NOVEL FEATURE REPRESENTATION STRATEGIES FOR TIME SERIES FORECASTING WITH PREDICTED FUTURE COVARIATES

Jimeng Shi, Rukmangadh Sai Myana, Vitalii Stebliankin, Azam Shirali, Giri Narasimhan

Keywords: time series forecasting, future covariates, shifting, padding, periodicity, deep learning

Abstract: Accurate time series forecasting is a fundamental challenge in data science. Unlike traditional statistical methods, conventional machine learning models, such as RNNs and CNNs, use historical data consisting of previously measured variables including the forecast variable and all its covariates. However, in many applications, some of the covariates can be predicted with reasonable accuracy for the immediate future. Note that the input may also contain some covariates that cannot be accurately predicted. We consider the problem of predicting water levels at a given location in a river or canal system using historical data and future covariates, some of which (e.g., precipitation, tide) may be predictable. In many applications, for some covariates of interest, it may be possible to use historical data or accurate predictions for the near future. Traditional methods to incorporate future predictable covariates have major limitations. The strategy of simply concatenating the future predicted covariates to the input vector is highly likely to miss the past-future connection. Another strategy that iteratively predicts one step at a time can end up with prediction error accumulation. We propose two novel feature representation strategies to solve those limitations -- shifting and padding, which create a framework for contextually linking the past with the predicted future, while avoiding any accumulation of prediction errors. Extensive experiments on three well-known datasets revealed that our strategies when applied to RNN and CNN backbones, outperform existing methods. Our experiments also suggest a relationship between the amount of shifting and padding and the periodicity of the time series.

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TL;DR: We propose two novel feature representation strategies for time series forecasting with predicted future covariates.