Patent Description:
The present disclosure claims the Paris convention priority of European patent applications <CIT>, <CIT> and <CIT>.

Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.

Third and fourth generation wireless communications systems, such as those based on the third generation partnership project (3GPP) defined UMTS and Long Term Evolution (LTE) architecture are able to support sophisticated services such as instant messaging, video calls as well as high speed internet access. 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. However, whilst fourth generation networks can support communications at high data rate and low latencies from devices such as smart phones and tablet computers, it is expected that future wireless communications networks will need to support communications to and from a much wider range of devices, including reduced complexity devices, machine type communication (MTC) devices, devices which require little or no mobility, high resolution video displays and virtual reality headsets. As such, supporting such a wide range of communications devices can represent a technical challenge for a wireless communications network.

A current technical area of interest to those working in the field of wireless and mobile communications is known as "The Internet of Things" or IoT for short. The 3GPP has proposed to develop technologies for supporting narrow band (NB)-IoT using an LTE or <NUM> wireless access interface and wireless infrastructure. Such IoT devices are expected to be low complexity and inexpensive devices requiring infrequent communication of relatively low bandwidth data. It is also expected that there will be an extremely large number of IoT devices which would need to be supported in a cell of the wireless communications network. Furthermore such NB-IoT devices are likely to be deployed indoors and /or in remote locations making radio communications challenging.

<CIT> relates generally to wireless communications networks, and more particularly to enhancing frequency stability of a user terminal.

<FIG> provides a schematic diagram illustrating some basic functionality of a mobile telecommunications network / system operating in accordance with LTE principles and which may be adapted to implement embodiments of the disclosure as described further below. Various elements of <FIG> and their respective modes of operation are well-known and defined in the relevant standards administered by the 3GPP (RTM) body, and also described in many books on the subject, for example, Holma H. It will be appreciated that operational aspects of the telecommunications network which are not specifically described below may be implemented in accordance with any known techniques, for example according to the relevant standards.

The mobile telecommunications system, where the system shown in <FIG> includes infrastructure equipment including base stations <NUM>. The infrastructure equipment <NUM> may also be referred to as a base station, network element, enhanced NodeB (eNodeB (eNB)) or a coordinating entity for example, and provides a wireless access interface to the one or more communications devices within a coverage area or cell represented by a broken line <NUM>. One or more mobile communications devices <NUM> may communicate data via the transmission and reception of signals representing data using the wireless access interface. The core network <NUM> may also provide functionality including authentication, mobility management, charging and so on for the communications devices served by the network entity.

The mobile communications devices <NUM> of <FIG> may also be referred to as communications terminals, user equipment (UE), terminal devices and so forth, and are configured to communicate with one or more other communications devices served by the same or a different coverage area via the network entity. These communications may be performed by transmitting and receiving signals representing data using the wireless access interface over the two way communications links.

As shown in <FIG> eNodeBs <NUM> are connected to a serving gateway S-GW <NUM> which is arranged to perform routing and management of mobile communications services to the communications devices <NUM> as they roam throughout the mobile radio network. In order to maintain mobility management and connectivity, a mobility management entity (MME) <NUM> manages the enhanced packet service (EPS) connections with the communications devices <NUM> using subscriber information stored in a home subscriber server (HSS) <NUM>. Other core network components include the policy charging and resource function (PCRF) <NUM> a packet data gateway (P-GW) <NUM> which connects to an internet network <NUM> and finally to an external server <NUM>.

Mobile communications systems such as those arranged in accordance with the 3GPP defined Long Term Evolution (LTE) architecture use an orthogonal frequency division modulation (OFDM) based interface for the radio downlink (so-called OFDMA) and a single carrier frequency division multiple access scheme (SC-FDMA) on the radio uplink.

<FIG> provides a simplified schematic diagram of the structure of a downlink of a wireless access interface that may be provided by or in association with the eNB of <FIG> when the communications system is operating in accordance with the LTE standard. In LTE systems the wireless access interface of the downlink from an eNB to a UE is based upon an orthogonal frequency division multiplexing (OFDM) access radio interface. In an OFDM interface the resources of the available bandwidth are divided in frequency into a plurality of orthogonal subcarriers and data is transmitted in parallel on a plurality of orthogonal subcarriers, where bandwidths between <NUM> and <NUM> bandwidth may be divided into <NUM> to <NUM> orthogonal subcarriers for example. Each subcarrier bandwidth may take any value but in LTE it is conventionally fixed at <NUM>. However it has been proposed in the future [<NUM>][<NUM>] to provide also a reduced subcarrier spacing of <NUM> for certain parts of the LTE wireless access interface for the uplink. As shown in <FIG>, the resources of the wireless access interface are also temporally divided into frames where a frame <NUM> lasts <NUM> and is subdivided into <NUM> subframes <NUM> each with a duration of <NUM>. Each subframe is formed from <NUM> OFDM symbols and is divided into two slots each of which comprise six or seven OFDM symbols depending on whether a normal or extended cyclic prefix is being utilised between OFDM symbols for the reduction of inter symbol interference. The resources within a slot may be divided into resources blocks <NUM> each comprising <NUM> subcarriers for the duration of one slot and the resources blocks further divided into resource elements <NUM> which span one subcarrier for one OFDM symbol, where each rectangle <NUM> represents a resource element. More details of the downlink structure of the LTE wireless access interface are provided in Annex <NUM>.

<FIG> provides a simplified schematic diagram of the structure of an uplink of an LTE wireless access interface that may be provided by or in association with the eNB of <FIG>. In LTE networks the uplink wireless access interface is based upon a single carrier frequency division multiplexing FDM (SC-FDM) interface and downlink and uplink wireless access interfaces may be provided by frequency division duplexing (FDD) or time division duplexing (TDD), where in TDD implementations subframes switch between uplink and downlink subframes in accordance with predefined patterns. However, regardless of the form of duplexing used, a common uplink frame structure is utilised. The simplified structure of <FIG> illustrates such an uplink frame in an FDD implementation. A frame <NUM> is divided in to <NUM> subframes <NUM> of <NUM> duration where each subframe <NUM> comprises two slots <NUM> of <NUM> duration. Each slot is then formed from seven OFDM symbols <NUM> where a cyclic prefix <NUM> is inserted between each symbol in a manner equivalent to that in downlink subframes. In <FIG> a normal cyclic prefix is used and therefore there are seven OFDM symbols within a subframe, however, if an extended cyclic prefix were to be used, each slot would contain only six OFDM symbols. The resources of the uplink subframes are also divided into resource blocks and resource elements in a similar manner to downlink subframes. More details of the LTE uplink represented in <FIG> are provided in Annex <NUM>.

As explained above, it has been proposed to develop an adaptation of a mobile communications network to accommodate narrow band communications within an existing wireless access interface which has been developed to provide broadband wireless communications. For example, in 3GPP a project relating to improvements to LTE wireless access interfaces to provide for a Narrowband Internet of Things (NB-IoT) was agreed [<NUM>]. This project is aimed at improved indoor coverage, support for massive number of low throughput devices, low delay sensitivity, ultra-low device cost, low device power consumption and (optimised) network architecture. An example of such a device is a smart meter. It has been proposed that an NB-IoT communications system supports a bandwidth of only <NUM> and can have three operational modes:.

One of the objectives of NB-IoT is to allow the cost of devices to be as low as possible. This is also an objective of Low Complexity Machine Type Communication (LC-MTC). LC-MTC terminal devices (UEs) also implement new LTE features which are currently being specified in 3GPP. The main features of LC-MTC UE are low complexity (and therefore low cost), coverage enhancement and reduced power consumption.

<FIG> illustrates MTC and NB-IoT operation in various modes of coverage. As seen in <FIG>, an infrastructure equipment sits inside the centre-most of three concentric rings of coverage. These coverage areas are, from the centre-most and smallest, area C1 (normal coverage), area C2 (extended coverage) and area C3 (extreme coverage). As can be seen in <FIG>, MTC-UE devices are able to operate in both normal and extended coverage modes (C1 and C2) but not in extreme coverage mode (C3). NB-IoT UEs are able to operate in normal, extended and extreme coverage modes (C1, C2 and C3).

NB-IoT UEs are expected to use low cost oscillators (e.g. Digital Controlled Crystal Oscillators (DCXOs) or free-running crystal oscillators (XOs)) in order to reduce the cost. However, such components are expected to have more imperfections than more accurate and costly oscillators. In particular, such oscillators may lack frequency stability over changes in temperature.

NB-IoT UEs can be operated in normal coverage, extended coverage, and extreme coverage, as depicted in <FIG> and described above. In the extreme coverage enhancement case (<NUM> dB coverage enhancement), NB-IoT UEs can support a data rate of <NUM> bps or greater. In the GERAN study (as detailed in 3GPP TR45. <NUM>), a mobile autonomous reporting (MAR) application has a packet size of up to <NUM> bytes. The application layer packet of <NUM> bytes can be segmented into smaller packets. If a maximum transport block size (TBS) of <NUM> bits in the uplink and <NUM> bps data rate are assumed then it will take around <NUM> seconds to transmit each transport block. Such a condition sets a challenge for meeting a very low frequency error target of ±<NUM> ppm as defined in the 3GPP specifications, since the frequency stability of the oscillator needs to be sufficient to meet this ±<NUM> ppm requirement without correction from other parts of the UE signal processing functions. Large frequency errors can be introduced by the temperature change caused by, for example, power amplifier self-heating during long continuous transmissions. Large frequency error can introduce inter-carrier interference (ICI) at the receiver (eNodeB) and can significantly degrade the link quality performance (e.g. throughput).

There are various models for the frequency of the signal produced by a free running local oscillator. A simple model is described in equation (<NUM>) below: <MAT> where fosc is the output frequency of the local oscillator, finit is the initial frequency of the local oscillator at time t<NUM>, fdrift, is the frequency drift rate (measured in Hz / second) and t is the time. In an LTE modem, the initial frequency can be determined by, for example, monitoring the synchronisation and reference signals transmitted in the LTE downlink.

In a full-duplex FDD modem, the UE can continuously monitor the local oscillator frequency error (for example, through monitoring synchronisation and reference signals). Hence the term 't - t<NUM>' never grows large, even in the presence of frequency drift.

In a half-duplex (HD) FDD modem however, the UE is unable to monitor the synchronisation and reference signals while it is transmitting in the uplink. Hence the term 't - t<NUM>' can increase, causing a significant difference between the local oscillator frequency at the UE and the frequency at the eNodeB. This effect is shown in <FIG>.

<FIG> illustrates an example of a local oscillator frequency as a function of time for an HD-FDD UE. As can be seen, during the periods when the UE is operating in the downlink (time period <NUM> up to tA and time period <NUM> between tB and tC), the UE is able to correct its local oscillator frequency, keeping it within an acceptable range (e.g. ±<NUM> ppm). However, when the UE is transmitting in the uplink, it is unable to correct its local oscillator frequency and that frequency hence drifts (at a rate of fdrift). Such periods are shown between times tA and tB (time period <NUM>) and from time tC (time period <NUM>). During these time periods <NUM> and <NUM>, the frequency drift becomes greater than the error requirement of ±<NUM> ppm, as can be seen in shaded regions <NUM> and <NUM>.

<FIG> shows a high level block diagram of the UE architecture of an HD-FDD modem. This modem contains a switch <NUM> close to an antenna <NUM>. The switch <NUM> either allows signals from a power amplifier (PA) <NUM> to the transmitted by the antenna <NUM> or signals received from the antenna <NUM> to reach a low noise amplifier (LNA) <NUM>. In this architecture, it is not possible for the downlink signals to be received by the LNA <NUM> whilst signals are being transmitted by the PA <NUM>. The amplified signal from the LNA <NUM> is demodulated by an RF demodulator <NUM>. One of the components of the RF demodulator <NUM> is a mixer, which downconverts the received signal, based on a signal produced by a local oscillator <NUM>. The local oscillator is one example of a reference frequency source. A receiver processing function <NUM> performs various functions, such as fast Fourier transforms (FFT), physical channel processing, transport channel processing and channel estimation. Signals from the receiver processing function <NUM> are provided to a frequency estimation block <NUM>, which estimates a frequency error between the UE's local oscillator <NUM> and the eNodeB's oscillator (using, for example, the primary and secondary synchronisation signals, NB-PSS, NB-SSS and reference signals such as narrowband reference signals (NB-RS), cell-specific reference signals (CRS)) and controls the frequency of the signal produced by the local oscillator <NUM>. As such, there is a feedback loop based on the downlink signal that controls the frequency of the local oscillator <NUM>. The signal produced by the local oscillator <NUM> is also used by an RF modulator <NUM> to upconvert the signal produced by a transmitter processing block <NUM> for transmission to the eNodeB. By virtue of the UE being able to monitor the downlink signal in the frequency estimation function <NUM>, the UE is able to control the frequency of the uplink transmission to be within the tolerance required by the eNodeB. The ability of the UE to monitor the downlink signal is impaired when there are long uplink transmissions.

The eNodeB architecture is implementation specific, and <FIG> shows a high level block diagram of an example eNodeB architecture of an HD-FDD modem. The eNodeB operates in full duplex mode, being able to transmit to some HD-FDD UEs in the downlink while simultaneously receiving from other HD-FDD UEs in the uplink. Hence, the eNodeB contains a duplexer <NUM> close to the antenna <NUM>. The duplexer <NUM> allows signals from a power amplifier (PA) <NUM> to be transmitted by the antenna <NUM> on a DL carrier frequency and for signals to be received from the antenna <NUM> to simultaneously reach a low noise amplifier (LNA) <NUM>. The amplified signal from the LNA <NUM> is demodulated by an RF demodulator <NUM>. One of the components of the RF demodulator <NUM> is a mixer, which downconverts the received signal, based on a signal produced by a local oscillator <NUM>. A receiver processing function <NUM> performs various functions, such as fast Fourier transforms (FFT), physical channel processing, transport channel processing and channel estimation. The signal produced by the local oscillator <NUM> is also used by an RF modulator <NUM> to upconvert the signal produced by a transmitter processing block <NUM> for transmission to the UE.

As can be seen in <FIG>, a main difference between the eNodeB and UE architectures is that the eNodeB architecture does not include a frequency estimation block. The eNodeB assumes that the UE has performed frequency estimation and correction (based on the UE's measurement of the eNodeB's downlink transmit signal) and thus that the frequency tolerance of the UE's transmission is within a specified tolerance of the eNodeB's local oscillator frequency (e.g. ±<NUM> ppm).

Other eNodeB architectures may include a frequency estimation block that operates on a per UE basis (i.e. one frequency estimation block operates to estimate the frequency error of one UE, and there are plural estimation blocks for plural UEs). Such an arrangement can lead to improved demodulation performance at the eNodeB.

Two methods and architectural implementations are proposed in the present disclosure in order to solve the problem of frequency drift of an NB-IoT UE. The first of these embodiments ensures that the frequency error of the NB IoT device is kept as low as possible, and as such within the required frequency error range, while the UE is transmitting for long time durations. The second of these embodiments ensures that large frequency errors (i.e. those which are outside of the required frequency error range) accumulated by the UE during uplink transmissions of long time durations may be tolerated by the eNodeB.

A first embodiment of the present technique can provide an arrangement in which a mobile communications device or UE <NUM> can operate to communicate in a wireless communications system via a base station or infrastructure equipment. <FIG> is a part schematic block diagram of a communications device <NUM> and an infrastructure equipment <NUM>, and part message flow diagram illustrating a process of receiving a message which may have been transmitted with a frequency error from the communications device <NUM> at the infrastructure equipment <NUM> in accordance with an embodiment of the present technique. Each of the infrastructure equipment <NUM> and communications device <NUM> comprise a transmitter <NUM>, <NUM>, a receiver <NUM>, <NUM> and a controller <NUM>, <NUM> to control the transmitter <NUM>, <NUM> and receiver <NUM>, <NUM>. The communications device <NUM> further comprises a local oscillator <NUM> configured to control an output frequency of the signals transmitted by the transmitter <NUM> of the communications device <NUM>.

The receiver <NUM> of the infrastructure equipment <NUM> is configured to receive signals <NUM> comprising data from the communications device <NUM> in accordance with a wireless access interface <NUM> of the wireless communications system. The controller is configured in combination with the receiver and the transmitter to measure <NUM> a frequency error of the signals <NUM> received from the communications device, the frequency error being an amount by which a carrier frequency of the received signals <NUM> differs from a predetermined frequency, and to transmit, in one or more temporal periods <NUM>, <NUM>, during which reception of the signals transmitted by and received from the one of the communications devices is paused, a frequency correction signal <NUM> to the one of the communications devices, the frequency correction signal providing an indication of a correction to compensate for the measured frequency error. During a long transmission <NUM>, <NUM>, such as of the signal <NUM>, the communications device <NUM> is configured to insert temporal gaps <NUM>, <NUM> into the transmission <NUM>, <NUM>, in order to allow for the infrastructure equipment <NUM>, on measuring <NUM> a potential frequency error <NUM> of the communications device <NUM> to transmit the frequency correction signal <NUM> in the form of a bit or plurality of bits. The temporal gaps <NUM>, <NUM> may include transmissions from the infrastructure equipment and time to allow for scheduling of the transmissions <NUM>. The frequency correction signal <NUM> may be an exact value or a quantised value, and may be equal to the (potentially quantised) measured frequency, instructing the communications device <NUM> that its output frequency is offset from the expected output frequency by the value of the frequency correction signal <NUM>. The frequency correction signal <NUM> may alternatively be a frequency correction command equal and opposite to the (potentially quantised) measured frequency, instructing the communications device <NUM> to correct its output frequency by the value of the frequency correction signal <NUM>.

In arrangements of this first embodiment of the present technique, the frequency error can be measured by the eNodeB by one or more of the following techniques:.

The temporal periods, or transmission gaps, are inserted within the uplink transmission, as shown in <FIG>. As can be seen in <FIG>, a long uplink transmission <NUM> of duration T0 is split up <NUM> into shorter uplink transmissions <NUM> of duration T1 with gaps <NUM> of duration T2. During the gaps of duration T2, the eNodeB may transmit frequency correction signals to the UE. Typically, the transmission period T1 may be of the order of <NUM>, while the transmission gap period may be of the order of <NUM>. The transmission period T1 should be chosen to be less than the time at which the UE's frequency could drift to such an extent that it cannot decode the eNodeB's downlink transmissions (due to excess frequency error).

The frequency error correction signals can be sent in various different manners:.

The UE corrects its local oscillator in response to the frequency error correction signals and continues its uplink transmission.

Advantages of the first embodiment of the present technique include that it allows for a half-duplex UE to operate with a lower cost frequency oscillator, and that the burden of frequency correction is moved to the eNodeB, which has greater processing power and is less cost sensitive than the UE. The eNodeB is also best placed to measure frequency error when the UE is transmitting.

A second embodiment of the present technique can provide an arrangement in which a mobile communications device or UE <NUM> can operate to communicate in a wireless communications system via a base station or infrastructure equipment. <FIG> is a part schematic block diagram of a communications device <NUM> and an infrastructure equipment <NUM>, and part message flow diagram illustrating a process of receiving a message which may have been transmitted with a frequency error from the communications device <NUM> at the infrastructure equipment <NUM> in accordance with a second embodiment of the present technique. Each of the infrastructure equipment <NUM> and communications device <NUM> comprise a transmitter <NUM>, <NUM>, a receiver <NUM>, <NUM> and a controller <NUM>, <NUM> to control the transmitter <NUM>, <NUM> and receiver <NUM>, <NUM>. The communications device <NUM> further comprises a local oscillator <NUM> configured to control an output frequency of the signals transmitted by the transmitter <NUM> of the communications device <NUM>.

The receiver <NUM> of the infrastructure equipment <NUM> is configured to receive signals <NUM> comprising data from the communications device <NUM> in accordance with a wireless access interface <NUM> of the wireless communications system. The controller is configured in combination with the receiver and the transmitter to determine <NUM> whether a duration of the reception of the signals <NUM> from the communications device <NUM> exceeds a predetermined threshold, and if so subsequently to delay transmission of signals to the one of the communications devices for a predetermined frequency adjustment period <NUM> following the reception of the signals <NUM> from the communications device <NUM>. The communications device <NUM> is configured to, following the transmission of the signals <NUM> to the infrastructure equipment <NUM>, receive no signals from the infrastructure equipment <NUM> for a predetermined frequency adjustment period <NUM>. In arrangements of the second embodiment of the present technique, the communications device <NUM>, if it is determined that signals have not been received from the infrastructure equipment <NUM> for longer than the predetermined frequency adjustment period <NUM> following the transmission of the signals <NUM> to the infrastructure equipment <NUM>, subsequently to synchronise the output frequency in accordance with a received synchronisation signal, which may be received from the infrastructure equipment or from another communications device within range of the communications device <NUM>.

In arrangements of this second embodiment of the present technique, the infrastructure equipment <NUM> is configured to communicate to the communications device <NUM> that, for any PUSCH repetition that exceeds a threshold, the communications device <NUM> would have a prolonged frequency adjustment period <NUM> after the PUSCH transmission. This threshold can be defined in the specifications or RRC signalled to the communications device <NUM>. Alternatively, the infrastructure equipment <NUM> is configured to indicate in DCI signalling (for example, uplink grant) that the communications device <NUM> can expect the prolonged frequency adjustment period <NUM> after the PUSCH transmission. During the frequency adjustment period <NUM>, the communications device <NUM> can resynchronise to the network.

In arrangements of this second embodiment of the present technique, the eNodeB can operate in a mode that is tolerant of large frequency offsets by:.

<FIG> shows an assignment of subcarriers to allow for transmissions from a UE with a low accuracy frequency oscillator. Accurate UEs may be assigned subcarriers <NUM> to <NUM>. A subcarrier <NUM> may be assigned to a frequency-inaccurate UE, such that the assigned subcarrier <NUM> is surrounded by unassigned subcarriers <NUM> to <NUM> that allow the transmission from the frequency inaccurate UE to drift away from its assigned frequency (as shown by the arrow <NUM>) without drifting into a frequency assigned to the accurate UEs.

Alternatively, the eNodeB can treat the signals received from UEs with a large frequency error as interference into transmissions from other UEs and use advanced receiver algorithms (such as successive interference cancellation) to tolerate the inter-carrier interference created from these UEs.

<FIG> shows a timing diagram of UE and eNodeB transmissions according to the second embodiment of the present technique. The UE transmits in the uplink for a long time <NUM> between tA and tB. During this time, the frequency error of the UE transmission may become large. The eNodeB implements a receiver processing algorithm that is tolerant to a frequency error. At time tB, the UE's uplink transmission terminates. The UE may then re-synchronise to the downlink (e.g. using the NB-PSS and NB-SSS synchronisation signals, the NB-PBCH and / or the NB-RS reference signals).

During the time period <NUM> tB to tC, the eNodeB does not transmit NB-PDCCH or NB-PDSCH (or equivalent for another technology) to the UE. The eNodeB still transmits other signals in the downlink (to other UEs and broadcast signals, such as NB-PSS, NB-SSS, NB-PBCH, NB-RS). The eNodeB may transmit a UE-specific synchronisation signal to help the UE (that transmitted the long uplink transmission) to regain frequency synchronisation. Example UE-specific signals may be based on the NB-PSS or NB-SSS, but using a different scrambling sequence (to avoid the creation of false alarms with the main NB-PSS / NB-SSS). Alternatively any sequence that is known between the UE and eNodeB can be transmitted by the eNodeB. In some arrangements of the second embodiment, these synchronisation signals may be power boosted or beamformed. In some arrangements of the second embodiment, the synchronisation signals may be transmitted as device-to-device (D2D) communications to the UE from other UEs in the network, following a command transmitted to the other UEs by the eNodeB.

After time tC, the UE is able to receive downlink transmissions from the eNodeB. At time tD, the eNodeB initiates a downlink transmission <NUM> to the UE, which may be for example, an acknowledgement (ACK / NACK) relating to the previous uplink transmission. At time tE, the eNodeB finishes the downlink transmission to the UE.

During the resynchronisation time period <NUM> between tB and tC the eNodeB does not transmit downlink signals to the UE. As explained previously, during this time period <NUM>, the UE can resynchronise to the eNodeB by, for example, using the NB-PSS, NB-SSS or NB-PBCH in the anchor carrier. This resynchronisation time period <NUM> is known to the eNodeB and the UE. For example, it may be:.

In arrangements of this second embodiment of the present technique, the eNodeB is configured to tolerate the frequency error from the UE, and to transmit a command in the time period <NUM> to the one UE at a frequency shifted from a preconfigured frequency of transmission of the infrastructure equipment by an amount equal to a frequency error of the UE. This command indicates to the UE that the frequency of its transmissions should be corrected by an amount equal and opposite to the frequency error.

In arrangements of this second embodiment of the present technique, uplink transmissions during the time period <NUM> between tA and tB may be discontinuous, with transmission gaps inserted for frequency drift correction at the UE. However, the final transmission period after the final transmission gap may still be long enough for the UE frequency to drift, and so a time period <NUM> is required for the UE to correct its frequency before signals may be received on the downlink from the eNodeB.

Advantages of the second embodiment of the present technique include that it allows for a half-duplex UE to operate with a lower cost frequency oscillator, and that the burden of frequency correction is moved to the eNodeB, which has greater processing power and is less cost sensitive than the UE. Further, transmission gaps do not need to be inserted into the uplink transmission. This allows the UE to terminate transmission of its uplink/downlink message sequence earlier, which in turn allows the UE to turn its modem off earlier, thus saving power.

A third embodiment of the present technique can provide an arrangement in which a mobile communications device or UE <NUM> can operate to communicate in a wireless communications system via a base station or infrastructure equipment <NUM>. Each of the infrastructure equipment <NUM> and communications device <NUM> comprise a transmitter, a receiver and a controller to control the transmitter and receiver. The communications device <NUM> further comprises a local oscillator configured to control an output frequency of the signals transmitted by the transmitter of the communications device <NUM>.

The receiver of the infrastructure equipment <NUM> is configured to receive uplink signals comprising data from the communications device <NUM> in accordance with a wireless access interface of the wireless communications system in a plurality of transmission periods, each of the plurality of transmission periods being separated from a next transmission by a predetermined period in which the communications device <NUM> receives downlink signals from the infrastructure equipment to correct a transmission frequency with respect to a carrier frequency of allocated communications resources. After a last of the transmission periods in which the uplink signals are received from the communications device <NUM>, the controller of the infrastructure equipment <NUM> is configured in combination with the receiver and the transmitter of the infrastructure equipment 101to determine whether the duration of reception of the signals from the communications device 104in the last of the transmission periods exceeded a predetermined threshold, and if so to control the transmitter to delay transmission of signals to the communications device <NUM> for a second predetermined period following the reception of the signals from the communications device <NUM>. The first and second predetermined periods may be the same, or alternatively may have different temporal lengths.

<FIG> illustrates an example of a timing diagram of UE and eNodeB transmissions according to the third embodiment of the present disclosure. This third embodiment differs from the second embodiment in that the communications device inserts transmission gaps into its uplink transmissions to the infrastructure equipment. However, it is still potentially the case that, even with the transmission gaps, each transmission period or segment may be of a sufficient temporal length for frequency drift to occur at the local oscillator of the communications device so as to impair the performance of the UE when the UE subsequently decodes the eNodeB's transmissions.

Transmission of a signal comprising data is split into three transmission periods <NUM>, <NUM> and <NUM>. Between transmission period <NUM> and transmission period <NUM> is a first transmission gap <NUM>, and between transmission period <NUM> and transmission period <NUM> is a second transmission gap <NUM>. Following the final transmission period <NUM>, if it is determined that the final transmission period <NUM> exceeded a predetermined threshold, a further transmission gap <NUM> is applied, in order for the communications device to correct a frequency offset which is judged to have occurred due to frequency drift during long transmissions. Following this transmission gap <NUM>, the eNodeB initiates a downlink transmission <NUM> to the UE, which may be for example, an ACK / NACK relating to the previous uplink transmission.

In arrangements of the present embodiment, if the time taken between the transmission period <NUM> and the transmission period <NUM> is X, and the time taken for the transmission gap <NUM> and the transmission gap <NUM> is Y, the next downlink transmission is at a time that is greater than or equal to the start time of transmission period <NUM> + X + Y + the frequency offset. In other words, the last transmission <NUM> is treated as though it were a full "period X" and insert a "gap Y" of the normal duration. The offset (which typically, the normal defined timing relationship from NB-PUSCH to A/N is that the time is >= <NUM>). In this case, it is not necessary to compare the last transmission period <NUM> duration to a predetermined threshold.

The transmission periods previously discussed in the present disclosure take account of invalid uplink subframes. For example, if every subframe <NUM> of a radio frame is invalid, then transmission period <NUM> is the time including the time taken up by these invalid subframes.

<FIG> shows a second example of a timing diagram of UE and eNodeB transmissions according to the third embodiment of the present technique. The UE transmits in the uplink for a long time between tA and tB. This transmission is split into segments <NUM>, <NUM> and <NUM> interspersed with transmission gaps <NUM> and <NUM>. During the transmission gaps, the UE <NUM>, <NUM>, the UE is able to correct the frequency error of its transmissions, e.g. via the method of frequency offset indication previously discussed, or by some other method of frequency error correction. At time tB, the UE's uplink transmission terminates. The UE may then re-synchronise to the downlink (e.g. using the NB-PSS and NB-SSS synchronisation signals, the NB-PBCH and / or the NB-RS reference signals).

During the time period <NUM> tB to tC, the eNodeB does not transmit NB-PDCCH or NB-PDSCH (or equivalent for another technology) to the UE. The eNodeB still transmits other signals in the downlink (to other UEs and broadcast signals, such as NB-PSS, NB-SSS, NB-PBCH, NB-RS). The eNodeB may transmit a UE-specific synchronisation signal to help the UE (that transmitted the long uplink transmission) to regain frequency synchronisation. Example UE-specific signals may be based on the NB-PSS or NB-SSS, but using a different scrambling sequence (to avoid the creation of false alarms with the main NB-PSS / NB-SSS). Alternatively any sequence that is known between the UE and eNodeB can be transmitted by the eNodeB. In some arrangements of the third embodiment, these synchronisation signals may be power boosted or beamformed. In some arrangements of the third embodiment, the synchronisation signals may be transmitted as device-to-device (D2D) communications to the UE from other UEs in the network, following a command transmitted to the other UEs by the eNodeB.

After time tC, the UE is able to receive downlink transmissions from the eNodeB. At time tD, the eNodeB initiates a downlink transmission <NUM> to the UE, which may be for example, an ACK / NACK relating to the previous uplink transmission. At time tE, the eNodeB finishes the downlink transmission to the UE.

During the resynchronisation time period <NUM> between tB and tC the eNodeB does not transmit downlink signals to the UE. As explained previously, during this time period <NUM>, the UE can resynchronise to the eNodeB by, for example, using the NB-PSS, NB-SSS or NB-PBCH in the anchor carrier. This resynchronisation time period <NUM> is known to the eNodeB and the UE. For example, it may be, as in the second embodiment:.

In arrangements of this third embodiment of the present technique, the eNodeB is configured to tolerate the frequency error from the UE, and to transmit a command in the time period <NUM> to the one UE at a frequency shifted from a preconfigured frequency of transmission of the infrastructure equipment by an amount equal to a frequency error of the UE. This command indicates to the UE that the frequency of its transmissions should be corrected by an amount equal and opposite to the frequency error.

Advantages of the third embodiment of the present technique include that it allows for a half-duplex UE to operate with a lower cost frequency oscillator, and that the burden of frequency correction is moved to the eNodeB, which has greater processing power and is less cost sensitive than the UE. This is the case even when the transmissions from the UE are not continuous, and there are transmission gaps between transmission periods of the uplink transmissions.

There are cases where the eNodeB cannot tolerate a frequency drift from the UE and supports neither of the following:.

In this case the eNodeB can configure the UE not to insert uplink transmission gaps (either by UE-specific signalling or via system information). However, the UE implements a low cost crystal oscillator and its frequency can drift beyond the specification of <NUM>. 1ppm if uplink transmissions are greater than a certain amount, T_UL_MAX. For example, this maximum uplink transmission period, T_UL_MAX may be <NUM>.

When the UE is configured to insert not UL transmission gaps, the following arrangements are applicable:.

In arrangements of the fourth embodiment, the eNodeB configures the UE not to insert uplink transmission gaps through system information signalling:.

In other words, the communications device is configured to receive from the infrastructure equipment an indication of communications resources in which the transmitter can transmit signals to the infrastructure equipment, to determine whether a period required to transmit an uplink transmission to the infrastructure equipment in the indicated communications resources exceeds a predetermined threshold, and if so, subsequently to control the transmitter not to transmit signals to the infrastructure equipment using the indicated communications resources. If the period required to transmit the uplink transmission to the infrastructure equipment exceeds the predetermined threshold, the communications device is configured to search for a second infrastructure equipment to which the uplink transmission can be transmitted. The communications device may determine the period required to transmit the uplink transmission to the infrastructure equipment based on a coverage level of the communications device.

In arrangements of the fourth embodiment, when the eNodeB does not support uplink transmission gaps, it indicates (e.g. implicitly) that coverage levels which would lead to large uplink transmission gaps (of NB-PRACH or NB-PUSCH) of greater than T_UL_MAX are not supported. In this case, UEs have the following behaviours:.

In other words, the reference frequency source of the communications device has a predetermined accuracy relating to an amount of frequency drift of the output frequency with respect to time. If the period required to transmit the uplink transmission to the infrastructure equipment exceeds the predetermined threshold, the communications device is configured to determine whether the amount of frequency drift caused by the reference frequency source with the predetermined accuracy is within a predetermined limit, so that if the frequency drift is within the predetermined limit (depending upon an accuracy of the reference frequency source (having a predetermined accuracy) ) a controller of the communications device is configured to control the transmitter and the receiver to transmit signals to and to receive signals from the infrastructure equipment, using the indicated communications resources. This is because the communications resources can nevertheless be used, notwithstanding a temporal length of the transmission, because the accuracy of the reference frequency source (crystal oscillator) is high enough that the frequency drift is still within a tolerable limit.

In a sub-embodiment of these arrangements of the fourth embodiment, there are two lists of coverage levels indicated by the eNodeB (e.g. in system information):.

In this case, the UE reads the appropriate list of coverage levels and PRACHs to the cell (or not) accordingly.

Although the present disclosure has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. 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 any manner suitable to implement the technique.

The simplified structure of the downlink of an LTE wireless access interface presented in <FIG>, also includes an illustration of each subframe <NUM>, which comprises a control region <NUM> for the transmission of control data, a data region <NUM> for the transmission of user data , reference signals <NUM> and synchronisation signals which are interspersed in the control and data regions in accordance with a predetermined pattern. The control region <NUM> may contain a number of physical channels for the transmission of control data, such as a physical downlink control channel PDCCH, a physical control format indicator channel PCFICH and a physical HARQ indicator channel PHICH. The data region may contain a number of physical channel for the transmission of data, such as a physical downlink shared channel PDSCH and a physical broadcast channels PBCH. Although these physical channels provide a wide range of functionality to LTE systems, in terms of resource allocation and the present disclosure PDCCH and PDSCH are most relevant. Further information on the structure and functioning of the physical channels of LTE systems can be found in [<NUM>].

Resources within the PDSCH may be allocated by an eNodeB to UEs being served by the eNodeB. For example, a number of resource blocks of the PDSCH may be allocated to a UE in order that it may receive data that it has previously requested or data which is being pushed to it by the eNodeB, such as radio resource control RRC signalling. In <FIG>, UE1 has been allocated resources <NUM> of the data region <NUM>, UE2 resources <NUM> and UE resources <NUM>. UEs in a an LTE system may be allocated a fraction of the available resources of the PDSCH and therefore UEs are required to be informed of the location of their allocated resources within the PDCSH so that only relevant data within the PDSCH is detected and estimated. In order to inform the UEs of the location of their allocated communications resources, resource control information specifying downlink resource allocations is conveyed across the PDCCH in a form termed downlink control information DCI, where resource allocations for a PDSCH are communicated in a preceding PDCCH instance in the same subframe. During a resource allocation procedure, UEs thus monitor the PDCCH for DCI addressed to them and once such a DCI is detected, receive the DCI and detect and estimate the data from the relevant part of the PDSCH.

Each uplink subframe may include a plurality of different channels, for example a physical uplink shared channel PUSCH <NUM>, a physical uplink control channel PUCCH <NUM>, and a physical random access channel PRACH. The physical Uplink Control Channel PUCCH may carry control information such as ACK/NACK to the eNodeB for downlink transmissions, scheduling request indicators SRI for UEs wishing to be scheduled uplink resources, and feedback of downlink channel state information CSI for example. The PUSCH may carry UE uplink data or some uplink control data. Resources of the PUSCH are granted via PDCCH, such a grant being typically triggered by communicating to the network the amount of data ready to be transmitted in a buffer at the UE. The PRACH may be scheduled in any of the resources of an uplink frame in accordance with a one of a plurality of PRACH patterns that may be signalled to UE in downlink signalling such as system information blocks. As well as physical uplink channels, uplink subframes may also include reference signals. For example, demodulation reference signals DMRS <NUM> and sounding reference signals SRS <NUM> may be present in an uplink subframe where the DMRS occupy the fourth symbol of a slot in which PUSCH is transmitted and are used for decoding of PUCCH and PUSCH data, and where SRS are used for uplink channel estimation at the eNodeB. Further information on the structure and functioning of the physical channels of LTE systems can be found in [<NUM>].

In an analogous manner to the resources of the PDSCH, resources of the PUSCH are required to be scheduled or granted by the serving eNodeB and thus if data is to be transmitted by a UE, resources of the PUSCH are required to be granted to the UE by the eNodeB. At a UE, PUSCH resource allocation is achieved by the transmission of a scheduling request or a buffer status report to its serving eNodeB. The scheduling request may be made, when there is insufficient uplink resource for the UE to send a buffer status report, via the transmission of Uplink Control Information UCI on the PUCCH when there is no existing PUSCH allocation for the UE, or by transmission directly on the PUSCH when there is an existing PUSCH allocation for the UE. In response to a scheduling request, the eNodeB is configured to allocate a portion of the PUSCH resource to the requesting UE sufficient for transferring a buffer status report and then inform the UE of the buffer status report resource allocation via a DCI in the PDCCH. Once or if the UE has PUSCH resource adequate to send a buffer status report, the buffer status report is sent to the eNodeB and gives the eNodeB information regarding the amount of data in an uplink buffer or buffers at the UE. After receiving the buffer status report, the eNodeB can allocate a portion of the PUSCH resources to the sending UE in order to transmit some of its buffered uplink data and then inform the UE of the resource allocation via a DCI in the PDCCH. For example, presuming a UE has a connection with the eNodeB, the UE will first transmit a PUSCH resource request in the PUCCH in the form of a UCI. The UE will then monitor the PDCCH for an appropriate DCI, extract the details of the PUSCH resource allocation, and transmit uplink data , at first comprising a buffer status report, and/or later comprising a portion of the buffered data, in the allocated resources.

Although similar in structure to downlink subframes, uplink subframes have a different control structure to downlink subframes, in particular the upper <NUM> and lower <NUM> subcarriers/frequencies/resource blocks of an uplink subframe are reserved for control signaling rather than the initial symbols of a downlink subframe. Furthermore, although the resource allocation procedure for the downlink and uplink are relatively similar, the actual structure of the resources that may be allocated may vary due to the different characteristics of the OFDM and SC-FDM interfaces that are used in the downlink and uplink respectively. In OFDM each subcarrier is individually modulated and therefore it is not necessary that frequency/subcarrier allocation are contiguous however, in SC-FDM subcarriers are modulation in combination and therefore if efficient use of the available resources are to be made contiguous frequency allocations for each UE are preferable.

Claim 1:
An infrastructure equipment (<NUM>) forming part of a mobile communications network configured to transmit signals to and receive signals from one or more communications devices (<NUM>), the infrastructure equipment comprising
a receiver configured to receive signals on the uplink from the one or more communications devices via a wireless access interface of the mobile communications network,
a transmitter configured to transmit signals on the downlink to the one or more communications devices via the wireless access interface, and
a controller configured to control the receiver to receive the signals and to control the transmitter to transmit the signals, wherein the controller is configured in combination with the receiver and the transmitter
to determine whether a duration of reception of signals from one of the communications devices exceeds a predetermined threshold, wherein the predetermined threshold is configured by the infrastructure equipment based on measurements performed by the infrastructure equipment, and if so subsequently
to delay transmission of data or control signals to the one of the communications devices for a predetermined re-synchronisation period following the reception of the signals from the one of the communications devices, wherein the length of the predetermined re-synchronisation period is configured by the infrastructure equipment based on measurements performed by the infrastructure equipment.