1,010 research outputs found
Information Rates and Error Exponents for Probabilistic Amplitude Shaping
Probabilistic Amplitude Shaping (PAS) is a coded-modulation scheme in which
the encoder is a concatenation of a distribution matcher with a systematic
Forward Error Correction (FEC) code. For reduced computational complexity the
decoder can be chosen as a concatenation of a mismatched FEC decoder and
dematcher. This work studies the theoretic limits of PAS. The classical joint
source-channel coding (JSCC) setup is modified to include systematic FEC and
the mismatched FEC decoder. At each step error exponents and achievable rates
for the corresponding setup are derived.Comment: Shortened version submitted to Information Theory Workshop (ITW) 201
Probabilistic Shaping for Finite Blocklengths: Distribution Matching and Sphere Shaping
In this paper, we provide for the first time a systematic comparison of
distribution matching (DM) and sphere shaping (SpSh) algorithms for short
blocklength probabilistic amplitude shaping. For asymptotically large
blocklengths, constant composition distribution matching (CCDM) is known to
generate the target capacity-achieving distribution. As the blocklength
decreases, however, the resulting rate loss diminishes the efficiency of CCDM.
We claim that for such short blocklengths and over the additive white Gaussian
channel (AWGN), the objective of shaping should be reformulated as obtaining
the most energy-efficient signal space for a given rate (rather than matching
distributions). In light of this interpretation, multiset-partition DM (MPDM),
enumerative sphere shaping (ESS) and shell mapping (SM), are reviewed as
energy-efficient shaping techniques. Numerical results show that MPDM and SpSh
have smaller rate losses than CCDM. SpSh--whose sole objective is to maximize
the energy efficiency--is shown to have the minimum rate loss amongst all. We
provide simulation results of the end-to-end decoding performance showing that
up to 1 dB improvement in power efficiency over uniform signaling can be
obtained with MPDM and SpSh at blocklengths around 200. Finally, we present a
discussion on the complexity of these algorithms from the perspective of
latency, storage and computations.Comment: 18 pages, 10 figure
Achievable Information Rates for Probabilistic Amplitude Shaping: An Alternative Approach via Random Sign-Coding Arguments
Probabilistic amplitude shaping (PAS) is a coded modulation strategy in which
constellation shaping and channel coding are combined. PAS has attracted
considerable attention in both wireless and optical communications. Achievable
information rates (AIRs) of PAS have been investigated in the literature using
Gallager's error exponent approach. In particular, it has been shown that PAS
achieves the capacity of the additive white Gaussian noise channel (B\"ocherer,
2018). In this work, we revisit the capacity-achieving property of PAS and
derive AIRs using weak typicality. Our objective is to provide alternative
proofs based on random sign-coding arguments that are as constructive as
possible. Accordingly, in our proofs, only some signs of the channel inputs are
drawn from a random code, while the remaining signs and amplitudes are produced
constructively. We consider both symbol-metric and bit-metric decoding.Comment: 19 pages, 6 figures (v3: proofs of Theorems 3 and 4 are generalized
for M-ASK.
Required and received SNRs in coded modulation
Coded modulation techniques aim at reducing the required signal-to-noise ratio (SNR) over the Gaussian channel with an average energy constraint; however, such techniques tend to degrade the received SNR. We studied the balance of required and received SNRs for a realistic system design
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