Sectorized Wireless Scheduling for Hidden Node Collision Avoidance
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Solution Overview
Problem
In larger wireless local area networks (WLANs), the carrier sense multiple access with collision avoidance (CSMA/CA) technique is less effective due to the hidden node problem, where mobile stations outside each other's transmission range simultaneously transmit to a base station, causing collisions, especially with the emergence of next-generation Wi-Fi standards like IEEE 802.11ah featuring large cells and low-power sensor devices.
Innovation Solution
Scheduling transmissions in different sectors during distinct time periods, using beamformed beacon signals to communicate sector-specific scheduling, ensuring that mobile stations within the same sector are more likely to detect each other's transmissions and avoid collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CSMA/CA technique is used for uplink channel access in large WLANs, then collision avoidance is achieved through carrier sensing, but hidden node collisions occur when STAs are outside each other's transmission range
Solution Approach 1:
The coverage area is divided into multiple sectors, and STAs are assigned to specific sectors. Each sector is scheduled to transmit during different time periods, effectively segmenting the hidden node problem into isolated sector-specific issues rather than network-wide collisions
Solution Approach 2:
Different sectors are assigned periodic time slots for transmission. STAs in each sector transmit only during their designated time period, creating a periodic transmission pattern that eliminates simultaneous transmissions from hidden nodes in different sectors
2Use of energy by moving object
If STAs use low transmit power in large WLANs, then energy consumption is reduced, but transmission range is limited causing increased hidden node collisions
Solution Approach 1:
By segmenting the network into sectors with dedicated time slots, STAs can maintain low transmit power while their transmissions are guaranteed not to collide with STAs in other sectors, as those STAs transmit at different times
Solution Approach 2:
The base station acts as an intermediary that coordinates transmission schedules among sectors. It assigns specific time periods to different sectors, mediating the conflict between low power consumption and collision avoidance by organizing transmissions in a structured temporal pattern
3Reliability
If sectorized scheduling is implemented, then hidden node collisions are reduced, but system complexity increases due to scheduling coordination
Solution Approach 1:
The system changes the temporal parameter by assigning different time periods to different sectors. This parameter change simplifies the coordination problem by using time division rather than spatial or frequency division, making the scheduling mechanism more straightforward to implement and manage
Data Source
AI summary
The hidden node problem can be avoided by scheduling stations in different sectors to perform transmissions during different time periods. Sectorized scheduling can be communicated to stations through transmission of beamformed beacon signals at the beginning of respective time periods. For instance, a first beamformed beacon signal may be transmitted to stations in a first sector at the beginning of a first time period, while a second beamformed beacon signal may be transmitted to stations in a second sector at the beginning of a second time period.