- The paper introduces a coded modulation strategy that leverages probabilistic amplitude shaping to operate within 1 dB of AWGN capacity.
- It integrates DVB-S2 LDPC codes with rate adaptation and eliminates iterative demapping for efficient bipolar ASK and QAM performance.
- The method achieves significant spectral and energy efficiency gains, demonstrating up to a 4 dB improvement at high spectral efficiencies.
Bandwidth Efficient and Rate-Matched Low-Density Parity-Check Coded Modulation
This paper presents a novel approach to coded modulation, focusing on bandwidth efficiency and adaptability to varying signal-to-noise ratios (SNR) over the additive white Gaussian noise (AWGN) channel. The proposed scheme integrates a distribution matcher and a systematic binary encoder at the transmitter for probabilistic signal shaping and channel coding, avoiding iterative demapping at the receiver. This design is directly applicable to bipolar amplitude shift keying (ASK) and two-dimensional quadrature amplitude modulation (QAM) constellations, utilizing DVB-S2 low-density parity-check (LDPC) codes.
Key Components and Methodology
- Probability Amplitude Shaping (PAS): The core of this scheme lies in probabilistic amplitude shaping, which mediates between shaping gains and coding gaps by optimizing amplitude distribution. Specifically, amplitudes are assigned probabilities based on Maxwell-Boltzmann distributions. The proposed method allows the system to operate within 1 dB of channel capacity for various spectral efficiencies.
- Rate Adaptation: The modulation scheme adapts its rates by adjusting amplitude distributions and constellation scale. This offers a finer granularity in modes compared to previous DVB-S2 standards, significantly improving energy efficiency, especially at high spectral efficiencies. The method demonstrates gains of up to 4 dB for certain spectral efficiencies, showcasing effective rate adaptation mechanisms.
- Bit-Metric Decoding: A binary decoder processes the output of a bitwise demapper at the receiver. Notably, the system foregoes iterative demapping, as traditionally required in methods founded on Gallager’s scheme or superposition coding.
- Universal Code Design: The scheme employs DVB-S2 LDPC codes across various code rates and modulations, optimizing bit-mapping to match distinct channel conditions effectively. This is further enhanced by using a constant composition distribution matcher to provide a binary interface and facilitate rate adaptation.
Numerical Results and Analysis
The authors provide rigorous numerical results demonstrating the system's performance across spectral efficiencies between 1 and 5 bits/s/Hz, achieving within 1 dB of the AWGN capacity. For 64-ASK constellation and a code rate of 9/10, the system exhibits a spectral efficiency advantage over conventional equiprobable signaling schemes. These outcomes underscore the practical viability of the proposed system to substantially enhance bandwidth and power efficiency.
Implications and Future Directions
This research holds significant promise for communications systems requiring flexible and efficient resource usage, notably within satellite and broadband applications employing DVB-S2 standards. The ability to closely approach theoretical limits of channel capacity with practical coding and modulation schemes presents opportunities for enhancing data throughput and reducing power expenditure.
Future inquiries should consider the application of this modulation scheme within multi-input multi-output (MIMO) frameworks and examine performance under varying channel conditions, including those with rapid fading and interference. Additionally, expanding on short block length scenarios could confirm the broader applicability of this approach within latency-sensitive applications.
In summary, this paper introduces a significant advancement in coded modulation methodologies, achieving efficient rate matching and probabilistic shaping to closely approach AWGN capacity, all within a feasible and scalable framework.