WO1997003522A1

WO1997003522A1 - Videoconferencing

Info

Publication number: WO1997003522A1
Application number: PCT/GB1996/001640
Authority: WO
Inventors: David Connolly
Original assignee: Hong Kong Telecommunications Limited
Priority date: 1995-07-10
Filing date: 1996-07-09
Publication date: 1997-01-30
Also published as: AU6366296A; GB9800578D0; GB2318018A; GB9514004D0

Abstract

A videoconferencing network comprises a plurality of desktop (PC) units (16) each having a small video camera (18) to provide simple video analogue signals. The units each have an MPEG decoder (17). A central controller or exchange (10) for the network includes an MPEG (10A) coder which is shared by all the desktop units and used for compressing signals for transmission to other networks. This means that each desktop unit user may be provided with a relatively low cost MPEG decoder and effectively share the relatively high cost of the MPEG coder with other users in the network.

Description

VIDEOCONFERENCING

The invention relates to videoconferencing.

In a personal videoconferencing service, the user typically has a small video camera placed above or near the screen of a personal computer (PC) , the PC screen being used to receive moving pictures form the distant party.

To minimize the transmission costs of the video pictures, it is desirable to use standard forms of telecom transmission in digital form. The most common of these is currently the H.320 standard, operating over the Integrated Services Digital Network (ISDN) using circuit switching at 64 or 128 Kbps which includes the audio channel. In this arrangement, both the video compression of the camera signal and the decompression of the transmitted signal for display are carried out in the desktop (PC) unit. In order to achieve minimum digital transmission capacity and cost, the H.320 system provides picture quality lower than normally expected in a TV programme.

A second facility which is emerging is the Motion Picture Exports Group (MPEG) coding standard for video pictures. The digital compression is complex but the decompression for display is simple and low cost. This asymmetric coding arrangement is ideal for pre-recorded material stored in digital form, for example in a Video on Demand (VOD) service or on Compact Disc (CD-ROM) for use in a PC. MPEG transmission is at rates of 1.5 to 6 Megabits/second, significantly higher than for H.320 compression, but with quality comparable with a normal TV picture.

The MPEG system is becoming popular for PC use, particularly to replay video from an internal CD-ROM source. The PC with CD ROM and MPEG decoding will therefore become commonplace at the desktop. However the complexity and cost of a realtime coder for MPEG compression prevents its use in a desktop unit for videoconferencing, despite the benefit of improved picture quality.

It is an object of the invention to at least reduce this problem.

According to the invention, there is provided a videoconferencing system including a number of personal computers in a network, each computer having an MPEG decoder, and a video camera for generating video analogue signals, in which a MPEG coder is provided for the network to compress the analogue signals of the personal computers in the network for transmission to other networks.

The invention also provides a personal computer for a videoconferencing network having a MPEG decoder and a video camera for generating video analogue signals for transmission to other personal computers in the network.

A videoconferencing network according to the invention will now be described by way of example with reference to the accompanying schematic drawings in which:

Figure 1 shows the network; and

Figure 2 shows the arrangement of each communicating unit of the network.

Referring to the drawings, a network controller or exchange 10 is connected to a number of communication units 11 to 15 such as desk top (PC) units by unshielded twisted pair cables. The controller 10 is also connected to transmit to and receive transmissions from other like networks. The controller 10 includes an MPEG coder 10A and is controlled to receive signals from each of the units 11 to 15, one at a time and on demand, and to compress these signals for transmission to the other networks. The controller passes on any MPEG coded signals it receives from other networks for selected destinations at any of the units 11 to 15 in their compressed coded format. For communications within the network, that is between the units 11 to 15 however, the MPEG coder is not normally employed. In Figure 2, each unit includes a personal computer 16 and a MPEG decoder 17. The computer 16 is equipped to display visual images on its screen in the normal way based on MPEG coded signals received for the central controller 10. The computer 16 can also provide a display corresponding to analogue signals passed from other units in the same network. Each unit also has a video camera 18 and a convertor 19 that develops analogue signals which are passed to and via the central controller 10 and to other units in the network, as appropriate.

Thus, in the personal videoconferencing service, each PC is equipped with Video On Demand (VOD) service and a relatively low cost MPEG decoder. The PC may also have CD-ROM capability for local access to video material. The video camera at each PC is connected to a simple analogue transmission system which transmits a conventional analogue signal over a short distance and so can use conventional Unshielded Twisted Pair (UTP) cable to a central building for the network. At the central building, the analogue camera signals are converted to a compressed digital signal using the MPEG coder. However, this digital compression facility is shared among all the users of the network, and is occupied only while each call is in progress. In this way, the relatively high cost of the PEG compression can be allocated on a per call basis, rather than being dedicated to each PC in the network. As such. videoconference networks can be provided a reasonable individual cost, because the signifcantly high cost of each analogue MPEG coder can be in effect shared between a significant number of video work stations in each network. At the same time the encoding is carried out on original analogue signals, provided by video cameras, permitting conventional switching means to be used.

Videoconference calls are transmitted over a metropolitan area using the MPEG Coding Scheme for high picture quality, or over greater distances using the H.320 Coding Scheme. Each PC configuration for each user is the same for both coding standards, but for H.320 operation a digital transcoder H.320/MPEG will be required, which can be centrally located for the network.

Claims

1. A videoconferencing network including a number of personal computers in the network, each computer having an MPEG decoder, and a video camera for generating video analogue signals, in which a MPEG coder is provided for the network to compress the analogue signals of the personal computers in the network for transmission to other networks.

2. A personal computer for a videoconferencing network having a MPEG decoder and a video camera for generating video analogue signals for transmission to other personal computers in the network.