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Implications of Power Control in Wireless Networks: A Quantitative Study

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

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Implications of Power Control in Wireless Networks: A Quantitative 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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