Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-06-18
2002-07-02
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000
Reexamination Certificate
active
06414948
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric power controlling system for variable bit rate CDMA transmission which is applied to a mobile telephone system (cellular mobile telephone system) or the like using a direct spread code-division multiple accessing (DS-CDMA) system. More particularly, the invention relates to an electric power controlling system for variable bit rate CDMA transmission in which a plurality of bit rates are switched, and a mobile telephone system adopting the system.
2. Description of the Prior Arts
Hitherto, as a mobile telephone system of this kind adopting the direct spread code-division multiple accessing (DS-CDMA) system, IS-95 Standard of North American Standards TIA/EIA is widely known. In the IS-95 Standard, at the time of a reverse link from a mobile terminal as a transmitting side to a base station as a receiving side, one of four kinds of bit rates of 9.6 kbps, 4.8kbps, 2.4 kbps, and 1.2 kbps is selected for transmission. When 9.6 kbps is set to a basic rate and data is transmitted at bit rates of ½, ¼, and ⅛ of the basic rate, the variable rate transmission is executed in such a manner that transmission data is thinned to ½, ¼, and ⅛, respectively, and the resultant data is transmitted.
That is, one frame (20 msec) is divided into 16 slots each having an interval of 1.25 msec and, when data is transmitted at the basic rate of 9.6 kbps, the data is transmitted with all of 16 slots. In case of the bit rate of 2.4 kbps, 2.4 kbps, or 1.2 kbps, data is transmitted with only 8, 4, or 2 slots per one frame and transmission of other slots is stopped. In the method, the slot transmission is merely turned ON/OFF and a transmission electric power does not depend on the bit rate.
In the reverse link in the cellular mobile telephone system adopting the CDMA system, it is necessary to control a transmission electric power of a mobile terminal so that reception electric powers from respective mobile terminals such as a mobile telephone, and an information terminal are equalized. Particularly, in case of the variable bit rate system in which a bit rate of the mobile terminal dynamically changes, it is necessary to execute a control to equalize a reception electric power per information of one bit.
A control of the transmission electric power in the reverse link in OS-95 Standard will now be explained.
Since the base station cannot previously know a bit rate at which the mobile terminal transmits, the base station compares the reception electric power with a reference value for all slots and instructs the mobile terminal to increase or decrease the transmission electric power so that the reception electric power coincides with the reference value. The mobile terminal is controlled in accordance with only the instruction of the base station for the slots which have actually been transmitted and ignores the instruction to slots which have not been transmitted.
As mentioned above, in the transmission electric power control by the variable bit rate CDMA system, only the turn ON/OFF on a slot unit basis whereby the transmission electric power control is executed can be performed. Since the selection of bit rates is limited, an intra-frame interleave is restricted at a low bit rate, so that an effect of an error correction coding process is reduced. Therefore, since intervals of slots in which the reception electric power can be measured is widened, the control for the transmission electric power cannot follow a fast fading, so that its transmitting characteristics deteriorate. Since a burst transmission is executed, a hazard noise occurs. In this case, there is such a problem that an erroneous operation occurs due to the noise in, for example, a hearing aid or medical instruments located nearby.
On the other hand, in a forward link serving as an operation from the transmission of the base station to the reception of the mobile terminal of IS-95 Standard as well, the transmission in which one of the four kinds of bit rates of 9.6 kbps, 2.4 kbps, 2.4 kbps, and 1.2 kbps is selected can be similarly executed. However, it is different from a realizing method for the variable bit rate of the reverse link. In the forward link, the low bit rate is not realized by turning ON/OFF the transmission on a slot unit basis, namely, thinning in a manner similar to the reverse link. But, for example, in case of 4.8 kbps as shown in
FIG. 1
, the transmission electric power per one time is controlled to ½ instead of executing the transmission by repeating the same bit twice.
Similarly, in case of the bit rates of 2.4 kbps and 1.2 kbps, the electric powers per one time are set to ¼ and ⅛, respectively, instead of repeating the same bit four times and eight times, respectively. By the above-mentioned process, the transmission electric power per one bit can be held to be constant. In the variable bit rate processing method for the forward link as mentioned above, the problems involved in the reverse link as explained above, namely, a deterioration in characteristics due to the restriction of the interleave and hazard noise caused by with the burst transmission can be solved. However, since the transmission electric power is dynamically changed depending upon the bit rate in use, it is difficult to control the transmission electric power without previously knowing the bit rate so that the reception electric power per 1-bit information is equalized.
The reason why the realizing method for the variable bit rate for the forward link is different from that for the reverse link in IS-95 Standard is that the forward link uses a method in which it is unnecessary to execute a high-speed transmission electric power control and in which a deterioration in characteristics is small.
As such examples, “Spread Spectrum Transmitting Method” disclosed in Japanese Patent Application Laid-Open No. 5-102943 (1993) and “Transmission Bit Rate Discriminating Method and Apparatus” disclosed in Japanese Patent Application Laid-Open No. 8-130535 (1996) are known. In Japanese Patent Application Laid-Open No. 5-102943 (1993), a variable bit rate transmitting and receiving method similar to that for the forward link in IS-95 Standard is disclosed but the above-described problems associated with the transmission electric power control are difficult to solve.
Further, in Japanese Patent Application Laid-Open No. 5-102943 (1993), an improvement in the determination of the transmission bit rate in the variable bit rate system is shown. However, since the bit rate can be determined only after completion of the reception of a reception signal of one frame (20 msec in IS-95 Standard), such transmission electric power control as executed for every slot (1.25 msec in IS-95 Standard)is not applicable. Similarly, as a method of determining a bit rate after completion of the reception of a reception signal of one frame, a method of comparing a likelihood when a CRC check is executed at a plurality of bit rates or when a maximum likelihood decode is performed to a convolution code by a Viterbi algorithm or the like is known. In this case, however, a timing of the transmission electric power cannot be processed.
In order to solve the problem of the variable bit rate transmitting system for the reverse link in IS-95 Standard, namely, a deterioration in transmitting characteristics caused by delays of the control for the interleave and control for the transmission electric power, there has been also proposed another variable bit rate transmission method for transmitting only part of slots without turning ON/OFF the transmission on a slot unit basis on which the transmission electric power controlled is executed in a manner similar to that in the reverse link of IS-95 Standard. For example, a method of transmitting a frame which is transmitted at a bit rate that is ½ of the basic rate by using the whole slot in such a manner that the transmission of only the former half of one slot is ON and that of the lat
Chin Wellington
Dickstein, Shapiro, Morin & Oshinsky L.L.P.
NEC Corporation
Pham Brenda
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