CN106937404B - Method for reducing random access time delay on unauthorized frequency spectrum - Google Patents
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- H04W74/0833—Random access procedures, e.g. with 4-step access
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- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
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Abstract
The invention discloses a method for reducing random access time delay on an unauthorized frequency spectrum, belonging to the technical field of mobile communication. The invention adopts a method of 'LBT sequence indication', a base station adopts multi-carrier scheduling for random access of a terminal, and an eNB indicates the sequence of LBT of each configured unauthorized carrier wave for random access by the UE based on a signaling before PRACH transmission of the UE by introducing a physical indication signal, so that the UE can access a channel as soon as possible. The base station transmits the physical indication signal on the appointed idle carrier, so the base station plays a role of channel reservation to a certain extent, thereby further increasing the probability of successful monitoring of the idle carrier of the terminal for the first time and reducing the time delay of the random access process.
Description
Technical Field
The invention belongs to the technical field of mobile communication, relates to an auxiliary authorized access (LAA) system, and particularly relates to a method for reducing random access time delay on an unauthorized frequency spectrum.
Background
In a Long Term Evolution (LTE) system, User Equipment (UE) can perform uplink transmission only after establishing a connection with a cell through a random access procedure and acquiring 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 randomly selects one preamble from a preamble resource pool configured by a network to transmit, so that a situation that multiple users use the same preamble may occur, thereby causing preamble collision. In the non-contention based random access process, the network allocates a specific preamble to the user, and the problem of preamble collision is avoided because other users cannot use the preamble. Specifically, the procedure of non-contention based random access is as follows: (1) when a subframe # n (n is a subframe sequence number), a base station informs UE of needing to initiate random access through a PDCCH order, and designates Preamble Index and PRACH Mask Index which the UE should use; (2) the UE sends a specified preamble in the first available PRACH subframe from the subframe # n + k, wherein k is more than or equal to 6; (3) after the UE sends the preamble, the UE monitors the PDCCH within a Random Access Response (RAR) time window to obtain a Timing Advance (TA) value.
Because the conventional LTE only works on the licensed spectrum, in a 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). And a newly introduced secondary licensed access system (LAA system) allows the unlicensed spectrum and the licensed spectrum to be jointly deployed in a CA manner, and configures a licensed carrier as a PCell and an unlicensed carrier as a secondary cell (SCell). Since the operating frequency of the PCell is usually at 800MHz or 2GHz, while the operating frequency of the LAA SCell may be up to 5.8GHz, the frequency difference between the two cells is so large that it is difficult to make the PCell and the SCell in the same TAG, and therefore it is necessary to perform a random access procedure on the LAA SCell. To address this issue, the third generation partnership project (3GPP) agreed to the following at RAN1#84 conferences: non-contention based random access compliant Listen Before Talk (LBT) is supported in the LAA SCell. In other words, random access of the unlicensed carrier will be triggered by the PDCCH order sent by the base station.
Another scenario requiring random access on an unlicensed carrier is a dual connectivity scenario: the UE needs to simultaneously maintain parallel connections with the macro base station (MeNB) and the secondary base station (SeNB). In this scenario, it is also necessary for the UE to have random access to the SeNB on an unlicensed carrier if the UE's connection to the SeNB is entirely based on unlicensed spectrum.
When random access is performed to the unlicensed spectrum in the LAA system, the UE may send a preamble on the unlicensed carrier. Due to the unknown condition of the unlicensed carrier channel, the LBT may fail before the preamble is transmitted by the UE, and therefore, the preamble to be transmitted will wait for the next available PRACH subframe to be transmitted or be directly discarded, thereby causing a delay of the whole random access process.
In order to reduce the unexpected delay of the random access procedure, the access opportunity for PRACH transmission needs to be increased. However, as known from the current random access procedure, the UE has only one opportunity of PRACH transmission before the end of the Random Access (RA) response window, and to solve this problem, some companies propose to configure multiple PRACH transmission opportunities in the "PRACH transmission time window". In addition, some companies propose one PDCCH order to schedule UEs for random access to multiple unlicensed carriers in the same TAG, considering the different channel conditions on different unlicensed carriers (3GPP R1-162669, R1-162803). For the second approach, the UE will randomly select or LBT using one carrier designated by the base station on the first available PRACH subframe. If LBT fails, the UE selects another carrier on the next available PRACH subframe for LBT, and so on until detecting an idle carrier and then sending a preamble.
Disclosure of Invention
The invention mainly solves the problem that the time delay of the whole random access process is higher due to the low channel access probability of the random access in an LAA system. In the prior art, a base station (eNB) schedules a UE to perform LBT-compliant random access on multiple carriers in the same TAG by using one PDCCH order, and due to uncertainty of availability of unlicensed carriers, the order of performing LBT on each scheduled carrier may affect the delay of the whole random access process and the load of LBT. The invention provides a method for reducing random access time delay on an unauthorized frequency spectrum, which adopts a method of 'LBT sequence indication', and by introducing an additional signaling (called as a physical indication signal), an eNB indicates the UE to execute the LBT sequence on each configured unauthorized carrier wave for random access based on the signaling before the PRACH transmission of the UE, so that the UE can access a channel as soon as possible, thereby reducing the random access time delay.
The invention has the advantages that:
(1) the LBT is carried out on each carrier wave in advance through the base station side, the channel state of each carrier wave is informed to the UE through the physical indication signal, the UE carries out the LBT on the carrier wave with the best channel condition firstly, the successful probability of the LBT is improved, and the random access time delay is effectively reduced.
(2) The physical indication signal is configured on the carrier wave with the best channel state considered by the eNB for transmission, so that the channel reservation function is achieved to a certain extent, the probability of the first LBT success of the UE is improved, and the time delay of the random access process is further reduced.
(3) The UE performs LBT on each carrier according to the indication of the eNB and the sequence of the quality of the channel, thereby avoiding frequent failure caused by randomly selecting the carrier for LBT, reducing the frequency of LBT and further saving electric quantity to a certain extent.
(4) Since the sequence of performing LBT on each carrier by the UE is notified by the eNB, the eNB will also know which carrier the UE will perform LBT on in a certain specific subframe, so as to monitor the received signal on the corresponding carrier, thereby avoiding the eNB monitoring the signal on the N carriers at the same time, and thus reducing the number of decoding times of the eNB to a certain extent.
Drawings
Fig. 1 is a schematic diagram of an eNB side and a UE side performing a random access procedure based on an unlicensed spectrum.
Fig. 2 is a flowchart of a method for reducing a random access delay at an eNB end in a random access process based on an unlicensed spectrum.
Fig. 3 is a flowchart of a method for reducing a random access delay at a UE side in a random access process based on an unlicensed spectrum.
Detailed Description
The following describes a method for reducing random access delay on an unlicensed spectrum according to the present invention in detail with reference to the accompanying drawings and embodiments.
The invention provides a method for reducing random access time delay on an unauthorized frequency spectrum in an LAA system. In subframe # n, the base station sends a PDCCH order to inform the UE of performing multi-carrier random access in the LAA SCell. In a subframe # N + k-1, the invention introduces a new signaling (called physical indication signal) for carrying channel state information of N (N is more than or equal to 2) carriers, specifically, an eNB carries out LBT on the N carriers, then obtains the channel state information of the N carriers according to the LBT result, and sequences the information; and 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 a subframe # n + k (k is more than or equal to 6), the UE performs LBT on each carrier according to the LBT sequence indicated by the base station, and performs PRACH transmission on the monitored first idle carrier. Since the eNB has previously performed channel estimation 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 procedure.
With reference to fig. 1, fig. 2 and fig. 3, the method for reducing random access delay on an unlicensed spectrum according to the present invention includes a base station end and a UE end, and includes the following specific processes:
a base station end:
(1) the base station configures N carriers (such as CC1, CC2, CC3) under the same TAG to be scheduled through high layer signaling.
(2) In subframe # n (where n is a subframe number), the eNB sends a random access request (PDCCH order) to the UE, where the random access request includes information such as a Preamble Index and a PRACH Mask Index, and indicates a Preamble available to the UE and a time-frequency resource for PRACH transmission, respectively.
(3) Assuming that the first available subframe is # n + k, in the subframe # n + k-1, the eNB performs LBT on each scheduled carrier, determines the channel idle condition of each carrier, and transmits a physical indication signal on the carrier with the idle and best channel state. For example, if the eNB finds that CC2 is idle and the channel status is the best, the eNB sends a physical indication signal to the UE on carrier CC2 to notify the UE of the LBT order for each carrier (for example, CC2- > CC1- > CC3 indicates that CC2 has the highest priority for PRACH transmission). Note that here the eNB transmitting the physical indicator signal on the highest priority CC2 may act as a reserved channel, further increasing the probability of successful LBT of the UE on CC 2.
(4) If the base station receives the preamble in the PRACH transmission time window, such as a subframe # n + m (m is more than or equal to k), the eNB estimates the TA value and sends RAR to the UE in the RAR 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).
The UE end:
(A) the UE learns N PRACH candidate carriers in the same TAG for random access in a high-layer signaling, and initializes i to 1.
(B) The UE receives the PDCCH order in the subframe # n, acquires indication information (random access request) comprising information such as PreambleIndex and PRACH Mask Index, acquires time-frequency resource information transmitted by the PRACH according to the information, and then configures time-frequency resources to be transmitted.
(C) In subframe # n + k-1, the UE receives a physical indicator signal of the base station to obtain priority information of PRACH transmission, and performs LBT on a carrier having the physical indicator signal. According to the example proposed by the eNB, if the eNB sends a physical indication signal to the UE on the carrier CC2, the UE performs LBT on the CC2 at the end symbol of the subframe # n + k-1;
(D) if LBT succeeds on the current carrier (e.g., CC2), the UE will send preamble on the carrier CC2 in subframe # N + k, otherwise the UE performs LBT on the i +1 th carrier CC1 in the last symbol of # N + k, and so on, if LBT still fails by the nth carrier CC3, it needs to receive the physical indicator 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. 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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| CN105992347B (en) * | 2015-01-29 | 2021-11-12 | 北京三星通信技术研究有限公司 | Uplink signal sending method, user equipment and base station |
| KR102394622B1 (en) * | 2017-09-06 | 2022-05-09 | 삼성전자주식회사 | Apparatus and method for controlling uplink transmission timing in internet of things environment |
| CN109803444B (en) * | 2017-11-17 | 2021-01-15 | 中国移动通信有限公司研究院 | Transmission method and terminal for physical random access channel |
| CN110636614A (en) | 2018-06-21 | 2019-12-31 | 维沃移动通信有限公司 | Random access method, terminal and network equipment |
| CN109156015B (en) * | 2018-07-20 | 2023-12-22 | 北京小米移动软件有限公司 | Random access processing method and device |
| JP7390357B2 (en) * | 2018-08-01 | 2023-12-01 | オッポ広東移動通信有限公司 | Random access methods, terminal devices and network devices |
| CN110830205B (en) * | 2018-08-10 | 2020-10-09 | 展讯通信（上海）有限公司 | Monitoring and indicating method and device for non-authorized spectrum PDCCH, storage medium, terminal and base station |
| CN111181663A (en) * | 2018-11-09 | 2020-05-19 | 普天信息技术有限公司 | Fast initial access method and device on unlicensed spectrum |
| US20220078850A1 (en) * | 2019-01-18 | 2022-03-10 | Beijing Xiaomi Mobile Software Co., Ltd. | Access feedback method, base station, terminal, and storage medium |
| CN111263465B (en) * | 2019-02-01 | 2021-12-07 | 维沃移动通信有限公司 | Transmission method and equipment of random access message |
| US20220256609A1 (en) * | 2019-04-30 | 2022-08-11 | Nokia Technologies Oy | Mechanism for Providing Multiple Transmission Opportunities |
| US20220217783A1 (en) * | 2019-05-17 | 2022-07-07 | Beijing Xiaomi Mobile Software Co., Ltd. | Method, system and device for acquiring random access configuration information |
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