Optimal Channel Changing Delay for Mobile TV over DVB-H

摘要

This paper provides an analysis on the optimal channel changing delay in DVB-H (Digital Video Broadcasting for Handhelds) channels for Mobile Television. DVB-H uses a time-sliced transmission scheme to reduce the power consumption used for radio reception in DVB-H receivers. Channel changing delay, i.e. changing from one audio-visual service to another, is increased due to the time slicing scheme in DVB-H. One of the significant factors in channel changing delay is the Decoder Refresh Delay. The Decoder Refresh Delay is the time from the start of video decoding to the start of correct output from decoder. This delay is minimized when a time-slice starts with a random access point picture such as an instantaneous decoding refresh (IDR) picture in H.264/AVC standard. In DVB-H, encapsulation into time-slices is performed independently from content encoding. At the time of encoding, the exact time-slice boundaries are typically unknown, and therefore it is impossible to align the location of IDR pictures to time-slice boundaries. The average decoder refresh delay can decrease by frequent IDR pictures in the bit stream. However, using very frequent IDR pictures drops the compression efficiency and the quality of compressed video dramatically. Another factor in channel changing delay is the delay required to compensate the variation in bit rate. In video streaming over DVB-H the improved quality and compression efficiency obtained by using variable bit rate should be exploited. Higher quality and compression performance can be provided by higher delay. Moreover, when changing channels, a delay is required until the start of the desired time-slice and a further delay is incurred to complete the reception of the entire time-slice. These delays depend on the time-slicing parameters that define the power saving percentage obtained as the result of the time-slice scheme. The lower the receiver power consumption, the higher delay is required. Therefore, there is a strong multilateral relationship between the quality of compressed video, the channel changing delay and the power consumption in the receiver. Simulations were conducted and based on the simulation results an optimal operating area is proposed.