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Definition of Discovery Latency in PAC

This document discusses the definition and importance of discovery latency in PAC networks and explores different protocols and tradeoffs in energy consumption.

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Definition of Discovery Latency in PAC

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [ Definition of discovery latency in PAC] Date Submitted: [ December 3rd, 2012] Source: [Marco Hernandez] Company: [NICT] Address: [] Voice:[] Fax:[] E-Mail:[] Re: [In response to call for technical guidance document contributions TG8] Abstract: [ ] Purpose: [Material for discussion in 802.15.8 TG] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Marco Hernandez (NICT)

  2. Discovery Latency Definition • Discovery latency refers to the delay between the moment two active PAC devices are within communication range to the moment when they first discover each other. • The distribution of discovery latencies (fraction of discoveries vs discovery latency), as well as the tail of this distribution (worst-case discovery latency), are both important metrics for a neighbor discovery protocol. • The worst-case discovery latency determines the minimum amount of time two devices need to be in communication range to ensure discovery. Marco Hernandez (NICT)

  3. Study case • PAC networks are envisioned to be mobile and energy constrain. • Energy efficient discovery protocols for mobile networks is challenging and requires an adaptive tune of parameters such as inquiry duration and interval. • Indeed, constant inquiry intervals are optimal to minimize the discovery-missing probability, at the cost of high power consumption. • Tradeoff: energy consumption vs discovery-missing probability Marco Hernandez (NICT)

  4. Study case • A clear example is Bluetooth and Wi-Fi discovery. • Bluetooth is a low power radio, but device discovery is longer than Wi-Fi (active scanning): • ≈5 sec for Bluetooth vs ≈1 sec for Wi-Fi • Although Wi-Fi is known to be power hungry for mobile devices. • Caveat: Both discovery protocols consider limited mobility. Marco Hernandez (NICT)

  5. Study case II • Birthday discovery protocols • Asynchronous neighbor discovery for static ad-hoc networks • Quorum discovery protocol • 802.11 based multi-hop ad-hoc networks • Discovery latency: • In birthday, it is a function of the beacon/listen probability of each node. • In quorum, it is a function of a grid rows & cols choices (mxm) and group size m2 =intervals or slots. Each node can choose an independent duty cycle Marco Hernandez (NICT)

  6. Study case II • Choosing for birthday probabilities: pt=pr=0.05 (5% duty cycle) and for quorum: m=40 (5% duty cycle) • The discovery latency CDF with 50% fraction of discoveries for: • 4.7 sec discovery latency in quorum • 2.81 sec discovery latency in birthday • Caveat: birthday is a random algorithm that does not provide predictable rendezvous times and quorum specifies a global constant for all devices duty cycle. Marco Hernandez (NICT)

  7. PAC case • As PAC networks are relative new (different requirements respect to other technologies), we cannot specify discovery latency values for the TGD. • The previous examples may give a guideline to proposers based on other current technologies and proposals. • However, we can give the definition of discovery latency as: “Discovery latency refers to the delay between the moment two active PAC devices are within communication range to the moment when they first discover each other. The worst-case discovery latency determines the minimum amount of time two devices need to be in communication range to ensure discovery.” Marco Hernandez (NICT)

  8. References • [1] M. Mcglyn, S. Borbash, “Birthday protocols for low energy deployment and flexible neighbor discovery in ad hoc wireless networks”, MobiHoc 2001. • [2] Y. Tseng, et.al., “Power saving protocols for IEEE802.11-based multi-hop and ad-hoc networks”, Joint conference of the IEEE computer and communication society, 2002. • [3] Google: Bluetooth Special Interest Group. Marco Hernandez (NICT)

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