Device-to-device communication (D2D) is a key enabler for connecting devices together to form the Internet of Things (IoT)[1]. A growing issue with IoT networks is the increasing number of IoT devices congesting the spectral resources of the cellular bands. Operating D2D in unlicensed band alleviates this issue by offloading network traffic from the licensed bands, while also reducing the associated licensing costs. To this end, we present a new low-cost radio access technology (RAT) protocol, called sidelink communications on unlicensed bands (SCUBA), which can be implemented on cellular devices such that it coexists with the legacy cellular protocol by operating as a secondary RAT in a time division multiplexed manner using the existing radio hardware. SCUBA is compatible on different types of cellular devices including the low-complexity half-duplex frequency-division duplex machine type communication (MTC) user equipments. SCUBA provides flexible sidelink (SL) latency and battery life tradeoff using a discontinuous reception procedure, which ensures that it is applicable across a wide range of use cases. We prove the effectiveness of our protocol with analyses and simulation results of the medium access control layer of SCUBA using different types of MTC traffic for both SL and the underlying cellular communication.

Device-to-device (D2D) communication finds widespread applicability in enabling connectivity for the Internet of Things. Leveraging the unlicensed frequency bands for D2D communication reduces the spectrum licensing costs, and offloads network traffic from the limited licensed spectral resources. Towards achieving a cost-efficient solution, we study the feasibility of integrating such a D2D operation in the unlicensed band (D2D-U) within legacy cellular devices as a secondary radio access technology in a time division multiplexed manner. To this end, we evaluate the constraints faced in incorporating D2D-U in various challenging environments, such as within devices that use a single radio architecture and a half-duplex with frequency division duplexed cellular operation. We propose time instances that can be exploited to multiplex D2D-U without violating regulatory restrictions imposed on using different unlicensed frequency bands. Based on our analyses and simulation results, we suggest guidelines for a prospective D2D-U protocol that can achieve efficient sidelink communications while also ensuring coexistence with legacy cellular operation.

Narrowband Internet of Things (NB-IoT) is one of the most prominent low power wide area (LPWA) technologies to support massive connections among low-cost devices with enhanced coverage. Addressing the further increase in the number of supported connections in IoT applications, we investigate the use of real-valued modulated signals together with widely linear detection (WLD) to NB-IoT. In this paper, we show that the use of WLD to resolve collisions of two simultaneously transmitted real- valued signals generated from two user equipments (UEs) enhances the capability of NB-IoT systems to facilitate massive connectivity. More specifically, to demonstrate the performance improvements, we analyze the uplink transmission reliability and the device density supported in NB-IoT systems with WLD in a grant-free scenario. The numerical results show that, for a 1% probability of decoding failure, the supported device density can be increased by one order of magnitude compared to that of conventional complex-valued signalling schemes.

In this paper, we address the problem of improving the medium access control (MAC) layer efficiency in indoor broadband power line communication networks. Several overheads in the MAC layer, like random back-offs and collision recovery, degrade the MAC efficiency. To reduce these overheads, we apply in-band full-duplexing (IBFD), which enables medium-aware transmission at all the network nodes. Specifically, we propose two new schemes called contention-free pre-sensing and mutual preamble detection to minimize the time spent during contentions and collisions. Considering the non-idealities of IBFD, we analytically show the feasibility of our solutions. We further design a comprehensive simulation model with multiple priority data frames and Poisson network traffic arrival to emulate a real in-home network traffic. We then present numerical results for both the classical saturated network model and the comprehensive traffic model, to show through OMNeT++ simulations that our presented solutions achieve over 95% of the optimum MAC efficiency that can only be attained in the idealized case of no contentions or collisions.

Although in-band full-duplexing (IBFD) has long been implemented in various communication media, it was only recently that an IBFD solution was presented for broadband power line communications (BB-PLCs). The maximum attainable echo suppression using this solution is, however, limited by the dynamic range of the analog-to-digital converter (ADC). To counter this critical constraint, we propose echo cancellation in the analog domain, while persisting with a low-complexity frequency domain digital echo estimation. By formulating an expression for the number of ADC bits lost in IBFD over a conventional half-duplex operation, we show that the ADC dynamic range is no longer a limiting factor for our solution. We further extend our solution to present an analog cancellation method for multiple-input multiple-output IBFD BB-PLC systems. Finally, we present simulation results of echo cancellation and data rate gains obtained under realistic in-home BB-PLC settings, to demonstrate that our solution is capable of doubling bidirectional transfer rates in a large number of the tested network conditions.

In this paper, we introduce a new scheme called Mutual Preamble Detection (MPD) to reduce the collision recovery time in broadband power line communication (BB-PLC) networks. Although latest BB- PLC products deliver a physical layer data rate of over 1000 Mbps, this is not efficiently translated into the medium access control (MAC) layer throughput due to several factors, including the long time intervals taken to recover from collisions. To address this, we use in-band full duplex operation to enable network nodes to transmit and simultaneously detect preambles, making them aware of a potential frame collision. With the detection of such a potential collision, we compel the network nodes to refrain from frame transmission in order to avoid the lengthy collision recovery time. The near-zero values of detection error and false alarm probabilities ensure the feasibility of our scheme in typical in-home BB-PLC networks. We present OMNeT++ simulation results to demonstrate the considerable increase in MAC efficiency obtained by using our proposed MPD scheme, over a traditional BB-PLC protocol.

We introduce in-band full duplexing (IBFD) for broadband power line communication (BB-PLC) systems. Inspired by the use of IBFD in digital subscriber lines, Ethernet, cable communication, and recently in wireless communication, we investigate the constraints and requirements for a successful IBFD implementation in BB-PLC. We propose a two-stage IBFD structure consisting of an initial analog isolation using an active hybrid circuit, and a simplified mixed-domain digital echo cancellation procedure to suppress the self-interference. Furthermore, we enhance the digital cancellation filter to better adapt to linear periodically time-varying channel conditions, commonly encountered in PLC scenarios. We evaluate our solution under diverse power line channel and noise conditions to examine the overall data rate gains that can be achieved. Last, we extend IBFD to multiple-input multiple-output (MIMO) BB-PLC systems that enable faster and/or more robust data transmission.