CN106937404A - A kind of method that Stochastic accessing time delay is reduced on unlicensed spectrum - Google Patents

Abstract

The invention discloses a method for reducing random access time delay on an unlicensed frequency spectrum, belonging 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. By introducing a physical indication signal, the eNB instructs the UE to configure random access based on this signaling before the UE performs PRACH transmission. Each unlicensed carrier performs LBT sequence, so that the UE can access the channel as soon as possible. Since the base station transmits the physical indicator signal on the specified idle carrier, it plays a role of channel reservation to a certain extent, thereby further increasing the chance of the terminal succeeding in the first idle carrier monitoring and reducing the time delay of the random access process.

Description

A Method for Reducing Random Access Latency on Unlicensed Spectrum

technical field

The invention belongs to the technical field of mobile communication, relates to an assisted authorized access (LAA) system, and specifically refers to a method for reducing random access time delay on an unlicensed frequency 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 preamble conflicts. In the non-contention-based random access process, the network will assign a specific preamble to the user, and since other users will not use this preamble, the problem of preamble conflict is avoided. Specifically, the process of non-contention-based random access is: (1) In subframe #n (n is the subframe sequence number), the base station notifies the UE of the need to initiate random access 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 starting from subframe #n+k, where k≥6; (3) After the UE sends the preamble, it will Monitor the PDCCH in the random access response (RAR) time window to obtain the timing advance (TA) value.

Since traditional LTE only works on the licensed spectrum, in the carrier aggregation (CA) scenario, when all cells are deployed as the same Timing Advance Group (TAG), the UE only needs to establish random access with the primary cell (PCell) . The newly introduced assisted authorized access system (LAA system) allows unlicensed spectrum and licensed spectrum to be jointly deployed in the form of CA, and the licensed carrier is configured as a PCell, and the unlicensed carrier is configured as a secondary cell (SCell). Since the working frequency of PCell is usually 800MHz or 2GHz, and the working frequency of LAA SCell may be as high as 5.8GHz, the frequency difference between the two cells is so large that it is difficult for PCell and SCell to be in the same TAG, so it is necessary to perform LAA SCell random access process. In order to solve this problem, the 3rd Generation Partnership Project (3GPP) reached an agreement in the RAN1#84 meeting as follows: in the LAA SCell, non-contention-based random access subject to Listen Before Dialogue (LBT) is supported. 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: UE needs to maintain parallel connections with a macro base station (MeNB) and a secondary base station (SeNB) at the same time. In this scenario, if all connections between the UE and the SeNB are 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 the unlicensed spectrum in the LAA system, the UE will send a preamble on the unlicensed carrier. Due to the unknown channel status of the unlicensed carrier, the UE may fail the LBT before transmitting the preamble, so 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 to transmit PRACH 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 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 to perform LBT on the first available PRACH subframe. If LBT fails, the UE will select another carrier for LBT on the next available PRACH subframe, and so on, until it detects an idle carrier and then sends a preamble.

Contents of the invention

The present invention mainly solves the problem that in the LAA system, the low probability of random access channel access leads to high time delay in the whole 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 on multiple carriers in the same TAG. Due to the uncertainty of the availability of unlicensed carriers, LBT is performed on each scheduled carrier. The order will affect the delay of the whole random access process and the load of LBT. The present invention proposes a method for reducing the random access delay on the unlicensed spectrum. The method adopts the method of "LBT order indication". By introducing an additional signaling (called a physical indication signal), the eNB will Based on this signaling before PRACH transmission, the UE is instructed 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 by the base station side, and the channel status of each carrier is notified to the UE through a physical indication signal. The UE will first perform LBT on the carrier with the best channel condition, which improves the probability of successful LBT and effectively reduces Random access delay.

(2) Since the physical indicator signal will be configured to be transmitted on the carrier that the eNB considers to be the best channel state, it plays the role of reserving the channel to a certain extent, improving the probability of the UE's first LBT success, and further reducing the randomness. Access delay.

(3) The UE performs LBT on each carrier according to the order of channel quality according to the instructions of the eNB, avoiding frequent failures caused by random selection of carriers for LBT, reducing the number of times of LBT, thereby saving 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 in a specific subframe, so as to monitor the received signal on the corresponding carrier, avoiding the eNB Signals are monitored on the N carriers at the same time, thereby reducing the decoding times of the eNB to a certain extent.

Description of drawings

Fig. 1 is a schematic diagram of the execution process of 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 flow chart of a method for reducing random access delay at a UE side in a random access process based on an unlicensed spectrum.

detailed description

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

The present invention proposes a method for reducing the random access delay on the unlicensed frequency spectrum in the LAA system. In the method, first, the base station configures multiple unlicensed Carriers are 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 channel state information of N (N≥2) carriers, specifically, the eNB LBT is performed on the N carriers, and then the channel state information of the N carriers is obtained according to the LBT results, and sorted; then a physical indication signal is sent on the carrier with the best channel state, and the UE is notified by this physical indication signal The order in which LBT is performed on the N carriers. Starting from subframe #n+k (k≥6), UE performs LBT on each carrier according to the sequence of LBT 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 scheduled carrier, according to the order 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 Fig. 1, Fig. 2 and Fig. 3, the method for reducing the random access delay on the unlicensed spectrum provided by the present invention includes two parts, the base station end and the UE end, 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-layer signaling.

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

(3) Assuming that the first available subframe is #n+k, in subframe #n+k-1, eNB performs LBT on each scheduled carrier, judges the channel idleness of each carrier, and The physical indication signal is sent on the best carrier. For example, when the eNB finds that CC2 is idle and the channel status is the best, it sends a physical indication signal to the UE on the carrier CC2 to inform the UE of the order of LBT for each carrier (for example, CC2->CC1->CC3 indicates the priority of CC2 for PRACH transmission Highest). Note here that the eNB transmits the physical indication signal on the CC2 with the highest priority to reserve the channel, further improving the probability of the UE succeeding in LBT on the 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 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 return to step (3).

UE side:

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

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

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

(D) If the LBT on the current carrier (such as CC2) is successful, then the UE will send the preamble on the carrier CC2 in the subframe #n+k, otherwise the UE will send the preamble to the i+1th carrier CC1 at the end of #n+k Carry out LBT, and so on, if the LBT still fails when reaching the Nth carrier CC3, you need 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 return to step (C ).

Claims (3)

1. it is a kind of on unlicensed spectrum reduce Stochastic accessing time delay method, it is characterised in that：First, base station is believed by high-rise The N number of unauthorized carrier wave that order is configured with same TAG is used for Stochastic accessing；In subframe #n, base station sends PDCCH order Notify that UE carries out multicarrier Stochastic accessing in LAA SCell；In subframe #n+k-1, eNB carries out LBT to described N number of carrier wave, Then the result according to LBT draws the channel condition information of this N number of carrier wave, and is ranked up；It is then best in channel status Physics indication signal is sent on carrier wave, and notifies to carry out the suitable of LBT to this N number of carrier wave after UE by this physics indication signal Sequence；Since subframe #n+k, the order of the LBT that UE is indicated according to base station carries out LBT to each carrier wave, and in first for monitoring PRACH transmission is carried out on individual idle carrier wave.

2. it is according to claim 1 it is a kind of on unlicensed spectrum reduce Stochastic accessing time delay method, it is characterised in that： It is in the method for base station end reduction Stochastic accessing time delay：

(1) base station configures the N number of carrier wave under same TAG that will be dispatched by high-level signaling；

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

(3) assume that first available subframe is #n+k, in subframe #n+k-1, eNB carries out LBT to each carrier wave dispatched, and judges Go out the channel idle situation of each carrier wave, and physics indication signal is sent on the idle and best carrier wave of channel status, notify UE The order of LBT is carried out to each carrier wave；

(4) if base station receives preamble in PRACH transmission time windows, eNB will estimate TA values, and in RAR Between RAR is sent in window to UE；

If base station does not receive preamble at the appointed time, first available PRACH after the RAR time windows The previous subframe of frame carries out LBT to each carrier wave, returns to step (3).

3. it is according to claim 1 it is a kind of on unlicensed spectrum reduce Stochastic accessing time delay method, it is characterised in that： It is in the method for UE end station reduction Stochastic accessing time delay：

(A) UE knows the N number of PRACH candidate carriers in the same TAG for Stochastic accessing in high-level signaling；

(B) UE receives PDCCH order in subframe #n, obtains configured information, UE according to these information acquisitions PRACH transmit when Frequency resource information, then configures the running time-frequency resource that will be sent；

(C) in subframe #n+k-1, UE receives the physics indication signal of base station so as to obtain the precedence information that PRACH is transmitted, LBT is performed on carrier wave with physics indication signal；

(D) if LBT successes on current carrier, UE will send preamble on the carrier wave during subframe #n+k, and otherwise UE is in # The end symbol of n+k carries out LBT to i+1 carrier wave, the like, if still failed to LBT during n-th carrier wave, need The previous subframe of next available PRACH subframes that will be after RAR time windows receives the physics indication signal that base station sends, Return to step (C).