ABSTRACT We consider joint power allocation (PA) and relay positioning in a dual‐hop regenerative relay system with multiple antennas equipped at the destination. With a fixed relay location, an adaptive PA strategy at the source and relay under a sum power constraint that minimizes the system outage probability is presented. With a fixed PA strategy, the optimal relay location is derived. We then propose to jointly optimize PA and relay location. It is shown that employing more destination antennas and/or choosing an appropriate relay location can significantly save the power needed at the relay. Numerical results are presented to demonstrate the performance of the proposed PA and relay positioning algorithms. Copyright © 2011 John Wiley & Sons, Ltd.

We analyze the achievable diversity-multiplexing tradeoff (DMT) in MIMO fading channels with two-way channel training. We first consider a typical training scenario, where the transmitter transmits training symbols followed by data symbols, and the receiver performs channel estimation using the training symbols and then uses the imperfect channel estimates to decode the data symbols. It turns out that as long as the training power is equal to the data power, the obtained DMT based on imperfect channel state information at receiver (CSIR) is the same as the original DMT result with perfect CSIR given in Zheng and Tse's seminal work. We further extend our analysis to two-way training scenarios, with single and multiple training rounds. Our results show that two-way training together with power control further significantly improves the achievable diversity gain. In particular, we show that if the multiplexing gain is larger than a certain value, no training can help get any diversity and therefore the achievable diversity is zero.

We investigate the impact of imperfect channel state information at the transmitter (CSIT) on the diversity gain in dynamic decode-and-forward (DF) relaying channels. A diversity and multiplexing tradeoff analysis is presented, which reveals that power control based on imperfect CSIT significantly improves the achievable diversity gain. It is found that if the multiplexing gain is higher than 1/2, the achievable diversity gain only depends on the CSIT of the source-destination (S-D) link and the relay-destination (R-D) link; otherwise the CSIT of the source-relay (S-R) link might also contribute. It is also found that the CSIT of the R-D link does not contribute to the overall diversity gain if the source has no CSIT. The presented results show that dynamic DF relaying supports not only a higher multiplexing gain but also a higher diversity gain than conventional DF relaying protocols.

We analyze the impact of imperfect channel state information at the transmitter and receiver (CSITR) on the achievable diversity gain in multi-input multi-output (MIMO) fading channels with joint rate and power control. With rate control only, we consider the system with and without a minimum spatial multiplexing gain constraint, respectively. With joint rate and power control, we show that the achievable diversity gain can be improved significantly. The conducted analysis adopts the diversity-multiplexing tradeoff framework and uses the notions of diversity gain and multiplexing gain to study the impact of noisy CSITR in MIMO fading channels.

The achievable diversity and multiplexing tradeoff (DMT) in MIMO fading channels with channel training is analyzed in this paper. We first consider a typical training scenario, where the transmitter transmits training symbols followed by data symbols, and the receiver performs channel estimation using the training symbols and then uses the imperfect channel estimates to decode the data symbols. From the DMT perspective, our results show that as long as the training power is equal to the data power, the obtained DMT result based on imperfect channel state information at receiver (CSIR) is the same as the original DMT result with perfect CSIR given in Zheng and Tse's seminal work . We extend the analysis to two-way training scenarios, with single and multiple training rounds. Our results show that two-way training together with power control can substantially improve the achievable diversity gain. Specifically, the achievable DMT with multiple training rounds can be described as a single straight line; while in the case of single training round, the achievable DMT is much lower and can be described as a single straight line or a collection of line segments, depending on the underlying training strategy and channel qualities.

In this paper, we study the impact of imperfect channel state information at the transmitter and receiver (CSITR) on the diversity-multiplexing tradeoff in single-input multi-output (SIMO)/multi- input single-output (MISO) fading channels with two- way training. We consider two two-way training strategies: 1) the destination initiates the training, and 2) the source initiates the training. We show that for time division duplex (TDD) systems, imperfect CSITR significantly improves the optimal diversity gain through two-way training and power control.

In this paper, we investigate the impact of imperfect channel state information at the transmitters (CSIT) on the achievable diversity gain in a cooperative relaying channel with multiple destination antennas, where the CSIT comes from channel estimation at the transmitters. Both decode-and-forward (DF) and amplify-and-forward (AF) relaying protocols are considered. We show that transmit power control based on the imperfect CSIT significantly improves the achievable diversity gain. The diversity and multiplexing tradeoff (DMT) as a function of the CSIT quality of the source-relay link, source-destination link and relay-destination link is derived for each of the considered relaying schemes. An upper bound on the DMT of the relaying channel is also provided.

Two-way amplify-and-forward relaying is considered in this paper. We propose adaptive power allocation (PA) algorithms to maximize the instantaneous achievable rate and minimize the system outage probability, respectively. Both single- and multi-relay systems are considered. It is shown that the proposed adaptive PA algorithms significantly outperform the uniform PA algorithms. Furthermore, exploiting multiple relays obtains higher diversity order and lower outage probability than using only one relay, at the price of a lower achievable information rate. The relay locations and relay selection are also taken into account to further improve the system performance.

In this paper, we investigate the impact of imperfect channel state information at the transmitter (CSIT) on the fundamental tradeoff of diversity and multiplexing in multi-input multi-output (MIMO) fading channels. We show that through power adaptation, a higher diversity gain as well as a more efficient diversity-multiplexing tradeoff can be achieved than the reported results in literature. Our analysis reveals that imperfect CSIT significantly improves the achievable diversity gain while enjoying the full spatial multiplexing gain.

In this paper, we consider the uplink of a Direct Sequence Code Division Multiple Access (DS-CDMA) system, where the source users cooperate in relaying each other's message to the destination node based on the decode-and-forward relaying protocol. We study the following partner selection strategies: 1. each user helps all other users (All-Cooperate); 2. each user helps all successfully decoded users (Sue-Cooperate); 3. each user helps a user with the maximum observed signal-to-(interference plus noise) ratio (Max-Cooperate). To mitigate the multiple access interference (MAI) due to the usage of non-orthogonal spreading codes, we develop MMSE multiuser detectors at both the cooperative users and the destination node and evaluate the bit-error-rate (BER) performance. Simulation results show that the cooperative relaying significantly outperforms the direct transmission. Among the three partner selection strategies, Max- Cooperate achieves the lowest average BER. It is found that when the number of users increases, the BER performance of direct transmission gets worse, but the BER performance of Max- Cooperate improves significantly. For All-Cooperate and Sue- Cooperate selection strategies, the number of users does not have much impact on the BER performance.

The authors consider a dual-hop multi-relay cooperative relay system in this study. Both decode-and-forward (DF) and amplify-and-forward (AF) protocols are considered. Under different relay selection strategies, the authors derive closed-form outage probability expressions. With the second-order channel statistics, the authors propose to jointly optimise power allocation (PA) and relay positions in order to minimise the system outage probability. Simulation results show that the proposed adaptive allocation algorithms significantly outperform fixed allocation algorithms. With the proposed joint optimisation algorithm, AF relaying outperforms DF relaying when multiple relays are selected to help. When only the best relay is selected to help, DF relaying is shown to have better performance.

We consider a two-hop relaying system with multiple antennas deployed at the destination node in this paper. The relay node is regenerative and working in half-duplex mode. We propose adaptive power allocation (PA) algorithms under joint transmit power constraint in order to minimize outage probability, instantaneous symbol-error-rate (SER) upper bound and average SER upper bound with the assumption that perfect channel state information (CSI) is known at all nodes. Simulation results show that the proposed adaptive PA algorithms outperform uniform PA and direct transmission. It is also found that the more antennas are deployed at the destination, the less power will be needed to allocate to the relay node in order to satisfy the optimization criteria.