This paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modelling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used for performing time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. The paper also considers a software radio implementation of MIMO-OFDM. OFDM is a block modulation scheme where a block of N information symbols is transmitted in parallel on N subcarriers. The time duration of an OFDM symbol is N times larger than that of a single carrier system. An OFDM modulator can be implemented as an inverse discrete Fourier transform (IDFT) on a block of N information symbols followed by an analog to digital converter (ADC). To mitigate the effects of intersymbol interference (ISI) caused by channel time spread, each block of N IDFT coefficients is typically preceded by a cyclic prefix (CP) or a guard interval consisting of G samples, such that the length of the CP is at least equal to the channel length, M. Under this condition, a linear convolution of the transmitted sequence and the channel is converted to a circular convolution. As a result, the effects of the ISI are easily and completely eliminated. Moreover, the approach enables the receiver to use fast signal processing transforms such as a fast Fourier transform (FFT) for OFDM implementation. Similar techniques can be employed in single carrier systems as well, by preceding each transmitted data block of length N by a cyclic prefix of length G, while using frequency domain equalization at the receiver. Multiple antennas can be used at the transmitter and receiver, an arrangement called a multiple-input multiple-output (MIMO) system. A MIMO system takes advantage of the spatial diversity that is obtained by spatially separated antennas in a dense multipath scattering environment. MIMO systems may be implemented in a number of different ways to obtain either a diversity gain to combat signal fading, or to obtain a capacity gain. Generally there are three categories of MIMO techniques. The first aims to improve the power efficiency by maximizing spatial diversity. Such techniques include delay diversity, space-time block codes (STBC), and space-time trellis codes (STTC). The second class uses a layered approach to increase capacity. One popular example of such a system is V-BLAST suggested by Foschini et al. where full spatial diversity is usually not achieved. Finally, the third type exploits the knowledge of channel at the transmitter. It decomposes the channel coefficient matrix using Singular Value Decomposition (SVD) and uses these decomposed unitary matrices as pre and post filters at the transmitter and the receiver to achieve near capacity. OFDM has been adopted in the IEEE802.11a LAN and IEEE802.16a LAN/MAN standards. OFDM is alsoThis paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modelling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used for performing time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. The paper also considers a software radio implementation of MIMO-OFDM. OFDM is a block modulation scheme where a block of N information symbols is transmitted in parallel on N subcarriers. The time duration of an OFDM symbol is N times larger than that of a single carrier system. An OFDM modulator can be implemented as an inverse discrete Fourier transform (IDFT) on a block of N information symbols followed by an analog to digital converter (ADC). To mitigate the effects of intersymbol interference (ISI) caused by channel time spread, each block of N IDFT coefficients is typically preceded by a cyclic prefix (CP) or a guard interval consisting of G samples, such that the length of the CP is at least equal to the channel length, M. Under this condition, a linear convolution of the transmitted sequence and the channel is converted to a circular convolution. As a result, the effects of the ISI are easily and completely eliminated. Moreover, the approach enables the receiver to use fast signal processing transforms such as a fast Fourier transform (FFT) for OFDM implementation. Similar techniques can be employed in single carrier systems as well, by preceding each transmitted data block of length N by a cyclic prefix of length G, while using frequency domain equalization at the receiver. Multiple antennas can be used at the transmitter and receiver, an arrangement called a multiple-input multiple-output (MIMO) system. A MIMO system takes advantage of the spatial diversity that is obtained by spatially separated antennas in a dense multipath scattering environment. MIMO systems may be implemented in a number of different ways to obtain either a diversity gain to combat signal fading, or to obtain a capacity gain. Generally there are three categories of MIMO techniques. The first aims to improve the power efficiency by maximizing spatial diversity. Such techniques include delay diversity, space-time block codes (STBC), and space-time trellis codes (STTC). The second class uses a layered approach to increase capacity. One popular example of such a system is V-BLAST suggested by Foschini et al. where full spatial diversity is usually not achieved. Finally, the third type exploits the knowledge of channel at the transmitter. It decomposes the channel coefficient matrix using Singular Value Decomposition (SVD) and uses these decomposed unitary matrices as pre and post filters at the transmitter and the receiver to achieve near capacity. OFDM has been adopted in the IEEE802.11a LAN and IEEE802.16a LAN/MAN standards. OFDM is also