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White Paper T290i/T290c
32 October 2004
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.
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.