News Column

Patent Issued for Base Station, Mobile Communication System and Radio Signal Quality Measurement Method

August 27, 2014



By a News Reporter-Staff News Editor at Telecommunications Weekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventor Takahashi, Mamoru (Kawasaki, JP), filed on May 31, 2012, was published online on August 12, 2014.

The patent's assignee for patent number 8805447 is Fujitsu Limited (Kawasaki, JP).

News editors obtained the following quote from the background information supplied by the inventors: "In a mobile communication system, a base station and a mobile station can both measure quality of received radio signal, so that the radio signal received from an apparatus of a wireless connection destination can be appropriately reproduced. Then, the base station and the mobile station can determine a transmission power control (TPC) value used as an index for determining transmission power of a radio signal according to the measured quality, and transmit the TPC value to the apparatus at the wireless connection destination.

"The base station and the mobile station measure, for example, a signal-to-interference ratio (SIR) to determine the quality of the received radio signal.

"For example, in cases where a code division multiplexing access (CDMA) is adopted as a multiplex system, a base station detects pilot symbols by applying a despreading operation to the received radio signal. The base station performs channel estimation using the detected pilot symbols, and then performs Rake combination. Then, after performing the Rake combination, the base station measures a receiving power of a pilot symbol period in an uplink-dedicated physical control channel (UL-DPCCH) and a power of interference signals. The base station acquires an SIR estimation value by dividing the received power of the Pilot symbol period by the power of the interference signals. Then, the base station compares the SIR estimation value with an SIR target value and determines a TPC bit value based on the comparison result. The base station transmits an uplink TPC bit value to the mobile station over a downlink-dedicated physical control channel (DL-DPCCH). Inner loop power control is realized by these operations.

"Conventionally, a base station and mobile station automatically control gain (AGC) of the radio signal so that the radio signal received through an antenna can be reproduced. Therefore, the power value of the received signal and the power value of the interference signal, which are used to calculate the SIR estimation value in the base station, are relative to a total power value of the radio signal received by the base station. Thus, a change in the total power value of the radio signal received by the base station causes the power value of the received signal and the power value of the interference signals to change. For example, when the total power value of the radio signal received by the base station increases, each of the power values of the received signal from each mobile station and the power value of the interference signals relatively decrease.

"The power value of the interference signal is measured by averaging signal distribution values of the pilot symbols in respective time slots over a plurality of slots. In order to estimate the power value of the interference signals correctly, the length of the period used for the averaging is set, for example, as a length corresponding to a plurality of frames, such as ten frames. However, a case may occur where the total received power in the base station is rapidly changed due to a change in the number of the mobile station connected with the base station in a same cell. In such case where the rapid change of the total received power occurs, the power value of the interference signals may be unable to follow the rapid change of the total received power since the power value of the interference signals is an average value of the values measured over a certain period as described above. Therefore, an error between the SIR estimation value and the actual value of SIR may become large, and as a result, there is a possibility that the mobile communication system may not perform normal transmission power control.

"Techniques for adjusting the length of the period for calculating the estimate value of the interference signals according to the change of the power value of the received signal have been developed (refer to Japanese Laid-open Patent Publication No. 2001-197017 and Japanese Laid-open Patent Publication No. 2005-167710, for example).

"For example, in such known techniques, while the apparatus for measuring the SIR detects desired wave power by the received signal, the apparatus detects interference wave power from the received signal. The apparatus applies an averaging process of earlier and later interference wave power detection values over a long period slot and an averaging process thereof over a short period slot. Furthermore, the apparatus obtains a difference of the two average values, thereby detecting an amount of the change of the interference wave power. The apparatus selects the average value over the short period in cases where the detected amount of the change of the interference wave power is large, and selects the average value over the long period in cases where the detected amount of the change of the interference wave power is small. Then, the apparatus obtains a ratio of the selected average value and the desired wave power.

"According to another example of a known technique, a calculator for instantaneous interference wave power calculates a spread value of reverse modulation symbols in a predetermined period, and outputs the value as an instantaneous interference wave power value. Moreover, a calculator for the number of averaging interference wave power calculates a number of averaging interference wave power, which is short if the amount of interference wave power change calculated by a calculator for the amount of interference wave power change is more than a threshold, and calculates a number of averaging interference wave power, which is long if it is less than a threshold. An interference wave power averaging device performs an averaging process to the number of the instantaneous interference wave power values corresponding to the number of averaging interference wave power, and outputs the averaged value as an interference wave power value. Moreover, the calculator for the number of averaging interference wave power calculates the number of averaging interference wave power according to an estimate value of propagation channel environment. The estimate value of propagation channel environment is calculated based on any of the amount of phasing change, the amount of other cell interference, the number of multipasses and the number of other cell paths, or combinations thereof."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "In the above-described known techniques, the apparatus which receives the radio signal calculates information for estimating whether or not the interference signal power may be changed, based on the received radio signal. Therefore, the apparatus receiving the radio signal may not adjust the measurement period for averaging the interference signal until a power change actually occurs. Thus, according to the conventional techniques, a case may occur where the apparatus receiving the radio signal, is subject to a rapid power change and may not adjust the length of the measurement period of the interference signal appropriately, and may be unable to reduce the difference amount between the estimate value and the actual value of SIR.

"According to one embodiment, a base station is provided. The base station includes: a received signal power measurement unit that calculates a radio signal power of a radio signal received from a mobile station which is connected by radio connection; a measurement period decision unit that decides a measurement period which is to be used for calculating an interference power based on a first index representing a transmission rate of received data transmitted from the mobile station and one of a second index representing a resource assigned to the mobile station and a third index representing an amount of data buffered in the mobile station and to be transmitted; an interference power measurement unit that calculates an interference power over the decided measurement period; a received signal quality measurement unit that calculates signal quality of the radio signal received from the mobile station based on the radio signal power and the interference power; and a transmission power decision unit that decides a transmission power control value to the mobile station based on the signal quality.

"According to another embodiment, a mobile communication system including a mobile station and a base station is provided. In the mobile communication system, the base station includes: a received signal power measurement unit that calculates a radio signal power of a radio signal received from the mobile station which is connected by radio connection; a measurement period decision unit that determines whether or not a transmission rate change of the data transmitted from the mobile station is expected to occur based on a first index representing a transmission rate of received data transmitted from the mobile station and, one of a second index representing a resource assigned to the mobile station and a third index representing an amount of data buffered in the mobile station and to be transmitted, sets a measurement period which is to be used for calculating an interference power to a first length when a period in which the transmission rate change is expected not to occur exceeds a certain period, while sets the measurement period to a second length shorter than the first length when the transmission rate change is expected to occur; an interference power measurement unit that calculates interference power by averaging power of interference wave over the measurement period; a received signal quality measurement unit that calculates signal quality of the radio signal received from the mobile station based on the radio signal power and the interference power; and a transmission power decision unit that decides a transmission power control value to the mobile station so as to cause the mobile station to increase the transmission value when the signal quality is lower than a target value, while decides the transmission power control value to the mobile station so as to cause the mobile station to decrease the transmission value when the signal quality is higher than the target value.

"According to still another embodiment, a radio signal quality measurement method is provided. The radio signal quality measurement method includes: calculating a radio signal power of a radio signal received from an apparatus of radio communication destination; determining whether or not a transmission rate change of data transmitted from the apparatus of radio communication destination is expected to occur based on a first index representing a transmission rate of received data transmitted from the apparatus of radio communication destination and, one of a second index representing a resource assigned to the apparatus of radio communication destination and a third index representing an amount of data buffered in the apparatus of radio communication destination and to be transmitted, setting a measurement period which is to be used for calculating an interference power to a first length when a period in which the transmission rate change is expected not to occur exceeds a certain period, while setting the measurement period to a second length shorter than the first length when the transmission rate change is expected to occur; calculating an interference power by averaging power of interference wave over the measurement period; and calculating signal quality of the radio signal received from the mobile station based on the radio signal power and the interference power.

"The purpose and advantage of the present invention are realized and achieved by elements especially indicated in the claims and combinations thereof.

"It should be understood that both the general description described above and the detailed description which will be described later, provide examples for illustrative purposes and are not intended to limit the present invention."

For additional information on this patent, see: Takahashi, Mamoru. Base Station, Mobile Communication System and Radio Signal Quality Measurement Method. U.S. Patent Number 8805447, filed May 31, 2012, and published online on August 12, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8805447.PN.&OS=PN/8805447RS=PN/8805447

Keywords for this news article include: Fujitsu Limited.

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Source: Telecommunications Weekly


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