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MAC Header Design for Small Data Packet for 802.11ah . Date: 2012-01-18. Authors:. Slide 1. Abstract. This contribution presents some considerations on MAC overhead reduction and an MAC header suitable for small data packet is proposed for 802.11ah STAs. Slide 2.

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  1. MAC Header Design for Small Data Packet for 802.11ah Date:2012-01-18 Authors: Slide 1 Lv kaiying, ZTE Corporation

  2. Abstract This contribution presents some considerations on MAC overhead reduction and an MAC header suitable for small data packet is proposed for 802.11ah STAs. Slide 2 Lv kaiying, ZTE Corporation

  3. 802.11ah traffic overview 802.11ah STAs work at low data rate and exchange small data packets in most cases. We list some traffic parameters for use case1&2[1]. ═>Small data packet is a typical feature in 802.11ah. Slide 3 Lvkaiying, ZTE Corporation

  4. MAC overhead analysis(1) • MAC overhead comes from: • —MAC header：24bytes for 802.11n data frame, excluding Add4, HT • control, QoS control and FCS. • —IFS：SIFS /PIFS/DFIS is expanded to 160/208/ 256µs due to • downclock，which is almost ten times than Clause 20(High Throughput • PHY specification). • —Any frames needed for data transmission: like RTS(20bytes), • CTS(14bytes),ACK(14bytes) • —Backoff:aSlotTime is also expanded to 48µs in 802.11ah, compared to • 9µs in 5GHz band in Clause 20. • … • There is already a contribution [3] about MAC overhead calculating. Slide 4 Lv kaiying, ZTE Corporation

  5. MAC overhead analysis(2) • Such huge MAC overhead will downgrade 802.11ah MAC efficiency when small data packets comprise a significant proportion of traffic in 802.11ah. • Most of 802.11ah devices work with low duty cycle, MPDU aggregation for small data packets overhead reduction is hardly applied. • There could be two ways to reduce MAC overhead: • —By optimizing MAC function and flow to improve MAC efficiency • —By compressing MAC header • We are trying to figure out an efficient way to reduce MAC header overhead with less modifications to the current MAC header format. Slide 5 Lv kaiying, ZTE Corporation

  6. MAC header design(1) A Reduced MAC Header is proposed, and the format is shown as follows: Reduced MAC Header vs Original MAC Header Slide 6 Lv kaiying, ZTE Corporation

  7. MAC header design(2) • The proposed Reduced MAC Header consists of the following fields: • Frame Control field • Keep this field the same as 802.11n/802.11ac Frame Control field; • May need to add new subtypes of data frame. • AID field • Set to the AID of the Transmitter when Reduced MAC Header is applied; • Since AID is allocated to a STA when it performs association, AP itself has no “AID” value. AP could uses a special “AID ” value in downlink transmission, for example ,Bit0~13 of AID field set to 0,and Bit 14~15 set to 1. • Add1 field (RA field) • Set to the MAC address of the receiver. • Add3 field • Same setting rules with 802.11n/802.11ac Add3 field. (Could be removed but need further consideration and evaluation) • SN • Could be further reduced to less bits ( but need further study). • QoS control field and HT control field • Optional field for Reduced MAC Header (could be removed if some subfields can be replace by other methods, eg. SIG) Slide 7 Lv kaiying, ZTE Corporation

  8. MAC header design(2) • The reasons why using AID instead of TA(Add2) for transmitter are: • AID can uniquely identify a STA in a BSS; • There are more uplink traffics(from STAs to AP) than downlink traffics(from AP to STAs) in most of the 802.11ah use case, sometimes only uplink streams(use case 1f).Using 2 bytes AID instead of 6bytes TA could reduces the overhead during data communication. • No Duration value exists in a Reduced MAC Header, the NAV setting rules is similar to the PS-Poll receiving situation: • Upon receipt of a data frame with the Reduced MAC Header, a STA shall update its NAV settings as appropriate under the data rate selection rules using a duration value equal to the time required to transmit one ACK frame plus one SIFS interval, but only when the new NAV value is greater than the current NAV value. • QoS control field will be present if Reduced MAC Header applies to QoS data. • HT control field is also optional depending on whether STAs need to perform Link Adaption in some scenarios by using Reduced MAC Header. Slide 8 Lv kaiying, ZTE Corporation

  9. Conclusion • Considering the data rate and frequency bandwidth, 802.11ah MAC overhead should be reduced to improve MAC efficiency. • We suggest applying a Reduced MAC Header for small data packet in 802.11ah, and at least 6 bytes MAC address could be reduced. • When to choose Reduced MAC header format for data frames transmission is application dependent. • There are some other alternative methods to optimize the overhead. Further study and discussion may be needed. Slide 9 Lv kaiying, ZTE Corporation

  10. References [1] 11-11-0457-00-00ah-potential-compromise-of-802-11ah-use-case-document [2]11-11-1137-03-00ah-specification-framework-for-tgah [3]11-11-1254-00-00ah-considerations-on-short-packet-transmission-overhead Slide 10 Lv kaiying, ZTE Corporation

  11. Thank you! Slide 11 Lv kaiying, ZTE Corporation

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