Multi-carrier code division multiple access (MC-CDMA) technique is a combination of two radio access techniques: CDMA and orthogonal frequency division multiplexing and has the advantages of both techniques. The paper...
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Multi-carrier code division multiple access (MC-CDMA) technique is a combination of two radio access techniques: CDMA and orthogonal frequency division multiplexing and has the advantages of both techniques. The paper presents the design of transmitter and receiver for MC-CDMA radio interface. It also presents encoders and decoders of turbo codes which were used in simulation of the MC-CDMA technique. Two turbo codes with 8-state recursive systematic convolutional were used in the simulation. The simulation results of the transmission quality in additive white Gaussian noise (AWGN) channel presented in the paper show bit error rate and frame error rate performance of MC-CDMA technique with the turbo codes and allow for comparison the performance of both turbo codes.
The paper presents the construction of encoders and decoders turbo codes with different number of states. Simulation results of the transmission quality of turbo codes were presented. Decoders for turbo codes have bee...
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ISBN:
(纸本)9781457714115
The paper presents the construction of encoders and decoders turbo codes with different number of states. Simulation results of the transmission quality of turbo codes were presented. Decoders for turbo codes have been tested with a fixed number of iterations and with mechanisms that reduce the number of iterations. The data were transmitted in an Outdoor to Indoor & Pedestrian B environment for a data rate of 384 kbps. The sova algorithm was used for turbo decoders.
In this paper, we propose a novel and simple approach for dealing with the exaggerated extrinsic information produced by the soft-output Viterbi algorithm (sova). The proposed remedy is based on mathematical analysis ...
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In this paper, we propose a novel and simple approach for dealing with the exaggerated extrinsic information produced by the soft-output Viterbi algorithm (sova). The proposed remedy is based on mathematical analysis and it involves using two attenuators, one applied to the immediate output of the sova and another applied to the extrinsic information before it is passed to the other decoder (assuming iterative decoding). The use of these attenuators aims at reducing the inherent strong correlation between the intrinsic information (input to the sova) and extrinsic information (output of the sova). We examine the modified sova (Msova) on additive white Gaussian noise (AWGN) and flat fading channels for parallel concatenated codes (PCCs) and serial concatenated codes (SCCs). We show that the Msova provides substantial performance improvements over both channels. For example, it provides improvements of about 0.8 to 1.0 dB at P-b = 10(-5) in AWGN, and about 1.4 to 2.0 dB at P-b = 10(-5) on fading channels. We also show that there are cases where the Msova is superior to the a posteriori probability (APP) algorithm. With this motivation, we extend the proposed modification to the APP algorithm with favorable results. We demonstrate that the modified APP (MAPP) provides performance improvements between 0.3 to 0.6 dB at P-b = 10(-5) relative to the APP. We lastly mention that the proposed modifications, while they provide considerable performance improvements, keep the complexity of these decoders almost, the same, which is remarkable.
Most of results in channel coding theory have been accomplished basing on the additive white Gaussian noise (AWGN) channels assumption. This hypothesis is not fulfilled in realistic environments in communications appl...
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ISBN:
(纸本)9781424443451
Most of results in channel coding theory have been accomplished basing on the additive white Gaussian noise (AWGN) channels assumption. This hypothesis is not fulfilled in realistic environments in communications applications. In this paper, we investigate the robustness of the turbo code decoding algorithm in presence of a generalized Gaussian (GG) noise. This noise model has been proposed for modeling in many applications such as audio and speech processing. The probability density function (PDF) of such model depends on a shape parameter which determines the decay rate of the distribution. This paper presents the decoding performances of turbo code in terms of bit error rate (BER) when the noise PDF departs from Gaussianity into a GG distribution.
Soft output Viterbi algorithm （sova） is a turbo decoding algorithm that is suitable for hardware implementation. But its performance is not so good as maximum a posterior probability（MAP） algorithm. So it is very ...
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Soft output Viterbi algorithm （sova） is a turbo decoding algorithm that is suitable for hardware implementation. But its performance is not so good as maximum a posterior probability（MAP） algorithm. So it is very important to improve its performance. The non-correlation between minimum and maximum likelihood paths in sova is analyzed. The metric difference of both likelihood paths is used as iterative soft information, which is not the same as the traditional sova. The performance of the proposed sova is demonstrated by the simulations. For 1 024-bit frame size and 9 iterations with signal to noise ratio from 1 dB to 4 dB, the experimental results show that the new sova algorithm obtains about more 0. 4 dB and 0. 2 dB coding gains more than the traditional sova and Bi-sova algorithms at bit error rate（BER） of 1 × 10^-4 , while the latency is only half of the Bi-direction sova decoding.
In this paper, we propose a novel and simple approach for dealing with the exaggerated extrinsic information produced by the soft-output Viterbi algorithm (sova). We first identify the reason behind these exaggerated ...
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In this paper, we propose a novel and simple approach for dealing with the exaggerated extrinsic information produced by the soft-output Viterbi algorithm (sova). We first identify the reason behind these exaggerated values and then propose a simple remedy for it. We argue that what leads to this optimistic extrinsic information is the inherent strong correlation between the intrinsic information (input to the sova) and extrinsic information (output of the sova). Our proposed remedy is based on mathematical analysis, and it involves using two attenuators, one applied to the immediate output of the sova and another applied to the extrinsic information before it is passed to the other decoder (assuming iterative decoding). We examine the modified sova (Msova) on idealized partial response (PR) channels and the Lorentzian channel equalized to a PR target. We consider both parallel concatenated codes (PCCs) and serial concatenated codes (SCCs). We show that the Msova provides substantial performance improvements over both channels. For example, it provides improvements of about 0.8 to 1.6 dB at P-b = 10(-5). Finally, we note that the proposed modifications, while they provide considerable performance improvements, introduce only two additional multipliers to the complexity of the sova algorithm, which is remarkable.
This paper investigates the performance of a turbo-coded system transmitted over a correlated Rician flat fading channel using quaternary partial response Continuous Phase Modulation (CPM). The system provides an attr...
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ISBN:
(纸本)0780385217
This paper investigates the performance of a turbo-coded system transmitted over a correlated Rician flat fading channel using quaternary partial response Continuous Phase Modulation (CPM). The system provides an attractive option for spectral efficient communications systems. We compare the performances of a Maximum A Posteriori (MAP) algorithm and a Soft Output Viterbi algorithm (sova). The paper considers the hybrid concatenation of a parallel designed turbo encoder and a partial response quaternary CPM modulator. Based on the decomposition theory of CPM, the quaternary CPM modulator is decomposed into a quaternary ring Continuous Phase Encoder (CPE) and a Memoryless Modulator (MM). This allows a quaternary convolutional encoder to be combined with the CPE without the need of a mapper. The hybrid design combined with iterative decoding yield very good performances. The results show the considerable superiority of the MAP algorithm to that of the sova.
Parallel concatenated spa ce time trellis code modulation, called Turbo STCM, can efficiently increase the coding gains of the space time codes. However, the complexity of the iterat iv e decoding restricts its ap...
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Parallel concatenated spa ce time trellis code modulation, called Turbo STCM, can efficiently increase the coding gains of the space time codes. However, the complexity of the iterat iv e decoding restricts its application. This paper introduces a lower complex deco ding algorithm based on soft output Viterbi algorithm (sova) for Turbo STCM. S imulational results show that the new sova algorithm for the Turbo STCM outperf orms the original space time trellis code (STTC) by 4~6 dB. At the same time, compared with the Max Log MAP (maximum a posteriori) algorithm, the new scheme requires a lower complexity and approaches the performance of Turbo STCM decod ing w ith Max Log MAP.
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