Communication using MFSK modulation in an OFDM transmitter

Abstract

A transmitting apparatus and method for low signal-to-noise ratio, SNR, communications. An example method comprises transmitting (610) in a first mode, in which an Orthogonal Frequency Division Multiplexing, OFDM, waveform having an OFDM symbol length is formed using Inverse Discrete Fourier Transform, IDFT, functionality and transmitted. The method further comprises transmitting (620) in a second mode, in which an integer number of multiple-frequency-shift keying, MFSK, symbols per the OFDM symbol length are formed using the same IDFT functionality and transmitted, and selectively switching (605) between transmitting in the first mode and transmitting in the second mode. In embodiments, switching between the first and second transmission modes may be based on an estimate of signal-to-noise ratio, SNR, for a received signal and a target symbol-error-rate.

Description

[0001] P112076W001

[0002] COMMUNICATION USING MFSK MODULATION IN AN OFDM TRANSMITTER

[0003] TECHNICAL FIELD

[0004] The present disclosure is generally related to radio transmitters and is more particularly related to the design of transmitters for lowsignal-to-noise ratio (SNR), multiple frequency-shift keying (MFSK)-based, Orthogonal Frequency-Division Multiplexing (OFDM) communication.

[0005] BACKGROUND

[0006] In recent generations of cellular systems, Orthogonal Frequency-Division Multiplexing (OFDM) modulation is used, providing efficient ways to handle effects of delay spread in the wireless channel. This serves most communication scenarioswell, and the communication equipment is thus customized to this type of modulation, typically with dedicated hardware to perform the Fast Fourier Transforms (FFTs), inverse-Fast Fourier Transforms (iFFTs), and other operations that underly most OFDM transceiver implementations. However, OFDM modulation is not ideal for all scenarios - in some situations, different types of modulations may be beneficial.

[0007] In G. Al-Juboori, etal., “A Comparison of OFDM and GFDM-based MFSK Modulation Schemes for Robust loT Applications”, IEEE, 2017, a modulation scheme called OFDM-MFSK is presented, to improve communication performance of OFDM equipment in low-SNR conditions. In International Patent Application Publication WO 2024 / 186248 A1, filed 28 February 2024, the use of continuous-phase MFSK modulation (Multiple Frequency-Shift Keying, interchangeably known as M-ary Frequency-Shift Keying) in an OFDM system for a wake-up-signal (WUS) is proposed. In the latter reference, the authors applied time-shift to align the cyclic prefix. According to the proposed scheme, the transmitter side is configured to transmit MFSK symbol in an OFDM symbol usingP112076W001

[0008] OFDM modulation. The receiver node includes first and second receivers, where the second receiver (configured to receive MFSK transmission) consumes less operation power than first receiver (configured to receive OFDM transmission), and where the second receiver is configured to wake up the first receiver when a WUS is received.

[0009] In the G. Al-Juboori publication referenced above, the authors describe OFDM-MFSK and Generalized Frequency Division Multiplexing (GFDM)-MFSK systems intended to enable low SNR communication for internet-of-Things (loT) applications. The described OFDM-MFSK system groups sub-carriers into groups of sub-carriers and then applies MFSK modulation in each group by making the amplitude of just one of the sub-carriers non-zero. Each MFSK symbol then occupies the same time duration as one OFDM symbol. In the described GFDM-MFSK system, by contrast, multiple MFSK symbols are transmitted in consecutive time intervals within one GFDM symbol, where the GFDM symbol interval is the same as an OFDM symbol interval. Notably, however, the GFDM transceiver chain is more complicated than a regular OFDM transmitter.

[0010] One issue with the OFDM-MFSK and GFDM-MFSK schemes described above is that multiple MFSK frequency tones are transmitted simultaneously, one per sub-carrier group, which creates high peak-to-average power ratio (PAPR). (The term “tone” or “frequency tone” as used herein refers to a specific frequency alternative, among several possible alternatives, where the MFSK modulation maps particular data values to each of the alternatives.) This leads to out-of-band (OOB) emissions, which in the case of long-range transmissions lead to spectrum leakage and potential interference to devices not targeted by the transmitter, over a large geographical area. This can be especially severe in the case of above-the-horizon (AtH) transmissions, such as transmissions for drone communication, which may interfere with satellite communications. In addition, designing aP112076W001

[0011] new GFDM transceiver is costly, and the GFDM scheme is largely incompatible with existing products for OFDM-based systems.

[0012] The International Patent Application Publication WO 2024 / 186248 A1 referenced above addresses a simple OFDM-based MFSK symbol mapping that is not optimized to achieve the highest possible data rates, as the target application, i.e. , WUS, doesn’t require it. The authors mapped one MFSK symbol to each OFDM symbol, which is not desirable for transmitting communication data. In addition, the proposed multi-tone MFSK does not have a constant envelope for each MFSK symbol, which again might cause undesirable out-of-band emissions.

[0013] SUMMARY

[0014] Embodiments of the inventive techniques, apparatuses, and systems described herein address at least some of these problems by providing a transmitter that selectively switches between transmitting with a conventional OFDM waveform, having a certain OFDM symbol length, and transmitting in a mode in which one or more MFSK symbols are transmitted within that same OFDM symbol length. The latter mode may be selected, in various embodiments, based on SNR conditions, and / or direction of transmission, and / or one or more other factors.

[0015] An example method in a transmitting apparatus thus comprises transmitting in a first mode, in which an OFDM waveform having an OFDM symbol length is formed using Inverse Discrete Fourier Transform (IDFT) functionality and transmitted and transmitting in a second mode, in which an integer number of MFSK symbols per the OFDM symbol length are formed using the same IDFT functionality and transmitted. This example method further comprises selectively switching between transmitting in the first mode and transmitting in the second mode.P112076W001

[0016] A corresponding transmitting apparatus, according to various embodiments, comprises radiofrequency (RF) transmitter circuitry and processing circuitry operatively coupled to the RF transmitter circuitry, where the processing circuitry is configured to use the RF transmitter circuitry to transmit in a first mode, in which an OFDM, waveform having an OFDM symbol length is formed using IDFT functionality and transmitted, as well as to transmit in a second mode, in which an integer number of MFSK symbols per the OFDM symbol length is formed using the same IDFT functionality and transmitted. The processing circuitry is further configured to selectively switch between transmitting in the first mode and transmitting in the second mode.

[0017] Advantages arising from at least some embodiments of the techniques and apparatuses described in detail below include that MFSK symbols can be transmitted with peak power while achieving low OOB emission, using hardware commonly found in conventional OFDM transmitters. In scenarios or situations when regular OFDM transmissions do not work, e.g., when a required symbol error rate is not satisfied due to low SNR, it is possible to switch from OFDM transmissions to use of an MFSK waveform, using the same transmitter hardware to perform the required communication.

[0018] Embodiments may also be used in scenarios involving communicating with far away drones or loT devices, where the use of the techniques described herein can reduce interference caused by OOB emissions.

[0019] Further details and advantages of these and other embodiments are provided in the attached figures and the detailed description that follows.

[0020] BRIEF DESCRIPTION OFTHE FIGURES

[0021] Figure 1 is a block diagram of a system model of the transmitting and receiving chains.

[0022] Figure 2 shows mapping of MFSK symbols to an OFDM symbol interval.P112076W001

[0023] Figure 3 illustrates a comparison of the number of bits that can be transmitted per OFDM symbol interval, for a symbol error rate (SER) less than 1%, for various combinations of M and N.

[0024] Figure 4 is a process flow diagram illustrating an example control scheme for switching between OFDM and OFDM-based MFSKtransmissions.

[0025] Figure 5 is a block diagram illustrating components of an example transmitter, according to some embodiments described herein.

[0026] Figure 6 is an example method, accordingto some embodiments.

[0027] Figure 7 is a block diagram of an example transmitting apparatus in which techniques described herein may be implemented.

[0028] DETAILED DESCRIPTION

[0029] As discussed briefly above, while OFDM transmitters are widely used, conventional OFDM transmissions are not optimal for some low-SNR scenarios. While many alternative modulation schemes, including MFSK, are well known, various implementations of these schemes may generate excessive OOB emissions and / or require the use of new hardware designs that cannot readily re-use existing OFDM hardware. Thus, various embodiments of the techniques, apparatuses, and systems described provide a transmitter that selectively switches between transmitting with a conventional OFDM waveform, having a certain OFDM symbol length, and transmitting in a mode in which one or more MFSK symbols are transmitted within that same OFDM symbol length. The latter mode may be selected, in various embodiments, based on SNR conditions, and / or direction of transmission, and / or one or more other factors.P112076W001

[0030] When an SNR estimate is used to determine which mode should be used for transmitting, the SNR may be estimated in the receiver targeted by or to be targeted by the transmission, in some embodiments, and fed back to the transmitting device, e.g., using previously standardized mechanisms and / or using new messaging. Alternatively, in some embodiments, the SNR may be estimated in a receiver co-located with the transmitter, and attributed (possibly with adjustments) to the targeted receiver, e.g., based on an assumption that the channels in each direction are reciprocal or approximately reciprocal.

[0031] In either case, if the estimated SNR is below a certain limit, a switch to MFSK may be performed for coming transmission. There can also be different MFSK settings used, depending on the SNR. In otherwords, the mode of transmission involvingthe use of MFSK symbols may be one of multiple target modes, or sub-modes, with those multiple target modes having, for example, different combinations of (a) number of bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol, based on the estimate of SNR and (b) a target symbol-error rate (SER) or target bit-error rate (BER). Again, an MFSK “tone,” or alternatively an MFSK frequency or MFSK frequency alternative, is a selected one of several possible tones or frequencies, where the MFSK modulation maps data bits to particular ones of those tones or frequencies. An MFSK mapping scheme is thus based on a number of MFSK tone alternatives per symbol. Thus, for example, if there are four MFSK tone alternatives per MFSK symbol, the mapping process maps each possible value for two data bits to one of the four MFSK tone alternatives. As another example, if there are 32 MFSK tone alternatives, each possible for a group of five bits can be mapped to one of the 32 MFSK tone alternatives.

[0032] According to various embodiments, the MFSK signal is transmitted using a regular FFT-based OFDM transmitter, e.g., an OFDM transmitter designed for transmitting signals according to 3GPP’s 4G or 5G standards or according to standards and specifications for Wi-Fi transmitters. The MFSK signalP112076W001

[0033] can have multiple symbols per OFDM symbol, which are generated in the time domain, and then taken to the frequency domain by an IFFT, so that the signal can be processed by the regular OFDM transmitter. The MFSK symbol duration may be chosen as an integer fraction of an OFDM symbol duration, with the specific fraction depending on the SNR in some embodiments. The number of frequency alternatives in the MFSK modulation may then be chosen in a trade-off between error rate and bit rate. The cyclic prefix of the OFDM transmitter is beneficial in reducing the effects of multipath propagation on signal reception.

[0034] In some embodiments, control communication between transmitter and receiver can take place using the longest MFSK symbols, with few frequency alternatives, to ensure control communication in very low SNR. This may be done by default, in some embodiments, such that this control communication can be used to set up a communication link, for example, and to agree upon or signal what modulation parameters should subsequently be used.

[0035] MFSK modulation, as an alternative to “normal” OFDM transmission, can be used to improve coverage in low SNR. Alternatively or in addition, it can be used when communicating in sensitive directions, e.g., when the transmission is an above-the-horizon (AtH) transmission. A determined direction of transmission can be used in addition to or instead of SNR as a criteria for switching from OFDM to MFSK.

[0036] A system model suitable for evaluating the performance of the proposed solution is shown in Figure 1. This model has been evaluated in a Matlab simulation environment to show the benefits of the proposed solution as compared to a conventional OFDM system. Note that Figure 1 does not show a complete transmitter and receiver and does not represent an illustration of the invention itself, but shows blocks that form part of the system model. Details of how an example OFDM-MFSKP112076W001

[0037] transmitter may reuse certain components of an OFDM transmitter to implement the solutions described herein are provided further below, in connection with Figure 5.

[0038] As seen in Figure 1, the transmitter side of the illustrated model takes, as input, random bits as shown at block 110. In practical applications, the input will generally not be random bits, but data that is arbitrarily generated, e.g., to convey commands and / or application / user data. The transmitter side further includes time-domain MFSK-symbol mapping functionality, as well as phase accumulation or correction, as shown at block 120. The function of this block depends on how many bits are mapped to each MFSK symbol, which in turn depends on how many frequency tones / frequency alternatives are used for the MFSK modulation. In some embodiments, this number may vary, depending on conditions, in which case the mapping functionality of block 120 will vary accordingly. The phase accumulation or correction functionality of block 120 ensures that the time-domain output of this block will have a continuous phase.

[0039] The remaining blocks on the transmitter side include up-sampling and filtering block 125, filter delay computation and compensation block 130, and analog / RF / power amplifier block 135, the latter of which may include various combinations of digital-to-analog conversion, amplification, filtering, and up-conversion. Some or all of these may be re-used from a conventional OFDM transmitter, when implementing the inventive techniques described herein.

[0040] On the receiver side, the system model includes decimation and filter block 140, symbol extraction & correlation block 145, symbol detection block 150, demapping block 155, and received bit sequency & SER computation block 160. In practical implementations, these blocks may be based on re-use and / or adaptation of circuit blocks from conventional OFDM receivers.P112076W001

[0041] As can be seen, on the transmitter side, randomly generated bits are mapped to MFSK symbols, where each symbol consists of L = log2(M) bits. M is the number of MFSK frequency / tone alternatives that are available to represent each symbol. For example, if M = 32, then L (one MFSK symbol) becomes 5 bits.

[0042] The distance between each MFSK tone / frequency alternative is defined by (1 ):

[0043]

[0044] where BW is the bandwidth and T^yF^ is the MFSK symbol period. The bandwidth BW is the bandwidth to be used by the system for the transmission - it may be the total bandwidth made available to the transmitter for the transmission, in some embodiments, in which case it provides for the most robust transmissions in low SNR conditions, or in some portion of the total available bandwidth, in others. The MFSK symbol period is dependent on the number of MFSK symbols (N) to be included in each OFDM symbol period

[0045]

[0046] as described in equation (2):

[0047] TSymb (?) rpSymb > ‘ OFDM ' '

[0048] ‘ MFSK ~

[0049] Again, including only one MFSK symbol per OFDM symbol period provides for the greatest degree of robustness, in adverse signal conditions, but actual signal conditions may allow for the use of multiple MFSK symbols per OFDM symbol period to improve data throughput.

[0050] Figure 2 shows the time-frequency resource mapping of MFSK symbols in an OFDM symbol in an OFDM-based-MFSK system according to the presently disclosed techniques. In the example of Figure 2, M = 8 and N = 16.P112076W001

[0051] The total number of information bits I that can be packed in each OFDM symbol is a function of N and L as in Equations (3) and (4).

[0052] I = N * L (3)

[0053] I = N log2M (4)

[0054] Once the frequency separation, fd, is defined then each of the MFSK frequency tones (ft) are defined as in Equation (5).

[0055] ft = fc+ (2i - 1 - M) * fd(5)

[0056] where fcis the carrier frequency and i e [1, 2, ...M], The basics of MFSK modulation are described in, for example, Chapter 7 of C. Beard and W. Stallings, Wireless Communication Networks and Systems, 1stEdition, 2016.

[0057] Based on the above parameters, the time domain in-phase and quadrature components of the signal are generated, e.g., using time-domain MFSK symbol mapping block 120 of Figure 1. This is shown in Equation (6), where A is the amplitude and t is a time vector for the duration of an MFSK symbol. Using conventional OFDM hardware, this may be done by mapping a non-zero value to only a single one of the OFDM subcarrier frequencies in the available bandwidth, with that OFDM subcarrier frequency corresponding to one of the M MFSK frequencies / tones. Alternatively, an MFSK tone could occupy multiple OFDM subcarriers, such that a non-zero value is mapped to each of two or more adjacent OFDM sub-carriers, in which case the resulting MFSK tone is wider than an OFDM subcarrier. Simulations indicate improved performance when the MFSK “subcarrier” formed in this way occupies more bandwidth than a single OFDM subcarrier. (When discussing MFSK, the terms “MFSK frequency” or “MFSK tone” may be used interchangeably.”) To eliminate the phaseP112076WG01

[0058] discontinuity, a phase accumulation and correction is applied, e.g., using phase accumulation and correction block 120 in Figure 1 :

[0059] x = Acos(2nfit) + Asin 2nfit) (6)

[0060] Then an up sampling and anti-alias filtering of the signal follows, e.g., as shown at up-sampling block and filtering block 125 in Figure 1, before it is fed to analog, radio-frequency (RF), and power amplifier (PA) components, as shown at block 135. Because the techniques described herein produce constant envelope signals, distortion from non-linearities in the output stages, especially from the PA, are minimized. For the system model, a non-linear 3rd-order memoryless power amplifier (PA) can be used to validate the techniques. This may be modeled, for example, as in Equation (7):

[0061] y = ct* x + c2* x3(7)

[0062] where x is an input signal to the PA, ct= l, and c2= —0.0006 are the coefficients of the polynomial and y is the output of the PA. Then the output of the PA is fed to an antenna to be transmitted.

[0063] The radio channel through which the transmitted signal passes before it reaches the receiver may be modeled as an additive white Gaussian noise (AWGN) channel with zero-mean and variance a2drawn from normal distribution n~N(0, o-2). At the receiver, the signal gets decimated and filtered, e.g., using decimation and filtering block 140 in Figure 1 , before the symbol extraction (shown at block 145 in Figure 1), by computing the correlation of each of the symbols against the list of frequencies defined in Equation (5). The symbol detection, shown at block 150 in Figure 1, is performed by finding which signal frequency ft has the highest correlation to the received signal.P112076W001

[0064] Then, demappingof symbols to bits is performed, e.g., as shown at block 155 in Figure 1, followed by a symbol error rate (SER) computation, e.g., as shown at block 160.

[0065] In some implementations of the techniques described herein, the number of MFSK symbols per OFDM symbol used for transmission may be communicated, via a control signal, to the receiver to assist the decoding. (Some embodiments or implementations may use only a single option of MFSK symbols per OFDM symbol, in which case this communication may be unnecessary, or replaced with signaling that, for example, simply indicates that the mode of transmission has changed from OFDM to MFSK.) In various embodiments, this control communication may be handled via only a few MFSK symbols (i.e., the longest MFSK symbols), with few frequency alternatives, to support communication in very low SNR. As an example, the parameters M=8 and N=8, might be used.

[0066] Figure 3 illustrates a comparison of the number of bits that can be transmitted per OFDM symbol interval, for a symbol error rate (SER) less than 1 %, for various combinations of M and N. Notably, the illustrated combinations of M and N can be used to support reliable transmissions of data at SNRs ranging from approximately 5 dB down to about -26 dB. In comparison, while conventional OFDM modulation using data symbols modulated with BPSK, 4-QAM, QPSK, 16-QAM, and 64-QAM modulations can support transmission of a higher number of bits per OFDM symbol, e.g., from about 4.3 bits / OFDM symbol to 5 bits / OFDM symbol, the minimum SNR needed to achieve an SER less than 1% with these scheme ranges from about 7 dB to over 24 dB. The illustration in Figure 3 is based on the system model described above; differing models will provide different results.

[0067] Likewise, different choices of SER or bit-error rate (BER) may be used, and will also provide different results.

[0068] Thus, the conventional OFDM waveform is suited for high SNR and high data rate transmission. Figure 3 shows that OFDM-based-MFSK as described herein, on the other hand, is suited for lowP112076W001

[0069] SNR transmissions, while maintaining a reasonable data rate for an extended range of SNRs.

[0070] OFDM-based-MFSKand regular OFDM waveforms may thus be selectively used depending on the SNR level.

[0071] As can be seen in the figure, smaller values of M and N generally allow for robust communication at lower SNRs, but the specifics vary in ways that are not straightforward. For example, Figure 3 shows that an SER less than 1% can be achieved at SNRs greater than -20 dB using M / N combinations of 64 / 8, 8 / 16, 64 / 16, and 512 / 16, among several others, but the numberof bits transmitted per OFDM symbol interval varies for each of these schemes. In some embodiments or implementations, a look-up table may be used to select from among multiple M / N combinations or, equivalently, L / N combinations, since L, the number of bits per MFSK symbol, is directly related to M, the number of MFSKfrequencies / tones. Such a table may be indexed by estimated SNR or by ranges of estimated SNR, with each table entry specifying the combination of M / N (or L / N) that yields the best throughput for the given SNR or SNR range. Note that such a look-up table is specific to a chosen target for maximum SER or maximum BER. Multiple look-up tables, based on different SER or BER targets, may be used in embodiments or instances where different targets for maximum SER or BER may be used at different times.

[0072] Figure 4 illustrates a process flow diagram illustrating an example control scheme for switching between the two types of waveforms, i.e., for switching between the use of OFDM and OFDM-based MFSK as described herein.

[0073] As shown at block 410, the illustrated process begins with measuring or estimating an expected SNR for a next transmission. This measurement or estimate is compared to a threshold, as shown at block 420. If the expected SNR is greater than the threshold, then transmission can be performed using a conventional OFDM waveform, as shown at block 430. Otherwise, if the SNR is less than theP112076W001

[0074] threshold (or, depending on the specific implementation, less than or equal to the threshold), then transmission is performed using an MFSK-based-OFDM waveform as described herein. This is shown at block 440.

[0075] As an example, given the minimum SNR requirements for each of the various alternatives for OFDM-based MFSK transmission shown in Figure 3, the threshold SNR level for switching between the two waveform types, shown in Figure 4 as SNRthresh, might be set to 4dB, for a given implementation, to satisfy a maximum SER of 1%.

[0076] Transmitting with an MFSK-based-OFDM waveform includes picking a configuration for the MFSK-based-OFDM waveform, e.g., selecting a combination of the parameters M and N discussed above. This is shown at block 450 of Figure 4. For a fixed SNR, increasing the number of MFSK frequencies M increases data rate while satisfying the required SER. Moreover, when SNR increases, it is beneficial to increase the number of MFSK symbols per OFDM symbol, N, to achieve a higher data rate. This is highlighted at block 450 of the flowchart of Figure 4, in terms of picking the configuration for the tuple <M, N> that ensures the highest bit rate per an OFDM symbol. In some embodiments, the different combinations of <M, N> and their corresponding bit rates can be stored in the transmitting device, in a database, or calculated on the fly. In some embodiments or implementations, a look-up table may be used to select from among multiple <M, N> combinations or, equivalently, <L, N> combinations, since L, the number of bits per MFSK symbol, is directly related to M, the number of MFSKfrequencies / tones. Such a table may be indexed by estimated SNR or by ranges of estimated SNR, with each table entry specifying the combination of M / N (or L / N) that yields the best throughput for the given SNR or SNR range. In some embodiments, e.g., where the device is very far from the base station or in a bad signaling condition, then the SNR measurement / estimation could be performed for a transmission that uses OFDM-based-MFSKP112076W001

[0077] based transmission with the lowest bit rate and lowest configuration <M, N> (e.g., <8, 8>) before starting the actual data transmission.

[0078] Referring backto Figure 3, it can be seen that for a given minimum SNR level, e.g., minimum SNR = 4dB, there are several configurations for <M and N> that satisfy the SER requirement of .001. These show up in Figure 3 as groups of configurations, e.g., the group of <8, 256>, <16, 256>, <32, 256>, <64, 256> satisfies the condition of a minimum SNR of 4 dB. In each of these groups of configurations, N is fixed while M varies from 8 to 64. Thus, to choose the best configuration, the amount of information bits that can be transmitted for each configuration is computed based on equation (4). For the group just mentioned, 11 = 768 bits, I2 = 1024 bits, I3 = 1280 bits, and I4 = 1536 bits. The number of bits between the lowest configuration, <8, 256>, to the highest, <64, 256>, has

[0079] increased by a factor of ^4, where M4andMtare the number of MFSK frequencies that

[0080] represent each MFSK symbol for the highest and lowest configurations, respectively. It is therefore advantageous to choose the highest configuration with configuration M4.

[0081] Similarly, when comparing configurations for two SNR values, e.g., SNR = 4dB with SNR = -8dB, for SNR = 4dB configuration <64, 256> will be chosen based on above description and for SNR = -8dB configuration <128, 128> will be selected. However, if the number of frequencies for MFSK symbols is fixed to 64, i.e., selecting <64, 128> for SNR = -8dB for easy comparison, the number of bits for configuration <64, 256> is I2 = 1536 bits and for configuration <64, 128> becomes 11 = 768 bits.

[0082] N

[0083] Then the increase in number of bits from 11 to I2 is proportional to the ratio . Thus, increasing SNR

[0084]

[0085] improves the number of bits proportional to the number of MFSK symbols that can be used per OFDM symbol at higher SNR.P112076W001

[0086] Simulations, e.g., with M = 256, N=512, and SNR = 4dB, have shown that normalized signals at the input and output of the power amplifier exactly overlap one another, indicating that the non-linear effects of the PA do not appreciably affect the MFSK waveform. The insensitivity to non-linear effects in the PA is a desirable characteristic to reduce or eliminate unwanted out-of-band (OOB) emissions, especially when communicating over long range.

[0087] Figure 5 is a block diagram illustrating a simplified viewof transmitter circuitry configured to implement the techniques described above. The illustrated transmitter circuit includes processing circuitry 510, which produces data for use in generating a conventional CP-OFDM waveform. This may be user data and / or control data, in various instances or examples. Processing circuitry 510 may convert binary data to data symbols, e.g., using Quadrature Phase-Shift Keying (QPSK), 16-quadrature amplitude modulation (16-QAM), etc., and output these data symbols in parallel form for input to IDFT functionality. In parallel with processing circuitry 510 is OFDM- MFSK waveform generation circuitry 520, which is configured to produce one (or more) of the OFDM-MFSK waveforms discussed above. Like processing circuitry 510, OFDM-MFSK waveform generation circuitry 520 may be configured to provide the OFDM-MFSK waveform in the form of data symbols, in parallel form, for input to the IFFT (or, more generally, Inverse Discrete Fourier Transform, IDFT) functionality.

[0088] Mode selection circuitry 530 is configured to select between the outputs of processing circuitry 510 and OFDM-MFSK waveform generation circuitry 520. This selection, as described in detail elsewhere herein, may be based on SNR and / or direction of transmission, for example, and is represented in Figure 5 as switching between the outputs from processing circuitry 510 and OFDM-MFSK waveform generation circuitry 520. It will be appreciated that processing circuitry 510, OFDM-MFSK waveform generation circuitry 520, and mode selection circuitry 530 may beP112076W001

[0089] implemented using one or more digital signal processors, microprocessors, microcontrollers, or the like, alone or in combination with specialized digital circuitry, and that the illustrated switch driven by mode selection circuitry 530 may thus be implemented within a processor or microcontroller, using appropriately configured firmware and / or software.

[0090] The output from processing circuitry 510 orOFDM-MFSK waveform generation circuitry 520, as selected by mode selection circuitry 530, is supplied to the inverse Fast-FourierTransform (IFFT) circuitry 540. In some embodiments, OFDM-MFSK waveform generation circuitry 520 may include a Fast Fourier Transform (FFT) to convert a time-domain input signal to the frequency-domain input provided to IFFT circuitry 540. The IFFT is an efficient algorithm for computing an IDFT, and thus represents an example (albeit a widely used example) of IDFT functionality -its use in OFDM transmitters is extensive and well understood. The output of IFFT circuitry 540 is followed by parallel-to-serial converter 550 and cyclic-prefix insertion 560 -these, again, are widely used in OFDM transmitters and well-understood. IFFT circuitry 540, parallel-to-serial converter 550, and cyclic-prefix (CP) insertion 560 may be implemented using one or more digital signal processors, microprocessors, microcontrollers, or the like, alone or in combination with specialized digital circuitry.

[0091] When the input to the IFFT circuitry 540 is from processing circuitry 510, the signal supplied to RF circuitry 570 corresponds to a conventional OFDM waveform transmitted by RF circuitry 570, PA 580, and antenna 590, e.g., as used in 4G and 5G communications. When the input to the IFFT circuitry 540 is from OFDM-MFSK waveform generator 520, on the other hand, the signal supplied to RF circuitry 570 corresponds to an OFDM-MFSK waveform transmitted by RF circuitry 570, PA 580, and antenna 590. In either case, the output from CP insertion 560 may be provided to radiofrequency (RF) circuit 570, which may include various combinations of digital-to-analogP112076W001

[0092] conversion, amplification, filtering, and up-conversion, with the RF output from RF circuit 570 then being supplied to power amplifier (PA) 580 and antenna 590. As discussed above, OOB emissions radiated from antenna 590 will generally be lower in the mode in which an OFDM-MFSK waveform is used, than when a conventional OFDM waveform is used. The IDFT-based processing-the processing including IFFT circuitry 540 in this example, can be used, without change, in both of these modes.

[0093] Keeping all of the above details and examples in mind, it will be appreciated that Figure 6 is a process flow diagram illustrating an example method for facilitating low-SNR communications, according to several embodiments and instances of the techniques described herein. Note that the process illustrated in Figure 6 is intended to be a generalization of and to encompass many, if not all, of the transmitter-based techniques described above, and thus where there are differences between the terminology used to describe Figure 6 and that used in the discussion above, the terminology used to describe Figure 6 should be understood to at least encompass the related terminology used above, unless the context clearly indicates otherwise.

[0094] As shown at block610, the method comprises transmitting, in a first mode, in which an OFDM waveform having an OFDM symbol length is formed and transmitted. This may be performed with IDFT functionality, e.g., processing that utilizes an IFFT, as described in examples above. As shown at block 620, the method further comprises transmitting in a second mode, in which an integer number of MFSK symbols per the OFDM symbol length are formed and transmitted. The integer number of MFSK symbols per the OFDM symbol length may be greater than one, in some embodiments. The same IDFT functionality may be used to form the resulting OFDM-MFSK waveform as was used for generating the OFDM waveform. The steps shown at blocks 610 and 620 can occur in either order, and may be alternately selected, to switch between the two modes. Thus,P112076W001

[0095] as shown at block 605, the method comprises selectively switching between transmitting in the first mode, as in block610, and transmitting in the second mode, as in block620. In any ofvarious embodiments, this selective switching may be based on any one or more of: an estimate of SNR or other signal quality estimate for a received signal, an indication of signal quality (e.g., SNR) for a previous transmission by the transmitting apparatus, and a direction of transmission. The estimate of SNR may be obtained from a receiver co-located with the transmitting apparatus, for example. As another example, the estimate of SNR or the indication of signal quality may be received over a radio link from a remote apparatus.

[0096] As was discussed in some of the examples described above, selectively switching between transmitting in the first mode and transmitting in the second mode may comprise selecting, for the second mode, from among a plurality of choices for a number of MFSK symbols per the OFDM symbol length, based on the estimate of SNR and a target SER or target bit-error rate (BER). In some embodiments or instances, selectively switching between transmitting in the first mode and transmitting in the second mode as shown at block 605 may comprise selecting, for the second mode, from among a plurality of choices for a number of bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol, based on the estimate of SNR and a target SER or target biterror rate BER.

[0097] In some embodiments or instances, selectively switching between transmitting in the first mode and transmitting in the second mode as shown at block 605 may comprise selecting, for the second mode, from among a plurality of combinations of (a) number of bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol and (b) number of MFSK symbols per the OFDM symbol length, based on the estimate of SNR and a target symbol-error rate (SER) or target bit-error rate (BER). In some of these embodiments or instances, selecting from among the pluralityP112076W001

[0098] of combinations comprises selecting, forthe second mode, a combination of (a) numberof bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol and (b) number of MFSK symbols per the OFDM symbol length, using the estimate of SNR and a look-up table indexed by SNR.

[0099] In some embodiments or instances, selectively switching between transmitting in the first mode and transmitting in the second mode as shown at block 605 comprises determining to transmit in the first mode for transmissions in a non-protected direction or in a range of non-protected directions and determining to transmit in the second mode for transmissions in a protected direction or range of protected directions. The protected direction or range of protected directions may be determined based on whether the transmission direction is towards, below, or above a geographic horizon, for example.

[0100] In some embodiments or instances, selectively switching between transmitting in the first mode and transmitting in the second mode as shown at block 605 is based on a location of the transmitting apparatus. In some of these and in some other embodiments or instances, the selection may be based on a maximum allowed power for transmitting or on an actual equivalent transmission power. Similarly, the selection may be instead or additionally based on a frequency band or a range of frequencies used for transmissions.

[0101] The techniques described herein may, in some embodiments or instances, be implemented in a wireless terminal configured for use in a wireless network, such as a user equipment (UE) configured for operation in a 4G, 5G, or 6G, or in a radio base station or other radio network node in a wireless network, such as a 4G, 5G, or 6G base station. Figure 7 thus illustrates an example transmitting apparatus 700, which may be configured to carry out a method like that shown in Figure 6 and described above. The functionality and circuit blocks shown in Figure 5, for exampleP112076W001

[0102] may be implemented in the processing circuitry and communication interface circuitry shown in Figure 7.

[0103] The transmitting apparatus 700 includes processing circuitry 702 that is operatively coupled via a bus 704 to an input / output interface 706, a power source 708, a memory 710, a communication interface 712, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 7. The level of integration between the components may vary from one implementation of the apparatus to another. Further, certain transmitting apparatuses may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0104] The processing circuitry 702 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in the memory 710. The processing circuitry 702 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 702 may include multiple central processing units (CPUs).

[0105] In the example, input / output interface 706 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. This may be particularly relevant when the transmitting apparatus 700 is a user equipment (UE), for example. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. AnP112076W001

[0106] input device may allow a user to capture information into the apparatus 700. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[0107] In some embodiments, the power source 708 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. The power source 708 may further include power circuitry for delivering power from the power source 708 itself, and / or an external power source, to the various parts of the UE 700 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 708. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 708 to make the power suitable for the respective components of the UE 700 to which power is supplied.

[0108] The memory 710 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 710 includes one or more application programs 714, such as an operating system, web browser application, a widget, gadget engine, or other application, andP112076W001

[0109] corresponding data 716. The memory 710 may store, for use by the UE 700, any of a variety of various operating systems or combinations of operating systems.

[0110] The memory 710 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and / or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUlCC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ The memory 710 may allow the UE transmitting apparatus to access instructions, application programs and the like, stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in the memory 710, which may be or comprise a device-readable storage medium.

[0111] In implementations where the transmitting apparatus 700 is a UE or other access terminal, the processing circuitry 702 may be configured to communicate with an access network or other network using the communication interface 712. Similarly, in implementations where the transmitting apparatus 700 is a base station or other access point, the processing circuitry 702 may be configured to communicate with one or more UEs or other access terminals, using communication interface 712. The communication interface 712 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 722.P112076W001

[0112] The communication interface 712 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., a UE or a network node in an access network). Each transceiver may include a transmitter 718 and / or a receiver 720 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 718 and receiver 720 may be coupled to one or more antennas (e.g., antenna 722) and may share circuit components, software or firmware, or alternatively be implemented separately. Processing circuitry 702, together with memory 710, may be configured to utilize radio frequency (RF) transceiver circuitry and baseband processing circuitry to carry out the method shown in Figure 6, as described above, or variants thereof.

[0113] In the illustrated embodiment, communication functions of the communication interface 712 may include cellular communication, Wi-Fi communication, LPWAN communication, communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in accordingto one or more communication protocols and / or standards, such as IEEE 802.11 , Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / internet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0114] A transmitting apparatus 700 that is a UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limitedP112076W001

[0115] to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a wearable for tactile augmentation or sensoryenhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to the transmitting apparatus 700 shown in Figure 7.

[0116] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements, and transmits the results of such monitoring and / or measurements to another UE and / or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-loT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.P112076W001

[0117] Whether implemented in a UE or network node or some other transmitting apparatus, embodiments of the presently disclosed techniques, apparatuses, and systems comprise RF transmitter circuitry and processing circuitry operatively coupled to RF transmitter circuitry, where the processing circuitry is configured to use the RF transmitter circuitry to carryout a method like any of the variations discussed above for Figure 4 and Figure 6, i.e., to: transmit in a first mode, in which an OFDM waveform having an OFDM symbol length is formed using IDFT, functionality and transmitted; transmit in a second mode, in which an integer number of multiple-frequency-shift keying (MFSK) symbols per the OFDM symbol length is formed using the same IDFT functionality and transmitted; and selectively switch between transmitting in the first mode and transmitting in the second mode.

[0118] The techniques, apparatuses, and systems described herein may be used to provide several advantages. As an example, using a regular OFDM transmitter, MFSK symbols can be transmitted with peak power while achieving low OOB emissions. This can be an advantageous approach for operations that require long range, low SNR transmissions. In cases when regular OFDM transmissions do not work, i.e., required SER is not satisfied due to low SNR, it is possible to switch to MFSK waveform using the same transmitter / hardware to perform the required communication.

[0119] Interesting use cases where this transmitter could be used include scenarios when communicating with far away drones and loT devices. The solutions described herein can be implemented in UEs and / or in 5G base stations (aka gNBs), for example.

[0120] The cyclic prefix used by the OFDM hardware can reduce the impact of multipath channel on the MFSK signal reception. Other advantages may be apparent in some embodiments of the techniques and apparatuses described herein.P112076W001

[0121] In certain embodiments, some or allot the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and / or by end users and a wireless network generally.

Claims

P112076W001CLAIMSWhat is claimed is:

1. A method, in a transmitting apparatus, the method comprising:transmitting (610) in a first mode, in which an Orthogonal Frequency Division Multiplexing, OFDM, waveform having an OFDM symbol length is formed using Inverse Discrete Fourier Transform, IDFT, functionality and transmitted; andtransmitting (620) in a second mode, in which an integer number of multiple-frequency-shift keying, MFSK, symbols per the OFDM symbol length are formed using the same IDFT functionality and transmitted; andwherein the method further comprises selectively switching (605) between transmitting in the first mode and transmitting in the second mode; and wherein the integer number of MFSK symbols per the OFDM symbol length is greater than one.

2. The method of claim 1 , wherein the selectively switching (605) is based on at least one of: an estimate of signal-to-noise ratio, SNR, for a received signal; an indication of signal quality for a previous transmission by the transmitting apparatus; and a direction of transmission.

3. The method of claim 2, wherein the estimate of SNR is obtained from a receiver co-located with the transmitting apparatus.

4. The method of claim 2, wherein the method comprises receiving the estimate of SNR or the indication of signal quality over a radio link from a remote apparatus.

5. The method of any one of claims 1-4, wherein selectively switching (605) between transmitting in the first mode and transmitting in the second mode comprises selecting, for the second mode, from among a plurality of choices for a number of MFSK symbols per the OFDM symbol length, based on an estimate of SNR and a target symbol-error rate, SER, or target bit-error rate, BER.

6. The method of any one of claims 1-5, wherein selectively switching (605) between transmitting in the first mode and transmitting in the second mode comprises selecting, for the second mode, from amonga plurality of choices fora number of bits per MFSKsymbolor numberof MFSK toneP112076W001alternatives per MFSK symbol, based on an estimate of SNR and a target symbol-error rate, SER, or target bit-error rate, BER.

7. The method of any one of claims 1-5, wherein selectively switching (605) between transmitting in the first mode and transmitting in the second mode comprises selecting, for the second mode, from among a plurality of combinations of (a) number of bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol and (b) number of MFSK symbols per the OFDM symbol length, based on an estimate of SNR and a target symbol-error rate, SER, or target bit-error rate, BER.

8. The method of claim 7, wherein selecting from among the plurality of combinations comprises selecting, for the second mode, a combination of (a) number of bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol and (b) number of MFSK symbols per the OFDM symbol length, using the estimate of SNR and a look-up table indexed by SNR.

9. The method of any one of claims 1-8, wherein selectively switching (605) between transmitting in the first mode and transmitting in the second mode comprises determining to transmit in the first mode for transmissions in a non-protected direction or in a range of non-protected directions and determining to transmit in the second mode for transmissions in a protected direction or range of protected directions.

10. The method of claim 9, wherein the protected direction or range of protected directions is determined based on whether the transmission direction is towards, below, or above a geographic horizon.

11. The method of anyone of claims 1-10, wherein selectively switching (605) between transmitting in the first mode and transmitting in the second mode is based on a location of the transmitting apparatus.

12. The method of anyone of claims 1-11 , wherein selectively switching (605) between transmitting in the first mode and transmitting in the second mode is based on a maximum allowed power for transmitting or on an actual transmission power.P112076W00113. A transmitting apparatus, comprising:radio-frequency, RF, transmitter circuitry (718); andprocessing circuitry (702) operatively coupled to the RF transmitter circuitry (718), wherein the processing circuitry (702) is configured to use the RF transmitter circuitry (718) to:transmit in a first mode, in which an Orthogonal Frequency Division Multiplexing, OFDM, waveform having an OFDM symbol length is formed using Inverse Discrete FourierTransform, IDFT, functionality and transmitted; and transmit in a second mode, in which an integer number of multiple-frequency-shift keying, MFSK, symbols per the OFDM symbol length is formed using the same IDFT functionality and transmitted, the integer number of MFSK symbols per the OFDM symbol length being greater than one; and wherein the processing circuitry (702) is configured to selectively switch between transmitting in the first mode and transmitting in the second mode.

14. The transmitting apparatus of claim 13, wherein the processing circuitry is configured to selectively switch between transmitting in the first mode and transmitting in the second mode based on at least one of: an estimate of signal-to-noise ratio, SNR, for a received signal; an indication of signal quality for a previous transmission by the transmitting apparatus; and a direction of transmission.

15. The transmitting apparatus of claim 14, wherein the estimate of SNR is obtained from a receiver co-located with the transmitting apparatus.

16. The transmitting apparatus of claim 14, wherein the method comprises receiving the estimate of SNR or the indication of signal quality over a radio linkfrom a remote apparatus.

17. The transmitting apparatus of anyone of claims 13-16, wherein the processing circuitry (702) is configured to select, for the second mode, from among a plurality of choices for a number of MFSK symbols per the OFDM symbol length, based on the estimate of SNR and a target symbol-error rate, SER, or target bit-error rate, BER.P112076W00118. The transmitting apparatus of anyone of claims 13-17, wherein the processing circuitry (702) is configured to select, for the second mode, from among a plurality of choices for a number of bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol, based on the estimate of SNR and a target symbol-error rate, SER, or target bit-error rate, BER.

19. The transmitting apparatus of any one of claims 13-17, wherein the processing circuitry (702) is configured to select, for the second mode, from among a plurality of combinations of (a) number of bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol and (b) number of MFSK symbols per the OFDM symbol length, based on the estimate of SNR and a target symbolerror rate, SER, or target bit-error rate, BER.

20. The transmitting apparatus of claim 19, wherein the processing circuitry (702) is configured to select, for the second mode, a combination of (a) number of bits per MFSK symbol or number of MFSK tone alternatives per MFSK symbol and (b) number of MFSK symbols per the OFDM symbol length using the estimate of SNR and a look-up table indexed by SNR.

21. The transmitting apparatus of any one of claims 13-20, wherein the processing circuitry (702) is configured to selectively switch between transmitting in the first mode and transmitting in the second mode so as to transmit in the first mode for transmissions in a non-protected direction or in a range of non-protected directions and transmit in the second mode for transmissions in a protected direction or range of protected directions.

22. The transmitting apparatus of claim 21 , wherein the protected direction or range of protected directions is determined based on whether the transmission direction is towards, below, or above a geographic horizon.

23. The transmitting apparatus of any one of claims 13-22, wherein the processing circuitry (702) is configured to selectively switch between transmitting in the first mode and transmitting in the second mode based on a location of the transmitting apparatus.P112076W00124. The transmitting apparatus of any one of claims 13-23, wherein the processing circuitry (702) is configured to selectively switch between transmitting in the first mode and transmitting in the second mode based on a maximum allowed power for transmitting or an actual equivalent transmission power.

25. A mobile communication device comprising a transmitting apparatus according to any one of claims 13-24.

26. A network node for use in a wireless communications network, the network node comprising a transmitting apparatus according to anyone of claims 13-24.32

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