Diversity Gain Loss Research Articles

Performance Analysis of Buffer-Aided Hybrid NOMA/OMA in Cooperative Uplink System

This paper investigates a cooperative uplink system where two users wish to send messages to a base station with the help of a buffer-aided relay. Transmission modes in terms of both non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) are considered. For the considered system, the probability for the user-to-relay channels to successfully perform NOMA is first theoretically derived in two scenarios of dynamic and fixed power controls (PCs) at users. Then, an efficient buffer-aided hybrid NOMA/OMA based mode selection (MS) scheme is proposed, which adaptively switches between the NOMA and OMA transmission modes according to the instantaneous strength of wireless channels and the buffer state. The state transmission matrix probabilities of the corresponding Markov chain is also derived, and the performance of the proposed hybrid NOMA/OMA scheme is analyzed with closed-form expressions, in terms of sum throughput, outage probability, diversity gain, and average packet delay. For both the dynamic and fixed PCs, the proposed scheme is proved to achieve a diversity gain of two when the buffer size is not smaller than three, which means that fixed PC will not lead to a loss of diversity gain.

Outage Performance of Cognitive Relay Networks With Wireless Information and Power Transfer

In this paper, we consider underlay cognitive radio (CR) networks with one primary receiver, one cognitive transmitter–receiver pair, and one energy harvesting relay. The transmission power of the secondary source is opportunistically determined by its interference to the primary receiver, and the relay transmission is powered by the energy harvested from the radio-frequency observations at the relay. For the considered CR networks with simultaneous wireless information and power transfer (SWIPT), we derive analytical expressions for the outage probability, as well as their high signal-to-noise ratio (SNR) approximations in closed form. The developed analytical results demonstrate that the use of SWIPT will not cause any loss in diversity gain, but the outage probability achieved by the SWIPT-CR scheme asymptotically decays as ${\log \mbox{SNR}}/\mbox{SNR}$ , whereas a decaying rate of ${\mbox{1}}/\mbox{SNR}$ is achieved by a conventional CR network. Computer simulation results are also provided to demonstrate the accuracy of the presented analysis.

Outage performance of amplify-and-forward multiple-input multiple-output relay networks with outdated channel state information and co-channel interference

In this paper, we investigate the outage performance of a dual-hop amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network, considering beamforming transmission with outdated channel state information (CSI) and an arbitrary number of co-channel interferers at both the relay and the destination. The exact closed-form expression for the outage probability is derived, and the asymptotic behavior of the outage probability is also presented to provide further insights into the system performance. Our results show that the system suffers a diversity gain loss caused by the outdated CSI, and the interference only degrade the coding gain of the system. Moreover, increasing antennas can achieve more performance gains, however, the gains decrease as the delay of the CSI increases.

Performance Analysis of MU-MIMO Systems Using HMRS Technique for Various Transmission Modes

It is the fact that the bandwidth of wireless communication system is such a limited resource that several techniques are selectively applied to increase the bandwidth efficiency. The highest bandwidth efficiency can be taken by applying Multi-User Multiple-Input Multiple-Output (MU-MIMO) technique. For this technique, the complexity of detection is rapidly increased by increasing the number of users. Thus the lower complex detection is necessarily required for MU-MIMO system. Recently, the simple detection technique called hybrid-MIMO receiver scheme (HMRS) has been proposed by the authors. However, that study neglected the demands of multiple users for transmitting MIMO modes which are crucially unpredictable in practice. In this paper, the performance analysis of MU-MIMO system using HMRS technique to support various types of user transmission modes is presented. Moreover, the nearly exact symbol error rate (SER) analysis of HMRS with the nonlinear error propagation effect over Rayleigh channels is originally presented. The recursive procedure is adopted to derive the nearly closed-form expressions of the error probability of each user. The results indicate that HMRS technique can improve the error rate more than the existing hybrid-MIMO about 8 dB at 10e−4 SER, increasing the total number of user and number of SM user introduce the diversity gain loss. The simulation results illustrate the performance accuracy of the proposed analysis.

Resource Block Assignment to Reduce Peak to Average Power Ratio in Multi-User OFDM

SUMMARY This paper proposes the assignment of resource blocks (RBs) to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) in a multi-user OFDM system. This system ranks the users according to the channel state information (CSI) for RB assignment. In our proposed technique, an RB is assigned to either the first- or second-ranked mobile station (MS) to minimize the PAPR of the OFDM signal. While this process reduces the PAPR, the throughput is also reduced because of the user diversity gain loss. A PAPR-throughput tradeoff is then established. Theoretical analyses and computer simulations confirm that when the number of MSs becomes large, the PAPR-throughput tradeoff is eased because of the minimal effect of the diversity gain loss. Therefore, significant PAPR reduction is achieved with only a slight degradation in the throughput.

BER analysis of TDD downlink multiuser MIMO systems with imperfect channel state information

In downlink multiuser multiple-input multiple-output (MU-MIMO) systems, the zero-forcing (ZF) transmission is a simple and effective technique for separating users and data streams of each user at the transmitter side, but its performance depends greatly on the accuracy of the available channel state information (CSI) at the transmitter side. In time division duplex (TDD) systems, the base station estimates CSI based on uplink pilots and then uses it through channel reciprocity to generate the precoding matrix in the downlink transmission. Because of the constraints of the TDD frame structure and the uplink pilot overhead, there inevitably exists CSI delay and channel estimation error between CSI estimation and downlink transmission channel, which degrades system performance significantly. In this article, by characterizing CSI inaccuracies caused by CSI delay and channel estimation error, we develop a novel bit error rate (BER) expression for M-QAM signal in TDD downlink MU-MIMO systems. We find that channel estimation error causes array gain loss while CSI delay causes diversity gain loss. Moreover, CSI delay causes more performance degradation than channel estimation error at high signal-to-noise ratio for time varying channel. Our research is especially valuable for the design of the adaptive modulation and coding scheme as well as the optimization of MU-MIMO systems. Numerical simulations show accurate agreement with the proposed analytical expressions.

High-Throughput Multi-Source Cooperation via Complex-Field Network Coding

Physical-layer network coding over wireless networks can provide considerable throughput gains with respect to traditional cooperative relaying strategies at no loss of diversity gain. In this paper, a novel cooperation protocol is developed based on complex-field wireless network coding. Sources transmit efficiently information symbols linearly combined with symbols from other sources. Different from existing wireless network coding protocols, transmissions are not restricted to binary symbols, and do not have to be received simultaneously. In a network with N sources, the developed protocol can achieve throughput up to approximately 1/N symbols per source per channel use, as well as diversity of order N. To deal with decoding errors at sources, selective- and adaptive-forwarding protocols are also developed at no loss of diversity gain. Analytical results corroborated by simulated tests show considerable performance gains with respect to distributed space-time coding, and bit-level network coding protocols.

Dynamic Coded Cooperation Using Multiple Turbo Codes in Wireless Relay Networks

In this paper, we propose a dynamic coded cooperation using multiple turbo codes in wireless relay networks where both relay and destination are equipped with a sensing device and the relay is assumed to determine autonomously if it should cooperate or not. We first elucidate the fact that the puncturing patterns of the multiple turbo codes determine the achievable diversity order by deriving their pairwise error probabilities (PEP). This is followed by a derivation of a simple power detector at the destination that can estimate a precise duration of cooperation phase upon decoding information. Furthermore, we investigate the impact of process delay due to cognitive processing at the relay, which results in the loss of diversity gain, and propose a simple null padding as its countermeasure. Computer simulations show that our proposed approach is able to achieve a full diversity and the frame error rate (FER) performance superior to that of conventional cooperative communications that make use of turbo coding structure even in practical scenarios.

Performance analysis of code selection algorithm based on quasi-orthogonal space–time block code

A quasi-orthogonal space–time block code (QO-STBC) has a rate one but a loss of diversity gain, compared with an orthogonal space–time block code such as Alamouti code. In this study, a code selection algorithm between QO-STBCs is proposed for a diversity gain improvement of a system based on a QO-STBC with four transmit antennas. The proposed algorithm improves diversity gain without a rate loss and provides better performance than the conventional closed-loop algorithm based on QO-STBC. Advantageously, the proposed algorithm can be applied to simple linear receivers, such as the zero-forcing receiver and minimum mean square error receiver, instead of the maximum likelihood receiver, which has a high computational complexity problem. The probability density function of two signal-to-interference and noise ratios (SINRs) is derived and by the derived pdf, an approximated bit error rate (BER) performance of the proposed system is also derived. The BER performance of the proposed system outperforms previous algorithms at least by about 0.5 dB SNR gain at BER 10−4.

The RF-chain limited mimo system- part I: optimum diversity-multiplexing tradeoff

The large gain promised by the multi-input multioutput (MIMO) technology comes with a cost. In particular, multiple analog radio frequency (RF) chains, which are expensive and power consuming, are required at both the transmitter and receiver sides. On the other hand, the antennas connecting to the RF chains are less expensive. Hence, one engineering compromise is to implement more antennas than RF chains and to use only a subset of them based on some antenna selection (AS) algorithm. An interesting question therefore arises: given a RF chain limited MIMO system, what is the fundamental performance gain by adding more antennas? In this two-part paper, we answer this question by using the diversity-multiplexing (D-M) gain tradeoff metric. Consider a Rayleigh fading channel with M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) antennas and L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ⩽ M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) RF chains at the transmitter while M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> antennas and L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ⩽ M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) RF chains at the receiver. We obtain the fundamental D-M tradeoff as a function of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> , M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , and min(L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ). Referring to the special case where L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> = M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) and L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> as the RF unlimited system (or full system) and RF limited system (or pruned system) otherwise, we prove that the pruned system with optimal channel-dependent AS has the same D-M tradeoff as the full system if the multiplexing gain is less than some integer threshold P, while it suffers from some diversity gain loss for multiplexing gains larger than P. In particular, if min(L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) = K = min(M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ), then P = K, i.e. the D-M tradeoffs of the pruned system and the full system are the same. Moreover, this result can be extended to more general fading channels such as Nakagami channel. A fast and D-M tradeoff-optimal AS algorithm is proposed as a byproduct of our analysis. Index Terms?Antenna selection, diversity gain, fast algorithm, MIMO, Nakagami fading, outage probability, Rayleigh fading, spatial multiplexing gain, tradeoff.

Analysis of Dual-Band Helical Antenna for Diversity on Mobile Phones

Antenna diversity on a mobile phone is considered using two dual-band, GSM900/1800, helical antennas. The received signals in mobile Rayleigh fading channel are modeled using a new field simulation technique that involves the three-dimensional (3D) radiation pattern of antennas, 3D angle of arrivals (AoAs) and Doppler frequency. Statistical tools prove the validity of the field simulator. The signals correlation coefficient and diversity gain are computed for different mobile propagation environments by considering AoAs. It is shown that the diversity gain is slightly influenced by the environment models. The experimental prototype is developed and measured. Antenna characteristics: return loss, coupling, 3-D radiation patterns and antenna efficiency are obtained by the measurements and simulations. The diversity performance of the array configuration is measured in the rich wave scattering environment of a reverberation chamber (RC). Results including: signals correlation coefficient, average power of diversity branches, apparent/effective diversity gain and antenna efficiency in RC are provided. The influence of the mobile user is measured as well. Diversity gain of the helical array in both operating frequencies is fairly good. The signals correlation with user's head increases in GSM900 and slightly decreases in GSM1800. In the former band, the diversity gain loss due to imbalance branch powers is found more important than in the later.

Shannon Capacity and Symbol Error Rate of Space-Time Block Codes in MIMO Rayleigh Channels With Channel estimation Error

Space-time block coding (STBC) is an attractive solution for improving quality in wireless links. In this paper, we analyze the impact of channel estimation error on the ergodic capacity and symbol error rate (SER) for space-time block coded multiple-input multiple-output (MIMO) systems. We derive a closed-form capacity expression over MIMO Rayleigh channels with channel estimation error. Moreover, we derive an exact closed-form SER for general PAM/PSK/QAM with channel estimation error. We show that, as expected, channel estimation error introduces the capacity loss and diversity gain loss. Furthermore, as the number of transmit and receive antennas increases, the sensitivity of the STBC system to channel estimation error increases. Simulation results demonstrate the accuracy of our analysis.

Closed-Loop Quasi-Orthogonal STBCs and Their Performance in Multipath Fading Environments and When Combined With Turbo Codes

Quasi-orthogonal space-time block codes (QO-STBCs) achieve full code rate at the expense of loss in diversity gain. We propose two feedback methods for QO-STBCs to achieve full diversity and full code rate. In the first method, signals radiated from various antennas are rotated by phasors according to feedback from the receiver, whereas the second method is based upon antenna weighting/selection. For high to moderate feedback error rates, it is demonstrated that the proposed methods outperform the quantized transmit beamformer. The performance improvement is also investigated for these closed-loop methods when the transmitted signal is error control coded.

Microdiversity reception of spread-spectrum signals on Nakagami fading channels

An analytical framework to evaluate the performance of different predetection diversity techniques in various mobile radio environments is developed. The average bit-error rate analysis applies to phase coded spread-spectrum systems, over Nakagami multipath fading channels. A simple and practical selection combining rule is considered. Our numerical results reveal that this new low-complexity receiver structure exhibits comparable performance to that of an optimum linear diversity combiner when the channel does not experience severe fading and for small diversity orders, conditioned on the situation that all the diversity branches have identical mean signal strengths. In this study, we also investigate the effect of variations in the mean signal and noise power levels on each of the independent diversity branches. This is an important consideration because in practice equal mean signal strengths rarely occur, which results in loss of diversity gain. We found that the signal-plus-noise-and-interference selection model outperforms the traditional signal-to-interference-plus-noise ratio selection scheme if the discrepancy between the mean signal strengths are small, owing to the statistical nature of the multiple-access interference.