AUTOMATIC GAIN CONTROL

Abstract

A method of operating a radio receiver device comprises receiving a plurality of signals with a plurality of corresponding frequencies; applying respective gains to each of the plurality of signals; and storing the gain applied to each signal and its corresponding frequency. The method comprises subsequently receiving a further signal with a further frequency; and applying a further gain to the further signal. The further gain is determined using at least one of the stored gains according to a difference between the further frequency and at least one of the plurality of corresponding frequencies.

Claims

1. A method of operating a radio receiver device comprising: receiving a plurality of signals with a plurality of corresponding frequencies; applying respective gains to each of the plurality of signals; and storing the gain applied to each signal, its corresponding frequency, and a time at which the gain was applied; wherein the method comprises subsequently: receiving a further signal with a further frequency; and applying a further gain to the further signal; wherein the further gain is determined using at least one of the stored gains according to a difference between the further frequency and at least one of the plurality of corresponding frequencies and according to a comparison between a time at which the further signal is received and at least one of the stored times.

2. The method of operating a radio receiver device as claimed in claim 1, wherein applying respective gains to each of the plurality of signals comprises optimising the respective gains using automatic gain control.

3. The method of operating a radio receiver device as claimed in claim 1, comprising setting the further gain to be equal to a stored gain with a corresponding frequency that is a closest of the plurality of corresponding frequencies to the further frequency.

4.-5. (canceled)

6. The method of operating a radio receiver device as claimed in claim 1, comprising disregarding all stored gains with a corresponding frequency that differs from the further frequency by more than a threshold value.

7. The method of operating a radio receiver device as claimed in claim 1, comprising assigning each previously-applied gain a distance metric based upon its difference in both frequency and time from the further signal.

8. The method of operating a radio receiver device as claimed in claim 7, wherein the distance metric comprises a weighted combination of the differences.

9. The method of operating a radio receiver device as claimed in claim 7, comprising setting the further gain to be equal to the gain to which a minimum distance metric has been assigned.

10. The method of operating a radio receiver device as claimed in claim 1, comprising deriving the further gain from one or more stored gains subject to a refinement according to a frequency separation and/or time separation between the stored gain and the further gain.

11. The method of operating a radio receiver device as claimed in claim 1, comprising setting the further gain to a value interpolated between two or more stored gains.

12. The method of operating a radio receiver device as claimed in claim 1, wherein the plurality of signals comprises signals transmitted according to an LTE standard.

13. The method of operating a radio receiver device as claimed in claim 12, wherein the plurality of frequencies comprises a plurality of narrowbands defined according to an LTE standard.

14. A radio transceiver device comprising: an antenna; an amplifier module; and a memory; wherein the device is configured to: receive a plurality of signals with a plurality of corresponding frequencies; apply respective gains to each of the plurality of signals using the amplifier; and store each gain, its corresponding frequency, and a time at which the gain was applied in the memory; wherein the device is configured to receive subsequently a further signal with a further frequency and to apply a further gain to said further signal using the amplifier; wherein the further gain is determined using at least one of the stored gains according to a difference between the further frequency and the plurality of corresponding frequencies and according to a comparison between a time at which the further signal is received and at least one of the stored times.

15. The radio transceiver device as claimed in claim 14, which operates according to an LTE standard.

16. The radio transceiver device as claimed in claim 14, wherein the amplifier module comprises an adjustable gain low noise amplifier.

17. The radio transceiver device as claimed in claim 14, further comprising a digital signal processor arranged to optimise the respective gains using automatic gain control.

18. The method of operating a radio receiver device as claimed in claim 1, comprising disregarding stored gains which were applied at a time before a threshold.

19. The method of operating a radio receiver device as claimed in claim 18, comprising setting the further gain to be equal to a remaining stored gain with a corresponding frequency that is closest to the further frequency.

20. The method of operating a radio receiver device as claimed in claim 18, comprising setting the further gain to be equal to a remaining stored gain that was applied most recently.

Description

[0048] One or more non-limiting examples of the present disclosure will now be described with reference to the accompanying Figures, in which:

[0049] FIG. 1 is a block diagram of an eMTC radio receiver device according to an embodiment of the present invention;

[0050] FIG. 2 is a timing diagram illustrating frequency hopping within an LTE signal; and

[0051] FIG. 3 is a timing diagram illustrating operation of the eMTC radio device shown in FIG. 1.

[0052] FIG. 1 shows an eMTC radio receiver device 2. The receiver 2 is implemented as a system-on-chip (SoC) and comprises: an analogue RF front-end circuit portion 4; a digital circuit portion 6; and a baseband circuit portion 8. The structure and operation of each of these circuit portions 4, 6, 8 are described in turn below.

[0053] The analogue RF front-end circuit portion 4 is arranged to be connected to an antenna 10 via an antenna terminal 12 for receiving LTE eMTC radio signals received over-the-air. The analogue circuit portion 4 comprises: a variable gain pre-amplifier 14; a mixer 16; a local oscillator 18; an in-phase amplifier 20; a quadrature amplifier 22; two bandpass filters 24, 26; an in-phase ADC 28, and a quadrature ADC 30.

[0054] When an incoming LTE radio signal 32 is received via the antenna 10, it is first input to the variable gain pre-amplifier 14 which amplifies the signal 32 to a level suitable for processing by downstream circuitry. Typically, the variable gain pre-amplifier 14 is a low-noise amplifier (LNA), a type of amplifier known in the art per se that is particularly suited to amplifying a signal of interest while rejecting unwanted noise.

[0055] The resulting amplified signal 34 is input to the mixer 16, which is also arranged to receive a signal 36 generated by the local oscillator 18 as a further input. The signal 36 generated by the local oscillator 18 is set to the frequency of interest (i.e. the carrier frequency associated with the channel to which the receiver 2 is currently tuned). This downmixes the amplified signal 34 to baseband and generates an in-phase signal 38 and a quadrature signal 40.

[0056] The in-phase signal 38 and the quadrature signal 40 are passed through the in-phase amplifier 20 and the quadrature amplifier 22 respectively to provide further amplification of each of these signals 38, 40. The resulting amplified in-phase signal 42 and amplified quadrature signal 44 are each passed through a respective band-pass filter 24, 26, where the bandpass filters 24, 26 are tuned to reject signals outside a particular frequency range. This results in a filtered in-phase signal 46 and a filtered quadrature signal 48.

[0057] The filtered in-phase and quadrature signals 46, 48 are input to the in-phase ADC 28 and the quadrature ADC 30 respectively. These ADCs 28, 30 convert the analogue filtered signals 46, 48 to a digital in-phase signal 50 and a digital quadrature signal 52. The resulting digital signals 50, 52 are then input to the digital circuit portion 6.

[0058] The digital circuit portion 6 includes a processor 54 which is connected to a memory 56. The processor is arranged to carry out digital processing of the digital signals 50, 52 in order to decode them, i.e. to retrieve the data within the received sub-frame. Once the processor 54 decodes the received eMTC sub-frame, the resulting data 58 is passed to the downstream baseband circuitry 8, which will use the data for the desired application.

[0059] The strength of the incoming LTE radio signal 32 can vary significantly for a multitude of reasons, including a changing distance to a base station or local environmental effects (e.g. interference or signal attenuation by intervening objects). The digital circuit portion 6 is, therefore, further configured to provide automated gain control (AGC) to the receiver 2. This is provided by the digital circuit portion estimating the amplitudes of the filtered in-phase and quadrature signals 46, 48 using the digital signals 50, 52 from the ADCs 28, 30. The digital circuit portion 6 uses this estimation to provide a control signal 60 the variable gain pre-amplifier 14 to maximise the utilisation of the dynamic range of the ADCs 28, 30 (while avoiding saturating the ADCs 28, 30) for any strength of incoming signal 32.

[0060] For instance, if the incoming signal 32 is weak, such that the estimated amplitudes of the filtered in-phase and quadrature signals 46, 48 are below a maximum input amplitude of the ADCs 28, 30, the digital circuit portion 6 provides a control signal 60 which increases the gain provided by the variable gain pre-amplifier 14. This increases the amplitudes of the filtered in-phase and quadrature signals 46, 48, increasing the utilisation of the ADCs' 28, 30 dynamic range and thus the resolution of their outputs 50, 52. Contrastingly, if the incoming signal 32 is strong, such that estimated amplitudes of the filtered in-phase and quadrature signals 46, 48 are so large as to saturate the ADCs 28, 30, the digital circuit portion 6 provides a control signal 60 which decreases the gain provided by the variable gain pre-amplifier 14. This reduces the likelihood of data being lost during the analogue to digital conversion.

[0061] Operation of the receiver 2 in accordance with an embodiment of the present invention will now be described with further reference to FIG. 2.

[0062] The LTE eMTC radio signals received by the receiver 2 are transmitted within one of eight 1.4 MHz narrowbands 200-207 (which make up a 10 MHz LTE radio channel). The narrowband 200-207 within which the signals are transmitted is changed periodically, following a pseudo-random pattern known in advance by the receiver 2. This is known as frequency hopping.

[0063] This frequency hopping behaviour is shown in FIG. 2, which is a timing diagram showing the active narrowband over time. At an initial time 102 the LTE radio signal 32 is transmitted in a seventh narrowband 207. At the end of a first sub-frame, at time 104, the signal 32 hops to a second narrowband 202. At time 106 the signal 32 hops back to the seventh narrowband 207. At time 108 the signal 32 hops to a third narrowband 203 and then at time 110 the signal 32 hops back to the second narrowband 202.

[0064] The strength of the signal 32 received by the receiver 2 varies with time (e.g. due to movement of a receiver relative to a base station, or changing environmental conditions) but also with the changing narrowbands 200-207 in which it is transmitted (e.g. due to varying multi-path effects or frequency-dependent attenuation). As such, to achieve optimal operation, a different gain needs to be applied by the pre-amplifier 14 as the transmission narrowband 200-207 changes. The conventional automatic gain control provided by the digital circuit portion 6 to the pre-amplifier 14 operates using feedback from the ADCs 28, 30 and thus features an inherent delay. As such, it cannot react immediately to changing gain requirements as the active narrowband 200-207 changes. As explained above, this may result in sub-optimal operation or even lost data.

[0065] The digital circuit portion 6 is configured to mitigate this delay by applying immediately an estimated gain when the signal 32 hops to a different narrowband 200-207, as will be explained in more detail below with reference to FIG. 3.

[0066] Every time the signal 32 hops from one narrowband 200-207 to another (i.e. at times 102, 104, 106 and 108), the gain applied by the pre-amplifier 14 to the signal is recorded in the memory 56, along with the current time and the narrowband for which that gain was applied. A new gain, selected for the narrowband to which the signal 32 is hopping, is then applied.

[0067] As mentioned above and as shown in FIG. 3, at the initial time 102 the transceiver 2 receives a signal on the seventh narrowband 207. The digital circuit portion 6 reads a gain g.sub.7 from the memory 56 which had been previously applied to a signal on the seventh narrowband 207 at a time t.sub.7 and instructs the pre-amplifier 14 to apply this gain to the incoming signal 32. Between times 102 and 104 the signal 32 is demodulated and data extracted. Throughout this period the digital circuit portion 6 refines the gain applied by the pre-amplifier 14 based upon feedback from the ADCs 28, 30.

[0068] At time 104 the digital circuit portion 6 stores the refined value of the gain g.sub.7 for the seventh narrowband 207 in the memory 56 (i.e. the value of g.sub.7 stored in the memory is updated). The digital circuit portion 6 also updates the time t.sub.7 to equal the time 104 at which the refined gain g.sub.7 was applied. The signal 32 hops to the second narrowband 202 and the digital circuit portion 6 retrieves a gain g.sub.2 from the memory 56 which had been previously applied to a signal on the second narrowband 202 at a time t.sub.2. This gain is applied immediately to the signal 32 by the pre-amplifier 14.

[0069] At time 106 the signal 32 hops to the sixth narrowband 206. However, the receiver has not received a signal 32 in the sixth narrowband 206 before and as such, there is not yet a value for the gain to be applied stored in the memory 56. However, instead of continuing to use the gain g.sub.2 which was applied to the signal 32 in the second narrowband 202, the digital signal processor 6 reads the (previously updated) gain g.sub.7 from the memory 56 and applies it to the signal 32.

[0070] While the gain g.sub.7 used for the seventh narrowband 207 may not be optimal for the signal 32 in the sixth narrowband 206, it is likely to be closer than the gain g.sub.2 used for the second narrowband 202, as the frequency difference between the sixth and seventh narrowbands 206, 207 is much less than that between the sixth and second narrowbands 206, 202. Gain g.sub.7 therefore serves as the best estimate the digital signal processor 6 can make of the optimal gain for the sixth narrowband 206 at time 106.

[0071] Alternatively, the digital signal processor 6 may interpolate between two (or more) previously stored gains to determine an estimate for the gain to be applied to the signal 32 in the sixth narrowband 206. For example, the gain for the sixth narrowband 206 may be calculated as a weighted average of g.sub.7 and g.sub.2 (e.g. 0.8× g.sub.7+0.2× g.sub.2)— with the weights being calculated, for example, according to how recently g.sub.7 and g.sub.2 were stored.

[0072] As described above, the gain g.sub.6 applied to the sixth narrowband is refined over time by feedback from the ADCs 28, 30. At time 108, the signal 32 hops to another narrowband, and a refined gain g.sub.6 for the sixth narrowband is stored in the memory 56, along with the time t.sub.6.