=Paper=
{{Paper
|id=Vol-1689/paper7
|storemode=property
|title=Performance Study of Frame Aggregation Mechanisms in the New Generation WiFi
|pdfUrl=https://ceur-ws.org/Vol-1689/paper7.pdf
|volume=Vol-1689
|authors=Mohand Yazid,Louiza Bouallouche-Medjkoune,Djamil Aïssani
|dblpUrl=https://dblp.org/rec/conf/vecos/YazidBA16
}}
==Performance Study of Frame Aggregation Mechanisms in the New Generation WiFi ==
https://ceur-ws.org/Vol-1689/paper7.pdf
Performance Study of Frame Aggregation
Mechanisms in the New Generation WiFi
Mohand Yazid Louiza Medjkoune-Bouallouche Djamil Aı̈ssani
Research Unit LaMOS Research Unit LaMOS Research Unit LaMOS
Faculty of Exact Sciences Faculty of Exact Sciences Faculty of Exact Sciences
University of Bejaia University of Bejaia University of Bejaia
06000 Bejaia, Algeria 06000 Bejaia, Algeria 06000 Bejaia, Algeria
yazid.mohand@gmail.Com louiza medjkoune@yahoo.fr lamos bejaia@hotmail.com
The new generation WiFi (Widely Fidelity), which is called 802.11ac, has the goal of reaching at least 1 Gbps
on bands below 6 GHz. This is why, the standard has been extended with new features at both PHYsical
(PHY) and Medium Access Control (MAC) layers level. One of the key features of MAC layer is the ability of
aggregating frames in order to reduce temporal overheads that significantly harm the performance of 802.11
networks. Three forms of aggregation exist, namely Aggregate MAC Service Data Unit (A-MSDU), Aggregate
MAC Protocol Data Unit (A-MPDU) and hybrid A-MSDU/A-MPDU Aggregation (A-hybrid). In this paper, we
study the impact of Frame Aggregation Mechanisms (FAMs) for improving the overall throughput of 802.11ac
networks. Furthermore, we highlight the need of PHY/MAC cross-layer communications for optimizing the
wireless bandwidth utilization. Simulation results demonstrate the gains offered by the FAMs.
IEEE 802.11ac, Frame Aggregation Mechanisms, Physical Data Rates, Simulation and Performance Study.
1. INTRODUCTION Several key enhancements have been proposed to
both the PHY and MAC layers of the IEEE 802.11ac
More than any time ever before, today technology standard in order to reach gigabit throughput rates
has a significant impact on people’s lives. The pro- (Charfi et al. (2013)). On the one hand, substantial
liferation of slim, mobile, and portable devices such modifications are required at the PHY layer in order
as notebooks, ultrabooks, tablets, and smartphones to increase the PHY data rates (Ismail el. (2013)).
is a clear testament to the importance of wireless On the other hand, the IEEE 802.11ac standard
communications in modern society (Cordeiro et al. specifies the use of different Frame Aggregation
(2013)). The most notable example of wireless sys- Mechanisms (FAMs) at the MAC layer level in
tems with data rates greater than 1 Gbps, includes order to increase the channel utilization and MAC
the IEEE 802.11ac amendment to the base IEEE efficiency (Charfi et al. (2012)). The IEEE 802.11ac
802.11 standard (IEEE 802.11ac Standard (2013)). standard boasts better MAC layer efficiency through
Several companies have announced products imple- innovative mechanisms such as Frame Aggregation
menting this technology, with a few of those prod- (FA) and Block Acknowledgment (ACK) (Yazid et al.
ucts already available, or soon to be available, to (2015)). Three forms of aggregation exist, namely:
consumers (Cordeiro et al. (2013)). The data rates Aggregate MAC Service Data Unit (A-MSDU),
provided by IEEE 802.11ac can meet the needs of Aggregate MAC Protocol Data Unit (A-MPDU) and
many applications, with replacement of Wired Digital hybrid A-MSDU/A-MPDU Aggregation (A-hybrid).
Interface (WDI) cables arguably the most promi- These involve aggregating several MPDU/MSDU
nent new use of this technology. To this end, the frames (called sub-frames) into one larger frame,
IEEE 802.11ac Task Group (TGac) is working on an and as a result only require a single MAC layer
amendment that has the goal of reaching maximum header for it to be accepted by the PHY layer
aggregate network throughputs of at least 1 Gbps (Al-Adhami et al. (2012)). Thus, the laborious
on bands below 6 GHz (Yazid et al. (2014)). Due to channel access of the Carrier Sense Multiple Access
the significant rate increase achieved by 802.11ac, with Collision Avoidance (CSMA/CA) protocol is
the term Very High Throughput (VHT) is also used considerably reduced by the sharing of the PHY
in reference to this new amendment (Bejarano et al. header and channel access mechanism among the
(2013)). MPDUs of the A-MPDU. Hence, the MAC layer
Performance Study of Frame Aggregation Mechanisms
Yazid • Bouallouche-Medjkoune • Aı̈ssani
efficiency is considerably improved (Redieteab et al. followed by the MSDU arrived from the Logical Link
(2012)). Control (LLC) layer and 0-3 bytes of padding. A
major drawback of using A-MSDU is under error-
The main contribution of this paper is to analyze prone channels. By compressing all MSDUs into a
the potential benefits in terms of MAC throughput single MPDU with a single Frame Check Sequence
gains of IEEE 802.11ac WLANs over various (FCS), for any MSDUs that are corrupted, the entire
Frame Aggregation Mechanisms and practical PHY A-MSDU must be retransmitted (Skordoulis et al.
data rates. In the same way, we highlight the (2008)).
need to cross-layer communications between the
PHY and MAC layers in order to increase the
efficiency of the wireless channel utilization. In
addition, we demonstrate that hybrid A-MSDU/A-
MPDU aggregation yields the best throughput for the
IEEE 802.11ac WLANs.
The reminder of this paper is organized as follows:
Section 2 presents the different mechanisms of
Frame Aggregation introduced in the IEEE 802.11ac
standard. Section 3 gives a review of existing studies
on Frame Aggregation Mechanisms. Simulation Figure 1: Aggregate MSDU.
results and performance analysis are presented
in Section 4. Finally, our main conclusions are 2.2. Aggregate MPDU
summarized in Section 5.
The concept of A-MPDU aggregation is to join
multiple MPDUs with a single leading PHY header.
2. FRAME AGGREGATION MECHANISMS
A key difference from A-MSDU aggregation is that A-
There are three methods available to perform frame MPDU operates after the MAC header encapsulation
aggregation: Aggregate MAC Service Data Unit (A- process. The utmost number of MPDUs that it can
MSDU), Aggregate MAC Protocol Data Unit (A- hold is 64 because a Block ACK bitmap field is 128
MPDU) and hybrid A-MSDU/A-MPDU Aggregation bytes in length, where each MPDU is mapped using
(A-hybrid) (Charfi et al. (2012)). The main distinction two bytes (Charfi et al. (2012)). The basic structure
between an MSDU and an MPDU is that the former is shown in Figure 2.
corresponds to the information that is imported to
or exported from the upper part of the MAC layer A set of fields, known as MPDU header is inserted
from or to the higher layers, respectively. Whereas, before each MPDU and padding bits varied from 0-3
the latter relates to the information that is exchanged bytes are added at the tail. The basic operation of the
from or to the PHY layer by the lower part of the MAC MPDU header is to define the MPDU position and
layer. Aggregate exchange sequences are made length inside the A-MPDU. The Cyclic Redundancy
possible with a protocol that acknowledges multiple Check (CRC) field in the MPDU header is used to
MPDUs with a single Block ACK (BA) in response verify the authenticity of the 16 preceding bits. After
to a Block ACK Request (BAR) (Skordoulis et al. the A-MPDU is received, a de-aggregation process
(2008)). is initiates. First it checks the MPDU header for any
errors based on the CRC value. If it is correct, the
2.1. Aggregate MSDU MPDU is extracted, and it continues with the next
MPDU till it reaches the end of the PHY Service
The principle of the A-MSDU is to allow multiple Data Unit (PSDU). Otherwise, it checks every four
MSDUs sent to the same receiver to be concate- bytes until it locates a valid MPDU header or the end
nated in a single MPDU. This definitively improves of the PSDU. The delimiter has a unique pattern to
the efficiency of the MAC layer, specifically when assist the de-aggregation process while scanning for
there are many small MSDUs. For an A-MSDU to be MPDU header (Skordoulis et al. (2008)).
formed, a layer at the top of the MAC receives and
buffers multiple MSDUs. The A-MSDU is completed 2.3. Hybrid A-MSDU/A-MPDU Aggregation
when the size of the waiting MSDUs reaches the
maximal A-MSDU threshold (Charfi et al. (2013)). The hybrid aggregation as shown in Figure 3
comprises a blend of A-MSDU and A-MPDU over
In Figure 1, we describe a simple structure of an A- two stages. In the first stage, MSDUs received
MSDU. Each MSDU consists of a MSDU header, by MAC from the upper layer are buffered for a
which contains the Destination Address (DA), the short time until A-MSDUs are formed according to
Sender Address (SA) and the length of the MSDU, their traffic identifier, destination, source, and the
2
Performance Study of Frame Aggregation Mechanisms
Yazid • Bouallouche-Medjkoune • Aı̈ssani
et al. (Cha et al. (2012)) compared the performance
of the two down-link user multiplexing schemes: MU-
MIMO and frame aggregation in IEEE 802.11ac. The
authors showed that, if each user’s data stream has
a similar length, the MU-MIMO scheme yields better
average throughput. Whereas, if each user’s data
stream has a different length, the frame aggregation
scheme outperforms the MU-MIMO scheme in terms
of average throughput. Chung et al. (Chung et
al. (2013)) proposed an aggregated MPDU using
fragmented MPDUs with a compressed Block ACK
Figure 2: Aggregate MPDU.
mechanism for use in IEEE 802.11ac MU-MIMO
transmission. The authors showed that, by allowing
maximum size of A-MSDU. The complete A-MSDUs the use of fragmentation with the A-MPDU, the waste
and other non-aggregate MSDUs then enter the of medium resources in terms of meaningless A-
second stage to form an A-MPDU. Only complete MPDU padding can be eliminated.
A-MSDUs and MSDUs, not the fragments of A-
It is clear that, the frame aggregation and block
MSDUs or MSDUs, could be contained in an A-
acknowledgement are the most important MAC
MPDU. The entire aggregation scheme completes
mechanisms proposed in the new generation IEEE
when A-MPDU is created (Wang et al. (2009)).
802.11ac WLANs standard for achieving a very high
throughput. This is due to their efficiency of reducing
the temporal overheads caused mainly by the PHY
and MAC headers, inter-frame spacing, backoff timer
and frame ACK. However, non of the existing studies
has been devoted to evaluate the performance level
and quantify the throughput gains offered by the
frame aggregation mechanisms. This is why, we
dedicate this work to separately study how each
frame aggregation mechanism allows increasing the
overall throughput in an IEEE 802.11ac WLAN.
In the same way, we identify, for the first time
in the literature, some issues risen to the use
Figure 3: Hybrid A-MSDU/A-MPDU aggregation. of frame aggregation mechanisms with practical
physical data rates. These drawbacks should be
taken into account, in order to enhance the IEEE
3. RELATED WORKS AND MOTIVATIONS
802.11ac WLAN.
The Frame Aggregation Mechanisms, which are
designed for improving channel utilization and MAC 4. SIMULATION RESULTS AND ANALYSIS
efficiency have received a large interest by the
research community. In the field, Redieteab et al. In this section, we analyze the impact of the MAC
(Redieteab et al. (2010)) proposed a new cross- layer to increase the overall throughput in the VHT
layer aggregation scheme that increases throughput IEEE 802.11ac WLAN. Especially, we study how
as a compromise between robustness to collisions the frame aggregation mechanisms allow enhancing
and channel diversity exploitation in a WLAN the utilization of the scarce wireless bandwidth and
multichannel context. Ong et al. (Ong et al. (2011)) improving the achievable throughput in an IEEE
compared the MAC performance between 802.11ac 802.11ac WLAN. Furthermore, we highlight the need
and 802.11n over three different frame aggregation to cross-layer communications between the PHY
mechanisms, and indicated that 802.11ac with a and MAC layers to accommodate the use of the
configuration of 80 MHz and single spatial streams different frame aggregation mechanisms according
outperforms 802.11n with a configuration of 40 MHz to the offered physical data rates.
and two spatial streams in terms of throughput by
28%. Bellalta et al. (Bellalta et al. (2012)) proposed In order to analyze the gains of the different frame
and evaluated a simple reference scheme covering aggregation mechanisms over several physical data
the fundamental properties of frame aggregation rates in an IEEE 802.11ac WLAN, we have
and MU-MIMO transmission in order to demonstrate implemented the IEEE 802.11ac frame aggregation
that the combination of both techniques is able to mechanisms in a custom-made simulator written in
significantly improve the system performance. Cha C++ programming language under Linux operating
3
Performance Study of Frame Aggregation Mechanisms
Yazid • Bouallouche-Medjkoune • Aı̈ssani
system. The values of parameters used to obtain the A-MSDU/A-MPDU aggregation. This scheme
simulation results are given in Table 1. allows the same maximum number of MPDUs
as in A-MPDU aggregation. However, in
Table 1: 802.11ac PHY and MAC Parameters. the hybrid aggregation, a single MPDU can
encapsulate several MSDUs, conditioned by
Parameter Numerical value the size of MPDU which does not exceed 4095
Signal propagation delay 1 µs bytes.
DIFS 34 µs
SIFS 16 µs • Finally, we give a comparative study between
Slot time 9 µs the maximum throughput reached with the
Minimum PHY hdr time 40 µs different frame aggregation mechanisms in
Maximum PHY hdr time 68 µs an IEEE 802.11ac WLAN according to the
Minimum CW 32 network size.
Maximum CW 1024
Maximum MAC hdr size 36 bytes
Maximum MPDU size 11454 bytes
ACK length 14 bytes
Block-ACK length 64 bytes
Maximum MSDU size 2304 bytes
The goal of the following obtained simulation
results is to show the relation existing between
the data rates (offered by the PHY layer) and
frame aggregation mechanisms (available at MAC
layer level), allowing an efficient use of the scarce Figure 4: Bandwidth utilization versus data rate.
wireless bandwidth while improving the achievable
throughput in an IEEE 802.11ac WLAN. Therefore,
In Figure 4, we study the bandwidth utilization
our analysis is organized as follows:
according to the physical data rate without using
• Firstly, we study the bandwidth utilization the frame aggregation. Therefore, we have used
rate according to various physical data a middle MPDU length (1000 bytes), an average
rates without applying frame aggregation. network size (15 stations), and we have varied the
The objective of this study is to show physical data rate from 50 Mbps to 300 Mbps.
that, increasing the physical data rate does We observe from the Figure 4 that, the bandwidth
not increase systematically the bandwidth utilization is decreasing with the increase of physical
utilization. So, the frame aggregation is data rate; the greater the used physical data rate,
required for increasing the bandwidth utilization the lower the bandwidth utilization rate. We note
and MAC efficiency. that, with a physical data rate of 54 Mbps, the
bandwidth utilization rate is 37%. The bandwidth
• Secondly, we evaluate the first existing frame utilization decreases to 12%, when the physical data
aggregation scheme, which is the A-MSDU rate reaches 300 Mbps. This is mainly due to the
aggregation. So, we quantify the achievable PHY and MAC headers which harm the bandwidth
throughput with the A-MSDU aggregation utilization and the achievable throughput of IEEE
scheme according to the A-MSDU length. With 802.11 WLANs. By enabling new features (like wider
the A-MSDU aggregation, we already note the channels and MU-MIMO transmission) at the PHY
benefit gain of the frame aggregation in an layer, it is true that, the physical data rate is highly
IEEE 802.11ac WLAN. increased. However, as we have shown in Figure
4, the channel bandwidth is less and less utilized.
• Thirdly, we evaluate the second frame aggre-
This can be explained by the fact that the physical
gation scheme, which is the A-MPDU aggre-
data rates are only used to transmit the payload
gation. This scheme offers greater length to
of the 802.11 frame (the useful data). However,
the aggregated frame, up to 64 MPDUs in the
the PHY and MAC headers are always transmitted
same A-MPDU, where the payload length of
by using the physical basic rate, which is very
each MPDU does not exceed 2304 bytes. Sev-
low compared to the physical data rates. This is
eral simulation results will be given according
why, when increasing the physical data rate, the
to the number of MPDUs with different MPDU
time duration spent to transmit the PHY and MAC
lengths and physical data rates.
headers becomes larger and larger compared to the
• Fourthly, we report on the third and last time duration spent to transmit the frame payload.
frame aggregation scheme, which is the hybrid Consequently, the channel bandwidth is less utilized.
4
Performance Study of Frame Aggregation Mechanisms
Yazid • Bouallouche-Medjkoune • Aı̈ssani
So, increasing the data rate at the PHY layer does with different MPDU frame lengths (1000 bytes and
not systematically increase the bandwidth utilization 2000 bytes), and over various physical data rates (54
and MAC efficiency. Thereby, the frame aggregation Mbps, 100 Mbps and 150 Mbps).
and block acknowledgment are required at MAC
layer level in order to share among several frames
the overheads mainly generated by the PHY and
MAC headers, and inter-frame spacing.
Figure 6: Throughput versus A-MPDU length over a data
rate of 54 Mbps.
We remark from Figure 6 that, the achievable
Figure 5: Throughput versus A-MSDU length. throughput with the A-MPDU aggregation increases,
at the beginning, with the increase of the number of
In Figure 5, we analyze the achievable throughput MPDU frames in an A-MPDU frame, for both MPDU
in an IEEE 802.11ac WLAN, when using the A- frame lengths 1000 bytes and 2000 bytes. However,
MSDU frame aggregation mechanism at the MAC when the number of MPDU frames exceeds 40
layer level, according to the number of MSDU frames MPDUs and 16 MPDUs respectively for the MPDU
aggregated in an A-MSDU frame. Therefore, we frame lengths of 1000 bytes and 2000 bytes, the
have fixed the PHY data rate at 54 Mbps, the network achievable throughput decreases along the increase
size at 15 stations, and we have varied the number of the number of MPDU frames. This degradation
of MSDUs in an A-MSDU frame from 1 to 7 (i.e., in more remarkable in case of MPDU frame length
we have varied the length of the A-MSDU frame of 2000 bytes, where the throughput increases first
from 1000 bytes to 7000 bytes). We observe from from 26 Mbps (with 1 MPDU) to 37 Mbps (with
Figure 5 that, the larger the A-MSDU frame length, 16 MPDUs), then it decreases to 27 Mbps (with
the greater the achievable throughput in the IEEE 64 MPDUs). Through these results, we show for
802.11ac WLAN. We remark that, with an A-MSDU the first time in the literature that, with a specific
frame of 1000 bytes the achievable throughput is value of physical data rate (54 Mbps, for example),
17 Mbps, it increases to 30 Mbps with an A-MSDU there is an optimum length of the A-MPDU frame
frame of 7000 bytes. In terms of channel bandwidth, which allows the IEEE 802.11ac WLAN to achieve
by enabling the A-MSDU aggregation at MAC layer the maximum throughput. Beyond of this A-MPDU
level, the bandwidth utilization increases from 32% length, the achievable throughput will decrease with
to 56% when the A-MSDU frame length increases the increase of A-MPDU length. Traditionally, we
from 1000 bytes to 7000 bytes. This significant think that, increasing the amount of transmitted data
improvement level, in terms of achievable throughput means automatically an increase of the achievable
and bandwidth utilization, is provided by the A- throughput. Here, we prove that, for a given physical
MSDU frame aggregation mechanism which allows data rate, the best achievable throughput in an IEEE
several MSDU frames to be transmitted with the 802.11ac WLAN is conditioned by an optimum A-
same PHY and MAC headers during one channel MPDU length. Before reaching this A-MPDU length,
access. Thereby, the overheads caused by the there is a problem of overheads which harm the
PHY and MAC headers, inter-frame spacing and throughput. But, after this value, there is an other
channel access time, are shared among several problem which is the collision time that becomes
MSDU frames. This is why, by enabling the A-MSDU more and more important with the increase of the
aggregation, the overheads are significantly reduced A-MPDU length.
and the amount of transmitted useful data is highly
increased. In Figures 7 and 8, we illustrate the achievable
throughput by applying the A-MPDU aggregation
In Figures 6, 7 and 8, we analyze the achievable scheme on IEEE 802.11ac network over 100 Mbps
throughput in an IEEE 802.11ac WLAN, by enabling and 150 Mbps, respectively. We note on both Figures
the A-MPDU frame aggregation mechanism at MAC 7 and 8 that, the throughput increases with the
layer level, according to the number of MPDU frames increase of the number of MPDU frames in an A-
in an A-MPDU frame (from 1 MPDU to 64 MPDUs), MPDU frame, for both MPDU frame lengths 1000
5
Performance Study of Frame Aggregation Mechanisms
Yazid • Bouallouche-Medjkoune • Aı̈ssani
Figure 7: Throughput versus A-MPDU length over a data Figure 9: Throughput versus A-hybrid length over a data
rate of 100 Mbps. rate of 100 Mbps.
Figure 8: Throughput versus A-MPDU length over a data Figure 10: Throughput versus A-hybrid length over a data
rate of 150 Mbps. rate of 200 Mbps.
bytes and 2000 bytes. The maximum achievable
throughputs with the maximum length of A-MPDU
frame (64 MPDU frames of 2000 bytes for each
of them) over the physical data rates 100 Mbps
and 150 Mbps, are respectively 71 Mbps and 104
Mbps. This significant improvement, in terms of
achievable throughput, is due to the collision time
of the A-MPDU frame which is significantly reduced
when using high data rates at the PHY layer level.
So, when the length of the MAC frame is large,
it is necessary to increase the data rate at the Figure 11: Throughput versus A-hybrid length over a data
PHY layer in order to reduce the collision time and rate of 300 Mbps.
consequently to improve the achievable throughput.
However, there is a limit that the physical data
rate should not exceed. Otherwise, the channel frame. The achievable throughput is given for two
bandwidth will be less utilized because of temporal MPDU frame lengths: 2000 bytes and 4000 bytes,
overheads. This why, with the physical data rate and over three different physical data rates: 100
of 100 Mbps, the rate of bandwidth utilization is Mbps, 200 Mbps and 300 Mbps.
71%. It is decreased to 69% with the physical data
From Figure 9, we note that, with a MPDU frame
rate of 150 Mbps. Therefore, for a given length of
length of 4000 bytes and over a physical data rate
MAC frame, there is an optimum physical data rate
of 100 Mbps, the maximum throughput of the hybrid
which reduces the collision time and minimizes the
frame aggregation is reached with 32 MPDUs. In
temporal overheads. Consequently, the achievable
Figure 10, we show that, although the physical
throughput is improved and the bandwidth utilization
data rate used is high (200 Mbps), the achievable
is enhanced.
throughput decreases when the number of MPDU
In Figures 9, 10 and 11, we evaluate the A-MSDU/A- frames exceeds 48 frames. So, when the hybrid
MPDU hybrid frame aggregation scheme according frame aggregation scheme is enabled at the MAC
to the number of MPDU frames in an A-MPDU frame, layer level, it is required to employ the very high
where each MPDU frame encapsulates an A-MSDU data rate available at the PHY layer level in order to
achieve a very high throughput in the IEEE 802.11ac
6
Performance Study of Frame Aggregation Mechanisms
Yazid • Bouallouche-Medjkoune • Aı̈ssani
WLAN. This is why, we note on Figure 11 that, over IEEE Wireless Telecommunications Symposium
the physical data rate of 300 Mbps, the achievable (WTS), pp. 1–7.
throughput does not decrease whatever the length
of the A-MPDU frame. Bejarano, O., Knightly, E. W., Park, M. (2013)
IEEE 802.11ac: From Channelization to Multi-User
MIMO. In proceedings of IEEE Communications
Magazine, pp. 84–90.
Bellalta, B., Barcelo, J., Staehle, D., Vinel, A.,
Oliver, M. (2012) On the Performance of Packet
Aggregation in IEEE 802.11ac MU-MIMO WLANs.
IEEE Communications Letters, 16(10), 1588–
1591.
Cha, J., Jin, H., Jung, B. C., Sung, D. K.
(2012) Performance Comparison of Downlink User
Multiplexing Schemes in IEEE 802.11ac: Multi-
Figure 12: Throughput variation according to the network
size. User MIMO vs. Frame Aggregation. IEEE Wireless
Communications and Networking Conference
(WCNC), pp. 1514–1519.
In Figure 12, we compare the maximum achievable
throughput by the different frame aggregation Charfi, E., Chaari, L., Kamoun, L. (2012) Upcoming
schemes in the IEEE 802.11ac WLAN according WLANs MAC Access Mechanisms: An Overview.
to the network size. Therefore, we have fixed the In proceedings of IEEE 8th International Sympo-
physical data rate to 300 Mbps, and we have used sium on Communication Systems, Networks and
the maximum length of each frame aggregation Digital Signal Processing (CSNDSP), pp. 1–6.
scheme. Through this figure, we show clearly that,
the hybrid frame aggregation scheme provides the Charfi, E., Chaari, L., Kamoun, L. (2013) PHY/MAC
best bandwidth utilization and MAC efficiency in the Enhancements and QoS Mechanisms for Very
IEEE 802.11ac WLAN over a physical data rate of High Throughput WLANs: A Survey. In proceed-
300 Mbps. ings of IEEE Communications Surveys and Tutori-
als, pp. 1–22.
5. CONCLUSION Chung, C., Chung, T., Kang, B., Kim, J. (2013)
A-MPDU Using Fragmented MPDUs for IEEE
In this paper, we are interested at presenting 802.11ac MU-MIMO WLANs. In proceedings of
and studying the Frame Aggregation Mechanisms TENCON 2013-2013 IEEE Region 10 Conference
introduced in the IEEE 802.11ac standard for (31194), pp. 1–4.
very high throughput WLANs. Indeed, Frame
Cordeiro, C. (2013) The Pursuit of Tens of
Aggregation Mechanisms allow enhancing MAC
Gigabits Per Second Wireless Systems Industry
efficiency and bandwidth utilization. The presented
Perspectives. IEEE Wireless Communications
simulation results show that, the Frame Aggregation
Magazine, 20(1), 3–5.
Mechanisms are required at MAC layer level for
reducing temporal overheads and consequently IEEE 802.11 ac Standard (2013) Wireless LAN
increasing the achievable throughput and bandwidth Medium Access Control (MAC) and Physical Layer
utilization. However, when the length of the (PHY) specifications: Enhancements for Very High
aggregated MAC frame is very large, it is necessary Throughput for Operation in Bands below 6 GHz.
to use a higher physical data rate in order to reduce
the collision time of this aggregated frame. Thereby, Ismail, S. Z., Chavali, N. K. (2013) Impact of Spatial
we have identified, for the first time in the literature, Expansion on Channel Estimation Accuracy in HT
the need to cross-layer communications between the and VHT Wireless LAN Systems. In proceedings
PHY and MAC layers for accommodating the use of of IEEE International Conference on Advances
the different Frame Aggregation Mechanisms over in Computing, Communications and Informatics
the available physical rates. (ICACCI), pp. 643–648.
Ong, E. H., Kneckt, J., Alanen, O., Chang, Z.,
REFERENCES Huovinen, T., Nihtila, T. (2011) IEEE 802.11ac:
Enhancements for Very High Throughput WLANs.
Al-Adhami, M., Al-Dubai, A. Y., Romdhani, I. (2012) In proceedings of IEEE 22nd International
Experimental Investigation of Link Layer Adapta- Symposium on Personal Indoor and Mobile Radio
tion in IEEE 802.11n WLANs. In proceedings of Communications (PIMRC), pp. 849–853.
7
Performance Study of Frame Aggregation Mechanisms
Yazid • Bouallouche-Medjkoune • Aı̈ssani
Redieteab, G., Cariou, L., Christin, P., Hélard, J.
(2010) Cross-Layer Multichannel Aggregation
for Future WLAN Systems. In proceedings of
IEEE International Conference on Communication
Systems (ICCS) pp. 740–745.
Redieteab, G., Cariou, L., Christin, P., Hélard,
J. F. (2012) SU/MU-MIMO in IEEE 802.11ac:
PHY+MAC Performance Comparison for Single
Antenna Stations. In proceedings of IEEE Wire-
less Telecommunications Symposium (WTS), pp.
1–5.
Skordoulis, D., Ni, Q., Chen, H. H., Stephens,
A. P., Liu, C., Jamalipour, A. (2008) IEEE
802.11n MAC Frame Aggregation Mechanisms
for Next-Generation High-Throughput WLANs. In
proceedings of IEEE wireless Communications,
pp. 40–47.
Wang, C. Y., Wei, H. Y. (2009) IEEE 802.11n
MAC Enhancement and Performance Evaluation.
Mobile Networks and Applications 14, 760–771.
Yazid, M., Ksentini, A., Bouallouche-Medjkoune, L.,
Aı̈ssani, D. (2014) Performance Analysis of the
TXOP Sharing Mechanism in the VHT IEEE
802.11ac WLANs. IEEE Communications Letters,
18(9), 1599–1602.
Yazid, M., Ksentini, A., Bouallouche-Medjkoune,
L., Aı̈ssani, D. (2015) Enhancement of the
TXOP Sharing designed for DL-MU-MIMO IEEE
802.11ac WLANs. In proceedings of IEEE Wire-
less Communications and Networking Conference
(WCNC), pp. 908–913.
8