Relay-oriented source power allocation for MIMO selective decode-and-forward relaying

This paper considers the two-hop relay broadcast channel (BC) in a wireless cellular network where the downlink transmission from the base station (BS) to mobile users is assisted by a fixed relay station (RS). Assuming both the BS and RS equipped with multi-antennas, we consider joint optimization of beamforming weights and power allocations at the BS and RS so as to minimize their weighted sum-power consumption under the minimum signal-to-interference-noise-ratio (SINR) constraints at user terminals. We extend the two well-known criteria for design of linear precoding in the conventional MIMO-BC without relay, namely, the SINR balancing and the channel-inversion, to the MIMO relay BC. First, an iterative SINR-balancing algorithm is proposed that in each iteration optimizes transmit parameters at one station (BS or RS) with those at the other fixed. Secondly, a joint BS and RS channel-inversion algorithm is proposed together with a novel technique termed eigenmode switching at the RS. Simulation results show that optimized joint beamforming and power control are able to achieve substantial power savings for the MIMO relay BC.

We propose a broadcasting relay scheme in which the source-to-relay link is a multiple input multiple output (MIMO) channel and the relay-to-destination link is a broadcast channel. The operation for relay station consists of receive beamforming, amplifying and transmit beamforming (R-A-T). We study joint MIMO beamforming and power adaptation to transmit parallel data streams to multiple users with different quality-of-service (QoS) constraints. We derive the optimal solution for the beamforming weights and power adaptation at the base station and the relay station transmitters for the R-A-T scheme, and propose iterative algorithms for joint beamforming weights and power adaption. Simulation results are presented to show that the proposed iterative algorithms achieve the respective target signal-to-interference-plus-noise ratio (SINR) of mobile receivers.

In wireless communication, Multiple Input Multiple Output (MIMO) technology has proven to improve reliability through spatial diversity. Cooperative relay transmission is an emerging concept, which involves the users to share their resources to improve overall system performance. In this work, Selective Decode and Forward (SDF) cooperative relaying scheme is analyzed. This paper describes power optimization in relay nodes for a dual hop half-duplex SDF based cooperative relay communication system, with nodes using multiple antenna. For the proposed system model, average end-to-end probability of error is derived, leading to evaluation of asymptotically tight upper bound under high signal to noise ratio. Optimal power allocation to minimize the bit error rate (BER) is formulated and a closed form solution for this convex optimization problem is derived and verified through simulation. The BER performance of the system is compared with that of cooperative relay network having single antenna at the participating nodes. Results show sharp decline in error rate with increase in the number of participating antenna. Simulation results reveal that cooperate scheme with optimal power allocation has an improved performance, compared to its direct link counterpart.

This paper considers uplink multiuser (MU) multiple-input and multiple-output (MIMO) communication with millimeter-wave beamforming in unmanned aerial vehicle (UAV)-assisted cellular networks. We aim to improve uplink system capacity by using the MU-MIMO technique between a relay station (RS) and users and applying a spatial multiplexing technique such as line-of-sight (LOS) MIMO between the RS and a base station. In such systems, locations and orientations of RSs should be determined appropriately since severe interference might be caused depending on user locations relative to the RS. Therefore, we propose a UAV-RS deployment method for MU-MIMO capacity maximization. In the proposed method, a combination of the location and orientation of each RS is sequentially selected based on estimated MU-MIMO capacity from pre-defined candidates. The uplink system level simulations assuming a scenario where three RSs cover the celledge area of the base station demonstrate that the proposed method can improve the system capacity by about 32% compared to a fixed deployment where the RSs are deployed concentrically at equal angular intervals.

This paper addresses channel state information (CSI) estimation in a wireless relay network, which consists of a base station (BS), a relay station (RS), and a mobile station (MS). We propose a method for the BS to obtain the instantaneous CSIs of the three links (BS-RS, BS-MS, and RS-MS links) with minimized overhead. The CSI availability plays an important role for the BS to adapt its transmission strategies to the given channel conditions. Our proposed method exploits the fact that the link condition between fixed BS and fixed RS tends to be stable, and the frequent CSI update is not necessary for this link. In order for the BS to obtain the CSI of the distant link (i.e. RS-MS link), RS amplifies a pilot signal received from MS with a pre-defined amplification factor, and forwards it to BS. This enables the BS to obtain the CSI of the RS-MS link based on the received pilot signal and pre-knowledge on the CSI of BS-RS link. We show by computer simulation that our proposed method can reduce the required overhead for CSI estimation with little degradation on the accuracy of the obtained CSI.

This letter proposes a robust joint linear precoding scheme based on the minimum mean squared error (MMSE) criterion for amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay broadcast systems with limited feedback, where only the quantized channel direction information (CDI) of the forward channel is available for the base station (BS) and the relay station (RS). The proposed scheme employs an iterative algorithm which alternately optimizes the BS and RS precoders to jointly minimize the expected MSE conditioned on the quantized CDI.

An adaptive resource allocation scheme is proposed for regenerative relay-based orthogonal frequency division multiplexing access systems. This scheme allocates subchannels to guarantee fairness between users, and also saves energy by minimising the transmission power. The subchannel allocation for data rate fairness is considered between direct link users and relay stations in the first time subslot and among relay link users in the second time subslot by introducing a proportional fair scheduling algorithm. However, the data rate between the two hop links of each RS will still be mismatched under equal power allocation, so the transmission power of the base station and the relay stations will adjust adaptively in terms of the data rate difference between the two hop links. In this way, the data rate on the two hop links of one relay station will be matched and the total transmission power will be reduced. Simulation results comparing this approach with standard scheduling methods show that this approach achieves an overwhelming performance improvement on the long-term fairness of the user data rate and the total transmission power of base station and relay stations can be reduced greatly.

This paper studies the two-hop relay broadcast channel (BC) for a relay-assisted wireless cellular network where the multiuser independent downlink signals from the base station (BS) are first transmitted to a fixed relay station (RS), and then forwarded by the RS to multiple mobile users. Assuming both the BS and RS are equipped with multiantennas, we study the joint optimization of linear beamforming and power control at the BS and RS so as to minimize their weighted sum-power consumption under the user minimum signal-to-interference-noise-ratio (SINR) - quality-of-service (QoS) - constraints. We apply two well-known criteria in the literature, namely, the ldquoSINR balancingrdquo and the ldquochannel-inversion,rdquo for the design of linear precoding in the traditional nonrelay-assisted multiantenna BC to the relay-assisted multiantenna BC. First, a convergence-ensured iterative SINR-balancing algorithm is proposed to successively in turn optimize the transmit parameters at one station (BS or RS) with those at the other station being fixed. Second, a joint BS and RS channel-inversion algorithm is proposed together with a novel technique, termed ldquoeigenmode switching,rdquo at the RS to reduce the power penalty of the channel inversion. Simulation results show that the proposed joint beamforming and power control schemes provide substantial power savings to achieve the assigned user QoS constraints.

In a cellular communication system, deploying a relay station (RS) is an effective alternative to installing a new base station (BS). A dual-hop network enhances the throughput of mobile stations (MSs) located in shadow areas or at cell edges by installing RSs between BSs and MSs. Because additional radio resources should be allocated to the wireless link between BS and RS, a frame to be transmitted from BS is divided into an access zone (AZ) and a relay zone (RZ). BS and RS communicate with each other through the RZ, and they communicate with their registered MSs through an AZ. However, if too many MSs are registered with a certain BS or RS, MS overloading may cause performance degradation. To prevent such performance degradation, it is very important to find the proper positions for RSs to be deployed. In this paper, we propose a method for finding the sub-optimal RS deployment location for the purpose of load-balancing and throughput enhancement. The advantage of the proposed method is the efficiency in find the sub-optimal location of RSs and its reliable tradeoff between load-balancing throughput enhancement. Since the proposed scheme finds the proper position by adjusting the distance and angle of RSs, its computational complexity lower than other global optimization approach or learning-based approach. In addition, the proposed scheme is constituted with the two stages of load-balancing and throughput enhancement. These procedures result in the appropriate tradeoff between load-balancing and throughput enhancement. The simulation results support these advancements of the proposed scheme.

Performance enhancement of repacking and borrowing mechanisms for IEEE 802.16j multihop resource scheduling

Energy-efficient and reliable data transmission is a challenging task in wireless relay networks (WRNs). Energy efficiency in cellular networks has received significant attention because of the present need for reduced energy consumption, thereby maintaining the profitability of networks, which in turn makes these networks “greener”. The urban cell topography needs more energy to cover the total area of the cell. The base station does not cover the entire area in a given topography and adding more number of base stations is a cost prohibitive one. Energy-efficient relay placement model which calculates the maximum cell coverage is proposed in this work that covers all sectors and also an energy-efficient incremental redundancy-hybrid automatic repeat request (IR-HARQ) power allocation scheme to improve the reliability of the network by improving the overall network throughput is proposed. An IR-HARQ power allocation method maximizes the average incremental mutual information at each round, and its throughput quickly converges to the ergodic channel capacity as the number of retransmissions increases. Simulation results show that the proposed IR-HARQ power allocation achieves full channel capacity with average transmission delay and maintains good throughput under less power consumption. Also the impact of relaying performance on node distances between relay station and base station as well as between user and relay station and relay height for line of sight conditions are analyzed using full decode and forward (FDF) and partial decode and forward (PDF) relaying schemes. Compared to FDF scheme, PDF scheme provides better performance and allows more freedom in the relay placement for an increase in cell coverage.

In cellular systems, BSs (base stations) are ideally desired to be located in the center of cells, but it is sometimes impossible because of the physical and/or social restrictions on the BS setting space. This paper considers the influence of the displacement of the BS location on BS cooperation (BSC) scheme in MIMO (multiple input multiple output) cellular system. For this aim, BS locations are given on fixed points of circles with different radius and rotation angle. The performances of transmission algorithms with and without BSC are quantitatively evaluated under several typical BS locations through computer simulations. The results show the BS location has certain impact, but the BSC is still effective under the BS displacement.

This paper proposes interference-based decode and forward scheme that utilizes relay stations (RSs). In Long-Term-Evolution (LTE-) Advanced, heterogeneous networks in which femto- and picocells are overlaid onto macrocells are extensively discussed. However, interference between macro- and pico(femto)cells arises due to their different transmit power levels. Unlike conventional cooperative transmission schemes, the RS decodes interference in the first transmit timing period and forwards it to the user equipment (UE) in the second period. Moreover, cooperative transmission can be achieved without stopping the transmission from the base station (BS) to UE when forwarding the interference from the RS to the UE by utilizing the fact that signal-to-noise power ratio (SNR) between the RS and UE is much greater than that between the BS and UE. The basic performance of the proposed method is shown based on computer simulation. Moreover, the interference temperature and shadowing effect are measured when considering the coexistence between macro- and femtocells, and the performance of the proposed method is verified using measured shadowing effect.

In this paper, we consider transceiver design for multiuser cellular two-way relay network (cTWRC), where a multi-antenna base station (BS) exchanges information with multiple single-antenna mobile stations (MSs) with the help of a multi-antenna relay station (RS). We propose a low complexity two-way relaying scheme for cTWRC via signal space alignment. In our scheme, the precoders at the BS and MSs are jointly designed that the two data streams delivered to and from the same MS fall in the same spatial direction at the RS. With such signal space alignment, interference-free physical-layer network coding can be performed at the relay. We analyze the end-to-end sum bit error rate (BER) performance of the proposed scheme and investigate the optimal power allocation at the BS and RS to improve the BER performance. Numerical results demonstrate that our scheme is superior to the existing amplify-and-forward based signal alignment schemes.

The IEEE 802.16j mobile multi-hop relay (MMR) is studied to improve throughput, extend coverage, and increase capacity. Mobile relay stations attached to vehicles make arbitrary movements and have interference with other base stations or relay stations, thus lowering service functions. This study sets out to suggest an interference detection and avoidance method and evaluates its performance in order to help introduce a mobile relay station for vehicle mounting in a mobile multi-hop relay network. The proposed approach would be implemented by the addition of MAC management messages at a base or relay station instead of the change of mobile station.