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TopI. Introduction
CONTEMPORARY communication systems are required to provide robust design in rapidly changing channel environment. While the fifth generation (5G) of mobile technology is rapidly deployed now and the internet of things (IoT) revolution is coming, many applications such as industrial sensors, wearables, and medical devices are operated in either stationary or mobile fading channels. Regardless of the operation condition, the interference mitigation is important to maintain quality of service in the communication link.
Many baseband block coding schemes, such as space-time (ST), space-frequency (SF), and space-time-frequency (STF) techniques (Bauch, 2003; Eilert, 2008; Idris, 2008) have been studied recently in conjunction with the orthogonal frequency division multiplexing (OFDM) to enhance system performance. OFDM is a combination of multi-carrier modulation and multiplexing system. It is well known that OFDM is to partition a high-data-rate signal into smaller low-data-rate signals so that the data can be sent over many low-rate subchannels in parallel. OFDM is popular and applied to 3G, 4G, and 5G since it has high spectral efficiency due to overlapping subcarrier spectra. The ST-OFDM system provides the spatial and temporal diversities offered in the multi-antenna system. One of the disadvantages of ST-OFDM systems is the sensitivity of its performance to synchronization error, such as frequency error. The Doppler effects in mobile fading channels, can lead to a loss in orthogonality between subcarriers at the receiver and results in intercarrier interference (ICI), and significant bit error rate (BER) degradation.
Many ICI mitigation schemes have been proposed, such as ICI self-cancelation (SC) (Zhao & Haggman, 2001), extended Kalman filter (Shi, 2010), OFDM symbol time compression in one half duration (El-Bakry, 2017), parallel cancellation (PC) (Yeh & Wang, 2004; Yeh & Wang, 2007; Yeh & Yao, 2012; Yeh et al., 2016), and conjugate cancellation (CC) (Wang et al., 2013; Yeh, 2015; Yeh et al., 2009; Yeh et al., 2007). The PC scheme employs the two-path transmission technique architecture to transmit one OFDM symbol in two parallel OFDM blocks. Although the redundancy causes a reduction in bandwidth efficiency, it can be compensated by using a larger signal alphabet size to regain the bandwidth efficiency as that of the regular ST scheme due to its excellent ICI suppression.