Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-01-08
2002-06-18
Pham, Chi (Department: 2734)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S342000, C375S231000
Reexamination Certificate
active
06408038
ABSTRACT:
TECHNICAL FIELD
The invention relates to a receiving apparatus suitable for Eureka DAB (Digital Audio Broadcasting) System, in particular, to an improvement on an influence of a multi-path to a timing detection signal.
BACKGROUND ART
As an example of digital audio broadcast systems, Eureka DAB System developed by European Eureka
147
Project is known. In Eureka DAB System, MPEG (Moving Picture Experts Group) layer
2
is used as an audio encoding method. In addition, OFDM (Orthogonal Frequency Division Multiplexing) is used as a modulating method. With such methods, Eureka DAB System broadcasts six channels of high quality stereo programs and one channel of data in a transmission band of 1.50 MHZ.
FIG. 1
shows the structure of the transmitter side of Eureka DAB System. In
FIG. 1
, audio data is supplied to an input terminal
101
. The audio data is supplied from the input terminal
101
to an audio encoder
102
. The audio encoder
102
compresses the audio data.
In Eureka DAB System, as a compressing process of audio data, MPEG layer
2
is used. The MPEG layer
2
audio compressing method is a sub-band encoding method in which an input signal is divided into a plurality of frequency bands and each divided signal is independently encoded. In other words, input audio data is divided into 32 sub-bands with a bandwidth of 750 Hz by an analyzing filter bank. In addition, an FFT (Fast Fourier Transform) process is performed for the input audio data so as to analyze individual components of these bands. Corresponding to the result of the FFT process, masking is calculated and bits are assigned to the individual bands.
An output signal of the audio encoder
102
is supplied to a channel encoder
103
. The channel encoder
103
performs an encoding process for the compressed audio data with an error correction code such as a convolutional code.
An output signal of the channel encoder
103
is supplied to a time interleaving circuit
104
. The time interleaving circuit
104
interleaves the signal received from the channel encoder
103
in the time direction. An output signal of the time interleaving circuit
104
is supplied to a multiplexer
105
.
General data is supplied to an input terminal
106
. The general data is information such as weather information and traffic information. General data received from the input terminal
106
is supplied to a data encoder
107
. The data encoder
107
arranges the data received from the input terminal
106
in a predetermined format. An output signal of the data encoder
107
is supplied to a channel encoder
108
. The channel encoder
108
performs an encoding process for the signal received from the data encoder
107
with an error correction code such as a convolutional code. An output signal of the channel encoder
108
is supplied to a time interleaving circuit
109
.
The time interleaving circuit
109
interleaves the signal received from the channel encoder
108
in the time direction. An output signal of the time interleaving circuit
109
is supplied to a multiplexer
105
. Thus, the multiplexer
105
multiplexes the audio data received from the terminal
101
with the general data received from the terminal
106
.
An output signal of the multiplexer
105
is supplied to a frequency interleaving circuit
111
. An FIC generating circuit
115
supplies FIC (Fast Information Channel) data to the frequency interleaving circuit
111
. The frequency interleaving circuit
111
interleaves the output signal of the multiplexer
105
and an output signal of the FIC generating circuit
115
in the frequency direction. An output signal of the frequency interleaving circuit
111
is supplied to an OFDM circuit
112
. A sync generating circuit
113
supplies a TFPR signal and a null symbol to the OFDM circuit
112
. Thus, the TFPR signal and null symbol are added to the output signal of the frequency interleaving circuit
111
.
The OFDM (orthogonal Frequency Division Multiplexing) method is a multi-carrier modulating method using a plurality of carriers that are perpendicular to each other. The OFDM circuit
112
correlates digital data with data in frequency region and performs an IFFT (Inverse Fast Fourier Transform) process so as to convert data in frequency region into digital data in time region.
An output signal of the OFDM circuit
112
is obtained from an output terminal
114
. The output signal is modulated by &pgr;/4 QPSK modulating method and converted into a signal with a predetermined transmission frequency.
FIG. 2
shows the structure of a transmission frame transmitted in Eureka DAB System. As shown in
FIG. 2
, at the beginning of the transmission frame, a null symbol is disposed (thus, the relevant RF signal is not transmitted). The null symbol is used to coarsely synchronize with the received signal. The null symbol is followed by a TFPR signal. The TFPR signal is a reference symbol for controlling the frequency and synchronization of the received signal. The TFPR signal is followed by FIC (Fast Information Channel) data. The FIC data is control data that includes service information, display data, program service label, time and date, broadcast station ID, presence/absence of simultaneous service, and broadcast information of other channels. The FIC data is followed by MSC (Main Service Channel) data. The MSC data is general data such as music data, weather information, traffic information, and program list.
Eureka DAB System broadcasts signals through a satellite and VHF ground broadcasting stations. In Europe, the following three bands of frequencies have been assigned to Eureka DAB System.
Band 1 (47 MHz to 68 MHz)
Band 3 (174 MHz to 240 MHz)
L Band (1.452 GHz to 1.492 GHz)
In addition, depending on a frequency for use, as a hybrid method, both ground broadcasting stations and a satellite can be used.
When a mobile substance such as an automobile receives a signal of a conventional FM broadcast or a conventional AM broadcast, the signal is subject to fading due to an interference of a wave reflected by a building or the like to a direct wave. In addition, since the signal is analog, the sound quality is not high and the signal is subject to noise.
On the other hand, in Eureka DAB System, since an audio signal which is transmitted is a digital signal, the audio signal quality is high and the audio signal is not subject to noise. In Eureka DAB System, the OFDM method is used. In the OFDM method, since data is allotted to many carriers, the duration of one symbol is long. In the OFDM method, since a guard interval is placed on the time axis, even if a multi-path of which the delay time of a reflected wave is smaller than the interval is present, the transmission characteristic does not deteriorate. Since the waveform of a digital signal of the OFDM method has a resistance to random noise, the signal does not adversely affects other communications. In addition, the signal is not adversely affected by other communications. When carriers are allocated at particular intervals on the frequency axis, a frequency interleave effect is substantially obtained. In a combination with an adequate error correction code, the signal has a resistance to frequency selective fading.
In Eureka DAB System, in addition to high quality of an audio signal, multi-lingual broadcasts and general information such as weather information and traffic information are available. In Eureka DAB System, general information can be used for paging and still pictures can be transmitted as general information.
By the way, as shown in
FIG. 2
, in each transmission frame used in Eureka DAB System, a null symbol is disposed at the beginning. The null symbol is followed by a synchronous TFPR signal. With the TFPR signal, the frequency and timing of the having received signal or the receiving signal are controlled.
FIG. 3
shows the structure of a channel decoder of a conventional receiver for Eureka DAB System. In
FIG. 3
, an intermediate frequency signal is supplied to an input terminal
131
. The signal received from the input terminal
131
is supplied to an A/D
Al-Beshrawi Tony
Maioli Jay H.
Pham Chi
Sony Corporation
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