Handoff and New Call Blocking Probability Reducing Technique Using Auxiliary Stations Seema Pankaj Mahalungkar, Santosh S. Sambare Abstract In cellular network, there are no of parameters which are affecting on quality of service of the network. There are various techniques which are used to improve it. One of the parameter is rejection of a call due to unavailability of the free channel. Call can be new call or handoff call. Proposed scheme is combination of existing techniques which also uses auxiliary stations to reduce call blocking probability and improved the quality of service. Index Terms Cellular Network, Handoff Management, Blocking Probability, Auxiliary Stations(AS), Received Signal Strength(RSS), Base Station(BS), Mobile Station(MS). I. INTRODUCTION For cellular networks here proposed a scheme through which we can easily reduce call blocking probability by making use of auxiliary stations which are placed in base station coverage area. When new connection request comes and all channels are busy then without rejecting that call it should be hold for some specific time period by auxiliary station. Thus new call blocking probability will get reduced. Handoff management becomes very much essential in mobile communication system. When mobile moves from current access point to new access point, its actually switching from one cell frequency to different cell frequency without any interruption we call it handoff. So to avoid handoff call rejection due to unavailability of free channels we can use auxiliary stations to hold the call for specific amount of time. It will help to reduce handoff call blocking probability. II. RELATED WORK By using reservation based channel assignment technique, according to call duration we can assign channel groups to user groups so that short duration calls will not be blocked due to long duration calls. Here long duration calls may get blocked.[1] In hierarchical based scheme dual-band cellular mobile communication network is considered where each cell i.e the macro and microcells are served by different base stations which are situated at center. Call is sent to the macro cell, if user s speed is determined to be fast, else if the user were slow then the call would be sent to microcell to be served. When a call is sent to the microcell but the required bandwidth of the call is larger than the available bandwidth, then the call would be forwarded to the macro cell. But in hierarchical cellular network problems like call setup and signaling protocol for mobile terminal will become complex. [1] Hybrid channel allocation is the combination of fixed channel allocation and dynamic channel allocation. When a mobile host needs a channel for its call, and all the fixed set channels are busy, only then channels from the dynamic set is taken. After using the channels base station must return back channels to MSC otherwise there will not be channels in dynamic set for further requests and call will get rejected [1] Call blocking can also be reduced using auxiliary stations. When channels of base station (BS) are not free, failure probability can be minimized if the handoff request is served by an Auxiliary Station (AS) closest to the mobile station (MS). The mobile station, being in the auxiliary station, will send requests to the base station within fixed time intervals and when it will find free channels are available in base station it will automatically connect with it, rejecting the connection of the auxiliary station (AS). This process effectively reduces the handoff failure probability. But this approach may result in handoff failure when all the channels of nearest AS are busy. Call transfer time is required when nearest AS has no free channels and call forwarded to second nearest AS [2] 419
III. PROPOSED SCHEME Here proposed a improved scheme which is the combination of above discussed schemes and overcomes the limitations of it. By using proposed scheme we can surely reduce the handoff call blocking probability as well as new call blocking probability. As we can see in the following fig.1 NCBPR (New call blocking probability reducing) using AS, here three AS are placed in the coverage area of main cell (MC), also we can see when MS moves from one cell to other cell it sets up the connection with base station. If all channels of the BS are busy then connection request is rejected. To reduce this call blocking probability AS will play main role. Instead of rejecting the connection request, that request is send to the AS for fixed amount of time in between it has to check availability of the free channels in the BS. If free channels are available then call will connect to BS and remove the connection from AS. In [6] if all the channels of AS are busy then request will send to next nearest AS till free channel get available with BS. When all the AS are busy then connection request will be rejected. To overcome this, in proposed algorithm we are allocating AS s according to call duration. For long duration call s one AS, for short duration call s one AS, and if both AS are busy and BS is also busy then we have to check RSS (received signal strength) of the MS. If RSS is weak and it is registered with adjacent cell then terminate that MS connection request from AS. If BS is busy and AS also have free channel available then AS can accept the incoming connection request. If AS for short duration call and long duration call both are busy and BS is also busy then connection request is handled by reserved AS for some amount of time. Reserved AS is used only when both short and long duration AS s channel are fully utilized. Fig.1. NCBPR using AS Assume 3 A.S, t time required by incoming M.S 1. M.S comes under M.C and want to connect with B.S 2. M.S send request to MSC for checking channel availability 3. If (c! =0), then connect to B.S Else CheckAS () to perform handoff a. If (t<=ti), connect M.S to ASi b. Else if ( t>ti), connect M.S to ASj 4. After fixed time interval check availability of free channels a. If (c!=0), connect to B.S and remove connection from A.S b. Else Check if (Aux(fully utilised)=yes and B.S(fully utilised) ) = yes Check if ( MS s RSS weak and registered with adjacent cell ) Terminate that M.S connection request from A.S Else if (RSS strong) Incoming connection request is handled by ASk 420
5. End IV. RESULTS AND DISCUSSIONS NS2.34 is a well known network simulator which is used here for simulation. We can see comparison of existing scheme and improved scheme through which we can understand how improved scheme is better than existing scheme. As shown in fig.2 NAM window, base stations are marked by red color, mobile stations are marked by green color and channels are shown by circles using different colors randomly. Fig. 2 Simulation of Mobile Nodes Fig.3 Comparison of Handoff_Count 421
Fig.4 Comparison of Call Blocked_Count As shown in Fig.3 and Fig.4 interval is taken as horizontal axis against which compared handoff count and new call blocked count respectively. We can see failure probability of existing and improved scheme also how improved scheme is better than existing scheme as shown in Fig.5 Fig.5 Failure Probability of Existing and Improved Scheme Through the results we can see how improved scheme is better than existing scheme. 422
V. CONCLUSION Proposed method is simple to implement and flexible to point diverse fields of implementation with the help of appropriate improvements and modifications. As the number of AS will increase the possibility of ping pong effect will also increase. Using proposed algorithm we can reduce handoff failure when all the channels of the nearest AS will be busy. Also call transfer time was required to move from one auxiliary station to other auxiliary station is totally removed. By using proposed algorithm your call will never get rejected, so call blocking probability is reduced. We can also improve the traffic distribution between AS and BS in future. Proposed method is flawless and effective for practical purposes. REFERENCES [1] Seema P. Mahalungkar, Santosh S. Sambare Survey of Call Blocking Probability Reducing Techniques in Cellular Network, IJSRP, Volume 2, Issue 12, December 2012 1 ISSN 2250-3153. [2] Seema P. Mahalungkar, Santosh S. Sambare Improved Call Blocking Probability Reducing Technique Using Auxiliary Stations IJSER, Volume 4, Issue3, March-2013 1ISSN 2229-5518odd page. [3] Abhijit Sharma, Deepak kumar Call Blocking Performance of New Reservation based Channel Assignment Scheme in Cellular IJCA Special Issue on 2nd National Conference- Computing, Communication and Sensor Network CCSN, 2011. [4] Saravanan Kandasamy, Prihandoko, Borhanuddin Mohd.Ali New Call Blocking Probability (NCBP) in Improved Adaptive Quality of Service (AdQoS) for Wireless Multimedia Communications using Hierarchical Cellular Approach 2003. [5] Rana Ejaz Ahmed, A Channel Allocation Algorithm for Hot-Spot Cells in Wireless Networks journal of advances in information technology, vol. 1, no. 3, august 2010 [6] Debabrata Sarddar, Shubhajeet Chatterjee Minimization of Call Blocking Probability using Auxiliary Stations International Journal of Computer Applications (0975 8887)Volume 25 No.7, July 2011 [7] Poonam B Bhilare Seamless handoff in Next Generation Wireless System (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 2 (6), 2011 [8] M.L.S.N.S. Lakshmi1 An insight to call blocking probabilities of Channel assignment schemes International Journal of Advances in Engineering & Technology, May 2012. [9] Jayshri Joshi, Girish Mundada A Hybrid Channel Allocation Algorithm to Reduce Call blocking probability using Hot-spot Notification [10] Moshe Sidi and David Starobinski New call blocking versus handoff blocking in cellular networks Wireless Networks 3. 1997 [11] Jon M. Peha and Arak Sutivong Admission Control Algorithms for Cellular Systems ACM/Baltzer Wireless Networks, 1999 [12] http://en.wikipedia.org/wiki/cellular_network. 423