A Many Antenna High Rate Wireless System
  We describe a TDD MIMO wireless system designed to operate at high bandwidth and low SNR. Signals are transmitted as a direct sequence. In the uplink (Multiple Access Channel), signal detection is done by a space-time whitening filter followed by a matched filter. In the downlink (Broadcast Channel), precoding is done by the transpose of these filters.   We further describe an implementation of this system that uses an array of 32 antennas to communicate with 32 single-antenna clients simultaneously on the same frequencies between 512-608 and 614-698 MHz. At close range, all 32 links achieve the full PHY data rate, both uplink and downlink, with less than 1\% Block Error Rate on each link. The total system rate is 3.8 Gb/s. The system spectral efficiency is 21.7 b/s/Hz for both uplink and downlink.   We close with some projections to the not-to-distant future. 
Philip Gossett, Jeremy Thorpe, Bob Nuckolls, Brett Coon, Dan   McCloskey, David Chang, Greg Steuck, Paul Rodman, Sasha Levit...
cs.IT math.IT