International Journal of Informatics Society, VOL.13, NO.2 (2021) 55-66

55

Regular Paper

Sub-1 GHz Wireless Coexistence of IEEE 802.15.4g and IEEE 802.11ah Using
Hybrid CSMA/CA
Yukimasa Nagai† *, Jianlin Guo‡ , Takenori Sumi† , Philip Orlik‡ , and Hiroshi Mineno*†

Mitsubishi Electric IT R&D Center, Japan
Mitsubishi Electric Research Laboratories, USA* Graduate School of Science and Technology, Shizuoka University, Japan
Nagai.Yukimasa@ds.MitsubishiElectric.co.jp‡

Abstract - As more and more wireless technologies havebeen developed to support emerging Internet of Things (IoT)
applications, the coexistence of these heterogeneous wirelesstechnologies presents challenges. IEEE 802.15.4g and IEEE
802.11ah are two of such wireless technologies specified
for the outdoor IoT applications and designed to operate
in the Sub-1 GHz (S1G) frequency band. Due to theconstrained spectrum allocation in the S1G band, two typesof devices may be forced to coexist, i.e., share frequency
spectrum. Therefore, the coexistence of 802.15.4g and802.11ah should be addressed. To investigate coexistence
behavior of these two wireless technologies, we first identify
coexistence issues using our developed NS-3 based S1Gband coexistence simulator. Simulation results confirm that802.15.4g performance can significantly degrade due to the802.11ah interference. Accordingly, we propose a hybrid
CSMA/CA mechanism for 802.15.4g to address the identified
coexistence issues. We then present several distributedand network assisted methods for 802.15.4g devices toestimate 802.11ah interference severity and switch channel
access mode for interference mitigation. The performance
analysis shows that the proposed hybrid CSMA/CA canimprove 802.15.4g performance without sacrificing 802.11ah
performance1 .
Keywords: Wireless coexistence, interference mitigation,
hybrid CSMA/CA, Sub-1 GHz band, IEEE 802.15.4g, IEEE
802.11ah

1

INTRODUCTION

The Internet of Things (IoT) applications are rapidly
growing. A broad range of wireless technologies have beendeveloped to cater diverse applications. As heterogeneous
wireless technologies are emerging, wireless coexistence
becomes a critical issue to be addressed. IEEE 802.15.4g[2], marketed as Wi-SUN, operates in the Sub-1 GHz (S1G)
frequency band for outdoor IoT applications. IEEE 802.11ah[1], marketed as Wi-Fi HaLow, is the first 802.11 standard
designed to operate in the S1G band. The unlicensed
1 This paper is an extended version of our work published in [5].
We extend our previous work by adding distributed and network assisted
methods for 802.15.4g devices to estimate 802.11ah interference severity.
These methods are indispensable for 802.15.4g devices to assess 802.11ah
interference and therefore, switch channel access mode for interference
mitigation.

spectrum allocation is limited, especially in the S1G band
compared with other bands such as 2.4 GHz band. For
example, Japan only allocates 7.6 MHz spectrum in 920
MHz band for active radio devices in the standard ARIB
STD-T108 (20 mW) [3]. This standard also regulates otherpassive radio devices to use this spectrum. The constrained
spectrum allocation indicates that 802.15.4g devices and802.11ah devices may be forced to coexist, i.e., sharefrequency spectrum. In addition, 802.15.4g network and802.11ah network can have thousands of nodes. Bothtechnologies have communication range of 1000 meters for
IoT applications. These features significantly increases
the coexistence potential. Therefore, ensuring harmonious
coexistence of these two wireless technologies is important.
802.11ah mandates the support of 1 MHz channel, which
is much narrower than the 20 MHz channel for conventional
802.11 in 2.4 GHz band. As a result, the existing coexistence
technologies designed for 2.4 GHz band may not be suitable
for the coexistence of 802.11ah and 802.15.4g in the S1Gband, e.g., the cooperative busy tone method proposed in[10] assumes 22 MHz 802.11 channel. Therefore, thecoexistence of 802.11ah and 802.15.4g needs to be further
investigated. Accordingly, IEEE New Standards Committee
and Standard Board formed IEEE 802.19.3 Task Group in
December 2018 to develop an IEEE 802 standard for thecoexistence of 802.11ah and 802.15.4g in the S1G frequency
band [4]. Authors of this paper have been leading thisstandard development.
J. Guo, et al. propose a prediction based self-transmission
control method for 802.11ah to ease its interference impact
on 802.15.4g [6]. Y. Liu, et al. introduce α-Fairness energy
detection clear channel assessment (ED-CCA) method for802.11ah to mitigate its interference on 802.15.4g causedby its higher energy detection (ED) threshold [7]. To
address the interference caused by the faster backoff of
802.11ah, Y. Liu, et al.
also propose a Q-Learning
based backoff mechanism for 802.11ah to avoid interferingwith 802.15.4g packet transmission process [7]. However,these coexistence technologies improve the performanceof 802.15.4g at the expense of 802.11ah. This paper
aims to develop coexistence technologies for 802.15.4g toimprove 802.15.4g performance without degrading 802.11ah
performance. We first evaluate coexistence behavior andidentify coexistence issues by using the developed S1G band

ISSN1883-4566 © 2021 - Informatics Society and the authors. All rights reserved.

56

Y. Nagai et al. / Sub-1 GHz Wireless Coexistence of IEEE 802.15.4g and IEEE 802.11ah Using Hybrid CSMA/CA

Table 1: The majority of available performance evaluation, and conventional coexistence researches.
Reference
This article and [5]J. Guo, P. Orlik [6]Y. Liu, J. Guo et al.[7]W. Yuan et al. [8]E.D.N Ndih et al. [9]X. Zhang, et al. [10]J.Hou et al. [11]J.W. Chong et al. [12]B. Badihi et al. [13]R. Ma et al. [14]

Year
2020
2017
2018
2010
2016
2011
2009
2015
2013
2017

Target System
11ah & 15.4g
11ah & 15.4g
11ah & 15.4g
11b & 15.4
11 & 15.4
11 & 15.4
11 & 15.4
11 & 15.4
11ah & 15.4
11b & 15.4

Band
Sub-1 GHz
Sub-1 GHz
Sub-1 GHz
2.4 GHz
2.4 GHz
2.4 GHz
2.4 GHz
2.4 GHz
Sub-1 GHz
2.4 GHz

Objective
delivery rate and latency at coexistencedelivery rate and latency at coexistencedelivery rate and latency at coexistence
throughput
delivery rate
analytical model, throughput
delivery rate
throughput
throughput and energy consumption
analytical model, throughput

coexistence simulator. We then propose a hybrid carrier sense
multiple access/collision avoidance (CSMA/CA) mechanism
for 802.15.4g to achieve better coexistence with 802.11ah.
Furthermore, we present the distributed techniques for802.15.4g devices to assess 802.11ah interference and switch
channel access mode for interference mitigation.
The rest of this paper is organized as follows. Section
2 presents related work. Section 3 evaluates coexistence
behavior and issue of 802.11ah and 802.15.4g. We introduce
the proposed hybrid CSMA/CA mechanism in Section 4.
Section 5 presents distributed methods to estimate 802.11ah
interference severity. Section 6 shows network assisted
802.11ah interference severity estimation. In Section 7, weintroduce our S1G band coexistence simulator. Performance
evaluation of hybrid CSMA/CA mechanism is conducted in
Section 8. We conclude our work in Section 9.

2

RELATED WORK

There are existing coexistence technologies developed forconventional 802.15.4 to address its coexistence with 802.11
in 2.4 GHz band. W. Yuan, et al. propose a decentralized
approach to mitigate interference by adaptively adjusting ED
threshold [8]. E.D.N. Ndih, et al. propose an adaptive backoffmechanism to survive coexistence with 802.11 [9]. X. Zhang,
et al. design a cooperative busy tone method via a special
device to enable 802.11 to be aware of 802.15.4 transmission[10]. J. Hou, et al. propose a hybrid device to coordinate802.11 and 802.15.4 transmissions [11]. J.W. Chong, etal. propose an adaptive interference mitigation scheme for802.15.4 to control its frame length based on the measured
802.11 interference via a hybrid device [12].
Before the work in [6] and [7], to the best of ourknowledge, no other existing work addresses the coexistenceof 802.11ah and 802.15.4 in the S1G band. The related
studies are done either for 802.11ah or 802.15.4g only. B.
B. Olyaei, et al. compare the performance of 802.11ah andconventional 802.15.4 in the S1G band. The results revealthat 802.11ah network achieves higher channel efficiency
than 802.15.4 network [13]. R. Ma, et al. investigate thecoexistence issues of 802.11b and 802.15.4g in 2.4 GHz
band. It shows that 802.11b can significantly interfere with
802.15.4g [14]. However, our investigation shows that theexisting studies only reveal one side of the story. Table 1

Validation Tool
ns-3
ns-3
ns-3
OPNET
MATLAB
analytical, ns-2
experiments
analytical
OMNeT++
analytical & unknown simulatorshows majority of available 802.11 and 802.15.4 performance
evaluation and conventional coexistence researches.

3

802.11AH AND 802.15.4G COEXISTENCEBEHAVIOR AND ISSUE

Before conducting coexistence performance evaluation
using our S1G band coexistence simulator, we briefly
introduce the functional differences between 802.11ah and802.15.4g, which affect the coexistence behavior of 802.11ah
and 802.15.4g.
802.11ah defines OFDM PHY and uses the ED-CCA witha threshold of -75 dBm per MHz for coexistence control withother non-802.11 systems. 802.15.4g specifies MR-FSK,
MR-OFDM and MR-O-QPSK PHYs and only addresses
coexistence among devices using different 802.15.4g PHYs.
802.15.4g ED threshold is lower than -75 dBm, e.g., its ED
threshold is in [-100 dBm, -78 dBm] for FSK PHY.
802.11ah channel width is in the unit of MHz, i.e., 1
MHz/2 MHz/4 MHz/8 MHz/16 MHz. However, 802.15.4g
channel width is in the unit of kHz, i.e., 200 kHz/400 kHz/600
kHz/800 kHz/1200 kHz. 802.11ah data rate ranges from 150kbps to 78 Mbps for even one spatial stream. On the other
hand, 802.15.4g data rate ranges from 6.25 kbps to 800 kbps.
802.11ah CSMA/CA and 802.15.4g CSMA/CA are muchdifferent. 1) 802.11ah allows immediate channel access.
802.15.4g, however, requires backoff no matter how longchannel has been idle. 2) 802.11ah backoff is much faster than802.15.4g backoff due to much smaller parameters as shownin Table 2, where 802.15.4g parameters are for FSK PHY
operating in 920 MHz band. 3) 802.11ah requires backoffsuspension, i.e., 802.11ah device must perform clear channel
assessment (CCA) in each backoff slot and can decrease
backoff counter only if the channel is idle. On the other
hand, 802.15.4g has no backoff suspension. 802.15.4g device
performs CCA after the backoff procedure completes.
The ED threshold, channel width, data rate and first two
CSMA/CA features are in favor of 802.11ah. However,
the third CSMA/CA feature is in favor of 802.15.4g.
Theoretically, an 802.11ah packet can be infinitely delayed,
but an 802.15.4g packet has bounded delay.
Based on forementioned functional differences, thepurpose of 802.11ah and 802.15.4g coexistence simulation
is to explore how network traffic and network size affect theInternational Journal of Informatics Society, VOL.13, NO.2 (2021) 55-66

57

Table 2: 802.11ah and 802.15.4g CSMA/CA Parameters802.11ah Param.
CCA Time
Slot Time
SIFS Time
DIFS Time

Value
40 µs
52 µs
160 µs264 µs

802.15.4g Param.
phyCCADuration
UnitBackoffPeriod
AIFS Time
SIFS TimeValue
160 µs1160 µs1000 µs1000 µs

coexistence behavior of 802.11ah and 802.15.4g as well as
what are the critical coexistence issues to be addressed.
We use packet delivery rate and packet latency as metrics
to evaluate the coexistence performance. The packet delivery
rate is measured as the ratio of number of packets successfully
delivered and total number of packets transmitted. The packet
latency is measured as time difference from the time at packet
transmission process starts to the time at the packet receiving
is successfully confirmed. In other words, the packet
latency is given by Backof f T ime + DataT XT ime +AckW aitingT ime + AckRXT ime. The simulation setup
is described in section 7.
In Figs. 1 and 2, solid lines represent 802.11ah network
performance and dash lines illustrate 802.15.4g network
performance. In addition, 50-20-20 indicates 50 nodes foreach network, 20 kbps offered load for 802.11ah network, 20kbps offered load for 802.15.4g network, and so on.
Fig. 1 shows packet delivery rate of 802.11ah network
and 802.15.4g network. We have following findings: 1)
For all scenarios, 802.11ah network delivers nearly 100%of the packet, which indicates that network traffic andnetwork size have less impact on 802.11ah packet delivery
rate. 2) 802.11ah network traffic has impact on 802.15.4g
packet delivery rate. 802.15.4g network packet delivery
rate decreases as 802.11ah network traffic increases. 3)
802.15.4g network traffic affects more on its packet delivery
rate. 802.15.4g network packet delivery rate decreases
significantly as its network traffic doubles. 4) The network
size has little effect on 802.15.4g network packet delivery
rate.
Fig. 2 depicts the corresponding packet latency. We
have following observations: 1) For all scenarios, 802.15.4g
network achieves similar packet latency, which indicates that802.15.4g packet is either delivered with the bounded delay
or dropped and therefore, network traffic and network size
have little impact on 802.15.4g packet latency. 2) 802.11ah
network traffic has impact on its packet latency. 802.11ah
packet latency increases as its network traffic increases.
3) 802.15.4g network traffic has more impact on 802.11ah
packet latency. 802.11ah network packet latency increases
more as 802.15.4g network traffic doubles. 4) Network size
has major influence on 802.11ah packet latency. 802.11ah
packet latency increases significantly as the number of nodes
doubles, which verifies that 802.11ah packet can be infinitely
delayed.
These results show that 802.11ah network and 802.15.4g
network interfere with each other. This observation isdifferent from that drawn by existing studies that only reveal
the 802.11ah interference on 802.15.4g. Based on thesefindings, coexistence technologies need to improve 802.15.4g
delivery rate and reduce 802.11ah packet latency.

Figure 1: Packet Delivery Rate

Figure 2: Packet Latency

4

HYBRID CSMA/CA FOR 802.15.4G TO
COEXIST BETTER WITH 802.11AH

This section presents the proposed hybrid CSMA/CA for802.15.4g to improve 802.15.4g delivery rate and reduce
802.11ah packet latency. The proposed hybrid CSMA/CA
for 802.15.4g allows 802.14.g device to perform immediatechannel access.
An 802.15.4g device cannot communicate with an
802.11ah device. Therefore, 802.15.4g devices cannot
coordinate with 802.11ah devices for interference mitigation
without special assistance. However, 802.15.4g devices
can explore the weakness of 802.11ah devices to increase
their channel access opportunity when they detect severeinterference from 802.11ah devices. An 802.11ah device
must perform backoff process after the busy channel. Before
the backoff process, 802.11ah device must wait for a DCF
inter frame space (DIFS) (264 µs) time period. This 264µs waiting time plus random backoff time gives 802.15.4g
devices opportunity to start transmission before 802.11ah
devices if 802.15.4g devices are allowed to have immediatechannel access capability, which is not allowed in the802.15.4g standard.
To compete with more aggressive 802.11ah for channel
access, we propose a hybrid CSMA/CA mechanism for802.15.4g. Depending on severity of 802.11ah interference,
the hybrid CSMA/CA switches between two modes:
immediate channel access disabled mode when 802.11ah
interference is not severe and immediate channel accessenabled mode when 802.11ah interference is severe. In thefirst mode, the standard 802.15.4g CSMA/CA is applied. In
the second mode, the proposed immediate channel accessenabled CSMA/CA is employed.
Fig. 3 shows the hybrid CSMA/CA mechanism for58

Y. Nagai et al. / Sub-1 GHz Wireless Coexistence of IEEE 802.15.4g and IEEE 802.11ah Using Hybrid CSMA/CA

therefore, reduces 802.11ah packet latency.
The core of the hybrid CSMA/CA is to determine 802.11ah
interference severity. In Sections 5 and 6, we present pure andnetwork assisted distributed methods to estimate 802.11ah
interference severity.

5

DISTRIBUTED 802.11AH
INTERFERENCE SEVERITY
ESTIMATIONThis section presents three pure distributed methods for802.15.4g to estimate 802.11ah interference severity, inwhich 802.15.4g devices estimate 802.11ah interference
severity distributively without any assistance. An 802.15.4g
device should select a method for better performance basedon the given performance metric.

Figure 3: Hybrid CSMA/CA for IEEE 802.15.4g
802.15.4g. To decide a CSMA/CA mode, the hybrid
CSMA/CA first determines the severity of 802.11ah
interference. If the 802.11ah interference is not severe,
the standard 802.15.4g CSMA/CA is applied.
If the802.11ah interference is severe, the immediate channel accessenabled CSMA/CA is used. In this mode, the hybrid
CSMA/CA enables 802.15.4g devices to have immediatechannel access capability. The blue blocks show the flow
chart of the immediate channel access. Considering thatthe immediate channel access by multiple 802.15.4g devices
within a neighborhood may also cause collision, the hybrid
CSMA/CA computes an optimal probability for stochastic
decision making, i.e., perform immediate channel access orbackoff.
To compute the optimal probability, an 802.15.4g
device first determines number of 802.15.4g neighbors bymonitoring neighbor’s packet transmission. Assume there
are Ng 802.15.4g devices in a neighborhood and each device
has probability p to take immediate channel access andprobability 1 − p to perform backoff. Let X denote binomial
PNg grandom variable i=1
Xi , where Xig (i = 1, 2, ..., Ng ) is
random variable representing decisionof 802.15.4g neighbori. Then P (X = k) = Nkg pk (1 − p)Ng −k and E[X] =Ng p. To avoid collision among 802.15.4g transmissions due
to immediate channel access, optimal strategy is that the
expected number of 802.15.4g devices that take immediatechannel access is one and rest of 802.15.4g devices performbackoff, i.e., E[X] = 1, which gives optimal probability
po = N1g .
Based on the optimal probability po , the hybrid CSMA/CA
decides if immediate channel access or backoff is performed.
The Yes decision leads to CCA operation. If the CCA
returns idle channel, the immediate channel access takes
place. The No decision leads to backoff. To do so, 802.15.4g
device increases backoff parameters to avoid collision withtransmission process of immediate channel access device andalso give 802.11ah device opportunity to transmit next andA) Channel Access Failure Rate Caused by 802.11ah
IEEE 802.15.4g performs carrier sense before startingtransmission to check if channel is available. IEEE 802.15.4g
can detect other system is transmitting if received signal
over IEEE 802.15.4g ED threshold cannot be decoded, anddetermine channel access failure caused by other system. In
this paper, IEEE 802.11ah is assumed to be other system.
Let Ncaf be the total number of channel access failure
observed by an 802.15.4g device for total Ntx transmissionhattempts. Ncaf can be decomposed into Ncaf = Ncaf+ghNcaf , where Ncaf is the number of channel access failuregcaused by 802.11ah and Ncaf
is the number of channel
access failure caused by 802.15.4g. 802.15.4g device is ablegto compute Ncaf
by using carrier sense mechanism. To
guarantee packet header sensing, 802.15.4g device may start
carrier sense early, e.g., start channel sense before backoff
counter reaches to zero. Therefore, channel access failure ratehcaused by 802.11ah Rcaf
can be computed as
h
Rcaf
=

g
h
Ncaf − Ncaf
Ncaf
=
Ntx
Ntx

(1)

g
If Ncaf = Ncaf
, no interference from 802.11ah, else (likegNcaf − Ncaf > 0, 802.11ah presence. 802.15.4g device
switches to the immediate channel access.

B) 802.11ah Channel Occupancy Probability
An 802.15.4g device can estimate the channel busy time
Tb by continuously sensing channel for a time period T . Itstransmission time and reception time are considered as busy
time. Its turnaround time is considered as idle time. In
addition, 802.15.4g device is able to determine the busy time
consumed by 802.15.4g transmissions Tbg via carrier sense.
hTherefore, 802.11ah channel occupancy probability Ptx
canbe estimated as
Tb − Tbg
h
.
(2)
Ptx
=
T
h
If Pedis higher than 802.15.4g system predeterminedthreshold, 802.15.4g device switches to the immediatechannel access.

International Journal of Informatics Society, VOL.13, NO.2 (2021) 55-66

59C) 802.11ah Energy Detection Ratio
Using energy detection mechanism, an 802.15.4g device
can detect energy that is higher than or equal to 802.15.4g ED
threshold. Let EDtotal be the total number of such detection
by an 802.15.4g device within a time period T . Using carrier
sensing mechanisms, an 802.15.4g device can determine if
the detected signal is 802.15.4g signal or not. For 802.15.4g
and 802.11ah coexistence, if the signal is not 802.15.4g
signal, it is either 802.11ah signal or collided signal. Let
EDah be the number of non 802.15.4g signal detected.
h802.11ah energy detection ratio Red
can be estimated as
h
Red
=

EDah
.
EDtotal(3)

If 802.15.4g device detects EDah during observationhtime period T and Red
is higher than 802.15.4g systempredetermined threshold, 802.15.4g device switches toimmediate channel access.

6

NETWORK ASSISTED 802.11AH
INTERFERENCE SEVERITY
ESTIMATION

Some of performance metrics such as packet delivery
rate can not be estimated locally by an 802.15.4g device
alone and therefore, network assistance is needed. The
advantage is that metric can be more accurately assessed. The
disadvantage is that network assistance may not be available.
Due to the fact that 802.15.4g devices can not distinguishbetween collision caused by 802.11ah or 802.15.4g, we use
the probability of the 802.11ah transmission colliding with
802.15.4g transmission as a metric to estimate 802.11ah
interference severity.
This section presents a network assisted distributed method
for 802.15.4g devices to estimate 802.11ah interference
severity. Using this method, 802.11ah network provides its
node distribution, traffic pattern, and the random backoff
period length of its nodes to 802.15.4g network. Nodedistribution and traffic pattern only need to be provided once,
and the length of random backoff period needs to be provided
repeatedly, since the traffic pattern and terminal location
are assumed not to change dynamically for sensor networks
that enable IoT application. Node distribution is used todetermine 802.11ah neighbors of an 802.15.4g node. The
determined number of 802.11ah neighbors, traffic pattern andthe length of random backoff period are then used to estimate
the collision probability caused by 802.11ah.
An 802.11ah transmission can interfere with an 802.15.4g
transmission only if their transmission time periods overlap.
Fig. 4(A) shows the collision scenarios.
In the IEEE 802 standards, a data transmission is successful
only if its transmission process completes. Therefore, we
consider interference effect of 802.11ah transmission process
on 802.15.4g transmission process.
An 802.11ah transmission process can interfere with agiven 802.15.4g transmission only if the corresponding
802.11ah data arrives within a potential time period. The

Figure 4: 802.11ah TX interfering with 802.15.4g TX
length of this time period is used to estimate the collision
probability caused by 802.11ah.
In this section, we first present a method to estimate
the length of potential 802.11ah data arriving time period.
Based on 802.11ah traffic pattern and the estimated lengthof potential 802.11ah data arriving time period, we thencompute the probability of 802.11ah transmission processinterfering with 802.15.4g transmission process.
A) Potential 802.11ah Data Arriving Time Period
802.11ah channel access can be divided into
1. Immediate access, in which if data arrives, channel isidle and idle channel continues for more than DIFS
time period, the data is transmitted without backoff.
2. Deferred access, in which if data arrives, channel
is busy, then backoff process is invoked and datatransmission is deferred.
An 802.11ah device ignores 802.15.4g transmission if thedetected energy level is below 802.11ah CCA-ED threshold,which is -75 dBm for 1 MHz channel, and detects 802.15.4g
transmission if the detected energy level is above 802.11ah
CCA-ED threshold. Therefore, the 802.11ah interference
scenarios can be classified into following four cases:• Case-1: 802.11ah performs immediate channel accessand ignores 802.15.4g transmission• Case-2: 802.11ah performs delayed channel access andignores 802.15.4g transmission• Case-3: 802.11ah performs immediate channel accessand detects 802.15.4g transmission• Case-4: 802.11ah performs delayed channel access anddetects 802.15.4g transmission
Let Tgd , Tga , Thd and Tha be 802.15.4g data transmissiontime, 802.15.4g ACK transmission time, 802.11ah data

60

Y. Nagai et al. / Sub-1 GHz Wireless Coexistence of IEEE 802.15.4g and IEEE 802.11ah Using Hybrid CSMA/CA

transmission time and 802.11ah ACK transmission time,
respectively.
For Case-1, Fig. 4(B) illustrates the length of potential
802.11ah data arriving period that can cause 802.11ah
transmission process interfering with the given 802.15.4g
ig= T2 −
transmission. The period length is given by Tim
T1 = Thd + SIF S + Tha + Tgd . It is obvious thatthe latest interfering 802.11ah transmission process can takeplace since 802.11ah device ignores 802.15.4g transmission.
Is it possible for the earliest interfering 802.11ah transmission
process to occur without being detected by 802.15.4g device?
Yes, 802.15.4g turnaround time is 1000 µs. 802.11ah SIFS is
160 µs. There are 840 µs left for 802.11ah data transmission
and ACK transmission. Even with 1 MHz channel, 802.11ah
PHY rate ranges from 300 kbps to 16 Mbps. Using 3 Mbps
PHY rate, a 100 byte packet only takes 267 µs. The remaining
573 µs is long enough to transmit 802.11ah ACK.
For Case-2, when 802.11ah data arrives for transmission,
802.11ah CCA returns channel status as busy. Therefore,
802.11ah device has to do backoff. Fig. 4(C) depicts thelength of potential 802.11ah data arriving period that cancause 802.11ah transmission process interfering with the802.15.4g transmission. In this case, the earliest interfering802.11ah transmission process performs backoff with backoff
period length greater than zero. The latest interfering802.11ah transmission process happens to select a zeroig
backoff period length. The period length is given by Tdf=hT2 − T1 = max{Thd , Tgd } + Tbo+ Thd + SIF S + Tha +Tgd , where max{Thd , Tgd } indicates that the busy channel
status returned by 802.11ah CCA can be caused by 802.11ahhis thetransmission and/or 802.15.4g transmission and Tbo
hlength of random backoff period of 802.11ah device. Tbo
israndom with a lower bound 0. For light traffic without backoffhsuspension, Tbo
has an upper bound CWmin ∗ 52µs, whereh
CWmin is typically 15. However, for heavy traffic, Tbo
could
be theoretically unbounded.
Combining Case-1 and Case-2, if 802.11ah device
ignores 802.15.4g data transmission, the length of potential
802.11ah data arriving time period that can cause 802.11ah
transmission process interfering with 802.15.4g datatransmission can be estimated as
ig
ig
ig
Titd
= Pi Tim+ (1 − Pi )Tdf

= Thd + SIF S + Tha + Tgd

hmax{Thd , Tgd } + Tbo+ Thd + SIF S + Tha .
Combining Case-3 and Case-4, if 802.11ah device
detects 802.15.4g data transmission, the length of potential
802.11ah data arriving time period that can cause 802.11ah
transmission process interfering with 802.15.4g datatransmission can be estimated as
dt
dt
dt
Titd
= Pi Tim+ (1 − Pi )Tdf

= Thd + SIF S + Tha(5)h+ (1 − Pi )(max{Thd , Tgd } + Tbo).

B) Collision Probability Caused by 802.11ah
The probability of 802.11ah transmission colliding with
802.15.4g transmission depends on traffic pattern of 802.11ah
network. This section considers Poisson data arrival anduniform data arrival traffic scenarios.
In addition, we also assume that 802.15.4g transmission
device has Nh 802.11ah neighbors with Nh > 0. Otherwise,
the 802.15.4g transmission device does not switch CSMA/CA
mode and always applies standard CSMA/CA.
B.1) Poisson Data Arrival
Assume 802.11ah device has Poisson data arriving
distribution with mean arriving rate λ. In a time period T ,the probability an 802.11ah neighbor having no data arriving
is e−λT and the probability all 802.11ah neighbors having nohdata arriving is e−Nh λT . Let Ppd
be the probability at leastone 802.11ah neighbor having data arriving in time period T ,hand Ppd
is given byhPpd= 1 − e−Nh λT .

ig
For the immediate access, plugging Titd
into (6), we obtain
the probability 802.11ah transmission process interferingwith the given 802.15.4g data transmission as
ig

ig
Ppd
= 1 − e−λNh Titd .

h+ (1 − Pi )(max{Thd , Tgd } + Tbo),

where Pi is the channel idle probability and can be estimatedbby using similar approach used in Section 5.
as Pi = T −T
T
Case-3 is similar as Case-1, but in this case, the latest
interfering 802.11ah transmission process can not start at
the end of 802.15.4g transmission since during 802.15.4g
transmission, channel is considered as busy. Therefore, thelatest interfering 802.11ah transmission process can only startat the start of 802.15.4g transmission. As a result, the lengthof potential interfering 802.11ah data arriving time period isdtTim= Thd + SIF S + Tha .
Similarly, for Case-4, the length of potential interferingdt
802.11ah data arriving time period is given by Tdf=(7)

Similarly, for the deferred access, the probability 802.11ah
transmission process colliding with the given 802.15.4g datatransmission is given by
dt

(4)

(6)

dt
Ppd
= 1 − e−λNh Titd .

(8)

ig
ig
dt
dt
Notice that Ppd< Ppd
since Titd
< Titd,which is reasonable because if 802.11ah detects 802.15.4g
transmission, it takes action to avoid interference.
Besides interfering with 802.15.4g data transmission,
802.11ah transmission can also interfere with 802.15.4g ACK
transmission. 802.15.4g ACK transmission waiting time
AIFS is 1000 µs, which is much longer than 802.11ah
DIFS time of 264 µs. Therefore, 802.11ah devices canstart transmission process in between 802.15.4g data and802.15.4g ACK. The transmission process can interfere with
802.15.4g ACK transmission.
Consider that 802.15.4g ACK is transmitted only if
802.15.4g data transmission is successful, the probabilityof 802.15.4g ACK transmission is 1 − Pcg , where Pcg isInternational Journal of Informatics Society, VOL.13, NO.2 (2021) 55-66

61

the 802.15.4g collision probability caused by both 802.11ah
transmission and 802.15.4g transmission. 802.15.4g device
can compute Pcg using number of transmission attempts andnumber of ACK received.
The probability of 802.11ah transmission processinterfering with 802.15.4g ACK transmission can besimilarly computed as for the 802.15.4g data transmission. In
this case, however, the busy channel is caused by 802.15.4g
data transmission.
For the immediate access, the probability 802.11ah
transmission process colliding with 802.15.4g ACK
transmission is given by

>>

dt

W,z

Z&ͲŚĂŶŶĞů

For uniform data arriving, if T ≥ Tih , the hybrid
CSMA/CA is always on the immediate access enabled mode.
Otherwise, the hybrid CSMA/CA switches mode based on thecollision probability caused by 802.11ah.
h
For the case T < Tih , Pud
is simplified as
h
Pud
=1−(

Tih − T Nh
) .
TihWƌŽƉĂŐĞƚŝŽŶ
ĞůĂǇDŽĚĞů

(13)

Similarly as for Poisson data arriving scenario, plugging
ig
ig
dt
dt
Titd
, Titd, Titaor Tita
into Eq.(13), we can obtain the
ig
dt
ig
dt
probability Pud , Pud , Puaor Pua. The probability of^ϭ'&ƌĂŵĞ
,ĞĂĚĞƌ
tŝĨŝZĞŵŽƚĞ
^ƚĂƚŝŽŶDĂŶĂŐĞƌ

tŝĨŝWŚǇͬzĂŶƐtŝĨŝWŚǇ

/ŶƚĞƌĨĞƌĞŶĐĞ,ĞůƉĞƌ
ͬƌƌŽƌZĂƚĞDŽĚĞů

tŝĨŝŚĂŶŶĞů

WƌŽƉĂŐĂƚŝŽŶ>ŽƐƐDŽĚĞůEŽƚŝĨǇϴϬϮ͘ϭϱ͘ϰŐdǆ /ŶĨŽ͘/ϴϬϮ͘ϭϱ͘ϰŐŵŽĚƵůĞ

/ϴϬϮ͘ϭϭĂŚŵŽĚƵůĞ

;ͿWƌǆϰŐ͗ZĞĐĞŝǀĞĚƉŽǁĞƌĨƌŽŵϴϬϮ͘ϭϱ͘ϰŐŶŽĚĞWƌǆĂŚ͗ZĞĐĞŝǀĞĚƉŽǁĞƌĨƌŽŵϴϬϮ͘ϭϭĂŚŶŽĚĞϴϬϮ͘ϭϱ͘ϰŐŚĂŶŶĞů
ϴϬϮ͘ϭϭĂŚŚĂŶŶĞů

&ƌĞƋƵĞŶĐǇ
;ͿFigure 5: Sub-1 GHz Band Coexistence Simulator Model
Interface
the 802.11ah transmission process colliding with the given
802.15.4g transmission process Pcu is given by
 ig
ig
Pud + Pua,
P dt + P ig ,
ua
ud
Pcu =
ig
dt

P
+
P

ua ,

 ud
dt
dt
Pud
+ Pua
,

7

i

ZtŽŶĨŝŐƵƌĂƚŝŽŶ
/ŶƚĞƌĨĂĐĞ

EŽƚŝĨǇϴϬϮ͘ϭϭĂŚdǆ/ŶĨŽ͘(10)B.2) Uniform Data Arrival
Assume 802.11ah device has uniform data arriving withtime interval Tih , i.e., one data arriving per Tih time period.
For a time period T , the probability of no 802.11ah packet
arriving is 0 if T ≥ Tih and is ((Tih − T )/Tih )Nh if T < Tih .
Therefore, the probability at least one 802.11ah neighborhhaving data arriving Pud
is given by(1,
if T ≥ Tih
h
h
(12)
Pud =
T −T
1 − ( iT h )Nh , if T < Tih .

DĂĐZǆDŝĚĚůĞ

DĂĐ>Žǁ

D

(9)

dt
h
where Tita
= Thd + SIF S + Tha + (1 − Pi )(Tgd + Tbo
).
ig
dt
ig
dt
We can also see that Pca < Pca since Tita < Tita .
Finally, combining all cases, the probability of 802.11ah
transmission process colliding with the given 802.15.4g
transmission process for Poisson 802.11ah data arriving Pcp
is given by
 ig
ig, if 15.4g data & ACK ignored
Ppd + PpaP dt + P ig , if only 15.4g data detected
pa
pd
(11)
Pcp =
ig
dt

P
+
P
, if only 15.4g ACK detected

pa
pd

 dt
dt
, if 15.4g data & ACK detected.
Ppd + Ppa

ĐĂdǆŽƉͬĚĐĂdǆŽƉE

ĐĨDĂŶĂŐĞƌ

igh= Thd +SIF S +Tha +Tga +(1−Pi )(Tgd +Tbo).
where Tita
For the deferred access, the probability 802.11ah
transmission process interfering with 802.15.4g ACK
transmission is given bydt
Ppa= (1 − Pcg )(1 − e−λNh Tita ),;ƉtŝĨŝDͬ^ƚĂtŝĨŝDĂĐͿ^^^

ZyWŽǁĞƌ

ig

ig
Ppa
= (1 − Pcg )(1 − e−λNh Tita ),hƉƉĞƌ>ĂǇĞƌ

if 15.4g data & ACK ignored
if only 15.4g data detected(14)
if only 15.4g ACK detected
if 15.4g data & ACK detected.

802.11AH AND 802.15.4G COEXISTENCESIMULATORThe existing simulation tools for 802.11 and 802.15.4,
e.g., NS-3 [15], MATLAB, QualNet and OMNeT++, do not
implement 802.11ah and 802.15.4g. Accordingly, we havedeveloped an NS-3 based coexistence simulator for 802.11ah
and 802.15.4g, in which we adopt the third party 802.11ah
module [16] and implement 802.15.4g FSK PHY in 920 MHz
band. NS-3 (version 3.23) is used because of supported
version in [16]. The challenges include the interfacing
independent 802.11ah module and 802.15.4g module and thereceived power conversion.
Fig. 5(A) shows the developed interface between 802.11ah
module and 802.15.4g module, where two modules
notify each other with their transmission via a TX
Info (Transmission Information) message that contains
device position, transmission duration, transmission power,
frequency, bandwidth, antenna gain, etc. Upon receiving
TX Info message from other party, 802.11ah device and802.15.4g device first compute the corresponding RX power
Prx4g and Prxah , respectively, as shown in Fig. 5(B), wheresame transmission power is assumed. In other words,
802.11ah device computes 802.15.4g received power Prx4g as
if it was an 802.15.4g device and 802.15.4g device computes

62

Y. Nagai et al. / Sub-1 GHz Wireless Coexistence of IEEE 802.15.4g and IEEE 802.11ah Using Hybrid CSMA/CA

Table 3: Simulation Scenarios−30
LoS
NLoS Suburban
NLoS Urban
802.11ah ED Threshold
802.15.4g ED Threshold

RX Power[dBm]

−40
−50
−60

Scenario-1
Scenario-2
Scenario-3
Scenario-4
Scenario-5

−70
−80
−90
−100
0

20

40

60

80

Network Size
[node]
11ah
15.4g
50
50
50
50
50
50
100
100
100
100

Offered Load[kbps]
11ah
15.4g
20
20
40
20
20
40
40
20
40
20

Propagation
Model

Suburban NLoS
Urban NLoS

100

Distance[m]8Figure 6: ITU-R P.1411-9 Propagation Model
802.11ah received power Prxah as if it was an 802.11ah
device. Using the received power computed, 802.11ah device
and 802.15.4g device compute interference power level fromother party as
4g
Pint=Prxah [dBm] − 10 log10 (CHah /CH4g )[dBm],ah
Pint=Prx4g [dBm],(15)
ahwhere Pint
is interference power to 802.11ah from 802.15.4g
4gtransmission, Pint
is interference power to 802.15.4g from802.11ah transmission, CHah and CH4g represent thechannel width of 802.11ah channel and 802.15.4g channel,
respectively.
Using the interference power level andtransmission duration, 802.11ah device and 802.15.4g device
perform the enhanced CCA operation such that if theinterference power is above the corresponding CCA-ED
threshold, the channel status is considered as busy no matter
what channel status is returned by their respective CCA
operation.

Propagation model is another key component for practicalsimulation. NS-3 implements eight propagation models
designed for general use scenarios without considering the
emerging IoT applications. Both 802.11ah and 802.15.4g
target the outdoor applications such as smart utility andsmart city. Therefore, we adopt ITU-R P.1411-9 model for
propagation between terminals located from below roof-top
height to near street level. The median value of the
Non-Line-of-Sight (NLoS) loss is given by
Lmedian
N LoS (d) = 9.5+45 log10 f +40 log10 (d/1000)+Lurban ,(16)
where f is the frequency, Lurban depends on the urban
category and is 0 dB for suburban, 6.8 dB for urban, and dis the distance. Fig. 6 shows the propagation loss of LoS
model, Suburban NLoS model and Urban NLoS model fortransmission power of 13 dBm. With -78 dBm ED threshold,the intersection of the red curve and green dash line represents
the effective energy detection distance for 802.15.4g, which
is about 50 meters for Suburban NLoS model and 34 metersfor Urban NLoS model. For 802.11ah with -75 dBm ED
threshold, the corresponding distances are 42 meters and 28
meters, respectively.

HYBRID CSMA/CA PERFORMANCEEVALUATIONIn this section, we evaluate the performance of Hybrid
CSMA/CA proposed in Section 4 to compare with standard
802.15.4g CSMA/CA. We adopt the simulation parameters
recommended by IEEE 802.19 Working Group [17]. Table
4 shows simulation parameters for IEEE 802.11ah and IEEE
802.15.4g coexistence performance. The frequency is in 920
MHz band, transmission power is 13 dBm, 1 MHz channel for802.11ah, 400 kHz channel for 802.15.4g, 802.11ah OFDMPHY rate is 300 kbps and 802.15.4g FSK PHY rate is 100kbps. And, ITU-R P.1411-9 propagation model is employedin the simulations. We use 802.11ah energy detection ratio
method to assess 802.11ah interference severity. We define
PDR (Packet Delivery Rate) and packet latency as metrics toevaluate the coexistence performance.
Five typical scenarios for 50-node and 100-node are
simulated with simulation conditions in [17]. Table 3 shows
the simulation cases. One 802.15.4g network consists of
50 or 100 nodes uniformly deployed in a circle centered at
PANC (Personal Area Network Coordinator) with radius ofeffective energy detection distance. The PANC is locatedat (0, 0). Three 802.11ah networks are deployed inside802.15.4g network with each 802.11ah network having 17
or 33 nodes uniformly distributed in a circle centered atcorresponding AP with radius of effective energy detection
distance. Based on propagation model, three APs are locatedat (8, 0), (-4, 6.928), (-4, -6.928) and (6, 0), (-3, 5.196), (-3,-5.196), respectively. The offered network load is 20 kbps or
40 kbps. The offered network load is uniformly distributed
among network nodes. The packet size is 100 bytes.
In addition to five typical scenarios, individual performanceof IEEE 802.11ah and IEEE 802.15.4g was conducted for(node, of f eredload) = (50 nodes, 20 kbps). Packet arrival
rate in a single network for is 100% for IEEE 802.11ah and98.5 % for IEEE 802.15.4g, respectively. Packet latency at
CDF 0.9 is 10 ms for IEEE 802.11ah and 40 ms for IEEE
802.15.4g.
Scenario-1: The offered load for both networks is 20kbps, i.e., 400 bps offered load per node, which leads to0.13 % duty cycle for 802.11ah node and 0.4 % duty cyclefor 802.15.4g node. These duty cycles are much lower than
the 10 % duty cycle specified in ARIB STD T108 standard[3]. With 100 bytes of packet size, each node generates 0.5
packet per second. For both standard CSMA/CA and hybrid
CSMA/CA, Fig. 7 shows that 802.11ah network delivers 100% of the packet. The standard CSMA/CA delivers 92.37 % of
802.15.4g packet. The hybrid CSMA/CA delivers 95.77 % of

International Journal of Informatics Society, VOL.13, NO.2 (2021) 55-66

63

Table 4: Simulation parameters for IEEE 802.11ah and IEEE
802.15.4g coexistence performance
Parameters

Value [Unit]

Note

Network offered load
Network offered load
Tx Power
11ah Bandwidth
15.4g Bandwidth
aSlotTimeaSIFSTime
aCCATime
aRxTxTurnaroundTIme
CW (min, max)
phyCCADuration
aTurnaroundTime

20-40 kbps
20-40 kbps
20 mw
1 MHz
400 kHz
52 usec
160 usec<40 usec
Less than 5 usec
15, 1023
140 usec
1000 usec
300 usec or more,
1000 usec or lessLess than 300 usec1000 usec
1140 usec
5 ms
3 to 8 (Default 5)
0 to macMaxBE(Default 3)
0 to 5 (Default 4)
0 to 7 (Default 4)

11ah
15.4g
11ah & 15.4g
11ah
15.4g
11ah
11ah
11ah
11ah
11ah
15.4g
15.4g

Rx to Tx TrunaroundTime
Tx to Rx TurnaroundTIme
macMinLIFSPeriod
aUnitBackoffPeriod
macAckWaitDuration
macMaxBE
macMinBE
macMaxCSMABackoffs
macMaxFrameRetries

Figure 7: Scenario-1: Packet Delivery Rate

15.4g
15.4g
15.4g
15.4g
15.4g
15.4g
15.4g
15.4g
15.4g

802.15.4g packet, i.e., 3.4 % improvement without degrading
802.11ah packet delivery. Fig. 8 shows that packet latency forboth 802.11ah and 802.15.4g, Standard CSMA/CA achieves
shorter packet latency than the hybrid CSMA/CA due toless 802.15.4g packet delivered. 802.11ah has shorter packet
latency than 802.15.4g. In this case, the hybrid CSMA/CA
increases 802.11ah packet latency slightly.
Scenario-2: The offered load is 40 kbps for 802.11ah
network and 20 kbps for 802.15.4g network, i.e., the offeredload is 800 bps for 802.11ah node and 400 bps for 802.15.4g
node, which leads to 0.26 % duty cycle and 0.4 % duty cycle,
respectively. These duty cycles are much lower than the 10% duty cycle limit. Each 802.11ah node generates 1 packet
per second and each 802.15.4g node generates 0.5 packet per
second. Fig. 9 shows that both standard CSMA/CA andhybrid CSMA/CA deliver near 100 % of 802.11ah packet.
The hybrid CSMA/CA improves 802.15.4g packet delivery
rate from 86.2 % given by standard CSMA/CA to 90.7%. This 4.5 % improvement is done without degrading
802.11ah packet delivery. It indicates that as 802.11ah
network traffic increases, the hybrid CSMA/CA provides
more improvement on 802.15.4g packet delivery rate. Fig.
10 shows that 802.11ah and 802.15.4g have similar packet
latency. For 802.15.4g, standard CSMA/CA achieves slightly
shorter packet latency than the hybrid CSMA/CA due to less802.15.4g packet delivered. However, the hybrid CSMA/CA
maintain overall 802.11ah packet latency, i.e., the hybrid
CSMA/CA does not degrade 802.11ah performance.
Scenario-3: The offered load is 20 kbps for 802.11ah
network and 40 kbps for 802.15.4g network, i.e., the offeredload is 400 bps for 802.11ah node and 800 bps for 802.15.4g
node, which leads to 0.13 % duty cycle and 0.8 % duty cycle,
respectively. These duty cycles are much lower than the 10% duty cycle limit. Each 802.11ah node generates 0.5 packet
per second and each 802.15.4g node generates 1 packet per

Figure 8: Scenario-1: Packet Latency

second. Fig. 11 shows that both standard CSMA/CA andhybrid CSMA/CA deliver near 100 % of 802.11ah packet.
The hybrid CSMA/CA improves 802.15.4g packet delivery
rate from 59.8 % given by standard CSMA/CA to 61.3 %, i.e.,
1.5 % of improvement without degrading 802.11ah packet
delivery. It indicates that as 802.15.4g traffic increases, thehybrid CSMA/CA provides less improvement on 802.15.4g
packet delivery rate. Fig. 12 shows that 802.11ah delay
packet longer than 802.15.4g does due to high 802.15.4g
network traffic. For both 802.11ah and 802.15.4g, standard
CSMA/CA achieves slightly shorter packet latency than the
hybrid CSMA/CA due to less 802.15.4g packet delivered.
In this case, the hybrid CSMA/CA delays 802.11ah further
longer.
Scenario-4: In this case, each of 802.11ah network and802.15.4g network has 100 nodes. The offered load, the duty
cycle and the number of packet per second are same as in the
Scenario-2 of the 50-node scenario. Fig. 13 shows that bothstandard CSMA/CA and hybrid CSMA/CA deliver near 100% of 802.11ah packet. For 802.15.4g, the hybrid CSMA/CA
improves packet delivery rate from 86.1 % given by standard
CSMA/CA to 92.9 % without degrading 802.11ah packet
delivery rate. This 6.8 % improvement is better than 4.5% improvement in the Scenario-2 of 50-Node scenario.
Fig. 14 shows that 802.15.4g achieves lower packet latency
than 802.11ah. For 802.15.4g, the standard CSMA/CA
delays packet shorter than the hybrid CSMA/CA due to less802.15.4g packet delivered. For 802.11ah, however, thehybrid CSMA/CA achieves shorter packet delay than thestandard CSMA/CA does. This is because for the standard
CSMA/CA, the range of the 802.15.4g backoff period length

64

Y. Nagai et al. / Sub-1 GHz Wireless Coexistence of IEEE 802.15.4g and IEEE 802.11ah Using Hybrid CSMA/CA

Figure 9: Scenario-2: Packet Delivery Rate

Figure 11: Scenario-3: Packet Delivery Rate

Figure 10: Scenario-2: Packet Latency

Figure 12: Scenario-3: Packet Latency

is smaller, which results in more concentrated 802.15.4g
packet transmission and therefore, causes the longer delayof 802.11ah transmission. On the other hand, the hybrid
CSMA/CA allows the longer range of the 802.15.4g backoff
period, which spreads 802.15.4g transmission and gives
802.11ah opportunity to transmit early. Therefore, 802.11ah
achieves shorter packet delay. In this case, the hybrid
CSMA/CA not only improves 802.15.4g packet delivery rate
but also improves 802.11ah packet latency. This case also
demonstrates that as the number of network node increases,
the hybrid CSMA/CA becomes more effective.
Scenario-5: In this case, network size, the offered load,
the duty cycle and the number of packet per second aresame as in Scenario-4. The difference from Scenario-4 ispropagation model from Suburban NLoS model to Urban
NLoS Propagation model. Again, Fig 15 shows that bothstandard CSMA/CA and hybrid CSMA/CA deliver near 100% of 802.11ah packet. The standard CSMA/CA delivers
76.87 % of 802.15.4g packet. The hybrid CSMA/CA delivers
82.18 % of 802.15.4g packet, i.e., 5.31 % improvement
without degrading 802.11ah packet delivery. However, using
Urban NLoS model, both standard CSMA/CA and hybrid
CSMA/CA achieve lower packet delivery rate compared withthe corresponding results using Suburban NLoS model (ason Scenario-4) due to the higher node density, which causes
more channel access failure for 802.15.4g nodes. It indicatesthat as node density increases, 802.15.4g packet delivery
rate decreases. Fig. 16 shows that packet latency forboth 802.11ah and 802.15.4g, the standard CSMA/CA delays
packet less than the hybrid CSMA/CA due to more packet
drop by standard CSMA/CA. However, compared with the
Suburban NLoS mode case (as on Scenario-4), Urban NLoS

Table 5: Packet Delivery Rate Comparison

Scenario-1
Scenario-2
Scenario-3
Scenario-4
Scenario-5

802.11ah
Standard
Hybrid
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %
100 %

Standard
92.4 %
86.2 %
59.8 %
86.1 %
78.8 %

802.15.4g
Hybrid95.8 %
90.7 %
61.3 %
92.9 %
82.1 %

Diff.
3.4 %
4.5 %
1.5 %
6.8 %
5.3 %

model has shorter packet delay due to less 802.15.4g packet
delivery.
In summary of all network traffic and network size
scenarios, simulation results show that the proposed hybrid
CSMA/CA improves 802.15.4g packet delivery rate without
degrading 802.11ah packet delivery rate. In some case,it can improve performance of both 802.11ah network and802.15.4g network. As number of the node increases,
the hybrid CSMA/CA demonstrated more superiority. In
addition, the Suburban NLoS model outperforms Urban
NLoS model. Packet delivery rate of 802.11ah and 802.15.4g
for both standard 802.15.4g CSMA/CA and the proposed
hybrid CSMA/CA for 802.15.4g are shown in Table 5.

9

CONCLUSION

The heterogeneous wireless technologies developed for
IoT applications increase the coexistence potential andpresent coexistence challenges. This paper takes IEEE
802.15.4g and IEEE 802.11ah as target technologies toinvestigate the Sub-1 GHz band coexistence. We evaluated802.15.4g and 802.11ah coexistence behavior and identified
802.15.4g packet delivery rate and 802.11ah packet latency

International Journal of Informatics Society, VOL.13, NO.2 (2021) 55-66

65

Figure 13: Scenario-4: Packet Delivery Rate

Figure 15: Scenario-5: Packet Delivery Rate

Figure 14: Scenario-4: Packet Latency

Figure 16: Scenario-5: Packet Latency

as the coexistence issues to be addressed. Accordingly, we
proposed a hybrid CSMA/CA mechanism for 802.15.4g toachieve better coexistence with 802.11ah. To contend forchannel access with more aggressive 802.11ah, the hybrid
CSMA/CA allows 802.15.4g to perform immediate channel
access. Two classes of the distributed methods are introducedfor 802.15.4g devices to estimate the severity of 802.11ah
interference and switch the CSMA/CA mode for interference
mitigation. Using the developed Sub-1 GHz band coexistence
simulator with use case scenarios and parameters proposed byIEEE 802.19.3 Task Group, we conducted the performance
analysis of the proposed hybrid CSMA/CA. Compared withthe standard 802.15.4g CSMA/CA, simulation results showthat the hybrid CSMA/CA can improve 802.15.4g packet
delivery rate by 6.8% without degrading 802.11ah packet
delivery rate in our scenario. As the number of nodes in
the network traffic increases under the same conditions, thehybrid CSMA/CA can also reduce 802.11ah packet latency.

Amendment 3: Physical Layer (PHY) Specifications
for Low-Data-Rate, Wireless, Smart Metering Utility
Networks,” IEEE 802.15.4g-2012, IEEE, (2012).
[3] ARIB STD-T108,“920MHz-Band Telemeter,
Telecontrol and Data Transmission Radio Equipment,”
https://www.arib.or.jp/english/html/overview/doc/
5-STD-T108v1 0-E1.pdf, (2012).
[4] B. A. Rolfe, “PAR as approved by REVCOM Dec
2019,” IEEE802.19-18-0093r0, https://mentor.ieee.org/
802.19/documents/2018/ IEEE 802.19, (2018).
[5] Y. Nagai, J. Guo, T. Sumi, P. Orlik and H. Mineno,“Hybrid CSMA/CA for Sub-1 GHz Frequency Band
Coexistence of IEEE 802.11ah and IEEE 802.15.4g,”
14th International Workshop on Informatics (IWIN),INFSOC, (2020).
[6] J. Guo and P. Orlik, “Self-transmission control in IoTover heterogeneous wireless networks,” 2017 Ninth
International Conference on Ubiquitous and Future
Networks, pp. 898-903, Milan, (2017).
[7] Y. Liu, J. Guo, P. Orlik, Y. Nagai, K. Watanabe
and T. Sumi, “Coexistence of 802.11ah and 802.15.4g
networks,” 2018 IEEE Wireless Communications andNetworking Conference, pp. 1-6, Barcelona, (2018).
[8] W. Yuan, J. M. G. Linnartz and I. G. M. M. Niemegeers,“Adaptive CCA for IEEE 802.15.4 Wireless Sensor
Networks to Mitigate Interference,” 2010 IEEE WirelessCommunication and Networking Conference, Sydney,
NSW, pp. 1-5, (2010).
[9] E. D. N. Ndih and S. Cherkaoui, “Adaptive 802.15.4
backoff procedure to survive coexistence with 802.11 inextreme conditions,” 2016 13th IEEE Annual Consumer
Communications and Networking Conference, Las

REFERENCES[1] IEEE 802.11ah-2016, “IEEE Standard for Information
technology–Telecommunications and informationexchange between systems - Local and metropolitan
area networks–Specific requirements - Part 11: Wireless
LAN Medium Access Control (MAC) and PhysicalLayer (PHY) Specifications Amendment 2: Sub 1 GHz
License Exempt Operation,” IEEE 802.11ah-2016,
IEEE, 2016.
[2] IEEE 802.15.4g-2012, “IEEE Standard for Local
and metropolitan area networks–Part 15.4: Low-RateWireless Personal Area Networks (LR-WPANs)

66

Y. Nagai et al. / Sub-1 GHz Wireless Coexistence of IEEE 802.15.4g and IEEE 802.11ah Using Hybrid CSMA/CA

Vegas, NV, pp. 556-561, (2016).
[10] X. Zhang and K. G. Shin, “Enabling Coexistence ofHeterogeneous Wireless Systems: Case for ZigBee and
WiFi,” the 12 th ACM International Symposium on
Mobile Ad Hoc Networking and Computing, ACM,
(2011).
[11] J. Hou, B. Chang, D.-K. Cho, and M. Gerla,“Minimizing 802.11 Interference on Zigbee Medical
Sensors,” the Fourth International Conference on Body
Area Networks, ICST, (2009).
[12] J. W. Chong, C. H. Cho, H. Y. Hwang, and D. K. Sung,“An Adaptive WLAN Interference Mitigation Scheme
for ZigBee Sensor Networks,” International Journal ofDistributed Sensor Networks, vol. 11, no. 8, pp. 1-16,(2015).
[13] B. B. Olyaei, J. Pirskanen, O. Raeesi, A. Hazmi,
and M. Valkama, “Performance Comparison Between
Slotted IEEE 802.15.4 and IEEE802.11ah in loT Based
Applications,” in 1st International Workshop on Internetof Things Communications and Technologies, IEEE, pp.
332-337, (2013).
[14] R. Ma, S. Chen, H. Chen and W. Meng, “Coexistenceof Smart Utility Networks and WLANs in Smart
Grid Systems,” IEEE Transactions on WirelessCommunications, vol. 15, no. 12, pp. 8313-8324, (Dec.
2016).
[15] The ns-3 network simulator, http://www.nsnam.org/.
[16] L. Tian, L. Latre, and J. Famaey, “Implementation andvalidation of an IEEE 802.11ah module for NS-3,” inWorkshop in NS3, ACM, (2016).
[17] Y. Nagai, J. Guo, T. Sumi, P. Orlik, and H.
Mineno, “S1G Coexistence Simulation Profile,”
IEEE802.19-19-0021r2, https://mentor.ieee.org/802.19/
documents/2019/, IEEE 802.19, (May 2019).
(Received October 29, 2020)(Accepted July 6, 2021)

Yukimasa Nagai received B.E. degree and M.E.
degree in Information and Communication
Engineering
from
The
UniversityofElectro-Communications, Tokyo, Japan in1998 and 2000, respectively.
He has beenworking at Information Technology R&D Centerof Mitsubishi Electric Corporation (2000 2016, 2020- ) and Mitsubishi Electric ResearchLaboratories (2016 - 2020).
His research
work has covered various topics on wirelesscommunication systems, signal processing andconnected car, and he has acted as a key part of getting standardizationgroups formed in Wi-Fi Alliance and IEEE 802.11/15/19. Wi-Fi Alliance
DSRC MTG Vice Chair (2015 - 2018), Wi-Fi Alliance Automotive MSTG
Vice Chair (2013 - present), IEEE Senior member, and IPSJ member.

Jianlin Guo is a Senior Principal Research
Scientist at Mitsubishi Electric ResearchLaboratories in Cambridge, Massachusetts, USA.
He received his Ph.D. in Applied Mathematics
in 1995 from University of Windsor, Windsor,
Ontario, Canada. His research interests include
coexistence of the heterogeneous wirelessnetworks, time sensitive networking, edge
computing for vehicular networks, networked
control systems, anomaly detection in factory
automation, routing and resource management
in wireless IoT networks, and nonlinear stability of convection in porous
medium. He is IEEE Senior Member and IEEE 802.19.3 Task Group
Technical Editor.

Takenori Sumi received B.E. degree and M.E.
degree in Faculty of Engineering of Doshisha
University, Kyoto, Japan in 2005 and 2007,
respectively. He has been working as a seniorresearcher at Information Technology R&D
Center of Mitsubishi Electric Corporation from2007. His current research interests include
spectrum sharing, wireless coexistence and V2X.
He is also engaged in the Wi-Fi architect andnetwork architect for embedded system. IEEE
Senior member and IEICE member.

Philip Orlik received the B.E. degree in 1994
and the M.S. degree in 1997 both from the State
University of New York at Stony Brook. In 1999
he earned his Ph. D. in electrical engineering also
from SUNY Stony Brook. Since 2000 he has beenwith Mitsubishi Electric Research Laboratories
Inc. located in Cambridge, MA where he iscurrently the Manager of the Signal Processing
Group. His primary research focus is on advanced
wireless and wired communications, sensor/IoT
networks.
Other research interests include
vehicular/car-to-car communications, mobility modeling, performance
analysis, and queuing theory.

Hiroshi Mineno received his B.E. and M.E.
degrees from Shizuoka University, Japan in 1997
and 1999, respectively. In 2006, he received his
Ph.D. degree in information science and electricalengineering from Kyushu University, Japan.
Between 1999 and 2002, he was a researcher
in the NTT Service Integration Laboratories. In
2002, he joined the Department of Computer
Science of Shizuoka University as an AssistantProfessor. He is currently a Professor. His
research interests include Intelligent IoT systems
as well as heterogeneous network convergence. He is a senior member ofIEEE, IEICE and IPSJ, a member of ACM and the Informatics Society.