Transmitter for Transmitting a Data Transmission Signal and Receiver for Receiving the Data Transmission Signal Each of Which can Switch Between Coding and/or Modulating Schemes in Dependency of an Additional Information Signal

Abstract

A transmitter for transmitting a data transmission signal in a reception area is provided with an input for receiving an information signal (IS) to be transmitted, a codingand/or modulation unit for coding and/or modulating the information signal with a certain codingand/or modulation scheme into the data transmission signal, and an output for supplying the data transmission signal, and an output for supplying the data transmission signal. In accordance with the invention, the codingand/or modulation unit is adapted to code and/or modulate the information signal with n different codingand/or modulation schemes (n2), and further is adapted to transmit an additional information signal by changing between these n codingand/or modulation schemes. The invention also relates to a receiver for receiving the data transmission signal transmitted by the transmitter

Claims

1. A transmitter for transmitting a data transmission signal in a reception area, which transmitter is provided with an input for receiving an information signal (IS) to be transmitted, a codingand/or modulation unit for coding and/or modulating the information signal with a certain codingand/or modulation scheme into the data transmission signal, and an output for supplying the data transmission signal, wherein, the codingand/or modulation unit is adapted to code and/or modulate the information signal with n different codingand/or modulation schemes (where n is an integer for which holds: n2), and further is adapted to switch between these n codingand/or modulation schemes in dependency of an additional information signals (ZI) to be transmitted.

2. The transmitter as claimed in claim 1, characterized in that, the codingand/or modulation unit is provided with an input for receiving the additional information signal (ZI).

3. The transmitter as claimed in claim 1, wherein the codingand/or modulation unit is adapted to code and/or modulate the information signal with two different codingand/or modulation schemes in dependency of a binary additional information signal to be transmitted.

4. The transmitter as claimed in claim 1, wherein in case no additional information signal is to be transmitted, the codingand/or modulation unit is adapted to code and/or modulate the information signal with a certain first codingand/or modulation scheme having a certain robustness, and during transmission of the additional information signal the codingand/or modulation unit is adapted to code and/or modulate the information signal with the first codingand/or modulation scheme and at least a second codingand/or modulation scheme, which at least second codingand/or modulation scheme has a higher robustness than the first codingand/or modulation scheme.

5. The transmitter as claimed in claim 1, wherein the codingand/or modulation unit is adapted to code the information signal with at least two different coding schemes in dependency of the additional information signal to be transmitted, and that the codingand/or modulation unit is further adapted to modulate the coded information signal with a certain modulation scheme.

6. The transmitter as claimed in claim 5, wherein the at least two coding schemes differ between each other by a next higher robustness.

7. The transmitter as claimed in claim 1, wherein the codingand/or modulation unit is adapted to code the information signal with a certain coding scheme, and the codingand/or modulation unit is further adapted to modulate the coded information signal with at least two different modulation schemes in dependency of the additional information signal to be transmitted.

8. The transmitter as claimed in claim 7, wherein the at least two modulation schemes differ between each other by a next higher robustness.

9. The transmitter as claimed in claim 1, wherein the additional information signal is a warning broadcast signal.

10. A receiver for receiving a data transmission signal, which receiver is provided with an input for receiving the data transmission signal, a demodulationand/or decoding unit for demodulating and/or decoding the data transmission signal with a certain demodulationand/or decoding scheme into an information signal, and an output for supplying the information signal, wherein, the demodulationand/or decoding unit is adapted to demodulate and/or decode a data transmission signal which is in the form of an information signal which is coded and/or modulated with n codingand/or modulation schemes (where n is an integer for which holds: n2), and the receiver is further adapted to derive from the switching-overs between the n coding and/or modulation of the received data transmission signal an additional information signal, and to supply the additional information signal to an output.

11. The receiver as claimed in claim 10, wherein, the receiver is adapted to demodulate and/or decode a data transmission signal which has been transmitted by a transmitter.

12. The receiver as claimed in claim 11, for demodulating and/or decoding a data transmission signal transmitted by the transmitter wherein the demodulationand/or decoding unit is adapted to demodulate and/or decode the data transmission signal that has been coded and/or modulated with two coding and/or modulation schemes, and the receiver is further adapted to derive the binary additional information signal from the switching-overs between the two coding and/or modulation schemes.

13. The receiver as claimed in claim 10, wherein the receiver is provided with an arrangement to detect whether a data transmission signal received by the receiver is a distorted data transmission signal, and to derive a control signal in dependency of the amount of distortion detected, and that the receiver is further provided with an arrangement for generating a feedback signal in dependency of the control signal and to transmit the feedback signal to a transmitter.

Description

SHORT DESCRIPTION OF DIAGRAMS

[0012] The invention is represented in more detail using some implementation examples in the diagram description that follows. In these diagrams:

[0013] FIG. 1 is an implementation example of a transmitter according to the invention,

[0014] FIG. 2 is an implementation example of the transmitter's coding and/or modulation scheme,

[0015] FIG. 3 is a second implementation example of the transmitter's coding and/or modulation scheme,

[0016] FIG. 4 is an implementation example of a receiver according to the invention,

[0017] FIG. 5 is a second implementation example of a receiver according to the invention,

[0018] FIG. 6 is a second implementation example of a transmitter according to the invention,

[0019] FIG. 7 is an implementation example of the transmitter's coding and/or modulation scheme according to FIG. 6,

[0020] FIG. 8 is an application of the MCS conversion process according to the invention for an additional information signal that is pre-coded using a Manchester Code, and

[0021] FIG. 9 is an implementation example of the MCS conversion process according to the invention, wherein an additional information signal is enclosed in the data transmission signal using (n=) 4 MCS schemes.

DETAILED DESCRIPTION OF DIAGRAMS

[0022] In a coding and modulation scheme in a transmitter, there are always two separate signal processing levels implemented one after the other on the information signal that is to be transmitted. However, a transmitter's coding and modulation schemes are always given together for this transmitter.

[0023] A modulation scheme refers to the modulation of a signal, i.e., how it is modulated and transmitted from a transmitter into a carrier. There are various modulation processes; BPSK, QPSK, QAM etc. The most common process used in communications engineering is currently quadrature amplitude modulation (QAM)in which modulation takes on a power of 4 (4n)which is most easily understood using the four quadrants in the IQ constellation diagram41->4QAM/4.sup.2->16-QAM/4.sup.3->64-QAM/44->256-QAM/45->1024-QAM etc.

[0024] A coding scheme (also called a code rate) is error protection coding. The code rate of the error protection coding always gives the ratio of useful bits to total bits (useful bits +error correction bits) and therefore can never be larger than one (1). For example: the code rate 3/4 means that 4 bits total contain 3 bits of information and one protection bit. Or: a code rate of 5/6 means that 6 bits total contain 5 bits of information and one protection bit.

[0025] FIG. 1 shows an implementation example of a transmitter. The transmitter 100 is equipped with an input 102 to receive the information signal (IS) to be sent. Input 102 is coupled with an error protection coding unit 104 using an input terminal. The IS is error protection coded into the error protection coding unit 104 and the error protection coded information signal is given to an output terminal. The output terminal of the error protection coding unit 104 is coupled with a modulation unit 106 using an input terminal. The modulation unit 106 modulates the error protection coded information signal into a modulated information signal, which is given to an output 108 as a data transmission signal via the output terminal of the modulation unit 106. The data transmission signal can then (after a corresponding conversion from digital to analogue) be transmitted in the transmission area using an antenna 110.

[0026] The transmitter is further equipped with a control unit 112. The control unit 112 controls the error protection coding unit 104 and the modulation unit 106 using control signals 114 or 116, which are supplied on the control input of the error protection coding unit 104 or on a control input of the modulation unit 106 and thereby control the transmitter's 100 coding and/or modulation scheme (MCS). The control unit 112 controls the error protection coding unit and the modulation unit 106 under the influence of an additional information signal AI, which is supplied via a second input 120 in the transmitter to an input terminal of the control unit 112 and derives control signals 114 and 116 from this.

[0027] The additional information signal could, as an example, be a warning broadcast signal.

[0028] FIG. 2 shows an implementation example of how the transmitter's coding and modulation scheme could change over time under the influence of the additional information signal. If there is no additional information signal to transmit, the information signal to be transmitted that is supplied at input 102 will be coded and modulated with a coding and modulation scheme of, for example, 16-QAM3/4. This means that under the influence of the control signal 114, the error protection coding unit 104 adds one error protection bit to three information bits. Under the influence of the control signal 116, the modulation unit 106 modulates the information signal that has been error protection coded in this way with 16-QAM modulation. This is shown in FIG. 2 for the time t<t1.

[0029] If an additional information signal, AI, must be transmitted, the coding and modulation scheme is altered as follows. In this implementation example, the additional information signal is given as a digital (binary) signal in FIG. 2, namely by the series of bits in zeros and ones: 1001011011001010011011 . . . .

[0030] This series of bits in ones and zeros is essentially the sequence of a series of bytes (8-bit-long words) B1, B2, B3, . . . of the additional information signal.

[0031] As FIG. 2 demonstrates, the coding and modulation scheme are altered in that for a bit equal to logic 1, the coding and modulation scheme changes to 16-QAM 2/3. For logic 0 bits, the coding and modulation scheme changes back to 16-QAM 3/4.

[0032] This means that modulation 16-QAM remains unchanged, but the error protection coding changes under the influence of the additional information signal between the code rate 3/4 and 2/3.

[0033] As shown in FIG. 2, if no additional information signal is to be transmitted, i.e., for times t<t1, the coding and modulation scheme is 16-QAM 3/4. This coding and modulation scheme means a specified robustness of data transmission and therefore a specified transmission area in which receivers can receive the data transmission signal without error as far as possible. In the time intervals in which the additional information signal is transmitted, the second coding and modulation scheme is: 16-QAM 2/3. This coding and modulation scheme means a greater robustness of data transmission than 16-QAM 3/4 and therefore a somewhat larger transmission area in which receivers can receive the data transmission signal without error as far as possible. This is advantageous, therefore, because the change in coding and/or modulation scheme in the time intervals in which an additional data signal is transferred does not negatively affect the size of the desired transmission area because the 16-QAM 2/3 scheme is used, i.e., the useful signal transmission itself is not affected.

[0034] FIG. 3 shows another implementation example of how the transmitter's coding and modulation scheme could change over time under the influence of the additional information signal. If there is no additional information signal to transmit, the information signal to be transmitted that is supplied at input 102 will be modulated with a modulation scheme of, for example, 16-QAM. This means that according to the invention, the error protection coding unit 104 has no significance in this case, and may be configured to a specified error protection coding (code rate) or may even be absent. Under the influence of the control signal 116, the modulation unit 106 modulates any information signal that has been error protection coded in this way with 16-QAM modulation. This is shown in FIG. 3 for the time t<t1.

[0035] If an additional information signal, AI, must be transmitted, the coding and modulation scheme is altered as follows. In this implementation example, the additional information signal is given as a digital (binary) signal again, as in FIG. 2.

[0036] As FIG. 3 demonstrates, the coding and modulation scheme are altered by changing the modulation scheme to 8-QAM for a bit equal to logic 1. For logic 0 bits, the modulation scheme changes back to 16-QAM.

[0037] As shown in FIG. 3, if no additional information signal is to be transmitted, i.e., for times t<t1, the modulation scheme is 16-QAM. This modulation scheme means a specified robustness of data transmission and therefore a specified transmission area in which receivers can receive the data transmission signal without error as far as possible. In the time intervals in which the additional information signal is transmitted, the second modulation scheme is 8-QAM. This modulation scheme means a greater robustness of data transmission than 16-QAM and therefore a larger transmission area in which receivers can receive the data transmission signal without error as far as possible. As can be seen from the description to the FIGS. 2 and 3, the additional information signal is a digital additional information signal, and the changes in the MCS scheme occur on a bit basis of the digital additional information signal. That means that for each bit in the digital additional information signal, it is decided whether a change in the MCS scheme should occur or not, in dependence of the bit value of that bit of the digital additional information signal. This is advantageous, therefore, because the change in modulation scheme in the time intervals in which an additional data signal is transferred does not negatively affect the size of the desired transmission area because the 8-QAM scheme is used, i.e., the useful signal transmission itself is not affected.

[0038] FIG. 4 shows an implementation example of a receiver 400 for receiving the transmitter's data transmission signals from FIG. 1. The data transmission signal is received with an antenna and forwarded to an input 404 of the receiver 400. Input 404 is coupled with a demodulation unit 406 using an input terminal. An output terminal of demodulation unit 406 is coupled with an error correction unit 408 using an input terminal. An output terminal of the error correction unit 408 is coupled with an output 416. Furthermore, a control unit 412 is provided to control the demodulator unit 406 and the error correction unit 408, so that the data transmission signal that is received can be demodulated and/or error-corrected using the correct demodulation and/or decoding scheme.

[0039] The control unit 412 is configured to determine with which coding and/or modulation scheme the transmission signal is coded and/or modulated. In the case of the implementation example from FIG. 2, the control unit 412 determines that the transmission signal is coded and modulated with either 16-QAM 3/4 or 16-QAM 2/3. The control unit 412 uses this to generate two control signals 420 and 422 to control the demodulator unit 406 and the error correction unit 422, so that demodulation and error correction are carried out correctly and a replica of the transmitted information signal is received.

[0040] In the time intervals in which an additional information signal is transmitted through a change in the coding and/or modulation scheme, the control unit can additionally derive the transmitted additional information signal from these changes to the coding and/or modulation schemes and pass them on at an output 418.

[0041] In the case of the implementation example from FIG. 3, the control unit 412 determines that the transmission signal is modulated with either 16-QAM or 8-QAM. The control unit 412 uses this to generate a control signal 422 to control the demodulator unit 406, so that demodulation is carried out correctly and a replica of the transmitted information signal is received. As mentioned in the description to FIG. 3, this similarly means here that according to the invention, the error correction unit 408 is of no importance in this case and may be configured to a specified error correction value or may even be absent.

[0042] As described in, for example, U.S. Pat. No. 5,423,059 or in EP 1076427A2, errors may occur during reception of transmission signals from a transmitter. Known receivers are configured for this purpose to determine whether a data transmission signal from a transmitter is received by the receiver with an error and to generate a feedback signal depending on these errors. This feedback signal is transmitted to the transmitter and the transmitter switches to a more robust coding and/or modulation scheme on the basis of this feedback signal.

[0043] FIG. 5 shows a second implementation example of a receivers 500 according to the invention that is also configured to generate a feedback signal and to transmit the feedback signal to a transmitter.

[0044] The receiver 500 according to FIG. 5 is formed in the same way as the transmitter 400 according to FIG. 4. Matching elements that are indicated in FIG. 4 with 4xy are given in FIG. 5 with 5xy. In addition to what it shown in FIG. 4, the receiver in FIG. 5 contains another device 514 to (in the way already discussed) generate a control signal depending on the scale of the error in the received data transmission signal, which device 514 is further configured to transmit the control signal as a feedback signal 530 to the transmitter using an antenna 536.

[0045] FIG. 6 shows a second implementation example of a transmitter 600 according to the invention that is additionally configured to receive the feedback signal 630 that has been transmitted by the receiver 500 in FIG. 5 as a feedback signal 530.

[0046] The transmitter 600 according to FIG. 6 is formed in the same way as the transmitter 100 according to FIG. 1. Matching elements that are indicated in FIG. 1 with 1xy are given in FIG. 6 with 6xy. In addition to what is shown in FIG. 1, the transmitter in FIG. 6 contains another device 628 (e.g., another antenna) to receive the feedback signal 630. This feedback signal is also passed on to the control unit 612, also in order to control the transmitter's coding and/or modulation scheme.

[0047] The transmitter's functioning according to FIG. 6 is further explained in FIG. 7. In normal operation and under good conditions for transmission, but when no additional information signal is to be transmitted, the transmitter 600 words with a coding and/or modulation scheme of, for example, 16-QAM 5/6. If an additional information signal AI1 is to be transmitted, at time t=t1, this additional information signal AI1 is transmitted by switching between coding and modulation schemes 16-QAM 5/6 and 16-QAM 3/4 in a way already described with FIG. 2. However, in this case, only the error protection coding changes between 5/6 (i.e., an error correction bit is transmitted with 5 information bits of the information signal to be transmitted) and 3/4 (i.e., an error correction bit is transmitted with 4 information bits of the information signal to be transmitted).

[0048] Then, the transmitter 600 receives a feedback signal that informs it that the reception quality of the received transmission signal has reduced. In response to this, the control unit 612 switches the transmitter to a more robust coding and/or modulation scheme. This is shown in FIG. 7 at time t=t2, where the modulation scheme is converted from 16-QAM 5/6 to 8-QAM 5/6.

[0049] If an additional information signal AI2 is to be transmitted again, at time t=t3, this additional information signal AI2 is transmitted by switching between coding and modulation schemes 8-QAM 5/6 and 8-QAM 3/4 again in a way already depicted in FIG. 2. In this case, the error protection coding changes again between 5/6 and 3/4.

[0050] Then, the transmitter 600 receives a feedback signal again that informs it that the reception quality of the received transmission signal has reduced further. In response to this, the control unit 612 switches the transmitter to an even more robust coding and/or modulation scheme. This is shown in FIG. 7 at time t=t4, where the modulation scheme is converted from 8-QAM 5/6 to 4-QAM 5/6.

[0051] If an additional information signal AI3 is to be transmitted again, at time t=t5, this additional information signal AI3 is transmitted by switching between coding and modulation schemes 4-QAM 5/6 and 4-QAM 3/4 again in a way already described with FIG. 2. In this case, the error protection coding changes again between 5/6 and 3/4.

[0052] However, a conversion of the modulation and coding scheme may take place because of poorer reception within the transmission time of an information signal, such as at time tx, see FIG. 7. This can lead to bit errors during decoding of the AI signal. For example, an MCS conversion from 16-QAM 5/6 to 16-QAM 3/4 at time tx can be interpreted erroneously as a bit change in the AI signal as a result of deteriorating reception on the receiver side, even though NO bit change has occurred in the AI signal at this time. To avoid these errors, in particular in additional information signals that are not transmitted repeatedly (in this case, a bit error may be detected because of the multiple transmission), additional error protection is implemented on the additional information signal. The additional information signal (AI) can be provided with Forward Error Correction for the AI signal (FECZI) before it is modulated into the useful signal by the MCS change. For example, a protection bit may be added for every 3 useful bits in the AI signal, corresponding to a coderate_AI of 3/4.

[0053] Synchronization in transmission of the additional information signal between transmitter and receiver must be ensured. There is an opportunity here to select a fixed bit clock that is known to both the transmitter and the receiver. This means it is possible for the receiver to recognize longer zero and one sequences in the additional information signal data bits (in this case there will not always be a change in the MCS scheme from bit to bit).

[0054] A second opportunity is the use of a special differential phase modulation (phase shift keying) for the AI signal, see FIG. 8. Differential Manchester code has the following coding specification:

[0055] When transmitting a logic 0, the clock signal is not inverted (turned 180 during the phase) for output relative to previous phasing

[0056] When transmitting a logic 1, the clock signal is inverted (turned) 180 for output relative to previous phasing

[0057] The clock can be recovered in the receiver from the transmitted differential Manchester coded AI signal. As applied in this invention, this means that any time a phase change occurs in differential Manchester code, the MCS scheme changes correspondingly, as described above, between MCS 1 and MCS 2. Or the inverse: the MCS is always changed correspondingly when the phase changes. The exact bit sequence of the additional information can be derived at the receiver from the recovered clock and the times of the phase changes (MCS changes).

[0058] FIG. 9 shows an implementation example of the MCS conversion process according to the invention, wherein an additional information signal is enclosed in the data transmission signal using (n=) 4 MCS schemes.

[0059] The additional information signal that is to be transmitted is, again, the digital (binary) signal that was already given in FIG. 2, namely, the series of 0 and 1 bits: 1001011011001010011011 . . . .

[0060] Two consecutive bits are always taken together. There are four possibilities for two bits: 00, 01, 10 and 11. As shown in FIG. 9, if no additional information signal is to be transmitted, i.e., for times t<t1, the coding and modulation scheme is 64-QAM 3/4. This coding and modulation scheme means a specified robustness of data transmission and therefore a specified transmission area in which receivers can receive the data transmission signal without error as far as possible. The first two-bit word of the additional information signal 10 causes a new change in the MCS scheme from 64-QAM 3/4 to 16-QAM 3/4. Two two-bit words of the additional information signal 01 follow this. This causes a change in the MCS scheme from 16-QAM 3/4 to 64-QAM 2/3. Following this is another two-bit word 10, which causes a change in the MCS scheme from 64-QAM 2/3 to 16-QAM 3/4. Following this is a two-bit word 11, which leads to a change from 16-QAM 3/4 to 16-QAM 1/2. Following this is a two-bit word 00, which leads to a change from 16-QAM 1/2 to 64-QAM 3/4.

[0061] This process leads to a lower change frequency between the different MCS schemes in comparison with the conversion process discussed in FIG. 2. This is advantageous because the MCS change scheme must then be interfered with less than if every bit change were to lead to an MCS change. A higher FEC could also be used, which would generate additional protection bits, also generating a few more MCS changes, but this could then be better managed because of the lower change rate.

[0062] It should also be noted that the invention is not limited to the example implementations discussed here. The invention also bears upon examples of implementation that differ from these examples in ways that are not crucial to the invention. For instance, n (the number of different MCS schemes) could differ from that described. For a number of n equal to, for example, three, a ternary additional information signal would have to be accommodated through changes between the three different MCS schemes in the data transmission signal. The invention also has applications in single-frequency networks (SFNs). Because the MCS does not usually change in SFNs, it is obvious when the MCS scheme does change that an additional information signal is being transmitted. The additional error correction mentioned above would then not be necessary and the transmission system would then become simpler (and therefore cheaper).