FIELD OF INVENTION

The present invention relates to wireless communications systems and methods, and in particular to a system, method, base station and terminal device for communicating using a subordinate carrier of a host carrier.

BACKGROUND OF THE INVENTION

Mobile communication systems have evolved over the past ten years or so from the GSM System (Global System for Mobile communications) to the 3G system and now include packet data communications as well as circuit switched communications. The third generation partnership project (3GPP) is developing a fourth generation mobile communication system referred to as Long Term Evolution (LTE) in which a core network part has been evolved to form a more simplified architecture based on a merging of components of earlier mobile radio network architectures and a radio access interface which is based on Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) on the uplink.

Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architectures, are able to support a more sophisticated range of services than 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.

The anticipated widespread deployment of third and fourth generation networks has led to the parallel development of a class of devices and applications which, rather than taking advantage of the high data rates available, instead take advantage of the robust radio interface and increasing ubiquity of the coverage area. Examples include so-called machine type communication (MTC) applications, also known as machine-to-machine (M2M) communications, some of which are in some respects typified by semi-autonomous or autonomous wireless communication devices (i.e. MTC devices) communicating small amounts of data on a relatively infrequent basis. Examples include so-called smart meters which, for example, are located in a customer's home and periodically transmit data back to a central MTC server relating to the customer's consumption of a utility such as gas, water, electricity and so on.

Whilst it can be convenient for a terminal such as an MTC-type terminal to take advantage of the wide coverage area provided by a third or fourth generation mobile telecommunication network there are at present disadvantages. Unlike a conventional third or fourth generation mobile terminal such as a smartphone, a primary driver for MTC-type terminals will be a desire for such terminals to be relatively simple and inexpensive. The type of functions typically performed by a MTC-type terminal (e.g. simple collection and reporting of relatively small amounts of data) do not require particularly complex processing to perform, for example, compared to a smartphone supporting video streaming. However, third and fourth generation mobile telecommunication networks typically employ advanced data modulation techniques and support wide bandwidth usage on the radio interface which can require more complex and expensive radio transceivers to implement. It is usually justified to include such complex transceivers in a smartphone as a smartphone will typically require a powerful processor to perform typical smartphone type functions. However, as indicated above, there is now a desire to use relatively inexpensive and less complex devices to communicate using LTE type networks.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a wireless communications system, comprising a base station, one or more terminal devices of a first type and one or more terminal devices of a second type. The base station is operable to communicate with the terminal devices of the first type using a host carrier comprising radio resource segments distributed in time, each radio resource segment providing radio resources across a first frequency band. The base station is operable to communicate with the terminal devices of the second type using a subordinate carrier comprising radio resources within a second frequency band of a subset of the radio resource segments of the host carrier, the second frequency band being narrower than and contained within the first frequency band.

In this way, an efficient and flexible mechanism for specifying and controlling an amount and location of radio resources to be dedicated to a subordinate earner for use by a particular (e.g. reduced capability) type of device can be provided.

One way of achieving this differentiated access between the terminal devices of the first type and second type is to allocate a part of the carrier resource that is dedicated to the second type of device (e.g. MTC traffic) using normal eNB (base station) scheduling. The eNB differentiates between MTC and non-MTC (example of the first type of device) UEs and only schedules MTC UEs within the reserved part of the earner resource and only schedules non-MTC UEs outside of the reserved part of the carrier resource. While this solution is viable, the simple scheduling approach places some restrictions on the MTC subordinate carrier that can be realised. For instance, it would be necessary to use the same carrier characteristics and/or reference signals. If it were advantageous to use different carrier characteristics or to use additional or modified reference signals then this may not be possible in an MTC subordinate carrier implemented purely by eNB scheduling.

The radio resource segments may be sub-frames of radio frames, each radio frame comprising a plurality of sub-frames. In this case, the sub-frames may be allocated to the subordinate carrier using a subordinate carrier sub-frame allocation set, the subordinate carrier sub-frame allocation set determining which sub frames within a repeating group of one or more radio frames are allocated to the subordinate carrier. The subordinate carrier sub-frame allocation set may be defined by one or more reserved sub-frame allocation patterns. The one or more reserved sub-frame allocation patterns may comprise all or a sub-set of all reserved sub-frame allocation patterns defined for the host carrier.

In one example, the subframes selected for the subordinate carrier are so-called MBSFN (Multimedia Broadcast/multicast service over a Single Frequency Network) subframes. This embodiment relies on the fact that such subframes do not have to be used exclusively for MBSFN. The LTE Rel. 8/9/10 specifications define a means (in the standard LTE SystemInformationBlockType2—SIB2) by which certain subframes can be excluded from normal allocation to the Physical Downlink Shared Channel (PDSCH). Furthermore, the specifications define signalling within the standard system information which allows some or all of these excluded subframes to be used for other defined purposes, such as MBMS (in SystemInformationBlockType13—SIB 13), relay and positioning reference signal transmission. However, reading of this system information may require reception across the whole carrier bandwidth.

Acquisition information required for a terminal device of the second type to receive the subordinate carrier may be allocated for inclusion in sub-frames of the subordinate carrier using at least a portion of the subframes in one or more of the reserved sub-frame allocation patterns defining the subordinate carrier.

The base station may be operable to transmit an indication of the radio resources of all reserved sub-frames to terminal devices of the first type. In this way, the first type of device is informed of subframes which are reserved for the subordinate carrier, another subordinate carrier, and for other purposes such as relay backhaul. A particular device of the first type is not required to know why a particular sub-frame is reserved, merely that it is not available to that device. This indication may be presented to the terminal devices of the first type as a reserved subframe allocation within a system information block transmitted using frequency resources not necessarily limited to the second frequency band of the subordinate carrier. In this way, it is possible to exclude non-MTC devices from a resource reserved for the subordinate carrier.

The base station may be operable to transmit, using radio resources within the second frequency band, subordinate carrier information indicating that a subordinate carrier is available within the host carrier. A terminal device of the second type may be responsive to subordinate carrier information indicating that a subordinate carrier is not available within the host carrier to terminate a camp-on procedure for camping on to the network.

The subordinate carrier information may be provided within first acquisition information transmitted on radio resources within the second frequency band, the first acquisition information being required for a terminal device of the first type to receive the system information of the host carrier. The first acquisition information may be a master information block transmitted on a physical broadcast channel within radio resources of the host earner. In this way it is possible to signal via the first acquisition information, to terminal devices of the second type, the presence of an MTC subordinate carrier existing within the reserved resource and using only a restricted bandwidth. If the subordinate carrier information is not present then the camp-on process by a terminal device may be terminated early, thereby reducing time and power wastage at the terminal device.

The first type of terminal device may be capable of receiving the full bandwidth of the first frequency band, and the second type of terminal device may not be capable of receiving the full bandwidth of the first frequency band but be capable of receiving the full bandwidth of the second frequency band. The bandwidth of the subordinate carrier may be predetermined and be known in advance to terminal devices of the second type. Alternatively, the base station may be operable to transmit, using radio resources within the second frequency band, an indication of the bandwidth of the subordinate carrier. In this case the bandwidth need not necessarily be predetermined. The indication of the bandwidth of the subordinate carrier may be provided within first acquisition information transmitted on radio resources within the second frequency band, the acquisition information being provided to permit a terminal device of the first type to receive the host carrier downlink and camp on to the host carrier. Alternatively, the base station may be operable to transmit, using radio resources of the subordinate carrier, an indication of the bandwidth of the subordinate carrier.

The base station may be operable to transmit, using radio resources of the subordinate carrier, second acquisition information required for a terminal device of the second type to receive the subordinate carrier downlink and camp on to the subordinate carrier. The second acquisition information may be transmitted on predetermined radio resources which are known in advance to terminal devices of the second type. The second acquisition information may comprise an indication of the bandwidth of the subordinate carrier. In this way, it is possible to signal system information defining the characteristics of the MTC subordinate carrier using only resources within the MTC subordinate carrier.

The radio resource segments may be sub-frames of radio frames in the time direction, each radio frame comprising a plurality of sub-frames. The second acquisition information may be transmitted in at least some of the sub-frames allocated to the subordinate carrier. A terminal device of the second type may be operable to determine whether a sub-frame contains second acquisition information from a current radio frame number and a first sub-frame allocation set for allocating the second acquisition information to sub-frames within the subordinate carrier, said first sub-frame allocation set identifying which sub-frames within a repeating group of one or more radio frames contain the second acquisition information.

The current radio frame number may be determined from first acquisition information transmitted on radio resources within the second frequency band, the first acquisition information being required for a terminal device of the first type to receive the host carrier downlink and camp on to the network. The first sub-frame allocation set may be predetermined and known in advance to terminal devices of the second type. The second acquisition information may comprise an indication of the current radio frame number. Accordingly, once the second acquisition information is available to a mobile terminal, it may from that point on obtain the current radio frame number from the second acquisition information rather than having to refer back to the first acquisition information.

A terminal device of the second type may be operable to determine whether a sub-frame is allocated to the subordinate carrier from a current radio frame number and a second sub-frame allocation set for the subordinate carrier, said second sub-frame allocation set identifying which sub-frames within a repeating group of one or more radio frames are allocated to the subordinate carrier. The current radio frame number may be determined from the second acquisition information. Alternatively, the current radio frame number may be determined from the first acquisition information and updated by counting radio frames.

The second sub-frame allocation set may be predetermined and known in advance to terminal devices of the second type. Alternatively, the second sub-frame allocation set may be specified in the second acquisition information. It will be appreciated that the second sub-frame allocation set may be different to the first sub-frame allocation set, but will include all of the sub-frames of the first sub-frame allocation set (and probably additional sub-frames as well).

The first type of terminal device may be an LTE device and the second type of device may be a low data rate device. The first type of terminal device may be an LTE device and the second type of device may be a low data rate device for providing machine-to-machine (M2M) communication.

It will be appreciated that different radio resource segments of the same or a different frequency band may be used to support a further subordinate carrier.

At least a portion of the radio resources outside of the second frequency band of the subset of the radio resource segments of the host earner allocated to the subordinate carrier may be allocated to another subordinate carrier. In other words, a different frequency band of the same resource segments (in time) may support another carrier.

At least a portion of the radio resources outside of the second frequency band of the subset of the radio resource segments of the host carrier allocated to the subordinate carrier may be used for communicating with terminal devices of the first type. In other words, a different frequency band of the same resource segments (in time) may support the host carrier.

Viewed from another aspect, there is provided a base station for communicating with terminal devices. The base station is operable to communicate with terminal devices of a first type using a host carrier comprising radio resource segments distributed in time, each radio resource segment providing radio resources across a first frequency band. The base station is operable to communicate with terminal devices of a second type using a subordinate carrier comprising radio resources within a second frequency band of a subset of the radio resource segments of the host carrier, the second frequency band being narrower than and contained within the first frequency band.

Viewed from another aspect, there is provided a terminal device for communicating with a base station which supports a host carrier comprising radio resource segments distributed in time, each radio resource segment providing radio resources across a first frequency band. The terminal device is operable to communicate with the base station using a subordinate carrier comprising radio resources within a second frequency band of a subset of the radio resource segments of the host carrier, the second frequency band being narrower than and contained within the first frequency band.

Viewed from another aspect, there is provided a method of communicating between a base station and terminal devices of a first type and a second type. The method comprises communicating between the base station and terminal devices of a first type using a host carrier comprising radio resource segments distributed in time, each radio resource segment providing radio resources across a first frequency band, and communicating between the base station and terminal devices of a second type using a subordinate carrier comprising radio resources within a second frequency band of a subset of the radio resource segments of the host carrier, the second frequency band being narrower than and contained within the first frequency band.

Viewed from another aspect, there is provided a method of communicating with a base station from a terminal device, comprising communicating with the base station using a subordinate carrier of a host carrier comprising radio resource segments distributed in time, each radio resource segment of the host carrier providing radio resources across a first frequency band, the subordinate carrier comprising radio resources within a second frequency band of a subset of the radio resource segments of the host carrier, the second frequency band being narrower than and contained within the first frequency band.

It will be appreciated that features of the above-described aspects and embodiments of the invention may be combined with features of other aspects and embodiments of the invention as appropriate and in combinations other than those explicitly set out. For example, optional features of the first aspect of the invention may equally optionally be incorporated in embodiments according to other aspects of the invention, for example where the different aspects have corresponding features.

