JPH06507053A - Method and device for differential modulation of signals in multichannel transmission systems - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Method and device for differential modulation of signals in multichannel transmission systems The present invention provides that a data stream is transmitted over a plurality of subcarriers arranged sequentially in the frequency domain. Relating to a digital modulation method and apparatus for a multichannel transmission system divided into .

The present invention is particularly applicable to COFDM (coded orthogonal frequency (Several division multiplexing) (Coded Orthogonal Frequency) Division (Multiplexing) method.

In multichannel modulation methods for digital data transmission, the data stream to be transmitted is divided into a certain number (for example, hundreds) of subcarriers arranged sequentially in the frequency domain. subcarrier spectra may overlap each other.

This mode of operation allows each subcarrier to maintain its original data rate. A data rate that is several orders of magnitude lower is transmitted, so that the symbol duration is It grows accordingly. This is advantageous when echoes occur in the transmission channel. do. By appropriately setting the number of subcarriers, the multichannel modulation method can be The symbol duration is always large compared to the maximum possible echo delay propagation time. The specifications can be designed as follows.

The effect of echo is e.g. when two consecutive symbols are transmitted without transmitting them immediately one after the other. A guard tag is used to attenuate the echo of the first transmitted symbol during each symbol. This can be completely eliminated by providing a time frame.

The technical realization method of the multi-channel modulation method is, for example, as a digital method, e.g. , the transmitting side calculates the transmitted signal at the composite baseband or at the intermediate frequency. and executed as a program on at least one microprocessor. If Known analog technology methods set (convert) the transmitted signal to the carrier frequency position. can do. Correspondingly, in the receiver the signal is first received in analog form and then downconverted from baseband or intermediate frequency and then digital will continue to be processed in the file.

A multi-channel modulated signal consists of time-frequency slots. The time slot is The frequency slot is formed by a frequency-related symbol clock. formed by the rear frequency interval. Means for attenuating echoes, e.g. When the guard time described above is provided, each time-frequency slot The effects of the wireless channel on the transmission are attenuation and phase rotation. Attenuation and phase rotation are Typically time and frequency variable.

As a modulation method for the subcarriers of a multichannel signal, the known phase shift method is advantageously used. key is used. The different data symbols then depend on the different phase characteristics of the transmitted signal. Displayed as progress. Then for demodulation, the phase defined by the channel The rotation acts as a disturbance quantity, which must be compensated by suitable means. .

Known methods are differential demodulation and differential bricoding (predictive coding). child In the case of It is transmitted as a phase difference between symbols. Multichannel methods involve differential demodulation and Bricoding (predictive coding) is performed separately on each subcarrier be done.

Differential precoding (predictive coding) is performed at the transmitter (Figure 1A) and Differential demodulation is performed at the receiver (Figure 1B).

The multiplication of complex numbers corresponds to the addition of their phases, and the formation of conjugate complex numbers corresponds to the addition of their phases. Corresponds to reversal. "D" is the delay of one symbol in Figures 1A and 1B. where * represents a conjugate complex component.

Differential demodulation or differential bricoding is a method in which the phase rotation due to the channel is one It is based on the assumption that symbols do not change from one symbol to the next. but Relatively long symbol durations, especially in time-varying radio channels This assumption is often not fulfilled in multi-channel methods with time. the In this case, transmission errors occur even in noise-free conditions.

Therefore, it is an object of the present invention to improve the transmission quality of unstable wireless channel signals. It is an object of the present invention to provide a modulation method and apparatus for a multi-channel transmission system.

This object is achieved by the features described in the characterizing parts of claims 1 to 4. another The structure of is described in claim 5.

The present invention will now be described by way of example with reference to the accompanying drawings.

In the embodiment of FIG. 2, portions of the transmitter and receiver equipment may A... k-1, and +1... are shown, and they are and on the receiving side, the data of adjacent subcarriers are combined each time. Contains a multiplier. For example, in the transmitter, the subcarrier is multiplied by -1, The data sent to the subcarrier is fed to a +l multiplier and the subcarrier is fed to a +l multiplier. Multiplied by data. At the receiver side, this signal with ten i subcarriers The carrier is multiplied by the conjugate complex signal. This method is called frequency difference modulation. Ru.

The method implemented by this device is to move from one subcarrier to the next subcarrier. It is based on the assumption that the phase rotation due to the channel does not change until child The assumption is similar to that in the well-known differential modulation, except that Wavenumber invariance has been replaced. However, the latter method is preferable for multi-channel modulation methods. Occurs often. This is because the small frequency of the subcarriers is This is because the number intervals are corresponding.

In another embodiment of FIG. 3, temporally consecutive data symbols of subcarriers and the data of adjacent subcarriers are also mutually combined, the transmitter and the receiver equipment is shown. For example, in the transmitter subcarrier +], two consecutive The data transmitted as a phase difference between successive data symbols is is supplied to the multiplier together with the data multiplied by -1 and by. In the receiver, This complex signal multiplied by +1 on the subcarrier becomes the conjugate complex signal on the subcarrier. The numbers are multiplied. This multiplied signal is subsequently delayed in time. It is also supplied to another multiplier together with the conjugate complex signal. These two differential modulations Therefore, at the transmitter, the subcarrier signals are first differentially pre-encoded and then is frequency differentially precoded and then first differentially demodulated at the receiver. and subsequently frequency differential demodulation. The two differential modulations are performed on the transmitter side and On the receiver side, it is also carried out first by frequency difference modulation and then by differential modulation. be done.

Due to the two-time differential modulation, compared to conventional differential modulation and frequency differential modulation, However, the assumption of time invariance of the phase rotation due to the channel and the assumption of frequency invariance channel phase characteristics with respect to time and frequency into one signal space characteristic. The particular advantage is that it is more closely approximated by the spatial plane. This approximation is based on the radio channel is significantly better than the approximation by a constant phase course with respect to time or frequency. It's good.

F old, IA FIG, IB Transmitter Receiver F old 2 Transmitter Receiver

Claims (5)

[Claims] 1. Divide the data stream into multiple subcarriers that are sequential in the frequency domain In the multi-channel modulation method, Transmit data as a phase difference between adjacent subcarriers A multi-channel modulation method characterized by: 2. Data is calculated based on the phase difference between adjacent subcarriers and temporally continuous data. Claim 1 wherein the data symbols are transmitted on each subcarrier as a phase difference between data symbols. A multi-channel modulation method as described in the general concept of. 3. At least one subcarrier path in each subcarrier path at the receiving and transmitting ends. This multiplier combines data of adjacent subcarriers. Ru A receiver for the multi-channel modulation method according to claims 1 and 2, characterized in that: and transmitter equipment. 4. One multiplier is included for each subcarrier on the receiving and transmitting sides. The multiplier multiplies the data of two temporally consecutive data symbols, respectively. on each subcarrier and subsequently on adjacent subcarriers. Another multiplier is provided to combine the data. A receiver and a transmitter for the multi-channel modulation method according to claim 2, Transmission device. 5. One multiplier is included for each subcarrier on the receiving and transmitting sides. The multiplier combines the data of adjacent subcarriers and subsequently , the data of two temporally consecutive data symbols are transferred to each subcarrier. Another multiplier is provided that combines A receiver and a transmitter for the multi-channel modulation method according to claim 2, Transmission device.