REV Journal on Electronics and Communications
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Joint Optimization of Precoder and Decoder in Multiuser MIMO Systems
Get PDFThis paper considers the joint optimization of precoder and decoder for both uplink and downlink transmissions in multiuser multiple-input, multiple-output (MU-MIMO) systems. Focusing on the scenario when an improper constellation such as binary phase shift-keying (BPSK) or M-ary amplitude shift-keying (M-ASK) is employed, novel joint linear precoders and decoders are proposed to minimize the total mean squared error (TMSE) of the symbol estimation. The superiority of the proposed transceivers over the previously-proposed designs is thoroughly verified by simulation results
Standard-Compliant Content Adaptation in IPTV Systems
Get PDFIPTV, which is based on the universal IP infrastructure, has the inherent nature of heterogeneity in terms of content, networks, terminals, and users. An important solution to cope with such heterogeneity is content adaptation. This paper reviews the standardization issues related to content adaptation in IPTV standards. We first describe the basic architecture of content adaptation and its integration into the ITU-T IPTV architecture. Then typical methods of content adaptation in practical IPTV systems are discussed in detail. Especially, we highlight the standard metadata tools that are potential to support adaptation methods within ITU-T IPTV architecture. Some recent developments in other standard bodies are also discussed
Constructing High-Rate QC-LDPC Codes with Large-Girth based on Shortened Array Codes
Get PDFIn this paper, we aim at constructing high-rate quasi-cyclic low-density parity-check (QC-LDPC) codes with girth-10 based on shortened array codes. Our first contribution is the derivation of analytic results on the maximum number of columns for shortened array codes of different girths. Then, inspired by the analysis, we propose a code construction method for column-weight-three codes. We further compare the minimum length and the error performance of the column-weight-three codes constructed by the proposed algorithm and those found by the conventional greedy construction algorithm. We show that the proposed method is more effective than the conventional greedy algorithm in the sense that the minimum length of the codes constructed using the proposed method to achieve different code rates is comparative or much shorter than those constructed using the greedy construction
Design, Simulation, and Performance Analysis of an INS/GPS System using Parallel Kalman Filters Structure
Get PDFThanks to the strong growth of MEMS technology, the Inertial Navigation System (INS) is widely applied to navigation and guidance of moving objects. However, there exist errors in the inertial sensor’s signals that cause unacceptable drifts. To minimize these effects on the INS system, a GPS is usually employed simultaneously with an INS in order to increase the dimension of the system; the desired parameters are estimated by Kalman filtering technique applied to the enlarged system. In this paper, we present the design, simulation and performance analysis of an INS/GPS system using two parallel Kaman filters in order to increase the accuracy of the parameter estimation process. The results show that this system could be efficiently brought to practical applications
Performance Analysis of Adaptive Modulation for Distributed Switch-and-Stay Combining with Single Relay
Get PDFIn this paper we present our investigation of the performance of a distributed switch-and-stay scheme and a solution for low-complexity cooperative relaying under adaptive transmission. We are able to derive the closed-form expressions of the occurrence probability, the outage probability, the bit error probability, and the achievable spectral efficiency of the proposed scheme for Rayleigh fading channels. Simulations are performed to verify the analytic results. It is shown that, by applying adaptive modulation, the achievable spectral efficiency of the system is improved significantly, and the proposed scheme achieves the same spectral efficiency as compared to that of the incremental relaying but with a lower relay activation time
Jointly Optimal Precoder and Power Allocation for an Amplify-and-Forward Half-Duplex Relay System
Get PDFThis paper investigates the optimal precoder design and power allocation between the source and relay for a half-duplex single-relay non-orthogonal amplify-and-forward (NAF) system. Based on the pair-wise error probability (PEP) analysis, an optimal class of 2 × 2 precoders is first derived for the traditional power allocation scheme, where one-third of the system power is spent at the relay node, while two-thirds are spent at the source node. Different from optimal unitary precoders proposed earlier, the derived class of precoders indicates that the source should spend all its power transmitting a superposition of the symbols in the broadcast phase, while being silent in the cooperative phase, for optimal asymptotic performance. We then further address the problem of jointly optimal precoder and power allocation for the system under consideration. It is shown that the total power should be equally distributed to the source and the relay, and the source should again spend no power during the cooperative phase for the best asymptotic performance. Analytical and simulation results reveal that the proposed precoders not only exploit full cooperative diversity, but also provide significant coding gain over the optimal unitary precoders. For instance, a coding gain of around 1dB can be attained at the practical BER level of 10 − 5 for various modulation schemes
Opportunistic Unsynchronized Cognitive Radio Networks
Get PDFThe challenge of opportunistic networks is to maximize the usage of the spectrum by offering quick and easy access to independent systems and their users. A physical layer able to operate efficiently in an unsynchronized environment is needed and it is shown that the filter bank multicarrier (FBMC) technique can meet the objectives in terms of performance and flexibility. Then, a protocol must be developed to ensure global convergence and an overall transmission capacity close to the optimal possible value at a given place and a given time. An approach called “good neighbour” is presented, which consists of building the capacity requested by the users through a threshold regulated local search and with minimum changes in frequency band allocation to reduce interference non-stationarity to other systems. Finally, potential applications of opportunistic networks are reviewed and the conditions for proliferation of this kind of network are discussed
Defining Quantiles for Estimating IP Packet Delay Variation in NGN Core Networks
Get PDFTraffic delay is one of the important metrics used for evaluating network performance. Delay and delay variation characteristics of IP packets transferred over multi-section networks can be derived, estimated or composed from component distributions of IP package delay in each network section. Approximate methods are needed in the cases of unknown or complicated delay distribution functions, which are unavailable or unusable in practice. The ITU-T has proposed a method for estimating IP packet delay variation. One of noticeable factors affecting the estimation accuracy is the packet delay population quantile which has not been adequately considered. The objective of this paper is to examine the optimal range of quantiles used for estimating the IP packet delay variation in the NGN (Next Generation Network) core networks. The paper is composed from the following ideas. Firstly, several concepts and mathematical formulas related to delay metrics based on probability and statistics theory are defined. The approximate method of ITU-T for estimating the IP packet delay variation in a multi-section network is revised. Then, another method based on convolution for composing the empirical IPTD distribution functions is proposed for the same target as the first one. Secondly, a number of test cases are implemented to measure the IP packet delay on several sections of an NGN core network. Sample data are used for computing and estimating the IP packet delay variation for multi-section networks by two methods with certain hypotheses. Finally, these methods are compared and evaluated both theoretically and empirically in regards to the estimation accuracy versus quantiles of the IP packet transfer delay. The best range of quantiles is determined to ensure the accuracy of the estimation method applied for the NGN core network
ACO-Based Multi-User Detection in Cooperative CDMA Networks
Get PDFIn this paper, the cooperative diversity is investigated in the uplink of a Code Division Multiple Access (CDMA) network in which users cooperate by relaying each other’s messages toward the Base Station (BS). It is assumed that the spreading waveforms are not orthogonal and hence, Multiple Access Interference (MAI) exists at the relay nodes as well as the BS. MAI degrades the signal quality at both relays and BS and decreases the cooperative diversity gain. To alleviate this problem, an Ant Colony Optimization (ACO) based Multi-User Detector (MUD) has been proposed to efficiently combine the received signals from the direct and relay paths and sub-optimally extract transmitted bits at the BS. The computational complexity of proposed algorithm is significantly lower than that of the Maximum Likelihood (ML) detector. More explicitly, for a cooperative network supporting 15 users, the computational complexity of the proposed ACO algorithm is a factor of 103 lower than that of the optimum Bayesian detector. Simulation results show that the performance of the proposed ACO-based detector can closely approach the maximum diversity in terms of BER and efficiently cancel the MAI at the BS
Gram-Schmidt Combined LLL Lattice-Reduction Aided Detection in MIMO Systems
Get PDFThis paper proposes an improved lattice-reduction aided (LRA) MMSE detection scheme, based on the Gram-Schmidt (GS) procedure. The proposed scheme reduces the column vectors of the MIMO channel matrix, by using the LLL algorithm followed by the GS procedure in order to transform the channel matrix into a new one which has mutually purely orthogonal column vectors. Compared to the conventional LRA MMSE detector, the proposed detector achieves a very good BER performance, almost equivalent to those using the ML detector in the 4 × 4 MIMO system at the cost of a slightly larger computational complexity