Hamidreza Shariatmadari

Machine-type communications: current status and future perspectives toward 5G systems

Machine-type communications (MTC) enables a broad range of applications from mission- critical services to massive deployment of autonomous devices. To spread these applications widely, cellular systems are considered as a potential candidate to provide connectivity for MTC devices. The ubiquitous deployment of these systems reduces network installation cost and provides mobility support. However, based on the service functions, there are key challenges that currently hinder the broad use of cellular systems for MTC. This article provides a clear mapping between the main MTC service requirements and their associated challenges. The goal is to develop a comprehensive understanding of these challenges and the potential solutions. This study presents, in part, a roadmap from the current cellular technologies toward fully MTC-capable 5G mobile systems.

Analysis of transmission methods for ultra-reliable communications

Fifth generation of cellular systems is expected to widely enable machine-type communications (MTC). The envisioned applications and services for MTC have diverse requirements which are not fully supported with current wireless systems. Ultra-reliable communications (URC) with low-latency is an essential feature for mission-critical applications, such as industrial automation, public safety, and vehicular safety applications. This feature guarantees a communication service with a high level of reliability. This paper investigates the feasibility and efficiency of URC over wireless links. It also analyzes the effectiveness of different transmission methods, including spatial diversity and support of hybrid automatic repeat request (HARQ). Finally, the importance of reliable feedback information is highlighted.

Link adaptation design for ultra-reliable communications

The fifth generation (5G) of cellular networks is expected to provide connectivity for a wide range of services. This requires the network to encounter novel features. Ultra-reliable communications (URC) is one of the considered features, which provides a certain level of communication service almost all the time. This is essential in order to support mission-critical applications, such as industrial automation, public safety, and vehicular communications. This paper studies link adaptation optimization for URC, considering errors in both data and feedback channels. As the implementation of optimal link adaptation is challenging, particularly, for downlink transmissions due to the limited feedback channel, a simple link adaption scheme is also proposed. Results reveal that the performances of the proposed and optimal link adaptation schemes are close. Hence, the proposed scheme can be utilized to efficiently support URC in cellular networks.

Delay analysis of network architectures for machine-to-machine communications in LTE system

Machine-to-machine communications has emerged to provide autonomic communications for a wide variety of intelligent services and applications. Among different communication technologies available for connecting machines, cellular-based systems have gained more attention as backhaul networks due to ubiquitous coverage and mobility support. The diverse ranges of service requirements as well as machine constraints require adopting different network architectures. This paper reviews three M2M network architectures to integrate machines into the LTE system and analyzes their associated communication delays. It also presents how the appropriate networks can be selected for some machine-to-machine applications, fulfilling their latency constraints.

Channel ranking based on packet delivery ratio estimation in wireless sensor networks

Wireless sensor networks (WSNs) operating in 2.4 GHz unlicensed bands must explore favorable channels in order to mitigate the effects of induced interference by co-existing wireless systems and frequency selective fading. In this context, we develop a packet delivery ratio (PDR) estimation method for channel ranking in WSNs. The PDR, in general, is defined as a function of signal-to-noise ratio (SNR) and signal-to-interferenceplus-noise ratio (SINR) at the sensor and the packet collision-time distribution of the sensor link. The collision-time distribution depends on the packet size and packet inter-arrival time distributions of both networks. Under limited channel measurements, the collision-time cannot be estimated satisfactorily. In order to bypass the collision-time estimation process, the proposed PDR estimation method utilizes signal level, interference and noise characteristics identified by spectrum measurements adjusted to the intended traffic pattern of the sensor link. The proposed method is validated against the empirical PDR using off-the-shelf sensor platform in emulated multi path wireless fading channels. The results reveal that the method is accurate in modeling the empirical PDR with limited channel energy measurements. In addition, we used the estimated PDR as a metric for channel ranking and verified its effectiveness by ranking the available channels to a WSN under interference from multiple WLANs in a real environment.

Data aggregation in capillary networks for machine-to-machine communications

As machine-to-machine applications using cellular systems become pervasive, it is an important concern that their deployment does not jeopardize the performance of the cellular systems. Support for a massive number of machines brings technical challenges affecting the performance of the random access channel and efficiency of radio resource allocation. Capillary networks are considered as an extensions to the cellular systems for providing large-scale connectivity. This paper proposes an aggregation scheme for capillary networks connected to the LTE network to improve their communication efficiency. A gateway, an intermediate unit between machines and the base station, aggregates packets from the machines during a predefined time, and then delivers them to the LTE network. In addition, this paper analyzes the trade-offs between random access interaction, resource allocation, and communication latency. Results reveals that accepting the extra latency for accumulating packets can significantly reduce the random access requests and the required resources for the data transmissions.

Optimized transmission and resource allocation strategies for ultra-reliable communications

Fifth generation (5G) wireless systems will provide connectivity for a wide range of new applications with diverse requirements. In part, the network needs to support ultra-reliable communications with low-latency (URLLC) for mission-critical applications. For these applications, the generated data should be delivered with a limited number of transmission attempts with high success probability. This paper considers the optimal transmission and resource allocations for URLLC in cellular systems. The resource allocations are derived for the fixed and adaptive transmission attempt assignments. The analysis results reveal that both fixed and adaptive transmission assignments, applicable to automatic repeat request (ARQ) and hybrid ARQ (HARQ) schemes, can reduce the required resources compared to the equal transmission assignment.

Control channel enhancements for ultra-reliable low-latency communications

The cellular wireless systems are gaining more attention among other connectivity solutions for supporting machine-type communications (MTC). The efficient support of MTC relies on incorporating new features in the communication networks. Ultra-reliable low-latency communications (URLLC) is one of the considered features that is essential for the support of mission-critical applications, such as industrial automation, e-health, public safety, and future vehicular communications. Enabling URLLC requires employing enhanced transmission techniques to meet the reliability requirements for both data and control channels. This paper develops general communication models for URLLC in uplink and downlink, considering the errors of data and control channels. The models help in determining the reliability constraints on control information, that should be considered in the design of the future cellular systems. In addition, the paper proposes some enhancement techniques that allow relaxing the stringent reliability requirements of control information.

Resource Allocations for Ultra-Reliable Low-Latency Communications

Ultra-reliable low-latency communications (URLLC) is a new feature to be considered for the fifth generation (5G) cellular systems. This feature is essential for the support of envisioned mission-critical applications, particularly in the realm of machine-type communications. These applications require that the messages, which are generally short-length packets, to be exchanged between a source and a destination with the high level of reliability and within a short period of time. The characteristics of URLLC do not fit directly in the conventional communication models. For instance, most of the existing communication models are developed considering moderate levels of reliability, neglecting the small effects of the feedback errors. However, even such small errors cannot be ignored for URLLC. This paper proposes a communication model for URLLC considering the reliabilities of both data and control channels. Then, the optimal and sub-optimal resource allocations are derived. We show that the proposed sub-optimal resource allocations have lower computational complexities with a negligible performance degradations compared to that of the optimal solutions. The results reveal that the possibility of performing only one retransmission can significantly reduce the required radio resources needed for data delivery compared to the case of performing a single transmission round.

Achieving Ultra-Reliable Low-Latency Communications: Challenges and Envisioned System Enhancements

URLLC have the potential to enable a new range of applications and services: from wireless control and automation in industrial environments to self-driving vehicles. 5G wireless systems are faced by different challenges for supporting URLLC. Some of the challenges, particularly in the downlink direction, are related to the reliability requirements for both data and control channels, the need for accurate and flexible link adaptation, reducing the processing time of data retransmissions, and the multiplexing of URLLC with other services. This article considers these challenges and proposes state-of-the-art solutions covering different aspects of the radio interface. In addition, system-level simulation results are presented, showing how the proposed techniques can work in harmony in order to fulfill the ambitious latency and reliability requirements of upcoming URLLC applications.