Long Term Evolution In Unlicensed Spectrum Research Articles

Application of LTE-U Technology in Train-Ground Communication of Urban Rail Transit

With the development of intelligentizing of Urban Rail Transit (URT), the data that need to be transmitted between train and OCC (Operational Contral Center) has increased significantly, and the licensed spectrum range is gradually unable to satisfy the data transfer task of URT communication systems(URT-cs). Therefore, this article considers to use LTE-U (Long-Term-Evolution in unlicensed spectrum) technology to deploy this communication system in unlicensed spectrum. In view of the interference caused by the introduction to WLAN system which have already been deployed in unlicensed spectrum, a dynamic spectrum range duty cycle adjustment scheme based on Q-learning algorithm is proposed to achieve coexistence of the two system. The scheme takes spectrum range as state, modelling the spectrum range allocation as a Markov Decision Process, obtains the spectrum range allocation strategy through Q-learning algorithm. Simulation results show that, compared with fixed spectrum allocation, the proposed scheme has a higher throughput and user satisfaction. Realizing the transmission task of URT-cs while meeting the user satisfaction of the WLAN system, and the problem of spectrum resources insufficiency of URT-cs is well solved.

CQI-Based Interference Detection and Resource Allocation With QoS Provision in LTE-U Systems

Long-Term Evolution in unlicensed spectrum (LTE-U) is a promising solution to address the spectrum scarcity in the cellular networks. However, the LTE-U and WiFi systems may interfere with each other and degrade the performance. Thus, many works have focused on coexistence design and proposed various solutions. Nevertheless, the hidden terminal problem has not been well studied in the LTE-U system. In this paper, we investigate joint interference detection and resource allocation in the LTE-U system to maximize the overall system throughput while guaranteeing each user's quality-of-service (QoS) requirements. Firstly, to solve the hidden terminal problem and avoid the co-channel interference between the WiFi and LTE-U users, we adopt a cluster-based algorithm to find the potential WiFi interference for each LTE-U user according to their channel quality indicator (CQI) feedback and location information. Secondly, we formulate a joint subcarrier and power allocation problem over the licensed and unlicensed bands with each user's QoS provision. To make the original problem more tractable, we separate it into licensed and unlicensed subproblems and then derive the optimal solution. Moreover, we propose a low-complexity resource allocation scheme. The simulation results show that the proposed schemes can significantly improve the system performance and outperform the existing schemes.

A Complete Solution to LTE-U and Wi-Fi Hidden Terminal Problem

With the exponential growth in mobile data traffic, mobile operators are facing the unfortunate limit on the availability of licensed spectrum which has however, led to the popularity of long term evolution (LTE) in unlicensed spectrum (LTE-U). Undeniably, it is expected from LTE-U that it fairly shares the spectrum with Wi-Fi. Along with fair sharing, efficient utilization of the unlicensed spectrum is also equally important, which in some sense requires coordination between the two radio access technologies (RATs) viz. , LTE-U and Wi-Fi. In particular, the hidden terminal scenario between LTE-U and Wi-Fi, resulting mainly due to lack of coordination, threatens the spectrum utilization of unlicensed spectrum. Focusing on this hidden terminal problem between LTE-U and Wi-Fi, we highlight the deficiency of existing technologies from the Wi-Fi perspective, both at the user level and at the network level. We then propose a novel coexistence technique (similar to RTS-CTS mechanism in Wi-Fi) that solves the hidden terminal problem between LTE-U and Wi-Fi, and subsequently addresses the spectrum underutilization problem caused by hidden terminal collisions. The proposed mechanism achieves this by using a modified CTS frame of Wi-Fi. We have validated our proposed mechanism using a mathematical framework demonstrating its credibility.

New Radio Beam-Based Access to Unlicensed Spectrum: Design Challenges and Solutions

This paper elaborates on the design challenges, opportunities, and solutions for New Radio-based access to Unlicensed spectrum (NR-U) by taking into account the beam-based transmissions and the worldwide regulatory requirements. NR-U intends to expand the applicability of 5th generation New Radio access technology to support operation in unlicensed bands by adhering to Listen-Before-Talk (LBT) requirements for accessing the channel. LBT was already adopted by different variants of 4th generation Long Term Evolution (LTE) in unlicensed spectrum, i.e., Licensed-Assisted Access and MulteFire, to guarantee fair coexistence among different radio access technologies. In the case of beam-based transmissions, the NR-U coexistence framework is significantly different as compared to LTE in unlicensed spectrum due to the use of directional antennas, which enhance the spatial reuse but also complicate the interference management. In particular, beam-based transmissions are needed in the unlicensed spectrum at millimeter-wave (mmWave) bands, which is an attractive candidate for NR-U due to its large amount of allocated spectrum. As a consequence, some major design principles need to be revisited to address coexistence for beam-based NR-U. In this paper, different problems and the potential solutions related to channel access procedures, frame structure, initial access procedures, re-transmission procedures, and scheduling schemes are discussed. A simulation evaluation of different LBT-based channel access procedures for NR-U/Wi-Fi indoor mmWave coexistence scenarios is also provided.

Proactive Resource Management for LTE in Unlicensed Spectrum: A Deep Learning Perspective

Performing cellular long term evolution (LTE) communications in unlicensed spectrum using licensed assisted access LTE (LTE-LAA) is a promising approach to overcome wireless spectrum scarcity. However, to reap the benefits of LTE-LAA, a fair coexistence mechanism with other incumbent WiFi deployments is required. In this paper, a novel deep learning approach is proposed for modeling the resource allocation problem of LTE-LAA small base stations (SBSs). The proposed approach enables multiple SBSs to proactively perform dynamic channel selection, carrier aggregation, and f ractional spectrum access while guaranteeing fairness with existing WiFi networks and other LTE-LAA operators. Adopting a proactive coexistence mechanism enables future delay-tolerant LTE-LAA data demands to be served within a given prediction window ahead of their actual arrival time thus avoiding the underutilization of the unlicensed spectrum during off-peak hours while maximizing the total served LTE-LAA traffic load. To this end, a noncooperative game model is formulated in which SBSs are modeled as homo egualis agents that aim at predicting a sequence of future actions and thus achieving long-term equal weighted fairness with wireless local area network and other LTE-LAA operators over a given time horizon. The proposed deep learning algorithm is then shown to reach a mixed-strategy Nash equilibrium, when it converges. Simulation results using real data traces show that the proposed scheme can yield up to 28% and 11% gains over a conventional reactive approach and a proportional fair coexistence mechanism, respectively. The results also show that the proposed framework prevents WiFi performance degradation for a densely deployed LTE-LAA network.

A Q-Learning Scheme for Fair Coexistence Between LTE and Wi-Fi in Unlicensed Spectrum

During the last years, the growth of wireless traffic pushed the wireless community to search for solutions that can assist in a more efficient management of the spectrum. Toward this direction, the operation of long term evolution (LTE) in unlicensed spectrum (LTE-U) has been proposed. Targeting a global solution that respects the regional regulations worldwide, 3GPP has published the LTE licensed assisted access (LAA) standard. According to LTE LAA, a listen before talk (LBT) procedure must precede any LTE transmission burst in the unlicensed spectrum. However, the proposed standard may cause coexistence issues between LTE and Wi-Fi, especially in the case that the latter does not use frame aggregation. Toward the provision of a balanced channel access, we have proposed mLTE-U that is an adaptive LTE LBT scheme. According to mLTE-U, LTE uses a variable transmission opportunity (TXOP), followed by a variable muting period. This muting period can be exploited by co-located Wi-Fi networks to gain access to the medium. In this paper, the system model of the mLTE-U scheme in coexistence with Wi-Fi is studied. In addition, mLTE-U is enhanced with a Q-learning technique that is used for autonomous selection of the appropriate combinations of TXOP and muting period that can provide fair coexistence between co-located mLTE-U and Wi-Fi networks. Simulation results showcase the performance of the proposed model and reveal the benefit of using Q-learning for self-adaptation of mLTE-U to the changes of the dynamic wireless environment, toward fair coexistence with Wi-Fi. Finally, the Q-learning mechanism is compared with conventional selection schemes showing the superior performance of the proposed model over less complex mechanisms.

LTE-U and Wi-Fi Coexistence Algorithm Based on Q-Learning in Multi-Channel

Due to the lack of resources in the low spectrum, long term evolution (LTE) in unlicensed spectrum (LTE-U) technology has been proposed to extend LTE to unlicensed spectrum. LTE-U undertakes the task of streaming data traffic for licensed spectrum, which can greatly enhance the capacity of the system. However, the introduction of LTE-U technology also gives rise to the problem of coexistence with Wi-Fi systems. In this paper, an LTE-U and Wi-Fi coexistence algorithm is proposed in multi-channel scenarios based on Q-learning. By taking the idea of alternately transferring data in LTE-U and Wi-Fi, the algorithm takes into account both the fairness and the performance of the system and optimizes the duty cycle. The simulation results show that the proposed algorithm can effectively improve the throughput of the system in the premise of ensuring fairness.

Full-Duplex Assisted LTE-U/Wifi Coexisting Networks in Unlicensed Spectrum

With the boosting of mobile services, licensed spectrum for wireless networks becomes more and more crowded. To explore new spectrum for cellular users, more and more mobile operators are interested in deploying the long-term evolution in unlicensed spectrum (LTE-U), which utilizes the unlicensed spectrum occupied by Wi-Fi. Because the medium access control (MAC) protocols of LTE-U and Wi-Fi are different, the synchronization between the LTE-U users and Wi-Fi users cannot be guaranteed for LTE-U/Wi-Fi coexisting networks, thus resulting in the throughput deterioration of LTE-U and Wi-Fi users. In this paper, we propose the full-duplex two-threshold spectrum sensing (FDTT-SS) algorithm for LTE-U/Wi-Fi coexisting networks, where both LTE-U and Wi-Fi users adopt the listen-before-talk mechanism, with adaptive priority for LTE-U. Using our proposed FDTT-SS scheme, the LTE-U/Wi-Fi average transmission time can be guaranteed by avoiding the collisions among LTE-U/Wi-Fi users. We further develop the FDTT-MAC protocol that can significantly increase the sum throughput while guaranteeing the fairness for LTE-U/Wi-Fi coexisting networks. Numerical results show that our proposed fair FDTT-MAC protocol can improve the channel utilization in unlicensed spectrum and can increase the throughput of Wi-Fi without greatly degrading the throughput of LTE-U for coexisting wireless networks as compared with existing schemes.

Opportunistic Coexistence of LTE and WiFi for Future 5G System: Experimental Performance Evaluation and Analysis

To alleviate the problem of scarce spectrum resources and meet the ever-increasing of mobile broadband data traffic demands, Licensed Assisted Access (LAA)-Long Term Evolution (LTE), operating in the unlicensed spectrum, is a promising solution. Considering that the unlicensed spectrum is shared by a few incumbent systems, such as IEEE 802.11 (i.e., WiFi), one main target is to guarantee the friendly and harmonious coexistence of LTE with other wireless systems in the unlicensed spectrum. Both listen-before-talk (LBT) and duty cycle methods are regarded as effective ways to solve the coexistence problem in academia and industry so far. Although there are a large number of theoretical researches on LTE in unlicensed spectrum (LTE-U), field trail results are still lacking. In this paper, an experimental testing platform is deployed to model the realistic environment. This paper focuses on three aspects. First, a typical indoor field trial scenario in 5.8 GHz unlicensed bands is deployed, and the performance of LTE-U and WiFi, including coverage and capacity, is evaluated. Specifically, a methodology to determine the proper clear channel assessment energy detection (CCA-ED) threshold for LTE-U is proposed to implement the friendly coexistence between LTE-U and WiFi systems. Second, supplementary downlink (SDL) and Cell ON/OFF mechanisms are investigated to verify the fair coexistence between LAA and WiFi in the unlicensed spectrum. Third, the Enhanced Cell ON/OFF scheme, which introduces Clear to Send (CTS)-to-Self (CTS2S) message, is discussed and evaluated. Based on the built testbed, we obtain threefold conclusions. First of all, introducing LTE into unlicensed spectrums can greatly improve the spectrum efficiency and optimize wireless resources. Furthermore, test results and analyses show that a proper CCA-ED threshold is necessary for coexisting friendly and fairly among different systems, and experiments are also provided to validate the feasibility of the suggested method in various scenarios. Second, experimental results show that SDL mechanism guarantees relatively friendly and harmonious coexistence between LAA and WiFi only in the sparse scenario, while basic Cell ON/OFF mechanism is more effective to ensure coexistence between LAA and WiFi than the SDL. Finally, with the introduction of CTS2S message, the Enhanced Cell ON/OFF scheme is able to achieve more peaceful coexistence between LTE and WiFi users employed in the same bands compared with the Basic Cell ON/OFF scheme.

Cooperation Techniques between LTE in Unlicensed Spectrum and Wi-Fi towards Fair Spectral Efficiency.

On the road towards 5G, a proliferation of Heterogeneous Networks (HetNets) is expected. Sensor networks are of great importance in this new wireless era, as they allow interaction with the environment. Additionally, the establishment of the Internet of Things (IoT) has incredibly increased the number of interconnected devices and consequently the already massive wirelessly transmitted traffic. The exponential growth of wireless traffic is pushing the wireless community to investigate solutions that maximally exploit the available spectrum. Recently, 3rd Generation Partnership Project (3GPP) announced standards that permit the operation of Long Term Evolution (LTE) in the unlicensed spectrum in addition to the exclusive use of the licensed spectrum owned by a mobile operator. Alternatively, leading wireless technology developers examine standalone LTE operation in the unlicensed spectrum without any involvement of a mobile operator. In this article, we present a classification of different techniques that can be applied on co-located LTE and Wi-Fi networks. Up to today, Wi-Fi is the most widely-used wireless technology in the unlicensed spectrum. A review of the current state of the art further reveals the lack of cooperation schemes among co-located networks that can lead to more optimal usage of the available spectrum. This article fills this gap in the literature by conceptually describing different classes of cooperation between LTE and Wi-Fi. For each class, we provide a detailed presentation of possible cooperation techniques that can provide spectral efficiency in a fair manner.

Embedding LTE-U within Wi-Fi Bands for Spectrum Efficiency Improvement

Driven by growing spectrum shortage, Long-term Evolution in unlicensed spectrum (LTE-U) has recently been proposed as a new paradigm to deliver better performance and experience for mobile users by extending the LTE protocol to unlicensed spectrum. In the paper, we first present a comprehensive overview of the LTE-U technology, and discuss the practical challenges it faces. We summarize the existing LTE-U operation modes and analyze several means for LTE-U coexistence with Wi-Fi medium access control protocols. We further propose a novel hyper access-point (HAP) that integrates the functionalities of LTE small cell base station and commercial Wi-Fi AP for deployment by cellular network operators. Our proposed LTE-U access embedding within the Wi-Fi protocol is non-disruptive to unlicensed Wi-Fi nodes and demonstrates performance benefits as a seamless and novel LTE and Wi-Fi coexistence technology in unlicensed band. We provide results to demonstrate the performances advantage of this novel LTE-U proposal.

Optimizing Unlicensed Spectrum Sharing for LTE-U and WiFi Network Coexistence

Long-term evolution in unlicensed spectrum (LTE-U) is an emerging technology for expanding cellular network capacity without additional spectrum cost. This paper investigates effective spectrum sharing for coexisting Wi-Fi and LTE-U services. Based on a novel hyper access point (HAP) we introduced for effectively embedding LTE-U in unlicensed Wi-Fi band, LTE-U can directly take advantage of the Wi-Fi point coordination function protocol. To facilitate the coexistence, our HAP dedicates a contention-free period to LTE-U users and allows a contention period (CP) for traditional Wi-Fi users. We investigate the optimization of joint user association and resource allocation to further improve system throughput and user fairness. We formulate a network utility maximization problem based on the Nash bargaining solution (NBS), for which we derive a closed-form expression for the optimal CP length under a given user association. We analyze this NBS-based utility maximization and the performance of the proposed algorithm under log-normal fading, Rayleigh fading, and Rician fading channel models, respectively. Our numerical results corroborate our analysis and demonstrate effective improvement of the system performance by the proposed HAP algorithm against traditional LTE-U deployment.

A Compact and Low-Profile Loop Antenna With Six Resonant Modes for LTE Smartphone

In this paper, a novel six-mode loop antenna covering 660–1100, 1710–3020, 3370–3900, and 5150–5850 MHz has been proposed for the application of long-term evolution (LTE) including the coming LTE in unlicensed spectrum and LTE-Licensed Assisted Access. Loop antennas offer better user experience than conventional planar inverted-F antennas (PIFAs), inverted-F antennas (IFAs), and monopole antennas because of their unique balanced modes ( $1\lambda $ , $2\lambda , \ldots $ ). However, the bandwidth of loop antennas is usually narrower than that of PIFA/IFA and monopole antennas due to these balanced modes. To overcome this problem, a novel monopole/dipole parasitic element, which operates at an unbalanced monopole-like $0.25\lambda $ mode and a balanced dipole-like $0.5\lambda $ mode, is first proposed for loop antennas to cover more frequency bands. Benefiting from the balanced mode, the proposed parasitic element is promising to provide better user experience than conventional parasitic elements. To the best of the authors’ knowledge, the balanced mode for a parasitic element is reported for the first time. The proposed antenna is able to provide excellent user experience while solving the problem of limited bandwidth in loop antennas. To validate the concept, one prototype antenna with a size of $75 \times 10\times 5$ mm3 is designed, fabricated, and measured. Both simulations and experimental results are presented and discussed. Good performance is achieved.

Throughput and Fairness Analysis of Wi-Fi and LTE-U in Unlicensed Band

Shortage of available licensed spectrum is a major barrier to the development of 5G networks. The deployment of long term evolution (LTE) in unlicensed spectrum (LTE-U) is a promising solution to overcome such a barrier. However, the interaction between LTE-U and Wi-Fi in unlicensed spectrum has not been well understood. In this paper, we use stochastic geometry to develop a framework for a multi-radio access technologies (multi-RAT) heterogeneous network, which consists of an LTE-U tier and a Wi-Fi tier. To reduce the intra- and inter-RAT interference, LTE-U employs an ALOHA-like random access scheme and Wi-Fi performs carrier sensing and energy detection before transmission. We derive the coverage probability and spatial throughput of Wi-Fi and LTE-U networks, and perform the asymptotic analysis when the density of Wi-Fi and LTE-U nodes approach infinity. Based on our analysis, we investigate the effect of network parameters on the coverage probability and spatial throughput of these networks. Furthermore, in order to achieve weighted max-min fairness, we optimize the retention probability of LTE-U nodes to maximize the minimum weighted spatial throughput of Wi-Fi and LTE-U networks.