On the MIMO Channel Capacity of Multi-Dimensional Signal Sets

In this contribution we evaluate the capacity of Multi-Input Multi-Output (MIMO) systems using multi-dimensional PSK/QAM signal sets. It was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and the AWGN channel. However, since this gap becomes narrower when the receiver diversity order is increased, for higher-order receiver diversity the performance advantage of transmit diversity diminishes. A MIMO system having full multiplexing gain has a higher achievable throughput than the corresponding MIMO system designed for full diversity gain, although this is attained at the cost of a higher complexity and a higher SNR. The tradeoffs between diversity gain, multiplexing gain, complexity and bandwidth are studied

Turbo-Detected Unequal Protection MPEG-4 Wireless Video Telephony using Multi-Level Coding, Trellis Coded Modulation and Space-Time Trellis Coding

Most multimedia source signals are capable of tolerating lossy, rather than lossless delivery to the human eye, ear and other human sensors. The corresponding lossy and preferably low-delay multimedia source codecs however exhibit unequal error sensitivity, which is not the case for Shannon’s ideal entropy codec. This paper proposes a jointly optimised turbo transceiver design capable of providing unequal error protection for MPEG-4 coding aided wireless video telephony. The transceiver investigated consists of space-time trellis coding (STTC) invoked for the sake of mitigating the effects of fading, in addition to bandwidth efficient trellis coded modulation or bit-interleaved coded modulation, combined with a multi-level coding scheme employing either two different-rate non-systematic convolutional codes (NSCs) or two recursive systematic convolutional codes for yielding a twin-class unequal-protection. A single-class protection based benchmark scheme combining STTC and NSC is used for comparison with the unequal-protection scheme advocated. The video performance of the various schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the proposed scheme requires about 2.8 dBs lower transmit power than the benchmark scheme in the context of the MPEG-4 videophone transceiver at a similar decoding complexity

Capacity of Underspread Noncoherent WSSUS Fading Channels under Peak Signal Constraints

We characterize the capacity of the general class of noncoherent underspread wide-sense stationary uncorrelated scattering (WSSUS) time-frequency-selective Rayleigh fading channels, under peak constraints in time and frequency and in time only. Capacity upper and lower bounds are found which are explicit in the channel's scattering function and allow to identify the capacity-maximizing bandwidth for a given scattering function and a given peak-to-average power ratio.Comment: To be presented at IEEE Int. Symp. Inf. Theory 2007, Nice, Franc

The Impact of Hard-Decision Detection on the Energy Efficiency of Phase and Frequency Modulation

The central design challenge in next generation wireless systems is to have these systems operate at high bandwidths and provide high data rates while being cognizant of the energy consumption levels especially in mobile applications. Since communicating at very high data rates prohibits obtaining high bit resolutions from the analog-to-digital (A/D) converters, analysis of the energy efficiency under the assumption of hard-decision detection is called for to accurately predict the performance levels. In this paper, transmission over the additive white Gaussian noise (AWGN) channel, and coherent and noncoherent fading channels is considered, and the impact of hard-decision detection on the energy efficiency of phase and frequency modulations is investigated. Energy efficiency is analyzed by studying the capacity of these modulation schemes and the energy required to send one bit of information reliably in the low signal-to-noise ratio (SNR) regime. The capacity of hard-decision-detected phase and frequency modulations is characterized at low SNR levels through closed-form expressions for the first and second derivatives of the capacity at zero SNR. Subsequently, bit energy requirements in the low-SNR regime are identified. The increases in the bit energy incurred by hard-decision detection and channel fading are quantified. Moreover, practical design guidelines for the selection of the constellation size are drawn from the analysis of the spectral efficiency--bit energy tradeoff.Comment: To appear in the IEEE Transactions on Wireless Communication

Near-capacity iterative decoding of binary self-concatenated codes using soft decision demapping and 3-D EXIT charts

In this paper 3-D Extrinsic Information Transfer (EXIT) charts are used to design binary Self-Concatenated Convolutional Codes employing Iterative Decoding (SECCC-ID), exchanging extrinsic information with the soft-decision demapper to approach the channel capacity. Recursive Systematic Convolutional (RSC) codes are selected as constituent codes, an interleaver is used for randomising the extrinsic information exchange of the constituent codes, while a puncturer helps to increase the achievable bandwidth efficiency. The convergence behaviour of the decoder is analysed with the aid of bit-based 3-D EXIT charts, for accurately calculating the operating EbN0 threshold, especially when SP based soft demapper is employed. Finally, we propose an attractive system configuration, which is capable of operating within about 1 dB from the channel capacity