Multiplexed Principal Modes in Few-Mode Fiber Links With Limited Delayed Feedback

The use of channel state information (CSI) at the transmitter significantly enhances the performance of wireless communication systems. However, the requirement of CSI feed-back increases the burden on the reverse link, especially in links that employ multiple-input multiple-output (MIMO), where CSI takes the form of scalar parameters of the Principal Modes (PMs). Typical deployments use quantization and feedback of CSI at certain wavelengths of the dense wavelength division multiplexing (DWDM) grid, with interpolation to fill in missing CSI at the transmitter. Past work has used the Linde-Buzo-Gray algorithm (LBG) algorithm for quantization and interpolation of CSI. This paper includes the parameterization of the PMs into scalar parameters that are subjected to quantization and interpolation. we exploit another degree of flexibility by the ordering of the singular vectors of unitary PMs. This results in significant savings over the previous approaches to quantize PMs without any loss in performance. Further, simulations reveal that the proposed Flag manifold quantization and interpolation effectively enhance achievable rates with limited complexity.