NLOS TDD Wireless Backhaul Frame Structure
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Solution Overview
Problem
Current wireless backhaul systems for small cell deployments face challenges in Non-Line-Of-Sight (NLOS) environments, particularly in outdoor settings where wired backhaul is not available, due to high interference and the limitations of conventional single carrier waveforms designed for point-to-point Line-Of-Sight (LOS) channels, and existing solutions like in-band LTE relays suffer from high latency and high block error rates.
Innovation Solution
A NLOS Time Division Duplex (TDD) wireless backhaul design is implemented, utilizing a 0.5 ms slot-based Transmission Time Interval (TTI) and 5 ms UL and DL frames for compatibility with TD-LTE, along with a special slot structure including Sync Signal, Physical Broadcast Channel, Pilot Signals, and Guard Period, and employing Forward Error Correction methods like turbo codes and Reed Solomon codes to minimize latency and maximize spectrum reuse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional single carrier waveforms with time domain equalization are used in wireless backhaul systems, then the system can operate in point-to-point line-of-sight channels, but the system becomes less practical in point-to-multipoint non-line-of-sight environments with high interference
Solution Approach 1:
The patent changes the fundamental waveform parameter from single carrier with time domain equalization to orthogonal frequency division multiple access (OFDMA) structure. This parameter change transforms the system's adaptability to NLOS environments while maintaining reliability through the robustness of orthogonal frequency division multiplexing in multipath channels.
Solution Approach 2:
The patent implements dynamic time division duplex (TDD) frame structures that can adaptively allocate uplink and downlink time slots based on traffic conditions and channel quality. This dynamic adjustment allows the system to optimize performance in varying NLOS conditions while managing interference between access and backhaul links.
2Adaptability or versatility
If in-band LTE relays are deployed to provide wireless backhaul connectivity, then wireless backhaul can be established in outdoor small cell deployments, but the system experiences high latency and high block error rates
Solution Approach 1:
The patent segments the transmission time interval into smaller slot units within the TDD frame structure, enabling more granular scheduling and faster retransmission of erroneous data packets. This segmentation reduces the effective latency by allowing quicker error recovery without waiting for complete subframe cycles.
Solution Approach 2:
The patent implements periodic reference signals and pilot tones embedded within the OFDMA structure, enabling continuous channel estimation and tracking. This periodic action maintains reliable connectivity in NLOS conditions while minimizing latency through efficient channel state information feedback.
3Productivity
If spectrum resources are shared between access links and backhaul links in TD-LTE systems, then frequency resources are utilized efficiently, but significant intercell interference occurs between access links and backhaul links
Solution Approach 1:
The patent employs periodic time division multiplexing where access links and backhaul links are allocated specific time slots within TDD frames. This periodic separation in time domain allows spectrum sharing while minimizing interference, as transmit and receive operations are coordinated across different time periods.
Solution Approach 2:
The patent implements dynamic TDD configuration that can adjust the proportion of uplink and downlink time slots based on traffic demands and interference conditions. This dynamic adjustment optimizes spectral efficiency while managing interference between access and backhaul operations in real-time.
Data Source
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AI summary
In described examples, a method of operating a wireless communication system includes communicating by a first data frame (506) having a first transmit time interval with a first wireless transceiver (504) and communicating by a second data frame (502) having a second transmit time interval different from the first transmit time interval with a second wireless transceiver (500). Data is transferred between the first data frame (506) and the second data frame (502).