Mobile Velocity Estimation In Next-Generation Mobile Communication Systems

The next generation or beyond 3rd generation (B3G) systems have become one of the hottest areas in the field of mobile communications. The bandwidth efficiency, multi-path robustness and expandability leads orthogonal frequency division multiplexing (OFDM) to be one of the most competitive technologies in next generation mobile communication systems. Estimation of the mobile terminals (MTs) velocity or, equivalently, the maximum Doppler spread, is useful in improving network control algorithms, such as handoff or cell-layer-assignment, and necessary for the optimal tuning of parameters for systems that adapt to changing channel conditions. This dissertation focuses on velocity estimation in OFDM mobile communication systems.Firstly, the time-frequency fading which the signal undergoes in wireless communications is introduced, and three typical methods of velocity estimation for single carrier system, zero-crossing rate (ZCR), level-crossing rate (LCR), and covariance function (COV), are presented.A velocity estimator for OFDM or other multi-carrier systems is proposed. Instead of using received signal, this method relies on the channel estimates. Except input, implementation of the proposed method is the same as the typical velocity estimator. The steps of LCR, ZCR and COV estimators for OFDM are designed separately. Their performance in additive white gaussian noise (AWGN) channel are analyzed and compared. Simulations show that they have the same performance. Finally, based on the characteristic of performance in AWGN, a useful application is available by improving channel estimation.Additionally, an accurate scheme based on COV estimator is proposed. This method corrects the estimation errors by adjusting estimation interval. Considering the effect of interval on the original estimation accuracy and noise factors, the optimal interval, which minimizes estimation errors, is derived. It is related with MT's velocity. In order to reach the optimal interval, joint velocity estimation and interval calculation are applied. Finally, the feasibility of proposed algorithms is discussed.Field-programmable gate arrays (FPGA) design of the proposed velocity estimator for OFDM is accomplished with Verilog hardware description language (HDL). Utilizing some equivalent algorithms, the implementation structures of numerical calculations are optimized, and the circuit scale is largely reduced. Finally, an experimental system has been developed for practical verification of FPGA design. It offers a platform for future development.