Radioplan GSMCase Study

Optimizing GSM cell configurations reduces network interference

to just 1%

1

0.8

0.6

0.4

0.2

0

Rela

tive

Freq

uenc

y

-55.32 -41.93 -28.55 -15.17 -1.78 7.14 16.06 29.44

Automatic cell planning has for the past couple of years revolutionized the way in which UMTS planning and optimization is performed. Not surprisingly, results have been impressive and savvy wireless operators now benefit from a reduction in both CAPEX investment and OPEX spend.

For GSM networks, however, it is a different story. Optimization here is generally limited to changing the frequency plan and fixing quality issues. But as one major North American operator discovered, when demand for high-speed data services (such as GPRS and EDGE) gathers momentum, an efficient strategy to minimize cell interference is essential to maintain the high quality service their customers demand. Their solution? Automatic cell planning combined with automatic frequency planning.

Having engaged with Actix on a previous project, the operator’s optimization manager asked Actix to make a full study of one of their main markets – one which included 47 sites – to see what improvements could be made. The study included the following steps:

1. Site audit. This included making sure that the planning tool database was up-to-date with the right information relating to each site’s configuration

2. Drive test of the area. To be used in the path-loss tuning exercise

3. Pathloss tuning using Actix Radioplan

4. Tilt optimization using Actix Radioplan

5. Benchmarking the results

Reducing CAPEX investment and OPEX spend

Pathloss Tuning

www.actix.com

2Actix Case Study Radioplan GSM

Figure 1. Standard prediction model Figure 2. Tuned pathloss model

Once the site audit was verified and the drive test conducted, attention turned to pathloss tuning. To get an accurate view of the network, site information and the planning database’s pathloss files were imported into the Actix Radioplan’s pathloss tuning application. Then, having imported the drive test data from the same area, pathloss tuning was simply a case of adjusting the pathloss sector-by-sector based on the signal levels from the drive test.

Next, the standard prediction model and the tuned pathloss model from Actix Radioplan were compared.

1

0.8

0.6

0.4

0.2

0

Rela

tive

Freq

uenc

y

-15.17 -1.78 7.14 16.06 29.44

1

0.8

0.6

0.4

0.2

0

Rela

tive

Freq

uenc

y

-15.17 -11.43 -5.08 1.27 5.50 9.74 13.97 20.32 29.44

When comparing the differences in the predicted coverage between both models, the coverage area of the tuned pathloss model was also better than had been anticipated:

This indicated that the network was experiencing more interference than was currently known from the planning department. Nevertheless, overall interference could be easily improved, either by making manual changes or by automatic cell planning.

www.actix.com

3Actix Case Study Radioplan GSM

In contrast, the standard prediction model appeared somewhat conservative with what looked like cell coverage designed for a denser network. The downside of this was that interference conditions within the network were worse than expected:

Figure 3. Coverage with standard prediction model Figure 4. Coverage with tuned pathloss model

Figure 5. Interference (C/I) with standard prediction model Figure 5. Interference (C/I) with tuned pathloss model

The result for the standard prediction model was a mean error of 4.8dB and a standard deviation of 7.9dB. After pathloss tuning, the mean error dropped to 2.1dB and standard deviation 4.3dB – a significant improvement.

Won over by the fast, accurate and robust results of Actix Radioplan’s tuned pathloss application, the operator’s optimization manager decided to reduce the network’s interference using the Actix Radioplan automatic cell planning (ACP) application. This activity involved electrical tilts and mechanical tilts at various sites. This improvement depends on the tuned pathloss matrices used in the optimization, and on the ability of the Actix Radioplan solution to detect mismatches between the planned and actual network configuration, allowing the optimization process to commence form a better initial starting point. Without pathloss tuning and automatic mismatch detection, the results would be less impressive. The results are shown below:

Automatic cell planning

www.actix.com

4Actix Case Study Radioplan GSM

This improvement depends on the tuned pathloss matrices used in the optimization, and on the ability of the Actix Radioplan solution to detect mismatches between the planned and actual network configuration, allowing the optimization process to commence form a better initial starting point. Without pathloss tuning and automatic mismatche detection, the results would be less impressive.

Figure 6. Coverage before ACP Figure 7. Coverage after ACP

Figure 8. Interference (C/I) before ACP Figure 9. Interference (C/I) after ACP

www.actix.com

5Actix Case Study Radioplan GSM

The results can also be viewed in tabular form via Actix Radioplan’s user interface.

As the above plots illustrate, cell coverage improved only slightly beyond the initial tuned pathloss optimization, as expected. However, interference levels were dramatically enhanced using Actix Radioplan’s ACP – invariably leading to a much higher quality network. Generally, in GSM coverage optimisation is not the goal. Operators have been planning and running GSM network for 15 years now, so there is a broad understanding of how to achieve good coverage. The really new thing about Actix’ focus is reducing cell overlap, which has been neglected in the traditional approach, because there was typically more than enough spectrum. Optimizing cell overlap becomes more and more critical, especially in case of spectrum rebanding.

With ever tighter budgets and fewer resources, automatic cell planning and frequency planning can be used to efficiently support network optimization, often with astounding results. While pathloss tuning using Actix Radioplan ensures an accurate picture of the coverage and interference conditions in the network, the Actix Radioplan ACP enabled this wireless operator to achieve the optimum network configuration.

As this operator’s optimization manager commented, “The Actix Radioplan platform quickly gave my engineers precise and realistic predictions for cell coverage and interference. This enabled them to focus on key optimization tasks to enhance the network. Results were far better than we could have ever imagined – we have more or less removed all interference in the network, moving the area of C/I < 12dB down from 14% to just 1%. That’s quite an achievement.”

Automated planning tools yield outstanding results

Coverage >84dB >70dB

Before 96% 53%

After 98% 54%

Interference (C/I) >12dB >16dB

Before 86% 68%

After 99% 95%

Americas T +1 703 707 4777 F +1 703 707 4778

China T +86 21 5396 0670 F +86 21 5396 0676

Germany T +49 351 40429 0 F +49 351 40429-50

Hong Kong T +852 2295 6677 F +852 2295 6687

India T +91 11 41683064 F +91 11 41683080

Japan T +81 422 45 4720 F +81 422 45 4720

Singapore T +65 6333 7428 F +65 6333 5540

Sweden T +46 42 38 99 00 F +46 42 21 05 85

UK T +44 (0)20 8735 6300 F +44 (0)20 8735 6301

www.actix.com