377 research outputs found
Fast-SSC-Flip Decoding of Polar Codes
Polar codes are widely considered as one of the most exciting recent
discoveries in channel coding. For short to moderate block lengths, their
error-correction performance under list decoding can outperform that of other
modern error-correcting codes. However, high-speed list-based decoders with
moderate complexity are challenging to implement. Successive-cancellation
(SC)-flip decoding was shown to be capable of a competitive error-correction
performance compared to that of list decoding with a small list size, at a
fraction of the complexity, but suffers from a variable execution time and a
higher worst-case latency. In this work, we show how to modify the
state-of-the-art high-speed SC decoding algorithm to incorporate the SC-flip
ideas. The algorithmic improvements are presented as well as average
execution-time results tailored to a hardware implementation. The results show
that the proposed fast-SSC-flip algorithm has a decoding speed close to an
order of magnitude better than the previous works while retaining a comparable
error-correction performance.Comment: 5 pages, 3 figures, appeared at IEEE Wireless Commun. and Netw. Conf.
(WCNC) 201
Faulty Successive Cancellation Decoding of Polar Codes for the Binary Erasure Channel
We study faulty successive cancellation decoding of polar codes for the
binary erasure channel. To this end, we introduce a simple erasure-based fault
model and we show that, under this model, polarization does not happen, meaning
that fully reliable communication is not possible at any rate. Moreover, we
provide numerical results for the frame erasure rate and bit erasure rate and
we study an unequal error protection scheme that can significantly improve the
performance of the faulty successive cancellation decoder with negligible
overhead.Comment: As presented at ISITA 201
Faulty Successive Cancellation Decoding of Polar Codes for the Binary Erasure Channel
In this paper, faulty successive cancellation decoding of polar codes for the
binary erasure channel is studied. To this end, a simple erasure-based fault
model is introduced to represent errors in the decoder and it is shown that,
under this model, polarization does not happen, meaning that fully reliable
communication is not possible at any rate. Furthermore, a lower bound on the
frame error rate of polar codes under faulty SC decoding is provided, which is
then used, along with a well-known upper bound, in order to choose a
blocklength that minimizes the erasure probability under faulty decoding.
Finally, an unequal error protection scheme that can re-enable asymptotically
erasure-free transmission at a small rate loss and by protecting only a
constant fraction of the decoder is proposed. The same scheme is also shown to
significantly improve the finite-length performance of the faulty successive
cancellation decoder by protecting as little as 1.5% of the decoder.Comment: Accepted for publications in the IEEE Transactions on Communication
MIMO Transmission with Residual Transmit-RF Impairments
Physical transceiver implementations for multiple-input multiple-output
(MIMO) wireless communication systems suffer from transmit-RF (Tx-RF)
impairments. In this paper, we study the effect on channel capacity and
error-rate performance of residual Tx-RF impairments that defy proper
compensation. In particular, we demonstrate that such residual distortions
severely degrade the performance of (near-)optimum MIMO detection algorithms.
To mitigate this performance loss, we propose an efficient algorithm, which is
based on an i.i.d. Gaussian model for the distortion caused by these
impairments. In order to validate this model, we provide measurement results
based on a 4-stream Tx-RF chain implementation for MIMO orthogonal
frequency-division multiplexing (OFDM).Comment: to be presented at the International ITG Workshop on Smart Antennas -
WSA 201
Comparison of Polar Decoders with Existing Low-Density Parity-Check and Turbo Decoders
Polar codes are a recently proposed family of provably capacity-achieving
error-correction codes that received a lot of attention. While their
theoretical properties render them interesting, their practicality compared to
other types of codes has not been thoroughly studied. Towards this end, in this
paper, we perform a comparison of polar decoders against LDPC and Turbo
decoders that are used in existing communications standards. More specifically,
we compare both the error-correction performance and the hardware efficiency of
the corresponding hardware implementations. This comparison enables us to
identify applications where polar codes are superior to existing
error-correction coding solutions as well as to determine the most promising
research direction in terms of the hardware implementation of polar decoders.Comment: Fixes small mistakes from the paper to appear in the proceedings of
IEEE WCNC 2017. Results were presented in the "Polar Coding in Wireless
Communications: Theory and Implementation" Worksho
Blind Detection of Polar Codes
Polar codes were recently chosen to protect the control channel information
in the next-generation mobile communication standard (5G) defined by the 3GPP.
As a result, receivers will have to implement blind detection of polar coded
frames in order to keep complexity, latency, and power consumption tractable.
As a newly proposed class of block codes, the problem of polar-code blind
detection has received very little attention. In this work, we propose a
low-complexity blind-detection algorithm for polar-encoded frames. We base this
algorithm on a novel detection metric with update rules that leverage the a
priori knowledge of the frozen-bit locations, exploiting the inherent
structures that these locations impose on a polar-encoded block of data. We
show that the proposed detection metric allows to clearly distinguish
polar-encoded frames from other types of data by considering the cumulative
distribution functions of the detection metric, and the receiver operating
characteristic. The presented results are tailored to the 5G standardization
effort discussions, i.e., we consider a short low-rate polar code concatenated
with a CRC.Comment: 6 pages, 8 figures, to appear at the IEEE Int. Workshop on Signal
Process. Syst. (SiPS) 201
Feedback-Aware Precoding for Millimeter Wave Massive MIMO Systems
Millimeter wave (mmWave) communication is a promising solution for coping
with the ever-increasing mobile data traffic because of its large bandwidth. To
enable a sufficient link margin, a large antenna array employing directional
beamforming, which is enabled by the availability of channel state information
at the transmitter (CSIT), is required. However, CSIT acquisition for mmWave
channels introduces a huge feedback overhead due to the typically large number
of transmit and receive antennas. Leveraging properties of mmWave channels,
this paper proposes a precoding strategy which enables a flexible adjustment of
the feedback overhead. In particular, the optimal unconstrained precoder is
approximated by selecting a variable number of elements from a basis that is
constructed as a function of the transmitter array response, where the number
of selected basis elements can be chosen according to the feedback constraint.
Simulation results show that the proposed precoding scheme can provide a
near-optimal solution if a higher feedback overhead can be afforded. For a low
overhead, it can still provide a good approximation of the optimal precoder.Comment: 7 pages, 5 figures, to appear at the IEEE International Symposium on
Personal, Indoor and Mobile Radio Communications (PIMRC) 201
Sliding Window Spectrum Sensing for Full-Duplex Cognitive Radios with Low Access-Latency
In a cognitive radio system the failure of secondary user (SU) transceivers
to promptly vacate the channel can introduce significant access-latency for
primary or high-priority users (PU). In conventional cognitive radio systems,
the backoff latency is exacerbated by frame structures that only allow sensing
at periodic intervals. Concurrent transmission and sensing using
self-interference suppression has been suggested to improve the performance of
cognitive radio systems, allowing decisions to be taken at multiple points
within the frame. In this paper, we extend this approach by proposing a
sliding-window full-duplex model allowing decisions to be taken on a
sample-by-sample basis. We also derive the access-latency for both the existing
and the proposed schemes. Our results show that the access-latency of the
sliding scheme is decreased by a factor of 2.6 compared to the existing slotted
full-duplex scheme and by a factor of approximately 16 compared to a
half-duplex cognitive radio system. Moreover, the proposed scheme is
significantly more resilient to the destructive effects of residual
self-interference compared to previous approaches.Comment: Published in IEEE VTC Spring 2016, Nanjing, Chin
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