# Performance Analysis of MIMO System with Single RF Link Based on Switched Parasitic Antenna
## 1 Introduction  
With the rapid growth of mobile data services, the requirement for the communication speed and communication quality in today's wireless communication system is increasing constantly [1]. High speed, high spectral efficiency, high capacity and high reliability will be the dominant factors of modern communication system [2]. However, with increasingly complex wireless communication environment, channel fading caused by multipath propagation [3] is becoming more and more serious. At the same time, traditional multiplex communication technologies (frequency division multiplexing, time division multiplexing, code division multiplexing) are becoming increasingly difficult to cope with the tense situation of spectrum resources [4; 5; 6]. Under such circumstances, the MIMO system is put forward to solve the problem. The multipath signal transmission in traditional communication theory has always been the negative factor [7]; however, the MIMO technology can make full use of the multipath fading in the free space and exponentially increases the system transmission rate and the communication capacity [8]. Communication quality has been greatly improved for the limited spectrum resources and fixed transmit power by this technology [9]. The most prominent advantage of MIMO systems is that it can increase channel capacity and spectrum efficiency without increasing bandwidth and antenna transmit power [10], which will maximize the spatial multiplexing gain and diversity gain. In fact, the nature of improving the spatialmultiplexing gain is to maximize the spectrum utilization and improve channel capacity by introducing multi antennas [11; 12]. The nature of improving the diversity gain is to improve the channel reliability and reduce the system bit error rate by time-space encoding [13]. However, in MIMO communication technology, there are still some defects that limit development. First, in order to increase the spatial reuse of the MIMO system, the correlation between the MIMO channels and the mutual coupling between multi-antennas should be reduced as much as possible. However, the antenna dimension usually increases to at least half a wavelength and it is difficult to realize such large feed structure in the portable terminal device. Second, the MIMO system needs to equip the transmit antennas and receive antennas with a radio link, and the high cost and high power consumption in the amplifier and mixer will increase the overall system complexity. Therefore, improvement of the efficiency of the corresponding feeder system and simplification of the RF link in the MIMO system is a challenging issue in the field of MIMO technology. In order to reduce channel dependence, the decoupling network [14; 15] was used to ensure the isolation between antennas, but the network design is complex and the system bandwidth is too narrow. In order to simplify the RF link, the signal processing in the transmitter and receiver antenna will adopt the selection algorithm [16]. The algorithm selects the best transmission performance antennas as the transmitter and the receivers using the RF switch [17]. The antenna selection algorithm is considered to be the best when the system channel capacity reaches maximum [18]. In [19], a method for source separation based on the single source point identification and time frequency-smoothed \(l_{0}\) norm in non-cooperative electromagnetic case is proposed. In addition, some researchers have implemented space coding and time coding using spatial modulation [20] or the beamforming algorithm [21], which can be implemented in the RF domain and can effectively reduce the complexity of the system. However, with the increasing size of the MIMO system, the number of RF links is still very large and the simplification of the RF link has not been fundamentally solved. The single-link MIMO system based on SPA was proposed [22; 23].