Simplified HCF Access Point Scheduler for VoIP QoS

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Solution Overview

Problem

Current 802.11e draft standard for Quality of Service (QoS) in wireless networks is inadequate for interactive voice in enterprise environments, particularly due to the complexity of Hybrid Coordination Function (HCF) implementation and error recovery mechanisms, and lacks a simple power-save method that does not require fast Beacon rates or keep stations awake for VoIP stations.

Innovation Solution

A simplified HCF implementation for access points that uses strict priority queues, periodic polling schedules synchronized with timer synchronization functions, and a unified power-save method that coincides with polling times, allowing for efficient channel access and error recovery without complex timer recalculations or frequent station wake-ups.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If HCF is implemented as originally defined in 802.11e draft, then QoS for interactive voice is improved, but AP implementation complexity increases significantly

Engineering Contradiction:

ImproveQoS for interactive voiceVSAvoidAP implementation complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the HCF implementation into distinct components: a simplified poll generation mechanism, separate strict priority queues for different traffic types, and independent error recovery handling. This segmentation allows each component to be implemented and tested independently, reducing overall implementation complexity while maintaining QoS functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts and removes complex timer recalculations and synchronization mechanisms from the HCF implementation. By taking out these complicated elements and replacing them with simpler polling schedules that don't require frequent timer adjustments, the patent maintains the essential QoS functionality while dramatically reducing AP implementation complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If current 802.11e error recovery mechanism is used for HCF polled access, then error recovery capability is provided, but collision frequency increases due to repeated collisions

Engineering Contradiction:

Improveerror recovery capabilityVSAvoidcollision frequency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

Instead of having both HC and station initiate error recovery simultaneously (which causes repeated collisions), the patent inverts the approach by having only the station initiate error recovery when it detects a missing poll response. This inversion eliminates the simultaneous initiation problem and reduces collision frequency while maintaining reliable error recovery.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent implements a feedback mechanism where the station monitors whether it receives an expected poll response within a specified time window. If the poll response is missing, the station generates a feedback signal to initiate error recovery. This feedback-based approach ensures error recovery is triggered only when necessary, reducing unnecessary collisions.

Inventive Principle:

Principle #23Feedback

3Device complexity

If APSD method is used for power-save, then implementation simplicity is improved, but station wakefulness requirement increases

Engineering Contradiction:

Improvepower-save implementation simplicityVSAvoidstation wakefulness duration

Core Design Contradiction:

Device complexityVSDuration of action of stationary object

Solution Approach 1:

The patent merges the power-save mechanism with the existing HCF polling structure. By combining these two functions, the patent allows stations to remain in power-saving mode longer while still receiving timely polls for VoIP traffic. This merging reduces the frequency and duration of station wakefulness compared to traditional APSD, while maintaining implementation simplicity.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS7801092B2Method for a simple 802.11e HCF implementation

Publication Date: 2010.09.21 CISCO TECHNOLOGY INC

AI summary

A Hybrid Coordination Function (HCF) implementation wherein an access point's existing (E)DCF transmit queues are augmented by at least one strict priority HCF transmit queue. The HCF queues are only used to schedule downlink data and CF-Poll transmissions are used for admitted downlink flows and for uplink flows. The 802.1D user priority value is used to select the HCF queue for an admitted flow. The strict priority HCF transmit queues are always serviced first, in priority order before any other (E)DCF transmit queue. The channel is considered busy to (E)DCF transmit queues while the strict priority queues are being serviced. An admissions control mechanism is used to control data flows and prevents the strict priority traffic from starving (E)DCF traffic. A single, simple AP scheduler is used for scheduling both polling times and station wakeup times.