A New Architecture of Wireless Mesh Networks Based IEEE 802.11s ...

This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2011 proceedings 

A new architecture of wireless mesh networks 

based IEEE 802.11s directional antennas 

Jalel Ben-Othman 

Laboratoire CNRS-Prism 

University of Versailles 

jbo@prism.uvsq.fr 

Lynda Mokdad 

Laboratoire LACL 

University of Paris 12 

Lynda.mokdad@univ-paris12.fr 

Abstract—This paper tackle the problem of coverage in IEEE 

802.11 using mesh mode. Instead of omnidirectional coverage, 

we propose to use directional coverage. The use of directional 

antenna have two main advantages. The first is to increase the 

performance of QoS of considered services. The second is that 

using directional antenna allows to improve the spatial reuse 

of the wireless channel, which allows nodes to communicate 

simultaneously without interference, and potentially establish 

links between nodes far away from each other, and the number of 

routing hops can be fewer than that of omnidirectional antennas. 

We also propose an new amendment to reduce the routing 

overhead related to the use of multiple interfaces. We have 

evaluated the performance of the proposed architecture and we 

show with numerical results that the use of directional coverage 

outperform the omnidirectional coverage. 

I. INTRODUCTION 

Today IEEE 802.11 is the most widely used standard in 

WLAN. Since the first deployment several amendments have 

been developed to adapt this standard for different use as the 

IEEE 802.11s for mesh networks. The Wireless Mesh Networks 

(WMN) are designed to communicate between nodes 

using the air interface organized in mesh topology. In this 

network the Mesh Point (MP) nodes communicate directly 

by the meduim of transmission radio with their neighbors 

through a multihop routing protocol. The extension of IEEE 

802.11 MAC standard has been done by defining new wireless 

configuration that manage the topology, the quality of radio 

link and the routing protocols to increase the effective coverage 

area. In this Draft, the DS of an AP can be replaced with 

wireless links or multi-hop paths between multiple APs. 

In IEEE 802.11s, the network nodes are divided into two 

classes : The nodes that support mesh services and those who 

do not support see figure 1. 

• Mesh points (MPs): Are entities that support mesh 

services (such as path selection and forwarding ...etc), 

i.e. they participate in the formation and operation of the 

mesh network. 

• Mesh Access Point : The configuration of an MP that is 

collocated with an Access Point is referred to as a Mesh 

Access Point (MAP). 

• Mesh portals (MPPs): Interface the network to other 

IEEE 802 LAN segments. 

• Stations : do not participate in mesh functionalities. 

978-1-61284-231-8/11/$26.00 ©2011 IEEE 

Mohamed Ould Cheikh 

Laboratoire LAMSADE 

University of Paris-dauphine 

ouldcheikh@lamsade.dauphine.fr 

Figure 1. Mesh containing MPs, MAPs, MPP, and STAs[1]. 

Using wireless link between nodes in WMN conduct to 

the deployment of more access point due to the limitation 

of the IEEE 802.11 technology radio coverage. The use of 

directional antennas increases the radio coverage and thus can 

decrease the number of AP. This study tackle this last point by 

proposing a directional coverage in a deployment of a WMN 

based on IEEE 802.11s. We want to take the advantage of 

directional antennas while keeping the compatibility of the 

IEEE 802.11 standard. The rest of this paper is organised 

as flowing : after a presentation of the related work in the 

section II, the proposed architecture is presented in section 

III. In this section we start by describing the mechanism used 

to reduce the routing overhead, then we present the directional 

antenna modeland implementation on NS3 simulator. In this 

section we discuss the influence of the coverage angle size 

of each sector on the network performance as well. This 

architecture has been evaluated by simulations under NS3, 

the description of implementations and numerical results are 

detailed in section IV. Finally, we summarize the main 

contribution of this paper and we give the perspectives of this 

study in section V.


II. RELATED WORK 

Directionnal Antennas (DA) have received increasing interest 

in recent years, especially in the context of an ad hoc 

network, due to their better performance. By using DA in 

IEEE 802.11s backbone, the nodes can communicate simultaneously 

without interference, and potentially establish links 

between nodes far away from each other, and the number of 

routing hops can be fewer. However, the existing IEEE 802.11 

(mesh) standards does not gain with the implementation of DA 

and poses additional technical challenges such as deafness 

and hidden- and exposed terminal problems arisen due to 

directional transmissions[5]. Deafness is caused when a node, 

C, attempts to initiate dialog with a node, A, while A is 

engaged in communication with another node [6], as shown 

in figure 2. 

Figure 2. A scenario illustrating the problem of deafness [6]. 

Most work on directional antennas (they are often in the 

context of ad hoc network) propose to change the MAC 

layer, to take advantage of these benefits and to solve the 

deafness and hidden- and exposed terminal problems. In 

DMAC (Directionnal MAC) [7] all frames are transmitted 

directionally except for the CTS (Clear To Send). In MMAC 

(Multi-hop RTS MAC) [7] the authors proposes the multi-hop 

RTS (Request To Send) to take advantage of the higher gain 

obtained by directional antennas. In [6], the authors propose 

ToneDMAC to solve the problem of deafness. However, most 

of these works are not compatible with the 802.11 standard 

(problem of the interoperability and evolution). To the best of 

our knowledge no work has been done on using directional 

antenas in IEEE 802.11s. 

In this paper, we propose a new deployment of IEEE 

802.11s that take the advantage of directional antennas while 

keeping the compatibility of the IEEE 802.11standard. 

III. OUR PROPOSAL 

In our proposal, we use a sectorial antenna, which consists 

of multiple fixed beam antennas aimed in different directions, 

each covering a different sector of space, all of them together 

giving full 2π coverage. A fixed beam antenna is the traditional 

directional antenna which is pre-fixed in particular 

direction ( has a fixed gain profile with a primary lobe pointing 

in a single direction). Steering the beam is only possible by 

physically changing the orientation of the antenna[10]. Using 

this configuration allows to solve the deafness problem. 

The main purpose of our proposal is to take the advantage 

of directional antennas while keeping the compatibility of the 

IEEE 802.11 MAC and to reduce the routing overhead. In the 

flowing we describe the mechanism that we propose to reduce 

the routing overhead, then we present the directionnal antenna 

model and their implementation in NS3 simulator that we use 

for the simulations. 

A. Sector-HWMP 

The mechanism defined in the following is valid for the two 

modes (Proactive tree building mode and On demand mode). 

In this mechanism, if a source MP A needs to find a path to 

a destination MP B : 

• if node A knows the position of node B, the PREQ is 

transmitted only by the fixed beam antenna that the MP 

B is inside of their three-dimensional radiation beam. 

• Otherwise, the PREQ is broadcasted by all beam antennas. 

In our proposal, each node has a table where it keeps the 

list of others nodes positions. The PREQ and PREP messages 

format are modified to carry the sender potision. Before an 

MP sends PREQ or reply with PREP , it puts its potision. 

When an MP receives a PREQ or PREP, it updates its 

positions table by adding the new entries ( new positions, if 

exists). 

The PREQ element is used for discovering a path to one 

or more destinations. Whenever an MP have to send or have 

to forward a PREQ to a set of destinations, it checks if it 

exists an entry in the positions table for each destination. The 

PREQ which will be sent by the interface i must contain 

only the subset of destinations address of the MPs that are 

inside of their three-dimensional radiation beam. By this way 

we reduce the overhead : Some interfaces my have a subset 

empty (No PREQ have to send on these interfaces or the 

size of PREQ is reduced) and the number of intermediates 

MP are reduced. To determines if a MP destination is inside 

of the three-dimensional radiation beam of the beam antenna 

of the interface i, the MP uses the algorithm described in 

[9]. The subset of destinations address that not exist in 

positions table of the MP (Sender, intermediate ) will be 

set in each preq broadcasted(see figure 3). When three 

consecutive attempts fail at path discovery towards a given


(set of) destination(s), this subset of destinations address will 

be set in each broadcasted preq. 

Figure 3. Figure illustrating Sctor-HWMP. 

In Figure 3, we assume that the source MP has three fixed 

beam antennas aimed in different directions, each covering an 

angle of 120 degrees. In this figure, if a MP source knows the 

position of the MP destination then, the destination address 

of this MP will be set only in the PREQ copy that must be 

transmited the antenna 1. Otherwise, this address must be 

added in all PREQ broadcasted by 1,2 and 3. 

1) sectorization issues : In this section we discuss the 

influence of the coverage angle size of each sector on the 

network performance. 

Figure 4. Figure illustrating sectorization issues on the network performance. 

B. Directionnal antenna model 

A directional antenna is defined as: ”having the property of 

radiating or receiving electromagnetic waves more effectively 

in some directions than in others” [3]. In practice, when one 

wants to describe how a particular antenna works, some basic 

characteristics common to all types of antennas, are given: 

Impedance, radiation pattern, Polarization and Gain. 

In wireless network simulations, we are interested only 

to determines when and with what reception power a signal 

arrives at a receiver. The signal strength is used to determine 

whether the frame is transmitted successfully. There is several 

propagation models to predict the power received signal (Free 

Space, Two Ray Ground, Shadowing,....etc ). 

Free Space model is used to simulate path loss of wireless 

communication when line-of-sight path exists between transmitter 

and receiver. Two Ray Ground model is used when 

line-of-sight path exists and reflection of ground is considered. 

Shadowing model simulates shadow effect of obstructions 

between the transmitter and receiver. 

For example, the free-space attenuation can be computed 

using Friis modernized equation : 

where : 

PRx = PTx∗GRx∗GTx∗λ2 

(4∗π∗d) 2 ∗L 

• PRx,PTx are reception and transmission power in watt; 

• GRx,GTx are reception and transmission gain; 

• L is a general dimensionless system loss coefficient; 

• λ is the wavelength; 

• and d is the distance in meters between sender and 

receiver. 

Most of the current implementations of the IEEE 802.11 

physical models (802.11a/b/g...etc.) in a packet-based network 

simulators uses only omnidirectional antennas models ( 

GRx =1and GTx =1). These implementations use an object 

(wifichannel in NS3, WirelessChannel in NS2) to models the 

radio signal transmission. This object keeps a list of all nodes 

, or the list of their physical components on this channel ( all 

the nodes participate in the simulation). It works just like a 

physical media : receives packets from nodes and assigns them 

to all possible destination and following the reception power, 

the receiving node decides whether the packet is correct or 

not. 

In directional antenna models, the electromagnetic waves 

is mainly radiated in some directions and consequently the 

reception and transmission gains are calculated differently. 

Also, the received packets by the wifichannel object do not 

assigned to all nodes in the simulation but only to the receivers 

inside the three-dimensional radiation beam. 

The gain of an antenna (in a given direction) is defined as 

”the ratio of the intensity, in a given direction, to the radiation 

intensity that would be obtained if the power accepted by the 

antenna were radiated isotropically (the power accepted (input) 

by the antenna divided by 4π)” [4]. 

Gain =4π U(θ,φ) 

Pin 

Since all of the accepted (input) power is not radiated 

(because of losses),the total radiated power (Prad) is related 

to the total input power (Pin )by: 

Prad = ecdPin 

where ecd, is the radiation efficiency of the antenna. 

Gain = ecd[4π U(θ,φ) 

Prad ] 

The maximum value of the gain can be expressed according 

to the beam solid angle : 

U(θ, φ) =B0F (θ, φ) 

Prad = ◦ �� 

Ω 

Gainmax = ecd 

U(θ, φ)dΩ =B0 

Gainmax = ecd 4π 

ΩA 

� 2π 

0 

� π 

F (θ, φ)sinθdθdφ 

0 

� 4π 

2π � π 

[ F (θ,φ)sinθdθdφ]/F (θ,φ)|max 

0 0


Table I 

SIMULATION PARAMETERS 

Parameters Value 

CBR (DataRate (Mb/s)) 1 

CBR (PacketSize ) 1000 

MPEG 4 based on a stream trace file (See [11,12]) 

PHY OFDM 5 GHz 

Channel 20MHz 

txPower 16.0206 dBm 

txGain 6.0206 dB 

rxGain 6.0206 dBm 

EnergyDetectionThreshold -96.0 dBm 

propagation loss model log-distance 

DataMode wifia-6mbs 

Simulation time 250 (seconds) 

Number of nodes 25 

Where ΩA is the beam solid angle. 

For our simulations, we consider an antenna formed by a 

cone (The beam width of this antenna is 2ϕ and ecd =1) with 

spherical cap model , which is a mathematical approximation 

for simplicity, the solid angle : 

ΩA =2π(1 − cos ϕ) 

The gain can be expressed as : 

4π 

GRx = GTx = ecd[ 

2π(1−cos ϕ) ] 

2 

GRx = GTx =[ (1−cos ϕ) ] 

To check if a receiver is inside the three-dimensional 

radiation beam of the antenna, we use the algorithms defined 

in [9]. 

The figure 5 shows an UML diagram illustrating directionnal 

antenna implementation. In this figure we show only the 

part of IEEE 802.11 models provided in ns-3 that we have 

changed. 

IV. SIMULATION RESULTS 

We present and discuss in this section our simulation results 

for the performance study of our multipath routing protocol. 

We used NS3 for our simulations. The simulations are 

executed using the parameters of Table I . 

Figure 6 represents the reception power according to the 

distance and the antenna gain. For these simulations we used 

two different type of antennas. The firs is directional with 

120 degrees of beamwidth while the second is omnidirectional. 

The numerical results are based on the log propagation model. 

The figure shows for omnidirectional antenna the link between 

two nodes is efficient for a distance less than 170m. For a 

directional antenna the distance between two nodes is efficient 

up to 370 m. These results confirm that using directional 

antenna can improve the distance between nodes. 

In Figure 7 and 8 we have plotted the throughput and the 

end-to-end delay according to the distance respectively. The 

considered traffic is composed by two different sources one 

CBR and a multimedia traffic. We can notice from the both 

figures that better performances are for a distance less than 

220m. 

Figure 6. Directional Vs Omnidirectional antenna 

Figure 7. global throughput 

Figure 8. PDR 

V. CONCLUSION 

IEEE 802.11s is the amendment of IEEE 802.11 that enable 

the mesh mode. The current deployment is made using 

omnidirectional antenna. Recently, the directional antenna 

has received intensive research due to its variety of potential


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benefits for wireless communication systems. It is expected to 

provide significant improvements. In this study we propose a 

new improvements of HWMP protocol (Sector-HWMP) that 

take into account the using of directional antennas. These 

improvements are intend to reduce the routing overhead related 

to the use of multiple interfaces, and to take the advantage of 

directional antenna. In order to evaluate the performance of 

our proposal, we have made an antenna directionnal antenna 

model. We show the benefits of directional antennas through 

simulation under NS3. Numerical results show that the 

distance between nodes is increased and we show that the 

global QoS is increased as well. We intend to extend this 

architecture by taking into account the MAC layer in the 

routing process in order to increase number of radios in each 

sector. 

REFERENCES 

[1] IEEE 802.11s. (2007). Draft STANDARD for Information Technology- 

Telecommunications and information exchange between systems-Local 

and metropolitan area networks-Specific requirements-Part 11: Wireless 

LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications. 

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Figure 5. UML diagram illustrating directionnal antenna implementation 

[2] Sana, G., Sonia, M. G., and Farouk, K. (2010). Comparison of Proposed 

Path Selection Protocols for IEEE 802.11s WLAN Mesh Networks. 

Boston: Springer , 17-28. 

[3] Ian F. Akyildiz, Xudong Wang, Weilin Wang ”Wireless mesh networks: 

a survey” 

[4] Constantine A. Balanis ”Antenna Theory: A Review”. PROCEEDINGS 

OF THE IEEE, VOL. 80, NO. 1, JANUARY 1992. 

[5] Romit Roy Choudhury, Xue Yang, Ram Ramanathan.. and Nitin H. 

Vaidya ”Using Directional Antennas for Medium Access Control in Ad 

Hoc Networks” 

[6] Romit Roy Choudhury and Nitin H. Vaidya ”Deafness: A MAC Problem 

in Ad Hoc Networks when using Directional Antennas” 

[7] Romit Roy Choudhury, Xue Yang, Ram Ramanathan and Nitin H. Vaidya 

”Using Antennas for Medium Access Control in Ad Hoc Networks” 

[8] ”Ad Hoc Networking with Directional Antennas: A Complete System 

Solution” 

[9] Saravanan Kandasamy, Ricardo Morla, and Manuel Ricardo. ”Improving 

the Performance of IEEE802.11s Networks using Directional Antennas 

over Multi-Radio/Multi-Channel Implementation The Research Challenges” 

[10] Michael Neufeld and Dirk Grunwald. ”Deafness and Virtual Carrier 

Sensing with Directional Antennas in 802.11 Networks”. May 2004 

[11] stream trace file http://www.tkn.tu-berlin.de/research/trace/ 

pics/FrameTrace/mp4/ Verbose Jurassic 10.dat 

[12] The ns-3 network simulator : http ://www.nsnam.org/

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