Wide-Band Digital Transmission over Analog Radio Relay Links

An experimental investigation has been performed to assess the feasibility of 8-phase phase-shift-keyed (PSK) signal transmission through a 6-GHz band microwave radio link with a 30-MHz nominal RF bandwidth. Only a portion of this bandwidth is currently being utilized to transmit one analog TV program or 1800channel frequency-division-multiplexed (FDM)/FM telephony. The link has been modified to have a 40-MHz bandwidth for this experiment. The digital modem is a 36-MHz bandwidth, 8-phase coherent PSK (CPSK), 36-Msymbol/s (108 Mbit/s) system. The work which has been performed includes the following: 1) study of the link bit error rate as a function of link carrier-carrier-to-noise ratio with the transmitter TWT power output as a parameter; 2) study of the effects of an adjacent 1800-channel carrier (center-to-center separation of 36 MHz) on the error rate of the PSK carrier; and 3) perturbation of the 1800-channel FM carrier top channel noise power ratio (NPR) by an adjacent-channel 8-phase carrier (center-to-center separation of 36 MHz). In addition, experiments have been conducted through a four hop test simulator to examine the cumulative effect of transmission deviations such as group delay and TWT AM-PM transfer effect on the error rate performance for two different TWT power outputs, namely 2 and 4 W.