Maximum-Likelihood Detection of Nonlinearly Distorted Multicarrier Symbols by Iterative Decoding (2003)

This paper presents several techniques for the VLSI implemen- tation of the MAP algorithm. In general, knowledge about the implementa- tion of the Viterbi algorithm can be applied to the MAP algorithm. Bounds are derived for the dynamic range of the state metrics which enable the de- signer to optimize the word length. The computational kernel of the algo- rithm is the Add-MAX operation, which is the add-compare-select oper- ation of the Viterbi algorithm with an added offset. We show that the crit- ical path of the algorithm can be reduced if the Add-MAX operation is re- ordered into an offset-add-compare-select operation by adjusting the loca- tion of registers. A general scheduling for the MAP algorithm is presented which gives the tradeoffs between computational complexity, latency, and memory size. Some of these architectures eliminate the need for RAM blocks with unusual form factors or can replace the RAM with registers. These architectures are suited to VLSI implementation of turbo decoders. Abstract—This paper proposes a precoding technique for the complete elimination of both multiple-access interference and intersymbol interfer- ence in the uplink of a code-division multiple-access system based on burst transmission, with reduction of the minimum mean-square error joint de- tector to a simple filter matched to the total impulse responses. If the re- ceived power is fixed, this system minimizes the variance of the symbol esti- mation error. An infinity of solutions exists to the orthogonalize the system. Two objectives are added: a possible progression in the number of users, and a minimization of the average emitted power. In an ideal progressive system, users can enter or leave the system easily without recomputing the codes of the other users. The minimization of the emitted power is a com- plex optimization problem. An appropriate solution is proposed. It is shown that the system introduced in this paper outperforms burst systems using a conventional set of codes. The authors are with the UVL Communications and Remote Sensing Labo- ratory, B-1348 Louvain-la-Neuve, Belgium. Abstract—Progressive image transmission is difficult in the presence of a noisy channel, mainly due to the propagation of errors during the de- coding of a progressive bitstream. Excellent results for this problem are made possible through combined source-channel coding—a method that matches the channel code to the source operational rate distortion as well as channel conditions. This paper focuses on the key component of combined source-channel coding: rate allocation. We develop a parametric method- ology for rate allocation in progressive source-channel coding. The key to this technique is an empirical model of decoded bit error rate as a function of the rate of channel codes. We investigate several scenarios. In the case of the memoryless channel, we present closed-form results. For the fading channel and channels with feedback, where closed-form solutions are elu- sive, our analysis leads to low-complexity algorithms. The results presented in this paper are applicable to any progressive source code and any family of channel codes. Abstract—This paper proposes a new method for decoding multicarrier symbols with severe nonlinear distortion. The first part evaluates mutual information expressions for practical nonlinear models and shows the per- formance bounds for commonly used receiver structures. Then, we derive the maximum-likelihood (ML) sequence estimator, which, unfortunately, has an exponential complexity due to the nonlinear distortion. This ex- tremely large complexity can be reduced with a simple algorithm that it- eratively estimates the nonlinear distortion, thereby reducing the exponen- tial ML to the standard ML without nonlinear distortion. The proposed method can be used to reduce the peak-to-average power ratio of multicar- rier signals by clipping the transmit sequence. It can also be used to correct any nonlinear distortion present in transmitter/receiver amplifiers that are operating close to saturation.