Effect of MT s Power ON/OFF State Management on Mobile Communication Networks Based on IS-41

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1 Effect of MT s Power ON/OFF State Management on Mobile Communication Networks Based on IS- un Won Chung, Min oung Chung y, Sun Jong Kwon, and Dan Keun Sung Dept. of EE, KAIST, 7- Kusong-dong usong-gu, Taejon 5-7, Korea y ETRI, 6 Kajong-dong usong-gu, Taejon 5-5, Korea ywchung@cnr.kaist.ac.kr Abstract This paper presents two mobile terminal s (MT s) power ON/OFF state management schemes, that are designed to reduce the cost of failed call attempts. Performance comparisons between the two schemes and the conventional Interim Standard - (IS-) at radio interface, signaling network, and database (DB) are analyzed based on the modeling of MT s power ON/OFF state transitions. Result shows that management of MT s power ON/OFF state information in visitor location register/home location register (VLR/HLR) yields good performance and the performance of each scheme is closely related with the MT s power ON/OFF state transition characteristics. I. Introduction Mobility management is one of key issues in mobile communication. Mobility management usually requires location, routing, and state information. Location information includes mobile users current location area identities (LAIs). Routing information contains the addresses of mobile service switching center (MSC) and temporary addresses such as temporary local directory numbers (TLDNs) in IS- and mobile station roaming numbers (MSRNs) in Global Systems for Mobile (GSM), and is used to setup calls to destination MSCs from origination MSCs. State information includes the current state of MTs, i.e., either busy or idle, in which the idle state can be further divided into reachable (power on) and unreachable (power ) substates. This state information can be stored in VLR or HLR in an appropriate manner. Several efficient mobility management strategies were proposed to reduce network signaling load and call setup delay [] - [5]. These previous studies usually focused on the efficient management of location and routing information to improve the performance of mobile communication networks assuming that MT s power state is always on. However, in real personal communications services (PCS) environments, many MTs would be turned due to short battery life time, unwanted incoming calls, and undesirable subscriber behavior [6] and the probability that a mobile user s terminal is may be significant in today s system [5]. Therefore, although a mobile terminated call occurs and all the base transceiver stations (BTSs) in mobile user s current LA broadcast paging signals through the forward control channel (FOCC), they cannot receive any response from MT. This results in a failed call attempt. According to Lee et al. [7], [8], paging traffic is a major contributor of the FOCC bottleneck problem and failed call attempts cause to make the problem worse. In addition, failed call attempts waste network path reserved from origination MSCs to destination MSCs during the call setup procedure. However, if MT s power state is efficiently managed in the network, the FOCC bottleneck can be alleviated and the waste in the network path can be reduced. Concerning about the works dealing with MT s power state information, Meier-Hellstern et al. [9] assumed that the probability that MT is in power state is.5 and used it to calculate the number of call originations in some area. Markoulidakis et al. [] considered various state types of MT, such as switched on, switched, busy, and idle and analyzed a periodic attachment scheme to detect the MT switched state. However, they did not consider detachment requests occurring when the state of MTs is changed from on to. Since no detachment request is sent to the network when an MT is switched,themt s power state is considered to be on until network finds that the MT is in state by periodic attachment. Therefore, if any incoming call to the MT occurs in that period, network makes an attempt to connect this call to the MT but results in the waste of FOCC and network path. Kim et al. [6] assumed two mobile user types. The first type is that the MT s power state is always on. The second type is that the MT s power state is on only in case of making a call. Then, they computed the ratio of active mobile users and analyzed signaling traffic load. However, previous studies mentioned above are not sufficient to show the effect of MT s power ON/OFF state management on mobile communication networks. In this paper, two MT s power ON/OFF state management schemes are proposed to investigate the effect of MT s power ON/OFF state management on mobile communication networks and the performance is evaluated after modeling the power state transition of MT. The rest of this paper is organized as follows. In section II, a PCS environment is introduced and IS- call setup protocols are explained. In Section III, MT s power ON/OFF state management schemes are proposed. MT s power ON/OFF state transition is analyzed in Section IV. Some numerical examples are given in Section V and conclusions are given in Section VI. II. PCS Environments And IS- Call Setup Protocol A PCS network architecture is consiedred to employ VLR/HLR based techniques, as shown in Fig. [5]. It consists of three zones: s current zone, s current zone, and s home zone, in which and denote mobile users. In each zone there is a pair of VLR/HLR to store mobile user s temporary and permanent data, respectively. Each mobile user has a permanent home zone and a temporary visiting zone. Mobile user s location information is stored in his/her HLR and routing information is stored in his/her current VLR. Each MSC manages calls from/to mobile users located in the MSC area. Each MSC area is divided into several LAs and each LA consists of a group of cells. The LA and the cell are assumed to be both square-shaped. VLR has LAIs of all the users currently located in its zone and upon arrival of an incoming call setup request, a paging request is sent to all the BTSs

2 START Wireline Network MSC. MSC. VLR/ HLR MSC. MSC. MSC. VLR/ HLR [q] Is in 's Zone? Zone : 's current zone Zone : 's current zone es No [-q] Base Trsnsceiver Station Mobile service Switching Center [t] Is in 's home? MSC. MSC es VLR/ VLR/ HLR HLR Zone : 's home zone Fig.. PCS network architecture Visiting & Home Location Register es [s] No [-t] Is in His Home Zone? in the LA corresponding to the LAI of the terminating mobile user. Calls are originated and terminated through radio interfaces with base transceiver stations (BTSs) which manage all the radio resources. The following assumptions Mobile user is currently located in zone ; Mobile user has home zone and is currently located in zone ; Mobile user makes a call to ; Only a mobile-to-mobile call is considered. The following notations are introduced to analyze the effect of the relationship between zone and on the performance of MT s power ON/OFF state management schemes: q : Probability that and are in the same zone; s : Probability that is in his/her home zone; t : Probability that is in s home zone. Let Z i (i =; ; ; ) denote the probability that the relationship between zone and belongs to case i. Fig. shows four cases of the relationship and the Z i can be calculated by using the parameters q, s, andt. IS- [] is considered as a reference call setup protocol. Fig. shows an IS- call setup procedure. When originates a call to, a local lookup is initiated at s own VLR (VLR) for s routing information. If there is no s routing information, VLR sends a query to s home HLR (HLR). Then, HLR requests s routing information to s current VLR (VLR) and VLR delivers this request to the s MSC. If is not busy, the MSC allocates a TLDN to the call and returns the TLDN to VLR. VLR also returns the TLDN to HLR and HLR sends the TLDN back to VLR. VLR gives the TLDN to s MSC and a call setup to s MSC is established using the TLDN. In this call setup procedure, a network path from s MSC to s MSC is reserved. Then, s MSC sends a paging request to all the BTSs in s current LA and BTSs broadcast paging signals through FOCC to find the user. If there is a response from, s MSC sends acknowledgement to s MSC and the call setup is completed. If does not respond to the page request, the call setup fails. III. MT s Power ON/OFF State Management Schemes Mobile call setup protocols such as IS- and GSM require to reserve network paths irrespective of the MT s power ON/OFF state. If there is no paging response from MT, network determines that the MT is in power state or out of range and releases the network path. This results in waste of network path and radio resource. However, if network can manage MT s power ON/OFF states, this waste can be avoided. Therefore, two MT s power Fig.. Four relationships of zones between a caller and a callee 7 Zone : 's current zone No [-s] Zone : 's home zone Fig.. IS- call setup procedure Zone : 's current zone ON/OFF state management schemes are proposed, and the effect of the two schemes on mobile communication networks is analyzed. We compare the performance with the conventional IS- scheme without managing MT s power ON/OFF state. We explain each management scheme in the following sections. A. Scheme Network does not manage MT s power ON/OFF state. Therefore, when a call is terminated to a mobile user, network follows the general IS- call setup procedure, as showninfig.. B. Scheme Network manages MT s power ON/OFF state in the VLR of MT s current zone. When a MT s power state is changed from to on, the MT sends an attach request to its associated VLR and receives acknowledgement from the VLR. When the MT s power state is changed from on to, the MT sends a detach request to its associated VLR and there is no acknowledgement in this case. Fig. shows a failed call attempt procedure in scheme. In this scheme the VLR of the s current zone has the information that is in state. Therefore, when the VLR receives a routing information request, it sends s state information to s HLR. When s HLR receives this information, it returns this information to s MSC and s MSC informs that is in state. C. Scheme Network manages MT s power ON/OFF state in both the VLR of MT s current zone and the HLR of MT s home zone. In this scheme attach and detach requests are sent

3 G : LA residence time * n 6 time Zone : 's current zone Zone : 's current zone LA enterance time LA departure time 5 Power on request Incoming all arrival Power request Fig. 6. Timing diagram of the state change of an MT Zone : 's home zone Fig.. Failed call attempt procedure in scheme Zone : 's current zone Zone : 's home zone Zone : 's current zone Fig. 5. Failed call attempt procedure in scheme to the VLR/HLR whenever MT s power state is changed. Fig. 5 shows a failed call attempt procedure in scheme. In this scheme, the HLR of the s home zone has a information that is in state. Therefore, when s HLR receives a location information request, it sends s state information immediately to s VLR instead of sending a routing request to the s VLR. IV. Modeling of MT s Power ON/OFF State Transitions MT s power ON/OFF state transitions are modeled during mobile user s LA residence time. There are four MT s power ON/OFF state transition cases when a mobile user enters and leaves an LA. As an example, there is a case where a mobile user enters and leaves the LA with the MT s power on state. In order to analyze the MT s power ON/OFF state transition, the following assumptions The state of an MT is changed according to an alternating renewal process; A mobile user enters an LA at time ; Incoming calls to a mobile user occur as a Poisson process with parameter. The following notations are also made: time instant of a mobile user s departure from an LA. number of transitions from the on state to the state of an MT during mobile user s LA residence time. number of transitions from the state to the on state of an MT during mobile user s LA residence time. Mobile user s LA residence time. on duration of MT. duration of MT. t Non! N!on G The state of an MT can be modeled as an alternating renewal process []. In the case where a mobile user enters an LA in the on state at time, Fig. 6 illustrates a timing diagram of the state transitions of an MT. It is initially in the on state and will remain in the on state for a time duration, the residual life time of. The state undergoes a transition to the state and will remain in the state for a time duration. It is then changed into the on state for a time duration, and so forth. A renewal is assumed to occur when the state of an MT is changed from the state to the on state. Let F and F denote the distribution of n and n, respectively. Under the condition that a mobile user enters the LA in the on state at time and the mobile user leaves an LA in the on state at time t, the conditional probability that n renewals occur during (;t] and that the MT is still in the on state at time t is given by: PrfN(t) =n; on state at time tjon state at time ; G= tg =PrfV n + Wn t<v n + Wn+jon state at time ; G= tg =PrfV n + Wn tjon state at time ; G= tg, PrfV n + Wn+ tjon state at time ; G= tg = F Vn+WnjG (t), F Vn+W n+jg(t); () P P n where V n = i= i, W n = + n i= i,andn (t) denotes the number of renewals occurred during (;t]. Let S on,on (t) denote the sum of durations during (;t] in the above case. Suppose that a mobile user enters an LA in the on state at time and leaves the LA at time t. The conditional probability density function of S on,on (t) under the condition that n renewals occur during (;t] and that the MT is still in the on state at time t is given by: g(n; s; t) = f V njg (s) [F WnjG (t, s), F W n+ j G (t, s)]: () Themeanvalueofthesumof durations during mobile user s LA residence time is given by: on,on g = Z n= Z t The mean number of renewals is given by: EfN on,on g = Z n n= s g(n; s; t)ds dfg(t): () Z t g(n; s; t)ds dfg(t): () The mean number of transitions N on,on on! (t) N on,on!on and (t) from the on state to the state during (;t] and from the state to the on state during (;t], respectively, are the same as the mean number of renewals given in Eq.(). Similarly, the probability density functions of duration during (;t] and the mean number of transitions for other cases can be obtained. The mean value of the sum of durations is obtained as the weighted sum of mean values of durations for all cases. g = + on,on g + on, g Pon,on g +, g P ; (5)

4 where P on and P denote the mean probability that an MT is in power on and states at any instant, respectively and are given by the following equations: Pon = P = Efong Efong +Efg ; (6) Efg Efong +Efg : (7) The mean number of failed call attempts in unit time N FCA is given by: EfNFCAg = g ; (8) EfGg where denotes the incoming call arrival rate to a mobile user. The mean numbers of transitions in unit time N on! and N!on from the on state to the state and from the state to the on state are obtained as: + EfN on! g = hh i EfNon! on,on g +EfNon, on! g P on h i i EfNon!,on g,+efn, on! g, P = EfGg; (9) hh i EfN!on g = EfN!on on,on g +EfNon,!on g P on h i i + EfN!on,on g +EfN,!on g P = EfGg: () Finally, if a mobile terminal is in the on state when the mobile user enters or leaves an LA, there is a location update/cancellation and the mean number of location update/cancellations in unit time N LUC is given by: EfNLUC g = P on + PonP + P Pon : () EfGg V. Numerical Evaluations For numerical evaluation, the following procedures are considered: failed call attempt, attach, detach, and location update/cancellation. In each procedure, different messages at radio interface, signaling network, and DB are required in each scheme. At radio interface, paging request uses much more radio resources than other radio access requests because paging request is sent to all the BTSs in one LA and is broadcast through FOCC. In signaling network, signaling messages between network entities in the same zone are neglected and only signaling messages between different zones are considered. Call path setup and other signaling messages are separately considered because in call path setup, network resource such as bearer circuit is used and this results in more cost than other network signaling. In DB, number of query/update messages are considered. For numerical evaluations, the following notations CR cost on the radio interface due to one message exchange between MT and BTS. CS cost on the fixed network due to one message exchange between zones. CD cost on the DB due to one query/update message. Cpaging weighting factor of paging on CR. weighting factor of call path setup on CS. Cpathsetup Parameter TABLE I INPUT PARAMETERS Value q 8 s t 8 :5 calls=hour hour hour hours In the above notations, C paging is equal to the number of cells in one LA and it is assumed that one LA consists of n n cells. Let R i;j;k denote the cost at radio interface, where i is the case of relationship between zones, j the scheme, and k the procedure considered. For example, R ;; is C R + C paging C R. In a similar way, S i;j;k and D i;j;k denote the cost in signaling network and DB, respectively. Let CR j, CS j,andcd j be the total cost at the radio interface, signaling network, and DB in scheme j, respectively and can be obtained as: CRj = CSj = CDj = k= i= k= i= k= i= ZiRi;j;kEk; () ZiSi;j;kEk; () ZiDi;j;kEk; () where E k (k = ; ; ; ) correspond to EfN FCA g, EfN on! g, EfN!on g, and EfN LUC g, respectively. It is assumed that the distribution of mobile user s LA residence time, G, on duration of MT,, and duration of MT, follow exponential distributions with parameters,,and, respectively. Table I shows input parameter values referred from references [5], [6], [] for numerical evaluations. Fig. 7 shows the cost ratio of schemes and to scheme at the radio interface for varying the ratio of to on duration when the mean values of on duration are hour, hours, and hours, respectively. In this figure, the values of C R and C paging are set as and 6, respectively. Schemes and have the same cost at the radio interface and it decreases as the ratio of to on duration increases and it increases as the mean value of on duration increass. In all ranges of the ratio of to on duration considered, schemes and have smaller cost than scheme. This shows that management of MT s power ON/OFF state can reduce the waste of radio resources and alleviate the FOCC bottleneck problem. Fig. 8 shows the cost ratio of schemes and to scheme at the radio interface for varying the number of cells in an LA. The cost ratio decreases as the number of cells in the LA increases. From this figure, if the number of cells in the LA is approximately more than, management of MT s power ON/OFF state can yield better performance in all the ratios of to on duration from. to.

5 Cost ratio at the radio interface Schemes, (on = hour) Schemes, (on = hours) Schemes, (on = hours) Cost ratio in the signaling network Scheme (on = hour) Scheme (on = hour) Scheme (on = hours) Scheme (on = hours) Scheme (on = hours) Scheme (on = hours).. Ratio of to on duration Fig. 7. Cost ratio at the radio interface for varying the mean value of on duration.. Ratio of to on duration Fig. 9. Cost ratio in the signaling network for varying the mean value of on duration Cost ratio at the radio interface No. cells in LA = 6 No. cells in LA = 6 No. cells in LA = 6 No. cells in LA = Cost ratio in the DB Scheme (on = hour) Scheme (on = hour) Scheme (on = hours) Scheme (on = hours) Scheme (on = hours) Scheme (on = hours). Ratio of to on duration Fig. 8. Cost ratio at the radio interface for varying the number of cells in LA Fig. 9 shows the cost ratio of schemes and to scheme in the signaling network for varying the ratio of to on duration when the mean values of on duration are hour, hours, and hours, respectively. In this figure the values of C S and C callsetup are set at and, respectively. Scheme has better performance than scheme in all ranges of the ratio of to on durations and does not experience a large variation in the cost ratio for varying the ratio of to on duration and the mean value of on duration. On the contrary, the cost of scheme significantly changes for varying the ratio of to on duration and it decreases as the mean value of on duration increases. However, schemes and yield better performance than scheme in most ranges. Fig. shows the cost ratio of schemes and to scheme in the DB for varying the ratio of to on duration when the mean values of on duration are hour, hours, and hours, respectively. In this figure, the value of C D is set at. From the viewpoint of DB processing, scheme yields better performance than other schemes in the low range of ratio of to on duration. VI. Conclusions Two MT s power ON/OFF state management schemes are proposed and the performance is evaluated in terms of cost at the radio interface, signaling network, and DB based on the modeling of MT s power ON/OFF state transitions. Result shows that management of MT s power ON/OFF state in VLR/HLR yields better performance than other schemes in the parameter values considered. We also show that the performance of each scheme is closely related with the MT s power ON/OFF.5. Ratio of to on duration Fig.. Cost ratio in the DB for varying the mean value of on duration state transition characteristics. As a further study, two schemes are further evaluated based on the real field data of MT s power ON/OFF state transition characteristics. References [] I. F. Akyildiz et al., Movement-Based Location Update and Selective Paging for PCS Networks, IEEE Trans. Veh. Technol., vol., no., pp , Aug []. B. Lin, Reducing Location Update Cost in a PCS Network, IEEE Trans. Veh. Technol., vol. 5, no., pp. 5 -, Feb [] A. Hac, and. Zhou, Locating Strategies for Personal Communication Networks: A Novel Tracking Strategy, IEEE J. Select. Areas Comm., vol. 5, no. 8, pp. 5-6, Oct [] C. L. I et al., PCS mobility management using the reverse virtual call setup algorithm. IEEE/ACM Transactions on Networking, vol. 5, no., pp. -, 997. [5]. Cui et al., Efficient PCS Call Setup Protocols, Infocom 98, pp , 998. [6] K. S. Kim et al., Analysis of Power Up and Down Registration in CMS, ICUPC 95, pp. 9 -, 995. [7] H. C. Lee and J. Sun, Mobile Location Tracking by Optimal Paging Zone Partitioning, ICUPC 97, pp. 68-7, 997. [8] H. C. Lee and J. Sun, Multilayered Model Strategy for Optimal Mobile Location Tracking, PIMRC 97, pp. 9 -, 997. [9] K. S. Meier-Hellstern et al., The use of SS7 and GSM to support high density personal communications, ICC 9, pp.698-7, 99. [] J. G. Markoulidakis and M. E. Anagnotou, Periodic Attachment in Future Mobile Telecommunications, IEEE Trans. on Vehicular Technology, vol., no., pp , Aug [] M. D. Gallagher, and R. A. Snyder, Mobile Telecommunications Networking With IS-, McGraw-Hill, 997. [] S. M. Ross, Stochastic processes, John Wiley & Sons, 98.