Multidimensional Index Modulation for 5G and Beyond Wireless Networks

This study examines the flexible utilization of existing IM techniques in a comprehensive manner to satisfy the challenging and diverse requirements of 5G and beyond services. After spatial modulation (SM), which transmits information bits through antenna indices, application of IM to orthogonal frequency division multiplexing (OFDM) subcarriers has opened the door for the extension of IM into different dimensions, such as radio frequency (RF) mirrors, time slots, codes, and dispersion matrices. Recent studies have introduced the concept of multidimensional IM by various combinations of one-dimensional IM techniques to provide higher spectral efficiency (SE) and better bit error rate (BER) performance at the expense of higher transmitter (Tx) and receiver (Rx) complexity. Despite the ongoing research on the design of new IM techniques and their implementation challenges, proper use of the available IM techniques to address different requirements of 5G and beyond networks is an open research area in the literature. For this reason, we first provide the dimensional-based categorization of available IM domains and review the existing IM types regarding this categorization. Then, we develop a framework that investigates the efficient utilization of these techniques and establishes a link between the IM schemes and 5G services, namely enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communication (URLLC). Additionally, this work defines key performance indicators (KPIs) to quantify the advantages and disadvantages of IM techniques in time, frequency, space, and code dimensions. Finally, future recommendations are given regarding the design of flexible IM-based communication systems for 5G and beyond wireless networks.Comment: This work has been submitted to Proceedings of the IEEE for possible publicatio

IQI mitigation for narrowband iot systems with OFDM-IM

WOS: 000444509800001The crucial aim for 5G narrowband Internet of Things (NB-IoT) is to support massive connectivity with wide coverage area, low power consumption, low hardware complexity, and low data rate. Direct conversion receiver (DCR) has a simple structure to fulfill NB-IoT requirements. However, a significant degradation has been observed on the performance of orthogonal frequency division multiplexing (OFDM) systems with the DCR due to in-phase and quadrature imbalance (IQI) at RF front-end. Estimation and mitigation of IQI in OFDM systems require an iterative receiver at the expense of high complexity and power consumption. In this paper, OFDM with index modulation (OFDM-IM) is proposed as a promising candidate in order to meet the demands of NB-IoT use cases. OFDM-IM-based systems carry data information not only by modulated subcarriers but also by indices of fractionally used subcarriers. A non-iterative and efficient receiver that exploits inactive subcarriers is introduced to mitigate the effect of IQI for NB-IoT with OFDM-IM. Cyclic redundancy check algorithm is used to investigate the accuracy of the receiver under IQI. Theoretical analysis and computer-based simulations show that the proposed non-iterative receiver for OFDM-IM in NB-IoT under IQI works very well in various scenarios. Moreover, our findings show that the OFDM-IM under IQI provides higher signal-to-interference ratio in comparison with classical OFDM