On The Performance Of MIMO MRC Systems And Grating-Lobe Suppression Technique Of Antenna Array

With the rapid development of wireless communication, one has the requirement of higher data rates and link quality. However, frequency spectral resource has become increasingly precious. Meanwhile fading and multipath distortion of wireless transmission cannot be ignored. Multiple-input multiple-output (MIMO) systems employing multiple antennas at both transmitter and receiver are capable of exploiting spatial resource and can provide significant improvements in capacity and link performance without requiring extra power or bandwidth. This thesis presents the research on performance of MIMO systems with maximum ratio transmission at the transmitter and maximum ratio combining (MRC) at the receiver, simply called MIMO MRC, and grating-lobe suppression technique of antenna array.Firstly, performance of MIMO MRC systems is investigated in the presence of co-channel interferences (CCI). MIMO MRC system model is established when CCI and channel estimation error are considered together. Based on the model, closed-form expressions for cumulative distribution function (CDF) of the output signal-to-interference plus noise ratio and symbol error rate (SER) of MIMO MRC systems with equal-power and unequal-power CCI are derived respectively. By using these expressions, the impact of CCI and channel estimation error on system performance can be easily obtained without any numerical integrations or statistical simulations. Results show that in the presence of CCI, the SER performance is less sensitive to estimation error. Next, by using the matrix theory and multivariate statistical analysis, probability density function and CDF for the largest eigenvalue of the correlated complex Wishart matrix are provided. Exact expressions for capacity performance, including outage capacity and average capacity, of MIMO MRC systems with correlation at the transmitter and receiver are derived respectively. And the impact of spatial correlation is investigated.Then, the impact of spatial correlation on the combination of spatial diversity and multiuser diversity is investigated. Exact expressions for outage capacity and average capacity of multiuser diversity system combined with MIMO space-time block coding (STBC) and MIMO MRC respectively are derived in receive-correlated channels. Based on them, system capacity is analyzed. The analytical results are validated by the simulated results.Finally, the grating-lobe suppression methods for narrow-band and wideband arrays are discussed based on the analysis of the mechanism of producing the grating lobes. For narrow-band signals, three uniform linear arrays, whose grating lobes are not overlapped by setting the angles between the arrays and the same pointing of main-lobes, are used and then multiplication of three patterns is operated to reduce the grating lobes of large-spaced array, which makes the array operate in broad band. For wideband or ultra-wideband signals, array pattern in the whole frequecy band is identical by designing the frequency-dependent weighting coefficients based on the Bessel function, and therefore grating lobes in high frequency parts are suppressed.