WO2015144221A1

WO2015144221A1 - Improved radio receiver desensitization

Info

Publication number: WO2015144221A1
Application number: PCT/EP2014/056113
Authority: WO
Inventors: David OTTOSSON; Anders Lamm
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-03-27
Filing date: 2014-03-27
Publication date: 2015-10-01

Abstract

A method in a network node for receiving a first wireless signal from a first wireless device, the method comprising the steps of receiving S1 a aggregated radio signal comprising the first wireless signal, and extracting S2 the aggregated radio signal to extract the first wireless signal, as well as generating S3 a first interference signal f₁(n(t)) based on at least one first pre- determined reference interference signal level, and also adding S4 the first interference signal f₁(n(t)) to the extracted first wireless signal prior to detecting the first wireless signal.

Description

IMPROVED RADIO RECEIVER DESENSITIZATION

TECHNICAL FIELD

The present disclosure relates to wireless communication systems, and in particular to transmit power control of wireless devices.

BACKGROUND

In wideband code division multiple access, WCDMA, networks, a plurality of wireless devices, or user equipments, UEs, transmit wireless signals simultaneously in a shared frequency band over an uplink to one or more radio base stations, RBSs.

Radio transmissions in the uplink of a WCDMA network are not perfectly orthogonal, meaning that interference is generated in the WCDMA uplink. This interference can contribute to degraded network performance, and is especially burdensome when attempting to receive a weak wireless signal comprised in a received aggregated radio signal where there are also significantly stronger wireless signals present.

To alleviate this interference problem, many wireless networks, and WCDMA networks in particular, implement transmit power control, TPC, schemes which aim at reducing interference effects in the network. A conventional TPC scheme controls the output power of wireless devices to maintain estimated Signal-to-lnterference plus Noise Ratios, SINRs, close to pre-set target values at a receiving RBS.

A potential problem can arise when a wireless signal transmitted by a wireless device is received and decoded at more than one network node, e.g., at a first serving RBS, or NodeB, and also at a second non-serving RBS. This situation can, for instance, occur if a wireless device is undergoing soft handover between two network nodes in a WCDMA network. In such scenarios, it is possible that the received power of the wireless signal, and thus also the corresponding signal to interference and noise ratio, SINR, differs at the two network nodes due to, e.g., differences in propagation distance. A network node experiencing high SINR may then, as part of a TPC routine, request transmit power reduction, which transmit power reduction can lead to unwanted loss of data at the second network node where SINR could be significantly worse than at the first network node.

This phenomenon is especially pronounced where small cells are bordering larger cells, which is often the case in heterogeneous networks. Thus, large power imbalances between network nodes in a WCDMA system can lead to large differences in UpLink Raise Over Thermal, UL RoT, which can have implications especially during Soft Handover, SHO, of wireless devices between, e.g., a larger macro cell and a smaller cell, since, during SHO the transmit power of a UE is controlled by more than one NodeB.

To give an example, suppose a non-serving cell NodeB measures a high SINR on a wireless signal received from a given UE, and that a serving cell NodeB measures a lower SINR on the same wireless signal. The non-serving cell may then repeatedly send transmit power control, TPC, messages to the UE requesting transmit power reduction. Consequently, the detection performance of, e.g., HS-DPCCH in the serving cell can be significantly degraded and in the end, the HSDPA throughput can be affected. So-called desensitization has been proposed to compensate for large power imbalances in, e.g., DL CPICH power between cells in heterogeneous network cell configurations in WCDMA networks. During desensitization an artificial interference is, according to current practice, added to the received aggregated radio signal in a network node, such as the non-serving cell NodeB in the example above. Hence, a received aggregated radio signal, comprising one or more wireless signals transmitted by one or more wireless devices to a network node, is purposely injected with interference in order to bring down the measured SINR. By this action of interference injection, all measured SINRs on all wireless signals will be lowered, allowing, e.g., for the SINR of a UE in a non-serving cell to be aligned with the SINR of the same UE in the serving cell. The UL-TPC will then not only be controlled by the non-serving cell NodeB and the HS-DPCCH detection performance in the serving cell of the above example can be maintained at an acceptable level.

There are, however, potential problems associated with current desensitization practice. For instance, all users that have a radio link setup in a cell where desensitization is performed are affected by the desensitization. Current desensitization practice will therefore unnecessarily limit, e.g., battery life-time of users which transmit a wireless signal received at a single network node and which are not suffering from, or contributing to, the power unbalance problem described above. Also, the Raise Over Thermal, RoT, in the cell doing the desensitization will be increased which can lead to degradation of the UL throughput in the cell.

Hence, there is a need for improved desensitization mechanisms for radio receivers, and in particular for improved desensitization mechanisms for WCDMA radio receivers.

SUMMARY

An object of the present disclosure is to provide network nodes and methods which seek to mitigate, alleviate, or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and to provide improved desensitization mechanisms.

This object is obtained by a method in a network node implementing power control, for receiving a first wireless signal from a first wireless device. The method comprises the steps of receiving an aggregated radio signal comprising the first wireless signal, and extracting the first wireless signal from the aggregated radio signal, as well as generating a first interference signal based on at least one first pre-determined reference interference signal level, and also adding the first interference signal to the extracted first wireless signal prior to detecting the first wireless signal, wherein said detection involves generating power control input data for controlling the transmit power of the first wireless device transmitting the first wireless signal.

Thus, instead of adding artificial noise, i.e., the interference signal, directly to the received aggregated radio signal in a network node, it is proposed herein to first process the received aggregated radio signal in order to extract a first wireless signal corresponding to one or more signals transmitted by a specific UE in the network. Then, interference is purposely added to the specific first wireless signal independently of other received wireless signals, as opposed to being added to all received wireless signals at once, which leads to improved control over the desensitization process since desensitization can be done on a per user basis instead of for all users at once. Consequently, all users that have a radio link setup in a cell where desensitization is done are not necessarily affected by the desensitization. It is thus, by the present teaching, provided a method to only desensitize the wireless signals where desensitization is beneficial, i.e., where there is a power and/or SINR balance problem as described above, e.g., for a wireless device undergoing soft handover. Thus, according to an aspect, the wireless device is undergoing a soft handover routine for handover between the network node and a further network node.

Further, all demodulated physical channels for a specific user need not necessarily be desensitized as is the case when interference is added directly to the received aggregated radio signal. This means that the decoding performance of physical channels which is not in need of desensitizing is not degraded. Examples of such channels which are commonly not in need of desensitization are the HS-DPCCH, and the E-DPCCH.

Also, advantageously, the RoT in the desensitizing cell will be lower by the present technique compared to when applying interference directly to the received aggregated radio signal, thus UL throughput in the cell is not necessarily degraded. According to an aspect, the method further comprises the step of sending a transmit power control, TPC, message to the first wireless device based on the generated power control input data.

Thus, the present desensitization mechanism can be exploited for improving the transmit power control of the first wireless device, allowing, e.g., for the SINR of a specific UE in a non- serving cell to be aligned with the SINR of the same UE in the serving cell, independently of other UEs.

According to an aspect, the step of extracting the first wireless signal comprises de-spreading and descrambling, DS, the aggregated radio signal. According to another aspect, the step of extracting further comprises any of amplification by a low-noise amplifier, LNA, automatic gain control, AGC, channel compensation, CH-COMP, maximum ratio combining, MRC, soft scaling, rake finger combining, and generalized rake finger combining. According to an aspect, the step of generating a first interference signal further comprises generating the first interference signal based on signal processing steps applied to the aggregated radio signal in extracting the first wireless signal.

Consequently, the interference injection in the first wireless signal is adapted based on the specific processing that is undertaken in order to extract the first wireless signal. The effect of the interference injection can then, e.g., mimic the effect obtained from injecting interference, or noise, directly into the received aggregated radio signal.

According to an aspect, the first wireless signal comprises at least one first wireless signal component, and, according to an aspect, one of the at least one wireless signal component is received over any of a Dedicated Physical Control Channel, DPCCH, an Enhanced Dedicated Physical Data Channel, E-DPDCH, or a Physical Random Access Channel, P-RACH.

Thus, the present teaching also provides for handling wireless signals comprising sub-signals or components. The components being signals received via different channels in the WCDMA communication system, and having different purposes in the WCDMA communication system.

According to an aspect, the first interference signal comprises at least one interference signal component. The step of adding then comprises adding each of the at least one interference signal component to at least one respective first wireless signal component.

This is potentially beneficial in that different channel signals can be injected with different levels of interference, which is advantageous in that it allows a greater detail of network control and optimization. According to an aspect, each of the at least one interference signal component is a scaled replica of a common interference signal component, which common interference signal component is generated from a sequence of pre-determined interference signal values.

The use of a scaled replica provides for ease of implementation. According to an aspect, the method is applicable for receiving also a second wireless signal from a second wireless device. The received aggregated radio signal then further comprises the second wireless signal. The method then further comprises: extracting the second wireless signal from the aggregated radio signal, generating a second interference signal based on at least one second predetermined reference interference signal level, as well as adding the second interference signal to the extracted second wireless signal prior to detecting the second wireless signal, wherein said detection involves generating further power control input data for controlling the transmit power of the second wireless device transmitting the second wireless signal.

Accordingly, the present teaching provides for injecting different interference signals to different extracted wireless signals, since there may be no need for interference injection in all extracted wireless signals, as discussed above. Further, by injecting different interference signals in the different extracted wireless signals, different UEs can be aligned in SINR to different RBSs.

According to an aspect, the method further comprises the step of sending a transmit power control, TPC, message to the second wireless device based on the generated further power control input data.

Thus, aspects of the present desensitization mechanism are exploited for improving transmit power control of the second wireless device.

The object is also obtained by a computer program comprising computer program code which, when executed in a network node, causes the network node to execute the methods disclosed above.

The object is further obtained by a network node implementing power control, the network node comprises: a communication interface configured to enable communication with at least a first wireless device transmitting a first wireless signal;

a processor; and a memory storing computer program code which, when run in the processor, causes the network node:

- to receive an aggregated radio signal comprising the first wireless signal,

- to extract the first wireless signal from the aggregated radio signal, and

- to generate a first interference signal fl(n(t)) based on at least one first

-determined reference interference signal level, as well

- to add the first interference signal fl(n(t)) to the extracted first wireless signal prior to detecting the first wireless signal, said detection involving to generate power control input data for controlling the transmit power of the first wireless device transmitting the first wireless signal.

According to an aspect, the network node further comprises a TPC message transmitter unit configured to send a transmit power control, TPC, message to the first wireless device based on the generated power control input data.

According to an aspect, the communication interface is further configured to enable communication with a second wireless device transmitting a second wireless signal. The memory is then storing computer program code which, when run in the processor, causes the network node: to extract the second wireless signal from the aggregated radio signal (426), and to generate a second interference signal f2(n(t)) based on at least one second determined reference interference signal level, as well

to add the second interference signal f2(n(t)) to the extracted second wireless signal prior to detecting the second wireless signal, said detection involving to generate further power control input data for controlling the transmit power of the second wireless device transmitting the second wireless signal.

According to an aspect, the network node further comprises a TPC message transmitter unit configured to send a transmit power control, TPC, message to the second wireless device based on the generated further power control input data.

The object is also obtained by a network node implementing power control. The network node comprises a receiver arranged to receive an aggregated radio signal from at least a first wireless device. The aggregated radio signal comprises a first wireless signal transmitted by the first wireless device. The receiver comprises an antenna unit adapted to receive the aggregated radio signal, and a signal processing unit arranged to extract the first wireless signal from the aggregated radio signal. The receiver also comprises an interference signal generator module arranged to generate a first interference signal fl(n(t)) based on at least a first pre-determined reference interference signal level, as well as an interference addition module adapted to add the first interference signal fl(n(t)) to the extracted first wireless signal prior to detecting the first wireless signal by a detector unit comprised in the receiver, wherein said detection involves generating power control input data for controlling the transmit power of the first wireless device transmitting the first wireless signal.

The computer program and the network nodes display advantages corresponding to the advantages already described in relation to the methods performed in the network node.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features, and advantages of the present disclosure will appear from the following detailed description, wherein some aspects of the disclosure will be described in more detail with reference to the accompanying drawings, in which:

Figure 1 is a schematic overview of a radio access network.

Figure 2 is a schematic overview of cells in a cellular radio access network. Figure 3 is a flowchart illustrating embodiments of method steps.

Figures 4-5 are block diagrams illustrating embodiments of radio receivers.

Figure 6 is a block diagram of an embodiment of a network node.

Figure 7 is a block diagram of an embodiment of a wireless device. DETAILED DESCRI PTION

Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The nodes, devices, computer program and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout, except for a prefix digit in the number which represents the figure in which the element is to be found.

The terminology used herein is for the purpose of describing particular aspects of the disclosure only, and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Abbreviations

3GPP 3rd Generation Partnership Project

BLER Block Error Ratio

CPICH Common Pilot Channel

DL DownLink

DPCCH Dedicated Physical Control Channel

E-DCH Enhanced - Dedicated Channel

E-DPCCH E-DCH Dedicated Physical Control Channel

E-DPDCH Enhanced Dedicated Physical Data Channel

FI R Finite Impulse Response

HSDPA High Speed Downlink Packet Access

HS-DPCCH Dedicated Physical Control Channel (uplink) for HS-DSCH

HS-DSCH High Speed Downlink Shared Channel IS Interference Suppression

MRC Maximal Ratio Combining

OLPC Outer Loop Power Control

P-RACH Physical Random Access Channel

RBS Radio Base Station

RoT Raise Over Thermal

SHO Soft Handover

SINR Signal to Interference and Noise Ratio

SNR Signal to Noise Ratio

TPC Transmit Power Control

UE User Equipment

UL UpLink

UL-TPC UpLink Transmit Power Control

WCDMA Wideband Code Division Multiple Access

Figure 1 shows a schematic overview of a radio access network. There are two network nodes 102, 103, arranged to receive wireless signals comprised in radio signals 109a, 109b transmitted from a respective first 101 and a second 110 wireless device. The first wireless device 101 is shown to receive radio signals 104, 105 transmitted from the two network nodes 102, 103. Due to differences in propagation distance, the SINR of received wireless signals can be expected to differ at the two network nodes 102, 103.

Consider now the first wireless device 101, and suppose it is undergoing soft handover between the leftmost network node 102 and the rightmost network node 103. The optimal UL 107 and DL 108 handover distance thresholds are shown as dashed lines, and it is observed that the two thresholds do not co-incide. Thus, it can be understood from looking at Figure 1 that a power imbalance problem such as the one mentioned above can occur here, since the SINR at the rightmost network node is likely to be higher than the SINR at the leftmost network node. Thus, the rightmost network node may transmit TPC messages to the first wireless device asking for transmit power reduction. However, should the wireless device comply with the TPC messages, there is a danger that data loss occur at the leftmost network node 102. For instance, HS-DPCCH and E- DPCCH data may be lost due to insufficient receiver SINR at the leftmost network node 102.

The present desensitization technique is applicable to a wide variety of wireless signals in a wide variety of communication systems. However, the following physical channels in a WCDMA network are likely to be subjected to desensitization:

DPCCH: The reason for desensitization of DPCCH is to lower the estimated SINR at an RBS and force UL-TPC up commands, i.e., transmit power increase commands, when using a RAKE receiver.

E-DPDCH: The reason for desensitization of E-DPDCH is to decrease the SINR of the E-DPDCH soft symbols into a Turbo decoding function. By this action, a linear increase in block error rate, BLER, is obtained. This will prevent that the Outer Loop Power Control, OLPC, acts to decrease the SINR target of the UE which would work against the goal to increase the transmit power for the UE.

Figure 2 is a schematic overview of cells in a cellular radio access network. A large cell A 211, e.g., a macro cell is shown bordering a smaller cell a 212. It is noted, based on the discussion above, that power unbalance problems can occur for wireless devices located in the intersection between the large cell A 211 and the smaller cell a 212.

There are also shown two additional smaller cells b 213 and c 214. Wireless devices located in the intersection between smaller cell b 213 and smaller cell c 214 are, however, not likely to suffer from problems related to power unbalance. The same can be said of wireless devices located in the intersection area between a 212 and b 213, and between a 212 and c 214.

Thus, in some cell configurations, a small cell might not overlap with a bigger cell in any cell region, c.f., e.g., cells b and c in Figure 2. There is no need to desensitize a user in SHO between cell a 212 and cell b 213, nor is there a need to desensitize a user in SHO between cell b 213 and cell c 214. By doing desensitization on wireless device level, i.e., per user and even per user channel, it is provided a more refined way of when to do desensitization and when to refrain from desensitization. This stands in contrast to current practice of desensitizing all wireless devices in a cell at all times by injecting interference into the received aggregated radio signal, which received aggregated radio signal comprises all wireless signals from all wireless devices in the cell.

If a user leaves SHO between the large cell and one of the smaller cells in Figure 2, and obtains the small cell as its serving cell, the desensitization state shall be terminated, since there is no longer any need for desensitization of the wireless signal. In case the interference signal added to the wireless signal is a scaled generated interference signal, termination of desensitization state is, according to an aspect, done by setting the scaling factor to zero.

Figure 3 is a flowchart illustrating embodiments of method steps. An embodiment of a radio receiver 420a, arranged to perform the method steps, is shown in Figure 4.

In particular, Figure 3 shows a method in a network node 103 implementing power control, for receiving a first wireless signal from a first wireless device 101.

Thus, the method is applicable in the type of network shown in Figures 1 and 2, and discussed above. Consequently, according to an aspect, the aggregated radio signal is an uplink signal in a WCDMA radio access network. Also, according to another aspect, the network node 103 is a non-serving NodeB of the first wireless device 101. The method comprises receiving SI an aggregated radio signal 426 comprising the first wireless signal. As noted above, the aggregated radio signal is according to one aspect an uplink signal in a WCDMA communication system. The first wireless signal is then a part of the uplink signal which wireless signal can comprise a number of channels, or components, wherein each such component originates from the wireless device 101. The wireless device 101 can be a UE in a WCDMA network, and the network node 103 can be an RBS in the WCDMA network.

The method further comprises the step of extracting S2 the first wireless signal 427a from the aggregated radio signal 426. A collection of signal processing units for performing the step of processing is in Figure 4 shown as f(ui). Details of this processing will be given below in connection to Figure 5. However, in general, said processing pertains to extracting the first wireless signal from the aggregated radio signal. Thus, according to an aspect, the step of processing comprises de-spreading of the aggregated radio signal into one or more components originating from the first wireless device 101. The method also comprises generating a first interference signal fi(n(t)) based on at least one first pre-determined reference interference signal level. This interference signal plays a part in aligning measured SIN Rs at two different RBSs. If, e.g., the RBS measuring a smaller of the SIN Rs performs the method illustrated in Figure 3, then that measured SN R will selectively change for a given user or wireless device independently of measured SIN Rs of other wireless devices in the cell.

The interference signal can be generated in a number of different ways. I n some cases it is preferred to mimic a desensitization technique which injects interference into the received aggregated radio signal, and thus affects the SIN R of all wireless devices in the cell. This injection point 422 for injecting interference into the received aggregated radio signal 426 is shown in Figure 4, where the injected interference signal is shown as n(t). However, it should be noted that the present technique does not require using this addition point, nor using the interference signal n(t) for desensitization.

It can be preferred to use a pre-computed sequence of interference signal values stored in, e.g., a memory of the network node. This pre-computed sequence of interference signal samples can then be scaled depending on which signal processing steps that have been executed in order to extract the first wireless signal, in order to affect SIN R in the same way regardless of where in the signal processing chain the first interference signal is injected.

I n other cases is could be preferred to have a more refined interference signal corresponding more closely to some ideal interference signal. I n such cases a pre-computed and stored sequence of interference signal samples can be passed through a linear filter, such as a Finite I mpulse Response, FIR, filter 428 having a pre-determined transfer function to mimic, e.g., the impact to a noise in a received aggregated radio signal to a sequence of signal processing steps. The first p re-determined reference interference signal level is, according to an aspect configured by a network operator, or, according to another aspect, dynamically adjusted according to a pre-configured set of adjustment criteria. According to yet another aspect, the first pre-determined reference interference signal level is transmitted to the network node by an operator of a radio network comprising the network node.

The method further comprises the step of adding S4 the first interference signal fi(n(t)) to the extracted first wireless signal 427a prior to detecting the first wireless signal. Here, the detection involves generating power control input data for controlling the transmit power of the first wireless device transmitting the first wireless signal. For instance, according to aspects, transmitter power control of UEs can be based on measured SIN R, BLER, or similar metrics, which are all measured following detection of the first wireless signal. Therefore, the addition of the interference signal will have a direct effect on measurement of, e.g., SIN R, and an indirect effect on TPC via measurement of, e.g., SI NR.

Thus, a first wireless signal with lower SI NR than an SINR corresponding to the quality of the wireless signal actually received by the network node can be generated. However, instead of adding artificial noise, i.e., an interference signal, directly to the received aggregated radio signal in a network node, it is proposed herein to first process the received aggregated radio signal in order to extract a first wireless signal corresponding to one or more signals transmitted by a specific UE in the network. Then, interference is purposely added to the specific first wireless signal independently of other received wireless signals, as opposed to being added to all received wireless signals at once.

Consequently, all users that have a radio link setup in a cell where desensitization is done are not necessarily affected by the desensitization. It is thus, by the present teaching, provided a method to only desensitize the wireless signals where desensitization is beneficial, i.e., where there is a power and/or SIN R balance problem as described above, e.g., for a wireless device undergoing soft handover.

Thus, according to an aspect, the wireless device is undergoing a soft handover routine for handover between the network node and a further network node. Further, all demodulated physical channels for a specific user need not necessarily be desensitized as is the case when interference is added directly to the received aggregated radio signal. This means that the decoding performance of physical channels which is not in need of desensitizing is not degraded. Examples of such channels which are not in need of desensitization are the HS-DPCCH and the E-DPCCH.

Also, advantageously, the RoT in the desensitizing cell can be lowered by the present technique compared to when applying interference directly to the received aggregated radio signal, thus UL throughput in the cell is not necessarily degraded.

According to an aspect, the method further comprises the step of sending S5 a transmit power control, TPC, message to the first wireless device based on the generated power control input data.

Thus, the present desensitization mechanism is exploited for improving transmit power control of the first wireless device.

Turning now to Figure 4, where a block diagram illustrating an embodiment of a radio receiver implementing power control is shown.

As noted above, the basic concept of the present teaching is to perform desensitization when the wireless signal corresponding to a specific user, or UE, has been extracted, as opposed to performing desensitization directly on the received aggregated radio signal 426. This principal is outlined in Figure 4. The receiver 420a shown in Figure 4 is arranged to receive an aggregated radio signal 426 from at least a first wireless device 101. The aggregated radio signal 426 comprises a first wireless signal.

Towards this end, the receiver 420a comprises an antenna unit 421 adapted to receive the aggregated radio signal 426, and a signal processing unit 423a arranged extract the first wireless signal 427a from the aggregated radio signal 426.

In addition to the first signal processing unit 423a, there is also shown further signal processing units 423b-423c arranged to process the aggregated radio signal 426 to extract a second 427b up to an N-th wireless signal. There is also shown in Figure 4 an addition point 422 for artificial interference n(t), such as the addition of interference which is used according to current practice in order to desensitize a received aggregated radio signal. This addition point is shown as reference only, and is not a necessary component of the receiver 420a shown in Figure 4, which is why the addition point 422 is shown using a dashed line.

The receiver 420a further comprises an interference signal generator module 428 arranged to generate at least a first interference signal fi(n(t)) based on at least a first pre-determined reference interference signal level.

The interference signal can be generated in a number of different ways. I n some cases it is preferred to mimic a desensitization technique which injects interference into the received aggregated radio signal, and thus affects the SIN R of all wireless devices in the cell. I n this case, it can be preferred to use a pre-computed sequence of interference signal values stored in, e.g., a memory of the network node. This pre-computed sequence of interference signal samples can then be scaled depending on which signal processing steps that have been executed in order to extract the first wireless signal.

The pre-determined reference interference signal level can be determined from theoretical calculation, or from experimentation, or from computer simulation to achieve a target effect on the first wireless signal such as a target or maximum BLER.

I n other cases is could be preferred to have a more refined interference signal corresponding more closely to some ideal interference signal. I n such cases a pre-computed and stored sequence of interference signal samples can be passed through a linear filter, such as a Finite I mpulse Response, FI R, filter having a pre-determined transfer function to mimic, e.g., the impact to a noise in a received aggregated radio signal to a sequence of signal processing steps. To summarize, according to aspects, an interference sequence is generated by, e.g., using a pseudo-random number generator. The sequence, having a pre-determined length, is stored in memory. To do desensitization, the sequence is read from memory, possibly scaled by a scaling factor, or filtered by an FIR filter, and then added to the extracted wireless signal. The amount of scaling, or the transfer function of the FIR filter is configured to attain a controlled impact on, e.g., the SINR measured on the wireless signal.

The receiver 420a also comprises interference addition modules 424a-c adapted to add the corresponding interference signals fi(n(t))-

to the respective extracted wireless signals 427a-c prior to detecting the wireless signals by detector units 425a-c comprised in the receiver 420a.

According to an aspect, the amplitudes of the interference signals fi(n(t))- f_N(n(t)) to add to the extracted wireless signals 427a-c are set to mimic the effect of adding interference n(t) with a given power directly to the received aggregated radio signal 426, i.e., as shown in Figure 4 by the optional interference addition point 422. In this case, the first through N-th interference signals added to respective wireless signals are derived from the corresponding aggregated radio signal interference signal n(t) scaled by approximately the gain factor up until the respective at least one point of addition. The gain factor consists of a static and a dynamic part where the interference amplitude scaled by the static part will be referred to as the reference level of the interference amplitude. To adapt the reference level of the interference in real time to current wanted level, the reference interference level is dynamically scaled.

Moreover, according to an aspect, the interference sequence corresponding to the reference level is pre-calculated and stored in an external memory table at radio link setup in non- serving cell where desensitization shall be applied. The length of table will determine the repetition time of the interference sequence.

As mentioned above, according to current practice, desensitization is done on the input signal y(t). Contrary to this, the present technique comprises determining how the functions (U_]_)— f(u_N) operate on an interference signal n(t) applied to y(t) such that the desensitization can be done later in the signal processing flow. In case a straight forward scaling is used, i.e., in case, e.g., fi(n(t))=a*n(t), it has been found out that is possible to calculate the scaling factor a that specifies how the amplitude of the interference, n(t), is affected by the different functions f(u) 423a-c. The notation f(u) in this context is the combined effect of a number of signal processing steps that are performed on the received aggregated radio signal 426. Examples of such steps which are often common for a plurality of wireless signals are: root raised cosine filtering of the aggregated radio signal 426, dynamic scaling of the input aggregated radio signal by an automatic gain controller, AGC. The function is required to keep a constant reference input power to the base band parts of the receiver 420a and thereby limit the required bit width into the demodulator.

Examples of such steps which are specific for a given wireless signals, i.e., for a given UE, are: descramble and despread of a particular physical channel,

channel compensation and maximum ratio combining over different propagation delays of the aggregated radio signal,

soft scaling prior to Turbo decoding of a physical data channel.

As discussed above, the method proposed herein can be extended for receiving also a second wireless signal from a second wireless device 110, in which case the received aggregated radio signal 426 further comprises the second wireless signal. Turning back now to Figure 3, the method, according to aspects, further comprises: extracting S21 the second wireless signal 427b from the aggregated radio signal 426, and generating S31 a second interference signal f₂(n(t)) based on at least one second pre-determined reference interference signal level, as well as adding S41 the second interference signal f₂(n(t)) to the extracted second wireless signal 427b prior to detecting the second wireless signal, wherein said detection involves generating further power control input data for controlling the transmit power of the second wireless device transmitting the second wireless signal.

Here, the detection involves generating input data for controlling the power of the UE transmitting the second wireless signal. For instance, according to aspects, transmitter power control of the second wireless device transmitting the second wireless signal can be based on measured SINR, BLER, or similar metrics, which are all measured following detection of the first wireless signal. Therefore, the addition of the interference signal will have a direct effect on measurement of, e.g., SINR, and an indirect effect on TPC of the UE transmitting the second wireless signal.

The second pre-determined reference interference signal level is, according to an aspect configured by a network operator, or, according to another aspect, dynamically adjusted according to a pre-configured set of adjustment criteria. According to yet another aspect, the second pre-determined reference interference signal level is transmitted to the network node by an operator of a radio network comprising the network node. It is observed that the first and the second reference interference signal levels are not necessarily equal.

According to an aspect, the method further comprises the step of sending S51 a transmit power control, TPC, message to the second wireless device based on the generated further power control input data. Thus, the present desensitization mechanism is exploited for improving transmit power control of the second wireless device.

According to an aspect, as with the first interference signal, the step of generating S31 a second interference signal further comprises generating the second interference signal based on signal processing steps applied to the aggregated radio signal 426 in extracting the second wireless signal 427b.

Also, as already mentioned above, the first, the second, or any other wireless signal is according to aspects received over any of a Dedicated Physical Control Channel, DPCCH, an Enhanced Dedicated Physical Data Channel, E-DPDCH, or a Physical Random Access Channel, P-RACH. Turning now to Figure 5, where a more detailed signal processing in a receiver 520b is shown. Here, the received aggregated radio signal 526 is amplified by fixed 530 and variable 531 amplifiers, i.e., by the fixed amplifier 530 followed by the AGC unit 531. The aggregated radio signal is then de-scrambled and de-spread into two different channels, E-DPDCH and DPCCH. DPCCH is used for channel estimation by a channel estimator unit 533. Thus, according to an aspect, the first wireless signal comprises at least one first wireless signal component 539a, 539b, one of the at least one wireless signal component 539a, 539b being received over any of a Dedicated Physical Control Channel, DPCCH, an Enhanced Dedicated Physical Data Channel, E-DPDCH, or a Physical Random Access Channel, P-RACH. Examples of the wireless signal components are shown in Figure 5, where the wireless signal components comprise the E-DPDCH and DPCCH transmission by the wireless device 101.

Also, according to an aspect, the first interference signal fi(n(t)) comprises at least one interference signal component fn(n(t)), fi₂(n(t)), and the step of adding S4 comprises adding each of the at least one interference signal component fn(n(t)), fi₂(n(t)) to at least one respective first wireless signal component 539a, 539b.

According to an aspect, each of the at least one interference signal component is a scaled replica a*n(t) of a common interference signal component n(t), which common interference signal component is generated from a sequence of pre-determined interference signal values.

Note the point of desensitization 539b prior to the signal processing step of channel estimation by the channel estimator unit 533.

The E-DPDCH, naturally, is subjected to more signal processing steps than DPCCH is subjected to. The E-DPDCH channel is first despread 534 by a despreading unit, then subjected to channel compensation by a channel compensation unit 535, following which maximum ratio combining is done in an MRC unit 536. After MRC soft scaling is applied to the signal by a soft scaling unit 537. The point of addition of the interference signal fn(n(t)) is here shown as being arranged immediately prior to detection of the E-DPDCH channel by the detector unit 538. However, as marked by dashed arrows, interference signals fn_a(n(t)), fn_b(n(t)), and fn_c(n(t)) can be arranged at any point in the signal processing chain.

Thus, according to an aspect, the step of extracting S2 comprises any of amplification by a low- noise amplifier, LNA, automatic gain control, AGC, de-spreading, DS, channel compensation, CH-COMP, maximum ratio combining, MRC, soft scaling, and Rake finger combining.

In order to do desensitization on a per user basis is that the interference signal must be added after the aggregated radio signal has been descrambled and despread. It is preferred, in some cases, to find how the interference variance is affected by the descramble and despread function. This knowledge can be obtained from experimentation, or from theoretical calculations, or from computer simulation.

There is further disclosed herein a computer program comprising computer program code which, when executed in a network node, causes the network node 102 to execute the method according to any preceding claim.

Assuming now that the generated interference signals by the interference generator unit 428, 528 are scaled replicas of a reference interference signal n_D stored, e.g., in a memory of the receiver 420a, 520b. Examples will now be given of how the scaling factors can be derived in practice. Handling of RAKE receivers

In the RAKE case only the DPCCH channel is used in the estimation function of SINR for UL-TPC. The SINR used for UL-TPC in the RAKE case is calculated as

where h_{r r} is the slot channel estimate of RAKE finger rfr and N_rf_r is the estimated slot interference of RAKE finger rfr. As mentioned above, by desensitizing the DPCCH channel by addition of the interference signal a_DPccHⁿD_> ^{Λ iS} possible to lower the estimated SINR for UL-TPC by the variance of opccHⁿD, opccH being the scaling factor applied to the reference interference signal having a pre-determined reference interference signal level. The configured amplitude of the scaled interference signal, a_DPccHⁿD depends on the amount of desensitization wanted, N, and also on the gain factors in the signal processing chain up until the point of addition.

The interference scaling a_DPCCH at this point will substantially equal

( 2 )

aDPCCH - ^aAGC ' ^ ^■ K ·

Dynamic part

Reference noise

amplitude of n_d where a_AGC is the dynamical scaling of aggregated radio signal made by the automatic gain controller, SF is the spreading factor of the DPCCH channel and K is the static amplification of the aggregated radio signal made in the TRX. The last term, the reference interference level, arise from solving the amplitude from a uniform distribution with variance N.

Handling of Interference Suppression, IS When using IS the SINR is calculated as ( 3 )

where R_u\s an interference covariance matrix for all RAKE fingers, w and h are vectors of generalized channel weights and the channel estimates for all RAKE fingers and symbols in a slot respectively. By desensitizing the input data to the covariance estimation, R_u in ( 3 ), by addition of the interference signal a_DPccHⁿD_> ^tne SINR for UL-TPC will be lowered as intended.

The scaling of the interference signal is calculated as in ( 2 ) but with SF adjusted according to a corresponding channel spreading factor.

Desensitization of E-DPDCH The desensitization of the E-DPDCH by addition of the real or imaginary part of the interference signal <¾_DPDCHn_D, depending on the physical channel mapping of the E-DPDCH, is, according to an aspect, made after the received information symbols comprised in the wireless signal have been soft scaled. The signal processing steps made until this point can be seen in Figure 5. To mimic the scaling until this point the scale factor in ( 2 ) needs to be complemented with the influence of channel compensation, MRC and soft scaling. The interference scaling at this point will substantially equal

Reference noise

amplitude of n^ where P here corresponds to the number of MRCed RAKE fingers. The scale factor £^" [|w|²] derives from the channel compensation signal processing step and the scale factor δ is the scaling of the E-DPDCH soft symbols. The other variables, a_AGC, SF and the reference interference level where explained in connection to ( 2 ) above. An example of how a reference interference sequence can be generated will now be given.

At setup of a new radio link to a non-serving cell where desensitization shall be applied, a complex interference vector is pre-calculated and stored in a memory area in the RBS. The reference level of the interference is calculated as seen in ( 2 ) and ( 4 ). The interference is then generated using M Linear Feedback Shift Registers, LFSRs, and saved in an external memory. The number of LFSRs, M, is calculated from the reference level of the interference as

M = ceil(log2 (Reference level)^ + 1 ( 5 )

Where ceil(x) represents the smallest integer value larger than x. During runtime the interference is tabulated and dynamically scaled to correct level for the concerned channel as described in ( 2 ) and ( 4 ).

The interference will be added per antenna and RAKE finger in case it is the DPCCH which is being desensitized. It is preferred that the added interference on RAKE finger basis must be uncorrelated between the RAKE fingers. It must thus be guaranteed that the interference vector is large enough to extract the maximum number of uncorrelated sequences that could be needed during runtime. But even though the desensitization of the DPCCH channel is made per RAKE finger, the constraint on how long the interference vector must be is given by the maximum number of soft symbols in the E-DPDCH channel.

Figure 6 is a block diagram of an embodiment of a network node configured to perform the method steps disclosed herein. In particular, there is shown a network node 640 implementing power control. The network node 640 comprises:

- a communication interface 645 configured to enable communication with at least a first wireless device 101 transmitting a first wireless signal;

- a processor 641; and - a memory 646 storing computer program code which, when run in the processor 641, causes the network node 640:

- to receive an aggregated radio signal 426 comprising the first wireless signal, - to extract the first wireless signal 427a from the aggregated radio signal

426, and

- to generate a first interference signal fi(n(t)) based on at least one first predetermined reference interference signal level, as well as

- to add the first interference signal fi(n(t)) to the extracted first wireless signal 427a prior to detecting the first wireless signal, wherein said detection involves generating power control input data for controlling the transmit power of the first wireless device 101 transmitting the first wireless signal.

According to an aspect, the network node 640 further comprises a TPC message transmitter unit 642 configured to send a transmit power control, TPC, message to the first wireless device 101 based on the generated power control input data.

According to an aspect, the communication interface 645 is further configured to enable communication with a second wireless device 110 transmitting a second wireless signal. The memory 646 is then also storing computer program code which, when run in the processor 641, causes the network node 640: to extract the second wireless signal 427b from the aggregated radio signal 426, to generate S31 a second interference signal f₂(n(t)) based on at least one second pre-determined reference interference signal level, and to add S41 the second interference signal f₂(n(t)) to the extracted second wireless signal 427b prior to detecting the second wireless signal, wherein said detection involves generating further power control input data for controlling the transmit power of the second wireless device 110 transmitting the second wireless signal. According to an aspect, the network node 640 further comprises a TPC message transmitter unit 642 configured to send a transmit power control, TPC, message to the second wireless device 110 based on the generated further power control input data.

Figure 7 is a block diagram of an embodiment of a wireless device 750, such as the first wireless device 101 or the second wireless device 110 shown in Figure 1. The wireless device 750 comprises a communications interface 751 for communicating with at least a network node such as the network node 647 shown in Figure 6. The wireless device further comprises a controller 752 for transmitting wireless signals, and also a memory 753 for storing data and instructions for executing method steps.

Claims

A method performed in a network node (103) implementing power control, for receiving a first wireless signal from a first wireless device (101), the method comprising: receiving (SI) an aggregated radio signal (426) comprising the first wireless signal, extracting (S2) the first wireless signal (427a) from the aggregated radio signal (426), generating (S3) a first interference signal fi(n(t)) based on at least one first predetermined reference interference signal level, and adding (S4) the first interference signal fi(n(t)) to the extracted first wireless signal (427a) prior to detecting the first wireless signal, wherein said detection involves generating power control input data for controlling the transmit power of the first wireless device (101) transmitting the first wireless signal.

The method according to claim 1, further comprising the step of sending (S5) a transmit power control, TPC, message to the first wireless device (101) based on the generated power control input data.

The method according to any preceding claim, wherein the aggregated radio signal is an uplink signal in a WCDMA radio access network.

The method according to any preceding claim, wherein the network node (103) is a non- serving NodeB of the first wireless device (101).

The method according to any preceding claim, wherein the method is performed when the wireless device (101) is undergoing a soft handover routine for handover between the network node (103) and a further network node (102).

The method according to any preceding claim, wherein the step of extracting (S2) the first wireless signal (427a) comprises de-spreading and descrambling, DS, the aggregated radio signal (426).

The method according to claim 6, wherein the step of extracting (S2) further comprises any of amplification by a low-noise amplifier, LNA, automatic gain control, AGC, channel compensation, CH-COMP, maximum ratio combining, MRC, soft scaling, and Rake finger combining.

8. The method according to any preceding claim, the step of generating (S3) a first interference signal further comprising generating the first interference signal based on signal processing steps applied to the aggregated radio signal in extracting the first wireless signal.

9. The method according to any preceding claim, wherein the first wireless signal comprises at least one first wireless signal component (539a, 539b).

10. The method according to claim 9, one of the at least one wireless signal component (539a, 539b) being received over any of a Dedicated Physical Control Channel, DPCCH, an Enhanced Dedicated Physical Data Channel, E-DPDCH, or a Physical Random Access Channel, P-RACH.

11. The method according to any preceding claim, the first interference signal fi(n(t)) comprising at least one interference signal component fn(n(t)), fi₂(n(t)), the step of adding (S4) comprising adding each of the at least one interference signal component fn(n(t)), fi₂(n(t)) to at least one respective first wireless signal component (539a, 539b).

12. The method according to claim 11, wherein each of the at least one interference signal component fn(n(t)), fi₂(n(t)) is a scaled replica of a common interference signal component, which common interference signal component is generated from a sequence of pre-determined interference signal values.

13. The method according to any preceding claim, wherein the aggregated radio signal comprises at least a second wireless signal transmitted from a second wireless device (110), the received aggregated radio signal (426) further comprising the second wireless signal, the method further comprising: - extracting (S21) the second wireless signal (427b) from the aggregated radio signal (426), generating (S31) a second interference signal f₂(n(t)) based on at least one second pre-determined reference interference signal level, adding (S41) the second interference signal f₂(n(t)) to the extracted second wireless signal (427b) prior to detecting the second wireless signal, wherein said detection involves generating further power control input data for controlling the transmit power of the second wireless device (110) transmitting the second wireless signal.

14. The method according to claim 13, further comprising the step of sending (S51) a transmit power control, TPC, message to the second wireless device (110) based on the generated further power control input data.

15. The method according to claim 13, wherein the network node (103) is a non-serving NodeB of the second wireless device.

16. The method according to any of claims 13-15, the step of generating (S31) a second interference signal further comprising generating the second interference signal based on signal processing steps applied to the aggregated radio signal (426) in extracting the second wireless signal (427b). 17. The method according to any preceding claim, the first and/or the second wireless signal being received over any of a Dedicated Physical Control Channel, DPCCH, an Enhanced Dedicated Physical Data Channel, E-DPDCH, or a Physical Random Access Channel, P- RACH.

18. A computer program comprising computer program code which, when executed in a network node, causes the network node (102) to execute the method according to any preceding claim.

19. A network node (640) implementing power control, the network node comprising:

- a communication interface (645) configured to enable communication with at least a first wireless device (101) transmitting a first wireless signal; - a processor (641); and

- a memory (646) storing computer program code which, when run in the processor (641), causes the network node (640): - to receive an aggregated radio signal (426) comprising the first wireless signal,

- to extract the first wireless signal (427a) from the aggregated radio signal (426), and

- to add the first interference signal fi(n(t)) to the extracted first wireless signal (427a) prior to detecting the first wireless signal, wherein said detection involves generating power control input data for controlling the transmit power of the first wireless device (101) transmitting the first wireless signal.

The network node (640) according to claim 19, further comprising a TPC message transmitter unit (642) configured to send a transmit power control, TPC, message to the first wireless device (101) based on the generated power control input data.

The network node (640) according to any of claims 19-20, the communication interface (645) further being configured to enable communication with a second wireless device (110) transmitting a second wireless signal, wherein the memory (646) is storing computer program code which, when run in the processor (641), causes the network node (640): to extract the second wireless signal (427b) from the aggregated radio signal (426), to generate (S31) a second interference signal f₂(n(t)) based on at least one second pre-determined reference interference signal level, to add (S41) the second interference signal f₂(n(t)) to the extracted second wireless signal (427b) prior to detecting the second wireless signal, wherein said detection involves generating further power control input data for controlling the transmit power of the second wireless device (110) transmitting the second wireless signal.

22. The network node (640) according to claim 21, further comprising a TPC message transmitter unit (642) configured to send a transmit power control, TPC, message to the second wireless device (110) based on the generated further power control input data.

23. A network node (103) implementing power control, the network node comprising a receiver (420a) arranged to receive a aggregated radio signal (426) from at least a first wireless device (101), the aggregated radio signal (426) comprising a first wireless signal transmitted by the first wireless device (101), the receiver (420a) comprising an antenna unit (421) adapted to receive the aggregated radio signal, and a signal processing unit (423a) arranged to extract the first wireless signal (427a) from the aggregated radio signal (426), the receiver (420a) further comprising an interference signal generator module (428) arranged to generate a first interference signal fi(n(t)) based on at least a first pre-determined reference interference signal level, as well as an interference addition module (424a) adapted to add the first interference signal fi(n(t)) to the extracted first wireless signal (427a) prior to detecting the first wireless signal by a detector unit (425a) comprised in the receiver (420a), wherein said detection involves generating power control input data for controlling the transmit power of the first wireless device (101) transmitting the first wireless signal.