8 research outputs found
Robust Successive Compute-and-Forward over Multi-User Multi-Relay Networks
This paper develops efficient Compute-and-forward (CMF) schemes in multi-user
multi-relay networks. To solve the rank failure problem in CMF setups and to
achieve full diversity of the network, we introduce two novel CMF methods,
namely, extended CMF and successive CMF. The former, having low complexity, is
based on recovering multiple equations at relays. The latter utilizes
successive interference cancellation (SIC) to enhance the system performance
compared to the state-of-the-art schemes. Both methods can be utilized in a
network with different number of users, relays, and relay antennas, with
negligible feedback channels or signaling overhead. We derive new concise
formulations and explicit framework for the successive CMF method as well as an
approach to reduce its computational complexity. Our theoretical analysis and
computer simulations demonstrate the superior performance of our proposed CMF
methods over the conventional schemes. Furthermore, based on our simulation
results, the successive CMF method yields additional signal-to-noise ratio
gains and shows considerable robustness against channel estimation error,
compared to the extended CMF method.Comment: 44 pages, 10 figures, 1 table, accepted to be published in IEEE
Trans. on Vehicular Tec
Integer Forcing-and-Forward Transceiver Design for MIMO Multi-Pair Two-Way Relaying
In this paper, we propose a new transmission scheme, named as Integer
Forcing-and-Forward (IFF), for communications among multi-pair multiple-antenna
users in which each pair exchanges their messages with the help of a single
multi antennas relay in the multiple-access and broadcast phases. The proposed
scheme utilizes Integer Forcing Linear Receiver (IFLR) at relay, which uses
equations, i.e., linear integer-combinations of messages, to harness the
intra-pair interference. Accordingly, we propose the design of mean squared
error (MSE) based transceiver, including precoder and projection matrices for
the relay and users, assuming that the perfect channel state information (CSI)
is available. In this regards, in the multiple-access phase, we introduce two
new MSE criteria for the related precoding and filter designs, i.e., the sum of
the equations MSE (Sum-Equation MSE) and the maximum of the equations MSE
(Max-Equation MSE), to exploit the equations in the relay. In addition, the
convergence of the proposed criteria is proven as well. Moreover, in the
broadcast phase, we use the two traditional MSE criteria, i.e. the sum of the
users' mean squred errors (Sum MSE) and the maximum of the users' mean squared
errors (Max MSE), to design the related precoding and filters for recovering
relay's equations by the users. Then, we consider a more practical scenario
with imperfect CSI. For this case, IFLR receiver is modified, and another
transceiver design is proposed, which take into account the effect of channels
estimation error. We evaluate the performance of our proposed strategy and
compare the results with the conventional amplify-and-forward (AF) and
denoise-and-forward (DF) strategies for the same scenario. The results indicate
the substantial superiority of the proposed strategy in terms of the outage
probability and the sum rate.Comment: 30 pages, 7 figures, Submitted to a IEEE journa
Wireless Network-Coded Accumulate-Compute-and-Forward Two-Way Relaying
For the physical-layer network-coded wireless two-way relaying, it was observed by Koike-Akino et al. that adaptively changing the network coding map used at the relay according to channel conditions greatly reduces the impact of multiple-access interference, which occurs at the relay, and all these network coding maps should satisfy a requirement called exclusive law. We extend this approach to an accumulate-compute-and-forward protocol, which employs two phases: a multiple access (MA) phase consisting of two channel uses with independent messages in each channel use and a broadcast (BC) phase having one channel use. Assuming that the two users transmit points from the same 4-phase-shift keying (PSK) constellation, every such network coding map that satisfies the exclusive law can be represented by a Latin square of side 16, and conversely, this relationship can be used to get the network coding maps satisfying the exclusive law. Two methods of obtaining this network coding map to be used at the relay are discussed. Using the structural properties of the Latin squares for a given set of parameters, the problem of finding all the required maps is reduced to finding a small set of maps for the case. Having obtained all the Latin squares, a criterion is provided to select a Latin square for a given realization of fade state. This criterion turns out to be the same as the one used byMuralidharan et al. for two-stage bidirectional relaying
Buffer-Aided Two-Way Relaying with Lattice Codes
The achievable sum-rate of the two-way relaying becomes far below the cut-set outer bound if the signal-to-noise-ratio (SNR) from one node to the relay is significantly different from the SNR from the other node to the relay, and particularly so for decode-and-forward or compute-and-forward type relaying. In this paper, we propose a buffer-aided compute-and-forward two-way relaying with lattice codes to improve the sum-rate in asymmetric SNR two-way relay channels (TWRCs). Specifically, the relay can store some amount of data received in the multiple access phase before forwarding it, thereby controlling the amount of data to be transmitted to each direction in the broadcast phase. Simulation results show that the sum-rate can be improved with the use of buffers compared to the conventional two-way relaying without buffers