FIELD

The invention relates to downlink and uplink transmission scheduling, particularly though not exclusively in relation to the 3GPP 5G radio communication standard.

BACKGROUND

Recent developments in the 3GPP 5G radio communication protocol have introduced a new type of user equipment, named Reduced Capability or RedCap, with reduced complexity (e.g. reduced computational resources, reduced power consumption, reduced bandwidth, reduced number of antennas, reduced cost of manufacture, etc.) when compared to legacy devices. RedCap devices are particularly well suited for applications such as the Internet of Things (loT), as their low power consumption and low cost of manufacture enables increased battery life and mass production. RedCap devices are particularly well suited for wireless sensors and other similar devices.

The development of RedCap devices brings with it a number of hurdles which need to be overcome in order to enable those devices to successfully integrate with other devices configured to operate in accordance with the 3GPP 5G communication protocol. In particular, it is desired to keep computational resources and power consumption to a minimum (e.g. to reduce cost of manufacture and increase battery life).

In light of this goal, the 5G standard is being developed in order to allow for the reduced complexity of RedCap devices, while still enabling more powerful and legacy devices to coexist with the RedCap devices. In particular, it is desired to avoid RedCap devices being required to perform excess parallel processing for radio communications, as parallel processing requires increased computational resources (i.e. more powerful processors, increases memory, etc.). RedCap devices being required to perform an excess of parallel processing in order to conform to the 5G standard increases their power consumption and manufacture cost, and so modifications to the 5G standard are sought in order to keep RedCap device complexity to a minimum, while still allowing smooth coexistence with non- RedCap or RedCap UEs of earlier releases.

The present invention aims to address at least some of the issues set out above.

SUMMARY OF THE INVENTION

When viewed from a first aspect, the invention provides a digital radio transceiver configured to: receive a downlink signal or channel addressed to the transceiver; begin transmission of an uplink signal or channel after a time gap following receipt of the downlink signal or channel; wherein: when the downlink signal or channel and the uplink signal or channel both belong to a first predetermined set of signals and channels, said time gap has a first value; and when at least one of the downlink signal or channel and the uplink signal or channel belongs to a second predetermined set of signals and channels, said time gap has a second value, the second value being shorter than the first value.

Thus is will be seen by those skilled in the art that in accordance with the invention, the time gap between transmission and reception is dependent on the nature of the signals or channels being transmitted and received. After receiving the downlink signal or channel, the receiver requires an amount of time in order to decode the received downlink signal or channel, and to prepare the uplink signal or channel for transmission. The Applicant has recognised that some types of downlink signals or channels e.g. downlink shared data channels, require more computational resources and time for the transceiver to decode than other types of signals or channels e.g. control channels and/or reference signals. Similarly, the Applicant has recognised that some types of uplink signals or channels e.g. uplink shared data channels, require more computational resources and time for the transceiver to prepare for transmission than other types of signals or channels e.g. control channels and/or reference signals.

In light of this, where the transceiver is a low-complexity device e.g. a RedCap device, simultaneous decoding of some types of downlink signals or channels and preparation of some types of uplink signals or channels e.g. using parallel processing is generally undesirable, as this places a minimum processing power requirement on the transceiver that is higher than desired for a low-complexity RedCap device. Simultaneous decoding of a downlink signal or channel and preparation of an uplink signal or channel of other types on the other hand may be feasible without increasing the processing power required by the device, however, due to the lower processing requirements for preparation of these. Similarly, simultaneously decoding of a downlink signal or channel of other types and preparation of an uplink signal is also feasible due to their lower processing requirements.

In light of this, the Applicant has recognised that complexity of the receiver can be kept to a minimum by enabling it, sequentially, to decode a received downlink signal or channel of a specific type included in the first predetermined set e.g. a received downlink shared data channel, and to prepare for transmission an uplink signal or channel of a specific type included in the first predetermined set e.g. an uplink shared data channel, but that this is not necessary for other types of downlink and uplink signals or channels. As such, a longer time gap is provided between the end of receiving a downlink signal or channel included in the first predetermined set, e.g. a downlink shared data channel, and beginning of transmission of an uplink signal or channel also included in the first predetermined set, e.g. an uplink shared data channel, than between other types of signals or channels. A shorter time gap is provided where at least one of the downlink and uplink signal or channel belongs to the second predetermined set, as the transceiver is able to employ parallel processing where this is the case.

As a result, embodiments of the present invention provide improved downlink/uplink transmission sequencing, whereby a transceiver is not required to perform excessive parallel processing - e.g. of a received downlink shared data channel and an uplink shared data channel for transmission, but advantageously retains a high level of transmission scheduling flexibility of other signals and channels.

The first predetermined set of signals and channels and the second predetermined set of signals of channels typically do not overlap - i.e. any signal or channel that belongs to the first predetermined set does not also belong to the second predetermined set, and vice versa. In a set of embodiments, the first and second predetermined sets together include all possible signals and channels that the transceiver is configured to be able to receive or transmit respectively when operating in accordance with a predetermined communication protocol - i.e. there are no types of signals or channels that the transceiver could transmit and/or receive which are not included in either the first predetermined set or the second predetermined set.

However, in other embodiments there may be uplink and/or downlink signals or channels that do not belong to either the first or the second predetermined set. In such embodiments the transceiver may be configured to apply a time gap of a different value to the first and second values where at least one of the downlink signal or channel or the uplink signal or channel does not belong to either predetermined set. Alternatively, the transceiver may be configured to ignore and/or drop transmission of any signals or channels that do not belong to either predetermined set.

In a set of embodiments, the first predetermined set of signals and channels comprises downlink shared data channels and uplink shared data channels. The first predetermined set may comprise only downlink shared data channels and uplink shared data channels. The first predetermined set may comprise Physical Downlink Shared Channels (PDSCH) and Physical Uplink Shared Channels (PUSCH).

In a set of embodiments, the second predetermined set of signals and channels comprises downlink control channels, downlink reference signals, uplink control channels and uplink reference signals. The second predetermined set may comprise only downlink control channels, downlink reference signals, uplink control channels and uplink reference signals. The second predetermined set may comprise Physical Downlink Control Channels (PDCCH), Channel State Information Reference Signals (CSI-RS), Physical Uplink Control Channels (PUCCH) and Sounding Reference Signals (SRS).

In a set of embodiments, the first predetermined set of signals and channels comprises downlink control channels coded using polar coding and uplink control channels coded using polar coding. The first predetermined set may comprise Physical Downlink Control Channels (PDCCH) coded using polar coding and Physical Uplink Control Channels (PUCCH) coded using polar coding. In a set of embodiments, the downlink control channels and the uplink control channels in the second predetermined set of signals and channels are not coded using polar coding - i.e. the second predetermined set may comprise PDCCH not coded using polar coding and PUCCH not coded using polar coding.

The processing requirements for decoding downlink control channels (e.g. PDCCH) that are coded using polar coding, and preparing uplink control channels (e.g. PUCCH) that are coded using polar coding for transmission, may be greater than those for downlink and uplink control channels coded using other types of coding. Thus, these may belong to the first predetermined set in order to avoid parallel processing thereof. Conversely, downlink and uplink control channels coded using other types of coding - e.g. Reed-Miller coding or a Zadoff-Chu sequence - may have lower processing requirements and thus may instead belong to the second predetermined set instead.

In a set of embodiments, decoding the downlink signal comprises one or more of baseband processing, demodulation, decoding, performing checksum checks, etc.

In a set of embodiments, preparing the uplink signal for transmission comprises one or more of baseband processing, mixing, encoding, generating checksums, retrieving data from a memory, etc.

In a set of embodiments, the transceiver comprises a low-complexity device - i.e. it is configured to operate in either a reception mode of operation or a transmission mode of operation at any given time, but not both simultaneously. As such, the first and second values of the time gap should provide sufficient time for the transceiver to switch from the reception mode to the transmission mode. The transceiver may comprise a single antenna which is used for downlink signal reception when the transceiver is operating in the reception mode, and used for uplink signal transmission when the transceiver is operating in the transmission mode.

The transceiver may comprise a user equipment device, and the transceiver may comprise a RedCap device. The transceiver may support a bandwidth of less than 20MHz, preferably less than 10MHz, more preferably equal to 5MHz. The transceiver may be configured to communicate using half-duplex frequency division duplexing (HD-FDD), or using time division duplexing (TDD). Advantageously, by only permitting half-duplex communications or time-division duplex communications, the transceiver may not be required to include a duplexer, thereby reducing the complexity of the transceiver.

In a set of embodiments, the second value of the time gap provides sufficient time for the transceiver to switch from a reception mode to a transmission mode. The time required for the transceiver to switch from the reception mode to the transmission mode may for example be 13ps.

The first value of the time gap may be significantly greater than the second value - e.g. at least 50 times the second value. In a set of embodiments, the first value of the time gap provides sufficient time for the transceiver to process the downlink signal or channel and the uplink signal or channel without performing parallel processing of the downlink and uplink signal or channel - i.e. sufficient time to allow them to be processed sequentially. The first value of the time gap may, for example, provide sufficient time for the transceiver to sequentially decode a downlink shared data channel and prepare an uplink shared data channel for transmission.

In a set of embodiments, the first value of the time gap is equal to at least a sum of a time for the transceiver to switch from the reception mode to the transmission mode and a time required for the transceiver to process the downlink signal or channel and the uplink signal or channel without performing parallel processing.

In a set of embodiments, the first and/or second value of the time gap further provides sufficient time for the transceiver to accommodate a timing advance specific to the transceiver.

The timing advance specific to the transceiver may be less than or equal to a predetermined maximum. Transmitting the uplink signal or channel using the timing advance may comprise advancing the uplink transmission by a period of time such that the uplink signal or channel is received from the transceiver e.g. at a base station at the correct reference timing. In a set of embodiments, the timing advance specific to the transceiver is equal to the sum of a propagation delay for the downlink signal or channel and a propagation delay for the uplink signal or channel. The timing advance specific to the transceiver may be dependent on at least the distance between the UE and the base station, and it may change over time.

In a set of embodiments, the first value of the time gap is equal to one subframe period, the subframe period typically comprising twelve symbol periods. In a set of embodiments, the second value of the time gap is equal to three symbol periods. The first value of the time gap may be equal to 1ms, and the second value of the time gap may be equal to 213ps.

In accordance with the invention, although the first value of the time gap may be provided between receipt of a specific downlink signal or channel, such as a downlink shared data channel, and a specific uplink signal or channel, such as an uplink shared data channel, other signals which are much less computationally intensive to process, such as control channels and/or reference signals, can still be transmitted during the extended part of the time gap. In a set of embodiments, the transceiver is configured to begin transmission of the uplink signal or channel at a time that ensures a period of time greater than or equal to the second period of time is provided between said other downlink signals or channels and the uplink signal or channel. This advantageously ensures that the transceiver never begins transmission of an uplink signal or channel too soon after receipt of a downlink signal or channel, even if the longer gap which may be provided in accordance with the invention is not required.

In a set of embodiments, the transceiver is configured to receive within the downlink signal or channel or a further downlink signal or channel, grant information indicating a time at which the transceiver should begin transmission of the uplink signal or channel and to use the grant information to schedule the uplink transmission. In other words, the time at which the transceiver should begin transmission of the uplink signal or channel is determined dynamically by a transmitter of the downlink signal or channel - e.g. a base station radio transceiver - and communicated ad-hoc to the transceiver via one or more downlink signals or channels. This advantageously enables increased scheduling flexibility. In another set of embodiments, the transceiver is configured to determine a time at which to begin transmission of the uplink signal or channel based on one or more pre-configured computer-readable instructions stored on a local non-transitory memory. In other words, the time at which the transceiver should begin transmission of the uplink signal or channel is determined at protocol-level, and the transceiver is pre-configured to function accordingly. This advantageously reduces computation burden on the transmitter of the downlink signal or channel - e.g. a base station - as it is not required to transmit grant information to the transceiver in order to schedule the transmission of an uplink signal or channel.

In a set of embodiments, the transceiver is configured to receive the grant information and to use the grant information to schedule the uplink transmission but to determine the time at which to begin transmission of the uplink signal or channel based on one or more preconfigured computer-readable instructions stored on a local non-transitory memory only when no grant information is received. Such a configuration provides a hybrid configuration whereby a transmitter of the downlink signal (e.g. a base station) can dynamically schedule the transmission of the uplink signal or channel through transmission of the grant information, but where the transceiver will still appropriately provide the first and second values of the time gap between the respective downlink and uplink signals or channels, where no grant information is received.

In a set of embodiments, the transceiver is configured to delay or drop at least part of the transmission of the uplink signal or channel if: the uplink transmission is scheduled to begin after a time gap following receipt of the downlink signal or channel that is less than the first value, when the downlink signal or channel and the uplink signal or channel both belong to the first predetermined set of signals and channels; or the uplink transmission is scheduled to begin after a time gap following receipt of the downlink signal or channel that is less than the second value, when at least one of the downlink signal or channel and the uplink signal or channel belongs to the second predetermined set of signals and channels. In a set of embodiments, the transceiver is configured to ignore at least part of the received downlink signal or channel if: the uplink transmission is scheduled to begin after a time gap following receipt of the downlink signal or channel that is less than the first value, when the downlink signal or channel and the uplink signal or channel both belong to the first predetermined set of signals and channels; or the uplink transmission is scheduled to begin after a time gap following receipt of the downlink signal or channel that is less than the second value, when at least one of the downlink signal or channel and the uplink signal or channel belongs to the second predetermined set of signals and channels.

In other words, the transceiver may be configured to delay or drop transmission of the uplink signal or channel, or ignore the received downlink signal or channel, or both, when the uplink transmission is scheduled at a time that does not provide the respective appropriate time gap after reception of the downlink signal or channel. This is sometimes referred to as a collision between the downlink signal or channel and the uplink signal or channel.

The downlink shared data channel may comprise a payload of a downlink data packet, and the uplink shared data channel may comprise a payload of an uplink data packet. The control channels may comprise one or more control parameters required to decode corresponding shared data channels e.g. rate, length, the modulation and coding scheme (MCS) used, etc. The reference signals may be used for channel estimation by the transceiver or by a transmitter of the downlink signals e.g. a base station.

The downlink shared data channel may comprise a Physical Downlink Shared Channel (PDSCH). The downlink control channel may comprise a Physical Downlink Control Channel (PDCCH). The downlink reference signal may comprise a Channel State Information Reference Signal (CSI-RS). The uplink shared data channel may comprise a Physical Uplink Shared Channel (PUSCH). The uplink control channel may comprise a Physical Uplink Control Channel (PUCCH). The uplink reference signal may comprise a Sounding Reference Signal (SRS). When viewed from a second aspect, the invention provides a base station radio transceiver configured to: transmit a downlink signal or channel addressed to a user equipment radio transceiver; begin receipt of an uplink signal or channel from the user equipment radio transceiver after a time gap following the end of the transmission of the downlink signal or channel; wherein: when the downlink signal or channel and the uplink signal or channel both belong to a first predetermined set of signals and channels, said time gap has a first value; and when at least one of the downlink signal or channel and the uplink signal or channel belongs to a second predetermined set of signals and channels, said time gap has a second value, the second value being shorter than the first value.

It will be appreciated that such a base station is advantageous in supporting User Equipment (UE) transceivers in accordance with the first aspect of the invention. Similarly the optional features and benefits set out for the transceiver are applicable with suitable adaption to the perspective of the base station, to the second aspect of the invention.

When viewed from a third aspect, the invention provides a digital radio communications network comprising a base station radio transceiver and a user equipment radio transceiver, wherein: the base station radio transceiver is configured to transmit a downlink signal or channel addressed to the user equipment radio transceiver; the user equipment radio transceiver is configured to transmit an uplink signal or channel to the base station radio transceiver after a time gap following the end of the transmission of the downlink signal or channel; wherein: when the downlink signal or channel and the uplink signal or channel both belong to a first predetermined set of signals and channels, said time gap has a first value; and when at least one of the downlink signal or channel and the uplink signal or channel belongs to a second predetermined set of signals and channels, said time gap has a second value, the second value being shorter than the first value. When viewed from a fourth aspect, the invention provides a method of operating a digital radio transceiver, comprising: receiving a downlink signal or channel addressed to the transceiver; beginning transmission of an uplink signal or channel after a time gap following receipt of the downlink signal; wherein: when the downlink signal or channel and the uplink signal or channel both belong to a first predetermined set of signals and channels, said time gap has a first value; and when at least one of the downlink signal or channel and the uplink signal or channel belongs to a second predetermined set of signals and channels, said time gap has a second value, the second value being shorter than the first value.

Features of any aspect or embodiment described herein may, wherever appropriate, be applied to any other aspect or embodiment described herein. Where reference is made to different embodiments or sets of embodiments, it should be understood that these are not necessarily distinct but may overlap.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of an exemplary radio communications network in accordance with an embodiment of the present invention;

Figure 2 shows a prior art downlink/uplink transmission sequence and a prior proposal for a downlink/uplink transmission sequence;

Figure 3 shows a first downlink/uplink transmission sequence in accordance with an embodiment of the present invention;

Figure 4 shows a second downlink/uplink transmission sequence in accordance with an embodiment of the present invention;

Figure 5 is a table illustrating which of two gaps are applied when switching from scheduled downlink signals to scheduled uplink signals, for each possible pair of signal type; and Figure 6 is a flowchart of a method for determining which of two gaps to apply between a scheduled downlink signal and a subsequently scheduled uplink signal.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic diagram of an exemplary radio communications network 100. The network 100 includes a base station radio transceiver 102, a first user equipment (UE) radio transceiver 106, and a second UE radio transceiver 110. The base station 102, first UE 106 and second UE 110 each comprise a respective antenna 104, 108, 110 for transmission and receipt of wireless radio signals.

The base station 102 is in wireless radio communication with each UE 106, 110, and can thus transmit wireless signals to, and receive wireless signals from, each UE 106, 110. In order to transmit information to the first UE 106, the base station 102 transmits using its antenna 104 a first downlink signal 114 which is addressed to the first UE 106, and the first UE 106 receives this first downlink signal 114 using its antenna 108. Similarly, the base station 102 also transmits using its antenna 104 a second downlink signal 118 which is addressed to the second UE 110, and the second UE 110 receives this second downlink signal 118 using its antenna 112.

In order to transmit information to the base station 102, the first UE 108 transmits using its antenna 108 a first uplink signal 116 which is addressed to the base station 102, and the base station 102 receives this first uplink signal 116 using its antenna 104. Similarly, the second UE 110 transmits using its antenna 112 a second uplink signal 120 which is addressed to the base station 102, and the base station 102 receives this second uplink signal 120 using its antenna.

The base station 102 and UEs 106, 110 are configured to operate in accordance with a predetermined communication protocol - which in this particular embodiment is 3GPP NR 5G, though the principles outline herein are not limited to 3GPP NR 5G and may be equally applied to other predetermined communication protocols e.g. Wi-Fi, Bluetooth, LTE, 3GPP 4G, etc.

Though only one respective antenna is shown for the base station 102 and the UEs 106, 110, it will be appreciated that these may each comprise any number of antennas in order to enable various communication modes e.g. spatial multiplexing, multiple-input-multiple-output (MIMO), single-input-multiple-output (SIMO), etc. However, in this particular embodiment, the UEs 106, 110 comprise low-complexity reduced capacity (RedCap) devices typically, but not always, with only a single antenna, as shown in Figure 1. Such RedCap devices are configured to have a smaller bandwidth of 20MHz, compared to 100MHz for a standard, non-RedCap New Radio UE. RedCap devices are typically battery-powered devices with relatively low processing capabilities (e.g. sensors) for applications like internet of things (loT).

It will also be appreciated that the base station 102 and the UEs 106, 110 may include additional electronic components that are not shown in Figure 1 , including but not limited to radio transmission/reception circuitry, amplifiers, filters, analogue- to-digital converters (ADCs), digital-to-analogue converters (DACs), processors, memory, storage, etc. Furthermore, the network 100 is not limited to a single base station 102 and two UEs 106, 110 as shown in Figure 1 - the network 100 may comprise any number of base stations and UEs.

The base station 102 and the UEs 106, 110 support half-duplex frequency-division- duplex (HD-FDD) modes of communication. In other words, the UEs 106, 110 support communications whereby frequency division is employed in order to transmit and receive data over a plurality of frequency subcarriers simultaneously, but where uplink and downlink signals are scheduled at different times and are not transmitted simultaneously. As such, each UE 106, 110 can operate either in a reception mode or in a transmission mode. Advantageously, by only permitting halfduplex communications, the UEs 106, 110 are not required to include a duplexer, thus reducing the overall complexity of the UEs 106, 110. While operating in reception mode, the UEs 106, 110 are able to receive the respective downlink signals 114, 118 using their respective antennas 108, 112. While operating in transmission mode, the UEs 106, 110 are able to transmit the respective uplink signals 116, 120 using their respective antennas 108, 112. As the UEs 106, 110 are each low-complexity RedCap devices in this embodiment, they can only operate in one of the reception mode or the transmission mode at any given time. The base station 102 schedules, dynamically or semi-statically, the timings of the downlink and uplink transmissions in order to ensure the UEs 106, 110 are able to receive the respective downlink signals 114, 118 and transmit the respective uplink signals 116, 120. Scheduling downlink and uplink signals in this manner enables the UEs 106, 110 to operate in the correct mode of operation at the correct time and reduces any cross-interference that may occur between the downlink and uplink signals 114, 116, 118, 120. In some circumstances, the base station may schedule the downlink signals 114, 118 and the uplink signals 116, 120 such that they collide - i.e. overlap or occur too close together to allow the UE to process the downlink signals and prepare the uplink signals. However, in such circumstances the UEs 106, 110 respond to such collisions between downlink and uplink signals by dropping a scheduled uplink signal if it collides with a scheduled downlink signal, or by ignoring a received downlink signal if it collides with a scheduled uplink signal. The scheduling of downlink and uplink transmissions may be performed dynamically by the base station 102 while it is in communication with each UE 106, 110, and communicated ad-hoc to the respective UEs 106, 110 via the one or more respective downlink signals 114, 118. Alternatively, the scheduling of downlink and uplink transmissions may be predetermined at protocol level, e.g. Radio Resource Control (RRC) protocol.

Figure 2 shows an example of a prior art downlink/uplink transmission timing sequence 200 between a base station and a UE, and a prior proposal for a downlink/uplink transmission timing sequence 250 between a base station and a UE. For the sake of simplicity, the timing sequences shown herein only consider uplink and downlink signals transmitted between a single base station and a single UE. In the timing sequences shown herein, the horizontal axis shows the flow of time, and the vertical axis shows the frequency subcarriers used, as is known in the art for wireless radio communications. White boxes indicate downlink signals transmitted from a base station to a UE, and black boxes indicate uplink signals transmitted from a UE to a base station. Diagonally hatched sections are used to indicate that no signals are transmitted over those particular subcarriers at that particular time.

In the prior art timing sequence 200, a base station transmits a first downlink control channel (PDCCH) 202, followed by a first downlink shared data channel (PDSCH) 204, followed by a second PDCCH 206 and then followed by a second PDSCH 208. The first PDCCH 202 contains downlink control information (DCI) for the first PDSCH 204, and the second PDCCH 206 contains DCI for the second PDSCH 208. The DCI contains the information required for a UE to successfully receive and decode the respective PDSCH, including but not limited to parameters such as data rate, the modulation and coding scheme used, the transmission mode used (e.g. MISO, SISO, etc.) and, where transmission timings are determined dynamically by the base station, transmission timing information. The UE operates in its reception mode while the base station transmits the channels 202, 204, 206, 208.

Then, after a predefined period of time or gap 220, the UE transmits a first uplink data block 210. The UE operates in the transmission mode while transmitting the uplink data block 210. In this prior art example, the gap 220 between the end of the final downlink signal 208 and the beginning of the first uplink signal 210 is dynamically determined and equal to three symbol periods in this specific example, one symbol period being approximately equal to 71 ps when corresponding to a subcarrier spacing of 15kHz (and thus three symbol periods being approximately equal to 213ps).

The gap 220 provides a sufficient period of time to cover the time that the UE takes to switch from the reception mode to the transmission mode, as well as a UE- specific timing advance (TA) that ensures uplink signals from all UEs arrive at the base station at the same reference timing. It takes approximately 13ps for the UE to switch from the reception mode to the transmission mode. The UE-specific timing advance is equal to the propagation delay for the downlink signals 202, 204, 206, 208 plus the propagation delay for the uplink signal 210, and is thus dependent on at least the distance between the UE and the base station. Thus, the UE-specific timing advance may change over time. In this example, the sum of the UE-specific timing advance and the reception-to-transmission mode switching time is less than three symbol periods, and thus three symbol periods is sufficient for the gap 220.

As mentioned above, the gap 220 is determined dynamically by the base station. The minimum size of the gap 220 is equal to just the reception-to-transmission mode switching time for the UE, assuming a propagation delay of 0s for both uplink and downlink signals. The maximum size of the gap 220 is equal to the sum of the reception-to-transmission mode switching time for the UE and the predetermined maximum timing advance supported by the UE, though in practice the actual timing advance of the UE is likely to be smaller than the predetermined maximum. It will therefore be seen that the gap 220 is not fixed at three symbol periods as shown in the transmission sequence 200, but may be any value within the above-mentioned range, depending on the UE-specific timing advance.

Contained within this uplink block 210, but not shown for the sake of simplicity, are a sounding reference signal (SRS), an uplink control channel (PUCCH) and an uplink shared data channel (PUSCH). The PUSCH contains the payload of the uplink data block 210. The SRS is a reference signal transmitted by the UE in order to enable the base station to determine the quality of the uplink channel, and to respond accordingly. The PUCCH contains uplink control information (UCI) which can include a Scheduling Request, acknowledgements/negative acknowledgements (ACK/NACK) for received PDSCH, PDCCH and/or channel state information (CSI), etc.

Typically, in prior art transmission sequences such as the sequence 200 shown in Fig. 2, the SRS and PUCCH are initially transmitted over one or more subcarriers within the uplink block 210 and the PUSCH is transmitted over one or more subcarriers after transmission of the SRS and PUCCH is completed. However, in the prior art transmission sequence 200, the uplink block 210 is treated as a single uplink signal in terms of scheduling - i.e. no distinction is made between the SRS, PUCCH and/or PUSCH contained within the uplink block 210. The gap 220 between the end of the final downlink signal 208 and the beginning of the uplink signal 210 is independent of whether an SRS, PUCCH or PUSCH is transmitted initially within the uplink block 210.

In order to access the data contained in the channels 202, 204, 206, 208, a UE must demodulate and decode the downlink signals it receives. Demodulation and decoding can be somewhat processor intensive, depending on the size and complexity of the data received. In particular, the data channels 204, 208 are generally complex and it takes an amount of time after fully receiving these channels for a UE to be able to decode them. It also takes an amount of time for a UE to prepare the SRS, PLICCH and PLISCH within the uplink block 210 for transmission (e.g. encoding, modulation, generating checksums, etc.).

The dynamically scheduled gap 220 in the prior art timing sequence 200 is short, comprising only three symbol periods. In fact, the gap 220 is too short to enable the UE to switch from the reception mode to the transmission mode, transmit with the UE-specific timing advance, and sequentially decode the final PDSCH 208 and prepare the uplink block 210 for transmission - the UE must simultaneously decode the PDSCH 208 and prepare the uplink block 210 using e.g. parallel processing. This places a minimum processing power requirement on the UE. This is particularly undesirable where a UE comprises a low-complexity RedCap device as the UE must include a processor with sufficient processing capabilities and sufficient memory to be able to simultaneously decode the PDSCH 208 and prepare the uplink block 210 for transmission, thereby increasing the complexity of the UE and therefore manufacturing cost, power consumption, etc.

While the gap 220 is shown in the prior art timing sequence 200 between the end of the PDSCH 208 and the beginning of the uplink block 210, such prior art implementations use the same dynamically scheduled gap 220 between the end of any final downlink signal and the beginning of any uplink signal. For example, the final downlink signal may alternatively be a PDCCH, or a channel state information reference signal (CSI-RS) which isn’t shown in the timing sequence 200. The gap 220 is applied regardless of the type of downlink signal scheduled immediately before an uplink signal is scheduled.

The previously proposed timing sequence 250 is much the same as the prior art timing sequence 200, with like reference numerals (though increased by fifty) being used to indicate like uplink and downlink signals. However, an extended gap 270 is provided between the end of the final downlink signal 258 and the beginning of the uplink signal 260. The extended gap 270 is fixed at protocol level, unlike the gap 220 shown in the prior art timing sequence 200 which is dynamically scheduled by the base station. Furthermore, the extended gap 270 is significantly longer than the gap 220: the extended gap 270 is equal to one subframe - e.g. approximately 1ms - whereas the gap 220 is only equal to three symbol periods - e.g. approximately 213ps. As well as providing a sufficient period of time to cover the reception-to- transmission mode switching time of the UE as well as a maximum timing advance supported by the UE (i.e. the maximum supported value of the UE-specific timing advance value), the extended, fixed gap 270 is provided in order to prevent the need for a UE to simultaneously decode the PDSCH 258 and prepare the uplink block 260 for transmission, in order to reduce complexity requirements of the UE and therefore manufacturing cost and power consumption. While the extended gap 270 accomplishes this goal, it brings a different issue in the form of reduced scheduling flexibility for a base station e.g. with other UEs and/or with other uplink/downlink signals between the base station and the UE. Furthermore, no downlink or uplink signals may be transmitted between the base station and the UE in the gap 270, resulting in an undesirable excess amount of downtime in the communication link between the base station and the UE. This reduces the overall data rate that can be accomplished between the base station and the UE.

Figure 3 shows a first downlink/uplink timing sequence 300 between the base station 102 and the UE 106 in accordance with an embodiment of the present invention. Like with the prior art timing sequences 200, 250, the base station 102 transmits a first PDCCH 302, followed by a first PDSCH 304, followed by a second PDCCH 306 and then followed by a second PDSCH 308. The UE 106 transmits an SRS 314 over one or more subcarriers following a gap 320 after the end of the PDSCH 308. Then, after one symbol period, the UE transmits a first PUCCH frequency hop 316 over one or more subcarriers. Immediately after transmission of the first PUCCH 316, the UE 106 transmits a second PUCCH frequency hop 318 over different subcarriers to the first PUCCH 316. The second PUCCH 318 frequency may in some embodiments be a repeat of the first PUCCH 316. In this example, the PUCCH frequency hops 316, 318 are not coded using polar coding - instead they are coded using e.g. Reed-Miller coding or a Zadoff-Chu sequence.

For the sake of simplicity, the timing sequences shown herein in accordance with embodiments of the invention only consider uplink and downlink signals transmitted between the base station 102 and a single UE 106, though it will be appreciated that the timing sequences may equally apply to a group of UEs 106, 110. After an extended gap 322 from the end of the PDSCH 308, the UE 106 transmits a PLISCH 312. The beginning of the transmission of the PLISCH 312 and the end of the transmission of the second PLICCH frequency hop 318 happen to fall at the same time in this example, though this is not required. In other embodiments, the PLICCH 316, 318 and the SRS 314 are transmitted over different subcarriers and at different times to those illustrated in the timing sequence 300 - e.g. the first PLICCH frequency hop 316 may be transmitted after the PDSCH 308 (with the smaller gap 320 therebetween), immediately followed by the second PLICCH frequency hop 318, and the SRS 316 may be transmitted after the second PLICCH frequency hop 318 or no SRS 316 may be transmitted at all. However, the smaller gap 320 is always provided between the end of the PDSCH 308 and the first uplink signal which is not the PLISCH 312 or a PLICCH which /s coded using polar coding (i.e. the PLICCH 316, 318 or the SRS 314), and the extended gap 322 is always provided between the end of the final PDSCH 308 and the beginning of the first PLISCH 312 or a PLICCH which /s coded using polar coding.

The processing requirements for preparation of the PLICCH 316, 318 and the SRS 314 for transmission by the UE 106 are significantly lower than those required for preparation of the PUSCH 312. In light of this, the UE 106 requires lower processing power and smaller amounts of memory to prepare the PUCCH 316, 318 and the SRS 314, and these can therefore be performed at the same time as decoding the PDSCH 308. As a result, the gap 320 between the end of the PDSCH 308 and the beginning of SRS 314 can be significantly smaller than the gap 322 between the PDSCH 308 and the PUSCH 312, without requiring increased complexity of the UE 106.

Thus, in the timing sequence 300, the smaller gap 320 between the PDSCH 308 and the SRS 314 is equal to three symbols. The smaller gap 320 provides a sufficient amount of time for the UE 106 to switch from the reception mode to the transmission mode, and the current UE-specific TA for the UE 106. The gap 320 is also sufficiently long for the UE 106 to prepare the SRS 314 for transmission, but this has such low processing requirements that the gap 320 does not require extending beyond the sum of the Rx-Tx switching time of the UE 106 and the UE- specific TA of the UE 106 in order to allow the UE 106 to prepare the SRS 314 for transmission. The UE 106 prepares the SRS 314 for transmission at the same time as decoding the PDSCH 308, in parallel. The smaller gap 320 is dynamically scheduled by the base station 102 in dependence on the UE-specific timing advance of the UE 106 at a particular moment in time, as explained previously. In some embodiments, the gap 320 is the same as the gap 220 used in the prior art timing sequence 200.

The extended gap 322 between the PDSCH 308 and the PLISCH 312 is substantially longer than the gap 320, and consists of a period of time equal to one subframe - e.g. 1ms. The extended gap 322 is equal to the sum the reception-to- transmission mode switching time of the UE 106, the UE-specific TA of the UE 106, and a sufficient amount of time for the UE 106 to prepare the PUSCH 312 for transmission without needing to do so at the same time as decoding the PDSCH 308 in the majority of cases. A gap of one subframe is sufficient for this purpose in this example. Like the smaller gap 320, the extended gap 322 is also dynamically scheduled by the base station 102 in dependence on the UE-specific timing advance of the UE 106 at a particular moment in time, as explained previously.

As outlined previously, the scheduling of the downlink and uplink signals shown in the timing sequence 300 may be performed dynamically by the base station 102 while it is in communication with the UE 106, and communicated ad-hoc to the UE 106 within the DCI contained within the PDCCH 302, 306, or within the PDSCH 304, 308. Alternatively, the scheduling of downlink and uplink transmissions may be predetermined at protocol level. Either way, the UE 106 is provided with RRC configured grant or dynamically received grant to transmit the respective uplink signals 314, 316, 318, 320 by the base station 102, the grant consisting of the time at which the UE 106 is allotted to begin transmission of these respective signals. As can be seen from the timing sequence 300, the UE is provided with different grant for each uplink signal 314, 316, 318, 320.

Figure 4 shows a second downlink/uplink timing sequence 400 between the base station 102 and the UE 106 in accordance with an embodiment of the present invention. Like with the timing sequences 200, 250, 300 the base station 102 transmits a first PDCCH 402, followed by a first PDSCH 404, followed by a second PDCCH 406 and then followed by a second PDSCH 408. However, unlike the timing sequences 200, 250, 300, the base station 102 then transmits a further PDCCH 409 and, after a short period of time, a CSI-RS 415. In this example, the PDCCH 409 is not transmitted using polar coding - e.g. it is coded using Reed- Miller coding or a Zadoff-Chu sequence. Then, after a gap 420, which is equal to the gap 320 shown in the timing sequence 300, the UE 106 transmits a PLISCH 412. The transmission by the UE 106 of the PUSCH 412 also provides an extended gap 422 after the PDSCH 408 which is equal to the extended gap 322 shown in the timing sequence 300. In this example, these two gaps end at the same time - i.e. the beginning of the transmission of the PUSC 412 - but this may not be the case in other examples.

As before, because the processing requirements for decoding the PDCCH 409 (which is not coded using polar coding) and the CSI-RS 415 are significantly lower than those required for decoding the PDSCH 408 this can be performed in parallel with decoding the PDSCH 408 or preparing the PUSCH 412 for transmission but the extended gap 422 between the PDSCH 408 and the PUSCH 412 allows the former to be decoded and the latter prepared for transmission sequentially, i.e. without requiring increased complexity of the UE 106.

It will be seen from Figs. 3 and 4 that, in effect, the extended gaps 322, 422 are provided between a final PDSCH 308, 408 of a set of downlink signals and the first PUSCH 312, 412 of a set of uplink signals. Other types of downlink and uplink signals - e.g. the PUCCH 314, 318 (which are not coded using polar coding), the SRS 316, the PDCCH 409 (which is not coded using polar coding) and the CSI-RS 415 - can be transmitted within the extended gaps 322, 422, provided that there is a smaller gap 320, 420 provided between any downlink signal and a subsequent uplink signal where one of those signals is not a shared data channel. While not shown in Figs. 3 and 4, in examples where the PUCCH 314, 318 and the PDCCH 409 are coded using polar coding, the extended gaps 322, 422 are provided between the polar-coded PUCCH, polar-coded PDCCH, PUSCH and PDSCH where appropriate.

The gaps 320, 322, 420, 422 are applied only when switching from downlink signals to uplink signals. A different configuration is typically used when switching from uplink signals to downlink signals. As used herein, the shorter gap 320, 420, is equivalent to the second value of the time gap referred to previously, and the extended gap 322, 422 is equivalent to the first value of the time gap.

Figure 5 shows a table 500 illustrating which gap is applied when switching from downlink signals to uplink signals for each possible pair of signal type. It will be seen from the table 500 that the extended gap 322, 422, is only applied when a PLISCH or a polar-coded PLICCH is scheduled for transmission after a PDSCH, and when a PLISCH or a polar-coded PLICCH is scheduled for transmission after a polar-coded PDCCH. The shorter gap 320, 420, is used for all other pairs of downlink/uplink signal types.

Figure 6 shows a flowchart of a method for determining which gap to apply between a scheduled downlink signal and a subsequently scheduled uplink signal. At step 602, an uplink signal is scheduled for transmission after a downlink signal. At step 604, it is determined whether the scheduled uplink signal belongs to a first predetermined set of signals and channels and, if so, the method proceeds to step 606. If not, the method proceeds to step 610. The first predetermined set in this embodiment includes downlink shared data channels (i.e. PDSCH 308, 408), uplink shared data channels (i.e. PLISCH 312, 412), downlink control channels (i.e. PDCCH) that are coded using polar coding and uplink control channels (i.e. PLICCH) that are coded using polar coding.

At step 606, it is determined whether the scheduled downlink signal belongs to the first predetermined set of signals and channels and, if so, the method proceeds to step 608. If not, the method proceeds to step 610. At step 608, the extended gap 322, 422, is applied between the scheduled uplink signal and the scheduled downlink signal. At step 610, the shorter gap 320, 420, is applied between the scheduled uplink signal and the scheduled downlink signal.

In this embodiment, all possible signals and channels shown in the table 500 of Fig. 5 are included in either the first predetermined set of signals and channels, or a second predetermined set of signals and channels, and the first predetermined set and the second predetermined set do not overlap - i.e. there are no signals or channels shown in Fig. 5 that do not belong to either the first predetermined set or the second predetermined set. Thus, in this embodiment, when it is determined that the uplink or downlink signal does not belong to the first predetermined set at step 604 or 606, it is automatically determined that the uplink or downlink signal belongs to the second predetermined set.

The second predetermined set includes downlink control channels that are not coded using polar coding, downlink reference signals, uplink control channels that are not coded using polar coding and uplink reference signals - i.e. PDCCH 409, CSI-RS 415, PUCCH 316, 318 and SRS 314. Thus, the first and second predetermined sets of signals and channels include all possible signal/channel types shown in Fig. 5, hence there is no need for the flowchart shown in Fig. 6 to include a further step of determining whether the uplink/downlink signals are included in the second predetermined set.

It will be appreciated that in other embodiments where e.g. more than two predetermined sets of signals and channels are used (and, accordingly, more than two different time gaps between reception and transmission) or where there are further types of signal not included in either the first or second predetermined set, the flowchart shown in Fig. 6 can be readily adjusted accordingly. It will also be appreciated that the first and second predetermined sets of signals and channels could in other embodiments include additional and/or different channels and signals to those outlined above, depending on implementation.

It will be appreciated by those skilled in the art that the invention has been illustrated by describing one or more specific embodiments thereof, but is not limited to these embodiments; many variations and modifications are possible within the scope of the appended claims.