Patent Abstract:
In a mobile communication system having a plurality of radio packet channels of different transmission rate with each other between a base station and a mobile station, undesirable interference to adjacent cells of adjacent base stations is decreased. Signal quality of a receive signal at a mobile station is measured, and the better said signal quality is, the higher packet channel is assigned. Thus, although signal quality is poor because of long distance between a base station and a mobile station, no increase of transmission power of a base station is requested. Thus, interference to adjacent cells is decreased. When high rate packet channel is selected, short packet transmission time may be assigned so that amount of data transmission is kept uniform in spite of said signal quality.

Full Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to mobile communication system between a mobile station and a base station having a plurality of radio packet channels with different transmission rate with each other. 
   Conventionally, a mobile communication system for packet communication has a plurality of packet channels each having a single common transmission rate between a mobile station and a base station. In that system, when a free packet channel is selected, a duration for a packet transmission, or a number of frames for continuous transmission, is assigned. 
   On the other hand, in a future mobile communication system, such as IMT-2000 standard, packet channels having a plurality of transmission rates are possible. In that system, a packet channel having a desired transmission rate must be, first, selected, and then, a duration for a packet transmission can be assigned. 
     FIG. 1  shows a configuration of a mobile communication system, in which there are a plurality of communication cells each located adjacently, and each cell comprises a base station  2  and a plurality of mobile stations  1 . A base station  2  is controlled by a control station  3  which is installed for a plurality of base stations  2 . An assignment of a packet is controlled either by a base station  2  or a control station  3 . 
   In a mobile communication system, when distance between a base station and a mobile station is defined, the higher transmission power is requested for the higher transmission rate. On the other hand, when a transmission rate of a packet is defined, the higher transmission power is requested, the longer the distance between a base station and a mobile station is. 
   Therefore, when the distance between a base station and a mobile station is long, and a transmission rate of a packet is high, the highest transmission power is requested. 
   However, when the distance between a base station and a mobile station is long, in other words, the mobile station locates close to a border of the cell of the own mobile station and the adjacent cell, the radio wave to/from said mobile station would affect interference to communication of adjacent cells. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to overcome the disadvantages and limitations of a prior packet assignment system by providing a new and improved packet assignment system in a mobile communication system. 
   It is also an object of the present invention to provide a packet assignment system in a mobile communication system, so that a radio packet is adaptively assigned so that no interference is affected to adjacent cells. 
   The above and other objects are attained by a mobile communication system having a plurality of radio packet channels having different transmission rate from each other between a base station and a mobile station; said mobile station comprising; means for measuring a signal quality of a receive signal from a base station, means for assigning packet rate relating to said signal quality thus measured, means for transmitting said packet rate to a base station, and data terminal for transmitting and receiving data to and from the base station with said packet rate. 
   Preferably, said signal quality is defined by propagation loss which is obtained by transmission power of a pilot signal at a base station and receive power of said pilot signal at a mobile station. 
   Preferably, said base station comprises; means for receiving packet rate from a mobile station, means for determining number of frames for continuous transmission for each packet rate, and means for transmitting said number of frames thus determined to a mobile station so that communication with said mobile station is carried out with the determined packet rate and the determined number of frames. 
   Still preferably, a short packet transmission time is assigned when a high transmission rate packet channel is selected, and a long packet transmission time is assigned when a low transmission rate packet channel is selected. 
   Still preferably, a small number of frames for continuous transmission and a large amount of data in each frame are assigned when a high transmission rate packet channel is selected, and a large number of frames for continuous transmission and a small amount of data in each frame are assigned when a low transmission rate packet channel is selected, so that data amount to be transmitted is uniform irrespective of selected transmission rate of a packet channel. 
   Preferably a packet channel is set a number of frames of continuous transmission for each transmission rate. Still preferably, said number of frames is adaptively adjusted. 
   Still preferably, when a high transmission rate packet channel is selected, a short packet transmission time is assigned, and when a low transmission rate packet channel is selected, a long packet transmission time is assigned, so that a mobile station takes a uniform amount of data to be transmitted or received, in spite of location relation of a base station and a mobile station. Preferable, when a high transmission rate packet channel is selected, a number of frames of continuous transmission is small and an amount of data for each frame is large, and when a low transmission packet channel is selected, a number of frames of continuous transmission is large and an amount of data for each frame is small. 
   Still preferably, a base station, upon finishing transmission or reception of a number of continuous frames to/from a mobile station, begins transmission or reception of a number of continuous frames to/from a next mobile station, so that a mobile station which communicates with a base station is switched recursively. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features, and attendant advantages of the present invention will be appreciated as the same become better understood by means of the following description, wherein; 
       FIG. 1  shows a system configuration of a conventional mobile communication system, 
       FIG. 2  is a system configuration of an embodiment of a mobile communication system according to the present invention, 
       FIG. 3  is a system configuration of another embodiment of a mobile communication system according to the present invention, 
       FIG. 4  is a system configuration of still another embodiment of a mobile communication system according to the present invention, 
       FIG. 5  shows a block diagram of a base station according to the present invention, 
       FIG. 6  is a block diagram of a mobile station according to the present invention, and 
       FIG. 7  shows signal sequence between a base station and a mobile station according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5  is a block diagram of a base station according to the present invention,  FIG. 6  is a block diagram of a mobile station according to the present invention, and  FIG. 7  shows signal sequence between a base station and a mobile station. 
   It is assumed in the present invention that no transmission power control is carried out in a base station and/or a mobile station, in other words, a base station and/or a mobile station transmits with the maximum power which is allowed to the base station and/or the mobile station, irrespective of transmission rate. 
   In  FIG. 5 , a base station comprises an antenna  10 , an antenna duplexer  11  for common use of a single antenna both for transmission and reception, a receiver  12  for receive process including frequency conversion from radio frequency to baseband frequency and demodulation, a transmitter  13  for transmit process including frequency conversion from baseband frequency to radio frequency and modulation. The numeral  13 A is a means for transmitting a pilot signal and a transmission power of the own base station, and is coupled with the transmitter  13 . The numeral  14  is a transmit/receive process for packeting/unpacketing, multiplexing/demultiplexing, and transmission of a number of continuous frames depending upon a determined communication ratio. The transmit process  14  is coupled with a network  16  through an interface  15 . 
   The numeral  20  is a packet rate receiver, coupled with the transmit process  14 , for receiving a packet rate which is transmitted by a mobile station. An output of the Packet rate receiver  20  is applied to a frame number decision process  22  which determines a number of frames transmitted continuously depending upon a packet rate. According to the present invention, when a packet rate is high, a number of frames transmitted continuously is small, and when a packet rate is low, said number is large, so that a number of frames in each transmission is almost uniform irrespective of a packet rate. The frame number decision process  22  has a table for determining a number of frames for continuous transmission for each packet rate received from a mobile station. 
   An output of the frame number decision process  22  is applied to a transmission queue  24  which shows whether there is a transmission queue of another mobile station in the base station or not. If the answer is yes, a mobile station which is waiting for transmission for the longest duration is determined (process  26 ), and a packet is transmitted or received to or from the determined mobile station (process  30 ). If the answer in the process  24  is no, a packet is transmitted or received to or from the mobile station which supplied a packet rate (process  28 ). 
   An output of the transmit/receive packet process  28  and an output of the transmit/receive packet process  30  are applied to the transmit/receive process  14 , for transmission/reception of a packet through a transmitter  13  or a receiver  12  and an antenna  10 . 
   A mobile station shown in  FIG. 6  comprises an antenna  40 , an antenna duplexer  41 , a receiver  42  for receive process including frequency conversion and demodulation, a transmitter  43  for transmit process including frequency conversion and modulation, a transmit/receive process  44  for packeting/unpacketing, multiplexing/demultiplexing, and reception of a number of frames for continuous transmission. 
   The transmit/receive process  44  is coupled with a handset  46  for speech and a data terminal  47  through an interface  45 . The data terminal  47  transmits/receives data. 
   The numeral  50  is a receive signal quality measure which measures a receive signal quality, which may be a propagation loss which is calculated by a receive level of a pilot signal and a transmission power of a base station. In the embodiment of  FIG. 6 , the process  52  receives the data of transmission power of a pilot signal by a base station, the process  54  measures receive power of a pilot signal at a mobile station, and the process  56  calculates the propagation loss which is the difference of the transmit power of a pilot signal at a base station and the receive power of a pilot signal at a mobile station. 
   The numeral  60  is a table search which determines a packet rate according to measured signal quality. When a signal quality is good, a packet rate is determined to be high, and when a signal quality is poor, a packet rate is determined to be low. A plurality packet rates are listed in a table corresponding to each signal quality, and one of the packet rate is selected according to the receive signal quality. 
   The determined packet rate is applied to a packet rate advice  62 , and is transmitted to a base station. 
     FIG. 7  shows a signal sequence between a base station and a mobile station for determining a packet rate and a number of continuous frames. 
   In  FIG. 7 , upon establishing a circuit between a base station and a mobile station, a base station transmits a mobile station a transmit power data (process  70 ). Alternatively, said transmit power data may be broadcast by a base station. That transmit power data is received by the mobile station (process  80 ), then the mobile station measures receive power of a pilot signal (process  82 ). The propagation loss (process  84 ) is calculated as the difference between the transmit power of a pilot signal at a base station and the receive power of a pilot signal at a mobile station. 
   Then, the mobile station searches a table (process  86 ) to determine a packet rate according to a signal quality (propagation loss) thus measured. The mobile station transmits the determined packet rate to the base station (process  88 ). 
   The base station receives the packet rate (process  74 ), then, determines a number of continuous frames according to the packet rate through a table search (process  76 ). The number of continuous frames thus determined is transmitted to the mobile station (process  78 ). 
   The mobile station receives the number of continuous frames (process  89 ). 
   Then, the mobile station and the base station begin the packet communication based upon the determined packet rate and the determined number of continuous frames (process  100 ). Thus, a data terminal  47  ( FIG. 6 ) begins the communication with another mobile station or a network through a base station with the determined packet rate. 
   Now, some modifications of the present invention will be described. The modifications concern how a signal quality is defined. 
     FIG. 2  shows an explanatory figure of a channel assignment for a packet according to the present invention, in which a signal quality at a mobile station is defined by a distance between a mobile station and a base station. A distance between a mobile station and a base station is first measured. When the distance is short, a high rate packet channel is assigned, and when the distance is long, a low rate packet channel is assigned. As shown in  FIG. 2 , a mobile station A located close to a base station is assigned a high rate packet channel, and a mobile station B located far from a base station is assigned a low rate packet channel. Thus, no interference is affected to an adjacent base station, and further, receive level at a base station of a signal from a mobile station is essentially controlled to be almost uniform. 
   In another modification, instead of measuring a distance between a base station and a mobile station, a signal quality is defined by a receive level of a signal received by a mobile station. A high receive level implies that a distance between a base station and a mobile station is short, and a low receive level implies the distance is long. Therefore, a base station transmits a pilot signal, and a mobile station measures a receive level S of a pilot signal from the base station. When the receive level S is high, a high rate packet channel is assigned, and when the receive level S is low, a low rate packet channel is assigned, as shown in the table 1. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               S 
               Packet channel 
               Comments 
             
             
                 
                 
             
           
           
             
                 
               Low 
               low rate packet channel 
               Mobile station B far 
             
             
                 
                 
                 
               from base station 
             
             
                 
               High 
               high rate packet channel 
               Mobile station A near 
             
             
                 
                 
                 
               to base station 
             
             
                 
                 
             
           
        
       
     
   
   In still another modification, a signal quality at a mobile station is defined by a distance between a mobile station and a border of a cell which the mobile station belongs covers. When a distance between a mobile station and a border is long, it means that a distance between a mobile station and a base station is short, and when a distance between a mobile station and a border is short, it means that a distance between a mobile station and a base station is long. Therefore, as shown in  FIG. 3 , a mobile station A which locates far from a border is assigned a high rate packet channel, and a mobile station B which locates close to a border is assigned a low rate packet channel. 
   In still another modification, a signal quality at a mobile station is defined by a receive level of a signal from a base station which the mobile station belongs, and receive levels of signals from adjacent base stations. A first base station which a mobile station belongs, and other base stations adjacent to said first base station transmit a pilot signal. The mobile station measures a receive level S 1  of a pilot signal from the first base station which the mobile station belongs, and receive levels S 2 -S n , of pilot signals from other base stations located adjacent to said first base station. Then, the maximum receive level S max  among receive levels S 2  through S n  is selected, and the difference ΔS between the first receive level S 1 , and said maximum receive level S max is calculated (ΔS=S 1 -S max ). When ΔS is large, it implies that a distance between a mobile station and a border of a cell from the mobile station is long, and when ΔS is small, it implies that the distance is short. Therefore, when ΔS is large, a high rate packet channel is assigned, and when ΔS is small, a low rate packet channel is assigned, as shown in the table 2. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 2 
             
             
                 
                 
             
             
                 
               ΔS 
               Packet channel 
               Comments 
             
             
                 
                 
             
           
           
             
                 
               Small 
               low rate packet channel 
               mobile station B close to 
             
             
                 
                 
                 
               border 
             
             
                 
               Large 
               high rate packet channel 
               mobile station A far from 
             
             
                 
                 
                 
               border 
             
             
                 
                 
             
           
        
       
     
   
   In still another modification, a receive signal quality at a mobile station is defined by an interference level I at a mobile station. When an interference level I is high, it means that there exist many other mobile stations near the own station. Therefore, it is essential to decrease transmission power so that interference affects less. On the other hand, when an interference level I is low, it is recognized that there exist less other mobile stations near the own station, and therefore, interference affects less even if transmission power is high. 
   Therefore, when an interference level I is low, high rate packet channel is assigned, and when interference level I is high, low rate packet channel is assigned. Table 3 shows the relations between an interference level I and packet channel to be assigned. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 3 
             
             
                 
                 
             
             
                 
               I 
               Packet channel 
               Comments 
             
             
                 
                 
             
           
           
             
                 
               Low 
               High rate packet channel 
               Less other mobile stations 
             
             
                 
               High 
               Low rate packet channel 
               Many other mobile stations 
             
             
                 
                 
             
           
        
       
     
   
   In still another modification, a receive signal quality at a mobile station is defined by receive SIR, or signal to interference ratio at a mobile station. When receive SIR is low, there exist many other mobile stations near own mobile station, and therefore, transmission power must be low so that interference affects less. On the other hand when receive SIR is high, there exist less mobile stations near own mobile station, and therefore, transmission power may be high. 
   Therefore, when receive SIR is low, low rate packet channel is assigned, and when receive SIR is high, high rate packet channel is assigned. Table 4 shows the relations between receive SIR and packet channel. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 4 
             
             
                 
                 
             
             
                 
               SIR 
               Packet channel 
               Comments 
             
             
                 
                 
             
           
           
             
                 
               High 
               High rate packet channel 
               Less mobile stations 
             
             
                 
               Low 
               Low rate packet channel 
               Many mobile stations 
             
             
                 
                 
             
           
        
       
     
   
   In still another modification, a receive signal quality at a mobile station is defined as follows. It is assumed the maximum transmission power P max  assigned to a packet channel at a base station, transmission loss L measured between a base station and a mobile station, interference power I measured at a mobile station, desired SIR designated for each packet channel, process gain G designated for each packet channel, and compensation factor A for compensating characteristics of an antenna and equipment. Then, the highest rate packet channel is assigned on the condition that the following inequality Is satisfied.
 
 P   max   &gt;=I−L+SIR−G +A 
 
   With the above scheme, the maximum rate packet channel available at the location of the mobile station is assigned. The closer to a base station the higher rate packet channel is assigned, and the farer from a base station, the lower rate packet channel is assigned. 
   As described above the present invention has the feature that a packet channel depends upon a receive signal quality at a mobile station or location relation of a mobile station and a base station. Therefore, rate of a packet channel to be assigned depends upon location where a mobile station locates. 
   Next, the present invention further provides a system which assures a predetermined uniform amount of data transmission to all the mobile stations, in spite of transmission rate of a packet channel. 
   In still another modification, a packet channel may be assigned a number of frames of continuous transmission for each transmission rate. Preferably, said number of frames of continuous transmission may be adaptively adjusted. 
   In still another modification, when high rate packet channel is assigned, short packet transmission time is assigned, and when low rate packet channel is assigned, long packet transmission time is assigned. Short packet transmission time means that the maximum number N max  of frames to be transmitted continuously is small, and long packet transmission time means that the value N max  is large. 
   In still another modification, when high rate packet channel is selected, a number of frames to be transmitted continuously is assigned small and amount of data for each frame is assigned large, and when low rate packet channel is selected, a number of frames to be transmitted continuously is assigned large and amount of data for each frame is assigned small. Amount of data for each frame is called as a frame payload, which is large for high rate packet channel. Table 5 shows an example. Thus, the same amount of data transmission is assured to all the mobile stations, in spite of rate of a packet channel. 
   
     
       
             
             
             
             
           
             
             
             
             
           
         
             
               TABLE 5 
             
             
                 
             
             
                 
               Number of frames 
                 
                 
             
             
               Packet 
               N max  of continuous 
               Frame 
               Amount 
             
             
               channel 
               transmission 
               Payload 
               of data 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               High (1024 Mbps) 
               1 
               128 kbytes 
               1.024 Mbps 
             
             
                 
                 
               (1024 kbits) 
             
             
               Low (16 kbps) 
               64 
                2 kbytes 
               1.024 Mbps 
             
             
                 
                 
               (16 kbit) 
             
             
                 
             
           
        
       
     
   
   In still another modification, when the base station finishes transmission or reception of the maximum continuous number of frames with a certain mobile station, the base station starts transmission or reception of the maximum continuous number of frames with another mobile station, so that a mobile station communicating with the base station is switched recursively. 
   With the above scheme, amount of data transmission of each mobile station is kept uniform. 
   Two priority modes in operation of communication control of the whole system are possible as follows.
         First priority mode; amount of data of each mobile station is kept constant.   Second priority mode; amount of data of a base station is kept constant.       

   In the above embodiments and modifications, it is assumed that the first priority mode is taken. As for the second priority mode, amount of data of a base station may be the maximum by assigning the value N max  of high rate packet channel large and the value N max  of low rate packet channel small. Thus, the flexible control of operation of a mobile communication system is possible merely by assigning a value of N max . 
   As described above, according to the present invention which assigns a radio packet adaptively, a transmission rate and/or transmission time of a packet is assigned adaptively according to location relation of a base station and a mobile station. Therefore, communication between a base station and a mobile station interferes less with adjacent cells of adjacent base stations. Further, a predetermined uniform amount of data transmission is assigned to each mobile station, in spite of location relation of a base station and a mobile station. Further, flexible control is a mobile communication system is possible. 
   From the foregoing, it will now be apparent that a new and improved mobile communication system which assigns a radio packet channel adaptively has been found. It should be understood of course that the embodiments disclosed are merely illustrative and are not intended to limit the scope of the invention. Reference should be made to the appended claims, therefore, for indicating the scope of the invention.

Technology Classification (CPC): 7