Group Power Save for IEEE 802.11ah Sensor Networks
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Solution Overview
Problem
Wireless sensor and metering networks face challenges in power saving, particularly with large numbers of stations competing for medium access, leading to signal collisions and inefficiency, as existing sleep modes do not adequately address the stringent power-saving needs of these networks.
Innovation Solution
The solution involves grouping stations by sequential AID numbers, with each group having separate wake times and using modified Traffic Identification Maps (TIM) to manage sleep intervals, allowing for efficient power management and reduced collisions by optimizing beacon transmission and reception times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If stations use traditional sleep modes with synchronized wake times, then power saving is achieved, but signal collisions occur when many stations wake simultaneously to contend for medium access
Solution Approach 1:
The patent divides the network stations into multiple groups (Group 0, Group 1, etc.) based on their Association ID (AID) numbers. Each group is assigned a different wake time offset relative to the beacon interval. For example, even AIDs wake at one offset while odd AIDs wake at another offset. This segmentation prevents simultaneous wake-up contention and eliminates signal collisions while maintaining power saving benefits.
2Speed
If stations wake up frequently to check for data, then network responsiveness is improved, but power consumption increases
Solution Approach 1:
The patent implements periodic wake-up behavior where stations wake up at regular intervals determined by their group assignment and beacon interval settings. Stations can be configured with different wake frequencies - some wake every beacon interval while others wake less frequently. This periodic action maintains network responsiveness for time-sensitive applications while allowing power-saving mode for less critical traffic.
3Quantity of substance
If the network supports a large number of stations, then network capacity is improved, but medium access contention and collisions increase
Solution Approach 1:
The patent segments the large population of stations into multiple groups using modulo operations on their AID numbers. For instance, with 2 groups, stations with AID % 2 == 0 form Group 0 and stations with AID % 2 == 1 form Group 1. Each group has dedicated wake time slots, effectively dividing the contention window and reducing the number of simultaneous contending stations from N to N/k where k is the number of groups.
Solution Approach 2:
The patent introduces a temporal dimension to station access by assigning different wake time offsets to different groups. Instead of all stations competing in the same time window, the system adds a time-based dimension to medium access control. This transforms a one-dimensional contention problem into a multi-dimensional problem where stations are separated both by group membership and wake time offset.
Data Source
AI summary
Methods and systems are disclosed for reduced power consumption in communication networks, including sensor networks implemented according to IEEE 802.11ah, by organizing stations into groups having long sleep periods. By organizing the stations of the network into groups, the access point can match each group's traffic identification map with its target beacon transmit time. One embodiment organizes the stations sequentially by AID numbers. Other embodiments organize the stations by similar power save requirements and/or nearby geographical location. Forms of an Extended Traffic Identification Map are matched with an awaken Target Beacon Transmit Time of the group.