AF Relaying

In this thesis, performance of cooperative relaying with multi-antenna system in Rayleigh/Nakagami-m fading channels has been investigated. The relay is assumed to operate in adaptive decode and forward mode and perform threshold based decoding. Installation of multiple receiving antennas on infrastructure based fixed relay is feasible thereby increasing the probability of relay participation and hence diversity order may be increased for systems which contain such relays. Such systems in different configurations have been analyzed in various path-loss conditions, severity of fading, relay placement at different locations and antennas installed on it. It has been found that for some locations of relay placement, performance of system depends only marginally on the number of antennas installed on relay and combining schemes at relay and destination. System performance can be improved significantly by appropriately positioning the relay. For such positioning, system performance depend...

The core aim of this work is the maximization of the achievable data rate of the secondary user pairs (SU pairs), while ensuring the QoS of primary users (PUs). All users are assumed to be equipped with multiple antennas. It is assumed that when PUs are present, the direct communications between SU pairs introduces intolerable interference to PUs and thereby SUs transmit signal using the cooperation of other SUs and avoid transmitting in the direct channel. In brief, an adaptive cooperative strategy for multiple-input/multiple-output (MIMO) cognitive radio networks is proposed. At the presence of PUs, the issue of joint relay selection and power allocation in Underlay MIMO Cooperative Cognitive Radio Networks (U-MIMO-CCRN) is addressed. The optimal approach for determining the power allocation and the cooperating SU is proposed. Besides, the outage probability of the proposed communication protocol is further derived. Due to high complexity of the optimal approach, a low-complexity approach is further proposed and its performance is evaluated using simulations. The simulation results reveal that the performance loss due to the low-complexity approach is only about 14%, while the complexity is greatly reduced.

A virtual multiple-input multiple-output (MIMO) system based on cooperative communication is studied actively. This system is formed between base station and source node with using of two or more nodes around itself. These transmitters are equipped with a single antenna. This system is one of the solution methods for deterioration in communication quality from that the power supply of the node is battery when it use a high frequency band than at present in uplink. In this paper, we have focused on virtual MIMO system based on Amplify-and-Forward (AF) algorithm and Decode-and-Forward (DF) algorithm, and proposed a design method of realizing eigenbeam-space division multiplexing (E-SDM) based on these algorithms. Our proposed method is optimizing the whole channel with eigenvalue decomposition. Finally, we have shown that the proposed method is effectiveness by computer simulation. These results indicate that BER performance has been improved by proposed method and the effect of increasing transmitters and antenna elements of receivers.

Non-orthogonal multiple access (NOMA) is being widely considered as a potential candidate to enhance the spectrum utilization in beyond fifth-generation (B5G) communications. In this article, we derive closed-form expressions for the ergodic rate and outage probability of a multiple-antennaassisted NOMA-based cooperative relaying system (CRS-NOMA). We present the performance analysis of the system for two different receive diversity schemes-selection combining (SC) and maximal-ratio combining (MRC), in Nakagami-m fading. We also evaluate the asymptotic behavior of the CRS-NOMA to determine the slope of the ergodic rate and diversity order. Our results show that in contrast to the existing CRS-NOMA systems, the CRS-NOMA with receive diversity outperforms its orthogonal multiple access (OMA) based counterpart even in the low-SNR regime, by achieving higher ergodic rate. Diversity analysis confirms that the CRS-NOMA achieves full diversity order using both SC and MRC schemes, and this diversity order depends on both the shape parameter m and the number of receive antennas. We also discuss the problem of optimal power allocation for the minimization of the outage probability of the system, and subsequently use this optimal value to obtain the ergodic rate. An excellent match is observed between the numerical and the analytical results, confirming the correctness of the derived analytical expressions. INDEX TERMS Non-orthogonal multiple access, cooperative communications, relaying, Nakagami-m fading, ergodic rate, outage probability, diversity order. 1. Note that the analysis of the ergodic rate in the high-SNR regime was not presented in [10].

In deterministic networks where relay nodes are stationary, combined relay selection is an efficient relay selection scheme, which is capable of achieving the near-optimal outage performance with much lower system complexity. However, the efficiency of combined relay selection is only validated upon fixed topological settings. To investigate the performance of combined relay selection in spatially random networks (SRNs), we employ the Poisson point process to model the dynamical nature of cooperative networks and study the outage performance of the proposed system. It is surprising that the equivalence principle of combined relay selection appearing in deterministic networks does not hold in SRNs.

The ever-increasing demand for mobile Internet and high-data-rate applications poses unique challenging requirements for 5G mobile networks, including spectrum limitations and massive connectivity. Cognitive radio and carrier aggregation (CA) have recently been proposed as promising technologies to overcome these challenges. In this paper, we investigate joint relay selection and optimal power allocation in an underlay cooperative cognitive radio with CA, taking into account the availability of multiple carrier components in two frequency bands, subject to outage probability requirements for primary users (PUs). The secondary user network employs relay selection, where the relay that maximizes the end-to-end sum rate is selected, assuming both decode-andforward and amplify-and-forward relaying. The resulting optimization problems are optimally solved using convex optimization tools, i.e., dual decomposition and an efficient iterative method, allowing their application in practical implementations. Simulation results illustrate that the proposed configuration exploits the available degrees of freedom efficiently to maximize the SU rate, while meeting the PU average outage probability constraints.

In this paper, we investigate joint relay selection and optimal power allocation, as a means to maximize the achievable rate of an underlay cooperative cognitive radio with carrier aggregation, taking into account the availability of multiple carrier components in two different bands and primary users (PUs) with specific average outage probability requirements. For the acquisition of the interference thresholds, which are set by the PUs on the secondary user (SU), we incorporate a minimum feedback strategy into the problem formulation, based on the minimization of the PUs outage probabilities. The resulting nonconvex optimization problem is transformed into a convex one and optimally solved using dual decomposition and an efficient iterative method with closed-form power policies. Simulation results illustrate that the proposed configuration exploits the available degrees of freedom in an efficient way which maximizes the SU throughput while the average outage probability of the PUs is kept at acceptable levels.

This paper considers a Gaussian network where N half-duplex multiple-antenna relays assist the communication between a source and a destination. A novel antenna switching policy is proposed, where each relays' antenna can be configured to either receive or transmit independently of the others. The rate achieved by noisy network coding is shown to be to within a constant gap from the cut-set bound, where the gap only depends on the total number of antennas in the system. Moreover, the optimal number of different relay antenna configurations needed to attain the constant gap is proved to be at most N + 1, that is, it only depends on the number of relays but not on the total number of antennas. Such a relay scheduling policy is referred to as simple. Through an example, it is shown that independently switching the antennas at the relays not only achieves in general strictly higher rates compared to using the antennas for the same purpose, but can actually provide a strictly larger pre-log factor. This implies that in broadband wireless networks with half-duplex multiple-antenna relays, the relay antennas should be dynamically configured to either transmit of receive depending on the channel conditions. Index Terms-Approximate capacity, half-duplex networks, multiple-antenna nodes, relay scheduling policies.

In this paper, we propose a general method to analyze the achievable rate and to characterize the optimal powerallocation (PA) scheme for a wide range of half-duplex singlerelay amplify-and-forward (AF) protocols over Rayleigh fading channels in high and low signal-to-noise-ratio (SNR) regimes. These include one-way (OW) dual-hop AF (DHAF) systems, OW nonorthogonal AF (NAF) systems, and two-phase two-way AF (2P TWAF) systems using either fixed-gain (FG) or variable-gain (VG) amplification coefficients. At high-SNR regimes, our main idea is to exploit the capacity of a two-branch maximal-ratio combining (MRC) system to obtain tight yet simple approximations to the achievable rates. In low-SNR regions, we use a simple approximation to the logarithm to compute the asymptotic achievable rates. For all considered AF protocols, the closed-form approximations are tight and easy to analyze since they involve only the exponential integral. Then, using the derived approximations, we analytically quantify the asymptotic PA schemes among the nodes to achieve the maximum rate and the sum rate for OW and TW schemes, respectively. The OW and TW protocols of interest are finally compared with the direct transmission (DT) scheme. Although OW relaying is inferior in terms of capacity in high-and low-SNR regimes, the 2P TW system might become advantageous in terms of sum-rate performance at high SNRs under the right channel conditions. Index Terms-Achievable rate, amplify-and-forward (AF), capacity, exponential integral, Rayleigh fading, relay channel, sum rate. I. INTRODUCTION R ELAY communications have recently received considerable research attention due to the advantage in increasing range and reliability in wireless networks. In general, relaying strategies can be categorized as decode-and-forward, compressand-forward, and amplify-and-forward (AF) schemes. Among these strategies, the AF technique is transparent to the

This paper introduces an amplify-and-forward (AF) relaying technique that employs phase dithering and intentional delay within single carrier-frequency domain equalizer (SC-FDE) systems. The proposed relaying technique aims to increase the gain of both frequency diversity and time diversity in slow fading channels. To achieve this, the proposed technique introduces random phase rotation and random intentional delay. The relaying scenario assumes two-hop communication with relaying between the source and destination. It is assumed that many nodes are densely distributed, allowing for many relay nodes to participate in relaying. To verify the performance through computer simulation, the number of relays is 1, 2, 3, 5, 15, and 25, and three modulation coding schemes (MCSs) are considered: QPSK with R=1/3, 16QAM with R=3/4, and 8PSK with R=7/8. The simulation results demonstrate that the proposed relaying technique improves the bit error ratio (BER) performance. The performance improves...

This paper introduces an amplify-and-forward (AF) relaying technique that employs phase dithering and intentional delay within single carrier-frequency domain equalizer (SC-FDE) systems. The proposed relaying technique aims to increase the gain of both frequency diversity and time diversity in slow fading channels. To achieve this, the proposed technique introduces random phase rotation and random intentional delay. The relaying scenario assumes two-hop communication with relaying between the source and destination. It is assumed that many nodes are densely distributed, allowing for many relay nodes to participate in relaying. To verify the performance through computer simulation, the number of relays is 1, 2, 3, 5, 15, and 25, and three modulation coding schemes (MCSs) are considered: QPSK with R=1/3, 16QAM with R=3/4, and 8PSK with R=7/8. The simulation results demonstrate that the proposed relaying technique improves the bit error ratio (BER) performance. The performance improves as the number of relays increases.

We examine the impact of multiple primary transmitters and receivers (PU-TxRx) on the outage performance of cognitive decode-and-forward relay networks. In such a joint relaying/spectrum-sharing arrangement, we address fundamental questions concerning three key power constraints: 1) maximum transmit power at the secondary transmitter (SU-Tx), 2) peak interference power at the primary receivers (PU-Rx), and 3) interference power at SU-Rx caused by the primary transmitter (PU-Tx). Our answers to these are given in new analytical expressions for the exact and asymptotic outage probability of the secondary relay network. Based on our asymptotic expressions, important design insights into the impact of primary transceivers on the performance of cognitive relay networks is reached. We have shown that zero diversity order is attained when the peak interference power at the PU-Rx is independent of the maximum transmit power at the SU-TX.

A salient feature of millimeter-wave (mmW) wireless systems is their large bandwidths. A direct consequence is that radio frequency (RF) non-idealities, such as phase noise, I-Q imbalance, and non-ideal frequency response of bandpass filters, become more pronounced compared to existing systems operating below 6 GHz. However, investigations of the impact of such nonidealities and techniques for their compensation are limited. In this paper, the problem of I-Q mismatch is investigated, motivated by the authors' recent work on mmW prototype design and development. First, a model for the non-ideal system is developed by modeling the in-phase (I) and quadrature (Q) passband channels separately, rather than the common complex baseband representation. The resulting channel matrix reveals the structure of interference introduced across I-Q channels and frequencies. Second, a new approach is developed for estimating the non-ideal channel using the new model. Third, a linear receiver architecture is developed to compensate for the interference caused by the I-Q mismatch. Finally, the performance of the new proposed system is compared to a baseline conventional system which ignores I-Q mismatch. The results indicate significant loss in performance even for modest values of I-Q mismatch parameters. In particular, the baseline system exhibits a saturation of output signal-to-interference-and-noise ratio (SINR) regardless of the input SNR. The new proposed system does not suffer from such saturation and its SINR can be increased indefinitely by increasing the input SNR. The analytical results are validated with experimental evaluation on a 28 GHz mmW wireless testbed.

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Non-orthogonal multiple access (NOMA) is being widely considered as a potential candidate to enhance the spectrum utilization in beyond fifth-generation (B5G) communications. In this article, we derive closed-form expressions for the ergodic rate and outage probability of a multiple-antennaassisted NOMA-based cooperative relaying system (CRS-NOMA). We present the performance analysis of the system for two different receive diversity schemes-selection combining (SC) and maximal-ratio combining (MRC), in Nakagami-m fading. We also evaluate the asymptotic behavior of the CRS-NOMA to determine the slope of the ergodic rate and diversity order. Our results show that in contrast to the existing CRS-NOMA systems, the CRS-NOMA with receive diversity outperforms its orthogonal multiple access (OMA) based counterpart even in the low-SNR regime, by achieving higher ergodic rate. Diversity analysis confirms that the CRS-NOMA achieves full diversity order using both SC and MRC schemes, and this diversity order depends on both the shape parameter m and the number of receive antennas. We also discuss the problem of optimal power allocation for the minimization of the outage probability of the system, and subsequently use this optimal value to obtain the ergodic rate. An excellent match is observed between the numerical and the analytical results, confirming the correctness of the derived analytical expressions. INDEX TERMS Non-orthogonal multiple access, cooperative communications, relaying, Nakagami-m fading, ergodic rate, outage probability, diversity order. 1. Note that the analysis of the ergodic rate in the high-SNR regime was not presented in [10].