GB2557209A

GB2557209A - Multi-rate wireless communication network

Info

Publication number: GB2557209A
Application number: GB1620293.9A
Authority: GB
Inventors: Zhang Lei; Ijaz Ayesha; Quddus Atta; Tafazolli Rahim; Xiao Pei
Original assignee: University of Surrey
Current assignee: University of Surrey
Priority date: 2016-11-30
Filing date: 2016-11-30
Publication date: 2018-06-20
Anticipated expiration: 2036-11-30
Also published as: GB2557209B; GB201620293D0

Abstract

Transmitting and receiving data in a wireless communication network is described. Data is transmitted 305 by transforming 301 plural data symbols ak to be transmitted on a plurality of subcarrier frequencies within a frequency sub band into a time-domain multicarrier signal, upsampling 302 the time-domain multicarrier signal at a selected appropriate upsampling rate, filtering 303 the upsampled signal to remove upsampling images, and transmitting the filtered upsampled signal over a wireless communication channel. A complementary receiver (Figure 4) converts the received signal to a digital signal at a selected sampling rate, which may be selected according to signaling provided by the network, transforms the digital signal from the time-domain into a plurality of frequency-domain subcarrier signals, and performs equalization on the frequency-domain subcarrier signals to obtain an estimated data symbol. Methods of cancelling interference between sub-bands (inter-subband interference) are also disclosed. The arrangement may take as input sub-bands of data of different sampling rates (i.e. multi-rate data) and converts the data such that the signals received in the multiplexing stage 304 have the same sampling rate as each other (i.e. different upsampling rates may be selected for each sub-band).

Description

(71) Applicant(s):

University of Surrey (Incorporated in the United Kingdom)

GUILDFORD, Surrey, GU2 7XH, United Kingdom (56) Documents Cited:

EP 3001629 A1 EP 1336267 A1

WO 2016/195296 A1 US 6252909 B1 (58) Field of Search:

INT CL H04J, H04L

Other: WPI, EPODOC, XPI3E, XP3GPP, XPESP (72) Inventor(s):

Lei Zhang Ayesha Ijaz Atta Quddus Rahim Tafazolli Pei Xiao (74) Agent and/or Address for Service:

Venner Shipley LLP

The Surrey Technology Centre,

The Surrey Research Park, 40 Occam Road, Guildford, Surrey, GU2 7YG, United Kingdom (54) Title of the Invention: Multi-rate wireless communication network Abstract Title: Multi-rate wireless communication network (57) Transmitting and receiving data in a wireless communication network is described. Data is transmitted 305 by transforming 301 plural data symbols a_k to be transmitted on a plurality of subcarrier frequencies within a frequency sub band into a time-domain multicarrier signal, upsampling 302 the time-domain multicarrier signal at a selected appropriate upsampling rate, filtering 303 the upsampled signal to remove upsampling images, and transmitting the filtered upsampled signal over a wireless communication channel. A complementary receiver (Figure 4) converts the received signal to a digital signal at a selected sampling rate, which may be selected according to signaling provided by the network, transforms the digital signal from the time-domain into a plurality of frequency-domain subcarrier signals, and performs equalization on the frequency-domain subcarrier signals to obtain an estimated data symbol. Methods of cancelling interference between sub-bands (inter-subband interference) are also disclosed. The arrangement may take as input sub-bands of data of different sampling rates (i.e. multi-rate data) and converts the data such that the signals received in the multiplexing stage 304 have the same sampling rate as each other (i.e. different upsampling rates may be selected for each sub-band).

FIG. 3

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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FIG. 1

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c) Service-based subband filtering

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FIG. 12

- 1 Multi-Rate Wireless Communication Network

Technical Field

The present invention relates to a wireless communication network. More particularly, 5 the present invention relates to wireless communication networks in which different sampling rates are used for different sub-bands.

Background

It is expected that future wireless communication systems will need to support a greater density of users whilst providing higher rates of data throughput, ultra-high reliability, and ultra-low latency communications. However, the differing requirements of various types of services can result in different optimal frame structure design criteria for different services.

For example, services for machine type communications (MTC) and Internet of Things (IoT) applications may be required to support a large number of devices, which can tolerate relatively long delays in communication (i.e. high latency). Accordingly, the optimal frame structure for MTC and IoT services may be one with a relatively small subcarrier spacing and long symbol duration, so as to support a high number of devices,

On the other hand, services for vehicle to vehicle (V2V) communications may have much more stringent latency requirements than MTC or IoT services. Therefore, the optimal frame structure for a V2V service may have a much shorter symbol duration than that for MTC or IoT services. These conflicting requirements make it difficult to design a unified frame structure that can meet the requirements of all types of services in the same wireless communication network.

The invention is made in this context.

Summary of the Invention

According to a first aspect of the present invention, there is provided a method of transmitting data in a wireless communication network, the method comprising transforming a plurality of data symbols to be transmitted on a plurality of subcarrier frequencies within a frequency subband into a time domain multicarrier signal, selecting an appropriate upsampling rate for the time domain multicarrier signal, upsampling the time domain multicarrier signal at the selected upsampling rate, filtering the upsampled signal to remove upsampling images, and transmitting the filtered upsampled signal over a wireless communication channel.

In some embodiments according to the first aspect, a plurality of time domain multicarrier signals are obtained for a plurality of frequency subbands, and a different upsampling rate is selected for at least two of the time domain multicarrier signals.

In some embodiments according to the first aspect, the at least two time domain 10 multicarrier signals each have a different sampling rate before upsampling, and the upsampling rates for the at least two time domain multicarrier signals are selected so that the at least two upsampled signals have the same sampling rate, the method further comprising a step of combining the at least two upsampled signals to obtain a multiplexed signal.

In some embodiments according to the first aspect, the method further comprises a step of receiving sampling rate information from the wireless communication network, and wherein the upsampling rate is selected in accordance with the received sampling rate information.

In some embodiments according to the first aspect, the plurality of frequency subbands are arranged into a plurality of service bands each comprising one or more of the sub-bands, the plurality of service bands including a first service band configured to use a first subcarrier spacing and a second service band configured to use a second subcarrier spacing different to the first subcarrier spacing, and the method further comprises steps of obtaining a first precoding matrix configured to compensate for interference between the first and second service bands due to the different subcarrier spacings, and applying the first precoding matrix to sub-bands at the edge of the first and second service bands, before transmitting the filtered upsampled signal.

In some embodiments according to the first aspect, the method further comprises steps of obtaining a second precoding matrix configured to compensate for interference between the at least two of the time domain multicarrier signals due to the upsampling, and applying the second precoding matrix to the data symbol to be transmitted on the plurality of subcarrier frequencies, prior to the time domain transformation.

-3According to a second aspect of the present invention, there is provided a method of receiving data in a wireless communication network, the method comprising receiving a signal over a wireless communication channel, selecting a first sampling rate, converting the received signal to a digital signal at the selected first sampling rate, transforming the digital signal from the time domain into a plurality of frequencydomain subcarrier signals, and performing equalization on the frequency-domain subcarrier signals to obtain an estimated data symbol.

In some embodiments according to the second aspect, converting the received signal to 10 the digital signal at the first sampling rate comprises converting the received signal to a digital signal at a second sampling rate higher than the first sampling rate, and downsampling the digital signal to the first sampling rate, wherein the transforming and equalization steps are performed on the downsampled digital signal.

According to a third aspect of the present invention, there is provided apparatus for transmitting data in a wireless communication network, the apparatus comprising a time domain conversion unit configured to transform a plurality of data symbols to be transmitted on a plurality of subcarrier frequencies within a frequency subband into a time domain multicarrier signal, an upsampling unit configured to upsample the time domain multicarrier signal, wherein the apparatus is configured to select an appropriate upsampling rate for the time domain multicarrier signal, a subband filter configured to filter the upsampled signal to remove upsampling images, and one or more antennas configured to transmitting the filtered upsampled signal over a wireless communication channel.

In some embodiments according to the third aspect, the apparatus further comprises a plurality of time domain conversion units each configured to obtain a plurality of time domain multi carrier signals for a plurality of frequency sub-bands, by transforming a plurality of data symbols to be transmitted on a plurality of subcarrier frequencies within each sub-band into a time domain multicarrier signal, a plurality of upsampling units each configured to upsample one of the plurality of time domain multicarrier signals, wherein at least two of the plurality of upsampling units are configured to use a different upsampling rate, and a plurality of sub-band filters each configured to filter one of the plurality of upsampled signals to remove upsampling images.

-4In some embodiments according to the third aspect, the time domain multicarrier signals upsampled by said at least two upsampling units each have a different sampling rate before upsampling, and the upsampling rates for said at least two upsampling units are selected so that the upsampled signals outputted by said at least two upsampling units have the same sampling rate, and the apparatus further comprises a multiplexing stage configured to combining the at least two upsampled signals to obtain a multiplexed signal.

In some embodiments according to the third aspect, the plurality of frequency sub10 bands are arranged into a plurality of service bands each comprising one or more of the sub-bands, the plurality of service bands including a first service band configured to use a first subcarrier spacing and a second service band configured to use a second subcarrier spacing different to the first subcarrier spacing, and wherein the apparatus is configured to obtain a first precoding matrix configured to compensate for interference between the first and second service bands due to the different subcarrier spacings, and further comprises an inter-service-band interference pre-cancellation unit configured to apply the first precoding matrix to sub-bands at the edge of the first and second service bands before transmitting the filtered upsampled signal.

In some embodiments according to the third aspect, the apparatus is configured to obtain a second precoding matrix configured to compensate for interference between the at least two of the time domain multicarrier signals due to upsampling, and further comprises a precoding unit configured to apply the second precoding matrix to the data symbol to be transmitted on the plurality of subcarrier frequencies, prior to the time domain transformation.

According to a fourth aspect of the present invention, there is provided apparatus for receiving data in a wireless communication network, the apparatus comprising one or more antennas configured to receive a signal over a wireless communication channel, signal conversion apparatus configured to convert the received signal to a digital signal at a first sampling rate selected by the apparatus, a frequency domain conversion unit configured to transform the digital signal from the time domain into a plurality of frequency-domain subcarrier signals, and an equalization unit configured to perform equalization on the frequency-domain subcarrier signals to obtain an estimated data symbol.

-5In some embodiments according to the fourth aspect, the apparatus further comprises an analogue to digital converter configured to convert the received signal to the digital signal at a second sampling rate higher than the first sampling rate, and a downsampling unit configured to downsample the digital signal to the first sampling rate and send the downsampled digital signal to the frequency domain conversion unit.

In some embodiments according to the fourth aspect, the apparatus is configured to receive bandwidth information defining a frequency band allocated to the apparatus, the apparatus further comprises a tunable bandpass filter, and the apparatus is configured to tune the bandpass filter to select the allocated frequency band.

In some embodiments according to the fourth aspect, the tunable bandpass filter is a tunable analogue filter with a fixed bandwidth, such that the allocated frequency band is selected before the received signal is converted from analogue to digital.

In some embodiments according to the fourth aspect, the tunable bandpass filter is a tunable baseband filter with a fixed bandwidth, and the apparatus further comprises an analogue bandpass filter configured to filter the received signal with a passband width equal to or greater than a bandwidth of a service band which includes the allocated frequency band, wherein the apparatus is configured to convert the filtered analogue signal to a baseband digital signal at the first sampling rate, and pass the baseband digital signal through the tunable baseband filter to select the allocated frequency band.

According to a fifth aspect of the present invention, there is provided a wireless communication network comprising a transmitting apparatus comprising the apparatus according to the third aspect, a first receiver comprising the apparatus according to the fourth aspect, and a second receiver comprising the apparatus according to the fourth aspect. The first receiver can be configured to convert the received signal to a digital signal at a first sampling rate and then downsample the digital signal to a second sampling rate lower than the first sampling rate. The second receiver can be configured to convert the received signal to a digital signal at a first sampling rate and then perform baseband processing, including equalization, without downsampling. The first sampling rate used by the first receiver may be different to the first sampling rate used by the second receiver. In some embodiments, the first sampling rate used by the first receiver is a higher sampling rate than the first sampling rate used by the second receiver.

-6In some embodiments according to the fifth aspect, the transmitting apparatus is configured to transmit bandwidth information to the second receiver, the bandwidth information defining a frequency band allocated to the second receiver, the second receiver comprises a tunable bandpass filter, and the second receiver is configured to tune the bandpass filter to select the allocated frequency band.

In some embodiments according to the fifth aspect, the tunable bandpass filter is a tunable analogue filter with a fixed bandwidth, such that the allocated frequency band is selected before the received signal is converted from analogue to digital.

In some embodiments according to the fifth aspect, the tunable bandpass filter is a tunable baseband filter with a fixed bandwidth, and the second receiver further comprises an analogue bandpass filter configured to filter the received signal with a passband width equal to or greater than a bandwidth of a service band which includes the allocated frequency band, wherein the second receiver is configured to convert the filtered analogue signal to a baseband digital signal at the first sampling rate, and pass the baseband digital signal through the tunable baseband filter to select the allocated frequency band.

Brief Description of the Drawings

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

Figure 1 illustrates a frame structure in a wireless communication network, according to an embodiment of the present invention;

Figure 2 illustrates alternative subband filtering schemes for the multicarrier system of Fig. 1, according to embodiments of the present invention;

Figure 3 illustrates apparatus for transmitting a multiplexed signal in the downlink direction in a wireless communication network, according to an embodiment of the present invention;

Figure 4 illustrates apparatus for receiving a multiplexed signal in the downlink direction in a wireless communication network, according to an embodiment of the present invention;

Figure 5 illustrates apparatus for transmitting a signal in the uplink direction in a wireless communication network, according to an embodiment of the present invention;

-ΊFigure 6 illustrates apparatus for receiving a plurality of signals in the uplink direction in a wireless communication network, according to an embodiment of the present invention;

Figure 7 illustrates the baseband processing stage in the second device of Figs. 4 and 5, 5 according to an embodiment of the present invention;

Figure 8 illustrates the baseband processing stage in the second device of Figs. 4 and 5, according to an alternative embodiment of the present invention;

Figure 9 illustrates apparatus for applying ISBI and ISubBI pre-cancellation at a base station, according to an embodiment of the present invention;

Figure 10 illustrates apparatus for cancelling ISBI and ISubBI in received uplink signals at a base station, according to an embodiment of the present invention;

Figure 11 is a graph showing an improvement in the information symbol estimation MSE versus subcarrier index when ISBI pre-cancellation is applied, according to an embodiment of the present invention; and

Figure 12 is a graph showing the improvement in the information symbol estimation MSE versus subcarrier index when ISubBI pre-cancellation is applied, according to an embodiment of the present invention.

Detailed Description

In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments maybe modified in various different ways, all without departing from the scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

Referring now to Fig. 1, a frame structure in a wireless communication network is illustrated, according to an embodiment of the present invention. In the embodiment shown in Fig. 1, physical resource blocks (PRBs) in the wireless communication network are allocated among a plurality of services. As such, the network maybe referred to as a multi-service (MS) wireless communication network. In the present embodiment, data is transmitted across a plurality of subcarriers within each PRB, and hence the network may be also referred to as a multi-carrier (MC) network. The frequency range allocated to each service may be referred to as a ‘service band’. In

-8some embodiments, a guard interval maybe provided between adjacent service bands to reduce or eliminate interference between services on adjacent frequencies.

In the present embodiment the PRBs are divided among first, second and third service 5 bands. For example, the first service band may be allocated to a high capacity service such as an MTC service, the second service band may be allocated to a high data rate service, and the third service band may be allocated to a low-latency service such as a V2V service. It should be understood that these are merely examples of types of services that could be supported by the wireless communication network, and in other embodiments the PRBs may be allocated to different types of service to those described in the present embodiment.

In general, each service may support one or more users, and each user can be allocated an arbitrary number of consecutive or non-consecutive PRBs. In addition, within each

PRB data is transmitted on a plurality of subcarriers. Figure 2 illustrates examples of alternative subband filtering schemes that can be used in the multicarrier network of Fig. 1, according to embodiments of the present invention. In the examples illustrated, each service supports two users. In the first and third service bands each user is allocated an equal bandwidth, whilst in the second service band one user is allocated more bandwidth than the other user.

In a MS-MC system such as the one shown in Fig. 1, interference between adjacent services can be mitigated by using subband filtering. Here, the term ‘subband’ is used to refer to the frequency block over which filtering is performed. The subbands may be defined differently depending on the embodiment. For example, each subband may be equivalent to either a PRB, a user bandwidth allocation, or a service band, as shown in Figs. 2 a) to c) respectively.

In example a) in Fig. 2, PRB-based subband filtering is illustrated, meaning that each individual PRB is filtered using a separate subband filter. This approach offers the largest design flexibility, albeit at the expense of increased computational complexity due to the number of filters that are required. PRB-based subband filtering also offers the advantage that filters with a steeper roll-off can be used since the passband width of each filter is relatively narrow, increasing the isolation between adjacent subbands.

-9In example b) in Fig. 2, user-based subband filtering is illustrated, meaning that the bandwidth allocated to each user is treated as a single subband and filtered separately to other user’s bandwidth allocation. In this example, each subband filter may have a passband width equivalent to a plurality of PRBs, depending on the number of PRBs allocated to that particular user. This approach reduces the system complexity in comparison to PRB-based subband filtering since fewer filters are needed.

In example c) in Fig. 2, service based subband filtering is illustrated, meaning that each service band is treated as a single subband and filtered separately. This approach has io the lowest computational complexity in comparison to examples a) and b), and the users (and PRBs) in one service band can share the same filter design parameters.

For communications in the downlink direction, a BS can employ any of the subband filtering schemes illustrated in Fig. 2. Since orthogonality is preserved between subcarriers within a service band, a user can apply an RF passband filter with a bandwidth equal to the service band to isolate signals in the relevant service band, and can then separate the orthogonal subcarriers. For communications in the uplink direction, the transmitter (e.g. a UE device) may apply either of the subband filtering schemes in examples a) and b) of Fig. 2.

Referring now to Figs. 3 and 4, apparatus for transmitting and receiving signals in the downlink direction in a wireless communication network is illustrated, according to an embodiment of the present invention. Here, ‘downlink’ is used in the conventional sense, to refer to signals being transmitted from a base station (BS) to one or more devices in the wireless communication network, such as user equipment (UE) devices. Apparatus for generating a multiplexed signal at the BS is schematically illustrated in Fig. 3. The apparatus comprises a plurality of subband processing chains, each of which is configured to receive data to be transmitted on a plurality of subcarrier frequencies within one subband and to generate a multicarrier signal. In more detail, each subband processing chain comprises a time domain conversion unit 301, an upsampling unit 302, and a subband filter 303. The apparatus further comprises a multiplexing stage 304 and a transmitter 305.

The plurality of time domain conversion units 301 are configured to obtain a plurality of time domain multicarrier signals for a plurality of frequency sub-bands, by transforming a plurality of data symbols to be transmitted on a plurality of subcarrier

- 10 frequencies within each sub-band into a time domain multicarrier signal. In the present embodiment each time domain conversion unit is configured to perform an inverse discrete Fourier transform (IDFT) to convert the plurality of data symbols (a_J5a₂,..., ακ) from the frequency domain to the time domain. In other embodiments a different type of frequency-to-time transformation may be used, for example an inverse fast Fourier transform (IFFT).

Here, cu to ak denote a plurality of vectors each carrying n data symbols, where n is the number of subcarriers in the relevant subband. In some embodiments, different ones of the plurality of subbands may include different numbers of subcarriers n. If the system is configured to apply PRB-based subband filtering, as shown in example a) of Fig. 2, each subcarrier in one subband carries different data symbols from one user. Similarly, if the system is configured to apply user-based subband filtering, as shown in example b) of Fig. 2, each subcarrier in one subband carries different data symbols from one user. On the other hand, if the system is configured to apply service-based subband filtering, as shown in example c) of Fig. 2, each subcarrier in one subband may carry data symbols from different users, if a plurality of users have been allocated bandwidth within the particular service band.

Each of the plurality of upsampling units 302 is configured to upsample one of the plurality of time domain multicarrier signals. At least two of the plurality of upsampling units maybe configured to use a different upsampling rate, such that the signals received by the multiplexing stage 304 have the same sampling rate as each other. In some embodiments the sampling rates of the baseband digital signals produced by the IDFT units 301 may differ from one another, for example as a result of different subbands having different bandwidths, and/or different numbers of subcarriers, resulting in different IDFT sizes being used. In such embodiments, the upsampling rate for each subband can be selected such that the upsampled signals all have the same higher sampling rate, allowing the upsampled signals to be multiplexed, while enabling a flexible frame structure since subbands with different bandwidths and/or different numbers of subcarriers may be used. This arrangement can be referred to as a multi-rate system, since different upsampling rates maybe used for different subbands. In some embodiment, a cyclic prefix (CP) may be added to the time-domain signal before upsampling is performed.

- 11 Upsampling at different rates enables the BS to simultaneously support a plurality of services with different subcarrier spacings, since the BS can set an appropriate upsampling rate for each subband based on the subcarrier spacing currently in use in that subband. Since the computational complexity increases as the sampling rate is increased, using different upsampling rates for different subbands allows different IDFT sizes to be used for different subbands, thereby avoiding unduly increasing the system complexity any further than is necessary. In the present embodiment, the upsampling rate is selected so that the upsampled signals all have the same higher sampling rate and can be added together in the multiplexing stage 304.

Depending on the frame structure used in a particular embodiment, different subbands within the same service band may be upsampled at the same upsampling rate or at different upsampling rates. For example, when first and second subbands within the same service band have different bandwidths, the first and second subbands will contain different numbers of subcarriers since the subcarrier spacing will be constant within the service band. As a result, a different IDFT size can be selected for each of the first and second subbands. The upsampling units for the first and second subbands can then be set to use different upsampling rates, such that the resulting upsampled signals for the first and second subbands have the same higher sampling rate and can be added together in the multiplexing stage 304.

The BS may transmit sampling rate information to each user on the network, wherein the sampling rate information transmitted to a particular user identifies the sampling rate to be used for the subband which includes subcarrier frequencies allocated to that user. Depending on the embodiment, the sampling rate information may define the sampling rate in absolute terms, by specifying an actual sampling rate, or in relative terms, by specifying an upsampling or downsampling rate (i.e. a ratio between a higher sampling rate and a lower sampling rate). The user can then set its own sampling rate according to the sampling rate information specified by the BS.

Each upsampled baseband signal is then filtered using a subband filter 303 that is configured to reject images introduced during the upsampling stage. The filter 303 may therefore be referred to as an ‘anti-image filter’.

The upsampled and filtered signals from the plurality of subband processing chains are then combined in the multiplexing stage 304 to obtain a multiplexed signal. In the

- 12 present embodiment, the multiplexing stage 304 receives baseband signals from the subband processing chains and shifts each baseband signal to a different centre frequency so that the signals do not overlap with one another. This process may be referred to as spectrum shifting. The multiplexing stage 304 is further configured to sum the spectrum-shifted signals and convert the multiplexed signal to a radiofrequency (RF) signal. In the present embodiment, the spectrum shifters are configured to convert the baseband signals to an intermediate frequency (IF), and the IF signals are then added together to obtain a multiplexed signal. The multiplexed signal is then converted to RF and transmitted over a wireless communication channel via a suitable transmitter 305. In another embodiment, the spectrum shifters may convert the baseband signals directly to RF, in which case the additional RF chain after the summation node in Fig. 1 may be omitted.

Referring now to Fig. 4, two different device architectures for receiving multiplexed signals from the apparatus of Fig. 3 are schematically illustrated, according to an embodiment of the present invention. In general, in embodiments of the present invention a receiver may demultiplex a received multiplexed signal using either a baseband or RF subband filter. A baseband subband filter has relatively high accuracy, high flexibility, and can allow a smaller guard interval to be used. On the other hand, an RF subband filter has lower complexity, and so may be more suitable for low cost

IoT devices.

In Fig. 4, a first device is illustrated comprising an RF chain 401, spectrum shifting stage 402, anti-aliasing filter 403, downsampling unit 404, frequency domain conversion unit 405, and an equalization unit 406. The RF chain 401 is configured to filter the multiplexed signal, and then convert the filtered RF signal from analogue to digital at a sampling rate selected in accordance with the sampling rate information provided by the BS. Then, the spectrum shifting stage 402 converts the filtered RF signal to baseband, and the baseband signal is filtered in the anti-aliasing filter 403.

The passband of the RF chain 401 can be set to be equal to or greater than the system bandwidth in order to receive all frequencies in the multiplexed signal without distortion. The baseband signal is therefore a combination of all services transmitted by the BS. For example, if the bandwidth of the whole system, including all service bands, is too megahertz (MHz), the passband of the RF chain 401 can be set to be greater than or equal to too MHz. In other words, in the present embodiment the RF chain 401 does not separate the multiplexed multi-service signals. Instead, in the

-13present embodiment the multi-service demultiplexing is performed during baseband processing. In the present embodiment, the passband of the anti-aliasing filter 403 is configured to only pass signals on subcarrier frequencies allocated to the current user, thereby performing demultiplexing at baseband.

Next, the filtered baseband signal is down-sampled in the downsampling unit 404. Here, the first device may set the downsampling rate to be equal in magnitude to the upsampling rate applied at the transmitter. The BS and first device may agree on a suitable downsampling/upsampling rate in advance. For example, the downsampling/upsampling rates to be used in communications between the BS and first device may be selected during a scheduling and resource allocation operation.

Next, the downsampled baseband signal is converted from the time domain to the frequency domain in the frequency-domain conversion unit 405. In the present embodiment the frequency-domain conversion unit 405 is configured to perform a fast Fourier transformation (FFT), but in other embodiments a different type of time-tofrequency transformation may be used. The frequency-domain conversion unit 405 separates the individual subcarrier frequencies, and the equalization unit 406 then performs per-subcarrier equalization to obtain an estimate of the original data symbol

a.!.

Figure 4 also illustrates a second device comprising an RF chain 411 followed by a baseband processing stage 412. The baseband processing stage 412 can include baseband processing components similar to the ones illustrated in the first device, such as a spectrum shifting stage, frequency domain conversion unit and equalization unit. The baseband processing stage 412 can also include a passband filter similar to the anti-aliasing filter 403 of the first device, for rejecting signals from adjacent subbands. The RF chain 411 in the second device is configured to perform analogue to digital conversion at the same low sampling rate used in the BS, and a passband of the RF 411 chain is set to be narrower than the system bandwidth. Depending on the embodiment, the passband of the RF chain 411 may be set to only pass the signals in the frequency band allocated to the second device, or may be set to pass all signals in the service band for which the lower sampling rate is used.

This differs from the method used in the first device, which performs analogue to digital conversion at a high sample rate and then downsamples the signal to reduce the

-14sampling rate. In the present embodiment, the second device is a low-cost IoT device. Since the second device converts the analogue signal directly to the lower sampling rate, the complexity is reduced in comparison to the first device. For example, the downsampling unit 404 of the first device can be omitted in the second device, since analogue-to-digital conversion is performed at the lower sampling rate. The architecture used in the second device of Fig. 4 may be particularly suited to IoT devices, which may be required to have a lower cost and complexity than other wireless communication devices.

The first and second devices in Fig. 4 are configured to use different sampling rates when converting a received analogue RF signal to a digital signal. The sampling rate used in each device can be selected in accordance with the sampling rate information provided by the BS. Since the BS of Fig. 3 can support multiple different low sampling rates in different subbands, both the first and second devices can participate in the network at the same time, and communicate simultaneously with the BS.

Referring now to Figs. 5 and 6, apparatus for transmitting and receiving signals in the uplink direction in a wireless communication network is illustrated, according to an embodiment of the present invention. The apparatus illustrated in Fig. 5 can be included in the first and second devices of Fig. 4, to allow the UE devices to communicate in the uplink direction with the BS. Figure 6 schematically illustrates apparatus for use at the BS to receive a plurality of signals from devices such as the ones shown in Fig. 5.

In the embodiment shown in Fig. 5, the first device comprises a time domain conversion unit 501, upsampling unit 502, filter 503, spectrum shifting unit 504, and RF chain 505. The time domain conversion unit 501 operates at a low sampling rate, reducing the complexity of the IFFT calculation. The time-domain signal is then upsampled to a higher sampling rate, allowing a filter 503 with a sharper roll-off to be used, and thereby reducing interference due to upsampling images. The filter 503 may be referred to as an anti-image filter, since the filter 503 is configured to remove upsampling images from the upsampled signal. The spectrum shifting unit 504 and RF chain 505 perform a similar function to those described above in relation to Fig. 3, by converting the baseband signal to the appropriate RF transmission frequency and performing digital-to-analogue conversion.

-15The second device of the present embodiment includes a baseband processing stage 511 and RF chain 512, which are configured to perform an inverse sequence of operations to those described above in relation to Fig. 4. As such, as detailed description of similar aspects will not be repeated here. The RF chain 512 is configured to convert the digital baseband signal to an analogue RF signal at a low sampling rate, thereby reducing the cost and complexity of the device.

In the above-described embodiments, two different receiver and transmitter architectures are illustrated in Figs. 4 and 5. The lower-complexity architecture described above in relation to the second device can be particularly suitable for low cost devices, such as IoT devices.

Referring now to Fig. 6, the signal receiving apparatus at the BS comprises a demultiplexing stage 601 which is configured to demultiplex the received signal into separate subbands. The apparatus further comprises a plurality of subband processing chains, each of which comprises an anti-aliasing filter 602, downsampling unit 603, frequency domain conversion unit 604, and equalization unit 605. Each subband processing chain operates in a similar manner to the baseband processing chain in the first device of Fig. 4, and a detailed description will not be repeated here.

It should be noted that in the embodiments shown in Figs. 3 and 6, the BS uses one unified RF chain for all services. This reduces the cost and complexity of the apparatus in comparison to having a separate RF chain for each subband. However, in some embodiments separate RF chains could be provided, for example if the service bands are not close enough in frequency to permit a single RF chain to be used. If separate RF chains are provided, an RF chain for receiving signals from the second device of Fig. 5 could be configured to directly convert the received analogue signal to a digital signal at the low sampling rate, meaning that the downsampling unit on the corresponding subband processing chain can be omitted.

Figures 7 and 8 illustrate two alternative architectures for the baseband processing stage in the second device of Figs. 4 and 5, according to embodiments of the present invention. The embodiments of Figs. 7 and 8 are described in the context of a wireless communication network in which a service band allocated to low-complexity devices, such as an IoT service, has a total bandwidth of 1 MHz divided into five equal PRBs of 200 kilohertz (kHz) each. It will be understood that these numbers are provided purely

-ι6by way of an example, and should not be construed as limiting. Furthermore, although the embodiments of Figs. 7 and 8 are shown as receiving a downlink signal, it will be understood that a similar principle could be applied in reverse to generate and transmit an uplink signal.

In the embodiment illustrated in Fig. 7, the second device comprises a tuneable narrow band RF filter 711 that can be tuned to select any one of the five PRBs of 200 kHz. In this way, demultiplexing is performed by the RF filter 711, which outputs a demultiplexed analogue signal. After the filtering, the analogue signal will only include the signal intended for the current device, since signals in PRBs allocated to other devices will have been filtered out. The analogue signal is then converted to a digital signal in an analogue-to-digital converter (ADC) 712, which is configured to use a low sampling rate as described above in relation to Fig. 4. Then, the digital signal is converted to the frequency domain by an FFT unit 713 to obtain a plurality of subcarrier signals. An equalization unit 714 then performs equalization to obtain an estimated data symbol άκ·

In the embodiment illustrated in Fig. 8, the second device comprises an RF filter 811 which has a fixed bandwidth that is set to cover the full service band. The second device further comprises an ADC 812, FFT 814 and equalization unit 815 which perform similar functions to those described above in relation to Fig. 7. However, in the present embodiment the de-multiplexing is performed by a subband filter 813, after analogueto-digital conversion and before the frequency transformation. The passband of the subband filter 813, which operates at baseband, can be adjusted by changing the filter coefficients. In comparison with the embodiment of Fig. 7, the present embodiment has reduced cost and complexity since a low-complexity fixed RF filter 811 is used, and the tuneable RF filter 711 of Fig. 7 has a higher complexity than the subband filter 813. However, in this embodiment, the sampling rate of the ADC 812 should be set higher than that used in Fig. 7 since the ADC 812 has to cover a wider bandwidth, converting all analogue signals within the service band into the digital domain.

As described above, in some embodiments different services may use different subcarrier spacings. When different subcarrier spacings are used, the subcarriers in adjacent service bands may no longer be orthogonal, and may therefore interfere with one another. Interference between subcarriers in adjacent subbands can be referred to as inter-service-band-interference (ISBI). For example, an MTC service and a high data

-17rate service may use different subcarrier spacings and hence may interfere with each other. The interference level may depend on the subcarrier spacing difference between subbands. In some embodiments, a guard band may be inserted between subband to reduce interference between adjacent services with different subcarrier spacings.

However, inserting a guard band reduces the spectral efficiency of the system, by reducing the available bandwidth for data transmission.

In addition, interference between adjacent sub-bands may occur when upsampling is used. This type of interference can be referred to as inter-subband-interference (ISubBI), and can occur within the same service band.

Methods and apparatus for cancelling ISBI and ISubBI will now be described with reference to Figs. 9 and 10. The ISBI cancellation and ISubBI cancellation are both performed using baseband signal processing, either at the transmitter-end or the receiver-end. In the embodiments shown in Figs. 9 and 10, both ISBI and ISubBI cancellation is performed. However, in other embodiments one type of cancellation maybe performed without the other, depending on whether or not a particular device and/or the network as a whole will experience ISBI or ISubBI. In general only the subcarriers at edges of service bands may be significantly affected by ISBI, and so devices which are allocated subbands away from the edges of service bands may not suffer from ISBI. Similarly, a device may only suffer from ISubBI when the system only includes a single service and upsampling is applied to subbands within the service to reduce the complexity.

Referring now to Fig. 9, apparatus for applying ISBI and ISubBI pre-cancellation at a BS is illustrated, according to an embodiment of the present invention. In Fig. 9, certain elements of the BS are omitted to preserve clarity. The apparatus comprises an ISBI pre-cancellation unit 901 configured to apply a first precoding matrix to subbands at the edge of the first and second service bands before transmitting the multiplexed signal. The apparatus further comprises a plurality of precoding units 902, each of which is configured to apply a second precoding matrix to the data symbol to be transmitted on the plurality of subcarrier frequencies, prior to the time domain transformation by a time domain converting unit (not shown in Fig. 9). Methods of obtaining the first and second precoding matrices, denoted respectively by Pisbi and

PisubBi, will now be described.

-18Method for obtaining Ptsrt

Figure 9 illustrates an example of a generalized synchronized (GS) system comprising two service bands (service 1 and service 2) which are adjacent to each other in frequency, and which use different subcarrier spacings. Service bands 1 and 2 contain

Vi and V2 subbands, respectively. The last subband of service 1 (i.e., Vi-th subband of service 1) and the first subband of service 2 are adjacent subbands that have different subcarrier spacings to each other, and may therefore experience ISBI.

In the present embodiment, the first precoding matrix PISBI is obtained by first 10 determining the ISBI cancellation bandwidth, which is the number of subcarriers to be considered in the ISBI cancellation. In general terms the number of subcarriers in the Vi subband of service 1 can be defined as N_can,i and the number of subcarriers in the first subband of service 2 can be defined as N_can,2· The ISBI cancellation bandwidth can be set according to the subcarrier differences and guard band between two adjacent services, and the quality of service (QoS) requirements of the adjacent services. A suitable cancellation algorithm can also be selected, for example zero forcing (ZF) or minimum mean square error estimation (MMSE).

Next, the BS acquires all information necessary to calculate Pisbi, which may include channel and noise power information if MMSE-based cancellation is selected, filter coefficients, ISBI cancellation bandwidth, and any relevant system parameters such as subcarrier spacing, LCM symbol duration, and so on.

Figure 11 is a graph showing an improvement in the information symbol estimation

MSE versus subcarrier index when ISBI pre-cancellation is applied. Figure 11 illustrates the MSE of the symbol estimation for different bandwidths N_can for ISBI cancelation, specifically N_can = N_can,i = N_can,2 = 4, 8, and 20 subcarriers. In the present embodiment, an ISBI cancellation bandwidth N_can = 20 means that all subcarriers in the subbands are considered. When all subcarriers are taken into consideration for interference cancelation, the MSE at all subcarriers can reach noise power level.

Taking the frame structure illustrated in Fig. 1 as an example, the symbol durations in the first, second and third services can be denoted respectively by ΔΤ,, Δ75, and ΔΤ₃, and the width of the first, second and third service bands can be denoted respectively by Δ/i, Δή», and Δ/₃. The received signals of users 1 and 2 can be combined together as follows:

-19c_c =H_cEa_c +b_c where

H_c =Blkdiag{H_1Via//,H_21a//}

Hi.v, = Blkdiag{H_1Vi, N_syml}

Η^,αίί =Blkdiag{H₂₁,2V_sym2}

Here, H_ly denotes a sub-matrix obtained by taking the last N_can,i columns and rows of the channel matrix Ηι,η, H₂, denotes a sub-matrix obtained by taking the first N_can,2 columns and rows of the channel matrix H₂,i, and a_c is the considered information symbols vector for ISBI cancellation, expressed as:

^a = [^aiy, ,i ’ · · · ’ ^aiy, .NvmA > ^a2,i,i > · · · > ^a2.i.Nvmr2 f where ΰι,η,ί comprises the last N_can,i symbols of ai,yi,z for ISBI cancellation, given by:

^aiy_l,Z ~ kkr, ,Z (^1,½ — N can,\ — N can,\ ⁺ ^)’· · · ’ ^ai.V, ,i ~ l)J a₂,i,i comprises the first N_can,2 symbols of a₂,i,i for ISBI cancellation, given by:

^a2,l,i ^— [^Ω2,1,ί (θ)’ ^a2,i,i CO’ · · · ’ ^a2.l.i can.2 ~ 0] and b_c is the interference plus noise. In some embodiments all subcarriers may be considered in the cancellation algorithm, in which case N_can,i = Z^vi- A matrix E can be defined as follows:

E = f^E,J M

T²·¹ ^2,2 j where

- 20 Ϊ ^Ei,i = — BlkdiagfF,, N_sym4) Ay, ^E2,2 =— ^Blkdiag(^E2,P^_m,₂) Ay ^Ei,2 ^— Blkdiag(f)_{l v}, _2JVi ' [^2,1,1’·

P2.1 ^E2,i ^— Blkdiag(f)_212JV '

Ay with Fj _v being the sub-matrix obtained by taking the last N_can,i columns and rows of the filter response matrix Fi,yj, and F₂₄ being the sub-matrix obtained by taking the first N_can,2 columns and rows of the filter response matrix Fi,_w. G, _{v ;} is obtained by taking the [(i-i)L₂+i]-th to the i£₂-th rows of G_ly = Blkdiag(A_ly D_ly , N_sym4), and

Dj _v is obtained by taking the last N_can,i columns of Diyj. Similarly, G₂ j,. is obtained by taking the [(i-i)Li+i]-th to the i'Li-th rows of G₂₄ = Blkdiag(A₂₄D₂₄, A ₂), and D₂ j is obtained by taking the first N_can,2 columns of D₂₄.

This provides a complete signal model. In the downlink scenario, the precoding matrix

Pisbi for pre-cancelling the ISBI at the BS can be determined as follows:

A =H_cEP_/SB/a_c +b_c +v_c

A suitable method, such as a zero-forcing (ZF) or minimum mean square error (MMSE) method, can then be used to derive the optimal Pisbi. An MMSE-based precoding matrix may depend on channel state information and other interference, whereas a ZFbased precoding matrix may depend only on the filter design and other fixed systemrelated parameters. Accordingly, when ZF is used to determine the first precoding matrix Pisbi, the first precoding matrix Pisbi maybe calculated offline, that is, maybe calculated in advance to reduce the computational complexity. Therefore, in some embodiments a plurality of first precoding matrices for different system configurations may be calculated in advance and stored. Then, during use, the transmitter can simply

- 21 retrieve the appropriate stored pre-calculated first precoding matrix for the current system configuration and apply the retrieved precoding matrix to cancel the ISBI.

Although one approach for determining the first precoding matrix Pisbi has been 5 described above, it should be understood that this is merely one example, and in other embodiments the first precoding matrix may be determined using a different method.

Method for obtaining Ptsubbt

For downlink transmissions, ISubBI cancellation can be performed at the BS side by precoding the transmitting signals that belong to adjacent subbands. For uplink transmissions, ISubBI cancellation can be performed at the BS side by using joint detection across subbands to eliminate the interference by taking the advantage of the overall signal and channel information available to the BS. In the present embodiment, the ISubBI pre-cancellation matrix PisubBi is obtained using a similar method as that described above for obtaining Pisbi. First, the ISubBI cancelation bandwidth is determined. Then, the BS acquires all relevant information and calculates PisubBi according to the determined cancellation bandwidth.

Figure 12 is a graph showing the improvement in the information symbol estimation

MSE versus subcarrier index when ISubBI pre-cancellation is applied, in comparison to a system without ISubBI pre-cancellation applied. As shown in Fig. 12, the MSE of subcarrier after interference cancellation shows significant gain in comparison to a system without interference cancellation.

Taking the downlink scenario as an example, a method of determining the second precoding matrix PisubBi is as follows. The received signal y at the receiver after the FFT operation, but before channel estimation, can be written as:

y = TPa + y,,,. +y,._ci +v where

- 22 % ζ₂ Ο Ο Ο

Zj ζ_θ ζ₂ ο ο

Ο Zj ζ₀ ζ₂ ο

Ο ··· Ο Ο Zj Ζ_θ Ζ₂ _ΫΟ ··· Ο Ο Ο Zj Z_Oy

Ζ„ =G[^HlH_t.,F_t ^[wl + tG^'W^F?·'¹

Ζ, =0/-¾^¾^{10 11 * * * 15 * * * * 20 * * * * 25} -t-GWHjW ζ₂ =GWH_tFW +gS,h_uif£;'1

F/'¹ =diag(f_e ^MX G[l = diag(gW).and

H_t =diag(h₍)

Here, and gri'] respectively denote the k^th subband filter response at the m^th subband at the transmitter and receiver, h* denotes the channel frequency response at the k^th subband, and v, yisi and yid respectively denote the noise, inter-symbol interference and inter-carrier interference. The second precoding matrix, Pis.ibm, can then be determined using a suitable method, for example ZF or MMSE.

In the above-described method of determining the second precoding matrix Pisubm, T is a function of the channel. Accordingly, the second precoding matrix Pis.ibm or second detection matrix Disubsi may need to be recalculated for each received symbol, based on knowledge of the channel state information at the time the symbol was transmitted. To further reduce the computational complexity, in some embodiments a method of deriving the second precoding matrix Pis.ibm or second detection matrix

Disubsi may be used which does not rely on channel state information, allowing the second precoding matrix Pis.ibm and/or second detection matrix Disubsi to be calculated offline for various different system configurations and stored in memory.

For example, by assuming that the channel frequency selectivity is flat among the three considered subbands for ISubBI, the received signal y can be written as follows:

-23y = HTa + y_I,_; +y_ici +v where T has a similar structure to the example described above, but with Z_o, Zi and Z₂5 replaced respectively with Z_o, Zj, Z₂, where:

Zo ~ Η^Ζθ, z₁₌hX Zo ~ Η*Ζ₀ and — _|_ζΥΐλ]ρΐΑ] _|_ Q'h+ilp^h+i]

Z,

Z, =θ'ΥΜ -t-GMF'Y

This enables the second precoding matrix PisubBi and/or second detection matrix DisubBi to be calculated in advance without knowledge of the channel conditions.

Referring now to Fig. io, apparatus for cancelling ISBI and ISubBI in received uplink signals at a BS is illustrated, according to an embodiment of the present invention. The apparatus comprises an ISBI joint detection unit toot configured to perform joint detection over two adjacent subbands at the edges of adjacent service bands, based on a first detection matrix Disbi. The apparatus further comprises a plurality of ISubBI joint detection units 1002 each configured to perform detection based on a second detection matrix DisubBi. Disbi and DisubBi can be determined using a similar method to that described above for Pisbi and PisubBi, specifically, by determining the appropriate cancellation bandwidth, acquiring relevant information, and then calculating the detection matrix.

For example, the first detection matrix Disbi can be applied to an equalized signal c_c as follows:

-24^ac ^ISBI^Cc where a_c is the estimated signal for the considered frequency bandwidth. As with the first precoding matrix Pisbi, the first detection matrix Disbi can be determined based 5 on a suitable method such as ZF or MMSE. An MMSE-based detection matrix may depend on instantaneous channel and other interference, whereas a ZF-based detection matrix may only depend on the filter design and other fixed system-related parameters. Accordingly, in some embodiments a ZF-based first detection matrix Disbi can be calculated offline in advance to reduce the computational complexity. As with the first precoding matrix, in some embodiments a plurality of first detection matrices for different system configurations may be calculated in advance and stored. Then, during use, the receiver can simply retrieve the appropriate stored pre-calculated first detection matrix for the current system configuration and apply the retrieved detection matrix to cancel the ISBI.

In uplink transmission, individual devices that belong to different types of services may not be able to communicate with one another and so may not be able to cooperate in order to pre-cancel the ISBI. Therefore uplink signals transmitted by the devices at the edges of adjacent service bands which use different subcarrier spacings may suffer from

ISBI. However the BS may have access to the information required to cancel the ISBI during symbol detection. In the present embodiment, the ISBI cancellation in received signals is performed after channel equalization, as shown in Fig. 10.

As explained above, ISubBI may occur when signals transmitted on adjacent subbands are generated using different sampling rates. Like ISBI, ISubBI only affects adjacent subbands. For example, subbands 1, 2 and 3 can denote three adjacent subbands in the same service band, which use different sampling rates. Subband 2 will cause ISubBI in subbands 1 and 3 and will experience ISubBI from subbands 1 and 3. However, subband 1 may not cause any significant ISubBI in subband 3 since the two subbands are not adjacent to one another. The second detection matrix DisubBi can be configured to compensate for interference in one subband that is introduced by the adjacent subbands on either side.

As an example, in the uplink scenario the second detection matrix DisubBi at the receiver can be determined as follows:

-25^a,,₇ = ϋ/Μ,/,/,νΥ = O_ISubBI (Ta + y_isi + y_/c/ + v)

Whilst certain embodiments of the invention have been described herein with reference 5 to the drawings, it will be understood that many variations and modifications will be possible without departing from the scope of the invention as defined in the accompanying claims.

Claims

Claims

1. A method of transmitting data in a wireless communication network, the method comprising:

5 transforming a plurality of data symbols to be transmitted on a plurality of subcarrier frequencies within a frequency subband into a time domain multicarrier signal;

selecting an appropriate upsampling rate for the time domain multicarrier signal;

io upsampling the time domain multicarrier signal at the selected upsampling rate;

filtering the upsampled signal to remove upsampling images; and transmitting the filtered upsampled signal over a wireless communication channel.
2. The method of claim l, wherein a plurality of time domain multicarrier signals are obtained for a plurality of frequency subbands, and a different upsampling rate is selected for at least two of the time domain multicarrier signals.

20
3. The method of claim 2, wherein the at least two time domain multicarrier signals each have a different sampling rate before upsampling, and the upsampling rates for the at least two time domain multicarrier signals are selected so that the at least two upsampled signals have the same sampling rate, the method further comprising:

25 combining the at least two upsampled signals to obtain a multiplexed signal.
4. The method of claim l, 2 or 3, further comprising:

receiving sampling rate information from the wireless communication network, wherein the upsampling rate is selected in accordance with the received

30 sampling rate information.
5. The method of claim 2,3 or 4, wherein the plurality of frequency sub-bands are arranged into a plurality of service bands each comprising one or more of the subbands, the plurality of service bands including a first service band configured to use a

35 first subcarrier spacing and a second sendee band configured to use a second subcarrier spacing different to the first subcarrier spacing, the method further comprising:

-2ηobtaining a first precoding matrix configured to compensate for interference between the first and second service bands due to the different subcarrier spacings; and applying the first precoding matrix to sub-bands at the edge of the first and second service bands, before transmitting the filtered upsampled signal.
6. The method of any one of claims 2 to 5, further comprising:

obtaining a second precoding matrix configured to compensate for interference between the at least two of the time domain multicarrier signals due to the upsampling; and

10 applying the second precoding matrix to the data symbol to be transmitted on the plurality of subcarrier frequencies, prior to the time domain transformation.
7. A method of receiving data in a wireless communication network, the method comprising:

15 receiving a signal over a wireless communication channel;

selecting a first sampling rate;

converting the received signal to a digital signal at the selected first sampling rate;

transforming the digital signal from the time domain into a plurality of 20 frequency-domain subcarrier signals; and performing equalization on the frequency-domain subcarrier signals to obtain an estimated data symbol.
8. The method of claim 7, wherein converting the received signal to the digital 25 signal at the first sampling rate comprises:

converting the received signal to a digital signal at a second sampling rate higher than the first sampling rate; and downsampling the digital signal to the first sampling rate, wherein the transforming and equalization steps are performed on the

30 downsampled digital signal.
9. Apparatus for transmitting data in a wireless communication network, the apparatus comprising:

a time domain conversion unit configured to transform a plurality of data 35 symbols to be transmitted on a plurality of subcarrier frequencies within a frequency subband into a time domain multicarrier signal;

- 28 an upsampling unit configured to upsample the time domain multicarrier signal, wherein the apparatus is configured to select an appropriate upsampling rate for the time domain multicarrier signal;

a subband filter configured to filter the upsampled signal to remove upsampling 5 images; and one or more antennas configured to transmitting the filtered upsampled signal over a wireless communication channel.

io. The apparatus of claim 9, further comprising:
10 a plurality of time domain conversion units each configured to obtain a plurality of time domain multicarrier signals for a plurality of frequency sub-bands, by transforming a plurality of data symbols to be transmitted on a plurality of subcarrier frequencies within each sub-band into a time domain multicarrier signal;

a plurality of upsampling units each configured to upsample one of the plurality 15 of time domain multicarrier signals, wherein at least two of the plurality of upsampling units are configured to use a different upsampling rate; and a plurality of sub-band filters each configured to filter one of the plurality of upsampled signals to remove upsampling images.

20
11. The apparatus of claim 10, wherein the time domain multicarrier signals upsampled by said at least two upsampling units each have a different sampling rate before upsampling, and the upsampling rates for said at least two upsampling units are selected so that the upsampled signals outputted by said at least two upsampling units have the same sampling rate, the apparatus further comprising:

25 a multiplexing stage configured to combining the at least two upsampled signals to obtain a multiplexed signal.
12. The apparatus of claim 10 or 11, wherein the plurality of frequency sub-bands are arranged into a plurality of service bands each comprising one or more of the sub30 bands, the plurality of service bands including a first service band configured to use a first subcarrier spacing and a second sendee band configured to use a second subcarrier spacing different to the first subcarrier spacing, wherein the apparatus is configured to obtain a first precoding matrix configured to compensate for interference between the first and second service bands

35 due to the different subcarrier spacings, and further comprises:

-29an inter-service-band interference pre-cancellation unit configured to apply the first precoding matrix to sub-bands at the edge of the first and second service bands before transmitting the filtered upsampled signal.

5
13. The apparatus of claim 10,11 or 12, wherein the apparatus is configured to obtain a second precoding matrix configured to compensate for interference between the at least two of the time domain multicarrier signals due to the upsampling, and further comprises:

a precoding unit configured to apply the second precoding matrix to the data 10 symbol to be transmitted on the plurality of subcarrier frequencies, prior to the time domain transformation.
14. Apparatus for receiving data in a wireless communication network, the apparatus comprising:
15 one or more antennas configured to receive a signal over a wireless communication channel;

signal conversion apparatus configured to convert the received signal to a digital signal at a first sampling rate selected by the apparatus;

a frequency domain conversion unit configured to transform the digital signal 20 from the time domain into a plurality of frequency-domain subcarrier signals; and an equalization unit configured to perform equalization on the frequencydomain subcarrier signals to obtain an estimated data symbol.

15. The apparatus of claim 14, wherein the signal conversion apparatus comprises:

25 an analogue to digital converter configured to convert the received signal to the digital signal at a second sampling rate higher than the first sampling rate; and a downsampling unit configured to downsample the digital signal to the first sampling rate and send the downsampled digital signal to the frequency domain conversion unit.
16. A wireless communication network comprising:

a transmitting apparatus comprising the apparatus of any one of claims 10 to 13; a first receiver comprising the apparatus of claim 15; and a second receiver comprising the apparatus of claim 14.

-3017· The wireless communication network of claim 16, wherein the transmitting apparatus is configured to transmit bandwidth information to the second receiver, the bandwidth information defining a frequency band allocated to the second receiver, and wherein the second receiver comprises a tunable bandpass filter, and the second

5 receiver is configured to tune the bandpass filter to select the allocated frequency band.
18. The wireless communication network of claim 17, wherein the tunable bandpass filter is a tunable analogue filter with a fixed bandwidth, such that the allocated frequency band is selected before the received signal is converted from analogue to

10 digital.
19. The wireless communication network of claim 17, wherein the tunable bandpass filter is a tunable baseband filter with a fixed bandwidth, and the second receiver further comprises:

15 an analogue bandpass filter configured to filter the received signal with a passband width equal to or greater than a bandwidth of a service band which includes the allocated frequency band, wherein the second receiver is configured to convert the filtered analogue signal to a baseband digital signal at the first sampling rate, and pass the baseband digital
20 signal through the tunable baseband filter to select the allocated frequency band.

Intellectual

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Application No: GB 1620293.9