EE-IoT: An Energy-Efficient IoT Communication Scheme for WLANs

While Narrow-Band Internet of Things (NB-IoT) has been standardized by 3GPP to provide wireless Internet access for IoT devices, this service is expected to come with a monthly fee (e.g., $1 or $2 per month per device). As the number of IoT devices tends to be large, the service charge will impose a considerable financial burden on the end users. In this paper, we propose an Energy-Efficient IoT (EE-IoT) communication scheme by taking advantage of the existing WiFi infrastructure that is widely available in home, office, campus, and city environments. EE-IoT will not only avoid monthly service charge for the end users but also maintain a low power consumption for IoT devices. The key component of EE-IoT is an asymmetric physical (PHY) design, which enables an OFDM-based broadband AP to communicate with multiple QAM-based narrowband IoT devices at a low sampling rate (250 ksps) in both uplink and downlink. The trick in our design is that, instead of using the same carrier frequency as the AP, each IoT device tunes its carrier frequency to a particular subcarrier of the AP's OFDM signal, making it possible to encode/decode the data on that subcarrier at a low sampling rate. Based on this new PHY, we propose a MAC protocol to enable EE-IoT in WLANs. We have built a prototype of EE-IoT on a USRP2 wireless testbed and evaluated its performance in an office building environment. Experimental results show that an AP can serve 24 IoT devices simultaneously and each IoT device can achieve more than 187 kbps in the downlink and more than 125 kbps in the uplink.