In this paper, based on sum-difference co-array analysis, a new fourth-order sparse array called sum-difference-FODC (SD-FODC) is proposed, allowing the construction of a fourth-order DCA with long consecutive lags using the continuous segments in the second-order DCA and SCA of the original array. It has a closed-form expression for sensor positions that can be generated by two arbitrary nonuniform linear arrays (NLAs) called generators. If the second-order SCA and DCA of the generators have long consecutive segments, the designed fourth-order sparse array can achieve a large number of uDOFs. Numerical results are provided to demonstrate the superior performance of the proposed design.

Effectively utilizing multimodal information (e.g., heart rate and acceleration) is a promising way to achieve wearable sensor based human activity recognition (HAR). In this paper, an activity recognition approach MARCEL (Multimodal Activity Recognition with Classifier Ensemble) is proposed, which exploits the diversity of base classifiers to construct a good ensemble for multimodal HAR, and the diversity measure is obtained from both labeled and unlabeled data. MARCEL uses neural network (NN) as base classifiers to construct the HAR model, and the diversity of classifier ensemble is embedded in the error function of the model. In each iteration, the error of the model is decomposed and back-propagated to base classifiers. To ensure the overall accuracy of the model, the weights of base classifiers are learnt in the classifier fusion process with sparse group lasso. Extensive experiments show that MARCEL is able to yield a competitive HAR performance, and has its superiority on exploiting multimodal signals.