On the multiple-access capacity of multitone-CDMA communications

This letter derives a bit-error-probability expression for an asynchronous multitone-code-division multiple access (CDMA) system and shows that the multiple-access (MA) capacity of this system is identical to that of a conventional (single-carrier) direct-sequence spread-spectrum system under conditions of equal bandwidth and equal bit rate. It is also shown that using more subcarriers to increase the processing gain does not increase the MA capacity.published_or_final_versio

A low-complexity multitone-CDMA communication technique

Digital implementation of multitone-(MT-) CDMA systems often involves considerable complexity. Assuming the spreading-sequence length, N, is a multiple of the number of subcarriers, M, this paper proposes a new digital MT-CDMA technique that achieves low-implementation complexity. In particular, for the case of rectangular chip waveform, it is shown that the MT-CDMA technique proposed earlier and the technique proposed in this paper require α + αlog2 αN and 1 + (M/N)log2 M multiplications per chip, respectively, where α ≥ 1 is the number of samples per chip. The reduction in complexity is particularly considerable when N is large.published_or_final_versio

Spectrally Shaped Generalized MC-DS-CDMA with Dual Band Combining for Increased Diversity

A new multicarrier spread spectrum modulation scheme is proposed in this paper. This scheme uses sinusoidal chip waveforms to shape the spectrum of each subcarrier of a multicarrier direct sequence spread spectrum (DS-SS) signal. As a result, each subcarrier has two distinct spectral lobes, one a lower sideband (LSB) and the other an upper sideband (USB). By properly selecting the parameters of the sinusoidal chip waveforms, the two sideband signals can be made to undergo independent fading in a dispersive fading channel. These two independently-faded sideband signals, when combined at the receiver, provide diversity gain to the system. Our analysis and simulation results show that by properly selecting the chip waveform parameter and the intersubcarrier frequency separation, the bit error ratio (BER) performance of the proposed scheme is superior to that of the conventional MC-DS-CDMA system in dispersive fading channels. In addition, spectral sidelobes are naturally reduced by our scheme