Code Acquisition at Low SINR in Spread Spectrum Communications

We consider the problem of code acquisition at low signal to interference and noise ratio (SINR) in packet- based spread spectrum communications, where a centralized "pilot" synchronization signal and high-precision oscillators are not available. Such problems arise in the context of ad-hoc networks, for example, which require fast code acquisition times and gradual degradation of the network with decreasing SINR. We motivate the use of the "postdetection integration" ap- proach, which utilizes the energy of multiple bits in a packet, for code acquisition at low SINR. We present the implementation of a fully parallel architecture which simultaneously looks at all possible code alignments over multiple bits. This leads to a drastic reduction in acquisition time compared to serial search based methods. We report some preliminary simulation and experimental results from a hardware prototype of a transceiver on which the code acquisition algorithm was implemented.