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This article was published in the April 1997 issue of
IEEE Personal Communications.

ABSTRACT

 

Korea Telecom (KT), Korea's main telephone operator, is planning to launch PCS service in 1998, and is developing PCS systems with local manufacturers. This article describes KT's PCS marketing strategies, PCS network implementation directions, and the current status of system developments. In early 1996, prototypes of each network element are to be completed, which will be followed by testing and system integration. The PCS will not only open up a new market for KT; it will be a major revenue source. This KT-PCS will also be the basis for the next generation of wireless communications in the 2000s.

 

 

Current Status and Development Strategy of Personal Communications Services of Korea Telecom

 

Myung-Sung Lee, Won-Pyo Hong, Tae-Geun Kim, Yang-Ho Choi,
Kyung-Soo Lee, Yoon-Hak Bang, and Sang-Chul Lee
Korea Telecom

 

The telecommunication industry is going through environmental changes due to the vast trend of globalizing and opening the telecommunication market. In response, the Korean government is promoting competition and initiating privatization in the telecommunication market by restructuring the industry. The first restructuring occurred in 1994, in which the government officially announced its plan to introduce new services, such as PCS, into the market. Because the government is encouraging more intense competition in the mobile phone business, the technological development and commercialization of PCS are being expedited as a viable competitor against the cellular industry. Moreover, in the early stage of the development, the government is planning to select a company with the capability to establish an efficient communication network and expand the service base. In response to this movement, Korea Telecom (KT) is accelerating its PCS development. KT's objective is to pilot the service under the name KT-PCS (KT Personal Communications Services) in 1997–1998. About 250 million people worldwide are expected to subscribe to this kind of service by the year 2005, and KT is expected to make PCS one of its major business lines. In this article, the current status and future directions of the KT-PCS strategies and research and development (R&D) activities are described. The remainder of this article is organized as follows. In the second section, KT-PCS strategies are explained with respect to the key issues of service requirements. In the third section, PCS network implementation directions are explained, and the network architecture strategy to establish a cost-effective nationwide PCS network is illustrated. In the fourth section, the current status of system development and R&D activities are described. In the fifth section, other technical achievements are described. The final section summarizes the article.

KT-PCS Strategies

KT-PCS will take into account the demand of potential customers, economy of scale, and national competitiveness. The main PCS strategies are established on the three principles of ubiquity of service, profitability, and staged growth.
The PCS strategies need to be established through efficient and cooperative relationships among a number of related organizations within KT. It is expected that once the service launches, the PCS business will go through four major stages: preparation, introduction, growth, and maturity. The directions, objectives, and characteristics of each stage are described below.

Preparation Stage

This stage is to prepare for the commercial service, which requires completion of system development and network deployment followed by examination of the network reliability and stability through field trials and services. During this stage, the service trend of potential customers, including the usage pattern and call duration, also needs to be confirmed. Training and education of the network operation personnel as well as computerization of sales procedures will be also carried out.

Introduction Stage

At the beginning of commercial service, market take-off is expected to be slow. Therefore, the main goal at this stage is to help potential customers recognize the strength of the KT service by differentiating KT-PCS from regular cellular services, especially by emphasizing its low service charge and advanced services, such as the short message service and voice/fax mail. Furthermore, KT will also meet the needs of special business customers by providing special services for business applications.

Growth Stage

Once the strength of PCS is recognized, and consequently the acceptance and subscription rate increase, the market size is expected to grow significantly. In order to increase the market share and spread the service into every market sector, KT needs to broaden the customer base by providing nation-wide service in addition to developing a number of supplementary services.

Maturity Stage

During this stage, the significant increase of competition and subsequent slowdown of market growth will demand that KT prepare a transition strategy by providing global roaming and initiating wireless multimedia services. KT will focus its marketing strategy on raising current customers' usage rates and developing new markets, especially international markets. As for the former, KT will need to provide a variety of intelligent network services, high-speed data services, and advanced multimedia services by emphasizing the enhancement of advanced services in addition to low price.

KT-PCS Network Implementation

Principles of Network Deployment

The construction of the KT-PCS network will be carried out to meet the following requirements in order to meet the customer demands. First, from the service cost point of view, KT should build a network that can maximize the effectiveness of resource allocation by cutting down the facility cost and integrating/automating the operation procedures. This will enable KT to provide competitive services by minimizing the cost for implementing and operating the networks. Second, since an early establishment of the domestic service is urged, KT should take an approach of deploying and stabilizing the network at the earliest possible time. Third, the network should be capable of handling high traffic rates and, more important, should be expandable in order to maintain high quality of service. In other words, when the traffic increase is unexpectedly high, the addition of subscriber lines should be easily achieved. Furthermore, network redundancy should be established to ensure continuity of service. Since the air interface of KT-PCS is upbanded GSM (Global System for Mobile Communications), the voice quality will be that of GSM; therefore, KT-PCS plans to achieve a high quality of service with a well-planned and well-managed network.

Directions for Network Implementation

For the last two decades, KT has built a modern national telephone network through expanding the network into rural areas, lowering the tariff on long distance calls, and providing a number of new services. For instance, the transition from analog to digital trunked facilities and switching systems is complete. Furthermore, advances in telecommunications networks have been achieved by deploying TDX (Time-Division eXchange, a domestically developed switching system) digital switching systems and SS7 (Signaling System No. 7) signaling networks. Therefore, in order to make full use of current PSTN (public switched telephone network) facilities in establishing an efficient PCS network, the KT-PCS network will be integrated with the PSTN network. This will enable KT to quickly build a nation-wide PCS network and will also ensure the stability of the service. Moreover, this will lead to the efficiency and economy of the KT-PCS network during the growth stage of the service.
PCS Network Elements -- Figure 1 schematically shows a PCS network consisting of the PCX (personal communication exchange, the PCS switching system), PBC (PCS base station controller), PBS (PCS base station), and HLR (home location register) connected to PCX through an SS7 signaling network. Note that the PCS network is integrated with the PSTN network. In contrast to the other implementations where a PCS-1900 network works via a message switching center (MSC) to the PSTN, PCX handles MSC functions such as mobility management and PSTN switch functions. PCX executes a series of procedures associated with call control, including call setup/release, inquiry of subscriber information to the HLR, control of services, and billing. A group of PBSs will be connected to a PBC through DS1 (E1) transmission lines.
A Nation-Wide PCS Network -- Figure 2 illustrates a schematic diagram of a nation-wide PCS network showing the interconnection strategy between PCS networks of major cities, between PCS networks and PSTN, and between KT networks and other companies' networks. A call from a PCS subscriber will require a connection to a local exchange (LE) through the PSTN's toll or tandem switching systems. On the other hand, a call from the PSTN to a PCS subscriber will require toll or tandem switching systems to access and inquire for subscriber location information from the HLR. Then a call will be routed to the PCX where the subscriber is located.
In the early stage of PCS network implementation, a few PCXs (currently five) are planned to be deployed. Hence, a direct mesh interconnection among the PCXs is expected to provide an efficient and economical way of operating the network. However, when the number of PCXs expands beyond a certain level, an integration of the PCS network into the PSTN will be established by interconnecting PCXs through toll or tandem switching systems. This will enable KT to make full use of the intelligent network capability and existing transmission facilities of PSTN.
In addition, KT will provide other telecommunication operators with equal access to the KT-PCS network. In particular, the internal gateway system (IGS) has been used in order for other operators' networks to access KT's PSTN. The same IGS will be utilized for other wireless service providers such as regular cellular providers.
Since the Korean government has decided that CDMA technology will be used for digital cellular, KT-PCS needs to be able to operate with a CDMA cellular network. As KT-PCS will cover the whole South Korean territory, communication services will be provided seamlessly to KT-PCS subscribers, but roaming through a dual-mode terminal between KT-PCS and a digital cellular network may not be required initially. As KT-PCS matures, however, interoperability with various other cellular networks will be provided.

KT-PCS System Development

Directions of System Development

System development is underway with the aim that the capabilities of PSTN, ISDN (integrated service digital network), and IN (intelligent network) will be fully employed such that a reliable and economical network will be established, and therefore KT will be positioned to be able to provide low-cost ubiquitous wireless services of high quality. The main directions of system development are:
  • Develop a "total system" consisting of a PCX, PBC, an HLR, and a ROMS (radio operation and maintenance system).
  • Formulate joint development between KT and domestic system manufacturers, in which KT will play a major role in defining the system specifications and designing the basic architecture of each network element.
  • Use the basic architecture of the digital TDX-10 switching system for the design of PCX and PBC, leading to enhancing the competitiveness of the domestic system industry.
  • Develop a system capable of providing a variety of advanced services, including personal number (PN) service and short message services (SMS), by interacting with ISDN and IN.
  • Adopt the wireless access protocols of GSM-based PCS-1900 as the system's common air interface protocol between the PBS and personal station (PS).

Current Status of System Development

Recently, high-level system designs of physical and functional structures of all network elements, including the PCX, PBC, PBS, and HLR, have been completed under a joint development project between KT and local system manufacturers. A detailed plan for the low-level system design based on the mentioned implementation directions has been also laid out. In this section, development directions and current development status, especially high-level system designs, are described for each network element.
PCX -- Currently, KT and local system manufacturers are jointly developing a next-generation digital switching system named TDX-10 (ISDN/SSP, service switching point). This TDX-10 is the basis of the PCX; therefore, the PCX will be capable of handling PSTN, ISDN, and wireless calls. One of the key development directions of the PCX was that the VLR (visitor location register) be placed inside the PCX as a subsystem of the PCX. This decision was made by taking into account the cost and operation and maintenance efficiency.
Figure 3 shows the schematic diagram of the PCX structure illustrating three main subsystems: ASS (access switching subsystem), INS (interconnection network subsystem), and CCS (common control subsystem). The system has been designed to be able to accommodate more than 200,000 subscribers. The traffic-handling capacity is designed to be higher than 22,000 Er, which means that the average traffic per subscriber is assumed to be 0.06 Er (0.034 for originating and 0.026 for terminating). Each subsystem uses a 32-bit control processor with a main memory of 32 MB. The system has 128 SS7 signaling links. Each PCX is designed to accommodate maximum 15 ASS-W (ASS-Wireless) units, while each ASS-W can provide 960 (1 k) traffic channels.
The PCX performs the following functions:
  • Call control/management
  • Inter-PBC handover control
  • Supporting supplementary services: call forwarding, call transfer, call waiting, closed user group, multiparty call, and so on
  • Short message service
  • Billing
  • Operation and maintenance
  • SS7 link management
  • Control of VLR
PBC -- It is predicted that the main part of the PCS network will comprise small microcells the typical cell radius of which is estimated to be in the range of 400–600 m. The need to deploy microcells results from the forecast of high traffic demand, especially in a few major cities. Thus, it is expected that thousands of PBSs will be deployed nation-wide. As a result, it is very critical to design the PBC and PBS in such a way that most complex and intelligent functions are performed at the PBC, while simplifying the structure and function of the PBS as much as possible. The key design guidelines for the PBC have been modularity for capacity expansion and dual structure for secure reliability.
The PBC's key role is to manage allocated radio resources and to control all the PBSs connected to each PBC in all aspects. Figure 4 shows the schematic diagram of the PBC structure. It consists of two main subsystems: the RCIS (radio control and interworking subsystem) and the BMS (BSC management subsystem). RCIS is responsible for radio control and interworking functions, while BMS is responsible for system operation maintenance. The traffic capacity of each PBC is designed to be 960 traffic channels; thus, one PBC corresponds to one ASS-W unit of the PCX. The basic hardware of the PBC also utilizes that of the TDX-10 switching system. The system is designed to be modular such that the total capacity can be expanded up to 3920 traffic channels (4 k). TSU, one of the key components of RSIC, performs 64 kb/s time slot switching.
The functions the PBC performs are:
  • Radio resources management
  • Channel allocation and release
  • Down-/uplink power control
  • Inter-PBS handover control
  • Transcoding and rate adaptation
  • Discontinuous transmission control
  • Operation and maintenance of the PBC and related PBSs
PBS -- As we project that microcells and picocells will be deployed for outdoor and indoor uses, respectively, it is very critical to address the cost effectiveness and flexibility of PBS; hence, the system should be compact. On the other hand, when installed outdoors, it should be well packaged to maintain high performance under severe weather conditions. Moreover, the system needs to be so modular that the system capacity can easily be expanded by adding more RF (radio frequency) channels, and should be able to adopt new technologies of the wireless access protocol.
The system contains the following features:
  • Three sectorized antennas
  • Maximum number of TRXs (omni/sect): 8/24
  • Slow frequency hopping
  • Down-/uplink discontinuous transmission
  • Down-/uplink power control
Figure 5 illustrates the PBS structure consisting of five subsystems, including DDS (digital distribution subsystem), RTS (radio transceiver subsystem), and AAS. A more detailed block diagram of the AAS and part of the RTS is shown in Fig. 6. As mentioned earlier, the air interface protocol is based on that of GSM-based PCS-1900. Therefore, the RF channel spacing is 200 kHz, the modulation scheme is GMSK (Gaussian minimum shift keying), the coding uses RPE-LTP (regular pulse excitation -- long-term prediction), and FDD (frequency-division duplexing) is used. In designing the PBS, system reliability was given a high priority. The PBS has been designed to operate with decreased capacity or performance under a part of the subsystem failure by maintaining the independence between subsystems and duplicating critical subsystems such as TFS (timing function subsystem). The sectorized antenna will be employed when the cell planning warrants its use. The design of PBS, however, should be able to support the use of sectorized antennas.
HLR -- The HLR is the centralized database system to which all the PCXs are connected through an SS7 network. Its main functions include subscriber location information management, call control for supplementary services, subscriber authentication, and personal handset authentication. The downtime of the HLR system should be less than 3 min/year; thus, its reliability is critical to service quality. Moreover, since all the executions are carried out in real time, the system is designed to have a fully fault-tolerant structure.
The SMS (subscriber management system) handles subscriber registration, subscriber data management, and handset registration and data management, and is connected to the HLR though X.25. The SMS database is considered the master database, while the HLR database is considered as a slave to the SMS database. The separation of the HLR/SMS follows the principle that real-time operations related to call processing are processed at HLR, while non-real-time service management operations are processed at the SMS. This physical separation of HLR/SMS allows more flexible and reliable design.
Figure 7 shows the system architecture of HLR, consisting of two databases and several other subsystems. The MMDBS (main memory database system) stores service data requiring high-speed execution, whereas DBMS (database management system) is responsible for system operation management and maintenance. By adopting two separate databases, two main functions, service data control and operation management, are conducted on separate databases, which will minimize the effect of the operation and management tasks on the time-sensitive call processing tasks. This will speed up the service operation. The system is also designed to enhance the system flexibility and open architecture characteristics. Currently, the geographical redundancy structure is under consideration in order to increase its availability.
ROMS -- Network management is another important area in which KT can be significantly differentiated from competitors in terms of maintaining service quality and service reliability. The current plan is to construct two layer structures in establishing network management functions (i.e., the network management and network element management layers). ROMS, a system at the network management layer, is responsible for conducting operation and maintenance functions for the PCX, PBCs, and PBSs in the same location.
Figure 8 shows the hardware architecture of ROMS. The system platforms are as follows:
  • Hardware platform: RISC (reduced instruction set computer) computer, two to three redundant CPUs, mirrored disk storage (a few GB), and DAT (digital audio tape) drive
  • Software platform: UNIX, RDBMS (relational DBMS, e.g., SYBASE), SQL, X Windows, OSF/Motif user interface, Transmission Control Protocol/Internet Protocol (TCP/IP), and X.25 communication protocol
The ROMS executes functions with respect to the following areas:
  • Administration and control
  • Security
  • Operation and performance
  • Change
  • Maintenance

Other Technical Achievements

DECT-Based Small PCS System

Recently, KT has developed a small PCS system, a full system consisting of an SPCX (small PCX), an SPC (SPCX controller), a PBS, and a PS (personal station) (Fig. 9). The system employs DECT (Digital European Cordless Telecommunications) air interface protocol. The system is under operation as a trial system for indoor applications at KT's Wireless Communications Laboratory with the transmitting power level of 250 mW in the frequency range of 1880–1887 MHz. Certain valuable operation data are being collected, and eventually the system will be utilized for establishing the performance testing procedures of the PCS system.

MMICs

KT strongly supports R&D activities in the area of key components, including RF circuits and digital processing ASICs. In particular, some key GaAs MMIC (monolithic microwave integrated circuit) RF components are under development, which are expected to lead to considerable cost reduction of PSs (handsets). Figure 10 shows a photograph of an S-band (2–4 GHz) GaAs MMIC VCO (voltage controlled oscillator). An ion-implanted GaAs MESFET (metal-semiconductor field effect transistor) has been used as a transistor, an active device of the circuit. In addition to VCO, other RF components, including an LNA (low-noise amplifier), a mixer, and an HPA (high-power amplifier), are also under development.

Summary

It is a great challenge to launch a commercial service with high service quality at low service charges. For the last two decades, KT's main business has been concentrated on PSTN services, but at a considerable growth rate. The PCS will not only open up a new market opportunities to KT; it will also be a major revenue source. This KT-PCS will also be the basis of the next-generation wireless communications in the 2000s, as GSM provides a viable network model with proper improvements on a common air interface.

Note

Since this article was written, the Korean government has decided that the PCS service should employ CDMA technology. Since then, Korea Telecom has decided to follow Korean government policy. At the time of this writing (December 26, 1995), Korea Telecom has suspended its PCS-1900 system development, and is re-evaluating its PCS strategy and development plan. This article, however, describes the PCS-1900 system that Korea Telecom's Wireless Communication Laboratory has been developing. The authors, however, believe that this article still provides valuable information, particularly on KT's PCS service strategy and its PCS network architecture. Furthermore, there are still continued PCS-1900 system development efforts among Korean manufactures for the international market. Those PCS-1900 systems will be based on the architecture described in this article.

Acknowledgments

The authors wish to thank their colleagues at Korea Telecom's Wireless Communications Laboratory for their hard work in developing the architecture and high-level design of the KT-PCS system, and colleagues at the Korea Telecom Wireless Communication Business Group for useful discussions.

Additional Reading

[1] Korea Telecom Research Center, "KT-PCS PBC System Requirements," Aug. 11, 1995.
[2] Korea Telecom Research Center, "KT-PCS PBS System Design," Aug. 4, 1995.
[3] Korea Telecom Research Center, "KT-PCS HLR System Design," June 30, 1995.
[4] Korea Telecom Research Center, "KT-PCS System Protocol Description," Nov. 7, 1995.

 

References

Biographies
 Myung-Sung Lee is an associate professor at the Department of Computer Engineering of Sejong University, Seoul, Korea, where he is also director of the Center for Telecommunication Research. He was the managing director of Korea Telecom until February 1996, where he was in charge of the PCS Division. From 1986 to 1992, he was a member of technical staff at AT&T Bell Laboratories, working on architecture, performance and reliability analysis, and development of the SS7 signaling network and intelligent network. He received his Ph.D. in computer engineering from the University of Michigan, Ann Arbor, in 1986, and a B.S. in electrical engineering from Seoul National University, Korea, in 1977.
Won-Pyo Hong is managing director at the Korea Telecom Research Center, where he leads the PCS Division. His group currently works on wireless access technologies and system integration in preparation for PCS, planned to be launched in early 1998. Before joining Korea Telecom in 1994, he was at Bellcore, where he led a group in the area of high-capacity network R&D. He received his doctoral degree and M.S. from the University of Michigan, Ann Arbor, in 1987 and 1984, respectively, and his B.S. from Seoul National University, Korea, in 1983.
Tae-Geun Kim received a B.S. degree in electrical engineering from the University of Hankook Aviation and an M.S. degree in electrical engineering from the Korea Advanced Institute of Science and Technology, Korea, in 1981 and 1983, respectively. He received a Ph.D. degree in electrical system engineering from the University of Essex, England, in 1991. From 1983 to 1987 he worked for Korea Telecom in evaluating and planning of the digital switching systems. Since 1991, he worked in the R&D areas of Personal Communications Services which include the wireless switching system, network protocols and value added services.
Yang-Ho Choi received the B. S. degree in electrical engineering from Yonsei University in 1982, the M.S. and Ph.D. degrees in electrical engineering from Korea Advanced Institute of Science and Technology, Seoul, in 1984 and 1989, respectively. He has been employed at Korea Telecom since 1989. His research interests include wireless access technologies and adaptive signal processing for mobile communications.
Kyung-Soo Lee received the B. S. degree in electrical engineering from the Kyung-book National University, Korea, in 1986. He received the M.S. and Ph.D. degrees in electrical engineering from the Korea Advanced Institute of Science and Technology in 1988 and 1992, respectively. He is employed at Korea Telecom, where, since 1992, he has worked in R&D on wireless communications, including channel analysis, network protocols, and radio resource management.
Yoon-Hak Bang's biography was unavailable when this article went to press.
Sang-Chul Lee's biography was unavailable when this article went to press.