Predictable 802.11 packet delivery from wireless channel measurements
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References
Fundamentals of Wireless Communication
Wireless communications
Understanding Packet Delivery Performance In Dense Wireless Sensor Networks
Related Papers (5)
Frequently Asked Questions (17)
Q2. How can the authors evaluate the effectiveness of SNR?
The authors have also shown that effective SNR can be implemented on commodity NICs and evaluated it over real wireless channels with mobile and fixed clients.
Q3. What is the way to achieve good performance in a wide range of environments?
Modern wireless NICs provide a large and growing range of physical layer configurations to obtain good performance across this range of environments.
Q4. What is the way to handle OFDM over faded links?
It uses the notion of effective SNR to handle OFDM over faded links, works for MIMO configurations, and needs no calibration of target links.
Q5. What is the way to adapt to varying channel conditions?
Many rate adaptation algorithms have been proposed that use packet delivery statistics [5, 29], RSSI-based packetSNR [6, 10], or symbol-level details of packet reception [23, 28] to adapt to varying channel conditions.
Q6. What is the concept of an effective SNR for a multi-carrier channel?
Their model uses the concept of an effective SNR for a multi-carrier channel [18], such as OFDM, in which there are different subcarrier SNRs, plus approximations for coding, interference between MIMO streams, and decoding algorithms.
Q7. What is the method for calculating the supported rate on a link?
At each reduced transmit power level, the authors estimate the best supported rate on a link based on appropriate thresholds, and continue the reduction if the original rate is sustained.
Q8. What is the biggest potential weakness of the SNR protocol?
This is one of the largest potential weaknesses of this technique, because effective SNR is based on measurements taken only during the packet preamble.
Q9. How do the authors compute the effective SNR?
If the authors ignore coding for the moment, then the authors can compute the effective SNR by averaging the subcarrier BERs and then finding the corresponding SNR.
Q10. How do the authors measure the reception rate of a packet?
Then the authors collect packet reception rate (PRR) statistics for all 8 rates using 1, 2, and 3 spatial streams as the authors vary the power between −10 dBm and 16 dBm in steps of 2 dB.
Q11. What is the rate for a given SNR?
Except for extremely low and high SNRs, nearly all SNRs have at least two and up to five different rates as suitable choices for the best rate.
Q12. What does the study conclude that the presence of interference does not cause wild swings in transmit rate?
The authors conclude that the mere presence of interference does not completely invalidate effective SNR values, and thus transient interference will not cause wild swings in transmit rate.
Q13. What is the way to convert CSI to effective SNR?
The authors convert CSI to effective SNR in a way that better matches the equal modulation and power allocation used by 802.11n and offer a better API for practical use.
Q14. What is the way to understand how transition windows map to packet delivery predictions?
To understand how transition windows map to packet delivery predictions, the authors analyze their measurements for the highest supported rate (PRR≥ 90%) for each link and all NIC settings.
Q15. How can the authors predict the transmission power of a wireless link?
Their example in §5 suggests that, with a good predictive model, the authors can directly and confidently select a reduced transmit power without degrading link performance.
Q16. How is the Eff SNR line used to show that the link is tight?
To show that this trimming is tight, the authors also consider trimming towards slightly lower thresholds (Effective SNR− 0.5 dB, solid line).
Q17. How did the authors change the transmit power of the node designated as the interferer?
The authors also varied the transmit power of the node designated as the interferer from low to high to induce a large range of interfering channels.