# Thread: help for Q function query

1. ## help for Q function query

I have got a solution of a question but i m unable to understand this equation

Q (a) > 99 %

so a < -2.33

i know Q function and know to read its table but how -2.33 has come here.plz explain

2. Originally Posted by moonnightingale
I have got a solution of a question but i m unable to understand this equation

Q (a) > 99 %

so a < -2.33

i know Q function and know to read its table but how -2.33 has come here.plz explain
What youve posted makes no sense. Please post the entire question, including the part where Q is defined.

3. I have attached the solution.
Kindly tell me why he has written -2.33

4. Originally Posted by moonnightingale
I have attached the solution.
Kindly tell me why he has written -2.33
The solution does not define any of the notation that is used. So, again, you are asked to provide the entire question.

5. The question is

In this problem we will explore the impact of different log-normal shadowing parameters on outage probability.Consider a a cellular system where the received signal power is distributed according to a log-normal
distribution with mean
μ dBm and standard deviation σψ dBm. Assume thereceived signal power must beabove 10 dBm for acceptable performance.

(a) What is the outage probability when the log-normal distribution has
μψ = 15 dBm and σψ = 8dBm?
(b) For
σψ = 4dBm, what value of μψ is required such that the outage probability is less than 1%, a typical
value for high-quality PCS systems?

Solution is

attached file

6. ## Q function query

1 - Q(a) < 0.01
1 + Q(-a) < 0.01
Q(-a) > 0.99

from table
-a > 2.33, which is same as a < -2.33

hope it helps

7. ur last statement stillnot clear