Reducing peak-to-average power ratio in cellular communication systems

Abstract

Reducing Peak-to-Average Power Ratio in Cellular Communication Systems An apparatus is described, comprising: means for allocating transmission resources to a first group of one or more transmitters (202) and to a second group of one or more transmitters (204), such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first (B1) and second (B2) frequency bands, and additional frequency resources outside of the second frequency band (304A) and which overlap with the first frequency band (B1) are allocated to the transmitters of the second group (204). Preferably, the resources might be allocated for the purpose of peak-to-average power reduction. The apparatus may also comprise means for forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group.

Description

[0001] Reducing Peak-to-Average Power Ratio in Cellular Communication Systems

[0002] Field

[0003] Example embodiments relate in general to cellular communication systems and, more specifically, to an apparatus and method for reducing peak-to-average power ratio, PAPR, in such systems.

[0004] Background

[0005] Peak-to-Average Power Ratio, PAPR, may occur, for example, in multicarrier communication systems, wherein different sub-carriers may be out of phase compared to each other, thereby causing a peak in an output envelope. Reduction of PAPR is thus important at least in various cellular networks, such as in networks operating according to Long Term Evolution, LTE, and / or fifth generation, 5G, radio access technology. 5G radio access technology may also be referred to as New Radio, NR, access technology. 3rdGeneration Partnership Project, 3GPP, still develops LTE, and also standards for 5G / NR. Reduction of PAPR may also be beneficial in other wireless communication networks in the future as well, such as in 6G networks.

[0006] Summary

[0007] The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0008] According to a first aspect, there is described an apparatus, comprising means for allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands; and additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and means for forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group. Preferably, the additional frequency resources might be allocated for the purpose of peak-to-average power reduction.

[0009] In some example embodiments, the means for allocating transmission resources is further configured such that additional frequency resources outside of the first frequency band and which overlap with the second frequency band are allocated to the transmitters of the first group, and the apparatus further comprises means for forming receive beams for the second frequency band in the direction of the transmitters of the second group whilst reducing interference from the transmitters of the first group.

[0010] In some example embodiments, the receive beams may be formed by computing a set of antenna weights for respective elements of an antenna array for receiving the in-band data using the first and second frequency bands.

[0011] In some example embodiments, the set of antenna weights for a particular frequency band may be computed by: determining in-band channel estimates for the one or more transmitters allocated to transmit in-band data using frequency resources corresponding to the particular frequency band; determining one or more covariance matrices over the additional frequency resources allocated to said one or more transmitters outside of the particular frequency band; and determining the set of antenna weights for the particular frequency band based on the in-band channel estimates and the one or more covariance matrices.

[0012] In some example embodiments, the apparatus may further comprise: means for receiving reference signals from the one or transmitters allocated to transmit in-band data using frequency resources corresponding to the particular frequency band, wherein the in-band channel estimates for said one or more transmitters are determined using the received reference signals. The reference signals may comprise sounding reference signals.

[0013] In some example embodiments, determining the set of antenna weights for the particular frequency band comprises multiplying the in-band channel estimates with an inverted version of the covariance matrix.

[0014] In some example embodiments, the apparatus further comprises means for providing the determined antenna weights to a combiner associated with the antenna array. The additional frequency resources may be used for transmission of one or more reserved tones. The one or more reserved tones may comprise peak cancellation signal(s). The additional frequency resources may be allocated either side of the frequency band.

[0015] In some example embodiments the apparatus comprises a wireless network node, e.g. an enhanced NodeB, a next generation NodeB (gNB) or Transmit Reception Point (TRP).

[0016] According to a second aspect, there is described a method, comprising: allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands; additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group. Preferably, the additional frequency resources might be allocated for the purpose of peak-to-average power reduction.

[0017] In some example embodiments, the additional frequency resources allocated outside of the first frequency band and which overlap with the second frequency band are allocated to the transmitters of the first group, and the apparatus further comprises means for forming receive beams for the second frequency band in the direction of the transmitters of the second group whilst reducing interference from the transmitters of the first group.

[0018] In some example embodiments, the receive beams may be formed by computing a set of antenna weights for respective elements of an antenna array for receiving the in-band data using the first and second frequency bands.

[0019] In some example embodiments, the set of antenna weights for a particular frequency band may be computed by: determining in-band channel estimates for the one or more transmitters allocated to transmit in-band data using frequency resources corresponding to the particular frequency band; determining one or more covariance matrices over the additional frequency resources allocated to said one or more transmitters outside of the particular frequency band; and determining the set of antenna weights for the particular frequency band based on the in-band channel estimates and the one or more covariance matrices. In some example embodiments, the method may further comprise: receiving reference signals from the one or transmitters allocated to transmit in-band data using frequency resources corresponding to the particular frequency band, wherein the in-band channel estimates for said one or more transmitters are determined using the received reference signals. The reference signals may comprise sounding reference signals.

[0020] In some example embodiments, determining the set of antenna weights for the particular frequency band comprises multiplying the in-band channel estimates with an inverted version of the covariance matrix.

[0021] In some example embodiments, the method may further comprise providing the determined antenna weights to a combiner associated with the antenna array. The additional frequency resources may be used for transmission of one or more reserved tones. The one or more reserved tones may comprise peak cancellation signal(s).

[0022] The additional frequency resources may be allocated either side of the frequency band.

[0023] In some example embodiments the method may be performed at a wireless network node, e.g. an enhanced NodeB, a next generation NodeB (gNB) or Transmit Reception Point (TRP).

[0024] According to a third aspect, there is described a computer program product, comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out a method, comprising allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands; additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group. In some example embodiments, the third aspect may include any other feature mentioned with respect to the method of the second aspect.

[0025] According to a fourth aspect, there is described a non-transitory computer readable medium comprising program instructions stored thereon to cause the apparatus to carry out a method, comprising allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands; additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group. Preferably, the additional frequency resources might be allocated for the purpose of peak-to-average power reduction.

[0026] In some example embodiments, the fourth aspect may include any other feature mentioned with respect to the method of the second aspect.

[0027] According to a fifth aspect, there is described an apparatus comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processing core, cause the apparatus to allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands; additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group. Preferably, the additional frequency resources might be allocated for the purpose of peak-to-average power reduction.

[0028] In some example embodiments, the fifth aspect may include any other feature mentioned with respect to the method of the second aspect. Drawings

[0029] Example embodiments will be described, by way of non-limiting example, with reference to the accompanying drawings, in which:

[0030] Figure 1 illustrates a first network scenario which is useful for understanding example embodiments;

[0031] Figure 2 illustrates a second network scenario in accordance with at least some example embodiments;

[0032] Figure 3 illustrates allocation of uplink frequency resources in accordance with at least some example embodiments;

[0033] Figure 4 illustrates the forming of receive beams and nulls for a first group of user equipment (UEs) in accordance with at least some example embodiments;

[0034] Figure 5 illustrates the forming of receive beams and nulls for a second group of user equipment (UEs) in accordance with at least some example embodiments;

[0035] Figure 6 is a flow diagram illustrating operations that may be performed in accordance with at least some example embodiments;

[0036] Figure 7 is another flow diagram illustrating other operations that may be performed in accordance with at least some example embodiments;

[0037] Figure 8 illustrates an example apparatus capable of supporting at least some example embodiments; and

[0038] Figure 9 illustrates a non-transitory medium for carrying computer-readable instructions that, when executed by one or more processors of an apparatus, may perform at least some example embodiments.

[0039] Detailed Description

[0040] Example embodiments relate in general to cellular communication systems and, more specifically, to an apparatus and method for reducing peak-to-average power ratio, PAPR, in such systems.

[0041] Example embodiments are described in relation to uplink, UL, communication over an air interface between, for example, a user equipment, UE, and a wireless network node.

[0042] Energy efficiency and coverage are important considerations in cellular communication systems. Both quantities are determined by the PAPR. A low PAPR allows a power amplifier of a transmitting apparatus to be operated with a lower backoff which improves the efficiency of the power amplifier by reducing power consumption whilst also allowing for higher transmit power, improving coverage.

[0043] Increasing UL throughput involves use of complex modulation schemes such as higher- order quadrature amplitude modulation, QAM and / or by use of Orthogonal Frequency- Division Multiplexing, OFDM, waveforms with support for multi-antenna communications. Such schemes tend to increase the PAPR in the UL and may limit their use to situations where the UE is close to the wireless network node. For example, in 5G / NR technology OFDM may be employed when the UE is close to the wireless network node and waveforms such as discrete Fourier Transform-Spread-Orthogonal Frequency- Division Multiplexing, DFT-s-OFDM, which have a lower PAPR may be employed when the UE is further away from the wireless network node. However, waveforms that have a lower PAPR tend also to have lower throughputs. For example, 5G / NR has 71 / 2 -binary phase shift keying, BPSK, in the UL that can operate using a power amplifier backoff of less than 0.5 dB but with a low spectral efficiency of less than 1 bit per second, bps, per hertz. Also, DFT-s-OFDM can operate at twice the spectral efficiency of TT / 2 -BPSK while requiring a higher power amplifier backoff of approximately 2.5 dB. These modulation schemes may employ frequency domain spectral shaping, FDSS, which may further reduce the PAPR at the cost of spectral efficiency.

[0044] The use of OFDM waveforms that have a relatively high PAPR and the use of relatively lower PAPR waveforms such as DFT-s-OFDM can have a relatively higher PAPR when used with carrier aggregation. Multi-antenna precoding may also increase the PAPR of OFDM waveforms.

[0045] Known methods for reducing PAPR include tone reservation for OFDM and spectral extension for DFT-s-OFDM.

[0046] Tone reservation may involve reserving some of the total number of tones (e.g. as a percentage) for a UE to accommodate a peak-cancelling signal that is known to lower PAPR. In spectral extension for DFT-s-OFDM, additional resource elements maybe reserved on both sides of a desired UL bandwidth and the spectrum is effectively symmetrically extended. This allows for UL spectral efficiency to be traded-off for reduced PAPR. Both methods can reduce PAPR but increase transmission overhead and reduce spectral efficiency. Example embodiment apparatuses and methods are shown to reduce transmission overhead when using tone reservation and / or spectral extension methods for OFDM / DFT-s-OFDM for a given PAPR.

[0047] Figure i illustrates a network scenario useful for understanding at least some example embodiments. According to the example network scenario of Figure 1, there may be a cellular communication system, which comprises a UE no, a wireless network node 120 and core network element 130. The UE no may be connected to the wireless network node 120 via an air interface 115 and the wireless network node 120 may be further connected to the core network element 130 via a wired interface 125. In some example embodiments, the air interface 115 may be a beam-based interface.

[0048] The UE 110 may comprise, for example, a smartphone, a cellular phone, a Machine-to-Machine, M2M, node, Machine-Type Communications, MTC, node, RedCap UE (Reduced Capability UE) node, an Internet of Things, loT, node, a car telemetry unit, a laptop computer, a tablet computer or, indeed, any kind of suitable wireless terminal, like a relay. The wireless network node 120 may be considered as a serving node for the UE 110 and one cell of the wireless network node 120 may be a serving cell for the UE 110.

[0049] The air interface 115 between the UE 110 and the wireless network node 120 may be configured in accordance with a Radio Access Technology, RAT, which both the UE 110 and the wireless network node 120 are configured to support. Examples of cellular RATs include

[0050] Long Term Evolution, LTE, New Radio, NR, which may also be known as fifth generation, 5G, radio access technology and MulteFire. For example, in the context of LTE, the wireless network node 120 may be referred to as an eNB while wireless network node 120 may be referred to as a gNB in the context of 5G / NR. In some example embodiments, the wireless network node 120 may be referred to as a Transmission and Reception Point, TRP, or may control multiple TRPs that may be co-located or non-co-located. In some example embodiments, the wireless network node 120 may be a relay.

[0051] In any case, example embodiments of the present disclosure are not restricted to any particular wireless technology. Instead, example embodiments maybe exploited in any wireless communication network wherein reduction of PAPR is desirable. The wireless network node 120 may be connected, directly or via at least one intermediate node, with the core network element 130 via interface 125. The core network element 130 may be, in turn, coupled via interface 135 with another network (not shown in Figure 1) via which connectivity to further networks may be obtained, for example via a worldwide interconnection network. The wireless network node 120 may be connected, directly or via at least one intermediate node, with the core network element 130 or with another core network.

[0052] In some example embodiments, the network scenario may comprise a relay node instead of, or in addition to, the UE 110 and / or the wireless network node 120. Relaying may be used, for example, when operating on millimetre-wave frequencies. One example of the relay node may be an Integrated Access and Backhaul, IAB, node. The IAB node may be referred to as a self-backhauling relay as well. Another example of a relay may be an outband relay. In general, the relay node may comprise two parts:

[0053] 1) a Distributed Unit, DU, part which may facilitate functionalities of wireless network node 120, such as a gNB. Thus, in some example embodiments, the DU part of a relay may be referred to as the wireless network node 120 and the DU may perform tasks of the wireless network node 120;

[0054] 2) a Mobile Termination, MT, part which may facilitate functionalities of the UE 110, i.e., a backhaul link which may be the communication link between a parent node (DU), such as a DU part of the wireless network node 120, and the relay, such as an IAB node.

[0055] In some example embodiments, the MT part may be referred to as the UE 110 and perform tasks of the UE 110.

[0056] Figure 2 illustrates another network scenario useful for understanding at least some example embodiments.

[0057] The example network scenario of Figure 2 is the same as the Figure 1 example network scenario but there are now multiple, in this case first to fifth, UEs 110A - 110E. Otherwise, the same considerations mentioned above for Figure 1 still apply. In other example embodiments there maybe fewer or a larger number of UEs, for example only two UEs. The first to fifth UEs noA - noE may be configured for uplink transmissions by information or indicators received in downlink communications from the wireless network node 120. The information or indicators may enable the first to fifth UEs 110A - 110E to determine a precoder to use for uplink transmissions.

[0058] For example, the first to fifth UEs 110A - 110E may be grouped by the network into two or more groups of UEs with UEs of said groups being allocated (or scheduled) uplink transmission resources corresponding to respective non-overlapping uplink frequency bands (or bandwidths) for transmission of in-band signals such as PUSCH data.

[0059] In Figure 2, the first to third UEs 110A - 110C are shown allocated to a first group 202 of UEs and maybe allocated uplink resources corresponding to a first frequency band Bi. The fourth and fifth UEs 110D - 110E are shown allocated to a second group 204 of UEs and may be allocated uplink resources corresponding to a second frequency band B2. In other embodiments not shown in the Figures, one or both groups 202, 204 may only comprise one UE.

[0060] Figure 3 is a graphical representation of how uplink transmission resources maybe allocated according to one or more example embodiments.

[0061] With reference to Figure 3, the first group 202 of UEs, comprising the first to third UEs 110A - 110C, are shown allocated to respective MIMO layers 322A - 322C. The first frequency band Bi for transmission of in-band signals is indicated by reference numeral 302. The second group 204 of UEs, comprising the fourth and fifth UEs 110D - 110E. are shown allocated to respective MIMO layers 322D - 322E. The second frequency band B2 for transmission of in-band signals is indicated by reference numeral 304. The first and second frequency bands Bi, B2, 302, 304 do not overlap but maybe adjacent in the frequency domain.

[0062] As will be seen in Figure 3, further frequency resources 302A, 302B, 304A, 304B are allocated on both sides of the first and second frequency bands Bi, B2, 302, 304 as part of known PAPR reduction methods. These may be referred to as reserved tones or reserved bands in the context of tone reservation methods (which transmit peak cancellation signals along with the in-band signals) or extended bands in the context of spectral extension methods. It will be assumed hereinafter that said further frequency resources 302A, 302B, 304A, 304B are reserved tones or reserved bands for transmitting peak cancellation signals, although example embodiments are applicable to spectral extension methods.

[0063] For example, either side of the first band 302 are allocated reserved tones 302A, 302B. For example, either side of the second band 304 are allocated reserved tones 304A, 304B.

[0064] In some example embodiments, at least some of the reserved tones 302B for the first group 202 of UEs are allocated or scheduled to overlap the second frequency band B2, 304 used for uplink transmission of in-band signals by the second group 204 of UEs. In some example embodiments, at least some of the reserved tones 304A for the second group 204 of UEs are allocated or scheduled to overlap the first frequency band Bi, 302 used for uplink transmission of in-band signals by the first group 202 of UEs.

[0065] In respect of the first frequency band Bi 302, the MIMO layers 322A - 322C may be real layers. In respect of the additional frequency resources allocated for reserved tones 302B, the MIMO layers 322A - 322C are virtual layers and only carry peak cancelling signals or extended parts of the spectrum. The term “virtual layers” is used here to denote that these layers are not meant to be carrying useful, or in-band data.

[0066] In some example embodiments, some or all of the first to fifth UEs 110A - 110E may be equipped with only a single antenna port.

[0067] Allocation or scheduling in this way may reduce transmission overhead for the first to fifth UEs 110A - 110E when using tone reservation and / or spectral extension methods for OFDM / DFT-s-OFDM for a given PAPR. Allocating additional frequency resources for the reserved tones 302B, 304 using the explained overlapping method uses less frequency resources, and therefore less transmission overhead, than if they were not to overlap or if they were to overlap each other rather than respectively overlapping the second and first frequency bands B2, Bi.

[0068] There may be a need, however, to supress uplink interference from reserved tones of one group of UEs, for example the first group 202 of UEs, being within in-band signals of the other group of UEs, for example the second group 204, or vice versa.

[0069] In some example embodiments, therefore, the wireless network node 120 may be configured to use spatial processing methods to supress such interference. With reference to Figure 4, the wireless network node 120 may for example be configured to form receive beams 210A - 210C for receiving in-band data in the first frequency band Bi, 302 in the respective directions of the first to third UEs 110A - 110C of the first group 202 of UEs. At the same time, the wireless network node 120 may be configured to place receive nulls for uplink transmissions in frequency resources 304A which is or are part of the first frequency band Bi, 302 in the respective directions of the third and fourth UEs 110D - 110E of the second group 204 of UEs. The nulls may therefore supress interference from reserved tones transmitted by any of the third and fourth UEs 110D - 110E of the second group 204 of UEs.

[0070] With reference to Figure 5, the wireless network node 120 may also be configured to form receive beams 210D - 210E for receiving in-band data in the second frequency band B2, 304 in the respective directions of the third and fourth UEs 110D - 110E of the second group 204 of UEs. At the same time, the wireless network node 120 may be configured to place receive nulls for uplink transmissions in frequency resources 302B which is or are part of the second frequency band B2, 304 in the direction of the respective directions of the first to third UEs 110A - 110C of the first group 202 of UEs. The nulls may therefore supress interference from reserved tones transmitted by any of the first to third UEs 110A - 110C of said first group 202 of UEs.

[0071] It is noted that the Figure 4 and Figure 5 scenarios may occur simultaneously but over the different, non-overlapping bandwidths Bi, B2.

[0072] The wireless network node 120 may be configured to form the respective receive beams by computing a set of antenna weights for respective elements of an antenna array for receiving in-band data using the first and second frequency bands 302, 304.

[0073] The wireless network node 120 may, for this purpose, compute the set of antenna weights for a spatial combiner function or similar. An example method will now be explained although it will be appreciated that alternative or variation methods may be used.

[0074] One approach for computing antenna weights is to consider maximising the overall signal to interference noise ratio, SINR. Consider a wireless network node with M antenna elements serving up to K users or UEs over a given bandwidth. In Figures 2 to 5 above, K = 3 for the first frequency band Bi allocation and K = 2 for the second frequency band B2 allocation.

[0075] Then, if hk[n] is the channel vector between the kthUE and the wireless network node 120 at the nthresource element, RE, the received signal at the nthresource element can be written as: is the group of UEs that are transmitting payload data (in-band signals) in the nthRE and iZ[n] are the UEs that transmit the peak cancelling signals on the same RE.

[0076] For example, in Figure 4, V.n= [1, 2, 3] and Hn= [4, 5].

[0077] Further, xfc[n] e C is the transmitted payload data, e.g. physical uplink shared channel (PUSCH) data, ek[n] e C is the peak cancellation signal, and 77 [n] is additive white Gaussian noise (AWGN) at the wireless network node 120 with noise variance u2. pkis the transmit power for the kthUE.

[0078] Estimates of the channel vector hk[n] for the users or UEs in Unare assumed to be known or can be obtained which is reasonable because estimates can be obtained from respective uplink sounding reference signals (SRS) transmitted by said UEs. As will be known, channel estimation may be performed by a receiving node, for example by the wireless network node 120 shown in Figure 2, having knowledge of pilot symbols, which represent a type of reference signal, e.g., SRS in the case of uplink signals, that will be transmitted by a particular transmitting node, e.g. one of the UEs 110A - 110E shown in Figure 2. More specifically, the receiving node may have prior knowledge of the time and frequency resources on which the SRSs will be transmitted by the transmitting node and characteristics of said SRSs. Upon receiving SRSs from the transmitting node, the receiving node may compare characteristics of the received SRSs with those of the known SRS and thereby estimate or model certain parameters of the channel over which the SRS was transmitted. This may be in the form of a channel matrix. Such parameters may include path loss, propagation delay and received signal strength (RSS). Known channel estimators include Least Square Error (LSE) and Linear Minimum Mean Square Error (LSSE) estimators.

[0079] However, estimates of the channel vector hk[n] for the users or UEs in Hnare assumed unavailable because they typically need not transmit outside of their allocated frequency band. In this case, we may assume that a (long-term) spatial covariance matrix is available for these users or UEs. The spatial covariance matrix may be estimated by averaging outer products of channel vector hfc[n].

[0080] Denoting the spatial covariance matrix of the kthUE as Rk, we can express the SINR as: where wke is a vector containing the combining weights for the kthUE.

[0081] The combining vector can be obtained by maximizing the SINR for the kthUE as: subject to w11hk[n] = 1

[0082] (3)

[0083] In this optimization problem, the objective and the constraint are, respectively, the denominator and numerator of the SINR. Because the optimization problem minimizes the denominator of the SINR while fixing the numerator, it effectively maximizes the SINR.

[0084] The optimization problem can be solved in closed form to obtain weights for the kthUE: The weights w^ptfor each UE for each of the first and second frequency bands Bi, B2 may therefore be computed and provided to a combiner, e.g. a zero-forcing (ZF) combiner, at the wireless network node 120 which forms the respective beams and nulls in said first and second frequency bands.

[0085] Figure 6 is a flow diagram indicating operations 600 according to one or more other example embodiments. The operations maybe performed in hardware, software, firmware or a combination thereof. For example, the operations may be performed individually, or collectively, by a means, wherein the means may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the operations.

[0086] A first operation 601 may comprise allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in a sub-operation 602, in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands, and in a sub-operation 603, additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group.

[0087] A second operation 602 may comprise forming receive beams for the first frequency band in the direction of the transmitters of the first group whilst minimizing interference from the direction of transmitters of the second group (for the first frequency band).

[0088] The allocation of transmission resources may comprise allocation of uplink transmission resources, as is the case for the above-described embodiments, wherein the transmitters are for example UEs.

[0089] In alternative example embodiments, the allocation of transmission resources may comprise allocation of downlink transmission resources.

[0090] In some example embodiments, other operations may be performed. For example, other operations may comprise: allocating transmission resources such that frequency resources outside of the first frequency band and which overlap with the second frequency band are allocated to the transmitters of the first group, and forming receive beams for the second frequency band in the direction of the transmitters of the second group whilst minimizing interference from the direction of transmitters of the first group (for the second frequency band).

[0091] Figure 7 is a flow diagram indicating operations 700 according to one or more other example embodiments. The operations 700 may comprise at least part of the abovedescribed operation(s) for forming receive beams, whether for one or each of the first and second frequency bands. The operations may be performed in hardware, software, firmware or a combination thereof. For example, the operations may be performed individually, or collectively, by a means, wherein the means may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the operations.

[0092] An operation 701 indicates that the subsequent operations are performed for one or each particular frequency band of the first and second frequency bands Bi, B2302, 304.

[0093] Another operation 702 may comprise, for the particular frequency band, determining in- band channel estimates for the one or more transmitters allocated to transmit in-band data using frequency resources corresponding to the particular frequency band.

[0094] For example, for the first frequency band Bi 302 in the Figure 3 allocation, in-band channel estimates may be determined for the first to third UEs 110A - 110C of the first group 202 of UEs.

[0095] For example, for the second frequency band B2304 in the Figure 3 allocation, in-band channel estimates may be determined for the fourth and fifth UEs 110D, 110E of the second group 204 of UEs.

[0096] In some example embodiments, the channel estimates may be determined in the operation 702 based on receiving one or more reference signals transmitted by the transmitters, e.g., the above-mentioned UEs of the first and second groups 202, 204 of UEs. The reference signals may be Sounding Reference Signals (SRS) or other forms of reference signals suitable for this purpose.

[0097] Reference numeral 703 indicates an operation of transmitting SRSs but it will be appreciated that this operation is performed by the individual transmitters, or UEs in the above examples, and not the wireless network node 120.

[0098] Another operation 704 may comprise determining a covariance matrix over the additional frequency resources allocated to said one or more transmitters outside of the particular frequency band.

[0099] The operation 704 maybe performed before, after or at the same time as the second operation 702.

[0100] For example, for the first frequency band Bi 302 in the Figure 3 allocation, a covariance matrix may be determined over the additional frequency resources 302B for the transmitters 110D - 110E of the second group.

[0101] For example, for the second frequency band B2304 in the Figure 3 allocation, a covariance matrix may be determined over the additional frequency resources 304A for the transmitters 110A - 110C of the first group.

[0102] Another operation 705 may comprise determining a set of antenna weights for the frequency band based on the in-band channel estimates and the covariance matrix.

[0103] For example, the operation 705 may comprise multiplying the in-band channel estimates from the operation 702 with an inverted version of the covariance matrix from the operation 704.

[0104] Another operation 706 may comprise providing the determined set of antenna weights to a combiner associated with an antenna array.

[0105] With computed sets of antenna weights for the first and second frequency bands Bi, B2 302, 304 the combiner has the required information for forming beams and nulls usable in the example scenarios of Figures 3 - 5. It will be appreciated that the operations described with reference to Figures 5 and 6 are applicable to any number of transmitter or UE groups, e.g., more than two groups.

[0106] Simulation Results

[0107] Figure 8 is a graphical illustrating simulation results where the horizontal axis represents PAPR in dBs and where the vertical axis represents throughput in bps / hertz. An upper plot line 810 indicates results from an apparatus configured according to an example embodiment and a lower plot line 820 indicates baseline results from a conventional apparatus using tone reservation. For the simulation, a wireless network node 120 with 64 elements (8 rows, 2 columns, 2 polarizations) serving four UEs was assumed, with a system bandwidth of Bs= 10 MHz. The four UEs were arranged in two groups of two UEs and each were allocated to half the system bandwidth Bs, i.e. 5 MHz. The UEs were assumed to utilize CP-OFDM to communicate in the uplink with the number of reserved tones for PAPR reduction taken from the set {o, 6.25%, 12.5%, 18.75%, 25%}. A zeroforcing (ZF) combiner was utilized as the baseline combiner for the conventional apparatus. The overall system was simulated with the 3GPP Umi channel model (3.5 GHz, 3 kph mobility).

[0108] It will be seen from Figure 8 that both the PAPR and throughput are dependent on the number of reserved tones for PAPR reduction. Reference numerals 812 - 816 respectively indicate the number of tones used from the set {o, 6.25%, 12.5%, 18.75%, 25%}. As can be seen for the lower plot line 820, as the number of reserved tones are increased, the PAPR is reduced as is the throughput. As can be seen for the the upper plot line 810, the same trend occurs but the overhead associated with use of tone reservation is significantly reduced by allocating the reserved tones of one group of UEs in the frequency band of another group of UEs. It can be seen, for example, that even with 25% tone reservation (see reference numeral 816), which achieves significantly lower PAPR, there is only an 8% drop in throughput compared with a 25% drop for the conventional apparatus.

[0109] Similar results can be observed where spectral extension methods are used instead of tone reservation.

[0110] In addition to increased throughout for a given PAPR, further advantages include the ability to perform processing for supressing interference at the wireless network node 120 rather than at UEs noA - noE. Also, example embodiments work with UEs noA - noE any of which may have only a single antenna port, such a reduced-capability UEs.

[0111] Example Apparatus

[0112] Figure 9 illustrates an example apparatus capable of supporting at least some embodiments. Illustrated is a device 900, which maybe referred to as, for example, any of the first to fifth UEs 110A - 110E, or the wireless network node 120, or a device configured to control the functioning thereof.

[0113] Comprised in device 900 is a processor 910, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. The processor 910 may comprise, in general, a control device. The processor 910 may comprise more than one processor. The processor 910 may be a control device. A processing core may comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Steamroller processing core produced by Advanced Micro Devices Corporation. The processor 910 may comprise at least one Qualcomm Snapdragon and / or Intel Atom processor. The processor 910 may comprise at least one Application-Specific Integrated Circuit, ASIC. The processor 910 may comprise at least one Field-Programmable Gate Array, FPGA. The processor 910 maybe means for performing method steps in device 900. The processor 910 may be configured, at least in part by computer instructions, to perform actions.

[0114] A processor may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with embodiments described herein. As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as any of the first to fifth UEs 110A - 110E or the wireless network node 120, or a device configured to control the functioning thereof, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0115] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0116] The device 900 may comprise a memory 920. The memory 920 may comprise random access memory and / or permanent memory. The memory 920 may comprise at least one RAM chip. The memory 920 may comprise solid-state, magnetic, optical and / or holographic memory, for example. The memory 920 may be at least in part accessible to processor 910. The memory 920 maybe at least in part comprised in processor 910. The memory 920 may be means for storing information. The memory 920 may comprise computer instructions that processor 910 is configured to execute. When computer instructions configured to cause the processor 910 to perform certain actions are stored in the memory 920, and the device 900 overall is configured to run under the direction of the processor 910 using computer instructions from the memory 920, the processor 910 and / or its at least one processing core may be considered to be configured to perform said certain actions. The memory 920 may be at least in part comprised in the processor 910. The memory 920 may be at least in part external to the device 900 but accessible to the device 900.

[0117] The device 900 may comprise a transmitter 930. The device 900 may comprise a receiver 940. The transmitter 930 and the receiver 940 maybe configured to transmit and receive, respectively, information in accordance with at least one cellular or non-cellular standard. The transmitter 930 may comprise more than one transmitter. The receiver 940 may comprise more than one receiver. The transmitter 930 and / or the receiver 940 maybe configured to operate in accordance with Global System for Mobile Communication, GSM, Wideband Code Division Multiple Access, WCDMA, 5G / NR, 5G-Advanced, i.e., NR Rel- 18, 19 and beyond, Long Term Evolution, LTE, IS-95, Wireless Local Area Network, WLAN, Ethernet and / or Worldwide Interoperability for Microwave Access, WiMAX, standards, for example. The device 900 may comprise a Near-Field Communication, NFC, transceiver 950. The NFC transceiver 950 may support at least one NFC technology, such as NFC, Bluetooth, Wibree or similar technologies.

[0118] The device 900 may comprise a User Interface, UI, 960. The UI 960 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 900 to vibrate, a speaker and a microphone. A user maybe able to operate the device 900 via the UI 960, for example to accept incoming telephone calls, to originate telephone calls or video calls, to browse the Internet, to manage digital files stored in memory 920 or on a cloud accessible via the transmitter 930 and the receiver 940, or via NFC transceiver 950, and / or to play games.

[0119] The device 900 may comprise or be arranged to accept a user identity module 970.

[0120] The user identity module 970 may comprise, for example, a Subscriber Identity Module, SIM, card installable in device 900. The user identity module 970 may comprise information identifying a subscription of a user of device 900. The user identity module 970 may comprise cryptographic information usable to verify the identity of a user of device 900 and / or to facilitate encryption of communicated information and billing of the user of the device 900 for communication effected via device 900.

[0121] The processor 910 may be furnished with a transmitter arranged to output information from processor 910, via electrical leads internal to the device 900, to other devices comprised in the device 900. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to the memory 920 for storage therein. Alternatively to a serial bus, the transmitter may comprise a parallel bus transmitter.

[0122] Likewise the processor 910 may comprise a receiver arranged to receive information in The processor 910, via electrical leads internal to the device 900, from other devices comprised in the device 900. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from the receiver 940 for processing in the processor 910. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver.

[0123] The device 900 may comprise further devices not illustrated in Figure 9. For example, where the device 900 comprises a smartphone, it may comprise at least one digital camera. Some devices 900 may comprise a back-facing camera and a front-facing camera, wherein the back-facing camera may be intended for digital photography and the frontfacing camera for video telephony. The device 900 may comprise a fingerprint sensor arranged to authenticate, at least in part, a user of the device 900. In some embodiments, the device 900 lacks at least one device described above. For example, some devices 900 may lack a NFC transceiver 950 and / or user identity module 970.

[0124] The processor 910, memory 920, transmitter 930, receiver 940, NFC transceiver

[0125] 10 950, UI 960 and / or user identity module 970 may be interconnected by electrical leads internal to the device 900 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to the device 900, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the embodiment various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the present invention.

[0126] Figure 10 shows a non-transitory media 1000 according to some embodiments. The non- transitory media 1000 is a computer readable storage medium. It maybe e.g. a CD, a DVD, a USB stick, a blue ray disk, etc. The non-transitory media 1000 stores computer program instructions, causing an apparatus to perform the method of any preceding process for example as disclosed in relation to the flow diagrams in this specification and related features thereof.

[0127] The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0128] While the forgoing examples are illustrative of the principles of the embodiments in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0129] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependant claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

[0130] Acronyms List

[0131] 3GPP 3rd Generation Partnership Project

[0132] ACLR Adjacent Channel Leakage Ratio

[0133] ASIC Application-Specific Integrated Circuit

[0134] BS Wireless network node

[0135] CP-OFDM Cyclic Prefix -OFDM

[0136] CSI-RS Channel State Information-Reference Signal

[0137] D2D Device-to-Device

[0138] DFT-s-OFDM Discrete Fourier Transform-Spread-OFDM

[0139] DMRS Demodulation Reference Signal

[0140] DU Distributed Unit

[0141] EVM Error Vector Magnitude

[0142] FPGA Field-Programmable Gate Array

[0143] FR Frequency Range

[0144] GSM Global System for Mobile communication

[0145] IAB Integrated Access and Backhaul

[0146] IBE In-band Emissions loT Internet of Things

[0147] LTE Long-Term Evolution

[0148] KT-DFT-s-OFDM Known Tail-DFT-s-OFDM

[0149] M2M Machine-to-Machine

[0150] MT Mobile Termination

[0151] MTC Machine-Type Communications

[0152] NFC Near-Field Communication

[0153] NR New Radio

[0154] OBO Output Power Backoff OCB Occupied Bandwidth

[0155] OFDM Orthogonal Frequency Division Multiplexing

[0156] PA Power Amplifier

[0157] PAPR Peak-to-Average Power Ratio

[0158] PCS Peak Cancellation Signal

[0159] PUSCH Physical Uplink Shared Channel

[0160] RAN Radio Access Network

[0161] RAT Radio Access Technology

[0162] RRC Radio Resource Control

[0163] SIM Subscriber Identity Module

[0164] SIR Signal-to-Interference Ratio

[0165] SRS Sounding Reference Signal

[0166] TPMI Transmitted Precoding Matrix Indicator

[0167] TRP Transmission and Reception Point

[0168] UE User Equipment

[0169] UI User Interface

[0170] WCDMA Wideband Code Division Multiple Access

[0171] WiMAX Worldwide Interoperability for Microwave Access

[0172] WLAN Wireless Local Area Network

Claims

Claims1. An apparatus, comprising: means for allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands; additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and means for forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group.

2. An apparatus according to claim 1, wherein the means for allocating transmission resources is further configured such that additional frequency resources outside of the first frequency band and which overlap with the second frequency band are allocated to the transmitters of the first group, and the apparatus further comprises means for forming receive beams for the second frequency band in the direction of the transmitters of the second group whilst reducing interference from the transmitters of the first group.

3. An apparatus according to claim 1 or claim 2, wherein the receive beams are by formed by computing a set of antenna weights for respective elements of an antenna array for receiving the in-band data using the first and second frequency bands.

4. An apparatus according to claim 3, wherein the set of antenna weights for a particular frequency band are computed by: determining in-band channel estimates for the one or more transmitters allocated to transmit in-band data using frequency resources corresponding to the particular frequency band;determining one or more covariance matrices over the additional frequency resources allocated to said one or more transmitters outside of the particular frequency band; and determining the set of antenna weights for the particular frequency band based on the in-band channel estimates and the one or more covariance matrices.

5. The apparatus according to claim 4, further comprising: means for receiving reference signals from the one or transmitters allocated to transmit in-band data using frequency resources corresponding to the particular frequency band, wherein the in-band channel estimates for said one or more transmitters are determined using the received reference signals.

6. The apparatus according to claim 5, wherein the reference signals comprise sounding reference signals.

7. The apparatus according to any of claims 4 to 6, wherein determining the set of antenna weights for the particular frequency band comprises multiplying the in-band channel estimates with an inverted version of the covariance matrix.

8. The apparatus according to any of claims 4 to 7, further comprising means for providing the determined antenna weights to a combiner associated with the antenna array.

9. The apparatus according to any preceding claim, wherein the additional frequency resources are used for transmission of one or more reserved tones.

10. The apparatus according to claim 9, wherein the one or more reserved tones comprise peak cancellation signal(s).

11. The apparatus according to any preceding claim, wherein the additional frequency resources are allocated either side of the frequency band.

12. The apparatus according to any preceding claim, wherein the apparatus comprises a wireless network node, e.g. an eNB, gNB or TRP.

113. A method, comprising: allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands; additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group.

14. The method according to claim 13, wherein allocating the transmission resources further comprises allocating additional frequency resources outside of the first frequency band and which overlap with the second frequency band to the transmitters of the first group, and forming receive beams for the second frequency band in the direction of the transmitters of the second group whilst reducing interference from the transmitters of the first group.

15. The method according to claim 13 or claim 14, wherein the receive beams are by formed by computing a set of antenna weights for respective elements of an antenna array for receiving the in-band data using the first and second frequency bands.

16. The method according to claim 15, wherein the set of antenna weights for a particular frequency band are computed by: determining in-band channel estimates for the one or more transmitters allocated to transmit in-band data using frequency resources corresponding to the particular frequency band; determining one or more covariance matrices over the additional frequency resources allocated to said one or more transmitters outside of the particular frequency band; and determining the set of antenna weights for the particular frequency band based on the in-band channel estimates and the one or more covariance matrices.17- The method according to claim 16, further comprising: receiving reference signals from the one or transmitters allocated to transmit in- band data using frequency resources corresponding to the particular frequency band, wherein the in-band channel estimates for said one or more transmitters are determined using the received reference signals.

18. The method according to claim 17, wherein the reference signals comprise sounding reference signals.

19. The method according to any of claims 16 to 18, wherein determining the set of antenna weights for the particular frequency band comprises multiplying the in-band channel estimates with an inverted version of the covariance matrix.

20. The method according to any of claims 16 to 19, further comprising providing the determined antenna weights to a combiner associated with the antenna array.

21. The method according to any of claims 13 to 20, wherein the additional frequency resources are used for transmission of one or more reserved tones.

22. The method according to claim 21, wherein the one or more reserved tones comprise peak cancellation signal(s).

23. The method according to any of claims 13 to 22, wherein the additional frequency resources are allocated either side of the frequency band.

24. The method according to any of claims 13 to 23, wherein the apparatus comprises a wireless network node, e.g. an eNB, gNB or TRP.

25. A computer program product, comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out a method, comprising: allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands;additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group.

26. A non-transitory computer readable medium comprising program instructions stored thereon to cause the apparatus to carry out a method, comprising: allocating transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and non-overlapping first and second frequency bands; additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and forming receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group.

27. An apparatus comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processing core, cause the apparatus to: allocate transmission resources to a first group of one or more transmitters and to a second group of one or more transmitters, such that: in-band data is transmitted by the transmitters of the first and second groups using frequency resources corresponding to respective and nonoverlapping first and second frequency bands; additional frequency resources outside of the second frequency band and which overlap with the first frequency band are allocated to the transmitters of the second group; and to form receive beams for the first frequency band in the direction of the transmitters of the first group for receiving in-band data transmitted by the transmitters of the first group whilst reducing interference from the transmitters of the second group.

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