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11/12/2005: "Thoughts on system block diagram and flow of project"
After doing some research in Telecommunication Breakdown by C. Richard Johnson Jr. and William A. Sethares, I think there needs some revision to the system level block diagram that is being currently worked on:
The transmitter portion of the system block diagram is almost correct. The level of each block is not quite the same but it shows the dataflow through the system. Pulse shaping, if anything, could be added before the QAM modulator to make better use of the bandwidth of each channel. The need for this will depend on the implementation of OFDM and needs to be researched.
The transmitter needs a couple of additions, depending on the amount of corruption that is used in the channel model. Initially we should have complete control over the channel model used. A complete model would add a varible gain/attenuation, delay due to the channel, multipath interference, and interference from other sources. Once an ideal transmitter/receiver is working, these interferences will be added one at a time. The most important interference is the delay of the signal.
Delaying the transmitted signal will make synchronization necessary in the receiver. This is a major part of the project. The block diagram already shows carrier synchronization. This will align the phase and frequency of the transmitter and receiver. However, there are two additional forms of synchronization that need to be considered. These are symbol synchronization and frame synchronization. Symbol synchronization is sampling each pulse at the right moment to ensure the data is extracted from the pulse most accurately. This will extract the 1s and 0s out of the stream. Frame synchronization is knowing when the messages stops and ends in these 1s and 0s. This is important because an offset of just one bit will throw the whole message off. This could be implemented by looking for a known sequence, but there are issues that need to be considered with this also.
After the project works with the channel model in place with all the necessary corruption models, it can be replaced with running the signal out through the D/A converter and back in through the D/A converter. Various corruptions can be done between the D/A and A/D converters, eventually targeting radio frequency circuitry and possibly an antenna.
Preliminary steps/phases for the project can be summarized below (assuming full project completion):
1. Research transmitter/receiver design
2. Design and simulate an ideal transmitter/receiver pair (no channel corruption) and implement on DSP board.
3. Add delay to the channel model and get the 3 levels of synchronization working in simulation. Implement on DSP board.
4. Add other channel corruptions (gain/attenuation and multipath). Verify operation of radio in simulation and on DSP.
5. Remove channel model and run signal through D/A and A/D. Verify operation of radio on DSP board.
6. Introduce interference to physical signal and verify operation.
7. Procure RF circuitry and look into actual wireless transmission.