MAC Partial Proposal for TGn

1. MAC Partial Proposal for TGn Nokia Yousuf Saifullah Naveen Kakani Srinivas Sreemanthula Nico van Waes Nico van Waes, Nokia

2. Introduction • MAC efficiency is an important aspect of the goal of achieving 100 Mbps at the MAC SAP in a robust, economically attractive fashion. • Power Efficiency is a critical aspect of making 802.11n suitable for the handset market. • The following MAC features are proposed for achieving these goals: • Multi data rate frame aggregation • Power Efficiency in aggregation • MAC Header Compression • Aggregate ACK Nico van Waes, Nokia

3. Multi Data Rate Frame Aggregation • STAs use different data rates due to different radio environment. Performing aggregation on multi rate increases the usability of aggregation. Thus, increases the data throughput. • Experiment results show improvement is Channel Efficiency (Data Throughput), Channel Occupancy, and Power Savings, over Single Rate Aggregation. • Introduce Num Rates, RATE #x, and Offset RATE-x in Aggregation Control Header (ACH). Could be introduced in the PHY or MAC Header. Nico van Waes, Nokia

4. Num Rates=3 RATE #1 OffsetRATE-1 # ofSTAs # ofSTAs RATE #2 OffsetRATE-2 OffsetRATE-3 # ofSTAs FCS RATE #3 STAInfo STAInfo STAInfo MRate-ACH MPDU1 MPDU2 Midamble MPDU3 MPDU4 Midamble MPDU5 Multi Data Rate Frame Aggregation • Codecs need to be emptied and reset between two different MCS. This interruption (one OFDM symbol) is filled with single symbol Midamble for improvement of channel estimation. • Proposed structure allows flexible insertion of different size preamble (including full preamble copy) in rare cases when MCS change requires this. Nico van Waes, Nokia

5. Exp No Rate (Mbps) M-Rate Scenario App1 users App2 Users % Ch Efficiency Improv. App3 Users % Ch Occupancy Improv. Total Users % Power Saving 126 1 0 1 2 1 11111100000 37.68 27.37 70.07 108 0 1 1 2 2 10011100110 39.98 28.56 57.09 96 0 1 1 2 3 00011111111 29.27 22.64 53.20 72 1 1 0 2 63 0 1 0 1 4 00011111000 30.90 23.60 60.02 54 0 0 1 1 5 11100001111 21.22 17.51 50.36 48 1 0 0 1 6 10101010101 40.00 24.24 47.39 36 0 0 1 1 7 11101010111 33.47 25.08 54.74 24 0 1 0 1 12 1 0 0 1 8 11100110011 24.12 19.43 51.27 6 1 0 0 1 9 11111111100 36.16 26.55 74.41 10 00111111100 36.67 25.75 67.46 M-Rate Aggregation Performance Results • Experiments are run with a a mix of users at different rates and different application traffic mix • Table-1: Appl User 1, MSDU=50; Appl User 2, MSDU=120; Appl User 3, MSDU=1500 bytes; • Table-2 shows an M-Rate scenario with results. Each bit under M-Rate Scenario indicates the inclusion (1) or exclusion (0) of the data rate rows in Table-1. Top row is indicated by MSB. Nico van Waes, Nokia

6. Power Efficiency • Power efficiency is important for small handheld devices. These devices will be an important segment of WLAN High Throughput products. • Power efficiency should not be compromised in Frame Aggregation. • Provide power efficiency by placing MPDU lengths along with the receiving STA’s MAC address in the ACH. Doesn’t compromise MAC throughput efficiency • A STA reads ACH determines the position of its MPDUs and reads them only without reading MPDUs of other STAs. Nico van Waes, Nokia

7. MAC Header Compression • With the High Throughput need and new applications (e.g. VoIP), MAC header (36 bytes) is becoming a significant overhead • Nokia proposes a very efficient MAC Header Compression method by • Starting compression from the very first MPDU, • Making long lived compression context, and • equally applicable on MPDUs in Frame Aggregation (FA) • MAC Header Compression Procedure • An AP creates a mapping between 1 byte unique Compression ID (CID) and the set of addresses in the MAC Header (Addr 1 through 4). • AP establishes the same CID in the non-AP STA by introducing “CID Association” procedure. For example: AP and STA exchange a CID Association Request followed by ACK. • The CID is established prior to exchanging any data frames • AP and STA start exchanging Compressed Header (CH) MPDU Nico van Waes, Nokia

8. FrameBody Seq Control QoSControl FrameControl Duration /ID Addr 3 Addr 4 Addr 2 Addr 1 FCS Compressed Header MPDU Format • MAC HC procedure is applicable for adhoc mode • CID has to be unique between two STAs performing MAC HC • BSSID (infra) is added in first frame (FA) to remove ambiguity in cases where same CID is used in neighboring APs for different STAs • RA (adhoc) is added in the first frame to remove ambiguity between two pairs of STAs Octets: 2 2 6 6 6 2 6 2 n 4 Existing MAC Header Octets: 2 2 1 2 2 n 4 FrameBody Duration /ID QoSControl Seq Control FrameControl FCS CID CH-MPDU Octets: 2 2 2 1 2 2 n 4 FrameBody Seq Control QoSControl Duration /ID FrameControl BSSID/RA FCS CID CH-MPDU with BSSID/RA Nico van Waes, Nokia

9. MAC HC Benefit Analysis • Assumptions • 5 individual MPDUs, each in “n” aggregated frames • Only 3 MAC Header address fields compressed • WithoutMAC HC • MAC Header bytes in n aggregated frames are n* 5*36. For n=10, MAC header bytes are 1800. • With MAC HC • One time signaling overhead is 41 bytes: CID Establishment Request is 27 bytes and ACK is 14 bytes. • For each 5 MPDUs in one aggregated frame • First 2 are “CH-MPDU with AP MAC Address”. Robustness assumption: 2 such MPDUs sent. Each MPDU saves (12-1) bytes, and 2 MPDUs save 22 bytes. • Next 3 MPDUs (CH-MPDU) have savings of 3*(18-1) = 51 bytes • Total savings in one aggregated frame: 22+51= 73 bytes • For “n” aggregated frames: -41+ n*73; For n=10, Total savings = 689 bytes • This provides 38% savings in the MAC header bytes over no MAC header compression in 50 MPDUs. The higher the number of MPDUs exchanged the more will be the savings. Nico van Waes, Nokia

10. ACK aggregation • Frame Aggregation (FA) feature sends multiple MPDUs together. For the MPDUs needing ACK, the receiving STAs could send either Block ACK or Normal ACK in the reverse link. • There is significant redundancy in using both, even if FA is used in the reverse link. • Normal ACK adds considerable overhead in the traffic, even in an aggregated frame, since an ACK frame (14 bytes) is sent for each MPDU • A Block ACK frame size is 152 bytes. It has additional signaling overhead needed for adding, requesting, and deleting Block ACK. Moreover, Block ACK is defined on a TID basis. An aggregated frame may contain MPDUs with different TIDs for a STA. This would still result into multiple Block ACK Req and Block ACK per STA. Nico van Waes, Nokia

11. Solution: Aggregate ACK • Aggregate-ACK (A-ACK) retains frame format as Normal ACK but adds 2 additional fields to acknowledge individual MPDU within an aggregated frame • A-ACK follows the Normal ACK rules in 802.11 MAC. Thus, it doesn’t have any signaling overhead like Block ACK Nico van Waes, Nokia

12. Aggregate ACK Benefit Analysis • A-ACK Overhead • Frame size of an A-ACK = 14 + 1 + n*3. • For n=10, overhead = 45 bytes • Normal ACK Overhead • Frame size of on ACK = 14 bytes • For n MPDUs, Frame size = n*14. • For n=10, overhead = 140 bytes • Block ACK Overhead • Assume n MPDUs in 3 TIDs, requiring Block ACK. • Exclude ADD/DEL BA signaling overhead. • Overhead due to 3 Block ACK Req/Block ACK = 3 (24 + 152) = 528 • A-ACK saves 68% over Normal ACK • A-ACK saves 91% over Block ACK Nico van Waes, Nokia

13. Aggregate ACK Benefit Analysis • The proposed MAC features substantially improve MAC throughput, as well as power efficiency, which is critical for handset applications • The features can be introduced easily by modifying/enhancing the existing procedures and frame structures • Analysis has been provided to show the benefit Nico van Waes, Nokia