WO2009056482A2

WO2009056482A2 - Signal processor for selectively performing spectral shaping

Info

Publication number: WO2009056482A2
Application number: PCT/EP2008/064363
Authority: WO
Inventors: Iikka Urvas
Original assignee: Nokia Corporation
Priority date: 2007-10-30
Filing date: 2008-10-23
Publication date: 2009-05-07
Also published as: WO2009056482A3; GB0721305D0

Abstract

A signal processor comprising means for determining if a signal to be transmitted requires spectral shaping; and means for providing spectral shaping only if said determining means determines that said signal to be transmitted requires spectral shaping, wherein a delay of the signal to be transmitted when said spectral shaping means provides spectral shaping is substantially the same as the delay of a signal to be transmitted when no spectral shaping is provided.

Description

A TRANSMITTER Field of the invention

The present invention relates to a transmitter and to a method of processing a signal for transmission. The present invention also relates to a signal processor for processing a signal for transmission.

Background of the Invention

A communications system is a facility which facilitates communication between two or more entities such as communication devices, network entities and other nodes. A communication system may be provided by one or more interconnect networks. It is noted that although a communications system typically comprises at least one communication network, for example a fixed line network or a wireless or mobile network, in its simplest form a communications system is provided by two entities communicating with each other. The communication may comprise, for example, communication of data for carrying communications such as voice, electronic mait (email), text messages, multimedia and so on. A user may communicate by means of an appropriate communication device.

An appropriate access system allows a communication device to access a communications system. An access to the communications system may be provided by means of a fixed line or wireless communication interface, or a combination of these. Examples of wireless access systems include cellular access networks, various wireless local area networks (WLANs), wireless personal area networks (WPANs), satellite-based communication systems and various combinations of these.

A communications system typically operates in accordance with a standard and/or certain specifications and protocols which set out what the various elements of the system are permitted to do and how that should be achieved. For example, it is typically defined if the user, or more precisely a user device, is provided with a circuit switched bearer or a packet switched bearer, or both. Also, the manner in which communication and various aspects thereof should be implemented between the user device and the various elements of the communication and their function and responsibilities are typically defined by a predefined communication protocol.

Typically, wireless communication transmitters have tight requirements for the spectral shape of a transmitted signal in order to obtain high data transmission speeds with as small a usage of the radio spectrum as possible. Typically, the minimum requirements of the shape of the spectrum are governed by a particular standard and must be fulfilled by any transmitter operating in accordance with that standard.

In the case of a mobile phone, the transmitted spectrum shaping is implemented in the digital baseband part using integrated circuit technology. Depending on the requirements of the particular standard in question, the spectrum shaping filters may have tight requirements for the spectral shape of the transmitted signal. This results in a complex filter structure with a significant power consumption.

For example, in the proposed E-UTRAN (evolved UMTS (universal mobile telecommunications system) terrestrial radio access network) implementation, the integrated circuit requires a complex digital transmit filter to provide the spectrum shaping required by the standard.

Known systems such as GSM (global system for mobile communications) and WCDMA (wideband code division multiple access) use spectrum shaping. For example, in WCDMA, the spectrum shaping is required as it affects the received signal.

EP1737134 describes a communication device which is used in a communication system. The communication device has a detector for detecting an interfering signal. In response to that detection, transfer characteristics of a shaping filter are modified.

US 20070183520 discloses techniques for performing spectra! shaping to achieve a desired peak-to-average ratio. !t is an aim of one or more embodiments of the present invention to address or at least mitigate one or more of the problems discussed above.

Summary of invention

According to one aspect of the present invention, there is provided a signal processor comprising means for determining if a signal to be transmitted requires spectral shaping; and means for providing spectral shaping only if said determining means determines that said signal to be transmitted requires spectral shaping wherein a delay of the signal to be transmitted when said spectral shaping means provides spectral shaping is substantially the same as the delay of a signal to be transmitted when no spectral shaping is provided,

According to a further aspect of the present invention, there is provided a signal processor comprising a filtering arrangement; means for determining if a signal to be transmitted requires filtering by said fiitering arrangement; control means for controlling the filtering arrangement such that if said determining means determines that said signal to be transmitted does not require fiitering, at least part of said filtering arrangement is bypassed.

According to another aspect of the present invention, there is provided a signal processor comprising a filtering arrangement; means for determining if a signal to be transmitted requires filtering by said filtering arrangement; control means for controlling the filtering arrangement such that if said determining means determines that said signal to be transmitted does not require filtering, at least part of said filtering arrangement is switched off.

According to a further aspect of the present invention, there is provided a signal processor comprising a controiler configured to determine if a signal to be transmitted requires spectral shaping; and a spectral shaping filter configured to provide spectral shaping only if said controiler determines that said signal to be transmitted requires spectral shaping, wherein said processor is configured such that a delay of the signal to be transmitted when said spectral shaping filter provides spectral shaping is substantially the same as a delay of a signal to be transmitted when no spectral shaping is provided.

According to another aspect of the present invention, there is provided a signal processor comprising a filtering arrangement; and a controller configured to determine if a signal to be transmitted requires filtering by said filtering arrangement and to control the filtering arrangement such that if the controller determines that said signal to be transmitted does not require filtering, at least part of said filtering arrangement is bypassed,

According to another aspect of the present invention, there is provided a signal processor comprising a filtering arrangement; a controller configured to determine if a signal to be transmitted requires filtering by said filtering arrangement and to control the filtering arrangement such that if said controller determines that said signal to be transmitted does not require filtering, at least part of said filtering arrangement is switched off.

According to another aspect of the present invention, there is provided a method comprising determining if a signal to be transmitted requires spectral shaping; and providing spectral shaping only if the determining determines that said signal to be transmitted requires spectral shaping, wherein a delay of the signal to be transmitted when said spectral shaping is provided is substantially the same as the delay of a signal to be transmitted when spectral shaping is provided.

Brief Description of the Drawings

For a better understanding of the present invention and as to how the same may be carried into effect, reference will now be made by way of example only to the accompanying drawings in which:

Figure 1 shows a schematic representation of a communications system in which embodiments of the present invention may be used;

Figure 2 shows a transmitter in which embodiments of the present invention may be incorporated; Figures 3a and b show in detail first and second embodiments of the spectra! shaping filtering arrangement;

Figure 4a and b shows a graph illustrating a E-UTRAN 5MHz signal with partial bandwidth usage; Figures 5a and b show an alternative spectral shaping filtering arrangement usable in the transmitter of Figure 2;

Figure 6 shows the impulse response of the filter of Figure 5, when the filter is on;

Figure 7 shows the impulse response of the filter of Figure 5 when deactivated; and

Figure 8 shows a further spectral shaping filter arrangement.

Detailed Description of Preferred Embodiments of the Present Invention

Before explaining in detail a few exemplifying embodiments, a brief explanation of the general principles of wireless communications in a system comprising a base station and a communication device such as mobile station is given with reference to Figure 1.

A communication device, for example a user device, can be used for accessing various services and/or applications provided via a communications system. In wireless or mobile systems the access is provided via an access interface between a user device 1 and an appropriate wireless access system. The user device can typically access wirelessly a communication system via at least one base station 10 or similar wireless transmitter and/or receiver node via a wireless connection 11. Non-limiting examples of access nodes are a base station of a cellular system and a base system of a wireless local area network (WLAN). Each user device may have one or more radio channels open at the same time and may be connected to more than one base station.

The base station may be connected to other system, for example, a data network 12. A gateway function between a base station node and other network may be provided by means of any appropriate gateway node 14, for example a packet data gateway and/or an access gateway. A base station is typically controlled by at least one appropriate controller entity 16. The controller entity can be provided for managing of the overall operation of a base station and communications via the base station. The controller entity is typically provided with memory capacity and at least one data processor. Functional entities may be provided in the controller by means of a data processing capability thereof, The functional entity provided in the base station controller may provide functions relating to radio resource control, access control, packet data context control and so forth.

Certain embodiments of the present invention can be used in the long term evolution (LTE) radio system. This system provides an evolved radio access system that is connected to a packet data system. Such an access system may be provided, for example, based on architecture that is known from the E-UTRA (evolved UMTS terrestrial radio access) and based on the use of the E-UTRAN node Bs (eNBs). An E-UTRAN consists of E-UTRAN node Bs which are configured to provide base station and control functionalities. For example, the eNBs nodes can provide independently radio access network features such as user plane radio link control/medium access control/physical layer control and control plane radio resource control RRC protocol terminations towards the user devices.

It is noted that Figure 1 shows this architecture only to give an example of a possible communications system where the embodiment described below may be provided and that other arrangements and architectures are also possible. For example, the user device may communicate with a different access system.

The user device 1 can be used for various tasks such as making and receiving phone calls, for receiving and sending data from and to a data network and for experiencing, for example, multimedia or other content. For example, a user device may access data applications provided by a data network. For example, various applications may be offered in a data network that is based on the internet protocol (IP) or any other appropriate protocol. An appropriate user device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS), a portable computer provided with a wireless interface card or other wireless interface faculty, personal data assistant (PDA) provided with wireless communication capabilities, or any combination of these or the like.

A mobile device may communicate by an appropriate radio interface arrangement of the mobile device. The interface arrangement may be provided for example by means of a radio part 7 and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

A mobile device is typically provided with at least one data processing entity 3 and at least one memory 4 for use in tasks such as it is designed to perform. The data processing and storage entities can be provided on an appropriate circuit board, on an integrated circuit and/or in chip sets. This is denoted by reference 6.

Also shown is a modulator component 9 connected to the other elements. It should be noted that the modulator functions may be arranged to be provided by the data processing entity 3 instead of by a separate component.

The user can control operation of the mobile device by means of a suitable user interface such as a keypad 2, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 5, a speaker and a microphone are also typically provided. Furthermore, a mobile device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands free equipment thereto.

Reference is now made to Figure 2 which shows in more detail a transmitter. The transmitter shown in Figure 2 is incorporated in the user device 2. However, it should be appreciated that the transmitter can be incorporated in any other suitable device, for example the node B or base station. The transmitter shown in Figure 2 is used in an E-UTRAN system and provides spectrum shaping. Symbol generator 100 is responsible for generating the baseband signal. The baseband signal output by the symbol generator 100 is input to a prefix block 101 which adds a cyclic prefix to the baseband signal received from the symbol generator 100.

As will be described in more detail, the output of the cyclic prefix box 101 is optionally subjected to spectrum shaping by spectrum shaping block 102. This will be described in more detail afterwards.

The signal which has optionally been subjected to spectrum shaping is input to the digital to analog converter 103. The digital to analog converter 103 converts a signal from the digital domain to the analog domain.

The analog signal is output by the digital to analog converter 103 to a low pass filter 104 which filters the received signal. The function of this low pass filter 104 is to remove spurious responses or signals caused by the digital to analog converter 103.

The filtered signal is input into an IQ modulator 105. The IQ modulator 105 converts the baseband signal to the required radio frequency. To achieve this, the

IQ modulator 105 receives a radio frequency signal from an RF oscillator 109.

The modulated I and Q RF signals are output by the IQ modulator 105 to a power amplifier 106 which amplifies the RF signal to the desired output power level. As will be discussed later, this may cause spectral spreading due to intermodulation products.

The amplified signal is input to an RF filter 107 which removes wideband interference such as noise.

The filtered output is input to the transmit antenna 108 which transmits the signal.

Controller 110 is arranged to control the spectrum shaping as will be described in more detail later. The amplification provided by the power amplifier 106 is controlled by the transmission power controller 1 11. The power controller 111 is arranged to provide an output not only to the power amplifier 106 but also to the controller 110. The controller 1 10 is arranged to provide an input to the spectrum shaping block 102 and to receive inputs from the symbol generator 100.

As mentioned, one embodiment of the invention described is in the context of an E-UTRAN mobile transmitter although embodiments of the invention may be applicable to some other standards. The E-UTRAN transmitter has several variable parameters that affect the spectral shape of the modulated signal. The spectral shape filtering, such as woufd be provided by the spectral shaping filter 102 is necessary for the transmitter in order to meet the spectrum emission mask requirements at the output of the transmitter, that is at the antenna. It has been appreciated by the inventor that there are a limited number of cases where the signal properties are such that the spectral shaping is actually required.

Embodiments of the present invention are arranged such that spectral shaping is used only when necessary. In some situations, mostly, the spectral shaping is not required. Accordingly, in the embodiment illustrated in Figures 2 and 3, the spectral shaping filter can be effectively bypassed and thus, power consumption can be reduced.

In one example, the E-UTRAN transmitter has a 5MHz operating band. The transmit bandwidth of the modulated signal is limited to 90% of the operating band, that is 4.5MHz. This is divided into 25 resource blocks that are 18OkHz wide. The bandwidth can be divided between ail mobile transmitters based on the amount of traffic and capacity needed by each user so that a single user can use from 1 up to 25 adjacent resource blocks at a given time. The allocation of the resource blocks for a user can change dynamically, in one example, the allocation of the resource blocks can change between transmitted frame pairs, that are 10 ms iong.

The need for spectral shaping may be determined by the spectrum emission mask and adjacent channel leakage ratio specifications. There are two contributions to the out of band unwanted spectral components in an E-UTRAN uplink transmitter: 1) the so-called SINC (sine cardinal) response of the signal caused by the discontinuities between the transmitted symbol and 2) the intermodulation caused by the power amplifier. The spectral shaping filter is attenuating a spectral spreading caused by the discontinuity between the symbols in the time domain, As the spectral shaping takes place before the power amplifier, it is not possible to filter the intermodulation results. Typically, the power amplifier operation becomes more non-linear at high power levels which results in higher intermodulation products. The spectral shaping is designed so that the baseband signal is clean enough to provide an output signal that fulfils a specification after the power amplifier, that is after the signal has been amplified by the power amplifier.

The power amplifier may be the main distortion source in some embodiments, but other components in the radio frequency path may alternatively or additionally generate intermodulation components. Typically the power amplifier intermodulation contribution is larger than the rest. However embodiments of the invention are able to leave more margin for the power amplifier distortion by removing unwanted spectral components. If the baseband distortion level is clearly below the intermodulation it will not significantly contribute thus leaving more room for power amplifier nonlinearity.

The strength of the output signal provided by the power amplifier can be controlled by changing the power level of the input signal to the power amplifier and/or by changing the gain provided by the power amplifier. At high input and output power levels intermodulation products occur.

In those cases, where the spectrum emission mask is likely to be exceeded, spectral filtering can be provided. This would particularly occur in those circumstances where the power amplifier may be providing a high transmit power, that is where the power amplifier is not operating in a linear mode.

Reference is now made to Figure 3a which shows the principles of the operating of the spectral shaping filter.

The controller 110 is arranged to receive information from the symbol generator 100 indicating which resource blocks will be transmitted in the next symbol. The transmit power controller 1 1 1 provides information to the control logic as to the signal level required by the output of the power amplifier. In other words, it provides information as to output power provided by the power amplifier 106. This allows a determination as to whether or not the power amplifier is likely to be operating in a linear or non linear manner. The controller 1 10 uses this information which it has received in order to determine whether or not spectral shaping is required.

In one embodiment, the controller 1 10 is provided with a lookup table. In an alternative embodiment of the present invention, the coπtro! logic may execute an algorithm or carry out a calculation which provides an indication as to whether or not spectral shaping filtering is required. Thus, the control logic is able to determine if the combination of the transmitted resource blocks requires spectral shaping to meet the specification at the used output power level.

Thus one method is to estimate the transmitted spectrum based on the information of the transmitted signal characteristics such as one or more of the bandwidth, frequency allocation and power level. These are the most significant parameters in some embodiments. However in alternative embodiments of the invention one or more other parameters may additionally or alternatively be considered.

!n addition, or alternatively information about the intermodulation product generation of the power amplifier may be used. This information may for example be obtained from a look up table using for example output power level of the power amplifier as an input to the look up table.

In addition or alternatively, the decision as to whether to apply spectra! shaping filtering can use the bandwidth of the modulated signal, its centre frequency, or the frequency range of the modulated signal from X to Y Hz. Alternatively or additionally, the minimum and maximum frequency of the modulated signal could be used, allowing for gaps in the bandwidth.

One alternative method is to measure the output spectrum after the power amplifier and make the decision as to whether or not to filter based on that. In one alternative embodiment, feedback is obtained from the base station indicating if spectrum shaping is required.

It should be appreciated that there are several possible parameters in the output signal that might be used to select whether to use the spectral shaping or not. Examples of parameters are the frequency allocation, power level and the modulation of the signal. Additionally there are issues related to the power amplifier in order to improve its performance. It has already been discussed that the intermodulation depends on performance of the power amplifier as a function of the output power. In digital modulation the signal power is not constant but there are peaks in the time domain. The higher the peak-to-average ratio (PAR) of the signal, the more intermodulation results are reproduced when driven into a nonlinear device like the power amplifier. Clipping is a technique to reduce the PAR of the signal in a controlled manner so that the PA requirements can be reduced. The clipping typically has an impact on the spectrum shape so it could be one parameter that affects the decision if spectrum shaping is required. Clipping can be used in base stations or mobile stations. Accordingly in some embodiments of the invention, a signal clipper may be provided to carry out clipping.

Based on the information discussed previously, in one embodiment of the invention, the controller 110 sends a control word or signal to the spectral shaping block. If spectra! shaping is not required, the spectral shaping filter shuts down the filter and bypasses it. If needed, the spectral shaping filter is used. As shown in Figure 3a₍ the spectral shaping filter comprises a spectral shaping filter 1 12, a switch 1 13 and a bypass path 1 14. The output of the cyclic prefix block 101 (not shown) is input to the spectral shaping filter 102. The position of the switch 1 13 is controlled by the output of the controller 110.

When the switch is in a first position, as shown in Figure 3a, the output of the cyclic prefix block 101 is connected to the bypass path 1 14 and accordingly bypasses the spectral shaping filter 112. However, when the switch 113 is controlled by the output of the controller 1 10 to be in a second position in which the switch is connected to the output of the spectral shaping filter 112, the output of the cyclic prefix block 101 is input to the spectral shaping filter 1 12, the output of which is connected to the digital to analog converter.

It should be appreciated that the switch 113 shown in Figure 3a can be an electronic switch.

In some embodiments of the present invention, a transition from spectral shaping being off to spectral shaping being on and vice versa may create a discontinuity in the transmission. In some embodiments of the invention, here is a need to compensate for a delay differences caused by switching on and off the filter. In embodiments of the present invention, the spectral shape filter can be controlled in order to mitigate this effect.

Reference is now made to Figure 3b which shows an alternative to the embodiment of Figure 3a. Those elements which are the same as in Figure 3a are marked with the same reference numerals. As with the embodiment of Figure 3a, a controller 110, a symbol generator 100 and a transmit power controller 111 are provided,

In this embodiment, the spectral shaping filter 102 comprises a spectrum shaping filter 112, a delay element 1 13, a sealer 1 14 and a multiplexer 1 15. The output of the symbol generator 100 is input both to the spectral shaping filter 1 12 and the delay element 113. It should be appreciated that the output of the symbol generator 100 will be via the cyclic prefix block 101 (not shown) to the spectral shaping filter 1 12 and the delay element 113.

The output of the delay element 113 is input to the sealer 114. The output of the spectrum shaping filter 112 and the output of the sealer 114 are input to the multiplexer 115 which outputs the signal received from one of the spectrum shaping filter 1 12 and the sealer 114. The controller 110 provides control signals to each of the delay element 113, the sealer 1 14, the spectrum shaping filter 112 and the muitiplexer 115. The bypass path is thus provided by the delay element and the scaler 1 14. Thus, the filter path has the same delay as the bypass path. The sealer 1 14 provides the same gain as the filter. The controller 110 can turn on and off on the one hand the spectral shaping filter 1 12 and on the other hand the delay element 1 13 and the scaler 114 typically so that if one path is on then the other path is off. Thus either the spectral filter is on or the delay element 1 13 and the scaler 114 is on. The multiplexer 115 is controlled to select data from the active path.

Reference is now made to Figures 5a and b which show a modification to the arrangements shown in Figure 3a and b. Figure 5a shows the normal mode whilst Figure 5b shows the power saving mode. Referring to Figures 5a and b, this shows a spectral shaping FIR (finite impulse response) filter 300 with 2N-1 taps. The filter 300 comprises 2N-1 delay elements 302. The first delay element 302 receives the input signal. The output of each delay element 302 (except for the last delay element) connects to the input of the next delay element 302. The output of each of the delay elements are connected to the input of a respective multiplier 304. Each multiplier 304 also receives a respective filter coefficient C input from block 303. Each coefficient has a separate value that may correspond to a respective impulse response shown in Figure 6. The output of each multiplier 304 represents a tap and is input to an adder 305. The adder 305 provides a summed output 306 of each of the outputs of the multipliers 304. .

Reference is now made to Figure 5b which shows the configuration of the same filter as shown in Figure 5a but in the power saving mode. The input to the filter is referenced 401 , In this mode, the input signal passes only through N of the delay elements 302, with the remaining delay elements being bypassed. The output 405 is taken from the multiplier 304 associated with the Nth delay element 302. Block 303 represents the multiplier coefficient used, corresponding to the center tap of the normal mode (but the coefficient value is typically not the same),

In a practical implementation the normal mode and power save mode can be a single filter that is reprog rammed and the unnecessary elements are shut down. In an alternative embodiment, Figure 5a represents a normal path and Figure 5b represents an additional path which is used in the power save mode. In this modification, it is an aim so that the delay of the signal is not changed as compared to when the filter is turned on/off or off/on.

In order to avoid delay changes of the signal in the filter when changing state (i.e. switching the filter on or off) in this modification, most of the functionality of the filter is turned off, rather than bypassing the entire structure.

When the filter is in the partially deactivated state, in this example of a 2N-1 tap filter, the first N delay elements remain operational. In other words, the signal is input to the first delay element 302. The signal is then output by the first delay element 302 to the input of the next delay element 302 and so on for the first N blocks. It should be appreciated that the other elements of the first N blocks, that is the multiplier, the coefficient block and the output are not functional. The centre multiplier, that is the multiplier 304 of the Nth block remains functional. However, the filter coefficients can be scaled so that when the spectral shaping is off the multiplier coefficient is 1. In other words, the coefficient provided would be 1 in this option so there would be no multiplication required in this state. The remaining blocks are switched off completely and are effectively bypassed. Thus, the output of summer would be the single output from the multiplier 304 of the Nth block 302.

Reference is made to Figure 6 which shows the impulse response provided by the filter of Figure 5a, that is when the spectral shaping is on. In other words, each of the impulse response samples shown in Figure 6 represents the output of one of the taps. In this example, after the convolution of the signal and the filter impulse response the signal energy will be concentrated around the centre tap so the delay experienced in the filter is 13 samples. By way of example only, Figure 6 shows 25 taps.

Figure 7 shows the corresponding Figure to that of Figure 6 but for the filter arrangement in the off state. The delay of the signal is equal to that of the on state, that is N delay elements. The taps are scaled so that the signal power remains the same in both filters. In one embodiment, the off state centre tap maybe scaled to 1 so that there wϋl be no need for multiplication when the filter is off. The centre tap multiplier may be used only in the on state. As shown in Figure 7, there is a single tap corresponding to the Nth block 302.

It should be appreciated that the size of the filter, that is a 2N-1 tap FIR filter is given by way of example only and that any other suitably sized filter can of course be used in embodiments of the present invention. In the modification shown in

Figure 5, the signal energy is shown as being centred on the centre tap. It should be appreciated that in alternative embodiments of the present invention, the filters can be designed so that the energy is not provided by a central tap but to one side. In such a modification, the number of delay elements used would correspond merely to where the filtered signal is concentrated. This may be the centre tap but for asymmetric FIR filters, this may be a different tap

In some embodiments of the invention, it may be possible to control the length of the delay path used. This may be controlled by the controller.

Embodiments of the present invention provide an advantage that the spectral shape filter is turned off or at least partially deactivated. The spectral shaping filter may increase the impulse response of the transmitted signal. If the impulse response of the spectrum shaping filter is relatively long compared to the cyclic prefix, the spectral shaping filter may cause intersymbol interference that reduces the data transfer performance. This problem is reduced as the spectrum shaping filter is used only when necessary.

In the described embodiments, the delay provided when spectral shaping is not performed is shown as being in parallel to the spectral shaping path. In alternative embodiments of the invention, it is possible to provide the delay compensation in a different location in the transmission chain.

An example of such an alternative is shown in Figure 8. For convenience those elements that are the same as in previous embodiments are referenced by the same number. The output of the symbol generator 100 is input both to a delay element 113 and a multiplexer 116. The output of the delay element 113 is aiso input to the multiplexer 1 16. The output of the multiplexer 116 is input to function unit 117. The output of function unit 117 is input both to the spectrum shaping filter 112 and the sealer 1 14. The output of the spectrum shaping filter as well as the output of the sealer 114 is input to a multiplexer 115. The delay is separated from the spectrum shaping by the functionality of block 117. Thus, the input signal comes from, for example, the cyclic prefix block to the input of the multiplexer 116 as well as the delay element 113, The block 117 performs the associated function. This function can be any suitable function required by the system. If spectrum shaping is required, then the control logic 1 10 selects the direct input to the multiplexer 116 and the input to the multiplexer 1 15 from the spectrum shaping filter. When the spectrum filtering is changed from being on to off, a delay element 113 is used. The delay element is optionally used all the time with its output not selected by the multiplexer 116 when spectrum filtering is carried out. Preferably the delay element is switched off when the spectrum shaping filter is used.

When spectrum shaping is not required, the multiplexer 116 selects the output of the delay element 113 whilst the second multiplexer 1 15 selects the input from the sealer 114. This spectrum shaping filter is preferably switched off. It should be appreciated that when changing from on to off, it is necessary to load values to the delay element. Likewise, when changing from the spectrum filtering being off to on, the spectrum shaping filter needs to be loaded, that is turned on so that its delay elements are loaded with data. Only at that point would the delay element 113 and the sealer 114 be shut down.

It should be appreciated that this alternative embodiment is only one other alternative and various other options for the location of the delay element and the spectrum shaping filter may be used in embodiments of the invention.

Reference is now made to Figures 4a and 4b which illustrate how the need for spectrum shaping fitter is determined by the allocation of signal bandwidth and the location thereof. The power level of the signal i.e. the PA output power is such that reducing the output power could be considered as shifting the spectrum down so there would be more margin to the mask. Figure 4b shows a close up of region 208 of Figure 4a.

As shown by line 202, there is an output spectrum with eight edge resource block transmission, with the spectrum shaping filter off, As compared to the spectrum emission mask 206, the spectrum emission mask is not breached.

As shown by line 200, there is an output spectrum with one edge resource block transmission and spectrum filtering off. The spectrum mask 206 is breached.

As shown by line 204, there is an output spectrum with one edge resource block transmission and spectrum filtering on. The spectrum mask 206 is now not breached.

Thus in some situations, even without the power amplifier intermodulation results, spectrum shaping may be required under certain conditions. This may depend on the allocated signal bandwidth and its frequency allocation.

It should be appreciated that whilst embodiments of the present invention have been described in relation to a transmitter and user devices, such as mobile stations and network devices such as base stations, embodiments of the present invention are applicable to any other type of apparatus suitable for data communication where spectral shaping is required some but not all of the time.

It is also noted that although certain embodiments have been described by way of example with reference to certain exemplifying architectures for wireless networks, technologies and standards, embodiments maybe applied to any other suitable form of communication systems and may be at least partially implemented by a computer program.¹ For example, the function provided by the controller 110 may be provided by a computer program running on a suitable processor or the like.

It is also noted herein that whilst the above-described exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

Claims

CLAIMS:

1. A signal processor comprising: means for determining if a signal to be transmitted requires spectral shaping; and means for providing spectral shaping only if said determining means determines that said signal to be transmitted requires spectral shaping, wherein a delay of the signal to be transmitted when said spectral shaping means provides spectral shaping is substantially the same as the delay of a signal to be transmitted when no spectral shaping is provided.

2. A signal processor as claimed in claim 1 , wherein said means for determining is arranged to use at least one of: information received from an intended recipient of said signal to be transmitted; allocated resource blocks for said signal to be transmitted; bandwidth of said signal to be transmitted; centre frequency of the signal to be transmitted; frequency range of the signal to be transmitted, minimum frequency of signal to be transmitted; maximum frequency of signal to be transmitted; transmission power level; information related to intermodulation products; frequency allocation; spectrum of said signal to be transmitted; modulation of the signal.

3. A signal processor as claimed in claim 1 or 2, wherein said means for providing spectral shaping comprises a spectral shaping filter.

4. A signal processor as claim in claim 2 wherein said spectral shaping filter comprises a finite impulse response filter.

5. A signal processor as claimed in claim 3 or 4, wherein said spectral shaping filter comprises a plurality of delay elements.

6. A signal processor as claimed in claim 5, wherein some but not all of said delay elements are turned off if the determining means determines that said signal does not require spectral shaping.

7. A signal processor as claimed in claim 6, wherein the delay elements which are bypassed comprise delay elements after one or more delay elements on which signal energy is substantially concentrated when said spectral shaping filter provides spectra! shaping.

8. A signal processor as claimed in any preceding claim, comprising bypass means for bypassing said means for providing spectral shaping means

9. A signal processor as claimed in claim 8, wherein switch means are provided, said switch means being operable to connect to said spectral shaping means if spectral shaping is required and to said bypass means if spectral shaping is not required.

10. A signal processor as claimed in claim 9, wherein said switch means are controlled by said determining means.

1 1. A signal processor as claimed in any preceding claim, wherein at least part of said means for providing spectral shaping is shut down if no spectral shaping is required.

12. A signal processor as claimed in any preceding claim, wherein said determining means comprises a look up table.

13. A signal processor comprising: a filtering arrangement; means for determining if a signal to be transmitted requires filtering by said filtering arrangement; control means for controlling the filtering arrangement such that if said determining means determines that said signal to be transmitted does not require filtering, at least part of said filtering arrangement is bypassed.

14. A signal processor comprising: a filtering arrangement; means for determining if a signal to be transmitted requires filtering by said fiitering arrangement; control means for controlling the fiitering arrangement such that if said determining means determines that said signal to be transmitted does not require filtering, at least part of said filtering arrangement is switched off.

15, A processor as claimed in claim 13 or 14, wherein said fiitering arrangement comprises a filter

16. A signal processor comprising: a controller configured to determine if a signal to be transmitted requires spectral shaping; and a spectral shaping filter configured to provide spectral shaping only if said controller determines that said signal to be transmitted requires spectra! shaping, wherein said processor is configured such that a delay of the signal to be transmitted when said spectral shaping filter provides spectra! shaping is substantially the same as a delay of a signal to be transmitted when no spectral shaping is provided.

17. A signal processor comprising: a filtering arrangement; and a controller configured to determine if a signal to be transmitted requires filtering by said filtering arrangement and to control the filtering arrangement such that if the controller determines that said signal to be transmitted does not require filtering, at least part of said filtering arrangement is bypassed.

18. A signal processor comprising: a filtering arrangement; a controller configured to determine if a signal to be transmitted requires filtering by said filtering arrangement and to control the filtering arrangement such that if said controller determines that said signal to be transmitted does not require filtering, at least part of said filtering arrangement is switched off.

19, A user equipment comprising a signal processor as claimed in any preceding claim.

20. A method comprising: determining if a signal to be transmitted requires spectral shaping; and providing spectral shaping only if the determining determines that said signal to be transmitted requires spectral shaping, wherein a delay of the signal to be transmitted when said spectral shaping is provided is substantially the same as the delay of a signal to be transmitted when spectral shaping is provided.

21 . A computer program comprising computer program code means adapted to perform any of the steps of claim 20 when the program is run on a processor.

22. A transmitter comprising a signal processor as claimed in any of claims 1 to 18.