day 08 cell planning
TRANSCRIPT
7/31/2019 Day 08 Cell Planning
http://slidepdf.com/reader/full/day-08-cell-planning 1/6
Cellular Mobile Systems and Services (TCOM1010) 2009-June
Cell Planning.doc Dr. Monzur Kabir, P.Eng Page 1 of 6
Cell Planning
1 WHAT IS CELLULAR MOBILE SYSTEMS................................................................................................................2
2 CELL PLANNING PRELIMINARIES...........................................................................................................................32.1 CO-CHANNEL INTERFERENCE (CCI) .............................................................................................................................4
3 CELL PLANNING CRITERIA.......................................................................................................................................5
4 NETWORK CAPACITY..................................................................................................................................................6
4.1 FREQUENCY REUSE FACTOR AND TRUNKING GAIN......................................................................................................6
Disclaimer: This document is a draft and intended for the author’s
consumption only. It is by no means complete and error free.
7/31/2019 Day 08 Cell Planning
http://slidepdf.com/reader/full/day-08-cell-planning 2/6
Cellular Mobile Systems and Services (TCOM1010) 2009-June
Cell Planning.doc Dr. Monzur Kabir, P.Eng Page 2 of 6
1 What is Cellular Mobile Systems• The access network is wireless but core network is based on standard telephony system (ISDN)
• Coverage area is divided into small cells each of which covered by one antenna station. Smaller coverage area of an
antenna means low transmission power requirement (longer battery life and/or smaller light-weight battery needed).
This is one of the most important advantages of a cellular system.
• Total allocated frequency channel (a licensed band) is divided among a set of channels. In the following figure the
set of cannel includes 7 cells (Cell A, B, C, D, E, F and G). This set is called cluster. All other cluster will reuse the
same set of frequencies. This is one of the most important advantages of a cellular system. The reuse of say 7 times
means 6 times more traffic using no additional frequency band.
• Allows long-haul mobility. To manage the mobility the network has mobility management capability which
performs ‘handover’ a mobile station from one-cell to another in order to continue a call. This is another important
advantage of a cellular system.
• Allows roaming from one network to another (including international roaming). The user database of different
networks can share information as needed basis to let a mobile station of one network use another network for call
connection.
7/31/2019 Day 08 Cell Planning
http://slidepdf.com/reader/full/day-08-cell-planning 3/6
Cellular Mobile Systems and Services (TCOM1010) 2009-June
Cell Planning.doc Dr. Monzur Kabir, P.Eng Page 3 of 6
2 Cell Planning Preliminaries
A cell-cluster is a group of adjacent cells, which are allocated all the frequency channels without duplication.Cluster-size (number of cells in a cluster), Ncluster = i
2+ ij + j
2, where i = 0, 1, 2 … and j = 0, 1, 2 …
i= 0 1 2 3 4
j = 0 x 1 4 9 16
1 1 3 7 13 21
2 4 7 12 19 28
3 9 13 19 27 37
4 16 21 28 37
5
Frequency Reuse Distance (FRD), cellcluster FRD R N D .3=
The cell size (in radius) can be tens of meters (pico cell), hundreds of meters (microcell) and tens of kilometers (macro cell)
depending on the design criteria (discussed later)
7/31/2019 Day 08 Cell Planning
http://slidepdf.com/reader/full/day-08-cell-planning 4/6
7/31/2019 Day 08 Cell Planning
http://slidepdf.com/reader/full/day-08-cell-planning 5/6
Cellular Mobile Systems and Services (TCOM1010) 2009-June
Cell Planning.doc Dr. Monzur Kabir, P.Eng Page 5 of 6
3 Cell Planning CriteriaCell planning depends on a number of criteria. Some examples are given below. There are some requirements which are
mutually conflicting.
• Co-channel interference limit (it puts a lower limit of cell size)
• Traffic volume per cell together with GOS (Grade of Service) sets the minimum channel requirements
• For a given spectral width (a given set of frequency channels), more channels per cell means smaller cluster size
• Smaller cell means lower transmission power
• Smaller cell => More reuse => more capacity ----- good for city center
• Bigger cell => less number of radio antenna station but less capacity ----- good for rural area
• Bigger cell preferred for high-speed traffic in order to reduce frequent handover
• High-speed traffic through high-call area => overlay cell (more than one cell at a place; one is bigger than the other)
7/31/2019 Day 08 Cell Planning
http://slidepdf.com/reader/full/day-08-cell-planning 6/6
Cellular Mobile Systems and Services (TCOM1010) 2009-June
Cell Planning.doc Dr. Monzur Kabir, P.Eng Page 6 of 6
4 Network CapacityLet us calculate capacity and channels per cell
• A Teletraffic engineer estimates calls/hour (Q) for a cell, estimates average call-duration (T in minutes) and calculates
Erlangs60QT A = => Erlang (A) is total call-hours per hour (since it is hour/hour Erlang does not have unit)
Erlang B Formula
http://www.stuffsoftware.com/trafficerlangb.html
Calculator: http://www.erlang.com/calculator/erlb/ Table: http://www.sis.pitt.edu/~dtipper/2720/erlang-table.pdf
When Erlang value and the Grade-of-Service (or blocking probability) is known the number of required channel (N) can be
calculated using Erlang formula calculator.
Example: A GSM network cell s have arrival rate = 2000 calls/hour/cell, average call duration = 1.8 minutes and blocking
probability = 1%. Assume cluster size = 7 cells. Calculate the number of frequencies required for the network.
=> A = 2000*1.8/60 = 60
Using the online calculator with A = 60 and Blocking Probability = 1% ,
Number of traffic Channel, NTraffic = 75
In Time-Division-Multiplexed (TDM) system a frequency-channel is divided into a number of TDM time-slots (for
example, GSM divides a frequency-channel into 8 time-slots) each of which is equivalent to a voice-traffic-channel.
Traffic-channels-per- frequency-channel (Nslot) specifies how many voice-grade-traffic-channels a frequency channel cansimultaneously accommodate.
Number of Frequency Channel per cell, Ncell-f = NTraffic /NSlot
Here, NTraffic = 75, NSlot = 8 => Ncell-f = ceiling(75/8) = 10
If total number of frequency channel per cluster is Ncluster-f , = NCluster × NCell-f
Here, NCell-f = 10, NCluster = number of cells per cluster = 7 => Ncluster-f = 10 × 7 = 70
4.1 Frequency Reuse Factor and Trunking Gain
Frequency Reuse Factor (FRF),
cluster
reuse N
N
SizeCluster
Cellsof Number TotalF ==
_
___
The traffic-channels, which carry actual voice (or subscribers’ data), are not dedicated to but shared by subscribers. They
are dynamically allocated to subscribers on demand. Usually, number of subscriber is many-times larger than total
number of traffic channel. The ratio,ChannelsTrafficof Number
sSubscriber of Number Gtrunking
___
__= is called Trunking-Gain.