Fengchun Zhang

Frequency Invariant Uniform Circular Array for Wideband mm-Wave Channel Characterization

A new approach for designing frequency-invariant (FI) uniform circular array (UCA) is proposed, and its application to wideband multipath estimation at millimeter-wave (mm-wave) bands is studied. Both numerical simulations and channel sounding results at mm-wave bands are provided to demonstrate the effectiveness and improvement of the proposed method in channel parameter estimation over the conventional FI UCA method.

Analysis of Simulated and Measured Indoor Channels for mm-Wave Beamforming Applications

Ray tracing- (RT-) assisted beamforming, where beams are directly steered to dominant paths tracked by ray tracing simulations, is a promising beamforming strategy, since it avoids the time-consuming exhaustive beam searching adopted in conventional beam steering strategies. The performance of RT-assisted beamforming depends directly on how accurate the spatial profiles of the radio environment can be predicted by the RT simulation. In this paper, we investigate how ray tracing-assisted beamforming performs in both poorly furnished and richly furnished indoor environments. Single-user beamforming performance was investigated using both single beam and multiple beams, with two different power allocation schemes applied to multibeamforming. Channel measurements were performed at 28–30 GHz using a vector network analyzer equipped with a biconical antenna as the transmit antenna and a rotated horn antenna as the receive antenna. 3D ray tracing simulations were carried out in the same replicated propagation environments. Based on measurement and ray tracing simulation data, it is shown that RT-assisted beamforming performs well both for single and multibeamforming in these two representative indoor propagation environments.

Virtual Large-Scale Array Beamforming Analysis Using Measured Subarray Antenna Patterns

An accurate and reliable massive MIMO channel model is crucial for supporting design and performance evaluation of such systems in the future. However, massive MIMO channel sounding systems are cost prohibitive and complicated, where a large number of antenna elements and associated radio frequency transceiver chains are needed. Virtual large-scale arrays have been extensively utilized as an alternative for massive MIMO channel characterization. In this paper, we investigate virtual large-scale array systems formed by repositioning a real subarray system for channel characterization. With this scheme, we have the flexibility to scale between system cost and system channel sounding capability. Based on this scheme, general beampatterns of subarrays and subarray-based virtual large-scale arrays are derived, based on measured complex antenna patterns of antenna elements on the subarray. Three real subarray antenna systems, i.e., a 16-element uniform rectangular array (URA) at 3.5 GHz, an 8-element uniform circular array at 3.5 GHz, and an 8-element uniform linear array (ULA) at 10 GHz, were utilized to form the respective large-scale virtual arrays, i.e., a 128-element URA, a 48-element uniform cylinder array, and a 64 element ULA, respectively. Beamforming analysis based on the measured complex radiation patterns of the real arrays is provided to demonstrate that virtual large-scale arrays can significantly improve the capability of multipath parameter detection compared with the subarrays. Therefore, such cost-effective systems are promising for characterization massive MIMO propagation channels.