Showing papers by "Yi-Bing Lin published in 1994"

Queueing priority channel assignment strategies for PCS hand-off and initial access

Abstract: 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. >

A caching strategy to reduce network impacts of PCS

Abstract: We propose an auxiliary strategy, called per-user caching, for locating users who move from place to place while using Personal Communications Services (PCS). The caching strategy augments the basic location strategy proposed in existing standards such as GSM and IS-41, with the objective of reducing network signaling and database loads in exchange for increased CPU processing and memory costs. Since technology trends are driving the latter costs down, the auxiliary strategy will become increasingly attractive. The idea behind caching is to reuse the information about a called user's location for subsequent calls to that user, and is useful for those users who receive calls frequently relative to the rate at which they change registration areas. This idea attempts to exploit the spatial and temporal locality in calls received by users, similar to the idea of exploiting locality of file access in computer systems. We use a reference PCS architecture and the notion of a user's local call-to-mobility ratio (LCMR) to quantify the costs and benefits of using caching and classes of users for whom it would be beneficial. We also present two simple algorithms for estimating users' LCMR and the situation in which each is preferable. We show that under a variety of assumptions caching is likely to yield significant net benefits in terms of reduced signaling network traffic and database loads. >

Determining the user locations for personal communications services networks

Abstract: 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. >

Eliminating the boundary effect of a large-scale personal communication service network simulation

Abstract: Eliminating the boundary effects is an important issue for a large-scale personal communication service (PCS) network simulation. A PCS network is often modeled by a network of hexagonal cells. The boundary may significantly bias the ouput statistics if the number of hexagonal cells is small in a PCS network simulation. On the other hand, if the simulation is to be completed within a reasonable time on the available computing resources, the number of cells in the simulation cannot be too large. To avoid the inaccuracy caused by the boundary effect for a PCS network simulation with limited computing resources, we propose wrapping the hexagonal mesh into a homogeneous graph (i.e., all nodes in the graph are topologically identical). We show that by using the wrapped hexagonal mesh, the inaccuracy of the output measures can be limited even though the number of cells in the simulation is small. We can thus obtain the same statistical accuracy while using significantly less computation power than required for a simulation without cell wrapping.

Analyzing the trade off between implementation costs and performance: PCS Channel Assignment Strategies for Hand-off and Initial Access

Abstract: YI-BING LIN, SESHADRI MOHAN, AND ANTHONY NOERPEL ersonal communications is expected to provide low-power/high-quality wireless access to the public switched telephone network (PSTN) [4,5]. The service area of a network providing personal communications services (PCS) is populated with a large number of ports, with each port providing coverage in its vicinity. Each port is assigned a group of channels (time slots, frequencies, spreading codes, or a combination of these) that can be either fixed or dynamic. This article assumes a fixed or quasi-static channel assignment [9]. The results may be extensible to dynamic channel assignment schemes [lo]. When a subscriber wishes to make or receive a phone call, the portable attempts to seize an available traffic channel for the call. For some PCS radio systems, the portable launches an access request on a common signaling channel and is then directed to a traffic channel (CT-2 Plus [14]). In other PCS radio systems the access attempt can be made directly on an available traffic channel (DECT [8], or Bellcore WACS [l]’). Owing to the limited number of servers or transceivers in a port, when a port is blocked there is no idle transceiver for the signaling channel. There is usually no provision (either no channel or no protocol, or both) for a portable to signal the need for a traffic channel to a blocked port and therefore access attempts cannot be queued by the network. If there is no available traffic channel or common signaling channel, the call is blocked. (An exception to this is the WACS system, which reserves a time slot channel called the system broadcast channel.) If there is an available traffic channel it is used for the call. The channel is released eitherwhen the call iscompleted or the portable (or the PCS subscriber) moves out of the coverage area. When a user moves from one coverage area to another while a call is in progress, a hand-off to the new port is required to maintain continuity and quality of the call. If the new port does not have an idle channel, the call may be dropped o r forced terminated. The forced termination probability is an important criterion in the performance evaluation of a PCS network. Forced termination of an ongoing call is considered less desirable than blocking of a new call attempt. Radio tech-

Distributed simulation of large-scale PCS networks

Abstract: There has been rapid growth an demand for mobile communications over the past few years that has led to intensive research and development of complex PCS (personal communication service) networks. Capacity planning and performance modeling are necessary to maintain a high quality of service to the mobile subscriber while minimizing the cost. Simulation is widely used in such studies, however, because these models are extremely time consuming to execute, only small-scale PCS networks have previously been simulated. In this paper, we examine the use of the Time Warp distributed simulation mechanism in simulating large scale (1024 or more cells) PCS networks. An object-oriented, distributed, discrete event simulator using Time Warp has been developed, and initial performance measurements completed. Speedups in the range of 2.8 to 7.8 using 8 Unix workstations have been obtained, enabling simulation runs that require 20 hours on a single workstation to be completed in only 3.5 hours. >

Implicit deregistration in a PCS network

Abstract: 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. >

A non-blocking channel assignment strategy for hand-offs

Abstract: A new 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 (non-prioritizing) schemes and the previously proposed prioritizing schemes. The "costs" for this scheme are presented and discussed, as well as the additional procedural complexity to implement on-the-fly sub-rating, and the impact of continuing the conversation on a lower rate channel (which may have lower speech quality or increase battery drain). Simulation experiments investigating the traffic impacts are presented, as are the results which show that even in the highest offered load considered, a 3 minute conversation in the busy hour experiences less than half a second of sub-rated conversation on average, and only about 1% of the calls experience more than 30 seconds of sub-rated conversation. This scheme can increase capacity by 8% to 35% for systems with 1% call incompletion probability. >

Queueing channel assignment strategies for PCS hand-off and initial access

Abstract: The forced termination probability (the probability that a hand-off call is blocked) is an important criterion in the performance evaluation of the 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 a 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 previous published results because the present models capture features not considered in those studies >

A flexible graphical user interface for performance modeling

Abstract: We identify three goals for the graphical user interface (GUI) of a network simulation environment: user friendliness, model re-usability, and application extensibility. We address the user friendliness issue by proposing a simple yet efficient approach to setup parameters for the simulation models. We address the application extensibility issue by a two-layer GUI architecture. The two layers are loosely-coupled, and the first layer can be easily replaced (without affecting the other components of the simulation environment). We address the model re-usability issue by subnetworks. Unlike most existing simulation packages where subnetwork is simply a method to group the nodes, the subnetwork construct in our approach is an integral part of the simulation environment (i.e., all operations for a basic node also apply to a subnetwork). The port concept is used to explicitly define the I/O relationship between a subnetwork and the outside world. Parameter dialog boxes are used to set up the parameters for a subnetwork conveniently. Finally, a simple stack mechanism is proposed to measure subnetwork-wide output statistics. >

Implicit deregistration in a PCS network

Abstract: 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. 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. The 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 the study indicates that good performance can be achieved if k/spl sime/5N. >