Frequency-Domain Oversampling for Cognitive CDMA Systems: Enabling Robust and Massive Multiple Access for Internet of Things

Toward the era of mobile internet and Internet of Things (IoT), numerous sensors and devices are being introduced and interconnected. To support such amount of data traffic, traditional wireless communication technologies are facing challenges both in terms of increasingly shortage of spectrum resource and massive multiple access. In this paper, cognitive code division multiple access (Cognitive-CDMA) is proposed by combining the concept of cognitive radio with dynamic noncontinuous spectrum bands and code division multiple access. In order to suppress multiple access interference resulting from the non-orthogonality of partial available spectrum bins, carrier frequency offset, and spectrum sensing mismatch, an enhanced receiver design using frequency-domain oversampling (FDO) with linear minimum mean square error (MMSE) is considered in this paper for Cognitive-CDMA systems. By spectrum sensing to mitigate spectral interference in the transceiver and by utilizing FDO in the receiver to project received signal to a higher dimension, the proposed Cognitive-CDMA is able to support robust and massive multiple access for IoT applications. The simulation results show that the cognitive-CDMA with FDO-MMSE receiver outperforms that with conventional per-user MMSE receiver in the presence of multipath fading channels, carrier frequency offset, and spectrum sensing mismatch.