Personal Communications Services Systems Research Articles

Handoff Optimization for Wireless and Mobile Networks using Fuzzy logic

The most important issue in Personal Communication Services (PCS) is the mobility management. And the efficiency of this PCS system is dependent on the maintenance of a reliable and optimal radio link between the mobile user and the fixed system. When the mobile user moves out of his coverage area, handoff is required to enjoy continuation of services. In this paper, a handoff algorithm termed as Fuzzy controller for Handoff Optimization (FCHO) is introduced based upon fuzzy logic. Traditional algorithms for handoff using fixed values of parameters can perform well only in specific environment but FCHO exploits attractive features of several existing algorithms, and adds more capabilities to provide adaptation to the dynamic environment. Simulation results reveal that the proposed FCHO algorithm eliminates the problem of corner effect by dynamically changing the value of threshold and hysteresis with the change in the RSSI and the velocity of the mobile station. General Terms Wireless Networks and Mobile Networks

TDMA for North American PCS systems

This paper compares the two time division multiple access (TDMA)-based North American personal communications services (PCS) systems (DAMPS-1900 and PCS-1900) by examining their logical channel structure, framing, modulation schemes, speech and channel coding, and system capacity. The contents of the paper should be helpful to PCS network planners and designers in choosing a TDMA system for their networks.

More efficient location tracking in PCS systems using a novel distributed database system

In personal communication services (PCS), the complete location information and subscribers' profiles are kept in a database called the home location register (HLR). Another database, the visitor location register (VLR), is used to store partial location information. When a mobile user is called, the system queries the HLR to determine the location of the called party. Distributed databases have been introduced to improve the efficiency of querying the HLR. This paper presents an alternative means of constructing a distributed database. The proposed database design employs fixed pointers to link distributed data. Each database contains a portion of the system's information as well as several pointers. The pointers identify the location of real data, enabling the system to obtain the required information efficiently. The database of the proposed design is markedly smaller than the fully distributed databases since each database of the proposed design stores only partial information. Subscriber information is stored only in one database, thus allowing a single database, rather than multiple databases, to be updated. The single update presented herein notably reduces the signal traffic load. If the caller is in the registration area of some HLR, which holds the called party's information, the response time is significantly decreased since the transactions are served only by the local database. This phenomenon is referred to as the calling locality. The proposed method effectively shares the database and the network loading that originates from several databases' tracking mobile users in a PCS system. According to the results presented, this method is highly effective for systems with a heavy load and high calling locality. The single update feature of the proposed design reduces the traffic in the signaling link and the processing load of a database. However, the proposed method includes no fault tolerance and therein differs from the fully distributed design.

Adaptive region-based location management for PCS systems

The personal communications services (PCSs) systems can provide ubiquitous and customized services. The key issue, which affects the performance of the whole system, is the location management. We propose a region-based location strategy by taking advantage of the user's movement behavior to improve the performance of the conventional systems. Each mobile user is associated with a set of regions, which are derived from the user's movement patterns. The registration processes in the same region can be eliminated such that the cost of location management can be significantly reduced. Several design issues are studied by considering the workload balance and the call-to-mobility ratio for a user. The proposed strategy can be dynamically adjusted based on different system parameters and user behavior. A performance analysis on the signaling cost and the database access cost is given to justify the benefits of this approach.

A Low Latency Handoff Algorithm for Voice over IP Traffics in the Next Generation Packet-Based Cellular Networks: Cellular Mobile IPv6

In the mobile communication environments, Mobile IP is defined to provide users roaming everywhere and transmit information freely. It integrates communication and network systems into Internet. The Mobile IPv6 concepts are similar to Mobile IP, and some new functions of IPv6 bring new features and schemes for mobility support. Two major problems in mobile environments are packet loss and handoff. To solve those problems, a mobile management scheme – the cellular mobile IPv6 (CMIv6) is proposed. Our approach is based on the Internet Protocol version 6 and is compatible with the Mobile IPv6 standard. Besides, it also combines with the cellular technologies which is an inevitable architecture for the future Personal Communication Service system (PCS). In this paper, {Cellular Mobile IPv6 (CMIv6)}, a new solution migrated from Mobile IPv6, is proposed for mobile nodes moving among small wireless cells at high speed. This is important for future mobile communication trends. CMIv6 can solve the problems of communication break off within smaller cellular coverage during high-speed movement when packet-switched data or the real-time voice messages are transmitted. Voice over IP (VoIP) packets were chosen to verify this system. The G.723.1 Codec scheme was selected because it has better jitter resistance than GSM and G729 in a packet-based cellular network. Simulation results using OPNET show smooth and non-breaking handoffs during high-speed movement.

An overview and analysis of mobile Internet protocols in cellular environments

Notes that cellular is the inevitable future architecture for the personal communication service system (PCS). This is important for wireless mobile communications and will eventually be integrated with the Internet. Recent initiatives to add mobility to the Internet and packet data services for the next generation cellular systems are being considered by many mobile service providers, and providing a seamless support for IP‐based packet switched services is an important issue. Mobile Internet Protocol version 6 (Ipv6) is a new version of the Internet Protocol that was standardized by the Internet Engineering Task Force (IETF). It supports mobility and is presently being standardized by the IETF Mobile IP Working Group. Discusses the current cellular support based on Ipv6 and points out the shortfalls of using Mobile IP. Highlights protocols especially for mobile management schemes which can optimize a high speed mobile station moving among small wireless cells.

The Design of Location Regions Using User Movement Behaviors in PCS Systems

The personal communications services (PCS) systems provide ubiquitous and customized services. The key issue, which affects the performance of the whole system, is the location management. Current systems group cells into location regions to reduce the location management cost which includes the location tracking cost and the registration cost. In this paper, by considering users' movement behaviors, four strategies are proposed to derive location regions. These strategies attempt to simultaneously reduce the location tracking cost and the registration cost. Simulations are performed to compare the performance of these methods with the existing strategies to show the superiority of our approaches.

Seamless Support for Mobile Internet Protocol Based Cellular Environments

Cellular is the inevitable architecture for the Personal Communication Service system (PCS) in the coming future. Access to the Internet via cellular networks is expected to become an essential portion of future wireless service offerings. Providing seamless support for IP based packet switched services has become an important issue.

The implication of the next-generation wireless network design: cellular mobile IPv6

The initiatives to add mobility to the Internet and packet data services for next-generation cellular systems are being considered by many mobile service providers. IPv6 is a new version of the Internet protocol that was standardized by the Internet Engineering Task Force (IETF). It supports mobility and is presently being standardized by the IETF Mobile IP Working Group. At the same time, cellular is an inevitable and developing architecture for the Personal Communication Service system (PCS). In this paper, cellular mobile IPv6 (CMI), a new algorithm that is migrated from mobile IPv6 is proposed for mobile nodes moving among small wireless cells at high speed. It is important for future mobile communication environments and should eventually, integrate its functions with the Internet. The purpose of this paper is to solve the problems of a communication break within smaller cellular coverage during high-speed movement with packet-switched data or the real-time voice messages. Thus, voice over IP (VoIP) packets were chosen to implement the system. Simulation results show smooth and non-breaking handoff during high-speed movement using the proposed algorithm.

Experiences with network-based user agents for mobile applications

Wireless networks are characterized by simple end devices and limited bandwidth. One solution to address these and other limitations of the wireless mobile environment that has been widely pursued is the placement of proxies, or agents, inside the network to assist with application processing that would normally take place on end devices. These agents can additionally manipulate data to reduce bandwidth requirements and assist in providing services. The design and implementation of a user agent is heavily impacted by the application it supports. In this paper we present our experiences with user agents in two different types of applications: telephony-based Personal Communication Services (PCS) and two-way messaging. To provide low latency service, the PCS user agents are mobile so that they may be kept close to their end devices. The design of the PCS agents limits migration overhead to the transfer of approximately 100 bytes of information in about 150 milliseconds. To provide advanced messaging services, the messaging user agent supports flexible messages while limiting air interface bandwidth usage. The messaging agents reduce uplink bandwidth usage by approximately 35% when applied to a cellular PCS system, and reduce message payloads by 97%.

Satellite systems for personal communications

A number of industrial groups are planning to construct satellite systems to provide personal communications services (typically voice, data, and fax) to users who will employ small, hand-held, cellular-type telephones. Some of these systems (e.g., Iridium and Globalstar) will be constructed using satellites in low Earth orbit. Two (Odyssey and ICO) will employ medium Earth orbit (six-hour period), and still others (ACeS and Agrani) will operate from geostationary altitude. The origin and evolution of mobile satellite communications is discussed first, including the INMARSAT system and several land-based mobile satellite systems in operation. The rival approaches to the personal communications services (PCS) market are then described, and some of the technical challenges inherent in each are indicated. The paper concludes with speculation on the factors influencing the likelihood of business success for the various PCS systems.

Calling for control

A cordless telephone system (or as it is sometimes called a low power personal communications services system) provides telephone services to moving users. The Cordless Telephone Second generation (CT2) is a digital cordless telephone system developed in Europe in 1989. The CT2 system provides high speech quality (32 kb/s speech rate) with low power consumption (the maximum transmit power is 10 mW). While the radio aspect of CT2 has been extensively discussed, the network aspect is seldom mentioned in the literature. This article introduces the CT2 call control procedures (specifically, call origination and call delivery) from the network aspect. We first describe the call control procedures for a private CT2 system in a company building. Then we describe the procedures for a public CT2 system.

A data request scheduling policy for PCS networks

This paper proposes a scheduling policy called latest preempted, earliest resumed (LPER) for personal communications services (PCS) systems that support voice services as well as the circuit mode data services. The policy gives priority to the voice services over the data services. The scheduling of voice requests is performed as if no data requests exist. Thus, if no idle channel is available when a voice request arrives, a data channel (if exists) is interrupted and the channel will be used for the voice request. The interrupted data request will be resumed when an idle channel is available. In LPER, the data channel selected for interruption is the one that serves the latest outstanding data request (i.e., other outstanding requests enter the system earlier than this request). When an occupied channel is released, LPER resumes the earliest request that entered the system. An analytic model is proposed to study the performance of LPER and provides guidelines to select the input parameters for the PCS systems.

Per-user profile replication in mobile environments: algorithms, analysis, and simulation results

We consider per-user profile replication as a mechanism for faster location lookup of mobile users in a personal communications service system. We present a minimum-cost maximum-flow based algorithm to compute the set of sites at which a user profile should be replicated given known calling and user mobility patterns. We show the costs and benefits of our replication algorithm against previous location lookup approaches through analysis. We also simulate our algorithm against other location lookup algorithms on a realistic model of a geographical area to evaluate critical system performance measures. A notable aspect of our simulations is that we use well-validated models of user calling and mobility patterns.

Phone number portability for PCS systems with ATM backbones using distributed dynamic hashing

Current cellular subscribers have a geographic phone number (e.g., in AMPS and US digital cellular systems) or a number which contains the network provider's identity (e.g., in GSM), and whenever subscribers register or receive (and possibly, originate) a call, a home location register (HLR) database has to be queried. The wired infrastructure supports a function called global title translation (GTT) that converts the subscriber's number to an HLR database address. A special feature of next generation wireless access service will be to support personal communication services (PCS) and wireless subscribers with portable personal numbers, or nongeographic phone numbers (NGPNs), that do not indicate the service provider or HLR database serving the user. In addition, the GTT function may not be available when the wired backbone is an ATM network. Thus a key function required in future wireless access systems with wired ATM backbones will be the ability to translate an NGPN to the identity of the HLR which serves the subscriber, a process we call NGPN translation. We discuss the requirements of NGPN translation and some alternative schemes. We propose two schemes for fast, efficient, scalable and flexible NGPN translation which use ideas of dynamic hashing, caching, and indirection. The schemes use a hash function in the visiting location registers (VLRs) (or serving SCP) and a set of distributed translation servers which store the NGPN-to-HLR mapping. We discuss how the operations required to maintain the translation information can be performed. Finally, we perform a simplified analysis of the scalability of the alternative schemes as well as the hash-based schemes we propose.

A narrowband approach to efficient PCS spectrum sharing through decentralized DCA access policies

This article addresses spectrum sharing and open access for personal communications services (PCS). Traditional regulation has allocated electromagnetic spectrum through fragmentation into mutually exclusive frequency blocks. Block allocation schemes produce trunking inefficiencies in the use of multiple narrowband RF channels. Broadband allocation schemes such as code division multiple access (CDMA) can accommodate multiple users on a single RF channel. Due to the near-far problem, the only way competing CDMA operators could share common spectrum is through collocation of cell sites, which hinders market mechanisms. An alternative approach is narrowband spectrum sharing through a decentralized dynamic channel assignment (DCA) approach, such as autonomous reuse partitioning (ARP). Multiple-operator DCA allocation schemes for low-tier PCS systems have been proposed in some countries. Under such an approach, competing operators use a common air interface to share the available spectrum. Open access can improve opportunities for competition in the provision of PCS. Other things being equal, a multi-operator DCA system outperforms that achievable by multiple carriers under a traditional fragmented spectrum, even for overlapping networks and unequal traffic loads. In this article we use a discrete event simulation to explore the spectrum efficiency implications of adopting a narrowband decentralized DCA/ARP spectrum-sharing policy. We explore as well regulatory measures so operators will deploy infrastructure instead of appropriating channels from competitors.

Performance of simulcast wireless techniques for personal communication systems

Broadband analog transport facilities using fiber or fiber/coax cable can play a significant role in the evolution of the network infrastructure for personal communications services (PCSs). Low-power PCS systems require a dense grid of radio ports to provide connectivity to the telephone network. Analog transport has a number of important advantages over digital transmission facilities, including the flexibility to support a variety of air interface formats, shared infrastructure cost with other services such as video distribution, and centralized call processing allowing the use of low cost and simple radio ports. A simulcast technique can be used in such systems to permit low rates of handoff (no handoff within each simulcast area) and sharing of hardware resources among multiple radio ports. This paper provides a detailed model and a simulation analysis of the cochannel interference and noise performance as well as the resource sharing benefit of a simulcast PCS system. Several potential PCS air interfaces are considered, including time division multiple access (TDMA) and code division multiple access (CDMA) techniques. Our investigation shows that the impact of multiple antenna noise in a simulcast system is offset by the improved signal-to-interference (SIR) ratio brought about by distributed antennas. Even with distributed antennas, multiple antenna noise places a limit on the maximum number of radio ports that can be assigned to each simulcast group. This limit, however, is shown to have little impact on the achievable resource sharing benefit of simulcasting (i.e., grouping beyond this limit has diminishing returns). A saving of 40% to 60%, in terms of the required central hardware resources, is typical for both TDMA and CDMA systems in suburban environments.

A comparison study of the two-tier and the single-tier personal communications services systems

A two-tier PCS system integrates the high tier PCS system and the low tier PCS systems into a single system to provide the advantages of both tiers. Such a system is expected to provide better service (more available and more cost effective to the users) at the expense of the extra tier switching management. We compare the performance of the two-tier PCS system and the single low tier system in two aspects: the registration traffic and the service availability. Because of the tier management, the two-tier system generates more registration traffic than the single low tier system. Under the range of the input parameters in our study, we show that the two-tier system generates less than 10cases and generates less than 20system is better than the single one tier system. We also study the probability that a call is forced terminated 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).

Heterogeneous personal communications services: integration of PCS systems

Personal communications services (PCS) are being introduced to offer ubiquitous communication. In its first phase PCS consists of a plethora of systems that address cellular, vehicular, cordless phone, and a variety of other services. The integration of these different systems is referred to as heterogeneous PCS (HPCS). We describe the various PCS systems available and address in detail the issue of PCS systems integration. Key implementation issues for integrating PCS systems are defined and discussed.

Intelligent network: a key platform for PCS interworking and interoperability

The Tl and TIA standards committees in the United States have worked jointly on the development of the first phase of personal communication services (PCS) standards, which were approved in December 1995. PCS systems based on these standards are currently under development. As these systems are deployed, the variety of wireless systems will grow, making interworking and interoperability a key challenge. This article provides an overview of PCS standards and explores how the different types of wireless systems (PCS and cellular) will utilize the capabilities of the intelligent network to provide seamless roaming.