Transmit Antenna Selection Research Articles

TAS-Based Incremental Hybrid Decode–Amplify–Forward Relaying for Physical Layer Security Enhancement

In this paper, a transmit antenna selection (TAS)-based incremental hybrid decode–amplify–forward (IHDAF) scheme is proposed to enhance physical layer security in cooperative relay networks. Specifically, TAS is adopted at the source in order to reduce the feedback overhead. In the proposed TAS-based IHDAF scheme, the network transmits signals to the destination adaptive select direction transmission (DT) mode, AF mode, or DF mode depending on the capacity of the source-relay link and source-relay link. In order to fully examine the benefits of the proposed TAS-based IHDAF scheme, we first derive its secrecy outage probability (SOP) in a closed-form expression. We then conduct asymptotic analysis on the SOP, which reveals the secrecy performance floor of the proposed TAS-based IHDAF scheme when no channel state information is available at the source. Theoretical analysis and simulation results demonstrate that the proposed TAS-based IHDAF scheme outperforms the selective decode-and-forward, the incremental decode-and-forward, and the noncooperative DT schemes in terms of the SOP and effective secrecy throughout, especially when the relay is close to the destination. Furthermore, the proposed TAS-based IHDAF scheme offer a good tradeoff between complexity and performance compared with using all antennas at the source.

Transmit Antenna Selection Schemes for Spatial Modulation Systems: Search Complexity Reduction and Large-Scale MIMO Applications

Euclidean distance optimized antenna selection (EDAS) has proven to be able to achieve high transmit diversity gains for spatial modulation (SM) multiple-input multiple-output (MIMO) systems, but the exhaustive search over all possible antenna subsets may result in an intractable search complexity, especially for large-scale MIMO (LS-MIMO) systems. In this paper, a novel EDAS-equivalent criterion, relaying on matrix dimension reduction, is proposed to reduce the search complexity. Based upon this criterion, for small-scale SM-MIMO systems, a pair of transmit antenna selection (TAS) schemes, namely, the tree search based antenna selection (TSAS), and the decremental antenna selection (D-AS) schemes, are developed. Specifically, the TSAS scheme works by iteratively splitting the original Euclidean distance (ED) matrix into submatrices with smaller dimensions. TSAS achieves the same bit error rate (BER) performance as that of the exhaustive search at the cost of exponential search complexity. To address this issue, D-AS is carried out by excluding one specific transmit antenna from all the possible candidates in each iteration based on the channel information. D-AS is able to offer a near-optimal BER performance with a further reduction in terms of the search complexity. Moreover, we extend the D-AS scheme to LS-SM-MIMO systems by sorting all the ED elements with the low-complexity heapsort algorithm. Our simulation results show that the proposed D-AS algorithm outperforms conventional TAS schemes conceived for LS-SM-MIMO systems.

Secure communication via an energy-harvesting untrusted relay with imperfect CSI

This paper studies the secure communication of an energy-harvesting system in which a source communicates with a destination via an amplify-and-forward (AF) untrusted relay. The relay uses the power-splitting policy to harvest energy from wireless signals. The source is equipped with multiple antennas and uses transmit antenna selection (TAS) and maximum ratio transmission (MRT) to enhance the harvested energy at the relay; for performance comparison, random antenna selection (RAS) is examined. The relay and destination are single-antenna nodes. To create a positive secrecy capacity, destination-assisted jamming is deployed. Because the use of multiple antennas can cause the imperfect channel state information (CSI), the channel between the source and the relay is examined in two cases: perfect CSI and imperfect CSI. To evaluate the secrecy performance, analytical expressions for the secrecy outage probability (SOP) and the average secrecy capacity (ASC) for the TAS, MRT, and RAS schemes are derived. Moreover, a high-power approximation for the SOP is presented. The accuracy of the analytical results is verified by Monte Carlo simulations. The results show the benefit of using multiple antennas in improving the secrecy performance. Specifically, MRT performs better than TAS, and both of them outperform RAS. Moreover, the results provide valuable insight into the effects of various system parameters, such as the channel correlation coefficient, energy-harvesting efficiency, secrecy rate threshold, power-splitting ratio, transmit powers, and locations of the relay, on the secrecy performance.

Low‐complexity transmit antenna selection algorithm exploiting null space in spatial multiplexing UWB MIMO systems

In this paper, a new transmit antenna selection algorithm for spatial multiplexing ultra‐wideband multiple‐input multiple‐output systems is proposed. It utilizes the null space of the channel matrix spatially and temporally combined for available transmit antennas. A selection strategy is used to successively find and remove the transmit antennas having the largest contribution to the null space. Its error performance is shown to be close to that of the optimal antenna selection algorithm with low complexity. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Huffman Coding-Based Adaptive Spatial Modulation

Antenna switch enables multiple antennas to share a common RF chain. It also offers an additional spatial dimension, i.e., antenna index, that can be utilized for data transmission via both signal space and spatial dimension. In this paper, we propose a Huffman coding-based adaptive spatial modulation that generalizes both conventional spatial modulation and transmit antenna selection. Through the Huffman coding, i.e., designing variable length prefix codes, the transmit antennas can be activated with different probabilities. When the input signal is Gaussian distributed, the optimal antenna activation probability is derived through optimizing channel capacity. To make the optimization tractable, closed form upper bound and lower bound are derived as the effective approximations of channel capacity. When the input is discrete QAM signal, the optimal antenna activation probability is derived through minimizing symbol error rate. Numerical results show that the proposed adaptive transmission offers considerable performance improvement over the conventional spatial modulation and transmit antenna selection.

Performance analysis for non‐orthogonal multiple access in energy harvesting relaying networks

Non-orthogonal multiple access (NOMA), which uses the power domain for multiple users, has been considered as an emerging candidate for fifth generation downlink transmission. Energy harvesting (EH), a promising technology to prolong the lifetime of energy-constrained wireless networks, has attracted significant attention. In this study, the authors first combine NOMA with EH (NOMA–EH) to enhance system spectral efficiency and user fairness. An NOMA-based relaying network is analysed, where the relay node is equipped with EH device, and functions as the bridge between the base station and the multiple users. The outage performance of the NOMA–EH scheme-based relaying network is studied, where the transmitting antenna selection is applied at the base station and maximal ratio combining is applied at the multiple users. Furthermore, closed-form expression for the system outage probability is also derived. On the basis of the computer simulations, they show the correctness of the numerical analysis and confirm the superiority of the proposed NOMA–EH scheme.

Secure Multiple Amplify-and-Forward Relaying Over Correlated Fading Channels

This paper quantifies the impact of correlated fading on secure communication of multiple amplify-and-forward (AF) relaying networks. In such a network, the base station (BS) is equipped with multiple antennas and communicates with the destination through multiple AF relays, while the message from the relays can be overheard by an eavesdropper. We focus on the practical communication scenario, where the main and eavesdropper’s channels are correlated. In order to enhance the transmission security, transmit antenna selection is performed at the BS, and the best relay is chosen according to the full- or partial-relay selection criterion, which relies on the dual-hop relay channels or the second-hop relay channels, respectively. For these criteria, we study the impact of correlated fading on the network secrecy performance, by deriving an analytical approximation for the secrecy outage probability and an asymptotic expression for the high main-to-eavesdropper ratio. From these results, it is concluded that the channel correlation is always beneficial to the secrecy performance of full relay selection. However, it deteriorates the secrecy performance if partial-relay selection is used, when the number of antennas at the BS is less than the number of relays.

SER of TAS-MRC With Relay and User Selection in MIMO-Relay Systems Over Non-Identical Nakagami Fading Channels

We investigate the symbol error rate (SER) of a transmit antenna selection (TAS)-maximal ratio combining (MRC) with relay and user selection in multiple-input multiple-output systems over non-identical Nakagami fading channels. This letter derives the exact cumulative density function (cdf) of the effective signal-to-noise ratio for the proposed system. Using the cdf, this letter derives the exact closed-form expressions of the TAS-MRC with relay and user selection for the SER with M-ary quadrature amplitude modulation over non-identical Nakagami fading channels including quantification of the diversity order using asymptotic analysis.

Performance analysis of scheduled TAS‐MRC MIMO systems with multiple interferers

The authors present the performance analysis of a scheduled transmit antenna selection with maximal ratio combining (TAS-MRC) for multiple-input multiple-output transmission in the presence of multiple interferers. They derive the probability density function of the instantaneous post-processing signal to interference plus noise ratio for the scheduled TAS with MRC over the Rayleigh fading channels under multiple interferers. Using the distribution, the closed-form expressions of the scheduled TAS with MRC are derived for symbol error rate (SER), outage probability and ergodic capacity in the presence of multiple interferers. From the analysis results, the performance of the scheduled TAS-MRC in the presence of multiple interferers is mainly determined by the signal-to-interference ratio. The performance of SER and ergodic capacity is less sensitive to the number of interferers.

Outage and energy-efficiency analysis of cognitive radio networks: A stochastic approach to transmit antenna selection

Cognitive radio networks have recently attracted significant research attention owing to their promise for application in future cellular communication. In this light, given the intense power consumption of wireless networks, considerable research is now being directed at designing random cognitive radio networks with enhanced energy efficiency. In this study, we investigate the outage probability and energy efficiency in a cognitive radio network, modeling the locations of the primary users and cognitive users as a Poisson point process. We derive closed-form expressions for the outage probability and energy efficiency with consideration of the probabilities of unoccupied (not utilized by the primary users) channel selection and successful transmission for imperfect detection in an interference-limited environment of cognitive radio network. Furthermore, we propose a transmit antenna selection method for the cognitive transmitter in such networks and accordingly develop closed-form expressions for the outage probability and energy efficiency. The study reported here highlights the importance of combining the capabilities of unoccupied channel selection and successful transmission in cognitive radio networks to achieve optimal performance regarding outage probability and energy efficiency. In terms of energy efficiency, there is an optimal threshold that maximizes the energy efficiency. For implementation in transmit antenna selection, the outage probability can be significantly decreased by increasing the number of transmit antennas, even though the energy efficiency is maximized at the target outage probability.

Analytical BER Calculation of TAS/MRC-Based Two Hop UWB Communication System Over IEEE 802.15.4a Channel

ABSTRACTIn this paper, we calculate the bit error rate (BER) of the orthogonal binary signals in the two hop ultra-wideband (UWB) communication system with the transmit antenna selection scheme at the source and the relay terminals. In the two hop UWB system, relay is configured to perform the decode and forward cooperative strategy. In order to calculate the BER of the investigated UWB system, we consider the characteristic function- based approach to model the sum of path gains of the IEEE 802.15.4a channel. We assume that all the IEEE 802.15.4a channel links are independent and identically distributed and perfect channel state information is available at the transmitter. The results exhibit that the derived BER is a good match with the simulations and it has been significantly improved over the BER of the conventional UWB systems.

Secrecy Outage Analysis in Random Wireless Networks With Antenna Selection and User Ordering

This letter investigates the secrecy outage probability in the downlink with ordered user equipment (UE) based on two ordering metrics. UEs and independently acting eavesdroppers (EDs) are positioned randomly according to a Poisson point process. We consider a transmit antenna selection (TAS) scheme at the base station (BS) to enhance secrecy performance and propose two metrics to order the UEs: one based on long-term average channel gain information from the BS to the UEs, and the other based on instantaneous channel gains. We derive closed form expressions for the secrecy outage probability subject to each of these ordering policies and verify our calculations through Monte Carlo simulations. Our results show that while TAS yields a performance improvement relative to single-antenna systems, the secrecy outage probability for TAS systems actually increases with the path loss exponent. Furthermore, we show that the importance of the specific user ordering policy that is adopted in these systems is reduced for high path loss environments or situations where large numbers of antennas are employed.

Transmit Antenna Selection for Power Adaptive Underlay Cognitive Radio With Instantaneous Interference Constraint

The high hardware cost associated with multiple antennas at the secondary transmitter of an underlay cognitive radio (CR) can be reduced by antenna selection. This paper analyzes different power adaptive transmit antenna selection (TAS) schemes for an underlay CR, which ensure that the instantaneous interference caused by the secondary transmitter to the primary receiver is below a predetermined level. We consider the optimal continuous power adaptive TAS and present a low-complexity antenna and power level selection scheme, named sequential antenna and power level selection scheme (SAPS), for discrete power adaptation. Exact statistical characterizations of the signal-to-interference plus noise ratio at the secondary receiver are derived for the considered schemes. Based on the newly derived statistics, we prove that the considered schemes achieve the highest diversity order equaling the number of antennas at the secondary transmitter. Further, we also derive a closed-form expression of the ergodic capacity for the underlay CR with SAPS scheme. Finally, we show that the proposed scheme outperforms existing schemes in terms of ergodic capacity.

Low Complexity Capacity Maximizing Transmit Antenna Selection Schemes for Massive MIMO Wireless Communications

Recently massive MIMO systems have attracted a lot of attention. A serious limitation in implementing massive MIMO is the number of RF chains required, which is due to its high implementation cost and power consumption. Antenna selection is a wise remedy, that not only reduces the number of required RF chains, but also improves the system’s performance. In this work, two low complexity capacity-maximizing transmit antenna selection (TAS) schemes, one for low SNR region and one for medium to high SNR region, are proposed. It is shown that the proposed antenna selection schemes enhance the MIMO link’s capacity at low SNRs, and select only one antenna in more than $$90\%$$ of channel realizations, which in terms of numbers of required RF chains is very promising. The performance of the proposed schemes are compared to an existing high performance greedy TAS technique in terms of average capacity and complexity. Finally, a close analytical approximation for average capacity of the proposed capacity-based subset selection scheme is presented.

Energy efficiency optimisation of large‐scale multiple‐input–multiple‐output system with transmit antenna selection

The rapid development of wireless communication comes at the cost of dramatically increasing energy consumption, which makes the optimisation of energy efficiency (EE) extremely important. In this study, the authors focus on maximising EE of large-scale multiple-input–multiple-output system by optimising the transmit power and the number of selected base station antennas. First, the EE optimisation problem, i.e. finding the optimal EE-based values of each parameter, when the other one is fixed, is investigated. Then, the optimisation problem jointly considering these two parameters to maximise EE is studied. Moreover, the EE optimisation problem is extended to multi-user (MU) system. Owing to the formulation of EE, the EE optimisation problem is reformulated as the fractional programming problem, and the Dinkelbach method is proposed to deal with this problem instead of the binary search algorithm (BSA) by switching the objective function to a weighted sum of rate and power. Simulation results show that the EE can be improved with the proposed Dinkelbach method, and it has a faster convergence speed than the BSA without any performance loss for both single-user system and MU system.

Performance Study of MIMO Transmissions with Joint Channel Allocation and Relay Assignment

Multiple-input multiple-output (MIMO) techniques have shown numerous benefits in improving communication reliability and spectrum efficiency in wireless communication. In this paper, performance of MIMO transmission schemes with joint channel allocation and relay assignment (JCARA) in MIMO cooperative cognitive radio network (CRN) is studied. The problem of maximizing the spectrum efficiency among multiple CR source–destination pairs under different number of antenna configurations is studied. In order to improve the spectrum efficiency, multiple antennas are exploited at cognitive radio (CR) sources, CR relays, and CR destinations in a cooperative CRN . In this concern, we obtain the spectrum efficiency for various settings of MIMO maximum ratio transmission (MIMO-MRT) and MIMO transmit antenna selection (MIMO-TAS) schemes, which are applied at CR transmitter (i.e., CR sourc/relay) and maximum ratio combining (MRC) is applied at CR receivers (i.e., CR relay/destination), with JCARA. Extensive numerical results are presented to show the effectiveness of the MIMO-MRT and MIMO-TAS schemes. It is also shown that as the number of transmit–receive antenna increases the spectrum efficiency of both the MIMO-MRT and MIMO-TAS schemes increases as compared to single transmit–receive antenna case. Moreover, it is shown that relay assignment offers more benefit of maximization of minimum transmission rate with the MIMO-TAS scheme than the MIMO-MRT scheme.

Joint effect of jamming and noise on the secrecy outage performance of wiretap channels with feedback delay and multiple antennas

AbstractIn this paper, we investigate the secrecy performance of multiple‐input–multiple‐output wiretap channels with outdated channel state information (CSI) at the transmitter. The joint effect of multiple jamming signals and noise at the eavesdropper is studied assuming that the transmitter adopts a transmit antenna selection technique, while both the legitimate receiver and the eavesdropper use a maximal‐ratio combining scheme to achieve spatial diversity in reception. Exact closed‐form expressions for the nonzero secrecy rate probability and the secrecy outage probability for an arbitrary number of power distributed jamming signals are derived, by assuming both perfect and imperfect CSI. The general secrecy outage probability expressions are simplified for 2 special cases, ie, different and equal power distributed interferers. Furthermore, we conduct an asymptotic secrecy outage analysis at high signal‐to‐noise ratio, which reveals that the expected diversity gain cannot be realized for imperfect CSI and full diversity order can only be achieved under the perfect CSI condition. In addition, our results reveal that the number of antennas at the eavesdropper as well as the number of jamming signals do not affect the system diversity order. Simulation results are performed to illustrate the effects of imperfect feedback and other key system parameters on the secrecy performance. Finally, our analytical results are validated through Monte Carlo simulations.

Relay Selection in Adaptive Buffer-Aided Space-Time Coding with TAS for Cooperative Wireless Networks

In this work, we propose an adaptive buffer-aided space-time coding scheme for cooperative wireless networks. A maximum likelihood receiver and adjustable code vectors are considered subject to a power constraint with an amplify-and forward cooperation strategy. Each relay is equipped with a buffer and is capable of storing the received symbols before forwarding them to the destination. We also present an adaptive relay selection and a new hybrid relay selection protocol, in which the instantaneous signal to noise ratio in each link is calculated and compared at the destination. The transmit antenna selection (TAS) is adopted at the destination where a single transmit antenna at the transmitter and relay that maximizes the instantaneous received signal-to-noise ratio is selected for further transmissions to improve the performance of co-operative network. A stochastic gradient algorithm is then developed to compute the parameters of the adjustable code vector with reduced computational complexity. Simulation results show that the proposed buffer-aided schemes with TAS obtain performance gains over existing schemes.

Source Transmit Antenna Selection for Space Shift Keying With Cooperative Relays

In this letter, we propose a cooperative multiple-input multiple-output (MIMO) scheme combining transmit antenna selection (TAS) and space shift keying (SSK). In this scheme, source transmit antennas are selected and SSK is applied by using the selected antennas. Besides the direct link transmission, the relays, that decode the source signal correctly, take part in the transmission. Exact expressions and a considerably accurate approximate expression for the symbol error rate of the proposed SSK system are derived. It is shown that the proposed scheme outperforms the SSK system without TAS and also the conventional cooperative MIMO system, which employs source TAS, at practical signal-to-noise ratio values for especially high data rates and sufficient number of receive antennas at the destination.

Secrecy Outage Analysis for Downlink Transmissions in the Presence of Randomly Located Eavesdroppers

We analyze the secrecy outage probability in the downlink for wireless networks with spatially (Poisson) distributed eavesdroppers (EDs) under the assumption that the base station employs transmit antenna selection (TAS) to enhance secrecy performance. We compare the cases where the receiving user equipment (UE) operates in half-duplex (HD) mode and full-duplex (FD) mode. In the latter case, the UE simultaneously receives the intended downlink message and transmits a jamming signal to strengthen secrecy. We investigate two models of (semi)passive eavesdropping: (1) EDs act independently and (2) EDs collude to intercept the transmitted message. For both of these models, we obtain expressions for the secrecy outage probability in the downlink for HD and FD UE operation. The expressions for HD systems have very accurate approximate or exact forms in terms of elementary and/or special functions for all path loss exponents. Those related to the FD systems have exact integral forms for general path loss exponents, while exact closed forms are given for specific exponents. A closed-form approximation is also derived for the FD case with colluding EDs. The resulting analysis shows that the reduction in the secrecy outage probability is logarithmic in the number of antennas used for TAS and identifies conditions under which HD operation should be used instead of FD jamming at the UE. These performance trends and exact relations between system parameters can be used to develop adaptive power allocation and duplex operation methods in practice. Examples of such techniques are alluded to herein.