Adaptive APSD: A low power scheduling protocol for IEEE 802.11 Wireless LANs

IEEE 802.11e recommends two mechanisms for support of low power operation in handheld and battery operated devices, called scheduled automatic power save delivery (S-APSD) and unscheduled APSD (U-APSD). U-APSD has an advantage under variable bit rate traffic, while S-APSD is more efficient for moderate to heavily loaded networks with predictable traffic. This paper introduces a new scheduling algorithm that combines efficient aggregation and bursting schemes in combination with support for low power devices in a wireless LAN. It consists of two key components; the first is a dynamic scheduling scheme based on embedding the schedule information in downlink frames and the second is a signaling mechanism used to determine whether legacy APSD mechanisms or dynamic scheduling is to be used. The result is a very flexible scheme – adaptive APSD – that allows the scheduler embedded in the access point (AP) to adaptively switch to the scheduling strategy best suited to the prevailing traffic conditions.