GB2552307A

GB2552307A - Methods and devices for link adaptation under conditions of intermittent interference in wireless communication systems

Info

Publication number: GB2552307A
Application number: GB1612107.1A
Authority: GB
Inventors: Katranaras Efstathios; Liu Guang; Winiecki Thomas
Original assignee: TCL Communication Ltd
Current assignee: TCL Communication Ltd
Priority date: 2016-07-12
Filing date: 2016-07-12
Publication date: 2018-01-24
Also published as: CN110036659B; WO2018010542A1; CN110036659A; GB201612107D0

Abstract

Link adaptation of a downlink between an eNB and a User Equipment (UE) in an LTE system operating in unlicensed spectrum is based upon information in Channel Quality Indicator (CQI) reports which monitors and reports on an individual sub-frame periodically. If the downlink is subject to intermittent interference, the sub-frame reported on my not be affected and therefore the CQI will not reflect this. By reporting a CQI value for every sub-frame, intermittent interference will be detected. This information is used by the eNB to select an appropriate Modulation Coding Scheme (MCS) based on the channel conditions. The ratio between sub-frames affected by interference to those not affected by interference may also be calculated to determine which MCS is most appropriate. Alternatively, the CQI reports may be used to determine the duty cycle of the source of any intermittent interference and use the duty cycle information at the eNB to select a MCS. A higher order MCS will provide a higher throughput but will necessitate frequent retransmissions or a lower order MCS will require frequent retransmissions but will have the disadvantage of a lower throughput.

Description

(54) Title of the Invention: Methods and devices for link adaptation under conditions of intermittent interference in wireless communication systems

Abstract Title: Link adaptation under conditions of intermittent interference in wireless communication systems (57) Link adaptation of a downlink between an eNB and a User Equipment (UE) in an LTE system operating in unlicensed spectrum is based upon information in Channel Quality Indicator (CQI) reports which monitors and reports on an individual sub-frame periodically. If the downlink is subject to intermittent interference, the subframe reported on my not be affected and therefore the CQI will not reflect this. By reporting a CQI value for every sub-frame, intermittent interference will be detected. This information is used by the eNB to select an appropriate Modulation Coding Scheme (MCS) based on the channel conditions. The ratio between sub-frames affected by interference to those not affected by interference may also be calculated to determine which MCS is most appropriate. Alternatively, the CQI reports may be used to determine the duty cycle of the source of any intermittent interference and use the duty cycle information at the eNB to select a MCS. A higher order MCS will provide a higher throughput but will necessitate frequent retransmissions or a lower order MCS will require frequent retransmissions but will have the disadvantage of a lower throughput.

FIG. 2 of 3

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FIG. 1 of 3

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FIG. 3

Methods and devices for link adaptation under conditions of intermittent interference in wireless communication systems

Technical Field

Embodiments of the present invention generally relate to wireless communication systems and in particular to devices and methods for optimising performance of communication links over the air interface in the presence of bursty or intermittent interferers.

Background

Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project (3GPP). The 3^rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs) to communicate with wireless communication devices within a relatively large geographical coverage area. Typically, wireless communication devices, or User Equipment (UEs) as they are often referred to, communicate with a Core Network (CN) of the 3G wireless communication system via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of radio network subsystems, each radio network subsystem comprising one or more cells to which UEs may attach, and thereby connect to the network. Each macro-cellular RNS further comprises a controller, in a form of a Radio Network Controller (RNC), operably coupled to the one or more NodeBs. Communication systems and networks have developed towards a broadband and mobile system. The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) and LTE advanced solutions, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network, and a System Architecture Evolution (SAE) solution, namely, an Evolved Packet Core (EPC), for a mobile core network. A macrocell in an LTE system is supported by a base station known as an eNodeB or eNB (evolved NodeB).

Current wireless communications networks operate using licensed radio spectrum in which multiple accesses to the communications resources of the licensed radio spectrum is strictly controlled. Each user of the network is essentially provided a “slice” of the spectrum using a variety of multiple access techniques such as, by way of example only but not limited to, frequency division multiplexing, time division multiplexing, code division multiplexing, and space division multiplexing or a combination of one or more of these techniques. Even with a combination of these techniques, with the popularity of mobile telecommunications, the capacity of current and future networks is still very limited, especially when using licensed radio spectrum. Unlicensed radio spectrum may also be used by network operators in order to increase or supplement capacity. For example, a network based on the Long Term Evolution (LTE)/LTE advanced standards has an enhanced downlink that uses a Licensed-Assisted-Access (LAA) procedure to operate on unlicensed spectrum. This enables the operation of a telecommunication network based on LTE in the 5GHz unlicensed spectrum for low power secondary cells based on regional regulatory power limits using carrier aggregation.

The current 3GPP standard lays out a strategy for link adaptation. In the downlink, the UE measures the link quality and sends reports to the eNB regarding the Channel State Information (CSI). One of these indicators is the Channel Quality Indicator (CQI) which reflects how good or bad the communication channel quality is. CQI is coded in terms of a target modulation and coding scheme (MCS) to essentially inform the eNB about the MCS that can be used to receive data with a block error rate (BLER) up to 10% under the current link conditions. Typically, CQI is an index having a value between 0 and 15 which the eNB uses to select an appropriate MCS between 0 and 28. So in practice, the granularity of the MCS chosen by the eNB can be greater than the target MCS that is suggested by the UE in a CQI report. If the link quality is good, a signal can be sent with a complex modulation scheme and little redundancy. Conversely, if the link quality is poor due to high losses or the presence of interferes, the modulation scheme is simplified and more redundancy is added to make the signal more robust and easier to decode by the receiving device.

Existing strategies assume that the link conditions are relatively stable, at least over durations of a few milliseconds which is the case in licensed frequency bands where transmissions between all devices are co-ordinated and scheduled at least per TTI (Transmission Time Interval) period (e.g. a subframe of 1ms in LTE system). The duration over which the link quality is assumed stable is called coherence time. It takes several milliseconds to evaluate the link conditions, to report the measurements and for the eNB to switch into a new MCS.

In unlicensed bands however where different technologies share the same frequency spectrum, intermittent interference may occur, yielding fast (typically less than 1ms) variations in the link quality. Similar types of interference may also be perceived in licensed bands operating at high frequencies.

Consider for example an eNB and a UE using an unlicensed frequency carrier (e.g. 5GHz spectrum shared with WiFi devices). The eNB and WiFi transmitter (or access point) will normally try to avoid simultaneous transmission by employing the socalled Listen Before Talk procedure whereby a device will postpone transmission on a particular channel if it detects energy on that channel. However, the threshold for detecting this energy is relatively high and as long as the eNB and WiFi access point are far enough apart, they could consider the channel available and so transmit simultaneously. Thus, a UE using the channel to communicate with the eNB could suffer from severe interference from the WiFi transmissions. Consequently, the UE will report poor channel conditions to the eNB (low CQI) and the eNB will react by lowering MCS to a level that can be sustained at low block error rates. However, this will not necessarily correspond to the optimum operating point of the system. Furthermore, a lower MCS can result in a lower throughput and a waste of spectral efficiency. On the other hand, an MCS set too high can result in demodulation errors and the need for frequent re-transmissions.

It would be advantageous to provide a means for optimising the air interface link under conditions of intermittent and bursty interference.

Summary

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

The invention provides methods and systems which employ a 'modified* form of the conventional CQI reporting from a wireless communication device to a base station, in order for the base station (an eNB in certain examples) to be able to prepare Modulation and Coding Schemes (MCS), not only in the conventional way, but also by disregarding reports relating to subframes affected by intermittent interference. The 'modified' form of a CGI report may include additional information as described in more detail below.

According to a first aspect of the present invention there is provided a wireless communication device for enabling link adaptation in a wireless communication system, the wireless communication device comprising a receiver for receiving, from a base station supporting communications in the wireless communication system, a downlink transmission burst comprising a plurality of sub-frames, a signal processor for monitoring the quality of the received downlink transmission burst for every subframe and for computing, for each received sub-frame, a Channel Quality Indicator (CGI) value which is coded in terms of a target modulation and coding scheme (MCS) that can be used to receive data with a block error rate (BLER) up to a predetermined value, and a transmitter for reporting to the base station, the computed CGI value for every received sub-frame.

By reporting a CQI value for every receive sub-frame (of a reference signal sent by the base station for the purpose of link adaptation, for example), the existence of intermittent interference, which may affect only a small proportion of sub-frames comprising a downlink burst (which may be configured by the base station), is made known to the base station. Making the base station aware of the existence of intermittent or 'bursty' interference, allows the base station to estimate the relative improvement of the use of a higher MCS versus a lower and more robust MCS.

Therefore the base station is provided with the flexibility to trade off higher throughput for the higher auxiliary signalling that is associated with retransmissions.

The wireless communication system may be an LTE system and the base station may be an eNB. The wireless communication device may be a User Equipment or other mobile communications device. In one embodiment, the base station and wireless communication device communicate using unlicensed spectrum and may be arranged to operate a Licence Assisted Access procedure and to support a Listen Before Talk (LBT) procedure.

According to a second aspect of the invention there is provided a base station for enabling link adaptation in a wireless communication system, the base station comprising a receiver arranged to receive from a wireless communication device in the wireless communication system, for every sub-frame of a downlink transmission burst, a report including a CQI (Channel Quality Indicator) value which is coded in terms of a target modulation and coding scheme (MCS) that can be used to receive data at the wireless communication device with a block error rate (BLER) up to a predetermined value, and a signal processor for selecting a MCS depending on the received report.

In the specific example of 3GGP LAA, a 'downlink transmission burst' refers to a number of continuous-in-time downlink subframes. For link adaptation, in general, the base station may consider one or several CQI reports received from the wireless communication device regarding a number of 'X' past downlink subframes in order to estimate the general channel quality.

The base station, in a link adaptation procedure, may choose a higher (or more aggressive) MCS by considering the reported channel conditions in only those subframes which are unaffected by intermittent or bursty interference. Alternatively, the base station, in a link adaptation procedure, may choose a lower (more robust) MCS by considering the reported channel conditions of all sub-frames. In the former case, the BLER value will be higher than in the latter case. Preferably, the base station has the ability to handle the higher re-transmission rates that will result from a higher BLER. The choice of an intermediate MCS does not necessarily provide any advantage. An intermediate MCS will give a lower throughput in undisturbed subframes but will still fail to be decoded in sub-frames suffering from interference.

The choice of a higher order MCS is beneficial for higher interferer power (because higher interferer power normally causes the MCS and therefore the throughput to be reduced to low values). Also, the benefit of a higher order MCS increases with decreasing interferer duty cycles. This is because a lower duty cycle will result in fewer ill-received transport blocks and fewer re-transmissions. It has been found that for large interferer power, the increase in throughput if a higher order MCS is selected can potentially be very great. Although a higher order MCS means a worse block error rate and therefore an increase in the number of re-transmissions for a UE, the transmission of a UE file will happen faster. So on average, each UE will occupy a channel for less time and there will be a global gain in system capacity.

Consider the example of a UE capable of operating at 3.5GHz and in proximity to radar transmitters using the same frequency band. The radar pulses are typically short and infrequent affecting only a small percentage of LTE subframes and they have a very high power level which makes it nearly impossible to demodulate affected sub-frames. In such a case, rather than lowering the MCS to allow affected sub-frames to be decoded it may be advantageous overall to ignore sub-frames lost due to radar interference and optimize throughput for the majority of unaffected subframes.

According to a third aspect of the invention, there is provided a wireless communication device comprising a receiver for monitoring quality of a downlink channel in a wireless communication system, a signal processing circuit for computing a Channel Quality Indicator (CQI) report, wherein the report includes an indication of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and information relating to a ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference, and wherein the wireless communication device comprises a transmitter for transmitting the channel quality indicator report to a base station supporting communications in the wireless communication system.

Optionally, HARQ (Hybrid Automatic Repeat Request) may be disabled at the wireless communication device in cases of high INR (interference to noise ratio). This is preferred because with high power interference the raw data received is not very useful even if several re-transmitted copies are combined. Furthermore, when corrupted data is combined with data received in sub-frames that are not affected by the interferer the combined signal quality is degraded. So for high INR it is a better strategy to completely discard ill-received data and fully rely on re-transmissions.

A high INR is equivalent to a high variation (or spread) in the values of the calculated CQI. Therefore, a decision to enable or disable HARQ can be made based on the difference between the highest and lowest reported CQI values in a given number of reports. So, for a large spread (i.e. high interferer power), HARQ may be disabled but for a small spread, HARQ is retained.

According to a fourth aspect of the invention, there is provided a base station for enabling link adaptation in a wireless communication system, the base station comprising a receiver for receiving from a wireless communication device in the wireless communication system, a Channel Quality Indicator (CQI) report, wherein the report includes an indicator of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and information relating to a ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference, and wherein the base station comprises a signal processor for selecting a modulation and coding scheme MCS depending on the received CQI reports.

In one embodiment, the base station sends a request to the wireless communication device to send it a Channel Quality Indicator report which includes said information relating to the ratio of the number of sub-frames in the group of sub-frames which are least affected by interference to the number of sub-frames in the group of sub-frames which are most affected by interference. In addition to or as an alternative to ratio information, the base station may also ask the wireless communication device for information relating to, for example, CQI values per downlink subframe, lowest CQI values, highest CQI values, CQI values for only those subframes unaffected by interference

In a situation where many UEs report local interference and a higher order MCS would be beneficial for many UEs, the base station may limit the number of UEs targeting a higher order MCS so that the number of overall re-transmissions (and associated buffer sizes and signalling overheads) does not become limiting. The rate of reception errors and therefore necessary re-transmissions will be of the order of, or slightly higher than, the rate of interference events. If this rate is reported by a wireless communication device to the base station, the base station can predict the number of re-transmissions likely to occur. Thus, it will be possible for the base station to optimize the allocation of higher order MCS across the population of all wireless communication devices in the base stations region of coverage based on their collective reports on interferer duty cycles and differences in CQI for affected and non-affected sub-frames.

According to a fifth aspect of the invention, there is provided a method for enabling link adaptation in a wireless communication system, the method comprising, at a wireless communication device, monitoring quality of a downlink channel in the wireless communication system, computing a Channel Quality Indicator (CQI) report, wherein the report includes an indication of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and information relating to a ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference, and transmitting a channel quality indicator report to a base station supporting communications in the wireless communication system.

According to a sixth aspect of the invention, there is provided a method for enabling link adaptation in a wireless communication system, the method comprising, at a base station, receiving from a wireless communication device in the wireless communication system, a Channel Quality Indicator (CQI) report, wherein the report includes an indication of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and information relating to a ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference, and transmitting a channel quality indicator report to a base station supporting communications in the wireless communication system, and selecting a modulation and coding scheme (MCS) depending on the received CQI report.

According to a seventh aspect of the invention, there is provided a method for enabling link adaptation in a wireless communication system, the method comprising, at a base station receiving from a wireless communication device in the wireless communication system, a Channel Quality Indicator (CQI) report, wherein the report includes an indication of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value, monitoring ACK/NACK messages from the wireless communication device to determine an indication of a duty cycle of an interferer, and selecting a modulation and coding scheme (MCS) depending on the received CQI report and the indication of said duty cycle duty.

According to an eighth aspect of the invention, there is provided a non-transitory computer readable medium having computer readable instructions stored thereon for execution by a processor to perform the method according to the fifth, sixth or seventh aspects.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

Figure 1 is a simplified block diagram of a part of a wireless communication system and operating in accordance with an example embodiment;

Figure 2 is a simplified flow chart illustrating a first method for assisting a link adaptation procedure; and

Figure 3 is a simplified flow chart illustrating a second method for assisting a link adaptation procedure.

Detailed description of the preferred embodiments

Those skilled in the art will recognise and appreciate that the specifics of the examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings.

Referring now to FIG.1, an example of part of an LTE cellular communication system operating in accordance with embodiments of the invention is illustrated and indicated generally at 100 and comprises an evolved Node B (eNB) 101 supporting an LTE cell 102. In other embodiments, the eNB 101 may support a multiplicity of cells. The cell 102 can be considered to be a cell using licensed frequency spectrum or can be a LAA cell using unlicensed spectrum. The LAA downlink is arranged in subframes. The eNB 101 and UE 103 have the capability of operating a Listen Before Talk procedure. The evolved Node B 101 comprises a part of a radio access network which in this example is an E-UTRAN. User Equipment 103 is located within the area of coverage of the cell 102. Just one User Equipment is shown in FIG. 1 but more User Equipments may be located in the cell 102 and be in a connected mode at any given time. An evolved packet core (EPC) of the Wireless Communications System of FIG.1 includes a Packet Gateway P-GW 104 and a Serving GPRS (General Packet Radio System) Support Node (SGSN) 105. The P-GW 104 is responsible for interfacing the radio access network with a packet data network, e.g. a Packet Switched Data Network (PSDN) (such as the Internet). The SSGN 105 performs a routing and tunnelling function for traffic to and from the cell 102, while the P-GW 104 links with external packet networks. The EPC also comprises a Mobility Management Entity 106. The eNB 101 is linked to the SSGN 105 through the Mobility Management Entity (MME) 106. The eNB 101 is also connected with the PGW 104 through the MME 106 and a Service Gateway S-GW 107. The MME 106 handles signalling control and mobility while the S-GW 107 is a local anchor point for user data.

The eNB 101 is provided with a receiver circuit 108 for receiving messages from one or more UEs and also a transmitter circuit 109 for transmitting messages to one or more User Equipments. The eNB is also provided with a signal processor 110 whose purpose will be described below. The User Equipment 103 includes a receiver 111 for receiving messages from the eNB 101 a transmitter 112 for transmitting messages to the eNB101 and a signal processing circuit 113 whose function will be described below. The eNB 101 supports communications with the UE 103 using licensed and unlicensed spectrum. First and second access points 114 and 115 provide WiFi signals using unlicensed spectrum for use by communications devices within their coverage areas. The first access point 114 is in close proximity to the UE 103 and more distant from the eNB 101. The second access point 115 is in close proximity to the eNB and more distant from the UE.

In operation, the signal processing circuit 113 in the UE 103 computes a CQI value by measuring the link quality (that is the downlink) using reference signals which are transmitted from the eNB 101. These measurements can done across the whole of the receive channel bandwidth (wideband CQI) or over narrow frequency ranges (sub band CQI). As is conventional, CQI reports can be either periodic or a periodic. In the case of periodic reports, the UE 103 cycles through different sub bands from one reporting instance to the next, in order to reduce overhead. In the case of eNBselected aperiodic reports, the UE 103 reports the sub band CQI for each band in a single feedback report. In the case of a UE-selected aperiodic report, the UE reports the sub band CQI for bands with highest CQI values. It will be noted that UE 103 is also capable of monitoring link quality on the uplink. For example, in the case of a TDD (Time Division Duplex) system, in which uplink and downlink use the same frequency band, the information on the link quality at a given moment on the downlink can provide relevant information for the uplink channel too, because of channel reciprocity. For an FDD (Frequency Division Duplex) system, uplink and downlink are carried over different frequency bands, and additional methods are used to estimate the quality of the uplink link, for example the use of a SRS (Sounding Reference Signal).

In a first example, the UE 103 is monitoring the downlink of an LAA unlicensed channel supported by the eNB 101 and the access point 114 is transmitting (intermittently) in the same unlicensed spectrum (5GHz say). The access point 114 is sufficiently distant from the eNB 101 so that its transmissions are not detected in a Listen Before Talk procedure carried out by the eNB 101 yet is close enough to the UE 103 for the UE to be able to detect its transmissions as noise or intermittent interference. In this example it is assumed that the duty cycle of the transmissions from the access point 114 are such that one out of every three subframes of the LAA downlink monitored by the UE 103 are affected by bursty interference from the access point 114. Conventionally, a CQI report is triggered from a group of CSI reference signals within a downlink transmission burst from an eNB. If this conventional procedure is followed, then the eNB 101 will receive from the UE 103 a CQI report indicating a low MCS although only one in three subframes is affected by the interference. The eNB will not be able to extract any information from the report regarding the type of interference within the reported subframe group and will not know if the interference is bursty or if all subframes are affected by the same interfering signal. In a first method, this drawback is overcome by arranging for the UE 103 to report a CQI value on every valid TTI (Transmission Time Interval).

Referring to figures 1 and 2, at 201, the UE 103 commences to monitor the downlink quality of the unlicensed spectrum. At 202, the Wi-Fi access point 114 starts to transmit with a particular duty cycle. At 203, the UE detects that the downlink quality is now affected by bursty interference (from the access point 114) and the signal processing module 113 computes a CQI value for every downlink sub-frame which it codes in terms of the target MCS that can be used to receive data with a block error rate (BLER) up to 10% under the current link conditions. At 204, the UE 103 transmits to the eNB 101 a computed CQI value for every sub-frame. Therefore, for sub-frames which are not affected by the Wi-Fi transmissions a higher CQI will be reported and for sub-frames which are affected by the Wi-Fi transmissions a lower CQI will be reported. At 205, the eNB 101 receives the CQI values (which convey the target MCS). At 206 using the received CQI values, the signal processor 110 in the eNB 101 computes a ratio of sub-frames affected by interference to those unaffected by interference in a downlink burst and also computes a longer term statistical distribution of CQI values. From these computations the signal processor 110 can determine an MCS for ensuring optimum throughput. In a first alternative, at 207, the signal processor in the eNB ignores the CQI reports for sub-frames affected by bursty interference (i.e. those subframes reported with comparatively low CQI values) and uses the MCS value corresponding to those CQI reports for the other, unaffected sub-frames and suffers an increased necessity for retransmissions. If there is just one strong interferer, the rate of retransmissions will correspond to the ratio of subframes affected by the interferer. In a second alternative, at 208, the signal processor in the eNB considers reports in respect of all subframes and so selects a lower MCS value. The second alternative ensures an increased resilience to interference for all sub-frames. It will be noted that in the current standards, with an average CQI, the situation is non-optimal because unaffected sub-frames would get a lower MCS than is achievable whereas affected sub-frames cannot be decoded

Reporting a CQI for every downlink sub-frame (that is; every valid TTI) necessitates significant signalling overhead and can reduce the throughput that LAA services are aiming to achieve. In a second example, this drawback may be overcome as follows. With reference to figure 1, the UE 103 monitors the downlink of an LAA unlicensed channel supported by the eNB 101 and the access point 114 transmits (intermittently) in the same unlicensed spectrum (5GHz). The access point 114 is sufficiently distant from the eNB 101 so that its transmissions are not detected in a Listen Before Talk procedure carried out by the eNB 101 yet is close enough to the UE 103 for the UE to be able to detect its transmissions as noise or intermittent interference. In this example it is assumed that the duty cycle of the transmissions from the access point 114 is 20 per cent. This bursty interference is detected by the UE 103 as an increase in INR. The duty cycle of 20 per cent will raise the noise floor of the UE 104 for two out of 10 sub-frames.

With reference now to figures 1 and 3, at 301, the UE 103 commences to monitor the downlink quality of the unlicensed spectrum. At 302, the Wi-Fi access point 114 starts to transmit with a 20 per cent duty cycle. At 203, the UE detects that the downlink quality is now affected by bursty interference (from the access point 114) and the signal processing circuit 113 computes a CQI value which it codes in terms of a target MCS that can be used to receive data with a block error rate (BLER) up to 10% under the current link conditions. The signal processing circuit 113 also computes a value for the ratio of sub-frames that are affected by interference from the access point 114 to the ratio of sub-frames that are unaffected by interference from the access point (that is, 2:10 in this example). At 304, the UE 103 transmits to the eNB 101 a CQI report which contains the CQI value (coded in terms of the target MCS) and the ratio. The CQI report (and subsequent CQI reports) is triggered from a group of CSI reference signals within each downlink transmission burst from the eNB. (An alternative method may involve aperiodic reporting where a CQI report is triggered explicitly by the eNB using e.g. an uplink grant.) At 305, the CQI report is received at the eNB 101. At 306, in the signal processor 110 in the eNB a MCS is determined based on the information received in the CQI report. For example, the eNB 101 may choose to use a MCS having a high resilience against interference but a comparatively low peak throughput. Such an MCS is tuned to the channel conditions of the worst affected sub-frames. Alternatively, knowing that the ratio of affected sub-frames to unaffected sub-frames is comparatively low (2 in every 10) the eNB 101 may choose to use a higher order MCS than that conveyed by the UE 103 but with the expectation that many sub-frames will be lost. The higher order MCS is based on the channel conditions in the 8 sub-frames per every 10 which are unaffected by the interference from the access point 114. An intermediate MCS will give lower a throughput in undisturbed sub-frames and will still fail to be decoded in sub-frames suffering from interference.

In the second example, the UE 103, optionally, measures values for signal-to-noise ratio (SNR) and interference to noise ratio (INR) on the downlink and sends these measured values to the eNB 101. These additional values the signal processor 110 in the eNB 101 takes into account when determining an MCS.

As another option, instead of computing a value for the ratio of affected sub-frames to unaffected sub-frames, the signal processing circuit 113 in the UE 103 computes the duty cycle of the interfering signal and includes this in the CQI report (instead of the value for the ratio). The signal processor 110 in the eNB 101 then uses this duty cycle value along with the received CQI value to determine an MCS.

In another embodiment, graph-maps are standardised and stored as search tables and used by the signal processor 110 in the eNB 101 such that a UE can just report a few (indicator) bits representing the downlink situation (SNR, INR, duty cycle) matching closest to its channel measured statistics. Such indicator bits may be sent at the request of the base station.

As a further option, instead of the UE 103 computing a duty cycle of the interfering signal or a value for the ratio of the number of sub- frames affected by interference to the number of sub-frames unaffected by interference and sending either of these parameters to the eNB 101, an indication of either of these parameters is computed in the signal processor 110 of the eNB 101 by monitoring ACK/NACK messages from the UE 103.

In other, 'UE-centric' embodiments, instead of the UE providing extra information to the eNB, operating standards may re-define what a UE is allowed to collect and report in an environment of intermittent interference. For example, upon detecting a bursty interference environment, the UE can start collecting different types of statistics regarding its CQI (e.g. best CQI, worst CQI over a period) and signal processing functionality in the UE can compute an optimum MCS under the prevailing circumstances and report such computed MCS to the eNB. In one embodiment, the UE computes a MCS based only on the CQI values of unaffected sub-frames and ignores affected sub-frames. Advantageously, minimal extra signalling between the UE and the eNB is needed and the link adaptation process can stay the way it is currently. So in this embodiment, the definition of CQI is redefined so that, for LAA DL link adaptation, for example, a UE is able to produce and report a CQI value corresponding to a MCS that can be used to receive data with a block error rate (BLER) higher than 10% under the current link conditions, disregarding the periods where bursty interference is experienced. Further, the eNB is aware that handling a re-transmission rate higher than 10% may be needed.

Intermittent interference can also occur on an uplink. Referring to fig 1, the access point 115 is close to the eNB 101 but distant from the UE 103. In this situation, the access point 114 and the UE 103 are sufficiently far apart so that each considers that their channel is occupied and therefore may transmit simultaneously. The eNB 103 receiving the UE's uplink signal is thus disturbed by the transmissions from the access point 114. In LTE, the uplink link adaptation is fully under the control of the eNB and not standardized. However similar extra information, as described for the downlink case, can be made available at the UE and improve link adaptation for bursty interference.

The signal processing functionality of the embodiments of the invention especially the signal processor of the eNB and the signal processing circuit of the UE may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms ‘computer program product’, ‘computer-readable medium’ and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’, ‘an’, ‘first’, ‘second’, etc. do not preclude a plurality.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements.

Claims

1. A wireless communication device for enabling link adaptation in a wireless communication system, the wireless communication device comprising a receiver for receiving, from a base station supporting communications in the wireless communication system, a downlink transmission burst comprising a plurality of sub-frames, a signal processing circuit for monitoring the quality of the received downlink transmission burst for every sub-frame and for computing, for each received sub-frame, a Channel Quality Indicator (CQI) value which is coded in terms of a target modulation and coding scheme (MCS) that can be used to receive data with a block error rate (BLER) up to a predetermined value, and a transmitter for reporting to the base station, the computed CQI value for every received sub-frame.

2. A base station for enabling link adaptation in a wireless communication system, the base station comprising a receiver arranged to receive from a wireless communication device in the wireless communication system, for every sub-frame of a downlink transmission burst, a report including a CQI (Channel Quality Indicator) value which is coded in terms of a target modulation and coding scheme (MCS) that can be used to receive data at the wireless communication device with a block error rate (BLER) up to a pre-determined value, and a signal processor for selecting a MCS depending on the received report.

3. The base station of claim 2 adapted to select a MCS based on reported channel conditions in sub-frames that are unaffected by interference.

4. The base station of claim 2 adapted to select a MCS based on reported channel conditions in all sub-frames.

5. A wireless communication device comprising a receiver for monitoring quality of a downlink channel in a wireless communication system, a signal processing circuit for computing a Channel Quality Indicator (CQI) report, wherein the report includes an indicator of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and information relating to a ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference, and wherein the wireless communication device comprises a transmitter for transmitting the CQI report to a base station supporting communications in the wireless communication system.

6. A base station for enabling link adaptation in a wireless communication system, the base station comprising a receiver for receiving from a wireless communication device in the wireless communication system, a Channel Quality Indicator (CQI) report, wherein the report includes an indicator relating to a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and information relating to a ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference, and wherein the base station comprises a signal processor for selecting a modulation and coding scheme MCS depending on the received CQI report.

7. A method for enabling link adaptation in a wireless communication system, the method comprising, at a wireless communication device, monitoring quality of a downlink channel in the wireless communication system, computing a Channel Quality Indicator (CQI) report, wherein the report includes an indication of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and information relating to a ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference, and transmitting a CQI report to a base station supporting communications in the wireless communication system.

8. A method for enabling link adaptation in a wireless communication system, the method comprising, at a base station, receiving from a wireless communication device in the wireless communication system, a Channel Quality Indicator (CQI) report, wherein the report includes an indication of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and information relating to a ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference, and selecting a modulation and coding scheme (MCS) depending on the received CQI report.

9. A method for enabling link adaptation in a wireless communication system, the method comprising, at a base station receiving from a wireless communication device in the wireless communication system, a Channel Quality Indicator (CQI) report, wherein the report includes an indication of a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub- frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value, monitoring ACK/NACK messages from the wireless communication device to determine an indication of a duty cycle of an interferer, and selecting a modulation and coding scheme (MCS) depending on the received CQI report and the indication of said duty cycle duty cycle.

10. The method of claim 7 comprising, at the wireless communication device, disabling Hybrid Automatic Repeat Request (HARQ) when a difference between the highest and lowest CQI values in a given number of reports reaches a pre-determined value.

11. The method of claim 8 comprising, at the base station, sending a request to the wireless communication device for information relating to the ratio of the number of sub-frames in the group of sub-frames which are most affected by interference to the number of sub-frames in the group of sub-frames which are least affected by interference.

12. A method for enabling link adaptation in a wireless communication system, the method comprising, at a wireless communication device, monitoring quality of a downlink channel in the wireless communication system, detecting intermittent interference on the downlink channel, computing Channel Quality Indicator (CQI) values and comparing said computed CQI values over a pre-determined period, from the comparison, determining a target modulation and coding scheme (MCS) that can be used to receive data in a group of sub-frames comprising a downlink transmission burst with a block error rate (BLER) up to a predetermined value and, and transmitting a CQI report indicating the target MCS to a base station supporting communications in the wireless, and at the base station, using the MCS as coded in the received CQI in subsequent transmissions to the wireless communication device.

13. A non-transitory computer readable medium having computer readable instructions stored thereon for execution by a processor to perform the method according to any of claims 7, 8, 9 or 12.

14. The non-transitory computer readable medium of claim 13 comprising at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read

10 Only Memory, EPROM, an Electrically Erasable Programmable Read

Only Memory and a Flash memory.

Intellectual

Property

Office

GB1612107.1

1-4