379 research outputs found
Turbo Packet Combining for Broadband Space-Time BICM Hybrid-ARQ Systems with Co-Channel Interference
In this paper, efficient turbo packet combining for single carrier (SC)
broadband multiple-input--multiple-output (MIMO) hybrid--automatic repeat
request (ARQ) transmission with unknown co-channel interference (CCI) is
studied. We propose a new frequency domain soft minimum mean square error
(MMSE)-based signal level combining technique where received signals and
channel frequency responses (CFR)s corresponding to all retransmissions are
used to decode the data packet. We provide a recursive implementation algorithm
for the introduced scheme, and show that both its computational complexity and
memory requirements are quite insensitive to the ARQ delay, i.e., maximum
number of ARQ rounds. Furthermore, we analyze the asymptotic performance, and
show that under a sum-rank condition on the CCI MIMO ARQ channel, the proposed
packet combining scheme is not interference-limited. Simulation results are
provided to demonstrate the gains offered by the proposed technique.Comment: 12 pages, 7 figures, and 2 table
DMT Optimality of LR-Aided Linear Decoders for a General Class of Channels, Lattice Designs, and System Models
The work identifies the first general, explicit, and non-random MIMO
encoder-decoder structures that guarantee optimality with respect to the
diversity-multiplexing tradeoff (DMT), without employing a computationally
expensive maximum-likelihood (ML) receiver. Specifically, the work establishes
the DMT optimality of a class of regularized lattice decoders, and more
importantly the DMT optimality of their lattice-reduction (LR)-aided linear
counterparts. The results hold for all channel statistics, for all channel
dimensions, and most interestingly, irrespective of the particular lattice-code
applied. As a special case, it is established that the LLL-based LR-aided
linear implementation of the MMSE-GDFE lattice decoder facilitates DMT optimal
decoding of any lattice code at a worst-case complexity that grows at most
linearly in the data rate. This represents a fundamental reduction in the
decoding complexity when compared to ML decoding whose complexity is generally
exponential in rate.
The results' generality lends them applicable to a plethora of pertinent
communication scenarios such as quasi-static MIMO, MIMO-OFDM, ISI,
cooperative-relaying, and MIMO-ARQ channels, in all of which the DMT optimality
of the LR-aided linear decoder is guaranteed. The adopted approach yields
insight, and motivates further study, into joint transceiver designs with an
improved SNR gap to ML decoding.Comment: 16 pages, 1 figure (3 subfigures), submitted to the IEEE Transactions
on Information Theor
Turbo Packet Combining Strategies for the MIMO-ISI ARQ Channel
This paper addresses the issue of efficient turbo packet combining techniques
for coded transmission with a Chase-type automatic repeat request (ARQ)
protocol operating over a multiple-input--multiple-output (MIMO) channel with
intersymbol interference (ISI). First of all, we investigate the outage
probability and the outage-based power loss of the MIMO-ISI ARQ channel when
optimal maximum a posteriori (MAP) turbo packet combining is used at the
receiver. We show that the ARQ delay (i.e., the maximum number of ARQ rounds)
does not completely translate into a diversity gain. We then introduce two
efficient turbo packet combining algorithms that are inspired by minimum mean
square error (MMSE)-based turbo equalization techniques. Both schemes can be
viewed as low-complexity versions of the optimal MAP turbo combiner. The first
scheme is called signal-level turbo combining and performs packet combining and
multiple transmission ISI cancellation jointly at the signal-level. The second
scheme, called symbol-level turbo combining, allows ARQ rounds to be separately
turbo equalized, while combining is performed at the filter output. We conduct
a complexity analysis where we demonstrate that both algorithms have almost the
same computational cost as the conventional log-likelihood ratio (LLR)-level
combiner. Simulation results show that both proposed techniques outperform
LLR-level combining, while for some representative MIMO configurations,
signal-level combining has better ISI cancellation capability and achievable
diversity order than that of symbol-level combining.Comment: 13 pages, 7 figures, and 2 table
Frequency Domain Hybrid-ARQ Chase Combining for Broadband MIMO CDMA Systems
In this paper, we consider high-speed wireless packet access using code
division multiple access (CDMA) and multiple-input multiple-output (MIMO).
Current wireless standards, such as high speed packet access (HSPA), have
adopted multi-code transmission and hybrid-automatic repeat request (ARQ) as
major technologies for delivering high data rates. The key technique in
hybrid-ARQ, is that erroneous data packets are kept in the receiver to
detect/decode retransmitted ones. This strategy is refereed to as packet
combining. In CDMA MIMO-based wireless packet access, multi-code transmission
suffers from severe performance degradation due to the loss of code
orthogonality caused by both interchip interference (ICI) and co-antenna
interference (CAI). This limitation results in large transmission delays when
an ARQ mechanism is used in the link layer. In this paper, we investigate
efficient minimum mean square error (MMSE) frequency domain equalization
(FDE)-based iterative (turbo) packet combining for cyclic prefix (CP)-CDMA MIMO
with Chase-type ARQ. We introduce two turbo packet combining schemes: i) In the
first scheme, namely "chip-level turbo packet combining", MMSE FDE and packet
combining are jointly performed at the chip-level. ii) In the second scheme,
namely "symbol-level turbo packet combining", chip-level MMSE FDE and
despreading are separately carried out for each transmission, then packet
combining is performed at the level of the soft demapper. The computational
complexity and memory requirements of both techniques are quite insensitive to
the ARQ delay, i.e., maximum number of ARQ rounds. The throughput is evaluated
for some representative antenna configurations and load factors to show the
gains offered by the proposed techniques.Comment: Submitted to IEEE Transactions on Vehicular Technology (Apr 2009
Finite-SNR Diversity-Multiplexing-Delay Tradeoff in Half-Duplex Hybrid ARQ Relay Channels
International audienceIn this paper, we consider a delay-limited hybrid automatic repeat request (HARQ) protocol that makes use of incremental redundancy over the three-node decode-and-forward (DF) relay fading channel where one source cooperates with a relay to transmit information to the destination. We provide an estimate of the diversity-multiplexing tradeoff (DMT) at finite signal to noise ratio (SNR) based on tight bounds on outage probabilities for two channel models. The results for the long term quasi-static channel highlight the distributed diversity, ie. the cooperative space diversity, and the HARQ coding gain, achieved by soft combining the successive transmitted punctured codewords via incremental redundancy. On the other hand, the results for the short term quasi-static channel illustrate the diversity gains obtained thanks to cooperative space diversity and time diversity, along with the HARQ coding gain. Using the DMT formulation, we show that equal power partitioning between the source and the relay nodes provides close to optimal performance. Furthermore, thanks to the extension of the finite-SNR DMT to the finite-SNR diversity-multiplexing-delay tradeoff, we show that, unlike the asymptotic SNR analysis, the ARQ delay, defined as the number of retransmissions rounds, impacts the performance of the HARQ relay protocol for high effective multiplexing gain
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