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October 20, 2008

Comments

Harmeet

Hi,

I have the following design problem..

Hello,

I have the following design problem...

Assume the FCC has opened a band of spectrum for commercial use. The spectrum is centered around 3 GHz. Your company has decided to use this spectrum to deploy a wireless voice telephony service to
compete with the existing cell phone services. Your boss in this imaginary company has charged you with working out possible system designs, and deciding which to use. However, the spectrum has some strange constraints. Transmit power levels are limited to 2 Watts per RF carrier (so a base station could transmit more than this since it might have more RF carrier frequencies). The TOTAL bandwith available in this spectrum band is 2 MHz.

No other constraints are there. We can be fairly liberal in our assumptions.. Now i need to know what things that I can research to make this as detailed as possible. It is not going to be a thesis its just a design problem and I am required to write a paper listing all the different thing in which the goal can be achieved. I think the major part will be to determine which system design (CDMA, TDMA etc ) will be better suited for the problem.. kindly let me know any comments have on this.

Brough Turner

Harmeet, I can't offer to do your homework for you. :-) But let me point out a gap in your specification and then throw out some thoughts you might investigate...

First, you say 2 watts per RF carrier but then don't specify the bandwidth per carrier. Typically, power limits are specified in watts per Hz, KHz or MHz. If it's watts per carrier you have to specify the carrier width.

Other thoughts: You will have a hard time competing with 3G cellular operators with only 2 MHz total spectrum. The cellular operators typically have much more spectrum -- minimum 10 MHz for 3G UMTS. So competitively, you will need a lot of cell sites to achieve comparable capacity, not to mention needing more cell sites in order to achieve full coverage at 3 GHz.

For a design-from-scratch, the most efficient current technology is based on OFDMA and variations. Look at what's used in WiMAX and LTE. They are very similar and state-of-the-art. Including multiple input multiple output (MIMO) technology and that's likely to be the best you'll do with current semiconductor technology.

If you want to go out on a limb, it might be interesting to consider combining full power use of the permitted 2 MHz of bandwidth with ultra wideband transmissions below the noise floor of everyone else between 3 GHz and 10 GHz (or perhaps from DC to ultra-violet - just kidding...).

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