User's Manual

10 68P80801E35-A 9/1/2001
Base Radio EBTS System Manual - Vol 2
Generation 2 Single Channel 800 MHz Base Radio Overview
Generation2 Single Channel BR Theory of Operation
The BR operates in conjunction with other site controllers and equipment that are
properly terminated. The following description assumes such a configuration.
Figures 5 shows an overall block diagram of the BR.
Power is applied to the DC Power input located on the BR backplane. The DC
Power input is connected if -48 VDC or batteries are used in the site.
Power is applied to the BR by setting the Power Supply power switch to the ON
position. Upon power-up, the BR performs self-diagnostic tests to ensure the
integrity of the unit. These tests are primarily confined to the EBRC and include
memory and Ethernet verification routines.
After the self-diagnostic tests are complete, the BR reports any alarm conditions
present on any of its modules to the site controller via Ethernet. Alarm conditions
may also be verified locally using service computer and the STATUS port located
on the front of the EBRC.
The software resident in Flash Memory on the EBRC registers the BR with the site
controller via Ethernet. Once registered, the BR software is downloaded via
resident FLASH- or Ethernet and is executed from RAM. Operating parameters
for the BR are included in this download. This software allows the BR to perform
call processing functions.
The BR operates in a TDMA (Time Division Multiple Access) mode. This mode,
combined with voice compression techniques, provides an increased channel
capacity ratio of as much as 6 to 1. Both the receive and transmit signals of the BR
are divided into 6 individual time slots. Each receive slot has a corresponding
transmit slot; this pair of slots comprises a logical RF channel.
The BR uses diversity reception for increased coverage area and improved
quality. The Receiver module within the BR contains up to three receivers. Two
Receivers are used with two-branch diversity sites, and three Receivers are used
with three-branch diversity sites.
All Receivers within a given BR are programmed to the same receive frequency.
The signals from each receiver are fed to the EBRC where a diversity combining
algorithm is performed on the signals. The resultant signal is processed for error
correction and then sent to the site controller via Ethernet with the appropriate
control information regarding its destination.
The transmit section of the BR is comprised of two separate FRUs, the Exciter and
Power Amplifier (PA). Several PA FRUs are available, covering different
applications and power levels; these are individually discussed as applicable in
later subsections.
The Exciter processes the information to transmit from the EBRC in the proper
modulation format. This low level signal is sent to the PA where it is amplified to
the desired output power level. The PA is a continuous keyed linear amplifier. A
power control routine monitors the output power of the BR and adjusts it as
necessary to maintain the proper output level.