An Integrated Scheduling and Retransmission Proposal for Firm Real-Time Traffic in IEEE 802.11e

This work investigates the problem of scheduling network resources in the context of a cooperative mobile multi-robot system that exchanges messages with firm real-time constraints using a wireless network compliant with the recently created IEEE 802.11e amendment. Given the physical characteristics of wireless communication, message retransmission becomes a crucial issue, especially in a realtime application. Experiments performed in the context of this work show that the regular approach for retransmission proposed in the IEEE 802.11e is not suitable for real-time applications that require a certain level of reliability. To tackle this problem, the current work proposes a new mechanism called Integrated Scheduling and Retransmission Approach (ISRA) that integrates messages scheduling and retransmission in a unified manner at the MAC layer. Our proposal is able to deal with residual transmission errors and thereby increases the reliability level of the real-time messages. Our approach is evaluated through simulations for different scenarios of traffic load and compared with the standard approach of the 802.11e for scheduling and retransmission of real-time messages. Obtained results show that ISRA presents a high adaptability and does not get affected by variations in the network load or topology.