Performance Verification of LMR Systems

Using TIA TSB-88.3c Methodologies2011APCO Western Regional Conference, Ontario, CA

David Buchanan

This series of documents was prepared in response to requests from APCO, LMCC and the NCC

These organizations recognized that new technologies and the drive for more efficient use of spectrum required better methods for frequency coordination.

TSB-88 also covers:◦ Independent Methods of Performance Modeling◦ Propagation and Noise

TSB-88 History

Area Coverage Covered Area Reliability Delivered Audio Quality (DAQ) Mean and Median Signal Levels and other

ugly statistical terms Outdoor Coverage testing Developing a test methodology to verify

system performance

What We Will Cover

What Do We Mean by Coverage Boundary?

Example of a coverage Boundary

Yucaipa, CA

% of the Area? % of the Area with X% of Confidence What level of signal? Faded or not faded? What % of time Why do we need all these statistics? Unfortunately radio propagation is not

constant over time and area It can only be characterized using statistics

Define Coverage!

Start with signal level

Why don’t we decide on a method to define coverage!

Inferred Noise Floor -123 dBm

Static Threshold-116 dBm

Faded Threshold

-106 dBm

Higher value for Interference limited systems or Portable coverage

-94 dBm

We need to divide our coverage area into tiles to test for the signal level throughout the coverage area

Test Tiles

Estimate of proportions Tt = Z2pq/e2

Where:Tt = number of test tilesZ = Standard Deviate unit (confidence level

97% = 1.881)p = Service Area Reliability (95% = .95) q = 1-pe = Sampling error allowance (e =2% = .02)And Tt >= 100

So How many Tiles?

Tt = Z2pq/e2

Tt = 2.2362*.95*(1-.95)/.022 = 5942.236 = 99% confidence level as

recommended by TSB-88594>100 so Service area needs to be divided

into 594 equal area tilesAlso for outside tests Tile size ≥ 100λ x 100λ

but less than 2 km x 2 km

Example for Number of tiles

We now need to test each tile one time to determine the signal level

How do you test outdoors? You need to measure 50 subsamples to produce

a 90% confidence level that the measured value is within +/- 1 dB of the true value. Also the subsamples should be measured over 40 wavelengths. Use the median value of these measurements for each tile.

A tile passes if the measured value is >= to the CPC value (level from slide 7)

The “Greater Than” Test

To find out divide the number tiles that pass by the total number of tiles. Example: 594 total tiles and 580 passed = .976 or 97.6 %. If your criteria was 97% area coverage – the system passes. If not your vendor has some problems.

You should also do subjective voice checks for analog systems particularly for simulcast systems as they can show good levels but not be optimized in the overlap areas. For digital systems measure the bit error rate to check for voice quality.

Does My System Pass?

Use an automated system for the testing Don’t mix mobile and portable testing if the

service areas differ Not all tiles may be accessible for testing and

should be excluded Some tiles may be critical to have coverage

and those should be noted to the vendors before system design

There are methods for indoor coverage testing and mobile data system testing in the document

A Few Other Notes