JP4117138B2 - CDMA base station apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a CDMA base station apparatus used in a CDMA (Code Division Multiple Access) cellular mobile radio communication system using an array antenna. In consideration of the influence on the communication quality of an existing mobile station in communication, whether to allocate a new communication channel to a mobile station of a new user is determined.
[0002]
[Prior art]
One of the third generation mobile communication systems is W-CDMA (Wide band-Code Division Multiple Access), and high-speed and wide-band communication such as moving images as well as voice is expected. Recently, the study of the 4th generation mobile communication system aiming at high-speed and broadband transmission about 10 times that of the 3rd generation system has begun. In order to provide a high-speed service with limited frequency resources, it is necessary to make further effective use of frequencies. As one of countermeasures, use of an adaptive array antenna for a base station is being studied.
In a CDMA communication system, a large number of users can communicate simultaneously in the same frequency band by using different spreading codes. However, if the number of simultaneous communication users increases, intersymbol interference cannot be ignored. Therefore, if an adaptive array antenna is used as the base station antenna, interference signals can be reduced.
[0003]
However, when a new communication channel assignment request is received when a new call (outgoing call, incoming call) for which communication is newly requested occurs, the directivity characteristics of the adaptive array antenna are changed, and the communication of the mobile station in communication In some cases, the quality is greatly deteriorated and communication cannot be continued.
FIG. 7 is an explanatory diagram showing an example of a CDMA mobile communication system using an adaptive array antenna.
In FIG. 7A, 21 is a mobile station of user 1, 22 is a mobile station of user 2, 24 is a base station, 25 is an adaptive array antenna of the base station, and 25a and 25b are antenna elements thereof. The number of elements is arbitrary. The reception beam pattern can be freely controlled by controlling the antenna weight by which the output signal of each antenna element is multiplied during reception. Reference numeral 26 denotes a cover area (cell) of the base station 24.
In the uplink where the base station 24 receives transmission waves from the mobile stations 21 and 22, the mobile station 21 of the user 1 receives the beam pattern shown as the user 1 directivity 31. The user 1 directivity 31 has a main lobe in the direction of the mobile station 21 of the user 1 and a beam null in the direction of the mobile station 22 of the user 2. The same applies to the user 2 directivity 32 with respect to the mobile station 22 of the user 2.
However, the number of beam nulls that can be controlled by the adaptive array antenna is determined by the degree of freedom (number of elements of the array antenna-1). However, in a CDMA communication system, communication is usually performed simultaneously with users exceeding the number of elements of the array antenna.
[0004]
FIG. 7B shows a case where the mobile station 23 of the user 3 newly requests communication in the state where two users equal to the number of antenna elements are simultaneously communicating as shown in FIG. Indicates. There are a case where the mobile station 23 of the user 3 makes a call and a case where the user's call located inside or outside the cover area 26 calls the mobile station 23 of the user 3 via the base station 24. .
If the mobile station 23 of the user 3 newly starts communication, the number of users in communication exceeds the number of antenna elements, so that beam null cannot be directed to other stations. In addition, when the number of users is less than the number of antenna elements and the angle difference between each user is close to the resolution or more, the directivity of a certain user approaches the beam null direction with respect to other users. There is also a problem that the gain decreases and the amount of interference increases.
In this way, the amount of interference varies greatly depending on the angle relationship including the mobile station 23 of the new user 3, the mobile station 21 of the user 1 in communication, and the mobile station 22 of the user 2. Further, this interference greatly affects the communication quality of the mobile station 21 of the user 1 and the mobile station 22 of the user 2 that are already communicating.
[0005]
Therefore, even when the mobile station 23 of the new user 3 requests allocation of a new communication channel for a new call, the communication quality of the mobile stations 21 and 22 of other users (users 1 and 2) already in communication However, depending on the position of the mobile station 23 of the new user 3, not only the communication quality of the mobile station 23 of the new user 3, The communication quality of the mobile station 22 of the user 2 may also deteriorate, and communication may be disabled during communication.
Therefore, in the adaptive array antenna, new communication channel allocation control for determining whether or not to accept a new communication channel allocation request for a new call (outgoing call, incoming call) for newly requesting communication is very important. However, when an adaptive array antenna is applied to the CDMA system, a new communication channel assignment control method in which users who far exceed the number of antenna elements perform simultaneous communication has not been studied.
[0006]
Considering the case of using a normal omni antenna or sector antenna in the CDMA system without using an adaptive array antenna, the interference level in the same cell is set to the number of mobile stations in communication (or one mobile by the transmission power control). If a station can use multiple communication channels, it can be considered to be almost proportional to the number of communication channels in communication), so when a new call occurs, the total number of mobile stations currently in communication (or all The number of communication channels) and the transmission speed of each mobile station are compared with the total number of mobile stations (or the total number of communication channels) that can be accommodated in the base station, taking into account the amount of interference from surrounding cells. Then, it is possible to easily determine whether new communication channels can be allocated.
However, when an adaptive array antenna is applied, the directivity pattern of the adaptive array antenna changes depending on the number of users in communication and its position, so that the method for determining whether or not to allocate the new communication channel becomes complicated.
[0007]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems. Even when a new communication channel assignment request signal is received when a new user makes or receives a call, the communication quality of the user in communication is guaranteed and the communication is in progress. An object of the present invention is to provide a CDMA base station apparatus that can perform communication with an interference signal reduced by using an array antenna without worrying about communication quality fluctuations associated with traffic fluctuations in the wireless zone. is there.
[0008]
[Means for Solving the Problems]
  In the invention according to claim 1, the present invention provides:Angle-divided into multiple sectorsBetween multiple mobile stations in the wireless zoneA plurality of each sector arrangedWith array antenna, For each sectorA CDMA base station apparatus that performs communication by code division multiple access,
  Control channel receiving means for receiving a new communication channel assignment request signal from the array antenna using a control channel from a new mobile station requesting assignment of a new communication channel among the plurality of mobile stations;
  Of the plurality of mobile stations, the estimated arrival direction and the estimated received power for each incoming wave from the communicating mobile station and the new mobile station are obtained using the received signal of the array antenna.For each sector in which the communicating mobile station and the new mobile station are locatedEstimating means for estimating;
  When the control channel receiving means receives the new communication channel assignment request signal, the received signal of the array antenna, the new communication channel assignment request signal, and the estimated arrival direction related to the individual incoming waves estimated by the estimating means and Communication channel assignment control means for deciding whether or not to assign a new communication channel to the new mobile station based on communication quality information based on the estimated received power;
  The communication channel allocation control means is estimated by the reception signal of the array antenna and the new communication channel allocation request signal and the estimation means when the control channel reception means receives the new communication channel allocation request signal, The communication quality information based on the information on the individual incoming waves received from the communicating mobile stations located in all the sectors in the radio zone and the antennas of the corresponding sectors from the new mobile stations, Determining whether the new communication channel can be allocated to a mobile station;
  The new mobile station communicates using the communication channel.If you doThe new mobile station andWithin the radio zoneWhen it is determined that at least one mobile station among the mobile stations in a call cannot perform communication satisfying the communication quality defined in advance, a new communication channel assignment to the new mobile station is rejected. is there.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a flowchart for explaining an embodiment of a CDMA base station apparatus of the present invention.
FIG. 2 is an explanatory diagram showing an example of a communication channel management table and information on a mobile station in communication used in an embodiment of the present invention.
FIG. 2 (a) is a communication channel management table, and FIG. 2 (b) is an explanatory diagram showing information on mobile stations in communication.
Although the configuration of the embodiment of the CDMA base station apparatus of the present invention is not shown, a new communication using a control channel is performed from a new mobile station that requests allocation of a new communication channel among a plurality of mobile stations. A control channel receiver that receives a channel allocation request signal from the array antenna, and information on individual incoming waves from the mobile station in communication and the new mobile station among the plurality of mobile stations, using the received signal of the array antenna And when the control channel receiving unit receives a new communication channel assignment request signal, the received information of the array antenna and the new communication channel assignment request signal and information on individual incoming waves estimated by the estimating means, Channel assignment to determine whether new communication channels can be assigned to new mobile stations based on communication quality information based on With a control unit.
[0011]
With reference to FIGS. 1 and 2, a new communication channel assignment control operation for determining whether or not a new communication channel can be assigned when a new call (calling or incoming call) to a new user's mobile station occurs will be described.
Here, in particular, only when the number of requested communication channels of the new user is equal to or less than the number of unused communication channels and the estimated communication quality of all the mobile stations satisfies the respective required communication quality, the new communication channel is used for a new call. The case of assignment is taken up and illustrated.
In the flowchart of FIG. 1, reading and writing of required data from the communication channel management table shown in FIG. 2A and estimation of arrival wave information regarding an incoming wave from a mobile station in communication are performed by a new communication channel. It is described separately from the flow of the allocation control operation.
That is, the communication channel management table shown in FIG. 2 (a) manages the state of the communication channel currently in use separately from the flow of FIG. 1, and is updated as needed as the communication channel is secured and released. This is for distinguishing between a communication channel in use and an unused communication channel and making a call loss when there is a new communication channel allocation request exceeding the number of unused communication channels.
The total number of communication channels of the base station is Nc, the total number of users in communication is K, and the mobile station number identifying each user k (k = 1 to K) is k₁~ K_KAnd
[0012]
In this table, the mobile station number k, which is information for identifying the user using each communication channel, corresponding to the communication channel numbers 1 to Nc.₁~ K_KHas been written. For example, if user 2 is using two communication channels of communication channel numbers 1 and 2, mobile station number k corresponds to communication channel numbers 1 and 2, respectively.₂Has been written. For communication channels that are not used, information indicating “empty” is written corresponding to the communication channel number.
The total number K of users in communication and the total number N of channels used by all users can be calculated from the information in the above-described table, but may be directly written in this communication channel management table.
If it is assumed that each user uses only one channel, the number of used channels N = the number of users K.
The information on the mobile station in communication shown in FIG. 2B is information on the mobile station necessary for the communication quality during the new communication channel assignment control. This information on mobile stations in communication is information that needs to be managed separately from the flow of FIG.
[0013]
With reference to FIG.2 (b), an example of the content of the mobile station information collected is demonstrated first.
Individual in-communication mobile station information regarding users in communication (k = 1 to K) is estimated arrival direction θ._k, Estimated received power P_kCommunication channel allocatable CINR (Carrierto Interference plus Noise Ratio) γ^(k)req etc.
Estimated direction of arrival θ_kIs the direction of the mobile station of user k as seen from the base station, and the estimated received power P_kIs the received power of the incoming wave from this mobile station. Note that the array propagation vector v_kThe estimated direction of arrival θ_kIs unnecessary.
The estimation unit described above uses the estimated arrival direction θ as the arrival wave information about the arrival wave from each mobile station in communication._k(Or array propagation vector v_k) And estimated received power P_kIs estimated at any time using the received signal of the array antenna (the array input signal of each element of the array antenna).
The arrival wave can be estimated by a well-known MUSIC (MUltiple SIgnal Classification), ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques), or a beamformer method.
CINR is a parameter of communication quality in the carrier wave band. The communication quality parameter used for the new communication channel assignment control only needs to be mutually convertible with CINR. For example, SINR (Signal to Interference plus Noise Ratio) or BER (Bit Error Rate) in the baseband may be used.
Since these pieces of information are necessary when it is necessary to estimate the communication quality described above, they need to be managed and stored as a table like the communication channel management table shown in FIG. There is no. However, in order to speed up the communication quality estimation process, it may be stored as one piece of information in the communication channel management table.
[0014]
In FIG. 1, when there is a new communication channel assignment request at the time of a call from a new mobile station (new user k = K + 1), the number of requested communication channels is Nreq. When the transmission rate from the mobile station is high, one user uses a plurality of communication channels and transmits using spreading codes assigned to each communication channel.
First, the number N of all communication channels used by all users in communication is read from the communication channel management table shown in FIG.
In S1, it is determined whether or not the value obtained by adding Nreq to N is equal to or less than the total number of communication channels Nc held by the base station. If it is Nc or less, the process proceeds to S2, and if it exceeds Nc, there is no room in the communication channel, so the acceptance of a new communication channel allocation request is rejected. As a result, new calls are also rejected.
In S2, the arrival wave estimation of the received signal from the mobile station of the new user is performed based on the new communication channel allocation request signal at the time of the call received from the mobile station of the new user (k = K + 1).
Here, the in-communication mobile station information of each user k (k = 1 to K) in communication shown in FIG. 2B is collected. That is, the estimated arrival direction θ_k, Estimated received power P_k, Which is the CINR threshold that can be assigned to the communication channel, γ^(k)Collect req. Γ which is the CINR threshold value that can be assigned to the communication channel of new user k = K + 1^{(K + 1)}req is determined according to the number of requested channels Nreq of the new user, or is collected if it is determined in advance.
[0015]
In S3, the optimum weight w when it is assumed that a communication is performed by accepting a new communication channel assignment request at the time of calling a new user (k = K + 1)_kCalculate Here, k = 1 to K + 1, which is performed for each user's mobile station and new user's mobile station in communication. Next, in S4, k = 1 is first set and the process proceeds to S5.
In S5, it is determined whether or not k is equal to or less than K + 1. If K + 1 or less, the process proceeds to S6, and if it exceeds K + 1, the process proceeds to S7.
In S6, if the new user is accepted, the CINR of the kth user^(k)Predict. Specifically how CINR^(k)As to whether or not is to be calculated, description thereof will be omitted here. In S8, this CINR^(k)Is the required CINR of the kth user γ^(k)Determine whether or not req is greater than or equal to γ^(k)If req or more, the process proceeds to S9, and γ^(k)If it is less than req, it refuses acceptance of a new communication channel allocation request for a new call, and proceeds to a process of rejecting acceptance of a new call. Therefore, receive CINR^(k)Is γ^(k)If a user k that does not satisfy req is detected, the received CINR for the mobile station of the remaining users^(k)At that time, the acceptance of the new communication channel assignment request for the new call is rejected. As a result, the acceptance of the new call is rejected, and the generated new call is regarded as a call loss.
Note that γ which is the above-described communication channel assignable CINR threshold value^(k)Since the value of req is for determining whether or not a new communication channel can be allocated, an arbitrary value that allows the mobile station to perform communication may be defined. Normally, the required CINR value during communication using the communication channel is made to match, but it is not always necessary to match this required CINR value. In addition, this threshold value may be changed depending on traffic conditions.
In S9, the value of k is incremented by 1, and the user of the next number is made to repeat the steps from S5.
[0016]
On the other hand, the process proceeds from S5 to S7 for all users including the user of the new call.^(k)Is γ^(k)This is a case where a condition equal to or higher than req is satisfied. In S7, the number of requested communication channels Nreq of the new user is added to the number of all communication channels N used by all users in communication to update the value of N to update the weight and allocate the communication channel for the new call. Thus, the process proceeds to accepting a new call.
At that time, a new user (k = K + 1) is registered in the communication channel management table shown in FIG. 2B, and the mobile station number k of the new user corresponding to the assigned communication channel number._{K + 1}Write.
Here, the weight update is the optimum weight w calculated when the new communication channel allocation request at the time of outgoing call of the new user (k = K + 1) received in S3 is accepted._kThis means that (k = 1 to K + 1) is set as a weight for the mobile station of each user k (k = 1 to K + 1) in communication including a new user.
[0017]
The flow described above corresponds to the function of the communication channel assignment control unit described above when viewed as a whole.
However, the step of S2 is a function executed by the estimation unit that estimates information on each incoming wave described above with respect to the mobile station of the new user.
In S6, the communication channel allocation control unit performs communication with the new mobile station based on communication quality information based on the received signal from the array antenna, the new communication channel allocation request signal, and the information on the individual incoming waves estimated by the estimation unit. Whether or not to allocate a new communication channel has been determined. In particular, when a new mobile station communicates using a communication channel, at least one mobile station out of the new mobile station and each mobile station in communication cannot perform communication satisfying communication quality defined in advance. If it is determined, the new communication channel assignment to the new mobile station is rejected.
[0018]
In the above-described flow, the determination process in S1, that is, the determination of whether or not there are free communication channels equal to or greater than the required communication channel number Nreq can be omitted. This can be omitted if a sufficient number of communication channels Nc is set in the base station. If, as a result of omitting this determination, the number of simultaneously connected communication channels becomes too large, it is found that the received CINR has deteriorated in S7, so the acceptance of a new call is rejected.
Note that the optimal weight calculation in S3 does not necessarily have to be performed for all mobile stations of k = 1 to K + 1. For example, a mobile station whose reception CINR is estimated to be sufficiently large or sufficiently smaller than γ (k) req without needing to perform weight calculation from the magnitude of the reception power is omitted. It is also possible. In the latter case, the processing of S4 to S9 can be skipped and the new call acceptance rejection can be immediately performed.
[0019]
FIG. 3 is an explanatory diagram showing how a new communication channel assignment request at the time of a call from a plurality of users is processed in the embodiment of the present invention. Here, the CINR threshold γ that can be assigned to the communication channel^(k)req is the required CINR value.
In the figure, the call event is indicated by a white circle, the call end event is indicated by a black circle, the call loss is indicated by ×, the CINR prediction calculation is indicated by Δ, and the time series of each of the users 1 to K is described on the horizontal axis. CINR prediction calculation means processing by steps S2 to S9 in FIG. In FIG. 1, the request communication channel determination is performed. In FIG. 3, a case where the request communication channel determination is not performed or the request communication channel determination result is always OK will be described.
[0020]
At time 1, user 1 makes a new communication channel assignment request at the time of outgoing call with no user in communication. The determination result of whether or not the required CINR is satisfied for the predicted CINR of user 1 is OK. As a result, a new communication channel assignment request for a new call of user 1 is accepted.
At time 2, user 2 makes a new communication channel assignment request at the time of calling and performs CINR prediction calculation for users 1 and 2. For the predicted CINRs of users 1 and 2, the determination result whether or not the required CINR is satisfied is OK. As a result, a new communication channel assignment request for a new call of user 2 is also accepted.
At time 3, user 3 makes a new communication channel assignment request at the time of calling and performs CINR prediction calculation for users 1, 2, and 3. The determination result of whether or not the desired CINR is satisfied for at least one of the predicted CINRs of the users 1, 2, and 3 is NG. As a result, the new communication channel assignment request for the new call of user 2 is rejected, and a call loss occurs.
At time 4, user 2 terminates communication and ends the call, and a free communication channel is generated.
[0021]
At time 5, the user 3 makes a communication channel assignment request at the time of calling again, and performs CINR prediction calculation for the users 1 and 3. As for the predicted CINRs of the users 1 and 3, the determination result as to whether or not the desired CINR is satisfied is OK. As a result, a new communication channel assignment request for a new call of user 3 is accepted this time.
At time 6, user K makes a new communication channel allocation request at the time of calling and performs CINR prediction calculation for users 1, 3, and K. For at least one of the predicted CINRs of users 1, 3, and K, the determination result as to whether or not the desired CINR is satisfied is NG. As a result, the new communication channel assignment request for the new call of user K is rejected and a call loss occurs.
At time 7, the user 3 ends the communication and is terminated.
At time 8, user K makes a new communication channel allocation request at the time of calling and performs CINR prediction calculation for users 1 and K. For the predicted CINR of users 1 and K, the determination result of whether or not the desired CINR is satisfied is OK. As a result, a new communication channel allocation request for a new call of user K is accepted this time.
At time 9, user 1 is terminated, and at time 10, user K is terminated.
[0022]
In the above description, the CINR prediction calculation for the mobile station of the user in communication becomes necessary when a new user makes a call. Therefore, arrival wave estimation and optimum weight calculation necessary for predicting CINR may be performed at the time when a call is made. However, since the calculation takes time, the incoming wave estimation for the user's mobile station during communication is performed at any time during communication, for example, at a predetermined time interval, regardless of whether there is a new call. At the time of occurrence, the immediately preceding estimated value or measured value may be used.
Moreover, the optimum weight calculation for the mobile station in communication is necessary for the directivity control of the adaptive array antenna in communication. This optimum weight also changes depending on the change in the location of the user's mobile station or the occurrence of a call termination. Therefore, in order to further improve the communication quality, it may be performed during communication, for example, at predetermined time intervals and / or when a call termination event occurs.
[0023]
In the above description, a case has been described in which the new communication channel assignment request for a new call is a new communication channel assignment request at the time of a call from a mobile station of a new user in the cell. On the other hand, when the new communication channel assignment request for the new call is a new communication channel assignment request at the time of the incoming call to the mobile station of the new user in the cell, it can be made in the same manner.
For example, the new communication channel allocation request at the time of the incoming call is made as a response signal from the mobile station to the incoming request signal from the base station to the mobile station. In this case, since the required number of communication channels is known first on the base station side, step S1 is executed. Here, if acceptance of a new communication channel allocation request for a new incoming call is not rejected, an incoming request signal is then transmitted from the base station to the new user, and then a response is received from the mobile station of this new user. A signal is received using the control channel. Based on this response signal, the arrival direction estimation and the reception power estimation of the new user mobile station are performed in S2, and the steps after S3 are executed. Similarly, the wait request and the new incoming call channel request acceptance or the new Refusal to accept new communication channel assignment request for incoming call.
[0024]
Here, the arrival wave estimation for the received signal from the mobile station of the new user K + 1, the optimum weight w when the new user is accepted_kAn example of calculation and CINR prediction will be supplementarily described.
The mobile station of the new user K + 1 transmits a new communication channel assignment request signal for a new call using the uplink common control channel (random access channel), and requests the base station to assign a new communication channel. To do. That is, the communication link establishment is requested.
A new communication channel assignment request signal at the time of outgoing call from the mobile station of the new user K + 1 is received by the base station, and a new communication channel assignment request signal at the time of outgoing call is received using the pilot signal included in the received signal. Direction of arrival θ_{K + 1}Is estimated. Since these processes are performed in a very short time interval, the direction of arrival hardly changes even when user data is transmitted to the base station using the dedicated communication channel. Direction of arrival θ during communication_{K + 1}Can be considered.
[0025]
On the other hand, the received power P of the incoming wave at the stage where user data is transmitted from the mobile station K + 1 of the new user using the communication channel._{K + 1}Can be determined by, for example, the transmission rate (mobile station transmission rate). In the case of DS-CDMA, transmission power proportional to the transmission rate is required for the same modulation scheme. Since this transmission rate information normally has a correspondence relationship with the required communication channel number Nreq, it can also serve as the required communication channel number Nreq.
If the transmission rate information is included in the new communication channel allocation request signal, the required communication channel number Nreq can also be obtained. Further, the requested communication channel number Nreq may be included in the new communication channel allocation request signal together with the transmission rate information.
Received power P_{K + 1}In addition, based on the received power of the new communication channel allocation request signal received using the control channel, the received power P when received using the communication channel_{K + 1}May be estimated.
[0026]
Arrival direction θ of the incoming wave from the mobile station of new user K + 1 described above_{K + 1}And received power P_{K + 1}Based on the above, the reception signal of the array antenna (the array input signal of each element) based only on the incoming wave from the mobile station of the new user K + 1 is calculated. The array antenna received signal from the mobile station of the new user K + 1 described above is added to the array antenna received signal in the current state during communication with the mobile station k (k = 1 to K). Is a received signal of the array antenna when it is assumed that the new user K + 1 is included. The optimum weight w of the mobile station k (k = 1 to K + 1) at the time of accepting a new user according to the received signal of this array antenna_k(Hereafter, w_k') Is calculated based on, for example, the least square error method (MMSE).
[0027]
Next, the explanation of CINR will be supplemented.
Nobuyoshi Kikuma “Adaptive signal processing by array antenna”, Science and Technology Publication (1998-11) p.26, 27, SINR (Signal to Interference plus Noise Ratio) for the output of the array antenna (Corresponding to the value normalized by PG).
CINR of a certain user k^(k)Is the array antenna output power (I + N) of the interference wave including the thermal noise of the array antenna output power (C) of the desired wave, which is included in the output signal of the array antenna despread with the spreading code of the target user k. )).
[0028]
The array antenna output power (C) of the desired wave of a certain user k is the arrival wave (estimated arrival direction θ_k, Estimated received power P_k) The optimum weight w after assuming that the received signal of the array antenna at each antenna element of FIG._kIt is calculated as electric power when it is combined and output using ′. More specifically, the estimated arrival direction θ_kAnd estimated received power P_kAutocorrelation matrix calculated from the optimal weight w described above_k'
On the other hand, the array antenna output power (I + N) of the interference wave including the thermal noise is equal to the optimum weight w described above when the received signal of the array antenna is assumed to include the new user K + 1._kIt is calculated as a value obtained by subtracting the above-described array antenna output power (C) of the desired wave of the user k from the power when combined and output using ′.
Communication quality CINR of a certain user k^(k)To estimate the optimal weight w_k′, Estimated arrival direction θ_k, And estimated received power P_kIt is only necessary to know, and other users need not be understood. Therefore, step S3 in FIG. 1 may be executed between step S5 and step S6. Therefore, optimum weight w_kThe calculation of 'is also the CINR in S6^(k)Like the received CINR^(k)Is γ^(k)If a user k that does not satisfy req is detected, the calculations for the mobile stations of the remaining users can be omitted.
[0029]
Communication quality CINR described above^(k)For the direction of arrival θ_kThere is no need to estimate the information directly. θ_kInstead of array placement, frequency, direction of arrival θ_kThe array propagation vector v determined by_kMay be estimated directly, and a correlation matrix may be calculated using this to estimate communication quality. For the array propagation vector, see the above-mentioned adaptive signal processing by array antennas, pages 28-31.
Note that the interference wave is not generated only by another user who performs communication using the communication channel. In the CDMA communication system, the control channel for communication channel allocation already described and the control channel for mobile station location registration, etc. are used, and the code spread signal is transmitted even when communication is not performed using the communication channel. Sending. Therefore, the interference wave described above includes signals transmitted during non-communication that does not use these communication channels other than interference from other users who are communicating using the communication channels, and other wireless zones ( Interference due to radio waves coming from neighboring cells is also included.
[0030]
In the CDMA communication system described above, as shown in FIG. 7, the cover area (cell) of the base station 24 is an isotropic omnicell. On the other hand, in order to improve the frequency utilization efficiency, as illustrated in FIG. 5 described later, a cover area that is an omni cell may be divided into a plurality of sectors. A cellular mobile communication system is designed by replacing each individual sector with an omni cell.
In a CDMA cellular mobile radio communication system using such a sector, an array antenna is arranged for each sector, and code division multiple access is performed for each sector.
[0031]
Communication channel assignment control for determining whether or not to accept a new communication channel assignment request signal for a new call (outgoing call or incoming call) shown in FIG. 1 is performed for each sector. The communication channel management table shown in FIG. 2 is also managed for each sector. The estimation means for estimating information on each incoming wave estimates for each sector in which a communicating mobile station and a new mobile station are located. Mobile station information relating to a mobile station in communication using a communication channel is collected for each sector in which the mobile station in communication is located.
However, if each sector is operated at the allowable limit of the reception CINR, interference from other sectors will have an effect. Therefore, when the control channel receiving unit receives the new communication channel assignment request signal, the communication channel assignment control unit described above includes the received signal of the array antenna, the new communication channel assignment request signal, and the estimation means. Whether to allocate the new communication channel to the new mobile station is determined based on communication quality information based on the information on the individual incoming waves from the mobile station in communication and the new mobile station located in all sectors To do.
[0032]
FIG. 4 is an explanatory diagram showing how a new communication channel request at the time of a call from a plurality of users is processed in the sectorized system according to the embodiment of the present invention. The symbols in the figure are the same as those in FIG. The sector to which each user belongs is indicated by a subscript number of the user number.
At time 1, user 1₁Makes a new communication channel allocation request at the time of a call with no user in communication. User 1₁The determination result of whether or not the predicted CINR satisfies the desired CINR is OK. As a result, user 1₁A new communication channel assignment request for a new call is accepted.
At time 2, user 1 in the second sector₂Makes a new communication channel assignment request at the time of call, and user 1₁, 1₂Perform CINR prediction calculation. User 1₁, 1₂For the predicted CINR, the determination result of whether or not the desired CINR is satisfied is OK. As a result, user 1₂New communication channel assignment requests for new calls are also accepted.
User 3 in sector 3 at time 3_ThreeMakes a new communication channel assignment request at the time of call, and user 1₁, 1₂, 1_ThreePerform CINR prediction calculation. User 1₁, 1₂, 1_ThreeFor the predicted CINR, the determination result of whether or not the desired CINR is satisfied is OK. As a result, user 1_ThreeNew communication channel assignment requests are also accepted.
At time 4, the user 21 in the first sector makes a new communication channel allocation request at the time of calling, and user 1₁, 2₁, 1₂, 1_ThreePerform CINR prediction calculation. User 1₁, 2₁, 1₂, 1_ThreeFor the predicted CINR, the determination result of whether or not the desired CINR is satisfied is OK. As a result, user 2₁New communication channel assignment requests are also accepted.
[0033]
At time 5, user 3 in sector 1₁Makes a new communication channel assignment request at the time of call, and user 1₁, 2₁, 3₁, 1₂, 1_ThreePerform CINR prediction calculation. User 1₁, 2₁, 3₁, 1₂, 1_ThreeThe determination result of whether or not the desired CINR is satisfied for at least one of the predicted CINRs is NG. As a result, user 3₁The new communication channel allocation request is rejected and a call loss occurs.
User 1 at time 6_ThreeBut user 1 at time 7₂However, the communication is terminated and the call is terminated.
At time 8, user 3₁Makes a new communication channel assignment request at the time of outgoing call,₁, 2₁, 3₁Perform CINR prediction calculation. User 1₁, 2₁, 3₁For the predicted CINR, the determination result of whether or not the desired CINR is satisfied is OK. As a result, this time user 3₁The new communication channel allocation request is accepted.
User 3 at time 9₁But user 2 at time 10₁But at time 12 user 1₁However, the communication is terminated and the call is terminated.
When there are a plurality of cells, it is desirable to consider the interference given to neighboring cells when a new communication channel is assigned. CINR threshold γ that can be assigned to the communication channel of each base station^(k)By setting a large threshold value with a margin in advance with respect to req, it is possible to consider interference given to surrounding cells.
[0034]
FIG. 5 is an explanatory diagram of a sectorized cell.
FIG. 5A is an explanatory diagram of a cell model, and FIG. 5B is an explanatory diagram showing an example of a directivity pattern of an adaptive array antenna in a sectorized cell.
In FIG. 5A, 11 is a sectorized hexagonal cell, and the omnicell is divided into three sectors. Reference numeral 12 denotes an array antenna provided in each sector, and 13 denotes individual directivity characteristics of the antenna elements constituting each array antenna.
In FIG.5 (b), 14, 15, and 16 are the mobile stations of the users 1-3. The case where the mobile station of one user is located in one sector is shown. The number of elements of the array antenna in each sector is 8, and 17 (solid line), 18 (broken line), and 19 (dashed line) indicate the directivity characteristics. The main lobe is directed toward the target user, and the beam null is directed toward the other user direction.
[0035]
The simulation was performed using the cell model with eight antenna elements shown in FIG. Since it has a three-sector configuration, the total number of antenna elements is 8 × 3 = 24.
The mobile station is uniformly distributed within the cell, with the isolated cell having no interference from neighboring cells. The new communication channel assignment request signal at the time of calling follows the occurrence of Poisson with an average generation interval Ta within one sector. All communication channels requested by the mobile station are assumed to be one communication channel. It is assumed that the transmission power from each mobile station is adjusted so as to compensate for the variation in distance to the base station.
The required CINR for satisfying the communication quality required by each communication channel is assumed to be constant γreq = 10 dB for all users, and it is assumed that all users communicate at the same speed. Since there is no complete orthogonality between the spreading codes in the uplink, the amount of interference is 1 / PG when the spreading factor (processing gain by spreading code) is PG. Here, the simulation results are shown with PG = 20 dB.
Assuming that the arrival directions and received power of all the mobile stations can be accurately estimated, the optimum weight of the adaptive array antenna is obtained for each user, and the received CINR is estimated. The user who has received the new communication channel assignment request is disconnected after using the communication channel for the holding time ts seconds. This holding time was determined so that the average holding time Ts (= ρTa) had an exponential distribution of 120 seconds.
[0036]
FIG. 6 is a graph showing a simulation result of the embodiment of the present invention and the prior art.
FIG. 6A is a graph showing the cumulative probability of CINR, which is a communication quality parameter. The cumulative probability on the vertical axis indicates the probability that the value of CINR is less than or equal to the value on the horizontal axis. A call volume of ρ = 25 erlangs per sector is generated. The required value γreq of CINR is 10 dB for all users. The number of base station communication channels was not limited.
A solid line indicates a simulation result when new communication channel allocation control is performed, and a broken line indicates a simulation result when new communication channel allocation control is not performed.
When the new communication channel allocation control is not performed, there is a cumulative probability of approximately 1% that the CINR is less than the required value of 10 dB. This value means the CINR degradation rate during communication. On the other hand, when new communication channel allocation control is performed, a call loss almost equal to the CINR deterioration rate occurs. However, once the communication channel is assigned, the CINR does not become 10 dB or less during communication, and it can be seen that call control is working effectively.
[0037]
FIG. 6B is a graph showing the characteristics of the call loss rate with respect to the amount of calls made, with call control.
FIG. 6C is a graph showing the characteristics of the call loss rate with respect to the amount of calls made when no call control is performed.
In either case, the number of communication channels (number of facilities) assigned to each sector of the base station is 20 ch to 50 ch, the solid line indicates the call loss rate, and the broken line indicates the CINR deterioration rate. The same scale is used for the call loss rate and the CINR deterioration rate. It should be noted that the CINR deterioration rate in 20ch of FIG. 6C is not shown because it is below the range shown.
[0038]
As can be seen from FIG. 6B, when the above-described new communication channel allocation control is performed, the received CINR (communication quality) does not deteriorate regardless of the number of communication channels and the number of calls generated.
On the other hand, as can be seen from FIG. 6B, when the new communication channel assignment control is not performed, the degradation rate of the received CINR greatly varies depending on the number of communication channels and the amount of calls made. Therefore, in order to suppress deterioration below a predetermined value without call control, it is necessary to limit two parameters such as the number of communication channels and the number of calls generated in advance, and the control becomes complicated. Therefore, the performance of the adaptive array antenna cannot be fully utilized.
In this way, by performing the above-described new communication channel allocation control, the communication quality does not deteriorate even if the amount of outgoing calls or the number of communication channels changes. Can do.
[0039]
In the above description, the call control method is to determine whether or not to accept a new communication channel assignment request when a new call is generated by paying attention to uplink communication quality. The downlink communication quality was not considered because it was difficult to evaluate. However, if the communication quality of the downlink is also evaluated, it is desirable to determine whether or not to accept the communication channel assignment request in consideration of this evaluation.
[0040]
【The invention's effect】
As is apparent from the above description, according to the present invention, when performing code division multiple access with a plurality of mobile stations in a cell using an array antenna, the communication quality of the uplink during communication is guaranteed. There is an effect that communication with reduced interference signals can be performed using the array antenna without worrying about any communication quality fluctuations due to fluctuations in traffic in the cell during communication.
[Brief description of the drawings]
FIG. 1 is a flowchart for explaining an embodiment of a CDMA base station apparatus of the present invention.
FIG. 2 is an explanatory diagram showing an example of a communication channel management table used in an embodiment of the present invention.
FIG. 3 is an explanatory diagram showing how a new communication channel allocation request at the time of a call from a plurality of users is processed in the embodiment of the present invention.
FIG. 4 is an explanatory diagram showing how a new communication channel allocation request at the time of a call from a plurality of users is processed in the sectorized system in the embodiment of the present invention.
FIG. 5 is an explanatory diagram of a sectorized cell.
FIG. 6 is a graph showing a simulation result of the embodiment of the present invention and the prior art.
FIG. 7 is an explanatory diagram showing an example of a CDMA mobile communication system using an adaptive array antenna.
[Explanation of symbols]
21 ... User 1 mobile station, 22 ... User 2 mobile station, 23 ... User 3 mobile station, 24 ... Base station, 31 ... User 1 directivity, 32 ... User 2 directivity, 25 ... Adaptive array antenna, 25a ... Antenna element

Claims (1)

CDMA that performs communication by code division multiple access for each sector using a plurality of array antennas arranged for each sector with a plurality of mobile stations in a radio zone that is angle-divided into a plurality of sectors A base station device,
Control channel receiving means for receiving a new communication channel assignment request signal from the array antenna using a control channel from a new mobile station requesting assignment of a new communication channel among the plurality of mobile stations;
Among the plurality of mobile stations, an estimated arrival direction and estimated received power for each incoming wave from the communicating mobile station and the new mobile station are used to obtain the estimated mobile station and Estimating means for estimating for each sector in which the new mobile station is located ;
When the control channel receiving means receives the new communication channel assignment request signal, the received signal of the array antenna, the new communication channel assignment request signal, and the estimated arrival direction related to the individual incoming waves estimated by the estimating means and Communication channel assignment control means for deciding whether or not to assign a new communication channel to the new mobile station based on communication quality information based on the estimated received power;
The communication channel allocation control means is estimated by the reception signal of the array antenna and the new communication channel allocation request signal and the estimation means when the control channel reception means receives the new communication channel allocation request signal, The communication quality information based on the information on the individual incoming waves received from the communicating mobile stations located in all the sectors in the radio zone and the antennas of the corresponding sectors from the new mobile stations, Determining whether the new communication channel can be allocated to a mobile station;
Wherein when a new mobile station performs communication using the communication channel, said one of the new mobile station and each mobile station in the call in the wireless zone, satisfies the communication quality at least one mobile station previously defined If it is determined that communication cannot be performed, the new communication channel assignment for the new mobile station is rejected.
A CDMA base station apparatus.

Images