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Underwater wireless communication systemTo cite this article J H Goh et al 2009 J Phys Conf Ser 178 012029

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Underwater Wireless Communication System

J H Goh A Shaw A I Al-Shammarsquoa

Liverpool John Moores University General Engineering Research Institute (GERI) RF and Microwave Group Byrom Street Liverpool L3 3AF UK

E-mail jhgoh2006ljmuacuk

Abstract Underwater communication has a range of applications including remotely operated vehicle (ROV) and autonomous underwater vehicle (AUV) communication and docking in the offshore industry Current underwater transmission techniques is primarily utilise sound waves for large distance at lower frequencies and the velocity of sound in water is approximately 1500ms the resultant communications have problems with multi-path propagation and low bandwidth problems The use of electromagnetic (EM) techniques underwater has largely been overlooked because of the attenuation due to the conductivity of seawater However for short range applications the higher frequencies and much higher velocity can prove advantageous This paper will outline a project which will utilise recent investigations that demonstrate EM wave propagation up to the MHz frequency range is possible in seawater

1 Introduction The present technology for underwater communication involves either light or sound Both of these techniques have their advantages and limitations In optical systems which use lasers the light is rapidly attenuated in shallow water due to the backscatter and is therefore limited to very short distances Acoustic techniques are the most widely used in water communications The velocity of sound in water is approximately 1500ms They are severely affected by multi-path propagation [1] which is shown in Figure 1 The multi-path propagation in water is including reflection and refraction Reflection of signals occurs at the ocean surface and at the ocean floor Reflection is when the direction of the wave front is changed at an interface between two different mediums and the wave front returns into the original medium Refraction occurs when a wave passes from one medium to another medium and the direction of the wave is changed This results in multiple propagation paths from the transmitter to the receiver as shown in Figure 1 d is the direct path 1d and 2d are possibly

indirect paths This means the signal following the 1d and 2d paths arrive at different times and slightly after the direct path This results in a pulse spreading This pulse spreading limits the data rates of transmissions and can be a cause of higher error probability

As a result a new method was introduced which is electromagnetic (EM) wave propagation The high EM frequency at megahertz (MHz) is used to propagate in the water over short and long distances The speed of an EM wave in vacuum is sm 103 8times The speed of an EM wave in water is

affected by a factor rr microε where rε is the relative permittivity and rmicro is the relative permeability

The rε for the water at the frequencies considered is approximately 81 rmicro is 1 therefore the speed of the EM wave in water is

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

ccopy 2009 IOP Publishing Ltd 1

smc

crr

vacuumwater 10333

181

103 78

timesasymptimes

timesasympasympmicroε

d

1d

2d

1θ

2θ

Figure 1 Multi-path Propagation in Water

Maxwellrsquos equations [23] are used to predict EM wave propagation in water The electric field

strength xΕ and the magnetic field strength yΗ are presented for a linearly polarized plane wave

propagating in the z direction in equations (1) and (2)

)(0

ztjx e γω minussdotΕ=Ε (1)

)(0

ztjy e γω minussdotΗ=Η (2)

where is the angular frequency given as fπω 2= (3)

and is the propagation constant given as βαγ j+= (4)

where is the attenuation constant and is the phase constant the phase constant is given as

λπβ 2= (5)

Although EM wave propagation is also affected by multi-path propagation the higher attenuation will reduce these effects and the higher frequencies and faster velocity will enable higher data rates and bandwidth

2 Modulation and Demodulation Modulation is a process of adding the information signal onto the carrier signal and must be accomplished cost effectively and accurately for maximum range and minimum interference [Lathi 1998] Demodulation is a process of removing the information signal from the carrier frequency (retranslate back the signal to its original position)

21 On-Off Keying (OOK) The amplitude of the carrier frequency is varied to represent binary lsquo1rsquo and lsquo0rsquo in OOK which is shown in Figure 2 The frequency and phase of the signal remain the same only the amplitude is changes The signal region (1 bit) which has voltage level (amplitude) is represent binary lsquo1rsquo and binary lsquo0rsquo is represented by no voltage The advantage for the OOK is the amount of transmitted energy that required for transmit information is very low The bit duration for the peak amplitude of the signal is always constant

22 OOK Modulation The OOK signal can be generated by using an OOK modulator [4] which is shown in Figure 3 It consists of a multiplier which multiplies the square waveform and the carrier frequency to obtain an OOK signal When an input signals binary lsquo1rsquo (represented by pulse) multiplies with the sine wave

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

2

(carrier frequency) then it will results an analog signal which has voltage level (amplitude) When an input signals binary lsquo0rsquo (no pulse) multiplies with the sine wave (carrier frequency) then it will results an analog signal which no voltage

)(tVm

)cos( tV cc ω

)(tVOOK

Figure 2 OOK Signal Figure 3 Block Diagram of OOK Modulator

23 OOK Demodulation Figure 4 shows the block diagram of OOK demodulator [5] It consists of a multiplier a low-pass filter (LPF) and a comparator The multiplier is use to multiplies the OOK signal and the local carrier frequency which same frequency as the transmitter The higher frequency (sum-frequency) output of the multiplier is rejected by LPF and the lower frequency (difference-frequency) output of the multiplier is passed through the LPF The output of the LPF is then fed into the comparator to obtain the original digital signal )(tVm The function of the comparator is to compare the voltage level

(amplitude) and make a decision for that signal If the voltage level is more than 0 then is binary lsquo1rsquo otherwise is binary lsquo0rsquo

)(tVm

)cos( tV cc ω

)(tVOOK )(0 tV

Figure 4 Block Diagram of OOK Demodulator

3 Loop Antenna Loop antenna is the directional type antenna which has one or more complete turns of conductors [6] The loop antenna has a very low radiation resistance because it acts as inductive component like a large inductor [7] The advantages of the loop antenna is strongly responds to the magnetic field (Η ) of the EM waves and less affected by the man-made interference because it has strong electric field ( Ε ) The loop antenna is also picks up less noise and provided better signal to noise ratio (SNR) The wavelength equation of the loop antenna is given as [8]

dπλ = (6) where is the diameter of the loop antenna

A double loop antenna with 32cm of diameter is used for the experiment which is shown in Figure 5 By theoretical the wavelength of this antenna can be calculated by using the equation (6) This double loop antenna has two turns and the circumference isdπ2 and it is half-wavelength antenna Therefore

md 024)320(422

asymp== ππλ

and the frequency of this antenna

MHzc

f 75024

103 8

asymptimes==λ

If the antenna is in water then the wavelength of this antenna was affected by a factorrr microε

Therefore the wavelength in water can be calculated as

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

3

MHzc

frr

8024181

103 8

asymptimestimes

times=sdot

=λmicroε

Figure 5 Double Loop Antenna with 32cm of diameter

4 Experiment and Results Figure 6 shows the experiment setup for modulation and demodulation A RF switch ZASWA-2-50DR is used to generate the OOK signal The RF switch is used to select the on or off signal for two input frequencies A +5V and -5V voltage is supplied to active the RF switch The two output ports of the RF switch are used as input and the input port of the RF switch is used as output The direct digital synthesis (DDS) generator is used to generate the carrier frequency that represent binary lsquo1rsquo and the ground (no frequency) represent binary lsquo0rsquo The square wave generator is used to generate the square wave which used to control the switching of the RF switch The output of the RF switch is a OOK signal and connected to the transmitter (Tx) The OOK signal is transmit by the transmitter (Tx) the signal is transmit from the Tx to receiver (Rx) and then Rx received the signal A voltage controlled oscillator (VCO) ZOS-300+ is uses to generate a local carrier frequency which same frequency as the transmitter frequency or more or less than the transmitter frequency The frequency mixer ZX05-1MHW is uses to subtract the received signal (RF) from the local carrier frequency (LO) and provided the intermediate frequency (IF) as output of the frequency mixer The output signal (intermediate frequency) of frequency mixer is connected to the power detector follow by LPF and 50 terminator The demodulated signal (output of the 50 terminator) is then displayed on oscilloscope The square wave that generated from square wave generator is also connected to the oscilloscope as trigger function

The experiment for underwater transmission is take place in the large cylinder tank filled with 27000 litres of water which is shown in Figure 7a and Figure 7b shows the dimension of the cylinder tank The cylinder tank has a 34m diameter and a 235m height the depth of the water was 185m The gantry is attached on top of the cylinder tank in order to place the receiver (Rx) on top of it the gantry has a 36m length and a 01m height The steel rack was used to hold the transmitter and receiver when put both of it into the water The receiver was mounted from a gantry on moveable support The transmitter (Tx) was put into bottom of the tank The Rx was placed vertically with the Tx in water The distance between Rx and Tx mx 411=

Both of the Tx and Rx are needed to test in order to know the best transmission frequency that can use in water Figure 8 shows the received signal strength in water From Figure 8 the higher power level for the received signal is -605dBm at 6MHz and -605dBm at 10MHz Therefore the 6 and 10 MHz are considered as the best transmission frequency in water

Figure 9 shows the amplitude of the received signal for 6 MHz and 107 MHz as a function of horizontal distance in water for the experiment The vertical distance between the Tx and Rx is 14m 6 MHz and 107 MHz were used because these two frequencies were the best for the double loop antenna The start position at 0cm represents the position of the transmitter (Tx) From Figure 9 the received signal strength for 6MHz decreases as Rx moved away from Tx and the received signal strength is begins to increase at 130cm because Rx also received the reflected signal from the metal

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

4

tank At 107MHz the signal strength also falls with distance bur begins to increase beyond 170cm for the same reason Based on Figure 9 it can be conclude that the 6MHz frequency can provide a higher receive power level compare to the 107MHz frequency but 107MHz can transmit longer distances in water compared to 6 MHz

Figure 10 shows the voltage level transition of the OOK modulated signal for 6 MHz and 107 MHz in water The highest voltage level transition for 6MHz frequency is mV450 at the near field (0 and 10cm) and the lowest voltage level transition is mV70 at the far field (110 to 140cm) The transition levels lower than mV150 are considered very small and are difficult to detect and demodulate Therefore the maximum transmission distance for 6MHz in the water is 90cm The highest voltage level transition for 107MHz is mV250 at the near field (0 to 20cm) and lowest voltage level transition is mV58 at the far field (170cm) Therefore the maximum distance for 107MHz frequency to transmit in water is 130cm with a transition voltage ofmV160

Figure 6 Experiment Setup for Modulation and Demodulation

x

Figure 7a Water Tank filled with 27000 litres of

water Figure 7b Experiment Setup for Underwater

Transmission in Water Tank

5 Conclusion In this paper it proved the propagation of EM waves at high frequency in the water is possible Underwater communications by using the EM wave propagation method has a bright future and very useful for many applications Propagation of EM waves in water is affected by parameters including permittivity )(ε conductivity )(σ Although the EM wave propagation has high attenuation in the near field it has been shown that a far field region exists that would allow transmission over longer

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

5

distance than previously thought The advantages of the EM wave are low power potentially covert useful bandwidth for many applications such as compress video radar data telemetry and useful Range

-100

-95

-90

-85

-80

-75

-70

-65

-60

4 6 8 10 12 14 16 18 20DDS Frequency (MHz)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

Figure 8 Received Signal Strength for Different DDS Frequency in Water

-85

-80

-75

-70

-65

-60

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

6 MHz107 MHz

50

100

150

200

250

300

350

400

450

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Vo

ltag

e T

ran

siti

on

(m

V)

6 MHz107 MHz

Figure 9 Received Signal Strength for 6 MHz and 107 MHz versus Horizontal Distance in Water

Figure 10 Voltage Level Transition of the OOK modulated signal for 6 MHz and 107 MHz Water

References [1] Ahmed I Al-Shammarsquoa Andrew Shaw and Saher Saman ldquoPropagation of Electromagnetic

Waves at MHz Frequencies Through Seawaterrdquo IEEE Transactions on Antenna and Propagation Vol 52 No 11 November 2004 pp 2843-2849

[2] John D Kraus ldquoElectromagnetics 4th Editionrdquo McGraw-Hill International Editions 1992 [3] David H Staelin Ann W Morgenthaler and Jin Au Kong ldquoElectromagnetic Wavesrdquo Prentice

Hall International Inc 1994 [4] Ifiok Otung ldquoCommunication Engineering Principlesrdquo Palgrave 1998 [5] Alberto Leon-Garcia and Indra Widjaja ldquoCommunication Networks Fundamental Concepts

and Key Architecturerdquo McGraw-Hill International Editions 2006 [6] Constantine A Balanis ldquoAntenna Theory Analysis and Design 3rd Editionrdquo John Wiley amp

Sons Inc 2005 [7] Joseph Carr ldquoAntenna Toolkit 2nd Editionrdquo Newnes 2001 [8] John D Kraus and Ronald J Marhefka ldquoAntennas For All Applicationsrdquo McGraw-Hill

International Editions 2002

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

6

smc

crr

vacuumwater 10333

181

103 78

timesasymptimes

timesasympasympmicroε

d

1d

2d

1θ

2θ

Figure 1 Multi-path Propagation in Water

Maxwellrsquos equations [23] are used to predict EM wave propagation in water The electric field

strength xΕ and the magnetic field strength yΗ are presented for a linearly polarized plane wave

propagating in the z direction in equations (1) and (2)

)(0

ztjx e γω minussdotΕ=Ε (1)

)(0

ztjy e γω minussdotΗ=Η (2)

where is the angular frequency given as fπω 2= (3)

and is the propagation constant given as βαγ j+= (4)

where is the attenuation constant and is the phase constant the phase constant is given as

λπβ 2= (5)

Although EM wave propagation is also affected by multi-path propagation the higher attenuation will reduce these effects and the higher frequencies and faster velocity will enable higher data rates and bandwidth

2 Modulation and Demodulation Modulation is a process of adding the information signal onto the carrier signal and must be accomplished cost effectively and accurately for maximum range and minimum interference [Lathi 1998] Demodulation is a process of removing the information signal from the carrier frequency (retranslate back the signal to its original position)

21 On-Off Keying (OOK) The amplitude of the carrier frequency is varied to represent binary lsquo1rsquo and lsquo0rsquo in OOK which is shown in Figure 2 The frequency and phase of the signal remain the same only the amplitude is changes The signal region (1 bit) which has voltage level (amplitude) is represent binary lsquo1rsquo and binary lsquo0rsquo is represented by no voltage The advantage for the OOK is the amount of transmitted energy that required for transmit information is very low The bit duration for the peak amplitude of the signal is always constant

22 OOK Modulation The OOK signal can be generated by using an OOK modulator [4] which is shown in Figure 3 It consists of a multiplier which multiplies the square waveform and the carrier frequency to obtain an OOK signal When an input signals binary lsquo1rsquo (represented by pulse) multiplies with the sine wave

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

2

(carrier frequency) then it will results an analog signal which has voltage level (amplitude) When an input signals binary lsquo0rsquo (no pulse) multiplies with the sine wave (carrier frequency) then it will results an analog signal which no voltage

)(tVm

)cos( tV cc ω

)(tVOOK

Figure 2 OOK Signal Figure 3 Block Diagram of OOK Modulator

23 OOK Demodulation Figure 4 shows the block diagram of OOK demodulator [5] It consists of a multiplier a low-pass filter (LPF) and a comparator The multiplier is use to multiplies the OOK signal and the local carrier frequency which same frequency as the transmitter The higher frequency (sum-frequency) output of the multiplier is rejected by LPF and the lower frequency (difference-frequency) output of the multiplier is passed through the LPF The output of the LPF is then fed into the comparator to obtain the original digital signal )(tVm The function of the comparator is to compare the voltage level

(amplitude) and make a decision for that signal If the voltage level is more than 0 then is binary lsquo1rsquo otherwise is binary lsquo0rsquo

)(tVm

)cos( tV cc ω

)(tVOOK )(0 tV

Figure 4 Block Diagram of OOK Demodulator

3 Loop Antenna Loop antenna is the directional type antenna which has one or more complete turns of conductors [6] The loop antenna has a very low radiation resistance because it acts as inductive component like a large inductor [7] The advantages of the loop antenna is strongly responds to the magnetic field (Η ) of the EM waves and less affected by the man-made interference because it has strong electric field ( Ε ) The loop antenna is also picks up less noise and provided better signal to noise ratio (SNR) The wavelength equation of the loop antenna is given as [8]

dπλ = (6) where is the diameter of the loop antenna

A double loop antenna with 32cm of diameter is used for the experiment which is shown in Figure 5 By theoretical the wavelength of this antenna can be calculated by using the equation (6) This double loop antenna has two turns and the circumference isdπ2 and it is half-wavelength antenna Therefore

md 024)320(422

asymp== ππλ

and the frequency of this antenna

MHzc

f 75024

103 8

asymptimes==λ

If the antenna is in water then the wavelength of this antenna was affected by a factorrr microε

Therefore the wavelength in water can be calculated as

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

3

MHzc

frr

8024181

103 8

asymptimestimes

times=sdot

=λmicroε

Figure 5 Double Loop Antenna with 32cm of diameter

4 Experiment and Results Figure 6 shows the experiment setup for modulation and demodulation A RF switch ZASWA-2-50DR is used to generate the OOK signal The RF switch is used to select the on or off signal for two input frequencies A +5V and -5V voltage is supplied to active the RF switch The two output ports of the RF switch are used as input and the input port of the RF switch is used as output The direct digital synthesis (DDS) generator is used to generate the carrier frequency that represent binary lsquo1rsquo and the ground (no frequency) represent binary lsquo0rsquo The square wave generator is used to generate the square wave which used to control the switching of the RF switch The output of the RF switch is a OOK signal and connected to the transmitter (Tx) The OOK signal is transmit by the transmitter (Tx) the signal is transmit from the Tx to receiver (Rx) and then Rx received the signal A voltage controlled oscillator (VCO) ZOS-300+ is uses to generate a local carrier frequency which same frequency as the transmitter frequency or more or less than the transmitter frequency The frequency mixer ZX05-1MHW is uses to subtract the received signal (RF) from the local carrier frequency (LO) and provided the intermediate frequency (IF) as output of the frequency mixer The output signal (intermediate frequency) of frequency mixer is connected to the power detector follow by LPF and 50 terminator The demodulated signal (output of the 50 terminator) is then displayed on oscilloscope The square wave that generated from square wave generator is also connected to the oscilloscope as trigger function

The experiment for underwater transmission is take place in the large cylinder tank filled with 27000 litres of water which is shown in Figure 7a and Figure 7b shows the dimension of the cylinder tank The cylinder tank has a 34m diameter and a 235m height the depth of the water was 185m The gantry is attached on top of the cylinder tank in order to place the receiver (Rx) on top of it the gantry has a 36m length and a 01m height The steel rack was used to hold the transmitter and receiver when put both of it into the water The receiver was mounted from a gantry on moveable support The transmitter (Tx) was put into bottom of the tank The Rx was placed vertically with the Tx in water The distance between Rx and Tx mx 411=

Both of the Tx and Rx are needed to test in order to know the best transmission frequency that can use in water Figure 8 shows the received signal strength in water From Figure 8 the higher power level for the received signal is -605dBm at 6MHz and -605dBm at 10MHz Therefore the 6 and 10 MHz are considered as the best transmission frequency in water

Figure 9 shows the amplitude of the received signal for 6 MHz and 107 MHz as a function of horizontal distance in water for the experiment The vertical distance between the Tx and Rx is 14m 6 MHz and 107 MHz were used because these two frequencies were the best for the double loop antenna The start position at 0cm represents the position of the transmitter (Tx) From Figure 9 the received signal strength for 6MHz decreases as Rx moved away from Tx and the received signal strength is begins to increase at 130cm because Rx also received the reflected signal from the metal

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

4

tank At 107MHz the signal strength also falls with distance bur begins to increase beyond 170cm for the same reason Based on Figure 9 it can be conclude that the 6MHz frequency can provide a higher receive power level compare to the 107MHz frequency but 107MHz can transmit longer distances in water compared to 6 MHz

Figure 10 shows the voltage level transition of the OOK modulated signal for 6 MHz and 107 MHz in water The highest voltage level transition for 6MHz frequency is mV450 at the near field (0 and 10cm) and the lowest voltage level transition is mV70 at the far field (110 to 140cm) The transition levels lower than mV150 are considered very small and are difficult to detect and demodulate Therefore the maximum transmission distance for 6MHz in the water is 90cm The highest voltage level transition for 107MHz is mV250 at the near field (0 to 20cm) and lowest voltage level transition is mV58 at the far field (170cm) Therefore the maximum distance for 107MHz frequency to transmit in water is 130cm with a transition voltage ofmV160

Figure 6 Experiment Setup for Modulation and Demodulation

x

Figure 7a Water Tank filled with 27000 litres of

water Figure 7b Experiment Setup for Underwater

Transmission in Water Tank

5 Conclusion In this paper it proved the propagation of EM waves at high frequency in the water is possible Underwater communications by using the EM wave propagation method has a bright future and very useful for many applications Propagation of EM waves in water is affected by parameters including permittivity )(ε conductivity )(σ Although the EM wave propagation has high attenuation in the near field it has been shown that a far field region exists that would allow transmission over longer

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

5

distance than previously thought The advantages of the EM wave are low power potentially covert useful bandwidth for many applications such as compress video radar data telemetry and useful Range

-100

-95

-90

-85

-80

-75

-70

-65

-60

4 6 8 10 12 14 16 18 20DDS Frequency (MHz)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

Figure 8 Received Signal Strength for Different DDS Frequency in Water

-85

-80

-75

-70

-65

-60

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

6 MHz107 MHz

50

100

150

200

250

300

350

400

450

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Vo

ltag

e T

ran

siti

on

(m

V)

6 MHz107 MHz

Figure 9 Received Signal Strength for 6 MHz and 107 MHz versus Horizontal Distance in Water

Figure 10 Voltage Level Transition of the OOK modulated signal for 6 MHz and 107 MHz Water

References [1] Ahmed I Al-Shammarsquoa Andrew Shaw and Saher Saman ldquoPropagation of Electromagnetic

Waves at MHz Frequencies Through Seawaterrdquo IEEE Transactions on Antenna and Propagation Vol 52 No 11 November 2004 pp 2843-2849

[2] John D Kraus ldquoElectromagnetics 4th Editionrdquo McGraw-Hill International Editions 1992 [3] David H Staelin Ann W Morgenthaler and Jin Au Kong ldquoElectromagnetic Wavesrdquo Prentice

Hall International Inc 1994 [4] Ifiok Otung ldquoCommunication Engineering Principlesrdquo Palgrave 1998 [5] Alberto Leon-Garcia and Indra Widjaja ldquoCommunication Networks Fundamental Concepts

and Key Architecturerdquo McGraw-Hill International Editions 2006 [6] Constantine A Balanis ldquoAntenna Theory Analysis and Design 3rd Editionrdquo John Wiley amp

Sons Inc 2005 [7] Joseph Carr ldquoAntenna Toolkit 2nd Editionrdquo Newnes 2001 [8] John D Kraus and Ronald J Marhefka ldquoAntennas For All Applicationsrdquo McGraw-Hill

International Editions 2002

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

6

(carrier frequency) then it will results an analog signal which has voltage level (amplitude) When an input signals binary lsquo0rsquo (no pulse) multiplies with the sine wave (carrier frequency) then it will results an analog signal which no voltage

)(tVm

)cos( tV cc ω

)(tVOOK

Figure 2 OOK Signal Figure 3 Block Diagram of OOK Modulator

23 OOK Demodulation Figure 4 shows the block diagram of OOK demodulator [5] It consists of a multiplier a low-pass filter (LPF) and a comparator The multiplier is use to multiplies the OOK signal and the local carrier frequency which same frequency as the transmitter The higher frequency (sum-frequency) output of the multiplier is rejected by LPF and the lower frequency (difference-frequency) output of the multiplier is passed through the LPF The output of the LPF is then fed into the comparator to obtain the original digital signal )(tVm The function of the comparator is to compare the voltage level

(amplitude) and make a decision for that signal If the voltage level is more than 0 then is binary lsquo1rsquo otherwise is binary lsquo0rsquo

)(tVm

)cos( tV cc ω

)(tVOOK )(0 tV

Figure 4 Block Diagram of OOK Demodulator

3 Loop Antenna Loop antenna is the directional type antenna which has one or more complete turns of conductors [6] The loop antenna has a very low radiation resistance because it acts as inductive component like a large inductor [7] The advantages of the loop antenna is strongly responds to the magnetic field (Η ) of the EM waves and less affected by the man-made interference because it has strong electric field ( Ε ) The loop antenna is also picks up less noise and provided better signal to noise ratio (SNR) The wavelength equation of the loop antenna is given as [8]

dπλ = (6) where is the diameter of the loop antenna

A double loop antenna with 32cm of diameter is used for the experiment which is shown in Figure 5 By theoretical the wavelength of this antenna can be calculated by using the equation (6) This double loop antenna has two turns and the circumference isdπ2 and it is half-wavelength antenna Therefore

md 024)320(422

asymp== ππλ

and the frequency of this antenna

MHzc

f 75024

103 8

asymptimes==λ

If the antenna is in water then the wavelength of this antenna was affected by a factorrr microε

Therefore the wavelength in water can be calculated as

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

3

MHzc

frr

8024181

103 8

asymptimestimes

times=sdot

=λmicroε

Figure 5 Double Loop Antenna with 32cm of diameter

4 Experiment and Results Figure 6 shows the experiment setup for modulation and demodulation A RF switch ZASWA-2-50DR is used to generate the OOK signal The RF switch is used to select the on or off signal for two input frequencies A +5V and -5V voltage is supplied to active the RF switch The two output ports of the RF switch are used as input and the input port of the RF switch is used as output The direct digital synthesis (DDS) generator is used to generate the carrier frequency that represent binary lsquo1rsquo and the ground (no frequency) represent binary lsquo0rsquo The square wave generator is used to generate the square wave which used to control the switching of the RF switch The output of the RF switch is a OOK signal and connected to the transmitter (Tx) The OOK signal is transmit by the transmitter (Tx) the signal is transmit from the Tx to receiver (Rx) and then Rx received the signal A voltage controlled oscillator (VCO) ZOS-300+ is uses to generate a local carrier frequency which same frequency as the transmitter frequency or more or less than the transmitter frequency The frequency mixer ZX05-1MHW is uses to subtract the received signal (RF) from the local carrier frequency (LO) and provided the intermediate frequency (IF) as output of the frequency mixer The output signal (intermediate frequency) of frequency mixer is connected to the power detector follow by LPF and 50 terminator The demodulated signal (output of the 50 terminator) is then displayed on oscilloscope The square wave that generated from square wave generator is also connected to the oscilloscope as trigger function

The experiment for underwater transmission is take place in the large cylinder tank filled with 27000 litres of water which is shown in Figure 7a and Figure 7b shows the dimension of the cylinder tank The cylinder tank has a 34m diameter and a 235m height the depth of the water was 185m The gantry is attached on top of the cylinder tank in order to place the receiver (Rx) on top of it the gantry has a 36m length and a 01m height The steel rack was used to hold the transmitter and receiver when put both of it into the water The receiver was mounted from a gantry on moveable support The transmitter (Tx) was put into bottom of the tank The Rx was placed vertically with the Tx in water The distance between Rx and Tx mx 411=

Both of the Tx and Rx are needed to test in order to know the best transmission frequency that can use in water Figure 8 shows the received signal strength in water From Figure 8 the higher power level for the received signal is -605dBm at 6MHz and -605dBm at 10MHz Therefore the 6 and 10 MHz are considered as the best transmission frequency in water

Figure 9 shows the amplitude of the received signal for 6 MHz and 107 MHz as a function of horizontal distance in water for the experiment The vertical distance between the Tx and Rx is 14m 6 MHz and 107 MHz were used because these two frequencies were the best for the double loop antenna The start position at 0cm represents the position of the transmitter (Tx) From Figure 9 the received signal strength for 6MHz decreases as Rx moved away from Tx and the received signal strength is begins to increase at 130cm because Rx also received the reflected signal from the metal

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

4

tank At 107MHz the signal strength also falls with distance bur begins to increase beyond 170cm for the same reason Based on Figure 9 it can be conclude that the 6MHz frequency can provide a higher receive power level compare to the 107MHz frequency but 107MHz can transmit longer distances in water compared to 6 MHz

Figure 10 shows the voltage level transition of the OOK modulated signal for 6 MHz and 107 MHz in water The highest voltage level transition for 6MHz frequency is mV450 at the near field (0 and 10cm) and the lowest voltage level transition is mV70 at the far field (110 to 140cm) The transition levels lower than mV150 are considered very small and are difficult to detect and demodulate Therefore the maximum transmission distance for 6MHz in the water is 90cm The highest voltage level transition for 107MHz is mV250 at the near field (0 to 20cm) and lowest voltage level transition is mV58 at the far field (170cm) Therefore the maximum distance for 107MHz frequency to transmit in water is 130cm with a transition voltage ofmV160

Figure 6 Experiment Setup for Modulation and Demodulation

x

Figure 7a Water Tank filled with 27000 litres of

water Figure 7b Experiment Setup for Underwater

Transmission in Water Tank

5 Conclusion In this paper it proved the propagation of EM waves at high frequency in the water is possible Underwater communications by using the EM wave propagation method has a bright future and very useful for many applications Propagation of EM waves in water is affected by parameters including permittivity )(ε conductivity )(σ Although the EM wave propagation has high attenuation in the near field it has been shown that a far field region exists that would allow transmission over longer

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

5

distance than previously thought The advantages of the EM wave are low power potentially covert useful bandwidth for many applications such as compress video radar data telemetry and useful Range

-100

-95

-90

-85

-80

-75

-70

-65

-60

4 6 8 10 12 14 16 18 20DDS Frequency (MHz)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

Figure 8 Received Signal Strength for Different DDS Frequency in Water

-85

-80

-75

-70

-65

-60

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

6 MHz107 MHz

50

100

150

200

250

300

350

400

450

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Vo

ltag

e T

ran

siti

on

(m

V)

6 MHz107 MHz

Figure 9 Received Signal Strength for 6 MHz and 107 MHz versus Horizontal Distance in Water

Figure 10 Voltage Level Transition of the OOK modulated signal for 6 MHz and 107 MHz Water

References [1] Ahmed I Al-Shammarsquoa Andrew Shaw and Saher Saman ldquoPropagation of Electromagnetic

Waves at MHz Frequencies Through Seawaterrdquo IEEE Transactions on Antenna and Propagation Vol 52 No 11 November 2004 pp 2843-2849

[2] John D Kraus ldquoElectromagnetics 4th Editionrdquo McGraw-Hill International Editions 1992 [3] David H Staelin Ann W Morgenthaler and Jin Au Kong ldquoElectromagnetic Wavesrdquo Prentice

Hall International Inc 1994 [4] Ifiok Otung ldquoCommunication Engineering Principlesrdquo Palgrave 1998 [5] Alberto Leon-Garcia and Indra Widjaja ldquoCommunication Networks Fundamental Concepts

and Key Architecturerdquo McGraw-Hill International Editions 2006 [6] Constantine A Balanis ldquoAntenna Theory Analysis and Design 3rd Editionrdquo John Wiley amp

Sons Inc 2005 [7] Joseph Carr ldquoAntenna Toolkit 2nd Editionrdquo Newnes 2001 [8] John D Kraus and Ronald J Marhefka ldquoAntennas For All Applicationsrdquo McGraw-Hill

International Editions 2002

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

6

MHzc

frr

8024181

103 8

asymptimestimes

times=sdot

=λmicroε

Figure 5 Double Loop Antenna with 32cm of diameter

4 Experiment and Results Figure 6 shows the experiment setup for modulation and demodulation A RF switch ZASWA-2-50DR is used to generate the OOK signal The RF switch is used to select the on or off signal for two input frequencies A +5V and -5V voltage is supplied to active the RF switch The two output ports of the RF switch are used as input and the input port of the RF switch is used as output The direct digital synthesis (DDS) generator is used to generate the carrier frequency that represent binary lsquo1rsquo and the ground (no frequency) represent binary lsquo0rsquo The square wave generator is used to generate the square wave which used to control the switching of the RF switch The output of the RF switch is a OOK signal and connected to the transmitter (Tx) The OOK signal is transmit by the transmitter (Tx) the signal is transmit from the Tx to receiver (Rx) and then Rx received the signal A voltage controlled oscillator (VCO) ZOS-300+ is uses to generate a local carrier frequency which same frequency as the transmitter frequency or more or less than the transmitter frequency The frequency mixer ZX05-1MHW is uses to subtract the received signal (RF) from the local carrier frequency (LO) and provided the intermediate frequency (IF) as output of the frequency mixer The output signal (intermediate frequency) of frequency mixer is connected to the power detector follow by LPF and 50 terminator The demodulated signal (output of the 50 terminator) is then displayed on oscilloscope The square wave that generated from square wave generator is also connected to the oscilloscope as trigger function

The experiment for underwater transmission is take place in the large cylinder tank filled with 27000 litres of water which is shown in Figure 7a and Figure 7b shows the dimension of the cylinder tank The cylinder tank has a 34m diameter and a 235m height the depth of the water was 185m The gantry is attached on top of the cylinder tank in order to place the receiver (Rx) on top of it the gantry has a 36m length and a 01m height The steel rack was used to hold the transmitter and receiver when put both of it into the water The receiver was mounted from a gantry on moveable support The transmitter (Tx) was put into bottom of the tank The Rx was placed vertically with the Tx in water The distance between Rx and Tx mx 411=

Both of the Tx and Rx are needed to test in order to know the best transmission frequency that can use in water Figure 8 shows the received signal strength in water From Figure 8 the higher power level for the received signal is -605dBm at 6MHz and -605dBm at 10MHz Therefore the 6 and 10 MHz are considered as the best transmission frequency in water

Figure 9 shows the amplitude of the received signal for 6 MHz and 107 MHz as a function of horizontal distance in water for the experiment The vertical distance between the Tx and Rx is 14m 6 MHz and 107 MHz were used because these two frequencies were the best for the double loop antenna The start position at 0cm represents the position of the transmitter (Tx) From Figure 9 the received signal strength for 6MHz decreases as Rx moved away from Tx and the received signal strength is begins to increase at 130cm because Rx also received the reflected signal from the metal

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

4

tank At 107MHz the signal strength also falls with distance bur begins to increase beyond 170cm for the same reason Based on Figure 9 it can be conclude that the 6MHz frequency can provide a higher receive power level compare to the 107MHz frequency but 107MHz can transmit longer distances in water compared to 6 MHz

Figure 10 shows the voltage level transition of the OOK modulated signal for 6 MHz and 107 MHz in water The highest voltage level transition for 6MHz frequency is mV450 at the near field (0 and 10cm) and the lowest voltage level transition is mV70 at the far field (110 to 140cm) The transition levels lower than mV150 are considered very small and are difficult to detect and demodulate Therefore the maximum transmission distance for 6MHz in the water is 90cm The highest voltage level transition for 107MHz is mV250 at the near field (0 to 20cm) and lowest voltage level transition is mV58 at the far field (170cm) Therefore the maximum distance for 107MHz frequency to transmit in water is 130cm with a transition voltage ofmV160

Figure 6 Experiment Setup for Modulation and Demodulation

x

Figure 7a Water Tank filled with 27000 litres of

water Figure 7b Experiment Setup for Underwater

Transmission in Water Tank

5 Conclusion In this paper it proved the propagation of EM waves at high frequency in the water is possible Underwater communications by using the EM wave propagation method has a bright future and very useful for many applications Propagation of EM waves in water is affected by parameters including permittivity )(ε conductivity )(σ Although the EM wave propagation has high attenuation in the near field it has been shown that a far field region exists that would allow transmission over longer

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

5

distance than previously thought The advantages of the EM wave are low power potentially covert useful bandwidth for many applications such as compress video radar data telemetry and useful Range

-100

-95

-90

-85

-80

-75

-70

-65

-60

4 6 8 10 12 14 16 18 20DDS Frequency (MHz)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

Figure 8 Received Signal Strength for Different DDS Frequency in Water

-85

-80

-75

-70

-65

-60

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

6 MHz107 MHz

50

100

150

200

250

300

350

400

450

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Vo

ltag

e T

ran

siti

on

(m

V)

6 MHz107 MHz

Figure 9 Received Signal Strength for 6 MHz and 107 MHz versus Horizontal Distance in Water

Figure 10 Voltage Level Transition of the OOK modulated signal for 6 MHz and 107 MHz Water

References [1] Ahmed I Al-Shammarsquoa Andrew Shaw and Saher Saman ldquoPropagation of Electromagnetic

Waves at MHz Frequencies Through Seawaterrdquo IEEE Transactions on Antenna and Propagation Vol 52 No 11 November 2004 pp 2843-2849

[2] John D Kraus ldquoElectromagnetics 4th Editionrdquo McGraw-Hill International Editions 1992 [3] David H Staelin Ann W Morgenthaler and Jin Au Kong ldquoElectromagnetic Wavesrdquo Prentice

Hall International Inc 1994 [4] Ifiok Otung ldquoCommunication Engineering Principlesrdquo Palgrave 1998 [5] Alberto Leon-Garcia and Indra Widjaja ldquoCommunication Networks Fundamental Concepts

and Key Architecturerdquo McGraw-Hill International Editions 2006 [6] Constantine A Balanis ldquoAntenna Theory Analysis and Design 3rd Editionrdquo John Wiley amp

Sons Inc 2005 [7] Joseph Carr ldquoAntenna Toolkit 2nd Editionrdquo Newnes 2001 [8] John D Kraus and Ronald J Marhefka ldquoAntennas For All Applicationsrdquo McGraw-Hill

International Editions 2002

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

6

tank At 107MHz the signal strength also falls with distance bur begins to increase beyond 170cm for the same reason Based on Figure 9 it can be conclude that the 6MHz frequency can provide a higher receive power level compare to the 107MHz frequency but 107MHz can transmit longer distances in water compared to 6 MHz

Figure 10 shows the voltage level transition of the OOK modulated signal for 6 MHz and 107 MHz in water The highest voltage level transition for 6MHz frequency is mV450 at the near field (0 and 10cm) and the lowest voltage level transition is mV70 at the far field (110 to 140cm) The transition levels lower than mV150 are considered very small and are difficult to detect and demodulate Therefore the maximum transmission distance for 6MHz in the water is 90cm The highest voltage level transition for 107MHz is mV250 at the near field (0 to 20cm) and lowest voltage level transition is mV58 at the far field (170cm) Therefore the maximum distance for 107MHz frequency to transmit in water is 130cm with a transition voltage ofmV160

Figure 6 Experiment Setup for Modulation and Demodulation

x

Figure 7a Water Tank filled with 27000 litres of

water Figure 7b Experiment Setup for Underwater

Transmission in Water Tank

5 Conclusion In this paper it proved the propagation of EM waves at high frequency in the water is possible Underwater communications by using the EM wave propagation method has a bright future and very useful for many applications Propagation of EM waves in water is affected by parameters including permittivity )(ε conductivity )(σ Although the EM wave propagation has high attenuation in the near field it has been shown that a far field region exists that would allow transmission over longer

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

5

distance than previously thought The advantages of the EM wave are low power potentially covert useful bandwidth for many applications such as compress video radar data telemetry and useful Range

-100

-95

-90

-85

-80

-75

-70

-65

-60

4 6 8 10 12 14 16 18 20DDS Frequency (MHz)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

Figure 8 Received Signal Strength for Different DDS Frequency in Water

-85

-80

-75

-70

-65

-60

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

6 MHz107 MHz

50

100

150

200

250

300

350

400

450

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Vo

ltag

e T

ran

siti

on

(m

V)

6 MHz107 MHz

Figure 9 Received Signal Strength for 6 MHz and 107 MHz versus Horizontal Distance in Water

Figure 10 Voltage Level Transition of the OOK modulated signal for 6 MHz and 107 MHz Water

References [1] Ahmed I Al-Shammarsquoa Andrew Shaw and Saher Saman ldquoPropagation of Electromagnetic

Waves at MHz Frequencies Through Seawaterrdquo IEEE Transactions on Antenna and Propagation Vol 52 No 11 November 2004 pp 2843-2849

[2] John D Kraus ldquoElectromagnetics 4th Editionrdquo McGraw-Hill International Editions 1992 [3] David H Staelin Ann W Morgenthaler and Jin Au Kong ldquoElectromagnetic Wavesrdquo Prentice

Hall International Inc 1994 [4] Ifiok Otung ldquoCommunication Engineering Principlesrdquo Palgrave 1998 [5] Alberto Leon-Garcia and Indra Widjaja ldquoCommunication Networks Fundamental Concepts

and Key Architecturerdquo McGraw-Hill International Editions 2006 [6] Constantine A Balanis ldquoAntenna Theory Analysis and Design 3rd Editionrdquo John Wiley amp

Sons Inc 2005 [7] Joseph Carr ldquoAntenna Toolkit 2nd Editionrdquo Newnes 2001 [8] John D Kraus and Ronald J Marhefka ldquoAntennas For All Applicationsrdquo McGraw-Hill

International Editions 2002

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

6

distance than previously thought The advantages of the EM wave are low power potentially covert useful bandwidth for many applications such as compress video radar data telemetry and useful Range

-100

-95

-90

-85

-80

-75

-70

-65

-60

4 6 8 10 12 14 16 18 20DDS Frequency (MHz)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

Figure 8 Received Signal Strength for Different DDS Frequency in Water

-85

-80

-75

-70

-65

-60

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Rec

eive

d S

ign

al S

tren

gth

(d

Bm

)

6 MHz107 MHz

50

100

150

200

250

300

350

400

450

-40 -20 0 20 40 60 80 100 120 140 160 180 200Distance (cm)

Vo

ltag

e T

ran

siti

on

(m

V)

6 MHz107 MHz

Figure 9 Received Signal Strength for 6 MHz and 107 MHz versus Horizontal Distance in Water

Figure 10 Voltage Level Transition of the OOK modulated signal for 6 MHz and 107 MHz Water

References [1] Ahmed I Al-Shammarsquoa Andrew Shaw and Saher Saman ldquoPropagation of Electromagnetic

Waves at MHz Frequencies Through Seawaterrdquo IEEE Transactions on Antenna and Propagation Vol 52 No 11 November 2004 pp 2843-2849

[2] John D Kraus ldquoElectromagnetics 4th Editionrdquo McGraw-Hill International Editions 1992 [3] David H Staelin Ann W Morgenthaler and Jin Au Kong ldquoElectromagnetic Wavesrdquo Prentice

Hall International Inc 1994 [4] Ifiok Otung ldquoCommunication Engineering Principlesrdquo Palgrave 1998 [5] Alberto Leon-Garcia and Indra Widjaja ldquoCommunication Networks Fundamental Concepts

and Key Architecturerdquo McGraw-Hill International Editions 2006 [6] Constantine A Balanis ldquoAntenna Theory Analysis and Design 3rd Editionrdquo John Wiley amp

Sons Inc 2005 [7] Joseph Carr ldquoAntenna Toolkit 2nd Editionrdquo Newnes 2001 [8] John D Kraus and Ronald J Marhefka ldquoAntennas For All Applicationsrdquo McGraw-Hill

International Editions 2002

Sensors amp their Applications XV IOP PublishingJournal of Physics Conference Series 178 (2009) 012029 doi1010881742-65961781012029

6