Studies On Segment Minimum Mean Square Error Channel Estimation And Multi-Layer Dedicated Reference Signal Design For OFDM Systems

With the rapid progress of mobile communication and internet, broadband mobile access is the absolute trend for the next generation of mobile communication. Orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO), being able to achieve higher data rate and better spectrum efficiency, are assumed to be the key technologies of physical layer in the next generation of mobile communication. This dissertation focused on MIMO-OFDM system and made a thorough research on the key theories and technologies including channel estimation and dedicated reference signal design. The major work and contribution of this dissertation are summarized as follows:1. Research on the OFDM channel estimation based on reference signalThis dissertation summarized the classical algorithms of channel estimation and proposed an improved OFDM channel estimation scheme-segment minimum mean squared error (SMMSE) channel estimation. Firstly, the system bandwidth was consecutively divided into several subbands of uniform size. Then the minimum mean squared error (MMSE) channel estimation was performed in the frequency direction within every subband in the OFDM symbols with reference signals, and the channel estimation results of the whole system bandwidth on these OFDM symbols were derived. Finally, on every tone, the MMSE channel estimation was performed in the time direction using the former result of the OFDM symbols with reference signals. The complexity analysis and block error ratio (BLER) performance showed that, this scheme simplified the former MMSE algorithm and reduced the computation to a large extent with little performance loss. With this scheme, the MMSE channel estimation can be efficiently applied to practical system.2. Research on the OFDM parametric channel estimationConsidering that the MMSE channel estimation need prior statistic information of channel, this dissertation proposed an OFDM parametric channel estimation scheme with little delay and low computation based on the SMMSE channel estimation above, and the specific implementation was also provided. This scheme including that:the estimation of multi-path parameter, the estimation of maximum Doppler frequency shift and the combination of channel parameter estimation and SMMSE channel estimation. In this scheme, few subframes were needed and the delay was little, which assured the validity of the estimation result. Additionally, this scheme used the operations with less computation to limit the overall complexity. The simulation results showed that, the channel parameters can be estimated accurately in this scheme, making the SMMSE channel estimation applicable to various channel environments. Further more, the simulation results showed that this scheme outperformed the classical parametric channel estimation method.3. Design of dedicated reference signal in MIMO-OFDM systemDedicated reference signal has many advantages over common reference signal on multi-layer transmission. This dissertation thoroughly studied the design of dedicated reference signal in terms of density, multiplexing method and location for two-layer transmission in MIMO-OFDM system. For the density of dedicated reference signal, the effects on channel estimation performance and transmission resource occupation were considered together. These two effects were translated into the equivalent signal to interference plus noise ratio (SINR) respectively, and the overall equivalent SINR was derived from Shannon limit. Among the candidate densities, the density with least SINR loss was chosen as the best one. For the multiplexing method and location of dedicated reference signal, two methods to implement the orthogonality of dedicated reference signal accross layers were deduced-frequency division multiplexing and code divison multiplexing. For each multiplexing method, the best location of dedicated reference signal was studied targeting on the spectrum efficiency and the practicability. Finally, by comparing these two multiplexing methods and the spectrum efficiency of different patterns, the best dedicated reference signal pattern for two-layer transmission was derived. The research method can be extended to higher rank transmission, and the research result can also be regarded as the basis for higher rank design.The research productions related to this dissertation are accepted as papers in IEEE journals and conference.