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Embedded computer systems equipped with wireless communication transceivers are nowadays used in a vast number of application scenarios. Energy consumption is important in many of these scenarios, as systems are battery operated and long maintenance-free operation is required. To achieve this goal, embedded systems employ low-power communication transceivers and protocols. However, currently used protocols cannot operate efficiently when communication channels are highly erroneous. In this study, we show how average diversity combining (ADC) can be used in state-of-the-art low-power communication protocols. This novel approach improves transmission reliability and in consequence energy consumption and transmission latency in the presence of erroneous channels. Using a testbed, we show that highly erroneous channels are indeed a common occurrence in situations, where low-power systems are used and we demonstrate that ADC improves low-power communication dramatically.

A switchable-rate quasi-cyclic low-density parity-check (QC-LDPC) coding scheme has been proposed for integration within the legacy and next-generation high-frequency internet protocol (HF-IP) systems. The novelty in this work is based upon using a class of switchable-rate short-block-length ( lt;;1500 bits) QC-LDPC codes for the HF fading channel modelled by the ITU-R F.1487 for all latitudes and conditions. The QC-LDPC codes are constructed using a switchable-rate approach based on finite fields which provides the ability to switch among three rates to combat varying channel conditions using a single encoder/decoder structure. The proposed structure enables low-complexity implementation of the low-density parity-check encoder/decoder for use within the existing data link (DL) layer of the standardisation agreement (STANAG) 5066 profile. The performance of the proposed scheme has been evaluated comprehensively for all the HF channel conditions and latitudes. A comparison between the proposed and the current coding scheme in HF-IP systems (based on convolutional coding) shows an improvement in error-rate performance.

This paper investigates the multiple emitting multiple receiving points diversity technique as one of the ways of meeting the tripartite conditions of high data rate, less transmit power, and low unwanted electromagnetic radiations of the frequency-selective power-line channels. To be resilient to the intersymbol interference present in frequency-selective fading, the diversity technique must be used in conjunction with wideband multicarrier modulation. We propose an efficient space-frequency and space-time-frequency (STF)-coded multitone M-ary multilevel frequency-shift keying (M3FSK) for high-rate indoor communications over the multiwire power-line channels. We show that coding by using three dimensions of space, frequency, and time, the STF system is capable of achieving up to 8-dB diversity gain. Simulation results are provided to demonstrate the performance improvement of the STF over other diversity schemes as well as over single-wire M3FSK systems in a highly impulsive power line.

This paper presents new methods for constructing efficiently encodable quasi-cyclic LDPC codes based on special balanced incomplete block designs (BIBD's). Codes constructed perform well over both the AWGN and binary erasure channels with iterative decoding.

Health and usage monitoring of structures and active systems has received a wealth of attention in recent years. Microsystems are seen as a core technology for the realisation of these monitors as they offer the potential for multi-sensor integration with active electronics, wireless connectivity and in the future a self-powering capability. This article focuses on solutions for aircraft wiring systems where on-line detection of degradation and incipient failure would deliver improved safety and enhanced maintenance efficiency. Several approaches are presented to the problem of wire degradation detection in terms of both test and monitoring strategies. Both electric and mechanical (acoustic) methods will be presented together with simulation and experimental results.

We present a turbo coding scheme whose constituent codes are designed using convolutional encoders with time-varying coefficients. These encoders are finite state sequence machines that operate over the Galois field GF(q). The scheme includes an encryption polynomial whose coefficients are changed periodically by means of a user key. The trellis coding procedure thus hops from one trellis to another, following a random sequence taken over a set of subtrellises which correspond to different convolutional encoders. The proposed scheme is introduced as a turbo code with encryption properties, and is presented in two forms, the systematic and the nonsystematic schemes.

The recently published letter by Li and Hu (see ibid., vol.39, no.8, p.670-1, 2003) contains a number of incorrect statements and omissions. These are set out.

Parallel combinatory orthogonal frequency division multiplexing (PC-OFDM yields lower maximum peak-to-average power ratio (PAR), high bandwidth efficiency and lower bit error rate (BER) on Gaussian channels compared to OFDM systems. However, PC-OFDM does not improve the statistics of PAR significantly. In this chapter, the use of a set of fixed permutations to improve the statistics of the PAR of a PC-OFDM signal is presented. For this technique, interleavers are used to produce K-1 permuted sequences from the same information sequence. The sequence with the lowest PAR, among K sequences is chosen for the transmission. The PAR of a PC-OFDM signal can be further reduced by 3-4 dB by this technique. Mathematical expressions for the complementary cumulative density function (CCDF)of PAR of PC-OFDM signal and interleaved PC-OFDM signal are also presented.

A new signal set is constructed using 4QAM and Walsh-Hadamard functions and is applied in ring-block coded modulation (ring-BCM) schemes. These 4QAM (M/2)-dimensional signal set ring-BCM schemes show better performance than equivalent MPSK ring-BCM schemes. Asymptotic coding gains of 7 to 8 dB are obtained, in comparison to uncoded BPSK.