EMF measurements of LTE

Transcription

1 EMF measurements of LTE COST BM 0704, Working Group Meeting Ljubliana Peter Fritschi, Jean-Michel Vannay, Hugo Lehmann Swisscom (Switzerland) Ltd. Beat Mühlemann Federal Office of Metrology (METAS) Markus Riederer Federal Office of Communications (OFCOM) Motivation: Compliance with legal requirements 2 Source: Federal Authorities of the Swiss Confederation

2 Motivation Swisscom: first LTE field trail in Switzerland 3 LTE Proof of concept field trial in Grenchen: 4 Map source: Federal Office of Communications

3 Some on site impressions: 5 Operating band in field trial: 6

4 Scheduling block: 7 Signalling: Reference Signals (downlink): 8

5 Scheduling block on duty (downlink): 9 Total signal -> «Patchwork»: 10 f t

6 Signalling: Total signal (downlink): 11 Signal measured with a spectrum analyzer: 12 LTE: «connected» danach «full traffic», Ch. BW = 20 MHz Analyser: RBW = 1 MHz, CF = 2'630 MHz, CLRWR, RMS Power coupling: -20dB(Dir.Coupl.) -8.18dB(Cable 10m) -10dB(Att.) +107 = db RS PBCH PBCH PBCH RS & PBCH 80 RS S-SS P-SS FSU8-Eingang [dbµv] Time [ms]

7 Difficulties of spectrum analyzer measurements (i): 13 Theoretical RBW filter Real RBW filter Perfect RBW-Filter, RBW = 1 MHz, [µw] 1 Subcarriers of LTE-Signal full traffic 1 MHz Reference --> total Power of all Subcarriers within 1 MHz Real RBW-Filter, RBW = 1 MHz, e.g. R&S FSU8, [µw] 1 Subcarriers of LTE-Signal full traffic Measurement Result e.g. Reference db Frequency [MHz] Frequency [MHz] Difficulties of spectrum analyzer measurements (ii): 14 Real RBW filter Real RBW-Filter, RBW = 20 MHz, e.g. R&S FSU8, [µw] 1 Subcarriers of LTE- Transmission Bandwidth 18 MHz Signal full traffic Underestimation e.g db Frequency [MHz]

8 Difficulties of spectrum analyzer measurements (iii): 15 Real RBW filters Real RBW-Filter, RBW = 1 MHz, e.g. R&S FSU8, [µw] 1 Subcarriers of LTE- Synchnonization Signal 0.93 MHz Measurement Result e.g. Reference db Real RBW-Filter, RBW = 1 MHz, e.g. R&S FSU8, [µw] 1 Subcarriers of LTE- Broadcast Signal 1.08 MHz Measurement Result e.g. Reference db Frequency [MHz] Frequency [MHz] Spectrum analyzer: a closer view LTE: «connected» danach «full traffic», Ch. BW = 20 MHz Analyser: RBW = 1 MHz, CF = 2'630 MHz, CLRWR, RMS Power coupling: -20dB(Dir.Coupl.) -8.18dB(Cable 10m) -10dB(Att.) +107 = db FSU8-Eingang [dbµv] RMS 95.5 dbµv RMS dbµv RMS dbµv RS S-SS RMS dbµv P-SS RS & PBCH RMS dbµv PBCH PBCH PBCH RS Time [ms]

9 Signalled LTE parameters (downlink): 17 REFERENCE SIGNAL Energy Per Resource Element: Reference-signal-power ( * ) P B( * ) referencesignalpower (#) PHYSICAL DOWNLINK SHARED CHANNEL Energy Per Resource Element: P A( * ) = = = p-b (#) p-a (#) downlink user dependant The cases according Table ( * ) show, which PHYSICAL DOWNLINK SHARED CHANNEL Resource Elements are affected. Table ( * ) respectively P B( * ) show the linear Level Ratio between ρ B( * ) and ρ A( * ). ρ A( * ) can be derived from P A( * ) (P A( * ) in [db]) ( * ) TS , Chapter 5.2 (#) TS , ca. Page 119 These parameters give the following information: 18 B A REFERENCE SIGNAL Energy Per Resource Element Table 5.2-1: The cell-specific ratio B / A for 1, 2, or 4 cell specific antenna ports

10 Other LTE parameters (downlink): 19 Spectrum analyzer measurements (and its worst case extrapolation) are not influenced by LTE-traffic if every single level of: PHYSICAL DOWNLINK SHARED CHANNEL Energy Per Resource Element ( * ) REFERENCE SIGNAL Energy Per Resource Element (#) PHYSICAL DOWNLINK CONTROL CHANNEL Energy Per Resource Element PHYSICAL HYBRID ARQ INDICATOR CHANNEL Energy Per Resource Element PHYSICAL CONTROL FORMAT INDICATION CHANNEL Energy Per Resource Element lower or equal higher or equal PRIMARY SYNCHRONIZATION CHANNEL Energy Per Resource Element SECONDARY SYNCHRONIZATION CHANNEL Energy Per Resource Element PHYSICAL BROADCAST CHANNEL Energy Per Resource Element ( * ) includes both ρ B and ρ A (#) strictly speaking: Average Physical Downlink Shared Channel Energy Per Resource Element across one single Symbol of the Antenna Port «Code-selective» measurement of LTE: 20 Source: manufacturers and probably many more

11 LTE measurements field strengths (location close to Mattenstr. 5): 21 * (* extrapolated to total transmitted bandwidth power) LTE measurements field strengths (close to Archstr. 36): 22 * (* extrapolated to total transmitted bandwidth power)

12 Conclusions: 23 Our analysis shows that legally required measurements for LTE can be performed with the same order of precision and quality as commonly (at least in Switzerland) expected and required for GSM and UMTS measurements. Even though spectrum analyzer measurements for LTE are less traffic dependant than for UMTS, it will never be possible to distinguish the contribution from different cells in the network. Furthermore, to check the conditions in which a spectrum analyzer measurement might give correct results and to derive the correction factors for a given spectrum analyzer is somehow cumbersome. Moreover, this process represents an important source of error for the measurement. Therefore a code selective method seems to be the best solution. There are still open questions to be answered: How have the different signal paths to be handled?? Questions? 24 Parts of this presentation can be found in a previous presentation hold at the LTE-Workshop of the Forschungsstiftung Mobilkommunikation available under ethz ch/dienstlei ( --> hugo.lehmann@swisscom.com )

13 References: 26 Standardization: Document information 27 Doc ID Classification Scope of application Document owner - Version 1.0 Issue date - Status - Valid from - Valid until - File location - Document name - Update interval - Archiving _LTE_Cost0704_HL_PF.ppt C2 Swisscom (Switzerland) Ltd.

14 Document pointers 28 Change control Version Date Changed by Remarks/Nature of the change Peter Fritschi, Hugo Lehmann Checking Issue Version Date Changed by Remarks/Nature of the change Hugo Lehmann Review Release Version Date Changed by Remarks/Nature of the change Peter Fritschi Release Contact information 29 Swisscom (Switzerland) Ltd. Hugo Lehmann SCS-SIS-INI-ENV Postfach CH-3050 Bern Phone Fax Mail