Gain control in radio chains of a receiver

There is provided automatic gain control of radio chains of a receiver. At least two radio frequency (RF) signals are received. Each RF signal is received on an individual radio chain from an antenna array. By comparing the at least two RF signals to a threshold it is determined whether to perform gain control or not of at least one of the at least two RF signals before analog combining of the at least two RF signals. A notification is sent to a detector regarding whether gain control is performed or not. Analog combining of the at least two RF signals is performed, thereby generating a single input to the detector.

TECHNICAL FIELD

Embodiments presented herein relate to automatic gain control, and particularly to a method, a receiver, a computer program, and a computer program product for automatic gain control of radio chains of a receiver.

BACKGROUND

In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.

For example, one parameter in providing good performance and capacity for a given communications protocol in a communications network is the capabilities of the radio transceiver devices operating in the communications network. Examples of such radio transceiver devices include both radio access network nodes and portable wireless devices. For example, the radio transceiver devices comprise receivers in order to receive signals from another radio transceiver device or node in the communications network.

As is known by the skilled person, a receiver in a radio transceiver device comprises circuitry configured to perform operations on received signals. One such operation is gain control, or automatic gain control (AGC).

AGC currently exist in radio access network nodes with antennas where the different antenna signal chains are independent of each other. Current radio access network nodes are based on a receiver architecture where there typically are a low number of parallel receiver branches (say, about 2-4) with separate detectors and control loops in each receiver branch. Such an antenna architecture is not possible to implement in an array antenna system using combining before detection.

More particularly, in antenna array systems with a large number of antennas (say, more than 4 antennas), each antenna is connected to low noise amplifiers and then combined into one received signal. In this combined received signal distributed to a detector it is not possible to control the individual antenna signal paths based on the combined received signal at the detector. It is not possible to detect if the signal in one path is saturated and thus distort the combined received signal.

Hence, there is still a need for an improved gain control in a receiver in a radio transceiver device.

SUMMARY

An object of embodiments herein is to provide improved gain control in a receiver in a radio transceiver device.

A particular object of embodiments herein is to provide improved gain control in a receiver in a radio transceiver device where the receiver uses analogue combined beam forming.

According to a first aspect there is presented a method for automatic gain control of radio chains of a receiver. The method is performed by a controller. The method comprises receiving at least two radio frequency (RF) signals. Each RF signal being received on an individual radio chain from an antenna array. The method comprises determining, by comparing the at least two RF signals to a threshold, whether to perform gain control or not of at least one of the at least two RF signals before analogue combining of the at least two RF signals. The method comprises sending a notification to a detector regarding whether gain control is performed or not. The method comprises performing analogue combining of the at least two RF signals, thereby generating a single input to the detector.

Advantageously this provides efficient gain control in a receiver in radio transceiver device.

Advantageously this provides efficient gain control in a receiver in radio transceiver device where the receiver uses analogue combined beam forming.

Advantageously this enables the number of signals between the receiver and the gain control to be reduced from many to one without affecting the gain control functionality in the receiver.

According to a second aspect there is presented a computer program for automatic gain control of radio chains of a receiver, the computer program comprising computer program code which, when run on a processing unit, causes the processing unit to perform a method according to the first aspect.

According to a third aspect there is presented a computer program product comprising a computer program according to the second aspect and a to computer readable means on which the computer program is stored.

According to a fourth aspect there is presented a receiver for automatic gain control of radio chains of a receiver. The receiver comprises a processing unit. The processing unit is configured to receive at least two radio frequency (RF) signals. Each RF signal being received on an individual radio chain from an antenna array. The processing unit is configured to determine, by comparing the at least two RF signals to a threshold, whether to perform gain control or not of at least one of the at least two RF signals before analogue combining of the at least two RF signals. The processing unit is configured to send a notification to a detector regarding whether gain control is performed or not. The processing unit is configured to perform analogue combining of the at least two RF signals, thereby generating a single input to the detector.

Advantageously such a receiver may be combined with an antenna array used for beam-forming in the analog domain and where the detector is integrated in a chip with many antenna receiving elements, e.g., so-called massive multiple-input multiple-output (MIMO). Massive MIMO is in the literature also known as Large-Scale Antenna Systems.

According to a fifth aspect there is presented a radio access network node for automatic gain control of radio chains of a receiver of the radio access network node. The radio access network node comprises an antenna array.

The radio access network node comprises a detector. The radio access network node comprises a receiver according to the fourth aspect.

According to a fifth aspect there is presented a portable wireless device for automatic gain control of radio chains of a receiver of the portable wireless device. The portable wireless device comprises an antenna array. The portable wireless device comprises a detector. The portable wireless device comprises a receiver according to the fourth aspect.

It is to be noted that any feature of the first, second, third, fourth, fifth and sixth aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, fourth, fifth, and/or sixth aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

DETAILED DESCRIPTION

In general terms, in existing receivers in radio access network nodes and portable wireless devices the RF signal from one separate receiver branch is transformed to baseband and then converted into a digital signal by an analog-to-digital converter (ADC). The digital signal is then monitored and it is determined if a gain change of the signal is needed or not. The monitoring and gain change are typically performed independently in each receiver branch in receivers with multiple receiver branches. In some cases the gain changes are determined by measuring on one or more receiver branches and then gain changes are set in all receiver branches.

In the case of receivers in radio access network nodes and portable wireless devices having array antenna systems using analog RF combining these methods are not applicable. Each antenna element, or sub-array of antenna elements in the antenna array, are connected to a low noise amplifier and then combined into one received RF signal connected to a detector.FIG. 1is a schematic diagram illustrating such a known radio signal processing arrangement10. The radio signal processing arrangement10comprises an antenna array11, a receiver12, and a detector13.

The antenna array11is configured to receive radio frequency (RF) signals on individual antenna elements and to provide the received RF signals to the receiver12. The antenna array11comprises n receiver chains.

The receiver12comprises an analogue combiner17. The analogue combiner17is configured for analogue combining of the RF signals. The analogue combiner17combines the RF signals into one signal which is provided to the detector13.

All signals are thus combined before distributed to the detector13. It will therefore not be possible to, for the radio signal processing arrangement10, determine in a detected signal from which path any gain problem has occurred. It will thus not, for the radio signal processing arrangement10, be possible to determine how to provide a compensated gain and which receiver branch (i.e., which radio chain14a,14b, . . .14n) to compensate.

A first possible way to adapt the radio signal processing arrangement10to larger antenna arrays11(corresponding to many individual antenna elements), for example in order to make the radio signal processing arrangement10suitable for so-called massive multiple-input multiple-output (MIMO) could be to scale the radio signal processing arrangement10. However, this may be expensive. A second possible way to adapt the radio signal processing arrangement10to larger antenna arrays11could be to re-build the known radio signal processing arrangement10and change the architecture of the gain elements. Currently, automatic gain control is performed based on measurements made in the digital domain. Hence, the first possible way and the second possible way are not readily combinable.

FIG. 2is a schematic diagram illustrating a radio signal processing arrangement20where embodiments presented herein can be applied. The radio signal processing arrangement20comprises an antenna array21, a receiver22, and a detector23.

The functionalities of the antenna array21, the receiver22, and the detector23correspond to the functionalities of the antenna array11, the receiver12, and the detector13of the radio signal processing arrangement10inFIG. 1, except that the receiver22further comprises a controller28and gain control elements29a,29b, . . . ,29ncontrolled by the controller28.

The antenna array21is thus configured to receive radio frequency (RF) signals on individual antenna elements and to provide the received RF signals to the receiver22. The antenna array21comprises n receiver chains.

The receiver22further comprises gain control elements29a,29b, . . . ,29n. The gain control elements29a,29b, . . . ,29nare controlled by a controller28. In general terms, a new function block in terms of a controller28may thus be added to the radio signal processing arrangement20, where the controller28is operatively connected to the RF signal on each radio chain24a,24b, . . . ,24n. The controller28is operatively connected to the RF signal on each radio chain24a,24b, . . . ,24nbefore the gain control elements29a,29b, . . . ,29n, the individual gain elements26a,26b, . . . ,26nand the analogue combiner27. The controller28may thus detect the RF signal before the gain control elements29a,29b, . . . ,29nand the optional individual gain elements26a,26b, . . . ,26naffect the RF signals. In brief, the controller28detects if any of the RF signals crosses a threshold and based on this determines if gain control should be performed or not by activating or deactivating the gain control elements29a,29b, . . . ,29n. For example, the controller28may control all gain control elements2929a,29b, . . . ,29nwith one control signal, setting the gain control on or off. The controller28indicates to the detector23whether gain control (of the gain control elements29a,29b, . . . ,29n) is activated or not. Hence the controller28may have a communications interface to the detector23. Further detailed disclosure of the gain control elements29a,29b, . . . ,29nand the controller28will be provided below.

The receiver22thus comprises an analogue combiner27. The analogue combiner27is configured for analogue combining of the RF signals. The analogue combiner27combines the RF signals into one signal which is provided to the detector23.

The embodiments disclosed herein relate to automatic gain control of radio chains of a receiver. In order to obtain automatic gain control of radio chains of a receiver there is provided a receiver, a method performed by the receiver, a computer program comprising code, for example in the form of a computer program product, that when run on a processing unit, causes the processing unit to perform the method.

FIG. 3aschematically illustrates, in terms of a number of functional units, the components of a receiver22according to an embodiment. A processing unit31is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc., capable of executing software instructions stored in a computer program product41(as inFIG. 4), e.g. in the form of a storage medium33. Thus the processing unit31is thereby arranged to execute methods as herein disclosed. The storage medium33may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The receiver22may further comprise a communications interface32for communications with the antenna array21and the detector23. The processing unit31controls the general operation of the receiver22e.g. by sending data and control signals to the communications interface32and the storage medium33, by receiving data and reports from the communications interface32, and by retrieving data and instructions from the storage medium33. Other components, as well as the related functionality, of the receiver22are omitted in order not to obscure the concepts presented herein.

FIG. 3bschematically illustrates, in terms of a number of functional modules, the components of a receiver22according to an embodiment. The receiver22ofFIG. 3bcomprises a number of functional modules; a send and/or receive module31a, a determine module31b, and a perform module sic. The receiver22ofFIG. 3bmay further comprises a number of optional functional modules, such as any of an activate and/or deactivate module31d. The functionality of each functional module31a-dwill be further disclosed below in the context of which the functional modules31a-dmay be used. In general terms, each functional module31a-dmay be implemented in hardware or in software. Preferably, one or more or all functional modules31a-dmay be implemented by the processing unit31, possibly in cooperation with functional units32and/or33. The processing unit31may thus be arranged to from the storage medium33fetch instructions as provided by a functional module31a-dand to execute these instructions, thereby performing any steps as will be disclosed hereinafter.

The receiver22may be provided as a standalone device or as a part of a further device. For example, the receiver22may be provided in a radio transceiver device, such as a radio access network node51or a portable wireless device61. The radio access network node51may be a base transceiver station (BTS), a Node B, an evolved node B (eNB), a repeater, a backhaul node, or the like. The wireless terminal61may be a user equipment (UE), a mobile phone, a tablet computer, a laptop computer, etc. or the likeFIG. 2illustrates a radio transceiver device51,61comprising a receiver22. According toFIG. 2the radio transceiver device51,61further comprises an antenna array21, and a detector23, and a receiver22. The receiver22inter alia comprises the controller28.

The receiver22may be provided as an integral part of the radio transceiver device51,61. That is, the components of the receiver22may be integrated with other components of the radio transceiver device51,61; some components of the radio transceiver device51,61and the receiver22may be shared. For example, if the radio transceiver device51,61as such comprises a processing unit, this processing unit may be arranged to perform the actions of the processing unit31associated with the receiver22. Alternatively the receiver22may be provided as a separate unit in the radio transceiver device51,61.

FIG. 4shows one example of a computer program product41comprising computer readable means43. On this computer readable means43, a computer program42can be stored, which computer program42can cause the processing unit31and thereto operatively coupled entities and devices, such as the communications interface32and the storage medium33, to execute methods according to embodiments described herein. The computer program42and/or computer program product41may thus provide means for performing any steps as herein disclosed.

FIGS. 5, 6, and 7are flow chart illustrating embodiments of methods for automatic gain control of radio chains of a receiver. The methods are performed by the receiver22. The methods are advantageously provided as computer programs42.

Reference is now made toFIG. 5illustrating a method for automatic gain control of radio chains24a,24b, . . . ,24nof a receiver22as performed by the receiver22according to an embodiment.

S102: The receiver22receives at least two radio frequency (RF) signals. Each RF signal is received on an individual radio chain24a,24b, . . . ,24nfrom an antenna array21. The processing unit31may be configured to perform step S102by executing functionality of the functional module31a. The computer program42and/or the computer program product41may thus provide means for this step.

S106: The receiver22determines whether to perform gain control or not of at least one of the at least two RF signals. The determination is in the receiver22performed by the controller28. The processing unit31may be configured to perform step S106by executing functionality of the functional module31b. The computer program42and/or the computer program product41may thus provide means for this step. The gain control is to be performed before analogue combining of the at least two RF signals. The receiver22determines whether to perform gain control or not of at least one of the at least two RF signals by comparing the at least two RF signals to a threshold. Examples of how the at least two RF signals may be compared to the threshold as well as examples of the threshold will be provided below.

S108: The receiver22, upon having determined whether to perform gain control or not of at least one of the at least two RF signals, sends a notification to a detector23. The notification is in the receiver22sent by the controller28. The processing unit31may be configured to perform step S108by executing functionality of the functional module31a. The computer program42and/or the computer program product41may thus provide means for this step. The notification regards whether gain control is performed or not.

S112: The receiver22performs analogue combining of the at least two RF signals. The analogue combining is in the receiver22performed by the analogue combiner27. The processing unit31may be configured to perform step S112by executing functionality of the functional module31c. The computer program42and/or the computer program product41may thus provide means for this step. A single input to the detector23is generated by the analogue combining.

The gain control disclosed herein will improve performance of the antenna array21using analogue combining, thereby extending the dynamic range of the receiver22. The receiver may thereby be enabled to receive signals from devices at varying distances to the antenna array21. Further, this may enable the antenna array21to be suitable for antenna arrays21with many individual antenna elements, say about 100 or more antenna arrays simultaneously serving many tens of portable wireless devices61in the same coverage area, and for beam forming with fixed beams in different directions in the coverage area.

Reference is now made toFIG. 6illustrating methods for automatic gain control of radio chains24a,24b, . . . ,24nof a receiver22as performed by the receiver22according to further embodiments.

There may be different ways to determine whether to perform gain control or not of at least one of the at least two RF signals. Different examples relating thereto will now be disclosed.

For example, the determination in step S106may be based on one or more RF signals crossing the threshold, as in optional step S106a.

S106a: The receiver22may determine whether to perform gain control or not of at least one of the at least two RF signals by determining whether to activate or to deactivate performing gain control in case at least one individual RF signal of the at least two RF signals crosses the threshold. The determination is in the receiver22performed by the controller28. The processing unit31may be configured to perform step S106aby executing functionality of the functional module31b. The computer program42and/or the computer program product41may thus provide means for this step.

The receiver22may be configured to perform gain control of at least one of the at least two RF signals by activating or deactivating the gain control elements29a,29b, . . . ,29n. The activation/deactivation is in the receiver22performed by the controller28. There may be different ways to perform the gain control of at least one of the at least two RF signals. Different examples relating thereto will now be disclosed.

For example, activating performing gain control may comprise subjecting at least one of the two RF signals to a gain value. For example, deactivating performing gain control may comprise stopping subjecting at least one of the two RF signals to a gain value. Hence (the controller28in) the receiver22may be configured to deactivate at least one of the gain control elements29a,29b, . . . ,29n.

Either a common gain value for all the at least two RF signals may be used or individual gain values for each one of the at least two RF signals may be used. Thus, as a first example, performing gain control may comprise subjecting all those of the at least two RF signals on which gain control is to be performed to a single gain value. Hence all the gain control elements29a,29b, . . . ,29nmay have one single common gain value. Thus, as a second example, performing gain control may comprise subjecting each one of those of the at least two RF signals on which gain control is to be performed to an individual gain value. Hence at least two of the gain control elements29a,29b, . . . ,29nmay have different gain values.

There may be different ways to determine the individual gain values to be used by the gain control elements29a,29b, . . . ,29n. For example, the individual gain values may depend on properties of the antenna array21. More particularly, the individual gain values may depend on how antenna elements of the antenna array21are combined before low noise amplification.

Further, the gain control may be performed on all of the at least two RF signals or on less than all of the at least two RF signals. Hence, some of the gain control elements29a,29b, . . . ,29nmay be activated whilst some of the gain control elements29a,29b, . . . ,29nmay be deactivated.

There may be different ways to select the threshold. For example, the threshold may comprise a first threshold and a second threshold. The first threshold may be used for determining to activate gain control and the second threshold may be used for determining to deactivate gain control. The first threshold may be higher than the second threshold. Different examples relating thereto will now be disclosed.

For example, the determination in step S106may further comprise comparing the at least two RF signals to a first threshold, as in optional step S106b. The comparing is in the receiver22performed by the controller28.

S106b: The receiver22may activate gain control of at least one of the at least two RF signals in case at least one of the at least two RF signals exceeds a first threshold. The activation is in the receiver22performed by the controller28. The processing unit31may be configured to perform step S106bby executing functionality of the functional module31d. The computer program42and/or the computer program product41may thus provide means for this step. Step S106bmay be performed in case gain control of at least one of the at least two RF signals currently is deactivated.

For example, the determination in step S106may further comprise comparing the at least two RF signals to a second threshold, as in optional step S106c. The comparing is in the receiver22performed by the controller28. The processing unit31may be configured to perform step S106cby executing functionality of the functional module31d. The computer program42and/or the computer program product41may thus provide means for this step.

S106c: The receiver22may deactivate gain control of at least one of the at least two RF signals in case at least one of the at least two RF signals is less than a second threshold. The deactivation is in the receiver22performed by the controller28. The processing unit31may be configured to perform step S106cby executing functionality of the functional module31d. The computer program42and/or the computer program product41may thus provide means for this step. Step S106cmay be performed in case gain control of at least one of the at least two RF signals currently is activated.

The upper part ofFIG. 8schematically illustrates an example of amplitude variation of an RF signal81of the at least two RF signals over time. The lower part ofFIG. 8schematically illustrates how gain control of at least one of the at least two RF signals is activated (inFIG. 8illustrated by gain control being on) and deactivated (inFIG. 8illustrated by gain control being off) based on the to behaviour of the RF signal81. The activation and the deactivation of the gain control is based on comparing the RF signal81to a first threshold (inFIG. 8denoted Threshold_1) and a second threshold (inFIG. 8denoted Threshold_2), respectively. In the outset it is assumed that gain control is deactivated and hence not used. In the illustrative example ofFIG. 8, at time t1the RF signal81exceeds the first threshold and as a result thereof gain control is activated (i.e., inFIG. 8gain control goes from being off to being on). Applying gain control on the RF signal81causes the amplitude of the RF signal81to sink below the first threshold. In the illustrative example ofFIG. 8, at time t2the RF signal81is less than the second threshold and as a result thereof gain control is deactivated (i.e., inFIG. 8gain control goes from being on to being off). Removing application of gain control on the RF signal81causes the amplitude of the RF signal81to rise above the second threshold. In the illustrative example ofFIG. 8, at time t3the RF signal81again exceeds the first threshold and as a result thereof gain control is again activated (i.e., inFIG. 8gain control again goes from being off to being on). Applying gain control on the RF signal81causes the amplitude of the RF signal81to again sink below the first threshold.

Reference is again made toFIG. 6illustrating methods for automatic gain control of radio chains24a,24b, . . . ,24nof a receiver22.

The receiver22may be configured to send further notifications than the notification sent in step S108. The sending is in the receiver22performed by the controller28. For example, such further notifications may relate to how many RF signal that crossed the threshold, and/or which RF signal(s) crossed the threshold, as in optional steps S114and S116.

S114: The receiver22may send a notification regarding how many RF signals of the at least two RF signals that crosses the threshold. The processing unit31may be configured to perform step S114by executing functionality of the functional module31a. The computer program42and/or the computer program product41may thus provide means for this step.

S116: The receiver22may send a notification regarding which RF signals of to the at least two RF signals that crosses the threshold. The processing unit31may be configured to perform step S116by executing functionality of the functional module31a. The computer program42and/or the computer program product41may thus provide means for this step.

The receiver22may be configured to perform further operations of the RF signals, such as low noise amplification and/or further gain operations, as in optional steps S104and S110.

S104: The receiver22may be configured to selectively activate/deactivate low noise amplification on the at least two RF signals before determining whether to perform gain control or not on the at least two RF signals. The processing unit31may be configured to perform step S104by executing functionality of the functional module31d. The computer program42and/or the computer program product41may thus provide means for this step. The low noise amplification is in the receiver22performed by the low noise amplifiers25a,25b, . . . ,25n.

S110: The receiver22may be configured to selectively activate/deactivate individual further gain operations on the at least two RF signals according to antenna beam weights after determining whether to perform gain control or not on the at least two RF signals. The selectively activating/deactivating is in the receiver22performed by the by the controller28. The processing unit31may be configured to perform step S110by executing functionality of the functional module31d. The computer program42and/or the computer program product41may thus provide means for this step. The individual further gain operations is in the receiver22performed by the by the individual gain element26a,26b, . . . ,26n.

The individual further gain operations may be performed before performing the analogue combining, as in step S112. Hence, the individual further gain operations may be performed between the performing the gain control and performing the analogue combining.

Reference is now made toFIG. 7illustrating a method for automatic gain control of radio chains24a,24b, . . . ,24nof a receiver22as performed by the receiver22according to a particular embodiment.

S202: The receiver22receives RF signals on individual radio chains24a,24b, . . . ,24nfrom an antenna array21. Each RF signal in the radio chains is thereby continuously monitored by the receiver22. One way of implementing step S202is to perform step S102.

S204: It is checked whether gain control currently is activated (AGC=“set”→Yes) or deactivated (AGC=“set”→No). If gain control is activated step S212is entered. If gain control is deactivated step S204is entered.

S206: The receiver22compares the received RF signals to a first threshold (Threshold_1). If the received RF signal exceeds the first threshold step S208is entered. If the received RF signal does not exceed the first threshold step S202is entered. One way of implementing step S206is to perform any of steps S106, S106a, and S106b.

S208: The receiver22activates gain control on all received RF signals. One way of implementing step S208is to perform any of steps S106, S106a, and S106b.

S210: The receiver22sends a notification that gain control is activated (by setting “send notification”=“on”). One way of implementing step S210is to perform step S108.

S212: The receiver22compares the received RF signals to a second threshold (Threshold_2). If the received RF signal is lower than the second threshold step S214is entered. If the received RF signal is not lower than the second threshold step S202is entered. One way of implementing step S212is to perform any of steps S106, S106a, and S106c.

S214: The receiver22deactivates gain control on all received RF signals. One way of implementing step S214is to perform any of steps S106, S106a, and S106c.

S216: The receiver22sends a notification that gain control is deactivated (by setting “send notification”=“off”). One way of implementing step S216is to perform step S108.

Thus, according to the embodiment illustrated inFIG. 7the controller28of the receiver22has two states; “AGC on” and “AGC off” (step S204). If the state is “AGC off” and if any of the RF signals are measured above Threshold_1gain control is activated on all RF signals (step S208) and the controller28sets the notification signal “AGC out” to state “on” (step S210). In the “AGC on” state if any of the measured RF signal is below Threshold level_2gain control is deactivated on all RF signals (step S214) and the controller28sets the notification signal “AGC off” to state “off” (step S216). In all other cases the state of the controller28remains unchanged.