Research On The Key Technologies Of Broadband Wireless Access In High Speed Scenario

The development of China Railway High Speed attracts the world's attention. There is a technology bottleneck between high mobility scenario and broadband wireless data transmission either the services for the passengers' wireless demands or for railway control system in High-Speed Railway Communication (HRC). While the mobile telecommunications technology evolved from the second generation to what is known today as beyond third generation (B3G), the same occurred with the telecommunication systems used in HRC. In this paper we will focus on the key technologies to enhance the performance of the broadband wireless access under high speed conditions.The wireless communication demands for the high speed railway is analyzed, and then the advantages and disadvantages are referred. We propose an architecture called High Speed and Mobile Cell (Himocell) to fulfill the broadband wireless needs for High-Speed Railway. The superiorities and drawbacks are evaluated. Additionally, the wireless channel of HRC is studied that the wireless channel of HRC is a double selective fading channel.Doppler spread is particularly detrimental to wireless communication performance especially for transmitting a long packet. In this case, the packet experiences rapidly varying fading compared with transmitting over the static channel. To deal with this problem, the uniform linear antenna (ULA) was proposed to compensate Doppler spread. The ULA consists of a linear antenna array which can be used as space samplers to estimate a virtual point that does not move during packet transmission but without the diversity gain. In this paper, we propose the optimal time diversity position with the ULA compensator over the time-varying Rayleigh fading channel. During transmission, this scheme can not only keep the channel quasi-static but also achieve the optimal time diversity by setting the virtual diversity receiving points at zeros of the time autocorrelation function. When combined with the orthogonal space time block code (STBC), it is proved that this scheme performs even better than that over the static channel with Monte Carlo simulation.Orthogonal frequency division multiplexing (OFDM) should estimate and track the wireless channel in the double selective fading channel. Generally, the comb-pilot number is more than the wireless channel order which makes the noise suppression difficult. We will propose a novel frequency diversity channel estimation method via groups of pilots combining which can reduce the noise. Doppler frequency offset due to the high speed movement destroys the orthogonality of the subcarriers resulting in the intercarrier interference (ICI), and degrades the performance of the system at the same time. We will propose a novel OFDM channel estimation algorithm with ICI mitigation based on the ICI self-cancellation scheme. With this method, more accurate channel estimation is obtained by comb-type double pilots and then ICI coefficients can be obtained to mitigate the ICI on each subcarrier under the assumption that the channel impulse response (CIR) varies in a linear fashion. The theoretical analysis and simulation results show that the BER and spectral efficiency performances are improved significantly under high-speed mobility conditions (350km/h-500km/h) in comparison to the classical ICI self-cancellation scheme.The sectorized antenna can be employed for Doppler mitigation and obtaining Doppler diversity gain. In this paper we will focus on the performances of this directional antenna. We will present the preferable partition scheme for the omnidirectional antenna and the Doppler compensation frequency. And the uncorrelated property of the signal received from the different sectorised antennas will be demonstrated which is utilized for Doppler diversity gain. Finally, it is proved by the simulation results that this architecture will show superior performance under high-mobility conditions.Fast verification of the prototype design upon software radio platform has become one of the most important content in communication assessment. This paper introduces the fundamental method of float-point and fixed-point simulation and rapid prototype design flow. Then some key issues such as OFDM frame synchronization, symbol timing, channel estimation, and so on are optimized, which significantly reduced the usage of hardware resources. The validness is illustrated here with experimental results from the implementation of OFDM burst frame transceiver.