CDMA communication system having means for controlling access in dependence on communication quality

Abstract: In order to control access from mobile terminals in a code division multi-access communication system, a terminal communication with one of the base station measures data relating to quality of a downlink signal during a predetermined time interval to inform as downlink signal quality data to the base station. The base station also measures data relating to quality of an uplink signal during the predetermined time interval to produce uplink signal quality data. A base station control device defines from the downlink signal quality data and the uplink signal quality data communication quality within the service zone of the base station and sends an access confinement signal to the base station when defining the communication quality bad. Thus, the base station carries out a busy processing for a fresh calling to and from other mobile radio terminals therefrom and thereto.

Description: Background of the Invention: This invention relates to a code division multiple access (CDMA) communication system and, in particular, to confinement of access from mobile terminals in such CDMA communication system. A known CDMA communication system comprises a plurality of mobile radio terminals, a plurality of base stations having different radio service zones, and a base station control device. In a communication system, a particular one of the plurality of mobile radio terminals communicates with a particular one of the plurality of base stations having a particular one of the radio service zones in which the particular mobile radio terminal currently is situated. As is known in the art, the CDMA communication system uses a spectrum spread technique wherein a carrier signal is, in a transmitting side, spectrum spread by use of a pseudo- noise (PN) code and is transmitted. In the receiving side, the transmitted signal is received as a received signal, which is, in turn, correlated with the PN code signal to derive the carrier signal from the received signal. In the CDMA communication system using the spectrum spread technique, many channels can be made by use of different PN codes without use of different carrier frequencies and can be protected from cross talk to each other as well as interception. However, the CDMA communication system has the graceful degradation that is the communication quality degrades as increase of the communication traffic or the number of calls. This means that a data communication requiring a high communication quality cannot be completed when the traffic is excessively increased during the communication. In order to resolve the problem of the graceful degradation in the CDMA communication, JP-A-5 145516 discloses provision of a memory for storing attributes of terminals accommodated in the system and maximum traffic values acceptable for attributes of the terminals to thereby control accesses from terminals to maintain the traffic by the terminals below the maximum traffic values. According to the resolve by JP-A-5 145516, it is undesirably required before use of the system to actually measure the radio transmission for various attributes of the terminals such as telephone terminals, facsimile terminals, data transmission terminals and others within each of the radio service zones so as to determine the acceptable maximum traffic values. Further, since the accessible maximum traffic values are fixedly determined for every attribute of the terminals, it is often impossible to efficiently use the frequency. This is because the accessible traffic values are dependent on traffic values and radio transmission conditions which always vary. In other related prior art, WO-A-94/27384 discloses a method and a device based on threshold values on the load value of a connection as a quality measurement for optimising the setting up of channels, the changing of channels and handover procedures in a mobile telecommunications system. EP-A-0652680 discloses a communications system and method using an access confinement signal ("GoAway"-Message) to mark a cell as barred for access by a mobile station, according to the value of a "Cell Barred"-parameter. Summary of the Invention: Therefore, it is an object of at least the preferred embodiments of this invention to provide a method for controlling access from terminals to a service zone of a base station in a CDMA communication system by currently monitoring the communication quality in the radio service zone without predetermining the maximum traffic values for attributes of the terminals, so as to maintain the high communication quality with the high efficiency in the use of the frequency. It is another such object to provide the method for controlling the accesses from terminals to the base station in the CDMA communication system also with a the maximum number of calls which can be adjusted in dependence on the current communication quality as monitored. It is another such object to provide a CDMA communication system which can carry out the access control method. According to an aspect of this invention, there is obtained an access controlling method in a code division multi-access communication system comprising a plurality of mobile radio terminals, a plurality of base stations having different radio service zones, and a base station control device, a particular one of the plurality of mobile radio terminals communicating with a particular one of the plurality of base stations having a particular one of the radio service zones in which communication with the particular mobile radio terminal currently exists. The method comprises steps of; the particular mobile radio terminals receiving a downlink signal transmitted from the particular base station and measuring data relating to quality of the downlink signal during a predetermined time interval to inform as downlink signal quality data to the particular base station; the particular base station receiving an uplink signal transmitted from the particular mobile station and measuring data relating to quality of the uplink signal during the predetermined time interval to produce uplink signal quality data, the particular base station informing of the downlink signal quality data and the uplink signal quality data to the base station control device; the base station control device defining, from the downlink signal quality data and the uplink signal quality data, communication quality within the particular radio service zone, the base station control device sending an access confinement signal to the particular base station when defining that the communication quality is bad; and the particular base station responsive to the access confinement signal to carry out a busy processing for a fresh call initiated to and from one of the mobile radio terminals therefrom and thereto. Further, this invention is applicable to a code division multi-access communication system comprising a plurality of mobile radio terminals, a plurality of base stations having different radio service zones, and a base station control device, each one of the plurality of mobile radio terminals communicating, as a particular mobile radio terminal, with a particular one of the plurality of base stations havin a particular one of the radio service zones in which communication with the each one of the mobile radio terminals currently exists. According to this aspect of the invention, the code division multi-access communication system comprises; each of the mobile radio terminals comprising, means for receiving a downlink signal transmitted from the particular base station, and means for measuring data relating to quality of the downlink signal during a predetermined time interval to inform as downlink signal quality data to the particular base station; each of the base stations comprising, means for receiving an uplink signal transmitted from the particular mobile station, and means for measuring data relating to quality of the uplink signal during the predetermined time interval to produce uplink signal quality data, the particular base station informing of the downlink signal quality data and the uplink signal quality data to the base station control device; and the base station control device comprising means for defining, from the downlink signal quality data and the uplink signal quality data from the particular base station, communication quality within the particular radio service zone and being arranged to send an access confinement signal to the particular base station when defining that the communication quality is bad, whereby the particular base station responsive to the access confinement signal is arranged to carry out a busy processing for a fresh call initiated to and from one of the mobile radio terminals therefrom and thereto. Brief Description of the Drawings The invention now will be described merely by way of example with reference to the accompanying drawings wherein: Fig. 1 is a schematic diagram view of a CDMA communication system according to an embodiment of this invention; and Fig. 2 is a chart illustrating an access control operation flow of the system in Fig. 1. Description of Preferred Embodiments: Referring to Fig. 1, there is shown a block diagram of a digital mobile communication system using the CDMA system according to an embodiment of this invention. The digital communication system shown therein comprises mobile radio terminals 11 (only one of them is shown), base stations 13-1 through 13-n (n is a natural number equal to 2 or more, collectively identified as 13), a base station control device 15, and a mobile communication switch 17. Each of the mobile stations 11 communicates with the nearest one (13-k) of the base stations 13-n. Each of the mobile stations 11 has a pilot signal measuring portion 19. Each of the base stations 13-1 through 13-n is provided with a plurality of (m: a natural number equal to 2 or more) channel control portions 21-n-1 though 21-n-m (collectively identified as 21) which are corresponding to calls, respectively. The base station control device 15 is provided with a plurality of (n) statistical processing portions 23-1-1 through 23-1-n (collectively identified as 23) which are corresponding to the base stations 13-1 through 13-n, respectively, and an access control portion 25. The statistical processing portions 23 and the access control portion 25 in the base station control device 15 function as a quality defining means for instructing access confinement to the base stations 13 including ones currently communicating in dependence on the communication quality. Therefore, it is unnecessary to predetermine acceptable traffic values for the base stations 13, respectively. The access control or confinement can be performed in dependence on traffic distribution condition for each of the base stations 13, so that the desired communication quality can always be insured with high efficiency in use of the given frequency band. Upon receipt of the channel confinement, the channel control portions 21 carry out the busy processing for a fresh calling to and from the other mobile radio terminals 11. According to another embodiment, the channel control portions 21 in the base stations 13 further function the access confinement to the all of channels in dependence on the maximum calling number storing in a memory (not shown). The maximum calling number is adjusted in response to the communication quality condition, as described below. Therefore, even if a number of calls occur or rush during a short period, it is possible by adapting the current traffic distribution to maintain the desired communication quality. Referring to Fig. 2, there is shown a flow chart illustrating an example of a sequence of access control in the digital mobile communication system using the CDMA system as shown in Fig. 1. Referring to Figs. 1 and 2, description will be made as regards an example of the access control in the digital mobile communication system using the CDMA system according to an embodiment of this invention, below. During communication, the mobile station 11 measures the pilot signal which is always transmitted from the base stations 13. At a unit of measuring frame number corresponding to a unit time t1 (for example 2 seconds) indicated from the base station control device 15, for example, at a unit of 100 frames under each frame being 20 msec. the mobile station reports to the base station 13 data of the average reception signal level and the number of error frames in a downward signal transmitted from the base station 13. The measuring frame number can be noticed to all of mobile stations 11 through the base stations 13 as broadcast information before start of any calling. When the average receiving signal level cannot be measured after, for example, the received signal is gain controlled, an average relative value of a receiving level to noise and interference which is determined by Eb/(N0+I0) can be used in place of the average receiving signal level, where Eb is a receiving energy per one tip of the pilot signal, (N0+I0) being an entire spectral density of the noise and interference as received. In a communicating one of the base stations 13, one of the chanel control portions 21 corresponding to each of the mobile stations 11 and each of the channels measures the number of error frames in an upward signal transmitted from the corresponding mobile station at a unit of frame numbers indicated by the base station control device 15, for, example, at a unit of 100 frames, and calculates the frame error rate (FER) in the upward signal. At the unit of frame numbers indicated by the base station control device 15, for example, at a unit of 100 frames, each of the channel control portions 21 reports to each of the statistic processing portions 23 the FER of the upward signal, and the average receiving signal level (or the average relative value Eb/(N0+I0)) and the number of error frames in the downward signal. The base station control device 15 calculates the FER of the downward signal from the downward number of error frames and the measuring frame number. Then, the base station control device 15 compares a predetermined value α % with the FER calculated to produce a first probability x (= Prob. (FER > α %))that the downward signal FER exceeds the predetermined value α %, and also compares the predetermined value α % with each of a set of the FER of the upward signal to produce a second probability y (= Prob. (FER > α %)) that the upward signal FER exceeds α %, as shown at step S1 in Fig. 2. Then, the base station control device is compares the probabilities x and y with another predetermined value β % at step S2, and generates an access confinement signal as shown at step S3 when both of probability x and y are larger than β %. On the other hand, when the both of probability x and y are not larger than β % at step S2, the base station control device 15 generates the acceptance signal as shown at step S4. The access confinement signal is applied to the base station 13 concerned and adjacent base stations. Upon reception of the access confinement signal, each of the base stations performs the busy processing for fresh callings. Each of the base stations 13 further holds a maximum number of calls and a current number of calls between the base station 13 and the mobile terminals , as described above. When the the current number of calls becomes the maximum number of calls, each of the base stations carries out the busy processing for the new call therefrom and thereto in no relation to whether or not both of the probabilities x and y are larger then β %, Thus, it can be avoided that the communication quality is degraded even if there are many calls at a quite short time before determining whether or not both of the probabilities x and y are larger then β %. The maximum number of calls can be adjusted by the statistical processing portions 23 in the base station control device 15 through steps S5-S9 and S10-S16 in Fig. 2, during a steady time period when many calls do not rush for a quite short time. At steps S5-S10 in Fig. 2, Cup and Cdn represent a number of calls continuously accepted and a number of calls continuously rejected, respectively. Nup and Ndn represent the maximum numbers (for example, both being 5) of Cup and Cdn, respectively. MAXCALLS represents the maximum number of calls. In the steady condition of the call occurrence, Cup is set "0" at step S5 after step S3, and Cdn is increased by "1" at step S6. Then, Cdn and Ndn are compared at step S7. If Cdn does not reach Ndn, MAXCALLS is maintained without change. If Cdn reaches Ndn, MAXCALLS is decreased by "1" at step S8, and then Cdn is set "0" at step S9. While, after the new call is accepted at step S4, the number of calls which are now accepted or communicating is compared with MAXCALLS at step S10. When they are equal to each other, Cdn is set "0" at step S11, and then Cup is increased by "1" at step S12. Then, Cup is compared with Nup at step S13, when Cup does not reach Nup, the MAXCALLS is maintained without change. When Cup is equal to Nup, MAXCALLS is increased by "1" at step S14 and then Cup is set "0" at step S15. When the number of calls is equal to MAXCALLS at step 10, Cdn is set "0" at step S16. If the MAXCALLS is set "1" when the system starts, MAXCALLS is adjusted at the steady condition by the operation through steps S5-S16. The MAXIMCALLS adjusted is informed from the base station control device 15 to the base stations 13 in which the MAXCALLS is renewed. As an example in the above embodiment, α and β may be 1 and 5, respectively. Further, α can be different from attributes of the mobile radio terminals. For example, α is determined as 1 and 0.1 for an audio terminal and a data terminal. The text of the abstract filed herewith is repeated here as part of the specification. In order to control access from mobile terminals in a code division multi-access communication system, a terminal communication with one of the base station measures data relating to quality of a downlink signal during a predetermined time interval to inform as downlink signal quality data to the base station. The base station also measures data relating to quality of an uplink signal during the predetermined time interval to produce uplink signal quality data. A base station control device defines from the downlink signal quality data and the uplink signal quality data communication quality within the service zone of the base station and sends an access confinement signal to the base station when defining the communication quality bad. Thus, the base station carries out a busy processing for a fresh calling to and from other mobile radio terminals therefrom and thereto.

Claims: An access controlling method in a code division multi-access communication system comprising a plurality of mobile radio terminals (11), a plurality of base stations (13-1, 13-n) having different radio service zones, and a base station control device (15), a particular one of said plurality of mobile radio terminals (11) communicating with a particular one of said plurality of base stations (13-1, 13-n) having a particular one of said radio service zones in which communication with said particular mobile radio terminal currently exists, which comprises steps of; said particular mobile radio terminal (11) receiving a downlink signal transmitted from said particular base station (13-1, 13-n) and measuring data relating to quality of the downlink signal during a predetermined time interval to inform as downlink signal quality data to said particular base station; said particular base station (13-1, 13-n) receiving an uplink signal transmitted from said particular mobile terminal (11) and measuring data relating to quality of the uplink signal during said predetermined time interval to produce uplink signal quality data, said particular base station (13-1, 13-n) informing of said downlink signal quality data and said uplink signal quality data to said base station control device; said base station control device (15) defining, from said downlink signal quality data and said uplink signal quality data, communication quality within said particular radio service zone, said base elation control device (15) sending an access confinement signal to said particular base station when defining that said communication quality is bad; and said particular base station responsive to said access confinement signal to carry out a busy processing for a fresh call initiated to or from one of said mobile radio terminals (11). The method as claimed in Claim 1, wherein said base station control device (15) further sending out said access confinement signal to specific ones of said base stations (13-1, 13-n) which have radio service zones adjacent to said particular radio service zone; and each of said specific base stations responsive to said access confinement signal to carry out a busy processing for a fresh calling to or from one of said mobile radio terminals (11). The method as claimed in Claim 1, said particular base station transmitting a pilot signal spectrum spread, said particular mobile radio terminal receiving said pilot signal spectrum spread as a received signal and demodulating said received signal into said pilot signal, wherein said downlink signal quality data comprise an average receiving level of said received signal during said predetermined time interval and a number of error frames occurring in said pilot signal demodulated. The method as claimed in Claim 3, wherein an average relative value of a receiving level to noise and interference which is determined by Eb/(N0+I0) is used in place of said average receiving level of said received signal, Eb being a receiving energy per one tip of said pilot signal and (N0+I0) being an entire spectral density of said noise and interference as received. The method as claimed in Claim 3, said uplink signal having subsequent frames, wherein said uplink signal quality data comprise an uplink signal frame error rate occurring in said uplink signal as received at said particular base station during said predetermined time interval. The method as claimed in Claim 5, wherein said base station control device defines said communication quality by calculating a downlink signal frame error rate from said number of error frames and said predetermined time interval, comparing a first predetermined value with each of a set of downlink signal frame error rates obtained during a predetermined time period longer than said predetermined time interval to produce a first probability that the downlink signal frame error rate exceeds said first predetermined value, comparing a second predetermined value with each of a set of uplink signal frame error rates obtained during another predetermined time period longer than said predetermined time interval to produce a second probability that the uplink signal frame error rate exceeds said second predetermined value, and comparing said first and said second probability with a third predetermined value, said base station control device generating said access confinement signal when both of said first and said second probability are larger than said third predetermined value. The method as claimed in Claim 6, wherein said particular base station (13-1, 13-n) memorizes, as a current call number, a number of calls which are currently established at said particular base station and stores a maximum number of calls which can be allowed at said particular base station, said particular base station (13-1, 13-n) comparing said current call number with said maximum number of calls in no relation whether or not both of said first and said second probability are larger than said third predetermined value, and carrying out the busy processing for fresh call therefrom and thereto when said current call number reaches the maximum number of calls. The method as claimed in Claim 6, wherein said maximum number of calls is adjusted at said base station control device (15) during a steady state conflition when many calls do not rush during a quite short time and is renewed at the particular base station (13-1, 13-n). A code division multi-access communication system comprising a plurality of mobile radio terminals (11), a plurality of base stations (13-1, 13-n) having different radio service zones, and a base station control device (15), each one of said plurality of mobile radio terminals (11) communicating, as a particular mobile radio terminal (11), witch a particular one of said plurality of base stations (13-1, 13-n) having a particular one of said radio service zones in which communication with said each one of said mobile radio terminals (11) currently exists, which comprises; each of said mobile radio terminals (11) comprising, means for receiving a downlink signal transmitted from said particular base station (13-1, 13-n), and means for measuring data relating to quality of the downlink signal during a predetermined time interval to inform as downlink signal quality data to said particular base station (13-1, 13-n); each of said base stations comprising, means for receiving an uplink signal transmitted from said particular mobile terminal (11), and means tor measuring data relating to quality of the uplink signal during said predetermined time interval to produce uplink signal quality data, said particular base station (13-1, 13-n) informing of said downlink signal quality data and said uplink signal quality data to said base station control device (15); said base station control device (15) comprising means for defining, from said downlink signal quality data and said uplink signal quality data from said particular base station (13-1, 13-n), communication quality within said particular radio service zone and being arranged to send an access confinement signal to said particular base station when defining that said communication quality is bad, whereby said particular base station responsive to said access confinement signal is arranged to carry out a busy processing for a fresh call initiated to or from one of said mobile radio terminals (11). The code division multi-access communication system as claimed in Claim 9, wherein said base station control device (15) further comprises means for sending out said access confinement signal to specific ones of said base stations (13-1, 13-n) which have radio service zones adjacent to said particular radio service zone; each of said specific base stations being responsive to said access confinement signal to carry out a busy processing for a fresh call initiated to or from one of said mobile radio terminals.

Inventors: UEDA TETSURO, UEDA, TETSURO
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1997
Main classification: H04Q7
IPC codes: H04B7, H04J13, H04W72, H04W48