Patent US4114403A successfully refreshed from Google Patents.
EP0762701A2
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EP
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MCM system, with a plurality of data streams, each with its own transmission parameters
Assignee: Advanced Digital Television Broadcasting Laboratory
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Filing: 1996-09-04
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Granted: —
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Expires: 2016-09-04
Abstract
Abstract Data sequences (D1 through DL) correspond to L different parameter sets (effective symbol length, guard interval length, the number of carrier waves) and transformed into parallel data by respective serial/parallel converters (111 through 11L), which are allocated to respective carrier waves for OFDM and subjected to inverse discrete Fourier transform by inverse discrete Fourier transformers (121 through 12L) to produce sampled values for the transmission waveform in the time domain. The sampled values are transformed into serial sequences of sampled values by parallel/serial converters (131 through 13L) and then into a single temporal sampling sequence by a temporal sampling sequence switching unit (14). A frame synchronizing symbol is added to the temporal sampling sequence and then transformed into an analog base band OFDM signal before it is converted up to a transmission signal. The frequency bandwidth of the OFDM signal is made smaller than a predetermined value defined by the bandwidth of the available transmission channel. As a result, an OFDM signal that can be received well regardless of the mode of reception can be transmitted.
Inventors
- 👤 Masafumi Saito
- 👤 Tetsuomi Ikeda
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 15:51
CPC Classifications
H; H04; H04L; H04L5/00; H04L5/003; H04L5/0048; H04L27/00; H04L27/26; H04L27/2601; H04L27/2602; H04L27/2605; H04L27/2607; H04L5/0001; H04L5/0003; H04L5/0005; H04L5/0007
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
124 words
An orthogonal frequency division multiplexing (hereinafter referred to as OFDM) transmission system for transmitting data by means of OFDM and digital modulation/demodulation, characterized in that, if the time interval of OFDM sampling points is denoted as T, the effective symbol length NiT (Ni being a positive integer), the guard interval length MiT (Mi being zero or a positive integer) and the number of carrier waves Ki (Ki being a positive integer) of the i-th data transmission symbol in an OFDM transmission frame, Ni, Mi and Ki can take a plurality of respective different values that can be arbitrarily selected, provided that Ki/NiT is kept smaller than a constant value W (W being a positive real number) determined by the bandwidth of the transmission channel.
Claim 2
Dependent Claim
139 words
An orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that, if the effective symbol length NaT (Na being a positive integer), the guard interval length MaT (Ma being zero or a positive integer) and the number of carrier waves Ka (Ka being a positive integer) of a specific data transmitting symbol in an OFDM transmission frame are known by the receiver along with the modulation techniques selected for the carrier waves of the specific symbol, at least part of the data on the effective symbol lengths, the guard interval lengths, the number of carrier waves and the modulation techniques selected for the respective carrier waves of all the data transmitting symbols other than said specific data transmitting symbol in the frame are transmitted from the transmitter to the receiver by means of said specific symbol.
Claim 3
Dependent Claim
76 words
An orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that data transmitting symbols are transmitted in such an order that the data transmitting symbols having an identical effective symbol length and a guard interval length are continuously arranged on the time base and the number of switching points where two adjacent data transmitting symbols having at least mutually different effective symbol lengths or mutually different guard interval lengths are located is minimized.
Claim 4
Dependent Claim
58 words
An orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that said OFDM transmission frame comprises data transmitting symbols having a relatively long effective symbol length and a relatively long guard interval length for fixed reception and those having a relatively short effective symbol length and a relatively short guard interval length for mobile reception.
Claim 5
Dependent Claim
21 words
An orthogonal frequency division multiplexing transmission system according to claim 4, characterized in that it is used for digital television broadcasting.
Claim 6
Dependent Claim
83 words
An orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that, if the average transmission power required for the i-th data transmitting symbol is Pi in the OFDM frame of the above embodiment, Pi is determined as a function of Ni that defines the effective symbol length in the frame so that Pi and Ni provide a one-to-one correspondence and that, if there are L different values Ni can take, there are also provided L different values Pi can take.
Claim 7
Dependent Claim
59 words
An orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that, if the value of Ni is selected from A1, A2, ..., AL and Amax is the largest value of A1, A2, ..., AL, all the numbers Al, A2, ..., AL are so selected as to be divisors of Amax that can exactly divide the latter.
Claim 8
Dependent Claim
20 words
An orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that Mi can take a single value.
Claim 9
Dependent Claim
41 words
An orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that the frequencies of the carrier waves for the data transmitting symbols in said OFDM transmission frame are shifted with a predetermined period and a predetermined frequency interval.
Claim 10
Dependent Claim
47 words
An orthogonal frequency division multiplexing transmission system according to claim 4, characterized in that at least one data transmitting symbols having a relatively short effective symbol length and a relatively short guard interval length for mobile reception are transmitted at a predetermined time interval within a frame.
Claim 11
Dependent Claim
56 words
An orthogonal frequency division multiplexing transmission system according to claim 2, characterized in that at least one of the effective symbol length, the guard interval length, the number of carrier waves and the modulation techniques is modified for each OFDM transmission frame by means of a specific data transmitting symbol on an OFDM transmission frame basis.
Claim 12
Dependent Claim
56 words
A transmitter adapted to an orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that, if L FFT points are used for the modulation of data transmitting symbols in inverse discrete Fourier transform, a total of L inverse discrete Fourier transformers (121, 122, ..., 12L) are provided for each number of FFT points.
Claim 13
Dependent Claim
54 words
A receiver adapted to an orthogonal frequency division multiplexing transmission system according to claim 1, characterized in that, if L FFT points are used for the demodulation of data transmitting symbols in discrete Fourier transform, a total of L discrete Fourier transformers (421, 422, ..., 42L) are provided for each number of FFT points.
References Cited (Backward Citations)
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