Telecommunications – Transmitter and receiver at separate stations – With control signal
Reexamination Certificate
1999-02-04
2002-01-29
Vo, Nguyen T. (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
With control signal
C455S522000
Reexamination Certificate
active
06343206
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to transmission power control apparatuses and radio communication apparatuses used for digital cellular mobile communications, etc.
2. Description of the Related Art
A multiple access system means a line access system when a plurality of stations carry out communications simultaneously using a same band. For example, CDMA (Code Division Multiple Access) refers to code division multiple access, a technology realizing multiple access through spread spectrum communications transmitting an information signal with its spectrum spread over a sufficiently wide band relative to the original information bandwidth.
This technology is sometimes called “spread spectrum multiple access (SSMA).” The mainstream of this CDMA system is a direct spreading system in which a spreading system code is carried on an information signal as is when it is spread.
Since a plurality of communications share a same frequency in the direct spreading CDMA system, the system has a problem (near-far problem) of equalizing the intensity of an interference wave (communication wave of a different station) with that of a desired radio wave at a receiving end and how to overcome this problem is a prerequisite to implement the CDMA system. The perspective problem becomes critical when a base station receives radio waves from many stations at different locations simultaneously, and thus it is essential for a mobile station to control transmission power according to the state of each transmission path.
As a transmission power control method, two methods are available; open-loop control performed based on the reception level of a mobile station and closed-loop control performed by a base station by feeding back information of its reception level to a mobile station as a control signal.
Mobile station transmission power Ti at transmission timing i (i=0 1, . . . ) in open-loop control is expressed as shown in expression (1) using transmission power PBS of the base station and reception level target value Rtg of the base station. In expression (1), Ri stands for the reception power of a desired radio wave.
Ti=Rtg+(P
BS
−Ri) (1)
A CDMA/TDD system which applies a TDD (Time Division Duplex) system that carries out communications by time-dividing a same radio frequency between transmission and reception to the CDMA system, is known to have the ability to implement dynamic and high-precision transmission power control relatively easily by means of open-loop control taking advantage of the high correlativity in characteristics of the propagation path between transmission and reception.
FIG. 1
is a block diagram showing the configuration of transmission power control apparatus
1
that performs open-loop control in conventional CDMA transmission. In this apparatus, reception power calculation circuit
11
calculates the reception power of a desired radio wave using the correlator output. Here, the reception system is provided with an AGC circuit, etc. and if the apparatus has a configuration in which the level of a received signal is adjusted before correlation operations, reception power calculation circuit
11
calculates correct reception power using not only the correlator output but also the adjustment value (AGC gain) above.
The correlator output is input to demodulation circuit
12
, and a control signal included in the received signal for controlling transmission power is demodulated and sent to transmission power calculation circuit
13
. Transmission power calculation circuit
13
calculates a transmission power set value (Ti of expression (1)) based on the reception power (Ri of expression (1)), transmission power (P
BS
of expression (1)) and desired reception level (Rtg of expression (1)) of the communication counterpart and outputs it.
On the other hand, transmission power Ti in closed-loop transmission power control is expressed as shown in expression (2) using transmitted power Ti−1 in the immediately preceding control cycle.
T
i
=T
i−1
+U
i
(2)
More precisely, Ui in expression (2) means a variation of power controlled by the control signal and generally indicates a preset value of power variation (hereinafter referred to as “step”) by which the transmission power is increased/decreased in response to the control signal which is an instruction for increasing/decreasing the transmission power. In further explanations, Ui will mean the value described above.
FIG. 2
shows transmission/reception intervals of a mobile station in a communication system which uses the TDD system as the communication system, its cycle (TDD cycle), MS reception power R on the downlink at that time, control signal (TPC for uplink) U and an example of the timing of MS transmission power T.
In
FIG. 2
, transmission power Ti of MS in TDD cycle i is calculated from expression (1) based on average reception power Ri in the immediately preceding reception interval, known base station transmission power P
BS
and desired reception level Rtg of the base station in open-loop control, while in closed-loop control it is calculated from expression (2) using received control signal Ui. Thus, in the CDMA/TDD transmission system using the transmission power control apparatus for mobile stations, power received from the base station is controlled so that it may be always fixed at a certain level for all mobile stations.
However, as is clear from expression (1), in open-loop control, the conventional transmission power control apparatus above has a problem that transmission power P
BS
of the base station and desired reception level Rtg of the base station must be known in order to calculate transmission power Ti from reception power Ri. It also has another problem that it is difficult to perform transmission power control on the downlink.
On the other hand, in closed-loop transmission power control, it has a problem that the transmission speed of the control signal transmitted from the base station to mobile stations increases in order to implement high precision transmission power control according to fading, which will reduce the frequency utilization efficiency.
SUMMARY OF THE INVENTION
The present invention has been implemented taking into account the points described above and it is an objective of the present invention to provide a transmission power control apparatus and radio communication apparatus in the CDMA radio system that allow dynamic transmission power control which is a feature of open-loop control without requiring information of the communication counterpart such as Rtg and P
BS
above, and also realize transmission power control at an equivalent control speed on the reverse line.
The present inventor et al. came to implement the present invention after taking notice of the fact that in the transmission power control apparatus, information on the reception power need not be transmitted from the communication counterpart on the uplink and downlink, discovering that the transmission power can be controlled accurately by storing the reception power of the preceding communication and calculating the transmission power from a difference from the actual reception power of communication using said information, without using the received transmission power P
BS
of the base station and desired reception level Rtg of the base station.
In other words, the main point of the present invention is to provide a transmission power control apparatus installed on the transmitting side comprising means for calculating desired radio wave reception power from a received signal, means for storing the reception power, means for storing past transmission power, means for demodulating a control signal included in the received signal and means for determining a transmission power set value, and determine the transmission power set value above using the past transmission power, desired radio wave reception power and control signal.
Furthermore, in addition to the above means, said transmission power contro
Hayashi Masaki
Kitade Takashi
Miya Kazuyuki
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Vo Nguyen T.
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