Showing papers by "NTT DoCoMo published in 1994"

Correlation detector and communication apparatus

Abstract: A correlation detector for CDMA communication receivers, which can establish synchronization at a high speed, can extract mutually correlated components, and can perform highly accurate tracking. The received signal (21) is fed to a matched filter (43) when the initial synchronization is established. When a synchronization judging circuit (45) judges that the filter (43) detects synchronization, the switching circuit (42) feeds the signal (21) to multipliers (47, 48), and resets a VCCG (29) and a spread-spectrum code replica generator (30). After the synchronization is established, the spread-spectrum signal is detected quasi-synchronously, the received signal quasi-synchronously detected is multiplied by replical codes having advanced and lagged phases, and correlation detection signals are extracted from the multiplication results. The square components are generated, added together in opposite phases, and averaged in the time direction. The received spread-spectrum signal is multiplied by the codes whose phases are synchronous, and the results are integrated over chips. The signal, after the averaging processing, is reversely modulated by use of the identification signal of the received data obtained by compensation for the phase error of the received signal in order to generate a phase error signal. The replica code generator is driven by a clock the phase of which is controlled by the phase error signal.

Mobile radio communications system

Abstract: Transmission quality and throughput are improved when communication is carried out using fixed-length packets in wire circuits between radio base stations and a mobile switching center in mobile radio communications systems. Low bit-rate digital information signals are converted to short packets by a plurality of information data assembly/disassembly circuits provided in parallel. A plurality of these short packets are transmitted after being inserted into a long fixed-length packet by means of a fixed-length packet assembly/disassembly circuit, and a plurality of short packets are extracted from the fixed-length packet and then restored to the low bit-rate digital information signals by information data assembly/disassembly circuits. This enables high throughput, economical communication paths to be constructed.

Automatic gain control apparatus, communication system, and automatic gain control method

Abstract: An automatic gain control apparatus of a spread spectrum signal receiver which can quickly follow distance variations, median variations, and instantaneous variations due to Rayleigh fading. An output of a variable gain amplifier 22 is quadrature-detected, the detected outputs are A/D converted, the digital output thereof are supplied to a despreading processor 34 through a digital level corrector 33, and the despreading output undergoes the instantaneous envelope detection by an instantaneous envelope detector 37. The envelope-detected signal is supplied to a symbol timing generator 38 which extracts data symbol timing component using a peak signal as a trigger, and a time window through which a desired signal enters is calculated from the symbol timing. Within the time window, the output of the instantaneous envelope detector 37 undergoes time integration by a level detector 43, and its output shifts the level of the digital level corrector 33, thereby making the output constant. The output of the level detector 43 is averaged over a few symbol length by a level detector 44 whose output controls the gain of the variable gain amplifier 22, thereby making its output constant.

Receiver for spread spectrum communication

Abstract: A receiver for spread spectrum communication which does not require any highly accurate, highly stable VCO for its local signal generator. The receiver has a correcting circuit which corrects base-band signals obtained by compression-back, a RAKE circuit which demodulates the corrected base-band signals to reproduce information, and a re-modulating circuit which generates signals similar to primary modulated signals on the transmission side by re-modulating demodulated signals outputted from the RAKE circuit, a multiplying circuit which multiplies the complex conjugate of the output of the re-modulating circuit by the base-band signals and outputs signals obtained by eliminating the modulated components of the base-band signals from the product, an averaging circuit which removes the noise component of the base-band signals by averaging the output of the multiplying circuit and outputs only the frequency offset component of the received signals and local signals, and a circuit which obtains the angular velocity of the frequency offset component and uses, as correcting signals, the signals having the angular velocity and the polarity opposite to that of the base-band signals. The receiver eliminates the frequency offset components by means of the correcting circuit.

Code Division Multiple Access Transmitter and Receiver

Abstract: A code division multiple access transmitter and receiver that makes it possible to reduce its size by designating a spreading code and a carrier frequency in a baseband. It includes a primary modulator for performing primary modulation by transmission information, thereby producing a primary modulated I signal and a primary modulated Q signal, a spreading code generator for generating a spreading code with a frequency higher than a rate of the transmission information, a secondary modulator for spread-modulating the primary modulated I signal and Q signal by using the spreading code, thereby outputting spread I-channel data and spread Q-channel data, a frequency offset circuit for offsetting the center frequency of the spread I-channel data and Q-channel data by a designated offset frequency, thereby outputting frequency offset data, and a transmitting circuit for converting the frequency offset data into a transmitted signal.

Automatic gain control apparatus and method for a spread spectrum signal receiver

Abstract: An apparatus for automatically controlling the gain of a spread spectrum signal receiver, which follows up at a high speed the instantaneous variation resulting from change in the distance, change in the median, and Rayleigh fading. The output of a variable gain amplifier (22) is orthogonally detected. The detected output is converted by an A/D converter. This digital output signal is fed to compressor (34) through a digital level corrector (33). The compressed spectrum output is instantaneously detected by an instantaneous envelope detector (37). The data symbol timing component of the signal detected is extracted by a symbol timing extractor (38) using the peak signal as trigger. From this symbol timing, the width of the window of time at which a desired wave arrives is calculated. Over this width of the window, the output of the instantaneous envelope detector (37) is integrated with respect to time by a level detector (43). By this output, the level of the digital level corrector (33) is shifted, thus making its output constant. Also, the values of the output of the level detector (43) are averaged by a level detector (44) over several symbols. By this output, the gain of the variable gain amplifier (22) is controlled, thus making its output constant.

CDMA communication with multiplex transmission of data over a long distance with a low to a high rate

Abstract: of EP0652650A CDMA communications method capable of multiplex transmission of data over a wide range from a low rate to high rate such as image data without a considerable increase in a circuit scale. A fundamental transmission rate is determined, for example, at 32 kbps, a rate higher than 8 kbps conventionally used. The data whose transmission rate is equal to the fundamental transmission rate is transmitted in frames including no vacant portion. Data whose transmission rate is lower than the fundamental transmission rate (16 kbps, for example) are transmitted in frames including vacant portions. The vacant portions are not transmitted. This makes it possible to receive data through other channels during a time period associated with the vacant portions. Data of a higher transmission rate, 128 kbps, for example, can be multiplexed and transmitted through four channels using different spreading codes.

Wireless call system

Abstract: In a mobile communication system for calling mobile unit by repeatedly transmitting the same call signal by n call frames, each call frame is constituted by n sub-frames each containing a call signal and having a predetermined length, a sub-frame containing a new call signal is disposed at one of the ends of the call frame, and the sub-frames are shifted in their sequence each time after the first call. According to this construction, the number of times of transmission can be known on the receiver side without transmitting additional information, and time diversity reception can be made on the reception side.

Device for Testing an Amplifier

Abstract: A plurality of PN modulators (28) are provided corresponding to a plurality of oscillators (22) at stages preceding or following them, or fluctuation is given to division ratios at the oscillators (22). Since each of n carriers combined by a combiner (24) contains phase fluctuation, the possibility that the peaks will overlap each other or that the carriers having opposite phases will negate each other is very low. The peak power in signals supplied to the amplifier (14) to be tested is unlikely to vary, enabling accurate evaluation or testing.

Method and apparatus for receiving FDMA signals

Abstract: of EP0656701A communication apparatus capable of measuring levels of carrier signals used in adjacent zones during telecommunication with a small circuit scale, and capable of simultaneously transmitting/receiving to FDMA-system signals through a plurality of communication channels. All of transmission signals received through the communication channels under use are wholly converted into an intermediate signal by a mixer. The intermediate signal is quadrature-detected (24) and then A/D-converted into digital I/Q-channel signals by A/D-converters (26, 27). Thereafter, the digital I/Q-channel signals are frequency-converted by frequency converting circuits(43, 44) in such a manner that center frequencies of these I/Q-channel signals become zero, two sets of I/Q-channel signals may be demodulated by two sets of demodulating circuits (28). Otherwise, one of these I/Q-channel signals is demodulated by a single demodulating circuit(28), and the other is level-detected by a level detecting circuit (45).

A frequency error correction in a DSSS receiver

Abstract: A frequency correction device for a spread-spectrum communication receiver requiring no high-accuracy, high-stable VCO as a local signal oscillator. It includes a quasi-coherent quadrature detector (12) detecting an intermediate frequency signal using a local signal from a fixed frequency local oscillator (41), a correlation detector (17) producing a despread signal by demodulating the output of the detector, a clock signal generating portion (47) generating a pair of clock signals whose frequency is deviated a little with respect to a clock signal for driving the correlation detector (17). The pair of clock signals are used to drive two correlation detectors (48 and 49), and the amplitude of the outputs of the correlation detectors are squared, and then subtracted, thereby generating a correlation output error signal. Since the correlation output error signal has one to one correspondence with the frequency difference between the chip frequency of the spread spectrum signal outputted from the quasi-coherent quadrature detector and the frequency of the clock signal, a frequency correction signal can be generated by converting the correlation output error signal into the frequency error. The frequency difference between despread signal and the clock signal, which arises from the difference between the center frequency of a received signal and the local signal, can be corrected by correcting the frequency of the despread signal by the frequency correction signal.

Apparatus for automatically controlling gain, communication apparatus, and method for automatically controlling gain

Abstract: An apparatus for automatically controlling the gain of a spread spectrum signal receiver, which follows up at a high speed the instantaneous variation resulting from change in the distance, change in the median, and Rayleigh fading. The output of a variable gain amplifier (22) is orthogonally detected. The detected output is converted by an A/D converter. This digital output signal is fed to compressor (34) through a digital level corrector (33). The compressed spectrum output is instantaneously detected by an instantaneous envelope detector (37). The data symbol timing component of the signal detected is extracted by a symbol timing extractor (38) using the peak signal as trigger. From this symbol timing, the width of the window of time at which a desired wave arrives is calculated. Over this width of the window, the output of the instantaneous envelope detector (37) is integrated with respect to time by a level detector (43). By this output, the level of the digital level corrector (33) is shifted, thus making its output constant. Also, the values of the output of the level detector (43) are averaged by a level detector (44) over several symbols. By this output, the gain of the variable gain amplifier (22) is controlled, thus making its output constant.

Code division multiplex transmitter/receiver

Abstract: A code division mutiplex transmitter/receiver the size of which is reduced by performing the designation of the spread codes and carrier frequency by using a base-band signal. This transmitter/receiver is equipped with a primary modulating circuit which generates primary modulated I and Q signals by performing primary modulation based on transmitted information, spread code generating means which corresponds to each channel and generates spread codes having a frequency higher than that of the transmission rate of transmitted information, a secondary modulating circuit which spread-modulates the primary modulated I and Q signals by using the spread codes and outputs spread I- and Q-channel data, a frequency offsetting circuit which offsets the center frequencies of the spread I- and Q-channel data by designated offset frequencies and outputs frequency-offset data, and a transmitting circuit which converts the frequency-offset data into transmission signals.

Quadrature receiver for spread spectrum signals

Abstract: A received signal is downconverted to and intermediate frequency, in a quadrature mixer (24), sampled (26,27), and then further downconverted (43,44) to baseband I and Q signals. The I and Q signals are despread in a matched-filter correlators (57,58).