LTE and Wi−Fi Coexistence in Unlicensed Spectrum with Application to Smart Grid: A Review
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paper_title: Modeling and Analyzing the Coexistence of Licensed-Assisted Access LTE and Wi-Fi

paper_content:

Licensed-assisted access (LAA) is a feature of Long-Term Evolution (LTE) which enables operation in the unlicensed spectrum. LAA guarantees fair coexistence with Wi-Fi by implementing the listen- before-talk (LBT) mechanism. In this paper, we leverage stochastic geometry to characterize key performance metrics of neighboring LAA and Wi-Fi networks. Our analysis is focused on a single unlicensed frequency band, where the locations for coexisting LTE eNodeBs (eNBs) and Wi-Fi access points (APs) are modeled as two independent homogeneous Poisson point processes (PPPs). Based on an analytical modeling of the channel access procedure, we have derived the medium access probability (MAP), the signal-to- interference-plus-noise ratio (SINR) distribution, the density of successful transmissions (DST), and the data rate distribution for both LAA and Wi-Fi. We show that compared to the baseline scenario where Wi-Fi coexists with an additional Wi-Fi network, LAA can improve the DST and data rate performance of Wi-Fi by adopting more sensitive clear channel assessment thresholds and/or larger contention window sizes. Meanwhile, LAA is demonstrated to achieve acceptable data rate performance despite using LBT.
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paper_title: Efficient Coexistence of LTE With WiFi in the Licensed and Unlicensed Spectrum Aggregation

paper_content:

The exploitation of unlicensed bands by the LTE-advanced (LTE-A) system has become a reality through the proposal of licensed assisted access (LAA) that relies on the carrier aggregation concept within the 3GPP framework. The efficient coexistence of LTE-A and WiFi in the unlicensed spectrum bands requires advanced intelligent techniques. This paper first investigates the concept of LAA, which consists of four main functionalities: 1) carrier selection (CS); 2) listen-before-talk; 3) discontinuous transmission (DTX); and 4) transmit power control (TPC). Second, the LAA functionality implementation is provided using an open source LTE-A downlink link level simulator. Third, we devise an enhanced learning technique for CS and DTX for efficient coexistence among LTE-A and WiFi users. In particular, we provide a Q-learning mechanism for the advanced learning of the unlicensed band activity resulting in the efficient coexistence. Finally, we enhance the coexistence further through a double Q-learning method as a proposal for CS that takes into account both DTX and TPC improving both LTE and WiFi performance. Simulation results are provided for all the use cases that reveal the benefit of exploiting unlicensed bands in next generation mobile cellular networks.
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paper_title: Coexistence of Wi-Fi and Heterogeneous Small Cell Networks Sharing Unlicensed Spectrum

paper_content:

As two major players in terrestrial wireless communications, Wi-Fi systems and cellular networks have different origins and have largely evolved separately. Motivated by the exponentially increasing wireless data demand, cellular networks are evolving towards a heterogeneous and small cell network architecture, wherein small cells are expected to provide very high capacity. However, due to the limited licensed spectrum for cellular networks, any effort to achieve capacity growth through network densification will face the challenge of severe inter-cell interference. In view of this, recent standardization developments have started to consider the opportunities for cellular networks to use the unlicensed spectrum bands, including the 2.4 GHz and 5 GHz bands that are currently used by Wi-Fi, Zigbee and some other communication systems. In this article, we look into the coexistence of Wi-Fi and 4G cellular networks sharing the unlicensed spectrum. We introduce a network architecture where small cells use the same unlicensed spectrum that Wi-Fi systems operate in without affecting the performance of Wi-Fi systems. We present an almost blank subframe (ABS) scheme without priority to mitigate the co-channel interference from small cells to Wi-Fi systems, and propose an interference avoidance scheme based on small cells estimating the density of nearby Wi-Fi access points to facilitate their coexistence while sharing the same unlicensed spectrum. Simulation results show that the proposed network architecture and interference avoidance schemes can significantly increase the capacity of 4G heterogeneous cellular networks while maintaining the service quality of Wi-Fi systems.
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paper_title: Experimental study of concurrent transmission in wireless sensor networks

paper_content:

We undertake a systematic experimental study of the effects of concurrent packet transmissions in low-power wireless networks. Our measurements, conducted with Mica2 motes equipped with CC1000 radios, confirm that guaranteeing successful packet reception with high probability in the presence of concurrent transmissions requires that the signal-to-interference-plus-noise-ratio (SINR) exceed a critical threshold. However, we find a significant variation of about 6 dB in the threshold for groups of radios operating at different transmission powers. We find that it is harder to estimate the level of interference in the presence of multiple interferers. We also find that the measured SINR threshold generally increases with the number of interferers. Our study offers a better understanding of concurrent transmissions and suggests richer interference models and useful guidelines to improve the design and analysis of higher layer protocols.
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paper_title: Licensed-assisted access for LTE in unlicensed spectrum: A MAC protocol design

paper_content:

Licensed-assisted access (LAA), which conveys data information via both licensed and unlicensed bands through spectrum aggregation, becomes a promising solution to enhance the capacity of wireless systems. In view of the potential impact on the incumbent system operating in unlicensed bands, the medium access control (MAC) protocol design for LAA system to harmonically coexist with its neighboring incumbent users is one of the most critical and challenging issues. In this paper, we consider a long-term evolution-based LAA (LAA-LTE) system operating in the WiFi unlicensed spectrum, for which the listen-before-talk-based MAC protocol is carefully designed. By quantifying the WiFi throughput and packet delay in the coexisting system, we formulate the constraints of LAA-LTE transmission time to fairly maintain WiFi services. The conditions of known and unknown network size of incumbent WiFi system are each considered separately. Then, the feasible region of LAA-LTE transmission time is determined, and the LAA-LTE protocol is optimized for maximizing the LAA-LTE throughput or the overall throughput contributed by both LAA-LTE and WiFi system. The theoretical analysis is validated via simulation, which also illustrates important observations when LAA-LTE and WiFi systems coexist. This paper offers guidelines to design the LAA-LTE system, paving the way to a controllable, not only harmonious, coexistence of LAA-LTE and WiFi systems in the unlicensed spectrum.
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paper_title: A SURVEY OF LTE WI-FI COEXISTENCE IN UNLICENSED BANDS

paper_content:

With the rapid growth of mobile data, many LTE operators are interested in leveraging unlicensed bands to enhance data rates and user experience. Th is paper investigates the problem of the coexistence of LTE and Wi-Fi in 5 GHz unlicensed bands. We fi rst introduce the current rules for the 5 GHz unlicensed bands and the carrier aggregation technique. We then discuss four deployment scenarios and two LTE-unlicensed (LTE-U) coexistence scenarios. Further, we provide a feature comparison between LTE and Wi-Fi in the PHY/MAC layers, and review the coexistence methods for LTE-U and Wi-Fi without or with the Listen- Before-Talk (LBT) mechanism. Th is paper is concluded by an examination of Wi-Fi link aggregation and in-device coexistence issues.
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paper_title: Multi-armed bandit for LTE-U and WiFi coexistence in unlicensed bands

paper_content:

In order to cope with the phenomenal growth of mobile data traffic, unlicensed spectrum can be utilized by the Long Term Evolution (LTE) cellular systems. However, ensuring fair coexistence with WiFi is a mandatory requirement. In one approach, periodically configurable transmission gaps can be used to facilitate a coexistence between WiFi and LTE. In this paper, a Multi-Armed Bandit (MAB) based dynamic duty cycle selection method is proposed for configuration of transmission gaps ensuring a better coexistence for both technologies. Then the concept is further strengthened with downlink power control mechanism using the same algorithm leading to a high energy efficiency and interference reduction. Performance results are given for different user equipment and WiFi station densities in which it is shown that significant improvements in overall throughput and energy efficiency can be achieved.
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paper_title: Performance Analysis of LAA and WiFi Coexistence in Unlicensed Spectrum Based on Markov Chain

paper_content:

License-assisted access (LAA) is a candidate feature in 3GPP Rel-13 to meet the explosive growth of traffic demand. The main idea of LAA is to deploy LTE in the unlicensed band (mainly the 5GHz band), which is abundant with available spectrum. However, the major concern is the coexistence between WiFi and LAA in the same band. This paper presents a new framework to evaluate the downlink performance of coexisting LAA and WiFi networks. By using Markov chain, analytical models are established based on WiFi distributed coordination function (DCF) and two listen-before- talk (LBT) schemes. These two LBT schemes are Cat 3 and Cat 4 LBT, which mainly differ in medium access schemes in terms of backoff procedure. Unlike most existing works, which focus on the impact on WiFi performance posed by LAA, the performance of LAA is also evaluated. Our analysis shows that throughput of a WiFi network can be enhanced by adding or replacing WiFi access points (APs) with LAA E-UTRAN Node Bs (eNBs), at the expense of different levels of WiFi performance degradation. A trade-off between WiFi protection and LAA-WiFi system performance enhancement is observed. WiFi throughput and delay are less affected by Cat 4 LBT scheme, while Cat 3 LBT scheme provides higher LAA-WiFi system throughput. The choice of LBT schemes relies on the network planning priority, WiFi performance protection and LAA system performance requirements.
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paper_title: A review of wireless communications for smart grid

paper_content:

Smart grid is envisioned to meet the 21st century energy requirements in a sophisticated manner with real time approach by integrating the latest digital communications and advanced control technologies to the existing power grid. It will connect the global users through energy efficiency and awareness corridor. This paper presents a comprehensive review of Wireless Communications Technologies (WCTs) for implementation of smart grid in a systematic way. Various network attributes like internet protocol (IP) support, power usage, data rate etc. are considered to compare the communications technologies in smart grid context. Techniques suitable for Home Area Networks (HANs) like ZigBee, Bluetooth, Wi-Fi, 6LoWPAN and Z-Wave are discussed and compared in context of consumer concerns and network attributes. A similar approach in context of utilities concerns is adopted for wireless communications techniques for Neighborhood Area Networks (NANs) which include WiMAX and GSM based cellular standards. Smart grid applications, associated network issues and challenges are elaborated at the end.
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paper_title: Simultaneous transmission opportunities for LTE-LAA smallcells coexisting with WiFi in unlicensed spectrum

paper_content:

LTE License-Assisted Access (LTE-LAA) in unlicensed spectrum has drawn a lot of attention due to its appealing data traffic offloading potential. However, the coexistence of LTE and WiFi technologies in the same unlicensed bands needs careful design to avoid severe interference between them. In this paper, we propose a coexistence scheme to create opportunities for LTE-LAA small cells and WiFi devices to transmit simultaneously. We combine Multiple Signal Classification (MUSIC) direction of arrival (DOA) estimation with null steering techniques to avoid collisions between LTE-LAA and WiFi transmissions. We assume that the LTE-LAA small cells are equipped with the latest 802.11 receivers for monitoring WiFi transmissions and for capturing simultaneous transmission timing. The performance of the proposed scheme in terms of collision avoidance and channel occupancy time ratio is evaluated via simulations. The results show that with DOA estimation and null steering, LTE-LAA small cells can transmit simultaneously with nearby WiFi devices without causing significant interference to them. As a result, LTE-LAA small cells can gain much more channel access opportunities and longer channel occupancy time while being “invisible” to coexisting WiFi networks.
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paper_title: LAA-based LTE and ZigBee coexistence for unlicensed-band smart grid communications

paper_content:

The advent of smart grid introduces abundant number of smart meters which require bidirectional reliable communication. The deployment of advanced metering infrastructure (AMI) in smart grid networks will be auspicious if the existing infrastructure of LTE networks can be utilized. On the other hand, use of LTE infrastructure and spectrum by AMIs will further load the already congested broadband wireless networks. Recently, use of the unlicensed spectrum by the LTE technology is seen as a promising approach to offload the existing traffic from the licensed spectrum. In our study, we investigate the coexistence of LTE and ZigBee networks at the unlicensed frequency band of 2.4 GHz. We consider a time division duplexing (TDD)-LTE system accompanied by ZigBee network with FTP traffic model for system level simulations. The simulation results demonstrate that the simultaneous operation of LTE and ZigBee on the 2.4 GHz band reduces ZigBee's performance, but still meets the data communication requirements for AMI as prescribed by Department of Energy (DoE).
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paper_title: Licensed-assisted access for WiFi-LTE coexistence in the unlicensed spectrum

paper_content:

One of the effective ways to address the exponentially increasing traffic demand in mobile communication systems is to use more spectrum. Although licensed spectrum is always preferable for providing better user experience, unlicensed spectrum can be considered as an effective complement. Before moving into unlicensed spectrum, it is essential to carry out proper coexistence performance evaluations. In this paper, we analyze WiFi 802.11n and Long Term Evolution (LTE) coexistence performance considering multi-layer cell layouts through system level simulations. We consider a time division duplexing (TDD)-LTE system with an FTP traffic model for performance evaluation. Simulation results show that WiFi performance is more vulnerable to LTE interference, while LTE performance is degraded only slightly. However, WiFi throughput degradation is lower for TDD configurations with larger number of LTE uplink sub-frames and smaller path loss compensation factors.
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paper_title: Hybrid Wi-Fi/LTE aggregation architecture for smart meter communications

paper_content:

The 3GPP Long Term Evolution (LTE) technology and its evolutions are promising candidate technologies to support smart meter communications. However, smart meter traffic is uplink heavy and needs large number of simultaneously connected users. This reduces LTE's potential to be employed for smart meter communications. To improve the overall performance, in this paper, we propose a hybrid WiFi-LTE aggregation data communication architecture. Specifically, two IEEE 802.11 based layers (IEEE 802.11b/g/n and IEEE 802.11s) are added to the bottom of the LTE architecture to aggregate local smart grid data and pass the aggregated data through limited number of LTE enabled nodes. These hybrid network architectures are evaluated using extensive ns-3 simulations, and their performance are compared with baseline LTE under smart grid traffic profile. Results show that proposed architectures can improve control channel and random access channel performance, at the cost of tolerable latency degradation.
---
paper_title: Efficient Coexistence of LTE With WiFi in the Licensed and Unlicensed Spectrum Aggregation

paper_content:

The exploitation of unlicensed bands by the LTE-advanced (LTE-A) system has become a reality through the proposal of licensed assisted access (LAA) that relies on the carrier aggregation concept within the 3GPP framework. The efficient coexistence of LTE-A and WiFi in the unlicensed spectrum bands requires advanced intelligent techniques. This paper first investigates the concept of LAA, which consists of four main functionalities: 1) carrier selection (CS); 2) listen-before-talk; 3) discontinuous transmission (DTX); and 4) transmit power control (TPC). Second, the LAA functionality implementation is provided using an open source LTE-A downlink link level simulator. Third, we devise an enhanced learning technique for CS and DTX for efficient coexistence among LTE-A and WiFi users. In particular, we provide a Q-learning mechanism for the advanced learning of the unlicensed band activity resulting in the efficient coexistence. Finally, we enhance the coexistence further through a double Q-learning method as a proposal for CS that takes into account both DTX and TPC improving both LTE and WiFi performance. Simulation results are provided for all the use cases that reveal the benefit of exploiting unlicensed bands in next generation mobile cellular networks.
---
paper_title: Experimental study of concurrent transmission in wireless sensor networks

paper_content:

We undertake a systematic experimental study of the effects of concurrent packet transmissions in low-power wireless networks. Our measurements, conducted with Mica2 motes equipped with CC1000 radios, confirm that guaranteeing successful packet reception with high probability in the presence of concurrent transmissions requires that the signal-to-interference-plus-noise-ratio (SINR) exceed a critical threshold. However, we find a significant variation of about 6 dB in the threshold for groups of radios operating at different transmission powers. We find that it is harder to estimate the level of interference in the presence of multiple interferers. We also find that the measured SINR threshold generally increases with the number of interferers. Our study offers a better understanding of concurrent transmissions and suggests richer interference models and useful guidelines to improve the design and analysis of higher layer protocols.
---
paper_title: Efficient Coexistence of LTE With WiFi in the Licensed and Unlicensed Spectrum Aggregation

paper_content:

The exploitation of unlicensed bands by the LTE-advanced (LTE-A) system has become a reality through the proposal of licensed assisted access (LAA) that relies on the carrier aggregation concept within the 3GPP framework. The efficient coexistence of LTE-A and WiFi in the unlicensed spectrum bands requires advanced intelligent techniques. This paper first investigates the concept of LAA, which consists of four main functionalities: 1) carrier selection (CS); 2) listen-before-talk; 3) discontinuous transmission (DTX); and 4) transmit power control (TPC). Second, the LAA functionality implementation is provided using an open source LTE-A downlink link level simulator. Third, we devise an enhanced learning technique for CS and DTX for efficient coexistence among LTE-A and WiFi users. In particular, we provide a Q-learning mechanism for the advanced learning of the unlicensed band activity resulting in the efficient coexistence. Finally, we enhance the coexistence further through a double Q-learning method as a proposal for CS that takes into account both DTX and TPC improving both LTE and WiFi performance. Simulation results are provided for all the use cases that reveal the benefit of exploiting unlicensed bands in next generation mobile cellular networks.
---
paper_title: Multi-armed bandit for LTE-U and WiFi coexistence in unlicensed bands

paper_content:

In order to cope with the phenomenal growth of mobile data traffic, unlicensed spectrum can be utilized by the Long Term Evolution (LTE) cellular systems. However, ensuring fair coexistence with WiFi is a mandatory requirement. In one approach, periodically configurable transmission gaps can be used to facilitate a coexistence between WiFi and LTE. In this paper, a Multi-Armed Bandit (MAB) based dynamic duty cycle selection method is proposed for configuration of transmission gaps ensuring a better coexistence for both technologies. Then the concept is further strengthened with downlink power control mechanism using the same algorithm leading to a high energy efficiency and interference reduction. Performance results are given for different user equipment and WiFi station densities in which it is shown that significant improvements in overall throughput and energy efficiency can be achieved.
---
paper_title: LTE in the unlicensed spectrum: Evaluating coexistence mechanisms

paper_content:

The Long Term Evolution (LTE) in unlicensed spectrum is an emerging topic in the 3rd Generation Partnership Project (3GPP), which is about an operation of the LTE system in the unlicensed spectrum via license-assisted carrier aggregation. The 5 GHz Unlicensed National Information Infrastructure (U-NII) bands are currently under consideration, but these bands are also occupied by Wireless Local Area Networks (WLAN), specifically those based on the IEEE 802.11a/n/ac technologies. Therefore, an appropriate coexistence mechanism must be augmented to guarantee a peaceful coexistence with the incumbent systems. With this regard, our focus lies on the evaluation of all the proposed coexistence mechanisms so far in a single framework and making a fair comparison of them. The coexistence mechanisms covered in this work includes static muting, listen-before-talk (LBT), and other sensing-based schemes that make a use of the existing WLAN channel reservation protocol.
---
paper_title: Hybrid Wi-Fi/LTE aggregation architecture for smart meter communications

paper_content:

The 3GPP Long Term Evolution (LTE) technology and its evolutions are promising candidate technologies to support smart meter communications. However, smart meter traffic is uplink heavy and needs large number of simultaneously connected users. This reduces LTE's potential to be employed for smart meter communications. To improve the overall performance, in this paper, we propose a hybrid WiFi-LTE aggregation data communication architecture. Specifically, two IEEE 802.11 based layers (IEEE 802.11b/g/n and IEEE 802.11s) are added to the bottom of the LTE architecture to aggregate local smart grid data and pass the aggregated data through limited number of LTE enabled nodes. These hybrid network architectures are evaluated using extensive ns-3 simulations, and their performance are compared with baseline LTE under smart grid traffic profile. Results show that proposed architectures can improve control channel and random access channel performance, at the cost of tolerable latency degradation.
---
paper_title: Frequency band for HAN and NAN communication in Smart Grid

paper_content:

Smart Grid metering and control applications require fast and secured two-way communication. IEEE 802.15.4 based ZigBee is one of the leading communication protocols for Advanced Metering Infrastructure (AMI). In North America, ZigBee supports two distinguished frequency bands — 915MHz and 2.4GHz. In Home Area Network (HAN) of AMI, home appliances communicate with smart meters whereas the communication among neighboring meters is termed as Neighborhood Area Network (NAN). In this study, optimum frequency bands for NAN and HAN communication have been proposed based on the throughput, reliability and scalability. We evaluated and compared the performance of bands 868/915MHz and 2.4GHz for AMI context. The solution also meets the requirements for Smart Grid communication standards as recommended by the US Department of Energy (DOE).
---
paper_title: Multi-armed bandit for LTE-U and WiFi coexistence in unlicensed bands

paper_content:

In order to cope with the phenomenal growth of mobile data traffic, unlicensed spectrum can be utilized by the Long Term Evolution (LTE) cellular systems. However, ensuring fair coexistence with WiFi is a mandatory requirement. In one approach, periodically configurable transmission gaps can be used to facilitate a coexistence between WiFi and LTE. In this paper, a Multi-Armed Bandit (MAB) based dynamic duty cycle selection method is proposed for configuration of transmission gaps ensuring a better coexistence for both technologies. Then the concept is further strengthened with downlink power control mechanism using the same algorithm leading to a high energy efficiency and interference reduction. Performance results are given for different user equipment and WiFi station densities in which it is shown that significant improvements in overall throughput and energy efficiency can be achieved.
---
paper_title: Licensed-assisted access for WiFi-LTE coexistence in the unlicensed spectrum

paper_content:

One of the effective ways to address the exponentially increasing traffic demand in mobile communication systems is to use more spectrum. Although licensed spectrum is always preferable for providing better user experience, unlicensed spectrum can be considered as an effective complement. Before moving into unlicensed spectrum, it is essential to carry out proper coexistence performance evaluations. In this paper, we analyze WiFi 802.11n and Long Term Evolution (LTE) coexistence performance considering multi-layer cell layouts through system level simulations. We consider a time division duplexing (TDD)-LTE system with an FTP traffic model for performance evaluation. Simulation results show that WiFi performance is more vulnerable to LTE interference, while LTE performance is degraded only slightly. However, WiFi throughput degradation is lower for TDD configurations with larger number of LTE uplink sub-frames and smaller path loss compensation factors.
---
paper_title: Efficient Coexistence of LTE With WiFi in the Licensed and Unlicensed Spectrum Aggregation

paper_content:

The exploitation of unlicensed bands by the LTE-advanced (LTE-A) system has become a reality through the proposal of licensed assisted access (LAA) that relies on the carrier aggregation concept within the 3GPP framework. The efficient coexistence of LTE-A and WiFi in the unlicensed spectrum bands requires advanced intelligent techniques. This paper first investigates the concept of LAA, which consists of four main functionalities: 1) carrier selection (CS); 2) listen-before-talk; 3) discontinuous transmission (DTX); and 4) transmit power control (TPC). Second, the LAA functionality implementation is provided using an open source LTE-A downlink link level simulator. Third, we devise an enhanced learning technique for CS and DTX for efficient coexistence among LTE-A and WiFi users. In particular, we provide a Q-learning mechanism for the advanced learning of the unlicensed band activity resulting in the efficient coexistence. Finally, we enhance the coexistence further through a double Q-learning method as a proposal for CS that takes into account both DTX and TPC improving both LTE and WiFi performance. Simulation results are provided for all the use cases that reveal the benefit of exploiting unlicensed bands in next generation mobile cellular networks.
---
paper_title: Frequency band for HAN and NAN communication in Smart Grid

paper_content:

Smart Grid metering and control applications require fast and secured two-way communication. IEEE 802.15.4 based ZigBee is one of the leading communication protocols for Advanced Metering Infrastructure (AMI). In North America, ZigBee supports two distinguished frequency bands — 915MHz and 2.4GHz. In Home Area Network (HAN) of AMI, home appliances communicate with smart meters whereas the communication among neighboring meters is termed as Neighborhood Area Network (NAN). In this study, optimum frequency bands for NAN and HAN communication have been proposed based on the throughput, reliability and scalability. We evaluated and compared the performance of bands 868/915MHz and 2.4GHz for AMI context. The solution also meets the requirements for Smart Grid communication standards as recommended by the US Department of Energy (DOE).
---
paper_title: Modeling and Analyzing the Coexistence of Licensed-Assisted Access LTE and Wi-Fi

paper_content:

Licensed-assisted access (LAA) is a feature of Long-Term Evolution (LTE) which enables operation in the unlicensed spectrum. LAA guarantees fair coexistence with Wi-Fi by implementing the listen- before-talk (LBT) mechanism. In this paper, we leverage stochastic geometry to characterize key performance metrics of neighboring LAA and Wi-Fi networks. Our analysis is focused on a single unlicensed frequency band, where the locations for coexisting LTE eNodeBs (eNBs) and Wi-Fi access points (APs) are modeled as two independent homogeneous Poisson point processes (PPPs). Based on an analytical modeling of the channel access procedure, we have derived the medium access probability (MAP), the signal-to- interference-plus-noise ratio (SINR) distribution, the density of successful transmissions (DST), and the data rate distribution for both LAA and Wi-Fi. We show that compared to the baseline scenario where Wi-Fi coexists with an additional Wi-Fi network, LAA can improve the DST and data rate performance of Wi-Fi by adopting more sensitive clear channel assessment thresholds and/or larger contention window sizes. Meanwhile, LAA is demonstrated to achieve acceptable data rate performance despite using LBT.
---
paper_title: A SURVEY OF LTE WI-FI COEXISTENCE IN UNLICENSED BANDS

paper_content:

With the rapid growth of mobile data, many LTE operators are interested in leveraging unlicensed bands to enhance data rates and user experience. Th is paper investigates the problem of the coexistence of LTE and Wi-Fi in 5 GHz unlicensed bands. We fi rst introduce the current rules for the 5 GHz unlicensed bands and the carrier aggregation technique. We then discuss four deployment scenarios and two LTE-unlicensed (LTE-U) coexistence scenarios. Further, we provide a feature comparison between LTE and Wi-Fi in the PHY/MAC layers, and review the coexistence methods for LTE-U and Wi-Fi without or with the Listen- Before-Talk (LBT) mechanism. Th is paper is concluded by an examination of Wi-Fi link aggregation and in-device coexistence issues.
---
paper_title: Simultaneous transmission opportunities for LTE-LAA smallcells coexisting with WiFi in unlicensed spectrum

paper_content:

LTE License-Assisted Access (LTE-LAA) in unlicensed spectrum has drawn a lot of attention due to its appealing data traffic offloading potential. However, the coexistence of LTE and WiFi technologies in the same unlicensed bands needs careful design to avoid severe interference between them. In this paper, we propose a coexistence scheme to create opportunities for LTE-LAA small cells and WiFi devices to transmit simultaneously. We combine Multiple Signal Classification (MUSIC) direction of arrival (DOA) estimation with null steering techniques to avoid collisions between LTE-LAA and WiFi transmissions. We assume that the LTE-LAA small cells are equipped with the latest 802.11 receivers for monitoring WiFi transmissions and for capturing simultaneous transmission timing. The performance of the proposed scheme in terms of collision avoidance and channel occupancy time ratio is evaluated via simulations. The results show that with DOA estimation and null steering, LTE-LAA small cells can transmit simultaneously with nearby WiFi devices without causing significant interference to them. As a result, LTE-LAA small cells can gain much more channel access opportunities and longer channel occupancy time while being “invisible” to coexisting WiFi networks.
---
paper_title: Licensed-assisted access for WiFi-LTE coexistence in the unlicensed spectrum

paper_content:

One of the effective ways to address the exponentially increasing traffic demand in mobile communication systems is to use more spectrum. Although licensed spectrum is always preferable for providing better user experience, unlicensed spectrum can be considered as an effective complement. Before moving into unlicensed spectrum, it is essential to carry out proper coexistence performance evaluations. In this paper, we analyze WiFi 802.11n and Long Term Evolution (LTE) coexistence performance considering multi-layer cell layouts through system level simulations. We consider a time division duplexing (TDD)-LTE system with an FTP traffic model for performance evaluation. Simulation results show that WiFi performance is more vulnerable to LTE interference, while LTE performance is degraded only slightly. However, WiFi throughput degradation is lower for TDD configurations with larger number of LTE uplink sub-frames and smaller path loss compensation factors.
---
paper_title: A review of wireless communications for smart grid

paper_content:

Smart grid is envisioned to meet the 21st century energy requirements in a sophisticated manner with real time approach by integrating the latest digital communications and advanced control technologies to the existing power grid. It will connect the global users through energy efficiency and awareness corridor. This paper presents a comprehensive review of Wireless Communications Technologies (WCTs) for implementation of smart grid in a systematic way. Various network attributes like internet protocol (IP) support, power usage, data rate etc. are considered to compare the communications technologies in smart grid context. Techniques suitable for Home Area Networks (HANs) like ZigBee, Bluetooth, Wi-Fi, 6LoWPAN and Z-Wave are discussed and compared in context of consumer concerns and network attributes. A similar approach in context of utilities concerns is adopted for wireless communications techniques for Neighborhood Area Networks (NANs) which include WiMAX and GSM based cellular standards. Smart grid applications, associated network issues and challenges are elaborated at the end.
---

Title: LTE and Wi−Fi Coexistence in Unlicensed Spectrum with Application to Smart Grid: A Review

Section 1: INTRODUCTION
Description 1: This section introduces the motivations behind LTE and Wi−Fi coexistence in unlicensed spectrum, emphasizing the increasing data traffic from smart devices and smart grid networks.

Section 2: Wi-Fi Technology
Description 2: This section covers the basic principles and operational mechanisms of Wi-Fi technology, including its advantages and MAC layer mechanisms.

Section 3: LTE Technology
Description 3: This section explains the fundamentals of LTE technology, its architecture, and the types of LTE deployment in unlicensed spectrum.

Section 4: COEXISTENCE CHALLENGES IN SMART GRID
Description 4: This section discusses the challenges faced in the coexistence of Wi-Fi and LTE within smart grid communication networks, highlighting interference and compatibility issues.

Section 5: COEXISTENCE MECHANISM
Description 5: This section presents two LTE-U coexistence scenarios: coexistence between Wi-Fi and LTE and coexistence between LTE of different operators, explaining why different mechanisms are necessary.

Section 6: LTE vs Wi-Fi
Description 6: This section examines the coexistence between Wi-Fi and LTE, discussing the differences in radio frame structure, transmission scheduling, and their impact on channel usage.

Section 7: LTE-U vs LTE-U
Description 7: This section explores the coexistence issues between LTE-Us from different operators, focusing on the interference and coordination required for spectrum efficiency.

Section 8: TECHNIQUES FOR COEXISTENCE
Description 8: This section reviews various techniques developed for coexistence, both with and without regulatory Listen Before Talk (LBT) requirements, and their effectiveness.

Section 9: Coexistence without LBT
Description 9: This section details coexistence mechanisms in countries without LBT requirements, including Channel Selection, Carrier-Sensing-Adaptive Transmission, and Opportunistic Supplementary Downlink.

Section 10: Coexistence Based on LBT Mechanism
Description 10: This section discusses coexistence mechanisms that adhere to LBT regulations, including Frame-based Equipment and Load-based Equipment methods.

Section 11: CONCLUSION
Description 11: This section summarizes the key findings of the paper, offering insights into how coexistence mechanisms can ensure fair and efficient use of unlicensed spectrum in smart grid communication networks.