Method for controlling radio channel access in a single frequency network, communication system, and single frequency network radio access controller

Abstract

The present invention provides a method, a communication system, and a single frequency network radio access controller for controlling radio channel access in a single frequency network, wherein multiple base stations simultaneously send the same data to a UE device, and the method includes: sending a set of random access parameters common to the first multiple base stations of the single frequency network from a first multiple base station; receiving a random access preamble code sent by the UE device by a second multiple base station, the second multiple base stations being the same as the first multiple base stations or being a subset of the first multiple base stations; sending multiple responses to the random access preamble code from a third multiple base station of the single frequency network, the third multiple base stations being the same as the second multiple base stations or being a subset of the second multiple base stations; and receiving a preset transmission in response to the multiple responses by a fourth multiple base station, the fourth multiple base stations being the same as the third multiple base stations or being a subset of the third multiple base stations.

Description

[0001] This application is a divisional application of the following original application:

[0002] -- Filing date of original application: November 18, 2016

[0003] --Original application number: 201680067571.4

[0004] --Title of the invention of the original application: Method for controlling radio channel access in a single frequency network, communication system, and single frequency network radio access controller Technical Field

[0005] The present invention relates to a mechanism for performing random access to a single frequency network (SFN). Background Art

[0006] In a single-frequency network (SFN), multiple base stations transmit data simultaneously using the same resources. These base stations appear as a single frequency network and, therefore, appear as a single cell to mobile devices. Furthermore, base stations can be added to and removed from a group of base stations currently transmitting data to a specific mobile device (user equipment, UE) based on the UE's movement, in order to cover the area where the UE is expected to move next. This means that with respect to transmissions to a specific UE, some cells are switched on and some are switched off, depending on the UE's movement. If a base station does not need to transmit to any UE, it can also be completely switched off (powered down). Summary of the Invention

[0007] In the context of the present invention, the term SFN can be understood as a group of synchronously operated base stations that typically covers a larger extended area, but can also be understood as a subset of base stations from this larger group (a so-called SFN cluster). In order to avoid interference between adjacent SFN clusters, the resources used in the respective SFN clusters can be orthogonal to each other.

[0008] The present invention mainly relates to uplink services and how to efficiently configure and establish the initial connection setup, ie the random access procedure for a single frequency network.

[0009] The random access procedure is known in the art and varies between radio access technologies. For example, in LTE described in 3GPP TS 36.321, the message flow for random access includes: (1)

[0011] The UE reads the system information broadcast by the eNB in ​​each cell and receives, among other things, the following parameters for random access:

[0012] Available PRACH resources (time slots) for sending random access preambles

[0013] Available random access preambles

[0014] Initial preamble power

[0015] Random access response (time) window size (2)

[0017] After the UE has decided to use the random access procedure, it randomly selects a preamble and resources from the available preambles and resources.

[0018] (3) UE sends random access preamble

[0019] (4) The UE selects the eNB that serves it (i.e., the eNB on which the UE resides)

[0020] Receive the preamble. Since neighboring eNBs intentionally use different preambles, only one eNB can receive the random access preamble. (5)

[0022] The eNB prepares and sends a random access response. The sending timing is flexible but must be completed within the configured random access response window.

[0023] (6) After receiving the response, the UE prepares and sends the scheduled transmission.

[0024] (7) After receiving the preset transmission, the eNB prepares and sends the contention resolution message.

[0025] CN102196518B describes a cell switching process including a random access process.

[0026] EP2534873A2 describes another random access procedure in an LTE system, in particular in combination with a Minimization of Drive Test (MDT) metric.

[0027] US 2013 / 0089034 A1 describes a method for selecting a base station from multiple base stations to serve a UE in the uplink (UL). A single base station already serving the UE in the downlink (DL) controls the method, which involves the UE transmitting reference signals in the UL to multiple base stations. The base stations receive and decrypt the signals and transmit the received signal strength to the controlling base station, which then selects a base station to serve the UE in the UL. This selection is fixed; the selected base station serves the UE.

[0028] In known random access procedures, such as in LTE, the UE must select a base station before a random access request can be sent. Therefore, the UE must perform cell selection regularly in idle mode to discover and select the most suitable base station. These idle mode procedures are power-consuming for the mobile device. In addition, compared with the multi-base station solution of the present invention (i.e., provided by the SFN cluster), ... perform cell selection regularly in idle mode to discover and select the most suitable base station.

[0029] In comparison, the reception quality of a single base station is worse. The access procedure according to the prior art is more likely to result in unsuccessful and power-wasting transmissions.

[0030] In the case where multiple base stations establish a synchronized subnet like an SFN, known conventional random access schemes will fail because a base station is intentionally prohibited from receiving random access preambles from neighboring base stations.

[0031] WO 2014 / 204365 A1 describes a method for controlling multiple antenna points by a network node. The network node forms pico cells and accordingly uses orthogonal radio resources and does not form a single frequency network in which multiple access points use the same radio resources to transmit the same signal.

[0032] WO 2013 / 178612 A1 describes timing advance management in the presence of repeaters and remote radio heads, with the remote radio heads served by an eNB. A UE receives signals from multiple radio heads, and radio heads communicating with similar timing advances are assigned to a timing advance group for timing advance management. There is no indication that the radio heads form a single frequency network.

[0033] US 2013 / 0170385 A1 describes a contention resolution method in a mobile communication system, wherein a UE receives BCH signals broadcast by two base stations using a multimedia broadcast single frequency network radio transmission format.

[0034] The present invention provides a method for controlling radio channel access in a single frequency network, wherein multiple base stations simultaneously transmit the same data to a UE device.

[0035] The present invention also provides a method for a user equipment (UE) to access a radio channel in a single frequency network, wherein multiple base stations transmit the same data simultaneously.

[0036] According to preferred embodiments of the present invention, further preferred aspects of the method of the present invention are also provided.

[0037] In another aspect, the present invention provides a UE device adapted to access a radio channel in a single frequency network, wherein multiple base stations transmit the same data simultaneously.

[0038] In a further aspect, the present invention provides a Single Frequency Network Radio Access (SFN-RA) controller arranged to control a plurality of base stations forming a single frequency network so that the plurality of base stations each transmit simultaneously.

[0039] The present invention provides a random access procedure in which multiple base stations (eNBs) are capable of receiving and responding to random access preambles. This is advantageous because the probability of successful transmission increases due to the multiple receiver / transmitter scheme. Consequently, access is faster, battery consumption of mobile devices is reduced, and radio resources (for retransmissions) are conserved. Furthermore, the SFN random access scheme is advantageous because the execution of idle mode procedures related to mobility can be reduced, i.e., the UE must read system information (the random access portion of system information) very rarely, as the initial random access configuration remains valid as long as it remains in the corresponding SFN cluster (even when the UE moves).

[0040] The present invention provides the following benefits:

[0041] The SFN-RA controller (e.g., a functional entity that can be part of the SFN cluster management unit or resource control unit) can configure important random access-related parameters for all small cells within a single frequency network (or SFN cluster). All base stations within the SFN (or SFN cluster) can simultaneously receive the random access preamble, making the reception of the random access preamble more reliable.

[0042] All base stations within the SFN (or SFN cluster) can respond to the received random access preamble at the same time, making the reception of the random access response more reliable.

[0043] All base stations within the SFN (or SFN cluster) can transmit the received “preset transmission”

[0044] Forwarded to the SFN-RA controller. The SFN-RA controller is able to combine the received multiple "scheduled transmissions" and resolve any conflicting information therein. This provides the advantage of more reliable reception of the "scheduled transmissions".

[0045] The SFN-RA controller can direct all base stations or a subset of all base stations in the SFN (or SFN cluster) to send "contention resolution" signals simultaneously.

[0046] Message. Which base stations are to send the message is decided based on the reception quality reported by the base stations, e.g. a subset of base stations may be sufficient for highly reliable collective DL transmission of the message. The base stations are able to receive the contention resolution message from the SFN-RA controller and forward the contention resolution message to the UE using resources (time slots and subcarriers) as directed by the SFN-RA controller. These provide "contention resolution"

[0047] Advantage of more reliable reception of messages. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0049] Figure 1 A schematic diagram showing a single frequency network;

[0050] Figure 2 shows the message exchange between the SFN controller, small cells and UE; and

[0051] Figure 3 The diagram includes the transmission of a random access preamble and the subsequent message exchange. DETAILED DESCRIPTION

[0052] To illustrate the present invention, Figure 1 An exemplary schematic diagram showing a single frequency network arrangement 10 is shown, comprising two clusters, namely cluster M and cluster N. Three small cells SC_n to SC_n+2 are shown configured as a single frequency network (SFN cluster N) for a mobile device "UE1". Two small cells SC_m and SC_m+1 are shown configured to form a second cluster, namely SFN cluster M. Each of the small cells SC_n to SC_n+2 and SC_m to SC_m+1 is connected to a SFN random access SFN-RA controller 12 that configures the small cells. Figure 1 As shown, the SFN-RA controller 12 is a cluster-specific radio control unit RCU

[0053] 14 , the RCU 14 in turn is connected to the SFN cluster management unit 20 .

[0054] As shown in the figure, the SFN cluster management unit 20 includes a SFN controller 22, a location determination unit 24, a central resource control unit (RCU) 26 and a cluster segmentation unit 28. The SFN cluster management unit 20 also communicates with the LTE Mobility Management Entity (MME) 30.

[0055] The central SFN-RA controller can communicate with the central resource control unit (RCU)

[0056] 26 association without having a separate SFN-RA controller attached to each cluster-specific RCU.

[0057] It should be noted that the term "small cell" used may be, for example, a Node B, NB, evolved Node B, eNB or other forms of base station.

[0058] The first aspect of the SFN random access procedure is that all base stations in the SFN (or SFN cluster) use the same random access configuration. The SFN-RA controller configures eight parameters for the base stations (some of which are already used in the known LTE random access procedure).

[0059] Compared to known procedures, the base station implementing the SFN random access procedure does not have the freedom to choose its own parameters.

[0060] (1) Available random access resources (time slots) for sending random access preambles

[0061] (2) A set of available random access preamble codes

[0062] (3) Initial preamble transmission power

[0063] (4) Size of the random access response window

[0064] (5) Backoff parameter value

[0065] Additionally, the following new parameters are configured by the SFN-RA controller:

[0066] (6) Requirement to send a (positive) random access response

[0067] (7) Timing for sending random access response message (8)

[0069] Timing Alignment Configuration. Timing alignment is the timing used by a UE to transmit a signal earlier in order to cause a base station to synchronize reception of signals from different UEs.

[0070] The SFN-RA controller configuration parameters are as follows:

[0071] Parameters (1) and (2)

[0072] The selection is based on the current capacity requirement for random access. If more capacity is needed, more time slots and preambles can be provided. Therefore, if the capacity needs change, reconfiguration is performed.

[0073] Parameters (3)

[0074] is chosen so that the first transmitted preamble can be correctly received in most cases. The nominal value of this parameter depends on the size of the cell's coverage area. Since our new scheme may significantly increase the perceived coverage area, a scheme with multiple reception points should be considered here.

[0075] Parameter (4) is selected based on the performance of the configured base station group to respond to all random access requests within the time window.

[0076] Parameter (5) indicates the backoff parameter value used in the random access backoff procedure. With this parameter, the SFN-RA controller can instruct the base station to initiate a backoff algorithm in the requesting UE to delay the next (several) random access preamble transmission attempts. The random access procedure stops when the maximum number of random access preambles has been transmitted in the uplink direction without any positive feedback from the base station.

[0077] Parameter (6) indicates under what circumstances the configured base station group sends a positive response to the requesting UE, that is, allows the UE to continue the "preset transmission" in the uplink direction

[0078] For example, if the preamble is received correctly, if no contention is detected, and if resources on the air interface and on the core network interface are free, then this would be a valid case for issuing a positive response.

[0079] Parameter (7) indicates which time slots must be used to send the response message.

[0080] Parameter (8) indicates the method by which the timing alignment value is derived (described below). In the event that method 1 is configured, the timing alignment value to be used is included. This is a fixed value used by all base stations.

[0081] The SFN-RA controller then sends these parameters (at least one of them) to each base station as a configuration message. All base stations of the same SFN (or SFN cluster) will get the same set of parameters. Base stations from another SFN (or SFN cluster) will get parameters that may differ from those of other SFNs (or SFN clusters).

[0082] Cluster) with the same or different parameters.

[0083] This is implemented after the base stations of the SFN cluster N receive a configuration message from the SFN-RA controller containing some, all, or more of the eight parameters described above. The base stations configure their receivers to receive random access preambles and their transmitters to broadcast random access parameters relevant to the UE. Once this is done, they are ready to receive any of the available random access preambles in the configured time slot.

[0084] exist Figure 1 In the exemplary arrangement of , the small cells SC_n to SC_n+2 will start broadcasting random access parameters synchronously as part of the system information broadcast (SIB), ie by using the same time slot and the same subcarrier.

[0085] refer to Figure 2 , shows a typical message exchange between the SFN-RA controller and the small cells, and between the small cells and the UE. Configuration messages from the SFN-RA controller to each of the small cells are shown as messages 34′, 34″, and 34′″. The small cells then broadcast the configuration messages represented by messages 36′, 36″

[0086] and 36'' show the SIB. Message 36'' is shown as a dotted line to indicate that the parameters are being sent.

[0087] However, due to the large distance between the small cell and the UE, the small cell will not make a significant contribution to the received signal at UE1.

[0088] Note that, as in 3GPPTS

[0089] As described in 36321, the UE also needs more parameters for random access, which are also broadcasted. For simplicity, they are not described further here because they are used for normal random access as usual.

[0090] In the LTE random access process, the timing calibration value is dynamically derived by the base station based on the reception timing of the random access preamble. This method is not applicable to SFN.

[0091] Because it usually results in different timing alignment values ​​for each base station. When the data (i.e. timing alignment values) are different for each base station, synchronous transmission is impossible. This problem is solved by one of the following three methods:

[0092] Semi-static value:

[0093] The SFN-RA controller configures the timing alignment value. It chooses a value based on the average distance from any UE in the SFN to the nearest base station, for example r / 2, where

[0094] r is the radius of the coverage area. This value is sent to the base station and applied to the random access response message. This method is advantageous because it enables a fast response from the base station and reduces the amount of signaling.

[0095] Coordination of dynamic values ​​with the help of SFN-RA controller

[0096] After the base station receives the random access preamble, it calculates the time offset delta_T between the received preamble and the downlink timing. This value is sent to the SFN-RA controller. The SFN-RA controller selects a value for timing alignment based on multiple received time offsets. For example, the timing alignment value is derived by considering only the lowest time offset value. Alternatively, the average (mean or

[0097] average) deviation value to determine the calibration value.

[0098] Dynamic value selected by UE:

[0099] After the base station receives the random access preamble, it calculates the time offset delta T between the received preamble and the downlink timing and uses it to derive the timing correction value. Each base station will derive

[0100] An own value. This value is sent to the UE within the random access response message. The transmission is done simultaneously by all base stations. Without further means, the reception of these multiple different messages on the same resource will fail. Therefore, orthogonal codes are used so that different values ​​can be distinguished at the UE. For example, different orthogonal spreading codes are assigned to the base stations by the SFN-RA controller, and the base stations will spread the timing alignment value by using the assigned codes. These codes are known in each UE, for example they are pre-configured. After receiving the response message by the UE, it will decode the different timing alignment values ​​and will calculate a value for subsequent transmission. For example, it uses the lowest value or the average value.

[0101] Now refer to Figure 3 Describes the random access procedure performed by the UE.

[0102] As a prerequisite, it is assumed that the UE, UE1, has received important UE-related parameters required for random access from any one (or multiple) base stations in the SFN cluster. (1)

[0104] UE1 selects a random access preamble and timeslot from the configured group and transmits the preamble at the configured power. As shown, SC_n and SC_n+1 correctly receive the preamble. SC_n+2 does not receive the preamble (indicated by the dashed line) due to, for example, a large UE-to-base station separation. Because the preconditions for parameter 5 are met, SC_n and SC_n+1 decide to issue a positive acknowledgment response. SC_n and SC_n+1 generate the parameters for the response message as instructed by the SFN-RA controller. (2)

[0106] SC_n and SC_n+1 synchronously send random access response messages to UE 1. They precisely use the time slots to send the response messages that have been configured by the SFN-RA controller.

[0107] Note: In this step, all base stations (e.g., eNBs)

[0108] The same response has been generated for this request alone and they are both sent using the same resources. Unlike in the known random access response transmission, the base station does not have any freedom to choose the transmission timing, the transmission window is just a parameter indicated by the SFN-RA controller to schedule the base station's transmission and used by the UE to stop probing.

[0109] This ensures SFN-like transmission and timely response to UE1's random access attempt, which is not possible when the base stations coordinate their joint response before transmission. UE1 receives the response message without identifying the individual transmission points (base stations SC_n and SC_n+1).

[0110] (3) UE1 sends a preset send message, which in this example is assumed to be received by SC_n and SC_n+1.

[0111] (4) SC_n and SC_n+1 will include information about reception quality (e.g. UL signal strength)

[0112] The SFN-RA controller combines a plurality of messages that may be received taking into account reception quality to prepare a common "contention resolution" message.

[0113] (5) The SFN-RA controller selects a group of suitable base stations that should send a common "contention resolution" message to UE1. This selection can be based on reception quality, i.e. only the small cells with the highest reception quality are selected for sending the "contention resolution" message.

[0114] Message. The SFN-RA controller sends a "contention resolution" message to the selected small cells.

[0115] News. Figure 3 In the example, only SC_n and SC_n+1 are selected.

[0116] When messages are exchanged between the SFN-RA controller and the selected base station, they may include information about resources to be used by the base station to send the “contention resolution” message to UE1. (6)

[0118] SC_n and SC_n+1 send contention resolution messages synchronously according to the instruction of the SFN-RA controller. After UE1 successfully receives the message, the random access procedure is completed.

[0119] The multiple reception point approach of the random access procedure described above leads to new situations, which have to be handled by the mobile network.

[0120] If a scheduled transmission is not correctly received by one or more base stations, the SFN-RA controller addresses the issue. As described above, the base station forwards the received message and an indicator of reception quality (or perceived UL signal strength, reliability, etc.) to the SFN-RA controller. The SFN-RA controller then discards messages with poor reception quality and only uses messages with good reception quality. In another embodiment, the base station forwards messages using so-called "soft bits."

[0121] This means that the base station does not decode the received message into binary bits ("0" or "1"). Instead, it simply forwards the received symbols to the SFN-RA controller, where the actual decoding takes place.

[0122] The SFN-RA controller will combine the "soft bits" from all base stations.

[0123] The reception quality (or perceived UL signal strength, or reliability indication, etc.) of each instance of the received message is taken into account simultaneously and the message is decoded. This will result in optimal receiver performance.

[0124] Preamble collisions may also occur due to transmissions from multiple UEs. The current behavior of the known random access procedure is as follows: In the event that two or more UEs are transmitting the same preamble to the same base station at the same time (i.e., using the same time slot), all requests except one will be rejected by the base station by sending a corresponding "contention resolution" message. The rejected UE will have to initiate the random access procedure again.

[0125] The current random access procedure behaves differently. In the event that two or more UEs in the same SFN simultaneously transmit the same preamble to different base stations, the base stations will respond with separate messages so that the UEs will continue their individual "scheduled transmissions" in the uplink direction. These messages are all forwarded to the SFN-RA controller. The SFN controller detects that these messages originate from different UEs (based on the included UE IDs).

[0126] In this case, the SFN controller will not combine the multiple messages into a single message but will interpret them independently and will allocate different resources to the base station for each UE for submitting the "contention resolution" message in the DL direction. Therefore, the method of the present invention is advantageous because it will result in a smaller number of rejected requests and thus save radio resources and battery power.

Claims

1. A user equipment (UE) device, comprising a transmitting module and a receiving module, adapted to access a wireless channel in a single frequency network, wherein multiple base stations in the single frequency network simultaneously transmit the same data by using the same resources, such that data received by the UE device from the multiple base stations in the single frequency network appears to the UE device as data received from a single cell, wherein the UE device is configured to: Receiving, by the receiving module, a set of random access parameters common to the plurality of base stations in the single frequency network from the first plurality of base stations; The sending module sends a random access preamble; The receiving module receives a plurality of responses to the random access preamble, the plurality of responses having been simultaneously transmitted from a second plurality of base stations of the single frequency network using the same resources including the same exact time slots, wherein: the second plurality of base stations being the same as or a subset of the first plurality of base stations; and The sending module sends a preset sending in response to the multiple responses, The UE device is configured to determine an actual timing alignment value by receiving a timing alignment value from each of the second plurality of base stations of the single frequency network in response to the random access preamble code, and determine the actual timing alignment value from the plurality of received timing alignment values, wherein each of the received timing alignment values ​​is received in a coded state such that the timing alignment values ​​received from different base stations of the second plurality of base stations of the single frequency network are orthogonally coded with respect to each other, and the UE device is configured to decode each of the received coded timing alignment values ​​by using a code pre-configured in the UE device.

2. The UE device according to claim 1, wherein: The UE device is configured to determine the actual timing alignment value by selecting one of a minimum value and an average value among the plurality of received timing alignment values.

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