WO2019001691A1

WO2019001691A1 - Guard band utilization

Info

Publication number: WO2019001691A1
Application number: PCT/EP2017/065903
Authority: WO
Inventors: Jan Hellmann; Marko FLEISCHER
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2017-06-27
Filing date: 2017-06-27
Publication date: 2019-01-03

Abstract

There are provided measures for guard band utilization. Such measures exemplarily comprise transmitting a first signal, receiving a second signal, wherein said second signal is influenced by said first signal, generating a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and correcting said second signal based on said crosstalk cancellation signal.

Description

Title

Guard band utilization Field

The present invention relates to guard band utilization. More specifically, the present invention exemplarily relates to measures (including methods, apparatuses and computer program products) for realizing guard band utilization.

Background

The present specification generally relates to the usage of guard bands between uplink (UL) and downlink (DL) bands for the service of frequency division duplex (FDD) access nodes such as base transceiver stations (BTS).

Generally, in the radio field, a guard band is an unused part of the radio spectrum between radio bands for the purpose of preventing interference, i.e. mutual influence of the involved radio bands. In particular, the guard band is a narrow frequency range used to separate two wider frequency ranges to ensure that both can propagate simultaneously without interfering with each other. The guard band may be used in both wired or wireless communications, so that adjacent frequency bands on the same media can avoid interference.

More specifically, in mobile communications, in relation to the FDD technique a guard band is established for a paired frequency band which is a pair of frequency bands, namely of an UL band and a DL band. In the present context, guard band specifications take into consideration that a certain gap between UL and DL bands must be established to allow state-of-the-art duplex filters to sufficiently suppress transmitter (TX) spurious emissions and to guarantee high receive sensitivity. Thus, guard band size definition within 3^rd Generation Partnership Project (3GPP) was a compromise for FDD to keep performance and costs balanced and scarifying frequencies unusable for service. Duplex filters are part of radio modules and are responsible to connect supported UL bands and DL bands (i.e. receiver (RX) and transmitter (TX)) to a common antenna.

Besides this functionality to limit the necessary performance of utilized duplex filters, the frequency resources of a guard band are unused for the corresponding FDD (paired) frequency band and in particular communications/services handled utilizing the corresponding FDD (paired) frequency band. For mobile network operators, it would be beneficial to acquire such resources, and thus to gain additional frequency spectrum to increase network capacity.

Figure 4 is a schematic diagram illustrating frequency responses of an exemplary duplex filter. In particular, Figure 4 illustrates an example of duplex filter key performance parameters in a Band 3 context, where the provided guard band is indicated by chain dotted lines, and a potential guard band reduction is suggested by arrows starting from the chain dotted lines.

Here, on the left portion of Figure 4, the exemplary duplex filter is schematically illustrated as comprising a TX (band pass) filter connected to a TX via terminal 1 and an RX (band pass) filter connected to an RX via terminal 3, via terminal 2, wherein the TX (band pass) filter and the RX (band pass) filter are respectively connected to an antenna via terminal 2.

The graph s21 corresponds to the (TX) insertion loss between terminal 1 and terminal 2. The graph s32 corresponds to the (RX) insertion loss between terminal 2 and terminal 3. The graph s31 corresponds to the (TXRX) isolation between terminal 1 and terminal 3. Utilizing an additional frequency spectrum laying inside the guard band would, however, require a more stringent performance of the duplex filters associated with additional resonators.

In particular, an increase in duplex filter performance in terms of TX to RX isolation and a TX transfer characteristic would be required. Namely, guard band reduction would generally go along with still steeper filter edges. Steeper filter edges would raise requirements on the respective filter in terms of for example size, weight, material, etc. In some cases, steeper filter edges are not implementable at all considering acceptable costs and mechanical designs and bulkiness of devices. Namely, for transmission bands with small duplex distances such as (3GPP) [evolved] Universal Mobile Telecommunications System Terrestrial Radio Access ([evolved] UMTS Terrestrial Radio Access, [E-]UTRA) Band 3, this has even major impact on hardware cost, weight and size while maintaining RX sensitivity and TX spurious emissions.

Neglecting the requirement to steeper filters would result in lacking TX to RX isolation which would lead to violation of RX sensitivity limits.

Hence, the problem arises, that although present filter performance requirements are to be kept when utilizing the guard band, the lacking TX to RX isolation performance is to be avoided or to be compensated.

Sum mary

Various exemplary embodiments of the present invention aim at addressing at least part of the above issues and/or problems and drawbacks.

Various aspects of exemplary embodiments of the present invention are set out in the appended claims.

According to an exemplary aspect of the present invention, there is provided a method comprising transmitting a first signal, receiving a second signal, wherein said second signal is influenced by said first signal, generating a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and correcting said second signal based on said crosstalk cancellation signal.

According to an exemplary aspect of the present invention, there is provided an apparatus, comprising at least one processor, at least one memory including computer program code, and at least one interface configured for communication with at least another apparatus, the at least one processor, with the at least one memory and the computer program code, being configured to cause the apparatus to perform transmitting a first signal, receiving a second signal, wherein said second signal is influenced by said first signal, generating a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and correcting said second signal based on said crosstalk cancellation signal.

According to an exemplary aspect of the present invention, there is provided an apparatus, comprising transmitting circuitry configured to transmit a first signal, receiving circuitry configured to receive a second signal, wherein said second signal is influenced by said first signal, generating circuitry configured to generate a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and correcting circuitry configured to corrected said second signal based on said crosstalk cancellation signal.

According to an exemplary aspect of the present invention, there is provided a computer program product comprising computer-executable computer program code which, when the program is run on a computer (e.g. a computer of an apparatus according to any one of the aforementioned apparatus-related exemplary aspects of the present invention), is configured to cause the computer to carry out the method according to any one of the aforementioned method-related exemplary aspects of the present invention.

Any one of the above aspects enables an efficient crosstalk cancellation to thereby solve at least part of the problems and drawbacks identified in relation to the prior art.

By way of exemplary embodiments of the present invention, there is provided guard band utilization. More specifically, by way of exemplary embodiments of the present invention, there are provided measures and mechanisms for realizing guard band utilization.

Namely, according to exemplary embodiments of the present invention, measures for making spectrum in FDD systems which is currently part of the guard band available for data traffic are provided. Thus, additional frequency spectrum is available while todays filter requirements can be maintained.

Thus, improvement is achieved by methods, apparatuses and computer program products enabling/realizing guard band utilization.

Brief description of the drawings

In the following, the present invention will be described in greater detail by way of non-limiting examples with reference to the accompanying drawings, in which

Figure 1 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention,

Figure 2 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention,

Figure 3 is a schematic diagram of a procedure according to exemplary embodiments of the present invention, Figure 4 is a schematic diagram illustrating frequency responses of an exemplary duplex filter, Figure 5 is a schematic diagram illustrating signal levels at an antenna port of an exemplary macro base station with reduced guard band,

Figure 6 is a schematic diagram illustrating guard band utilization and TXRX crosstalk cancellation according to exemplary embodiments of the present invention,

Figure 7 is a block diagram schematically illustrating reference signal extraction according to exemplary embodiments of the present invention, Figure 8 is a block diagram schematically illustrating reference signal extraction and cancellation signal generation according to exemplary embodiments of the present invention,

Figure 9 is a block diagram schematically illustrating reference signal extraction and cancellation signal generation according to exemplary embodiments of the present invention,

Figure 10 is a schematic diagram of an example of a frequency spectrum of an RX band according to exemplary embodiments of the present invention generally illustrating crosstalk cancellation effects,

Figure 11 is a schematic diagram of an example of a frequency spectrum of an RX band according to exemplary embodiments of the present invention particularly illustrating crosstalk cancellation effects within the guard band,

Figure 12 is a block diagram alternatively illustrating an apparatus according to exemplary embodiments of the present invention.

Detailed description of drawings and embodiments of the present invention The present invention is described herein with reference to particular non- limiting examples and to what are presently considered to be conceivable embodiments of the present invention. A person skilled in the art will appreciate that the invention is by no means limited to these examples, and may be more broadly applied.

It is to be noted that the following description of the present invention and its embodiments mainly refers to specifications being used as non-limiting examples for certain exemplary network configurations and deployments. Namely, the present invention and its embodiments are mainly described in relation to 3GPP specifications being used as non-limiting examples for certain exemplary network configurations and deployments. As such, the description of exemplary embodiments given herein specifically refers to terminology which is directly related thereto. Such terminology is only used in the context of the presented non-limiting examples, and does naturally not limit the invention in any way. Rather, any other communication or communication related system deployment, etc. may also be utilized as long as compliant with the features described herein. Hereinafter, various embodiments and implementations of the present invention and its aspects or embodiments are described using several variants and/or alternatives. It is generally noted that, according to certain needs and constraints, all of the described variants and/or alternatives may be provided alone or in any conceivable combination (also including combinations of individual features of the various variants and/or alternatives).

According to exemplary embodiments of the present invention, in general terms, there are provided measures and mechanisms for (enabling/realizing) guard band utilization.

In general, according to exemplary embodiments of the present invention, extension of the spectrum in FDD systems by guard band utilization is combined with TX to RX crosstalk cancellation to keep RX sensitivity figures without changing TX to RX isolation requirements for duplex filters. Based thereon, guard band utilization requires to shift RX and TX band edges in a way that the guard band is narrowed. This would result in a violation of the required TX to RX isolation, as discussed above, which would negatively impact RX sensitivity. To ensure the required TX to RX isolation, according to exemplary embodiments of the present invention, crosstalk cancellation is used to compensate for the lacking duplex filter suppression. Figure 6 illustrates guard band utilization and TXRX crosstalk cancellation to ensure TXRX isolation according to exemplary embodiments of the present invention.

Thus, according to exemplary embodiments of the present invention, when utilizing the guard band, former filter performance requirements can be kept and the lacking TX to RX isolation performance is compensated by TX to RX crosstalk cancellation.

Hence, exemplary embodiments of the present invention allow the reduction of the guard band without changing duplex filter performance requirements and thus to keep costs, weight and size.

It is foreseeable that utilization or tighten the guard band/bands for FDD systems (as enabled by the measures according to exemplary embodiments of the present invention) would need a change in 3GPP standardization or other regulation bodies.

Figure 5 is a schematic diagram illustrating signal levels at an antenna port of an exemplary macro base station with reduced guard band. In particular, according to the example shown in Figure 5 illustrating TXRX crosstalk cancellation to achieve a required sensitivity limit, the extended RX band allocates parts of the former guard band. Furthermore, for this example it is assumed that an intermodulation product from the own TX hits the RX band in this area ("IM3 level RX band" line in Figure 5). This would reflect worst case requirements on a duplex filter used in such scenario. While keeping the same duplex filter performance, it is not possible to deal with this narrowed guard band and to suppress any intermodulation (crosstalk) sufficiently. However, according to exemplary embodiments of the present invention, TX to RX crosstalk cancellation is used to close the gap to the required sensitivity limit. Exemplary embodiments of the present invention are explained below in general terms with reference to Figures 1 to 3.

Figure 1 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention. The apparatus may be a network node 10 such as a base transceiver station comprising transmitting circuitry 11, receiving circuitry 12, generating circuitry 13, and correcting circuitry 14. The transmitting circuitry 11 transmits a first signal. The receiving circuitry 12 receives a second signal, wherein said second signal is influenced by said first signal. The generating circuitry 13 generates a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal. The correcting circuitry 14 corrects said second signal based on said crosstalk cancellation signal. Figure 3 is a schematic diagram of a procedure according to exemplary embodiments of the present invention. The apparatus according to Figure 1 may perform the method of Figure 3 but is not limited to this method. The method of Figure 3 may be performed by the apparatus of Figure 1 but is not limited to being performed by this apparatus. As shown in Figure 3, a procedure according to exemplary embodiments of the present invention comprises an operation of transmitting (S31) a first signal, an operation of receiving (S32) a second signal, wherein said second signal is influenced by said first signal, an operation of generating (S33) a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and an operation of correcting (S34) said second signal based on said crosstalk cancellation signal.

Figure 2 is a block diagram illustrating an apparatus according to exemplary embodiments of the present invention. In particular, Figure 2 illustrates a variation of the apparatus shown in Figure 1. The apparatus according to Figure 2 may thus further comprise creating circuitry 21, modelling circuitry 22, modifying circuitry 23, converting circuitry 24, filtering circuitry 25, determining circuitry 26, and/or adding circuitry 27.

In an embodiment at least some of the functionalities of the apparatus shown in Figure 1 (or 2) may be shared between two physically separate devices forming one operational entity. Therefore, the apparatus may be seen to depict the operational entity comprising one or more physically separate devices for executing at least some of the described processes.

According to the foregoing remarks, the second signal is influenced by said first signal. The influence of the first signal on the second signal is embodied by an interference between said second signal and said first signal. In particular, this means that the first signal is crosstalked onto said second signal.

In this regard, crosstalking means any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an (undesired) effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another.

In the duplex filter shown in the example of Figure 4, the crosstalk appears between terminal 1 and terminal 3, such that the first signal (i.e. the signal (to be) transmitted via the duplex filter and an antenna) creates an effect on the second signal (i.e. the signal received via the antenna and the duplex filter). The coupling may take place in the duplex filter and/or the elements/circuits connected to terminals 1 and 3, respectively, and influencing each other.

According to a variation of the procedure shown in Figure 3, exemplary additional operations are given, which are inherently independent from each other as such. According to such variation, an exemplary method according to exemplary embodiments of the present invention may comprise an operation of creating said first signal as an analogue signal based on a transmission digital baseband signal. Here, the transmission reference signal is said transmission digital baseband signal.

This variation corresponds to option 2 shown in Figure 7 explained below. Further details of this variation are discussed below in relation to Figure 9.

According to a variation of the procedure shown in Figure 3, exemplary details of the generating operation (S33) are given, which are inherently independent from each other as such.

Such exemplary generating operation (S33) according to exemplary embodiments of the present invention may comprise an operation of modelling crosstalk influence of said first signal on said second signal, and an operation of modifying said transmission reference signal based on a result of said modelling.

According to a variation of the procedure shown in Figure 3, exemplary additional operations are given, which are inherently independent from each other as such. According to such variation, an exemplary method according to exemplary embodiments of the present invention may comprise an operation of creating said first signal as an analogue signal based on a transmission digital baseband signal. Here, the transmission reference signal is said first signal.

This variation corresponds to option 1 shown in Figure 7 explained below. Further details of this variation are discussed below in relation to Figure 8.

Such exemplary generating operation (S33) according to exemplary embodiments of the present invention may comprise an operation of converting said transmission reference signal utilizing a radio frequency receiver.

According to further exemplary embodiments of the present invention, the said creating said first signal is effected utilizing an amplifier.

Such exemplary generating operation (S33) according to exemplary embodiments of the present invention may comprise an operation of filtering said transmission reference signal. Preferably, the modified transmission reference signal or the converted transmission reference signal (dependent on the implemented option) is filtered according to this variation.

According to further exemplary embodiments of the present invention, the filtering is effected utilizing a finite impulse response filter based on filter coefficients for said finite impulse response filter.

According to a variation of the procedure shown in Figure 3, exemplary additional operations are given, which are inherently independent from each other as such. According to such variation, an exemplary method according to exemplary embodiments of the present invention may comprise an operation of determining said filter coefficients based on said transmission reference signal and said second signal. According to a variation of the procedure shown in Figure 3, exemplary details of the correcting operation (S34) are given, which are inherently independent from each other as such. Such exemplary correcting operation (S34) according to exemplary embodiments of the present invention may comprise an operation of adding said crosstalk cancellation signal to said second signal. The above measures allow to utilize (parts of) the guard band for transmissions while nevertheless the requirements on the duplex filter are not toughened, since the disadvantages adjoined with narrowing the guard band (i.e. decreased TX to RX isolation which leads to violation of RX sensitivity limits) are compensated by the advantages of the measures according to exemplary embodiments of the present invention enabling crosstalk compensation.

In the following, exemplary embodiments of the present invention are described in more specific terms with reference to Figures 7 to 11.

The implementation of exemplary embodiments of the present invention exploits TX to RX crosstalk cancellation in digital domain, which targets on generating a cancellation signal suited to be added to the digital RX signal for cancellation purpose. The necessity to cancel the crosstalk is caused by the guard band reduction and the circumstance that the TX to RX suppression (s31) is not sufficient in such case.

The cancellation signal (cane) is derived from a reference signal (ref). There are two general options to generate the correcting or reference signal (ref) from the TX as shown in Figure 7 schematically illustrating reference signal extraction according to exemplary embodiments of the present invention. Figure 7 in particular illustrates TX to RX crosstalk cancellation and positions of cancellation and reference signals according to exemplary embodiments of the present invention.

The reference signal (ref) has two purposes. Namely, on the one hand, the reference signal (ref) serves as input to estimate a filter (FIR) with coefficients h_cr0ss. Further, on the other hand, the estimated filter is used to provide the cancellation signal (cane) from/based on the reference signal (ref). When combining/superimposing the cancellation signal and the main signal (main), a cleaned main signal (clean) is achieved.

In line with the tow options in relation to sources for the reference signal (ref), there are also two general implementation architectures according to exemplary embodiments of the present invention.

Figure 8 is a block diagram schematically illustrating reference signal extraction and cancellation signal generation according to exemplary embodiments of the present invention and in particular a TX to RX crosstalk cancellation based on an analogue reference signal (ref). Hence, Figure 8 corresponds to option 1 shown in Figure 7.

Figure 8 in particular shows how the reference signal (ref) is derived from the analogue TX signal (after a transmitter incl. digital pre-distortion (DPD) and a power amplifier (PA)) and fed, via an RX filter, to an extra cancellation receiver.

An advantage of this architecture is an exact representation of the inter- modulations interfering with the user signal in former guard band. All radio frequency (RF) impairments as TX wide noise and PA distortions are contained in the reference signal. However, additional costs may accrue for the cancellation receiver chain. Figure 9 is a block diagram schematically illustrating reference signal extraction and cancellation signal generation according to exemplary embodiments of the present invention and in particular a TX to RX crosstalk cancellation based on a digital reference signal (ref). Hence, Figure 9 corresponds to option 2 shown in Figure 7.

Figure 9 in particular shows how the reference signal (ref) is derived from the digital baseband signal which is then subjected to a chain of modelling the TX to RX crosstalk (inter-modulation (IM) modelling). An advantage of this architecture is the capability for complete implementation in the digital domain without the need for additional RF hardware. However, additional modelling of the inter-modulations is needed, and TX wide noise impairments and DPD distortions cannot be corrected according to this option.

According to exemplary embodiments of the present invention, the finite impulse response (FIR) filter shown in Figures 8 and 9 is effective to determine, based on the reference signal (in particular based on a signal (ref) derived from the reference signal (ref) as explained above by means of an RX filter and a cancellation receiver (option 1) or by means of IM modelling (option 2)), the cancellation signal (cane) to be superimposed with the main signal provided by the main receiver. Here, the Fl R filter is provided with filter coefficients h_cross.

According to exemplary embodiments of the present invention, the filter coefficients h_cr0ss may be calculated during an identification phase. This calculation may be effected by software. This would require that reference and main signals as shown in Figures 7 to 9 are accessible (in terms of captured signals) by the entity effecting the calculation, e.g. the calculation software.

According to exemplary embodiments of the present invention, the filter coefficients h_CToss are periodically updated to ensure sufficient cancellation results over changing conditions such as temperature.

In one embodiment, for determining the filter coefficients h_cr0Ss, the Rx band is filtered, and the reference signal (ref) and the main signal (main) are time aligned.

An auto- correlation matrix R_xx and a coss- correlation vector r_xy are used as an input to calculate complex filter coefficients h cross — Rxx ^ ¹ rxy. A cancellation signal (cane) is generated by filtering the aligned/derived reference signal (ref) with h_cross.

When combining/superimposing the cancellation signal and the main signal (main), a cleaned main signal (clean) can be achieved.

The use case of both general architectures explained above is to increase the TX to RX isolation in case of guard band reduction to gain additional frequency spectrum. Thus, the former/present duplex filter performance can be kept and heavier and more bulky filters can be avoided. Contrary thereto, without TX to RX crosstalk cancellation according to exemplary embodiments of the present invention, keeping filter performance and avoidance of heavier and more bulky filters might not be possible. In this regard, it is noted that the advantages/use cases of TX to RX crosstalk cancellation according to exemplary embodiments are explained in the context of resource gain by narrowing the guard band.

However, in addition to narrowing the guard band/duplex gap or as an alternative thereto, crosstalk cancellation also enables that the duplex filter are relaxed, thereby achieving e.g. smaller, lighter (less bulky) filters with new materials.

Figures 10 and 11 are schematic diagrams illustrating examples of frequency spectra of an RX band according to exemplary embodiments of the present invention. In particular, Figures 10 and 11 show some results measured with real existing hardware with a setup based on the cancellation receiver architecture as outlined above. Here, while Figure 10 illustrates crosstalk cancellation effects in general, Figure 11 illustrates in particular crosstalk cancellation effects within the guard band.

The TX to RX crosstalk considered for the examples shown in Figures 10 and 11 was generated as intermodulation product 3rd order (IM3) out of two LTE5 carriers in a way that the IM3 hits the RX channel under investigation. Figure 10 shows a reconstruction of a user signal by TXRX crosstalk cancellation. In particular, Figure 10 shows that an LTE5 user signal can be reconstructed from the received RX (main) by the above explained measures even if it is completely covered by crosstalk.

In detail, the dotted line represents the main signal (main) including a received LTE5 user signal and the TXRX crosstalk.

The solid line represents the cleaned main signal (clean) which corresponds to the received user signal without substantial distortion. Here, in particular the bar shaped peak which protrudes from the plateau in the middle of the spectrum corresponds to the active LTE5 user signal, while the more or less flat plateau corresponds to the noise reference as also indicated by the dashed line.

The dotted line (i.e. the main signal) also covers the bar shaped peak representing the active LTE5 user signal, i.e., also includes the active LTE5 user signal. Thus, Figure 10 shows the general ability to remove crosstalk from an "uncleaned" main signal such that the cleaned signal is nearby the noise reference level for frequencies without the active LTE5 user signal and corresponds to the active LTE5 user signal for frequencies of the active LTE5 user signal.

Figure 11 shows an RX noise floor increase. In particular, Figure 11 shows that cancellation close to noise floor is possible. This is also valid for duplex filter TX to RX isolations as they can be typically found within the guard band, in particular if notches are included.

In detail, in contrast to Figure 10 above, the dotted line in Figure 11 represents the main signal (main) including the TXRX crosstalk but without the received LTE5 user signal. The active user signal is omitted in order to emphasize the behavior and capability of the crosstalk cancellation according to exemplary embodiments in particular in relation to band gaps. Namely, as can be seen in Figure 11, within the frequency range of the LTE5 user signal (indicated by the chain dotted lines) there is a notch (drop) in the main signal including the TXRX crosstalk. This/these one or more notches is/ are a result of utilizing the band gap with filters not having the needed filter steepness.

However, Figure 11 shows the ability to remove crosstalk from an "uncleaned" main signal even if, as in the present case, one or more notches are contained in the "uncleaned" main signal. Accordingly, the cleaned signal is nearby the noise reference level (as shown), and would also correspond to the active LTE5 user signal for frequencies of the active LTE5 user signal (not shown in order not to cover the notches).

For explanations before, Band 3 is used as an example which is non-limiting and the present invention can also be applied to other specified Bands and to band gaps lying on arbitrary (center) frequencies.

However, for the exemplary case of a deployment in the Band 3 (i.e. 1800 MHz in Europe, having FDD guard band (gap) of 20 MHz from 1785 to 1805 MHz), it is expected that the guard band can be narrowed by 5 to 10 MHz without the necessity to modify the filter requirements, which amounts to 25 to 50 % of the "original" guard band of 20 MHz.

Of course, as already mentioned before, utilization or tighten the guard band/bands for FDD systems is likely to need a change in 3GPP standardization or other regulation bodies. In particular, both access network related hardware as well as the user equipments (UE) need to support the allocation on the new frequency resources.

In this regard, an utilization scenario is foreseeable, according to which an operator may deploy FDD equipment supporting the above explained narrowing of the guard band and FDD equipment not supporting the above explained narrowing of the guard band in parallel.

Such lack of accordance in features obviously affecting allocation, scheduling, synchronization etc. can only be solved by coordination which is expected to be made by means of standardization approaches by regulation bodies like e.g. 3 GPP/ FCC.

One option to overcome this lack of accordance in features would be to only provide the features of the less equipped network entity, i.e., all participants of a network (section) use frequency resources of the guard band or do not. Another option to overcome this lack of accordance in features would be to only provide the features of the less equipped network entity of a specific connection, i.e., all participants of specific connection use frequency resources of the guard band or do not for that connection. The present invention is not limited to the examples given above.

The above-described procedures and functions may be implemented by respective functional elements, processors, or the like, as described below.

In the foregoing exemplary description of the network entity, only the units that are relevant for understanding the principles of the invention have been described using functional blocks. The network entity may comprise further units that are necessary for its respective operation. However, a description of these units is omitted in this specification. The arrangement of the functional blocks of the devices is not construed to limit the invention, and the functions may be performed by one block or further split into sub-blocks. When in the foregoing description it is stated that the apparatus, i.e. network entity (or some other means) is configured to perform some function, this is to be construed to be equivalent to a description stating that a (i.e. at least one) processor or corresponding circuitry, potentially in cooperation with computer program code stored in the memory of the respective apparatus, is configured to cause the apparatus to perform at least the thus mentioned function. Also, such function is to be construed to be equivalently implementable by specifically configured circuitry or means for performing the respective function (i.e. the expression "unit configured to" is construed to be equivalent to an expression such as "means for").

In Figure 12, an alternative illustration of apparatuses according to exemplary embodiments of the present invention is depicted. As indicated in Figure 12, according to exemplary embodiments of the present invention, the apparatus (network node) 10' (corresponding to the network node 10) comprises a processor 121, a memory 122 and an interface 123, which are connected by a bus 124 or the like. The apparatus may be connected to other apparatuses (e.g. device 120, i.e., an interface of device 120) via link 125, respectively. The processor 121 and/or the interface 123 may also include a modem or the like to facilitate communication over a (hardwire or wireless) link, respectively. The interface 123 may include a suitable transceiver coupled to one or more antennas or communication means for (hardwire or wireless) communications with the linked or connected device(s), respectively. The interface 123 is generally configured to communicate with at least one other apparatus, i.e. the interface thereof.

The memory 122 may store respective programs assumed to include program instructions or computer program code that, when executed by the respective processor, enables the respective electronic device or apparatus to operate in accordance with the exemplary embodiments of the present invention.

In general terms, the respective devices/ apparatuses (and/or parts thereof) may represent means for performing respective operations and/or exhibiting respective functionalities, and/or the respective devices (and/or parts thereof) may have functions for performing respective operations and/or exhibiting respective functionalities. When in the subsequent description it is stated that the processor (or some other means) is configured to perform some function, this is to be construed to be equivalent to a description stating that at least one processor, potentially in cooperation with computer program code stored in the memory of the respective apparatus, is configured to cause the apparatus to perform at least the thus mentioned function. Also, such function is to be construed to be equivalently implementable by specifically configured means for performing the respective function (i.e. the expression "processor configured to [cause the apparatus to] perform xxx-ing" is construed to be equivalent to an expression such as "means for xxx-ing"). According to exemplary embodiments of the present invention, an apparatus representing the network node 10 comprises at least one processor 121, at least one memory 122 including computer program code, and at least one interface 123 configured for communication with at least another apparatus. The processor (i.e. the at least one processor 121, with the at least one memory 122 and the computer program code) is configured to perform transmitting a first signal (thus the apparatus comprising corresponding means for transmitting), to perform receiving a second signal, wherein said second signal is influenced by said first signal (thus the apparatus comprising corresponding means for receiving), to perform generating a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal (thus the apparatus comprising corresponding means for generating), and to perform correcting said second signal based on said crosstalk cancellation signal (thus the apparatus comprising corresponding means for correcting).

For further details regarding the operability/f unctionality of the individual apparatuses, reference is made to the above description in connection with any one of Figures 1 to 11 , respectively.

For the purpose of the present invention as described herein above, it should be noted that

- method steps likely to be implemented as software code portions and being run using a processor at a network server or network entity (as examples of devices, apparatuses and/or modules thereof, or as examples of entities including apparatuses and/or modules therefore), are software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved;

- generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the embodiments and its modification in terms of the functionality implemented;

- method steps and/or devices, units or means likely to be implemented as hardware components at the above-defined apparatuses, or any module(s) thereof, (e.g., devices carrying out the functions of the apparatuses according to the embodiments as described above) are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor- Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Circuit)) components, FPGA (Field-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components;

- devices, units or means (e.g. the above-defined network entity or network register, or any one of their respective units/means) can be implemented as individual devices, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, unit or means is preserved;

- an apparatus like the user equipment and the network entity /network register may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor;

- a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example.

In general, it is to be noted that respective functional blocks or elements according to above-described aspects can be implemented by any known means, either in hardware and/or software, respectively, if it is only adapted to perform the described functions of the respective parts. The mentioned method steps can be realized in individual functional blocks or by individual devices, or one or more of the method steps can be realized in a single functional block or by a single device.

Generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the present invention. Devices and means can be implemented as individual devices, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device is preserved. Such and similar principles are to be considered as known to a skilled person.

Software in the sense of the present description comprises software code as such comprising code means or portions or a computer program or a computer program product for performing the respective functions, as well as software (or a computer program or a computer program product) embodied on a tangible medium such as a computer-readable (storage) medium having stored thereon a respective data structure or code means/portions or embodied in a signal or in a chip, potentially during processing thereof.

The present invention also covers any conceivable combination of method steps and operations described above, and any conceivable combination of nodes, apparatuses, modules or elements described above, as long as the above-described concepts of methodology and structural arrangement are applicable.

In view of the above, there are provided measures for guard band utilization. Such measures exemplarily comprise transmitting a first signal, receiving a second signal, wherein said second signal is influenced by said first signal, generating a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and correcting said second signal based on said crosstalk cancellation signal.

Even though the invention is described above with reference to the examples according to the accompanying drawings, it is to be understood that the invention is not restricted thereto. Rather, it is apparent to those skilled in the art that the present invention can be modified in many ways without departing from the scope of the inventive idea as disclosed herein.

List of acronyms and abbreviations

3GPP 3rd Generation Partnership Project

BTS base transceiver station

DL downlink

DPD digital pre-distortion

E- UTRA evolved UMTS Terrestrial Radio Access

FIR finite impulse response

FDD frequency division duplex

IM inter-modulation

PA power amplifier

RF radio frequency

RFSW radio frequency software

RX receiver

TX transmitter

UE user equipment

UL uplink

UMTS Universal Mobile Telecommunications System

UTRA UMTS Terrestrial Radio Access cane cancellation signal

clean cleaned main signal

main main signal ref reference signal ref aligned/derived reference signal

Claims

1. A method comprising

transmitting a first signal,

receiving a second signal, wherein said second signal is influenced by said first signal,

generating a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and

correcting said second signal based on said crosstalk cancellation signal.

2. The method according to claim 1 , further comprising

creating said first signal as an analogue signal based on a transmission digital baseband signal, wherein

said transmission reference signal is said transmission digital baseband signal.

3. The method according to claim 2, wherein

in relation to said generating said crosstalk cancellation signal, the method further comprises

modelling crosstalk influence of said first signal on said second signal, and

modifying said transmission reference signal based on a result of said modelling.

4. The method according to claim 1 , further comprising

said transmission reference signal is said first signal.

5. The method according to claim 4, wherein

in relation to said generating said crosstalk cancellation signal, the method further comprises converting said transmission reference signal utilizing a radio frequency receiver.

6. The method according to any of claims 2 to 5, wherein

said creating said first signal is effected utilizing an amplifier.

7. The method according to any of claims 1 to 6, wherein

filtering said transmission reference signal.

8. The method according to claim 7, wherein

said filtering is effected utilizing a finite impulse response filter based on filter coefficients for said finite impulse response filter.

9. The method according to claim 8, further comprising

determining said filter coefficients based on said transmission reference signal and said second signal.

10. The method according to any of claims 1 to 9, wherein

in relation to said correcting said second signal, the method further comprises

adding said crosstalk cancellation signal to said second signal.

11. An apparatus, comprising

at least one processor,

at least one memory including computer program code, and

at least one interface configured for communication with at least another apparatus,

the at least one processor, with the at least one memory and the computer program code, being configured to cause the apparatus to perform :

transmitting a first signal,

receiving a second signal, wherein said second signal is influenced by said first signal, generating a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and

correcting said second signal based on said crosstalk cancellation signal.

12. The apparatus according to claim 11 , wherein

the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform:

creating said first signal as an analogue signal based on a transmission digital baseband signal, and wherein

13. The apparatus according to claim 12, wherein

in relation to said generating said crosstalk cancellation signal, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform: modelling crosstalk influence of said first signal on said second signal, and

14. The apparatus according to claim 11 , wherein

the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform :

said transmission reference signal is said first signal.

15. The apparatus according to claim 14, wherein in relation to said generating said crosstalk cancellation signal, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform: converting said transmission reference signal utilizing a radio frequency receiver.

16. The apparatus according to any of claims 12 to 15, wherein

the at least one processor, with the at least one memory and the computer program code, is configured to cause the apparatus to perform said creating said first signal utilizing an amplifier.

17. The apparatus according to any of claims 11 to 16, wherein

in relation to said generating said crosstalk cancellation signal, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform: filtering said transmission reference signal.

18. The apparatus according to claim 17, wherein

the at least one processor, with the at least one memory and the computer program code, is configured to cause the apparatus to perform said filtering utilizing a finite impulse response filter based on filter coefficients for said finite impulse response filter.

19. The apparatus according to claim 18, wherein

20. The apparatus according to any of claims 11 to 19, wherein

in relation to said correcting said second signal, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform:

adding said crosstalk cancellation signal to said second signal.

21. An apparatus, comprising

transmitting circuitry configured to transmit a first signal,

receiving circuitry configured to receive a second signal, wherein said second signal is influenced by said first signal,

generating circuitry configured to generate a crosstalk cancellation signal based on a transmission reference signal, wherein said transmission reference signal is indicative of said first signal, and

correcting circuitry configured to corrected said second signal based on said crosstalk cancellation signal.

22. A computer program product comprising computer-executable computer program code which, when the program is run on a computer, is configured to cause the computer to carry out the method according to any one of claims 1 to 10.

23. The computer program product according to claim 22, wherein the computer program product comprises a computer-readable medium on which the computer-executable computer program code is stored, and/or wherein the program is directly loadable into an internal memory of the computer or a processor thereof.