US 6,137,788 AGranted

CDMA demodulating apparatus

AssigneeNTT Mobile Communications Network, Inc.

InventorsMamoru Sawahashi, Hidehiro Andou, Yoshinori Miki, Kenichi Higuchi

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Abstract

A CDMA demodulating apparatus with an improved interference canceling effect when there are a large number of communicators. A reception signal having a frame configuration in which a pilot signal of a known pattern is inserted between information signals is received from a plurality of communicators. Transmission data of each communicator is demodulated, an interference canceler for estimating is provided in a plurality of stages, in each channel of each stage, a variation of transmission path is estimated in each path to achieve data demodulation and estimation of interference replica. The later the stage, the more error of interference signal replica can be reduced, thereby improving the interference canceling effect. An even better effect can be obtained when interference canceling is performed after detecting a reception level of each channel by summation of reception power of each path of each channel, and channel ranking is determined in the order of higher reception level.

Claims29

Dependent claims

A CDMA (Code Division Multiple Access) demodulating apparatus for use in a CDMA communication system that performs spreading information data by a spreading code faster than an information rate to a wideband signal and the wideband signal is transmitted to achieve multiple access transmission, wherein a pilot symbol of know pattern is received to estimate channel variation, individual reception signals received through a plurality of channels are compensated by the estimated channel variation, and the compensated reception signal is demodulated to reproduce the information data, comprising:

a correlation detector using a spreading code as a spreading code replica synchronized with a reception timing of each path of each of the channel for correlation detection of the spreading code replica with the reception signal of each path;
a received level detector for determining a sum of a reception power of a corresponding path of said correlation detector and detecting a desired wave reception signal level;
a channel ranking unit for controlling order of demodulation of the user according to the reception signal level of each user detected by said received level detector;
and
an interference canceler of a plurality of stages for making interference canceling according to a control signal outputted from said channel ranking unit, in each of the plurality of stages, making estimation of channel variation using the pilot symbol on each channel, compensating the reception signal of the channel by the estimated channel variation, and respreading the compensated reception signal to produce an interference signal replica.

2 more elements

A CDMA (Code Division Multiple Access) demodulating apparatus for use in a CDMA system that performs multiple access transmission by transmitting a spread signal, the spread signal being generated by spreading information data into a wideband signal with a spreading code whose rate is higher than an information rate, wherein a pilot symbol of a known pattern to estimate a channel variation, each reception signal received through a plurality of channels is compensated by the estimated channel variation, and the compensated reception signal is demodulated to reproduce the information data, the demodulating apparatus comprising:

a correlation detector, using a spreading code in phase with reception timing of each path of each channel, for detecting correlation of the spreading code with the reception signal of each path;
a received level detector for determining a sum of a reception power of a corresponding path of the correlation detector and detecting a desired wave reception signal level;
a channel ranking unit for controlling order of demodulation of the user according to the reception signal level of each user detected by said received level detector;
an interference canceler of a plurality of stages for despreading the reception signal for individual users according to an order determined by the control signal outputted from said channel ranking unit, respreading the despread signal, and subtracting an interference signal replica of other users obtained by respreading from the reception signal of the corresponding user;
and
a pilot interpolation/coherent detector for estimating a channel variation using the pilot symbol in the signal after subtracting by an interference amount of other users in said interference canceler of the last stage in the plurality of stages, compensating the information data using the estimated channel variation to perform absolute synchronization detection of the compensated information data.

3 more elements

Dependencies are inferred from the claim text.