Section: 5.1.1 Random Access Procedure initialization
Content: The Random Access procedure described in this clause is initiated by a PDCCH order, by the MAC sublayer itself or by the RRC sublayer. Random Access procedure on an SCell shall only be initiated by a PDCCH order. If a MAC entity receives a PDCCH transmission consistent with a PDCCH order, as specified inTS 36.212 [5], masked with its C-RNTI, and for a specific Serving Cell, the MAC entity shall initiate a Random Access procedure on this Serving Cell. For Random Access on the SpCell a PDCCH order or RRC optionally indicate the ra-PreambleIndex and the ra-PRACH-MaskIndex, except for NB-IoT where the subcarrier index is indicated; and for Random Access on an SCell, the PDCCH order indicates the ra-PreambleIndex with a value different from 000000 and the ra-PRACH-MaskIndex. For the pTAG preamble transmission on PRACH and reception of a PDCCH order are only supported for SpCell. If the UE is an NB-IoT UE, the Random Access procedure is performed on the anchor carrier or one of the non-anchor carriers for which PRACH resource has been configured in system information. Before the procedure can be initiated, the following information for related Serving Cell is assumed to be available for UEs other than NB-IoT UEs, BL UEs or UEs in enhanced coverage, as specified in TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8], unless explicitly stated otherwise: - the available set of PRACH resources for the transmission of the Random Access Preamble, prach-ConfigIndex. - the groups of Random Access Preambles and the set of available Random Access Preambles in each group (SpCell only): The preambles that are contained in Random Access Preambles group A and Random Access Preambles group B are calculated from the parameters numberOfRA-Preambles and sizeOfRA-PreamblesGroupA: If sizeOfRA-PreamblesGroupA is equal to numberOfRA-Preambles then there is no Random Access Preambles group B. The preambles in Random Access Preamble group A are the preambles 0 to sizeOfRA-PreamblesGroupA – 1 and, if it exists, the preambles in Random Access Preamble group B are the preambles sizeOfRA-PreamblesGroupA to numberOfRA-Preambles – 1 from the set of 64 preambles as defined in TS 36.211[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation ]  [7]. - if Random Access Preambles group B exists, the thresholds, messagePowerOffsetGroupB and messageSizeGroupA, the configured UE transmitted power of the Serving Cell performing the Random Access Procedure, PCMAX, c, as specified in TS 36.101[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception ]  [10], and the offset between the preamble and Msg3, deltaPreambleMsg3, that are required for selecting one of the two groups of Random Access Preambles (SpCell only). - the RA response window size ra-ResponseWindowSize. - the power-ramping factor powerRampingStep. - the maximum number of preamble transmission preambleTransMax. - the initial preamble power preambleInitialReceivedTargetPower. - the preamble format based offset DELTA_PREAMBLE (see clause 7.6). - the maximum number of Msg3 HARQ transmissions maxHARQ-Msg3Tx (SpCell only). - the Contention Resolution Timer mac-ContentionResolutionTimer (SpCell only). NOTE 1: The above parameters may be updated from upper layers before each Random Access procedure is initiated. The following information for related Serving Cell is assumed to be available before the procedure can be initiated for NB-IoT UEs, BL UEs or UEs in enhanced coverage, as specified in TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [8]: - if the UE is a BL UE or a UE in enhanced coverage: - the available set of PRACH resources associated with each enhanced coverage level supported in the Serving Cell for the transmission of the Random Access Preamble, prach-ConfigIndex. - for EDT, the available set of PRACH resources associated with EDT for each enhanced coverage level supported in the Serving Cell for the transmission of the Random Access Preamble, prach-ConfigIndex. - the groups of Random Access Preambles and the set of available Random Access Preambles in each group(SpCell only): - except for EDT: - if sizeOfRA-PreamblesGroupA is not equal to numberOfRA-Preambles: - Random Access Preambles group A and B exist and are calculated as above; - else: - the preambles that are contained in Random Access Preamble groups for each enhanced coverage level, if it exists, are the preambles firstPreamble to lastPreamble. - for EDT, the preambles that are contained in Random Access Preamble groups for each enhanced coverage level, if it exists, are the preambles firstPreamble to edt-LastPreamble if PRACH resources configured by edt-PRACH-ParametersCE are different from the PRACH resources configured by PRACH-ParametersCE for all enhanced coverage levels and edt-PRACH-ParametersCE for all other enhanced coverage levels, otherwise the preambles for EDT are the preambles lastPreamble+1 to edt-LastPreamble. NOTE 2: When a PRACH resource is shared for multiple enhanced coverage levels, and enhanced coverage levels are differentiated by different preamble indices, Group A and Group B is not used for this PRACH resource. - if the UE is an NB-IoT UE: - the available set of PRACH resources supported in the Serving Cell on the anchor carrier, nprach-ParametersList, and on the non-anchor carriers, in ul-ConfigList. - for EDT, the available set of PRACH resources associated with EDT on anchor carrier, nprach-ParametersList-EDT, and on the non-anchor carriers, in ul-ConfigList. - for random access resource selection and preamble transmission: - a PRACH resource is mapped into an enhanced coverage level. - each PRACH resource contains a set of nprach-NumSubcarriers subcarriers which can be partitioned into one or two groups for single/multi-tone Msg3 transmission by nprach-SubcarrierMSG3-RangeStart and nprach-NumCBRA-StartSubcarriers as specified in TS 36.211[ Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation ]  [7], clause 10.1.6.1. Each group is referred to as a Random Access Preamble group below in the procedure text. - a subcarrier is identified by the subcarrier index in the range: [nprach-SubcarrierOffset, nprach-SubcarrierOffset + nprach-NumSubcarriers -1] - each subcarrier of a Random Access Preamble group corresponds to a Random Access Preamble. - when the subcarrier index is explicitly sent from the eNB as part of a PDCCH order ra-PreambleIndex shall be set to the signalled subcarrier index. - the mapping of the PRACH resources into enhanced coverage levels is determined according to the following: - the number of enhanced coverage levels is equal to one plus the number of RSRP thresholds present in rsrp-ThresholdsPrachInfoList. - each enhanced coverage level has one anchor carrier PRACH resource present in nprach-ParametersList and zero or one PRACH resource for each non-anchor carrier signalled in ul-ConfigList. - for EDT, each enhanced coverage level has zero or one anchor carrier PRACH resource present in nprach-ParametersList-EDT and zero or one PRACH resource for each non-anchor carrier signalled in ul-ConfigList. - enhanced coverage levels are numbered from 0 and the mapping of PRACH resources to enhanced coverage levels are done in increasing numRepetitionsPerPreambleAttempt order. - when multiple carriers provide PRACH resources for the same enhanced coverage level, the UE will randomly select one of them using the following selection probabilities: - the selection probability of the anchor carrier PRACH resource for the given enhanced coverage level, nprach-ProbabilityAnchor, is given by the corresponding entry in nprach-ProbabilityAnchorList - the selection probability is equal for all non-anchor carrier PRACH resources and the probability of selecting one PRACH resource on a given non-anchor carrier is (1- nprach-ProbabilityAnchor)/(number of non-anchor NPRACH resources) - the criteria to select PRACH resources based on RSRP measurement per enhanced coverage level supported in the Serving Cell rsrp-ThresholdsPrachInfoList. - the maximum number of preamble transmission attempts per enhanced coverage level supported in the Serving Cell maxNumPreambleAttemptCE. - the number of repetitions required for preamble transmission per attempt for each enhanced coverage level supported in the Serving Cell numRepetitionPerPreambleAttempt. - the configured UE transmitted power of the Serving Cell performing the Random Access Procedure, PCMAX, c, as specified in TS 36.101[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception ]  [10]. - the RA response window size ra-ResponseWindowSize and the Contention Resolution Timer mac-ContentionResolutionTimer (SpCell only) per enhanced coverage level supported in the Serving Cell. - for EDT, the Contention Resolution Timer mac-ContentionResolutionTimer configured for EDT (SpCell only) per enhanced coverage level supported in the Serving Cell. - the power-ramping factor powerRampingStep and optionally powerRampingStepCE1. - the maximum number of preamble transmission preambleTransMax-CE. - the initial preamble power preambleInitialReceivedTargetPower and optionally preambleInitialReceivedTargetPowerCE1. - the preamble format based offset DELTA_PREAMBLE (see clause 7.6). - for NB-IoT, the use of contention free random access ra-CFRA-Config. The Random Access procedure shall be performed as follows: - flush the Msg3 buffer; - set the PREAMBLE_TRANSMISSION_COUNTER to 1; - if the UE is an NB-IoT UE, a BL UE or a UE in enhanced coverage: - set the PREAMBLE_TRANSMISSION_COUNTER_CE to 1; - if the starting enhanced coverage level, or for NB-IoT the starting number of NPRACH repetitions, has been indicated in the PDCCH order which initiated the Random Access procedure, or if the starting enhanced coverage level has been provided by upper layers: - the MAC entity considers itself to be in that enhanced coverage level regardless of the measured RSRP; - else: - if the RSRP threshold of enhanced coverage level 3 is configured by upper layers in rsrp-ThresholdsPrachInfoList and the measured RSRP is less than the RSRP threshold of enhanced coverage level 3 and the UE is capable of enhanced coverage level 3 then: - the MAC entity considers to be in enhanced coverage level 3; - else if the RSRP threshold of enhanced coverage level 2 configured by upper layers in rsrp-ThresholdsPrachInfoList and the measured RSRP is less than the RSRP threshold of enhanced coverage level 2 and the UE is capable of enhanced coverage level 2 then: - the MAC entity considers to be in enhanced coverage level 2; - else if the measured RSRP is less than the RSRP threshold of enhanced coverage level 1 as configured by upper layers in rsrp-ThresholdsPrachInfoList then: - the MAC entity considers to be in enhanced coverage level 1; - else: - the MAC entity considers to be in enhanced coverage level 0; - set the backoff parameter value to 0 ms; - for the RN, suspend any RN subframe configuration; - proceed to the selection of the Random Access Resource (see clause 5.1.2). NOTE 3: There is only one Random Access procedure ongoing at any point in time in a MAC entity. If the MAC entity receives a request for a new Random Access procedure while another is already ongoing in the MAC entity, it is up to UE implementation whether to continue with the ongoing procedure or start with the new procedure. NOTE 4: An NB-IoT UE measures RSRP on the anchor carrier.