Fair Rate Allocation in IEEE 802.11e Wireless Networks
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Solution Overview
Problem
Existing wireless networks face challenges in achieving per-station and per-flow fairness due to location-dependent transmission rates and transmission errors, which lead to inefficient resource allocation and reduced system throughput, especially in IEEE 802.11 wireless LANs where stations have different transmission rates and experience varying error probabilities.
Innovation Solution
A single timing parameter, CWmin[UP], is used to regulate the number of attempts for gaining exclusive transmission access to the medium, with values updated based on outcomes, ensuring that the product of expected rates and delays approaches a constant over time, thereby maintaining fair share opportunities across stations with varying priorities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If stations use different transmission rates based on location, then transmission efficiency is improved, but fairness in resource allocation deteriorates
Solution Approach 1:
The patent applies local quality by allowing each station to use transmission rates appropriate to its location and channel conditions, while simultaneously applying a location-dependent weighting factor to the contention window parameter. This enables each station to have optimized local transmission characteristics while maintaining overall network fairness through the weighted random backoff mechanism.
Solution Approach 2:
The patent changes the parameter CWmin from a fixed value to a location-dependent variable CWmin[i]. This parameter change allows the system to adapt the contention window size based on each station's position and transmission rate, thereby resolving the contradiction between transmission efficiency and fairness by making the backoff probability inversely proportional to transmission rate.
2Productivity
If stations with higher transmission rates are given equal access opportunities, then system throughput is improved, but air time fairness deteriorates
Solution Approach 1:
The patent applies anti-weight by introducing a counterbalancing mechanism where stations with higher transmission rates are assigned larger contention window values. This counterweights the advantage of higher transmission rates, ensuring that faster stations back off more often and thus achieve air time fairness while still allowing the network to benefit from their higher throughput capability when they do transmit.
3Device complexity
If a single contention window parameter is used for all stations, then device complexity is reduced, but fairness in multi-rate environments deteriorates
Solution Approach 1:
The patent applies dynamics by making the contention window parameter dynamic and location-dependent rather than static and uniform. Each station i has its own CWmin[i] value that is determined based on its transmission rate and position in the network, allowing the system to adapt to varying conditions while maintaining fairness without requiring complex centralized control.
Data Source
AI summary
Wireless stations (108-1-108-N) contending for exclusive access for a predetermined period of time (S232) to transmit on a communication medium (112) are regulated by a common external controller (104) using a single timing parameter (S204). Attempts at transmission access are preceded by respective delays that are expired simultaneously and at a common rate by the stations at times when the stations sense the medium to be idle (S224). The delays are pseudo-randomly selected to avoid collisions among stations in their respective access attempts (S208). Default, initial values of the respective delays (S204) applied to the stations, when multiplied by the respective expected number of transmission attempts by the stations over the long term over periods of time when no transmission attempt is unsuccessful, yield respective products equal to a constant value common to all stations (S312). The default values therefore serve as a knob by which the controller regulates air time opportunity.