We describe a multilayered video transport scheme for wireless channels capable of adapting to channel conditions in order to maximize end-to-end quality of service ( QoS). This scheme combines a scalable H. 263+ vide...
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We describe a multilayered video transport scheme for wireless channels capable of adapting to channel conditions in order to maximize end-to-end quality of service ( QoS). This scheme combines a scalable H. 263+ video source coder with unequal error protection ( UEP) across layers. The UEP is achieved by employing different channel codes together with a multiresolution modulation approach to transport the different priority layers. Adaptivity to channel conditions is provided through a joint source-channel coding ( JSCC) approach which attempts to jointly optimize the source and channel coding rates together with the modulation parameters to obtain the maximum achievable end-to-end QoS for the prevailing channel conditions. In this work, we model the wireless links as slow-fading Rician channel where the channel conditions can be described in terms of the channel signal-to-noise ratio ( SNR) and the ratio of specular-to-diffuse energy zeta(2). The multiresolution modulation/coding scheme consists of binary rate-compatible punctured convolutional ( RCPC) codes used together with nonuniform phase-shift keyed ( PSK) signaling constellations. Results indicate that this adaptive JSCC scheme employing scalable video encoding together with a multiresolution modulation/coding approach leads to significant improvements in delivered video quality for specified channel conditions. In particular, the approach results in considerably improved graceful degradation properties for decreasing channel SNR. Copyright (c) 2007 Y. Pei and J. W.
In this paper, we propose a modified iterative decoding algorithm to decode a special class of quasi-cyclic low-density parity-check (QC-LDPC) codes such as QC-LDPC codes used in the IEEE 802.16e standards. The propos...
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ISBN:
(纸本)9781424402632
In this paper, we propose a modified iterative decoding algorithm to decode a special class of quasi-cyclic low-density parity-check (QC-LDPC) codes such as QC-LDPC codes used in the IEEE 802.16e standards. The proposed decoding is implemented by serially decoding block codes with identical parity-check matrix H, derived from the parity-check matrix H of the QC-LDPC codes. The dimensions of H, are much smaller than those of H. Extrinsic values can be passed among these block codes since the code bits of these block codes are overlapped. Hence, the proposed decoding can reduce the number of iterations required by up to forty percent without error performance loss as compared to the conventional message-passing decoding algorithm. A partially-parallel very large-scale integration (VLSI) architecture is proposed to implement such a decoding algorithm. The proposed VLSI decoder can fully take advantage of the proposed decoding to increase its throughput. In addition, the proposed decoder only needs to store check-to-variable messages and hence is memory efficient.
This letter studies the effect of signal constellation expansion on the achievable diversity of pragmatic bit-interleaved space-time codes in quasistatic multiple antenna channels. Signal constellation expansion can b...
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This letter studies the effect of signal constellation expansion on the achievable diversity of pragmatic bit-interleaved space-time codes in quasistatic multiple antenna channels. Signal constellation expansion can be obtained either by increasing the size of the constellation in the complex plane or by using multidimensional linear mappings. By means of two simple constructions, we provide a comparison of the two options with message passing decoding. We show that multidimensional expansion achieves Some performance advantage over complex-plane expansion at the cost of significantly higher decoding complexity and larger peak-to-average power ratio of the transmitted signals.
Adaptive modulation has emerged as a prime technique in wireless systems to improve system capacity and spectral efficiency. Its basic idea is to adapt the modulation scheme to the fading channel quality, using differ...
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ISBN:
(纸本)0780374428
Adaptive modulation has emerged as a prime technique in wireless systems to improve system capacity and spectral efficiency. Its basic idea is to adapt the modulation scheme to the fading channel quality, using different schemes for different channel conditions. Therefore a primary issue is to determine the switching thresholds between the modulation schemes. Typically these thresholds are fixed Recently a novel adaptive learning approach capable of dynamically adjusting the thresholds to maximize a performance criterion, for example the data throughput, was introduced. This paper presents further simulation results for this new method.
This paper studies a memory-based pulse shaping and travelling wave tube precompensation technique applied to high data rate satellite communications. Baseband I and Q waveforms are synthesized from data stored in a d...
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This paper studies a memory-based pulse shaping and travelling wave tube precompensation technique applied to high data rate satellite communications. Baseband I and Q waveforms are synthesized from data stored in a distributed arithmetic architecture. The waveforms are adjusted to minimize intersymbol interference, spectral bandwidth and travelling wave tube distortion. We evaluate its performance in a simulated BPSK link. The results show that memory-based precompensation has great potential to improve link performance.
Steiner Systems constitute an example of codes that achieve asymptotic error-free transmission for the Gaussian channel. In contrast to simplex and orthogonal codes which also have this property, these codes make more...
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Steiner Systems constitute an example of codes that achieve asymptotic error-free transmission for the Gaussian channel. In contrast to simplex and orthogonal codes which also have this property, these codes make more efficient use of the bandwidth by reducing the required dimensionality to generate the M signals. Tight upper bounds for the symbol error probability are derived for coherent and noncoherent detection that include previously reported results as special cases.
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