In this section, the design of power adaptive DVB-T system that includes DVB-T system block andthe adaptive power control block will be discussed. The main DVB-T system that was used during thesimulation process using Simulink software is shown in Figure 1. As shown in Figure 1, DVB-T transmission system takes the input from file in MPEG2-TS or MPEG2Transport Stream format. Input data is segmented into frames with the length of 188 bytes per frame.
Thechannel encoders consist of outer and inner encoders. For outer encoders, Reed Solomon (RS)(255,188) codewas used. This is the reason behind 188 bytes as an input frame length. For the inner encoder, puncturedconvolutional code with rate 3/4 was used 8. Outer and Inner interleaver were also used to reduce the impactof burst errors by improving the performance of forward error correction codes. The modulation scheme usedin the experiment is 64-QAM with 2K-mode Orthogonal Frequency Division Multiplexing (OFDM)transmitter.
Outer and Inner decoders were used in the receiver, where Viterbi decoder was used as the innerdecoder. The channel used during the simulation is adaptive white Gaussian noise (AWGN) channel. Thesystem block produced 188 bytes of output frame for every 188 bytes of input frame.
As shown in Figure 2, the proposed DVB-T adaptive power control method is presented. The methodconsists of picture quality assessment algorithm, feedback channel, and power adaptation scheme. Many different picture quality assessment methods can be used, such as full-reference (a received image is comparedwith the original or source picture), reduced-reference (features from the received picture are extracted andcompared with corresponding stored features of the original or source picture), and no-reference (does notrequire prior knowledge about the original or source image but performs assessment of the receivedimage/blind assessment) 9. However, for real-time picture quality monitoring, the no-reference (NR) is themost suitable method, since no extra information is needed to be communicated to the receiver, as well as noprior knowledge about the original picture is required. For real implementation, the feedback or return channelfrom the receiver to the transmitter for DVB-T system can be based-on general packet radio service (GPRS)or other suitable methods, since the picture quality data is only a few bits in length. The measurement intervalcan be predefined, for example every 50 frames or every 100 frames. The quality will be the average qualityof 50 frames or 100 frames, which will be depended upon the selected predefined interval.
Power adaptationscheme will be based on this quality information. When the quality is below a certain predefined qualitythreshold, then the power will be increased. The power will be decreased when the quality is greater or equalto the threshold. By adapting the power of the transmitter, the picture quality will be maintained in good qualitywhile at the same time maintaining the power efficiency.