Pushing the Envelope of Indoor Wireless Spatial Reuse using Directional Access Points and Clients

1. Pushing the Envelope of Indoor Wireless Spatial Reuse using Directional Access Points and Clients Xi Liu1, Anmol Sheth2, Konstantina Papagiannaki3, Michael Kaminsky3, Srinivasan Seshan1, Peter Steenkiste1 1Carnegie Mellon University 2Intel Labs Seattle 3Intel Labs Pittsburgh

2. Driving Demand for Wireless Capacity • Wide adoption of wireless technologies causes dense deployment of wireless devices • Examples include conference rooms, enterprise networks, and home • Interference is becoming a serious issue future home will have 1000 radios

3. Directional Antennas Can Reduce Interference • Less power to undesired directions • More power to desired directions • Directional antennas systems can manage interference and improve spatial reuse Omnidirectional Directional

4. Limitations of Directional Antennas in Indoor Environments Outdoor: Use LOS direction Indoor: LOS Blocked Indoor : unintended interference • Indoor space is rich-scattered • LOS may be blocked • May cause unintended interference • Recent work focuses on directional APs that are centrally controlled [DIRC, Sigcomm 2009] intended rx unintended rx

5. What This Talk is About

6. Outline • Where should directional antennas be deployed (AP, client, or both)? • How to deploy directional antennas on clients? • How to coordinate the nodes to exploit spatial reuse? • Evaluation

7. Which Side(s) to Put Directionality On? Directional APs and clients Directional APs Directional clients Omnidirectional Is it worth putting additional directionality on clients?

8. Two Indoor Testbeds • Six AP and client pairs in each scenario • APs and clients are equipped with directional and omnidirectional antennas Campus: offices with thick walls Lab: cubicles with more open space

9. Benefits of Directionality on Both APs and Clients • Significant gain from additional directionality on clients • Directional APs and clients outperforms Directional APs even with weaker directionality 1.2X 1.4X 1.6X 1.2X Capacity (Mbps)

10. Limitations of Directional APs in Dense Client Deployments • Directional APs and clients significantly improves spatial reuse in dense deployments, e.g., conference rooms

11. Outline • Where should directional antennas be deployed (AP, client, or both)? • Partitioning directionality across both APs and clients is a good choice • How to deploy directional antennas on clients? • How to coordinate the nodes to exploit spatial reuse? • Evaluation

12. How to Deploy Antennas on Clients? • Phased array antennas: too big, too expensive • Patch antennas: easy to miniaturize, inexpensive, but fixed sector too big for wireless clients

13. How to Deploy Antennas on Clients? • Phased array antennas: too big, too expensive • Patch antennas: easy to miniaturize, inexpensive, but fixed sector perfect candidates

14. Provisioning Directional Antennas for Coverage Over-provisioning (>= 8 sectors of 45⁰) Under-provisioning • Common practice is over-provisioning • Such provisioning is unnecessary in indoors scenarios

15. A Small Number of Narrow Beams Suffice Signal • 4 sector of 35⁰ antennas provide 96% coverage • Additional omnidirectional antenna for 4% of the cases • Gain of directionality can be achieved with practical antenna setup on indoor clients

16. Outline • Where should directional antennas be deployed (AP, client, or both)? • Partitioning directionality across both APs and clients is a good choice • How to deploy directional antennas on clients? • Four patch antennas + one omni antenna suffice • How to coordinate the nodes to exploit spatial reuse? • Evaluation

17. Speed Overview • Directional APs • Directional clients • Multiple administration domains

18. How to Orient and Control Antennas? MaxSNR: ignores interactions→poor performance & distributed control MaxCAP: consider all interactions→high performance & centralized control

19. Speed Operation new client / periodically environment changes

20. Collecting Measurements • Construct a conflict graph using the SINR model • Measurements: signal strength from all APs to all clients with all tx and rx directions • Each AP scans once • Clients report signal strength measurements to APs Measurements collected: S(AP1, C1, , ) AP1 S(AP1, C2, , ) S(AP2, C1, , ) S(AP2, C2, , ) AP2 C1 C2

21. Distributed Channel Reservation • Idea: a new reservation can be made if it does not interfere with existing reservations • Each node choose orientations to maximizes its signal strength yet minimizes interference • Simple greedy algorithm that only considers current and existing reservations AP1, C1, , , 54Mbps AP1, C1, , , 54Mbps AP1, C1, , , 54Mbps Reservations Made: AP2, C2, , , 36Mbps AP2, C2, , , 36Mbps AP2, C2, , , 36Mbps AP1 AP2 C1 C2

22. Transmission • Clients: directional receive, use standard CSMA, omni send • APs: directional send, use selective carrier sensing • Defer to client and external traffic • Automatically synchronized with other APs to transmit regardless of carrier sensing AP1, C1, , , 54Mbps Reservations Made: AP2, C2, , , 36Mbps AP1 AP2 C1 C2

23. Outline • Where should directional antennas be deployed (AP, client, or both)? • Partitioning directionality across both APs and clients is a good choice • How to deploy directional antennas on clients? • Four patch antennas + one omni antenna suffice • How to coordinate the nodes to exploit spatial reuse? • Speed: greedy orientation + timeslot based MAC • Evaluation

24. List of Experiments in the Paper • Comparing Speed with MaxCAP • Speed End-to-End Performance (UDP & TCP) • Breaking Down Speed’s Performance Improvement • Ability to React to Node Mobility • Association Process

25. Comparing Speed with MaxCAP • Speed’s algorithm is simple, yet performs better than MaxSNR • Speed’s algorithm a bit worse than MaxCAP, but can be implemented distributedly Capacity

26. Speed End-to-End UDP Performance 1.3X 1.5X 1.7X 2.4X Capacity UDP Performance Speed can significantly improve over directional AP only solution and OMNI

27. Conclusion • Partitioning directionality across APs and clients can improve indoor network performance in dense deployments • Speed is a lightweight and distributed system that exploits the benefits of directional APs and clients • 30% and 70% improvement across two indoor testbeds

28. Thanks!