Receiver Design for Dual-Mode Index Modulation Aided OFDM

Nowadays, variants of Spatial Modulation (SM) are studied by a lot of researchers in order to increase Spectral Efficiency (SE) more. One of the important variants of SM is known as Orthogonal Frequency Division Multiplexing Index Modulation (OFDM-IM). In OFDM-IM, selection of active subcarriers is based on the idea of the selection of active antennas in the SM. Then, to take OFDM-IM a step further in terms of SE, Dual Mode OFDM-IM (DM-OFDM-IM) has been proposed that activates entire subcarriers unlike that of OFDM-IM. However, in all these studies same assumption is made, i.e., channel is perfectly known at the receiver. However, this assumption is not accurate for practical applications. For this reason, the presented simulation results and theoretical analysis without channel estimation cannot represent the real system performance. In this study, a pilot symbol aided channel estimation for DM-OFDM-IM scheme is considered. We investigate the effect on Bit Error Rate (BER) performance of five different interpolation techniques. The simulation results illustrate that, interpolation techniques perform similiar BER performance for low and moderate Signal-to-Noise Ratio (SNR) range. However, at the high SNR values (SNR> 30 dB), Low-Pass and SPLINE interpolation techniques give the highest performance among all considered techniques.

I. Introduction

Since its first introduction in 2006, Spatial Modulation (SM) has received considerable attention from the academic community [1]. SM provides a new dimension to carry data bits besides well-known constellation mapping. Inspired by the underlying idea of SM, Subcarrier Index Modulation (SIM) and enchanced SIM are proposed for Orthogonal Frequency Division Multiplexing (OFDM) [2], [3]. Then, in 2013, OFDM-IM method has been introduced by Basar et.al. [4]. According to [4], subcarriers are split into subblocks. In each subblock, some of the subcarriers are activated to convey symbols and the remains are unused. While active subcarriers are determined to index bits, conveying symbols are created by bits entering constellation mapper. Not only providing high Spectral Efficiency (SE) in OFDM-IM, but also the better Bit Error Ratio (BER) is obtained compared to classical OFDM at the same time. In 2016, Dual Mode OFDM-IM (DM-OFDM-1M) has been proposed which activates all subcarriers to convey symbols. In this manner, more SE is provided compared the OFDM-IM. Within a very short period of time, various DM-OFDM methods have been proposed that further increase SE [5]–[7]. All these studies assume that channel knowledge is perfectly known at the receiver. However, Channel Estimation (CE) methods for DM-OFDM-IM based systems have not been studied yet. Addressing this gap, various interpolation techniques for channel estimation method are investigated for DM-OFDM-IM technique in Rayleigh fading channel.