Method and apparatus for power optimization in wireless systems with large antenna arrays
A method and apparatus for communication between a wireless base station and a population of one or more terminals are provided, involving, in each of a plurality of iterations, transmitting a block of forward-link data from an array of multiple base station antennas to the terminal population. In each iteration, a forward-link power level is updated for each said terminal using a distributed algorithm and purely local information. Meanwhile, a set of beamforming coefficients based on channel state information (CSI) obtained from reverse-link pilot signals is periodically updated, and each data block is precoded with the most recently updated beamforming coefficients. Each data block is transmitted at the most recently updated forward-link power levels.
1. A method of communication between a wireless base station and a population of one or more terminals, comprising:
in each of a plurality of iterations, transmitting a block of forward-link data from an array of multiple base station antennas to the population of one or more terminals;
in each of said iterations, updating a forward-link power level based on a convergence algorithm for each terminal based on SINR feedback data returned by the population of one or more terminals in response to the forward-link data transmitted in a previous iteration, wherein the forward-link power level substantially converges toward an asymptotic value as a result of the plurality of iterations;
during said plurality of iterations, periodically updating a set of beamforming coefficients based on channel state information (CSI) obtained from reverse-link pilot signals, wherein the CSI is obtained once per a CSI-update period long enough that the CSI obtained in each period is decorrelated from the CSI obtained in a previous period; and
precoding each data block prior to transmission with most recently updated beamforming coefficients, wherein:
each data block is transmitted at most recently updated forward-link power levels; and
the power levels are updated using local information.
2. The method of claim 1 , wherein the beamforming coefficients are updated frequently enough to beamform to a mobile population of terminals traveling at vehicular velocities.
3. The method of claim 1 , wherein the array comprises at least twenty base station antennas.
4. The method of claim 1 , further comprising periodically receiving pilot signals concurrently transmitted from the terminals of the population of one or more terminals.
5. The method of claim 1 , further comprising, in each iteration, receiving SINR feedback data from each terminal of the population of one or more terminals.
6. The method of claim 5 , wherein the SINR feedback data comprises information derived from an indication of useful signal power (P sig ) and an indication of interference power (P int ) of each terminal of the population of one or more terminals.
7. The method of claim 1 , performed concurrently with a plurality of other base stations.
8. The method of claim 1 , wherein:
the forward-link power levels have an adaptation time within which the forward-link power levels substantially reach an asymptotic value for static CSI; and
the adaptation time is at least thirty CSI-update periods.
9. The method of claim 1 , wherein the precoding of the data block creates a transmit signal vector that is distributed across the antennas of the array.
10. A wireless base station for communication with a population of one or more terminals, comprising:
a module configured to transmit, in each of a plurality of iterations, a block of forward-link data from an array of multiple base station antennas to the population of one or more terminals;
a module configured to update, in each of said iterations, a forward-link power level based on a convergence algorithm for each terminal based on SINR feedback data returned by the population of one or more terminals in response to the forward-link data transmitted in a previous iteration, wherein the forward-link power level substantially converges toward an asymptotic value as a result of the plurality of iterations;
a module configured to periodically update, during said plurality of iterations, a set of beamforming coefficients based on channel state information (CSI) obtained from reverse-link pilot signals, wherein the CSI is obtained once per a CSI-update period long enough that the CSI obtained in each period is decorrelated from the CSI obtained in a previous period; and
a module configured to precode each said data block, prior to transmission, with most recently updated beamforming coefficients, wherein:
the transmission module is configured to transmit each said data block at most recently updated forward-link power levels; and
the power-level updating module is configured to update the power levels using local information.
11. The base station of claim 10 , configured to update the beamforming coefficients frequently enough to beamform to a mobile population of terminals traveling at vehicular velocities.
12. The base station of claim 10 , wherein the array comprises at least twenty base station antennas.
13. The base station of claim 10 , further comprising a module configured to periodically receive pilot signals concurrently transmitted from the terminals of the population of one or more terminals.
14. The base station of claim 10 , further comprising a module configured to receive, in each iteration, SINR feedback data from each terminal of the population of one or more terminals.
15. The base station of claim 10 , wherein the precoding of the data block creates a transmit signal vector, and the base station is configured to distribute said vector across the antennas of the array.