Design and Prototyping of Hybrid Analog–Digital Multiuser MIMO Beamforming for Nonorthogonal Signals

Abstract

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 lowcost 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 lowcost 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.Index Terms-Beamforming, multiple input multiple output (MIMO), multiuser, hybrid precoding, Internet of Things (IoT), non-orthogonal, software defined radio (SDR), prototyping.

Identification and practical validation of spectrally efficient non-orthogonal frequency shaping waveform

“…Unlike pulse shaping signals, such a high out-of-band power leakage signal design is not suitable for omni-directional co-existence communication scenarios because it would cause interference to adjacent signals. For future communications, directional transmission link will be the dominated technique where antenna array or directional antenna can generate narrow beams 48 to specific users and therefore inter-user interference can be avoided. In such cases, the out-of-band power leakage from NOFS is not a limiting factor anymore and should not be counted as the occupied bandwidth.…”

Partial OFDM Symbol Recovery to Improve Interfering Wireless Networks Operation in Collision Environments

“…Interference alignment [17] (IA) techniques use multiple antennas to align different interfering transmissions, and have been realised in both wireless LAN [18] and cellular [19] settings. A practical three-stage hybrid analog-digital precoding architecture, occupying fewer RF chains, is proposed aiming for a nonorthogonal Internet of Things (IoT) signal 198 in low-cost multiuser MIMO systems [20]. For the physical 199 layer cross-technology communication (CTC), the work of 200 ZigFi [21] leverages the channel state information of the 201 received frames to enable WiFi receivers to decode data from 202 ZigBee senders.…”

An Experimental Proof of Concept for Integrated Sensing and Communications Waveform Design

“…In this experiment, the phase shifter is merely used for holding the omnidirectional antenna without any phase control functions. However, the activation of the phase control function in each phase shifter will enable a more power efficient hybrid analog-digital multiuser MIMO system design [47], which could be the future research direction of ISAC. In total, six antennas are placed in a uniform linear array (ULA) format at the top of the testbed with the spacing of half wavelength.…”