PDCP Layer Average Throughput calculation in LTE

It is common for operators to measure average throughput of the User Plane because this is what most subscribers can/want to see. Calculating throughput for other LTE layers can sometimes be confusing and using different methods / counters could give drastically different results. Measuring the throughput only for payload is not enough for operators to closely monitor the health of their LTE network.

Following is an explanation of how to calculate the average throughput for PDCP layer in LTE network. The main services and functions of the PDCP sublayer are:

  • User plane: Header compression and decompression: ROHC only; Transfer of user data; In-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM; Duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM; Retransmission of PDCP SDUs at handover for RLC AM; Ciphering and deciphering; Timer-based SDU discard in uplink.
  • Control plane: Ciphering and Integrity Protection; Transfer of control plane data.

Different measurements are listed in ETSI TS 136 314 documentation: PRB usage, Received Random Access Preambles, Number of active UEs, Packet Delay, Data Loss and Scheduled IP Throughput.

For Scheduled IP Throughput (measured over Uu the IP throughput independent of traffic patterns and packet size), the measurement is performed per QCI per UE and it can be calculated in the following way:

  • DL: Throughput of PDCP SDU bits in downlink for packet sizes or data bursts that are large enough to require transmissions to be split across several TTIs, by excluding transmission of the last piece of data in a data burst. Only data transmission time is considered,

    If sum(ThpTimeDl>0) à sum(ThpVolDl)/sum(ThpTimeDl)x1000 (kbits/s).

    Where

    ThpTimeDl: The time to transmit a data burst excluding the last piece of data transmitted in the TTI when the buffer is emptied.

    ThpVolDl: The volume of a data burst, excluding the data transmitted in the TTI when the buffer is emptied

    If sum(ThpTimeDl=0)à 0

    For small data bursts, where all buffered data is included in one initial HARQ transmission: ThpTimeDl = 0, otherwise ThpTimeDl =T1T2 [ms]

    Where

    T1: The point in time after T2 when data up until the second last piece of data in the transmitted data burst which emptied the PDCP SDU available for transmission for the particular E-RAB was successfully transmitted, as acknowledged by the UE

    T2: The point in time when the first transmission begins after a PDCP SDU becomes available for transmission, where previously no PDCP SDUs were available for transmission for the particular E-RAB.

  • UL: same as DL. eNB estimate of the throughput of PDCP SDU bits in uplink for packet sizes or data bursts (where a UL data burst is the collective data received while the eNB estimate of the UE buffer size is continuously above zero) that are large enough to require transmissions to be split across several TTIs, by excluding transmission of the last piece of data. Only data transmission time is considered

    If sum(ThpTimeUl>0) à sum(ThpVolUl)/sum(ThpTimeUl)x1000 (kbits/s).

    Where

    ThpTimeUl: The time to transmit a data burst excluding the last piece of data transmitted in the TTI when the buffer is emptied.

    ThpVolUl: The volume of a data burst, excluding the data transmitted in the TTI when the buffer is emptied

    If sum(ThpTimeUl=0) à 0

    For small data bursts, where all buffered data is included in one initial HARQ transmission

    ThpTimeUl = 0

    otherwise:

    ThpTimeUl =T1T2 [ ] ms

    Where

    T1 The point in time when the data up until the second last piece of data in data burst has been successfully received for a particular E-RAB and

    T2: The point in time when transmission is started for the the first data in data burst for a particular E-RAB

    For more information on measurements, counters or any Radio Network related query don’t hesitate to contact 3DB CONSULT at: toomas.sarv@3dbconsult.com

    Additional info


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