Wednesday, April 3, 2013

RSSI,SINR,RSRP and RSRQ in LTE

RSSI,SINR,RSRSP and RSRQ : These are  the basic measurement quantities used in LTE.
RSSI - Received Signal Strength Indicator
SINR - Signal to Interference & Noise Ratio
RSRP - Reference Signal Received Power
RSRQ - Reference Signal Received Quality

RSRP is a measure of signal strength. It is of most importance as it used by the UE for the cell selection and reselection process and is reported to the network to aid in the handover procedure. 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 determined for a considered cell as the linear average over the power contributions (Watts) of the resource elements that carry cell specific Reference Signals within the considered measurement frequency bandwidth."

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

RSRQ is a measure of signal quality. It is measured by the UE and reported back to the network to aid in the handover procedure. For those used to working in UMTS WCDMA is it equivalent to CPICH Ec/N0. Unlike UTMS WCDMA though it is not used for the process of cell 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 the ratio: N×RSRP/(E -UTRA carrier RSSI) where N is the number of Resource Blocks of the E-UTRA carrier RSSI measurement bandwidth."

The new term that appears here is RSSI (Received Signal Strength Indicator). RSSI is effectively 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, adjacent cell power, background noise, everything. As RSSI applies to the whole spectrum we need to multiple the RSRP measurement by N (the number of resource blocks) which effectively applies the RSRP measurement across the whole spectrum and allows us to compare the two.

Finally SINR is a measure of signal quality as well. Unlike RSRQ, it is not defined in the 3GPP specs but defined by the UE vendor. It is not reported to the network. SINR is used a lot by operators, and the LTE industry in general, as it better quantifies the relationship between 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 physical downlink shared channels (PDSCHs) are mainly involved

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

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

4 comments:

  1. Hi Ashok,

    Thanks for sharing this information.

    Is RSRP calculated by taking linear average of all the reference signals present in the OFDMA symbol or it is measured in single RE that carrier the reference signals.

    -RB

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  2. now a days technology improves wireless technology better
    av consultant

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  3. Hi Askok,
    Thanks for the good explanation. There is an error in describing how RSSI is calculated according to 3GPP specs.

    Regarding RSSI, this is what 36.214 says:

    E-UTRA Carrier Received Signal Strength Indicator (RSSI), comprises the linear average of the total received power (in [W]) observed only in OFDM symbols containing reference symbols for antenna port 0, in the measurement bandwidth, over N number of resource blocks by the UE from all sources, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise etc.

    Hence RSSI is only measured in the carriers (resource-elements) where the reference symbol is contained, and not over the entire spectrum.

    Regards
    Irfan

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