White Paper. TETRA QoS evaluation and monitoring

Transcription

1 White Paper TETRA QoS evaluation and monitoring

2 Content Executive summary... 2 Evaluation vs. monitoring... 3 How to measure QoS?... 4 What QoS Parameters should be measured?. 4 What to do with the results?... 5 Take Control of your Network Quality... 6 Executive summary `Maximum coverage and reliability at minimal costs is often the motto for applying or operating a TETRA Network. Other than public cellular networks TETRA Networks have only relatively few users and thus the cost of coverage per user seems often to be very high. However, the requirements for TETRA networks are due to their use for PMR and public safety rather high especially regarding the coverage and redundancy. While the users have high expectations in the network and in the terminals leading into a higher number of smaller low power radios with additional features rather than high power vehicle mounted devices with solid antennas. SAMDALE has been working over 20 years with the aim of analysing and improving TETRA Networks and based on that experience developed the PEGASUS System. The following document describes SAMDALES understanding of how a TETRA network should be evaluated and monitored to access the best Quality of Service from the underlying coverage and with that run the network most effectively both in an economical and operational way. 2

3 Evaluation vs. monitoring While and after the installation of a TETRA network there is naturally a huge interest in evaluating the coverage of the network to make sure that the planned services are achieved in reality. For this purpose field surveys have to be performed to capture various parameters from the network afterwards the results have to be analysed which should result on one side in coverage maps, but on the other side also in statistics about the QoS of the Network. The results of the evaluation can have a huge impact on the network performance if they are analysed correctly. This can rather consist of simple changes of frequencies to avoid interference, changes of parameters to improve the handovers or in some cases it even leads into the realisation that BS positions are obsolete/ missing/ can be changed. After the network is deployed there is often a change of responsibility for the network which enhances often with a change of specific interests. The results of the evaluation however show the status of the network at a specific time, mostly before having the users on the network. For the operator and users the results of the evaluation are important information but due to the fact that an operating network changes its behaviour depending on load, weather, faults, temporally interference, etc. it is further more important for the daily work that it can be assured that the QoS level which has initially been evaluated is being maintained or even improved. For that purpose an on-air monitoring system is necessary, which means that measurement tools have to capture constantly data from the TETRA air interface, analyse it and report automatically faults to the network management. 3

4 How to measure QoS? Due to the fact that a TETRA network has two main parts, the SwMI and the terminals there are naturally two main access points to measure the QoS. One is to monitor the traffic and results in the SwMI and the other one is to monitor the behaviour of the terminals. The data from the SwMI can provide a lot of interesting statistics about the load and the behaviour of the network and there are quite some errors that can be found analysing this data. But these data can never reflect the actual behaviour of a terminal moving through a network. To measure the QoS from the terminal/ user perspective it is essential to act like a terminal, which means surveying the network. The only problem of surveys is that they happen to be very expensive. What QoS Parameters should be measured? Quality of service (QoS) is defined by Schmitt J. (2001) as the well-defined and controllable behaviour of a system with respect to quantitative parameters. However, the opinion what quality level a network achieves differs in reality often depending on who you ask. A Radio engineer might look at the RSSI level, a service manager at the bit error rate and the user will only consider the voice quality as a valid parameter to define the Quality of service. In fact to measure the QoS of a network all of this and a lot more has to be taken into consideration. We consider three groups of parameters. - Physical (Radio) Parameters These are mainly parameters that have a direct relation to the RF carrier like modulation, frequency and power stability of the carrier, RSSI, C/I ratio, bit error rate etc.. These parameters allow a good overview of the basic physical health of the network and it s absolutely necessary to measure those for acceptance test, finding problems with slow/ fast fading or reflection, as well as finding an interfering frequency or hardware problems in a BS etc.. - Mobility Parameters Mobility parameters are the details that are being generated inside a terminal 4

5 while it is moving through a network registering from cell to cell. These are parameters like, LAC code of the current serving cell and the one visit before, broadcast and C1/ C2 parameters, amount of handovers, time for handovers, difference between attempted and completed handovers and lots more. These parameters have to be measured using some kind of TETRA Protocol like it runs in Terminals and the measurement tool has to actively take part in the communication between the base station and terminal to receive the full scope of parameters. - Service Parameters The service parameters reflect the end user view of the network chain, which means parameters like voice quality, data throughput, lost SDS s, speech delay etc. The overall point is that all these points are related to each other and in every group there are effects that can have an impact on to the general QoS. What to do with the results? The truth is that in a lot of cases surveys are performed which produce tons of separate data in a specific format that can only be analysed by certain trained and experienced people. From that reality comes one of the most important questions. How do I analyse, present, export and, very important, archive the data? This can only be achieved with a coherent system architecture that allows storing and using the data in a flexible but well defined form. The main points that have to be taken in account are: - Standard central storing of data. - Clear and open presentation of the data, that allows users with different knowledge to drill down to different levels of detail. - Easy export of data to standard formats. - View of current and historical data. - Stand alone and controlled operation possibilities. - Variable automatic instant alert functionality. 5

6 - Secure flexible accessibility for different users groups. Take Control of your Network Quality Samdale s PEGASUS TETRA Service Monitoring system delivers pro-active Quality of Service maintenance via a network of real-time monitoring probes. Each Probe operates autonomously, automatically buffering data and uploading data to the PEGASUS Server when a connection is present. The PEGASUS Server provides a comprehensive suite of analysis tools for viewing probe data on maps & charts. PEGASUS provides the most detailed view of performance by detecting the widest range of offair problems that are often not reported by traditional network monitoring systems. Key Benefits - Usability for initial surveys and long term monitoring. - Covering o Physical Parameter o Mobility Parameter o Service Parameter in one measurement tool. - All data stored in one server. - Passive or Active Monitoring - Fixed or Roaming Probes - Easy Trend Monitoring & Analysis - Instant Alerts to Key Personnel - Easy view/ prove of historical data. - Cost-effective because it can be used in operational vehicles. References Schmitt, J. (2001). Heterogeneous Network Quality of Service Systems. Kluwer Academic Publishers. ISBN: X. 6

7 Tel: +44 (0) ~ fax: +44 (0) info@samdale.com Samdale Limited Spectrum House West Station Business Park Spital Road, Maldon, Essex United Kingdom. CM9 6FF