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 Vol. 5, No. 2 | July – December 2021 
 

 

 

SJCMS | P-ISSN: 2520-0755| E-ISSN: 2522-3003 | Vol. 5 No. 2 July – December 2021 

59 

Orthogonal Zones for Interference Migration in 2.4 

GHz Mesh Backhaul

Shazia Abbasi1, Muhammad Memon1, Khalil Khoumbati2, Shahzad Memon1 

Abstract: 

Managing interference in the multi-radio networks is critical challenge; problem becomes 

even more serious in 2.4 GHz band due to minimal availability of orthogonal channels. This 

work attempts to propose a channel assignment scheme for interference zones of 2.4 GHz 

backhaul of Wireless Mesh Networks (WMN). The static nodes of Infrastructure based Backhaul 

employing directional antennas to connect static nodes, orthogonal channel zones introducing 

Interference are formatted with the selection of single tire direct hop and two-tier directional 

hopes. The effort maintains the orthogonality of channels on system thus reduce the co-channel 

interference between inter flow and intra flow links. Group of non-overlapping channels of 

selected band are obtained by a mathematical procedure, interference is modeled by directed 

graph and Channel assignment is carried out with the help of greedy algorithms. Experimental 

analysis of the technical proposal is done by simulation through OPNET 14. Our framework can 

act as an imperative way to enhance the network performance resulting a leading improvement 

in system throughput and reduction in system delay 

Keywords: Wireless Mesh Networks (WMN), Backhaul, Orthogonal,Non-orthogonal 

1. Introduction  

The wireless networks are going to 
restructure for the ultimate communication 
service comparable in the performance of 
wired Ethernet [1], [2]. Advance wireless 
networks support some resource allocation 
procedures for the effective utilization of 
spectrum [3], which makes efficient use the 
simultaneous communication channels of 
spectrum; interference has been a central issue 
in this type of networking, There is a 
possibility that same channel allocate to 
several nodes which create co-channel 
interference between simultaneous 
communications, or there may be adjacent 
channel interference when adjoining channels 
allocate to neighboring nodes [4]. In such 
conditions WMN backhaul is a potential 

 
1Faculty of Engineering and Technology Institute of Business studies 
2University of Sindh, Jamshoro 

Corresponding Author: shazia.abbasi@usindh.edu.pk  

network to offer preferred performance [5], the 
fact is only to observer 

and manages the backhaul links to reduce 
interference [6]. In the condition of WMN 
infrastructure, backhaul links are concurrently 
working on dissimilar channels; the 
arrangement of channels for backhaul links 
may enhance or reduce interference of system 
[7]. However, if the channels are not properly 
assigned to nodes then the performance of 
system drops proportionally with the amount 
of nodes and interfaces. Interference in any 
form can be reduced by using a suitable 
arrangement for the allocation of channels. 

In general, two methods are used for the 
allocation of channels: Static channel (SC) 
assignment and dynamic channel (DC) 
assignment. Dynamic scheme support the 
mechanism where channels assign to 

mailto:shazia.abbasi@usindh.edu.pk


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interfaces animatedly [8], nodes have ability to 
sweep channels to meet the required criteria of 
system, in this respect dynamic channel 
assignment is effective in use for mobile 
communication, on the other hand static 
allocation of channels is suitable for fixed 
nodes [9], under static allocation, channels 
allotted to interfaces, remains permanent and 
fixed for required time. In our previous work, 
the employed strategy was used by backhaul 
links of Wireless local area network [10], here 
the proposed strategy is employed on 
infrastructure based WMN backhaul. The 
backhaul is working on 2.4 GHz band and 
linked by directional antennas. The key 
consideration of this work is formatting the 
interference zones and selection of orthogonal 
channels for such zones to reduce co channel 
interference, whereas improper (non-
orthogonal) arrangement of channels under 
directional antennas creates serious level of 
interference as the signals would have more 
power in particular direction and covers 
maximum areas. To cover such parameter the 
zones of interference in proposed to covers 
both inter-flow links (single tier of direct hop), 
and intra-flow links (two tiers of directional 
hop) of directional antenna. 

In doing so this paper presents 7 sections. 
Section 2 presents review of the literature; 
section 3 provides mathematical procedure to 
find orthogonal sets. Section 4 discusses about 
the modelling of the proposed system. Section 
5 presents greedy algorithm for channel 
assignment. Results and discussion on 
orthogonal channel zones of 2.4 GHz system is 
presented in section 6. Finally, section 7 
provide conclusion.  

2. Literature Review 

 The litratutre review reflects lot of 
research work to deal the problem of 
interfernce introduced by partially overlapped 
channels. The concept of utilizing Partially 
overlapped channels with the alteration of 
energy masks was presented by the authors of 
[11], [12], [13]. This technique introduces, 
loss of information relative to the overlapped 
frequency range of partially overlapped 
channels. In other work, orthogonal channels 

are modeled as Least Congested Channel 
Search (LCCS), where periodically channel’s 
traffic is observed, in the case of overflow of 
traffic from threshold level, channel sweeps to 
LLC [14]. Their work was limited and does 
not support sudden change of traffic. The 
work of [15], tried to solve the problem of 
interfernce in multi channel (POC) 
environment by multicasting. They employed 
rational nodes to form multicast trees from 
soure to destination. Every node of tree, 
eqqiped with gateway which reduce the 
interference by limitting the broadcasting of 
POS channels. Their work aspects the 
bottelneck problem in heavy traffic. The bottel 
neck problem is some how overcomed the 
recent work of [16] where links were ranked 
on mobility data. The mobility data derived by 
traffic load and topology of network. Ranking 
links through multiple data types interduce 
system latency. The work of [17 and 18] 
focused on Interference of directional antennas 
in multi hop networks, Interference among the 
signals of directional antennas are measured in 
[17], both antennas are at 90 degree phase 
change in alignment the work did not contains 
data regarding spatial separation. The 
Performance of 802.11g system is observed 
with the support of multi radio [18], they try to 
prove with quantity study that the overall 
network efficiency is depended on the 
employment position of directional antennas, 
the position consider antennas alignment and 
distance. Algorithm “directionality as needed 
(DAN)”, is presented in [19], this work meets 
two aims: network with minimum interference 
with limited budget. The work of [20] presents 
the behavior of channel assignment in the 
environment of directional antennas. They 
present Outdoor testbed-based measurement 
of 802.11a, the system connected by 
directional antenna, in that system they 
estimate adjacent channel interference with the 
help of the antenna’s physical position, 
transmitted power of the interfaces and WMN 
throughput. Research work of [21], [22], [23] 
assignment of partially overlapped channels 
discuss about interfering signal and noise ratio 
(SINR) based novel model for channel 
allocation, the authors considered that the use 
of the channel partiality at some affordable 



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interference focused collective interference. 
Therefore, they are able to model only physical 
interference. A MICA algorithm-based 
allocation of partially Overlapped Channels 
(POS) is presented in [22], their focus was to 
enhance performance while decreasing 
interference of system. They sustain channel 
separation and node orthogonality with the 
consideration of Physical distance of nodes. 
Another technique to reduce interference is 
adopted in [23], where alternate channels in the 
form of odd number are selected for allocation, 
their results are equivalent with channel 
assignment where only limited orthogonal 
channel are used. A greedy channel 
assignment algorithm for Multi radio Multi 
Channel WMN is presented in [24] the total 
interference of static nodes is approximated 
and assigned channels with the nodes having 
minimum interference. The suggested work in 
this paper solved the bottel neck problem by 
directional antennas at physical layer with 
minimum latency. Static channels assign to 
perticular antenna this maintain the 
orthogonality and channel spacing between 
channels. Thus there was no loss of energy 
produced by masking of energy.  

3. Mathematical Procedure to Find 
Groups of Orthogonal Channels 

 Traditionaly the orthogonal channels are 
drived by using energy masks [11,12,13], 
discussed in litrature review. This process 
consumes times and introduce losses of 
energy w.r.t overlapped portion of two 
channels. Here a set theory is used to find out 
the groups of non-overlapped and overlapped 
channels for the (channel 1 to channel 11) on 
frequency band 2.4 GHz. Universal set “S”, of 
2.4GHz band is combination of two sets: 
Orthogonal and Non-orthogonal.  

S = {Orthogonal channels, Non-orthogonal 
channels} 

S = {On,NOn} 

Orthogonal channels “O”, contain all non-
overlapped channels related to the channel 
number “n” can be find out as, 

On = ∪N 

m=1 = {|(m− n)| > 4} 

Non-orthogonal channels “NO”, contain 
all overlapped channels related to channel 
number “n”, and can be find out as,  

 

 

Fig. 1. Interference zone of different AP’s NOn 
= {S\On} 

4. Modelling of Proposed System 

The network graph G for proposed work is 
identified as G = (U, V,L). The network 
consists of n mesh routers, distributed 
uniformly and independently over unit area. 
All nodes are connected by directional 
antennas for backhaul connectivity. The Area 
is divided into non overlapping directional 

Interference zones “Iz”. The system must 
satisfy the following considerations. 

• Number of interference zones = number 
of interfaces for backhaul connectivity 

• Beamwidth of directional zone = 360 deg 
/ number of zones 

• Linear area of zones = 2 directional nodes 
(2 Tier of directional hop) 

• Vertical area of zone = 1 direct node 
(single tire of direct hop) 

• Minimum number of zones = 1  



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Area of system is divided in zones, equal to 
the number of interfaces of node, each zone has 
a mesh router that is responsible for serving 
clients within the zone and linked with other 
zones by directional antenna. To deal with 
interferences, it is important to identify the 
interference nodes in Interference zones “Iz” in 
the network. Work considered two sources of 
interference, directional and direct links, here 
the nodes of directional links are identified “u” 
and nodes with direct links are identified as 
“v”, these nodes are connected by links “L”. 

The network graph G for proposed work is 
identified as G = (U, V,L). As stated in 
proposed work, every node have interference 
area up to second hop of directional antennas 
“u” and “u+1” and up to single hop for direct 
connected node “v” (as the directed node is in 
different direction of directional antenna). 
Using neighbouring directed coloring graph 
the identified interference zone is expressed as 
Iz = (u, u+1, v). For our work, we modeled 2.4 
GHz backhaul via OPNET 14. The system is 
designed with two scenarios.  

• Allocation of non-orthogonal channels to 
interference zones of WMN backhaul 

• Allocation of orthogonal channels to 
interference zones of WMN backhaul. 

Both scenarios comprise Multiple Access 
points, every access point have 3 interfaces, 2 
interfaces are reserved for backhaul link, there 
for it comprises 2 interference zones. The third 
interface is used for user access. Running 
application for system is FTP, which serves 
users in uniform pattern. In 1st scenario the 
channels are randomly assign to all nodes of 
zones without any care of orthogonal channels. 
While in 2nd scenario the group of orthogonal 
channels formatted by proposed mathematical 
process assigned to different interference 
zones. This maintains the orthogonality of 
channels within zones resulting minimum 
interference.  

5. A. Greedy Algorithm for 2.4 GHz 
backhaul link 

Following section illustrates the    
pseudocode of greedy algorithm for channel 
assignment of 2.4 GHz backhaul links. 

The core idea is to select, identified 
interference links and set of orthogonal 
channels, then assign channels to every link of 
in interference. That procedure will repeat until 
channels assigned to complete network. Every 
time selected interference links and channel set 
must be different. With this the network 
sustains orthogonality to reduce channel 
interference. 

 B. Algorithm Greedy channel Assign 
for 2.4 GHz backhaul 

Input: Graph G = (U, V,E); 

Available channels 1, 2, 3, ・ ・ ・ , 11 
1) Find conflict links Ec for each node v 

belongs to G = (U, V,E) 

2) For each interference zone Iz = (u, u + 1, 

v), select set of orthogonal channels of 

channel “n” by, On = ∪N m=1 = {|(m − n)| 
> 4} 

3) Assign channel, member of On = uj , 

4) Assign channel, member of On = uj+1, 

5) Assign channel, member of On = Vi, 

6) Iz 6= Iz of (1) and Orthogonal channels 

for n 6= n of (1) 

7) Repeat from 1 to 5 for every node 

belongs to G 

8) end 

6. Results and Discussion 

Proposed work analyzed the throughput 
and delay of orthogonal and non-orthogonal 
channel schemes for interference zones. Figure 
2 presents the comparative results of two 
scenarios in terms of average throughput, 
throughput of both scenarios of system is in 
quiet mode up to 50 sec, which is time taken 
by server to respond to users. 

 
Fig. 2. Average throughput of both schemes 



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63 

 

 

 

 
 

Fig. 3. Average delay of both schemes 
Fig. 2 illustrate the association of both 

scenarios by average throughput, this 
comparison shows that non-orthogonal 
allocation throughput drops after certain 
events while throughput of orthogonal 
allocation is constantly increasing, further it is 
observed that performance of proposed 
scheme sweeps 70% more than non-
orthogonal. 

Fig: 3 expressed the performance of both 
scenarios in terms of average delay, it shows 
that the maximum delay for 

orthogonal interference zones is less than 
0.003 sec, while for some events of non-
orthogonal interference zones, the delay 
reaches to 0.008 sec. Approximately we can 
reduce the delay in system by half with 
orthogonal interference zones. 

This can be further justified from Fig. 4 and 
5, where the average throughput and average 
delay is plotted with number of users. The 
number of users varies with the difference of 
10 and provides 10 different points to observe 
the results. Both results show the considerable 
enhancement in system performance when we 
use the proposed channel assignment scheme 
for backhaul links. With respect to simulation 
analysis, the simulation model is 

repeated for multiple times with different 

number of users and find out the different 

confidence intervals. The Table II shows the 

statistical data for two scenarios of 2.4 GHz 

backhaul. For the given statistical values, Fig. 

6 and 7 presents the plots for normal 

distribution of both scenarios 

 
Fig. 4. Average throughput/No. of users of 

both schemes 

 

 
Fig. 5. Average delay / No. of users of both 

schemes 

 



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64 

 
Fig. 6. Normal distribution of orthogonal 

interference zone 

 
Fig. 7. Normal distribution of non-orthogonal 

interference zone 

7. Conclusion  

An effective channel assignment scheme is 
presented where channels of 2.4 GHz are 
statically arranged as orthogonal channels to 
the Inter flow and Intra flow links of WLAN 
backhaul. Co-channel interference from 360 
degrees is initially controlled by directional 
antennas, further the proposed channel 
arrangement sustaining orthogonality between 
direct (inter-flow) and directional (Intra-flow) 
links, this reduces the co-channel interference 
among these nodes.  

In suggested work the interference is 
controlled at two phases: 1st by reducing 
interference directions (degrees), 2nd by 
allocating orthogonal channels to selected 
links. This study found significant 

improvement in system performance with the 
increase in system throughput and reduction in 
delay. Simulated results clearly illustrate that 
orthogonal scheme reaches approximately 
twice the performance in comparison with the 
non-orthogonal scheme. 

REFERENCES 

[1] Mannava, P., 2018. A Comprehensive Study 
on The Usage of Big Data Analytics for 
Wireless and Wired Networks. International 
Journal of Scientific Research in Science and 
Technology (IJSRST), Online ISSN: 2395-
602X, Print ISSN: 2395, 6011, pp.724-732. 

[2] Pang, Z., Luvisotto, M. and Dzung, D., 2017. 
Wireless high-performance communications: 
The challenges and opportunities of a new 
target. IEEE Industrial Electronics Magazine, 
11(3), pp.20-25. 

[3] Papavassiliou, S., Tsiropoulou, E.E., 
Promponas, P. and Vamvakas, P., 2020. A 
Paradigm Shift Toward Satisfaction, Realism 
and Efficiency in Wireless Networks 
Resource Sharing. IEEE Network.  

[4] Tabata, H., Suganuma, H. and Maehara, F., 
2021. Impact of adjacent-channel interference 
on transmission performance in asynchronous 
FBMC/OFDM systems. IEICE 
Communications Express, p.2020XBL0183.  

[5] Iqbal, S., Abdullah, A.H. and Qureshi, K.N., 
2020. An adaptive interference‐aware and 
traffic‐aware channel assignment strategy for 
backhaul networks. Concurrency and 
Computation: Practice and Experience, 
32(11), p.e5650. 

[6] Harkusha, S. and Yevdokymenko, M., 2021. 
The Development of Routing Flow Model in 
IEEE 802.11 Multi-radio Multi-channel Mesh 
Networks, Shown as a Konig Graph. In Data-
Centric Business and Applications (pp. 513-
528). Springer, Cham.  

[7] Hou, Y., Li, M. and Zeng, K., 2017, January. 
Throughput optimization in multi-hop 
wireless networks with reconfigurable 
antennas. In 2017 International Conference on 
Computing, Networking and Communications 
(ICNC) (pp. 620-626). IEEE.  

[8] Jeffrey G. Andrews, Arunabha Ghosh, and 
Rias Muhamed. Fundamentals of WiMAX: 
Understanding Broadband Wireless 
Networking. Prentice Hall, 2007. page 269-
365. 

[9] W. Zhou, X. Chen, and D. Qiao. Practical 
routing and channel assignment scheme for 
mesh networks with directional antennas. In 
IEEE International Conference on 
Communications, pages 3181–3187, May 
2008. 



Shazia Abbasi (et al.), Orthogonal Zones for Interference Migration in 2.4 GHz Mesh Backhaul 
 (pp. 59 - 65) 

Sukkur IBA Journal of Computing and Mathematical Science - SJCMS | Vol. 5 No. 2 July – December 2021 

65 

[10] S. Abbasi, Q. Kalhoro, and M. A. Kalhoro. 
Efficient use of partially overlapped channels 
in 2.4 ghz wlan backhaul links. In 
International Conference on Innovations in 
Information Technology, pages 7–11, April 
2011. 

[11] Arunesh Mishra, Vivek Shrivastava, Suman 
Banerjee, and William Arbaugh. Partially 
overlapped channels not considered harmful. 
ACM SIGMETRICS Performance Evaluation 
Review, 34(1):63–74, June 2006. 

[12] Z. Feng and Y. Yang. How much 
improvement can we get from partially 
overlapped channels? In 2008 IEEE Wireless 
Communications and Networking 
Conference, pages 2957–2962, March 2008. 

[13] Liu, K., Li, N. and Liu, Y., 2017, December. 
Min-interference and connectivity-oriented 
partially overlapped channel assignment for 
multi-radio multi-channel wireless mesh 
networks. In 2017 3rd IEEE International 
Conference on Computer and 
Communications (ICCC) (pp. 84-88). IEEE. 

[14] Arunesh Mishra, Suman Banerjee, and 
William Arbaugh. Weightedcoloring based 
channel assignment for wlans. ACM 
SIGMOBILEMobile Computing and 
Communications Review, 9(3):19–31, July 
2005. 

[15] Shahmirzadi, M.A., Dehghan, M. and 
Ghasemi, A., 2018. An optimization 
framework for multicasting in MCMR 
wireless mesh network with partially 
overlapping channels. Wireless Networks, 
24(4), pp.1099-1117.  

[16] 11 b Al-rimy, B.A.S., Kamat, M., Ghaleb, 
F.A., Rohani, M.F., Abd Razak, S. and Shah, 
M.A., 2020. A user mobility-aware fair 
channel assignment scheme for wireless mesh 
network. In Computational Science and 
Technology (pp. 531-541). Springer, 
Singapore. 

[17] Derdouri, L., Pham, C., Zouaoui, E.M.E.A. 
and Zeghib, N., 2019. Performance analysis of 
self-organised multicast group in multi-radio 
multi-channel wireless mesh networks. IET 
Communications, 14(4), pp.693-702. 

[18] V. Ramamurthi, A. Reaz, S. Dixit, and B. 
Mukherjee. Directionality as needed - 
achieving connectivity in wireless mesh 
networks. In 2008 IEEE International 
Conference on Communications, pages 3055–
3059,May 2008. 

[19] W. Zhou, X. Chen, and D. Qiao. Practical 
routing and channel assignment scheme for 
mesh networks with directional antennas. In 
2008 IEEE International Conference on 
Communications, pages 3181– 3187, May 
2008. 

[20] K. Zhou, X. Jia, L. Xie, Y. Chang, and X. 
Tang. Channel assignment for wlan by 
considering overlapping channels in sinr 
interference model. In International 
Conference on Computing, Networking and 
Communications (ICNC), pages 1005–1009, 
Jan 2012. 

[21] Gimenez-Guzman, J.M., Crespo-Sen, D. and 
Marsa-Maestre, I., 2020, December. A 
Cluster-Based Channel Assignment 
Technique in IEEE 802.11 Networks. In 
Telecom (Vol. 1, No. 3, pp. 228-241). 
Multidisciplinary Digital Publishing Institute. 

[22] W. Wang, B. Liu, M. Yang, J. Luo, and X. 
Shen. Max-cut based overlapping channel 
assignment for 802.11 multi-radio wireless 
mesh networks. In Proceedings of the 2013 
IEEE 17th International Conference on 
Computer Supported Cooperative Work in 
Design (CSCWD), pages 662–667, June 2013. 

[23] G. S. Uyanik, M. J. Abdel Rahman, and M. 
Krunz. Optimal guardband-aware channel 
assignment with bonding and aggregation in 
multichannel systems. In 2013 IEEE Global 
Communications Conference (GLOBECOM), 
pages 4769–4774, Dec 2013. 

[24] Jun Xu, Chengcheng Guo, and Jianfeng Yang. 
Interference-aware. greedy channel 
assignment in multi-radio multi-channel wmn. 
In 25th Wireless and Optical Communication 
Conference (WOCC), pages 1–4, May 2016