Mark Cudak

Heterogeneous cellular networks: From theory to practice

The proliferation of internet-connected mobile devices will continue to drive growth in data traffic in an exponential fashion, forcing network operators to dramatically increase the capacity of their networks. To do this cost-effectively, a paradigm shift in cellular network infrastructure deployment is occurring away from traditional (expensive) high-power tower-mounted base stations and towards heterogeneous elements. Examples of heterogeneous elements include microcells, picocells, femtocells, and distributed antenna systems (remote radio heads), which are distinguished by their transmit powers/ coverage areas, physical size, backhaul, and propagation characteristics. This shift presents many opportunities for capacity improvement, and many new challenges to co-existence and network management. This article discusses new theoretical models for understanding the heterogeneous cellular networks of tomorrow, and the practical constraints and challenges that operators must tackle in order for these networks to reach their potential.

Millimeter-Wave Enhanced Local Area Systems: A High-Data-Rate Approach for Future Wireless Networks

Wireless data traffic is projected to skyrocket 10 000 fold within the next 20 years. To tackle this incredible increase in wireless data traffic, a first approach is to further improve spectrally efficient systems such as 4G LTE in bands below 6 GHz by using more advanced spectral efficiency techniques. However, the required substantial increase in system complexity along with fundamental limits on hardware implementation and channel conditions may limit the viability of this approach. Furthermore, the end result would be an extremely spectrally efficient system with little room for future improvement to meet the ever-growing wireless data usage. The second approach is to move up in frequency, into an unused nontraditional spectrum where enormous bandwidths are available, such as at millimeter wave (mmWave). The mmWave option enables the use of simple air interfaces since large bandwidths can be exploited (e.g., 2 GHz) to achieve high data rates rather than relying on highly complex techniques originally aimed at achieving a high spectral efficiency with smaller bandwidths. In addition, mmWave systems will easily evolve to even higher system capacities, because there will be plenty of margin to improve the spectral efficiency as data demands further increase. In this paper, a case is made for using mmWave for a fifth generation (5G) wireless system for ultradense networks by presenting an overview of enhanced local area (eLA) technology at mmWave with emphasis on 5G requirements, spectrum considerations, propagation and channel modeling, air-interface and multiantenna design, and network architecture solutions.

Air interface design and ray tracing study for 5G millimeter wave communications

To meet the explosive growth in traffic during the next twenty years, 5G systems using local area networks need to be developed. These systems will comprise of small cells and will use extreme cell densification. The use of millimeter wave (Mmwave) frequencies, in particular from 20 GHz to 90 GHz, will revolutionize wireless communications given the extreme amount of available bandwidth. However, the different propagation conditions and hardware constraints of Mmwave (e.g., the use of RF beamforming with very large arrays) require reconsidering the modulation methods for Mmwave compared to those used below 6 GHz. In this paper we present ray-tracing results, which, along with recent propagation measurements at Mmwave, all point to the fact that Mmwave frequencies are very appropriate for next generation, 5G, local area wireless communication systems. Next, we propose null cyclic prefix single carrier as the best candidate for Mmwave communications. Finally, systemlevel simulation results show that with the right access point deployment peak rates of over 15 Gbps are possible at Mmwave along with a cell edge experience in excess of 400 Mbps.

Moving Towards Mmwave-Based Beyond-4G (B-4G) Technology

Availability of large untapped spectrum resources in the millimeter wave (Mmwave) band is suitable for providing a gigabit experience with true local feel using high capacity small cells. Unlike traditional cellular systems, millimeter wave transmissions do not benefit from diffraction and dispersion making it difficult for them to propagate around obstacles thus resulting in higher shadowing loss. They also have less favorable link budgets due to lower power amplifier (PA) output powers and greater pathloss at these higher frequencies. Also, current costs of the Mmwave circuits are higher, but the costs will become much lower when the technology becomes mainstream. One advantage of millimeter wave, however, is that the smaller wavelengths allow for the fabrication of antenna arrays having a much higher number of antenna elements in a much smaller area than is typical at microwave bands. In this article, we outline a framework for Beyond-4G (B-4G) local area network in the millimeter wave band for both access and backhaul including air-interface, antenna-arrays and IC technology. It is shown that Mmwave B-4G small cell technology can provide peak and cell edge rates greater than 10 Gbps and 100 Mbps respectively with latency less than 1msec for local area network.

Experimental mm wave 5G cellular system

Bolstered by the ever increasing processing power of smart devices and combined with the new innovative applications, cellular data traffic demand is expected to increase a 10000x by 2025. Simultaneously, the telecommunication industry is converging on a common set of 5G requirements specifying 10x peak rates, 10x reductions in latency and 100x increases in cell edge rates over 4G cellular. Researchers are now looking to higher frequencies to meet demand and achieve the new requirements. This paper describes an experimental 5G system designed to operate at 73.5 GHz with a 1 GHz BW. The system communicates using a 28 dB gain antenna having a narrow 3 degree half-power beamwidth serving fully mobile user devices moving at pedestrian speeds. This experimental system is implemented in collaboration with Nokia and NTT DOCOMO [1][2].

Performance of coded higher order modulation and hybrid ARQ for next generation cellular CDMA systems

A key requirement for next generation CDMA systems is to provide a high bit rate packet data service and improved sector throughput for both low and high mobility applications. A 1.25 MHz DS-CDMA evolution called 1XTREME (Third Generation Enhanced Modulation and Encoding) has been proposed. 1XTREME uses a forward shared channel (F-SHCH) that is shared by multiple packet data users and is capable of supporting peak rates of up to 5 Mbps, compared to third generation CDMA system indoor peak data rates of 460 kbps and 2 Mbps for IS-2000 and W-CDMA, respectively. In this paper the link performance of the F-SHCH is evaluated for different modulation and coding scheme (MCS) configurations. Based on the link results, the average sector throughput is presented for two simple scheduling algorithms, as well as performance as a function of the maximum allowed FER operating point.

Field Experiments on 5G mmW Radio Access with Beam Tracking in Small Cell Environments

This paper presents field experiments on the downlink throughput performance of a beam tracking proof-of-concept system targeting 5G millimeter wave radio access in the following typical small cell environments: a courtyard, lobby, and underground parking area. The majority of the area in the tested environments is Line-Of-Sight (LOS) with cell radii of less than 60 m. The results show that the maximum throughput of over 2 Gbps is achieved in 87%, 40%, and 51% of each of the respective environments in the defined course. The beam tracking characteristics of each environment are nearly identical since the direct path is selected in LOS environments. Furthermore, under Non-LOS (NLOS) conditions, even though reflections degrade the signal quality, it is still possible for the user device (UD) to connect to the access point (AP) through the reflected paths. The NLOS connection is possible due to the relative position of the AP, UD, and reflectors in the environment.

Handoff Rates for Millimeterwave 5G Systems

Millimeterwave band is a promising candidate for 5th generation wireless access technology to deliver peak and cell-edge data rates of the order of 10 Gbps and 100 Mbps, respectively, and to meet the future capacity demands. The main advantages of the millimeterwave band are availability of large blocks of contiguous bandwidth and the opportunity of using large antenna arrays composed of very small antenna elements to provide large antenna gains. The line-of-sight operation requirement in this band, due to its unique propagation characteristics, makes it necessary to build the network with enough redundancy of access points and the users may have to frequently handoff from one access point to another whenever its radio link is disrupted by obstacles. In this paper we investigate the handoff rate in such an access network. Based on analysis of various deployment scenarios, we observe that, typical average handoff interval is several seconds, although for certain types of user actions the average handoff interval can be as low as 0.75 sec.

Experimental evaluation of downlink transmission and beam tracking performance for 5G mmW radio access in indoor shielded environment

This paper presents experimental results on downlink transmission and beam tracking performance in an indoor shielded room environment using a Proof-of-Concept (PoC) system targeting 5G millimeter wave (mmW) radio access. Experiments in mmW targeting under mobility and beam tracking with narrow beams in reflective environment have not yet been conducted. The mmW transceiver is implemented with analog beamforming using a switched feeder array and a dielectric antenna. The experimental results show that a throughput of greater than 2 Gbps is achieved while employing beam tracking and a lens antenna. Furthermore, the performance in an anechoic camber was also evaluated. We conclude that the indoor shielded room has low reflections comparable to an anechoic chamber when using the mmW transceiver.

Field experimental evaluation of beamtracking and latency performance for 5G mmWave radio access in outdoor mobile environment

In the fifth generation mobile communications system (5G), it is expected to use millimeter wave (mmW) radio access with very wide frequency bandwidths of more than 1 GHz. To achieve good coverage and availability, high gain antennas or arrays are essential in order to compensate for the higher propagation loss experienced at mmW frequencies relative to current cellular bands. This paper presents the beamtracking performance and throughput performance of a 5G mmW Proof-of-Concept (PoC) system in field experiments conducted at up to 20 km/h vehicular speeds in outdoor line-of-sight (LOS) conditions. In addition, this paper recomposes the frame structure for low latency and evaluates latency performance in the vehicular experiments.