Unambiguous Processing Techniques of Binary Offset Carrier Modulated Signals - Global Navigation Satellite Systems: Signal,Theory and Applications - page 62

main peak. However, this technique has some limitations, for it is only applicable to sine-
BOC( n , n ) signals. Some other side-peaks cancellation methods have been proposed recently
(Dovis, et al., 2005; Fante, 2003; Musso et al., 2006; Nunes et al., 2007).

However, the design of SC algorithms is still scarce of uniform theoretical frame and
analytical method. There is no easy handling design method for SC algorithms
development. The key of SC methods is the selection of local auxiliary signal chip
waveforms. Due to lack of mathematical analysis tools, the selection of local signal chip
waveforms is mainly based on intuition and trail-and-error. In new SC algorithm design, the
shape of auxiliary signal waveforms is limited by the imagination of the designer, thus
concentrating on some common shapes such as rectangular pulse, square wave with sine
phase or cosine phase, and return to zero (RZ) code wave. When the chip waveform of the
received signal is simple, for instance, Manchester code which is used in BOC( n , n ) signals, it
is easy to find a corresponding auxiliary chip waveform by using trail-and-error method.
However, when the chip waveform of target signal gets more complicated, the design
process becomes tough, and a mathematical analysis method is needed.

In the next section, a SC analytic design framework is presented. In this framework, the local
auxiliary signal chip waveform can be designed under this framework by means of
mathematic analysis so that the waveform shape selection can be more flexible.

4. SC analytic design framework
4.1 SCS waveform

The main difficulty of SC method design is how to select the spreading code chip
waveform of local signals. It is desired to define a parameterized local signal model the
chip waveform of which has a high degrees of freedom and is easy to generate in receivers
to provide more opportunities for waveform optimization. Although there are few
investigations about general local signal model for receiver designers since most of the
signal receiving techniques are based on matched correlator in GNSS, it is interesting to
note that some generalized waveform models are proposed for satellite signal design in
order to offer degrees of freedom for shaping the signal spectrum, such as the binary coded
symbols (BCS) (Hegarty et al., 2004). The advanced idea can be instructive for SC algorithm
design.

For BCS signals, in order to ensure constant modulus, the envelope of p ( t ) is restricted to 1.
However, when considering auxiliary chip waveform in SC techniques, since local signals
do not relate to amplifying and transmitting, they do not need to satisfy the request of
constant modulus but their chip waveform should be easy to generate. Therefore, we
expand the definition of BCS signal, restricting the chip waveform to being real-valued and
having normalized energy. The chip waveform is divided into M segments, each with equal
length TTM = / , and in each segment the level remains constant.

s c

Since such waveform looks like steps, for expressional simplicity, we call this kind of chip
waveform the step-shape code symbol (SCS) waveform, and call the signal which uses this
waveform the SCS signal hereafter. Sticking with the terms used for BOC signals, M is
referred to as the order of SCS signal. Some examples of SCS waveforms are shown in
Figure 8.