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A distributed optimization algorithm is presented for resource allocation in wireless relay networks. This algorithm is particularly useful in multiple-source, multiple-relay wireless networks employing fractional cooperation, in which each relay contributes only a fraction of its resources to each source; in this case, the algorithm is used to find the optimal fractions. The advantage of this distributed...
Energy consumption in wireless communication system is rapidly increasing due to the growth in wireless multimedia access. Combating the adverse effects of excessive energy consumption demands for energy-aware system design called green communication, which has become the major focus of many researchers recently. In this paper, we propose user selection and power allocation schemes for a multi-user...
In this paper, we formulate an optimization problem for resource allocation and scheduling in orthogonal frequency division multiple access (OFDMA) half-duplex decode-and-forward (DF) relay assisted networks. Our problem formulation takes into account artificial noise generation to combat a multiple antenna eavesdropper. The secrecy data rate, power, and sub-carrier allocation policies are optimized...
Log-likelihood ratios (LLRs) are efficient metrics used in the decoding of modern channel codes such as low-density parity-check and turbo codes. LLR calculation, however, can be a complex task since LLRs are usually complicated nonlinear functions of the channel output. In multi-input multioutput (MIMO) channels, the complexity of the calculation increases exponentially with the number of antennas...
In this article, a new method to design the flexible-length S-random interleaver is proposed for storage optimization in a turbo coding system. In this method, the high-spread property s-random interleaver is constructed by selecting appropriate position and element that can improve spread property of interleaver in each iteration in which length of interleaver is increased. Using this method, interleavers...
In this paper, we consider a slow-fading nt ×nr multiple-input multiple-output (MIMO) channel subjected to block fading. Reliability (in terms of achieved diversity order) and rate (in number of symbols transmitted per channel use) are of interest in such channels. We propose a new precoding scheme which achieves both full diversity (nt ×nrth order diversity) as well as full rate (nt symbols per channel...
We propose two scheduling protocols which are applicable to two-hop relay networks based on mobile WiMAX system: the first protocol adopts a persistent scheduling (PS) scheme in both hops, called the PS-PS protocol, while the second protocol adopts the PS scheme only in the first hop and the dynamic scheduling (DS) scheme in the second hop, called the PS-DS protocol. We optimize the above two protocols...
Adaptive cooperation with conflict-free relay assignment in a network setting is a challenging problem. The problem becomes even more difficult when users have quality-of-service (QoS) requirements but the available spectrum resource is limited, where admission control may be required. In this paper, we jointly study relay assignment and admission control in cooperative radio networks (CRNs). A one-stage...
Switch-and-stay combining (SSC) is a low-complexity alternative of selection combining in diversity schemes with two receiving antennas. Its operation is based upon activating a single diversity branch and maintaining it active for as long as the corresponding channel is sufficiently strong, regardless of the quality of the remaining branch. In this respect, we optimize here the switching threshold...
In this paper, we present a new non-data-aided (NDA) maximum likelihood (ML) time delay estimator based on importance sampling (IS). We show that a grid search and lack of convergence from which most iterative estimators suffer can be avoided. It is assumed that the transmitted data are completely unknown at the receiver. Moreover the carrier phase is considered as an unknown nuisance parameter. The...
Current communication schemes rely on instantaneous adaptation, which increases the system complexity and is memoryless. We propose a scheme for adapting system parameters based on a priori knowledge of the channel statistics to reduce feedback requirements. As a vital parameter in OFDM system, cyclic prefix (CP) length depends mainly on two channel characteristics: the channel gains and the root...
It has long been recognised that a wireless communication system can be more efficient if link-layer parameters such as modulation order, symbol rate and packet size, are (adaptively) optimised. A common optimising criterion is to maximise spectral efficiency (bits per second per Hertz (bps/Hertz)) subject to a very low bit-error constraint. But a packet-oriented criterion for link adaptation seems...
In this paper we consider a single cognitive radio seeking a transmission opportunity by sequentially sensing a number of statistically independent primary channels. We study the joint optimization of the time spent to sense a channel, the decision threshold to determine whether the channel is free or busy, together with the order with which the channels are sensed. The sensing time and decision threshold...
In this paper, we consider the analysis of a cooperative relay-based amplify-and-forward system in terms of average and outage capacity over fading channels. We first optimize the relay gain with the objective of maximizing the received signal-to-noise-ratio (SNR) at the destination, given that the fading statistics of the links in the cooperative system are known at the relay node. The Gaussian finite...
Transmission power control can significantly improve energy-efficiency of wireless sensor network communications. Power consumption models are typically based on dependence of channel attenuation on distance. However, in practice, information on distance is usually not available and the dependence of channel attenuation on distance is not sufficiently accurate. Therefore, we propose more accurate...
A novel cross-layer routing protocol is presented for Decode-and-Forward multi-hop relaying systems which lead to optimal power allocation for a given power budget by maximizing the capacity of source to destination. The problem of rate maximization by jointly allocating power and selecting relays nodes with limited total power constraint of network nodes is formulated when the channel state information...
We consider the Noisy MIMO Interference Channel (IFC) with linear transmitters and receivers and full CSI. The maximization of the Weighted Sum Rate (WSR) or transceiver design for Interference Alignment (IA) lead to cost functions with many local optima. Deterministic annealing is an approach that allows to track the variation of the known solution of one version of the problem into the unknown solution...
This paper focuses on the optimization of the 2D geometry of sensor arrays for 2D direction-of-arrival (DOA) estimation. Such arrays can be used for radar imaging purposes. Due to the optimization, the number of array channels can be kept quite small, which reduces hardware costs, while highly accurate DOA estimation accuracy can be achieved. Therefore, we derive a very simple expression of the 2D...
In this paper, resource allocation and scheduling in an orthogonal frequency division multiple access (OFDMA) downlink network is studied. The considered problem is modeled as an optimization problem which takes into account a multiple antenna eavesdropper and artificial noise generation for secure communications. Power, secrecy data rate, and subcarrier allocation are optimized for maximization of...
In the paper the optimization is applied to determine the threshold of wavelet coefficients in image de-noising aiming at grayscale image corrupted by additive white Gaussian noise and Daubechies wavelet transform. In the method the entropy of an image is the optimality criteria, which makes image de-noising a process of optimizing objective index of an image. The example proves that the presented...
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