Changes between Version 5 and Version 6 of U-Connect
- Timestamp:
- 02/11/2010 01:36:22 AM (7 months ago)
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U-Connect
v5 v6 7 7 problem, whereas existing protocols like Quorum and Disco are 2-approximation algorithms. Please refer to () for details. 8 8 9 = Protocol Overview=9 == Protocol Overview == 10 10 U-Connect is an unified protocol to address both the symmetric and asymmetric asynchronous neighbor discovery problems. 11 11 The intuition behind the protocol design is as follows. Consider a protocol in which a node picks a prime number ''p'' and stays active for ''1'' slot every ''p'' slots. Any two primes are by definition relatively prime with each other. Hence, two nodes choosing different primes will discover one another. If the nodes choose the same pair of 12 12 primes, discovery can still be ensured by each node staying active for slightly longer than half the prime period ''p''. 13 13 14 The protocol has been implemented on a custom designed light-weight, small and rechargeable mobile sensor-networking hardware platform called '''FireFly-Badge'''. In the implementation, the node listens at the slots that are multiples of ''p''. This operation is fundamentally ''Low14 The protocol has been implemented on a custom designed light-weight, small and rechargeable mobile sensor-networking hardware platform called [wiki:FireFly-Badge]. In the implementation, the node listens at the slots that are multiples of ''p''. This operation is fundamentally ''Low 15 15 Power Listening'' (LPL), where the listen period is 16 16 ''p'' slots. The node transmits continuously for ''{p + 1}/2'' slots for every hyper-cycle. This periodic transmission … … 19 19 to spread the packet transmission over multiple slots, thereby enabling much lower slot sizes. The operation is depicted in the figure below. 20 20 21 [[Image(operation.png)]] 21 [[Image(operation.png, 300px)]] 22 23 == Interoperability == 24 In applications where the mobile nodes use infrastructure support, 25 interoperability of the neighbor discovery protocol with the MAC 26 protocol used by the infrastructure nodes for data flows is a desired feature. 27 For example, the networks deployed as part of Sensor Andrew use BMAC as 28 the MAC protocol. 29 U-Connect achieves interoperability with LPL-based MAC protocols such as 30 B-MAC by transmitting for duration equal to BMAC's check-period, whenever a packet needs to be sent to an infrastructure node. Also U-Connect will be able to receive any BMAC packet 31 as long as the listen period of U-Connect is less than the 32 check period used by BMAC. 33 34 == Slot Non-Alignment == 35 In practice, slots will rarely be aligned since nodes run independently 36 and do not adjust for clock skews or set up a global time-reference. We 37 need to ensure that two nodes will discover each other regardless of how 38 their slots overlap. In U-Connect, when in LPT mode of operation, 39 an unmodulated preamble is transmitted for $\rho$ consecutive slots. 40 The actual data, which is the node id in our implementation, is sent at the end of this 41 preamble. Any other node that wakes up during this LPT will find the channel 42 busy and will receive the data at the end of the preamble. When this 43 happens, both nodes will attempt to transmit at the same time resulting 44 in a collision. To avoid collisions in our protocol a CCA check is done before transmitting. 45 Also, since the probability of two nodes being exactly phase-aligned to come in contact is low, we have not taken any explicit measures to overcome this.
