Research On Heterogeneous Connection For Internet Of Things

In various Internet of Things(IoT)scenarios,different wireless technologies coexist in the shared frequency medium as well as the physical space.Such wireless co-existence may lead to serious cross technology interference(CTI)problems.Compared with tra-ditional methods like interference avoidance and tolerance,direct connection among het-erogeneous devices is therefore a fundamental requirement to ensure the usability,inter-operability and reliability of the IoT.The research on heterogeneous connection in IoT faces the following challenges:(i)As heterogeneous wireless devices adopt different pro-tocol standards,a reliable and generable side-channel needs to be built to transmit mes-sages among these devices.(ii)There are distinguishable asymmetries among hetero-geneous devices,e.g.modulation mechanism,coding rate and computation ability.We should find the compatibility among various protocols to achieve more fine-grained signal control.(iii)Energy and cost limit the large-scale deployment of IoT devices.Therefore,how to achieve the connection of active wireless devices and passive wireless devices is important for reducing the energy consumption.This paper focuses on the research of heterogeneous connection for IoT devices.The main problems to be solved in this paper mainly include: enhancing the reliabil-ity of heterogeneous connection,improving the transmission efficiency of heterogeneous connection,and reducing the power consumption of heterogeneous connection.The con-tributions of this paper are summarized as follows.(1)Research on active heterogeneous connection based on packet-level features.(i)We leverage the packet energy as the side-channel to transmit cross-technology communi-cation(CTC)messages from WiFi to ZigBee.We establish a theoretical model to clearly describe the relationship between bit error rate(BER)and signal to noise ratio(SNR).We further employ modulation techniques in both the amplitude and temporal dimensions to optimize the throughput over a noisy channel.(ii)We explore the feasibility of chan-nel state information(CSI)to achieve the CTC from ZigBee to WiFi.We transform the CTC decoding problem into a problem of CSI classification with support vector machine(SVM).We also design a receiver-initiated CTC protocol for the practical application.The evaluation results demonstrate the throughput of WiFi to ZigBee CTC is 153.85 bps and the throughput of ZigBee to WiFi CTC is 215.9bps.(2)Research on active heterogeneous connection based on physical-level signals.(i)We present a transmitter-transparent CTC from ZigBee to WiFi based on cross-demapping.By reusing the existing WiFi modules,the WiFi receiver can decode ZigBee phase sequences with the throughput of 213.6Kbps.(ii)Different from existing analog emulation,we propose a novel method named digital emulation,which emulates the phase shift of ZigBee signals by changing the payload of WiFi packets.We explore the opportu-nity to select an appropriate phase sequence and achieve a more reliable CTC from WiFi to ZigBee with the packet reception ratio(PRR)of 86.2%.(iii)We present comprehensive understanding on emulation errors and propose the method of split encoding.By leverag-ing the asymmetry between the coding bandwidth of WiFi and the decoding rate of BLE,the emulation errors are controlled at specific sampling positions.Finally,we achieve a physical-level CTC from WiFi to BLE with the throughput of 522.2Kbps.(3)Research on passive heterogeneous connection based on backscatter technol-ogy.We revisit the classic ON-OFF keying(OOK)modulation and propose a backscatter system that takes the ambient LoRa transmissions as the excitation and piggybacks the in-band OOK modulated signals over the LoRa transmissions.This method achieves the connection of active wireless networks and passive wireless networks.The low-power backscatter tag can pick up the ambient LoRa signals from other signals.A novel clustering-based decoding algorithm at the LoRa receiver is proposed to demodulate the backscatter signal.Experimental results show this system can achieve 39.5Kbps data rate at 200 m communication distance.