CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of International Application No. PCT/KR2019/006914 filed on Jun. 7, 2019, which claims priority to India Patent Application No. 201841021102 filed on Jun. 6, 2018 and India Patent Application No. 201841021102 filed on Jun. 5, 2019, the disclosures of which are herein incorporated by reference in their entirety.

BACKGROUND

1. Field

The present disclosure relates to a random access response reception by a User Equipment (UE) in a wireless communication system, and more particularly to a method and system for handling the random access response reception for an extended Random Access Response (RAR) timer or window in the wireless communication system.

2. Description of Related Art

To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.

In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.

In the recent years, several broadband wireless technologies have been developed to meet the growing number of broadband subscribers and to provide more and better applications and services. The second generation wireless communication system has been developed to provide voice services while ensuring the mobility of users. Third generation wireless communication system supports not only the voice service but also data service. In recent years, fourth wireless communication system has been developed to provide high-speed data service. However, currently, the fourth generation wireless communication system suffers from lack of resources to meet the growing demand for high speed data services. So fifth generation wireless communication system is being developed to meet the growing demand for high speed data services, support ultra-reliability and low latency applications.

The fifth generation wireless communication system will be implemented not only in lower frequency bands but also in higher frequency (mmWave) bands, e.g., 10 GHz to 100 GHz bands, so as to accomplish higher data rates. In order to mitigate propagation loss of the radio waves and increase the transmission distance, the beamforming, massive Multiple-Input Multiple-Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are being considered in the design of the fifth generation wireless communication system. In addition, the fifth generation wireless communication system is expected to address different use cases having quite different requirements in terms of data rate, latency, reliability, mobility etc. However, it is expected that the design of an air-interface of the fifth generation wireless communication system would be flexible enough to serve the UEs having quite different capabilities depending on the use case and market segment the UE cater service to the end customer. Few example use cases the fifth generation wireless communication system wireless system is expected to address is enhanced Mobile Broadband (eMBB), massive Machine Type Communication (m-MTC), ultra-reliable low latency communication (URLL) etc. The eMBB requirements like tens of Gbps data rate, low latency, high mobility so on and so forth address the market segment representing the conventional wireless broadband subscribers needing internet connectivity everywhere, all the time and on the go. The m-MTC requirements like very high connection density, infrequent data transmission, very long battery life, low mobility address so on and so forth address the market segment representing the Internet of Things (IoT)/Internet of Everything (IoE) envisioning connectivity of billions of devices. The URLL requirements like very low latency, very high reliability and variable mobility so on and so forth address the market segment representing the Industrial automation application, vehicle-to-vehicle/vehicle-to-infrastructure communication foreseen as one of the enabler for autonomous cars.

In the 5th generation (also referred as NR or New Radio) wireless communication system, the random access (RA) procedure is used to achieve uplink time synchronization. The RA procedure is used during initial access, handover, RRC connection re-establishment procedure, scheduling request transmission, beam failure recovery, SCG addition/modification and data or control information transmission in uplink by non-synchronized UE in RRC CONNECTED state. During the 4 step contention based RA procedure, the UE first transmits random access preamble (also referred as Msg1) and then waits for random access response (RAR) or Msg2 in the RAR window. In the RAR window, the UE monitors for PDCCH addressed to a random access radio network temporary identifier (RA-RNTI). The PDCCH search space for monitoring RAR is configured by GNB. The PDCCH addressed to RA-RNTI schedules DL TB (over PDSCH) which includes a RAR MAC PDU. Several RARs for various Random Access Preambles detected by the gNB can be multiplexed in the same RAR MAC PDU by gNB. An RAR in MAC PDU corresponds to UE's Random Access Preamble transmission if it includes RAPID of Random Access Preamble transmitted by it. If the RAR corresponding to its Random Access Preamble transmission is not received during the RAR window and the UE has not yet transmitted the Random Access Preamble for a configurable (configured by gNB in RACH configuration) number of times then, the UE retransmits the Random Access Preamble. If the RAR corresponding to its Random Access Preamble transmission is received, the UE transmits Msg3 in UL grant received in RAR. The Msg3 includes message such as RRC Connection Request, RRC Connection Re-establishment request, RRC handover confirm, scheduling request, RRC resume, SI request etc. It also includes the UE identity (i.e. C-RNTI or S-TMSI or a random number). After transmitting the Msg3, the UE starts a contention resolution timer. While the contention resolution timer is running, if the UE receives a PDCCH addressed to C-RNTI included in Msg3, contention resolution is considered successful, contention resolution timer is stopped and RA procedure is completed. While the contention resolution timer is running, if the UE receives contention resolution MAC CE including the UE's Contention Resolution Identity (first X bits of CCCH SDU transmitted in Msg3), contention resolution is considered successful, contention resolution timer is stopped and RA procedure is completed. If the contention resolution timer expires and the UE has not yet transmitted the Random Access Preamble for a configurable number of times, the UE retransmits the Random Access Preamble.

In the 5th generation (also referred as NR or New Radio) wireless communication system, 2 step contention-free RA (CFRA) procedure is also supported. The contention free RA procedure is used for scenarios such as handover where low latency is required, timing advance establishment for Scell, etc. the GNB assigns to UE non-contention RA preamble in dedicated signaling. The UE transmits the assigned non-contention RA preamble. The UE then waits for Random Access Response (RAR) or Msg2 in the RAR window. In the RAR window UE monitors for PDCCH addressed to RA-RNTI. PDCCH addressed to RA-RNTI schedules DL TB which includes RAR MAC PDU. Contention free RA procedure terminates after receiving the RAR corresponding to the transmitted RA preamble.

In order to reduce the latency of 4 step CBRA procedure, a 2 step CB RA procedure is also supported in NR. The 2 step RACH refers to the procedure which can complete RACH procedure in two steps and wherein PUSCH payload is also transmitted in addition to RA preamble in first step. It comprises of 2 messages i.e. msgA and msgB. The channel structure of msgA includes PRACH Preamble and PUSCH carrying payload. PRACH Preamble and PUSCH in the msgA is TDMed. In the 2 step CBRA procedure, UE sends additional information i.e. UE ID along with PRACH preamble in first step (i.e. MsgA). The UE ID can be one of Random ID, S-TMSI, C-RNTI, Resume ID, IMSI, idle mode ID, Inactive Mode ID, I-RNTI etc. The UE ID can be different in different scenarios in which UE performs the 2 step RA procedure. When the UE performs 2 step RA procedure after power on (before it is attached/registered to the network) then the UE ID is the random ID. When the UE perform 2 step RA procedure in IDLE state after it is attached/registered to the network, the UE ID is S-TMSI. If UE has an assigned C-RNTI (e.g. in connected state) the UE ID is C-RNTI. In case UE is in INACTIVE state, the UE ID is resume ID. In case MsgA includes dedicated RACH preamble, the UE ID can be skipped (i.e. not included) in Msg1. In this case gNB can identify the UE based on a dedicated preamble.

In 2 step CBRA procedure, after transmitting MsgA, UE monitors for MsgB in response window (similar to RAR-window). The PDCCH for MsgB is also addressed to RA-RNTI. Upon receiving the MsgB including the UE ID which UE has transmitted in MsgA, random access procedure is successfully completed.

In the RA procedure, RA-RNTI identifies the time-frequency resource (also referred as PRACH Occasion or PRACH TX Occasion or RACH Occasion) in which Random Access Preamble was detected by gNB. The maximum size of RAR Window is one radio frame i.e. 10 ms. The RA-RNTI is calculated as follows: RA-RNTI=1+s_id+14*t_id+14*80*f_id+14*80*8*ul_carrier_id, where

I. s_id is the index of the first OFDM symbol of the PRACH occasion where UE has transmitted Msg1 i.e. RA preamble; 0≤s_id≤14. OFDM symbols in a slot are sequentially numbered from zero.

II. t_id is the index of the first slot of the PRACH occasion (0≤t_id≤80). Slots in a radio frame are sequentially numbered from zero.

f_id is the index of the PRACH occasion within the slot in the frequency domain (0≤f_id≤8)

ul_carrier_id is the UL carrier used for Msg1 transmission (0 for NUL (normal uplink carrier) and 1 for SUL (supplementary carrier).

For a case of unlicensed operation gNB needs to check whether channel is free or not and it can transmit RAR and/or MsgB only if channel is free. As a result time for which the UE monitors for the RAR and/or MsgB can extend beyond 10 ms (i.e. 1 system frame or radio frame) period, in which case it is possible that multiple UEs monitor PDCCH scrambled with same RA-RNTI value at the same time even if their PRACH transmission occasions are different. This happens because even if two different UEs perform the PRACH transmission over different system frames, but if there PRACH occasion within a system frame is same (i.e. have s_id, t_id and f_id) than a computed RA-RNTI is common for both of the given UEs. Such a phenomenon can lead to an increased contention for the random access procedure thereby reducing an overall random access performance. In licensed operation also time for which the UE monitors for the RAR and/or MsgB can extend beyond 10 ms (i.e. 1 system frame or radio frame) period to provide enough processing time to gNB to prepare and transmit RAR and/or MsgB.

Thus, it is desired to address the above mentioned disadvantages or other shortcomings or at least provide a useful alternative.

The principal object of the embodiments herein is to provide a method and system for performing a random access response reception for an extended RAR timer or window in a wireless communication system.

SUMMARY

Accordingly, the embodiments herein provides a method for handling a RAR in a wireless communication system. The method includes transmitting, by a User Equipment (UE), a Physical Random Access Channel (PRACH) preamble. Further, the method includes determining, by the UE, a frame index value for the transmitted PRACH preamble based on at least one of a system frame number, a Channel Occupancy Time (COT) number, a subframe number and a time duration number. Further, the method includes monitoring, by the UE, the RAR in a RAR window based on the determined frame index value.

In an embodiment, monitoring, by the UE, the RAR in the RAR window based on the determined frame index value includes determining a Random Access Radio Network Temporary Identifier (RA-RNTI) based on the frame index value, monitoring a PDCCH addressed to the determined RA-RNTI, receiving the RAR corresponding to a RAPID of the PRACH preamble transmitted by the UE, wherein a transport block comprising the RAR is scheduled by the PDCCH addressed to the determined RA-RNTI, and declaring a successful reception of the RAR upon receiving the RAR corresponding to the RAPID of the PRACH preamble transmitted by the UE.

In an embodiment, monitoring, by the UE, the RAR in the RAR window based on the determined frame index value includes monitoring a PDCCH addressed to a RA-RNTI, receiving the PDCCH addressed to the RA-RNTI, wherein a DCI includes the determined frame index value, receiving the RAR corresponding to the RAPID of the PRACH transmitted by the UE, where a transport block including the RAR is scheduled by the received PDCCH, and declaring successful reception of the RAR upon receiving the RAR corresponding to the RAPID of the PRACH transmitted by the UE.

In an embodiment, monitoring, by the UE, the RAR in the RAR window based on the determined frame index value includes monitoring a PDCCH addressed to a RA-RNTI, receiving the PDCCH addressed to the RA-RNTI, receiving the RAR including a RAPID of the PRACH transmitted by the UE and the determined frame index, wherein a transport block including the RAR is scheduled by the received PDCCH, and declaring successful reception of the RAR upon receiving the RAR including the RAPID of the PRACH transmitted by the UE and the determined frame index value. The determined frame index value is present in one of a RAR MAC sub-header and a RAR payload.

In an embodiment, monitoring, by the UE, the RAR in the RAR window based on the determined frame index includes monitoring a PDCCH addressed to a RA-RNTI, wherein monitoring is performed in a DL radio resource corresponding to determined frame index value, receiving the PDCCH addressed to the RA-RNTI, receiving the RAR including a Random Access Preamble Identifier (RAPID) of the PRACH transmitted by the UE wherein a transport block including the RAR is scheduled by the received PDCCH, and declaring successful reception of the RAR upon receiving the RAR including the RAPID of the PRACH transmitted by the UE.

In an embodiment, further, the method includes initiating, by the UE, a RAR timer. Further, the method includes monitoring, by the UE, a PDCCH transmission addressed to a RA-RNTI value. Further, the method includes determining, by the UE, that the RAR is not received at an end of an ongoing PRACH period. Further, the method includes determining, by the UE, that an occurrence of a RACH failure in response to determining that the RAR is not received at the end of the PRACH period. Further, the method includes determining, by the UE, that a RAR monitoring period is greater than the PRACH period. Further, the method includes stopping, by the UE, a downlink RAR monitoring procedure. Further, the method includes performing, by the UE, actions applicable on the RACH failure in response to determining that the RAR monitoring period is exceeds the ongoing PRACH period and the RAR is not received at the end of the PRACH period.

In an embodiment, monitoring, by the UE, the RAR in the RAR window based on the determined frame index value includes monitoring a PDCCH addressed to a RA-RNTI, receiving the PDCCH addressed to the RA-RNTI, receiving and decoding TB scheduled by the PDCCH addressed to the RA-RNTI, determining that the RAR contains a backoff indicator, processing the backoff indicator based on the determination, determining that the RAR comprises a RAPID transmitted by the UE, determining whether the RAR includes the RAPID only, and performing one of: declaring successful reception of the RAR based on the successful determination, and processing a timing advance and received uplink grant within the RAR based on unsuccessful determination.

In an embodiment, further, the method includes starting, by the UE, a RAR timer. Further, the method includes monitoring, by the UE, a PDCCH transmission addressed to a RA-RNTI. Further, the method includes determining, by the UE, that the PDCCH transmission addressed to the RA-RNTI is received and a RAR is decoded. Further, the method includes processing, by the UE, a backoff-indicator included within the RAR based on the determination. Further, the method includes stopping, by the UE, the RAR timer. Further, the method includes determining, by the UE, that the RAR comprises the RAPID transmitted by the UE. Further, the method includes determining, by the UE, whether the RAR includes only RAPID. Further, the method includes performing, by the UE one of: in response to determining that the RAR includes the only RAPID, stopping a random access procedure and stopping the RAR timer (140), and in response to determining that the RAR does not include the only RAPID, determining that an uplink radio resource of an uplink grant included within the RAR is associated with the frame index value corresponding to the PRACH determined by the UE processing a timing advance within the RAR, processing an uplink grant, and stopping the RAR timer.

In an embodiment, the UE continuous to monitor the PDCCH transmission addressed to the RA-RNTI, if the uplink radio resource of the uplink grant included within the RAR is not associated with the frame index value corresponding to the PRACH determined by the UE

In an embodiment, the monitoring is performed in the DL radio resource corresponding to the determined frame index value by initiating, by the UE a RAR timer, determining, by the UE, whether a random access preamble is not selected by a medium access control (MAC) entity of the UE, performing, by the UE, one of: in response to determining that the random access preamble is not selected by the MAC entity of the UE determining that a downlink radio resource which is common to all frame index values, and in response to determining that the random access preamble is selected by the MAC entity of the UE determining that the downlink radio resource is associated with the frame index value.

In an embodiment, the RA-RNTI is obtained based on a first parameter and a second parameter, wherein the first parameter comprises a symbol index within a slot, a slot index within a system frame, a frequency index, an uplink carrier of the PRACH transmission, and wherein the second parameter comprises at least one of a function of the system frame number and the COT number, a system frame number period, a system frame number, a RAR window length, and a COT duration.

In an embodiment, the downlink radio resource comprises at least one of a CORESET, a PDCCH search space, a time domain radio resource, a frequency domain radio resource, and a bandwidth part.

In an embodiment, the uplink radio resource comprises at least one of a CORESET, a PDCCH search space, a time domain radio resource, a frequency domain radio resource, and a bandwidth part.

Accordingly, the embodiments herein provides a method for handling a RAR reception in a wireless communication system. The method includes determining, by a base station, at least one of an RA-RNTI value and a frame index value for a random access response message based on at least one of a system frame number, a Channel Occupancy Time (COT) number, a subframe number and a time duration number. Further, the method includes sending, by the base station, one or more of downlink transmissions associated to the random access response message based on at least one of the RA-RNTI value and the frame index value to a UE.

In an embodiment, the frame index value is included in one of a downlink Control Information (DCI) identified by a RA-RNTI which schedules RAR message, a RAR MAC sub-header of the random access response and a RAR payload of the random access response.

Accordingly, the embodiments herein provides a UE for handling a RAR in a wireless communication system. The UE includes a processor coupled with a memory. The processor is configured to transmit a PRACH preamble and determine a frame index value for the transmitted PRACH preamble based on at least one of a system frame number, a COT number, a subframe number and a time duration number. Further, the processor is configured to monitor the RAR in a RAR window based on the determined frame index value.

Accordingly, the embodiments herein provides a base station for handling a RAR reception in a wireless communication system. The base station includes a processor coupled with a memory. The processor is configured to determine at least one of an RA-RNTI value and a frame index value for a random access response message based on at least one of a system frame number, a COT number, a subframe number and a time duration number. The processor is configured to send one or more of downlink transmissions associated with the random access response message based on at least one of the RA-RNTI value and the frame index value to a UE.

These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

According to aspects of the present disclosure, a method and system for performing a random access response reception for an extended RAR timer or window in a wireless communication system are provided.

