HK1098603B - Orthogonal code synchronization system and method for spread spectrum cdma communications - Google Patents

Description

Orthogonal code synchronization system and method for spread spectrum CDMA communications

The present application is a divisional application of a patent application entitled "orthogonal code synchronization system and method for spread spectrum code division multiple access communication" filed on 26/2/1998 with application number 200510074074.0(PCT/US 98/03861).

Technical Field

The present invention relates to spread spectrum communications, and more particularly to a system and method for adjusting and aligning the phase of an information channel using orthogonal codes and information of the distance between a mobile terminal and a base station to achieve orthogonality at the base station.

Background

Referring to fig. 1, the spread spectrum modulator 51 utilizes a message-chip-code (Message-chip-code) signal g₁(t) processing the message data d (t) to produce a spread spectrum data signal. The transmitter 52 is used at the carrier frequency f₀Processes the spread spectrum data signal and is transmitted over the communication channel 53.

At the receiver, a spread spectrum demodulator 54 despreads the received spread spectrum signal and recovers the message data as received data via a synchronous data demodulator 60. The synchronous data demodulator 60 synchronously demodulates the despread spread spectrum signal using a reference signal. It is known in the art to generate a reference signal from a received modulated data signal using a square-law device 55, a band-pass filter 56 and a frequency divider 57. A costas phase lock loop or other reference signal generating circuit is suitable for this purpose.

In a fading channel, such as the ionosphere or any channel containing multipath, or more generally any channel in which the amplitude of the received signal fluctuates over time, synchronous demodulation cannot be carried out because the phase of the input signal is generally not the same as the phase of the reference signal.In this case, Differential Phase Shift Keying (DPSK) is used. The received signal is delayed by one symbol using DPSK and multiplied by the base signal. If the resulting phase is less than 90 deg., a 0-bit is declared, otherwise a 1-bit is declared. Such a system is complex and is at 10^-2There is a degradation of the error rate of about 6 dB.

The prior art does not provide a system and method for using spread spectrum modulation to communicate synchronously with a base station and to obtain orthogonality at the base station in conjunction with using the distance to the mobile terminal.

Disclosure of Invention

A general object of the present invention is a geolocation system and method that can be used as a personal communications service.

An object of the present invention is a system and method for synchronously transmitting a modulated data signal embedded in a CDMA signal and geographically locating remote units that performs well regardless of whether the signal is fading.

Another object of the present invention is a geolocation system and method that uses a separate spread spectrum channel as the pilot signal for the data link to geolocate a remote unit and to demodulate a modulated data signal embedded in a CDMA signal.

An additional object of the present invention is to synchronize spread spectrum communications with a geolocation system.

Still another object of the present invention is a spread spectrum system and method that utilizes orthogonal codes and known distances to mobile terminals to obtain orthogonality of mobile terminal user data signals at a base station.

It is yet another object of the present invention to provide a system and method for utilizing orthogonal codes on the reverse link of a duplex wireless channel.

Current cellular CDMA systems do not use orthogonal codes on the reverse link. In practice IS-95 systems use non-coherent detection on the reverse link. This is because it is difficult to synchronize the spreading codes with each other when they arrive at the base station from multiple mobile users. In order for the codes to be orthogonal, the different codes must start at substantially the same time and end at the appropriate time. Thus, even if all signals are synchronized as they leave the mobile station, the different path lengths of the signals as they arrive at the base station will cause them to be out of synchronization, since the mobile subscriber station is at different distances from the base station, and may be in motion.

At least three different signals may be gained in the detection process if the sampling is done at the appropriate time or if the predetermined waveforms are properly aligned in time. These two concepts, i.e., sampling at the appropriate time or aligning known waveforms, are generally referred to as synchronization. In the case of carrier synchronization, the correct carrier phase must be tracked. This means that the correct frequency is also followed and thus the known waveforms are phase aligned. In the case of PN code synchronization, the phase of the locally generated PN code must be shifted with reference to the received PN code until the two signals have accurate phase alignment; this alignment is maintained by locking the chip clock of the locally generated PN code to the clock of the received PN code. This is also the phase alignment to the known waveform.

In the case of an information signal, some degree of uncertainty must be involved, or there may be no information transmitted. Thus, if the information is transmitted on a bit-by-bit basis, the decision is made during each bit of the information. If a noise averaging filter or integrator is matched to a predetermined bit rate rather than to a predetermined phase of a predetermined waveform and if sampling is performed at the end of a bit period to maximize the integration process, the phase or amplitude of the received signal can be measured to determine the content of the information. For example, one is at f_cThe carrier sine wave of the predetermined waveform of (2) lasts for several hundred cycles at a predetermined phase. The information signal may then shift the phase to another predetermined and acceptable phase angle. This change in phase may represent a code containing information bits. The prior art includes many techniques for even receivingTechniques for maintaining a synchronized local carrier as the carrier changes its phase occasionally due to information.

In a CDMA system, there is a better way to derive a clean local carrier at the receiver than from the information channel. In a CDMA system, the same RF carrier may be transmitted, but with a different PN code superimposed thereon. Such signals have no unknown information on them; it is a completely predetermined signal known at both ends of the link. Since such a signal has a code different from the user information channel code, it can be completely distinguished from the user information channel. Thus, both signals may occupy the same frequency spectrum at the same time and cause only little interference with each other. This signal is called the pilot channel and can be filtered at the receiver with a narrow band filter that makes it a very stable reference signal. The user information channel phase is then compared to this clean reference to determine what changes to make to reflect the information on the user information channel. On the forward link, the same pilot channel is used as a reference for many mobile subscriber stations. As a result, the power of the pilot channel can be made several times larger than the power of an individual user information channel, while still having a small impact on the total power transmitted by the base station. This power factor, coupled with the fact that all signals have the same starting point and the same timing source, makes it easy to use orthogonal codes on such forward transmission links. All mobile users receive the same composite CDMA forward transmission signal and use the same pilot channel to extract their assigned user information channels from the composite CDMA signal.

The complexity of deriving and detecting orthogonal codes results in the actual orthogonal codes being relatively short, i.e., 64 chips for IS-95 systems, with some other proposals being 128 chips. These short codes limit the available pre-detection processing gain. Since these codes are repeated consecutively, the resulting spectral structure is made up of a small number of rows with large row spacing; this is not a desirable strong noise-like code. Thus, as in the case of IS-95, a longer, stronger noise-like code IS superimposed over the orthogonal code. If the pilot channel code is also one of the orthogonal codes, it will not provide noise into the information channel. In the case of IS-95, the pilot IS Walsh (Walsh) code 0, which means that it IS simply a superimposed noise-like code since Walsh 0 codes are all zeros. To achieve sufficient cancellation of the accompanying orthogonal codes, the codes must be perfectly aligned with all the zero crossings that happen at exactly the same time. Any misalignment will produce unmatched glitches that will interfere with the desired signal. On the forward link, a plurality of signals transmitted to all mobile stations are summed together to form a composite CDMA signal. As a result, the signals are perfectly aligned with each other and since all signals travel the same path, they will remain aligned. Therefore, the orthogonal code is practical and can be directly implemented. The only disadvantages are limited processing gain, and the limited number of available codes.

Applying orthogonal codes on the reverse link is more difficult because different codes originate from different mobile stations that are randomly distributed as a function of distance from the base station that all signals must arrive in perfect alignment. This means that in order for all signals to arrive at the base station synchronously, each mobile station must start its reference point at a different time to compensate for the change in path length. This has been considered too difficult to be practical in current systems. U.S. patent No. 5,404,376 proposes having the base station establish and broadcast a relationship between the C/I received by the mobile station and the distance that is continuously updated based on the measurement data. Based on this relationship, the mobile station estimates the PN code phase that will cause the PN code to arrive at the base station nearly synchronously with the transmissions of other mobile stations. There are a number of problems with this approach. In particular, it is difficult to maintain a consistent relationship between C/I and distance from the base station. Even in the best case, this relationship will depend on the direction of the propagation path. U.S. patent No. 5,404,376 proposes sophisticated techniques by which to add correction factors to accommodate the direction or sector in which the mobile station is located. The best result is also only one estimate and there is still a large amount of uncertainty that must be sought. The present invention overcomes these difficulties by determining the distance of a mobile station from a base station in a unique, simple and straightforward manner.

In accordance with the present invention, there is provided, as embodied and broadly described herein, a spread spectrum Code Division Multiple Access (CDMA) communication system and method for communicating over a duplex wireless channel, including at least one base station and a plurality of mobile terminals. Message data is communicated between the base station and the mobile terminal. Message data includes, but is not limited to, digital voice, computer data, facsimile data, video data, and the like. The base station transmits base message data to the plurality of mobile terminals over a forward channel. The mobile terminal transmits the remote message data to the base station over the reverse link. Base message data is defined herein as message data originating from a base station and remote message data is defined herein as message data originating from a mobile terminal.

The remote message data is spread spectrum processed with a pseudo noise code to produce spread spectrum processed remote message data. The spread spectrum processed remote message data is combined with a remote pilot signal to produce a remote CDMA signal. The remote-CDMA signal includes a remote pilot signal and a data signal.

The remote-CDMA signal is transmitted from the mobile terminal to the base station on a reverse channel of the duplex radio channel. The base station receives the remote-CDMA signal and separates the remote-CDMA signal into a pilot channel and a data channel. The base station generates a base station pilot signal and a base station pilot reference signal. The base pilot reference signal is separated and delayed to produce an on-time signal for the base pilot reference signal, an early signal for the base pilot reference signal, and a late signal for the base pilot reference signal. The on-time, early and late signals of the remote pilot signal are correlated using the on-time, early and late signals of the base pilot reference signal, respectively. The base station also generates a base station data reference signal and correlates the data signal using the base station data reference signal.

The phase of the remote pilot signal is tracked and an acquisition signal indicating synchronization of the remote pilot signal with the base station pilot reference signal is output in response to a peak in the remote pilot signal. In response to the acquisition signal, a code phase difference between the base station pilot signal and the base station pilot reference signal is measured to determine a distance between the mobile terminal and the base station. The range is transmitted on the forward channel to the mobile terminal, which adjusts the phase of the pseudo-noise code in response to the range to adjust the time of arrival of the data signal at the base station and to obtain orthogonality with other mobile terminal data signals arriving at the base station.

The base station may receive data from the mobile terminal on the reverse link of the duplex channel using one of four control modes. In the first mode, the mobile terminal transmits a separate user pilot on the reverse link that is not synchronized with the base station pilot and synchronizes the user data channel to this separate user pilot. In the second mode, the mobile terminal slaves its user pilot to the pilot it receives from the base station and synchronizes the user data channel with this slave user pilot. The second mode allows the user terminal to receive round trip delay information for purposes of geolocation and rapid reacquisition. In the third mode, the mobile terminal slaves its pilot to the incoming base station pilot, as in the case of mode two, but the user data channel operates in an orthogonal mode using the ranging information received from the base station. The phase relationship between the user pilot channel and the user data channel is calibrated. The user pilot carrier is also a carrier of the user data channel and can be used as a carrier reference for detecting the user data channel. In the fourth mode, acquisition is performed using the mode three secondary pilot, but after acquisition, the phase of the user pilot code is shifted to synchronize with the user data channel, thus making it an orthogonal channel as well. In this mode, the pilots no longer cause interference to the user data channels within the cell and can be transmitted at higher power levels.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention.

FIG. 1 is a prior art scheme for synchronizing recovery message data;

FIG. 2 illustrates a synchronous spread spectrum system having a bit synchronizer synchronized to a generic chip code generator in accordance with the present invention;

FIG. 3A illustrates a synchronous spread spectrum transmitter system for multiple message data;

FIG. 3B shows a spread spectrum receiver that receives a plurality of spread spectrum processed signals using a synchronous detector;

FIG. 3C shows a spread spectrum receiver that receives a plurality of spread spectrum processed signals using a nonsynchronous detector;

FIG. 4 illustrates a synchronous spread spectrum demodulation method;

FIG. 5 is a block diagram of a base station for synchronously communicating with and geographically locating remote units;

FIG. 6 is a block diagram of a remote unit for communicating with and geographically locating base stations;

fig. 7 is a block diagram of a mobile terminal in accordance with the orthogonal code synchronization system and method of the present invention; and

fig. 8 is a block diagram of a base station for an orthogonal code synchronization system and method.

Detailed Description

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout the several views.

The spread spectrum communication and orthogonal code synchronization system and method of the present invention is a continuation of the invention disclosed in U.S. patent No. 5,228,056, now published as serial No. 07/626,109 and filed on 1990, 12/14/d, and filed by donaldl. For complete disclosure, the following discussion includes the disclosure section presented in the original patent application and subsequently enters the discussion of orthogonal code synchronization in accordance with the present invention.

The spread spectrum signal of the present invention is designed to be "transparent" to other users, i.e., the spread spectrum signal is designed to have negligible interference with communications of other existing users. The presence of spread spectrum signals is difficult to determine. Such characteristics are referred to as Low Probability of Interception (LPI) and Low Probability of Detection (LPD). The LPI and LPD characteristics of spread spectrum allow transmissions between users of a spread spectrum CDMA communication system without the existing users of the mobile cellular system experiencing significant interference. The present invention utilizes LPI and LPD with respect to predetermined channels in a mobile cellular system or a fixed service microwave system. By having the power level of each spread spectrum signal below a predetermined level, the total power from all spread spectrum used within a cell will not interfere with mobile users in a mobile cellular system, or microwave users in a fixed service microwave system.

Spread spectrum is also resistant to "blocking" or interference. Spread spectrum receivers spread the spectrum of interfering signals. This reduces the interference from the interfering signal so that it does not significantly degrade the performance of the spread spectrum system. This interference reduction feature makes spread spectrum useful for commercial communications, i.e., spread spectrum waveforms can be superimposed over existing narrowband signals.

The present invention uses direct sequence spread spectrum using phase modulation techniques. Direct sequence spread spectrum takes the power to be transmitted and spreads it over a wide bandwidth, thus minimizing the power per unit bandwidth (watts/hertz). When this is done, the transmitted spread spectrum power received by the mobile cellular or microwave user, which has a relatively narrow bandwidth, is only a fraction of the actual transmitted power.

In a fixed service microwave system, for example, if a spread spectrum signal having 10 milliwatts is spread over a fixed service microwave bandwidth of 10MHz, and microwave users use a communication system having a channel bandwidth of only 2MHz, then in a narrowband communication system, the effective interference power caused by a spread spectrum signal is reduced by a factor of 10MHz/2 MHz. For fifty simultaneous spread spectrum users, the power of the interfering signal caused by the spread spectrum increases fifty times.

The nature of the spread spectrum resulting in interference reduction is that the spread spectrum receiver actually spreads the energy of any interference received over the same wide bandwidth, in this case 10MHz, and compresses the bandwidth of the desired received signal to its starting bandwidth. For example, if the starting bandwidth of the desired message data is only 30kHz, the power of the interference signal generated at the base station is reduced by a factor of 10MHz/30 kHz.

Direct sequence spread spectrum spreading is accomplished by modulating the original signal with a strong wideband signal relative to the data bandwidth. This wideband signal is chosen to have two possible amplitudes, +1 and-1, and these two amplitudes are periodically switched in a "pseudo-random" manner. Thus, at each equally spaced time interval, a determination is made as to whether the wideband modulated signal should be +1 or-1. If this determination is made by throwing a coin, the resulting sequence will be truly random. However, in such a case, the receiver will not know the sequence a priori and will not receive the transmitted signal properly. Instead, a chip-code generator electronically generates an approximately random sequence, called a pseudorandom sequence, which is known a priori to both the transmitter and the receiver.

Code division multiple access

Code Division Multiple Access (CDMA) is a direct sequence spread spectrum system in which a plurality, at least two, spread spectrum signals are communicated simultaneously, each operating on the same frequency band. In a CDMA system, each user is given a particular chip code. This chip code identifies the user. For example, if the first user has a first chip code g₁(t) the second user has a second chip code g₂(t), etc., then a receiver wishing to listen to the first user receives all of the energy transmitted by all users on its antenna. However, after despreading the first user's signal, the receiver outputs the full energy of the first user, while only a small portion of the energy transmitted by the second, third, etc., users is output.

CDMA is interference limited. That is, the number of users that can use the same spectrum and still have acceptable performance is determined by the total interference power generated in the receiver by all users as a whole. Unless power control is of great concern, those CDMA transmitters that are close to the receiver will cause overwhelming interference. This effect is known as the "near-far" (near-far) problem. In a mobile environment, the near-far problem may be a major effect. The power of each individual mobile remote user may be controlled such that the power received from each mobile remote user is the same. This technique is called "adaptive power control". See U.S. patent No. 5,093,840 entitled "adaptive power control for spread spectrum systems and methods", published 3.3.1992 by donaldl.schilling, which is incorporated herein by reference.

The spread spectrum communication system of the present invention is a Code Division Multiple Access (CDMA) system. Spread spectrum CDMA can significantly improve spectrum utilization. With CDMA, each user in a cell uses the same frequency band. However, each CDMA signal has a separate pseudo-random code that enables the receiver to distinguish the desired signal from the remaining signal. Remote users in adjacent cells use the same frequency band and the same bandwidth and thus "interfere" with each other. As the number of user signals received by the PCN base station increases, the received signals may exhibit greater noise.

Each unwanted user signal generates a certain interference power, the magnitude of which depends on the processing gain. Assuming that the remote users are evenly distributed among all neighboring cells, the remote users in the neighboring cells increase the expected interference energy by approximately 50% compared to the remote users within a particular cell. Since the interference increase factor is not severe, frequency reuse is not employed.

Each spread spectrum cell may use the full 10MHz band for transmission and the full 10MHz band for reception. Thus, using a chip rate of five million chips per second and an encoding data rate of 4800bps results in a processing gain of approximately 1000 chips per bit. As is known to those skilled in the art, the maximum number of CDMA remote users that can simultaneously use a frequency band is approximately equal to the processing gain.

Orthogonal code

The pilot on the return link is now considered feasible because it reduces the C/I required to achieve the desired Eb/No as disclosed in U.S. patent No. 5,506,864 and U.S. patent No. 5,544,156. This improvement comes from the ability to use synchronous or coherent detection. As described in these patents, the use of pilot or generic chip codes improves the performance of both orthogonal and non-orthogonal coded links. For orthogonal channels, the number of current users is reduced by two, since each mobile terminal requires a unique pilot and information code. This may have a serious impact if there is a limited number of codes. U.S. patent No. 5,506,864 measures the distance between a base station and a mobile terminal using non-orthogonal codes using pilots from the mobile terminal. The invention extends this patent to include orthogonal codes and uses information of the distance to the mobile terminal to adjust the phase of the information channel so that it is aligned with other mobile signals arriving at the base station. The mobile terminal receives the pilot or generic-chip-code signal from the base station and uses the timing and phase of the base station pilot signal to originate the remote pilot signal it transmits to the base station. That is, the returned pilot passes through the mobile terminal without delay; the returned pilot appears to be a radar reflection from the mobile terminal. Since there are many remote pilots to be returned to the base station, it is of course stronger in signal strength, a different but similar pseudo-noise code to the base station pilot pseudo-noise code.

The base station receives the pilot signals from all current mobile terminals and measures the phase difference between the returned pseudo-noise sequence and the transmitted pseudo-noise sequence to each remote mobile station, possibly down to 0.1 chips. Measured is the round trip delay; the actual distance is half the number measured in chips to the nearest 0.1 chip. This information is transmitted to the mobile user and, if the mobile user is operating in an orthogonal mode on the return link, the mobile user uses this information to adjust the phase of the PN code on the remote message to arrive at the base station at a predetermined time as established by the base station. Thus, the PN codes of the remote pilot and remote user message channels are at different phases, but they both have the same carrier signal, and the pilot carrier can be used to generate a reference for coherent detection in the user message channel.

The data sampling point is typically dependent on the repetition rate of the PN sequence and is adjusted in phase to coincide with the timing of the data on the user message channel. Thus, the mutual interference caused by the user message channels that are communicating with one common base station can be significantly reduced.

Interference from mobile users in neighboring cells is not orthogonal and appears as non-orthogonal interference. Most orthogonal code CDMA systems utilize sector antennas to achieve code multiplexing and reduce interference. Thus, at the edge of a cell across the surface of a sector, the mobile users in each cell transmit at maximum power and cause radiation to both cells at maximum energy. However, as mobile users in neighboring cells move towards their base stations, they reduce their power so that they remain the same as they did at the cell edge. Assuming a quarter power decay curve, they reduce their power at a rate of a quarter power to distance ratio, and since they are also leaving the interfering base station, their reduced transmit power level (reduced to a quarter power) travels a distance that is also reduced by a quarter power factor. This doubles the effect of the quarter power factor, which means that the interference from the mobile user's neighboring cell is much less than if power control was not used. Thus, the external interference introduced at the original base station, i.e., the interference from mobile users operating with other base stations, is at least 6db lower than the interference caused within the cell from other mobile users operating with the original base station. Therefore, the number of users can be increased by four times. As described above, each current mobile user transmits a pilot channel and an information or message channel. The information channels are adjusted so that they are orthogonal when arriving at the base station. But the pilot channels are not orthogonal, but the pilot channel power is reduced by 6db after the information channel is active. Thus, even with external interference and pilot channels, the result of the present invention is to double the capacity.

Another improvement can be achieved by shifting the phase of the remote pilot after acquisition so that it coincides with the user information channel. When this is done, the far-end pilots also become orthogonal, and the only interference is external interference radiated into the original cell from users in neighboring cells. As described above, this interference is reduced by at least 6db, resulting in a four-fold increase in capacity. Code tracking on the reverse link becomes more difficult since errors are generated in the base station and the oscillator voltage controlled by this error is in the mobile station. Therefore, this error voltage must be transmitted to the mobile station using the forward link. Typically the distance change is relatively slow and remote control of such a mobile code clock is not a problem. When sudden fluctuations occur that are sufficient to cause rapid and severe misalignment, the mobile station moves the remote pilot code back to the acquisition mode. Once reacquisition and the necessary adjustments to bring the information channel back into proper alignment are completed, the mobile station switches back to the orthogonal tracking mode. Thus, the non-orthogonal remote pilots only contribute a small fraction of the time, with little impact on capacity. If there are enough orthogonal codes in the code set to actually take advantage of this, the capacity should still be close to four times that of a non-orthogonal code system.

Synchronous spread spectrum communications

As shown in fig. 2, a spread spectrum Code Division Multiple Access (CDMA) communication system for use over a communication channel 110 is provided that includes a general purpose device, a message device, a spreading device, an adder device, a transmitting device, a general spread spectrum processing device, a message spread spectrum processing device, an acquisition and tracking device, a detection device, and a synchronization device. The generic means and the message means are embodied as a transmitter-generic-chip-code generator 101 and a transmitter-message-chip-code generator 102. The expansion device is shown as an exclusive-or device 103, which may be an exclusive-or gate. The adder means is a combiner 105 and the transmitting means comprises a transmitter embodied as a signal source 108 coupled to a modulator 107. The transmitter-message-chip-code generator 102 is coupled to an exclusive-or device 103. The transmitter-generic-chip-code generator 101 is shown coupled to a transmitter-message-chip-code generator 102 and a message-data source. The exclusive-or device 103 and the transmitter-generic-chip-code generator 101 are coupled to a combiner 105. Modulator 107 is coupled between combiner 105 and communication channel 110.

At the receiver, the generic-spread-spectrum-processing means are embodied as a receiver-generic-chip-code generator 121, a generic mixer 123, and a generic-bandpass filter 125. The generic mixer 123 is coupled between the receiver-generic-chip-code generator 121 and the generic-bandpass filter 125. The message-spread-spectrum-processing means is embodied as a receiver-message-chip-code generator 122, a message mixer 124, and a message-bandpass filter 126. The message mixer 124 is coupled between the receiver-message-chip-code generator 122 and the message-bandpass filter 126. A power splitter 115 is coupled between the communication channel 110 and the common mixer 123 and the message mixer 124.

The acquisition and tracking means are embodied as an acquisition and tracking circuit 131. The acquisition and tracking circuit 131 is coupled to an output of the generic-bandpass filter 125 and to the receiver-generic-chip-code generator 121. The receiver-message-chip-code generator 122 is preferably coupled to the receiver-generic-chip-code generator 121.

The detection means is embodied as a detector 139. The detector 139 is coupled to the message bandpass filter 126 and the generic bandpass filter 125. The detector 139 may be a non-synchronous detector, such as an envelope detector, or a square law detector. Alternatively, the detector 139 may be a synchronous detector that utilizes the recovered carrier signal from the general bandpass filter 125.

The synchronization means comprise a bit means, a low pass filter 128, and an electronic switch 130. The bit means is embodied as a bit synchronizer 129. The low pass filter 128 and the electronic switch 130 are coupled to a bit synchronizer 129. As shown in fig. 2, the bit synchronizer 129 is preferably coupled to the receiver-generic-chip-code generator 121. Alternatively, the bit synchronizer 129 may be coupled to an output of the detector 139.

Transmitter-generic-chip-code generator 101 generates a generic-chip-code signal g₀(t) the transmitter-message-chip-code generator 102 generates a message-chip-code signal g₁(t) of (d). In fig. 2, the message data d is provided by a generic-chip-code signal₁(t), and the synchronization timing of the message-chip-code signal, although other sources may be used, such as a common clock signal for synchronization. The exclusive-or device 103 generates a spread spectrum signal by spread spectrum processing the message data with a message-chip-code signal. Spread spectrum processing may be accomplished by modulo-2 addition of the message data to the message-chip-code signal. The combiner 105 combines the generic-chip-code signal with the spread-spectrum-processed signal. The combined generic-chip-code signal and spread-spectrum-processed signal may be a multi-level signal having the instantaneous voltage levels of the generic-chip-code signal and the spread-spectrum-processed signal.

The modulator 107 as a transmitter component is used at a carrier frequency f₀Of the carrier signal cos omega₀t modulates the combined generic-chip-code signal and the spread-spectrum-processed signal.The modulated generic-chip-code signal and the spread-spectrum-processed signal are transmitted over a communication channel 110 as a Code Division Multiple Access (CDMA) signal x_c(t) transmitting. Thus, a CDMA signal includes a generic-chip-code signal and a spread-spectrum-processed signal as if each were at the same carrier frequency f₀Are individually and synchronously modulated on separate carrier signals and transmitted over a communication channel.

At a receiver, a common spread spectrum processing device derives CDMA signal x_c(t) recovering the carrier signal cos ω₀t and message spread spectrum processing means despreads the CDMA signal x_c(t) becomes a modulated data signal d₁(t) of (d). More specifically, referring to fig. 2, the power splitter 115 separates CDMA signals received from the communication channel 110. The receiver-generic-chip-code generator 121 generates a generic-chip-code signal g₀(t) a replica signal. The generic mixer 123 despreads the CDMA signal x from the power splitter 115 with a replica of the generic-chip-code signal_c(t) becomes a recovered carrier signal. With generic-chip-code signal g₀(t)cosω₀the spread spectrum channel of the CDMA signal of t generally does not include data, and thus despreading the CDMA signal produces only a carrier signal. The generic-bandpass filter 125 filters the recovered-carrier signal at the carrier frequency, or equivalently at an intermediate frequency. The generic-bandpass filter 125 may have a very narrow bandwidth for filtering the recovered-carrier signal, as compared to the message-bandpass filter 126, which has a sufficiently wide bandwidth for filtering the modulated-data signal. The very narrow bandwidth of the generic-bandpass filter 125 helps to extract the recovered-carrier signal from the noise.

Acquisition and tracking circuit 131 acquires and tracks the recovered carrier signal from the output of general purpose bandpass filter 125. A replica of the generic-chip-code signal from the receiver-generic-chip-code generator 121 is synchronized to the recovered carrier signal via acquisition and tracking circuit 131.

The receiver-message-chip-code generator 122 generates a message-chip-code signal g₁(t) a replica signal. The message chip code signal g₁(t) the replica signal and the generic-chip-code signal g from the receiver-generic-chip-code generator 121₀The replica signal of (t) is synchronized. Thus, the receiver-message-chip-code generator 122, which is synchronized to the receiver-generic-chip-code generator 121, has the same synchronization as the transmitter-message-chip-code generator 102, which is synchronized to the transmitter-generic-chip-code generator 101. Thus, a spread spectrum communication channel having a generic-chip-code signal provides coherent spread spectrum demodulation of a spread spectrum channel with data.

Message mixer 124 despreads the CDMA signal from power splitter 115 with a replica of the message-chip-code signal to produce a modulated data signal d₁(t)cosω₀t. The modulated data signal is actually message data modulated with a carrier signal. The message bandpass filter 126 filters the modulated data signal at a carrier frequency, or equivalently, at an Intermediate Frequency (IF). A down-converter converting the modulated data signal to IF may be used alternatively without changing the cooperative function or teaching of the present invention.

The detector 139 demodulates the modulated data signal into a detected signal. The detected signal is filtered by a low pass filter 128, sampled by an electronic switch 130, and used as received data d₁And (t) outputting. The received data without errors is identical to the message data. The low pass filter 128 and the electronic switch function as an "integrate and dump" respectively, under the control of the bit synchronizer 129.

The bit synchronizer 129 controls the integration and dump of the low pass filter 128 and the electronic switch 130. The bit synchronizer 129 preferably derives synchronization using a replica of the generic-chip-code signal from the receiver-generic-chip-code generator 121 as shown in fig. 2. The bit synchronizer 129 may also derive synchronization from the output signal of the detector 139 as shown in fig. 1.

In a preferred embodiment, the bit synchronizer 129 receives the generic-chip-code signal g from the receiver-generic-chip-code generator 121₀(t) a replica signal. Copies of the generic-chip-code signal, e.g. may comprise a copy of the generic-chip-code signal having 825A chip codeword of 0 chips. Assuming a codeword of 11 bits per chip, there are 750 chips per data bit. Since the replica of the generic-chip-code signal provides the bit synchronizer 129 with information about where the chip codeword starts, the bit synchronizer 129 knows the timing of the corresponding bits for synchronization.

The present invention may also include transmitting a plurality of spread spectrum processed signals for processing a plurality of information data as CDMA signals. In this case, the present invention includes a plurality of message devices and a plurality of extension devices. Referring to fig. 3A, the plurality of message means may be embodied as a plurality of transmitter-message-chip-code generators and the plurality of spreading means may be embodied as a plurality of exclusive-or gates. A plurality of transmitter-message-chip-code generators generates a plurality of message-chip-code signals. In fig. 3A, a plurality of transmitter-message-chip-code generators are shown as: generating a first message-chip-code signal g₁(t) a first transmitter-message-chip-code generator 102 for generating a second message-chip-code signal g₂(t) to a second transmitter-message-chip-code generator 172 to generate an Nth message-chip-code signal g_N(t) nth transmitter message chip code transmitter 182. A plurality of exclusive-or gates are shown: a first exclusive-or gate 103, a second exclusive-or gate 173, through an nth exclusive-or gate 183. Multiple exclusive-or gates pass multiple message data d₁(t)，d₂(t)，…，d_N(t) are respectively associated with a plurality of message-chip-code signals g₁(t)，g₂(t)，…，g_N(t) modulo-2 addition produces a plurality of spread spectrum processed signals. More specifically, the first message data d₁(t) and a first message-chip-code signal g₁(t) modulo-2 addition, second message data d₂(t) and a second message-chip-code signal g₂(t) modulo-2 addition to the Nth message data d_N(t) and Nth message-chip-code signal g_N(t) modulo-2 addition.

The transmitter-generic-chip-code generator 101 is coupled to the plurality of transmitter-message-chip-code generators and for the plurality of message data d₁(t)，d₂(t)，…，d_N(t) source of (t). In a preferred embodiment, generic chip codesSignal g₀(t) is a plurality of message-chip-code signals g₁(t)，g₂(t)，…，g_N(t), and a plurality of message data d₁(t)，d₂(t)，…，d_N(t) providing synchronization timing.

The combiner 105 combines the generic-chip-code signal and the plurality of spread-processed signals by linear addition of the generic-chip-code signal and the plurality of spread-processed signals. The combined signal is typically a multilevel signal having the instantaneous voltage levels of the generic-chip-code signal and the plurality of spread-spectrum-processed signals.

The modulator 107 as a transmitter component is used at the carrier frequency f₀Of the carrier signal cos omega₀t modulating the combined generic-chip-code signal and the plurality of spread-spectrum-processed signals. Passing the modulated generic-chip-code signal and the plurality of spread-spectrum-processed signals through communication channel 110 as CDMA signal X_C(t) transmitting. CDMA Signal X_C(t) has the form:

thus, a CDMA signal includes a generic-chip-code signal and a plurality of spread-spectrum-processed signals as if each were individually and synchronously at the same carrier frequency f₀Modulated on a separate carrier signal and transmitted over a communication channel.

The present invention includes receiving a CDMA signal having a plurality of spread spectrum processes. The receiver further comprises a plurality of message spread spectrum processing means, a plurality of detection means, and a plurality of synchronization means. As shown in fig. 3B, the plurality of message spread spectrum processing means may be embodied as a plurality of message-chip-code generators, a plurality of message mixers, and a plurality of message-bandpass filters. A mixer is coupled between a corresponding message-chip-code generator and the message-bandpass filter. The plurality of message mixers are coupled to a power splitter 115. More specifically, the plurality of message-chip-code generators are specifically shown as a first message-chip-code generator 122, a second message-chip-code generator 172, through an Nth message-chip-code generator 182. The plurality of message mixers are shown specifically as first message mixer 124, second message mixer 174, through nth message mixer 184. The plurality of message bandpass filters are specifically shown as a first message bandpass filter 126, a second message bandpass filter 176, through an Nth message bandpass filter 186.

The plurality of detector means may be embodied as a plurality of synchronous detectors shown as a first synchronous detector 127, a second synchronous detector 177 through an Nth synchronous detector 187. Each of the plurality of synchronous detectors is coupled to one of the plurality of message bandpass filters.

The plurality of synchronization means may comprise a bit synchronizer 129, a plurality of low pass filters, and a plurality of electronic switches. The plurality of low pass filters are shown as: a first low pass filter 128, a second low pass filter 178, through an Nth low pass filter 188. The plurality of electronic switches are shown as: a first electronic switch 130, a second electronic switch 180, through an Nth electronic switch 190. Each of the plurality of synchronous detectors is coupled to an output of the generic-bandpass filter 125. The recovered carrier signal from the general bandpass filter 125 is used as a reference signal for synchronously demodulating each of the plurality of message data signals into a plurality of received data d by a plurality of synchronous detectors₁(t)，d₂(t)，…，d_N(t)。

Alternatively, the detection means may be embodied as a plurality of non-synchronous detectors, for example envelope detectors 139, 189, 199, as shown in fig. 3C. The non-synchronous detector generally does not require a recovered carrier signal.

Bit synchronizer 129 derives a generic-chip-code signal g from the chip-code signal₀(t) deriving a timing from the replica signal and controlling a timing of an integrate and dump function of the plurality of low pass filters and the plurality of electronic switches.

With the present invention embodied in fig. 3B, as described above, the common spread spectrum channel that is part of the CDMA signal provides a recovered carrier signal. The acquisition and tracking circuit 131 acquires and tracks the recovered carrier signal from one output of the generic-bandpass filter 125. A replica of the generic-chip-code signal from the receiver-generic-chip-code generator 121 is synchronized to the recovered carrier signal via the acquisition and tracking circuit 131. The receiver-generic-chip-code generator 121 generates a generic-chip-code signal g₀(t) that provides timing to the bit synchronizer 129 and to the plurality of receiver-message-chip-code generators 122, 172, 182.

The present invention also includes a method for synchronously demodulating a CDMA signal. Message data is input to the expansion device. Referring to fig. 4, the method includes the step of generating 403 a generic-chip-code signal. The method further includes generating 405 message data synchronized to the generic-chip-code signal and generating 407 a message-chip-code signal synchronized to the generic-chip-code signal. Message data is processed with the message-chip-code signal using a spread spectrum modulator to produce a spread spectrum processed signal. The generic-chip-code signal is combined 409 with the spread-spectrum-processed signal. The method transmits the combined generic-chip-code signal and spread-spectrum-processed signal as a CDMA signal over a communication channel on a carrier signal.

At the receiver, the method includes recovering 413 the carrier signal from the CDMA signal and despreading 415 the CDMA signal into a modulated data signal. The recovered carrier signal is used for the steps of synchronously despreading the CDMA signal and optionally for synchronously demodulating 417 and outputting 419 the modulated data signal as received data.

In FIG. 3In use of the system shown in a, a transmitter-generic-chip-code generator 101 generates a generic-chip-code signal g₀(t) of (d). Using EXCLUSIVE-OR device 103 with message-chip-code signal g from transmitter-message-chip-code generator 102₁(t) spread spectrum processing the message data. The combiner 105 combines the generic-chip-code signal with the spread-spectrum-processed signal. The combined signal may be, for example, a multi-level signal resulting from linearly adding the voltage levels of the generic-chip-code signal and the spread-spectrum-processed signal, or a generic-chip-code signal and the voltage levels of a plurality of spread-spectrum-processed signals. The transmitter having a carrier frequency f₀Transmits the combined generic-chip-code signal and the plurality of spread-spectrum-processed signals on a carrier signal. The CDMA signal is transmitted over a communication channel 110.

As shown in fig. 3B, at the receiver, the generic-spread-spectrum-processing means is embodied as a receiver-generic-chip-code generator 121, a generic mixer 123, and a generic-bandpass filter 125 that cooperate to recover the carrier signal from the CDMA signal. The message-spread-spectrum-processing means is embodied as a receiver-message-chip-code generator 122, a message mixer 124, and a message-bandpass filter 126 that cooperate to despread the CDMA signal into a modulated-data signal. The receiver-message-chip-code generator 122 is preferably synchronized to the replica of the generic-chip-code signal from the receiver-generic-chip-code generator 121. A plurality of receiver-message-chip-code generators synchronized to the replica of the generic-chip-code signal may be used. Embodied as a synchronization means of the synchronous detector 127 synchronized to the recovered carrier signal, demodulates the modulated data signal into received data.

The low pass filter 128 and electronic switch 130 integrate and dump the received data under the control of the bit synchronizer 129. The bit synchronizer 129 preferably uses a replica of the generic-chip-code signal to synchronize the integrate-and-dump function.

Spread spectrum geolocation

A spread spectrum Code Division Multiple Access (CDMA) communication and geolocation system and method for use over a communication channel includes at least one base station and a plurality of remote units. The remote units may be mobile or in a fixed stationary position. Message data is communicated between the base station and the remote unit. Message data includes, but is not limited to, digitized voice, computer data, facsimile data, video data, and the like. The base station communicates base station message data to a plurality of remote units. The remote unit communicates remote message data to the base station. Base message data is defined herein as message data originating from a base station, and remote message data is defined herein as message data originating from a remote unit. In the following discussion, a preferred embodiment is discussed in which the distance between the base station and the remote unit is determined at the base station. The roles of base station and remote unit may be reversed, with the distance being determined at the remote unit, as would be equivalent to one skilled in the art.

In the example configuration shown in fig. 5, the base station includes a base station extension means, a base station general means, a base station combiner means, a base station transmitter, and a base station antenna. The term "base station" as used as a prefix refers to an element located at, or originating from, a base station.

Spread spectrum processing base station message data d by base station spreading device₁(t) of (d). The base station spreading means is embodied as a base station spread spectrum modulator. The base-spread-spectrum modulator is shown as a message-chip-code generator 502 and an exclusive-or gate 503. The exclusive-or gate 503 is coupled to the message-chip-code generator 502. Message-chip-code generator 502 uses a chip codeword to generate base-message data d for spread-spectrum processing₁The chip code sequence of (t). The chip-code sequence from message-chip-code generator 502 is spread-spectrum processed by modulo addition with exclusive-or gate 503. Those skilled in the art will recognize that there are many equivalent circuits that can be used in a base-spread-spectrum modulator including, but not limited to, a product device for multiplying the chip-code sequence by the base-message data, a matched filter, and a surface-acoustic-wave device having an impulse response that matches the chip-code sequence.

The base-generic means generates a base-generic-chip-code signal. The term "generic" is used as a prefix to indicate that the generic-chip-code signal is an unmodulated, or low-data-rate, direct-sequence spread-spectrum signal, which can be used as a pilot channel. The pilot channel allows the user to acquire timing and provides a phase reference for coherent demodulation. The base-generic means is embodied as a base-generic-chip-code generator 501. The base-generic-chip-code generator 501 generates a base-generic-chip-code signal using a chip codeword shared by all remote units in communication with the base station. The message-chip-code generator 501 is coupled to a base-generic-chip-code generator 502 for deriving the common timing. Alternatively, a common clock may be used to provide timing signals for the message-chip-code generator 502 and the base-generic-chip-code generator 501.

The base combiner means combines the base generic-chip-code signal with the spread-spectrum-processed base message data to produce a base-CDMA signal. The base combiner means is embodied as a base combiner 505. The base combiner 505 is coupled to the base-generic-chip-code generator 501 and the EXCLUSIVE-OR gate 503. The base combiner 505 linearly adds the base-generic-chip-code signal to the spread-spectrum-processed base-message data from the exclusive-or gate 503. The resulting signal at the output of the base combiner 505 is a Code Division Multiple Access (CDMA) signal, here denoted a base CDMA signal. Various alternative non-linear combinations may also be used, so long as the resulting base station CDMA signal enables its channel to be detected at the spread spectrum receiver.

The base transmitter means transmits base CDMA signals from the base station to the remote unit. The base station transmitter apparatus is embodied as a signal source 508 and a product device 507. The product device 507 is coupled between the base combiner 505 and the signal source 508. The signal source 508 is at a first carrier frequency f₁A first carrier signal is generated. The multiplication device 507 multiplies the base CDMA signal output from the base combiner 505 by the first carrier signal. It is known in the art that other transmitting devices may be used to place the desired signal at a selected carrier frequency.

The base station antenna 509 is coupled to the base transmitter means through an isolator 513. The base station antenna 509 radiates base station CDMA signals at a first carrier frequency.

As shown in fig. 6, the remote unit comprises a remote antenna 511, remote detection means, remote extension means, remote combiner means, and remote transmitter means. Each remote unit may also include remote generic devices. The term "remote" as used as a prefix refers to an element located at, or originating from, a remote unit.

The remote antenna 511 receives the base-station CDMA signal radiated from the base station.

The remote detection means is coupled to a remote antenna 511. The remote-detection means detects a base-generic-chip-code signal embedded in the base-CDMA signal. Using the detected base-generic-chip-code signal, the remote-detection means recovers the base-message data propagated from the base station. The remote unit may retransmit the detected base-generic-chip-code signal, or alternatively, may cause the remote-generic means to generate a different remote-generic-chip-code signal.

In fig. 6, the far-end detection means is embodied as a product device 536, a band-pass filter 537, an acquisition and tracking circuit 538, a general-purpose chip code generator 539, a message-chip code generator 541, a product device 542, a band-pass filter 543, a data detector 544, a low-pass filter 545, and a bit synchronizer 540. Other devices and circuits may be used to perform the same function, as is well known in the art, including, but not limited to, matched filters, surface acoustic wave devices, and the like. This circuit captures and tracks the base-generic-chip-code signal embedded in the base-CDMA signal. The base station CDMA signal is received at remote antenna 511 and passed through isolator 534 and power splitter 535. The base-generic-chip-code signal is detected using a product device 536, a bandpass filter 537, an acquisition and tracking circuit 538, and a generic-chip-code generator 539. The function of this circuit is the same as described in the previous section. Using message-chip-code generator 541, product device 542, bandpass filter 543, data detectionThe detected base-generic-chip-code signal is used by a detector 544, a low pass filter 545, and a synchronizer 540 to recover the base-message data embedded in the base-CDMA signal. The data detector 544 may operate coherently or non-coherently. Detected base message data as detected data d_R1And (t) outputting.

If the base-generic-chip-code signal is to be combined as part of the remote-CDMA signal, then generic-chip-code generator 546 is not needed because the base-generic-chip-code signal at the output of generic-chip-code generator 539 is available. If a remote-generic-chip-code signal is used that is different from the base-generic-chip-code signal, then a generic-chip-code generator 546 may be used to generate the remote-generic-chip-code signal. In the latter case, the remote-generic-chip-code signal is timed or synchronized to the detected base-generic-chip-code signal. For purposes of discussion, the remote-generic-chip-code signal is considered to be transmitted from the remote unit to the base station, it being understood that the remote-generic-chip-code signal may be the same as, or the same as, the detected base-generic-chip-code signal.

The remote spreading means spreads the spectrum to process the remote message data. The remote spreading means is embodied as a remote spread spectrum modulator. The remote-spread-spectrum modulator is shown as a message-chip-code generator 548 and an exclusive-or gate 547. The EXCLUSIVE-OR gate 547 is coupled to the message-chip-code generator 548. Message-chip code generator 548 utilizes a chip codeword to generate remote-message data d for spread-spectrum processing₂The chip code sequence of (t). An exclusive-or gate 547 performs spread-spectrum processing on the chip-code sequence from message-chip-code generator 548 with modulo addition. Those skilled in the art will recognize that many equivalent circuits may be used as the remote spreading means, including, but not limited to, product devices for multiplying chip code sequences by base station message data, matched filters and surface acoustic wave devices.

The remote combiner means combines the remote generic-chip-code signal and the spread-spectrum-processed remote message data into a remote CDMA signal. The remote combiner arrangement is embodied as a remote combiner 549. The remote combiner 549 is coupled to the EXCLUSIVE-OR gate 547, and to the remote-generic-chip-code generator 546, or alternatively to the generic-chip-code generator 539. The remote combiner 549 linearly sums the remote-generic-chip-code signal with the spread-spectrum-processed remote-message data from the EXCLUSIVE-OR gate 547. The signal generated at the output of the remote combiner 549 is a Code Division Multiple Access (CDMA) signal, here denoted a remote CDMA signal. Various other non-linear combinations may alternatively be used, so long as the resulting remote-CDMA signal is capable of having its channel detected at the spread-spectrum receiver.

The remote unit also includes remote transmitter means for transmitting a remote CDMA signal from the remote unit to the base station. The remote transmitter apparatus is embodied as a signal source 551 and a product device 550. The product device 550 is coupled between the remote combiner 549 and the signal source 551. The signal source 551 is at the second carrier frequency f₂A carrier signal is generated. The product device 550 multiplies the remote-CDMA signal from the output of the remote combiner 549 by the second carrier signal. Other transmitting devices are known in the art for placing the desired signal at the selected carrier frequency. The second carrier frequency may be the same or different from the first carrier frequency.

The remote antenna 511 is coupled to the remote transmitter means through an isolator 534. The remote antenna 511 radiates the remote CDMA signal at the second carrier frequency.

Each base station further comprises base detection means and distance means. The base-detection means is coupled to a base antenna 509 through an isolator 513 and a power splitter 515. The base-detection means detects the remote-generic-chip-code signal embedded in the remote-CDMA signal. As shown in fig. 5, the base-detection means may be embodied as a base-detector, which may include a product device 523, a bandpass filter 525, an acquisition and tracking circuit 531, a generic-chip-code generator 521, a message-chip-code generator 522, a product device 524, a bandpass filter 526, a data detector 527, a lowpass filter 528, and a bit synchronizer 529. Other devices and circuits performing the same function may be used to implement the base-detection apparatus, other devices and electrical circuits, as is well known in the artThe circuit includes, but is not limited to, a matched filter, a surface acoustic wave device, and the like. This circuit acquires and tracks the remote-generic-chip-code signal embedded in the remote-CDMA signal. The remote CDMA signal is received at the base station antenna 509 and passes through an isolator 513 and a power splitter 515. The remote-generic-chip-code signal is detected by product device 523, bandpass filter 525, acquisition and tracking circuit 531 and generic-chip-code generator 521. The function of this circuit is as described previously. The detected remote-generic-chip-code signal is used to recover the remote-message data embedded in the remote-CDMA signal by message-chip-code generator 522, product device 524, bandpass filter 526, data detector 527, lowpass filter 528, and bit synchronizer 529. The data detector 527 may operate coherently or non-coherently. Detected remote message data as detected data d_R2And (t) outputting. Thus, the base detector recovers the remote message data transmitted from the remote unit using the detected remote generic-chip-code signal.

The distance means determines the distance delay between the remote unit and the base station using the detected remote-generic-chip-code signal and the base-generic-chip-code signal. The range means is embodied as a range delay device 530 that compares the timing between the base-generic-chip-code signal from the generic-chip-code generator 501 and the detected-remote-generic-chip-code signal from the generic-chip-code generator 521.

The present invention may further comprise the steps of: spread spectrum processing base station message data; generating a base station generic chip code signal; combining the base-generic-chip-code signal with the spread-spectrum-processed base-message data, thereby generating a base-CDMA signal; transmitting a base CDMA signal from the base station to the remote unit; detecting a base-generic-chip-code signal embedded in the base-CDMA signal; recovering base station message data using the detected base station generic chip code signal; spread spectrum processing remote message data; generating a remote-CDMA signal using the detected generic-chip-code signal and the spread-spectrum-processed remote data; transmitting a remote-CDMA signal from the remote unit to the base station; detecting a remote-generic-chip-code signal embedded in the remote-CDMA signal; recovering the remote message data using the detected remote generic-chip-code signal; and determining the range delay between the remote unit and the base station using the detected remote-generic-chip-code signal and the base-generic-chip-code signal.

In use, the base station spread spectrum processes base message data with a message-chip-code signal and combines the spread-spectrum processed base message data with the base-generic-chip-code signal. The combined signal is a base-CDMA signal transmitted over the communication channel to the at least one remote unit.

The remote unit receives the base-CDMA signal, detects the base-generic-chip-code signal embedded in the base-CDMA signal, and uses the detected base-generic-chip-code signal to recover the base-message data embedded in the base-CDMA signal.

The detected base-generic-chip-code signal is delayed to a remote-generic-chip-code signal or used to set the timing for a different remote-generic-chip-code signal transmitted from the remote unit to the base station. The remote unit spread spectrum processes the remote-message data with the remote-chip-code signal and combines the spread-spectrum-processed remote-message data with the remote-generic-chip-code signal into a remote-CDMA signal. The remote-CDMA signal is transmitted to the base station through a communication channel.

At the base station, a remote-generic-chip-code signal is detected from the remote-CDMA signal, and the detected remote-generic-chip-code signal is used to detect remote-message data embedded in the remote-CDMA signal. In addition, the detected remote-generic-chip-code signal is compared with the base-station-generic-chip-code signal in a range delay circuit to determine the range of the remote unit from the base station. In practice, the distance between the remote unit and the base station is a function of the timing between transmission of the sequence of chip codes that produced the base-generic-chip-code signal and reception of the sequence produced by the chip code that produced the remote-generic-chip-code signal.

The concept of determining distance using Radio Frequency (RF) signals is known in the art. The RF signal should have a fixed propagation rate, 3X 10⁸M/s. At which the RF signal arrivesThe receiver leaves the transmitter some time before. A specific sequence of the base-generic-chip-code signal and the remote-generic-chip-code signal is used as a time stamp. The time difference between the base-generic-chip-code signal sequence seen at the receiver of the remote unit and the sequence at the base transmitter is directly related to the distance between the base station and the remote unit. Likewise, the time difference between the sequence of the remote-generic-chip-code signal seen at the receiver of the base station and the sequence at the transmitter of the remote unit is directly related to the distance between the remote unit and the base station.

The use of the base-generic-chip-code signal and the far-end-generic-chip-code signal is of the same type as the echo ranging method used in radar systems. Many radar systems simply pulse out RF energy and then wait for a portion of the energy to return due to the pulse reflecting off of the target. The radar marks the time from the moment the pulse is transmitted until it returns. The time required for the pulse to return is a function of the round trip distance to the target. The distance is easily determined from the propagation speed of the signal.

The spread spectrum signals of the present invention have the same distance/time relationship. The spread spectrum signal of the present invention has the advantages of: its phase is easily resolved. The base resolution of the base-station-chip-code signal or the remote-chip-code signal sequence is one code chip. Thus, the higher the chip rate, the better the scalability. Thus, at a chip rate of 10 Mchips/second, the base range resolution is 10^-7Seconds, or 30 meters. Additional delays that may be encountered in the remote unit circuitry are also taken into account. These delays can be compensated for at the base station when determining the distance between the base station and the remote unit.

Orthogonal code synchronization

The present invention may also be embodied as a system and method for adjusting and aligning the phase of an information channel using orthogonal codes and information of the distance to a mobile terminal in order to obtain orthogonality at a base station antenna.

The system for obtaining orthogonality at a base station antenna using information of an orthogonal code and a distance to a mobile terminal includes: a plurality of mobile terminals and a base station. Each of the plurality of mobile terminals includes remote spread spectrum processing means, remote pilot means, combining means, remote transmitting means, and code phase adjusting means.

The remote spread spectrum processing means and the remote pilot means are coupled to the combining means. The remote transmitting device is coupled to the combining device.

The base station comprises receiving means, first base station pilot means, second base station pilot means, first delay means, second delay means, correlator means, tracking means, distance delay means, and base station transmitting means.

The remote spread spectrum processing means processes the remote message data using the pseudo noise code. The remote pilot means generates a remote pilot signal. The combining means combines the remote pilot signal with the spread spectrum processed remote message data to produce a remote composite signal. The remote composite signal has a remote pilot signal and at least one remote user information channel. The remote transmitting means transmits the remote composite signal to the base station on a reverse channel of the duplex radio channel.

At the base station, the receiving device receives the far-end composite signal. The first base station pilot means generates a base station pilot signal. The second base station pilot means generates a base station pilot reference signal. The first delay means generates an on-time, an early, and a late signal of the base station pilot reference signal. The second delay means generates an information reference signal. The information reference signal is synchronized with the on-time signal of the base station pilot reference signal. Correlator means multiplies the remote composite signal by the on-time, early and late signals of the base pilot reference signal to correlate an on-time, an early and a late signal, respectively, of the remote pilot signal. The correlator means also multiplies the remote composite signal by the information reference signal to correlate out the remote user information channel.

The tracking device tracks the phase of the remote pilot signal and outputs a capture signal in response to the peak of the remote pilot signal. The acquisition signal represents synchronization of the remote pilot signal with the base station pilot reference signal.

In response to the acquisition signal, the range delay means calculates a phase difference between the base station pilot signal and the base station pilot reference signal to determine a range between the mobile station and the base station. The base station transmitting means transmits the distance from the base station to the mobile terminal through a forward channel of the duplex radio channel.

In response to the distance information received from the base station, code phase adjustment means at the mobile terminal adjusts the phase of the pseudo noise code to determine the time of arrival of spread spectrum processed remote message data at the base station.

In adjusting the phase of the pseudo noise code, the remote spread spectrum processing device may adjust the pseudo noise code in code chip increments. The base station processor compares the signal strength levels of the spread spectrum processed remote message data as the mobile terminal adjusts the pseudo noise code. In response to a code chip increment that maximizes operating characteristics, the base station calibrates the relationship between the remote pilot signal and the spread-spectrum-processed remote-message data having the code chip increment.

The spread spectrum CDMA cellular wireless communications system may further include base station spreading means and base station combining means. The base station spreading means spreads the spectrum to process the base station message data. The base station extension means may include means for processing base station message data for a particular mobile terminal with a selected chip code. The base station combining means combines the spread spectrum processed base station message data and the base station pilot signal into one composite base station signal. The composite base station signal includes a common spread spectrum pilot signal and at least one dedicated spread spectrum user information channel for each mobile terminal. The spreading code of each of the shared spread spectrum pilot signal and the dedicated spread spectrum user information channel may comprise one orthogonal symbol. The remote pilot signal may be slaved to the common spread spectrum pilot signal as a reference for the phase and timing of the remote pilot signal.

The remote pilot signal and the spreading code of the remote user information channel for each mobile terminal may comprise an orthogonal symbol. In addition, the remote user information channel may be synchronized to the remote pilot signal.

The system may also include base station delay lock loop means for generating an error signal and tracking the remote pilot signal. The mobile terminal adjusts the phase of the orthogonal pseudo noise code in response to the error signal received from the base station so as to compensate for the change in distance as the mobile terminal moves within the cell.

More particularly, the mobile terminal of the present invention includes a remote user data source, a first orthogonal code set generator, a first type of noise code generator, a remote pilot data source, a signal combiner, a first modulo-2 adder, a second modulo-2 adder, a third modulo-2 adder, a fourth modulo-2 adder, a modulator, an antenna assembly, a code phase adjuster, and a processor.

The first modulo-2 adder is coupled to a remote user data source and to a first orthogonal code set generator. The second modulo-2 adder is coupled to an output of the first modulo-2 adder and to the first class of noise code generator. The third modulo-2 adder is coupled to the first orthogonal code set generator and the remote pilot data source. The fourth modulo-2 adder is coupled to an output of the third modulo-2 adder and to the first class noise code generator. The signal combiner is coupled to the fourth modulo-2 adder and the second modulo-2 adder. The modulator is coupled to the signal combiner. The code phase adjuster is coupled to the first orthogonal code set generator and the first type noise code generator. The processor is coupled to the code phase adjuster.

A remote user data source generates a user data signal. A first orthogonal code set generator generates a first orthogonal code and a first remote pilot code. A first modulo-2 adder spreads the spectrum processed user data signal with a first orthogonal code to produce a spread signal. A first type of noise code generator generates a first pseudo noise code. A second modulo-2 addition processes the spread signal with the first pseudo-noise code to produce a spread spectrum user data signal.

A remote pilot data source generates a pilot data signal. The pilot data signal may consist entirely of 1 s. Alternatively, the remote pilot data source may generate a pilot data signal consisting entirely of 0 s.

The third modulo-2 addition processes the pilot data signal using the first remote pilot code spread spectrum to produce a spread pilot signal. The fourth modulo-2 addition processes the spread pilot signal with the first pseudo noise code to produce a remote spread spectrum pilot data signal.

A signal combiner combines the remote spread spectrum pilot data signal and the spread spectrum user data signal into a combined spread spectrum data signal. The modulator modulates the combined spread spectrum data signal onto a carrier to become a combined spread spectrum modulated data signal. The antenna apparatus transmits the combined spread spectrum modulated data signal on a reverse channel of a duplex radio channel. The antenna apparatus also receives a composite spread spectrum modulated carrier signal transmitted from the base station on a forward channel of the duplex radio channel. The composite spread spectrum modulated carrier signal on the forward channel has a common spread spectrum pilot signal and a dedicated spread spectrum user information channel for the mobile terminal.

A code phase adjuster, responsive to input from the processor and the common spread spectrum pilot signal, adjusts the phase of the first orthogonal code to adjust the time of arrival of the spread spectrum user data signal at the base station. This phase adjustment operation adjusts the arrival time of the spread spectrum user data signal so that it is orthogonal to other arriving spread spectrum user data signals. The phase of the first remote pilot code is slaved to the common spread spectrum pilot signal to enable the base station to determine the distance between the base station and the mobile terminal using the round trip delay. The processor generates processor inputs and stores the distance between the base station and the mobile terminal.

The code phase adjuster may also adjust the phase of the first orthogonal code to have the same phase as the first pseudo noise code. The length of the first pseudo noise code is an integer multiple of the length of the first orthogonal code. The code phase adjuster may also shift the phase of the first remote pilot code in response to acquisition so that it is synchronized with the spread spectrum user data signal.

The mobile terminal of the present invention may further comprise a power divider, a second orthogonal code set generator, a second type noise code generator, a mode control and acquisition device, a clock generator, a fifth modulo-2 adder, a sixth modulo-2 adder, a first delay device, a second delay device, a first multiplier/correlator, a second multiplier/correlator, a third multiplier/correlator, a fourth multiplier/correlator, a delay-locked loop, and a phase-locked loop oscillator.

The mode control and acquisition device is coupled between the second orthogonal code set generator and the second type noise generator. The clock generator is coupled to the pattern control and acquisition device, the first orthogonal code set generator, and the first type of noise code generator. The fifth modulo-2 adder is coupled to the second orthogonal code set generator and the second type noise code generator. The sixth modulo-2 adder is coupled to the second orthogonal code set generator and the second type noise code generator. The first delay device is coupled to the fifth modulo-2 adder. The first, second, and third multiplier/correlators are each coupled to the power divider and the first delay device. The second delay device is coupled to the sixth modulo-2 adder and the processor. The fourth multiplier/correlator is coupled to the second delay device and the power splitter. The delay locked loop is coupled to the second and third multiplier/correlators. The phase locked loop oscillator is coupled to the first multiplier/correlator.

The power splitter splits the composite spread spectrum modulated carrier signal into a pilot channel and a data channel. A second orthogonal code set generator, responsive to commands from the base station, generates a plurality of locally generated pilot codes, any one of which, or any plurality of which, may be generated and/or used at any given time.

A second type of noise code generator generates a second pseudo noise code. The pattern control and acquisition device receives timing information from the base station and generates clocks for a second orthogonal code set generator and a second type noise code generator. The mode control and capture device also generates a synchronization signal. The clock pulse generator provides a synchronous clock signal. The clock pulse generator may have its own oscillator or may be locked to the clock from the mode control and capture device.

A fifth modulo-2 adder combines the first locally generated pilot code and the second pseudo-noise code to form a first local spread spectrum pilot reference signal. A sixth modulo-2 adder combines a particular orthogonal code and the second pseudo-noise code to form the first local spread spectrum information reference signal. A first delay device, responsive to the processor, delays the first local spread spectrum pilot reference signal to produce an on-time, an early, and a late signal of the first local spread spectrum pilot reference signal.

First, second and third multiplier/correlators multiply the composite spread spectrum modulated carrier signal with the on-time, early and late signals of the first local spread spectrum pilot reference signal to correlate out the on-time, early and late signals, respectively, of the common spread spectrum pilot signal. The second delay device provides an information reference signal that is synchronized with the on-time signal of the first local spread spectrum pilot reference signal. A fourth multiplier/correlator multiplies the composite spread spectrum modulated carrier signal with the first local spread spectrum information reference signal to correlate out the dedicated spread spectrum user information channel. The delay locked loop tracks the phase of the input common spread spectrum pilot signal and outputs a clock signal and a capture signal to the mode control and capture device in response to the correlation peak. The phase-locked loop oscillator focuses on the correlation peak and provides a coherent carrier reference to the local data detector and the delay-locked loop.

With the system just described, the base station can determine the distance between the base station and the mobile terminal by measuring the code phase difference between the common spread spectrum pilot signal and the first remote pilot code. The common spread spectrum pilot signal may contain orthogonal symbols. The first remote pilot code may also comprise orthogonal symbols.

In the spread spectrum CDMA digital cellular radio system of the present invention, the system also includes a base station. The base station comprises a base station user data source, a first orthogonal code set generator, a first class noise code generator, a first modulo-2 adder, a second modulo-2 adder, a system data source, a system data spreading device, a base station pilot frequency data source, a pilot frequency data spreading device, a signal combiner, a modulator, an antenna device, a pilot frequency reference signal generating device, a clock pulse generator, a distance delay device and a processor.

The first modulo-2 adder is coupled to a base station user data source and to a first orthogonal code set generator. The second modulo-2 adder is coupled to an output of the first modulo-2 adder and to the first class of noise code generator. The signal combiner is coupled to the pilot data signal spreading means, the system data spreading means, and the second modulo-2 adder. The modulator is coupled to the signal combiner. The clock generator is coupled to the first orthogonal code set generator and the first type of noise code generator. The distance delay means is coupled to an output of the pilot data spreading means and an output of the pilot reference signal generating means.

The base station user data source generates a base station user data signal. A first orthogonal code set generator generates a first orthogonal code and a first base station pilot code. A first modulo-2 addition processes the base station user data signal with a first orthogonal code spread spectrum to produce a spread signal. A first type of noise code generator generates a first pseudo noise code. A second modulo-2 addition processes the spread signal with the first pseudo noise code to produce a spread spectrum user data signal. The system data source generates system data to be transmitted to the plurality of mobile terminals. The system data spreading means spreads the spectrum processing system data. The base station pilot data source generates a base station pilot data signal. The pilot data signal spreading means spread spectrum processes the base pilot data signal with the first base pilot code into a common spread spectrum pilot signal.

The signal combiner combines the common spread spectrum pilot signal, the spread spectrum system data, and the spread spectrum user data signal into a combined spread spectrum data signal. The modulator modulates the combined spread spectrum data signal onto a carrier to become a combined spread spectrum modulated data signal. The antenna arrangement transmits the combined spread spectrum modulated data signal. The antenna apparatus also receives a plurality of composite spread spectrum modulated carrier signals transmitted from a plurality of mobile terminals, respectively. Each composite spread spectrum modulated carrier signal has a received remote spread spectrum pilot signal and an information channel for each mobile terminal.

The pilot reference signal generating means generates a pilot reference signal. The clock pulse generator maintains full system time. The range delay means calculates a phase difference between the pilot reference signal and the common spread spectrum pilot signal as a first value. The processor stores a first value and uses the first value to provide a processor output signal representative of the round trip delay to the mobile terminal.

The pilot data signal spreading means may comprise a third modulo-2 adder, and a fourth modulo-2 adder. The third modulo-2 adder is coupled to the first orthogonal code set generator and the base station pilot data source. The fourth modulo-2 adder is coupled to an output of the third modulo-2 adder and to the first class noise code generator.

The third modulo-2 addition processes the pilot data signal using the first base station pilot code spread spectrum to produce a spread pilot signal. A fourth modulo-2 addition processes the spread pilot signal with the first pseudo noise code to produce a common spread spectrum pilot signal.

The system data expansion means may comprise a fifth modulo-2 adder and a sixth modulo-2 adder. The fifth modulo-2 adder is coupled to the first orthogonal code set generator and the system data source. The sixth modulo-2 adder is coupled to an output of the fifth modulo-2 adder and to the first class noise code generator.

The first orthogonal code set generator generates a second orthogonal code. A fifth modulo-2 addition spreads the spectrum processed system data with a second orthogonal code to produce a spread spectrum data signal. A sixth modulo-2 adder processes the spread spectrum data signal with the first pseudo noise code to produce a spread spectrum system data signal.

The base station may further comprise a power divider, a second orthogonal code set generator, a second type noise code generator, a pattern control and acquisition device, a seventh modulo-2 adder, an eighth modulo-2 adder, a first delay device, a second delay device, a first multiplier/correlator, a second multiplier/correlator, a third multiplier/correlator, a fourth multiplier/correlator, a delay-locked loop, and a phase-locked loop oscillator.

The pattern control and acquisition device is coupled between the second orthogonal code set generator and the second type noise code generator. The seventh modulo-2 adder is coupled to the second orthogonal code set generator and the second type noise code generator. The eighth modulo-2 adder is coupled to the second orthogonal code set generator and the second type noise code generator. The first delay device is coupled to the seventh modulo-2 adder. The second delay device is coupled to the eighth modulo-2 adder and the processor. The first, second, and third multiplier/correlators are each coupled to the power divider and the first delay device. The fourth multiplier/correlator is coupled to the second delay device and the power splitter. The delay locked loop is coupled to the second and third multiplier/correlators. The phase locked loop oscillator is coupled to the first multiplier/correlator.

The power splitter splits the composite spread spectrum modulated carrier signal into a pilot channel and a data channel. The second orthogonal code set generator generates a third orthogonal code. A second type of noise code generator generates a second pseudo noise code. The mode control and capture device provides clock and control signals.

A seventh modulo-2 adder combines the assigned pilot orthogonal code and the second pseudo-noise code to form a first spread-spectrum pilot reference signal. An eighth modulo-2 adder combines the assigned data orthogonal code and the second pseudo noise code to form a first spread spectrum data reference signal.

A first delay device, responsive to the processor, delays the first spread spectrum pilot reference signal to generate on-time, early, and late signals of the first spread spectrum pilot reference signal. First, second, and third multiplier/correlators multiply the composite spread spectrum modulated carrier signal with the on-time, early, and late signals of the first spread spectrum pilot reference signal to correlate out the on-time, early, and late signals, respectively, of the received remote spread spectrum pilot signal.

The second delay device provides an information reference signal that is synchronized with the on-time signal of the first spread spectrum pilot reference signal. A fourth multiplier/correlator multiplies the composite spread spectrum modulated carrier signal with the information reference signal to correlate out the information channel.

The delay locked loop tracks the phase of the received remote spread spectrum pilot signal. In response to the correlation peak, the delay locked loop outputs a clock signal and a capture signal to the mode control and capture device. The phase-locked loop oscillator provides a coherent carrier reference to the local data detector and the delay-locked loop.

With the system just described, the base station can determine the distance to each mobile terminal by measuring the code phase difference between the common spread spectrum pilot signal and the received remote spread spectrum pilot signal.

The mobile terminal may adjust the code phase of the information channel of each composite spread spectrum modulated carrier signal in response to the round trip delay to coincide with a particular time stamp when the composite spread spectrum modulated carrier signal arrives at the base station. The base station may set the specific time stamp to an absolute value in time to satisfy the cellular orthogonality criterion.

As shown in fig. 7, the mobile terminal of the present invention includes a remote antenna 727, a remote data source 700, a remote pilot data source 701, remote quadrature code set generators 702, 740, noise-like code generators 703, 741, six modulo-2 adders 710 and 715, a combiner 716, a radio frequency modulator/converter 720, a clock generator 730, a processor 732, a code phase adjuster 731, a mode control and acquisition device 733, four band pass filters 754, 755, 756, 757, a bit synchronizer 759, a coherent detector 758, an integrate and dump circuit 760, a delay locked loop, two delay elements 752, 753, four multiplier correlators 725, 726, 728, 729, a phase locked loop oscillator 750, a power divider 722, a duplexer 721, and a carrier generator 719. Fig. 7 also shows processor input/output port 771, user data input port 770, and radio frequency input/output port 773.

The remote data source 700 of fig. 7 is information provided to the mobile terminal by a remote user. This information may be voice, data, fax, or any other form of information that a user wishes to send to another user, machine or system via his mobile terminal. The processor 732 also generates messages for use by the wireless system or other remote user and provides these messages to the remote user data source via the user data input port 770 where they are multiplexed with the user data. The remote user data source provides the multiplexed user data signal to a modulo-2 adder 710 where an assigned orthogonal code operating at a much higher bit rate than the user data is superimposed on the user data signal. The orthogonal code spreads the user data signal so that several similar signals can occupy the same frequency spectrum and be recovered at the base station. The modulo-2 adder 711 superimposes an additional PN code on the spread signal to make the resulting spread spectrum signal more like random noise. The PN code is generated by a noise-like code generator 703. The spread spectrum user data signal is combined with the spread spectrum pilot data signal in combiner 716. RF modulator/converter 720 places the combined spread spectrum data signal at carrier frequency W_CAnd (4) performing upper modulation. The spread spectrum modulated data signal is passed to the remote antenna 727 through the duplexer 721 which allows the remote antenna 727 to be used for transmission and reception. The remote antenna 727 transmits the composite spread spectrum modulated carrier signal over the air to the base station antenna apparatus from which it is received. Those skilled in the art will appreciate that it can be implemented in many other ways. For example, the orthogonal code and the noise-like code may be combined before adding them to the data. Modulation can be performed at baseband by using orthogonal carrier components and combining the components at radio frequency. Different PN codes may be used on different orthogonal components to increase the randomness of the composite signal. These are all techniques known to those skilled in the art.

The orthogonal code set generator 702 may generate any code belonging to a predetermined code set and is instructed by the processor 732 to generate a dedicated code. The processor 732 in turn receives instructions from the base station control device sent to it over a control channel via input/output port 771. As described above, the orthogonal code set generator 702 creates and generates the assigned codes, and the orthogonal codes are used to spread the user data signals in the modulo-2 adder 710. Orthogonal code set generator 702 also generates an orthogonal code for spreading the second allocation of pilot data signals in modulo-2 adder 712. The phases of the codes are adjusted independently, but the clock frequencies of the two codes are the same. After acquisition, the clock pulse generator 730 is slaved to the input received from the mode control and acquisition device 733, or base station timing and clock, for all modes of operation. During the acquisition mode, clock generator 730 uses an internal oscillator that operates at approximately the expected frequency to be received from the base station. This internal oscillator may be set slightly above or below the clock frequency to enable scanning of the incoming composite spread signal. Once captured, the mode control and capture device 733 provides a clock synchronization signal to the clock generator 730.

The phase of the orthogonal code may be adjusted to be the same as the phase of the pilot code input from the base station. This makes the transmitted user pilot signal appear as a reflection from the mobile terminal and the base station can measure the round trip delay to each particular mobile terminal. The round trip delay measured in code chips is transmitted to the mobile terminal and stored in the processor 732. One half of the round trip delay is the distance between the mobile terminal and the base station measured in code chips. The accuracy of the range can be improved by using increments of one-eighth or one-tenth of a chip multiple and determining the peak output power from the base station correlator and then transmitting the delay time to the mobile terminal with an accuracy of a fraction of a chip.

The mobile terminal has the ability to adjust the phase of the orthogonal code with a precision of a fraction of a chip, e.g., one eighth, one tenth or one sixteenth, under the instruction of the code phase adjuster 731, and the code phase adjuster 731 determines the phase of the received pilot signal and converts it to an initial state appropriate for the remote pilot spreading code, with the aid of the processor 732.

When the signal arrives at the base station, in order for the transmitted, reverse link, spread spectrum user data signals to be orthogonal to other transmitted spread spectrum user data signals, the phase of the code transmitted by each user must be adjusted to compensate for the different path lengths, or distances, to each individual user. Each mobile terminal has stored in its memory the distance to the base station. Using this information, processor 732 determines the phase adjustment required to cause the spread spectrum user data signal to arrive at the base station at a particular time. The code phase adjuster 731 then provides the initial code settings to the orthogonal code set generator 702 and starts the generator at the appropriate time. The base station user data channel calibration detector detects the error voltage to maximize coherent output power at an accuracy of a fraction of a chip, and transmits a correction signal to the mobile terminal providing incremental adjustments to the user data quadrature code phase to fine tune the relative position of the transmitted signal. These incremental adjustments compensate for normal movement of the mobile terminal and track the mobile terminal as it moves through the area, using the pilot tracking error signal.

Rapid changes in code phase require re-acquisition of the data signal by repeating the range measurement technique with the pilot as described above. The noise-like code generator 703 is phase adjusted by a code phase adjuster 731 to have the same phase as the orthogonal code set generator 702. Since the noise-like PN code is much longer than the orthogonal code, the orthogonal code and the noise-like PN code are adjusted to appear to start at the same time, the orthogonal code will repeat multiple times during each cycle of the noise-like PN code, and they will end at the same time. Thus, they both start at the start of a signal epoch, which is the length of the noise-like PN code. The length of the orthogonal code is an even integer of the longer noise-like PN code. All users use the same noise-like PN code and become the digital carrier for all user data signals. When the noise-like PN code is synchronously detected, the resolution between different orthogonal codes is not influenced.

The above processing results in a transmitted user data signal and a transmitted pilot having different absolute phases with respect to the system time reference. Thus, the pilot spread spectrum signal cannot be orthogonal to the user data signal, which means that if half of the signal appears as random noise and the other half does not cause interference, then the interference has been reduced by 3db, assuming that each user terminal also has a pilot signal. The pilot data from the remote pilot data source 701 may all be 0 s, all be 1 s or actually have a low data rate information signal input onto the pilot channel. Assuming an "all 1" input to the remote pilot data source 701, the pilot channel transmits only the addition of the orthogonal code selected for the pilot and the noise-like PN code.

As described above, the phase and timing of the remote pilot is slaved to the input pilot from the base station. The pilot is slaved so that it appears without delay as it passes from the mobile terminal. This is a key feature of the present invention and enables the base station to accurately measure the round trip delay. The base station provides this round trip delay information to the mobile terminal, which uses this information to adjust the phase of the transmitted user data signal during acquisition, thus enabling the base station to quickly acquire the user data signal in the quadrature mode of operation. Since the mobile terminal uses the same carrier for both the pilot and user data signals, the pilot carrier is used to detect the user data coherently. As described above, after acquisition, range information from the pilots is not necessary during normal transitions of the data pattern. Accordingly, the mobile terminal includes a mode for use after acquisition has occurred in which the pilot code phase is shifted to have the same phase as the user data channel. In this mode, if the assigned pilot code is an entry of an orthogonal code set, then the pilots are also orthogonal. This feature of the present invention further almost doubles the system capacity. This also indicates that the pilot can be transmitted at a relatively high power level since the pilot does not cause interference to other signals. Although this does mean that the number of users has been reduced if the capacity is limited due to the limited number of orthogonal codes rather than the processing gain. Since this feature is controlled from the base station, the base station can make an estimate of which mode will give the best operating characteristics with the largest capacity and act accordingly.

The pilot data is modulo-2 added to the code assigned to the pilot in adder 712 to generate a spread spectrum reverse link pilot signal. A noise-like PN signal is also added to this signal at adder 713 and the pilot signal is made to behave more like a random noise spread spectrum signal at adder 713. The noise-like spread spectrum pilot signal is combined with the spread spectrum user data signal in combiner 716 to form a composite spread spectrum signal, which is then modulated onto a carrier in modulator/converter 720. This modulated composite spread spectrum signal passes through duplexer 721 to antenna 727.

The antenna 727 also receives a composite spread spectrum signal transmitted from the base station. This signal passes through duplexer 721, which isolates it from the transmit signal, and is separated into a pilot channel and a data channel in power splitter 722. The pilot channel may track the carrier and spreading code using three different correlators; these three correlators are formed by multipliers/correlators 726, 728, 729 plus integrator/bandpass filters 754, 756, 757. Delay-locked loop 751 tracks the phase of the incoming codes and synchronizes the local pilot code generated by the modulo-2 addition of the locally generated orthogonal and noise-like codes to the composite spread spectrum signal transmitted by the base station. The local pilot code is multiplied with the incoming complex spread signal in multipliers/correlators 726, 728, 729. Delay element 752 delays the reference pilots input to multipliers/correlators 726, 728, 729 in an appropriate manner so that an on-time, an early, and a late signal of the reference pilots are generated, respectively. Delay locked loop 751 tracks the input signal using early and late signals multiplied by multipliers/correlators 728, 729, respectively. When the code is phase aligned with the input signal from the power splitter to the three multipliers/correlators 726, 728, 729, a maximum signal appears at the output of each multiplier/correlator 726, 728, 729. When the input signal is thus tracked, the delay locked loop 751 sends a clock signal and a capture signal to the mode control and capture device 733. It will be appreciated by those skilled in the art that any equivalent error generating means may be used to perform the function of the delay locked loop.

Delay element 752 also provides an on-time path for use by phase-locked loop oscillator 750. The phase locked loop oscillator 750 focuses on the correlation peak and provides the maximum carrier signal strength. The data channel delay element 753 also causes the data channel to have the same alignment, on-time, and maximum carrier strength as the phase locked loop path. Phase-locked loop oscillator 750 provides a coherent carrier reference to coherent detector 758 and delay-locked loop 751. The orthogonal code set generator 740 provides an orthogonal code assigned by the base station via processor 732 to the modulo-2 adder 715 where it is combined with the output of the noise-like code generator 741 to form the local data spread spectrum reference signal. Since the base station pilot code and user data code channels are synchronized and transmitted on the same RF carrier, the phase of the local code and the carrier phase of the pilot channel after acquisition can be used to demodulate the user data channel. Delay element 753 delays the reference signal from adder 715 and multiplies the incoming received combined spread spectrum signal in multiplier/correlator 725 to correlate out the user data channel. The output of multiplier/correlator 725 is integrated in bandpass filter 755 so that the information channel arrives at correlation peak used by coherent detector 758 for detection. Integrate and dump circuit 760 integrates the output of coherent detector 758 over the information bit period. The integrate and dump circuit 760 samples the output at a time determined by the bit synchronizer 759. The bit synchronizer 759 is synchronized with the orthogonal code set generator 740 so that when the codes are synchronized, the data bits are also automatically synchronized. This occurs because the data in the base station transmitter is also synchronized with the base station orthogonal code generator. The output signal 775 is user data multiplexed with channel-specific additional data, which is separated from the data signal by a demultiplexer, not shown, and transmitted to the processor 732. Such additional data includes power control messages, code phase alignment messages, mode change messages, and the like. These messages are input to the processor via processor input/output port 771.

Orthogonal code set generator 740 is identical to orthogonal code set generator 702 and noise-like code generator 741 is identical to noise-like code generator 703. The orthogonal code set generator 740 and the noise-like code generator 741 are clocked by the mode control and acquisition device 733. Prior to capture, the mode control and capture device 733 provides timing to the code generator with a stable internal clock; after acquisition, PLL oscillator 750 is slaved to a clock derived from delay locked loop 751. The clock pulse generator 730 also depends on the output of the mode control and capture device 733.

As shown in fig. 8, the base station according to the present invention includes a base station antenna 827, a user data source 800, a pilot data source 801, orthogonal code set generators 802, 840, noise-like code generators 803, 841, eight modulo-2 adders 810, 818, a signal combiner 816, a radio frequency converter/modulator 820, a clock generator 830, a distance delay device 834, a processor 832, a controller 836, a code phase adjuster 831, a mode control and acquisition device 833, four band pass filters 854, 855, 856, 857, a bit synchronizer 859, a coherent detector 858, an integrate and dump circuit 860, a delay locked loop 851, delay elements 852, 853, four multiplying correlators 825, 826, 828, 829, a phase locked loop oscillator 850, a power divider 822, a multicoupler 821, and a carrier generator 819. Fig. 8 also shows processor input/output port 871, user data input port 870, user data output port 875, and radio frequency input/output port 873.

Fig. 8 is an illustrative diagram of a base station showing features of the invention. There are many similarities between the base station of fig. 8 and the mobile terminal of fig. 7. In the following discussion, the differences between the base station and the mobile terminal are emphasized.

In fig. 8, there are three data sources. In addition to the user data and pilot data as shown in fig. 7, system data transmitted to all users connected to the base station is required. This type of data includes general system parameters, paging information, system synchronization markers, control information, and channel assignments. Many of these system information originate at a network centric controller and are sent over landlines to base station controllers 836 adapted for the respective cells. The processor 832 works in conjunction with the controller 836 to access these messages to the base station. This is information that is typically broadcast so that all users can receive it before they are assigned to a dedicated channel.

System information transmitted to a specific user while the mobile terminal operates on an allocated channel is input to a user data device at the input port 870 and multiplexed with user data. In adder 817, the system data is also spread with the unique orthogonal code generated by orthogonal code set generator 802 and further randomized by adding an additional noise-like PN code in adder 818. The noise-like PN code is generated by a noise-like code generator 803.

There may be several system data channels, each spread with a unique orthogonal code, but all channels use the same noise-like PN code. The same noise-like PN code is added to all channels including all data channels, all system channels, and the pilot channel. There is only one pilot channel and it uses one of the unique orthogonal codes, usually all 0 codes. This indicates that the noise-like PN code is essentially a pilot code, but it is also a component of all other codes. The concept of pilots on the forward link is commonly accepted and documented in the prior art; see U.S. patent No. 5,228,056; us patent No. 5,420,896; U.S. patent No. 5,103,459 and U.S. patent No. 5,416,797. There are also several means of generating different pilots for different base stations, including deliberately introducing a fixed code phase shift; see U.S. patent No. 5,103,459 and U.S. patent No. 5,416,797.

For illustrative purposes, fig. 8 shows only one user data source 800, but there will typically be many user data sources or channels, one for each current user. Will assign a unique to each current userOrthogonal codes and each current user will use the same noise-like PN code. Thus, the input to combiner 816 will typically include a number of user data channels, a number of system channels, and a pilot channel. The output of combiner 816 is a composite spread spectrum signal that is applied to a carrier W in converter/modulator 820_CAnd (4) performing upper modulation. The modulated composite spread spectrum signal is transmitted by the multicoupler 821 to the base station antenna 827. The multi-way coupler 821 not only provides isolation between transmit and receive signals as is done in mobile terminals, but must also isolate multiple transmit signals from each other. An alternative approach is to combine low power level signals and use a linear amplifier in the final stage.

Clock generator 830 is derived from a stable oscillator and is the basic clock for the entire cell. Absolute time is maintained throughout the system. This absolute time at all base stations enables the mobile terminal to determine the absolute time delay to several base stations, resulting in an accurate geographical position determination. Clock pulse generator 830 clocks quadrature code generator 802 and noise-like code generator 803. It also clocks orthogonal code generator 840 and noise-like code generator 841 when the reverse link is operating in an orthogonal code mode. When the receiver is not operating in the orthogonal code mode and it has acquired an assigned user signal, the orthogonal code generator 840 and the noise-like code generator 841 use the clock generated by the delay-locked loop 851 as their clock source.

When the pilot receive channel has acquired the user pilot signal on the reverse link and delay lock loop 851 is tracking the input pilot signal, the reference pilot code generated by the addition of the outputs of orthogonal code set generator 840 and noise-like code generator 841 in summer 814 is perfectly synchronized with the pilot signal from the user. When this occurs, the output of summer 814 is accepted by range delay device 834 and the phase of this pilot code is compared to the phase of the base station pilot code obtained from the output of summer 813. With the aid of the processor 832, the range delay device 834 calculates the phase difference between the two signals and stores this value in a memory in the processor 832. The round trip delay value is also communicated to the mobile terminal that is transmitting the user pilot signal through the input port 870 of the user data source 800 or as part of the assignment channel setup command.

When the mobile terminal is in the pilot ranging orthogonal mode of operation, the base station sends the user terminal ranging information and the user terminal sends back user data on the return link in the orthogonal mode. There may be a small fixed offset between the pilot channel distance measurement and the correct phase to achieve maximum noise reduction on the quadrature channel. To remove this offset, processor 832 sends a command to the mobile terminal to move the phase relationship between the user pilot and the user data channel by a fraction of a chip, e.g., one eighth, one tenth, or one sixteenth, while processor 832 observes the output level of integrate and dump circuit 860. When a peak output signal level is observed, the offset is locked and held. This process calibrates the relationship between the user pilot and the user data channel. Once the optimum result is reached, this relationship is no longer significantly changed during normal transmission. It can always be reconstructed after a fixed time interval.

When the mobile terminal is in a mode that also transmits an orthogonal pilot synchronized to the user data channel, the delay lock loop 851 error voltage is fed to the processor 832, analyzed and compensated with a predetermined component, and transmitted to the mobile terminal for correction of the phase of the composite signal transmitted back by the mobile terminal. Since the error is detected at the base station and the correction is made at the mobile station, there is an inherent delay in the loop. However, this delay is small compared to the normal movement of the user, and since the user's movement does not generally change direction rapidly, a prediction can be made from the last measurement. If the path length has a sudden jump of several chips, the mobile terminal is commanded to return to the previous mode and reacquire using the ranging information. This occurs only if a strong primary multipath radiation fades rapidly and there are no existing secondary rays, but a new secondary ray appears immediately after the primary ray disappears.

Therefore, according to the present invention, the base station receiver can receive data from the mobile terminal in one of four modes. The first mode enables the mobile terminal to transmit a separate user pilot on the reverse link that is not synchronized with the base station, and the user data channel is synchronized with this separate user pilot. The second mode requires that the user terminal slaves its user pilot to the pilot it receives from the base station and that the user data channel is synchronized with this slaved user pilot. The second mode enables the user terminal to receive round trip delay information for purposes of geolocation and rapid reacquisition. The third mode requires the user terminal to have its user pilot slaved to the incoming base station pilot as in the case of mode 2, but the user data channel operates in an orthogonal mode using the ranging information received from the base station. Calibrating the phase relation between the user pilot channel and the user data channel; one technique is described above, but many others will be known to those skilled in the art. The user pilot carrier is also a carrier for the user data channel and can be used as a carrier reference for detecting the user data channel. The fourth mode performs acquisition using the pilot-slaved scheme of mode 3, but after acquisition, the phase of the user pilot code is shifted to be synchronized with the user data channel, so the pilot is also made to be one orthogonal channel. This means that the pilots no longer cause interference to the user data channels within the cell and can be transmitted at higher power levels.

The present invention may further comprise a spread spectrum CDMA cellular wireless communications method for transmitting remote message data from a mobile terminal to a base station over a duplex wireless channel. The method includes using pilots on the return link to achieve orthogonality at the base station antennas.

The method comprises the following steps: the method includes the steps of spread spectrum processing remote message data using a pseudo noise code, generating a remote pilot signal, and combining the remote pilot signal with the spread spectrum processed remote message data to generate a remote CDMA signal. The remote-CDMA signal includes a remote pilot signal and a data signal.

The method then comprises the steps of: transmitting a remote-CDMA signal from the mobile terminal to the base station on a reverse channel of the duplex radio channel; the base station receives the remote-CDMA signal and separates the remote-CDMA signal into a pilot channel and a data channel. The method then comprises the steps of: generating a base station pilot signal and generating a base station pilot reference signal; separating and delaying the base pilot reference signal to produce an on-time signal of the base pilot reference signal, an early signal of the base pilot reference signal, and a late signal of the base pilot reference signal; an on-time, an early, and a late signal of the remote pilot signal are correlated using the on-time, early, and late signals of the base pilot reference signal, respectively.

The method then comprises the steps of: generating a base station data reference signal and correlating the data signal with the base station data reference signal; tracking the phase of the remote pilot signal and outputting a capture signal indicating synchronization of the remote pilot signal with the base station pilot reference signal in response to a peak in the remote pilot signal; in response to the acquisition signal, the remote pilot signal may be shifted in phase to synchronize with the data signal. The remote pilot signal may also be slaved to the base station pilot signal.

The method then comprises the steps of: measuring a code phase difference between a base station pilot signal and a base station pilot reference signal in response to the acquisition signal to determine a distance between the mobile terminal and the base station; the distance is transmitted to the mobile terminal, and in response to the distance, the mobile terminal adjusts the phase of the pseudo noise code, thereby adjusting the time of arrival of the data signal at the base station and achieving orthogonality at the base station.

It will be apparent to those skilled in the art that various modifications can be made to the spread spectrum communication system and method of the present invention without departing from the scope or spirit of the invention, and it is intended that the invention encompass modifications and variations of the spread spectrum communication system and method described herein insofar as they come within the scope of the appended claims and their equivalents.

Claims (2)

1. A wireless code division multiple access system for geographically locating mobile terminals, the system comprising:

a plurality of base stations having fixed locations, each base station comprising:

a transmitter configured to transmit a first spread spectrum signal, the first spread spectrum signal having an associated base station pilot reference signal;

a receiver configured to receive a second spread spectrum signal, the second spread spectrum signal having an associated remote pilot signal;

a transmitter configured to output an acquisition signal indicating that the first spread spectrum signal is synchronized with the second spread spectrum signal;

wherein each base station is configured to separate and delay the base pilot reference signal to produce an on-time signal of the base pilot reference signal, an early signal of the base pilot reference signal, and a late signal of the base pilot reference signal, the on-time signal, the early signal, and the late signal of the base pilot reference signal being used to correlate out the on-time signal, the early signal, and the late signal of the far-end pilot signal, respectively;

wherein each base station is configured to determine a distance between the mobile terminal and the base station by measuring a code phase difference between the first spread spectrum signal and the second spread spectrum signal in response to the acquisition signal; and

the transmitter is further configured to transmit the distance to the mobile terminal; and

the mobile terminal includes:

a receiver configured to receive the first spread-spectrum signal from the base station;

a transmitter configured to transmit the second spread spectrum signal, the second spread spectrum signal having its associated remote pilot signal time-synchronized with the first spread spectrum signal, wherein the second spread spectrum signal has its associated remote pilot signal time-synchronized with the first spread spectrum signal via an associated base station pilot reference signal utilizing the first spread spectrum signal;

wherein the receiver of the mobile terminal is further configured to receive said distance from at least one of said base stations; and

wherein the transmitter of the mobile terminal is further configured to transmit a third spread spectrum signal having a timing adjusted in response to the distance, wherein the third spread spectrum signal includes a data bearer channel and a pilot bearer channel.

2. The system of claim 1, wherein the base stations are synchronized in timing with each other.