The rapid progress of power line communications (PLC) for data transmission over electric power supply systems is now opening ways for special applications such as train automation in local transportation and mass transit (MT) systems. These DC-powered traction networks can be used as communication links between wayside equipment and the moving trains. As MT networks significantly differ from usual electricity supply systems, the usage of existing models and communication equipment for conventional PLC channels turns out infeasible. Therefore, the work reported in this paper focuses on MT channel investigation and modeling, in order to develop novel adapted solutions. The outcome is a stochastic MT channel model, which-besides multipath and time-variance-also includes peculiar properties such as the behavior of ring structures and the impact of the Doppler effect invoked by moving trains. In addition, a very special interference scenario is treated, caused by the rectifiers in these DC-powered environments. Besides a complete simulation model, this paper presents detailed guidelines for building emulation hardware, so that channel adapted PLC system design for MT networks can now be successfully started without further expensive field trials.

In the low signal-to-noise ratio regime, the performance of concatenated coding schemes is limited by the convergence properties of the iterative decoder. Idealizing the model of iterative decoding by an independence assumption, which represents the case in which the codeword length is infinitely large, leads to analyzable structures from which this performance limit can be predicted. Mutual information transfer characteristics of the constituent coding schemes comprising convolutional encoders and soft-in/soft-out decoders have been shown to be sufficient to characterize the components within this model. Analyzing serial and parallel concatenations is possible just by these characteristics. In this paper, we extend the method of extrinsic information transfer charts, that is limited to the case of a concatenation of two component codes, to the case of multiple turbo codes. Multiple turbo codes are parallel concatenations of three or more constituent codes, which, in general, may not be identical and may not have identical code rates. For the construction of low-rate codes, this concept seems to be very favorable, as power efficiencies close to the Shannon limit can be achieved with reasonable complexity

When the same data sequence is transmitted over two independent channels, or when a data sequence is transmitted twice but independently over the same channel, the independent observations can be combined at the receiver side. From an information-theory point of view, the overall mutual information between the data sequence and the received sequences represents a combination of the mutual information of the two channels. This concept is termed information combining. A lower bound and an upper bound on the combined information is presented, and it is proved that these bounds are tight. Furthermore, this principle is extended to the computation of extrinsic information on single code bits for a repetition code and for a single parity-check code of length three, respectively. For illustration of the concept and the bounds on information combining, two applications are considered. First, bounds on the information processing characteristic (IPC) of a parallel concatenated code are derived from its extrinsic information transfer (EXIT) chart. Second, bounds on the EXIT chart for an outer repetition code and for an outer single parity-check code of a serially concatenated coding scheme are computed.

Bit interleaved coded space-time modulation with iterative decoding (BICSTM-ID) [1], [2] is an attractive strategy to achieve high power efficiency close to capacity limit by applying turbo principle to multiple-input and multiple-output (MIMO) channels. In this paper, Information Processing Characteristic (IPC) analysis [3] is extended to MIMO systems in order to fully characterize the BICSTM-ID scheme based on a new equivalent model of combined binary input channels. The analysis results show that the IPC analysis offers an unified aspect for BICSTM and BICSTM-ID from an information theoretical point of view and provides a valuable design guideline for BICSTM-ID as well. Moreover, IPC based upper and lower bounds on BER performance [4] are applied to BICSTM-ID, which are confirmed by simulations and seem to be very useful for performance estimation of coding schemes for space-time coded MIMO channels.

Asymptotical analysis of concatenated codes with EXIT charts (ten Brink, S., 1999) or the AMCA (Huettinger, S. and Huber, J., 2002) has proven to be a powerful tool for the design of power-efficient communication systems. However, the result of the asymptotical analysis is usually a binary decision, whether convergence of iterative decoding is possible at the chosen signal-to-noise ratio, or not. We show how to obtain the information processing characteristic (IPC) introduced by Huettinger et al. for concatenated coding schemes (see Proc. 39th Allerton Conf. on Commun., Control and Computing, 2001). If asymptotical analysis is performed under the assumption of infinite interleaving and infinitely many iterations, this IPC is a lower bound. Furthermore, it is also possible to estimate the performance of realistic coding schemes by restricting the number of iterations. Finally, the IPC can be used to estimate the resulting bit error ratio for the concatenated coding scheme. As an upper and a lower bound on the bit error ratio for a given IPC exist, we are able to lower bound the performance of any concatenated coding scheme and give an achievability bound, i.e. it is possible to determine a performance that can surely be achieved if sufficiently many iterations are performed and a large interleaver is used.

We propose a novel design method, which is an extension to the EXIT charts introduced by ten Brink (see IEE Electronics Letters, vol.35, no.10, p. 806-808, 1999), for low-rate power-efficient codes. An exemplary design of a rate -1/4 code shows more than 1 dB more coding gain than the original turbo-code of rate -1/2. Using this code in a CDMA scheme while reducing the spreading by a factor of 2 helps improving the overall performance of the multi-user scheme significantly.

A hierarchically designed channel coding scheme protects a few number of input data streams, so-called layers, with a decreasing amount of redundancy from layer 0 to layer L. Such a code design clearly leads to unequal error protection, but as shown by Huettinger and Huber (see Winter School on Coding and Information Theory, Reisensburg, December 2000) it can be superior in the average bit error rate compared to an equal error protection (EEP) design, if the protection of layers is not too different. This is due to the fact, that a near-EEP hierarchical design can match the properties of the iterative decoder. We extend the result to woven convolutional codes (WCC). Based on asymptotical analysis of the convergence of iterative decoding by means of EXIT charts we show that for an infinite interleaver size the hierarchical structure is superior. Furthermore, we show that even for practical block sizes used in modern communication systems a significant improvement is possible by the hierarchical design.