Pulse or digital communications – Receivers
Utility Patent
1998-04-30
2001-01-02
Bocure, Tesfaldet (Department: 2731)
Pulse or digital communications
Receivers
C375S340000
Utility Patent
active
06169768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a receiving apparatus and a receiving method and, more particularly, to a receiving apparatus and a method for receiving an orthogonally modulated information sequence.
2. Description of the Related Art
As a digital modulation method, PSK (Phase Shift Keying), QAM (Quadrature Amplitude Modulation), which assign information to phase and amplitude, and the like, are often used.
Meanwhile, as these digital modulation methods, there is a single-carrier method for modulating a single-carrier wave by a method such as that described above and transmitting it, and a multicarrier method for modulating a plurality of carrier waves and transmitting them.
In the single-carrier transmission method, a single-carrier wave is modulated by PSK, QAM, and the like, and transmitted. In comparison, in the multicarrier transmission, a plurality of carrier waves which are formed into a narrower band are modulated by the above-described PSK, QAM, and the like, and transmitted. In the multicarrier transmission method, since the band width of each carrier wave is narrower than that of the single-carrier transmission method, it is possible to suppress the amplitude and the delay deviation within each carrier-wave band to a small amount even in an environment with frequency selective phasing, and therefore, it is possible to suppress deterioration of the bit error rate.
FIG. 9
shows an example of the construction of the transmission apparatus of the multicarrier transmission method. A serial/parallel (hereinafter, referred to as S/P) conversion circuit
2
converts input serial data (data to be transmitted)
1
into parallel data. D/A (Digital to Analog) conversion circuits
3
to
6
convert output data of the S/P conversion circuit
2
into corresponding analog signals.
LPFs (Low Pass Filters)
7
to
10
remove unwanted high-frequency components contained in the output of the D/A conversion circuits
3
to
6
. Orthogonal conversion circuits
11
to
14
orthogonally convert the output of the LPFs
7
to
10
in accordance with the signals of frequencies f
1
to f
4
output from local oscillation circuits
15
to
18
, respectively.
The local oscillation circuits
15
to
18
output signals of frequencies f
1
to f
4
and supply them to the orthogonal conversion circuits
11
to
14
, respectively. BPFs (Band Pass Filters)
19
to
22
perform a band limitation on the output of the orthogonal conversion circuits
11
to
14
, respectively, and supply the obtained signals to an addition circuit
23
. The addition circuit
23
adds together the output of the BPFs
19
to
22
and generates a multicarrier signal.
The BPF
24
appropriately shapes the spectrum of the output signal of the addition circuit
23
and then outputs it to an RF converter
25
. The RF converter
25
converts the frequency band of a multicarrier signal output from the BPF
24
into an RF band and then sends it from an antenna
26
.
FIG. 10
shows an example of the construction of a receiving apparatus of the multicarrier transmission method. In this figure, an antenna
32
receives an RF signal transmitted from the antenna
26
of a transmission apparatus shown in FIG.
9
. An IF converter
33
converts the RF signal received by the antenna
32
into an IF (intermediate frequency) band signal.
A wave-branching circuit
34
separates and extracts each carrier-wave component from the IF signal. BPFs
35
to
38
perform band limitation on each carrier wave output from the wave-branching circuit
34
and extracts a carrier wave having each of the center frequencies of f
1
to f
4
.
Orthogonal demodulation circuits
39
to
42
multiply signals output from the local oscillation circuits
43
to
46
with signals output from the BPFs
35
to
38
, respectively, and demodulate them into respective baseband signals. The local oscillation circuits
43
to
46
generate signals of a frequency f
1
, to f
4
and supply them to the orthogonal demodulation circuits
39
to
42
, respectively.
LPFs
47
to
50
remove unwanted high-frequency components from the baseband signals output from the orthogonal demodulation circuits
39
to
42
. A/D (Analog to Digital) conversion circuits
51
to
54
convert output signals of the LPFs
47
to
50
into digital signals.
A parallel/serial (hereinafter, referred to as P/S) conversion circuit
55
converts parallel signals output from the A/D conversion circuits
51
to
54
into a serial signal and outputs it as a received digital signal
56
.
In the above multicarrier transmission method, only one carrier wave (carrier) is assigned to one frequency. However, in order to enhance the use efficiency of frequency, a method in which each carrier is formed of two subcarriers with different phases (perpendicular to each other along the frequency axis) has been proposed.
FIG. 11
shows a transmission apparatus based on what is commonly called an OFDM (Orthogonal Frequency Division Multiplexing) in which subcarriers are placed so as to be perpendicular to each other along the frequency axis.
In this figure, a mapping circuit
62
converts a digital input signal
61
into a corresponding same phase (I) component and an orthogonal (Q) component in accordance with a modulation method, such as QPSK or 16QAM. An IDFT (Inverse Discrete Fourier Transform) circuit
63
converts data converted into a predetermined signal point by the mapping circuit
62
into a signal in the time domain.
Memories
64
and
65
add a guard interval indicating the beginning and end of each symbol to the signal in the time domain output from the IDFT circuit
63
. D/A conversion circuits
66
and
67
convert the signal in the time domain to which the guard interval is added into a corresponding analog signal.
LPFs
68
and
69
remove folded components (high-frequency components) which occur by D/A conversion, and then output them to an orthogonal modulation circuit
70
. The orthogonal modulation circuit
70
orthogonally modulates the output signal of the LPFs
68
and
69
in accordance with the signal of a frequency f
1
supplied from a local oscillation circuit
71
.
A BPF
72
extracts only the signal in the intermediate frequency (IF) band from the output signal of the orthogonal modulation circuit
70
. An RF converter
73
converts the signal in the IF band into a signal in the RF band, and then transmits it from an antenna
74
.
FIG. 12
is a view illustrating an example of the construction of a receiving apparatus for receiving information transmitted from the transmission apparatus of the OFDM method shown in FIG.
11
.
In this figure, an IF converter
83
frequency-converts the signal in the RF band received by an antenna
82
into a signal in the IF band. An orthogonal demodulation circuit
84
orthogonally demodulates the signal output from the IF converter
83
in accordance with the signal of a frequency f
1
, supplied from a local oscillation circuit
85
.
LPFs
86
and
87
remove unwanted high-frequency components contained in the output signals of the orthogonal demodulation circuit
84
. A/D conversion circuits
88
and
89
convert signals output from the LPFs
86
and
87
into corresponding digital signals and supply them to a DFT (Discrete Fourier Transform) circuit
90
.
The DFT circuit
90
converts the digital signals output from the A/D conversion circuits
88
and
89
into signals in the frequency range and outputs them to a demapping circuit
91
.
The demapping circuit
91
reproduces the original digital data from the I components and the Q components which are converted into the frequency range and outputs it as received data
92
.
In such an OFDM method as above, since each carrier wave is formed of two subcarriers whose carrier waves are perpendicular to each other, the use efficiency of frequency can be enhanced.
Meanwhile, with an increase in types of communication configuration and broadcasting configuration, a transmission method capable of appropriately changing a modulation method and an error correction met
Ikeda Tamotsu
Ito Osamu
Okada Takahiro
Bocure Tesfaldet
Lerner David Littenberg Krumholz & Mentlik LLP
Sony Corporation
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