Konstantinos Theofilis’s research while affiliated with National Institute of Information and Communications Technology and other places

While the Internet of Things (IoT) is usually envisioned to support powerful functionality, like in self-driving cars, there is also increasing interest in simpler IoT applications that can be employed on massive scales at high densities, like in data gathering at meetings with large audiences. The latter vision requires low-cost devices consuming little energy, and it tends to come with a relaxed need for high-speed communication. Its realization necessitates the development of wireless protocols that are simple, yet that can effectively arbitrate multi-access to communication channels. Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) is usually deployed in such contexts, but it tends to work less well when large numbers of nodes attempt to simultaneously access a wireless channel. Asynchronous Pulse Code Multiple Access (APCMA) has been developed with simultaneous asynchronous access to communication channels in mind by using a sparse representation of pulses to encode messages, but being relatively recent, its performance has never been systematically compared to CSMA/CA. This paper compares APCMA’s performance with that of CSMA/CA in terms of the success probability (i.e., absence of errors) of message transmissions through the use of simulations and analytical models, under the assumption of equivalence in throughput. We find that APCMA with four pulses per code word performs worse than CSMA/CA, but the roles are reversed if five or six pulses are used.

For the realization of an Internet of Things (IoT) with high densities of devices it is necessary that wireless communication protocols are developed that offer (1) low energy consumption, (2) simplicity of encoding and decoding, (3) an asynchronous mode of communication, and (4) an effective but simple method to deal with interference between transmissions. This paper presents the implementation, experimentation, and analysis of a protocol on the MAC sublayer that encodes information in terms of silent intervals between pulses. Based on the representation of patterns of sparse pulses, this encoding has the potential for extremely low power consumption at the transmitter side. It also results in only few conflicts between messages that are broadcast on the same band overlapped in time, while no synchronization between transmitters and receivers is necessary. The protocol is demonstrated experimentally on the 315 MHz band with 100 senders and one receiver configured in a Star topology. Theoretical analysis confirms that the probability of conflicts between messages is low, even if the number of devices increases to the order of ten thousand. This protocol facilitates the implementation of IoT devices that are restricted in terms of hardware and energy resources.

An Internet of Things (IoT) employing resource-restricted (e.g., battery-limited) IoT devices at high densities will require an effective multiplexing protocol that can be implemented with low energy consumption, while being able to effectively avoid collisions between the transmissions from multiple IoT devices. Asynchronous Pulse-Code Multiple Access (APCMA) has been proposed as a communication protocol based on pulse-encoded signals that allows multiple senders to simultaneously transmit their messages. Even if multiple messages on the same band overlap in time during transmission, they are disentangled at the receiver by a decoding algorithm that is based on pattern matching of pulse trains. In this paper, we implement the APCMA protocol on an FPGA and evaluate its performance in wireless communication. We also implement a decoding algorithm that matches pulses by logical operations on a shift register. Our experiments show that the APCMA protocol can realize multiplexing with low overhead and that the error rate caused by misdetection during decoding is reduced with longer pulse trains.