Apparatus for receiving data

Details Apparatus for receiving data Apparatus for receiving data

1998-06-05

2001-05-29

Pham, Chi (Department: 2631)

Pulse or digital communications

Receivers

Particular pulse demodulator or detector

C375S262000, C714S794000, C714S795000

Reexamination Certificate

active

06240145

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an apparatus for receiving data, and more particularly to an apparatus for receiving data that is applied to a portable radio telephone and the like and carries out decoding while following a time variation based on the characteristics of a channel of a radio circuit and the like.
BACKGROUND OF THE INVENTION
Conventional apparatuses for receiving data applied to portable telephones include, for example, “Data Receiver” disclosed in Japanese Patent Laid-Open No. 166332/1988. According to the conventional apparatus for receiving data, the path memory length of a Viterbi decoder is varied depending upon the channel state. Specifically, the path memory length of the Viterbi decoder is varied depending upon the quality of the channel, and, when the quality of the channel is good, the delay within the Viterbi decoder is reduced to improve the transmission efficiency.
In the conventional apparatus for receiving data, however, the number of states in the Viterbi decoder is not taken into consideration, and, even when the transmission quality of the channel is good, the number of states is used which matches the average channel state. In other words, even when the transmission quality of the channel is good, the computation quantity of the Viterbi decoder cannot be reduced, resulting in increased power consumption, and, at the same time, the computation quantity cannot be minimized, unfavorably making it impossible to conduct high speed processing.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an apparatus for receiving data that, when the transmission quality of the channel is good, can reduce the quantity of computation in the Viterbi decoder to reduce the power consumption and, at the same time, can minimize the quantity of computation to realize high speed processing.
According to the invention, an apparatus for receiving data, adapted for outputting data of decoding decision results of a received signal by maximum likelihood serial estimation using Viterbi algorithm, comprises decoding means for specifying the number of states in Viterbi algorithm to an assigned value and carrying out decoding based on the control of the determined Viterbi algorithm.
In the preferred embodiment, the decoding means comprises:
channel estimation means for estimating the state of channel;
control means for the number of states which, based on the channel state estimated by the channel estimation means, determines the magnitude and delay quantity of delay wave contained in the received signal to determine the number of states of predetermined Viterbi decoding and, based on the number of states, controls the decoding; and
Viterbi decoding means for carrying out decoding according to the control based on the number of states determined by the control means for the number of states.
In the preferred embodiment, the Viterbi decoding means comprises:
a branch metric generating section which calculates and generates branch metric with necessary number of states from the control means for the number of states using an input signal and an impulse response estimation value as estimation of the channel state by the channel estimation means;
a computing section which adds the path metric from the preceding time period within each of the number of states to the branch metric from the branch metric generating section to determine the path metric at the current time for the necessary number of states, sends the path metric selected as a survival path which is the largest path metric in two paths created in each time, and sends information on survival path;
a path memory which receives information on the survival path from the computing section to renew a transition record on a memory; and
a maximum likelihood decision section which compares the size of path metric of the information on the survival path from the computing section, selects path memory series corresponding to the maximum path metric from the path memory, withdraws the oldest data recorded in the data series, and sends the oldest data as output decoded data.
In the preferred embodiment, the estimation of the channel state in the channel estimation means is carried out by estimation of the impulse response of the channel.
In the preferred embodiment, the apparatus is applied to a portable radio telephone.
According to the apparatus, for receiving data, having the above construction, data of decision results of decoding of a received signal are output by maximum likelihood serial estimation using Viterbi algorithm. The number of states in the Viterbi algorithm is specified to any assigned value, and decoding is carried out based on the control of the determined Viterbi algorithm.
Consequently, unlike the prior art, the number of states, which matches the average channel state, is not used when the transmission quality of the channel is good. That is, when the transmission quality of the channel is good, the quantity of computation in the Viterbi decoder is reduced to reduce the power consumption and, at the same time, the quantity of computation can be minimized to realize high speed processing.


REFERENCES:
patent: 5644603 (1997-07-01), Ushirokawa
patent: 97/24849 (1997-07-01), None
patent: 2252221 (1992-07-01), None
patent: 63-166332 (1988-07-01), None
patent: 0615347 (1994-09-01), None
patent: 0691770 (1996-01-01), None
Guren, et al.,IEEE, “Decision Feedback Sequence Estimation for Continous Phase Modulation on a Linear Multipath Channel”, vol. 41, No. 2, Feb. 1993, pp. 280-284.

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