Research On Cloud Transmission Technology In Digital Terrestrial Television System

In order to ensure the communication quality of radio and television, a lot of TV white space(TVWS) is reserved between different frequency bands to avoid the interference, resulting in the waste of a large amount of spectrum resources. In the case that the spectrum resources become increasingly scarce, it demands that the next generation digital terrestrial television system make full use of the TVWS. Cloud transmission technique provides a solution to solve the problem, which uses efficient error-correcting code and layer-division-multiplexing technology to overcome the co-channel interference and achieve the parallel transmission for multiple data streams in one radio frequency channel. Thus the TVWS is reduced or eliminated and the spectrum utilization is significantly improved.It is only two more years from the proposition of the cloud transmission technique to now. There are a number of research areas that need to be investigated in conjunction with the implementation and application of Cloud Transmission system. As the orthogonal frequency division multiplexing(OFDM) technique is widely used in radio and television standards, this dissertation will do research on the OFDM based cloud transmission system in the field of digital terrestrial television. And an in-depth analysis of its performance is given. In view of the trait of the cloud transmission, a research on the application of cloud transmission technique in the system parameter transmission for the cognitive radio(CR) communication is carried out. A novel adaptive system based on cloud transmission for CR communication and its carrier frequency synchronization schemes are proposed by the thesis. The main work includes the following aspects:1. A comprehensive theoretical analysis is presented on the characteristics of cloud transmission technology and an in-depth study on the OFDM based cloud transmission system is carried out. A two-layer cloud transmission system based on OFDM is built in VS2010 and matlab. The performance of the superposition in frequency domain and time domain is analyzed and two cancellation algorithms in frequency domain are compared. Then the advantages of the cloud transmission technology relative to the time-division multiplexing(TDM) or frequency division multiplexing(FDM) technique are analyzed. The influence of the system performance from the power allocation of the transmitter and error propagation in the cancellation stage is studied.2. Cloud transmission for the system parameter transmission in the CR network is first studied. A novel adaptive system based on cloud transmission is proposed for dynamic CR communication. For this purpose, the code shift keying(CSK) modulation based on kasami sequence is studied. Its theoretical performance is evaluated and the relevant formula is modified. In the design of the system, the CR system parameter information is precoded by kasami sequences as the secondary and then superimposed onto OFDM data, i.e., the primary link. Then the corresponding operation mechanism is proposed. The symbol-wise parameter adaptation between the transmitter and receiver is realized via the proposed system. The latency is significantly shortened during the initialization or channel transition for the CR communication.3. The carrier frequency synchronization schemes are proposed for the cloud transmission based CR system. By utilizing the special structure of the secondary link that the kasami sequences are repeated a few times in each OFDM symbol, two synchronization schemes are designed for the system. Carrier frequency synchronization of the proposed system can be achieved. As such, additional benefit without extra resource overhead is obtained.