Digital implementation of time domain equalizers for digital microwave systems

Line-of-sight microwave links are currently used to transmit high speed data in the telecommunication network. The trend in modulation formats is typically towards multilevel quadrature amplitude modulation (OAM) with symbol rates in the range 20-75 Mbaud and carrier frequencies in the region of 2-20 GHz. For systems operating at the lower carrier frequencies long hops are feasible, requiring adaptive equalization to overcome the effects of distortion caused by multipath propagation in the radio channel. The design of a prototype fully-digital equalizer, which is being developed as a test-bed for examining equalization techniques and approaches to VLSI implementation, aimed at providing a range of next-generation adaptive equalization products is described. A 2×34 Mbits/s 16QAM system, with adaptation under the control of a zero-forcing algorithm, was initially chosen as the experimental vehicle