A method of random access procedure in cellular networks

Abstract

A method of random access procedure in a cellular network is described. The method com- prises receiving at least one first SSB beam from at least one SSB burst from at least one gNB. The method further comprises receiving a RACH configuration comprising scheduling of at least one first RO and at least one of at least one first value for the number of SSB beams sharing an RO and at least one second value for the number of contention based (CB) pream- bles. An SSB beam is determined from the at least one first SSB beam and at least one second RO corresponding to the SSB beam based on the RACH configuration. At least one PRACH is transmitted in the at least one second RO.

Description

A METHOD OF RANDOM ACCESS PROCEDURE IN CELLULAR NETWORKSFIELD OF THE INVENTION

[0001] The present invention relates to random access procedure in cellular communication, and more particularly to management of RACH Occasions and RACH preambles in a random access procedure.BACKGROUND OF THE INVENTION

[0002] Initial Access procedure is a sequence of processes by which user equipment (UE) establishes a connection with the base station (BS) and the network. The procedure enables UE to acquire downlink and uplink synchronization and obtain essential information i.e. system information to establish and maintain connection with network. The synchronization signal block (SSB) is a periodic message broadcasted by the BS to enable the UEs to acquire DL synchronization and to convey first set of system information to the UE. The UE, when needed, searches for SSB transmitted in a predefined time and frequency locations. SSB comprises of primary synchronization sequence (PSS), secondary synchronization sequence (SSS) and master information block (MIB). The PSS and SSS sequences are used by the UE to obtain the cell identity, obtain the frame boundary and also can be used to measure information about the channel, whereas the MIB is used by the UE to obtain crucial initial broadcast information like the frame information, the scheduling information for control information, etc. The BS broadcasts control information within the scheduled set of resources (a.k.a, CORESETO) and it provides scheduling information for system information block 1 (SIB1), which provides essential information about the cell and necessary configurations to perform various operations to latch on to the cell. E.g., information about the set of SSB associated with the cell, information about other system information blocks transmitted in the cell, configuration to perform random access channel (RACH) procedure, the DL / UL transmission pattern of the cell, etc.

[0003] RACH procedure is an essential part of wireless communication systems, and it plays a significant role in acquiring UL synchronization with the network, obtain specified ID for the radio access communication, etc. The RACH procedure is the first point of contact or the front door for the UE to the network. When a UE wants to connect to a network for the first time or after a period of inactivity, it uses the RACH to request access to the network. Further, the UEinitiate the RACH procedure for beam failure recovery (BFR), demand other system information blocks, handover, etc.

[0004] The RACH procedure in fifth generation (5G) new radio (NR) is broadly classified into two types: contention-based RACH procedure (CB-RACH) and contention-free RACH procedure (CF-RACH). In CB-RACH, the UE randomly selects a random access preamble from a pool of preambles configured and transmit the selected preamble to the BS in certain time frequency resources. The pool of preambles and the time frequency resources are determined by the UE based on RACH configuration provided in SIB1 and the measurement of SSBs by the UE. The time frequency resource for transmitting RACH preamble is also known as RACH occasions (RO). The pool of preambles is common for a set of UEs and can lead to contention if multiple UEs select the same preamble from the pool and transmit in same RO. Hence the procedure is termed CB-RACH. Using physical random access channel (PRACH) occasion, the BS determine information about the SSB beam selected by the UE, the propagation delay with the UE, timing misalignment at the UE, etc. and sends a response called MSG2, also known as random access response (RAR). The MSG2 consists of several critical information, such as the time advance (TA) command for timing adjustment, the RAPID (random access preamble ID) matching the preamble sent by the UE, an initial uplink grant for the UE, a temporary identifier called RA-RNTI (random access radio network temporary identifier) to the UE, etc.

[0005] After transmitting a preamble, the UEs wait for MSG2 in preconfigured set of resources, where the configuration for RAR window is provided to UE in SIB 1. After receiving MSG2 and performing the required timing adjustment, the UE transmits MSG3 using the uplink grant received in MSG2. The MSG3 is transmitted after applying TA and in physical UL shared channel (PUSCH). The MSG3 contains the UE identity, C-RNTI if UE was previously connected in the network or identity provided by the CORE network. In the case of contention, multiple UE transmit MSG3 in same resource. However, the BS decode only one MSG3 and sends MSG4 for contention resolution along with the identity of the UE contained in decoded MSG3. The UE compare identity received in MSG4 with identity transmitted in MSG3 and report RACH success only when a match is found. E.g., if UE has transmitted C- RNTI in MSG3 and received MSG4 on control channel addressed by C-RNTI. Since C-RNTI s unique, only intended UE will decode MSG4.OBJECTS OF THE INVENTION

[0006] A general objective of the present invention is to minimize wastage of ROs in a random access procedure.

[0007] Another obj ective of the present invention is to improve utilization of RACH preambles in a random access procedure.SUMMARY OF THE INVENTION

[0008] The summary is provided to introduce aspects related to random access procedure in cellular networks, and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[0009] In one embodiment, a method of random access procedure in a cellular network is described. The method comprises receiving, by a User Equipment (UE), at least one first Synchronization Signal Block (SSB) beam from at least one SSB burst from at least one gNB. The method further comprises receiving, by the UE, a RACH configuration comprising scheduling of at least one first RACH occasion (RO) and at least one of at least one first value for the number of SSB beams sharing an RO and at least one second value for the number of contention based (CB) preambles. The method further comprises determining, by the UE, an SSB beam from the at least one first SSB beam and at least one second RO corresponding to the SSB beam based on the RACH configuration. The method further comprises transmitting, by the UE, at least one physical random access channel (PRACH) in the at least one second RO.

[0010] In an aspect, at least one of the at least one first value and the at least one second value is applicable to the at least one second SSB beam.

[0011] In an aspect, the at least one second SSB beam is received in a radio resource control (RRC) message using GroupPresence information element (IE).

[0012] In an aspect, the method further comprises determining a number of fields used for indicating the at least one first value based on one of number of at least one active SSB beam in the at least one SSB burst, and number of at least one second SSB beam.

[0013] In an aspect, the method further comprises determining a number of fields used for indicating the at least one second value based on the at least one first value.

[0014] In an aspect, the at least one second value comprises at least one of number of CB preambles available for an SSB beam, number of CB preambles available for an SSB beam in the RO, number of CB preambles available in the RO, and a ratio of sharing CB preambles among SSB beams sharing the RO.

[0015] In an aspect, receiving the RACH configuration further comprises receiving at least one of an indication of the at least one active SSB beam, a threshold value of RSRP, total number of preambles available in a RO from the at least one first RO, duration of the RACH configuration, and periodicity.

[0016] In an aspect, the scheduling of at least one first RO comprises at least one of time domain position of the at least one first RO, frequency domain positions of the at least one first RO, number of RO, from at least one first RO, multiplexed in frequency domain, and an index from a predefined table comprising time resources for the at least one first RO.

[0017] In an aspect, the indication of at least one active SSB beam is received in radio resource control (RRC) message using ssb-PositionsInburst information element (IE).

[0018] In an aspect, the RACH configuration is received using system information block.

[0019] In an aspect, the RACH configuration is received in RRC message using RACH- ConfigCommon information element (IE).

[0020] In an aspect, determining the SSB beam comprises determining at least one RSRP value for the at least one first SSB beam, and determining the SSB beam based on an RSRP value from the at least one RSRP value.

[0021] In an aspect, the RSRP value is the highest value of the at least one RSRP value.

[0022] In an aspect, determining the at least one second RO comprises mapping the at least one first RO to the at least one active SSB beam based on at least one of at least one first value and at least one second value.

[0023] In an aspect, mapping is based on the order of an active SSB beam from the at least one active SSB beam in the at least one SSB burst.

[0024] In an aspect, mapping comprises determining an active SSB beam from the at least one active SSB beam, determining a second SSB beam from the at least one second SSB beam corresponding to the active SSB beam,determining a first value from the at least one first value corresponding to the second SSB beam, and assigning at least one RO from the at least one first RO to the active SSB beam based on the first value.

[0025] In an aspect, the active SSB beam has lowest index from the at least one active SSB beam and is not mapped to the at least one first RO.

[0026] In an aspect, the at least one RO starts from earliest RO the at least one first RO which is not mapped to the at least one active SSB beam.

[0027] In an aspect, transmitting the at least one PRACH comprises determining plurality of preambles for the SSB beam in the at least one second RO, and obtaining the at least one PRACH by selecting at least one preamble from the plurality of preambles in a random manner.

[0028] In an aspect, determining the plurality of preambles comprises determining number of CB preambles available in the at least one second RO, determining number of SSB beams sharing the at least one second RO, and dividing the number of CB preambles among the number of SSB beams

[0029] In an aspect, dividing the number of CB preambles is based on at least one of number of contention based (CB) preambles per SSB beam, and ratio of sharing CB preambles among SSB beams sharing the at least one second RO.

[0030] In an aspect, the method further comprises determining an association period. Determining the association period comprises at least one of determining total number of CB preambles needed for the at least one active SSB beam, and determining the minimum number of ROs from the at least one first RO required for the total number of preambles.

[0031] In an aspect, determining the association period is based on at least one of the at least one first value, number of at least one active SSB beam, number of CB preambles available for the at least one active SSB beam, and number of CB preambles available in an RO from the at least one first RO.

[0032] In an aspect, the at least one second RO is a subset of the at least one first RO.

[0033] In one embodiment, a method of random access procedure in a cellular network is described. The method comprises receiving, by a UE, at least one first Synchronization SignalBlock (SSB) beam from at least one SSB burst. The method further comprises receiving, by the UE, RACH configuration comprising scheduling of at least one first RACH occasion (RO) and information about RACH association period. Information about the RACH association period comprises at least one of number of RACH configuration period within the association period, total number of ROs from at least one first RO in the association period, total number of preambles in the association period, starting time resource, number of time resources, and periodicity. The method further comprises determining, by the UE, an SSB beam from the at least one first SSB beam and at least one second RO corresponding to the SSB beam based on the RACH configuration. The method further comprises transmitting, by the UE, at least one physical random access channel (PRACH) in the at least one second RO.

[0034] In an aspect, information about the RACH association period further comprises a mapping pattern.

[0035] In an aspect, the mapping pattern comprises information about dividing the RACH association period among at least one active SSB beam from the at least one SSB burst.

[0036] In an aspect, the mapping pattern comprises at least one ratio for dividing total number of preambles in the association period among the at least one active SSB beam, at least one ratio for dividing total number of preambles in an RO among the at least one active SSB beam, at least one ratio for dividing total number of ROs in the association period among the at least one active SSB beam, number of preambles associated with the at least one active SSB beam, number of ROs associated with the at least one active SSB beam, and at least one pattern for interleaving.

[0037] In an aspect, receiving RACH configuration further comprises receiving at least one active SSB beam from the at least one SSB burst in one of system information block and radio resource control (RRC) message using ssb-PositionsInburst information element (IE).

[0038] In an aspect, the at least one pattern for interleaving comprises at least one of information about grouping ROs in the association period, information about grouping ROs in the at least one second RO, and a time offset between at least one third RO and at least one fourth RO from the at least one second RO.

[0039] In an aspect, the RACH configuration further comprises at least one of an indication of at least one active SSB beam, a threshold value of RSRP, total number of preambles available in a RO from the at least one first RO, duration of the RACH configuration, and periodicity.

[0040] In an aspect, the scheduling of at least one first RO comprises at least one of time domain position of the at least one first RO, frequency domain positions of the at least one first RO, number of the at least one first RO multiplexed in frequency domain, and an index from a predefined table comprising time resources for the at least one first RO.

[0041] In an aspect, the RACH configuration is received in system information block.

[0042] In an aspect, the RACH configuration is received in radio resource control (RRC) message using RACH-ConfigCommon information element (IE).

[0043] In an aspect, determining the SSB beam comprises determining at least one RSRP value for the at least one first SSB beam, and determining the SSB beam based on an RSRP value from the at least one RSRP value.

[0044] In an aspect, the RSRP value is the highest value of the at least one RSRP value.

[0045] In an aspect, determining the at least one second RO comprises at least one of determining the number of at least one active SSB beam, determining one of total number of ROs and total number of preambles in the association period, and mapping one of the total number of ROs and the total number of preambles to the at least one active SSB beam.

[0046] In an aspect, mapping is based on the order of an active SSB beam from the at least one active SSB beam in the at least one SSB burst.

[0047] In an aspect, determining the at least one second RO comprises receiving at least one pattern for interleaving, dividing the association period into plurality of group of ROs depending on the at least one pattern, determining one of total number of ROs and total number of preambles in at least one group from the plurality of groups, andmapping one of the total number of ROs and the total number of preambles in the at least one group to the at least one active SSB beam.

[0048] In an aspect, transmitting the at least one PRACH comprises determining plurality of preambles for the SSB beam in the at least one second RO, and obtaining the at least one PRACH by selecting at least one preamble from the plurality of preambles in a random manner.

[0049] In an aspect, determining the plurality of preambles comprises determining number of CB preambles available in the at least one second RO, determining number of SSB beams sharing the at least one second RO, and dividing the number of CB preambles among the number of SSB beams.

[0050] In an aspect, dividing the number of CB preambles is based on at least one of number of contention based (CB) preambles per SSB beam, and at least one ratio for dividing total number of preambles in an RO among the at least one active SSB beam.

[0051] In an aspect, the at least one second RO is a subset of the at least one first RO.

[0052] A method of random access procedure in a cellular network is described. The method comprises transmitting, by a base station (BS), at least one first Synchronization Signal Block (SSB) beam from at least one SSB burst. The method further comprises transmitting, by the BS, a RACH configuration comprising scheduling of at least one first RACH occasion (RO) and at least one of at least one first value for the number of SSB beams sharing a RO, at least one second value for the number of contention based (CB) preambles, and information about the RACH association period. The method further comprises receiving, by the BS, at least one physical random access channel (PRACH) in at least one second RO. The method further comprises determining, by the BS, an SSB beam from the at least one first SSB beam based on the at least one PRACH and the at least one second RO.

[0053] In an aspect, at least one of the at least one first value and the at least one second value is applicable to the at least one second SSB beam.

[0054] In an aspect, the at least one second SSB beam is received in a radio resource control (RRC) message using GroupPresence information element (IE).

[0055] In an aspect, the at least one second SSB beam is a subset of the at least one first SSB beam.

[0056] In an aspect, the at least one second value comprises at least one ofnumber of CB preambles available for an SSB beam, number of CB preambles available for an SSB beam in an RO, number of CB preambles available in an RO, and a ratio of sharing CB preambles among SSB beams sharing an RO.

[0057] In an aspect, transmitting the RACH configuration further comprises transmitting at least one of an indication of the at least one first SSB beam, a threshold value of RSRP, total number of preambles available in a RO from the at least one first RO, duration of the RACH configuration, and periodicity.

[0058] In an aspect, transmitting the indication of at least one first SSB beam is in radio resource control (RRC) message using ssb-PositionsInburst information element (IE).

[0059] In an aspect, transmitting the RACH configuration is using at least one of system information block and radio resource control (RRC) message using RACH-ConfigCommon information element (IE).

[0060] In an aspect, the scheduling of at least one first RO comprises at least one of time domain position of the at least one first RO, frequency domain positions of the at least one first RO, number of RO, from at least one first RO, multiplexed in frequency domain, and an index from a predefined table comprising time resources for the at least one first RO.

[0061] In an aspect, determining the SSB beam comprises determining the identity of the SSB beam and identity of at least one UE, and transmitting at least one response in the SSB beam.

[0062] In an aspect, the at least one PRACH is received from the at least one UE.

[0063] In an aspect, information about the RACH association period further comprises a mapping pattern.

[0064] In an aspect, the mapping pattern comprises information about dividing the RACH association period among the at least one first SSB beam from the at least one SSB burst.

[0065] In an aspect, the mapping pattern comprises at least one ratio for dividing total number of preambles in the association period among the at least one first SSB beam,at least one ratio for dividing total number of preambles in an RO among the at least one first SSB beam, at least one ratio for dividing total number of ROs in the association period among the at least one first SSB beam, number of preambles associated with the at least one first SSB beam, number of ROs associated with the at least one first SSB beam, and at least one pattern for interleaving.

[0066] In an aspect, the at least one pattern for interleaving comprises at least one of information about grouping ROs in the association period, information about grouping ROs mapping to an SSB beam, and a time offset between at least one second RO and at least one third RO mapping to an SSB beam.

[0067] In an aspect, receiving the at least one PRACH comprises receiving at least one preamble.

[0068] In an aspect, determining the SSB beam from the at least one first SSB beam comprises mapping the at least one first SSB beam to the at least one first RO based on the RACH configuration, and determining at least one third SSB beam mapping to the at least one second RO,

[0069] In an aspect, determining the SSB beam from the at least one first SSB beam comprises determining one of total number of ROs and total number of preambles in the association period, mapping the at least one first SSB beam to one of the total number of ROs and the total number of preambles, and determining at least one third SSB beam mapping to the at least one second RO.

[0070] In an aspect, determining the SSB beam from the at least one first SSB beam comprises dividing the association period into plurality of group of ROs depending on at least one pattern for interleaving, determining one of total number of ROs and total number of preambles in at least one group from the plurality of groups, mapping the at least one first SSB beam to one of the total number of ROs and the total number of preambles in the at least one group, and determining at least one third SSB beam mapping to the at least one second RO.

[0071] In an aspect, the method further comprisesdetermining at least one preamble associated with the at least one second RO, dividing the at least one preamble among the at least one third SSB beam, and determining the SSB beam based on a preamble received in the at least one PRACH.BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Fig. 1 illustrates time domain configuration of RACH occasions.

[0073] Fig. 2 illustrates RACH association period and association pattern period.

[0074] Fig. 3 illustrates allocation of ROs in RACH association pattern period.

[0075] Fig. 4a illustrates continuous mapping of ROs of RACH association pattern period among SSBs.

[0076] Fig. 4b illustrates interleaved mapping of ROs of RACH association pattern period among SSBs.DETAILED DESCRIPTION OF THE INVENTION

[0077] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0078] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This disclosure may however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those of ordinary skill in the art. Moreover, all statements herein reciting embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).Configuration for RACH

[0079] In NR, the SSB is transmitted in multiple beams known as SSB burst set. In frequency range 1 (FR1), the SSB burst set can have a maximum of 8 beams, whereas in frequency range 2 the SSB burst set can have up to 64 beams. The actual SSBs transmitted in an SSB burst set is indicated to the UE using following information element (IE).• ssb-PositionsInburst: Indicate the time domain position of transmitted SSB in an SSB burst set. This IE has following fields: o groupPresence: In NR the SSBs can be grouped into 8 groups and each group can have 8 SSBs each. This bit string of length 8 indicates which groups of SSBs are present out of 8 groups. Value 0 in the bitmap indicates that the corresponding SS / PBCH group is not present while value 1 indicates that the corresponding SS / PBCH group is present. This field is present only in the case of FR2, where the total number of SSBs is larger than 8. o inOneGroup: This bit string of length 8 indicates which SSBs are present within a group. Value 0 in the bitmap indicates that the corresponding SS / PBCH block is not transmitted while value 1 indicates that the corresponding SS / PBCH block is transmitted. Further, the first / leftmost bit corresponds to SS / PBCH block index 0, the second bit corresponds to SS / PBCH block index 1, and so on.

[0080] The UE measures multiple beams in the SSB burst set, identifies the best beam based on measurement. Further, UE determines the RACH preambles and ROs corresponding to the best beam. The configuration to select the best beam, determine ROs and map SSB with the RO are provided to UE in SIB1, using IE RACH-ConfigCommon using the following fields.• rsrp-thresholdSSB'. This field configures the minimum reference signal received power (RSRP) value that an SSB beam should have. The UE determine RSRP value corresponding to multiple SSB beams received, compare the RSRP values with the threshold configured and select the SSB beam with RSRP value crossing threshold as the best beam. If none of the SSB beam crosses the threshold configured, then the UE select randomly one beam from the burst set.• totalNumberOfRA-Preambles: This field indicate the total number of preambles per PRACH occasion which are available for both the Contention Based and Contention Free RACH. In NR, a maximum of 64 preambles can be configured per RO and these preambles are divided into three groups: for CB-RACH, for CF-RACH and for other purpose. The other purpose include preamble for requesting other system informationblocks. E.g., if totalNumberOfRA-Preambles=5Q then out of 64 preambles, 50 are available for Contention Based and Contention Free RACH.• ssb-perRACH-OccasionAndCB-PreamblesPerSSB: This field conveys two parameters: o The first part indicates the number of SSBs sharing a RO. E.g., value of oneEighth corresponds to one SSB associated with 8 RACH occasions, value Four corresponds to 4 SSBs sharing a RACH occasion and so on. o The second part indicates the number of Contention Based preambles per SSB per valid RACH occasion. E.g. value n4 corresponds to 4 Contention Based preambles per SSB in a RO, value n8 corresponds to 8 Contention Based preambles per SSB in a RO, and so on.

[0081] These two parameters together indicate the number of CB preambles per RO and number of CF preambles. E.g., if ssb-perRACH-Occasion = 1 / 2 and CB-PreamblesPerSSB = 40 then each SSB beam span across 2 RO and 40 CB preambles are available to an SSB beam in a valid RO. Therefore, a total of 80 Contention Based preambles available to each SSB beam. Further, in a RO the difference between value indicated by totalNumberOfRA-Preambles and number of preambles available for CB-RACH gives the number of preambles available for CF- RACH. E.g., if totalNumberOfRA-Preambles=5Q and 40 preambles are for CB-RACH then remaining 10 preambles for CF-RACH. In another e.g., if totalNumberOfRA-Preambles=5lQ and ssb-perRACH-OccasionAndCB-PreamblesPer SSB = (2, n24) then, a total of 50 preambles are available for RACH, two SSBs will share a RO and n24 implies 24 preambles / SSB in a RO. Therefore, total number of CB preambles in a RO = 2 SSB / RO*24 preambles / SSB=48 Preambles. Remaining 2 preambles, out of total 50, are for contention free RACH. In general, the total number of CB preambles per RO is given by below equation.CBpreambles / RO = CBpreambles / SSB). Max l, SSB / RO)• prach-Configurationindex: Used to indicate the time domain positions of the ROs. The indicated value points to a row in RRC configured look up table, which provide preamble format to use (e.g., short or long preamble), the frame in which RO is present (i.e., even frame or odd frame), subframe / slots in which RO is present, the number of slots having RO in a subframe, number of RO within each slot, starting symbol of RO and duration of RO. o E.g., prach-Configuration / index indicates the following values: x = 2, y = 1, subframe number = (4, 9), PRACH slots within subframe = 2, PRACH occasion within PRACH slot = 3, PRACH duration = 4, and starting symbol = 0. Systemframe number satisfying condition, n_SFN mod x = y, only has RO. Applying x and y in formula only odd frames will have ROs. Field subframe number = (4, 9) implies subframes 4 and 9 within odd frame has RO. Further, each subframe has 2 slots, each slot has 3 ROs starting from symbol 0 and each RO is of duration 4 symbols. The time domain allocation of RO is illustrated in Fig. 1.• msgl-FDM'. Specifies the number of RO which are multiplexed in the frequency domain. E.g., msgl-FDM= implies 4 RO are multiplexed in frequency domain.• msg 1 -FrequencyStart'. Indicate the frequency domain positions of the RO. The field indicate the position of the lowest PRB belonging to the first RO. The indication is using a frequency offset with respect to starting PRB of the channel bandwidth. Number of PRBs in a RO depend on SCS of PUSCH, SCS of PRACH and length of RACH preamble. o E.g., For RACH SCS = 15 KHz and short preamble of 139 subcarriers, the preamble occupied BW = 2085 KHz. For SCS of PUSCH = 30 KHz, number of PRBs occupied by preamble = 2085 KHz / (12><30 KHz) = 6 PRBs.

[0082] Once UE obtains information about SSB, preambles and RO, the next step is to identify the RO corresponding to the SSB beams measured and determine the RO for the selected SSB beam. The SS / PBCH block indexes provided by ssb-PositionsInBurst are mapped to valid ROs in the below mentioned order: i. First, in increasing order of preamble indexes within a single RO ii. Second, in increasing order of frequency resource indexes for frequency multiplexed ROs iii. Third, in increasing order of time resource indexes for time multiplexed ROs within a RACH slot iv. Fourth, in increasing order of indexes for PRACH slotsTiming associated with RACH Process

[0083] Following timing relations has been defined in NR for RACH configuration and associated procedures:• RACH configuration period: Time duration for which time domain configuration provided for RACH, in prach-Configuration / index, get repeated. o E.g., if x and y provided in prach-Configurationindex is 2 and 1, respectively, then only odd system frames have ROs. Therefore, the RACH configuration period is 20 ms.• RACH association period: The RACH association period, starting from frame 0, for mapping SS / PBCH block indexes to ROs is the smallest number of RACH configuration period, from a predefined set, such that all SSB indices, provided in ssb-Posi- tionslnburst, are mapped at least once to the PRACH occasions. The possible number of PRACH configuration periods that can be counted in RACH association period is predefined in NR standards and is given in Table 1 provided below.Table 1 : Possible set of values for RACH association period

[0084] In one example, if there are 32 SSB beams, SSB / RO = 2 and 48 ROs within a 20 ms PRACH Configuration Period, then a total of 16 ROs are needed to cover all the SSBs. Since a single RACH configuration period has 48 ROs, each SSB can be mapped 3 times within a RACH configuration period. Therefore, RACH association period is 1 in this case.

[0085] In another example, if there are 64 SSB beams, 1 SSB / RO and 24 ROs within a 20 ms RACH Configuration Period then, a total of 64 ROs are needed to map all SSBs at least once. Therefore, 3 RACH configuration periods are needed to get the 64 ROs. However, the predefined set of values for association period does not include 3. Therefore, association period is considered as 4 RACH configuration periods, having a total of 96 ROs. Since there are 64 SSB beams, 64 ROs are used by SSB beams, out of 96 ROs, and the remaining 32 are unused.

[0086] The number of ROs in a RACH configuration period varies depending on the configuration of high priority signals and channels. E.g., if a configuration for SSB overlaps with RACH configuration period, then ROs within that period are not counted as valid ROs. Similarly, if at least one symbol of a RO is configured as DL by configuration, then the RO is not considered as valid. Therefore, the number of configuration period within a RACH association period keeps on varying.• RACH association pattern period: An association pattern period includes one or more association periods and is determined so that a pattern between ROs and SSB indices repeats at most every 160 msec. The ROs that are not associated with SSB indices after an integer number of association periods, if any, are not used for RACH transmissions.

[0087] For example, if there are 8 SSB beams and 1 SSB / RO, then association period should have 8 ROs. Further, RACH configuration period is assumed to be 10 ms and SSB periodicity is assumed to be 80 ms. Due to configuration for high priority signals and DL pattern the number of RO varies across RACH configuration period as: no valid RACH occasions are assumed in frames having SSB, 8 ROs in even frames and 6 ROs in odd frames. The RACH association period and the RACH association pattern period are illustrated in Fig. 2. As illustrated, one association period is represented using blue color, second association period is represented using yellow, and likewise. The first RACH association period (indicated in blue) comprises of 4 RACH configuration periods with 20 ROs, where each SSB is mapped twice (8 x 2 = 16 ROs) and the remaining 4 ROs are wasted. The second RACH association period (indicated in yellow) comprises 1 RACH configuration period with 8 ROs, where each SSB is mapped once. The mapping continues in a similar manner. The last association period (indicated in red) comprises 14 ROs and each of 8 SSBs is mapped once (8 x 1 = 8 ROs) and the remaining 6 ROs are wasted. Similarly, the last RACH configuration period in 160 ms window (illustrated in grey) has 6 ROs and it cannot be mapped to 8 SSBs. Therefore, ROs in the last RACH configuration period remain unused.

[0088] Currently in NR, the ROs are distributed uniformly across the SSB beams, irrespective of the user density, user arrival rate, etc. However, the user density or user arrival rate can vary across SSB beams depending on the characteristics of the region covered by the beam. Therefore, uniform allocation of RO and RACH preambles across SSBs can lead to wastage of preambles in some cases and contention in another case. E.g., consider an SSB beam 1 pointing to a shopping mall, where there is a high chance of the UE trying to connect to the network and SSB beam 2 pointing to highway with much lower UE arrival rate. Currently, if RACH- ConfigCommon indicates SSB / RO = 1 and CB preambles / SSB = 40 then SSB beam 1 and SSB beam 2 are associated with a pool of 40 preambles each. The UEs have to select one preamble for RACH from the pool. Since more UEs are trying to connect to SSB beam 1, there is a high probability that more than one UE selects the same preamble from the pool of 40, whereas the preambles assigned to SSB beam 2 may get wasted because of the small number of UEs trying to connect. Further, the contention increases the delay during initial access and processing atthe nodes, as the entire RACH process is to be repeated. Therefore, non-uniform allocation of RACH occasions and preambles is essential to avoid unnecessary delay in connecting to network, to ensure efficient utilization of RACH preambles and to minimize the processing at the node. Various methods to allocate the RACH preambles / occasions to SSB beams are proposed in present invention.

[0089] Further, the current NR framework results in wastage of ROs and preambles. E.g., the ROs, in a RACH association period, which doesn’t have enough preambles to map to all SSBs in the SSB burst set are left unused. The unused set increases because of the limited number of RACH configuration periods possible within a RACH association period. E.g., NR supports only 1, 2, 4, 8 or 16 RACH configuration periods within a RACH association period (See e.g. 2 under RACH association period in previous section). Similarly, the ROs, in RACH association pattern period, which doesn’t have enough preambles to map to all SSBs in SSB burst set are left unused (for ex. as described above in RACH association pattern period and shown in Fig. 2). Present invention also proposes methods to minimize the wastage of ROs and to improve utilization of RACH preambles.Method for Non-uniform Allocation of RACH occasions to SSB

[0090] Following methods can be used for non-uniform allocation of RO and preambles to the SSBs:

[0091] Method 1 : Configure multiple values for SSB per RO and CB preambles per SSB, where each value can be applicable to SSB or a group of SSB.

[0092] In one option, configure multiple ssb-perRACH-OccasionAndCBPreamblesPerSSB in RACH-ConfigCommon where each value is applicable for the SSB groups indicated by GroupPresence in ssb-PositionsInburst. The number of SSB in each Group and its index is given by InOneGroup in ssb-PositionsInburst.

[0093] For example, GroupPresence = 10110100, ssb-perRACH-OccasionAndCBPreambles PerSSB = { 1 / 2, 20}, {2, 20}, {8, 5}, { 1 / 4, 20}. The GroupPresence indicates 4 SSB groups are active, Groupl, 3, 4 and 6. Also, 4 different values are given for SSB / RO and CBpreambles / SSB. Therefore, Group 1 maps to {1 / 2, 20}, Group 3 maps to {2, 20} and so on. Further, based on configuration given, the SSB in Group 1 occupies 2 ROs and 20 CBpreambles / SSB in each RO. Therefore, each SSB in Group 1 has a total of 40 CB preambles. Similarly, in Group 3, two SSBs share a RO and each SSB has 20 CB preambles. Therefore, 40 CB preambles per RO.

[0094] The number of CB preambles per RO will vary from one RO to another depending on the SSB mapped to a RO and number of preambles assigned to that SSB. Consequently, the number of CF preambles per RO also varies from one RO to another. For the e.g., given above for RO mapping to SSB in Group 1, the CB preambles per RO is 20 whereas for RO mapping to SSB in Group 3, the CB preambles per RO is 40. If totalNumberOfRA-Preambles = 50, then the number of CF preambles / RO for first case is 30, whereas for second case it is 10.

[0095] In another option, indicate multiple CBpreambles / SSB in ssb-perRACH- OccasionAndCB-PreamblesPerSSB. This method can distribute preambles non-uniformly across SSBs when multiple SSBs share a RO or in case of single SSB share multiple ROs. In one example, ssb-perRACH-OccasionAndCB-PreamblesPerSSB = {4, 16, 12, 4, 8} indicating 4 SSB share a RO, SSB1 get 16 CB preambles, SSB2 gets 12, SSB3 gets 4 and SSB4 gets 8 preambles. In another example, ssb-perRACH-OccasionAndCB-PreamblesPerSSB = { 1 / 4, 30, 20, 10, 8} indicating each SSB gets 4 ROs, 30 CB preambles / SSB in first RO, 20 CB preambles in second RO, 5 CB preambles in third occasion and 8 CB preambles in fourth RO.

[0096] In this method, UE determines the number of values for CBpreambles / SSB indicated in ssb-perRACH-OccasionAndCB-PreamblesPerSSB based on number of SSB / RO. For the first e.g., given above SSB / RO = 4, and therefore, UE assumes 4 fields for CB preambles / SSB. In another option, various combinations of SSB / RO and CB preambles per SSB can be defined and the configuration can select one combination from the set. Further, in this method, the number of CB preambles per RO can be fixed across RO and only the division across SSBs sharing RO can be varied. Consequently, the number of CF preambles per RO remains the same across ROs.

[0097] In yet another option, indicate the ratio in which the CB preambles to be shared among SSBs sharing a RO. The UE determines the number of CB preambles per RO using SSB / RO and CB preambles / SSB and uses the ratio indicated to divide the number of CB preambles among SSBs. In first example, ssb-perRACH-OccasionAndCB-PreamblesPerSSB = {2, n20, 1 / 4, 3 / 4} implies 2 SSBs share a RO, 20 CB preambles per SSB / RO (implying 40 preamble / RO), first SSB gets 10 CB preambles and second SSB gets 30. In second example, ssb-perRACH-OccasionAndCB-PreamblesPerSSB = {4, nl6} ratio = { 1 / 4, 1 / 2, 1 / 8, 1 / 8} indicating 4 SSBs share RO, each SSB get 16 preambles (64 preambles per RO), SSB1 gets 16, SSB2 gets 32, SSB3 gets 8 and SSB4 gets 8. In third example, ssb-perRACH- OccasionAndCB-PreamblesPerSSB = { 1 / 4, nl6} and ratio = { 1, 1 / 2, 1 / 8, 1 / 4}, where first part is same as legacy indicating one SSB occupy 4 ROs and the SSB get 16 preambles. However,the ratio modifies the allocation of CB preambles / SSB in each RO. The ratio = 1 implies all 16 CB preambles are assigned to SSB in first RO out of 4, ratio = 1 / 2 implies the SSB is assigned 8 preambles in second RO out of 4, SSB gets 2 preambles in third RO and 4 preambles in fourth RO.

[0098] The ratio can be indicated to UE along with ssb-perRACH-OccasionAndCB- PreamblesPerSSB (as in first example mentioned above) or as a separate entity (as in second example mentioned above). UE determines the number of fields for indicating ratio based on the value of SSB / RO. For the e.g.1 above, SSB / RO=2, therefore two fields for ratio. Similarly, for second example, SSB / RO=4. Therefore, 4 fields indicate the ratio in which the preambles are divided among SSBs. The advantage with the method illustrated in second example and third example above is that the content of ssb-perRACH-OccasionAndCB-PreamblesPerSSB and the interpretation of the contents does not change. Further, in this method, the number of CB preambles per RO can be fixed across RO and only the division across SSBs sharing RO can be varied. Consequently, the number of CF preambles per RO can be the same across ROs.

[0099] Method 2: Configure CB preambles / RO and SSBs / RO. Instead of providing CB preambles per SSB to UE, configure CB preambles per RO. Introduce new IE ssb-perRACH- OccasionAndCB-PreamblesPerRO in RACHConfigCommon which indicates SSB per RO and CB preambles per RO. The indication can be applicable for each SSB or for group of SSBs.• In one option, configure multiple CB preambles / RO and SSB / RO to the UE, where each value is applicable for the SSB groups indicated by GroupPresence in ssb-Posi- tionslnburst. The number of SSB in each Group and its index is given by InOneGroup in ssb-PositionsInburst. For example, GroupPresence = 10110100, ssb-perRACH-Oc- casionAndCBPreambles PerRO = { 1 / 2, 20}, {2, 20}, {8, 20}, { 1 / 4, 20}. The GroupPresence indicates 4 SSB groups are active, Groupl, 3, 4 and 6. Also, 4 different values are given for SSB / RO and CBpreambles / RO. Therefore, Group 1 maps to { 1 / 2, 20}, Group 3 maps to {2, 20} and so on. Further, based on configuration given, the SSB in Group 1 occupies 2 ROs and 20 CB-preambles / RO. Therefore, each SSB in Group 1 has a total of 40 CB preambles. Similarly, two SSBs in Group 3 share a RO. Therefore, 20 preambles associated with RO are divided among the 2 SSBs.• In another option, configure CB preambles / RO, SSB / RO and division of preambles among SSBs sharing RO to the UE. The division can be indicated in terms of ratio or number of preambles per SSB. The division can be indicated along with ssb-perRACH- OccasionAndCBPreamblesPerRO or as a separate quantity. The UE determines thenumber of fields for indicating division based on the value of SSB / RO. In one example, CB based preambles / RO = 40, SSB / RO = 2, ratio = (3 / 4, 1 / 4). 40 CB based preambles will be divided among 2 SSBs, the first SSB gets 30 and second one gets 10. In another example, CB based preambles / RO = 40, SSB / RO = 2, CB-preamble / SSB = (30, 10). 40 CB based preambles in a RO will be divided among 2 SSBs, the first SSB gets 30 and second one gets 10.

[0100] The advantage with this method is that the number of CB preambles per RO can be fixed across ROs and only the division across SSBs sharing a RO can be varied. Consequently, the number of CF preambles per RO remains the same across ROs.

[0101] Method 3 : Configure CB preambles / RO and CB preambles needed for each SSB or group of SSB, using which the UE derive the mapping between SSB and RO.

[0102] In one example, CBPreamblesPerRO = 40, CBPreamblesPerSSB = {20, 10, 25, 45} and 4 active SSBs are configured then, first SSB is assigned 20 CB preambles, second SSB is assigned 10 CB preambles and so on. The first 20 preambles among 40 CB preambles in a RO is mapped to SSB1, next 10 preambles are mapped to SSB2, and remaining 10 preambles are mapped to SSB3. The remaining 15 preambles for SSB3 are assigned from the second RO. The SSB4 is assigned 25 preambles from second RO and remaining 20 preambles from third RO. Therefore, the first RO is shared by SSB1 (20 preambles), SSB2 (10 preambles) and partially by SSB3 (10 preambles out of 25). The second RO is shared partially by SSB3 (15 preambles out of 25) and SSB 4 (25 preambles out of 45). Finally, the third RO is assigned to SSB4 (20 preambles out of 45).

[0103] In another example, each value of the CB preambles / SSB indicate CB preambles for SSBs in a specific group. GroupPresence = 10110100, InOneGroup = 11001011, CBPreamblesPerRO = 40 and CBPreamblesPerSSB = {20, 10, 5, 15}. Here, SSB groups 1, 3, 4 and 6 are active. SSBs in group 1 are assigned with 20 CB preambles, SSBs in group 3 are configured with 10 CB preambles each, and so on.

[0104] In yet another example, the values of CB preambles / SSB indicate CB preambles for SSBs within a group. GroupPresence = 10110100, InOneGroup = 11001011, CBPreamblesPerRO = 40 and CBPreamblesPerSSB = {20, 10, 5, 15, 4}. Here, there are 4 active SSB groups, each group having 5 SSBs. The first SSB in each group is assigned with 20 CB preambles, second SSB in each group is assigned with 10 CB preambles, third SSB configured with 5 preambles and so on.

[0105] The advantage with this method is that the number of CB preambles and CF preambles remain the same across the ROs. Also, more flexibility is available for sharing preambles among SSBs. Also, the wastage of preambles and RO can be minimized.Impact of non-uniform allocation on timings associated with RACH

[0106] The non-uniform allocation of RO across SSB beams will have impact on calculation of total number of ROs needed to cover full SSB and hence on association period.• In one option, the ROs needed for each SSB in SSB burst set have to be counted to determine the total ROs needed in association period. For example, GroupPresence = 10110100, InOneGroup = 11001011, ssb-perRACH-OccasionAndCBPreambles PerSSB = { 1 / 2, 20}, {2, 20}, {5, 5}, { 1 / 4, 15}, then there are 4 active SSB groups in SSB burst set and each group has 5 SSBs. Further, each SSB in group 1 spans across 2 ROs, hence 5 SSBs in group 1 need 10 ROs. Similarly, 2 SSBs in group 3 share a RO and hence 5 SSBs need 3 ROs. 5 SSBs share RO in group 4, hence only 1 RO is needed to cover 5 SSBs in group 4. One SSB in group 6 spans across 4 ROs and hence 5 SSBs together needs 20 ROs. Therefore, in the e.g., the association period should have a total of 34 ROs (i.e., 10+3+1+20).• In another option, the total number of preambles needed for all SSBs in an SSB burst set can be counted, the count can be used to determine the total number of ROs needed and to determine the association period. For example, GroupPresence = 10110100, InOneGroup = 11001011, CBPreamblesPerRO = 40 and CBPreamblesPerSSBgroup = {20, 10, 5, 15}. Each SSB in group 1 needs 20 CB preambles, hence a total of 100 CB preambles. Similarly, CB preambles needed for SSBs in group 3, group 4 and group 6 are 50, 25, and 75, respectively. Hence, a total of 250 preambles (i.e., 100+50+25+75) are needed to cover all the SSBs. The number of ROs to get 250 preambles is 7 (i.e., ceil (250 / 40)). Hence, the association period should have 7 ROs. In another example, GroupPresence = 10110100, InOneGroup = 11001011, CBPreamblesPerRO = 40 and CBPreamblesPerSSBingroup = {20, 10, 5, 15, 4}. Here, the first SSB in each group needs 20 CB preambles, second SSB in each group needs 10 CB preambles and so on. Hence, a total of 54 preambles (i.e., 20+10+5+15+4) are needed per group. Total no. of preambles needed = {s\im(CBPreamblesPerSSBingroup)}zno. of groups = 216 preambles and no. of RO needed = ceil(Total no. of preambles needed I CBPreamblesPerRO) = 6 ROs for all SSBs. Hence, the RACH association period should have 6 ROs.• In yet another option, the total number of preambles needed for all the SSBs in an SSB burst set can be counted and can be used to determine the association period. The advantage with this method is that wastage of RACH preambles for counting in terms of RO can be avoided. For example, GroupPresence = 10110100, InOneGroup = 11001011, CBPreamblesPerRO = 40 and CBPreamblesPerSSBgroup = {20, 10, 5, 15}. Each SSB in group 1 needs 20 CB preambles, hence a total of 100 CB preambles. Similarly, CB preambles are 50, 25, and 75 for SSBs in group 3, group 4 and group 6, respectively. Hence, a total of 250 preambles (i.e., 100+50+25+75) are needed to cover all SSBs. Hence, the association period should have a total of 250 CB RACH preambles.Method for avoiding wastage of ROs / preambles

[0107] As mentioned earlier, the ROs and associated preambles in a RACH association period which are left out after completely mapping to available SSB beams are unused, leading to wastage of resources. For improving efficiency and to minimize collisions all the available ROs need to be mapped to SSB beams. Following methods can be used for such purpose:

[0108] In one method, the number of RACH configuration periods possible in a RACH association period can be increased, so that the wastage of ROs is minimized. Currently, the values supported are { 1, 2, 4, 8, 16} as illustrated in Table 1. Include more values like 3, 5, 6, etc. so that more flexibility is available in choosing the RACH association period.

[0109] For example, the configuration indicates 8 SSB beams and 1 SSB / RO then association period should have 8 ROs. If RACH configuration period is assumed to be 10 ms and SSB periodicity is assumed to be 80ms. Due to configuration for high priority signals and DL pattern the number of RO varies across RACH configuration period as: no valid RACH occasions are assumed in frames having SSB, 8 ROs in even frames and 6 ROs in odd frames. The scenario is shown in Fig. 3 illustrating allocation of ROs in RACH association pattern period. Now, the first association period will have 3 RACH configuration period comprising 14 ROs of which 8 will be assigned to SSBs. The second association period consists of 2 configuration period and will have 14 ROs of which 8 will be assigned to SSB and so on.

[0110] In another method, the RACH configuration can provide the ratio in which the ROs or preambles in an association period has to be divided among SSB beams. Hence the association period is computed using SSB / RO and number of configuration periods needed to map every SSB with a RO. The total number of ROs in the association period is computed andis divided among the SSBs as per ratio configured. Similarly, the ROs remaining after complete mapping in association pattern period can also be divided among SSBs based on the ratio indicated.

[0111] For example, the configuration indicates 8 SSB beams, 1 SSB / RO and ratio = { 1 / 8, 1 / 8, 14, 1 / 16, 1 / 16, 1 / 16, 1 / 16, 1 / 4}, then association period should have 8 ROs. If RACH configuration period is assumed to be 10ms and SSB periodicity is assumed to be 80ms. Due to configuration for high priority signals and DL pattern the number of RO varies across RACH configuration period as: no valid RACH occasions are assumed in frames having SSB, 8 ROs in even frames and 6 ROs in odd frames. The scenario is illustrated in Fig. 3. The first association period should have 4 RACH configuration periods comprising 20 ROs. Now, divide the 20 ROs among 8 SSBs based on the ratio indicated so that SSB land SSB2 gets 2.5 ROs (=20x 1 / 8), SSB3 gets 5 ROs, SSB4-SSB7 gets 1.25 and SSB8 gets 5 ROs. Further, SSB1 gets complete CB preambles in first two ROs and first half of preambles in third ROs. For SSB2 the preamble allocation starts from the second half of preambles in RO3 and complete set of CB preambles in RO4 and RO5. The second association period has 8 ROs and is divided among SSBs according to the ratio configured. The number of CB preambles per RO can be configured to the UE or can be determined based on conventional method using SSB / RO and CB-preamble / SSB. o For e.g., above, if minimum of 8 ROs is taken for association period and continue then at the end of 160ms association pattern period 6 ROs will remain (See e.g., in Fig. 2). Currently, this set of ROs remains unused, whereas in the proposed method, this set can be divided among the SSBs based on the ratio configured. i.e., SSB1 and SSB2 get 1 / 8x6 ROs, SSB3 gets 1 / 4x6 ROs and so on.• In another method, the total number of ROs or preambles available in association pattern period can be determined and can be divided among the SSBs. The ratio in which the ROs / preambles has to be divided among SSBs is configured to the UE. If the division is uniform, then the wastage will be minimized whereas in case of non-uniform division the wastage of RO and preamble can be avoided. o E.g., Consider RACH association pattern period of 160ms comprising 16 RACH configuration periods, as illustrated in Fig. 3. The number of ROs in even RACH configuration period is 8 whereas for odd RACH configuration period is 6. Further, the configuration period overlapping with SSB is not having valid ROs. Therefore, 160 ms RACH configuration period has total of 96 ROs(i.e., 6><8ROs+8x6ROs). In case of 8 SSB beams, the set of 96 ROs can be divided such that all 96 are configured to one of the SSB beams. In case ratio = { 1 / 8, 1 / 8, %, 1 / 16, 1 / 16, 1 / 16, 1 / 16, 1 / 4} then SSB1 and SSB2 gets 12 ROs (= 1 / 8x96 ROs), SSB3 gets 24 ROs (= 1 / 4x96 ROs), and so on. o In one option the ROs allocated to an SSB beam can be continuous. For the e.g., above, first 12 ROs are configured to SSB 1, SSB2 gets next 12 ROs, following 24 ROs are assigned to SSB3, SSB4-SSSB7 gets 6 ROs and SSB8 gets 24 ROs. The continuous mapping of ROs of RACH association pattern period among SSBs is illustrated in Fig. 4a. o In another option the ROs allocated to SSB can be interleaved. In that case the configuration will provide the number of sections into which the association pattern period has to be divided. For e.g., if number of sections is 4, then 12 ROs of SSB1 is divided into 4 blocks of 3 ROs each and is mapped to each section. Similar is the case with SSB2-SSB8. Hence, section 1 comprises 24 ROs, of which the first 3 are assigned to SSB1 followed by 3 ROs of SSB2, 6 ROs of SSB3, 1.5 ROs each from SSB4-SSB7 and 6 ROs from SSB8. The same pattern repeats across the sections. The interleaved mapping of ROs of RACH association pattern period among SSBs is illustrated in Fig. 4b.

[0112] In the above detailed description, reference is made to the accompanying drawings that form a part thereof, and illustrate the best mode presently contemplated for carrying out the invention. However, such description should not be considered as any limitation of scope of the present invention. The structure thus conceived in the present description is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence.

Claims

We Claim:

1. A method of random access procedure in a cellular network, the method comprising: receiving, by a User Equipment (UE), at least one first Synchronization Signal Block(SSB) beam from at least one SSB burst from at least one gNB; receiving, by the UE, a RACH configuration comprising scheduling of at least one first RACH occasion (RO) and at least one of at least one first value for the number of SSB beams sharing an RO and at least one second value for the number of contention based (CB) preambles; determining, by the UE, an SSB beam from the at least one first SSB beam and at least one second RO corresponding to the SSB beam based on the RACH configuration; and transmitting, by the UE, at least one physical random access channel (PRACH) in the at least one second RO.

2. The method as claimed in claim 1, wherein at least one of the at least one first value and the at least one second value is applicable to the at least one second SSB beam.

3. The method as claimed in claim 2, wherein the at least one second SSB beam is received in a radio resource control (RRC) message using GroupPresence information element (IE).

4. The method as claimed in claim 1, further comprises determining a number of fields used for indicating the at least one first value based on one of number of at least one active SSB beam in the at least one SSB burst, and number of at least one second SSB beam.

5. The method as claimed in claim 1, further comprises determining a number of fields used for indicating the at least one second value based on the at least one first value.

6. The method as claimed in claim 1, wherein the at least one second value comprises at least one of number of CB preambles available for an SSB beam, number of CB preambles available for an SSB beam in the RO, number of CB preambles available in the RO, and a ratio of sharing CB preambles among SSB beams sharing the RO.

7. The method as claimed in claim 1, wherein receiving the RACH configuration further comprises receiving at least one of an indication of the at least one active SSB beam, a threshold value of RSRP, total number of preambles available in a RO from the at least one first RO, duration of the RACH configuration, and periodicity.

8. The method as claimed in claim 1, wherein the scheduling of at least one first RO comprises at least one of time domain position of the at least one first RO, frequency domain positions of the at least one first RO, number of RO, from at least one first RO, multiplexed in frequency domain, and an index from a predefined table comprising time resources for the at least one first RO.

9. The method as claimed in claim 7, wherein the indication of at least one active SSB beam is received in radio resource control (RRC) message using ssb-PositionsInburst information element (IE).

10. The method as claimed in claim 1, wherein the RACH configuration is received using system information block.

11. The method as claimed in claim 1, wherein the RACH configuration is received in RRC message using RACH-ConfigCommon information element (IE).

12. The method as claimed in claim 1, wherein determining the SSB beam comprises determining at least one RSRP value for the at least one first SSB beam, and determining the SSB beam based on an RSRP value from the at least one RSRP value.

13. The method as claimed in claim 12, wherein the RSRP value is the highest value of the at least one RSRP value.

14. The method as claimed in claim 1, wherein determining the at least one second RO comprises mapping the at least one first RO to the at least one active SSB beam based on at least one of at least one first value and at least one second value.

15. The method as claimed in claim 14, wherein mapping is based on the order of an active SSB beam from the at least one active SSB beam in the at least one SSB burst.

16. The method as claimed in claim 14, wherein mapping comprises determining an active SSB beam from the at least one active SSB beam, determining a second SSB beam from the at least one second SSB beam corresponding to the active SSB beam, determining a first value from the at least one first value corresponding to the second SSB beam, and assigning at least one RO from the at least one first RO to the active SSB beam based on the first value.

17. The method as claimed in claim 16, wherein the active SSB beam has lowest index from the at least one active SSB beam and is not mapped to the at least one first RO.

18. The method as claimed in claim 16, wherein the at least one RO starts from earliest RO the at least one first RO which is not mapped to the at least one active SSB beam.

19. The method as claimed in claim 1, wherein transmitting the at least one PRACH comprises determining plurality of preambles for the SSB beam in the at least one second RO, and obtaining the at least one PRACH by selecting at least one preamble from the plurality of preambles in a random manner.

20. The method as claimed in claim 19, wherein determining the plurality of preambles comprises determining number of CB preambles available in the at least one second RO, determining number of SSB beams sharing the at least one second RO, and dividing the number of CB preambles among the number of SSB beams21. The method as claimed in claim 20, wherein dividing the number of CB preambles is based on at least one of number of contention based (CB) preambles per SSB beam, and ratio of sharing CB preambles among SSB beams sharing the at least one second RO.

22. The method as claimed in claim 1, further comprises determining an association period; wherein determining the association period comprises at least one of determining total number of CB preambles needed for the at least one active SSB beam, and determining the minimum number of ROs from the at least one first RO required for the total number of preambles.

23. The method as claimed in claim 22, wherein determining the association period is based on at least one of the at least one first value, number of at least one active SSB beam, number of CB preambles available for the at least one active SSB beam, and number of CB preambles available in an RO from the at least one first RO.

24. The method as claimed in claim 1, wherein the at least one second RO is a subset of the at least one first RO.

25. A method of random access procedure in a cellular network, the method comprising: receiving, by a UE, at least one first Synchronization Signal Block (SSB) beam from at least one SSB burst; receiving, by the UE, RACH configuration comprising scheduling of at least one first RACH occasion (RO) and information about RACH association period, wherein information about the RACH association period comprises at least one of number of RACH configuration period within the association period, total number of ROs from at least one first RO in the association period, total number of preambles in the association period, starting time resource, number of time resources, and periodicitydetermining, by the UE, an SSB beam from the at least one first SSB beam and at least one second RO corresponding to the SSB beam based on the RACH configuration, and transmitting, by the UE, at least one physical random access channel (PRACH) in the at least one second RO.

26. The method as claimed in claim 25, wherein information about the RACH association period further comprises a mapping pattern.

27. The method as claimed in claim 26, wherein the mapping pattern comprises information about dividing the RACH association period among at least one active SSB beam from the at least one SSB burst.

28. The method as claimed in claim 26, wherein the mapping pattern comprises at least one ratio for dividing total number of preambles in the association period among the at least one active SSB beam, at least one ratio for dividing total number of preambles in an RO among the at least one active SSB beam, at least one ratio for dividing total number of ROs in the association period among the at least one active SSB beam, number of preambles associated with the at least one active SSB beam, number of ROs associated with the at least one active SSB beam, and at least one pattern for interleaving.

29. The method as claimed in claim 25, wherein receiving RACH configuration further comprises receiving at least one active SSB beam from the at least one SSB burst in one of system information block and radio resource control (RRC) message using ssb-PositionsInburst information element (IE).

30. The method as claimed in claim 28, wherein the at least one pattern for interleaving comprises at least one of information about grouping ROs in the association period, information about grouping ROs in the at least one second RO, anda time offset between at least one third RO and at least one fourth RO from the at least one second RO.

31. The method as claimed in claim 25, wherein the RACH configuration further comprises at least one of an indication of at least one active SSB beam, a threshold value of RSRP, total number of preambles available in a RO from the at least one first RO, duration of the RACH configuration, and periodicity.

32. The method as claimed in claim 25, wherein the scheduling of at least one first RO comprises at least one of time domain position of the at least one first RO, frequency domain positions of the at least one first RO, number of the at least one first RO multiplexed in frequency domain, and an index from a predefined table comprising time resources for the at least one first RO.

33. The method as claimed in claim 25, wherein the RACH configuration is received in system information block.

34. The method as claimed in claim 25, wherein the RACH configuration is received in radio resource control (RRC) message using RACH-ConfigCommon information element (IE).

35. The method as claimed in claim 25, wherein determining the SSB beam comprises determining at least one RSRP value for the at least one first SSB beam, and determining the SSB beam based on an RSRP value from the at least one RSRP value.

36. The method as claimed in claim 35, wherein the RSRP value is the highest value of the at least one RSRP value.

37. The method as claimed in claim 25, wherein determining the at least one second RO comprises at least one of determining the number of at least one active SSB beam,determining one of total number of ROs and total number of preambles in the association period, and mapping one of the total number of ROs and the total number of preambles to the at least one active SSB beam.

38. The method as claimed in claim 37, wherein mapping is based on the order of an active SSB beam from the at least one active SSB beam in the at least one SSB burst.

39. The method as claimed in claim 25, wherein determining the at least one second RO comprises receiving at least one pattern for interleaving, dividing the association period into plurality of group of ROs depending on the at least one pattern, determining one of total number of ROs and total number of preambles in at least one group from the plurality of groups, and mapping one of the total number of ROs and the total number of preambles in the at least one group to the at least one active SSB beam.

40. The method as claimed in claim 25, wherein transmitting the at least one PRACH comprises determining plurality of preambles for the SSB beam in the at least one second RO, and obtaining the at least one PRACH by selecting at least one preamble from the plurality of preambles in a random manner.

41. The method as claimed in claim 40, wherein determining the plurality of preambles comprises determining number of CB preambles available in the at least one second RO, determining number of SSB beams sharing the at least one second RO, and dividing the number of CB preambles among the number of SSB beams.

42. The method as claimed in claim 41, wherein dividing the number of CB preambles is based on at least one of number of contention based (CB) preambles per SSB beam, andat least one ratio for dividing total number of preambles in an RO among the at least one active SSB beam.

43. The method as claimed in claim 25, wherein the at least one second RO is a subset of the at least one first RO.

44. A method of random access procedure in a cellular network, the method comprising: transmitting, by a base station (BS), at least one first Synchronization Signal Block(SSB) beam from at least one SSB burst, transmitting, by the BS, a RACH configuration comprising scheduling of at least one first RACH occasion (RO) and at least one of at least one first value for the number of SSB beams sharing a RO, at least one second value for the number of contention based (CB) preambles, and information about the RACH association period, receiving, by the BS, at least one physical random access channel (PRACH) in at least one second RO, and determining, by the BS, a SSB beam from the at least one first SSB beam based on the at least one PRACH and the at least one second RO.

45. The method as claimed in claim 44, wherein at least one of the at least one first value and the at least one second value is applicable to the at least one second SSB beam.

46. The method as claimed in claim 44, wherein the at least one second SSB beam is received in a radio resource control (RRC) message using GroupPresence information element (IE).

47. The method as claimed in claim 45, wherein the at least one second SSB beam is a subset of the at least one first SSB beam.

48. The method as claimed in claim 44, wherein the at least one second value comprises at least one of number of CB preambles available for an SSB beam, number of CB preambles available for an SSB beam in an RO, number of CB preambles available in an RO, anda ratio of sharing CB preambles among SSB beams sharing an RO.

49. The method as claimed in claim 44, wherein transmitting the RACH configuration further comprises transmitting at least one of an indication of the at least one first SSB beam, a threshold value of RSRP, total number of preambles available in a RO from the at least one first RO, duration of the RACH configuration, and periodicity.

50. The method as claimed in claim 49, wherein transmitting the indication of at least one first SSB beam is in radio resource control (RRC) message using ssb-PositionsInburst information element (IE).

51. The method as claimed in claim 44, wherein transmitting the RACH configuration is using at least one of system information block and radio resource control (RRC) message using RACH-ConfigCommon information element (IE).

52. The method as claimed in claim 44, wherein the scheduling of at least one first RO comprises at least one of time domain position of the at least one first RO, frequency domain positions of the at least one first RO, number of RO, from at least one first RO, multiplexed in frequency domain, and an index from a predefined table comprising time resources for the at least one first RO.

53. The method as claimed in claim 44, wherein determining the SSB beam comprises determining the identity of the SSB beam and identity of at least one UE, and transmitting at least one response in the SSB beam.

54. The method as claimed in claim 53, wherein the at least one PRACH is received from the at least one UE.

55. The method as claimed in claim 44, wherein information about the RACH association period further comprises a mapping pattern.

56. The method as claimed in claim 55, wherein the mapping pattern comprises information about dividing the RACH association period among the at least one first SSB beam from the at least one SSB burst.

57. The method as claimed in claim 55, wherein the mapping pattern comprises at least one ratio for dividing total number of preambles in the association period among the at least one first SSB beam, at least one ratio for dividing total number of preambles in an RO among the at least one first SSB beam, at least one ratio for dividing total number of ROs in the association period among the at least one first SSB beam, number of preambles associated with the at least one first SSB beam, number of ROs associated with the at least one first SSB beam, and at least one pattern for interleaving.

58. The method as claimed in claim 57, wherein the at least one pattern for interleaving comprises at least one of information about grouping ROs in the association period, information about grouping ROs mapping to an SSB beam, and a time offset between at least one second RO and at least one third RO mapping to anSSB beam.

59. The method as claimed in claim 44, wherein receiving the at least one PRACH comprises receiving at least one preamble.

60. The method as claimed in claim 44, wherein determining the SSB beam from the at least one first SSB beam comprises mapping the at least one first SSB beam to the at least one first RO based on the RACH configuration, and determining at least one third SSB beam mapping to the at least one second RO,61. The method as claimed in claim 44, wherein determining the SSB beam from the at least one first SSB beam comprisesdetermining one of total number of ROs and total number of preambles in the association period, mapping the at least one first SSB beam to one of the total number of ROs and the total number of preambles, and determining at least one third SSB beam mapping to the at least one second RO.

62. The method as claimed in claim 44, wherein determining the SSB beam from the at least one first SSB beam comprises dividing the association period into plurality of group of ROs depending on at least one pattern for interleaving, determining one of total number of ROs and total number of preambles in at least one group from the plurality of groups, mapping the at least one first SSB beam to one of the total number of ROs and the total number of preambles in the at least one group, and determining at least one third SSB beam mapping to the at least one second RO.

63. The method as claimed in claim 17 or 18 or 19, further comprises determining at least one preamble associated with the at least one second RO, dividing the at least one preamble among the at least one third SSB beam, and determining the SSB beam based on a preamble received in the at least one PRACH.

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