CN106937404B - Method for reducing random access time delay on unauthorized frequency spectrum - Google Patents

Abstract

The invention discloses a method for reducing random access delay on unlicensed frequency spectrum, and belongs to the technical field of mobile communication. The present invention adopts the method of "LBT sequence indication", the base station adopts multi-carrier scheduling for the random access of the terminal, and by introducing a physical indication signal, the eNB instructs the UE to configure the random access signal based on this signal before the UE performs PRACH transmission. The sequence of performing LBT on each unlicensed carrier enables the UE to access the channel as soon as possible. Since the base station transmits the physical indication signal on the designated idle carrier, it plays the role of channel reservation to a certain extent, thereby further increasing the chance of the terminal to successfully monitor the idle carrier for the first time and reducing the delay of the random access process.

Description

A method for reducing random access delay in unlicensed spectrum

technical field

The present invention belongs to the technical field of mobile communication, and relates to an authorized access (LAA) system, in particular, to a method for reducing random access delay on an unlicensed spectrum.

Background technique

In a Long Term Evolution (LTE) system, a user equipment (UE) can perform uplink transmission only after establishing a connection with a cell through a random access procedure and obtaining uplink synchronization. Two random access procedures are defined in the LTE standard, namely contention-based random access and non-contention-based random access. In the contention-based random access process, the UE will randomly select a preamble from the network-configured preamble resource pool to send, so multiple users may use the same preamble, resulting in a preamble conflict. In the non-contention-based random access process, the network assigns a specific preamble to the user, which avoids the problem of preamble conflict because other users will not use this preamble. Specifically, the process of non-contention-based random access is: (1) In subframe #n (n is the subframe sequence number), the base station informs the UE that random access needs to be initiated through the PDCCH order, and specifies the Preamble that the UE should use Index and PRACH Mask Index; (2) The UE sends the specified preamble in the first available PRACH subframe from subframe #n+k, where k≥6; (3) After the UE sends the preamble, it sends Monitor the PDCCH within a random access response (RAR) time window to obtain a timing advance (TA) value.

Since traditional LTE only works on the licensed spectrum, in the carrier aggregation (CA) scenario, when all cells are deployed in the same Timing Advance Group (TAG), the UE only needs to establish random access with the primary cell (PCell) . The newly introduced Auxiliary Authorized Access System (LAA system) allows the joint deployment of unlicensed spectrum and licensed spectrum in the form of CA, and configures licensed carriers as PCells and unlicensed carriers as secondary cells (SCells). Since the operating frequency of PCell is usually 800MHz or 2GHz, and the operating frequency of LAA SCell may be as high as 5.8GHz, the frequency difference between the two cells is so huge that it is difficult to make PCell and SCell in the same TAG. random access procedure. In order to solve this problem, the 3rd Generation Partnership Project (3GPP) reached an agreement at the RAN1 #84 meeting to support non-contention based random access in the LAA SCell subject to Listen Before Session (LBT). In other words, the random access of the unlicensed carrier will be triggered by the PDCCH order sent by the base station.

Another scenario that requires random access on an unlicensed carrier is a dual connectivity scenario: the UE needs to maintain parallel connections with the macro base station (MeNB) and the secondary base station (SeNB) at the same time. In this scenario, if the connection between the UE and the SeNB is all based on unlicensed spectrum, it is also necessary for the UE to perform random access to the SeNB on the unlicensed carrier.

When performing random access to unlicensed spectrum in the LAA system, the UE will send a preamble on the unlicensed carrier. Due to the unknown channel conditions of the unlicensed carrier, the UE may fail in LBT before transmitting the preamble. Therefore, the preamble to be transmitted will wait for the next available PRACH subframe to be transmitted or be discarded directly, thus causing a delay in the entire random access process.

In order to reduce the unexpected delay of the random access process, it is necessary to increase the access opportunity of PRACH transmission. However, according to the current random access process, the UE has only one chance of PRACH transmission before the end of the random access (RA) response window. In order to solve this problem, some companies propose to configure multiple PRACH transmissions in the "PRACH transmission time window" Chance. In addition, considering the different channel conditions on different unlicensed carriers, some companies propose a PDCCH order to schedule the UE to perform random access to multiple unlicensed carriers in the same TAG (3GPP R1-162669, R1-162803). For the second method, the UE will randomly select or use a carrier designated by the base station for LBT on the first available PRACH subframe. If the LBT fails, the UE will select another carrier for LBT on the next available PRACH subframe, and so on, until an idle carrier is detected and then the preamble is sent.

SUMMARY OF THE INVENTION

The present invention mainly solves the problem that in the LAA system, the channel access probability of random access is low, resulting in high time delay of the entire random access process. In the prior art, the base station (eNB) uses a PDCCH order to schedule the UE to perform LBT-compliant random access to multiple carriers in the same TAG. Due to the uncertainty of the availability of unlicensed carriers, LBT is performed on each scheduled carrier. The sequence will affect the delay of the entire random access process and the load of the LBT. The present invention proposes a method for reducing random access delay on unlicensed spectrum. The method adopts the method of "LBT sequence indication". Before performing PRACH transmission, the UE is instructed based on this signaling to perform LBT sequence on each unlicensed carrier configured for random access, so that the UE can access the channel as soon as possible, thereby reducing the random access delay.

The advantages of the present invention are:

(1) LBT is performed on each carrier in advance through the base station side, and the channel status of each carrier is notified to the UE through a physical indication signal. Random access delay.

(2) Since the physical indication signal will be configured to be transmitted on the carrier with the best channel state considered by the eNB, it plays a role in reserving the channel to a certain extent, improving the probability of the UE's first LBT success, and further reducing randomness. The latency of the access process.

(3) According to the instructions of the eNB, the UE performs LBT on each carrier in the order of channel quality, which avoids frequent failures caused by randomly selecting carriers for LBT, reduces the number of LBTs, and saves power to a certain extent.

(4) Since the order in which the UE performs LBT on each carrier is notified by the eNB, the eNB will also know which carrier the UE will perform LBT on on a specific subframe, so as to monitor the received signal on the corresponding carrier, avoiding the need for the eNB Signals are monitored on these N carriers at the same time, thereby reducing the number of decoding times of the eNB to a certain extent.

Description of drawings

FIG. 1 is a schematic diagram of the execution process on the eNB side and the UE side in the random access process based on the unlicensed spectrum.

FIG. 2 is a flow chart of a method for reducing random access delay at the eNB side in a random access process based on an unlicensed spectrum.

FIG. 3 is a flowchart of a method for reducing random access delay at the UE end in an unlicensed spectrum-based random access process.

Detailed ways

A method for reducing random access delay in unlicensed spectrum according to the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

The present invention proposes a method for reducing random access delay on an unlicensed spectrum in an LAA system. In the method, first, the base station configures multiple unlicensed TAGs in the same TAG through high-level signaling. The carrier is used for random access. In subframe #n, the base station sends a PDCCH order to notify the UE to perform multi-carrier random access in the LAA SCell. In subframe #n+k-1, the present invention introduces a new signaling (called a physical indication signal) for carrying the channel state information of N (N≥2) carriers. Perform LBT on the N carriers, and then obtain the channel state information of the N carriers according to the LBT results, and sort them; then send a physical indication signal on the carrier with the best channel state, and notify the UE through the physical indication signal. The sequence of performing LBT on these N carriers. Starting from subframe #n+k (k≥6), the UE performs LBT on each carrier according to the LBT sequence indicated by the base station, and performs PRACH transmission on the first monitored idle carrier. Since the eNB has previously performed channel evaluation on each of the scheduled carriers, according to the sequence indicated by the eNB, the UE can access the channel as soon as possible to reduce the delay of the random access process.

With reference to Figure 1, Figure 2 and Figure 3, the method for reducing random access delay on unlicensed spectrum provided by the present invention includes two parts: a base station and a UE, and the specific process is as follows:

Base Station:

(1) The base station configures N carriers (such as CC1, CC2, and CC3) under the same TAG to be scheduled through high-level signaling.

(2) In subframe #n (n is the subframe sequence number), the eNB sends a random access request (PDCCH order) to the UE, including information such as Preamble Index, PRACH Mask Index, etc., indicating the available preamble and PRACH transmission of the UE respectively. time-frequency resources.

(3) Assuming that the first available subframe is #n+k, in subframe #n+k-1, the eNB performs LBT on each scheduled carrier, determines the channel idle condition of each carrier, and determines the idle and channel status of each carrier. The physical indication signal is sent on the best carrier. For example, if the eNB finds that CC2 is idle and the channel state is the best, it sends a physical indication signal to the UE on the carrier CC2, informing the UE of the sequence of performing LBT on each carrier (for example, CC2->CC1->CC3 indicates the priority of CC2 for PRACH transmission). Highest). Note that the eNB transmits the physical indication signal on CC2 with the highest priority here, which can play the role of reserving the channel, which further improves the probability of the UE succeeding in LBT on CC2.

(4) If the base station receives the preamble within the PRACH transmission time window, such as subframe #n+m (m≥k), the eNB will estimate the TA value and send the RAR to the UE within the RAR time window.

If the base station does not receive the preamble within the specified time, perform LBT on each carrier in the subframe before the first available PRACH subframe after the RAR time window, and go back to step (3).

UE side:

(A) The UE acquires N PRACH candidate carriers in the same TAG for random access in high-layer signaling, and initializes i=1.

(B) The UE receives the PDCCH order in subframe #n, and obtains indication information (random access request), including information such as PreambleIndex, PRACH Mask Index, etc. The UE obtains the time-frequency resource information of PRACH transmission according to these information, and then configures the upcoming Time-frequency resources sent.

(C) In subframe #n+k-1, the UE receives the physical indication signal of the base station to obtain priority information of PRACH transmission, and performs LBT on the carrier with the physical indication signal. According to the example proposed by the eNB side above, if the eNB sends a physical indication signal to the UE on the carrier CC2, the UE will perform LBT on CC2 at the end symbol of subframe #n+k-1;

(D) If the LBT on the current carrier (such as CC2) is successful, the UE will send the preamble on the carrier CC2 in subframe #n+k, otherwise the UE will send a preamble to the i+1th carrier CC1 at the end symbol of #n+k Perform LBT, and so on. If LBT still fails when the Nth carrier CC3 is reached, it is necessary to receive the physical indication signal sent by the base station in the previous subframe of the next available PRACH subframe after the RAR time window, and go back to step (C). ).

Claims (3)

1. A method for reducing random access delay in an unlicensed spectrum, comprising: firstly, a base station configures N unauthorized carriers in the same TAG timing advance group for random access through high-level signaling; in a subframe # n, a base station sends a PDCCH order random access request to inform UE of carrying out multi-carrier random access in an LAA SCell auxiliary authorization access auxiliary cell; in a subframe # N + k-1, the eNB monitors the N carriers before LBT conversation, then obtains the channel state information of the N carriers according to the LBT result, and sequences the N carriers; then, sending a physical indication signal on the carrier with the best channel state, and informing the UE of the LBT sequence of the N carriers through the physical indication signal; starting from the subframe # n + k, the UE performs LBT on each carrier according to the LBT sequence indicated by the base station, and performs PRACH physical random access channel transmission on the monitored first idle carrier.

2. The method of claim 1, wherein the method for reducing random access delay on unlicensed spectrum comprises: the method for reducing the random access time delay at the base station end comprises the following steps:

(1) a base station configures N carriers to be scheduled under the same TAG through a high-level signaling;

(2) in a subframe # n, the eNB sends a random access request PDCCH order to UE user equipment to indicate available time-frequency resources of the UE;

(3) assuming that the first available subframe is # n + k, in the subframe # n + k-1, the eNB carries out LBT on each scheduled carrier, judges the channel idle condition of each carrier, and sends a physical indication signal on the idle carrier with the best channel state to inform the UE of the LBT sequence of each carrier;

(4) if the base station receives preamble in the PRACH transmission time window, the eNB estimates a TA timing advance value and sends RAR to the UE in the RAR random access response time window;

and (4) if the base station does not receive the preamble within the specified time, carrying out LBT on each carrier in a subframe before the first available PRACH subframe after the RAR time window, and returning to the step (3).

3. The method of claim 1, wherein the method for reducing random access delay on unlicensed spectrum comprises: the method for reducing the random access time delay at the UE end station comprises the following steps:

(A) the UE acquires N PRACH candidate carriers in the same TAG for random access in a high-level signaling;

(B) the UE receives the PDCCH order in the subframe # n, acquires the indication information, acquires the time-frequency resource information transmitted by the PRACH according to the information, and then configures the time-frequency resource to be transmitted;

(C) in a subframe # n + k-1, the UE receives a physical indication signal of a base station so as to obtain priority information of PRACH transmission, and performs LBT on a carrier with the physical indication signal;

(D) if the LBT on the current carrier is successful, the UE will send preamble on the carrier when subframe # N + k, otherwise the UE performs LBT on the i +1 th carrier at the last symbol of # N + k, and so on, if LBT still fails when the nth carrier is reached, it needs to receive the physical indication signal sent by the base station in the previous subframe of the next available PRACH subframe after the RAR time window, and returns to step (C).

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