Re: dBm

Ed Casas (edc@ece.ubc.ca) Wed, 12 Apr 2000 11:08:12 -0700 

Date: Wed, 12 Apr 2000 11:08:12 -0700
From: Ed Casas <edc@ece.ubc.ca>
Subject: Re: dBm



On Wed, Apr 12, 2000 at 10:41:27AM -0700, sergio gonzalez wrote:

> In the solutions handout for assignment #1, on the solution for problem
> 3.16, it is indicated that the threshold (gamma)=noise_floor(dBm)+SNR(dB).
> Is it really correct to add dBm to dB?. 

Yes, this is correct.  Values in dB are dimensionless so the
result will be in dBm.  In linear terms we are multiplying
milliwatts by a (dimensionless) ratio.

> Also, on the next page (39) of the solutions set, it shows the equation:
> 
> Pr(dmax)=Pr(d0)[dBm]-10 x n x log (dmax/d0), whereas in the textbook, eq.
> 3.68 (pag 102) shows the same equation with a "+" sign, not a "-". 
> 
> Same questions apply for solution of prob. 3.17

The sign in the above equation is correct (the received power
should decrease with increasing dmax).  However, if the ratio is
d0/dmax then the opposite sign would be used.

-- 
Ed Casas   edc@ece.ubc.ca   http://casas.ece.ubc.ca   +1 604 822-2592