Critical communications networks: planning for transition

As the transition from PMR to mobile broadband draws nearer effective network planning is needed now more than ever, as Richard Martin discovers

Public safety communications are in a state of flux; we are in a transition from PMR/LMR systems to broadband cellular systems. This is happening at different speeds across the world. In some cases, the intent is to make the transition rapidly, as in the UK; in others, the transition is a process of evolution with both working alongside each other, as in the USA. In many cases the use of 4G and 5G for public safety is being trialled or studied, as is the case in Canada.

In terms of planning for a public safety network there are several cases to consider.

First, a dedicated network which can be a PMR technology such as TETRA or P25, or a standalone cellular network such as GSM-R or 3G or even private LTE. Next, a new cellular network which may be shared between public and mission-critical users. The particular needs of public safety users will need to be met in terms of coverage and resilience. In the third case, an existing public network is offered; this may need to be expanded into low-population areas to provide extra coverage or other enhancements.

With the increasingly rapid roll-out of 5G we have to ponder how long it will be before this too is used for critical communications. 5G is expected to be deployed in densely populated areas and use high frequencies – it will pose network planning challenges of its own.

Planning basics
The basic steps in network planning can be reduced to the following:

A clear view of service requirements for the public safety users, including KPIs. For public safety users, coverage will be a key factor from the outset, together with resilience and security.

Fundamental to the planning which follows will be the budget – high resilience and secure networks or network expansions will come at a cost.

Link budgeting will establish the maximum cell size in rural areas, particularly when commercial networks are to be extended to lightly populated areas. This calculation adds up the losses from sources in the base station and the mobile, and this is subtracted from the base station or mobile transmitter power. Propagation loss is then included to calculate cell sizes for the expected base station configurations.

In dense urban areas, cell sizes and capacity will be driven by user numbers; the addition of public safety users may not greatly increase traffic but will require priority service. Frequency planning and cell capacity calculations come into play in this case.

The other challenge is the need to ensure in-building coverage [for more on this topic, see “Building confidence” in our April issue – Ed].

The site survey may also identify adaptations to the proposed base station configurations, the sectors proposed and the need for special antenna types.

Naturally even the most careful plan will need to be tested once installed. A more detailed discussion of this is covered in Critical Communications Today’s August 2018 issue.

A bridge from old to new
Our scene shifts to South Korea, where the country’s Safe-Net mission-critical broadband network is being rolled out. To what extent (if any) is it reusing existing LMR or public cellular network sites?

“The coverage range of the private LTE network under construction for Korea Safe-Net is different than those of the existing LMR network due to using a separate 700MHz frequency band. And LMR sites are not shared with the PS-LTE sites.” says Young Sam Hong, outreach committee chair of Safe-Net Forum. “Therefore, [nobody has reported any coexistence issues]. We are implementing 15,000+ new sites dedicated to PS-LTE but expect some coverage shadow areas (such as underground locations, farming and fishing villages, and mountains). For those limited areas we are planning to also use some of the public cellular network’s existing eNodeBs through RAN sharing, this would improve service quality for the public safety users”.

He adds that where PS-LTE (public safety LTE) and commercial networks share sites, it is mainly the building facilities, antenna towers and backhaul that are shared, but “redundancy and security are separately implemented”.

“Planning and design has been carried out by network operators and industries under the supervision of the government in [South] Korea, and the Safe-Net Forum is providing technical support including consultation. Evolved packet cores (EPCs), eNodeBs, applications and security are dedicated to PS-LTE, all are separately implemented for PS-LTE. There will be a full set of core equipment at each regional operation centre including EPC, MCPTT, eMBMS (evolved Multimedia Broadcast Multicast Service), IMS (IP Multimedia Subsystem), NMS (network management system) and common applications. To be clear, Safe-Net is a private network.”

Hong concludes by saying that “[the South Korean] government is not planning to implement 5G networks dedicated for PPDR within four to five years due to technical and frequency spectrum characteristics, budget, etc. As cellular operators have been already implementing 5G commercial networks in [South Korea], we are studying how to utilise them in connection with 4G.”

There is much more to mission-critical network design than the radio access technology. One issue for TETRA networks of a certain age is their use of circuit-switched technology, which employs time-division multiplexing (TDM) and synchronous protocols such as E1 and T1 for the links between the switches and base stations. If these are to reap the full benefits of modern technology – particularly the ability to use commercial off-the-shelf (COTS) hardware – such networks need to be migrated over to internet protocol (IP).

Our next port of call is in Germany, where the world’s biggest TETRA network is being upgraded to become an all-IP system, as BDBOS’s Barbara Held explains. “This entails a new simplified architecture that will reduce the number of switches from 64 to 21 by using new technical features for virtualisation. At the same time, all 6,500 base stations will be upgraded while the network stays in full operation. The users have been promised TETRA voice service at least until 2030.

“In parallel, BDBOS plans to prepare for basic broadband data services in the 450MHz area, once this spectrum is allocated to public safety usage. Radio experts estimate that an additional 1,200-1,500 base stations will be necessary to establish a broadband network in these bands that will cover the entire German territory. The basic broadband network will deliver the same mission-critical qualities as the current TETRA network and will be used to manage additional capacities in other bands.”

More broadband services and capacity will be reached by adding (unharmonised) bands in the 700MHz area that were allocated to public safety in 2018. RAN-sharing with the commercial providers in neighbouring bands is also being considered. The scenario will be complemented by roaming services acquired from commercial providers, thus delivering a state-of-the-art hybrid critical communications system.

What’s in the toolbox?
Given the highly complex nature of modern network planning and the many different (and inter-related) technical and commercial factors that have to be considered, it is not a surprise to see that a number of suppliers provide tools for public safety network planning.

Jason Suplita, regional executive at Ranplan Americas, says that it offers an all-in-one heterogeneous network planning, optimisation and simulation solution for small cells, DAS and Wi-Fi across indoor and outdoor environments. The company provides modern indoor/outdoor HetNet design capabilities supporting all connectivity technologies. With the ability to accurately model coverage and interference through the use of a true 3D ray-tracing propagation model, the Ranplan solution addresses the complexities associated with designing modern public safety communications networks for large venues, campus settings and theme parks. Accurate predictions using advanced building structure modelling from floors and stairs to tunnels offers the public safety industry an alternative to traditional design software that only takes into account in-building areas or outdoor areas in a separate manner.

“First-responders require dependable radio coverage prior to and when entering any emergency situation. Precision [is] key [when] designing modern public safety connectivity within and alongside current public safety networks. We need to ensure that we exceed today’s compliance requirements and be ready to meet those in the future. Ranplan’s in-building design capabilities coupled with our outdoor network visualisation capabilities mean that public safety organisations have the best possible chance of understanding where they have indoor-to-outdoor radio accessibility,” says Suplita.

Other providers include TEOCO, which offers its ASSET planning tool for LTE capacity planning and PRB dimensioning. iBwave specialises in planning for indoor coverage; its tools consider the needs of fire and medical teams in particular who will need to access difficult areas inside a building including staircases, corridors and other rooms without an external wall or window. The EDX Wireless SignalPro tools also focus on planning for public safety needs covering frequencies from 30MHz to 100GHz and are able to show how different technologies work together. This is helpful during the transition to an all-4G/5G network.

A closer look….
Based on a live deployment, this case study outlines the challenges and risks associated with deploying a public safety network, alongside other connectivity systems, into a very complex environment.

Radio One is a turnkey systems integrator and one of the largest authorised Motorola Solutions channel partners in the US. Working with Ranplan it is responsible for aiding the deployment and maintenance of the public safety system for one of the country’s largest theme parks.

The project had to overcome a number of challenges. These included the sheer scale of the network, given that it had to cover a large site consisting of several physical parks, each with their own indoor and outdoor coverage requirements, making it harder to visualise. The site also had high capacity needs, due to the large amount of footfall. There was also the mission-critical nature of the network to consider – any errors could potentially put the park’s patrons at risk, as well as potentially leading to a large monetary cost over the project’s lifecycle. Finally, there were a large number of internal and external stakeholders to manage.

Just as a public safety agency team might struggle to have a clear picture of a large complex and evolving incident, so too can it be difficult for network planners and project managers to keep track of a similarly challenging roll-out and ensure that everyone is working with the latest documents and plans. This can be made much easier through the use of cloud-based applications, to provide everyone with a common operational picture. This project used Ranplan’s cloud-based Public Safety Collaboration Hub Platform, which has project visualisation (including 2D and 3D floor design views), workflow management, and project monitoring and auditing functions.

It effectively guided walk test and design resources so that they could correctly identify non-compliant buildings inside the campus. This was made possible through the visualisation of the wider campus using high-quality geo-data that combined detailed models of the campus’s in-building and outdoor areas. It also allowed the project management team to enforce best practices in terms of input control and to standardise reporting for all stakeholders. Finally, it provided the team with data protection and security by allowing them to set user access controls for files, protected against data loss and ensured the smooth flow of data in standardised formats.

Planning for 5G
5G is still on the horizon from the perspective of critical communications but planning may need to start soon.

Huawei has identified the specific challenges that 5G creates for network planners, with two key ones being the use of Massive MIMO (multiple input, multiple output), which replaces sector-level wide beams with user-centric dynamic narrow beams, with users sharing frequencies; and multi-user MIMO, which allows multiple spatially distinct users to share the same frequency. The company’s network planning tools include ray-tracing, UMi (urban micro) and UMa (urban macro) propagation models, Massive MIMO modelling, balancing uplink and downlinks, 2D and 3D coverage prediction and automatic cell and
site planning.

The whole picture
The focus of this article has been on planning the radio element of the network. This is vital as cell sizes, quality of service, data throughput and backhaul all begin with these first steps. But the next stages will be to plan in terms of the data transmission network, core elements and switching; all have to be dimensioned, costed and planned. As we are considering public safety, resilience and security requirements will also be a consideration. An intriguing question for future study will be self-optimising networks and the use of artificial intelligence. The capabilities and complexities of 5G networks may well lend themselves to AI.

The radio network plan is just the start of the planning process which itself will have to be revisited when there are significant changes to the physical environment, frequencies, user needs, or regulations. As legacy PMR systems are replaced by 4G and 5G, the same or better levels of service must be maintained. As two-way radio has long been a foundation of public safety operations, planning for this transition has to be securely based on reliable tools and processes. We can’t miss a step.