This invention relates to characterizing transmit channels from an antenna array to a transceiver, and more particularly, to eliminating a need for channel feedback from the transceiver. In some embodiments, the characterized transmit channels are used for beamforming to a transceiver or in MIMO communication to a plurality of transceivers from the antenna array.
The high cost of cellular spectrum has motivated network providers to seek advanced MIMO techniques to improve spectral efficiency. Yet, only point-to-point MIMO multiplexing can be performed efficiently in current networks. More advanced MIMO solutions such as massive MIMO, coordinated multi-point, distributed MIMO, and multi-user MIMO, all require the base station to know the downlink channels prior to transmission. In the absence of this information, the base station cannot effectively beamform its signal to its users. A prior way to learn the downlink channels is to have the remote device (e.g., a user's cellphone, or other “user equipment”) perform the measurements and send the channels back to the base station. Measuring the channels on the one thousand LTE subcarriers for every antenna on the base station, and feeding those measurements back to the base station would generate much overhead. This feedback overhead is excessive even in today's networks which have a limited number of antennas on the base station—about 4.6 Mb/s of signaling per user in a 20 MHz 4×2 network. The problem escalates in future 5G networks which rely on large MIMO systems with many antennas (massive MIMO, CoMP, etc.). In fact, the LTE standardization body that is investigating high-order MIMO systems with up to 64 antennas (Release 13), has declared this problem as a major challenge for future LTE networks.