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The GPS signal consists of several signals transmitted at the L1, L2, and L5 carrier frequencies. The signal at L1 = 1575.42 MHz and L2 =1227.6 MHz consists of the civilian C/A code signals with pseudorandom sequences of length 1023 and chipping frequency of 1.023 MHz and the P(Y) code signals of length 1 week and chipping frequency of 10.23 MHz. The new L5 signal is QPSKmodulated, centered on 1176.45 MHz. Its two components have each a different spreading code at chipping frequency of 10.23 MHz. The in-phase component carries the navigation message, at 100 symbols per second (50 bits per second with a convolutional encoder) while the quadrature component, called the pilot channel, carries no message at all. Most GPS receivers, whether military or civilian, are designed in a way that the acquisition of the P(Y) code depends on the acquisition and tracking of the C/A code. Moreover, if the acquisition of the P(Y) code is lost, due to reasons that are explained in the paper, then the reacquisition of the P(Y) code will again depend on the acquisition and tracking of the C/A code. Therefore, for most commercially available receivers, the reliable acquisition and tracking of the C/A code is critical for the entire operation of a GPS receiver. 1 However, it is well-known the vulnerability of the GPS C/A code signal, to unintentional interference or jamming. The main theme of this paper is the reexamination of the GPS C/A code signal acquisition and tracking under the situation of the unintentional interference or jamming. A variety of jamming signals are considered such as: (1) periodic, deterministic; (2) aperiodic, deterministic; and (3) noisy type signals or non-deterministic. However, the majority of vendors are still producing correlator type receivers. As shown by the simulation results of this paper and other previous publications a sliding correlator type of receiver used to acquire and track the C/A code or L5 code can be easily jammed by a similar C/A code replica or L5 code replica at power levels 10 dB or higher above noise power. GAMES, GILS, and GIANT are not the most economically viable solutions in the market to handle GPS protection of the civilian receivers. A maximum likelihood GPS receiver which considers all the signals in the environment can be used to acquire and track successfully the C/A and the L5 GPS signals when the jamming signal power are in the range or 10dB or higher above the noise power. In summary, the direction of designing acquisition and tracking receivers for future C/A L1 code or L5 GPS signals should go towards joint signal acquisition and tracking. There are three main challenges with these types of receivers: (1) algorithm complexity, (2) computational power, and (3) test with real data. All these remain to be studied and analyzes further in the future. I think it is going to be a breakthrough in the state of the art of GPS receivers when these algorithms are ultimately implemented and a lot more work is required to arrive at that point which some of it is going to be published in future publications.

GPS L5 Signal Acquisition and Tracking under Unintentional Interference or Jamming