MARINE COMMUNICATION“Short history”

•The correct use of marine radios

communication is paramount to safe

boating and in the right hands, a

marine radios can save life and

property.

Presenter: Sagun Subedi

MOKPO NATIONAL UNIVERSITY

It is necessary to understand difference the between the term marine and maritime communication. There is very little difference. Both come from the Latin word for 'sea' which is mare, Maris. Thus, 'marine' directly relates to the sea, while 'maritime' relates to things associated with the sea.

Marine

• Marine is an adjective meaning of or pertaining to the sea, as in 'marine biology,' the study of life in the sea.

• He was a marine in World War II.

Maritime

• Maritime is an adjective meaning pertaining to objects or actions related to or conducted on the sea, as in 'maritime history,' which is the study of events that have occurred on the high seas, shipping, commerce, discovery.

• We enjoyed maritime activities such as kayaking and deep sea diving.

Marine communication• As it is known that earth consists of 70% water and it can be predicted

that marine communication is vast than terrestrial communication.

• Marine communication refers to the Information exchange between sea things as ships or other equipment floating or under sea\ocean.

• Initially for this communication flag semaphore were used.Flag semaphore is the telegraphy system conveying information at a distance by means of visual signals with hand-held flags,

rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags; it is read when the flag is in a fixed position.

• Earlier in the 17th century ship to ship or ship to shore communication was watched by the skilled radio officers which latter was replaced by radio telegraphy using Morse code.

• Marine communication between ship to shore and ship to ship is carried out by very high frequency (VHF) radio. Digital selective calling (DSC) is now being integrated with VHF as per SOLAS (safety of life at sea) convection.

• DSC come with digital remote commands to transmit or receive distress alert, urgent or safety and routine priority message.

Progress in Marine Radio Communication• Marine communication is believed to accelerate with the invention of the RMS Queen Mary(1936-

1967).

• A paper entitled “A survey of Marine Radio Progress, with special reference to RMS Queen Mary” was presented at the meeting of the wireless section of the institution of Electrical Engineers. This paper summarizes the progress such as radio equipment used in cargo and passenger vessels, radio problems encountered , way to solve the problems and the actual radio station of the RMS Queen Mary.

#Queen Mary constructed by john brown and company in Clydebank, Scotland route between Southampton,

Cherbourg and New York. Also serves as military ship for troops during WWII. Currently it is in New York as

Tourist attraction.

• This installation comprises four transmitters and nine or ten

receivers; the control room can handle four independent

duplex circuits, and provision is made for high-speed

transmission and reception, and simultaneously

communication on both telegraphy and telephony with both sides of the Atlantic.

Marine communication

INMARSAT

It is British satellite telecommunication company, offering global mobile services.

The organization was created to establish and operate a satellite communications network for the maritime community.

COSPAS-SARSAT

The International Cospas-Sarsat Program is a satellite-based search and rescue (SAR) distress alert detection and information distribution system.

As of 2011, 26 country ( including republic of Korea), regional governments and one organization (Chunghwa Telecom) are providers of ground segments.

Cell phones age:

• In early 70s, cell phones were developed, though they provide the convenience of simple, easy-to-use, inexpensive, private and generally reliable telephone service to home, office, automobile or other locations yet they weren’t and still aren’t used as the mean of communication in marine system. Here are some reasons behind them.

• Most cell phones are designed for a land-based service. Their coverage offshore is limited, and may change without notice .

• If distress call is made on the cell phones only one party you call will be able to hear you.

• Locating a cell caller is hard to do. If you don’t know your location, the coast guard will have difficulty finding your location on the water.

VHF radios• VHF marine radios were designed with safety in mind, i.e. if you are in distress, calls can be received

not only by the coast guard but by ships which may be in position to give immediate assistance.

• A VHF marine radio also helps ensure that storm warnings and other urgent marine information broadcasts are received.

• VHF radios can be used anywhere around the world.

“VHF radios”

“MSI- receivers” “S-EPIRB”

For international operational requirements, the global maritime distress safety system (GMDSS) has divided world into four sub areas.

• Area A1: lies within range of shore-based VHF coast stations (up to about 20 NM);

• VHF equipment, S-EPIRB or VHF EPIRB, MSI receiver.

• Area A2: lies within range of shore based MF coast stations (excluding A1 areas) (up to about 150 NM) ;

• VHF and MF equipment, S-EPIRB, MSI receiver.

• Area A3: lies within the coverage area of INMARSAT communications satellites (excluding A1 and A2 areas- approximately between latitude 70 degrees north to latitude 70 degrees south);

• VHF, MF and HF or satellite equipment, S-EPIRB, MSI receiver.

• Area A4: comprises the remaining sea areas outside A1, A2, A3 (the polar regions);• VHF, MF and HF equipment, 406 MHZ S-EPIRB, MSI receiver.

# NM/M/nmi is unit of distance that is approximately one minute of arc measured along any meridian i.e. 1,852 meter or 6,076 feet.

“Marine communication over-view”

GENERAL INTRODUCTION

Brief definition on EPIRB, signal processing at LOESAR & LEOLUT and slight focus on Doppler’s shift.

EPIRBs/PLBs

SAR SERVICES

SATELLITES

INMARSAT COSPAS-SARSAT

LEO-SAR GEO-SAR

406 MHz

LUT/MCC

NATIONAL/INTERNATIONAL NETWORKS

COAST/RADIO STATIONS

RESC

UE C

OO

RD

INA

TION

C

ENTER

EARTH’S SURFACE

85

0 K

m

Introduction to EPIRB;

• EPIRB stands for emergency position-indicating radio beacon. It is a device that is designed to transmit signal if you get in trouble. No matter where you are in the world, and EPIRB sends a signal to emergency responders through a satellite system called COSPAS-SARSAT.

• A modern EPIRB is a sophisticated device that contains:-• Antenna

• Sea switch

• Activation switch

• Test button

• Lanyard

• Strobe light

• LEDs and BUZZER

• Internal battery supply for at least 48 hours

• GPS position fixing system.• #EPIRB may either be portable and capable of being manually activated or they must be able to be deployed automatically without any operator intervention.

Working mechanism of EPIRB;

• On the activation of the EPIRB, it sends the signal (frequency varying from 406 to 406.1 MHz) which is picked up by LEOSAR. This communication is rather one way.

• Each 406 MHz EPIRB incorporates a unique identification code (if it is properly

registered).

• Once the satellite receives the beacon’s signals, the Doppler's shift is measured and the beacon’s digital data is recovered from the signal. The digital data include a maritime identification digit (MID, a three digit number identifying the administrative country) and either a ship station identifier (SSI, a 6 digit number assigned to specific ships), a ship radio call sign or a serial number to identify the ship in distress.

• # This data is then stored in DRU of the LEOSAR and then transmit back to the LUT/MCC for further processing such as locating and sending rescue team (SARs) towards the vessel.

LEOSAR• 406 MHz receiver

• The 406 MHz ELTs utilize a Bi-Phase-L type modulation (Manchester coding) transmitting for 500ms every 50 seconds.

• Bandwidth calculations for the 406 are slightly different since the transmitted signal uses BPSK modulation. The modulation bandwidth (Bm) is the wanted input to the link budget and is found using the spectral efficiency factor (η) for BPSK which is 0.5 bps/Hz. Solving for Hz in the equation below, the modulation bandwidth is simple twice the maximum bit data rate(R) of the 406, which is 404 bps.

• η = 1/2= R(bps)/ Bm(Hz)

• Bm = 2R= 2*404= 808hz

• Thus 808 Hz is the minimum noise bandwidth of the processed signal as input to the A/D. also needed for the 406 MHz link calculations is the receiver IF bandwidth. For this BPSK signal the minimum receiver noise is the modulation bandwidth plus the transmitter stability of current ELT beacons, which is ±5KHz.

406 Link analysis:

• Link calculations for the 406 receiver still utilize the S/N method even though the 406 MHz signal is Bi-Phase-L modulation with a five year oscillator stability of ±5KHz, uplink side. This is because by applying similar FFT processing to 406 MHz transmissions the signal recovery becomes more reliant on a relationship between the signal strength and the noise floor.

• The calculation method in below table model the ground ELT as having an isotropic antenna with a power out of 5W.

Parameter AMSAT link calculator STK

Received power -150 dBw (decibel watt) -147 dBw

G/T -23.4 dB/K -23 dB/K

S/N 25 dB 25 dB

• Beacon’s signals aren’t time synchronized i.e. this signals received by satellite antenna are random. Hence

signals from different beacons may overlap, which is referred to as random access with time.

• 406 MHz i.e. the carrier frequency is assigned to particular frequency channel in accordance to frequency

management plan. Within this frequency channel, beacon frequency are distributed around the center

frequency due to variation in oscillator frequency, ageing and temperature. Moreover the frequency received

by the satellite may overlap thereby creating frequency overlapping also called random access with

frequency.

BASIC LEOSAR SYSTEM CHARACTERISTICS• Beacon transmission times are not synchronized and beacon message arrival times at the satellite receiver antenna are

random.

• Therefore, bursts from different beacons may overlap in time.

τ= duration of each beacon burst,

b= frequency bandwidth of each burst,

T= beacon repetition period (beacon can continuously burst for 40 hours).

Hence at period (t1 + T);

Beacon overlap at frequency domain may disappear {which is true in every case} i.e. each beacon’s frequency is different ranging from 406 MHz to 406.1MHz.

Also, the message repetition period of both beacons may be slightly different, a collision in time domain maynotnecessarily repeat after few signal transmission.

When any two beacon’s signal overlapped at time and frequency domain have equivalent signal power then both the signals are lost which is worst case and probably never occurring one.

If overlapped signal at [t and f] have different signal power than signal having high power is received correctly while the weaker message is lost.

SARP AND SARR processing channel.

These are the two processing channels in the LOESAR.

• 406 MHz signal received through the SARP channel are processed on board i.e. information is extracted and stored on

board and continuously transmitted to LEOLUT.

• The LEOLUT processed the data to compute a Doppler position and generates a distress message for distribution to SAR services.

The SARP channel that includes a satellite memory unit, provides the system global coverage as simultaneous satellite visibility of a

LEOLUT.

#: In the SARP channel, 406 MHz signal is assigned to the real time specific processing unit. The data recovery unit (DRU) remains occupied by for a given processing time. If all the DRU are busy at

certain period of time, 406 signal arriving at the SARP may be lost. On the basis of the current characteristics of the SARP instrument and memory unit, and the number of LEOLUTs in the system, it is

assumed that no data is lost before its transmission to a LEOLUT.

Control unit

Receiver

DRU 1

DRU 2

DRU 3

Frame

FormatterAnd

Memory

Mission telemetry

RF input

Fig: SARP Block Diagram

• Whereas the 406 MHz beacon messages received through the SARR channel are only repeated by the

satellite SARR instrument and all the processing (data recovery, timing, shift measurement and Doppler

location computation) is carried out at LEOLUT.

Similarly in SARR channel, LEOLUT ground processing can be adapted as necessary to meet the required

traffic.

DOPPLER’S SHIFT;

• Doppler’s shift:

• As we know Doppler shift is given by the equation:

𝐹𝑟 = (1 +𝑉𝑟𝑎𝑑𝑖𝑎𝑙

𝑉𝑝𝑟𝑜𝑝) × 𝐹𝑡 ………. (1)

= 1 −𝑉𝑟𝑎𝑑𝑖𝑎𝑙

𝑉𝑝𝑟𝑜𝑝× 𝐹𝑡 … . . . (2)

• +,- signs are for observer moving towards and away form the transmitter.

• Change in frequency is given by:∆𝐹𝑟 = 𝐹𝑟 − 𝐹𝑡

= ±𝑉𝑟𝑎𝑑𝑖𝑎𝑙

𝑉𝑝𝑟𝑜𝑝×Ft, v=f𝜆 → 𝜆=v/f

= ±𝑉𝑟𝑎𝑑𝑖𝑎𝑙

𝜆…………….(3)

With this equation we can plot the graph between frequency and time.

frequ

en

cyTime

Point of inflection

y

x

β

• Point of inflection in the curve represents where satellite was closest to the transmitter i.e. {EPIRB} also called time of closest approach {TCA}.

• Slope of the curve at TCA determines the distance of the transmitter form the satellite. • Slope (m) = tan β, where β must be greater than 6.80 , in order to locate the beacon.

Point of inflection

• After the determination of β, it is possible to locate two lines where transmitter could have been. These two lines are parallel line to the satellite track.

• Now, we could draw perpendicular line form the point on the satellite to these line which represent the distance between the transmitter and the satellite track.

• Thus, we get two possible location of the transmitter, one being real and another being imaginary.

• We find the actual location of the transmitter by coordinating with other satellite. • Another way to locate the real location is the rotation of earth, which speed is about 463 ms-1

.

Satellite tracking

OA=OB= perpendicular distance from the satellite track to the parallel lines.

The beacon is either located at position A or B.

Rotation of the earth or synchronization with other satellite gives the exact position. A B

O

Satellite track

β β

satellite

감사합니다

THANK YOU