a simple neighbor discovery procedure for bluetooth ad hoc networks miklós aurél rónai and eszter...
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A Simple Neighbor Discovery Procedure for Bluetooth Ad Hoc Networks
Miklós Aurél Rónai and Eszter Kail
GlobeCom 2003
Speaker: Chung-Hsien Hsu
Presented at TKU Group Meeting
January 29, 2004
Outline
Introduction Simple Neighbor Discovery Procedure Performance of the SND Procedure Comparison of SND and Inquiry Conclusion
Introduction
Current Bluetooth neighbor discovery procedure Three weaknesses:
Taking a lot of time. Transmitting data simultaneously with the inquiry is very
inefficient. Assuming asymmetric roles is not well suited to an ad hoc
network of peer nodes.
Simple Neighbor Discovery Procedure
Main concept: Every node sends beacon messages regularly at
pseudo-randomly selected slots. Containing BD_ADDR and clock
A node wants to discover or update information about its neighbors:
To perform Scanning
Simple Neighbor Discovery Procedure- Sending beacon packets
Priority: Beacon packet > Data and ack packets
Simple Neighbor Discovery Procedure- Sending beacon packets
Beacon Containing BD_ADDR and clock. Predictable. (option)
Packet loss: Automatic Retransmission Query (ARQ) mechanism.
Not every Bluetooth frequency is used as beacon frequency.
To ensure faster discovery of nodes. Be sent with one of the 63 DIAC access code.
The nodes are aware of SND.
Simple Neighbor Discovery Procedure- Scanning
Scanning Objective
To discover the neighbors. To update the status information about its neighbors.
The length and the timing of the scan periods are not fixed.
Randomly selects frequencies for scanning. During a scan period the node listens only on one frequency.
Simple Neighbor Discovery Procedure- Scanning
Performance of the SND procedure
Environment: A discrete event driven. Simulator: Plasma (object oriented) Nodes: 2 The interval between scanning periods: 0 ~ 1000 slots Scanning duration: 10 slots Frequency used for scanning: 32 channels
Performance of the SND procedure - Experiment 1
If a node sends beacons more often,the probability of discovery is higher.
Performance of the SND procedure - Experiment 1
The reception of a beacon packet at a scanning node is successful:
errbcn
s
BCN
PT
T
NP
1
21
11
The number of beacon and scanning frequencies.
The length of a timeslot.
Beacon period length of the node performing the neighbor discovery.
The probability of interference occurs.
Performance of the SND procedure - Experiment 1
The reception of a beacon packet at a scanning node is successful:
errbcn
s
BCN
PT
T
NP
1
21
11
The probability of using the same frequency.
The probability that the beacon packet cannot be detected.
The probability that the beacon packet be detected.
The probability of having received the beacon successfully.
Performance of the SND procedure - Experiment 1
The probability of discovering:
SCAN
tot
T
T
BCN
SCANdisc P
T
TP
111
The period of a node performs scanning.
The beacon period of a neighbor node sends a beacon.
The total amount of time spent with scanning.
Performance of the SND procedure - Experiment 1
The probability of discovering:
SCAN
tot
T
T
BCN
SCANdisc P
T
TP
111
The probability of having a beacon in a scan period.
Performance of the SND procedure - Experiment 1
The probability of discovering:
SCAN
tot
T
T
BCN
SCANdisc P
T
TP
111
BCN
tot
T
TP
disc eP1
1
Performance of the SND procedure - Experiment 1
2.9s
5.8s
99%
90%
Performance of the SND procedure - Experiment 2
Analyzing 2 different kinds of scanning schemes: Deterministic scanning periods. Random scanning periods.
Performance of the SND procedure - Experiment 2
Comparison of SND and Inquiry
Comparison of SND and Inquiry
Four difference: Inquiry messages vs. beacon packets. Asymmetric roles vs. equal roles. Deterministic vs. probabilistic. Guarantees 100% probability of the discovery in a
fixed time interval vs. trade-off between the discovery time and overhead.
Comparison of SND and Inquiry
Comparing procedures in two case: Asymmetric roles. Symmetric roles.
Comparison of SND and Inquiry - Asymmetric roles
Wake-up period 16 slots
64 slots
10 slots
Comparison of SND and Inquiry - Asymmetric roles
Comparison of SND and Inquiry - Symmetric roles
Comparison of SND and Inquiry - Symmetric roles
Conclusion
Proposed a Simple Neighbor Discovery procedure: Well suited to systems where peer nodes are
communicating. Flexible mechanism. Be performed with low overhead during data
transmissions. Taking less time than the Bluetooth inquiry. Be configurable in the trade-off between discovery time
and overhead.