4G/LTE - Basic Procedures  




Decoding Uplink Signal

'Decoding Uplink Singal' means 'decoding PUCCH and PUSCH'. Overall Procedure is as follows :

    i) UE transmit PUSCH (or PUCCH) to eNodeB

    ii) eNodeB detect DMRS (DeModulation Reference Signal : PUSCH DMRS , PUCCH DMRS)

    iii) if DMRS detection is successful, eNodeB decode PUSCH (PUCCH) data. UL CRC Check happens at this stage.

Overall logic is simple, but eNodeB normally get Uplink signal from multiple UEs and each of the UE may be in different distance and under different channel condition. So docoding uplink channel would not be easy. To help eNodeB decode these uplink channel, UE transmit a reference signal.

There are a few different uplink signal as listed below.

Item iii) would not be a mandatory component, but UE must send item i) and ii). Otherwise, eNodeB fail to decode PUCCH or PUSCH even though UE transmit it in proper format.

Detailed implementation of UL reference signal is described in TS 36.211 section 5.5 and TS 36.213. You will notice a lot of parameters are involved in UL reference signal generation and the following is brief list of these parameters. See Physical Channel : PUSCH DMRS  and Physical Channel : PUCCH DMRS page if you are interested in how these parameters are used in PUSCH/PUCCH DMRS signal generation.

  • n_1_pucch : N(1)PUCCH described in 3GPP TS36.213
  • GroupHopping : in TS36.211
  • Cell ID :
  • Pucch format : 5.5 in TS36.211
  • N_1_CS :
  • N_2_RB :
  • delta Pucch shift :
  • RNTI :
  • UL CP Configuration :
  • systemBW :
  • u_even : sequence-group number even slot (TS36.211
  • u_odd : sequence-group number odd slot (TS36.211
  • n_cs_even#0~#6 : Cyclic Shift for even slot in a subframe (TS36.211 5.4.1,
  • n_cs_odd#0~#6 : Cyclic Shift for odd slot in a subframe (TS36.211 5.4.1,
  • n_oc_bar_even : orthogonal sequence for even slot in a subframe (TS36.211
  • n_oc_bar_odd : orthogonal sequence for odd slot in a subframe (TS36.211
  • n_oc_even : orthogonal sequence for even slot in a subframe (TS36.211 5.4.1)
  • n_oc_odd : orthogonal sequence for odd slot in a subframe (TS36.211 5.4.1)
  • n_PRB_even : Physical resource block number for even slot in a subframe (TS36.211 5.4.3)
  • n_PRB_odd : Physical resource block number for odd slot in a subframe (TS36.211 5.4.3)

As you notice, quite a lot of parameters are involved and it is not easy to understand all of these in detail, but at the initial phase of chipset development or when you try to duplicate live network environment with network simulator you have to make it sure that all of these parameters are properly setup not only in UE but also in network simulator.

Can UE set these parameters arbitrarily whatever it likes to do ? No.. in that case eNode B would not know how to detect the reference signal and in result eNode B would not be able to decode PUCCH/PUSCH. Then how UE can know which value it has to use for Uplink Reference Signal Creation ?

The most critical information on UL Reference Signal is tranmitted by SIB2 message and there are different parameters that are involved in PUCCH reference signal detection and PUSCH reference signal detection :

Following is the list of IEs related to PUCCH reference signal detection.

  • radioResourceConfigCommon.pucch_ConfigCommon.deltaPUCCH_Shift
  • radioResourceConfigCommon.pucch_ConfigCommon.nRB_CQI
  • radioResourceConfigCommon.pucch_ConfigCommon.nCS_AN
  • radioResourceConfigCommon.pucch_ConfigCommon.n1PUCCH_AN

Following is the list of IEs related to PUSCH reference signal detection.

  • radioResourceConfigCommon.pusch-ConfigCommon.ul-ReferenceSignalsPUSCH.groupHoppingEnabled
  • radioResourceConfigCommon.pusch-ConfigCommon.ul-ReferenceSignalsPUSCH.groupAssignmentPUSCH
  • radioResourceConfigCommon.pusch-ConfigCommon.ul-ReferenceSignalsPUSCH.sequenceHoppingEnabled
  • radioResourceConfigCommon.pusch-ConfigCommon.ul-ReferenceSignalsPUSCH.cyclicShift