Supporting the Department of Homeland Security

Sunday, 12 February 2012

RESOURCE CENTRE

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Government Security, Technology

1 March 2010

How Motorola’s Federal Technical Centre handles radio support for new P25 digital radio systems, while ensuring top-notch radio communications for federal agencies.

With the deployment of new digital radio technologies like P25, radio support operations are faced with new requirements for testing and validating these radios.

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SPOTLIGHT

Using the latest methods for testing and aligning radios, the Motorola Federal Technical Centre (FTC) in Lanham, Maryland provides dedicated and continuous support for federal agencies. Equipped with state-of-the-art processes and systems, this centre provides rapid response for repair, maintenance and upgrades of the nation’s federal radio operators.

With new P25 digital radios, our primary focus is to quickly verify the reported issue, perform preventative maintenance and upgrade radio firmware. The first step is to triage the radio and then deal with the issue in the most appropriate manner.

Using a unique triage process, the centre uses a combination of non-technical personnel, computer systems and test instrumentation to sort and speed the initial determination of what needs to be fixed in the radio.

The incoming process is the most critical to efficient processing of the radio equipment received. During this process, the radio is logged into the service facility, inspected and sorted into groups. This sorting process allows for the most efficient use of personnel and speeds response time through the centre.

Experienced technicians look at a variety of performance indicators to determine whether the radio meets rigid OEM specifications and conforms to the P25 standard. This activity takes about 75% to 80% of the experience technician’s time and is critical to the overall operational performance of the radio.

While efficiency is important, performance is the primary objective for the FTC. The P25 digital radio standard includes a number of parameters to verify the digital performance of the radio‘s RF transmission and receiver characteristics. These parameters include radio transmitter parameters that include modulation fidelity, frequency error and power, and Bit Error Rate (BER) for determining the radio‘s digital sensitivity.

The P25 radio transmits and receives digital data using a type of modulation called C4FM. This modulation imparts the “1s” and “0s” by using four distinct frequency states. For proper analysis of these signals, the FTC utilizes test instruments that can analyze four critical parameters of the C4FM modulation:

1. Symbol Clock Error: The primary reference to ensure that the digital data is encoded and decoded correctly. Errors in the symbol clock can cause digital “jitter”.

2. Symbol Frequency Error: Each of the four frequency states have to occur at precise deviations at the symbol clock time. These frequency states occur at -1800Hz, -600Hz, +600Hz and +1800Hz in reference to the carrier.

3. RF Frequency Error: Due to the nature of P25 signals, conventional frequency counters cannot accurately measure RF error. Specific instruments are needed to verify proper operation in the P25 mode.

4. Modulation Fidelity: This measurement shows how closely the overall modulation is performing.

Once the reprogramming and repair are completed, the radio undergoes a final test and alignment and an over-the-air test. Radios must be aligned to specification before being returned to the customer. In the past this has been a manual process that would take the technician several minutes.

Since the 3920 replaces the computer and can directly control the radio and perform complete test and alignment in just a few minutes, we are looking at moving these units into earlier stages of our testing process. If a simple alignment can correct an issue, then there is no need to run the radio through additional troubleshooting. Plus, using specific tests, we can automatically isolate different failure modes, such as power amplifier versus reference oscillator issues, where the repair entails different procedures.”

Cost savings are a major part of any radio service operation. Service organisations would much rather have their technical resources working on higher value testing and repair, rather than routine radio testing. Using a streamlined process coupled with new test systems, the end user can, for the first time, test P25 digital radios accurately and align them without the need for a technician or engineer.