Radio and broadcast


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Please try to limit the opinions of other people's ideas and save it for the discussion pages. If you think someone has a particularly good or bad idea, say so in the discussion page. This discussion/argument/feud can be noted in the article, but in a less familiar style.


Broadcast texts over shortwave radio

A major challenge is providing a continuing source of content for the OLPC. Access to the Internet in most of the regions of the world where children will benefit from the OLPC program is severely limited. However, most of these regions can receive shortwave radio signals, even in mountainous areas.


The OLPC is (1) a tool for accessing information and (2) a tool for self-driven learning through investigation. A problem with the former role is "from whence cometh the information?". With the limited storage resources, "pre-loading" the information on the machines seems like an untenable approach. The crux of this proposal is that having easy and reliable access to a small library of information will be more useful than having spotty access to the entire Internet, even through mesh networking.


Continuosly broadcast e-book content over shortwave radio with the same content repeating at different times of the day to work around intermittent reception areas. Have the books broken up into chunks, and all the texts from a library interleaved in time. If possible, transmit different interleaving sequences on a set of different channels. The basic circuitry for a shortwave radio demodulator can be very simple, particularly if the decoding is done in software sitting behind a straightforward RF and analog front-end. When a child wants information on a topic, the implemented system captures fragments of a text relating to the topic off the air, and over time, the whole text is collected.

I wouldn't suggest using software radio on this platform, implementing a hardware radio (which returns either unerrorcorrected binary or even better values between 0 to 255 for a bit is either 0 or 1) is very simple, even for relativly fast data transmission modes over "ordinary" AM amateur radio transmitting equipment. I'll try and post a very basic design for one on a USB port if I find time --Ikarus 00:35, 16 November 2006 (EST)
The system could be used for a) Long lasting information - eBooks, software, media-files, teaching material, etc. and b) Short-lived information - Web-pages/text-file with News, OLPC Project/School News, group-email Newsletters, etc. Both would be repeated at regular intervals. Even at low data rates, a large library could be accumulated over time.
Some people may think that only full 2-way access to the internet is good enough, but if you were in the position of having no information at all from the outside world, having a 1-way stream of information would be very much better than nothing. --Ricardo 14:46, 19 August 2007 (EDT)
I had the Idea of Internet over Shortwave the other day. Didn't know about this page then. Some problems would be the laptops would not have strong enough transmitters to do 2-way unless shortwave towers were installed to receive the data transmit it over regular wifi with a meraki network so people can connect the laptops would then make up another mesh internet network then data can go from laptops back to the tower to be transmitted on short wave then onto the internet again. I will try to post a diagram of this later. ~DeSalvionjr (
Here is the diagram ( the diagram shows that a short wave tower broadcasts the internet which is recieved by another shortwave tower which is connected to a meraki mesh network ( the laptops within the meraki network's range will recieve the internet and create another mesh network to conect laptops outside of the meraki networks range. Packets from laptops go to laptop to meraki (or if in range it will go directly to meraki) then to the tower to be broadcasted then recieved by the other tower and put on internet incomming packets follow that route in reverse. Path to internet: laptop network > Meraki Network> shortwave tower 2 > shortwave tower 1 > ISP > Internet ~DeSalvionjr (


Purely as an example, let the library of e-books being transmitted consist of

  1. Project Gutenberg texts
  4. Wikipedia.

All the content is broken up into packets of some size, encoded, all the packets interleaved according to some scheme, and the entire interleaved stream repeatedly transmitted. The infrastructure for transmitting the data streams need not even be in the nation or on the continent where the recipients are. Let, for example, the entire stream take two months to transmit. 4GB of encoded data at 1200 baud will take ~40 days. 1200 baud for a packet radio seems feasible, though I can't say how complex the hardware would be. Bear in mind we're only talking about receiving, not a full-blown modem. It could be as simple as a shortwave radio with a patch cord between its earphone jack and the microphone input of the OLPC.


You can imagine having N different interleavings, which are transmitted on N different channels. When a child wants information on some topic, the request is sent out to at least N other OLPCs, over the mesh wireless network. All the machines start picking up chunks for the text on one of the N different channels. The chunks are sent to the requester over the mesh network. This is similar to the way in which the hosts on a P2P file sharing network cooperate to transfer files from far away into their local area.

Existing technology that can be adapted

There are various existing technologies that could be adopted or adapted to achieve this.

Digital Signal Processing for Ham Radio

The Ham Radio community has a vast amount of experience with weak-signal transmission (and reception of data) beginning with slowscan TV back in the 60's. Phil Karn, the developer of a popular DOS application to run TCP/IP over shortwave, has done some work that could be used. The Geode chipset does have MMX instructions which can be used to do DSP functions.

Digital Radio Mondiale

There is a new standard that is now beginning to be used for international shortwave broadcasting called Digital Radio Mondiale. This already has a subchannel allocated for transmission of data.

An Open Source implementation of a software Digital Radio Mondiale decoder, called DReaM already exists.. It can decode international broadcasts, such as the BBC World Service, Voice of America etc. and can decode single sideband AM. As the decoding for Upper Sideband uses a flip filter, I can't see it being to hard to decode AM, and if FM decoding in software and a simple Superhet front end were added, would be perfect.. The User Interface would require modification as it is aimed at Radio Experimenters, and is too technical for children.

HF radio

The ham radio community has mature technology for sending data over long distances at low speeds over narrow high-frequency (3-30 MHz) channels using PC sound cards as data modems. This technology could be used for e-mail to remote regions.

I think this would be a good idea since some children live a mile or more in there towns and villages. Having data travel over long distances will help them keep in touch with each other through the network. I'm sure thought this will have to be approve by the IEEE as a new networking standard, but I'm sure this can be done.


Currently, PSK31 supports text-mode "chat" via HF radio. PSK31 software is being ported to the XO by TommyGober. Currently there are not any truly outstanding PSK applications for Linux (at least, not in the same capacity as DigiPan or MixW that Windows offers). gPSK does offer built in ALSA support and has a simple interface, psk31lw has a super simple ncurses interface that could have a GUI wrapped around it. Other packages exist but may not offer ALSA support, or require graphics libraries not in use on the XO.


PACTOR or other email reflector modes would also be useful for the XO (especially for file transers to remote areas). Solid linux-based software for PACTOR is unknown at the time, use of a TNC for PACTOR is also unknown.

Another historical note about radio broadcast of programs

Back in the 8-bit era, when floppies were still not cheap enough, some computers had a cassette recorder so you could store your programs in cassette. A local radio used to broadcast Atari programs so you could record them at your radio receiver and then play them on your Atari. It wasn't very reliable, since line noise could spoil the recording, but it was a nice idea back then. .:|you could broadcast boot code, mesh-networking software patches, and links to P2P resources. Just include a standard FM receiver (but why not a programmable transmitter as well!), record and process audio into bits, but don't listen to the noise ... oww! N888-9-AE|:.

Luis González

See Basicode 17:02, 17 March 2006 (EST)

12 March 2006

Broadcasting files over radio should work a lot better nowadays, now that the fast processor in the OLPC can perform Digital Signal Processing to filter-out noise and detect the signal (see below - The 'Signal format' section of Embedding Data as Hidden-Sounds within a Radio-Station’s Audio-Stream). -- 14:26, 19 August 2007 (EDT)

Satellite Broadcast

MIT's Technology Review web site has an article about narrowband (128 Kb/s) satellite broadcasting being used in Africa. This could be used to send updates to schools.

Some interesting experiments in using direct satellite broadcasting for education took place in the 1970s using the ATS-6 experimental satellite.

EduVision - This article, Eduvision - Beaming Books, describes a system where electronic books are beamed via the commercial WorldSpace geostionary satellites to satellite receivers. These have palm-size antennas, because the company normally does satellite radio, unlike other systems that require large dishes. The system transfers files at 128Kbps. It takes a while to receive the books, but then they are available to anyone after that. Since it's a 1-way broadcast, any number of users can receive the books. It doesn't slow down as you add users.

USB addons

Well, first of all, the OLPC has 4 USB ports. There is no reason why someone could not manufacture such a radio system as an accessory for the OLPC, to be used in those countries and those regions where this would be a good idea. This would most definitely be a dumb idea in the capital city of Thailand, for instance. But in mountainous western China it would be a very good idea, indeed.

For an example of how small an simple radio circuitry can be, look at this plan for a 3 penny radio. Note that he refers to using a lemonade battery to power it, i.e. electrodes dangling in a glass of lemonade. To use this as a shortwave receiver you just need to adjust the tuning circuitry to bring in the shortwave bands. Here is a circuit specifically for receiving shortwave bands that uses the same radio IC. A receiver like this could actually feed directly into the OLPC's microphone input, however some extra work could interface it with a USB port. This is an example of a microphone input via USB. If it was built as a USB device, it would be powered from the USB port and receive data in the background while the user reads e-books in monochrome mode.

Decoding the transmission in software is alot more "expensive" in terms of battery use then in hardware. --Ikarus 00:37, 16 November 2006 (EST)

Vertical retrace data channel

One way to mass download info, at least in areas that have TV reception, is to use the vertical retrace interval to send data.

TV signals have a very limited range, using a subchannel on a existing AM radio transmitter (of any carrier frequency) increases the range tremendously, yet requires almost no expense for the organisation doing the transmissions, or the carrier. --Ikarus 00:39, 16 November 2006 (EST)


Support for this and mention of telesoftware and of MHP

Yes, good idea.

You might like to consider using telesoftware, that is the unidirectional cyclic broadcasting of software and its selective use, to broadcast software packages for the laptop as well.

The following webspace about the DVB-MHP (Digital Video Broadcasting - Multimedia Home Platform) interactive televison system might be of interest.

The MHP system broadcasts Java programs to interactive television sets.

The following idea, not implemented as far as I know, might be of interest in relation to digital radio.

William Overington

5 March 2006

For Telesoftware, see Telesoftware file transfer using Teletext Pages section below. Teletext is a fore-runner to MHP. --Ricardo 03:57, 20 August 2007 (EDT)

There is now a page about the possibility of an MHP to laptop interface

There is now a page about the possibility of an MHP to laptop interface.


One way connection to internet helps nothing. This is passive usage like watching tv. Software distribution with USB is easy.

  • Yet in areas of the world where a two-way link is impossible, a one-way system where lots of software and data such as electronic textbooks can be received from direct to school broadcasts from a geosynchronous television broadcasting satellite and stored localy, telesoftware could be very advantageous.

Distance and the Mesh Network

As I understand these laptops will have intergraded wireless with the 802.11 b and g standards. The problem I see is that in some countries, like Africa, the children live sometimes a half mile or so apart from each other. The 802.11 b and g IEEE standard only has a reach of 100 feet or more with out modifications. This means the only time the children will be networked with each other is when they are at school. What needs to be done is the wireless in each laptop needs to reach up to at least a mile so the children’s computers are always connected to the network even in their home. The wireless b and g standard can be mod up to 10 miles of reach but to do that requires either a large antenna or an amplifier that would consume too much power. My suggestion is that you create a new wireless networking standard with low radio frequencies like every one has been suggesting. I would like to see it so the children’s computers are always part of the network when they are at home, because as I see it most of the programs on the laptop except the office programs can’t work with out a network.

  • Yeah, Thats true and current problem in commuication field. But i heard a new low-power, long-range communications technology called xMax®[2]. xMax uses single cycle modulation to boost the range of wired and wireless communication devices. Incorporated into products as a new physical layer PHY chipset, xMax also reduces a device's RF output power resulting in improved battery life and high data rate over a distance of about 13 miles.I think sounds like very good and i am request to OLPC team contact the xG Technologyfor using such technology in the OLPC project. If everything is done, The OLPC become a great project in the human era. Reason is good education is best mould of making best community. Muhammad Ismail .H 14:15, 15 July 2006 (IST)
    • WiMax [3] might be suitable for this.

Speeds and data integrity

If I remember my modem hardware correctly, 1200baud is simple FM over half of a telephone channel. This would be more like a FAX channel where the entire frequency width of the channel is available; all normal fax modulations have a baud rate of 2400, with bps of 4800 to 14400.

The processor in this machine would be more than enough to demodulate this in software and decode some serious forward error correction eg par files

Radio distribution of content

The basic suggestion is to adapt existing technology for broadcasting data over the radio and use it as a widespread distribution tool for content to the laptops or, more likely, to some central site in the village. Once in the village it can be distributed further using the built-in wi-fi of the OLPCs. The radio would presumably be similar to existing USB DVB-T receivers available in Europe to receive digital television broadcasts. This could be done in one of two ways. One way is to fill up a shared library in each village. The other way is to constantly repeat the same documents so that villages do not need to have large storage capability.

MHP has been suggested as a possible source of this technology.

Mesh * xMax / MIMO = "The End of Telcos"

Take the automagically connected 'mesh' network, multiply by 'xMax' and divide into 'MIMO'.

Everybody is a node, but needn't be 'near' each other and receives and transmits from and through every other user. The very high speed and the numerous sources could avoid the latency problem when accessing internet servers through many hops.

And the very low power consumption of xMax is an interesting asset indeed.

I back Muhammad Ismail .H 's claim: contact xG Technology, they should be very interested in producing something between 5 and 10 million chips for the OLPC.

(From:general-products) Single cycle AM frequency communications is far easier than people realise, as it can be handled by direct connection to a low speed CPU or equivalent. Im afraid Ive been trying to find someone to consider uses of my single cycle, chaos modulation method since 1997, and have dated notes to prove it, but am no good at all in selling or following up. Anyone who is interested is welcome to the hardware and software block diagrams, under Open Source style ideas. I also apologise for my belief that Bluetooth was deliberatly crippled from its initial form, to prevent it being used in such a Telco replacing Free Mesh network. See BT and South Wales Mesh network tests.(28/04/2007) (From:general-products)

--S112 04:39 16 August 2006 (EST)

Satellite TV Multi-Language Sub-Carriers

This is a method for the 1-way broadcasting of information and files to schools, free-of-charge.

Satellite TV systems are able to provide sound to go with their pictures in several languages, on separate sound-tracks or sub-carriers. The viewer selects which one to listen to using their set-top box’s on-screen menu.

It is often the case that programmes are transmitted with just one or two language sound-tracks, leaving the others un-used. If the OLPC project could get the co-operation of a satellite company which broadcasts free-to-air programmes to a developing country or continent, these spare audio-tracks could be used to broadcast audio-signals containing up-to-date or long-lasting information to the schools (news, OLPC news, eBooks, software, web-pages, open/protected emails, newsletters, broadcasting schedule, etc).

Some of the information might be of interest to home/business users, not just schools. The satellite company could benefit by using the same file-broadcasting system for commercial purposes.

Depending on the type of audio data-signal that is used, the amount of data per day would be :-

  • 8 Megabytes in 24 Hours at 1000 bits-per-second.
  • 43 Megabytes in 24 Hours at 5000 bits-per-second.
  • 424 Megabytes in 24 Hours at 48K bits-per-second (the speed of a fax-machine).
  • 495 Megabytes in 24 Hours at 56K bits-per-second (the speed of a dial-up modem).

File-compression might improve this.

Even a small amount of information/files each day at low data-rates would be useful to schools with no other link to the outside world. At 48/56Kbps, it would be even more useful.

Using Satellite TV means that data would be available to schools over a very large area.

The signal might be based on an existing Packet Radio standard, but with 1-way forward error-correction instead of 2-way data-packet acknowledgements, re-tries, etc, since there is no way of transmitting back to the satellite.

A satellite dish and decoder would be required to receive the broadcast (costing about 200 US Dollars in 2007). This would be expensive if each user had to buy their own, but sharing the cost of a single receiver among many local users might deal with this issue (school(s), homes and businesses). There is no on-going cost. A paid-subscription would not be required if it just receives free-to-air programmes. The equipment cost is much less than data-broadcast by satellite systems, such as VSAT terminals (1000 US Dollars in 2007).

The system might be used to send data to remote towns and villages, then another broadcasting system which uses cheaper receivers could distribute it locally (such as data-broadcasting by radio, Wi-Fi, Sneakernet on USB Flash Drive/CD/DVD or Embedding Data as Hidden-Sounds within a Radio-Station’s Audio-Stream).

To receive the data, the audio-output of the satellite decoder would be connected via an audio-lead to the microphone/audio-in socket of a computer/OLPC laptop and software would be used to sample it and convert it back to bits, bytes, data-packets and files.

If anyone is interested in developing it, please post your comments on the OLPCWiki discussion page for this article or contact me at [].

--Ricardo 01:01, 11 August 2007 (EDT)

Embedding Data as Hidden-Sounds within a Radio-Station’s Audio-Stream


I think that 1-way broadcasting of information and files to schools (OLPC and non-OLPC), free-of-charge, would provide a very useful service. It would be welcome in parts of the world where there is no internet-access and no other source of digital information, eBooks, software, web-pages or files. It's a bit like a one-way internet.

It would allow a school to build up a library of information and eBooks over time and have some up-to-date news and information every day.

People often talk about "How can we bridge The Digital Divide?" (between the industrialised and developing countries). Broadcasting useful files for free may go part-way toward bridging the digital divide. Part-way is better than nothing, having no access to information at all. Feel free to add your own thoughts about this to the discussion page.

There are several existing services to transmit data by radio, but they use expensive equipment or need an expensive monthly subscription. This system is much cheaper, with no subscription and very cheap equipment.

One possible method of broadcasting files to schools would be to embed the digital data as hidden sound-signals within an existing radio-station’s music/speech audio-signal. Embedding the data within the audio would allow data-files to be received without any special equipment, using ordinary cheap radios connected to a computer via an audio-lead.

There are many potential or existing technologies for 1-way broadcasting of data. This idea is just one of them.

Software at the transmitting-station would convert the data into an audio signal representing the binary bits, bytes, data-packets and files. It would then be mixed digitally, or via the radio station’s analogue mixing-desk, with the music or speech to produce the final audio-signal for transmission (music with hidden data).

The data would be received by connecting the headphone socket of an ordinary, cheap, analog radio (5 US dollars in 2007) to a computer’s audio-in/microphone socket. Alternatively, you could use a Radio that plugs into a USB socket (about 10 US Dollars in 2007). Receiving-software would sample the audio stream using the sound-card's Analogue-To-Digital Convertor, extract the data-signal out of the music using digital filtering software and convert it back to bits, bytes, data-packets and files.

The key advantages of this system are :-

  1. It doesn't require a new license for part of the radio spectrum from the government. Data is broadcast within the music of an existing radio-station.
  2. For the listeners/data-users, using ordinary radio's would be very much cheaper than satellite or digital radio receivers, making it affordable to schools and individuals in developing countries.

The radio-station could obtain the long-term/slowly-changing data to be broadcast (electronic books, software, web-pages, etc) on CD/DVD/Flash Memory Drive/etc. Up-to-date information could be obtained daily via the internet or satellite receiver, if the station has one. If not, then it could come from another international, national or regional radio station, via the same 'cheap radio + computer' system. The station would just re-broadcast it to it's local area.

This method could be used to transmit files to any type of computer in developing countries, not just One Laptop Per Child computers. It could also be used in industrialised countries, wherever there is no internet-access (countryside, camping trips, vacations, boats, etc).

Ideally, the software would be free open-source software, so that it's widely adopted, then people could make money from encrypted or password-protected data services if they wish.

Development status

This is an idea that has not yet been developed. It's almost entirely a software project. The development could be a university project or spare-time open source project. This may be pointing out the obvious, but once the software is written, an unlimited number of copies could be produced for nothing, for any number of users. Unlike hardware, there is no per-user cost.

There are any number of ways the data could be encoded, based on existing methods or a new one. As an experienced software developer, familiar with the transmission-methods of the last 20 years, I know that the software development is perfectly feasible and wouldn't take too long. I could do it myself, but it would be better to make it a university or open-source-group project, so a team can work on it together and consult with potential users.

Comparison with other methods

This method, where data is embedded into the audio signal, allows ordinary radios to be used as receivers. Some alternative systems for sending digital data as part of a radio-broadcast rely on more expensive receivers, which receive data on a separate sub-carrier frequency. For example, the RDS Radio Data System, which sends current programme information on a sub-carrier frequency (see Wikipedia - ). In contrast, an embedded-audio system would keep everything within the normal audio-signal.

Data Representation

The signal-format for embedding data into the music/speech could be one of these :-

  1. Steganography – Several existing methods for hiding data within audio signals. (See Wikipedia - )
  2. ‘Digital Watermarking’, as used to embed copyright information into CD-tracks. The fact that digital watermarking is known to work provides a ‘proof of concept’. It shows that data can be embedded into audio and then recovered. Digital-watermarks are quite robust, surviving attempts to remove the copyright information by such measures as recording CD-tracks to tape then re-digitizing the track. However, most existing digital-watermarking systems are proprietary and would require license-fees.
  3. An existing non-proprietary way of representing data as tones (public-domain or patent-expired).
  4. A new format of our own - so there are no commercial license-fees to pay.

Signal format

Initially, to simplify development, the encoding could use a simple signal-format for the data, such as a pair of tones at two different audio-frequencies representing binary 0s and 1s, for example 10KHz and 20Khz. This is known as Audio Frequency Shift Keying (AFSK), as used in amateur radio file-transfer, early dial-up modems, Emergency Warning Systems and in 1980s home-computers, to load games from cassette-tape using the Kansas City Standard (see Wikipedia FSK - Applications).

The signal would be at a much lower volume than the music or speech, making it inaudible to the human ear, but recoverable by digital filtering. To ensure that a low-volume data-signal can be recovered, a long tone consisting of 10 or more cycles could be used for each binary bit. Later, a more sophisticated format than AFSK could be used, capable of higher data-rates.

Here is what the signal-waveforms would look like :-

Data Embedded in Music as AFSK (Audio Frequency Shift Keying) Audio-Tones

Quantity of data

If 1000 bits per second can be achieved, then the following amounts of data can be sent :-

  • 3 Megabytes can be received in an 8 Hour school-day.
  • 14 Megabytes can be received in a week (5 days x 8 hours per day).

Files would be compressed to transfer as much data as possible.

This would be enough to recieve daily news, individual web-pages, newsletters, group emails, and for the slow accumulation of eBooks, software and one or two small websites per week. A large library of eBooks, software, websites, etc. could be accumulated over many weeks and months. Children would then have access to hundreds of eBooks for years to come.


Although hiding data in the audio signal wouldn’t achieve such a high data-rate as subcarrier systems or dedicated data channels, this system does have several points in its favour...

Cheap Hardware

No expensive hardware is required for transmission or reception. Most of it would be carried out in software. At the transmission-end, it would use purely software for encoding, embedding and mixing the audio. At the receiving-end, it just requires a cheap radio (which a school may already have), a 3.5mm stereo-to-mono jack lead to connect the radio to the microphone socket of the OLPC laptop (for one stereo channel only, about 2 US Dollars in 2007) and some decoding-software. If the radio is connected to a conventional PC, then you would use a stereo-to-stereo lead and monitor just one left/right signal. To avoid using batteries, a radio that plugs into the USB port may be preferable, since USB 2.0 provides power for re-charging the radio's battery as well as data.

Very Important - No need for new Radio-licenses

Since it uses existing radio-stations, it wouldn’t require a new expensive radio-licence (for part of the radio-spectrum), as you would require if you set up a brand-new data broadcasting station. It just needs a partnership with one or more radio stations that are prepared to carry the data as a community-service.

Short development time

It can be based on proven, existing techniques for embedding data in audio.

Long distance transmission

It can use the powerful transmitter of a radio-station to transmit data over long distances.

Wide coverage of data transmission

A single short/medium/long-wave radio-station can cover a wide area (thousands of square miles). In addition, there are thousands of FM stations worldwide which can broadcast data to schools within their local area.

Multiple receivers

Because the hardware is so cheap, a school could have several radios connected to different computers on the mesh-network listening to several radio-stations at the same time which transmit different files. The received files could be passed from each of the receiving computers to the mesh-server and other computers on the network.

Independence from the Transmission-Medium

The system is independent of the underlying transmission-medium. Any transmission-medium with an audio signal can transmit embedded data, including AM/FM radio-stations, terrestrial TV, satellite TV, internet-radio, etc. Internet radio-stations could embed data into their audio signal, so that it can be streamed via the internet to anywhere in the world, then without modification, re-broadcast by radio to a local area or a whole country.

Re-broadcasting Data

Sometimes, local FM stations receive a programme from a national or international radio-station and re-broadcast it on a different wave-band to their local area. For example, the British BBC World Service is transmitted from the UK, received by radio or the internet in many countries and re-broadcast on local FM stations. It allows people without a short-wave radio to receive it on an FM radio.

Embedding data within the music/speech audio-signal means that data from the national/international-station can be passed on without the local FM station having to do anything at all to the audio signal.

In a developing country, data could be embedded into a programme by a national radio station, then received by local stations and re-transmitted on FM in their area.

One variation on this is for local stations to continuously extract just the data from a national broadcast and re-embed it into different local programmes. They are not forced to carry the music or speech content of the national broadcast, just because they use the data.

Multiple data-sets

Perhaps more than one set of data could be embedded into the music/speech audio-signal for national and locally-developed content. This could be on 2 separate hidden sound signals, on the left/right stereo channels or just interleaved in time within one signal.


Since it’s a software-based system and it uses audio-signals and it is independent of the transmission medium, most of the development work and improvements can be done by software developers, with no special knowledge of radio-equipment or electronics. This provides a larger pool of people with the skills to work on it than a hardware-based solution. Also, a great deal of the development work can be done on computers, without any special radio hardware. Obviously, the team still needs some experienced radio-engineers.


Slower data-rate than other systems

The amount of data per hour may be quite low compared with a system that uses the full capacity of a radio-channel for transmitting data. However, receiving data from several stations at a time could offset this to some extent. Also, if the maximum data-rate does prove to be very slow, it’s still quick and cheap to develop and could act as a stop-gap until a better system is developed. Since, it is software based, it is capable of constant improvement once it is up and running. There’s no reason why more than one data-broadcasting method shouldn’t operate at the same time. It isn’t necessarily an either/or situation.

The slow data-rate doesn’t necessarily rule this system out. Even with a low data-rate service, a school could still build-up a library of useful eBooks and software over a few weeks or months.


Verifying the data before transmission

To make sure that each data-packet is transmitted correctly and not obscured by a particularly loud sound at the audio frequencies used by the data, the software would monitor the mixed music + data output signal, check each data-packet is recoverable by filtering and then mix-in another copy of the packet after a short delay, if necessary. In this way, one would know that recoverable data-packets are present in the signal at the point of transmission. This is just an option. It may not even be needed.

Keeping the Data Inaudible

Some method may be required to avoid transmitting data during periods of silence, such as abandoning a data-packet if the music/speech stops, then re-transmitting it when the music/speech starts again.


The service could be useful, not just for information of long-term value, like eBooks and software, but also for short-term information, such as news. The data transmitted could include a transmission-schedule of files, a range of popular web-pages, news, weather, sports results, farm/market-prices, public-health bulletins, voice-mail files, pictures, text, MP3s, MIDI music files, system maintenance information, OLPC news, etc..

Layered Services

The service is just a platform for data-transmission, like a one-way internet. Any number of services could be built on top, equivalent to one-way versions of email, ftp file-transfer, instant-messaging and the World Wide Web (a selection of popular web-pages). It could send any type of file for any type of service.


This might be done in 4 stages :-

  1. Software-only – Encode some data into an audio-file, then decode it and check it.
  2. Cable Loop-back – Transmit the signal from the audio-out socket of a computer to the audio-in socket of another/the same computer via a stereo jack lead.
  3. Transmit and receive the signal on FM radio - As a transmitter, we could use one of those cheap transmitters that broadcasts an MP3 Player’s headphone-output as an FM radio signal to a car radio that doesn’t have an input-socket. We would output the signal from the audio-out socket of a computer, broadcast it using the FM transmitter-device, and receive it on an FM radio plugged into the audio-in socket of another computer or the same computer. Alternatively, use a USB FM Radio or laptop PCMCIA radio-card.
  4. Transmit and receive data on Short-Wave – Use professional short-wave equipment over various distances, such as across a lab, a university campus and longer distances.

Upgrading the Encoding-Standard

The first encoding standard that is used for the hidden data isn’t fixed forever. A simple, slow encoding method could be used for a start, then upgraded later via software-updates.

Development Partners

Development might be speeded-up if people in the industrialised countries, including radio-stations, advertisers and other high-tech companies, became interested in using and developing the standards and software and services based on them. This type of data-transmission service could provide people with a steady stream of useful information in situations where the internet is unavailable and there is no mobile phone coverage, such as in remote countryside areas, on vacations overseas, on trekking/camping trips, on boats, etc. Some people may just use it because it's cheap.

Receiving Equipment

Many types of receiving equipment with a built-in radio could make use of it, with suitable software – OLPC laptops, ordinary desktop/laptop computers, hand-held devices/PDAs, mobile-phone handsets with FM radio, FM Radio/MP3 players, games consoles, etc. It could be useful in any situation where people want news, weather, sport, software, eBooks, text-files, popular web-pages, entertainment, radio-station news, stock-market prices, etc, for free.

Streaming real-time or pre-prepared audio encoding

The system I've described encodes the data in real-time and mixes it into the music audio stream. Since a lot of stations play MP3 music files for each song, an alternative is to prepare MP3 files with specific embedded data files in advance of transmission. One particular song would have one or more particular eBooks, web-pages, etc. It means that data can't be changed easily at the last minute for news, but for eBooks, etc, it avoids having to use the mixing desk. It's just an option.

Two-Way Transmission - Benefits for Radio-Stations and Schools

This part is an optional advanced usage. Feel free to ignore it on first-reading.

In addition to a 1-way data broadcasting service, this system of embedding data in radio-station transmissions could provide a 2-way link between nearby radio-stations and whole chains/networks of radio-stations in those parts of the world where there is limited phone or internet access or none at all. Each station transmits its data to the other station within its own music/speech broadcast and receives data in the opposite direction in the same way, by receiving the other station’s output on a radio + computer, like the schools. Since it’s a 2-way system, it can include Acknowledgement and Retry messages for reliable data-delivery, like TCP/IP.

The system could be used by the radio-stations to...

  1. Swap news, emails and music-files among themselves, perhaps with automatic file-sharing and synchronisation of file-collections.
  2. Receive files for broadcast to the schools from another radio-station, somewhere else on the chain/network with internet-access to an OLPC website or with better reception of international data broadcasts.
  3. Accumulate a library of files over several weeks or months, which local schools can pick up in person on an OLPC laptop, CD, DVD or Flash Memory Drive.
  4. Send the occasional message from one school to another in a different part of the world, if the sender brings the message in to the station.
  5. Upload locally-produced content produced by the schools, to an OLPC file-server or website, for /publishing/broadcasting to other schools (web-pages, eBooks, artwork, music, articles, teaching materials, etc).
  6. Send requests on behalf of the schools to the controller of the transmission-schedule, for particular files to be broadcast. This makes the system to some extent ‘interactive’, not just passive.

Higher Data-Rates using Data in TV Pictures

Hiding data in the sound-signal is quite simple, but there is also the possibility that data could be hidden in Terrestrial/Satellite TV pictures, using steganographic techniques, to allow a higher data rate.

It could be done in real-time or by pre-processing each programme’s video file in software. It wouldn’t require any additional hardware at each broadcasting station, which is an advantage compared with schemes which add data using electronic circuitry.

Note that, like the audio-system, the picture-system is independent of the transmission-medium. It doesn’t matter whether the picture is broadcast over digital or analogue, terrestrial or satellite TV. The data is embedded in the picture, not in the TV signals of the particular transmission-standard. The data would still be present, even if the programmes is relayed through several different TV systems, uplinks/downlinks, or recorded onto DVD, Hard Disk or tape.

Wider Use of Data by Radio

In developing countries, many people would ideally like to have 2-way access to the internet, so they can choose what to look at. However, if the internet is unavailable or unaffordable in their area, any of the 1-way data-broadcasting methods on this page could still provide a lot of people with access to a range of free digital information for the first time. This scheme and any of the 1-way broadcasting systems might be called a ‘One-Way Web’, extending the internet in a limited way to thousands more people, over large areas, for free.

The scheme could benefit people with any type of computer, not just participants in the OLPC project. If a lot of radio-stations were involved in the scheme, large parts of developing countries could be covered. It would cover the time until they get affordable 2-way internet-access in their area.


I think this embedded-audio scheme provides plenty of options for broadcasting data to schools, either by using this scheme as described or by including elements of it in other schemes.

If anyone is interested in developing it, please post your comments on the OLPCWiki discussion page for this article or contact me at [].

--Ricardo 06:13, 7 August 2007 (EDT)

Very long distance Wi-Fi

Very long distance Wi-Fi might be a suitable, cheap technology for connecting schools to the internet in isolated areas.

See this eBook Wireless Networking in the Developing World for all aspects of Long Distance Wi-Fi links, including Radio Physics, Equipment, Antennas, Security, Lessons from Trials, etc (a .pdf file). The HTML version from is easier to read on-screen.

In April 2007, a group from the Venezuelan APC (Association for Progressive Communications) member EsLaRed, in conjunction with Professor Eric Brewer and his team from the University of California at Berkeley, set a new Wi-Fi Distance Record, transmitting and receiving data over a distance of 382 Kilometres (237 miles). They achieved a data-rate of 3 Megabits Per Second in each direction, first using Professor Brewer’s equipment and again using APC's Linksys Wi-Fi equipment, costing less than 60 US Dollars.

Please see this article on the APC website, which has photos of the equipment they used, including domestic Wi-Fi home-network equipment and parabolic open-lattice dishes.

See also :-

Wired Blog Network - New WiFi Record: 237 Miles - New Wi-Fi distance record: 382 kilometers

If data can be transmitted over these distances so cheaply, schools could link to a place with internet access directly or via a chain of schools. In this way, only one 60 USD link per school is needed (less than the cost of one OLPC laptop).

But the cost per month in the future can be high.

--Ricardo 14:48, 20 August 2007 (EDT)

Telesoftware file transfer using Teletext Pages

In most countries, analog and digital TV services have additional Teletext information, a system allowing TVs with a Teletext decoder to display a few thousand pages of text/block-graphics information such as news, weather, entertainment, share-prices, etc.

In analog Terrestrial TV systems, the TV signal includes a few hidden lines of digital Teletext information, in the Vertical Blanking interval.

For OLPC schools, we could use a Telesoftware system to send files as blocks of ASCII text on Teletext pages.

Telesoftware is a fore-runner to MHP - Multimedia Home Platform. It’s not as sophisticated and it’s non-interactive, but it may have the advantages of being simpler and more understandable to users, system builders and programmers and using older, cheaper equipment.

Users of a Teletext system can see the pages on a TV with a built-in Teletext decoder or on a TV with an external Teletext Decoder box. The remote control switches between TV and Text and lets the user select which page to view. The whole set of pages are broadcast repeatedly and stored in the decoder until the user selects one.

In the UK, in the 1980s, before the World Wide Web, some Teletext pages were used to broadcast ‘Telesoftware’, such as games and educational programs for the BBC microcomputer. Program files were encoded into ASCII text on Teletext pages. The computer used an external Teletext decoder box to receive the pages and had software to convert the ASCII pages back to binary files.

We could use a similar Telesoftware system to send files to OLPC schools in those countries (on those TV stations) that have a Teletext service. Terrestrial TV doesn't require a subscription and would have the advantage of cheap receiving equipment (an aerial/antenna and Teletext card/box for the server computer), but the range is limited. Satellite TV equipment is more expensive (a dish and satellite-receiver plus Teletext decoder), but it would cover a wider area, such as remote regions of Africa and South America. Each school would also need a satellite TV subscription. We only want the data, but if anyone wants to see the TV picture and Teletext pages, a TV set or a TV card for the school server could be used.

If Teletext is available, then files containing news/software/web-page/etc, would be converted to 7-bit ASCII characters, perhaps in the UUENCODE or BINHEX format, and uploaded via the internet to the TV station’s Teletext-server computer. They would then be broadcast repeatedly on a fixed page number until a new version is uploaded. The page can have several ‘frames’, to transmit multiple blocks of a file e.g. Page 501, frame 1 of 10.

To receive the files, some software is needed to retrieve each page from the Teletext decoder, UUDECODE the ASCII data and save each file to hard disk.

Commercial TV stations with Teletext allow advertisers, such as package-tour companies, to use some of the Teletext pages. The OLPC project or the governments supplying the laptops could pay a subscription to use one or more pages, like another advertiser. Although this costs money, it would benefit thousands of schools.

The OLPC project could change their page(s) throughout the day via internet uploads, to send many different files. They would change pages much more often than normal advertisers. One of the files would be a transmission schedule for the other files.

The effective data row is quite low, so it would probably be best to use it for short-lived information, such as OLPC project news, school news, group-emails, etc and for schools to slowly update their library of eBooks, software, etc over many weeks.

Non-OLPC schools could receive the files as well, on ordinary computers. Any files which are private to OLPC could be encrypted and password-protected.

--Ricardo 03:48, 20 August 2007 (EDT)

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