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The paper presents several novel residual recurrent neural network (RNN) models for digital predistortion of radio-frequency power amplifiers. Then, unstructured and structured neural network (NN) pruning algorithms are proposed to reduce the per-sample computational complexity and the required memory, without compromising their modeling performance. The mathematical equations of the complexity and the memory are derived to analyze the hardware cost and design low cost models. An experimental platform is developed to measure the modeling performance in terms of adjacent channel leakage ratio (ACLR), normalized mean square error, error vector magnitude (EVM) and bit error rate. The platform uses an envelope tracking PA excited by 80 MHz IEEE 802.11ac signals. Compared with the state-of-the-art RNN model in (Sun et al., 2019), the proposed models reduce the per-sample complexity and required memory by $94\hbox{--}99$ %, they also improve the ACLR and EVM by at least 3 dB and 1 dB at 0.45 dB and 3.15 dB gain compression, respectively. Furthermore, an observation path with time alignment is used to remove the transmit latency in the state-of-the-art approach. At 3.15 dB gain compression, the proposed models outperform the state-of-the-art feedforward and convolutional NN models by at least 1.3 dB in EVM, outperform the general memory polynomial model by at least 3.3 dB in EVM. The above evidences indicate that the proposed RNN models can be implemented with relatively low hardware cost and achieve the best EVM in high power efficiency scenario. [ABSTRACT FROM AUTHOR]

In this paper, we propose a reference-modulated permutation index differential chaos shift keying (RM-PI-DCSK) over multipath fading channels. Due to quasi-orthogonal property between different permutated chaotic signals, the proposed scheme can remarkably suppress the inter-sequence interference to recover the desired information. Moreover, the proposed RM-PI-DCSK has one more modulation bit in the reference segment than the conventional permutation index differential chaos shift keying (PI-DCSK). Both the reference signal in the first time-slot and a permuted replica of the reference in the second time-slot are modulated for efficient transmission. The theoretical bit-error-rate (BER) performance and the highly consistent simulation results demonstrate that the proposed RM-PI-DCSK can achieve a performance gain 3 dB over the conventional PI-DCSK at a BER of $10^{-4}$ , and this gain becomes larger in a high-delay-spread channel. In particular, the performance superiority of the RM-PI-DCSK is further demonstrated in a typical ultra-wideband (UWB) channel with narrow-band interference. Therefore, this proposed scheme can be deemed as an efficient transmission alternative for chaotic-based wireless communications, such as in wireless local area network (WLAN) applications and indoor applications of the transmitted-reference UWB. [ABSTRACT FROM AUTHOR]

In nonsaturated 802.11 distributed coordination function (DCF) networks, existing studies had observed a salient phenomenon: the maximum stable throughput may be far higher than the saturation throughput and last for a long duration (say, months). Such a maximum stable throughput is called the presaturation throughput peak. The long-duration peak suggests that 802.11 DCF networks may provide a far higher stable throughput than what we generally believe, without worrying about a sudden deterioration of quality of service (QoS). This paper is devoted to developing a general theoretical framework to predict the peak. In the framework, we define a backoff entropy to quantify the uncertainty of the inherent random backoff process of 802.11 DCF networks, and then innovatively introduce a BackoffEntropy-Peak linearity property (i.e., the peak is linearly proportional to the backoff entropy) for the peak prediction. This framework is applicable for a general configuration of contention windows (CWs). It enables us to reveal the most essential dependency of the peak on the initial CW size and the number of network nodes. Further, we design peak-based call admission control (CAC) schemes that can be performed quickly and easily, without requiring network performance measurements and complex calculations. We verify our framework and CAC schemes via widely adopted 802.11 DCF ns2 and ns3 simulators (mostly with typical 802.11 standard settings). Extensive simulations show that our framework and CAC schemes trade within 9% peak prediction errors for making 802.11 DCF networks provide high stable throughput with good QoS (such as short delay and low collision probability). This paper is the first to propose applying the information entropy to study the throughput-stability problem. We believe that this study makes a crucial breakthrough in thoroughly investigating nonsaturated performance and network stability of random access wireless networks. [ABSTRACT FROM AUTHOR]

A novel low-profile wideband antenna is proposed with high-gain, high-isolated, and dual-polarized properties. It consists of two mutually-orthogonal bowtie-shaped dipole radiators, four rectangular parasitic elements, and a cylindrical artificial magnetic conductor (AMC) cavity. By introducing parasitic elements, additional resonance is generated, and the bandwidth is widened. The gain is mainly improved by the cylindrical metallic wall and wideband AMC of the cavity. The AMC operates in ±90o reflection phase band-gap bandwidth of 2.35-4.25 GHz, and its equivalent circuit model is developed to understand the working mechanism. The orthogonal placement of two dipole radiators ensures polarization diversity and high isolation. The impacts of various environmental conditions on antenna performance are investigated. To verify the concept of design and demonstrate its excellent performance features, a prototype is fabricated and measured. The proposed wideband antenna has a height of 0.18 wavelength at the center frequency. The measured -10-dB impedance bandwidth is from 2.16 to 3.96 GHz, where the realized gain is 8.34-10.96 dBi and the radiation efficiency is more than 81.8%. High isolation of > 28.65 dB and low envelop correlation coefficient (ECC) of < 2.74 × 10-3 are also achieved between antenna elements. It can be used in the base station for intelligent Internet of Vehicle (IoV) applications, covering the bands of WLAN, WiMAX, Bluetooth, LTE, and 5G sub-6 GHz. [ABSTRACT FROM AUTHOR]

Support for an asymmetric transmission topology involving two user stations, one for downlink and one for uplink, is essential in full-duplex wireless LANs to handle asymmetric and heterogeneous traffic demands as well as heterogeneous station capabilities. The main challenge presented by this asymmetric topology is interstation interference from the uplink-transmitting station to the downlink-receiving station. In this paper, we develop a novel medium access control (MAC) protocol and an associated station selection algorithm that exploit successive interference cancellation (SIC) to resolve the interstation interference. To understand the problem and find design rationales, we establish concepts of distinct transmission types and conduct a formal analysis of decodability with SIC, based on which we show that a transmission-type-specific design is necessary due to the type-dependent information requirements and asymmetric availability of information. We define, identify, and illustrate the SIC-eligible, interference and noninterference regions, each of which has different decodability characteristics. The developed MAC protocol is designed to guarantee coexistence with legacy wireless LANs. The developed station selection algorithm is designed to handle all possible transmission cases of full-duplex communication in both the centralized and distributed operation modes, which differ in terms of the signaling overhead and achieved performance; moreover, this algorithm can be combined with a wide range of access point schedulers. Through comprehensive simulation, we demonstrate that the proposed scheme considerably enhances the system and per-station throughputs compared with conventional schemes, approaching the ideal case with no interstation interference. [ABSTRACT FROM AUTHOR]

Wireless blockchain network is proposed to enable a decentralized and safe wireless networks for various blockchain applications. To achieve blockchain consensus in wireless network, one of the important steps is to broadcast new block using wireless channel. Under wireless network protocols, the block transmitting will be affected significantly. In this work, we focus on the consensus process in blockchain-based wireless local area network (B-WLAN) by investigating the impact of the media access control (MAC) protocol, CSMA/CA. With the randomness of the backoff counter in CSMA/CA, it is possible for latter blocks to catch up or outpace the earlier one, which complicates blockchain forking problem. In view of this, we propose mining strategies to pause mining for reducing the forking probability, and a discard strategy to remove the forking blocks that already exist in CSMA/CA backoff procedure. Based on the proposed strategies, we design Block Access Control (BAC) approaches to effectively schedule block mining and transmitting for improving the performance of B-WLAN. Then, Markov chain models are presented to conduct performance analysis in B-WLAN. The results show that BAC approaches can help the network to achieve a high transaction throughput while improving block utilization and saving computational power. Meanwhile, the trade-off between transaction throughput and block utilization is demonstrated, which can act as a guidance for practical deployment of blockchain. [ABSTRACT FROM AUTHOR]

Two-Way Ranging (TWR) is a widely used method for distance estimation in asynchronous wireless networks, but the deviation between the clocks can lead to errors in distance estimation. The ultra-wideband (UWB) technology provides the best accuracy in distance estimation, but total emission time is drastically limited by harmonized standards. Localization accuracy, latency and network scalability are key performance metrics in wireless location characterization. This article advances a new sequencing of the localization process, called Double-Beacon Two-Way Ranging (DB-TWR) algorithm, and presents the related time-of-flight (ToF) estimation formula, which is able to compensate for clock error and to reduce the localization period. The Fine Time Measurement (FTM) protocol, specified by the Wireless LAN (WLAN) standard, uses the TWR method and as a result the clock deviation leads to systematic errors in ToF estimation. The paper proposes two additional timestamp s captures and a new ToF computation formula which compensates for clock deviation. The article provides a theoretical analysis and extensive simulations of errors propagation in the ranging process, both as a mean and as an uncertainty, and proves that the designed algorithms cancel the clock offsets entirely. [ABSTRACT FROM AUTHOR]

As a complementary technology to existing Radio Frequency (RF)-based solutions such as Cellular V2X (C-V2X) and Dedicated Short Range Communication (DSRC), Vehicular VLC (V-VLC) is gaining more attention in the research community as well as in the industry. This paper introduces a complete IEEE 802.11 compliant V-VLC system. The system relies on Universal Software Radio Peripheral (USRP) software defined radios programmed using the GNU Radio framework, a typical car headlight plus a custom driver electronics for the high-power car LEDs (sender), and a photodiode (receiver). Building upon our earlier work, we, for the first time, experimentally explore the communication performance in outdoor scenarios, even in broad daylight, and show that rather simple optical modifications help to reduce the ambient noise to enable long distance visible light communication. Our system also supports Orthogonal Frequency-Division Multiplexing (OFDM) with a variety of Modulation and Coding Schemes (MCS) up to 64-QAM and is fully compliant with IEEE 802.11. We performed an extensive series of experiments to explore the performance of our system, even using higher order MCS in daylight. Our results demonstrated a high reliability for distances up to 75m with the presented system, regardless of the time of the day. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical framework to evaluate distance statistics of first arriving multi-path components at millimeter wave (mm-Wave) frequencies in a typical indoor environment. The proposed modeling approach is based on a numerically tractable channel model that accounts for the line-of-sight (LoS) component and first-order reflection components from surrounding walls. Based on the derived statistics, an approximation for coverage probability of mm-Wave indoor wireless local area networks (WLAN)s is obtained. Further, the coverage probability for an access point (AP) to user node link is determined after accounting for blockage of LoS component and optimal antenna beamforming in the modeling framework. The analysis of coverage probability provides useful insights which can be applied to plan optimum AP location layout in a typical mm-Wave indoor WLAN. [ABSTRACT FROM AUTHOR]

Millimeter wave (mmWave) systems have attracted considerable attention as a benefit of their Gbps services. Therefore, wireless-gigabit (WiGig) transmission has been developed based on the IEEE 802.11ad and 802.11ay standards of wireless local area networks (WLANs) in the 60-GHz band. To overcome the high path loss of mmWave, beamforming and beam-sector based training protocols are specified in 802.11ad/ay. With the increase in service demand, more WiGig access points (APs) will be deployed, hence the transmission frame structure of beam control should be adjustable for supporting both multiple APs and multiple users. The conventional exhaustive beam search (EBS) scheme has a potentially excessive complexity for high number of beams. Furthermore, assigning fixed training slots for users will lead to high-latency beam training under EBS. Hence, we design an advanced protocol for multiple APs and multiple users. Based on this protocol, we propose coordinated multiple AP multiuser training (CMMBT) including variable length framing and adjustable beam training. Our simulations demonstrate that CMMBT provides flexible training control and achieves the lowest training latency and highest average throughput performance amongst the state-of-the-art solutions in the open literature. [ABSTRACT FROM AUTHOR]

The increasing number of low power communication devices in the era of Internet of Things (IoT) has resulted in challenges in maintenance and continuous energy supply. In this paper, the ambient energy harvesting is integrated with wireless local area network (WLAN), where low-power users adopt a distributed coordination strategy for their random access, namely ambient energy harvesting carrier-sense-multiple-access with collision avoidance (AEH-CSMA/CA). All users harvest ambient energy to power their data uploading. In order to increase the uplink throughput and to reduce the energy outage probability, a classic deep reinforcement learning (DRL) algorithm, namely deep Q-learning (DQL), is adopted by a smart user for intelligently adjusting its initial backoff window size during the backoff process. Simulation results demonstrate that the proposed DQL algorithm is capable of substantially improving the throughput performance, while gauranteeing the energy outage probability of the smart user lower than a certain threshold. [ABSTRACT FROM AUTHOR]

Conventional design of wireless transmissions mainly focuses on manipulating end devices to better adapt to the transmission environments, such as channel coding and modulation techniques, whose performance is significantly affected by the quality of the transmission environments. In this paper, we propose an innovative idea to proactively manipulate, reconfigure, and augment wireless transmission environments to better support end-to-end services. Specifically, we implement this idea into the commercialized millimeter-wave (mmWave) wireless local area networks (WLANs) to address the vulnerability to blockages in mmWave bands. Without damaging the aesthetic nature of environments, we deploy multiple small-piece highly-reflective metallic reflecting surfaces as tunable reflectors, where alternative indirect line-of-sight links are created by tuning the orientations of the reflecting surfaces. To demonstrate our idea, we devise a novel adaptive mechanism, mmRef, to enable the implementation of tunable reflectors in mmWave WLANs, where the system architecture, operational procedures, and the signaling process are developed, respectively. To theoretically quantify the expected benefits, we characterize the outage probability and system throughput of mmRef mechanism based on stochastic geometry theory. Simulation and numerical results demonstrate the effectiveness of implementing mmRef and the significantly improved system performance. [ABSTRACT FROM AUTHOR]

Millimeter wave (mmWave) in the unlicensed 60 GHz band provides extremely large spectrum utilization, which is a promising technique due to the rapid growth of wireless communication services. With wireless devices explosively increasing, the limited number of association and beamforming training (A-BFT) opportunities in conventional protocol leads to high packet collisions. In this paper, we design a novel non-slotted A-BFT frame structure for multi-users in order to alleviate packet collisions providing flexible training slots. To further reduce collision occurrence, we propose two association mechanisms including the time-based distributed coordination function (TDCF) and time-based beam collision avoidance (TBCA) schemes. The theoretical closed-forms of both TDCF and TBCA methods are also derived, and proved to outperform the random association. Furthermore, the adaptive beam search (ABS) and dynamic A-BFT adjustment (DAA) schemes are proposed to consider historical beam training information by adjusting the number of training beams and A-BFT length, respectively. Simulations are conducted to show that our proposed ABS, DAA, and TDCF/TBCA mechanisms outperform existing methods; whereas higher spectrum efficiency can be achieved by proposed non-slotted frame structure compared to conventional slotted structure. [ABSTRACT FROM AUTHOR]

The energy consumption of wireless interface is critical to power-constrained mobile devices. To improve energy efficiency for WLAN stations, power saving mode (PSM) is proposed, to manage the time spent in idle listening (IL) state. The hurdle is that the receiver has no knowledge about when the pending data will arrive under end-to-end communication protocols (TCP/IP), making each station spend enormous time in IL to wait for the pending data. To overcome this limitation, in this paper, we propose a named data networking (NDN) enabled PSM, namely, NDN-PSM, which leverages NDN communication architecture to cut down unnecessary IL time. In particular, we devise two new power states in NDN-PSM, i.e., light doze and deep doze, to precisely map to the underlying data arriving states. The inherent receiver-driven pattern of NDN can effectively drive the stations to the deep doze state for power saving, and to light doze state for timely data reception. Considering the IL time waste during channel contention, we further design a channel contention control mechanism in NDN-PSM, in which stations will switch to the light doze state if the channel is perceived to be busy. The power consumption model of the proposed NDN-PSM is theoretically analyzed and verified via numerical results. At last, we implement NDN-PSM in NS-3 by adopting the ndnSIM module and conduct extensive simulations to demonstrate the efficacy of NDN-PSM. Specifically, compared to the existing PSM mechanism, NDN-PSM reduces 56% power consumption by cutting down unnecessary IL time, and meanwhile enables low-delay transmission. [ABSTRACT FROM AUTHOR]

With dramatically increased data traffic, the traditional low-frequency (LF) wireless local area networks (WLAN) are facing several difficulties, particularly, limited available spectrum resources and low network efficiency. While the use of millimeter-wave (mmWave) could bring more spectrum, WLAN in high-frequency (HF) suffers poor reliability. In addition, the current distributed WLAN architecture and the coupled data and control planes lead to inefficient management and poor performance with increased network scale, which cannot meet the stringent requirements from diverse applications. In overcoming these difficulties, the control plane and data plane decoupled network architecture and sub-6 GHz and mmWave dual-band cooperation are considered to be the critical solutions to improve the system performance in 5th-Generation (5G) and beyond networks. Therefore, to improve the throughput and reliability of the future WLAN, we propose a control plane and data plane decoupled WLAN architecture in this paper that supports both sub-6 GHz and mmWave based on the existing control plane and data plane decoupled WLAN concept. Furthermore, new multi-beam transmission and sub-6 GHz and mmWave dual-band cooperation mechanisms are developed to improve the throughput and reliability in our proposed WLAN architecture. Performance analysis and simulation show that with the multi-beam transmission and sub-6 GHz and mmWave dual-band cooperation mechanisms in our proposed WLAN architecture, throughput and reliability are both significantly improved when compared with the traditional distributed WLAN architecture and operation mechanism. [ABSTRACT FROM AUTHOR]

Vehicular ad hoc networks (VANETs) are wireless networks formed of moving vehicle stations, that enable safety-related packet exchanges among them. Their infrastructure-less, unbounded nature allows the formation of dense networks that present a channel sharing issue, which is harder to tackle than in conventional WLANs, due to fundamental differences of the protocol stack. Optimizing channel access strategies is important for the efficient usage of the available wireless bandwidth and the successful deployment of VANETs. We present a Q-learning-based approach to wirelessly network a big number of vehicles and enable the efficient exchange of data packets among them. More specifically, this work focuses on a IEEE 802.11p-compatible contention-based medium access control protocol for efficiently sharing the wireless channel among multiple vehicular stations. The stations feature algorithms that “learn” how to act optimally in a network in order to maximize their achieved packet delivery and minimise bandwidth wastage. Additionally, via a collective contention estimation mechanism, which we embed on the Q-learning agent, faster convergence, higher throughput, and short-term fairness are achieved. [ABSTRACT FROM AUTHOR]

The advancement of integrated millimeter-wave products opens the possibility of leveraging communications in 60-GHz band to meet the unprecedented traffic demand in WLAN. Despite the vast bandwidth available, millimeter-wave signals suffer from high attenuation and weak diffraction ability. Therefore, wireless communication at 60 GHz is characterized by the inherent directivity and susceptibility to blockage. Multiple Access Point (AP) architecture is proposed for 60-GHz WLAN to enhance spatial reuse and survive blockage. In the presence of multiple APs in the network, this paper addresses the important problem of user-AP association and resource allocation. We study three schemes of different complexity and investigate how to maximize user throughput with joint consideration of AP assignment and transmission scheduling. To solve the formulated problem, we propose a branch-and-cut-based solution procedure. We perform a detailed comparative analysis of the three schemes and advocate to use one-shot AP assignment-based scheduling scheme due to its simplicity and good performance. To deal with real-time traffic and human blockage, we propose an online algorithm to implement the one-shot AP assignment-based scheme to avoid frequent service disruption. Our results show that the proposed online algorithm is competitive when compared with the optimal offline algorithm. [ABSTRACT FROM AUTHOR]

The latest standard of IEEE 802.11 WLANs embraces multi-user (MU) transmission via orthogonal frequency-division multiple access (OFDMA), multi-user multiple-input and multiple-output (MU-MIMO), or a mixture of both. However, due to the frame-basis transmission of WLANs, all concurrent user frames must have an identical transmission duration so as to fit in a common MU frame, which requires shorter frames padded with dummy bits, thus reducing transmission efficiency. Since stations are likely to have heterogeneous traffic demands and transmission bit rates in real networks, such inefficiency arises as a practical problem. To address this challenge, first we analyze how different overhead components impact the efficiency of MU transmission. Then, we propose a scheme to construct an MU frame with an optimal length maximizing its transmission efficiency, which provides a unified framework for OFDMA and MU-MIMO in both downlink and uplink. Through simulation, we demonstrate that the proposed scheme integrated with various scheduling algorithms reduces transmission delay and enhances traffic delivery ratio considerably compared to basic approaches. [ABSTRACT FROM AUTHOR]

Recently, solutions based on mobile edge computing paradigm have been widely discussed in academia and industry. This paradigm offers solutions to address limitations, in terms of battery lifetime and processing power, of mobile and constrained devices. Despite the ever-increasing capabilities of these devices, resource requirements of applications can often transcend what is available within a single device. Offloading intensive computation tasks to a distant server can help applications reach their desired performances. In this work, we tackle the problem of offloading heavy computation tasks of unmanned aerial vehicles (UAVs) while achieving the best possible tradeoff between energy consumption, time delay, and computation cost. We focus on a scenario of a fleet of small UAVs performing an exploration mission. During their mission, these constrained devices have to carry-out highly intensive computation tasks such as pattern recognition and video preprocessing. We formulate the problem using a non-cooperative theoretical game with N players and three pure strategies. We provide a comprehensive proof for the existence of a Nash equilibrium and implement accordingly a distributed algorithm that converges to such an equilibrium. Extensive simulations are performed in order to provide thorough results and assess the performances of the approach compared to three other models. Results show that our algorithm outperforms all the three approaches. Our approach achieved in average about 19%, 58%, and 55% better results compared to local computing, offloading to the edge server, and offloading to base station, respectively. [ABSTRACT FROM AUTHOR]

This paper uses an information-theoretic lens to view the error bound of wireless local area network (WLAN) localization, which is recognized as one of the superior candidate localization techniques in the GPS-denied environment. Interestingly, we analogize the process of WLAN localization into one of information propagation in a parallel Gaussian noisy channel, and then derive the corresponding localization error bound from the channel capacity of the analogical information propagation system. Experimental results show that compared with the widely-known Cramer-Rao Lower Bound (CRLB), the proposed approach performs better in localization error bound estimation under most of the cases of different access point deployment and reference point calibration. [ABSTRACT FROM AUTHOR]

IP flow mobility (IFOM) enables a user equipment to offload data traffic at the IP flow level. Although the procedure of IFOM-based flow offloading has been specified by 3GPP, how many IP flows should be offloaded and when offloading should be performed are not defined. Consequently, IP flows may be routed to a target access network that has a strong signal strength but with backhaul congestion or insufficient access capability. In this paper, we propose two algorithms, referred to as proportional offloading (PO) and proportional and preemption-enabled offloading (PPO), respectively, for IP flow offloading in hybrid cellular and wireless local area networks. The PO algorithm decides an optimal proportion of IP flows, which could be offloaded by considering available resources at the target access network. In the PPO algorithm, both service continuity and network utilization are taken into consideration. Furthermore, a detailed analytical model is developed in order to evaluate the behavior of the proposed algorithms. The analytical model is validated through extensive simulations. The results show that by dynamically adjusting the percentage of traffic flows to be offloaded, PO can reduce blocking probability and increase resource utilization. PPO further improves the performance at the cost of slightly higher offloading overhead. [ABSTRACT FROM AUTHOR]

Device-to-device (D2D) communication is a promising technology towards 5G networks. D2D communication can offload traffic using licensed/unlicensed band by establishing a direct communication between two users without traversing the base station or core network. However, one of the major challenges of D2D communication is resource allocation and guaranteeing quality-of-service (QoS). In this paper, we establish an optimal queuing scheduling and resource allocation problem for three-tier heterogeneous network based on LTE Wi-Fi aggregation, to offload voice/multimedia traffic from licensed band to unlicensed band using scalable MAC protocol (SC-MP) under various static delay constraints. The access mechanism used for Wi-Fi in SC-MP is point coordination function, which further offloads the multimedia traffic using D2D communication in unlicensed band. Resource allocation and optimal joint queuing scheduling problems are formulated with diverse QoS guarantee between licensed and unlicensed band to minimize the bandwidth of licensed band. Furthermore, an iterative algorithm is proposed to express the nonconvex problem as a series of subproblems based on block coordinate descent and difference of two convex functions (D.C) program. We have simulated the proposed scheme using two scenarios: voice traffic using licensed band and voice traffic using both licensed and unlicensed band, whereas multimedia traffic uses unlicensed band for both the scenarios. The simulation results show that both the schemes perform better than the existing scheme and scenario 2 outperforms scenario 1. [ABSTRACT FROM AUTHOR]

In this paper, we study the connectivity between two fixed terminal nodes within a geometrically bounded network of relay nodes and fixed infrastructure nodes. We assume that a communication path, between the terminal nodes, can be established by direct connection (1-hop), via a relay node (2-hop) or via the infrastructure network; the choice is based on link viability in a Rayleigh fading environment. We adopt a probabilistic approach to our analysis considering a homogeneous spatial distribution of relay nodes and an inhomogeneous spatial distribution of infrastructure nodes. Our analysis of the relationship between relay and infrastructure densities for a prescribed outage probability shows that reliance on infrastructure connectivity can be appreciably reduced by employing direct and 2-hop connectivity. We further show that, as the relay density increases, optimum connectivity is achieved by employing a non uniform spatial thinning of the infrastructure, which is dependent upon the geometric extent of the network. Our analysis provides an insight into multi-mode connectivity in bounded network domains and has application in many fields including cellular and vehicle-to-infrastructure (V2X), which are often modelled as having finite extent and where reducing the reliance on fixed infrastructure can effectively reduce operating expenditure costs. [ABSTRACT FROM AUTHOR]

The bidirectional transmission based-protocols have been proposed to resolve an uplink (UL)/downlink (DL) unfairness problem of an infrastructure mode WLAN. However, they do not guarantee the fairness in an error-prone channel. We propose two protocols enhancing the UL/DL fairness, named negative acknowledgement (NACK)-based channel reservation and hybrid automatic repeat request-based bidirectional media access control (MAC) (HyBiM). We analyze the throughput of the two protocols by proposing a new Markov chain model. The analytical and simulation results show that the HyBiM protocol guarantees the UL/DL fairness even in the error-prone channel. [ABSTRACT FROM AUTHOR]

The hidden terminal problem degrades the uplink system throughput of wireless local area network seriously. In this paper, we propose the optimum allocation (OA) scheme of the location-based virtual sector (VS) method, which solves the hidden terminal problem without massive overheads like request-to-send and clear-to-send (RTS/CTS) packets. The VS method forms sectors virtually to make short-distance mobile terminal (MT) groups using MTs’ location information. In the group, all MTs can sense the transmission of all other MTs. In the proposed method, rough time slot control is implemented for intersector control, which does not need a highly functional centralized controller. The proposal OA scheme of the VS method improves the fairness among MTs by optimizing active periods of VS according to the number of MTs in each VS. By computer simulations, we show that the proposed method can increase the system throughput from the RTS/CTS and improve fairness among MTs even in the condition that positioning error is 1/10 of cell radius. [ABSTRACT FROM AUTHOR]

Wireless LAN (WLAN) based networks can rely on the concept of automatic repeat request to overcome temporary channel outages, such as those due to interference. However, the used acknowledgement scheme for unicast transmissions blocks other transmissions until a message has either been successfully transmitted or until the retry limit has been reached. We investigate this head of line blocking problem, its impact, and first steps toward a final solution. As a research methodology, we build upon an analytical model, computer simulations, and also experimentation in a lab environment. We consider the effects for a single node in a small and static network as well as studying the application layer performance in a highly dynamic network—we investigate Vehicular Ad Hoc Networks (VANETs) as a prime example—spanning several kilometers. Aside from considering the case of malicious users conducting easy active and passive attacks, we show that in highly dynamic networks this blocking behavior can (massively) be observed as local topologies change. Here, the discussed effects can lead to massive message loss and increased latencies in the order of seconds. [ABSTRACT FROM AUTHOR]

An L-sleeve L-monopole (LSLM) antenna fitting a shark-fin module is proposed for vehicular long-term evolution (LTE) communication. Starting with classical sleeve monopole antennas, a low-profile evolution is introduced to explain the working principle of the LSLM. The influence of the ground plane, placement position, and bent of the LSLM is analyzed to fit different shark-fin modules. Designed prototypes (the LSLM and bended LSLM) cover the frequency range of 698–2700 MHz (VSWR < 3), which would serve major LTE standards. One tab monopole antenna covering the frequency range of 5–6 GHz can be integrated into the shark-fin module and provide services for wireless local area network and car-to-car communications. Low mutual coupling (lower than –23 dB) between the two antennas is achieved in the frequency range of 698–6000 MHz without any additional filters, and the design method is presented for better understanding the underlying physics. The proposed antenna is fabricated on an affordable printed circuit board, which is useful for vehicular applications. [ABSTRACT FROM AUTHOR]

Recently, the interest in operating long term evolution (LTE) in unlicensed bands (i.e., LTE-U) has increased. However, since LTE does not sense for channel vacancy prior to transmissions, whereas a wireless local area network (WLAN) is based on carrier sensing multiple access, LTE interference severely degrades the performance of WLAN. To maximize the LTE throughput while maintaining fairness between LTE and WLAN, we formulate a joint optimization problem of channel selection and frame scheduling in LTE. As a practical solution of this problem, we propose a low-complexity heuristic algorithm called the sequential operation algorithm (SOA). Evaluation results demonstrate that SOA can achieve an LTE throughput comparable to that of the optimal solution, while maintaining fairness between LTE and WLAN by selecting appropriate channels and conducting effective frame scheduling. [ABSTRACT FROM AUTHOR]

Dynamic spectrum access (DSA) allows the spectrum to be utilized efficiently through opportunistic access. Cognitive radio (CR) is a technology used to enable DSA. Unlike a wireless local area network (WLAN) that operates in unlicensed band, cognitive WLAN allows CRs to identify spectrum holes in licensed bands and opportunistically use it. DSA makes the design of the medium access control (MAC) layer in the cognitive WLAN challenging. In this paper, we design and carry out performance analysis of IEEE 802.11 DCF based MAC protocol for multichannel cognitive WLAN. Our main contributions are as follows: 1) A Markov chain model for CRs and 2) another Markov chain to model the joint usage of the channel by the licensed users and CRs. These coupled Markov chain models are then solved for stationary probability distribution. Using the above models, we derive throughput and delay of the CRs and study their variation against the number of CRs, the number of channels, and spectrum availability. Theoretical results are validated using simulation and compared with results from existing literature. [ABSTRACT FROM AUTHOR]

With increasing popularity of wireless local area network (WLAN) and emerging real-time applications, seamless mobility has become one of the primary concerns. Hence, the choice of a proper handover algorithm is of utmost importance. Various performance evaluation metrics for handover algorithms have been proposed in this regard. We argue that in a multiple access point (AP) scenario, the load on each of the APs, the requested data rate of the mobile terminal, and the soft handover have significant impact on these metrics. In this paper, we present an analytical framework to measure various handover performance evaluation metrics under both load condition and soft handover for a specific data rate request. Our approach is based on finding the circular region centered around an AP within which the requested data rate can be satisfied. We have considered WLAN usage efficiency, handover failure probability, and unnecessary handover probability as evaluation metrics. We have analyzed the impact of load and soft handover on these metrics. The impact of velocity on these metrics has also been analyzed. We also have derived lower bounds on both handover failure probability and unnecessary handover probability by formulating the problem into three circle intersection problem. The circular coverage assumption used in the framework is also validated through simulation. [ABSTRACT FROM PUBLISHER]

Identifying line-of-sight (LOS) and non-LOS channel conditions can improve the performance of many wireless applications, such as signal strength-based localization algorithms. For this purpose, channel state information (CSI) obtained by commodity IEEE 802.11n devices can be used, because it contains information about channel impulse response (CIR). However, because of the limited sampling rate of the devices, a high-resolution CIR is not available, and it is difficult to detect the existence of an LOS path from a single CSI measurement, but it can be inferred from the variation pattern of CSI over time. To this end, we propose a recurrent neural network (RNN) model, which takes a series of CSI to identify the corresponding channel condition. We collect numerous measurement data under an indoor office environment, train the proposed RNN model, and compare the performance with those of existing schemes that use handcrafted features. The proposed method efficiently learns a nonlinear relationship between input and output, and thus, yields high accuracy even for data obtained in a very short period. [ABSTRACT FROM PUBLISHER]

Femtocell provides a potential solution for poor coverage and capacity limitation in the indoor environment. For wireless service providers (WSPs), the emerging femtocell market brings new opportunities as well as challenges. In this paper, we propose an economic framework for an oligopolistic femtocell market, where selfish WSPs try to maximize their net profits by price competition and resource allocation. When analyzing the optimal strategy for each WSP, we are facing two major challenges. On the one hand, it is difficult for a WSP to acquire complete information about its rival to make well-informed decisions. On the other hand, the market share of a WSP is not only determined by its own price and quality of service (QoS), but also affected by prices and QoS of other WSPs. To address these problems, we formulate the oligopolistic femtocell market as a Bayesian game, where WSPs with incomplete information of their competitors optimize pricing and resource allocation strategies based on a well-round market analysis. We first study the scenario where all WSPs enter the femtocell market at the same time and unaware of each other's strategy. Then, we consider the scenario where WSPs enter the femtocell market sequentially, and the newcomers can observe the strategy of the incumbent. We derive the optimal pricing and resource allocation strategy for each WSP and obtain the Bayesian Nash equilibrium of the whole game. We conduct simulations to evaluate the proposed economic framework in terms of market entry sequence, information status, and strategy space. [ABSTRACT FROM AUTHOR]

With the increase of the popularity of voice over wireless local area networks (VoWLANs), how to improve the capacity of VoWLANs is being actively investigated. A recent technology to allow simultaneous transmission and reception, i.e., full duplex (FD) communications, can be a promising candidate for improving the capacity of VoWLANs. In this paper, we develop an analytical model of an FD medium access control protocol for VoWLANs, and study its capacity. Extensive simulation results are given to show the effects of FD communications, different voice over IP (VoIP) codecs, and data connections on the VoIP capacity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

About 60-GHz millimeter wave (mmWave) unlicensed frequency band is considered as a key enabler for future multi-Gbps WLANs. IEEE 802.11ad (WiGig) standard has been ratified for 60-GHz wireless local area networks (WLANs) by only considering the use case of peer to peer (P2P) communication coordinated by a single WiGig access point (AP). However, due to 60-GHz fragile channel, multiple number of WiGig APs should be installed to fully cover a typical target environment. Nevertheless, the exhaustive search beamforming training and the maximum received power-based autonomous users association prevent WiGig APs from establishing optimal WiGig concurrent links using random access. In this paper, we formulate the problem of WiGig concurrent transmissions in random access scenarios as an optimization problem, and then we propose a greedy scheme based on (2.4/5 GHz) Wi-Fi/(60 GHz) WiGig coordination to find out a suboptimal solution for it. In the proposed WLAN, the wide coverage Wi-Fi band is used to provide the control signalling required for launching the high date rate WiGig concurrent links. Besides, statistical learning using Wi-Fi fingerprinting is utilized to estimate the suboptimal candidate AP along with its suboptimal beam direction for establishing the WiGig concurrent link without causing interference to the existing WiGig data links while maximizing the total system throughput. Numerical analysis confirms the high impact of the proposed Wi-Fi/WiGig coordinated WLAN. [ABSTRACT FROM PUBLISHER]

Device-free wireless localization and activity recognition is an emerging technique, which could estimate the location and activity of a person without equipping him/her with any device. It deduces the state of a person by analyzing his/her influence on surrounding wireless signals. Therefore, how to characterize the influence of human behaviors is the key question. In this paper, we explore and exploit a radio image processing approach to better characterize the influence of human behaviors on Wi-Fi signals. Traditional methods deal with channel state information (CSI) measurements on each channel independently. However, CSI measurements on different channels are correlated, and thus lots of useful information involved with channel correlation may be lost. This motivates us to look on CSI measurements from multiple channels as a radio image and deal with it from the two-dimensional perspective. Specifically, we transform CSI measurements from multiple channels into a radio image, extract color and texture features from the radio image, adopt a deep learning network to learn optimized deep features from image features, and estimate the location and activity of a person using a machine learning approach. Benefits from the informative and discriminative deep image features and experimental results in two clutter laboratories confirm the excellent performance of the proposed system. [ABSTRACT FROM PUBLISHER]

From experience, it has been well known that the performance of IEEE 802.11 wireless local area networks significantly drops in dense settings, largely driven by poor capacity of the medium access control (MAC) layer. The current 802.11 MAC mechanism utilizes a contention window (CW) for random access, and the CW size is dictated to take discrete values from a bounded finite set. In this paper, with focus on a saturated network scenario, we closely investigate the impacts of the aforementioned constraint and show that the limitations on the CW size are the main MAC bottleneck in dense conditions. Then, in order to tackle this bottleneck, we propose a new backoff scheme that does not attempt to tune the CW but makes a small modification in the backoff freezing process to determine the optimal configuration. We prove that our backoff scheme can achieve the maximum network throughput even under densely populated networks (i.e., many contenders), while a maximal compliance with the mentioned constraints is maintained. Then, we turn our attention to minimizing the channel access delay, and propose a variant of our backoff algorithm to accomplish this aim. We further present a new result on the theoretical relation between the optimal configurations for which the throughput is maximized and the delay is minimized. Finally, we note that our modified backoff mechanism does not penalize legacy users and is, therefore, practical for implementation in existing networks, which removes co-existence concerns. [ABSTRACT FROM PUBLISHER]

The 802.11ac version of the popular IEEE 802.11 protocol aims to boost performance by increasing the channel bandwidth and allowing downlink multiuser multiple-input multiple-output (MIMO)—i.e., simultaneous transmission to multiple clients in the downlink direction. In this paper, we evaluate the performance improvements of multiuser Transmission Opportunity (MU-TXOP) sharing in this scenario under nonsaturated load and non-ideal channel condition, using a novel analytical model based on discrete Markov chain and E-limited M/G/1 queuing model. Our results show that MU-TXOP sharing achieves up to 105% gain in throughput compared to the case without MU-TXOP sharing. Moreover, the low-priority traffic benefits most from MU-TXOP sharing, with up to 150% throughput gain at low traffic intensity due to availability of additional transmission opportunities for secondary ACs. [ABSTRACT FROM PUBLISHER]

A software-defined wireless local area network (SDWLAN) has gained significant interest recently from both the academic and industrial communities and initiated a paradigmatic reconsideration on the stereotyped management and control of current WLAN due to its flexibility and programmability. However, with the proliferation of mobile devices, efficient client association with quality of service (QoS) guarantees in the high-density SDWLAN is a very challenging issue. In this paper, we study the client association problem in the SDWLAN with new features, including centralized association, global network state awareness, seamless handoff, and flow-level association. We formulate the client association in a high-density scenario as an optimization problem aiming to minimize the interpacket delay of individual flows, based on an unsaturated and heterogeneous Markovian analytical model. Furthermore, we interpret the optimization problem as an NP-hard supermodular set function minimization problem, which is solved by two low-complexity heuristic methods, namely the greedy algorithm and the bounded local search algorithm. Through simulations, we demonstrate the effectiveness of our proposed client association solution. [ABSTRACT FROM AUTHOR]

This paper introduces novel schemes for indoor localization, outlier detection, and radio map interpolation using wireless local area networks. The localization method consists of a novel multicomponent optimization technique that minimizes the squared \ell 2-norm of the residuals between the radio map and the online received signal strength (RSS) measurements, the \ell 1-norm of the user's location vector, and weighted \ell 2-norms of layered groups of reference points (RPs). RPs are grouped using a new criterion based on the similarity between the so-called access point (AP) coverage vectors. In addition, since AP readings are prone to containing inordinate readings, called outliers, an augmented optimization problem is proposed to detect the outliers and localize the user with cleaned online measurements. Moreover, a novel scheme to record fingerprints from a smaller number of RPs and estimate the radio map at RPs without recorded fingerprints is developed using sparse recovery techniques. All localization schemes are tested on RSS fingerprints collected from a real environment. The overall scheme has comparable complexity with competing approaches, while it performs with high accuracy under a small number of APs and finer granularity of RPs. [ABSTRACT FROM PUBLISHER]

To meet the dramatic growth in mobile traffic, wireless local area networks (WLANs) have been integrated with cellular networks. We investigate the user equipment (UE) association problem in WLAN/cellular integrated networks from game-theoretic perspective by taking into account throughput and power consumption. In the case of WLAN offloading, random uplink traffic from UEs inevitably brings contention and collisions into WLANs; thus, the capacity of a WLAN system is decreased. To eliminate this side effect, UEs are encouraged to deliver uplink traffic over contention-free cellular networks. However, UEs will consume much more power when their uplink traffic is delivered over cellular networks instead of WLANs. Observing the above contradiction between throughput and power consumption, we define a utility function to reconcile the contradiction and formulate the UE association problem as a game. An incentive mechanism is involved to encourage UEs with enough energy to redirect their uplink traffic over cellular networks. We prove that this game is an exact potential game with at least one pure-strategy Nash equilibrium. Then, a distributed algorithm is proposed for each UE to determine its uplink association. Finally, extensive numerical simulations validate the feasibility and effectiveness of the proposed association strategy. [ABSTRACT FROM PUBLISHER]

A fine-grained carrier sense threshold (CST) adaptation method, which controls CST, depending on both the interferer and destination nodes, is proposed to improve spatial reuse in wireless local area networks (WLANs). The proposed method utilizes predefined functions in the WLAN standard, thus making itself easily implementable in commercial WLAN devices. A supplementary clear channel assessment (CCA) method is also proposed to further enhance network performance by reducing CCA overhead. The performance of the proposed methods is comparatively evaluated via ns-3 simulation. Simulation results show that the proposed methods significantly improve network throughput compared with the legacy method in a two-cell environment. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a sounding control scheme for IEEE 802.11ac multiuser multiple-input multiple-output (MU-MIMO). The proposed scheme comprehensively considers the long-term characteristics of a network environment, including the downlink traffic loads and channel coherence times of wireless links, and jointly determines the sounding node set and sounding interval to maximize the long-term expected MU-MIMO throughput gain in consideration of sounding overhead. To this end, we analytically formulate an MU-MIMO throughput gain maximization problem, considering the network environment and sounding overhead. We conduct MIMO channel measurement in practical wireless local area network (WLAN) environments and evaluate the performance of the proposed scheme by employing the real channel data traces. Simulation results verify that the proposed scheme adaptively determines the sounding node set and sounding interval, according to the network environment, and outperforms the existing scheme, which considers the channel coherence times only. [ABSTRACT FROM PUBLISHER]

Recently, there has been an increasing interest in operating long-term evolution (LTE) in unlicensed bands (i.e., LTE-U). However, since LTE and wireless local area networks (WLANs) are designed to operate in different bands, they have no coexistence mechanism, which leads to significant performance degradation. In particular, since LTE does not sense channel vacancy prior to transmissions, the LTE interference severely affects the WLAN operation. To address this problem, we propose a fair listen-before-talk (F-LBT) algorithm for coexistence of LTE-U and WLAN in unlicensed bands. F-LBT jointly considers the total system throughput and the fairness between LTE-U and WLAN and then allocates an appropriate idle period for WLAN. Evaluation results demonstrate that F-LBT can improve the total system throughput while providing the fairness between LTE-U and WLAN. [ABSTRACT FROM PUBLISHER]

Flow assignment and packet scheduling are two processes of deploying limited wireless resources to support high-data-rate transmissions. Optimizing these processes is critical in improving the traffic performance and network utilization. In this paper, we investigate the flow assignment and packet scheduling for multihomed communication of delay-constrained traffic over heterogeneous wireless networks. With regard to the inherent channel diversity and unreliability, large end-to-end delay and burst packet losses pose crucial challenges to guarantee goodput performance of real-time traffic. To address these critical issues, we present an Adaptive Flow Assignment and Packet Scheduling (AFAPS) framework. First, we introduce a “horizontal water filling” algorithm, which effectively integrates the channel resources in heterogeneous wireless networks to maximize the aggregate goodput. Second, we propose an alternative path interleaving scheme, which spreads out the packets' departures over multiple communication paths within the delay constraint to mitigate burst losses. The performance of the proposed AFAPS framework is evaluated through semi-physical emulations in EXata involving real Internet traffic traces. Experimental results show that AFAPS outperforms existing multipath data distribution models, in terms of goodput and end-to-end delay. [ABSTRACT FROM PUBLISHER]

In this paper, the problem of joint data-rate allocation and mobile terminal (MT) assignment is investigated in a heterogeneous wireless network (HetNet) environment that consists of wireless local area network (WLAN) access points (APs) and cellular base stations (BSs) for a best-effort service. MTs are equipped with multiple radio interfaces and have multihoming capabilities. As a result, MTs can connect simultaneously to more than one wireless network (e.g., cellular network BS and WLAN AP) and aggregate the offered bandwidths from these networks to support applications with high required data rates. Unlike the existing research, to account for the MT's limited number of radio interfaces and the abundant wireless network options, the joint MT assignment and data-rate allocation problem is formulated to select the optimal subset of networks for each MT and allocate the optimal data rate share from this subset to maximize the HetNet total utility. The problem is formulated as a mixed-integer nonlinear program (MINLP), and due to its intractability and computational complexity, we transform the problem into a convex optimization problem via a binary variable relaxation approach. Based on the mathematical analysis of the problem, we present a heuristic algorithm for joint MT assignment and data-rate allocation. Numerical results demonstrate that the proposed solution achieves a near-optimal MT assignment and data-rate allocation at reduced computational complexity. [ABSTRACT FROM PUBLISHER]

With the pervasive use of IEEE 802.11 wireless local area networks (LANs), increasingly more application flows with different quality-of-service (QoS) requirements will be deployed therein, e.g., home multimedia. This paper is concerned with providing utility-optimal throughput guarantees when diverse application flows share the limited bandwidth. Our proposal provides the absolute throughput guarantees for inelastic flows (such as Internet Protocol television) and the proportional throughput guarantees for elastic flows (such as text message) while maximizing the entire system bandwidth utilization. To this end, we first establish a general theoretical framework on the utility-optimal problem. We then present the exact and approximate solutions and prove the existence and uniqueness of the approximate solution. Finally, extensive simulations are performed, which validate that the approximate solution can well achieve the desired objectives. [ABSTRACT FROM PUBLISHER]

Carrier sense multiple access with collision notification (CSMA/CN) is a typical representation of physical-layer (PHY)/medium access control (MAC) co-designs, where the MAC control frames are implemented or detected using PHY techniques. With CSMA/CN, the sender detects an unsuccessful transmission, with the aid of a collision notification (CN) from the receiver. In this paper, we first theoretically study the crucial impact of the CN attributes (namely, the detection threshold and the length) on system throughput in a wireless local area network (WLAN). We identify that the false-alarm probability of CN (more generally, the control frames in PHY/MAC co-designs) is a dominating metric that influences system performance. This paper will help developers select optimal CN attributes to balance various factors influencing CN detection performance. Extensive simulation results verify that our performance model is very accurate. [ABSTRACT FROM PUBLISHER]

In this paper, we focus on enhancing the energy efficiency in open-access femtocell networks where many femto base stations (BSs) are deployed in a large public area such as airports, shopping malls, etc. In those areas, the femtocells are overlapped and underutilized during most of the operation time because femto BSs are densely deployed to support the peak traffic load. Therefore, if we properly coordinate the user association (UA) with BSs and put the femto BSs having no associated users to sleep, the energy consumption can be saved remarkably. In this paper, we propose a scheme that jointly decides the operation modes (e.g., active or sleep) of femto BSs and the association between users and the active BSs to minimize the energy consumption in the network. Simulation results show that the proposed scheme can significantly reduce the total energy consumption in the open-access femtocell networks. [ABSTRACT FROM AUTHOR]

In general, an access point (AP) in wireless local area networks (WLANs) can be easily congested since all related data traffic goes through it. To satisfy the quality-of-service (QoS) requirement for its customers, a protocol-independent redundancy elimination (RE) technique can effectively mitigate the congestion at the AP by reducing redundant data traffic. In this paper, we propose an overhearing-aided RE (OARE) scheme for multirate WLANs by leveraging the broadcast nature of a wireless medium. In OARE, the AP estimates overhearing probabilities of partially sliced chunks from an incoming packet for a destination mobile terminal by considering an adaptive modulation and coding technique. Then, the original packet is encoded by means of RE to minimize its transfer time to the destination, depending on the estimated overhearing probabilities. Extensive simulation results demonstrate that OARE can reduce the packet transfer time by 7.8%–23.2%, compared with non-RE (or nonencoded) transmissions. [ABSTRACT FROM AUTHOR]