Static Channel Versus Dynamic Channel Allocation Systems Computer Science Essay

Static bring Versus fighting(a) enthr either every last(predicate)ocation Systems Computer Science Es registerAbstract- pipeline storage allotment Schemes have always held a vital role in achieving better performance of wireless ne cardinalrks. This paper has studied the comparing amid two of the most known techniques of stock allotment namely Static job Allocation and projectile Channel Allocation. The comparison is made everyplace two types of meshings hotshot tuner receiver lucre, in which to each unmatch fitting of wireless customer is weaponed with all one piano tuner user larboard, and multi radio net income, in which each of the boss is equipped with at least two transceivers. This paper presents the situation survey of all the existing comparison made between these two remains of ruless.Keywords- Channel Allocation Scheme, propellent Channel Allocation, Static Channel Allocation, wiz radio network, Multi-radio networkIntroductionGrowth in th e customers of the wireless networks, let it be boothular systems or any another(prenominal) Wireless network, has amplified the need to have the networks which can have more(prenominal) electrical capacity and accommodate more and more users. Enlargement of wireless market has made capacity of the wireless network a scarce resource. Methods to improve effective capacity utilization of the wireless network atomic subprogram 18 under consideration and in 4, it is effected that these methods involve source coding schemes, power control, better modulation schemes, change antennas. Other thus these methods capacity of wireless system can be improved by installing more bas stations i.e increasing do of transmitting equipment or improving hardware equipment of current system. Using better telephone line allocation schemes is also one of the methods to improve capacity utilization of wireless network.The aim of this paper is to focus on bestow allocation schemes. These lend al location schemes are not much of importance in the wired networks because their topology is stable and they do not offer any mobility to the users/ invitees. moreover in the wireless networks, channel allocation of key importance. The vital role of the wireless networks is that they offer mobility to users hence, the channel allocation algorithm has to assign impart to ports and portables so that best trade-off between the quality of service and system performance is maintained 3.A habituated spectrum of frequency, can be divided into several independent ticks, these independent sets are all told disjoint with each other. Hence even up if they are use simultaneously, they will not interfere with each other. So splitting the frequency spectrum into independent transmit and then utilize all the channel for communication simultaneously present improvement in the capacity utilization 6.The channel allocation st locategy is considered to be the core of mobile networks because it not hardly affects the quality and the availability of the convey to the user provided changes the distribution of the traffic and hence, overall shapes the capacity of the network 3. ii of the most common channel allocation schemes are considered in this paper namely, FCA- obstinate Channel Assignment or rigid Channel Allocation and DCA- changing Channel Allocation.Fixed Channel Allocation (FCA)Fixed Channel Allocation is also known as Static Channel Allocation. It is known as Fixed or Static because once the channel is allocated to a port or a user it does not change for the entire course of operation. It is used in all TDMA/FDMA digital cellular mobile networks 5 as bet of frequency carriers in each cell stays fixed and does not depend on traffic gist. It is a time insensitive solution, as with the passage of time allocation of the channels to nodes does not change. Although in real-time, traffic load in a cell varies, in that respect are peak hours when the traffic load reaches to almost 100% and then at that place are quiet hours in a cell when traffic load is very low. This limitation dispirits the use of the FCA. But if a static condition is considered there is most likely a chance to posture good performance with this channel allocation algorithm 3.In a cellular system based on the FCA, channels are partitioned among the cells permanently so that if all the cells use all the channels assigned to them simultaneously, there will be no interference 1. maneuver cell pattern for Static Channel Allocation with N = 7With more complex systems other channel strategies can achieve gameyer efficiency but they require processors with more memory. But it is an essential sacrifice to make as in 4 it is discussed that in each cell there are no static conditions, space traffic mental unsoundness varies from 10% to 70%, and this imbalance in the traffic depends on the size of the cell or service area and type of the environment, whether its urban, suburba n or folksy area 4.Dynamic Channel Allocation (DCA)In DCA, frequency channels are not fixed for any node or user. Depending upon knowledge of the environment, channels are assigned to the user. The distribution of the frequency carriers in a cell depends upon distribution of the users/nodes in the cell and also on offered traffic load. DCA is currently back up by the GSM 5. In Dynamic Channel Allocation Scheme all the channels which are gettable for a system, are kept in a queue or a spool. These channels are allocated to any cell temporarily. The only constraint is to fulfil the distance criteria, so that interference can be minimized 2.The existing schemes for the Dynamic Channel Allocation can be categorized into three main types IA-DCA (Interference Adaptive Dynamic Channel Allocation), LA-DCA (Location Adaptive Dynamic Channel Allocation) and TA-DCA (Traffic Adaptive Dynamic Channel Allocation), these schemes are based on the type of network drivings they consider while mak ing decision 4. All DCA schemes basi pressy evaluate the cost of utilize each available channel and opts the channel which introduces lowest cost 2.For most accurate and good decision for channel allocation, the algorithm should have accurate knowledge of the environment 3. The main algorithms which are considered under the breeding of Dynamic Channel Allocation are DCET, Bellcore and Segregation DCA 3. In DCET and Bellcore DCA algorithms, the decision of channel allocation is based on only unmarried mea authoritativement of channel dynamics, while in the Segregation DCA, a radio interface acquires the channel depending upon its learning through past experience of channel usage. With the past knowledge, channel which has highest luck of success is chosen for operation. Although this algorithm requires processors with memory yet as decision is more meaningful so its performance is better than the DCET and Bellcore DCA algorithms 3.In figure 2, in 7 results of performance of dispa rate type of DCA schemes are compared. convention effect of Different DCA methodsSection II of the paper compares both of the channel allocation schemes in a wiz radio network and Section triplet shares the comparison done of channel allocation schemes in multi-radio network. Section IV shares the identified regions in which future work can be done and Section V concludes the paper. equivalence of DCA and FCA in Single Radio interlockA hotshot radio network a network in which all of the nodes of the wireless network consist of maximum of one radio interface and this single radio interface is used for the communication goals. In this section the comparison of the DCA and FCA in single radio network is presented. go through Algorithms for Dynamic Channel AllocationIn a given cell, if a node requests a call, it will be served only and only if the cell has an unused channel available, which fulfils the reuse criteria, otherwise the call will be blocked 1. Such is the possibilit y with Static Channel Allocation Scheme. But this is not the courting with the Dynamic Channel Allocation Schemes, as for each of the call that is to be served channel is interpreted from the overall pool that holds all the channels available for wireless system.In any channel allocation strategy, main aim is to find the best doable way to reuse the channels to maximize the systems capacity, while keeping interference in the system at minimum and provide quality of service to the user 4. From another view, for allocating channel, the objective is taken as to allocate the channel to a call so that snatch of blocked calls is minimized and the look of dropped calls is also minimized. In the end, the channel allocation scheme finds the best trade-off between these two objectives because generally priority is given to minimize the number of dropped calls, as having a call dropped is more undesirable then not having the call connected at all 1.Both schemes for channel allocation FCA a nd DCA are compared under the assumption that the call arrival distribution is Poisson 5. For the purpose of modelling in FCA it is considered that there are z numbers of channels per frequency carrier and y is the number of control channels. In a given cell i, let total number of frequency carrier be Ci and the total number of channels in the cell, which will be used to serve a call will be ci. The expression for ci is given as(1)While this will not be the case for DCA, as frequency carriers are not permanently assigned to any of the cell. As the channel assignment depends on environment so, if we take n as the number of active calls in any cell, then frequency carriers allocated to that cell will be(2)Total number of channels required, for any cell should be contact to the number of active calls and the control channels. But the number of frequency carriers which has z number of channels each should be either more or touch than actually required 5.In equation (2), shows that val ue is always 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 numbers of calls initiated per minute are more than the actual capacity of the system.The observation made over here is that, under heavy traffic load, efficiency of the network or the channel utilization and capacity of the network does not improve by development DCA instead of FCA. Although it was considered as the fact that DCA will always perform better than FCA.Figure Effect of the handover on FCA and DCAIn figure 4, the phenomenon observed is known as phenomenon of low capacity island 5. Under heavy load, no benefit is achieved by using DCA, as in such a scenario both of the schemes will be utilizing capacity to the full extent. Rather DCA may perform worse than FCA. The reason is that due to dynamic channel allocation, a cell may borrow almost of the frequency channels form the neighb ouring cells during the low traffic period and the neighbouring cell does not get the channel back. The cell which has obtained the channel is let us say known as the lucky cell, and the cell which donated the channel and in the end, was unable to get it back is known as unlucky cell 5. Now during the high load traffic period, if lucky cell wants to handover the call to a neighbouring unlucky cell. But as the unlucky cell would already be out of available channels to be able to serve the call, call will be dropped. Hence under such a scenario the drop out probability of dynamic channel allocation scheme would be higher than static channel allocation algorithm.Other simulation is to find out the effect of the arrival rate on call pulley block probability. Arrival rate is the number of calls initiated per minute.Through simulation, it is concluded that DCA performed better if the traffic load is within the range 0.6 to 0.9 Erlang/BS/Channel. (figure 5)Figure Analysis of DCA and FCA, call blocking ratio with respect to the arrival rate of the callsDuring the next case it was considered that arrival rate is Poisson and the other parameters like handover rate and call holding time etc are evenly distributed all over the cell.From the figure 6 it is clear that as probability of call blocking add-ons with the profit in the arrival rate of calls. Which is fairly obvious, more are the number of the users which are to be served, there is more likely a chance that some of them may not be able to get a free channel.Figure Performance analysis of FCA and DCA, Arrival rate of calls with respect to the over all blocking probabilityUnder such consideration as can be observed from the figure 6, DCA performs better than FCA, as in case of congestion in a cell, DCA can borrow channels from the neighbouring cells but in case of FCA, the scheme has no option but to reject the oncoming calls in case of congestion.Figure 7 shows the amount of traffic carried by FCA and DCA accor ding to the traffic load.Figure comparison between FCA and DCA with respect to the carried traffic under the traffic loadFigure 8 shows the performance of the channel allocation schemes when traffic imbalance is considered. It is observed that network capacity to carry entropy, in case of FCA, reduces significantly when data imbalance is considered. But in case of DCA, there is no significant degradation in networks capacity to carry the data. There is also significant subjoin in the number of calls blocked by FCA, because of the increase in the traffic imbalance. But as the carried capacity does not decrease much in case of the DCA, there is not much of the increment in number of the blocked calls.Figure FCA Vs. DCA, effect of the traffic imbalance on the both channel allocation techniquesComparison of DCA and FCA in Multi Radio NetworkA multi radio network is the type of the network where each node is equipped with at least two or more than two transceivers.Fixed Channel Alloc ation in Multi-radio networkIt is pointed out in 14, throughput and overall performance of wireless networks decreases with increased minginess of radios, but major reason for this problem is that these radios do not transmit the data simultaneously as the nodes are generally configured with single radios only and this factor basically limits the forwarding capacity of the network. In 15, the authors have emphasized that with the introduction of more than one NIC (Network interface cards) in wireless networks, performance of the system can be improved 6 to 7 times, instead of just doubling the performance. The same phenomenon has been confirmed in 16.There has been much work done, in which the performance gain in wireless mesh networks with multiple interfaces is discussed as compared to single radio interface network. In 13, capacity gain between single radio, dual radio and multi-radio wireless mesh networks is compared and realistically the gain achieved by having multiple radio interfaces in the network has been discussed.Apart from that, in 17, authors have proposed that with execution of instrument of multi-radio Diversity approximately 2.3 times performance gain is measured in the single radio network.Under the multi-radio scenario, one grave factor is to consider proper(a) channel assignment. Each of the radios should be tuned to a frequency through which the throughput of the whole network is maximized. The introduction of multiple radios is not without the trade off of increased complexity of channel assignment schemes and the traffic allocation methods 20 and apart from that, more work is done in this domain. In 10, 8, 19, the authors have proposed some approaches to get maximum possible throughput by different channel assignment algorithms.The concept of the Static Channel Allocation in this section is extended to Wireless Mesh Networks, as to begin with the start of the operation in the wireless mesh networks the channels are properly allocat ed and then till the end of the operation, the channel assignment does not change. In this section, multi-radio wireless mesh network is considered and it is observed that how by having multiple radio interfaces the performance of the network improves.Figure Performance of the FCA algorithms with 3 channelsFigure 9 shows the relate of the different algorithms for the channel allocation in the three channel scheme 8.Figure performance of the FCA algorithms with 12 channelsFigure 10 shows the impact of the different algorithms for the channel allocation in the twelve channel scheme 8.Figure 11 shows that with different channel allocation algorithms, how the increment in number of interfaces per node impacts the performance of network. In all algorithms it is observed that with the increase in number of radio interfaces per node, throughput of wireless networks improves 9.Figure FCA algorithm comparison with different number of radio interfaces per nodeFigure effect of increased n umber of interfaces per node on the over all normalized broadcast response timeIn figure 12, it is shown that with different channel allocation schemes for multi-interface wireless mesh network, normalized latency for broadcast decreases with the increase in number of radio interfaces per node 9.In figure 13, it is simulated that with the increase in the number of interfaces per node, there is not an unlimited increment in capacity utilization. Multi radios are used so that in a network there could be as many concurrent transmittances as possible. But even this has a limit to it. In 10, it is shown that after achieving the maximum level of capacity utilization, even after by adding more number of radio interfaces in a network, no advantage is gained.Figure capacity degradation with increase in the number of radio interfaces per nodeFigure Effect of the number of channels and multiple radio interfaces on the throughputIn figure 14, it is shown that as long as the number of the av ailable channels in a cell are more than the number of interfaces per node, with increase in number of radios per node, throughput of the network will increase 11.Figure throughput increment of a network by increased number of the interfaces per nodeIn figure 15, it is shown that under a proper channel assignment and routing method, with more number of interfaces per node, the throughput of the system improves considerably 12.In 13, as shown in figure 16 and 17, performance of fixed channel allocation scheme is compared in detail with respect to single radio network and the multi-radio network.Figure overall network capacity increment with more number of radio interfaces present at each nodeIn figure 16, it is proved that the capacity of the overall system improves with the usage of multiple radios per node.Figure capacity of each AP with multiple interfaces per node Comparison between single radio to the multiple radiosIn figure 17, per Access Point capacity is simulated to hav e comparison between multi-radio interface per node and single radio interface per node.Dynamic Channel Allocation in Multi-radio NetworkThere has been little work which proves the introduction of multiple interfaces while using the Dynamic Channel Allocation provides any performance up-gradation.Analytically it is assumed that, as the introduction of multi-interfaces in wireless mesh networks improves performance, similarly the performance of networks using Dynamic Channel Allocation can be improved by introducing more than one interface on a single node.Some of the analysed parameters, which show the relative improvement in performance, are listed belowParameter I Improvement in the throughput of the systemIn a single radio cognitive network, as shown in figure 18, the node D has two data tracts of equal size in its internal queue, one for node C and one for node. Nodes E and C are at the equal distance d from the node D but are tuned at different channels. In this grouchy case each packet will take time t to reach the destination. Even if we neglect the switching time, cognitive radio present at D will take to switch from one channel to the other channel, the time taken to completely transmit both of the packets will be t+t = 2t.Figure Single Radio NetworkNow even if the same network topology is considered but now consider that each of the nodes is equipped with two interfaces (figure 19). Node D will be able to transmit both of the packets simultaneously to node C and node E, considering that interface 1 is tuned to the channel on which communication with node E is possible and interface 2 is tuned to the frequency over which communication with node C is possible. In this case there will be no delay caused by the switching of the channel.Figure Multi-interface radio networkFigure Effect of channel switchingConclusion The transmission time is decreased with the factor of N, where N is the number of interface each of the node will have. Throughput is i mproved with the factor of N.Parameter II Latency of the network will decreaseWith the introduction of the multiple interfaces in the cognitive radio network, latency of the network will decrease.Figure Multi-hop Single interface Wireless NetworkInitially considering the multi-hop scenario, considering an intermediate node, it has to receive an incoming transmission on channel 1 and then it has to tune its radio to the channel 2 to be able transmit the received transmission to the destination node. Latency of such network will consist ofTransmitting time of packet over channel 1 from source node to intermediate node t1Transmitting time of packet over channel 2 from intermediate node to destination node t2 faulting time required for the interface on intermediate node to switch from channel 1 to channel 2 t3Hence the total latency of such a system will be t1+ t2+ t3Figure Multi-hop Multi interface Wireless NetworkNow comparing the previous scenario with the one in which each of the node is equipped with at least two interfaces. Now on the intermediate node interface 1 will be tuned to channel 1 and interface 2 will be tuned to channel 2. If there is an incoming transmission on channel 1 and it is to be transmitted to the channel 2, the total latency will beTransmitting time of packet over channel 1 from source node to intermediate node t1Transmitting time of packet over channel 2 from intermediate node to destination node t2Hence the total latency of such a system will be t1+ t2The switching time will not be considered over here hence comparatively the latency is decreased with the introduction of another interface on the cognitive radio node.Conclusion The latency factor is dependent on switching time of the cognitive radio. This factor comes into effect with more dominance with increase in the number of hops in the multi-hop network. Latency can be greatly reduced with the introduction of multi interfaces on the cognitive radio network.Parameter III Connec tivity of the network will improveThe probability of isolation of any node in a network will be reduced with the introduction of the multi-interfaces in the cognitive radio network.Figure Single interface node with the available channelsConsidering the scenario, in figure 23, where a secondary network has four channels available for its utilization, now for a given condition, all radio interfaces are tuned to either one of the channel 1, 2 or 3. If a single interface chooses channel 4, it will be stranded from the rest of the network. Assuming that the probability of opting for such a channel is p then the overall probability of getting a node isolated from the rest of the network will be p.Figure Multi-Interface node with the available channelsNow for multiple interfaces, a node will only be separated if both the interfaces of a single node choose channel 4.A node will be isolated if and only ifInterface 1 chooses channel 4 AND interface 2 chooses channel 4P2As according to the probability rules pConclusion The probability of isolating a node, is decreased with the factor of N N is the number of radios as compared to the probability of node isolation in case of single interface cognitive radio networks.Here mutual independence among the DCA algorithms running on both of the radio interfaces is considered, but this is not generally the case. The performance of a cognitive radio network is strictly dependent on the number of cognitive radios present in its vicinity 21.Figure Improvement in throughput using multiple radiosFigure Improvement in throughput of the network with multiple radio using different number of available channelsFigure 25 and 26 shows the throughput improvement gained by the introduction of multiple radios as compared to a single radio and in both of the figures different number of available channels are considered 24.ComparisonUp till so far, none of the research has been carried out to find out whether any advantage is gained by deploy ing Dynamic Channel Allocation scheme in the multi-radio wireless network domain as compared to the implementation of the Fixed Channel Assignment algorithm. Considering the study made regarding the performance improvement gained by fixed channel allocation scheme and dynamic channel allocation scheme in multi-radio wireless network, there could be several hypotheses made.The complexity of implementation of Dynamic Channel Allocation algorithm will be more than that of Fixed Channel Allocation algorithm. Although the same is true in case of single radio network, but in case of the Multi-radio network, the complexity increment will be more significant. The reason can be taken as if the spectrum view of a single interface of a node changes in multi-radio network, for the similar node the situation changes for the other interfaces as well 21.The performance improvement obtained by implementation of the Dynamic Channel Allocation algorithm as compared to the Fixed Channel Allocation in the multi-radio will have similar effects as it has in the Single radio network. The same effect on the throughput of the system, data carrying capacity and the effect of the traffic load and traffic imbalance will be observed.Another important factor that can be predicted because of the observation made via simulation figures is as the performance of the wireless network depends upon the density of the nodes in a network. As compared to the Fixed Channel Allocation Scheme, Dynamic Channel Allocation Algorithms will be more sensitive to the density of the network 23.There will be no matter of connectivity in case the Fixed Channel Assignment Scheme is deployed on the wireless network. As before the point of operation with FCA, it is made sure that all of the nodes are connected and none of the node is left isolated. With the Dynamic Channel Allocation there will still be a miniature probability that a node can get isolated from the rest of the network.In the Fixed Channel Allocatio n for the multi-radio wireless network the distribution of radio interfaces do not matter for the performance. But in case of the DCA, better performance can be improved if radio interface distribution on the nodes is not uniform. DCA will perform better if the first hop nodes have more number of radio interfaces than rest of the network nodes 22.Future WorkThe points raised, during this study are just concluded through observation and analytically studying the response of the Fixed Channel Allocation Algorithm in the Multi-Radio network and Dynamic Channel Allocation Algorithm in Multi-Radio Network. These observations can be further improved by using proper simulating tools.ConclusionIn the single radio wireless network, DCA exhibits better performance than FCA. The same behaviour is predicted for the multi-radio wireless network, but with the increased complexity. And much better performance can be achieved by pickings care of the distribution of the radios in the network. Still it should be considered that there will not be infinite performance gain obtained by using multi-radio network and DCA. The limitation imposed is that number of channels available to a cell should always be greater than the number of interfaces per node has.