Area-Efficient Universal Code Generator for Multi-GNSS Receivers

Abstract

Although conventional global navigation satellite systems (GNSS) receivers were originally designed for single signals, studies on multi-signal receiver design have recently been actively conducted to achieve high accuracy, precision, and reliability. However, in order for a multi-signal receiver to support various codes, the receiver should support the generation of individual codes. Therefore, the resulting problem of increased complexity must be solved. This paper proposes a hardware structure for an area-efficient linear feedback shift register (LFSR)-based multi-frequency universal code generator. Whereas the existing universal code generators were configured so that feedback polynomials, output registers, and initial values can be selected by placing read-only memories (ROMs), multiplexers (MUXs), and exclusive ORs (XORs) by register bit, in the case of the proposed universal code generator; the circuit was implemented by applying the hardwiring technique to those register bits that have fixed values. According to the results of field programmable gate array (FPGA) implementation, the proposed LFSR-based universal code generator can improve look up table (LUT) by up to 37% and register by up to 78% when compared to conventional code generators, and LUT by up to 36% when compared to the previous universal code generator. Therefore, the proposed universal code generator is a good candidate for implementing multi-frequency receivers to achieve high precision and high reliability.

Design of Universal Code Generator for Multi-Constellation Multi-Frequency GNSS Receiver

“…The conventional universal code generator [5] is characterized by a sophisticated hardware architecture that configures specific initial ROMs, feedback ROMs, and output ROMs for each register bit. By inputting different signal types and satellite numbers, code generators SR1 and SR2 are assigned with their respective initial ROMs, feedback ROMs, and output ROMs.…”

“…The proposed multi-frequency universal code generator in Ref. [5] eliminates unnecessary ROM, MUX, and XOR resources by eliminating unused bits and directly connecting relevant configuration bits. In comparison to conventional multi-frequency universal spread spectrum code generators, this approach significantly reduces redundant hardware resources.…”

“…Therefore, the greater the number of fixed bits at zero and one, the more unnecessary hardware resources can be removed. As depicted in Figure 10, literature [5] proposes a compatible type code generator structure that enables the generation of spread spectrum codes for GPS, Galileo, GLONASS, and BDS navigation systems. This structure corresponds to four sets of independent code generator structures, one for each system.…”

“…Significant global research has been conducted on the design of compatible code generators [1][2][3][4][5]. The linear feedback shift register (LFSR) is widely used for generating a majority of GNSS signals.…”

“…In Ref. [5], an area-efficient universal code generator based on linear feedback shift registers is proposed. It can be configured with shift registers and tap positions to generate different signal spread spectrum codes, resulting in significant savings of hardware resources.…”