Jointly Optimal Precoder and Power Allocation for an Amplify-and-Forward Half-Duplex Relay System

To improve the bandwidth efficiency, a semi-blind channel estimation method using data nulling superimposed pilots (DNSP) is designed for orthogonal frequency division multiplexing (OFDM) system without data rate loss. However, the data distortion is introduced by rank-deficient precoding. To minimize the data distortion, the optimal precoder is found to minimize the Euclidean distance between precoded sequence and source sequence. Further, the impact of power allocation between training sequence and data information on effective signal noise ratio (SNR) is analytically derived, effective SNR is found to be a quadratic function for the percentage allocated for training sequence, and the optimal power allocation is provided to maximize the effective SNR. Simulation results show that our optimal precoder design and power allocation scheme obtain the optimal performance of symbol detection.

For data services over satellite networks, the efficient management of satellite downlink communication resources is crucial for economic competitiveness of the medium. To support a broad spectrum of users with small terminals at high rates, narrow transmit spotbeams on the satellite will be used. Since satellite transmitter resources are expensive and there can be many spotbeam-coverage cells within the satellite service area, it is attractive to use some form of agile scanning beam system and to time-share these precious resources. An optimized design of the multibeam antenna pattern and scheduling can further improve the efficiency of transmission and power management. In this paper, the advantage of parallel multibeams in terms of spectral efficiency and power gain is shown, and the issue of multibeam power allocation based on traffic demands and channel conditions over satellite downlinks with power and delay constraints is addressed. The study indicates that the use of a parallel multibeam scheme with optimum power allocation can achieve a substantial power gain and reasonable proportional fairness. By coupling power allocation with multibeam scheduling when the number of active beams is smaller than the number of cells, the authors show that a modest number of active parallel beams are sufficient to cover many cells efficiently.

This paper proposes an optimal power allocation method for two-way decode-and-forward (DF) relay networks when transmit power values at source nodes are the same. In this paper we consider the multiple access (MAC) capacity for DF relaying scheme. Using case studies, it analytically determines the optimal power values for the two source nodes and one relay node. The achievable sum rate is maximized under a sum power constraint for given squared magnitude of the channel coefficients. Finally, numerical results show that the achievable sum rate for proposed optimum power allocation is greater than or equal to that for equal power allocation.

In this paper, we propose a dynamic power allocation scheme for a single-relay network based on orthogonal frequency division multiplexing (OFDM) modulation with limited feedback.We consider an Amplify-and-Forward (AF) cooperative diversity model, where one source node communicates with one destination node assisted by one half duplex relay. The power allocation scheme employs a codebook of quantized power allocation vectors designed offline equipped on the source, relay, and destination. The destination, who has full knowledge of channel state information (CSI), chooses the best power allocation vector and sends back its index to the source and relay nodes, which results in a dramatic reduced overhead over conventional resource allocation. First we achieve the optimal power allocation solution as the function of channel realizations with maximum capacity. Then we present an adaptation of the Lloyd algorithm to construct a codebook to quantize the optimal power allocation vectors subject to the amount of feedback. Simulations show that a negligible performance loss could be achieved with just a few feedback bits at different levels of SNRs.

In this paper, we investigate the optimal power and time allocation for a wireless relay network, called BCFR (Broadcasting Channel with Fixed Relay), where the relay node is limited by the half-duplex operation. Introducing a relay in two-node broadcasting channel for a node which has a link of bad quality or requires higher transmission rate enlarges the rate region with well-designed power and time allocation. Also, BCFR is a common component of many relay networks, in which either orthogonal or non-orthogonal transmission can be adopted at the information source node. In particular, for the non-orthogonal transmission, the layered transmission with superposition coding is applied at the source node. By deriving the optimal power and time-fraction allocation at each node of BCFR, we show that the non-orthogonal structure enhances the capacity region and achieves higher log-sum capacity than the orthogonal transmission.

Virtual multiple-input-multiple-output (MIMO) systems using multiple antennas at the transmitter and a single antenna at each of the receivers have recently emerged as an alternative to point-to-point MIMO systems. This paper investigates the relationship between energy efficiency (EE) and spectral efficiency (SE) for a virtual-MIMO system that has one destination and one relay using compress-and-forward (CF) cooperation. To capture the cost of cooperation, the power allocation (between the transmitter and the relay) and the bandwidth allocation (between the data and cooperation channels) are studied. This paper derives a tight upper bound for the overall system EE as a function of SE, which exhibits good accuracy for a wide range of SE values. The EE upper bound is used to formulate an EE optimization problem. Given a target SE, the optimal power and bandwidth allocation can be derived such that the overall EE is maximized. Results indicate that the EE performance of virtual-MIMO is sensitive to many factors, including resource-allocation schemes and channel characteristics. When an out-of-band cooperation channel is considered, the performance of virtual-MIMO is close to that of the MIMO case in terms of EE. Considering a shared-band cooperation channel, virtual-MIMO with optimal power and bandwidth allocation is more energy efficient than the noncooperation case under most SE values.

In this paper, we study the power allocation of suggested cognitive relay network model to minimize the system outage probability subject to total and individual power constraints for cognitive relays and subject to interference constraints for primary user nodes. In suggested model, a source is assisted by cognitive relay nodes which allow coexisting with primary user nodes by imposing severe constraints on the transmission power so that they operate below the noise floor of primary nodes. A relay transmission scheme, namely, amplify-and-forward (AF) is considered. We present an optimal power allocation (OPA) scheme to minimize the system outage probability, based on complete channel state information among the source, destination and relay nodes and mean channel gains between primary user nodes and cognitive relays. The analytical power allocation strategies have been validated through numerical simulations. The results indicate that the AF with OPA has significantly better outage behavior and average throughput than AF scheme.

In this paper, PEP (pairwise error probability) is derived for MIMO systems in the presence of channel estimation error, where the channel is estimated using training insertion and linear channel estimation. This training-based PEP expression is utilized to design the training sequence and for optimal power allocation between the training and data symbols. The loss of coding gain due to the training is quantified at high SNR. It is shown that both the proposed PEP-based and the existing capacity-based optimal training approach of B. Hassibi and B. Hochwald (IEEE Trans. Inform. Theory, vol. 49, no. 4, pp. 951-963, 2003) reveal the same power allocation for constant modulus (CM) constellations. The performance of our optimal power allocation scheme falls between the nonoptimized equal power allocation and perfectly known channel cases, and converges to the latter for larger data transmission intervals. Numerical and simulation results are presented to justify the usefulness of our analytical findings.

In this paper, we propose a cooperative spectrum sharing protocol based on OFDM two-way relaying with joint optimal subcarrier and power allocation. Specifically, the secondary system helps the primary system achieve their target rates through OFDM two-way relaying, where the secondary system forwards the primary signal by using a fraction of subcarriers and power. In return, the secondary system can gain spectrum access by using the remaining subcarriers and power to transmit its own signal. Joint optimal subcarrier and power allocation is derived aiming to maximize secondary transmission rate with primary transmission rate constraint. Simulation results demonstrate a significant enhancement in spectrum efficiency compared with several benchmark schemes.

This paper investigates an unmanned aerial vehicle (UAV) enabled full-duplex relaying system. By assuming that the UAV follows a circular trajectory and applies decode-and-forward relaying strategy, we study the joint design of beamforming and power allocation to maximize the instantaneous data rate, under both the individual and the sum power constraints over the source and relay nodes. As the problem is non-convex, we propose an efficient sub-optimal solution based on block-coordinate descent method by decomposing the problem into two sub-problems: a beamforming optimization sub-problem with given power allocation and a power allocation sub-problem with fixed beamforming. For the beamforming design sub-problem, the optimal solution is obtained based on the semi-definite relaxation technique. For the power allocation sub-problem, the optimal solution is obtained in closed form. Then, the closed-form cumulative distribution function and outage probability expressions for sub-optimal beamforming with both uniform power allocation and optimal power allocation are derived. In addition, simple and informative high signal-to-noise ratio (SNR) approximations for outage probability expressions are presented to gain insights. Finally, the optimal flying altitude that minimizes the average outage probability is obtained via one-dimensional search.

We consider power allocation and relay positioning with the objective to minimize system error probability in a dual-hop regenerative relaying system operating under co-channel interference. First, assuming fixed relay location, adaptive power allocation at the source and the relay nodes under joint power constraint is presented. Then considering fixed power allocation scheme, the optimal relay position is obtained. Results show that optimum power allocation, optimum relay location and joint optimization of the power allocation and relay positioning significantly improve the system performance in terms of error probability compared to uniform power allocation and mid-point distance location for the relay node.

Cognitive radio (CR) technology has been developed to solve the spectrum-underutilization problem. In CR networks, the CR users have opportunities to access the licensed spectrum bands assigned to the primary users (PUs). Since the PUs have priorities to use the bands, the CR users are not allowed to generate unacceptable interference to them. In this paper, we investigate power allocation schemes for source and relay nodes in CR with direct and relay link. We show that there is a significant benefit to the system rate by jointly distributing the transmitting power. Three schemes are considered, where particularly the scheme based on analogue network coding shows significant superior performance to other two classic schemes. The optimum power allocation is derived analytically. The proposed schemes are verified by the simulations which also show the impact of different positions of relay node and the primary user locations on power allocation solutions.

In this paper, we consider an amplify-and-forward wireless relay system where multiple source nodes communicate with their corresponding destination nodes with the help of relay nodes. Conventionally, each relay equally distributes the available resources to its relayed sources. This approach is clearly sub-optimal since each user experiences dissimilar channel conditions, and thus, demands different amount of allocated resources to meet its quality-of-service (QoS) request. Therefore, this paper presents novel power allocation schemes to i) maximize the minimum signal-to-noise ratio among all users; ii) minimize the maximum transmit power over all sources; iii) maximize the network throughput. Moreover, due to limited power, it may be impossible to satisfy the QoS requirement for every user. Consequently, an admission control algorithm should first be carried out to maximize the number of users possibly served. Then, optimal power allocation is performed. Although the joint optimal admission control and power allocation problem is combinatorially hard, we develop an effective heuristic algorithm with significantly reduced complexity. Even though theoretically sub-optimal, it performs remarkably well. The proposed power allocation problems are formulated using geometric programming (GP), a well-studied class of nonlinear and nonconvex optimization. Since a GP problem is readily transformed into an equivalent convex optimization problem, optimal solution can be obtained efficiently. Numerical results demonstrate the effectiveness of our proposed approach.

Optimal power allocation for a full-duplex multicarrier decode-forward relay system with or without direct link

We investigate a power allocation optimization problem under the scenario of multiple cooperative relays and one destination with multiple receiving antennas. We consider the relay protocol, decode and forward (DAF). An optimal power allocation scheme (OPA), through singular value decomposition (SVD) of the channel matrix, is developed among the relay nodes under a certain power constraint to achieve the maximum channel capacity. The expression of the optimal power allocation coefficient is derived using Lagrange multiplier. Simulation results show that the OPA can obtain higher capacity gain and lower outage probability comparing with the uniform power allocation (UPA) scheme. Moreover, we show that the OPA with DAF has better performance than it with AAF.