Another function of the MPC860 is to control the operation of the radio. It contains programming
data for the modulator and demodulator unit, as well as frequency assignment of the uplink and downlink
channels. The operation parameters of the radio, such as data rate, modulation scheme, frequency channel
assignment, etc., can be modified by programming a different table into the MPC860 memory. The radio
is designed to include the capability of changing operating parameters on the fly. This feature allows
the radio to operate more efficiently under different conditions.
Modulator and Demodulator UnitThe modulator unit utilizes a 240MHz IF local-oscillator (LO) carrier. Current radio design allows
binary and quadrature modulation (BPSK and QPSK). Baseband data is first differentially encoded, and
then passed directly to the modulator for BPSK modulation, or split into in-phase (I) and quadrature
(Q) data before reaching the modulator for QPSK operation. A 240MHz IF carrier is chosen for the
modulator in order to avoid interference with the IF carrier at the demodulator.
The demodulator is a mixed analog and digital design. RF signal is first down-converted to IF at
70MHz. This IF frequency is widely accepted, which leads to more convenience in obtaining off-the-shelf
components. The 70MHz IF signal is then sub-sampled by a high-speed analog-to-digital converter (ADC).
Harris Semiconductor's digital quadrature tuner (DQT) and digital costas loop (DCL) chip set processes
the digital data to bring the information signal back to baseband. The baseband data is finally passed
to the PowerPC processor for final processing back to ethernet packets.
RF Front-EndThe RF front-end up-converts the transmit IF signal to the proper frequency, and down-converts the
receiving signal to the proper receive IF frequency. Each front-end is divided into transmit and receive
section. Both of them achieve the desired frequency stability by using a phase-lock loop (PLL) and
a very stable reference oscillator. As mentioned previously, the radio can operate in different
frequency bands by using the appropriate front-end. At this point the radio is connected to a 5.3GHz
AntennaThe transmit signal from the RF front-end will further be amplified before hitting the antenna. The
transmit antenna assembly contains a patch antenna with an integrated power amplifier at the back.
This arrangement avoids signal loss between the antenna and the final power amplifier stage to ensure
maximum power transfer.
The receive antenna is very similar to the transmit antenna, except that the power amplifier is
replaced by a low-noise amplifier (LNA). The LNA is connected as close to the antenna as possible to
minimize signal loss and to maximize signal-to-noise ratio (SNR) at the input and output of the LNA.
A MS PowerPoint slide
is provided here with pictures and performance data of the antennas used in the RDRN radio.
Radio Performance Testing
There is a section dedicated to radio performance testing. Please refer to the page
Field Tests on the left column.
Last Update: December 16, 1999 05:00pm (GMT-0600)