Resource allocation in cooperative relay MIMO systems

ABSTRACTBy combining Spatial modulation (SM) with cooperative communication, the diversity gain brought by cooperative relaying and high rate of SM can be obtained. In this paper, considering amplify-and-forward (AF) protocol, the performance of cooperative SM system with imperfect channel state information (CSI) over Rayleigh channel is analyzed. According to the performance analysis, the moment generating functions (MGFs) of effective signal-to-noise ratios (SNRs) are derived. With the MGFs, closed-form expressions of the error probability of antenna index detection and the error probability of symbol detection for imperfect CSI are achieved. Thereby, the approximate overall average bit error ratio (BER) is obtained, and these theoretical expressions include those under perfect CSI as special cases. Besides, the asymptotically approximate BER for large SNR is also derived. Based on this, a suboptimal power allocation (PA) scheme is developed, and the corresponding PA coefficients are attained by minimizing the asymptotical BER. As a result, closed-form PA can be attained for the system with multiple receive antennas. Computer simulations show that the theoretical BERs are close to the corresponding simulated results, which illustrates the effectiveness of the derived theoretical expressions. Compared with the conventional equal PA scheme, the proposed PA scheme enhances the BER performance efficiently.

In this paper, cross-layer design methods are proposed for jointly detecting data streams and dynamically allocating power within a multiple-input multiple-output two-phase cooperative wireless communication system operating in a spatial multiplexing configuration and with single and multiple decode-and-forward (DF) relays. The proposed joint detection and power allocation schemes employ a maximum likelihood rule, which gives rise to an efficient cooperative sphere detector and algorithms to adjust the power levels of all links in an alternating strategy. Simulation results show Bit Error Rate (BER) comparisons between the system with no cooperation, equally distributed power allocation with cooperation, and the proposed power allocation scheme for single and multiple relay systems for different conditions and scenarios.

A multihop regenerative relay system is considered. We explore adaptive power allocation (PA) under a total power constraint to minimize the system error probability when the perfect channel state information (CSI) is known at the transmitters. We propose adaptive PA schemes with limited feedback when the transmitters have no perfect knowledge of CSI. Simulation results demonstrate the good performance of the proposed PA scheme with perfect CSI. When no perfect CSI is available at the transmitters, the proposed PA schemes with a small number of feedback bits are able to achieve very close performance to the adaptive PA with perfect CSI.

This paper considers a two-hop orthogonal frequency division multiple (OFDM) wireless communication systems with a source, a decode-and-forward (DF) relay and a destination. We develop a low complexity rate adaptive power allocation strategy at the source and the relay, with respect to individual transmit power constraints, if the channel state information at the transmitter is given. To further enhance the rate of the considered systems, the OFDM sub-carriers of source to relay (SR) and relay to destination (RD) are selected and paired according to their actual channel states. Computer simulations are carried out to evaluate the proposed power allocation and sub-carriers selecting-pairing approaches.

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.

For the next generation wireless communication system, Multi carrier Code Division Multiple Access (MC-CDMA) has become very appealing scheme due to due to high data rates and interference limiting factors. In this research work we analyzes the capacity of MC-CDMA system using adaptive power and sub-channel allocation under perfect, imperfect and predicted channel state information (CSI). The transmitter and receiver both have been targeted in this paper. The proposed scheme is a novel idea that divides the sub-channels into small groups. Each group is assigned power according to the Eigen values and gain of the each sub-channel in that specific group. The receiver calculates optimal feedback vector for the transmitter by calculating the bit error rates using the above strategy and selects the optimal feedback vector. The simulations show that the usage of joint power and sub-channel allocation outperforms the capacity of the system. The capacity of the system is highly improved using adaptive power and sub-carriers allocation along with CSI prediction. The simulation results have been carried out for other power allocation schemes available in literature and results have been compared with perfect, imperfect and predicted CSI.

In this paper, we investigate the joint optimization of power allocation and subcarrier assignment in the OFDM bidirectional systems where two users exchange data assisted by multiple decode-and-forward (DF) relays. We assume the availability of imperfect channel state information (CSI) that contains a probabilistic uncertainty component and consider its worst effect when performing resource allocation. Moreover, we adopt dynamic network coding to exploit channel diversity. The objective of the resource allocation problem is to maximize the weighted sum rates of the two users subject to quality-of-service (QoS) requirements and individual power constraints. We formulate the problem as a mixed integer programming problem and solve it efficiently in an asymptotic manner by using the dual method. Simulation results show that the proposed scheme is robust to imperfect CSI and provides better performance compared to the scheme with static network coding.

Wireless amplify-and-forward relay networks in which the source communicates with the relays and destination in the first phase and the relays forward signals to the destination in the second phase over orthogonal and uncorrelated Rayleigh fading channels are considered. Convex programming is used to obtain optimal and approximately optimal power allocation schemes to maximize the average signal-to-noise ratios at the output of the receiver filters under two different assumptions of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">partial</i> channel state information (CSI). Analysis and simulation results demonstrate the superiority of the proposed power allocation schemes over the equal-power allocation scheme. Performance comparison to the extreme cases of i) direct transmission between the source and destination and ii) having full CSI is made to illustrate the gain and loss, respectively, of the proposed schemes. The impact of power allocation between the source and relays is also investigated by computer simulation.

This paper addresses the downlink transmission strategies with dynamic resource allocation for multiuser MIMO-OFDM systems. The ultimate objective is to maximize the sum rate capacity subject to average power constraints. Considering that the performance of conventional Orthogonal Frequency Division Multiple Access (OFDMA) is limited by users' exclusive use to subcamer, while Dirty Paper Coding (DPC) is capable of supporting multiple users, we propose joint subcarrier and power allocation and precoding schemes based on OFDMA combined with DPC, which is called DPC-OFDMA. The analysis is considered in two stages with channel state information (CSI) at transmitter. The first stage applies water-filling method to address subcarriers allocation, in which users are allowable to share subcarriers. The second stage employs DPC combined with preceding to deal with simultaneous transmissions of the users sharing the same subcarriers. An efficient algorithm to choose the best possible ordering of users for DPC and the optimal preceding design of each user are also involved. To reduce the complexity for practice, two simplified strategies are proposed. One is called suboptimal DPC-OFDMA, where the number of users using the same subcamer is restricted. Another employs beamfonning (BF) at every subcamer referred as BF-DPC-OFDMA. Simulation results show that the proposed simplified strategies can approach the optimal performance for most cases, and have higher spectral efficiency than conventional time-sharing OFDMA.

This paper proposes using cooperative relays to improve the ergodic secrecy capacity (ESC) of a multi-hop decode-and-forward (DF) relaying system where communication takes place in the presence of multiple non-colluding eavesdroppers. The proposed scheme is based on a recent approach to generate artificial noise in which transmitter of each hop allocates a portion of its power for generating an intentional interference at the eavesdroppers. Under the assumption that the transmitters can only use limited transmit power, a power allocation strategy has been developed which maximizes the secrecy capacity by optimally distributing the power between the original signal and the artificial noise. Since the optimal solution depends on the channel state information (CSI) of the eavesdroppers, which is difficult to obtain in practice, a sub-optimal solution is also presented in which the CSI of the eavesdroppers is not needed.

We consider the secure transmission of information over an ergodic fading channel in the presence of an eavesdropper. Our eavesdropper can be viewed as the wireless counterpart of Wyner's wiretapper. The secrecy capacity of such a system is characterized under the assumption of asymptotically long coherence intervals. We analyze the full channel state information (CSI) case, where the transmitter has access to the channel gains of the legitimate receiver and eavesdropper, and the main channel CSI scenario, where only the legitimate receiver channel gain is known at the transmitter. In each scenario, the secrecy capacity is obtained along with the optimal power and rate allocation strategies. We then propose a low-complexity on/off power allocation strategy that achieves near-optimal performance with only the main channel CSI. More specifically, this scheme is shown to be asymptotically optimal as the average SNR goes to infinity, and interestingly, is shown to attain the secrecy capacity under the full CSI assumption. Remarkably, our results reveal the positive impact of fading on the secrecy capacity and establish the critical role of rate adaptation, based on the main channel CSI, in facilitating secure communications over slow fading channels.

In this paper, we analyze and compare the outage probabilities of selection relaying protocols for cooperative communications in wireless networks. Depending on the quality of the source-relay channel, the relay may choose either decode-and-forward (DF), amplify-and-forward (AF), or direct-transmission (DT) to forward signals. It turns out that in terms of outage probability, two selection relaying protocols are better than others: either selection between DF and AF protocols (DF-AF) or selection between DF and DT protocols (DF-DT). We show that with an equal power allocation at the source and the relay, both the DF-AF and DF-DT selection protocols have the same asymptotic outage probability. However, with an optimum power allocation strategy, the DF-AF selection is in general better than the DF-DT selection. Simulations are also presented to validate the analytical results.

In this letter, the outage probabilities of selection relaying protocols are analyzed and compared for cooperative wireless networks. It is assumed that both source and relay use equal allocated time in transmission. Depending on the quality of the source-relay channel, the relay may choose either Decode-and-Forward (DF), Amplify-and-Forward (AF), or Direct-Transmission (DT) to forward signals. It turns out that in terms of outage probability, two selection relaying schemes are better than others: selecting between DF and AF protocols (DF-AF) or selecting between DF and DT protocols (DF-DT). It is shown that with an equal power allocation, both of the DF-AF and DF-DT selection relaying protocols have the same asymptotic outage probability. However, with an optimum power allocation strategy, the DF-AF selection scheme is in general better than the DF-DT selection scheme. Note that the optimum power allocations depend on channel variances, not on instantaneous channel gains. When the quality of the relay-destination link is much better than that of the source-relay link, observed from simulation, the outage probability of the DF-AF selection protocol with its optimum power allocation is 1.5 dB better than that of the DF-DT selection with its own optimum power allocation. Extensive simulations are presented to validate the analytical results.

A low complexity power allocation scheme for NOMA-based indoor VLC systems

In this paper, the optimal channel capacity of cooperative system with or without channel state information (CSI) has been analyzed by simultaneously taking both relay location and power allocation into consideration. The proposed model is a dual-hop relay system with signal from a source to a destination through the relay using the decode-and-forward (DF) strategy. The numerical results show that the optimal channel capacity of system with CSI is significantly better than the one without CSI.