Nec Corporation

Oki Electric Industry Co., Ltd.

Shigeru Ono

Mariko Matsumoto

Hiroshi Katsuragawa

Satoru Araki

Hiroshi Hayashi

Yoshihiro Ono

Yoshihito Shimazaki

Hideo Sano

Noriaki Kondoh

Tomoko Tanaka

Mariko Matsu Moto

A portable radio terminal for realizing automatic frequency control (AFC) for automatically controlling the oscillation frequency of an oscillator includes a unit for intermittently performing AFC operation, and a unit for shortening an AFC operation stop period when the frequency shift of the oscillation frequency is large. An AFC control method is also disclosed.

Portable radio terminal and AFC control method

A receiver for a code division multiple access system includes a pilot symbol producing section, a frequency offset estimating section and a local signal generating section. The pilot symbol producing section produces pilot symbols of complex vector expression from a received radio frequency (RF) signal based on a first local frequency signal and a second local frequency signal. The first local frequency signal has a frequency obtained by shifting a frequency of a carrier signal by an IF frequency and the second local frequency signal has a frequency equal to the IF frequency. The pilot symbols have been subjected to inverse modulation to remove a modulation component. The frequency offset estimating section carries out in-phase adding operations to the pilot symbols of the complex vector expression over a predetermined interval in accordance with a predetermined pattern. Then, the frequency offset estimating section carries out a complex adding operation of results of the in-phase adding operations, and determines a frequency offset from a result of the complex adding operation. The local signal generating section generates the first and second frequency signals based on the determined frequency offset.

CDMA receiver capable of estimation of frequency offset in high precision

A portable radio system, a portable radio equipment to be used in the same and a frequency error prediction method can be adapted to large frequency error by making tap number smaller and frequency error smaller. The portable radio system employs an automatic frequency control for detecting a frequency shift of an internal oscillator of a portable radio equipment with reference to a received wave transmitted from a base station having higher precision of frequency and adjusting the frequency of the internal oscillator by feeding back the frequency shift to the internal oscillator. Coordinate rotation digital computation (CORDIC) is employed for calculation of arctangent in the automatic frequency control.

Portable radio system and portable radio equipment to be used in the same and frequency error prediction method used therefor

A metric calculating means calculates a first metric corresponding to a transmitted symbol sequence estimated by an adaptive equalizer, then calculates a second metric corresponding to a symbol sequence in which a symbol located at a position where a soft decision is made in the transmitted symbol sequence is inverted in polarity. Thereafter a subtracting portion subtracts the second metric from the first metric. Further, a multiplying portion multiplies the subtraction result from the subtracting portion by the symbol located at a position where the soft decision is made in the transmitted symbol sequence to generate a soft decision.

Soft decision estimation unit and maximum-likelihood sequence estimation unit

A correlation unit,de-spreads reception signal in a reception physical channel and a physical channel for channel estimation with a de-spread timing signal designated by a path control unit,and supplies the portions of reception symbols in the de-spread reception signal, corresponding to the pilot symbols and the reception symbols corresponding to the reception physical channel, to weighting coefficient estimation units,and a weighting circuit,, respectively. The weighting coefficient estimation unit,carries out channel estimation corresponding to paths for individual finger units,-,through,-,. The weighting circuit,multiplies a complex conjugate of the estimated weighting coefficient by the reception signal to produce the multiplication result to a RAKE combiner unit,. The RAKE combiner unit,carries out maximum-ratio combining of the weighted reception signals supplied from the finger units,-,through,-,and produces the combination result via an output terminal

Spread spectrum communication system

In order to differentially detect a multiple-phase shift keying (MPSK) signal, a predetermined number of phase signals are stored at successive symbol time points. Next, a plurality of phase differences between the phase signals stored in the above are calculated. Subsequently, a symbol value of the MPSK signal is determined or estimated at a current symbol time point using the calculated phase differences and using symbol values already determined at a plurality of preceding symbol time points.

Method and arrangement for differentially detecting an MPSK signal using a plurality of past symbol data

A Rake receiving system distributes parts of a receiving signal to fingers for producing weighted parts, and supplies the parts of receiving signal to a pass controlling sub-system; the pass controlling sub-system checks the parts to see whether or not the correlative electric power of each part is equivalent to an average noise power, and each finger calculates a ratio of electric power between an expected receiving signal and non-expected receiving signal; when the correlative electric power is equivalent to a noise power, the associated weighted part is deleted from the Rake synthesis; when the ratio is lower than a threshold, the associated weighted part is also deleted from the Rake synthesis.

Rake receiving system with fingers selectively participating rake

Buffers 101 and 103 are provided in an input and an output of a signal processing circuit 102 for performing a data transformation between a first digital data signal and a second digital data signal, respectively, and data of one of the first and second digital data signals is interpolated by a data interpolation circuit 106 on the basis of a deviation between sampling frequencies of the first and second digital data signals detected by an out-of-sync detection circuit 104 on the basis of two clocks driving the buffers 101 and 103. Further, an amount of jitter between the two clocks driving the respective buffers 101 and 103 is detected by a jitter detection circuit 105 and the amount of interpolation data is controlled in the data interpolation circuit 106 on the basis of the amount of jitter.

Digital signal processor for detecting out-of-sync and jitter from two

The connection between a plurality of antenna output signals and a plurality of finger units is switched in dependence upon a reception state of each multipath propagation path at each antenna branch to controllably select those finger units to be subjected to RAKE combination. A particular finger unit is excluded from RAKE combination if the reception state does not satisfy a predetermined condition.

Rake reception method for a spread spectrum signal

A first vector quantizer generates output codevectors corresponding in number to a number determined by a predetermined number of bits through linear coupling of integer coefficients of a predetermined number of base vectors stored in a base vector memory. A second vector quantizer determines coefficients of the base vectors according to at least one of output indexes of the output codevectors.

Vector quantizer with first quantization using input and base vectors

A demodulator performs both synchronization and decoding concurrently by decoding a received preambleless signal according to Viterbi-decoding scheme and determining a time alignment function n(t) which indicates where the decoded sequence is located in a time period of the received signal. After converting the received preambleless signal to a received sequence in a sampling rate which is at least the predetermined symbol rate, a Viterbi decoder is synchronized with the received sequence while determining the time alignment function n(t) so that the Viterbi-decoded sequence is closest to the received sequence.

Digital demodulator and method of operation

In a first aspect of the invention, a Viterbi decoding circuit stores comparison result bits in a bit-accessible path memory unit. A back-trace is performed by setting a state value in a shift register, then shifting comparison result bits from the path memory unit into the shift register. A certain number of bits at the shift-in end of this register are supplied as read address bits to the path memory unit. In a second aspect of the invention, a Viterbi decoding circuit has selectors that first select old path metric values and branch metric values, which are added or subtracted to produce candidate path metric values, then select the candidate path metric values, which are subtracted to produce a comparison result bit representing the sign of their difference. These additions and subtractions are performed by the same arithmetic unit.

Viterbi decoding method and circuit with accelerated back-tracing and

A method and a device for signal decision, a receiver and a channel condition estimating method for a coding communication system are disclosed. A plurality of add, compare and select (ACS) circuits each sequentially determines metrics at a particular trellis tracing rate assigned thereto. The metrics are sequentially added in order to select the most probable path. An M break-up circuit 30 compares the path metrics of the most probable paths and breaks up unlikely paths over a plurality of circuits. The path metrics of probable paths are sequentially written to respective metric memories and again fed to the ACS circuits for trellis tracings. This is repeated until the M break-up circuit 30 selects M paths out of paths fed from N (N&gt;M) ACS circuits. The M paths are delivered to a decision circuit while survivor paths are written to respective path memories. The decision circuit selects one of the M path metrics having the smallest value, reads the path out of the path memory, traces it back, and then outputs decoded bits via an output terminal.

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Tokyo, Japan

Shigeru Ono