Millimeter wave (mmWave) frequency bands, ranging from 24 GHz to 100 GHz, are primarily considered for the low latency communication in fifth generation mobile technology (5G). This article investigates path loss modeling atthe 24 GHz industrial, scientific, and medical (ISM) band in indoor industrial environments. Radio channel measurements were carried out to study the narrow-band channel characteristics in three different industrial environments in Sweden. The measurements were conducted using an affordable but highly competent in-house assembled mmWave testbed, reusing several radio instruments available in our lab. A comprehensive study isperformed to investigate the path loss based on three different models.

Millimeter wave (mmWave) wireless technology is primarily considered for low latency communication in fifth-generation mobile technology (5G) and has the potential to revolutionize industrial automation and manufacturing processes. This article investigates multipath radio propagation in indoor industrial environments at the 24 GHz industrial, scientific and medical (ISM) mmWave frequency band. The wideband radio channel measurements were carried out in four different industrial environments in Sweden. The measurements were conducted using an affordable but highly competent in-house assembled mmWave testbed, reusing radio instruments available in our lab. The measurement environments were chosen based on their radio wave reflection characteristics. The multipath propagation characteristics are analyzed with respect to the power delay profile (PDP), coherence bandwidth, and root mean square (RMS) delay spread. Additionally, the Saleh-Valenzuela model parameters are estimated for these industrial environments.

Experimental characterization of an amplifier's nonlinear properties at 24 GHz is presented in single and dual-band operation using orthogonal frequency-division multiplex signals. A test system for characterizing an amplifier's nonlinear properties at millimeter-wave frequencies for single and dual-band excitation is presented. The use of standard instrument enables a feasible test system. Analytical expressions based on a statistical analysis of signals and hardware impairments were used to analyze the experimental data versus power level and found to describe well the experimental results, including inter- and cross-modulation distortion. Parameters are derived that could be used in system studies.

Human civilization is now staring at the fourth industrial revolution, where wireless technologies will play a pivotal role in its success. Wireless sensors’ role is also becoming more significant in the present day to facilitate industrial automation and manufacturing processes and address health, safety, and environmental concerns. However, wireless communication is primarily unreliable due to noise, interference, and channel fading. Several factors, like hardware quality of the sensors, imperfect calibration, harsh environment, and deployment locations, can also affect the sensors’ observation, which throws further challenges for information reliability and latency. These challenges must be addressed urgently for the success of Industry 4.0.

The scope of this Ph.D. research works is broadly divided into two research problems. The first research problem, this dissertation investigates, is how to retrieve and process the local detection of wireless sensors in critical industrial applications. Diversity techniques are known to improve the reliability of wireless communication. Therefore, various spatial diversity techniques using an antenna array with a large number of elements at the receiver are investigated first to find out the suitability of wireless communication for critical industrial applications. Moreover, in order to improve sensors’ detection performance, distributed detection methods are popularly used. This Ph.D.thesis proposes techniques and algorithms to transmit and fuse local decisions from non-identical wireless sensors, e.g., sensors with different detection capabilities. The fusion center utilizes the spatial diversity or spatial multiplexing based scheme to retrieve the sensors’ local decisions.

In order to design a reliable wireless communication system, it is highly desirable to understand the channel characteristics of the wireless medium. The second research problem this dissertation address is to characterize the radio propagation channel in one of the millimeter wave frequency bands. Millimeter wave wireless technologies bring several benefits, which can further revolutionize the industrial manufacturing and automation processes. In this.D. research work, the radio channel measurements were carried out at the24 GHz ISM band in various industrial environments within Gävle, Sweden, with the help of highly competent in-house assembled affordable testbeds. Several radio propagation aspects, like, the large scale fading, small scale fading, multipath propagation, and Doppler effect, are studied.

Mänskligheten ser nu med tillförsikt fram emot den fjärde industriella revolutionen, där trådlös teknik kommer att spela en central roll i dess framgång. Trådlösa sensorer blir också allt viktigare för att underlätta industriell automatisering och tillverkningsprocesser men även hälsa, säkerhet och miljö. Tillförlitligheten hos trådlös kommunikation påverkas dock av brus, störningar och kanalfädning. Ytterligare faktorer, som sensorns hårdvarumässiga kvalitet, ofullständig kalibrering, tuff omgivande miljö och begränsade placeringsmöjligheter, kan också påverka sensorernas observation, vilket ger ytterligare utmaningar för latens och tillförlitlighet i informationsflödet. Dessa utmaningar måste hanteras snarast för att Industry 4.0 ska lyckas.

Innehållet i denna doktorsavhandling är generellt sett uppdelat i två forskningsfrågor. Den första forskningsfrågan som denna avhandling undersöker, är hur man kan hämta och bearbeta information från fristående lokala sensorer i kritiska industriella applikationer. Diversitetstekniker är kända för att förbättra tillförlitligheten hos trådlös kommunikation. Därför undersöks inledningsvis olika spatiella divsersitetstekniker med ett stort antal antennelement vid mottagaren för att ta reda på lämpligheten för trådlös kommunikation för kritiska industriella applikationer. För att förbättra sensorernas detekteringsprestanda används dessutom distribuerade detekteringsmetoder. Denna doktorsavhandling föreslår metoder och algoritmer för att överföra och kombinera lokala beslut från icke-identiska trådlösa sensorer, t.ex. sensorer med olika detekteringsfunktioner. Sensorernas lokala beslut samlas ihop med hjälp av spatiell diversitet eller multiplexering till ett centralt detektionsbeslutet

För att utforma ett pålitligt trådlöst kommunikationssystem är det nödvändigt att förstå kanalegenskaperna för den trådlösa miljön. Den andra forskningsfrågan, som denna avhandling behandlar, är att karakterisera radioutbredningskanaler i ett av frekvensbanden för millimetervågor. Trådlös kommunikation med millimetervågor ger flera fördelar, vilket kan revolutionera industriella tillverknings- och automatiseringsprocesser ytterligare. I denna doktorsavhandling utfördes radiokanalmätningarna vid 24 GHz i ISM-bandet vid olika industriella miljöer i Gävle, Sverige, med hjälp av prisvärda, internt designade, testbäddar baserade på högprestandainstrument. Flera radioutbredningsaspekter har studerats, så som flervägsutbredning, dopplereffekt samt storskalig och småskalig fädning.

This article investigates the wide-band channel characteristics at 24 GHz ISM band in a mobile radio environment. The mobility in the test environment is achieved by attaching the transmit antenna to a KUKA robot’s arm. The radio measurements were carried out inside the robotics lab at the University of Gävle, Sweden. The radio channel measurements were carried out at various situations, e.g., line of sight (LOS), non-line of sight (NLOS), regular lab environment, reflective environment, and different velocities of the robot’s arm. The influence of these situations on the power delay profile, Doppler spectral density, root mean square (RMS) delay spread, RMS Doppler spread, coherence bandwidth and coherence time, has been studied.

In this research paper, fusion in the air (FIA) and fusion at the receiver (FAR) - two different approaches of multi-hypotheses distributed detection for wireless sensor networks with decision fusion center (DFC) - are investigated. The DFC is equipped with multiple antennas, whereas each of the sensors has a single antenna. The performance of these schemes is evaluated in two different scenarios; with identical sensors and non-identical sensors, in terms of their detection capabilities. For a global event, identical sensors observe an equal number of hypotheses, whereas the number of hypotheses detected by the non-identical sensors can be different. When all the sensors in the network are identical, the FIA based technique has a higher detection probability in transmit power constrained situations. However, the FAR scheme performs better when the transmit power budget is higher. Additionally, in the network with non-identical wireless sensors, the FAR based technique is unable to exploit the benefits from the local decisions of the low capability sensors. Therefore the FAR scheme has a lower detection probability than the FIA based approach.

In this paper, a multi-hypothesis distributed detection technique with non-identical local detectors is investigated. Here, for a global event, some of the sensors/detectors can observe the whole set of hypotheses, whereas the remaining sensors can either see only some aspects of the global event or infer more than one hypothesis as a single hypothesis. Another possible option is that different sensors provide complementary information. The local decisions are sent over a multiple access radio channel so that the data fusion is formed in the air before reaching the decision fusion center (DFC). An optimal energy fusion rule is formulated by considering the radio channel effects and the reliability of the sensors together, and a closed-form solution is derived. A receive beamforming algorithm, based on a modification of Lozano's algorithm, is proposed to equalize the channel gains from different sensors. Sensors with limited detection capabilities are found to boost the overall system performance when they are used along with fully capable sensors. The additional transmit power used by these sensors is compensated by the designed fusion rule and the antenna array gain. Additionally, the DFC, equipped with a large antenna array, can reduce the overall transmit energy consumption without sacrificing the detection performance.

There has been very little exploration when it comes to design distributed detection techniques and data fusion rules with non-identical sensors. This concept can be utilized in many possible applications within industrial automation, surveillance and safety. Here, for a global event, some of the sensors/detectors in the network can observe the full set of the hypotheses, whereas the remaining sensors infer more than one hypotheses as a single hypothesis. The local decisions are sent to the decision fusion center (DFC) over a multiple access wireless channel. In this paper, a fusion rule based on minimization of variance of the local mis-detection is proposed. The presence of sensors with limited detection capabilities is found to have a positive impact on the overall system performance, both in terms of probability of detection and transmit power consumption. Additionally, when the DFC is equipped with a large antenna array, the overall transmit power consumption can be reduced without sacrificing the detection performance. 

Industrial automation and safety applications demand low latency and ultra reliable communication. Currently deployed wireless communication technologies are mostly developed for non-critical applications and hence, they are not suitable for these kind of applications. On the other hand, cable based communication is widely popular in industries, even though it has limitations towards cost of installment and is susceptible towards mechanical wear and tear. This paper reviews the feasibility of large antenna arrays at the receiver to achieve low latency and ultra reliable communication for up-link scenarios. The suitability of both coherent and non-coherent multiple input multiple output (MIMO) receivers are investigated. Non-coherent MIMO receiver is found to be a promising option as signal to noise power ratio (SNR) is fairly reasonable in achieving the desired reliability. The effect of antenna correlation at the transmitter and at receiver on reliability are also looked into. Its influence on the system performance is very nominal. Moreover, in certain scenarios, antenna correlation at the transmitter gives a significant improvement in system performance. Furthermore, having a single antenna at the sensors is found not to be a limiting factor in achieving the desired performance goal.