Design and implementation of UWB transceivers for Internet of Things applications
In today's world, daily life is influenced significantly by the connectivity between millions of individuals and devices all around the world, which exchange information and data via the internet. The main architecture in which all internet-enabled objects are connected is called the Internet of Things (IoT). The IoT has various applications in smart cities, smart farming, smart industry, e-health, etc. In the case of smart cities, the IoT e.g. enables to improve the citizens’ quality of life, as well as to facilitate urban services. In smart homes, as another example, the objective is, amongst others, to reduce the energy consumption of a building.
In order to realize the desired level of quality of IoT services, a first challenge is a need for a reliable, secure and user-friendly interconnection between hardware and software layers. Although individual layers can be designed independently, the related interconnections cause challenges in terms of interoperability of heterogeneous systems using different communication technologies, security and privacy, etc. A second important challenge is the implementation of a low-power, low-cost communication device, which enables the different IoT nodes to interact with each other.
To accelerate the above described IoT paradigm, this thesis aims to overcome some of the bottlenecks for IoT implementations in smart home and eHealth applications.
First, we discuss the interoperability of heterogeneous devices applied in a smart home platform together with the design of a low-power sensor node for a multi-standard event-driven energy management system. The developed energy management system at both software and hardware layers uses wireless sensor networks (WSN) to improve the energy efficiency of a building without construction work needed.
At the software level, various communications technologies have been integrated into the same middleware by utilizing an integration layer as an interface between the hardware and the software. This middleware allows the exploitation of both existing and future emerging wired and wireless technologies. In order to add a power-efficient technology to the existing wireless solutions, we have developed a prototype of a low-energy wireless sensor node based on pulsed UWB communication. The UWB transceiver has been designed and implemented at both system and circuit level. The radio system comprises an integrated low-power transmitter fabricated in 130 nm CMOS technology. It generates a signal with a 1.1 ns pulse width in the 3 - 5GHz band and consumes only 39 μW at a 1 Mbps rate. To enable data reception, a commercial off-the-shelf-component receiver has been implemented and directly interfaced with the data management system. The pulsed UWB design consumes only 5.31 nJ per transmitted bit which presents a ten times better DC energy consumption per pulse compared to the other off-the-shelf products integrated into the same middleware The developed demonstrator is the first example of an IoT system based on pulsed UWB technology directly interfaced with a multi-standard centralized system. As an example of an IoT application, a heating, ventilation and air conditioning (HVAC) control strategy has been developed that uses the information of the deployed sensor nodes. These sensor nodes are used to measure the temperature of several rooms, as well as the energy consumption of heating and cooling appliances. The system has been tested experimentally in an office setting. For this experiment, an average energy savings of 71% has been achieved during the test period of three days in summer.
A low-cost implementation is crucial for IoT sensor nodes. To this end, this thesis also targeted a fully digital implementation of the communication transceiver, to achieve low-cost and technology-scalable sensor nodes. The second part of this thesis, therefore, describes the system and circuit-level design of a fully-digital asynchronous UWB receiver compliant with the IEEE 802.15.6 standard, targeting a wireless body area network for eHealth applications. The fully-digital receiver implemented in 65nm CMOS technology uses inverter amplifiers in the RF front-end to convert RF UWB signals centered at 4GHz to digital pulses for demodulation in the baseband. The event-driven and asynchronous baseband demodulates the incoming signals. To benefit from the pulsed nature of the impulse UWB signals for power reduction, a duty-cycling control unit has been designed and implemented. It enables not only the periodic switching of the receiver’s front-end but also provides IEEE 802.15.6 standard compliance to the receiver. The duty-cycling control works asynchronously to the transmitter using a local low-power all-digital oscillator, hence avoiding the need for a high power reference oscillator.
The prototype fully digital receiver has been implemented in 65nm CMOS technology. Based on the simulation results, the fully digital receiver demonstrates a sensitivity of -91dBm with a gain of 110dB in the front-end. The receiver consumes an average power of 18.5 mW. The measured duty cycle of 18.75% for the receiver with an overhead power consumption of 74 µW has been achieved in the duty cycling block.
This thesis hence proposes two IR-UWB systems for two different IoT applications. The focus was on overcoming interoperability issues and enabling low-cost implementations of the IoT sensor nodes. This brings us one step closer to the ultimate goal of having low-power, low-cost autonomous, reconfigurable and easily integrable sensor nodes for a wide variety of IoT applications.