Multistage beamforming of multiple-antenna communication system

A base station for multistage beamforming in a wireless communication network, the base station comprising:

• a data unit configured to implement a frequency domain beamforming stage, the data unit comprising:
• a frequency domain precoding module configured to receive and precode K data streams into M precoding output streams in a frequency domain by applying frequency domain precoding matrices,
• M pairs of an Inverse Fast Fourier Transform (IFFT) processing block coupled to M cyclic prefix processing block, each pair configured to transform the M precoding output streams into M orthogonal frequency-division multiplexing (OFDM) time-domain signals, wherein each IFFT processing block is configured to receive a frequency-domain signal, map the frequency-domain signal to resource elements in a frequency domain, transform the received frequency-domain signal to a stream of time domain samples, and each cyclic prefix processing block is configured to add a cyclical prefix to the stream of time domain samples to generate the M precoding output streams;
• and
• a remote radio head (RRH) configured to implement a time-domain broadband beamforming stage by converting the M OFDM time-domain signals into N transmit streams of time-domain samples based on beamforming control signals received from the data unit, the beamforming control signals indicating a wide-band precoding matrix or a set of indicators to construct the wideband precoding matrix, the RRH comprising:
• a time-domain broadband beamforming module configured to receive and precode the M output streams into N precoded output signals using a wide-band precoding matrix,
• a transmit antenna array configured to transmit the N transmit streams that together form broadcast beams and user-specific beams, the antenna array including a plurality of physical antennas,
• wherein the number N of transmit streams is greater than the number M of precoding output streams in the time domain, and
• wherein N. M. and K are positive integers.

A multistage beamforming method comprising:

• implementing a frequency domain beamforming stage by converting K data streams in a frequency-domain into M precoding output streams in a frequency domain, wherein converting the K data streams into M precoding output streams comprises receiving and precoding the K data streams into M precoding output streams by applying frequency domain precoding matrices;
• transforming the M output streams to M orthogonal frequency-division multiplexing (OFDM) time-domain signals by:
• mapping the M output streams to resource elements in a frequency domain to generate M mapped frequency-domain signals,
• transforming the M mapped frequency-domain signals to M streams of time domain samples using Inverse Fast Fourier Transform (IFFT), and
• adding a cyclical prefix to each of the M streams of time domain samples yielding the M OFDM time-domain signals:
• implementing a time-domain broadband beamforming stage by converting the M OFDM time-domain signals into N transmit streams of time-domain samples based on beamforming control signals received, the beamforming control signals indicating a wide-band precoding matrix or a set of indicators to construct the wideband precoding matrix;
• and
• transmitting, by a transmit antenna array including a plurality of physical antennas, the N transmit streams that together form broadcast beams and user-specific beams,
• wherein the number N of transmit streams is greater than the number M of precoding output streams, and
• wherein N. M. and K are positive integers.