WO2021105546A1 - Reducing peak to average power ratio in wireless communication systems - Google Patents

Abstract

According to an example aspect of the present invention, there is provided a method for a wireless transmitter,comprisingdetermining a complete set of symbols of a constellation diagram for bit-to-symbol mapping, determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation, mapping M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols, modulating a signal using said selected N consecutive symbols and transmitting the modulated signal to a wireless receiver.

Description

REDUCING PEAK TO AVERAGE POWER RATIO IN WIRELESS COMMUNICATION SYSTEMS FIELD

[0001] Various example embodiments relate in general to wireless communication systems and more specifically, to reducing Peak-to-average Power Ratio, PAPR, in such systems. BACKGROUND

[0002] 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 important for various cellular networks, such as, networks operating according to Long Term Evolution, LTE, and/or 5G radio access technology. 5G radio access technology may also be referred to as New Radio, NR, access technology. 3rd Generation Partnership Project, 3GPP, still develops LTE and also standards for 5G/NR. Reduction of PAPR is also beneficial in other wireless communication networks as well, such as, for example, in Wireless Local Area Networks, WLANs, or satellite communications in the context of Non- Terrestrial Networks, NTNs.

SUMMARY

[0003] According to some aspects, there is provided the subject-matter of the independent claims. Some embodiments are defined in the dependent claims. [0004] 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.

[0005] According to a first aspect, there is provided a first method for a wireless transmitter, comprising determining a complete set of symbols of a constellation diagram for bit-to-symbol mapping, determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation, mapping M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols, modulating a signal using said selected N consecutive symbols and transmitting the modulated signal to a wireless receiver.

[0006] According to a second aspect, there is provided a second method for a wireless receiver, comprising receiving a modulated signal from a wireless transmitter, determining a complete set of symbols of a constellation diagram for bit-to-symbol mapping, determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for demodulation, demodulating the modulated signal using N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols and demapping M consecutive bits from said N consecutive symbols.

[0007] Embodiments of the first or the second aspect may comprise at least one feature from the following bulleted list:

• each subset of symbols to be used for modulation at the time instant may comprise at least neighbour symbols of the previous symbol;

• the determination of the complete set of symbols and/or the determination of the subsets of symbols to be used for modulation may comprise optimisation of peak-to- average power ratio of the transmited signal;

• the first or the second method may further comprise selecting a bit-to-symbol mapping table and selecting said N consecutive symbols based on the selected bit- to-symbol mapping table; • in some embodiments, the selection of bit-to-symbol mapping table may comprise selection for reducing error rate of a decoded signal at the receiver and/or the selection of bit-to-symbol mapping table may comprise selection for reducing complexity of the receiver;

• the bit-to symbol mapping table may be selected such that a number of changing bits per the selected N consecutive symbols depends on a Euclidean distance between the symbols;

• rach subset of symbols to be used for modulation may comprise at least 1 , 2, 3 or 4 of symbols closest on the constellation diagram to a symbol used for modulation at a previous time instant;

• rach subset of symbols to be used for modulation further may comprise a symbol used at a previous time instant;

• the constellation diagram from which each subset of symbols is determined may be rotated by p/K compared to a constellation diagram of the previous symbol, wherein K denotes a number of symbols in the complete set of symbols;

• a size of the subsets of symbols to be used for modulation may be four symbols and each subset may comprise the symbol used for modulation at a previous time instant, first-order neighbour symbols of the previous symbol and one second-order neighbour symbol of the previous symbol;

• the second-order neighbour symbol may be selected from a particular side of the previous symbol depending on whether a symbol to be selected is odd or even;

• a number of symbols in the complete set of symbols may be at least three and at most eight;

• said M consecutive bits may be jointly mapped to said N consecutive symbols;

• in some embodiments, M= 3 or M=4 and N=2;

• in some embodiments, M/N may be a fraction;

• in some embodiments, N>= M/log2(k), k denotes a number of symbols in the subset and N is an integer;

• the determination of the subset and/or the complete of symbols may comprise at least one of the following: determination based on external trigger; determination based on executing optimisation algorithm and determination based on pre-defined setting; • the selection of bit-to-symbol mapping comprises at least one of the following: selection based on the determined subset and/or the complete of symbols; selection based on external trigger; selection based on executing optimisation algorithm and selection based on a pre-defmed setting;

• the subsets of symbols may be of the same size.

[0008] According to a third aspect of the present invention, there is provided an apparatus, such as a wireless transmitter, comprising means for determining a complete set of symbols of a constellation diagram for bit-to-symbol mapping, determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation, mapping M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols, modulating a signal using said selected A consecutive symbols and transmitting the modulated signal to a wireless receiver. The apparatus may further comprise means for performing the first method.

[0009] According to a fourth aspect of the present invention, there is provided an apparatus, such as a wireless receiver, comprising means for receiving a modulated signal from a wireless transmitter, determining a complete set of symbols of a constellation diagram for bit-to-symbol mapping, determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for demodulation, demodulating the modulated signal using N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols and demapping M consecutive bits from said N consecutive symbols.

[0010] According to a fifth aspect of the present invention, there is provided an apparatus, such as a wireless transmitter, 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 at least to perform determine a complete set of symbols of a constellation diagram for bit- to-symbol mapping, determine a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation, map M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols, modulate a signal using said selected N consecutive symbols and transmitting the modulated signal to a wireless receiver. The at least one memory and the computer program code, with the at least one processing core, may further cause the apparatus at least to perform the first method.

[0011] According to a sixth aspect of the present invention, there is provided an apparatus, such as a wireless receiver, 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 at least to perform receive a modulated signal from a wireless transmitter, determine a complete set of symbols of a constellation diagram for bit-to-symbol mapping, determine a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for demodulation, demodulate the modulated signal using N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols and demap M consecutive bits from said N consecutive symbols. The at least one memory and the computer program code, with the at least one processing core, may further cause the apparatus at least to perform the second method.

[0012] According to a seventh aspect of the present invention, there is provided non- transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform the first method. According to an eighth aspect of the present invention, there is provided non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform the second method.

[0013] According to a ninth aspect of the present invention, there is provided a computer program configured to perform the first method. According to a tenth aspect of the present invention, there is provided a computer program configured to perform the second method. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIGURE 1 illustrates an exemplary network scenario in accordance with at least some example embodiments;

[0015] FIGURE 2 illustrates a first example of a high-level flow diagram of operations of a wireless transmitter and a wireless receiver in accordance with at least some embodiments;

[0016] FIGURE 3 illustrates a second example of a high-level flow diagram of operations of a wireless transmitter and a wireless receiver in accordance with at least some embodiments; [0017] FIGURE 4 illustrates an example apparatus capable of supporting at least some embodiments;

[0018] FIGURE 5 illustrates a first example of constrained modulation with 6-PSK constellation and with 4 options per time instant allowed in accordance with at least some embodiments; [0019] FIGURE 6 illustrates a second example of constrained modulation with 6-PSK constellation and with 4 options per time instant allowed in accordance with at least some embodiments;

[0020] FIGURE 7 illustrates an example of constrained modulation with 6-PSK constellation and with 3 options per time instant allowed in accordance with at least some embodiments;

[0021] FIGURE 8 illustrates an example of constrained modulation with 6-PSK constellation and with 4 options and with constellation rotation in accordance with at least some embodiments;

[0022] FIGURE 9 illustrates a Trellis diagram evolution example for constrained modulation with 6-PSK constellation and with 4 options in accordance with at least some embodiments;

[0023] FIGURE 10 illustrates a flow graph of a first method in accordance with at least some embodiments; [0024] FIGURE 11 illustrates a flow graph of a second method in accordance with at least some embodiments;

[0025] FIGURE 12 illustrates a complex eye-diagram for a constrained modulation with 6-PSK constellation and with 3 options in accordance with at least some embodiments; [0026] FIGURE 13 illustrates a complex eye-diagram for a constrained modulation with 6-PSK constellation and with 4 options in accordance with at least some embodiments;

[0027] FIGURE 14 illustrates a complex eye-diagram for a constrained modulation with 8-PSK constellation and with 3 options in accordance with at least some embodiments;

[0028] FIGURE 15 illustrates a complex eye-diagram for a constrained modulation with 8-PSK constellation and with 4 options in accordance with at least some embodiments;

[0029] FIGURE 16 illustrates a power spectral density, PSD, for a constrained modulation with 6-PSK constellation and with 4 options modulated signal without using different mapping for even and odd symbols in accordance with at least some embodiments;

[0030] FIGURE 17 illustrates a PSD for a constrained modulation with 6-PSK constellation and with 4 options modulated signal when using different mapping for even and odd symbols in accordance with at least some embodiments;

[0031] FIGURE 18 illustrates examples of the achievable PAPR for a constrained modulation with different constellations and with 3 options in accordance with at least some embodiments; [0032] FIGURE 19 illustrates examples of the achievable PAPR for a constrained modulation with different constellations and with 4 options in accordance with at least some embodiments;

[0033] FIGURE 20 illustrates uncoded link performance examples of constrained modulation with 5-PSK constellation, C5PSK, and with 6-PSK constellation, C6PSK, with 3 options with two different bits-to-symbols mapping tables in accordance with at least some embodiments; [0034] FIGURE 21 illustrates uncoded link performance examples of constrained modulation with C5PSK and C6PSK with 3 options with a specific bits-to-symbols mapping table in accordance with at least some embodiments;

[0035] FIGURE 22 illustrates examples of the achievable PAPR for a constrained modulation with different constellations and with 4 options, when the constellation is rotated at every other symbol time instant in accordance with at least some embodiments;

[0036] FIGURE 23 illustrates a complex eye-diagram for a constrained modulation with 6-PSK constellation and with 4 options, when the constellation is rotated at every other symbol time instant in accordance with at least some embodiments; [0037] FIGURE 24 illustrates a complex eye-diagram for a constrained modulation with 8-PSK constellation and with 4 options, when the constellation is rotated at every other symbol time instant in accordance with at least some embodiments;

[0038] FIGURE 25 illustrates an example of constrained modulation with 8-PSK constellation and with 4 options and with fixed bits-to-symbols mapping in accordance with at least some embodiments.

EMBODIMENTS

[0039] Peak-to-Average Power Ratio, PAPR, may be reduced in wireless communication systems by the procedures described herein. In general, a wireless communication system may comprise a wireless transmitter and a wireless receiver. In some embodiments of the present invention, the wireless transmitter and the wireless receiver may determine one subset of symbols for each of N consecutive symbols out of a complete set of symbols, wherein each subset may be determined based on a previous symbol selected for modulation, i.e., each subset may depend on the previous symbol. Said N consecutive symbols may be then selected from the subsets to be used for mapping of M consecutive bits of a digital sequence. The wireless transmitter may modulate a signal using said N consecutive symbols and transmit the modulated signal. Upon receiving the modulated signal, the wireless receiver may demodulate the signal using said selected N consecutive symbols. [0040] FIGURE 1 illustrates an exemplary network scenario in accordance with at least some example embodiments. According to the example scenario of FIGURE 1, there may be a wireless communication network comprising one or more wireless terminals 110, wireless network node 120, and core network element 130. In the example network of FIGURE 1, wireless terminals 110 may communicate wirelessly with wireless network node 120, or with a cell of wireless network node 120, via air interface 115. In some example embodiments, wireless network node 120 may be considered as a serving Base Station, BS, for wireless terminal 110. Alternatively, or in addition, wireless terminals 110 may be connected directly to each other via air interface 115 or some other suitable air interface, e.g., for performing direct Device-to-Device, D2D, communications. Embodiments of the present invention may be applied for satellite communications in the context of Non- Terrestrial Networks, NTNs, as well.

[0041] Wireless terminals 110 may comprise, for example, a User Equipment, UE, a smartphone, a cellular phone, a Machine-to -Machine, M2M, node, Machine-Type Communications node, MTC, an Internet of Things, IoT, node, a D2D node, a car telemetry unit, a laptop computer, a tablet computer or, indeed, any kind of suitable wireless terminal or station. In the example system of FIGURE 1, wireless terminal 110 may communicate wirelessly with wireless network node 120, or with a cell of wireless network node 120, via air interface 115.

[0042] Air interface 115 may be configured in accordance with a Radio Access Technology, RAT, which wireless terminal 110 and wireless network node 120 are configured to support. Examples of cellular RATs include Long Term Evolution, LTE, New Radio, NR, which may also be known as fifth generation, 5G, radio access technology and MulteFire. On the other hand, examples of non-cellular RATs include Wireless Local Area Network, WLAN, and Worldwide Interoperability for Microwave Access, WiMAX.

[0043] For example, in the context of LTE, wireless network node 120 may be referred to as eNB while wireless network node 120 may be referred to as gNB in the context of NR. Wireless terminal 110 may be similarly referred to as a UE, e.g., in the context of LTE and NR. Also, for example in the context of WLAN, wireless network node 120 may be referred to as an access point while wireless terminal 110 may be referred to as a mobile station. In any case, example embodiments are not restricted to any particular wireless technology. Instead, example embodiments may be exploited in any wireless communication network or system wherein it is desirable to achieve low PAPR.

[0044] Wireless network node 120 may be connected, directly or via at least one intermediate node, with core network 130 via interface 125. Core network 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. Wireless network node 120 may be connected with at least one other wireless network node as well via an inter-base station interface (not shown in FIGURE 1), even though in some example embodiments the inter-base station interface may be absent. Wireless network node 120 may be connected, directly or via at least one intermediate node, with core network 130 or with another core network.

[0045] In general, a wireless transmitter, TX, may perform modulation of a signal and transmit the modulated signal to a wireless receiver, RX. Upon receiving the modulated signal, the receiver may demodulate the received signal. In case of downlink transmissions, wireless network node 120 may be referred to as the wireless transmitter and wireless terminal 110 may be referred to as the wireless receiver. On the other hand, in case of uplink transmission wireless terminal 110 may be referred to as the wireless transmitter and wireless network node 120 may be referred to as the wireless receiver. In case of D2D communications, one wireless terminal 110 may be referred to as the wireless transmitter and another wireless terminal 110 may be referred to as the wireless receiver. Thus, embodiments of the present invention are related to the wireless transmitter and/or the wireless receiver in general, but not limited to any specific device that would be the wireless transmitter and/or the wireless receiver.

[0046] Embodiments of the present invention may be exploited in various wireless communication systems, such as in 5G networks or WLANs. For example, in 5G NR networks communications may be performed using millimeter wave frequencies, such as frequencies above 52.6 GHz, wherein main implementation issues comprise low power amplifier efficiency and phase noise induced distortion. Waveforms with low PAPR are typically required to improve power amplifier efficiency and such waveforms should tolerate well phase noise distortion to improve link performance and to provide improved link budget gain. Embodiments of the present invention therefore enable optimization of PAPR while maximizing robustness against phase noise.

[0047] Even though the present invention is not limited to any specific frequency bands, other potential high mm-wave bands for 5G and beyond systems comprise at least 70/80/92-114 GHz. Ranges, use cases, deployment scenarios and requirements for such frequency spectrum are being discussed in 3rd Generation Partnership Project, 3GPP, Radio Access Network, RAN, meetings. Objectives discussed in the meetings comprise waveform design for operation beyond 52.6GHz and study of physical layer design for above 52.6GHz. The design should take into consideration at least efficient transceiver design, including power efficiency and complexity, improvement of coverage to cope with extreme propagation loss and inheriting physical layer channel design for below 52.6 GHz from NR Rel-15 whenever applicable.

[0048] At least wireless communication systems operating on frequencies above 52.6 GHz will have to cope with increased path loss, larger antenna arrays, and less efficient radio frequency components like power amplifiers. Hence the systems above 52.6 GHz will likely be more noise limited especially at cell edges which will drive the need to obtain more power from the power amplifiers. Also the high phase noise degrades the performance and must be addressed for a viable solution. Embodiments of the present invention therefore enable improved operation on millimeter wave frequencies, such as frequencies above 52.6 GHz. Embodiments of the present invention are not limited to millimeter wave frequencies though and may be exploited for communication on other frequencies as well.

[0049] Moreover, embodiments of the present invention may be exploited for various wireless communication systems. For instance, embodiments of the present invention may be exploited for different Orthogonal Frequency Division Multiplexing, OFDM, schemes and single carrier modulation based systems. Embodiments of the present invention may be used, e.g., for Discrete Fourier Transform - spread - OFDM, DFT-s-OFDM, with or without cyclic prefix for 5G NR. That is to say, in some embodiments the signal may be an OFDM signal. That is to say, in some embodiments, the signal may be related to a single carrier wave signal, such as Single Carrier - Frequency Division Multiple Access, SC-FDMA, /DFT- s-OFDM -signal. In addition, embodiments of the present invention may be exploited for multicarrier modulation, such as Cyclic Prefix, CP, -OFDM. [0050] In some embodiments of the present invention, PAPR of a signal, such as a single carrier signal, may be significantly reduced by applying a constraint which limits a set of available constellation points (i.e., limits a complete set of symbols to a subset of symbols) that may be used for modulation in a constellation diagram per time instant, such as Phase Shift Keying, PSK, modulation. Constrained modulation with PSK may be referred to as a Constrained PSK, CPSK. Embodiments of the present invention may be applied for other constellation diagrams and modulations as well. For instance, embodiments of the present invention may be applied for Amplitude and Phase Shift Keying, APSK, in general, such as for Quadrature Amplitude Modulation, QAM.

[0051] The constraint may refer to a subset of symbols that may be used for modulation at a certain time instant. That is to say, the constraint may vary from one time instant to another depending on previous symbol that was used for modulation. In some embodiments of the present invention, the constraint may be used to reduce PAPR by allowing transition at least to closest neighbours on the constellation diagram, but not to all symbols on the constellation diagram.

[0052] Moreover, in some embodiments of the present invention, a bits-to-symbol(s) mapping table may be used to improve performance of the wireless receiver uncoded Bit Error Rate, BER, operation. Performance of the wireless receiver may be improved at least for low channel coding rate operation. Selection of the mapping table may be done independently of the constellation constraint, i.e., subset of symbols to be used for modulation, but for each case similar design principles can be used to achieve good performance under severe phase noise distortion.

[0053] In addition, or alternatively, in some embodiments of the present invention mapping of bits-to-symbol(s) may be varied in time to remove distortion. For instance, if a number of options per symbol, i.e., size of a subset that may be used for modulation, requires unsymmetric mapping in a direction of rotation, the direction of asymmetry may be changed in every second symbol or group of symbols, depending on whether the current symbol or group of symbols is odd or even.

[0054] Embodiments of the present invention may be thus exploited to reduce PAPR.

For instance, CPSK in accordance with at least some embodiments of the present invention may be used to reduce PAPR compared to QPSK, and in some cases compared to pulse shaped pi/-2 Binary PSK, BPSK.

[0055] FIGURE 2 illustrates a first example of a high-level flow diagram of operations of a wireless transmitter and a wireless receiver in accordance with at least some embodiments. At steps 210 and 215, TX and RX may determine a constellation (underlying constellation to which the constraint is applied), respectively. The constellation may be referred to as a complete set of symbols of a constellation diagram for bit-to-symbol mapping. Determination of the constellation may affect PAPR and/or BER and it may be triggered externally.

[0056] In some embodiments of the present invention, external triggering may refer to defining the constellation by a control channel indicator, such as a modulation and coding scheme index in LTE and 5G NR systems, for example. The control channel indicator may point to a specific configuration written in a table or the constellation may be indicated directly by the control channel indicator. On the other hand, in some embodiments, TX and RX may always use a specific constellation in a specific system, similarly as a fixed modulation and coding scheme may be used for simple devices, such as narrowband IoT devices.

[0057] At steps 220 and 225, TX and RX may determine a number of options per time instant (defines together with the constellation the PAPR performance and also the number of bits carried by symbol), respectively. The number of options per time instant may be referred to as a subset of symbols of the constellation to be used for modulation at a certain time instant. So both, TX and RX, may determine one subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation. Determination of the number of options may affect PAPR and/or Power Spectral Density, PSD, and it may be triggered externally similarly as the determination of the constellation.

[0058] Using N=2 as an example, a first subset of symbols to be used for modulation may be determined for a first symbol based on a previous symbol selected modulation. Thus, the first subset of symbols may be associated with the first symbol. Then, a second subset of symbols to be used for modulation may be determined for a second symbol based on the first symbols, wherein the second subset of symbols may be associated with the second symbol. That is to say, the second subset of symbols may be restricted by the first symbol. The first symbol may be selected from the first subset of symbols and the second symbol may be selected from the second subset of symbols and a signal may be modulated/demodulated using the first symbol and the second symbol.

[0059] At steps 230 and 235, TX and RX may select said N consecutive symbols from the subsets of symbols to be used for modulation of M consecutive bits of a digital signal sequence. For instance, TX may map M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols.

[0060] TX and RX may also select bits-to-symbols mapping which defines the BER performance in a specific channel. The bits-to-symbols mapping may also be selected to minimize the RX complexity. The bits-to-symbols mapping may be selected from a mapping table. Selection of the number of options may affect BER, RX complexity, and/or PSD and it may be triggered externally similarly as the determination of the constellation. For instance, if TX has knowledge about a detection algorithm of RX, the mapping table may be selected to optimize the performance with a specific detector, e.g., if RX is using a differential detector. Alternatively, the mapping table may be selected so that the performance may be optimized with simpler RX detection algorithms, such as a differential detector or a coherent, memoryless detector.

[0061] At step 240, TX may modulate a signal, such as a single carrier signal, using said selected N consecutive symbols and transmit the modulated bit sequence, i.e., the modulated signal, over air interface 115 shown in FIGURE 1 to RX and upon reception of the modulated bit sequence RX may demodulate the received, modulated signal using said selected N consecutive symbols at step 245, wherein each of said N consecutive symbols is selected from an associated subset of symbols. Upon demodulating the received, modulated signal, RX may demap, i.e., determine, consecutive bits from said A consecutive symbols.

[0062] FIGURE 3 illustrates a second example of a high-level flow diagram of operations of a wireless transmitter and a wireless receiver in accordance with at least some embodiments. At step 310, TX may read a constellation, number of options per time instant and mapping table from a memory for example. Similarly, at step 315 RX may read a constellation, number of options per time instant and a mapping table from a memory. Steps 310 and 315 may be triggered by an external trigger indicating a predefined modulation, such as a predefined CPSK modulation.

[0063] At step 320, TX may perform modulation and transmit the modulated bit sequence, i.e., the modulated signal, over air interface 115 shown in FIGURE 1 to RX and upon reception of the modulated bit sequence RX may demodulate the received bit sequence at step 325.

[0064] So if for instance all these parameters, i.e., the constellation, number of options per time instant, and bits-to-symbols mapping are defined in a standard specification, such as a 3GPP standard specification similar to current modulations, the parameters may be signalled similarly as the modulation and coding scheme index for example. That is to say, in some embodiments wireless network node 120 may transmit the parameters to wireless terminal 110.

[0065] FIGURE 4 illustrates an example apparatus capable of supporting at least some embodiments. Illustrated is device 400, which may be referred to as, for example, a wireless transmitter, TX, or a wireless receiver, RX. Comprised in device 400 is processor 410, 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. Processor 410 may comprise, in general, a control device. Processor 410 may comprise more than one processor. Processor 410 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. Processor 410 may comprise at least one Qualcomm Snapdragon and/or Intel Atom processor. Processor 410 may comprise at least one Application-Specific Integrated Circuit, ASIC. Processor 410 may comprise at least one Field-Programmable Gate Array, FPGA. Processor 410 may be means for performing method steps in device 400. Processor 410 may be configured, at least in part by computer instructions, to perform actions.

[0066] 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 UE 110 or BS 120, 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.

[0067] 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.

[0068] Device 400 may comprise memory 420. Memory 420 may comprise random- access memory and/or permanent memory. Memory 420 may comprise at least one RAM chip. Memory 420 may comprise solid-state, magnetic, optical and/or holographic memory, for example. Memory 420 may be at least in part accessible to processor 410. Memory 420 may be at least in part comprised in processor 410. Memory 420 may be means for storing information. Memory 420 may comprise computer instructions that processor 410 is configured to execute. When computer instructions configured to cause processor 410 to perform certain actions are stored in memory 420, and device 400 overall is configured to run under the direction of processor 410 using computer instructions from memory 420, processor 410 and/or its at least one processing core may be considered to be configured to perform said certain actions. Memory 420 may be at least in part comprised in processor 410. Memory 420 may be at least in part external to device 400 but accessible to device 400.

[0069] Device 400 may comprise a transmitter 430. Device 400 may comprise a receiver 440. Transmitter 430 and receiver 440 may be configured to transmit and receive, respectively, information in accordance with at least one cellular or non-cellular standard. Transmitter 430 may comprise more than one transmitter. Receiver 440 may comprise more than one receiver. Transmitter 430 and/or receiver 440 may be configured to operate in accordance with Global System for Mobile Communication, GSM, Wideband Code Division Multiple Access, WCDMA, 5G/NR, Long Term Evolution, LTE, IS-95, Wireless Local Area Network, WLAN, Ethernet and/or Worldwide Interoperability for Microwave Access, WiMAX, standards, for example.

[0070] Device 400 may comprise a Near-Field Communication, NFC, transceiver 450. NFC transceiver 450 may support at least one NFC technology, such as NFC, Bluetooth, Wibree or similar technologies.

[0071] Device 400 may comprise User Interface, UI, 460. UI 460 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 400 to vibrate, a speaker and a microphone. A user may be able to operate device 400 via UI 460, 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 420 or on a cloud accessible via transmitter 430 and receiver 440, or via NFC transceiver 450, and/or to play games.

[0072] Device 400 may comprise or be arranged to accept a user identity module 470. User identity module 470 may comprise, for example, a Subscriber Identity Module, SIM, card installable in device 400. A user identity module 470 may comprise information identifying a subscription of a user of device 400. A user identity module 470 may comprise cryptographic information usable to verify the identity of a user of device 400 and/or to facilitate encryption of communicated information and billing of the user of device 400 for communication effected via device 400.

[0073] Processor 410 may be furnished with a transmitter arranged to output information from processor 410, via electrical leads internal to device 400, to other devices comprised in device 400. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to memory 420 for storage therein. Alternatively to a serial bus, the transmiter may comprise a parallel bus transmitter. Likewise processor 410 may comprise a receiver arranged to receive information in processor 410, via electrical leads internal to device 400, from other devices comprised in device 400. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver 440 for processing in processor 410. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver.

[0074] Device 400 may comprise further devices not illustrated in FIGURE 4. For example, where device 400 comprises a smartphone, it may comprise at least one digital camera. Some devices 400 may comprise a back-facing camera and a front-facing camera, wherein the back-facing camera may be intended for digital photography and the front facing camera for video telephony. Device 400 may comprise a fingerprint sensor arranged to authenticate, at least in part, a user of device 400. In some embodiments, device 400 lacks at least one device described above. For example, some devices 400 may lack a NFC transceiver 450 and/or user identity module 470.

[0075] Processor 410, memory 420, transmitter 430, receiver 440, NFC transceiver 450, UI 460 and/or user identity module 470 may be interconnected by electrical leads internal to device 400 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to device 400, 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.

[0076] FIGURE 5 illustrates a first example of constrained modulation example with 6-PSK constellation and with 4 options per time instant allowed in accordance with at least some embodiments. Constrained modulation with 6-PSK constellation and with 4 options may be denoted as C6PSK/4 modulation. FIGURE 5(a) demonstrates allowed transitions for even symbols (in this example clockwise rotation) and FIGURE 5(b) demonstrates allowed transitions for odd symbols (in this example counter-clockwise rotation).

[0077] As shown in FIGURES 5(a) and 5(b), if the previous symbol is SO for example the subset of the symbol to be selected for modulation comprises at least the closest neighbours of SO, i.e., SI and S5. The closest neighbours may refer to the closest symbols with a Euclidean distance. In some embodiments, the closest neighbours may be referred to as first-tier neighbours. The subset may also comprise the previous symbol SO. In the example of FIGURE 5(a) the subset may also comprise one second-tier neighbour S4 of the previous symbol SO. Thus, a current symbol may be associated with the subset of symbols comprising SO, SI, S4 and S5.

[0078] In the example of FIGURE 5(b) the subset may also comprise another second- tier neighbour S2 of the previous symbol SO, but not the symbol S4. Thus, a current symbol may be associated with the subset of symbols comprising SO, SI, S2 and S5. In some embodiments, the second order neighbour symbol may be selected from a particular side of the previous symbol depending on whether a symbol to be selected is odd or even.

[0079] FIGURE 6 illustrates a second example of constrained modulation example with 6-PSK constellation and with 4 options per time instant allowed in accordance with at least some embodiments. As shown in FIGURE 6, in some embodiments the previous symbol may be excluded from subset of symbols and in such a case the subset of symbols may comprise the first-tier and the second-tier neighbours of the previous symbol. So if the previous symbol is SO, the subset may comprise symbols SI, S2, S4 and S5, but not SO. That is to say, FIGURE 6 depicts transitions, wherein it is not allowed to send the same symbol in consecutive time instants. Thus, a current symbol may be associated with the subset of symbols comprising SI, S2, S4 and S5.

[0080] FIGURE 7 illustrates an example of constrained modulation example with 6- PSK constellation and with 3 options per time instant allowed in accordance with at least some embodiments. Constrained modulation with 6-PSK constellation and with 3 options may be denoted as C6PSK/3 modulation. Similarly as in FIGURE 5, FIGURE 7(a) demonstrates allowed transitions for even symbols (in this example clockwise rotation) and FIGURE 7(b) demonstrates allowed transitions for odd symbols (in this example counter clockwise rotation). In the example of FIGURE 7, the previous symbol may be excluded from the subset of symbols and in such a case the subset may comprise the first-tier neighbours of the previous symbol and one second-tier neighbour depending on whether the symbol to be modulated is odd or even, similarly as in the example of FIGURE 6. Thus, in case of FIGURE 7(a) a current symbol may be associated with the subset of symbols comprising SI, S4 and S5 and in case of FIGURE 7(b) a current symbol may be associated with the subset of symbols comprising SI, S2 and S5. In some embodiments, applying rotation per symbol (or symbol sequence) to the constellation makes it possible to avoid of using separate mappings to even and odd symbols or symbol sequences. [0081] FIGURE 8 illustrates an example of constrained modulation with 6-PSK constellation and with 4 options and with constellation rotation in accordance with at least some embodiments. To further reduce the PAPR, e.g., with CPSK modulations having 4 options per time instant, a rotation of the underlying constellation per symbol time instant may be applied. FIGURE 8(a) shows the constellation of the previous symbol and FIGURE 8(b) shows the rotated constellation to be used for the current symbol. In some embodiments, the constellation diagram from which each subset of symbols may be determined may be rotated by p/K compared to a constellation diagram of the previous symbol, wherein K denotes a number of symbols in the complete set of symbols. In FIGURE 6, symbols Si denote possible constellation points for even symbols, and Si^' denote the possible constellation points for odd symbols, where ie (0,1, 2, 3, 4, 5}. This allows a significant reduction of the PAPR, e.g., of the CPSK modulated signal with 4 options.

[0082] In some embodiments of the present invention, optimization of the PAPR and the link performance may be separate steps. First, the constellation and number of options, i.e., the subset of symbols that may be used for modulation, may be selected to achieve desired PAPR performance and spectral efficiency. After the selection of the constellation and the number of options, a proper bits-to-symbols mapping may be determined, from a mapping table for example. Said bits-to-symbols mapping may be used for improving the link performance with selected modulation, such as CPSK modulation, for example by assuming that the TX is aware of the radio environment. Alternatively, or in addition, said bits-to-symbols mapping may depend on assumptions made about RX detector implementation.

[0083] In some embodiments of the present invention, the bits-to-symbols mapping may be thus adapted to improve the link performance in a desired communications link. Some example mapping tables for the bits-to-symbols are shown below. For C5PSK/3 and C6PSK/3 modulations, two example mappings are defined in tables 1 - 4, wherein each symbol carries 1.5 bits and thus 2 symbols are required to carry 3 bits. Tables 5 and 6 denote the 4 option mapping tables for the C6PSK/4 wherein each symbol carries 2 bits and thus 1 symbol is required to carry 2 bits. Table 7 denotes the 4 option mapping table for C8PSK/4 wherein each symbol carries 2 bits. In tables 1 - 7 the top row defines the previous state (e.g., the previous transmitted symbol) and the left-hand column shows the input bits. In Tables 5-6, transitions for even/odd symbols are provided for those cases in which the direction of rotation may be changed to avoid spectrum degradation. In Table 7, transitions for even/odd symbols are provided for those cases where there is equal distance to closest candidates, in which case the direction of rotation may be changed to avoid spectrum degradation.

[0084] The mapping in tables 1, 3, and 5 may be for a differential detector, allowing detection of the modulated bit sequence based on only the symbol transitions, without coherent detection of the symbol itself. Tables 2, 4, and 6 define transition tables that maximize the number of transitions from different states leading to the same modulated bit sequence. The mapping in tables 2, 4 and 6 may be used to improve the performance with a simple, memoryless, coherent detector. In all tables, the previous symbol is shown on the top row and input bits are shown in the left-hand column.

[0085] The input bits may be referred to as M consecutive bits of a digital signal sequence, i.e., bits of an input sequence, as well. So in case of Table 1 for example, if said M consecutive bits are 000 and the previous symbol is SO, the subset of a first symbol may be determined as (SO, SI, S4} based on the previous symbol. From the subset of the first symbol, SO may be selected. Then, a subset of a second symbol may be determined as (SO, SI, S4} based on the selected first symbol. From the subset of the first symbol, SI may be selected. Thus, in this example a number of consecutive symbols N=2 and the selected symbols may be SO and SI for modulation of said M consecutive bits. The signal may be then modulated using SO and SI. That is to say, two symbols, SO and SI, may carry 3 consecutive bits.

[0086] Similarly, if said consecutive bits are 010 and the previous symbol is S3, the subset of a first symbol may be determined as (S2, S3, S4} based on the previous symbol. From the subset of the first symbol, S4 may be selected. Then, a subset of a second symbol may be determined as (SO, S3, S4} based on the selected first symbol. From the subset of the first symbol, SO may be selected. Thus, in this example a number of consecutive symbols N=2 and the selected symbols may be S4 and SO for modulation of said M consecutive bits. The signal may be then modulated using S4 and SO. Again two symbols, S4 and SO, may carry 3 consecutive bits. [0087] In some embodiments, it may be required that N>= M/log2(k), wherein k denotes a number of symbols in the subset. In some embodiments, N may be an integer. So for instance if M= 7 and k=4, then N=4, because 7/log₂(5) gives 3.01 which may be rounded up (take the ceiling) to the next integer, i.e., N=4. Table 1: Example mapping a) for C5PSK with 3 options, e.g., for a differential detector/receiver.

Mapping of table 2 may be used to maximize the similarity of bit mappings related transitions from previous state (symbol), thereby allowing minimization of the error probability with memoryless, coherent detector.

Table 2: Example mapping b) for C5PSK with 3 options, e.g., for a memoryless detector/receiver.

Table 3: Example mapping a) for C6PSK with 3 options, e.g., for a differential detector/receiver.

Table 4: Example mapping b) for C6PSK with 3 options, e.g., for a memoryless detector/receiver.

Table 5: Example mapping C6PSK with 4 options, e.g., for a differential detector/receiver.

Table 6: Example mapping b) for C6PSK with 4 options, e.g., for a memoryless detector/receiver.

[0088] Also, in Tables 1 - 4, the transition S_XS_X when previous transmitted symbol is

S_x may not be used to make the transitions over a sequence of symbols symmetric in different directions, in clockwise and counter clockwise directions, as shown conceptually in FIGURE 6 for example. Thus, transitions may be symmetric over a sequence of A transmitted symbols and some symbol combinations may not be allowed within the sequence of N transmitted symbols. The deterioration of the signal spectrum may thus be avoided. As another option, S_xS_x may be included in the possible transitions, to have mapping that changes direction from symbol sequence to another, as shown conceptually in FIGURES 5(a) and 5(b) for example.

[0089] In Table 7, an example of constrained modulation for 8-PSK constellation with 4 options and with fixed bits-to-symbols mapping per constellation point is shown and further illustrated in FIGURE 25. In this case, the constraint needs to be noted only in the transmitter, TX, side and in the receiver, RX, a traditional 8-PSK receiver may be used. For example, constrained modulation using a fixed bits-to-symbols mapping per constellation point can be done when the size of the constellation is K=b2^M.

Table 7: Mapping table for C8PSK/4 with modulation constraint only in the TX. For RX, plain 8-PSK detector can be used.

[0090] Embodiments of the present invention may be used for uplink and downlink transmission. For instance, in case of downlink transmissions the RX complexity may be similar to widely used QAM modulations if memoryless coherent detectors or differential detectors are used, but the complexity may be more critical as the RX may be a UE or other wireless terminal It should be noted that modulation, such as CPSK, may not be related to the implementation of a channel code (unlike, e.g., in traditional Trellis-coded-modulation, wherein the channel code and the modulation are optimized jointly), and may be directly implemented instead of traditional modulators in the TX chain, without effect on system specific (e.g., 5G NR) channel codec.

[0091] In some embodiments of the present invention, the detection of CPSK may be done without noting the memory, based on plain PSK detector assuming a PSK constellation over a sequence of N symbols. The detection of CPSK modulation while incorporating the memory may be done based on Trellis-based detector using well known algorithms, such as Viterbi or BCJR algorithm.

[0092] In some embodiments of the present invention, the number of options, i.e., a size of a subset of symbols that may be used for modulation, per symbol may correspond to an integer number of bits. In such a case, the Trellis of the modulation may have K states corresponding to the number of constellation points. The number of constellation points may correspond to a size of a complete set of symbols of the constellation diagram. There may then be k possible transitions from each state, following the constraint imposed on the modulation. That is to say, the size of the subset of symbols that may be used for modulation may be denoted by k. [0093] FIGURE 9 illustrates a Trellis diagram evolution example for C6PSK/4 modulation. First three symbol time instants are shown. In the example of FIGURE 9, it is assumed that first transmitted symbol 910 is set to be SO. First transmitted symbol 910 may be a previous symbol for a current symbol to be used for modulation, wherein the current symbol is denoted by 920. As previous symbol 910 may be SO, the subset of symbols for current symbol 920 may comprise symbols SO, SI, S2 and S5. Possible transitions from previous symbol 910 are denoted by 912, 914, 916 and 918 in FIGURE 9. Hence, current symbol 920 to be used for modulation may be selected from the subset comprising SO, SI, S2 and S5, i.e., the subset depends on previous symbol SO. Thus, a current symbol may be associated with the subset of symbols comprising SO, SI, S2 and S5.

[0094] If the transmission of modulated symbols, such as CPSK modulated symbols, is done in multiple blocks, it may be assumed for example that different sets of 4 initial states is allowed for transmission of 2 bits transmission over the first symbol of each CPSK block, assuming that the constellation size is at least K= 4. In some embodiments, it may also be assumed, that each block is started with a symbol or a sequence of symbols known by both, the TX and RX, which can be used as a reference signal for different purposes, such as phase noise estimation. Such block transmission may be used to allow the RX to run multiple Trellis detectors in parallel for each CPSK block.

[0095] FIGURE 10 is a flow graph of a first method in accordance with at least some embodiments. The phases of the illustrated first method may be performed by a wireless transmitter, or by a control device configured to control the functioning thereof, possibly when installed therein.

[0096] The first method may comprise, at step 1010, determining a complete set of symbols of a constellation diagram for bit-to-symbol mapping. At step 1020, the first method may comprise determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation. At step 1030, the first method may comprise mapping M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols. Moreover, at step 1040, the first method may comprise modulating a signal using said selected N consecutive symbols. Finally, at step 1050, the first method may comprise transmitting the modulated signal to a wireless receiver.

[0097] FIGURE 11 is a flow graph of a second method in accordance with at least some embodiments. The phases of the illustrated second method may be performed by a wireless receiver or by a control device configured to control the functioning thereof, possibly when installed therein.

[0098] The second method may comprise, at step 1110, receiving a modulated signal from a wireless transmitter. At step 1120, the second method may comprise determining a complete set of symbols of a constellation diagram for bit-to-symbol mapping. At step 1130, the second method may comprise determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for demodulation. Moreover, at step 1140, the second method may comprise demodulating the modulated signal using N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols. Finally, at step 1150, the second method may comprise demapping M consecutive bits from said N consecutive symbols.

[0099] FIGURE 12 illustrates a complex eye-diagram for a C6PSK with 3 options. FIGURE 13 illustrates a complex eye-diagram for a C6PSK with 4 options. From FIGURES 12 and 13 it can be seen how constraining the symbol transitions to closest symbols and limiting the number of options to 3 per symbol reduces PAPR.

[00100] FIGURE 14 illustrates a complex eye-diagram for a C8PSK with 3 options. FIGURE 15 illustrates a complex eye-diagram for a C8PSK with 4 options.

[00101] From FIGURES 12 to 15 it can be observed that reducing the number of options, with a constraint, i.e., a subset of symbols, that allows the use of the closest neighbour symbols based on Euclidian distance metric, reduces the variation around the unit circle, which would correspond to a constant envelope signal. Thus, the PAPR of the signal is reduced by decreasing the number of options, when the constellation size is fixed. Similarly, the PAPR of the signal may be reduced if the number of options is fixed, but the size of the constellation is increased. In addition, well known techniques, such as pulse shaping or frequency domain filtering, can be used to further reduce the PAPR of the CPSK modulated signal.

[00102] FIGURE 16 illustrates PSD of C6PSK/4 modulated signal without using different mapping for even and odd symbols. FIGURE 17 illustrates PSD of C6PSK/4 modulated signal when using different mapping for even and odd symbols. That is to say, FIGURE 16 illustrates PSD without changing direction of rotation between even and odd symbols and FIGURE 17 illustrates PSD when changing direction of rotation between even and odd symbols.

[00103] FIGURE 18 illustrates examples of the achievable PAPR with different constellations and with 3 options.

[00104] FIGURE 19 illustrates examples of the achievable PAPR with different constellations and with 4 options.

[00105] FIGURE 20 illustrates example of C5PSK and C6PSK with 3 options performance with two different bits-to-symbols mapping tables. The uncoded BER with memoryless receiver is shown for a system operating in a AWGN channel, illustrating that the mapping tables have significant effect on the link performance

[00106] FIGURE 21 illustrates uncoded link performance with different constellations and with 3 options per symbol. The uncoded BER for the link is shown for a system operating at 60 GHz carrier frequency, using 120 kHz subcarrier spacing, and when 3 GPP TR 38.803 Section 6.1.11 UE phase noise model is applied in the TX and RX and ideal common phase error, CPE, compensation is assumed for all modulations in the RX.

[00107] FIGURE 22 illustrates examples of the achievable PAPR with different constellations and with 4 options, when the constellation is rotated at every other symbol time instant. [00108] FIGURE 23 illustrates a complex eye-diagram for a C6PSK/4 with constellation rotation. FIGURE 24 illustrates a complex eye-diagram for a C8PSK/4 with constellation rotation. In FIGURES 23 and 24 the amount of original symbols is doubled, as both even and odd time instant constellation points are included. [00109] FIGURE 25 illustrates an example of C8PSK/4 modulation with a specific bits- to-symbols mapping (defined in Table 7) which allows to apply the constraint only in the TX. For RX this corresponds to a fixed mapping (s7=“10” always). RX may use traditional 8 PSK detector for receiving 2 symbols per bit.

[00110] It is to be understood that the embodiments disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[00111] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[00112] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and examples may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations.

[00113] In an exemplary embodiment, an apparatus, such as, for example, a wireless transmitter or a wireless receiver, may comprise means for carrying out the embodiments described above and any combination thereof. [00114] In an exemplary embodiment, a computer program may be configured to cause a method in accordance with the embodiments described above and any combination thereof. In an exemplary embodiment, a computer program product, embodied on a non-transitory computer readable medium, may be configured to control a processor to perform a process comprising the embodiments described above and any combination thereof

[00115] In an exemplary embodiment, an apparatus, such as, for example, a wireless transmitter or a wireless receiver, may comprise at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform the embodiments described above and any combination thereof

[00116] Furthermore, 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.

[00117] 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.

[00118] 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 depending 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. INDUSTRIAL APPLICABILITY

[00119] At least some embodiments of the present invention find industrial application in wireless communication systems wherein it is desirable to reduce PAPR, such as in networks operating according to 3GPP or WLAN standards. In addition, at least some embodiments of the present invention find industrial application in satellite communications and wide coverage sensor communications.

ACRONYMS FIST

3 GPP 3rd Generation Partnership Project

APSK Amplitude and Phase Shift Keying

ASIC Application-Specific Integrated Circuit

BER Bit Error Rate

BPSK Binary PSK

BS Base Station

CP-OFDM Cyclic Prefix -OFDM

CPE Common Phase Error

CPSK Constrained PSK

D2D Device-to-Device

DFT-s-OFDM Discrete Fourier Transform - spread - OFDM

FPGA Field-Programmable Gate Array

GSM Global System for Mobile communication

IoT Internet of Things

FTE Fong-T erm E vo lution

M2M Machine-to -Machine

NFC Near-Field Communication

NR New Radio

NTN N on-T errestrial N etwork

OFDM Orthogonal Frequency Division Multiplexing

PAPR Peak-to-Average Power Ratio PSD Power Spectral Density

PSK Phase Shift Keying

QAM Quadrature Amplitude Modulation

QPSK Quadrature PSK RAN Radio Access Network

RAT Radio Access Technology

RX Receiver

SC-FDMA Single Carrier - Frequency Division Multiple Access SIM Subscriber Identity Module TX Transmitter

UE User Equipment

UI User Interface

WCDMA Wideband Code Division Multiple Access WiMAX Worldwide Interoperability for Microwave Access WLAN Wireless Local Area Network

REFERENCE SIGNS LIST

Claims

CLAIMS:

1. A method for a wireless transmitter, comprising:

- determining a complete set of symbols of a constellation diagram for bit-to-symbol mapping;

- determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation;

- mapping M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols;

- modulating a signal using said selected N consecutive symbols; and

- transmitting the modulated signal to a wireless receiver.

2. A method for a wireless receiver, comprising:

- receiving a modulated signal from a wireless transmitter;

- determining a complete set of symbols of a constellation diagram for bit-to-symbol mapping;

- determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for demodulation;

- demodulating the modulated signal using N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols; and

- demapping M consecutive bits from said N consecutive symbols.

3. A method according to claim 1 or claim 2, wherein each subset of symbols to be used for modulation at the time instant comprises at least neighbour symbols of the previous symbol.

4. A method according to any of the preceding claims, wherein the determination of the complete set of symbols and/or the determination of the subsets of symbols to be used for modulation comprises optimisation of peak-to-average power ratio of the transmitted signal.

5. A method according to any of the preceding claims, further comprising: - selecting a bit-to-symbol mapping table; and - selecting said N consecutive symbols based on the selected bit-to-symbol mapping table.

6. A method according to claim 5, wherein the selection of bit-to-symbol mapping table comprises selection for reducing error rate of a decoded signal at the receiver.

7. A method according to claim 5 or claim 6, wherein the selection of bit-to-symbol mapping table comprises selection for reducing complexity of the receiver.

8. A method according to any of claims 5 to 7, wherein the bit-to symbol mapping table is selected such that a number of changing bits per the selected N consecutive symbols depends on a Euclidean distance between the symbols.

9. A method according to any of the preceding claims, wherein each subset of symbols to be used for modulation comprises at least 1, 2, 3 or 4 of symbols closest on the constellation diagram to a symbol used for modulation at a previous time instant.

10. A method according to any of the preceding claims, wherein each subset of symbols to be used for modulation further comprises a symbol used at a previous time instant.

11. A method according to any of the preceding claims, wherein the constellation diagram from which each subset of symbols is determined is rotated by p/K compared to a constellation diagram of the previous symbol, wherein K denotes a number of symbols in the complete set of symbols.

12. A method according to any of the preceding claims, wherein a size of the subsets of symbols to be used for modulation is four symbols and each subset comprises the symbol used for modulation at a previous time instant, first-order neighbour symbols of the previous symbol and one second-order neighbour symbol of the previous symbol.

13. A method according to claim 12, wherein the second-order neighbour symbol is selected from a particular side of the previous symbol depending on whether a symbol to be selected is odd or even.

14. A method according to any of the preceding claims, wherein a number of symbols in the complete set of symbols is at least three and at most eight.

15. A method according to any of the preceding claims, wherein said M consecutive bits are jointly mapped to said N consecutive symbols.

16. A method according to any of the preceding claims, wherein M=3 or M=4 and N=2.

17. A method according to any of the preceding claims, wherein M/N is a fraction.

18. A method according to any of the preceding claims, wherein

N>= M/log2(k), k denotes a number of symbols in the subset and N is an integer.

19. A method according to any of the preceding claims, wherein the determination of the subset and/or the complete of symbols comprises at least one of the following:

- determination based on external trigger; determination based on executing optimisation algorithm and determination based on pre-defined setting.

20. A method according to any of the preceding claims, wherein the selection of bit-to- symbol mapping comprises at least one of the following:

- Selection based on the determined subset and/or the complete of symbols; selection based on external trigger; selection based on executing optimisation algorithm and selection based on a pre-defined setting.

21. A method according to any of the preceding claims, wherein the subsets of symbols are of the same size.

22. 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 at least to perform:

- determine a complete set of symbols of a constellation diagram for bit-to-symbol mapping;

- determine a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation;

- map M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols;

- modulate a signal using said selected N consecutive symbols; and

- transmit the modulated signal to a wireless receiver.

23. An apparatus according to claim 22, wherein the at least one memory and the computer program code are further configured to, with the at least one processing core, cause the apparatus at least to perform a method according to any of claims 3 - 21.

24. 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 at least to perform:

- receive a modulated signal from a wireless transmitter;

- determine a complete set of symbols of a constellation diagram for bit-to-symbol mapping;

- determine a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for demodulation;

- demodulate the modulated signal using N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols; and

- demap M consecutive bits from said N consecutive symbols.

25. An apparatus according to claim 24, wherein the at least one memory and the computer program code are further configured to, with the at least one processing core, cause the apparatus at least to perform a method according to any of claims 3 - 21.

26. An apparatus comprising:

- means for determining a complete set of symbols of a constellation diagram for bit- to-symbol mapping;

- means for determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for modulation;

- means for mapping M consecutive bits of an input sequence to N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols;

- means for modulating a signal using said selected N consecutive symbols; and

- means for transmitting the modulated signal to a wireless receiver.

27. An apparatus according to claim 26, further comprising means for performing a method according to any of claims 3 - 21.

28. An apparatus comprising:

- means for receiving a modulated signal from a wireless transmitter;

- means for determining a complete set of symbols of a constellation diagram for bit- to-symbol mapping;

- means for determining a subset of symbols for each of N consecutive symbols out of the complete set of symbols, wherein each subset is associated with one symbol and each subset is determined based on a previous symbol selected for demodulation;

- means for demodulating the modulated signal using N consecutive symbols, wherein each of said N consecutive symbols is selected from an associated subset of symbols; and

- means for demapping M consecutive bits from said N consecutive symbols.

29. An apparatus according to claim 28, further comprising means for performing a method according to any of claims 3 - 21.

30. A non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform a method according to any of claims 1 - 21.

31. A computer program configured to perform a method according to any of claims 1 - 21.