1. Real-Time Caption Streaming over WiFi Network Balaji Vasu (vbalaji@cs.ucla.edu) Joseph Joswig (joswig@cs.ucla.edu) CS 218

2. Outline Project Description Assumptions Demo Results

3. Motivation for Caption Streaming Each student can visualize in real-time and store the captions of the ongoing lesson Useful in many real situations:  to help the comprehension of  foreign students, students with hearing impairment, or just as  a support to notes taking during classes (students can focus on the lecture)

4. Project Overview Speech recognition algorithm running in the central host Multicast transmission via IEEE802.11b from the central host (sender) to the devices (receivers) Receivers do not acknowledge receipt of packets

5. Streaming Protocol Instructor is equipped with a headset and an IEEE802.11b enabled station, running a speech detection software. The voice of the lecturer is captured by the headset, converted into a text file by the speech recognition software Sent via a IEEE802.11b multicast transmission to all the students. The lecturer’s host runs a client program which handles the multicast transmission Wirelessly connected to the receiving stations that run a server program able to receive the packets and display the speech in a real- time fashion.

6. Redundant Transmission Protocol Each multicast packet contains N fragments of spoken text. Fragments sent within a packet are determined by a sliding window protocol. First packet delivers P to P + 3, second P + 1 to P + 4 etc. Even if one out of 4 packets reaches the receiver, all the fragments would reach the receiver.

7. Redundant Transmission Protocol (cont’d) Greater the N, the greater the channel is robust to errors. Larger the N, the more bandwidth is wasted on redundancy. At the end of the lecture, receivers can ask for any missing packets from the host. These will be retransmitted over TCP.

8. Redundant Packet Protocol SS+1S+2S+3S+1S+2S+3S+4S+2S+3S+4S+5

9. Platform Choices Java  Operating System Independence  Easy to use networking tools. Speech Recognition  Sphinx  Dragon Naturally Speaking  IBM ViaVoice

10. Programming Notes Speech to text program writes to an ascii file, and holds a write lock on the file. N = 4, in this case, with results for other values of N shown later Packet size is 512 bytes + 4 bytes for sequence number. Each segment is 128 bytes.

11. Simulation Simulated program by pulling data from a text file. Measure the percentage of packets that different window sizes and different error rates. Calculate the number of packets that are lost during the broadcast. Simulated Error is much larger than anticipated actual transmission error.

12. Simulation Results

13. Remaining Issues PDA’s Robust Speech Recognition Program