M2M Massive Access in LTE: RACH Performance Evaluation in a Smart City Scenario

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by  Michele Polese

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M. Polese, M. Centenaro, A. Zanella, and M. Zorzi, M2M Massive Access in LTE:
RACH Performance Evaluation in a Smart City Scenario, 2016 IEEE International Conference
on Communications (ICC), Kuala Lumpur, 2016, pp. 1-6.
BibTex:
@INPROCEEDINGS{7511430,
author={M. Polese and M. Centenaro and A. Zanella and M. Zorzi},
booktitle={2016 IEEE International Conference on Communications (ICC)},
title={M2M massive access in LTE: RACH performance evaluation in a Smart City scenario},
6 year={2016},
1
pages={1-6},
0
keywords={Long Term Evolution;multi-access systems;public domain software;
2
smart cities;Internet of Things;LTE Random Access Channel;
t
c LTE cellular standard;LTE module;LTE random access procedure;
O Long Term Evolution cellular standard;M2M massive access;RACH;
Smart City scenario;mobile terminals;open-source network simulators;
5
system-level simulators;Delays;Indexes;Internet of things;

] Long Term Evolution;Signal to noise ratio;Smart cities;Uplink},
I
doi={10.1109/ICC.2016.7511430},
N
month={May},}
.
s
c
[

4
v
8
9
0
5
0
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a
ThispaperwasacceptedforpresentationattheIEEEICC2016
conference,May23-27,2016,KualaLumpur,Malaysia.
M2M Massive Access in LTE: RACH Performance
Evaluation in a Smart City Scenario
Michele Polese, Marco Centenaro, Andrea Zanella, and Michele Zorzi
Department of Information Engineering, University of Padova – Via Gradenigo, 6/b, 35131 Padova, Italy
Email: {polesemi,marco.centenaro,zanella,zorzi}@dei.unipd.it
Abstract—Several studies assert that the random access proce- to study the impact of M2M traffic in LTE networks in
dure of the Long Term Evolution (LTE) cellular standard may urban scenarios. Simulation results show that if a few hundred
not be effective whenever a massive number of simultaneous
smart sensors simultaneously require network access, e.g., to
connectionattemptsareperformedbyterminals,asmayhappenin
report some kind of failure event, an MTD would experience
atypicalInternetofThingsorSmartCityscenario.Nevertheless,
simulation studies in real deployment scenarios are missing extremely long delays to complete the access procedure, thus
because many system-level simulators do not implement the LTE not respecting the delay constraints of important Smart City
random access procedure in detail. In this paper, we propose a applications, such as alarms.
patch for the LTE module of ns–3, one of the most prominent
Theremainderofthepaperisorganizedasfollows.InSec.II,
open-source network simulators, to improve the accuracy of
the random access procedure in LTE is described and issues
the routine that simulates the LTE Random Access Channel
(RACH). The patched version of the random access procedure related to massive access are briefly explained. In Sec. III the
is compared with the default one and the issues arising from implementation of LTE Random Access Channel (RACH) in
massive simultaneous access from mobile terminals in LTE are ns–3 is discussed and its weaknesses are highlighted; then, a
assessed via a simulation campaign.
patchtothedefaultroutineisproposedtoenhancetheaccuracy
of the simulator. In Sec. IV the patched routine is compared
with the default one and is used to evaluate the impact of a
I. INTRODUCTION
massive number of simultaneous access attempts in a realistic
Ahugeincreaseinfullyautomatedcommunicationsbetween SmartCitiesscenario.Finally,conclusionsaredrawninSec.V.
devices is forecasted in the next few years as new use cases,
II. THERANDOMACCESSPROCEDUREINLTE
e.g., connected cars, e-health, environmental monitoring, are
being identified. This new paradigm is called Machine-to- The RA procedure in LTE is initiated when (i) a User
Machine(M2M)communication,sinceitistypicallyperformed Equipment (UE) is in the RRC_CONNECTED state1 and has
withoutanyhumanintervention,andisconsideredafundamen- new data to transmit or receive but no uplink synchronization;
tal enabler of the Internet of Things (IoT) vision. (ii) it recovers after radio link failure; (iii) it switches from
AdesirablerequirementforthedeploymentofMachine-Type RRC_IDLE to RRC_CONNECTED, or, finally, (iv) it performs
Devices (MTDs) is the place & play concept [1], i.e., MTDs a handover. The procedure takes place in a dedicated physical
should just need to be deployed in a certain area to be ready channelcalledPhysicalRandomAccessChannel(PRACH)[6],
to operate. Indeed, the expected number of devices (40 MTDs which is multiplexed in time and frequency with the Physical
per household according to [2]) makes a manual configuration Uplink Shared Channel (PUSCH). The PRACH consists of 6
infeasible. For this reason, the cellular network infrastructure Resource Blocks (RBs) for an overall bandwidth of 1.08 MHz
is suitable to provide connectivity for M2M communications, and has a duration between 1 and 4 subframes. Its periodicity
sinceitcanprovision(ideally)worldwide,ubiquitouscoverage, is variable and is defined by the PRACH Configuration Index,
in contrast to many ad hoc proprietary technologies. However, which is broadcast by the base station (eNodeB, eNB) on
deploying such a huge number of devices in current cellular the System Information Broadcast 2 (SIB2) along with the
networks, e.g., the Long Term Evolution (LTE), poses new following signaling information:
issues that need to be addressed. In particular, an important • numContentionPreambles, i.e., the number of
problem is the overload of the LTE Random Access (RA) preamblesreservedforcontention-basedRA(atmost64);
procedureunderamassivenumberofsimultaneousconnection • preambleInitialReceivedTargetPower, i.e.,
attempts, since the LTE standard has been designed to provide the target power (in dBm) to be reached at the eNB for
high-rate access to a fairly limited number of terminals. transmissions on PRACH;
In this paper, we aim at evaluating the delay that a device • powerRampingStep,i.e.,thepowerrampingstepused
may undergo while accessing an LTE network in the case of to increase the transmission power after every failed
a massive number of access requests in a real deployment. attempt;
In particular, we address a Smart City scenario using one of • preambleTransMax, i.e., the maximum number of
themostaccurateopen-sourcesystem-levelnetworksimulators, preamble transmission attempts.
i.e., network simulator 3 (ns–3, [3]). We found that the current
1A UE is in the RRC_CONNECTED state when a Radio Resource Control
implementation of the RA procedure in ns–3 is idealized;
(RRC)connectionhasbeenestablished;ifthisisnotthecase,theUEisinthe
therefore, we developed a patch to make the routine suitable RRC_IDLEstate[4,Sec.4.2.1].
532 F.J.López-Martínezetal./DigitalSignalProcessing22(2012)526–534
Table3
PRACHmisseddetectionrequirementsfornormalmode.
Numberof Propagation Burst0 Burst1 Burst2 Burst3
RXantennas conditions(FO)
2 AETWUG7N0((207H0zH)z) −148.2dBdB −147..82ddBB −1160..04ddBB −1106..15ddBB
− − − −
4 AETWUG7N0((207H0zH)z) −1162..91ddBB −1161..77ddBB −1194..01ddBB −1183..89ddBB
− − − −
Werecallthatthepreambleisasignaturecomposedofacyclic
prefix and a Zadoff-Chu (ZC) sequence that is obtained by
shifting a root sequence, which is common to all the UEs
connected to a certain eNB. Preambles containing different
sequencesareorthogonaltooneanother.2 Thereare4different
preambleformats,withdurationfrom1to4subframes,inorder
to guarantee coverage of different cell sizes.
The RA procedure consists of 4 messages as follows.
a) Preamble Transmission: The UE selects a random ZC
sequence and transmits a preamble on one of the resources
specified by the PRACH Configuration Index. The eNB will Figure 1: PFmig.i8s.sMDvPsvsSSNRN.2RanteΓnn,as,tAaWkGeN.n from [14].
detectthesequencebyapplyingacorrelatorandapeakdetector
to the received signal [6]. However, since the number of ZC
sequences is finite, it may happen that more than one UE repeats the RA procedure from the beginning after a random
select the same sequence, thus incurring in a collision. If the backofftime.Again,whenthenumberofunsuccessfulattempts
colliding UE preambles are received with high enough Signal- reachessomespecifiedmaximumvalue,thenetworkisdeclared
to-NoiseRatio(SNR),andaresufficientlyspacedapartintime, unavailable by the UE and an access problem exception is
two energy peaks separated by a time that is longer than the raised to the upper layers.
Maximum Delay Spread (MDS) are detected and the eNB will
interpret this event as due to a collision. On the other hand, if A. Massive Random Access
onlyoneofthecollidingpreamblesisreceivedwithhighSNR, The LTE RA process is efficient when a small number of
orthedelayofthedifferentpreamblesissimilar,3 theeNBwill devices require access to the network, which is the typical
not be able to recognize the collision. case for Human-to-HFigu.9m.MaDPnvs(SNHR.24Hant)enntars,aAWffiGNc.. However, the num-
We remark that MDS and the preamble detection algorithm ber of terminals is envisioned to grow exponentially in IoT
are not standardized but left to the eNB vendor. However, the scenarios, especially for what concerns Smart Cities where
3GPP report [11] requires a missed detection probability lower smart meters will be deployed to monitor a large variety of
than 10−2 for an SNR value of −14.2 dB and a 2-antenna parameters, from air pollution to supply levels. In the case of
receiver in AWGN channel. extraordinary events, e.g., power outages, many MTDs may
b) RandomAccessResponse(RAR): TheeNBanswersto be activated simultaneously, thus causing a PRACH overload.
correctly decoded preambles (including those with undetected The consequences are that the constraints of delay-sensitive
collision) by sending a RAR message on the Downlink Shared M2M applications can be violated, the power consumption of
Channel (DLSCH). RAR carries the detected preamble index, the sensors is increased, and the Quality of Service (QoS) of
which corresponds to the sequence sent by the UE, a timing H2H applications can be degraded.
alignment to synchronize the UE to the eNB, a temporary In this paper we aim at evaluating how this massive event-
identifier (RNTI), and an uplink scheduling grant that specifies triggered reporting mFiga.1y0.MiDmPvpsaSNcRt.2tahnteennaLs,TETEU70.network performance
the resources assigned to the UE to transmit in the next phase in a Smart City scenario using a well-known open-source
oftheRAprocedure.IfaUEreceivesaRAR,thenitproceeds network simulation tool, i.e., ns–3, written in C++, which is
with the third step; otherwise, it restarts the RA procedure particularly suitable to simulate an urban propagation environ-
anew (unless it has reached the maximum number of preamble ment. Other open-source simulation platforms are available,
transmission attempts) after a backoff time that is uniformly e.g., the LTE Vienna Simulator [9], which is based on Matlab,
distributed in the interval [0,BI], where BI is the Backoff and Omnet++ [8] and LTE-sim [7], both written in C++.
Indicator carried by the RAR. If the counter of consecutive However,theycannotbedirectlyusedforourpurposes.Infact,
unsuccessful preamble transmissions exceeds the maximum the Vienna Simulator is a link level simulator for the uplink,
number of attempts, a RA problem is indicated to the upper andthereforelackssomeofthenecessaryfeaturestoadequately
layers. model a network of MTDs, whereas Omnet++ and LTE-sim
c) Connection Request: The UE transmits a Radio Re- focus on the higher networking layers through an idealized
source Control (RRC) message containing its core-network abstraction of the lower layers, and therefore do not capture
terminal identifier in the uplink grant resources and starts a the level of detail we need to model the RACH performance.
ContentionResolutiontimer.NotethattheUEsthattransmitted
the same preamble but whose collision remained undetected III. LTERACHINNS–3
will transmit on the same resources, colliding again. In this section the LTE RACH implementation in ns–3
d) Contention Resolution: If the eNB correctly receives is addressed and an enhancement to evaluate IoT traffic is
theRRCmessage,itreplieswithanRRCConnectionSetupthat proposed.
signals to the UE that the RA phase is successfully completed. We refer to version 3.23 of the ns–3 simulator, which
Instead, if the Contention Resolution timer expires, the UE uses the LTE-EPC Network simulAtor (LENA) [10] module
to simulate the LTE protocol stack and the Evolved Packet
2For eNBs with a large coverage area there may be more than one root
Core (EPC) network. In the current implementation of LENA,
sequence.Howeverthesequencesobtainedhavelowcross-correlation[5].
3ThisistypicalinSmallCellsscenarios[6]. however, the RACH preamble is an ideal message, i.e., not
Parameter Value
DUowplninliknkcacrarrireirerfrferqeuqeunecnycy 994050MMHHzz 250
AvaRilBabbleanbdawniddwthidth 15800RkHBz 200
eNBesNHbBeexasmafgowornideatalhcsh(emcsteaocirntsorlobe) 3(co6-l51o◦cated) Y [m] 150
TXpowerusedbyeNBs 43dBm 100
MaxTMXeNTpBDownneooriissueesfiefidgguubrryeeMTDs 2335dddBBBm 50
Shadowing log-normalwithσ=8 0
Numberofbuildings 96
0 50 100 150 200 250 300 350 400
Apartmentsforeachfloor 6
Floorsforeachbuilding 3 X [m]
MTDspeed 0Km/h
Figure 2: Smart City network deployment example. The rect-
NumberofMTDsN {50,100,150,200,300,400,500,600}
Simulationtime∀N {60,60,120,120,300,300,400,400}s angles are the buildings, the small triangles are the MTDs, and
the black square is the position of the three co-located eNBs.
Table I: Simulation parameters [2].
Parameters Value
and transmits it in the next PRACH opportunity. Note that
PRACHConfigurationIndex 1 we are assuming that, in a PRACH-dedicated subframe, no
BackoffIndicatorBI 0ms
PUSCHtrafficisallocatedbythescheduler,whilethePRACH
preambleInitialReceivedTargetPower −110dBm
powerRampingStep 2dB is allocated in the first 6 RBs available. The power (in dBm)
numContentionPreambles 54 for the transmission is computed according to the standard as
preambleTransMax ∞
[12]
Contentionresolutiontimer 32ms
P =min{P ,
Table II: Simulation parameters of LTE RACH. prach UE,max (1)
PREAMBLE_RECEIVED_TARGET_POWER+P }
lc
where P is the maximum transmit power
UE,max
subject to radio propagation; moreover, Connection Request
for a UE, P is the estimated pathloss and
lc
and Connection Resolution messages are not modeled and,
PREAMBLE_RECEIVED_TARGET_POWER is given by
therefore, all collisions are detected and solved at the first
the MAC layer, as [13]
step of the RA procedure. Furthermore, we found that it is
not possible to simulate the connection and disconnection of PREAMBLE_RECEIVED_TARGET_POWER=
UEs during runtime, since LENA allows every UE to switch preambleInitialReceivedTargetPower
only once from RRC_IDLE to RRC_CONNECTED states at (2)
+∆ +(PREAMBLE_TX_COUNTER−1)
preamble
the beginning of the simulation. Therefore, we implemented
×powerRampingStep
a more realistic RA procedure, along with the possibility to
disconnectUEsfromtheeNB(i.e.,switchingfromRRC_IDLE where PREAMBLE_TX_COUNTER is the number of consec-
toRRC_CONNECTEDandviceversa).Theenhancedmoduleis utive preamble transmissions and ∆ = 0 for format
preamble
called LENA+. 4 However, to maintain the backward compat- 0. The other parameters are given by the eNB with SIB2, as
ibility with the current release, an option has been introduced explainedinSec.II.AttheeNBside,theSNRiscomputedfor
to use the idealized LENA RA procedure if desired. In the each preamble and a decision on correct or missed detection is
following, we describe in detail the features of LENA+ that made.In[14]differenteNBdetectionalgorithmsareintroduced
were not present in LENA. and evaluated in terms of missed detection probability vs SNR
atthereceiver.Themisseddetectionprobabilityperformanceof
A. PRACH Characterization
these algorithms is reported in Fig. 1. Note that our improved
PRACH is implemented as a real physical channel, re-
PRACH model for ns–3 assumes a time domain detector with
lying on the already developed and tested channel model.
decimation (denoted with LT in the legend), which is the
Nonetheless, PRACH preambles are now subject to noise and
simplest algorithm which satisfies the 3GPP requirements in
radio propagation, since they are sent on specific time and
[14], as can be seen from Fig. 1. The ns–3 LTE module has
frequency physical resources, and therefore the eNB can fail
alsobeenmodified,inordertohandlethereceptionofmultiple
their detection. We remark that only format 0 of PRACH
signals in the same time and frequency resources. Indeed, the
preambles is implemented. Whenever a UE starts the RA
default implementation raises an exception whenever two or
procedure,itcheckswhetherithasreceivedSIB2,whichcarries
more signals are received in the same time and frequency
the RACH configuration. Then, it chooses a random index
resources by the eNB, since the MAC scheduler forbids mul-
drawn uniformly in [0, numContentionPreambles - 1]
tiple transmissions in physical channels other than PRACH.
In PRACH, indeed, transmissions cannot be scheduled and the
4The source code is available at https://github.com/
signetlabdei/lena-plus. ZCsequencesallowmultipleaccessbyCodeDivisionMultiple
1 1 1
0.8 0.8 0.8
0.6 0.6 0.6
F F F
D D D
C C C
E 0.4 E 0.4 E 0.4
0.2 LENA 0.2 LENA 0.2 LENA
LENA+ LENA+ LENA+
0 0 0
10−2 100 102 10−2 100 102 10−2 100 102
Delay[s] Delay[s] Delay[s]
(a)N =100 (b)N =200 (c)N =300
1 1 1
LENA LENA LENA
LENA+ LENA+ LENA+
0.8 0.8 0.8
0.6 0.6 0.6
F F F
D D D
C C C
E 0.4 E 0.4 E 0.4
0.2 0.2 0.2
0 0 0
10−2 100 102 10−2 100 102 10−2 100 102
Delay[s] Delay[s] Delay[s]
(d)N =400 (e)N =500 (f)N =600
Figure 3: ECDFs of access delay for N ∈{100, 200, 300, 400, 500, 600}. The x-axis is expressed in logarithmic scale.
Access (CDMA). If a preamble is correctly received but there LENA, has been added as well.
aretwoormorepreambleswiththesameZCsequence,thenthe
collisionisdetectedornotaccordingtothefollowingheuristic. IV. PERFORMANCEEVALUATION
Since the PDP of different users is not simulated in a system- In this section the proposed enhanced version of the LENA
level simulator such as ns–3, as a rule of thumb a collision is module is evaluated and compared with the current release.
detected if Moreover, we will use our module to evaluate the impact of
d −d
max min >T , (3) massive simultaneous accesses to an LTE network in a Smart
c chip
City scenario.
where d and d are the distances from the eNB of the The scenario we simulated is compliant with the specifica-
max min
farthest and closest colliding UE, respectively, c is the speed tions in [2]; the main simulation parameters are in Table I,
oflight,T =1/(2B),andB =1.08MHzisthebandwidth while the RACH-related parameters can be found in Table II.
chip
of PRACH. We refer to an urban environment with a high density of tall
RAR message transmission was already implemented as buildings; the deployment of buildings and MTDs is depicted
a message on the DLSCH. For each not-collided preamble in Fig. 2. For what concerns the radio propagation model,
or undetected collision, an uplink grant is allocated by the we employed the ns–3 Hybrid Buildings Propagation Loss
schedulerandaddedtotheRARresponse;theBackoffindicator Model, which exploits different propagation models to account
has also been added. for several factors, such as the positions of the UE and the
Connection Request transmission on granted resources was eNB (both indoor, both outdoor, one indoor and the other
already implemented, as well. However, since in the default outdoor), the external wall penetration loss of different types
implementation of RACH all the collisions are resolved at the of buildings (i.e., concrete with windows, concrete without
first step, collisions of messages 3 were not handled and the windows,stoneblocks,wood),andtheinternalwallpenetration
simulatorraisedanexception.Thisexceptionhasbeenhandled loss. We remark that all the MTDs have been placed inside
as follows. Firstly, no capture effect has been considered. the buildings and their positions are not changed during the
Then, if two or more Connection Request messages collide, simulation according to the specifications found in [2].
they are considered as received with errors, triggering an Let us denote with N the number of MTDs that are trying
HARQ (layer 2) retransmission until the maximum number of to simultaneously access the LTE network. For every value of
attempts is reached; after that, the RA procedure starts again. N ∈ {50,100,150,200,300,400,500,600}, 10 Monte Carlo
The Contention Resolution timer, that was also not present in simulations have been run and the Empirical Cumulative Dis-
1
50
pts 40 100
0.8 51000 Attem 125000
H
ECDF 00..46 123450000000 cessfulRAC 20 345600000000
c
0.2 500 Su
600
0
0 0 2 4 6 8 10
10−2 10−1 100 101 102
Time[s]
Delay[s]
Figure 5: Successful RACH attempts vs time.
Figure 4: ECDF for various values of N. The x-axis is
expressed in logarithmic scale.
of the higher number of collision events. For N > 300, we
N Meanµ[s] Std.Dev.σ [s] µ/σ cannot observe any meaningful peak, denoting that the RACH
50 0.235 1.855 0.127 is congested and the success probability is very low.
100 0.498 2.608 0.191
150 0.780 2.605 0.300
V. CONCLUSION
200 1.481 4.453 0.333
300 5.268 5.359 0.983 TheimplementationofamorerealisticmodeloftheLTERA
400 21.400 15.126 1.415
procedureinthenetworksimulatorns–3hasbeenproposedand
500 64.234 52.852 1.215
600 77.423 59.256 1.307 evaluated in a Smart City scenario. An enhanced ns–3 LENA
module, called LENA+, has been developed to overcome the
Table III: Statistics of the access delay experienced by the
limitationsofthedefaultroutine,whichisratheridealized.The
MTDs that succeeded in completing the access procedure.
simulation results show that the default release of the LENA
module underestimates the impact of M2M traffic in cellular
networksandconfirmstheconcernsaboutLTERACHoverload
tribution Functions (ECDFs) of the access delays have been
incaseofmassivesimultaneousaccessattempts.Aspartofour
produced.Fig.3showstheECDFsofthedelay(inlogarithmic
futurework,wewillenrichtheLENA+implementation,totest
scale) for the various values of N, obtained using both the
the effectiveness of some of the strategies proposed in [1] to
defaultLENAmoduleandtheLENA+module.Weremarkthat,
relieve the RACH overload problem.
forwhatconcernstheLENA+performancecurves,theaverage
ECDF is represented by the solid line and we plotted the REFERENCES
ECDFs of the individual Monte Carlo simulations with dashed
lines to show the dispersion around the average value. It can [1] A. Biral, M. Centenaro, A. Zanella, L. Vangelista, and M. Zorzi, “The
challengesofM2Mmassiveaccessinwirelesscellularnetworks,”Digital
be seen that the idealized RACH implemented in LENA gives CommunicationsandNetworks,Vol.1,Issue1,pp.1-19,Feb.2015
quite unrealistic results, where all the MTDs would succeed in [2] 3GPP, “Cellular System Support for Ultra Low Complexity and Low
completing the RA procedure in less than 1 s for all values of ThroughputInternetofThings,”TR45.820,V.1.3.1,June2015
[3] https://www.nsnam.org
N. The simulations that have been carried out using LENA+,
[4] 3GPP, “Radio Resource Control (RRC) – Protocol specification,” TS
instead,showthat,asN grows,theaccessdelayincreases,upto 36.331,V.12.6.0,June2015
hundreds of seconds for most MTDs, which is not acceptable [5] M. Amirijoo, P. Frenger, F. Gunnarsson, J. Moe, K. Zetterberg, “On
self-optimization of the random access procedure in 3G Long Term
for many delay-constrained Smart City applications, such as
Evolution,” in Proceedings of the IFIP/IEEE International Symposium
alarms. Moreover, using our module, we are able to observe onIntegratedNetworkManagement-Workshops,pp.177-184,June2009
that some UEs (approximately 5% of the total in each simu- [6] P.BertrandandJ.Jiang,“RandomAccess,”inS.Sesia,I.Toufik,andM.
Baker(editors),“LTE–TheUMTSLongTermEvolution:FromTheory
lation) do not succeed in completing the RA procedure during
toPractice,”JohnWiley&Sons,pp.421-457,2009
the simulation, despite the unlimited number of transmission [7] G. Piro, L. A. Grieco, G. Boggia, F. Capozzi, and P. Camarda, “Sim-
attempts allowed (i.e., preambleTransMax = ∞). This is ulating LTE Cellular Systems: An Open-Source Framework,” in IEEE
TransactionsonVehicularTechnology,Vol.60,No.2,pp.498-513,Feb.
due to their unfavorable position, e.g., inside buildings which
2011
are far away from the eNB. An overall comparison among the [8] A.Virdis,G.Stea,andG.Nardini,“SimuLTE-Amodularsystem-level
average ECDFs for all the values of N is provided in Fig. 4, simulatorforLTE/LTE-AnetworksbasedonOMNeT++,”inProceedings
of the International Conference on Simulation and Modeling Method-
whichclearlyshowsthattheaccessdelayincreasesasN grows.
ologies,TechnologiesandApplications(SIMULTECH),pp.59-70,Aug.
As a further insight, we invite the reader to refer to Table III, 2014
which contains the average value and standard deviation of the [9] J. Blumenstein, J. Ikuno, J. Prokopec, and M. Rupp, “Simulating the
long term evolution uplink physical layer,” in Proceedings ELMAR, pp.
delays of successful MTDs. The statistics confirm the trend.
141-144,Sept.2011
Finally, Fig. 5 represents the number of successful RACH [10] N. Baldo, M. Miozzo, M. Requena, J. Nin Guerrero, “An Open Source
attempts vs time for different values of N. Note that, as N Product-OrientedLTENetworkSimulatorbasedonns-3,”inProceedings
of the 14th ACM International Conference on Modeling, Analysis and
increases, the maximum number of successful RACH attempts
SimulationofWirelessandMobileSystems(MSWIM),pp.293-298,Nov.
decreases, and is achieved later in time, as a consequence 2011
[11] 3GPP,“BaseStation(BS)radiotransmissionandreception,”TS36.104,
V.13.0.0,July2015
[12] 3GPP,“Physicallayerprocedures,”TS36.213,V.12.6.0,June2015
[13] 3GPP, “Medium Access Control (MAC) protocol specification,” TS
36.321,V.12.6.0,June2015
[14] F.J.López-Martínez,E.delCastillo-Sánchez,E.Martos-Naya,J.Tomás
Entrambasaguas, “Performance evaluation of preamble detectors for
3GPP-LTEphysicalrandomaccesschannel,”inDigitalSignalProcess-
ing,Vol.22,Issue3,pp.526-534,May2012