Spectrally efficient digital mobile fronthaul with discrete cosine transform and multi-band quantization

A spectrally efficient digital mobile fronthaul (MFH) with discrete cosine transform and multi-band quantization (DCT-MBQ) is first proposed and experimentally demonstrated. In this approach, the baseband orthogonal frequency division multiplexing (OFDM) symbols are segmented into individual blocks and independently transformed by DCT to obtain a set of transform coefficients. Different from digitizing each OFDM sample with the same number of quantization bits (QBs) in previous digital MFH, MBQ is introduced to separately digitize different parts of the coefficients with different numbers of QBs according to the significance of these coefficients. Furthermore, the part of transform coefficients with little significance is discarded. Thus, the total number of required QBs for digitizing an OFDM symbol can be greatly reduced and, thereby, high bandwidth efficiency can be achieved. In the experiment, the proposed DCT-MBQ-based digital MFH transmission is demonstrated over a 25 Gb/s four-level pulse amplitude modulation intensity modulation-direct detection optical link supporting up to 16×100  MHz 5G new radio carriers with 1024 QAM, achieving an error vector magnitude of 0.65%. The equivalent common public radio interface rates from 55 to 158 Gb/s are supported.