OFDM Carrier Blocking for Adjacent Channel Interference
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Solution Overview
Problem
The current ATSC 8-VSB modulation system is vulnerable to multipath propagation and Doppler Effect, particularly in metropolitan areas and when delivering content to portable/handheld/vehicular devices, and new broadcast systems like ATSC 3.0 face challenges in co-existing with legacy systems due to adjacent channel interference.
Innovation Solution
Implementing a multi-carrier modulation system like OFDM, which temporarily blocks carriers at the edge of the spectrum during transition to reduce adjacent channel interference without complex filtering, while maintaining compatibility with legacy systems, and later unblocks these carriers when the interference becomes less significant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multi-carrier modulation system (OFDM) is deployed to replace legacy 8-VSB system, then resistance to multipath propagation and Doppler Effect is improved, but adjacent channel interference increases
Solution Approach 1:
The patent segments the available carriers into three distinct groups: first carriers (causing interference to legacy systems), second carriers (used by both systems), and third carriers (protected from interference). This segmentation allows the multi-carrier system to operate while minimizing harm to legacy receivers by restricting which carriers can be actively used during coexistence periods.
Solution Approach 2:
The patent implements dynamic carrier allocation where the set of usable carriers changes over time based on system state. During transition periods when legacy systems are still operational, only second and third carriers are permitted for use. Once legacy systems are decommissioned, the system dynamically transitions to utilizing all carriers including the first group, thereby eliminating the interference constraint.
2Object-generated harmful factors
If filtering is applied to reduce adjacent channel interference, then interference to legacy systems is reduced, but device complexity and cost increase
Solution Approach 1:
Instead of modifying the physical characteristics of the transmitted signal through filtering, the patent changes the operational parameters by selectively enabling or disabling specific carrier groups. This parameter-based control achieves interference reduction through intelligent carrier selection rather than analog filtering, avoiding the complexity and cost associated with sophisticated filter designs.
3Adaptability or versatility
If carriers are blocked to reduce interference during transition, then compatibility with legacy systems is improved, but bandwidth efficiency decreases
Solution Approach 1:
The patent implements preliminary carrier blocking of the first carrier group before legacy systems are fully decommissioned. This preliminary action ensures legacy compatibility is maintained during the transition period. The blocked carriers are held in reserve and activated once the preliminary condition (legacy system operation) no longer applies, thereby recovering the lost bandwidth efficiency at the appropriate time.
Data Source
AI summary
Methods and apparatuses are provided with a solution to adjacent channel interference when a multi-carrier modulation system (e.g., OFDM) replaces a legacy modulation system and co-exists with it for a period of time. The adjacent channel interference can be reduced by blocking (setting to 0) and not using some of the carriers at the edge of the spectrum during the transition period. This effectively reduces the bandwidth of the channel and consequently, the adjacent channel interference caused by the multi-carrier signal. However, at some point in time, the legacy system will be turned off and the adjacent channel interference into the original channels will no longer be important. The present principles propose a mechanism to allow for the unblocking of the removed carriers once the interference problem becomes less strict.