Link-level Measurements from an b Mesh Network Daniel Aguayo John Bicket Sanjit Biswas Glenn Judd † Robert Morris M.I.T. Computer Science and Artificial Intelligence Laboratory {aguayo, jbicket, biswas, † Carnegie Mellon University Devin Barillari Advanced Topics in Wireless Networks

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks The Experimental Setup Effect of distance Effect of SNR (Signal vs. Noise Ratio) Effect of transmit bit-rate Interference from other b sources Effect of Multi-path Output power b Laptops +8 db omni directional roof mounted antenna Channel 3 (2.422Ghz) Prism wireless cards in “pseudo-IBSS” Ad- Hoc mode to prevent network partitioning Each node transmits as all other nodes receive and record each successful frame.

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks The Experimental Setup Effect of distance Effect of SNR (Signal vs. Noise Ratio) Effect of transmit bit-rate Interference from other b sources Effect of Multi-path Output power Figure 5: These maps show the delivery probabilities from three senders to all other nodes. The sender is marked S, and each receiver is indicated by a circle with radius proportional to the fraction of packets it received. There is a correlation to distance but it is not always consistent.

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks The Experimental Setup Effect of distance Effect of SNR Effect of transmit bit-rate Interference from other b sources Effect of Multi-path Output power In ideal conditions there is a 3db difference in signal strength that gives 10% to 90% loss rates. Many nodes have mid-range loss rates, Does this mean there are many nodes with a signal in this 3db range? No. In real conditions the 3db range is much greater due to obstacles and attenuation. Ideal Emulated Conditions Observed Real-World Conditions

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks The Experimental Setup Effect of distance Effect of SNR (Signal vs. Noise Ratio) Effect of transmit bit-rate Interference from other b sources Effect of Multi-path Output power Lower bitrates are usually more robust. A higher bitrate may have better data throughput with loss rates above 50%. Performance at low bitrates are no indication of performance at higher bitrates.

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks Much of the “other source” noise is due to beacons. Channel 6 is very busy (usually the default configuration for commercial products. The Experimental Setup Effect of distance Effect of SNR (Signal vs. Noise Ratio) Effect of transmit bit-rate Interference from other b sources Effect of Multi-path Output power

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks The Experimental Setup Effect of distance Effect of SNR (Signal vs. Noise Ratio) Effect of transmit bit-rate Interference from other b Effect of Multi-path Output power Multipath differs greatly from an Small indoor area to a wide outdoor urban area. Larger Distances introduce delays longer then multipath filters cannot identify. (rake < s) No loss occurs if reflection has more then 4db weaker. Δt = 10 nanoseconds Δd = 3 Meters Indoor Sender Receiver Δt = 1 microseconds Δd = 300 Meters Outdoor Sender Receiver

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks The Experimental Setup Effect of distance Effect of SNR (Signal vs. Noise Ratio) Effect of transmit bit-rate Interference from other b Effect of Multi-path Output power

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks The Experimental Setup Effect of distance Effect of SNR (Signal vs. Noise Ratio) Effect of transmit bit-rate Interference from other b sources Effect of Multi-path Output power Quadrupeling the output power will increase effective radius by around 2 times. The effect of varying the transmit power level on the delivery probability, for 1 Mbit/s. For example, raising the power level from 10 to 40 milliwatts almost doubles the number of nodes that have delivery probabilities of 40% or more.

802.11b networks in an wide urban environment: Devin Barillari Advanced Topics in Wireless Networks The Experimental Setup Effect of distance Effect of SNR (Signal vs. Noise Ratio) Effect of transmit bit-rate Interference from other b sources Effect of Multi-path Output power Conclusion: Links with intermediate levels of loss are the common case; there is no clear distinction between “working” and “non-working” links. Link distance and S/N ratio do have an effect on loss rates, but the correlation is weak.