4 research outputs found
Relay Selection for Two-way Relaying with Amplify-and-Forward Protocols
In this paper, we propose a relay selection amplify-and-forward (RS-AF)
protocol in general bi-directional relay networks with two sources and
relays. In the proposed scheme, the two sources first transmit to all the
relays simultaneously, and then a single relay with a minimum sum symbol error
rate (SER) will be selected to broadcast the received signals back to both
sources. To facilitate the selection process, we propose a simple sub-optimal
Min-Max criterion for relay selection, where a single relay which minimizes the
maximum SER of two source nodes will be selected. Simulation results show that
the proposed Min-Max selection has almost the same performance as the optimal
selection with lower complexity. We also present a simple asymptotic SER
expression and make comparison with the conventional all-participate
amplify-and-forward (AP-AF) relaying scheme. The analytical results are
verified through simulations. To improve the system performance, optimum power
allocation (OPA) between the sources and the relay is determined based on the
asymptotic SER. Simulation results indicate that the proposed RS-AF scheme with
OPA yields considerable performance improvement over an equal power allocation
(EPA) scheme, specially with large number of relay nodes.Comment: 19 pages, 6 figure
Soft information based protocols in network coded relay networks
Future wireless networks aim at providing higher quality of service (QoS) to mobile users. The emergence of relay technologies has shed light on new methodologies through which the system capacity can be dramatically increased with low deployment cost. In this thesis, novel relay technologies have been proposed in two practical scenarios: wireless sensor networks (WSN) and cellular networks. In practical WSN designs, energy conservation is the single most important requirement. This thesis draws attention to a multiple access relay channels model in the WSN. The network coded symbol for the received signals from correlated sources has been derived; the network coded symbol vector is then converted into a sparse vector, after which a compressive sensing (CS) technique is applied over the sparse signals. A theoretical proof analysis is derived regarding the reliability of the network coded symbol formed in the proposed protocol. The proposed protocol results in a better bit error rate (BER) performance in comparison to the direct implementation of CS on the EF protocol. Simulation results validate our analyses. Another hot topic is the application of relay technologies to the cellular networks. In this thesis, a practical two-way transmission scheme is proposed based on the EF protocol and the network coding technique. A trellis coded quantization/modulation (TCQ/M) scheme is used in the network coding process. The soft network coded symbols are quantized into only one bit thus requiring the same transmission bandwidth as the simplest decode-and-forward protocol. The probability density function of the network coded symbol is derived to help to form the quantization codebook for the TCQ. Simulations show that the proposed soft forwarding protocol can achieve full diversity with only a transmission rate of 1, and its BER performance is equivalent to that of an unquantized EF protocol
Optimum Power Allocation for Cooperative Communications
Cooperative communication is a new class of wireless communication techniques in which wireless nodes help each other relay information and realize spatial diversity advantages in a distributed manner. This new transmission technique promises significant performance gains in terms of link reliability, spectral efficiency, system capacity, and transmission range. Analysis and design of cooperative communication wireless systems have been extensively studied over the last few years. The introduction and integration of cooperative communication in next generation wireless standards will lead to the design of an efficient and reliable fully-distributed wireless network. However, there are various technical challenges and open issues to be resolved before this promising concept becomes an integral part of the modern wireless communication devices.
A common assumption in the literature on cooperative communications is the equal distribution of power among the cooperating nodes. Optimum power allocation is a key technique to realize the full potentials of relay-assisted transmission promised by the recent information-theoretic results. In this dissertation, we present a comprehensive framework for power allocation problem. We investigate the error rate performance of cooperative communication systems and further devise open-loop optimum power allocation schemes to optimize the performance. By exploiting the information about the location of cooperating nodes, we are able to demonstrate significant improvements in the system performance.
In the first part of this dissertation, we consider single-relay systems with amplify-and-forward relaying. We derive upper bounds for bit error rate performance assuming various cooperation protocols and minimize them under total power constraint. In the second part, we consider a multi-relay network with decode-and-forward relaying. We propose a simple relay selection scheme for this multi-relay system to improve the throughput of the system, further optimize its performance through power allocation. Finally, we consider a multi-source multi-relay broadband cooperative network. We derive and optimize approximate symbol error rate of this OFDMA (orthogonal frequency division multiple access) system
Mathematical optimization and signal processing techniques for cooperative wireless networks
The rapid growth of mobile users and emergence of high data rate multimedia and interactive services have resulted in a shortage of the radio spectrum. Novel solutions are therefore required for future generations of wireless networks to enhance capacity and coverage. This thesis aims at addressing this issue through the design and analysis of signal processing algorithms. In particular various resource allocation and spatial diversity techniques have
been proposed within the context of wireless peer-to-peer relays and coordinated base station (BS) processing.
In order to enhance coverage while providing improvement in capacity, peer-to-peer relays that share the same frequency band have been considered and various techniques for designing relay coefficients and allocating powers optimally are proposed. Both one-way and two-way amplify and forward (AF) relays have been investigated. In order to maintain fairness, a signal-to-interference plus noise ratio (SINR) balancing criterion has been adopted. In order to improve the spectrum utilization further, the relays within the context of cognitive radio network are also considered. In this case, a cognitive peer-to-peer relay network is required to achieve SINR balancing while maintaining the interference leakage to primary receiver below a certain threshold.
As the spatial diversity techniques in the form of multiple-input-multipleoutput (MIMO) systems have the potential to enhance capacity significantly, the above work has been extended to peer-to-peer MIMO relay networks. Transceiver and relay beamforming design based on minimum mean-square error (MSE) criterion has been proposed. Establishing uplink downlink MSE duality, an alternating algorithm has been developed. A scenario where multiple users are served by both the BS and a MIMO relay is considered and a joint beamforming technique for the BS and the MIMO relay is proposed. With the motivation of optimising the transmission power at both the BS and the relay, an interference precoding design is presented that takes into account the knowledge of the interference caused by the relay to the users served by the BS.
Recognizing joint beamformer design for multiple BSs has the ability to reduce interference in the network significantly, cooperative multi-cell beamforming design is proposed. The aim is to design multi-cell beamformers to maximize the minimum SINR of users subject to individual BS power constraints. In contrast to all works available in the literature that aimed at balancing SINR of all users in all cells to the same level, the SINRs of users in each cell is balanced and maximized at different values. This new technique takes advantage of the fact that BSs may have different available transmission powers and/or channel conditions for their users