Lte Rf Conditions Classi

thoughts, news, investigations on radio access networks, GSM, GPRS, UMTS & LTE

radio accessSunday, 25 November 2012

LTE RF conditions classification

It is common sense that the performance of any wireless system has a direct relationshipwith the RF conditions at the time. To aid with performance analysis then, we typicallydefine some ranges of RF measurements that correspond to some typical RF conditionsone might find themselves in.

When it comes to LTE, I came across the above table that presents a good classification.The source of this table is a EUTRAN vendor and has been complied during the RF tuningprocess for a major US operator. Of course there are no rules as to how various RFconditions are classified, so different tables will exist but to a great extent you can expectthem to align.

In this particular example, three measurement quantities are used. RSRP (ReferenceSignal Received Power), RSRQ (Reference Signal Received Quality) and SINR (Signal toInterference & Noise Ratio).

RSRP is a measure of signal strength. It is of most importance as it used by the UE for thecell selection and reselection process and is reported to the network to aid in the handoverprocedure. For those used to working in UMTS WCDMA it is equivalent to CPICH RSCP.

The 3GPP spec description is "The RSRP (Reference Signal Received Power) is determinedfor a considered cell as the linear average over the power contributions (Watts) of theresource elements that carry cell specific Reference Signals within the consideredmeasurement frequency bandwidth."

In simple terms the Reference Signal (RS) is mapped to Resource Elements (RE). Thismapping follows a specific pattern (see below). So at any point in time the UE willmeasure all the REs that carry the RS and average the measurements to obtain an RSRPreading.

Page1 of 4radio access: LTE RF conditions classification

11/20/2013http://radioaccess.blogspot.in/2012/11/lte-rf-conditions-classification.html

RSRQ is a measure of signal quality. It is measured by the UE and reported back to thenetwork to aid in the handover procedure. For those used to working in UMTS WCDMA is itequivalent to CPICH Ec/N0. Unlike UTMS WCDMA though it is not used for the process ofcell selection and reselection (at least in the Rel08 version of the specs).

The 3GPP spec description is "RSRQ (Reference Signal Received Quality) is defined as theratio: N×RSRP/(E -UTRA carrier RSSI) where N is the number of Resource Blocks of theE-UTRA carrier RSSI measurement bandwidth."

The new term that appears here is RSSI (Received Signal Strength Indicator). RSSI iseffectively a measurement of all of the power contained in the applicable spectrum (1.4,3, 5, 10, 15 or 20MHz). This could be signals, control channels, data channels, adjacentcell power, background noise, everything. As RSSI applies to the whole spectrum we needto multiple the RSRP measurement by N (the number of resource blocks) which effectivelyapplies the RSRP measurement across the whole spectrum and allows us to compare thetwo.

Finally SINR is a measure of signal quality as well. Unlike RSRQ, it is not defined in the3GPP specs but defined by the UE vendor. It is not reported to the network. SINR is useda lot by operators, and the LTE industry in general, as it better quantifies the relationshipbetween RF conditions and throughput. UEs typically use SINR to calculate the CQI(Channel Quality Indicator) they report to the network.

The components of the SINR calculation can be defined as:

S: indicates the power of measured usable signals. Reference signals (RS) and physicaldownlink shared channels (PDSCHs) are mainly involved

I: indicates the power of measured signals or channel interference signals from other cellsin the current system

N: indicates background noise, which is related to measurement bandwidths and receivernoise coefficients

So that is it! I have also included a real life measurement from a Sierra Wireless card thatincludes the above mentioned metrics so you can see what is the typical output from aUE. Using that and the table above you should be able to deduce the RF conditioncategory it is in at the time of measurement.



Posted by radio access blogger at 17:58

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3 comments:

Vineet Singh 15 July 2013 07:11

Hi Mark,

Awesome blog very informative thanks for doing thisbut i think there is some silly mistakes in the RF condition table RSRQ section (lessthan and greater than signs it should be >=-10 for excellent ).

Reply

radio access blogger 27 July 2013 21:54

Thanks for spotting the typo.

Reply

Rafael Cardenas 11 November 2013 02:19

I don't know how to calculate the RSRQ from the RSSI and the RSRP, from thevalues after given it gives me, Log(50(-79/-61)) = 1.81 dB. I really don't knowwhat i'm missing. Best regards

Reply



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