The difference between Repeater and Relay Station..

The Relay Station nearly has all the functionality of a base station. In the following part, I will make some comparison between the Relay Station and the Repeater.

The advantages of using Repeater:

1. With the same coverage area, the investment of repeater is much lower.
2. The shape of coverage is more flexible. Normally a base station has circle coverage, while multiple repeaters can make multiple coverage shapes, such as "--", "L", "N" and "M".
3. In the beginning of forming the network, because the number of users is small and the benefit of investment is low, some repeaters can be used instead of base stations. When the users expand, they can be changed into base stations. And the replaced repeaters can be used in further places.
4. Because the building and transmission circuit are not needed, the network can be rapidly established.

The disadvantages of Repeater:

1. It cannot increase system capacity.
2. After the introduction of repeater, it will increase more than 3dB noise to base station. It makes the working environment of base station worse and decreases its coverage. So in a sector of one base station, the maximum of two repeaters can be used.
3. Repeater can only use frequency division, but not code division. One repeater usually amplifies the signal of multiple base stations and multiple sectors. If there are a lot of repeaters, it makes mess in base station phases and pilots. The improvement is hard and it increses a lot of unnecessary soft handovers.
4. The network management functionality and device detection is far from relay station. If there is something wrong with the repeater, it is not easily to be conscious.
5. Because of the limitation of separation requirement, the installation environment for a repeater is much more critical than a relay station. This makes its function not be sufficiently performed.
6. If there is interferencing source around the repeater, it will make severe influence on the original network. If the repeater antenna is high, it will effect larger area. CDMA is a co-frequency system, maybe all the base stations around it will be destroyed by congestion.

From some statistical results, in China, the installation ratio between repeaters and base stations is as high as or higher than 2:1. And because the people density of the country is quite high, the installation ratio should not be too large. If there is no fiber repeater, only for radio coupling outdoor repeater, this ratio should not be larger than 1. When it is the time for system plan, the repeaters work as transition devices for continuous development. The repeaters installed for long term use should be further decreased. In large or middle sized cities or high density areas, radio coupling outdoor repeaters should not be used.

On the other hand, because in CDMA system the frequency reuse is 1. So usage of the repeaters in CDMA system and the ones in GSM systems has difference. The use of repeaters has relation with the whole system performance. While in GSM sytem the use of repeaters only has relation with several corresponding channel performance. Therefore, proper plan of repeater network, strict project survey and implementation have much importance in improving CDMA network performance.