Patent Description:
A technique is under study in which a plurality of antennas are arranged with high density, and communication with a terminal apparatus is performed using some of the plurality of antennas. With this technique, as a result of different antennas being used for each terminal apparatus, a cell is virtually configured for the terminal apparatus, and the terminal apparatus is approximately present at the center of the virtual cell (refer to NPL <NUM>). According to such a technique, the terminal apparatus can achieve uniform communication quality regardless of the position.

Further background art is provided in a paper by <NPL>), which discusses <NUM>-step CFRA (Contention Free Random Access) for handover, and in <CIT>, which discloses a random access method and equipment thereof.

Any procedure for establishing connection has not been determined for performing communication between a terminal apparatus and a base station apparatus in an aforementioned system in which antennas are arranged with high density, and at least some of the antennas are selectively used. Therefore, it is requested to define a procedure for efficiently establishing connection between a base station apparatus and a terminal apparatus.

The present invention provides a technique for enabling efficient establishment of connection between a base station apparatus and a terminal apparatus, in a system in which some of a plurality of antennas are selected and used for performing communication between the base station apparatus and the terminal apparatus.

More particularly, the present invention provides a control apparatus as defined in Claim <NUM> of the appended claims. Also provided is a terminal apparatus as defined in Claim <NUM>, communication methods as defined in Claims <NUM> and <NUM>, and programs as defined in Claims <NUM> and <NUM>. Details of certain embodiments are set out in the dependent claims.

A control apparatus according to one aspect of the present invention is a control apparatus that wirelessly communicates with a terminal apparatus, and includes control means for, when a message corresponding to a random access preamble is received from the terminal apparatus, if the message is not based on a setting notified to the terminal apparatus by the control apparatus, scrambling communication with the terminal apparatus after the message was received, using a scrambling sequence that is based on second identification information that is different from first identification information corresponding to the control apparatus.

A terminal apparatus according to another aspect of the present invention includes communication means for including, in a message corresponding to a random access preamble, identification information for specifying a scrambling sequence to be used by a control apparatus that has received the message to scramble communication with the terminal apparatus, transmitting the message, and, after transmitting the message, performing communication with the control apparatus, the communication being scrambled using the scrambling sequence.

According to the present invention, connection between a base station apparatus and a terminal apparatus can be efficiently established, in a system in which some of a plurality of antennas are selected and used for performing communication between the base station apparatus and the terminal apparatus.

The accompanying drawing are included in and make up a portion of the specification, illustrate embodiments of the present invention, and are used along with the description thereof for describing the principle of the present invention.

<FIG> shows an exemplary configuration of a wireless communication system according to a present embodiment. As shown in <FIG>, in the wireless communication system according to the present embodiment, a plurality of antennas are planarly arranged with high density, and the antennas are connected to control apparatuses <NUM> such as base station apparatuses using optical fibers, for example. A control apparatus <NUM> connects to a terminal apparatus <NUM> via at least one antenna and performs communication therewith. Note that, although only a small number of control apparatuses <NUM> and one terminal apparatus <NUM> are shown in <FIG> in order to simplify the description, there may be of course a larger number of these apparatuses than illustrated in <FIG>.

Note that, in the following, description will be given assuming that the antennas are arranged in a distributed manner and are connected to the control apparatuses. However, only the antennas may be arranged with high density, or antenna units having an RF processing function such as an RF (radio frequency) filter may also be arranged with high density. The control apparatuses <NUM> execute communication processing other than the processing to be performed on the antenna side. That is, baseband processing regarding received signals and signal processing in an upper layer thereafter are performed by the control apparatuses <NUM>. As shown in <FIG>, when constructing a system in which a very large number of antennas are used, it is envisioned that a plurality of control apparatuses <NUM> are each connected to a plurality of antennas and perform signal transmission and reception, considering a computation load or the like. Note that this system can be configured using a known centralized radio access network (C-RAN), in which each antenna may correspond to a transmission/reception point (TRP) of C-RAN, and the control apparatus <NUM> may correspond to a baseband unit (BBU) of C-RAN.

The terminal apparatus <NUM> connects to a control apparatus <NUM> via an antenna that is present in the vicinity, and performs communication. The control apparatus <NUM> performs communication with the terminal apparatus <NUM> using at least some of the antennas that are connected to the control apparatus <NUM>, in a state in which the connection with the terminal apparatus <NUM> has been established. Here, two or more control apparatuses <NUM> can establish connection with the terminal apparatus <NUM> and perform communication in parallel. Accordingly, one or more control apparatuses <NUM> can configure a virtual area with the terminal apparatus <NUM> being at the center (may also be referred to as a user centric area), and provide a high quality and highly stable communication service, regardless of the position of the terminal apparatus <NUM>.

In contrast, any study has not been made regarding the processing that is performed when starting establishment of connection in such a system in which a plurality of antennas are used. In a conventional cellular wireless communication system of LTE (long term evolution) or the like, cell-specific scrambling corresponding to identification information of a cell (a cell ID) is applied to a reference signal sequence or user data. Accordingly, interference between cells is randomized, and it is possible to improve the communication quality. In addition, in a conventional cellular wireless communication system, terminal-specific scrambling can be further applied to a reference signal sequence or user data. Due to such terminal-specific scrambling, when different cells corresponding to different cell IDs perform cooperative communication, interference is randomized, and simultaneous transmission in cooperative communication is enabled. On the other hand, when a conventional technique is applied to a system such as that shown in <FIG>, it is envisioned that, in random access processing (hereinafter, may be referred to as "RACH" or "RACH processing") for establishing connection, after cell-specific scrambling is applied and connection is established, terminal-specific scrambling is set in the terminal apparatus as necessary, and, after this, scrambling specific to that terminal apparatus is applied and communication is performed. However, two or more control apparatuses <NUM> respectively correspond to different cell IDs, and thus, when the terminal apparatus <NUM> performs RACH processing, only an antenna that is connected to the control apparatus <NUM> with which an attempt is made to establish connection through that RACH processing is used. As a result, it is not possible to sufficiently improve the communication quality of the RACH processing performed by the terminal apparatus <NUM> by using a large number of antennas, and the probability that the RACH processing will fail can increase. In addition, after the terminal apparatus <NUM> performs RACH processing and is then connected to a predetermined control apparatus <NUM>, until a scrambling sequence specific to the terminal apparatus <NUM> is shared by two or more control apparatuses <NUM> that perform communication with that terminal apparatus <NUM>, it is not possible to provide high-quality communication to the terminal apparatus <NUM>. In view of such a situation, the present embodiment provides a technique for improving a method to be used when the terminal apparatus <NUM> establishes initial connection with one or more control apparatuses <NUM>.

In the present embodiment, a first control apparatus determines whether or not a random access preamble received from the terminal apparatus <NUM> (for example, included in a message A of two-step RACH, or as a message <NUM> of four-step RACH) is based on a setting notified from the first control apparatus itself to the terminal apparatus. If the random access preamble is based on the setting of the first control apparatus, then, after this, the first control apparatus performs communication using a first scrambling sequence corresponding to a first cell ID of the first control apparatus itself. On the other hand, if the random access preamble is not based on the setting notified from the first control apparatus itself to the terminal apparatus, then, in communication after this, the first control apparatus does not use the first scrambling sequence corresponding to the first cell ID, but uses a second scrambling sequence corresponding to a second cell ID.

The second cell ID can be the cell ID of a second control apparatus that is in a neighboring relationship with the first control apparatus, for example. Accordingly, the first control apparatus can perform communication with the terminal apparatus <NUM> that has transmitted the random access preamble to the second control apparatus, using the scrambling sequence corresponding to the cell ID of the second control apparatus. Accordingly, the first control apparatus and the second control apparatus can cooperate with each other to execute processing after transmission of a response message to the random access preamble, and it is possible to improve the reliability of RACH processing. In addition, as a result of the scrambling sequence corresponding to the second cell ID being used also after RACH processing, there is no need to newly set a scrambling sequence specific to the terminal apparatus <NUM>. For this reason, it is possible to provide a high-quality wireless communication service to the terminal apparatus <NUM> immediately after connection is established.

Note that, for example, a first control apparatus can acquire, in advance, information regarding a cell ID from a control apparatus for which a neighboring relationship is set, and hold the information. In addition, for example, a configuration may be adopted in which, when a random access preamble is received, if the random access preamble is not based on the setting notified from the first control apparatus to the terminal apparatus, the first control apparatus transmits the random access preamble to a second control apparatus that is in a neighboring relationship therewith, inquires about a cell ID, and acquires a second cell ID. If, for example, the received random access preamble is based on the setting notified from the second control apparatus to the terminal apparatus, the second control apparatus can perform notification of the second cell ID thereof. Note that a configuration may be adopted in which a control apparatus holds, in advance, information regarding cell IDs related to one or more second control apparatuses, and, by transmitting a random access preamble, acquires only a response as to whether or not the random access preamble is based on the setting notified to the terminal apparatus by the second control apparatus to which the inquiry was made. In this case, the control apparatus that has received the inquiry may notify "ACK" as a response to the control apparatus that has made the inquiry if the received random access preamble is based on the setting notified from the control apparatus (that has received the inquiry) to the terminal apparatus, and notify "NACK" if not. Note that information of a small number of bits such as one bit indicating whether or not the random access preamble is based on the setting notified from the control apparatus that has received the inquiry to the terminal apparatus, other than ACK/NACK, may be transmitted/received. In addition, the first control apparatus may store a cell ID and setting information such as a seed for generating a sequence of a random access preamble (information that enables a random access preamble to be specified) in association, for each of one or more second control apparatuses. In this case, the first control apparatus specifies which control apparatus the received random access preamble is associated with, for example, by performing correlation detection using a sequence that is based on a seed associated with the second control apparatus in addition to a sequence that is based on a seed associated with the first control apparatus itself. When a random access preamble is detected based on a seed associated with an apparatus other than the first control apparatus, the first control apparatus specifies the cell ID stored in association with that seed, and, in communication after this, uses a scrambling sequence corresponding to the specified cell ID.

In addition, for example, in PUSCH (Physical Uplink Shared Channel) that is transmitted in a message A of two-step RACH in addition to the random access preamble, the terminal apparatus <NUM> may transmit a virtual cell ID. In this case, the first control apparatus can use this virtual cell ID as the above-described second cell ID regardless of whether or not the destination of the random access preamble is the first control apparatus itself. Accordingly, starting from transmission of a message B after the message A has been received, the control apparatus that has received the message A uses a scrambling sequence that is based on this virtual cell ID as a scrambling sequence specific to the terminal apparatus, and a plurality of control apparatuses can cooperate to transmit a signal. Note that it suffices that information that is notified from the terminal apparatus is any information that enables a scrambling sequence to be specified, and the information does not need to be a virtual cell ID.

As described above, in the present embodiment, starting from a response to transmission of a random access preamble of RACH processing, a plurality of control apparatuses can use a shared scrambling sequence, and thus it is possible to improve the wireless quality during RACH processing, and provide a high-quality communication environment to a terminal apparatus promptly after connection is established.

Next, the configuration of the control apparatus that executes processing described above will be described. Note that the terminal apparatus can have a similar configuration. <FIG> shows an exemplary hardware configuration of the control apparatus. The control apparatus includes a processor <NUM>, a ROM <NUM>, a RAM <NUM>, a storage apparatus <NUM>, and a communication circuit <NUM>, in one example. In the control apparatus, a computer readable program for realizing the functions of the control apparatus, which is recorded in any of the ROM <NUM>, the RAM <NUM>, and the storage apparatus <NUM>, for example, is executed by the processor <NUM>. Note that the processor <NUM> may be replaced by one or more processors such as an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), and a DSP (digital signal processor).

The control apparatus performs communication with a partner apparatus (e.g., a terminal apparatus, another control apparatus, an upper node, or the like) by the processor <NUM> controlling the communication circuit <NUM>, for example. Note that, a schematic diagram in which the control apparatus includes one communication circuit <NUM> is shown in <FIG>, however there is no limitation thereto. For example, the control apparatus may include a communication apparatus for communicating with a terminal apparatus and a communication apparatus for communicating with another control apparatus or an upper node.

<FIG> shows an exemplary functional configuration of the control apparatus. The control apparatus includes, for example, a communication control unit <NUM>, a scrambling sequence setting unit <NUM>, an information acquiring unit <NUM>, and an information notifying unit <NUM>. The communication control unit <NUM> controls communication with a terminal apparatus. The communication control unit <NUM> receives a random access preamble from the terminal apparatus, and transmits a random access response (for example, included in the message B of two-step RACH, or as a message <NUM> in four-step RACH) in response to that, for example, and thereby establishes connection with the terminal apparatus.

The scrambling sequence setting unit <NUM> sets settings of a scrambling sequence that is to be used. If, for example, the random access preamble is not based on the setting notified to the terminal apparatus by the control apparatus, the scrambling sequence setting unit <NUM> of the control apparatus sets settings of the communication control unit <NUM> such that a scrambling sequence that is based on a second cell ID that is different from a first cell ID of the control apparatus is used. The second cell ID can be a cell ID of another control apparatus that is in a neighboring relationship, for example. Note that, if PUSCH included in the message A from the terminal apparatus includes a virtual cell ID, the scrambling sequence setting unit <NUM> sets the communication control unit <NUM> such that a scrambling sequence that is based on the virtual cell ID. Note that, if notification of such a virtual cell ID has been performed, the scrambling sequence setting unit <NUM> can set settings of the communication control unit <NUM> such that a scrambling sequence that is based on the virtual cell ID is used, regardless of whether or not the random access preamble is based on the setting notified to the terminal apparatus by the control apparatus. On the other hand, if notification of a virtual cell ID has not been performed, and the random access preamble is not based on the setting notified to the terminal apparatus by the control apparatus, the scrambling sequence setting unit <NUM> of the control apparatus can set the settings of the communication control unit <NUM> such that a scrambling sequence that is based on the cell ID of the control apparatus is used.

The information acquiring unit <NUM> acquires the aforementioned second cell ID. An inquiry that includes the random access preamble is transmitted to another control apparatus that is in a neighboring relationship, for example. The information acquiring unit <NUM> then specifies whether or not the received random access preamble is based on the setting notified to the terminal apparatus by this other control apparatus, by receiving a response to the inquiry. If the received random access preamble is based on the setting notified to the terminal apparatus by this other control apparatus, the information acquiring unit <NUM> uses the cell ID of this other control apparatus as the second cell ID. Note that the information acquiring unit <NUM> may acquire, from another control apparatus, information indicating only whether or not the received random access preamble is based on the setting notified to the terminal apparatus by this other control apparatus, or may acquire the cell ID itself of this other control apparatus. When a similar inquiry is given from another control apparatus, the information notifying unit <NUM> notifies the other control apparatus that has made the inquiry, of the cell ID and information indicating whether or not the random access preamble included in the inquiry is based on the setting notified to the terminal apparatus by the control apparatus (that has received the inquiry). Note that a configuration can be adopted in which, for example, the information acquiring unit <NUM> stores seeds of random access preambles and cell IDs in association, specifies which seed the received random access preamble corresponds to, and specifies the cell ID associated with the specified seed as the second cell ID.

<FIG> shows an exemplary functional configuration of the terminal apparatus that adds a virtual cell ID to the message A of two-step RACH and transmits the message A. The terminal apparatus includes a communication processing unit <NUM> and a cell ID notifying unit <NUM>, for example. The communication processing unit <NUM> establishes connection with a control apparatus, and performs wireless communication. The cell ID notifying unit <NUM> transmits the message A in which the PUSCH portion includes the virtual cell ID, to a nearby control apparatus. Note that the virtual cell ID is exemplary, and any information that enables a scrambling sequence specific to the terminal apparatus to be specified may be notified to the control apparatus.

Next, some examples of the processing flow to be executed in the wireless communication system according to the present embodiment will be described. Note that description of the details may be omitted regarding the operations described above. Note that detailed description above is not repeated here, and only the processing flow will be schematically described.

<FIG> shows a first example of the processing flow. First, each of the control apparatuses transmits notification information that includes parameters to be used for transmitting a random access preamble for the control apparatus itself (S501, S502). Note that the parameters include information regarding a seed for generating a sequence of a random access preamble, information regarding the time/frequency resource for transmitting the random access preamble, and the like. The terminal apparatus then transmits the random access preamble (that is included in the message A of two-step RACH, or as the message <NUM> of four-step RACH, for example) to the control apparatus A, for example, based on notification information A received from the control apparatus A (S503). The control apparatus A receives the random access preamble that is based on the notification information A provided from the control apparatus A itself, and, after this, the control apparatus A thereby scrambles communication with the terminal apparatus using a scrambling sequence that is based on the cell ID (the cell ID-A) of the control apparatus A (S506). On the other hand, the control apparatus B receives the random access preamble that is based on the notification information A that is different from notification information B provided from the control apparatus B itself, and thus, the control apparatus B attempts to acquire the cell ID, for example, by making an inquiry that includes the random access preamble to another control information that is in a neighboring relationship (S504). The control apparatus B then receives, from the control apparatus A that transmitted the notification information A used for generating the random access preamble, the cell ID of the control apparatus A (the cell ID-A) (S505). Note that the control apparatus B can also make a similar inquiry to another control apparatus, but this other control apparatus does not correspond to the random access preamble that is based on notification information thereof, and thus does not perform notification of the cell ID (not illustrated). After this, the control apparatus B scrambles communication with the terminal apparatus using the scrambling sequence that is based on the cell ID acquired in S505 (the cell ID-A) (S506). In this technique, by inquiring about the cell ID each time, it is possible to flexibly handle a change in the neighboring relationship between control apparatuses and the like.

Note that each control apparatus may store, therein, information including information regarding a random access preamble (for example, a sequence of a random access preamble itself or a seed for generating the sequence) and a cell ID associated with each other, and may specify a cell ID based on a received random access preamble. <FIG> shows an example of the processing flow in this case. In <FIG>, the control apparatus B executes processing for specifying the cell ID corresponding to the received random access preamble, from the information stored therein (S601) instead of performing S504 and S505 in <FIG>. With this technique, there is no need to make an inquiry, and thus it is possible to reduce the processing time.

In addition, a configuration may be adopted in which the terminal apparatus adds a virtual cell ID to be used for generating a scrambling sequence to the message A of two-step RACH and transmits the message, and the control apparatus perform communication using the scrambling sequence that is based on that virtual cell ID. <FIG> shows an example of this processing flow. In <FIG>, the terminal apparatus transmits a message A that includes a random access preamble that is based on notification information A provided from the control apparatus A and PUSCH that includes a cell ID-C as a virtual cell ID (S701). The control apparatus A then detects the random access preamble based on parameters transmitted in the notification information A by the control apparatus A itself, and acquires the cell ID-C from next PUSCH. In addition, for example, as shown in <FIG>, the control apparatus B acquires, in advance, information regarding a seed for generating a preamble sequence of a random access preamble to be used by another control apparatus that is in a neighboring relationship, and the like, and thereby acquires information similar to information that is notified using the notification information A. Similarly to the control apparatus A, the control apparatus B then detects the random access preamble, and acquires the cell ID-C from next PUSCH. The control apparatus A and the control apparatus B then perform communication after that using a scrambling sequence that is based on the notified cell ID-C (S702).

According to the above-described processing examples, a plurality of control apparatuses can use a shared scrambling sequence, from a response to transmission of a random access preamble of RACH processing. For this reason, it is possible to improve the wireless quality during RACH processing, and to provide a high-quality communication environment to the terminal apparatus promptly after connection is established.

Claim 1:
A control apparatus (<NUM>) configured to wirelessly communicate with a terminal apparatus (<NUM>), the control apparatus (<NUM>) comprising:
control means (<NUM>, <NUM>) configured to, in a case where each of the control apparatus (<NUM>) and another control apparatus (<NUM>) notifies the terminal apparatus (<NUM>) of information including a setting regarding a random access preamble and when the control apparatus (<NUM>) receives the random access preamble from the terminal apparatus (<NUM>), if the random access preamble is not based on a setting notified by the control apparatus (<NUM>), use a scrambling sequence that is based on second identification information different from first identification information corresponding to the control apparatus (<NUM>) to scramble communication with the terminal apparatus (<NUM>) after receiving the random access preamble.