The proliferation of location-based applications inside various handheld electronic devices, such as mobile phones and internet tablets, demands the GPS system to have low power consumption, small form-factor and be co-located on the same device with other radio systems, such as cellular, BT, and WLAN. The conventional GPS solution often uses two SAW filters, before and after an external LNA, to meet the requirements of low noise and multi-radio coexistence. Nevertheless, it is highly desirable to remove the external LNA and interstage SAW filter due to size and cost, which presents a great design challenge to achieve high out-of-band linearity with very low power consumption. To fulfill these stringent requirements, a more comprehensive approach is needed to tar get a radio architecture with a proper RX system budgeting and optimal circuit design. In addition, a GPS system can be desensitized by unexpected in-band blockers generated from other subsystems on the same platform, such as LCD display, PMU, CPU system clocks, etc. The GPS digital baseband processor must possess the capability to withstand in-band blockers without significant performance degradation. This paper presents a GPS/Galileo SoC with an adaptive in-band blocker cancellation scheme, which is implemented in a 65nm CMOS process.

As the trend of integrating GNSS (Global Navigation Satellite System) with other wireless communications becomes prevalent, jamming tolerance ability is emerging as an essential topic. In an anti-jamming system, the design of AGC (Automatic Gain Control) operation has significant influences on the jamming immunity of the receiver. However, conventional AGC which are designed for some assumptive input signal model cannot guarantee the optimal control under various ambient jamming scenarios and cause extra degradation in the output CN0 (power-to-noise power density ratio). The purpose of this research is to find an AGC control algorithm to perform properly regardless of the changing input signal models. Therefore, a novel AGC control methodology, the Entropy AGC, is proposed. The Entropy AGC estimates the proper occurrence probabilities of each ADC step without the need for a priori information of the environment. To evaluate the AGC performance, various jamming environmental tests are simulated using the Monte-Carlo method. It is verified that an Entropy AGC can reach optimal gain control in the presence of interferences as well as in a jamming-free environment. The jamming mitigation ability of the proposed AGC with anti-jamming system is also shown in the paper.

As code acquisition in the baseband digital signal processing is still one of the major computational bottleneck limiting the time to first fix (TTFF) in navigation devices, this paper proposed a new code acquisition method that results in a lower computational complexity architecture and is more appropriate for searching multiple satellites. We transformed the traditional code acquisition problem into a multiple constant multiplications problem such that the technique of subexpression elimination can be utilized to reduce the addition complexity within code acquisition. A fast acquisition engine based on the proposed method is also demonstrated for its usability for GPS coarse/acquisition (C/A) codes. According to the simulation results, the number of required additions given the number of simultaneously processing satellites is larger than six can be decreased by about 70%, compared to the traditional architecture.

In this paper, a new code for code acquisition in a navigation receiver is proposed. Conceptually, the code is derived by cyclically shifting a spreading code multiple times and combining all the shifted codes. This cyclically shift-and-combine (CSC) code, like the original spreading code, can be used to despread the received signal and extract the code-phase information. A corresponding acquisition and verification structure with respect to the CSC code is also presented. Because the period of the CSC code is shortened, the search space of the code phases shrinks and the computation of the code correlations reduces. Simulation results show that the CSC-base code acquisition works efficiently given the received signal strength is satisfactory, while it still benefits from a longer integration time if the signal is weak. Using the proposed code, operations and hardware complexity of matched filter based correlators can be approximately decreased by 75%.