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Method and apparatus for receiving gps/glonass signalsRelated Patent Categories: Pulse Or Digital Communications, Spread Spectrum, Direct Sequence, Receiver, Multi-receiver Or Interference CancellationMethod and apparatus for receiving gps/glonass signals description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20050276316, Method and apparatus for receiving gps/glonass signals. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] This application is a divisional application which claims priority under 35 U.S.C. .sctn.120, 121 from U.S. patent application Ser. No. 09/196,658, filed Nov. 19, 1998, and which is incorporated by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to an electronic system and its components and to methods of operating the system and its components for receiving spread spectrum signals, for example, signals from a global positioning system such as Global Positioning System (GPS) and/or Global Orbiting Navigation Satellite System (GLONASS). Description of the Related Technology [0004] An increasing number of applications and systems for communicating information nowadays make use of the spread spectrum technique. The spread spectrum technique is a digital modulation technique in which a digital signal is spread over a wide frequency band so that it has a noise-like spectrum. This can be done by breaking up or "chopping" each data bit of the digital signal into multiple sub-bits (commonly called chips) that are then modulated and up-converted to a carrier frequency. The chopping may be done by multiplying the digital information signal with a so-called pseudo-random code or PN code. By using orthogonal codes for different communication links, the same frequency band can be used for different simultaneous communication links. [0005] Using the same PN code as the transmitter, a receiver can correlate the received, spread signal and reconstruct the data signal while other receivers that use other codes or other transmission techniques cannot. One of the advantages of using the spread spectrum communication technique is the robustness to narrow band interference signals. Because spread-spectrum receivers are rapidly being introduced in applications and systems meant for the consumer markets, the cost of the receiver system is a major determining factor in order to remain competitive. [0006] A specific class of spread spectrum systems are devices and receivers for position determination. Such devices are gaining importance for both the consumer market and for high precision applications. Most of the existing systems are based on the American Global Positioning System (GPS). Because this is also a military system, a precise position determination can be made difficult by the satellite operator deliberately introducing errors (called "anti-spoofing"). Moreover, in many areas the number of visible satellites can be too limited to determine an accurate position. These two problems can be reduced by also using a second positioning system such as the Russian Global Orbiting Navigation Satellite System (GLONASS) system. [0007] Combined GPS and GLONASS receivers have been reported, e.g., S. Riley, N. Howard, E. Aardoom, R. Daly, and P. Silvestrin, in "A combined GPS/GLONASS high precision receiver for space applications," ION-GPS 95, Palm Springs, USA, September 1995, or Japanese patent application JP 7128423-950519, "Receiver Common to GPS and GLONASS." [0008] A GPS receiver is disclosed in U.S. Pat. No. 5,293,170 that can be used with P-code modulated signals, which have been modulated with an unknown code. Implementations of this known device require a lot of registers. [0009] U.S. Pat. No. 5,600,670 describes a GPS receiver that includes a hierarchical chain of channel modules which includes slave modules and a master module. The known system does not provide sufficient flexibility. SUMMARY OF CERTAIN INVENTIVE ASPECTS [0010] One aspect of the present invention provides a method and an apparatus for processing received spread spectrum signals, particularly signals from a global navigational system, which allows an optimal flexibility in processing capabilities while reducing power consumption and manufacturing costs. [0011] Another aspect of the present invention provides a method and an apparatus for processing received spread spectrum signals, in particular signals from a global navigational system, which is suitable for implementation of at least one sub-system as an ASIC while maintaining an optimal flexibility in processing capabilities and reducing power consumption and chip area. [0012] Another aspect of the present invention provides a method and an apparatus for processing received signals from a global navigational system in which the processing of signals modulated with an unknown code is more efficient. [0013] Another aspect of the present invention provides an apparatus for processing received spread spectrum signals modulated with a unique pseudo-random code, comprising: a plurality of channel modules each including a correlator; means for hierarchically chaining a plurality of the channel modules in series, the means including a selector for selecting one channel module from at least two candidate channel modules for the next channel module of the chain. [0014] Another aspect of the present invention provides an apparatus for processing received spread spectrum signals modulated with a unique pseudo-random code, comprising: a plurality of channel modules each including a correlator; means for hierarchically chaining a plurality of the channel modules in series, code and/or control signals and/or carrier signals being passed from one channel module of the chain to the next; and a selector for selecting to transmit the code and/or control signals and/or carrier signals to the next channel module in the chain with a delay or without a delay. [0015] Another aspect of the present invention provides a method of processing received spread spectrum signals using a plurality of channel modules each including a correlator, the method comprising: selecting one of two further modules to include within a chain of a plurality of channel modules; selecting to transmit code and/or control and/or carrier signals to the next channel module in a chain of a plurality of channel modules with or without delay. [0016] Another aspect of the present invention provides an apparatus for tracking received spread spectrum signals modulated with a unique pseudo-random code and for obtaining a correlation profile, comprising: a generator for generating a first replica of the pseudo-random code; a first demodulator for sequentially demodulating the received spread spectrum signals with the replica of the pseudo-random code at regular time intervals; a first integrator for integrating the output of the first demodulator; a second generator for generating a plurality of second versions of the first locally generated replica of the pseudo-random code, each second version having, in any one time interval, a selectably different timing compared with the timing of the first replica; a second demodulator for sequentially demodulating the received spread spectrum signal at regular integration time intervals with different ones of the second versions of the first replica and outputting the results; and a second single integrator for integrating each output of the second demodulator separately. [0017] Another aspect of the present invention provides a method for tracking received spread spectrum signals modulated with a unique pseudo-random code to obtain a correlation profile, comprising: generating a first locally generated replica of the pseudo-random code; sequentially demodulating the received spread spectrum signals with the first locally generated replica of the pseudo-random code at regular time intervals and integrating the result of each demodulation in a first integration using a first integrator; generating a plurality of second versions of the first locally generated replica of the pseudo-random code, each second version having a selectably different timing compared with the timing of the first replica in any one time interval; sequentially demodulating the received spread spectrum signal with different ones of the second versions of the first replica at regular time intervals and integrating each demodulation result separately in second integrating steps using a single second integrator. [0018] In one embodiment, the apparatus or method described in [0012]-[0014 ] may be used in combination with the apparatus or method described in [0015]-[0016]. In particular, the apparatus or method described in [0012]-[0014] may be useful in both rapid acquisition and efficient tracking of spread spectrum signals, whereas the apparatus or method described in [0015]-[0016] may be useful in obtaining a correlation profile during tracking of the signals. [0019] Another aspect of the present invention provides an apparatus for despreading received spread spectrum signals, at least a part of the received signals being modulated with a first unique coarse acquisition pseudo-random code and a second precision unique pseudo-random code; comprising: a first plurality of correlators, a second plurality of correlators; and a switching device for switching any one of the first plurality of correlators to correlate the received spread spectrum signals with respect to one of the first and second unique pseudo-random codes. [0020] Another aspect of the present invention provides a method of despreading received spread spectrum signals, at least a part of the received signals being modulated with a first unique coarse acquisition pseudo-random code and a second precision unique pseudo-random code using a first plurality of correlators and a second plurality of correlators, the method comprising: selecting for any one of the first plurality of correlators so that this correlator correlates the received spread spectrum signals with respect to one of the first and second unique pseudo-random codes. [0021] In one embodiment, the apparatus or method described in [0018]-[0019] may be used in combination with at least one of the apparatuses and methods described in [0012]-[0017]. This embodiment may provide the advantage of flexibility of selecting correlators to correlate either CA-code or P-code signals of a GLONASS (Global Orbiting Navigation Satellite System) or GPS global positioning system. 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