We consider the full-duplex (FD) two-way amplify-and-forward relay system with imperfect cancelation of loopback self-interference (SI) and investigate joint design of relay and receive beamforming for minimizing the mean square error under a relay transmit power constraint. Due to loopback channel estimation error and limitation of analog-to-digital converter, the loopback SI cannot be completely canceled. Multiple antennas at the relay can help loopback SI suppression but beamforming is required to balance between the residual SI suppression and the desired signal transmission. Moreover, the relay beamforming matrix should be updated every time slot because the residual SI in the previous time slot is amplified by the current beamforming matrix and added to the received signals from the two sources in the current time slot. We derive the optimally balanced relay beamforming and receive beamforming matrices in closed form based on minimum mean square error, taking into account the propagation of the residual loopback SI from the first to the current time slot. We also propose beamforming design using only the channels of the m latest time slots, not from the first time slot. Based on our numerical results, we also identify when FD is beneficial and propose selection between FD and half-duplex according to signal-to-noise ratio and interference-to-noise ratio.
This paper proposes an optimal power allocation method for two-way decode-and-forward (DF) relay networks when transmit power values at source nodes are the same. In this paper we consider the multiple access (MAC) capacity for DF relaying scheme. Using case studies, it analytically determines the optimal power values for the two source nodes and one relay node. The achievable sum rate is maximized under a sum power constraint for given squared magnitude of the channel coefficients. Finally, numerical results show that the achievable sum rate for proposed optimum power allocation is greater than or equal to that for equal power allocation.Index Terms-Two-way relay channel, power allocation, decode-and-forward, network coding, sum rate.
I. INTRODUCTIONIn a two-way relay channel (TWRC), two source nodes exchange messages with each other via a common relay. The two source nodes transmit messages to the relay through the multiple access (MAC) in the first time slot, and the relay transmits received messages to both source nodes through the broadcast (BC) in the second time slot. Amplify-and forward (AF) and decode-and-forward (DF) are typical relay ing schemes [1]-[4]. This paper assumes the DF relay. The each source node removes its own information, called self interference, and decodes the other source node ' s information.In order to maximize the achievable rate, the signal-to-noise ratio (SNR) of the received signal should be the maximum. By allocating the sum power to the sources and relay nodes in an optimal way, a maximum achievable rate can be obtained. To maximize an achievable rate, an optimal power allocation method for a one-way relay channel using DF was presented in [5]. The outage probability of a TWRC with a DF strategy was studied in [6]. An optimal power allocation scheme for a TWRC using AF and DF with data rate fairness was proposed in [7]. The physical-layer network coding (PNC) technique is presented in [8], and the optimal power allocation scheme for a TWRC using PNC has been presented in [9]. While the paper [9] does not consider a MAC capacity, this paper considers the MAC capacity and for the sake of simplicity assumes that transmit power at the two source nodes are the
This paper considers a hybrid relay network consisting of the source, the amplify-and-forward (AF) relay, the decode-and-forward (DF) relay, and the destination. In hybrid three-hop relay systems, the transmitted signal from source can be received at the destination after processing the signals through two relays. If the first relay amplifies and forwards the received signal, and the second relay decodes and forwards the received signal, the system model is considered to be an AF-DF relay system. The reverse case is considered for the DF-AF relay system. The AF-DF and DF-AF relay systems have different error rates and achievable throughput with respect to the channel conditions between two nodes. We propose optimal power allocation schemes for two different relays in order to maximize the achievable rate under a sum relay power constraint for given channel gains and transmit power from the source. By solving the optimization problem to maximize the achievable rate for each relay network, the transmit power values in closed form are derived. When the channel gains are the same, the optimal power allocation scheme for the AF-DF relay network proves that greater power should be allocated at the first relay to maximize the achievable rate. In the case of the DF-AF relay network, we derive an optimal power allocation scheme for the four possible cases. Under the same signal-to-noise ratio (SNR) condition, at the first hop we show that the achievable rate of the AF-DF relay network is greater than that of the DF-AF relay network when the channel gain between two relays is greater than that between the second relay and destination. Simulation results show that the proposed power allocation schemes provide a higher achievable rate than the equal power allocation scheme and the grid search schemes.
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iii OPTIMAL AMPLIFY-AND-FORWARD PRECODE AND RELAY AMPLIFYING MATRICESThe following faculty members have examined the final copy of this thesis for form and content, and recommend that it be accepted in partial fulfillment of the requirement for the degree of Master of Science with a major in Electrical Engineering. Hu for being part of the adjudicating committee. Lastly, I express my sincere gratitude to the Republic of Korea Air Force, which provided me the opportunity to study abroad. This experience has proven to be very valuable, and I promise to make a commitment to my country.
_________________________________________vi ABSTRACT A cooperative amplify-and-forward (AF) wireless relay scheme consisting of M sources, N relays, and L destinations all equipped with a single antenna was studied in this thesis. The main objective was to design jointly and iteratively the closed form of the minimum mean square error (MMSE)-based source precode and relay amplifying matrices under a jamming environment with various power constraints: (1) transmit, (2) aggregate, (3) source, and (4) relay. With the derived optimal source precode and relay amplifying matrices, the jamming influence of various power constraints on system performance were examined numerically usingMonte-Carlo simulations.vii
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