Combined GPS/GLONASS satellite positioning system receiver

• US 5,923,287 A
• Filed: 04/01/1997
• Issued: 07/13/1999
• Est. Priority Date: 04/01/1997
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Lennen, Gary R.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US08/831,095
• Time in Patent Office: 833 Days
• Field of Search: 342/357, 455/314, 701/213
• US Class Current: 342/357.73
• CPC Class Codes: G01S 19/33 Multimode operation in different systems which transmit time stamped messages, e.g. GPS/GLONASS
• CPC Class Codes: G01S 19/36 relating to the receiver frond end

Abstract

A combined GPS/GLONASS Receiver is disclosed. The GLONASS system of satellites operates at a higher orbit inclination than GPS satellites (64° for GLONASS, 55° for GPS). This leads to GLONASS having better coverage at higher latitudes, e.g. in the State of Alaska or Northern Europe. The combined GPS/GLONASS receiver incorporates this advantage. Another advantage of using the GPS/GLONASS receiver is that GLONASS can become a back up system when the US Government intentionally degrades the GPS system accuracy via Selective Availability (SA). The combined GPS/GLONASS Receiver can receive signals from more satellites and therefore has more resistance to jamming than a single GPS or GLONASS Receiver.

Claims

1. An apparatus for receiving satellite signals generated by a GPS satellite system and a GLONASS satellite system, wherein said GPS system generates L1_GPS and L² GPS signals, wherein said GLONASS system generates L1_GLONASS and L² GLONASS signals;

said apparatus comprising;

a Receiver circuit configured to receive the satellite signals from each said satellite system;

said Receiver circuit further including;

an Antenna configured to receive said L1_GPS, L2_GPS, L1_GLONASS, and L2_GLONASS signals;

a Filter/LNA circuit conductively connected to said Antenna, wherein said Filter/LNA is configured to perform the filtering and low noise amplification of said L1_GPS, L2_GPS, L1_GLONASS, and L2_GLONASS signals;

wherein said Filter/LNA determines the signal-to-noise (SNR) ratio of the received signals;

a Downconverter circuit conductively connected to said Filter/LNA, wherein said Downconverter is configured to convert down in frequency said L1_GPS, L2_GPS, L1_GLONASS, and L2_GLONASS signals; and

an IF processor conductively connected to said Downconverter, wherein said IF processor is configured for further frequency translating and digitizing said L1_GPS, L2_GPS, L1_GLONASS, and L2_GLONASS signals;

a plurality of Digital Channel Processor circuits connected to said Receiver circuit, wherein each said Digital Channel Processor is configured to process received satellite signals emanating from a single satellite; and

a Microprocessor connected to each said Digital Channel Processor, wherein said Microprocessor is configured to extract the navigational information from each said received satellite signal.

2. The apparatus of claim 1 further comprising a master oscillator block configured to generate a single clock frequency MASTER_-- CLK, a GPS clock frequency OSC_GPS, and a GLONASS clock frequency OSC_GLONASS, wherein said GPS clock frequency OSC_GPS and GLONASS clock frequency OSC_GLONASS are both derived from said single clock frequency MASTER_-- CLK.

3. The apparatus of claim 2 further comprising a frequency synthesizer connected to said master oscillator, wherein said frequency synthesizer is configured to synthesize LO₁, LO₂, LO₃, LO₄, msec, and sclk clock signals.

4. The apparatus of claim 2, wherein said master oscillator further comprises:

a master clock generator configured to generate a MASTER_-- CLK frequency signal;

a first divider block connected to said master clock generator, wherein said first divider is configured to divide said MASTER_-- CLK frequency signal and configured to generate said OSCGPS frequency clock signal;

a first phase detector connected to said first divider block, wherein said first phase detector is configured to phase detect said first divided MASTER_-- CLK signal against a first reference signal;

a first loop Filter connected to said first phase detector, wherein said first loop Filter is configured to filter out high the high frequency component signal and to output a first filtered signal, wherein said first filtered signal includes low frequency voltage noise;

a second phase detector connected to said first loop Filter, wherein said second phase detector is configured to phase compare said first filtered signal against a second reference signal;

a second loop Filter connected to said second phase detector, wherein said second loop Filter is configured to filter out high and low frequency voltage noise in order to close the phase-locked loop;

a first voltage controlled oscillator (VCO₁) connected to said second loop Filter, wherein said VCO₁ is configured to generate said first reference signal and said OSC_GLONASS signal; and

a second divider block connected to said first divider block, wherein said second divider is configured to generate said second reference signal.

5. The apparatus of claim 2, wherein said master oscillator further comprises:

a master clock generator configured to generate a 10 MHZ (MASTER_-- CLK) frequency signal;

a "Divide by 2" block connected to said master clock generator, wherein said "Divide by 2" block is configured to divide said 10 MHZ frequency signal and configured to generate a 5 MHz (OSC_GPS) frequency clock signal;

a first phase detector connected to said "Divide by 2" block, wherein said first phase detector is configured to phase detect said 5 MHz signal against a first reference signal;

a first loop Filter connected to said first phase detector, wherein said first loop Filter is configured to filter out high the high frequency component signal and to output a first filtered (100 kHz) signal, wherein said first filtered (100 kHz) signal includes low frequency voltage noise;

a second phase detector connected to said first loop Filter, wherein said second phase detector is configured to phase compare said first filtered 100 kHz signal against a second reference 100 kHz signal;

a second loop Filter connected to said second phase detector, wherein said second loop Filter is configured to filter out high and low frequency voltage noise in order to close the phase-locked loop;

a first voltage controlled oscillator (VCO₁) connected to said second loop Filter, wherein said VCO₁ is configured to generate said first reference (5.1 MHz) signal and said 5.1 MHz (OSC_GLONASS) signal; and

a "Divide by 50" block connected to said "Divide by 2" block, wherein said second divider is configured to generate said second reference 100 kHz signal.

6. The apparatus of claim 3, wherein said frequency synthesizer block further comprises a GLONASS synthesizer block and a GPS synthesizer block.

7. The apparatus of claim 6, wherein said GLONASS synthesizer block further comprises:

a "Divide by 5" block configured to generate a third reference signal;

a third phase detector connected to said "Divide by 5" block, wherein said third phase detector is configured to compare said 5.1 MHz (OSC_GLONASS) signal with said third reference signal;

a third loop Filter circuit connected to said third phase detector, wherein said third loop Filter is configured to filtering out high frequency voltage noise;

a second voltage controlled oscillator (VCO₂) connected to said third loop Filter, wherein said VCO₂ is configured to generate said LO₂ (1428 MHz) clock signal;

a "Divide by 8" block connected to said VCO₂, wherein said "Divide by 8" block is configured to divide said 1428 MHz VCO₂ output signal by 8 to obtain said LO₄ (178.5 MHz) clock signal;

a "Divide by 7" block connected to said "Divide by 8" block, wherein said "Divide by 7" block is configured to divide said 178.5 MHz signal by 7 to obtain a 25.5 MHz signal; and

a "Divide by 5" block connected to said "Divide by 7" block, wherein said "Divide by 5" block is configured to divide said 25.5 MHz signal by 5 to obtain said third reference (5.1 MHz) signal.

8. The apparatus of claim 6, wherein said GPS synthesizer block further comprises:

a "Divide by 5" block configured to generate a fourth reference signal;

a fourth phase detector connected to said "Divide by 5" block, wherein said fourth phase detector is configured to compare said 5 MHz (OSC_GPS) signal with said fourth reference signal;

a fourth loop Filter circuit connected to said fourth phase detector, wherein said fourth loop filer is configured to filter out the high frequency voltage noise;

a third voltage controlled oscillator (VCO₃) connected to said fourth loop Filter, wherein said VCO₃ is configured to generate said LO₁ (1400 MHz) clock signal;

a "Divide by 8" block connected to said VC0₃, wherein said "Divide by 8" block is configured to divide said 1400 MHz VCO output signal by 8 to obtain said LO₃ (175 MHz) clock signal;

a "Divide by 7" block connected to said "Divide by 8" block, wherein said "Divide by 7" block is configured to divide said 175 MHz signal by 7 to obtain said sclk (25 MHz) wide digital sampling clock signal;

a "Divide by 5" block connected to said "Divide by 7" block, wherein said "Divide by 5" block is configured to divide said 25 MHz signal by 5 to obtain said fourth reference (5 MHz) signal; and

a "Divide by 25000" block connected to said "Divide by 5" block, wherein said "Divide by 25000" block is configured to generate a 1 kHz (msec) clock signal used by each said Digital Channel Processor as a reference clock timing signal.

9. The apparatus of claim 1, wherein said filter/LNA circuit further comprises:

a power splitter connected to said Antenna, wherein said power splitter is configured to power split a single L1/L2 signal received by said Antenna into two separate L1 and L2 signal paths, and wherein said L1 signal has bandwidth L1_-- BAND that includes both L1_GPS and L1_GLONASS signals; and

wherein said L2 signal has bandwidth L2_-- BAND to include both L2_GPS and L2_GLONASS signals;

a first Bandpass Filter connected to said power splitter, wherein said first Bandpass Filter is configured to filter said L1 signal, and wherein said first Bandpass Filter has a bandwidth at least as wide as the L1_-- BAND bandwidth;

a second Bandpass Filter connected to said power splitter, wherein said second Bandpass Filter is configured to filter said L2 signal, and wherein said second Bandpass Filter has a bandwidth at least as wide as the L2_-- BAND bandwidth;

a first low noise amplifier (LNA₁) connected to said first Bandpass Filter, wherein said first low noise amplifier is configured to maintain the signal-to noise ratio (SNR) of said apparatus in the L1 path; and

a second low noise amplifier (LNA₂) connected to said second Bandpass Filter, wherein said second low noise amplifier is configured to maintain the signal-to noise ratio (SNR) of said apparatus in the L2 path.

10. The apparatus of claim 1, wherein said Downconverter circuit further comprises:

a first power splitter configured to split the L1 signal generated by said first LNA₁ amplifier into the L1_-- GPS signal path and into the L1_-- GLONASS signal path;

a second power splitter connected to said first power splitter, wherein said second power splitter is configured to split the L2 signal generated by said second LNA₂ amplifier into the L2_-- GPS signal path and into the L2_-- GLONASS signal path;

a first mixer connected to said first power splitter, wherein said first mixer is configured to frequency translate the L1 GPS signal from center frequency 1575.42 MHz to 175.42 MHz;

a first Filter connected to said first mixer, wherein said first Filter has a center frequency of 175.42 MHz and a bandwidth of 25 MHz, and wherein said first Filter is configured to output the L1 GPS signal having 175.42 MHz frequency;

a fist amplifier connected to said first Filter, wherein said first amplifier is configured to amplify said L1 GPS signal and outputs an L1_GPS signal;

a second mixer connected to said first power splitter, wherein said second mixer is configured to frequency translate the L1 GLONASS signal from center frequency 1606.78125 MHz to 178.78125 MHz;

a second Filter connected to said second mixer, wherein said second Filter has a center frequency of 178.78125 MHz and a bandwidth of 25 MHz, and wherein said second Filter is configured to output the L1 GLONASS signal having 178.78125 MHz frequency;

a second amplifier connected to said second Filter, wherein said second amplifier is configured to amplify said L1 GLONASS signal and outputs an L1_GLONASS signal;

a third mixer connected to said second power splitter, wherein said third mixer is configured to frequency translate the L2 GPS signal from center frequency 1227.6 MHz to 172.4 MHz;

a third Filter connected to said third mixer, wherein said third Filter has a center frequency of 172.4 MHz and a bandwidth of 25 MHz, and wherein said third Filter is configured to output the L2 GPS signal having 172.4 MHz frequency;

a third amplifier connected to said third Filter, wherein said third amplifier is configured to amplify said L2 GPS signal and outputs an L2_GPS signal;

a fourth mixer connected to said second power splitter, wherein said fourth mixer is configured to frequency translate the L2 GLONASS signal from center frequency 1249.71875 MHz to 178.28125 MHz;

a fourth Filter connected to said fourth mixer, wherein said fourth Filter has a center frequency of 178.28125 MHz and a bandwidth of 25 MHz, and wherein said fourth Filter is configured to output the L2 GLONASS signal having 178.28125 MHz frequency; and

a fourth amplifier connected to said fourth Filter, wherein said fourth amplifier is configured to amplify said L2 GLONASS signal and outputs an L2_GLONASS signal.

11. The apparatus of claim 1, wherein said IF processor further comprises:

a first IF Downconverter and Sampler block configured to frequency translate to 420 kHz the L1_GPS signal using the LO₃ clock signal and to digitally sample the 420 kHz L1_GPS signal using the sclk signal in order to generate the inphase and quadrature components I_L1 GPS and Q_L1 GPS ;

a second IF Downconverter and Sampler block configured to frequency translate to (-2.6) MHz the L2_GPS signal using the LO₃ clock signal and to digitally sample the (-2.6) MHz L2_GPS signal using the sclk signal in order to generate the inphase and quadrature components I_L2 GPS and Q_L2 GPS ;

a third IF Downconverter and Sampler block configured to frequency translate to 281.25 kHz the L1_GLONASS signal using the LO₄ clock signal and to digitally sample the 281.25 kHz L1_GLONASS signal using the sclk signal in order to generate the inphase and quadrature components I_L1 GLONASS and Q_L1 GLONASS ; and

a fourth IF Downconverter and Sampler block configured to frequency translate to (-218.75) kHz the L2_GLONASS signal using the LO₄ clock signal and to digitally sample the (-218.75) kHz L2_GLONASS signal using the sclk signal in order to generate the inphase and quadrature components I_L2 GLONASS and Q_L2 GLONASS.

12. The apparatus of claim 11, wherein each said IF Downconverter and Sampler block further comprises:

a power splitter configured to split the input signal S_i into two components S_i1 and S_i2 ;

a first mixer connected to said power splitter, wherein said first mixer is configured to mix the S_i1 signal with the inphase component of the local clock signal LO to generate the frequency translated (S_i1 -Inphase LO) signal;

a first low pass Filter connected to said first mixer, wherein said first low pass Filter is configured to pass the low frequency component of the mixed (S_i1 -Inphase LO) signal;

a first amplifier connected to said first low pass Filter, wherein said first amplifier is configured to amplify the low frequency component of the (S_i1 -Inphase LO) signal;

a first quantizer connected to said first amplifier, wherein said first quantizer is configured to quantize the low frequency component of the (S_i1 -Inphase LO) signal;

a first flip-flop connected to said first quantizer, wherein said first flip-flop is configured to sample the quantized (S_i1 -Inphase LO) signal;

a second mixer connected to said power splitter, wherein said second mixer is configured to mix the S_i2 signal with the quadrature component of the local clock signal LO to generate the frequency translated (S_i2 -Quadrature LO) signal;

a second low pass Filter connected to said second mixer, wherein said second low pass Filter is configured to pass the low frequency component of the mixed (S_i2 -Quadrature LO) signal;

a second amplifier connected to said second low pass Filter, wherein said second amplifier is configured to amplify the low frequency component of the (S_i2 -Quadrature LO) signal;

a second quantizer connected to said second amplifier, wherein said second quantizer is configured to quantize the low frequency component of the (S_i2 -Quadrature LO) signal; and

a second flip-flop connected to said second quantizer, wherein said second flip-flop is configured to sample the quantized (S_i2 -Quadrature LO) signal.

13. The apparatus of claim 12, wherein said first quantizer comprises a 1-bit quantizer;

and wherein said second quantizer comprises a 1-bit quantizer.

14. The apparatus of claim 12, wherein said first quantizer comprises a multi-bit quantizer;

and wherein said second quantizer comprises a multi-bit quantizer.

15. The apparatus of claim 1, wherein each said Digital Channel Processor circuit further comprises:

a first multiplexer configured to select for further processing the I_L1 GPS, Q_L1 GPS, I_L1 GLONASS, and Q_L1 GLONASS signals;

a first signal tracker connected to said first multiplexer, wherein said first signal tracker is configured to process the I_L1 GPS, Q_L1 GPS, I_L1 GLONASS, and Q_L1 GLONASS signals;

a second multiplexer configured to select for further processing the I_L2 GPS, Q_L2 GPS, I_L2 GLONASS, and Q_L2 GLONASS signals; and

a second signal tracker connected to said second multiplexer, wherein said second signal tracker is configured to process the I_L2 GPS, Q_L2 GPS, I_L2 GLONASS, and Q_L2 GLONASS signals;

wherein said first signal tracker and said second signal tracker are synchronously clocked at the sclk clock rate to facilitate the digital signal tracking and code and carrier phase measurements for L1 and L2 signals in conjunction with said Microprocessor system μ

P.

16. The apparatus of claim 15, wherein each said signal tracker further comprises:

a carrier mixer configured to further frequency translate the I and Q components of the incoming satellite signals to d. c. carrier frequency (0 Hz carrier frequency) I and Q components of the incoming satellite signals;

a carrier numerically controlled oscillator (NCO) circuit connected to said carrier mixer, wherein said block carrier NCO is configured to close the carrier tracking loop via the control of said Microprocessor system μ

P;

a code mixer circuit connected to said carrier mixer, wherein said code mixer is configured to mix the d. c. I and Q carrier components of the incoming satellite signals with the locally generated code L_c signals at three time points Early (E), Punctual (P), and Late (L) on the autocorrelation function formed between the satellite code and local code;

a code generator connected to said code mixer, wherein said code generator is configured to generate the code signals L_c ;

a code NCO connected to said code generator, wherein said code NCO is configured to drive said code generator; and

a correlators block connected to said code mixer, wherein said correlators block is configured to integrate the signals outputted by said code mixer over an integer period of C/A epoch signals;

wherein said Microprocessor system μ

P uses said correlators output signal to form the code and carrier tracking loops via the feedback to said code NCO and said carrier NCO.

17. The apparatus of claim 16, wherein said code generator further comprises:

a GPS C/A code generator configured to generate a GPS C/A code signal;

a GPS P(Y) code generator configured to generate a GPS P(Y) code signal;

a GLONASS C/A code generator configured to generate a GLONASS C/A code signal;

a GLONASS P code generator configured to generate a GLONASS P code signal; and

a multiplexer 3 configured to select the local code L_c from GPS C/A, GPS P(Y), GLONASS C/A, and GLONASS C/A locally generated codes depending on what signals said Digital Channel Processor is required to track.

18. The apparatus of claim 1, wherein said GPS system generates L1_GPS signal, wherein said GLONASS system generates L1_GLONASS signal;

and wherein said Receiver circuit further includes;

an Antenna configured to receive said L1_GPS and L1_GLONASS signals;

a Filter/LNA circuit conductively connected to said Antenna, wherein said Filter/LNA is configured to perform the filtering and low noise amplification of said L1_GPS and L1_GLONASS signals;

wherein said Filter/LNA determines the signal-to-noise ratio (SNR) of the received signals;

a Downconverter circuit conductively connected to said Filter/LNA, wherein said Downconverter is configured to convert down in frequency said L1_GPS and L1 _GLONASS signals; and

an IF processor conductively connected to said Downconverter, wherein said IF processor is configured to further frequency translate and digitize said L1_GPS and L1_GLONASS signals.

19. The apparatus of claim 1, wherein each said Digital Channel Processor circuit further comprises:

a multiplexer configured to select for further processing the I_L1 GPS, Q_L1 GPS, I_L1 GLONASS, and Q_L1 GLONASS signals; and

a signal tracker connected to said first multiplexer, wherein said signal tracker is configured to process the I_L1 GPS, Q_L1 GPS, I_L1 GLONASS, and Q_L1 GLONASS signals;

wherein said signal tracker and said signal tracker are synchronously clocked at the sclk clock rate to facilitate the digital signal tracking and code and carrier phase measurements for L1_GPS and L1_GLONASS signals in conjunction with said Microprocessor system μ

p.

20. The apparatus of claim 1, wherein said GPS system generates L2_GPS signal, wherein said GLONASS system generates L2_GLONASS signal;

and wherein said Receiver circuit further includes;

an Antenna configured to receive said L2_GPS and L2_GLONASS signals;

a Filter/LNA circuit conductively connected to said Antenna, wherein said Filter/LNA is configured to perform the filtering and low noise amplification of said L2_GPS and L2_GLONASS signals;

wherein said Filter/LNA determines the signal-to-noise ratio (SNR) of the received signals;

a Downconverter circuit conductively connected to said Filter/LNA, wherein said Downconverter is configured to convert down in frequency said L2_GPS and L2_GLONASS signals; and

an IF processor conductively connected to said Downconverter, wherein said IF processor is configured to further frequency translate and digitize said L2_GPS and L2_GLONASS signals.

21. The apparatus of claim 1, wherein each said Digital Channel Processor circuit further comprises:

a multiplexer configured to select for further processing the I_L2 GPS, Q_L2 GPS, I_L2 GLONASS, and Q_L2 GLONASS signals; and

a signal tracker connected to said first multiplexer, wherein said signal tracker is configured to process the I_L2 GPS, Q_L2 GPS, I_L2 GLONASS, and Q_L2 GLONASS signals;

wherein said signal tracker and said signal tracker are synchronously clocked at the sclk clock rate to facilitate the digital signal tracking and code and carrier phase measurements for L2_GPS and L2_GLONASS signals in conjunction with said Microprocessor system μ

P.

22. A method for receiving satellite signals generated by GPS and GLONASS satellite systems, each said satellite system comprising a plurality of satellites, said method employing an apparatus comprising a Receiver circuit, a plurality of Digital Channel Processor circuits, wherein each said Digital Channel Processor is configured to track one said satellite, and a Microprocessor, said method comprising the steps of:

(a) selecting the GPS or GLONASS satellite system;

(b) if the GPS system is selected, tracking first said GPS satellite and extracting from the tracked satellite signals prn X(1) code;

(c) computing which GPS satellites are above the horizon based on the orbital almanac information extracted from said first GPS satellite prn X(1) code, wherein each said (i) GPS satellite has its unique prn X(i) code, `i` being an integer;

(d) selecting said second GPS satellite for tracking by determining its prn X(2) code and by determining carrier frequencies of L1 and L2 signals for said second GPS satellite;

(e) setting the correct code clock rate for said second GPS satellite;

(f) initializing the generator of local code signals;

(g) generating locally the GPS C/A;

(h) tracking C/A code;

(i) performing a handover operation to locally generate the GPS P code;

(j) setting the expected value of final intermediate carrier frequency, wherein for tracking the L1 GPS signal the expected carrier frequency is equal to (420 kHz+Doppler offset between said apparatus and said satellite being tracked), and wherein for L2 GPS signal the expected carrier frequency is equal to (-2.6 MHz+Doppler offset between said apparatus and said satellite being tracked);

(k) searching for signal power by adjusting the locally generated signals;

(l) repeating said steps (d)-(k) for `k` number of visible GPS satellite, wherein `k` is less or equal to the number of all visible GPS satellites, k being an integer;

(m) if the GLONASS satellite system is selected, tracking a GLONASS satellite;

(n) identifying a plurality of visible GLONASS satellites by the GLONASS satellite vehicle identification number SV_-- ID Y acquired from the GLONASS almanac data obtained from said tracked GLONASS satellite, wherein although the GLONASS C/A and P codes are identical C/A and P codes for all GLONASS satellites, the nominal carrier transmission frequency is unique for each said GLONASS satellite;

(o) selecting one said visible Y GLONASS satellite for tracking;

(p) setting the correct code clock rate for said selected Y GLONASS satellite;

(q) initializing the generator of local code signals;

(r) generating locally the GLONASS C/A and P codes;

(s) setting the carrier frequency to expected nominal frequency for said Y GLONASS satellite plus Doppler offset between said apparatus and said Y GLONASS satellite;

(t) searching for signal power by adjusting the locally generated signals; and

(y) repeating said steps (o)-(t) for `m` number of visible GLONASS satellite, wherein `m` is less or equal to the number of all visible GLONASS satellites.

23. A method for combined GPS/GLONASS measurement processing after the lock on a GPS satellite and a lock on a GLONASS satellite is acquired, said method employing an apparatus comprising a Receiver circuit, a plurality of Digital Channel Processor circuits, wherein each said Digital Channel Processor is configured to track one said GPS or GLONASS satellite, and a Microprocessor, said method comprising the steps of:

smoothing a GPS satellite pseudo range measurement with said GPS satellite'"'"'s equivalent carrier phase measurements to obtain the resulting position and velocity solution in the WGS 84 coordinate reference system and the time solution referenced to GPS system time or UTC (USNO);

smoothing a GLONASS satellite pseudo range measurement with said GLONASS satellite'"'"'s equivalent carrier phase measurements to obtain the resulting position and velocity solution in the SGS 90 coordinate reference system and the time solution referenced to GLONASS system time or UTC (SU); and

using combined GPS/GLONASS pseudo range measurements with combined GPS/GLONASS carrier phase measurements to obtain the resulting position and velocity solution in the composite WGS 84 and SGS 90 coordinate reference systems and the time solution that provides the offset between GPS and GLONASS system times.

24. The method of claim 23, wherein if the transformation matrix is available for transformation the WGS 84 coordinate system into the SGS 90 coordinate system, said method further comprises the step of:

transforming the obtained pseudo range measurements from the WGS 84 coordinate system to the SGS 90 coordinate system and vice versa.

25. A method for receiving satellite signals generated by GPS and GLONASS satellite systems, each said satellite system comprising a plurality of satellites, said method employing an apparatus comprising a Receiver circuit, a plurality of Digital Channel Processor circuits, wherein each said Digital Channel Processor is configured to track one said satellite, and a Microprocessor, said method comprising the steps of:

(a) selecting the GPS or GLONASS satellite system;

(b) if the GPS system is selected, tracking first said GPS satellite and extracting from the tracked satellite signals prn X(1) code;

(c) computing which GPS satellites are above the horizon based on the orbital almanac information extracted from said first GPS satellite prn X(1) code, wherein each said (i) GPS satellite has its unique prn X(i) code, `i` being an integer;

(d) selecting said second GPS satellite for tracking by determining its prn X(2) code and by determining carrier frequencies of L1 signal for said second GPS satellite;

(e) setting the correct code clock rate for said second GPS satellite;

(f) initializing the generator of local code signals;

(g) generating locally the GPS C/A;

(h) tracking C/A code;

(i) performing a handover operation to locally generate the GPS P code;

(j) setting the expected value of final intermediate carrier frequency, wherein for tracking the L1 GPS signal the expected carrier frequency is equal to (420 kHz+Doppler offset between said apparatus and said satellite being tracked);

(k) searching for signal power by adjusting the locally generated signals;

(l) repeating said steps (d)-(k) for `k` number of visible GPS satellite, wherein `k` is less or equal to the number of all visible GPS satellites, k being an integer;

(m) if the GLONASS satellite system is selected, tracking a GLONASS satellite;

(n) identifying a plurality of visible GLONASS satellites by the GLONASS satellite vehicle identification number SV_-- ID Y acquired from the GLONASS almanac data obtained from said tracked GLONASS satellite, wherein although the GLONASS C/A and P codes are identical C/A and P codes for all GLONASS satellites, the nominal carrier transmission frequency is unique for each said GLONASS satellite;

(o) selecting one said visible Y GLONASS satellite for tracking;

(p) setting the correct code clock rate for said selected Y GLONASS satellite;

(q) initializing the generator of local code signals;

(r) generating locally the GLONASS C/A and P codes;

(s) setting the carrier frequency to expected nominal frequency for said Y GLONASS satellite plus Doppler offset between said apparatus and said Y GLONASS satellite;

(t) searching for signal power by adjusting the locally generated signals; and

(y) repeating said steps (o)-(t) for `m` number of visible GLONASS satellite, wherein `m` is less or equal to the number of all visible GLONASS satellites.

26. A method for receiving satellite signals generated by GPS and GLONASS satellite systems, each said satellite system comprising a plurality of satellites, said method employing an apparatus comprising a Receiver circuit, a plurality of Digital Channel Processor circuits, wherein each said Digital Channel Processor is configured to track one said satellite, and a Microprocessor, said method comprising the steps of:

(a) selecting the GPS or GLONASS satellite system;

(b) if the GPS system is selected, tracking first said GPS satellite and extracting from the tracked satellite signals prn X(1) code;

(c) computing which GPS satellites are above the horizon based on the orbital almanac information extracted from said first GPS satellite prn X(1) code, wherein each said (i) GPS satellite has its unique prn X(i) code, `i` being an integer;

(d) selecting said second GPS satellite for tracking by determining its prn X(2) code and by determining carrier frequencies of L2 signal for said second GPS satellite;

(e) setting the correct code clock rate for said second GPS satellite;

(f) initializing the generator of local code signals;

(g) generating locally the GPS C/A;

(h) tracking C/A code;

(i) performing a handover operation to locally generate the GPS P code;

(j) setting the expected value of final intermediate carrier frequency, wherein for tracking the L2 GPS signal the expected carrier frequency is equal to (-2.6 MHz+Doppler offset between said apparatus and said satellite being tracked);

(k) searching for signal power by adjusting the locally generated signals;

(l) repeating said steps (d)-(k) for `k` number of visible GPS satellite, wherein `k` is less or equal to the number of all visible GPS satellites, k being an integer;

(m) if the GLONASS satellite system is selected, tracking a GLONASS satellite;

(n) identifying a plurality of visible GLONASS satellites by the GLONASS satellite vehicle identification number SV_-- ID Y acquired from the GLONASS almanac data obtained from said tracked GLONASS satellite, wherein although the GLONASS C/A and P codes are identical C/A and P codes for all GLONASS satellites, the nominal carrier transmission frequency is unique for each said GLONASS satellite;

(o) selecting one said visible Y GLONASS satellite for tracking;

(p) setting the correct code clock rate for said selected Y GLONASS satellite;

(q) initializing the generator of local code signals;

(r) generating locally the GLONASS C/A and P codes;

(s) setting the carrier frequency to expected nominal frequency for said Y GLONASS satellite plus Doppler offset between said apparatus and said Y GLONASS satellite;

(t) searching for signal power by adjusting the locally generated signals; and

(y) repeating said steps (o)-(t) for `m` number of visible GLONASS satellite, wherein `m` is less or equal to the number of all visible GLONASS satellites.