Sequential chip mixed frequency correlator array system
A global navigation satellite system (GNSS) receiver including a sequential chip mixed frequency correlator array system (SCMFCAS) is provided. The SCMFCAS includes P signal generators, each receiving N samples of intermediate frequency (IF) data of a GNSS signal. Each signal generator includes a primary mixer, a pseudo random noise code generator, and Q mixed frequency correlators (MFCs). Each MFC generates accumulated correlation components of the N samples of the IF data by processing the N samples of the IF data. Adders and subtractors operably connected to the SCMFCAS are time division multiplexed for generating correlation values of a positive frequency and a negative frequency of the N samples of the IF data by combining the accumulated correlation components. Time division multiplexing the adders and the subtractors across the SCMFCAS and generation of the correlation values reduce logic area of the SCMFCAS, thereby reducing power consumption of the GNSS receiver.
1. A method for generating correlation values for a positive frequency and a negative frequency of a global navigation satellite system signal received by a radio frequency down converter of a global navigation satellite system receiver, said method comprising:
providing a radio frequency (RF) down converter, a global navigation satellite system baseband engine, and a coprocessor, wherein said global navigation satellite system baseband engine comprises a carrier frequency offset module, a satellite signal acquisition module and a tracking module, wherein said satellite signal acquisition module comprises a carrier generator and mixer, a sequential chip mixed frequency correlator array system, a selector, a post correlation unit and a peak detector, wherein said sequential chip mixed frequency correlator array system comprises P signal generators deployed in a global navigation satellite system baseband engine, wherein P is a positive integer corresponding to number of signal generators, wherein each of said P signal generators comprises a primary mixer, a local carrier generator, a pseudo random noise code generator, a linear feedback shift register, and Q mixed frequency correlators, wherein Q is a positive integer corresponding to number of mixed frequency correlators, wherein each of said Q mixed frequency correlators comprises secondary mixers operably connected to said primary mixer, and accumulator and dump units operably connected to corresponding said secondary mixers, wherein said post correlation unit comprises final stage adders and subtractors, a coherent accumulator, and a non-coherent accumulator, and wherein said final stage adders and subtractors are operably connected to said sequential chip mixed frequency correlator array system via said selector;
receiving N samples of intermediate frequency data from said radio frequency down converter, by said primary mixer of said each of said P signal generators;
generating inphase components and quadrature phase components of said received N samples of said intermediate frequency data, by said primary mixer of said each of said P signal generators, by mixing said received N samples of said intermediate frequency data with a carrier reference signal locally generated by a local carrier generator, wherein said N samples of said intermediate frequency data correspond to a global navigation satellite system signal received by said radio frequency down converter;
receiving said generated inphase components, said generated quadrature phase components, and a pseudo random noise code bit sequence, by said each of said Q mixed frequency correlators, wherein said pseudo random noise code bit sequence corresponds to said received global navigation satellite system signal, and wherein said pseudo random noise code bit sequence is generated using said pseudo random noise code generator;
generating, by said secondary mixers of said each of said Q mixed frequency correlators, discrete correlation components of said received N samples of said intermediate frequency data by mixing said generated inphase components and said generated quadrature phase components of said received N samples of said intermediate frequency data with said pseudo random noise code bit sequence;
generating accumulated correlation components of said received N samples of said intermediate frequency data by coherently accumulating and dumping said generated discrete correlation components of said received N samples of said intermediate frequency data, by said accumulator and dump units of said each of said Q mixed frequency correlators; and
sequentially generating said correlation values for said positive frequency and said negative frequency of said received N samples of said intermediate frequency data, by time division multiplexing of said final stage adders and subtractors operably connected to said sequential chip mixed frequency correlator array system, by combining said accumulated correlation components of said each of said Q mixed frequency correlators from said each of said P signal generators, wherein said time division multiplexing of said final stage adders and subtractors after said accumulation and said dumping of said generated discrete correlation components of said received N samples of said intermediate frequency data, and said generation of said correlation values for said positive frequency and said negative frequency of said received N samples of said intermediate frequency data using said accumulated correlation components of said each of said Q mixed frequency correlators from said each of said P signal generators reduce logic area of said sequential chip mixed frequency correlator array system in said global navigation satellite system baseband engine, thereby reducing power consumption of said global navigation satellite system receiver.
2. The method of claim 1 , wherein said carrier frequency offset module comprises an auxiliary local carrier generator and an auxiliary mixer operably connected to said auxiliary local carrier generator and said radio frequency down converter, wherein said auxiliary local carrier generator generates an offsetting carrier reference signal, wherein said auxiliary local carrier generator operates at a sampling rate f s , and wherein said auxiliary mixer offsets carrier frequency of said N samples of said intermediate frequency data to zero by mixing said N samples of said intermediate frequency data with said offsetting carrier reference signal, for further reducing said power consumption of said global navigation satellite system receiver.
3. The method of claim 1 , wherein said local carrier generator operates at a frequency greater than twice of maximum Doppler frequency supported by said global navigation satellite system receiver, thereby precluding operation of said local carrier generator at said sampling rate f s within said sequential chip mixed frequency correlator array system, and further reducing said power consumption of said global navigation satellite system receiver.
4. The method of claim 3 , further comprising selecting said frequency of operation of said local carrier generator using a Nyquist criterion.
5. The method of claim 1 , further comprising performing coherent integration of said generated correlation values corresponding to said positive frequency and said negative frequency of said received N samples of said intermediate frequency data over a predetermined duration of time to generate coherent integration values corresponding to said positive frequency and said negative frequency of said received N samples of said intermediate frequency data, by a coherent accumulator operably connected to said final stage adders and subtractors.
6. The method of claim 5 , further comprising performing non-coherent integration of said generated coherent integration values to generate non-coherent integration values corresponding to said positive frequency and said negative frequency of said received N samples of said intermediate frequency data, by a non-coherent accumulator operably connected to said coherent accumulator.
7. The method of claim 6 , further comprising performing acquisition checks on said generated non-coherent integration values corresponding to said positive frequency and said negative frequency of said received N samples of said intermediate frequency data against a threshold value, by a peak detector operably connected to said non-coherent accumulator.
8. The method of claim 1 , wherein said N samples of said intermediate frequency data comprise one of complex intermediate frequency data and real intermediate frequency data.