Zachary Bagley

Indoor MIMO channel measurements using dual polarized patch antennas

A mobile 4/spl times/4 multiple input multiple output (MIMO) system containing dual polarized patch antennas is used to perform wireless measurement campaigns on nonline of sight (NLOS) channels in an indoor office setting. The MIMO system uses orthogonal 500 kchips/s Walsh coded signals that are filtered and simultaneously transmitted at 916 MHz. The patch antennas have high isolation between their two ports and are used at both transmitter and receiver stations. The complex MIMO channel matrices obtained in the campaigns were used to calculate the theoretical capacity for a 4/spl times/4 system. Our mean measured capacity for the campaign is 21.3 bits/use and the 90/sup th/ percentile channel capacity is 19.5 bits/use. These values are slightly higher than those (mean of 21.1 bits/use and 90/sup th/ percentile channel capacity of 18.9 bits/use) obtained for an identical campaign which used single polarized whip antennas.

Transmitter layering for multiuser MIMO systems

A novel structure for multiple antenna transmissions utilizing space-time dispersion is proposed, where the original data stream is divided into substreams which are modulated onto all available transmit antennas using stream-specific transmit signature sequences. In order to achieve this, the transmit antennas are partitioned into groups of antennas, called partitions. The signals from the data streams are independently interleaved by partition over the entire transmission frame. The interleaved partitions are then added over all substreams prior to transmission over the MIMO channel. At the receiver, a low-complexity iterative detector adapted from recent CDMA multiuser detection research is used. It is shown that with careful substream power assignments this transmission methodology can efficiently utilize the capacity of rank-deficient channels as it can approach the capacity limits of the multiple antenna channel closely over the entire range of available signal-to-noise ratios and system sizes. This transmission methodology and receiver structure are then applied to multiuser MIMO systems where several multiple antenna terminals communicate concurrently to a joint receiver. It is shown that different received power levels from the different MIMO terminals can be beneficial and that higher spectral efficiencies can be achieved than in the single-terminal case.

Low-complexity processing of randomly correlated signals

edu Abstract - Linear pre-processing of systems with large numbers of concurrent channels such as asyn- chronous CDMA systems or MIMO systems is used to transform the multi-access channel into parallel single-user channels. The linear filters such as decor- relator and MMSE filters typically have a cubic com- plexity in terms of the filter size. We study the infor- mation capacities of low-complexity iterative approxi- mations of these linear filters, and show that for large operation ranges, these simple iterative filters provide nearly the same capacity as original complex filters. Conditional correlation reception of multi-access signals is limited by mutual interference, hence joint detection method have been studied for a number of years to improve the spec- tral efficiency. The optimal detection (2) has an exponential complexity, and is feasible only for very small systems. As a result, linear filters (l, 3)are considered as the low-complexity alternatives. Linear pre-processing can be understood as conditioning the channel between a single transmitter and its designated receiver. These filters turn the noise and interference into a Gaussian noise source affecting the equivalent single-user channel. The information theoretic capacity is then calculated using Shannon capacity formula for the AWGN channel (4). The linear reception of multi-access signals bears the general form as