Japan PROPOSED MODIFICATION OF OF THE WORKING DOCUMENT TOWARDS A PDNR ITU-R SM.[UWB.MES] MEASUREMENT INITIALIZATION FOR RMS PSD

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1 INTERNATIONAL TELECOMMUNICATION UNION RADIOCOMMUNICATION STUDY GROUPS Document -8/83-E 5 October 004 English only Received: 5 October 004 Japan PROPOSED MODIFICATION OF OF THE WORKING DOCUMENT TOWARDS A PDNR ITU-R SM.[UWB.MES] MEASUREMENT INITIALIZATION FOR RMS PSD Introduction Working document towards a PDNR ITU-R SM.[UWB.MES] was described by the third meeting of ITU-R Task Group /8. The objective of this contribution is to revise the description about measurement initialization for RMS PSD in the document. Discussion In Section of the current WDPDNR (Doc. -8/6, Annex 4), the RMS power measurement by using a spectrum analyser is described. It deploys the subband measurement and the power sum law. However, the present scheme is not only time consuming, but also is incompatible with other Recommendations in the similar context. This contribution proposes the modification of Section to be compatible with other ITU-R Recommendations. In Recommendation ITU-R SM.39-0 Unwanted emissions in the spurious domain, the relation between the reference bandwidth and the resolution bandwidth is described as follows. Note that italic font is deployed just to clarify the points, and not used in the original Recommendation. 4. Recommended reference bandwidths A reference bandwidth is a bandwidth in which spurious domain emission levels are specified. (specific values and detailed conditions are listed) NOTE The reference bandwidth is a bandwidth in which the spurious domain emission limit is specified, but does not mean a bandwidth in which spurious domain emissions should be measured. Annex describes the resolution bandwidth in which spurious domain emissions should be measured. As a general guideline, the resolution bandwidth should be equal to the reference bandwidth. However, to improve measurement accuracy, sensitivity and efficiency, the resolution bandwidth can be different from the reference bandwidth as described in Annex. The contribution proposes the use of the resolution bandwidth equal to the reference bandwidth. C:\DOCUMENTS AND SETTINGS\TAKADA\DESKTOP\R03-TG.8-C_0506_083659_96_JYTAKADA\R03-TG.8-C-083!!MSW-E.DOC

2 - - -8/83-E Accordingly, two additional techniques are proposed:. Strict limitation of the sweep time When the (average) pulse repetition frequency is much lower than the sweep time, the RMS power for the same pulse waveform is inversely proportional to the sweep time. In other words, the pulse magnitude can be arbitrarily large when sweep time is not restricted. Therefore, the sweep time shall be strictly limited.. Use of linear detector and video filter for RMS measurement Off-the-shelf low cost spectrum analyzers usually do not have RMS measurement function. However, they still have linear (envelope) detectors and video filters. The contribution also proposes an RMS power measurement using the linear detector and the video filter. 3 Proposal This contribution proposes modification of Section as shown in following Annex, and addition of Section 7 of Appendix as shown in following Annex, in WDPDNR ITU-R SM.[UWB.MES]. The modified items are listed below: the subband measurement of RMS PSD is replaced by the full RBW measurement; sweep time is redefined; RMS power measurement method for low cost spectrum analyzers without RMS measurement function is newly added. Annexes: C:\DOCUMENTS AND SETTINGS\TAKADA\DESKTOP\R03-TG.8-C_0506_083659_96_JYTAKADA\R03-TG.8-C-083!!MSW-E.DOC

3 /83-E Annex Proposed text for Section Measurement initialization for RMS PSD Set the resolution bandwidth (RBW) of the spectrum analyser to 0 kmhz. Set the video bandwidth (VBW) to be three times the resolution bandwidth or 30 k3mhz. Set the frequency span to Mhzzero span. Set the detector to sample. The sweep time remains a coupled functionset the sweep time to ms. Take a single sweep. Detailed procedure For each MHz bin, extract the data points from the analyser.measurement shall be done for each MHz bin. RMS value can be obtained by one of the following equivalent methods: a. Use RMS detector of the analyser to directly obtain RMS value. b. Use linear (envelope) detector and the video filter to obtain RMS value. The detailed procedure is described in section 7 of Appendix. c. Extract the data points from the analyser. After converting the data from logarithmic to numerical terms, find the RMS value in the bin by squaring all the values, calculate the mean of the squares and square root the mean. The RMS value is corrected to account for the noise power bandwidth of the spectrum analyser. This value is plotted on a graph with the centre frequency of the bin along the X-axis and the power spectral density value of the bin on the Y-axis. The analyser s centre frequency is stepped in MHz increments over the frequency range of interest and the value of each bin plotted as before. The display points arerms value is recovered from the instrument and post processed with the following formula: alternative: P n = 0log 0 Sp NBW () () n 0 P i 0 i= C:\DOCUMENTS AND SETTINGS\TAKADA\DESKTOP\R03-TG.8-C_0506_083659_96_JYTAKADA\R03-TG.8-C-083!!MSW-E.DOC

4 P = 0 log /83-E n 0 n i= Sp NBW P( i) 0 n K P = 0 log 0 0 n i= P( i) 0 where: P = total RMS power in the span in dbm; Sp = span size in MHz n = number of data points in the spansweep; P(i) = power reading on spectrum analyser at data point i in dbm; NBW = equivalent noise bandwidth of the spectrum analyser in MHz where NBW = RBW * K (the value of K provided by the equipment manufacturer) PSD = P/Sp in dbm/mhz. K = RBW/ABW(the value of ABW is actual RBW filter bandwidth of the spectrum analyser). C:\DOCUMENTS AND SETTINGS\TAKADA\DESKTOP\R03-TG.8-C_0506_083659_96_JYTAKADA\R03-TG.8-C-083!!MSW-E.DOC

5 /83-E Annex Proposed text for Section 7 of Appendix 7 A conversion from linear average to RMS Off-the-shelf low cost spectrum analyzers usually do not have RMS measurement function. However, they still have linear (envelope) detectors and video filters. The RMS power measurement using the linear detector and the video filter is described below. 7. Theory The probability density function of the envelope R ( t) of UWB signal in RBW MHz shall be given by p ( R). Since the probability that the envelope ( t) r + is p ()dr r, the following equation is obtained. c = nd ( moment of p() r ) st moment of p() r ( ) = R is in the range between r and dr ( RMS value of R() t ) ( average value of R() t ) The value c is called the conversion factor. When unmodulated carrier, thermal noise, and impulse sequence of constant pulse repetition frequency (PRF) are fed into spectrum analyzers, the average and RMS values of the linear detector output 0.707R() t and the conversion factor are shown in Table. TABLE Conversion factor of average to RMS conversion IF waveform Average value RMS value Conversion factor c Sine wave* a a Thermal noise** Gaussian pulse train*** 0.886s s.8 PRF a PRF a RBW RBW *: The RMS value of the sine wave is a Volt. **: The RMS value of the thermal noise is s Volt. ***: The adjacent Gaussian pulses in the train do not overlap each other. PRF.03 RBW As a result of setting VBW to f c = khz, the video filter outputs the RMS voltage value 0.707R ( t) of the envelope in the equivalent integration time of = ms. When the video filter output is f c multiplied by c, the video filter output is changed into the RMS value. The average power in RBW MHz portion of UWB signal connected to the RF input port of the spectrum analyzer is obtained by squaring and dividing by 50 ohms of the RMS voltage value. That is, C:\DOCUMENTS AND SETTINGS\TAKADA\DESKTOP\R03-TG.8-C_0506_083659_96_JYTAKADA\R03-TG.8-C-083!!MSW-E.DOC

6 Averagepower in RBW MHz = ( 0.707R ( t) ) c /83-E If pulse gating is employed where the transmitter is quiescent for intervals that are long compared to the nominal pulse repetition interval, measurements shall be made with the pulse train gated on. 7. Measurement procedure Set the RBW filter to MHz. Set the IF detector to the linear mode. Set the display detector to the positive peak mode. Set the VBW to 0 khz. Read the RMS voltage value ( t) 0.707R displayed on the screen. Recover the average power with the following formula, using the conversion factor c of Table. ( 0.707R () t ) Average power = 50 c C:\DOCUMENTS AND SETTINGS\TAKADA\DESKTOP\R03-TG.8-C_0506_083659_96_JYTAKADA\R03-TG.8-C-083!!MSW-E.DOC