User's Manual Part 1

ADCP-75-187 • Preliminary Issue 1B • November 2005 • Section 1: OVERVIEW
Page 1-7
© 2005, ADC Telecommunications, Inc.
3 SYSTEM FUNCTIONS AND FEATURES
This section describes various system level functions and features of the Digivance system.
3.1 Fiber Optic Transport
In a typical Digivance LRCS system, the HU is connected to the RU over two single-mode
optical fibers. One fiber is used to transport the forward path optical signal. The other fiber is
used to transport the reverse path optical signal. Because the optical signal is digital, the input
and output RF signal levels at the HU or the RU are not dependent on the level of the optical
signal or the length of the optical fiber. A diagram of the fiber optic transport system for a
typical Digivance LRCS system is shown in Figure 1-7.
Figure 1-7. LRCS System Fiber Optic Transport - Typical
The maximum length of the optical links is dependent on the loss specifications of the optical
fiber, the losses imposed by the various connectors and splices, and the RF modulation protocol
response timing limitations. The basic system provides an optical budget of 25 dB (typical)
when used with 9/125 single-mode fiber.
In SCS applications, the forward path and reverse path optical signals from an HU/RU pair are
combined onto a single optical fiber. This is accomplished by using a passive bi-directional
Wavelength Division Multiplexer (WDM) system. The optical wavelengths used in the
Digivance system are 1550 nm for the forward path and 1310 nm for the reverse path. Because
different wavelengths are used for the forward and reverse paths, both signals can be combined
on a single optical fiber. A WDM module (accessory) is installed with the HU at the host site
The SCS RU, which is equipped with an internally mounted WDM, is installed at the remote
site as shown in Figure 1-8.
Figure 1-8. SCS System Fiber Optic Transport with Wavelength Division Multiplexer
HOST UNIT
18526-A
REMOTE
UNIT
FORWARD PATH
REVERSE PATH
FIBER OPTIC
LINK
20721-A
HOST UNIT
REMOTE
UNIT
FORWARD AND
REVERSE PATH
WDM
WDM
FIBER OPTIC LINK