BER and optimal power allocation for amplify-and-forward relaying using pilot-aided maximum likelihood estimation

Bit error rate (BER) and outage probability for amplify-and-forward (AF) relaying systems with two different channel estimation methods, disintegrated channel estimation and cascaded channel estimation, using pilot-aided maximum likelihood method in slowly fading Rayleigh channels are derived. Based on the BERs, the optimal values of pilot power under the total transmitting power constraints at the source and the optimal values of pilot power under the total transmitting power constraints at the relay are obtained, separately. Moreover, the optimal power allocation between the pilot power at the source, the pilot power at the relay, the data power at the source and the data power at the relay are obtained when their total transmitting power is fixed. Numerical results show that the derived BER expressions match with the simulation results. They also show that the proposed systems with optimal power allocation outperform the conventional systems without power allocation under the same other conditions. In some cases, the gain could be as large as several dB's in effective signal-to-noise ratio

Dispensing with channel estimation: differentially modulated cooperative wireless communications

As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective

Non-coherent successive relaying and cooperation: principles, designs, and applications

Cooperative communication is capable of forming a virtual antenna array for each node (user) in a network by allowing the nodes (users) to relay the messages of others to the destination. Such a relay aided network may be viewed as a distributed multiple-input multiple-output (MIMO) system relying on the spatially distributed single antennas of the cooperating mobiles, which avoids the correlation of the antenna elements routinely encountered in conventional MIMO systems and hence attains the maximum achievable diversity gain. Therefore, the family of cooperative communication techniques may be regarded as a potential solution for future wireless networks. However, constrained by the half-duplex transmit/receive mode of most practical transceivers, the cooperative networks may impose a severe 50% throughput loss. As a remedy, successive relaying can be employed, which is capable of mimicking a full-duplex relay and thereby recovering much of the 50% throughput loss. Furthermore, for the sake of bypassing power-hungry and potentially excessive-complexity channel estimation, noncoherent detection techniques may be employed for multiple-antenna aided systems, because estimating all the associated channels may become unrealistic. Explicitly, the mobile-stations acting as relays cannot be realistically expected to estimate the source-to-relay channels. In order to motivate further research on noncoherent successive relaying aided systems, a comprehensive review of its basic concepts, fundamental principles, practical transceiver designs and open challenges is provide

Performance analysis for cooperative wireless communications

Cooperative relaying has been proposed as a promising solution to mitigate and combat the deleterious effects of fading by sending and receiving independent copies of the same signal at different nodes. It has attracted huge attention from both industry and academia. The purpose of this thesis is to provide an analytical performance evaluation of the cooperative wireless systems while taking some realistic conditions into consideration. To achieve this, first, performance analysis of amplify-and-forward (AF) relaying using pilot-aided maximum likelihood estimation is studied in this thesis. Both disintegrated channel estimation (DCE) and cascaded channel estimation (CCE) are considered. Based on this analysis, optimal energy allocation is proposed. Then, performance analysis for AF relaying corrupted by interferers are investigated. Both randomly distributed and fixed interferers are considered. For random interferers, both the number and the locations of the interferers are random while for fixed interferers, both the number and the locations are fixed. Next, multihop relaying and multiple scattering channels over α - μ fading are analyzed. Channels with interferences and without interferences are considered. Exact results in the form of one-dimensional integral are derived. Also, approximate results with simplified structure and closed-form expressions are provided. Finally, a new hard decision fusion rule that combines arbitrary numbers of bits for different samples taken at different nodes is proposed. The best thresholds for the fusion rules using 2 bits, 3 bits and 4 bits are obtained through simulation. The bit error rate (BER) for hard fusion rule with 1 bit is provided. Numerical results are presented to show the accuracy of our analysis and provide insights. First, they show that our optimal energy allocation methods outperform the conventional system without optimal energy allocation, which could be as large as several dB’s in some cases. Second, with the increase of signal-to-interference-plus-noise ratio (SINR) for AF relaying with interference, the outage probability decreases accordingly for both random and fixed interferers. However, with the change of interference-to-noise ratio (INR) but with the SINR fixed, the outage probability for random interferers change correspondingly while the outage probability for fixed interferers remains almost the same. Third, our newly derived approximate expressions are shown to have acceptable performances in approximating outage probability in wireless multihop relaying system and multiple scattering channel considering interferences and without interferences. Last, our new hard decision fusion rule is shown to achieve better performance with higher energy efficiency. Also they show that there is a tradeoff between performance and energy penalty in the hard decision fusion rule

Pilot-based channel estimation for AF relaying using energy harvesting

In existing channel estimators for amplify-andforward relaying, pilots are often sent from the relay to the destination which consumes the relay’s own energy. This limits the relay’s participation in the network. In this paper, several moment-based channel estimators for amplify-and-forward relaying are proposed that harvest energy from the source and using the harvested energy to send pilots to the destination for channel estimation. Both time-switching and power-splitting strategies are considered. Numerical results show that the two schemes that perform channel estimation only at the destination have worse performances than the two schemes that perform channel estimation at both the relay and the destination. They also show that the bit error rate performances of all schemes are close to the perfect case when exact knowledge of the channel state information is available such that there is no channel estimation error in the demodulation. The assumption that the two schemes only perform channel estimation at the destination makes them simpler, as they do not require channel estimation at the relay or feed the channel estimate back to the destination