512/256 kbps $30K +2995/month 384/128 kbps $30K +$412/month
USAT (Ultra Small Aperture Terminals) with reflector sizes of only 60 cm (24") opens up internet access at fixed monthly prices to a huge market of much smaller vessels that could not support the size and weight of a full fledged 1 meter antenna.
Until recently, traditional Ku-Band VSAT was restricted to antennas of 1 meters or greater, whose beamwidth was small enough not to interfere with adjacent satellites. The larger the antenna, the narrower the beamwidth.
Using conventional modulation methods, this size was required in order to prevent the uplink transmission interfering with the adjacent satellites which are often spaced only 2 degrees or less from the target satellite.
New modulation methods, employing spread spectrum technology have allowed the bandwidth to be spread out over multiple frequencies thus lowering the spectral density of the signal and the level of interference from ultra small (60 cm) miniature VSATs.
While the cost of the terminals is substantially less than 1 meter systems, it actually cost providers more to deliver services to the smaller antennas, due to the extra bandwidth required. Consequently airtime rates are not necessarily lower, however, to fit the smaller vessel budget, some providers are offering some very attractive rates, most likely at higher contention ratios.
Your selection of a marine satellite network would depend mostly on your communication budget, your bandwidth requirements, and frequency of use. Basically they can be divided into three groups:
- Dedicated bandwidth (SCPC),
- Shared bandwidth, Fixed Price (TDMA)
- Pay per use bandwidth (Inmarsat / Iridium).
ALWAYS ON - FIXED PRICE. Technically, all parabollic dish satellite terminals less than 3.8 m could be called Very Small Aperture Terminals, or VSATs, but the term VSAT generally refers to transmit/receive (TX/RX) satellite terminals used for two way, data and voice traffic, like internet and telephone. The term "small" compares to the huge 25 meter Standard A teleport antennas.
A VSAT service is typically billed on a monthly contract, rather than by the minute, or by the megabyte like Inmarsat satcoms.
There are quite few stabilized VSATs in operation when you consider that there are less than 10 000 active terminals worldwide.
A VSAT service is typically billed on a monthly contract, rather than by the minute, or by the megabyte like Inmarsat satcoms.
There are quite few stabilized VSATs in operation when you consider that there are less than 10 000 active terminals worldwide.
Single Carrier Per Channel circuits provide a dedicated channel between ship and shore where the full bandwidth is always on and available to you alone, whether you are using it or not.
Satellite space segment is pricey by any standards, due to the extreme cost of developing, building, deploying, and operating a satellite in space. You would need good reasons to justify a dedicated service just for you, unless you are a very heavy, around the clock, bandwidth user with an unlimited budget. Dedicated bandwidth is like having a whole train, reserved only for you, and you need to use all the space to make it worthwhile.
There are several variations of SCPC where, for example, a shipping company might secure dedicated bandwidth and then share the bandwidth, using various technologies such as FDMA, across their fleet of ships.
Satellite space segment is pricey by any standards, due to the extreme cost of developing, building, deploying, and operating a satellite in space. You would need good reasons to justify a dedicated service just for you, unless you are a very heavy, around the clock, bandwidth user with an unlimited budget. Dedicated bandwidth is like having a whole train, reserved only for you, and you need to use all the space to make it worthwhile.
There are several variations of SCPC where, for example, a shipping company might secure dedicated bandwidth and then share the bandwidth, using various technologies such as FDMA, across their fleet of ships.
Since the way that most of us use bandwidth is sporadic (or bursty) , it is far more economical and practical for users to share a satellite connection with other users. If the satellite provider sizes the pipe and number of users appropriately, most often one is unaware that circuit is being shared by many users. Most modern technologies provide extremely secure separation between users making it almost impossible for data or voice traffic to be compromised.
TDMA is the common form of securely sharing bandwidth, where each second or millisecond is sliced up into microseconds and shared between several users. This is timeshare in the sky except that you are not buying a week or two per year, but rather a few milliseconds every second. While you are downloading your Internet, or speaking on the phone, you don‘t even realize that there are several other users doing the same thing on the same satellite link. When there are fewer people using the link, there is more bandwidth available for you, and when there are more people, you will have a bit less.
TDMA is difficult to implement on mobile marine circuits, due to the remote units changing their positions, and therefore their distance from the satellite and the time it takes for the signal to travel to the satellite. It is important for the controller to know the exact position of the remote terminals so that timeslots can be accurately allocated. This usually requires a GPS input to the satellite modem.
The most common iDirect networks use TDMA technology.
TDMA is difficult to implement on mobile marine circuits, due to the remote units changing their positions, and therefore their distance from the satellite and the time it takes for the signal to travel to the satellite. It is important for the controller to know the exact position of the remote terminals so that timeslots can be accurately allocated. This usually requires a GPS input to the satellite modem.
The most common iDirect networks use TDMA technology.
CDMA- Code Division Multiple Access works much the same as TDMA for sharing the circuit, except that instead of allocating timeslots for each burst of information, everyone just talks at the same time. Due to special coding, each listener listens only to his own data messages and ignores the rest. It is like several songs being sung in the same room at the same time, but we can still tune out the others and follow just one of the songs at a time.
