WO2012080068A1

WO2012080068A1 - Apparatus, method and method of manufacturing apparatus for interference mitigation

Info

Publication number: WO2012080068A1
Application number: PCT/EP2011/072165
Authority: WO
Inventors: Harri Narhi
Original assignee: Nokia Siemens Networks Oy
Priority date: 2010-12-13
Filing date: 2011-12-08
Publication date: 2012-06-21

Abstract

An apparatus for a communications network is provided. The apparatus includes an antenna configured to receive a first signal and a filter configured to filter the first signal. A directional coupler is arranged between the antenna and the filter and a receiver is coupled to the directional coupler. The directional coupler is configured to couple the first signal to the receiver, and the receiver is configured to convert the first signal to a second signal having a bandwidth larger than a reception bandwidth of the communications network.

Description

METHOD AND METHOD OF MANUFACTURING APPARATUS FOR INTERFERENCE

FIELD OF THE INVENTION

The invention generally relates to an apparatus for communications network. More particularly, the in vention relates to mitigating interference of re ceived signals in wireless communications networks.

BACKGROUND OF THE INVENTION

Interference is a big problem in wireless communica tions networks as it can severely reduce the perfor mance of communication.

Figures 1 and 2 schematically show frequency band diagrams illustrating situations in which interference can be a particular problem.

Figure 1 shows adjacent channel interference, whereby a downlink frequency band of a first radio network slightly overlaps with the uplink frequency band of a second network to which the base station belongs and an edge of the downlink frequency band of the first network is captured by the receiver of the base station. The part of the downlink frequency band of the first network captured by the receiver then inter- feres with the received uplink signals from the receiver's own network.

Figure 2 shows blocking interference In this case, an uplink frequency band received at the base station belonging to a radio network is visible on the receiver of the base station. However, the input filter frequency response of the base station receiver is wider than the reception bandwidth of the network. This means that the receiver filter can capture some of the downlink bandwidth of another radio network, which interferes with the uplink signals from the network in which the base station belongs .

One way of reducing the problem of interference is to decrease the sensitivity of the receiver of the base station or NodeB . However, this desensitization of the receiver leads to reduced network coverage.

Furthermore, the network operator may not be aware of interference problems such as those set out above and illustrated in Figures 1 and 2, or such interference problems may arise at a later stage when a network is already mature .

In order to solve interference problems currently, the interference must be measured by sending a technician to visit the site of the affected base station. Firstly, the base station must be switched off. The technician then measures the interference using separate measurement equipment, for example a spectrum analyser. This requires the antenna cable to be disconnected from the base station and connected to the measurement equipment, which is inconvenient, costly and causes delays and disruption during the time when the base station must be switched off.

Therefore a solution is required to the above problems, which allows interference to be mitigated in a convenient way without causing delays or service interruptions to communication in the wireless network.

SUMMARY OF THE INVENTION

Accordingly, the invention provides an apparatus for a communications network. The apparatus includes an antenna configured to receive a first signal, with a filter being provided, which is configured to filter the first signal. A directional coupler is arranged between the antenna and the filter and a receiver is couplable to the directional coupler, such that the directional coupler is configured to couple the first signal to the receiver. The receiver is configured to convert the first signal to a second signal having a bandwidth larger than a reception bandwidth of the communications network.

The received signal is coupled to a receiver before it is filtered. The receiver then converts the frequency of the received signal so that a signal is produced derived from the received signal, which has a bandwidth that is larger than the normal bandwidth over which signals are received in the network. The first signal can be converted inside the receiver from the time domain to the frequency domain by means of a Fourier transform, for example, in order to obtain the second signal.

In this way, a wideband spectrum is produced, which allows interference to be sensed that would not normally be detected, for example due to signals being picked up at the antenna from another network. This allows the network management functions to then automatically move reception to interference-free channels without the need for time-consuming and inefficient manual interference measurements of base stations where there is a problem. Therefore, the apparatus according to the invention provides the further advantage of being able to be used in a self- organising communications network.

A mixer can be arranged in the receiver, which is configured to up-convert the frequency of the first, received signal to produce the second signal having a higher bandwidth than the reception bandwidth of the network .

A low noise amplifier can be arranged between the directional coupler and the receiver for amplifying the first signal before it is converted by the receiver to the second signal.

The receiver may be coupled to a signal generator configured to apply a conversion signal to the first signal in the receiver so as to convert the first signal to the second signal. The signal generator can be configured to feed a signal to the receiver having a frequency such that the first, received, signal is up-converted to the required bandwidth. The signal generator may also be tunable so that the received signal may be converted to a tunable wideband signal and the bandwidth of the second signal may be further increased .

Preferably, the apparatus includes a sensor configured to detect interference over a frequency range of the second signal. This enables interference to be automatically sensed over a wider bandwidth than the reception bandwidth of the network, which allows problematic interference to be detected that would not normally be found. The interference information may then automatically be sent to management functions of the network, which avoids the need for manual interference measurements .

In an advantageous embodiment, the apparatus includes an interference mitigation means configured to mitigate against signal interference . The interference mitigation means can be configured to automatically block reception on channels that have been found to contain interference by the wideband interference sensing information made available to the network management functions . In this way, only interference-free uplink signals are received.

The invention further provides a network node. The network node includes an apparatus having an antenna configured to receive a first signal. A filter is provided, which is configured to filter the first signal. A directional coupler is arranged between the antenna and the filter and a receiver is coupled to the directional coupler, such that the directional coupler is configured to couple the first signal to the receiver . The receiver is configured to convert the first signal to a second signal having a bandwidth larger than a reception bandwidth of the communications network. The network node may be a base station or Node B, for example . The received signal is coupled to a receiver before it is filtered. The receiver then converts the frequency of the received signal so that a signal is produced from the received signal, which has a bandwidth that is larger than the normal bandwidth over which signals are received in the network. The first signal can be converted inside the receiver from the time domain to the frequency domain by means of a Fourier transform, for example, in order to obtain the second signal.

In this way, a wideband spectrum is produced at the network node, which allows wideband interference information to be obtained so that interference can be detected that would not be expected to affect the reception bandwidth of the network. This means that interference measurement can be automated and allows the network node to be employed in a self-organising communications network. Furthermore, communication via the network node does not have to be disrupted in order for the network operator to be made aware of interference problems, since the antenna cable is not required to be disconnected from the network node to perform a manual measurement .

A mixer can be arranged in the receiver, which is configured to up-convert the frequency of the first, received signal to produce the second signal having a higher bandwidth than the reception bandwidth of the network at the network node .

The receiver may be coupled to a signal generator configured to apply a conversion signal to the first signal in the receiver so as to convert the first signal to the second signal. The signal generator can be configured to feed a signal to the receiver having a frequency such that the first, received, signal is up-or down-converted to the required bandwidth. Furthermore the signal generator may be tunable so that signals having a range of frequencies can be applied to the first signal. This provides the advantage that the second signal may have a range of bandwidths wider than the reception bandwidth of the network.

Preferably, the network node includes a sensor configured to detect interference over a bandwidth of the second signal. This enables the network node to automatically perform wideband interference sensing itself. Furthermore it enables interference to be sensed over a wider bandwidth than the reception bandwidth of the network, which means that the network operator can be automatically made aware of interference problems not normally detectable. This also allows the network operator to automatically move reception of signals at the network node to unoccupied channels that are free of interference.

In an advantageous embodiment, the network node includes an interference mitigation means configured to mitigate against signal interference . The interference mitigation means can be configured to automatically block reception on channels that have been found to have interference problems by the wideband interference sensing information made available from the network node to the network management functions .

The invention further provides a method of processing a signal in a wireless communications network. The method includes receiving a first signal, filtering the first signal, directionally coupling the first signal to a receiver before the first signal is filtered, and converting the first signal in the receiver to a second signal having a bandwidth outside a reception bandwidth of the wireless network. This produces a wideband spectrum and provides the advantage that interference of a received signal can be sensed over a wideband spectrum. The method according to the invention can then be used in a self- organising network and it is not required to take interference measurements manually.

Preferably, the method further includes sensing interference over a bandwidth of the second signal. This provides the advantage that interference information from the wideband spectrum can automatically be made available to network management functions, which avoids the need for time-consuming and inefficient manual interference measurements .

In an advantageous embodiment, the method further includes moving a connection between a subscriber station and the communications network to a channel that the step of sensing has determined to be free of interference. This means that signals can be received in an unoccupied channel without interference. Furthermore, the method may include mitigating against signal interference, which can be achieved automatically once interference has been sensed over the bandwidth of the second signal.

The invention also provides a method of manufacturing an apparatus for a wireless communications network. The method includes coupling an antenna to a filter via a directional coupler, and coupling the directional coupler to a receiver .

The method may further include coupling the receiver to an interference sensor so that interference measurements can be taken automatically and be made available to network management functions .

The invention will now be described, by way of example only, with reference to specific embodiments and to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic frequency band diagram illustrating a type of interference in a wireless communications network;

Figure 2 is a schematic frequency band diagram illustrating a type of interference in a wireless communications network;

Figure 3 is a simplified schematic block diagram wireless communications network according to an bodiment of the invention; Figure 4 is a simplified schematic block diagram of an apparatus according to an embodiment of the inven- tion ;

Figure 5 is a simplified schematic block diagram of an apparatus according to an embodiment of the inven- tion ;

Figure 6 is a more detailed diagram of the apparatus shown in Figures 4 and 5;

Figure 7 is a simplified schematic block diagram of an apparatus according to another embodiment of the invention ;

Figure 8 is a simplified schematic block diagram of an apparatus according to another embodiment of the invention; and

Figure 9 is a more detailed diagram of the apparatus shown in Figures 7 and 8.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Figure 3 schematically shows a radio access network, for example a UMTS network, although the invention as described below could apply to any other wireless network or broadcast network. Access to the network is provided via a Node B 1 controlled by a radio network controller (RNC) 2 (In the case of an LTE net- work, the functionality of the RNC and the Node B would be included in a single eNode B module) over an Iub interface. A radio module is provided inside the Node B 1.

The RNC 2 is connected to a core network, which includes an operation and management facility O&M.

Figures 4 and 5 show a radio module 3 according to a first aspect of the invention, which is a component of the Node B 1 in the case where the Node B 1 employs FDD (frequency division duplex) modulation for received signals .

The radio module 3 includes an antenna Al for receiving uplink signals, which is coupled by an antenna line LI to a duplex filter DF . A directional coupler DC1 is coupled between the antenna Al and the duplex filter DF . An amplifier unit Ampl is coupled to the duplex filter DF and to an intermediate frequency module IF1 The intermediate frequency module IF1 is connected to a base band processing unit BB1.

In the radio module 3 shown in Figure 4, the directional coupler DC1 is directly coupled to the base band processing unit BB1 so that the directional coupler DC1 and base band processing unit BB1, used for interference spectrum sensing, can be completely separate from the rest of the components in the radio module 3.

Alternatively, as shown in Figure 5, the directional coupler DC1 is directly coupled to the intermediate frequency module IF1. In this embodiment, part of the predistortion feedback receiver of the power amplifier Ampl can be used for wideband reception (with the intermediate frequency module IF1 containing the predistortion feedback receiver of the amplifier Ampl .

The directional coupler DC1 is configured to couple signals received at the antenna Al via a low noise amplifier LNA1 to a frequency conversion module, which is shown in Figure 6. The frequency conversion module includes a mixer Ml coupled via an amplifier IFA1 to an interference filter IFF1 and an analog to digital conversion unit AD1. The mixer Ml is also coupled to a signal generator SI .

In operation, uplink signals having a frequency range 1920 - 1980 MHz over the defined reception bandwidth of the network are received at the Node B 1 through the antenna Al . The received signals are filtered by the duplex filter DF . However, since the directional coupler DC1 is arranged between the antenna Al and the duplex filter DF, a portion of the received signals are directionally coupled to the mixer Ml in the frequency conversion module before being filtered.

In the mixer, Ml a signal from the signal generator SI is applied to the received signal and it is converted by a Fourier transform process from an analog signal in the time domain to a signal in the frequency domain having a bandwidth of 150 MHz larger than the reception bandwidth of the wireless network. Any interference from networks operating in adjacent or proximal frequency bandwidths that have been picked up by the Node B 1 may then be detected in the received signal.

In one embodiment of the invention, any interference present in the converted signals is amplified by the amplifier IFA1, filtered by the filter IFF1 and processed in the base band processing unit BB1 after being converted to a digital signal in the A/D converter AD1 to obtain a wideband interference spectrum. Interference in the processed signals is then detected and measured, whereby the interference spectrum is measured in the A/D converter AD1 and converted by fourier transform FFT to the frequency domain in the base band processor BB1. Interference in channels over the whole bandwidth of the converted received signals may then be detected.

The interference measurements taken in the radio module are then automatically transmitted by the Node B 1 to the O&M facility in the core network.

In one embodiment of the invention, channels that have been found to contain interference are automatically blocked. This is achieved by using the duplex filter DF as a selective band pass filter which only allows channels having a frequency outside that of the channel affected by interference to be received.

Alternatively, an interference blocker or attenuator is used to mitigate interference in the received signals, which attenuates the interference in the received signals . The level of blocking carried out by the interference blocker is determined by the interference sensing in the radio module 3. If, for exam- pie, the level of interference has been determined to be 8 dB, a -8 dB interference blocker (attenuator) is provided in the frequency range of the channel affected by interference .

In a further embodiment of the invention, the Node B 1 automatically switches the channel on which signals are received to an unoccupied channel that the radio module 3 has detected to be free of interference .

Figures 7 and 8 show a radio module 13 according to a second aspect of the invention, which is a component of the Node B 1 in the case where the Node B 1 employs TDD (time division duplex) modulation for received signals.

The radio module 13 includes an antenna A2 for receiving uplink signals, which is coupled by an antenna line L2 to a filter F and an isolator I (the filter F and the isolator I replace the duplex filter DF of the FDD radio module shown in Figures 4 and 5) . A directional coupler DC2 is coupled between the antenna A2 and the filter F. An amplifier unit Amp2 is coupled to the filter F and to an intermediate frequency module IF2. The intermediate frequency module IF2 is connected to a base band processing unit BB2.

In the radio module 3 shown in Figure 7, the directional coupler DC2 is directly coupled to the base band processing unit BB2 so that the directional coupler DC2 and base band processing unit BB2, used for interference spectrum sensing, can be completely separate from the rest of the components in the radio module 13. Alternatively, as shown in Figure 8, the directional coupler DC2 is directly coupled to the intermediate frequency module IF2. In this embodiment, part of the predistortion feedback receiver of the power amplifier Amp2 can be used for wideband reception (with the intermediate frequency module IF2 containing the predistortion feedback receiver of the amplifier Amp2.

The directional coupler DC2 is configured to couple signals received at the antenna A2 via a low noise amplifier LNA2 to a frequency conversion module or receiver, which is shown in Figure 9. The frequency conversion module includes a mixer M2 coupled via an amplifier IFA2 to a filter IFF2 and an analog to digital conversion unit AD2. The mixer M2 is coupled to a signal generator S2. However, in the TDD radio module shown in Figure 8, in which the directional coupler DC2 is directly coupled to the intermediate frequency IF2, the mixer M2 is not required if the interference frequency is wideband. In this case the feedback path of the power amplifier Amp2 is uti- lized. If the interference frequency is narrowband, the mixer M2 is required as it performs the signal transformation from close to passband frequencies on antenna frequencies to the base band processor BB2.

In operation, uplink signals having a frequency range 1910-1920 MHz over the defined reception bandwidth of the network are received at the Node B 1 through the antenna A2. The received signals are filtered by the filter F.

Since the directional coupler DC2 is arranged between the antenna A2 and the filter F, a portion of the received signals are directionally coupled to the mixer M2 in the frequency conversion module before being filtered. The time domain analog signal is fed to the mixer M2 and transformed to the frequency domain by means of a Fourier transform. In the mixer M2, a signal from the signal generator S2 is applied to the received signal and it is converted to a wideband frequency spectrum with a bandwidth 150 MHz larger than the reception bandwidth of the wireless network. Any interference from networks operating in adjacent or proximal frequency bands that have been picked up by the Node B 1 may then be detected in the received signals .

In one embodiment of the invention, any interference present in the converted signals is amplified by the amplifier IFA2, so that an interference sensing bandwidth is determined by the interference filter IFF2 and the A/D converter AD2. Interference in the processed signals is then detected and measured in the A/D converter AD2 after the signals have been processed in the base band processing unit BB2 by FFT . The radio module 13 is able to detect interference in channels over the whole frequency bandwidth of the converted received signals .

The interference spectrum derived from measurements taken by the radio module 13 is then automatically transmitted by the Node B 1 to the management facility O&M in the core network.

In one embodiment of the invention, channels that have been found to contain interference are automatically blocked by the Node B 1. This is achieved by using the filter F as a selective band pass filter (which only allows channels having a frequency outside that of the channel affected by interference to be received.

Alternatively, an interference blocker can be used, which automatically attenuates the interference in the received signals . The level of blocking is de- termined by the interference sensing in the radio module 13. If, for example, the level of interference has been determined to be 8 dB, a -8 dB interference blocker (attenuator) is provided in the frequency range of the channel affected by interference .

In a further embodiment of the invention, the Node B 1 automatically switches the channel on which signals are received to an unoccupied channel that the radio module 13 has detected to be free of interference.

In a further embodiment of the invention, the signal generator S2 is tunable so that the received signals may be converted to signals having a tunable bandwidth and the interference spectrum may be further increased.

Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further al- ternatives will occur to the skilled person, which lie within the scope of the invention as claimed.

For example, although the above embodiments of the invention have been described with reference to a wireless communications system, they may be applied in any broadcast system.

Claims

1. An apparatus for a communications network, the apparatus comprising:

an antenna configured to receive a first signal;

a filter configured to filter the first signal;

a directional coupler arranged between the antenna and the filter; and

a receiver couplable to the directional coupler, wherein the directional coupler is con- figured to couple the first signal to the receiver, and the receiver is configured to convert the first signal to a second signal having a bandwidth larger than a reception bandwidth of the communications network .

2. The apparatus according to claim 1, wherein a mixer is arranged in the receiver .

3. The apparatus according to claim 1 or claim 2, further comprising a low noise amplifier arranged between the directional coupler and the receiver .

4. The apparatus according to any of claims 1 to 3, wherein the receiver is couplable to a signal generator configured to apply a conversion signal to the first signal in the receiver so as to convert the first signal to the second signal.

5. The apparatus according to any of claims 1 to 4, further comprising a sensor configured to detect interference over a frequency range of the second signal.

6. The apparatus according to claim 5, further comprising means configured to mitigate against signal interference.

7. A network node for a communications network, comprising an apparatus according to any preceding claim.

8. A method of processing a signal in a wireless communications network, the method comprising receiving a first signal, filtering the first signal, directionally coupling the first signal to a receiver before the first signal is filtered, and converting the first signal in the receiver to a second signal having a bandwidth outside a reception bandwidth of the wireless network.

9. The method according to claim 8, further comprising sensing interference over a frequency range of the second signal.

10. The method according to claim 9, further comprising moving a connection between a subscriber station and the communications network to a channel that the step of sensing has determined to be free of interference .

11. The method according to claim 10, further comprising mitigating against signal interference.

12. A method of manufacturing an apparatus for a wireless communications network, the method comprising coupling an antenna to a filter via a directional coupler, and coupling the directional coupler to a receiver .

13. The method according to claim 12, further comprising coupling the receiver to an interference sensor .