Slot Assignment in Restricted Access Windows
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Solution Overview
Problem
Existing wireless communication systems face challenges in efficiently assigning slots to stations in a restricted access window, particularly in IEEE 802.11ah systems, which can lead to overloading of beacons and inefficient data transmission, especially for low-power devices like sensors.
Innovation Solution
A slot assignment scheme using traffic indication map (TIM) and restricted access window (RAW) parameter set information elements to determine a station-to-slot mapping function, allowing stations to contend for channel access based on a pre-defined mapping function that adjusts for fairness and power-saving protocols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional beacon-based slot assignment is used in IEEE 802.11ah systems, then all stations can be served, but beacon overloading occurs and power consumption increases for low-power devices
Solution Approach 1:
The patent segments the beacon frame's traffic indication map into multiple pages, where each page serves a specific group of stations. This segmentation allows the system to manage slot assignments for different station groups separately, preventing beacon overloading while maintaining comprehensive coverage. The first page handles initial slot assignments, while subsequent pages handle additional stations, distributing the information load across multiple structured segments.
Solution Approach 2:
The patent implements preliminary slot assignment within the beacon frame using the traffic indication map, allowing stations to determine their restricted access window slots before the actual data transmission. This preliminary action enables low-power devices to calculate and prepare their access timing in advance, reducing the need for continuous beacon monitoring and subsequent contention resolution, thereby improving overall assignment efficiency.
2Measurement precision
If continuous beacon monitoring is implemented for slot assignment, then accurate slot allocation is achieved, but power consumption increases for low-power devices
Solution Approach 1:
The patent enables low-power devices to perform preliminary calculations of their restricted access window slots using the association identifier and traffic indication map information received in beacons. Devices can compute their slot positions using predefined formulas based on their AID and the TIM structure, allowing them to enter sleep mode between beacons while still accurately determining their access timing, thus reducing power consumption without sacrificing allocation accuracy.
Solution Approach 2:
The patent implements a self-service mechanism where each station independently calculates its own slot assignment based on its association identifier and the traffic indication map structure. Rather than requiring the access point to explicitly assign slots or requiring stations to continuously monitor for assignments, each station autonomously determines its restricted access window timing, reducing the signaling overhead and power consumption for beacon monitoring.
3Use of energy by moving object
If restricted access windows are implemented for power-saving, then low-power device support is improved, but slot assignment complexity increases
Solution Approach 1:
The patent employs a universal slot assignment mechanism that works for both power-saving and non-power-saving scenarios. The same traffic indication map structure and association identifier-based calculation method serve all stations regardless of their power requirements. This multi-functional approach allows the system to support restricted access windows for power-saving devices while maintaining compatibility with traditional access methods, avoiding the need for separate complex assignment mechanisms.
Solution Approach 2:
The patent utilizes parameter changes in the traffic indication map structure, specifically the page-based organization and association identifier mapping, to control slot assignments. By modifying the TIM parameters (page number, bit position within page) based on station AID, the system dynamically assigns restricted access windows without requiring complex dedicated protocols. The parameter-based control simplifies the overall mechanism while enabling power-saving functionality.
Data Source
Figure 1
Figure 1A~1B
Figure 1C
AI summary
Logic may implement a slot assignment scheme that uses information provided in traffic indication map (TIM) information element (IE) and restricted access window (RAW) parameter 5 set (PS) IE to determine a station-to-slot mapping function for communication of slot assignments to stations for RAWs. The TIM IE may comprise a bitmap indicating paged and unpaged stations. The RAW PS IE may comprise a duration and a slot duration. Logic may implement the station-to-slot function by determining the number of slots in a RAW and correlating slot assignments for stations based upon a position for the station in the TIM bitmap. 10 The TIM bitmap may identify each station via a bit on a page in the bitmap based upon an assignment of the station to a position in the TIM bitmap. The station-to-slot mapping function may use an offset for fair access.