A Flexible Beam Training Protocol for 60GHz mm-Wave Communication (TGad)

1. A Flexible Beam Training Protocol for 60GHz mm-Wave Communication (TGad) Authors: Date: 2010-05-17 Junyi Wang, NiCT

2. Abstract Overview of beamforming (BF) related contributions for 802.11ad and suggestions for BF proposal based on those contributions. Junyi Wang, NiCT

3. Comparing with 2.4GHz/5GHz WLAN, a high propagation, attenuation loss in 60GHz link budget shall be compensated with antenna gain. Interferences from other systems can be mitigated with BF techniques. Coexistence capability can also be improved with directional transmission. Why BF? Junyi Wang, NiCT

4. In IEEE Std 802.15.3c™-2009, a BF protocol is specified on the top of multiple PHY modes. • In 09/0572r0, the authors show that in 60GHz, most usages (07/2988r4) require directional communication in order to meet link budget requirements. • In 09/0572r0, the authors also believe that TGad should reuse as much as possible from 802.11+amendments. • In 09/1153r0, the authors conclude that BF is one of the most important features in the TGad 60GHz specification and will be decisive in enabling successful 60GHz products. Overview of BFcontributions in TGad (1/2) Junyi Wang, NiCT

5. In 09/1153r0, the authors summary the BF requirements in TGad • One BF protocol for all usages/scenarios • The BF protocol shall support different antenna types and does not assume antenna reciprocity • The BF protocol shall allows fast BF link (re-)establishment and tracking • The BF protocol should accommodate devices/usages with different levels of complexity • The BF protocol should supports pre-network entry and post-network entry BF • In 10/0231r3, the authors propose to use 802.11a/b/g/n to assistant 802.11ad for signalling. • In 10/430r0 and 10/450r1, the authors propose beamforming protocol for sector sweeping, beam refinement and beam tracking • In 10/493r0, the authors propose to find the optimum weight vector for beamforming. Overview of BFcontributions in TGad (2/2) Junyi Wang, NiCT

6. Network model Infrastructure mode Ad-hoc mode • In infrastructure mode, a beamformed link shall be set up between Access Point • (AP) and any Station (STA). • In Ad-hoc mode, a beamformed link shall be set up between any two STAs. • In 60GHz WLAN, both of them shall support CSMA/CA and TDMA mode Junyi Wang, NiCT

7. The objective of the proposed BF is to find the optimal transmit and receive antenna weight vector through MAC operation in order to optimize a cost function that measures the link quality metric. In this paper, signal to interference plus noise ratio (SINR) is selected as the metric. BF model Junyi Wang, NiCT

8. All STAs shall support one or more directional antenna patterns, which are generated by the pre-defined beam codebooks. • A beam codebook is a matrix where each column specifies a BF weight vector. Each column also specifies a pattern. • Either of the following ways shall be supported for signaling (including BF request/response). • All BF capable STAs support 2.4G/5G WLAN (IEEE 802.11a/b/g) • At least AS supports omni (or quasi-omni) transmission with low date rate by using advanced modulation and coding scheme that compensates for the lack of antenna gain. Basic assumptions for BF Junyi Wang, NiCT

9. The BF operation starts from either of following initial status by acquiring synchronization with AS Initial status 2.4GHz/5GHz Omni By switching directional pattern to acquiring timing in 60Ghz Through 2.4G/5G omni antenna to acquiring time for 60GHz Junyi Wang, NiCT

10. Beam searching between two STAs CSMA/CA based CSMA/CA or TDMA based CSMA/CA or TDMA based Junyi Wang, NiCT

11. Beam searching between AP and STA CSMA/CA based CSMA/CA or TDMA based CSMA/CA or TDMA based Junyi Wang, NiCT

12. Beam refinement CSMA/CA based CSMA/CA or TDMA based CSMA/CA or TDMA based Junyi Wang, NiCT

13. Function • Handshaking for BF • Exchange BF capability • If the beam searching is performed in TDMA time slot, then the initial BF capability has been exchanged during association or by beacon, the “BF capability” field in initial BFRqt or BFRsp command shall be empty. • Set network allocation vector for other NAV if beam training is performed in CSMA/CA mode • Transmission • The BFRqt and BFRsp shall be sent in CSMA/CA mode. • AP shall send or receive command with (1) omni/quasi-omni pattern with advanced modulation and coding rate to compensate the propagation loss; or (2) in 2.4GHz or 5GHz WLAN. • The handshaking period may be omitted in beam refinement stage if the field “More training” is set to 1 in the BFfdbk command. • BFRqt/BFRsp Frame • BFRqt/BFRsp Frame is control frame with framebody information shown in next page. Initial substage Junyi Wang, NiCT

14. Address 1: the address of the source Address 2: the address of the destination Address 3: the address of the BF target Rqt/Rsp: Set to 1 when it is BFRqt command, otherwise set to 0 Training mode: set 1 if BF is to perform in reserved service period (SP), set to 0 otherwise. Quasi-omni capable : Set to 1 when the selected is quasi-omni capable, otherwise set to 0. BF capable: Set to 1 when the STA is BF capable. # of Tx beams: Number of transmit beam pattern of the beamformer. # of Rx beams: Number of receive beam pattern of the beamformer. Searching /Refinement: set to 1 if the stage is searching stage, otherwise set to 0. BFRqt/BFRsp frame format Junyi Wang, NiCT

15. Training procedure in beam training stage • As shown in Figure (a) Supposing beamformer has M directions, beamformee has N directions. Each training period is composed of M cycles of N repetitions. Each cycle shall be sent from each of beamformer’s transmit directions. The repetitions shall be received by each of receive direction of beamformee. • Training in Beam refinement • Cover the same space of the selected pattern with more now narrower beams, and select the best beam pair among all transmit and receive beam combinations. • Beam refinement stage submay repeat to further narrow down the beam until both of STAs are satisfied. Training substage(1/2) (a) Beam training (b) Beam refinement Junyi Wang, NiCT

16. Training starting time • The training shall start after receiving BFRsp or BFFdbk command following by a “SIFS” interval. • Training sequences • Training sequences is a control frame with following framebody • Tx pattern ID: the pattern ID in which the training sequences is sent • Training sequence counter: the index of training sequences • Total training sequences : Total training sequences to be sent continuously. • The PLCP preamble can used as the training sequences for each direction, the “long training sequence ” in the preamble can be used for SNR estimation. Training substage(2/2) Junyi Wang, NiCT

17. Function • Feed back the selected best transmit pattern. • Transmission • The BFFdbk command can be sent in CSMA/CA mode, or a TDMA time slot. • The first feedback after first training period shall be sent in all transmit direction of a STA so that beamformed may receive at least any one of them. • BFRqt/BFRsp Frame • BFRqt/BFRsp Frame is control frame with the following framebody information. • Address 1: the address of the source • Address 2: the address of the destination • Address 3: the address of the BF target • Best pattern ID: the index of the best pattern • SNR of best pattern: the SNR of the best pattern, for beamformer to select proper modulation and coding scheme. • More training: Set to1 if following is a beam refinement stage, otherwise set to 0 • BF capability: same with the field in BFrqt/BFrsp, however may be omitted if “More training” is set to 0. Feedback substage Junyi Wang, NiCT

18. STA1 is BF capable, however STA2 is not • STA2 shall help STA1 finish BF operation by using omni/quasi-omni transmission. • STA1 is capable of beam refinement, however STA2 is not. • STA2 could not refine its pattern into finer beams. STA2 shall use his latest found pattern to help STA1 finish BF operation, in this case, STA2 shall set the # of Tx beam and # of Rx beam to 1. • If all devices involved in BF support 2.4GHz/5GHz transmission, or all devices involved in BF support omni/quasi-omni transmission, the beam refinement protocol can be directly used for beam searching. Some rules for some special cases Junyi Wang, NiCT

19. Necessarity of beam tracking • Possible channel variation • Possible block • Beam tracking • Beam tracking is performed together with data streaming periodically. • The training sequences are attached at the end of data • the beam for data streaming (called working beam in the following context) and its adjacent beams ( and the wider pattern which cover the working beam and its adjacent pattern may be tracked prepared for contingencies of the working beam’s blocking) Beam tracking Junyi Wang, NiCT

20. The proposed BF protocol is beam codebook based proposal, which selects the best beam pattern from pre-defined beam codebook, and setup a beamformed communication link between any STAs. The proposed BF includes beam searching, beam refinement and beam tracking. The proposed BF protocol supports different level of codebook complexities, no training stage limitation. STAs are able to request further beam refinement as long as they need. Beam searching and beam refinement stage can be easily combined and separated, significantly improve the flexibility of BF protocol. The proposed BF protocol is available in both DCF (CSMA/CA) mode and PCF (TDMA) mode, compliant with the full proposals in TGad, and also compliant with currently implemented IEEE 802.11 MAC. The proposed BF protocol can also be extended to support AP directional transmission. Conclusions Junyi Wang, NiCT

21. References • IEEE Std 802.15.3c™-2009 • 11-07-2988-04-00-00ad Wi-Fi Alliance (WFA) VHT Study GroupUsage Models • 11-09-0572-00-00-00ad MAC Channel Access in 60 GHz • 11-09-1153-00-00-00ad Motivation and Requirements on 60 GHz Beamforming • 11-10-0259-02-00-00ad 802.11ad New Technique Proposal • 11-10-0430-00-00-00ad NT-11 Beamforming Introduction • 11-10-0450-01-00-00ad NT-12 on Beamforming (BRP) • 11-10-0493-00-00-00ad Beamforming training for IEEE 802.11ad Junyi Wang, NiCT

22. Do you support complete or partial inclusion of beamforming technique, as described in 10/0496r1 in the TGad draft amendment? Yes: . No: . Abstain: . Straw poll Junyi Wang, NiCT