9,957 research outputs found
Multi-slot Coded ALOHA with Irregular Degree Distribution
This paper proposes an improvement of the random multiple access scheme for
satellite communication named Multislot coded ALOHA (MuSCA). MuSCA is a
generalization of Contention Resolution Diversity Slotted ALOHA (CRDSA). In
this scheme, each user transmits several parts of a single codeword of an error
correcting code instead of sending replicas. At the receiver level, the decoder
collects all these parts and includes them in the decoding process even if they
are interfered. In this paper, we show that a high throughput can be obtained
by selecting variable code rates and user degrees according to a probability
distribution. With an optimal irregular degree distribution, our system
achieves a normalized throughput up to 1.43, resulting in a significant gain
compared to CRDSA and MuSCA. The spectral efficiency and the implementation
issues of the scheme are also analyzed.Comment: 6 pages, 8 figure
Turbo-Coded Adaptive Modulation Versus Space-Time Trellis Codes for Transmission over Dispersive Channels
Decision feedback equalizer (DFE)-aided turbocoded wideband adaptive quadrature amplitude modulation (AQAM) is proposed, which is capable of combating the temporal channel quality variation of fading channels. A procedure is suggested for determining the AQAM switching thresholds and the specific turbo-coding rates capable of maintaining the target bit-error rate while aiming for achieving a highly effective bits per symbol throughput. As a design alternative, we also employ multiple-input/multiple-output DFE-aided space–time trellis codes, which benefit from transmit diversity and hence reduce the temporal channel quality fluctuations. The performance of both systems is characterized and compared when communicating over the COST 207 typical urban wideband fading channel. It was found that the turbo-coded AQAM scheme outperforms the two-transmitter space–time trellis coded system employing two receivers; although, its performance is inferior to the space–time trellis coded arrangement employing three receivers. Index Terms—Coded adaptive modulation, dispersive channels, space–time trellis codes
List Decoding Tensor Products and Interleaved Codes
We design the first efficient algorithms and prove new combinatorial bounds
for list decoding tensor products of codes and interleaved codes. We show that
for {\em every} code, the ratio of its list decoding radius to its minimum
distance stays unchanged under the tensor product operation (rather than
squaring, as one might expect). This gives the first efficient list decoders
and new combinatorial bounds for some natural codes including multivariate
polynomials where the degree in each variable is bounded. We show that for {\em
every} code, its list decoding radius remains unchanged under -wise
interleaving for an integer . This generalizes a recent result of Dinur et
al \cite{DGKS}, who proved such a result for interleaved Hadamard codes
(equivalently, linear transformations). Using the notion of generalized Hamming
weights, we give better list size bounds for {\em both} tensoring and
interleaving of binary linear codes. By analyzing the weight distribution of
these codes, we reduce the task of bounding the list size to bounding the
number of close-by low-rank codewords. For decoding linear transformations,
using rank-reduction together with other ideas, we obtain list size bounds that
are tight over small fields.Comment: 32 page
Codes for protection from synchronization loss and additive errors
Codes for protection from synchronization loss and additive error
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