9 Modulation accuracy at GMSK modulation

3GPP51.026Base Station System (BSS) equipment specificationPart 4: RepeatersRelease 17TS

9.1 Test purpose

This clause applies only to repeater systems using frequency shift and describes the test of the phase error.

9.2 Test case

The repeater system shall be levelled according to the recommendations of the manufacturer. For the purpose of the frequency synchronisation of the repeater system it might be necessary to connect the system to a BTS or equivalent test equipment like a mobile tester. In all cases an accurate frequency synchronisation source has to be used to synchronise the measurement setup.

For the measurement of the phase error a continuous and synchronised GMSK signal modulated with a pseudo random bit sequence shall be fed successively at one frequency of the relevant MS or BTS transmit frequency band into the relevant input port of the repeater. The power level of the RF input signal shall be at least 5 dB below the power level which would produce, when applied within the pass band, maximum rated output power, as declared by the manufacturer. This is to ensure that the equipment is operating in the linear output range.

The phase trajectory shall be measured at the equivalent output of the repeater system and the calculation of the phase error shall be performed according to 3GPP TS 51.010-1 [9] or 3GPP TS 51.021 [10].

The phase error of single elements within the repeater system such as master unit or remote unit may be measured as well.

The GMSK signal source shall have a phase error below the following values:

– 5 degrees rms;

– 20 degrees peak.

Test environment: Normal

Extreme temperature

9.3 Conformance requirement

The phase error of a complete repeater system shall not exceed:

– 7 degrees rms;

– 28 degrees peak.

If tested, the phase error of a single repeater unit shall not exceed:

– 6.1 degrees rms;

– 24.5 degrees peak.

9.4 Reference requirement

3GPP TS 45.005 [13], annex E.