1. ® Copyright© Intel Corporation 2000-2004 Making Radios More Like Human Ears Jing Zhu, Xingang Guo, L. Lily Yang, W. Steven Conner Intel Corp. Lakshman Krishnamurthy Principal Engineer Intel Corp.

2. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 2 Three points  We can improve performance by making radios like our ears  And behaving like people – talk even though you hear others  Mesh can give more bandwidth – not less  Stop working on routing and NS2!

3. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 3 Problem overview  Mesh network  An ad-hoc group of nodes relaying each other’s traffic  Logically flat hierarchy – AP mesh, station mesh, hybrid mesh  Spatial reuse – use the same channel at spatially separated locations  Enable simultaneous communications to improve overall network throughput  Applicable to large-scale wireless networks * Third party brands/names are property of their respective owners

4. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 4 Physical carrier sensing  802.11 MAC based on CSMA/CA  CS (Carrier Sensing) to avoid interference  Carrier sensing – a station listens before transmit  Listen – sample the radio energy (interference) in the air  Carrier sensing threshold  Decide transmit or wait  Current devices – static, not independently tunable  Make the threshold tunable, and network throughput can be improved dramatically with properly tuned threshold

5. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 5 Network throughput  Large-scale 802.11 networks, in each channel Link date rate – R 11 Mbps Link date rate – R 11 Mbps # of simultaneous comm. – N 10 # of simultaneous comm. – N 10 X). X). Network throughput (R*N) 110 Mbps Network throughput (R*N) 110 Mbps  “N” determined by spatial reuse  Reuse the same channel in separated location  Tuning CS threshold can leverage spatial reuse

6. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 6 Communication model  Each data rate has its own requirement on channel quality  SNIR threshold  Spatial reuse  Properly separate simultaneous comm.  Different rates will require different require different separation distances separation distances  CS threshold reflects separation distance

7. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 7 A B TX D RX Anatomy of interference R I X C

8. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 8 Optimal sensing threshold  Let  P C – carrier sensing threshold  P D – receiving power threshold, or sensitivity  S 0,r – SNIR threshold for data rate r  γ – pathloss exponent  Define relative sensing threshold P cs_t = P C / P D  Then  P cs_t = (1+ S 0,r 1/γ ) -γ  S 0,r >>1  P cs_t = 1/S 0,r,  In a large network, TX and RX almost co-locate

9. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 9 Simulating chain network  90-node chain, 90- hop e2e path  Tx range tuned to node distance  Measure e2e throughput while varying P cs_t  E2e throughput changes dramatically  Optimal P cs_t depends on data rate

10. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 10 Effectiveness of PCS tuning PCS tuning maximizes spatial reuse in chain networks

11. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 11 Simulating grid network  10x10 grid, comm. w/ immediate neighbors  Tx range tuned to node distance  Measure aggregate throughput while varying P cs_t  E2e throughput changes dramatically  Optimal P cs_t NOT depending on propagation environment

12. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 12 RTS/CTS?  Protocol exchange may fail when outside of Tx range A B TX D RX R I C  VCS failed to take full advantage of higher pathloss to increase spatial reuse

13. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 13 Conclusion  Properly tuned carrier sensing achieves optimal spatial reuse  Dramatically improves network throughput  Computational efficient  Complementary to RTS/CTS  Non-disruptive enhancement to 802.11 MAC  Make the carrier sensing tunable in all 802.11 devices

14. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 14 Overview: Experimental evaluation of an 802.11b home mesh network Upper Level Office Lower Level Living Room Den Back Yard B C D A 70 71 72 73 74 75 76 77   Experiments performed in house (~2000 sq. ft.) in Hillsboro, OR (August, 2003)   Topology: 8 Client Laptops and 4 AP routers   In a real home network scenario, some of the laptops would likely be replaced by other 802.11 enabled devices (e.g., DVRs, media servers, stereo systems, etc.)   Traffic: Experiments assume network traffic is not limited to Internet surfing on a broadband link   Clients share significant amount of data within the home (e.g., A/V content sharing, photo storage, data backup, etc.)

15. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 15 5.182 1.572 0.85 0 0 1 2 3 4 5 6 Throughput (Mbps) OfficeLiving Room DenBackyard 70 (O) 73 (D) 75 (L) 77 (B) Multi-Hop ESS Individual Node Throughput 5.179 2.679 2.686 1.8 0 1 2 3 4 5 6 Throughput (Mbps) OfficeLiving Room DenBackyard 70 (O) 73 (D) 75 (L) 77 (B) Individual Node Throughput Non-Mesh BSS Individual Node Throughput Out of range 1.7X  3.1X  Connected!

16. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 16 Multi-Node Throughput Out of range Non-Mesh BSS Aggregate Throughput 5.338 2.878 1.994 1.520 Multi-Hop ESS Aggregate Throughput 5.322 3.910 3.880 3.284 1.3X  1.9X  2.1X 

17. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 17 Multi-Node Throughput cont. Aggregate Throughput with 8 Clients Out of range 1.719 3.709 2.1X 

18. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 18 Client-to-Client Throughput Non-Mesh BSS Client-to-Client Throughput Out of range Multi-Hop ESS Client-to-Client Throughput 2.4X  3.4X  Note: Direct client-to-client links can help here as well

19. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 19 Network Latency Non-Mesh BSS End-to-End Latency Out of range Multi-Hop ESS End-to-End Latency Highly dependent on implementation ~ 2ms increase per hop

20. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 20 Shorter range radio hops offer higher throughput Source: Intel Corporation

21. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 21 Summary of home testbed Results  A multi-hop mesh is beneficial, even for a relatively small-scale home network  Multi-hop topologies:  Can be built with standard 802.11 hardware  Can improve network performance in comparison to traditional 1-hop BSS networks  These experiments used 1 radio on each AP/router; multi-radio per AP/router would allow even better performance (multi-channel)

22. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 22 Mesh test bed and Platforms 25-35 nodes Laptops and embbeded Xscale boards (PXA-255 and IXP425) Boards, software available for research Performance comparison of mesh and wireless network self organization

23. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 23  Microsoft Research  Intel Routing Protocol Median Throughput of 100 TCP transfers LQSR w/ shortest path (No link quality metric) 1155 Kbps LQSR w/ ETX (MIT 2002) 1379 Kbps LQSR w/ ETX++ (MSR 2003) 1601 Kbps AODV w/ link filtering (Intel 2003) 1460 Kbps Topology and Transmit power have significant impact Routing Protocol Median Throughput of 100 TCP transfers LQSR w/ shortest path (No link quality metric) LQSR w/ ETX (MIT 2002) 7334 Kbps 1935 Kbps LQSR w/ ETX++ (MSR 2003) AODV w/ link filtering (Intel 2003) 11709 Kbps 2079 Kbps Need self-configuration algorithms

24. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 24 802.11S MESH standard Lowering the Barriers to 802.11 Mesh Deployment  Standardize Multi-Hop ESS Mesh  Interoperability  Radio/Metric-Aware L2 Routing/Switching  Security  Self-Configuration / Management  Enhance MAC Performance for Mesh  Scalability  Scheduling (managing collisions/ interference) Major focus of new Mesh Task Group (802.11s)  Leverage 802.11i/k where possible Influence current/ future MAC enhancement efforts to improve scalability for mesh  Leverage 802.11e/n where possible  Mesh-specific MAC enhancements can be made in ESS Mesh TG Parallel Efforts:

25. Communications Technology Lab Leveraging spatial reuse with enhanced physical carrier sensing Copyright© Intel Corporation 2000-2004 25 Thank you