Gps l2 downconverter

The L2 frequency was implemented after the L1. It also has a military code and a civilian use code. The L2 uses the frequency This allows the signal to better travel through obstacles such as cloud cover, trees, and buildings.

Because of this, it cannot be used on its own: it must be used along with L1 frequencies. It is the most advanced GNSS signal yet, but it is still in its infancy, with deployment scheduled for It will eventually become another signal available for civilian users. First, the L1 signal can be used on its own. This will give you about a centimeter of accuracy when also using RTK , but it is slow, taking about 10 minutes to reach that level of accuracy.

Since the L2 signal has a higher frequency, it can travel much more easily through obstacles. This means that errors caused by particles in the air can be calculated and eliminated by comparing the two signals. There are also two military signals at the L2 frequency. Civilians with dual-frequency GPS receivers enjoy the same accuracy as the military or better. For professional users with existing dual-frequency operations, L2C enables faster signal acquisition, enhanced reliability, and greater operating range.

However, L2C remains pre-operational and should be employed at the user's own risk until it is declared operational. Return to top of page. L5 is the third civilian GPS signal, designed to meet demanding requirements for safety-of-life transportation and other high-performance applications.

L5 is broadcast in a radio band reserved exclusively for aviation safety services. It features higher power, greater bandwidth, and an advanced signal design.

In addition to enhancing safety, L5 use will increase capacity and fuel efficiency within U. Beyond transportation, L5 will provide users worldwide with the most advanced civilian GPS signal. Through a technique called trilaning, the use of three GPS frequencies may enable sub-meter accuracy without augmentations, and very long range operations with augmentations. This will result in a small loss in signal power for GLONASS satellites that transmit frequencies close to the low and high edges of this band.

Thus, all signals are band limited to 25 MHz to satisfy the Nyquist sampling theorem for a subsequent sample rate, sclk, of 25 MHz. This ensures the optimal conversion from the analog to the digital domain which occurs in the IF Processor block of FIG. The IF Processor performs frequency translation and digitization operations.

The input signal S i is power split and mixed separately with inphase and quadrature versions of the local oscillator signal LO in mixer 1 and in mixer 2 The inphase version of the mixed signal is then filtered in Filter 1 , amplified in Amplifier 1 before being hardlimited in Hardlimiter 1 and sampled in flip-flop 1 The output signal 1 represents a frequency translated , filtered, amplified and digitized version of the input signal S i The quadrature signal is similarly processed.

In one embodiment, the Hardlimiter of FIG. In another embodiment, the Hardlimiter comprises an n-bit quantizer, n being an integer. If this is the case, the signal-to-noise ratio SNR and the anti-jamming performance are improved.

Referring back to FIG. The selected signals are further processed in the first Signal Tracker 1 The operation of the similar block has been fully described by Gary Lennen in the U. The Carrier Mixer I and Q output signals are further processed by the Code Mixer block that mixes the I and Q samples with the local code L c generated by the Code generator The mixing or correlation process performed by the Code Mixer is performed at 3 time points E-early, P-punctual and L-late on the autocorrelation function graph formed between the satellite code and local code.

However, the output of the Correlators block itself is not sufficient for code tracking because it does not provide an indication of the sign of the delay error of a tracking reference signal. This clock CODE NCO drives the Code Generator block in such a manner that if the clock Code NCO is lagging in phase, the correction signal drives the clock faster and the reference code speeds up and runs in coincidence with the received signal. Thus, the reference code is tracking the received code.

The epoch time ticks are then a measure of the received signal time. If the received signal delay increases suddenly because of user platform motion the delay error increases momentarily and the correction signal increases from zero.

The reference code then slows down and increases its delay until it matches the received signal at which point the correction signal decreases to zero again. Thus, given an initial small error and sufficiently slow dynamics of delay change relative to the filter bandwidth, the Delay-Lock-Code-Loop will track the incoming signal. The Code generator block is designed to provide the correct local code L c The Multiplexer 3 is used to make the selection.

See discussion above. When more channels are available than satellites the criteria can be the visibility above the horizon of a satellite. When setting up for a GPS satellite the distinguishing feature of each satellite is its prn X code. Signal Trackers 1 and 2 in this channel will now operate on these signals: Signal tracker 1 on L1, and Signal Tracker 2 on L2.

The next step is to set the expected value of final IF carrier frequency. For GPS L2 this is If signal power is not found then small adjustments can be made to the Code NCO output phase and the Carrier NCO output frequency to widen the search area step The Digital Channel Processor is ready for the signal power search step The process of performing code and carrier phase measurements has been fully described in the U.

The U. Currently, this term is of the order of one microsecond, which translates into meters in distance. If unaccounted for, this term can cause a significant error in position. Firstly, all pseudo range measurements are smoothed step by their equivalent carrier phase measurements, providing lower noise pseudo ranges. If only GPS pseudo ranges are available, then the standard and well documents solution for the system of simultaneous equations formed by the equation 1 for each GPS satellite is solved step Similarly, if only GLONASS pseudo ranges are available, the standard solution to a system of equations of the type 1 is obtained step The offset between the two is not known exactly yet but is known to be less than 10 meters in any axis.

The description of the preferred embodiment of this invention is given for purposes of explaining the principles thereof, and is not to be considered as limiting or restricting the invention since many modifications may be made by the exercise of skill in the art without departing from the scope of the invention.

What is claimed is: 1. The apparatus of claim 2 further comprising a frequency synthesizer connected to said master oscillator, wherein said frequency synthesizer is configured to synthesize LO 1 , LO 2 , LO 3 , LO 4 , msec, and sclk clock signals.

The apparatus of claim 6, wherein said GLONASS synthesizer block further comprises: a "Divide by 5" block configured to generate a third reference signal;. The apparatus of claim 6, wherein said GPS synthesizer block further comprises: a "Divide by 5" block configured to generate a fourth reference signal;.

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 ;.

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

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;.

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.

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