Designing and Planning a GSM-R Network
The first step in the provisioning of a GSM-R network are the design and planning phases. The following describes the most important procedures and considerations for a typical GSM-R network.
Nominal Cell Planning
Translation of operator/customer requirements
For network planning, the coverage level is defined in terms of the area and time where the minimum signal criteria are achieved. This we do in full compliance with the EIRENE specifications and with the customer’s requirements, which in the case of GSM-R typically consist of or include government requirements. The typical level of coverage should be at least 95% of the time over 95% of the designated coverage area for a radio installed in a vehicle containing an external antenna.
A GSM-R system must provide communication for mobile devices travelling at speeds from 0 km/h to at least 140 km/h. However, individual clients specify the maximum speed needed to support their trains; this in turn influences the cell overlap in the nominal design.
For radio network planning, the minimum coverage level is defined as the power measured at the antenna port of an isotropic antenna (antenna gain: 0dBi) on the roof of the train; this is usually 4 meters above the track. This criterion will be met with a certain probability in the coverage area, as the target coverage power level is dependent on the statistical fluctuations caused by the actual propagation conditions. The minimum coverage level might be different, depending on special requirements from railway operators.
Although a network could be designed for minimal cost, a common recommendation is to use the following values:
- A minimum coverage level of 90dBm
- Probability 95%
- C/I greater than 12dB
In addition to the coverage and quality being specified for a train, other factors can be taken into account as well. This can include the required levels for handheld mobile equipment in shunting areas, or indoor for station staff and security operatives. Obviously, customers can specify other factors which may impact the radio network design; for example, the required redundancy in the network can be higher and call for the utilization of a full redundant coverage ETCS design or the Hot Standby TRX option.
The link budget is created from the translation of the customer requirements into specific coverage/quality levels. This is a theoretical calculation based on a number of assumptions, which provide the radio design engineers with a framework of radio losses and gains for both the downlink and uplink paths.
The information gleaned from the link budget provides a sound assumption for what the cell radius for the coverage will be, as well as an indication of the signal levels sent and received at the antennas. This is essential information for the radio engineers in establishing the site count, handover overlaps and other aspects of the Nominal Cell Plan.
Nominal Cell Plan
The Nominal Cell Plan (NCP) is an official document with specifications of parameters and equipment used for the radio access. It also gives an estimate of the number of sites needed. The nominal cell plan is usually the starting point in the rollout of a GSM-R network.
A typical Nominal Cell Plan contains the following information:
- Explanation, description and specification of parameters and equipment used in the document
- Nominal site location, with specified search area per site (country specific coordinates, usage of railway kilometer to specify the site location
- Use of friendly sites: public GSM sites; analogue sites of the 450MHz train system, Railway Operator’s building. Use of these sites can contribute to a faster rollout and cost reduction
- Cell site configuration (Composite cell/sector), number of sectors, directions, power level and antenna type
- Propagation model description
- Number of carriers (estimation based on the traffic model or specified from customer)
- Initial frequency plan
- Nominal antenna height above ground, or above mean sea level
- Engineering tolerances (antenna heights, accuracy of the digital map, etc.)
- Coverage prediction plots for the total area
Final Cell Planning
Train Line/Track Survey
A Track and Line Survey is optional, but this can be a very useful exercise before the detailed planning commences.
For a Track and Line survey a train is used in which basic survey equipment is installed (GPS, mapping data). Records on a Tablet PC provide details such as the ground heights and the exact route the track takes. This is coupled with notes taken at various distance markers along the track of features such as bridges, cuttings, tunnels and locations where the track runs through towns or thick forest areas. Together with the GPS reading, a camcorder records the line so that the radio engineers can minimize the number of surveys
Continuous Wave Measurements
Continuous Wave Measurements (CW-measurements) are used in preliminary radio path calculations, to derive initial qualitative and quantitative information in order to design BTS site configurations and in particular to support antenna design. In addition, data obtained here will validate the computing algorithms of the radio planning tool used and adapt them to reality in order to comply with GSM-R requirements; this provides the engineers with accurate topology losses, which add further accuracy to the Final Cell Plan. This is known as model tuning.
CW measurements should be carried out in a variety of environments including cuttings, embankments, bridges, tunnels, routes in built up areas, as well as routes in both flat and hilly terrain. The measurements taken at varying base antenna heights ensure that the analysis takes into account the variation in base station antenna heights.
It is vital that the engineers carrying out this survey have experience conducting radio surveys and look at the situation through “radio eyes“. If possible, the survey team should be joined by trained radio network engineers who have already performed surveys in other network rollouts.
The required details for a proper site survey are:
All the details above should be included in a Site Survey Report, in so far this is feasible. If there is a choice in sites, these should be ranked from most to least suitable. The relevant parties, including the engineer, acquisition manager and build manger, should then select the best option for inclusion in the Final Cell Plan.
- Complete, up-to-date maps, showing the exact course of the railway line and the corresponding profile of same scale
- A unique number and unique name of the site location (tower or building)
- Photos of site location (towers, buildings, etc.)
- Geographic coordinates in degrees, minutes and seconds (country specific)
- Exact address
- Complete height of tower above ground level
- Site location height above sea level
- Usable range of possible antenna mounting heights for all reasonable antenna directions marked in a sketch or plan, giving the heights above ground level in meters
- Exact site location marked on a map of appropriate scale (the map has to contain the course of the railway). Direct distance to railway line should be seen or given in meters.
- Photos into both main directions, if possible from a roof top (in case of a building) or from possible antenna mounting height location (in case of towers). The whole course of the railway to be covered from that site should be visible on the image, included all possible obstructions interfering the radiation in the directions of interest; these should be marked.
- In case of a building a drawing indicating the possible exact antenna mounting locations for both directions must be given (location on the roof, if edge or pole) and the definite antenna mounting height above ground level.
- Exact description of all obstructions, especially in the directions of the radiating antenna, with approximate distances.
- Rough classification of all areas along the railway track to be covered according to topological, morphological and vegetation aspects (e.g. urban, suburban, open, field, light forest, dense forest, hilly terrain, mountains, ascending/descending terrain in both directions of interest, ...), marked in the corresponding maps.
- Maximum speed of the trains (e.g. 200km/h) at the track section
- Number of parallel tracks
- Type of track section (main station, station, goods/freight station, shunting areas, tracks for personal traffic, tracks for freight traffic)
- Distance in kilometers to the next and previous sites on the route
- Exact specification of infrastructure parameters (access availability, power and telecom supply)
- Specified distance in meters from public houses (hospitals, schools, etc.)
- Surrounding conditions that might prevent the site from being built (national park area, tourist area, etc.)
Final Cell Plan
The Final Cell Plan is a detailed document which contains information about specific sites, site positions, antenna types, antenna heights, BTSE type and so forth, on which the rollout of the GSM-R network will be based. The Final Cell Plan includes a detailed Traffic Plan and a Frequency Plan. Depending on customer’s requirements, it may include BCC and LAC codes, a neighbor list for the network and a specification of Voice Group Call Areas. The Final Cell Plan typically contains a number of pictures taken at the site surveys.
The release of the Final Cell Plan is the trigger to start the implementation and building of the sites required for the GSM-R network.
Clear CinCom and GSM-R Network Design and Planning
Clear CinCom is a telecom consultancy with extensive experience in GSM-R network design and planning in Europe and elsewhere. You can read more about our services, the technologies we work with, projects we have recently completed and our specific experience with GSM-R.