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Determination of EMF Exposition
at LTE transmitter sites with
SRM-3006
Worst – Case Extrapolation
Measuring LTE = ‘BIG ?’
DISCUSSION ABOUT
MEASUREMENT PROCEDURE IN EUROPE
Issues with Spectrum Measurements
Interference with neighboring carriers
Low signal quality and noise of common Spectrum Analyzer (sensitivity)
Issues with Demodulation
Possible interferences
Demodulation during handoffs (movements with high speed) or between cells
Needs to be considered:
Versatility of signal
EU wants to minimize investments into new equipment for measuring LTERequirement for CENELEC Guidelines i.e. EN50492 could be: RBW = 1 MHz, Span = 40 MHz, Detectors: Peak, sample peak and averaging
Summary of technical details
Channel Bandwidth:1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz
DL Multiple Access: OFDMA
Duplexing: FDD and TDD
Sub-carrier spacing of 15 kHz
Data Modulation: QPSK, 16QAM, 64 QAM
FFT size (5MHz): 512
Channel Coding:Convolutional coding and turbo coding
MIMO: Multi layer pre-coded spatial multi-placing space time / frequency block coding, switched transmit diversity, and cycle delay diversity
Measuring LTE
Facts
center consists of 6 resource blocks with two types of signals which will probably be transmitted at max. power:
• primary and secondary synchronization signals
• PBCH (physical broadcast channel)
Used carriers of a system with a carrier spacing of 15 kHz
• synchronization signals use the central 62 carriers
• PBCH uses the central 72 carriers.
The synchronization signals or the PBCH are noise-like bursts with a total duration of
• 2 symbol interval (142.7 �s)
• or 4 symbol intervals (285.4 �s)
The synchronization signals pulse occurs twice within a 10 ms frame, the PBCH occurs only one time.
The PBCH pulse occurs always immediately after the synchronization signals pulse.
LTE Nomenclature
Freq AccyFreq AccyFrequency Accuracy
EVMRhoEVM (Signal Quality)
TrafficTrafficPDSCH (Physical Downlink Shared Channel)
P/S-CCPCH & PICHPagingPDCCH (Physical Downlink Control Channel)
n.a.n.a.PHICH (Physical Hybrid ARQ Indicator Channel)
BCCHPagingPBCH (Physical Broadcast Channel)
n.a.n.a.PCFICH (Physical Control Format Indicator
Channel) �
S-SCHn.a.S-SS (Secondary Synchronizing Signals)
P-SCHSyncP-SS (Primary Synchronizing Signals)
CPICHPilot RS (Reference Signal)
~ W-CDMA / UMTS~ CDMALTE
Assumptions
Assumptions:
The resource blocks of the following signals are transmitted
with the highest or equal power compared to any other
resource block:
1. primary and secondary synchronization signals
2. PBCH
3. Both the primary and secondary synchronization signals and the
PBCH
If one the assumptions can be verified by LTE operator
following procedure can be used.
Assumption 2 will most likely be verified.
LTE Spectrum – Broadcast Channel
Broadcast Channel +
Sync Channel = 1 MHz
LTE Spectrum can be measured with zero
span and
1 or 20 MHz (RBW) => Scope or Level Meter
Mode
96 % Traffic
LTE Signal in Scope Mode – 1 Frame
Recommended Measurement of LTE
Measure LTE in Level Recorder
=> offering best (lowest) measurement uncertainty
Set-up SRM-3006 as follows
• RBW = 800 kHz
broadest RBW to minimize spectrum fluctuation
• VBW = 1.25 kHz for single axis and assumption 2 or
VBW = 1.6 kHz for three axis and assumption 2
offering best compromise between settling time and reduction of
fluctuations due to noise like structure of signal
• Set right Center Frequency of LTE Band
• Select correct Detector: Peak
LTE Signal in ‘Real Time’ Level Meter Mode
Extrapolation
Extrapolation of worst case scenario:
Pmax = Maximum transmitted Power
Ppmax = Measured Peak Power
Fc = correction Factor (depending on settings)
Correction factor for SRM-3006 three axis measurement: 0.925
Correction factor for SRM-3006 single axis measurement: 0.875
TBW = Transmission Bandwidth of LTE signal
NBW = Noise Bandwidth from measurement device= 0.96 * RBW (for SRM-3006 in Scope Mode / Level Recorder)
Please Noteworst-case power is based on assumption that all available resource blocks are transmitted with same power as measured resource blocks. This will often not be real-life case. However, in such cases the assumed knowledge about the relationship between measured signals and full traffic power can be used for extrapolation.
An additional correction must be applied to extrapolate the worst-case emission if the synchronization signals or the PBCH were not transmitted at their maximum power.
Pmax =Ppmax * Fc * TBW
NBW
Measurement Uncertainty
Measurement Uncertainty
(to be added to ‘normal’ measurement uncertainty)
for three axis measurement: 0.42 / -0.47 dB
for single axis measurement: 0.34 / -0.37 dB
There are other possible measurement procedures, but there are
less accurate.