This paper investigates the sensitivity of several multiple-access techniques to narrow-band interference. The analysis covers time-division multiple access (TDMA), code-division multiple access (CDMA), and orthogonal frequency-division multiple access (OFDMA). The study is carried out under the assumption that all the considered multiple-access systems occupy the same total bandwidth, and the bit rates of all active users are identical. A major finding of this study is that CDMA with pseudonoise spreading sequences is more sensitive to narrow-band interference than TDMA. We point out that the signal-to-jammer power ratio at the decision device input is in fact identical for both multiple-access techniques, but the amplitude distribution of the jammer term at the threshold detector input is more favorable to TDMA, which turns out to be more robust in terms of bit-error rate. Another finding is that in terms of sensitivity to narrow-band interference, orthogonal CDMA (OCDMA) is closer to TDMA than to CDMA with pseudonoise sequences, because the degradation is not the same for all users. Finally, we discuss the relationship of OCDMA and TDMA and highlight the superiority, in terms of capacity over the narrow-band interference channel, of TDMA to the other multiple-access techniques considered in this paper.

This paper deals with the derivation and comparison of some promising TDMA and OFDM/CDMA receiver structures for communication over the return path channel of the cable TV (CATV) network. Regarding TDMA, it is shown that the performance substantially improves by using equalization. Given the slowly varying, frequency selective nature of the ingress noise, OFDM seems an interesting possible access technique to employ. Here it is considered in combination with CDMA. With respect to the performance in terms of the SNR at the input of the decision device, the TDMA structure gives better results than the OFDM/CDMA schemes. Also with respect to the design complexity TDMA seems more interesting.

In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered. The degradation of the bit error rate (BER), caused by the presence of carrier frequency offset and carrier phase noise is analytically evaluated. It is shown that for a given BER degradation, the values of the frequency offset and the linewidth of the carrier generator that are allowed for OFDM are orders of magnitude smaller than for single carrier systems carrying the same bit rate.>

An investigation is made on the compatibility of the video formats, standard TV (625/50/2:1/4:3), EDTV (625/50/1:1/16:9), HDTVint (1250/50/2:1/16:9) and HDTVpro (1250/50/1:1/16:9) in three-dimensional subband coding. A hierarchical method is proposed leading to a more reasonable joint solution for the issues of digital transmission evolution and interlace-to-progressive scanning conversion in the frame work of bit rate compression. Conventional HDTVint with the diamond shaped spectrum is proposed to be replaced by a kind of "switching" HDTVint signal which consists of three components and motion detection bits (MDB). The first component and the MDB represent TV. The first plus the second component and the MDB represent EDTV. HDTVpro is split into switching HDTVint and an extra component. The switching threshold and the length of temporal filter banks are discussed. Rearranging the pixels in subbands is recommended. Based on the proposed method, the transmission system can evolve through four steps: TV, EDTV, HDTVint, and HDTVpro. Results of bit rate compression are also presented. TV, EDTV, HDTVint, and HDTVpro are compressed to approximately 40, 80, 128, and 256 Mb/s, respectively. Interlace scanning has drawbacks such as line flicker and line crawling as the eye follows the line structure in the picture. Progressive version switching TV and HDTVint could be reconstructed using one frame memory without the problems of handling temporal-vertical diamond shaped spectra of conventional TV and HDTVint based on one-frame memory algorithm in the receiver.>