[ieee 2010 ieee asia-pacific conference on applied electromagnetics (apace 2010) - port dickson...

Proceedings of 2010 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2010)

Xplore Compliant ©2010 IEEE

The effects of foliage on 5.8GHz Broadband Fixed Wireless Access (BFWA)

N.A. Muhammad, T.A.Rahman, and S.K.A.Rahim

Wireless Communication Center, Faculty of Electrical Engineering,

Universiti Teknologi Malaysia, 81300 Skudai, Johor, Malaysia.

[email protected]

Abstract— This paper investigates the foliage effect on fixed wireless links based on IEEE 802.11a standard operating at frequency 5.8GHz of Unlicensed National Information Infrastructure (UNII) bands. Based on the studies of the measured received signal profiles under two different links, it is observed that the foliage obstruction gives significant effects on the link performance. The results from measurements performed are discussed and presented in term of their statistical distribution.

Keywords-Foliage, Propagation, Line of Sight, Non-Line of Sight.

I. INTRODUCTION

Wireless communication has created a continuing demand for high speed data, increased bandwidth and better quality of services. Nowadays, wireless technology has been recognized as an important option for delivering mobile, fixed and broadband services to the end users. Wireless access services are including Fixed Wireless Access (FWA), Mobile Wireless Access (MWA) and Broadband Wireless Access (BWA) [1]. Fixed wireless links can be defined when the position of both transmitter and receiver are static or at a fixed location during operation such as on top of, below of a building’s rooftop or mounted on the wall.

In order to have excellent performance of wireless link, advance knowledge on the surrounding environment is crucial. Even though the line of sight (LOS) is often desired to ensure a good wireless link performance, the propensity of trees appearing in the vicinity between the transmitter and receiver antennas is unavoidable especially when the system applied in suburban area.

This scenario refers to the problem occurred during the deployment of wireless network within the Universiti Teknologi Malaysia. Since the location of the students’ accommodation in Universiti Teknologi Malaysia are scattered, connection via wired system is consider as impractical solution. Alternatively, replacing the cable network with a wireless system such as BFWA is less expensive especially when the distance between subscribers are several kilometers apart. However, the presence of trees in the vicinity of this area can cause signal to fade which subsequently affect overall wireless link performance.

Vegetation gives a significant role in the fading phenomena in fixed wireless access links [2-7]. The leaves and branches of individual trees scatter electromagnetic waves which will degrade the performance of the received signal. Furthermore, the changes of trees such as growth over time of measurement will affect the condition of the link performance. Hence, the effects of foliage should be taken into consideration in fixed terrestrial links.

Foliage penetration loss is more complicated to analyze compared to the building penetration loss due to random and changing structure of foliage. Numerous study has been conducted which considered the effects of foliage in microwave links. A review of radio wave attenuation in forest environment consists of classic analytical and empirical methods have been presented in [8]. Radio wave propagation measurements through vegetation over a range of frequencies between 50 to 800MHz have been previously accounted in rain forests of India [9]. The transmission loss was found to increase with the increment of separation distance between transmitter and receiver. Besides, M. H. Hashim and S. Stavrou in [5], examines the effect of moving vegetation in various wind condition. According to Al-Nuaimi and Stephens in [10], the presence of vegetation in the form of a single tree, a line of trees, or a forest in the radio path of point-to-point links significantly influences the propagation of radio waves at frequencies above 1 GHz. Meanwhile, several residential radio penetration studies show that path loss and penetration loss increase as the frequency increases [11-13].

The main objective of this paper is to investigate the different performance for line of sight and foliage blocked of line of sight link. A series of trees obstruction measurement campaigns were carried out over a period of two weeks in April 2010 during the intermonsoon season in Malaysia.

II. MEASUREMENT APPROACH

A. Outdoor Environment The measurement campaigns were performed within the

Universiti Teknologi Malaysia over a period of two weeks in April 2010. The foliage chosen in this study are approximately 10 meters in height and the leaves size is between 3.5cm to 6.5cm. Two experimental sites were identified, Site 1: Line of



sight link, Site 2: Non-line of sight link. The photograph of the location under consideration for Site 1 and Site 2 are shown in Figure 1 and 2 respectively. Figure 3 shows the image captured from Google Earth where the measurements were conducted.

Figure 1: Site 1 (Line of Sight)

Figure 2: Site 2 (Non-Line of Sight)

Figure 3: Measurement locations

B. Measurement set up The path loss measurements were carried out using

equipment developed by Wireless Communication Centre (WCC), Universiti Teknologi Malaysia which is currently known as WCC Broadband system. This system operating at 5.8GHz UNII frequency bands in which it is consists of Radial Line Slot Array (RLSA) antenna, wireless radio and router board to provide both broadband wireless bridging and last mile access services. The antennas used for both links are linearly polarized Radial Line Slot Array (RLSA) antennas with gain and size of 7dBi and 13cm respectively. Figure 4 shows the equipment set up for a point-to-point link internet access. The transmitter antennas for both sites were remained in fixed positions at the rooftop of the building, while the receiver antennas were mounted on the wall. The distance between the transmitter and receiver for Site 1 is 66.86 meters whereas 127.9 meters for Site 2.

III. DATA ANALYSIS AND DISCUSSION

A. Main results By employing the concept of remote data logging, power

received measurements were acquired constantly via a remote server for 24 hours and seven days a week from two links. Then, the data logged were sent to remote server which running on a data acquisition system.

Total path loss, L calculated is the summation of free space

loss and excess loss. It is worth noting that excess loss is inclusive of foliage loss and other losses. The excess path loss can be computed by the subtraction of the total path loss from free space loss as shown in the equation 1 and 2 [14].

L = Lf + Le (1)

Lf = 32.44 + 20 log d (km) + 20 log f (MHz) (2)

Pr = Pt + Gt + Gr –L (3)

where,

Pr = Power received in dBm

Pt = Power transmitted in dBm

Gt = Gain of the transmitter in dBi

Gr = Gain of the receiver in dBi

Lf = Free space loss in dB

Le = Path loss in excess of free space loss in dB



Figure 4: The equipment set up for internet access.

Table 1 shows the frequency used for respective site as well as the calculated free space loss. The typical received signal strength was recorded in the measurement campaign for Site 1 (LOS) and Site 2 (NLOS) as illustrated in Figure 5. The received signal strength in Site 1 on that day was found to fall until the lowest signal strength of -55dBm from the maximum signal strength of -46.35dBm. By further analysis on both plots, it was observed that the received signal strength variations and deep fades were more noticeable at the Site 2. It was believed that the received signal strength for fixed wireless link was dependent on the obstacles appear between the transmitter and receiver. In addition, the excess path loss has been calculated to further investigate the loss value in the vicinity of the link. Figure 6 illustrates the excess path loss based on equation 3.

Table 1: Calculated Free Space Loss for both sites

Link Frequency (MHz)

Distance (km)

Free Space Loss (dB)

Site 1 (LOS) 5805 0.06686 84.22

Site 2 (NLOS) 5765 0.1279 89.79

Figure 5: Received Signal Strength

Figure 6: Excess Path Loss

0 200 400 600 800 1000 1200 1400-95

-90

-85

-80

-75

-70

-65

-60

-55

-50

-45

-40

Time (minutes)

Rec

eive

d S

igna

l Str

engt

h (d

Bm

)

Site 1 (LOS)

Site 2 (NLOS)

0 200 400 600 800 1000 1200 1400-25

-20

-15

-10

-5

0

5

10

15

20

25

30

Time (minutes)

Exc

ess

Pat

h Lo

ss (

dB)

Site 1(LOS)

Site 2 (NLOS)



B. Comparison to Known Distributions The distribution functions of excess path loss constructed

from the measured data were compared to the commonly known distributions associated with wireless communication systems, namely Gaussian, Rician, Rayleigh Nakagami, and Weilbull distributions [5]. Figure 7 and Figure 8 depict the probability distribution function (PDF) for LOS and NLOS respectively. From the visual inspection figures, it was obvious that Gaussian distribution is the most suitable to describe the excess path loss for LOS link. On the other hand, the measured data for NLOS can be fitted to Gaussian, Rician and Nakagami distributions.

Figure 7: Typical PDF for LOS link.

Figure 8: Typical PDF for LOS link.

IV. CONCLUSION

In order to study the effects of foliage blockage on 5.8GHz UNII bands, measurements were carried out over a period of two weeks within Universiti Teknologi Malaysia. The experiment results indicated that the received signal strength variation were clearly noticeable at the link which blocked by a tree. Further investigation and measurements in different vegetation depth, weather effect such as rain are vital since rain still an unclear factor for low frequency signal propagation through forested area.

ACKNOWLEDGMENT

The authors are most grateful to the anonymous reviewers for their thorough reviews and their constructive comments for this paper. They also wish to express their appreciation and thanks to Universiti Teknologi Malaysia for supporting the research work under the Wireless Campus Project.

REFERENCES

[1] R. Pandya, Introduction to WLLs: Application and Deployment for Fixed and Broadband Services: Piscataway, N.J.: Prentice Hall, 2003J. Clerk Maxwell, A Treatise on Electricity and Magnetism, 3rd ed., vol. 2. Oxford: Clarendon, 1892, pp.68–73.

[2] M. O. Al-Nuaimi and A. M. Hammoudeh, "Measurements and predictions of attenuation and scatter of microwave signals by trees," Microwaves, Antennas and Propagation, IEE Proceedings -, vol. 141, pp. 70-76, 1994.

[3] J. C. R. Dal Bello, et al., "Theoretical analysis and measurement results of vegetation effects on path loss for mobile cellular communication systems," Vehicular Technology, IEEE Transactions on, vol. 49, pp. 1285-1293, 2000.

[4] E. R. Pelet, et al., "Effect of wind on foliage obstructed line-of-sight channel at 2.5 GHz," Broadcasting, IEEE Transactions on, vol. 50, pp. 224-232, 2004.

[5] M. H. Hashim and S. Stavrou, "Measurements and modelling of wind influence on radiowave propagation through vegetation," Wireless Communications, IEEE Transactions on, vol. 5, pp. 1055-1064, 2006.

[6] M. Yu Song, et al., "Wind and rain influences on forested radiowave propagation," in Antennas and Propagation Society International Symposium, 2007 IEEE, 2007, pp. 3748-3751.

[7] M. J. Gans, et al., "Propagation measurements for fixed wireless loops (FWL) in a suburban region with foliage and terrain blockages," Wireless Communications, IEEE Transactions on, vol. 1, pp. 302-310, 2002.

[8] M. Yu Song, et al., "Study of propagation loss prediction in forest environment," Progress In Electromagnetics Research B, vol. 17, pp. 117-133, 2009.

[9] R. K. Tewari, et al., "Radio wave propagation through rain forests of India," Antennas and Propagation, IEEE Transactions on, vol. 38, pp. 433-449, 1990.

[10] M. O. Al-Nuaimi and R. B. L. Stephens, "Measurements and prediction model optimisation for signal attenuation in vegetation media at centimetre wave frequencies," Microwaves, Antennas and Propagation, IEE Proceedings -, vol. 145, pp. 201-206, 1998.

[11] D. M. J. Devasirvatham, et al., "Four-frequency CW measurements in residential environments for personal communications," in Universal Personal Communications, 1994. Record., 1994 Third Annual International Conference on, 1994, pp. 140-144.

-6 -5 -4 -3 -2 -1 0 1 2 30

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Excess Path Loss for Site 1 (LOS)

Den

sity

Excess Path Loss

Gaussian

10 15 20 25 300

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Excess Path Loss for Site 2 (NLOS)

Den

sity

Excess Path Loss

Rayleigh

NakagamiWeibull

Gaussian

Rician



[12] S. Aguirre, et al., "Radio propagation into buildings at 912, 1920, and 5990 MHz using microcells," in Universal Personal Communications, 1994. Record., 1994 Third Annual International Conference on, 1994, pp. 129-134.

[13] G. Durgin, et al., "Measurements and models for radio path loss and penetration loss in and around homes and trees at 5.85 GHz," Communications, IEEE Transactions on, vol. 46, pp. 1484-1496, 1998.

[14] H. R. Anderson, Fixed Broadband Wireless Sytem Design: UK: John Wiley&Sons, 2003.

[ieee 2010 ieee asia-pacific conference on applied electromagnetics (apace 2010) - port dickson...

Documents