Symbol-by-symbol CDMA spreading gain adaptation and detection using OVSF sequences

We present a spreading gain adaptation protocol between a transmitter and a receiver communicating with each other through a direct-sequence spread spectrum system. This protocol does not require the transfer of an explicit control message indicating the change of spreading gain from the transmitter to the receiver. Also, according to this protocol, the transmitter can change the spreading gain "symbol by symbol" (SBS) as opposed to "frame by frame" (FBF); this enables extremely fast adaptation to the time-varying wireless channel and/or to the rate variation of the traffic. The proposed scheme uses the orthogonal variable spreading factor (OVSF) codes to enable the receiver to detect the spreading gain used by the transmitter. Our analysis indicates that fast adaptation can significantly improve the average throughput over a slow or no adaptation.