Code Acquisition at Low SINR in Spread Spectrum Communications

Abstract

Abstract-We consider the problem of code acquisition at low signal to interference and noise ratio (SINR) in packetbased 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" approach, 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.

A low SINR synchronization system for direct-sequence spread-spectrum communications: radio prototype, verification testbed and experimental results

“…During the reception of the preamble, the SB performs a post-detection integration (PDI) based parallel code acquisition [4,6,8] operation for fast synchronization at low SINR. Parallel code acquisition, which leads to fast acquisition, involves simultaneous testing of all hypotheses for correct alignment of the incoming received signal and the locally generated spreading code for accurate despreading operation.…”

“…Code acquisition [8] ensures correct despreading operation in the receiver by aligning the spreading code in the incoming packet with a local copy of the spreading code at the receiver. Once the acquisition is achieved, tracking [9,10] maintains the alignment of the local spreading code with the received signal over the reception of the entire packet.…”