RF Planning for Ground Transportation

Some years ago I was involved in building out a large wide area wireless network in the South East of the UK, delivering wireless broadband services to rural areas underserved by wireline technology such as DSL. Before any physical deployment could take place, it was vital to identify where multi-sector base stations had to be placed in order to provide sufficient RF coverage of the target areas, and how these locations could be linked together with point-to-point connections for backhaul. This RF coverage planning stage enables the network operator to understand infrastructure requirements in terms of location and cost, but also to predict throughput and capacity, and mitigate dead zones due to obstructions by landscape topography, buildings and dense seasonal foliage. Transit operators are facing similar issues with a range of wireless initiatives including rebanding, narrowbanding and vehicle connectivity for Positive Train Control (PTC), passenger Internet and other needs. Accurate radio coverage planning on the desktop will help reduce deployment time and make more efficient use of budget. There are a number of vendors in this space who make the software systems required for wide area network, multi-frequency planning, including EDX , ATDI and AWE . Unwired caught up with Mark Chapman, CEO of EDX Wireless, at the recent IWCE conference in Las Vegas for an of outline how transit agencies can benefit from radio planning. Unwired: What are some of the key challenges facing transit operators as they prepare for federally mandated wireless initiatives such as narrowbanding and PTC? Chapman: One of the biggest challenges is ensuring that current network performance is maintained or improved as it is upgraded and expanded.  It is easy for an operator to overlook the importance of the planning stage of the project.  A good RF design will reduce project costs, minimize rework and ensure that network performance meets or exceeds objectives. A well-planned network will also use spectrum in an efficient manner, preserving this critical and increasingly scarce resource as rail networks expand. [caption id="attachment_804" align="aligncenter" width="300" caption="Signal strength analysis along rail route"][/caption] Unwired: What are the key functions of desktop radio planning software? Chapman: Well, one of the key functions of radio planning software is to predict network performance before committing capital expense to a new network build or the expansion or modification of an existing network.  Radio planning software allows the engineer to visualize the effects of planned or proposed changes or additions to the network before the expensive civil works and electronics purchases are made. It's worth noting that the needs of an efficient Rail PTC system differ greatly from standard wireless solutions and require a different approach to planning and optimizing. These links are designed primarily for communication and control along a rail line, making the radio coverage and interference off the tracks or Right of Way less relevant to PTC operation.  For example EDX PTC tool SignalRT, concentrates calculations along the rail lines creating a high-resolution study that can be run more efficiently and quickly than a comparable study using conventional planning tools. The result is a more accurate representation of the interference, coverage and quality of RF service along the route of interest. The focus on the specific rail route, rather than an area, translates into more efficient use of scarce and valuable spectrum, higher performance, greater reliability and redundancy, and lower equipment costs. Unwired: Can the same software be used for UHF/VHF narrowbanding, 800MHz rebanding, and trackside network design, for example at 5.8GHz? Chapman: A good RF planning tool can allow the user to perform a wide variety of network simulations.  Most professional tools can predict radio network performance on a wide variety of networks that operate between 30 MHz and 100 GHz including Land Mobile analog and digital networks, PTC, cellular and other systems using area, route, link, mesh and multipoint studies and simulations. Unwired: Where does ‘clutter’ data (representing obstructions to RF propagation such as topography and buildings) come from, and how accurate is it? Chapman: Terrain and land use (“clutter”) is needed in RF modeling to provide accurate predictions of radio link performance.  The choice of clutter data depends on the project.  Network designs in rapidly growing densely populated areas need up-to-date high-resolution clutter data whereas rural areas that haven’t seen much development can be designed using older low-resolution clutter data that can be obtained for free, at least in the U.S., from the USGS website.  There are several vendors of high-resolution, high-quality clutter data. Interestingly, one recent innovation is the use of Clutter Carving. This technique allows the use of easily obtainable digitized street and rail data to improve accuracy of predicted RF coverage by modeling RF transmission down the ‘canyons’ created by roads or rail lines through the ground clutter. Suited to both planning and deployment phases, Clutter Carving allows the use of low-cost, low-resolution clutter data while still giving accurate propagation predictions. The benefit is that a user can employ freely available data that better represents the propagation environment, thereby improving accuracy while lowering cost. Unwired: Many transit operators are considering 4G networks for vehicle connectivity; how accurate are the coverage maps supplied by mobile carriers, and can desktop software be used to plan cellular coverage? Chapman: The mobile carriers use sophisticated radio planning software to plan their network, but their publicly available network coverage maps tend to be a lower resolution historical snapshot of network coverage.  They can give an idea of how good the coverage is in an area, but it is unlikely they could be used to reliably plan a mission-critical system that would use the carrier’s network. Unwired: How does radio planning take into account railway tunnels, and how much more is designing radio coverage in underground metro systems easier or more complex? Chapman: Great question. Outdoor coverage is simpler to model.  Indoor and tunnel coverage requires more sophisticated models using more detailed building and tunnel databases.  Many planners choose to use a microcell/indoor models that can perform detailed analysis using ray tracing for indoor and tunnel radio coverage predictions. Ray tracing essentially considers all the various paths the signal can take including reflections etc., to build up a detailed model of performance. Obviously this is massively computationally challenging so part of our art is in developing mathematical ray tracing techniques which intelligently compute the performance in a way which allows the simulation to be run accurately even on a laptop. Unwired: Does desktop software take into account differences between equipment vendors and radio/antenna types? If so, how? Chapman: Depending on the engineering requirements, predictions can be made for generic transmitters, but more usually technology and vendor specific models are employed to predict actual performance. These models are built into the software or can be defined by the user if a particular vendor’s equipment is not supported. Most vendors are pretty good about publishing and sharing their data so it can be used in modeling software. Unwired: How does radio planning help transit operators improve their return on investment? Chapman: It is a lot cheaper to simulate a network in software before making the expensive upgrades.  Buying electronics and doing civil works is the expensive part of the project.  Radio planning software allows the engineer to do trade-off studies to ensure that the network is designed to meet or exceed design goals while saving expensive equipment. This process also allows “what-if” scenarios to be rapidly analyzed and simplifies the comparison of various architectures and vendor equipment and their effect on overall performance In addition, a well-planned network will provide a higher degree of communication reliability and redundancy, increasing overall safety. Planning tools can determine the number of wireless servers that are available at any point along a route, essentially indicating what is available should a primary server fail. The combination of route analysis and clutter carving releases inefficiently used spectrum which can then be deployed to create additional back-up servers, offering an increased measure of resilience and redundancy. This is not strictly equipment ROI but certainly will be a factor if an operator is buying or licensing spectrum as well as building the network. Unwired: What are some of the key differences when planning for voice traffic versus data? Chapman: There is the simplistic approach of looking at only RF coverage that works for simpler FM types of networks.  But with digital systems carrying voice and data, the quality of service is equally, if not more important, to model. Most commercial RF planning software contains many specific tools and analysis studies to predict quality of service for digital systems as well as basis coverage. Unwired: How does RF planning software account for in-building coverage of wide area networks? Chapman: Buildings present quite an RF challenge as they are really good at absorbing RF. Many wireless network operators and planners now are considering an indoor to outdoor implementation process rather than trying to serve a building purely from an external system. This is particularly relevant as high-speed data service becomes important. As I mentioned before, if an operator has dedicated in-building systems then the Microcell/indoor Module and its sophisticated ray-tracing capability can accurately predict indoor coverage from indoor micro and pico cells, as well as the contribution and service from outdoor sites. Unwired: Does RF planning help mitigate interference when designing network in unlicensed bands, such as 900MHz, 2.4GHz and 5GHz? Chapman: Yes and no.  It is possible to predict the interference that your own network causes, but unlicensed bands are a “wild west” of a variety of RF sources that really need to be field-tested to ensure interference-free operation. Unwired: Some transit operators want to use a combination of network types such as high-capacity Wi-Fi mesh in unlicensed bands for rail wayside video systems, and 3G/4G cellular for road vehicle connectivity. Will desktop software work with all types of network topology including multi-hop mesh? Chapman: A comprehensive RF planning tool can allow the user to perform a wide variety of network simulations.  For example, EDX SignalPro can predict radio network performance on a wide variety of networks that operate between 30 MHz and 100 GHz, including Land Mobile analog and digital networks, PTC, cellular and other systems using area, route, link, mesh and multipoint studies and simulations. We also have a dedicated mesh Module that performs detailed mesh calculations on large scale networks.   This software is used for designing municipal Wi-Fi networks of a few hundred nodes up to large urban area Smart Grid AMI mesh systems with 100,000's of nodes. [caption id="attachment_805" align="aligncenter" width="300" caption="Multi-hop mesh network modeling in an urban environment."][/caption] Unwired: What key advice do you have regarding wireless network planning for CIOs and communication managers within transit organizations? Chapman: Everything starts with planning so don’t try to save money by taking short cuts in the planning process. Wireless networks are complex, expensive and ever-changing systems, but with a proper focus on RF planning, operators will achieve higher performance and improved reliability with faster deployment, while benefiting from lower implementation and equipment costs. -- Jim Baker is managing partner at Xenventure, a market strategy and private equity firm based in San Francisco and London. A C-level wireless industry veteran, Baker has been involved in many deployments of wireless technologies on passenger transportation worldwide and is a recognized industry expert on Wi-Fi, 3G and 4G convergence. He is Chair of the Technology Committee at the Joint Council on Transit Wireless Communications which is developing a strategic plan for implementation of wireless technologies in mass transit. Contact Baker via LinkedIn or follow him on Twitter.

Loading