User's Manual Chapter 13

Chapter 7: Operational Description
AT&T Wireless Services
7-101
FCC Type Acceptance Application
10991 Rev. 1.0 7/6/99
7.2.5 PWAN Voice Traffic Channel (VTch) Functional Description
The Voice Traffic channel (VTch) provides a circuit-switched airlink
connection between the Base and an RU for the duration of the call.
Each RU is capable of supporting up to two simultaneous VTch
connections.
Each base is capable of supporting between 60 and 92 VTch
connections per sector. The exact number of VTch resources available
can be provisioned by Base and is dependent upon the size of the high-
speed data service partition. At a minimum, all Bases will be
provisioned for high speed data services as shown in Figure 7.13—,
where 32 FTRs are dedicated to the data service, leaving 92 resources
available for voice traffic. Heavy data traffic loading in some cells may
call for the Base to support additional data resources. In such cases, the
Base may be provisioned to support two high-speed data service
partitions (64 FTRs), leaving 60 resources available for voice traffic.
VF traffic, which appears as 64 kbps PCM to both the Base and RU, is
compressed to a 16 kbps data stream using Low Delay-Codebook
Excited Linear Prediction (LD-CELP). The LD-CELP bit stream is
mapped into data symbols for transmission over the airlink using either
16-QAM or QPSK modulation.
The Radio Management Entity (RME) maintains and accounts for FTR
utilization. The Base RME may allocate FTRs that are independent in
time to maintain the RU Effective Isotropic Radiated Power (EIRP)
budget. Regardless of the type of modulation in use, it is not necessary
for the downlink and the uplink FTRs to be paired.
7.2.5.1 Associated Control Channel Functional Description
The Associated Control Channel (ACC) is a small (10%) partition
within the VTch data frame which serves as the primary airlink
signalling channel for voice traffic call processing. This channel exists
only after a voice traffic channel has been established between the Base
and the RU. In addition to airlink signalling, the ACC can also be used
to support channel management functions such as power control and
active delay compensation. Other undefined services are possible over
the ACC as well.