There are lots of needs for a unified platform that allows efficient GNSS (Global Navigation Satellite System) receiver development and testing for various applications. With the current functionality of the GPS constellation and the promise of the future Galileo constellation, many efforts have been focused on the 1575.42MHz L1 signals for the GNSS software receiver implementation. GPS (Global Positioning System) L1 or Galileo E1, particularly when coupled with SBAS (Space Based Augmentation System) such as WAAS (Wide Area Augmentation System) or EGNOS (European Geostationary Navigation Overlay System) are likely to fulfill the most navigation needs including accuracy and integrity. Particular interest to receiver researcher is the open service BOC(1,1) (Binary Offset Carrier) modulation format to be transmitted by Galileo at the E1 frequency. Recently MBOC(6,1,1/11) (Multiplexed BOC) is considered as base signal for both Galileo and GPS III. In preparation for mass product receiver before the transmission of the first Galileo signals from satellite, development of GPS/Galileo receiver, capable of tracking the basic BOC(1,1) signals, has been initiated. Bump jump (or known as Very Early – Very Late) correlator, Non-coherent processing in SSB(Single Side Band), Deconvolution correlator and correlator with dual discriminator are well known method to acquire and track correct peak.

In order to develop and test the GNSS signal processing algorithms such as signal acquisition and tracking, a generalized GNSS IF(Intermediate Frequency) signal generator has been designed. The signal generator is capable of processing the wide bandwidth necessary to the Galileo BOC(1,1) signal. This signal generator generates digital samples in the host computer for the software receiver test. Many GPS software receivers have been already implemented in C language by many research groups and they are capable of performing GNSS satellite acquisition and tracking on both real and simulated GNSS data [1]. In this paper, the design and implementation of GPS/ Galileo software receiver is given. The GPS software receiver already working in our laboratory is extended to GPS/ Galileo software receiver. The BOC(1,1) signal acquisition and tracking method and its performance are emphasized.

The GPS C/A code is a binary phase shift keying (BPSK) signal with a chipping rate of 1.023 MHz. The notation BPSK(fc) is used to describe the signal, where fc represents a factor of 1.023MHz[2]. The Galileo Open Service signal on L1 will use a BOC modulated signal. For BOC signals, the spreading code is mixed with a square wave at a given subcarrier frequency. The notation BOC(fs, fc) is used, where fs represents the square wave subcarrier frequency in units of 1.023 MHz, and fc represents the chipping rate in units of 1.023 MHz. The generation of a BOC(1,1) signal is shown in Figure 1, where the top line is a 1.023 MHz square wave, the middle line is a 1.023 MHz spreading code, and the bottom line is the resulting BOC(1,1) modulation signal.

The normalized ideal autocorrelation function for a BPSK(1) signal is shown in Figure 2. The autocorrelation function for a BOC(1,1) signal is shown in Figure 3. Compared to the BPSK(1) autocorrelation function, the square wave subcarrier modulation used with BOC(1,1) causes the autocorrelation function to have a sharp main peak, and two smaller negative side peaks. The sharp main peak will result in improved code tracking performance for the BOC(1,1) signal, as well as improved multipath mitigation performance.