The Personal Handyphone System (PHS) service was commercially launched in Japan in 1995. Today, more than 10 countries and regions have provisioned commercial PHS services.
PHS standardization activities were initiated by the Association of Radio Industries and Businesses (ARIB) and Telecommunication Technology Committee (TTC) of Japan. The PHS air interface was standardized in 1993 by ARIB, and the details are described in RCR STD-28 [1].
PHS uses Time Division Multiple Access / Time Division Duplex (TDMA/TDD) for radio channel access. PHS voice codec is 32-kbps Adaptive Differential Pulse Code Modulation (ADPCM) based on the ITU-T Recommendation G.726 [2]. The ADPCM compresses speech data without degrading speech quality. The PHS system is used for data transmission as well as speech communications. Modern PHS phone operators also support many value-added services such as high speed wireless data (64-kbps and higher), Internet connection, WWW access, e-mailing, text messaging, and color image transfer.
The PHS Common Air Interface (CAI) is standardized in RCR STD-28 [1], and its User-Network and Network-Network Interfaces (UNI and NNI) are defined in ITU-T Q-series standards [3]. The PHS Internet Access Forum (PIAF) was organized in July 1995 in order to promote PHS multimedia communications. The promotional works were inherited from the PIAF to Mobile Internet Access Forum (MITF) and then to the ARIB. The PIAF Standard (PIAFS) V1.0 was finalized in 1996, which is a data transmission procedure that supports 32-kbps unrestricted PHS digital bearer [4]. The 32-kbps unrestricted data transmission service was commercialized in Japan on April 1, 1997. In November 1997, the ARIB standardized RCR STD-28 V3.0 [1] to specify a data transmission procedure that supports
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64-kbps digital bearer. Accordingly, PIAFS V2.0 was enhanced to support 64-kbps unrestricted PHS digital bearer in October 1998. The current specification number is ARIB STD-T76 [4].
PABX: Private Automatic Branch eXchange PS: Personal Station
PSC: PHS Switching Center
PSTN: Public Switched Telephone Network
TE: Terminal Equipment
WAC: WLL/FWA Access Controller WCS: WLL/FWA Cell Station
WLL/FWA: Wireless Local Loop/Fixed Wireless Access WPS: WLL/FWA Personal Station
Figure 1. Network Configurations for PHS Service Domains
Figure 1 shows five PHS network configurations in public and private telecommunications service domains [5]. In this figure, Public Switched Telephone Network (PSTN) is a circuit-switched telephone network system designed to allow transmission of voice and data
over ordinary telephone copper wires. The PHS service domains connected to PSTN are described as follow:
z Public Digital Cordless Telephone (Figure 1 (1)) enables public wide area communications service with mobility. In this configuration the PHS Switching Center (PSC) is a digital switching system installed with PHS service software. The PSC connects the calls from the Personal Stations (PSs) to the PSTN through the Cell Station (CS). The CS interfaces with the PSC through a modified ISDN protocol that supports PHS-specific functions such as location registration, authentication, and handover. A PS communicates with the CS via the PHS air interface.
z Wireless Local Loop/Fixed Wireless Access (WLL/FWA) system (Figure 1 (2)) substitutes the existing telephone twisted pair to provide subscribers with telephone services. The WLL/FWA Access Controller (WAC) has a Local Exchange (LE) interface and a WLL/FWA Cell Station (WCS) interface. The WAC controls call connection, and performs location registration and authentication. The WCS communicates with WLL/FWA Subscriber Unit (WSU) and/or the WLL/FWA Personal Station (WPS) using the PHS air interface. The WCS is typically installed on the top of a pole or the roof of a building. The number of subscribers per cell can be increased by using multiple transceiver facilities of the WCS. The WSU converts signals between the Terminal Equipment (TE) and the WCS. In order to serve as a subscriber line to the telephone, a WSU includes features such as DP (Dial Pulse)/DTMF (Dual Tone Multi-Frequency signaling) transmission/reception and the generation of the howler/ringer. The WPS is a mobile subscriber terminal similar to the public PHS PS.
z Wireless Private Automatic Branch eXchange (PABX) system (Figure 1 (3)) provides office mobility and greater flexibility in the office environments. The digital wireless PABX system consists of PSs, CSs, and a digital PABX. The air interface between PSs and CSs complies with the PHS air interface standard. Mobility management functions
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such as location registration and authentication are installed in the PABX. The CSs can be directly connected to the PABX through the interface cards. Alternatively, the CSs and the PSs can be controlled by the PHS adapter that treats each PS as an ordinary extension line for the PABX.
z Home Digital Cordless Telephone (Figure 1 (4)) consists of PSs and a CS that provides cordless base unit function. PHS terminal mobility is an important concept of PHS. This concept enables the users to move seamlessly between public and private PHS services.
In the public environment, the PS can be a mobile terminal of the public PHS service. At home, the same PS can be an extension of a home digital cordless telephone. When the PS is within the range of both the public and the private systems, the PS can be paged from both systems.
z Transceiver (walkie-talkie) Mode (Figure 1 (5)) enables a PS to communicate directly with another PS without the involvement of the CS.
Based on the PIAFS, Figure 2 shows several types of PHS data terminals for the public digital cordless phone service domain. The Gateway supports interworking between the PSTN and the Internet, and converts the data packets between the PIAFS and the standard TCP/IP [6]
[7].
z In the integrated type (Figure 2 (1)), the telephone and the PIAFS functions are physically merged. The handset can also be connected to a TE to serve as a wireless modem.
z In the combined type (Figure 2 (2)), a PS without PIAFS is connected to a TE through a PIAFS adapter via, e.g., a cable with Universal Serial Bus (USB) interface.
z In the data-oriented type (Figure 2 (3)), a TE connects a built-in PHS module with PIAFS in a PC Card, a Compact Flash (CF) card, or a Secure Digital (SD) card.
z In the embedded type (Figure 2 (4)), the PHS module with PIAFS is built in a TE.
PS without PIAFS
Figure 2. PHS Data Terminal Types
Current PIAFS version supports 64-kbps data communications for PHS, which uses multiple 32-kbps channels simultaneously to provide high transmission speed. A standard PHS cell station supports 4 channels where 3 channels are used for voice and packet data, and the fourth channel is pre-assigned as the control channel. The packet data transmission service can also utilize the control channel when the control channel’s time slots are not occupied. In this way the radio frequency efficiency can be improved.
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PIAFS uses either PHS’s 32 or 64-kbps unlimited digital bearer and provides transmission control procedures (comparable to OSI reference model layer 2) for high quality data transmission. Data compression can be optionally selected when the parameters are set at the beginning of a communication session.
The PIAFS specifies inband negotiation and Automatic Repeat reQuest (ARQ) transmission control. Inband negotiation is the process of choosing one data-link protocol out of multiple data-link protocols through the occurrence of terminal negotiations before data-link establishment. ARQ transmission supports error control in layer 2 in the PHS communication phase. It requests only the error frames to be resent to improve the data transmission rate.
Figure 3 shows the PIAFS protocol stacks [7]. Figure 3 (1) is the integrated type data terminal and Figure 3 (2) is the combined type.
PIAFS
(2) PIAFS protocol stack of combined type data terminal PS
PIAFS
Physical
Figure 3. PIAFS Protocol Stacks
Global System for Mobile Communications (GSM) is a digital wireless network stand designed by standardization committees from major European telecommunication operators and manufacturers. The GSM standard provides a common set of compatible services and capabilities to all mobile users across Europe and several million customers worldwide.
General Packet Radio Service (GPRS) reuses the existing GSM infrastructure to provide end-to-end packet-switched services for bursty data applications such as e-mail and WWW.
GPRS also provides a smooth path to evolve from GSM to the third-generation mobile network [8].
In this thesis, we investigate the development of a GPRS/PHS dual mode handset which can process both radio access systems. Such dual mode handset will allow a user to enjoy the advantages of both PHS and GPRS networks. While PHS provides high-quality speech and high-speed data communication with low mobility, GPRS supports larger radio coverage and enhanced mobility.
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This thesis describes how to develop a GPRS/PHS dual mode handset architecture to support Internet applications such as Wireless Application Protocol (WAP) browser or e-mail on the GPRS platform, and to access the applications through GPRS or PHS bearer networks at a user’s choice. Users may switch the data service between the two systems depending on factors such as the cost, the data speed, or the signal strength. We choose the integrated type PHS data terminal (see Figure 2 (1)) to implement PIAFS. In this approach, a user may surf the Internet by WAP browser on the phone and by a computer via using the dual mode handset as a modem.