Technical Field

The invention relates to a transmitting device and a network node comprising such a transmitting device. Furthermore, the invention also relates to corresponding methods, a computer program, and a computer program product.

Background

Within 3GPP there are ongoing discussions about new waveform contenders for conveying information for the next generation of cellular systems, i.e. 5G systems.

Today, in 4G systems, the waveform contenders are using a form of cyclic prefix. The main intention of using the cyclic prefix is to mitigate the impact of the multipath spread of the radio propagation channel. Without a cyclic prefix, multipath channels will create so-called inter- symbol-interference ( IS I) deteriorating the orthogonality of the transmitted waveforms, and force the receiving devices to choose between the implementation of expensive channel equalizers or just accept poor performance.

Some of the new waveforms contenders, that are discussed in the context of 5G systems, use a guard interval (sometimes called a guard space or guard period) between each transmitted symbol, instead of using a cyclic prefix. The guard interval is intended for the same purpose as the cyclic prefix, i.e. to mitigate the impact of multipath channels and maintain the orthogonality of the transmitted waveforms. In this new class of waveforms, we find for example Zero-Tailed Universal Frequency Multi-Carrier (ZT-UFMC), Zero tailed OFDM (ZT-OFDM), Zero tailed DFT-S-SCMA (ZT-DFT-S-SCMA), Unique Words DFT-S-OFDM (UW-DFT-S- OFDM) and many others.

The use of a cycle prefix or guard interval has a price. The transmission medium cannot be used 100% of the time for transferring data.

Summary

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions using guard interval. Another objective of embodiments of the invention is to provide a solution which provides improved utilization of the transmission medium. An "or" in this description and the corresponding claims is to be understood as a mathematical OR which covers "and" and "or", and is not to be understand as an XOR (exclusive OR).

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous implementation forms of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a transmitting device for a communication system, the transmitting device being configured to

obtain a set of delay spreads for a corresponding set of receiving devices, wherein each delay spread in the set of delay spreads is associated with a channel between the transmitting device and a receiving device in the set of receiving devices,

classify receiving devices in the set of receiving devices into a subset of receiving devices if the corresponding delay spread for a receiving device is less than or equal to a delay spread threshold value,

transmit a first sequence of data symbols with a first transmission power to the set of receiving devices, wherein the first sequence of data symbols comprises at least one guard interval arranged between two data symbols in the first sequence of data symbols,

transmit a second sequence of data symbols with a second transmission power to the subset of receiving devices, wherein the second sequence of data symbols comprises at least one additional data symbol in the guard interval of the first sequence of data symbols.

The first sequence of data symbols is addressed for the set of receiving devices whilst second sequence of data symbols is addressed for the subset of receiving devices.

The channel is a radio channel in wireless communication systems.

The transmitting device according to the first aspect provides a number of advantages over conventional solutions. One such advantage is improved utilization of the transmission medium in the time domain. Thereby, improved data rates and reduced latency is possible in the wireless communication system. The transmission of the second sequence of data symbols could in some cases be implemented as an add-on service on top of existing services in communication systems. By deciding based on the delay spread if the additional second sequence of data symbols using the guard interval it can be ensured that the transmission of the second sequence data symbols does not interfere with the transmission of the first sequence of data symbols at the receiving devices. In a first possible implementation form of a transmitting device according to the first aspect, the delay spread threshold value is less than the duration of the guard interval. The first implementation form means that the second sequence of data symbols will not interfere with the first sequence of data symbols.

In a second possible implementation form of a transmitting device according to the first implementation form of the first aspect, the transmitting device is further configured to

determine the symbol duration for the additional data symbol based on the set of delay spreads and the duration of the guard interval.

The second implementation form means that the symbol duration for the additional data symbol can be determined more exactly since both the delay spreads and the duration of the guard interval are considered.

In a third possible implementation form of a transmitting device according to the second implementation form of the first aspect, the transmitting device is further configured to

control at least one of the duration of the guard interval and the symbol duration for the additional data symbol so as to control the number of receiving devices classified into the subset of receiving devices.

The duration of the guard interval and the symbol duration for the additional data symbol can be used as design parameters for controlling the number of receiving devices classified into the subset of receiving devices. Thereby, the communication resources (such as time and frequency) used for the additional data symbols can be allocated for optimising higher data rates, lower latency, or other performance measures.

In a fourth possible implementation form of a transmitting device according to any of the preceding implementation forms of the first aspect or to the first aspect as such, the transmitting device is further configured to

receive a set of Power Delay Profiles, PDPs, for the corresponding set of receiving devices, wherein each PDP in the set of PDPs is associated with a radio channel between the transmitting device and a receiving device in the set of receiving devices,

obtain the set of delay spreads based on the set of PDPs.

The fourth implementation form is a convenient and low complex way of obtaining the set of delay spreads since in most existing systems the PDPs are already available.

In a fifth possible implementation form of a transmitting device according the fourth implementation form of the first aspect, the transmitting device is further configured to

compute a set of received powers for the corresponding set of receiving devices based on the set of PDPs,

classify the receiving device into the subset of receiving devices if the corresponding delay spread for the receiving device is less than or equal to the delay spread threshold value and if the corresponding received power for the receiving device is larger than an interference power threshold value.

The fifth implementation form provides a feedback mechanism for interference control. If the received power is too low for a receiving device, such a receiving device should not belong to or be removed from the subset of receiving devices.

In a sixth possible implementation form of a transmitting device according to the fourth or fifth implementation form of the first aspect, the transmitting device is further configured to

compute the second transmission power based on the set of PDPs. The sixth implementation form provides a low complex solution of computing the second transmission power for interference control when transmitting the additional data symbols.

In a seventh possible implementation form of a transmitting device according to the sixth implementation form of the first aspect, the second transmission power is less than the first transmission power.

The seventh implementation form means that the interference can be held low. By choosing the second transmission power lower than the first transmission power it can be achieved that close receive devices with a low delay spread can receive and decode the first sequence of data packets and the second sequence of data packets. However, it can also be achieved that distant receive devices with a higher delay spread can receive and decode the first sequence of data packets without being interfered by the second sequence of data packets.

In an eighth possible implementation form of a transmitting device according to any of the preceding implementation forms of the first aspect or to the first aspect as such, the transmitting device is further configured to

transmit the additional data symbol in the centre of the guard interval. By transmitting the additional data symbol in the centre of the guard interval inter symbol interference is minimized. In a ninth possible implementation form of a transmitting device according to any of the preceding implementation forms of the first aspect or to the first aspect as such, the transmitting device is further configured to

modulate the first sequence of data symbols and the second sequence of data symbols using the same modulation scheme.

The ninth implementation form has the benefit that most parts of the hardware in the transmitting device can be used for both the the first sequence of data symbols and the second sequence of data symbols. Thereby, reduced hardware implementation cost is achieved. In a tenth possible implementation form of a transmitting device according to any of the preceding implementation forms of the first aspect or to the first aspect as such, the additional data symbol comprises at least one of: a reference signal and control information.

The tenth implementation form means that reduced latency in the communication system is possible. For example, fast Acknowledgment (ACK) and Negative Acknowledgment (NACK) response is an important feature in many communication systems. By transmitting NACK and ACK in additional data symbols reduced feedback latency is achieved. Further, pilots and other type of reference signals can be transmitted in additional data symbols to prepare the receiver for transmission of the next ordinary data symbol(s) transmission. The receiver can therefore perform channel estimation, clock compensations, etc., such that the receiver will be better prepared for processing the ordinary data symbol(s) transmitted in the next transmission.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a network node for a communication system, the network node comprising a transmitting device according to any of the preceding implementation forms of the first aspect or to the first aspect as such.

According to a third aspect of the invention, the above mentioned and other objectives are achieved with a method for a transmitting device, the method comprises:

obtaining a set of delay spreads for a corresponding set of receiving devices, wherein each delay spread in the set of delay spreads is associated with a channel between the transmitting device and a receiving device in the set of receiving devices, classifying receiving devices in the set of receiving devices into a subset of receiving devices if the corresponding delay spread for a receiving device is less than or equal to a delay spread threshold value,

transmitting a first sequence of data symbols with a first transmission power to the set of receiving devices, wherein the first sequence of data symbols comprises at least one guard interval arranged between two data symbols in the first sequence of data symbols,

transmitting a second sequence of data symbols with a second transmission power to the subset of receiving devices, wherein the second sequence of data symbols comprises at least one additional data symbol in the guard interval of the first sequence of data symbols.

The channel is a radio channel in wireless communication systems.

The first sequence of data symbols is addressed for the set of receiving devices whilst second sequence of data symbols is addressed for the subset of receiving devices.

In a first possible implementation form of a method according to the third aspect, the delay spread threshold value is less than the duration of the guard interval.

In a second possible implementation form of a method according to the first implementation form of the third aspect, the method comprises

determining the symbol duration for the additional data symbol based on the set of delay spreads and the duration of the guard interval.

In a third possible implementation form of a method according to the second implementation form of the third aspect, the method comprises

controlling at least one of the duration of the guard interval and the symbol duration for the additional data symbol so as to control the number of receiving devices classified into the subset of receiving devices. In a fourth possible implementation form of a method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the method comprises receiving a set of Power Delay Profiles, PDPs, for the corresponding set of receiving devices, wherein each PDP in the set of PDPs is associated with a radio channel between the method and a receiving device in the set of receiving devices,

obtaining the set of delay spreads based on the set of PDPs.

In a fifth possible implementation form of a method according the fourth implementation form of the third aspect, the method comprises

computing a set of received powers for the corresponding set of receiving devices based on the set of PDPs,

classifying the receiving device into the subset of receiving devices if the corresponding delay spread for the receiving device is less than or equal to the delay spread threshold value and if the corresponding received power for the receiving device is larger than an interference power threshold value.

In a sixth possible implementation form of a method according to the fourth or fifth implementation form of the third aspect, the method comprises

computing the second transmission power based on the set of PDPs.

In a seventh possible implementation form of a method according to the sixth implementation form of the third aspect, the second transmission power is less than the first transmission power.

In an eighth possible implementation form of a method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the method comprises transmitting the additional data symbol in the centre of the guard interval.

In a ninth possible implementation form of a method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the method comprises modulating the first sequence of data symbols and the second sequence of data symbols using the same modulation scheme.

In a tenth possible implementation form of a method according to any of the preceding implementation forms of the third aspect or to the third aspect as such, the additional data symbol comprises at least one of: a reference signal and control information. The advantages of any method according to the second aspect are the same as those for the corresponding device claims according to the first aspects.

The invention also relates to a computer program, characterized in code means, which when run by processing means causes said processing means to execute any method according to the present invention. Further, the invention also relates to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

Further applications and advantages of the present invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different embodiments of the present invention, in which:

- Fig. 1 shows a transmitting device according to an embodiment of the invention.

- Fig. 2 shows a method according to an embodiment of the invention.

- Fig. 3 shows a symbol-wise time interleaved transmission of additional information.

- Fig. 4 shows a guard interval between data symbols and insertion of additional data in between the data symbols.

- Fig. 5 shows transmitted and received power of ordinary data symbols and additional data symbols at a transmitting device, a far-end receiving device and a near-end receiving device.

- Fig. 6 shows a wireless communication system according to an embodiment of the invention.

- Fig. 7 shows a ZT-UFMC downlink modulator according to an embodiment of the invention.

Detailed Description

A signal transmitted by a transmitting device, such as a network node or a server, can encounter a number of obstacles during its way to a receiving device, such as a client device. Thereby, causing reflections, diffractions and scattering of the transmitted signal over the wireless and/or the wired transmission medium. When the signal arrives at the receiving device it will look like a superposition of signals, each signal with a different delay, attenuation and phase.

Mathematically a simple model of multipath can be expressed with the impulse response of the channel

where p _n e ^j(Pn and τ _η are the complex amplitude and delay of the n-th path, respectively. Real channel impulse responses are time varying meaning that the number of paths and its complex amplitudes and delays are changing continuously with time. However, for simplicity without limiting embodiments of the invention thereto it is assumed that the channel is static and time invariant.

The delay spread T of the channel is defined as the difference between the maximum path delay and minimum path delay of the channel.

Typically, so called far-end receiving devices (or distant receiving devices) are subjected to a radio channel with long delay spread. The radio propagation channel of so called near-end receiving devices (or close receiving devices) and especially those with a direct line of sight has a very dominant path (i.e. large complex amplitude) over the rest of the paths arriving from far-end reflections, diffractions and scattering. Thus near-end receiving devices are exposed to a radio channel that can be approximated with an impulse response with a much shorter delay spread. In 4G, the cyclic prefix length of the cyclic prefix OFDM symbols is in principle fixed with a value such that the duration of the cyclic prefix is longer than the delay spread of the channels that receiving devices in the cell are typically exposed to. By selecting a cyclic prefix length that is longer than the typical delay spread, the receiving devices are protected from severe ISI.

In the same way, guard intervals between symbols are intended to protect receiving devices against ISI and the reserved guard interval is therefore selected to be valid for all receiving devices in the network or cell. It has however been realized that near-end receiving devices are exposed to channels with very short delay spread and the guard interval reserved for multipath protection is therefore in most cases unnecessarily long for these receiving devices.

We can define the time efficiency of the communication system Γ as follows

r ₌ N _s - N _G where N _s is the duration of a data symbol, and N _G is the duration of a guard interval. Clearly 0 < Γ < 1 and it is an objective to achieve a value as close to one as possible in order to use as much of the time as possible for data transmission.

Therefore, embodiments of the invention relate to utilize part of the guard interval for transmission of additional data symbols between the transmitting device and one or more selected near-end receiving devices. The additional data symbols could be used for ordinary traffic data, control information complementing or supporting the data transmitted in the ordinary data signals, reference signals, synchronization signals, channel estimation signals, or any other type of data or signals.

According to an embodiment of the invention the transmission of additional data symbols is performed by a transmitting device 100, as shown in Fig. 1 . The transmitting device 100 comprises a processor 1 02 coupled to a transceiver 1 04. The processor 1 02 and the transceiver 1 04 are coupled to each other by means of communication means 106 known in the art. The transceiver 1 04 comprises a modulator and transmitting block 110 configured to modulate and transmit both the ordinary data symbols and the additional data symbols. The functions of the modulator and transmitting block 110 is further described below with reference to Fig. 7. The transmitting device 100 further comprises an antenna 108 and/or a wired communication interface 112 coupled to the transceiver 104, which means that the receiving device 100 is configured for wireless and/or wired communications in a communication system. The transmitting device 100 is configured to obtain a set of delay spreads T for a corresponding set of receiving devices R (see Fig. 6). Each delay spread in the set of delay spreads T is associated with a channel between the transmitting device 100 and a receiving device 300 (see Fig. 6) in the set of receiving devices R. The transmitting device 100 is further configured to classify receiving devices 300a, 300b, ..., 300i in the set of receiving devices R into a subset of receiving devices R _Sub (see Fig. 6) if the corresponding delay spread for a receiving device 300 is less than or equal to a delay spread threshold value T _Th . In other words, if a receiving device has a corresponding delay spread than or equal to a delay spread threshold value T _Th then this receiving device is classified (as a near-end device) into the subset of receiving devices R _Sub . The transmitting device 100 is further configured to transmit a first sequence of data symbols S ₁ with a first transmission power P _t to the set of receiving devices R and to transmit a second sequence of data symbols S ₂ with a second transmission power P ₂ to the subset of receiving devices R _Sub . The first sequence of data symbols S ₁ comprises at least one guard interval Gl (see Fig. 3) arranged between two data symbols in the first sequence of data symbols S ₁ and the second sequence of data symbols S ₂ comprises at least one additional data symbol in the guard interval G l of the first sequence of data symbols S ₁ .

The receiving devices classified into the subset of receiving devices R _Sub may in some cases in this disclosure be denoted as near-end receiving devices. Correspondingly, the receiving devices not classified into the subset of receiving devices R _Sub may in some cases in this disclosure be denoted as far-end receiving devices. Therefore, a near-end receiving device belongs to the subset of receiving devices R _Sub and a far-end receiving device does not belong to the subset of receiving devices R _Sub if not otherwise stated herein.

Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a transmitting device 1 00, such as the one shown in Fig. 1 . The method 200 comprises obtaining 202 a set of delay spreads T for a corresponding set of receiving devices R . Each delay spread in the set of delay spreads T is associated with a channel between the transmitting device 100 and a receiving device 300 in the set of receiving devices R . The method 200 further comprises classifying 204 receiving devices 300a, 300b, ... , 300i in the set of receiving devices R into a subset of receiving devices R _Sub if the corresponding delay spread for a receiving device 300 is less than or equal to a delay spread threshold value T _Th . The method 200 further comprises transmitting 206 a first sequence of data symbols S ₁ with a first transmission power P ₁ to the set of receiving devices R . The first sequence of data symbols S ₁ comprises at least one guard interval G l arranged between two data symbols in the first sequence of data symbols S . The method 200 further comprises transmitting 208 a second sequence of data symbols S ₂ with a second transmission power P ₂ to the subset of receiving devices R _Sub . The second sequence of data symbols S ₂ comprises at least one additional data symbol in the guard interval G l of the first sequence of data symbols S^ In Fig. 2 the transmission method steps 206 and 208 are shown in series. However, the order of these two steps are not limited to this scenario and is typically even performed at the same time more or less in parallel. This means that first sequence of data symbols S ₁ and the second sequence of data symbols S ₂ are in some cases transmitted in an interleaved or superposed fashion with respect to each other.

The first sequence of data symbols S ₁ and second sequence of data symbols S ₂ are exemplarily illustrated in Fig. 3. In the first sequence of data symbols S ₁ a guard interval G l having duration N _G is reserved between each data symbol as shown in Fig. 3. The transmission of the additional data symbol(s) in the second sequence of data symbols S ₂ is aligned with said guard interval Gl, meaning that at least one additional data symbol having duration N _A is transmitted in the guard interval G l. Fig. 3 further illustrates that the first sequence of data symbols S ₁ is transmitted with a first transmission power P ₁ and the second sequence of data symbols S ₂ is transmitted with a second transmission power P ₂ . Typically the second transmission power P ₂ should be chosen to be smaller than the first transmission power P . In order to not jeopardize the orthogonality of the transmission signals Si[Pi] and S ₂ [P ₂ ] the duration of the additional data symbol N _A should be carefully selected. The relationship between the duration of the guard interval N _G and the duration of the additional data symbol N _A is illustrated in Fig. 4 in more detail. It is assumed that the guard interval used by the waveform has a duration of N _G digital samples. The value of N _G is chosen to accommodate the typical delay spreads, e.g. found in a cell of a cellular system. The transmission scheme illustrated in Fig. 4 comprises transmitting one data symbol every N _s samples with a guard interval of N _G samples between each data symbol in the first sequence of data symbols S . In the guard interval an additional data symbol is inserted having the duration of N _A digital samples. The subscript A is to indicate that this is an additional data symbol however another wording is possible.

It is advantageous to select the position of the additional symbol and the duration of the additional data symbol N _A in such a way that the orthogonality of the transmission signals is preserved. The parameters to be considered here are the duration of the guard interval N _G and the delay spread of the channels for the near-end receiving devices, i.e. the duration of the additional data symbol N _A should be determined based on said two parameters. Especially, the difference between the duration of the guard interval N _G and the duration of the additional symbol N _A should be longer than the delay spread of the channels for the near-end receiving devices. In this way, the additional data symbols do not cause too much interference to the data symbols sent in the intervals N _s — N _G . In addition, the additional data symbols should be transmitted in the centre of the guard interval to allow for spreading of the additional data symbol on both sides.

Clearly, the additional data symbols will propagate to far-end receiving devices through a channel with longer delay spread and cause interference to the far-end receiving devices. But since the target of these additional data symbols is a group of near-end receiving devices the transmission power P ₂ used for transmitting these additional data symbols can be set to be significantly lower compared to the power used for transmitting ordinary data symbols to the far-end receiving devices. In other words, the second transmission power P ₂ of the second sequence of data symbols S ₂ can be significantly lower than the first transmission power P _t of the first sequence of data symbols S ₁ . Thus the level of interference that the additional data symbols will cause can be held under control so it does not impact the performance and the capacity of the far-end receiving devices.

Fig. 5 captures how the additional data symbols will be spread when propagating through a radio channel to a far-end receiving device (denoted as RD in Fig. 5) and a near-end receiving device. Observe that at the far-end receiving device the additional data symbols will overlap with the far-end receiving device signal, but the signal level for the additional data symbols will be lower and under acceptable levels if the transmission power of the additional data symbols is correctly set. At the near-end receiving devices, the additional data symbols will not overlap and thus the near-end receiving devices are able to maintain orthogonal transmission and receive the additional data symbols. Further, for improved performance the guard intervals cannot be used for transmission of additional data symbols without considering how it impacts the whole system, i.e. the impact on both near-end and far-end receiving devices. The performance of the whole system is therefore considered by classifying the receiving devices into the subset R _Sub or not and only enable transmission in the guard intervals that will not generate ISI and negatively impact the overall system performance.

To classify the receiving devices into the subset of receiving devices R _Sub some means or mechanism for measuring the downlink radio channel from the transmitting device 1 00 to the active receiving devices 300a, 300b,... , 300i can be foreseen. As an example, a useful parameter to extract from each receiving device 300 is the power delay profile, PDP, of the channel associated with a receiving device 300. The PDP gives the intensity of a signal received through a multipath channel as a function of time delay. The time delay is the difference in travel time between multipath arrivals to the receiving device 300 from the transmitting device 1 00. Therefore, from the PDPs it is easy to extract the delay spread that each connected receiving device 300 is experiencing. The PDPs may also be used to derive the transmission power needed to reach each receiving device 300 with a reasonable signal level. The PDPs associated with the receiving devices may in one example be directly transmitted by the receiving devices to the transmitting device 100 which is illustrated in Fig. 6.

Fig. 6 shows a communication system 500 according to an embodiment in which the transmitting device 100 is comprised in a network node 400 configured to operate in a wireless communication system in this particular case. The communication system 500 may however be a wired communication system or a combined wireless and wired communication system.

The communication system 500 in Fig. 6 comprises a network node 400 and a transmitting device 100 comprised in said network node 400. In addition, the communication system 500 comprises a plurality of receiving devices 300a, 300b, ..., 300i. The receiving devices 300a, 300b, ... , 300i form a set of receiving devices R. Each receiving device 300 is configured to signal its PDP to the transmitting device 100 as shown in Fig. 6. The transmitting device 1 00 obtains the delay spreads T associated with the set of receiving devices R based on the received PDPs. Based on the obtained delay spreads T the transmitting device 100 classifies the receiving devices 300a, 300b, ... , 300i in the set of receiving devices R into a subset of receiving devices R _Sub . The transmitting device 1 00 transmits the previously described first sequence of data symbols S ₁ to the set of receiving devices R and the previously described second sequence of data symbols S ₂ to the subset of receiving devices R _Sub . The first sequence of data symbols S ₁ and the second sequence of data symbols S ₂ are transmitted in an interleaved or superposed fashion in Fig. 6.

As described above, when the transmitting device 100 knows the delay spread of the channels to each receiving device 300, the transmitting device 1 00 is able to classify the receiving devices 300a, 300b, ..., 300i in the set R into at least one subset of receiving devices R _Sub . A receiving device 300 having index i = 0,1, ... , 1 - 1 will be a member of the subset R _Sub if the delay spread T _t of its channel to the transmitting device 100 is below the delay spread threshold value T _Th where T _Th can be determined by the inequality

and if the maximum intensity of its PDP is above a threshold value P _TH , i.e.

These classification conditions guarantees that the receiving devices in the subset R _Sub will not be experiencing ISI when the additional data symbol is transmitted and further that the transmitted additional data symbol will be strong enough for being decoded by all members of the subset R _Sub . Recall that we want to keep the transmission power of these additional data low to prevent creating high interference on the signals received by the receiving devices 300a, 300b, ... , 300i in the set R which do not belong to the subset R _Sub . A communication system 500 normally has some requirements on interference levels. Based on the requirements of interference levels and on the PDPs of all receiving devices 300a, 300b, ... , 300i in the set R, the appropriate transmission power P ₂ for the additional data symbols can be decided. The sum PDP, i.e.∑ _k PDP _{i k} , is a measure of the received power of receiving device i over multipath channels k for a transmitted signal with unit power. Let the transmitted signal power for the additional data symbol be denoted as P ₂ . The transmitted signal for the additional data symbol will arrive at receiving device i with power

P ₂ dB + 1 0log1 0(∑ _fe PDP ). If receiving device i is a so called far-end receiving device, meaning that the delay spread constraint, T _t ≤ T _Th , is not satisfied, the received power at this receiving device ί must be below a noise floor level P _NO ise dB to avoid creating too much interference to receiving device i. We can then select P _TH to be max∑ _k PDP _{i k} of all far-end receiving devices to avoid that any far- i

end receiving devices experience too much interference. From that definition we can also compute the maximum transmit power P ₂ for the second set of data symbols by solving the inequality:

P ₂ dB + 10log10(iy„) < / _e dB. Now suppose we have a so called near-end receiving device i, i.e. a receiving device satisfying the delay spread constraint, T _t ≤ T _Th . If for that receiving device i the sum PDP is less than a threshold, i.e.∑ _k PDP _{i k} ≤ P _TH , we have PidB + 10log10(∑ _fe PDP ) < P _Noise dB. This means that it is a waste of resources, such as power and bandwidth, to transmit any additional data to that receiving device. Thus it does not make sense to include that receiving device in the subset R _Sub .

Therefore, the transmitting device 100 is configured to obtain the PDP information from all receiving devices in the set R and perform the classification into the subset R _Sub based on the obtained PDP information. As described above each PDP is associated with a radio channel between the transmitting device 100 and a receiving device 300. The PDP measurements are already performed in many current communication systems for other purposes. So, the PDP measurements are already available in these communication systems.

Moreover, when the receiving devices 300a, 300b,..., 300i in the set R have been classified, the first sequence of data symbols S ₁ and the second sequence of data symbols S ₂ have to be properly modulated. Therefore, the transmitting device 100 in one embodiment comprises a modulator and transmitting block 110 as illustrated in Fig. 7. The modulator and transmitting block 110 in Fig. 7 comprises a first modulator 112 for the first sequence of data symbols and a second modulator 112 ^' for the second sequence of data symbols. The modulator and transmitting block 110 further comprises a radio front end 114 coupled to the first modulator 112 and the second modulator 112 ^' , respectively. The first modulator 112 in turn comprises a N inverse discrete Fourier transform (IDFT), a parallel to serial (P/S) conversion and a filter F _t for each receiving device i in the set R. The second modulator 112 ^' in turn comprises a M- IDTF, a P/S and a filter Gj for each receiving device in the subset R _Sub .

The additional data symbols of the second sequence are positioned between the ordinary data symbols in the guard intervals of the first sequence of data symbols. Fig. 7 illustrates an exemplary modulator and transmitting block 110 based on the ZT-UFMC technology. Without going into detail about the ZT-UFMC technology we can easily identify the conventional ZT- UFMC first modulator 112 in the upper half of Fig. 7 and the added second modulator 112 ^' for transmitting the additional data symbols in the lower part of Fig. 7.

The first modulator 112 works as follows. The receiving devices in the set R are allocated to different frequency sub-bands of the wireless communication system 500. The data intended for each receiving device i = 0,1, - 1, e.g. in form of quadrature amplitude modulation (QAM) symbols, is collected in different N-dimensional vectors x _t in the positions that corresponds to their allocated frequencies or subcarriers. Vector positions corresponding to non-allocated frequencies are filled with zeros which means that vectors for any two different receiving devices will never have nonzero values on the same positions. The N-points IDFTs of these vectors are computed and the resulting time-domain vectors are serialized and filtered by the sub-band filters F _t that are band pass filters with a bandwidth equal to the assigned sub- band width and centered over the same sub-band. The filter outputs are all superposed in the summer∑ to generate a baseband signal that is fed to the radio front end 114.

With filters having an impulse response length L _f the duration of the data symbols in the first sequence of data symbols is N + L _f - 1. Hence the first modulator 112 shall add a tail of N _s - N - L _f + 1 zeros to create a guard interval of length N _G .

The second modulator 112 ^' for the additional data symbols in the second sequence of data symbols works in a similar way. The data intended for the receiving devices in the subset j = 0,1, ... ,/ - 1, e.g. in form of QAM symbols, is collected in different -dimensional vectors y _t in the positions that corresponds to their allocated frequencies or subcarriers.

It should however be noted that the IDFT in the second modulator 112 ^' is of size M, hence M- IDFT M is not necessarily equal to N as the appropriate value for M and N depend on the system configuration of N _s , N _G , subcarrier separation, sampling clock frequency, etc.

The sub-band filters of the second modulator 112 ^' are denoted as G _j since they might have a different impulse response compared to the filters in the first modulator 112, and the number of sub-bands are denoted as /, wherein / ≤ \A \. The number of sub-bands / is not necessarily equal to the cardinality of the subset R _Sub . If/ is selected equal to one, the additional data symbols would be transmitted as broad-cast transmission to all receiving devices in the set R . However, if / is selected to be greater than one, the additional data symbols could be transmitted as any mix of multi-cast and uni-cast transmissions.

With filters having an impulse response length L _g the duration of these data symbols is M + L _g - l. Hence, the second modulator 112 ^' should create a gap of length ^{Ng ~Na} samples. The second modulator 11 2 ^' shall also synchronize the transmission so the additional data symbol is transmitted in the middle of the guard interval as shown Fig. 4.

The two baseband digital signals from the first modulator 11 2 and the second modulator 112' are converted to an analogue baseband signal in the digital to analogue converters (DAC) 116 and thereafter amplified in amplifiers A1 and A2, respectively. The two signals are then superposed into a superposed signal S in the summer∑ of the radio front end 114. The superposed signal S is up-converted to the radio frequency (RF) in the baseband to RF up- converter 11 8 before it is provided to an antenna or a wired communication interface (not shown in Fig. 7).

The control of the transmission powers of the first modulator 112 and the second modulator 11 2 ^' is done separately by the power amplifiers A1 and A2 in the radio front end 114. Since the additional data symbols are sent to the receiving devices in the subset ¾ _u &the power of this signal P ₂ can be kept much lower than the power for the first sequence of data symbols P _{l t} i.e. P ₂ « Pi, to avoid interference with the received signal for the receiving devices not in the subset R _Sub . Recall that the receiving devices not in the subset R _Sub experience longer channel delay spread, and thus the additional data symbols will be spread by the channel while it is propagated through the radio channel. However, by controlling the power for the second sequence of data symbols P ₂ the level of interference the additional data symbol might create can be held low, and optimally below the noise floor level of the receiving devices in the set R.

In this example one implementation based on ZT-UFMC has been described, but the modulators 11 2 and 112 ^' could be using any other suitable waveform technology. The requirement is that the transmission of the additional data symbols should be done in the guard intervals of the first sequence of data symbols S ₁ .

In the case that the additional data symbol is using the same modulation scheme, the hardware implementation could be the same. The modulators 11 2 and 112 ^' would in such an example only differ in some minor parameter settings, such as in N and M. Further, if the transmissions of the first sequence of data symbols S-^nd the second sequence of data symbols S ₂ \s performed in different time regions only one single DAC is needed which means reduced hardware. This case is however not shown in Fig. 7.

Furthermore, the duration of the guard interval N _G or the duration of the additional symbols N _A can be adapted with the objective that, e.g. 1 % of the active receiving devices are classified into the subset R _Sub . From the expression T _t < ^Ng~Na we can see that by increasing the duration of the guard interval N _G or decreasing the duration of the additional data symbol N _A it becomes easier for a receiving device to meet that constraint. Thus, more receiving devices will be classified into the subset R _Sub . Conversely, by decreasing N _G or increasing N _A fewer receiving devices will meet that constraint. Thus by adjusting these two parameters, N _G or N _A , it is possible for the transmitting device 100 to control the number or percentage of receiving devices in subset R _Sub . It is also possible to adjust the power threshold P _TH for controlling the number or percentage of receiving devices in the subset R _Sub . The network node herein may also be denoted as a radio network node, an access network node, an access point, or a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", "eNodeB", "NodeB" or "B node", depending on the technology and terminology used. The radio network nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The network node may also be a base station corresponding to the fifth generation (5G) wireless systems. The client device herein may be denoted as a user device, a User Equipment (UE), a mobile station, an internet of things (loT) device, a sensor device, a wireless terminal and/or a mobile terminal, is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 - conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The client device 1 00 may also be configured for communication in 3GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation wireless technologies, such as New Radio.

Any method according to embodiments of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

Moreover, it is realized by the skilled person that embodiments of the transmitting device 100 comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the present solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the present solution.

Especially, the processor 102 of the transmitting device 100 may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression "processor" may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like.

Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.