Broadband Communities

MAR-APR 2017

BROADBAND COMMUNITIES is the leading source of information on digital and broadband technologies for buildings and communities. Our editorial aims to accelerate the deployment of Fiber-To-The-Home and Fiber-To-The-Premises.

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28 | BROADBAND COMMUNITIES | | MARCH/APRIL 2017 RURAL BROADBAND mmW spectrum for true 5G can be deployed. ere are enormous complexities to interworking and reconciling these dissimilar and competing networks and standards, which are anticipated to be pre-5G propositions. No one should stake a long-term, publicly funded commitment on them until after 2020, when mmW bands and devices that can handle them begin to become ubiquitously and globally standardized and licensed, with channels auto- managed among users in the case of shared-use spectrum and generally available for genuine 5G. Reducing the number of users per cell. e last means of increasing capacity for an entire system is by reducing the number of users per cell. is is accomplished by placing cells closer and closer together so the same capacity once afforded to a large coverage footprint of one cell utilizing a radio channel can be applied many times over with multiple, smaller cells in the same coverage footprint, all reusing that same channel. is is nothing new. Since first- generation cellular networks, when cells were on 500-foot towers and dozens of miles apart, cells have been placed lower and closer together to reuse available spectrum and increase capacity. Today, 4G cells are typically no more than 100 feet off the ground, except in sparsely populated rural areas, and they are placed every few blocks in urban areas. 5G "small cells" are a natural evolution of this cell-splitting technique. And the laws of physics will indeed necessitate that they be small. One cannot improve a system's overall capacity simply by moving the same cells closer together and serving only customers within the cells' close-in, high-throughput coverage areas, however. Signal still propagates from an access point to the edge of its otherwise usable coverage, whether it is used or not. Attempts to place cells closer together in this manner will raise the noise floor significantly for neighboring cells and reduce the overall efficiency of the multicell system as a whole. Intersite distance and coverage overlaps must be planned carefully to minimize interference to neighboring cells so they can maintain capacity. Placing cells closer together requires reducing signal power by lowering transmitter powers, lowering antenna elevations, and/or tilting antennas radically downward. Any of these strategies forces the cells to be much smaller, shrinking their capacity footprints correspondingly. In a 5G network, the resulting small cells indeed will need to be quite small. Moving cells closer together is especially difficult if a provider uses currently available sub-6 GHz spectrum that propagates too well for dense small-cell applications. Designs that meet the 5G bandwidth targets and accommodate future mmW ranges have made their coverage areas typically less than 1,000 feet in diameter – often half of this – and placed antennas only about 20 feet off the ground, with equipment deployed on streetlights and utility poles. Some estimates put 5G small-cell deployments at 10 times the number of sites as their current 4G macrocell counterparts. e hurdles to such a dense deployment include the vastly increased need for backhaul for so many cells so close together, particularly the dark fiber optic cable that most current configuration designs require for "fronthaul" (connections between base stations and radio antennas). All these sites will also need power. Both can be exceedingly difficult to coordinate and accomplish. In addition, user devices will have to incorporate many bands and have vastly expanded MIMO capabilities. is will require software-tunable, radio frequency (RF) components and antennas, which are just emerging from labs, plus very capable device processors, none of which are expected to be developed and generally available until after 2020. DOES 5G HAVE ENOUGH CAPACITY? Let's assume that 5G will one day be able to achieve its goal of 10 Gbps peak data rate per small cell. Applying the practical cell throughput factor of around 15 percent, this falls to around 1.5 Gbps of likely actual usable throughput available per cell, shared among all users. is bandwidth, even shared, might seem like a lot compared with today's typical broadband speed of around 41 Mbps. But again, it is reasonable to expect median wireline broadband speed to approach 100–150 Mbps by 2020 and 1 Gbps by the 5G equipment end of life. In addition, wireline providers, particularly FTTP providers, typically do not have to limit monthly usage to avoid oversubscribing their shared broadband resources. Today, IP video drives wireless providers to limit oversubscription of shared broadband resources. IP video is critical for distance learning, telemedicine, entertainment and other purposes. In days when bursty web-browsing traffic dominated the internet, broadband capacity could be significantly oversubscribed. High- volume data streams (such as video), on the other hand, require constant bit rates. is largely undermines or defeats any ability to oversubscribe a resource among active users. Increasingly, the only remaining basis for any oversubscription is the likely percentage of active subscribers. Dimensioning system capacity based on forecasts of the number of active users can be risky and easily lead to serious cell congestion if activity is heavier than normal. Most of Vantage Point's fixed wireless clients have difficulty oversubscribing access point capacity by more than 5:1 today, and many have had to resort to nondiscriminatory, across-the-board measures to limit video. is situation will only worsen as data demands, including but not limited to IP video traffic, grow as projected by Cisco and others. If 1 Gbps is a reasonable household broadband service expectation within the 5G equipment's service life, then the maximum 5G small-cell throughput expectation of about 1.5 Gbps will be a mediocre, if not very poor, solution for tomorrow's fixed

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