VSAT Service Providers

VSAT Service Providers ( VSAT服务提供商 )

http://www.marinesatellitesystems.com/index.php?page_id=22

 

Satellite Networks and Technologies ( 卫星网络与技术 )

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:

( 您对海洋卫星网络的选择主要取决于您的通信预算，带宽要求和使用频率。 基本上，它们可以分为三类： )

• Dedicated bandwidth (SCPC),  ( 专用带宽（SCPC）， )
• Shared bandwidth, Fixed Price (TDMA)   ( 共享带宽，固定价格（TDMA） )
• Pay per use bandwidth (Inmarsat / Iridium).  ( 按使用付费带宽（Inmarsat /铱星）。 )

 

VSAT - Very Small Aperture Terminal ( VSAT-小孔径终端 )

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.
( 永远在线-固定价格。 从技术上讲，所有小于3.8 m的抛物面碟形卫星终端都可以称为甚小孔径终端，或VSAT，但术语VSAT通常是指用于数据和语音通信等两种方式的发射/接收（TX / RX）卫星终端，例如 互联网和电话。 术语“小”与巨大的25米标准A传送天线相比。 )
A VSAT service is typically billed on a monthly contract, rather than by the minute, or by the megabyte like Inmarsat satcoms. 
( VSAT服务通常按月合同计费，而不是按分钟计费，也不像Inmarsat卫星通讯这样按兆字节计费。 )
There are quite few stabilized VSATs in operation when you consider that there are less than 10 000 active terminals worldwide.

( 当您考虑到全球活动终端不到10000台时，运行中的稳定VSAT很少。 ) 

 

USAT, Ultra Small, Fixed Price, Internet at sea. ( USAT，超小型，固定价格，海上互联网。 )

512/256 kbps $30K +2995/month     384/128 kbps $30K +$412/month

( 512/256 kbps $30K + 2995美元/月 384/128 kbps $30K + 412美元/月 )
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.
( USAT（超小孔径终端）的反射器尺寸仅为60厘米（24英寸），以固定的月租价格向一个巨大的市场提供互联网接入，这些船只的尺寸和重量无法满足一个完整的1米天线的尺寸和重量。 )
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.
( 直到最近，传统的Ku波段VSAT仅限于1米或更大的天线，其波束宽度足够小，不干扰相邻卫星。天线越大，波束宽度越窄。 )
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.
( 使用传统的调制方法，为了防止上行链路传输干扰通常与目标卫星只有2度或更小间距的相邻卫星，需要这样的尺寸。 )
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.
( 采用扩频技术的新调制方法允许带宽在多个频率上分布，从而降低了信号的频谱密度和超小型（60 cm）小型VSAT的干扰水平。 )
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.

( 虽然终端的成本基本上不到1米系统，但由于需要额外的带宽，供应商向较小的天线提供服务的成本实际上更高。因此，广播时间费率不一定较低，但是，为了满足较小的船舶预算，一些供应商提供了一些非常有吸引力的费率，很可能是在更高的竞争比率下。 )

 

SCPC - Dedicated, One-on-one circuits ( SCPC-专用的一对一链路 )

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.
( 每通道单载波电路提供了船与岸之间的专用信道，无论您是否使用它，总带宽始终保持打开状态，并且您可以单独使用。 )
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.
( 由于在太空中开发，建造，部署和运营卫星的极高成本，按任何标准衡量，卫星太空市场的价格都是昂贵的。 您将有充分的理由为您量身定制专用服务，除非您是一个非常忙碌的全天候带宽无限预算的用户。 专用带宽就像拥有一整列火车，只为您保留，您需要利用所有空间使其物有所值。 )
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.

( SCPC有多种变体，例如，一家运输公司可以确保专用带宽，然后使用FDMA等各种技术在其整个船队中共享带宽。 )

 

Shared Bandwidth: ( 共享带宽： )

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.  

( 由于我们大多数人使用带宽的方式是偶发性的（或突发性的），因此用户与其他用户共享卫星连接更加经济实用。 如果卫星提供商适当地确定管道的数量和用户数量，则大多数情况下，人们不会意识到许多用户正在共享电路。 大多数现代技术在用户之间提供了极为安全的隔离，几乎不可能破坏数据或语音流量。 )

 

TDMA - Time Division Multiple Access: ( TDMA-时分多址： )

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是安全共享带宽的常见形式，其中每秒或毫秒被切分为几微秒，并在多个用户之间共享。这是天空中的分时度假，除了您不是每年购买一两个星期，而是每秒购买几毫秒。当您下载Internet或通过电话讲话时，您甚至没有意识到还有其他几个用户在同一卫星链接上执行相同的操作。当使用链接的人数减少时，可以为您提供更多的带宽，而当人数增加时，您的带宽就会减少一些。 )
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.
( 由于远程单元会更改其位置，从而更改其与卫星的距离以及信号传播到卫星所花费的时间，因此在移动海洋电路上难以实现TDMA。对于控制器而言，重要的是要知道远程终端的确切位置，以便可以准确分配时隙。这通常需要GPS输入到卫星调制解调器。 )
The most common iDirect networks use TDMA technology.
( 最常见的iDirect网络使用TDMA技术。 )

 

CDMA- Code Division Multiple Access ( CDMA-码分多址 )

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.
( CDMA码分多址与TDMA共享电路的工作原理几乎相同，只是每个人都在同一时间讲话，而不是为每个信息突发分配时隙。 由于特殊的编码，每个侦听器仅侦听自己的数据消息，而忽略其余的消息。 就像是在同一房间同时演唱多首歌曲，但我们仍然可以调出其他歌曲并一次只听一首歌曲。 )

 

PCMA - Paired Carrier Multiple Access ( PCMA-成对载波多址接入 )

http://www.viasat.com/broadband-networks/paired-carrier-multiple-access-pcma

 

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