Mobile communication system with autonomous distributed type dynamic channel allocation scheme

A mobile communication system using an autonomous distributed type dynamic channel allocation scheme, in which each base station manages allocation priority levels for the available radio channels according to past records of channel use for each radio channel, and updates the allocation priority level of each radio channel by weighting past allocation accept/reject judgement results for each radio channel with weight factors which vary according to time intervals of the past allocation accept/reject judgement results from a current time. The mobile stations can be grouped into N groups according to states of the mobile stations and N sets of allocation priority levels for each radio channel in correspondence to these N groups can be managed at each base station. The thresholds for grouping the mobile stations can be determined according to past records of states of the mobile stations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a mobile communication system formed by 
base stations and mobile stations, and more particularly, to a channel 
allocation scheme used by each base station in establishing communications 
with mobile stations. 
2. Description of the Background Art 
A well known type of the mobile communication system currently in practical 
use as a portable telephone system or an automobile telephone system is a 
cellular system in which a communication service is provided by 
distributing a number of base stations over its service area, where each 
base station serves for a radio zone with a radius of about several km. 
In general, in order to utilize a finite amount of available radio channel 
resources efficiently, this type of a mobile communication system adopts 
the geographically repeated utilization of the radio channels in which the 
identical radio channel is used by more than one geographically distanced 
base stations. In this case, by making a channel reuse distance between 
the base stations which uses the identical radio channel as small as 
possible, the higher frequency utilization efficiency can be achieved, so 
that the system capacity can be increased within a condition of a constant 
frequency bandwidth given to the system. 
However, this channel reuse distance cannot be made unlimitedly smaller, 
because when this channel reuse distance is made smaller, there arises a 
problem of the interference from the identical radio channel or the 
interference from the neighboring radio channel in a case of an interleave 
scheme in which each radio channels are formed by allowing overlaps in the 
power at the side band of each radio channel in an FDMA (Frequency 
Division Multiple Access) system, which significantly lowers a 
communication quality. For this reason, there is a need to restrict the 
repeated utilization of the identical radio channel only among those base 
stations which are sufficiently distanced spatially to keep the 
interference within a certain tolerable level. 
The schemes for realizing this repeated utilization of the radio channels 
within such a practical condition include a fixed channel allocation 
scheme and a dynamic channel allocation scheme, of which the dynamic 
channel allocation scheme further includes a centralized control type 
dynamic channel allocation scheme in which a control station for 
controlling the channel allocations is provided with respect to a 
plurality of base stations, and an autonomous distributed type dynamic 
channel allocation scheme in which each base station allocates the radio 
channels autonomously and distributedly. 
The fixed channel allocation scheme fixedly allocates the radio channels to 
each base station according to the radio wave propagation state and the 
traffic distribution within the service area obtained either by the actual 
measurements or by the theoretical calculations. In general, this fixed 
channel allocation scheme is associated with problems that an enormous 
amount of efforts are required in obtaining a design for determining the 
fixed allocations, and that the re-designing is required at a time of the 
system expansion such as the addition of base stations, so that it has a 
very low adaptivity to a system expansion. In addition, the available 
radio channels of the entire system are to be divided into some number of 
groups and allocated to a number of base stations, so that there is a loss 
of efficiency of large groups, and therefore it cannot achieve the high 
frequency utilization efficiency. 
On the other hand, in the dynamic channel allocation scheme, it is possible 
to allocate the radio channels flexibly to some extent in accordance with 
the temporal variation and the spatial bias of the traffic, and all the 
available radio channels of the entire system are made to be usable by any 
base station of the system, so that the large grouping effect can be 
obtained, and consequently the frequency utilization efficiency can be 
improved compared with the fixed channel allocation scheme. 
However, in order to suppress the call loss rate or the interference 
probability to the minimum level, an enormous amount of data and quite 
complicated controls are necessary in general, and in a case of the 
centralized control type dynamic channel allocation scheme, it requires a 
considerable amount of signal traffic between each base station and the 
control station, while in a case of the autonomous distributed type 
dynamic channel allocation scheme; it requires many processing steps 
before the actual channel allocation can be made so that the connection 
delay becomes large. Thus, in the dynamic channel allocation scheme, how 
to realize a channel allocation scheme capable of achieving a less control 
load and a higher frequency utilization efficiency at the same time 
presents an important practical issue to be resolved. 
To this end, there has been a proposition of a channel allocation scheme 
for realizing such an autonomous distributed type dynamic channel 
allocation by a relatively simple control method, as disclosed in Japanese 
Patent Application No. 61-244137 (1986) and Japanese Patent Application 
No. 62-91033 (1967). 
In this channel allocation scheme, an allocation priority level of each 
radio channel is calculated from the past records of the channel use, 
i.e., records concerning whether each radio channel had allocated or not 
in the past, and the judgement as to whether each radio channel is to be 
allocated or not is made sequentially from a radio channel with a highest 
allocation priority level. Then, when it is judged to be allocated, the 
allocation of that radio channel is made accordingly, whereas otherwise 
the judgement for a next radio channel with a next highest allocation 
priority level is made. 
More specifically, the aforementioned Japanese Patent Application No. 
61-244137 proposed a radio communication scheme in which each channel is 
given a priority level which is dynamically determined according to the 
past records of the channel use and the channels are sequentially used in 
an order of their priority levels. On the other hand, the aforementioned 
Japanese Patent Application No. 62-91033 proposed a transmission channel 
control scheme in which a transmission success rate for each channel is 
memorized and the channels are sequentially used in an order of their 
transmission success rates at a time of transmission, while the 
transmission success rates are updated according to the transmission 
result. 
However, in such a conventional autonomous distributed type dynamic channel 
allocation scheme, the allocation priority level of each radio channel has 
been determined by equally weighting all the past records of the channel 
use, and using a large number of the past records of the channel use, so 
that there has been a problem that an enormous amount of time is required 
in order to follow the changes in the radio wave propagation state and the 
traffic distribution after the system has reached a stationary state. 
Here, the changes in the radio wave propagation state and the traffic 
distribution are caused by newly constructed buildings in the surrounding 
of each base station, newly constructed base stations, and/or the 
starting/ending of the operations of movable type base stations, and the 
conventional autonomous distributed type dynamic channel allocation scheme 
using the past records of the channel use has been unable to follow such 
changes of the radio wave propagation state and the traffic distribution, 
so that there has been problems of large call loss rate, interference 
probability, and connection delay. 
Moreover, in such a conventional autonomous distributed type dynamic 
channel allocation scheme which calculates the allocation priority level 
of each radio channel according to the past records of channel use and 
makes the radio channel allocation according to the calculated allocation 
priority levels, only one priority level has been assigned to each radio 
channel, so that the repeated utilization of each radio channel is limited 
to the repeated utilization in units of the radio zones. As a result, the 
advantage in the frequency utilization efficiency in comparison with the 
fixed channel allocation scheme has been limited only to the improvement 
due to the large grouping effect obtained as all the available radio 
channels of the entire system are made to be usable by any base station of 
the system. 
There has also been a proposition of a channel allocation scheme for 
realizing an autonomous distributed type dynamic channel allocation by a 
relatively small control load, as disclosed in Japanese Patent Application 
No. 1-306417 (1989). 
In this channel allocation scheme, all the radio communication channels are 
divided into a plurality of channel groups, and in order to use these 
channel groups in accordance with the reception level in the 
communication, a lower limit of the reception level required in the 
communication between the mobile station and the base station using a 
channel of each channel group is set for each channel group. Then, a radio 
communication channel to be allocated to a communication set up request 
occurring in each radio zone is selected to be a channel of the channel 
group for which the reception level in the communication obtained from the 
reception level in the radio control channel between the requesting mobile 
station and the base station satisfies the aforementioned lower limit 
while the carrier to interference power ratio satisfies the required 
communication quality condition when this channel is allocated for setting 
up the requested communication. 
However, in this conventional autonomous distributed type dynamic channel 
allocation scheme, it is necessary to determine thresholds to be used in 
determining the grouping of different channel groups by means of the 
thoroughly analysis of the radio wave propagation state and the traffic 
distribution within each radio zone using the actual measurements or the 
theoretical calculations, in order to suppress the control load required 
in the radio channel allocation at the minimum level, to maintain the high 
frequency utilization efficiency, and to satisfy the required 
communication quality. 
But, such a thorough analysis over all the numerous radio zones existing 
within the service area of the system requires an enormous amount of time 
and efforts, and there is also a problem that the re-designing is 
necessary at a time of the system expansion such as the addition of base 
stations. Moreover, apart from the system expansion, a large variation in 
the radio wave propagation state and the traffic distribution can be 
caused by new construction and destruction of buildings, roads, etc. in 
the surrounding of each base station, so that the re-designing is 
necessary in order to cope with such a variation. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a mobile 
communication system and a channel allocation scheme adaptive to the 
system expansion and having a superior load variation follow-up 
characteristic, such that the degradation of the call loss rate, the 
interference probability, and the connection delay can be prevented 
regardless of the practically unavoidable changes in the radio wave 
propagation state and the traffic distribution caused by newly constructed 
buildings in the surrounding of each base station, newly constructed base 
stations, and/or the starting/ending of the operations of movable type 
bake stations. 
It is another object of the present invention to provide a mobile 
communication system and a dynamic channel allocation scheme of an 
autonomous distribution type capable of reducing the control load and 
improving the frequency utilization efficiency. 
It is another object of the present invention to provide a mobile 
communication system and a channel allocation scheme in which each base 
station can determine thresholds to be used in determining the grouping by 
its own autonomous processing, without requiring a cumbersome designing 
which takes enormous amounts of efforts and time. 
According to one aspect of the present invention there is provided a method 
of allocating radio channels to communications between base stations and 
mobile stations in a mobile communication system, comprising the steps of: 
(a) managing allocation priority levels for the radio channels available 
in the mobile communication system, according to past records of channel 
use for each radio channel at each base station; (b) sequentially 
selecting each currently unused radio channel in an order of the 
allocation priority levels managed at the step (a), and sequentially 
making an allocation accept/reject judgement concerning whether each 
selected radio channel is usable or not, at said each base station; (c) 
updating the allocation priority level managed at the step (a) of each 
radio channel selected at the step (b) by weighting past allocation 
accept/reject judgement results for said each radio channel with weight 
factors which vary according to time intervals of the past allocation 
accept/reject judgement results from a current time; and (d) allocating 
one radio channel which is judged as usable at the step (b) to a 
communication between said each base station and one mobile station. 
According to another aspect of the present invention there is provided a 
method of allocating radio channels to communications between base 
stations and mobile stations in a mobile communication system, comprising 
the steps of: (a) grouping the mobile stations into N groups according to 
states of the mobile stations at each base station, where N is an integer; 
(b) managing N sets of allocation priority levels for each radio channel 
available in the mobile communication system in correspondence to said N 
groups at each base station; (c) for each mobile station, sequentially 
selecting each radio channel which is currently unused in an order of one 
of said N sets of the allocation priority levels managed at the step (b) 
which corresponds to one of said N groups grouped at the step (a) to which 
said each mobile station belongs to, and sequentially making an allocation 
accept/reject judgement concerning whether each selected radio channel is 
usable or not, at said each base station; and (d) allocating one radio 
channel which is judged as usable at the step (c) to a communication 
between said each base station and said each mobile station. 
According to another aspect of the present invention there is provided a 
method of allocating radio channels to communications between base 
stations and mobile stations in a mobile communication system, comprising 
the steps of: (a) determining thresholds for grouping the mobile stations 
according to past records of states of the mobile stations; (b) grouping 
the mobile stations into N groups at each base station according to the 
thresholds for grouping determined at the step (a), where N is an integer; 
(c) for each mobile station, sequentially selecting each radio channel 
which is currently unused and sequentially making an allocation 
accept/reject judgement concerning whether each selected radio channel is 
usable or not, at said each base station, according to a procedure 
prescribed for one of said N groups grouped at the step (b) to which said 
each mobile station belongs to; and (d) allocating one radio channel which 
is judged as usable at the step (c) to a communication between said each 
base station and said each mobile station. 
According to another aspect of the present invention there is provided a 
mobile communication system, comprising: mobile stations; and base 
stations for communicating with the mobile stations by allocating radio 
channels, each base station including: a memory for managing allocation 
priority levels for the radio channels available in the mobile 
communication system, according to past records of channel use for each 
radio channel; and control means for sequentially selecting each currently 
unused radio channel in an order of the allocation priority levels managed 
in the memory and sequentially making an allocation accept/reject 
judgement concerning whether each selected radio channel is usable or not 
so as to allocate one radio channel which is judged as usable to a 
communication between said each base station and one mobile station, and 
updating the allocation priority level of each selected radio channel in 
the memory by weighting past allocation accept/reject judgement results 
for said each radio channel with weight factors which vary according to 
time intervals of the past allocation accept/reject judgement results from 
a current time. 
According to another aspect of the present invention there is provided a 
mobile communication system, comprising: mobile stations; and base 
stations for communicating with the mobile stations by allocating radio 
channels, each base station including: a memory for managing N sets of 
allocation priority levels for each radio channel available in the mobile 
communication system in correspondence to N groups into which the mobile 
stations are grouped according to states of the mobile stations, where N 
is an integer; and control means for sequentially selecting each radio 
channel which is currently unused, for each mobile station, in an order of 
one of said N sets of the allocation priority levels managed in the memory 
which corresponds to one of said N groups to which said each mobile 
station belongs to, and sequentially making an allocation accept/reject 
judgement concerning whether each selected radio channel is usable or not, 
so as to allocate one radio channel which is judged as usable to a 
communication between said each base station and said each mobile station. 
According to another aspect of the present invention there is provided a 
mobile communication system, comprising: mobile stations; and base 
stations for communicating with the mobile stations by allocating radio 
channels, each base station including: memory for managing thresholds for 
grouping the mobile stations according to past records of states of the 
mobile stations, such that the mobile stations are grouped into N groups 
according to the thresholds for grouping, where N is an integer; and 
control means for sequentially selecting each radio channel which is 
currently unused and sequentially making an allocation accept/reject 
judgement concerning whether each selected radio channel is usable or not, 
for each mobile station, according to a procedure prescribed for one of 
said N groups to which said each mobile station belongs to, so as to 
allocate one radio channel which is judged as usable to a communication 
between said each base station and said each mobile station. 
Other features and advantages of the present invention will become apparent 
from the following description taken in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, the first embodiment of a mobile communication system and a channel 
allocation scheme according to the present invention will be described. 
In this first embodiment, the mobile communication system has an overall 
configuration as shown in FIG. 1 which comprises a plurality of base 
stations 11 distributed over an entire service area of this mobile 
communication system, and a number of mobile stations 12 moving within the 
service area. Here, total M radio channels (M is an integer) are available 
for this mobile communication system as a whole, and an i-th base station 
11 is equipped with K.sub.i sets (K.sub.i is an integer) of transceiver 
devices capable of radio transmission and reception through any one of the 
M radio channels given to this mobile communication system, while each 
mobile station 12 is also equipped with a transceiver device capable of 
radio transmission and reception through any one of the M radio channels. 
Here, each base station 11 has a functional configuration relating to the 
radio channel allocation as shown in FIG. 2, which includes total Ki sets 
of transceivers 13 (13.sub.1 to 13.sub.Ki), a transceiver controller 14 
connected with the transceivers 13, a radio channel controller 15 
connected with the transceiver controller 14, a call processing controller 
16 connected with the radio channel controller 15, and a memory 17 
connected with the radio channel controller 15. 
The memory 17 is used for managing allocation priority levels of the radio 
channels, and stores a predetermined weight constant .lambda. 
(0.ltoreq..lambda.&lt;1) given by a system operator, and a table of a channel 
ID (ch.sub.1 to ch.sub.M) of each radio channel, a used/unused flag 
indicating whether each radio channel is currently used or unused, and an 
allocation priority level assigned to each radio channel, as shown in FIG. 
2. 
The radio channel controller 15 carries out reading, updating, and writing 
of the allocation priority level of a radio channel stored in the memory 
17 and specified by a request from the call processing controller 16, and 
manages the radio channel currently used by each base station. The 
transceiver controller 14 carries out a management of the transceivers 
13.sub.1 to 13.sub.Ki, and makes an allocation accept/reject judgement for 
a radio channel specified from the radio channel controller 15. 
In this configuration of FIG. 2, the radio channel allocation operation is 
carried out according to the flow chart of FIG. 3 as follows. 
When there is a radio channel allocation request with respect to a new call 
or a radio channel switching from the call processing controller 16, the 
radio channel controller 15 checks whether there exist radio channels 
which are currently unused or not, by reading the used/unused flags in the 
memory 17 (step S1). In a case all the radio channels ch.sub.1 to ch.sub.M 
are currently used, this fact is notified to the call processing 
controller 18 and the operation is terminated. 
In a case there exist radio channels which are currently unused, next the 
radio channel controller 15 inquires the transceiver controller 14 as to 
whether there exist transceivers 13 which are currently unused or not 
(step S2). In a case there is no transceiver 13 which is currently unused, 
the transceiver controller 14 notifies this fact to the call processing 
controller 16 through the radio channel controller 15 and the operation is 
terminated. 
In a case there exist transceivers 13 which are currently unused, next the 
radio channel controller 15 selects a channel ID of one radio channel 
which has the highest allocation priority level among those radio channels 
which are currently unused, by referring to the allocation priority levels 
in the memory 17, and notifies the selected channel ID to the transceiver 
controller 14 (step S3). 
In response, the transceiver controller 14 makes the allocation 
accept/reject judgement regarding whether the selected radio channel is 
usable or not as described in detail below, and returns the result of this 
allocation accept/reject judgement to the radio channel controller 15 
(step S4). 
Then, when the result of the allocation accept/reject judgement indicates 
that the selected radio channel is usable, the radio channel controller 15 
sets a factor A to be used for updating the allocation priority level as 
one of the two values having opposite signs which are predetermined with 
respect to two possible results (accept and reject) of the allocation 
accept/reject judgement, which is +1 in this first embodiment (step S5), 
and then updates the allocation priority level P.sub.j of this selected 
radio channel according to the following formula (1): 
EQU P.sub.j (new)=P.sub.j (old).times..lambda.+A (1) 
and writes this updated allocation priority level P.sub.j (new) into the 
corresponding entry of this selected radio channel in the memory 17 (step 
S6). 
Then, the radio channel controller 15 notifies the channel ID of the 
selected radio channel to the call processing controller 16, and rewrites 
the used/unused flag in the corresponding entry of this selected radio 
channel in the memory 17 to "1" for indicating that it is currently used, 
so as to effectuate the radio channel allocation processing (step S7). 
On the other hand, when the result of the allocation accept/reject 
judgement indicates that the selected radio channel is not usable, the 
radio channel controller 15 sets the factor A to as another one of the two 
values having opposite signs which are predetermined with respect to two 
possible results (accept and reject) of the allocation accept/reject 
judgement, which is -1 in this first embodiment, and then updates the 
allocation priority level P.sub.j of this selected radio channel according 
to the above formula (1) and writes this updated allocation priority level 
P.sub.j (new) into the corresponding entry of this selected radio channel 
in the memory 17 (step S8). 
Then, unless this selected radio channel is a last radio channel which are 
currently unused (step S11 NO), the radio channel controller 15 selects a 
channel ID of one radio channel which has the next highest allocation 
priority level among those radio channels which are currently unused, by 
referring to the allocation priority levels in the memory 17, and notifies 
this selected channel ID to the transceiver controller 14 (step S10), and 
the operation from the step S4 on as described above is repeated for this 
next selected radio channel. 
In a case the result of the allocation accept/reject judgements for all the 
radio channels which are currently unused indicate that these radio 
channels are not usable as a result of repeated operation (step S11 YES), 
the radio channel controller 15 notifies this fact to the call processing 
controller 16, and the operation is terminated. 
As a result of this operation, the allocation priority level P.sub.j of the 
j-th radio channel ch.sub.j is going to be updated as: 
EQU P.sub.j =A.sub.1 +.lambda.A.sub.2 +.lambda..sup.2 A.sub.3 + . . . 
+.lambda..sup.(L-1) A.sub.L (2) 
according the allocation accept/reject judgement results A.sub.1, A.sub.2, 
. . . , A.sub.L of the past L cases, where L is an integer and A.sub.i 
(i=1, 2, . . . , L) has a value +1 or -1 as described above. Here, the 
weight constant .lambda. is a constant value in a range of 
0.ltoreq..lambda.&lt;1, so that in this updated allocation priority level 
P.sub.j, the contribution from the immediately previous allocation 
accept/reject judgement result is the largest, and the earlier allocation 
accept/reject judgement results have sequentially smaller contributions. 
Thus, in this first embodiment, it is possible to weight the past 
allocation accept/reject judgement results inversely proportional to the 
time order of these past allocation accept/reject judgement results by an 
extremely simple operation. 
Moreover, in this first embodiment, it suffices for the memory 17 to have a 
sufficient memory capacity for storing the allocation priority levels, the 
radio channel utilization state (i.e., the used/unused flags), and a 
constant .lambda., so that this memory 17 can be formed by a relatively 
small capacity memory device suitable for high speed accesses. 
In the above described radio channel allocation operation, the allocation 
accept/reject judgement of the selected radio channel at the step S4 can 
be made by various methods, such as a method in which the selected radio 
channel is tentatively set to one of the currently unused transceivers 13 
and the radio signals are received at this transceiver 13 in order to 
determine the reception level (i.e., the interference level), and it is 
judged that the selected radio channel is usable when the determined 
reception level is less than or equal to a prescribed threshold, or a 
method in which the target mobile station is also notified to tentatively 
set the selected radio channel and the radio signals transmitted from the 
target mobile station through this selected radio channel is received at 
the base station in order to determine the carrier to interference power 
ratio for this selected radio channel, and it is judged that the selected 
radio channel is usable when the determined carrier to interference power 
ratio is greater than or equal to a prescribed threshold. 
Now, the convergence of the allocation priority level P.sub.j when the 
allocation accept/reject judgement results with respect to the j-th radio 
channel happen to be either acceptances or rejections alone consecutively 
will be considered. Here, it is assumed that the allocation accept/reject 
judgement result which is an acceptance is represented by a value A=.rho., 
while the allocation accept/reject judgement result which is a rejection 
is represented by a value A=-.rho. (where .rho. is a positive constant), 
and the allocation priority level P.sub.j is to be sequentially updated 
according to the above formula (1). 
When the acceptances occur consecutively for L times, the allocation 
priority level P.sub.j is given by: 
##EQU1## 
Then, using the following formula which holds for any number x in a range 
of -1&lt;x&lt;1: 
##EQU2## 
when the limit of the above expression (3) is taken, it follows that the 
limit of the allocation priority level P.sub.j is given by: 
##EQU3## 
Similarly, when the rejections occur consecutively for L times, the limit 
of the allocation priority level P.sub.j is given by: 
##EQU4## 
Thus, the allocation priority level P.sub.j of this first embodiment 
converges to a finite value in either case. In other words, even when the 
allocation priority level for a certain radio channel happens to be the 
highest consecutively, this allocation priority level is not going to be 
infinitely large, and bounded by the finite value .rho./(1-.lambda.) as 
described above, so that a value of the allocation priority level never 
become so large as to overflow from the memory 17, as long as the memory 
17 has a memory capacity sufficient for storing a value .rho./(1-.lambda.) 
at most. 
As described, according to this first embodiment, the past allocation 
accept/reject judgement results are weighted inversely proportional to the 
time order of these past allocation accept/reject judgement results, i.e., 
the older allocation accept/reject judgement result is weighted by a 
smaller weight, so that even when the interference state changes as a 
result of the changes in the radio wave propagation state caused by newly 
constructed buildings in the surrounding of each base station, newly 
constructed base stations, and/or the starting/ending of the operations of 
movable type base stations, and/or the changes in the traffic distribution 
caused by the construction or destruction of a large building, it is 
possible to prevent the degradation of the connection quality such as the 
call loss rate, the interference probability, and the connection delay, as 
the allocation priority level of each radio channel also changes 
adaptively by following the environmental change to take a value suitable 
for the new environmental conditions. 
In addition, in this first embodiment, it is possible to freely adjust the 
flexibility in the load variation follow-up characteristic with respect to 
the changes in the radio wave propagation state and the traffic 
distribution, by adjusting the value of the weight constant .lambda.. 
Namely, by setting the weight constant .lambda. to be a smaller value, the 
decrease of the influence of the older allocation accept/reject judgement 
result on the allocation priority level can be made faster, such that the 
allocation priority level of each radio channel can be adapted to the 
changes in the radio wave propagation state and the traffic distribution 
more quickly, i.e., the flexibility of the load variation follow-up 
characteristic is raised. On the contrary, by setting the weight constant 
.lambda. to be a larger value, the influence of the older allocation 
accept/reject judgement result on the allocation priority level lasts 
longer, so that the flexibility of the load variation follow-up 
characteristic is reduced. Consequently, it is preferable to set the 
weight constant .lambda. to be relatively large when the changes in the 
radio wave propagation state and the traffic distribution are relatively 
small. 
It is to be noted that, in this first embodiment, in calculating the 
allocation priority level according to the allocation accept/reject 
judgement result at a time of newly allocating the radio channel, when the 
interference occurs during the communication such that the switching of 
the communication to the other radio channel becomes necessary, it is also 
possible to account for the occurrence of the switching due to the 
interference as well. Namely, such an occurrence of the switching due to 
the interference can be accounted in updating the allocation priority 
level by the above formula (1) similarly as in a case of the allocation 
accept/reject judgement result which is the rejection, but using another 
value A such as -0.5 for instance. 
Now, the result of the computer simulation for confirming the effect of the 
above described first embodiment will be described. This computer 
simulation used a model as shown in FIGS. 4A to 4C in which radio zones 
21.sub.1 to 21.sub.5 having respective base stations 11.sub.1 to 11.sub.5 
are assumed to be in forms of hexagonal cells with omni-directional 
antennas which are arranged one dimensionally. In this-model, the call is 
assumed to be generated according to the Poisson distribution, spatially 
uniformly throughout these radio zones, while the holding time is assumed 
to be in accordance with the exponential distribution with a mean equal to 
120 sec., and the behavior of call within each radio zone is assumed to be 
identical. In addition, the mobile station which is going to make a call 
or receive a call is assumed to have selected the radio zone in advance by 
measuring the reception power of the perch channel (control channel) 
transmitted at the constant transmission power from the base station, 
while a number of radio channels available in the system as a whole is 
assumed to be 20, and only the identical channel interference is accounted 
as the interference. 
In the practical mobile communication system, a frequently encountered 
situation is that, because of the increasing number of requests for making 
calls to or receiving calls from an area (region) for which the base 
station is not provided, it becomes necessary to provide a new base 
station in that area in order to facilitate the expanded service covering 
that area. In the above described computer simulation model, this 
situation is modelled as follows. As shown in FIG. 4A, for the first five 
days from the start of the simulation, the base station 11.sub.3 for the 
radio zone 21.sub.3 is absent and there is no call generated within this 
radio zone 21.sub.3. Then, as shown in FIG. 4B, from the sixth day to the 
tenth day of the simulation, the base station 11.sub.3 for the radio zone 
21.sub.3 is still absent but the calls are generated in this radio zone 
21.sub.3 just as in any other radio zone. Then, as shown in FIG. 4C, on 
the eleventh day of the simulation, the base station 11.sub.3 for the 
radio zone 21.sub.3 is newly provided to facilitate the expanded service 
covering this radio zone 21.sub.3. 
The result obtained by this computer simulation is indicated in FIGS. 5A to 
5D, where FIG. 5A shows a call loss rate at the base station 11.sub.3 on 
the eleventh day of the simulation, FIGS. 5B and 5C show interference 
probabilities in the upward link (from the mobile station to the base 
station) and the downward link (from base station to the mobile station) 
for eleventh day of the simulation, respectively, and FIG. 5D shows a 
number of allocation accept/reject judgements required in making a radio 
channel allocation with respect to one call on the eleventh day of the 
simulation. In each of FIGS. 5A to 5D, the horizontal axis is set to be an 
offered traffic per one radio zone. 
It can be seen from this computer simulation result that, in comparison 
with the conventional radio channel allocation scheme using the past 
records of the channel use, at a level of an offered traffic per one radio 
zone equal to 7 [Erl/Cell] for instance, the radio channel allocation 
scheme of this first embodiment can realize a considerable improvement of 
2.02% for the call loss rate in contrast to conventional 3.13%, 1.05% for 
the interference probability in the upward link in contrast to 
conventional 2.11%, 0.54% for the interference probability in the downward 
link in contrast to conventional 1.6%, and 1.56 times for the number of 
allocation accept/reject judgements required in making a radio channel 
allocation with respect to one call in contrast to conventional 1.93 
times. 
Thus, it can be confirmed that the radio channel allocation scheme of this 
first embodiment is indeed capable of preventing the degradation of the 
connection quality such as the call loss rate, the interference 
probability, and the connection delay due to an increased number of 
allocation accept/reject judgements, and realizing the radio channel 
allocation with a small control load, even in a presence of the changes in 
the radio wave propagation state and the traffic distribution caused by 
newly constructed buildings in the surrounding of each base station, newly 
constructed base stations, and/or the starting/ending of the operations of 
movable type base stations. 
It is to be noted here that the values of A=1 for a case of the allocation 
acceptance, A=-1 for a case of the allocation rejection, and A=-0.5 for a 
case of the channel switching due to the interference which are used in 
the above description are only exemplary values, and it basically suffices 
to use any positive value for a case of the allocation acceptance and any 
negative values for a case of the allocation rejection and a case of the 
channel switching due to the interference. 
In particular, it is not necessary for the two values with opposite signs 
to be set in correspondence to the acceptance and the rejection to have an 
identical absolute value as in A=.rho. for the acceptance and A=-.rho. for 
the rejection as described above, and these two values may be set to have 
different absolute values. For example, it is possible to use a setting of 
A=1.0 for the allocation acceptance and A=-1.2 for the allocation 
rejection, such that when a new base station is provided in the 
surrounding of the old base station, the radio channels used at the old 
base station with high allocation priority levels become lower and it 
becomes easier to select the radio channels at the new base station. On 
the other hand, in a case of providing a plurality of base stations over a 
wide service area, and starting the service operation of all these base 
stations simultaneously from an initial state in which the allocation 
priority levels of all the radio channels are zeros, it is possible to use 
a setting of A=1.2 for the allocation acceptance and A=-1.0 for the 
allocation rejection, such that the allocation priority levels can reach 
high values quickly. 
Moreover, a case of the channel switching due to the interference is 
handled similarly as in a case of the allocation rejection by using a 
value A=-0.5, i.e., a value with a smaller absolute value than a value 
A=-1 used in a case of the allocation rejection, in consideration for 
accounting the fact that the previous allocation priority level was high, 
but it is also possible to drop this consideration and use the same value 
A=-1 for both a case of the allocation rejection as well as a case of the 
channel switching due to the interference, if desired. 
In addition, the weight for each allocation accept/reject judgement result 
is sequentially reduced as each allocation accept/reject judgement result 
becomes older with respect to the current allocation accept/reject 
judgement result in the above description, but it is not absolutely 
necessary to reduce this weight every time a new allocation accept/reject 
judgement result is made, and it may be modified such that this weight is 
reduced in every two or three times of making new allocation accept/reject 
judgement results, for example. In order to reduce this weight in every 
two times, it suffices to carry out the calculation of P.sub.i 
.times..lambda.+A and the calculation of P.sub.i +A alternately in 
updating the allocation priority level P.sub.i. 
Moreover, instead of reducing the weight in every prescribed number of 
times, the number of times for which the identical weight is used can be 
increased for the older allocation accept/reject judgement result. It is 
also possible to use a certain weight for a prescribed number, such as 
three for instance, of the allocation accept/reject judgement results 
counted from the latest one, while using another smaller weight for all 
the allocation accept/reject judgment results older than these, i.e., to 
reduce the weight once at least as the allocation accept/reject judgement 
result becomes older. It is also possible to set the weight of the three 
times earlier allocation accept/reject judgement result as the maximum 
possible weight for the current allocation accept/reject judgement result 
in some cases, if desired. 
As for the radio channels to be used in this first embodiment, it is 
possible to consider the use of the radio frequencies in the FDMA system, 
the use of the time slots in the TDMA (Time Division Multiple Access) 
system, and the repeated use of the spread codes or the frequency hopping 
patterns in the CDMA (Code Division Multiple Access) system, and the radio 
channel allocation scheme of this first embodiment is equally applicable 
to any of these cases, by making the allocation accept/reject judgement 
according to the measurement of the interference level or the carrier to 
interference power ratio as described above, for the substantially similar 
effects. 
Now, the second embodiment of a mobile communication system and a channel 
allocation scheme according to the present invention will be described. 
In this second embodiment, the mobile communication system has an overall 
configuration similar to that shown in FIG. 1 described above, where each 
base station 11 has a functional configuration relating to the radio 
channel allocation as shown in FIG. 6 which includes total Ki sets (Ki is 
an integer) of transceivers 13 (13.sub.1 to 13.sub.Ki), a transceiver 
controller 14 connected with the transceivers 13, a radio channel 
controller 15A connected with the transceiver controller 14, a call 
processing controller 16 connected with the radio channel controller 15A, 
a memory 17A connected with the radio channel controller 15A, a mobile 
station feature measurement device 18 for measuring a feature of each 
mobile station, and a mobile station feature measurement device controller 
19 connected with the mobile station feature measurement device 18 and the 
radio channel-controller 15A. 
The radio channel controller 15A carries out reading, updating, and writing 
of the data stored in the memory 17A and specified by a request from the 
call processing controller 16, and manages the radio channel currently 
used by each base station. The transceiver controller 14 carries out a 
management of the transceivers 13.sub.1 to 13.sub.Ki, and makes an 
allocation accept/reject judgement for a radio channel specified from the 
radio channel controller 15A. 
Here, the radio channels are allocated by dividing the mobile stations into 
a plurality of groups according to the features of the mobile stations 
such as the distances, the moving directions, and the moving speeds with 
respect to each base station. For this reason, the memory 17A is used for 
managing allocation priority levels of the radio channels, and stores a 
table of a channel ID (ch.sub.1 to ch.sub.M) of each radio channel, a 
used/unused flag indicating whether each radio channel is currently used 
or unused, and a priority level table registering N sets of allocation 
priority levels assigned to each radio channel, as shown in FIG. 7A, as 
well as a table of a priority level table number (#1 to #N) of each 
priority level table, and corresponding thresholds for the distance, the 
moving direction, and the moving speed to be used in dividing the mobile 
stations into N groups, as shown in FIG. 7B. 
In this configuration of FIG. 6, the radio channel allocation operation is 
carried out according to the flow chart of FIG. 8 as follows. 
When there is a radio channel allocation request with respect to a new call 
or a radio channel switching from the call processing controller 16, the 
radio channel controller 15A checks whether there exist radio channels 
which are currently unused or not, by reading the used/unused flags in the 
memory 17A (step 110). In a case all the radio channels ch.sub.1 to 
ch.sub.M are currently used, this fact is notified to the call processing 
controller 16 and the operation is terminated. 
In a case there exist radio channels which are currently unused, next the 
radio channel controller 15A inquires the transceiver controller 14 as to 
whether there exist transceivers 13 which are currently unused or not 
(step 120). In a case there is no transceiver 13 which is currently 
unused, the transceiver controller 14 notifies this fact to the call 
processing controller 16 through the radio channel controller 15A and the 
operation is terminated. 
In a case there exist transceivers 13 which are currently unused, next the 
radio channel controller 15A commands the mobile station feature 
measurement device controller 19 to control the mobile station feature 
measurement device 18 such that the extraction of the features of the 
mobile station to which the radio channel is to be allocated such as the 
distance, the moving direction, and the moving speed is carried out by the 
mobile station feature measurement device 18 (step 130). 
Then, the mobile station feature measurement device controller 19 notifies 
the measurement result received from the mobile station feature 
measurement device 18 to the radio channel controller 15A, and in 
response, the radio channel controller 15A compares the notified 
measurement result with the thresholds for determining the priority level 
table number stored in the memory 17A, so as to determine the appropriate 
priority level table number (step 140). 
Then, the radio channel controller 15A selects a channel ID of one radio 
channel which has the highest allocation priority level among those radio 
channels which are currently unused by referring to the allocation 
priority level registered in the priority level table on the memory 17A 
which is specified by the priority level table number determined at the 
step 140, and notifies the selected channel ID to the transceiver 
controller 14 (step 150). 
In response, the transceiver controller 14 makes the allocation 
accept/reject judgement regarding whether the selected radio channel is 
usable or not as described in detail below, and returns the result of this 
allocation accept/reject judgement to the radio channel controller 15A 
(step 160). 
Then, when the result of the allocation accept/reject judgement indicates 
that the selected radio channel is usable, the radio channel controller 
15A raises the allocation priority level with respect to the selected 
radio channel on that priority level table (step 170) so as to update the 
allocation priority level on the memory 17A, and then, the radio channel 
controller 15A notifies the channel ID of the selected radio channel to 
the call processing controller 16, and rewrites the used/unused flag in 
the corresponding entry of this selected radio channel in the memory 17A 
to "1" for indicating that it is currently used, so as to effectuate the 
radio channel allocation processing (step 175). 
On the other hand, when the result of the allocation accept/reject 
judgement indicates that the selected radio channel is not usable, the 
radio channel controller 15A lowers the allocation priority level with 
respect to the selected radio channel on that priority level table (step 
180) so as to update the allocation priority level on the memory 17A, and 
then, unless this selected radio channel is a last radio channel which are 
currently unused (step 190 NO), the radio channel controller 15A selects a 
channel ID of one radio channel which has the next highest allocation 
priority level among those radio channels which are currently unused, by 
referring to the allocation priority levels in the memory 17A, and 
notifies this selected channel ID to the transceiver controller 14 (step 
200), and the operation from the step 160 on as described above is 
repeated for this next selected radio channel. 
In a case the result of the allocation accept/reject judgements for all the 
radio channels which are currently unused indicate that these radio 
channels are not usable as a result of repeated operation (step 190 YES), 
the radio channel controller 15A notifies this fact to the call processing 
controller 18, and the operation is terminated. 
By means of this radio channel allocation operation, it is possible to 
realize the separate use of the radio channels for different mobile 
stations within each base station automatically according to the features 
of the mobile stations, as well as the separate use of the radio channels 
among different base stations automatically, such that it is possible to 
realize the radio channel allocation scheme with high frequency 
utilization efficiency and communication quality by using a simple 
control. 
In the above radio channel allocation operation, the allocation 
accept/reject judgement of the selected radio channel at the step 160 can 
be made by various methods, such as a method in which the selected radio 
channel is tentatively set to one of the currently unused transceivers 13 
and the radio signals are received at this transceiver 13 in order to 
determine the reception level (i.e., the interference level), and it is 
judged that the selected radio channel is usable when the determined 
reception level is less than or equal to a prescribed threshold, a method 
in which the target mobile station is also notified to tentatively set the 
selected radio channel and the radio signals transmitted from the target 
mobile station through this selected radio channel is received at the base 
station in order to determine the carrier to interference power ratio for 
this selected radio channel, and it is judged that the selected radio 
channel is usable when the determined carrier to interference power ratio 
is greater than or equal to a prescribed threshold, or a method in which 
the target mobile station is also notified to tentatively set the selected 
radio channel and the interference level or the carrier to interference 
power ratio is also measured at the mobile station side, and it is judged 
that the selected radio channel is usable by comparing the determined 
interference level or the carrier to interference power ratio with 
predetermined threshold. 
The threshold for the interference level or the carrier to interference 
power ratio to be used in this allocation accept/reject judgement of the 
selected radio channel at the step 160 may be set to be identical for all 
the groups, or to be different for each group. For example, the threshold 
for the carrier to interference power ratio can be set to have a smaller 
margin with respect to a desired value for the mobile station with slow 
moving speed as such a mobile station is expected to have a smaller 
variation in the communication state, and to have a larger margin with 
respect to the desired value for the mobile station with fast moving speed 
as such a mobile station is expected to have a larger variation in the 
communication state. Similarly, the threshold for the interference level 
can be set to have a larger value for the mobile station in a vicinity of 
the base station and to have a smaller value for the mobile station in a 
vicinity of a cell edge, so as to satisfy the required communication 
quality. 
In the above radio channel allocation operation, the state of the mobile 
station is measured by the base station at a time of the radio channel 
allocation, but it is also possible to modify this aspect of the above 
radio channel allocation operation such that the measurement of the state 
of the mobile station is carried out by the mobile station itself. In such 
a case, it is possible to utilize a method in which the mobile station 
measures its own state in response to a command issued from the base 
station at a time of calling or call receiving, and reports the measured 
state to the base station, or a method in which the mobile station 
measures its own state autonomously at a time of calling or call 
receiving, or at a time of being in an idle state, and reports the 
measured state to the base station, for example. This second embodiment is 
equally applicable to either one of these methods, for essentially the 
similar effects. 
Moreover, in the above radio channel allocation operation, the allocation 
priority level has been determined adaptively according to the allocation 
accept/reject judgement result for each group, but it is also possible to 
modify this aspect of the above radio channel allocation operation such 
that the allocation priority level is determined adaptively according to 
the allocation accept/reject judgement results for each group as well as 
other groups. For example, when the allocation accept/reject judgement 
result is the acceptance, the allocation priority level for that radio 
channel in that group is raised while the allocation priority levels of 
that radio channel in the other groups are lowered, such that the 
convergence time for the allocation priority level can be shortened. 
Now, an exemplary allocation priority level for each group and each base 
station will be explained according to the computer simulation result. 
This computer simulation concerns with an exemplary case of a system with 
two neighboring base stations 11 (BS#1 and BS#2) as shown in FIG. 9, where 
total five radio channels are available in the system as a whole. A number 
of priority level tables, i.e., a number of groups, is assumed to be 
three, and the grouping is made according to the distance from the base 
station 11 alone. Here, the distance of the mobile station 12 from the 
base station 11 is estimated by measuring the reception level at the base 
station 11 of the radio wave transmitted from the mobile station 12. Also, 
the call is assumed to be generated according to the Poisson distribution, 
spatially uniformly throughout the radio zones of these base stations 11, 
while the offered traffic is assumed to be identical in these two radio 
zones. Moreover, the allocation accept/reject judgement result is set to 
be the acceptance when the carrier to interference power ratios for the 
upward and downward links are greater than or equal to a prescribed 
threshold, and only the identical channel interference is accounted as the 
interference. 
The allocation priority levels at both base stations BS#1 and BS#2 after a 
sufficient amount of time has elapsed since the start of the simulation 
are indicated in FIGS. 10A to 10C, where FIG. 10A shows the allocation 
priority levels of the priority level table #1, which are used for the 
mobile station at a close distance to the base station, FIG. 10B shows the 
allocation priority levels used for the mobile station at a middle range 
distance from the base station, and FIG. 10C shows the allocation priority 
levels used for the mobile station at a far distance from the base 
station. In these FIGS. 10A to 10C, the higher value along the vertical 
axis indicates the higher allocation priority level. 
It can be seen that, in FIG. 10A, the channel #0 has the highest allocation 
priority level for both BS#1 and BS#2, so that the identical radio channel 
is used with the high allocation priority level in the neighboring radio 
zones for the mobile station at the close distance from the base station. 
On the other hand, in FIGS. 10B and 10C, the radio channels with the 
highest allocation priority level are different for BS#1 and BS#2. For 
example, in FIG. 10C, the radio channel #2 has the highest allocation 
priority level for BS#1 while the radio channel #4 has the highest 
allocation priority level for BS#2, such that the different radio channels 
are used in order to avoid the occurrence of the interference in each 
radio zone from the other radio zone. 
It can also be seen that the separate use of the radio channels among the 
groups is realized automatically. For example, for BS#1, the radio channel 
#0 has the high allocation priority level in FIG. 10A while this radio 
channel #0 has low allocation priority levels in FIGS. 10B and 10C, 
whereas the radio channel #3 has the high allocation priority level in 
FIG. 10B while this radio channel #3 has low allocation priority levels in 
FIGS. 10A and 10C. 
In general, for the mobile station which is far distanced from the base 
station and located near the edge of the radio zone, the carrier reception 
level is low for both upward and downward links, so that it is necessary 
for the radio channel to be allocated to such a mobile station to be 
utilized repeatedly over a relatively large distance in order to suppress 
the interference level from the other base station or mobile station in 
the surrounding to be low such that the degradation of the communication 
quality can be prevented. On the contrary, for the mobile station which is 
near the base station, the carrier reception level of a certain level can 
be secured so that there is no degradation of the communication quality 
due to the use of the radio channel with a relatively smaller channel 
reuse distance compared with a case of the mobile station located near the 
edge of the radio zone. 
Consequently, by separately using the radio channel with a large channel 
reuse distance and the radio channel with a small channel reuse distance 
according to the distances between the base station and the mobile 
station, it is possible to improve the frequency utilization efficiency. 
In the radio channel allocation scheme of this second embodiment, the 
separate uses of the radio channels within the base station as well as 
among different base stations according to the features of the mobile 
stations are automatically realized by the autonomous distributed control 
at each base station, so that it is possible to realize the radio channel 
allocation scheme with high frequency utilization efficiency and 
communication quality by using a simple control. 
Now, the result of the computer simulation for confirming the effect of the 
above described second embodiment will be described. This computer 
simulation used a model with a service area formed by 61 radio zones in 
forms of hexagonal cells with omni-directional antennas. In this model, 
the call is assumed to be generated according to the Poisson distribution, 
spatially uniformly throughout these radio zones, while the holding time 
is assumed to be in accordance with the exponential distribution with a 
mean equal to 120 sec., and the behavior of call within each radio zone is 
assumed to be identical. In addition, the mobile station which is going to 
make a call or receive a call is assumed to have selected the radio zone 
in advance by measuring the reception power of the perch channel (control 
channel) transmitted at the constant transmission power from the base 
station, while a number of radio channels available in the system as a 
whole is assumed to be 35, and only the identical channel interference is 
accounted as the interference. A number of priority level tables, i.e., a 
number of groups, is assumed to be seven, and the grouping is made 
according to the distance from the base station alone as the feature of 
the mobile station. Here, the distance of the mobile station from the base 
station is estimated by measuring the reception level at the base station 
of the radio wave transmitted from the mobile station. Moreover, the 
allocation accept/reject judgement result is set to be the acceptance when 
the carrier to interference power ratios for the upward and downward links 
are greater than or equal to a prescribed threshold. 
The result obtained by this computer simulation is indicated in FIGS. 11 
and 12, where a system capacity is defined by an offered traffic per one 
radio zone at the call loss rate of 3%, and FIG. 11 shows a call loss rate 
as a function of the offered traffic per one radio zone which is 
normalized by the system capacity in the conventional radio channel 
allocation scheme using a single allocation priority level, while FIG. 12 
shows a number of allocation accept/reject judgements required in making a 
radio channel allocation with respect to one call as a function of the 
call loss rate which is normalized by a number of allocation accept/reject 
judgements required in a case of the system capacity in the conventional 
radio channel allocation scheme. 
It can be seen from this computer simulation result that, in comparison 
with the conventional radio channel allocation scheme using a single 
allocation priority level, the radio channel allocation scheme of this 
second embodiment can realize a considerable improvement of approximately 
25% for the system capacity as well as a considerable reduction of 
approximately 10% for the number of allocation accept/reject judgements 
required in making a radio channel allocation with respect to one call in 
the system capacity. 
Thus, it can be confirmed that the radio channel allocation scheme of this 
second embodiment is indeed capable of improving the system capacity 
considerably while suppressing the control load to be sufficiently small, 
so that it is possible to realize a mobile communication system and a 
dynamic channel allocation scheme of an autonomous distribution type with 
a reduced control load and the improved frequency utilization efficiency. 
A case of using the moving direction and the moving speed of the mobile 
station as the features of the mobile station is similarly capable of 
achieving the similar effects by the similarly simple control. 
It is to be noted here that, when the radio channel allocation is made 
without accounting for the moving direction and the moving speed of the 
mobile station, there is going to be a high probability for the occurrence 
of the forceful call disconnection due to the mobile station moving at the 
high speed which tends to move from one radio zone to another frequently 
such that the radio channel allocation at the moving target radio zone 
cannot follow the movement of the mobile station, and the control load for 
switching the radio channels is going to be increased on both the base 
station side as well as the mobile station side. Also, in such a case, due 
to the presence of the fast moving mobile station, the interference 
condition varies largely in time, such that a probability for the 
occurrence of the interference increases for the fast moving mobile 
station as well as for the slow moving mobile station. Consequently, in a 
case the mobile stations with different moving speeds coexists within the 
service area, it is necessary to separately use the radio channels 
according to the moving directions and the moving speeds of the mobile 
stations. 
In the radio channel allocation scheme of this second embodiment, the 
mobile stations are divided into groups according to the moving directions 
and the moving speeds of the mobile stations, and the radio channels are 
allocated by using different allocation priority levels in correspondence 
to the different groups, so that the separate use of the radio channels 
can be realized automatically just as in a case of using the distance 
between the base station and the mobile station, and it is possible to 
suppress the control load as well as the lowering of the frequency 
utilization efficiency at the minimum levels. 
As for the radio channels to be used in this second embodiment, it is 
possible to consider the use of the radio frequencies in the FDMA system, 
the use of the time slots in the TDMA system, and the repeated use of the 
spread codes or the frequency hopping patterns in the CDMA system, and the 
radio channel allocation scheme of this second embodiment is equally 
applicable to any of these cases, by making the allocation accept/reject 
judgement according to the measurement of the interference level or the 
carrier to interference power ratio as described above, for the 
substantially similar effects. 
Now, the third embodiment of a mobile communication system and a channel 
allocation scheme according to the present invention will be described. 
This third embodiment concerns with a modification of the second embodiment 
in that, instead of determining the allocation priority level adaptively 
according to the allocation accept/reject judgement result within each 
group, the allocation priority level is determined adaptively according to 
the past records of the channel use in each group as well as in the other 
groups. 
In this third embodiment, the mobile communication system has an overall 
configuration similar to that shown in FIG. 1 described above, and each 
base station 11 has a functional configuration relating to the radio 
channel allocation as shown in FIG. 8 described above, with the memory 17A 
storing the data as shown in FIGS. 7A and 7B described above. 
In this third embodiment, the radio channel allocation operation is carried 
out according to the flow chart of FIG. 13, which differs from that of 
FIG. 8 in that the step 170 is replaced by the step 171 for carrying out 
the allocation priority level update processing according to the flow 
chart of FIG. 14 as follows. Here, it is assumed the groups are 
sequentially labelled by group IDs 1 to N, while the channels are 
sequentially labelled by channel IDs 1 to M, and the group corresponding 
to the priority level table number selected at the step 140, i.e., the 
group to which this mobile station belongs to, has a group ID=G, while the 
radio channel selected at the step 150, i.e., the radio channel which is 
successfully allocated to this mobile station, has a channel ID=CH. 
First, at the step 1711, the allocation priority levels are raised for all 
the channels with channel IDs less than CH in the groups with group IDs 
less than G, i.e., the channels belonging to a region I indicated in FIG. 
15. 
Next, at the step 1712, the allocation priority levels are lowered for all 
the channels with channel IDs less than or equal to CH in the groups with 
group IDs greater than G, i.e., the channels belonging to a region II 
indicated in FIG. 15. 
Next, at the step 1713, the allocation priority levels are lowered for all 
the channels with channel IDs greater than or equal to CH in the groups 
with group IDs less than G, i.e., the channels belonging to a region III 
indicated in FIG. 15. 
Next, at the step 1714, the allocation priority levels are raised for all 
the channels with channel IDs greater than CH in the groups with group IDs 
greater than G, i.e., the channels belonging to a region IV indicated in 
FIG. 15. 
Finally, at the step 1715, the allocation priority level is raised for the 
channel with a channel ID=CH in the group with a group ID=G, i.e., the 
channel located at a region V indicated in FIG. 15. 
It is to be noted that the resulting updated allocation priority levels are 
identical regardless of the order of carrying out these steps 1711 to 
1715, so that these steps 1711 to 1715 may be carried out in any desired 
order. 
By means of this radio channel allocation operation including the 
allocation priority level update processing of FIG. 14, It is possible to 
realize the separate use of the radio channels for different mobile 
stations within each base station automatically according to the features 
of the mobile stations, as well as the separate use of the radio channels 
among different base stations automatically, while the allocation priority 
level is determined adaptively according to the past records of the 
channel use in each group as well as in the other groups such that it is 
possible to realize the clearer separate use of the radio channels within 
each base station, and consequently it is possible to realize the radio 
channel allocation scheme with the frequency utilization efficiency even 
higher than that achieved in the second embodiment described above by 
using a simple control. 
In this third embodiment, the allocation accept/reject judgement of the 
selected radio channel at the step 160 can be made by various methods, 
such as those already described above for the second embodiment, and the 
threshold for the interference level or the carrier to interference power 
ratio to be used in this allocation accept/reject judgement may be set to 
be identical for all the groups, or to be different for each group, just 
as in the second embodiment. Moreover, the measurement of the state of the 
mobile station may be carried out by the mobile station itself, just as in 
the second embodiment. 
Now, the result of the computer simulation for confirming the effect of 
this third embodiment will be described. This computer simulation used a 
model with a service area formed by 61 radio zones in forms of hexagonal 
cells with omni-directional antennas. In this model, the call is assumed 
to be generated according to the Poisson distribution, spatially uniformly 
throughout these radio zones, while the holding time is assumed to be in 
accordance with the exponential distribution with a mean equal to 120 
sec., and the behavior of call within each radio zone is assumed to be 
identical. In addition, the mobile station which is going to make a call 
or receive a call is assumed to have selected the radio zone in advance by 
measuring the reception power of the perch channel (control channel) 
transmitted at the constant transmission power from the base station, 
while a number of radio channels available in the system as a whole is 
assumed to be 70, and only the identical channel interference is accounted 
as the interference. A number of priority level tables, i.e., a number of 
groups, is assumed to be 30, and the grouping is made according to the 
distance from the base station alone as the feature of the mobile station. 
Here, the distance of the mobile station from the base station is 
estimated by measuring the reception level at the base station of the 
radio wave transmitted from the mobile station. Moreover, the allocation 
accept/reject judgement result is set to be the acceptance when the 
carrier to interference power ratios for the upward and downward links are 
greater than or equal to a prescribed threshold. 
The result obtained by this computer simulation is indicated in FIG. 16, 
where a system capacity is defined by an offered traffic per one radio 
zone at the call loss rate of 3%, and FIG. 16 shows a call loss rate as a 
function of the offered traffic per one radio zone which is normalized by 
the system capacity in the conventional radio channel allocation scheme 
using a single allocation priority level. 
It can be seen from this computer simulation result that the radio channel 
allocation scheme of this third embodiment can realize a considerable 
improvement of approximately 60% for the system capacity compared with the 
conventional radio channel allocation scheme using a single allocation 
priority level, and a further improvement of approximately 28% for the 
system capacity compared with the second embodiment described above. 
Thus, it can be confirmed that the radio channel allocation scheme of this 
third embodiment is indeed capable of improving the system capacity 
considerably while suppressing the control load to be sufficiently small, 
so that it is possible to realize a mobile communication system and a 
dynamic channel allocation scheme of an autonomous distribution type with 
a reduced control load and the further improved frequency utilization 
efficiency. 
A case of using the moving direction and the moving speed of the mobile 
station as the features of the mobile station is similarly capable of 
achieving the similar effects by the similarly simple control. 
As for the radio channels to be used in this third embodiment, it is 
possible to consider the use of the radio frequencies in the FDMA system, 
the use of the time slots in the TDMA system, and the repeated use of the 
spread codes or the frequency hopping patterns in the CDMA system, and the 
radio channel allocation scheme of this third embodiment is equally 
applicable to any of these cases, by making the allocation accept/reject 
judgement according to the measurement of the interference level or the 
carrier to interference power ratio as described above, for the 
substantially similar effects, just as in the second embodiment described 
above. 
Now, the fourth embodiment of a mobile communication system and a channel 
allocation scheme according to the present invention will be described. 
In this fourth embodiment, the mobile communication system has an overall 
configuration similar to that shown in FIG. 1 described above, where each 
base station 11 has a functional configuration relating to the radio 
channel allocation as shown in FIG. 17 which includes total Ki sets (Ki is 
an integer) of transceivers 13 (13.sub.1 to 13.sub.Ki), a transceiver 
controller 14 connected with the transceivers 13, a radio channel 
controller 15B connected with the transceiver controller 14, a call 
processing controller 16 connected with the radio channel controller 15B, 
a first memory 17B connected with the radio channel controller 15B, a 
mobile station feature measurement device 18 for measuring a feature of 
each mobile station, a mobile station feature measurement device 
controller 19 connected with the mobile station feature measurement device 
18 and the radio channel controller 15B, a parameter controller connected 
with the first memory 17B and the mobile station feature measurement 
device controller 19, and a second memory 26 connected with the parameter 
controller 25. 
The radio channel controller 15B carries out reading, updating, and writing 
of the data stored in the first memory 17B and specified by a request from 
the call processing controller 16, and manages the radio channel currently 
used by each base station. The transceiver controller 14 carries out a 
management of the transceivers 13.sub.1 to 13.sub.Ki, and makes an 
allocation accept/reject judgement for a radio channel specified from the 
radio channel controller 15B. 
The parameter controller 25 receives the mobile station feature measurement 
results from the mobile station feature measurement device 18 through the 
mobile station feature measurement device controller 19, and updates the 
measurement results stored in the second memory 26, while also calculating 
the thresholds for grouping of the mobile stations according to the 
measurement results stored in the second memory 25, and updates the 
threshold data stored in the first memory 17B. Here, the first memory 17B 
and the second memory 26 are indicated as separate components in FIG. 17, 
but these first and second memories 17B and 26 may be integrally provided 
by a single memory device if desired. 
Here, the radio channels are allocated by dividing the mobile stations into 
a plurality of groups according to the features of the mobile stations 
such as the distances, the moving directions, and the moving speeds with 
respect to each base station. For this reason, the first memory 17B is 
used for storing a table of a channel ID (ch.sub.1 to ch.sub.W) of each of 
W radio channels (W is an integer), and a used/unused flag indicating 
whether each radio channel is currently used or unused, as well as a table 
of a group ID (#1 to #N) of each group of the radio channels, and 
corresponding thresholds for the distance, the moving direction, and the 
moving speed to be used in dividing the mobile stations into N groups, as 
shown in FIG. 18. On the other hand, the second memory 26 is used for 
storing a distance data table, a moving direction data table, and a moving 
speed data table for measured distances, moving directions, and moving 
speeds of the mobile stations in past X states (X is an integer) of the 
mobile stations, as shown in FIG. 19. Here, a number of past states for 
which the measurement results are to be registered in this second memory 
26 may be different for the distances, the moving directions, and the 
moving speeds, if desired. 
In this configuration of FIG. 17, the radio channel allocation operation is 
carried out according to the flow chart of FIG. 20 as follows. 
When there is a radio channel allocation request with respect to a new call 
or a radio channel switching from the call processing controller 16, the 
radio channel controller 15B checks whether there exist radio channels 
which are currently unused or not, by reading the used/unused flags in the 
first memory 17A (step 210). In a case all the radio channels ch.sub.1 to 
ch.sub.M are currently used, this fact is notified to the call processing 
controller 16 and the operation is terminated. 
In a case there exist radio channels which are currently unused, next the 
radio channel controller 15B inquires the transceiver controller 14 as to 
whether there exist transceivers 13 which are currently unused or not 
(step 220). In a case there is no transceiver 13 which is currently 
unused, the transceiver controller 14 notifies this fact to the call 
processing controller 16 through the radio channel controller 15B and the 
operation is terminated. 
In a case there exist transceivers 13 which are currently unused, next the 
radio channel controller 15B commands the mobile station feature 
measurement device controller 19 to control the mobile station feature 
measurement device 18 such that the extraction of the features of the 
mobile station to which the radio channel is to be allocated such as the 
distance, the moving direction, and the moving speed is carried out by the 
mobile station feature measurement device 18 (step 230). 
Then, the mobile station feature measurement device controller 19 notifies 
the measurement result received from the mobile station feature 
measurement device 18 to the radio channel controller 15B and the 
parameter controller 25, and in response, the radio channel controller 15B 
compares the notified measurement result with the thresholds for 
determining the group ID stored in the first memory 17A, so as to 
determine the appropriate group ID (step 240). 
Then, the currently usable radio channels among the radio channels of the 
group with the group ID determined at the step 240 are selected and 
allocated according to a prescribed radio channel allocation procedure 
(step 250). In a case there is no currently usable radio channel among the 
radio channels of the selected group, the radio channel controller 15B 
notifies this fact to the call processing controller 16 and the operation 
is terminated. 
Next, the parameter controller 18 updates the measurement results recorded 
in the second memory 26 according to the measurement result notified from 
the mobile station feature measurement device controller 19 (step 260), 
and then reads out the past measurement results recorded in the second 
memory 28, calculates the thresholds for grouping the mobile stations from 
the read out past measurement results according to a prescribed 
calculation procedure, and updates the thresholds stored in the first 
memory 17B by the calculated thresholds, and the operation is terminated 
(step 270). 
In this radio channel allocation operation, the state of the mobile station 
is measured by the base station at a time of the radio channel allocation, 
but it is also possible to modify this aspect of the above radio channel 
allocation operation such that the measurement of the state of the mobile 
station is carried out by the mobile station itself. In such a case, it is 
possible to utilize a method in which the mobile station measures its own 
state in response to a command issued from the base station at a time of 
calling or call receiving, and reports the measured state to the base 
station, or a method in which the mobile station measures its own state 
autonomously at a time of calling or call receiving, or at a time of being 
in an idle state, and reports the measured state to the base station, for 
example. This fourth embodiment is equally applicable to either one of 
these methods, for essentially the similar effects. 
In addition, it is also possible to modify this radio channel allocation 
operation such that the updating of the measurement results and the 
thresholds at the steps 260 and 270 are carried out only when the radio 
channel allocation is successful at the step 250, and the steps 260 and 
270 are skipped with the radio channel allocation is unsuccessful at the 
step 250. More specifically, in such a case, the radio channel allocation 
operation is carried out, according to the flow chart of FIG. 21 which 
differs from that of FIG. 20 in that there is provided an additional step 
255 between the steps 250 and 280 for judging whether the radio channel 
allocation made at the step 250 is successful or not. In a case the radio 
channel allocation is successful, the operation proceeds to the steps 260 
and 270, whereas otherwise the operation is terminated. 
In general, the call which was not connected for such reason as that the 
currently unused transceiver does not exist or that the currently usable 
radio channel does not exist will be handled as a call loss in a loss 
system or as a waiting call in a delay system. The call which is handled 
as the call loss in the loss system or the call which is handled as the 
waiting call in the delay system but eventually not connected because of 
the limit on the waiting time or the abandonment of the waiting due to 
excessively long waiting time causes a phenomenon of repeated call 
generations and will be referred as a repeated call. When the system falls 
into the congested state and many repeated calls are generated, there is a 
possibility for the measurement results recorded in the second memory 26 
to be largely deviated from the actual traffic distribution. However, by 
carrying out the updating of the measurement results and the thresholds at 
the steps 260 and 270 only when the radio channel allocation is successful 
at the step 250, it is possible to prevent the occurrence of such a 
deviation of the measurement results and consequently it becomes possible 
to determine more the thresholds more accurately. 
Now, using a model shown in FIG. 22, the detailed procedure for determining 
the thresholds at the step 270 in the above radio channel allocation 
operation will be described. Here, the similar manner of determining the 
threshold can be used for a case of using the distance of the mobile 
station from the base station as the feature of the mobile station, a case 
of using the moving direction as the feature of the mobile station, and a 
case of using the moving speed as the feature of the mobile station, so 
that only a case of using the distance will be described below. 
In the model shown in FIG. 22, the service area of the system are covered 
by nine base stations BS1 to BS9, where each of the base stations BS1 to 
BS3 provided at a central region with a relatively heavier traffic has a 
smaller cell radius, while each of the base stations BS4 to BS9 provided 
at a peripheral region with a relatively lighter traffic has a larger cell 
radius. The practical mobile communication system often adopts a scheme 
for providing more base stations with smaller cell radii at a metropolitan 
area with heavier traffic and less base stations with larger cell radii at 
a suburb area with lighter traffic, and the model of FIG. 22 effectively 
represents such a practical case. 
In this model of FIG. 22, the cumulative frequency distribution of the 
distances of the mobile station from the base station appears as indicated 
in FIG. 23 for the base station BS1 at the central region and the base 
station BS5 at the peripheral region. Here, the distances of the mobile 
station from the base stations are estimated from the reception levels 
which are normalized by a required reception level, i.e., a reception 
level required in securing the required signal to thermal noise ratio. 
Because of the difference in the cell radii, the base station BS5 with a 
larger cell radius has a lower reception level. Then, the thresholds 
obtained by using the recorded data at the base station BS1 and the base 
station BS5 are as indicated in FIGS. 24 and 25, respectively. These FIGS. 
24 and 25 show a case of using four groups and determining the thresholds 
to make sizes of these groups equal to each other. The recorded data are 
expressed by the relative cumulative frequency, and the reception levels 
for which the relative cumulative frequency becomes equal to 0.25, 0.5, 
and 0.75 are determined as the thresholds TH2, TH3, and TH4 while the 
threshold TH1 is set equal to the required reception level. 
In this manner, by using this fourth embodiment, the thresholds for 
grouping of the mobile stations can be determined according to the states 
of the mobile stations without requiring a tedious designing. It is to be 
noted that FIGS. 24 and 25 show a case of determining the thresholds to 
make sizes of the groups equal to each other, but this fourth embodiment 
is equally applicable to a case of determining the thresholds to make 
sizes of the groups different from each other by merely changing the 
relative cumulative frequency value to be referred in determining the 
thresholds. 
By means of the above described processing, it becomes possible to provide 
a mobile communication system and a channel allocation scheme in which 
each base station can determine thresholds to be used in determining the 
grouping by its own autonomous processing, without requiring a cumbersome 
designing which takes enormous amounts of efforts and time and a 
re-designing in conjunction with the system expansion or the variation of 
the radio wave propagation state and/or the traffic distribution in the 
surrounding of each base station. 
Next, a variation of the fourth embodiment described above which utilizes a 
manner of determining the thresholds for grouping according to the order 
statistic of the past mobile station feature measurement results will be 
described. 
In this case, as indicated in FIG. 26, in addition to the distance data 
table for the measured distances L.sub.1 to L.sub.X, the moving direction 
data table for the measured moving directions D.sub.1 to D.sub.X, and the 
moving speed data table for the measured moving speeds V.sub.1 to V.sub.X 
of the mobile stations in past X states of the mobile stations, the second 
memory 26 further stores a table of group sizes PL.sub.1 to PL.sub.r of 
the groups for the grouping by distances of the mobile station from the 
base station, where r is a number of groups resulting from this grouping 
by distances, a table of group sizes PD.sub.1 to PD.sub.s of the groups 
for the grouping by moving directions of the mobile station, where s is a 
number of groups resulting from this grouping by moving directions, and a 
table of group sizes PV.sub.1 to PV.sub.t of the groups for the grouping 
by moving speeds of the mobile station, where t is a number of groups 
resulting from this grouping by moving speeds. 
Each of these group sizes has a value predetermined by a system operator 
within a range of greater than 0 and less than 1 such that: 
EQU PL.sub.1 +PL.sub.2 + . . . +PL.sub.r =1 
EQU PD.sub.1 +PD.sub.2 + . . . +PD.sub.s =1 
EQU PV.sub.1 +PV.sub.2 + . . . +PV.sub.t =1 
It is to be noted here that FIG. 26 is depicted as if r&gt;s&gt;t, but this is 
only an exemplary case and the relationships among r, s, and t can be 
arbitrary. Also, a number X of past states for which the measurement 
results are to be registered in this second memory 26 may be different for 
the distances, the moving directions, and the moving speeds. In general, 
for a larger number of groups, a larger number of measurement results are 
required, so that the number of past states for which the measurement 
results are to be registered in this second memory 26 may be varied 
according to the required number of groups. 
Then, the threshold for grouping is determined by the parameter controller 
25 according to the following procedure. Here, the similar manner of 
determining the threshold can be used for a case of using the distance of 
the mobile station from the base station as the feature of the mobile 
station, a case of using the moving direction as the feature of the mobile 
station, and a case of using the moving speed as the feature of the mobile 
station, so that only a case of using the distance will be described 
below. 
(a) In order to determine the threshold, the parameter controller 25 reads 
out the distance data L.sub.1 to L.sub.X stored in the second memory 26, 
and rearrange them in ascending order of their values as follows. 
EQU L.sup.(1) .ltoreq.L.sup.(2) .ltoreq. . . . .ltoreq.L.sup.(X) 
where a bracketed superscript indicates a sequential order number after 
this rearrangement, which is not related with the order in which the 
distance data L.sub.1 to L.sub.X are stored in the second memory 26. 
(b) Next, a natural number j which satisfies: 
EQU j/X&lt;PL.sub.1 .ltoreq.(j+1)/X 
is obtained. 
(c) Next, using the natural number j obtained in (b), the threshold (for 
distance) TL.sub.1 is obtained by the following formula: 
EQU TL.sub.1 =L.sup.(j) +(PL.sub.1 .times.X-j).times.(L.sup.(j+1) -L.sup.(j)) 
(d) The above (b) and (c) are repeated for each of the other group sizes 
PL.sub.2 to PL.sub.r similarly. 
This procedure of (a) to (d) described above corresponds to the processing 
at the steps 260 and 270 in the flow chart of FIG. 20. The determination 
of the threshold using the order statistic corresponds to the estimation 
of the distribution function of the population according to the 
observation values obtained from the population, and it is a 
non-parametric estimation independent of the shape of the distribution 
function of the population. 
By means of the above procedure of (a) to (d), the determination of the 
threshold can be made simpler compared with a manner of determining the 
threshold from the distribution function as explained above in conjunction 
with FIGS. 24 and 25, and it becomes possible to determine the threshold 
for grouping in accordance with the various different states of the 
different base stations, without requiring the cumbersome designing. 
As for the radio channels to be used in this fourth embodiment, it is 
possible to consider the use of the radio frequencies in the FDMA system, 
the use of the time slots in the TDMA system, and the repeated use of the 
spread codes or the frequency hopping patterns in the CDMA system, and the 
radio channel allocation scheme of this fourth embodiment is equally 
applicable to any of these cases, for the substantially similar effects. 
It is to be noted that the first embodiment described above may be combined 
with the second or third embodiment described above, and/or the fourth 
embodiment described above, while the second or third embodiment described 
above may be combined with the fourth embodiment described above, so as to 
enjoy the various effects of these embodiments together. 
It is also to be noted that besides those already mentioned above, many 
modifications and variations of the above embodiments may be made without 
departing from the novel and advantageous features of the present 
invention. Accordingly, all such modifications and variations are intended 
to be included within the scope of the appended claims.