Tuesday, April 17, 2012

Basics of GSM network

Figure: GSM Network Architecture.
The GSM network consists of the following components:
a. Mobile Station (MS)
b. Base Transceiver Station (BTS)
c. Base Station Controller (BSC)
d. Mobile Switching Center (MSC)
e. Home Location Register (HLR)
f. Visitor Location Register (VLR)
g. Authentication Center (AuC)
h. Equipment Identity Register (EIR)
Functions of Base Transceiver Station (BTS):
The BTS is a part of the Base Station Sub system (BSS) and it contacts Mobile Station (MS) through the radio interface. The BTS is in charge of management of simultaneous transmission and reception on the radio interface.
Functions of Base station Controller (BSC):
The BSC is connected on one side to one or several Base transceivers (BTS) and on the other side to the Mobile Switching Center (MSC). The main function of the Base Station Controller (BSC) is allocation and release of radio channels(or allocated ARFCH) and the handover (HO) management.
Functions of Mobile Switching Center (MSC)
The Mobile Switching Center (MSC) responsible for the basic function of switching. The main function of the Mobile Switching Center (MSC) is to co-ordinate the setting up of calls to and from GSM users and the external network The Mobile Switching Center (MSC) has interface with the Base Station Subsystem (BSS) on one side and the external network on the other side.
Functions of Home Location Register (HLR)
The Home Location Register (HLR) together with the Mobile Switching Center (MSC), provide the call ­routing and roaming capabilities of GSM. The Home Location Register (HLR) contains all the administrative information of each subscriber registered in the related to GSM network, along with the current location of the mobile.
Functions of Visitor Location Register (VLR):
The Visitor Location Register(VLR) contains roaming information. Once the visited system automatically detects the mobile, the Visitor Location Register (VLR) of that system enquires the Home location Register (HLR) to make sure you are a valid subscriber. It temporarily stores the last location area visited by the Mobile Station (MS), the power the mobile uses, the special services the Mobile Station (MS) is subscribed to and so on.
Functions of Equipment Identity Register (EIR):
The Equipment Identity Register (EIR) is a database that stores data related to the mobile equipment. It contains a list of all valid mobile equipment on the network, where each mobile station (MS) is identified by International Mobile Equipment Identity(IMEI). This is useful when searching for stolen mobile equipment or when monitoring misuse of Mobile Station (MS). If a Mobile operators want to prevent the misuse of Mobile phone; It's not too difficult for them.
Functions of Authentication Centers (AuC):
The Authentication Center is a database that stores a copy of the secret key stored in each subscriber's in Subscriber Identity Module (SIM) card, which is used for authentication and ciphering of the radio channel.

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Saturday, March 24, 2012

RF Planning and Optimization question

Example of frequency reuse factor or pattern 1/4

Here is few question about RF planning and optimization, All the questions were collected from recruiter. these questions are frequently asked in viva board.

1। What is the basic procedure for RF planning using RF planning tool in GSM?

  • Analyze the system requirement and plan for data acquisition.
  • Select proper Planning Tool
  • Loading of digital map data of planning area on the planning tool
  • Model tuning for prediction of network on the planning tool
  • Nominal cell planning for the coverage area
  • Frequency planning and interference calculation.
  • Final system planning.
2। What are the different types of antennas used in a GSM network?
Antennas may be categorize based on antenna beam width and gain, In GSM we have
  • Cross polarized antenna
  • Omni directional antennas.
3। How do the power, orientation, beam width, tilt and height of the antenna affect the coverage?
Antenna output power, always proportional to the coverage area. So power increases coverage increases.
Proper Orientation
Orientation of an antenna gives us coverage on specific direction of desired planning area, Antenna orientation tuning is a major treatment when we prescribe for a network optimization.
Beam width and tilt
Antenna beam width and tilt improves the coverage of the planned area. Proper tuning of beam width and tilt gives better coverage and performance.
Antenna height
Increase in antenna height improves the coverage.
4। What is EIRP? How is it calculated?
Effective isotropic radiated power is the total output power of Base station
EIRP=BTS Output power + Antenna gain – {cable losses - other (combiner) losses}
5। What is frequency planning? Why is frequency reuse pattern used?
Frequency planning is to be done for the GSM network for a given operator with A set of GSM frequency band .Frequency reuse pattern is used for capacity planning and for effective resource utilization.
6। What are all the patterns available? How is frequency planning done on planning tool ?
7/21 pattern, 4/12 pattern, 3/9 pattern ।Automatic frequency planning can be done with planning tool।
7। What is co-channel interference and adjacent channel interference?
The interference caused by using same channels in a network is called co - channel interference and interference caused by adjacent channels of is called adjacent channel interference. To distinguish actual signal from interface minimum power difference should be -9db.
8। How do you minimize co-channel interference?
  • Proper frequency planning
  • Proper reuse pattern.
  • Physical parameter tuning (Orientation, Height, Beam width, tilt etc)
  • Finally resource addition ( Frequency and New BTS)
9. How do you minimize adjacent channel interference?
  • Proper frequency planning.
  • Physical parameter tuning (Orientation, Height, Beam width, tilt etc)
10. What is model tuning? Why is it used? Okarama Hatta model?
Model tuning is done for any network using planning tool to obtain proper prediction about network.
As there will be difference in actual and predicted data for planning tool. One of the Model is Okarama Hatta Model, generally known as Hatta model, is widely used which considers the signal propagation losses.
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Monday, March 19, 2012

Implementation Of 4G network in Bangladesh

English: Axiata Group Berhad
Implementation Of 4G network

4G network is global leading communication network across the globe. All most all leading giants in Telecom industry already launched their 4G service through (LTE, Wimax, HSPA etc). In Bangladesh there are more than 105 million active subscriber up to Feb,2012. Five global cellular mobile company establishes their network here including a local government owned company.

List of companies and market shares are given bellow:
Also there's some wireless broadband service providers are playing here with Mobile and Fixed wimax (802.16e and 802.16d). All the cellular mobile subscribers are providing their voice service through GSM-2.5G and CDMA-2X. But subscribers are demanding more service from provider. Hence cellular operators are thinking about network up gradation. First their demand was 3G, but government delays to give them license and frequency allocation. Now it's too late, 4G network deploying across the globe. Subscribers demanding more, standard of living has been developed in recent few years, hence operators are in dilemma 3G or 4G ?

Now comes to the point, according to our feasibility study 4G network is not viable here from the bussiness aspect and although the demand of 4G is too high, Here Wimax operators are straggling, changes their strategy of business. Truly their customer and network growing very slow and selling their services in lower prices to survive. Hence 4G will be out of general customer's purchasing power. Because 4G needs at least two and a half times more access network equipment and huge bandwidth for each network. On the other hand government is planning a high licensing and bandwidth charge. They have already announced for 3G licensing fee, which is 15000 thousands crore in local currency. Operators are treating is too high. In December,2012 government of Bangladesh, ministry of Telecommunication is planning for bid of 4G licensing, BTRC is mapping their schedule according to plan.

So in this circumstances operators are planning to go slow, but in right way.
Thanks By
Hassan Imam
Manager, Network Service.
Huawei-TDC project in Malaysia.

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Thursday, March 15, 2012

4G Network Dimensioning Procedure

Network Dimensioning procedure are just previous step of Network planning; it's a important part of network planning. The first step of network dimensioning procedure is collection of data. This data often collected from operators business plan. The data is analyzed very carefully and makes the requirement of network. Requirement consist of number of sites and amount of resources (like frequencies for access network and Microwave transmission network), types of network etc. Then plan for coverage and capacity of network. If you need any calibration in network try to simulate with software and tune in different planning parameter. Then recalculate the number of sites and resources. To meet the desired capacity and coverage, you need to plan a reliable transmission plan. Because if transmission have limitation, the total network will be disturb. So you should have to plan a balanced, dependable, flexible and functioning network.

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