Destination Antennas Research Articles

Transmission Schemes and Power Allocation for Multiuser Massive MIMO Relaying

This paper proposes and analyzes the performance of two simple transmission protocols for a multiuser massive multiple input multiple-output relaying system, where K single-antenna users transmit data to a massive-antenna destination through an N-antenna relay node. In the first transmission protocol, the relay does not need to know the CSI. It just amplifies and forwards the received signals to the destination. In the second protocol, the relay first estimates the channels from all users. It then uses the maximum-ratio combining (MRC) technique to combine all received signals and forwards them to the destination. In both protocols, the destination estimates the channels and employs MRC to decode the signals. We propose an efficient channel estimation method at the destination in which the destination estimates only the effective channels gains. As a consequence, the channel estimation overhead does not depend on the numbers of relay and destination antennas. We derive closed-form expressions for the spectral efficiency of the two transmission protocols. These results allow us to further analyze the system performance and to allocate the transmit powers. Particularly, a max-min power control algorithm is proposed which selects the transmit powers at the relay and users to maximize the lowest spectral efficiency of all users. We show that, by using the max-min power allocation algorithm, the spectral efficiency can be increased significantly, compared to uniform power allocation. Furthermore, if the distance between the users and the relay is large, the first transmission protocol is better and vice versa if this distance is small.

SWIPT Enabled Intelligent Transportation Systems With Advanced Sensing Fusion

Internet of Things (IoT) is the connections of embedded sensing technologies that can be integrated with intelligent transportation systems (ITS), which can take advantage of the advanced sensing fusion to implement the intelligent interaction. Moreover, the environmental wireless signals was harvested and utilized to power the charging sensors, which can be used to assist and enhance the ITS and have attracted extensive attentions in industries. The simultaneous wireless information and power transfer (SWIPT) enabled ITS was designed and proposed with the advanced sensing fusion, where the sensor nodes of the source and destination were all equipped with multiple antennas and the maximum ratio transmission (MRT) precoding and maximum ratio combination (MRC) were adopted respectively in the proposed system, where the sensing nodes can be embedded into the data addressing equipment to fusion the sensing information. For the established massive sensing node transmission system, the transmission power, the number of source antennas and destination antennas were considered to fuse and optimize to obtain the maximum energy efficiency (EE) of the ITS. Since the original fusion problem was non-convex and difficult to solve, which can be transformed to convex problem via the large SNR approximation method and thereby the optimal solution of the sensing fusion problem was derived through the Lagrange algorithm and the Lambert function W. The simulation results showed that the proposed fusion algorithm can achieve remarkable EE compared with other algorithms and be utilized to the massive sensors to improve the intelligent predication and transportation for vehicle network.

Joint Impact of Nodes Mobility and Imperfect Channel Estimates on the Secrecy Performance of Cognitive Radio Vehicular Networks Over Nakagami-m Fading Channels

This paper investigates the joint impact of nodes' mobility and imperfect channel estimates on the secrecy performance of an underlay cognitive radio vehicular network over Nakagami-m fading channels. Specifically, the secondary network consists of a single-antenna source vehicle, an N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> D</sub> -antenna destination vehicle, and an N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> E</sub> -antenna passive eavesdropper vehicle, whereas the primary network comprises of a single-antenna primary receiver vehicle. The time selective fading links arise due to nodes' mobility are modeled via first-order auto-regressive process, and the channel state information is estimated using linear minimum mean square error estimation method. Moreover, the transmit power of secondary source is constrained by both the interference threshold of the primary receiver and the maximum transmit power of secondary network. Under such a realistic scenario, we derive the analytical closed-form secrecy outage probability (SOP) and ergodic secrecy capacity expressions. Furthermore, we present asymptotic SOP analysis to obtain key insights into the system's secrecy diversity order. We also report several practical cases of interest to reveal valuable information about the system's secrecy behavior. Moreover, we illustrate the impacts of system/channel parameters, nodes' mobility, imperfect channel estimates, interference temperature limit, and the maximum available source power. Finally, the simulation studies corroborate our derived analytical findings.

Efficient time reversal strategy for MISO-OFDM systems

In this work, we are interested in implementing, developing, and evaluating a time reversal strategy for a multiple-input single-output orthogonal frequency division multiplexing system. This strategy enjoys a good trade-off between the computational complexity and performance in terms of bit error rate where it offers a good coding gain by forming a beam in the direction of the destination at a price of channel state information available at the transmitter. In time reversal technique, a higher coding and diversity gain can be achieved by increasing the number of transmitting antennas, which focuses the formed beam to the direction of the destination antenna. By achieving this, the received signal-to-noise ratio can be maximized which makes time reversal a good candidate for multiple-input single-output systems while keeping a low complexity. The performance of the proposed system is evaluated in terms of bit error rate where our simulations show that the proposed strategy enjoys the full diversity gain, which is equal to the number of transmitting antennas. Moreover, a robust channel estimation technique is proposed to improve the overall system in terms of bit error rate.

Enhanced development of communication between the network and the end user by eliminating the interference signals inMIMOchannel

AbstractThough the key technology for 5G communication is the massive Multiple input and multiple output (MIMO), it has a major drawback when the user generated inference signals are to be handled by several other users. When these interference signals are used in various users, issues concerning system ability, power management issues and QoS related issues arises with the involvement of MIMO channel. Though internet of things (IoT) making use of MIMO is still under development, the requirements of the IoT is quite different when compared to several other connections. Thus, taking into account the demands, the solutions were framed with the help of the proposed system. One such solution is the Partition Square and Cross‐Processing method that can possess several antennas at the given destination. Based on this solution obtained the data rate can be drastically increased correspondingly reducing the power consumed thus producing the most desirable result with high signal to noise ratio (SNR). Best victory is another such solution that solves the issues relating to power reduction thereby providing the best solution with minimum SNR. These solutions produced by the proposed system still has some disadvantages with respect to the following case: when the number of destination antennas is less than the number of source antennas. This case is considered as most common in the model proposed. For the above‐mentioned case, near optimal solution is produced by both the algorithms. In this article, the transmitters are represented by the source antenna and the receiver is represented by the destination antenna. Thus, with the help of IoT connectivity, major benefits can be bought to the massive MIMO channel.

Analysis of DF Relay Selection in Massive MIMO Systems With Hardware Impairments

We consider a massive multiple-input multiple-output (m-MIMO) system in which a source communicates with a destination with the help of multiple single-antenna decode-and-forward (DF) relays. Employing optimal relay selection, we analyze the system performance in presence of hardware impairments (HWI) for two m-MIMO scenarios: massive-antenna source and single-antenna destination (m-MIMO I), and massive-antenna source and destination (m-MIMO II). We obtain lower bounds on the average signal-to-noise plus distortion ratio (SNDR) of the system and show that in the m-MIMO II regime, the HWI levels at the relays become the only limiting factors. Employing extreme value theory, we demonstrate that as the number of relays increases the end-to-end SNDR of the system tends to Gumbel and Weibull distributions for the m-MIMO I and m-MIMO II systems, respectively. In addition, for both arbitrary numbers of source and destination antennas and m-MIMO scenarios, we provide closed form expressions for optimal power allocation between the source and the selected relay, and the effects of HWI level distributions between the receiving and the transmitting parts of the relay (which can be exploited for optimal system design under cost constraints).

General performance of detect-and-forward cooperative relaying in the presence of multiple interferers for optimum combining receivers

Detect-and-Forward (DF) is a cooperative technique based on the retransmission of a detected version of the transmit signal. It improves performance, throughput and cellular coverage. However, in cellular scenarios, it coexists with co-channel interference (CCI), which is the principal factor that affects the performance of cellular networks. On the other hand, Optimum Combining (OC) is a low complexity combining technique that maximizes the signal-to-interference-plus-noise ratio (SINR), achieving in this case diversity gain by eliminating the CCI. In the present paper, the performance of cooperative DF network in the presence of multiple CCI at relay and destination is analysed, where relay and destination are equipped with multiple antennas and OC. Furthermore, scenarios by considering multiple antenna transmission (MAT) and transmit antenna selection (TAS) technique at relay are supposed. For both MAT and TAS techniques, a tight approximation of the end-to-end instantaneous SINR is proposed. Subsequently, its moment-generating function is derived in closed-form in order to evaluate the average bit-error rate of the system. Analytical results are validated using Monte-Carlo simulations for several scenarios, showing that OC eliminates fully the CCI, even in the case of high-power CCI. The diversity gain depends on the number of destination antennas, relay antennas and interferers.

Designing Anti-Jamming Receivers for NR-DCSK Systems Utilizing ICA, WPD, and VMD Methods

In this brief, we consider an advanced noise reduction differential chaotic shift keying system in which a single antenna source communicates with a single antenna destination under the attack of a single antenna jammer. We design an anti-jamming receiver for the considered system. Particularly, we propose a variational mode decomposition—independent component analysis—wavelet packet decomposition (VMD-ICA-WPD) structure, in which VMD method is first exploited to generate multiple signals from the single received one. Second, ICA method is applied to coarsely separate chaotic and jamming signals. After that, WPD method is used to finely estimate and mitigate jamming signals that exist on all outputs of ICA method. Finally, an inverse ICA procedure is carried out, followed by a summation, and the outcome is passed through the conventional correlation receiver for recovering the transmitted information. Simulation results show that the proposed receiver provides significant system performance enhancement compared to that given by the conventional counterparts.

Interference Mitigation via Relaying

This paper studies the effectiveness of relaying for interference mitigation in an interference-limited communication scenario. We are motivated by the observation that in a cellular network, a relay node placed at the cell edge observes a combination of intended signal and inter-cell interference that is correlated with the received signal at a nearby destination, so a relaying link can effectively allow the antennas at the relay and at the destination to be pooled together for both signal enhancement and interference mitigation. We model this scenario by a MIMO Gaussian relay channel with a digital relay-to-destination link of finite capacity, and with correlated noise across the relay and destination antennas. Assuming a compress-and-forward strategy with Gaussian input distribution and quantization noise, we propose a coordinate ascent algorithm for obtaining a stationary point of the non-convex joint optimization of the transmit and quantization covariance matrices. For fixed input distribution, the globally optimum quantization noise covariance matrix can be found in closed-form using a transformation of the relay's observation that simultaneously diagonalizes two conditional covariance matrices by congruence. For fixed quantization, the globally optimum transmit covariance matrix can be found via convex optimization. This paper further shows that such an optimized achievable rate is within a constant additive gap of the MIMO relay channel capacity. The optimal structure of the quantization noise covariance enables a characterization of the slope of the achievable rate as a function of the relay-to-destination link capacity. Moreover, this paper shows that the improvement in spatial degrees of freedom by MIMO relaying in the presence of noise correlation is related to the aforementioned slope via a connection to the deterministic relay channel.

Designing an Energy Efficient Scheme in MANET using Reconfigurable Directional (RDA) Algorithm

Mobile Ad Hoc Networks (MANET) are autonomous, infrastructure less and self-configuring networks. MANETs has gained lots of popularity due to on the fly deployment i.e. small network setup time and ability to provide communication in obstreperous terrains. Major challenges in MANETs include routing, energy efficiency, network topology control, security etc. Primary focus in this article is to provide method and algorithm to ensure significant energy savings using re-configurable directional antennas. Significant energy gains can be clinched using directional antenna. Key challenges while using directional antenna are to find destination location, antenna focusing, signal power and distance calculations. Re-configurable directional antenna can ensure significant energy gains if used intelligently. This article provides a brief insight into improved energy savings using re-configurable directional antennas and an associated algorithm

On the Energy Efficient Multiple Pair Communications in Two-Way Massive MIMO Relaying Networks with Imperfect CSI

Multiple-pair two-way communication in massive multiple-input multiple-output (MIMO) relay network is studied in this article wherein K single antenna source nodes exchange their messages to the corresponding K single antenna destination nodes with the help of one relay provisioned with N(N &gt;&gt; K) antenna array. And the energy efficient two-way multiple-pair communication in Massive MIMO relay network through the precoding design at relay is addressed. It is shown hat, even with the imperfect channel state information at the relay, the maximum ratio combining-maximum ratio transmission (MRC/MRT) precoding and the zero-forcing reception zero-forcing transmission (ZFR/ZFT) precoding at relay can be employed to mitigate inter-pair interference. The asymptotic signal to interference plus noise ratio (SINR) analysis of four power-scaling schemes in the regime of very large number of antenna at relay shows that, the inter-pair interference can be eliminated, the effect of the small-scale fading can be averaged out; the total transmit power consumption can be reduced for a better energy efficient multiple-pair communication when the number of antenna at relay is large enough. Moreover, when the transmit power at relay is sufficient, both the MRC/MRT and the ZFR/ZFT based relaying strategy can effectively cope with the channel state information (CSI) error. Simulation results are presented to validate our analysis.

Runtime Tunable Transmitting Power Technique in mm-Wave WiNoC Architectures

Emerging on-chip communication technologies, like wireless networks-on-chip (WiNoCs), have been recently proposed as candidate solutions for addressing the scalability limitations of conventional multihop network on chip (NoC) architectures. In a WiNoC, a subset of network nodes, namely, radio hubs, are equipped with a wireless interface that allows them to wirelessly communicate with other radio hubs. Thus, long-range communications, which would involve multiple hops in a conventional wireline NoC, can be realized by a single hop through the radio medium. Unfortunately, the energy consumed by the RF transceiver into the radio hub (i.e., the main building block in a WiNoC), and in particular by its transmitter, accounts for a significant fraction of the overall communication energy. In order to alleviate such contribution, this paper presents a runtime tunable transmitting power technique for improving the energy efficiency of the transceiver in WiNoC architectures. The basic idea is tuning the transmitting power based on the physical location of the recipient of the current communication. Specifically, based on the destination address of the incoming packet, the radio hub tunes its transmitting power to a minimum level, but high enough to reach the destination antenna without exceeding a certain bit error ratio. The proposed technique is general and can be applied to any WiNoC architecture. Its application on different representative WiNoC architectures results in an average energy reduction up to 50% without any impact on performance and with a negligible overhead in terms of silicon area.

Power Allocation and Outage Probability Analysis of AF Relaying Systems with Multiple Antenna at Terminal Nodes

In this paper, the performance of a nonregenerative relaying network of multiple-antenna terminal nodes is analyzed with respect to the power allocation issue. Assuming that complete channel state information (CSI) of all links is known at the destination terminal, an optimal power allocation (OPA) approach is investigated subject to constant total power with the objective of maximizing the instantaneous signal-to-noise ratio (SNR) at the destination. Generally, by this OPA approach, the total available power in the system is appropriated to source and relay nodes proportional to channel properties with the aim of coordinating the source–relay and relay–destination hop quality. Closed-form expressions for the outage probability are analytically derived, considering both conventional and maximized SNRs. It is shown that OPA outperforms the conventional uniform power allocation, although the achieved improvement is more significant if the number of destination antennas is less than the number of source antennas. Moreover, the results indicate that the effect of OPA on the performance improvement is significant if the relay node is close to the source terminal. Moreover, it is seen that the minimum number of the source and destination antennas is a determinant parameter in the evaluation of the outage probability. Hence, it is demonstrated that for an efficient system design, the number of source antennas should be as close as possible to that of the destination antennas. In addition, the relay selection scheme is considered to further improve the performance of the system. Finally, simulation results are presented, which confirms the validity of the analysis.

Secrecy Enhancement Analysis Against Unknown Eavesdropping in Spatial Modulation

In multiple-input–multiple-output (MIMO) wireless communications, spatial modulation (SM) has recently emerged as a new transmission method. This letter explores the physical-layer security in typical SM systems. We present a secrecy rate analysis for multiple antenna destination and eavesdroppers receivers. Targeting against passive eavesdroppers in unknown locations, we study the efficacy of active security measure through joint signal and jamming transmission without the typical requirement of eavesdropper channel information. We demonstrate the secrecy rate and transmission power tradeoff in active source jamming by providing numerical results on achieved secrecy rate and the bit error rate (BER) at different receivers.

Ergodic Capacity Analysis of Full-duplex Mimo Relay Channel using Tracy-Widom Distribution with Processing Delay

We explore a full-duplex technique in wireless communication particularly for relay networks. We consider the relay to operate in full-duplex, which occurs when transmission and reception are conducted in the same channel. We investigate potential benefits of full-duplex technique in relay networks, which uses multiple antennas for transmission and reception combined with the Amplify-Forward (AF) scenario. We study the effects of multiple antennas in terms of relay capacity. We derive an ergodic capacity expression using the Tracy-Widom distribution. Using Singular Value Decomposition (SVD) and perfect Channel State Information (CSI), we investigate these three scenarios: First, we consider the relay to have an antenna larger than that of both source and destination. Second, we consider both relay and destination to have an antenna larger than that of the source. Third, we consider both relay and source to have antenna larger than that of the destination. We show the results that the capacity of the relay with a fullduplex technique is almost twice the capacity of an half-duplex. We show that increasing the number of destination antennas is not help much when one of the source antennas is small. Moreover, the capacity decreases due to a channel hardening effect, when the number of destination antennas is larger than that of the source.

MIMO Precoding and Relay Selection for the Decode-and-Forward Relay Networks

We consider the joint relay and pre-coder selection in the decode-and-forward (DaF) relay network, where multiple relays are employed with multiple antennas. Depending on the channel information, the destination informs the relay and pre-coder selection information to the source and relays with finite bits of information. The source and the selected relay use their own pre-coders to transmit the signal using orthogonal channels. We present a selection criterion based on an upper bound of the pair-wise symbol error probability and provide the conditions for the code-books to achieve the full diversity. For a single antenna destination, we show that the proposed criterion guarantees the diversity order of M_s + KM_r, where M_s,M_r are the numbers of antennas at the source and the relay respectively and K is the number of relays in the network.

Performance Analysis of Optimal Single Stream Beamforming in MIMO Dual-Hop AF Systems

This paper investigates the performance of optimal single stream beamforming schemes in multiple-input multiple-output (MIMO) dual-hop amplify-and-forward (AF) systems. Assuming channel state information is not available at the source and relay, the optimal transmit and receive beamforming vectors are computed at the destination, and the transmit beamforming vector is sent to the transmitter via a dedicated feedback link. Then, a set of new closed-form expressions for the statistical properties of the maximum eigenvalue of the resultant channel is derived, i.e., the cumulative density function (cdf), probability density function (pdf) and general moments, as well as the first order asymptotic expansion and asymptotic large dimension approximations. These analytical expressions are then applied to study three important performance metrics of the system, i.e., outage probability, average symbol error rate and ergodic capacity. In addition, more detailed treatments are provided for some important special cases, e.g., when the number of antennas at one of the nodes is one or large, simple and insightful expressions for the key parameters such as diversity order and array gain of the system are derived. With the analytical results, the joint impact of source, relay and destination antenna numbers on the system performance is addressed, and the performance of optimal beamforming schemes and orthogonal space-time block-coding (OSTBC) schemes are compared. Results reveal that the number of antennas at the relay has a great impact on how the numbers of antennas at the source and destination contribute to the system performance, and optimal beamforming not only achieves the same maximum diversity order as OSTBC, but also provides significant power gains over OSTBC.

On Capacity Scaling of Multi-Antenna Multi-Hop Networks: The Significance of the Relaying Strategy in the “Long Network Limit”

The sum-capacity <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$C$</tex></formula> of a static uplink channel with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex> </formula> single-antenna sources and an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> -antenna destination is known to scale linearly in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> , if the random channel matrix fulfills the conditions for the Marcenko-Pastur law: if each source transmits at power <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$P/n$</tex></formula> , there exists a positive <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$c_{0}$</tex></formula> , such that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lim_{n \ura{} \infty}C/n=c_{0}$</tex></formula> almost surely. This paper addresses the question to which extent this result carries over to multi-hop networks. Specifically, an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$L+1$</tex></formula> -hop network with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex> </formula> non-cooperative source antennas, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> fully cooperative destination antennas, and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L$</tex></formula> relay stages of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n_{\cal R}$</tex></formula> (cooperative or non-cooperative) relay antennas each is considered. Four relaying strategies are assessed based on the interrelationship between two sequences. For each considered strategy <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm XF}$</tex></formula> , there exists a sequence <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(c_{L}^{\rm XF})_{L=0}^{\infty}$</tex> </formula> , such that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$c_{L}^{\rm XF}=\lim_{n \ura{} \infty}R^{\rm XF}_{L}/n$</tex></formula> almost surely, where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$R^{\rm XF}_{L}$</tex></formula> denotes the supremum of the set of sum-rates that are achievable by the strategy over <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L\!+\!1$</tex> </formula> hops. This sequence depends on the sequence <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(P_{L})_{L=0}^{\infty}$</tex> </formula> , where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$P_{L}$</tex></formula> corresponds to the power of the source stage and each of the relay stages in an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L\!+\!1$</tex></formula> -hop network. Results are summarized as follows: <orderedlist continuation="restarts" numeration="bullet" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <listitem><para>Decode &amp; forward (DF): For <formula formulatype="inline"><tex Notation="TeX">$n_{\cal R}=n$</tex></formula>, <formula formulatype="inline"><tex Notation="TeX">$c^{\rm DF}_{L}$</tex></formula> is constant with respect to <formula formulatype="inline"> <tex Notation="TeX">$L$</tex></formula>, if also <formula formulatype="inline"><tex Notation="TeX">$P_{L}$</tex></formula> is constant with respect to <formula formulatype="inline"> <tex Notation="TeX">$L$</tex></formula>.</para></listitem></orderedlist>

Amplify-forward relaying for multiple-antenna multiple relay networks under individual power constraint at each relay

This article considers the design of an optimal beamforming weight matrix of multiple-antenna multiple-relay networks. It is assumed that each relay utilizes the amplify and forward strategy, i.e., it multiplies the received signal vector by a matrix, dubbed the relay weight matrix, and forwards the resulting vector to the destination. Furthermore, we assume that the source and the destination have the same number of antennas and that each transmit antenna is virtually paired to a different destination antenna. The relay weight matrices are concurrently designed to optimize the mean square error (MSE) criterion at the destination, assuming each relay node is subject to a power constraint. Accordingly, it is demonstrated that this problem can be cast as a convex optimization problem in which the individual power constraints are tackled by employing the method of Lagrange multipliers in two stages. First, the relay gain matrix is computed analytically in terms of Lagrange dual variables, thereby converting the original problem into a scalar optimization problem. Then, these scalar variables are computed numerically. The proposed scheme is evaluated through simulation with various numbers of relays and antennas to obtain MSE and bit error rate (BER) metrics and it is shown that the resulting MSE and BER achieved through using the proposed method outperforms that of MMSE-MMSE method introduced by Oyman et.al., which is regarded as the best known method for the underlying problem.

Opportunistic Relaying for MIMO Amplify-and-Forward Cooperative Networks

We consider a wireless relay network with multiple antenna terminals over Rayleigh fading channels, and apply distributed space-time coding (DSTC) in amplify-and-forward (A&F) mode. The A&F scheme is used in a way that each relay transmits a scaled version of the linear combination of the received symbols. It turns out that, combined with power allocation in the relays, A&F DSTC results in an opportunistic relaying scheme, in which only the best relay is selected to retransmit the source's space-time coded signal. Furthermore, assuming the knowledge of source-relay CSI at the source node, we design an efficient power allocation which outperforms uniform power allocation across the source antennas. Next, assuming M-PSK or M-QAM modulations, we analyze the performance of the proposed cooperative diversity transmission schemes in a wireless relay networks with the multiple-antenna source and destination. We derive the probability density function (PDF) of the received SNR at the destination. Then, the PDF is used to determine the symbol error rate (SER) in Rayleigh fading channels. We derived closed-form approximations of the average SER in the high SNR scenario, from which we find the diversity order of system R min{N s , N d }, where R, N s , and N d are the number of the relays, source antennas, and destination antennas, respectively. Simulation results show that the proposed system obtain more than 6 dB gain in SNR over A&F MIMO DSTC for BER 10?4, when R = 2, N s = 2, and N d = 1.