WLAN Hidden Node Resolution via Grouped Access Windows and CTS Signaling
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Solution Overview
Problem
Wireless networks with a large number of stations face collisions from hidden nodes during synchronized contention slots in restricted access windows, leading to inefficiencies and delays.
Innovation Solution
A method where a wireless access point manages restricted access windows, transmitting beacon frames with traffic indication maps to allow wireless terminal devices to contend for specific time slots, and uses Clear to Send packets to indicate availability, thereby avoiding collisions with hidden nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If synchronized contention slots are used in restricted access windows, then channel access efficiency is improved, but collisions from hidden nodes occur
Solution Approach 1:
The access point sends a CTS (Clear to Send) packet before the actual data transmission in each time slot to preliminarily indicate that the channel is available and no hidden node transmission is detected. This preliminary action allows terminal devices to prepare for transmission without risk of collision, resolving the contradiction between efficient synchronized access and collision avoidance from hidden nodes.
2Ease of operation
If restricted access windows are allocated to different groups, then channel access organization is improved, but hidden node problem persists
Solution Approach 1:
The access point acts as an intermediary by monitoring each time slot and sending CTS packets to indicate channel availability. This intermediary function resolves the hidden node problem while maintaining the organized group-based restricted access window structure, allowing groups to access channels efficiently without collisions from nodes outside their group.
Data Source
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AI summary
To overcome the problem of hidden nodes in an IEEE 802.11ah system with a large number of (MTC) devices, the devices are grouped in sleep groups which are assigned an access window for exclusive use. This is defined in TIM with group information in the access beacon. The actual access restriction to RAW restricted access window for a group is transmitted in the RAW. Embodiments of the invention provide signaling mechanisms for wireless networks composed of a large number of stations. An example method embodiment comprises: receiving by a wireless terminal device, a first message from an access point, the first message comprising information indicating a plurality of restricted access windows, each allocated for a different group of terminal devices associated to a wireless network managed by the access point; receiving by the terminal device, a second message from the access point, within a restricted access window of the plurality of restricted access windows, the restricted access window allocated to a group of terminal devices of which the terminal device is a member, the second message comprising information indicating that a communications channel is available; and determining by the terminal device, based on the second message, that the communications channel is not occupied by hidden ones of the terminal devices associated to the network.