Measurement of Modulation Spectrum on GSM/DCS/PCS Mobiles acc. to GSM.0- Application Note MA0_E Subject to change Roland Minihold 98-0 Products: Application Firmware FSE-K0 Spectrum Analyzer FSE + FSE-B7 Digital Radiocommunication Tester CMD 5/55/5
Contents. Overview. Problem. Solution 4. Activating the Burst Trigger Output on Option CMD-B7 5. Ordering Information. Annex: Setting Up an External Trigger Circuit. Overview Fast and correct measurement of the spectrum due to modulation of GSM900/DCS800/PCS900 mobile phones according to GSM.0- is problematic due to the IDLE bursts. The suggested solution using Radiocommunication Tester CMD and Option CMD-B7 allows fast measurement of the spectrum due to modulation with the FSE and the Application Firmware FSE-K0 in the complete frequency band without the measured values being affected by the IDLE burst.. Problem For measurements on GSM/DCS/PCS mobile phones using the FSE and Application Firmware FSE-K0, correct triggering is a precondition for accurate measurement of the spectrum due to modulation according to GSM.0-. General trigger capabilities of FSE with FSE-K0: VIDEO: Internal triggering to the video signal is only possible with measurements at the channel frequency (phase/frequency error, carrier power, power vs time). The internal video trigger cannot be used for out-ofchannel measurements (transient spectrum, spectrum due to modulation and spurious measurement). RF POWER: The internal trigger to RF power often is not sufficiently sensitive or broadband for measurements of the spectrum due to modulation in the TX or RX band. EXTERN: Using the FRAME trigger (eg of CMD) as an external trigger leads to incorrect results of the spectrum due to modulation measurement. The reason is the IDLE burst which occurs at every th frame (the mobile is IDLE at every th frame, see Fig. ). This is a problem especially when measuring the spectrum due to modulation where invalid measurement results will also be averaged (ie values measured during the IDLE burst). Using the MULTIFRAME signal of the CMD as an external trigger allows correct measurement of the spectrum due to modulation, but the measurement time would be increased significantly (the period of the MULTIFRAME signal is 0 ms). MULTIFRAME 0 0 4 5 FRAME (Frame Trigger) 0 0 4 5 Bursts Burst Trigger (output signal of digital circuit shown here) 0 0 4 5 IDLE Burst Fig. : Timing of the CMD signals MULTIFRAME, FRAME, the bursts and the burst trigger shown here. The bursts are delayed by slots (577 µs each) relative to the FRAME signal. Every th burst is an IDLE burst. MA0_E ROHDE & SCHWARZ
.. Solution A possible solution is the new option CMD-B7 for the CMD. It comprises a digital circuit which suppresses the IDLE burst and produces a real burst trigger. The CMD is used to configure the mobile phone according to the requirements and in addition it supplies the burst trigger signal for the FSE at the rear BNC connector RAMP/TRIG. Thus fast measurements can be made with the aid of FSE and FSE-K0, with the IDLE burst being suppressed. NOTE: The jumper at X on this option has to be changed from position - to - (factory setting is - ). The option CMD-B7 can also be retrofitted by any R&S service center. This BURST TRIGGER signal can of course be used to advantage for all the other TX measurements on the mobile that can be carried out with the FSE/FSE- K0 (phase/frequency error, carrier power, power vs time, transient spectrum and spurious measurement). ext. reference signal CMD 5/55/5 with options CMD-B/CMD-B FSE OUTPUT INTPUT ON Pin ( MULTIFRAME) Multifunction Connector Pin 9 (FRAME) with option CMD-B7: rear output: RAMP/TRIG Rear input: EXT TRIG GATE max. 0 dbm! Coupler FRAME TX / RX BURST TRIGGER MULTI FRAME As an alternative: external burst trigger device Mobile phone ABC DEF GHI 4 5 7 8 9 STU ÜVW XYZ 0. - RCL S C M Fig. : Block diagram of test setup with option CMD-B7 or alternatively with external burst trigger device. The coupler shall be designed so that the FSE input will not be overdriven (coupling 0 db to 5 db, depending on maximum output power of the mobile phone). MA0_E ROHDE & SCHWARZ
4. Activating the Burst Trigger Output on Option CMD-B7 5 IEEE 488 IQ IQ RAMP / TRIG Fig. : Rear-panel detail of CMD with Option CMD-B7. After undoing the marked screws, the option can be withdrawn for changing the jumper position. Fig. 4: The jumper on option CMD-B7 must be changed from position - (factory setting) to position -. MA0_E 4 ROHDE & SCHWARZ
Should option CMD-B7 not be available, an external trigger circuit can be configured. The required information can be found in the Annex. 5. Ordering Information Spectrum Analyzer Application Firmware Digital Radiocommunication Tester FSEA 0 ) 05.00.0 ) FSE-K0 057.09.0 CMD 55 ) 050.9008.55 ) I/Q Outputs CMD-B7 ) 099.00.0 ) All FSE 0 models (FSEA0, FSEB 0, FSEM 0, FSEK 0) can be used. ) Depending on the system (GSM 900/DCS800 or PCS 900), other CMD models can also be used. ) If in the CMD both the options CMD-B8/U8 and CMD-B are fitted, option CMD-B7 cannot be installed for reasons of space. (In this case the external trigger circuit has to be used.) ROHDE & SCHWARZ GmbH & Co. KG. P.O.B. 80 4 9. D-84 München Telephone +49 89 49-0 Telefax +49 89 49-777. Internet: http://www.rsd.de MA0_E 5 ROHDE & SCHWARZ
. Annex: Setting Up an External Trigger Circuit Pin assignment of 50-pin MULTIFUNCTION connector of CMD 5/55/5 (Option CMD-B required): 7 50 Pinbelegung Frontplatten-Draufsicht 8 4 Pin 9 of the 50-pin multifunction connector delivers the FRAME signal, pin the MULTIFRAME signal. Reference ground is available at pin. 9 0 5 7 4 4 4 8 9 0 44 45 4 47 5 48 FRAME 5 MULTIFRAME BITCLK MULTIFRAME USERTRIGGER SLOTOUT SUPERFRAME SER DUTRLSD SER DUTTXCLK SER DUTRXCLK SER DUTDTR SER DUTRI SER DUTCTS SER DUTDSR SER DUTTXDATA SER DUTRXDATA SER DUTRTS not assigned not assigned GSM-specific clock outputs (USERTRIGGER is input). Time reference is the CMD transmitter (only with option CMD-B) Serial data interface (I/O). Pin Signal designation Function 8 4 9 5 HANDSET OUT HANDSET IN DPG HFF DPG EXTRST DPG EXTD DPG EXTW Handset connection Data pattern generator 49 7 50 PRI EXTQ PRI EXTI AQ EXT AI EXT ) I/Q modulation inputs (synthesizer ) I/Q demodulator outputs (level is set to max. ±.5 V peak value via software, AC coupling) 4 5 7 0 7 8 9 SER DSR SER TXDATA SER RXDATA SER RTS SER RLSD SER TXCLK SER RXCLK SER DTR SER RI SER CTS Serial data interface (I/O) 8 4 40 4 BICLK BIDATA BIFRAME Bit interface MA0_E ROHDE & SCHWARZ
MULTIFRAME FRAME 5 D 74HCT04 +5V +5V R K R K 4 45 5 0 9 D 74HCT9 C CTR4 M G G4 D + - 7 D4 74HCT08 & R K R4 K 54 4 5 0 9 D 74HCT9 C CTR4 M G G4 D +- D 74HCT04 D 74HCT04 4 9 D 74HCT04 8 7 +5V R5 K S 4 D5 74HCT74 C D R 5 D4 74HCT08 4 & 5 BURST_TRIG Fig. : Circuit diagram of external trigger device MA0_E 7 ROHDE & SCHWARZ
Setting up the circuit The trigger device can easily be set up on a breadboard. Unused inputs should be connected to ground via kω resistors. should be low impedance (wire diameter mm or ground line of sufficient width). The +5 V supply voltage should be carefully blocked by soldering 00 nf capacitors between the IC's supply pin and ground. MA0_E 8 ROHDE & SCHWARZ