Kunal Amarnani, Ayush Bhardwaj, Angad Kumar Kapoor & Tejas Pargaonkar MULTIRADIO WLANS Kunal Amarnani, Ayush Bhardwaj, Angad Kumar Kapoor & Tejas Pargaonkar

Context, Problem Statement, Motivation Each version of 802.11 is assigned a spectrum of frequencies for use. The spectrum is divided into 20 MHz bands. Each band represents an orthogonal channel with an associated throughput. One wireless radio connects to one channel.

Context, Problem Statement, Motivation Study the issues with using multiple wireless radios from a single node. Measure the performance when multiple radios are used on each node. Attempt to solve any issues discovered when implementing multiple radios.

Context, Problem Statement, Motivation Determine why the aggregate throughput experienced when using multiple radios is not equal to the ideal expected throughput.

Key Project Milestones Set up a network – Accomplished Measure the aggregate throughput when utilizing all radios - Accomplished Determine why the aggregate throughput is not equal to the expected throughput - Accomplished Come up with solutions to solve the aggregate throughput problem - Accomplished Implement the best solution - Not-accomplished

Set up the Network Two computers were set up, each with a network card with 3 radios Access point and client setup Frequencies of 5.26, 5.28, and 5.3 GHz IP addresses of 10.10.10.x, 20.20.20.x, and 30.30.30.x

Commands used Iwconfig – Setup up radio configuration iwconfig ath0 essid "first" freq 5.26G rate 54M -Server iwconfig ath0 essid "first" rate 54M -Client Ifconfig – Setup IP configuration ifconfig ath2 30.30.30.1 netmask 255.255.255.0 -Server ifconfig ath0 10.10.10.2 netmask 255.255.255.0 -Client Iperf – Create UDP data streams. Measure throughput iperf -s -u -B 10.10.10.1 -p 3301 -i 1 -Server iperf -c 10.10.10.1 -u -p 3301 -b 65M -t 100 -i 1 -Client

Measure the Aggregate Throughput All 3 access points were listening while the 3 clients simultaneously transmitted UDP packets with 100 second intervals Ideal Throughput (Mbps) Observed 10.10.10.1 33.6 9.65 20.20.20.1 32 1.49 30.30.30.1 38.7 37.1 Aggregate 104.3 48.24

Figure 1. Orthogonal Channel Model The Problem Radios that use orthogonal channels should not theoretically suffer from interference. Radios that are physically close may experience interference due to power leakage.1 5.26 GHz 5.28 GHz 5.30 GHz Figure 1. Orthogonal Channel Model 1. Atul Adya, Paramvir Bahl, Jitendra Padhye, Alec Wolman, and Lidong Zhou, “A Multi-Radio Unification Protocol for IEEE 802.11 Wireless Networks”.

CSMA/CA Sender’s Side Power leakage occurs at the sender radios. Physical carrier sense detects power leakage as interference. The channels do not transmit data simultaneously. 5.26 GHz 5.28 GHz 5.30 GHz Figure 2. Power Leakage

CSMA/CA Receiver’s Side Power leakage occurs at the receiver radios. ACKed packets for one channel leak into received data packets of another. Data collision occurs

Recognizing the Problem All three channels were analyzed simultaneously with Wireshark. The analysis showed that the channels were not transmitting simultaneously. Radio 1 Radio 2 Radio 3

Proposed Solution (1) Structure loosely based on CSMA/CA protocol Assumptions: Disabled CSMA/CA at sender side Disabled ACK message at receiver side Perfect packet synchronization Ignoring multiradio hidden terminal problem

Proposed Solution (2) Setup: Wireless ad-hoc network Multiple nodes with variable number of radios

Proposed Solution (3) Sender Receiver RTS Step 1: Sending RTS RTS sent along channel 1 In the RTS, number of radios possessed by sender is stored Info of all the sender side radio and associated channels in 1 RTS Attempt to reserve multiple channels for transmission Sender Receiver RTS Radio 1 Radio 1 Radio 2 Radio 2 Radio 3 Radio 3

Proposed Solution (4) Sender Receiver CTS Step 2: Sending CTS CTS sent along same channel as before Informs sender of all the channel that are free for transmission sent Sender Receiver CTS Radio 1 Radio 1 Radio 2 Radio 2 Radio 3 Radio 3

Proposed Solution (5) Sender Receiver Data Data Data Step 3: Data Transmission All the channels that are identified as free for transmission are used simultaneously (possible due to disabling CSMA/CA) Sender Receiver Data Radio 1 Radio 1 Radio 2 Data Radio 2 Radio 3 Radio 3 Data

Proposed Solution (6) Sender Receiver SACK Step 4: Data Acknowledgement Selective ACK Sent from receiver to send letting sender know of packet loss or next expected packet (possible due to disabling ACK) SACK Sent along one path only Sender Receiver SACK Radio 1 Radio 1 Radio 2 Radio 2 Radio 3 Radio 3

Proposed Solution (7) Advantages of solution: Can support variable number of radios Can support sender/receiver pairs having different number of radios Allows for maximum utility of network as all possible channels are utilized

Proposed Solution (7) S2 S1 R1 R2 4 S2 S1 R1 1 1 2 2 3 3 4 2 1 4 R2 Here we can see both pair of sender/receiver being able to transmit data even though they have a different number of radios

Proposed Solution (8) S2 S1 R1 R2 4 S2 S1 R1 1 1 2 2 3 3 4 2 1 4 R2 Here S1 & R1 can only utilize channels 1 & 3 since 2 is being used by S2 & R2

Proposed Solution (9) Sender Receiver RTS ? ? Drawbacks: Multiradio hidden terminal problem As RTS with channel 1,2 and 3 information is being sent across channel 1, channel 2 and 3 are idle and unaware of this CTS/RTS transaction, therefore another node in the network can randomly use them since they are unaware of the CTS/RTS agreement Sender Receiver RTS Radio 1 Radio 1 ? Radio 2 Radio 2 ? Radio 3 Radio 3

Proposed Solution (10) Sender Receiver Data ? Data ? ? Data Multiradio wireless also manipulates itself when packets are not sent in perfect synchronization Sender Receiver Data ? Radio 1 Radio 1 Radio 2 Data ? Radio 2 Radio 3 Radio 3 ? Data

Conclusion Multiradio networks have great potential to increase network throughput substantially Main problem is the interference caused by the power leakage from radios in close proximity Main problem in implementing proposed solution was multiradio hidden terminal problem Unable to attempt milestone 5 due to lack of time

Questions?