Investigation and Implementation of Novel STBC MIMO-OFDM Time and Frequency Synchronization Techniques for WiMAX Systems

For satisfying the growing demand of high data rates and good quality in wireless communications, WiMAX (the Worldwide Interoperability for Microwave Access) seems to be a solution for future communication systems. WiMAX, a commercialized standard of the IEEE 802.16 Working Group, aims to provide business and consumer wireless broadband service on the scale of the Metropolitan Area Network (MAN). This technology has a target range of up to 31 miles and a target transmission rate of 100 Mbps for low mobility users and 1 Gbps for high mobility users. Since two powerful techniques, orthogonal frequency division multiplexing (OFDM) and multi-input multi-output (MIMO) antennas, have been combined as a main transmission scheme in WiMAX standard, the study of MIMO-OFDM system is an important subject for the future world. In this project, we focus on frequency synchronization and timing synchronization problems in the MIMO-OFDM systems. As we known, one major drawback of the OFDM technique is the high sensitivity of the frequency offset. Compared to single subcarrier systems, OFDM systems would cause high BER when a little amount of frequency offset exists. Accurate frequency offset estimation often requires correct timing synchronization to avoid the interference between OFDM symbols. Therefore, it is an important issue to develop low-complexity and high-performance frequency and timing synchronization methods for MIMO-OFDM systems. In this project, we plan to use the characteristics of the space-time block code (STBC) in MIMO systems to develop new timing and frequency synchronization techniques for MIMO-OFDM systems. We have designed a preliminary STBC structure for timing and frequency synchronization, and verified by computer simulation results this start-up algorithms have better synchronization performance than the existing synchronization methods. Although this preliminary method has an exciting result, we find this method is not an optimal solution and still has plenty space to improve. Based on these observations, we aim to develop low-complexity and high-performance frequency and timing synchronization methods for STBC MIMO-OFDM systems in this project and accomplish the corresponding floating-point and fixed-point simulations. We also want to implement the developed synchronization algorithms on Lyrtech SignalWAVe and Software-defined Radio (SDR) Development DSP+FPGA Platforms to form a prototype of a simplified MIMO-OFDM transmission system and evaluate the transmission performance in real systems. We expect to accomplish the following items in this project: (1.1) Develop suitable STBC coding structures for the synchronization (timing and frequency)of MIMO-OFDM systems. (1.2) Based on the developed STBC coding structures, design algorithms to achieve the timing and frequency synchronization of the MIMO-OFDM systems, and investigate the joint performance of the timing and frequency synchronization algorithms. (1.3) Verify the developed MIMO-OFDM STBC synchronization algorithms for multipath time and frequency selective channels and accomplish the corresponding floating-point and fixed-point simulations. (1.4) Implement the developed MIMO-OFDM STBC synchronization algorithms on Lyrtech SignalWAVe and SDR Development DSP+FPGA Platforms to verify the performance in real communication systems.

Project ID:PB9907-4027
External Project ID:NSC99-2221-E182-024