PMT Cache for Digital TV Channel Switching
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Solution Overview
Problem
Current digital television systems experience significant channel change delays due to the need for frequent updates of conditional access information, particularly the program map table (PMT), which can take up to 400 milliseconds to receive, leading to an unsatisfactory user experience.
Innovation Solution
A digital television receiver is designed with a PMT cache that stores the PMT information for the most recently accessed channel, allowing for immediate generation of the conditional access program map table (CA_PMT) without waiting for new in-band PMT information, thereby reducing channel change times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the receiver waits for new in-band PMT information to be broadcast before changing channels, then the conditional access information remains accurate and reliable, but the channel change time increases significantly (up to 400 milliseconds)
Solution Approach 1:
The receiver performs preliminary actions by extracting and storing PMT information in advance during the current channel's active period. This cached PMT data is prepared beforehand so that when a channel change is requested, the receiver can immediately use the pre-stored PMT information from the cache rather than waiting for the new channel's PMT to be broadcast, thus resolving the contradiction between reliability and channel change time.
2Loss of time
If the receiver stores complete PMT information in cache memory, then channel change time is reduced, but the memory requirements and device complexity increase
Solution Approach 1:
The invention extracts only the essential and frequently used PMT information that is needed for conditional access and channel switching operations. Rather than caching complete PMT data structures, the receiver extracts and stores only the critical descriptors and parameters required for immediate channel change functionality. This selective extraction reduces the memory burden while still achieving the goal of fast channel switching.
3Productivity
If the receiver caches PMT information from the most recently accessed channel, then immediate channel switching is enabled, but the information may become outdated for channels that have updated their PMT since the cache was populated
Solution Approach 1:
The PMT cache implementation is made dynamic by continuously monitoring and detecting when PMT information becomes available for the currently accessed channel. When an update is detected, the cache is automatically refreshed with the new PMT data. This dynamic approach ensures that the cached information remains current and reliable while still enabling fast channel switching, as the cache is updated in real-time without requiring full channel re-tuning.
Data Source
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AI summary
There is provided a method and apparatus for tuning a digital television channel. More specifically, in one embodiment, there is provided a method comprising receiving a request to access a first digital television channel, downloading a first program map table ("PMT") (109) associated with a frequency of the first digital television channel, storing the first PMT, receiving a request to access a second digital television channel, determining if the second digital television channel is associated with the frequency of the first digital television channel, and creating a conditional access PMT (108) for the second digital television channel based on the stored PMT if the second digital television channel is associated with the frequency.