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doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Slide 1 Authors: MAC Header Design for Small Data Packet for 802.11ah Date: 2012-01-18 Lv kaiying, ZTE Corporation
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Slide 2 Abstract Lv kaiying, ZTE Corporation This contribution presents some considerations on MAC overhead reduction and an MAC header suitable for small data packet is proposed for 802.11ah STAs.
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Slide 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 . ═>Small data packet is a typical feature in 802.11ah. Lv kaiying, ZTE Corporation Use caseSTA/AP communication Data rateTraffic type 1a smart grid2-way100kbpsContinuous/periodic/burst 1c Environmental/Agricultural Monitoring 2-way100kbpsPeriodic, event-based 1d Industrial Process Automation 2-way<1MbpsPeriodic (0.1s~100s), Burst 1e Indoor Healthcare System 2-way100kbpsPeriodic, event-based 2b Backhaul for industrial process automation 200kbps 1f Healthcare/Fitnes Hospital/clinicsendPeriodic: few KBytes every sub- seconds (e.g. blood pressure, ECG, …) Event-based: few 100 bytes per event Elderly care2-wayPeriodic: few 100 bytes every few ~ 10s minutes Event-based: few 100 bytes per event Personal fitnesssendPeriodic: few 100 bytes every minute Event-based: few 100 bytes per event
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Lv kaiying, ZTE Corporation 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  about MAC overhead calculating. Slide 4
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Lv kaiying, ZTE Corporation 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
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Lv kaiying, ZTE Corporation 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
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Lv kaiying, ZTE Corporation 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
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Lv kaiying, ZTE Corporation 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
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Lv kaiying, ZTE Corporation 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
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Lv kaiying, ZTE Corporation References  11-11-0457-00-00ah-potential-compromise-of-802-11ah-use-case- document  11-11-1137-03-00ah-specification-framework-for-tgah 11-11-1254-00-00ah-considerations-on-short-packet-transmission- overhead Slide 10
doc.: IEEE 802.11-12/0094r2 Submission Jan 2012 Thank you! Lv kaiying, ZTE CorporationSlide 11
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