Wireless solutions are rapidly growing in machine-to-machine communications in industrial environments. These environments provide challenging conditions in terms of radio wave propagation as well as electromagnetic interference. In this article, results from the characterization of radio channel properties are summarized in order to provide some guidelines for the choice of wireless solutions in industrial environments. In conclusion, it is essential to know the sensitivity of industrial processes to time delay in data transfer. Furthermore, it is important to be aware of the radio interference environment and the manner in which different wireless technologies react upon interference. These steps will minimize the risk of unforeseen expensive disturbances in industrial processes.

Challenges and conditions for wireless machine-to-machine communications in industrial environments

Wireless Machine-to-Machine Communications in Industrial Environments

Automatic repeat request (ARQ) schemes, and in particular hybrid-ARQ (HARQ) schemes, which jointly adopt forward error correction (FEC) and ARQ, are essential to provide reliable data transmission in wireless communications systems. However, the feedback from the receiver to the transmitter and the retransmission process used in ARQ incurs significant cost in terms of power efficiency, throughput, computational power and delay. Unfortunately, such drawbacks can limit their applications to several current and emerging technologies. More specifically, the increasing number of wireless users has create spectrum scarcity, relying on small-size batteries create power constraints, deployment of real-time applications boost the demand for ultra-low delay networks, and the ultra-small low-cost Internet of Things (IoT) devices has limited signal processing and computation capabilities. Consequently, extensive research efforts have been dedicated to overcome the limitations inherent in HARQ. This survey paper provides an extensive literature review of the state-of-the-art HARQ techniques and discusses their integration in various wireless technologies. Moreover, it provides insights on advantages and disadvantages of particular ARQ types and discusses open problems and future directions.

Hybrid Automatic Repeat Request (HARQ) in Wireless Communications Systems and Standards: A Contemporary Survey

Cognitive radio networks (CRN), in their quest to become the preferred next-generation wireless communication paradigm, will depend heavily on their ability to efficiently manage the limited resources at their disposal in meeting the demands of their numerous users and driving their operations. As a result, a considerable amount of research work has been recently dedicated to investigating and developing resource allocation (RA) models that capture the essentials of CRN. The various ideas put forward by researchers to address RA problems in CRN have been somewhat diverse, and somehow, there seem to be no links that bring cohesion and clarity of purpose and ideas. To address this problem and bridge the gap, in this paper, a comprehensive study on the prevalent techniques developed for addressing RA problems in CRN is carried out, with an intent to put some structure, relevance and meaning to the various solution approaches. The solution models are therefore grouped and/or classified based on certain outstanding criteria, and their strengths and weaknesses highlighted. Open-ended problems are identified, and suggestions for improving solution models are given. The study therefore gives good directions for further investigations on developing RA solutions in CRN.

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Solving resource allocation problems in cognitive radio networks : a survey

Reliable packet delivery within stringent delay constraints is of primal importance to industrial processes with hard real-time constraints, such as electrical grid monitoring. Because retransmission and coding techniques counteract the delay requirements, reliability is achieved through replication over multiple fail-independent paths. Existing solutions such as parallel redundancy protocol (PRP) replicate all packets at the MAC layer over parallel paths. PRP works best in local area networks, e.g., sub-station networks. However, it is not viable for IP layer wide area networks which are a part of emerging smart grids. Such a limitation on scalability, coupled with lack of security, and diagnostic inability, renders it unsuitable for reliable data delivery in smart grids. To address this issue, we present a transport-layer design: IP parallel redundancy protocol (iPRP). Designing iPRP poses non-trivial challenges in the form of selective packet replication, soft-state and multicast support. Besides unicast, iPRP supports multicast, which is widely using in smart grid networks. It duplicates only time-critical UDP traffic. iPRP only requires a simple software installation on the end-devices. No other modification to the existing monitoring application, end-device operating system or intermediate network devices is needed. iPRP has a set of diagnostic tools for network debugging. With our implementation of iPRP in Linux, we show that iPRP supports multiple flows with minimal processing and delay overhead. It is being installed in our campus smart grid network and is publicly available.

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iPRP: Parallel redundancy protocol for IP networks

Traffic generated by machine to machine (M2M) communication or online gaming will be a large and integral part of the traffic transported by LTE-advanced and beyond networks. This traffic is characterized by sporadic and low-throughput packet arrivals. It must be scheduled under a latency constraint. Sporadic traffic creates environments where the channel-quality information (CQI) is outdated or unavailable. Fast-fading, the non-stationarity of inter-cell interference and the heterogeneity of Rel-10 networks further exacerbates this issue. However, current LTE-Advanced schedulers and resource allocation schemes are not optimized for these particular scenarios. In this paper, we propose a scheduling and resource allocation mechanism for latency-constrained operation. Our solution significantly improves the spectral efficiency of delay-constrained networks by optimizing a joint hybrid-ARQ and adaptive modulation and coding (AMC) policy that changes the number of dimensions (physical resources) used in each round. With only one bit of feedback, obtained causally from hybrid-ARQ, we achieve a performance close to the ergodic capacity.

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Adaptive modulation and coding with Hybrid-ARQ for latency-constrained networks

LTE systems do not suffer from intra-cell interference, but they are affected by interference coming from adjacent cells. However, most of the research on resource allocation and repetition protocols has not paid attention to the interference case. In this paper, we consider the problem of dynamic resource allocation for IR-HARQ schemes under the presence of interference. We consider resource allocation by means of rate and physical dimensions adaptation in each HARQ round. We provide a mathematical framework that can be applied for the analysis of heterogeneous networks. Rather than performing extensive simulations, we take an information theoretic approach to derive analytical expressions that represent the long-term throughput of the network and we consider distributed resource allocation policies. Our policies are applicable for both the uplink and downlink channels.

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Dynamic resource allocation in heterogeneous networks

Femtocells are small cellular base stations targeting in-home usage and deployed by end-users Because of the unplanned nature of their deployment, they can suffer from severe inter-cell interference with neighboring femtocells in dense deployments In addition, coordination is hardly feasible due to delays induced by the backhaul infrastructure of these home femtocell networks We propose a novel and decentralized interference mitigation scheme that combines hybrid-ARQ and incremental redundancy with an interference cancellation decoder Our performance evaluation based on analytical modeling and Monte Carlo experiments shows that our scheme is effective at combating interference without requiring any coordination

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Interference management in femtocell networks with hybrid-ARQ and interference cancellation

M2M/online gaming are considered as key applications in LTE and LTE-advanced networks. However, for most of these applications whose traffic is sporadic and some of them require very low latency, they are not well supported by the current LTE and LTE-advanced systems due to the large signaling overhead. This paper proposes two methods to address this problem. The first method provides a co-optimization method for AMC and HARQ when CQI is outdated or unavailable and there is a latency constraint. The second method presents a contention based access method to reduce uplink channel access latency. Simulation results show that with these two methods a significant improvement in spectral efficiency can be achieved while greatly reducing latency or maintaining a latency constraint.

Tania Villa

Papers

Adaptive modulation and coding with Hybrid-ARQ for latency-constrained networks

Dynamic resource allocation in heterogeneous networks

Interference management in femtocell networks with hybrid-ARQ and interference cancellation

Adaptive transmission and multiple-access for sparse-traffic sources