JP4187100B2 - Mobile phone system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mobile station of a code division multiple access (CDMA) communication system and a communication method of the mobile station.
[0002]
[Prior art]
In recent years, mobile phone systems using a code division multiple access (CDMA) system have become widespread. In the CDMA system, a transmitting station uses a special code called a pseudo-noise (PN) sequence to spread and modulate a signal over a wide band, and the receiving station uses the same PN sequence as that on the transmitting side. The required signal is restored by despreading demodulation. Here, the PN sequence has the property that it has orthogonality and the cross-correlation value with other sequences is zero. Due to the nature of such a PN sequence, even when a plurality of transmitting stations transmit signals that are spread-modulated using different PN sequences, the receiving station uses a PN sequence corresponding to the desired transmitting station. By despreading the received signal, only the signal from the desired transmitting station can be separated and extracted.
[0003]
Next, a method for the mobile station to switch base stations to be connected for communication will be described. First, in a base station, a pilot signal (control signal) for use in searching for a communication connection destination of a mobile station is spread-modulated with a PN sequence unique to the base station and transmitted. Here, the offset value of the PN sequence is called a PN number and takes a value of 0 to 511. Since a base station can be uniquely identified by this PN number, a base station using a PN sequence having a PN number (offset value) of n is called a base station n. A base station in communication connection is called an active base station. Then, the active base station transmits a neighbor list indicating the numbers of base stations located in the vicinity of the active station to the mobile station. A base station included in the neighbor list is called a neighbor base station, and a remotely located base station that is neither an active base station nor a neighbor base station is called a main base station. The active base station also transmits a number R_INC that represents the interval of the PN numbers for searching the remote base station, which is used when the mobile station searches for a communication connection destination.
[0004]
The mobile station always searches for a better base station than the current active base station during a call. That is, the mobile station measures the signal strength from all the neighbor base stations and the main base station whose PN number is R_INC. Then, when there is a base station having a signal strength higher than that of the active base station, the mobile station performs handoff (connection switching) to the base station. Therefore, it may be handed off to a remote base station that is remote.
[0005]
[Problems to be solved by the invention]
By the way, when handing off to a remote remote base station, there are the following problems.
[0006]
First, since the remote base station is located remotely from the mobile station, a signal (uplink signal) from the mobile station is difficult to reach. This is because a mobile station cannot transmit a signal with strong energy. As a result, the communication connection cannot be established between the remote base station and the mobile station, and the handoff destination must be determined again, or the communication quality is extremely poor even if the communication connection is established.
[0007]
Second, when a remote main base station becomes an active base station, its neighbor base station also becomes a remote base station. In such a case, since the base station in the vicinity of the current location is the main base station, the base station is not necessarily the next search target (the main base station is searched every R_INC). Therefore, it is difficult to handoff to a base station in the vicinity of the current location (generally, the signal strength is higher than that of a remote location).
[0008]
On the other hand, as the mobile station moves, fading, that is, the radio wave propagation environment changes, and the intensity of the received signal may vary. In addition, the re-main base station has a long distance from the mobile station, and the signal passes through various propagation environments. Therefore, it can be said that the signal intensity is likely to be subject to temporal fluctuations accordingly. Therefore, even if the signal strength is high when measured, it may happen that it is only high at that time, and there is no guarantee that the signal strength is high at any time other than when it is measured.
[0009]
As described above, when handing off to the main base station, there are many adverse effects, so it is desirable to avoid handing off to the main base station as much as possible. However, in the conventional base station switching method, the main base station If the signal strength becomes higher than that of the active base station even once, it will be handed off immediately to the remote base station regardless of whether the signal strength is continuously high at other times.
[0010]
Therefore, the present invention has been made in view of such problems, and provides a mobile station of a CDMA communication system that avoids handing off to a remaining base station whose signal strength is not continuously high. Objective.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the mobile station of the present invention according to claim 1 is a mobile phone system that uses a code division multiple access system composed of at least a mobile station and a base station. Detection means for detecting the strength of a signal from the base station, means for searching for another base station having a signal strength greater than the signal strength from the currently connected base station, and the searched base station Means for determining whether it is a neighbor base station located in the vicinity of the base station to which the communication is connected, or a remaining base station other than that, and when it is determined to be a main base station, handoff to the main base station is performed. Handoff control means for temporarily prohibiting, and the handoff control means detects the signal strength from the remote base station in a state where handoff is temporarily prohibited. Means for detecting a predetermined number of times, and when the average value of the signal strength of the predetermined number of times is larger than the signal strength from the currently connected base station, canceling the prohibition and handing off to the main base station To do.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Configuration of mobile station>
FIG. 1 is a block diagram showing a configuration of a mobile station in the CDMA communication system according to the present embodiment. As shown in the figure, mobile station 100 in a CDMA communication system includes despreading modulation section 101, signal strength calculation section 102, search control section 103, search information storage section 104, and PN sequence generation section 105. Composed.
[0013]
The search information storage unit 104 includes a base station number in communication, a list of neighbor base station numbers sent from the active base station (referred to as a neighbor list), and an interval number R_INC for searching the main base station. Store search information. The neighbor list and R_INC are received and stored from the active base station. FIG. 2 shows an example of search information. As shown in the figure, the active base station is the base station 7, the neighboring base stations are the base station 2, the base station 8, the base station 10, the base station 12, and the base station 14, and the interval for searching the main base station The state where the number is 5 is shown.
[0014]
When the search control unit 103 instructs the base station number, the PN sequence generation unit 105 generates a PN sequence (spreading code) having the number as an offset and sends it to the despreading modulation unit 101.
[0015]
Despreading modulation section 101 performs inverse conversion modulation with the PN sequence sent from PN sequence generation section 105, and extracts a pilot signal from a base station that is spread-modulated with the PN sequence.
[0016]
The signal strength calculation unit 102 calculates the strength of the pilot signal for each base station transmitted from the despreading modulation unit 101. More specifically, a value Ec / Io obtained by dividing the energy Ec of the signal for each base station by the total energy Io of the signal is calculated and used as the signal strength.
[0017]
The search control unit 103 is the most characteristic component in the present embodiment. The search control unit 103 refers to the search control information storage unit 104, specifies a base station to be searched, and assigns the base station number to the PN sequence generation unit. Sent to 105.
[0018]
The search control unit 103 performs a search in the order shown in the following (A1). (A1) The search is repeated with this as one cycle in the order of the active base station, all neighbor base stations, and the main base station for each R_INC.
[0019]
For example, when the active base station is 7, the neighbor base station is {2, 8, 10, 12, 14} and R_INC is 5, as in the state shown in FIG. 2, {7, 2, 8, 10, 12 , 14, 0}, {7, 2, 8, 10, 12, 14, 5}, {7, 2, 8, 10, 12, 14, 15}... Here, regarding the third cycle, since the base station 10 is a neighbor base station, this is skipped, and the base station 15 having a number obtained by adding R_INC (= 5) is selected.
[0020]
Further, the search control unit 103 determines the handoff of the base station based on the following criteria (B1) and (B2).
(B1) If the maximum value of the signal strength of the neighbor base station is greater than the signal strength of the active base station, handoff to the maximum neighbor base station is performed.
[0021]
In other words, the signal strength of the neighbor base station was high when it happened to be measured, and even if it was originally small, it was handed off to a nearby base station that was more suitable immediately after handoff, and the signal strength was high. Even if there is no guarantee that this is continuing, there will be little adverse effects, so we will hand off immediately. (B2) If the signal strength of the main base station is greater than the signal strength of the active base station, the main base station is shifted to the confirmation mode with the main base station as the confirmation target main.
[0022]
That is, when the signal strength of the main base station is high, the mode immediately shifts to a confirmation mode in which the signal strength of the base station is confirmed without any handoff to the main base station. Here, in order to distinguish from the confirmation mode, the state before shifting to the confirmation mode is referred to as a normal mode.
[0023]
Next, a search method in the confirmation mode will be described.
[0024]
In the confirmation mode, the search control unit 103 performs a search in the order shown in (C1) below. (C1) After searching the set of active base stations and all neighboring base stations a predetermined number of times N, a search is performed for the confirmation target main base station, and this search is repeated as one cycle.
[0025]
For example, as in the state shown in FIG. 2, when the active base station is 7 and the neighbor base station is {2, 8, 10, 12, 14}, the predetermined number N is set to 3 and the base station 15 performs the confirmation target Then, in the order {7, 2, 8, 10, 12, 14, 7, 2, 8, 10, 12, 14, 7, 2, 8, 10, 12, 14, 15} Search is performed as one cycle.
[0026]
In the confirmation mode, the search control unit 103 determines handoff of the base station based on the following criteria (D1) and (D2). (D1) If the maximum value of the signal strength of the neighbor base station is larger than the signal strength of the active base station, handoff to the maximum neighbor base station is performed.
[0027]
That is, even in the confirmation mode, if a neighbor base station having a high signal strength is found, the handoff to that neighbor base station is assumed. (D2) If the signal strength of the main base station to be confirmed is greater than the signal strength of the active base station, the counter is incremented, and if the counter value reaches a predetermined value R, handoff to the main base station is performed. On the way, when the signal strength of the confirmation target main base station becomes equal to or lower than the signal strength of the active base station, the confirmation mode is terminated at that time and the normal mode is restored.
[0028]
In other words, the signal strength of the remaining base station is likely to fluctuate and the handoff to the remaining base station is bad, so only when it is confirmed that it is certain that the signal strength is high, It shall be handed off.
[0029]
<Search operation in normal mode>
Next, a search operation in the normal mode in the mobile station according to the present embodiment will be described.
[0030]
FIG. 3 is a flowchart showing a search operation procedure in the normal mode.
[0031]
First, the search control unit 103 refers to the search information storage unit 104, specifies a base station that is an active base station, and generates a PN sequence of the active base station, thereby generating a base station from the despreading modulation unit 101. The station signal is extracted, and the signal strength calculation unit 102 obtains the signal strength from the active base station (step S201).
[0032]
Next, the search control unit 103 refers to the search information storage unit 104 to identify a base station to be a neighbor base station, and in the same way as the active base station, the signal strength for all the neighbor base stations. Is obtained (step S202).
[0033]
When the maximum value of the signal strengths from the neighbor base station is larger than the signal strength from the active base station, the search control unit 103 performs handoff to the neighbor base station that outputs the signal having the maximum strength. (Steps S203 and S204).
[0034]
On the other hand, when the maximum value of the intensity of the signal is equal to or less than the intensity of the signal from the active base station, the search control unit 103 performs one main search. That is, the search control unit 103 refers to the search information storage unit 104, selects any one base station (remain base station) that is neither active nor a neighbor, and obtains signal strength for the base station (step S205). ).
[0035]
When the strength of the signal from the main base station is larger than the strength of the signal from the active base station, the search control unit 103 shifts to the confirmation mode with the main base station as the confirmation target main (steps S206 and S207).
[0036]
On the other hand, when the maximum value of the signal strength is less than or equal to the signal strength from the active base station, the search control unit 103 returns to step S201 and repeats the processing (step S206).
[0037]
In the next step S205, the search control unit 103 specifies a base station having a number obtained by adding the number of search intervals in the search information storage unit 103 to the number of the previously selected main base station, and the base station is active. However, if it is not a neighbor (remain), the base station is searched, and if the base station is not a main, the main station to be searched is checked by checking whether the base station with the number of search intervals added is the main. And conduct a search for the main.
[0038]
<Search operation in confirmation mode>
Next, the search operation in the confirmation mode in the mobile station according to the present embodiment will be described.
FIG. 4 is a flowchart showing a search operation procedure in the confirmation mode.
[0039]
First, the search control unit 103 sets r indicating the number of times of confirmation of the confirmation target remain (the number of times the signal strength has become greater than active) to 0, and sets n indicating the number of times the neighbor base station has searched to 0. (Steps S301 and S302).
[0040]
Next, the search control unit 103 refers to the search information storage unit 104, identifies the base station that is the active base station, and generates the PN sequence of the active base station, thereby generating the active from the despreading modulation unit 101. The signal of the base station is taken out, and the signal strength from the active base station is obtained from the signal strength calculation unit 102 (step S303).
[0041]
Next, the search control unit 103 refers to the search information storage unit 104 to identify a base station to be a neighbor base station, and in the same way as the active base station, the signal strength for all the neighbor base stations. Is obtained (step S304).
[0042]
When the maximum value of the signal strengths from the neighbor base station is larger than the signal strength from the active base station, the search control unit 103 performs handoff to the neighbor base station that outputs the signal having the maximum strength. (Steps S305 and S306).
[0043]
On the other hand, when the maximum value of the intensity of the signal is equal to or less than the intensity of the signal from the active base station, the search control unit 103 increments the search count n of the neighbor base station (step S307).
[0044]
When the number n of searches is less than the number N to be searched, the search control unit 103 returns to step S303 and repeats the active and neighbor search (steps S308 and S303).
[0045]
On the other hand, when the number n of searches reaches the number N of times to be searched, the search control unit 103 searches for the confirmation target main. That is, the search control unit 103 obtains the strength of the signal for the confirmation-target main base station in the same manner as for the active base station (step S309).
[0046]
When the signal strength of the confirmation target main base station is equal to or lower than the signal strength from the active base station, the search control unit 103 ends the confirmation mode, shifts to the normal mode, and starts from step S201 of the normal mode shown in FIG. Are performed (steps S310 and S311).
[0047]
On the other hand, when the strength of the signal of the confirmation target main base station is larger than the strength of the signal from the active base station, the search control unit 103 increments the number of times r of confirmation of the confirmation target main (step S312).
[0048]
When the number r of confirmed times is less than the number of times R to be confirmed, the search control unit 103 returns to step S302 and repeats the processing from the active search (steps S313 and S302).
[0049]
On the other hand, when the number r of times of confirmation becomes the number of times R to be confirmed, the search control unit 103 hands off to the confirmation target main (steps S313 and S314). <Summary>
As described above, in the mobile station in the CDMA communication system according to the present embodiment, when the signal strength of the main base station is larger than the signal strength of the active base station, immediately without handing off to the main base station, The signal strength of the remote base station is detected a predetermined number of times, and only when both of them are larger than the signal strength of the active base station, handoff to the remote base station is performed. Although it is large and is not large continuously, it is possible to avoid a situation in which handoff is performed to the main base station.
<Modification>
(1) About the confirmation method In this embodiment, the signal strength from the main base station is handed off to the main base station on condition that the signal strength from the active base station becomes larger all the time than the signal strength from the active base station. However, the present invention is not limited to this. For example, when the average value measured a predetermined number of times becomes larger than the signal strength of the active base station, the handoff to the main base station may be performed. Alternatively, if the number of times measured a predetermined number of times is larger than the signal strength of the active base station, handoff to the main base station may be performed.
(2) Maintenance of confirmation mode In the present embodiment, the fact that it was the confirmation target of the previous confirmation target main base station after handing off to the neighbor base station in the confirmation mode is not considered in the search. However, it is not limited to this.
[0050]
In the confirmation mode, when handing off to the neighbor base station, the subsequent search for the main base station may be performed from the main base station that was the confirmation target in the previous confirmation mode, or the The search may be continued only for the base station.
[0051]
Further, in the confirmation mode, after hand-off to the neighbor base station, when the same residual as the previous one is selected as the confirmation target residual, the counting may be performed from the previous counter value. For example, when it has been confirmed up to 10 times, the counter value may be incremented from 10.
[0052]
【The invention's effect】
As is apparent from the above description, the mobile station of the CDMA communication system according to the present invention includes a detecting means for detecting the strength of the signal from the base station, and a signal larger than the signal strength from the base station that is currently in communication connection. Means for searching for another base station having strength, and whether the searched base station is a neighbor base station located in the vicinity of the currently connected base station or another main base station. It is characterized in that it comprises means for determining and handoff control means for temporarily prohibiting handoff to the main base station when it is determined to be the main base station.
[0053]
As a result, when the signal strength from the remote base station is higher than the signal strength from the base station in communication connection, the signal strength continues rather than immediately handing off to the remote base station. Since the handoff to the remote base station is postponed until it is surely guaranteed, it is possible to avoid handing off to the remote base station that is not reliably guaranteed that the signal strength continues to be high.
[0054]
Here, the handoff control means causes the detection means to detect the signal strength from the remote base station a predetermined number of times while handoff is temporarily prohibited, and the average value of the signal strength of the predetermined number of times is actually communicated. When the signal strength from the connected base station is larger, the prohibition is canceled and the handoff to the main base station is performed.
[0055]
As a result, when the signal strength from the remote base station is larger than the signal strength from the base station in communication connection over all of the detected times, the signal strength from the remote base station continues with considerable certainty. Therefore, it is possible to avoid the handoff of the re-main base station that is not surely guaranteed that the signal strength is continuously high.
[0056]
Here, the handoff control means, while handoff is temporarily prohibited, causes the detection means to repeatedly detect the signal strength from the main base station and continuously detect the signal from the main base station a predetermined number of times. When the signal strength is larger than the signal strength from the currently connected base station, the prohibition is canceled and handoff to the relevant base station is performed.
[0057]
As a result, when the average value obtained by detecting the signal strength from the re-main base station a predetermined number of times is larger than the signal strength from the base station in communication connection, the signal strength from the re-main base station continues with considerable certainty. Therefore, it is possible to avoid the hand-off of the re-main base station that is not surely guaranteed that the signal strength is continuously high.
[0058]
Here, the handoff control means further causes the detection means to detect the signal strength from the neighbor base station between detection of the signal strength from the main base station, and the signal strength from the neighbor base station is actually connected to the communication. If it is larger than the signal strength from the base station in the middle, handoff to the neighbor base station is performed.
[0059]
As a result, if the signal strength from the neighbor base station becomes larger than the signal strength from the base station in communication connection while checking whether the signal strength from the remaining base station is continuously high, the neighbor Since handoff is performed to the base station, it is possible to handoff to a neighbor base station with less harmful effect after handoff than the main base station.
[0060]
Here, the handoff control means causes the detection means to detect the signal strength from the neighbor base station more frequently than the frequency to detect the signal strength from the main base station.
[0061]
As a result, the frequency of detecting the signal strength from the neighbor base station while checking whether the signal strength from the main base station is continuously high is high, so the neighbor base station in which the signal propagation environment is improved Can quickly discover and handoff to its neighbor base station.
[0062]
Here, the handoff control means is characterized in that, even after handing off to a neighbor base station, the detection means gives priority to detection of the signal strength from the remote base station.
[0063]
As a result, even when a handoff is performed to a neighbor base station, the main base station that has suspended the handoff last time is the most promising candidate for a base station that can be handed over, so the signal strength from the main base station should be detected with priority. Thus, a base station suitable for handover can be quickly found.
[0064]
Further, the communication method of the mobile station of the CDMA communication system according to the present invention includes a step of detecting the strength of a signal from the base station, and another signal having a signal strength greater than the signal strength from the currently connected base station. A step of searching for a base station, and a step of determining whether the searched base station is a neighbor base station located in the vicinity of the currently connected base station, or a remaining base station other than that, A step of temporarily prohibiting handoff to the remote base station when it is determined that the remote base station is determined.
[0065]
As a result, when the signal strength from the remote base station is higher than the signal strength from the base station in communication connection, the signal strength continues rather than immediately handing off to the remote base station. Since the handoff to the main base station is postponed until it is guaranteed with certainty, it is possible to avoid handing off to the main base station that is not reliably guaranteed that the signal strength continues to be high.
[0066]
As described above, the present invention can solve the most serious problem in the mobile communication system using the CDMA system in which communication connection with an inappropriate base station is established, and its practical effect is extremely large.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a mobile station in a CDMA communication system according to an embodiment of the present invention.
FIG. 2 shows an example of search information.
FIG. 3 is a flowchart showing a search operation procedure in a normal mode.
FIG. 4 is a flowchart showing a search operation procedure in a confirmation mode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Mobile station 101 Despreading modulation part 102 Signal strength calculation part 103 Search control part 104 Search information storage part 105 PN sequence generation part

Claims (1)

In a mobile phone system using a code division multiple access method composed of at least a mobile station and a base station,
The mobile station
Detecting means for detecting the intensity of the signal from the base station;
Means for searching for another base station having a signal strength greater than the signal strength from the currently connected base station;
Means for determining whether the searched base station is a neighbor base station located in the vicinity of the currently connected base station, or another main base station;
When it is determined as a remote base station, it comprises handoff control means for temporarily prohibiting handoff to the remote base station,
The handoff control means causes the detection means to detect the signal strength from the remote base station a predetermined number of times while handoff is temporarily prohibited, and the average value of the signal strength of the predetermined number of times is currently in communication connection. Canceling the prohibition and handing off to the concerned base station when the signal strength from the base station is larger than the signal strength;
A mobile phone system characterized by

Images