User Manual

Demand Assignment
System Overview GSI 002
605-0000-450
Draft Issue 1.3dr Date 8/02/00
Page 17 of 16
7.2. Demand Assignment
The “Demand Assigned” Radio interface makes a temporary call by call assignment of
channels, to Subscriber Terminals in residential telephony applications, where the per
line traffic allows the provision of Graded Service. The radio interface differs in that
links are allocated as either Traffic, or Control channels.
1 to N
STs
OAM
Channel
Expansion
TCHs
RF1 to 4
3.5 MHz
RW12
RW13
RW1 - 160 kbit/s
RW2 - 160 kbit/s
RW3 - 160 kbit/s
RW4 - 160 kbit/s
RW5 - 160 kbit/s
RW6 - 160 kbit/s
RW7 - 160 kbit/s
RW8 - 160 kbit/s
RW9 - 160 kbit/s
RW10 - 160 kbit/s
RW11 - 160 kbit/s
RW14 - 160 kbit/s
RW15 - 160 kbit/s
Traffic
Channels
(Pool)
Priority
Calls
Call
Control
RW3 - 160 kbit/s
144 kbit/s 16k
64 kbit/s 64 kbit/s
32k 32k 32k 32k
16k
16k
System Capacity
(per RF)
10-13 x 144kbit/s
20-26 x 64kbit/s
40-52x 32kbit/s
Figure 7. Demand Assigned Air-Interface Structure
Within each RF channel, a pool of traffic channels supports a mix of 32, 64, and
144kbit/s services. Pool management is dynamic so channels may be made available as
32, 64, and 144kbit/s on demand. The size of the traffic pool is automatically and
dynamically sized based on radio interface performance and the grade of service
requirements thus controlling the level of access noise. The pool can be extended if the
interference level permits, or reduced if access noise is too great. The DA access
protocol can also support one or more priority channels that allow guaranteed access
for emergency calls. The channels allocated to traffic are pooled and configured as
either 10 - 13 x 144kbit/s, 20 - 26 x 64kbit/s, or 40 - 52 x 32kbit/s. Two links are
reserved for OAM and Call Control.
Each link operates using a master RW code to provide a 160kbit/s channel. These links
are then sub-divided using 2
nd
level RW codes that allow the construction of 2 x
80kbit/s or 4 x 40kbit/s smaller granularity links, while maintaining the same Spectral
Density. Hence Traffic Channels (TCH) are composed of either 160kbit/s, 80kbit/s or
40 kbit/s links.
STs maintain communication with CT via the Call Control link, using an “Ethernet” like
protocol. All STs are continually polled, and receive regular downloads of available
TCHs and their channelisation (i.e. 144kbit/s, 64kbit/s or 32kbit/s).