Patent Application
20170367097
This application claims priority to and the benefit of Korean Patent Application Nos. 10-2016-0076043 and 10-2016-0091645, filed in the Korean Intellectual Property Office on Jun. 17, 2016 and Jul. 19, 2016, respectively, the entire contents of which are incorporated herein by reference.
The present invention relates to a method and apparatus for handling a radio link failure in a mobile communication system and, more particularly, to a method and apparatus for handling a radio link failure that frequently occurs due to movement of a terminal in a mobile communication system of a cloud radio access network (C-RAN) to which a millimeter wave-based remote radio head (RRH) is applied.
Research into the use of a millimeter wave (mmWave) band to secure an effective bandwidth of 1 GHz or greater, rather than an existing cellular band, has been actively conducted to enhance spatial reuse of a frequency and a data rate in a mobile communication system.
In addition, in order to enhance quality of a mobile communication service, as well as satisfying recently increased wireless data traffic demand, a size of cells is decreased, the number of cells is increased, and wireless access technologies tend to be more elaborate and complicated to increase spatial reuse efficiency of a frequency. The increase in cells and progress in network incur high cost for cell installation and operation, laying a considerable burden on communication providers. As a solution, C-RAN technologies using an RRH, one of methods of providing a high speed wireless data service, while minimizing cost for advanced communication network, has been developed. A method for configuring a user-centric virtual cell, capable of simplifying an unnecessary handover procedure, while maintaining a user experienced data to rate in consideration of enhancement of performance in a cell boundary regarding a user which is located in the cell boundary or has high mobility, a problem which remains unsolved in an existing cellular system, has also be studied.
However, in the case of the C-RAN structure using millimeter wave-based RRH, an area in charge of each RRH is limited due to constraints of pathloss due to the use of a high frequency, poor penetration, and in particular, guaranteeing a line of sight (LOS), unlike transmission using an existing cellular band. In addition, since LOS is not secured due to movement of a user equipment (UE), a radio link established between the UE and a base station (BS) is frequently cut off.
Therefore, a method for rapidly handling a failure of a radio link which frequently occurs due to movement of a UE which is located in a cell boundary or which has high mobility in a millimeter wave-based mobile communication system of a C-RAN environment to which an RRH reducing installation cost of a BS and facilitating management, compared with the related art BS system, is required.
The present invention has been made in an effort to provide a method and apparatus for handling a failure of a radio link in a mobile communication system having advantages of rapidly handling a failure of a radio link established between a base station (BS) and a user equipment (UE) due to a movement of the UE in the mobile communication system of a millimeter based-based RRH-applied C-RAN environment.
An exemplary embodiment of the present invention provides a method for handling a radio link failure in a base station (BS) of a mobile communication system. The method for handling a radio link failure may include: receiving, from a user equipment (UE), a candidate list including a candidate remote radio head (RRH) adjacent to the UE, excluding at least one serving RRH connected to the UE, among a plurality of RRHs; allocating a random access code index to at least one candidate RRH included in the candidate list; and transmitting, to the UE, the random access code index allocated to the at least one candidate RRH.
The method for handling a radio link failure may further include: when a failure in a radio link established between the at least one serving RRH and the UE is detected, processing a random access between a target candidate RRH with strongest signal strength received from the UE on the candidate list and the UE; and establishing a radio link between the target candidate RRH and the UE.
The processing of random access may include: receiving a random access preamble transmitted from the UE using the random access code index allocated to the target candidate RRH; and transmitting a random response message regarding the random access preamble.
The process of random access may further include: transmitting the random access code index allocated to the target candidate RRH to the target candidate RRH.
The method for handling a radio link failure may further include: transmitting a synchronization signal including a physical layer cell ID and a to reference signal including a unique identifier of a corresponding RRH through a plurality of RRHs, before the candidate list is received from the UE, wherein the candidate list includes a unique identifier of the candidate RRH.
The candidate list may further include a relative reference time difference of a signal received from the candidate RRH with respect to a reference signal of a signal received from the serving RRH, and the relative reference time difference is used as an uplink timing adjustment value for random accessing the candidate RRH.
When signal strength of a synchronization signal received by the UE continuously exceeds a preset first threshold by a predetermined first number of times and a unique identifier obtained through a reference signal is the same for the first number of times, an RRH which has transmitted the corresponding synchronization signal and the reference signal may be added as the candidate RRH to the candidate list, and when signal strength of a synchronization signal received by the UE does not continuously exceed a preset second threshold by a predetermined second number of times, a candidate RRH which has transmitted the corresponding synchronization signal and the reference signal may be deleted from the candidate list.
The allocating may include: allocating a random access code index to the candidate RRH when the candidate RRH is first reported through the candidate list; and maintaining the random access code index allocated to the candidate RRH until the candidate RRH is deleted from the candidate list.
Another exemplary embodiment of the present invention provides a method for handling a radio link failure in a user equipment (UE) of a mobile to communication system. The method for handling a radio link failure may include: configuring a candidate list including at least one candidate remote radio head (RRH) adjacent to the UE, excluding at least one serving RRH to which the UE is connected, among a plurality of RRHs; receiving a random access code index of the at least one candidate RRH allocated by a base station (BS), through the serving RRH; and adding the random access code index of the at least one candidate RRH to the candidate list.
The method for handling a radio link failure may further include: when a failure that occurs in a radio link established between the at least one serving RRH and the UE is detected, performing random access with a target candidate RRH using a random access code index of the target candidate RRH with strongest signal strength received from the UE on the candidate list; and establishing a radio link with the target candidate RRH.
The configuring may include: receiving synchronization signals including a physical layer cell ID and reference signals including a unique identifier of a corresponding RRH from the plurality of RRHs; selecting the serving RRH and the candidate RRH from among the plurality of RRHs using the synchronizations and the reference signals; and generating a candidate list including the candidate RRH and transmitting the generated candidate list to the BS through the serving RRH.
The selecting may include: selecting an RRH which has transmitted a synchronization signal with strongest signal strength among signal strengths of synchronization signals received from the plurality of RRHs, as the serving RRH; and when signal strength of a synchronization signal among to synchronization signals and reference signals received from the plurality of RRHs continuously exceeds a preset first threshold by a predetermined number of times and a unique identifier transmitted through a received reference signal is the same for the first number of times, selecting an RRH which has transmitted the corresponding synchronization signal and the reference signal as the candidate RRH.
The selecting may further include: when signal strength of a synchronization signal of the candidate RRH does not continuously exceed a preset second threshold by a predetermined second number of times, deleting the corresponding candidate RRH from the candidate list.
The transmitting may include: calculating a relative reference time difference of a synchronization signal received from the candidate RRH with respect to a reference time of a synchronization signal received from the at least one serving RRH; and generating a candidate list including a unique identifier of the candidate RRH obtained through the reference signal received from the candidate RRH and the relative reference time difference of the candidate RRH.
The performing of random access may include: adjusting an uplink timing based on a RRH with the fastest transmission time using relative reference time differences calculated with respect to the serving RRH and the target candidate RRH.
Yet another exemplary embodiment of the present invention provides an apparatus for handling a radio link failure in a user equipment (UE) of a mobile communication system. The apparatus for handling a radio link failure may to include: a candidate list configuring unit, a random access processing unit, and a radio link connection unit. The candidate list configuring unit may select a candidate remote radio head (RRH) adjacent to the UE, excluding a serving RRH to which the UE is connected, among a plurality of RRHs connected to a single baseband unit (BBU) pool, configure a candidate list including the candidate RRH, add a random access code index allocated to the candidate RRH to the candidate list, and manage the candidate list. The random access processing unit may perform random access with a target adjacent RRH using a random access code index allocated to the target adjacent RRH with strongest signal strength received from the UE, on the candidate list, when a failure occurs in a radio link established between the serving RRH and the UE. The radio link connection unit may connect the target candidate RRH and a radio link, when the random access is completed.
The apparatus for handling a radio link failure may further include: a transceiver unit receiving synchronization signals each including a physical layer cell ID and reference signals including a unique identifier of a corresponding RRH from the plurality of RRHs, wherein the candidate list configuring unit may select an RRH which has transmitted a synchronization signal with strongest signal strength among signal strengths of synchronization signals received from the plurality of RRHs, as the serving RRH, and when a signal strength of a received synchronization signal continuously exceeds a preset first threshold by a predetermined first number of times and a unique identifier transmitted through the received reference signal is the same for the first number of times, the candidate list configuring unit may select an RRH to which has transmitted the corresponding synchronization signal and the reference signal, as the candidate RRH.
The radio link connection unit may perform a radio resource control (RRC) connection re-establishment procedure to connect the target candidate RRH and a radio link.
The candidate list configuring unit may calculate a relative reference time difference of a synchronization signal received from the candidate RRH with respect to a reference signal of a synchronization signal received from the serving RRH, and the candidate list may include a unique identifier of the candidate RRH obtained through a reference signal received from the candidate RRH and a relative reference time difference of the candidate RRH.
The random access processing unit may adjust an uplink timing based on a RRH with the fastest transmission time using the relative reference time differences calculated with respect to the serving RRH and the target candidate RRH.
In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings to and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.
Throughout the specification and claims, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.
Throughout the specification, a terminal may refer to a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS), a high reliability mobile station (HR-MS), a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), or a user equipment (UE), and may include the entirety or a portion of functions of the MT, MS, AMS, HR-MS, SS, PSS, AT, or UE.
Also, a base station (BS) may refer to an advanced base station (ABS), a high reliability base station (HR-BS), a node B, an evolved node B (eNodeB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR)-BS, a relay station (RS) serving as a base station, a relay node (RN) serving as a base station, an advanced relay station (ARS) serving as a base station, a high reliability relay station (HR-RS) serving as a base station, small base stations (BSs) (e.g., a femto base station (BS), a home node B (HNB), a home eNodeB (HeNB), a pico BS, a metro BS, a micro BS, etc.), and the like, and may include the entirety or a portion of functions of an ABS, a node B, an eNodeB, an AP, an RAS, a BTS, an MMR-BS, an RS, an RN, an ARS, an HR-RS, a small BS, and the like.
Hereinafter, a method and apparatus for managing a remote radio head to (RRH) in a mobile communication system according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.
Referring to
The plurality of RRHs 200, 210, . . . , 260 are distributed within a cell managed by the BS and connected to the BBU pool 100 through an optical cable, or the like. Each of the plurality of RRHs 200, 210, . . . , 260 may use a millimeter wave frequency band of 10 GHz or higher as a carrier frequency, and use a bandwidth from hundreds of MHz to 1 GHz or higher for data transmission.
The plurality of RRHs 200, 210, . . . , 260 connected to the same BBU pool 100 simultaneously transmit a synchronization signal including the same physical layer cell ID (PCID) to user equipments (UEs) 300, 310, and 320 using the same radio resource. During this process, the plurality of RRHs 200, 210, . . . , 260 interfere with each other because they transmit different data using the same radio resource. Thus, the plurality of RRHs 200, 210, . . . , 260 transmit a unique identifier (ID) identifying each RRH to the UEs 300, 310, and 320 using to a reference signal for alleviating interference of signals transmitted by neighboring RRHs. Here, radio resource refers to a resource element of a time and frequency space defined in 3GPP LTE/LTE-A (Advanced) specification, and it is assumed that radio frames transmitted from the plurality of RRHs 200, 210, . . . , 260, subframes forming the radio frames, and symbols are in synchronization.
Referring to
The UE 300 belonging to an area of the plurality of RRHs 200, 210, and 220 receives the synchronization signals and the reference signals from the plurality of RRHs 200, 210, and 220 after the time delays δ0, δ1, and δ2.
The UE 300 sets a reference time using a synchronization signal of an RRH (e.g., 220) having the largest signal strength among the synchronization signals received from the plurality of RRHs 200, 210, and 220, and determines the RRH 220 as a serving RRH 220 using a unique identifier included in the reference signal of the RRH 220.
When the serving RRH 220 is determined using the synchronization signal and the reference signal, the UE 300 establishes a radio resource control (RRC) connection with the serving RRH 220.
When the UE 300 is switched from an RRC idle (RRC_IDLE) state to an RRC-connected (RRC_CONNECTED) state, the UE 300 continuously searches whether another RRH excluding the serving RRH 220 is present in the vicinity of the UE 300 from synchronization signals received from the plurality of RRHs 200, 210, and 220. The UE 300 starts monitoring to add RRHs 200 and 210, from which synchronization signals received by the UE 300 exceed a preset threshold TH1, to a candidate list. Here, the RRHs 200 and 210 transmitting synchronization signals whose strength exceeds the preset threshold TH1 will be referred to as adjacent RRH_1200 and an adjacent RRH_2210. When reception signal strength of the synchronization signals respectively received from the adjacent RRH_1200 and the adjacent RRH_2210 after monitoring starts continuously exceeds a preset threshold TH2 a predetermined number of times N1 and unique identifiers transmitted through the reference signals respectively received from the adjacent RRH_1200 and the adjacent RRH_2210 are the same the predetermined number of times N1, the UE 300 adds the adjacent RRH_1200 and the adjacent RRH_2210, as candidate RRHs, to a candidate list.
When the candidate list is created, the UE 300 transmits the candidate list to the BBU pool 100 through the serving RRH 220 at a predetermined period.
The candidate list transmitted to the BBU pool 100 may include unique identifiers of the adjacent RRH_1200 and the adjacent RRH_2210. Also, the candidate list may further include information regarding a relative reference time difference of the synchronization signals received from the candidate RRHs 200 to and 210 with respect to a reference time set on the basis of a synchronization signal from the serving RRH 220. The relative reference time different will be described in detail with reference to
The BBU pool 100 allocates contention-free-based random access code indices RAa and RAb which may be used in a radio link failure or during a handover process with respect to the adjacent RRH_1200 and the adjacent RRH_2210 included in the candidate list received from the UE 300 and subsequently transmit the random access code indices RAa and RAb to the UE 300 using the serving RRH 220.
The UE 300 adds the random access code indices RAa and RAb allocated to the adjacent RRH_1200 and the adjacent RRH_2210 to the candidate list. The candidate list may further include the contention-free-based random access code indices RAa and RAb regarding the adjacent RRH_1200 and the adjacent RRH_2210.
When receive strengths of the synchronization signals from the adjacent RRH_1200 and the adjacent RRH_2210 do not continuously exceed a preset threshold TH3 a predetermined number of times N2, the UE 300 may delete the adjacent RRH_1200 and the adjacent RRH_2210 included in the candidate list, from the candidate list.
When the candidate list is updated due to deletion of the adjacent RRH_1200 and the adjacent RRH_2210 from the candidate list, the UE 300 may transmit the updated candidate list to the BBU pool 100 using the serving RRH 220.
Allocation of the random access code indices RAa and RAb may be to performed when the adjacent RRH_1200 and the adjacent RRH_2210 in the vicinity of the UE 300 are first reported through the candidate list, and values of the random access code indices RAa and RAb may be maintained until the adjacent RRH_1200 and the adjacent RRH_2210 are deleted from the candidate list.
Referring to
As described above, the UE 300 sets a reference time of a reception signal using the synchronization signal received from the serving RRH 220.
The UE 300 calculates relative reference time differences (d1=δ1−δ0, d2=δ2−δ0) of the synchronization signals received from the adjacent RRH_1200 and the adjacent RRH_2210 with respect to the set reference time. Here, the values of the calculated reference time differences d1 and d2 are used as timing adjustment values for random-accessing to a high ranking candidate RRH_1200 on the candidate list when a radio link between the UE 300 and the serving RRH 220 is cut off.
Table 1 shows an example of a candidate list configured by the UE 300 according to
terminal
In the case of
Referring to
The UE 320 included in an area of the plurality of RRHs 240, 250, and 260 receives the synchronization signals and reference signals from the plurality of RRHs 240, 250, and 260 after time delays
Here, the UE 320 included in the area of the plurality of RRHs 240, 250, and 260 may be connected to a plurality of serving RRHs 240 and 250. In a state in which the UE 320 is not connected to an RRH therearound, an RRH (e.g., 240) having strength of a synchronization signal is greatest is determined as the serving RRH 240 and connection is established between the UE 320 and the serving RRH 240. Also, a candidate list is created using the RRH around the UE 320. After this process is completed, when an additional connection is required, an RRH (e.g., 250) whose signal strength is strong on the candidate list may be determined as the serving RRH 250 in a state in which the existing serving RRH 240 is maintained, and connection may be additionally established between the UE 320 and the serving RRH 250.
In an RRC-connected state in which the UE 320 is connected to the to plurality of serving RRHs 240 and 250, the UE 320 continuously searches whether another RRH excluding the serving RRHs 240 and 250 is present around the UE 320 on the basis of synchronization signals received from the plurality of RRHs 240, 250, and 260. Here, for the purposes of description, the two serving RRHs 240 and 250 will be referred to as a serving RRH_1240 and a serving RRH_2250, respectively. Among the serving RRH_1240 and the serving RRH_2250, it is assumed that the serving RRH_1240 is a main serving RRH having priority of every connection and the serving RRH_2250 is an auxiliary serving RRH, and distinguishment of the main serving RRH and the auxiliary serving RRH may be determined according to priority connected to the UE 320.
When signal strength of the synchronization signal received from the adjacent RRH 260, excluding the serving RRH_1240 and the serving RRH_2250, exceeds the preset threshold TH1, the UE 320 starts monitoring to add the adjacent RRH 260 to the candidate list.
When signal strength of the synchronization signal received from the adjacent RRH 260 continuously exceeds the preset threshold TH2 the predetermined number of times N1 and a unique identifier transmitted through the reference signal of the adjacent RRH 260 is the same the predetermined number of times N1, the UE 320 adds the adjacent RRH 260 as monitored, as a candidate RRH 260 to the candidate list.
When the candidate list is created, the UE 320 transmits the candidate list to the BBU pool 100 through the serving RRH_1240 and the serving RRH_2250 at a predetermined period, but the BBU pool 100 allocates a to contention-free-based random access code index (RAc) which may be used in the occurrence of a radio link failure or during a handover process to the adjacent RRH 260 included in the candidate list received from the UE 320 through the serving RRH_1240 as a main serving RRH. Also, the BBU pool 100 transmits the contention-free-based random access code index (RAc) allocated to the adjacent RRH 260 to the UE 320 using the serving RRH_1240 as a main serving RRH.
The candidate list may include information regarding a relative reference time difference of a synchronization signal received from the adjacent RRH 260 to a reference time of synchronization signals respectively received from the serving RRH_1240 and the serving RRH_2250 and the contention-free-based random access code index (RAc) allocated to the adjacent RRH 260, as well as the unique identifier of the candidate RRH 260.
When a receive strength of the synchronization signal from the adjacent RRH 260 added to the candidate list does not continuously exceed the preset threshold TH3 the predetermined number of times N2, the UE 320 deletes the candidate RRH 260 from the candidate list.
When the candidate list is updated due to deletion of the adjacent RRH 260 from the candidate list, the UE 320 transmits the updated candidate list to the BBU pool 100 using the serving RRH_1240.
Allocation of the random access code index (RAc) may be performed when the adjacent RRH 260 near the UE 320 is first reported through the candidate list, and the value of the random access code index (RAc) may be maintained until the adjacent RRH 260 is deleted from the candidate list.
Referring to
As described above, the UE 320 sets a reference time of a reception signal using the synchronization signals respectively received from the serving RRH_1240 and the serving RRH_2250.
The UE 320 may calculate relative reference times (d3=δ5−δ3, d4=δ5−δ4) with respect to a reference time of the synchronization signal received from the adjacent RRH 260 from a reference time of the synchronization signals respectively received from the adjacent RRH_1200 and the adjacent RRH_2210.
Here, the values of the calculated reference time differences d3 and d4 are used as timing adjustment values for random-accessing to a high ranking candidate RRH 260 on the candidate list when a radio link between the UE 320 and the serving RRHs 240 and 250 is cut off.
Table 2 shows an example of a candidate list configured by the UE 320 in accordance with
termi-
termi-
A relative reference time difference of the candidate RRH 260 on the candidate list to the adjacent RRH_1200 and the adjacent RRH_2210 connected to the UE 320 by a radio link is respectively present, and in cases where the number of contention-free-based random access code indices which may be allocated by the BBU pool 100 is limited, the BBU pool 100 may allocate the random access code indices only to M number of RRH in a high ranking on the candidate list and transmit the same to the UE 320. Here, candidate RRHs on the candidate list may be aligned in descending order, starting from a largest one of values obtained by averaging signal strengths of synchronization signals from the candidate RRH 260 received by the UE 320 the predetermined number of times N1.
Referring to
The BBU pool 100 receives a candidate list regarding neighbor RRHs to from the UE (S620).
The BBU pool 100 allocates a random access code index to each of the RRHs included in the received candidate list (S630) and subsequently transmits the allocated random access code index to the UE (S640). The BBU pool 100 may allocate the random access code index when a candidate RRH is first reported through the candidate list transmitted from the UE. Also, the allocated random access code index may be maintained until the corresponding candidate RRH is deleted from the candidate list. When the number of contention-free-based random access code indices which may be allocated is limited, the BBU pool 100 may allocate the random access code indices only to M number of RRH in a high ranking on the candidate list.
Referring to
The UE 300 selects a serving RRH using the received synchronization signals and reference signals, and when the UE 300 is connected to the serving
RRH in an RRC-connected state, the UE 300 performs a process of searching for and selecting a candidate RRH (S720).
When a candidate RRH is selected, the UE 300 calculates a relative reference time difference of a synchronization signal received from the to candidate RRH to a reference time of a synchronization signal received from the serving RRH (S730).
The UE 300 configures a candidate list using a unique identifier of the candidate RHH and the calculated reference time difference (S740).
The UE 300 transmits the configured candidate list to the plurality of RRHs (S750).
Thereafter, when a random access code index regarding the candidate RRH included in the candidate list from the serving RRH is received (S760), the UE 300 updates the candidate list including the received random access code index (S770).
Referring to
The UE 300 performs a process of searching for and selecting a candidate RRH using the received synchronization signals and reference signals. The process (step S806 to S810) of searching for and selecting the candidate RRH and configuring and managing the candidate list are the same as the contents described above with reference to
Meanwhile, when a failure regarding a radio link connected between the serving RRH 220 and the UE 300 occurs (S812), the serving RRH 220 transmits radio link failure occurrence information to the BBU pool 100.
Upon receiving the wireless link failure occurrence information, the BBU pool 100 transfers information regarding the random access code index allocated to the adjacent RRH_1200 to the candidate RRH positioned in a highest ranking on the candidate list, e.g., the adjacent RRH_1200 (S814).
The UE 300 adjusts an uplink timing using the reference time difference to d1 stored to correspond to the adjacent RRH_1200 positioned in the highest ranking on the candidate list (S816). Thereafter, the UE 300 generates a random access preamble using the random access code index allocated to the adjacent RRH_1200 and subsequently transmits the random access preamble to the adjacent RRH_1200 (S818).
When the random access preamble is detected, the adjacent RRH_1200 transmits a detection result to the BBU pool 100. The BBU pool 100 generates a random access response on the basis of the detection result transmitted from the adjacent RRH_1200 and subsequently transmits the random access response to the adjacent RRH_1200. The adjacent RRH_1200 transmits the random access response with respect to the random access preamble to the UE 300 (S820).
As the UE 300 receives the random access response, the random access procedure is completed and a radio link is established between the UE 300 and the adjacent RRH_1200 through an RRC connection re-establishment process between the UE 300 and the adjacent RRH_1200 (S822).
Referring to
The UE 320 performs a process of searching for and selecting a candidate RRH on the basis of the received synchronization signals and reference signals. The process (step S906 to S910) of searching for and selecting the candidate RRH and configuring and managing the candidate list are the same as the contents described above with reference to
Meanwhile, when a failure regarding a radio link connected between the serving RRH_1240 and the UE 320 occurs (S912), the serving RRH_1240 transmits radio link failure occurrence information to the BBU pool 100.
Upon receiving the wireless link failure occurrence information, the BBU pool 100 transfers information regarding the random access code index allocated to the adjacent RRH 260 to the adjacent RRH 260 positioned in a highest ranking on the candidate list (S914).
The UE 320 adjusts an uplink timing regarding the adjacent RRH 260 positioned
The UE adjusts the uplink timing based on the RRH (for example, serving RRH_2250) with the fastest transmission time using the reference time differences d3 and d4 stored to correspond to the serving RRH_2250 and the adjacent RRH 260 positioned in the highest ranking on the candidate list (S916).
The UE 320 generates a random access preamble using the random access code index allocated to the adjacent RRH 260 and subsequently transmits the random access preamble to the adjacent RRH 260 (S918).
When the random access preamble is detected considering the relative reference time difference d4 of the signal transmitted from the serving RRH_2250, the adjacent RRH 260 transmits a detection result to the BBU pool 100. The BBU pool 100 generates a random access response on the basis of the to detection result transmitted from the adjacent RRH 260 and subsequently transmits the random access response to the adjacent RRH 260. The adjacent RRH 260 transmits the random access response to the UE 320 (S920).
As the UE 320 receives the random access response, the random access procedure is completed and a radio link is established between the UE 320, the serving RRH_2250, and the adjacent RRH 260 through an RRC connection re-establishment process between the UE 320 and the adjacent RRH 260 (S922).
Referring to
The UE 320 performs a process of searching for and selecting a candidate RRH on the basis of the received synchronization signals and reference signals. The process (step S1006 to S1010) of searching for and selecting the candidate RRH and configuring and managing the candidate list are the same as the process (S906 to S910) illustrated in
Meanwhile, when a failure occurs in the radio link established between to the serving RRH_2250 corresponding to an auxiliary serving RRH and the UE 320 (S1012), the serving RRH_2250 transmits radio link failure occurrence information to the serving RRH_1240 corresponding to the main serving RRH through the BBU pool 100 (S1014).
The serving RRH_1240 transfers information regarding the random access code index allocated to the adjacent RRH 260 to the adjacent RRH 260 positioned in a highest ranking on the candidate list through the BBU pool 100 (S1016).
Since the radio link failure of the serving RRH_1 ( 240) corresponding to the main serving RRH did not occur, the UE 320 does not perform the step of adjusting the uplink timing.
The UE 320 generates a random access preamble using the random access code index allocated to the adjacent RRH 260 and subsequently transmits the random access preamble to the adjacent RRH 260 (S1018).
When the random access preamble is detected, the adjacent RRH 260 transmits a detection result to the BBU pool 100. The BBU pool 100 generates a random access response on the basis of the detection result transmitted from the adjacent RRH 260 and subsequently transmits the random access response to the adjacent RRH 260. The adjacent RRH 260 transmits the random access response to the UE 320 (S1020).
As the UE 320 receives the random access response, the random access procedure is completed and a radio link is established between the UE 320 and the adjacent RRH 260 through an RRC connection re-establishment process between the UE 320, the serving RRH_1240 and the adjacent RRH to 260 (S1022).
Referring to
The UE 320 performs a process of searching for and selecting a candidate RRH on the basis of the received synchronization signals and reference signals. The process (step S1106 to S1110) of searching for and selecting the candidate RRH and configuring and managing the candidate list are the same as the process (S906 to S910, and S1006 to S1010) illustrated in
Meanwhile, when failures occur at the same time in the radio link established between the serving RRH_1240 corresponding to a main serving RRH and the UE 320 and the radio link established between the serving RRH_2250 corresponding to an auxiliary serving RRH and the UE 320 (S1112), the serving RRH_1240 and the serving RRH_2250 transmit radio link failure occurrence information to the BBU pool 100, respectively (S1114).
The BBU pool 100 transfers information regarding the random access code index allocated to the adjacent RRH 260 to the adjacent RRH 260 to positioned in a highest ranking on the candidate list (S1116).
The UE 320 adjusts an uplink timing regarding the adjacent RRH 260 positioned in the highest ranking on the candidate list using the reference time difference d4 stored to correspond to the adjacent RRH 260 positioned in the highest ranking on the candidate list (S1118).
The UE 320 generates a random access preamble using the random access code index allocated to the adjacent RRH 260 and transmits the random access preamble to the adjacent RRH 260 (S1120).
When the random access preamble is detected, the adjacent RRH 260 transmits a detection result to the BBU pool 100. The BBU pool 100 generates a random access response on the basis of the detection result transmitted from the adjacent RRH 260 and subsequently transmits the random access response to the adjacent RRH 260. The adjacent RRH 260 transmits the random access response to the UE 320 (S1122).
As the UE 320 receives the random access response, the random access procedure is completed and a radio link is established between the UE 320 and the adjacent RRH 260 through an RRC connection re-establishment process between the UE 320 and the adjacent RRH 260 (S1124).
Referring to
The allocation unit 1210 may be implemented in a BBU pool, and the random access processing unit 1220, the radio link connection unit 1230, and the transceiver unit 1240 may be implemented in an RRH.
The allocation unit 1210 may perform the function of the BBU pool 100 described above with reference to
When a failure occurs in a radio link established between a serving RRH and the UE, the random access processing unit 1220 detects a random access preamble using a random access code index allocated to an adjacent RRH positioned in a highest ranking on the candidate list and transmits a random access response with respect to the random access preamble to the UE through the transceiver unit 1240. The random access response is transmitted to the UE through the transceiver unit 1240.
When the failure occurs in the radio link established between the serving RRH and the UE, the radio link connection unit 1230 performs a process of RRC connection re-establishment between the adjacent RRH positioned in the to highest ranking on the candidate list to establish a radio link between the adjacent RRH and the UE.
The transceiver unit 1240 may include a plurality of RRHs and may be connected to the allocation unit 1210, the random access processing unit 1220, and the radio link connection unit 1230 to transmit and receive a radio signal to and from the UE.
Referring to
The candidate list configuring unit 1310 may perform a function of the UE 300 described above with reference to
The candidate list is transmitted to a BS through the transceiver unit 1340 and through the serving RRH. Also, when the candidate list configuring unit 1310 receives a random access code index regarding the RRH included in the candidate list through the transceiver unit 1340 from the BS, the candidate list configuring unit 1310 updates the candidate list using the received random access code index.
When a failure occurs in a wireless link established between the serving RRH and the UE, the random access processing unit 1320 performs a random access procedure with an adjacent RRH positioned in a highest ranking on the candidate list. The random access processing unit 1320 generates a random access preamble using the random access code index allocated to the adjacent RRH positioned in the highest ranking on the candidate list, and receives a random access response from the BS. The random access preamble is transmitted through the transceiver unit 1340, and the random access response is received from the BS through the transceiver unit 1340.
When a failure occurs in the radio link established between the serving RRH and the UE, the radio link connection unit 1330 performs a process of RRC connection re-establishment with the adjacent RRH positioned in the highest ranking on the candidate list to establish a radio link between the adjacent RRH and the UE.
The transceiver unit 1340 is connected to the candidate list configuring unit 1310, the random access processing unit 1320, and the radio link connection unit 1330 to transmit and receive a radio signal to and from the BS. According to an exemplary embodiment of the present invention, when a failure of a radio link established between a BS and a UE is detected due to a frequent movement of the UE which is located in a cell boundary or has high mobility, the radio link failure is rapidly handled using candidate list information regarding an adjacent RRH managed by the UE in advance, whereby a user experience data rate in consideration of enhancement of performance in a cell boundary may be maintained.
The exemplary embodiments of the present invention may not necessarily be implemented only through the foregoing devices and/or methods but may also be implemented through a program for realizing functions corresponding to the configurations of the embodiments of the present invention, a recording medium including the program, or the like. Such an implementation may be easily conducted by a person skilled in the art to which the present invention pertains from the foregoing description of embodiments.
The exemplary embodiments of the present invention have been described in detail, but the scope of the present invention is not limited thereto and various variants and modifications by a person skilled in the art using a basic concept of the present invention defined in claims also belong to the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0076043 | Jun 2016 | KR | national |
| 10-2016-0091645 | Jul 2016 | KR | national |
