KR101049836B1 - 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 to reduce 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 for the client to locate 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 topological 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 present invention relates to a method and apparatus for reducing code phase search space for a receiver in a distributed system.

Satellite positioning systems include a set of orbiting satellites (so-called space vehicles or 'SVs') 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. In order 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 several minutes.

To obtain a GPS signal, the receiver must lock onto both the frequency of the carrier signal and the phase of the code modulated by 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 transmits a signal spread by a known digital pseudorandom (or 'pseudonoise') code called a dense 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 of signals transmitted by several SVs.

The code phase of the received SV signal is set by the position at a predetermined point within the CA code of the signal. Since the CA code is periodic, the possible location of the predetermined point (ie, possible code phase) may appear as a point along the circumference of the circle, as shown in FIG. The code phase determination of a received signal is determined by the correlation at each point on the circle (e.g., as indicated by the correlation peak generation) until the code is located within 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 the GPS signal is 1.575 GHz, it can be difficult to maintain signal locks in areas such as indoors, inside a car and / or under a tree canopy. If the portable GPS receiver loses signal lock, uncomfortable interruption of the positioning capability and loss of computer resources may continue while the receiver attempts to reacquire the signal. As the frequency offset changes somewhat slowly, resetting the frequency lock after a short break may only require limited effort. However, the code phase of the received signal changes faster and may require searching for lost signals over the entire 1,023 symbol code phase circle. For applications where accurate positioning information must be available on demand, the above delay is unacceptable. 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 cellular 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 consumption features such as aircraft and vehicle management support.

One option for adding location tracking to 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 inside a vehicle. On the other hand, the base station of the system is well located with respect to 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 the time reference important 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 may actually reduce the size of the code phase search criteria (e.g., from 1,023 symbols to 30 symbols).

However, in analog systems for wireless communications, such as the Enhanced Mobile Phone Service (AMPS) system, which is widely used in the United States, there is no time base between mobile stations and base stations. 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 that allows the base station to transmit significant 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 satellite locks. Therefore, it is desirable to reduce the code phase search space of the distributed GPS system.

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 about 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 proceed directly to the predicted code phase, thereby 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.

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 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 the 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) code phase of the first received signal and (2) two Time relationship between code phases of the received signal (e.g., 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 an 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 a local copy of a known CA code). Information relating to the time relationship between the code phases of the received signals 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 needs time related information to reduce the amount of space that must be searched to determine the code phase of the signal from the second SV 100. Use

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 carrier signal modulated 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 about the code phase of the received signal (operation P142), and the receiver of the information (eg, field receiver 110) is the time between code phases. Work to determine the difference.

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 aforementioned code phase information 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 the 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 may include two distinct units (GPS receiver 310-1 and communication receiver 310-2) as shown in FIG. It may also include.

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 information to the client 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 likelihood of receiving signals. For example, the server transmits information related to a code sequence (eg, the sequence itself, or one or more indices 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 can also send the satellite's timing (eg, one or more time differences between code phases) to the client. The server preferably transmits these three kinds 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 relative timing of the satellites by the server does not even use timing criteria at all at the client or no common time reference between the client and the server at all. 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 used in part or in whole as hardware, as a circuit configuration manufactured by a specific application integrated circuit, or as a software program loaded into a data storage medium as a firmware program loaded into a nonvolatile storage device or a machine-readable code. 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 (32)

A method for improving the acquisition time of positioning signals received by a mobile station, Receiving a plurality of positioning signals at a reference receiver remote from the mobile station, wherein receiving the plurality of positioning signals comprises determining a code phase of the plurality of positioning signals and receiving a composite signal Wherein each of the plurality of received signals is based at least in part on at least a portion of the composite signal, Determining the code phase of each of the plurality of received signals includes calculating a correlation between a corresponding code sequence and a signal based at least in part on the composite signal for each of the plurality of received signals; , Each of the plurality of received signals has a corresponding periodic code, Each of the code phases is associated with a corresponding predetermined location within the corresponding periodic code, The code sequence is at least partially related to the corresponding periodic code; Determining a time difference between code phases of at least first and second positioning signals of the plurality of received positioning signals; Transmitting the time difference to the mobile station; And Receiving the first and second positioning signals at the mobile station, wherein receiving the first and second positioning signals is based on the code phase of the second positioning signal based at least in part on the time difference. Reducing the search space for;-improving the acquisition time of the positioning signals. delete The method of claim 1, Wherein each of the plurality of received signals is based at least in part on a corresponding direct-sequence spread spectrum modulated signal. The method of claim 1, Wherein each of the plurality of received signals is based at least in part on a corresponding direct-diffusion pseudonoise modulated signal. The method of claim 1, The first positioning signal has a corresponding periodic code, the second positioning signal has a corresponding periodic code, Wherein each of the code phase of the first positioning signal and the code phase of the second positioning signal are associated with a corresponding predetermined position in the corresponding periodic code. The method of claim 1, Wherein the positioning signals are transmitted from spacecrafts and comprise one of GPS and GLONASS signals. The method of claim 1, Wherein the plurality of positioning signals are transmitted from corresponding plurality of space vehicles. The method of claim 1, And the mobile station and the reference receiver are not time synchronized. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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