R3 – Wireless Broadcast System

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This is a system that consist of server and client. The server broadcast news data and the client can connect to the channel and get the data.

As the server system, we used a Linux machine (Ubuntu 8.04, kernel version 2.6.19) with Intel Core 2 Duo 2GHz CPU, 4G RAM and 320G HDD. We used IEEE 802.11.g as the communication media. The server system sends UDP data packets continuously via Channel No. 7 (2.442 GHz), where the size of a packet is 1024 bytes and the receiver address is not specified.

As  a client device, we used Nokia N810 PDA. This device is equipped with TI OMAP 2420 processor, 128MB DDR SDRAM, 256MB Flash memory, and IEEE 802.11.b/g network interface card. A client module listens on the channel, and selectively receives data packets from the channel.

Since this PDA is not originally designed to support selective tune-in on the wireless stream, we used the DFS (Dynamic Frequency Scaling) technique and the ‘flight mode’ for the energy-saving mode. During the doze period, the frequency of the CPU clock is changed to 800MHz from 2GHz and all communication devices are temporarily mounted off. Through these techniques, the power consumption rate of the PDA in the doze mode was reduced to 300W from 480W in the active mode.

For the data set to broadcast, we used the LA Times news articles. There are 163 documents, and the total size of them is 687KB. After eliminating stop words with the Porter Stemmer, we extracted 6387 distinct words and made an inverted list and an index tree. The numbers of buckets of the index tree, inverted list, and data stream are 230, 232, and 755, respectively.