Performance Verification of LMR Systems

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Performance Verification of LMR Systems
Using TIA TSB-88.3c Methodologies 2011APCO Western Regional Conference, Ontario, CA David Buchanan

TSB-88 History 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

What We Will Cover 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 Do We Mean by Coverage Boundary?

Yucaipa, CA Example of a coverage Boundary

Define Coverage! % 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

Why don’t we decide on a method to define coverage!
Start with signal level Higher value for Interference limited systems or Portable coverage -94 dBm -106 dBm Faded Threshold Static Threshold -116 dBm Faded Threshold is value for Desired DAQ in the presence of Multipath fading. Noise limited system for portables maybe assume -10 db antenna gain Inferred Noise Floor includes the Noise Figure of the Receiver -123 dBm Inferred Noise Floor

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

So How many Tiles? Estimate of proportions Tt = Z2pq/e2 Where:
Tt = number of test tiles Z = Standard Deviate unit (confidence level 97% = 1.881) p = Service Area Reliability (95% = .95) q = 1-p e = Sampling error allowance (e =2% = .02) And Tt >= 100

Example for Number of tiles
Tt = Z2pq/e2 Tt = *.95*(1-.95)/.022 = = 99% confidence level as recommended by TSB >100 so Service area needs to be divided into 594 equal area tiles Also for outside tests Tile size ≥ 100λ x 100λ but less than 2 km x 2 km

The “Greater Than” Test
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) 2 tests greater than and acceptance window greater than is simpler of the 2. There is an equation to determine different confidence levels. Not recommended to measure over more than 100 λ.

Does My System Pass? 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.

A Few Other Notes 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