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Microwave Point-to-Point Transmission Impairment

over Malaysia Sea Tidal at 7 GHz

Ahmad Firdaus Hakim Muhammad, Mahamod Ismail, J.S.Mandeep and A.T. Adediji

Dept. of Electrical, Electronic & System EngineeringUniversiti Kebangsaan Malaysia, 43600 UKM Bangi Selangor, Malaysia

Email: firdaushakim@yahoo.com, {mahamod, mandeep}@eng.ukm.my, kunleadediji2002@yahoo.co.uk

Abstract Cellular radio deployment involved Point-to-Point

(P2P) microwave transmission and planning. Proper planning

and design must take into consideration various impairments

such as atmosphere, rain attenuation, terrain profile, signal

blockage, and others. In this paper, we analyze received signal

level performance for microwave link propagating over sea tidal.

Data was collected over one day for P2P link with path length of

14.26 km that constitute 73.63% sea tidal. The study showed that

the signal fade varied about 13 dB and at least over 20% of daytime below threshold level.

Keywords-component; propagation; line-of-sight; point-to-

point; sea tidal; multipath

I. INTRODUCTIONMicrowave line-of-sight (LOS) links, sometime referred as

microwave link, LOS microwave, Point-to-Point (P2P) or

radio links, are composed of point-to-point systems between

two terrestrial stations that transmit and receive signal. Thelinks are designed to preserve direct LOS propagation path as

the main propagation mechanism, but in practice other

component and anomalies coexists due to reflection,diffraction, refraction and multipath [1].

The availability of P2P connection between the stationsmust always be nearly perfect (99.99%) in order to ensure that

the transmitted voice/data maintain its integrity at the receiver.

The received signal level or received signal strength must be

above the link threshold to make sure the links have a strength

value to cater for the fade margin. Without adequate value of

fade margin, there will be signal loss within the link in thestations, hence the data/voice signal being transmitted will not

reach the target area and resulted in high bit error ratio (BER).

The challenge in ensuring good system performance is to

ensure that the P2P link can militate against any obstacle

between the medium of the microwave stations.

In this paper, the study of sea tidal as one of the factorsthat affect microwave P2P performance is undertaken.Although there are many other obstructions to microwave P2Ptransmission, such as; rain, dust, terrain obstacle, etc., sea tidalis an obstacle that is very complicated to analyze and itinvolves a solution to some rural area data/voice coverage.The effect of sea tidal or sea ground to microwave propagationis related to multipath fading phenomena.

Hence, in this work, we dealt more on multipath fadingpropagation effect using two prediction models; BarnettVigants, and ITU models. Received Signal Level (RSL)characteristics on a flat terrain are also discussed.

The paper is divided into five sections; the present sectionis the introduction, section II present microwave propagationmechanism due to reflection and multipath fading in particular

to sea tidal followed by site description and signal receptionover P2P links in section III. Section IV analyzes andcompares signal reception collected over one day period forsignal propagates over sea tidal and reflected from groundterrain. Finally in Section V, we conclude the impairment dueto signal propagation over sea tidal and some mitigationtechnique.

II. MICROWAVE PROPAGATION MECHANISMMicrowave P2P typically use LOS mechanisms but

subjected to either clear path (Fresnel Zone) or obstructed path

due to terrain, building, vegetation and others. Multipathpropagation phenomenon and fading occurs when radio signal

reaching the receiving antenna by two or more indirect pathdue to reflection. A rigorous study on the acceptable path

length subjected to the rain attenuation and other factors for

P2P at and above 7 GHz been presented in [2][3].

Tidal fading occurs as a result of the interference between

the direct line-of-sight path from the transmitter antenna to the

receiver antennas and the indirect path that reflect on the waterplane as in Fig.1.

Fig 1. The two ray model, showing (a) the direct path and (b) the indirect path

reflected off the water plane.

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As the tide rises and falls, the length of the reflected path

changes. This in turn causes a change in the phase difference

between the two paths. As the phase difference approaches180 degrees, the interference between the paths will be

increasingly destructive, resulting in a deeper fade. The

reflected path is longer and so may interfere destructively with

the direct path. Refraction is neglected in this diagram. The

ray paths are curved due to the flat-earth representation used

to clarify the reflection. The two phenomenons that getinvolved in the both fluctuated link are reflection and

multipath fading.

A.ReflectionReflection occurs when an electromagnetic wave strikes a

nearly smooth, large surface, such as a water surface, and a

portion of the energy is reflected from the surface and

continues propagating along a path that defines an angle with

the surface equal to that of the incident wave. Obstruction

dimensions are very large compared to the signal wavelength.

The strength of the reflected wave is determined by the

reflection coefficient; a value that depends on the frequencyand polarization of radiation, the angle of incidence, and the

roughness of the reflecting surface.

For shallow incidence angles and smooth seas, typical

values of the reflection coefficient are near unity, i.e., the

reflected wave is almost as strong as the incidence wavecausing the so-calledspecular reflection. The law of reflection

states that for specular reflection, the angle at which the wave

is incident on the surface equals the angle at which it is

reflected. Reflection rays from different surfaces may interfere

constructively or destructively at a receiver causing multipath

propagation or multipath fading.

B.Multipath FadingMultipath fading is the dominant fading mechanism for

frequencies lower than approximately 10 GHz. A reflected

wave causes a phenomenon known as multipath, meaning that

the radio signal can travel many paths to reach the receiver.

Typically, multipath occurs when a reflected wave reaches the

receiver at the same time as the direct wave that travels in a

straight line from the transmitter. Multipath propagation gives

rise to two kinds of signal fading effects, i.e., flat fading and

frequency selective fading. The flat fading effect is due tothermal noise and interference. Certainly, both flat and

selective fading typically occur in combination. Two scenariosof multipath are possible:

i. If the two signals reach the receiver in phase, then thesignal is amplified. This is known as an upfade.

Upfades can also occur when the radio wave is

trapped within an atmospheric duct. As can be seen

from equation (1), higher upfades are possible for

longer paths:

Upfademax = 10 log d 0.03d(dB) (1)

where dis the path length in km.

For example, ford= 14.26 km, the maximum upfade

can be up to 11.11 dB.

ii. If the two waves reach the receiver out of phase, theyweaken the overall received signal. If the two waves

are 180 apart when they reach the receiver, they can

completely cancel each other out which may result intotal loss of signal. A location where a signal is to

cancel out by multipath is called a null ordownfade.

In [4], measurement results show that most multipath

fading occurs at night during the inter-moon seasons when

there is low wind activity and high humidity. Under such

conditions, the sea surface is smooth and the reflected signal isstrong and produces deep and fast multipath fading. The sea

breeze observed over a LOS link situated in Visakhapatnam

operating at 6 GHz [5] brought about some distinct

characteristic changes in the LOS link signal strength.

III. MEASUREMENT SETUP AND DATA COLLECTIONThese comprise site selection, path profile, measurement

setup, and data collection.

A. Site SelectionFour study sites as shown in Figure 2 are selected for P2P

measurement between Station A and Station B with link

distances as summarized in Table 1, however only data for

Kuala Linggi Tanjung Bidara (KLTB/TB-KL) will be

analyzed in this paper.

Fig. 2: P2P Study site

Table 1: Characteristics of the Stations considered for the P2P

measurements.STATION A STATION B LATITUDE A LONGITUDE A LATITUDE B LONGITUDE B LINK DISTANCE(KM) SEA WATER DISTANCE(KM)

Kuala Linggi Tanjung Bidara 02 22 38.40 N 1 01 59 04.90 E 02 18 02.00 N 102 05 15.70 E 14.26 10.5

Pulau Perhentian Bukit Bintang 05 54 04.80 N 1 02 44 29.30 E 05 37 41.99 N 102 38 54.95 E 31.89 20

Pulau Pemanggil Sekakap 02 34 58.20 N 104 18 55.20 E 02 21 43.30 N 103 53 56.10 E 52.4 52

Taman Puteri Wangsa Desa Tebrau 01 35 29.10 N 1 03 47 55.00 E 01 33 30.15 N 103 47 20.84 E 3.8 0

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B. Path ProfileThe path profile is generated using P2P link planning tool,

namely Pathloss 4.0. Figure 3 show path profile for KL-TBthat propagates over sea tidal.

Fig 3. Terrain Profile Kuala Linggi - Tanjung Bidara

C.Measurement SetupThe experimentation set-up for TB-KL reported in this

paper is as shown in Table 2.

Table 2: Base station parameters

Parameter KL Station TB Station

Antenna Size, (m) 1.8 1.8

Frequency (GHz) 7.575

k-factor 1.33

RSL (dBm) -29

D.Data CollectionThe data was collected at three microwave PTP links.

Received signal level (dBm) for main Out Door Unit (ODU)reading was collected. The data was captured and recorded in

IDU monitoring software for one day. Pathloss 4.0 software

was used to generate link budget for all the links and estimated

RSL at receiving station for KL-TB link is -29 dBm as shown

in Table 2.

IV. RESULT AND DISCUSSIONWireless links over estuaries experience time-varying

dependent on height of the tide. This is a problem becauselinks experiencing such fading can degrade in quality or result

in total failure when the fade margin is insufficient. Figure 3and 4 shows the measured signal strength for the KL-TB link

distance of 14.26 km with water spanning 10.5 km of the

entire link between the stations.

Fig. 3: Received Signal Level at Kuala Linggi Station

Fig. 4: Received Signal Level at Tanjung Bidara Station

From the figures, it is observed that RSL fluctuated andfaded most of the time and did not achieve the estimated RSL.

This is because of unstable reflection effect from the sea that

needs further analysis.

A.

Sea Tidal Height AnalysisAs we know sea tidal height can change any time depends

on countrys climate. In this study, the changes of the tidal

height may have effect on the RSL reading. This is because as

the tidal height changes, more multipath fading results due to

effects from the water reflection.

Figures 5 and 6 show the multipath for TB-KL and KL-TBrespectively. There are many reflected and indirect waves

from sea are transmitted back to the receiver area, thus cause

interference to the direct wave and reduced RSL reading. The

interference effects from reflection wave and multipath fading

is called inter-system interference (ISI).

The multipath view only represents certain k-factor values.The ground-earth terrain may not be much affected by the k-

factor; however for sea surface the k-factor varies as sea tidal

height change although not significant.

Path length (14.26 km)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Elevation(m)

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

-80

-60

-40

-20

0

8:30:00AM

9:30:00AM

10:30:00AM

11:30:00AM

12:30:00PM

1:30:00PM

2:30:00PM

3:30:00PM

4:30:00PM

5:30:00PM

6:30:00PM

7:30:00PM

8:30:00PM

ReceivedS

ignalLevel(dBm)

Main ODU RSL Vs Time

Current RSL

Maximum RSL

Minimum RSL

-80

-60

-40

-20

0

8:30:00AM

9:30:00AM

10:30:00AM

11:30:00AM

12:30:00PM

1:30:00PM

2:30:00PM

3:30:00PM

4:30:00PM

5:30:00PM

6:30:00PM

7:30:00PM

8:30:00PM

ReceiveSign

alLevel(dBm)

Main ODU RSL Vs Time

Maximum RSL

Minimum RSL

Current RSL

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Fig. 5: Multipath from Tanjung Bidara-Kuala Linggi

Fig. 6: Multipath from Kuala Linggi-Tanjung Bidara

Figure 7 shows the reflection analysis for TB-KL link using

Pathloss 4.0 where RSL fluctuated when there is change in the

k-factors.

Fig. 7: Reflection Analysis.

We observed at Tanjung Bidara site, the RSL change

very badly during 1 PM to 2.45 PM due increase in the seatidal. Table 3 shows and the sea tidal reading Tanjung

Bidara during 9/03/2010 taken from Malaysia Metrological

Department. During that time the interference of reflected

signal strength was too high.

Table 3 Tide Level at Tanjung Bidara

Time Height

0221 1.54 (HIGH)

1200 1.02 (HIGH)

1330 1.03 (HIGH)

2021 0.62 (LOW)

B.Multipath Fading Probability Model

Microwave links as for other links is a must to have

accurate prediction method in order to reduce the different

between simulation results and real system performance.

Nevertheless many microwave links have been deployedaround the world; unfortunately many of these links are in

the short range which path length is less than 20 km.

Therefore to address these constraints, these links need to as

accurate as possible.

There are two famous models in microwave link

propagation prediction model. These are Vigants-Barnett

model and ITU-R Multipath Probability model. The two

outages models are expressed as follows:

Vigants-Barnett [6]:

= 2.5 106310/10 (2)

and ITU-R [7]:

0 = 3.2(1 + )0.97 100.0320.00085/10 (3)

where, f is the frequency, d is the distance K is the

geoclimatic, Cis the terrain factor, FM is the effective fade

margin is the link inclination and hL is the lowestantenna altitude above sea level.

The each link probability is evaluated for both models using

simulated fade margin with link over sea tidal (softwaresimulation) and the measured real fade margin (average per

day). The measured and estimated fade margins are shown

in Tables 4 and 5 respectively.

Table 4: Simulated and measured fade margin over TB-KL link

Table 5: Estimated Fade Margin for Vigants-Barnett and ITU-R Multipath

Probability model

Link Estimated FM (%) Measured FM (%)

Vigants-Barnett 99.99991526 99.99822947

ITU-R 99.99991526 99.99822947

From the tables, the simulated and measured fade margin be

difference at least by 13 dB due to link passing through the

flat sea water.

14.30 1 2 3 4 5 6 7 8 9 10 11 12 13-10

0

10

20

30

40

50

60

70

80

90

100

110

120

14.30 1 2 3 4 5 6 7 8 9 10 11 12 13-10

0

10

20

30

40

50

60

70

80

90

100

110

120

RelativeReceiveSignal(dB)

EarthRadius Factor - arctan(K) ()

53.133.8 36 38 40 42 44 46 48 50 52-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.00

H1=55.0m, H2=45.0m, F=7575.0MHz, V

Link Simulated Measured

TB-KL fade (dB) 37.20 24.0314

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V. CONCLUSIONThe propagation mechanism of a microwave P2P link over

sea tidal has been analyzed using data collected over one day.

The tidal height affects the RSL and deep fades have a

significant impact on link quality. Furthermore, unlike LOS

and ground reflection propagation, tidal effects may be the

primary cause of performance degradation. However, bettermodel should include weather information such as rain and

humidity. In the near future, mitigation methods such as slow

frequency hopping and space diversity strategies will be

investigated.

ACKNOWLEDGMENT

The authors are very grateful and express dear thanks to theUniversiti Kebangsaan Malaysia for funding this work underGPP-2013-006 research university grant.

REFERENCES

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[2] U. Kesavan, A. R. Tharek, and Md. Rafiqul Islam, Comparison ofMicrowave Path Lengths between Temperate and Tropical RegionBased on Effects of Rain, Progress In Electromagnetics ResearchSymposium Proceedings, Moscow, Russia, August 19-23, 2012, pp. 504-507.

[3] D. Narayana Rao, K. Krishna Reddy, T.R. Vijaya Kumar, S.V. BhaskaraRao, M.V.S.N. Prasad, D. Punyaseshudu, Study of path inclinationeffects on performance of LOS microwave links in southern India, IEEProc.-Microw. Antennas Propag., Vol. 142, No. 4, August 1995,pp.295-299.

[4] Jin-Teong Ong and Chu-Feng Hu, Propagation measurement on anOver-Water, Line-of-Sight Link in Singapore, Proc. InternationalConference on Information, Communications and Signal Processing(ICICS'97), 9-12 Sept. 1997, pp.1714-1718.

[5] G.S.V. Radha Krishna Rao and M. Purnachandra Rao, A Study on thelnfluence of Sea breeze on Line-Of-Sight links located inVisakhapatnam, Proc. of INMIC 2004, pp. 293-300.

[6] Barnett, W. T., Multipath propagation at 4, 6 and 11 GHz,Bell SystemTechnical Journal,Vol. 51, No. 2, 311-361, Feb. 1972.

[7] International Telecommunication Union, Propagation data andprediction methods required for the design of terrestrial line-of-sightsystems, ITU-R P. 530-12, 2005.