Spatial Discovery in 60 GHz

1. Spatial Discovery in 60 GHz Authors: Date: 2010-03-02 Saad Ahmad et.al., InterDigital

2. Abstract The proposal presented in this new technique presentation deals with the problem of device discovery using directional antennas in 60 GHz band. The presentation outlines the existing techniques, presents a new approach and provides a comparison Saad Ahmad et.al., InterDigital

3. Background • In 802.11, AP or devices are discovered using periodic beaconing • In 2.4/5 GHz 802.11, Omni-directional beacons are used • In 60Ghz Omni-directional beacon have limited range • Sending out directional beacon in all the directions can be problematic and time consuming Saad Ahmad et.al., InterDigital

4. Spatial Discovery – Problem Statement • Directional antenna makes neighbor discovery difficult • Need to efficiently discover all neighbors • Just to know that a neighbor is somewhere around you is not enough • Need to have good knowledge of the directional location of the neighbors • This can help to solve problems arising from directional communication e.g. deafness problem • We need to track devices to provide support for low mobility Saad Ahmad et.al., InterDigital

5. Existing Techniques • Low Rate PHY (LRP) • Omni directional discovery using a low rate channel. The bandwidth of the channel is also smaller than the high rate channel • Fixed Discovery Channel (FDC) • Devices listen to a low rate separate and known discovery channel at scheduled time slots to receive the beacon • Out Of Band Control Channel (OOB) • Devices discover each other and their 60 GHz capabilities such as 802.11g PHY • Scanning each sector with a directed beam using brute force (BF) Saad Ahmad et.al., InterDigital

6. Let’s see how these techniques do: • Comparison Metrics: • Reliability : Probability of successfully discovering neighbors • Discovery Speed : How quickly neighbor devices are discovered • Device Mobility : Does the discovery procedure support mobility of stations • Single PHY : Does the procedure require multiple radios • Neighborhood Location Information : After discovery, does the procedure provide location information Clearly there is room for improvement… Saad Ahmad et.al., InterDigital

7. Proposed Technique • In a nutshell... • Two types of beacons may be used i.e. Discovery beacon and Periodic beacon • Each of these beacons uses coarse sectors/ coarse beam • Periodic beacon may be transmitted only in discovered sectors • Data is transmitted and received using fine beam • Details are presented in the following slides • Slide 15 provides a qualitative comparison of existing techniques and the proposed technique Saad Ahmad et.al., InterDigital

8. Coarse Discovery (1 / 2) • The approach is to send out a coarse directional beam that carries beacons rotating in a Time Division fashion followed by a listening period • Beam for normal data transmission may be finer Saad Ahmad et.al., InterDigital

9. Coarse Discovery (2 / 2) In the initial discovery phase, STA sends discovery beacons in a randomly chosen coarse sector (Discovery Beacon) It then listens for the response for a specific duration and then moves on to the next sector After the initial phase, the beaconing STA may focus in direction of interest i.e. the sectors where it has found STAs Beaconing STA will exchange antenna training symbols using Beam forming protocol with discovered STAs to enable fine beam for data traffic (Fine Beam forming) Beaconing STA will only send periodic beacons in the sectors where STAs are discovered (Periodic Beacon) Beaconing STA may opportunistically send discovery beacons in all sectors, or only in those sectors without STAs, to check for new STAs Saad Ahmad et.al., InterDigital

10. Infrastructure BSS Scenario – AP Operation In this example, AP sends out beacon in each quarter. It finds 2 STAs in quarter 1 and 2 STAs in quarter 2 After all four STAs are associated, AP sends out periodic beacon (every Beacon Interval) only in quarter 1 & 2 AP will send out discovery beacon in all directions every ‘x’ beacon intervals or opportunistically during idle period Saad Ahmad et.al., InterDigital

11. Infrastructure BSS – STA Operation STA starts scanning; looks for a discovery beacon in each sector STA scan time for all sectors should be slightly less than the discovery beacon transmission time for the AP in each sector Once the STA is associated to the AP it will just look for the periodic beacon in the discovered sector (e.g. quarter D in this fig.) Saad Ahmad et.al., InterDigital

12. Infrastructure BSS – Discovery Signal Flow Signal flow for device discovery (management message exchange) for the network illustrated above Saad Ahmad et.al., InterDigital

13. Coarse-Fine Summary Saad Ahmad et.al., InterDigital

14. Channel Detection • STAs need to detect the channel where beacon is being sent. This can be done in several ways: • Scanning all the available frequencies • Implementing Common Mode Signaling (CMS) • Fixed/ known discovery channel • Sending beacon over multiple frequencies • Sending beacon on fixed channel(s) with a very high coding gain(Underlay approach) • Scanning Multiple frequencies at the same time (Coarse Scan) • Frequency identified by using another RAT technology or 2.4/5 GHz 802.11 Saad Ahmad et.al., InterDigital

15. Comparison Matrix A: Low Rate PHY B: Fixed Discovery Channel C: Out Of Band Control Channel D: Brute Force E: Proposed technique Saad Ahmad et.al., InterDigital

16. Conclusion Device discovery using directional antenna can be performed efficiently with a nominal overhead by using two beacons i.e. discovery beacon & periodic beacon By solving the spatial discovery problem, the location of the device is known; this can assist in solving other issues e.g. deafness and hidden node problem Saad Ahmad et.al., InterDigital

17. Straw Poll • Do you support inclusion of the technique – “Spatial Discovery in 60GHz” as described in 10/0245r1 in the TGad draft amendment? – Yes – No – Abstain Saad Ahmad et.al., InterDigital

18. References [1] ECMA-387 [2] “Overview of WirelessHD Specification Version 1.0a” [3] IEEE std 802.15.3c-2009 [4] 15-07-0629-00-003c “Automatic Device Discovery for Directional Antenna Devices” Saad Ahmad et.al., InterDigital