base on the shannon capacity limit,dicuss the possibility of transmitting information when siganl is lower than the noise? some ways of trasmitting would be be spreading the specturm,using reed coding method. what are some other ways to transmit information when signal is lower than the noise

# transmitting information when signal is lower than the noise

Started by ●January 7, 2006

Reply by ●January 7, 20062006-01-07

"omg" <jimmybai123@yahoo.com> wrote in message news:_JCdncegjus_ESLeRVn-pQ@giganews.com...> base on the shannon capacity limit,dicuss the possibility of transmitting > information when siganl is lower than the noise? > > some ways of trasmitting would be be spreading the specturm,using reed > coding method. > > what are some other ways to transmit information when signal is lower than > the noiseOne very obvious way is just to repeat the information until it finally gets through. Best of Luck - Mike

Reply by ●January 8, 20062006-01-08

Hi The shannon capacity limit is known as: C =1/2 * log2(1 + Pxx/Pnn) bits/channel use where C is the capacity, Pxx is the average signal power and Pnn is the average noise power per channel use. If the channel bandwidth is W, then during T seconds we have 2WT parallel channels. So the total capacity is multiplied by 2WT, CD = 2WT* 1/2 * log2(1 + Pxx/NoW) bits/channel use where we used NoW instead of Pxx. No is the spectral density of the noise having a bandwidth of W Hz. In the limit T -> Infinity C = lim (T->oo) (CD/T) = W*log2(1 + Pxx/NoW) bits/sec. The noise power Pxx maybe expressed as Pxx = Eb*Rb where, Eb is the energy per bit, and Rb is the bit rate. Now, using optimal coding we can have Rb = C. Therefore, C = W*log2(1+Eb/No * C/W) We can now express Eb/No as: 2^(C/W) - 1 Eb/No = ------------------ (C/W) and in the limit of (C/W) -> 0, we get Eb/No = ln(2) = -1.6 dB. That is, if we have an infinite bandwidth and we use an optimal coding scheme, we can communicate errorless when the bits energy is 1.6 dB less than the noise energy !!! Tsachi.