In this paper, we investigate the dynamic resource allocation adapted to spread spectrum multicarrier multiple access (SS-MC-MA) systems in a multiuser power line communication (PLC) context. The developed adaptive system is valid for uplink, downlink, as well as for indoor and outdoor communications. The studied SS-MC-MA system is based on classical multicarrier modulation like DMT, combined with a spread-spectrum (SS) component used to multiplex several information symbols of a given user over the same subcarriers. The multiple access task is carried out using a frequency division multiple access (FDMA) approach so that each user is assigned one or more subcarrier sets. The number of subcarriers in each set is given by the spreading code length as in classical SS-MC-MA systems usually studied in the wireless context. We derive herein a new loading algorithm that dynamically handles the system configuration in order to maximize the data throughput. The algorithm consists in an adaptive subcarrier, code, bit and energy assignment algorithm. Power spectral density constraint due to spectral mask specifications is considered as well as finite order modulations. In that case, it is shown that SS-MC-MA combined with the proposed loading algorithm achieves higher throughput than DMT in a multiuser PLC context. Because of the finite granularity of the modulations, some residual energy is indeed wasted on each subcarrier of the DMT spectrum. The combining of a spreading component with digital multitone (DMT) allows to merge these amounts of energy so that one or more additional bits can be transmitted in each subcarrier subset leading to significant throughput gain. Simulations have been run over measured PLC channel responses and highlight that the proposed system is all the more interesting than the SNR is low.

Abstract. This paper deals with spreading sequences selection for downlink and uplink Multi-Carrier Code Division Multiple Access (MC-CDMA) systems with the aim of minimizing the dynamic nnge of the tcansrnitted rnulticamer signal envelope and the multiple access interference. The crest factor of orthogonal and non-orthogonal sequences are compared analytically and by simulation for downlink and uplink phase shift keying MC-CDMA transmissions. Then, in order to minimize the multiple access interference produced by frequency selective channels, an optimized spreading sequence allocation procedure is presented. Finally, a selection of the spreading codes which jointly reduces the multiple access interference and the crest factor is proposed for downlink MC-CDMA systems.

: A novel detection technique for MC-CDMA systems based on the MMSE criterion applied per user is presented. Simulation results in a Rayleigh fading channel show very good performance, mainly for non full load systems. Introduction :Since 1993, Multi-Carrier Code Division Multiple Access (MC-CDMA) has been the subject of much research, and appears to be a very good candidate to support multimedia services in mobile radio communications [1]. The MC-CDMA transmitter spreads in the frequency domain the original data stream over different subcarriers using a given spreading code. For a synchronous system as the downlink mobile radio communication channel, the application of orthogonal codes such as Walsh-Hadamard codes guarantees the absence of Multiple Access Interference (MAI) in a Gaussian channel. However, through a frequency selective fading channel, all the subcarriers have different amplitude levels and different phase shifts, which results in a loss of the orthogonality among users and then generates MAI. So, after direct FFT and frequency deinterleaving, the received sequence must be "equalized" by using one tap adaptive equalizer per subcarrier to make up for the phase and amplitude distortions caused by the mobile radio channel. To combat the MAI, various basic detection techniques such as Maximum Ratio Combining (MRC), Equal Gain Combining (EGC), Orthogonal Restoring Combining (ORC) or Minimum Mean Square Error (MMSE) may be used. This last technique, based on the MMSE criterion applied independently on each subcarrier [2] achieves better performance. This letter describes a novel detection technique based on the MMSE criterion applied per user which provides performance improvements, mainly for non full load systems.

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This letter introduces a 3D space-time-space block code for future terrestrial digital TV systems. The code is based on a double layer structure designed for inter-cell and intra-cell transmissions in single frequency networks. Without increasing the complexity of the receiver, the proposed code is very efficient to cope with equal and unequal received powers in single frequency network scenarios.Nowadays, one of the most promising technologies for the second generation of future terrestrial digital TV, concerned with flexibility, high bit rate and, portable and mobile reception is the combination of multiple-input multipleoutput (MIMO) and orthogonal frequency division multiplexing (OFDM) techniques. To increase area coverage, single frequency networks (SFN) [1]