WO2017081490A1

WO2017081490A1 - Method of initialising physical downlink control channel (pdcch) for emtc and iot devices

Info

Publication number: WO2017081490A1
Application number: PCT/GB2016/053562
Authority: WO
Inventors: Siva SUBRAMANI
Original assignee: Vodafone Ip Licensing Limited
Priority date: 2015-11-12
Filing date: 2016-11-14
Publication date: 2017-05-18
Also published as: GB201519999D0; GB2544317A; GB2544317B

Abstract

Messages are transmitted between devices and eNodeBs when initialising random access and user-specific resource allocation. In extending LTE to ultra-low complexity "internet of things" devices, a UE-specific N-PDCCH design is discussed that addresses the requirements of control channel messaging involving such devices.

Description

METHOD OF INITIALISING PHYSICAL DOWNLINK CONTROL CHANNEL (PDCCH) FOR eMTC AND loT DEVICES

Field of the Disclosure

This disclosure relates to a system and method for initialising a control channel for low complexity devices in cellular telecommunications networks. In particular this disclosure concerns the physical downlink control channel (PDCCH) for use by narrowband internet of things (NB-loT) devices and enhanced machine- type communications (MTC) devices.

Background to the Invention

Cellular telecommunications networks characteristically offer wireless (radio frequency, RF) communication to (and between) communication devices (which are typically mobile) in accordance with a standardised radio access technology (RAT).

Various RATs are implemented: currently digital cellular networks are the most common and these are loosely classed as second generation (2G), third generation (3G), fourth generation (4G), etc. technologies according to whether the RAT achieves effective data communications that meet increasingly challenging requirements. In meeting these requirements, the technologies make different uses of the available radio frequency (RF) bandwidth: for example 4G technologies typically require wideband RF carriers divided into a plurality of orthogonal subcarriers.

To ensure effective coverage of a large geographic area, a plurality of cells (i.e. regions of radio coverage) are provided by respective network nodes referred to variously as base transceiver stations and base stations. Base (transceiver) stations are associated with one or more antenna arrays which in turn establish respective cells. They are controlled at least in part by other entities in the core network known as controllers (in 3G technologies such as UMTS these are referred to as radio network controllers, RNCs). More recently certain categories of base transceiver stations, referred to as eNodeBs or eNBs in the context of Long Term Evolution (LTE), implement both base station functionality and at least some controller functionality. The antenna arrays (and thus, often, the base stations) are geographically distributed so that the coverage of each cell typically overlaps with that of neighbouring cells only at the cell edge.

The communication devices accessing the cellular network are variously referred to as mobile terminals or user equipment (UE) and examples include: cellular phones (smartphones, feature phones, etc.), cellular enabled tablets/computers, as well as machine-type low complexity devices. Radio access from communication devices is provided through one or more base station under the management of a core network, with a radio "downlink" from base station to communication device and an "uplink" in the opposite direction.

Certain classes of telecommunications device, such as NB-loT devices and MTC devices (e.g. semi-autonomous or autonomous wireless communication terminals), support low complexity communication applications that are typically characterised by their low throughput (i.e. they transmit small amounts of data at relatively infrequent intervals). Devices suitable for such applications need only be provided with a simple receiver unit (or transceiver unit) having capabilities more commensurate with the amount of data likely to be transmitted to (or from) the terminal. This more limited capability contrasts with the capabilities of the conventional mobile telecommunications terminals, such as smartphones, which share access to the same telecommunications networks.

NB-loT devices typically operate in a more limited bandwidth than conventional LTE devices - the "narrowband" of 180kHz is used in both uplink and downlink directions.

To support MTC and NB loT terminals, it has been proposed to introduce specific additions to the existing communications standards. In the case of NB loT devices, a narrowband-specific physical data control channel (N-PDCCH) is contemplated that is complementary to the existing PDCCH of the current LTE standards (referred to as the "legacy PDCCH" hereafter). A similar MTC-specific PDCCH is also contemplated (i.e. M-PDCCH).

In certain cases, the edge of the cell coverage may be considered to occur at greater distances from the base station and/or deeper indoors or underground (provided a lower quality of service is acceptable). Standards setting bodies have made considerable efforts to consider coverage enhancements that are relevant to the use cases for eMTC and NB-IOT devices. Typical suggestions require a plurality of coverage enhancement levels (also referred to as coverage classes) to be supported by the devices so that devices experiencing different coverage constraints (such as attenuation) can have suitable support from the radio access network.

The main technique for enhanced coverage is to repeat and bundle communications (i.e. blocks of data are transmitted multiple times in consecutive subframes without waiting for messages to confirm safe receipt/decoding). The number of times a given block of data is transmitted (i.e. the repetition number) is varied to ensure that devices in the most difficult coverage classes are addressed with a greater number of repetitions. For each CE level, the bundling size (i.e. the number of repetitions before an acknowledgement message is required) and/or the repetition number is different among different physical channels.

The current signal exchange for LTE uses available physical channels inefficiently when carrying control information for low complexity communication devices.

It is therefore desirable to configure the operations of base station to support low complexity communication device with more effective use of the radio resources.

Summary of the Invention

According to a first aspect of present disclosure there is provided a base station apparatus for communicating data with at least one terminal in a wireless telecommunications system, the base station apparatus comprising: a transceiver configured to receive, from the at least one terminal, a request for access to at least one downlink data channel, said request including an indication of a repetition number; and processing circuitry configured to generate a response message and scheduling data for at least one control message, wherein the scheduling data is generated in accordance with the indicated repetition number; and wherein the transceiver is further configured to transmit the at least one control message in accordance with the scheduling data.

As a result of the above, the number of messages (signalling) transmitted by the MTC and/or IOT devices on the uplink is reduced. The user-specific downlink response message both acts as an acknowledgment of receipt of a request from a given device and assigns resources for the MTC/loT devices to transmit the information. In order to accomplish this reduced number uplink messages, the assignment of resources in control channel messages can be larger than legacy PDCCH.

Furthermore, the solution presented here allows low complexity loT devices to restrict their monitoring to selected control channel elements and, conveniently, to predetermined radio sub-frames. Once DCIs addressing the device are obtained, the solution allows the device to ignore/discard remaining repetitions of those same DCIs.

According to a second aspect of the present disclosure there is provided a method for communicating data between a base station apparatus and at least one terminal in a wireless telecommunications system, the method comprising: receiving, from the at least one terminal, a request for access to at least one downlink data channel, said request including an indication of a repetition number; generating a response message and scheduling data for at least one control message, the scheduling data being generated in accordance with the indicated repetition number; and transmitting the at least one control message in accordance with the scheduling data.

According to a third aspect of the present disclosure there is provided a terminal having a radio frequency, RF, transceiver configured to receive downlink signals from a base station, said downlink signals including one or more reference signals, said reference signals having been transmitted at a predetermined power level; a measurement unit configured to measure the received strength of the reference signals and to generate a received strength measurement in accordance with the measured strength; a processor configured to obtain the predetermined power level, to calculate the relative strength of the received reference signal, and to calculate a repetition number corresponding to the calculated relative strength, wherein the RF transceiver is further configured to transmit a request for access to at least one downlink data channel to the base station, said request including an indication of a repetition number and information uniquely identifying the terminal.

There is further provided computer software operable, when executed on a computing device, to cause one or more processors to perform a computer implemented method according to the above aspects of the present disclosure.

A further aspect provides machine-readable storage storing such a program.

Various respective aspects and features of the present disclosure are defined in the appended claims.

It is an aim of certain embodiments of the present disclosure to solve, mitigate or obviate, at least partly, at least one of the problems and/or disadvantages associated with the prior art. Certain embodiments aim to provide at least one of the advantages described below.

Brief Description of the Drawings Various embodiments of the present disclosure will now be described with reference to the accompanying drawings, in which:

Figure 1 provides a schematic diagram illustrating a conventional mobile telecommunications network;

Figure 2 provides a schematic diagram illustrating a mobile telecommunications network configured to support low complexity devices;

Figure 3 is a schematic diagram illustrating an LTE downlink radio frame; Figure 4 is a schematic diagram of a grid which illustrates the structure of a conventional downlink LTE slot;

Figure 5 illustrates a conventional LTE downlink radio sub-frame (two slots);

Figure 6 illustrates an assignment of a group of resource elements to N- PDCCH in accordance with the present disclosure;

Figure 7 illustrates a further assignment of a group of resource elements to N- PDCCH in accordance with the present disclosure;

Figure 8 illustrates a further example of the assignment of a group of resource elements to N-PDCCH where only six subcarriers are allocated;

Figure 9 illustrates yet another example of the assignment of groups of resource elements to N-PDCCH, segregated groups being allocated messages of different coverage classes; and

Figure 10 illustrates the signal flow between low complexity device and eNodeB in accordance with one aspect of the present disclosure.

Detailed Description of Preferred Embodiments

The present disclosure relates to the initialisation of downlink control channels for low complexity and/or low throughput devices in a telecommunications network architecture that includes a radio access network (RAN), a core network (CN) and a packet data network (PDN). Communication devices, such as mobile terminals, user equipment (UEs) and wireless access stations, establish wireless connections to the network by means of the RAN.

Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architecture are able to support more sophisticated services than the simple voice and messaging services offered by previous generations of mobile telecommunication systems. For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.

Figure 1 provides a schematic diagram illustrating some basic functionality of a conventional mobile telecommunications network.

The network includes a plurality of base stations 1 10 connected to a core network 120.

Each base station provides a coverage area 102 within which data can be communicated to and from terminal devices (also referred to as mobile terminals, MT or User equipment, UE) 130. Data is transmitted from base stations 1 10 to terminal devices 130 within their respective coverage areas 102 via a radio downlink. Data is transmitted from terminal devices 130 to the base stations 1 10 via a radio uplink. The core network 120 routes data to and from the terminal devices 130 via the respective base stations 1 10 and provides functions such as authentication, mobility management, charging and so on.

The range of devices, for which access to a wireless communication network is expected, has widened to include classes of telecommunications device, such as NB-loT devices and MTC devices (e.g. semi-autonomous or autonomous wireless communication terminals), that support low complexity communication applications. These devices are typically characterised by their low throughput (i.e. they transmit small amounts of data at relatively infrequent intervals). Devices suitable for such applications need only be provided with a simple receiver unit (or transceiver unit) having capabilities more commensurate with the amount of data likely to be transmitted to (or from) the terminal. This more limited capability contrasts with the capabilities of the conventional mobile telecommunications terminals, such as smartphones, which share access to the same telecommunications networks.

To support MTC and NB loT terminals, it has been proposed (in discussions around Release 13 of the 3GPP standard for LTE) to introduce specific additions to the existing communications standards. In the case of NB loT devices, a narrowband-specific physical data control channel (N-PDCCH) is contemplated that is complementary to the existing PDCCH of the current LTE standards (i.e. the "legacy PDCCH"). A similar MTC-specific PDCCH is also contemplated (i.e. M- PDCCH).

Figure 2 provides a schematic diagram illustrating some basic functionality of a mobile telecommunications network configured to support NB-loT devices and/or MTC devices.

As for Figure 1 , the network includes a plurality of base stations 1 10 connected to a core network 120.

Each base station provides a coverage area 202 within which data can be communicated to and from low complexity devices 230. Data is transmitted from base stations 1 10 to the devices 230 within their respective coverage areas 202 via a radio downlink. Data is transmitted from devices 230 to the base stations 1 10 via a radio uplink. As for Figure 1 , the core network 120 routes data to and from the devices 230 via the respective base stations 1 10 and provides functions such as authentication, mobility management, charging and so on.

The more basic communications requirements of NB-loT devices and MTC devices and their greater tolerance of delay mean that the range of coverage (i.e. coverage area 202) from any one base station may be extended from the "normal" range of coverage (i.e. the range of coverage providing adequate services to conventional UEs) to locations where wireless communications become increasingly unreliable and error prone. In Figure 2, this is illustrated schematically by the provision of successively larger "rings" (marked CL1 , CL2 & CL3 respectively) around base stations each representing successively more challenging coverage levels.

Coverage enhancements for LTE view the coverage provided in terms of the reference signal received power (RSRP) measured by UEs, with UEs being classified in one of a plurality of coverage classes according to the measured RSRP. Table 1 below illustrates a case where there are three coverage classes: Class 1 - "good" coverage; Class 2 - "deep" coverage; and Class 3 - "extreme" coverage.

Table 1 :

In Table 1 , threshold RSRP value THR1 is greater than threshold RSRP value

THR2.

Mobile telecommunications systems such as those arranged in accordance with the 3GPP defined Long Term Evolution (LTE) architecture use an orthogonal frequency division multiplex (OFDM) based interface for the radio downlink (so-called OFDMA) and the radio uplink (so-called SC-FDMA).

Figure 3 shows a schematic diagram illustrating an OFDM based LTE downlink radio frame 300. Here, the horizontal axis represents time while the vertical represents frequency. The LTE downlink radio frame 300 is transmitted from an LTE base station (known as an enhanced Node B, eNodeB, or eNB) and lasts 10 ms. The downlink radio frame comprises ten sub-frames 302, each sub-frame lasting 1 ms. Sub-frames 302 are themselves divided into two slots 304 (each 0.5ms). These slots are numbered to allow distinctions to be made between slots, thus Figure 3 shows slots #0, #1 ...#18, #19 in time order. Synchronisation signals are transmitted in certain sub-frames of the LTE radio frame to allow receiving UEs to maintain synchronisation with the radio transmissions of the eNodeB.

Figure 4 is a schematic diagram of a grid which illustrates the structure of an example conventional downlink LTE slot 400. As for Figure 3, the horizontal axis represents time while the vertical represents frequency. The frequency axis is divided into a predetermined number of orthogonal sub-carriers, 15kHz each, distributed across the bandwidth of the downlink radio carrier, say 10MHz. The slot 400 comprises a predetermined number of "symbols" 406, which are transmitted during the 0.5 ms interval of the slot.

It is noted that, in discussion of the provision of downlink sub-carriers for narrowband loT devices, the sub-carrier spacing may be smaller than 15 kHz (e.g. 3.75 kHz) within the 180kHz "narrowband". The example slot 400 shown in Figure 4 comprises seven OFDM symbols 406 and 600 sub-carriers (some of these are omitted for brevity) spread across a 10MHz bandwidth. The smallest allocation of user data for transmission in LTE is a "resource block" 402 comprising twelve sub- carriers transmitted over one slot. Control data may be allocated to smaller units known as resource elements, corresponding to a single sub-carrier of a given symbol - an example of a resource element is shown in Figure 4, (reference sign - 404).

Figure 5 shows a conventional sub-frame 500 of two slots. The example sub- frame shown in Figure 5 comprises 14 symbols and 600 sub-carriers spread across a 10MHz bandwidth.

In downlink LTE radio frames, physical downlink control information is sent over a Physical Downlink Control Channel (PDCCH) while user data is provided in a Physical Downlink Shared Channel (PDSCH). The control information includes downlink scheduling assignments, which are used to carry the information needed to receive data on the PDSCH, and uplink scheduling grants, which are used to indicate the shared uplink resources (Physical Uplink Shared Channel, PUSCH) the terminal uses to send data to the base station (eNodeB). In a downlink LTE subframe, the first three (or two) OFDM symbols carry LTE PDCCH (these symbols 502 are shown as the shaded columns to the left of Figure 5); the legacy LTE PDCCH typically span the entire bandwidth (10MHz, say) of the LTE carrier.

In the PDCCH region in DL radio frame, there can be many places where a specific PDCCH is located and UE searches all the possible locations. These locations are called control channel elements (CCE). Each CCE is a respective resource element. The possible location for a PDCCH differs depending on whether the PDCCH is UE-Specific or Common, and also depend on what aggregation level is used. The set of all the possible locations for PDCCH is called the 'search space' and each of the possible locations is called a 'PDCCH Candidate'.

The search space indicates the set of CCE locations where the UE may find its PDCCHs. Each PDCCH carries one downlink control information, DCI, message.

A DCI message is user-specific and carries N-PUSCH grants and N-PDSCH allocations for a given UE: the UE being identified by a suitable identifier, such as a temporary ID assigned to the UE (in LTE this might be the Radio Network Temporary Identifier, RNTI). DCI message may also carry random access request, RAR, response messages and paging messages. A DCI message contains information including: (i) acknowledging coverage-class / repetition number (ii) an indication of the modulation and coding scheme, MCS, and/or (iii) resource allocation messages.

There are (at least) two types of search space: the common search space and the UE-specific search space. A UE is required to monitor both common and UE- specific search space. There might be overlap between common & UE-specific search spaces for a UE (i.e. certain CCEs of the legacy PDCCH may be used for common or UE-specific DCI messages in different sub-frames).

The first three OFDM symbols of LTE subframes carry LTE PDCCH; to allow legacy LTE devices to operate unaffected by the discussed arrangements control channel elements (CCEs) in those OFDM symbols are protected.

For NB-loT, certain additional symbols or groups of resource elements within each radio (sub-)frame are assigned to carry N-PDCCH.

It is noted that conventional LTE subframes are "punctured" by synchronisation signals: predetermined resource elements are assigned to carry reference signals, even when these resource elements are allocated to control channels such as PDCCH. Where resource blocks of the conventional LTE carrier are allocated to N-PDCCH, the same puncturing may be expected - with a minority of the resource elements (between 20% and 35% depending upon allocation and sub-frame number) being incapable of carrying control data. The scheduler is therefore required to schedule control data in resource elements of the allocated resource blocks that are determined not to carry these reference signals.

Once assigned, the coverage class for a given NB-loT device requesting access to resources determines the number of times a given DCI for that device is repeated (in successive sub-frames). Successive sub-frame repetition facilitates continuous energy ramping (without any phase discontinuity). Table 2 illustrates a simple mapping between the illustrative coverage classes of Table 1 with typical numbers of repetitions. The precise number of repetitions is not however limited to the numbers given in Table 2, and may be varied depending upon the thresholds between coverage classes and/or the level to which communication failure is tolerated.

Table 2:

Figure 6 illustrates an assignment of a group of resource elements to N- PDCCH in addition to the legacy PDCCH. Here, the N-PDCCH for an "extreme" coverage level CL3 is shown. A selected number of resource elements are allocated as a block to N-PDCCH 602. The allocation of N-PDCCH CCEs in blocks is convenient as contiguous ranges of elements are more easily identified than discrete elements, thereby aiding simpler allocation and repetition. Among these resource elements, certain elements (here on the same sub-carrier) form the CCEs 604 for extreme coverage devices (shown as the elements in black). In the illustrated example, the CCEs shaded black are for a specific user device in CL3.

Figure 7 illustrates a similar assignment of a group of resource elements to N- PDCCH 702. Here the CCEs 704 for a user device in "deep" coverage class CL2 start from sub-frame 9 and CCEs 706 for a further user device in "good" coverage class CL1 begin at subframe 15 and are repeated at subframe 16.

To allow a given NB-loT device to restrict further which sub-frames it needs to monitor for DCIs on the relevant N-PDCCH CCEs, the eNodeB conveniently includes an indication of the starting subframe in which DCIs for that NB-loT device will be transmitted.

In Figure 6, for example, the NB-loT device in extreme coverage CL3 N- PDCCH would receive a message including an indication that the CL3 N-PDCCH CCEs start upon which DCIs for that device are transmitted will start at subframe n1 . While Figure 6 indicates that the DCIs for that device will be repeated in successive subframes until subframe n8, in practice, for a CL3 device they will typically be repeated even longer. If a user is restricted to monitoring only selected CCEs it reduces searching complexity; the N-PDCCH search space is reduced.

In certain embodiments, only resource elements in predetermined symbols and on selected sub-carriers may be used to map N-PDCCH DCI messages. While the legacy LTE PDCCH could be 2 or 3 OFDM symbols over the entire carrier bandwidth, say 10 MHz, N-PDCCH has been assumed to extend over a 200kHz bandwidth (corresponding to a single resource block). In Figure 8, which illustrates an example of such a case, only six subcarriers 802 are allocated to N-PDCCH.

In further embodiments, a plurality of distinct groups of resource elements (in predetermined symbols and on selected sub-carriers) may be used to map N- PDCCH DCI messages to devices reporting corresponding coverage classes. As illustrated in Figure 9, one group of resource elements 902 may be dedicated to map N-PDCCH DCI messages to devices reporting CL3, while a second group of resource elements 904 may be dedicated to map N-PDCCH DCI messages to devices reporting CL2, thereby segregating some sub-carriers for CL3 and some for CL2. In the Figure 9 example, subframe m includes some N-PDCCH resource elements for CL3 devices and some for CL2 devices. This configuration may be repeated for n subframes. After m+n subframes, some of the resource elements 906 are instead configured for devices reporting CL1 , while the first group of resource elements 902 remains assigned to the transport of DCIs for CL3 devices. DCIs for CL3 devices are repeated in far more subframes than those for CL2 devices, which in turn are repeated more often than those for CL1 , which may not be repeated at all.

A flow of signals and operations (i.e. the random access channel, RACH procedure) for the initialisation of a PDCCH between a cellular loT device 1030 (or an MTC device) and an eNodeB 1010 is illustrated in Figure 10.

Initially, the UE 1030 transmits a physical RACH, PRACH, request message in the uplink. This PRACH request message includes an indication of a repetition number for that device along with an identifier for that UE (e.g. the temporary identifier, RNTI). The UE 1030 selects a repetition number among the predefined repetition numbers based on a measurement (by the UE) of RSRP (reference signal received power) for a reference signal transmitted by the eNodeB (such as the synchronisation signal and/or another predetermined reference signals). The UE initiates random access process by selecting the preamble length. It is noted that this message may be configured to carry more data than a PRACH request message for conventional LTE.

Upon receiving the PRACH request message, the eNodeB 1010 composes a RAR (random access response) message. This message is sent over N-PDCCH (which is monitored by a requesting UE), and all the control information intended for the UE is then transmitted through user-specific N-PDCCH (in resource elements that the UE can determine from the RAR message).

At most one RAR message is sent per sub-frame. The number of repetitions of the RAR message depends on coverage classes and/or the type of UE (just as the number of repetitions of DCIs in the N-PDCCH depends on the coverage class reported by the NB-loT device). The repetition number is pre-defined for each coverage classes. The format of the DCI messages themselves may conveniently be configured to the reported coverage class and UE type (i.e. whether it is in fact an eMTC device or an NB-loT device). Conveniently, the assignment of resources in control channel messages for NB-loT (or eMTC) may be larger than that for legacy PDCCH.

The time of arrival of the PRACH request message is logged by the eNodeB 1010 and used to determine the subframe at which the DCIs for the UE 1030 will start being transmitted in N-PDCCH CCEs appropriate for the reported UE's coverage class (i.e. the "starting subframe").

The eNodeB conveniently calculates the number of repetitions of the N- PDCCH messages (i.e. the DCI messages) and communicates them to the loT device (in the RAR message). Conveniently then the RAR message includes an indication of the N-PDCCH repetition number for the NB-loT device. It is noted that the number of repetitions of the N-PDCCH need not be identical to the number of repetitions of RAR messages.

Repetition of RAR messages (on PDCCH) ensures that the loT device (or MTC device) receives the response to its request. On the reception of RAR message, depending on the loT device's coverage class, the device specifically searches the N-CCEs allocated to that coverage class. The search of CCEs conveniently only starts at the starting subframe indicated in the RAR message.

The loT device then receives one or more DCI messages in the searched N- CCEs and decodes N-PDSCH resource allocations, N-PUSCH grants, etc. from the DCI. Once the N-PDSCH resource allocations are known, the NB-loT device may ignore or discard remaining N-PDCCH repetitions of the same DCI message.

It is noted that In order to accomplish this reduced number uplink messages, the assignment of resources in control channel messages can be larger than legacy PDCCH.

It will be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the scope of the appended claims.

For example, whilst embodiments described in the foregoing description refer to NB-loT in LTE, it should be noted that the system and method described may equally be deployed in telecommunications networks providing services to eMTC devices. Furthermore as NB-loT is envisaged to make use of other cellular telecommunication architectures, for example GERAN architectures, such as 2G and EDGE; UTRAN systems such as UMTS and HSPA; LTE-Advanced (3GPP Release 10 onwards), future architectures (e.g., 5G), as well as WD-CDMA and WiMAX. In certain examples NB-loT signalling may be carried in bands of spectrum currently being used by GERAN systems and may even act as a replacement of one or more GSM carriers.

The lower complexity of NB-loT devices may also allow an expansion of the bands upon which it is feasible to carry signalling. While the preceding discussion, presumes that NB-loT signalling operates using certain resource blocks within a normal LTE carrier, so-called "in-band operation", the unused resource blocks that correspond to guard-bands in conventional LTE may also be utilized for NB-loT signalling - so called "guard band operation".

It will also be well understood by persons of ordinary skill in the art that whilst the described embodiments implement certain functionality by means of software, that functionality could equally be implemented solely in hardware (for example by means of one or more ASICs (application specific integrated circuit)) or indeed by a mix of hardware and software. As such, the scope of the present invention should not be interpreted as being limited only to being implemented in software.

Lastly, it should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features or embodiments herein disclosed irrespective of whether or not that particular combination has been specifically enumerated in the accompanying claims.

Claims

Claims:

1 . A base station apparatus for communicating data with at least one terminal in a wireless telecommunications system, the base station apparatus comprising:

a transceiver configured to receive, from the at least one terminal, a request for access to at least one downlink data channel, said request including an indication of a repetition number; and

processing circuitry configured to generate a response message and scheduling data for at least one control message,

wherein the scheduling data is generated in accordance with the indicated repetition number; and

wherein the transceiver is further configured to transmit the at least one control message in accordance with the scheduling data.

2. A base station apparatus as claimed in claim 1 , wherein the transceiver is further configured to transmit a reference signal at a predetermined power and wherein the repetition number is a number selected by the terminal from a plurality of predefined repetition numbers mapped to respective ranges of received signal strengths, the selection corresponding to a measurement of the signal strength of the reference signal at the terminal.

3. A base station apparatus as claimed in claim 1 or claim 2, wherein the repetition number corresponds to a respective one of a plurality of coverage classes.

4. A base station apparatus as claimed in claim 3, wherein the scheduling data for the at least one further message includes information identifying a downlink control channel upon which the response message is to be transmitted, there being a plurality of downlink control channels, each downlink control channel comprising a respective subset of resource blocks selected from a plurality of resource blocks within one or more radio frames, and

wherein the processing circuitry is configured to generate the scheduling data in accordance with the indicated repetition number by:

determining which coverage class the indicated repetition number corresponds to,

selecting a downlink control channel corresponding to said coverage class from the plurality of downlink control channels, and generating the scheduling data for the response message identifying the selected downlink control channel as the downlink control channel upon which the response message is to be transmitted.

5. A base station apparatus as claimed in any one of the preceding claims, wherein the request further includes information uniquely identifying the terminal, wherein the scheduling data is generated in accordance with the indicated repetition number and the information uniquely identifying the terminal.

6. A base station apparatus as claimed in claim 5, wherein the processing circuitry is further configured to append a timestamp to the received request, the timestamp indicating a time at which the request was received, and wherein the scheduling data is further generated in accordance with the timestamp.

7. A base station apparatus as claimed in claim 6, wherein the processing circuitry is further configured to generate scheduling data in accordance with the timestamp by scheduling the starting subframe for the transmission of the at least one control message at a predetermined interval after the time indicated in the timestamp.

8. A base station apparatus as claimed in any one of the preceding claims, wherein the response message includes downlink channel information and downlink channel allocation data.

9. A base station apparatus as claimed in claim 8, wherein the response message specifies a starting subframe within the or each radio frame and a repetition number corresponding to the number of times the at least one control messages are to be sent after the starting subframe.

10. A base station apparatus as claimed in claim 8 or claim 9, wherein the response message specifies the location of user-specific downlink control channel elements upon which the at least one control messages are to be sent.

1 1 . A base station apparatus as claimed any one of the preceding claims, wherein the processing circuitry is configured to generate scheduling data for the at least one control message by scheduling the at least one control message for transmission within one or more radio frames, the scheduling data indicating at least one of the following regions of the one or more radio frames: a symbol, a resource block or a predetermined plurality of control channel elements in which the at least one control message is to be transmitted.

12. A base station apparatus as claimed in claim 1 1 , wherein the indicated region to which the at least one control message is scheduled corresponds to the repetition number indicated by the at least one terminal, there being a respective region for each different coverage class.

13. A base station apparatus as claimed in any one of the preceding claims wherein the response message is specific to the requesting terminal.

14. A base station apparatus as claimed in any one of the preceding claims wherein the response message is transmitted to the requesting terminal in a physical downlink control channel, PDCCH.

15. A base station apparatus as claimed in any one of the preceding claims, wherein the processing circuitry includes a scheduler.

16. A method for communicating data between a base station apparatus and at least one terminal in a wireless telecommunications system, the method comprising: receiving, from the at least one terminal, a request for access to at least one downlink data channel, said request including an indication of a repetition number; generating a response message and scheduling data for at least one control message, the scheduling data being generated in accordance with the indicated repetition number; and

transmitting the at least one control message in accordance with the scheduling data.

17. A terminal having

a radio frequency, RF, transceiver configured to receive downlink signals from a base station, said downlink signals including one or more reference signals, said reference signals having been transmitted at a predetermined power level;

a measurement unit configured to measure the received strength of the reference signals and to generate a received strength measurement in accordance with the measured strength; a processor configured to obtain the predetermined power level, to calculate the relative strength of the received reference signal, and to calculate a repetition number corresponding to the calculated relative strength,

wherein the RF transceiver is further configured to transmit a request for access to at least one downlink data channel to the base station, said request including an indication of a repetition number and information uniquely identifying the terminal.

18. A terminal as claimed in claim 16, wherein the repetition number corresponds to a respective one of a plurality of coverage classes.

19. A terminal as claimed in claim 17, wherein the repetition number

corresponding to the calculated relative strength is calculated by looking up the relative received signal strengths in a table, the table mapping respective ranges of signal strength to a plurality of predefined repetition numbers.