Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-02-12
2003-03-25
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S522000
Reexamination Certificate
active
06539226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a mobile communication system, and a mobile station and a base station to be employed therein. More particularly, the invention relates to a transmission power control system in a code divided multi access (CDMA) cellular system, to which soft hand over is applied.
2. Description of the Related Art
In a code divided multi access (CDMA) cellular mobile telephone system, a base station transmission power control technology for controlling a transmission power of a signal to be transmitted from a base station equipment on the basis of a power control information from a mobile station equipment, is employed.
FIGS. 30 and 31
are illustrations respectively showing control blocks of a mobile station and a base station for explaining the conventionally typical base station transmission power control method in the CDMA cellular mobile telephone system.
At first, discussion will be given for a control for transmitting the power control information from the mobile station equipment with reference to FIG.
30
. In the mobile station, a transmission signal to be transmitted from the base station is received and demodulated by a transmission/reception common unit
1
, an RF portion
2
and a demodulation
3
, and a reception quality Rq [dB] is measured by a reception quality measuring device
4
. Here, the reception quality is measured as a ratio of a received power of the base station transmission signal and unwanted signal power, such as interference and so forth, or a ratio of a received power of the base station transmission signal and an arbitrary reference received power constant.
The received reception quality Rq is compared with a required quality Rth by a comparing portion
14
. When the reception quality Rq is greater than the required quality Rth, a transmission power control bit is set at “0” in a processing portion
15
. Otherwise, the transmission power control bit is set at “1” by a processing portion
16
. The set transmission power control bit is inserted in a transmission signal by a transmission power control bit inserting portion
17
. Also, an overhead symbol containing various control information and so forth is inserted in an overhead inserting portion
10
.
A transmission data containing the transmission power control bit and an overhead information is transmitted to the base station via a spreading portion
9
, a modulator
8
and an amplifier device
7
of the mobile station equipment.
Next, discussion will be given for a transmission power control in the base station on the basis of the power control information from the mobile station with reference to
FIG. 31. A
reception signal including various data or various control information from the mobile station is received and demodulated via a transmission/reception common unit
21
, an RF portion
22
, a down converter
23
, a despreading portion
24
and a reception data demodulator
25
. Then, the transmission power control bit is extracted in the transmission power control bit detector
31
.
The extracted transmission power control bit is judged whether the value thereof is “1” or not in a processing portion
32
. If the transmission power control bit is “1”, a fixed transmission power control amount &Dgr;P is added for a current transmission power control signal Pctl in a processing portion
33
. Otherwise, the fixed transmission power control amount &Dgr;P is subtracted. A transmission spreading RF signal
28
is amplified by a variable amplifier
29
taking the current transmission power control signal Pctl as a control value and transmitted to the mobile station via the transmission/reception common unit
21
.
As set forth above, by the transmission power control according to the transmission power control block diagram, the base station transmission power control, in which the reception quality in the mobile station becomes Rth, can be achieved.
In addition to the foregoing transmission power control system (hereinafter referred to as “system A”), some transmission power control systems have been invented. For example, in a transmission power control system (hereinafter referred to as “system B”) recited in Kikuchi, Higashi, Ono, Technical Report of the Institute of Electronics, information and Communication Engineers, RCS96-13, May, 1996, pp 34, right column, links
1
-
15
, there has been proposed a method, in which all of the base station collects communication quality information of all of the connected mobile stations to determine a transmission power unitarily so as to achieve a required quality. By this method, developing of the transmission power can be completed at high speed to restrict occurrence of excessive transmission power during a period required for developing the transmission power.
On the other hand, in the transmission power control system (hereinafter referred to as “system C”) recited in Hamabe, Yoshida, Ushirbkawa, Technical Report of the Institute of Electronics, Information and Communication Engineers, RCS-84, August, 1996, pp 126, Section 2.1, there has been proposed a method, in which distribution amounts of the transmission power of the base station for respective mobile stations are determined by the mobile stations on the basis of a pilot reception power, and the base station unitarily determines the transmission power for respective mobile stations on the basis of the distribution information. Instead of seeking for the transmission power control system achieving the reception quality at the desired quality in respective mobile stations as in the systems A and B, this system C is directed only to make the reception quality of all of the mobile stations uniform. Accordingly, while interference restriction effect is considered to be lower in comparison with the system A, high precision and stable control can be performed as system makes reference to the pilot signal transmitted with high power.
In the cellular mobile communication, hand over, in which connected base stations are switched, is effected according to movement of the mobile station. The mobile station in the CDMA cellular mobile communication system, in which all base stations use the same frequency simultaneously, interference for other radio link has to be minimized by constantly connecting to the base station, at which a propagation loss becomes minimum (primary base station), and by performing transmission power control. However, since certain period is required for hand over to new base station, delay in connection with the primary base station can be caused to encounter a drawback in that communication with excessive power is inherent. Therefore, a method that the mobile station is connected to a plurality of base stations to preliminarily take the primary base stations, is employed. This method is referred to as soft hand over (or soft hand off).
Concerning the base station transmission power control during soft hand over, control system disclosed in Japanese Unexamined Patent Publication No. Heisei 9-74378 (hereinafter referred to as “system D”).
In the system D, concerning distribution method of the transmission power per the base station, there has been disclosed three methods, i.e. a method effecting distribution for equalizing the reception powers from respective base stations in the mobile station, a method effecting distribution for making a ratios of the reception power from respective base stations in the mobile station to be equal to the pilot reception level ratio, and a method effecting distribution for making the transmission powers of respective base stations equal to the ratio of the pilot reception level in the mobile station.
On the other hand, a related art relating to the base station transmission power control during soft hand over has been disclosed in commonly owned U.S. patent application Ser. No. 09/090,013. With the disclosed technology, reception qualities of down signals from a plurality of base stations during hand over are monitored in the mobile station and a signal desi
Furukawa Hiroshi
Hamabe Kojiro
Yoshida Shousei
Hunter Daniel
Nguyen Thuan
Scully Scott Murphy & Presser
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