5,858 research outputs found
Space-Time Signal Design for Multilevel Polar Coding in Slow Fading Broadcast Channels
Slow fading broadcast channels can model a wide range of applications in
wireless networks. Due to delay requirements and the unavailability of the
channel state information at the transmitter (CSIT), these channels for many
applications are non-ergodic. The appropriate measure for designing signals in
non-ergodic channels is the outage probability. In this paper, we provide a
method to optimize STBCs based on the outage probability at moderate SNRs.
Multilevel polar coded-modulation is a new class of coded-modulation techniques
that benefits from low complexity decoders and simple rate matching. In this
paper, we derive the outage optimality condition for multistage decoding and
propose a rule for determining component code rates. We also derive an upper
bound on the outage probability of STBCs for designing the
set-partitioning-based labelling. Finally, due to the optimality of the
outage-minimized STBCs for long codes, we introduce a novel method for the
joint optimization of short-to-moderate length polar codes and STBCs
Space-time coding techniques with bit-interleaved coded modulations for MIMO block-fading channels
The space-time bit-interleaved coded modulation (ST-BICM) is an efficient
technique to obtain high diversity and coding gain on a block-fading MIMO
channel. Its maximum-likelihood (ML) performance is computed under ideal
interleaving conditions, which enables a global optimization taking into
account channel coding. Thanks to a diversity upperbound derived from the
Singleton bound, an appropriate choice of the time dimension of the space-time
coding is possible, which maximizes diversity while minimizing complexity.
Based on the analysis, an optimized interleaver and a set of linear precoders,
called dispersive nucleo algebraic (DNA) precoders are proposed. The proposed
precoders have good performance with respect to the state of the art and exist
for any number of transmit antennas and any time dimension. With turbo codes,
they exhibit a frame error rate which does not increase with frame length.Comment: Submitted to IEEE Trans. on Information Theory, Submission: January
2006 - First review: June 200
Source and Physical-Layer Network Coding for Correlated Two-Way Relaying
In this paper, we study a half-duplex two-way relay channel (TWRC) with
correlated sources exchanging bidirectional information. In the case, when both
sources have the knowledge of correlation statistics, a source compression with
physical-layer network coding (SCPNC) scheme is proposed to perform the
distributed compression at each source node. When only the relay has the
knowledge of correlation statistics, we propose a relay compression with
physical-layer network coding (RCPNC) scheme to compress the bidirectional
messages at the relay. The closed-form block error rate (BLER) expressions of
both schemes are derived and verified through simulations. It is shown that the
proposed schemes achieve considerable improvements in both error performance
and throughput compared with the conventional non-compression scheme in
correlated two-way relay networks (CTWRNs).Comment: 15 pages, 6 figures. IET Communications, 201
Precoding for Outage Probability Minimization on Block Fading Channels
The outage probability limit is a fundamental and achievable lower bound on
the word error rate of coded communication systems affected by fading. This
limit is mainly determined by two parameters: the diversity order and the
coding gain. With linear precoding, full diversity on a block fading channel
can be achieved without error-correcting code. However, the effect of precoding
on the coding gain is not well known, mainly due to the complicated expression
of the outage probability. Using a geometric approach, this paper establishes
simple upper bounds on the outage probability, the minimization of which yields
to precoding matrices that achieve very good performance. For discrete
alphabets, it is shown that the combination of constellation expansion and
precoding is sufficient to closely approach the minimum possible outage
achieved by an i.i.d. Gaussian input distribution, thus essentially maximizing
the coding gain.Comment: Submitted to Transactions on Information Theory on March 23, 201
Relay Assisted Cooperative OSTBC Communication with SNR Imbalance and Channel Estimation Errors
In this paper, a two-hop relay assisted cooperative Orthogonal Space-Time
Block Codes (OSTBC) transmission scheme is considered for the downlink
communication of a cellular system, where the base station (BS) and the relay
station (RS) cooperate and transmit data to the user equipment (UE) in a
distributed fashion. We analyze the impact of the SNR imbalance between the
BS-UE and RS-UE links, as well as the imperfect channel estimation at the UE
receiver. The performance is analyzed in the presence of Rayleigh flat fading
and our results show that the SNR imbalance does not impact the spatial
diversity order. On the other hand, channel estimation errors have a larger
impact on the system performance. Simulation results are then provided to
confirm the analysis.Comment: 5 pages, 3 figures, IEEE 69th Vehicular Technology Conferenc
Space-time autocoding
Prior treatments of space-time communications in Rayleigh flat fading generally assume that channel coding covers either one fading interval-in which case there is a nonzero “outage capacity”-or multiple fading intervals-in which case there is a nonzero Shannon capacity. However, we establish conditions under which channel codes span only one fading interval and yet are arbitrarily reliable. In short, space-time signals are their own channel codes. We call this phenomenon space-time autocoding, and the accompanying capacity the space-time autocapacity. Let an M-transmitter antenna, N-receiver antenna Rayleigh flat fading channel be characterized by an M×N matrix of independent propagation coefficients, distributed as zero-mean, unit-variance complex Gaussian random variables. This propagation matrix is unknown to the transmitter, it remains constant during a T-symbol coherence interval, and there is a fixed total transmit power. Let the coherence interval and number of transmitter antennas be related as T=βM for some constant β. A T×M matrix-valued signal, associated with R·T bits of information for some rate R is transmitted during the T-symbol coherence interval. Then there is a positive space-time autocapacity Ca such that for all R<Ca, the block probability of error goes to zero as the pair (T, M)→∞ such that T/M=β. The autocoding effect occurs whether or not the propagation matrix is known to the receiver, and Ca=Nlog(1+ρ) in either case, independently of β, where ρ is the expected signal-to-noise ratio (SNR) at each receiver antenna. Lower bounds on the cutoff rate derived from random unitary space-time signals suggest that the autocoding effect manifests itself for relatively small values of T and M. For example, within a single coherence interval of duration T=16, for M=7 transmitter antennas and N=4 receiver antennas, and an 18-dB expected SNR, a total of 80 bits (corresponding to rate R=5) can theoretically be transmitted with a block probability of error less than 10^-9, all without any training or knowledge of the propagation matrix
Distributed Space-Time Coding Based on Adjustable Code Matrices for Cooperative MIMO Relaying Systems
An adaptive distributed space-time coding (DSTC) scheme is proposed for
two-hop cooperative MIMO networks. Linear minimum mean square error (MMSE)
receive filters and adjustable code matrices are considered subject to a power
constraint with an amplify-and-forward (AF) cooperation strategy. In the
proposed adaptive DSTC scheme, an adjustable code matrix obtained by a feedback
channel is employed to transform the space-time coded matrix at the relay node.
The effects of the limited feedback and the feedback errors are assessed.
Linear MMSE expressions are devised to compute the parameters of the adjustable
code matrix and the linear receive filters. Stochastic gradient (SG) and
least-squares (LS) algorithms are also developed with reduced computational
complexity. An upper bound on the pairwise error probability analysis is
derived and indicates the advantage of employing the adjustable code matrices
at the relay nodes. An alternative optimization algorithm for the adaptive DSTC
scheme is also derived in order to eliminate the need for the feedback. The
algorithm provides a fully distributed scheme for the adaptive DSTC at the
relay node based on the minimization of the error probability. Simulation
results show that the proposed algorithms obtain significant performance gains
as compared to existing DSTC schemes.Comment: 6 figure
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