Prerequisite for a 3G network design
At the best of times, designing a cellular network is like doing a puzzle without any instructions. With 3G, you have the added complication of both the operator and customers holding back some of the pieces and planners having to force pieces to fit together because the edges are a bit rough!
Getting the required information for a network plan is the most crucial part in building a cost effective quality network. Unfortunately, some of the necessary data is confidential and not only that, it's anybody's guess as to what the 3G mobile service mix and usage will be. In an environment where operators need comprehensive designs and redesigns in a very short time frame, there's plenty to get jittery about. Other vendors are rumoured to give better coverage with fewer sites, operators claim that other vendor's products are superior and vendor sales people seem to be promising everything to get the deal. On top of that, timetables keep on changing, but of course, the network launch date remains fixed. For the vendor, the worst thing is that once you've won the contract, you actually have to build the network you promised!
A lot of different information from various sources is needed for initial network (roll-out) plan. Here is a non-exhaustive list of required data:
Operators business plan
This should define what kind of service the operator is planning to provide, how these services will be implemented and how much money is needed for the total roll-out. Sometimes this information is public knowledge and sometimes it is a well guarded secret.
Technical section of business plan
This should contain the desired coverage, capacity, quality, features, service mix and customer intake plans.
UMTS License agreement
This usually contains the coverage, capacity and service deployment plans as well as requirements to hire a predetermined amount of employees and perhaps the required amount of domestic goods and services that need to be purchased.
Operators funding plan
This should give guidelines of how the roll-out should progress. However, usually operators do not want to share this information. Quite a few UMTS networks are vendor financed and such information could help network planners estimate the roll-out pace.
Operators risk analysis documents
These documents show where bottlenecks will be and show the project's critical path. Often site acquisition is in the critical path, which means that site RF planning will have to compromise some of the desired sites. However, technically the air interface capacity is normally the network limiting capacity factor and so network roll-out planning should really be started from there.
Over the past few years, operators have asked a lot of consultants to do 3G roll-out analysis reports. Even though this information gets old quickly, these reports might have some helpful facts.
Operator's internal studies of mobile usage
Information on mobile usage is very helpful and can pinpoint where 3G customers and key corporate clients are likely to be. Also, whether the 3G network will be used as a platform for other wireless technologies. Mobile usage profiles and customer distribution information is required to simulate the network load.
Government sources can provide statistics of population type and information such as income, distribution of wealth, taxation, spending habits etc., which are useful to estimate future mobile usage in different areas.
In a real life all of this information is compressed into the operators request for quote. This typically calls for an estimation of how many base station locations each network vendor thinks is required to provide a network. The operator normally asks vendors to guarantee the level of coverage for a certain load level, using the minimum amount of base stations and cost. Vendors have to commit to these figures even when most of the sites are yet to be acquired and some of the performance parameters will be defined later. Vendors are expected to reply in a very short period of time with limited information, so it is easy to see why network quality is not the biggest consideration in initial planning. There is a tendency for operators to use this tactic to get the lowest possible initial quote from vendors.
An experienced network planner can produce a "quick and dirty" network base station requirement figure with only a few parameters. The most crucial parameters for the initial roll-out are:
Capacity requirements - the planned customers and service usage in each area of the network (with BTS site capacity calculation) should be known in order to get the required amount of base stations for capacity.
Coverage requirements - the link budget of high data rate services should be calculated in order to estimate the required base station amount in each network area to get the amount of base stations for coverage.
In each network area, take the larger number of capacity OR coverage base stations for that area, then add each area together to get a total. To get the final required number of base stations, the following formula can be used:
- Add 10% more quality sites to provide special coverage or a dominant server in difficult or important areas - tunnels, bridges, exhibition and sports venues, shopping centres, airports, big hotels, high rise buildings, MD's home and CEO sailing and polo club!
- Add additional 10% more sites to fix holes because not all planned sites can be acquired.
- By this time the sales team will tell you that your plan is 30% too expensive, so you need to cut 30% of your base stations (and 40% of your acquisition budget)
The total will tell you how many sites you need to build an initial 3G network. Don't tell your customer you found the formula on the Internet!
Next: Calculating the network coverage and base station requirements.
3G Network Planning Basics