Abstract-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. In this paper, 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.Index Terms-Extrinsic information, extrinsic information transfer (EXIT) chart, information combining, information processing characteristic (IPC), iterative decoding, mutual information, parallel concatenated codes.

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This paper studies detection algorithms for diffusion-based molecular communication systems, where molecules freely diffuse as information carrier from a transmitter to a receiver in a fluid medium. The main limitations are strong intersymbol interference due to the random propagation of the molecules, and the low-energy/low-complexity assumption regarding future implementations in so-called nanomachines. In this contribution, a new biologically inspired detection algorithm suitable for binary signaling, named adaptive threshold detection, is proposed, which deals with these limitations. The proposed detector is of low complexity, does not require explicit channel knowledge, and seems to be biologically reasonable. Numerical results demonstrate that the proposed detector can outperform the common low-complexity fixed threshold detector under certain conditions. As a benchmark, maximum-likelihood sequence estimation (MLSE) and reduced-state sequence estimation (RSSE) are also analyzed by means of numerical simulations. In addition, the effect of molecular denaturation on the detection performances is studied. It is shown that denaturation generally improves the detection performances, while RSSE is able to outperform MLSE in the case of no denaturation.

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SUMMARYDirect-sequence code-division multiple access (DS-CDMA) is often put on the same level with CDMA, ignoring the fact that many different CDMA techniques exist. A special CDMA technique which has recently become popular is interleave-division multiple access (IDMA). In this semi-tutorial, focus is on a generalisation of IDMA referred to as interleave-division multiplexing (IDM)/IDMA or multi-layer IDMA for short. Multi-layer IDMA is a special form of superposition coding, and can be interpreted as a joint modulation, channel coding and multiple access scheme. Motivated by information theoretical arguments and practical functionalities, a wide range of subjects (such as capacity bounds, power allocation, receiver analysis, quality of service aspects, multi-layer ARQ and possible applications) are covered. This semi-tutorial consists of three parts: in the first part, an introduction to IDMA (Section 1) and multi-layer IDMA (Section 2) is given. In the second part, practical issues such as functionalities of multi-layer IDMA (Section 3) and multi-layer ARQ (Section 4) are studied. In the third part, information theoretical bounds in conjunction with power allocation (Section 5) and a receiver analysis (Section 6) are provided, before conclusions are drawn in Section 7.

Compared to the open ocean where blue lightemitting diodes (LEDs) perform well for data communications, in coastal and harbor environments optical transmission becomes worse and the color of lowest attenuation shifts to green. Another problem concerns the "green-yellow gap" of LEDs, as the quantum efficiency of current commercially available green LEDs is poor. Since energy consumption is an important factor, particularly for battery-powered systems, using blue LEDs is a tradeoff. Recently, phosphor-converted green LEDs, which are pumped by highly efficient blue LEDs, have been introduced to the market, and this type of LED promises better performance. This paper compares the use of blue, green, and converted green LEDs for applications in optical underwater communication systems in coastal waters. Theoretical aspects of the overall LED-water-detector channel are presented. A method for determining individual system coefficients is developed, and the impact on the communication system performance is explained. Practical approaches are introduced, complemented by measurements in the Baltic Sea. Index Terms-Coastal waters, converted light-emitting diode (LED), green-yellow gap, optical underwater (u/w) communication.

In this article, an innovative approach for magnetic data communication is presented. For this purpose, the receiver coil of a conventional magneto-inductive communication system is replaced by a high-sensitivity wideband magnetic field sensor. The results show decisive advantages offered by sensitive magnetic field sensors, including a higher communication range for small receiver units. This approach supports numerous mobile applications where receiver size is limited, possibly in conjunction with multiple detectors. Numerical results are supported by a prototype implementation employing an anisotropic magneto-resistive sensor.

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