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Unlicensed spectrum has been utilized to open up additional capacity to support long-term evolution (LTE) service. LTE and wireless local area network (WLAN) Aggregation (LWA) is a perfect solution that satisfies this need. In 2017, Taiwan has deployed the first commercial LWA service. The deployed LWA network reuses and is nicely merged with the existing individual LTE and WLAN networks. To provide appropriate WLAN transmission bandwidth, the user equipment periodically measures the WLAN quality and reports the results to the eNB (the LTE base station). The eNB then decides if the transmission rate should be adapted. We investigate the performance of periodical reporting and then propose the enhanced event-triggered reporting to improve the performance of WLAN transmission rate adaption. We suggest how to select appropriate frequency to minimize the network traffic of periodical reporting. We also show that enhanced event-triggered reporting outperforms periodical reporting. Our solution utilizes the standard 3GPP protocols and does not modify the mobile phone's software.

As physical obstacles, vehicles have significant impacts on the efficient propagations of safety-related information in vehicular ad hoc networks (VANETs) by frequently obstructing the LOS links between transmitters and receivers. Obstructing effect will diminish the effective coverage of safety-related information and incur severe impact on road safety. However, this impact has not been addressed effectively. In this paper, we first present the definition of broadcast efficiency as the metric for quantizing the obstructing effect. We investigate the optimization issue for mitigating the impact of obstructing effect on the propagation of safety-related information and propose a graph theory-based optimization algorithm. For a distributed implementation of this optimization in VANETs, we further propose the maximum broadcast efficiency relaying (MBER) algorithm. MBER maximizes the effective coverage of information, meanwhile, meets delay and reliability constraints by incorporating broadcast efficiency and propagation distance in relay contention. Simulation results demonstrate that MBER promotes the effective coverage of safety-related information in VANETs with varying vehicular distribution.

Information dissemination in VANETs mainly focuses on, e.g., the propagation of cooperative awareness messages and decentralized environmental notification messages on the control channel. As vehicles advance toward higher automation levels, VANETs should support more complex traffic services, which generates the demand for the propagation of Internet Protocol (IP)-based information and service data in multichannel environment as specified by IEEE Standard for Wireless Access in Vehicular Environments (WAVE). Multisource propagation in the multichannel environments will incur multisource relay confliction (MRC) which leads to higher latency and lower information propagation speed (IPS). However, the problem of how to mitigate the impact of MRC and maintain high IPS has not been studied sufficiently. In this paper, we propose success probability based relay contention algorithm (SPRCA) for mitigating the impact of MRC under WAVE channel environments. SPRCA presents a vital metric, success probability, for each vehicle to determine whether to join the relay candidate set of certain source and execute relay contention algorithm. SPRCA explores both real time location information of vehicles and stochastic properties of vehicular distribution. We construct a theoretical model for analyzing the performance of SPRCA with a stochastic geometry-based approach and derive the properties of the performance of SPRCA. We further demonstrate the network performance and the practicality in dynamic VANETs of SPRCA through simulations with realistic traffic flow data.

Energy saving of small cells is an important issue for a mobile network deployed with a large number of small cells. These small cells are typically overlapped with macro cells. When the call traffic is light, a small cell enters the dormant mode to save energy. Therefore, its call traffic is directed to the overlapped macro cell. When the traffic load of the macro cell becomes heavy, the macro cell wakes up the dormant small cells to share the traffic load. It is a nontrivial task to wake up the “right” dormant cells. This paper proposes simple energy saving (SES), which is a simple yet novel scheme, to accurately wake up the dormant small cells. In a low-traffic environment, our scheme enables the small cells to quickly enter the dormant mode. When the macro cell is heavily loaded, it wakes up the dormant small cells to share its traffic load. Specifically, with 90% of energy saving in our scheme, a dormant small cell can be detected and reported to the macro cell in 1.3716 s. When the macro cell conducts the wakeup mechanism, with a probability of 0.9, more than 75% of the dormant small cells are not affected and can stay in the dormant mode. We also show that energy saving of the SES scheme is more effective when the macro cell covers a larger number of small cells.

The mobile ticket dispenser system (MTDS) allows customers to remotely draw tickets for service orders anywhere through a mobile handset. In our previous work, the MTDS was applied to a restaurant scenario in which both clerks and customers are patient, i.e., once a mobile ticketing (MT) customer remotely draws the ticket, his request can be served by the clerk when the clerk is available, regardless of when the customer arrives at the restaurant. In this paper, the MTDS is applied to a post office scenario in which the customers are patient, but the clerk is impatient since the original ticket drawn by the MT customer may be invalid if he/she does not arrive at the post office before his/her turn. In this case, the behavior of the MT customer is the same as the so-called in-person ticketing customer who needs to draw a ticket in person when he/she arrives at the service counter. We propose an analytical model to derive the probability that an MT customer misses his/her turn when he/she arrives at the post office. A discrete-event simulation model is developed to investigate the performance of the predicted time adjustment mechanism for the MTDS. We also use real data collected at a post office to observe the queuing behavior. Our study provides guidelines for arranging the time for an MT customer to arrive at the MTDS server.

The performance of single-segment short messaging service (SMS) (i.e., the message sizes are smaller than 140 octets) has been intensively investigated. On the other hand, multisegment messages (with sizes larger than 140 octets) are seldom evaluated in the literature. This paper proposes analytical models to study two transmission policies for multisegment short messages. We show how to improve the performance of multisegment short message delivery by selecting appropriate transmission parameters: the retransmission interval and the maximum number of transmissions. The proposed models are validated by measured data collected from the largest telecom operator in Taiwan over a period of six months. We provide useful guidelines to configure parameters for SMS transmission policy. Numerical examples showed that the performance can be improved by over 20% in terms of successful delivery ratio.

When a mobile operator migrates its network from the third generation (3G) system to Long Term Evolution (LTE), both 3G and LTE will coexist for a period of time. Since the 3G circuit-switched (CS) voice mechanism is more mature and available than that for the LTE Voice over Internet Protocol (VoIP), the operator may consider CS fallback (CSFB) as a solution for providing reliable voice calls. According to the 3G Partnership Project (3GPP) CSFB procedure, when a mobile user in the LTE network has an incoming or an outgoing call, the user equipment (UE) falls back from LTE to Universal Mobile Telecommunications System (UMTS). When the call is complete and released, the UE immediately returns to LTE. If the next activity for the UE is another voice call, immediately switching from UMTS to LTE may not be efficient. In this case, the UE has to perform another CSFB. To resolve this issue, we suggest delaying the returns to avoid unnecessary CSFBs, which is called delayed return (DR). Based on the measurements from the real UMTS and LTE networks, we develop an analytic model for investigating the performance of the CSFB with DR. This paper indicates that the DR scheme can effectively reduce the CSFB costs by up to 60%.

Telematics typically utilizes vehicle detectors and Global Positioning System (GPS)-based vehicle probes to compute the speeds of vehicles. When the detectors and the GPS probes are not available, vehicle speeds can be estimated by the cellular floating vehicle data technique, where the telecom network needs to spend extra effort to identify specific users and track their movements. This paper proposes the Speed Determination (SD) Algorithm, which uses standard statistics of telecom switches to compute the speeds of vehicles without extra effort in the telecom network. Simulation and field measurements indicate that the SD Algorithm can effectively report the vehicle speeds of two-way roads.

Existing mobile telecom operators allow subscribers to receive mobile phone services when they roam in other countries. However, call setup to an international roaming subscriber is indirectly routed through the home network of the subscriber, which results in the usage of two expensive international telephone trunks. In this paper, we propose a plug-in roaming gateway to avoid the international trunk connections. Our solution is especially attractive when both call parties are roamers.

Based on the basic principle of spread spectrum systems, this paper proposes a hybrid automatic-repeat-request (HARQ) scheme with interference mitigation for multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. The proposed hybrid media access control (MAC) and physical layer (PHY) design orthogonally spreads signals in the transmission domain to separate the desired signals from interferences. It not only improves the signal-to-noise ratio (SNR) but also suppresses intercarrier interference (ICI) and interantenna interference (IAI). Almost without increasing complexity, mathematical analyses and numerical simulations show that the proposed scheme outperforms the conventional Chase combining HARQ.

The IEEE 802.1X is utilized in mobile Worldwide Interoperability for Microwave Access (WiMAX) authentication. This procedure incurs a long delay in WiMAX handoff. To resolve this issue, this paper proposes a key caching mechanism to eliminate the nonnecessary IEEE 802.1X authentication cost in WiMAX handoff. This mechanism is investigated through analytic and simulation modeling. Our study indicates that the key caching scheme can effectively speed up the handoff process.

The 3rd generation partnership project (3GPP) Technical Specification 23.246 proposed the multimedia broadcast multicast service (MBMS) that efficiently multicasts multimedia content. During MBMS content transmission, data may be lost. Three file repair schemes were proposed to retransmit the corrupted MBMS data. However, these schemes may introduce extra data traffic or signaling overheads. This paper proposes the Reuse Bearer Service (RBS) file repair scheme to resolve this issue. We analyze the four file repair schemes by analytical models and simulation experiments. This paper shows that the proposed RBS scheme may significantly outperform the previously proposed schemes.

Mobile telecommunication services have become very popular recently, and many people bring mobile phones with them wherever they go. However, we observe that mobile phones can be modified to become remote microphones for eavesdropping. The eavesdropping technique only requires modifications to the mobile phone to be spied on and does not require any network changes. This paper describes mobile-phone eavesdropping and analyzes how serious it can be. Based on our study, we provide suggestions to avoid being eavesdropped upon.

Universal mobile-telecommunication system supports IP multimedia services through the IP multimedia core-network subsystem (IMS). This paper proposes a prepaid application server (PAS) to handle both the prepaid calls and messaging services in the IMS. When both voice and messaging are simultaneously offered, a potential problem is that the delivery of a message during a call may result in force-termination of that call due to credit depletion. To address this issue, we describe a strategy to determine if a prepaid message can be sent out during a call session. We propose an analytic model to investigate the performance of this strategy. This paper provides guidelines to select appropriate input parameters for the PAS

For the two-branch space-time (ST) block-coded direct-sequence code-division multiple-access (DS-CDMA) systems, the impacts of a time-varying multipath channel on the downlink transmission are analyzed. By considering the systems using the random binary spreading code (RBSC) and deterministic binary spreading code (DBSC), the effects of the multipath interference and multiuser interference are included in the analyses of the bit-error rate and bit-error outage. Also, for the performance analysis of the system employing the decision-feedback (DF) detector, the effect of error propagation is taken into account. It is known that enlarging the spreading factor can enhance the interference-rejection ability of a DS-CDMA system and, hence, can improve the performance. However, it also lengthens the symbol duration and, thus, stiffens the diversity penalty resulting from the channel variation within an ST-code-word duration. Thus, a moderate spreading factor should be chosen. In this paper, for the RBSC system using the simple-maximum-likelihood (SML) detector, we derive an optimum spreading factor that is optimum in the minimum-error-probability sense. Numerical results have revealed that the derived optimum spreading factor is a good estimate of the ones for the DBSC systems using the SML, zero-forcing, and DF detectors. Therefore, it is very useful for system designers in determining the system parameters

In a mobile telecommunications network, the period when a mobile station (MS) resides in a cell (the radio coverage of a base station) is called the cell residence time of that MS. The period between when a call arrives at the MS and when the MS moves out the cell is called the excess life of the cell residence time for that MS. In performance evaluation of a mobile telecommunications network, it is important to derive the excess life distribution from the cell residence times. This distribution determines if a connected call will be handed over to a new cell, and therefore significantly affects the call dropping probability of the network. In mobile-telecommunications-network simulation, generating the excess-life random numbers is not a trivial task, which has not been addressed in the literature. This paper shows how to generate the random numbers from the excess life distribution, and develop the excess-life random number generation procedures for cell residence times with gamma, Pareto, lognormal, and Weibull distributions. This paper indicates that the generated random numbers closely match the true excess-life distributions

Prepaid phone service requires a user to make payment before calling. In 2.5G or the 3G networks, a user may be engaged in multiple voice and/or data prepaid sessions at the same time. For such services, it is important to distribute appropriate amounts of prepaid credit units to simultaneously executed sessions of a user. By considering the universal mobile telecommunication system (UMTS) as an example, this paper studies the prepaid credit allocation for the prepaid sessions. To simultaneously accommodate more prepaid sessions for a user, we propose a credit reclaim mechanism called prepaid credit reclaim (PCR). Analysis and simulation experiments are conducted to investigate the performance of our mechanism. Our study indicates that PCR can significantly improve the performance of the prepaid mechanism.

In this paper, we propose a universal mobile telecommunications system (UMTS) and a wireless LAN (WLAN) interworking solution called WLAN-based general packet radio service (GPRS) support node (WGSN), which allows a UMTS/WLAN dual mode mobile station (MS) to access heterogeneous wireless services. To reduce the power consumption of an MS, most WGSN applications are not activated at the MS, and MS-terminated services, such as incoming voice over IP (VoIP) calls, are not supported. To address this issue, a push mechanism called session initiation protocol (SIP)-based push center (SPC) was implemented in the WGSN node. For an incoming call to an MS, the SPC utilizes the UMTS short message service to activate the SIP User Agent of the MS. We study the performance of the SPC. An analytic model is proposed to derive the expected number of lost calls during the activation period. The analytic results are validated against the simulation experiments. Our study quantitatively indicates how the SPC performance is affected by the activation time and the timeout period, and we also suggest how to select appropriate values of these two factors to optimize the SPC performance.

A multi-tier wireless system integrates the high-tier wireless systems and the low-tier wireless systems into a single system to provide the advantages of both tiers. Such a system is expected to provide better service (more service availability and more cost effectiveness to the users) at the expense of the extra tier-switching management. Examples of multi-tier systems include the interconnection network of a satellite communication network and a terrestrial cellular network, the integration of low-power systems such as wireless personal area networks and cellular systems, and the integration of higher mobility of cellular systems with low-mobility wireless local area networks. In such a system, mobility management is critical, because only when the location of a mobile user is known or tracked can the service quality for the user be guaranteed. In this paper, we study a few mobility management schemes for multi-tier wireless mobile networks under more realistic assumptions. Performance evaluation in terms of registration signaling traffic is carried out, and easy-to-use analytical results are obtained. It is also clear that for service availability, the two-tier system is better than the single one-tier system; we therefore study the probability that a call is forced to terminate in the single low-tier system because the low tier becomes unavailable during the call (such a call can be continued in the two-tier system).

GSM system provides measurements regarding the signal attenuations from serving and neighboring base stations for managing radio resources. This paper proposes a mobile location estimation based on differences of downlink signal attenuations, which yield circles along which the mobile may lie. Then, the curves intersect at the estimated mobile position. The proposed method does not require a known and accurate path loss modeling, reduces the impact of shadowing on location, and is capable of being applied in existing systems without hardware development. Performance simulations include environments involving different standard deviation and cross-correlation of shadowings, and different abilities to detect base stations. Simulations demonstrate encouraging performance with only three base stations being available in severe shadowing environments. Additionally, the results of driving measurement show that the proposed method outperforms the cell-ID method in a real GSM in urban Taipei.

Based on Alamouti code, Lee and Williams proposed two-branch transmit diversity block-coded orthogonal frequency-division multiplexing (TDBC-OFDM) systems, namely, space-time block-coded OFDM (STBC-OFDM) and space-frequency block-coded OFDM (SFBC-OFDM). However, they employed the simple maximum-likelihood (SML) detector, which was designed under the assumption that the channel is static over the duration of a space-time/frequency codeword. Therefore, STBC-OFDM/SFBC-OFDM suffers from the high time/frequency selectivity of the wireless mobile fading channel. In this paper, besides the original SML detector, three detectors proposed by Vielmon et al. are applied to improve the two-branch TDBC-OFDM systems. Additionally, assuming sufficient cyclic prefix, the performances of all systems in spatially uncorrelated time-varying multipath Rayleigh-fading channels are evaluated by theoretical derivation and computer simulation, as well. According to the derived bit-error rate (BER), we further derive the bit-error outage (BEO) to provide a more object judgment on the transmission quality within a fading environment. Numerical results have revealed that significant performance improvement can be achieved even when the systems are operated in highly selective channels.

In the universal mobile telecommunication system, the user equipment (UE) communicates with all cells in the active set through the air interface. Multiple radio links between the UE and the cells may reduce the transmission speed due to interference. In high-speed downlink packet access (HSDPA), only one serving cell is selected in the active set for high-speed downlink transmission. When the radio link quality between the serving cell and the UE degrades below some threshold, the best cell (in terms of the radio characteristics) in the active set is selected as the new serving cell and the UE switches from the old serving cell to the new serving cell. This action is referred to as frame synchronization. The frame-synchronization information may be delivered through more than one wireless transmission, which introduces long delay for the frame-synchronization process. In this paper, we propose an overflow-control scheme with module count for HSDPA, which guarantees that the frame-synchronization information is delivered through one wireless transmission and that when the UE switches wireless link to the new serving cell, no packet frames are lost.

Deregistration due to the departures of mobile users from their current visiting registration area may cause significant traffic in the wireless cellular networks. In this paper, we propose a hierarchical implicit deregistration scheme with forced registration in third-generation wireless cellular networks to reduce the remote/international roaming signaling traffic when home-location registers (HLRs), gateway-location registers (GLRs), and the visitor-location registers (VLRs) form a three-level database hierarchy. In this scheme, if a mobile phone arrives and the GLR/VLR is full, a random record is deleted and the reclaimed storage is reassigned to the new arriving mobile phone. When a call arrives and the callee's record is missing in the GLR/VLR, forced registration is executed to restore the GLR/VLR record before the call-setup operation proceeds. An analytic model is proposed to carry out the performance evaluation for the proposed scheme. Our results show that the proposed scheme not only reduces the local deregistration traffic between the GLR and the VLR, but also reduces the remote/international deregistration traffic between the HLR and the GLR, especially when the ratio of the cost of the remote/international traffic between GLR and HLR to the cost of local traffic between the VLR and the GLR is high.

The universal mobile telecommunications system utilizes a three-level location-management strategy to reduce the net costs of location update and paging in the packet-switched service domain. Within a communication session, a mobile station (MS) is tracked at the cell level during packet transmission. In the idle period of an ongoing session, the MS is tracked at the UTRAN registration area (URA) level to avoid frequent cell updates while still keeping the radio connection. If the MS is not in any communication session, the MS is tracked at the routing-area (RA) level. The inactivity counter mechanism was proposed in 3GPP 25.331 to determine when to switch between the three location-tracking modes. In this mechanism, two inactivity counters are used to count the numbers of cell and URA updates in an idle period between two packet transmissions. If the number of cell updates reaches a threshold K/sub 1/, the MS is switched from cell tracking to URA tracking. After that, if the number of URA updates reaches a threshold K/sub 2/, the MS is tracked at the RA level. The paper proposes analytical and simulation models to investigate the performance of the inactivity counter mechanism. Our study provides guidelines for K/sub 1/ and K/sub 2/ selection to achieve lower net costs of location update and paging.

Third Generation Partnership Project (3GPP) specification TR 25.950 proposed high-speed downlink packet access for the Universal Mobile Telecommunication System (UMTS). In this mechanism, an active set of cells is defined for every user equipment (UE) communication session. The cell with the best wireless link quality (called the serving cell) in the active set is selected for communication with the UE. When the wireless link quality of the old serving cell degrades below some threshold, a new serving cell in the active set is selected to continue the communication session. Our previous work proposed a high-speed downlink packet access (HSDPA) overflow control scheme with four frame synchronization algorithms to switch the serving cell, and formally proved the correctness of the scheme. We propose an analytic model to investigate the performance of these frame synchronization algorithms, and show how the user movement patterns affect the control message delivery costs of these algorithms.

In mobile communications networks, periodic location area update (PLAU) is utilized to detect the presence of a mobile station (MS). In the 3GPP Technical Specifications 23.012 and 24.008, a fixed PLAU scheme was proposed for the Universal Mobile Telecommunications System (UMTS), where the interval between two PLAUs is of fixed length. We observe that MS presence can also be detected through call activities and normal location area update (NLAU). Therefore, we propose a dynamic PLAU scheme where the PLAU interval is dynamically adjusted based on the call traffic and NLAU rate. An analytic model is developed to investigate the performance of dynamic and fixed PLAU schemes. This paper provides guidelines to select parameters for dynamic PLAU.

The mobile prepaid service has become an important mobile application with rapid growth of subscription rate. The most widely deployed prepaid solution today is the service node approach that deducts and updates the prepaid credit during a phone call. Implementation of the service-node approach may generate a large number of credit checks that significantly degrades the performance of a service node. We investigate how the number of credit checks affects the workload of the service node and the bad debt that a service provider may bear. We propose an analytic model to derive the optimal credit checking/updating frequency for the service node approach: The analytic analysis is validated against simulation experiments. Our study indicates that the number of credit checks increases rapidly when the call pattern is irregular. We also observe that in order to reduce the checking cost of the service node, the prepaid service provider should encourage the customer to make long calls by giving them discounts.

Based on the GSM radio architecture, the general packet radio service (GPRS) provides users data connections with variable data rates and high bandwidth efficiency. In the GPRS service, allocation of physical channels is flexible, i.e., multiple channels can be allocated to a user. We propose four algorithms for the GPRS radio resource allocation: fixed resource allocation (FRA), dynamic resource allocation (DRA), fixed resource allocation with queue capability (FRAQ), and dynamic resource allocation with queue capability (DRAQ). We develop analytic and simulation models to evaluate the performance for these resource allocation algorithms in terms of the acceptance rate of both GPRS packet data and GSM voice calls. Our study indicates that DRAQ (queuing for both new and handoff calls) outperforms other algorithms.

In this paper, we propose a new model for the portable movement in personal communications services (PCSs) networks. Based on this model with general interservice time and registration area residence time distributions, an analytic expression for the probability that a portable moves across K registration areas (RAs) is obtained. The busy-line effect on this quantity is also studied and an analytic expression is presented. The result given in this paper is very useful for cost analysis for location updating and paging.

This paper studies the soft-handoff mechanism and compares its performance with hard handoff. Our study indicates that although a handset may potentially consume extra radio links in soft handoff, the mechanism provides better opportunity to transfer the link successfully in the handoff procedure. Thus, by carefully planning the overlay areas of cells, soft handoff can outperform hard handoff.

Personal communication service (PCS) networks offer mobile users diverse telecommunication applications, such as voice, data, and image, with different bandwidth and quality-of-service (QoS) requirements. This paper proposes an analytical model to investigate the performance of an integrated voice/data mobile network with finite data buffer in terms of voice-call blocking probability, data loss probability, and mean data delay. The model is based on the movable-boundary scheme that dynamically adjusts the number of channels for voice and data traffic. With the movable-boundary scheme, the bandwidth can be utilized efficiently while satisfying the QoS requirements for voice and data traffic. Using our model, the impact of hot-spot traffic in the heterogeneous PCS networks, in which the parameters (e.g., number of channels, voice, and data arrival rates) of cells can be varied, can be effectively analyzed. In addition, an iterative algorithm based on our model is proposed to determine the handoff traffic, which computes the system performance in polynomial-bounded time. The analytical model is validated by simulation.

In a cellular phone system, the service area is partitioned into several location areas (LAs). Every LA is associated with a mobility database called visitor location register (VLR). When a mobile user enters an LA, the user must register to the VLR before receiving any cellular service. If the VLR is full, the registration procedure fails and the system cannot deliver services to the user under the existing cellular technology. To resolve this problem, we propose a VLR overflow control scheme to accommodate the incoming mobile users during VLR overflow. Our scheme only requires minor modifications to the existing cellular mobility management protocols. Particularly, no modification is made to the mobile phones. An analytic model is proposed to investigate the performance of the overflow control scheme. When exercising the scheme, the call setup procedure for an "overflow" user is more expensive than that for a "normal" user. Under the range of input parameters considered in our study, we show that even if the VLR overflow situation is serious, the overhead for exercising the overflow control scheme is very low.

Previous performance studies of PCS channel allocation assumed that call holding times have an exponential distribution. The exponential call holding time assumption is justified for existing cellular systems, where wireless calls are charged based on the length of the call holding time. Future PCS systems may exercise flat rate billing, and consequently a more general distribution is desirable to model the call holding times. This paper models the call holding times by the Erlang distribution (a generalization of the exponential distribution) to investigate the effect of the variance of the call holding times on the call completion probability. Our analysis indicates that the call completion probability decreases as the variance of the call holding times decreases. This effect becomes more pronounced as the variance of the cell residence times decreases.

It is predicted that by the year 2000, US cellular carriers will invest billions of dollars for cellular billing and customer care. Two of the most desirable attributes of the cellular billing systems are the flexibility of upgrade and the ability to inform the billing experts quickly about the status of the system to minimize any possible fraud and improve customer service. Although the second attribute can be realized by reporting the billing customer record in real time, this tends to congest the signaling channel, which is not desirable. We propose several schemes for the provision of a quick billing status report which maintains low-signaling traffic. The performance of these schemes is derived analytically. We expect that these results may provide a guideline for the future design of on-line billing systems in personal communication services (PCSs) networks.

Location tracking operations in a personal communications service (PCS) network are expensive. A location tracking algorithm called pointer forwarding has been proposed to reduce the location update cost. The key observation behind forwarding is that if users change PCS registration areas (RAs) frequently, but receive calls relatively infrequently, it should be possible to avoid registrations at the home-location register (HLR) database by simply setting up a forwarding pointer from the previous visitor-location register (VLR). Calls to a given user will first query the user's HLR to determine the first VLR, which the user was registered at, and then follow a chain of forwarding pointers to the user's current VLR. To reduce the "find" cost in call delivery, the PCS provider may distribute HLR databases in the network. This paper integrates the concept of distributed HLRs with pointer forwarding, and the new scheme is referred to as the pointer forwarding with distributed HLR (PFDHLR). Since no registration to the HLR is performed in the pointer forwarding scheme when a user moves to the new locations, the cost of updating multiple HLRs is eliminated in PFDHLR. Our study indicates that PFDHLR may significantly reduce the mobility management cost compared with the single HLR approach.

This paper studies three deregistration strategies (explicit, implicit, and timeout (TO) deregistration) for personal communication service (PCS) networks to determine the network conditions under which each strategy, gives the best performance. Two performance measures are considered: (1) the probability /spl alpha/ that a portable cannot register (and receive service) and (2) the number of deregistration messages sent in a strategy. For the same database size, /spl alpha/ is smaller for explicit deregistration (ED) than it is for TO or implicit deregistration (ID). On the other hand, ID does not create any deregistration message traffic. With an appropriate TO period, the deregistration message traffic for TO deregistration is much smaller than the traffic for ED. Suppose that there are N portables in a registration area (RA) on the average. To ensure that /spl alpha/

Two authentication schemes (ASs) have been proposed in the Electronic Industry Association/Telecommunications Industry Association's (EIA/TIA) Telecommunications Systems Bulletins (TSBs) 51 for incorporation in the cellular industry Interim Standard IS 41 Revision C. In the first scheme, which we refer to as the WS scheme, a unique secret key [also known as shared secret data (SSD)] is shared only between the authentication center (AC) and handset. In the second scheme, referred to as the S scheme, the SSD is also shared with the visited system. The performance of the two schemes can be compared by using the expected number of call originations/terminations between two consecutive registrations or call-to-mobility ratio (CMR). Based on the message flow (accesses to databases), it is apparent that the S scheme outperforms the WS schemes if the CMR ratio is large. The CMRs of users will likely span a wide range and, even for the same user, will perhaps vary from time to time. It is therefore desirable to switch between the ASs based on the users' CMR to reduce the signaling network traffic. We propose two adaptive algorithms to determine how and when to switch between the ASs for a given user. Our performance study indicates that as the CMR of a user changes, the adaptive algorithms automatically select the best AS in real time.

The cache scheme has been proposed to reduce the location tracking overhead of a personal communications services (PCS) network. In the previous papers, we studied the cache scheme under the assumptions that the home location register (HLR) access time is constant and the portable residence times have an exponential distribution. This paper compares the cache scheme with a basic scheme (such as IS-41). We generalize the previous models by considering the queueing effect of the HLR (i.e., we model the HLR by an M/G/1 queue) and by considering an arbitrary distribution for the portable residence times. Our study shows that the cache scheme is likely to outperform the basic scheme when (1) the net traffic to the HLR in the basic scheme saturates and the hit ratio in the cache scheme is larger than zero, (2) the portable mobility is low with respect to the call arrival rate, and (3) the variance of the HLR service time distribution is large (for a fixed mean service time). We also indicate an intuitive result that the cache hit ratio is high for a high call arrival rate and low portable mobility. For a fixed mean portable residence time, we show that a higher cache hit ratio is expected for a portable residence distribution with larger variance.

A new personal communications services (PCS) hand-off scheme is proposed. This scheme provides for hand-off to radio ports on which there is no free channel by "sub-rating" an existing connection. With sub-rating, an occupied full-rate channel is temporarily divided into two half-rate channels: one to serve the existing call and the other to serve the hand-off request. The blocking probabilities (combined forced terminations of existing calls and blocking of new call attempts) of this new scheme compare favorably with the standard scheme (nonprioritizing) and the previously proposed prioritizing schemes. The costs for this scheme are presented and discussed, as well as the additional procedural complexity of implementing on-the-fly sub-rating and the impact of continuing the conversation on a lower rate channel (which may lower speech quality of increase battery drain). Analytical models and simulations investigating the traffic impacts are presented, as are the results that show that even in the highest offered load considered a 3-min conversation in the busy hour experiences less than half a second of sub-rated conversation on average and only about 3% of the calls experience more than 5.12 s of sub-rated conversation. This scheme can increase capacity by 8-35% for systems with 1% call incompletion probability.

In a personal communications services system, it is required to locate the destination portable when an incoming call arrives. The author proposes a simple location tracking scheme called the T-threshold location cache scheme. In the scheme, a threshold T is used to determine whether a cached location record is obsolete. When the incoming call frequency changes, this scheme adaptively modifies the threshold to yield the best performance. An analytical model is proposed to study the T-threshold scheme. The analysis indicates that the T-threshold scheme effectively reduces the network traffic compared to the IS-41 scheme. >

The forced termination probability (the probability that a hand-off call is blocked) is an important criterion in the performance evaluation of personal communication service (PCS) networks. The forced termination of an ongoing call is considered less desirable than blocking the initial access of a new call. The paper proposes analytic and simulation models to study the performance of different channel assignment strategies for hand-off and initial access. The authors observe that giving priority to hand-off attempts over initial access attempts would dramatically improve the forced termination probability of the system without seriously degrading the number of failed initial access attempts. Some of the results are different from previously published results because the present models capture features not considered in those studies. >

Registration/deregistration is required in a PCS network when a portable moves between registration areas. Several schemes were proposed to deregister a portable after it moves out of a registration area (RA). A simple scheme called implicit deregistration totally eliminates network traffic due to deregistration. However, this scheme may delete valid registration records. Thus, the size of a registration database must be sufficiently large to ensure low probability that a valid registration record is deleted. This paper describes an analytic model to determine the size k of the registration database for an RA in the implicit deregistration scheme. If the expected number of portables in an RA is N, then our study indicates that good performance can be achieved if k/spl sime/5N. >