Cyclic Shift De-correlation for Wireless Sub-band Emission Control

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Solution Overview

Problem

In wireless communication systems, the non-linear properties of amplifiers introduce intermodulation distortion and significant out-of-band emissions, particularly in duplicate transmission modes like IEEE 802.11n, leading to reduced output power and signal quality due to regulatory band edge restrictions.

Innovation Solution

Applying diverse cyclic delay shifting across subcarriers in multiple sub-bands to de-correlate the signal, thereby reducing intermodulation effects and out-of-band emissions, while maintaining beamforming integrity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the same data is transmitted in multiple contiguous sub-bands, then transmission reliability is improved, but out-of-band emissions increase due to amplifier non-linearity

Engineering Contradiction:

Improvetransmission reliabilityVSAvoidout-of-band emissions

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The transmitted signal is segmented into multiple sub-bands, each carrying the same data. Different cyclic shifts are applied to each sub-band to de-correlate them, reducing intermodulation distortion while maintaining the diversity benefit of multiple sub-bands

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different cyclic shifts are applied locally to each sub-band based on its specific characteristics and position. This allows each sub-band to be optimized independently, with the cyclic shift amount adapted to local conditions while maintaining overall signal integrity

Inventive Principle:

Principle #3Local quality

2Object-generated harmful factors

If output power is reduced to meet regulatory band edge restrictions, then out-of-band emissions are controlled, but received signal quality deteriorates

Engineering Contradiction:

Improveout-of-band emissionsVSAvoidreceived signal quality

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

Cyclic shifts are applied in advance to the signal before amplification. This preliminary de-correlation prevents intermodulation distortion from occurring during amplification, allowing the amplifier to operate at higher power levels without generating excessive out-of-band emissions

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The cyclic shift parameter is modified across different sub-bands to change the correlation properties of the signal. By adjusting this parameter, the signal can be de-correlated to reduce intermodulation distortion while maintaining acceptable signal quality at the receiver

Inventive Principle:

Principle #35Parameter changes

3Object-generated harmful factors

If cyclic shifts are applied to de-correlate sub-bands, then out-of-band emissions are reduced, but signal processing complexity increases

Engineering Contradiction:

Improveout-of-band emissionsVSAvoidsignal processing complexity

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The signal processing is segmented into independent operations for each sub-band. Cyclic shifts are applied separately to each sub-band, allowing for modular implementation that reduces overall complexity compared to processing the entire signal as a single unit

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of applying complex processing to the entire signal, only partial cyclic shift operations are applied to specific sub-bands where needed. This selective approach reduces the total amount of processing required while still achieving the goal of reducing out-of-band emissions

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS8582517B2De-correlation of sub-bands using cyclic shifts

Publication Date: 2013.11.12 CISCO TECHNOLOGY INC

AI summary

Techniques are provided to de-correlate sub-bands of a packet to be transmitted. At a communication device, a signal (packet or frame) is generated for transmission. The packet or frame comprises a plurality of subcarriers in each of a plurality of sub-bands. Different cyclic delays are applied to the plurality of sub-bands of the signal. The signal is amplified after applying the different cyclic delays for transmission from the communication device.