JPH0693649B2 - Mobile communication system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a channel allocation method and a channel connection / switching control method for small-zone configuration mobile communication that achieves high frequency utilization.

(Prior Art) Conventionally, there is an interleaved channel arrangement as a technology for increasing the frequency utilization rate of mobile radio communication. The interleaved channel arrangement is a method of using frequencies offset by about 1/2 of the channel spacing in addition to the frequencies arranged at the normal channel spacing, and the number of usable channels can be greatly increased.

(Problems to be solved by the invention) However, since the distance from the adjacent channel becomes smaller than the occupied bandwidth, the adjacent channel interference becomes a problem, and the ratio D / U of the desired wave and the interference wave of the adjacent channel is a certain value. If the above is not secured, there is a drawback that the call quality deteriorates significantly. Further, in order to maintain good call quality, adjacent channels cannot be arranged in nearby zones, so that the equivalent increase in the number of channels becomes small, and there is a drawback that the frequency utilization rate cannot be improved. Furthermore, when the channels are arranged in the normal 1 / 2-spaced channel, the carrier of the adjacent channel drops to the frequency at the end of the reception filter for removing the signal of the adjacent channel due to a slight frequency shift, so the frequency shift As the call quality changes sensitively, strict frequency stability is required, or if frequency stability cannot be obtained, it is necessary to arrange a channel with a margin to allow for frequency shift, and the frequency utilization rate will decrease. There was a drawback. Adjacent channel interference depends on the modulation signal of the adjacent channel. For example, in the case of no conversion, the leakage power to the adjacent channel is small and sufficient quality can be obtained even if D / U is insufficient. Also, adjacent channels are arranged so that the call quality around the zone satisfies the specified value, but in this case, excessive D / U is obtained in the center of the zone. As described above, there is a drawback in that the use of frequency is wasteful.

An object of the present invention is to provide a small zone configuration mobile communication system with high frequency utilization rate by eliminating waste of frequency utilization and solving the problem that strict conditions for hardware such as frequency stability are imposed. .

(Means for Solving Problems) In the present invention, a plurality of types of groups having different adjacent channel interference probabilities are arranged in each zone, and a channel group is selected and connected / switched in accordance with an interference state at the time of each call. Control is the main feature. In the conventional technique, the degree of interference between adjacent channels of each channel is the same, but in the present invention, different types of channel groups are arranged, and adjacent channel interference is detected in each base station and mobile station. They differ in that they have means.

(Example) First, a general small zone configuration mobile communication system will be described.

FIG. 1 is a diagram for explaining a general small zone configuration mobile communication system. 1 is a service area, 2 is a wireless zone, 3 is a base station, and 4 is a mobile station. A large number of base stations 3 are provided in the service area 1, and when a call request is made between the base station 3 and a mobile station 4 in a wireless zone covered by the base station, a wireless channel is set and a call is made. . When the mobile station 4 moves across the zone, it is possible to switch to the empty channel of the base station of the transfer destination zone. FIG. 2 shows an example of wireless channels arranged in each zone. The number in each zone indicates the number of the wireless channel group to be arranged. Since the same channel can be used in the distant zones, the frequency is repeatedly used in units of the seven zones indicated by the bold lines in FIG. Channel numbers indicate the order on the frequency axis, and adjacent numbers indicate adjacent channels. In the example of FIG. 2, the channels in each zone are arranged so that adjacent channels exist in two zones out of six adjacent zones.

When different frequencies are used for communication from the base station to the mobile station (downlink) and from the mobile station to the base station (uplink), the channel numbers shown here represent the two radio frequencies of the uplink and downlink. You can think of it. For example, a car telephone system currently being used uses a pair of channels with a frequency difference of several tens of MHz at regular intervals, and if one is determined, the other is also determined.

Also, since the number of channels required for one wireless zone is plural, the numbers in FIG. 2 are interpreted as the numbers of the channel groups. For example, when six channels are required for each wireless zone, FIG. As shown in, the group number of 1 is considered to represent 6 channels of channel numbers 1, 8, 15, 22, 29, and 36.

FIG. 4 shows the channel arrangement of the embodiment of the present invention. FIG. 5 shows the channel numbers of the channels that make up the channel group of each number in FIG. Channels are classified into two groups, group A and group B. Group A is a channel group in which adjacent channels exist in two adjacent cells, and group B is a channel group in which the adjacent channels are not used in other zones. That is, as shown in FIG. 5, every other B is used. The group A is a channel group having a high adjacent channel interference probability, and the group B is a channel group having a small adjacent channel interference probability. In the present invention, a means for detecting the amount of adjacent channel interference is provided,
Channels to be assigned are selected from the A group and the B group according to the interference amount, and connection control and switching control are performed.

As means for detecting adjacent channel interference, conventionally used for detecting same channel interference (1) method by beat component of received signal envelope, (2) quality monitoring signal such as pilot tone or control signal during communication It is sufficient to use a method of detecting the deterioration of. Further, (3) the method of simultaneously using the reception level measurement of the own channel and the adjacent channel is more effective. The method (3) requires two receiving systems, so there is no particular problem in the base station, but it is disadvantageous in the mobile station in terms of economy and reduction in size and weight. However, considering that the interference states of the uplink and downlink have a certain degree of correlation, it is sufficient if the mobile station is equipped with the means (1) and (2).

FIG. 6 shows an example of a control flow chart for connection / switching control according to the first embodiment of the present invention. When a request for setting a wireless channel occurs when a mobile station originates a call or receives an incoming call, first, a group A channel having a high probability of interference is assigned. If the mobile station is in a disadvantageous position, or the frequency of the adjacent channel drifts and is approaching,
When the adjacent channel interference of the specified value or more occurs, the adjacent channel interference probability is judged by the interference detecting means and is small B
Switch to the group channel. If there is no adjacent channel interference, the group A channel is used as it is. If all the channels of the group A are used when selecting the channel at the start of the call, the channels of the group B may be used.

A connection control according to another embodiment of the present invention will be described.

By using the method of determining the interference state before the call channel is set, it is possible to allocate the channels of the group A having a high interference probability and avoid the temporary interference deterioration before switching when the interference occurs. To determine the interference state before setting the call channel, measure the reception level U of the adjacent channel of the channel to be newly allocated by using the electric field monitoring dedicated receiver equipped in the base station or an unused transceiver Since the state of the mobile device, that is, the distance to the base station and the like can be estimated from the reception level D at the time of transmitting and receiving the control signal for notifying the outgoing call or the incoming call, the interference state with the adjacent channel is estimated. it can. FIG. 7 shows an example of a flow chart of judgment for channel assignment. When the reception level D of the local station is larger than a certain threshold value Dth, the A group is basically allocated, and when not, the B group is allocated in principle. However, if there is no empty channel in the relevant channel group, the D / U satisfies the specified value. If it is OK to check, it is allowed to allocate the other group. In this setting method, it is determined whether the mobile station is in the peripheral portion or the central portion of the zone according to the reception level D of its own station, and it is determined which of the group A and the group B is to be assigned. If there is no empty channel to be assigned to the group A, even if it is assigned to the group B, interference does not occur in most cases, and therefore assignment is possible without any problem. If there is no empty channel to be assigned to group B, there is a high possibility that interference will occur if it is assigned to group A, but the adjacent channel is used by confirming that the level U of the adjacent channel measured in advance is very low. This is a method of assigning the A group when it can be determined that no interference occurs.

FIG. 8 shows an example of a control flow chart for connection control according to another embodiment of the present invention. This is a method in which when the call volume is large, the channel group with a high interference probability is assigned, and when the call volume is small, the channel with a low interference probability is assigned. According to this method, channel allocation is performed with the frequency utilization rate taken into consideration first when the bus is busy, and interference deterioration is likely to occur, but it is possible to reliably guarantee speech quality when traffic is low.

FIG. 9 shows an example of a control flow chart of switching control according to another embodiment of the present invention. Even after switching to group B due to interference, when the state changes and interference no longer occurs, A
It is a method of returning to the group. When D / U is below a required value (D / U) req, switching to group B is performed, and when D / U- (D / U) req exceeds a certain value Δ in group B, switching to group A is performed. By preventing the channel from staying in the group B in which the interference probability is unnecessarily small, it is possible to increase the probability that the empty channel remains when the group B is needed due to interference.

FIG. 10 shows an example of a control flow chart of switching control according to another embodiment of the present invention. If all the channels of the group B are in use when there is interference and it becomes necessary to switch, the mobile station that was talking after switching to the group B channel caused an interference in the middle of the call There is a possibility that it is in a good state, so it is a method of forcibly switching it to the A group and switching to the channel where interference is occurring now. As a method of selecting the channel to be forcibly switched, select the channel with the maximum D / U, select D / U- (D / U) req randomly from the channels that exceed a certain value Δ, connect to group B, and then It is conceivable to select the one with the longest elapsed time.

Next, switching control according to another embodiment of the present invention will be described.

As a switching algorithm, a method of positively switching channels within the same group is more effective. Since the interference probability is the same on the average since they are in the same group, the average value of the reception level (in the section of about 10 m) fluctuates by several dB when the mobile station moves for several tens of meters, so it is relatively short. This is because the interference state is different even within the same channel group if observed over time. When the frequency of channel switching within the same group is high, it can be judged that the long section average D / U does not meet the required value. Fig. 11 shows an example of the control flow chart. The number of times of switching within the group A is the number of times of switching per fixed time, for example, one minute, and when this exceeds Cth, the channel switching to the group B is performed. In this example, the determination for switching the channel from the B group to the A group is made by the switching control of the fifth item, that is, when the D / U exceeds a certain threshold value.

FIG. 12 shows an example of a control flow chart of switching control according to another embodiment of the present invention. This is a method of actively switching channels within the group as in the previous section. D / U is measured by both short-term average value and long-term average value, and the measured value is directly used for switching control. That is, the channels within the group are switched for the short-term average value, and the groups are switched for the long-term average value.

FIG. 13 shows an example of a control flow chart of connection control according to another embodiment of the present invention. Subscribers are divided into groups of different service grades at the time of subscription, and this is a method of selecting channels according to the subscriber groups and allocating channels. For example, by dividing into two types of subscriber groups, a low charge group (a type) and a high charge group (b type), good call quality is guaranteed for subscribers in the high charge group and Subscribers should be aware that interference is likely to occur at a low price. In this example, if an attempt is made to allocate a channel of group B for a subscriber of type b and all are in use, then an empty channel is assigned to group A if it is in use.
If the channels of group A are all in use to allocate channels of group a for subscribers of type a, if there are more empty channels than those in group B, then they are allocated.

In this way, by performing channel connection control / switching control according to the interference state, it is possible to improve the spatial spatial utilization rate and temporal utilization rate of the frequency, and especially to improve the frequency utilization rate described below. is there.

The first effect of the present invention is to reduce the load on the hardware for high stabilization of the radio frequency necessary for interleaving the radio channels. When the wireless channels are interleaved, adjacent channels (that is, channels with a shorter frequency difference than when not interleaved) can be used if the DU ratio of adjacent channel interference can be secured to a certain value or more. Figure 14 shows the relationship between the frequency difference between adjacent channels and the required D / U for adjacent channels. Required D / U is the D required for the baseband S / N or call quality to meet the specified value.
/ U. fsp indicates the channel spacing. Centered at fsp, this figure shows that the required D / U increases with decreasing frequency spacing due to frequency drift. In the case of interleaving at half intervals as shown in this figure, the carrier of the adjacent channel drops to the frequency at the end of the receiving filter for removing the signal of the adjacent channel due to a slight frequency shift, so The required D / U changes sensitively to the deviation. Therefore, if there is no frequency drift, even if the adjacent channel can be used in the adjacent zone or the next adjacent zone, it can be used only in the zone farther away if there is some frequency drift. If the present invention is not used, it is necessary to perform channel arrangement so as to guarantee the communication quality even for mobile stations that have drifted in frequency, so there are many restrictions on channel arrangement and the required number of channels is large. is necessary.
It is technically difficult and economically disadvantageous to obtain high frequency stability because the mobile station is used in a severe situation. However, not all mobile stations drift to the limit of the standard value of frequency stability, and only some mobile stations. Therefore, according to the conventional technology, since excessive D / U is guaranteed for many mobile stations, it is disadvantageous in terms of frequency utilization rate, and frequency drift is considered first and frequency drift is considered. If the channel arrangement is performed without doing so, the speech quality of some drifted mobile stations cannot be maintained, and that mobile station causes a problem of quality deterioration due to interference with other mobile stations. According to the present invention, a mobile station with little frequency drift is assigned a channel group of channels arranged so that the frequency utilization rate is high, and a channel that does not cause adjacent channel interference to a mobile station with frequency drift is assigned. assign. Therefore, it does not require high frequency stability,
It is possible to improve the frequency utilization rate by interleaving and ensure the call quality.

The second effect of the present invention is that the frequency utilization factor is improved by applying it to the modulated signal and selecting the channel interval.
When analog FM is used, the spread of the spectrum is determined by the modulation signal, and the spectrum hardly spreads during silence during voice communication. Therefore, the amount of adjacent channel interference is small, and the D / U to be secured may be small. In a normal conversation,
The rate of time that voice is present is less than 1/2, and there is a call with a small amount of adjacent channel interference depending on the conversation content. A voice switch (VO that turns transmission on / off depending on the presence or absence of voice)
X) is mainly a technique for reducing power consumption, but when this technique is used, the carrier disappears when there is no voice, so even in the situation where the carrier of the adjacent channel leaks due to frequency drift. Adjacent channel interference is reduced. In the prior art, a certain DU ratio was secured regardless of the spread of the modulation spectrum, so there was a waste of frequency utilization. According to the present invention, adjacent channels can be assigned to calls having a small spectrum spread even if D / U is not sufficient for a normal design value. When the spectrum spreads steadily due to data transmission using a modem and the adjacent channel interference becomes a problem, it is detected and the quality deterioration can be avoided by switching to the channel group which does not generate the adjacent channel interference. In this way, it is possible to eliminate waste of frequency use on the frequency axis without degrading quality.

The effect of increasing the frequency utilization rate according to the present invention described above is quantitatively evaluated by the increase amount of the subscriber capacity. Focusing on the long-term average value, the adjacent channel interference D / U is
It is determined by the distance ratio d ₁ / d ₂ of the U station. FIG. 15 is a diagram for explaining a region where interference occurs. 1a is its own base station, 2a is an interfering base station, 3a is its own zone, and 4a is an interference zone. In the D zone and U zone shown in FIG. 15, the area satisfying d ₁ / d ₂ corresponding to the required D / U when there is no frequency drift is indicated by A in the figure.
Within the area of. Required D / U when frequency drift occurs
, The area that satisfies the required D / U is significantly narrowed to fall within the area indicated by B, and the speech quality cannot be guaranteed for the mobile station in the shaded area in FIG. Channel spacing 12.5kHz, occupied bandwidth 1kHz
If you consider the frequency drift of 2-3kHz,
It is difficult to arrange adjacent channels in the next adjacent zone, interleaved channels cannot be arranged, and if the present invention is not used, group A cannot be arranged. When using the present invention,
In the mobile stations in the shaded area in the figure, interference is a problem due to frequency drift. The ratio of the mobile stations to the mobile stations in the entire zone is (1-p). Let it be p. The group A or the group B is assigned according to the interference state of each mobile station, but if there is no free space in the group A when trying to assign the group A, the group B is assigned and vice versa. However, in the former case, the channel of the B group can be used unconditionally, but in the latter case, the condition of the allocation is that the channel of the U zone having an interference relationship with the channel of the A group to be allocated is unused. As described above, when the overflow calls of both groups are processed, the overflow calls can be approximated by Poisson's occurrence, and the relationship between the a-erlang and the call loss rate B can be obtained for the call origination amount in the zone. Here, S ₁ and S ₂ are the channel numbers for the A group and the B group, respectively, which are arranged in each base station. If the total number of channels given to the system is S ₀ , then S ₀ = 7S ₁ + 14S ₂ . When S ₀ = 120,
Fig. 16 shows the relationship between (S ₁ ) / (S ₁ + S ₂ ) and the volume of call origination at a call loss rate of 3%. The horizontal axis is the ratio of the number of channels in Group A to the total number of channels in one station, and the horizontal axis = 0 is
The conventional method which does not arrange the channel of A group is shown.
There is an optimum point in the distribution of the number of channels to be allocated to the A group and the B group, and if the value is set to an appropriate value and the channel allocation is performed, evaluation is made with p = 0.7. It can be seen that the capacity can be increased.

FIG. 17 shows another example of the channel arrangement of the present invention. In this example, the B group is a channel group in which no adjacent channels are arranged, and the A group is a group in which adjacent channels are arranged in the next adjacent zone. Figure 18 shows the calculation results of the subscriber increase effect in this case. Since the effect of increasing the number of channels is small,
Although the effect seems smaller than that in Fig. 16, in the case of this arrangement method, since the interference probability of group A is small, it can be evaluated at a value of p larger than in the previous example.

In fact, the traffic distribution is uneven, and traffic is concentrated in some areas. The capacity of the system is mostly determined in the area where traffic is concentrated. The wireless zone in the area where traffic is concentrated has more channels than other wireless zones. There are some channels that are in interference with the channels placed in the wireless zone of the area where the traffic is concentrated, and some channels are not placed in the surrounding zones. A large number of channels can be arranged. Such an example is shown in FIG. The numbers in the figure represent channel numbers. If a large number of channels are required only in the wireless zones shown by the shaded areas, all the channels having adjacent channel interference relationships shown by double lines in the figure are not placed in the other wireless zones. Considering this, the present invention becomes more effective in a disadvantageous area where traffic is concentrated.

(Effects of the Invention) As described above, in the present invention, the channels adapted to the interference state of each call are allocated, so that the temporal, spatial, and frequency utilization efficiency of the frequency is improved, and the bandwidth usable as the system If is constant, the number of subscribers that can be accommodated can be greatly increased. Further, there is an advantage that the problem of high frequency stabilization, which is a problem when introducing the interleave channel arrangement, can be avoided.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a general small zone configuration mobile communication system. FIG. 2 shows an example of arrangement of wireless channels in general small zone mobile communication. FIG. 3 shows the correspondence between channel group numbers and channel numbers. FIG. 4 shows an example of the channel arrangement of the present invention. FIG. 5 shows the channel numbers of the channels that make up the channel group of each number in FIG. FIG. 6 shows an example of a flow chart of the channel connection operation of the second aspect of the present invention. FIG. 7 shows an example of a flow chart of the channel connection operation of the third aspect of the present invention. FIG. 8 shows an example of a flow chart of the channel connection operation of the fourth aspect of the present invention. FIG. 9 shows an example of a flow chart of the channel switching operation of the fifth aspect of the present invention. FIG. 10 shows an example of a flow chart of the channel switching operation of the sixth aspect of the present invention. FIG. 11 shows an example of a flow chart of the channel switching operation of the seventh aspect of the present invention. FIG. 12 shows an example of a flow chart of the channel switching operation of the eighth aspect of the present invention. FIG. 13 shows an example of a flow chart of the channel connection operation of the ninth aspect of the present invention. Fig. 14 shows the frequency difference between adjacent channels and the adjacent channels required.
The D / U relationship is shown. FIG. 15 is a diagram for explaining a region where interference occurs. Figure 16 shows the relationship between the allocation of channels and the volume of call origination at a loss rate of 3%. FIG. 17 shows another example of the channel arrangement of the present invention. Figure 18 shows the relationship between the allocation of channels and the volume of call origination at a loss rate of 3%. FIG. 19 shows another example of the channel arrangement of the present invention. DESCRIPTION OF SYMBOLS (FIG. 1) 1; service area, 2; wireless zone, 3; base station, 4; mobile station (FIG. 15) 1a; own base station, 2a; interfering base station, 3a; own zone, 4a Interference zone,

Claims (9)

[Claims] 1. A service area is divided into a number of zones,
In mobile communication where the same radio channel is repeatedly used in zones separated by a certain distance, frequency allocation is performed at a channel interval smaller than the occupied bandwidth of one radio channel, and adjacent channel interference is created by varying the adjacent channel interval in each radio zone. Arrangement of multiple types of channel groups with different probabilities and co-channel interference probabilities, equipped with means to measure the amount of adjacent channel interference in both or one of the base station and mobile station in each zone, and use according to the measurement results A mobile communication system characterized by selecting a wireless channel to be used from a plurality of types of channel groups and performing connection control and switching control. 2. In the mobile communication system according to claim 1, when a request for setting a radio channel is made when a mobile station originates or receives an incoming call, first, a channel of a group having the highest interference probability. Assign connection control, then
A mobile communication system characterized by performing channel switching control to a channel of a group having a lower interference probability when interference of a specified value or more is detected. 3. The mobile communication system according to claim 1, further comprising means for measuring a reception level, and transmitting with a reception level U of a channel to be assigned to a newly generated call and a reception level U of an adjacent channel. Alternatively, the reception level D at the time of exchanging a control signal for notifying an incoming call is measured, and when the reception level D of the local station is higher than a certain threshold Dth, a group having a high interference probability, otherwise, a low interference probability. Assign a group of channels, but if there is no empty channel in the channel group, check the D / U is more than a specified value and perform connection control that allows other groups to be assigned. Communication method. 4. A mobile communication system according to claim 1, wherein when a call is newly made, a channel having a high interference probability is assigned when a call volume during the past fixed time is large, and the past fixed time is allocated. A mobile communication system characterized by performing connection control in which a channel of a group having a lower interference probability is assigned to a smaller call volume. 5. In the mobile communication system according to claim 1, when the amount of interference of a channel during a call exceeds a prescribed value, the channel is switched to a group of channels having a low probability of interference, and the value is smaller than that value. A mobile communication method characterized in that switching control is performed to switch to a channel of a group having a high interference probability when the value falls below a certain specified value. 6. The mobile communication system according to claim 1, wherein when there is a request for switching to a channel of a group having a low interference probability when the amount of interference of a channel in communication exceeds a certain specified value, the interference probability. When all the channels in the low group are in use, one of the channels in use is forcibly switched to the channel in the high interference probability group,
A mobile communication system characterized by performing switching control for switching a call for which a switching request has occurred to a channel of a group having a low interference probability. 7. In the mobile communication system according to claim 1, when the interference amount exceeds a certain specified value, the channel is switched to an empty channel in the same group, and when the switching frequency exceeds a certain value. , A mobile communication system characterized by performing switching control for switching to a channel of a group with a low interference probability. 8. The mobile communication system according to claim 1, wherein the amount of interference is measured by a short-term average and a long-term average.
Measured by type, when the short term average interference amount exceeds a certain specified value, the channel switching within the same group is performed, and the channel switching control between different groups is controlled according to the long term average interference amount. Mobile communication method. 9. A mobile communication system according to claim 1, wherein the subscribers are divided into groups, and at the time of channel connection, a channel group corresponding to the subscriber group is selected for connection control. Characteristic mobile communication system.