GSM TOWARDS LTE NETWORKS

Lecture # 6

CELL PLANNING

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Cell

GSM Geographical Network Structure:

Cell

• The basic unit of a cellular system• It is defined as the area of radio coverage given by one BS antenna system.• Each cell is assigned a unique number called Cell Global Identity (CGI). • In a complete network covering an entire country, the number of cells can be quite high.

Cell Planning

• Cell Planning can be described as all the activities involved in

- Selecting the sites for the radio equipment - Selecting the radio equipment - Configuring the radio equipment

• Every cellular network requires cell planning in order to provide adequate coverage and quality.

Cells:• A cell may be defined as an area of radio coverage from one BTS antenna system• It is the smallest building block in a mobile network and is the reason why mobile networks are often referred to as cellular networks. • Typically, cells are represented graphically by hexagons.

Cells•There are two main types of cell:

Omni directional cell: An omni-directional cell (or omnicell) is served by a BTS with an antenna which transmits equally in all directions (360 degrees).

Sector cell: A sector cell is the area of coverage from an antenna, which transmits, in a given direction only (120 degree or 180 degree) - One BTS can serve one of these sectors (two or three) cells with a collection of BTS’s at a site serving more than one.

• Typically, omni-directional cells are used to gain coverage, whereas sector cells are used to gain capacity.

Cells (continued):• The border between the coverage area of two cells is the set of points at which the signal strength from both antennas is the same. • In reality, the environment will determine this line, but for simplicity, it is represented as a straight line.• If six BTS’s are placed around an original BTS, the coverage area, that is, the cell takes on a hexagonal shape.

LA and MSC Service Area

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cell 6

cell 1 cell 5

cell 4 cell 2 cell 3

MSC

LA1LA3

LA5LA4

VLR

Location Area (LA):• It is defined as a group of cells. • The identity of the current LA is stored in the VLR.• When an MS crosses the boundary between two cells belonging to different LA’s, it must report its new Location Area to the network. • If it crosses a cell boundary within a LA, it does not report its new cell location to the network. • When there is a call for an MS, a paging message is broadcast within all the cells belonging to the relevant LA.• One LA belongs to one MSC only.

MSC Service Area:• It made up of a number of LAs and represents the geographical part of the network controlled by one MSC. • In order to be able to route a call to an MS, the subscriber's MSC service area is also recorded and monitored.• The subscriber's MSC service area is stored in the HLR.

Public Land Mobile Network (PLMN) Service Area: • It is the entire set of cells served by one network operator• It is the area in which an operator offers radio coverage and access to its network. • In any country there may be several PLMN service areas, one for each mobile operator's network.

GSM Service Area It is the entire geographical area in which a subscriber can gain access to a GSM network. • It increases as more operators sign contracts agreeing to work together.

Cell Planning Process: The major activities involved in the cell planning process are shown below:

Traffic and Coverage Analysis: • Cell planning begins with traffic and coverage analysis which should produce information about the geographical area and the expected capacity (traffic load). • The types of data collected are:· Cost · Capacity · Coverage· Grade Of Service (GOS) · Available frequencies· Speech quality · System growth capability

• The basis for all cell planning is the traffic demand, i.e. how many subscribers use the network and how much traffic they generate.

• The Erlang (E) is a unit of measurement of traffic intensity. It can be calculated with the formula: A = n x T / 3600 ErlangWhere, A = offered traffic from one or more users in the systemn = number of calls per hour and T = average call time in seconds• The geographical distribution of traffic demand can be calculated by the use of demographic data such as:· Population distribution · Car usage distribution· Income level distribution · Land usage data· Telephone usage statistics· Other factors, like subscription/call charge and price of MSs

Clusters:• Groups of frequencies can be placed together into patterns of cells called clusters. • It is a group of cells in which all available frequencies are used once and only once• The frequency re-use distance must be kept as large as possible.• The re-use patterns recommended for GSM are the 4/12 and the 3/9 pattern. • 4/12 means that there are four three-sector sites supporting twelve cells using twelve frequency groups.

System Implementation and Tuning:• Once the system has been installed, it is continuously monitored to determine how well it meets demand. This is called system tuning which involves:- Checking that the final cell plan was implemented successfully- Evaluating customer complaints- Checking that the network performance is acceptable- Changing parameters and taking other measurements, if necessary

TEst Mobile Systems (TEMS):• It is a testing tool used to read and control the information sent over the air interface between the BTS and the MS.• It is used for radio coverage, field measurements and post processing• TEMS consists of an MS with special software, a laptop (PC) and a Global Positioning System (GPS).

CHANNELS

GSM Frequency Concepts

Introduction to Physical and Logical Channels:• Each timeslot on a TDMA frame is called a physical channel.• There are 8 physical channels per carrier frequency in GSM.• Physical channels can be used to transmit speech, data or signaling information• A physical channel may carry different messages, depending on the information that is to be sent. These messages are called logical channels.

GSM LOGICAL CHANNEL

BCCHFCHSCH

Broadcast Channel

SDCCHSACCHFACCH

Dedicated Control Channel

PAGCHAGCHRACHCBCHNCH

Common Control Channel

Control Channel

Full Rate TCH Half Rate TCH

Traffic Channel

Logical Channels

Broadcast Channels:

Common Control Channel:

Dedicated Control Channel:

Traffic Channels:• Once call set-up procedures have been completed on the control physical channel, the MS tunes to a traffic physical channel. It uses the Traffic CHannel (TCH) logical channel. There are two types of TCH:

· Full rate (TCH): transmits full rate speech (13 kbits/s). A full rate TCH occupies one physical channel.

· Half rate (TCH/2): transmits half rate speech (6.5 kbits/s). Two half rate TCH's can share one physical channel, thus doubling the capacity of a cell.

Enhanced Full Rate (EFR) speech coders improve the speech quality offered across one full rate TCH, but still use a full rate TCH logical channel.

Sample Traffic Case: Call to an MS:1. The MSC/VLR knows which LA the MS is located in. A paging message is sent to the BSCs controlling the LA.2. The BSC’s distribute the paging message to the BTS's in the desired LA. The BTS's transmit the message over the air interface using PCH.3. When the MS detects a PCH identifying itself, it sends a request for a signaling channel using RACH.4. The BSC uses AGCH to inform the MS of the signaling channel (SDCCH and SACCH) to use.5. SDCCH and SACCH are used for call set-up. A TCH is allocated and the SDCCH is released.6. The MS and BTS switch to the identified TCH frequency and time slot. The MS generates ring tone. If the subscriber answers, the connection is established. During the call, signals can be sent and received by the MS using SACCH.

PAKISTAN CELLULAR INDUSTRY UPDATES

PAKISTANMOBILE SUBSCRIBER STATISTICS

Network Subscriber

Mobilink 33378161

Telenor 26667079

Ufone 20533787

Warid 17387801

Zong 10927693

PAKISTAN CELLULAR INDUSTRY

‘90 ‘92 ‘98 ‘06‘05‘04‘03

Mobile Cellular Policy - 2004

Deregulation Policy – July ‘03

CELLULAR INDUSTRY EVOLUTION

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