Tutorial for Space-Time ICI Parallel Cancellation Techniques for OFDM Systems

Introduction

Orthogonal frequency division multiplexing (OFDM) communication systems have received substantial consideration as a bandwidth efficient modulation and multiplexing technical scheme for high data rate wireless applications, specifically for the 3rd, 4^th, and 5th generations (3G, 4G, 5G) of cellular technology. Many applications, such as internet of things (IOT), unmanned aerial vehicle (UAV), wearable devices, and health monitoring devices are identified in the daily operation and usages. However, the factors such as carrier frequency offset, time variations due to Doppler shift or phase noise led to a loss in the orthogonality between subcarriers and results in inter-carrier interference (ICI) which degrades the bit error rate (BER) performance of OFDM systems significantly. Many ICI mitigation schemes such as ICI self-cancellation (SC), frequency-domain equalization, and the time domain windowing scheme have been proposed (Alamouti, 1988; Yeh & Wang, 2004; Yu et al., 2007; Seyedi & Saulnier, 2005; Yeh et al., 2007). The well-known SC method in (Alamouti, 1988) applies the repetitive transmission in a per-subcarrier basis, while the parallel cancellation (PC) (Yeh & Wang, 2004; Yeh & Zhou, 2022) apply the repetitive transmission in a per-OFDM symbol basis.

Further developing the idea of the PC scheme to mitigate the ICI of OFDM systems, we expand this PC scheme into a space-time (ST) coded system (Alamouti, 1988; Li & Xia, 2008; Yusof & Zamani, 2008) and form a simple STPC-OFDM system. Since the ST scheme is robust to block size, the STPC scheme is also robust to block size. Additionally, the PC scheme provides a much higher signal-to-ICI ratio (SICIR) than does the regular OFDM system when Doppler shift or residual carrier frequency offset (CFO) exists. Hence the PC scheme lowers error floor for OFDM systems in frequency selective fading channels with Doppler frequency. This characteristic is extended to the STPC-OFDM system and improves the BER significantly. We focus on the architecture and BER performance comparison of the PC-, ST- and STPC-OFDM systems via simulations in frequency selective fading channels. Although our primary focus is the performance of STPC with frequency offset, STPC also performs well when ICI is caused by other factors, such as phase noise, timing error, and time varying channels. Since the scheme is very simple, they can be applied to mitigate ICI alone, or combined with techniques, such as channel coding schemes to further improve diversity gain and coding gain in multiple input single output (MISO) and multiple input multiple output (MIMO) systems with industrial and commercial applications, such as robots, and sensors, manufacture, and smart factory, etc. There are other software defined radio transceivers and networks (Chang et al., 2012, 2013; Yeh & Ingerson, 2010; Nasir et al., 2016; Wen et al., 2013; Ma, 2017; Kumar & Rao, 2018) which can be combined with MIMO to further enhance systems performance and lower cost. Moreover, (Yeh & Zhou, 2022) shows that a higher modulation scheme compensates the bandwidth efficiency in the STPC-OFDM and STCC-OFDM schemes.