Acquisition in direct-sequence spread-spectrum communication networks: An asymptotic analysis

If direct-sequence spread-spectrum (DS/SS) modulation is employed, the receiver must acquire the chip timing for incoming messages before these messages can be demodulated. If the system or network employs DS/SS multiple access, also known as code-division multiple access (CDMA), the acquisition process is more difficult because multiple messages are transmitted simultaneously and in the same frequency band. The effect of multiple-access interference on the acquisition of DS/SS signals is studied. A passive matched filter approach is employed, and the acquisition window length, which is the length of the matched filter, determines the complexity of the acquisition scheme. The acquisition-based capacity of a DS/SS system is defined to be the maximum number of simultaneous transmissions permissible while maintaining acceptable acquisition performance. The performance of the acquisition scheme is evaluated for large acquisition window length, and the asymptotic analysis yields the capacity as a function of the acquisition window length. If this length is linearly related to the processing gain, the acquisitionbased capacity is smaller than that obtained by consideration of post-acquisition criteria only (e.g., bit-error probability for the demodulated signal). The results indicate the relative importance of the acquisition problem and suggest directions for further research. Index rem-Code-division multiple access (CDMA), Directsequence spread spectrum, Acquisition