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Proceedings Articleβ€’DOIβ€’

Performance Analysis of Integrated Sub-6 GHz-Millimeter Wave Wireless Local Area Networks

TL;DR: Simulation results show that the proposed integrated mmW-sub 6 GHz MAC protocol yields significant performance gains, in terms of maximizing the saturation throughput and minimizing the delay experienced by the STAs.
Abstract: Millimeter wave (mmW) communications at the 60 GHz unlicensed band is seen as a promising approach for boosting the capacity of wireless local area networks (WLANs). If properly integrated into legacy IEEE 802.11 standards, mmW communications can offer substantial gains by offloading traffic from congested sub-6 GHz unlicensed bands to the 60 GHz mmW frequency band. In this paper, a novel medium access control (MAC) is proposed to dynamically manage the WLAN traffic over the unlicensed mmW and sub-6 GHz bands. The proposed protocol leverages the capability of advanced multi-band wireless stations (STAs) to perform fast session transfers (FST) to the mmW band, while considering the intermittent channel at the 60 GHz band and the level of congestion observed over the sub-6 GHz bands. The performance of the proposed scheme is analytically studied via a new Markov chain model and the probability of transmissions over the mmW and sub-6 GHz bands, as well as the aggregated saturation throughput are derived. In addition, analytical results are validated by simulation results. Simulation results show that the proposed integrated mmW-sub 6 GHz MAC protocol yields significant performance gains, in terms of maximizing the saturation throughput and minimizing the delay experienced by the STAs. The results also shed light on the tradeoffs between the achievable gains and the overhead introduced by the FST procedure.

SummaryΒ (2 min read)

Introduction

  • Such promising integrated mmW-πœ‡W protocols also provide substantial motivation to revisit the existing MAC solutions for traditional, yet important challenges of WLANs.
  • Simulation results are provided in Section IV.

II. MAC PROTOCOL INTEGRATION FOR MULTI-BAND

  • The contention-based medium access in the IEEE 802.11 DCF suffers from increased backoff time and excessive delays in congested scenarios [2], [3].
  • Prior to presenting the proposed scheme, the authors briefly overview some of the key definitions in the IEEE 802.11ad MAC protocol and 802.11 DCF that will be used in their analysis within the subsequent sections.
  • 1) sending directional beacon frames via an antenna sweeping mechanism, implemented within the beacon time interval (BTI), also known as 1. These modifications include.
  • The dynamic channel time allocation method includes a polling phase (PP) that enables STAs to request a channel time from the PCP/AP.
  • Moreover, the BC countdown is stopped, whenever the channel is sensed busy during a slot time.

C. Proposed Integrated MmW-Microwave MAC Protocol

  • The authors focus on the IEEE 802.11 DCF and IEEE 802.11ad dynamic channel time allocation, respectively, at the πœ‡W and mmW unlicensed bands.
  • Due to its omnidirectional MAC protocol, the DCF of IEEE 802.11 requires minimum coordination among STAs, which provides a fast and flexible medium access.
  • As the number of STAs increases, larger backoff times are required, resulting in more delay for packet transmissions.
  • The merit of using this control parameter will be elaborated in the next section.
  • This message is transferred over the 60 GHz band and FST is done once STA 1 receives the FST ACK Response frame from STA 2.

III. MODELING AND ANALYSIS OF THE PROPOSED MULTI-BAND MAC PROTOCOL

  • The authors present analytical results to evaluate the performance of the proposed multi-band MAC protocol.
  • First, the authors study the operation of an arbitrary STA that follows the proposed MAC protocol.
  • Then, the authors use these transmission probabilities to find a suitable expression for the saturation throughput.

A. Probability of Packet Transmission over mmW and πœ‡W Frequencies

  • In their analysis, the authors assume non-empty queues for all STAs, i.e., the network operates at a saturation condition.
  • In fact, while being at state (π‘š, 0), the STA can choose to either stay at the πœ‡W band and follow the DCF protocol or perform an FST to transmit over the mmW band.
  • Moreover, (1b) indicates that, after a successful packet transmission, an STA will randomly choose a BC from stage 0, i.e., π‘˜ is uniformly chosen from [0,π‘Š βˆ’ 1].
  • Furthermore, (1e) and (1f) indicate, respectively, that an STA will remain at stage π‘š with probability 1βˆ’π›½ after 2By choosing 𝛽 = 0, the proposed model will converge to the corresponding Markov chain for the conventional DCF in IEEE 802.11 standards.

B. Throughput Analysis of the Proposed Multi-band mmW-πœ‡W MAC Protocol

  • Next, the authors analyze the system throughput 𝑅 at the saturation conditions.
  • In multi-band WLANs, parallel streams of data can be sent simultaneously over different frequency bands.
  • In other words, only one STA can successfully transmit at a given time, otherwise, collision happens.
  • Clearly, there are (𝐽𝑒) distinct subsets with size 𝑒.
  • Therefore, the system throughput 𝑅 is calculated by finding the aggregated transmitted payload over both πœ‡W and mmW frequency bands, divided by the average time slot duration [𝑇 ] plus the time overhead associated with FST process: 𝑅 = 𝑃𝑠𝑃𝑑𝐡 πœ‡W + [𝐽mmW]𝐡mmW [𝑇 ] + [𝐽mmW]𝑇FST , (17) where π΅πœ‡W is the payload size over the πœ‡W frequency band.

IV. SIMULATION RESULTS

  • The authors validate their analytical results by simulating the proposed protocol in a multi-band WLAN.
  • From Fig. 4, the authors can see that the throughput increases as 𝛽 becomes large.
  • Interestingly, this performance gain is more evident for large network sizes, since the collision probability is higher and, thus, the proposed protocol sends more packets over the mmW band.
  • Stage π‘š and initiate FST to the mmW band.
  • Niemegeers, β€œPerformance analysis of IEEE 802.11ad MAC protocol,” IEEE Communications Letters, vol.

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Performance Analysis of Integrated
Sub-6 GHz-Millimeter Wave Wireless Local Area Networks
Omid Semiari
1
, Walid Saad
2
, Mehdi Bennis
3
, and Merouane Debbah
4
1
Department of Electrical Engineering, Georgia Southern University, Statesboro, GA, USA, Email: osemiari@georgiasouthern.edu
2
Wireless@VT, Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA, USA, Email: walids@vt.edu
3
Centre for Wireless Communications, University of Oulu, Finland, Email: bennis@ee.oulu.fi
4
Mathematical and Algorithmic Sciences Lab, Huawei France R&D, Paris, France, Email: merouane.debbah@huawei.com
Abstractβ€”Millimeter wave (mmW) communications at the 60
GHz unlicensed band is seen as a promising approach for
boosting the capacity of wireless local area networks (WLANs).
If properly integrated into legacy IEEE 802.11 standards, mmW
communications can offer substantial gains by offloading traffic
from congested sub-6 GHz unlicensed bands to the 60 GHz
mmW frequency band. In this paper, a novel medium access
control (MAC) is proposed to dynamically manage the WLAN
traffic over the unlicensed mmW and sub-6 GHz bands. The
proposed protocol leverages the capability of advanced multi-
band wireless stations (STAs) to perform fast session transfers
(FST) to the mmW band, while considering the intermittent
channel at the 60 GHz band and the level of congestion observed
over the sub-6 GHz bands. The performance of the proposed
scheme is analytically studied via a new Markov chain model
and the probability of transmissions over the mmW and sub-6
GHz bands, as well as the aggregated saturation throughput are
derived. In addition, analytical results are validated by simulation
results. Simulation results show that the proposed integrated
mmW-sub 6 GHz MAC protocol yields significant performance
gains, in terms of maximizing the saturation throughput and
minimizing the delay experienced by the STAs. The results also
shed light on the tradeoffs between the achievable gains and the
overhead introduced by the FST procedure.
I. INTRODUCTION
Advanced wireless stations (STAs) are capable of support-
ing multiple wireless local area network (WLAN) standards,
including legacy IEEE 802.11 over the sub-6 GHz (microwave)
unlicensed bands, as well as IEEE 802.11ad over the 60
GHz millimeter wave (mmW) band [1]. These modern STAs,
also known as tri-band WiGig devices, can potentially benefit
from high capacity mmW communications along with flexible,
simple, and more reliable networking at the sub-6 GHz bands.
Reaping the benefits of such a multi-band WLAN capability is
contingent upon adopting new medium access control (MAC)
protocols that can support flexible and dynamic traffic schedul-
ing over the aggregated mmW–microwave (πœ‡W) unlicensed
frequency bands
1
. Such promising integrated mmW-πœ‡Wpro-
tocols also provide substantial motivation to revisit the existing
MAC solutions for traditional, yet important challenges of
WLANs. One such problem is the excessive delay at the
contention-based medium access of the IEEE 802.11 standards
that prevents WLANs to meet the stringent quality-of-service
This research was supported by the U.S. National Science Foundation under
Grants CNS-1460316 and CNS-1526844, and by the ERC Starting Grant
305123 MORE.
1
Hereinafter, πœ‡W unlicensed band refers to either 2.4 GHz, 5 GHz, or both.
(QoS) requirements of emerging technologies, such as smart
home applications [2], [3].
The performance of IEEE 802.11 MAC protocols has been
thoroughly studied in the literature [4]–[8]. The seminal work
of Bianchi in [4] presents a comprehensive analysis for the
performance of the distributed coordination function (DCF)
of the IEEE 802.11. The authors in [5] study the modeling
and performance analysis of IEEE 802.11 DCF in unsaturated
scenarios with heterogeneous traffic arrival rates for STAs.
In [6], the authors propose a cooperative MAC protocol
that leverages spatial diversity across the network to increase
system throughput. The authors in [7] study the performance
of enhanced-DCF (EDCF) for IEEE 802.11e standard. More-
over, the work in [8] and references therein propose different
MAC protocols to improve QoS in IEEE 802.11. Although
interesting, the body of work in [4]–[8] solely focuses on the
WLAN standards at the πœ‡W unlicensed bands.
However, mmW communications over the 60 GHz unli-
censed band is one of the key enablers to support emerging
bandwidth-intensive technologies, such as virtual reality, in
WLANs [9]–[12]. In fact, the large available bandwidth at 60
GHz mmW band allows STAs to potentially achieve higher
data rates, compared with the data rates at the sub-6 GHz
unlicensed πœ‡W bands. However, mmW links are inherently
intermittent, due to extreme susceptibility of mmW signals
to blockage [13]. In addition, the challenges of bidirectional
transmissions at the 60 GHz band, such as deafness, increase
the complexity of MAC protocols.
In 2012, the IEEE 802.11ad standard [9] was introduced
as an amendment to IEEE 802.11 that enables bidirectional
transmissions over the unlicensed 60 GHz mmW frequency
band and support a variety of services with different QoS
requirements. In addition, this standard supports fast session
transfer (FST) that enables STAs to dynamically migrate from
one frequency band to another. This capability will enable
advanced multi-band STAs to jointly manage their traffic over
either 2.4, 5, or 60 GHz unlicensed frequency bands. The
performance of IEEE 802.11ad is studied in [10]–[12]. The
authors in [10] analyze the performance of IEEE 802.11ad
MAC protocol using a three-dimensional Markov chain model.
In [11], a directional cooperative scheme is proposed for
60 GHz mmW communications which is shown to improve
the system performance, compared with the standard IEEE
802.11ad. In [12], a throughput analysis of IEEE 802.11ad

Fig. 1: Beacon Interval structure [9].
under different modulation schemes is presented. The works
in [10]–[12] focus solely on performance analysis of the IEEE
802.11ad as a stand-alone system, although this standard has
been designed to coexist with legacy IEEE 802.11.
The main contribution of this paper is an integrated mmW-
πœ‡W MAC protocol that enables STAs to dynamically lever-
age the bandwidth available at the 60 GHz mmW band
and alleviate the excessive delay caused by the contention-
based medium access over the πœ‡W frequencies. In addition,
we present a comprehensive performance analysis for the
proposed protocol by adopting a Markov chain model for
backoff time that accommodates FST between mmW and πœ‡W
frequency bands. Furthermore, simulation results are provided
and shown to perfectly corroborate the derived analytical
results. Both analytical and simulation results show that the
proposed MAC protocol significantly increases the saturation
throughput and reduces the delay, compared with the legacy
IEEE 802.11 DCF. Moreover, the impact of different network
parameters, such as mmW link state, initial backoff window
size, and maximum backoff stage on the performance are
studied.
The rest of this paper is organized as follows. Section II
presents the proposed MAC protocol. Section III presents the
analytical results. Simulation results are provided in Section
IV. Section V concludes the paper.
II. MAC P
ROTOC OL INTEGRATION FOR MULTI-BAND
SUB-6 GHZANDMMW WLANS
The contention-based medium access in the IEEE 802.11
DCF suffers from increased backoff time and excessive delays
in congested scenarios [2], [3]. To alleviate this problem,
our goal is to leverage the multi-band operability of modern
STAs to avoid excessive backoff times for collided frames and
thus, decrease the associated contention delay for services in
WLANs. Prior to presenting the proposed scheme, we briefly
overview some of the key definitions in the IEEE 802.11ad
MAC protocol and 802.11 DCF that will be used in our
analysis within the subsequent sections.
A. IEEE 802.11AD MAC Protocol Overview
IEEE 802.11 standards, including IEEE 802.11ad, organize
the medium access using periodic recurring beacon intervals
(BIs). To accommodate bidirectional transmissions over the
60 GHz mmW band, some adjustments are introduced in
the IEEE 802.11ad BI structure, as shown in Fig. 1. These
modifications include: 1) sending directional beacon frames
via an antenna sweeping mechanism, implemented within the
beacon time interval (BTI). This sweeping process allows
to extend the communication range and resolve the issue
of STA discovery with unknown directions, 2) association
beamforming training (A-BFT) used by stations to train their
antenna sector for communication with the personal basic
service set (PBSS) control point (PCP)/access point (AP), and
3) the PCP/AP exchanges management information, including
scheduling, with beam-trained STAs prior to the data trans-
mission interval (DTI).
During DTI, three different medium access schemes are
supported, namely, 1) contention-based access, 2) scheduled
channel time allocation, and 3) dynamic channel time alloca-
tion. The first scheme which is conventional in IEEE 802.11
protocols allows STAs to access channel during contention-
based access periods (CBAPs). Two latter approaches are
based on time devision multiple access (TDMA) that dedicate
a service period (SP) to each pair of scheduled STAs. The
dynamic channel time allocation method includes a polling
phase (PP) that enables STAs to request a channel time from
the PCP/AP. The PCP/AP allocates the available channel time
according to these requests. This polling-based scheduling
mechanism is implemented within the beacon header interval
(BHI).
B. IEEE 802.11 DCF Overview
In this widely adopted protocol, STAs follow the contention-
based carrier-sense multiple access with collision avoidance
(CSMA/CA) scheme to reduce collisions [14]. That is, an
STA senses the channel prior to sending its packet. If channel
is sensed busy, the STA defers the transmission until the
channel is sensed idle for a DCF Interframe Space (DIFS)
time. Afterwards, the STA chooses a random backoff counter
(BC). Then, time is divided into slots and the BC will be
decremented after each idle slot time. Moreover, the BC
countdown is stopped, whenever the channel is sensed busy
during a slot time. The BC count down is reactivated once the
channel is sensed idle again for a DIFS. The STA sends its
packet immediately after BC reaches zero.
The BC is randomly selected from integers within an inter-
val [0, CW-1], where CW is called contention window. CW
depends on the number of transmissions failed for the packet.
Initially, CW is set equal to a value π‘Š , called minimum
contention window. After each unsuccessful transmission, π‘Š
is doubled, up to a maximum value of 2
π‘š
π‘Š . At this point, if
transmission fails again, the packet is either dropped or a new
BC is chosen randomly from [0, 2
π‘š
π‘Š βˆ’ 1].
C. Proposed Integrated MmW-Microwave MAC Protocol
In this work, we focus on the IEEE 802.11 DCF and IEEE
802.11ad dynamic channel time allocation, respectively, at
the πœ‡W and mmW unlicensed bands. In order to reduce the
excessive delay caused by the collisions at the IEEE 802.11
DCF, in this section, we propose a novel protocol that enables
STAs with multi-band capability to transfer their traffic to the
contention-free 60 GHz mmW band, whenever available, and
avoid intolerable large backoff times. The proposed protocol
is shown in Fig. 2. In this example scenario, STAs 1 and 2
are, respectively, the transmitting and receiving stations. The
communications between STAs 1 and 2 can be explained in
three following phases:

Fig. 2: Proposed Multi-Band MAC Protocol.
Phase 1: STA 1 aims to transmit its packet to STA 2, over
the πœ‡W band using a CSMA/CA scheme, as explained in Sec.
II-B. Due to its omnidirectional MAC protocol, the DCF of
IEEE 802.11 requires minimum coordination among STAs,
which provides a fast and flexible medium access. However,
as the number of STAs increases, larger backoff times are
required, resulting in more delay for packet transmissions. Ac-
cording to this protocol, STA 1 increases its backoff stage after
each unsuccessful transmission. After reaching the maximum
backoff stage π‘š, STA 1 initiates Phase 2 with probability 𝛽
and remains in Phase 1 with probability 1 βˆ’ 𝛽.Themerit
of using this control parameter will be elaborated in the next
section.
Phase 2: In this phase, STA 1 initiates an FST with STA 2.
FST capability is introduced in the IEEE 802.11ad Extended
version [9] that enables STAs to swiftly move their traffic from
one transmission band/channel to another. Since the FST is
managed at a separate control channel, it will not be prone to
collisions at the data channel. As shown in Fig. 2, to invoke
FST, the station management entity (SME) unit in STA 1 sends
an FST Setup Request to the πœ‡W MAC layer management
entity (MLME), followed by informing the STA 1’s MAC
to forward the FST Setup Request frame to STA 2. Then, a
handshaking procedure is done between STAs 1 and 2 in which
STA 2 confirms that it is ready to move the communication
to the 60 GHz band. Up to this stage, the control messages
between STAs 1 and 2 are exchanged at the πœ‡W band. Next,
an FST ACK Request is initiated by the STA 1’s mmW MLME
to request an FST ACK frame from STA 2. This message is
transferred over the 60 GHz band and FST is done once STA
1 receives the FST ACK Response frame from STA 2.
Here, we note that the FST procedure i s revoked if STA 1
does not receive ACK frames in any stage during Phase 2. This
can happen if the link between STAs 1 and 2 is blocked by
an obstacle, or A-BFT is failed. In that case, STA 1 continues
following the CSMA/CA in Phase 1.
Phase 3: This phase starts with the next BI of the IEEE
802.11ad, in which STA 1 participates in the polling within PP
of BI and requests a contention-free time for communication
with STA 2, as elaborated in Sec. II-A. Next, STA 1 will
transmit its packet to STA 2 during the allocated SP in DTI.
Afterwards, STA 1 will reset its CW to the minimum value
π‘Š and it will initiate Phase 1.
The proposed multi-band MAC benefits from the flexible
and simple CSMA/CA protocol at the πœ‡W unlicensed bands,
while preventing excessive delays caused by the contention-
based medium access. Next, we present analytical results to
evaluate the performance of the proposed MAC protocol.
III. M
ODELING AND ANALYSIS OF THE PROPOSED
MULTI-BAND MAC PROT OCO L
In this section, we present analytical results to evaluate
the performance of the proposed multi-band MAC protocol.
First, we study the operation of an arbitrary STA that follows
the proposed MAC protocol. In particular, we determine the
probability of packet transmissions over either mmW or πœ‡W
frequencies at a randomly chosen time slot. Then, we use these
transmission probabilities to find a suitable expression for the
saturation throughput.
A. Probability of Packet Transmission over mmW and πœ‡W
Frequencies
In our analysis, we assume non-empty queues for all STAs,
i.e., the network operates at a saturation condition. As such, a
new packet will be ready for transmission immediately after
each successful transmission. These consecutive transmissions
will require each STA transmitting over the πœ‡W frequency
band to wait for a random backoff time prior to sending the
next packet. In this regard, let 𝑏( 𝑑) be the stochastic process
for the BC of an arbitrary STA. A discrete and integer time
scale is adopted in which 𝑑 and 𝑑 +1 present the beginning
of two consecutive slot times, and the BC of each STA is
decremented at the beginning of each slot time. According
to the works in [4] and [5], the DCF of IEEE 802.11 can
be modeled as a two-dimensional discrete-time Markov chain
(𝑠(𝑑),𝑏(𝑑)), where 𝑠(𝑑) ∈{0, 1, β‹…β‹…β‹…π‘š} represents the backoff
stage of an STA at time 𝑑, with π‘š being the maximum backoff
stage. For an arbitrary backoff stage 𝑠( 𝑑)=𝑖, the CW will be
π‘Š
𝑖
=2
𝑖
π‘Š . In such Markov chain models, it is collectively
assumed that, regardless of state, a collision occurs with a
constant and independent probability 𝑝 as concretely discussed
in [4] and [5].
To study the performance of the proposed protocol, we
adopt a Markov chain model, as shown in Fig. 3, where each
state (𝑖, π‘˜ ) indicates that 𝑠(𝑑)=𝑖 and 𝑏(𝑑)=π‘˜, i.e., the BC of
an STA is at the π‘˜-th step of stage 𝑖. In addition, by introducing
anewstate Λ†π‘š, this model captures the capability of multi-band
STAs to operate at the mmW frequency band. In fact, while
being at state (π‘š, 0), the STA can choose to either stay at the
πœ‡W band and follow the DCF protocol or perform an FST to
transmit over the mmW band. We note that performing FST
by an arbitrary STA 𝑗 does not alter the collision probability
𝑝 for other packets, since the next backlogged packet of STA

Fig. 3: Markov Chain model for the backoff window size
𝑗 will be ready to be sent over the πœ‡W frequency band. In this
model, 𝛽 ∈ [0, 1] is a control parameter that allows an STA
to manage unnecessary FSTs to reduce signaling overhead or
avoid the mmW frequency band whenever the transmission of
a number of previous packets has failed, due to unsuccessful
A-BFTs. Moreover, 𝛽 provides backward compatibility for
legacy STAs with no mmW communications capability
2
.The
state of each mmW link is determined by a Bernoulli random
variable πœ‚ with success probability 𝛼. That is, with probability
𝛼
𝑗
, a transmitting STA 𝑗 and its desired receiving STA can
successfully perform the A-BFT and execute the transmission.
Here, the single-step nonzero transition probabilities are
{𝑖, π‘˜βˆ£π‘–, π‘˜ +1} =1,π‘–βˆˆ [0,π‘š],π‘˜ ∈ [0,π‘Š
𝑖
βˆ’2],(1a)
{0,π‘˜βˆ£π‘–, 0} = 𝑝
β€²
/π‘Š
0
,π‘–βˆˆ [0,π‘š] βˆͺ{Λ†π‘š} ,π‘˜ ∈ [0,π‘Š
0
βˆ’1],(1b)
{π‘š, π‘˜βˆ£ Λ†π‘š} =(1βˆ’ 𝛼)/π‘Š
π‘š
,π‘˜βˆˆ [0,π‘Š
π‘š
βˆ’1],(1c)
{𝑖, π‘˜βˆ£π‘– βˆ’ 1, 0} = 𝑝/π‘Š
𝑖
,π‘–βˆˆ [1,π‘š],π‘˜ ∈ [0,π‘Š
𝑖
βˆ’1],(1d)
{π‘š, π‘˜βˆ£π‘š, 0} = 𝑝(1 βˆ’ 𝛽)/π‘Š
π‘š
,π‘˜βˆˆ [0,π‘Š
π‘š
βˆ’1],(1e)
{ Λ†π‘šβˆ£π‘š, 0} = 𝛽𝑝, (1f)
where (1a) shows the backoff time count down at each time
slot. Moreover, (1b) indicates that, after a successful packet
transmission, an STA will randomly choose a BC from stage
0, i.e., π‘˜ is uniformly chosen from [0,π‘Š βˆ’ 1]. In (1b), 𝑝
β€²
is
equal to 1 βˆ’ 𝑝 and 𝛼, respectively, if 𝑖 ∈ [0,π‘š] and 𝑖 =Λ†π‘š.
In addition, (1c) captures an unsuccessful mmW transmission,
after which the STA will remain at the πœ‡W frequency band
and will choose a random backoff time at stage π‘š. (1d) shows
that backoff stage will incremented after an unsuccessful πœ‡W
transmission. Furthermore, (1e) and (1f) indicate, respectively,
that an STA will remain at stage π‘š with probability 1βˆ’π›½ after
2
By choosing 𝛽 =0, the proposed model will converge to the correspond-
ing Markov chain for the conventional DCF in IEEE 802.11 standards.
a collision, or will perform an FST with probability 𝛽.
For this Markov chain model, we next determine the station-
ary probability for each state (𝑖, π‘˜).Letβ„Ž
𝑖,π‘˜
= lim
π‘‘β†’βˆž
{𝑠(𝑑)=
𝑖, 𝑏(𝑑)=π‘˜}, 𝑖 ∈ [0,π‘š] βˆͺ{Λ†π‘š}, π‘˜ ∈ [0,π‘Š
𝑖
βˆ’ 1].Fromthe
Markov chain model in Fig. 3, it is easy to see that
β„Ž
𝑖,0
= π‘β„Ž
π‘–βˆ’1,0
= 𝑝
𝑖
β„Ž
0,0
,π‘–βˆˆ (0,π‘š). (2)
Furthermore, for 𝑖 = π‘š and Λ†π‘š, we note that
π‘β„Ž
π‘šβˆ’1,0
+ 𝑝(1 βˆ’ 𝛽)β„Ž
π‘š,0
+(1βˆ’ 𝛼)β„Ž
Λ†π‘š
= β„Ž
π‘š,0
, (3a)
π‘π›½β„Ž
π‘š,0
= β„Ž
Λ†π‘š
. (3b)
Using (2), we solve (3a) and (3b) with respect to β„Ž
π‘š,0
and
β„Ž
Λ†π‘š
, which yields
β„Ž
π‘š,0
=
𝑝
π‘š
1 βˆ’ 𝑝 + 𝛼𝛽𝑝
β„Ž
0,0
,β„Ž
Λ†π‘š
=
𝛽𝑝
π‘š+1
1 βˆ’ 𝑝 + 𝛼𝛽𝑝
β„Ž
0,0
. (4)
Next, by following the chain regularities, we can represent the
remaining stationary state probabilities as:
β„Ž
𝑖,π‘˜
= π‘Š
β€²
𝑖
ξ˜‚
ξ˜ƒ
ξ˜„
ξ˜ƒ
ξ˜…
1βˆ’π‘
π‘Š
0
ξ˜†
π‘š
𝑗=0
β„Ž
𝑗,0
+
𝛼
π‘Š
0
β„Ž
Λ†π‘š
,𝑖=0,
𝑝
π‘Š
π‘š
β„Ž
π‘šβˆ’1,0
+
𝑝(1βˆ’π›½)
π‘Š
π‘š
β„Ž
π‘š,0
+
1βˆ’π›Ό
π‘Š
π‘š
β„Ž
Λ†π‘š
,𝑖= π‘š,
𝑝
π‘Š
𝑖
β„Ž
π‘–βˆ’1,0
,π‘–βˆˆ (0,π‘š),
(5)
where π‘Š
β€²
𝑖
= π‘Š
𝑖
βˆ’ π‘˜, and π‘˜ ∈ (0,π‘Š
𝑖
βˆ’ 1]. In addition, we
note that
β„Ž
0,0
=(1βˆ’ 𝑝)
π‘š
ξ˜‡
𝑗=0
β„Ž
𝑗,0
+ π›Όβ„Ž
Λ†π‘š
. (6)
Thus, by using (2), (3a), and (6), β„Ž
𝑖,π‘˜
in (5) simplifies to:
β„Ž
𝑖,π‘˜
=
π‘Š
𝑖
βˆ’ π‘˜
π‘Š
𝑖
β„Ž
𝑖,0
,π‘–βˆˆ [0,π‘š],π‘˜ ∈ (0,π‘Š
𝑖
βˆ’ 1]. (7)
Finally, we find β„Ž
0,0
by noting that the sum of all state
probabilities is 1. That is,
1=
π‘š
ξ˜‡
𝑖=0
π‘Š
𝑖
βˆ’1
ξ˜‡
π‘˜=0
β„Ž
𝑖,π‘˜
+ β„Ž
Λ†π‘š
(8)
(a)
=
π‘š
ξ˜‡
𝑖=0
β„Ž
𝑖,0
π‘Š
𝑖
βˆ’1
ξ˜‡
π‘˜=0
π‘Š
𝑖
βˆ’ π‘˜
π‘Š
𝑖
+ β„Ž
Λ†π‘š
,
(b)
=
π‘šβˆ’1
ξ˜‡
𝑖=0
β„Ž
𝑖,0
π‘Š
𝑖
+1
2
+
π‘Š
π‘š
+1
2
𝑏
π‘š,0
+ β„Ž
Λ†π‘š
,
(c)
=

π‘šβˆ’1
ξ˜‡
𝑖=0
(π‘Š
𝑖
+1)𝑝
𝑖
+
(π‘Š
π‘š
+1)𝑝
π‘š
1 βˆ’ 𝑝 + 𝛼𝛽𝑝
+
2𝛽𝑝
π‘š+1
1 βˆ’ 𝑝 + 𝛼𝛽𝑝
ξ˜‰
β„Ž
0,0
2
.
In (8), (a) and (b) result from (7) and noting that
ξ˜†
π‘Š
𝑖
βˆ’1
π‘˜=0
(π‘Š
𝑖
βˆ’
π‘˜)/π‘Š
𝑖
=(π‘Š
𝑖
+1)/2, respectively. In addition, (c) results from
(2) and (4). From (8), we can find β„Ž
0,0
as follows:
β„Ž
0,0
=2

π‘Š
ξ˜‹
1 βˆ’ (2𝑝)
π‘š
1 βˆ’ 2𝑝

+
1 βˆ’ 𝑝
π‘š
1 βˆ’ 𝑝
+
(2
π‘š
π‘Š +1+2𝛽𝑝)𝑝
π‘š
1 βˆ’ 𝑝 + 𝛼𝛽𝑝

βˆ’1
. (9)
Next, we can compute the transmission probability over the
πœ‡W band, Θ
πœ‡W
, for an STA in a random time slot. To this
end, we note that πœ‡W transmission occurs only if the backoff
time countdown for an STA reaches zero. That is, an STA

transmits a packet if it is at any states (𝑖, 0),𝑖 ∈ [0,π‘š]. Thus,
Θ
πœ‡W
=
π‘š
ξ˜‡
𝑖=0
β„Ž
𝑖,0
=
1
1 βˆ’ 𝑝

1 βˆ’
𝛼𝛽𝑝
π‘š+1
1 βˆ’ 𝑝 + 𝛼𝛽𝑝

β„Ž
0,0
. (10)
Remark 1. Without mmW communications (𝛽 =0), we can
easily verify that Θ
πœ‡W
in (10) simplifies to
Θ
πœ‡W
=
2(1 βˆ’ 2𝑝)
(1 βˆ’ 2𝑝)(π‘Š +1)+π‘π‘Š (1 βˆ’ (2𝑝)
π‘š
)
, (11)
which is shown to be the transmission probability in DCF
protocol of the IEEE 802.11 [4].
Over the mmW frequency band, STAs that are in state
Λ†π‘š will be scheduled to transmit within the next available
DTI. Given that the mmW transmissions follow a TDMA
scheme during each SP, as proposed in IEEE 802.11ad, no
collision will happen. However, as mentioned in section II-A,
a mmW transmission is contingent upon a successful A-BFT
phase. Hence, the probability of transmission over the mmW
frequency band is
Θ
mmW
= {πœ‚ =1}β„Ž
Λ†π‘š
=
𝛼𝛽𝑝
π‘š+1
1 βˆ’ 𝑝 + 𝛼𝛽𝑝
β„Ž
0,0
. (12)
After deriving the transmission probability at both mmW and
πœ‡W frequencies for an arbitrary STA, our next step is to com-
pute the saturation throughput as a key performance metric.
B. Throughput Analysis of the Proposed Multi-band mmW-πœ‡W
MAC Protocol
Next, we analyze the s ystem throughput 𝑅 at the saturation
conditions. This throughput is defined as the average payload
that is successfully transmitted across the network during a
randomly chosen time slot, divided by the average time slot
duration [𝑇 ]. In multi-band WLANs, parallel streams of data
can be sent simultaneously over different frequency bands.
Thus, our analysis will focus on finding the throughput across
the aggregated mmW-πœ‡W frequencies.
Consider a WLAN, composed of 𝐽 STAs within a set π’₯ .
Over the πœ‡W frequency band, the protocol follows the standard
CSMA/CA. In other words, only one STA can successfully
transmit at a given time, otherwise, collision happens. In this
regard, 𝑃
πœ‡W
𝑑
is defined as the probability that at least one STA
is transmitting over the πœ‡W frequency band. Since each STA
𝑗 ∈π’₯ transmits with probability Θ
πœ‡W
𝑗
, 𝑃
πœ‡W
𝑑
is given by:
𝑃
πœ‡W
𝑑
=1βˆ’

π‘—βˆˆπ’₯
(1 βˆ’ Θ
πœ‡W
𝑗
). (13)
In addition, transmission of an arbitrary STA 𝑗 is successful,
if no other STA transmits at the same time. Hence, the
probability of successful transmission can be written as:
𝑃
πœ‡W
𝑠
=
ξ˜†
π‘—βˆˆπ’₯
Θ
πœ‡W
𝑗

𝑗
β€²
∈π’₯ βˆ–π‘—
(1 βˆ’ Θ
πœ‡W
𝑗
β€²
)
𝑃
πœ‡W
𝑑
. (14)
To compute [𝑇 ], we note that there are three possible cases
for the transmission scenarios over the πœ‡W band: 1) having
an empty slot which occurs with probability 1 βˆ’ 𝑃
πœ‡W
𝑑
, since
no STA is transmitting. 2) Successful transmission of a packet
during a time slot which happens with probability 𝑃
πœ‡W
𝑑
𝑃
πœ‡W
𝑠
,
and 3) collision scenario that occurs with probability 𝑃
πœ‡W
𝑑
(1βˆ’
TABLE I: Simulation parameters
Notation Parameter Value
𝐻
MAC
MAC header 272 bits
𝐻
PHY
PHY header 128 bits
𝐡
πœ‡W
πœ‡W packet payload 8184 bits
𝐡
mmW
mmW packet payload 81840 bits
ACK ACK 112 bits + PHY header
𝛿 Propagation delay 1 πœ‡s
𝜎 Slot time 50 πœ‡s
SIFS Short interframe space 28 πœ‡s
DIFS Distributed interframe space 128 πœ‡s
π‘Ÿ
πœ‡W
πœ‡W channel bit rate 1 Mbps
π‘Ÿ
mmW
mmW channel bit rate 1 Gbps
SETUP REQ FST setup request 240 bits
SETUP RES FST setup response 240 bits
𝑃
πœ‡W
𝑠
). Hence, the average slot time is
[𝑇 ]=(1βˆ’π‘ƒ
πœ‡W
𝑑
)𝜎+𝑃
πœ‡W
𝑑
𝑃
πœ‡W
𝑠
𝑇
𝑠
+𝑃
πœ‡W
𝑑
(1 βˆ’ 𝑃
πœ‡W
𝑠
)𝑇
𝑐
, (15)
where 𝑇
𝑠
, 𝑇
𝑐
, and 𝜎 denote the slot time duration, respectively,
in successful, collision, and no transmission scenarios.
For mmW transmissions, we must note that only FST is
performed over the πœ‡W band, while other phases during
BHI as well as payload transmissions in DTI will be done
simultaneously with the πœ‡W band transmissions. To properly
capture the mmW band contribution in the system throughput,
we consider the time overhead associated with performing FST
and we find the average number of STAs that can be scheduled
at the mmW frequency band within a coarse of [𝑇 ] time.
In this regard, let
Λ†
𝐽 ≀ 𝐽 be the maximum number of STAs
that can be scheduled over the mmW band during [𝑇 ], each
transmitting a payload of size 𝐡
mmW
bits. Considering π‘Ÿ
mmW
as the mmW channel bit rate,
Λ†
𝐽 = ⌊ [𝑇 ]π‘Ÿ
mmW
/𝐡
mmW
βŒ‹, where
⌊.βŒ‹ is the floor operand. Consequently, the average number of
STAs transmitting at the mmW frequency band, [𝐽
mmW
],is
[𝐽
mmW
]=
Λ†
𝐽
ξ˜‡
𝑒=1
(
𝐽
𝑒
)
ξ˜‡
𝑠=1
∣π’₯
β€²
∣=𝑒

𝑗=1
Θ
mmW
𝑗
, (16)
where the inner sum is done over all possible subsets π’₯
β€²
βŠ†π’₯
with ∣π’₯
β€²
∣ = 𝑒 number of STAs. Clearly, there are

𝐽
𝑒
ξ˜‘
distinct
subsets with size 𝑒. Moreover, the product is for all STAs in
the chosen subset π’₯
β€²
. In addition, since the protocol employs
TDMA scheme for mmW communications, no collision will
occur between multiple mmW transmissions during a DTI and
the probability of successful transmission is 𝑃
mmW
𝑠
=1.
Therefore, the system throughput 𝑅 is calculated by finding
the aggregated transmitted payload over both πœ‡W and mmW
frequency bands, divided by the average time slot duration
[𝑇 ] plus the time overhead associated with FST process:
𝑅 =
𝑃
𝑠
𝑃
𝑑
𝐡
πœ‡W
+[𝐽
mmW
]𝐡
mmW
[𝑇 ]+ [𝐽
mmW
]𝑇
FST
, (17)
where 𝐡
πœ‡W
is the payload size over the πœ‡W frequency band.
Given the high available bandwidth at the mmW band, 𝐡
mmW
is considered larger than 𝐡
πœ‡W
. Moreover, 𝑇
FST
is the required
time for performing an FST.
IV. S
IMULATION RESULTS
We validate our analytical results by simulating the pro-
posed protocol in a multi-band WLAN. The number of STAs
varies from 𝐽 =5to 50. The considered network is simulated
in MATLAB and the total simulation time extends to 500 sec-

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11 May 2003
TL;DR: The contention-based channel access mechanism, called enhanced distributed coordination function (EDCF), in comparison with the ECDF, is evaluated and it is concluded that the EDCF can provide differentiated channel access for different traffic types.
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Journal Articleβ€’DOIβ€’
TL;DR: This article surveys 802.11 QoS schemes, including service differentiation in the MAC layer, admission control and bandwidth reservation in MAC and higher layers, and link adaptation in the physical layer, designed to meet challenges by providing the necessary enhancements for the required QoS.
Abstract: Developed as a simple and cost-effective wireless technology for best effort services, IEEE 802.11 has gained popularity at an unprecedented rate. However, due to the lack of built-in quality of service support, IEEE 802.11 experiences serious challenges in meeting the demands of multimedia services and applications. This article surveys 802.11 QoS schemes, including service differentiation in the MAC layer, admission control and bandwidth reservation in MAC and higher layers, and link adaptation in the physical layer, designed to meet these challenges by providing the necessary enhancements for the required QoS. Furthermore, the article addresses issues that arise when end-to-end QoS has to be guaranteed in today's pervasive heterogeneous wired-cum-wireless networks. Among these challenges, protocol interoperability, multihop scheduling, full mobility support, and seamless vertical handoff among multiple mobile/wireless interfaces are specifically addressed.

316Β citations


"Performance Analysis of Integrated ..." refers background in this paper

  • ...Although interesting, the body of work in [4]–[8] solely focuses on the WLAN standards at the ΞΌW unlicensed bands....

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  • ...Moreover, the work in [8] and references therein propose different...

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  • ...thoroughly studied in the literature [4]–[8]....

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Frequently Asked Questions (1)
Q1. What have the authors contributed in "Performance analysis of integrated sub-6 ghz-millimeter wave wireless local area networks" ?

In this paper, a novel medium access control ( MAC ) is proposed to dynamically manage the WLAN traffic over the unlicensed mmW and sub-6 GHz bands.Β The performance of the proposed scheme is analytically studied via a new Markov chain model and the probability of transmissions over the mmW and sub-6 GHz bands, as well as the aggregated saturation throughput are derived.Β The results also shed light on the tradeoffs between the achievable gains and the overhead introduced by the FST procedure.Β