Abstract
Dual-mode (DM) or multi-mode (MM) index modulation (IM) techniques with the in-phase/quadrature (IQ) format have been investigated for improving the performance of the orthogonal frequency division multiplexing with IM (OFDM-IM) system in the frequency-selective Rayleigh fading channel. However, all subcarriers in these schemes must be activated so that the energy efficiency (EE) of the system inevitably decreases. In this paper, we propose a novel modulation scheme named quadrature tri-mode index modulation (QTM-IM) technique to achieve a trade-off between the spectral efficiency (SE) and EE. The proposed QTM-IM can also be flexibly extended into multi-mode form called MM with enhanced IQ (MM-EIQ). The multi-mode $M$ -ary pulse amplitude modulation (PAM) constellations containing the origin point are designed to map the information bits into the active subcarriers. On the other hand, the theoretical analysis of IM-based schemes over the Rician fading channel has been conducted since most previous papers only considered the Rayleigh fading channel. At the receiver, three kinds of detectors with different algorithm complexities are employed for signal demodulation. Finally, the computer simulation results demonstrate the enhancement of the proposed schemes. More specially, (i) QTM-IM achieves 4dB signal-to-noise ratio (SNR) gain at the BER level of 10−5 compared with quadrature DM (QDM) scheme with the same SE in the Rician fading channel and (ii) MM-EIQ harvests 0.89 bits/s/Hz SE gain and almost doubles the EE compared with MM-IQ scheme without any SNR loss over the Rayleigh fading channel.
Highlights
I NDEX modulation (IM), a novel modulation technique, has been considered for its application to the fifth-generation (5G) wireless networks [1,2,3,4], which can utilize the time slot [5], spreading codes [6], antenna index [7], and subcarrier index to implicitly transmit information bits without extra energy consumption.Recently, a promising IM technique known as spatial modulation (SM) has emerged which utilizes the spatial domain to transmit information bits besides the conventional signal constellations [7]
In order to increase the number of the index bits, a scheme named layered orthogonal frequency division multiplexing with IM (OFDM-IM) (L-orthogonal frequency division multiplexing (OFDM)-IM) was proposed in [14], where the subcarriers in a subblock are partitioned into several layers and the activated subcarriers and their symbols are determined in each layer separately
The signal-to-noise ratio (SNR) per bit is defined as Eb/N0, where Eb is the average energy per bit
Summary
I NDEX modulation (IM), a novel modulation technique, has been considered for its application to the fifth-generation (5G) wireless networks [1,2,3,4], which can utilize the time slot [5], spreading codes [6], antenna index [7], and subcarrier index to implicitly transmit information bits without extra energy consumption. In order to increase the number of the index bits, a scheme named layered OFDM-IM (L-OFDM-IM) was proposed in [14], where the subcarriers in a subblock are partitioned into several layers and the activated subcarriers and their symbols are determined in each layer separately. In [17], the dual-mode index modulation aided OFDM (DM-OFDM) is proposed to improve the achievable transmission rate of OFDM-IM in which only a part of subcarriers are activated for constellation symbol mapping. The IM process is independently executed on the in-phase and quadrature components, where the corresponding dual-mode pulse amplitude modulation (PAM) constellations are designed for constellation symbol mapping. In order to ensure EE of the proposed scheme, we set that k1 + k2 = k < l, where k is the number of active subcarriers in the in-phase component of a subblock. Based on the discussion about the signal demodulation, we will give the design principles of the constellation in subsection
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