non-ergadic channel
insatiable said:
hi, all
we use the shannon capacity and outage capacity in different case. can anyone talk about what decides the channel is ergodic or no-ergodic. is it the propagat environment or others?
thanks
Hi,
As many people said above, ergodic channel has a long term constant bit rate. Actually, guys who know random process will say that erogodic channel has same time and ensemble average. When we say the time average and the ensemble average, we have to begin from the observation with time. So ensemble means a set of signals observed, and time average means average for oberving time. Anyway, most of nature events (e.g channel) do not have ergodic property, but we should assume it to calculate the some results.
For example, you know, there are several channels the great have defined. The channel properties are different according to the environments, and it can be represented by the channel gain roughly, but the channel gain that we use is usually the function of time.
In the case of erogdic channel, the channel has constant capacity at the constant rate since the long term average of channel gain is constant.
However, in the case of non-ergodic channel, the channel gain is not the function of time, so that we can not say constant capacity such as shannon's.
Another important thing is the probability of the special rate. If a certain channel has the static characteristic at the special rate, or we can make such a condition(e.g. quasi-static channel), the capacity of that channel can be measured with special rate. That is outage probability.
It is all about what I know... please let me know my fault. Thanks.