This proposal is targeted at realizing the vision of a "green'' Internet of Things (IoT) and green communication using transmit-only devices. It is predicted that by 2020, there will be 50 billion embedded devices deployed in our ambient environment, most of which will be reporting data to the cloud through wireless communication. Thus, it is imperative to design green communication technologies in which power consumption is minimized and bandwidth utilization is optimized. Existing communication protocols, however, are not optimized for power consumption and bandwidth utilization because they were designed to facilitate reliable two-way exchange of information between communicating parties -- their requirements are completely different from those of IoT applications. The needs of emerging IoT applications, such as unidirectional communication flow, dense deployment, small packet sizes, are all opportunities for significantly simplifying network design. This project aims to simplify the protocol design by removing receiving functions from the embedded devices, such that they only spend radio resources on sending application data, thus minimizing power consumption and maximizing bandwidth utilization.
This project will study a set of algorithms that can achieve high throughput for wireless networks using transmit-only devices. The biggest challenge for a transmit-only network is the handling of packet collisions as the transmitters do not have any means of knowing whether others are transmitting at the same time. Transmit-only can be thought of as a single-input-multiple-output multiple access (SIMO-MAC) channel, but there is a fundamental difference between transmit-only and previous work in SIMO-MAC from the information theory community - in almost all of the previous studies, while transmitters do not communicate among themselves, they do rely on feedback from receivers to make transmission decisions related to encoding and/or scheduling. Transmit only, on the other hand, assumes once the network is deployed and in operation, each transmitter does not have any feedback from other transmitters or receivers. In this case, to reduce packet collisions, and to further ensure packet collisions do not lead to packet loss, this project proposes a set of strategies to pro-actively control the network topology as well as transmission schedules before network deployment. First, an optimal receiver placement strategy and a network dynamics based transmitter placement strategy are proposed to minimize the packet loss during a collision by exploiting the fact the stronger signal can be decoded at the receiver. Second, a transmission scheduling algorithm is proposed to overlap transmissions that can be decoded together (by different receivers) to minimize the collisions. The proposed scheduling algorithm also takes into consideration transmitter mobility to minimize their negative impact on the network throughput.
