Investigation and Implementation of SFBC MIMO-OFDM Peak-to-Average Power Ratio Reduction 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 peak-to-average power ratio (PAPR) reduction problems in the MIMO-OFDM systems. As we known, one major drawback of the OFDM technique is the high peak-to-average power ratio (PAPR) of the transmitter’s output signal. When an OFDM signal with high PAPR is passed through the nonlinear device, such as a transmit power amplifier, it may suffer from significant intermodulation distortion and out-of-band radiation. High PAPRs in OFDM signals also brings an increased complexity of the digital-to-analog and analog-to-digital converters and a reduced efficiency of the transmit power amplifier. Therefore, it is an important issue to develop a low-complexity and high-performance PAPR reduction method for MIMO-OFDM systems. In the first year of this project, we plan to use the extra degree of freedom, provided by the space-frequency block coded (SFBC) MIMO-OFDM systems, to develop PAPR reduction techniques. A preliminary method has been proposed in the 2009 IEEE Vehicular Technology Conference - Spring (VTC 2009-Spring) [98]. Compared with the conventional PAPR reduction method, this proposed scheme shows a better PAPR reduction performance without affecting the SFBC structure in MIMO-OFDM systems. 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 a general PAPR reduction method for SFBC MIMO-OFDM systems in this project and accomplish the corresponding floating-point and fixed-point simulations. We also note the problem of high computational complexity of the MIMO-OFDM PAPR reduction method and plan to apply our previous idea [95], proposed in the IEEE Transactions on Signal Processing, to develop a low-complexity PAPR reduction method for SFBC MIMO-OFDM systems. We also want to implement the developed low-complexity PAPR reduction algorithm 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 two years: The First Year (August 2009 ~ July 2010): (1.1) Develop a systematic method to find all the possible SFBC coding patterns for MIMO-OFDM PAPR reduction. (1.2) Investigate an optimal method to combine the above SFBC coding patterns to achieve significant PAPR reduction. (1.3) Develop PAPR reduction algorithms for SFBC MIMO-OFDM systems and accomplish the corresponding floating-point and fixed-point simulations. (1.4) Implement the developed PAPR reduction algorithm on Lyrtech SignalWAVe and SDR Development DSP+FPGA Platforms to verify the performance in real communication systems. The Second Year (August 2010 ~ July 2011): (2.1) Investigate the mathematical properties of the SFBC coding patterns found in step (1.1), finding the possible way to reduce the computational complexity of the encoding and decoding processes. (2.2) Utilize the method developed in [94] and [95] to reduce the computational complexity of the proposed SFBC MIMO-OFDM PAPR reduction algorithm (2.3) Develop a low-complexity and high-performance PAPR reduction algorithms for SFBC MIMO-OFDM systems and accomplish the corresponding floating-point and fixed-point simulations. (2.4) Implement the developed low-complexity and high-performance PAPR reduction algorithm in step (2.3) on Lyrtech SignalWAVe and SDR Development DSP+FPGA Platforms to verify the performance in real communication systems (2.5) Integrate the developed methods in step (1.4) and (2.4) to form a prototype of a simplified MIMO-OFDM transmission system and evaluate the transmission performance in real systems.

Project ID:PB9808-2400
External Project ID:NSC98-2221-E182-023