ResearchArticle Wi-Fi Coexistence with Duty Cycled LTE-Udownloads.hindawi.com/journals/wcmc/2017/6486380.pdf · Wi-Fi Coexistence with Duty Cycled LTE-U YiminPang, 1 AlirezaBabaei,

Research ArticleWi-Fi Coexistence with Duty Cycled LTE-U

Yimin Pang1 Alireza Babaei2 Jennifer Andreoli-Fang3 and Belal Hamzeh3

1Department of Electrical Computer and Energy Engineering University of Colorado Boulder Boulder CO 80309 USA2Ofinno Technologies Herndon VA USA3Cable Television Laboratories Louisville CO USA

Correspondence should be addressed to Yimin Pang yipa5803coloradoedu

Received 1 July 2016 Revised 17 September 2016 Accepted 18 October 2016 Published 15 January 2017

Academic Editor Adlen Ksentini

Copyright copy 2017 Yimin Pang et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Coexistence of Wi-Fi and LTE-Unlicensed (LTE-U) technologies has drawn significant concern in industry In this paper weinvestigate the Wi-Fi performance in the presence of duty cycle based LTE-U transmission on the same channel More specificallyone LTE-U cell and one Wi-Fi basic service set (BSS) coexist by allowing LTE-U devices to transmit their signals only inpredetermined duty cyclesWi-Fi stations on the other hand simply contend the shared channel using the distributed coordinationfunction (DCF) protocol without cooperation with the LTE-U system or prior knowledge about the duty cycle period or dutycycle of LTE-U transmission We define the fairness of the above scheme as the difference between Wi-Fi performance loss ratio(considering a defined reference performance) and the LTE-U duty cycle (or function of LTE-U duty cycle) Depending on theinterference to noise ratio (INR) being above or below minus62 dbm we classify the LTE-U interference as strong or weak and establishmathematical models accordingly The average throughput and average service time of Wi-Fi are both formulated as functions ofWi-Fi and LTE-U system parameters using probability theory Lastly we use the Monte Carlo analysis to demonstrate the fairnessof Wi-Fi and LTE-U air time sharing

1 Introduction

The rapidly growing demand of wireless network serviceshas led the mobile network operators (MNOs) to look intothe possibility of exploring unlicensed spectrum to offloadthe data traffic from the licensed bands Most recently3GPP and other industry alliances are considering extendingLTE into the unlicensed spectrum (3GPP has completedstandardization of license assisted access (LAA) in release13 (DL only) and enhanced LAA (eLAA) standardizationwhere UL access to unlicensed spectrum is also consideredand is currently ongoing in 3PP release 14 LAA and eLAAincorporate listen-before-talk (LBT) for their channel accessto the unlicensed spectrum In addition the LTE-U foruman industry alliance formed by some vendors and mobileoperators has released an LTE supplemental downlink (SDL)coexistence specification where an adaptive duty cycle basedcoexistence scheme is introduced The term ldquoLTE-Urdquo is usedinstead of ldquoLAArdquo in the LTE-U forum specification Sincethis paper focuses on duty cycle based LTE on unlicensed

spectrum we use the short term LTE-U for convenienceHowever the channel access approach introduced in thispaper is not completely aligned with the channel accessmethod introduced by the LTE-U forum specification due tononadaptive duty cycle) to offload part of the LTE data trafficonto the unlicensed spectrum Compared to data offloadusing Wi-Fi this approach has the advantage of seamlessintegration into the existing LTE evolved packet core (EPC)architecture In a proposal outlined in [1] three LTE-Umodesare introduced as supplement downlink TD-LTE-U carrieraggregation and standalone the first two of which wereproposed to 3GPP as possible candidates

Coexistence of heterogeneous networks such as Wi-Fiand LTE-U on the same band and their uncoordinated opera-tions can potentially cause significant interference degradingthe performance of both systems Solutions to manage theinterference between such systems are therefore necessaryfor their successful coexistence One straightforwardmethodis to split the common radio channel through air timesharing between the Wi-Fi and LTE-U subsystems With

HindawiWireless Communications and Mobile ComputingVolume 2017 Article ID 6486380 10 pageshttpsdoiorg10115520176486380

2 Wireless Communications and Mobile Computing

Duty cycle period

LTE offLTE on LTE on

Duty cycleTime

Wi-Fi access gapswhen LTE is off of cycle LTE is active

Figure 1 Air time sharing LTE-U

this approach LTE-U operates over the shared channelperiodically (more specifically the radio resources of LTE-Uthat reside in the unlicensed spectrum and are shared withWi-Fi are utilized periodically) and during each period (theso-called duty cycle period denoted as 119879) only a portion(defined by the LTE-U duty cycle 120572) of the time is utilized forthe LTE-U transmission as shown in Figure 1 In this schemeWi-Fi has no cooperation with LTE-U Wi-Fi stations haveneither knowledge about the time length of duty cycle periodnor the duty cycle they simply access the shared channel bystandard channel sensing and random back-off mechanisms

In an LTE system each user equipment (UE) commu-nicates with a base station (eNB) in a deterministic mannerthrough a centralized channel access controlmechanismTheaccess time and OFDM subcarriers of an LTE frame arepredetermined at eNB where the MAC scheduler considersthe radio measurement and quality of service needed foreach UE in its scheduling decisions Given the above timesharing scheme and the LTErsquos centralized access structurecomputation of the LTE-U performance in terms of through-put and service time is relatively simple and straightforwardHowever themedium accessmechanism used byWi-Fi con-trolled by distributed coordination function (DCF) protocoldefined in IEEE 80211 standard is random and distributedTherefore we focus on the impact of LTE-U interference onWi-Fi performance in this paper

11 Previous Works LTE-U and Wi-Fi coexistence are arelatively new area of research Previous works in thisarea are summarized as follows in [2] Wi-Fi and LTE-Ucoexistence in single floor and multiple floors environmentat various densities are simulated The results show thatwithout any interferencemanagement scheme LTE-U systemperformance is slightly affected from Wi-Fi whereas Wi-Fiis significantly impacted by the LTE-U transmissions Thisresult is reinforced in [3] by computing the Wi-Fi successfulchannel accessing probability in the presence of LTE-Utransmission However in [1] LTE-U is described as a betterneighbor to Wi-Fi than Wi-Fi to itself as long as a propercoexistence mechanism (called CSAT) is applied Authors in[4] present simulation results on spectrum efficiency com-parison between Wi-Fi and LTE-U in a sparse deploymentscenario The paper however lacks sufficient details on thecoexistence features and their effectiveness Cano and Leith[5] proposed a duty cycle mechanism for LTE-U which byselecting an appropriate probability to access the channeland transmission duration ensures proportional fairnessamong LTE-U and Wi-Fi nodes Specifications regardingduty cycled based LTE-U are released and maintained by

LTE-U forum [6] where CSAT is officially introduced as theaccess mechanism

On the other hand the 3GPP study item technicalreport document [7] has listed listen-before-talk (LBT) as therequired function for clear channel assessment for LTE LAAThe application of LBT may potentially enhance the coexist-ence behavior of Wi-Fi and LTE Some analysis and perfor-mance test have been reported in [8ndash10]

12 Main Results In this paper we define Wi-Fi averagesaturation throughputR(119879 120572H) (in terms of bitsWi-Fi slottime) and average service timeD(119879 120572H) (in terms ofWi-Fitime slots) to be functions of 119879 120572 and H = 119902 119871 119899 wherethe set H = 119902 119871 119899 represents 119899-clients Wi-Fi subsystemwith LTE-U to Wi-Fi collision probability (Wi-Fi transmis-sion failure probability due to LTE-U transmission) 119902 andWi-Fi data payload length 119871 (the length of MAC data payloadin terms of bytes) Given H the throughput fairness (cfDefinition 2) of (119879 120572) air time sharing scheme is measured bythe difference between average Wi-Fi saturation throughputloss ratio (with respect to the corresponding non-LTE-Udutycycle scenario (infin 0H) performance) and LTE-U duty cycle120572 that is (R(infin 0H) minus R(119879 120572H))R(infin 0H) minus 120572 Ina similar way the average service time fairness is defined as(D(119879 120572H) minus D(infin 0H))D(infin 0H) minus 120572(1 minus 120572) Thesetwo fairness measures indicate whether Wi-Fi will lose lessor more than 120572 portion of its performance (in the absence ofLTE-U transmission) if 120572 portion of the channel resource isshared with LTE-U

Our first step is to analytically formulateR(119879 120572H) andD(119879 120572H) using a probabilistic framework The followingtwo key techniques are employed

121 Only One Labeled Client Station among the 119899 Wi-Fi Stations Being Affected by LTE-U Interference As firstintroduced by [11] Wi-Fi DCF can be formulated into aMarkov chain model which was generalized later in [12 13]But when LTE-U is considered the Markov property nolonger holds because of the fact that when LTE-U is offthe Wi-Fi transmission failure probability is only Wi-Fi toWi-Fi collision probability when LTE-U is on the Wi-Fitransmission failure probability depends on both Wi-Fi toWi-Fi and LTE-U to Wi-Fi collision probability For thisissue we make an assumption that only one client stationamong the 119899 stations labeled as Sta-A is affected by theLTE-U interference The other 119899 minus 1 stations render theWi-Fi background traffic for the labeled station When 119899 ischosen to be large enough the background traffic could stillbe approximately modeled using the existing framework in[11ndash13] Under this assumption functions R(119879 120572H) andD(119879 120572H) are with respect to Sta-A

122 Different Interference Levels Lead to Different Formu-lations The Wi-Fi DCF employs CSMACA with binaryexponential back-off algorithm Depending on the energylevel being detected the back-off timer may or may not befrozen In short an LTE-U transmission with interferenceto noise ratio (INR) greater than minus62 dbm or a neighborWi-Fi station transmission with INR greater than minus82 dbm

Wireless Communications and Mobile Computing 3

will cause the interfered Wi-Fi station to freeze its back-offtimerWe refer toweak interference as the LTE-U interferencewith its INR being less than minus62 dbm and strong interferenceas interference with INR greater than minus62 dbm The mathe-matical formulations as well as the performance results arequite different between the cases of weak and strong LTE-Uinterference

Other assumptions are just inherited from the existingframework by [11ndash13] onWi-Fi DCF (1) a transmission fromone Wi-Fi station can be heard by all the other 119899 minus 1 Wi-Fi stations and Wi-Fi to Wi-Fi INR is always greater thanminus82 dbm (2) collisions among Wi-Fi or LTE-U to Wi-Fi arethe only causes to Wi-Fi failure transmission

Then we analyze the performance as well as the fairnessnumerically Both the analytical functions built for the weakand strong LTE-U interference are computationally ineffi-cient and characterizing the two performance functions inclosed form is hard On the other hand implementingMonteCarlo analysis based on these two functions is simple It isalso difficult and meaningless to show the fairness over allpossible combinations of119879 120572 andH We focus our attentionon the cases when LTE-U toWi-Fi collision probability 119902 = 1which has wide measure over real systems where LTE-U INRand Wi-Fi SNR are comparable Other parameters are alsoselected in a reasonable range according to practical systemsetting The results demonstrated in Section 4 support theconclusions below

(1) Fix 119902 = 1 under strong interference air time sharingscheme could approximately achieve the fairness forsome (119879 120572) under weak interference air time sharingscheme is generally unfair

(2) The fairness measure degrades almost linearly whenLTE-U to Wi-Fi collision probability 119902 increases

(3) The fairness measure degrades almost linearly whenWi-Fi payload length 119871 increases

The rest of the paper is organized as follows Section 2presents the Wi-Fi and LTE-U coexistence model and for-mulates the problem Section 3 characterizes the average Wi-Fi saturation throughput and average service time in thepresence of LTE-U duty cycle the impact of duty cycled LTE-U interference to Wi-Fi is discussed in Section 4 Section 5concludes the paper

2 System Model and Problem Formulation

In this section we first introduce the generalized Markovchain model for Wi-Fi DCF then we formulate the Wi-Fiand duty cycled LTE-U coexistence and lastly we define thefairness measure

21 Generalized Markov Chain Model for Wi-Fi DCF In[11] the Wi-Fi DCF is formulated into a two-dimensionalMarkov chain the 119894th floor in the Markov chain (refer toFigure 2) stands for the random back-off process before the119894th transmission attempt where 0 le 119894 le 119872 with contentionwindow size CW119894 = 2119894CW0 where CW0 is the contentionwindow size of the 0th back-off This Markov chain has

transition probability 119901(119894119899+1 119895119899+1 | 119894119899 119895119899) (with a slight abuseof notation we temporarily use 119899 to denote the state at 119899thdiscrete moment)

1 119894119899+1 = 119894119899 119895119899+1 = 119895119899 minus 1119895119899 = 0

1 minus 119901119894119899 119894119899+1 = 0 119894119899 = 119872 minus 1119895119899+1 isin 0 CW0 119895119899 = 0

1199011198941198992119894119899+1CW0 119894119899+1 = 119894119899 + 1 119894119899+1 = 119872 minus 1119895119899+1 isin 0 2119894119899+1CW0 119895119899 = 0

1 119894119899+1 = 0 119894119899 = 119872 minus 1119895119899+1 isin 0 CW0 119895119899 = 0

(1)

Let 120590 be the duration of the Wi-Fi system slot time asdefined in IEEE 80211 standard Throughout the paper wenormalize all the time variables to 120590 which means 1 s isnormalized to 1120590 During each (119894 0) state a Wi-Fi stationsenses the channel with probability119901119894 it detects clear channeland transmits (or retransmits) a packet If successful thestation stays idle or goes back to 0th contention level for a newpacket otherwise the failed packet will be retransmitted untilit reaches the maximum number of retry attempts119872 Beforethe 119894th attempt a random number is generated according tothe uniform distribution Unif(0CW119894 minus 1) and loaded intothe back-off timer The timer decreases the registered valueby one per slot time and once the back-off timer is reset thestation senses the channel for the 119894th attempt

Recall that a Wi-Fi station receiving Wi-Fi interferenceover minus82 dbm will freeze its back-off timer therefore thetransition time between two neighbor states in the Markovchain may be more than oneWi-Fi system slot time In orderto use this Markov chain model to analyze the Wi-Fi servicetime the Bianchi model in [11] is further generalized by[12 13] after incorporating the following two further assump-tions

(1) The transition time 119879119889 between any two neighborstates (we call this unit decrement time for shortnormalized to system slot time) is identically andindependently distributed and interference betweenany two Wi-Fi stations is above minus82 dbm threshold

(2) Based on assumption (1) and applying central limittheorem the time interval from a back-off timer loadswith an initial number 119869119894 before 119894th attempt to thetimer being reset is a Gaussian random variable withmean 119869119894119864(119879119889)

We adopt the generalized Markov model of Wi-Fi in thispaper

Next we describe the failure probability119901119894 in each retrans-mission trial Let 120582 be the probability that there is no packetready to transmit and let 120591 be the probability that a Wi-Fi station transmits (or retransmits) a packet in a randomlychosen time slot given a packet just left the buffer and is readyto be transmitted The number 120591 is a function of the number


1 1

1 1

11 1 1

1

1

111

0 0 0 1 0 2

1 0 1 1 1 2

1 minus P0

1 minus P1

1W0

0W0 minus 1

0W1 minus 1

P0W1

1 minus PMminus1

M minus 1 1M minus 1 0 M minus 1 2

M 0 M 1 M 2

PMminus2WMminus1

PMminus1WM

Mminus 1WMminus1 minus 1

MWM minus 1

middot middot middot





Figure 2 Markov model for Wi-Fi DCF (refer to [11])

of Wi-Fi stations 119899 and 119901119894 Without LTE-U interference theprobability119901119894 is simply the collision probability119901119888 that at leasttwo Wi-Fi stations transmit simultaneously which is

119901119894 = 119901119888 = 1 minus [1 minus (1 minus 120582) 120591]119899minus1 (2)

On the other hand we have

120591 = 119872minus1sum119894=0

(1 minus 119901119888) 119901 (119894 0) + (1 minus 119901119888) 119901 (119872 0) (3)

according to the transition probability defined in (1) where119901(119894 119895) is the stationary distribution of the Markov chainThere is no close form expression of the solution to 119901119894 and120591 but given the system parameters and number of stationsthey can be numerically computed When the Wi-Fi systemis saturated the buffer in each station is never empty that is120582 = 0 and 119901119888 = 1 minus (1 minus 120591)119899minus1

It remains to specify the distribution of unit decrementtime 119879119889 Let 119879119904 and 119879119888 be the time duration normalized tothe system slot time of one successful and failed (collided)transmission respectively If CTSRTSmechanism is used119879119904and 119879119888 can be calculated as follows

119879119904 = RTS + CTS +HDR + 119871 + ACK + 3 times SIFS

+ DIFS119879119888 = RTS + DIFS

(4)

otherwise

119879119904 = HDR + 119871 + ACK + SIFS + DIFS119879119888 = HDR + 119871 + DIFS (5)

In both cases 119871 denotes the length of the data payload of aWi-Fi frame Let 119901119904 be the probability that one of the other

119899 minus 1Wi-Fi station transmits successfully (note it is generallynot true that 119901119904 = 1 minus 119901119888) that is

119901119904 = (119899 minus 1) 120591 (1 minus 120591)119899minus2= (119899 minus 1) [(1 minus 119901119888)(119899minus2)(119899minus1) + 119901119888 minus 1] (6)

The unit decrement time 119879119889 has following pmf

119901119879119889 (119905119889) =

1 minus 119901119888 119905119889 = 1119901119888 minus 119901119904 119905119889 = 119879119888119901119904 119905119889 = 1198791199040 ow

(7)

22 Formulation ofWi-Fi andDutyCycled LTE-UCoexistenceConsider an infrastructure-based Wi-Fi network coexistingwith an LTE-U network on the same unlicensed band whereinterference is coming from LTE-U subsystem to the Wi-Fistation labeled Sta-A Considering a duty cycle period whichextends119879Wi-Fi system slots (refer to Figure 1) the eNB orUEin LTE-U subsystem transmits during the LTE-U ON stageof duration 120572119879 where 120572 isin [0 1] and keeps silence duringthe LTE-U OFF stage (as discussed in [3] even during LTE-Uquiet period the reference signalmay have same significantinterference to Wi-Fi transmission In this paper we assumethe LTE-U being completely off during its OFF stage) Thevariables 119879 and 120572 are defined to be LTE-U duty cycle periodand duty cycle respectively The Wi-Fi subsystem does notcooperate with LTE-U nor has any prior knowledge aboutLTE-U interference it simply transmits data frame based onthe DCF mechanism

As has been introduced before assuming only one outof the 119899 Wi-Fi stations receives LTE-U interference is for


the purpose of maintaining the Markov properties to modelthe rest of 119899 minus 1 stations so when 119899 is large enough thecollision probability119901119894 andunit decrement time119879119889 can still beapproximately computed using the generalizedMarkov chainmodel The 119899 minus 1 noninterference stations actually provide astationary background Wi-Fi traffic for Sta-A

We denote a Wi-Fi subsystem as H(119902 119871 119899) where 119902 isin[0 1] is the Wi-Fi collision probability subject to LTE-Uinterference (theWi-Fi transmission failure probability whenaWi-Fi frame and an LTE-U frame transmits simultaneouslyonly applies to Sta-A) 119871 is the data payload length in eachtransmission and 119899 is the number of clients in the Wi-Fisubsystem which determines the Wi-Fi to Wi-Fi collisionprobability (ie Wi-Fi collision probability in the absence ofLTE-U transmission) Furthermore let (119879 120572) denote an airtime sharing scheme with duty cycle period 119879 and LTE-Uduty cycle 120572

Instead of adopting the uniformed Wi-Fi throughputas in [11] we evaluate the Wi-Fi throughput (saturationthroughput of Sta-A the same premise keeps for futurediscussion) 119877(119879 120572H) as the number of bits can be suc-cessfully transmitted per Wi-Fi slot time The Wi-Fi servicetime 119863(119879 120572H) or the medium access delay is defined tobe the time interval (also normalized to system slot time)from the time instant that a packet becomes the head of thequeue and starts to contend for transmission to the timeinstant that either the packet is acknowledged for a successfultransmission or the packet is dropped Note both 119877(119879 120572H)and 119863(119879 120572H) are random variables according to abovedefinition Finally we define the average Wi-Fi throughputand average service time R(119879 120572H) (in terms of bitsWi-Fi slot time) and D(119879 120572H) (in terms of Wi-Fi time slots)respectively for a coexistence system with Wi-Fi subsystemH(119902 119871 119899) and air time sharing scheme (119879 120572) as

R (119879 120572H) = 119864 [119877 (119879 120572H)] D (119879 120572H) = 119864 [119863 (119879 120572H)] (8)

For convenience we sometimes omit the underlyingvariables (119879 120572H) and just use a simple notation as letter 119877orR = 119864[119877] for short23 Definition of Fairness It is a critical task to define whatfairnessmeans in this context since there could bemanywaysto describe the fairness in such a coexistence scenario Onestraightforward way is to compare the Wi-Fi performancewith and without the presence of LTE-U More specificallywe want to find answer to the questionWill the performanceloss (throughput degradation and service time increase) dueto time sharing be proportional to the duty cycle 120572 Alsowhat reference values should be used when we characterizethe performance loss The definition below gives an intuitiveway of measuring fairness

Definition 1 For a given H(119902 119871 119899) assume the referenceWi-Fi performance to be R(infin 0H) and D(infin 0H) Thethroughput fairness 120601119877(119879 120572H) is the difference between the

average throughput loss ratio and the LTE-U duty cycle 120572that is

120601119877 (119879 120572H) = R (infin 0H) minusR (119879 120572H)R (infin 0H) minus 120572 (9)

and service time fairness 120601119863(119879 120572H) is the difference ofaverage service time increase ratio to 120572(1 minus 120572) that is

120601119863 (119879 120572H) = D (119879 120572H) minusD (infin 0H)D (infin 0H) minus 1205721 minus 120572 (10)

Depending on H and (119879 120572) the fairness measures 120601119877and 120601119863 can be negative positive or zero If both these twoparameters (120601119877 and 120601119863) are zero Wi-Fi performs at exact(1 minus 120572) ldquoportionrdquo of the non-LTE duty cycle performanceWe consider such a time sharing scheme to be acceptableand reasonable From this perspective we have the followingdefinition

Definition 2 A Wi-Fi LTE-U coexistence system with Wi-Fi subsystem H and air time sharing scheme (119879 120572) is fairin throughput if 120601119877 le 0 and fair in service time if 120601119863 le 0If a scheme is both fair in throughput and service time thescheme is fair

Remark 3 Please note 119902 is a function of LTE-U toWi-Fi INRandWi-Fi SNR Formulating the collision probability 119902 is outof the scope of this paper It is obvious that very low INRSNRinterference causes almost no impact to Wi-Fi system whichis trivial that is 119902 asymp 0 and 120601119877 120601119863 le 0 This paper focuseson the situations when INR and SNR are comparable andin most subsequent discussions we assume 119902 = 1 whichmeans a Wi-Fi transmission will definitely fail if an LTE-Utransmission occurs at the same time Additionally we willshow in Section 4 how 120601119863 and 120601119877 decay when 119902 increasesfrom 1 to 0 in a numerical example Readers are reminded that119902 = 1 can happen to either strong or weak interference cases

3 Impact of Duty Cycled LTE-U Interference

During the LTE-U ON period the 119894th attempt of Wi-Fitransmission fails with probability

1199011015840119894 = 1 minus (1 minus 119901119888) (1 minus 119902) (11)

Whether the failure probability should be chosen as 119901119894 or1199011015840119894 depends on whether the LTE-U is on or off therefore theSta-A DCF could no longer be modeled by Markov chainInstead we characterize the Sta-A throughput and servicetime in three steps

(1) Suppose a Wi-Fi packet leaves Sta-A buffer at time1198790 = 1199050 where 1199050 isin 0 1 119879 minus 1 and at time 119879119890where 119879119890 isin 1199050 infin the packet will be either sentout successfully or dropped Conditioning on 1199050 wecompute the conditional distribution 119901119879119890|1198790(119905119890 | 1199050)of the finish time 119879119890 the conditional mean servicetime 119864[119863 | 1199050] and conditional mean throughput119864[119877 | 1199050]


(2) Let 1198791015840119890 be a function of 119879119890 that1198791015840119890 = 119879119890 mod (119879 minus 1) (12)

and the conditional distribution of 1198791015840119890 can be derivedfrom 119901119879119890|1198790(119905119890 | 1199050) as

1199011198791015840119890 |1198790 (1199051015840119890 | 1199050) = +infinsum119879119890119879119890 mod (119879minus1)=119905119890

119901119879119890|1198790 (119905119890 | 1199050) (13)

If we regard the119879 time slots (labeled as 0 119879minus1) ina duty cycle period as 119879 states those 119879 states form thestate space of a one-dimension Markov chain withtransition probability from state 1199050 to state 1199051015840119890 of

1199011198791015840119890 |1198790 (1199051015840119890 | 1199050) (14)

because knowing the start time 1199050 and the distributionof 1198791015840119890 does not depend on previous packet trans-mission start times The distribution 1199011198790(1199050) can becomputed as the stationary distribution over these 119879states

(3) Lastly the Sta-A mean throughput 119864[119877] and meanservice time 119864[119863] can be derived as 119864[119877] =sum119879minus11199050=0 1199011198790(1199050)119864[119877 | 1199050] and 119864[119863] = sum119879minus11199050=0 1199011198790(1199050)119864[119863 |1199050]

31 The Conditional Probability 119901119879119890|1198790119901(119905119890 | 1199050) under WeakLTE-U Interference When LTE-U interference is weak Sta-A keeps transmitting in the LTE-U ON stage wheneverpossible For some 1199050 consider an119898 dimension vectorw(119898) =(1199080 119908119898minus1) isin 0 CW0 minus 1 times sdot sdot sdot times 0 CW119898minus1 minus 1where 1 le 119898 le 119872 + 1 A vector w119898 with 1 le 119898 lt119872 + 1 fully determines a back-off pattern and also uniquelydetermines the transmission finish time 119905119890 When119898 = 119872+1depending on the last trial being successful or not the finishtime has two possibilities Hence the distribution 119901119879119890|1198790(119905119890 |1199050) can be derived by first getting the conditional distribution

119901W(119898)|1198790(w(119898) | 1199050) whereW(119898) is the corresponding randomvariable to w(119898)

The time of 119894th transmission attempt 120577119894 is also a functionof w that

120577119894 (w(119898)) = 1199050 + 119864 [119879119889] ( 119894sum119896=0

119908119896 + 119894119879119888)0 le 119894 le 119898 minus 1

(15)

and comparing 120577119894 with the values of 120572119879 119879 (1 + 120572)119879 2119879 itcould be figured out if the 119894th attempt falls within the LTE-UON period record the result by a bool function

119892 (120577119894)=

0 120572119879 le 120577119894 mod 119879 lt (120577119894 + 119879119904) mod 119879 lt 1198791 ow

(16)

and combining (11) and (16) we have

119901 (w(119898) | 1199050)= (119898minus2prod119894=0

1 minus (1 minus 119901119888) (1 minus 119902119892 [120577119894 (w(119898))])CW119894

)

sdot ((1 minus 119901119888) (1 minus 119902119892 [120577119898minus1 (w(119898))])CW119898minus1

) (17)

The end time 119879119890 is a function of random vectorW(119898) and119879119890(W(119898)) is the sum of the total waiting time and the timeof each transmission of back-off pattern W(119898) Let ℎ(W(119898))be a function of random variable W(119898) of the successfulretransmission probability of the119898th retrial

ℎ (W(119898)) = (1 minus 119901119888) (1 minus 119902119892 (120577119898minus1 (W(119898)))) (18)

According to the DCF the mapping 119891 (W(119898) 1199050) rarr 119879119890 is119891 (W(119898) 1199050)

=

1199050 + 119864 [119879119889] 120577119898minus1 + 119879119904 1 le 119898 lt 119872 + 11199050 + ℎ (W(119872)) 119864 [119879119889] (119872sum

119894=0

119882119894 +119872119879119888 + 119879119904) + (1 minus ℎ (W(119872))) 119864 [119879119889] (119872sum119894=0

119882119894 + (119872 + 1) 119879119888) 119898 = 119872 + 1(19)

Note in (19) to make 119891(W(119898) 1199050) a map we have to dealwith the map between (W(119872+1) 1199050) rarr 119879119890 so it has uniqueimage and we take the last retransmission duration to be itsexpectation The finish time 119879119890 has pmf

119901119879119890|1198790 (119905119890 | 1199050) = sumw119891(w)=119905119890

119901W|1198790 (w | 1199050) (20)

Knowing the distribution of 119879119890 the conditional mean 119864(119863 |1199050) can be written as

119864 [119863 | 1199050] = 119864 [119879119890 minus 1199050] (21)


For119864[119877 | 1199050] we need to find out the probability that a packettransmission started at 1199050 being dropped denoted as 119901dr(1199050)

119901dr (1199050) = sumw(119872+1)

119901W|1198790 (w(119872+1) | 1199050) [1 minus ℎ (w(119872+1))] (22)

and the conditional mean throughput can be written as

119864 [119877 | 1199050] = 119871 (1 minus 119901dr (1199050)) 119864 [ 1119863 | 1199050] (23)

32 The Conditional Probability 119901119879119890|1198790(119905119890 | 1199050) under StrongLTE-U Interference Under strong interference the Wi-Fiback-off timer will be blocked when LTE-U is on As will bedemonstrated later it effectively helps Wi-Fi to eliminate theLTE-U interference Not only does the LTE-U interferencecause the collision toWi-Fi but also the unit decrement time119879119889 atWi-Fi part will have a time variant pmfWhen LTE-U ison the Wi-Fi mean unit decrement time 119864[1198791015840119889] becomes 120572119879(when 120572119879 is chosen at a reasonable value eg 119879 ge 100) Asa result (15) and (19) which both reply on 119864[119879119889] no longerhold true Computation of 120577119894(w) and 119879119890 = 119891(W(119898) 1199050) needsiterative algorithm which is given below this algorithm hascomplexity 119874(1198992) Shortly speaking the counting processkeeps checking if 119879119890 mod 119879 lt 120572119879 in every iteration if it istrue then a constant (120572119879 minus 119878 mod 119879) is added to the partialsum of 119879119890

119879119890 = 1199050for 119894 = 0 119898 minus 1

for 119895 = 0 119908119894 minus 1if (119879119890 mod 119879 lt 120572119879)

119879119890 = 119879119890 + 120572119879 minus 119879119890 mod 119879else

119879119890 = 119879119890 + 119864[119879119889]end

end120577119894 = 119879119890if (119894 lt 119898 minus 1)

119879119890 = 119879119890 + 119879119888elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + 119879119904elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + (1 minus ℎ(w))119879119888 + ℎ(w)119879119904end

end

4 Fairness Evaluation Monte Carlo Analysis

It is computationally unpractical to characterize the distribu-tion of 119901119863(sdot | 1199050) as a function of 119901(W | 1199050) in closed formsince the sample space of randomvectorW(119872)119894 has cardinality

of prod119872minus1119894=0 CW119894 which is at the scale of 1011 However basedon the analytical discussion in the previous section it is easyto implement a Monte Carlo analysis for both the weak andstrong interference cases The essential idea of Monte Carloanalysis also named as Monte Carlo simulation is to userepeated random sampling to obtain numerical results andanalyze problems that might be deterministic in principleThe procedure in our evaluation is stepped as follows

(1) Let the first packet be generated at time 0 (slot time)and at the same time LTE-U starts its first duty cycle

(2) For each packet transmissionretransmission whichmay be affected by collision (either Wi-Fi to Wi-Fi or LTE-U to Wi-Fi or both) multiple trans-mission trials may occur during one transmis-sionretransmission and we uniformly generate asample vector w = 1199080 119908119872minus1 from its samplespace prod119872minus1119894=0 0 CW119894 minus 1 and then a Booleanvector 120598 = 1205980 120598119872minus1 indicating successfailurefor each trial whose distribution depends on (1)the value of w which determines if the 119894th Wi-Fi transmission trial 119894 isin 0 119872 minus 1 will beoverlapping with active LTE-U transmission (2) Wi-Fi to Wi-Fi collision probability 119901119888 (3) LTE-U to Wi-Fi collision probability 119902

(3) Based on the given w and 120598 we can deterministicallycompute the service time of the 119896th transmission andrecord it

(4) Let the next transmission start immediately (becausewe are evaluating saturate performance) and repeatsteps (2)-(3) until we derive enough numerical resultsfor analysis

(5) The average service time 119864[119863] as well as the through-put 119864[119877] can be approximated using recorded servicetime from each transmission

We refer to average throughput and average service timesimply as throughput and service time The impact of LTE-Uduty cycle is discussed in terms of the following parameters

(i) duty cycle period 119879(ii) the duty cycle 120572(iii) LTE-U to Wi-Fi collision probability 119902(iv) Wi-Fi payload length 119871

On the other hand the parameters below are fixed

(i) Wi-Fi system is saturated that is 120582 = 0(ii) RTSCTS is applied slot time120590 = 9 120583sWi-Fi physical

layer bit rate is 1Mbs for the random back-off 119872 =6 CW0 = 16 and other parameters are with respectto IEEE 80211n standard in the 5GHz band

(iii) The scenario contains 17 Wi-Fi client stationsaccording to [12] and we know the Wi-Fi to Wi-Ficollision probability 119901119888 = 03739


0

005

01

015

02

025

03

035

04

Weak interferenceStrong interference

200 300 400 500 600 700 800 900 1000100Duty cycle period T

120601R

(T 0

31

100

01

7)

120601R (T 03 1 1000 17)versus duty cycle period T

Wi-F

i thr

ough

put f

airn

ess

Wi-Fi throughput fairness

(a) Throughput fairness versus 119879

0

02

04

06

08

1

12

14

16

18



Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(T 0

31

100

01

7)

Wi-Fi service time fairness 120601D (T 03 1 1000 17)versus duty cycle period T

(b) Service time fairness versus 119879

Figure 3 Impact of duty cycle period 119879

005

01

015

02

025

03

Wi-F

i thr

ough

put f

airn

ess120601

R(5

00120572

1

100

01

7)

Wi-Fi throughput fairness 120601R (500 120572 1 1000 17)versus LTE-U duty cycle 120572


01 02 03 04 05 06 07 080LTE-U duty cycle 120572


minus1

0

1

2

3

4

5

6

7

120601D

(500

1205721

100

01

7)

120601D (500 120572 1 1000 17)versus LTE-U duty cycle 120572


01 02 03 04 05 06 07 080LTE-U duty cycle 120572

Wi-Fi service time fairness

Wi-F

i ser

vice

tim

e fai

rnes

s


Figure 4 Impact of duty cycle 120572

41The Role of Duty Cycle Period119879 Fixing the duty cycle 120572 =03 119902 = 1 and 119871 = 1KB Figure 3 shows the impact of dutycycle period119879 on throughput and service time for both weakand strong interference scenarios It can be observed that119879 le600ms (note one LTE-U frame duration is 10ms) will causesignificantWi-Fi performance degradation which is unfair toWi-Fi When 119879 is large enough the air time sharing tendsto cause less unfairness to Wi-Fi under strong interference

and more numerical results show (omitted due to the pagelimit) large119879 causing less unfairness under weak interferenceas well

42 The Role of Duty Cycle 120572 For 119879 = 500ms 119902 = 1 and119871 = 1KB the result is demonstrated in Figure 4 Whenthe interference is strong throughput loss ratio is almost 120572and is linear However if interference is weak but signifi-


minus04

minus03

minus02

minus01

0

01

02

03

02 04 06 08 10LTE-U to Wi-Fi collision probability q


Wi-Fi throughput fairness 120601R (500 03 q 1000 17)W

i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1

7) versus collision probability q


0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03

LTE-U to Wi-Fi collision probability q


Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)

Wi-Fi service time fairness 120601D (500 03 q 1000 17)versus collision probability q


Figure 5 The role of LTE-U to Wi-Fi collision probability 119902

cant (119902 = 1) there can be additional reduction on through-put When 120572 asymp 04 the air time sharing causes greatestthroughput unfairness When 120572 le 03 the delay seems tobe linear however when 120572 rarr 1 the service time increasesexponentially Recall the definition of fairness and it canbe inferred for in the given network setting a fair air timesharing scheme should have at least 120572 ≲ 03 Consideringthe throughput only strong interference approaches thethroughput fairness over almost any 120572 isin [0 1]43 LTE-U to Wi-Fi Collision Probability 119902 Fixing the dutycycle 119879 = 500ms and 120572 = 03 and 119871 = 1KB Figure 5 showshow the fairness varies with 119902 and it degrades almost linearlywith 119902 Particularly 119902 has less effect to fairness under stronginterference because interference over minus62 dbm will freezethe Wi-Fi back-up timer and the only possible LTE-U toWi-Fi collision occurrence is when an LTE-U transmission startsafter a Wi-Fi transmission

44 The Role of Wi-Fi Payload Length 119871 Fixing 119879 = 500ms119902 = 1 and 120572 = 03 Figure 6 illustrates the impact of datalength 119871 for both weak and strong interference and fairnessdegrades almost linearly with 11987145 Why Weak Interference Is Worse at 119902 = 1 In thestrong interference case Sta-A eliminates interference byfreezing the back-off timer and after LTE-U being off Sta-A could be immediately released from LTE-U interferenceso the total loss ratio of the performance is very close tothe duty cycle 120572 as can be seen in Figure 4 However wheninterference is weak Sta-A continues to contend the channeland it eliminates the interference by enlarging the contentionwindow size and increasing the number of attempts duringthe LTE-UON stage Once LTE-U switches off Sta-A will not

start transmitting until the current back-off timer is reset andin the worst case the recovery time could take as long as

26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)

119864[119879119889] in the above experiments is about 26ms In case 119879 isabout 100ms Sta-A would wait for 10 duty cycle periods longbefore sensing the channel again This effect is demonstratedclearly in Figures 3 and 4

From the information theory perspective when LTE-Uinterference is strong Wi-Fi has accurate and updated chan-nel state information (CSI) on whether LTE-U is on or offhenceWi-Fi could use this CSI to skip the interferenceWhenLTE-U interference is weak Wi-Fi has very delayed CSIsince the AP knows the interference only after detecting thefailure of a previous transmission which causes significantperformance degradation

5 Conclusion

In this paper we study the performance of an infrastructure-based Wi-Fi network when its operating channel in theunlicensed spectrum is air time shared with an LTE-Unetwork We define and characterize the Wi-Fi averageperformance and fairness in the presence of duty cycled LTE-U as functions of Wi-Fi subsystem parameters and the airtime sharing scheme being usedThroughMonte Carlo anal-ysis we numerically demonstrate the fairness under typicalcoexistence settings It can be observed from the results thatWi-Fi and LTE-U coexistence using simple air time sharingare generally unfair to Wi-Fi We conclude that some otherschemes (eg similar to the listen-before-talk mechanismused in 80211 networks) need to be developed for LTE-Unetworks in order to overcome the observed unfairness


500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045

Wi-Fi data payload length LWeak interferenceStrong interference

versus Wi-Fi data payload length L

120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess

120601R (500 03 1 L 17)Wi-Fi throughput fairness


500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18

Wi-Fi data payload length L


Wi-Fi service time fairness 120601D (500 03 1 L 17)

Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1

7) versus Wi-Fi data payload length L


Figure 6 Impact of Wi-Fi payload length 119871

Competing Interests

The authors declare that they have no competing interests

References

[1] ldquoExtending the benefits of LTE-A to unlicensed spectrumrdquoQualcommWhitepaper April 2014

[2] A M Cavalcante E Almeida R D Vieira et al ldquoPerformanceevaluation of LTE and Wi-Fi coexistence in unlicensed bandsrdquoin Proceedings of the IEEE 77th Vehicular Technology Conference(VTC rsquo13) pp 1ndash6 June 2013

[3] A Babaei J Andreoli-Fang and B Hamzeh ldquoOn the impactof LTE-U on Wi-Fi performancerdquo in Proceedings of the IEEEInternational Symposium on Personal Indoor and Mobile RadioCommunications (PIMRC rsquo14) Washington DC USA Septem-ber 2014

[4] U-LTE unlicensed spectrum utilization of LTE HuaweiWhitepaper 2014

[5] C Cano and D J Leith ldquoCoexistence of WiFi and LTE in unli-censed bands a proportional fair allocation schemerdquo in Pro-ceedings of the IEEE International Conference on Communica-tion Workshop (ICCW rsquo15) pp 2288ndash2293 June 2015

[6] ldquoLTE-U SDL Coexistence Specificationsrdquo LTE-U Forum[7] 3GPP TR 36889040 ldquoTechnical specification group radio

access network study on licensed-assisted access to unlicensedspectrum (Release 13)rdquo

[8] R Ratasuk NMangalvedhe and A Ghosh ldquoLTE in unlicensedspectrum using licensed-assisted accessrdquo in Proceedings of theIEEE GlobecomWorkshops (GCWkshps rsquo14) pp 746ndash751 IEEEAustin Tex USA December 2014

[9] A M Voicu L Simic and M Petrova ldquoCoexistence of pico-and femto-cellular LTE-unlicensed with legacy indoor Wi-Fi

deploymentsrdquo in Proceedings of the IEEE International Confer-ence on Communication Workshop (ICCW rsquo15) pp 2294ndash2300IEEE London UK June 2015

[10] R Kwan R Pazhyannur J Seymour et al ldquoFair co-existence ofLicensed Assisted Access LTE (LAA-LTE) and Wi-Fi in unli-censed spectrumrdquo in Proceedings of the 7th Computer Scienceand Electronic Engineering (CEEC rsquo15) pp 13ndash18 ColchesterUK September 2015

[11] G Bianchi ldquoPerformance analysis of the IEEE 80211 distributedcoordination functionrdquo IEEE Journal on Selected Areas inCommunications vol 18 no 3 pp 535ndash547 2000

[12] H Zhai Y Kwon and Y Fang ldquoPerformance analysis of IEEE80211 MAC protocols in wireless LANsrdquoWireless Communica-tions and Mobile Computing vol 4 no 8 pp 917ndash931 2004

[13] A Banchs P Serrano and A Azcorra ldquoEnd-to-end delay anal-ysis and admission control in 80211 DCF WLANsrdquo ComputerCommunications vol 29 no 7 pp 842ndash854 2006

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpswwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



Duty cycle period

LTE offLTE on LTE on

Duty cycleTime

Wi-Fi access gapswhen LTE is off of cycle LTE is active

Figure 1 Air time sharing LTE-U

this approach LTE-U operates over the shared channelperiodically (more specifically the radio resources of LTE-Uthat reside in the unlicensed spectrum and are shared withWi-Fi are utilized periodically) and during each period (theso-called duty cycle period denoted as 119879) only a portion(defined by the LTE-U duty cycle 120572) of the time is utilized forthe LTE-U transmission as shown in Figure 1 In this schemeWi-Fi has no cooperation with LTE-U Wi-Fi stations haveneither knowledge about the time length of duty cycle periodnor the duty cycle they simply access the shared channel bystandard channel sensing and random back-off mechanisms

In an LTE system each user equipment (UE) commu-nicates with a base station (eNB) in a deterministic mannerthrough a centralized channel access controlmechanismTheaccess time and OFDM subcarriers of an LTE frame arepredetermined at eNB where the MAC scheduler considersthe radio measurement and quality of service needed foreach UE in its scheduling decisions Given the above timesharing scheme and the LTErsquos centralized access structurecomputation of the LTE-U performance in terms of through-put and service time is relatively simple and straightforwardHowever themedium accessmechanism used byWi-Fi con-trolled by distributed coordination function (DCF) protocoldefined in IEEE 80211 standard is random and distributedTherefore we focus on the impact of LTE-U interference onWi-Fi performance in this paper

11 Previous Works LTE-U and Wi-Fi coexistence are arelatively new area of research Previous works in thisarea are summarized as follows in [2] Wi-Fi and LTE-Ucoexistence in single floor and multiple floors environmentat various densities are simulated The results show thatwithout any interferencemanagement scheme LTE-U systemperformance is slightly affected from Wi-Fi whereas Wi-Fiis significantly impacted by the LTE-U transmissions Thisresult is reinforced in [3] by computing the Wi-Fi successfulchannel accessing probability in the presence of LTE-Utransmission However in [1] LTE-U is described as a betterneighbor to Wi-Fi than Wi-Fi to itself as long as a propercoexistence mechanism (called CSAT) is applied Authors in[4] present simulation results on spectrum efficiency com-parison between Wi-Fi and LTE-U in a sparse deploymentscenario The paper however lacks sufficient details on thecoexistence features and their effectiveness Cano and Leith[5] proposed a duty cycle mechanism for LTE-U which byselecting an appropriate probability to access the channeland transmission duration ensures proportional fairnessamong LTE-U and Wi-Fi nodes Specifications regardingduty cycled based LTE-U are released and maintained by

LTE-U forum [6] where CSAT is officially introduced as theaccess mechanism

On the other hand the 3GPP study item technicalreport document [7] has listed listen-before-talk (LBT) as therequired function for clear channel assessment for LTE LAAThe application of LBT may potentially enhance the coexist-ence behavior of Wi-Fi and LTE Some analysis and perfor-mance test have been reported in [8ndash10]

12 Main Results In this paper we define Wi-Fi averagesaturation throughputR(119879 120572H) (in terms of bitsWi-Fi slottime) and average service timeD(119879 120572H) (in terms ofWi-Fitime slots) to be functions of 119879 120572 and H = 119902 119871 119899 wherethe set H = 119902 119871 119899 represents 119899-clients Wi-Fi subsystemwith LTE-U to Wi-Fi collision probability (Wi-Fi transmis-sion failure probability due to LTE-U transmission) 119902 andWi-Fi data payload length 119871 (the length of MAC data payloadin terms of bytes) Given H the throughput fairness (cfDefinition 2) of (119879 120572) air time sharing scheme is measured bythe difference between average Wi-Fi saturation throughputloss ratio (with respect to the corresponding non-LTE-Udutycycle scenario (infin 0H) performance) and LTE-U duty cycle120572 that is (R(infin 0H) minus R(119879 120572H))R(infin 0H) minus 120572 Ina similar way the average service time fairness is defined as(D(119879 120572H) minus D(infin 0H))D(infin 0H) minus 120572(1 minus 120572) Thesetwo fairness measures indicate whether Wi-Fi will lose lessor more than 120572 portion of its performance (in the absence ofLTE-U transmission) if 120572 portion of the channel resource isshared with LTE-U

Our first step is to analytically formulateR(119879 120572H) andD(119879 120572H) using a probabilistic framework The followingtwo key techniques are employed

121 Only One Labeled Client Station among the 119899 Wi-Fi Stations Being Affected by LTE-U Interference As firstintroduced by [11] Wi-Fi DCF can be formulated into aMarkov chain model which was generalized later in [12 13]But when LTE-U is considered the Markov property nolonger holds because of the fact that when LTE-U is offthe Wi-Fi transmission failure probability is only Wi-Fi toWi-Fi collision probability when LTE-U is on the Wi-Fitransmission failure probability depends on both Wi-Fi toWi-Fi and LTE-U to Wi-Fi collision probability For thisissue we make an assumption that only one client stationamong the 119899 stations labeled as Sta-A is affected by theLTE-U interference The other 119899 minus 1 stations render theWi-Fi background traffic for the labeled station When 119899 ischosen to be large enough the background traffic could stillbe approximately modeled using the existing framework in[11ndash13] Under this assumption functions R(119879 120572H) andD(119879 120572H) are with respect to Sta-A

122 Different Interference Levels Lead to Different Formu-lations The Wi-Fi DCF employs CSMACA with binaryexponential back-off algorithm Depending on the energylevel being detected the back-off timer may or may not befrozen In short an LTE-U transmission with interferenceto noise ratio (INR) greater than minus62 dbm or a neighborWi-Fi station transmission with INR greater than minus82 dbm













1 119894119899+1 = 119894119899 119895119899+1 = 119895119899 minus 1119895119899 = 0


1199011198941198992119894119899+1CW0 119894119899+1 = 119894119899 + 1 119894119899+1 = 119872 minus 1119895119899+1 isin 0 2119894119899+1CW0 119895119899 = 0

1 119894119899+1 = 0 119894119899 = 119872 minus 1119895119899+1 isin 0 CW0 119895119899 = 0

(1)








1 1

1 1

11 1 1

1

1

111

0 0 0 1 0 2

1 0 1 1 1 2

1 minus P0

1 minus P1

1W0

0W0 minus 1

0W1 minus 1

P0W1

1 minus PMminus1


M 0 M 1 M 2

PMminus2WMminus1

PMminus1WM


MWM minus 1










120591 = 119872minus1sum119894=0

(1 minus 119901119888) 119901 (119894 0) + (1 minus 119901119888) 119901 (119872 0) (3)




+ DIFS119879119888 = RTS + DIFS

(4)

otherwise






119901119879119889 (119905119889) =

1 minus 119901119888 119905119889 = 1119901119888 minus 119901119904 119905119889 = 119879119888119901119904 119905119889 = 1198791199040 ow

(7)







R (119879 120572H) = 119864 [119877 (119879 120572H)] D (119879 120572H) = 119864 [119863 (119879 120572H)] (8)



















119901119879119890|1198790 (119905119890 | 1199050) (13)


1199011198791015840119890 |1198790 (1199051015840119890 | 1199050) (14)






120577119894 (w(119898)) = 1199050 + 119864 [119879119889] ( 119894sum119896=0

119908119896 + 119894119879119888)0 le 119894 le 119898 minus 1

(15)


119892 (120577119894)=

0 120572119879 le 120577119894 mod 119879 lt (120577119894 + 119879119904) mod 119879 lt 1198791 ow

(16)


119901 (w(119898) | 1199050)= (119898minus2prod119894=0


)


) (17)




=

1199050 + 119864 [119879119889] 120577119898minus1 + 119879119904 1 le 119898 lt 119872 + 11199050 + ℎ (W(119872)) 119864 [119879119889] (119872sum

119894=0

119882119894 +119872119879119888 + 119879119904) + (1 minus ℎ (W(119872))) 119864 [119879119889] (119872sum119894=0

119882119894 + (119872 + 1) 119879119888) 119898 = 119872 + 1(19)


119901119879119890|1198790 (119905119890 | 1199050) = sumw119891(w)=119905119890

119901W|1198790 (w | 1199050) (20)


119864 [119863 | 1199050] = 119864 [119879119890 minus 1199050] (21)



119901dr (1199050) = sumw(119872+1)

119901W|1198790 (w(119872+1) | 1199050) [1 minus ℎ (w(119872+1))] (22)


119864 [119877 | 1199050] = 119871 (1 minus 119901dr (1199050)) 119864 [ 1119863 | 1199050] (23)


119879119890 = 1199050for 119894 = 0 119898 minus 1


119879119890 = 119879119890 + 120572119879 minus 119879119890 mod 119879else

119879119890 = 119879119890 + 119864[119879119889]end

end120577119894 = 119879119890if (119894 lt 119898 minus 1)

119879119890 = 119879119890 + 119879119888elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + 119879119904elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + (1 minus ℎ(w))119879119888 + ℎ(w)119879119904end

end
















0

005

01

015

02

025

03

035

04



120601R

(T 0

31

100

01

7)


Wi-F

i thr

ough

put f

airn

ess



0

02

04

06

08

1

12

14

16

18



Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(T 0

31

100

01

7)




005

01

015

02

025

03

Wi-F

i thr

ough

put f

airn

ess120601

R(5

00120572

1

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


minus1

0

1

2

3

4

5

6

7

120601D

(500

1205721

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


Wi-F

i ser

vice

tim

e fai

rnes

s







minus04

minus03

minus02

minus01

0

01

02

03




i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1



0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03



Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)







26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)



5 Conclusion



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation





















1 119894119899+1 = 119894119899 119895119899+1 = 119895119899 minus 1119895119899 = 0


1199011198941198992119894119899+1CW0 119894119899+1 = 119894119899 + 1 119894119899+1 = 119872 minus 1119895119899+1 isin 0 2119894119899+1CW0 119895119899 = 0

1 119894119899+1 = 0 119894119899 = 119872 minus 1119895119899+1 isin 0 CW0 119895119899 = 0

(1)








1 1

1 1

11 1 1

1

1

111

0 0 0 1 0 2

1 0 1 1 1 2

1 minus P0

1 minus P1

1W0

0W0 minus 1

0W1 minus 1

P0W1

1 minus PMminus1


M 0 M 1 M 2

PMminus2WMminus1

PMminus1WM


MWM minus 1










120591 = 119872minus1sum119894=0

(1 minus 119901119888) 119901 (119894 0) + (1 minus 119901119888) 119901 (119872 0) (3)




+ DIFS119879119888 = RTS + DIFS

(4)

otherwise






119901119879119889 (119905119889) =

1 minus 119901119888 119905119889 = 1119901119888 minus 119901119904 119905119889 = 119879119888119901119904 119905119889 = 1198791199040 ow

(7)







R (119879 120572H) = 119864 [119877 (119879 120572H)] D (119879 120572H) = 119864 [119863 (119879 120572H)] (8)



















119901119879119890|1198790 (119905119890 | 1199050) (13)


1199011198791015840119890 |1198790 (1199051015840119890 | 1199050) (14)






120577119894 (w(119898)) = 1199050 + 119864 [119879119889] ( 119894sum119896=0

119908119896 + 119894119879119888)0 le 119894 le 119898 minus 1

(15)


119892 (120577119894)=

0 120572119879 le 120577119894 mod 119879 lt (120577119894 + 119879119904) mod 119879 lt 1198791 ow

(16)


119901 (w(119898) | 1199050)= (119898minus2prod119894=0


)


) (17)




=

1199050 + 119864 [119879119889] 120577119898minus1 + 119879119904 1 le 119898 lt 119872 + 11199050 + ℎ (W(119872)) 119864 [119879119889] (119872sum

119894=0

119882119894 +119872119879119888 + 119879119904) + (1 minus ℎ (W(119872))) 119864 [119879119889] (119872sum119894=0

119882119894 + (119872 + 1) 119879119888) 119898 = 119872 + 1(19)


119901119879119890|1198790 (119905119890 | 1199050) = sumw119891(w)=119905119890

119901W|1198790 (w | 1199050) (20)


119864 [119863 | 1199050] = 119864 [119879119890 minus 1199050] (21)



119901dr (1199050) = sumw(119872+1)

119901W|1198790 (w(119872+1) | 1199050) [1 minus ℎ (w(119872+1))] (22)


119864 [119877 | 1199050] = 119871 (1 minus 119901dr (1199050)) 119864 [ 1119863 | 1199050] (23)


119879119890 = 1199050for 119894 = 0 119898 minus 1


119879119890 = 119879119890 + 120572119879 minus 119879119890 mod 119879else

119879119890 = 119879119890 + 119864[119879119889]end

end120577119894 = 119879119890if (119894 lt 119898 minus 1)

119879119890 = 119879119890 + 119879119888elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + 119879119904elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + (1 minus ℎ(w))119879119888 + ℎ(w)119879119904end

end
















0

005

01

015

02

025

03

035

04



120601R

(T 0

31

100

01

7)


Wi-F

i thr

ough

put f

airn

ess



0

02

04

06

08

1

12

14

16

18



Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(T 0

31

100

01

7)




005

01

015

02

025

03

Wi-F

i thr

ough

put f

airn

ess120601

R(5

00120572

1

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


minus1

0

1

2

3

4

5

6

7

120601D

(500

1205721

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


Wi-F

i ser

vice

tim

e fai

rnes

s







minus04

minus03

minus02

minus01

0

01

02

03




i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1



0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03



Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)







26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)



5 Conclusion



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










1 1

1 1

11 1 1

1

1

111

0 0 0 1 0 2

1 0 1 1 1 2

1 minus P0

1 minus P1

1W0

0W0 minus 1

0W1 minus 1

P0W1

1 minus PMminus1


M 0 M 1 M 2

PMminus2WMminus1

PMminus1WM


MWM minus 1










120591 = 119872minus1sum119894=0

(1 minus 119901119888) 119901 (119894 0) + (1 minus 119901119888) 119901 (119872 0) (3)




+ DIFS119879119888 = RTS + DIFS

(4)

otherwise






119901119879119889 (119905119889) =

1 minus 119901119888 119905119889 = 1119901119888 minus 119901119904 119905119889 = 119879119888119901119904 119905119889 = 1198791199040 ow

(7)







R (119879 120572H) = 119864 [119877 (119879 120572H)] D (119879 120572H) = 119864 [119863 (119879 120572H)] (8)



















119901119879119890|1198790 (119905119890 | 1199050) (13)


1199011198791015840119890 |1198790 (1199051015840119890 | 1199050) (14)






120577119894 (w(119898)) = 1199050 + 119864 [119879119889] ( 119894sum119896=0

119908119896 + 119894119879119888)0 le 119894 le 119898 minus 1

(15)


119892 (120577119894)=

0 120572119879 le 120577119894 mod 119879 lt (120577119894 + 119879119904) mod 119879 lt 1198791 ow

(16)


119901 (w(119898) | 1199050)= (119898minus2prod119894=0


)


) (17)




=

1199050 + 119864 [119879119889] 120577119898minus1 + 119879119904 1 le 119898 lt 119872 + 11199050 + ℎ (W(119872)) 119864 [119879119889] (119872sum

119894=0

119882119894 +119872119879119888 + 119879119904) + (1 minus ℎ (W(119872))) 119864 [119879119889] (119872sum119894=0

119882119894 + (119872 + 1) 119879119888) 119898 = 119872 + 1(19)


119901119879119890|1198790 (119905119890 | 1199050) = sumw119891(w)=119905119890

119901W|1198790 (w | 1199050) (20)


119864 [119863 | 1199050] = 119864 [119879119890 minus 1199050] (21)



119901dr (1199050) = sumw(119872+1)

119901W|1198790 (w(119872+1) | 1199050) [1 minus ℎ (w(119872+1))] (22)


119864 [119877 | 1199050] = 119871 (1 minus 119901dr (1199050)) 119864 [ 1119863 | 1199050] (23)


119879119890 = 1199050for 119894 = 0 119898 minus 1


119879119890 = 119879119890 + 120572119879 minus 119879119890 mod 119879else

119879119890 = 119879119890 + 119864[119879119889]end

end120577119894 = 119879119890if (119894 lt 119898 minus 1)

119879119890 = 119879119890 + 119879119888elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + 119879119904elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + (1 minus ℎ(w))119879119888 + ℎ(w)119879119904end

end
















0

005

01

015

02

025

03

035

04



120601R

(T 0

31

100

01

7)


Wi-F

i thr

ough

put f

airn

ess



0

02

04

06

08

1

12

14

16

18



Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(T 0

31

100

01

7)




005

01

015

02

025

03

Wi-F

i thr

ough

put f

airn

ess120601

R(5

00120572

1

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


minus1

0

1

2

3

4

5

6

7

120601D

(500

1205721

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


Wi-F

i ser

vice

tim

e fai

rnes

s







minus04

minus03

minus02

minus01

0

01

02

03




i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1



0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03



Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)







26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)



5 Conclusion



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













R (119879 120572H) = 119864 [119877 (119879 120572H)] D (119879 120572H) = 119864 [119863 (119879 120572H)] (8)



















119901119879119890|1198790 (119905119890 | 1199050) (13)


1199011198791015840119890 |1198790 (1199051015840119890 | 1199050) (14)






120577119894 (w(119898)) = 1199050 + 119864 [119879119889] ( 119894sum119896=0

119908119896 + 119894119879119888)0 le 119894 le 119898 minus 1

(15)


119892 (120577119894)=

0 120572119879 le 120577119894 mod 119879 lt (120577119894 + 119879119904) mod 119879 lt 1198791 ow

(16)


119901 (w(119898) | 1199050)= (119898minus2prod119894=0


)


) (17)




=

1199050 + 119864 [119879119889] 120577119898minus1 + 119879119904 1 le 119898 lt 119872 + 11199050 + ℎ (W(119872)) 119864 [119879119889] (119872sum

119894=0

119882119894 +119872119879119888 + 119879119904) + (1 minus ℎ (W(119872))) 119864 [119879119889] (119872sum119894=0

119882119894 + (119872 + 1) 119879119888) 119898 = 119872 + 1(19)


119901119879119890|1198790 (119905119890 | 1199050) = sumw119891(w)=119905119890

119901W|1198790 (w | 1199050) (20)


119864 [119863 | 1199050] = 119864 [119879119890 minus 1199050] (21)



119901dr (1199050) = sumw(119872+1)

119901W|1198790 (w(119872+1) | 1199050) [1 minus ℎ (w(119872+1))] (22)


119864 [119877 | 1199050] = 119871 (1 minus 119901dr (1199050)) 119864 [ 1119863 | 1199050] (23)


119879119890 = 1199050for 119894 = 0 119898 minus 1


119879119890 = 119879119890 + 120572119879 minus 119879119890 mod 119879else

119879119890 = 119879119890 + 119864[119879119889]end

end120577119894 = 119879119890if (119894 lt 119898 minus 1)

119879119890 = 119879119890 + 119879119888elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + 119879119904elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + (1 minus ℎ(w))119879119888 + ℎ(w)119879119904end

end
















0

005

01

015

02

025

03

035

04



120601R

(T 0

31

100

01

7)


Wi-F

i thr

ough

put f

airn

ess



0

02

04

06

08

1

12

14

16

18



Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(T 0

31

100

01

7)




005

01

015

02

025

03

Wi-F

i thr

ough

put f

airn

ess120601

R(5

00120572

1

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


minus1

0

1

2

3

4

5

6

7

120601D

(500

1205721

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


Wi-F

i ser

vice

tim

e fai

rnes

s







minus04

minus03

minus02

minus01

0

01

02

03




i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1



0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03



Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)







26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)



5 Conclusion



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













119901119879119890|1198790 (119905119890 | 1199050) (13)


1199011198791015840119890 |1198790 (1199051015840119890 | 1199050) (14)






120577119894 (w(119898)) = 1199050 + 119864 [119879119889] ( 119894sum119896=0

119908119896 + 119894119879119888)0 le 119894 le 119898 minus 1

(15)


119892 (120577119894)=

0 120572119879 le 120577119894 mod 119879 lt (120577119894 + 119879119904) mod 119879 lt 1198791 ow

(16)


119901 (w(119898) | 1199050)= (119898minus2prod119894=0


)


) (17)




=

1199050 + 119864 [119879119889] 120577119898minus1 + 119879119904 1 le 119898 lt 119872 + 11199050 + ℎ (W(119872)) 119864 [119879119889] (119872sum

119894=0

119882119894 +119872119879119888 + 119879119904) + (1 minus ℎ (W(119872))) 119864 [119879119889] (119872sum119894=0

119882119894 + (119872 + 1) 119879119888) 119898 = 119872 + 1(19)


119901119879119890|1198790 (119905119890 | 1199050) = sumw119891(w)=119905119890

119901W|1198790 (w | 1199050) (20)


119864 [119863 | 1199050] = 119864 [119879119890 minus 1199050] (21)



119901dr (1199050) = sumw(119872+1)

119901W|1198790 (w(119872+1) | 1199050) [1 minus ℎ (w(119872+1))] (22)


119864 [119877 | 1199050] = 119871 (1 minus 119901dr (1199050)) 119864 [ 1119863 | 1199050] (23)


119879119890 = 1199050for 119894 = 0 119898 minus 1


119879119890 = 119879119890 + 120572119879 minus 119879119890 mod 119879else

119879119890 = 119879119890 + 119864[119879119889]end

end120577119894 = 119879119890if (119894 lt 119898 minus 1)

119879119890 = 119879119890 + 119879119888elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + 119879119904elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + (1 minus ℎ(w))119879119888 + ℎ(w)119879119904end

end
















0

005

01

015

02

025

03

035

04



120601R

(T 0

31

100

01

7)


Wi-F

i thr

ough

put f

airn

ess



0

02

04

06

08

1

12

14

16

18



Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(T 0

31

100

01

7)




005

01

015

02

025

03

Wi-F

i thr

ough

put f

airn

ess120601

R(5

00120572

1

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


minus1

0

1

2

3

4

5

6

7

120601D

(500

1205721

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


Wi-F

i ser

vice

tim

e fai

rnes

s







minus04

minus03

minus02

minus01

0

01

02

03




i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1



0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03



Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)







26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)



5 Conclusion



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











119901dr (1199050) = sumw(119872+1)

119901W|1198790 (w(119872+1) | 1199050) [1 minus ℎ (w(119872+1))] (22)


119864 [119877 | 1199050] = 119871 (1 minus 119901dr (1199050)) 119864 [ 1119863 | 1199050] (23)


119879119890 = 1199050for 119894 = 0 119898 minus 1


119879119890 = 119879119890 + 120572119879 minus 119879119890 mod 119879else

119879119890 = 119879119890 + 119864[119879119889]end

end120577119894 = 119879119890if (119894 lt 119898 minus 1)

119879119890 = 119879119890 + 119879119888elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + 119879119904elseif (119898 = 119872 + 1)

119879119890 = 119879119890 + (1 minus ℎ(w))119879119888 + ℎ(w)119879119904end

end
















0

005

01

015

02

025

03

035

04



120601R

(T 0

31

100

01

7)


Wi-F

i thr

ough

put f

airn

ess



0

02

04

06

08

1

12

14

16

18



Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(T 0

31

100

01

7)




005

01

015

02

025

03

Wi-F

i thr

ough

put f

airn

ess120601

R(5

00120572

1

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


minus1

0

1

2

3

4

5

6

7

120601D

(500

1205721

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


Wi-F

i ser

vice

tim

e fai

rnes

s







minus04

minus03

minus02

minus01

0

01

02

03




i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1



0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03



Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)







26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)



5 Conclusion



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0

005

01

015

02

025

03

035

04



120601R

(T 0

31

100

01

7)


Wi-F

i thr

ough

put f

airn

ess



0

02

04

06

08

1

12

14

16

18



Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(T 0

31

100

01

7)




005

01

015

02

025

03

Wi-F

i thr

ough

put f

airn

ess120601

R(5

00120572

1

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


minus1

0

1

2

3

4

5

6

7

120601D

(500

1205721

100

01

7)



01 02 03 04 05 06 07 080LTE-U duty cycle 120572


Wi-F

i ser

vice

tim

e fai

rnes

s







minus04

minus03

minus02

minus01

0

01

02

03




i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1



0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03



Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)







26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)



5 Conclusion



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










minus04

minus03

minus02

minus01

0

01

02

03




i-Fi t

hrou

ghpu

t fai

rnes

s120601R

(500

03

q

100

0 1



0 02 04 06 08 1minus04

minus03

minus02

minus01

0

01

02

03



Wi-F

i ser

vice

tim

e fai

rnes

s 120601D

(500

03

q

100

0 1

7)







26CW0119864 [119879119889] asymp 1024119864 [119879119889] (24)



5 Conclusion



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










500 1000 1500 2000 2500 3000 3500 4000 4500 50000

005

01

015

02

025

03

035

04

045



120601R

(500

03

1

L 1

7)

Wi-F

i thr

ough

put f

airn

ess



500 1000 1500 2000 2500 3000 3500 4000 4500 50000

02

04

06

08

1

12

14

16

18




Wi-F

i ser

vice

tim

e fai

rnes

s120601D

(500

03

1

L 1




Competing Interests


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Documents

ResearchArticle Wi-Fi Coexistence with Duty Cycled LTE-Udownloads.hindawi.com/journals/wcmc/2017/6486380.pdf · Wi-Fi Coexistence with Duty Cycled LTE-U YiminPang, 1 AlirezaBabaei,