Hooman Shirani-Mehr

Validation of a Geometry-Based Statistical mmWave Channel Model Using Ray-Tracing Simulation

Next-generation wireless communications systems are expected to exploit frequency bands above 6 GHz. An important transition towards such bands will be design of channel models capable of supporting the design of efficient air-interface and networks. In this paper, we describe a geometry-based statistical channel model and apply ray-tracing simulation for its validation. Focusing on path loss and root-mean-square (RMS) delay spread as metrics, we show that the proposed modeling approach is flexible and realistic.

Practical downlink transmission schemes for future LTE systems with many base-station antennas

We consider downlink multi-user MIMO transmission of a wireless system in which the base station is equipped with a large number of antennas. We propose two downlink schemes based on random beamforming and subspace tracking and show that while reducing signaling overhead, these schemes can improve the system performance compared to conventional systems with a smaller number of antennas at the base station.

Progressive channel state information for advanced multi-user MIMO in next generation cellular systems

We propose an enhanced precision channel state acquisition scheme for downlink Multi-User MIMO (MU-MIMO) transmission with a large number of transmit antennas at the base station. The proposed scheme is an attempt to harvest the Channel State Information (CSI) at the transmitter by incrementally improving the precision of the channel knowledge. We show how, in an LTE-Advanced system, CSI harvesting mechanism followed by the conventional Zero-Forcing Beam-Forming (ZFBF) results in improved MU-MIMO performance, relative to the current method for acquiring CSI at the transmitter. The proposed progressive CSI harvesting scheme is also shown to yield significant saving in terms of feedback overhead. The implications of the larger MIMO systems and higher MU-MIMO ranks, and sensitivity to higher mobility are also discussed.

Millimeter wave channel model and system design considerations

In order to exploit millimeter wave (mmWave) bands for 5G communications, challenges mainly due to blockage and strong dependency on beamforming operation need to be overcome. In this work, we address some of the fundamental issues related to the use of mmWave bands for 5G communications, from propagation channel characteristics and modeling to the implications on system and network architecture design. A statistical mmWave channel model considering cluster-level spatial/temporal correlation is proposed. System-level simulation results based on the proposed model demonstrate the channel characteristics and system performance. Following that, key techniques in enabling mmWave system operation are discussed. Although we believe that mmWave bands can be utilized in 5G networks, significant efforts and time are needed in order to complete the air interface, device and network design which is shown to be quite different from the existing cellular design.