Sunday, 25 October 2015

The differences of area coverage reliability between simulation softer and link budget

Incident Description (Incident Phenomena)
 
We get the cell radius from the link budget, and deploy sites in the simulation tool, and configure these parameters to the simulation software, and maintain these parameters consistent between simulation software and link budget, and do the network simulation, and outputs the result, but the result of simulation is different with what we design in the link budget.
 
Deploying the site based on the radius of 80% cell area reliability and 90% cell area reliability, the link budget table in Annex "FDD LTE Link Budget-80%" and "FDD LTE Link Budget-90%", and the link budget need to consider the Cell edge reliability, such as 80% cell area reliability corresponding with 60% Cell edge reliability, 90% cell area reliability corresponding 75% Cell edge reliability, as shown follow figures 1.
 
the relationship between Cell edge reliability and cell area reliability
 
Figures 1 the relationship between Cell edge reliability and cell area reliability

Assume the value of Shadowing Standard Deviation is 8 db, the 80% cell area reliability corresponds to the value Shadowing Margin is 1.4db, the 90% cell area reliability corresponds to the value Shadowing Margin is 5.4db,
In the simulation the SINR coverage of 90% cell area reliability is significantly poorer than 80% cell area reliability, but there are inconsistent the higher percent reliability get better coverage with the idea of networks design. As following figures 2 shown
 the comparing figure for SINR
Figures 2 the comparing figure for SINR
 
 
 Networking Environment
 Problem Cause Analysis
 
In the edge for one cell, due to the interference come from other cell power is greater than the noise, the SINR formula can be abbreviated as follows LTE link budget guide):
X% stand for the cells load, the last chapter had described two link budget, the loads are same in 80% cell area reliability and 90% cell area reliability. Site distribution is in accordance with the radius of the uplink budget, the site is intensive for 90% cell area reliability, and the MAPL for 90% cell area reliability is less than 80%, then in the cell edge 90% cell area reliability the serving cell received power is greater than 80% cell area reliability, and the interference from other cells is also greater than 80% cell area reliability. In addition, according to the ATOLL engineers feedback, in the calculation for SINR, the power of other cells don’t considered shadow fading, and interference further larger for 90% cell area reliability, because the Shadowing Margin of 90% cell area reliability than 80% cell area reliability 3db, so the SINR of 90% cell area reliability is poor than 80% cell area reliability.
Whether the SINR coverage can be improved to reduce the distance between the two sites in the same cell area reliability to achieve the higher reliable coverage? In this situation the serving cell power and interference cell power both are heightened because of the short distance, the SINR don’t be sure to increase or reduce. Simulating that situation using the Atoll simulation software, the SINR doesn’t be improved, as following figures 3 shown:
the comparing figure for SINR
Figures 3 the comparing figure for SINR
 Solution
 
Discussing with other colleagues, the CDMA simulation software don’t considered the edge of coverage in the initial, the simulation software do the statistics from area coverage, for example, 90% coverage. The link budget is considered from the point; the link budget adds additional path loss in order to increase the reliable coverage, so the simulation doesn’t need to consider that. But there is another problem, the simulation software have the options for Cell edge reliability, what’s means in the simulation for the cell edge reliability, if we consider the cell edge reliability, there will turn up the situation that the higher reliability will lead to the worse SINR coverage.
 At actual simulation, we need to combine with the strategy of the project to determine whether we need to consider the edge reliability. The other an important reference, we can calculate RSRP from the link budget for the cell edge, to compare with RSRP in the simulation at the same distance, make the simulation as possible as consistent with and link budget.

Budi Prasetyo

About Budi Prasetyo

All About LTE

Subscribe to this Blog via Email :