Negative Ec/Io

[snabeel03]

Why Ec/Io is always negative in CDMA technology?

[s.sunilpal123]

I think it is just that the signal (S in SIR) in CDMA can be well beneath the noise level and still the receiver can correctly interpret & despread the signal to achieve the useful signal. That is because of the inherent processing gain in all CDMA technologies. A negative SIR is unheard of in GSM for exactly this reason: the absence of Processing gain....

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[s52d]

I think it is just that the signal (S in SIR) in CDMA can be well beneath the noise level and still the receiver can correctly interpret & despread the signal to achieve the useful signal. That is because of the inherent processing gain in all CDMA technologies. A negative SIR is unheard of in GSM for exactly this reason: the absence of Processing gain....

Pls add to my reputation if this helps!

Equivalence in GSM would be:
Ec is Energy of BCCH carrier
Io is Energy of all carriers + noise in GSM band, all 35 MHz.
Thus, Io is allways higher as Ec, and Ec/Io is negative.

In GSM, we filter out 200 kHz carrier by receiver filter.
In CDMA, we do same with descpreading and filtering.
On the filter output we have positive C/N ratio, thus commincation is possible.

BR
s52d

[dekili]

Multiplying by scrambling code at transmission side will spread signal energy in channel bandwidth (e.g. 5MHz). This will keep Ec/Io to be negative. Multiplying signal at receiver side, signal will shrink to original bandwidth keeping the energy received at channel bandwidth. Noise (interference from other users can be also modeled as thermal noise due to the fact that signals are uncorrelated) cannot shrink since noise as constant power spectral density so multiplying noise by scrambling code does not change its PSD.

[asdf1234]

Ec/Io = Ec / (Ec + I+N)

where I = Ec from other cell
N = noise

If I & N are 0, Ec/Io = 0

[da_manole]

Ec/Io is Always Negative
Because the Pilot channel power is always less than the total cell power, the ratio of the Pilot
power (Ec) to the total cell power (Io) is always less than one. Thus, when measured in decibels,
the value of Ec/Io is always negative.

Ec/Io
The quality of the received CDMA Pilot signal is measured in Ec/Io. This value is a measure of
the quality of the Pilot signal. The Pilot signal is called F-PICH in CDMA2000, and Common
Pilot Channel (CPICH) in UMTS. It is a reference overhead signal that is always transmitted
from the cell at the same power. These Pilot signals are used by the mobile for open loop power
control estimates, to help identify the cell/sector / Node B from which the mobile is receiving the
signal, and to help the mobile demodulate the Forward/Downlink signals.
Ec represents the energy in one chip of the Pilot signal.
Io represents the sum of all transmit power from a sector/ Node B and all interference received.
Because no spread spectrum processing gain is applied to this term, and no orthogonal coding, all
other channels are interference for the Pilot channel.
The ratio of Ec to Io is a measure of the quality or Signal-to-Noise Ratio of the Pilot signal. Note
that as the Base Station load increases, more channels are added, so more interference is
generated for the Pilot channel. This causes the Io to increase in power.

[dekili]

Ec/Io = Ec / (Ec + I+N)

where I = Ec from other cell
N = noise

If I & N are 0, Ec/Io = 0

If I and N are 0, which is never the case, Ec/Io is not zero!

[liukang]

Why Ec/Io is always negative in CDMA technology?

As you know:
Ec = Effect energy.
Io = Total energy and noise.
Ec/Io = 10.log[Effect energy / (total energy+noise)] < 10.log(1) = 0
So that Ec/Io always negative.

BR!

[Md.Moniruzzaman]

This is due to spreading of signal.Original Eb/Io (Energy per bit over Noise spectral density) is positive quantity but after spreading we get Ec/Io (Chip Energy over Noise spectral density) which is -ve one.
From our signal & system basic we know that while signal is spread its power decrease accordingly ,and vice-versa. Eb/Io=Ec/Io + PG

[asdf1234]

If I and N are 0, which is never the case, Ec/Io is not zero!

i never said it was the case. But what is the log(1/1)=?