- Internet at Sea

One of the questions we occasionally get asked is regarding internet and email at sea and in remote locations: what are the options? how does it work? Well the simple answer is that there are a number of complex options which all go to prove how technology has advanced in the last 15 years or so. In the early ‘90s Australia was asking what is email, what is the world wide web. Now some of us can’t take an extended trip without publishing a running commentary to the world via a blog. At the other end of the spectrum it is now possible to send secure data transmission to military forces in battlefield conditions. Your solution will depend on what you need and how reliable you need it to be...

Email and internet services for mariners and those in remote locations obviously rely on wireless transmissions, which are subject to the vagaries of propagation. The more complex your requirements, the more involved the technology needs to be. Basically, today you can get internet and email on your phone and computer via HF, VHF, UHF, SHF and microwave. You should not expect it to provide the same results as hard wired services although some solutions have become very sophisticated and are still evolving. The end results will depend on the nature of the transmission band and the propagation at these frequencies.

The challenge has been to devise protocols to make efficient use of low bandwidths, provide high efficiency error correction, and overcome problems associated with long transmission times. Systems have had to accommodate multicast messaging to multiple destinations, priority messaging in a high traffic environment and security considerations like ENCOM (Emission Control), where signals can be received but not sent. Recent technological advances have helped greatly to overcome many of the problems involved, not the least of which are those provided by ALE (Automatic Link Establishment).

Increasingly cellular providers are offering coverage in inshore waters with access to email and internet. Third generation cellular can now support fast data using technologies such as EVDO, HSDPA and UMTS on frequencies ranging from 800 to 2500 MHz (GSM 900/1800, 3G 2100, Next G 850). So, if you don’t need to wander far from civilisation, you may prefer to take your mobile with you. Performance and range are limited to the designed network coverage and to the efficiency of the antenna you are using. It will also be affected by propagation at these frequencies, where waves are short and subject to polarisation reversal and multi-path reflections. At sea the movement of the sea and the boat will also be factors. Cost may also be important as services are not cheap. Much will depend on your usage requirements.

In Australia coverage extends from 20 to 70 km out to sea in some areas along the coast, including the Great Barrier Reef, the Sydney to Melbourne coast and the Whitsundays. Of course charges at mobile rates apply and you would be wise to check with the service provider where coverage is available and where it is not before relying on it.

A full size external antenna can improve communications significantly provided you are within a cell and is recommended. Providers generally advise you to mount the antenna as high as possible to extend line of sight and gain maximum range. However, at these UHF/SHF frequencies you need to be aware that unless you are using suitable low loss coaxial cable, you may lose more than you gain by having extended runs. It is important to check what the losses are beforehand. Not all cables are designed to be used in the corrosive marine environment. Always use the best cable and you will save in the long term.

To attach a full size antenna to your phone you will need an RF connection on your phone. Mobile phone manufacturers often have their own proprietary connectors which are not easily available. To overcome this, they usually provide adaptors to FME connectors.

If you want to bring your computer on board and work, however, you will probably require something more sophisticated, something with better voice quality and reliable signal strength, like a 3G fixed wireless terminal with high speed broadband connections and greater range depending on the capability of the individual network you are connecting to and within the limits of the radio horizon. All you need to do is insert a sim card from your provider and connect the terminal to a computer via an Ethernet cable, Wi-Fi or router and away you go. It is also possible to connect a telephone handset and fax. In 3G networks you can use the phone and internet at the same time, but in 2G networks, the internet is usually put on hold when a call is received.

If you are venturing further afield, obviously you will need something with more range. For many users, the advances in HF technology have made HF internet a very attractive solution, as costs are minimal with free to air transmission via your radio. While propagation at HF can be variable, ALE has had a great impact on facilitating operations. So much so that military and peacekeeping forces are also finding HF increasingly useful for mobile email access and digital HF as technology continues to improve. If you are unable to take advantage of this, there may be times when conditions are not favourable, and you may like to up-date your equipment.

There are a wide range of frequencies and stations available around the world and a reasonable distribution of server stations. You may not always find one when you would like, remembering that they are usually manned by volunteers, but it does not take long to become familiar with their schedules.

What has made HF email and internet services possible at sea, is the Pactor radio modem protocol. Pactor modems are designed to transfer data over radio and have been around since 1991. Developed by Special Communications Systems GmbH, they evolved from AMTOR and packet radio, combining the bandwidth efficiency of packet radio with error correction (CRC) and AMTOR’s special form of RTTY protocol, which supports ARQ (Automatic Repeat Request) and FEC (Forward Error Correction).

Two significant improvements were error correction and online data compression. Data is compressed with memory ARQ error correction, where the last data packet received is held in memory and compared to the next , making it possible to maintain links in bad conditions through using data from corrupt packets to reconstruct the original packets. This is important as data signal reception can be subject to considerable attenuation over the typical long distances of 100-4,000km with a 100W transmitter, which must be set to reduced power (say 40W) to ensure distortion free data transmission.

Pactor radio modems use a very narrow waveform and occupy the same band space as Analog 300 baud packet. A very rapid Time-Division Duplexing is employed. Since Pactor I first arrived on the market, range and data transfer rates have increased significantly. The synchronous half duplex ARQ protoctol and DPSK (Differential Phase Shift Keying) modulation of Pactor II mean that the very narrow spectrum is virtually independent of the data rate.

With Pactor there are four different speed steps to suit different conditions. With the high correction decoder, weak and noisy links become viable and short error bursts or fadeouts lose their importance.

If there is enough data in the transmit buffer it is possible to switch to a triple cycle length creating relatively long data packets. The throughput of plain text is increased by a factor of 1.3, by assessing whether it is faster to send individual packets via Huffman coding, PMC (pseudo Markov coding) or normal ASCII transmission. Six different compression variations are possible. Run length coding minimises repetition of characters by indicating the number of repetitions with a number.

The latest Pactor III protocol is a software upgrade for Pactor II radio modems. The maximum occupied bandwidth is 2.4 kHz @ -40 dB with 400-2600 Hz audio passband:. Online data compression of around 5200 Bit/sec is possible for email via TCP/IP. This means that the new protocol is 3.5 to 5 times faster than Pactor II. Where it takes 7-8 minutes to download weather maps with Pactor II, it now takes around 2 minutes, thus saving time and battery power too. While both transmit and receive stations must support the protocol to use Pactor III, all versions are backwards compatible. The best mode is automatically selected.

There are two world-wide HF systems for mariners and remote users: Sailmail and Winlink. To join Sailmail you need an HF maritime ship station licence and an appropriate operator’s certificate of proficiency, to join Winlink you need to be a licensed amateur radio operator.

All you need is a properly licensed marine SSB, a Pactor radio modem with interface cables to suit your transceiver, an email client (like Airmail) and to join the association. The HF radio network is free to air, so the only costs are for the initial equipment, association membership fees and any internet access costs for backup services if you want them.

SailMail stations operate on 2 to 22 MHz. Each station has a range of up to 8000km. There are currently 17 shore-side coastal stations, scanning from 5 to 12 frequencies. They provide plain text email generally. Some attachments are possible and you can obtain weather data by using the SailDocs auto-responder. There is no bulletin board system or landline bulletin board system.

System protocol is designed to accommodate limited bandwidth and high latency as signal turnaround time can be long. Increased efficiency is achieved through reducing the number of link turnarounds, the use of compression, and virus, spam and attachment filtering. This can be around 10 times faster than conventional Pop 3/SMPT protocol, depending on the choice of radio modem.

With the latest Pactor III upgrade the rate varies from around 10 to 500 characters per second (approx 110-4800 baud), which is sufficient for email but not internet browsing. To reduce congestion members are limited to size of email (up to 10kB for Pactor III) and to an average of 90 minutes per week.

Although the system will operate with the earliest modems, apart from the speed and data capacity aspects, a serious encouragement to have a model that will permit frequency control via your computer. There are more than 115 frequencies that need to be monitored as well as weatherfax frequencies, so looking up frequencies and call signs which are organised numerically from 00 on the transceiver, can take a long time, especially when the station can’t be heard first time around, and considerably more prone to error.

If you have an amateur radio license or are a member of a supported organisation or agency, the Winlink 2000 Global Radio Email System or WL2K not for profit network offers greater geographic coverage through more stations, no limits on connect time and the ability to send and receive file attachments. You can also access weatherfax forecasts, satellite pictures, and wind wave forecasts. The system is not optimised for keyboarding or chat mode applications though this may be possible with the right software. FEC broadcast (unproto) mode is optional.

WL2K is a worldwide system of hundreds of amateur radio, MARS (Military Auxiliary Radio System) and other volunteer organisations providing services to emergency communicators and licensed radio operators who don’t have access to the internet. Their HF RMS (radio mail service) gateway stations use either WINMOR or PACTOR radio modems/protocols. Some operate public HF stations and concentrate on providing service to maritime mobile users, or users who have no other access to email, like remote medical teams or expeditions. Others maintain stations for emergency communications (EmComm). Many operate on VHF, UHF or SHF as well as HF. As with SailMail HF satellite or other connections are useful to ensure continuity of service in poor conditions.

The use of the system and all software is free provided you qualify. To create a radio email account you have to use radio email client software, like Airmail, Paclink or RMS, and make a connection using radio, or a connect directly to one of WL2K CMS (common message server) telnet servers with correctly configured client software.

WL2K only requires a simple computer soundcard-to-radio interface and runs as a ‘virtual TNC’ (the packet radio Terminal Node Controller) with Paclink and RMS (Radio Mail Server) software.

WINMOR is the radio transmission protocol for WL2K. It has been in operation since January 2010. The system complements Pactor HF protocols so that either WINMORE or PACTOR (1-3) modems can be used.

Winmore is designed to send both messages and data in conditions of generally low signal to noise levels, interference, poor to moderate propagation and multipath, frequency offset and drift, and sound card sampling rate error and drift. Currently there are two operating bandwidths, one 500 Hz (2 carriers), the other 1600 Hz (8 carriers) 46.875 Baud 4FSK or 93.75 baud PSK using TCM 4PSK, 8PSK or 16PSK.

Modulation is basic OFDM (Orthogonal Frequency Division Multiplexing) with a number of modulation modes and error correction mechanisms to adapt to changing conditions. Error correction is tailored specifically to accommodate types of errors found in HF communications using popular FSK and PSK modulation schemes. SRARQ (Selective Repeat Automatic Retry Request) protocol is used where receipt of data is acknowledged progressively by the receiving station. The system uses an error approach for improved efficiency: outer standard CRC sumcheck calculation on “corrected” data, Reed Solomon (R-S) FEC parity blocks (characters), Viterbi Encoded TCM (Pragmatic Trellis Coded Modulation) for PSK modes, and a final layer of Memory ARQ (Automatic Retry request). Both FEC (broadcast) and ARQ (connected) modes are supported. ARQ speeds range from 67 to more than 1300 bits per second, similar to PACTOR modes.

Military and peacekeeping forces are finding HF increasingly useful for mobile email access as digital HF technology continues to improve. Email clients like HUITSMail make it possible to capture, manipulate and compress images with a powerful wavelet compression engine on the fly before sending. Wireless messaging terminals can connect tactical radio links to LANs and WANs, including the internet, using HF, VHF, UHF, landline, or INMARSAT and the like. Predefined alternate pathways are automatically chosen if conditions are not viable. In addition, a wide range of encryption devices can be supported as well as SMTP and POP 3 email clients.

The HF data link protocols, HD and LDL, of 3G ARQ, known collectively as xDL, are described in STANAG 4538 which defines 3G HF with synchronous ALE and efficient data protocols. These protocols utilise code combining techniques and black side ARQ to deliver error free data over poor channels, even those experienced by war fighters. Together with the 2G modem standard of STANAG 4539, throughputs of greater than 10 kbps over 3 kHz channels are achieved. xDL protocols are time driven making it possible to adjust coding automatically and adaptively to match channel conditions, so that data can be transferred at the maximum possible rate.

Internet protocol (IP) is at the heart of network centric warfare operations. Systems can support voice, IP traffic, serial data services and email for ships, submarines, helicopters and aircraft as well as land forces. The amount of data transfer can be kept to a minimum by setting up edge proxy servers, and bandwidth can be increased by using ISB (Independent Side Band) links and combining separate channels in a multi channel system which can support circuits of 64 kb/s and higher. Dynamic frequency selection and other advanced communications management system optimise the use of the available frequency band. The result is reduced on air time (and opportunity for detection), rapid setup times and more efficient use of the available spectrum.

Going down the satellite path has its own share of propagational issues. Only frequencies above 100MHz can be used for satellite communications as lower frequencies do not penetrate the ionosphere; the higher the frequency, the wider the bandwidth and the greater the capacity of the link. However, higher satellite frequencies (Ku, K and Ka Bands, 12-40 GHz) are subject to greater atmospheric attenuation, and more rain and noise interference, requiring higher power for the same carrier to noise ratio. Antennas are harder to point as the beam is more directional.

By comparison, the relatively longer waves of the lower satellite bands (L, S, C and X Bands, 1-12 GHz) can penetrate many structures and materials and are least affected by cosmic noise, rainfade and other propagation losses. With more powerful satellite transmissions, smaller antennas have become possible. The C Band, in particular, has been used extensively for satellite communications since its inception and equipment, which is similar to that used for terrestrial microwave, troposcatter and radar, is widely available and relatively low cost.

However, these bands are also shared with commercial terrestrial services, including broadcast TV and DSS (decision support systems) and, on the X Band, with government and military satellite communications. As a result, they have now become crowded and frequency co-ordination has become a significant concern if interference is to be avoided.

Satellites are therefore increasingly being forced up the bands, primarily to the Ku and Ka Bands, which are affected by rainfade and atmospheric attenuation but not shared with terrestrial radio networks. Most modern satellites have a mixture of C and Ku transponders. Ku Band link margins are of the order of 8 dB compared with approximately 2 dB required in the C Band. While this can be compensated for by higher satellite powers, the higher fade margins make the Ku Band unsuitable for tropical regions. Fade margins are worst on the Ka Band which will become the home of the new satellites as the Ku Band is most allocated already. Drop outs can be common during travel, inclement weather and sunspot activity.

Satellite systems can be geostationary or geosynchronous in a fixed orbit around the earth’s equator at a height of approximately 35,800km or in medium earth orbit between 1,600 and35,800km (MEOs), or low earth orbit between 320 and 1,500km (LEOs) at different angles. MEOs can have a variety of orbits including elliptical whereas LEO orbits are typically circular. Today, MEO satellites are most commonly used in navigation systems including GPS and the Russian Glonass. The European Union’s new navigations system Galileo is expected to commence operations in 2013/2014.

System coverage will depend on the number of satellites and the nature of the orbits. Greater numbers of satellites are needed at lower altitudes generally. The geosynchronous Inmarsat system requires only four satellites with only one satellite being needed for satisfactory operation in a region, even in rough seas. The Iridium LEO system is in polar orbit at an inclination of 86.4 degrees, while the Globalstar LEO system is inclined to the equator at 56 degrees. Due to elevation angles, most systems do not provide coverage at the poles. At high latitudes communications may also be affected by multipath interference as the satellite appears low on the horizon. For these reasons, only Iridium provides a good service at the poles. The new Ob3 MEO system has an equatorial orbit and operates from only 45 degrees north to 45 degrees south latitude, while Globalstar and Inmarsat operate from 70 degrees north to 70 degrees south.

Signal routing is handled differently depending on the system. In geostationary systems the satellite completes one orbit in the same time as the earth turns on its axis. The connection is via the satellite to the network hub via a gateway teleport or earth station, and hence to the internet (and vice versa).

LEOs and MEOs can use a network of teleport earth stations, as in the Globalstar LEO system, in which signals are routed on to conventional terrestrial wireless (cellular) or landlines to another earth station then uplinked to another satellite and so on until the destination is reached. This is known as “Bent Pipe Routing”. Due to the lack of inter-satellite linking, a user must be in view of a gateway station in order to connect into the system. The O3B MEO system currently only has one teleport in operation servicing Asia, Africa, Europe and the Middle East and plans to implement multiple sites worldwide.

In the Irridium LEO system satellite to satellite routing is used directing the signal to the closest destination satellite for downlinking . Each satellite can communicate with two neighbours before and after in the same orbital plane and two in neighbouring planes. Only links between satellites orbiting in the same direction are supported due to the rapid handoffs required and large Doppler shifts.

Very Small Aperture Terminal (VSAT) services are also available, generally in the Ku or C bands. These are comprised of numbers of earth teleports connecting to a central teleport via a satellite in geosynchronous orbit. For one end user to communicate with another, each transmission has to go first to the teleport which connects to the other end user’s VSAT via the satellite. For private applications, companies can have total control of their own communications system.

The technical challenges for satellite systems are not confined to propagation issues associated with frequency bands. One of the most important factors is that associated with “latency”, deriving from the height of the satellite above the earth and time it takes for the signal to travel to and from the satellite. Naturally the most affected is the Inmarsat system which is in high geostationary orbit around the equator at 35,786 km.

As signal delay can be as much as 500 to 900 milliseconds extending to 1,000 to 1,400 milliseconds latency with handling by the service provider, this makes it unsuitable for real-time input applications.

Lower orbiting systems have lesser delays. MEO latency is around 120ms, close to that of a fibre network. Globalstar and Iridium LEO systems quote delays of less than 40ms.

Higher latency is not very compatible with Java Script heavy web-based applications. Where the internet is concerned, satellite systems have had to incorporate special TCP (Transmission Control Protocol) acceleration or IP spoofing techniques to prevent packets being discarded as lost during standard TCP/IP error correction procedures or all packets being sent at the slow start rate due to these time delays.

As data transmission did not feature prominently in existing satellite systems, second generation satellites are planned with improved bandwidth. L Band services with data speeds of around 9.6 to 150 Kbps are suitable for browsing as well as email. Inmarsat-C and mini-C 600 bits per second (bps) data services have slow speeds that do not support browsing and require protocol compatible email program. However they are an economical solution for basic text emails, position reports, weather information and emergency broadcasts. Inmarsat mini-M, 2.4 and 4.8 Kbps services are rather slow for browsing but good for email work with standard email applications. Inmarsat-B offers access speeds up to 64 Kbps for voice, fax, telex and data. The new Next Generation Inmarsat 4 satellites, however, provide L Band services up to 492 Kbps, making them useful for military applications.

With the pressures on data capacity, many satellite internet providers have implemented a ‘fair access policy’, slowing speeds to dial-up rates for about 24 hours after usage levels in excess of 200MB per day have been reached. Others have implemented restrictions based on monthly usage or sliding time window basis to reduce congestion at times of heavy usage. Obvious these can be very restrictive for those with intense usage requirements.

Obviously, there are many solutions out there for internet at sea. What is best for you will be determined by what services and speeds you need. In some instances a mixed solution may be required to ensure reliability in view of system access and propagation problems. If speed and bandwidth are prerequisites, then you will need to be prepared to pay.