APSK Modulation and Demodulation Algorithms with BICM-ID

Implementation of APSK modulation and demodulation algorithms in BICM-ID systems

APSK (Amplitude Phase Shift Keying) is an efficient digital modulation scheme that transmits information by simultaneously adjusting the amplitude and phase of the carrier wave. Compared to traditional PSK or QAM, APSK achieves a better balance between power efficiency and spectral efficiency, making it particularly suitable for nonlinear channel environments such as satellite communications. Code implementation typically involves creating constellation mapping tables and implementing amplitude/phase modulation functions.

BICM-ID System Overview BICM-ID (Bit-Interleaved Coded Modulation with Iterative Decoding) is a technique that combines channel coding and iterative detection. The core concept involves improving system bit error performance through bit interleaving and iterative decoding. In APSK modulation, BICM-ID fully utilizes both amplitude and phase information of symbols, enhancing decoding accuracy through soft information exchange. Algorithm implementation requires careful design of interleaver/deinterleaver functions and iterative feedback loops.

APSK Modulation Principles The APSK constellation diagram typically consists of multiple concentric circles, with different numbers of phase points distributed on each circle. This structure allows flexible allocation of power and phase to adapt to different channel conditions. During modulation, the input bit stream is mapped to APSK constellation points, where higher-power circles are typically used to transmit more important bits to improve system robustness. Implementation involves creating mapping functions that convert binary sequences to complex constellation symbols.

Demodulation and Iterative Detection The demodulator first calculates the log-likelihood ratio (LLR) for each bit based on the received signal. These soft metrics are then passed to the channel decoder (such as LDPC or Turbo codes). Within the BICM-ID framework, the decoder feeds updated soft information back to the demodulator, performing multiple iterations to gradually correct errors. This iterative process significantly improves system performance under low signal-to-noise ratio conditions. Code implementation requires LLR calculation algorithms and iterative message passing between demodulation and decoding modules.

Simulation and Applications Simulations can verify the combined performance of APSK and BICM-ID. Common evaluation metrics include bit error rate (BER) and packet error rate (PER). Results show that compared to traditional modulation schemes, APSK combined with BICM-ID achieves lower error rates at the same power level, making it particularly suitable for bandwidth-limited or power-constrained communication scenarios. Simulation code typically involves channel modeling, noise addition, and performance metric calculation functions.

Conclusion The combination of APSK modulation and BICM-ID algorithms provides an efficient and reliable solution for modern communication systems. Its flexible constellation design and iterative decoding mechanism enable excellent performance under complex channel conditions, showing broad application prospects in satellite communications and 5G/6G systems. Future implementations may focus on optimizing iterative algorithms and hardware-efficient designs.