JP2009224885A - Base station device, wireless communication system and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce loads on a base station or its host device in a communication system, where a preamble is transmitted to the base station when preamble is transmitted from a terminal. <P>SOLUTION: A base station device B1 is provided with preamble discarding parts 31, 33 and 34 for receiving preambles, including patterns selected from among a plurality of known patterns from a terminal UE, transmitting responses to the preambles to the terminal UE, selecting any of a plurality of preambles received, and discarding them. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a base station provided in a radio access network, and more particularly to a technique for reducing the processing load of a base station and its host device.

  In a cellular system, a user terminal immediately after power-on or immediately after handover performs initial communication with a base station using a random access channel. The base station periodically notifies the user terminal of a plurality of preamble patterns for initial communication used in the cell. The user terminal selects one appropriate one from the broadcasted preamble patterns, and transmits a preamble including the selected pattern to the base station.

  The base station performs correlation processing between all patterns that may be transmitted as a preamble and the pattern of the received signal, and determines that a preamble has been transmitted when a correlation peak that is equal to or greater than a set value is detected. A predetermined response to the preamble is transmitted. When receiving a response to the preamble, the user terminal sends a message such as its own terminal number, data type, and data amount to the base station to establish a communication link.

Patent Document 1 below discloses a base station apparatus that transmits call restriction information for restricting a call from a terminal when the number of times the preamble is received exceeds a threshold value.
Patent Document 2 below discloses that preamble congestion is controlled by notifying a mobile station of allowed slots of a random access channel.
Patent Document 3 below discloses that the time window of a random access channel is divided into two groups and these groups are assigned to priority classes.

JP 2005-354488 A JP 2007-97223 A JP 2000-151494 A

These signals may be congested in a process in which user terminals transmit all at once or a process in which location registration between a terminal and a base station is performed all at once. For example, such a situation is likely to occur in a train on which many people ride or an event where many people gather. When these signals are congested, the load on the base station and its host device increases, which may affect connected calls and subsequent processing.
Even if the number of terminals transmitting to a certain base station is small, the load on the host device of the base station may increase due to other reasons.

  An object of the disclosed apparatus and method is to reduce the load on a base station and its higher-level apparatus in a communication system in which a preamble is transmitted to a base station during transmission from a terminal.

  A disclosed apparatus is a base station apparatus that receives a preamble including a pattern selected from a plurality of known patterns from a terminal and transmits a response to the preamble to the terminal, and includes a plurality of received preambles A preamble discarding unit that selects and discards either of them is provided.

  Further, the disclosed method is a communication method in which a preamble including a pattern selected from a plurality of known patterns is transmitted from the terminal to the base station apparatus, and a response to the preamble is transmitted from the base station apparatus to the terminal. Then, the base station apparatus selects and discards one of the received plurality of preambles.

  A terminal whose preamble is discarded by the disclosed apparatus or method suppresses messages and data transmitted after the preamble, thereby reducing the load on the base station or its upper apparatus.

Hereinafter, embodiments will be described with reference to the accompanying drawings. FIG. 1 is a network configuration diagram of the disclosed communication system. The disclosed communication system 1 includes a core network NT1 and a radio access network NT2, and the radio access network NT2 includes base stations B1 to B3 that transmit and receive radio signals to and from a user terminal UE that is a mobile terminal. The core network NT1 includes nodes ND1 and ND2 that are higher-level devices of the base stations B1 to B3.
In the communication system 1, signals can be transmitted and received between the base stations B1 to B3 via the inter-base station interface I2, and between the base stations B1 to B3 and the nodes ND1 and ND2 Signals can be transmitted and received via the interface I1.

  For example, in the 3GPP-LTE system (Long Term Evolution) currently being studied in 3GPP, the nodes ND1 and ND2 provided in the core network NT1 provided as a packet core network are MME (Mobility Mobility) which is a logical node that performs mobility management control. Management Entity) and S-GW (Serving-Gateway). The S-GW is a gateway between the packet core network and a radio access network NT2 that is an E-UTRAN (Evolved Universal Terrestrial Radio Access Network).

  Also, for example, in the 3GPP-LTE system, the inter-base station interface I2 is called an X2 interface, and the inter-base station interface I1 connecting the MME and the base station (eNB) is called an S1-MME interface, and the S-GW and the base The inter-node base station interface I1 that connects stations (eNBs) is called an S1-U interface.

  FIG. 2 is a block diagram illustrating a configuration of a receiving unit of the disclosed base station B1. The configurations of the other base stations B2 and B3 are the same as the base station B1. The base station B1 includes an antenna 11 that receives a radio signal from the user terminal UE, a radio reception unit 12 that receives the radio signal, and baseband signal processing that performs signal processing of a baseband signal transmitted and received in the base station B1. Unit 13, control unit 14, call processing unit 15 that performs call processing, and communication network transmission that is an interface when communicating with other base stations B 2 and B 3 and nodes ND 1 and ND 2 via interfaces I 1 and I 2 An interface 16 is provided.

  The control unit 14 performs monitoring and control of the radio reception unit 12, the baseband signal processing unit 13, the call processing unit 15 and the like of the base station B1, and also controls the whole or a part of the base station, as well as the base stations B2 and B3, Communication between the nodes ND1 and ND2 and processing described below are executed.

The baseband signal processing unit 13 includes a reception unit interface 21, an uplink processing unit 22, a MAC / RLC unit 23, a baseband control unit 24, and another unit interface 25.
The receiving unit interface 21 is an interface between the wireless receiving unit 12 and the baseband signal processing unit 13, and the other unit interface 25 is an in-device interface between the baseband signal processing unit 13 and the other blocks 14 to 16. It is.

The uplink processing unit 22 performs demodulation and decoding processing on the signal received via the receiving unit interface 21.
The MAC / RLC unit 23 performs medium access control processing and radio link control processing of the signal demodulated and decoded by the uplink processing unit 22.
The baseband control unit 24 controls all or a part of the baseband signal processing unit 13 and executes processing described below.

  The base station B1 disclosed in FIG. 2 discards a part of the preamble transmitted by the user terminal UE under a predetermined condition and does not respond. Hereinafter, in this specification, the process of the base station B1 for discarding the preamble transmitted from the user terminal UE will be described, and the description of the other processes of the base station B1 will be omitted.

  FIG. 3 is a block diagram illustrating a configuration example of the uplink processing unit 22 related to discarding the preamble. The uplink processing unit 22 includes a demodulation / decoding unit 30 that demodulates and decodes a reception signal received via the reception unit interface 21, a preamble detection unit 31, a preamble count unit 32, a preamble generation unit 33, and a preamble. And a mask unit 34.

The preamble detector 31 performs a correlation process between the received signal demodulated and decoded by the demodulator / decoder 30 and a predetermined preamble pattern supplied from the preamble generator 33, and a correlation peak equal to or greater than a set value is detected. The detected preamble is detected, and only the detected preamble is output to the MAC / RLC unit 23.
The preamble count unit 32 detects a preamble by performing a correlation process between the preamble pattern of the predetermined pattern supplied from the preamble generation unit 33 and the received signal, and receives the number of detected preambles, that is, the preamble received by the base station B1. Count the number of times.

The preamble generation unit 33 sequentially generates a plurality of preamble patterns to be notified to the user terminal UE in advance for use by the base station B1, and supplies the preamble patterns to the preamble detection unit 31 and the preamble count unit 32.
The preamble mask unit 34 includes a pattern corresponding to the preamble sequence determined by the discard preamble determining unit 43 of the baseband control unit 24 described later in the preamble pattern supplied from the preamble generating unit 33 to the preamble detecting unit 31. So that the preamble pattern generated by the preamble generator 33 is masked.

The preamble pattern masked by the preamble mask unit 34 is not supplied from the preamble generation unit 33 to the preamble detection unit 31. Therefore, even if a signal including the same preamble pattern as the masked preamble pattern is received, the preamble detection unit 31 does not output to the MAC / RLC unit 23. For this reason, the signal including this preamble pattern is discarded, and the base station B1 does not respond to this preamble.
The preamble detection unit 31, the preamble generation unit 33, and the preamble mask unit 34 correspond to a preamble discard unit.

  FIG. 4 is a block diagram illustrating a first configuration example of the baseband control unit 24 regarding discard of the preamble. The baseband control unit 24 includes a mode determination unit 40, a discard rate determination unit 41, a discard preamble number determination unit 42, a discard preamble determination unit 43, and a discard information generation unit 44.

The mode determination unit 40 determines whether congestion is occurring or is in a normal state according to the number of preamble receptions per predetermined period counted by the preamble counting unit 32 described with reference to FIG. .
The discard rate determination unit 41 determines the discard rate according to the number of preamble receptions. That is, it determines how much of the received preamble should be discarded.

The discard preamble number determining unit 42 determines the number of preamble sequences for designating the preamble pattern included in the preamble to be discarded, according to the discard rate determined by the discard rate determining unit 41. Hereinafter, for simplicity of explanation, “a preamble sequence for designating a preamble pattern included in a preamble to be discarded” may be referred to as a “preamble sequence to be discarded”.
Here, the code string used for the preamble pattern by the disclosed base station B1 will be described. The base station B1 can use, for example, a Zadoff-Chu sequence that is a CAZAC sequence included in the specifications in the 3GPP-LTE system.

The Zadoff-Chu sequence can generate a plurality of orthogonal codes from one Zadoff-Chu sequence code by repeatedly performing a cyclic shift with a predetermined shift interval Q bits. For example, in the example illustrated in FIG. 5, a cyclic shift number s = 0, that is, a shift amount 0 Zadoff-Chu sequence code is provided to the user terminal UE # 0 as a preamble pattern.
The user terminal UE # 1 is provided with a code obtained by cyclically shifting the Zadoff-Chu sequence code given to the user terminal UE # 0 by one time (that is, by shifting the shift amount by Q bits). The user terminal UE # 2 is provided with a code obtained by cyclically shifting the Zadoff-Chu sequence code given to the user terminal UE # 0 by two times (that is, a shift amount shifted by 2 × Q bits). Hereinafter, the number of cyclic shifts performed on the Zadoff-Chu sequence code is referred to as “cyclic shift number”.

When the number of preamble patterns generated by the cyclic shift is insufficient, Zadoff-Chu sequence codes having different sequence numbers can be used.
Therefore, if N series of Zadoff-Chu series codes are used and a code obtained by cyclically shifting each Zadoff-Chu series code by 0 to (S-1) times is used as a preamble pattern, N × S in total. Number of preamble patterns can be used.

  Assuming that the sequence number of the Zadoff-Chu sequence code used for giving each preamble pattern is n (n = 0 to (N−1)) and the cyclic shift number is s (s = 0 to (S−1)). Each preamble pattern can be identified using p = n × S + s as an index. Hereinafter, this index p is referred to as a “preamble sequence” in the present specification. FIG. 6 shows an example of a preamble sequence when four Zadoff-Chu sequences are used (N = 4) and each code is used after being shifted eight times (S = 8). In this example, 32 preamble patterns are used as preamble patterns, and 0 to 31 in the table indicate the preamble sequence p.

  The code string that can be used as a preamble pattern by the base station B1 is not limited to the Zadoff-Chu sequence, and various code strings can be used. An example is shown in FIG. For example, instead of a plurality of Zadoff-Chu sequence codes, L-bit code sequences b01 to b0L, b11 to b1L, b21 to b2L, b31 to b3L for each of a plurality of sequence numbers 0, 1, 2, 3,. ... may be determined in advance and held in a table. Similarly to the Zadoff-Chu sequence, the code sequence of each sequence number may be cyclically shifted and used. In the following description, it is assumed that the base station B1 uses the preamble sequence shown in FIG. 6 for simplicity.

The discard preamble number determination unit 42 in FIG. 4 is masked by the number of preamble sequences to be discarded (that is, masked by the preamble mask unit 34 shown in FIG. 3) in the total number of preamble sequences predetermined for use in the base station B1. The number of preamble sequences to be discarded is determined such that the ratio of the number of preamble sequences to be discarded) is equal to or greater than the discard rate determined by the discard rate determination unit 41.
The discarded preamble determining unit 43 determines the number of preamble sequences determined by the discarded preamble number determining unit 42 from a plurality of preamble sequences determined in advance for use in the base station B1. Then, the determined preamble sequence is notified to the preamble mask unit 34 as a preamble sequence to be masked.
The discard information generation unit 44 includes the number of received preambles counted by the preamble count unit 32, the presence / absence of execution of preamble discard, the discard rate determined by the discard rate determination unit 41, the preamble sequence determined by the discard preamble determination unit 43, and the like. Predetermined discard information including information is created and output to the discard information notification unit 51 of the control unit 14 to be described later.

  FIG. 8 is a block diagram illustrating a first configuration example of the control unit 14 regarding the discard of the preamble. The control unit 14 includes a discard information notification unit 51 that notifies the discard information received from the discard information generation unit 44 to the other base stations B2 and B3 and the nodes ND1 and ND2.

Hereinafter, a process of discarding the preamble transmitted from the user terminal UE performed by the base station B1 will be described. FIG. 9 is a sequence diagram showing data exchange among the user terminal UE, the base station B1, and the node ND1 in the communication system 1.
In step S1, the user terminal UE to be transmitted or handed over transmits to the base station B1 a preamble including one pattern selected from a plurality of preamble patterns broadcast from the base station B1 in advance.

In step S2, the base station B1 that has received the preamble in step S1 transmits a response signal for the preamble to the user terminal UE.
In step S3, the user terminal UE that has received the response signal to the preamble transmits a connection request signal for requesting a line connection using a predetermined communication protocol to the base station B1.
In step S4, the base station B1 that has received the connection request signal transmits a connection setting signal for notifying parameters necessary for connection to the user terminal UE.
In step S5, the user terminal UE transmits a connection setting completion signal notifying that the connection setting has been completed to the base station B1, and in step S6, the base station B1 includes the identifier of the user terminal for which the connection setting has been completed. A terminal initial message is transmitted to the node ND1.

  For example, in the 3GPP-LTE system, the preamble in step S1 is a RACH (Random Access Channel) preamble message, the response signal in step S2 is a RACH response message, and the connection request signal in step S3 is RRC (Radio Resource Control) CONNECTION. It is a REQUEST message, the connection setup signal in step S4 is an RRC CONNECTION SETUP message, the connection setup completion signal in step S5 is an RRC CONNECTION SETUP COMPLETE message, and the terminal initial message in step S6 is an INITIAL UE message.

FIG. 10 is a flowchart illustrating a first example of preamble reception processing and response transmission processing in the base station B1.
First, in step S10, the mode determination unit 40 of the baseband control unit shown in FIG. 4 sets the operation mode of the base station B1 to “normal state” among “normal state” and “congestion state”.
In step S11, the radio reception unit 12 illustrated in FIG. 2 receives the preamble transmitted from the user terminal UE.
In step S12, the preamble count unit 32 of the uplink processing unit 22 shown in FIG. 3 counts the number of preambles received within a predetermined period.

In step S13, when the operation mode of the base station B1 is “normal state”, in step S14, the mode determination unit 40 determines whether or not congestion has occurred.
The mode determination unit 40 receives the preamble reception number Pcnt counted in step S12 from the preamble count unit 32, and determines that congestion has occurred when the preamble reception number Pcnt exceeds a predetermined congestion determination threshold Tsr. .

When it is determined that congestion has occurred, the mode determination unit 40 changes the operation mode of the base station B1 to “congestion state” in step S15, and returns to step S13. When the mode determination unit 40 determines that no congestion has occurred, the process proceeds to step S16.
In step S16, the preamble detection unit 31 shown in FIG. 3 performs a correlation process between the preamble pattern supplied from the preamble generation unit 33 and the pattern of the reception signal, and detects the preamble included in the reception signal. When the operation mode of the base station B1 is in the “normal state”, the preamble mask unit 34 does not perform the mask process for the preamble pattern generated by the preamble generation unit 33. Therefore, when the operation mode of the base station B1 is in the “normal state”, the preamble transmitted from the user terminal UE is not discarded.

FIG. 11A shows an example of a preamble sequence used in the base station B1 in the normal state, and FIG. 11B is an explanatory diagram of a preamble reception process in the base station B1 in the normal state. . The preamble sequence shown in FIG. 11A is the same as the preamble sequence described with reference to FIGS.
In this example, the base station B1 uses all the preambles 0 to 31 shown in FIG. 11A in the normal state. Accordingly, as shown in FIG. 11B, the preamble detection unit 31 of the uplink processing unit 22 detects all the preambles of the preamble sequences 2, 6, 8, 13, and 21 received by the radio reception unit 12. , Output to the MAC / RLC unit 23.
In step S17, a response signal to the preamble received by the MAC / RLC unit 23 is returned to the user terminal UE by a signal transmission unit (not shown).

When the operation mode of the base station B1 is changed to “congestion state” in step S15, the process proceeds to step S18 in the branch of step S13. In step S18, the mode determination unit 40 shown in FIG. 4 determines whether or not congestion has been eliminated.
The mode determination unit 40 determines that congestion has been resolved when the number of received preambles Pcnt received from the preamble count unit 32 is equal to or less than a predetermined congestion resolution determination threshold Tsp.

  When it is determined that the congestion has been eliminated, the mode determination unit 40 changes the operation mode of the base station B1 to “normal state” in step S19, and proceeds to step S21. When the mode determining unit 40 determines that the congestion has not been eliminated, the process proceeds to step S20. In step S20, a process of selecting and discarding at least a part of the preamble received by the wireless reception unit 12 is performed.

FIG. 12 is a flowchart of the preamble discarding routine S20 shown in FIG. In step S30, the discard rate determination unit 41 of the baseband control unit 24 shown in FIG. 4 determines the discard rate. Here, the discard rate is a ratio of the preamble received by the wireless reception unit 12 to the discarded preamble.
The discard rate determination unit 41 receives the preamble reception number Pcnt from the preamble count unit 32, and determines the discard rate according to the preamble reception number Pcnt.

For example, the discard rate determination unit 41 may determine the discard rate based on a predetermined calculation formula. For example, let the allowable upper limit number of preambles received within a predetermined period at the base station B1 be Pal, and let the target number of preambles processed during congestion be (allowable upper limit number Pal) × (target limiting rate Rtg (%)). For example, the discard rate r can be calculated by the following equation (1).
r = (Pcnt−Pal × Rtg) / Pcnt (1)

For example, the discard rate determination unit 41 stores in advance a lookup table of the discard rate according to the preamble reception number Pcnt, and searches the table for the discard rate r corresponding to the preamble reception number Pcnt received from the preamble count unit 32. Thus, the discard rate r may be obtained. The lookup table shown in FIG. 13 is a lookup table of the discard rate r corresponding to the preamble reception number Pcnt when the allowable upper limit number Pal is 200 times and the target limit rate Rtg is 70%.
Each value included in the lookup table may be fixed, and every time the allowable upper limit number Pal or the target limit rate Rtg is changed, it is calculated and updated again using the above formula (1). Also good.

A plurality of lookup tables corresponding to the plurality of allowable upper limit numbers Pal and the target limit rate Rtg may be stored in advance. Then, when the allowable upper limit number Pal or the target limit rate Rtg is changed, the table to be used may be switched from among the plurality of lookup tables. The lookup table shown in FIG. 14 is a lookup table of the discard rate r corresponding to the number of received preambles Pcnt when the allowable upper limit number Pal is 200 times and the target limit rate Rtg is 60% and 70%, respectively. .
4 notifies the discard preamble number determination unit 42 of the determined discard rate r.

In step S21 of FIG. 12, the preamble sequence masked by the preamble mask unit 34 is determined according to the discard rate r. FIG. 15 is a flowchart of a first example of the preamble sequence determination routine S31 to be discarded shown in FIG.
In step S40, the discard preamble number determination unit 42 in FIG. 4 determines the number of preamble sequences to be discarded according to the discard rate r. The designated unit of the preamble sequence to be discarded may be a preamble sequence, a cyclic shift number s, or a Zadoff-Chu sequence number n.
In the example of the preamble sequence shown in FIG. 6, if the preamble sequence designation unit is the cyclic shift number s, four preamble sequences are designated per cyclic shift number, and if the preamble sequence designation unit is the sequence number n, one preamble sequence is designated. Eight preamble sequences are designated per sequence number.

  For example, the discard preamble number determination unit 42 may determine the number of preamble sequences to be discarded based on a predetermined calculation formula. When the designated unit of the preamble sequence is a preamble sequence, the number p of preamble sequences to be discarded can be calculated by the following equation (2).

  p = roundup (S × N × r) (2)

Here, the range of the cyclic shift number s is 0 to (S-1), and the range of the sequence number n is 0 to (N-1) (S = 8, N in the example of the preamble sequence shown in FIG. 6). = 4), r is the discard rate r determined in step S30. Roundup (x) represents a minimum integer equal to or greater than x. The same applies to the following formulas (3) and (4).
When the designated unit of the preamble sequence is the cyclic shift number, the number s of cyclic shift numbers specifying the preamble sequence to be discarded can be calculated by the following equation (3).

  s = roundup (N × r) (3)

  When the preamble sequence designation unit is a Zadoff-Chu sequence number, the number n of sequence numbers for designating a sequence to be discarded can be calculated by the following equation (4).

  n = roundup (S × r) (4)

For example, the discard preamble number determination unit 42 stores in advance a lookup table that gives the number of preamble sequences to be discarded in accordance with the discard rate r, and stores the preamble sequence corresponding to the discard rate received from the discard rate determination unit 41. The number may be retrieved from this table. FIGS. 16 to 18 show examples of look-up tables when the preamble sequence designation unit is the preamble sequence, the cyclic shift number, and the sequence code sequence number, respectively.
The discarded preamble number determining unit 42 notifies the discarded preamble determining unit 43 of FIG. 4 of the determined number of preamble sequences.

In step S41, the discard preamble determining unit 43 specifies the number of preamble sequences specified by the discard preamble number determining unit 42. The discard preamble determining unit 43 notifies the preamble mask unit 34 shown in FIG. 3 of the designated preamble sequence as a preamble sequence to be discarded, that is, a preamble sequence to be masked.
For example, the discard preamble determining unit 43 stores in advance a lookup table that gives a preamble sequence to be discarded according to the number of preamble sequences specified by the discard preamble number determining unit 42, and is specified by the discard preamble number determining unit 42. A preamble sequence corresponding to the number may be retrieved from this table.

FIG. 19 shows an example of a look-up table that gives a preamble sequence to be discarded when the preamble sequence designation unit is a preamble sequence.
FIG. 20 shows an example of a look-up table that gives the cyclic shift number s that specifies the preamble sequence to be discarded when the preamble sequence designation unit is the cyclic shift number s.
FIG. 21 shows an example of a look-up table that gives a sequence number n that designates a preamble sequence to be discarded when the preamble sequence designation unit is a Zadoff-chu sequence number n.

  Further, for example, the discard preamble determining unit 43 randomly selects the number of preamble sequences specified by the discard preamble number determining unit 42 from all the preamble sequences 0 to 31 illustrated in FIG. It may be a series.

  When determining a preamble sequence to be discarded by any of the above methods, one or more preamble sequences may be specified in advance and excluded from the preamble sequence candidates to be discarded. For example, as in the preamble sequence shown in FIG. 22, among the preamble sequences 0 to 31, the preamble sequences 0, 10, 20 and 30 are excluded from the preamble sequence candidates to be discarded.

Since the preamble patterns corresponding to these preamble sequences 0, 10, 20, and 30 are not masked by the preamble mask unit 34, the preambles having these preamble patterns are not discarded by the preamble discarding process described in this specification. become.
Therefore, by assigning these preamble sequences to preambles such as emergency calls to the police and fire department and priority calls from priority subscribers, it becomes possible to preferentially handle these emergency calls and priority calls during congestion. .

  In step S32 of FIG. 12, the preamble mask unit 34 shown in FIG. 3 corresponds to the preamble sequence specified by the discarded preamble determination unit 43 in the preamble pattern supplied from the preamble generation unit 33 to the preamble detection unit 31. Mask processing of the preamble pattern generated by the preamble generation unit 33 is performed so that the pattern is not included. For example, when the preamble generation unit 33 sequentially generates each preamble pattern corresponding to the preamble sequences 0 to 31 shown in FIG. 6, the preamble mask unit 34 generates a pattern corresponding to the preamble sequence specified by the discard preamble determining unit 43. Prohibit occurrence.

  In step S33, the discard information generation unit 44 shown in FIG. 4 receives the number of preambles counted by the preamble count unit 32, whether or not to perform preamble discard, the discard rate r, and the preamble specified as the preamble sequence to be discarded. Predetermined discard information including information such as series is created and output to the discard information notification unit 51 shown in FIG. The discard information notification unit 51 notifies the discard information to other base stations B2 and B3 and nodes ND1 and ND2.

In step S21 of FIG. 10, the preamble detector 31 shown in FIG. 3 performs correlation processing between only the preamble pattern corresponding to the preamble sequence not masked by the preamble mask unit 34 and the received signal pattern, and is included in the received signal. The detected preamble is detected, and the process proceeds to step S17.
Therefore, when the operation mode of the base station B1 is “congestion state”, a preamble having a preamble pattern corresponding to the preamble sequence masked by the preamble mask unit 34 is discarded without being detected by the preamble detection unit 31. .

FIG. 23A shows an example of a preamble sequence used in the base station B1 in the congestion state, and FIG. 23B is an explanatory diagram of the preamble reception process in the base station B1 in the congestion state. . The preamble sequence shown in (A) of FIG. 23 is the same as the preamble sequence shown in (A) of FIG.
In this example, in the congestion state, the base station B1 discards the preamble having the preamble sequence pattern of the cyclic shift number s = 5, 6, and 7. Therefore, as shown in FIG. 11B, the preamble detection unit 31 of the uplink processing unit 22 does not detect the preambles of the preamble sequences 6, 13, and 21 among the preambles received by the radio reception unit 12. , Discard without outputting to the MAC / RLC unit 23.

According to the disclosed base station B1, since the preamble to be discarded can be designated by the preamble sequence, it is possible to provide a service according to the priority such as an emergency call or a priority call as described above.
Further, by performing a process of discarding at the time of reception of the preamble at the base station, it is possible to prevent the processing load for the user terminal UE that has issued this preamble from reaching the upper apparatus.
Furthermore, since it is not necessary to notify the user terminal UE of the call restriction, the processing load on the base station and the host device can be reduced without increasing the number of base station processes.
Furthermore, since it is possible to perform control immediately after detecting congestion as compared with the case of notifying transmission restriction to the user terminal UE, it is possible to reduce the processing load on the base station and the host device in a short period of time.

FIG. 24 is a flowchart of the second example of the preamble sequence determination routine S31 to be discarded shown in FIG.
In this example, the discard preamble determining unit 43 determines a preamble sequence to be discarded according to the discard rate r determined by the discard rate determining unit 41 (step S50). Therefore, in this example, the discard preamble determining unit 43 does not use the number of preamble sequences to be discarded determined by the discard preamble number determining unit 42. For this reason, in this method, the discard preamble number determination unit 42 may be omitted.

For example, the discard preamble determining unit 43 stores in advance a lookup table that gives a preamble sequence to be discarded according to the discard rate r, and the preamble sequence corresponding to the discard rate r designated by the discard rate determining unit 41 is stored from this table. You may search.
FIG. 25 shows an example of a look-up table that gives a preamble sequence to be discarded according to the discard rate r when the preamble sequence designation unit is a preamble sequence.
FIG. 26 shows an example of a look-up table that gives a cyclic shift number s that specifies a preamble sequence to be discarded according to the discard rate r when the preamble sequence designation unit is the cyclic shift number s.
FIG. 27 shows an example of a look-up table that gives a sequence number n that designates a preamble sequence to be discarded according to the discard rate r when the preamble sequence designation unit is a Zadoff-chu sequence number n.

Also, the discard preamble determining unit 43 determines a sequence rank that is the rank of each preamble sequence when the preamble sequences are arranged according to a predetermined procedure. The procedure for arranging the preamble sequences may be, for example, a random arrangement method.
Then, a sequence rank corresponding to the discard rate r specified by the discard rate determination unit 41 is searched from a lookup table that gives a sequence rank according to the discard rate r stored in advance, and the found sequence rank The corresponding preamble sequence may be determined as a preamble sequence to be discarded.

  FIG. 28 shows a correspondence table between the sequence order when the preamble sequences are arranged and the preamble sequence when the preamble sequence designation unit is a preamble sequence, and FIG. 29 shows a look that gives the sequence order corresponding to the discard rate. It is a figure which shows the example of an up table. Even if the designated unit of the preamble sequence to be discarded is the cyclic shift number s or the sequence number n of the sequence code, the preamble sequence to be discarded can be determined by the same method.

FIG. 30 is a block diagram illustrating a second configuration example of the baseband control unit 24 regarding discard of the preamble. In the baseband control unit 24 of this example, the preamble count unit 32 determines a preamble sequence to be discarded according to the number of preamble receptions within a predetermined period measured for each preamble sequence. For this reason, the baseband control unit 24 includes a cumulative frequency generation unit 45 that generates a cumulative frequency of the number of preamble receptions for the preamble sequence.
In this configuration example, the preamble count unit 32 shown in FIG. 3 measures the number of preamble receptions within a predetermined period for each preamble sequence.
The processes of the mode determination unit 40, the discard rate determination unit 41, and the discard information generation unit 44 are the same as the first configuration example of the baseband control unit 24 described with reference to FIG.

FIG. 31 is a flowchart of a third example of the preamble sequence determination routine S31 to be discarded shown in FIG. 12, which is performed by the baseband control unit 24 shown in FIG.
In step S60, the cumulative frequency generation unit 45 creates an ordered sequence in which the preamble sequences 0 to 31 are arranged according to a predetermined procedure.
FIG. 32 is a correspondence table between sequence ranks and preamble sequences when preamble sequences are arranged. The order in which the preamble sequences are arranged may be arranged in ascending or descending order or randomly arranged according to the number of preamble receptions measured by the preamble counting unit 32 shown in FIG. In addition, the rearrangement of the preamble sequences 0 to 31 may be omitted and the preamble sequences 0 to 31 may be arranged in the order of the preamble sequences.

In step S61, the cumulative frequency generation unit 45 generates a cumulative frequency of the number of receptions of each preamble sequence for the preamble sequences arranged in the order determined in step S61. FIG. 33 shows the cumulative frequency of the number of preamble receptions for the preamble sequence.
In step S62, the discard preamble determination unit 43 determines a preamble sequence to be discarded according to the discard rate r determined by the discard determination unit 41 and the cumulative frequency generated by the cumulative frequency generation unit 45, and determines the determined preamble sequence. Output to the preamble mask unit 34.

The discard preamble determination unit 43 determines the rank of the preamble sequence at the point where the cumulative frequency is equal to or higher than the discard rate r in the cumulative frequency generated by the cumulative frequency generation unit 45. Then, a preamble sequence having a numerical order lower than the determined order is determined as a preamble sequence to be discarded.
By determining in this way, the discard preamble determination unit 43 can determine a preamble sequence or a set thereof received at a rate equal to or greater than the discard rate r among the preambles received by the base station B1.

In the example shown in FIGS. 31 to 33 described above, the designated unit of the preamble sequence to be discarded is the preamble sequence. However, even if the cyclic shift number s or the sequence code sequence number n is the designated unit, it should be discarded in the same manner. A preamble sequence can be determined.
In addition, the preamble sequence determination method illustrated in FIG. 31 is merely an example, and the baseband control unit 24 receives at a rate equal to or higher than the discard rate determined by the discard rate determination unit 41 in the preamble received by the base station B1. Obviously, various methods can be used to determine the assigned preamble sequence or set thereof.

FIG. 34 is a block diagram illustrating a second configuration example of the control unit 14 related to preamble discarding, and FIG. 35 is a block diagram illustrating a third configuration example of the baseband control unit 24 regarding preamble discarding.
In the present embodiment, the discard rate of the preamble to be determined based on the number of calls processed by the call processing unit 15 and the load amount such as the MPU processing amount of the base station B1 and whether to be discarded or not. Determine r.

Therefore, the control unit 14 includes a processing load measurement unit 52, a load index determination unit 53, and a discard information notification unit 51. The processing load measurement unit 52 measures a processing load such as the MPU processing amount of the base station B1.
The load index determination unit 53 determines a predetermined load index indicating the load amount of the base station B1 according to the call processing amount within a predetermined period counted by the call processing unit 15 and the processing load measured by the processing load measurement unit 52. decide.
The discard information notification unit 51 adds information related to the processing load amount such as the call processing amount and the MPU processing amount to the additional information generated by the discard information generating unit 44 of the baseband control unit 24, so that the other base station B2 And B3 and the nodes ND1 and ND2.

The mode determination unit 40 of the baseband control unit 24 determines whether congestion is presently occurring or in a normal state according to the load index determined by the load index determination unit 53.
In the flowchart shown in FIG. 10, the load index determining unit 53 measures the load index in step S12.

In step S14 in which the operation mode of the base station B1 is in the “normal state”, the mode determination unit 40 determines that congestion has occurred when the measured load index Lg exceeds a predetermined congestion determination threshold Lsr.
In step S18 in which the operation mode of the base station B1 is in the “congestion state”, the mode determination unit 40 determines that the congestion is eliminated when the measured load index Lg is equal to or less than a predetermined congestion determination threshold Lsp. .

  The discard rate determination unit 41 determines the discard rate r according to the measured load index Lg. The processes of the discard preamble number determination unit 42, the discard preamble determination unit 43, and the discard information generation unit 44 are the same as the discard preamble number determination unit 42 and the discard preamble of the first configuration example of the baseband control unit 24 described with reference to FIG. Since it is the same as the process of the determination part 43 and the discard information generation part 44, description is abbreviate | omitted.

For example, the discard rate determination unit 41 may determine the discard rate based on a predetermined calculation formula. For example, the target value of the load index may be set as Ltg, and the discard rate may be calculated by the following equation (5).
r = (Lg−Ltg) / Lg (5)

The discard rate determination unit 41 stores, for example, a discard rate lookup table corresponding to the load index in advance, and searches the table for a discard rate r corresponding to the load index Lg received from the load index determination unit 53. The discard rate r may be obtained. The table shown in FIG. 36 is a lookup table when the load index Ltg of the target value is 70%.
Each value included in the lookup table may be fixed, or may be calculated and updated again using the above equation (5) each time the load index Ltg of the target value is changed.

  A plurality of lookup tables corresponding to the target value load index Ltg may be stored in advance. Then, when the load index Ltg of the target value is changed, a table to be used may be switched from among the plurality of lookup tables. The lookup table shown in FIG. 37 is a lookup table when the load index Ltg of the target value is 60% and 70%, respectively.

  Note that the mode determination unit 40 and the discard rate determination unit 41 determine whether or not it is in a congestion state and determine the discard rate r based on the load index Lt, in addition to the mode determination unit 40 shown in FIG. Similarly to the discard rate determination unit 41, it may be determined whether or not it is in a congestion state and determine the discard rate r based on the number of preamble receptions counted by the preamble count unit. At this time, for example, the discard rate determination unit 41 may employ a larger discard rate among the discard rate determined based on the load index Lt and the discard rate determined based on the number of preamble receptions.

  In addition, the same configuration as the configuration example described with reference to FIG. 30 is provided, and the preamble sequence received at a rate equal to or higher than the discard rate determined by the discard rate determination unit 41 among the preambles received by the base station B1 or The set may be determined as a preamble sequence to be discarded.

FIG. 38 is a block diagram illustrating a third configuration example of the control unit 14 related to preamble discarding, and FIG. 39 is a block diagram illustrating a fourth configuration example of the baseband control unit 24 regarding preamble discarding.
In this configuration example, when a discard instruction that is a control signal instructing discard of the preamble is received from any of the other base stations B2 and B3 and the nodes ND1 and ND2, the preamble discarding process is started. When a cancellation instruction for instructing cancellation of cancellation is received, the preamble cancellation processing is terminated.

  For this reason, the control unit 14 includes a discard instruction receiving unit 54 that receives the discard instruction and the cancel instruction from any of the other base stations B2 and B3 and the nodes ND1 and ND2, and a base instruction according to the discard instruction and the cancel instruction. A discard control unit 55 that controls processing for preamble discard performed by the band control unit 24 is provided. The processing of the discard information notification unit 51 is the same as the processing of the discard information notification unit 51 of the first configuration example of the control unit 14 described with reference to FIG.

The baseband control unit 24 includes a mode determination unit 40 that sets the operation mode of the base station B1 to either “execution of normal processing” or “execution of cancellation processing” according to control by the cancellation control unit 55; A discard rate determination unit 41 that determines the discard rate r according to the control by 55 is provided.
The discard rate determination unit 41 may determine the fixed discard rate r as the discard rate to be used, or the discard rate specified by the discard instruction received from the other base stations B2 and B3 and the nodes ND1 and ND2. r may be used.
The processes of the discard preamble number determination unit 42, the discard preamble determination unit 43, and the discard information generation unit 44 are the same as the discard preamble number determination unit 42 and the discard preamble of the first configuration example of the baseband control unit 24 described with reference to FIG. Since it is the same as the process of the determination part 43 and the discard information generation part 44, description is abbreviate | omitted.

FIG. 40 is a flowchart illustrating a second example of preamble reception and response transmission processing in the base station. First, in step S70, the mode determination unit 40 of the baseband control unit 24 shown in FIG. 39 sets the operation mode of the base station B1 to “execution of normal processing” among “execution of normal processing” and “execution of discard processing”. Set.
In step S71, the radio reception unit 12 illustrated in FIG. 2 receives the preamble transmitted from the user terminal UE.

  In step S72, when the operation mode of the base station B1 is “execution of normal processing”, in step S73, the mode determination unit 40 determines that the discard instruction reception unit 54 of the control unit 14 shown in FIG. It is determined whether a discard instruction has been received from any of B2 and B3 and nodes ND1 and ND2.

When receiving the discard instruction, the mode determination unit 40 changes the operation mode of the base station B1 to “execution of discard process” in step S74, and returns to step S72. When the mode determination unit 40 determines that no congestion has occurred, the process proceeds to step S75.
In step S75, the preamble detector 31 shown in FIG. 3 performs correlation processing between the preamble pattern supplied from the preamble generator 33 and the received signal pattern, and detects the preamble included in the received signal. Thus, when the operation mode of the base station B1 is “execution of normal processing”, the preamble transmitted from the user terminal UE is not discarded.
In step S76, a response signal to the preamble received by the MAC / RLC unit 23 is returned to the user terminal UE by a signal transmission unit (not shown).

When the operation mode of the base station B1 is changed to “execution of discarding process” in step S74, the process proceeds to step S77 in the branch of step S72. In step S77, the mode determination unit 40 determines whether a release instruction has been received.
When the cancellation instruction is received, the mode determination unit 40 changes the operation mode of the base station B1 to “execution of normal processing” in step S78, and proceeds to step S80. When the release instruction has not been received, the process proceeds to step S79. In step S79, processing for selecting and discarding at least a part of the preamble received by the wireless reception unit 12 is performed.

FIG. 41 is a flowchart of the preamble discarding routine shown in FIG. In step S90, a preamble sequence to be masked by the preamble mask unit 34 is determined according to the discard rate r determined by the discard rate determination unit 41. The process in step S90 may be the same as the process in step S31 illustrated in FIG.
In steps S91 and S92, as in steps S32 and S33 shown in FIG. 12, the preamble mask unit 34 performs preamble pattern masking, and the discard information notification unit 51 transmits discard information.

In step S80 of FIG. 40, the preamble detector 31 shown in FIG. 3 performs correlation processing between only the preamble pattern corresponding to the preamble sequence not masked by the preamble mask unit 34 and the pattern of the received signal, and is included in the received signal. The detected preamble is detected, and the process proceeds to step S76.
Therefore, when the operation mode of the base station B1 is “execution of discard processing”, the preamble having the preamble pattern corresponding to the preamble sequence masked by the preamble mask unit 34 is discarded without being detected by the preamble detection unit 31. Is done.

  It should be noted that by combining the components shown in FIG. 38 and FIG. 39 with the other embodiments described above, the preamble of any of the other base stations B2 and B3 and nodes ND1 and ND2 is also obtained in these embodiments. Configuration to start the preamble discarding process when receiving a discard instruction that is a control signal for discarding, and to terminate the preamble discarding process when receiving a release instruction for canceling the preamble discarding May be.

  The following additional notes are further disclosed with respect to the embodiment including the above examples.

(Appendix 1)
A base station apparatus that receives a preamble including a pattern selected from a plurality of known patterns from a terminal and transmits a response to the preamble to the terminal,
A base station apparatus comprising a preamble discarding unit that selects and discards any of the plurality of received preambles.

(Appendix 2)
The base station apparatus according to supplementary note 1, wherein the preamble discarding unit discards one or more preambles of a predetermined preamble sequence.

(Appendix 3)
A load measuring unit for measuring a predetermined load of the base station device;
A discarded preamble sequence determination unit that determines a preamble sequence in an amount corresponding to the measured load as the one or more predetermined preamble sequences;
The base station apparatus as set forth in Appendix 2.

(Appendix 4)
A discard amount determining unit that determines a discard amount indicating the amount of the preamble to be discarded within a predetermined period;
A reception amount measuring unit that measures a reception amount indicating the amount of the preamble received within the predetermined period for each preamble sequence;
A discarded preamble sequence determining unit that determines one or more preamble sequences whose total received amount is equal to or greater than the discarded amount as the one or more predetermined preamble sequences;
The base station apparatus as set forth in Appendix 2.

(Appendix 5)
A discard instruction receiving unit for receiving an instruction signal instructing discard of the preamble;
The base station apparatus according to supplementary note 1, wherein the preamble discarding unit discards the preamble according to the instruction signal.

(Appendix 6)
The base station apparatus according to appendix 1, further comprising a discard information notification unit that notifies the outside that the preamble has been discarded.

(Appendix 7)
A wireless communication system including a base station apparatus that receives a preamble including a pattern selected from a plurality of known patterns from a terminal and transmits a response to the preamble to the terminal,
The said base station is a radio | wireless communications system provided with the preamble discard part which selects and discards any one of the received several said preamble.

(Appendix 8)
A communication method in which a preamble including a pattern selected from a plurality of known patterns is transmitted from a terminal to a base station apparatus, and a response to the preamble is transmitted from the base station apparatus to the terminal,
A communication method in which the base station apparatus selects and discards any of the plurality of received preambles.

It is a network block diagram of the communication system of an indication. It is a block diagram which shows the receiving part structure of the disclosed base station. It is a block diagram which shows the structural example of the uplink process part regarding discard of a preamble. It is a block diagram which shows the 1st structural example of the baseband control part regarding discard of a preamble. It is explanatory drawing of a Zadoff-Chu series. It is a figure which shows the example of a preamble series in case of N = 4 and S = 8. It is a figure which shows the other example of the code sequence used as a preamble pattern. It is a block diagram which shows the 1st structural example of the control part regarding discard of a preamble. It is a sequence diagram which shows the exchange of data between the user terminal in this communication system, a base station, and a node. It is a flowchart which shows the 1st example of the reception process and response transmission process of a preamble in a base station. (A) is a figure which shows the example of the preamble series used in base station B1 in a normal state, (B) is explanatory drawing of the reception process of the preamble in base station B1 in a normal state. 11 is a flowchart of a preamble discarding routine shown in FIG. 10. It is a figure which shows the 1st example of the lookup table of the discard rate corresponding to the number of preamble reception. It is a figure which shows the 2nd example of the lookup table of the discard rate corresponding to the number of preamble reception. 13 is a flowchart of a routine for determining a preamble sequence to be discarded shown in FIG. It is a figure which shows the example of the look-up table which gives the number of preamble series which should be discarded. It is a figure which shows the example of the look-up table which gives the number of cyclic shift numbers which designate the preamble series which should be discarded. It is a figure which shows the example of the look-up table which gives the number of the sequence numbers which specify the preamble sequence which should be discarded. It is a figure which shows the example of the look-up table which gives the preamble series which should be discarded. It is a figure which shows the example of the look-up table which gives the cyclic shift number which designates the preamble series which should be discarded. It is a figure which shows the example of the look-up table which gives the sequence number which designates the preamble sequence which should be discarded. It is a figure which designates the preamble series excluded from the discard candidate. (A) is a figure which shows the example of the preamble series used in base station B1 in a congestion state, (B) is explanatory drawing of the reception process of the preamble in base station B1 in a congestion state. FIG. 13 is a flowchart of a second example of the preamble sequence determination routine S31 to be discarded shown in FIG. 12; FIG. It is a figure which shows the example of the look-up table which gives the preamble series which should be discarded corresponding to a discard rate. It is a figure which shows the example of the look-up table which provides the cyclic shift number which designates the preamble series which should be discarded corresponding to a discard rate. It is a figure which shows the example of the look-up table which provides the sequence number which designates the preamble sequence which should be discarded corresponding to a discard rate. It is a correspondence table between a sequence rank when preamble sequences are arranged and a preamble sequence. It is a figure which shows the example of the look-up table which gives a sequence | rank ranking corresponding to a discard rate. It is a block diagram which shows the 2nd structural example of the baseband control part regarding discard of a preamble. 13 is a flowchart of a third example of a preamble sequence determination routine S31 to be discarded shown in FIG. It is a correspondence table between a sequence rank when preamble sequences are arranged and a preamble sequence. It is a figure which shows the accumulation frequency of the frequency | count of preamble reception with respect to a preamble series. It is a block diagram which shows the 2nd structural example of the control part regarding discard of a preamble. It is a block diagram which shows the 3rd structural example of the baseband control part regarding discard of a preamble. It is a figure which shows the 1st example of the look-up table of the discard rate corresponding to a load index. It is a figure which shows the 2nd example of the lookup table of the discard rate corresponding to a load index. It is a block diagram which shows the 3rd structural example of the control part regarding discard of a preamble. It is a block diagram which shows the 4th structural example of the baseband control part regarding discard of a preamble. It is a flowchart which shows the 2nd example of the preamble reception and response transmission process in a base station. FIG. 41 is a flowchart of a preamble discarding routine shown in FIG. 40. FIG.

Explanation of symbols

B1 Base station 11 Antenna 13 Baseband signal processing unit 14 Control unit 22 Uplink processing unit 24 Baseband control unit 31 Preamble detection unit 32 Preamble count unit 33 Preamble generation unit 34 Preamble mask unit 41 Discard rate determination unit 43 Discard preamble determination unit 43 I1 Node interface between base stations I2 Interface between base stations

Claims (6)

A base station apparatus that receives a preamble including a pattern selected from a plurality of known patterns from a terminal and transmits a response to the preamble to the terminal,
A base station apparatus comprising a preamble discarding unit that selects and discards any of the plurality of received preambles.   The base station apparatus according to claim 1, wherein the preamble discarding unit discards one or more preambles of a predetermined preamble sequence. A load measuring unit for measuring a predetermined load of the base station device;
A discarded preamble sequence determination unit that determines a preamble sequence in an amount corresponding to the measured load as the one or more predetermined preamble sequences;
The base station apparatus according to claim 2, comprising: A discard amount determining unit that determines a discard amount indicating the amount of the preamble to be discarded within a predetermined period;
A reception amount measuring unit that measures a reception amount indicating the amount of the preamble received within the predetermined period for each preamble sequence;
A discarded preamble sequence determining unit that determines one or more preamble sequences whose total received amount is equal to or greater than the discarded amount as the one or more predetermined preamble sequences;
The base station apparatus according to claim 2, comprising: A wireless communication system including a base station apparatus that receives a preamble including a pattern selected from a plurality of known patterns from a terminal and transmits a response to the preamble to the terminal,
The said base station is a radio | wireless communications system provided with the preamble discard part which selects and discards any one of the received several said preamble. A communication method in which a preamble including a pattern selected from a plurality of known patterns is transmitted from a terminal to a base station apparatus, and a response to the preamble is transmitted from the base station apparatus to the terminal,
A communication method in which the base station apparatus selects and discards any of the plurality of received preambles.

Images