Indoor and Outdoor Coverage of MIMO-Based WLANs [620141]

Indoor and Outdoor Coverage of MIMO-Based WLANs
Murad Abusubaih

Palestine Polytechnic University, Palestine
Department of Electrical Engineering
[anonimizat]

Abstract – In this paper, we study the indoor and
outdoor coverage of Multi-Input Multi-Output
(MIMO)-based IEEE 802.11 Wireless Local Area
Networks (WLANs). The goal is to examine whether
newly emerged technologies do really provide the
argued coverage performance. We compare the
coverage of new technologies and the traditional
devices which are about to disappear from the market.
Our experimental results show that arguments of
vendors about the coverage of MIMO-based devices
are only theoretical and the real coverage is much
lower than what is provided in devices’ specifications.
Hence, in dense deployments, an enterprise should
really think about the per user throughput its backbone
network is able to guarantee and decides on the
installation of technology that fulfill users’ demand.

Keywords: Coverage; Range; MIMO; WLANs.

I. INTRODUCTION

Multi-Input Multi-Output (MIMO)–based Wireless
Local Area Networks (WLANs) have emerged as a
promising solution for broadband access. They are being
widely deployed in residential areas, hotels, campuses
and small business enterprises.

WLAN coverage is one of the most important concerns
to network administrators. They seek to provide services
to the largest number of users and at the same time
minimize interference among neighboring networks.
Also, WLAN coverage is one key issue that gets the
attention and focus of the manufacturers of wireless
networks and devices. Recently, designers of
networking devices are trying to take advantage of
various advanced technological methods to respond to
the market needs of high data rate devices that support
the huge plethora of applications and games.

It is known that multipath fading is a fundamental
phenomenon that impacts the coverage of WLANs,
especially indoors. It occurs due to signal reflections,
diffusions, scattering and diffraction. Fading does not
only cause degradation of signal strength, but also
provoke significant variations of received signals and
hence impacts both coverage and Quality of Service
(QoS).
The simple design of IEEE 802.11b, which is based on
Direct Sequence Spread Spectrum (DSSS), has been
replaced by Orthogonal Frequency Division
Multiplexing (OFDM)-based designs, such as 802.11g.
The IEEE 802.11n/ac task groups further tried to boost
the capacity and coverage of networking devices by
introducing more advanced Multi-Input Multi-Output
(MIMO) technologies as well as adopting multi-user
diversity and higher order modulation and coding
schemes [1][2].

Several researchers have been addressing the problem of
optimizing WLAN performance in terms of throughout,
coverage and users’ satisfaction. Studies have been
proposing a deployment of MIMO–based Acess Points
(APs) both indoor and outdoor to provide best and
sustainable performance. However, the cost of APs as
well as their installation indoors and outdoors is a real
challenge. It is very difficult to predict that certain
locations of APs will provide guaranteed access. Thus, it
is very common that enterprises deploy a number of APs
in the neighborhood of each other to ensure reliable
coverage and transparent handoff [3]. As a result,
efficient channel selection and interference mitigation
mechanisms are becoming crucial to alleviate degraded
performance and guarantee satisfactory quality of
service (QoS). On the contrary, other studies like [4]
noticed that in dense deployments, unreasonable
placement of APs exist, which is a waste of hardware
and energy. Such scenarios have been shifting research
to a new direction with a goal to optimize energy
consumption by turning off low loaded APs.

The legal question is that, do we need this number of
APs to provide access to users? Does MIMO-based
technology solve communication problems of previous
technologies like 802.11b, g? Does it provide better
coverage?

In this paper, we empirically study the indoor and
outdoor coverage capabilities of MIMO-based WLAN
technology. We are mainly interested in finding the
realistic coverage of technologies devices indoors and
outdoors. Further, we are compare the coverage of new
technologies and the traditional devices which are about
to disappear. The rest of the paper is organized as
follows: Section II discusses related work in the field.
Section III gives an overview of IEEE standards with a

focus on physical layer design. In section IV, we
describe the experimental setup. Results are presented
and discussed in Section V, before we conclude the
paper in section VI.

II. RELATED WORK

Due to the massive growth of IEEE 802.11-based
wireless networks in recent years, their coverage has
become a crucial and challenging issue for both network
designers and administrators.

The authors of [5] and [6] compare IEEE 802.11bgn
operating modes in terms of coverage and interference.
The authors performed indoor measurements and have
concluded that the signal strength of the IEEE 802.11b
and IEEE 802.11n modes was better than IEEE 802.11g
for short distances. For longer distances, the authors
have found that the signal strength of both IEEE
802.11b and IEEE 802.11g is higher than IEEE 802.11n.
However, their study is limited to indoor scenarios.

In [7], Banerji and Chowdhurys have shown that the
coverage area of an AP is generally around 20 meters
indoors and 100 meters outdoors. The authors of [8]
report results of measurements conducted to investigate
the coverage capability of IEEE 802.11g and IEEE
802.11n devices. They concluded that in an outdoor
environment, IEEE 802.11n provides better coverage
and throughput than IEEE 802.11g.

The authors of [9] study the performance of the IEEE
802.11ac technology in a typical office building. They
have shown that IEEE 802.11ac offers significantly
improved performance for small distances compared to
IEEE 802.11n. However, the improvements were also
found to be quite sensitive to channel conditions.
Therefore, the authors concluded that IEEE 802.11ac
may not deliver acceptable signal strength for long
distances.
The author of [10] compares the performance of IEEE
802.11ac and IEEE 802.11n technologies by measuring
the throughput and streaming rate of big data streaming.
The results of his study revealed that IEEE 802.11n
signals go further than IEEE 802.11ac.

The paper of [11] assesses coverage and overall
performance of IEEE 802.11ac WLANs through site
survey measurements and simulation for indoor
deployments. The authors of [12] tried to derive an
equation for coverage estimation for a university campus
based on site surveys. The authors pointed out that the
important parameter that determines the data rate and
QoS is the received signal power from APs.

To the best of our knowledge, none of the recent studies
has addressed the coverage of same devices that support
the different modes (i.e. b, g, and n) indoors and
outdoors. In addition, numerous studies in the literature
are only based on simulations [13]-[18]. III. RIVIEW OF IEEE STANDARDS

The IEEE 802.11b standard encodes data using the
DSSS. It uses Complementary Code Keying (CCK) and
Quadrature Phase Shift Keying (QPSK) modulation to
achieve a physical layer transfer of 11Mbps.
Furthermore, IEEE 802.11b implements rate adaptation,
where the data rate is selected based on channel
conditions. The maximum possible rate is 11Mbps.

IEEE 802.11g is an evolution of IEEE 802.11b. The
technology appeared in 2003. Same to IEEE 802.11b
devices, IEEE 802.11g works within the 2.4 GHz band.
IEEE 802.11g implements OFDM technology, which
enables the devices to transfer at a rate of 54Mbps at the
physical layer using 52 subcarriers. IEEE 802.11g
implements rate adaptation; it also supports the speeds
of IEEE 802.11b devices.

Emerging applications and anticipation of future speed
requirements have triggered efforts to enhance the
design of IEEE 802.11 to meet these requirements. In
this regard, the IEEE 802.11n is proposed to improve the
coverage and QoS performance of WLANs. The
technology is based on MIMO and OFDM and operates
in both the 2.4GHz and 5GHz frequency bands. IEEE
802.11n devices can theoretically deliver data rates at
600Mbps using the channel bonding mechanism,
wherein two 20MHz channels are combined and used as
one 40MHz channel. Furthermore, the IEEE 802.11n
uses smart antenna technology. Devices dynamically
adjust the transmitted beam to ensure that each user
receives stable signals. This was proposed as a method
for extending the coverage of typical devices.

Finally, the IEEE 802.11ac standard is proposed as a
viable solution for Gbps WLANs. The standard operates
in the 5GHz band and uses Quadrature Amplitude
Modulation (QAM). Though the modulation method is
the same as that used in IEEE 802.11n standard, IEEE
802.11ac standard optionally allows the use of 256
QAM. This increases the number of bits per subcarrier
to eight, resulting in up to a 33 percent increase in the
physical data rate. The IEEE 802.11ac standard supports
20, 40, and 80 MHz channels, with optional support for
contiguous 160 MHz channels or non-contiguous 80+80
MHz channels. Using sophisticated signal processing
algorithms and beamforming, IEEE 802.11ac devices
are expected to provide better coverage than IEEE
802.11n devices. Beamforming can be used to increase
throughput by improving the quality of the signal sent to
wireless clients. When this option is enabled, APs use
beamforming techniques to optimize the signal strength
for each individual wireless user.

A summary of the key specifications of the main three
variants of IEEE 802.11 is provided in Table 1.

TABLE 1. IEEE 802.11 Standards

Spec. 802.11b 802.11g 802.11n 802.11ac
Band 2.4GHz 2.4GHz 2.4GHz,
5GHz 5GHz
Channel
bandwidth 20MHz 20MHz 20/40
MHz 20/40/80
/160 MHz
Indoor
Coverage 25m 35m 75m 75m
Outdoor
Coverage 140m 140m 250m 250m

IEEE 802.11n manufacturers argue that their MIMO
APs can be placed a part from each other, because of the
increased range capabilities that MIMO provides.

III. EXPEREMENTAL SETUP AND
METHODOLOGY

A. Setup
The experiments were conducted in extensive
measurement campaigns inside the university labs
and outdoors. The iperf traffic generator was used
to send packets from a fixed source to a mobile
destination. The mobile node was moved and fixed
at the certain distances. As shown in Fig. 1, the AP
is dual band Linksys E3000. It has three antennas
for each band and can be configured to operate on
any of the four modes IEEE 802.11a/b/g/n. For
802.11ac experiments the D-Llink 802.11ac dual
band Gigabit router was used.

Fig. 1. Experiment Setup

B. Methodology
The fixed source node transmits packets to the
destination node. The destination node moves at
discrete distances away from the AP and then fixed,
namely 5m,10m,15m, etc. 1000 RSSI values have
been recorded at each distance after fixing the
destination node using three tools: InSSIDer,
Xirrus Wi-Fi Inspector and WirelessMon
Professional. Experiments are repeated for different
locations of the same distance. Same method is
used for outdoor measurements.

IV. RESULTS AND DISCUSSION
In this section, we present and discuss the results of the
experiments. Fig. 2 plots the received signal strength of
indoor measurements. The results show that MIMO-
based devices provide the best coverage for short distances. For distances above 15m, IEEE 802.11b
outperforms MIMO-based technology in terms of
coverage. The IEEE 802.11n/ac at 5GHz and IEEE
802.11a deliver acceptable signal strength just for short
distances. Despite that 802.11ac employs beamforming,
its range is comparable to 802.11n for indoor
installations.

Fig. 2. Signal Strength for Indoor Measurements

The results reveal that the range of all standards for
indoor deployments is just about 20m.

Fig. 3 summarizes the results of outdoor measurements.
The results reveal that the worst coverage is obtained
with the 5GHz devices. Other standards provide
comparable range performance. However, none of the
standards maintain an acceptable signal level after about
30m, even the MIMO-based ones. 802.11ac was found
to reach a bit farther distances in outdoor. This can be
attributed to the beamforming technology it employs.

Fig. 3. Signal Strength for outdoor Measurements

As seen from the results, the mostly recent MIMO-based
devices do not provide better coverage. The complexity
of MIMO-based devices is only able to maintain
comparable coverage to traditional devices which are
about to disappear. More APs are needed to cover areas;
this raises the issue of interference and the need of
methods to mitigate interference.

Finally, fig.4 compares the average throughput
performance of 802.11 technologies measured indoor at
15m from the AP. The results show that 802.11ac
technology provides a very high data rate compared to
other WLAN standards. This is due to MIMO and the
beamforming technique the 802.11ac supports.

IV. CONCLUSIONS

In this paper, we studied the coverage capabilities of
MIMO-based 802.11 standards. We compared the
coverage of MIMO-based devices with legacy devices.
We have found that those devices may benefit from
MIMO technology for range extension just at short
distances. The complex algorithms may fail to extend
the coverage to long distances, especially indoors.
Furthermore, the theoretical claimed range values are
difficult to be achieved, especially outdoors. Hence, in
practice, the new technology does not necessarily extend
the coverage of WLANs. i.e. the multi antenna systems
boost the rata rate rather than coverage.

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