Auditing and Optimizing a GSM-R Network
After designing and planning a GSM-R network, the next step in the deployment of a GSM-R network are audits, drive tests and optimization of the network.
Technical Site Surveys for Selected Site Options
When the Final Cell Plan (see Designing and Planning a GSM-R network) has been released, it contains the selected site options agreed upon for implementation in the radio network.
The survey team should be comprised of the radio design engineer who picked the site, a draughtsperson to compile the detailed drawings and perform physical measurements for feeder runs etcetera, the implementation manager to ensure compliance and legality of the design and the site landlord for any consultation issues.
The required details for a site survey are:
- Relevant details to complete an accurate scale drawing of the overall design
- Photo(s) of the site, with special attention to access points, ladders, fiber connection points and power supplies
- Geographic coordinates in degrees, minutes and seconds (country specific)
- Exact address
- Exact height of tower above ground level
- Site location height above sea level
- Required antenna type and tilts
- Required feeder type attained from a detailed measurement of the feeder cable runs
- Any build specific details, such as brackets and flanges, need to be recorded for inclusion on the design drawings
When the Technical Site Survey is completed and the detailed design drawings are issued and signed off as accurate by all relevant parties, the site can be built and prepared for implementation.
Built Site Audits
After the site has been built, it needs to be inspected by the relevant implementation/build manager and the radio engineer, in order to ensure it has been constructed in accordance with the detailed design drawings compiled after the technical site survey.
Every aspect should be inspected and ticked off on a check list. This includes the positioning and tilts of the antennas, inspection of the feeders and runs, weatherproofing of the joints between the feeders and tails, physical configuration of the BTS equipment, etcetera.
Once this has been completed and the installation is compliant, the BSS script files for the site can be implemented through the BSC and the site can be made active.
Individual Site Acceptance Testing
The last step for the implementation of the site is to conduct a SAT (Site Acceptance Test). This test comprises of the site being turned on and radiating, whilst a mobile test team drives a specified route and ensures the radio signal is propagating as it should. It will also indicate if the feeders are crossed or other issues which may degrade the effectiveness of the site in the completed network.
This test is recorded using various software applications connected to a receiver (such as an Agilent or Kapsch radio). The levels are recorded and processed for inclusion into a SAT report document. If the SAT is successful, the site can be integrated into the radio network.
Radio Network Delivery
Initial Drive Testing
When all the sites have been subjected to the various implementation tests and they are all compliant, the entire radio network can be tested in an end-to-end fashion.
The method commonly used for this important phase is the utilization of a train, fitted with the relevant measurement equipment and driven over the length of the network. This initial test will provide information and illustrate (in real time and within the actual environment) the handover behavior between cells and sites, any dropped calls (which can be caused through a number of issues such as low coverage, interference or poor handover behavior) and a number of other issues which can affect the quality of the radio environment.
The minimum requirement for the test is ensuring the coverage passes at the required levels and the quality (C/I) is acceptable and within the specified values. To achieve this, the train must be fitted with the relevant measurement equipment.
An example setup could be:
- PC and relevant software for recording the RxLevels (in dedicated mode)
- Measurement Radio such as a Kapsch radio or Trio Rail
- GPS equipment to record location data (used in conjunction with the coverage measurements)
- PC and relevant software for recording the C/I ratio
- GSM-R test handset (used in conjunction with the C/I measurements)
- Roof mounted antennas
Further tests can be conducted at customer’s request regarding the Bit Error Rate, Call Setup Success Rate and Idle Mode measurements to further measure the effectiveness of the radio environment. Ideally, the test train should be a dedicated unit allocated for testing. This will eradicate the variable results caused by the placement of antennas in different locations for other and subsequent tests. Consistency is the key to accuracy regarding train testing.
On completion of the initial train testing, the recorded results can be processed and analyzed. This will provide the radio engineers with data on which they can base optimization changes that will eradicate problems and improve performance.
This data, for example, may show areas where sites are overshooting and causing issues with other sites, therefore further tilts can be applied to improve overall network performance. Alternatively it may indicate poor handover behavior, which can be improved by simple adjustments to the BSC parameters to further improve the overall performance. These are just two examples of numerous issues which can affect a network; these will only be identified by following a correct and comprehensive testing procedure.
When the optimization changes have been implemented and completed, a final test drive can be conducted to gauge the effectiveness of the changes and to illustrate the improvements made.
Final Drive Test
The final drive test is a repeat of the initial drive test. However, this is to record the final state of the radio network (after the optimization changes) and is used as proof that the radio design now complies with the required specifications. The network is now ready to go live. At this stage, all results are documented and the radio network is prepared for handover to the client.
Clear CinCom and GSM-R Network Optimization
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.