4,134 research outputs found
On the Asymptotic Performance of Bit-Wise Decoders for Coded Modulation
Two decoder structures for coded modulation over the Gaussian and flat fading
channels are studied: the maximum likelihood symbol-wise decoder, and the
(suboptimal) bit-wise decoder based on the bit-interleaved coded modulation
paradigm. We consider a 16-ary quadrature amplitude constellation labeled by a
Gray labeling. It is shown that the asymptotic loss in terms of pairwise error
probability, for any two codewords caused by the bit-wise decoder, is bounded
by 1.25 dB. The analysis also shows that for the Gaussian channel the
asymptotic loss is zero for a wide range of linear codes, including all
rate-1/2 convolutional codes
Bit-Interleaved Coded Energy-Based Modulation with Iterative Decoding
This paper develops a low-complexity near-optimal non-coherent receiver for a
multi-level energy-based coded modulation system. Inspired by the turbo
processing principle, we incorporate the fundamentals of bit-interleaved coded
modulation with iterative decoding (BICM-ID) into the proposed receiver design.
The resulting system is called bit-interleaved coded energy-based modulation
with iterative decoding (BICEM-ID) and its error performance is analytically
studied. Specifically, we derive upper bounds on the average pairwise error
probability (PEP) of the non-coherent BICEM-ID system in the feedback-free (FF)
and error-free feedback (EFF) scenarios. It is revealed that the definition of
the nearest neighbors, which is important in the performance analysis in the FF
scenario, is very different from that in the coherent BICM-ID counterpart. The
analysis also reveals how the mapping from coded bits to energy levels
influences the diversity order and coding gain of the BICEM-ID systems. A
design criterion for good mappings is then formulated and an algorithm is
proposed to find a set of best mappings for BICEM-ID. Finally, simulation
results corroborate the main analytical findings
Performance Analysis of Bit-Interleaved Space-Time (BI-ST) Coded Systems Over Wireless Channels
In this paper a union bound on the bit error probability of bit-interleaved space-time (BI-ST) coded systems is derived. The derivation is based on the uniform interleaving assumption of the coded sequence prior to transmission over the multiple antennas. The performance of a BI-ST coded system is a function of how the bit errors are distributed over the signals in the codeword. In this paper, we derive this distribution as well as the corresponding pairwise error probability. The bound is a function of the distance spectrum of the code, the signal constellation used and the space-time (ST) encoding scheme. The bound is derived for a general BI-ST coded system and applied to two specific examples; namely, the BI space-time coded modulation (BI-STCM) and the BI space-time block codes (BI-STBC). Results show that the analysis provides a close approximation to the performance for a wide range of signal-to-noise ratios (SNR)
Performance Analysis of Bit-Interleaved Space-Time (BI-ST) Coded Systems Over Wireless Channels
In this paper a union bound on the bit error probability of bit-interleaved space-time (BI-ST) coded systems is derived. The derivation is based on the uniform interleaving assumption of the coded sequence prior to transmission over the multiple antennas. The performance of a BI-ST coded system is a function of how the bit errors are distributed over the signals in the codeword. In this paper, we derive this distribution as well as the corresponding pairwise error probability. The bound is a function of the distance spectrum of the code, the signal constellation used and the space-time (ST) encoding scheme. The bound is derived for a general BI-ST coded system and applied to two specific examples; namely, the BI space-time coded modulation (BI-STCM) and the BI space-time block codes (BI-STBC). Results show that the analysis provides a close approximation to the performance for a wide range of signal-to-noise ratios (SNR)
Bit-Interleaved Coded Modulation Revisited: A Mismatched Decoding Perspective
We revisit the information-theoretic analysis of bit-interleaved coded
modulation (BICM) by modeling the BICM decoder as a mismatched decoder. The
mismatched decoding model is well-defined for finite, yet arbitrary, block
lengths, and naturally captures the channel memory among the bits belonging to
the same symbol. We give two independent proofs of the achievability of the
BICM capacity calculated by Caire et al. where BICM was modeled as a set of
independent parallel binary-input channels whose output is the bitwise
log-likelihood ratio. Our first achievability proof uses typical sequences, and
shows that due to the random coding construction, the interleaver is not
required. The second proof is based on the random coding error exponents with
mismatched decoding, where the largest achievable rate is the generalized
mutual information. We show that the generalized mutual information of the
mismatched decoder coincides with the infinite-interleaver BICM capacity. We
also show that the error exponent -and hence the cutoff rate- of the BICM
mismatched decoder is upper bounded by that of coded modulation and may thus be
lower than in the infinite-interleaved model. We also consider the mutual
information appearing in the analysis of iterative decoding of BICM with EXIT
charts. We show that the corresponding symbol metric has knowledge of the
transmitted symbol and the EXIT mutual information admits a representation as a
pseudo-generalized mutual information, which is in general not achievable. A
different symbol decoding metric, for which the extrinsic side information
refers to the hypothesized symbol, induces a generalized mutual information
lower than the coded modulation capacity.Comment: submitted to the IEEE Transactions on Information Theory. Conference
version in 2008 IEEE International Symposium on Information Theory, Toronto,
Canada, July 200
Labeling Diversity for 2x2 WLAN Coded-Cooperative Networks
Labelling diversity is an efficient technique recently proposed in the literature and aims to improve the bit error rate(BER) performance of wireless local area network (WLAN) systems with two transmit and two receive antennas without increasing the transmit power and bandwidth requirements. In this paper, we employ labelling diversity with different space-time channel codes such as convolutional, turbo and low density parity check (LDPC) for both point-to-point and coded-cooperative communication scenarios. Joint iterative decoding schemes for distributed turbo and LDPC codes are also presented. BER performance bounds at an error floor (EF) region are derived and verified with the help of numerical simulations for both cooperative and non-cooperative schemes. Numerical simulations show that the coded-cooperative schemes with labelling diversity achieve better BER performances and use of labelling diversity at the source node significantly lowers relay outage probability and hence the overall BER performance of the coded-cooperative scheme is improved manifolds
Near-Capacity Turbo Trellis Coded Modulation Design
Bandwidth efficient parallel-concatenated Turbo Trellis Coded Modulation (TTCM) schemes were designed for communicating over uncorrelated Rayleigh fading channels. A symbol-based union bound was derived for analysing the error floor of the proposed TTCM schemes. A pair of In-phase (I) and Quadrature-phase (Q) interleavers were employed for interleaving the I and Q components of the TTCM coded symbols, in order to attain an increased diversity gain. The decoding convergence of the IQ-TTCM schemes was analysed using symbol based EXtrinsic Information Transfer (EXIT) charts. The best TTCM component codes were selected with the aid of both the symbol-based union bound and non-binary EXIT charts for the sake of designing capacity-approaching IQ-TTCM schemes in the context of 8PSK, 16QAM and 32QAM signal sets. It will be shown that our TTCM design is capable of approaching the channel capacity within 0.5 dB at a throughput of 4 bit/s/Hz, when communicating over uncorrelated Rayleigh fading channels using 32QAM
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