3. Basic Properties of Direct Sequence Spread Spectrum Signals

In order to utilize the frequent sign altering in the spreading codes to measure the distance accurately, and to achieve better performance of multiple access, multipath resistance, and anti-interference, direct sequence spread spectrum (DSSS) technology is used in satellite navigation signals. With different spreading chips, the time domain waveform and power spectrum shape of the signal will exhibit significant differences, which will affect many key performances. Therefore, the spreading chip waveform becomes the key factor in determining the intrinsic performance of the satellite navigation signal, and the spreading modulation design has become the core technology of the GNSS signal design. From this chapter, we will start our journey on the spreading modulation design of satellite navigation systems. In this chapter, we will discuss some basic concepts and properties of direct sequence spread-spectrum technology, illustrating the mathematical models of spreading modulated signals and their important characteristics in time and frequency domains. These characteristics will be used frequently in the following chapters.