Pushing the Envelope of Indoor Wireless Spatial Reuse using Directional Access Points and Clients Xi Liu 1, Anmol Sheth 2, Konstantina Papagiannaki 3, Michael Kaminsky 3, Srinivasan Seshan 1, Peter Steenkiste 1 1 Carnegie Mellon University 2 Intel Labs Seattle 3 Intel Labs Pittsburgh

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 Driving Demand for Wireless Capacity 2 future home will have 1000 radios

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 3 OmnidirectionalDirectional

Limitations of Directional Antennas in Indoor Environments 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] 8/19/20094 Outdoor: Use LOS direction Indoor: LOS Blocked Indoor : unintended interference intended rx unintended rx

What This Talk is About 5 Placing weaker directional antennas on both APs and clients provides better network performance compared to placing stronger directional antennas only on the APs Where should directional antennas be deployed (AP, client, or both)? Speed: Lightweight and distributed antenna control and MAC protocol that provides high performance How to coordinate the distributed nodes to exploit spatial reuse?

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 6

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

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 wallsLab: cubicles with more open space 8

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 Capacity (Mbps) 1.4X 1.6X 9 1.2X

Limitations of Directional APs in Dense Client Deployments Directional APs and clients significantly improves spatial reuse in dense deployments, e.g., conference rooms 10 Partitioning directionality across both APs and clients is a better choice

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 11

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

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

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 14

A Small Number of Narrow Beams Suffice 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 15 Signal

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 16

Speed Overview Directional APs Directional clients Multiple administration domains 17

How to Orient and Control Antennas? 18 MaxSNR: ignores interactions→poor performance & distributed control MaxCAP: consider all interactions→high performance & centralized control Can we design a directional antenna system that provides both high performance and distributed control?

Speed Operation 1. collect measurements 2. association3. reservation4. transmit environment changes new client / periodically 19 Speed: greedy orientation algorithm on timeslot-based MAC protocol

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 S(AP1, C1,, ) AP1 AP2 C1 C2 S(AP1, C2,, ) S(AP2, C1,, ) S(AP2, C2,, ) 20 Measurements collected:

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 AP2 C1 C2 Reservations Made: AP1, C1,,, 54Mbps AP2, C2,,, 36Mbps AP1, C1,,, 54Mbps AP2, C2,,, 36Mbps AP1, C1,,, 54Mbps AP2, C2,,, 36Mbps 21

Transmission AP1 AP2 C1 C2 AP1, C1,,, 54Mbps AP2, C2,,, 36Mbps 22 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 Reservations Made:

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 23

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 24

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 25 Capacity

Speed End-to-End UDP Performance UDP Performance Capacity 1.3X1.5X 1.7X2.4X 26 Speed can significantly improve over directional AP only solution and OMNI

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 27

28 Thanks!