HK1067818B - Diversity gain with a compact antenna - Google Patents

Description

Diversity gain for small antennas

Background

FIELD

The present invention relates generally to wireless communication systems, and more particularly to canceling interference from received signals in a wireless communication system.

Background

A typical wireless communication system will include a plurality of remote stations and a plurality of base stations. Generally, the communication system is bi-directional — a remote station receives signals from a base station and the remote station transmits signals to the base station. To facilitate receiving and transmitting signals over the wireless channel, the remote station includes a receiver and a transmitter.

The function of this receiver in the remote station is: the number of desired signals received is maximized while minimizing the number of any unwanted or interfering signals received. Typically, the desired signal is a radio wave from one (1) sector of three (3) sector base stations in close proximity to the remote station. The desired signal carries information to be decoded and used by the remote station. The unwanted or interfering signals include signals from the other two (2) sectors of the base station that "leak" into the serving sector. In addition, the unwanted or interfering signals may come from disparate base stations located nearby that are carrying transmitted information intended for other remote stations in the communication system. Signals received by a remote station intended for other remote stations may interfere with the reception of the desired signal by the remote station, making decoding of the desired signal more difficult.

Unwanted effects include "interference" and "fading". "interference" refers to all unwanted power "picked up" by the receiver in the remote station. "fading" is essentially a self-interference due to the multipath characteristics of the wireless channel. Typically, the desired signal will follow many paths to the remote station, as the desired signal radio waves "bounce" off buildings, cars, trees, etc. near the remote station. These multipath signals arrive at the remote station with an arbitrary set of phases, so that, from time to time, these signals add constructively, the signals are in phase, and receive additional power. Other times, these signals add destructively; these signals are out of phase, tending to cancel each other; and, receive lower power. The division may be such that for a highly dispersive environment, the multipath signal power may drop in strength to 1/100 which is the average over approximately 1% of the time. To compensate for the power loss in the multipath signal, the base station would need to transmit 100 times more power (as if there were no fading) to keep the receiver on for 99% of the time.

Therefore, there is a need in the art for an efficient method for combining signals in remote stations to maximize the available signals.

SUMMARY

Embodiments disclosed herein address the above stated needs by combining highly correlated signals in a remote station to maximize the available signals.

A remote station for use in a wireless communication system includes a receiver and a highly correlated multiple element small antenna. The multi-element antenna is configured to receive signals from at least one base station. The receiver includes a search engine configured to: a signal is received from each element of the antenna and a spatial signature (including the amplitude and phase of the received signal at each antenna element) is determined. The receiver also includes a weight factor engine that determines a set of weight factors for each base station signal in response to the spatial characteristics of the received signal. A combiner combines the signals received from each of the plurality of elements in the antenna using the weight factors to produce an optimal combined signal.

Brief Description of Drawings

Fig. 1 is a representative diagram representing a typical modern wireless communication system.

Fig. 2 is a representative diagram showing a cellular communication system.

Fig. 3 is a block diagram representing a typical handset with two highly correlated antennas.

Fig. 4 is a representative graph showing received signal strength at each antenna of a multiple antenna array.

Figure 5 is a block diagram illustrating one embodiment of a highly correlated antenna that may be used in a remote station.

Figure 6 is a block diagram of one embodiment of a dual antenna receiver in a remote station.

Figure 7 is a block diagram of one embodiment of a controller suitable for use in a dual antenna receiver in a remote station.

Detailed Description

A wireless communication system may include a plurality of remote stations and a plurality of base stations. FIG. 1 illustrates one embodiment of a terrestrial wireless communications system having three remote stations 10A, 10B and 10C and two base stations 12. In fig. 1, the three remote stations are shown as mobile telephone devices installed in a car 10A, a portable computer remote station 10B, and a fixed location remote station 10C such as might be found in a wireless local loop or meter reading system. The remote station may be any type of communication device, such as a handheld personal communication system device, a portable data device (e.g., a personal data assistant), or a fixed location data device (e.g., a meter reading equipment). Fig. 1 shows a forward link 14 from a base station 12 to a remote station 10 and a reverse link 16 from the remote station 10 to the base station 12.

Communication between the remote station 10 and the base station 12 over a wireless channel may be accomplished by using one of a variety of multiple access techniques that facilitate a large number of users in a limited frequency spectrum. These multiple-access techniques include Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and Code Division Multiple Access (CDMA). The industry standard for CDMA IS set forth in the "TIA/EIA temporary standard" (TIA/EIA/IS-95) and its derivatives (collectively referred to herein as "IS-95"), entitled mobile station-base station compatibility standard for dual mode wideband spread spectrum cellular systems, which are incorporated herein by reference in their entirety.

Generally, in a wireless communication system, signals are communicated between a series of base stations and a plurality of remote stations. For example, each base station transmits signals to remote stations located within the coverage area (also referred to as "base station cells") of the base station. A remote station located within the coverage area of a base station typically communicates with that base station (the remote station's preferred base station). A handoff occurs when a mobile remote station moves from the coverage area of a first base station to the coverage area of a second base station. When a handoff is performed, the remote station begins communication with the second base station and establishes the second base station as its preferred base station.

Figure 2 illustrates the coverage area of a plurality of base stations in a cellular-based communication system or network 19. In fig. 2, a remote station 20 is located within the coverage area of a preferred base station 22. Also shown in fig. 2 are neighboring base stations 24 and 26 and their respective coverage areas. As described above, the remote station 20 remains in communication with its preferred base station 22 as long as the remote station 20 remains within the coverage area of the preferred base station. If remote station 20 relocates to the coverage area of another base station (e.g., neighboring base station 24), then the remote station establishes base station 24 as its preferred base station and performs the handoff procedure. As the remote station passes through the cellular network 19, it will perform such a handover procedure as it moves from the coverage area of one base station to the coverage area of another. Although the coverage areas in fig. 2 are shown as being omni-directional, the coverage areas may be divided into sectors with the same base station using directional antennas to divide its coverage area into smaller sectors.

In a wireless communication system, a communication signal may travel along several distinct propagation paths as it travels between a base station and a remote station. In a wireless channel, multipath signals are created if the signal reflects off obstacles in the environment (e.g., buildings, trees, cars, and people). Multipath signals generated by the characteristics of the wireless channel present challenges to the communication system. One characteristic of a wireless channel that suffers from multipath effects is the time spread introduced in the signal being transmitted through the channel. For example, if an ideal pulse is transmitted over a wireless channel, the received signal appears as a stream of pulses with one pulse per multipath propagation path. Another characteristic of the multipath channel is: each path through the channel may subject the signal to a different fading factor. For example, if an ideal pulse is transmitted over a multipath channel, each pulse of the received pulse stream typically has a different signal strength than the other received pulses. Another characteristic of the multipath channel is: each path through the channel may cause a different phase on the received signal. For example, if an ideal pulse is transmitted over a multipath channel, each pulse of the received pulse stream typically has a different phase than the other received pulses.

Accordingly, the wireless channel is typically a time-varying multipath channel due to the relative motion of the various structures that create the multipath. For example, if an ideal pulse is transmitted over the time-varying multipath channel, the received pulse stream may vary in delay, fading, and phase as a function of the time that the ideal pulse is transmitted.

The multipath characteristics of the wireless channel can affect the received signal and, in particular, cause fading of the signal. Fading is a result of the phase variation characteristics of the multipath channel. Fading occurs when multipath vectors add destructively, causing the received signal to have a smaller amplitude than either vector alone. For example, if a sine wave is transmitted over a multipath channel with two paths, where the fading factor of the first path is x dB and the time delay is δ (with a phase shift of θ radians); the fading factor of the second path is x dB and the delay is delta (with a phase shift of theta + pi radians), then no signal is received at the output of the channel because the two signals (with the same amplitude and anti-phase) cancel each other out. Thus, fading (a type of self-interference or intra-cell interference) can have a severe negative impact on the performance of the wireless communication system.

Another feature of the cellular communication system is: interference from signals transmitted by other base stations; alternatively, the same base station is transmitting to different sectors of its coverage area, causing intra-cell interference. Intra-cell interference is typically maximized when the remote station is near a cell boundary where the signal level of the preferred base station is typically weakest and the interfering signals from neighboring base stations are maximized.

Intra-cell and inter-cell interference limits the system capacity of the forward link of a wireless communication system. For example, in a CDMA-based communication system, signals from the same base station are separated by a set of orthogonal codes (Walsh codes) that tend to minimize interference with signals of other users in the same base station cell. However, other signals from the preferred base station may still cause self-interference or fading. In addition, signals from neighboring base stations are identified by special short pseudo-random noise (PN) codes. All base stations use the same (but with different shifts) PN code. However, there is interference between cells due to non-zero autocorrelation.

One way to deal with the fading problem already mentioned is to: there are two separate antennas at the receiver. A separate antenna is a structure that produces separate signals or multiple signals. The separate antennas may be distinct antennas or may be multiple elements within a single antenna array.

The approach of using two separate antennas at the receiver is based in part on this concept: the two antennas will typically not receive the signal experiencing the "deep fade" simultaneously. If the two antennas are not completely correlated (not causal or complementary to each other), then fading effects can be reduced by determining the antenna with the strongest signal level and receiving the signal from that antenna for processing. In general, the two antennas will not be completely uncorrelated, but generally there must be a low degree of correlation (e.g., less than 0.7 envelope correlation). Envelope correlation is a commonly used measure of the correlation between two antennas. An envelope correlation of 1.0 indicates that: the two antennas are fully correlated and thus produce the same output signal. An envelope correlation value of 0 indicates: the two antennas are completely uncorrelated and the output signals of the two antennas are independent of each other.

If the envelopes of the two antennas are correlated by more than 0.7, then the signals received by the two antennas are highly correlated and the antennas may receive signals that are experiencing fading at the same time. Thus, the highly correlated antenna cancels the effectiveness of a two antenna system in a fading, multipath, communication environment.

The main method of making two antennas uncorrelated is by physically separating the two antennas. If the two antennas are separated, the correlation of the antennas may be reduced because the signal path from the transmitter to each of the antennas is different. Since the signal paths are different, the multipath signals or multipath vectors will add differently at each antenna. These multipath vectors represent the amplitude and phase of the received multipath signal. Thus, while these multipath vectors may add destructively, causing the received signal to be much smaller at one antenna (deep fading), the multipath vectors at the other antenna will be different, resulting in a different sum that will not be simultaneously subject to fading.

Typically, the antenna uncorrelation is achieved by spacing the antennas from each other by at least 0.2 λ of the communication signal (where λ is the wavelength of the signal). For receivers with uncorrelated antennas, several methods have been proposed to combine the antenna output signals in order to maximize the received signal strength. One approach is commonly referred to as "maximum ratio combining" (MRC), Joseph c.liberti, Jr and Theodore s.rappport wireless communication: the method IS described in IS-95 and smart antennas for third generation CDMA applications, which are incorporated herein in their entirety. In the MRC method, each signal received by the antennas is adjusted in its amplitude and phase by a set of weight terms. These adjusted signals are then combined. These weight terms are selected so as to maximize the signal-to-noise ratio (SNR) of the desired signal. However, MRC methods do not provide the ability to reject interfering signals, since these weighting factors are chosen to maximize the power of the desired signal, which may also increase the power of these interfering signals.

Another method of combining uncorrelated antenna signals is known as "best combining" (0C) or "Wiener-Hopf". In OC, a weight factor is determined that maximizes the quality of the signal or the signal-to-interference ratio (produced by combining the signals received by the two antennas). See wireless communications by Joseph c.liberti, Jr and Theodore s.rapppoport: IS-95 and smart antennas for third generation CDMA applications. The choice of the weighting factors has a significant impact on the ability to suppress interference.

The various methods described above for combining signals received by two antennas have been used for uncorrelated antennas. However, the size of remote station receivers (especially handsets) is decreasing. The reduced size of the receiver makes it difficult to position the antennas with sufficient separation (0.2 λ) to produce uncorrelated antenna signals.

Fig. 3 is a block diagram representing a typical handset 32 according to one embodiment, the typical handset 32 having highly correlated antenna elements 34 and 35. The two antenna elements 34 and 35 are connected to a diplexer 36. The duplexer passes signals from the transmitter circuit 37 to the two antenna elements 34 and 35 or from the two antennas to the receiver circuit 38. The transmitter circuit 37 interfaces with the receiver circuit 38 and is controlled by a controller 39. There is a high degree of correlation between the two antennas 34 and 35 because the elements 34, 35 that make up the dual antenna are placed close together.

Although fig. 3 shows two antenna elements 34, 35, the antenna may be comprised of any desired number of elements. For example, a multiple antenna array may consist of three antennas, four antennas, five antennas, or any desired number of antennas.

Fig. 4 is a representative diagram showing an interference field of a multipath signal received at each antenna of a multiple antenna array. In fig. 4, the vertical axis represents the signal intensity at each position as represented by the horizontal axis. The interference field 40 exhibits a plurality of peaks and valleys or fades corresponding to the areas of the constructive and destructive summation of these multipath signal instances, respectively. As shown in fig. 4, if multiple antennas (e.g., two antennas) are sufficiently spaced, it is unlikely that the two antennas will be located at a position that places the interfering field in a fading condition.

For example, in fig. 4, the signal strength at two different locations is shown for two antennas in the array. At a first location 42, the signal strength 43 at the first antenna is stronger than the signal strength 44 at the second antenna. Thus, the signal strength 44 at the second antenna is in a fading state, while the signal strength 43 at the first antenna is not in a fading state. The received signal strength at the two antennas differs, in part, due to the physical separation of the two antennas. As the receiver with the two antennas moves around, changing position, the signal levels at the two antennas will change. For example, if the two antennas are moved to a second position 46, the signal strengths at the first and second antennas correspond to signal strengths 47 and 48, respectively. In this example, if the receiver is moved from the first position 42 to the second position 46 such that at the second position 46 the first antenna is in a fading condition and the second antenna is not in a fading condition, the relative signal strengths of the two antennas are reversed.

As can be seen from fig. 4, the physical spacing of the various antennas in the antenna array contributes to the antennas having different signal strengths, and thus, the antennas are uncorrelated. As the spacing between antennas in an antenna array decreases, antenna correlation increases as the strength of the signals received by the two antennas approaches the same strength. In a typical interference field, the minimum separation between the peaks and valleys is about 0.25 λ. A spacing of 0.25 lambda or greater is typically used between the individual antennas in the antenna array and may result in an envelope correlation of less than about 0.7.

In a multipath environment, the antennas of a highly correlated antenna array are more likely to experience "deep fading" simultaneously. In highly correlated antenna systems, there is little phase difference between the individual signals received by each of these antennas. This results in a phase relationship of the multipath vectors received at nearly identical respective antennas. Thus, if these multipath vectors of the received signal add destructively at one antenna, causing deep fading, the vector sum of the multipath signals at the other antennas may also experience deep fading.

Furthermore, highly correlated antennas do not have as high "array gain" -a capability: the signals received from the multiple antenna elements are summed to sum the desired signal in phase and the interfering signal non-coherently. Typical interfering signals include adjacent base station signals (commonly referred to as "interference") received by the antenna. High array gain improves the ability of the receiver to reject interfering signals and improves the ability of the receiver to operate in a multipath environment. Conventionally, antennas designed to have high array gain and high diversity gain require that individual antenna elements be uncorrelated. Typically, this requires a large spacing between the individual antennas or antenna elements.

In a wireless communication system, it may be beneficial to use highly correlated antennas at the remote station and the base station. In particular, in remote stations, multiple antenna systems will typically be highly correlated. For example, remote stations (e.g., handheld wireless communication receivers) impose spatial constraints that may make it impractical to have sufficient antenna spacing to create uncorrelated antennas.

Techniques to improve the array and diversity gain of highly correlated antennas include: signals are received from the two antennas. In one embodiment, the signals from each of the two antennas are processed by separate receive circuitry. Then, the outputs of these receiving circuits are combined.

The complex signals at the outputs of the two antennas contain amplitude and phase information of these signals. The complex covariance matrix R is estimated using the complex signals.

The complex signal at the output of the two antenna receivers is used to estimate the complex spatial signature "c" of the desired signal. The complex spatial signature of a signal includes the signal amplitude and angle of arrival (AOA) of the signal. In CDMA based communication systems, a RAKE receiver is typically used. In a RAKE receiver, the complex spatial signature is estimated separately for each signal assigned to a receiver element or finger of the RAKE. For each finger of the RAKE, a weight vector is determined according to the following equation:

w＝((R-Rs)^-1)c

where Rs is a matrix formed by taking the outer product of c with a c-Hermite conjugate. Alternatively, w ═ R^-1c will provide similar results.

The weight vectors are used to condition the signals before the RAKE receiver receives them from the antennas. The signal received by each finger of RAKE receiver vc (t) is adjusted such that:

Vc(t)＝w1^*V1(t)+w2^*V2(t)

where V1(t) is the complex voltage current of antenna 1 and V2(t) is the complex voltage current of antenna 2. Weight term w1^*Is the complex conjugate of the first element of w as defined above. Weight term w2^*Is the complex conjugate of the second element of w as defined above.

The tests have indicated that: the above techniques may improve the sensitivity of a remote station receiver in a CDMA based wireless communication system by a factor of about 2, with diversity gain and interference gain. The test results have also indicated that: the gain provided by MRC combining in each case tested is greatly reduced.

The techniques described above may be used for antennas that are closely spaced to each other and thus highly correlated. In estimating the complex covariance matrix R, the high correlation of these signals is accounted for. Thus, even if there is only a small difference between the two signals, the weighting can be chosen to take advantage of this small difference. For example, the weighting selected as above would have the form:

w1＝1+z，w2＝-1+zORw1＝1-z，w2＝-1-z

where z is a small non-zero complex number. The value of z is based in part on the amount of correlation between the two antennas. For example, two highly correlated antennas would result in a smaller value of z, while two less highly correlated antennas would result in a larger value of z.

With respect to the example described above, there are two possible combined voltage streams that may be sent to the RAKE receiver. The two voltage streams correspond to the values of the two sets of possible weight terms. These corresponding voltage flows are:

VC1(t)＝(V1(t)-V2(t))+z^*(V1(t)+V2(t))

VC2(t)＝(V1(t)-V2(t))-z^*(V1(t)+V2(t))

the correlation between these two voltage currents is very small. The following will aid understanding: how to adjust the two highly correlated antenna signals so that they are no longer correlated. Since the two antennas are highly correlated, V1(t) and V2(t) have strong common modes. The strong common pattern between V1(t) and V2(t) means: to a large extent, both signals will change level together. Due to the strong common mode component in the two signals, the difference between the signals, V1(t) -V2(t), will be a small value. Further, z is a small value. Thus, if the sum of the two signals is multiplied by z (z × (V1(t) + V2(t))), the resulting product will be a small value. The values of z (V1(t) + V2(t)) and V1(t) -V2(t) are both small and generally approximately the same size.

Weighting and combining the two antenna signals produces a result that roughly adds and subtracts voltages of similar magnitude. This technique takes advantage of the small difference between the two antenna signals V1(t) and V2 (t). Combining the two antenna signals in this manner may produce adjusted signals VC1(t) and VC2(t) that have nearly completely uncorrelated fading characteristics. In addition, diversity is achieved by selecting the stronger of the two signals.

Fig. 5 is an illustrative diagram of one embodiment of a highly correlated antenna 50 that may be used, for example, in a remote station 52. The embodiment shown in fig. 5 is a small "stick" antenna. The antenna 50 is a dual element antenna and is mounted on a remote station 52. Within the remote station 52 are two receivers 53 and 54 corresponding to each element of the antenna 50. The outputs of these receivers are connected to a controller 55, the controller 55 having been adapted to receive a plurality of antenna inputs. The antenna 50 is composed of two planar antennas 56 and 58. The two antennas 56, 58 may be separated by a low dielectric constant spacer (e.g., polystyrene).

The two antennas 56, 58 may be spaced apart by approximately 0.01 to 0.02 wavelengths. In one embodiment, the two antennas 56, 58 are spaced apart by 0.05 inches, which corresponds to about.01 wavelengths at the design frequency.

In other embodiments, antennas 56, 58 may take different configurations (e.g., adjacent whip antennas, dual whip (where the two antennas are in a single small plastic strip), dual feed plates, adjacent stubs (stubs) or whip (whisp), and coaxial stub antennas (stub antenna)).

Figure 6 is a block diagram of one embodiment of a dual antenna receiver in a remote station. Each antenna 34 and 35 is connected to an antenna switch 60 (for simplicity, the connection of the antennas is not shown). The antenna switch 60 routes signals from a transmitter (not shown) to both antennas 34, 35 and routes signals from the antennas 34, 35 to the receiver circuit. The output of the antenna switch 60 is connected to the receiver chain 53. In the receiver chain 53, the output of the antenna converter 60 is connected to a low noise amplifier 61, and the output is amplified in the low noise amplifier 61. The output of the low noise amplifier 61 is connected to a mixer 62. A second input to the mixer 62 is a first local oscillator. The mixer 62 combines the two signals and outputs an IF signal. The output of the mixer 62 is connected to a band pass filter 63, which attenuates the out of band parts of the signal in the band pass filter 63. The output of the band pass filter 63 is connected to an in-phase/quadrature (I/Q) detector 64.

In the I/Q detector 64, the bandpass filter output is passed to an in-phase (I) mixer 65 and a quadrature (Q) mixer 66. A second input to the I-mixer 65 is a second local oscillator. To a second input of Q-mixer 66 is a phase shift 90⁰The second local oscillator of (1). I mixer 65 and Q mixer 66 combine the bandpass filter 53 output and the second local oscillator signal and output the baseband I and Q components of the received signal, respectively. The I and Q components are passed to analog-to-digital converters (ADCs) 67 and 68 where the signals are digitized. These digital outputs or ADCs 67 and 68 are communicated to the controller 55 antennas 0 and 1 and I and Q inputs, respectively.

Figure 7 is a block diagram of one embodiment of a controller 55 suitable for use in a dual antenna receiver in the remote station. As described above, the I component and the Q component of the two antenna signals are input to the controller 55 at the antenna 0 and antenna 1 input terminals, respectively. The I and Q signals from antenna 0 and antenna 1 are communicated to search engines 70 and 72, respectively. Further, the I and Q signals from the two antennas are passed to a combiner 74. Within the search engines 70 and 72, the antenna signals are evaluated and the covariance and time delays of the signal-carrying fingers and the spatial signatures of the signals received by the fingers are determined as described above and according to known techniques.

The outputs of the search engines 70 and 72 are connected to a weight factor engine 76, in which weight factors are determined for each signal received by the fingers.

The combiner 74 receives the weight factor w from the weight factor engine 76₁And w₂. In addition, a combiner 74 receives the I and Q components of the two antenna signals. According to one embodiment, combiner 74 generally produces one of two possible voltage streams, VC1(t) and VC2 (t). The voltage stream having the higher signal-to-noise ratio is used. These two voltage streams are passed to demodulator 78. In the demodulator 78, the two voltage streams are demodulated.

It should be understood that: as used herein, the relationship of "antenna" to "antenna element" and the relationship of "antenna array" to "antenna" are the same. Throughout, these two sets of terms are always applied interchangeably.

The various steps described for carrying out the methods according to the various aspects of the invention may be performed in a different order without departing from the scope of the invention. For example, the order of execution of the steps of the method of processing a multipath signal may be altered without departing from the scope of the invention.

Those skilled in the art will understand that: information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those skilled in the art will further understand that: the various illustrative logical blocks, modules, circuits, and operational steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly show this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or operation described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art; and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (39)

1. A remote station apparatus, comprising:

a multi-element antenna configured to receive signals from at least one transmitter and output highly correlated signals from the respective transmitters; and

a controller configured to: the highly correlated signals are received, spatial characteristics of each signal including amplitude and phase are determined, and the correlated signals are combined to reproduce the signal transmitted from the selected one of the at least one transmitter.

2. A remote station as defined in claim 1, wherein the multiple-element antenna is a dual-element antenna.

3. A remote station as defined in claim 1, wherein the multiple element antenna has an envelope correlation greater than approximately 0.7.

4. A remote station as defined in claim 1, wherein the controller determines a spatial signature of each signal received from the at least one transmitter.

5. A remote station as defined in claim 4, wherein the controller further comprises a weight factor engine configured to: a set of weighting factors is determined for each of the at least one transmitter signals in response to spatial characteristics of the received signal.

6. A remote station as defined in claim 5, wherein the controller further comprises a combiner configured to: combining the received signals using the weighting factors to reproduce the signal from the selected one of the at least one transmitter.

7. A remote station as defined in claim 6, wherein the received signals are combined using an optimal combiner.

8. A remote station as defined in claim 6, wherein the received signals are combined using a maximal ratio combiner.

9. A remote station as defined in claim 1, wherein the received signal is a CDMA signal.

10. A remote station apparatus, comprising:

a multi-element antenna configured to receive signals from at least one transmitter and output highly correlated signals from the respective transmitters; and the number of the first and second groups,

a controller configured to: the highly correlated signals are received from the multiple element antenna, spatial characteristics including amplitude and phase of each signal are determined, and the highly correlated signals are combined to maximize the ratio of the preferred signal amplitude to the signal amplitudes of the other received signals.

11. A remote station as defined in claim 10, wherein the multiple element antenna has an envelope correlation greater than approximately 0.7.

12. A remote station as defined in claim 10, wherein the multiple-element antenna is a dual-element antenna.

13. A remote station as defined in claim 10, wherein the controller further comprises at least two search engines, each search engine configured to receive an in-phase signal and a quadrature signal from the antenna unit.

14. A remote station as defined in claim 10, wherein the controller further comprises a weight factor engine configured to: a set of weighting factors is determined for each of the at least one transmitter signals in response to spatial characteristics of the received signal.

15. A remote station as defined in claim 10, wherein the controller further comprises a combiner configured to: the method includes receiving an in-phase signal and a quadrature signal from each antenna element, receiving a weight factor from a weight factor engine, and outputting optimized in-phase and quadrature signals.

16. A remote station as defined in claim 10, wherein the controller further comprises a demodulator configured to: receiving the optimized in-phase signal and quadrature signal, and outputting a demodulation signal.

17. A remote station as defined in claim 10, wherein the received signal is a CDMA signal.

18. A wireless communication system, comprising:

at least one base station configured to transmit communication signals; and

at least one remote station configured to receive communication signals from the at least one base station having a multi-element antenna, wherein the received communication signals are highly correlated and are combined to reproduce the communication signals transmitted from a selected one of the at least one base station, and the at least one remote station is configured to determine spatial characteristics of each signal including amplitude and phase.

19. The wireless communication system as defined in claim 18, wherein said multiple-element antenna is a dual-element antenna.

20. The wireless communication system as defined in claim 18, wherein the multiple-element antenna has an envelope correlation greater than about 0.7.

21. The wireless communication system as defined in claim 18, wherein the at least one remote station further comprises a controller configured to determine a spatial signature of each communication signal received from the at least one base station.

22. The wireless communication system as defined in claim 21, wherein the controller further comprises a weighting factor engine configured to: a set of weight factors is determined in response to the corresponding spatial features of each received communication signal.

23. The wireless communication system as defined in claim 22, wherein the controller further comprises a combiner configured to: the received communication signals are combined using the weighting factors to reproduce the signal from the selected one of the at least one transmitter.

24. A wireless communication system as defined in claim 23, wherein the received communication signals are combined using an optimal combiner.

25. A wireless communication system as defined in claim 23, wherein the received communication signals are combined using a maximal ratio combiner.

26. A wireless communication system as defined in claim 18, wherein the received signal is a CDMA signal.

27. A method of processing a multipath signal, comprising:

receiving signals from at least one transmitter at a plurality of antennas;

identifying a preferred transmitter of the at least one transmitter from which the desired signal was received;

generating signals from each antenna such that the generated signals are highly correlated and contain signal components of the desired signal from the preferred transmitter and an interference signal;

determining a spatial signature including amplitude and phase for each signal, an

Combining two or more of the highly correlated signals so as to maximize a ratio of desired signal amplitude to interference signal amplitude.

28. The method as defined in claim 27, wherein combining the received signals further comprises:

determining a spatial signature of each signal received from the at least one transmitter;

determining a set of weight factors for each received signal in response to the spatial characteristics of the received signal; and the number of the first and second groups,

using the weighting factor to reproduce a signal corresponding to the desired signal received from the preferred transmitter.

29. The method as defined in claim 27 wherein the received signals are combined using an optimal combiner.

30. The method as defined in claim 27 wherein the received signals are combined using a maximal ratio combiner.

31. A method as defined in claim 27, wherein the received signal is a CDMA signal.

32. A method of processing signals in a wireless communication system, the method comprising:

receiving signals from a plurality of transmitters with highly correlated multi-element antennas;

determining a spatial signature including amplitude and phase for each signal received from the plurality of transmitters;

determining a set of weight factors for each transmitter signal in response to spatial characteristics of the received signal; and the number of the first and second groups,

combining the received signals using the weighting factors to reproduce the signal from the selected one of the plurality of transmitters.

33. The method as defined in claim 32, wherein the multiple-element antenna is a dual-element antenna.

34. The method as defined in claim 32, wherein the multiple-element antenna has an envelope correlation greater than about 0.7.

35. A method as defined in claim 32, wherein the received signals are combined using an optimal combiner.

36. The method as defined in claim 32 wherein the received signals are combined using a maximal ratio combiner.

37. A method as defined in claim 32, wherein the received signal is a CDMA signal.

38. A remote station apparatus, comprising:

means for receiving signals from at least one transmitter at a plurality of antennas;

means for identifying a preferred transmitter of said at least one transmitter from which the desired signal was received;

means for generating a signal from each antenna such that the generated signals are highly correlated and contain signal components of the desired signal from the preferred transmitter and an interference signal;

means for determining a spatial characteristic of each signal, including amplitude and phase, an

Means for combining two or more of the highly correlated signals to maximize a ratio of desired signal amplitude to interference signal amplitude.

39. A wireless communication system, comprising:

means for transmitting a communication signal from at least one base station; and

means for receiving communication signals by at least one remote station configured to receive communication signals using a multi-element antenna, wherein the received signals are highly correlated, spatial characteristics including amplitude and phase are determined for each signal, and the received signals are combined to reproduce a signal from a selected one of the at least one base station.