1,321 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 Linear Receivers
Linear receivers are often used to reduce the implementation complexity of
multiple-antenna systems. In a traditional linear receiver architecture, the
receive antennas are used to separate out the codewords sent by each transmit
antenna, which can then be decoded individually. Although easy to implement,
this approach can be highly suboptimal when the channel matrix is near
singular. This paper develops a new linear receiver architecture that uses the
receive antennas to create an effective channel matrix with integer-valued
entries. Rather than attempting to recover transmitted codewords directly, the
decoder recovers integer combinations of the codewords according to the entries
of the effective channel matrix. The codewords are all generated using the same
linear code which guarantees that these integer combinations are themselves
codewords. Provided that the effective channel is full rank, these integer
combinations can then be digitally solved for the original codewords. This
paper focuses on the special case where there is no coding across transmit
antennas and no channel state information at the transmitter(s), which
corresponds either to a multi-user uplink scenario or to single-user V-BLAST
encoding. In this setting, the proposed integer-forcing linear receiver
significantly outperforms conventional linear architectures such as the
zero-forcing and linear MMSE receiver. In the high SNR regime, the proposed
receiver attains the optimal diversity-multiplexing tradeoff for the standard
MIMO channel with no coding across transmit antennas. It is further shown that
in an extended MIMO model with interference, the integer-forcing linear
receiver achieves the optimal generalized degrees-of-freedom.Comment: 40 pages, 16 figures, to appear in the IEEE Transactions on
Information Theor
Compute-and-Forward: Harnessing Interference through Structured Codes
Interference is usually viewed as an obstacle to communication in wireless
networks. This paper proposes a new strategy, compute-and-forward, that
exploits interference to obtain significantly higher rates between users in a
network. The key idea is that relays should decode linear functions of
transmitted messages according to their observed channel coefficients rather
than ignoring the interference as noise. After decoding these linear equations,
the relays simply send them towards the destinations, which given enough
equations, can recover their desired messages. The underlying codes are based
on nested lattices whose algebraic structure ensures that integer combinations
of codewords can be decoded reliably. Encoders map messages from a finite field
to a lattice and decoders recover equations of lattice points which are then
mapped back to equations over the finite field. This scheme is applicable even
if the transmitters lack channel state information.Comment: IEEE Trans. Info Theory, to appear. 23 pages, 13 figure
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
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