Electrical Engineering

The performance of a Turbo code with short block length depends critically on the interleaver design. There are two major criteria in the design of an interleaver: the distance spectrum of the code and the correlation between the information input data and the soft output of each decoder corresponding to its parity bits. This paper describes a new interleaver design for Turbo codes with short block length based on these two criteria. A deterministic interleaver suitable for Turbo codes is also described. Simulation results compare the new interleaver design to different existing interleavers.

A Pseudo-Maximum Likelihood Data Estimation (PML) algorithm f o r discrete channels with finite memory In additive white Gaussian noise is developed. Unlike the traditional methods which utilize the Viterbi Algorithm (VA) for data sequence estimation, the P M L algorithm offers an alternative solution to the problem which as much easier to implement. There is a trodeoff an the PML algorithm between computatzonal complexity and performance. The performance of PML is compared with the optimum receiver (VA iuzth known channel).

To compensate the performance degradation induced by polarisation mode dispersion (PMD) in high-speed optical transmission, a single-input multiple-output (SIMO) decision feedback equaliser (DFE) technique is proposed to combat all orders of PMD-induced distortion. The scheme is based on a new SIMO PMD channel model which utilises information embedded in both polarisation states. The performance analysis of the proposed PMD SIMO DFE scheme is provided along with explicit expressions for the filter coefficients. The analysis results show that the new scheme provides a significant improvement over using a first-order optical compensator and conventional DFE.

We investigate numerically the usefulness of Turbo and Reed-Solomon coding in the presence of Polarization-Mode Dispersion (PMD) using computer simulations. It is demonstrated that for a fixed level of PMD and a fixed data-rate, there is an optimal code overhead. This is in contrast to the case of negligible PMD, where high overhead codes perform best.

Opportunistic interference management (OIM) is an approach that can asymptotically achieve dirty paper coding (DPC) capacity in the downlink of wireless cellular networks with minimum feedback requirement. With K antennas at the base station and M mobile users in the cell, the proposed technique requires only K integer numbers related to channel state information (CSI). This multiplexing gain of K is achieved at the expense of M mobile users such that K = Θ(log M ). We introduce an antenna selection scheme at the base station to reduce the minimum number of required mobile users significantly at the expense of reasonable increase in feedback.

We demonstrate that the gain attained by network coding (NC) on the multicast capacity of random wireless ad hoc networks is bounded by a constant factor. We consider a network with n nodes distributed uniformly in a unit square, with each node acting as a source for independent information to be sent to a multicast group consisting of m randomly chosen destinations. We show that, under the protocol model, the persession capacity in the presence of arbitrary NC has a tight bound of Θ 1 √ mnlog (n) when m = O( n log(n) ) and Θ( 1 n ) when m = Ω( n log(n) ). Our result follows from the fact that prior work has shown that the same order bounds are achievable with pure routing based only on traditional store-and-forward methods.

A recent measurement campaign on spectrum utilization promoted by the Federal Communication Commission throughout the US has revealed that significant portions of the electromagnetic spectrum are rarely exploited for considerable intervals of time, thus paving the way to a number of possibilities for increasing bandwidth utilization among multiple users in shared radio networks. The clue to improve spectrum utilization, as well as efficiency, comes from communications systems exploiting the socalled Cognitive Radio technology, which at the physical layer, as well as at upper-levels of the network, can adaptively and dynamically allow users to access radio resources by switching among portions of unused bandwidth in different intervals of time. The cognitive radio technology is still in its infancy, and many problems at a theoretical as well as practical level have to be solved before this technology may be fully exploited in next generation wireless networks.

The paper presents a mathematical framework for Topology evolutions from nodes' mobility was not considered quantifying the overhead of proactive routing protocols in mobile in . In , information theoretic analysis is pursued to ad hoc networks (MANETs). We focus on situations where the bound the memory requirement and overhead for a hierarchical nodes are randomly moving around but the wireless transmisp sions can be decoded reliablely, when nodes are within commu-protocol in MANET upon entropy rate of topology evolutions. nication range of each other. We explicitly present a framework Such results provide good understanding of the scalability to model the overhead as a function of stability of topology and properties of routing overhead but are not sufficient to justify analytically characterize the statistical distribution of topology the practical impact from topology evolutions. However, to evolutions. The OLSR protocol is further singled out for a the best of our knowledge, there is no previous work that detailed analysis, incorporating the proposed analytical model. makes such analytical connection between routing overhead Results are compared against Qualnet simulations for random t movements, which corroborate the essential characteristics of and topology evolutions. Moreover, none ofthe past work has the analytical results. The key insight that can be drawn from analytically characterized topology evolutions as a function the analytical results of this paper is that nodal movements will of node mobility, a solution of which is crucial to make the drive up the overhead by a penalty factor, which is a function connection.

We present statistical models to accurately evaluate the distribution of the lifetime of a wireless link in a mobile ad hoc network (MANET) in which nodes move randomly within constrained areas. We show that link lifetime can be computed through a two-state Markov model and further apply the computed statistics to the optimization of segmentation schemes of information stream. Summarizing all these results, we further provide comprehensive analysis on throughput, delay, and storage requirements for MANETs with restricted node mobility.

We compute the capacity of mobile ad hoc networks (MANETs) when all the nodes in the network are endowed with M antennas. The derivation is based on a new communication scheme for wireless ad hoc networks utilizing the concept of cooperative many-to-many communication, called opportunistic cooperation, as opposed to the traditional approach that emphasizes on one-to-one communication. We demonstrate that the capacity of MANETs with multiple antennas is improved using cooperation as compared to non-cooperative schemes, i.e., point-to-point communication. Monte-Carlo simulation is used to validate the results.

Successful message relay, or the quality of the inter-user channel, is critical to fully realize the cooperative benefits promised by the theory. This in turn points out the importance of the relative location of the users. This paper investigates the impact of the location on the system capacity and outage probability for both amplify-forward (AF) and decodeforward (DF) schemes. Signal attenuation is modeled using power laws and capacity is evaluated using the max-flow mincut theory. The resemblance and difference between cooperative systems and multi-input multi-output (MIMO) systems are also discussed. Finally a capacity contour for DF, the more popular mode of the two, is provided to facilitate the derivation of engineering rules.