WO2013073746A1

WO2013073746A1 - Random access to the tp selected based on reception timing

Info

Publication number: WO2013073746A1
Application number: PCT/KR2012/001493
Authority: WO
Inventors: Dragan Vujcic
Original assignee: Lg Electronics Inc.
Priority date: 2011-11-14
Filing date: 2012-02-28
Publication date: 2013-05-23

Abstract

The present document is directed to a reception timing based TP (Transmission Point) selection and a random access procedure to the selected TP. According to one embodiment, a method comprises transmitting a random access preamble to the macro eNB and the RRHs; receiving a random access response, during a predetermined period of time after transmitting the random access preamble, from the macro eNB, wherein the random access response comprises a timing advanced command value and information about a specific transmission point (TP) to which the timing advanced command value corresponds, wherein the specific TP is selected from the macro eNB and the RRHs; and transmitting a message 3 to the specific TP based on the received timing advanced command value.

Description

RANDOM ACCESS TO THE TP SELECTED BASED ON RECEPTION TIMING

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present document is directed to a random access scheme to the network.

More specifically, the present document is directed to a reception timing based TP (Transmission Point) selection and a random access procedure to the selected TP.

Discussion of the Related Art

[0002] First of all, 3GPP LTE (3^rd generation partnership project) long term evolution: hereinafter called 'LTE') communication system is schematically described as a mobile communication system to which the present invention is applicable.

[0003] FIG. 1 is a schematic diagram of E-UMTS network structure as an example of a mobile communication system.

[0004] Referring to FIG. 1, E-UMTS (evolved universal mobile telecommunications system) is the system having evolved from UMTS (universal mobile telecommunications system) and its basic standardization is ongoing by 3GPP. Generally, the E-UMTS can be called LTE system.

[0005] E-UMTS network can be mainly divided into E-UTRAN (evolved-UMTS terrestrial radio access network) 101 and CN 102 (core network). The E-UTRAN 101 consists of a user equipment (hereinafter abbreviated UE) 103, a base station (hereinafter named eNode B or eNB) 104, and an access gateway (hereinafter abbreviated AG) 105 located at an end point of the network to be externally connected to an external network. The AG 105 can be divided into one part responsible for user traffic processing and the other part for processing control traffic. In this case, the AG for new user traffic processing and the AG for processing control traffic can communicate with each other using a new interface.

[0006] At least one cell can exist at one eNode B. Between eNode Bs, an interface for user or control traffic transmission is usable. And, the CN 102 can consist of a node for user registrations of the AG 105 and other UE 103. Moreover, an interface for discriminating the E-UTRAN 101 and the CN 102 is available.

[0007] Layers of a radio interface protocol between a user equipment and a network can be divided into LI (first layer), L2 (second layer) and L3 (third layer) based on three lower layers of the open system interconnection (OSI) reference model widely known in the field of communication systems. A physical layer belonging to the first layer provides an information transfer service using a physical channel. A radio resource control (hereinafter abbreviated RRC) located on the third layer plays a role in controlling radio resources between the user equipment and the network. For this, the RRC layers exchange RRC messages between the user equipment and the network. The RRC layers can be distributed to network nodes including the eNode B 104, the AG 105 and the like. Moreover, the RRC layer can be provided to the eNode B 104 or the AG 105 only.

[0008] FIG. 2 and FIG. 3 are diagrams for structures of a radio interface protocol between a user equipment and UTRAN based on the 3 GPP radio access network specifications.

[0009] Referring to FIG. 2 and FIG. 3, a radio interface protocol horizontally consists of a physical layer, a data link layer and a network layer. And, the radio interface protocol vertically consists of a user plane for data information transfer and a control plane for control signal delivery (signaling). In particular, FIG. 2 shows the respective layers of the radio protocol control plane and FIG. 3 shows the respective layers of the radio protocol user plane. The radio protocol layers shown in FIG. 2 and FIG. 3 can be divided into LI (first layer), L2 (second layer) and L3 (third layer) based on three lower layers of the open system interconnection (OSI) reference model widely known in the field of communication systems.

[0010] The respective layers of the radio protocol control plane shown in FIG. 2 and the respective layers of the radio protocol user plane shown in FIG. 3 are explained as follows.

[0011] First of all, a physical (PHY) layer of a first layer provides an upper layer with an information transfer service using a physical channel. The physical (PHY) layer is connected to a medium access control (MAC) layer on an upper layer via a transport channel. And, data is transported between the medium access control (MAC) layer and the physical (PHY) layer via the transport channel. In this case, the transport channel can be classified into a dedicated transport channel or a common transport channel according to whether a channel is shared or not. Moreover, data are transported via the physical channel between different physical layers, i.e., between a physical layer of a transmitting side and a physical layer of a receiving side.

[0012] Various layers exist in the second layer. First of all, a medium access control (hereinafter abbreviated 'MAC') layer plays a role in mapping various logical channels to various transport channels. And, the MAC layer also plays a role as logical channel multiplexing in mapping several logical channels to one transport channel. The MAC layer is connected to a radio link control (RLC) layer of an upper layer via a logical channel. And, the logical channel can be mainly categorized into a control channel for transferring information of a control plane and a traffic channel for transferring information of a user plane according to a type of the transferred information.

[0013] A radio link control (hereinafter abbreviated RLC) of the second layer performs segmentation and concatenation on data received from an upper layer to play a role in adjusting a size of the data to be suitable for a lower layer to transfer the data to a radio section. And, the RLC layer provides three kinds of RLC modes including a transparent mode (hereinafter abbreviated TM), an unacknowledged mode (hereinafter abbreviated UM) and an acknowledged mode (hereinafter abbreviated AM) to secure various kinds of QoS demanded by each radio bearer (hereinafter abbreviated RB). In particular, the AM RLC performs a retransmission function through automatic repeat and request (ARQ) for the reliable data transfer.

[0014] A packet data convergence protocol (hereinafter abbreviated PDCP) layer of the second layer performs a header compression function for reducing a size of an IP packet header containing relatively large and unnecessary control information to efficiently transmit such an IP packet as IPv4 and IPv6 in a radio section having a small bandwidth. This enables a header part of data to carry mandatory information only to play a role in increasing transmission efficiency of the radio section. Moreover, in the LTE system, the PDCP layer performs a security function as well. This consists of ciphering for preventing data interception conducted by a third party and integrity protection for preventing data manipulation conducted by a third party.

[0015] A radio resource control (hereinafter abbreviated RRC) layer located at a most upper part of a third layer is defined in the control plane only and is responsible for controlling a logical channel, a transport channel and physical channels in association with configuration, reconfiguration and release of radio bearers (hereinafter abbreviated RBs). In this case, the RB means a logical path provided by the first and second layers of the radio protocol for the data delivery between the user equipment and the UTRAN. Generally, configuring an RB means to stipulate characteristics of radio protocol layers and channels required for providing a specific service and also means to configure detailed parameters and operational methods thereof. The RB can be classified into a signaling RB (SRB) or a data RB DRB). The SRB is used as a path for sending an RRC message in a control plane (C-plane) and the DRB is used as a path for transferring user data in a user plane (U-plane).

[0016] As a downlink transport channel for transporting data to a user equipment from a network, there is a broadcast channel (BCH) for transmitting system information and a downlink shared channel (SCH) for transmitting a user traffic or a control message. Downlink multicast, traffic of a broadcast service or a control message can be transmitted on downlink SCH or a separate downlink MCH (multicast channel). Meanwhile, as an uplink transport channel for transmitting data to a network from a user equipment, there is a random access channel (RACH) for transmitting an initial control message or an uplink shared channel (SCH) for transmitting user traffic or a control message.

[0017] As a downlink physical channel for transmitting information transferred on a downlink transport channel to a radio section between a network and a user equipment, there is a physical broadcast channel for transferring information of BCH, a physical multicast channel (PMCH) for transmitting information of MCH, a physical downlink shared channel for transmitting information of PCH and downlink SCH or a physical downlink control (or called DL L1/L2 control channel) for transmitting control information provided by first and second layers.

[0018] As an uplink physical channel for transmitting information forwarded on an uplink transport channel to a radio section between a network and a user equipment, there is a physical uplink shared channel (PUSCH) for transmitting information of uplink SCH, a physical random access channel (PRACH) for transmitting RACH information or a physical uplink control channel (PUCCH) for transmitting such control information, which is provided by first and second layers, as HARQ ACK, HARQ NACK, scheduling request (SR), channel quality indicator (CQI) report and the like. [0019] An LTE User Equipment (UE) can only be scheduled for uplink transmission if its uplink transmission timing is synchronized. The LTE Random Access CHannel (RACH) therefore plays a key role as an interface between non-synchronized UEs and the orthogonal transmission scheme of the LTE uplink radio access.

[0020] The present proposal is related with heterogeneous networks scenarios consisting of a macro eNodeB and remote radio heads (RRHs). The UE would perform the random access with targeting its closest transmission point with minimal required access resources (e.g. RACH TTI allocation, RACH transmission power, preamble length). This would reduce interference in a cell and also save the UE's battery power.

[0021] In order to efficiently implement the above scheme, there is a need for how efficiently select the closest TP and random access scheme to access the selected TP.

SUMMARY OF THE INVENTION

[0022] Accordingly, the present invention is directed to a reception timing based TP (Transmission Point) selection and a random access procedure to the selected TP.

[0023] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

[0024] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for a user equipment (UE) to perform a random access to a network comprising a macro eNB and one or more remote radio heads (RRHs), the method comprising: transmitting a random access preamble to the macro eNB and the RRHs; receiving a random access response, during a predetermined period of time after transmitting the random access preamble, from the macro eNB, wherein the random access response comprises a timing advanced command value and information about a specific transmission point (TP) to which the timing advanced command value corresponds, wherein the specific TP is selected from the macro eNB and the RRHs; and transmitting a message 3 to the specific TP based on the received timing advanced command value is proposed.

[0025] Here, the specific TP may be a closest TP to the UE among the macro eNB and the RRHs.

[0026] The timing advanced command value may be calculated by the macro eNB based on reception timing information of the random access preamble by each of the macro eNB and the RRHs.

[0027] The random access response may further comprise a uplink grant information, and the uplink grant information may allocate uplink resource for transmitting the message 3 to the specific TP. That is, the uplink grant information may be determined based on the specific TP, not based on the macro eNB.

[0028] The random access response may further comprise a power adjustment parameter used for transmitting the message 3 to the specific TP.

[0029] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for a macro eNB to control a random access from a user equipment (UE) in a network comprising the macro eNB and one or more remote radio heads (RRHs), the method comprising: receiving a random access preamble from the UE; acquiring reception timing information of the random access preamble at the macro eNB; acquiring reception timing information of the random access preamble at the RRHs; selecting a specific TP among the macro eNB and the RRHs based on the reception timing information of the random access preamble at the macro eNB and the RRHs; and transmitting a random access response to the UE, wherein the random access response comprises a timing advanced command value and information about the specific transmission point (TP) to which the timing advanced command value corresponds is proposed.

[0030] Here, the specific TP may be a closest TP to the UE among the macro eNB and the RRHs.

[0031] The timing advanced command value may be calculated by the macro eNB based on reception timing information of the random access preamble by each of the macro eNB and the RRHs.

[0032] The random access response may further comprise a uplink grant information, and the uplink grant information may allocate uplink resource for transmitting the message 3 to the specific TP. That is, the uplink grant information may be determined based on the specific TP.

[0033] The random access response may further comprise a power adjustment parameter used for transmitting the message 3 to the specific TP.

[0034] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a user equipment (UE) for performing a random access to a network comprising a macro eNB and one or more remote radio heads (RRHs), the UE comprising: a transmitter configured to transmit a random access preamble to the macro eNB and the RRHs; a receiver configured to receive a random access response, during a predetermined period of time after transmitting the random access preamble, from the macro eNB, wherein the random access response comprises a timing advanced command value and information about a specific transmission point (TP) to which the timing advanced command value corresponds, wherein the specific TP is selected from the macro eNB and the RRHs; and a processor connected to the transmitter and the receiver, and configured to control the transmitter to transmit a message 3 to the specific TP based on the received timing advanced command value is proposed.

[0035] Here, the specific TP may be a closest TP to the UE among the macro eNB and the RRHs.

[0036] The timing advanced command value may be calculated by the macro eNB based on reception timing information of the random access preamble by each of the macro eNB and the RRHs.

[0037] The random access response may further comprise a uplink grant information, and the uplink grant information may allocate uplink resource for transmitting the message 3 to the specific TP.

[0038] The random access response may further comprise a power adjustment parameter used for transmitting the message 3 to the specific TP.

[0039] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a macro eNB for controlling a random access from a user equipment (UE) in a network comprising the macro eNB and one or more remote radio heads (RRHs), the macro eNB comprising: a receiver configured to receive a random access preamble from the UE, and receive reception timing information of the random access preamble at the RRHs; a processor connected to the receiver; configured to acquire reception timing information of the random access preamble at the macro eNB and the RRHs; and configured to select a specific TP among the macro eNB and the RRHs based on the reception timing information of the random access preamble at the macro eNB and the RRHs; and a transmitter connected to the processor, and configured to transmit a random access response to the UE, wherein the processor generate the random access response to comprise a timing advanced command value and information about the specific transmission point (TP) to which the timing advanced command value corresponds is proposed.

[0040] The specific TP may be a closest TP to the UE among the macro eNB and the RRHs.

[0041] The timing advanced command value may be calculated by the processor of the macro eNB based on reception timing information of the random access preamble by each of the macro eNB and the RRHs.

[0042] It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:

[0044] Figure 1 is a schematic diagram of E-UMTS network structure as an example of a mobile communication system;

[0045] Figures 2 and FIG. 3 are diagrams for structures of a radio interface protocol between a user equipment and UTRAN based on the 3 GPP radio access network specifications; T/KR2012/001493

[0046] Figure 4 shows the contention-based procedure consists of four-steps;

[0047] Figure 5 shows the non-contention-based procedure consists of two- steps;

[0048] Figure 6 shows LTE RACH preamble sequences to satisfy coverage requirement;

[0049] Figure 7 shows the concept of heterogeneous network to which the present proposal is directed;

[0050] Figure 8 shows the reception timing of the random access preamble from UE 0 at TPs 0-2 according to one example of the present invention;

[0051] Figure 9 is for the concept of timing advanced command value according to one embodiment of the present invention;

[0052] Figures 10 to 13 show the contents and formats for the message 2 of the present embodiment; and

[0053] Figure 14 shows apparatus to implement the embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0054] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In the following detailed description of the invention includes details to help the full understanding of the present invention. Yet, it is apparent to those skilled in the art that the present invention can be implemented without these details. For instance, although the following detailed description is made in detail on the assumption P T/KR2012/001493 that a mobile communication system is the 3GPP LTE system, it is applicable to other prescribed mobile communication systems by excluding unique items of the 3 GPP LTE.

[0055] Occasionally, the structures and devices known to the public are omitted to avoid conceptional vagueness of the present invention or can be illustrated as block diagrams centering on their core functions.

[0056] Besides, in the following description, assume that a terminal is a generic term of such a mobile or fixed user-end device as a user equipment (UE), a mobile station (MS) and the like. Moreover, assume that eNB is a generic name of such a random node of a network end, such as a base station, which communicates with a terminal, as a Node B, an eNnode B and the like.

[0057] As stated above, the present invention is directed to a reception timing based TP (Transmission Point) selection and a random access procedure to the selected TP. For better understanding of the invention, a random access procedure of the LTE system is first explained as an example.

[0058] The LTE random access procedure comes in two forms, allowing access to be either contention-based (implying an inherent risk of collision) or contention-free. A UE initiates a contention-based random access procedure for all use-cases listed as following.

[0059] (1) A UE in RRC CONNECTED state, but not uplink-synchronized, needing to send new uplink data or control information (e.g. an event-triggered measurement report);

[0060] (2) A UE in RRC CONNECTED state, but not uplink-synchronized, needing to receive new downlink data, and therefore to transmit correspondingACK/NACK in the uplink;

[0061] (3) A UE in RRC CONNECTED state, handing over from its current serving cell to a target cell; [0062] (4) A transition from RRCJDLE state to RRC CONNECTED, for example for initial access or tracking area updates;

[0063] (5) Recovering from radio link failure.

[0064] In this procedure, a random access preamble signature is randomly chosen by the UE, with the result that it is possible for more than one UE simultaneously to transmit the same signature, leading to a need for a subsequent contention resolution process.

[0065] For the use-cases (2) (new downlink data) and (3) (handover) the eNodeB has the option of preventing contention occurring by allocating a dedicated signature to a UE, resulting in contention-free access. This is faster than contention-based access - a factor which is particularly important for the case of handover, which is time-critical.

[0066] Unlike in WCDMA, a fixed number (64) of preamble signatures is available in each LTE cell, and the operation of the two types of RACH procedure depends on a partitioning of these signatures between those for contention-based access and those reserved for allocation to specific UEs on a contention-free basis.

[0067] The two procedures are outlined in the following.

[0068] FIGs. 4 and 5 are procedural diagrams illustrating Contention-based Random Access Procedure and Non-Contention-based Random Access Procedure.

[0069] The contention-based procedure consists of four-steps as shown in Figure 4:

• Step 1 : Preamble transmission (message 1);

• Step 2: Random access response (message 2);

• Step 3: Layer 2 / Layer 3 (L2/L3) message (message 3);

• Step 4: Contention resolution message (message 4).

[0070] ' The slightly unpredictable latency of the random access procedure can be circumvented for some use cases where low latency is required, such as handover and resumption of downlink traffic for a UE, by allocating a dedicated signature to the UE on a per-need basis. In this case the procedure is simplified as shown in Figure 5. The procedure terminates with the RAR.

[0071] The length of the LTE RACH preamble sequence was designed to satisfy coverage requirement.

[0072] Figure 6 shows LTE RACH preamble sequences to satisfy coverage requirement.

[0073] High cell coverage requires a longer CP (cyclic prefix) and GT (guard time) in order to absorb the corresponding round-trip delay. LTE Rel8 defines 4 PRACH formats as following:

[0074] Format 0: 1TTI (1 ms) burst for small-medium cells (up to ~ 14 km)

[0075] Format 1 : 2TTI (2 ms) burst for large cells (up to -77 km)

[0076] Format 2: 2TTI (2 ms) burst for medium cells (up to -29 km)

[0077] Format 3 : 3TTI (3 ms) burst for very large cells (up to - 100 km)

[0078] The number of TTIs for RACH preamble transmission is decided by eNB according to the cell coverage requirement. Due to round trip delay and delay spread of signal the UEs at cell edge require more TTIs for timing detection than those close to the eNB. Therefore the LTE reference scheme for all UEs within the cell is to satisfy the cell border UEs. However, this scheme can waist resource when considering the heterogeneous network.

[0079] Figure 7 shows the concept of heterogeneous network to which the present proposal is directed.

[0080] The present proposal is related with heterogeneous networks scenarios consisting of a macro eNodeB and remote radio heads (RRHs) as shown in figure 7. R2012/001493

Application of a RRH is effective in coordinating geographically separate cells with negligible coordination latency. Besides the well understood setup in which macro and RRHs are configured with different cell IDs, an alternative configuration was proposed in which all nodes share the same cell ID. In such a configuration both Macro cell and its RRH(s) can be referred as transmission points (TP) of one cell. Configuring the same cell ID at both macro eNodeB and RRHs makes these nodes appear as a single cell sharing the same radio resources. The UE would perform the random access with targeting its closest transmission point with minimal required access resources (e.g. RACH TTI allocation, RACH transmission power, preamble length). This would reduce interference in a cell and also save the UE's battery power.

[0081] Thus, in one aspect of the present proposal for a method for a user equipment (UE) to perform a random access to a network comprising a macro eNB and one or more remote radio heads (RRHs), the method comprises: transmitting a random access preamble to the macro eNB and the RRHs; and receiving a random access response, during a predetermined period of time after transmitting the random access preamble, from the macro eNB, wherein the random access response comprises (a) a timing advanced command value and (b) information about which of the macro eNB and the RRHs corresponds to the timing advanced command value. This method is explained with an example of the heterogeneous network shown in figure 7.

[0082] When the UE 1 wants to perform a random access to the network, the UE 1 may transmit the random access preamble to the macro eNB (TPO) and 2 RRHs (TPl and TP2). In this example, the reception timing of the random access preamble at TPs 0 - 2 can be represented as following Figure 8.

[0083] Figure 8 shows the reception timing of the random access preamble from UE 0 at TPs 0-2 according to one example of the present invention. [0084] This reception timing at each of TPs can be used to select the closest TP among the existing TPs. Referring to figure 8, the reception timing at TP 1 is the fastest, followed by that of TPO, and then that of TP 2. Based on these information, we can conclude that TP 1 is the closest TP among TPs 0-2.

[0085] For this end, this reception timing information may be forwarded to the macro eNB. Then, the macro eNB may inform the UE of the information about which of the TPs is to perform the rest of the random access procedure (that is, transmitting message 3 and receiving message 4) via the message 2. In this example, the UE1 receives message 2 indicating that the TP1 is the closest TP and the UE1 is to transmit message 3 to the TP1.

[0086] Further, the above mentioned reception timing information at each of TPs can be used to calculate the timing advanced command value transmitted also via the message 2. Explanation for the timing advanced command value is followed.

[0087] Figure 9 is for the concept of timing advanced command value according to one embodiment of the present invention.

[0088] Transmission of the uplink radio frame number ^ from the UE shall start (N_TA+N_TA offset ) ^x seconds before the start of the corresponding downlink radio frame at the UE, where 0 < N_TA≤ 20512, N_TA offset ^— 0 for frame structure type 1 and N_{TA of}f_set = 624 for frame structure type 2. Note that not all slots in a radio frame may be transmitted. One example hereof is TDD, where only a subset of the slots in a radio frame is transmitted.

[0089] The reason why the UE transmits uplink signals (-W TA ⁺ ^TA offset ) ^x ^s seconds before the start of the corresponding downlink radio frame is due to the different locations of the UE within the cell. That is, the UE far from the eNB should transmit earlier KR2012/001493 than the UE close to the eNB. This is a kind of uplink synchronization, and the value of NJA is received via the message 2 during the random access procedure.

[0090] Thus, according to the present proposal of heterogeneous networks, the reception timing information at each of TPs as shown in Figure 8 may be forwarded to the macro eNB, and the macro eNB may calculate the timing advanced command value (NTA) based on this information.

[0091] In this example, the UE1 receives message 2 indicating the timing advanced command indicating NTA calculated based on the random access preamble reception timing at TP 1. Then, the UE1 may transmit message 3 to the TP1 (NTA ⁺ ^TA offset ) ^x seconds before the start of the corresponding downlink radio frame, which is calculated based on the received timing advanced command value.

[0092] As shown in Figure 8, the amplitude the received random access preamble can be different due to the different distance from each of TPs, thus message 2 may informs the UE of the adjustment parameter for the amplitude of the message 3 (or all the uplink signals) based on this information.

[0093] In summary, the message 2 according to the present proposal may be represented as following.

[0094] Figures 10 to 13 show the contents and formats for the message 2 of the present embodiment.

[0095] A MAC PDU consists of a MAC header and zero or more MAC Random Access Responses (MAC RAR) and optionally padding as described in figure 13. The MAC header is of variable size. A MAC PDU header consists of one or more MAC PDU subheaders; each subheader corresponding to a MAC RAR except for the Backoff Indicator subheader. If included, the Backoff Indicator subheader is only included once and is the first subheader included within the MAC PDU header.

[0096] A MAC PDU subheader consists of the three header fields E/T/RAPID (as described in figure 10) but for the Backoff Indicator subheader which consists of the five header field E/T/R/R/BI (as described in figure 1 1).

[0097] A MAC RAR consists of the four fields I/Timing Advance Command/UL

Grant/Temporary C-RNTI (as described in figure 12). In this MAC RAR, 'Timing Advanced Command' field indicates (a) timing advanced command value (NTA) explained above, and T field indicates (b) information about which of the macro eNB and the RRHs corresponds to the timing advanced command value. That is, the T field indicates the specific TP among the macro and RRHs, closest to the UE.

[0098] UL grant field may indicate uplink resource allocated for transmission of the message 3 to the specific TP. That is, the resource allocated to the message 3 transmission is based on the radio condition between the UE and the specific TP, not between the macro eNB and the UE.

[0099] Padding may occur after the last MAC RAR. Presence and length of padding is implicit based on TB size, size of MAC header and number of RARs.

[00100] The UE receiving the above explained message 2 may select the TP to transmit message 3, and transmit the message 3 based on the information acquired from the message 2.

[00101] Based on the above explanation, the apparatus to implement the above method are explained.

[00102] Figure 14 shows apparatus to implement the embodiments of the present invention.

[00103] In figure 14, a wireless communication system includes a BS 10 and one or more UE 20. In downlink, a transmitter may be a part of the BS 10, and a receiver may be a part of the UE 20. In uplink, a transmitter may be a part of the UE 20, and a receiver may be a part of the BS 10. A BS 10 may include a processor 11, a memory 12, and a radio frequency (RF) unit 13. The processor 1 1 may be configured to implement proposed procedures and/or methods described in this document. The memory 12 is coupled with the processor 11 and stores a variety of information to operate the processor 1 1. The RF unit 13 is coupled with the processor 1 1 and transmits and/or receives a radio signal. A UE 20 may include a processor 21, a memory 22, and a RF unit 23. The processor 21 may be configured to implement proposed procedures and/or methods described in this application. The memory 22 is coupled with the processor 21 and stores a variety of information to operate the processor 21. The RF unit 23 is coupled with the processor 21 and transmits and/or receives a radio signal. The BS 10 and/or the UE 20 may have single antenna and multiple antenna. When at least one of the BS 10 and the UE 20 has multiple antenna, the wireless communication system may be called as multiple input multiple output (MIMO) system.

[00104] In figure 14, the BS 10 may represent Macro eNB in figure 7. The processor 21 of the UE 20 may control the RF unit 23 to transmit random access preamble to multiple TPs including the BS 10. The processor 1 1 of the BS 10 may acquire the reception timing information as shown in figure 8, and determine the information carried via message 2. This information may comprise information for the closest TP and timing advanced command value for the closest TP. Preferably, the information may comprise power adjustment parameter associated with the closest TP.

[00105] Based on this information, the processor 23 of the UE 20 may control the RF unit 23 to transmit message 3 to the closest TP with the information acquired from message 2. [00106] The above-described enhanced random access technology and apparatus are explained mainly with reference to the example that they are applied to the 3 GPP LTE system. However, they are applicable to various mobile communication systems, such as IEEE based system employing ranging procedure corresponding to the random access procedure of LTE.

Claims

WHAT IS CLAIMED IS:

1. A method for a user equipment (UE) to perform a random access to a network comprising a macro eNB and one or more remote radio heads (RRHs), the method comprising:

transmitting a random access preamble to the macro eNB and the RRHs; receiving a random access response, during a predetermined period of time after transmitting the random access preamble, from the macro eNB, wherein the random access response comprises a timing advanced command value and information about a specific transmission point (TP) to which the timing advanced command value corresponds, wherein the specific TP is selected from the macro eNB and the RRHs; and

transmitting a message 3 to the specific TP based on the received timing advanced command value.

2. The method of claim 1, wherein the specific TP is a closest TP to the UE among the macro eNB and the RRHs.

3. The method of claim 1, wherein the timing advanced command value is calculated by the macro eNB based on reception timing information of the random access preamble by each of the macro eNB and the RRHs.

4. The method of claim 1 , wherein the random access response further comprises a uplink grant information, and wherein the uplink grant information allocates uplink resource for transmitting the message 3 to the specific TP.

5. The method of claim 4, wherein the uplink grant information is determined based on the specific TP.

6. The method of claim 1, wherein the random access response further comprises a power adjustment parameter used for transmitting the message 3 to the specific TP.

7. A method for a macro eNB to control a random access from a user equipment (UE) in a network comprising the macro eNB and one or more remote radio heads (RRHs), the method comprising:

receiving a random access preamble from the UE;

acquiring reception timing information of the random access preamble at the macro eNB;

acquiring reception timing information of the random access preamble at the

RRHs;

selecting a specific TP among the macro eNB and the RRHs based on the reception timing information of the random access preamble at the macro eNB and the RRHs; and

transmitting a random access response to the UE, wherein the random access response comprises a timing advanced command value and information about the specific transmission point (TP) to which the timing advanced command value corresponds.

8. The method of claim 7, wherein the specific TP is a closest TP to the UE among the macro eNB and the RRHs.

9. The method of claim 7, wherein the timing advanced command value is calculated by the macro eNB based on reception timing information of the random access preamble by each of the macro eNB and the RRHs.

10. The method of claim 7, wherein the random access response further comprises a uplink grant information, and

wherein the uplink grant information allocates uplink resource for transmitting the message 3 to the specific TP.

1 1. The method of claim 10, wherein the uplink grant information is determined based on the specific TP.

12. The method of claim 7, wherein the random access response further comprises a power adjustment parameter used for transmitting the message 3 to the specific TP.

13. A user equipment (UE) for performing a random access to a network comprising a macro eNB and one or more remote radio heads (RRHs), the UE comprising:

a transmitter configured to transmit a random access preamble to the macro eNB and the RRHs; a receiver configured to receive a random access response, during a predetermined period of time after transmitting the random access preamble, from the macro eNB, wherein the random access response comprises a timing advanced command value and information about a specific transmission point (TP) to which the timing advanced command value corresponds, wherein the specific TP is selected from the macro eNB and the R Hs; and

a processor connected to the transmitter and the receiver, and configured to control the transmitter to transmit a message 3 to the specific TP based on the received timing advanced command value.

14. The UE of claim 13, wherein the specific TP is a closest TP to the UE among the macro eNB and the RRHs.

15. The UE of claim 13, wherein the timing advanced command value is calculated by the macro eNB based on reception timing information of the random access preamble by each of the macro eNB and the RRHs.

16. The UE of claim 13, wherein the random access response further comprises a uplink grant information, and

17. The UE of claim 13, wherein the random access response further comprises a power adjustment parameter used for transmitting the message 3 to the specific TP.

18. A macro eNB for controlling a random access from a user equipment (UE) in a network comprising the macro eNB and one or more remote radio heads (RRHs), the macro eNB comprising:

a receiver configured to receive a random access preamble from the UE, and receive reception timing information of the random access preamble at the RRHs; a processor connected to the receiver; configured to acquire reception timing information of the random access preamble at the macro eNB and the RRHs; and configured to select a specific TP among the macro eNB and the RRHs based on the reception timing information of the random access preamble at the macro eNB and the RRHs; and

a transmitter connected to the processor, and configured to transmit a random access response to the UE,

wherein the processor generate the random access response to comprise a timing advanced command value and information about the specific transmission point (TP) to which the timing advanced command value corresponds.

19. The macro eNB of claim 18, wherein the specific TP is a closest TP to the UE among the macro eNB and the RRHs.

20. The macro eNB of claim 19, wherein the timing advanced command value is calculated by the processor of the macro eNB based on reception timing information of the random access preamble by each of the macro eNB and the RRHs.