User Selection Scheme Research Articles

Performance analysis of MIMO DF relay network with the Nth-best user selection scheme in the presence of co-channel interference

In this paper, we study the performance of multi-user multiple-input multiple-output (MIMO) relay network in the presence of co-channel interference (CCI) as well as additive white Gaussian noise (AWGN). Specifically, the Nth-best user selection scheme is applied to attain multi-user diversity. Both exact and asymptotic closed-form expressions for the outage probability and average symbol error rate (SER) of the considered system are derived, and corroborated by the Monte Carlo simulations. Based on the asymptotic SER expression, the diversity order and array gain are characterized, and the optimum power allocation between the source and the relay is also designed. The results reveal that the diversity order is NR×min{NS, ND(K−N+1)}, where NS, NR and ND represent the number of antennas at the source, the relay, and each destination, respectively, K is the number of the destinations, and N (1≤N≤K) represents the rank of the user chosen. The findings of this paper show that the CCI deteriorates the system performance by reducing the array gain, and optimal power allocation achieves better performance than that of uniform power allocation by offering extra array gain. These findings provide a valuable insight into the practical system design.

Performance of a cooperative downlink multiplexing scheme using dynamic spectrum access principles

In this study, the authors propose a new cooperative multiplexing scheme for downlink transmission using dynamic spectrum access (DSA) principles. In this scheme, the base-station (BS) transmits to its distant user using a selected relay node in two hops. In the second hop, while the relay forwards information to the distant user, the BS transmits information to another selected user in its vicinity using DSA principles. Assuming peak power and peak interference constraints, the authors derive outage and ergodic rate performance of the user served by DSA assuming various user selection schemes. The authors consider gain-based selection, SINR based selection (SS), interference cancellation (IC), as well as a hybrid scheme that employs both SS and IC. The authors demonstrate that apportioning of time between the first and second hop of relaying can improve outage performance of the user served by DSA while ensuring certain guaranteed performance for the distant user. The presented analytical expressions are compared with computer simulation results.

Experimental Evaluation of Low Complexity User Selection Schemes for Multi-User MIMO Systems

Experimental Evaluation of Low Complexity User Selection Schemes for Multi-User MIMO Systems

Resource allocation for multiple input multiple output‐orthogonal frequency division multiplexing ‐based space division multiple access systems

The problem of the system throughput maximisation and the fairness issue among users is considered for the downlink multiuser multiple input multiple output-orthogonal frequency division multiplexing system with MMSE precoding. Since finding the optimal solution by using the exhaustive search has very high computational burden, the authors propose a low-complexity user selection strategy plus the optimal power allocation in this study. With resorting to the mathematical simplification process, the proposed user selection scheme is designed to compare the related value of SINR. The power allocation is performed after the user selection. However, the power allocation is not in interference-free environment but in the presence of crosstalk, which is a nonlinear non-convex optimisation problem. In this study, the authors use an optimisation technique to obtain the optimal solution of the constrained non-convex nonlinear problem by replacing the objective function with a difference of two convex functions. A bisection-based strategy to solve this problem with interference-awareness to find local optimal solutions is presented in this study. Simulation results show that the performance of the proposed algorithm is close to that of the optimal solution. The trade-off between the system throughput and the fairness among users is also considered.

Multiuser Cognitive Networks with Nth-Best User Selection and Imperfect Channel Estimation

The Nth-best user selection scheme is efficient in outdated channel information conditions where the user that was the best at the selection time instant could not be the best at the transmission time instant. Also, this scheme is useful when the scheduling unit fails in error in selecting the best user among all the available users. Furthermore, the Nth-best user selection scheme is efficient in situations where, while the best user is waiting to be scheduled by a certain base station or a scheduling unit, it gets scheduled by other unit. In the proposed scheme, the secondary user with the Nth-best end-to-end signal-to-noise ratio (SNR) is scheduled the system resources. In our paper, closed-form expressions are derived for the outage probability, average symbol error probability, and ergodic channel capacity assuming imperfect estimation of channel state information and Rayleigh fading channels. Furthermore, to further analyze the system performance, the system is studied at the high SNR regime. The derived analytical and asymptotic expressions are verified by Monte-Carlo simulations. Main results illustrate that the diversity order of the studied multiuser cognitive Nth-best user selection network is the same as its non-cognitive counterpart. Also, findings show that with perfect channel estimation of secondary users, the diversity order of the system linearly increases with decreasing the order of the scheduled user, and vice versa, whereas a zero diversity gain is achieved by the system and a noise floor appears in the results when the channels of secondary users are imperfectly estimated assuming constant estimation error variance. Finally, results illustrate that the imperfect estimation of the secondary cell-primary cell channel affects only the coding gain of the system without affecting the diversity order.

On the Performance of Multiuser Switched Diversity Systems with Co-channel Interference

We investigate the effect of co-channel interference on the performance of multiuser switched diversity (MUSwiD) systems. In such systems, the first checked user whose channel quality is greater than a predetermined switching threshold is assigned the system resources and allowed to conduct its uplink transmission. In this paper, we derive closed-form expressions for the end-to-end outage probability and symbol error probability (SEP) for the independent non-identically distributed and independent identically distributed cases of desired users channels. In the analysis, all system links are assumed to follow Rayleigh distribution with the interference is being considered at the base station. Approximate expressions for the outage probability and SEP are derived in the high signal-to-noise (SNR) regime which allow for an easy evaluation of the system performance. Monte Carlo simulations are provided to validate the derived analytical and asymptotic expressions. Results show that the system can still achieve performance gain when more desired users are available and the interference power is fixed. This happens at the values of switching threshold that are comparable to average SNR. Asymptotic results illustrate that the system has a diversity order of 1 and a coding gain that is affected by several parameters such as the switching threshold, number of interferers, and the outage threshold. Finally, findings show that the MUSwiD user selection scheme is efficient for systems which operate at the range of low SNR values and this makes it an attractive candidate to be implemented in the emerging mobile broadband communication systems.

A joint antenna and user selection scheme for multiuser MIMO system

In this paper, we present a low-complexity algorithm for real-time joint user scheduling and receive antenna selection (JUSRAS) in multiuser MIMO systems. The computational complexity of exhaustive search for JUSRAS problem grows exponentially with the number of users and receives antennas. We apply binary particle swarm optimization (BPSO) to the joint user scheduling and receive antenna selection problem. In addition to applying the conventional BPSO to JUSRAS, we also present a specific improvement to this population-based heuristic algorithm; namely, we feed cyclically shifted initial population, so that the number of iterations until reaching an acceptable solution is reduced. The proposed BPSO for JUSRAS problem has a low computational complexity, and its effectiveness is verified through simulation results.

Novel Closed-Form Expressions for Ergodic Capacity of MIMO-OSFBC-OFDM Systems Over Channel Adaptation Policies

In this work, closed-form expressions for capacities per unit bandwidth for MIMO-OFDM systems employing Orthogonal Space-Frequency Block Coding over multipath frequency-selective fading channels are derived for adaptation policies like optimal power and rate adaptation, optimal rate adaptation with constant transmit power, channel inversion with fixed rate, and truncated channel inversion polices. A Signal-to-Noise Ratio based user selection scheme is considered. Optimal power and rate adaptation policy provides the highest capacity over other adaptation policies. Capacity penalty is the highest for optimal rate adaptation with constant transmit power policy, while the performance of channel inversion with fixed rate policy and truncated channel inversion policy lie between that of OPRA and ORA policies.

Multiuser Diversity in Interfering Broadcast Channels: Achievable Degrees of Freedom and User Scaling Law

This paper investigates how multiuser dimensions can effectively be exploited for target degrees of freedom (DoF) in interfering broadcast channels (IBC) consisting of K-transmitters and their user groups. First, each transmitter is assumed to have a single antenna and serve a singe user in its user group where each user has receive antennas less than K. In this case, a K-transmitter single-input multiple-output (SIMO) interference channel (IC) is constituted after user selection. Without help of multiuser diversity, K-1 interfering signals cannot be perfectly removed at each user since the number of receive antennas is smaller than or equal to the number of interferers. Only with proper user selection, non-zero DoF per transmitter is achievable as the number of users increases. Through geometric interpretation of interfering channels, we show that the multiuser dimensions have to be used first for reducing the DoF loss caused by the interfering signals, and then have to be used for increasing the DoF gain from its own signal. The sufficient number of users for the target DoF is derived. We also discuss how the optimal strategy of exploiting multiuser diversity can be realized by practical user selection schemes. Finally, the single transmit antenna case is extended to the multiple-input multiple-output (MIMO) IBC where each transmitter with multiple antennas serves multiple users.

Analytical Derivation of Multiuser Diversity Gains with Opportunistic Spectrum Sharing in CR Systems

This paper investigates the multiuser diversity introduced by opportunistic user selection in cognitive radio (CR) networks, where multiple cognitive users request to access the spectral resources of the licensed (primary) user. We investigate a simple cognitive user selection strategy aiming at maximizing the received signal-to-interference-plus-noise ratio (SINR) for a given power budget, under interference constraints to the primary. We study the statistics of the SINR at the cognitive receiver, and derive exact analytical expressions of its probability density function (PDF). We then analytically calculate the diversity gains introduced in the system due to the selection of one cognitive user amongst multiple candidates compared to the case when only one cognitive user exists and no selection occurs. Furthermore, we utilize the PDF of the SINR to predict the bit error rate (BER) of the selected cognitive user. Finally, the asymptotic behavior of the diversity gains for the low transmit power region of the primary and cognitive links, and as the number of candidate links becomes large is also investigated. All three multiaccess scenarios are investigated, namely multiple access channel (MAC), broadcast channel (BC) and parallel access channel (PAC), and the results show that the analytically derived expressions closely match simulated performance.

A low-complexity user selection scheme in a multicell MIMO environment

Abstract An efficient user selection scheme for the downlink of multiuser MIMO systems is proposed in a multicell environment. In a multicell environment, the intercell interference is one of the most influential factors limiting the performance. Thus, a user selection scheme that considers intercell interference is essential to increase the sum rate. The proposed scheme is based on an interference-aware precoding. It sequentially selects users such that the sum rate is maximized. In particular, we develop a simple incremental metric for the sum rate. The use of the derived metric enables a significant reduction in the computational complexity of the user selection process, as compared to the optimal exhaustive search. Numerical results show that the proposed scheme provides near-optimal performance with substantially reduced complexity.

Performance Analysis of Distributed Beamforming in a Spectrum Sharing System

In this paper, we consider a distributed beamforming scheme (DBF) in a spectrum sharing system where multiple secondary users share the spectrum with some licensed primary users under an interference temperature constraint. We assume that the DBF is applied at the secondary users. We first consider optimal beamforming and compare it with the user selection scheme in terms of the outage probability and bit error rate performance metrics. Since perfect feedback is difficult to obtain, we then investigate a limited feedback DBF scheme and develop an analysis for a random vector quantization design algorithm. Specifically, the approximate statistics functions of the squared inner product between the optimal and quantized vectors are derived. With these statistics, we analyze the outage performance. Furthermore, the effects of channel estimation error and number of primary users on the system performance are investigated. Finally, optimal power adaptation and cochannel interference are considered and analyzed. Numerical and simulation results are provided to illustrate our mathematical formalism and verify our analysis.

후 순위 시스템의 성능 향상을 위한 언더레이 기반의 인지 무선 시스템의 사용자 선택 기법

최근 고속 데이터 서비스의 보급으로 데이터 사용량이 급증함에 따라 이를 수용하기 위한 주파수 자원의 효율적 사용 방법에 대한 연구가 주목받고 있다. 따라서 주파수 효율성을 향상시키기 위해 주파수 사용에 대한 우선권을 가진 사용자와 후순위에 있는 사용자가 해당 주파수 대역을 공유하는 기술인 인지 무선 기술(Cognitive Radio, CR)이 제안되었다. 본 논문에서는 CR 시스템에서 직교하는 채널 벡터를 이용하여 선순위 시스템에게 미치는 간섭을 줄이면서 후순위 시스템의 성능 향상을 동시에 고려한 사용자 선택 기법을 제안한다. 모의실험 결과 제안 기법을 적용했을 때 전체 시스템의 합 용량이 기존 기법보다 약 1.62bps/Hz의 이득을 가지는 것을 확인하였다. Recently, data traffic is significantly increased by high rate data service. As a result, radio spectrum is considered one of the most scarce and valuable resources for wireless communications. For the solution of this problem, cognitive radio(CR) has been proposed as an efficient means to opportunistic spectrum sharing between primary (licensed) users and cognitive radio users. In this paper, user selection scheme in CR networks is proposed for additional consideration of secondary system. The proposed user selection scheme mitigates interference to primary user by using orthogonal channel vectors while improves performance of secondary system. Simulation results show that the proposed scheme achieves 1.62bps/Hz higher average throughput of whole system than one of the existing scheme.

On the Achievable DoF and User Scaling Law of Opportunistic Interference Alignment in 3-Transmitter MIMO Interference Channels

In this paper, we propose opportunistic interference alignment (OIA) schemes for three-transmitter multiple-input multiple-output (MIMO) interference channels (ICs). In the proposed OIA, each transmitter has its own user group and selects a single user who has the most aligned interference signals. The user dimensions provided by multiple users are exploited to align interfering signals. Contrary to conventional IA, perfect channel state information of all channel links is not required at the transmitter, and each user just feeds back one scalar value to indicate how well the interfering channels are aligned. We prove that each transmitter can achieve the same degrees of freedom (DoF) as the interference free case via user selection in our system model that the number of receive antennas is twice of the number of transmit antennas. Using the geometric interpretation, we find the required user scaling to obtain an arbitrary non-zero DoF. Two OIA schemes are proposed and compared with various user selection schemes in terms of achievable rate/DoF and complexity.

User Fairness Scheme with Proportional Fair Scheduling in Multi-user MIMO Limited Feedback System

In Multi-user MIMO (MU-MIMO) downlink system, suitable user selection schemes can improve spatial diversity gain. In most of previous studies, it is always assumed that the base station (BS) knows full channel state information (CSI) of each user, which does not consider the reality. However, there are only limited feedback bits in real system. Besides, user fairness is often ignored in most of current user selection schemes. To discuss the user fairness and limited feedback, in this paper, the user selection scheme with limited feedback bits is proposed. The BS utilizes codebook precoding transmitting strategy with LTE codebook. Furthermore, this paper analyzes the influence of the number of feedback bits and the number of users on user fairness and system sum capacity. Simulation results show that in order to achieve better user fairness, we can use fewer bits for feedback CSI when the number of user is small, and more feedback bits when the number of users is large.

A novel low-complexity user selection scheme for multiuser MIMO downlink with zero-forcing beamforming

This letter proposed a user selection with swap (USS) algorithm based on zero-forcing beamforming (ZFBF). USS starts with an initial user group with the largest channel 2-norms, iteratively swap the “worst” user (has the minimal achieved rate) among the scheduled users with the “best” user (has the maximum channel 2-norm) among the remaining users. Based on the simulation results, we can confirm that the proposed USS algorithm can provide a comparable performance with previous algorithms with greatly reduced complexity of O(KN2).

Knapsack-based energy-efficient node selection scheme for cooperative spectrum sensing in cognitive radio sensor networks

A cognitive radio (CR) is the most promising candidate for the successful deployment of dynamic spectrum access (DSA). To embed DSA in a wireless sensor network, a CR is required to be installed on each sensor node. Such a sensor network is known as a cognitive radio sensor network (CRSN). Spectrum sensing is a prerequisite for a CR. Therefore every node in the CRSN consumes energy for spectrum sensing. To achieve a high-sensing accuracy, the nodes share sensing results among themselves, which is known as cooperative spectrum sensing (CSS). CSS improves sensing; however it increases energy consumption and shortens the lifetime of the network. As a CRSN is characterised as an energy constraint network, to prolong the lifetime of the network, the number of cooperating nodes should be minimum. This study presents a user selection scheme to minimise the overhead energy consumed by CSS in a CRSN. On the basis of the binary knapsack problem and its dynamic programming solution, the proposed technique selects the best nodes among the potential nodes subject to the energy constraint of the CRSN. The simulation results indicate the advantages of employing the proposed method, depending on the desired performance-energy consumption tradeoff.

Performance of a cooperative multiplexing scheme with opportunistic user and relay selection over Rayleigh fading channels

In this article, we analyze the performance of a cooperative spatial multiplexing scheme using amplify and forward relays over Rayleigh fading channels. We propose a simple user and relay selection scheme, and demonstrate that gains in spectral efficiencies are possible by such opportunistic selection. Using a bound on the outage performance, we develop a power control mechanism. We develop a bound on the ergodic rate of the proposed scheme. Computer simulation results are presented to demonstrate the performance of the scheme, and to validate the analytical expressions.

Secondary User Selection Scheme Using Adaptive Genetic Algorithms for Cooperative Spectrum Sensing Under Correlated Shadowing

Cooperative spectrum sensing has been shown to be an effective approach to improve the detection performance by exploiting the spatial diversity among multiple secondary users (or unlicensed users)...

Two-Way Amplify-and-Forward Multiple-Input Multiple-Output Relay Networks with Antenna Selection

Two new transmit/receive (Tx/Rx) antenna selection strategies are proposed and analyzed for two-way multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay networks. These two strategies select the best transmit and receive antennas at the two sources and the relay based on (i) minimizing the overall outage probability and (ii) maximizing the sum-rate. The performance of these selection strategies is quantified by deriving the overall outage probability, its high SNR approximation and the diversity order providing valuable insights into practical system-designs. Importantly, multiple relay and multiple user two-way relay network set-ups are also treated by proposing and analyzing (i) joint relay and antenna selection strategies, and (ii) joint user, relay and antenna selection strategies, respectively. Interestingly, our outage probability results reveal that the joint relay and antenna selection strategies achieve significant diversity and array gains over those of their single relay counterparts. In fact, the diversity orders of individual relayed-branches accumulate to yield the overall diversity of the multi-relay networks. For example, at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> outage probability, the dual-antenna relay provides a 14 dB gain over a single-antenna relay, and having two dual-antenna relays improves the gain by another 5 dB. Moreover, the performance degradation due to practical transmission impairments (i) feedback delays, (ii) spatially-correlated fading and (iii) non-identically distributed fading is quantified. Impact of channel prediction to circumvent outdated channel state information for antenna selection due to feedback delay is also studied. All the derivations are validated through Monte-Carlo simulations.