Sony Ericsson T226 manual Network-dependent features, SMS and EMS messaging

Network-dependent features

SMS and EMS messaging

The T226 is capable of sending and receiving SMS and EMS messages, and linked messages.

•With the Short Messaging Service, a user can send text messages containing up to 160 char- acters to and from GSM mobile stations

•With the linked SMS, the user can link up to 10 SMS messages together to create a longer mes- sage (network-dependent service)

A Service Center (SC) acts as a a storage and forwarding center. SMS consists of two basic services:

•Mobile Originated SMS

•Mobile Terminated SMS

For Mobile Originated SMS, an SMS message is sent from a Mobile Station to the SMS-C where it is forwarded to its destination. This can be another Mobile Station, or a terminal in the fixed network.

A Mobile Terminated SMS is delivered when an SMS message is forwarded from the SMS-C to a Mobile Station. When the Mobile Station receives the message, it returns a delivery report saying the transfer was successful.

Fixed dialing and Restricted calls

For a company or an organization, it can be useful to restrict phone calls. Fixed dialing allows the user to preset a number of digits, for example area codes. This restricts the user to making calls only to numbers which use the preset digits as leading digits. Fixed dialing makes use of the PIN2, and requires fixed dial fields on the SIM card.

The Restrict calls service allows the user to block outgoing or incoming calls in certain situations, for example international calls.

TTY

TTY (Text Telephony) refers to the capability for hearing impaired people to trasmit and receive text messages using teletype devices (TTY devices). These devices are composed of a keyboard, display, and modem that transforms typed characters into TTY signals to be transferred over the phone network. The standard TTY signal in the U.S. is a 45.45 bit/s FSK signal called Baudot. Traditionally, TTY users have communicated over the analog PSTN network. In the U.S., however, the FCC mandated that as of June 30, 2002 digital mobile systems should also support TTY for emergency 911 calls. Unfortunately, the integrity of Baudot decreases in poor radio conditions, due to

T226 White Paper

July 2003 (Rev C)

signal compression. To get around this problem, the GSM standards body adopted a more robust modem signal called CTM (cellular text modem), as described in 3 GPP TS 26.226 “Cellular Text Modem; General Description”. According to the standard, the Baudot signal gets converted to CTM, and it is the CTM signal that gets transmitted over the air. In the infrastructure side, a CTM node converts CTM back to Baudot (or vice versa).

CTM/Baudot conversion on the T226 side takes place in an accessory that interfaces between the T226 (with TTY enabled) and the user’s TTY device.

EOTD

EOTD is part of the GSM R99 location services. The T226 supports EOTD to satisfy the FCC E911 positioning requirements. Although EOTD is supported, it may not be enabled.

EOTD determines position of the mobile phone by measuring the signal propagation delay between the phone and multiple base stations. The mobile phone knows which BTS’s to measure against based on assistance data contained in the Measure Position Request received from the network. Some BTS’s may even be below the reference sensitivity of the mobile phone (-110 dBm). Since neither the phone nor BTS has knowledge of absolute time, the mobile phone measures time delay by looking at the burst arrival time differences between each BTS and a reference BTS. This time difference is known as the observed time difference value (OTD). The BTS’s are not synchronized in a typical network, and suffer from clock drift. A special device in the network, known as an LMU, is used to measure the Real Time Difference (RTD) between each BTS and the reference BTS. The network takes the OTD values from the mobile phone, interpolates the RTD from the LMU at the measurement time (the LMU typically only measures each BTS once per minute), and uses the known location and height of each BTS to calculate the phone position. Because the network calculates the position of the mobile phone, the term “MS-assisted” positioning is used.

The T226 supports Network Induced Location Request (NI-LR) which means that the T226 will calculate OTD values when it receives a Measure Position Request from the network during emergency calls.

AMR

The T226 supports the Adapative Multi-Rate (AMR) speech codec, which is a GSM speech service specified in Release 98/99. AMR is significantly different from the existing GSM speech codecs (FR,

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