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Description
Orthogonal frequency division multiplexing (OFDM) is a block transmission technique. In the baseband, complex-valued data symbols modulate a large number of tightly grouped carrier waveforms. The transmitted OFDM signal multiplexes several low-rate data streams and each data stream is associated with a given subcarrier. OFDM is implemented in broadband wireless access systems as a way to overcome wireless channel impairments and to improve bandwidth efficiency. OFDM is used today in wireless local area networks (LANs) as specified by the IEEE 802.11a and the ETSI HiperLAN/2 standards. It is also used for wireless digital radio and television transmissions, particularly in Europe. Multiple-input multiple-output (MIMO) communication refers to wireless communication systems using an array of antennas (i.e. multiple antennas) at either the transmitter or the receiver. Multiplexing would cause interference, but MIMO systems use smart selection and/or combining techniques at the receiving end to transmit more information and to improve signal quality. MIMO systems provide a significant capacity gain over conventional single antenna systems, along with more reliable communication. In this project, we will investigate MIMO techniques for OFDM systems in the context of WiFi and WiMax. We will conduct an extensive simulation-based study of MIMO-OFDM systems. We will analyze the performance of various MIMO techniques under different fading channel conditions. It is known that the complexity of OFDM with MIMO is overwhelming due to the necessity for multiple Fast Fourier Transforms (FFTs) at the receiver. In order to reduce system complexity, we also propose a novel combining technique that will exploit MIMO gains with only a single FFT at the receiver.
