Static Channel Versus Dynamic Channel Allocation Systems Computer Science Essay

Abstract- Channel Allocation Schemes have ever held a critical function in accomplishing better public presentation of radio webs. This paper has studied the comparing between two of the most known techniques of channel allotment viz. : Inactive Channel Allocation and Dynamic Channel Allocation. The comparing is made over two types of webs individual wireless web, in which each of radio node is equipped with merely one wireless interface, and multi wireless web, in which each of the node is equipped with at least two transceivers.

This paper presents the item study of all the bing comparing made between these two strategies.

Keywords- Channel Allocation Scheme, Dynamic Channel Allocation, Static Channel Allocation, Single wireless web, Multi-radio web

Introduction

Growth in the clients of the radio webs, allow it be cellular systems or any other Wireless web, has amplified the demand to hold the webs which can hold more capacity and suit more and more users. Expansion of radio market has made capacity of the radio web a scarce resource.

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Methods to better effectual capacity use of the radio web are under consideration and in [ 4 ] , it is realized that these methods involve beginning cryptography strategies, power control, better transition strategies, improved aerials. Other so these methods capacity of radio system can be improved by put ining more bas Stationss i.e increasing figure of conveying equipment or bettering hardware equipment of current system. Using better channel allotment strategies is besides one of the methods to better capacity use of radio web.

The purpose of this paper is to concentrate on channel allotment strategies.

These channel allotment strategies are non much of importance in the wired webs because their topology is stable and they do non offer any mobility to the users/nodes. But in the radio webs, channel allotment of cardinal importance. The critical function of the radio webs is that they offer mobility to users therefore, the channel allotment algorithm has to delegate channels to ports and portables so that best tradeoff between the quality of service and system public presentation is maintained [ 3 ] .

A given spectrum of frequence, can be divided into several independent sets, these independent sets are wholly disjoint with each other. Hence even if they are used at the same time, they will non interfere with each other. So dividing the frequence spectrum into independent channels and so utilizing all the channels for communicating at the same time present betterment in the capacity use [ 6 ] .

The channel allotment scheme is considered to be the nucleus of nomadic webs because it non merely affects the quality and the handiness of the channels to the user but changes the distribution of the traffic and hence, overall shapes the capacity of the web [ 3 ] .

Two of the most common channel allotment strategies are considered in this paper viz. , FCA- Fixed Channel Assignment or Fixed Channel Allocation and DCA- Dynamic Channel Allocation.

Fixed Channel Allocation ( FCA )

Fixed Channel Allocation is besides known as Inactive Channel Allocation. It is known as Fixed or Static because one time the channel is allocated to a port or a user it does non alter for the full class of operation. It is used in all TDMA/FDMA digital cellular Mobile webs [ 5 ] as figure of frequence bearers in each cell stays fixed and does non depend on traffic burden. It is a clip insensitive solution, as with the transition of clip allotment of the channels to nodes does non alter. Although in real-time, traffic burden in a cell varies, there are peak hours when the traffic burden reaches to about 100 % and so there are quiet hours in a cell when traffic burden is really low. This restriction dispirits the usage of the FCA. But if a inactive status is considered there is most likely a opportunity to acquire good public presentation with this channel allotment algorithm [ 3 ] .

In a cellular system based on the FCA, channels are partitioned among the cells for good so that if all the cells use all the channels assigned to them at the same time, there will be no intervention [ 1 ] .

Figure - cell form for Inactive Channel Allotment with N = 7

With more complex systems other channel schemes can accomplish higher efficiency but they require processors with more memory. But it is an indispensable forfeit to do as in [ 4 ] it is discussed that in each cell there are no inactive conditions, infinite traffic instability varies from 10 % to 70 % , and this instability in the traffic depends on the size of the cell or service country and type of the environment, whether its urban, suburban or rural country [ 4 ] .

Dynamic Channel Allocation ( DCA )

In DCA, frequence channels are non fixed for any node or user. Depending upon cognition of the environment, channels are assigned to the user. The distribution of the frequence bearers in a cell depends upon distribution of the users/nodes in the cell and besides on offered traffic burden. DCA is presently supported by the GSM [ 5 ] . In Dynamic Channel Allocation Scheme all the channels which are available for a system, are kept in a waiting line or a bobbin. These channels are allocated to any cell temporarily. The lone restraint is to carry through the distance standards, so that intervention can be minimized [ 2 ] .

The bing strategies for the Dynamic Channel Allocation can be categorized into three chief types: IA-DCA ( Interference Adaptive Dynamic Channel Allocation ) , LA-DCA ( Location Adaptive Dynamic Channel Allocation ) and TA-DCA ( Traffic Adaptive Dynamic Channel Allocation ) , these strategies are based on the type of web kineticss they consider while doing determination [ 4 ] . All DCA strategies fundamentally evaluate the cost of utilizing each available channel and opts the channel which introduces lowest cost [ 2 ] .

For most accurate and good determination for channel allotment, the algorithm should hold accurate cognition of the environment [ 3 ] . The chief algorithms which are considered under the survey of Dynamic Channel Allocation are: DCET, Bellcore and Segregation DCA [ 3 ] . In DCET and Bellcore DCA algorithms, the determination of channel allotment is based on merely individual measuring of channel kineticss, while in the Segregation DCA, a wireless interface acquires the channel depending upon its acquisition through past experience of channel use. With the past cognition, channel which has highest chance of success is chosen for operation. Although this algorithm requires processors with memory yet as determination is more meaningful so its public presentation is better than the DCET and Bellcore DCA algorithms [ 3 ] .

In figure 2, in [ 7 ] consequences of public presentation of different type of DCA strategies are compared.

Figure - Performance of Different DCA methods

Section II of the paper compares both of the channel allotment strategies in a individual wireless web and Section III portions the comparing done of channel allotment strategies in multi-radio web. Section IV portions the identified parts in which future work can be done and Section V concludes the paper.

Comparison of DCA and FCA in Single Radio Network

A individual wireless web a web in which all of the nodes of the radio web consist of upper limit of one wireless interface and this individual wireless interface is used for the communicating intents. In this subdivision the comparing of the DCA and FCA in individual wireless web is presented.

Figure - Algorithm for Dynamic Channel Allotment

In a given cell, if a node requests a call, it will be served merely and merely if the cell has an fresh channel available, which fulfils the reuse standards, otherwise the call will be blocked [ 1 ] . Such is the instance with Static Channel Allocation Scheme. But this is non the instance with the Dynamic Channel Allocation Schemes, as for each of the call that is to be served ; channel is taken from the overall pool that holds all the channels available for radio system.

In any channel allotment scheme, chief purpose is to happen the best possible manner to recycle the channels to maximise the systems ' capacity, while maintaining intervention in the system at lower limit and provide quality of service to the user [ 4 ] . From another position, for apportioning channel, the aim is taken as to apportion the channel to a call so that figure of out of use calls is minimized and the figure of dropped calls is besides minimized. In the terminal, the channel allotment strategy finds the best tradeoff between these two aims because by and large precedence is given to minimise the figure of dropped calls, as holding a call dropped is more unwanted so non holding the call connected at all [ 1 ] .

Both strategies for channel allotment FCA and DCA are compared under the premise that the call reaching distribution is Poisson [ 5 ] . For the intent of patterning in FCA it is considered that there are z Numberss of channels per frequence bearer and Y is the figure of control channels. In a given cell I, allow entire figure of frequence bearer be Ci and the entire figure of channels in the cell, which will be used to function a call will be ci. The look for curie is given as:

( 1 )

While this will non be the instance for DCA, as frequence bearers are non for good assigned to any of the cell. As the channel assignment depends on environment so, if we take n as the figure of active calls in any cell, so frequence bearers allocated to that cell will be:

( 2 )

Entire figure of channels required, for any cell should be equal to the figure of active calls and the control channels. But the figure of frequence bearers which has omega figure of channels each should be either more or equal than really required [ 5 ] .

In equation ( 2 ) , shows that value is ever taken equal or greater than `` a '' [ 5 ] .

For the first simulation, the arrival rate of the calls is set at the overload value ; this means that the overload period is considered where the Numberss of calls initiated per minute are more than the existent capacity of the system.

The observation made over here is that, under heavy traffic burden, efficiency of the web or the channel use and capacity of the web does non better by utilizing DCA alternatively of FCA. Although it was considered as the fact that DCA will ever execute better than FCA.

Figure - Consequence of the handover on FCA and DCA

In figure 4, the phenomenon observed is known as phenomenon of low capacity island [ 5 ] . Under heavy burden, no benefit is achieved by utilizing DCA, as in such a scenario both of the strategies will be utilizing capacity to the full extent. Rather DCA may execute worse than FCA. The ground is that due to dynamic channel allotment, a cell may borrow some of the frequence channels form the neighbouring cells during the low traffic period and the neighbouring cell does non acquire the channel back. The cell which has obtained the channel is let us state known as the lucky cell, and the cell which donated the channel and in the terminal, was unable to acquire it back is known as luckless cell [ 5 ] . Now during the high burden traffic period, if lucky cell wants to handover the call to a neighbouring luckless cell. But as the luckless cell would already be out of available channels to be able to function the call, call will be dropped. Hence under such a scenario the bead out chance of dynamic channel allotment strategy would be higher than inactive channel allotment algorithm.

Other simulation is to happen out the consequence of the reaching rate on call blocking chance. Arrival rate is the figure of calls initiated per minute.

Through simulation, it is concluded that DCA performed better if the traffic burden is within the scope 0.6 to 0.9 Erlang/BS/Channel. ( figure 5 )

Figure - Analysis of DCA and FCA, call barricading ratio with regard to the arrival rate of the calls

During the following instance it was considered that arrival rate is Poisson and the other parametric quantities like handover rate and name keeping clip etc are equally distributed all over the cell.

From the figure 6 it is clear that as chance of call blocking additions with the addition in the arrival rate of calls. Which is reasonably obvious, more are the figure of the users which are to be served, there is more likely a opportunity that some of them may non be able to acquire a free channel.

Figure - Performance analysis of FCA and DCA, Arrival rate of calls with regard to the over all blocking chance

Under such consideration as can be observed from the figure 6, DCA performs better than FCA, as in instance of congestion in a cell, DCA can borrow channels from the neighbouring cells but in instance of FCA, the strategy has no option but to reject the oncoming calls in instance of congestion.

Figure 7 shows the sum of traffic carried by FCA and DCA harmonizing to the traffic burden.

Figure - comparing between FCA and DCA with regard to the carried traffic under the traffic burden

Figure 8 shows the public presentation of the channel allotment strategies when traffic instability is considered. It is observed that web capacity to transport informations, in instance of FCA, reduces significantly when informations instability is considered. But in instance of DCA, there is no important debasement in webs capacity to transport the information. There is besides important addition in the figure of calls blocked by FCA, because of the addition in the traffic instability. But as the carried capacity does non diminish much in instance of the DCA, there is non much of the increase in figure of the out of use calls.

Figure - FCA Vs. DCA, consequence of the traffic instability on the both channel allotment techniques

Comparison of DCA and FCA in Multi Radio Network

A multi wireless web is the type of the web where each node is equipped with at least two or more than two transceivers.

Fixed Channel Allocation in Multi-radio web

It is pointed out in [ 14 ] , throughput and overall public presentation of radio webs decreases with increased denseness of wirelesss, but major ground for this job is that these wirelesss do non convey the information at the same time as the nodes are by and large configured with individual wirelesss merely and this factor fundamentally limits the forwarding capacity of the web. In [ 15 ] , the writers have emphasized that with the debut of more than one NIC ( Network interface cards ) in radio webs, public presentation of the system can be improved 6 to 7 times, alternatively of merely duplicating the public presentation. The same phenomenon has been confirmed in [ 16 ] .

There has been much work done, in which the public presentation addition in wireless mesh webs with multiple interfaces is discussed as compared to individual wireless interface web. In [ 13 ] , capacity addition between individual wireless, double wireless and multi-radio radio mesh webs is compared and realistically the addition achieved by holding multiple wireless interfaces in the web has been discussed.

Apart from that, in [ 17 ] , writers have proposed that with execution of multi-radio Diversity about 2.3 times public presentation addition is measured in the individual wireless web.

Under the multi-radio scenario, one of import factor is to see proper channel assignment. Each of the wirelesss should be tuned to a frequence through which the throughput of the whole web is maximized. The debut of multiple wirelesss is non without the trade off of increased complexness of channel assignment strategies and the traffic allotment methods [ 20 ] and apart from that, more work is done in this sphere. In [ 10 ] , [ 8 ] , [ 19 ] , the writers have proposed some attacks to acquire maximal possible throughput by different channel assignment algorithms.

The construct of the Static Channel Allocation in this subdivision is extended to Wireless Mesh Networks, as before the start of the operation in the radio mesh networks the channels are decently allocated and so till the terminal of the operation, the channel assignment does non alter. In this subdivision, multi-radio radio mesh web is considered and it is observed that how by holding multiple wireless interfaces the public presentation of the web improves.

Figure - Performance of the FCA algorithms with 3 channels

Figure 9 shows the impact of the different algorithms for the channel allotment in the three channel scheme [ 8 ] .

Figure - public presentation of the FCA algorithms with 12 channels

Figure 10 shows the impact of the different algorithms for the channel allotment in the 12 channel strategy [ 8 ] .

Figure 11 shows that with different channel allotment algorithms, how the increase in figure of interfaces per node impacts the public presentation of web. In all algorithms it is observed that with the addition in figure of wireless interfaces per node, throughput of radio webs improves [ 9 ] .

Figure - FCA algorithm comparing with different figure of wireless interfaces per node

Figure - consequence of increased figure of interfaces per node on the over all normalized broadcast latency

In figure 12, it is shown that with different channel allotment strategies for multi-interface radio mesh web, normalized latency for broadcast lessenings with the addition in figure of wireless interfaces per node [ 9 ] .

In figure 13, it is simulated that with the addition in the figure of interfaces per node, there is non an limitless increase in capacity use. Multi wirelesss are used so that in a web there could be as many coincident transmittals as possible. But even this has a bound to it. In [ 10 ] , it is shown that after accomplishing the maximal degree of capacity use, even after by adding more figure of wireless interfaces in a web, no advantage is gained.

Figure - capacity debasement with addition in the figure of wireless interfaces per node

Figure - Consequence of the figure of channels and multiple wireless interfaces on the throughput

In figure 14, it is shown that every bit long as the figure of the available channels in a cell ; are more than the figure of interfaces per node, with addition in figure of wirelesss per node, throughput of the web will increase [ 11 ] .

Figure - throughput increase of a web by increased figure of the interfaces per node

In figure 15, it is shown that under a proper channel assignment and routing method, with more figure of interfaces per node, the throughput of the system improves well [ 12 ] .

In [ 13 ] , as shown in figure 16 and 17, public presentation of fixed channel allotment strategy is compared in item with regard to individual wireless web and the multi-radio web.

Figure - overall web capacity increase with more figure of wireless interfaces present at each node

In figure 16, it is proved that the capacity of the overall system improves with the use of multiple wirelesss per node.

Figure - capacity of each AP with multiple interfaces per node - Comparison between individual wireless to the multiple wirelesss

In figure 17, per Access Point capacity is simulated to hold comparing between multi-radio interface per node and individual wireless interface per node.

Dynamic Channel Allocation in Multi-radio Network:

There has been small work which proves the debut of multiple interfaces while utilizing the Dynamic Channel Allocation provides any public presentation up-gradation.

Analytically it is assumed that, as the debut of multi-interfaces in radio mesh webs improves public presentation, likewise the public presentation of webs utilizing Dynamic Channel Allocation can be improved by presenting more than one interface on a individual node.

Some of the analysed parametric quantities, which show the comparative betterment in public presentation, are listed below:

Parameter - I: Improvement in the throughput of the system:

In a individual wireless cognitive web, as shown in figure 18, the node D has two informations packages of equal size in its internal waiting line, one for node C and one for node. Nodes E and C are at the equal distance `` vitamin D '' from the node D but are tuned at different channels. In this peculiar instance each package will take clip `` T '' to make the finish. Even if we neglect the shift clip, cognitive wireless nowadays at D will take to exchange from one channel to the other channel, the clip taken to wholly convey both of the packages will be t+t = 2t.

Figure - Single Radio Network

Now even if the same web topology is considered but now consider that each of the nodes is equipped with two interfaces ( figure 19 ) . Node D will be able to convey both of the packages at the same time to node C and node E, sing that interface 1 is tuned to the channel on which communicating with node E is possible and interface 2 is tuned to the frequence over which communicating with node C is possible. In this instance there will be no hold caused by the shift of the channel.

Figure - Multi-interface wireless web

Figure - Consequence of channel shift

Decision: The transmittal clip is decreased with the factor of `` N '' , where N is the figure of interface each of the node will hold. Throughput is improved with the factor of `` N '' .

Parameter - Two: Rotational latency of the web will diminish:

With the debut of the multiple interfaces in the cognitive wireless web, latency of the web will diminish.

Figure - Multi-hop Single interface Wireless Network

Initially sing the multi-hop scenario, sing an intermediate node, it has to have an incoming transmittal on channel 1 and so it has to tune its wireless to the channel 2 to be able transmit the received transmittal to the finish node. Rotational latency of such web will dwell of:

Conveying clip of package over channel 1 from beginning node to intercede node: t1

Conveying clip of package over channel 2 from intermediate node to finish node: t2

Switch overing clip required for the interface on intermediate node to exchange from channel 1 to impart 2: t3

Therefore the entire latency of such a system will be: t1+ t2+ t3

Figure - Multi-hop Multi interface Wireless Network

Now comparing the old scenario with the 1 in which each of the node is equipped with at least two interfaces. Now on the intermediate node interface 1 will be tuned to impart 1 and interface 2 will be tuned to impart 2. If there is an incoming transmittal on channel 1 and it is to be transmitted to the channel 2, the entire latency will be:

Conveying clip of package over channel 1 from beginning node to intercede node: t1

Conveying clip of package over channel 2 from intermediate node to finish node: t2

Therefore the entire latency of such a system will be: t1+ t2

The shift clip will non be considered over here ; therefore relatively the latency is decreased with the debut of another interface on the cognitive wireless node.

Decision: The latency factor is dependent on exchanging clip of the cognitive wireless. This factor comes into consequence with more laterality with addition in the figure of hops in the multi-hop web. Rotational latency can be greatly reduced with the debut of multi interfaces on the cognitive wireless web.

Parameter - Three: Connectivity of the web will better:

The chance of isolation of any node in a web will be reduced with the debut of the multi-interfaces in the cognitive wireless web.

Figure - Single interface node with the available channels

Sing the scenario, in figure 23, where a secondary web has four channels available for its use, now for a given status, all wireless interfaces are tuned to either one of the channel 1, 2 or 3. If a individual interface chooses channel 4, it will be isolated from the remainder of the web. Assuming that the chance of choosing for such a channel is p so the overall chance of acquiring a node isolated from the remainder of the web will be p.

Figure - Multi-Interface node with the available channels

Now for multiple interfaces, a node will merely be separated if both the interfaces of a individual node choose channel 4.

A node will be isolated if and merely if:

Interface 1 chooses channel 4 AND interface 2 chooses channel 4

P2

As harmonizing to the chance regulations p & lt ; =1, so p2 & lt ; P.

Decision: The chance of insulating a node, is decreased with the factor of `` N '' [ N is the figure of wirelesss ] as compared to the chance of node isolation in instance of individual interface cognitive wireless webs.

Here common independency among the DCA algorithms running on both of the wireless interfaces is considered, but this is non by and large the instance. The public presentation of a cognitive wireless web is purely dependent on the figure of cognitive wirelesss present in its locality [ 21 ] .

Figure - Improvement in throughput utilizing multiple wirelesss

Figure - Improvement in throughput of the web with multiple wireless utilizing different figure of available channels

Figure 25 and 26 shows the throughput betterment gained by the debut of multiple wirelesss as compared to a individual wireless and in both of the figures different figure of available channels are considered [ 24 ] .

Comparison:

Up boulder clay so far, none of the research has been carried out to happen out whether any advantage is gained by deploying Dynamic Channel Allocation strategy in the multi-radio radio web sphere as compared to the execution of the Fixed Channel Assignment algorithm. Sing the survey made sing the public presentation betterment gained by fixed channel allotment strategy and dynamic channel allotment strategy in multi-radio radio web, there could be several hypotheses made.

The complexness of execution of Dynamic Channel Allocation algorithm will be more than that of Fixed Channel Allocation algorithm. Although the same is true in instance of individual wireless web, but in instance of the Multi-radio web, the complexness increase will be more important. The ground can be taken as if the spectrum position of a individual interface of a node alterations in multi-radio web, for the similar node the state of affairs alterations for the other interfaces as good [ 21 ] .

The public presentation betterment obtained by execution of the Dynamic Channel Allocation algorithm as compared to the Fixed Channel Allocation in the multi-radio will hold similar effects as it has in the Single wireless web. The same consequence on the throughput of the system, informations transporting capacity and the consequence of the traffic burden and traffic instability will be observed.

Another of import factor that can be predicted because of the observation made via simulation figures is as the public presentation of the radio web depends upon the denseness of the nodes in a web. As compared to the Fixed Channel Allocation Scheme, Dynamic Channel Allocation Algorithms will be more sensitive to the denseness of the web [ 23 ] .

There will be no affair of connectivity in instance the Fixed Channel Assignment Scheme is deployed on the radio web. As before the point of operation with FCA, it is made certain that all of the nodes are connected and none of the node is left stray. With the Dynamic Channel Allocation there will still be a little chance that a node can acquire isolated from the remainder of the web.

In the Fixed Channel Allocation for the multi-radio radio web the distribution of wireless interfaces do non count for the public presentation. But in instance of the DCA, better public presentation can be improved if radio interface distribution on the nodes is non unvarying. DCA will execute better if the first hop nodes have more figure of wireless interfaces than remainder of the web nodes [ 22 ] .

Future Work

The points raised, during this survey are merely concluded through observation and analytically analyzing the response of the Fixed Channel Allocation Algorithm in the Multi-Radio web and Dynamic Channel Allocation Algorithm in Multi-Radio Network. These observations can be farther improved by utilizing proper simulating tools.

Decision

In the individual wireless radio web, DCA exhibits better public presentation than FCA. The same behavior is predicted for the multi-radio radio web, but with the increased complexness. And much better public presentation can be achieved by taking attention of the distribution of the wirelesss in the web. Still it should be considered that there will non be infinite public presentation addition obtained by utilizing multi-radio web and DCA. The restriction imposed is that figure of channels available to a cell should ever be greater than the figure of interfaces per node has.