6 research outputs found
Downlink Transmission under Heterogeneous Blocklength Constraints: Discrete Signaling with Single-User Decoding
In this paper, we consider the downlink broadcast channel under heterogenous
blocklength constraints, where each user experiences different interference
statistics across its received symbols. Different from the homogeneous
blocklength case, the strong users with short blocklength transmitted symbol
blocks usually cannot wait to receive the entire transmission frame and perform
successive interference cancellation (SIC) owing to their stringent latency
requirements. Even if SIC is feasible, it may not be perfect under finite
blocklength constraints. To cope with the heterogeneity in latency and
reliability requirements, we propose a practical downlink transmission scheme
with discrete signaling and single-user decoding, i.e., without SIC. In
addition, we derive the finite blocklength achievable rate and use it for
guiding the design of channel coding and modulations. Both achievable rate and
error probability simulation show that the proposed scheme can operate close to
the benchmark scheme which assumes capacity-achieving signaling and perfect
SIC.Comment: 7 pages, 1 figure, accepted for presentation at IEEE ICC 2023. arXiv
admin note: substantial text overlap with arXiv:2212.0173
Doubly-Irregular Repeat-Accumulate Codes over Integer Rings for Multi-user Communications
Structured codes based on lattices were shown to provide enlarged capacity
for multi-user communication networks. In this paper, we study
capacity-approaching irregular repeat accumulate (IRA) codes over integer rings
for -PAM signaling, . Such codes
feature the property that the integer sum of codewords belongs to the
extended codebook (or lattice) w.r.t. the base code. With it, \emph{%
structured binning} can be utilized and the gains promised in lattice based
network information theory can be materialized in practice. In designing IRA
ring codes, we first analyze the effect of zero-divisors of integer ring on the
iterative belief-propagation (BP) decoding, and show the invalidity of
symmetric Gaussian approximation. Then we propose a doubly IRA (D-IRA) ring
code structure, consisting of \emph{irregular multiplier distribution} and
\emph{irregular node-degree distribution}, that can restore the symmetry and
optimize the BP decoding threshold. For point-to-point AWGN channel with -PAM inputs, D-IRA ring codes perform as low as 0.29 dB to the capacity
limits, outperforming existing bit-interleaved coded-modulation (BICM) and IRA
modulation codes over GF(). We then proceed to design D-IRA ring codes for
two important multi-user communication setups, namely compute-forward (CF) and
dirty paper coding (DPC), with -PAM signaling. With it, a physical-layer
network coding scheme yields a gap to the CF limit by 0.24 dB, and a simple
linear DPC scheme exhibits a gap to the capacity by 0.91 dB.Comment: 30 pages, 13 figures, submitted to IEEE Trans. Signal Processin