a.)Fixed channel assignment
b.)Dynamic channel assignment
a.) Fixed
channel assignment
Ans:- With the limited frequency spectrum and an increasing
demand for cellular communication services, the problem of channel assignment
becomes increasingly important. However, finding a conflict-free channel
assignment with the minimum channel span is NP hard. Therefore, we formulate
the problem by assuming a given channel span. Our objective is to obtain a
conflict-free channel assignment among the cells, which satisfies both the
electromagnetic compatibility (EMC) constraints and traffic demand
requirements. We propose an approach based on a modified genetic algorithm
(GA). The approach consists of a genetic-fix algorithm that generates and
manipulates individuals with fixed size (i.e., in binary representation, the
number of ones is fixed) and a minimum-separation encoding scheme that
eliminates redundant zeros in the solution representation. Using these two
strategies, the search space can be reduced substantially. Simulations on the
first four benchmark problems showed that this algorithm could achieve at least
80%, if not 100%, convergence to solutions within reasonable time. In the fifth
benchmark problem, our algorithm found better solutions with shorter channel
span than any existing algorithms. Such significant results indicate that our
approach is indeed a good method for solving the channel-assignment problem.
b.) Dynamic channel assignment
Ans:- When there are more than
one user who desire to access a shared network channel, an algorithm is
deployed for channel allocation among the competing users. Dynamic channel
allocation encompasses the channel allocation schemes where channels are
allotted to users dynamically as per their requirements, from a central pool.
Working
Principle
In dynamic channel allocation schemes,
frequency channels are not permanently allotted to any user. Channels are assigned
to the user as needed depending upon the network environment. The available
channels are kept in a queue or a spool. The allocation of the channels is
temporary. Distribution of the channels to the contending users is based upon
distribution of the users in the network and offered traffic load. The
allocation is done so that transmission interference is minimized.
Dynamic
Channel Allocation Schemes
The dynamic channel allocation schemes
can be divided into three categories −
- Interference Adaptive Dynamic
Channel Allocation (IA-DCA)
- Location Adaptive Dynamic
Channel Allocation (LA-DCA)
- Traffic Adaptive Dynamic
Channel Allocation (TA-DCA)
All these schemes evaluate the cost of
using each available channel and allocates the channel with the optimum cost.
Advantages
Dynamic channel allocation schemes
allots channels as needed. This results in optimum utilization of network
resources. There are less chances of denial of services and call blocking in
case of voice transmission. These schemes adjust bandwidth allotment according
to traffic volume, and so are particularly suitable for bursty traffic.
Disadvantages
Dynamic channel allocation schemes
increases the computational as well as storage load on the system.
0 Comments