What is Ec/Io, How it is varied with traffic, Why Ec/Io is always negative

This is a key parameter of CDMA technology measure at mobile station. It shows signal strength of each sector individually. Now question is arises in our mind that signal strength can be measured with RSSI also then why Ec/Io is used because RSSI is sum of signal strength of all sectors received by mobile. To judge signal of each sector Ec/Io parameter is used. That’s why Ec/Io is used to decide handoffs.

Ec/Io is the ratio of pilot power to total power. Total power includes pilot channel power, paging channel power, sync channel power and traffic channel power.

Let’s consider following situation. Here pilot power is 2W and total power is 5.6W. Then Ec/Io is (2/5.6) and it is equal to -4 db (equation is 10* log (2/5.6)).

Traffic channel	2W	Io
Sync channel	1.4W
Paging channel	.2W
Pilot channel	2W

In following situation pilot power is 2W and total power is 9.6 W. Here Ec/Io is (2/9.6) and it is equal to -7 db (equation is 10* log (2/9.6)).

Traffic channel	6W	Io
Sync channel	1.4W
Paging channel	.2W
Pilot channel	2W

Why Ec/Io is always negative?

We can see that Ec/Io is ratio of pilot power to total power (including noise). Now pilot power is always less then total power and ratio value of these will always less than 1. Logarithm of any less than 1 value is always negative. This is the reason why Ec/Io is always negative.