WO2002011385A1

WO2002011385A1 - Modulation method for a multi-carrier system

Info

Publication number: WO2002011385A1
Application number: PCT/DE2000/002544
Authority: WO
Inventors: Ralf Kern; Juergen Kockmann; Theo Kreul; Henrik Wagener
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-08-01
Filing date: 2000-08-01
Publication date: 2002-02-07
Also published as: AU2000274021A1

Abstract

The invention relates to a modulation method for a multi-carrier system, for the transmission of signals (41) over a transmission band (3), comprising several sub-carriers (31-37), each with at least one sub-carrier. According to the invention, the signals are modulated groupwise in an adaptive manner on to the individual sub-carriers in the groups of sub-carriers, depending upon the current radio channel properties of the individual groups of sub-carriers (31-37). The modulation parameters (41-47) arising from the current radio channel properties are adaptively adjusted.

Description

description

Modulation method for a multi-carrier system

The present invention relates to a modulation method for a multi-carrier system for transmitting signals over a transmission band, which has several groups of subcarriers, each with at least one subcarrier.

In a multi-carrier system, e.g. B. an OFDM system, in which a transmission band is used, which has about 1000 immediately adjacent subcarriers, it comes because of the frequency-selective change in the amplitudes, that is, the signal attenuation, and the phases, that is, the transit time, at Signal transmission over broadband physical transmission channels to transmission errors that are noticeable by a deterioration in the received signal quality. This is done, for example, by increasing the bit error rate and can go so far that one or more subcarriers are completely unusable by interferers within the frequency band used.

So far, this problem has been solved in such a way that a method for predistortion of the transmitted signal, the amplitudes and the phase response has been used. This achieved a balance in the radio channel properties.

Furthermore, it was proposed to jointly adapt the modulation value of all individual subcarriers of a multi-carrier signal to the so-called QoS (Quality of Service). In the case of a digital modulation method, the modulation value of an individual carrier is understood to be the number of information per carrier channel that can be transmitted on this. This means that the value increases with a low signal-to-noise ratio. A high number of transmitted information is possible with an undisturbed subcarrier. In contrast, in the case of a severely disturbed ω ω tv> M h->h->

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A schematic representation of a channel transmission function and an interference function over a number of groups of subcarriers.

In the figure, the amplitude is plotted against the frequency. A total of 256 subcarriers are shown from a transmission band 3, which belong to an OFDM system, for example. The subcarriers are grouped into seven groups of subcarriers 31-37 as subcarrier bands. In the exemplary embodiment, the individual groups of subcarriers 31-37 are covered with 90, 30, 18, 10, 34, 10 and 64 subcarriers in accordance with their width. The groups of subcarriers 31-37 connect directly to one another in terms of their frequencies. The associated modulation weights 41-47 are given in the individual groups of subcarriers 31-37. The respective digits indicate the bits per group of subcarriers 31-37, that is to say the number of information items of the entire signal to be transmitted, which are transmitted simultaneously on the respective group of subcarriers 31-37. The second modulation value 42 and the fifth modulation value 45 are each equal to 0, which means that no information is transmitted on the associated group of subcarriers 32, 35. A modulation value of 1, as in the fourth and sixth group of subcarriers 34, 36, means that two pieces of information are transmitted in parallel. This is done, for example, using bi-phase shift keying (BPSK). The remaining groups of subcarriers 31, 33, 37 each have a modulation value 41, 43, 47 of three. This means that eight pieces of information are transported in parallel in the respective subband. This is done, for example, by quadrature amplitude modulation (QAM). With QAM it is possible to achieve modulation values of up to 8.1 bits. With the modulation value of two not shown, four pieces of information would be transmitted in parallel, which 00 00 O r P> F ¹ cn σ Cn o Cn O cn

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mixed, that is to say when the radio channel properties change or also periodically, that is to say at predetermined time intervals. This ensures that all groups of subcarriers 31-37 are optimally used. A disturbance of the transmitted information is largely excluded and at the same time the information is transmitted as quickly as possible.

Claims

claims

1. Modulation method for a multi-carrier system for transmitting signals (41-47) via a transmission band (3), which has several groups of subcarriers (31-37), each with at least one subcarrier, characterized in that the signals on the individual Subcarriers in the groups of subcarriers (31-37) are adaptively modulated in groups depending on the current radio channel properties of the individual groups of subcarriers (31-37), the modulation values (41-47) resulting from the current radio channel properties of the subcarriers being adaptive be adjusted.

2. Modulation method according to claim 1, characterized in that the adaptation takes place once during the initialization of a connection and / or several times during the duration of the connection.

3. Modulation method according to claim 2, characterized in that the adaptation is dynamic, i.e. when the radio channel properties change, or periodically, i.e. at predetermined intervals.

4. Modulation method according to one of the preceding claims, characterized in that the current radio channel properties are used as the basis for the adaptation, in particular on the basis of a predefined code word.

5. Modulation method according to one of the preceding claims, characterized in that A suitable assumption serves as the basis for the adaptation, in particular through the reconstruction of data symbols.

6. Modulation method according to one of the preceding claims, characterized in that the modulation value (41-47) of a group of subcarriers (31-37) is reduced in the case of a large disturbance in this group of subcarriers (31-37) and increased in the case of a minor disturbance - is eats.

7. Modulation method according to one of the preceding claims, characterized in that the data stream is subjected to interleaving in the time domain and / or in the frequency domain.