Irregular RIS Pattern Array-Based Index Modulation for Next-Generation RIS Communication

Abstract

Irregular reconfigurable intelligent surface (RIS)-assisted transmission has emerged as a promising candidate for beyond 6G communication because of its superiority to enhance spectral efficiency (SE). However, a sufficiently large number of grid at irregular array of RIS leads to unused patterns combination. This letter introduces a novel irregular-pattern-array-based index modulation (IPAIM) to exploit redundant patterns as an additional information to increase bits per channel usage (BPCU). In contrast with regular array and existing IM based RIS, the concept of IPAIM is to activate an arbitrary number of elements on irregular array grid. Therefore, a set number of unique irregular pattern array can be utilized as an index to convey additional bits. To verify the computer simulation results, this letter derive theoretical approximation for achievable rates, bit error rates (BER), and energy efficiency (EE) with spatially correlated channel model. Both simulation and theoretical indicate that IPAIM outperform conventional regular RIS based IM.