Radiotext: an application of computer and communication systems in distance teaching

Smith, P (1982). Radiotext: an application of computer and communication systems in distance teaching. PhD thesis The Open University.



To enhance the way in which the Open University is able to communicate with its students, learning at a distance, this study has involved the design of a system to allow material in the form of computer-coded text and graphics to be transmitted over an unmodified V.H.F. radio broadcast network. In addition to providing a low-cost rapid method of communication for course management, the system can be used for delivery of material such as audio-visual packages and computer software.

To enable the unmodified broadcast network and conventional radio receivers to be used, it is intended that Radiotext transmissions will take place at the end of the normal broadcast schedule. This implies that the system should be capable of unattended operation within the student's home. It is achieved by the use of a time-switched radio receiver and interface unit, together with an audio cassette recorder for storage of the received data. The received material may then be displayed on a television or printed out on a low-cost printer at a later, more convenient, time.

Each component of the system is described. The major emphasis is placed on the problem areas which sure either unique to this system or not adequately solved elsewhere. These include, choice of a modulation method for the transmission of data and the design of suitable encoder and decoder circuits, provision of a fast reliable method of storage of the received data, and the design of a suitable error correction procedure for use throughout the system.

The system design enables data to be transmitted, stored on audio cassette and finally displayed at a minimum data rate of 2400 baud. The error correction procedure reduces the probability of data error to less than 10-8 per transmitted bit, equivalent to an average of one error in every 10,000 low resolution pages, achieved with a code redundancy of 29%.

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