Research Of Carrier Synchronization And Antenna Array Calibration In Wideband Wireless Communication Systems

Multi-carrier and multiple antennas are important architecture in the next generation wireless communications to achieve broadband, high-speed, spectral-efficient communication performance. Orthogonal Frequency Division Multiplexing (OFDM) as a spectral-efficient form of frequency division multiplexing is a promising multi-carrier technology. For each sub-carrier, the channel can be considered as a flat-fading channel in OFDM systems. However, the vital problems when using OFDM in wireless communication systems are its sensitivity to carrier synchronization and high peak-to-average ratio. Thus, carrier synchronization technology is a key factor for OFDM.Meanwhile, multi-antenna technology, such as Multiple Input Multiple Output (MIMO), smart antenna and distributed antenna, is widely used in the next wireless communication systems as a spectral-efficient approach. Especially, smart antenna and MIMO defined in ITU-R report on technology trends can enhance by multiple folds the capacity of communication system and spectrum utilization without increasing bandwidth. Combining MIMO and OFDM will satisfy the demand of the next generation systems. MIMO-OFDM technology is a brand new technology that combines OFDM and MIMO to improve the quality of signals by using antenna array to realize spatial multiplexing and spatial diversity. It utilizes time, frequency and spatial diversity technologies to greatly enhance its tolerance to noise, interference and multipath. However, this combination is not a simple one that additionally creates several new technical challenges because there exists multiple parallel radio channels with different characteristics which complicates the problems.In a multiple antenna system, it is required in engineering that the amplitude and phase errors in the units of antenna array and radio frequency channels are rather small compared with theoretical design in order to guarantee system performance. Smart antenna has much high requirement for the units and channels to form accurate radio beams. However, for the reasons of manufacture, aging of apparatus and temperature variance, it is required for antenna, feed cable, and radio channel composed of analogue apparatus to correct first before using.