Two-way satellite-only communication

Two-way satellite Internet service involves both sending and receiving data from a remote very-small-aperture terminal (VSAT) via satellite to a hub telecommunications port (teleport), which then relays data via the terrestrial Internet. The satellite dish at each location must be precisely pointed to avoid interference with other satellites.
At each VSAT site the uplink frequency, bit rate and power must be accurately set, under control of the service provider hub.
There are several types of two way satellite Internet services, including time division multiple access (TDMA) and single channel per carrier (SCPC).
Normal VSAT dishes (1.2–2.4 m diameter) are widely used for VoIP phone services. A voice call is sent by means of packets via the satellite and internet. Using coding and compression techniques the bit rate needed per call is only 10.8 kbit/s each way.

System hardware components

The transmitting station (also called "teleport", "head end", "uplink facility", or "hub") has two components:

Internet connection: The ISP's routers connect to proxy servers which can enforce quality of service (QoS) bandwidth limits and guarantees for user traffic. These are then connected to a DVB encapsulator which is then connected to a DVB-S modulator. The radio frequency (RF) signal from the DVB-S modulator is connected to an up converter which is connected via feed line to the outdoor unit.
Satellite uplink: The block upconverter (BUC) and optional low-noise block converter (LNB), which may use a waveguide to connect to the optional orthomode transducer (OMT) which is bolted to the feed horn which is connected by metal supports to the satellite dish and mount.

System software components

Remote sites require a minimum of programming to provide authentication and set proxy server settings. Filtering is usually provided by the DVB card driver.
Often, non-standard IP stacks are used to address the latency and asymmetry problems of the satellite connection. Data sent over the satellite link is generally also encrypted, as otherwise it would be accessible to anyone with a satellite receiver.
Many IP-over-satellite implementations use paired proxy servers at both endpoints so that certain communications between clients and servers [1] do not need to accept the latency inherent in a satellite connection. For similar reasons, there exist special Virtual private network (VPN) implementations designed for use over satellite links because standard VPN software cannot handle the long packet travel times.
Upload speeds are limited by the user's dial-up modem, and latency is high, as it is for any satellite based Internet (minimum of 240 ms one-way, resulting in a minimum round-trip time of almost 500 ms). Download speeds can be very fast compared to dial-up.

K_u band

This symbol refers to (originally German: Kurz-unten)—in other words, the band directly below the K-band. In radar applications, it ranges from 12-18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521-2002

K_u band is primarily used for satellite communications, most notably for fixed and broadcast services, and for specific applications such as NASA's Tracking Data Relay Satellite used for both space shuttle and ISS communications. K_u band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network's studio for editing and broadcasting

Advantages

Compared with C-band, K_u band is not similarly restricted in power to avoid interference with terrestrial microwave systems, and the power of its uplinks and downlinks can be increased. This higher power also translates into smaller receiving dishes and points out a generalization between a satellite's transmission and a dish's size. As the power increases, the dish's size can decrease.^[4] This is because the purpose of the dish element of the antenna is to collect the incident waves over an area and focus them all onto the antenna's actual receiving element, mounted in front of the dish (and pointed back towards its face); if the waves are more intense, fewer of them need to be collected to achieve the same intensity at the receiving element.
Also, as frequencies increase, parabolic reflectors become more efficient at focusing them.

For Ku satellites in DBS (Direct Broadcast Satellite) service (12.2-12.7GHz in the U.S.) dishes much smaller than 1-meter can be used because those satellites are spaced 9 degrees apart. As power levels on both C and Ku band satellites have increased over the years, dish beam-width has become much more critical than gain.
The K_u band also offers a user more flexibility. A smaller dish size and a K_u band system's freedom from terrestrial operations simplifies finding a suitable dish site. For the end users K_u band is generally cheaper and enables smaller antennas (both because of the higher frequency and a more focused beam).^[5] K_u band is also less vulnerable to rain fade than the K_a band frequency spectrum.
The satellite operator's Earth Station antenna does require more accurate position control when operating at K_u band due to its much narrower focus beam compared to C band for a dish of a given size. Position feedback accuracies are higher and the antenna may require a closed loop control system to maintain position under wind loading of the dish surface.
Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) is a digital television broadcast standard that has been designed as a successor for the popular DVB-S system. It was developed in 2003 by the DVB Project, an international industry consortium, and ratified by ETSI (EN 302307) in March 2005. The standard is based on, and improves upon DVB-S and the electronic news-gathering (or Digital Satellite News Gathering) system, used by mobile units for sending sounds and images from remote locations world-wide back to their home television stations.
DVB-S2 is envisaged for broadcast services including standard and HDTV, interactive services including Internet access, and (professional) data content distribution. The development of DVB-S2 coincided with the introduction of HDTV and H.264 (MPEG-4 AVC) video codecs.
Two new key features that were added compared to the DVB-S standard are:

A powerful coding scheme based on a modern LDPC code.
VCM (Variable Coding and Modulation) and ACM (Adaptive Coding and Modulation) modes, which allow optimizing bandwidth utilization by dynamically changing transmission parameters.

Other features include enhanced modulation schemes up to 32APSK, additional code rates, and the introduction of a generic transport mechanism for IP packet data including MPEG-4 audio–video streams, while supporting backward compatibility with existing MPEG-2 TS based transmission.
DVB-S2 achieves a significantly better performance than its predecessors – mainly allowing for an increase of available bitrate over the same satellite transponder bandwidth. The measured DVB-S2 performance gain over DVB-S is around 30% at the same satellite transponder bandwidth and emitted signal power. When the contribution of improvements in video compression is added, an (MPEG-4 AVC) HDTV service can now be delivered in the same bandwidth that supported an early DVB-S based MPEG-2 SDTV service only a decade before.

Main features

Direct input of one or more MPEG-2 Transport Streams (TS). MPEG-TS is supported using a compatibility mode.
The native stream format for DVB-S2 is called Generic Stream (GS), and can be used to efficiently carry IP-based data, including MPEG-4 AVC/H.264 services.
Backward compatibility to DVB-S, intended for end users, and DVB-DSNG, used for backhauls and electronic news gathering.
Variable coding and modulation (VCM) to optimize bandwidth utilization based on the priority of the input data, e.g., SDTV could be delivered using a more robust setting than the corresponding HDTV service.
Adaptive coding and modulation (ACM) to allow flexibly adapting transmission parameters to the reception conditions of terminals, e.g., switching to a lower code rate during fading.
Four modulation modes:
- QPSK and 8PSK are proposed for broadcast applications, and can be used in non-linear transponders driven near to saturation.
- 16APSK and 32APSK are used mainly for professional, semi-linear applications, but can also be used for broadcasting though they require a higher level of available C/N and an adoption of advanced pre-distortion methods in the uplink station in order to minimize the effect of transponder linearity.
Improved rolloff: α = 0.20 and α = 0.25 in addition to the roll-off of DVB-S α = 0.35.
Improved coding: a modern large LDPC code is concatenated with an outer BCH code to achieve quasi-error-free (QEF) reception conditions on an AWGN channel. The outer code is introduced to avoid error floors at low bit-error rates. A single forward error correction or FEC frame may have either 64800 bits (normal) or 16200 bits (short). If VCM or ACM is used, the broadcast can be a combination of normal and short frames.
Several code rates for flexible configuration of transmission parameters: 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, and 9/10. Code rates 1/4, 1/3, and 2/5 have been introduced for exceptionally poor reception conditions in combination with QPSK modulation. Encoding values 8/9 and 9/10 behave poorly under marginal link conditions (where the signal level is below the noise level). However, with targeted spot Ku or Ka band downlinks these code rates may be recommended to prevent out-of-region viewing for copyright or cultural reasons.
Optional input stream synchronization to provide a constant end-to-end delay.

Depending on code rate and modulation, the system can operate at a C/N between -2.4 dB (QPSK, 1/4) and 16 dB (32APSK, 9/10) with a quasi-error free goal of a 10⁻⁷ TS packet error rate. Distance to the Shannon limit ranges from 0.7 dB to 1.2 dB.

iDirect

VT iDirect (iDirect) is a Herndon, Virginia based company that develops satellite-based IP communications technology. iDirect has customers in 50 countries.

About

Founded in 1994 as ComSoft Systems, iDirect changed their name to iDirect Technologies in 2000. The company became a wholly owned subsidiary of Vision Technologies Systems in 2005. iDirect has won numerous awards such as the 2005 Teleport Technology of the Year for its 5IF hub and broadband IP VSAT System and the 2008 World Teleport Technology of the Year for its DVB-S2/ACM product line, Evolution. In 2008, iDirect Government Technologies was established as a subsidiary of iDirect to serve the US federal market. iDirect made its first acquisition in late 2009 by purchasing UK-based Parallel Limited, who were best known for developing the network management software, SatManage.

Products

iDirect offers satellite-based IP communications products. Its products include universal satellite hubs, satellite remote routers, network accelerators, optimization solutions, and a network management system. Their Intelligent Platform is a satellite communications system with a variety of applications. Unlike many of their competitors iDirect does not operate a service arm - it only supplies equipment that is used by satellite service providers. A further differentiator is that their equipment is designed to provide services to high end enterprises or carriers rather than to consumers, hence there is an emphasis on the ability to deliver (and measure) the service level agreement requested by their clients.