EP3343818A1

EP3343818A1 - Reduction of de-synchronization effects in tdm signals including dvb-t2 frames

Info

Publication number: EP3343818A1
Application number: EP16306858.8A
Authority: EP
Inventors: Stefan ILSEN
Original assignee: Telediffusion de France ets Public de Diffusion
Current assignee: Telediffusion de France ets Public de Diffusion
Priority date: 2016-12-30
Filing date: 2016-12-30
Publication date: 2018-07-04
Also published as: WO2018122378A1; EP3343808A1

Abstract

The invention relates to processing a signal including a succession of DVB-T2 super-frames, and comprising at least one first part including DVB-T2 data, and one second part including non DVB-T2 data, and more particularly to reduce de-synchronization effects in that kind of signal between the DVB-T2 data reception and the non-DVB-T2 data reception. The invention proposes to process that signal so as to ensure signal transmission robustness above a first level (L1), and more particularly to process the signal at a beginning (T₂', T₄') of at least one of said first and second parts to ensure signal transmission robustness above a second level (L2) for said beginning, the second level being higher than the first level.

Description

The present invention generally relates to time division multiplexing (TDM) when multiplexing wireless signals of different protocols, including DVB-T2 protocol.
It finds applications, in particular while not exclusively, in time division multiplexing of DVB-T2 data and non DVBT-2 data. Such non DVB-T2 data can be communication data such as LTE data and more particularly LTE-Advance or "LTE-A+" data. The invention finds a possible (but non limitative) application when the aforesaid communication data are transmitted through an existing broadcast network, so-called Tower Overlay over LTE-A+.
Hereinafter "LTE-A+" refers to all wireless telecommunication standards which are extensions of the LTE eMBMS specifications and which support signal time division multiplexing with other standards.
Broadcasting an LTE-A+ signal in the context of Tower Overlay over LTE-A+ (TOoL+) aims at relieving mobile networks from the increasing load caused by popular content by offloading this data to existing broadcast networks. TOoL+ further supports a cooperative spectrum between DVB-T2 and LTE-A+. This is made possible by the fact that DVB-T2 provides super-frames including so-called "Future Extension Frame" (FEF), enabling time domain spectrum sharing with other wireless networks. Thus, as it is signal time division multiplexing, DVB-T2 receiver only decodes the regular DVB-T2 part of the signal and ignores the LTE-A+ part of the hybrid signal. Inversely, LTE-A+ receiver only decodes the regular LTE-A+ part of the signal included in the FEF and ignores the DVB-T2 part of the hybrid signal.
However, in such framework DVB-T2 receivers and even more LTE-A+ receivers, tend to desynchronize. Indeed, receivers while ignoring the other part of the hybrid signal do not receive any synchronization elements. For instance, the receivers cannot track decoding parameters like the OFDM window offset or frequency and sampling rate mismatches, typically.
Figures 2A and 2B clearly display the above situation.
However, at the start of every LTE-A+ part, LTE-A+ receivers require perfect synchronization to the LTE-A+ signal, inversely at the start of every DVB-T2 part, DVB-T2 receivers require perfect synchronization to the DVB-T2 signal, otherwise the decoding quality can be impaired which presents itself as an signal to noise ratio (SNR) loss, which may lead to loss of data, possible retransmissions and a reduction of the Quality of Service.
This problem is at least partially related to the receiver implementation and to the duration of the parts that are ignored by the receiver, which depends on the implementation of the DVB-T2 broadcast network. For instance DVB-T2/LTE-A+ frame durations are typically within the range of 70 to 210 milliseconds.
This problem does not only concern time division multiplexing of DVB-T2 and LTE-A+ signals, but time division multiplexing of signals from other wireless communication standards, on the condition that the two standards have at least a common frequency range.
The present invention aims to improve the situation.
To that end, the invention relates to a method implemented by computer means for processing a signal including a succession of DVB-T2 super-frames, comprising at least:

one first part including DVB-T2 data, and
one second part including non-DVB-T2 data,
- the method comprising a processing of said signal so as to ensure signal transmission robustness above a first level.

More particularly, the method comprises processing a beginning of at least one of said first and second parts to ensure signal transmission robustness above a second level for said beginning, the second level being higher than the first level.
The present invention enables thus ensuring higher signal transmission robustness at least at the beginning of at least one part including either DVB-T2 data or non-DVB-T2 data. Thus, enables to counterweight or at least to reduce the effect of de-synchronization due to the absence of synchronization elements when the receivers of either DVB-T2 data or non-DVB-T2 data, ignores the other part of the hybrid signal, leading to impairment of the decoding quality which presents itself as a signal to noise ratio (SNR) loss. According to the present invention the receiver encompasses all types of terminals, for instance mobile phones for example LTE user equipment, vehicle communication systems and all kinds of connected devices and more generally all end systems.
According to some embodiments of the invention, the first and second levels are predetermined (for instance: calculated by the computer means or predetermined by the network operator).
The second level is fixed so that the signal transmission robustness which is set up above this second level and applied to the signal at the beginning, at least reduces the decoding error due to de-synchronization of the receiver which is possibly at its maximum at the beginning.
For example it is possible to perform tests on specific receivers to set up a level that is not too high, to keep a good data rate. Indeed, generally enhancing robustness involves reducing the data rate.
In a further example the second level (L2) may be a multiple of the first level (L1). For instance the second level can be two times higher than the first level. These modes of defining the second level are particularly relevant when the first level is subject to changes for whatever purpose, consequently following modifications would be applied on the second level, therefore spontaneously taking into consideration the reasons that have led to the change of L2.
In a further example the second level can be determined as an increasing function of the duration of the part preceding the part on which is applied the signal transmission robustness above the second level. This embodiment is particularly relevant since the de-synchronization of the receiver is partially related to the duration of the parts that are ignored, and that these parts are not always of equal duration.
In a further example the level L2 may be set up during the beginning, as a decreasing function of the time. Indeed, since the synchronization of the receiver improves during the beginning it may be relevant to decrease the level of the signal transmission robustness consequently to keep a good ratio data rate/decoding error. That is to say to enhance the data rate while not significantly increasing the amount of decoding error due to the improvement of synchronization of the receiver.
According to some embodiments of the invention, the first and second levels are defined according to information relative to the quality of the transmission, this information being returned by at least one receiver of non-DVB-T2 data. Such information can be for example a Channel Quality Indicator (CQI) or equivalent information, returned by at least one receiver of non-DVB-T2 data.
Therefore, in that embodiment, for example the first level L1 can be dynamically defined according to the CQI estimated for one or several previous non DVB-T2 data parts. In this case, the second level L2 can be imposed to be N times (twice or more for example) a value defined for the first level L1 determined on the basis of the CQI. The value of N can be fixed and stored along with an instruction of a computer program in a memory of the transmitter (and of the received as well as presented below). However, in an alternative embodiment, the second level L2 can depend as well on the CQI estimated for a beginning of a previous non DVB-T2 data part.
In the case where the information related to quality of transmission is specifically a CQI, the non-DVB-T2 communication standard may need to offer a non-broadcast mode, or the receiver may need to offer another wireless communication standard offering a non-broadcast mode.
Then, the second level may be calculated indeed from a CQI or equivalent information, which refers to the quality of the transmission of at least one beginning of non-DVB-T2 data parts. For example the second level may be set up in accordance with the CQI based on the quality of the transmission of the beginning of the previous latest non-DVB-T2 part.
This is a different use of CQI's, compared to usual prior art. Indeed, in the context of the invention a usual implementation of the CQI's would lead to an important data loss at the beginning of each non-DVB-T2 part. Indeed at the end of the previous non-DVB-T2 data time period the signal transmission robustness would be fully synchronized, and consequently the receiver would send a high CQI index. Thus the level of signal transmission robustness at the beginning of the next non-DVB-T2 part would be weak, whereas at the beginning of this non-DVB-T2 data time period, the de-synchronization of the receiver can be possibly at its maximum. Consequently the loss of data may be significant, whereas the invention would have avoided this problem. In addition the usual CQI's use is not efficient enough to adapt quickly to the evolution of synchronization.
In the contrary, according to the invention, the level of signal transmission robustness applied at a certain time of a non-DVB-T2 part, and therefore the first and/or second level, may be determined according to the information on the quality of the transmission referring to a previous non-DVB-T2 part. For example, the second level L2 can be determined on the basis of CQI estimation in the beginning of that latest previous non-DVB-T2 part, while the first level L1 can be determined on the basis of CQI estimation on the remaining portion of that latest previous non-DVB-T2 part.
Of course, the first L1 and second L2 levels can be determined, one (L2) according to the other (L1), or separately (L2 being independent from L1), on the basis of the CQI (or an equivalent information). In the same way the duration of the beginning of non-DVB-T2 parts where the second level of robustness is applied can be also determined dynamically according to the CQI (or equivalent information).
Such embodiments enable to adapt the robustness according to the local circumstances to provide a better ratio data rate/decoding error.
Compared to a dynamic definition of the second level L2, the predetermined definition enables to avoid the need of the returns - stated above - from the receivers.
According to some embodiments of the invention, the non DVB-T2 data further comprises communication data, and more particularly LTE-Advanced type data, such as LTE-A+ type data.
Such embodiments enable to transmit data of such communication standard within the Future Extension Frame (FEF) of DVB-T2 super-frame, that is in a time division multiplex with DVB-T2 data. The communication standard can be any wireless communication standard, which supports signal time division multiplexing, and which share common frequency range with DVB-T2.
The invention may be particularly relevant in the case of LTE-A or LTE-A+ in broadcast mode such as eMBMS or other standard used in broadcast mode because they do not usually permit Automatic Repeat reQuest or at least it offers a new degree of freedom in this case for the trade-off between wasting transmission resources and having too many retransmissions. Therefore it is important to be able to parameterize transmitters and receivers to have relatively few decoding errors. Yet, decoding errors are directly impacted by de-synchronization of the receiver, which is offset by or at least reduced by the present invention.
According to some embodiments of the invention at least one of first and second parts comprises a succession of sub-frames, and the beginning comprises, at the most, one sub-frame which is the first sub-frame of the succession of sub-frames.
According to some embodiments of the invention the first part comprises a succession of N T2-Frames, and the beginning comprises, at the most, n T2-Frames of said succession of N T2-Frames, with n<N.
According to some embodiments of the invention the first sub-frame of the succession of sub-frames comprises a succession of slots, and wherein the beginning comprises, at the most, one slot which is the first slot in said succession of slots.
According to some embodiments of the invention the first slot of said succession of slots comprises a succession of N symbols, and wherein said beginning comprises, at the most, n first symbols of said succession of N symbols, with n<N.
The duration of the beginning can therefore be set up at different lengths. A short duration for instance one symbol allows to have a good data rate. A long duration for instance one sub-frame or T2-Frames or more ensures that the receiver is well synchronized when the beginning is finished, avoiding too much decoding error due to de-synchronization.
The duration of the beginning is optimally set up for the time required for the receiver to fully synchronize.
These time periods can be predetermined by the network operator, for example by operating tests or simply postulating their durations. Alternately, these time periods can be dynamically defined, for example: the receivers can send a Channel Quality Indicator (CQI), which enables to adapt these time periods according to the local circumstances and/or to the delay of synchronization.
In a further example the duration of the beginning can be determined as an increasing function of the duration of the part preceding the part on which is applied the signal transmission robustness above the second level. This embodiment is particularly relevant since the de-synchronization of the receiver is partially related to the duration of the parts that it ignored, and that these parts are not always of equal duration.
By imposing a higher signal transmission robustness for a wider beginning it enables to ensure data transmission during a time period long enough to improve the synchronization. The signal transmission robustness is set above the second level during all the beginning time period. For example the signal transmission robustness can be set above the second level and be gradually reduced during the beginning time period while the receiver synchronizes, this allows to opt for a good ratio data rate/decoding error.
According to an alternative, more than two levels above which the signal transmission robustness is ensured can be determined. Those levels can be determined either according to each other or separately. All the methods to determine the first and second level can therefore be applied either solely or in combination to those levels. For example, with three levels, L1, L2 and L3, L3 can be fixed independently from the two other levels by the network operator, for a first portion of the part, which was mentioned as the beginning. L2 can be defined according to L1, for instance as a multiple of L1, for a second portion of the part.
According to some embodiments of the invention to ensure signal transmission robustness the implementation of a Forward Error Correction (FEC) is performed and the level of signal transmission robustness of the signal may be a function of the chosen FEC code rate. For example the signal transmission robustness can be set above the second level by setting a low code rate and the signal transmission robustness can be gradually reduced during the beginning time period by increasing progressively the code rate. The code rate may as well be constant for all the beginning time period.
Such embodiments enable to ensure a signal transmission robustness above a certain level at the beginning of at least one part including either DVB-T2 data or non-DVB-T2 data, by changing the FEC code rate to a lower code rate.
Especially, according to some embodiments of the invention the Forward Error Correction applied can be a turbo code. Turbo codes are particularly efficient among FECs, enabling a good ratio SNR/data rate.
Especially, according in an embodiment, alternative or taken in combination with the embodiments where the Forward Error Correction (FEC) applied can be a turbo code, to ensure a signal transmission robustness above a certain level at the beginning of at least one part including either DVB-T2 data or non-DVB-T2 data, the FEC applied can be a Low-density parity-check (LPDC) code.
According in an embodiment, alternative or taken in combination with the embodiment where the implementation of a Forward Error Correction (FEC) is performed, to ensure signal transmission robustness the implementation of a modulation scheme having a chosen number of bits per symbol is performed and the signal transmission robustness is enhanced when using a modulation scheme having fewer bits per symbol. For example, the signal transmission robustness can be set above the second level by setting a modulation scheme having few bits per symbol and then the signal transmission robustness can be gradually reduced during the beginning time period by applying several successive modulation schemes that progressively increase the bits per symbol, hereinafter referred to as a sequence of modulation schemes. A single modulation scheme with the appropriate number of bits per symbol may as well be set up for all the beginning time period.
Such embodiments enable to ensure a signal transmission robustness above a certain level at the beginning of at least one part including either DVB-T2 data or non-DVB-T2 data, by changing the modulation scheme for a modulation scheme with fewer bits per symbol.
It is of course possible to change both, FEC codes rates and modulation schemes to achieve the desired signal transmission robustness level.
Other solutions to enhance the robustness can also be applied, for instance by increasing the power of the signal.
A second aspect of the invention concerns a transmitter configured to transmit a signal including a succession of DVB-T2 super-frames, comprising at least:

one first part including DVB-T2 data, and
one second part including non DVB-T2 data,
the transmitter being configured to process the signal so as to ensure signal transmission robustness above a first level,
wherein the transmitter is configured to process a beginning of at least one of the first and second parts to ensure signal transmission robustness above a second level for said beginning, the second level being higher than the first level.

A third aspect of the invention concerns a receiver configured to receive a signal including a succession of DVB-T2 super-frames, comprising at least:

one first part including DVB-T2 data, and
one second part including non DVB-T2 data,
the signal having been processed so as to ensure signal transmission robustness above at least a first level,
the receiver being configured to extract data from at least one among the first and second parts,
wherein the receiver is further configured to extract data from a beginning of at least one among the first and second parts while using a signal transmission robustness above a second level, the second level being higher than the first level.

Such embodiments enable the receiver to acquire the level of signal transmission robustness applied to the signal and thereby to be able to extract the data included in the signal. For example when the signal transmission robustness set up above the second level is ensured through a code rate scheme of an implemented FEC scheme and a sequence of modulation schemes, the receiver which has received these parameters is able to demodulate and decode the signal properly to extract the data.
A fourth aspect of the invention concerns a computer program comprising code instructions to implement the method according to any one of the embodiments of the invention.
An example of a flowchart implemented by the computer program is presented in the figures 3 and 4.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements and in which:

Figure 1 illustrates a Tower Overlay over LTE-A+ system representing a High Tower, High power (HTHP) transmitter covering many existing cellular towers.
Figure 2A represents the data structure of the signal, including a succession of DVB-T2 super-frames.
Figure 2B schematizes the evolution of the synchronization of the receiver (R2) towards the signal transmitting P2 and P4.
Figure 2C represents an example of the effective level of signal transmission robustness of the part of signal transmitting P2 and P4.
Figure 3 illustrates a flowchart representing the steps to process and emit the signal according to one embodiment of the invention.
Figure 4 illustrates a flowchart representing the steps to receive the signal and extract the data according to one embodiment of the invention.

Referring to Figure 1, there is shown a Tower Overlay over LTE-A+ system which comprises a High Tower, High power (HTHP) transmitter 1 covering many cellular towers 2.
The principle of Tower Overlay over LTE-A+ is to offload data transmitting through mobile networks, especially live video or popular content, to broadcast networks. Therefore the initial LTE-A+ data containing popular content is send through a HTHP transmitter 1 instead of a cellular tower. The User Equipment (UE) 3 - LTE receiver - receives the data from the HTHP transmitter, like if it was sent by the cellular tower which covers the LTE cell in which the UE is. This system enables to broadcast to all the UEs contained in many LTE cells covered by the HTHP transmitter, and therefore avoiding to distribute the popular content in many networks cells and possibly by several mobile network operators in parallel.
One relevant way of transmitting through HTHP transmitter is to use existing broadcast transmitter. In addition, TOoL+ further supports a cooperative spectrum between DVB-T2 and LTE-A+, this is made possible by the fact that DVB-T2 provides super-frames including Future Extension Frames (FEF), enabling time domain spectrum sharing with other wireless networks.
In this case LTE-A+ data is transmitted through a signal in time division multiplexing. Thus, as it is signal time division multiplexing, specific DVB-T2 receiver 4 only decodes the regular DVB-T2 part of the signal and ignores the LTE-A+ part of the hybrid signal, inversely specific LTE-A+ receiver 3 only decodes the regular LTE-A+ part of the signal included in the FEF and ignore the DVB-T2 part of the hybrid signal.
The LTE cellular towers 2 can as well be any cellular tower, and the communication standard can be any other wireless communication standard, which supports signal time division multiplexing, and which share common frequency range with DVB-T2. For example the invention can be applied with LTE and LTE Advanced instead of LTE-A+.
The receiver of DVB-T2 or non-DVB-T2 standard, comprises one receiver (RECE) 5, a demodulator (DEMO) 6, a FEC decoder (DECO) 7 and a memory unit (MEMO) 8 which are all control by a processor (PROC) 9. The MEMO comprises a non-volatile unit which retrieves the computer program and a volatile unit which retrieves the signal transmission robustness scheme and/or a code rate scheme of the implemented FEC scheme and a sequence of modulation schemes.
Referring to Figure 2A, there is shown a succession of parts, P1, P2, P3, and P4 including alternatively DVB-T2 data and non-DVB-T2 data. In this example and those that follow, P1 includes DVB-T2 data, P2 includes non-DVB-T2 data, P3 includes DVB-T2 data and P4 includes non DVB-T2 data. The same reasoning can be applied mutatis mutandis to all of the followings with, P1 includes non-DVB-T2 data, P2 includes DVB-T2 data, P3 includes non-DVB-T2 data and P4 includes DVB-T2 data.
The DVB-T2 standard enables to set the size and the structure of the super-frames, thus a super-frame can include several Future Extension Frames (FEF).
Each part can include one or several frames of a DVB-T2 super-frame or even several frames from several super-frames in a row. To sum up, the part including non-DVB-T2 data lasts until a DVB-T2 frame is transmitted, reciprocally the part including DVB-T2 data lasts until a FEF frame including non-DVB-T2 data is transmitted.
Thus the time period of each part is not defined in advance and so P1 and P3 or P2 and P4 can have a different time period.
The data included in the FEF can be from any wireless communication standard, which supports signal time division multiplexing, and which share common frequency range with DVB-T2. Since, LTE-A+ share common frequency range with DVB-T2, LTE-A+ signal can be time division multiplexed with a DVB-T2 signal, same can be done with LTE and LTE Advance.
To attempt, such succession of parts including alternately DVB-T2 data and non DVB-T2 data, it is possible to use a hybrid modulator, composed with two modulator, one of DVB-T2 and one of non DVB-T2, both modulators transmit there signal to a multiplexer/transmitter which transmits the signal of either one or the other modulator in accordance with the super-frame structure.
Referring to Figure 2B, there is shown schematically the evolution of the synchronization of the receiver (R2) towards the signal transmitting P2 and P4.
Only the synchronization of the receiver towards the signal transmitting P2 and P4 is represented on the figure 2B. A second case occurs with the receiver towards the signal transmitting P1 and P3 (R1), and the same reasoning could therefore be applied mutatis mutandis to this case to all that follow. These two cases according to the invention can be applied simultaneously.
During the time periods of the transmission of the signal transmitting P1 (T₁) and P3 (T₃), no signal is decoded by R2, thus during those hole time periods R2 will not receive any synchronization elements and will therefore tend to desynchronize. Consequently the de-synchronization depends on the duration of the P1 and P3 transmission time periods. At the end of T₁ and T₃ and at the beginning of P2 and P4 transmission time period (T₂ and T₄) the de-synchronization of R2 is possibly at its maximum. At the beginning of T₂ and T₄, R2 starts to re-synchronize with the signal transmitting P2 and P4.
As previously mentioned, in this example R2 is the non-DVB-T2 data receiver but R2 can indifferently be the DVB-T2 data receiver or the non-DVB-T2 data receiver. Furthermore, non-DVB-T2 can be any wireless communication standard which support signal time division multiplexing, and which share common frequency range with DVB-T2. Especially, non-DVB-T2 can be as well LTE, LTE-A or LTE-A+.
Referring to Figure 2C, there is shown an example of the effective level of signal transmission robustness of the part of signal transmitting P2 and P4.
At the beginning of T₂ and T₄ the de-synchronization of R2 is possibly at its maximum. Consequently the decoding quality will be impaired which presents itself as a signal to noise ratio (SNR) loss.
Therefore, signal transmission robustness is set up above a predetermined level, L2, during the beginning of T₂ and T₄. The level is selected to avoid or to reduce decoding error due to the de-synchronizations.
The level L2 may be predetermined calculated by computer means or set by the network operator. For example it is possible to perform tests on specific receivers to set up a level that is not too high, to keep a good data rate. Indeed, generally enhancing robustness involves reducing the data rate.
In a further example the level L2 may be a multiple of the first level, L1. For instance the L2 can be two times higher than L1. These modes of defining L2 are particularly relevant when the first level is subject to changes for whatever purpose, consequently following modifications would be applied on L2, therefore spontaneously taking into consideration the reasons that have led to the change of L2.
In a further example the level L2 can be determined independently for each beginning of T₂ and T₄ as a function of the duration of the precedent time periods T₁ and T₃. For example if L2 is set up at a X + L1 level for a duration of the precedent period of t₁, L2 may be set up at a 2X + L1 level for a duration of the precedent period of 2 times t₁. This embodiment is particularly relevant since the de-synchronization of the receiver is partially related to the duration of the parts that it ignored, and that these parts are not always of equal duration.
It is equally possible to not predetermine the level L2 but to define it dynamically, for example: the receivers can send a Channel Quality Indicator (CQI) through the cellular tower (2), which enables to adapt the robustness according to the local circumstances and/or to the level of de-synchronization to provide a better ratio data rate/decoding error.
However, the level, L2, is higher than the level, L1, of signal transmission robustness set up for the rest of T₂ and T₄ that occurs when R2 is synchronized.
To establish a robustness scale several techniques can be applied. For example, a data rate level can be considered to estimate a level of robustness.
The robustness scale can be defined also by determining levels and by mapping for each level a given couple of a modulation scheme and FEC code rate.
It may be as well the level of SNR returned by a receiver through the cellular tower, like mentioned above.
The time periods (T₂' and T₄') considered as the beginning of T₂ and T₄ optimally lasts the time required for R2 to fully resynchronize.
These time periods can be predetermined by the network operator, for example by operating tests or simply postulating their durations. Alternately, these time periods can be dynamically defined, for example: the receivers can send a Channel Quality Indicator (CQI) through the cellular tower (2), which enables to adapt these time periods according to the local circumstances and/or to the delay of synchronization.
In a further example T₂' and T₄' can be determined independently as a function of the duration of the precedent time periods T₁ and T₃. For example if T₂' is set up at t₂' for a duration of the precedent period of t₁, T₄' may be set up at a duration of 2 times t₂'.
When P2 and P4 comprise a succession of sub-frames, T₂' and T₄' can be defined as, at the most, the first sub-frame in the succession of sub-frames.
When P2 and P4 comprise a succession of sub-frames, and that the sub-frames comprise a succession of slots, T₂' and T₄' can be defined as, at the most, the first one slot in the succession of slots.
When P2 and P4 comprise a succession of sub-frames, and that the sub-frames comprise a succession of slots, and that the slots comprise a succession of N symbols, T₂' and T₄' can be defined as, at the most, the first n symbols in the succession of N symbols, with n<N.
If these time periods are broader it will ensure that R2 will be fully synchronized when T₂' and T₄' ends up.
Once the level and the time period considered as the beginning are defined the effective signal transmission robustness scheme to apply is set up and transmitted to R2 which registers it in the MEMO. The effective signal transmission robustness is at least above L2 and during at least T₂' and T₄'. It may be relevant to set up the effective signal transmission robustness as a decreasing function of the time, during T₂' and T₄'. Indeed, since the synchronization of the receiver improves during T₂' and T₄' it may be relevant to decrease the level of the signal transmission robustness consequently to keep a good ratio data rate/decoding error. That is to say to enhance the data rate while not significantly increasing the amount of decoding error due to the enhancement of the synchronization of the receiver.
Once the effective signal transmission robustness scheme is set up, the transmitter is configured to enhance signal transmission robustness of the signal transmitting P2 and P4 according to the signal transmission robustness scheme.
To proceed to such enhancement of the signal transmission robustness, many solutions are available, for instance by increasing the power of the signal according to the signal transmission robustness scheme.
Such enhancement of the signal transmission robustness can also be achieved by the implementation of a Forward Error Correction (FEC). Therefore redundant bits are added to the transmitted data. The code rate stands for the proportion of non-added bits on the total amount of bits. The more bits are added, the more the signal transmission robustness may be enhanced, and the lower the code rate is. Thus, the signal transmission robustness is a decreasing function of the FEC code rate. Consequently, the code rate scheme of the implemented FEC is chosen according to the signal transmission robustness scheme.
Especially, the Forward Error Correction implemented can be a turbo code. Turbo codes are particularly efficient among the FEC codes, enabling a good ratio SNR/data rate.
Such enhancement of the signal transmission robustness can also be achieved by the implementation of a modulation scheme having a chosen number of bits per symbol.
The signal transmission robustness may be enhanced when using a modulation scheme having fewer bits per symbol.
The signal transmission robustness may be reduced when using a modulation scheme having higher bits per symbol.
Accordingly, a chosen sequence of modulation schemes can be realized according to the signal transmission robustness scheme.
The effective signal transmission robustness scheme can be set up by combining several of solutions, for example using FEC codes rates combine with modulations schemes. Therefore, the code rate scheme of the implemented FEC and the sequence of modulation schemes are defined, according to the effective signal transmission robustness scheme.
Like pointed previously, non-DVB-T2 can be any wireless communication standard which support signal time division multiplexing and which share common frequency range with DVB-T2.
However the invention may be especially relevant in the case of LTE, LTE-A or LTE-A+, since these wireless communication standard provides re-transmissions. Therefore, when used in a broadcast mode, for example eMBMS, it can be relevant to implement the invention rather than to rely on re-transmissions, which could reduce the data rate and increase the latency, reducing the quality of service.
The invention may also be relevant in the case of LTE, LTE-A or LTE-A+, when not used in broadcast mode.
Indeed, DVB-T2 is a broadcast standard and therefore the HTHP is designed for transmitting and not receiving signals from the receivers, nonetheless while the downlink can be done between HTHP and the UE, the uplink can be done between the UE and the LTE cellular towers.
In such, a non-broadcast mode the UE will send a Channel Quality Indicator (CQI) to the LTE base station. At the end of the non-DVB-T2 data transmission time period for example P2, T₂, the R2 will be fully synchronized and therefore will send a high CQI index. At the beginning of the new non-DVB-T2 data transmission time period, T₄, the signal transmission robustness will be weak, when the de-synchronization of the UE will be maximal. Thus the loss of data may be significant, whereas the invention would have avoided this problem.
Referring to Figure 3, there is shown a flowchart summarizing the steps to process and emit the signal according to one embodiment of the invention.
At step 11 (S11), the network operator or the computer means define the level L2 and the time periods considered as the beginning.
At step 12 (S12), the network operator or the computer means set up the effective signal transmission robustness scheme to apply, which is at least above L2 and at least during the time period considered as the beginning. Therefore, a code rate scheme of the implemented FEC and a sequence of modulation schemes are defined. The same is done if other solutions are chosen to enhance the signal transmission robustness.
At step 13 (S13), the FEC coder and the modulator concerned by the signal transmitting P2 and P4, that is to say either DVB-T2 or non-DVB-T2 modulator component from the hybrid modulator, are configured in consequence.
At step 14 (S14), the signal transmission robustness scheme and/or the code rate scheme of the implemented FEC and the sequence of modulation schemes may be transmitted to the receiver R2 and then R2 registers it in the MEMO.
At step 21 (S21), the FEC coder runs the code rate scheme on P2 and P4.
At step 22 (S22), the modulator concerned by the signal transmitting P2 and P4 executes the modulation scheme according to the sequence of modulation schemes previously defined.
At step 23 (S23), the modulator concerned by the signal transmitting P2 and P4 transmits the signal to the multiplexer/transmitter which emits the signal of either one or the other modulator in accordance with the super-frame structure.
The steps 21, 22 and 23 can be repeated as long as the transmitter emits a signal and that the signal transmission robustness scheme is not changed.
Referring to Figure 4, there is shown a flowchart summarizing the steps to receive the signal and extract the data according to one embodiment of the invention. At step 31 (S31), R2 receives the signal transmission robustness scheme and/or the code rate scheme of the implemented FEC and the sequence of modulation schemes, and R2 registers them in the MEMO.
At step 32 (S32), R2 configures the demodulator and the FEC decoder according to the code rate scheme of the implemented FEC and the sequence of modulation schemes registered in the MEMO.
At step 41 (S41), R2 receives the signal transmitting P1, P2, P3 and P4.
At step 42 (S42), R2's demodulator demodulates the signal.
At step 43 (S43), R2's FEC decoder decodes the succession of bits and extract the P2 and P4 data.
The steps 41, 42 and 43 can be repeated as long as the transmitter emits a signal and that the signal transmission robustness scheme is not changed.
Of course, the present invention is not limited to the examples of embodiments described in details above, but encompasses also further alternative embodiments.
For instance, the invention further applies to the case where the beginnings of each parts, the ones including DVB-T2 data, and the ones including non-DVB-T2 data, have their signal transmission robustness enhanced above the second level.
Furthermore, the invention further applies to the case where more than two levels above which the signal transmission robustness is ensured, are determined.

Claims

A Method implemented by computer means for processing a signal including a succession of DVB-T2 super-frames, comprising at least:
one first part including DVB-T2 data, and

one second part including non DVB-T2 data,

the method comprising a processing of said signal so as to ensure signal transmission robustness above a first level,

wherein the method comprises processing a beginning of at least one of said first and second parts to ensure signal transmission robustness above a second level for said beginning, the second level being higher than the first level.
The method of claim 1, wherein said first and second levels are predetermined by said computer means.
The method of claim 1, wherein said first and second levels are defined according to information relative to a quality of a transmission, said information being returned by at least one receiver of non-DVB-T2 data.
The method according to any one of the preceding claims, wherein said non DVB-T2 data comprise communication data.
The method of claim 4, wherein said communication data comprise LTE-Advanced type data.
The method of claim 5, wherein said LTE-Advanced type data comprise LTE-A+ type data.
The method according to any one of the preceding claims, wherein said at least one of said first and second parts comprises a succession of sub-frames, and wherein said beginning comprises, at the most, one sub-frame which is the first sub-frame in said succession of sub-frames.
The method of claim 7, wherein said first sub-frame of said succession of sub-frames comprises a succession of slots, and wherein said beginning comprises, at the most, one slot which is the first slot in said succession of slots.
The method of claim 8, wherein said first slot of said succession of slots comprises a succession of N symbols, and wherein said beginning comprises, at the most, n first symbols of said succession of N symbols, with n<N.
The method according to any one of the preceding claims, wherein said first part comprises a succession of N T2-Frames, and wherein said beginning comprises, at the most, n first T2-Frames of said succession of N T2-Frames, with n<N.
The method according to one of the previous claim, wherein said processing of said signal to ensure signal transmission robustness is performed by implementation of a Forward Error Correction (FEC) and wherein said level of signal transmission robustness is a function of a chosen FEC code rate.
The method of claim 10, wherein the said Forward Error Correction is a turbo code.
The method of claim 11 or 12, wherein the said Forward Error Correction is a LPDC code.
The method according to one of the previous claim, wherein said processing of said signal to ensure signal transmission robustness is performed by implementation of a modulation scheme having a chosen number of bits per symbol, and wherein said signal transmission robustness is enhanced when using a modulation scheme having less bits per symbol.
A receiver configured to receive a signal including a succession of DVB-T2 super-frames, comprising at least:
one first part including DVB-T2 data, and

one second part including non DVB-T2 data,

said signal having been processed so as to ensure signal transmission robustness above at least a first level,

said receiver being configured to extract data from at least one among said first and second parts,

wherein said receiver is further configured to extract data from a beginning of said at least one among said first and second parts while using a signal transmission robustness above a second level, the second level being higher than the first level.
A transmitter configured to transmit a signal including a succession of DVB-T2 super-frames, comprising at least:
one first part including DVB-T2 data, and

one second part including non-DVB-T2 data,

said transmitter being configured to process said signal so as to ensure signal transmission robustness above a first level,

wherein said transmitter is configured to process a beginning of at least one of said first and second parts to ensure signal transmission robustness above a second level for said beginning, the second level being higher than the first level.
A computer program comprising code instructions to implement the method according to any one of claims 1 to 14 when said instructions are run by a processor.