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April 21, 2023 1
Mobile Computing COE 446
Network PlanningTarek Sheltami
KFUPMCCSECOE
http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm
Principles of Wireless Networks
K. Pahlavan and P. Krishnamurth
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Outline Channel Allocation Techniques and Capacity Expansion
Fixed Channel Allocation (FCA)
Channel Borrowing Techniques
Selecting Free Channels
Dynamic Channel Allocation (DCA)
Cell-based techniques
Interference-based techniques
Comparison between FCA and DCA
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Change the frequency allocation methodology
Channel Allocation Techniques and Capacity Expansion
1.Fixed Channel Allocation (FCA)
Divide the available spectrum by the cluster size to determine the number of radio channels per cell
Nc = W/B, Cc = Nc/N
Cc is then distributed in the cells in a manner to minimize the adjacent channel interference
In FDMA each radio channel corresponds to one user
TDMA and CDMA, each radio channel carries several time slots or codes associated with voice channels
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Change the frequency allocation methodology..
Fixed Channel Allocation (FCA)
Simple to implement if the traffic is uniform
In practice traffic changes with time due to the movement of MT high probability of call blocking in some cells and poor utilization of the available BW
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For a uniform distribution of the traffic, the calculated probability of blockage for each cell is 2%
If the traffic becomes non-uniform, the blockage rate will be changed and over all the average will not remain 2%
Our goal is to increase the number of channels in cells with the higher traffic load and decrease it in cells with lower traffic load so that overall blockage rate of the network is minimized
The number of channels per cell and the cost function to be minimized is the probability of call blocking
The minimization process is far complex than uniformly distributed traffic case
The optimization problem is now a function of Nc variables and, in addition, the regular frequency reuse pattern for FCA can not be used
Change the frequency allocation methodology..
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Channel Borrowing Techniques
High-traffic cells borrow channels from low-traffic cells
TemporaryTemporary channel borrowingchannel borrowing and StaticStatic channel channel borrowingborrowing
Temporary channel borrowingTemporary channel borrowing , high traffic cells return the borrowed channels after the call is completed
Static channel borrowingStatic channel borrowing, channels are distributed among cells according to the available statistics of the traffic and changed in a predictive manner
Change the frequency allocation methodology..
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Selecting Free Channels
1.1. Simple Borrowing SchemesSimple Borrowing Schemes
All the channels are available for borrowing
Better under light or moderate traffic loads
2.2. Hybrid borrowing schemeHybrid borrowing scheme
Channels are partitioned, some of them can be borrowed and other can not be borrowed
Some of the suggested borrowing techniques are found to be capable of supporting up to 35% more traffic than uniformly distributed FCA
Channels require additional computational complexity and frequent switching of channels
Change the frequency allocation methodology..
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Dynamic Channel Allocation (DCA) Channels are placed in a pool and they are assigned to a new
call according to the overall Sr in all cells
Each channel can be used in any cell as long as it satisfies Sr
requirement for the system
The channel is returned to the pool after the cellular call is terminated
According to some simulations, the capacity is maximized when Sr of every set of cochannels users is balanced around some level that is no larger than necessary
The downsize of this scheme, it is extremely complex and inefficient under high-traffic load conditions
Change the frequency allocation methodology..
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Dynamic Channel Allocation (DCA) Microcellular systems of high-density personal communication
networks have been shown to benefit the most out of the DCA (simulation)
The cost function quantitatively ranks the available channels based on the overall interference average probability of call-blockage or parameters that somehow related to there quantities
Cost function determine the appropriateness of the channel to be selected
The difference in DCA techniques lies in the selection and optimization of this cost function
Two DCA schemes: Centralize and Distributed schemes
Change the frequency allocation methodology..
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Dynamic Channel Allocation (DCA)
Centralized DCA, a central pool all channels exists
Distributed DCA are considered for microcellular systems where channel propagation is less predictable and traffic is denser
Distributed DCA are divided into two classes: Cell-based techniques and interference-based techniques
Cell-based techniques :
Each BS maintains and assigns the channel to the users in its cell
Cell-based techniques is very efficient, but the expense incurred additional inter-BS communication increases the traffic in the cell
Change the frequency allocation methodology..
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Dynamic Channel Allocation (DCA)
Interference-based techniques:
Each BS makes the channel assignment based on the RSS of the mobile in its vicinity
All channels are available to the BS and the BS makes its decision based on the local information without any need to communicate with other BSs
These schemes are self-organized, simple, efficient and fast but they suffer from additional unwanted cochannel interference which may result in channel interruption and network instability
Change the frequency allocation methodology..
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