A low energy architecture for fast PN acquisition

Spread spectrum systems are being widely deployed today and are becoming more prevalent as most next-generation wireless systems are adopting it for their common air interface. These systems include the digital cellular IS-95 A/B/C, IEEE 802.11 wireless local area networks, as well as third-generation wideband code-division multiple access systems. In spread-spectrum systems, the receiver must synchronize on to the transmitted pseudo-noise (PN) code to obtain the improvement performance achieved through spreading. Since PN acquisition must process the spread-spectrum signal at a speed much faster than the transmitted data rate, its energy consumption can become significant and should be minimized for portable applications. Typically, either matched filters or serial correlators are used to acquire the PN code timing. This paper describes a hybrid PN acquisition architecture which employs both matched filters and serial correlators to achieve a lower energy consumption and fast acquisition time as compared to the traditional approaches of using either matched filters or serial correlators alone. The hybrid architecture has been implemented in RTL VHDL and synthesized down to gate level in a 0.5 micron CMOS library. Synthesis results show a factor of four reduction in energy for the hybrid scheme as compared to the matched filters architecture and a factor of two reduction in energy as compared to the serial architecture.