In a typical GPRS/PHS dual mode handset, the GPRS is the master part and the PHS is the slave part. In our implementation, the GPRS part is implemented by using MediaTek MT6228, which includes the WAP and the modem modules. The PHS part is implemented by using Toshiba TC35605, which includes Toshiba PIAFS605 as the PIAFS Module. Figure 4 shows the architecture of our dual mode handset. The master part (GPRS) uses basic AT commands to communicate with the slave part (PHS) via Universal Asynchronous Receiver/Transmitter (UART; see Figure 4 (e) and (f)). In the UART interface, we have defined the extension commands for the dual mode handset such as network registration, network signal feedback, and hardware control commands. The PIAFS data transmission between the master and the slave is defined in the extended AT commands.
PHS
Figure 4. Dual Mode Handset Architecture
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z In the master part, the Man Machine Interface (MMI; see Figure 4 (a)) includes the input/output devices and software such as keypad, LCD screen, ringing tone, and user interface software. It allows a user’s request to surf Internet on the GPRS or the PHS service domain, and sets the data path flow of the WAP Module (Figure 4 (b)) and the Modem Interface (Figure 4 (c)). The WAP Module includes the WAP protocol stack, the lower interfaces to the bear networks (GPRS and PHS), and the upper interface to the MMI. The Modem Interface can be Bluetooth and/or USB that connect to TE when the GPRS/PHS handset serves as a wireless modem. The GSM/GPRS Communication Module (Figure 4 (d)) controls the GSM/GPRS data call request, the data flow paths, and the protocol stack for communication with GSM/GPRS network.
z In the slave part, the PHS Communication Module (Figure 4 (g)) controls the PHS data call request, the data flow paths, and the protocol stack for communication with the PHS network. The PIAFS Module (Figure 4 (h)) is responsible for the PIAFS data packet transmission with PHS network via the PHS Communication Module.
z UART: The WAP and the Modem modules interact with the PHS part through the Master UART and the Slave UART (see path [(c) , (b)] ↔ (e) ↔ (f) ↔ [(g) , (h)] in Figure 4).
As a layer 2 protocol in the OSI reference model [4], the PIAFS supports Point-to-Point Protocol (PPP) [9]. Figure 5 illustrates the PIAFS layer and others layers implemented in our dual mode handset. Figure 5 (a) shows the WAP protocol stack based on PIAFS. Figure 5 (b) shows the modem protocol based on PIAFS. In both cases, UART is used to bridge the master and the slave parts of the handset.
Figure 5. WAP and Modem Protocol Stacks over PIAFS
In this thesis, we develop several extended AT commands between the master part and the slave part. Table 1 shows the format of the AT commands sent from the master part to the slave part. The details are described as follows.
z The ATD command initiates a voice/data connection. The parameter <number> specifies
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the called telephone numbers. If the phone number field is followed by a semicolon, then it represents a data connection. Otherwise it represents a voice connection.
z The ATH command terminates a connection.
z The ATA command answers an incoming call.
z The AT+CFUN command sets slave part functionality. The parameter <state> can be, e.g., power on/off or network registration.
z The AT+PC command sends a data packet to the slave part. The parameter <size> is the length of the binary data packet in bytes. The master part transmits the desired packet to the slave part after this command is sent.
Table 1. The AT Commands of the Master Part ATD<number>[;] <number>: Called telephone numbers
[;]: Exists if it is a data call
ATH No parameters
ATA No parameters
AT+CFUN:<state> <state>: Power on/off or network registration request
AT+PC:<size> <size>: The size of the user data packet in bytes following this AT command
When the slave part receives an AT command from the master part, it executes the instruction, and then returns an “indication” to the master part. The format of an indication sent from the slave part to the master part is the form AT+PIND:<type>,<parameter>,<extend> (see Table 2). Several extended command types are described below:
z “RSSI” indicates the radio signal strength from the CS. The <parameter> is the Received Signal Strength Indication (RSSI).
z “Incoming Call” indicates that there is an incoming call from the PHS service network. If
the caller does not hide the telephone number, the <parameter> shows the number.
z “Call Event” indicates a call event from the PHS service network. It can be “connect” or
“disconnect”.
z “PIAFS” indicates the PIAFS status events and data transmission. The <parameter>
specifies an event or data transmission. The parameter <extend> shows an event such as PIAFS communication “start” or “stop”, or the size of the binary data packet. The slave part sends the packet to the master part after this indication is sent.
Table 2. The AT+PIND Indication Format
<type> <parameter> <extend>
RSSI Received Signal Strength
Indication (RSSI) from the CS
None
Incoming Call
The telephone number of the calling party
None
Call Event “Connect” or “Disconnect” None
PIAFS Events PIAFS communication “Start” or
“Stop”
Data The size of binary data packet
Figure 6 shows how binary data packets is delivered through the AT commands. In this figure, the solid lines represent commands and the dash lines represent binary data delivery. The Master UART sends the packet size to the Slave UART before sending the desired data packet (see message (1), (2), and (3) in Figure 6). Similarly, the Slave UART indicates the packet size before sending the packet (see message (4), (5), and (6) in Figure 6).
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Slave UART
Master UART 1. AT+PC: size
2. OK
3. Binary data
5. OK
4. AT+PIND: PIAFS, data, size
6. Binary data
Figure 6. Data Flow between the Master Part and the Slave Part