01 RF Measurement and Optimization

RF measurement quantities and optimization

Soc Classification level 1 © Nokia Siemens Networks

Presentation / Author / Date

Content • LTE RF measurement quantities in field measurements – – – –

RSRP RSSI RSRQ SINR

• RF optimization



SINR vs. RSSI vs. RSRP and RSRQ



Field measurement parameters • 3GPP is defining following measurements: – RSRP (Reference Signal Received Power) – RSRQ (Reference Signal Received Quality)

• Scanners and terminals are typically measuring following RF quantities: – – – – –

RSRP RSRQ RSSI (Received Signal Strength Indicator), Wideband channel power P-SCH, S-SCH power RS SINR, P-SCH/S-SCH SINR

• Understanding of different measurement quantities is very important for field performance analysis.



RSRP, 3GPP definition • RSRP is the average received power of a single RS resource element. • UE measures the power of multiple resource elements used to transfer the

reference signal but then takes an average of them rather than summing them. • Reporting range -44…-140 dBm



RSRP mapping 3GPP TS 36.133 V8.9.0 (2010-03) • The reporting range of RSRP is defined from -140 dBm to -44 dBm with 1 dB resolution. • The mapping of measured quantity is defined in the table below.

Reported value

Measured quantity value

Unit

RSRP_00

RSRP  -140

dBm

RSRP_01

-140  RSRP < -139

dBm

RSRP_02

-139  RSRP < -138

dBm

…

…

…

RSRP_95

-46  RSRP < -45

dBm

RSRP_96

-45  RSRP < -44

dBm

RSRP_97

-44  RSRP

dBm



RSSI • RSSI not reported to eNodeB by UE – Can be computed from RSRQ and RSRP that are reported by UE

• RSSI measures all power within the measurement bandwidth

– Measured over those OFDM symbols that contain RS – Measurement bandwidth RRC-signalled to UE



RSSI and RSRP • RSSI = wideband power= noise + serving cell power + interference power • Without noise and interference, 100% DL PRB activity: RSSI=12*N*RSRP – RSRP is the received power of 1 RE (3GPP definition) average of power levels received across all Reference Signal symbols within the considered measurement frequency bandwidth – RSSI is measured over the entire bandwidth – N: number of RBs across the RSSI is measured and depends on the BW • Based on the above, under full load and high SNR: RSRP (dBm)= RSSI (dBm) -10*log (12*N)



RSRQ • RSRQ = N x RSRP / RSSI – N is the number of resource blocks over which the RSSI is

measured, typically equal to system bandwidth – RSSI is pure wide band power measurement, including intracell power, interference and noise

• RSRQ reporting range -3…-19.5dB



RSRQ reporting range • RSRQ = N x RSRP / RSSI – N is the number of resource blocks over which the RSSI is

measured, typically equal to system bandwidth – RSSI is pure wide band power measurement, including intracell power, interference and noise

• RSRQ reporting range -3…-19.5dB Reported value

Measured quantity value

Unit

RSRQ_00

RSRQ  -19.5

dB

RSRQ_01

-19.5  RSRQ < -19

dB

RSRQ_02

-19  RSRQ < -18.5

…

…

…

RSRQ_32

-4  RSRQ < -3.5

dB

RSRQ_33

-3.5  RSRQ < -3

dB

RSRQ_34

-3  RSRQ

dB



dB

SINR definition • •

SINR is the reference value used in the system simulation SINR can be defined: 1. Wide band SINR 2. SINR for a specific subcarriers (or for a specific resource elements)

•

SINR = S/(I+N), all measured over the same bandwidth

• Most drive test UEs and scanners support SINR or SNR measurement

 Example: LG supports RS SNR measurement  Example: Samsung BT-3710 measures CINR from RS (e-mail info from Samsung)



SNR vs. RSRP • •

RSRP to SNR mapping RSRP is measured for a single subcarrier – noisepower_for_15KHz= -125.2dBm  

•

Noise figure = 7 dB Temperature = 290 K

Assumption: RSRP doesn’t contain noise power

SNR 

RSRP Pn _ RE

Pn _ RE  15 KHz _ noise _ power

This curve gives upper limit to SINR with certain RSRP. SINR is always lower than SNR in live network due to interference. Soc Classification level 12 © Nokia Siemens Networks


RSRQ to SINR mapping •

RSRQ depends on own cell traffic load, but SINR doesn’t depend on own cell load. – Used Resource Elements per Resource Block (RE/RB) in serving cell is an –

input parameter for RSRQ -> SINR mapping Assumption: RSRP doesn’t contain noise power

SINR 

RSRP *12 N Pi  Pn _ 12 N

Pn _ xN  Pn _ RE  xN x  RE / RB _ used N  # RBs RSSI  Pi  RSRP * xN  Pn _ 12 N RSRQ 

N * RSRP RSSI

SINR 


RSRP *12 N 12  N * RSRP 1  RSRP * xN x RSRQ RSRQ


RSRQ to SINR mapping Difficult to estimate SINR in this region from RSRQ, SINR very sensitive to RSRQ and cell load

• Equation used: SINR 

12 1 x RSRQ

– x=RE/RB

• 2RE/RB equals to empty cell. Only

Reference Signal power is considered from serving cell. • 12RE/RB equals to fully loaded serving cell. All resource elements are carrying data. • In practice, mapping from RSRQ to SINR seems difficult – Currently available measurement UEs and scanners report SINR directly



RSRP vs. DL throughput Example measurement •Drive test, 20MHz BW, ~2.6GHz •FTP download, no other interfering traffic in the network



SINR vs. DL throughput Example measurement •Drive test, 20MHz BW, ~2.6GHz



RF optimization Basic RF planning is important •Clear cell dominance areas •Avoid sites shooting over large areas with other cells Antenna tilting has big impact on other cell interference, at least in planning tool estimates •No LTE reference measurements available



Example from 3HK trial – reusing 3G sites Improving performance by blocking excess cells Ave SINR improved from 15.2dB to 17.4dB

All cells

• Overall SINR is improved due to

reduction of inter-cell interference • Locations with improved SINR are visible on the map • Improvement in throughput is even more significant (see next slide)

Blocked cells Soc Classification level 18

© Nokia Siemens Networks


Example from 3HK trial – reusing 3G sites Improving performance by blocking excess cells

Ave throughput improved from 23.34Mbps to 26.78Mbps, i.e. 14.7%

All cells

Key message: • The number of LTE cells when converted from all existing 3G sites seem to be more than sufficient, and cell overlapping and hence inter-cell interference seems to be excessive in outdoor environment. • Careful planning and cell/antenna selection process, and initial RF tuning is important to the LTE field performance Blocked cells Soc Classification level 19

© Nokia Siemens Networks


Quiz 1. If RSRP = -100 dBm, Calculate SINR. 2. For the SINR obtained in (1), what is the value of RSRQ for: i. Empty cell ii. Fully loaded cell



01 RF Measurement and Optimization

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