KR20030017641A - Method and apparatus for reducing code phase search space - Google Patents

Abstract

The present invention relates to a GPS communication system comprising a server and a client, each comprising a GPS receiver, which reduces the code phase search space of the GPS receiver of the client. The communication system includes a transmitter that transmits timing information from the server to the client side so that the client locates the first satellite, and a receiver that uses the timing difference between the satellites and synchronizes and locates other satellites. The code phase search space is reduced by reducing the number of phase hypotheses that must be calculated to establish communication between the server and the client.

Description

METHOD AND APPARATUS FOR REDUCING CODE PHASE SEARCH SPACE}

The satellite positioning system includes a set of orbiting satellites that broadcast a signal from which a receiver can determine a location. Two such systems are referred to herein (US Coast Guard Navigation Center, Alexandria, VA, 2nd Edition Satellite Positioning System June 2, 1995, as described in the Standard Positioning Service Signaling Standard) and Russia A satellite orbital navigation system (GLONASS) maintained by the Republic. To determine the three-dimensional position in the positioning system, the receiver must first acquire four SV signals. Initial acquisition of each SV signal is generally computationally intensive and can take a few minutes.

To obtain a GPS signal, the receiver must autotrack both the frequency of the carrier signal and the phase of the code modulated on the carrier. Because of the movement of the SV relative to the receiver and the resulting Doppler shift, the received carrier frequency can vary. Inaccuracies in the local oscillator of the receiver can cause additional frequency errors. Thus, autotracking of a carrier requires a receiver to search for a signal over a frequency range.

Each SV is spread by direct-sequence spread spectrum modulation. Specifically, each SV is spread by a known digital pseudorandom (or 'pseudonoise') code, which is termed a coarse acquisition (CA) code. This periodic code has a chip rate of 1.023 MHz and repeats every 1,023 symbols (ie, once per millisecond). The signal received at the receiver may be a composite signal transmitted by several SVs.

The code phase of the received SV signal is established by position at a predetermined positioning within the CA code of the signal. Since the CA code is periodic, the possible location of the predetermined positioning (ie, possible code phase) may appear as a point along the area of the circle, as shown in FIG. The code phase determination of the received signal is determined by the correlation at each position on the circle (e.g., as indicated by the correlation peak generation) until the code is located in the received signal (e.g., a code sequence based on a particular CA code). Correlation between the receiver and the receiver output.

Since the nominal carrier frequency of a GPS signal is 1.575 GHz, it can be difficult to maintain signal auto-tracking in areas such as indoors, inside a car and / or under a canopy of trees. If a portable GPS receiver loses signal autotracking, uncomfortable interruptions in positioning performance and loss of computer resources may continue while the receiver attempts to reacquire the signal. As the frequency offset changes somewhat slowly, reestablishing the frequency lock after a short break may require only limited effort. However, the code phase of the received signal changes more quickly and may require a lost signal search through the entire 1,023 symbol code phase circle. For applications where accurate positioning information should be available on demand, the above delay may not be acceptable. Of course, it can be beneficial to avoid long delays during initial acquisition.

It is desirable to supplement a given wireless system for mobile communication by adding a function to set the location of a specific mobile unit. One reason is the code issued by the Federal Communications Commission (Doct No. 94-102, adopted on 15 September 1999 and published 6 October 1999, Third Report and Regulations). These standards require all cellular carriers in the United States to track the location of cell phones making 911 calls within 50 meters for 67% of calls (within 150 meters for 95% of calls) in October 2001. do. Other uses for location tracking performance of wireless communication systems include value added consumer features such as aircraft and vehicle management support.

One option for adding location tracking for the communication system is to add GPS reception capability to the mobile unit. However, such a method has considerable difficulty in maintaining reliable reception of GPS signals in various areas where mobile units are generally used, such as indoors and in-vehicles. On the other hand, the base station of the system is well located in the sense of satellite visibility, and it is possible for the base station to assist the mobile station by collecting information (including code phase) on the SV signal and transmitting the information to the mobile station.

In a code division multiple access CDMA system for a wireless communication system, operations by mobile stations and base stations are synchronized to a common time reference (see FIG. 1). Because of this feature, the base station can transmit code phase information related to a meaningful time reference to the mobile station. Because of the difference in location of the base station and the mobile station, and because of the inaccuracy of the local oscillator of the mobile unit, the code phase information transmitted by the base station may not exactly match the code phase of the GPS signal received by the mobile unit. Nevertheless, the procedure can actually reduce the size of the code phase search criteria (eg, 30 symbols from 1,023 symbols).

However, in analog systems for wireless communications, such as the Enhanced Mobile Phone Service (AMPS) system widely used in the United States, there is no time reference between the mobile station and the base station. In addition, the operation of the station may not be synchronized within 1 millisecond (eg, time to pass through the entire code phase circle). Thus, there is no associated system reference point for the base station to transmit meaningful code phase information (see FIG. 2). Thus, in an AMPS system that supports GPS location tracking performance by a mobile station, full code phase circle search may be required for acquisition and reacquisition of phase locks. It is desirable to reduce the code phase search space of the distributed GPS system.

The present invention relates to a method and apparatus for reducing code phase search space for a receiver in a distributed system.

1 illustrates a CDMA system with a system reference time.

2 illustrates an AMPS system lacking system reference time.

Figure 3 shows how the code phase of a signal is determined from the time difference between (1) the code phase of another signal and (2) the code phase.

4 illustrates one method for representing the time difference between code phases for two or more signals.

5 illustrates another method of representing the time difference between code phases for two or more signals.

6 illustrates a system and multiple SVs 100 in accordance with an embodiment of the invention.

7 shows a block diagram of an apparatus 120 according to one embodiment of the invention.

8 shows a flowchart of a method according to an embodiment of the present invention.

9 shows a flowchart of a method according to another embodiment of the present invention.

10 shows a flowchart of a method according to an additional embodiment of the present invention.

11 shows a block diagram of a typical implementation of an apparatus 120 in accordance with an embodiment of the present invention.

12 shows a block diagram of an apparatus 110 in accordance with an embodiment of the present invention.

13 shows a block diagram of an exemplary implementation of an apparatus 110 in accordance with an embodiment of the present invention.

14 shows a block diagram of another exemplary implementation of an apparatus 110 in accordance with an embodiment of the present invention.

The present invention relates to a system, method and apparatus for reducing code phase search space in a code division multiple access receiver such as a GPS receiver. The reduction is obtained by applying information belonging to the time relationship between the code phases of the two received signals. The temporal relationship provides the ability to know the code phase of the second signal if the code phase of the first signal is known. By knowing the code phase of the second signal, the searcher can go directly to the predicted code phase, thus reducing the search space.

Advantages and principles of the present invention will become apparent from the following detailed description with reference to the accompanying drawings.

The following detailed description is made with reference to the accompanying drawings, which illustrate embodiments of the invention. Other embodiments are possible and modifications may be made to the embodiments without departing from the spirit and scope of the invention. Therefore, the following detailed description does not limit the invention. It is intended that the scope of the invention be defined by the claims appended hereto.

In a system, method and apparatus according to an embodiment of the present invention, the code phase of the second received signal is localized using the following time information item: (1) the code phase of the first received signal and the two received signals Time relationship between code phases (eg, time difference as shown in FIG. 3). This method provides an increased time difference (ie, for another received signal, as shown in FIG. 4) and / or a accumulated time difference (ie, for the first received signal, as in FIG. 5). This can be extended to allow localization of additional received signals.

6 shows a block diagram of a system according to an embodiment of the present invention including a field receiver 110 and a reference receiver 120. Reference receiver 120 receives at least first and second SVs 100 and determines the code phase of the received signal (eg, by correlation with local replication of a known CA code). Information pertaining to the time relationship between the code phases of the received signal is then transmitted to the field receiver 110. As the code phase of the signal is determined from the first SV 100, the field receiver 110 uses time related information to reduce the size of the space and determines the code phase of the signal from the second SV 100. You must perform a search.

7 shows a block diagram of a reference receiver 120 in accordance with an embodiment of the present invention. Within reference receiver 120, radio-frequency (RF) receiver 210 receives a modulated carrier signal from at least two SVs and outputs a corresponding demodulated signal to correlator 220. The correlator 220 determines the code phase of the received signal and outputs information related to the difference between the code phases to the transmitter 230 (eg, as shown in tasks P110 and P120 in FIG. 8).

The transmitter 230 transmits the information output by the correlator 220 as shown in task P140 of FIG. 8. In one example, correlator 220 determines the difference between code phases, and transmitter 230 transmits such a difference (eg, as shown in tasks P130 and P145 of FIG. 9). In the alternative example of FIG. 10, transmitter 230 transmits information regarding a received signal (task P142) code phase, and the receiver of the information (eg, field receiver 110) is a time difference between code phases. Perform the task to determine.

11 illustrates an example implementation of reference receiver 120. In this example, the RF receiver 210 receives a signal from the SV 100 via the GPS antenna 240. The code phase information described above is then transmitted by the transmitter 230 (eg, to one or more field receivers 110) via the communication antenna 250.

Reference receiver 120 may be combined with and / or integrated with a base station of a system for wireless communication. In this case, the position of the reference receiver 120 can generally be known with high accuracy.

As shown in FIG. 12, field receiver 110 according to an embodiment of the present invention includes a receiver 310 that receives signals from at least two SVs. The RF receiver 310 also receives a reference signal that derives a time relationship (eg, a difference) between code phases of the SV signal as received at the reference receiver.

In the signal received from the first SV, the correlator 320 determines the code phase. The correlator 320 combines the code phase information with the time relationship between the signal of the first SV and the signal of the second SV to reduce the code phase search space for the signal of the second SV.

In an exemplary implementation of the field receiver 110 as shown in FIG. 13, the RF receiver is a signal from the SV through the GPS antenna 340 and a reference signal through the communication antenna 350 (eg, a reference receiver ( 120). The RF receiver 310 may be an integrated unit, or the RF receiver 310 includes two distinct units (GPS receiver 310-1 and communication receiver 310-2) as shown in FIG. can do.

In the client-server architecture of the present invention as shown in FIG. 2, the central server has a GPS receiver that accurately informs of the position of the satellite in the air, the frequency of the satellite and the timing difference between the satellite and the server, among other information. The server may send the information to the client by identifying the satellite in view so that the client does not have to search for all the satellites, but to the extent that the client has a reasonable potential for the received signal. For example, the server transmits information related to a code sequence (eg, the sequence itself or one or more exponents within a predetermined table of code sequences) for the SV in the field of view. The server can also send satellite Doppler frequency information to the client. The server may also send the satellite's timing (eg, one or more time differences between code phases) to the client. The server preferably transmits these three types of information within the existing conditions.

Thus, in the present invention, the acquisition search space or time for the client's GPS receiver is significantly reduced. In the wireless GPS client-server architecture according to the embodiment of the present invention, the transmission of the relevant timing of the satellites by the server does not even use the timing reference at all at the client or at all the common time reference between the client and the server. If not, the search space for the client can be reduced.

The description of the preferred embodiment is provided to enable any person skilled in the art to make and use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments. For example, the present invention may be implemented in part or in whole as hardware, as a circuit configuration made of a specific application integrated circuit, or as a software program loaded into a data storage medium as a firmware program or machine-readable code loaded into a nonvolatile storage device. The code may be executable, or may be executable instructions by an array of logic elements such as a microprocessor or other digital signal processing unit. Accordingly, the invention is not limited to the described embodiments but is to be accorded the widest scope indicated in the principles and novel features disclosed herein.

Claims (25)

Determining each code phase among a plurality of received signals; And Transmitting information regarding a time relationship between at least one pair of code phases of the plurality of received signals. The method of claim 1, wherein the information comprises a time difference between the code phases. 2. The method of claim 1, wherein each of the plurality of received signals has a corresponding periodic code and each of the code phases is associated with a predetermined position within the corresponding periodic code. The method of claim 1, wherein each of the plurality of received signals is based on at least a portion of a corresponding direct-sequence spread spectrum modulated signal. The method of claim 1, wherein each of the plurality of received signals is based on at least a portion of a corresponding direct-sequence pseudonoise modulated signal. The method of claim 1, wherein the method further comprises receiving a composite signal, Wherein each of the plurality of received signals is based on at least a portion on at least a portion of a composite signal. 7. The method of claim 6, wherein determining each code phase of the plurality of received signals comprises calculating a correlation between a corresponding code sequence and a signal based on at least a portion of the composite signal for each of the plurality of received signals. Steps, Each of the plurality of received signals has a corresponding periodic code, Each of said code phases is associated with a corresponding predetermined location within a corresponding periodic code, and The code sequence is at least partially related to the corresponding periodic code. Determining a code phase of the first received signal; And Determining a code phase of a second received signal; Determining the code phase of the second received signal is based at least in part on information relating to a time relationship between the code phase of the first received signal and the code phase of the second received signal. 10. The method of claim 8, wherein the information comprises a time difference between the code phase of the first received signal and the code phase of the second received signal. The method of claim 8, wherein the first received signal has a corresponding periodic code, and the second received signal has a corresponding periodic code, Wherein a code phase of the first received signal and a code phase of the second received signal are each associated with a corresponding predetermined position in a corresponding periodic code. 9. The method of claim 8, wherein each of the first received signal and the second received signal is based on at least a portion of a corresponding direct-sequence spread spectrum modulated signal. 9. The method of claim 8, wherein each of the first received signal and the second received signal is based on at least a portion of a corresponding direct-sequence pseudonoise modulated signal. The method of claim 8, wherein the method further comprises receiving a composite signal, Wherein each of the first received signal and the second received signal is based on at least a portion of a portion of a composite signal. 15. The method of claim 13, wherein determining the code phase of the first received signal comprises calculating a correlation between a code sequence and a signal based at least in part on the composite signal, The first received signal has a corresponding periodic code and the second received signal has a corresponding periodic code, Each of the code phase of the first received signal and the code phase of the second received signal is related to a corresponding predetermined position in a corresponding periodic code, And said code sequence is at least partially related to a periodic code corresponding to said first received signal. A receiver configured to receive a plurality of signals; A correlator configured to determine a code phase for each of the plurality of received signals; And And a transmitter configured to transmit information regarding a time relationship between at least one pair of code phases among the plurality of received signals. 16. The apparatus of claim 15, wherein the information comprises a time difference between the code phases. The method of claim 15, wherein each of the plurality of received signals has a corresponding periodic code, Wherein each of the code phases is associated with a predetermined position within the corresponding periodic code. 16. The apparatus of claim 15, wherein each of the plurality of received signals is based on at least a portion of a corresponding direct-sequence spread spectrum modulated signal. 16. The apparatus of claim 15, wherein each of the plurality of received signals is based on at least a portion of a corresponding direct-sequence pseudonoise spectral modulated signal. 16. The apparatus of claim 15, wherein the correlator calculates a correlation between a corresponding code sequence and the plurality of received signals for each of the plurality of received signals to at least partially code phase for each of the plurality of received signals. Is further configured to determine, Each of the plurality of received signals has a corresponding periodic code, Each of said code phases is associated with a corresponding predetermined location within a corresponding periodic code, and Wherein the corresponding code sequence is at least partially related to a corresponding periodic code. A receiver configured to receive a first and a second signal and to receive a signal comprising information regarding a time relationship between the code phase of the first received signal and the code phase of the second received signal; And Determining at least one code phase of the first and second received signals for a predetermined code, wherein the predetermined code and the first and second received signals are based on a time relationship between the first and second received signals. And a correlator configured to correlate the other one of the signals. 22. The apparatus of claim 21, wherein the information comprises a time difference between the code phase of the first received signal and the code phase of the second received signal. 22. The apparatus of claim 21, wherein the correlator is further configured to determine at least some of the code phase for the second received signal from the information. A reference receiver configured to receive signals from a plurality of space vehicles and transmit information; And A field receiver configured to receive a signal from a plurality of space vehicles and receive the information; The reference receiver determines a reference code phase for each of at least a first signal and a second signal of the signal, The information relates to a temporal relationship between at least the first signal of the signal and the reference code phase for a second signal, The field receiver determines a field code phase for a first signal of the signal, And the field receiver determines at least in part a field code phase for the second signal of the signal from the information. 25. The system of claim 24, wherein the information comprises a time difference between the reference code phase for the first signal and the second signal of the signal.