| 1. |
- Basharat, S., et al.
(author)
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Reconfigurable Intelligent Surfaces : Potentials, Applications, and Challenges for 6G Wireless Networks
- 2021
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In: IEEE wireless communications. - : Institute of Electrical and Electronics Engineers Inc.. - 1536-1284 .- 1558-0687.
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Journal article (peer-reviewed)abstract
- Reconfigurable intelligent surfaces (RISs), with the potential to realize smart radio environments, have emerged as an energy-efficient and a cost-effective technology to support the services and demands foreseen for coming decades. By leveraging a large number of low-cost passive reflecting elements, RISs introduce a phase-shift in the impinging signal to create a favorable propagation channel between the transmitter and the receiver. In this article, we provide a tutorial overview of RISs for sixth-generation (6G) wireless networks. Specifically, we present a comprehensive discussion on performance gains that can be achieved by integrating RISs with emerging communication technologies. We address the practical implementation of RIS-assisted networks and expose the crucial challenges, including the RIS reconfiguration, deployment and size optimization, and channel estimation. Furthermore, we explore the integration of RIS and non-orthogonal multiple access (NOMA) under imperfect channel state information (CSI). Our numerical results illustrate the importance of better channel estimation in RIS-assisted networks and indicate the various factors that impact the size of RIS. Finally, we present promising future research directions for realizing RIS-assisted networks in 6G communication. IEEE
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| 2. |
- Beltramelli, Luca, et al.
(author)
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Energy efficiency of slotted LoRaWANcommunication with out-of-band synchronization
- 2021
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In: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662.
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Journal article (peer-reviewed)abstract
- Although the idea of using wireless links for covering large areas is not new, the advent of Low Power Wide area networks (LPWANs) has recently started changing the game. Simple, robust, narrowband modulation schemes permit the implementation of low-cost radio devices offering high receiver sensitivity, thus improving the overall link budget. The several technologies belonging to the LPWAN family, including the well-known LoRaWAN solution, provide a cost-effective answer to many Internet-of-things (IoT) applications, requiring wireless communication capable of supporting large networks of many devices (e.g., smart metering). Generally, the adopted medium access control (MAC) strategy is based on pure ALOHA, which, among other things, allows to minimize the traffic overhead under constrained duty cycle limitations of the unlicensed bands. Unfortunately, ALOHA suffers from poor scalability, rapidly collapsing in dense networks. This work investigates the design of an improved LoRaWAN MAC scheme based on slotted ALOHA. In particular, the required time dissemination is provided by out-of-band communications leveraging on Radio Data System(FM-RDS) broadcasting, which natively covers wide areas both indoor and outdoor. An experimental setup based on low-cost hardware is used to characterize the obtainable synchronization performance and derive a timing error model. Consequently, improvements in success probability and energy efficiency have been validated by means of simulations in very large networks with up to 10000 nodes. It is shown that the advantage of the proposed scheme over conventional LoRaWAN communication is up to 100% when short update time and large payload are required. Similar results are obtained regarding the energy efficiency improvement, that is close to 100% for relatively short transmission intervals and long message duration; however, due to the additional overhead for listening the time dissemination messages, efficiency gain can be negative for very short duration of message fastly repeating.
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| 3. |
- Beltramelli, Luca, et al.
(author)
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LoRa beyond ALOHA : An Investigation of Alternative Random Access Protocols
- 2021
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In: IEEE Transactions on Industrial Informatics. - 1551-3203 .- 1941-0050. ; 17:5, s. 3544-3554
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Journal article (peer-reviewed)abstract
- We present a stochastic geometry-based model to investigate alternative medium access choices for LoRaWAN a widely adopted low-power wide-area networking (LPWAN) technology for the Internet-of-things (IoT). LoRaWAN adoption is driven by its simplified network architecture, air interface, and medium access. The physical layer, known as LoRa, provides quasi-orthogonal virtual channels through spreading factors (SFs) and time-power capture gains. However, the adopted pure ALOHA access mechanism suffers, in terms of scalability, under the same-channel same-SF transmissions from a large number of devices. In this paper, our objective is to explore access mechanisms beyond-ALOHA for LoRaWAN. Using recent results on time- and power-capture effects of LoRa, we develop a unified model for the comparative study of other choices, i.e., slotted ALOHA and carrier-sense multiple access (CSMA). The model includes the necessary design parameters of these access mechanisms, such as guard time and synchronization accuracy for slotted ALOHA, carrier sensing threshold for CSMA. It also accounts for the spatial interaction of devices in annular shaped regions, characteristic of LoRa, for CSMA. The performance derived from the model in terms of coverage probability, throughput, and energy efficiency are validated using Monte-Carlo simulations. Our analysis shows that slotted ALOHA indeed has higher reliability than pure ALOHA but at the cost of lower energy efficiency for low device densities. Whereas, CSMA outperforms slotted ALOHA at smaller SFs in terms of reliability and energy efficiency, with its performance degrading to pure ALOHA at higher SFs.
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| 4. |
- Beltramelli, Luca, et al.
(author)
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Synchronous LoRa Communication by Exploiting Large-Area out-of-band Synchronization
- 2021
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In: IEEE Internet of Things Journal. - 2327-4662. ; 8:10, s. 7912-7924
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Journal article (peer-reviewed)abstract
- Many new narrowband low-power wide-area networks (LPWANs) (e.g., LoRaWAN, Sigfox) have opted to use pure ALOHA-like access for its reduced control overhead and asynchronous transmissions. Although asynchronous access reduces the energy consumption of IoT devices, the network performance suffers from high intra-network interference in dense deployments. Contrarily, adopting synchronous access can improve throughput and fairness, however, it requires time synchronization. Unfortunately, maintaining synchronization over the narrowband LPWANs wastes channel time and transmission opportunities. In this paper, we propose the use of out-of-band time-dissemination to relatively synchronize the LoRa devices and thereby facilitate resource-efficient slotted uplink communication. In this respect, we conceptualize and analyze a co-designed synchronization and random access communication mechanism that can effectively exploit technologies providing limited time accuracy, such as FM radio data system (FM-RDS). While considering the LoRa-specific parameters, we derive the throughput of the proposed mechanism, compare it to a generic synchronous random access using in-band synchronization, and design the communication parameters under time uncertainty. We scrutinize the transmission time uncertainty of a device by introducing a clock error model that accounts for the errors in the synchronization source, local clock, propagation delay, and transceiver’s transmission time uncertainty. We characterize the time uncertainty of FM-RDS with hardware measurements and perform simulations to evaluate the proposed solution. The results, presented in terms of success probability, throughput, and fairness for a single-cell scenario, suggest that FM-RDS, despite its poor absolute synchronization, can be used effectively to realize time-slotted communication in LoRa with performance similar to that of more accurate time-dissemination technologies.
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| 5. |
- Grimaldi, Simone, et al.
(author)
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Autonomous Interference Mapping for Industrial Internet of Things Networks Over Unlicensed Bands : Identifying Cross-Technology Interference
- 2021
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In: IEEE Industrial Electronics Magazine. - 1932-4529 .- 1941-0115. ; 15:1, s. 67-78
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Journal article (other academic/artistic)abstract
- The limited coexistence capabilities of current Internet of Things (IoT) wireless standards produce inefficient spectrum utilization and mutual performance impairment. The problem becomes critical in industrial IoT (IIoT) applications, which have stringent quality-of-service (QoS) requirements and very low error tolerance. The constant growth of wireless applications over unlicensed bands mandates then the adoption of dynamic spectrum-access techniques, which can significantly benefit from interference mapping over multiple dimensions of the radio space. In this article, we analyze the critical role of real-time interference detection and classification mechanisms that rely on only IIoT devices, without the added complexity of specialized hardware. The tradeoffs between classification performance and feasibility are analyzed in connection with the implementation on low-complexity IIoT devices. Moreover, we explain how to use such mechanisms for enabling IIoT networks to construct and maintain multidimensional interference maps at runtime in an autonomous fashion. Finally, we give an overview of the opportunities and challenges of using interference maps to enhance the performance of IIoT networks under interference.
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| 6. |
- Ilyas, Danish, et al.
(author)
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Performance of STBC Cooperative NOMA with Imperfect Successive Interference Cancellation
- 2021
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In: IEEE International Conference on Communications (ICC). - : IEEE.
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Conference paper (peer-reviewed)abstract
- This paper explores the performance gains achieved by space time block coding (STBC)-based non orthogonal multiple access (NOMA) scheme versus regular cooperative NOMA under the influence of imperfect successive interference cancellation (SIC). Imperfection in the SIC process of NOMA causes performance degradation which is proportional to the number of SIC operations involved. It is demonstrated through outage and sum-rate performance that STBC-NOMA maintains a considerable performance margin from conventional cooperative NOMA even under adverse imperfections in SIC. Furthermore, closed-form expressions of signal to interference ratio (SIR) at user equipment (UE) and outage probability for STBC-NOMA under imperfect SIC are also derived and validated.
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| 7. |
- Khodakhah, Farnaz, et al.
(author)
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Multiple Access-Enabled Relaying with Piece-Wise and Forward NOMA : Rate Optimization under Reliability Constraints
- 2021
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In: Sensors. - : MDPI AG. - 1424-8220. ; 21:14
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Journal article (peer-reviewed)abstract
- The increasing proliferation of Internet-of-things (IoT) networks in a given space requires exploring various communication solutions (e.g., cooperative relaying, non-orthogonal multiple access, spectrum sharing) jointly to increase the performance of coexisting IoT systems. However, the design complexity of such a system increases, especially under the constraints of performance targets. In this respect, this paper studies multiple-access enabled relaying by a lower-priority secondary system, which cooperatively relays the incoming information to the primary users and simultaneously transmits its own data. We consider that the direct link between the primary transmitter-receiver pair uses orthogonal multiple access in the first phase. In the second phase, a secondary transmitter adopts a relaying strategy to support the direct link while it uses non-orthogonal multiple access (NOMA) to serve the secondary receiver. As a relaying scheme, we propose a piece-wise and forward (PF) relay protocol, which, depending on the absolute value of the received primary signal, acts similar to decode-and-forward (DF) and amplify-and-forward (AF) schemes in high and low signal-to-noise ratio (SNR), respectively. By doing so, PF achieves the best of these two relaying protocols using the adaptive threshold according to the transmitter-relay channel condition. Under PF-NOMA, first, we find the achievable rate region for primary and secondary receivers, and then we formulate an optimization problem to derive the optimal PF-NOMA time and power fraction that maximize the secondary rate subject to reliability constraints on both the primary and the secondary links. Our simulation results and analysis show that the PF-NOMA outperforms DF-NOMA and AF-NOMA-based relaying techniques in terms of achievable rate regions and rate-guaranteed relay locations.
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| 8. |
- Minhaj, Syed Usama, et al.
(author)
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How SIC-enabled LoRa Fares under Imperfect Orthogonality?
- 2021
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In: IWCMC 2021. - : IEEE. - 9781728186160 ; , s. 729-734
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Conference paper (peer-reviewed)abstract
- With the increase of connected Internet-of-things (IoT) devices, the need for low-power wide-area networks (LP-WANs) is imminent, and LoRaWAN is one such technology that offers an elegant solution to the problem of long-range communication and battery consumption. A parameter of special interest in LoRaWAN is the spreading factor (SF), and it is often assumed that communication between different SFs is independent of each other. However, this claim has been practically debunked by many works, proving that SFs have imperfect orthogonality. To maximize connectivity and throughput, several techniques have been introduced, such as non-orthogonal-multiple-access (NOMA) and dynamic resource allocation. NOMA is getting a lot of attention recently, especially for IoT networks, because it embraces interference and tries to obtain desired information packets from corrupted ones. Furthermore, NOMA can be easily implemented on the base-station side by using the principle of successive interference cancellation (SIC). In this paper, we investigate how SIC, under the assumption of imperfect orthogonality of SF channels, can be used to increase the performance of the system. We find the expressions for success and coverage probability considering various SF allocation schemes and found the most efficient scheme for different scenarios.
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| 9. |
- Mugisha, Richard, et al.
(author)
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Joint Power and Blocklength Allocation for Energy-Efficient Ultra- Reliable and Low- Latency Communications
- 2021
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In: International Symposium on Wireless Communication Systems (ISWCS).
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Conference paper (peer-reviewed)abstract
- In this work, we address the problem of jointly optimizing the transmit power and blocklength of a two-users scenario for orthogonal multiple access (OMA) and non-orthogonal (NOMA) access schemes. We formulate an optimization problem to obtain the energy-optimal blocklength and transmit power under ultra-reliable and low-latency communications (URLLC) reliability and latency constraints. The aim is to minimize the energy consumption at short-blocklength regime. Due to the problem's complexity, we decompose it into two sub-problems for the OMA case, where the base station (BS) employs a 2D search for strong user, and the bisection method for the weak user. On the contrary, we find the sufficient transmit power conditions for NOMA to obtain the feasible solution. Our results show that the minimum required energy increases with the reliability requirement for both the OMA and NOMA, while NOMA consumes more energy than OMA for the same reliability target. Moreover, the results indicate that NOMA reduces latency due to better blocklength utilization compared to OMA when the channel gain disparity between the users is small.
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| 10. |
- Sisinni, Emiliano, et al.
(author)
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Wireless Communications for Industrial Internet of Things : The LPWAN Solutions
- 2021
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In: Wireless Networks and Industrial IoT. - Cham : Springer. - 9783030514723 - 9783030514730 ; , s. 79-103
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Book chapter (other academic/artistic)abstract
- Industrial Internet of things (IIoT) and machine-to-machine (M2M) connectivity are strictly related and represent the next step in the ever-evolving world of industrial communications. The lack of a single wireless technology capable of satisfying new requirements in terms of flexibility, scalability, and low-power consumption led to the proposal of many different protocols to support the plethora of brand new offered services. In this chapter, an overview of low-power wide-area network (LPWAN) technologies is provided. After a discussion about the common features of available LPWAN solutions, the focus will be moved to the LoRaWAN standard, which is attracting the most significant interest from both the industrial and academic domains. Finally, some considerations on the use of LPWAN solutions for industrial applications, and the need and availability of network simulation tools, will be sketched.
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