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A multiuser Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) broadcast channel is considered where both transmitter and receivers are equipped with multiple antennas. The Channel State Information (CSI) is quantized and provided through limited feedback links. In the first part of this work, the Maximum Expected SINR Combining (MESC) strategy for feedback decrease is investigated. Then a combination of MESC with subcarrier assigning is presented to further reduce the feedback load. The basic idea is the subcarriers are partitioned into resource blocks. For each block, only one quantized channel vector is feedback. The simulation results show MESC can obtain the performance gain over the relevant combiner strategies in MIMO-OFDM system. Moreover the effectiveness on the reduction of feedback overhead by the use of partitioning blocks in the studied system is evaluated.

Aimed at bridging the gap between the maximum likelihood and the suboptimal decoding schemes for short or medium LDPC codes, a generalised ordered statistic decoding (OSD), in the form of syndrome decoding, is presented in the paper. The OSD is invoked once when a nonzero decoding syndrome is returned for the preceded belief propagation (BP) or min-sum (MS) variants. With respect to the OSD with an accumulative reliability metric for the BP in the logarithmic likelihood ratio (LLR) domain, we extend the metric to the BP in the probability domain. Furthermore, the OSD with the metric specific for the MS variants, shows an appealing trade-off between performance and complexity. Meanwhile, when determining the optimal error pattern estimation, an alternative designed to reduce the number of the required real additions proves to be effective. Copyright © 2008 John Wiley & Sons, Ltd.

For one class of Low-Density Parity-Check (LDPC) codes with low row weight in their parity check matrix, a new Syndrome Decoding (SD) based on the heuristic Beam Search (BS), labeled as SD-BS, is put forward to improve the error performance. First, two observations are made and verified by simulation results. One is that in the SNR region of interest, the hard-decision on the corrupted sequence yields only a handful of erroneous bits. The other is that the true error pattern for the nonzero syndrome has a high probability to survive the competition in the BS, provided sufficient beam width. Bearing these two points in mind, the decoding of LDPC codes is transformed into seeking an error pattern with the known decoding syndrome. Secondly, the effectiveness of SD-BS depends closely on how to evaluate the bit reliability. Enlightened by a bit-flipping definition in the existing literature, a new metric is employed in the proposed SD-BS. The strength of SD-BS is demonstrated via applying it on the corrupted sequences directly and the decoding failures of the Belief Propagation (BP), respectively.

Bit-Interleaved Coded Modulation with Iterative Decoding (BICM-ID) is a bandwidth efficient transmission, where the bit error rate is reduced through the iterative information exchange between the inner demapper and the outer decoder. The choice of the symbol mapping is the crucial design parameter. This paper indicates that the Harmonic Mean of the Minimum Squared Euclidean (HMMSE) distance is the best criterion for the mapping design. Based on the design criterion of the HMMSE distance, a new search algorithm to find the optimized labeling maps for BICM-ID system is proposed. Numerical results and performance comparison show that the new labeling search method has a low complexity and outperforms other labeling schemes using other design criterion in BICM-ID system, therefore it is an optimized labeling method.

A novel method is proposed to analyze the capacity of future Code Division Multiple Access (CDMA) systems carrying multimedia services. The power level allocation is firstly investigated to meet each call’s Bit Error Rate (BER) requirement, then the system capacity is defined from the conditions for the existence of the physical meaning of these power levels. Simulation results have shown that the capacity analyzing methods can be well used in the performance evaluation of the system accommodating heterogeneous services and the spectral efficiency of this scheme is higher than the existing ones.

Multi-constrained quality-of-service routing (QoSR) is to find a feasible path that satisfies multiple constraints simultaneously, which is a big challenge for mobile ad hoc networks (MANETs) where the topology may change constantly. It has been proved that such a problem is NP-complete. Heuristic algorithms with polynomial and pseudo-polynomial-time complexities are often used to deal with this problem. However, existing solutions, most of which suffered either from excessive computational complexities or from low performance were proposed only for wired networks and cannot be used directly in wireless MANETs. In this paper a novel QoS routing algorithm based on Simulated Annealing (SA_RA) is proposed. This algorithm first uses an energy function to translate multiple QoS weights into a single mixed metric and then seeks to find a feasible path by simulated annealing. The paper outlines simulated annealing algorithm and analyzes the problems met when we apply it to QoSR in MANETs. Theoretical analysis and experiment results demonstrate that the proposed method is an effective approximation algorithms showing better performance than the other pertinent algorithm in seeking the (approximate) optimal configuration within a period of polynomial time.

Multi-constrained Quality-of-Service (QoS) routing is a big challenge for Mobile Ad hoc Networks (MANETs) where the topology may change constantly. In this paper a novel QoS Routing Algorithm based on Simulated Annealing (SA_RA) is proposed. This algorithm first uses an energy function to translate multiple QoS weights into a single mixed metric and then seeks to find a feasible path by simulated annealing. The paper outlines simulated annealing algorithm and analyzes the problems met when we apply it to Qos Routing (QoSR) in MANETs. Theoretical analysis and experiment results demonstrate that the proposed method is an effective approximation algorithms showing better performance than the other pertinent algorithm in seeking the (approximate) optimal configuration within a period of polynomial time.

A novel Least Squares Constant Modulus (LSCM) beam-forming algorithm in smart antenna Multi-Carrier Code Division Multiple Access (MC-CDMA) system is proposed in this paper. It adaptively beam-forms the multi-carrier antenna array signal using the LSCM Algorithm (LSCMA), and in the meantime, the beam-formed signals on every sub-carrier are combined by using Orthogonal Restore Combination (ORC), Equal Gain Combination (EGC) or Maximum Ratio Combination (MRC). Then the decision of the combined signals and the spread-code of the expected user are used to re-construct the signals on every sub-carrier. At last, the difference between the re-constructed signal and the output signal of the beam-former is used to control the coefficients of the beam-former. The bit error probability of the proposed algorithm is analyzed. We simulated and compared it with the conventional LSCM beam-forming algorithm. Simulation results show that the proposed algorithm is superior to the latter in Bit Error Rate (BER).

An alternative blind adaptive multiuser detection is investigated based on modified constrained constant modulus (CM) criterion. It is shown that the performance of a CM-based receiver is limited by the received power of the desired user. In this paper, we show that the limitation can be avoided using the noncanonical constraint CM criterion and that in the presence of channel noise the modified CM criterion function is strictly convex by properly selecting some constant. With analyzing the extrema of the cost function, we point out how to select the constant. Moreover, a simple stochastic gradient algorithm for implementing our scheme is presented, and the convergence properties of the algorithm are analyzed. Simulation examples are given to demonstrate the performance of the proposed scheme.

By applying a result from geometric Goppa codes, due to H.Schtenoth, the true dimension of certain alternant codes is calculated. The results lead in many cases to an improvement of the usual lower bound for the dimension.

I n this paper, we investigate the energy efficiency maximization problem of cognitive radio systems. We propose to study energy efficiency of cognitive relay transmission scheme based on cooperative spectrum sensing, since empirical studies have shown that optimal sensing time and transmit power are key factors for energy efficiency maximization. We design a method that simultaneously considers the parameters of spectrum sensing time and transmit power. Finally, we conduct deep experiments which show that our proposed approach can significantly improve the throughput and energy efficiency than the non-cooperative spectrum sensing method. DOI: http://dx.doi.org/10.11591/telkomnika.v11i8.2446

Cognitive radio is a promising technology. The spectrum scarcity problem can be overcome by enabling unlicensed users to access the licensed spectrum bands. In this paper, we focus on power efficiency maximization of cognitive system by jointly considering the parameters of spectrum sensing time and transmit power. In addition, we propose to investigate power efficiency of cognitive relay transmission scheme based on that of non-relay transmission. Finally, we provide the simulation results to show that the throughput and power efficiency of the proposed approach can be significantly improved compared to that of the non-relay transmission scheme in cognitive radio networks. Furthermore, numerical results demonstrate that there exist the optimal parameters to maximize power efficiency.

The channel model of distributed multiple input multiple output (MIMO) systems is provided and a novel fast antenna selection algorithm is proposed for the downlink transmit antenna selection in distributed MIMO systems. The performance of the proposed algorithm is compared with the algorithms described in references. Simulation results indicate that the proposed algorithm decreases the computational complexity without system capacity lost.

This paper investigates user selection scheme in the multiple-antennas multiuser downlink systems with the zero-forcing (ZF) beamforming transmit strategy. Among the numerous user selection algorithms, the sequential water-filling (SWF) algorithm based on LQ decomposition behave good performance in the throughput and the complexity. On another hand, setting a threshold value on channel gains can decrease evidently the search space of user selection. Considering the advantages of these two aspects, we combine them together, present a low complexity user selection scheme, and extend it to the multiple receive antennas scenario.

For original paper see IEEE Commun. Lett., vol.2, no.8, p.217-19 (1998 August). A linearly constrained constant modulus (LCCM) receiver was presented in the above paper by Miguez et al. In this letter, we point out that the analysis in the above paper is incomplete and show in the noise-free case that the LCCM approach can completely remove multiple-access interference if and only if the desired user amplitude is no less than the critical value 1/spl radic/3. The simulation examples demonstrate the results.

Ant based routing protocols for MANETs have been widely explored, but most of them are essentially of single-path which tends to have heavy burden on the hosts along the shortest path from source to destination. The robustness of these protocols is comparatively not good which is further weakened by the positive feedback mechanism of ant. Node-disjoint multi-path routing is more robust and can support QoS better than single-path routing in MANETs. In this paper we combine swarm intelligence and node-disjoint multi-path routing to solve the problem mentioned above. A novel approach named Ant colony based Multi-path Routing (AMR) is proposed. AMR establishes and utilizes multiple routes of node-disjoint paths to send data packets concurrently and adopts pheromone to disperse communication traffic, thus it can adapt to the dynamic changes of the network and support QoS better. The simulation results show that the proposed approach outperforms other pertinent algorithms

Wireless mesh networks (WMNs) are an emerging architecture based on multi-hop transmission. Improving the performance in face of unreliable wireless medium will support WMNs to be a very cost-effective solution for wireless ISPs. In this paper, we propose a new cross layer routing metric called expected transmission efficiency (ETE), which aims to find high throughput and low delay paths. ETE takes into account MAC-layer link quality as the number of packets retransmissions on wireless link and the contention level along the paths. The implementation of ETE metric in proactive routing protocol such as destination sequenced distance vector (DSDV) is also given. Simulation results show that our proposed cross layer routing metric achieves better performance in comparison to the traditional minimum hop metric

Two blind multiuser detection algorithms for antenna array in Code Division Multiple Access (CDMA) system which apply the linearly constrained condition to the Least Squares Constant Modulus Algorithm (LSCMA) are proposed in this paper. One is the Linearly Constrained LSCMA (LC-LSCMA), the other is the Preprocessing LC-LSCMA (PLC-LSCMA). The two algorithms are compared with the conventional LSCMA. The results show that the two algorithms proposed in this paper are superior to the conventional LSCMA and the best one is PLC-LSCMA.

Multi-constrained quality-of-service routing (QoSR) is to find a feasible path that satisfies multiple constraints simultaneously, as an NPC problem, which is also a big challenge for wireless mesh networks. There are few methods, which can solve this problem effectively so far. In this paper, we propose a novel routing scheme based on mean field network (MFN/spl I.bar/RS) to solve this problem. This algorithm first uses a function of the wireless link's delay and capacity both of which are QoS parameters as the cost function, and then seeks to find a feasible path by mean field annealing. Because MFN/spl I.bar/RS uses a set of deterministic equations to replace the stochastic process in simulated annealing (SA), and uses saddle point approximation in the calculation of the stationary probability distribution at equilibrium, thus the convergence time is much less than the algorithm based on SA. Simulation results demonstrate that MFN/spl I.bar/RS is an effective algorithm and is very fit for wireless mesh networks where the topology may be changing constantly.

Multi-constrained quality-of-service routing (QoSR) is to find a feasible path that satisfies multiple constraints simultaneously, as an NPC problem, which is also a big challenge for wireless mesh networks. In this paper, we propose a novel Routing Scheme based on Mean Field Annealing (MFA_RS) to solve this problem. MFA_RS first uses a function of the wireless link’s delay and capacity as the cost function, both of which are QoS parameters, and then seeks to find a feasible path by mean field annealing. Because MFA_RS uses a set of deterministic equations to replace the stochastic process in Simulated Annealing (SA), and uses saddle point approximation in the calculation of the stationary probability distribution at equilibrium, thus the convergence time is much less than the algorithm based on SA. Simulation results demonstrate that MFA_RS is an effective algorithm and is very fit for wireless mesh networks where the topology may be changing constantly.

Multi-constrained quality-of-service routing (QoSR) is to find a feasible path that satisfies multiple constraints simultaneously, as an NPC problem, which is also a big challenge for ad hoc networks. In this paper, we propose a novel heuristic routing algorithm based on Simulated Annealing (SA_HR). This algorithm first uses an energy function to translate multiple QoS weights into a single metric and then seeks to find a feasible path by simulated annealing. The paper outlines simulated annealing algorithm and analyzes the problems met when we apply it to QoSR in ad hoc networks. Theoretical analysis and experiment results demonstrate that the proposed method is an effective approximate algorithms showing good performance in seeking the (approximate) optimal configuration within a period of polynomial time.

In this letter we employ a genetic algorithm (GA) to synthesize binary sequences with good autocorrelation and crosscorrelation properties. The feasibility and robustness of this method are proved by the sequences obtained in simulation, which are better in auto- and crosscorrelation properties than those previously reported.