Ilya Bolotin

Evaluation of Joint Transmission CoMP in C-RAN based LTE-A HetNets with large coordination areas

Coordinated Multi-Point (CoMP) transmission is considered as one of the key technology enhancements for Rel-11 LTE-A systems. CoMP transmission is realized by exchanging coordination information between a set of transmission nodes, forming a so-called CoMP cluster. The size of the CoMP cluster is typically limited, which leads to cell-edge performance issues appearing at the CoMP cluster boundaries. However, in new radio access network (RAN) architectures such as Cloud RAN (C-RAN) the effect of cell-edge user performance degradation at the CoMP cluster boundaries can be minimized by considering larger CoMP coordination areas. In this paper, we investigate the Joint Transmission (JT) CoMP performance in a C-RAN implementation of LTE-A HetNet with large CoMP cluster sizes. Some approaches to minimize the CoMP processing requirements for this case are also discussed. As a baseline for comparison, the LTE-A time-domain enhanced Inter-Cell Interference Coordination (eICIC) scheme which has no coordination boundary issues is considered.

Quasi-deterministic approach to mmWave channel modeling in a non-stationary environment

There is increasing faith that mmWave technology will be part of 5G wireless networks in the wide frequency range 30-90 GHz. Experimental measurements are used to model mmWave channels addressing issues like human body shadowing or reflections due to moving vehicles. In this paper a new quasi-deterministic (Q-D) approach is introduced for modeling mmWave channels. The proposed channel model allows natural description of scenario-specific geometric properties, reflection attenuation and scattering, ray blockage and mobility effects. This new channel modeling approach is of utmost importance for further measurement campaigns planning, channel model characterization, system level simulations and network access capacity estimations.

Performance evaluation of dynamic point selection CoMP scheme in heterogeneous networks with FTP traffic model

High traffic demand is considered as one of the key challenge in modern wireless communication systems which are typically limited by amount of available spectrum. Recently heterogeneous networks (HetNet) have been proposed as an attractive approach to cope with this problem, by enabling cell splitting gain via deployment of an additional layer of pico-cells. While low power and small antenna height of pico-cell base stations simplify search of the site location, the efficiency of cell splitting gain in HetNet is typically limited by small coverage area of pico-cells. To address the issue of HetNet performance in LTE-A Rel-11, coordinated multipoint (CoMP) traffic management schemes were considered. In particular a combination of dynamic point selection (DPS) with dynamic point blanking (DPB) was identified as a promising mechanism to provide cell load balancing and interference mitigation in HetNet. Dynamicity of CoMP schemes is expected to provide performance benefits in various scenarios including non-full buffer traffic models, where scheduling decisions of DPS/DPB can be based on the instantaneous cells loading conditions. In this paper we provide detailed system level performance analysis for DPS/DPB CoMP scheme in HetNet scenario with non-full buffer FTP traffic model. The performance results are conducted for different traffic loadings of the cells and DPS/DPB scheduling decision granularities.

Highly Directional Steerable Antennas: High-Gain Antennas Supporting User Mobility or Beam Switching for Reconfigurable Backhauling

Modern millimeter-wave (mmWave) communication systems for large indoor areas and most outdoor scenarios require high-gain antennas with beam-steering ability to support user mobility or beam switching for reconfigurable backhauling. In this article, two new concepts for the development of highly directional steerable mmWave antennas are proposed and analyzed. The first one is modular antenna array (MAA) technology, which allows the creation of large-aperture, high-gain adaptive antenna arrays in a cost-effective and scalable manner. Two MAA configurations based on the existing phased subarray module are considered and analyzed for mmWave small-cell access and backhauling. The second prospective technology that fulfills the required antenna parameters for mmWave smallcell flexible backhauling is the lens-array antenna (LAA). The combination of the dielectric lens for aperture increasing with only one subarray module with beam-steering capabilities may provide 25-30-dBi total antenna gain with azimuth sector sweeping ±45°.

Partially adaptive arrays application for MU-MIMO mode in a MmWave small cells

In this paper we provide detailed system level performance analysis of MU-MIMO mode in the millimeter wave (mmWave) small cells (Wi-Fi hotspots) environment. Traditional way of MIMO implementation assumes a single RF chain per antenna element, with all spatial processing done in the baseband. To overcome high pathloss in the mmWave bands, the large-aperture, very high gain arrays with a large number of elements (several hundreds) are required. Therefore we introduce partially adaptive arrays with reduced number of degrees of freedom which are implemented based on the modular antenna arrays (MAA) architecture. The scalable practical design of MAA allows creation of large-aperture, high-power antenna arrays with reduced number of RF chains at cost of decreasing the adaptability. Employing recently proposed quasi-deterministic (Q-D) model for millimeter-wave channels, it was shown that partially adaptive MAA have very small degradation in comparison with ideal fully adaptive array (FAA) in a realistic scenarios. It was shown that application of MU-MIMO mode in a mmWave small cells allows achieving up to 15-30 Gbps total throughput per cell in a multipath environment (university campus scenario) with practical antenna array design.

Performance evaluation of interference mitigation techniques in the overlaying MmWave small cell network

In this paper we consider heterogeneous cellular network with a number of millimeter-wave (mmWave) small cells overlaying LTE macro cells. The impact of mutual interference in millimeter-wave band (57-64 GHz) is addressed and evaluated. We introduce several active interference cancellation techniques which are implemented at TX sides of mmWave small cell BSs equipped with adaptive antenna arrays. We started from the task of multi-stream intra-cell interference suppression in MU-MIMO mode by means of well-known Zero-Forcing (ZF) algorithm. Then more complex schemes involving coordinated multi-point (CoMP) operation of several neighboring BSs with Coordinated Scheduling (CS) and Coordinated Beamforming (CB) are investigated. Finally, performance evaluation and comprehensive comparative analysis are done by simulations for different mmWave small cell sizes and densification. Presented results allow to establish lower and upper bounds of interference impact and make reasonable selection of the suitable interference mitigation technique for mmWave overlaying network.

Virtual Antenna Array Methodology for Outdoor Millimeter-Wave Channel Measurements

The development of new outdoor millimeter-wave channel models requires processing of the experimental data which can be used to estimate multipath channel parameters with very high time and angular resolution. The virtual antenna arrays processing technique allows joint narrow beam forming and beam steering. The specific of outdoor experiment does not allow precise positioning of the antennas, like it possible under lab-conditions. So some special methodology should be developed to overcome this problem. In this paper we propose the virtual antenna array signal processing which allows for given experi-mental data to perform environment scanning with equivalent 1° antenna beamwidth and -30dB sidelobes rejection. As a result, the measurement environment was accurately reconstructed on the base of measurement data. High angular resolution of the proposed virtual antenna array signal processing allows estimat-ing the wall-reflected rays (channel clusters) power-angular spectrum parameters for a Laplacian model.

Performance evaluation of the isolated mmWave small cell

In this paper we introduce the performance evaluation of the isolated millimeter-wave (mmWave) small cell. The potential performance of the mmWave small cells is evaluated on the base of PHY layer technique with parameters similar to IEEE 802.11ad standard. Two important practical tasks are addressed in this paper: the efficiency of mmWave spectrum utilization and the small cell optimal coverage. Two approaches for spectrum utilization are considered: frequency reuse-1 (each cell sector operates in three channels) and frequency reuse-3 (each of three cell sectors operates in only one channel). We start from the comparison of these scenarios spectral efficiency. At the next step the interference mitigation techniques are applied in order to improve the system performance for both scenarios. Also we discuss the mmWave small cell coverage and its limits due to the regulator requirements. The impact of small cell radius on MU-MIMO mode performance is addressed and evaluated. Finally, the discussion and recommendations on the small cell size, frequency reuse scenario and interference mitigation techniques are provided.