Access Point Backoff Window Control for Wireless Collision Reduction
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Solution Overview
Problem
In wireless computer networks, the hidden node problem leads to increased collision rates during data transmission, resulting in data corruption and loss, as nodes that are not within each other's communication range cannot detect collisions, causing retransmissions to often overlap and collide again.
Innovation Solution
Implementing a method where an access point in the network determines backoff windows for message retransmission by defining collision patterns, setting a backoff window length based on the number of affected nodes and the frequency of collisions, and dividing this window into non-overlapping slots to ensure retransmissions occur at different times, thereby reducing collision probabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If nodes transmit messages immediately without backoff, then transmission speed is improved, but collision rate increases
Solution Approach 1:
The access point performs preliminary actions by defining collision patterns and calculating backoff window lengths before nodes attempt retransmission. The access point proactively sends instructions to nodes about when to retransmit, preventing collisions before they occur rather than reacting after collisions happen.
Solution Approach 2:
The backoff window length is made dynamic rather than fixed. The access point adjusts the backoff window length based on the number of sender nodes and collision frequency, allowing the system to adapt transmission timing to current network conditions, thereby balancing speed and collision avoidance.
2Reliability
If backoff window length is increased to reduce collisions, then collision rate decreases, but transmission delay increases
Solution Approach 1:
The backoff window length is dynamically adjusted based on network conditions. When collision frequency is high or many nodes are sending, the window length increases to reduce collisions. When conditions improve, the window length decreases to minimize delay. This dynamic adjustment resolves the contradiction between collision avoidance and transmission speed.
Solution Approach 2:
The system changes the parameter of backoff window length based on detected collision patterns and network state. By modifying this key parameter dynamically, the system optimizes the balance between reducing collisions and minimizing transmission delay for different network conditions.
3Reliability
If random backoff timing is used, then collision probability is reduced, but transmission efficiency decreases
Solution Approach 1:
The access point acts as an intermediary that coordinates retransmission timing among nodes. Instead of nodes independently choosing random backoff times, the access point receives collision pattern information, calculates appropriate backoff window lengths, and sends instructions to nodes about when to retransmit, thereby coordinating transmissions to avoid collisions while maintaining efficiency.
Solution Approach 2:
The system uses feedback from collision detection to adjust future retransmission timing. The access point monitors for collision patterns, determines when collisions occur, and uses this feedback to instruct nodes on appropriate backoff durations, creating a closed-loop control system that optimizes transmission efficiency while avoiding collisions.
Data Source
AI summary
A computer-implemented method of determining backoff windows in a wireless computer network is disclosed. The method comprises defining, by an access point in the wireless computer network, a plurality of collision patterns related to message transmission via one or more communication channels in the wireless computer network; detecting, by the access point, occurrence of one of the plurality of collision patterns involving a group of sender nodes in the wireless computer network that have each transmitted a message to the access point and received no acknowledgement message from the access point indicating successful transmission; setting to a first length a length of a backoff window for avoiding collision in data transmission based on a size of the group of sender nodes; sending a first message to a first plurality of nodes in the wireless computer network, the first message instructing performance of backoff during the backoff window having the first length.