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Chapter Three
The Cellular Concept:
System DesignFundamentals
BY : Adisu W.
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Objectives of the Chapter
In cellular system, the available radio spectrum is limited
E.g., because of regulatory issues
Hence, the number of simultaneous calls supported is limited
How to achieve high capacity (or support simultaneous calls at
the same time ) covering very large areas?
Frequency reuse by using cells
Overview of system design fundamentals on cellular
communication
Cell formation and associated frequency reuse, handoff,
interference, and power control
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Lecture Outline
Introduction
Cellular Concept and Frequency Reuse
ChannelAssignment Strategies
Handoff Strategies
Interference and System Capacity
Trunking and Grade of Services
Summary
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Used Acronyms• BS: Base station• MS: Mobile station• MSC: Mobile switching center • GOS: Grade of services• CCI : Co-channel interference•
ACI: Adjacent channel interference
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Introduction
Conventional Mobile Radio System and its Limitations
Single high power transmitter and large antenna towers Large size radios with large batteries
Provide limited number of channels
Poor quality of service
Still in use for some public/private organizations
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The coverage area called tower footprint of these towers was
theoretically circular in shape with radius around 50 km.
As long as cities being covered were far away from each other, no
interference occurred between the transmissions in different
cities.6
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The assigned spectrum (40 MHz) was used in every city being covered.
• But, full duplex transmission would require a total of 60 kHz per user
• Thus total number of users who can call or receive calls at the same
time in any city was around 660 users only.
• For a large city(for example with 10Million residents ) this is
extremely low and the system would get congested so easily.
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Due to the large distance between the MS and the BS (up to 50 km or
more), mobile phones had to transmit high powers.
This results in the need of large batteries and therefore phones were
large in size and inconvenient.
So what ?
• Cellular system with frequency reuse is the solution to avoid the
problem of spectral congestion , capacity and power budget.
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The Cellular System
High capacity is achieved by dividing the coverage area of each
BS to a small geographic region called a cell
Single, high power transmitter (large cell) are replaced with
many low power transmitters (small cells)
A portion of the total number of channels is allocated to each cell
Available group of channels are assigned to a small number of
neighbouring BS called cluster
Near by BS are assigned d/t groups of channels to minimize
interference
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Cellular System Architecture10
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The same channels ( frequencies/timeslots/codes ) are reused by
spatially separated base stations
Reuse distance and frequency reuse planning.
A switching technique called handoff enables a call to proceed
from one cell to another
As demand (# of users ) increases, the number of BS may be
increased to provide additional capacity:
Use smaller cells: e.g., Microcells, Picocell, Femtocell
Also cell sites in trucks to replace downed cell towers after
natural disasters, or to create additional capacity for large
gatherings(football games, rock concerts)
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The Cellular ConceptThe Cellular Idea
Divide the service area into several smaller cells
Put at least as many towers as the # of cells and reduce the transmitter
power of each BS
Reuse the allocated frequency spectrum (channels) as many times as
possible by controlling interference
Gains but with Pains
Greater system capacity with the cost of large infrastructure
Optimal frequency spectrum utilization attained by making system
more complicated
User equipment design made smarter at the cost of circuit complexity
and processing power 13
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Frequency Reuse Example14
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The Cell Shape
Actual radio coverage area of cell is amorphous(irregular shaped)
Obtained by field measurements or by using prediction modelsthrough computer simulation
This is known as footprints
•
(a) is theoretical coverage area and (b) measured coverage areawhere red, blue, green, and yellow indicate signal strength in
decreasing order
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All cells should have same shape and equal area
Circular (theoretical): If path loss was a decreasing function
of distance(say 1/d n) where d is the distance b/n BS & MS
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When using hexagon to model coverage areas, we may use:
Center excited cell: BS depicted as being in the center of the cell
• Omni-directional antenna is used
Edge excited cell: Placed on three of the six cell vertices
• Sectored directional antenna is used
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Geometry of Hexagons
Axes U and V intersect at 60 0
Assume unit distance is the distance between cell centers
If cell radius to point of hexagon is R, then
2Rcos 30 o = 1 or R = 1/3 (Normalized radius of a cell) To find the distance of a point P(U,V) from the origin, use XY to
UV coordinate transformation as
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Using this equation, to locate the co-channel cells, start from a
reference cell and move:
i-hexagons along the U-axis and
j- hexagons along the V-axis
The distance, D, between co-channel cells in adjacent cluster is
given by
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The number of cells in a cluster is given by
where i and j are non-negative integers
In real system , there are only certain cluster sizes and layouts
possible.
Typical values of N are 1, 3, 7, 12, …
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Locating Co-channel Cells
Observation: In the geometry of the hexagon, the number of
cells per cluster can only have values such that
Hence to find out the nearest co-channel neighbours of a
particular cell, do the following
Move i cells in the U direction
Then turn 60 0 CCW and move j cells in the V direction
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Example 1 : N=7, i=2,j=1
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Example 2 : N=28, i=4, j=2
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Frequency Reuse Principles
Let us assume a city of 10 Million mobile users
Let every user is allocated a radio spectrum for analog
speech of 4kHz bandwidth
Thus the required bandwidth is 4 kHz * 10 Million users =40 GHz!
This is clearly impractical!
No other services possible using a radio transmission
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Cellular radio systems rely on intelligent allocation and reuse of
channels through out the coverage area
Available group of channels are assigned to a cluster
Same group of frequencies are reused to cover another cell
separated by a large enough distance
• Hence a trade-off in the design is required
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To understand the frequency reuse concept, consider a cellular
system which has a total of S duplex channels available for use
If each cell is allocated a group of k channels (k
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If a cluster is repeated M times within the system, the total number
of duplex channels can be used as a measure of capacity and is
given by
C =MS= MkN
The factor N is called the cluster size and is typically values are1,3 , 7, 12,...
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The value N is a function of how much interference a mobile or
BS can tolerate while maintaining a sufficient quality of
communication.
Smallest possible value of N is desirable in order to maximize
capacity over a given coverage area
The frequency reuse factor of a cellular system is given by1/N
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Effect of Cell Size Trade-off
Advantages of smaller cell size:
Higher M (more replication of the cluster)
Higher system capacity
Lower power requirements for mobiles
Disadvantage of smaller cell size:
Additional base stations required
More frequent handoffs(Burden of MSC)
Extra possibilities for interference
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Effect of Cluster Size Trade offs
Each clusters have unique group of channels which are repeated
over clusters
Keeping cell size the same:
Large N: weak interference but lower capacity
Small N: higher capacity, more interference, need to maintain
certain S/I threshold level
• More clusters are required to cover area of interest,
• So capacity is directly prop. to replication factor for fixed area
• Results in larger co-channel interference
• May result in lower Quality of Service (QoS)31
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System Design ExamplesA total of 33 MHZ bandwidth is allocated to a particular FDD cellular phone system. If the simplex
voice/control channel bandwidth is 25 Khz, find the total # of channels available per cell if the
system uses (a) 4-cell frequency reuse (b) 7-cell frequency-reuse plan. If 1 MHZ out of the total
allocated bandwidth is used for control channels, determine an equitable distribution of the control
and voice channels in each cell in case of each frequency-reuse plan.
Solution:Total allocated bandwidth = 33 MHz, Duplex channel bandwidth = 25x2=50 K
Total # of Available(Voice/Control) Channels = 33,000/50 = 660 Channels.(a) N= 4, so total # of Channels/Cell = 660/4 = 165 Channels(b) N=7, so total # of Channels/Cell = 660/7 = 95 Channels
In case of 1 MHz bandwidth allocated for control channels, total # of control channels =1000/50=20 channels per systems. Out of 660 channels, 20 are used as control and remaining
640 as voice channels.(A)n=4, each cell can have 20/4=5 control channels and 640/4=160 voice channels. But, each cell
needs only one control channel, so, each cell will be assigned one control channel and 160 voicechannel.
(B)n = 7, each cell can have 20/7 = 3 control channels and 640/7=91 voice channels[plus 3 extra], but it needs only 1 control channel, so, we can assign 4 cells with 91 voice channels and one
control channels, and 3 cells with 92 voice channels and one control channels.
Hz
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The Channel Assignment Strategies Objective: maximize the system capacity while minimizing theinterference
A constrained optimization problem Classification:Fixed ChannelAllocationDynamic ChannelAllocation
Hybrid ChannelAllocationBorrowed ChannelAllocation Choice has impact on system
performance Handoff
Call InitiationMSC Processing Load
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Fixed Channel Assignment (FCA)
Each cell is allocated a predetermined set of voice channels.
Any call attempt within the cell can only be served by the unused
channels in that particular cell.
Any request for handoff , if all channels of this candidate cell are
in use, will not be treated.
MS may have to wait, call can drop even
Probability of blocking is high .
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Simple, but a busy cell will run out of channels before a neighbouring
cell
Service variations of fixed assignment strategy exit
System performance will be limited by the most crowded cell
Several solution to solve the problem:
Borrowing strategy Reserve some channels for handoff
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Borrowing channel assignment strategies
Modified from fixed channel assignment strategies.
A cell is allowed to borrow channels from a neighbouring cell if
all of its own channels are already occupied.
MSC supervises such borrowing procedures and ensures that
the borrowing of a channel does not disturb or interfere with
any of the calls in progress in the donor cell.
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The MSC allocates a channel to the requested cell following an
algorithm that takes into account :
The likelihood of future blocking within the cell
The frequency use of the candidate channel
The reuse distance of the channel, and Other cost functions.
DCA requires the MSC to collect real-time data on channel
occupancy, traffic distribution, and radio signal strength
indications (RSSI) of all channels on a continuous basis.
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Hence DCA
Reduces the call blocking probability and call drop
probability during hand off
Improves system Trunking capacity (traffic intensity/channel):
all channels are accessible by all cells
But adds the costs of storage and computational load on
MSC because
•
MSC must collect real-time channel occupancy data• Traffic distribution information
• Radio signal strength indications (RSSI) of all the channels
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The Handoff Strategies
In cellular network, the process to transfer the ownership of MS
from BS to another BS is termed as Handoff or Handover . MSC facilitates the transfer
In general, handoff involves
Identifying the new BS
Allocation of voice and control signals to channels on new BS
Usually, priority of handoff requests is higher than call
initiation requests when allocating unused channels.
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Handoffs must be performed
Successfully
As infrequently as possible, and
Must be imperceptible to the user
To meet these requirements, we must specify a minimum usable
signal level for acceptable voice quality at the base station
If the received power drops too low prior to handoff, the call
will be dropped.
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Handover Indicator : The parameters to determine HO occasion
RSSI: in ensemble average sense.
Bit Error Rate (BER)/Packet Error Rate (PER), more accurate.
By looking at the variation of signal strength from either base
station, it is possible to decide on the optimum area where handoff
can take place.
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Once a particular signal level is specified as the minimum usable
signal for acceptable voice quality at BS receiver (normally b/n
- 90 dBm and -100 dBm), a slightly stronger signal level is used asthreshold at which a handoff is made.
If Δ is too large: unnecessary handoffs may occur, burden on MSC
If Δ is too small: there may be insufficient time to complete a handoff,
calls may be loss or dropped.
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Example 1: Improper Handoff Situation
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Example 2: Proper Handoff Situation
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How to Prioritize Handoff
Guard Channel Method
A fraction of the total available channels is reserved for handoff
In case of fixed channel assignment, it affects system capacity.
But good in case of dynamic channel assignment
Queuing Handoff Request Method
Any handoff request, if can not be tackled immediately, it will be
placed in queue for sometime and answered before the signallevel goes below the minimum acceptable level.
Does not guarantee 100% success for all handoff requests46
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Handoff Styles
1. Network Controlled Handoff (NCHO)
Used in the 1G mobile cellular systemsHere each BS constantly monitors signal strength from MS in its
cell.
Based on the measurements, MSC decides if handoff is necessary
or not.
MS plays passive role in the process
Creates heavy burden on MSC
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2. Mobile Assisted Handoff (MAHO)
Used in 2 nd and above generation systems
MS measures received power from surrounding BS and report to
serving BS
Handoff is initiated when power received from neighboring cell
exceeds current value by a certain level or for a certain period of
time
Faster since measurements made by MS
MSC doesn ’t need to monitor the signal strength
• Simple burden on MSC
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3. Hard Handoff: Break before make
FDMA, TDMA (1G and 2G Systems)
The mobile has a radio link with only one BS at anytime.
Old BS connection is terminated before new BS connection is
made
4. Soft Handoff: Make before break
The mobile has simultaneous radio link with more than one BS at
any time (example CDMA systems ).
New BS connection is made before old BS connection is broken.
Mobile unit remains in this state until one BS clearly
predominates.
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5. Intersystem Handoff:
Used for MS found the border of the system(home service
provider ’s service area)MSC of the serving cell talks to the MSC of the neighboring
system or vice versa to transfer the call.
Several issues should be resolved before handoff can take place• Call type• Roaming is allowed or not•
Compatibility issues or standards• User authenticity and call charges issues
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Practical Handoff Problems
Problem 1: Simultaneous traffic of high speed and low speedmobiles.Small cell → high speed mobile → frequent handoff large cell → Reduce capacity
Solution: Umbrella Cell - cell split or hierarchical cell structure
By using different antenna heights and different power levels ,
it is possible to provide large and small cells which are co-
located at single location.
Small cell for low speed mobileLarge cell for high speed mobile
Need strong detection and handoff control.
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This concept minimizes the number of handoffs for high speed
users and provides additional micro cell channels for pedestrian
users.
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P bl 2 C ll D i
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Problem 2: Cell Dragging
Caused by pedestrian users that provide very strong signal to the
BS.
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Often occurs in an urban environment when there is line-of-sight
(LOS) radio path between the subscriber and the base station.
As the user travels away from the BS at very low speed, theaverage signal strength does not decay rapidly and the received
signal at the BS may be above the handoff threshold, thus handoff
may not be made.
Creates potential interference and traffic management problem .
Solution: Careful arrangement of handoff threshold and radio coverage
parameters.
Interference and System Capacity
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Interference and System Capacity
What is Interference : unwanted signal which affects the speech
quality and system capacity
Sources of interference includes:
Another mobile in the same cell
A call in progress in the neighboring cellOther BS operating in vicinity using the same frequency band
Some non cellular device/system leaking energy in the cellular
frequency band.
Two major types of interferences are:
Co-Channel Interference ( CCI )
Adjacent-Channel Interference( ACI )54
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It is a major Bottle Neck in system capacity : a trade off has to be
made between system capacity and information quality.
Interference in the voice channels causes crosstalk
A subscriber hears interference in the background due to an
undesired transmission
Interference in the control channels causes error in digital
signalling which causes
Missed calls
Blocked calls
Dropped calls
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To reduce co-channel interference , co-channel cells must be
physically separated by minimum distance to provide sufficient
isolation due to propagation .
So, when the size of each cell is approximately the same , and the
BS transmit the same power , the co-channel interference ratio is
independent of the transmitted power and becomes a function of
the radius of the cell (R) and the distance between centres of the
nearest co-channel cells (D)
By increasing the ratio of D/R , the spatial separation between co-
channel cells relative to the coverage distance of the cell is
increased.
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Thus interference is reduced from improved isolation of RF
energy from the co-channel cell
Co-channel Reuse Ratio (Q) : The spatial separation between co-
channel cells relative to the coverage distance of a cell .
For hexagonal geometry, it is related to the cluster size N
Small value of Q provides larger capacity since the cluster size is
small, whereas large value of Q improves the transmission
quality , due to smaller level of co-channel interference
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Co-channel reuse ratio for some values of N
Hence there is capacity versus interference trade off
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h l l f
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Co-Channel Signal to Interference Ratio
Let i 0 be the number of co-channel interfering cells , then the
signal-to- interference ratio (SIR) for a mobile receiver whichmonitors a forward channel can be expressed as
Where S is the desired signal power from the desired BS
I i is the interference power caused by the i th interfering
co-channel cell BS
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Propagation measurements in mobile radio channel show that the
average received signal strength at any point decays as a power
law of the distance between transmitter and receiver
The average received power P r at a distance d from the
transmitting antenna is then
Where P o is the received power at close reference distance in thefar-field and n is the path-loss exponent (mostly between 2 to 6)
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Now consider the forward link where the desired signal is the
serving BS and the interference is due to co-channel BS.
If D i is the distance of the i th interferer from the mobile, the
received power at given mobile due to the i th interfering cell will be
proportional to (D i)-n.
When the transmit power of each BS is equal and n is the same
throughout the coverage area, S/I for a mobile can be approximated
as
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For hexagonal cluster of cells with the MS situated at the edge of
the cell
Hence, as long as all cells are of the same size, S/I is
independent of the cell radius, R
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Example
If a signal to interference ratio of 15dB is required for satisfactory
forward channel performance of a cellular system, what is thefrequency reuse factor and the appropriate cluster size that
should be used for maximum capacity if the path loss exponent is
(a) n = 4 , (b) n = 3? Assume that there are 6 co-channels cells inthe first tier, and all of them are at the same distance from the
mobile. ( Hint: First consider 7 cell reuse pattern and decide the
practical cluster size.
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This is referred to as the near-far effect , where nearby
transmitter (which may or may not be of the same type as that
used by the cellular system) captures the receiver of the
subscriber.
Alternatively, the near-far effect occurs when mobile close to BS
transmits on channel close to one being used by weak mobile.
The BS may have difficulty in discriminating the desired
mobile user from close adjacent channel mobile.
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Near-far effect: This occurs when an interferer close to the BS
radiates in adjacent channel, while the subscriber is far away from
the BS
The BS may not discriminate the desired mobile user from the
“bleed ove r” caused by the close adjacent channel mobile
Or, an interferer which is in close range to the subscriber ’s
receiver is transmitting while the receiver receives from the
BS.
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In practice, power levels transmitted by every subscriber are under
constant control by the serving BS
Each MS transmits with the smallest power necessary
In power control
Reduces the transmit power level of MS close to the BS since
high T X power is not necessary in this case.
MS located far away must transmit with larger power than
those nearby
Power control reduces o ut-of-band interference , prolongs
battery life , and generally reduces even co-channel interference
on the reverse channel
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ACI can be minimized through careful filtering and channel
assignments .
By keeping the frequency separation between each channel in
given cell as large as possible , the adjacent channel interference
may be reduced considerably
Channels are allocated such that the frequency separation between
channels in a given cell is maximized.
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If a subscriber is at distance d 1 and the interferer is d 2 from the
base station, then SIR (prior to filtering) is
Example:
Suppose a subscriber is at d 1 = 1000m from the BS and an
adjacent channel interferer is at d 2 = 100m from the BS
Assume: Path loss exponent is n = 3
The signal-to-interference ratio prior to filtering is then
Hence we should use careful filtering to avoid this .
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Trunking and Grade of Services
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Trunking and Grade of Services
Trunking System : A mechanism to allow many users to share
fewer number of channels. Not every user calls at the same time.
Penalty: Blocking Effect.
If traffic is too heavy, call is blocked!!
Small blocking probability is desired.
There is trade-off between the number of available circuits and
blocking probability.
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T U d i T ki g Th
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Terms Used in Trunking Theory
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Setup time: The time required to allocate a radio channel to a requesting
user. Users request may be blocked or have to wait
Blocked Call: A call that cannot be completed at the time of request due
to congestion
Also called lost call => lost revenue( e.g., pick hours, holidays)
Holding Time(H): Average call duration in seconds
Depends on users and operator's tariff
Request (or call) Rate ( λ ): Average number of calls per unit time
Typically taken to be at the busiest time of day
Depends on type of users community: Office, residential, call center
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Erlang : The amount of traffic intensity carried by a channel that
is completely occupied.
For example, a radio channel that is occupied for 30 minutes
during an hour carries 0.5 Erlangs of traffic.
Grade of Service (GOS): is a measure of the ability of a user to
access a trunked system during the busiest hour.
GOS is typically given as the likelihood that a call is blocked ,
or the likelihood of a call experiencing a delay greater than acertain queuing time.
T ffi I i (A) M f h l i ili i hi h
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Traffic Intensity(A) : Measure of channel time utilization, which
is the average channel occupancy measured in Erlangs. This is a
dimensionless quantity and may be used to measure the time
utilization of single or multiple channels.
Load: Traffic intensity across the entire trunked radio system,
measured in Erlangs.
Grade of Service (GOS): A measure of congestion which is
specified as the probability of a call being blocked (Erlang B),
or the probability of a call being delayed beyond a certain
amount of time (Erlang C).
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Trunking Efficiency: is a measure of the number of users which
can be offered a particular GOS with a particular configuration of
fixed channels.
The way in which channels are grouped can substantially alter the
number of users handled by a trunked system.
From Table 3.4, for GOS=0.01
10 trunked channels can support 4.46 Erlangs.
Two 5 trunked channels can support 2x1.36=2.72 Erlang.
10 trunked channels support 64% more traffic than two 5
channel trunks do.
Computation of GOS
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Computation of GOS
Analysis
Average arrival rate( λ ): Average number of MSs requesting
service (call request/time)
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h ld i ( ) A d i f ll ( i f
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Average hold time(H): Average duration of a call (or time for
which MS requires service)
An average traffic intensity offered (generated) by each user
Example 1: If a user makes on average two calls per hour, and
that a call lasts an average of 3 minutes
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Then the total offered traffic intensity for U users are
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Then the total offered traffic intensity for U users are
In a C channel trunked system, if traffic is distributed equally among
channels, then traffic intensity per channel
In Example 1 , assume that there are 100 users and 20 channels
Then A = 100(0.1)= 10 andA c = 10/20 = 0.5
Note: Ac is a measure of the efficiency of channels utilization
Offered traffic is not necessarily the traffic carried by the trunked
system, only that is offered to the system
The maximum possible carried traffic is the total number of channels, C, in Erlangs
Example AMPS system is designed for a GOS of 2% blocking
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Example, AMPS system is designed for a GOS of 2% blocking
Channel allocations for cells are designed so that 2 out of 100 calls
will be blocked due to channel occupancy during the busiest hour
What do we do when a call is offered (requested) but all
channels are full?
Blocked calls cleared; Offers no queuing for call requests, ErlangB
Blocked calls delayed; Erlang C
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Types of trunked systems:
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yp y
1. Blocked Calls Cleared
No queuing for call requests: For every user who requests service, it is assumed there is no
setup time and the user is given immediate access to a channel if
channel is available.
If no channels are available, the requesting user is blocked
without access and is free to try again later.
GOS: Erlang B formula determines the probability that a call is
blocked.
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Erlang B is a measure of the GOS for a trunked system which
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Erlang B is a measure of the GOS for a trunked system which
provides no queuing for blocked calls
Setting the desired GOS, one can derive
Number of channels needed
The maximum number of users we can support as A = UAU
or
The maximum A U we can support (and set the number of
minutes on our calling plans accordingly)
Since C is very high, it is easier to use table or graph form
Blocking Probability: Erlang B Formula :
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Where C number of trunked channels andA total offered traffic
Assumption to the model
There are infinite number of users.
Call requests are memory less; both new and blocked users may request a
channel at any time.
Service time of a user is exponentially distributed
Traffic requests are described by Poisson model.
Inter-arrival times of call requests are independent and exponentially
distributed.88
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2. Blocked Calls Delayed
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A queue is provided to hold calls which are blocked.
Instead of clearing a call, put it in a queue and have it wait until achannel is available
First-in, first-out line; Calls will be processed in the order
received
If a channel is not available immediately, the call request may be
delayed until a channel becomes available.
GOS: Erlang C formula gives the likelihood that a call is
initially denied access to the system
There are two things to determine here
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g
The probability a call will be delayed (enter the queue), and
The probability that the delay will be longer than t seconds
The first time is no longer the same as Erlang B
It goes up, because blocked calls aren ’t cleared, they “stick
around” and wait for the first open channel
Meaning of GOS
The probability that a call will be forced into the queueAND it
will wait longer than t seconds before being served (for some
given t)
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Once it enters the queue, the probability that the delay is greater
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q , p y y g
than t (for t > 0) is given as
The marginal (overall) probability that a call will be delayedAND
experience a delay greater than t is then
The average delay for all calls in a queued system
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The Erlang C chart showing the probability of a call being delayed as a
function of the number of channels and traffic intensities in Erlangs
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Examples
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Consider a system with
• 100 cells• Each cell has C = 20 channels• Each user generates on average = 2 calls/hour • The average duration of each call (H) = 3 Minutes
How many number of users can be supported if the allowed
probability of blocking is
a . 2% b. 0.2%
Solution:
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a. From Erlang B Chart, total carried traffic = 13 Erlangs Traffic intensity per userA U = Hλ = 0.1 Erlangs The total number of users that can be supported by a cell = 13/0.1 =130 Users/cell
Therefore, the total number of users in the system is 13,000
b. Again from Erlang B Chart, total carried traffic = 10 Erlangs Traffic intensity per user A U = Hλ = 0.1 Erlangs The total number of users that can be supported by a cell = 10/0.1 =
100 Users/cell Therefore, the total number of users in the system is 10,000
We support less number of users here
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More Examples…
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1. How many users can be supported for 0.5% blockingprobability for the following number of trunked channelsin a blocked calls cleared system? Assume Au=0.1E
a) 1, b) 5, c) 10,d) 20, e) 1002. An urban area has a population of 2 million residents.three competing trunked mobile networks (system A, B
and C) provide cellular crevice in this area. System A has394 cells with 19 channels each, system B has 98 cellswith 57 channels each, and system C has 49 cells eachwith 100 channels.
Find the number of users that can be supported at 2%
Summary
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Concepts such as handoff, frequency reuse, Trunking
efficiency, and frequency planning are covered
Capacity of cellular system is a function of many things,
E.g: S/I that limits frequency reuse , which intern limits the
number of channels within the coverage area
Trunking efficiency limits the number of users that can access a
trunked radio system.
We may have a block call cleared or block call delayed
trunked system
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