Automatic gain control

Abstract

This application is concerned with adaptive gain control in a receiver, such as the receiver of user equipment (UE). A receiver's measurement of received signal strength indication (RSSI) may be inacc

Description

Field The present specification relates to automatic gain control, more particularly to automatic gain control in a mobile communications network. Background Automatic gain control in a mobile communications network is known. There remains a need for improvement in controlling gain of received signals. Summary In a first aspect, this specification provides an apparatus for controlling gain for received signals at a user device, the apparatus comprising: means for determining signal strength of at least one first received signal at a first beam acquisition window; means for determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number of total measured samples, wherein the clipping counter value indicates a number ofclipped samples; means for estimating a true signal strength of the received signal based, at least in part, on the clipping probability; and means for calculating a gain value for at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In some examples, the means for estimating the true signal strength is based, at least in part, on a predetermined relationship between the clipping probability and the true signal strength. Some examples further comprise means for incrementing the clipping counter value if one or more metrics of the determined signal strength is higher than a signal strength threshold. In some examples, the one or more metrics comprises a quadrature signal value. Some examples further comprise means for setting the signal strength threshold based, at least in part, on statistical reliability of the number of clipped samples. Some examples further comprise means for setting a clipping counter window size for determining the clipping counter, wherein the clipping counter window size is set to be shorter than a synchronisation signal block duration. Some examples further comprise means for determining whether the first beam acquisition window is complete, wherein the gain value is calculated after the first beam acquisition window is complete. In some examples, the means for calculating the gain value comprises reducing the gain value substantially proportionally to an increasing difference between the determined signal strength and the estimated true signal strength. Some examples further comprise means for determining a plurality of clipping probabilities corresponding to a plurality of clipping counter values respectively, wherein each of the plurality of clipping counter values are incremented if one or more metrics of the determined signal strength is higher than a plurality of signal strength thresholds respectively. In some examples, the signal strength is higher than a first signal strength saturation threshold or higher than a second signal strength saturation threshold. In some examples, the signal strength is indicated by a Received Signal Strength Indicator measurement. In some examples, the apparatus comprises: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: determining signal strength of at least one first received signal at a first beam acquisition window; determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; estimating a true signal strength of the received signal based, at least in part, on the clipping probability; and calculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In a second aspect, this specification describes a method comprising: determining signal strength of at least one first received signal at a first beam acquisition window; determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; estimating a true signal strength of the received signal based, at least in part, on the clipping probability; and calculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In some examples, estimating the true signal strength is based, at least in part, on a predetermined relationship between the clipping probability and the true signal strength. Some examples further comprise incrementing the clipping counter value if one or more metrics of the determined signal strength is higher than a signal strength threshold. In some examples, the one or more metrics comprises a quadrature signal value. Some examples further comprise setting the signal strength threshold based, at least in part, on statistical reliability of the number of clipped samples. Some examples further comprise setting a clipping counter window size for determining the clipping counter, wherein the clipping counter window size is set to be shorter than a synchronisation signal block duration. Some examples further comprise determining whether the first beam acquisition window is complete, wherein the gain value is calculated after the first beam acquisition window is complete. In some examples, calculating the gain value comprises reducing the gain value substantially proportionally to an increasing difference between the determined signal strength and the estimated true signal strength. Some examples further comprise determining a plurality ofclipping probabilities corresponding to a plurality of clipping counter values respectively, wherein each of the plurality of clipping counter values are incremented if one or more metrics of the determined signal strength is higher than a plurality of signal strength thresholds respectively. In some examples, the signal strength is higher than a first signal strength saturation threshold or higher than a second signal strength saturation threshold. In some examples, the signal strength is indicated by a Received Signal Strength Indicator measurement. In a third aspect, this specification describes an apparatus configured to perform any method as described with reference to the second aspect. In a fourth aspect, this specification describes computer-readable instructions which, when executed by computing apparatus, cause the computing apparatus to perform any method as described with reference to the second aspect. In a fifth aspect, this specification describes a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus to: determine signal strength of at least one first received signal at a first beam acquisition window; determine a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; estimate a true signal strength of the received signal based, at least in part, on the clipping probability; and calculate a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In a sixth aspect, this specification describes a computer-readable medium (such as a non-transitory computer-readable medium) comprising program instructions stored thereon for performing at least the following: determining signal strength of at least one first received signal at a first beam acquisition window; determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; estimating a true signal strength of the received signal based, at least in part, on the clipping probability; and calculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In a seventh aspect, this specification describes an apparatus comprising: at least one processor; and at least one memory including computer program code which, when executed by the at least one processor, causes the apparatus to: determine signal strength of at least one first received signal at a first beam acquisition window; determine a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; estimate a true signal strength of the received signal based, at least in part, on the clipping probability; and calculate a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In an eighth aspect, this specification describes an apparatus comprising: a first module configured to determine signal strength of at least one first received signal at a first beam acquisition window; a second module configured to determine a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; a third module configured to estimate a true signal strength of the received signal based, at least in part, on the clipping probability; and a fourth module configured to calculate a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In a ninth aspect, this specification describes a user device comprising an execution module for performing one or more of: channel filtering, image rejection filtering, direct current (DC) compensation, down conversion, analog to digital conversion on a signal received from a control module, and / or gain adjustment at one or more amplifiers. In a tenth aspect, this specification describes a user device comprising a control module for determining a gain value to be applied to at least one future received signal, wherein the control module comprises: a signal strength measurement module configured to determine signal strength of at least one first received signal at a first beam acquisition window, a clipping counter module for incrementing a clipping counter value if one or more metrics of the determined signal strength is higher than the signal strength threshold, and a gain calculation module for performing: determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; estimating a true signal strength of the received signal based, at least in part, on the clipping probability; and calculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In an eleventh aspect, this specification describes a system for implementing a gain control for received signals at a user device comprising: an execution module for performing one or more of: channel filtering, image rejection filtering, direct current compensation, down conversion, analog to digital conversion on a signal received from a control module, and / or gain adjustment at one or more amplifiers; and the control module for determining a gain value to be applied to at least one future received signal, wherein the control module comprises: a signal strength measurement module configured to determine signal strength of at least one first received signal at a first beam acquisition window, a clipping counter module for incrementing a clipping counter value if one or more metrics of the determined signal strength is higher than the signal strength threshold, and a gain calculation module for performing: determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; estimating a true signal strength of the received signal based, at least in part, on the clipping probability; and calculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In some examples, the execution module comprises a radio frequency front-end control interface, and the control module comprises a baseband front-end control interface. In some examples, the clipping counter module is implemented with a hardware accelerator module placed on a time domain sample stream at the baseband front-end control interface. Brief description of the drawings Example embodiments will now be described, by way of example only, with reference to the following schematic drawings, in which: FIGs. 1 to 3 are a block diagrams of example systems; FIG. 4 shows plots of example signals; FIG. 5 is a block diagram of an example system; FIG. 6 shows a plot of example signals; FIG. 7 is a flowchart of an algorithm in accordance with an example embodiment; FIG. 8 shows plots of signals in accordance with an example embodiment; FIG. 9 shows a plot in accordance with an example embodiment; FIGs. 10 and 11 are flowcharts of algorithms in accordance with example embodiments; FIG. 12 is a block diagram of a system in accordance with an example embodiment; FIG. 13 is a flowchart of an algorithm in accordance with an example embodiment; FIG. 14 shows a plot in accordance with an example embodiment; FIG. 15 is a block diagram of a system in accordance with an example embodiment; FIG. 16 shows a plot in accordance with an example embodiment; FIG. 17 is a flowchart of an algorithm in accordance with an example embodiment; FIG. 18 shows plots of signals in accordance with an example embodiment; FIG. 19 is a block diagram of a system in accordance with an example embodiment; FIG. 20 is a block diagram of components of a system in accordance with an example embodiment; and FIG. 21 shows an example of tangible media for storing computer-readable code which when run by a computer may perform methods according to example embodiments described above. Detailed description 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 the 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. In the description and drawings, like reference numerals refer to like elements throughout. Below is a list of abbreviations that may be used throughout the description: ADC Analog-to-Digital Converter AGC Automatic Gain Control BA Beam Acquisition BB BaseBand CSM Cell Search and Measurement DFT-S-OFDM DFT spread OFDM DL Downlink DRX Discontinuous Reception FR1 Frequency Range 1 FR2 Frequency Range 2 gNB MIB gNodeB Master Information Block NR New Radio OFDM Orthogonal frequency-division multiplexing PBCH Physical Broadcast Channel PSS Primary Synchronization Signal RA Random Access RefSen Reference Sensitivity RSSI Received Signal Strength Indicator SIB1 System Information Block #1 SNDR Signal to Noise and Distortion Ratio SSB Synchronization Signal Block sss Secondary Synchronization Signal UE User Equipment FIG. 1 shows a block diagram of an example system, indicated generally by the reference numeral 10. The system 10 comprises a base station 11 (gNB) and one or more user devices 13 (UE1) and 14 (UE2) in a mobile communications network, such as a 5G NR network. The base station 11 may utilize beamforming techniques for providing network communication to one or more user devices. For example, a plurality of radiofrequency beams 12 may correspond to the base station 11. The user devices 13 and 14 may each perform an initial cell search (e.g. beam acquisition), where the signal strength at the user device 13 is shown in plot 15 and the signal strength at the user device 14 is shown in plot 16. The signal strength is shown with respect to the respective directional beams detected by the UEs in the initial cell search. For example, based on the position of the user devices with respect to the base station 11, certain beams are received at a high signal strength by the user device 13, while certain other beams are received at high signal strength by the user device 14. As the signal strengths may vary largely, it is essential to apply appropriate gains in order to obtain a considerable signal strength. The user devices may use Automatic Gain Control (AGC) system for the purpose of maintaining a suitable signal amplitude at its output, despite variation of the signal amplitude at the input. However, if a gain applied is too high, signals may be clipped (i.e. signal strength clipped to a threshold) which may cause incorrect determination of true signal strength. FIG. 2 is a block diagram of an example system indicated generally by the reference numeral 20. The system 20 further elaborates on an initial cell search that may be performed by UEs. The system 20 shows a time-frequency plot 21 with respect to beam acquisition windows, such as a first beam acquisition (BA) window 22 and a second beam acquisition window 23. A plurality of synchronisation signal blocks (SSB) are shown, where the SSB periodicity is shown to be approximately 20ms. A zoomed in view of the plot 21 is shown in plot 24, showing a plurality of SSBs 25, corresponding respective SSB index 26. In this example, there may be no timing / frequency synchronization with the cell, as the BA window (22, 23) starts at arbitrary point of time without any timing information of SSB location / frame boundary. Signal strength information of the cell may not be available initially, which may then result in blind initial gain selection. Due to lack of frame or symbol synchronisation, the UE may be required to monitor signal strength for the whole SS block period, i.e., 20ms for 5G NR for a first frequency range (FR1; [-110...-20] dBm). During this period, the gain may be frozen to facilitate cell search operation. Failure to apply an appropriate gain may lead to the initial cell search operation to be extended to another SS block period. For a second frequency range (FR2; [-90...-20] dBm), the number of SS block periods may be multiplied by the number (e.g. 8) of wide receiver (Rx) beams at the user device, such that the total time period may be 160ms (8 x 20ms). As such, the determination of the appropriate gain to be applied may be a long process that may cause undesirable delays. FIG. 3 is a block diagram of a system, indicated generally by the reference numeral 30, in accordance with an example embodiment. The system 30 shows a user device 31, which may be monitoring the downlink signal from the serving cell. The monitoring may be performed at a plurality of Physical Downlink Control Channel (PDCCH) monitoring occasions 32 and / or 33. Incoming signals 36 may comprise one or more SSBs. Fora relatively long DRX cycle 34 (e.g. long connected discontinuous reception), long suspension of downlink reception activity may lead to deviation of gain tracking due to the channel evolution during the non-monitoring period, such that there may be a large difference between the latest known gain and an appropriate gain with respect to the actual channel). In order to have a proper gain at DRX ON duration, UE (e.g. UE 31) can briefly "wake-up" for gain acquisition / tracking to be prepared for an upcoming DRX ON duration. As SSB is one of the few always-on signals in 5G NR, UE can rely on the closest SSB occasion for wake-up (considering that SSBs are always-on signal in 5G NR). A UE can be "off" during (long) DRX cycle in order to reduce the power consumption, as shown in the portion 37a of the power plot 37. During this period, the UE be drifting away from the serving cell, from gain / time offset / frequency offset tracking perspective. The UE may need to wake up at the end of (long) DRX cycle in order to monitor PDCCH. In case UE's gain / timeOffset / freqOffset has been drifted away beyond a threshold, the UE may not be able to decode PDCCH accurately and may possibly fail to receive the data intended for it. Hence it is a common practice for UE modem to wake up during (long) DRX cycle near at the end of it (e.g. as shown in portion 37b of the plot 37), to acquire an appropriate gain &to estimate timing / frequency offset on SSB, in an effort to be tracking the serving cell reliably. Acquisition of appropriate gain is the pre-requisite for subsequent timeoffset / freq.offset estimation. As SSB can be found (at least) every 20ms according to 3GPP NR standard, it can serve as a good signal source of the serving cell for gain acquisition / timing &frequency offset estimation. For this brief reception of SSB, an automatic gain control (AGC) module should be able to monitor the incoming signal strength to calculate a proper gain for upcoming DRX ON duration, and if the AGC is unable to accurately monitor the signal strength, this may lead to misdetection of PDCCH during DRX ON duration. Based on the discussion above, a UE may not have a good guidance of the appropriate gain to be applied at the incoming signal (containing SSB). AGC scheme takes care of this and should be able to adjust gain for next reception opportunity, and this is done typically by making use of the incoming signal strength (RSSI) measurement and by calculating the next gain via comparison with the pre-defined target set point. So, in case that the initial gain was chosen not properly, at least the next gain should be adjusted for proper signal reception. FIG. 4 shows a plot, indicated generally by the reference numeral 40, of example signals. The plots 40 may illustrate Automatic gain control applied, based on known techniques. Plot 41 shows signals corresponding to a first BA window, and plot 42 shows signals corresponding to a second BA window (with corrected gain based on information obtained in the first BA window). FIG. 4 is viewed in conjunction with FIG. 5 for better understanding. FIG. 5 is a block diagram of a system, indicated generally by the reference numeral 50. The system 50 comprises a baseband 51 and a radiofrequency module 53. The baseband 51 comprises a LI control module 52, baseband front end module (BBFE) 54, a cell search and measurement (CSM) module 55, a beam management unit (BMU) 56, transmit signal generator module (TxSG) 57, channel estimator module (CHEST) 58, demodulator module (DEM) 59, and a decoder module (DEC) 60. Referring to the plot 41, for a first attempt at the first BA window, a high gain value (e.g., 48dB for FR1) may be configured and this gain is being applied for the whole duration of BA window. The plot 41 may depict one example of implementation of a NR receiver modem (e.g. the system 50 comprising a baseband 51 and a radiofrequency module 53). When samples are streamed to CSM (cell search &measurement) 55 via RF 53 and BBFE (baseband front-end) 54, signal strength (RSSI) may be monitored by AGC (automatic gain control) responsible unit (e.g. within the BBFE). CSM 55 may continuously compute correlation of the known synchronization sequences with the incoming samples over the whole BA window duration and keep this correlation scores for reporting to LI control. CSM 55 and / or CHEST 58 can also perform decoding of a physical broadcast channel (PBCH) for the highest score samples. After reception 8i processing of the first BA window is completed, LI control makes a decision based on CSM reports (cell search results). When a cell is found (successful PBCH decoding), then UE can move over to the next procedure, e.g., cell measurement, PDSCH reception for SIB1, etc. If no cell has been found, LI control adjusts the gain (by reducing gain by a certain number of dB) based on measured RSSI (which must have been reported by BBFE [AGC control unit]) and UE tries the second attempt of cell search on another BA window with an updated (reduced) gain. In case of FR2, UE is expected to sweep over its pre-defined Rx wide beams as well. In an example algorithm, which is based solely on measured RSSI, as shown by plots 41 (first BA window / first attempt) and 42 (second BA window / second attempt), a next delta gain (difference with respect to the previously applied gain; positive value: increase gain, negative value: decrease gain) may be calculated by assessing the difference to the target headroom (45a, 48a: -14dBFS, in this particular example), and by applying the predefined gain step (i.e., gain change is allowed for the multiples of this gain step only). As long as the measured RSSI lies within the safety zone (45b, 48b; targetHR + / - deltaDZ), next delta gain is 0 (RSSI already in good range; no update of gain). This way of measuring the next delta gain may be suitable if the measured RSSI approximates the true RSSI closely. As shown in plot 41 (FR1), when started with high gain (48dB), measured RSSI value (shown by the plot 43 comprising the portion 43a and 43b) is saturated (as shown by the saturation portion 43b) from input power of -48dBm or higher at the first BA attempt. This leads to no further delta gain (only down to -12dB; right y-axis) at this measured RSSI saturation range (refer to "flat-lined" &Gnext plot in the plot 42). As input power level increases, the gap between measured RSSI (plot 43) and true RSSI (plot 44) increases as well. As a consequence, even after UE calculates the next delta gain, based on the measured RSSI, the resulting signal level at the second BA attempt (e.g. shown by the plot 46) can be off from the safety zone 48b at the high input power level range (-45dBm or higher). Especially for the range of -45dBm or higher input power level, true signal strength at BB becomes -5dBFS or higher, up to +15dBFS (@-20dBm input power). This level is obviously still too high for reliable cell detection. In case of FR2, UE is assumed to have a small number (e.g., 8) of pre-defined Rx wide beams (analog beams for the initial beam acquisition). The FR2 initial cell search procedure is to find a suitable Rx beam index from UE side as well as an appropriate SSB (Tx beam) from gNB side. In this sense, "Tx beam sweeping with a fixed UE side beam" operation should be repeated over the predefined Rx wide beams in an effort to find out the best Tx-Rx beam pair. RSSI-based conventional AGC (e.g. as shown in the pseudocode below may not always guarantee successful initial cell search within 2 SSB burst periods, i.e., 2*20ms, for some corner cases (high signal level scenario) of FR1, as it is based on the measured RSSI only, which can deviate from the true RSSI. Note that in case of FR2, the required number of SSB burst periods to guarantee successful beam acquisition (Tx beam-Rx beam pair) for the corner cases is more than 2*NRxwideBeam*20ms, where NRxwideBeam' the number of Rx wide beams at UE. function [nextDeltaGainProposal] = calcDeltaGain(rssi,targetHR,deltaDZ, gainStep) nextDeltaGainProposal = 0; if (rssi <targetHR+deltaDZ &&rssi >targetHR-deltaDZ) nextDeltaGainProposal = 0; %within deadzone (safety zone) •■-.> no gain else rssiDist = abs(rssi - targetHR); s = sign(targetHR - rssi); nextDeltaGainProposal = floor(rssiDist / gainStep)*gainStep*s; end end One of the problems that may arise from RSSI-based AGC scheme (e.g. as described with respect to FIG. 4) is that when the incoming signal strength is too strong (>0 dBFS), RSSI metric fails to differentiate the signal strength beyond 0 dBFS (it saturates to 0 dBFS, irrespective of the true signal level). Therefore, it cannot serve as a reliable signal strength metric. From user experience perspective, it may be critical to acquire a cell as fast as possible. This means that it would be beneficial if UE can find a cell at one shot (after 1st attempt of BA window). However, this might not always be possible with the frozen-gain-for-BA-window scheme. When considering the wide range of possible input signal power, i.e., [-110...-20] dBm for FR1, [-90...-20] dBm for FR2 (reference sensitivity (RefSen) range has been taken into account for the lower end), it becomes clear that a single gain value cannot lead to "acceptable" received signal level suitable for PSS / SSS peak correlation detection &successful PBCH decoding at CSM for the whole input power range. FIG. 6 shows an example plot 61 shows an expected RSSI level at baseband (where cell search &measurement module is located) of the receive modem over possible input power range. Here, the initial gain configuration scheme is based on the following principles or assumptions: • High initial gain should be set such that there should be no RSSI measurement error due to discernibility issue at low end. o In the plot 61, 12 bit fixed point I / Q is assumed to serve up to 256QAM for FR1, whereas 10 bit fixed point I / Q for FR2 (to serve up to 64QAM). The lowest signal strength which can be represented by 12 (or 10) bit I / Q is -66dBFS (or -54dBFS), respectively, with consideration of 1 sign bit. 20*logl0(power (2,-11)) =-66.2266, 20*logl0(power (2,-9)) =-54.1854 o Measured RSSI cannot indicate a value lower than -66dBFS [FR1] or -54dBFS [FR2] when true (expected) RSSI <-66dBFS [FR1] or -54dBFS [FR2]. • Low initial gain should be set such that there should be no measured RSSI saturation due to clipping at high end. o Baseband signal processing unit at UE receives the signal which has gone through RFIC, implying that channel filtered, sampled &quantized digital samples mapped to the baseband frequency. Measured RSSI at baseband is in dBFS (dB full scale) unit, and its accuracy suffers near OdBFS range, and the difference between measured RSSI and true (expected) RSSI becomes bigger as the signal strength increases. Measured RSSI at BB tends to be saturated at OdBFS onwards. Considering the above principals or assumptions, the initial gain values have been selected to be 48dB, 42dB for FR1, FR2 respectively (plots 43, 44). The low initial gain case (denoted with a plus; + plots) shows RSSI floor at low input power range, which is not acceptable. Referring back to the scenario with a high initial gain, measured RSSI is being saturated at input power level of -48dBm (or -42dBm) onwards for FR1 (or FR2). A target headroom (45a, 48a) is assumed to be -14dBFS and safety zone (45b, 48b) is assumed to be with + / - 5dB range around it (e.g. no gain change required within this safety zone). This range in reality can be acquired by input power sweep on the actual cell searcher at UE in place (via link level simulation for example), to come up with the range in which PBCH decoding can be done successfully for the specifically designed CSM. The main objective of BA-AGC is to regulate the gain such that resulting received signal strength should lie within this safety zone. The problem is that UE cannot estimate the actual signal strength correctly (measured RSSI is OdBFS, irrespective of actual input power level), in case of input power >-48dBm for FR1 (or >-42dBm for FR2). In this highly clipped signal case, it is possible that UE cannot find the cell at the 1st attempt. In this case, UE should be able to find the cell (successful PBCH decoding) at the second attempt at least. For this to happen, an appropriate gain setting for (at most) the second BA window is mandatory. AGC based on the measured RSSI may not enable appropriate gain setting before the second BA window, due to its saturation behaviour at the high input power range. FIG. 7 is a flowchart of an algorithm, indicated generally by the reference numeral 70, in accordance with an example embodiment. The operations of algorithm 70 may be performed at a user device for controlling gain for received signals at the user device. The algorithm 70 may start at operation 71, where signal strength (e.g. RSSI) of at least one first received signal may be determined at a first beam acquisition (BA) window. A clipping probability may be determined based, at least in part, on a ratio of a clipping counter value and a number of total measured samples (e.g. total measured samples in the first BA window), wherein the clipping counter value indicates a number of clipped samples. For example, for a given time period (e.g. a first BA window) if a certain percentage of received signals were clipped, the clipping rate may be based on said percentage. The algorithm for determining the clipping probability is provided in further detail below. In an example embodiment, the clipping counter value may be incremented if one or more metrics of the determined signal strength is higher than a first (higher) signal strength saturation threshold. The one or more metrics may comprise a quadrature signal value. At operation 73, a true signal strength of the received signal may be determined based, at least in part, on the clipping probability. Next, at operation 74, a gain value may be calculated for at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. For example, the more the difference in the estimated true signal strength and the determined signal strength, the more that gain for the next BA window may be reduced. It would be appreciated that I / Q component of OFDM signal follows Gaussian (normal) distribution due to the central limit theorem. As such, clipping probability (clipping counter rate satisfying the condition (I / Q signal strength >threshold)) can be formulated as the Gaussian cumulative density function. This means that even at high input power level range in which measured RSSI at baseband is saturated due to clipping of the signal, the clipping probability may be a reliable and trustworthy indicator of the signal strength, as the clipping probability increases monotonically from 0 to 1 at RSSI range [X...+30] dBFS, where X e {-9,...,-3} depending on clipping rate threshold value (discussed in further detail below). The UE may therefore measure the clipping counter and map it to clipping probability, and may then use the clipping probability to determine a gain reduction when measured RSSI can be saturated. In one example, clipping probability to gain reduction mapping may be acquired offline and saved as a look-up table (e.g. explained further with reference to FIG. 9). In one example, the central limit theorem establishes that when independent and identically distributed (IID) random variables are summed up, their properly normalized sum tends toward a normal distribution even if the original variables themselves are not normally distributed. NR waveform, or OFDM signal in general, complies with this condition, as the input bit streams to be encoded on subcarriers can be formulated as IID random variables. Time domain OFDM signal is an aggregate of multiple subcarriers, each of which contains a modulated complex symbol which follows illD distribution. Based on the above theorem, achievable SNDR (Signal to Noise and Distortion Ratio) of OFDM signal may be analyzed as a function of bit resolution and clipping ratio at ADC (Analog-to-Digital Converter). In an example embodiment, the clipping probability may be determined as follows: ^clipping >x) = 2Q(x) Where Q(x) = 1 - 4>(x) Here, the function Tsx; is the Gaussian cumulative density function. 1 rx _t2 ^'(x) = —= I e 2 dr \ZTT J—oo The "clipping ratio" (on a ratio of a clipping counter value and a number of total measured samples) may be defined as the ratio of the maximum to the average output power at ADC (e.g. equivalent to a reciprocal of the linear RSSI after ADC). For example, the clipping ratio==—y2 = RSSllin x, where M: the number of quantization 4 levels per I / Q, and y A JNAES , where A: quantization step-size (assumption: uniform quantization), Na: the number of active subcarriers, Es: average power of the complex symbol Based on the definition of RSSI (RSSIdBFs = 10*logl0(RSSIiin)), the expression below may be derived: 4 RSSIdBFs —— -10 io M2 From the above expression, the following may be derived: x=-=y = J2-10 io , which needs to be inserted back to the clipping probability / rate function, after adopting concept of the clipping rate threshold (TRC e [0, ...,1]). The clipping rate threshold is introduced to allow configurable parameter when measuring the clipping rate on OFDM samples in practice. For normalized signal (I / Q components are confined to [-1 +1] range from the baseband perspective), the original clipping probability refers to the absolute clipping (PciipPing(x- >*), where x = 1), but it would be statistically not so reliable if UE counts the absolute clipping samples only, as NR SSB has only 240 subcarriers (the number of time domain OFDM symbol sample should be in a similar ball park). Hence, we'd better count I / Q samples with their absolute values being lager than a certain configurable threshold which is smaller than 1, in an effort to have statistically meaningful clipping counts. All-in-all, the probability of clipping, which takes into account the clipping rate threshold TRC, can be formulated as follows. / I RSS,dBFs\ Pciipping(TRc-x >TRC) = 2 ■ QI TR, -^2 ■ 10 io I, where TRC: clipping rate threshold (e [0,...,1]). The clipping probability is a function of clipping rate threshold and RSSI, and independent of the resolution of quantization. Be aware that a factor 2 comes from the practice of considering absolute value (| / | or |Q|), i.e., both ends of I or Q components. In an example embodiment, the UE may estimate a clipping probability based on a measuring a clipping rate (ratio of a clipping counter value and a number of total measured samples). The clipping rate may be used to supplement a measured RSSI to determine a true RSSI. For example, estimated true RSSI range can be segmentized with respect to the clipping rate, i.e., clipping rate range ([0.06 0.55], [0.55 0.85], [0.85 0.95], [0.95 1.0]) corresponds to true RSSI estimate range ([-5 +5], [+5 +15], [+15 +25], [+25 ...] dBFS), respectively in case of TRC =0.75. For each clipping rate segment above, AGnext value (e.g. change in gain to be applied in the next BA window) may be determined to be as (target headroom: -14dBFS - (+0, +10, +20, +30) dB), respectively. An example pseudo code is provided below for better understanding: [delxaGsinNext] » calcDeitaGain_CRb>ssad(probClipp<TRsslKsadro^O Rats based ds-RsaGain sal TRc « % ths see srs< based an sts ntapa -”> Htrdteded THcr » ($,$ tt st ttpt ,du rate thredholds wn TRc -- 5.75, ttith carrsRpoads tc RSFilBFS 2-S ad 4it 425? dBFS xssdRssi « £2 + -.2 +;>2 +22); Feudist Mei, taken frat IRc-lRlS case 3 irdtialikatiea deicaGain^ext * 2; if (prebel ipp <THcrCUJ dalcadaindezt « 2; ©Issif (piohClxpp <THcrCO) 2 2 322 i.n [-5 itp Raaaan .....> yagpp deibaGainNext » TSeslHaadxoaK - ’sedRa$i(U ; «lssif (prabClipp <Tllct(2)) 2 Rddl an [+5 + 15 j: radian ••"> llbdSRS daltasaiabaxt « TRsaiHesdtaain - RedRssi(l); elseaf (pxcbCXipp <THarf:)) 2 RSFi in 212 +25); median ......> +23dBR3 daltaGaiaNaxt » TRxsiKeadroom ~ jsadRssi (2); else % 2:3.31 1.-1 2’21 .,.-. a —> ad-:3dBF.S dalt~GaiaR~xt * TRssiHeadroosn - ^edRssi(4); end end In an example embodiment, the above method of clipping rate-based gain calculation (e.g. calculating gain based on clipping rate, rather than based on measured RSSI) may be used when measured signal strength (e.g. RSSI) is higher than a signal strength threshold (e.g. RSSI threshold) and / or clipping rate is higher than the predefined clipping rate threshold (for example 5%). For example, the measured signal strength being higher than the signal strength threshold or the clipping rate being higher than the clipping rate threshold may be an indication that the signal strength is saturated. If the signal strength is not saturated, conventional RSSI-based gain calculation scheme may be used. FIG. 8 shows plots, indicated generally by the reference numeral 80, in accordance with an example embodiment. Plot 81 shows signal strengths corresponding to a first beam acquisition window (e.g. for FR1: 48dBFS). Plot 82 shows signal strengths corresponding to a second beam acquisition window, where the gain calculation based on the clipping probability has been applied. The plot 81 shows measured RSSI 83, with a first portion 83a, and a saturated portion 83b (e.g. clipped signal due to RSSI being higher than a RSSI threshold e.g. -48dBm)). The plot 81 further shows an estimated true RSSI 85, a target headroom 84a, and a target safety zone 84b. The plot 82 shows a delta gain 86 (based on the right-side vertical axis showing the gain measurement [dB], measured RSSI and estimated true RSSI as represented by the line 87 (the measured RSSI and estimated true RSSI are shown to overlap fully), target headroom 88a and target safety zone 88b. As seen from the plot 82, the measured RSSI 87 is substantially within the target safety zone 88b due to the gain being controlled based on clipping probability, as discussed above. The delta gain 86 (AGnext) shows that after the signal strength exceeds -48dBm (e.g. which may be the signal strength threshold), the AGC may reduce the gain substantively (e.g. by allowing the gain to be reduced in large steps, e.g. up to 44dB gain reduction). FIG. 9 is a plot, indicated generally by the reference numeral 90, in accordance with an example embodiment. The plot 90 provides a relationship between a clipping probability and a true signal strength, such that it may be used as a look-up curve for estimating a true signal strength (e.g. operation 74) based on the determined clipping probability. For example, a first curve 91 is provided for the relationship between clipping probability and true signal strength (RSSI), said relationship corresponding to a clipping rate threshold of 1; a second curve 92 is provided for the relationship between clipping probability and true signal strength (RSSI), said relationship corresponding to a clipping rate threshold of 0.75; a third curve 93 is provided for the relationship between clipping probability and true signal strength (RSSI), said relationship corresponding to a clipping rate threshold of 0.5. The line 94 marks a clipping rate threshold of 5% (clipping probability threshold of 0.05). For example, based on the plot 90, when a clipping rate threshold is set to 1, the curve 91 is considered, and if the clipping probability is determined (e.g. based on the operation 72 for determining clipping probability based on a ratio ofclipped counter value and a number of total measured samples) to be 0.4, the true signal strength (RSSI) may be estimated to be 5dBFS, as shown by the point 95. For the same clipping probability of 0.4, if the clipping rate threshold is set to 0.75, the curve 91 is considered, and the true signal strength is estimated to be approximately 2dBFS. In some examples, as shown in the plot 90, the clipping probability curve may show a monotonic increase behavior from 0 to 1 throughout the high signal power region (RSSI >-lOdBFS or higher), which demonstrates that the clipping probability / rate can be used as a useful indicator for signal level determination. The clipping-rate based gain control may be able to differentiate +30dBFS true RSSI from OdBFS case, which could be a challenging task when solely relying on the measured RSSI. FIG. 10 is a flowchart of an algorithm, indicated generally by the reference numeral 100, in accordance with an example embodiment. The algorithm 100 may comprise operations that are carried out offline (e.g. setting predefined values). At operation 101, a signal strength threshold is set, for example, for use in incrementing the clipping counter value (e.g. clipping counter value is incremented if the measured signal strength exceeds the signal strength threshold). The signal strength threshold may be set based, at least in part, on statistical reliability of the number of clipped samples. For example, the number of clipped samples exceeding the signal strength threshold should ideally be a relatively high number, such as above 20 (e.g. this number may be determined based on simulations or experimentations), which may allow the clipping counter value to be a statistically meaningful number that is not too low or too high. In one example, when clipping counter window size is 2 OFDM symbol and sampling rate is 256 samples per symbol, clipping counter window size is 512 samples. When the clipping probability threshold is set to be 5%, then a threshold in terms of clipping count is 512*0.05=25.6, which can provide statistically meaningful number. In case clipping probability threshold is set to be 1% for the same case, clipping counter threshold would be 5.12 - perhaps too small number, to be prone to occasional outlier case. At operation 102, the clipping counter window size is set (e.g. predefined or set offline). The clipping counter window size may be set for determining the clipping counter, wherein the clipping counter window size is set to be shorter than a synchronisation signal block duration. For example, with the consideration that an SSB has a duration of 4 OFDM symbols, when clipping counter window size is set to be 2 OFDM symbol duration, it may be guaranteed that at least one clipping counter window should be completely immersed within SSB duration (e.g. also considering missing symbol / frame timing at UE) with arbitrary starting point of clipping counter window. As such, during the duration of the BA window (e.g. first BA window 22, second BA window 23), the UE may continuously calculate clipping counts over 2 OFDM symbol duration and keep track of maximum value of clipping probability over the entire BA window duration. FIG. 11 is a flowchart of an algorithm, indicated generally by the reference numeral 110, in accordance with an example embodiment. The operations of the algorithm 110 may be performed as part of calculating the gain value for a second beam acquisition window (e.g. operation 74 described above). At operation 111, an increasing difference between determined signal strength and estimated true signal strength may be detected. For example, referring to the plot 81 of FIG. 8, the RSSI is saturated after reaching 0 dBFS (input power at -48 dBm), and it can be seen that as the true RSSI 85 rises, the difference between true RSSI 85 and measured RSSI 83b increases. At operation 112, the gain value is reduced (i.e. next delta gain) substantially proportionally to said increasing difference between the determined signal strength and the estimated true signal strength. FIG. 12 is a block diagram of a system, indicated generally by the reference numeral 120, in accordance with an example embodiment. The system 120 shows an example hardware configuration for a clipping counter module (e.g. clipping counter module performing the incrementing of the clipping counter value if one or more metrics of the determined signal strength is higher than the signal strength threshold). For example, the system 120 shows a baseband (BB) digital signal 121 being divided into an in-phase component signal 121a and a quadrature component signal 121b and provided as an input to clipping counter module 123a and 123b respectively. A clipping rate threshold (TRC) 124 is also provided as an input to the clipping counter modules 123a and 123b. If a metric of the in-phase component signal 121a is determined to be higher than the clipping rate threshold 124, the clipping counter value is incremented at summation module 122a; similarly if a metric of the quadrature component signal 121b is determined to be higher than the clipping rate threshold 124, the clipping counter value is incremented at the summation module 122b. Outputs from the clipping counter modules 123a and 123b may be combined in the summation module 125 to obtain a total clipping counter value 126. FIG. 13 is a flowchart of an algorithm, indicated generally by the reference numeral 130, in accordance with an example embodiment. At operation 131, a plurality of clipping probabilities may be determined corresponding to a plurality of clipping counter values respectively. Each of the clipping counter values may be associated with a different clipping rate threshold. For example, a plurality of clipping rate thresholds may be set at 1%, 10%, and 75%. At operation 132, each of the plurality of clipping counter values may be incremented if one or more metrics of the determined signal strength is higher than a plurality of signal strength thresholds respectively. The plurality of clipping rate thresholds may be beneficial in allowing the system to be used for a wide range of RSSI measurements (e.g. not limited to very high or very low measurements). FIG. 14 shows a plot, indicated generally by the reference numeral 140, in accordance with an example embodiment. The plot 140 shows a relationship between clipping probability (y-axis) and estimated true signal strength (RSSI; x-axis) for three different clipping rate thresholds. For example, the curve 141 shows the relationship for a clipping rate threshold of 0.01, curve 142 shows the relationship for a clipping rate threshold of 0.10 and curve 143 shows the relationship for a clipping rate threshold of 0.75. The line 144 shows a clipping probability threshold of 5%, while the line 145 shows a clipping probability threshold of 95%. For example, when clipping probability is determined to be 5%, for a clipping rate threshold of 1%, the estimated true RSSI may be determined as -42.5 dBFS (e.g. based on a lookup), as shown by the point 146. For example, the motivation behind enabling RSSI estimation at a plurality ofclipping rate thresholds may be to enable the RSSI estimation range to be extended for enable statistically reliable mapping of clipping probability to determine true RSSI for high signal strengths, as well as relatively low signal strengths. For example, due to the monotonically increasing behavior of the RSSI with respect to the clipping probability, the RSSI may reliably be calculated based on clipping rate / probability, over the region [-42.5...+24.5] dBFS, with only 3 TRC variants (1%, 10%, 75%) [e.g. assuming that monitoring clipping probability region is between 5% up to 95%]. FIG. 15 is a block diagram of a system, indicated generally by the reference numeral 120, in accordance with an example embodiment. The system 150 shows an example hardware configuration for a clipping counter module (e.g. clipping counter module performing the incrementing of the clipping counter value if one or more metrics of the determined signal strength is higher than the signal strength threshold). The system 150 is similar to the system 120, while being able to implement a plurality of clipping rate thresholds for updating the clipping counter value. For example, the system 150 shows a baseband (BB) digital signal 151 being divided into an in-phase component signal 151a-l and a quadrature component signal 151 b-1 and provided as an input to clipping counter module 153a-l and 153b-l respectively. A clipping rate threshold (TRC) 154-1 is also provided as an input to the clipping counter modules 153a-l and 153b-l. If a metric of the in-phase component signal 151a is determined to be higher than the clipping rate threshold 154-1, the clipping counter value is incremented at summation module 152a-l; similarly if a metric of the quadrature component signal 151 b-1 is determined to be higher than the clipping rate threshold 154-1, the clipping counter value is incremented at the summation module 152b-l. Outputs from the clipping counter modules 153a-l and 153b-l may be combined in the summation module 155-1 to obtain a total clipping counter value 156-1. Similar steps may be performed for each of the clipping rate thresholds 154-2 and 154-3 respectively. In some examples, implementing a plurality of clipping rate thresholds may allow devices (e.g. low-cost devices like loT (Internet of Things)) to save on power consumption, hardware area and / or cycle count reduction. FIG. 16 is a plot, indicated generally by the reference numeral 160, in accordance with an example embodiment. The plot 160 comprises a curve 161 showing a relationship between clipping probability and an estimated true RSSI, and another curve 162 showing a next delta gain (e.g. gain calculation based on comparison of estimated true RSSI (based on clipping rate probability) and a measured RSSI. As shown by the curve 162, the gain is reduced based on the increasing RSSI (e.g. in order to avoid a difference between the true RSSI and measured RSSI to not exceed beyond a certain point). FIG. 17 is a flowchart of an algorithm, indicated generally by the reference numeral 170, in an example embodiment. The operations of algorithm 170 may be performed at a UE for calculating next gain (e.g. to be applied at a subsequent BA window), similar to algorithm 70 described above. The algorithm 170 may start at operation 171, and at operation 172, a signal strength, such as RSSI, of measured signal(s) may be determined, and the number of clipped samples (e.g. saturation due to RSSI being higher than an upper threshold) may be counted. Next, at operation 173, a clipping rate may be determined, for example, based on a ratio of the number of clipped samples and the total number of measured samples. At operation 174, if it is determined that a first beam acquisition window is not complete, the operations 172 and 173 may be repeated until the first beam acquisition window is complete. If it is determined that the first beam acquisition window is complete, operation 175 may be performed, where a next gain (e.g. for the next beam acquisition window) may be calculated based, at least in part, on the measured RSSI and the clipping rate. The delta gain next may be calculated accordingly in operation 175. The delta next gain is shown as an output 176. The operation 175 may be elaborated in the operations of algorithm 177. At operation 178, it is determined whether measured RRSI is higher than the RSSI threshold, or whether the measured clipping rate is higher than a clipping rate threshold. If yes, the delta next gain may be calculated at operation 179, based, at least in part, on the clipping probability. Alternatively, if it is determined that the measured RSSI is not higher than the RSSI threshold and the clipping rate is not higher than a clipping rate threshold, the delta next gain may be calculated at operation 180, based, at least in part, on the measured RSSI (e.g. conventional legacy AGC). The algorithm 170 may then end at operation 181. FIG. 18 shows plots, indicated generally by the reference numeral 180, in accordance with an example embodiment. The plots 180 comprise a plot 181 showing simulated data corresponding to a clipping probability for an analytical model with respect to empirical data collected. The analytical model (line) curve, a clipping rate (shown by circles along the plot), and a filtered signal (shown by * along the plot) are seen to fall on the same curve. As such, clipping probability shows a good match between the theoretical analytic model and the empirical data collected from simulations. In one example, a "filtered signal" may mean channel filtered signal seen from the baseband, i.e., (realistic) signal being clipped at +1 or -1 (normalized), whereas "raw signal" indicates hypothetical (true) signal which is clipping-free (allowed to have value higher than +1 or lower than -1). Empirical clipping rate shows good match with the analytic model, and it coincides with the hypothetical true signal case. The plots 180 further comprise a plot 182 showing an ideal RSSI (dashed line) curve, a raw true RSSI signal (denoted by circles mostly overlapping the ideal RSSI curve), a filtered RSSI signal (denoted by stars, overlapping the ideal RSSI curve until configured RSSI (x-axis) reaches around 2 dBFS), and a delta change in the filtered RSSI signal (denoted by diamond shaped points). It can be seen that the measured RSSI of the filtered (realistic) signal (*) starts deviating from that of the raw (true) signal (circle; o), which it shows saturation at the high input power range (configured RSSI >OdBFS). The configured RSSI value keeps increasing from 0 to +30dBFS, but the measured RSSI of the filtered signal (star; *) does not go higher than approximately +3dBFS (saturated). However, measured RSSI of the hypothetical true signal (circle; o) shows good match with the ideal case (dashed; - -). RSSI deviation level plot, ARSSIfilt (:= measured RSSI of the filtered signal - measure RSSI of the raw signal; diamond shape ❖; refer to right y-axis), shows that deviation starts from the configured RSSI of -3 dBFS and going deeper ever since, leading to 27dB underestimate at the configured RSSI of +30dBFS power level (refer to the right y-axis). The simulation-based numerical analysis in this subsection may not take into account RF non-linearity and possible impairments which should be implementation-specific. It may therefore be beneficial to perform input power sweep on a modem platform to collect {(input power level, clipping rate)} data to calibrate and create a mapping table, rather than solely rely on the analytical formula to reflect the actual modem implementation dependent characteristics. Once this mapping table is acquired via lab measurement and / or simulations, this table can be pre-loaded to modem for AGC feature. FIG. 19 is a block diagram of a system, indicated generally by the reference numeral 190, in accordance with an example embodiment. The system 190 may be used for implementing a gain control for received signals at a user device. The system 190 may comprise a radiofrequency frontend (RFFE) module 191 comprising an execution module 202 (AGC Slave) comprising one or more of a diplexer 193, low noise amplifier (LNA) 194, image rejection filter 195, a mixer 196, a local oscillator 203, an IF filter 197, a variable gain amplifier (VGA) 198, an analogue to digital conversion module 198, a filter module 200, a digital gain amplifier 201. The execution module may perform one or more of: channel filtering, image rejection filtering, direct current (DC) compensation, down conversion, analog to digital conversion on a signal received from a control module, and / or gain adjustment at one or more amplifiers. The system 190 may further comprise a baseband frontend (BBFE) module 192 comprising a control module 206 (AGC Master) for determining a gain value to be applied to at least one future received signal. The BBFE module 192 further comprises: a signal strength measurement module 203 configured to determine signal strength of at least one first received signal at a first beam acquisition window; a decimator 205; and a clipping counter module 204 for incrementing a clipping counter value if one or more metrics of the determined signal strength is higher than the signal strength threshold. The system may comprise a gain calculation module for performing operations of FIG. 7, such as: determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples; estimating a true signal; and calculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal. In one example the execution module comprises a radio frequency front-end control interface, and the control module comprises a baseband front-end control interface, where the clipping counter module is implemented with a hardware accelerator module placed on a time domain sample stream at the baseband front-end control interface. In some examples, the execution module 202 and the control module 206 are part of a single hardware device. Alternatively, the execution module 202 and the control module 206 are part of different hardware devices, and may be connected to each other by wired and / or wireless means. In this example, the NR UE receiver modem's AGC functionality is assumed to be split into two parts, i.e., AGC Master (control) at BBFE and AGC Slave (execution) at RFFE. This split may be made due to the following: • RFFE is responsible for channel filtering, image rejection filtering, direct current (DC) compensation, down conversion, and most importantly, ADC (analog-to-digital conversion). This means that sampling and quantization of the incoming analog signal takes place at RFFE. As the signal level at ADC plays a critical role for the quality (SNDR) of the resulting digital signal which is being streamed to baseband, signal scaling at ADC and possibly LNA at the further front of the analog signal processing module (via adjustment of analog gain) should be performed at RFFE. The residual gain ("digital gain" := total gain -analog gain) can be applied after ADC, before RF-BB interface. AGC execution (in terms of analog gain / digital gain split and scaling of the signal at ADC and other points like LNA, DGA) should be done at RFFE. • BBFE is in a position to have access to NR system knowledge, e.g., SSB structure and its periodicity, cell data base information (latest good known gain, frequency / time offset, etc.), CSM cell search outcome (peak correlation scores, PBCH decoding outcome, frame / symbol boundary), and to frequency domain samples as well as time domain samples (FFT is located in BB side). Due to this, BBFE is better positioned to make an informed decision for BA-AGC, like calculation of the next gain proposal, based on scenario detection result, measured RSSI and clipping counter values. Hence BBFE is assumed to play a role as an AGC Master (control) like the next gain calculation. This proposal of the next gain should be forward to RFFE for its timely execution. It may be appreciated that the "clipping counter" unit 204 at BBFE may support AGC function operation. Note that this clipping counter unit is located in front of the decimator (which is in turn located prior to CSM). The decimator 205 might be required in case that channel bandwidth of the baseband signal at RF-BB interface (and BB side from that point onwards prior to decimator) is wider than SSB bandwidth. In one example, clipping counter 204 should be located prior to decimator, as decimation could introduce distortion to the clipping probability behaviour. In case that the clipping counter unit is placed after decimator (e.g., at CSM, etc.) for some reason, an input power level-to-clipping rate mapping table should be generated via a lab measurement or a simulation to reflect any possible impact coming from signal decimation. In some examples, clipping counter increments its counter whenever its absolute value of I or Q component of incoming samples is higher than the configurable threshold, i.e., TRC, and these counter values for I / Q, i.e., Cnt_clip_re, Cnt_dip_im, are summed. This clipping counter value can be used as a signal strength indicator when input power level is high by making use of the relationship of (clipping counter = number of measured samples*clipping probability). HW accelerator module of Figure 13 can be placed on the streaming (complex) signals for probing, and the clipping counting can be done in run-time without costing cycle counts. For completeness, FIG. 16 is a schematic diagram of components of one or more of the example embodiments described previously, which hereafter are referred to generically as processing systems 300. A processing system 300 may have a processor 302, a memory 304 closely coupled to the processor and comprised of a RAM 314 and ROM 312, and, optionally, user input 310 and a display 318. The processing system 300 may comprise one or more network / apparatus interfaces 308 for connection to a network / apparatus, e.g. a modem which may be wired or wireless. Interface 308 may also operate as a connection to other apparatus such as device / apparatus which is not network side apparatus. Thus, direct connection between devices / apparatus without network participation is possible. The processor 302 is connected to each of the other components in order to control operation thereof. The memory 304 may comprise a non-volatile memory, such as a hard disk drive (HDD) or a solid-state drive (SSD). The ROM 312 of the memory 304 stores, amongst other things, an operating system 315 and may store software applications 316. The RAM 314 of the memory 304 is used by the processor 302 for the temporary storage of data. The operating system 315 may contain computer program code which, when executed by the processor implements aspects of the algorithms 70, 100, 110, and 170 described above. Note that in the case of small device / apparatus the memory can be most suitable for small size usage i.e. not always hard disk drive (HDD) or solid-state drive (SSD) is used. The processor 302 may take any suitable form. For instance, it may be a microcontroller, a plurality of microcontrollers, a processor, or a plurality of processors. The processing system 300 may be a standalone computer, a server, a console, or a network thereof. The processing system 300 and needed structural parts may be all inside device / apparatus such as loT device / apparatus i.e. embedded to very small size In some example embodiments, the processing system 300 may also be associated with external software applications. These may be applications stored on a remote server device / apparatus and may run partly or exclusively on the remote server device / apparatus. These applications may be termed cloud-hosted applications. The processing system 300 may be in communication with the remote server device / apparatus in order to utilize the software application stored there. FIG. 17 shows tangible media, specifically a removable memory unit 365, storing computer-readable code which when run by a computer may perform methods according to example embodiments described above. The removable memory unit 365 may be a memory stick, e.g. a USB memory stick, having internal memory 366 for storing the computer-readable code. The internal memory 366 may be accessed by a computer system via a connector 367. Other forms of tangible storage media may be used. Tangible media can be any device / apparatus capable of storing data / information which data / information can be exchanged between devices / apparatus / network. Embodiments of the present invention may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The software, application logic and / or hardware may reside on memory, or any computer media. In an example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a "memory" or "computer-readable medium" may be any non-transitory media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. Reference to, where relevant, "computer-readable storage medium", "computer program product", "tangibly embodied computer program" etc., or a "processor" or "processing circuitry" etc. should be understood to encompass not only computers having differing architectures such as single / multi-processor architectures and sequencers / parallel architectures, but also specialised circuits such as field programmable gate arrays FPGA, application specify circuits ASIC, signal processing devices / apparatus and other devices / apparatus. References to computer program, instructions, code etc. should be understood to express software for a programmable processor firmware such as the programmable content of a hardware device / apparatus as instructions for a processor or configured or configuration settings for a fixed function device / apparatus, gate array, programmable logic device / apparatus, etc. As used in this application, the term "circuitry" refers to all of the following: (a) hardware-only circuit implementations (such as implementations in only analogue and / or digital circuitry) and (b) to combinations of circuits and software (and / or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s) / software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a server, to perform various functions) and (c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. If desired, the different functions discussed herein may be performed in a different order and / or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined. Similarly, it will also be appreciated that the flow charts of Figures 7, 10, 11, 13, 17 are examples only and that various operations depicted therein may be omitted, reordered and / or combined. It will be appreciated that the above-described example embodiments are purely illustrative and are not limiting on the scope of the invention. Other variations and modifications will be apparent to persons skilled in the art upon reading the present specification. Moreover, the disclosure of the present application should be understood to include any novel features or any novel combination of features either explicitly or implicitly disclosed herein or any generalization thereof and during the prosecution of the present application or of any application derived therefrom, new claims may be formulated to cover any such features and / or combination of such features.

Claims

1. An apparatus for controlling gain for received signals at a user device, the apparatus comprising:means for determining signal strength of at least one first received signal at a first beam acquisition window;means for determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number of total measured samples, wherein the clipping counter value indicates a number of clipped samples;means for estimating a true signal strength of the received signal based, at least in part, on the clipping probability; andmeans for calculating a gain value for at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal.

2. An apparatus as claimed in claim 1, wherein the means for estimating the true signal strength is based, at least in part, on a predetermined relationship between the clipping probability and the true signal strength.

3. An apparatus as claimed in claim 1 or 2, further comprising means for incrementing the clipping counter value if one or more metrics of the determined signal strength is higher than a signal strength threshold.

4. An apparatus as claimed in claim 3, wherein the one or more metrics comprises a quadrature signal value.

5. An apparatus as claimed in any one of the claims 3 or 4, further comprising means for setting the signal strength threshold based, at least in part, on statistical reliability of the number of clipped samples.

6. An apparatus as claimed in any one of the preceding claims, further comprising means for setting a clipping counter window size for determining the clipping counter, wherein the clipping counter window size is set to be shorter than a synchronisation signal block duration.

7. An apparatus as claimed in any one of the preceding claims, further comprising means for determining whether the first beam acquisition window is complete,wherein the gain value is calculated after the first beam acquisition window is complete.

8. An apparatus as claimed in any one of the preceding claims, wherein the means for calculating the gain value comprises reducing the gain value substantially proportionally to an increasing difference between the determined signal strength and the estimated true signal strength.

9. An apparatus as claimed in any one of the preceding claims, further comprising means for determining a plurality ofclipping probabilities corresponding to a plurality of clipping counter values respectively, wherein each of the plurality of clipping counter values are incremented if one or more metrics of the determined signal strength is higher than a plurality of signal strength thresholds respectively.

10. An apparatus as claimed in any one of the preceding claims, wherein the signal strength is higher than a first signal strength saturation threshold.

11. An apparatus as claimed in any one of the preceding claims, wherein the signal strength is indicated by a Received Signal Strength Indicator measurement.

12. An apparatus as claimed in any one of the preceding claims, wherein the apparatus comprises:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:determining signal strength of at least one first received signal at a first beam acquisition window;determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples;estimating a true signal strength of the received signal based, at least in part, on the clipping probability; andcalculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal.

13. A system for implementing a gain control for received signals at a user device comprising:an execution module for performing one or more of: channel filtering, image rejection filtering, direct current compensation, down conversion, analog to digital conversion on a signal received from a control module, and / or gain adjustment at one or more amplifiers; andthe control module for determining a gain value to be applied to at least one future received signal, wherein the control module comprises:a signal strength measurement module configured to determine signal strength of at least one first received signal at a first beam acquisition window,a clipping counter module for incrementing a clipping counter value if one or more metrics of the determined signal strength is higher than the signal strength threshold, anda gain calculation module for performing:determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples;estimating a true signal strength of the received signal based, at least in part, on the clipping probability; andcalculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal.

14. The system of claim 13, wherein the execution module comprises a radio frequency front-end control interface, and the control module comprises a baseband front-end control interface.

15. The system of any one of claims 14, wherein the clipping counter module is implemented with a hardware accelerator module placed on a time domain sample stream at the baseband front-end control interface.

16. A method comprising:determining signal strength of at least one first received signal at a first beam acquisition window;determining a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples;estimating a true signal strength of the received signal based, at least in part, on the clipping probability; andcalculating a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal.

17. A computer program comprising instructions, which, when executed by an apparatus, cause the apparatus to:determine signal strength of at least one first received signal at a first beam acquisition window;determine a clipping probability based, at least in part, on a ratio of a clipping counter value and a number total measured samples, wherein the clipping counter value indicates a number of clipped samples;estimate a true signal strength of the received signal based, at least in part, on the clipping probability; andcalculate a gain value to be applied to at least one second received signal at a second beam acquisition window based, at least in part, on a comparison between the determined signal strength and the estimated true signal strength for the at least one received signal.

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