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Wireless Networks Power Control Implications Study

This study explores the effects of power control on interference levels and network-wide throughput in wireless networks. Experiments conducted on an indoor testbed reveal scenarios where power control enhances performance and fairness. Findings show varying impacts of power control in different interference scenarios, highlighting the trade-offs with RTS/CTS exchange. The study concludes that proper power control can benefit wireless deployments, improving throughput and fairness. Potential extensions include activating multiple links simultaneously and adjusting sensing thresholds.

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Wireless Networks Power Control Implications Study

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  1. Implications of Power Control in Wireless Networks: A Quantitative Study PAM 2007 Ioannis Broustis, Jakob Eriksson, Srikanth V. Krishnamurthy, Michalis Faloutsos Department of Computer Science and Engineering University of California, Riverside {broustis, jeriksson, krish, michalis}@cs.ucr.edu

  2. The problem • Increasing the transmission power may: • Increase throughput, due to increased signal quality • Increase interference levels in neighboring links • Conflict in providing the best network-wide throughput • Need to identify the possible interference scenarios • For these scenarios, need to examine: • Whether power control can help alleviate interference • Whether fairness is affected by power control • Whether the traditional Virtual Carrier Sensing (RTS/CTS exchange) can co-exist with power control

  3. In this work… • We conduct a set of experiments on an indoor wireless testbed • We focus on the interference between pairs of links • We identify 3 interference scenarios: • Overlapping • Neither power control nor RTS can improve performance • Hidden-terminal • Power control essential for fairness • RTS with power control degrades performance! • Potentially disjoint • Power control increases performance significantly • RTS with power control, however, results in lower throughput here as well

  4. Experimental set-up • Indoor wireless testbed • Nodes: 15 Soekris net4826 • Wireless: EMP-8602-6G Atheros AR5006 • MadWifi driver • Linux kernel v2.6, mounted over NFS • 802.11a for avoiding external interference

  5. Methodology • In our experiments we activate two links at a time • We observe the achieved throughput by each of the two links, for different power levels • Fully-saturated UDP traffic • iperf measurement tool • 30-sec back-to-back 1500-byte packets • Power is maintained at a constant level during each 30-sec experiment • After the end of the experiment, we vary the powers and start a new 30-sec session • Power levels: sequentially from 1 dBm to 16 dBm • Exhaustive search of different transmission power combinations (162) • We conduct experiments with and without RTS/CTS exchange

  6. Types of interference behavior • Overlapping case • The two links alwayscontend; power control not helpful • The channel between the two senders is typically better than the channel between sender and receiver

  7. Types of interference behavior (ii) • Hidden-terminal case • Most of the links under investigation belong to this category • Senders cannot sense each others’ tranmissions: PCS fails • This is not a problem if the strength of the desired signal is significantly higher than that of the interfering signal • Competition between signal andinterference • Fairness is consistently better along a diagonal (after a certainpower level)

  8. Types of interference behavior (iii) • Potentially disjoint case • Here, power control can greatly improve performance • May enable simultaneous transmissions • 15-16: 9 dBm • 22-31: 6 dBm • If power is different, the throughput is lower

  9. Without VCS With VCS Use of RTS/CTS • We repeat the experiments, with RTS enabled • Overlapping case with RTS • Worsened, due to the RTS/CTS transmission overhead

  10. Use of RTS/CTS (ii) • Hidden-terminal case with RTS • Consistently underperforms the plain vanilla CSMA in all considered scenarios! • Overall throughput is considerably lower • Fairness is also affected to a large degree ! Without VCS With VCS

  11. Use of RTS/CTS (iii) • Hidden-terminal case with RTS • A case where fairness is improved • However, RTS leads to large reduction in overall throughput Without VCS With VCS

  12. Use of RTS/CTS (iv) • Potentially disjoint case with RTS • RTS/CTS has a negative impact here as well • While the overall throughput is still higher than in the isolated link capacity, it is still lower than the achieved with the PCS alone • The regime of powers for achieving spatial reuse is also reduced • More precise power control is now required Without VCS With VCS

  13. Conclusion • Proper power control is beneficial in wireless deployments • The topology determines if power control will help • Power control improves throughput in potentially disjoint case, and fairness in hidden-terminal case • RTS/CTS cannot coexist with power control, while it degrades performance in indoor settings • Power control holds great promise for improving the performance of indoor wireless networks • Potential extensions of this work: • Import higher complexity, by activating more than two links at a time • Vary the sensing threshold as well

  14. Questions? Thank you

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