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Scheduled EDCA for Large Low Power BSS

This paper discusses the implementation of Scheduled EDCA to optimize medium access in large low-power BSS networks, reducing collisions and saving power.

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Scheduled EDCA for Large Low Power BSS

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  1. Date: May, 2012 Scheduled Medium Access For Large Low Power BSS Date: 2012-05-012 Authors: Liwen Chu Etc.

  2. Recap of Sensor Application in a BSS Most traffic are uplink traffic: sensor data report. Downlink data are used for sensor management etc. Traffic are periodic or event driven. Periodic traffic is the major part of the uplink traffic. A sensor may take long time to finish one data transmission by using EDCA. Collision with other transmission, Longer CW, Delay transmission in order to avoid collision, ACVI/ACVO transmission. A smart grid BSS may have about ~6000 STAs.

  3. Some Proposed Solutions in TGah and Baseline STAs in a BSS are separated in to different groups. Only some groups are allowed to send frames in a BI. Probability delay + backoff are used to further decrease the collision. Before transmit its frames, a STA needs to keep sensing the medium and backoff. PSMP with large STAs enhancement is used to save power. PSMP is a complex mechanism. A STA does not know when a PSMP sequence starts. HCCA can be used to save power. HCCA is a complex mechanism.

  4. Some Proposed Solutions in TGah and Baseline STAs in a BSS are separated in to different groups. Only some groups are allowed to send frames in a BI. Probability delay + backoff are used to further decrease the collision. Before transmit its frames, a STA needs to keep sensing the medium and backoff. PSMP with large STAs enhancement is used to save power. PSMP is a complex mechanism. A STA does not know when a PSMP sequence starts. HCCA can be used to save power. HCCA is a complex mechanism.

  5. Solution: Scheduled EDCA A low power STA reserve medium access resource with its associated AP through TS setup procedure. The AP reserve service period (SP) for the STA. SP include start time, SP periodicity, SP Duration. SP periodicity is 2n*BI or 2n*DTIMBI(beacon interval between two adjacent DTIM Beacon). Each SP does not overlap with other SPs. A STA wakes up at the start of its reserved SP to transmit and/or receive frames. A STA can go to doze during other time. Such kind of STAs may need to wake up to receive the beacon at the beginning of BI that include its SP to synchronize with the AP. SP Duration SP Start Time TBTT TBTT TBTT TBTT SP Periodicity

  6. Solution: Scheduled EDCA (Cont’d) During a STA’s SP duration, it has high priority to access. ACVO CW or PIFS can be used to contend the medium during its reserved SP duration. An AP can select to group SPs in BIs to a Scheduled EDCA Period. Other part of BIs are normal EDCA Period. An AP can notify scheduled EDCA period to its associated STAs. During such period, the STAs that does not reserve SP can not access the medium, and the STAs that are at the time other than its reserved SP can not access the medium or During such period, the STAs that does not reserve SP can not access the medium, and the STAs that are at the time other than its reserved SP uses ACBE CW to contend the medium. During time other than scheduled EDCA period, downlink traffic will be transmitted. During time other than scheduled EDCA period, burst sensing data that can not be transmitted in the reserved SP will be transmitted. TBTT TBTT Normal EDCA Period Scheduled EDCA Period

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