Problem
Research questions and friction points this paper is trying to address.
Code Index Modulation
Spreading-Code Indices
Information Allocation
Code-Domain Grouped Index Modulation for Spectrally Efficient Spread-Spectrum Communications
🤖 AI Summary
为提高扩频通信效率，提出了一种码域分组索引调制方法(CGIM)，通过将正交扩频码库分组并映射QAM符号到独立的码索引来实现信息的有效分配。
📝 Abstract
Efficient exploitation of spreading resources is important for improving the transmission efficiency of spread-spectrum communications. Code index modulation (CIM) conveys additional information through spreading-code indices without requiring extra radio-frequency chains. The fixed number of code-index branches in existing CIM schemes limits information allocation between the code-index and modulation-symbol domains as the target rate increases. This paper proposes code-domain grouped index modulation (CGIM), which partitions an orthogonal spreading-code bank into multiple groups and maps the in-phase and quadrature components of one quadrature amplitude modulation (QAM) symbol in each group onto two independent code indices. Group-wise despreading enables parallel detection. Group-wise maximum-likelihood (ML) and low-complexity greedy detection (GD) are developed, with both achieving joint ML decisions under the stated conditions. A pairwise error probability (PEP)-based bit error rate (BER) analysis is derived for Rayleigh and Nakagami-$m$ fading, with additive white Gaussian noise (AWGN) as a benchmark. Numerical results show that CGIM achieves better BER performance than traditional CIM benchmark schemes at the same transmission rate, owing to a more balanced distribution of information bits between the code-index and modulation-symbol domains.
Innovation
Methods, ideas, or system contributions that make the work stand out.
Code-Domain Grouped Index Modulation (CGIM)
Group-wise Despreading
Maximum-Likelihood Detection
Greedy Detection
Bit Error Rate Analysis
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