# Multi-tone carrier wave

Hi,

I know that USRP can send out carrier wave at one frequency. For
example, a
carrier wave at frequency 902MHz. The carrier wave sent is
sin(2pi902MHzt). Can we send a carrier wave at three frequencies? For
example, a carrier wave at frequency 902MHz, 915MHz, and 928MHz. The
carrier wave I want to send
is sin(2
pi902MHzt)+sin(2pi915MHzt)+sin(2pi928MHzt). Is
multi-tone
carrier wave feasible given USRP’s hardware? How could I implement this
on
USRP? Thanks.

Pengyu

You can add three sine waves and send them using a single carrier.
However,
in this approach, the separation of the sine wave frequency components
will
be limited by the sampling rate.

Let’s assume that you can obtain a 20 MS/s sampling rate in your system.
You can cover 10 MHz frequency band with this sampling rate. If you use
a
carrier frequency of 902 MHz, you can send different sine waves up to
912
MHz frequency in this approach.

Thanks,

Nazmul

On Thu, Aug 2, 2012 at 4:51 PM, pengyu zhang [email protected]
wrote:

Pengyu

[email protected]

Electrical & Computer Engineering
Wireless Information & Networking Laboratory
Rutgers, USA.

Also, remember that USRPs use quadrature down-conversion, so if you set
the
sample rate to 20 MS/s, you can see 20 MHz, not 10 MHz.

Cheers,
Ben

Nazmul – Thanks very much for pointing sampling rate out. Hope I
understand correctly. Sending carrier wave at three frequencies is
feasible
on USRP. However, the gaps between carrier wave frequencies are
determined
by receivers’ sampling rate. If the receiver has 20 MHz sampling rate,
the
gaps between carrier wave cannot be larger than 10 MHz (or 20 MHz as Ben
suggested).