User's Manual

385700-1006-006 OPERATIONS
Document use is restricted to that described on cover 4-1
CHAPTER 4
PRINCIPLES OF OPERATION
4.1 FUNCTIONAL DESCRIPTION OF EQUIPMENT
4.1.1 MOBILE DATA RADIO AND BASE DATA RADIO
The BDR and MDR are full duplex transceivers that operate as intentional radiators in the
FCC's 2400-2483.5 MHz industrial, scientific, and medical (ISM) band in North America and
within 2400-2500 MHz international band. They operate as unlicensed devices and are
compliant to the applicable FCC part 15 regulations.
The MDR employs both Code Division Multiple Access (CDMA) and Time Division Multiple
Access (TDMA) techniques. CDMA is a function of the Pseudo-random Noise (PN) code
selected for transmission and reception. The particular technique used in Andrew Base and
Mobile Data Radios is Direct Sequence Spread Spectrum (DSSS) technique. In the direct
sequence technique, the information spectrum is spread into a bandwidth many times wider
than the bandwidth of the data alone by using a pseudorandom noise sequence clocked at a
rate significantly greater than the information rate. Each data bit is encoded with a
pseudorandom spreading code. The receiver can recover the original data by using the same
sequence to decode the encoded data bits. Any other selected pseudorandom sequence
simply appears as additional noise at the receiver.
When power is applied to a radio, the radio configures the transmit and receiver spreading
sequences from data stored in the radio’s nonvolatile memory. After the radio configuration is
completed, the Control Equipment can change the spreading sequences. The base station
radios and mobile data radios maintain a pool of available PN codes or channels. Each radio
requires a code. The transmit and receive codes are different. The receive code of the MDR
or BDR must equal the other unit’s transmit code. Adjacent BDRs should not have the same
codes.
In normal operation, all MDR’s in the same control zone operate with the same set of transmit
and receive spreading codes. Time Division Multiple Access techniques are used to minimize
interference between the MDR’s.
Normally, the BDR keeps its transmitter on all the time. The MDR on the vehicle turns on its
transmitters in response to being specifically polled by a BDR. The BDR commands the MDR
to bring up its transmitter and send any pending poll responses from the vehicle control
equipment. The MDR turns off its transmitter if it fails to get confirmation in a certain period of
time that the BDR has “locked” to the MDR. Also, MDR will turn off its transmitter after the
BDR successfully “locks” to the MDR transmitter and the MDR sends its response to the BDR.