Licensed-Assisted Access System Research Articles

Learning-Assisted Clustered Access of 5G/B5G Networks to Unlicensed Spectrum

License-assisted access (LAA) to unlicensed spectrum is a potential solution to improve the resource availability and system scalability of 5G/ B5G networks. Challenges arise from coexistence between LAA and incumbent systems, especially the ubiquitous IEEE 802.11 WiFi systems. This article demonstrates that the coexistence can be substantially improved by leveraging learning-based clustering of small base stations (SBSs), referred to as learning-assisted clustered access (LACA), and improving the interoperability between licensed and unlicensed access. Fast signaling and a centralized control plane of licensed access can facilitate clustering SBSs for coordinated access to the unlicensed spectrum, hence reducing the number of parties contending for access and alleviating contention. Appropriate clustering of SBSs is important to the efficiency of LACA in 5G/B5G networks. LACA can quickly converge with strong locality, facilitating the coordination of the SBSs, for example, cooperatively connecting multiple users and conducting beamforming. Analytic evaluation and numerical tests confirm the improved coexistence through enlarged LAA-WiFi capacity regions, as well as reduced transmission delays.

Research on unlicensed spectrum access mechanism based on reinforcement learning in LAA/WLAN coexisting network

The efficient and fair coexistence of Licensed-Assisted-Access (LAA) and WLAN has become an urgent problem to be solved. According to the heat problems above, this thesis has conducted an in-depth research on access mechanism of LAA and WLAN systems in unlicensed frequency bands. The study firstly introduced an access mechanism based on reinforcement learning after making the summery of the existing coexistence mechanisms. This mechanism takes Listen Before Talk mechanism as a technical basis to have adaptive adjustment of the channel access probability, thus to increase the system capacity. Meanwhile, the system’s throughput is processed using a proportional fair utility function, and utility value is considered as the return value of the system to ensure fairness between the LAA and the WLAN. Simulation results indicate that the algorithm proposed in this study can effectively maximize the system throughput. In the case of different LAA and WLAN packet lengths, algorithm proposed can still guarantee fairness among users in coexistence system.

Modeling the Unlicensed Band Allocation for LAA With Buffering Mechanism

In this letter, we propose an analytical model and conduct simulation experiments to study listen-before-talk–based unlicensed band allocation with the buffering mechanism for the License Assisted Access (LAA) packets in the heterogeneous networks. In such a network, unlicensed band allocation for LAA and Wi-Fi is an important issue, which may affect the quality of service for both systems significantly. We evaluate the performance for these unlicensed band allocations in terms of the acceptance rate of both LAA and Wi-Fi packets. This letter provides the guidelines for designing channel occupation phase and buffer threshold of the LAA systems.

Traffic Offloading in Unlicensed Spectrum for 5G Cellular Network: A Two-Layer Game Approach.

Licensed Assisted Access (LAA) is considered one of the latest groundbreaking innovations to provide high performance in future 5G. Coexistence schemes such as Listen Before Talk (LBT) and Carrier Sensing and Adaptive Transmission (CSAT) have been proven to be good methods to share spectrums, and they are WiFi friendly. In this paper, a modified LBT-based CSAT scheme is proposed which can effectively reduce the collision at the moment when Long Term Evolution (LTE) starts to transmit data in CSAT mode. To make full use of the valuable spectrum resources, the throughput of both LAA and WiFi systems should be improved. Thus, a two-layer Coalition-Auction Game-based Transaction (CAGT) mechanism is proposed in this paper to optimize the performance of the two systems. In the first layer, a coalition among Access Points (APs) is built to balance the WiFi stations and maximize the WiFi throughput. The main idea of the devised coalition forming is to merge the light-loaded APs with heavy-loaded APs into a coalition; consequently, the data of the overloaded APs can be offloaded to the light-loaded APs. Next, an auction game between the LAA and WiFi systems is used to gain a win–win strategy, in which, LAA Base Station (BS) is the auctioneer and AP coalitions are bidders. Thus, the throughput of both systems are improved. Simulation results demonstrate that the proposed scheme in this paper can improve the performance of both two systems effectively.

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.

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.

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.

Design and Evaluation of Licensed Assisted Access LTE in Unlicensed Spectrum

Licensed assisted access (LAA) is a new feature for 3GPP LTE systems to operate in the unlicensed spectrum. Under LAA, licensed carriers will be aggregated with unlicensed carriers in order to opportunistically enhance user throughput, while still offering seamless mobility and outdoor coverage. In order to coexist with other technologies in the unlicensed bands, several new functionalities for LAA LTE have been introduced, including longterm channel selection, short-term channel sensing based on listen-before-talk (LBT), and discontinuous transmission on a carrier with limited maximum transmission duration. In this article, we present research findings behind the designs for LAA systems. We discuss the impact of several parameters of the LAA LBT framework on the channel access opportunities of LAA, and its coexistence performance toward co-channel networks based on extensive system-level simulation results. The investigation covers both single-channel as well as multi-channel operation and coexistence scenarios. In addition to the finalized designs for downlink LAA operations in Release 13, our findings in this article further shed light on the uplink LAA operations to be introduced in Release 14.

Licensed-Assisted Access for LTE in Unlicensed Spectrum: A MAC Protocol Design

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.

Energy Efficiency Optimization in Licensed-Assisted Access

To improve system capacity, licensed-assisted access (LAA) has been proposed for long-term evolution (LTE) systems to use unlicensed bands. However, the energy efficiency (EE) of the LTE system may be degraded by LAA since unlicensed bands are generally less energy-efficient than licensed bands. In this paper, we investigate the EE optimization of LAA systems. We first develop a criterion to determine whether unlicensed bands can be leveraged to improve the EE of LAA systems. We prove that unlicensed bands can be used to improve the EE only when the allocated licensed resource blocks (RBs) are not enough. We then investigate joint licensed and unlicensed RB allocation to maximize the EE of each small cell base station (SBS) in a multi-SBS scenario, taking into account fair resource sharing between LTE and WiFi networks. The complete Pareto optimal EE set can be obtained by the weighted Tchebycheff method. We also develop an algorithm to provide fair EE among different SBSs based on the Nash bargaining solution. Numerical results are presented to confirm our analysis and to demonstrate the effectiveness of the proposed algorithms.