Design of Manifolds Learning‐Aided SCMA‐OTFS With Index Modulation for Coordinated Multipoint Vehicular Communication Systems

ABSTRACT This work introduces a new SCMA‐OTFS (Sparse Code Multiple Access–Orthogonal Time Frequency Space) with index modulation (IM) for coordinated multipoint vehicular communication systems. The system is modeled as an uplink CoMP system with remote radio head and baseband unit. Users' messages are divided into data bits and index bits. The SCMA codebook encodes the data bits, while index bits specify active resources. Each data bit is converted into SCMA codewords using a variational transformer autoencoder with manifolds learning (VAE‐MFL)‐based codebook mapping. The SCMA‐IM aims to enhance spectrum efficiency and throughput by combining index modulation with the SCMA method. It uses the codebook index to encode information, allowing for extra information representation. The system uses SCMA and index modulation to encode data, identifying users by sparse codewords and index locations. The system then transforms the delay‐Doppler domain signal into the time domain to obtain a time domain symbol vector. These vectors travel across the wireless channel to a remote ratio head (RRH) mounted on road infrastructure. The RRHs wirelessly connect to a centralized baseband unit (BBU) after receiving signals from every user. The time‐domain symbol is estimated using a time‐domain LMMSE (linear minimum mean squared error)‐based OTFS detection technique. The delay‐Dopper domain received symbol is acquired, and user bits are recovered using SCMA decoding. A probabilistic recurrent‐based SCMA decoder is introduced to precisely recover user bits. As a result, ABER values of 2.00E‐05 for proposed bound and 2.25E‐05 for proposed Simulation are achieved with the proposed transmission power of 31 dBm.