I am implementing real time signal transmission on a hardware platform. I want to transmit and receive a signal between two GSM antennas (900-1800 MHz), what should be my input sinusoidal signal such that the power level at Rx antenna should not exceed -15 dBm.
Please make use of Friis transmission equation to get an idea of receiving power.
Dear Vatsala,
Your question is about the link budget.
In order to determine the required transmit power Pt for a given power level at the receiver Pr, you have to know Pt, the transmit power, the transmit antenna gain, the carrier frequency, the distance between the two antennas, the path loss and the receive antenna gain. The path loss depends on the propagation model.
There are some wireless channel model, the line of site,the Rayleigh, the Rice and other model such as Nakagami-m model practical models.
For calculating the link budget please refer to the book:Software Defined Radio for 3G (Wireless Communications (Artech House))
by Paul Burns (Author)
Best wishes
Adding to what Dr Zekry described, to answer this question, you will have to make certain assumptions. You can then work backwards, from your maximum allowable power at the receiver's antenna connection, -15 dBm, back to the maximum allowable transmitter power.
The links in the chain, going backwards to the transmitter, would be:
1. Receive antenna gain
2. Propagation loss, which depends on the model you use and on the range you assume from transmitter to receiver. If you want to make absolutely sure you don't exceed -15 dBm at the receiver, you will have to postulate a minimum practical range to the cell tower, and here's some wonderful news, you should also use the free space propagation loss model. Why? Because at minimum range, chances are very good that you're well within line of site, with no obstacles in the way. That's what you need to ensure you never saturate receivers. So, the propagation loss model is simple.
3. Transmit antenna gain.
4. Loss in the lead from transmitter to transmit antenna.
So, transmitter power in dBm has to be:
-15 >= Pt + RxAntGain - PropLoss + TxAntGain - TxLeadLoss
You can solve for Pt, then convert that Pt figure, which will be in dBm, to watts.
Propagation loss in dB = 32.45 + 20*log(freq in MHz) + 20*log(dist in km)
where those are log base 10.
Note that the receive antenna gain may possibly be negative. Probably you should search around for reasonable, real world numbers, maybe looking at the spec sheets of different brands.
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