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On Collision-Tolerant Transmission with Directional Antennas

On Collision-Tolerant Transmission with Directional Antennas. Hong-Ning Dai, Kam-Wing Ng, Min-You Wu. Outline. Introduction Analytical models and the probability of successful transmission Lightweight MAC protocol Conclusion. Motivation. Directional antennas can improve network capacity

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On Collision-Tolerant Transmission with Directional Antennas

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  1. On Collision-Tolerant Transmission with Directional Antennas Hong-Ning Dai, Kam-Wing Ng, Min-You Wu

  2. Outline • Introduction • Analytical models and the probability of successful transmission • Lightweight MAC protocol • Conclusion

  3. Motivation • Directional antennas can improve network capacity • Most of MAC protocols with directional antennas are based on RTS/CTS mechanism • The effectiveness of this mechanism with directional antennas is still questionable • Our paper focuses on the questions • How does the success transmission probability vary with the narrower beamwidth of directional antennas? • How effective is the RTS/CTS mechanism in wireless networks using directional antennas?

  4. Analysis Model • Antenna Model • A steerable beam antenna (beamwidth θ) • Antenna gain Gd • Interference Model • Transmission range Rt • Interference range Ri (1) where σis SINR threshold (under two ray ground model) (2)

  5. Directional Transmission and Directional Reception (DTDR) • There are four transmission and reception modes: • Omni-directional Transmission and Omni-directional Reception (OTOR); • Directional Transmission and Omni-directional Reception (DTOR); • Omni-directional Transmission and Directional Reception (OTDR) • Directional Transmission and Directional Reception(DTDR) • DTDR has the smallest interference area compared with OTOR, DTOR and OTDR. Only DTDR is considered in this work

  6. Related Work • Many studies focus on MAC protocols with directional antennas • Basic-DMAC, Circular-DMAC, DVCS, ToneDMAC, etc. • Capacity analysis on performance evaluation of directional antennas • However, there is no work that studies the connections between the beamwidth of directional antennas and interference, especially for narrow-beam antennas.

  7. Probability of Successful Transmissions • The probability that a successful transmission is equal to the probability that no nodes can cause collisions with a receiver • (3) where p is the probability that a node begins to transmit, • (4) • Under DTDR, the successful transmission probability is quite high when the beamwidth is lessened enough. ρthe node density

  8. Probability of Successful Transmissions (cont.) • When θ≤π/12 (i.e., 15°), the success probability is always above 98% • the transmission under DTDR is less vulnerable to interference when the beamwidth is narrow.

  9. Lightweight MAC protocol • We propose a lightweight MAC scheme denoted as Basic Directional Transmission and Directional Reception (BAS-DTDR) • This protocol turns off RTS/CTS • The competitor is RTC/CTS based Directional Transmission and Directional Reception (RTS-DTDR)

  10. Throughput is calculated by the proportion of time that a node spends transmitting data frames successfully on average We adopt a discrete Markov chain model Performance Evaluation

  11. Numerical Results (short data frame) N=10 N=20 N=30 N=40

  12. Results Analysis (short frame) • With the increased node density, both RTS-DTDR and BAS-DTDR degrade. • The BAS-DTDR has a much higher throughput than RTS-DTDR protocol. The peak value of BAS-DTDR is almost 20% higher than that of RTS-DTDR. • Reason: When the beamwidth is very narrow, the interfering nodes are so sparse that they cause nearly no collisions at that time.

  13. Numerical Results (long data frame) N=10 N=20 N=30 N=40

  14. Results Analysis (long frame) • Both RTS-DTDR and BAS-DTDR perform well under a narrow beam (e.g., beamwidth less thanπ/15) • BAS-DTDR still has a higher throughput than RTS-DTDR because it gets rid of the bulky RTS/CTS mechanism. • When the beamwidth is increased further, the collisions caused by interfering nodes become remarkable, both the throughput of RTS-DTDR and BAS-DTDR degrades. • There exists a trade-off between the arisen interfering nodes and the overhead of control frames

  15. Discussion • When the beamwidth is narrow enough, a transmission can yield a high success probability. • Under DTDR, if the beamwidth is less than π/12 (i.e., 15°), the probability of a successful transmission is greater than 99% • The transmission under this situation can be regarded as a collision-tolerant transmission (the collision probability is quite small) • Under this condition, the collision avoidance mechanisms, such as RTS/CTS, are not necessary to be used.

  16. Conclusion • This paper studies the performance wireless networks using directional antennas with a narrow beam. • The preliminary results show that RTS/CTS may not be necessary if a narrow beam antenna is used.

  17. Thank you

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