User's Manual Chapter 13

Chapter 7: Operational Description
AT&T Wireless Services
7-85
FCC Type Acceptance Application
10991 Rev. 1.0 7/6/99
users in known locations. In order to take advantage of this unique
relationship between the Base and multiple fixed users, each RU
employs a directional antenna and RF power control to minimize the
adverse effects of multipath propagation and reduce its contribution to
the overall interference environment.
RUs are situated at the subscriber’s location and serve as full-duplex
RDTs. Communication between the Base and the RU population
surrounding it may take place either as circuit-switched point-to-point
connections for telephony traffic or packet-switched point-to-
multipoint connections for high-speed data traffic. Each RU is capable
of supporting two simultaneous circuit-switched connections and a
concurrent packet-switched data link.
RUs are powered by an uninterruptible power supply (UPS) located
within the customer’s premises. The interface between an RU and the
customer’s existing telephone wiring is through a Network Interface
Device (NID) located on the exterior of the premises. The telephony
interface between the RU and the customer’s equipment is compliant
with the specifications set forth in Bellcore TR-57.
During the installation of an RU at the customer premises, the installer
utilizes a special Field Installation Tool (FIT) to obtain signal quality
information for each proposed mounting location on the structure.
Through the use of this tool, the installer can often select a mounting
location agreeable to the customer while optimizing the propagation
path between the RU and its serving Base.
7.1.4 PWAN Airlink Profile
The PWAN system is based upon the Open Systems Interconnect (OSI)
model depicted in Figure 7.2—. Subsequent sections in this chapter
will provide an overview of this model as it applies to the PWAN
airlink, and subsequent chapters will provide more detailed information
concerning the unique design aspects of the physical layer.