Licensed Assisted Access Research Articles

Delivering Fairness and QoS Guarantees for LTE/Wi-Fi Coexistence Under LAA Operation

Licensed assisted access (LAA) enables the coexistence of long-term evolution (LTE) and WiFi in unlicensed bands, while potentially offering improved coverage and data rates. However, cooperation with the conventional random-access protocols that employ listen-before-talk (LBT) considerations makes meeting the LTE performance requirements difficult, since delay and throughput guarantees should be delivered. In this paper, we propose a novel channel sharing mechanism for the LAA system that is capable of simultaneously providing the fairness of resource allocation across the competing LTE and Wi-Fi sessions as well as satisfying the quality-of-service guarantees of the LTE sessions in terms of their upper delay bound and throughput. Our proposal is based on two key mechanisms: 1) LAA connection admission control for the LTE sessions and 2) adaptive duty cycle resource division. The only external information necessary for the intended operation is the current number of active Wi-Fi sessions inferred by monitoring the shared channel. In the proposed scheme, LAA-enabled LTE base station fully controls the shared environment by dynamically adjusting the time allocations for both Wi-Fi and LTE technologies, while only admitting those LTE connections that should not interfere with Wi-Fi more than another Wi-Fi access point operating on the same channel would. To characterize the key performance trade-offs pertaining to the proposed operation, we develop a new analytical model. We then comprehensively investigate the performance of the developed channel sharing mechanism by confirming that it allows to achieve a high degree of fairness between the LTE and Wi-Fi connections as well as provides guarantees in terms of upper delay bound and throughput for the admitted LTE sessions. We also demonstrate that our scheme outperforms a typical LBT-based LAA implementation.

Throughput Analysis of LAA and Wi-Fi Coexistence Network With Asynchronous Channel Access

The licensed-assisted access (LAA) technology has been proposed as a promising solution to increase the network capability by extending the frequency bands for long term evolution networks. The performance evaluation of the LAA systems has been extensively studied in recent years. However, most existing works did not consider the fact that Wi-Fi stations and LAA equipments are typically not synchronized in such a heterogeneous network. They are not aligned in time domain because of different time-slot durations, channel access back off, and contention window sizes. Therefore, in this paper, we investigate the throughput performance of the LAA and Wi-Fi coexisting networks with asynchronous channel access. To deal with the asynchronism, we first introduce the concept of the heterogeneous network superframe based on the fact that the timing relation between LAA and Wi-Fi systems will be restored to a fixed pattern after a busy slot. Thereafter, we model the LAA and Wi-Fi channel access behaviors in superframes as 2-D Markov chains, respectively. Based on the Markov chains and the structure of the superframe, we analyze the throughput performance by fully considering the asynchronism of the heterogeneous channel access. The accuracy of our theoretical analysis is validated by numerical results. Meanwhile, we have also investigated the effects of the number of LAA equipments, Wi-Fi stations, and the maximum contention window size upon the system throughput.

Channel Access Scheme With Alignment Reference Interval Adaptation (ARIA) for Frequency Reuse in Unlicensed Band LTE: Fuzzy Q-Learning Approach

In licensed-assisted access using the LTE (LAA) standard, carrier sensing via the listen-before-talk (LBT) procedure is a vital feature for fair sharing with the Wi-Fi systems. Furthermore, it has been designed to support frequency reuse-1 operation among all cells by the virtue of licensed spectrum. As opposed to the two existing channel-access schemes for frequency reuse-1, transmission start time alignment (TSTA) and energy detection threshold adaptation (EDTA), which may not be able to maximize the LAA system throughput without violating the requirement of fair coexistence, we propose a new frequency-reuse-1 scheme, referred to as the alignment reference interval adaptation-based LAA (ARIA-LAA). It attempts to combine the advantages of TSTA and EDTA into a unified access framework, in which the alignment reference interval (ARI) is adaptively adjusted to control the channel-access probability for LAA and Wi-Fi systems. Meanwhile, to operate the ARIA-LAA effectively toward our design objective, we design the fuzzy Q-learning system that adapts the continuous variable ARI to the dynamically changing wireless network environment. Based on the analytical system models and formation of the optimization problem, it employs a model-free learning algorithm that interacts with the state, defined as the current level of fairness achieved by adaptation, and the Q-learning function to determine the ARI as a global action. Our simulation results demonstrate that the ARIA-LAA is a novel scheme of spectrum sharing with spatial reuse for LAA that enhances the overall system capacity while satisfying the fair-coexistence requirement in the unlicensed spectrum.

Delay and Reliability of Load-Based Listen-Before-Talk in LAA

With the release of the 5 GHz unlicensed spectrum has emerged licensed-assisted access, in which long-term evolution (LTE) operators compete with Wi-Fi users for a share of the unlicensed spectrum so as to augment their licensed spectrum. Subsequently, there has been the need to develop a LTE channel access mechanism that enables harmonious coexistence between Wi-Fi and LTE. Load-based listen-before-talk (LB-LBT) has been adopted as this LTE channel access mechanism by the 3rd Generation Partnership Project (3GPP). Theoretical modelling of LB-LBT schemes has focused on throughput and fair channel-time sharing between Wi-Fi and LTE technologies. We explore a LB-LBT scheme that belongs to LBT category 4, as recommended by the 3GPP, and develop a model for the distribution of the medium access control (MAC) delays experienced by the Wi-Fi packets and LTE frames. The model, validated by simulations, reveals design insights that can be used to dynamically adjust the LB-LBT parameters not only to achieve channel-time fairness, but also to guarantee MAC-delay bounds, with specified probability.

Performance of Interference Rejection Combining Receiver Employing Minimum Mean Square Error Filter for Licensed-Assisted Access

Performance of Interference Rejection Combining Receiver Employing Minimum Mean Square Error Filter for Licensed-Assisted Access

LTE on License-Exempt Spectrum

The radio frequency spectrum is classified as licensed and license-exempt/unlicensed spectrum. A traditional cellular communications system (e.g., LTE) operates unexceptionally on licensed spectrum. This paper explains the concept of cellular communications on both licensed and license-exempt carriers under a unified cellular architecture. It addresses the key challenges and describes a baseline communication framework that enables such operation, including carrier sensing based on listen-before-talk, discontinuous transmissions with limited channel occupation time, synchronization between licensed and license-exempt carriers, and coexistence with other incumbent systems like WiFi. These concept and techniques are further exemplified by a practical system, the LTE license-assisted access, including the downlink featured in Release 13 LTE and the most recent addition of uplink in Release 14 LTE.

Fairness vs. Performance in Rel-13 LTE Licensed Assisted Access

Wireless spectrum being a valuable resource, a large number of both non-profit and for-profit users rely on its unlicensed parts, usually to provide some sort of local area wireless coverage. When the cellular vendors and service providers expressed interest in the unlicensed spectrum, the incumbent community started to fear that the new technology would not respect the existing users. And although members of the incumbent community strongly influenced the design of licensed assisted access (LAA) in 3GPP, the fear has not dispersed yet. Representing a vendor with stakes in both communities, we attempt to disperse the fear by providing insight on the question of fairness and performance of LAA, openly discussing why it should generate less interference than WiFi and why it could be otherwise. We augment the discussion with insightful simulations, looking how detailed parameters of the channel access mechanism influence LAA's fairness and performance. Our investigations show that in common scenarios LAA is a fair neighbor to WiFi as is, and even in an extreme scenario only small adjustments to the channel access mechanism are needed to achieve the same outcome.

Extending LTE into the Unlicensed Spectrum: Technical Analysis of the Proposed Variants

The commercial success of LTE and the resulting growth in mobile data demand have urged cellular network operators to strive for new innovations. LTE in unlicensed spectrum has been proposed to allow cellular network operators to offload some of their data traffic by accessing the unlicensed 5 GHz frequency band. Currently, there are three proposed variants for LTE operation in the unlicensed band, namely LTE-U, licensed assisted access (LAA), and MulteFire. This article provides a comparative analysis of these variants and explains the current regulations of the 5 GHz band in different parts of the world. We present the technical details of the three proposed versions and analyze them in terms of their operational features and coexistence capabilities to provide an R&D perspective for their deployment and coexistence with legacy systems.

On a fair coexistence of LTE and Wi-Fi in the unlicensed spectrum: A Survey

To overcome the lack of spectrum resources, the proposal of extending LTE (Long Term Evolution) to the readily available unlicensed spectrum is receiving much attention. However, gaining capacity in a band where Wi-Fi is widely used and guaranteeing fairness between systems is not an easy to address issue. Analyzing the impact of operating LTE in the unlicensed band on the performance of Wi-Fi and devising solutions to minimize such an impact have been the goals of a considerable amount of work carried out by the research community, standardization bodies and telecom operators. In this paper, we first present a basic overview of Wi-Fi and LTE, which serves the purpose of illustrating why the fair coexistence of the two technologies in the unlicensed band is an issue. Basically, since LTE has been designed to operate in licensed bands, the centralized scheduling performed by LTE eNodeBs saturates all the channel resources, while Wi-Fi stations refrain from transmitting if the channel is sensed busy. Then, we illustrate the main approaches proposed to ensure a fair coexistence between Wi-Fi and LTE in the unlicensed band, namely Listen Before Talk (LBT) and Almost Blank Subframe (ABS), along with some other minor techniques. We describe the main solutions that are currently being developed by standardization bodies and telecom industry: LTE–U, Licensed Assisted Access (LAA) and MuLTEfire. Finally, we present an overview of the work appeared in the literature analyzing the impact of LTE on the performance of Wi-Fi and proposing solutions to mitigate such an impact.

Coexistence of Wi-Fi and LAA Networks With Adaptive Energy Detection

Licensed-assisted access (LAA) of the long term evolution (LTE) has been standardized by the Third Generation Partnership Project (3GPP) in Release 13 to address the urgent issues of ever-increasing traffic demands in cellular systems. However, challenges arise for the efficient coexistence of Wi-Fi and LAA in the same unlicensed spectrum. In this paper, the impact of LAA's energy detection thresholds on such coexistence are investigated from the perspective of collisions occurring during downlink transmissions. To facilitate the efficient coexistence of Wi-Fi and LAA, a distributed algorithm is proposed to adaptively change the energy detection thresholds of LAA per user or per base station, so that the system encourages more concurrent transmissions without introducing too many collisions. Simulation results validate the effectiveness of the proposed adaptive algorithm.

Performance bounds of different channel access priority classes in future Licensed Assisted Access (LAA) LTE networks

The growing demand on data to enhance the user experience has motivated research toward increasing the efficiency of spectrum utilization by extending cellular technology such as LTE toward the unlicensed bands. Several studies have been done regarding the fair coexistence of LTE with legacy technologies such as WiFi in the unlicensed bands. Most of these studies show that when LTE adopts appropriate technology such as LAA, it can be a good neighbor to WiFi. However, few studies have targeted the impact of coexistence of several LAA networks on the performance of each other in the unlicensed bands. Hence, within this scope, this is the first work that uses stochastic geometry to analyze the effect of channel access priorities of four traffic classes defined recently by 3GPP release 14, on the performance of the network and the degree of efficiency that can be achieved. In particular, we consider load based equipment (LBE) based MAC protocol where we use stochastic geometry to model and analyze the coexistence of four channel access priority classes of LTE-LAA networks with persistent downlink transmissions as defined by 3GPP. Mainly, we focus on a single unlicensed frequency band transmissions. The locations of LAA eNodeBs (eNBs) for the four classes are modeled as four independent homogeneous Poisson point processes. Furthermore, we derive analytical closed form expressions for a set of performance metrics which are the medium access probability (MAP), signal-to-interference-plus-noise ratio (SINR) coverage probability, and rate coverage probability. Our analysis demonstrates the impact of channel access priorities used by different classes on their network performance.

On The Modeling and Analysis of Uplink and Downlink IEEE 802.11ax Wi-Fi With LTE in Unlicensed Spectrum

The growing demand on data to enhance the user experience has motivated research toward increasing the efficiency of spectrum utilization by extending cellular technology, such as LTE, toward unlicensed bands. In order to study the fair coexistence of LTE and Wi-Fi, we consider the IEEE 802.11ax Wi-Fi standard, where we use stochastic geometry to model and analyze the coexistence of LTE with simultaneous uplink and downlink IEEE 802.11ax transmissions. Mainly, we consider LTE with continuous transmissions (no protocol change), LTE with discontinuous transmissions (LTE-U), and licensed-assisted access (LAA) coexistence mechanisms. In addition, we focus on single unlicensed frequency band transmissions, where the locations of Wi-Fi access points, Wi-Fi stations (users), and LTE eNodeBs (eNBs) are modeled as three independent homogeneous Poisson point processes. Then, we derive analytical expressions for a set of performance metrics, which are the medium access probability, signal-to-interference-plus-noise ratio coverage probability, density of successful transmissions, and Shannon throughput probability for both uplink and downlink of IEEE 802.11ax in addition to LTE. Our analysis quantifies both single-user and multi-user operation modes of the IEEE802.11ax and show that LTE-U or LAA can be a good neighbor for IEEE 802.11ax for different traffic types.

Harmonising Coexistence of Machine Type Communications With Wi-Fi Data Traffic Under Frame-Based LBT

The existence of relatively long LTE data blocks within the licensed-assisted access (LAA) framework results in bursty machine-type communications (MTC) packet arrivals, which cause system performance degradation and present new challenges in Markov modeling. We develop an embedded Markov chain to characterize the dynamic behavior of the contention arising from bursty MTC and Wi-Fi data traffic in the LAA framework. Our theoretical model reveals a high-contention phenomenon caused by the bursty MTC traffic, and quantifies the resulting performance degradation for both MTC and Wi-Fi data traffic. The Markov model is further developed to evaluate three potential solutions aiming to alleviate the contention. Our analysis shows that simply expanding the contention window, although successful in reducing congestion, may cause unacceptable MTC data loss. A TDMA scheme instead achieves better MTC packet delivery and overall throughput, but requires centralized coordination. We propose a distributed scheme that randomly spreads the MTC access processes through the available time period. Our model results, validated by simulations, demonstrate that the random spreading solution achieves a near TDMA performance, while preserving the distributed nature of the Wi-Fi protocol. It alleviates the MTC traffic contention and improves the overall throughput by up to 10%.

Effective Capacity of Licensed-Assisted Access in Unlicensed Spectrum for 5G: From Theory to Application

License-assisted access (LAA) is a promising technology to offload dramatically increasing cellular traffic to unlicensed bands. Challenges arise from the provision of quality-of-service (QoS) and the quantification of capacity, due to the distributed and heterogeneous nature of LAA and legacy systems (such as Wi-Fi) coexisting in the bands. In this paper, we develop new theories of the effective capacity to measure LAA under statistical QoS requirements. A new four-state semi-Markovian model is developed to capture transmission collisions, random backoffs, and lossy wireless channels of LAA in distributed heterogeneous network environments. A closed-form expression for the effective capacity is derived to comprehensively analyze LAA. The four-state model is further abstracted to an insightful two-state equivalent which reveals the concavity of the effective capacity in terms of transmit rate. Validated by simulations, the concavity is exploited to maximize the effective capacity and effective energy efficiency of LAA, and provide significant improvements of 62.7% and 171.4%, respectively, over existing approaches. Our results are of practical value to holistic designs and deployments of LAA systems.

Coexistence scheme of licensed-assisted access using long-term evolution and wireless local area network for wireless sensor networks

Wireless sensor networks have continuously evolved to provide better services and satisfy user demands. Through this, the number of wireless sensors and the amount of mobile traffic are exponentially growing every year. Long-term evolution technology can effectively resolve the problems caused by traffic growth; however, there are still limitations. Licensed-assisted access using long-term evolution technology has greatly improved the performance of existing long-term evolution heterogeneous networks with carrier aggregation. However, the existing wireless local area network sensor nodes remain a challenge. The licensed-assisted access using long-term evolution access point should efficiently handle the problem of monopolizing spectrum resources used by existing wireless local area network sensor nodes. In this article, we investigate an optimized time slot allocation technique for the coexistence of wireless local area network and licensed-assisted access using long-term evolution sensor nodes. In order to maximize the throughput of each wireless local area network and licensed-assisted access using long-term evolution sensor node in the proposed algorithm, we designed an objective function based on the number of wireless local area network/licensed-assisted access using long-term evolution sensor nodes and the queue size of each sensor, after which we developed the optimal parameters using Karush–Kuhn–Tucker conditions. Through extensive simulations, we show that the proposed scheme can significantly outperform the other existing techniques with respect to the throughput, channel utilization, delay, and transmission fairness.

Harmonious coexistence solution between stand‐alone LTE and WiFi in unlicensed band

AbstractTo fulfill the large spectrum requirements in the 5th‐Generation (5G) systems. The Third‐Generation Partnership Project has defined licensed assisted access (LAA) to extend its spectrum pool to unlicensed band. However, for these operators without licensed spectrum (eg, virtual operators), stand‐alone Long‐Term Evolution (LTE) in unlicensed band may be a more appealing choice since LAA is only suitable to these operators who have their licensed spectrum. Similar to LAA, fair coexistence between stand‐alone LTE system and other systems (eg, Wireless Fidelity [WiFi]) in unlicensed spectrum is also the dominated problem that should be solved. In this paper, 1 approach on stand‐alone LTE system in unlicensed spectrum is proposed. The proposed solution is based on adaptive power and bandwidth adjustment to guarantee the fair coexistence between stand‐alone LTE system and WiFi. The coexistence evaluation results between them indicate that the proposed one can improve the whole system throughput significantly and meanwhile the performance of WiFi is also guaranteed.

License assisted access-WiFi coexistence with TXOP backoff for LTE in unlicensed band

License assisted access (LAA) was proposed as a solution to the challenge of satisfying high throughput requirement in cellular network with limited licensed band. LAA uses long term evolution (LTE) carrier aggregation technique to combine licensed and unlicensed bands, specifically 5 GHz WiFi band, in order to achieve high data rates. However, LAA has several critical concerns for services provision on 5 GHz unlicensed band. In this article, an overview of the techniques concerning the coexistence of LTE and WiFi on the same unlicensed band is presented. We first present several general approaches including power control of LTE evolved Node B (eNB), carrier selection, LTE duty cycling, self clear to send (CTS) and request to send/CTS (RTS/ CTS), and listen before talk (LBT). Then, we focus on LBT techniques for LAA-WiFi coexistence and discuss how LBT based coexistence solutions can dynamically respond to the variations in network load and ensure fair coexistence in a distributed manner. Based on the LBT mechanism, we also present a fairness-aware LAA-WiFi coexisting scheme with TXOP (transmitted in a single transmission opportunity) backoff for LAA eNB. Finally, the performances of various LBT solutions for LAA-WiFi coexistence are evaluated using Markov chain analytical model.

Competition-based distributed BS power activation and user scheduling algorithm

Existing cellular technologies in unlicensed band such as license assisted access (LAA)-LTE do not capture inter-cell interference (ICI) management which becomes more important in modern small cell network environments. Moreover, existing ICI management techniques not only can be operated in only licensed frequency band due to their centralized properties, but also have high computational complexities. In this paper, by invoking distributed optimization, we propose a fully distributed base station (BS) activation and user scheduling framework which can be operated in even unlicensed band because of its competition properties. Our simulation results demonstrate that (i) proposed competitionbased BS activation and user scheduling framework (CBA) increases throughput of cell edge users by 112%–335% compared to conventional algorithms, (ii) the CBA properly catches up with the performance of optimal algorithm up to 93% in terms of overall performance and up to 95% in terms of edge user throughput, and (iii) the CBA also provides higher performance gains in the larger ratio of edge users and the smaller cell size, which indicates that the CBA well adapts to cellular network trend where cells are gradually smaller and densely deployed.

Licensed-Assisted Access to Unlicensed Spectrum in LTE Release 13

Exploiting the unlicensed spectrum is considered by 3GPP as one promising solution to meet the ever-increasing traffic growth. As a result, one major enhancement for LTE in Release 13 has been to enable its operation in the unlicensed spectrum via Licensed-Assisted Access (LAA). In this article, we provide an overview of the Release 13 LAA technology including motivation, use cases, LTE enhancements for enabling the unlicensed band operation, and the coexistence evaluation results contributed by 3GPP participants.

Efficient listen before technique for LTE-WiFi co-existence in unlicensed bands

In a moderate to high traffic scenario wireless fidelity (WiFi) performance degrades severely due to interference and back-off mechanism. Licensed assisted access (LAA) has been proposed by 3rd Generation Partnership Project (3GPP) to use long term evolution (LTE) in the un-licensed spectrum. As the centralised LAA has to co-exist with existing distributed wireless fidelity (WiFi), efficient listen before talk (LBT) technique is required to reduce interference and improve spectral efficiency of WiFi and LAA users. In this paper, we have proposed an LBT mechanism to share the medium in a fair manner and improves both WiFi-LAA combined system performances significantly. We have also analysed closed form solution for the LBT technique. We validated network performance of proposed LBT model using network simulator (NS-3) and Matlab. The results indicated that with proper choice of LAA channel occupancy and backoff counter, significant performance gains of WiFi-LAA can be achieved.