OFDM Preamble AGC Using Scheduled LPF Selection for Low Latency
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Solution Overview
Problem
Current wireless communication networks for power grid control, such as those using IEEE 802.11, suffer from high latency due to long preamble sequences required for automatic gain control (AGC), which limits the achievable latency and reliability in substation automation systems.
Innovation Solution
A method employing time-based scheduling of packets with a short preamble composed of a single OFDM symbol, where automatic gain control is applied using a selected low-pass filter (LPF) from a bank of LPFs, allowing rapid gain adjustments based on the packet transmitter, thereby reducing latency and ensuring reliable communications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If long preamble sequences are used for automatic gain control, then reliable message delivery is ensured, but transmission latency increases significantly
Solution Approach 1:
The patent segments the AGC process by using a bank of low-pass filters (LPFs) with different time constants, where each filter handles AGC for packets from specific transmitters. This allows parallel processing of AGC for multiple transmitters simultaneously, eliminating the need for long sequential preambles while ensuring reliable gain control for each transmitter-receiver pair.
Solution Approach 2:
The system performs preliminary action by pre-configuring a bank of LPFs with different time constants before packet transmission. Each LPF is pre-assigned to handle packets from specific transmitters based on time-based scheduling information, allowing immediate AGC processing upon packet reception without waiting for long preamble sequences.
2Reliability
If traditional AGC systems initialize gain setting to nominal value and process multiple packets sequentially, then AGC convergence is achieved, but settling time limits the achievable latency
Solution Approach 1:
The patent implements dynamics by making the AGC system adaptive to different transmitters through time-based scheduling. The packet receiver dynamically selects the appropriate LPF from the bank based on which transmitter is currently transmitting, allowing each transmitter to have its own optimized AGC parameters. This dynamic adaptation eliminates the need for repeated settling time for each packet while maintaining reliable AGC convergence.
Solution Approach 2:
The system changes parameters by using multiple LPFs with different time constants instead of a single fixed AGC parameter. Each LPF in the bank has optimized parameters for specific transmitters, allowing the system to switch parameters based on the active transmitter. This parameter variation enables fast AGC convergence without compromising reliability for different transmission scenarios.
3Speed
If short preambles are used to reduce latency, then transmission speed improves, but automatic gain control reliability deteriorates
Solution Approach 1:
The patent segments the AGC function across multiple parallel LPFs instead of relying on a single long preamble. Each LPF processes AGC for specific transmitters independently, allowing the system to use short preambles while maintaining AGC reliability through the segmented parallel processing architecture.
Solution Approach 2:
The system performs preliminary configuration of the LPF bank with transmitter-specific time constants before packet transmission. This preliminary action allows the receiver to immediately apply the correct AGC parameters upon receiving short preambles, eliminating the need for long preambles while ensuring reliable AGC performance.
Data Source
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 LPSs. Which LPF to apply depends on, according to the time based scheduling, from which packet transmitter the packet is received.