Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-07-27
2001-06-19
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S226100, C455S226200, C455S238100, C455S277100, C455S277200, C375S130000
Reexamination Certificate
active
06249682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for estimating the moving speed of opposing stations in mobile communications system.
2. Description of the Related Art
Conventionally, for a channel multiplex method in mobile communications system, a time division multiple access (TDMA) system, frequency division multiple access (FDMA) system, etc. have been used. However, the development of a method with a more efficient use of frequency is desired, and particularly, a direct sequence code division multiple access (DS-CDMA) system is a promising candidate, since a large volume of communications are available with this system.
The DS-CDMA system is one kind of spread spectrum communication system. In this system, on the transmitting side data signals are transmitted with the spread spectrum by using the same frequency for a plurality of channels and multiplying the data signals by an independent spread code with a broad band for each channel, and on the receiving side the data signals for each channel are restored by multiplying received signals by the same spread code. The multiplication of a spread code on the receiving side is called a despread. When this DS-CDMA system is applied to mobile communications, a searcher function, transmission power control function, absolute coherent detection function, etc. are indispensable.
A searcher function means a function for detecting a transmission path and a despread code timing being a timing for performing a despread. A transmission power control function means a function for modifying a transmission power for near-far problem due to the difference in distance between a mobile station and a base station, and an instantaneous fluctuation (fading) due to multi-paths. A coherent detection function means a function for adding a pilot signal to data signals in order to obtain a required bit error rate (BER) in a lower transmission power when transmitting, and performing a coherent detection.
In mobile communications, a stable communication is required in such a variety of dynamically changing environments that a mobile station may transit from a stationary status to a high-speed status, and a mobile station may transit from an urban environment to a suburban environment, etc. Particularly, in a multi-path environment accompanied by reflected waves and delayed waves passing through a plurality of transmission lines, countermeasures are indispensable, since fading (instantaneous value fluctuation) is generated by interference. In the DS-CDMA system too, effective fading countermeasures are desired in connection with each of the above-mentioned functions.
However, there are the following problems in mobile communications using the DS-CDMA system.
Generally speaking, although there are optimal values for parameters of each unit of a communication apparatus against a fading generated during the communication, each parameter is not always set to the optimal value, since the fluctuation speed of the fading changes depending on the moving speed of the mobile station (or fading pitch). Therefore, when the parameters are not optimized, degradation is generated in the receiving characteristics, and thereby the channel capacity is reduced. It is necessary to estimate the moving speed of the mobile station at the base station in order to optimize each parameter.
However, in the DS-CDMA system, since a plurality of channels are multiplexed on the same frequency, unlike a TDMA or FDMA system which are well known as other multiplex methods, it is difficult to estimate the moving speed based on the measurement of the receiving field strength.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus and method for estimating the moving speed of a mobile station in mobile communications using a spread spectrum system such as a CDMA system, etc.
The apparatus for estimating a moving speed of the present invention comprises an input unit, a receiver unit, a power composer unit and a speed estimation unit.
In the first aspect of the present invention the apparatus for estimating speed is used in mobile communications for controlling transmission power between a transmitting station and a receiving station. The input unit inputs a transmission power control command transmitted from the receiving station to the transmitting station. The speed estimation unit: estimates the moving speed of the receiving station using the transmission power control command, and outputs a control signal corresponding to the estimated moving speed.
Each of the transmitting station and the receiving station corresponds to a base station or a mobile station, respectively, in mobile communications. For example, The DS-CDMA system controls so that a transmission power may be optimally set against a fading generated due to the difference in distance between the base station and the mobile station and the multi-path transmission line.
In this control a transmission power control command is created on the receiving side, the command is transmitted to the transmitting side. On the transmitting side the transmission power is modified based on the received transmission power control command. Since the value of the transmission power control command changes according to an instantaneous fluctuation such as a fading following the travelling of the mobile station, the moving speed can be estimated if the change is detected. The speed estimation unit estimates the moving speed of the receiving station based on the change or an accumulated value of the transmission power control command.
In the second aspect of the present invention the apparatus for estimating speed is used in mobile communications between a transmitting station and a receiving station. The receiver unit extracts a desired signal from the received signals, and the power composer unit generates the desired signal power from the desired signal. Then, the speed estimation unit estimates the moving speed of the transmitting station using the desired signal power, and outputs a control signal corresponding to the estimated moving speed.
For example, in the DS-CDMA system, received signals are in a state where the spectrum is spread, and a plurality of channels are multiplexed. For this reason, signals experiencing fading from the transmitting station cannot be observed before being despread. However, by despreading the signals the desired signal can be extracted, the influence of the fading can be observed, and thereby the moving speed can be estimated.
The receiver unit despreads the received signals and extracts the desired signal. The power composer unit generates a desired signal power from the extracted signals. Then, the speed estimation unit estimates the moving speed of the transmitting station based on the sample value of the desired signal power.
In fact, since the base station and the mobile station have both the functions of the transmitting station and receiving station, the base and mobile stations can estimate the moving speed of an opposing station using both transmission power control command and desired signal power. The parameters of the communications apparatus can also be set to an optimal value against fading by using a control signal outputted from the speed estimation unit.
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Kubo Tokuro
Minowa Morihiko
Davis Temica M.
Fujitsu Limited
Helfgott & Karas P.C.
Maung Nay
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