# help for Q function query

• Mar 14th 2010, 03:11 AM
moonnightingale
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
• Mar 14th 2010, 06:08 PM
mr fantastic
Quote:

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.
• Mar 15th 2010, 03:45 AM
moonnightingale
I have attached the solution.
Kindly tell me why he has written -2.33
• Mar 15th 2010, 05:35 PM
mr fantastic
Quote:

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.
• Mar 16th 2010, 09:18 AM
moonnightingale
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

• Mar 16th 2010, 12:20 PM
rubic
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
• Mar 16th 2010, 03:13 PM
moonnightingale
ur last statement stillnot clear