A summary of the integrated broadcast-plus-communication network used to provide interactive features.

Broadcast networks like the DVB-H or DTMB systems are capable of providing services with both high data rate and high mobility. However, while most wireless access technologies work bi-directionally, broadcast networks are uni-directional and can only provide wideband data services in the downlink along with the video services, which is not suitable for the bi-directional IP transparent data transmissions. However, DVB-H and DTMB can work together with other systems as a return signalling channel (uplink) to accommodate the users’ request and acknowledgement. Systems such as cellular mobile radio systems (GSM/GPRS, UMTS), PSTN, ISDN etc. can all serve for this purpose. We may call it Integrated Communication Broadcasting Network (ISBN).

The architecture of the testbed network across the Tsinghua campus is depicted in the next figure; this is similar to the figure 1, with just DTMB as the downlink channel and WLAN as the uplink or feedback channel.

Obviously, the system can tolerate packets loss for the video and voice services, but for certain data services, packets loss is definitely unacceptable. Therefore, TCP should be adopted in the data communication systems, which requires a TCP link for the retransmission of the lost/error packets. Moreover, an uplink channel should be employed to provide the on-demand service. These are the primary design purposes of the signalling channel of the integrated network.

Similar systems are MEMO (Multimedia Environment for Mobiles), a hybrid DAB/GSM communication system for the mobile interactive multimedia services; while SABINA (System for Asymmetric Broad band Internet Access) is a prototype system concept for providing broad band, mobile Internet access via DVB-T and GSM.

Systems like MEMO or SABINA offer an asymmetric high-throughput downlink and interactive communication channels. This kind of combination is ideal for many services where the user wants to receive lots of data but sends only a few messages, the typical application is Internet browsing and MP3 or video download. However, the fixed combination of uplink (GSM) and downlink (DAB or DVB-T, respectively) in systems like MEMO and SABINA hasen’t used the advantage of the downlink capacity of the systems such as in GSM and this should be explored.

First the client sends out the connection request to the server, and then the server will accept or reject the request. After the acceptance of the request, the server should provide a list of the available services, such as file name and file size etc., similar as an ftp server. After the client has received the information of the available service, it will send out the request of service (bandwidth). The server will then use the bandwidth allocation algorithm to decide whether to reject or accept the request. After that, the client will give the “ready” message to the server, indicating that the client side is ready for the data transmission. Then the process of data transmission through the downlink channel is invoked. After the successful data transmission, the server will deliver the disconnect message. The complete process mentioned above is controlled by the timer, the process will automatically reset after waiting a certain period of time.

In order to guarantee the reliability of data transmission, a feedback mechanism of the received-packet status has to be designed. The design will be based on the unique video broadcast radio channels.