Transmit Antenna Diversity Research Articles

Sum Ergodic Capacity Analysis Using Asymptotic Design of Massive MU-MIMO Systems

This communication attempts to characterize the performance metrics of downlink Massive MU-MIMO systems impaired by cochannel interference and additive noise over a Rayleigh fading environment. We obtain close-form solutions for the probability density function of signal-to-interference-plus-noise ratio (SINR) and the sum ergodic capacity. The proposed work structures SINR in a quadratic form and thereby imposes a condition on its signal and interference power for a large transmit antenna diversity order; the conditional form is then analyzed using a distance correlation metric. Eventually, the sum ergodic capacity is expressed in a close-form by means of a residue theory approach and validated using the Monte Carlo simulation means.

Throughput Analysis of IEEE 802.11ac and IEEE 802.11n in a Residential Home Environment

IEEE 802.11ac is the latest WiFi standard that operates in 5GHz frequency band and promises high data rate than IEEE 802.11n. In this paper, the authors carry out experiments using commercial off-the-shelf equipment in a typical home environment and quantify the gain provided by IEEE 802.11ac compared to IEEE 802.11n. Their experimental results obtained in a typical home environment show that in 5GHz frequency band with a 2x2 MIMO configuration, IEEE 802.11ac provides much higher throughput than IEEE 802.11n. IEEE 802.11ac provides an average throughput gain of 94% and 91% at a distance of 3.6m and 8.5m from the wireless router, respectively. The authors further investigate the gain in average throughput that is provided by IEEE 802.11ac when the transmit antenna diversity on the wireless router is increased from two to three. They note that IEEE 802.11ac with a 3x2 MIMO configuration helps to combat multipath fading effect present in residential home environment and provides higher average throughput than 2x2 MIMO e.g. at a distance of 11m from the wireless router, 3x2 MIMO configuration provides a gain of 15.13% than the 2x2 MIMO configuration. The authors conclude based on their results (obtained via experiments in a typical home environment) that although IEEE 802.11ac wireless routers are more expensive than IEEE 802.11n wireless routers however, high throughput provided by IEEE 802.11ac justifies the high cost associated with its routers.

Joint Switched Multi-Spectrum and Transmit Antenna Diversity for Spectrum Sharing Systems

In spectrum sharing systems, a secondary user (SU) is allowed to share the spectrum with a primary (licensed) network under the condition that the interference observed at the receivers of the primary users (PU-Rxs) is below a predetermined level. In this paper, we consider a secondary network comprised of a secondary transmitter (SU-Tx) equipped with multiple antennas and a single-antenna secondary receiver (SU-Rx) sharing the same spectrum with multiple primary users (PUs), each with a distinct spectrum. We develop transmit antenna diversity schemes at the SU-Tx that exploit the multi-spectrum diversity provided by the existence of multiple PUs so as to optimize the signal-to-noise ratio (SNR) at the SU-Rx. In particular, assuming bounded transmit power at the SU-Tx, we develop switched selection schemes that select the primary spectrum and the SU-Tx transmit antenna that maintain the SNR at the SU-Rx above a specific threshold. Assuming Rayleigh fading channels and binary phase-shift keying (BPSK) transmission, we derive the average bit-error-rate (BER) and average feedback load expressions for the proposed schemes. For the sake of comparison, we also derive a BER expression for the optimal selection scheme that selects the best antenna/spectrum pair that maximizes the SNR at the SU-Rx, in exchange of high feedback load and switching complexity. Finally, we show that our analytical results are in perfect agreement with the simulation results.

Information‐guided communications in MIMO systems with channel state impairments

AbstractInformation‐guided channel hopping (IGCH) is a promising technique for high‐data‐rate communications using multiple antennas for information mapping at the transmitter and optional antenna diversity at the receiver. Compared with some popular multi‐antenna techniques, the advantage of this scheme is proven in ideal channel conditions, where the channel is spatially white and the perfect channel state information is assumed available at the receiver. The main objective of this paper is to present an information theoretical study on IGCH in realistic propagation environments with channel degeneracy due to spatial correlation and keyhole phenomena as well as imperfect channel estimation. It is proven that good performance promised by IGCH can be achieved in a variety of non‐ideal channel conditions. Moreover, the analysis in this paper provides a convenient tool for the corresponding system design in practical operating environments. Copyright © 2013 John Wiley & Sons, Ltd.

Error Performance of Spatial-temporal Combining-based Spatial Multiplexing UWB Systems Using Transmit Antenna Selection

This paper applies transmit antenna selection algorithms to spatial-temporal combining-based spatial multiplexing (SM) ultra-wideband (UWB) systems. The employed criterion is based on the largest minimum output signal-to-noise ratio of the multiplexed streams. It is shown via simulations that the bit error rate (BER) performance of the SM UWB systems based on the two-dimensional Rake receiver is significantly improved by antenna diversity through transmit antenna selection on a log-normal multipath fading channel. When the transmit antenna diversity through antenna selection is exploited in the SM UWB systems, the BER performance of the spatial-temporal combining-based zero-forcing (ZF) receiver is also compared with that of the ZF detector followed by the Rake receiver.

On Opportunistic Power Control for Alamouti and SM MIMO Systems

Transmit antenna diversity and single user spatial multiplexing have become attractive in practical systems, because they achieve performance gains without requiring sophisticated channel state information (CSI) feedback mechanisms. On the other hand, when fast and accurate CSI at the transmitter is available, opportunistic power control (OPC) is an attractive alternative to signal-to-interference-and-noise ratio (SINR) target following approaches, because it maximizes throughput by taking advantage of fast channel variations. In this paper we examine the question whether OPC is worth the pain of obtaining fast CSI by evaluating the gains of OPC for the downlink of a system employing multiple input multiple output (MIMO) systems with Alamouti and open loop spatial multiplexing (SM). We formulate the OPC problem as a throughput maximization task subject to power budget and fairness constraints. We solve this task by the Augmented Lagrangian Penalty Function and find that without fairness constraints, OPC in concert with SM provides superior throughput. With increasingly tight fairness constraints, Alamouti along with equal power allocation becomes a viable alternative to the SM OPC scheme. Both from fairness and throughput perspectives, Alamouti along with OPC is particularly efficient when adaptive MCS is employed and users with large differences in channel qualities have to share the total transmit power.

Peroformance analysis of decode-and-forward MIMO relay channels with OSTBCs

Performance analysis is presented for multiple-input multiple-output (MIMO) relay channels employing transmit antenna diversity with orthogonal space-time block codes (OSTBCs), where the source and the destination are equipped with N s and N d antennas, and communicate with each other with the help of a multiple-antenna relay operating in decode-and-forward (DF) mode. Over independent, not necessarily identical Rayleigh fading channels, exact closed-form symbol error rate (SER) expressions are derived for various digital modulation formats for both the OSTBC transmission with and without the direct link. The moment generating functions (MGFs) for overall system signal-noise ratios (SNRs) are also derived, based on which we present a unified SER analysis. The analysis shows that full spatial diversity order can be achieved for the DF MIMO relay channel by adopting OSTBC transmissions and maximal ratio combining (MRC) receptions. All the analytical results are confirmed through comparison with the results obtained using Mento Carlo simulations.

Performance Analysis of OSTBC Transmission in Amplify-and-Forward Cooperative Relay Networks

A performance analysis is presented for amplify-and-forward (AF) cooperative relay networks employing transmit antenna diversity with orthogonal space-time block codes (OSTBCs), where multiple antennas are equipped at the transmitter. We develop a symbol-error-rate (SER) and outage performance analysis for OSTBC transmissions with and without cooperative diversity over flat Rayleigh fading channels. We first derive exact probability density functions (pdf's) and cumulative distribution functions (cdf's) for the system SNR without direct transmission with an arbitrary number of transmit antennas and then present the exact closed-form SER and outage probability expressions. Next, we derive the moment-generating function (MGF) for the overall system SNR with direct transmission and present the exact SER and outage probability with joint transmit antenna diversity and cooperative diversity. The theoretical analysis is validated by simulations, which indicate an exact match between them. The results also show how the transmit antenna diversity and the cooperative diversity affect the overall system performance.

Transmit diversity vs. spatial multiplexing in modern MIMO systems

A contemporary perspective on transmit antenna diversity and spatial multiplexing is provided. It is argued that, in the context of most modern wireless systems and for the operating points of interest, transmission techniques that utilize all available spatial degrees of freedom for multiplexing outperform techniques that explicitly sacrifice spatial multiplexing for diversity. Reaching this conclusion, however, requires that the channel and some key system features be adequately modeled and that suitable performance metrics be adopted; failure to do so may bring about starkly different conclusions. As a specific example, this contrast is illustrated using the 3GPP long-term evolution system design.

Performance Comparison between CDTD and STTD for DS-CDMA/MMSE-FDE with Frequency-Domain ICI Cancellation

SUMMARY Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can provide a better bit error rate (BER) performance than rake combining. However, the residual inter-chip interference (ICI) is produced after MMSE-FDE and this degrades the BER performance. Recently, we showed that frequency-domain ICI cancellation can bring the BER performance close to the theoretical lower bound. To further improve the BER performance, transmit antenna diversity technique is effective. Cyclic delay transmit diversity (CDTD) can increase the number of equivalent paths and hence achieve a large frequency diversity gain. Space-time transmit diversity (STTD) can obtain antenna diversity gain due to the space-time coding and achieve a better BER performance than CDTD. Objective of this paper is to show that the BER performance degradation of CDTD is mainly due to the residual ICI and that the introduction of ICI cancellation gives almost the same BER performance as STTD. This study provides a very important result that CDTD has a great advantage of providing a higher throughput than STTD. This is confirmed by computer simulation. The computer simulation results show that CDTD can achieve higher throughput than STTD when ICI cancellation is introduced.

On the side-effects of proprietary solutions for fading and interference mitigation in IEEE 802.11b/g outdoor links

Experimental results are typically envisioned as the ultimate validation reference for any theoretical and/or simulation modelling assumptions. However, in the case of Wireless LANs, the situation is not as straightforward as it might seem. In this paper, we discuss to what (large) extent measurement results may depend on proprietary undocumented algorithms implemented in the vendor-specific card/driver employed. Specifically, we focus on the experimental study of IEEE 802.11b/g outdoor links based on the widely used Atheros/MadWiFi chipset/driver pair. We show that significant and unexpected performance degradation may occur as a consequence of two Atheros' proprietary algorithms: Transmit Antenna Diversity and Ambient Noise Immunity. Our findings appear quite critical in sight of the fact that part of the WLAN research community is often unaware of the existence of these proprietary mechanisms. Such lack of awareness is critical as it can lead to biased experimental trials and/or to erroneous interpretation of experimental results.

Space–time code selection for OFDM–MISO systems

In this paper, a space–time code selection technique for multiple transmit antenna OFDM systems is proposed, and a constant-rate transmission mode for the space–time code selection technique is introduced. Subcarriers are divided into subcarrier groups and a comparison of the equivalent SISO channel envelopes with a set of predetermined threshold levels for a central subcarrier of each group is performed at the receiver, which decides on the subcarriers to be used at each antenna and sends this information to the transmitter. The transmitter adjusts the space–time code to the number of selected antennas at each subcarriers group using four bits for feedback information per group. Simulation results show that the system performs well for a range of Doppler frequencies for correlated and uncorrelated channels, outperforming transmit antenna selection techniques and adaptive transmit antenna diversity systems for both variable-rate and constant-rate transmission modes.

Diversity eigenbeamforming for coded signals

Transmit antenna diversity without feedback has been widely investigated for various wireless communication systems. Especially, space-time codes are extensively studied to exploit the spatial diversity induced by multiple transmit antennas. Apart from these approaches, there can be different methods that provide a diversity gain using multiple antennas with conventional channel coding. In this paper, diversity eigenbeamforming is studied to exploit the spatial diversity when the channel covariance matrix is available at the transmitter. Diversity eigenbeamforming is based on eigenmode (of the spatial covariance matrix) switching that converts the spatial diversity into the temporal diversity which is exploited by channel coding. Optimized diversity eigenbeamforming is considered to take into account the spatial correlation. In addition, the trade-off between diversity and multiplexing gains is addressed. It is shown that the diversity eigenbeamforming can achieve optimal trade-off for the case of one receive antenna. Although, for simplicity, binary phase shift keying (BPSK) is used to derive diversity eigenbeamforming, any higher-order modulation scheme can also be used with diversity eigenbeamforming.

Comparison of open loop and closed loop schemes for multiple transmit antennas in OFDMA systems

The open loop transmit antenna diversity scheme and the closed loop beamforming technique are compared considering user mobility in OFDMA systems where both frequency distributed subchannelisation and frequency localised subchannelisation are provided. Outage capacity is considered for performance measurement.

Space–Time Code Selection for Transmit Antenna Diversity Systems

In this correspondence, a space-time code selection approach for transmit antenna diversity (TAD) systems is proposed. The receiver compares the equivalent single-input-single-output channel envelopes with a set of predetermined threshold levels, decides the antennas to be used, and sends this information to the transmitter, which adjusts the space-time code to the number of selected antennas using a small amount of feedback information. Threshold levels are found out-of-line based on the Doppler frequency in such a way that channel state information outdate at the transmitter is taken into account. Analysis and simulation results show that the system performs well for a wide range of Doppler frequencies, outperforming transmit antenna selection techniques and adaptive TAD systems.

An Optimal Closed-Loop Transmit Antenna Diversity With Average and Peak Power Constraints

In a closed-loop transmit-antenna-diversity system, a closed-form expression for the optimal transmitter weights that minimize the average bit error rate (BER) is derived with fixed average and peak transmit power constraints. It is shown that the peak-power limitation degrades the average BER performance more significantly as the available average power and/or the number of transmit antennas increase.

Exact error probability of Orthogonal Space-Time Block Codes over flat fading channels

Space time block coding is a modulation scheme recently discovered for the transmit antenna diversity to combat the effects of wireless fading channels. Using the equivalent Single-Input Single-Output (SISO) model, this paper presents closed-form expressions for the exact Symbol Error Rate (SER) and Bit Error Rate (BER) of Orthogonal Space-Time Block Codes (OSTBCs) with M-ary Phase-Shift Keying (MPSK) and M-ary Quadrature Amplitude Modulation (MQAM) over flat uncorrelated Nakagami-m and Ricean fading channels.

Turbo modulation and coding: design and evaluation of iterative bit‐interleaved coded modulation methods for wireless systems beyond 3G

AbstractWe give an overview of iterative techniques for bit‐interleaved coded modulation. We start with simple methods where a convolutional code is concatenated with a standard QAM modulation scheme. The mapping is carefully chosen different from Gray mapping such that significant gains can be obtained by an iterative (turbo) receiver. The idea can also be applied to transmit antenna diversity as well as spatial multiplexing (MIMO). We then consider various powerful iterative coding schemes which are under discussion in standardisation for wireless systems beyond 3G such as serial or parallel concatenated convolutional codes, repeat accumulate codes and LDPC codes. We give a comparison in terms of complexity and performance.The main intention is to provide an illustrative overview over relevant applications of the turbo principle in demodulation and decoding. It is a summary of results which have been obtained in collaboration between the Institute of Communications Engineering, TUM and DoCoMo Euro‐Labs. Copyright © 2007 John Wiley & Sons, Ltd.

Iterative Joint-Over-Antenna Detection and WNRA Decoding in Single-Carrier Multiuser MIMO Systems

In this paper, we propose a combined iterative detection and decoding technique that is capable of achieving the maximum diversity of order NTtimesLtimesNR over single-carrier multiple-input-multiple-output (MIMO) frequency-selective Rayleigh fading channels, where NT and NR denote the number of transmit and receive antennas, respectively, and L is the number of multipath components. The so-called space-time weighted-nonbinary-repeat-accumulate (ST-WNRA) codes are considered in our paper due to their ability to provide a full transmit antenna diversity and their relatively simple encoding and decoding algorithms. Multipath diversity is obtained using a joint-over-antenna turbo-equalization technique based on the minimum-mean-square-error filtering with soft interference cancellation. Computer simulations demonstrate that our proposed turbo-equalized system with ST-WNRA codes is capable of achieving the maximum diversity order with a relatively short codeword length and that the multiuser performance approaches the single-user bound so far as the number of users is smaller than or equal to the number of receive antennas in multiuser MIMO setups. We will also show that by modifying our proposed scheme to an equivalent multilevel coded system, higher bandwidth efficiency can be achieved at the expense of a performance loss while the system still retains the maximum diversity benefit

Matched-filter bounds for multicarrier communications systems with transmit diversity

In this paper, we consider wireless multicarrier communications systems applying different transmit-antenna diversity techniques. Whereas the transmitter has available multiple antennas, we assume a single antenna at the receiver. Thus, we consider multiple-input single-output multicarrier transmission systems which are of special interest for downlink mobile radio applications. For these systems, we investigate the matched-filter bounds (MFBs) which represent the performance in an environment free of any interference and, thus, are lower bounds on the achievable performance. Especially, we focus on the analytical determination of the MFBs for selection diversity (SD), since this transmit-antenna diversity technique requires the least amount of preprocessing at the transmitter. Based on the derived MFBs, SD is investigated in detail, and compared with other transmit-antenna diversity techniques which are based on the maximum-ratio and the equal-gain transmission principles, respectively