Patent Application
20180270013
The invention relates to a transmitter for the transmission of a data transmission signal within a transmission area in accordance with the claim preamble 1. The invention also relates to a receiver for receiving the data transmission signal.
A transmitter from the claim preamble 1 is known from US-20100260045A. In this document, a transmitter is described that is capable, inter alia, of modulating the information containing signal to be emitted using various modulation schemes dependent on the conditions of transmission in the transmission area and/or to encode according to various coding schemes, depending on good or bad reception conditions.
The purpose of the invention is the proposal of a transmitter and a receiver wherein the transmitter is equipped with a coding and/or modulation unit with an additional mode of operation and the receiver is also capable of working with the transmitter in this additional mode of operation.
The transmitter for the invention is therefore defined according to the notes in the claim 1. The receiver for the invention is also claimed.
Positive examples of the transmitter design and the receiver design are defined by select claims. 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.
The invention relates to the following information.
A transmitter and a receiver that are linked and exchange any modulation signal with each other (e.g., language, video, audio data) are linked on the physical layer (PHY) at specified points in time with entirely pre-defined modulation and coding schemes (MCS). The chosen MCS depends upon the receiver's reception conditions as well as the current conditions on the transmission channel. An important measure to determine this is the Signal-to-Interference-and-Noise Ratio—SINR—at the reception area.
In bidirectional connections (e.g., mobile phone connection to mobile transmission station), the receiving device constantly reports its reception conditions (at specified time intervals), whereupon the transmitter adjusts its MCS for the connection to the receiving device in such a way as to ensure the modulation signal is also received correctly by the receiving device (i.e., the signal is decoded correctly). For example, if the reception conditions in the location of the receiver deteriorate, the transmitter will adjust its MCS towards “more robust modulation”. This will reduce the transmissible net data rate. However, if the reception conditions in the location of the receiver improve, the transmitter will adjust its MCS towards “higher-order modulation”, increasing the transmissible net data rate. If the reception conditions in the location of the receiver remain the same over a certain period of time, then there will also be no change in the MCS in transmission from transmitter to receiver.
The invention then concerns the implementation of MCS changes (variations in the modulation and/or coding schemes) on the transmitter side in order to transmit specific data (additional information). The data/additional information is in the form of a binary sequence of bits (logic 0 and logic 1). The MCS will then be modified according to the bit sequence of the additional information (AI) in such a way that the robustness, based on the current MCS (as it has recently been selected for transmission without MCS variation from the transmission system), is first modified towards higher robustness and then back to the previous MCS.
For example: The MCS 64-QAM 3/4 is selected for transmission in a radio cell in order to ensure error-free reception at the receiving device if the cell is expanded. Now, for a specified, short time, depending on the additional information to be transmitted, the MCS will switch first to MCS 64-QAM 2/3 and then back to 64-QAM-3/4, and according to the bit sequence of the additional information, back and forth between these MCS until the data are completely reproduced. Disturbances in the transmission quality of the modulation data (video, audio, data) as a result of the modulated additional data will be avoided by always modulating to a “more robust MCS” relative to the current MCS.
Because transferal from the transmitter to the receiver entails a superimposition as part of the change in modulation and coding schemes, once triggered by the reception conditions and then another created by the transmission of the additional information, errors can occur on the receiver side during AI transmission. In the case of AI data that can be transmitted several times and repeatedly (identifiers, distress calls, etc.), this does not present a problem because the data will be received several times. The use of a suitable error protection mechanism (EPM) on the additional information's bit sequence can provide for error-free decoding, even of non-repeating additional information on the receiver side. But EPM also offers further, additional error protection for AI data that is transmitted several times and repeatedly.
The invention is represented in more detail using some implementation examples in the diagram description that follows. In these diagrams:
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.
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 (4̂n)—which is most easily understood using the four quadrants in the IQ constellation diagram—4̂1->4QAM/42->16-QAM/43->64-QAM/4̂4->256-QAM/4̂5->1024-QAM etc.
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.
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.
The additional information signal could, as an example, be a warning broadcast signal.
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
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.
As
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.
As shown in
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
As
As shown in
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
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.
In the case of the implementation example from
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.
The receiver 500 according to
The transmitter 600 according to
The transmitter's functioning according to
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
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
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
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
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
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).
A second opportunity is the use of a special differential phase modulation (phase shift keying) for the AI signal, see
When transmitting a logic 0, the clock signal is not inverted (turned 180° during the phase) for output relative to previous phasing
When transmitting a logic 1, the clock signal is inverted (turned) 180° for output relative to previous phasing
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).
The additional information signal that is to be transmitted is, again, the digital (binary) signal that was already given in
Two consecutive bits are always taken together. There are four possibilities for two bits: 00, 01, 10 and 11. As shown in
This process leads to a lower change frequency between the different MCS schemes in comparison with the conversion process discussed in
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).
| Number | Date | Country | Kind |
|---|---|---|---|
| 102015000035558 | Jul 2015 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/066910 | 7/15/2016 | WO | 00 |
