# What will it happen when the outage occur?

I saw this explanation about outage probability,it said: it is the probability that an outage will occur within a specified time period.

So what will it happen when the outage occur?

1. stop transmitting signal?

2. keep transmitting signal, but the information will be wrong easier?

• In which system does this outage occur? – Olli Niemitalo May 29 at 6:48
• Shineele, your question can't be answered, because all that is defined is that there is an outage. Not why that occurred, or what someone does. It's really that simple. – Marcus Müller May 29 at 7:28
• As with at least one of your other questions, if a paper doesn't defined reasons or forms in which something happens ("outage", "offloading"), it might simply be irrelevant to the paper in question. Maybe it's not, but then most likely, it's defined somewhere else in the paper. – Marcus Müller May 29 at 7:30
• In communication parlance, outage typically refers to a state where a realiable transmission from source to sink is not possible anymore, e.g., since the communication link became to weak (think of fading or blockage). Does this mean a transmission error? Typically yes, unless the receiver was good at guessing or enough redundancy was added to correct a short burst of outage. Does this mean the transmitter stops? Typically not immediately, since the transmitter has to be made aware of the interruption, which requires some signalling (or lack thereof that will become noticed after a timeout). – Florian May 29 at 13:52
• @Florian this is a good answer – shineele May 30 at 1:44

The outage probability of a communication system is defined as the probability that the transmission rate exceeds the capacity of the channel, which is defined as the maximum transmission rate that can be achieved with sufficiently low probability of error. Mathematically

$$\texttt{P_O} = \text{Pr}\left[\texttt{R} > \texttt{C}\right]$$

where $$\texttt{R}$$ and $$\texttt{C}$$ are the transmission rate and the capacity of the channel, respectively. This can be translated in terms of signal-to-noise ratio (SNR) by noting that

$$\texttt{C} = \log_2(1 + \texttt{SNR})$$

Which means that

$$\texttt{P_O} = \text{Pr}\left[\texttt{SNR} < \underbrace{2^{\texttt{R}} - 1}_{\texttt{SNR}_{\text{th}}}\right]$$

The above equation says that if the $$\texttt{SNR}$$ of the signal falls below a certain threshold $$\texttt{SNR}_{\text{th}}$$, then the system will be in outage.

So, what does that mean? From the beginning we said that outage probability by definition means that the transmission rate of the system exceeds the capacity of the channel, which means that the transmission cannot be decoded with sufficiently low probability, because the capacity is the maximum rate that can be decoded with sufficiently low probability of error using "some" coding and we exceeded that maximum rate.

What happens to the transmission in that case? If the transmitter keeps transmitting, important resources like transmission power and channel bandwidth will be wasted for nothing. So, it is better for the transmitter not to transmit.

In communication parlance, outage typically refers to a state where a realiable transmission from source to sink is not possible anymore, e.g., since the communication link became to weak (think of fading or blockage).

Does this mean a transmission error? Typically yes, unless the receiver was good at guessing or enough redundancy was added to correct a short burst of outage.

Does this mean the transmitter stops? Typically not immediately, since the transmitter has to be made aware of the interruption, which requires some signalling (or lack thereof that will become noticed after a timeout).