Communication systems are a key element for the industry 4.0 revolution, where the remote access to the machinery is a fundamental part for the automation of tasks related to monitoring and control of the different industrial processes. There is an increasing interest in performing such communications using a wireless medium, as they offer several advantages as a lower cost, greater flexibility or the ability to operate in moving elements. However, existing works have showed that the achievable performance in the sub-6 GHz frequency bands is insufficient to cope with all the requirements, which motivated the analysis of the millimeter wave spectrum for these use cases. Industrial environments present a harsh condition for electromagnetic wave propagation, where the abundance of reflective surfaces can present difficulties to properly exchange information. Thus, a thorough analysis and characterization of the propagation through this kind of environment is necessary to develop protocols and standards accordingly. This work provides the results of measurements carried out in two industrial facilities, which are a university workshop and a pit oven building from a steel company. Metrics of the results are computed and discussed as well, where a significantly larger losses can be seen for the pit oven measurements compared to other industrial scenarios.

This work discusses Access Point Coordination techniques for future 802.11 communications in the context of industrial Wireless TSN scenarios. A Coordinated OFDMA setup is proposed with a frame exchange scheme based on implicit wireless channel sounding prior to transmission. The scheduler assigns resource units to the users, trying to maximize the probability of all the STAs in the network to successfully deliver their data. In order to evaluate the quality of the channels without introducing overhead in the network, we propose a virtual sounding mechanism. We present simulation results first to validate the virtual sounding mechanism and, second, to show the achievable reliability of a Multi-AP network for a set of representative scenarios. These results highlight that Multi-AP can be effectively used to enhance the reliability of the network though special attention must be taken for time-varying scenarios.

The millimeter-wave (mmWave) bands contain some properties that can be key enablers for future wireless communications in industrial scenarios, but, despite the potential this new medium presents, very few efforts have been carried out to characterize such environments. This paper presents a cost-effective and flexible channel sounder that aims to measure indoor industrial setups in order to develop models that will assist in the development of future protocols and standards. The complete design and selected hardware (HW) of the sounder are discussed, and three preliminary tests carried out in laboratory and machining workshop scenarios are also presented, where the performance of the sounder is validated.

With the uprising of new fields such as robotics, IoT or Augmented Reality, one of the main objectives of industrial modernization is the incorporation of safe and secure wireless technologies in the factory floor. However, nowadays wireless protocols can not fulfill the communication requirements of industrial networks, among which reliability and bound guaranteed latency are probably the most stringent ones. The lack of guaranteed low latency and ultra-high reliability of wireless networks are mainly derived from the error-prone nature of wireless propagation. Multi-link techniques are expected to provide enhanced reliability, latency and also protection against external interference. In this work, we assess the reliability and latency enhancement of the Multi-Link technique proposed in 802.11be. The assessment is done through simulation means using realistic industrial propagation and interference models. The results shown in this paper prove that Multi-Link provides an enhancement in wireless reliability and latency.

Wireless communication technologies play an important role in today's society and, for that reason, wireless systems are almost ubiquitous. The keys of the success of wireless communications are, among others: reduced cost of wiring, implementation and maintenance or greater flexibility. Given these advantages, there is a growing interest in expanding the wired networks used in the most critical industrial applications to a wireless domain, fulfilling the real-time requirements of these applications. In addition, the incorporation of mobile devices to hybrid networks allows to expand the application area and obtain even more benefits from using wireless solutions. Nevertheless, guaranteeing the robustness and determinism required by factory automation applications where several Access Points (AP) are necessary to cover the entire wireless area is not an easy task. Therefore, in this paper, a novel soft-handover algorithm is presented. This algorithm guarantees an uninterrupted communication during the handover process required by the wireless devices together with a dynamic management of the resources within the hybrid (wired/wireless) scheme. To make this possible, the handover algorithm is combined with a slotted Medium Access Control (MAC) based on a superframe structure with a contention-free phase and a contention phase, where the contention-free phase is divided into uplink and downlink slots. The performance of the algorithm has been evaluated through OMNeT++ simulations.

In industrial automation systems, the introduction of wireless networks as an extension of the existing wired networks is increasing. However, with the existing wireless technologies, it is impossible to guarantee this coexistence for those applications with strict real-time and reliability requirements such as Networked Control Systems (NCS) or Distributed Control Systems (DCS). The main problem lies in the design of the Medium Access Control (MAC) protocol, as this plays a key role in fulfilling real-time and deterministic requirements. Moreover, the integration of both networks is fundamental to provide a seamless coexistence guaranteeing the demanding requirements of these applications. So, in order to expand the wired network used in NCS to a wireless domain, a hybrid IEEE 802.3/IEEE 802.11 real-time TDMA-based MAC scheme is proposed in this paper. The proposed scheme can support the transmission of periodic real-time traffic and aperiodic real-time traffic in a deterministic way, together with best-effort (BE) traffic. Moreover, with the aim of increasing the reliability of the communication system, retransmission mechanisms are defined. The performance of these MAC schemes has been evaluated over Rayleigh fading channel through OMNeT++ simulator. Provided results show that the transmission of periodic real-time traffic is not affected by the transmission of aperiodic or BE traffic. Moreover, results show that the transmissions and retransmissions are adapted to tight control cycles.

A Medium Access Control (MAC) protocol for time-critical wireless applications called Enhanced Priority MAC (EPMAC) is proposed in this paper. The proposed scheme supports three traffic categories prioritizing emergency traffic over non critical one and beacons are emitted to announce that the channel will be occupied. EP-MAC is designed so that the highest priority traffic postpones lowest priority transmissions. The performance of this protocol has been evaluated over several industrial channels through OPNET simulator. Compared with PriorityMAC, provided results show that EP-MAC is able to reduce the latency of all the traffic categories supported, whilst fulfilling the stringent requirements of time-critical applications.

The evaluation of Cognitive Radio (CR) for Wireless Sensor and Actuator Networks (WSANs) in industrial wireless automation applications is presented in this contribution. Current wireless solutions do not ensure enough performance for hard real-time and reliability requirements, based on time-critical data traffic. These industrial applications are characterized by harsh environments, where the robustness of wireless communications plays an important role. In these kinds of environments, CR can increase the system's reliability and robustness. Thus, several cognitive and non-cognitive MACs which ensure mission-critical and time-critical data transmission have been evaluated through OPNET network simulator over several fading and interference channels. The provided results show that CR-based MACs are able to maintain the performance of the network in harsh channels and under interference.

Designing energy-efficient cognitive radio transceivers requires joint optimization of medium access control and the physical layer implementation. In this paper we show an energy efficiency optimization strategy for IEEE 802.11n compliant transceivers in terms of energy consumed by the receiver per successfully received bit. To this end, we propose and explore several modifications of a conventional physical layer implementation, all of which target energy proportional behavior. The proposed modifications intentionally include operation modes and algorithm choices that are suboptimal with respect to throughput and error-rate performance. Yet, we show how (under ideal conditions) the rate adaptation at the medium access control layer can exploit these modifications to achieve superior energy efficiency that is 44% below that of a rate adaptation targeting only maximum goodput.

Last-generation and future wireless communication standards, such as DVB-T2 or DVB-NGH, are including multi-antenna transmission and reception in order to increase bandwidth efficiency and receiver robustness. The main goal is to combine diversity and spatial multiplexing in order to fully exploit the multiple-input multiple-output (MIMO) channel capacity. Full-rate full-diversity (FRFD) space-time codes (STC) such as the Golden code are studied for that purpose. However, despite their larger achievable capacity, most of them present high complexity for soft detection, which hinders their combination with soft-input decoders in bit-interleaved coded modulation (BICM) schemes. This article presents a novel low-complexity soft detection algorithm for the reception of FRFD space-frequency block codes in BICM orthogonal frequency-division multiplexing (OFDM) systems. The proposed detector maintains a reduced and fixed complexity, avoiding the variable nature of the list sphere decoder (LSD) due to its dependence on the noise and channel conditions. Complexity and simulation-based performance results are provided which show that the proposed detector performs close to the optimal log-maximum a posteriori (MAP) detection in a variety of DVB-T2 broadcasting scenarios.

This contribution analyzes the architecture design and FPGA implementation of high-throughput multiuser vector precoders. The most complex task of such precoders, i.e. the search of the perturbing vector over an infinite lattice, has been carried out by means of two tree search algorithms: a novel fully-pipelined complex-valued K-Best scheme and a fixed-sphere encoder (FSE). Both designs have been implemented in a Virtex-6 device, leading to precoding throughputs of up to 2.4 Gbps with 16-QAM modulation.

Recent and next-generation wireless broadcasting standards, such as DVB-T2 or DVB-NGH, are considering distributed multi-antenna transmission in order to increase bandwidth efficiency and signal quality. Full-rate full-diversity (FRFD) space-time codes (STC), such as the Golden code, have been reported to be excellent candidates, being their main drawback their detection complexity, which is enhanced when soft output is required when combined with a bit interleaved coded modulation (BICM) scheme based on low-density parity check (LDPC) codes. We present a novel low-complexity soft detection algorithm for the reception of Golden codes in LDPC based orthogonal frequency-division multiplexing (OFDM) systems. Complexity and simulation-based performance results are provided which show that the proposed detector performs close to the optimal detector in a variety of DVB-T2 broadcasting scenarios.

Besides the optimal but impractically complex dirty paper coding (DPC), linear precoding and vector precoding (VP) have been proposed for the vector broadcast channel (BC). Linear precoding is simple, as only a linear transform is applied to the data signals, whereas VP necessitates a closest-point search in a lattice to find the perturbation signal which reduces the necessary transmit power. In this paper, we analyze the high signal-to-noise ratio (SNR) performance of VP assuming optimal decoding. As the perturbation process hinders the analytical assessment of the VP performance, lower and upper bounds on the expected data rate of VP systems are reviewed and proposed. Based on these bounds, VP is compared to linear precoding w.r.t. the weighted sum rate, the power resulting from a quality of service (QoS) formulation, and the performance when balancing the rates.