Comparison of link layer of BLE and 802.15.4 : Running on Contiki OS

Abstract: There has been extensive research in the low power Wireless Sensor Network (WSN) community with 802.15.4 based platforms. A major factor for this is the support for 802.15.4 based platforms in lightweight Operating Systems (OS) for Internet of Things (IoT) devices. Bluetooth Low Energy (BLE) with its standardized protocol and wide adoption in mobile devices is well suited to all applications requiring direct interaction with a mobile device. BLE does not have support in any of these software platforms for IoT development. With this as motivation this thesis creates a port of Contiki OS to a BLE platform, specifically a platform based on nrf51822 System on Chip (SoC). This will enable direct communication of Contiki nodes with smart-phones and ease development of BLE based projects with Contiki. This thesis extends the research on BLE by comparing its link layer with 802.15.4’s Contiki- MAC and Null-RDC on four metrics, namely data rate, latency, reliability and energy consumption. Their behavior with and without external WiFi interference also has been looked into. The tests conducted showcases the performance of simple point to point communication 802.15.4, which is rarely benchmarked in research community that prefers testing complex topologies. The effect of the limits of the number of packets communicated per connection interval in different BLE stacks can be seen on the data rate achievable with BLE. The influence of frequency hopping on the reliability of BLE communication with the presence of external interference is assessed. Adaptive Frequency Hopping (AFH) has been emulated by manually choosing interference free channel map and its effect on mitigating interference has been evaluated. Tests also assesses the impact of BLE link layer configuration, especially creating an asymmetric connection by using non zero slave latency value on latency and energy consumption. With this asymmetric connection, the slave devices have been recorded to a latency of 16 ms with Radio Duty Cycle (RDC) of 0.6%.