Linewidth tolerance of digital coherent receiver using Viterbi & Viterbi RF carrier recovery for radio-over-fibre links

In this paper, we investigate the performance of the proposed digital coherent receiver using feedforward Viterbi & Viterbi RF carrier recovery algorithm in combination with squaring synchronizer. The advantage of the proposed scheme is simplicity since the RF carrier recovery is performed on only one sample per bit due to prior squaring synchronizer which performs timing recovery. We investigate the tolerance of the proposed scheme with respect to laser linewidth using numerical simulations and compare the results to traditional approach using feedforward maximum likelihood RF carrier phase recovery (MLCPE). We have shown that the proposed scheme improves the linewitdh tolerance by app. 1 dB and reduces the number of samples per bit required for the RF carrier recovery to one, compared to the traditional MLCPE.