Orthogonal Space-Time Codes for SFN Signal Quality
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Solution Overview
Problem
In Single Frequency Networks (SFN) using Orthogonal Frequency Division Multiplexing (OFDM), destructive signal interactions due to relative phase differences between base stations can lead to poor signal quality, necessitating higher transmit powers to meet coverage objectives, which may not be feasible, especially for mobile users with time-varying channels.
Innovation Solution
Assigning distinct column vectors of a generalized orthogonal space-time code matrix to each base station's coverage area ensures that signals from different base stations are transmitted using mutually orthogonal vectors, preventing destructive interference and improving signal quality without increasing transmit power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If OFDM is used in SFN to allow signals from multiple base stations to be added at the receiver, then receiver devices at cell edges can process aggregate signals from multiple base stations, but destructive interaction occurs between signals from different base stations due to relative phase differences
Solution Approach 1:
The patent applies parameter changes by modifying the phase relationships between signals from different base stations through orthogonal space-time codes. Instead of transmitting identical signals with arbitrary phase relationships, the system transforms the signal parameters to ensure orthogonal phase relationships, converting destructive interference into constructive signal aggregation that improves SINR at cell edges
2Reliability
If higher transmit powers are used to overcome poor signal quality caused by destructive interference, then coverage objectives can be met, but this increases energy consumption and may not be feasible for mobile users
Solution Approach 1:
The patent converts the harmful effect of signal interactions into a beneficial outcome by using orthogonal space-time codes. Instead of treating the combined signals from multiple base stations as interference to be overcome with higher power, the system transforms the scenario so that the same signal aggregation effect that previously caused destructive interference now produces constructive addition, improving coverage without increasing transmit power
3Productivity
If identical signals are transmitted by all base stations on the same sub-carriers in an SFN, then signals can be aggregated at the receiver, but phase differences cause destructive interaction that reduces signal quality
Solution Approach 1:
The patent applies local quality by assigning different orthogonal space-time code patterns to different base stations or different geographic regions. This allows the signal transmission to be locally optimized so that while all base stations transmit on the same sub-carriers, the local phase relationships are controlled to ensure constructive interference in each coverage area, improving the SINR distribution across the entire network
Data Source
AI summary
In one embodiment, a method of transmitting includes assigning column vectors of a generalized orthogonal space time code matrix to coverage areas of a plurality of base stations such that each coverage area is assigned one column vector. The same data is transmitted from each of the plurality of base stations in the coverage areas such that the data transmitted in each coverage area is transmitted using the column vector assigned to the coverage area.