An excess signaling concept with Walsh-Hadamard spreading and joint detection

We present a new signaling concept which consists of transmitting an additional data rate to the original data rate that is determined by the channel bandwidth, the modulation scheme, and other physical-layer functions of the transmission system. This is accomplished by overlaying M excess symbols to each block of N primary symbols, with the excess symbol period being equal to N times the primary symbol period. The resulting interference between primary and excess symbols is handled using a joint symbol detection technique. Our analysis shows that for BPSK or QPSK modulation and M=1 or M=3, transmission of the excess data rate does not degrade the minimum Euclidean distance when the excess symbol ratio M/N does not exceed 25%. Furthermore, our simulation results indicate that at bit error rate (BER) values in the order of 10/sup -3/ to 10/sup -5/, transmission of the additional data in these cases is achieved at the expense of a moderate to very small penalty in signal-to-noise ratio (SNR).