21923 - SCTE Broadband Aug2023 COMPLETE v1 (1)

102 Vol. 45 No. 3 - September 2023 Issue technical First, the back-end OFDM implementation introduces a high peak-to-average power ratio (>10 dB), even for the lowest order modulations. This is a known drawback for OFDM systems using large Fast Fourier Transform (FFT) sizes (2048 for each component carrier, in this case). Second, there is an input power mismatch between the LB and UB TX front-ends. The LB front-end needs an input signal with power lower than 0 decibel-milliwatts (dBm), and generates a maximum 13dBm output power. The UB front-end needs an input power of 10dBm to generate a 3dBm output at the desired harmonic. To address this, we precisely characterised the OFDM waveform power, and reduced the back-end output power to maintain the peak power under the limit of the UB front-end. The input to the LB front-end was then further attenuated to be below 0dB. Finally, to close the link margin for the 43m link, the LB and UB systems use 38dBi and 40dBi antennas, respectively. The TX and RX at both bands feature two mixing stages, part of the analogue front-ends shown in Fig. 1, thus forming a heterodyne system. However, due to the lack of RF lters at the considered frequency ranges, both LB and UB front-ends lack a sideband selection lter. This, combined with the high phase noise (due to the frequency multiplication process), may lead to drastic amplitude uctuations in the received Fig. 1 Prototype schematics and dual-band backhaul link deployment. a Deployment of the dual- band backhaul link over the Snell Engineering and Egan Research buildings at Northeastern University. b Components of the RX. c Components of the TX. d Block diagram with the components of the TX and RX. DC stands for Direct Current, NI for National Instruments, SPDT for Single-Pole Double- Throw, PSG for Performance Signal Generator, LB for Lower Band (123.5–140 GHz), UB for Upper Band (210–225 GHz), LO for Local Oscillator, IF for Intermediate Frequency, and RF for Radio Frequency.