HK1082851A - Reducing cross-interference in a combined gps receiver and communication system - Google Patents

Description

Reducing cross-interference in a combined GPS receiver and communication system

Technical Field

The present invention relates generally to the field of Satellite Positioning System (SPS) receivers, and more particularly to reducing cross-interference in a combined SPS receiver and communication system.

Background

The use of portable personal communication devices, such as cellular telephones and pagers, has increased dramatically in recent years. In addition, the use of portable navigation devices, such as Satellite Positioning System (SPS) receivers, has increased greatly as these devices become widely available. Recent technological developments have enabled the combination of an SPS receiver and a communication system within an integrated unit, such as a combination SPS receiver and cellular telephone unit. Such combined devices have many applications such as personal safety, emergency response, vehicle tracking, and inventory control. Some combination units use appropriate electronic interfaces to combine the separate SPS receiver and communication system. Others use shared circuitry and packaging. These combined units are characterized by the convenience advantages provided by a common housing and integrated user interface. However, such a combined unit may also exhibit certain disadvantages, such as increased power consumption and reduced performance.

One significant drawback inherent in many combination SPS and communication devices is the reduced performance of the SPS receiver portion of the combination unit. A common cause of such reduced performance is signal interference between the communication and SPS receiver stages. For example, in a combined cellular phone/SPS receiver, cellular transmissions from the cellular phone phase may generate strong interference that may degrade the performance of the SPS receiver.

The current approach to overcome cross interference between the communication and SPS phases is to use complex filters or high dynamic range circuits in the front-end section of the SPS receiver to limit in-band interference to an acceptable range. However, these approaches require the use of complex additional circuitry, which increases the cost and power consumption of the combined unit. For example, one approach to reducing cross-coupling in a combined cellular telephone/SPS receiver is to use several bandpass filters in the RF front end of the SPS transmitter to eliminate Radio Frequency (RF) interference from the cellular transmitter. However, this approach has several problems. First, several filters may be required to provide sufficient reduction in the signal energy coupled from the cellular transmitter into the SPS receiver RF circuitry. This increases the cost and size of the combined unit. Second, the use of a filter improves the noise characteristics of the SPS receiver, making it less sensitive to satellite navigation signals.

It is therefore desirable to provide a system that reduces cross-interference between the SPS and the communication portions of a combined SPS/communication receiver.

It would also be desirable to provide a system that improves SPS reception performance in a combined SPS/communication receiver without adversely affecting the cost and sensitivity characteristics of the SPS receiver.

Disclosure of Invention

A method of operating a mobile device is disclosed. A first behavior of a mobile device is detected. Performing the following two operations when the first behavior is detected: (i) wireless data transmission on a wireless data link from a mobile device communication unit is disabled for a period of time, and (ii) a first control signal is transmitted from the communication unit to a satellite positioning system receiver of the mobile device, the first control signal initiating processing of signal positioning system signals received by the receiver during the period of time.

The first action may be caused, for example, by a user of the mobile device performing an operation, such as pressing a button on the mobile device or lack of speech received by a microphone of the communication unit.

Wireless transmissions may be disabled and enabled in an alternating manner.

Other features of the present invention will become apparent from the accompanying drawings and from the detailed description that follows.

Drawings

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

fig. 1 is a block diagram of a combined Global Positioning System (GPS) receiver and communication system having a communication link to a base station in accordance with an embodiment of the present invention.

Fig. 2 is a block diagram of the components that comprise a GPS receiver and a communications transceiver within a mobile device in accordance with an embodiment of the present invention.

Fig. 3 illustrates a mobile telephone for use in a cellular telephone network in accordance with an embodiment of the present invention.

Fig. 4 is a timing diagram illustrating a method of operating a mobile device in accordance with the present invention.

Fig. 5 is a timing diagram illustrating another method of operating a mobile device in accordance with the present invention.

Fig. 6 is a flow chart illustrating operations for reducing cross-interference in a mobile device in accordance with a method of the present invention.

Detailed Description

A method and apparatus for reducing cross-interference within a mobile device that is a combination of a Satellite Positioning System (SPS) receiver and a communication device is described. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate explanation.

In the following discussion, embodiments of the present invention will be described with reference to applications related to the United states Global Positioning Satellite (GPS) System. It is clear, however, that these methods are equally applicable to similar satellite positioning systems, such as the russian Glonass system. Thus, the term "GPS" as used herein includes such other satellite positioning systems, including the Russian Glonass system. Likewise, the term "GPS signals" includes signals from other satellite positioning systems.

Mobile device

Fig. 1 is a block diagram of a mobile device 150, the mobile device 150 using a communication transmitter/receiver (transceiver) in combination with a GPS receiver in one embodiment of the invention. The mobile device 150 is a portable handheld unit that includes circuitry for performing the functions required for processing GPS signals as well as the functions required for processing communication signals transmitted and received over a communication link. The communication link, such as communication link 162, is typically a radio frequency communication link to another communication component, such as base station 160 having a communication antenna 164.

The mobile device 150 includes a GPS receiver 130, the GPS receiver 130 including acquisition circuitry and processing components. According to the conventional GPS method, the GPS receiver 130 receives GPS signals transmitted from orbiting GPS satellites and determines the arrival time of a unique pseudo-random noise (PN) code (referred to as a "pseudo-range") by comparing the time offset between the received PN code signal sequence and an internally generated PN signal sequence. The GPS signals are received by the GPS antenna 111 and input to an acquisition circuit which acquires the PN code of each received satellite. The navigation data (e.g., pseudoranges) generated by the acquisition circuit are processed by the processor for transmission by the communication transceiver 109.

The mobile device 150 also includes a communications transceiver section 109. A communications transceiver 109 is coupled to the communications antenna 100. The communication transceiver 109 transmits the navigation data processed by the GPS receiver 130 to a remote base station, such as base station 160, via a communication signal (typically RF). The navigation data may be the actual latitude, longitude and altitude of the GPS receiver, or it may be raw or partially processed data. The received communication signal is input to the communication transceiver 109 and passed to the processor for processing and possibly output through an audio speaker.

In accordance with an embodiment of the invention, pseudorange data generated by the GPS receiver 130 is transmitted in the mobile device 150 to the base station 160 over the communication link 162. The base station 160 then determines the location of the combined receiver 150 based on the pseudorange data from the combined receiver, the time at which the pseudoranges were measured, and ephemeris data received from its own GPS receiver or other source of such data. The location data is then transmitted back to the mobile device 150 or other remote station. The communication link 162 between the mobile device 150 and the base station 160 may be implemented in various embodiments including a direct link or a cellular telephone link. In one embodiment of the present invention, the communication transceiver section 109 is implemented with a cellular phone.

FIG. 2 provides a more detailed block diagram of a combination cellular telephone and GPS receiver according to one embodiment of the present invention. It will be appreciated by those skilled in the art that the system illustrated in fig. 2 is one embodiment and that many variations in the design and construction of a combined GPS receiver are possible in accordance with the principles of the present invention. For example, although the following discussion will assume that the communication portion is embodied in a cellular telephone, it will be appreciated that the present invention may be embodied in other communication devices, such as two-way pagers and similar two-way communicators.

In fig. 2, the mobile device 150 includes a GPS receiver 130 and a GPS antenna 111 (collectively referred to as the "GPS section"), and a cellular phone 109 and a cellular phone antenna 100 (collectively referred to as the "communication section"). The cellular telephone transmits signals to and receives signals from a remote base station (e.g., base station 160 in fig. 1) via antenna 100.

GPS section

In the GPS receiver 130 of the mobile device 150, a received GPS signal is input from the GPS antenna 111 to a Radio Frequency (RF) to Intermediate Frequency (IF) converter 113 through a signal line 120 and a switch 112. The frequency converter 113 converts the signal to a suitable intermediate frequency, for example 70 MHz. It is further converted to a lower intermediate frequency, such as 1 MHz. An output of the RF to IF converter 113 is coupled to an input of the GPS signal processing circuit 114. The GPS signal processing circuit 114 includes an analog-to-digital (a/D) converter that digitizes the output signal from the RF-to-IF converter 113.

In one embodiment of the present invention, the GPS signal processing circuit 114 further includes a digital snapshot memory coupled to the output of the a/D converter and capable of storing a record of the data to be processed. The snapshot memory is used to process GPS signals that are typically stored in a separate memory device coupled to GPS processing circuitry 114. Snapshot memories are typically employed for packetized communication signals, i.e., signals consisting of data burst bits followed by long periods of inactivity. Continuous signaling, such as many cellular-type signals, may also be processed by the processing circuitry in a continuous manner.

An output from the GPS signal processing circuit 114 is coupled to a microprocessor 115. The microprocessor 115 further processes the satellite signals received within the GPS receiver 130 and outputs the processed signals for transmission directly to a user interface or to a remote receiver (not shown) via a communication link.

In one embodiment of the present invention, the GPS receiver 130 is a conventional GPS receiver that uses a bank of correlators to demodulate the GPS signals. In one method of the invention, the gating signal either activates or deactivates the GPS receiver. When energized, a conventional GPS receiver can perform all of its normal functions, including demodulation of the 50 baud satellite data message. However, if the gating period becomes a large fraction of the data baud period, demodulation may become difficult or impossible. In this case, another type of GPS receiver may be used. For example, one type of GPS receiver only finds the relative times of arrival of a plurality of simultaneously received GPS signals and transmits these relative times of arrival (so-called "pseudo ranges") to a Remote station (see, for example, "An Application of the global positioning System to Search and research and Remote Tracking" by f.h. raab et al, aeronautical association press, vol. 24, No. 3, fall 1977, page 216-. The location of the mobile device is then determined by combining the pseudorange data with GPS satellite information collected by the mobile device using its own receiver or through some other source of such data. This configuration is particularly useful in various emergency response and tracking applications.

Although the embodiments of the present application are discussed with respect to a particular GPS receiver configuration, it will be apparent to those of ordinary skill in the art that there are several different GPS receiver configurations that can utilize the cross-interference reduction method of the present invention.

Also, although embodiments of the present invention are described with reference to GPS satellites, it will be appreciated that the principles are equally applicable to positioning systems utilizing pseudolites (pseudolites) or a combination of satellites and pseudolites. A pseudolite is a base transmitter that broadcasts a PN code modulated by a pair of L-band (or other frequency) carrier signals, typically synchronized with GPS time. Each transmitter may be assigned a unique PN code so as to be identifiable by a remote receiver. Pseudolites may be useful in situations where GPS signals from an orbiting satellite might be unavailable, such as tunnels, mines, buildings, or other enclosed areas. The term "satellite" as used herein includes pseudolites or equivalents of pseudolites, and the term "GPS signals" as used herein includes GPS-like signals from pseudolites or equivalents of pseudolites.

Communication part

The communication portion of mobile device 150 includes a receiver stage and a transmitter stage coupled to communication antenna 100 through a duplexer or transmit/receive switch 101. When a communication signal, such as a cellular telephone signal, is received from a communication base station (e.g., base station 160), switch 101 routes the input signal to RF-to-IF converter 202. The RF to IF frequency converter 102 converts the communication signal to an appropriate intermediate frequency for further processing. The output of RF to IF converter 102 is coupled to demodulator 103 which demodulates the communication signal to determine instructions in the communication signal or other data in the communication signal (e.g., digitized voice, doppler data, or data representing the ephemeris of the observed satellite). The demodulator 103 may be implemented as a digital demodulator. In this case, the frequency-converted communication signal may be passed through an analog-to-digital (a/D) converter that digitizes the output signal from the RF-to-IF converter 102 before being input to the demodulator 103.

In one embodiment of the invention, the output of the demodulator 103 is passed to a microprocessor 104. The microprocessor 104 performs any processing required for the communication receiving and transmitting functions.

The microprocessor 104 is also connected to a display and a microphone. The microphone can convert speech into voice data and provide the voice data to the microprocessor 104. When transmission is required over the communication link, the microphone 104 generates baseband digital samples (or representations thereof, e.g., mathematical models of the signals) of the data to be transmitted and the signals. It then uses the data to modulate a carrier signal with modulator 106. In recent systems, the modulation is typically digital, such as frequency shift keying or phase shift keying, although analog modulation (such as frequency modulation) may also be used. In this case, after modulation, the digital signal is converted from digital to analog within a digital-to-analog converter. The carrier frequency at which modulation is performed in modulator 106 may or may not be the final RF frequency of the communication signal; IF it is at an Intermediate Frequency (IF), an additional IF-to-RF converter 107 is used to convert the signal to the final RF frequency of the communication signal. The power amplifier 108 increases the signal level of the communication signal, and this increased signal is then transmitted to the communication antenna 100 through the switch 101.

In one method of the present invention, a communication signal containing data representing position information (e.g., pseudoranges to various satellites, or latitude and longitude of mobile device 150) is transmitted to base station 160 over communication link 162. The base station 160 can act as a processing station for calculating the location information of the portable GPS unit, or it can act as a relay station and retransmit information received from the mobile device 150.

In some cellular telephone systems, such as Time Division Multiple Access (TDMA) systems (including, for example, GSM, i.e., the global system for mobile telephony), the transmission and reception times of cellular signals are disjoint. In these cases, a simple switch 101 may be used to isolate the strong transmit signal 118 provided by the power amplifier 108 from the path 119 to the sensitive front-end receive circuitry (frequency converter 102). In particular, the receive circuit 102 may include a Low Noise Amplifier (LNA) that may be corrupted or significantly affected if the signal from the power amplifier is sent to the LNA without significant attenuation.

In other cellular systems, such as the IS-95 north american system based on Code Division Multiple Access (CDMA), there may be simultaneous signal transmission and reception through the antenna 100. To isolate RF circuitry 102 from high power signals 118, a device called a "diplexer" is used in place of switch 101. The duplexer 101 consists of two RF filters, one tuned to the transmit band and the other tuned to the receive band. The power amplifier output 118 is passed through a transmit filter and then to the antenna 100, while the receive signal from the antenna is passed through a receive filter. Thus, the transmission is separated from the RF circuitry 102 by an amount equal to the amount of isolation provided by the receive filter at the transmit frequency.

Signal gating for communication transceivers

In one embodiment of the invention, the mobile device 150 includes control circuitry that reduces cross-interference between the GPS receiver and cellular transceiver stages. Cross-interference is often a particularly serious problem in combined receivers, since the satellite signals received in GPS receivers are generally weak. Cross-interference typically occurs due to a high degree of coupling between cellular telephone signals transmitted through antenna 100 and GPS receive antenna 111. This is especially true when antenna units 100 and 111 are co-located or share portions of their mechanical components to conserve physical space or reduce cost.

In one embodiment of the invention, cross-interference between the communication and GPS sections of the combined unit is reduced by reducing the power of the transmitter (typically a cellular telephone) of the communication section. The power of the transmitter is reduced for a period of time during which the satellite positioning system signals can be processed, after which the transmitter is powered up again. The gating signal synchronizes the power control and GPS receiver operation. The operation of the gating signal according to an embodiment of the present invention is described with reference to the combined receiver of fig. 2.

In the cellular telephone portion 109 of the mobile device 150, a power level control signal 105 is sent from the microprocessor 104 to the power amplifier 108. In one embodiment of the invention, a first state of the power level control signal reduces power in the power amplifier and a second state of the signal restores a normal power level in the power amplifier. Alternatively, both signals are contained within the power level control signal. The first signal reduces the power in the power amplifier and the second signal restores the normal power level in the power amplifier. Depending on the power level of the amplifier 108 and the desired amount of reduction in cross-interference, the power level control signal 105 can turn off the power amplifier 108 completely or reduce its amplification power by a predetermined amount.

The power level control signal 105 is also sent to the GPS receiver 130. The signal is programmed to activate the GPS receiver to receive and process GPS signals relative to the power level of the communication power amplifier 108. When the power level control signal 105 reduces or turns off the power amplifier 108, the GPS receiver 130 is activated to receive GPS signals. Conversely, when the power level control signal maintains a normal power level within the power amplifier 108, the GPS receiver 130 is prevented from receiving GPS signals. Alternatively, the GPS receiver 130 may be programmed to receive GPS signals, but ignore these signals within its processing circuitry when the power level control signal indicates that the cellular telephone transmitter is at high power.

Within the GPS receiver 130, the gating signal 110 corresponds to the power level control signal 105. In one embodiment of the invention, gating signal 110 is sent to microprocessor 115 over line 122, to GPS processing circuit 114 over line 116, and to switch 112 over line 117. In one embodiment, switch 112 is controlled by gating signal 110 and power level control signal 105. When the power level control signal 105 reduces the power to the cellular telephone power amplifier 108, the switch 112 is turned on to enable data to pass from the GPS antenna 111 to the GPS receiver circuitry. Conversely, when the power level control signal 105 maintains the high power of the power amplifier 108, no data is passed to the GPS receiver when the switch 112 is turned off. In this way, the GPS signal is gated off (or blocked) during periods when the cellular telephone transmission is at high power, while the GPS signal is received at all other times.

In one embodiment of the invention, switch 112 is a gallium arsenide (GaAs) switch. Since the switch 112 is in the GPS input signal path, it causes some attenuation of the input GPS signal. GaAs switches minimize this attenuation. Furthermore, current switch devices at GPS frequency (1575.42MHz) provide approximately 0.5dB insertion loss.

In an alternative embodiment of the present invention, gating signal 110 is input only to microprocessor 115 rather than switch 117. In this configuration, the microprocessor 115 directly controls the switch 117 or GPS signal processing circuit 114 to gate the incoming GPS signals as the cellular telephone 109 transmits.

In a further alternative embodiment of the invention, GPS receiver 130 may not include GaAs switch 112. The switch may be omitted if the RF front-end circuitry of the GPS receiver 113 can withstand high power from a cellular telephone transmitter (e.g., with some sort of limiting circuitry). The omission of the switch 112 eliminates any possible signal attenuation through the switch. In this alternative embodiment, gating signal 110 is input to either or both of GPS signal processing circuit 114 and microprocessor 115. This signal causes the incoming GPS signals to be ignored by the processing circuitry during the time that the cellular telephone is transmitting, even though these signals are being received by the GPS receiver 130.

Most modern digital cellular telephone systems are capable of transmitting at full power for only a portion of the time. Thus, the gating signal method described herein is applicable to a wide range of digital cellular telephones. If cellular transmissions in these phones occur at 1/8 duty cycles (e.g., in the case of GSM digital cellular phones, or CDMA in reduced data throughput modes), then the sensitivity loss of the GPS receiver due to such gating is only about 0.5 dB.

Fig. 4 illustrates an example of how a mobile device may function. Fig. 4 is a timing chart with times T1, T2, and T3 on the abscissa and behaviors such as "speak", "send voice data", and "process GPS data" on the ordinate.

From time T1, a person may speak into the microphone before reaching time T2. Voice data is continuously sent from the mobile device during this time.

There is then a break in speech from time T2 to time T3, after which speech is resumed again. Since the interruption from T2 to T3 is less than a predetermined minimum amount, e.g., 1/2 seconds, the voice data transmission is not interrupted.

There will then be a further break (i.e., pause) in speech at time T4. The speech interruption lasts until time T7. The voice data transmission is stopped after the minimum interruption at time T5 due to the interruption or pause in speech being greater than the minimum interruption of 1/2 seconds. A control signal is sent at time T5 to enable GPS data processing. GPS data processing continues to time T6. The difference between time T6 and time T5 is large enough to allow the minimum amount of GPS data required to be processed, typically between one and two seconds. The minimum amount of GPS data is sufficient to triangulate the position of the mobile device.

Speech is resumed again at time T7 and can continue to time T8, after which there is a break in speech from time T8 to time T10. A speech minimum interruption of 1/2 seconds is reached at time T9, at which point the voice data transmission is stopped. GPS data processing is enabled at time T9. At time T10, the user can speak into the microphone again and continue speaking before time T12. Then, before time T11, the voice data transmission is stopped. The difference between time T11 and time T9 is, for example, two seconds, which is large enough to process a sufficient amount of GPS data. A signal is sent at time T9 to enable GPS data processing and another signal is sent at time T11 to stop GPS reception and processing. At time T11, voice data transmission is again enabled. In this example, a portion of the speaker's voice information (between times T10 and T11) is cut off due to the need to complete the GPS processing. In other embodiments, the resumed voice activity may cause the GPS processing cycle to terminate so that speech is not interrupted. However, this may result in unsuccessful completion of the GPS processing.

It should be noted that the time intervals for processing the GPS data need not be equal. For example, in the above example, the time intervals T5-T6 and T9-T11 need not be equal. This may be due to information obtained from processing of a previous interval (e.g., T5-T6) that may help reduce the processing time (e.g., T9-T11) required for subsequent processing of the GPS signals. For example, the previous GPS processing determines the time of arrival of the respective GPS signals. These times of arrival are projected forward in time to estimate the time of arrival of these signals at later samples in time. These trajectories reduce the processing required to determine the exact time of arrival of the GPS signals, which is required for an exact geographic location. It should also be noted that the time periods for performing the GPS processing (T5-T6 and T9-T11 in the above example) can either be predetermined or adaptive in nature. A simple procedure would utilize a fixed or predetermined period of time in a manner that would ensure successful GPS processing. A more complex procedure is one in which the GPS processing interval can be adapted depending on various adjustments. Once completed, the voice transmission resumes. The adjustment of the control interval length would include the received signal strength of the received SPS signal and a priori information about parameters of such signal, such as the uncertainty range of the doppler frequency and the time of arrival of such signal. As described above, the preceding SPS signal processing operation results in a reduction in the length of the interval required for subsequent processing. Alternatively, as described above, the speech cessation may determine the interval length.

The communication portion of the mobile device may enter half-duplex mode during the period when voice data transmission is stopped. It is thus possible to receive voice data and to cause the speaker that pronounces the voice to generate an audio signal, which is part of the mobile device. As shown in fig. 4, when voice data transmission is stopped, it is therefore possible to receive voice data within an interval starting from T5 and ending at T6. In other embodiments, both transmission and reception of voice data may be prevented during this interval.

Fig. 5 illustrates another method that a mobile device may operate. Assume that a person continuously speaks into the microphone from time T1 to T9. The voice data transmission begins at time T1 and continues through time T2.

The person presses a button at time T2 or, in another embodiment, the person may only need some other action with the mobile device. The button is pressed from time T2 and released at time T3. At time T3, after the button is released, the voice data transmission is stopped. A control signal is sent to enable GPS data processing.

Voice data transmission is then alternately disabled and enabled in an alternating time-based manner. Voice data is disabled for 7/8 of a frame and enabled for 1/8 of a frame. Each time voice data transmission is disabled, a control signal is sent that enables GPS data processing, and each time voice data transmission is enabled, a control signal is sent that disables GPS data processing. In the example given, voice data transmission is disabled at times T3, T5, and T7, and enabled at times T4, T6, and T8. The GPS data is processed at times T3 through T4, times T5 through T6, and times T7 through T8. The amount of GPS data accumulated and processed from the release of the button at time T3 until time T8 is sufficient to triangulate the position of the mobile device. Voice data transmission is no longer disabled since time T8 except when the button is pressed again. In this way, the mobile device user initiates and then ends the GPS processing as desired.

Each time voice data transmission is disabled, the mobile device also enters a half-duplex mode, enabling reception, processing of voice data, and generation of audio signals. The audio signals are typically sent to a speaker within the mobile device, which produces audio sounds.

Fig. 6 illustrates the basic operation according to the invention. In step 600, communications are established over a communications link. In step 602, it is determined whether a behavior is specified. The action may be, for example, the absence of speech detected by the microphone of the mobile device, as described with reference to fig. 4, or the pressing of a button, as described with reference to fig. 5. Other behaviors are also possible.

If a behavior is detected in step 602, step 604 is performed. In step 604, (i) voice data transmission is disabled for a period of time, and (ii) a control signal is sent to enable processing of satellite positioning system signal data. In FIG. 4, step 604 occurs at times T5 and T9 in FIG. 5, and in FIG. 5, step 604 occurs at time T3. When this time period has elapsed, step 606 is performed. In step 606, (iii) transmission of voice data is enabled, and (iv) processing of satellite positioning system signal data is disabled. In FIG. 4, step 606 occurs at times T6 and T11, and in FIG. 5, step 606 occurs at time T4. As previously described, the time period 604 may be predetermined or adaptive, depending on the processing strategy employed.

In the mobile device 150 of fig. 2, the circuitry within the GPS section and the communications section is illustrated as being dedicated and split between the two sections. It should be noted, however, that embodiments of the present invention may be used in mobile devices where one or more elements are shared between two portions. For example, the functions of the microprocessors 104 and 115 may be combined into a single processor or programmable digital circuit that can be shared between the GPS and communications sections. Also, one or more of the frequency converter, switch or antenna unit may be shared between the two parts.

In the foregoing discussion, a control signal is discussed that is sent to the GPS receiver and/or processing element to activate or deactivate GPS operation. The control signals are shown flowing through different paths, such as paths 110, 117, and 116. It should be appreciated that in some GPS implementations, both the GPS signal processing circuitry and the cellular telephone processing circuitry can be located within the same integrated circuit. In this case, the gating control signal is entirely present within the same integrated circuit and cannot be observed as an external physical line. Also, such control signals may be sent through a common microprocessor shared by multiple circuit elements, such as memory, keyboards, etc. The present invention should be understood to include these forms of control signals. Furthermore, as just described, the cellular telephone or other communication unit will not be completely distinct from the SPS receiver, also because they may share common circuitry, such as RF front end components, microprocessors, etc. However, the communication function and the SPS function may have some different parts of hardware elements and/or software. Thus, when referring to a "communication unit" and an "SPS receiver", this is not intended to be limiting as to being completely different or differing in major respects.

Cellular telephone/GPS network

As described above, one embodiment of the present invention is used in a mobile device, wherein the communications transceiver is a cellular telephone used in a cellular network. Fig. 3 illustrates the use of the mobile device 150 in the context of a cellular telephone network to form a combined GPS and cellular system 300. Area 306 represents a cell of a cellular telephone served by cell site 304. Cell site 304 transmits cellular telephone signals to, and receives cellular telephone signals from, cellular telephones and receivers, such as mobile device 302, within cell 306. Mobile device 302 comprises a mobile device, such as mobile device 150 in fig. 1. Mobile device 302 transmits cellular signals to cell site 304 via communication antenna 100 and receives GPS signals from GPS satellites via GPS antenna 111. Cell site 304 transmits cellular transmissions from mobile devices within cell 306 through cellular switching center 308 to land-based telephone network 310. The cellular switching center 308 routes the communication signals received from the mobile device 302 to the appropriate destination. In addition to cell 306, cellular switching center 308 may also serve several other cells. If the signal transmitted by the mobile device 302 is destined for another mobile device, a connection is made to a cell site that covers the area in which the mobile device is located. If the destination is land-based, the cellular switching center 308 connects to a land-based telephone network 310.

It should be noted that a cellular-based communication system is a communication system having more than one transmitter, each serving a different geographical area, which is predefined at any instant in time. Generally, each transmitter is a wireless transmitter serving a cell having a geographic radius of less than 20 miles, however, the area covered depends on the particular cellular system. There are many types of cellular communication systems such as cellular telephones, PCS (personal communication system), SMR (dedicated mobile radio), one-way and two-way paging systems, RAM, ARDIS, and wireless packet data systems. Generally, the predefined distinct geographic areas are referred to as cells, and a plurality of cells are grouped together to form a cellular service area, and these plurality of cells are coupled to one or more cellular switching centers that provide connectivity to land-based telephone systems and/or networks. The service area is typically used for billing purposes. Thus, more than one cell within a service area may be connected to a switching center. Alternatively, sometimes cells within a service area may be connected to different switching centers, especially in densely populated areas. In general, a service area is defined as a set of cells geographically located close to each other. Another type of cellular system consistent with the above description is satellite-based, where the cellular base stations are satellites that typically orbit the earth. In these systems, the cell sectors and service areas move as a function of time. Examples of such systems include the Iridium, Globalstar, Orbcomm and Odyssey systems.

In the system illustrated in FIG. 3, GPS location information transmitted by mobile device 302 is transmitted to GPS server base station 160 over land-based telephone network 310. The GPS base station 160 acts as a processing station for calculating the position of the GPS receiver in the remote unit 302. The GPS base station 160 may also receive GPS information from satellite signals received within the GPS receiver 312 (e.g., to provide a differential connection to mobile GPS information). GPS base station 160 may be directly connected to cell site 304 by a wired or wireless link to receive a corresponding cellular communication signal. Alternatively, the GPS base station 160 may receive a corresponding cellular communication signal from a cellular telephone 314, the cellular telephone 314 transmitting the signal to a cellular receiver within the GPS base station 160.

It should be noted that the cellular network system 300 of fig. 3 represents one embodiment of a use case of the present invention, and that other communication systems may be used to transmit GPS signals from a mobile device to a GPS base station in addition to a cellular telephone network.

Cellular communication system

Embodiments of the present invention may be used in several different cellular telephone systems. The particular cellular system or standard depends on the region in which the system is employed, as cellular standards may vary between different countries and regions.

In an embodiment of the invention, the combined communication device 150 is used in a GSM cellular system. GSM is an all-european digital cellular system using a Time Division Multiple Access (TDMA) method. When sending voice messages, the handset sends a burst of data in a time slot equal to 15/26 milliseconds. Each TDMA frame has 8 time slots and the handset transmits in only one of these frames, in the primary mode of operation. Thus, the transmitter is activated only 12.5% of the time. Thus, the control line of the system (i.e., gating signal 110 in FIG. 2) would indicate an active transfer 12.5% of the time. This causes the GPS receiver 130 to gate off and/or ignore incoming GPS data during this time. The "off" period is short, less than one GPS code period (977.5 microseconds), and only about 1/20 for one GPS data bit duration. The effective loss of sensitivity is a factor of 0.875 or-0.58 dB.

Another embodiment of the present invention may be used in IS-136 north american TDMA systems. The IS-136 system uses six slots in each 40 millisecond frame period. For full rate signaling, the voice traffic channel occupies two such time slots, namely 13.33 milliseconds. Thus, for full rate signaling, it is not always practical to receive GPS data messages along with transmission gating; however, it is still possible to perform measurements of the GPS PN periods (in order to determine the so-called "pseudoranges"). In this case, the resulting loss of sensitivity is 0.667 or-1.76 dB. If half rate signaling is used, the resulting loss of sensitivity is reduced to 0.833 or-0.76 dB.

Further embodiments of the present invention may be used in IS-95 north american Code Division Multiple Access (CDMA) systems. In IS-95 systems, signals are prevented from interfering with each other by using a different spreading code for each signal. The data is organized within 20 millisecond frames. However, when transmitting signals at low data rates (e.g., discontinuous speech), data is transmitted in bursts that occupy only a portion of a frame. For example, at 1200 baud, a burst of data occupies 1/8 of only one frame, and during the remainder of the frame, the transmit signal is transmitted at a reduced power level. During these reduced transmission times, the GPS receiver 130 can be activated. Also, during normal transmission, the GPS receiver 130 may be disabled, i.e., the receiver front end is turned off and/or the processing circuitry ignores incoming GPS data. The effective sensitivity loss to the GPS receiver for the 1200 baud transmission case is equal to the integration time reduction of 7/8, which is equivalent to-0.58 dB. For this 1200 baud case, the transmission time of the data burst period is only 1.25 milliseconds, which is a small fraction (20 milliseconds) of a GPS data bit. In this manner, a conventional GPS receiver can still demodulate satellite data messages in the presence of gating signal 110.

A system for reducing cross-interference in a combined GPS receiver and communication transceiver unit has been described above. Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the invention as set forth in the claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Claims (22)

1. A method of operating a mobile device, comprising:

detecting a first behavior of a mobile device;

upon detection of the first behavior:

(i) sending a wireless data transmission from a communication unit of a mobile device over a wireless data link; and

(ii) transmitting a first control signal from the communication unit to a satellite positioning system receiver of the mobile device, the first control signal beginning to process satellite positioning system signals received by the receiver during a time period in which the data transmission remains disabled even while a person speaks into a microphone of the mobile device.

2. The method of claim 1, wherein the first behavior is due to an operation implemented by a user of a mobile device.

3. The method of claim 2, wherein the operation is pressing a button on a mobile device.

4. The method of claim 2, wherein the operation is a lack of speech received by the communication unit.

5. The method of claim 1, wherein the wireless transmissions are alternately disabled and enabled.

6. The method of claim 5, wherein the disabling and enabling of the data transmission is time-based.

7. The method of claim 6, wherein the disabling and enabling of the data transmission is periodic.

8. The method of claim 2, wherein the wireless transmissions are alternately disabled and enabled.

9. The method of claim 1, wherein the wireless data transmission is disabled due to a user of the mobile device speaking into a microphone of the communication unit.

10. The method of claim 1, further comprising:

(iii) wireless data transmission from the communication unit over the wireless data link is enabled after a sufficient amount of satellite positioning system data is received.

11. The method of claim 10, further comprising:

(iv) transmitting a second control signal from the communication unit to the satellite positioning system receiver when wireless transmission is enabled, the second control signal inhibiting processing of satellite positioning system signals received by the receiver.

12. The method of claim 11, wherein (i) and (ii) are periodically alternated with (iii) and (iv).

13. The method of claim 1, wherein the period of time is predetermined.

14. The method of claim 1, wherein said time period is adaptive, and an end of said time period is determined during said processing of satellite positioning system signals.

15. A mobile device, comprising:

a satellite processing system antenna for receiving satellite positioning system signals from a plurality of satellite positioning system satellites;

receiver circuitry coupled to the satellite processing system antenna for processing the satellite positioning system signals;

a detector for detecting a behavior of the mobile device;

a microphone for converting speech into voice data;

a wireless transmitter operable to wirelessly transmit the voice data over a wireless data link;

an output amplifier coupled with the wireless transmitter; and

a communication unit circuit operable to control the output amplifier to wirelessly emit a signal from a wireless transmitter and, when the detector detects the action:

(i) disabling wireless transmission of the output amplifier; and

(ii) the first control signal is transmitted to the receiver circuit such that the receiver circuit begins processing satellite positioning system signals received by the satellite positioning system antenna for a period of time during which the output amplifier remains disabled even while a person speaks into the microphone.

16. The mobile device of claim 15, wherein the first behavior is due to an operation implemented by a user of the mobile device.

17. The mobile device of claim 16, further comprising:

a button that can be pressed by a user, the operation being pressing the button.

18. The mobile device of claim 16, wherein the operation is a lack of speech received by the communication unit.

19. The mobile device of claim 15, wherein the wireless transmission is alternately disabled and enabled.

20. The mobile device of claim 15, wherein the wireless data transmission is disabled while a user of the mobile device speaks into a microphone of the communication unit.

21. The mobile device of claim 15, wherein the period of time is predetermined.

22. The mobile device of claim 15, wherein said time period is adaptive, an end of said time period being determined during said processing of satellite positioning system signals.