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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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