187 research outputs found
Precoded Integer-Forcing Universally Achieves the MIMO Capacity to Within a Constant Gap
An open-loop single-user multiple-input multiple-output communication scheme
is considered where a transmitter, equipped with multiple antennas, encodes the
data into independent streams all taken from the same linear code. The coded
streams are then linearly precoded using the encoding matrix of a perfect
linear dispersion space-time code. At the receiver side, integer-forcing
equalization is applied, followed by standard single-stream decoding. It is
shown that this communication architecture achieves the capacity of any
Gaussian multiple-input multiple-output channel up to a gap that depends only
on the number of transmit antennas.Comment: to appear in the IEEE Transactions on Information Theor
Full Diversity Unitary Precoded Integer-Forcing
We consider a point-to-point flat-fading MIMO channel with channel state
information known both at transmitter and receiver. At the transmitter side, a
lattice coding scheme is employed at each antenna to map information symbols to
independent lattice codewords drawn from the same codebook. Each lattice
codeword is then multiplied by a unitary precoding matrix and sent
through the channel. At the receiver side, an integer-forcing (IF) linear
receiver is employed. We denote this scheme as unitary precoded integer-forcing
(UPIF). We show that UPIF can achieve full-diversity under a constraint based
on the shortest vector of a lattice generated by the precoding matrix . This constraint and a simpler version of that provide design criteria for
two types of full-diversity UPIF. Type I uses a unitary precoder that adapts at
each channel realization. Type II uses a unitary precoder, which remains fixed
for all channel realizations. We then verify our results by computer
simulations in , and MIMO using different QAM
constellations. We finally show that the proposed Type II UPIF outperform the
MIMO precoding X-codes at high data rates.Comment: 12 pages, 8 figures, to appear in IEEE-TW
Lattices from Codes for Harnessing Interference: An Overview and Generalizations
In this paper, using compute-and-forward as an example, we provide an
overview of constructions of lattices from codes that possess the right
algebraic structures for harnessing interference. This includes Construction A,
Construction D, and Construction (previously called product
construction) recently proposed by the authors. We then discuss two
generalizations where the first one is a general construction of lattices named
Construction subsuming the above three constructions as special cases
and the second one is to go beyond principal ideal domains and build lattices
over algebraic integers
Asymmetric Compute-and-Forward with CSIT
We present a modified compute-and-forward scheme which utilizes Channel State
Information at the Transmitters (CSIT) in a natural way. The modified scheme
allows different users to have different coding rates, and use CSIT to achieve
larger rate region. This idea is applicable to all systems which use the
compute-and-forward technique and can be arbitrarily better than the regular
scheme in some settings.Comment: in International Zurich Seminar on Communications, 2014; minor update
on example
Efficient Integer Coefficient Search for Compute-and-Forward
Integer coefficient selection is an important decoding step in the
implementation of compute-and-forward (C-F) relaying scheme. Choosing the
optimal integer coefficients in C-F has been shown to be a shortest vector
problem (SVP) which is known to be NP hard in its general form. Exhaustive
search of the integer coefficients is only feasible in complexity for small
number of users while approximation algorithms such as Lenstra-Lenstra-Lovasz
(LLL) lattice reduction algorithm only find a vector within an exponential
factor of the shortest vector. An optimal deterministic algorithm was proposed
for C-F by Sahraei and Gastpar specifically for the real valued channel case.
In this paper, we adapt their idea to the complex valued channel and propose an
efficient search algorithm to find the optimal integer coefficient vectors over
the ring of Gaussian integers and the ring of Eisenstein integers. A second
algorithm is then proposed that generalises our search algorithm to the
Integer-Forcing MIMO C-F receiver. Performance and efficiency of the proposed
algorithms are evaluated through simulations and theoretical analysis.Comment: IEEE Transactions on Wireless Communications, to appear.12 pages, 8
figure
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
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