Dynamic channel allocation in wireless ad-hoc networks Anup Tapadia Liang Chen Shaan Mahbubani
Background networks have experienced a tremendous growth in last few years networks have experienced a tremendous growth in last few years Access points work on a single static channel Access points work on a single static channel Contention & congestion Contention & congestion Low throughput due to inefficient channel allocation Low throughput due to inefficient channel allocation Presence of other interfering networks impacts performance Presence of other interfering networks impacts performance
Channel variations Traffic on Thursday 26 th April at Calit2 6 th floor
CogNet testbed setup at Calit2 CogNet is supported by NSF SGER-CogNet
CalNode Seokris 4521 Seokris 4521 Linux 2.6 Linux 2.6 Iperf Iperf Monitor Card Monitor Card Atheros w/ Mad Wifi Data Card Data Card Prism b Wired to UCSD network Wired to UCSD network
What may affect the channel performance? Interfering Traffic Interfering Traffic Packet count Packet count Rate Rate RSSI RSSI Other interference Other interference Bluetooth Bluetooth Cordless phones Cordless phones Microwaves Microwaves Our Focus
Challenge How do we select the channel that permits maximum throughput in an ad-hoc network ? How do we select the channel that permits maximum throughput in an ad-hoc network ?
Channel Controller (Java & C++) SQL Query Decision Logic Channel Switcher Iperf Test Scheduler CogNet DB Towards Nodes Connection Stub iwlib WiFi NIC WiFi NIC AP
Software Architecture Decision Logic Channel Switcher Channel Controller Connection Stub iwlib WiFi NIC WiFi NIC AP Connection Stub iwlib WiFi NIC WiFi NIC AP Connection Stub iwlib WiFi NIC WiFi NIC AP Connection Stub iwlib WiFi NIC WiFi NIC AP
Channel Switch Connection Stub Driver H/W Connection Stub Driver H/W iwlib Decision Logic Channel Switcher Channel Controller Probe Reply Switch Channel Switch Channel Channel Switch Message
Factors selection test Tx 15 sec silence
Factors affecting throughput :RSSI
Effect of our transmission rate on others RSSI Effect of our transmission rate on others RSSI
Factors affecting throughput : Rate
Factors affecting throughput :Packets
Channel Selection Algorithm We select the least interference channel dynamically We select the least interference channel dynamically Channel interference metric Channel interference metric where C i is the interference metric of channel i, N ip, N iq are the number of other packets captured at node p and q on channel i in a 120s window. where C i is the interference metric of channel i, N ip, N iq are the number of other packets captured at node p and q on channel i in a 120s window. Selected channel j, s.t. Selected channel j, s.t.
Experiment: Process Send a 3MB file using each scheme Send a 3MB file using each scheme 15s pause interval in between each transfer 15s pause interval in between each transfer Repeat Repeat SRD 15 sec silence 120 sec query window
Background Traffic
Results: Dynamic v. Static
Results: Dynamic v. Random
Results: Random v. Static
Channels picked
Results: Summary SchemeDynamicStaticRandom Avg Rate 4042 kbps 2100 kbps 2742 kbps Average Transfer Time (3MB) 6.08s11.7s8.96s
Effect of channel switching time t d = Tx time on dynamic channel t s = Tx time on static channel t c = Time to change r d = Rate on dynamic channel r s = Rate on static channel f = Size of file Our implementation
Future work Multi hop links Multi hop links More complex allocation schemes More complex allocation schemes Finer data granularity and patterns Finer data granularity and patterns Improve channel switching time Improve channel switching time Effect of frequency of channel switching Effect of frequency of channel switching
Conclusions Dynamic performed better than Static and Random Dynamic performed better than Static and Random Static on a free channel provides upper bound on Dynamic performance; improvements come when static channel is loaded (channel usage varies over time) Static on a free channel provides upper bound on Dynamic performance; improvements come when static channel is loaded (channel usage varies over time)