TECHNICAL FIELD

The present disclosure is related to wireless communication systems and more particularly to how such systems perform random access procedures for user equipment.

BACKGROUND

A random access (RA) procedure is a key function in a cellular system. In Long-Term Evolution (LTE), a user equipment (UE) that would like to access the network initiates the random access procedure by transmitting a preamble (Msg1) in the uplink on the Physical Random Access Channel (PRACH). A gNB (next generation Node B or Transmission and Reception Point (TRP), e.g., a base station or access node) receiving the preamble and detecting the random-access attempt will respond in the downlink by transmitting a random access response (RAR, Msg2). The RAR carries an uplink scheduling grant for the UE to continue the procedure by transmitting a following subsequent message in the uplink (Msg3) for terminal identification. A similar procedure is envisioned for New Radio (NR).FIG. 1illustrates an example 4-step initial access procedure performed by a UE10and a gNB20of a NR system.

Referring toFIG. 1, before transmission of the PRACH preamble, the UE10receives both a set of synchronization signals (SS) and configuration parameters on a broadcast channel in an SS-block (e.g., NR-PSS, NR-SSS, New Radio Physical Broadcast Channel (NR-PBCH)), possibly complemented with configuration parameters received on yet another channel.

A new 2-step random access procedure is being proposed for NR, where the Msg1 and Msg3 of the 4-step procedure are sent together as a first step, and in the second step Msg2 and Msg4 of the 4-step procedure are sent. This 2-step procedure may reduce the latency of the whole random-access procedure because there are only 2 steps involved and may be beneficial for unlicensed access because there will be fewer listen-before-talk (LBT) operations.

Msg3 Scheduling

Msg3 is transmitted by using a Physical Uplink Shared Channel (PUSCH) channel. Besides Msg3 payload, Demodulation Reference Signal (DMRS) is also transmitted to assist the data decoding at the eNB. In both LTE and NR, for a 4-step random access procedure, the initial transmission of Msg3 is scheduled by the UL grant contained in RAR. The retransmission of Msg3 is scheduled by UL grant over Physical Downlink Control Channel (PDCCH). In LTE, Msg3 repetition can be configured by the UL grant contained in RAR to improve the coverage.

For simulating data channel and for decoding of the data within a target, reference signals such as DMRS are very important. Selecting the right DMRS pattern plays an important role. For example, if the channel is varying very fast then more DMRSs per slot are needed to allow determination of smother channel estimates. However, it is important to minimize the number of DMRS transmissions to reduce radio resource utilization.

SUMMARY

According to some embodiments of inventive concepts, a method of random access procedure by a network node for use with a user equipment, UE, of a wireless communication system is provided. A demodulation reference signal, DMRS, configuration may be selected from among a set of DMRS configurations based on obtained information. A DMRS transmission may be controlled during the random access procedure based on the selected DMRS configuration.

Having a fixed DMRS pattern for different use cases and scenarios is not an efficient use of resources. Since Msg3 is unicasted by each UE and since the UE has a defined characteristic (e.g., low speed UE, high speed UE, power limited UE, low mobility, etc.), using one DMRS pattern for the different use cases and scenarios is not optimal in terms of resource efficiency, overhead, and for channel estimation. Various of these inventive concepts may operate to more efficiently use resources, for example, when a UE is a low mobility UE it is determined that a DMRS configuration providing 1+1+1 (3 DMRS per slot) is not needed, and instead a DMRS configuration providing only 1 DMRS per slot is therefore used. These operations reduce DMRS overhead, which means that information bits can be sent over radio resources that would otherwise be used for DMRS transmission. Resource utilization efficiency is thereby improved.

According to some embodiments of inventive concepts, a user equipment, UE, for performing a random access procedure with a network node of a wireless communication system is provided. An indication of a demodulation reference signal, DMRS, configuration may be received from the network node. The DMRS configuration may be selected from among a set of DMRS configurations based on the received indication. DMRS transmission may be controlled during the random access procedure based on the selected DMRS configuration.

According to some embodiments of inventive concepts, a network node for controlling a random access procedure with a user equipment, UE, of a wireless communication system is provided. The network node may select a demodulation reference signal, DMRS, configuration from among a set of DMRS configurations based on obtained information. The network node may control DMRS transmission during the random access procedure based on the selected DMRS configuration.

According to some embodiments of inventive concepts, a network node (20, 500) for controlling a random access procedure with a user equipment, UE, of a wireless communication system is provided that has a network interface, a processor connected to the network interface, and, a memory storing program code that is executed by the processor to perform operations. The operations performed by the processor may include selecting a demodulation reference signal, DMRS, configuration from among a set of DMRS configurations based on obtained information. The operations performed by the processor may include controlling DMRS transmission during the random access procedure based on the selected DMRS configuration.

According to some embodiments of inventive concepts, a user equipment, UE, for performing a random access procedure with a network node of a wireless communication system is provided. The UE may receive (300) an indication of a demodulation reference signal, DMRS, configuration from the network node. The UE may select the DMRS configuration from among a set of DMRS configurations based on the received indication. The UE may control DMRS transmission during the random access procedure based on the selected DMRS configuration.

According to some embodiments of inventive concepts, a user equipment, UE, for performing a random access procedure with a network node of a wireless communication system is provided. The UE has a network interface, a processor connected to the network interface, and a memory storing program code that is executed by the processor to perform operations. The operations performed by the processor may include receiving an indication of a demodulation reference signal, DMRS, configuration from the network node. The operations performed by the processor may include selecting the DMRS configuration from among a set of DMRS configurations based on the received indication. The operations performed by the processor may include controlling DMRS transmission during the random access procedure based on the selected DMRS configuration.

