21 research outputs found
Codebook Based Hybrid Precoding for Millimeter Wave Multiuser Systems
In millimeter wave (mmWave) systems, antenna architecture limitations make it
difficult to apply conventional fully digital precoding techniques but call for
low cost analog radio-frequency (RF) and digital baseband hybrid precoding
methods. This paper investigates joint RF-baseband hybrid precoding for the
downlink of multiuser multi-antenna mmWave systems with a limited number of RF
chains. Two performance measures, maximizing the spectral efficiency and the
energy efficiency of the system, are considered. We propose a codebook based RF
precoding design and obtain the channel state information via a beam sweep
procedure. Via the codebook based design, the original system is transformed
into a virtual multiuser downlink system with the RF chain constraint.
Consequently, we are able to simplify the complicated hybrid precoding
optimization problems to joint codeword selection and precoder design (JWSPD)
problems. Then, we propose efficient methods to address the JWSPD problems and
jointly optimize the RF and baseband precoders under the two performance
measures. Finally, extensive numerical results are provided to validate the
effectiveness of the proposed hybrid precoders.Comment: 35 pages, 9 figures, to appear in Trans. on Signal Process, 201
Design and Prototyping of Hybrid Analogue Digital Multiuser MIMO Beamforming for Non-Orthogonal Signals
To enable user diversity and multiplexing gains, a fully digital precoding
multiple input multiple output (MIMO) architecture is typically applied.
However, a large number of radio frequency (RF) chains make the system
unrealistic to low-cost communications. Therefore, a practical three-stage
hybrid analogue-digital precoding architecture, occupying fewer RF chains, is
proposed aiming for a non-orthogonal IoT signal in low-cost multiuser MIMO
systems. The non-orthogonal waveform can flexibly save spectral resources for
massive devices connections or improve data rate without consuming extra
spectral resources. The hybrid precoding is divided into three stages including
analogue-domain, digital-domain and waveform-domain. A codebook based beam
selection simplifies the analogue-domain beamforming via phase-only tuning.
Digital-domain precoding can fine-tune the codebook shaped beam and resolve
multiuser interference in terms of both signal amplitude and phase. In the end,
the waveform-domain precoding manages the self-created inter carrier
interference (ICI) of the non-orthogonal signal. This work designs over-the-air
signal transmission experiments for fully digital and hybrid precoding systems
on software defined radio (SDR) devices. Results reveal that waveform precoding
accuracy can be enhanced by hybrid precoding. Compared to a transmitter with
the same RF chain resources, hybrid precoding significantly outperforms fully
digital precoding by up to 15.6 dB error vector magnitude (EVM) gain. A fully
digital system with the same number of antennas clearly requires more RF chains
and therefore is low power-, space- and cost- efficient. Therefore, the
proposed three-stage hybrid precoding is a quite suitable solution to
non-orthogonal IoT applications