Packet CDMA Communication without Preambles

This paper applies a segmented matched filter for acquiring chip codephase alignment in direct-sequence CDMA packet communications. This alignment is essential for decoding the spread spectrum signal. The customary approach is to start each CDMA packet with a data-free preamble that facilitates codephase alignment in the receiver. Since packets can be short, processing must be rapid and so we use the parallel processing of a transversal matched filter correlator. We include segmentation of the matched filter to allow codephase testing even when there are data transitions. This eliminates the need for a preamble and the entire packet can contain data. Segmentation also increases tolerance to Doppler shifts caused by motion or by carrier frequency mismatch. To increase the probability of correct codephase acquisition, matched filter samples are accumulated over several code cycles prior to making the codephase decision. Correct detection probabilities exceeding 99% are indicated from simulations with 25 co-users and 10 kHz Doppler shift