1. Musical Instruments Connecting to a Mixer using 802.11 Tal Kesari & Shimon Korenman Advisor: Dr. Chen Avin

2. Outline Motivation Project Goal Background Related Work Our Solution Future Work

3. Motivation The world is becoming increasingly Wireless in all aspects of life. Musicians also aspire to get rid of the cables that restrict them. The available solution today is using simple analog radio communication. Disadvantage - it is prone to be affected by noises and interferences.

4. Outline Motivation Project Goal Background Related Work Our Solution Future Work

5. Project Goal To maintain wireless communication between several musical instruments and a central mixer.

6. Project Goal- cont. Crucial characteristics: Minimal Latency- hard real time (15ms). At least CD sound quality- wide bandwidth (44.1Khz sampling rate). Fairness- all instruments play concurrently and no starvation allowed.

7. Outline Motivation Project GoalBackground Related Work Our Solution Future Work

8. Background- 802.11 The prominent wireless protocol today is IEEE 802.11 (Wi-Fi). 802.11g operates at a raw rate of up to 54Mbps. There are two modes of operation - BSS & infrastructure. Collision avoidance protocol- CSMA/CA.

9. Background- CSMA/CA CSMA protocol: Station A wants to transmit- senses the line. If no other station is currently transmitting- transmit, else defer a random time. Collisions can still happen- won’t work for wireless due to hidden and exposed node problems. CSMA/CA protocol : Deferring for the duration in NAV. Decreasing wait time only while no carrier.

10. Background- Token Protocol Token Protocol allows fair communication in the network. Token is a small packet passed between the stations. Possession of the token grants the right to transmit. Each station can hold the token for a maximum period of time. For example: Token Ring.

11. Outline Motivation Project Goal Background Related Work Our Solution Future Work

12. Related Work “Real-Time Audio Transceiver Utilizing 802.11b Wireless Technology”. A wireless transmission between a guitar and an amplifier. Using programmable microcontroller ADCs and Wi-Fi cards. The major difference – concurrency.

13. Outline Motivation Project Goal Background Related Work Our Solution Future Work

14. Our Solution We looked for a solution that would answer all the demands listed. We chose to transmit over 802.11g because of its speed and bandwidth. But, it contradicts several of our demands: No fairness – CSMA/CA is best effort. High latency – CSMA/CA is slow.

15. Our Solution So, how do we solve it?

16. Our Solution We propose a software solution. Client-server based protocol using UDP sockets in C under Linux. Fairness is achieved by passing a token from the server to the clients. All elements work for a common goal and do not compete. Low latency is achieved by controlling the maximal token holding time.

17. Our Solution – the protocol Mixer (Server): Wait for instruments to register. Send acknowledgments to instruments Send Token to each instrument in its turn. Receive data and play it. Instrument (Client): Send registration request Receive acknowledgment When token received, transmit data else insert to buffer.

18. Outline Motivation Project Goal Background Related Work Our Solution Future Work

19. Is it a good enough solution? Minimizing delay further by sliming down the UDP packet. Examining the performance of the protocol. Adapting the program to a portable microcontroller.

20. Thank You!