Systems Development Life Cycle (SDLC)

Systems Development Life Cycle

Management and control

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.

What is Relay Station (RS)?

Definition in Wikipedia:

Generally, an intermediate station that passes information between terminals or other relay stations.

Definition in IEEE802.16j Terminology:
Mobile Multihop Relay (MMR): The concept of relaying user data and possibly control information between an MMR base station and an IEEE Standard 802.16 compliant mobile station through one or more relay stations.

Informative Notes: Licensed spectrum is used for relay. The purpose of enabling relay is to enhance coverage, range, throughput, and capacity of an MMR–BS, and to enable very low power devices to participate in the network. The adjective “mobile” used here refers to the fact that both mobile subscriber stations and mobile relay stations are supported. It may be possible to establish multiple communication paths between an MMR-BS and a MS and communicate the same user data and/or control information through both paths to improve performance.

What is Repeater?

Nowadays the mobile communication is developing very repidly. No matter what kind of communication coverage, there may be weak signal and blind areas. While in some far away areas and blind areas with very few users, the cost of building analog or digital base station is very high and the basic installation is also quite complicated. Therefore it is necessary to provide a device with low cost, easy installation, but with the functionality of base station--Repeater. So mobile communication service providers start setting repeaters in radio blind areas such as inside the buildings, basement, etc., to satisfy the service requirements of users to the maximum extent.

In the beginning of formation of repeater market in China, radio device and FM broadcast repeaters were used. Since the later part of 90s', as the mobile phones were more and more popular, repeater market has been developed continuously. Repeater can enlarge the coverage of already built analog and digital base station and it is an efficient and unexpensive method to solve blind and remote area problems.

• Repeater definition

A repeater is an electronic device that receives a weak or low-level signal and retransmits it at a higher level or higher power with the same frequency, so that the signal can cover longer distances without degradation. To use repeater as "small capacity, large coverage" method is mainly because that with the condition of not increasing the number of base stations to ensure network cover and its cost is much lower than cell system with the same effect.

Compared with base station, it has the advantages of simpler architecture, lower cost an easier installation. It can be used in many blind and weak areas, such as shopping mall, hotel, airport, port, station, subway, tunnel, highway, island, etc., to improve communication quality.

• Repeater types:

1. · GSM mobile communication repeater ·
2. CDMA mobile communication repeater ·
   
3. GSM/CDMA fiber repeater

• Repeater applications:

-Urban area with high density: because of the large number of users and base stations, normally the large signal blind area problem does exit. Repeater is usually used to cover blind areas and the areas inside the building. Wireless repeaters are often used. With the increase of the number of buildings, the number of required repeaters increases. Then the situation of one base station with multiple repeaters appears. However, the introduction of repeater will definitely cause the interference to base station. And the interference will increase with the increase of the number of repeaters. Especially when large power repeater is introduced, the system interference is much more severe. Therefore low power repeater (less than 1W) should be applied.

-Edge of city: in the beginning of CDMA network establishment, because the small number of base stations, large power wireless or fiber repeaters are used. It is mainly to solve coverage problem. In the areas with fibers, it is better to use fiber repeater with 10W output power. When there is no fiber resource, wireless repeater with 5W/10W is used to extend coverage, which equals to a base station output.

-Suburban and village: it is also to solve coverage problem. In the areas with fiber, it is better to use large power fiber repeater (10W/20W) to enlarge coverage. In the areas where there is no fiber resource but can receive signal from base station, wireless repeater can be used to solve coverage problem. And frequency shift repeater can be utilized to increase coverage distance.

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.

Why to develop IEEE802.16j?

Currently in the point-to-multipoint architecture, wireless communication easily has some hidden places. And the far away users' transmission speed decreases because of the drop of RSSI (Received Signal Strength Indication). IEEE 802.16 standard session started setting up Relay Task Group since the May of 2006 making the standard for supporting mobile user's multi-hop relay technology. The standard is designed to provide the signal relay between base station and mobile station to achieve the purposes of throughput enhancement and coverage extension. The IEEE802.16j is developed based on IEEE802.16e as its amendment.

• Scope

It specifies OFDMA physical layer and medium access control layer enhancements to IEEE Std 802.16 for licensed bands to enable the operation of relay stations. Subscriber station specifications are not changed.

• Purpose

The purpose of this amendment is to enhance coverage, throughput and system capacity of 802.16 networks by specifying 802.16 multihop relay capabilities and functionalities of interoperable relay stations and base stations.

• Reason

The multihop relay is a promising solution to expand coverage and to enhance throughput and system capacity for IEEE 802.16 system. It is expected that the complexity of relay stations will be considerably less than the complexity of legacy IEEE802.16 base station. The gains in coverage and throughput can be leveraged to reduce total deployment cost for a given system performance requirement and thereby improve the economic viability of IEEE802.16 systems. Relay functionality enables repid deployment and reduces the cost of system operation. These advantages will expand the market opportunity for broadband wireless access. This project aims to enable exploitation of such advantages by adding appropriate relay functionality to IEEE Std. 802.16 through the proposed amendment. Stakeholders include manufactures and operators of IEEE 802.16 networks.