OFDM Preamble AGC Using Scheduled LPF Selection
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Solution Overview
Problem
Current wireless communication standards for power grid control, such as WirelessHART and WIA-FA, suffer from high latency due to the use of non-optimized physical communication layers, particularly the long preamble sequences required for automatic gain control (AGC), which limits the achievable latency and reliability in wireless networks.
Innovation Solution
A method and system for automatic gain control in wireless communication networks that employs time-based scheduling of packets, using a single OFDM symbol preamble and selecting a low-pass filter (LPF) from a bank based on the packet transmitter, allowing rapid gain adjustment and reducing latency while maintaining reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If long preamble sequences are used for automatic gain control in IEEE 802.11, then reliable message delivery is ensured, but transmission latency increases significantly
Solution Approach 1:
The system performs automatic gain control adjustments during the preamble phase before the actual data transmission begins. The AGC circuitry uses the known preamble sequence to calibrate gain settings in advance, ensuring that when the real data arrives, the receiver is already properly configured for optimal signal reception, thus maintaining reliability without extending the critical data transmission time
Solution Approach 2:
The transmission is divided into distinct segments: a preamble phase dedicated to AGC calibration and a data phase for actual information transfer. This segmentation allows the system to allocate resources appropriately - using longer sequences when necessary (preamble) without proportionally increasing the latency of the critical data transmission portion, thereby resolving the contradiction between reliability requirements and latency constraints
2Loss of time
If the preamble duration is reduced below AGC settling time, then transmission latency decreases, but automatic gain control performance deteriorates
Solution Approach 1:
The system dynamically adjusts AGC parameters such as filter time constants and gain update rates based on the available preamble duration. By changing these parameters adaptively, the system can achieve adequate AGC performance even with shorter preambles, thus reducing latency while maintaining sufficient control performance for reliable communication
Solution Approach 2:
The AGC system transitions from static, conservative settings designed for long preambles to dynamic, adaptive settings that optimize performance for the actual available time. The system can adjust its response characteristics in real-time based on packet timing requirements, allowing it to achieve fast settling with shorter preambles while maintaining reliability when longer preambles are available
Data Source
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AI summary
There is provided mechanisms for automatic gain control in a wireless communication network for power grid control. The wireless communication network employs time based scheduling of packets. A method is performed by a packet receiver in the wireless communication network. The method comprises receiving a packet from a packet transmitter. The packet comprises a preamble. The preamble is composed of a single OFDM symbol. The preamble is represented by a sequence of samples. The method comprises applying automatic gain control to the sequence of samples after variable gain amplitude control has been applied to the sequence of samples. The automatic gain control involves applying an LPF to the sequence of automatic gain controlled samples. The LPF is selected from a bank of LPFs. Which LPF to apply depends on, according to the time based scheduling, from which packet transmitter the packet is received.