Showing papers by "NTT DoCoMo published in 1995"

Transmission power control for mobile radio using open and closed loop

Abstract: A transmission power control method of a mobile station in a CDMA (Code Division Multiple Access) system which primarily controls transmission power of the mobile station by using a closed loop control which enables high accuracy power control. When the received power at the base station of a signal from the mobile station suddenly increases owing to the state of buildings surrounding the mobile station, the transmission power of the mobile station must be quickly reduced to prevent the interference to other mobile stations. The mobile station measures an average value of the received power per transmission power control period of a desired signal from the base station, and detects the difference ΔRSSI between the current average value and that of one of the previous transmission power control periods. If ΔRSSI exceeds a reference power difference ΔPth, transmission power PT corresponding to ΔRSSI is set by using an open loop transmission power control to quickly reduce the transmission power of the mobile station. If ΔRSSI is lower than ΔPth, the transmission power PT is determined in accordance with the transmission power control bit sent from the base station.

CDMA demodulator and demodulation method

Abstract: A CDMA demodulator which can follow fast fading, and reduce interference components from other users in the same cell. A received input spread signal is despread by an orthogonal filer (103). The orthogonal filer provides the input spread signal with successive delays each of an amount of 1/m of the chip interval of a spreading code, multiplies the delayed signals by tap coefficients, and sums up the products, thereby outputting the despread signal. Pilot symbols in the despread signal are compared with known pattern pilot symbols by an absolute phase estimator/phase error compensator (107) to obtain phase fluctuations of the received pilot symbols. The phase fluctuations are interpolated to each information symbol, and each information symbol is phase compensated. The phase compensated information symbols are decided by a decision block (108). The tap coefficients are calculated by a tap coefficient controller (110) so that the mean square error of differences between signals before and after the decision is kept minimum, and the calculated values are fed back to the orthogonal filter.

Method and apparatus for transmission power control of a mobile station during soft handoff in a CDMA system

Abstract: A transmission power control method in CDMA, which is capable of increasing the capacity in terms of the number of subscribes by reducing transmission power by achieving highly accurate transmission power control during a soft handoff. A mobile station (PS1) determines its transmission power during the soft handoff by comparing a transmission power control bit from the old base station (BS1) with that from a new base station (BS2), and by selecting the transmission power control bit that indicates lower transmission power of the mobile station (PS1). In addition, the mobile station (PS1) determines the transmission power control bit for the base stations (BS1,BS2) by comparing the received SIR from the old base station (BS1) with that from the new base station (BS2), and by selecting the greater received SIR. This make it possible to reduce the transmission power, and increase the capacity in terms of the number of subscribers.

Transmission power control setting transmission power according to number of consecutive transmission power control bits having same value

Abstract: A transmission power control method of a spread-spectrum communication system which determines transmission power in accordance with a transmission power control bit. The transmission power control bit is extracted at a base station from a signal sequence obtained by receiving a signal transmitted from a mobile station, and by despreading and demodulating the received signal. When the same value of the transmission power control bit is consecutively received, the transmission power of the base station is controlled in accordance with transmission power control quantities which are predetermined in accordance with the consecutive number of receptions of the same value of the transmission power control bit. This is because the consecutive receptions of the same value of the transmission power control bit suggests that the received power of the other party (the mobile station in this case) changes greatly. Thus, an amount of an increment or a decrement in the transmission power is increased with the duration of the consecutive receptions. This makes it possible for the transmission power control to follow sudden changes in propagation paths.

Synchronous detector and synchronizing method for digital communication receiver

Abstract: A synchronous detecting method in which the transfer function of a propagation path is estimated by regarding the information symbols adjacent to pilot signals as known symbols and using the information symbols as pseudo-pilot signals. The method includes a step of estimating the transfer function by using the pilot signals, a step of performing interpolation synchronous detection of part of the information symbols by using the estimated transfer function, a step of storing the result of the interpolation synchronous detection as pseudo-pilot signals, a step of reestimating the transfer function related to information symbols corresponding to the pseudo-pilot signals from the pseudo-pilot signals and the received signals corresponding to the pseudo-pilot signal, regarding the pseudo-pilots as known correct signals, and a step of performing interpolation synchronous detection of each information symbol by using the reestimated transfer function. Thus, the detection characteristic can be improved by estimating the transfer function with high accuracy even when the number of symbols per pilot signal is small.

CDMA demodulation circuit and demodulation method

Abstract: A CDMA demodulation circuit which can reduce interference wave components from another user in the cell and can follow up high-speed fading. The frequency band of the received inputted spread-spectrum signals are compressed back by means of an orthogonalizing filter (103). The filter (103) successively gives a delay of 1/m of the chip period of the spread codes to the inputted spread-spectrum signals and outputs compressed-back signals by multiplying the inputted spread-spectrum signals by a tap factor and summing up the multiplied results. An absolute phase estimating and phase error compensating section (107) compares the pilot symbols in the compressed-back signals with the pilot symbols of a known pattern and finds the phase shifts of the received pilot symbols. The section (107) compensates the phase of each information symbol by interpolating the phase shifts in the respective information symbols. An identifying and judging section (108) identifies the phase-compensated information symbols. A tap factor control section (110) calculates the tap factor so that the mean square error of the errors of signals before and after the identification may be the minimum and feeds back the calculated tap factor to the filter (103).

Transmission power control method and apparatus for mobile communications using a cdma (code division multiple access) system

Abstract: A transmission power control method is disclosed for controlling transmission power of radio communications in a CDMA system. The transmission power of a first transmitted signal transmitted from a first station is determined by a transmission power control signal contained in a second transmitted signal sent from a second station. The first station receives the second transmitted signal in the form of convolutional codes, and decodes it by using a first Viterbi decoder and a second Viterbi decoder. The first and second Viterbi decoders includes path memories with the path history length of different first predetermined lengths. The transmission power control signal contained in the second transmitted signal is extracted from the output of the second Viterbi decoder, whereas the other information data is obtained from the output of the first Viterbi decoder. The first station controls the transmission power of the first transmitted signal on the basis of the extracted transmission power control signal.

Transmission power control for mobile radio

Abstract: A transmission power control method for a CDMA system including the steps of calculating an actual SIR (Signal-to-Interference Ratio) of a desired signal; deciding whether the actual SIR is greater than a predetermined reference SIR which satisfies a predetermined communication quality; forming a transmission power control bit on the basis of a result of deciding; inserting the transmission power control bit periodically into a forward frame, which steps are performed at the base station, and steps of calculating tentative reverse transmission power in accordance with the transmission power control bit in the forward frame; deciding reverse transmission power such that the reverse transmission power is made equal to the tentative reverse transmission power when the tentative reverse transmission power is less than a predetermined maximum transmission power, but otherwise made equal to the predetermined maximum transmission power; and transmitting a signal from the mobile station to the base station at the reverse transmission power, which steps are performed at the mobile station. This makes it possible to prevent the transmission power from diverging to the maximum output of a transmitter power amplifier.

Cellular mobile radiocommunication system soft-handover scheme

Abstract: A mobile communication scheme realizing highly reliable handover and improved service quality. The communication signals containing identical communication data are transmitted simultaneously from the mobile station to more than one base station at a time of the handover, such that reception signals are composed from the communication signals received by more than one base station by using the reliability information for the received communication signals. For the packet communication, the identification information for identifying each packet is attached to each packet, and the reliability information for each packet is measured, such that the reception packets can be obtained according to the identification information attached to each packet and the reliability information measured for each packet.

Transmission power control for mobile radio communications using a CDMA and Viterbi coding

Abstract: A transmission power control method for controlling transmission power of radio communications in a CDMA system. The transmission power of a first transmitted signal transmitted from a first station is determined by a transmission power control signal contained in a second transmitted signal sent from a second station. The first station receives the second transmitted signal in the form of convolutional codes, and decodes it by using a first Viterbi decoder (15) and a second Viterbi decoder (16). The first Viterbi decoder (15) includes a path memory with the path history length of a first predetermined length, and the second Viterbi decoder (16) includes a path memory with the path history length of a second predetermined length which is shorter than the first predetermined length. The transmission power control signal contained in the second transmitted signal is extracted from the output of the second Viterbi decoder, whereas the other information data is obtained from the output of the first Viterbi decoder. The first station controls the transmission power of the first transmitted signal on the basis of the extracted transmission power control signal. This makes it possible to achieve highly accurate, fast responsive transmission power control.

Mobile satellite communication system

Abstract: A transmission power control method in a mobile satellite communication system implementing accurate control of transmission power of a base station by obtaining an average received signal level at a mobile station at high accuracy. The mobile station measures an average received signal level Q k in a predetermined period (step SP2), and informs the base station of the average received signal level Q k and an actual measuring time T k (step SP3). The base station calculates a total measuring time t k which is the sum total of the actual measuring time T k (step SP16), a corrected average received signal level R k associated with the average received signal level during the total measuring time t k (step SP18), and a measuring error ΔD k (step SP17), and controls the transmission power on the basis of these values (step SP21). Estimating the measuring error ΔD k in the total measuring time t k longer than the individual actual measuring time T k makes it possible to reduce the measuring error, thereby implementing highly accurate transmission power control.

Mobile communication system having message-storing function and method thereof

Abstract: A mobile communication system in which an automatic answering function is provided both in a communication network (10) and in a mobile station (20). When the mobile station (20) does not respond, the communication network (10) responds and stores the message instead, and informs the mobile station of the storage of message. The mobile station requests the transfer of the stored message at any convenient time. This makes it possible to reliably transmit message even to mobile stations that are unavailable for communication for a long time.

Device and method for initially synchronizing spread-spectrum code of cdma transmission system

Abstract: A CDMA system which can quickly establish initial synchronization of long codes which are spread-spectrum codes having periods which are much longer than the symbol length. The system inserts a priori codes which have a correlation value of nearly zero with respect to the long codes and an autocorrelation value which changes triangularly into spread-spectrum signals whose bandwidth is spread by the long codes at regular intervals, detects the timing at which reception of a priori codes is started, and estimates the reception phase of the long codes. The system is provided with an a priori code inserting circuit on the transmitting side and an a priori code replica generating circuit on the receiving side. The system is also provided with a plurality of correlators for finding the correlation value between the received signal and the replica of the a priori signal and a circuit for finding the maximum correlation value among the correlation values and its reception starting timing. The system estimates the timing at which that a priori signal is received from the reception starting timing at which the maximum correlation value is obtained, and infers that the point of time at a fixed time interval from the estimated timing is the point of phase reception of the long codes.

Method for controlling transmission power for cdma system and device

Abstract: PURPOSE:To conduct high-accuracy transmission power control with high responsiveness by decoding only the transmission power connecting bit in a short period while using a simplified viterbi decoder, and controlling the transmission power based on this decoded result. CONSTITUTION:A received digital signal outputted from a reception radio part 12 is demodulated by a demodulating part 14 after diffusion is removed by an inverse diffusing part 13. The demodulated received signal is distributed to two systems. The received signal of the first system is decoded by a normal viterbi decoder 15 equipped with a path memory with and about five times restrict length. The received signal of the second system is decoded by a simplified viterbi decoder 16 equipped with a path memory of which the memory length is shorter. As an information data signal, the output of the normal viterbi decoder 15 is used. On the other hand, the transmission power control is performed while using the transmission power control bit of the signal decoded by the simplified viterbi decoder 16. A transmission power control bit extracting part 17 extracts the transmission power control bit from the signal decoded by the simplified viterbi decoder 16.

Mobile communication system using base station frequency correction scheme

Abstract: A mobile communication system having a high precision frequency base station device with a high precision frequency generator, and the other low precision frequency base station device with a low precision frequency generator which receives transmission waves from the high precision frequency base station device using a transmission frequency in a prescribed frequency precision, and carries out transmission and reception by controlling transmission and reception frequencies of own station in accordance with the frequency precision of the received transmission waves. It is also fine to provide a mobile station device for a mobile station which receives the transmission waves from the high precision frequency base station device, controls a reference frequency to be a reference for transmission and reception frequencies of own station in accordance with the frequency precision of the received transmission waves, and carries out transmission and reception with respect to a base station using transmission and reception frequencies according to the controlled reference frequency, and make the low precision frequency base station device to receive the transmission waves from the mobile station device carrying out transmission and reception using the transmission and reception frequencies according to the controlled reference frequency, control a reference frequency to be a reference for transmission and reception frequencies of own station in accordance with the frequency precision of the received transmission waves, and carry out transmission and reception with respect to the mobile station using transmission and reception frequencies according to the controlled reference frequency. (FIG. 1)

Speech information freeze-out control method and equipment in mobile satellite communication system

Abstract: A speech freeze-out method in a communication system for transmitting speech information, which is sent from public telephone terminals (1) to a control center (5) through voice channels, from the control center (5) to a base station (8) through time division multiplexing radio frequency channels (6), and from the base station (8) to mobile stations (17) through transponders (13). The freeze-out processing is carried out when the control center (5) feeds the speech information to the time division multiplexing radio frequency channels (6) so that the number of transmission channels from the base station (8) to the transponders (13) is limited within an upper limit value. The control center (5) sequentially detects the presence and absence of a speech spurt in each frame of respective voice channels during each time slot of the time division multiplexing radio frequency channels, counts the number of the channels including the speech spurt, and performs the speech freeze-out processing when the count value exceeds the upper limit value. The number of transmission channels from the base station (8) to the transponders (13) is positively limited within the upper limit value.

Mobile communication system using base station frequency correcting method

Abstract: A mobile communication system equipped with a high-accuracy frequency base station device having a high-accuracy frequency oscillator and a low-accuracy frequency base station device which has a low-accuracy frequency oscillator, receives radio waves of a frequency of prescribed frequency accuracy transmitted from the high-accuracy frequency base station device, and performs transmission/reception of radio waves by controlling the frequency accuracy of the transmission/reception in accordance with the frequency accuracy of the radio waves from the high-accuracy frequency base station. A mobile station device of a mobile station may be provided in the mobile communication system. The mobile station device receives radio waves transmitted from the high-accuracy frequency base station device, controls the reference frequency which is the reference of the own transmission/reception in accordance with the frequency accuracy of the received radio waves from the high-accuracy frequency base station, and performs transmission/reception to/from a base station with the transmission/reception frequencies based on the controlled reference frequency. The low-accuracy frequency base receives radio waves transmitted from the mobile station device, controls the reference frequency which is the reference of the own transmission/reception frequency in accordance with the frequency accuracy of the received radio waves from the mobile station, and transmits radio waves to the mobile station device with the transmission/reception frequency based on the controlled reference frequency.

Time diversity communication system

Abstract: The reception rate of a radio selective call receiver is improved by a time diversity system. Time diversity reception is applied to both the address signal and message signal constituting a call signal. Namely, the time diversity reception is executed for every error correcting or detecting code word which is the unit constituting the address and message signals irrespective of whether the signal is the address or message signal. For example, out of the code words having the same contents received several times, code words which are judged to be properly decoded in accordance with the error detection decoding logic are selected, and thus receiving signals composed of properly decoded code words can be obtained. Alternatively, a code word having the minimum possibility of error correction can be selected out of the corrected code words having the same contents received several times, by selecting the code word having the smallest number of error-corrected bits from among the code words which are judged to be properly decoded in accordance with the error correcting decoding logic. Thus, the reception rate of the radio selective call receiver is improved. When a code word is properly decoded, in addition, part of the radio selective call receiver is made in operative by inhibiting the reception of the code words having the same contents transmitted thereafter. As a result, the battery consumption of the receiver is reduced.

Mobile radio communication system and radio receiver

Abstract: A system which transmits a calling signal to radio sections to selectively call a radio receiver. The number of times of transmission of the calling signal from a base station is variable, so that the facility of the base station can be built at a relatively low cost even when the number of subscribers per service area is small.

Mobile machine to which subscriber number can be registered and subscriber number storage device

Abstract: PURPOSE: To set plural subscriber numbers stored in a storage device on a mobile machine. CONSTITUTION: A subscriber number storage device 1 is inserted into the reader 2 of the mobile machine. The mobile machine is controlled by a controller 4 and it reads the plural subscriber numbers stored in the subscriber number storage device 1 and mobile machine numbers and stores them in a storage device 3. The subscriber numbers and the mobile machine numbers, which are stored in the storage device 3, are held even if power is cut. The mobile machine reads the plural different subscriber numbers stored in the installed device, reads one or plural different subscriber numbers into the mobile machine and registers the subscriber number which is read to a network. Thus, different use in the communication of the subscriber numbers corresponding to the need of a user can be realized and the convenience of the user improves. COPYRIGHT: (C)1996,JPO

Mobile communications system and radio receiver

Abstract: In a system which transmits paging signals a plurality of times through the air by radio waves, said paging signals serving to selectively page radio receivers: base station facilities can be deployed at comparatively low cost even when there are few customers per service area, by variably setting the number of times that paging signals are transmitted from the base stations.

Power control in mobile satellite communication system

Abstract: A transmission power control method in a mobile satellite communication system implementing accurate control of transmission power of a base station by obtaining an average received signal level at a mobile station at high accuracy. The mobile station measures an average received signal level Q k in a predetermined period (step SP2), and informs the base station of the average received signal level Q k and an actual measuring time T k (step SP3). The base station calculates a total measuring time t k which is the sum total of the actual measuring time T k (step SP16), a corrected average received signal level R k associated with the average received signal level during the total measuring time t k (step SP18), and a measuring error ΔD k (step SP17), and controls the transmission power on the basis of these values (step SP21). Estimating the measuring error ΔD k in the total measuring time t k longer than the individual actual measuring time T k makes it possible to reduce the measuring error, thereby implementing highly accurate transmission power control.

Method and device for shutting out audio information in satellite mobile communication system

Abstract: In a communication system where audio information transmitted from a telephone terminal (1) through an audio channel to a control station (5) is transmitted from the control station (5) through a time-division multiplex line (6) to a base station (8) and further transmitted from the base station (8) through a satellite repeater (13) to a mobile station (17), audio signals are shut out when audio information is transmitted from the control station (5) through the time-division multiplex line (6) so as to decrease the number of transmission channels from the base station (8) to the satellite repeater (13) to below an upper limit. The presence/absence of audio signal in each frame of each audio channel is successively detected at every time-division multiplex time slot and the number of channels through which audio information is transmitted is counted. When the count value exceeds the upper limit value, the audio signals are shut out.