DSSS-OFDM Wireless LAN Range Extension
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Solution Overview
Problem
Current wireless LAN systems face range extension challenges while maintaining compatibility with legacy devices, as reducing bandwidth to enhance range leads to decreased data rates and interoperability issues with older 802.11a/802.11g systems, causing network chaos in dense deployments.
Innovation Solution
Implementing an orthogonal frequency division multiplexing scheme with direct sequence spread spectrum, where symbols are spread across subcarriers using predefined sequences, allowing for improved range extension without compromising compatibility by using a correlator receiver for maximum detection and maintaining orthogonality across subcarriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bandwidth is reduced to extend range, then receiver sensitivity is improved by 16DB, but data rate decreases by a factor of 24
Solution Approach 1:
The patent segments the data transmission by dividing each data symbol into multiple chips using DSSS spreading codes. Each chip carries a portion of the symbol information, allowing the system to maintain data rate while operating at lower bandwidth through processing gain from the spreading operation.
Solution Approach 2:
The patent changes the signal parameters by applying direct sequence spread spectrum modulation, transforming narrowband symbols into wideband chip sequences. This parameter transformation enables the system to achieve processing gain (10*log10(L)) that compensates for the reduced bandwidth, maintaining both range extension and data rate.
2Length of moving object
If symbol rate is divided by 24 to extend range, then range improves by at least 3 times, but data rate decreases by a factor of 24
Solution Approach 1:
The patent employs periodic spreading sequences (pseudorandom codes) that repeat at regular intervals. This periodic structure provides processing gain through correlation detection, enabling the receiver to detect signals at lower power levels (extending range) while maintaining data rate through the periodic reconstruction of the original symbol rate.
Solution Approach 2:
The patent creates multiple copies of the data symbol across different chips using spreading codes. Each chip is a copy of the original symbol information, but spread across a wider bandwidth. The receiver reconstructs the original symbol by correlating and summing these copies, achieving both range extension and data rate maintenance.
3Measurement precision
If narrow bandwidth signal is used for range extension, then receiver sensitivity improves, but interoperability with legacy systems deteriorates due to undetected BSS transmissions
Solution Approach 1:
The patent implements a universal signaling approach where the spread spectrum signal maintains compatibility with legacy 802.11a/g systems. The preamble and signaling structures are designed to be recognizable by both new and legacy devices, allowing the narrowband DSSS-OFDM system to coexist with wideband OFDM systems while maintaining improved range and sensitivity.
Solution Approach 2:
The patent uses a specialized preamble and training sequence as an intermediary that bridges legacy and new systems. These training symbols enable legacy devices to detect the presence of the new system's BSS and set their CCA bits appropriately, preventing network chaos while allowing the new system to operate with its improved range capabilities.
Data Source
AI summary
A system for implementing an orthogonal frequency division multiplexing scheme and providing an improved range extension. The system includes a transmitter for transmitting data to a receiver. The transmitter includes a symbol mapper for generating a symbol for each of a plurality of subcarriers and a spreading module for spreading out the symbol on each of the plurality of subcarriers by using a direct sequence spread spectrum. The symbol on each of the plurality of subcarriers is spread by multiplying the symbol by predefined length sequences. The receiver includes a de-spreader module for de-spreading the symbols on each of the plurality of subcarriers. The de-spreader module includes a simply correlator receiver for obtaining maximum detection. The correlator produces an output sequence of a same length as an input sequence and the de-spreader module uses a point of maximum correlation on the output sequence to obtain a recovered symbol.