SATMODE system - Engineering Seminar Report

ABSTRACT    

               The SATMODE system provides a revolutionary low cost solution for low data rate transmission over satellite, in  support  of  interactive  television services. This  low  cost is  achieved  through  the introduction  of  constant  envelope  modulation,  and efficient   channel  coding  techniques. The SATMODE system   specifications will be proposed as a  new  Cenelec  standard in Europe. The  lac k of an efficient and scalable  return path has always  limited  true  interactivity   over  satellite TV.  Remote   interactivity  is  the  key  element  needed  for  the  continuation   of  growth  of  digital    television through  the  introduction of new services. This interactivity requires a scalable, secured, always on permanent instantaneous connectivity.SATMODE answers this need, allowing the  connection of TV consumers individually, both ways with their iTV content providers, with other consumers, with other infrastructures  (GSM and internet)  in real time, at any time, all the time. The main characteristics  of SATMODE are:  always on connectivity,  packet transmission, ability to carry IP, bi t rate  adaptability  (1 to 64 kbit/s),  random  access  scheme,  flexible air-interface. Although compatible with existing satellites,  SATMODE  is  designed  to  be    ready  for new generations of space segments. The new  technology under  SATMODE  provides   interactivity for satellite television.  Previously,  interactivity  for  satellite television  was  only possible  through  terrestrial return  channels   such  as phone  connections   from   a viewer's  STB  (set-top box) to the TV content broadcast.

INTRODUCTION

SATMODE is a satellite return link system providing 'always-on' connectivity between digital TV set topboxes -- the interactive version of commercial satellite TV receivers --The SATMODE system is set to enable permanent, real time responses by millions of TV viewers to content provider's programmes. It will also allow additional services such as SMS, televoting, management of personal video recorders, access control, pay per view and other impulse transactions. ESA is committed to support developments that reduce the risk to implement commercially viable satcom innovations. In particular, the user terminal is one of the most critical factors for success in the consumer market. SATMODE is a prominent example of the special attention that ESA is devoting to user terminals and applications. Easily integrated into an existing or new, basic or DVR-powered, satellite TV set-top box, SATMODE is designed to enable broadcasters to deliver truly personalized, interactive and on-demand services directly to individual subscribers. Whether it’s in the hands of millions of voting American Idol fans, chatting friends and family members worldwide, or movie buffs ordering the latest release on-demand, the scalability of SATMODE would allow the transactions to be completed without delay. SATMODE is a low-cost always on transmission technology, designed to enable broadcasters and DBS providers to personalize the television experience for their subscribers. Services based on this technology can be easily integrated into existing or

New, basic and DVR-based set-top boxes, and will be offered with a turn-key option for service providers that prefer to leave the back office management to SATMODE.               

                          New proposals for highly immersive interactive TV, telemedicine and medical education for travelers, tele-psychiatry, e-government for a public-administration regional service, Internet access on high-speed trains, and dissemination of information to cars using satellite and WiFi have been selected as key areas for innovation’s is progressively addressing thematic areas that require specifications to improve the uptake of commercially viable initiatives. These areas - so far Broadband Access to All, Interactive TV,Tele-Home Care, Security/Civil Protection, Broadband to Trains,Infopoverty/Capacity Building - will host mid-sized Pilot Projects in the next phase of the Telecommunications Programmed. applications. The end-to-end system is currently undergoing final integration and validation and will soon be made available to application developers. SATMODE is being developed by consortium led by SES Astra, including Newtec,Thomson, NDS, STMicroelectronics and Spacebridge.

SATMODE WORKING

The SATMODE network consists of the terminals installed at the users homes, and a hub station installed at the broadcasters site.

SATMODE users need:

• an antenna

• the SATMODE interactive LNB (iLNB), which includes a low power transmitter (in addition to the normal low noise block converter function)

• a digital television receiver and decoder (Set-Top-Box) with interactive application software (interactive application client)

• the SATMODE satellite modem (Add On Box)

The SATMODE modem function can also be build into the set top box (interactive Set Top Box or iSTB).

The installation at the broadcaster’s site consists of:

• an antenna

• the SATMODE hub which receives the radio signals from the terminals and extracts the data and which transmits the digital television signals the broadcast centre where television programmes and associated data are distributed interactive application servers that process the data send by the terminals

The SATMODE hub station can be scaled according to the number of users in the networks, by adding capacity blocks. These capacity blocks are called ‘blades’. Typical capacity for the return channel .

INTERNAL STRUCTURE

Understanding modem's work is to look at its internal structure. A block diagram of a generic satellite modem is shown on the image. Almost all parts are optional. After a digital-to-analog conversion  in the transmitter the signal passes through a reconstruction filter Then its frequency is converted if needed. The purpose of the analog tract in the receiver is to convert signal's frequency, to adjust its power via an automatic gain control circuit and to get its complex envelope components.

          The input signal for the analog tract is at the intermediate frequency or in the L-band in the second case it must be firstly converted to IF. Then the signal is either sampled or processed by the four-quadrant multiplier which produces the complex envelope components (I,Q) through multiplying it by the heterodyne frequency.

See Super heterodyne receiver

At last the signal passes through an anti-aliasing filter and sampled (digitized).

Main article: Digital demodulator title

A digital modulator transforms a digital stream into a radio signal on Intermediate frequency (IF). A modulator is generally a much simpler device than a demodulator, because it doesn't have to recover symbol and carrier frequencies.

A demodulator is one of the most important parts of the receiver. The exact structure of the demodulator is defined by a modulation type. However, the fundamental concepts are similar. Moreover, it is possible to develop a demodulator which can process signals with different modulation types.

Digital demodulation implies that a symbol clock (and, in most cases, an intermediate frequency generator) at the receiving side have to be synchronous with those at the transmitting side. This is achieved by the following two circuits:

·timing recovery circuit determining the borders of symbols;

·carrier recovery circuit which determines the actual meaning of each symbol.

There are modulation types (like frequency shift keying that can be demodulated without carrier recovery (noncoherent) demodulation  but this method is generally worse

There are also additional components in the demodulator such as the Intersymbol interference .If the analog signal was digitized without a four-quadrant multiplier, the complex envelope has to be calculated by a digital complex mixer.Sometimes a digital automatic gain controlcircuit is implemented in the demodulator

FEC coding

Error correction  techniques are essential for satellite communications, because, due to satellite's limited power a signal to noise ratio at the receiver is usually rather poor. Error correction works by adding an artificial redundancy to a data stream at the transmitting side, and using this redundancy to correct errors caused by noise and interference.

A FEC encoder applies an error correction code to the digital stream, adding redundancy.

A FEC decoder decodes the Forward error correction code that is used in the specific signal. For example, Digital video broadcasting standard defines a concatenated code consisting of inner convolutional (standard NASA code, perforated, with rates 1 / 2, 2 / 3, 3 / 4, 5 / 6, 7 / 8), interleaving and outer Reed-Solomon code (block length: 204 bytes, information block: 188 bytes, can correct up to 8 bytes in the block).

Differential coding

Main article: Differential coding

There are several modulation types (such as PSK and QAM that have a phase ambiguity that is, a carrier can be restored in different ways. Differential coding is used to resolve this ambiguity.When differential coding is used, the data are deliberately made to depend not only on the current symbol, but also on the previous one.

Scrambling

Main article: Scrambler (randomizer)

Scrambling  is a technique used to randomize a data stream to eliminate long '0'-only and '1'-only sequences and to assure energy dispersal. Long '0'-only and '1'-only sequences create difficulties for timing recovery circuit. Scramblers and descramblers are usually based on linear feedback shift registers

A scrambler randomizes the data stream to be transmitted. Descrambler restores the original stream from the scrambled one.

Scrambling shouldn't be confused with encryption, since it doesn't protect information from intruders.

Multiplexing

A multiplexer transforms several digital stream into one stream.

Generally, a demultiplexer is a device which transforms one multiplexed data stream to several streams which it consists of. Satellite modem doesn't have so many outputs, so a demultiplexer here performs a [[drop and insert|drop] operation, allowing to choose channels that will be transferred to output.

A demultiplexer achieves this goal by maintaining a frame synchronization.

a.SATMODE Return Link Technical Features

The SATMODE return link is highly programmable and has the following main technical features:

• continuous phase modulation (GMSK, MSK and quaternary MSK are supported),

• symbol rate from 4 ksymbols/s to 128 ksymbols/s

• MF-TDMA burst transmission

• performing channel coding for data protection (supports several types of turbo-coding and coding rates)

• code rates ½ to 5/6

• Medium Access Protocol (MAC) = Aloha protocol, with selective repeat retransmission

• MAC packet size of 66 bytes

• MAC protocol is transparent to

network layer protocols

• rain fade mitigation by adaptive rate and coding, algorithm resides in terminal

• compatible with transmission in Ka band, Ku band or other bands

• low transmit powers (100 to 300mW).small antennas (~60cm)       

To reach that goal and nevertheless keep full interoperatibility of terminals, SATMODE uses a fully specified waveform toolbox.

Each building block has a well-defined space of operation and can be used without limitation in this space.

b.The building blocks of the SATMODE toolbox

·Binary or quaternary CPM.

·Symbol Rate: 2 kHz to 128 kHz

·Programmable phase filter for CPM modulations (GMSK being a specific case)

·Flexible Turbo or Turbo-like

·Programmable interleavers (3)

·Programmable constituent codes with bypass possibilities (2)

·Programmable Unique Word structure

·Tables extraction from a DVB TS (DVB-S or DVB-S2 broadcast)

All the parameters are sent by the HUB through DVB tables, even allowing changes during operation:

·FCT: Sprectrum organisation in Carrier Groups

·FAT: Spectrum Allocation to services

Signalisation information sent to specific terminals is also embedded in DVB tables (SMT tables).

The terminal is fully defined: it must be able to play the complete waveform space. The HUB usually only implements one scheme and sends the tables to the terminals to instruct them to play that scheme.

SATMODE is a joint program to develop a low-cost two-way communication channel by satellite for the satellite TV users

Connecting TV consumers individually, both ways:

·With their content providers,

·With other consumers, on TV,

·With other infrastructures (GSM, internet),

·In real time,

·At any time,

·All the time.

FEATURE’S OF SATMODE

The continuous phase modulation technique has been selected in SATMODE because it allows using saturated power amplifiers and frequency multiplication in the iLNB. This means no automatic level control or phase locked loops are necessary in the iLNB and the cost of the iLNB can be kept very low.

The flexible channel coding provided by SATMODE allows to profit from the latest technical developments in this field. Turbo-codes are available, that allow to operate with very low signal to noise ratios (for example required Eb/N0 = 3.7dB for code rate ½). This means that very small antennas and very low transmit powers can be used which again allow to keep the cost of the terminal down.

SATMODE main design drivers are:

Ultra low cost satellite return link for short & frequent interactions

Always-on , responsive, always connected, stand-alone and dedicated;

·        For both Pay-TV and FTA (Free-To-Air) mass markets;

·        Cheapest CPE and cost of ownership possible; < 50 Euros extra;

·        Low and flexible bit rate; average: few bit/s; short packets;

·        Compatibility with next generation space segment;

·        Replacement of the PSTN modems for targeted iTV applications;

·        Allow for shared ODUs (SMATV),

·        User-friendly installation (= 'regular' digital DTH installation),

·        Inter-working with existing terrestrial return channel solutions,

·        Compliance to environmental, legal & regulatory framework,

·         MHP support.

MODEM LAYERS

A "modem" stands for "modulator-demodulator". A satellite modem's main function is to transform an input bit stream to a radio signal and vice versa. There are some devices that include only a demodulator (and doesn't comprise any modulator) that are also referred to as "satellite modems". These devices are used in satellite Internet access.

               There is a wide range of satellite modems from cheap devices for home internet      access to expensive multifunctional equipment for enterprise use.

A satellite modem is not the only device needed to establish a communication channel. Other equipment that is essential for creating a satellite link. Data to be transmitted are transferred to a modem from Data terminal equipment .

The modem usually has Intermediate frequency IF) output (that is, 50-200 MHz), however, sometimes the signal is modulated directly to L-band .In most cases frequency has to be converted using an up converter before amplification and transmission.

                   Modulated signal is a sequence of symbols, pieces of data represented by a corresponding signal state, e.g. a bit or a few bits, depending upon a modulation. Recovering a symbol clock (making a local symbol clock generator synchronous with the remote one) is one of the most important tasks of a demodulator. Similarly, a signal received from a satellite is firstly down converted this is done by a Low-noise block converter ( LNB)then demodulated by a modem, and at last handled by data terminal equipment. The LNB is usually powered by the modem through the signal cable with 13 or 18 V DC

The modem layer is specified by a proposed CENELEC standard (prEN50478).

The SATMODE design having led to this specification was optimized for the iTV case.The choice of constant envelope modulations was made to minimize the terminal cost. Thanks to this property, very low cost ODUs operating at full saturation and in non-linear mode can be used.

                The moderate bit rates of SATMODE allow to use very low power transmitters (typically 100 mW), keeping the cost compatible with the mass-market.The selected access scheme -slotted ALOHA- is efficient on iTV traffic and very easy to scale up to a very high number of terminals only sending a few packets from time to time.

                The SATMODE modem specification aims at fully specifyinspecifying the behavior SATMODE modem function used in a terminal.To increase the applicability and the probability of commercial success of SATMODE, it was decided to design SATMODE as a system usable with existing space segments and ready for future satellites improved for point-to-point application.

SATELLITE CAPACITY

Typically a wide downlink coverage area in Ku band is used for DTH TV broadcast. The return channel can be implemented with a wide uplink coverage (Ku band) or spot beams (Ka band)

The satmode return channel is a Aloha system with typical spectral efficiency of about 8Hz/data bit.

Required return channel transponder capacity is mainly driven by applications such as televoting, where a large number of users need to send data in a short period.

For example in a network with 300000 users participating to a televoting that spans 5 minutes the required transponder bandwidth is calculates as follows:

·        nr of votes per second = 300000/300 = 1000

·        nr of data bytes = 64

·        aggregated bit rate in kbits/s = 64 x8 x1000/1000 = 512

·        required transponder bandwidth in kHz = 8 x 512 = 4096

Forward link data generated by the satmode network are multiplexed into the TV multiplex (DVB-S), required bandwidth is typically 10% of the required return link bandwidth

BENEFITS OF SATMODE

SATMode’s expected main benefits:

1. Scailability

 SATMODE is very scalable to address a mass market of several
Millions of users,Among them, the messages are sent through SATMODE without any establishment time with a total transmission time lower than a few seconds.The system is scalable up to the complete DTH market and is designed to minimize the terminal cost.The system is scalable up to the complete DTH market and is designed to minimize the terminal cost. Major Benefits Scalable addressing for a market of several millions of users per national market  Availability to all users within the satellite footprint  Always-on, permanent and instantaneous connectivity  Minimal costs of terminals and communication  Enhanced security "Simple to install Services Transactional (Push or Pull VOD, Music, Betting)  Personal Communication: Chat, SMS, e-mail  Tele-Voting, Polls, Play-along, Quiz  Games: standalone or multiplayer  Interactive advertising  Home Shopping  Personal Data Consultation/banking  Internet Services

 2. Flexibility

Considering this objective, it was considered as mandatory to have built-in flexibility in terminals deployed today and ready for the future.

This flexibility allows SATMODE to be used in extreme scenarios by adjusting the modem parameters:

·Very power limited scenarios (it’s the case for most VSAT Ku-band satellites)

·Aggressive multi-beam space segment, targeting high spectral efficiency.

3. Interactivity

SATMODE represents a significant innovation in the support of a new tier of interactive applications via DTH and places these services on par with the growing interactive services offered via cable,” The lack of an efficient return path has always limited true interactivity over satellite TV,” SATMODE will remove this major obstacle and will help accelerate wide deployment of interactive television. This is good news for the consumer, for the advertiser, and for the content creator. Remote interactivity is the key element needed for the continued growth of digital television. Indeed, there is a strong demand for TV enhancements using interactivity to allow the introduction of new services. This interactivity requires a secured, always-on, permanent, instantaneous connectivity, scalable to millions of viewers. The purpose of SATMODE is to connect TV consumers individually, both ways with their content providers, with other TV consumers and with other infrastructures, in real time, at any time, all the time. SATMODE is an ultra low cost interactive TV solution via satellite, targeting the mass-market through consumer products.

4.Real-time voting

SATMODE, an innovative technology designed to support real-time voting, chatting, messaging, commerce, video-on-demand, and other exciting applications at the remote control fingertips of DBS consumers worldwide,

·The SATMODE system is set to enable permanent, real time responses by millions of TV viewers to content provider’s programmes. It will also allow additional services such as SMS, televoting, management of

personal video recorders, access control, pay per view and other impulse transactions.
    

·home shopping

·impulse pay-per-view

·SMS, chat and emails from the TV interface, either synchronized with a show or as one TV to TV or GSM phone connections

·Interactive games and gambling.

·tele-voting

5.Low cost

ASTRA’s ability to provide satellite-based interactivity on a large scale, and at a low cost, will further encourage the development of additional interactive services.

Due to the nature of iTV traffic, SATMODE is also very competitive in terms of communication costs and thus in terms of total cost of ownership. Viewers will need SATMODE enabled set-top boxes and a transmit/ receive feed in order to use SATMODE services. This equipment will be made available by the pay-TV provider, or acquired at attractive prices. The antenna equipped with the new feed will be easy to install and will use the existing cable and 60 cm reflector. Market research shows that viewers who have ASTRA satellite dishes are statistically more interested in new technologies than other TV viewers and so can bring high growth

6. SATMODE provides 100% coverage (this is not the
case for xDSL or ISDN or Mobile Phone),

7.SATMODE performance closely matches end-user
requirements,

8. SATMODE performance closely matches the interactive provider
and TV bouquet provider requirements:

·Always-on,

·Sufficient QoS,

·Provide very low communication cost for the service provider,

·Enable the generation of new 'Telco' revenue,

·Enable the generation of premium rate fee,

9. Allows the bypassing of existing expensive Telecommunication
companies,

10. potential to improve the security of CA system

11. The installation of the ODU is as simple as the installation ofcurrent dishes.

From the end user's point of view, the following benefits can be derived from SATMODE

12. The main functions of a satellite modem are modulation and demodulation. .

Popular modulation types being used for satellite communications:

·Quadrature phase shift keying

·Orthogonal quadrature phase shift keying (

·8PSK

·Quadrature amplitude modulation (especially 16QAM. )

·Binary phase shift keying

13. Error correction codes and formats.

·Convolution codes

· constraint length(less than 10, usually decoded using a Viterbi algorithm

·constraint length  more than 10, usually decoded using a Fano algorithm

·Reed-Solomon codes usually concatenated with convolutional codes with an interleaving

·New modems support superior error correction codes (turbo codes )

SATMODE gets rid of the need to connect the Set-Top-Box to a PSTN line, thus removing an obstacle to using interactive applications,

SATMODE eliminates the conflict between simultaneous voice and interactive TV connections,

SATMODE provides an 'always on' connection.

From the broadcaster's point of view, such a return channel leads to substantial revenue increase: churn reduction, incomes from new services, interactive advertisement, piracy control, etc. SATMODE provides a scalable, universal solution, integrated with the TV satellite infrastructure. It also provides access to the end user Set-Top-Box for statistics, audience measurement and Personal Video Recorder management, etc.

FUTURE

New features Enhanced conditional access Audience metering Statistics gathering  Hard disk drive content management .Non broadcast applications may include tele-surveillance and process monitoring .Interactivity enabled by the ASTRA return link will greatly enhance future applications such as video-on-demand, messaging, gaming and growing audience interaction in various types of shows. Interactive television is a way to increase revenue for broadcasters of both pay-TV and free-to-air programming. Revenues are generated through the use of votes, games, messages, gambling and impulse pay-per -view. Interactive television also increases the quality of the entertainment experience by inviting individual involvement. This, in turn, attracts new viewers and reduces churn. To maximize these revenues, permanent connection between the set-top box and the provider is essential. ASTRA is a leading partner in the development of such connectivity: the SATMODE project, a satellite return system for interactive TV that connects individual TV viewers with their content providers. It is planned that SATMODE will be implemented in ASTRA homes as an additional revenue generation tool.

CONCLUSION 

SATMODE is currently in the latter stages of development The SATMODE system is set to enable permanent, real time responses by millions of TV viewers to content provider’s programmes.The system could also be exploited for anonymous statistic gathering, and especially for management of content on the set-top boxes equipped with a Personal Video recorder (PVR). SATMODE program comprises the development of an ultra low cost satellite interactive system, which includes all required activities, including commercial field trial .Although compatible with existing satellites; SATMODE is designed to be ready for new generations of space segments. SATMODE is a low cost interactive TV solution via satellite, targeting the mass-market through consumer products