Fixed dialling and Restricted calls, Eotd

Fixed dialling and Restricted calls

For a company or an organization, it can be useful to restrict phone calls. Fixed dialling 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 dialling 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.

EOTD

EOTD is part of the GSM R99 location services. The T290i/T290c 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, inter- polates 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 T290i/T290c supports Network Induced Loca- tion Request (NI-LR) which means that the T290i/ T290c will calculate OTD values when it receives a Measure Position Request from the network during emergency calls.

White Paper T290i/T290c

AMR

The T290i/T290c supports the Adapative Multi- Rate (AMR) speech codec, which is a GSM speech service specified in Release 98/99. AMR is signifi- cantly different from the existing GSM speech codecs (FR, HR, and EFR) in that it offers multiple speech and channel codec rates rather than a fixed ratio. Both half and full rate channel types are defined for AMR. Eight codec rates are defined for the full rate channel and 6 for the half rate.

AMR offers capacity advantages over the standard GSM speech codecs in two ways. First, the half rate mode exhibits significantly improved quality as compared with the existing HR speech codec. Use of the AMR half rate mode would double the number of users that can use a given frequency and, correspondingly, increase the network capac- ity without the need for added infrastructure or bandwidth. A secondary benefit of the half rate mode is that the talk time of the mobile phone would be increased due to the reduced duty cycle of the transmissions.

Second, the rate adaptability indirectly offers a potential increased capacity with regards to the cell repeat pattern of the system. Poor channel quality could be made acceptable by changing the AMR rate to have more channel coding. As a result, lower C/I ratios can be tolerated in the system. By allowing for a lower C/I ratio, a tighter re-use pat- tern may be used which increases the system capacity.

32	October 2004