Steven Ferrante

System capacity and coverage of a cellular network with D2D mobile relays

It has been predicted that the recent explosive growth in wireless data traffic will continue for the foreseeable future. To date, attempts to address this explosive growth have included increasing base station density through smaller cells, and to a lesser extent, by improving spectral efficiency using close-to-capacity channel coding and MIMO techniques. Providing further capacity and coverage improvements through ever shrinking cells could lead to large infrastructure costs and operating expenses. In this paper we propose a far less expensive alternate solution using a topology which employs mobile User Equipment (UE) nodes as virtual infrastructure to enhance the cellular capacity while also improving network coverage. The improvements in capacity and coverage are achieved by enabling cellular controlled direct Device to Device (D2D) links to carry relayed traffic. Each terminal UE (T-UE) with an active connection could potentially be assigned a Helper UE (H-UE), depending on the network conditions and traffic requirements to improve the system capacity. In addition, T-UEs which are out of coverage can also be assigned a H-UE, which would extend the typical coverage of a base station and lead to improved network coverage. In this paper, we present both coverage enhancement and system capacity results using Monte Carlo simulation techniques for both uplink and downlink communications. Our results indicate that cell edge percent throughput capacity improvements as well as percent throughput coverage improvements of more than 150% may be realized using idle UEs in the system as mobile relays.

mm Wave Initial Cell Search Analysis under UE Rotational Motion

Millimeter wave (mmW) communication has emerged as a promising component of the access link for 5G cellular systems. In order to overcome the higher free-space path loss at these frequencies, high gain, and therefore highly directional, antennas are being proposed at both ends of the link. Furthermore, in order to maintain a mobile connection with an acceptable quality of service (QOS), these highly directional antennas also need to be electronically steerable. This required dual-end steerability adds significant system complexity in terms of both initial access and connected mode procedures. Therefore, these various procedures which were originally designed for the current sub 6 GHz systems need to be re-investigated in light of this added complexity. Traditionally, sub 6 GHz mobility studies mainly focused on translational motion; however, with the dual-end highly directional links being proposed for mmW communications, rotational motion also becomes a concern. In this paper, we study the effects these steerable links have on initial network access procedures, especially in the presence of user equipment (UE) rotational motion.

Equalization for Outdoor mmW Deployments

Millimeter wave (mmW) frequencies are considered to be indispensable for next generation wireless systems, both cellular and Wi-Fi, primarily due to the large amounts of spectrum available in these bands. However, the higher frequency-dependent path loss at these frequencies needs to be overcome by the use of high-gain directional antenna arrays at both transmitter and receiver. Due to the complexity and peak to average power ratio (PAPR) requirements of OFDM, single-carrier is being considered for the physical layer, which brings up the question of appropriate equalization. In this paper we present a simulation study of equalization structures specifically for a mmW outdoor system, using realistic ray tracing simulation software to generate multipath channels depending on the transmit and receive antenna beam-widths. We then compare decision feedback equalization (DFE) with linear equalization (LE) for these channels and show that in an urban multipath environment the use of DFEs can offer significant gains even with very narrow antenna beams, while the gains are smaller in a suburban environment with less multipath.

mm Wave UE Antenna Configuration Study

Millimeter wave (mm wave) communication has emerged as a promising component of 5G cellular systems. The large losses in the Friis equation (due to the implied small apertures of mm wave antennas) suggest that high gain antennas are required. The high gain also implies steerability is required. Arrays of patch antennas are one possible low cost solution, but each array has a limited angular field of view. Multiple arrays per node can be used to improve the field of view. Choosing the correct antenna configuration requires a complex cost-benefit analysis and performance-complexity tradeoff. In this paper, we investigate these tradeoffs through system simulations. Our study uses ray tracing in 3D deployment scenarios and realistic patch antenna array models. MATLAB-based system simulation results are provided, and conclusions are drawn to provide insight into the performance vs. antenna complexity of a mm wave based system. Some of the key conclusions are: diminishing returns on performance as the number of arrays are increased, and the fact that a smaller number of larger arrays can outperform a larger number of smaller arrays. Iso-element curves are also presented as another way to perform a cost-benefit analysis.

Signal and noise power maximum likelihood estimation for fast AGC in packet based systems

Automatic Gain Control (AGC) system performance generally depends on the ability to accurately estimate receive signal power. The initial gain setting may be set high to ensure that low power signals can be detected. As the Variable Gain Amplifier (VGA) resides before the Analog to Digital Converter (ADC), there is a potential for heavy saturation at the output of the ADC, where this estimation is normally performed. This heavy saturation will cause power to be underestimated when using estimators that do not account for clipping, causing slow AGC convergence time. Fast AGC convergence time is desirable in general, but especially for high rate packet based systems (e.g. 802.11ad) which allow for only a limited number of updates in the early stages of a training period. Furthermore, optimal setting of the VGA gain requires statistics sufficient to estimate the received signal distribution. In this work, we propose Maximum Likelihood Estimation (MLE) based estimators of the signal power and noise power that account for saturation at the ADC. The performance of MLE based estimators of total power is compared to a traditional power estimator and results are shown through simulations.