WO2016202371A1

WO2016202371A1 - A communication transmitter and method

Info

Publication number: WO2016202371A1
Application number: PCT/EP2015/063511
Authority: WO
Inventors: Dror Regev; Shimi Shilo; Doron Ezri; Chirn Chye Boon; Xiang YI; Junping Zhang; Gengen HU; Dong Liang; Yannan MIAO
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2015-06-17
Filing date: 2015-06-17
Publication date: 2016-12-22
Also published as: CN107735954A; CN107735954B

Abstract

The invention relates to a communication transmitter (100) for transmitting a communication signal including a plurality of frequency channels, the plurality of frequency channels comprising a first frequency channel situated around a frequency f_RF1 and a second frequency channel situated around a frequency f_RF2 and defining a mutual spectral range of interest having a spectral bandwidth Δf and being situated around a frequency f_RF. The communication transmitter (100) comprises: a first modulator (103a) being configured to modulate a first base band frequency channel on the basis of a first local oscillator frequency f_LO1 to obtain a first modulated signal including the first frequency channel; a second modulator (103b) being configured to modulate a second base band frequency channel on the basis of a second local oscillator frequency f_LO2 to obtain a second modulated signal including the second frequency channel; a first combiner (105) being configured to add the first modulated signal and the second modulated signal to obtain a combined modulated signal; and a mixer (107) being configured to mix the combined modulated signal with a periodic mixing signal having a mixing frequency f_c for generating the communication signal, wherein the communication signal comprises the down-converted first frequency channel of the combined modulated signal and the up- converted second frequency channel of the combined modulated signal. A particular merit of this invention is its superior immunity to LO pulling and crosstalk that impair the performance of prior art parallel processing transmitters.

Description

DESCRIPTION

A communication transmitter and method TECHNICAL FIELD

The present invention relates to a communication transmitter and method. In particular, the present invention relates to a communication transmitter and method for transmitting a communication signal including a plurality of frequency channels.

BACKGROUND

Carrier, i.e. frequency channel, aggregation (CA) in wireless communications is becoming a key approach for increasing the bandwidth and data rate as well as optimally utilizing the generally fragmented spectra available in wireless communications (e.g., LTE, Wi-Fi). For non-contiguous CA (NC CA) to be a useful CA scenario transmitters are required that support NC CA transmission. In this context generally the following challenges must be addressed: a wider total processing bandwidth (BW) of the aggregated carriers, possibly spanning an entire band with interfering signals between desired carriers; the data rate and Error Vector Module (EVM) requirements for LTE and 802.1 1 ac employing high order QAMs are already stringent and CA influence will further enhance requirements for higher EVM performance; and EVM requirements for transceivers supporting CA should target full performance per each component carrier with minimal mutual interference

degradations.

A couple of transmitter technologies are known that support NC CA transmission, such as processing the entire band span covering all carriers, parallel processing of carriers and double complex processing of carriers. However, all of these known transmitter technologies have a couple of disadvantages, such as local oscillator (LO) pulling and/or LO coupling in parallel processing and the need for wide band tunable IF filtering and relatively very high image rejection ratios in double complex processing, that have prevented these technologies from gaining widespread acceptance as suitable for noncontiguous CA. Thus, there is a need for an improved communication transmitter and method, in particular an improved communication transmitter and method suitable for non-contiguous CA and not disadvantageously affected by LO pulling.

SUMMARY

It is an objective of the invention to provide an improved communication transmitter and method, in particular an improved communication transmitter and method suitable for non- contiguous CA and not disadvantageously affected by LO pulling and coupling or needing very wide band and high image rejecting processing circuitry that has many limitations.

This objective is achieved by the subject matter of the independent claims. Further implementation forms are provided in the dependent claims, the description and the figures.

According to a first aspect the invention relates to a communication transmitter for transmitting a communication signal including a plurality of frequency channels, the plurality of frequency channels comprising a first frequency channel situated around a frequency f_RFi and a second frequency channel situated around a frequency f_RF2 and defining a mutual spectral range of interest having a spectral bandwidth Af

and being situated around a frequency†RF. The communication transmitter comprises: a first modulator being configured to modulate a first base band frequency channel on the basis of a first local oscillator frequency f_Loi to obtain a first modulated signal including the first frequency channel situated around a frequency†RFI; a second modulator being configured to modulate a second base band frequency channel on the basis of a second local oscillator frequency f_L02 to obtain a second modulated signal including the second frequency channel situated around a frequency f_RF2; a first combiner being configured to add the first modulated signal and the second modulated signal to obtain a combined modulated signal; and a mixer being configured to mix the combined modulated signal with a periodic mixing signal having a mixing frequency f_c for generating the

communication signal, wherein the communication signal comprises the down-converted first frequency channel of the combined modulated signal and the up-converted second frequency channel of the combined modulated signal. Thus, a communication transmitter is provided, in particular suited for carrier aggregation, with a first frequency channel and a second frequency channel around the distant carrier frequencies f_Loi and f_L02 so that the corresponding F frequencies do not pull each other. In a first possible implementation form of the first aspect of the invention the frequency f_RFi of the first frequency channel, the first local oscillator frequency _οι and the mixing frequency are related by f_Loi =†RFI + fc, and the frequency f_RF20f the second frequency channel, the second local oscillator frequency f_L02 and the mixing frequency are related by

In a second possible implementation form of the first aspect of the invention the communication transmitter further comprises a third modulator being configured to modulate a third base band frequency channel on the basis of a third local oscillator frequency _03 to obtain a third modulated signal including a third frequency channel situated around a frequency f_RF3, wherein the third local oscillator frequency is given by fi_03 =†RF3, wherein the communication transmitter comprises a second combiner being configured to add the third modulated signal to the communication signal generated by the mixer. In a third possible implementation form of the second implementation form of the first aspect of the invention the communication transmitter further comprises a first local oscillator configured to provide a first local oscillator signal having the first local oscillator frequency f_Loi , a second local oscillator configured to provide a second local oscillator signal having the second local oscillator frequency f_L02 and a third local oscillator configured to provide a third local oscillator signal having the third local oscillator frequency _03-

This implementation form provides an efficient communication transmitter, where the LO signals are provided by local oscillators operating at fairly distant frequencies such that no risk of LO pulling exists.

In a fourth possible implementation form of the second or third implementation form of the first aspect of the invention the first, the second or the third modulator comprises a modulator mixer, wherein the modulator mixer of the first modulator is configured to mix the first base band frequency channel with a mixing signal having the first local oscillator frequency f_Loi , wherein the modulator mixer of the second modulator is configured to mix the second base band frequency channel with a mixing signal having the second local oscillator frequency fi_02, and wherein the modulator mixer of the third modulator is configured to mix third base band frequency channel with a mixing signal having the third local oscillator frequency f_L03.

In a fifth possible implementation form of the fourth implementation form of the first aspect of the invention the first, the second or the third modulator further comprises a low-pass filter being configured to filter the respective base band frequency channel. A low-pass filter upstream of the modulation removes unwanted frequency components from the communication signal.

In a sixth possible implementation form of the first aspect of the invention as such or any one of the first to fifth implementation form thereof the communication transmitter further comprises a power amplifier being configured to amplify the communication signal generated by the mixer.

In a seventh possible implementation form of the first aspect of the invention as such or any one of the first to sixth implementation form thereof the frequency of the mixing signal f_c is higher than spectral bandwidth Af _BPF of the mutual spectral range of interest of the communication signal.

In an eighth possible implementation form of the first aspect of the invention as such or any one of the first to seventh implementation form thereof the communication transmitter further comprises a detection and calibration unit configured to measure a leakage signal at the first frequency channel or the second frequency channel and a digital signal processor configured to pre-distort the first base band frequency channel and/or the second base band frequency channel to suppress any mutual leakage replica signals resulting from cross talk between L01 and L02 that may exist between the first frequency channel and the second frequency channel. Alternatively, such potential replicas can be filtered out at each channel.

In a ninth possible implementation form of the first aspect of the invention as such or any one of the first to eighth implementation form thereof the communication transmitter further comprises a band-pass filter configured to filter the communication signal generated by the mixer, wherein the bandwidth of the band-pass filter Af_Bp_F is situated around the frequency f_RF.

Such a communication transmitter allows rejecting unwanted images of the frequency channels within the spectral region of interest.

In a tenth possible implementation form of the first aspect of the invention as such or any one of the first to ninth implementation form thereof the periodic mixing signal is a sinusoidal mixing signal.

Such a communication transmitter allows for an easy provision of the periodic mixing signal. The frequency of the mixing signal f_c can be chosen such that f_c and its harmonics do not interfere with the re-centered spectral ranges of interest of the communication signal.

In an eleventh possible implementation form of the first aspect of the invention as such or any one of the first to tenth implementation form thereof the communication transmitter further comprises: a fourth modulator being configured to modulate a fourth base band frequency channel on the basis of a fourth local oscillator frequency f_L04 to obtain a fourth modulated signal including a fourth frequency channel situated around a frequency f_RF4; and a fifth modulator being configured to modulate a fifth base band frequency channel on the basis of a fifth local oscillator frequency _05 to obtain a fifth modulated signal including a fifth frequency channel situated around a frequency f_RF5; wherein the first combiner is configured to add the first modulated signal, the second modulated signal, the fourth modulated signal and the fifth modulated signal to obtain a combined modulated signal; and wherein the mixer is configured to mix the combined modulated signal with a square- wave signal having a mixing frequency f_c for generating the communication signal, wherein the communication signal comprises the down-converted first frequency channel of the combined modulated signal, the up-converted second frequency channel of the combined modulated signal, the down-converted fourth frequency channel of the combined modulated signal and the up-converted fifth frequency channel of the combined modulated signal.

In a twelfth possible implementation form of the eleventh implementation form of the first aspect of the invention the frequency f_RF4 of the fourth frequency channel, the fourth local oscillator frequency f_L04 and the mixing frequency are related by f_L04 = f_RF4 + 3f_c, and the frequency fRFs Of the fifth frequency channel, the fifth local oscillator frequency f_Los and the mixing frequency are related by f_Los =†RFS - 3f_c.

According to a second aspect the invention relates to a method of transmitting a communication signal including a plurality of frequency channels, the plurality of frequency channels comprising a first frequency channel situated around a frequency†RFI and a second frequency channel situated around a frequency f_RF2 and defining a spectral range of interest having a mutual spectral bandwidth Af and being situated around a frequency f_RF. The method comprising the steps of: modulating a first base band frequency channel on the basis of a first local oscillator frequency _οι to obtain a first modulated signal including the first frequency channel situated around a frequency f_RFi ; modulating a second base band frequency channel on the basis of a second local oscillator frequency f_L02 to obtain a second modulated signal including the second frequency channel situated around a frequency†RF2; adding the first modulated signal and the second modulated signal to obtain a combined modulated signal; and mixing the combined modulated signal with a periodic mixing signal having a mixing frequency f_c for generating the

communication signal, wherein the communication signal comprises the down-converted first frequency channel of the combined modulated signal and the up-converted second frequency channel of the combined modulated signal.

The method according to the second aspect of the invention can be performed by the communication transmitter according to the first aspect of the invention. Further features of the method according to the second aspect of the invention result directly from the functionality of the communication according to the first aspect of the invention and its different implementation forms described above.

According to a third aspect the invention relates to a computer program comprising program code for performing the method according to the second aspect of the invention when executed on a computer.

The invention can be implemented in hardware and/or software. BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect to the following figures, in which: Fig. 1 shows a schematic diagram of a communication transmitter according to an embodiment;

Fig. 2 shows a schematic diagram illustrating frequency plan aspects of a communication transmitter according to an embodiment;

Fig. 3 shows a schematic diagram illustrating image replica aspects of a communication transmitter according to an embodiment; Fig. 4 shows a schematic diagram of a communication transmitter with a LO cross talk calibration loop according to an embodiment;

Fig. 5 shows a schematic diagram of a communication transmitter for aggregating up to 5 communication carriers according to an embodiment;

Fig. 6 shows a schematic diagram illustrating frequency plan aspect of a communication transmitter for aggregating up to 5 communication carriers according to an embodiment; and Fig. 7 shows a schematic diagram of a communication method according to an

embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, reference is made to the accompanying drawings, which form a part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the disclosure may be practiced. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

It is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure 1 shows a schematic diagram of a communication transmitter 100 according to an embodiment. The communication transmitter 100 is configured to transmit a

communication signal including a plurality of frequency channels, wherein the plurality of frequency channels comprise a first frequency channel situated around a frequency f_RFi and a second frequency channel situated around a frequency†RF2 and wherein the plurality of frequency channels define a spectral range of interest having a mutual spectral bandwidth Af and being situated around a frequency f_RF.

In an embodiment, the communication transmitter 100 comprises an antenna 1 17 for transmitting the communication signal. An exemplary spectral range of interest comprising three frequency or communication channels identified as "ch1 ", "ch2" and "ch3" is shown in the upper right corner of figure 1.

The communication transmitter 100 comprises a first modulator 103a being configured to modulate a first base band frequency channel, for instance the first frequency channel

"ch1 " shown in figure 1 , on the basis of a first local oscillator frequency _οι to obtain a first modulated signal including the first frequency channel situated around a frequency†RFI and a second modulator 103b being configured to modulate a second base band frequency channel, for instance the second frequency channel "ch2" shown in figure 1 , on the basis of a second local oscillator frequency _02 to obtain a second modulated signal including the second frequency channel situated around a frequency†RF2-

The communication transmitter 100 further comprises a first combiner 105 being configured to add the first modulated signal provided by the first modulator 103a and the second modulated signal provided by the second modulator 103b to generate a combined modulated signal. In an embodiment, the combiner 105 can be just a simple circuit node that combines the currents representing the first modulated signal and the second modulated signal.

The communication transmitter 100 further comprises a mixer 107 being configured to mix the combined modulated signal provided by the first combiner 105 with a periodic mixing signal having a mixing frequency f_c for generating the communication signal such that the communication signal comprises the down-converted first frequency channel of the combined modulated signal and the up-converted second frequency channel of the combined modulated signal.

In an embodiment, the communication transmitter 100 further comprises a third modulator 103c being configured to modulate a third base band frequency channel, for instance the frequency channel "ch3" shown in figure 1 , on the basis of a third local oscillator frequency f_L03 to obtain a third modulated signal including a third frequency channel situated around a frequency†RF3. In an embodiment, the communication transmitter 100 comprises a second combiner 109 being configured to add the third modulated signal to the communication signal generated by the mixer 107.

In an embodiment, the periodic mixing signal used by the mixer 107 for generating the communication signal is a sinusoidal mixing signal. The frequency of the mixing signal f_c can be chosen such that f_c and its harmonics do not interfere with the re-centered spectral ranges of interest of the communication signal, as will be discussed in more detail below.

In an embodiment, the frequency of the mixing signal f_c is higher than the spectral bandwidth Af BPF of the mutual spectral range of interest of the communication signal.

In an embodiment, the first, second and third local oscillator frequencies are given by _οι =†RFI + fc, fi_02 =†RF2 - fc and f_L03 =†RF3, respectively. In an alternative embodiment, the first, second and third local oscillator frequencies are given by f_Loi =†RFI - fc, fi_02 =†RF2 + fc and fi_03 =†RF3, respectively. In an embodiment, the communication transmitter 100 further comprises a first local oscillator configured to provide a first local oscillator signal having the first local oscillator frequency f_Loi , a second local oscillator configured to provide a second local oscillator signal having the second local oscillator frequency f_L02 and a third local oscillator configured to provide a third local oscillator signal having the third local oscillator frequency f_L03-

In an embodiment, the first, second and/or third modulator 103a-c can comprise a respective modulator mixer 1 1 1 a-c. The modulator mixer 1 11 a of the first modulator 103a is configured to mix a base band input signal with a mixing signal having the first local oscillator frequency f _Loi■ The modulator mixer 1 1 1 b of the second modulator 103b is configured to mix a base band input signal with a mixing signal having the second local oscillator frequency f_L02- The modulator mixer 1 1 1c of the third modulator 103c is configured to mix a base band input signal with a mixing signal having the third local oscillator frequency f_L03- As indicated in figure 1 , the modulator mixers 1 1 1 a-c are configured to provide a frequency up conversion of the first, second and third base band frequency channels. The modulator mixers 1 1 1 a-c can be implemented in the form of a complex output mixer. As shown in figure 1 , the first, second and third modulator 103a-c and the modulator mixers 1 1 1 a-c can be configured to process an in-phase (I) and a quadrature (Q) component of the communication signal. In an embodiment, the first, the second and/or the third modulator 103a-c further comprise a low-pass filter (LPF) 1 13a-c being configured to filter unwanted frequency components from the respective base band input signals. In an embodiment, the low pass filter 1 13a-c can include an automatic gain control (AGC), as shown in figure 1. In an embodiment, the communication transmitter 100 further comprises a first, second and third digital to analog converter (DAC) 1 19a-c for providing the respective input signals in analog form to the first, second and third modulator 103a-c.

As shown in figure 1 , in an embodiment the communication transmitter 100 comprises upstream of the second combiner 109 a power amplifier (PA) 1 15 being configured to amplify the communication signal provided by the second combiner 109.

Figure 2 shows a schematic diagram illustrating frequency plan aspects of the communication transmitter 100 of figure 1.

The top portion of figure 2 shows the provision of the communication signal defining a mutual spectral range of interest having a spectral bandwidth being situated around a frequency f_RF and comprising a first frequency channel, i.e. "ch1 ", situated around a frequency f_RFi and a second frequency channel, i.e. "ch2", situated around a frequency †RF2 by means of the combiner 105 and the mixer 107.

As can be taken from the middle portion of figure 2, the communication transmitter 100 of figure 1 provides for a sufficient separation between the local oscillator frequencies _οι , f_L02 and f_L03 for providing the communication signal with the exemplary frequency or communication channels "ch1 ", "ch2" and "ch3" so that essentially no or only very little LO pulling between the local oscillator frequencies f_Loi , fi_02 and f_L03 occurs. In the bottom portion of figure 2 an exemplary relation between the local oscillator frequencies f_Loi , fi_02 and f_L03 and the mixing frequency f_c and its harmonic multiples is shown. As the person skilled in the art will appreciate, superior performance of the communication transmitter 100 and improved frequency plan flexibility can be achieved if the mixing frequency f_c and its multiples do not interfere with the communication channels provided by the modulators 103a-c.

In an embodiment, the communication transmitter 100 shown in figure 1 further comprises a band-pass filter (BPF) 1 16. In an embodiment, the band-pass filter 1 16 is configured to filter the communication signal generated by the mixer 107 and the second combiner 109. In an embodiment, the bandwidth of the band-pass filter 1 16 A†_BPF is determined as the widest spectral bandwidth that the specific communication technology supports, wherein the band-pass filter is situated around the frequency f_RF. The band-pass filter 1 16 allows rejecting unwanted images of the frequency channels outside the mutual spectral region of interest, as schematically illustrated in figure 3. The band-pass filter (BPF) 1 16 also blocks harmonic signals from being transmitted.

Figure 4 shows a schematic diagram of a communication transmitter 400 according to an embodiment. The main difference between the communication transmitter 400 shown in figure 4 and the communication transmitter 100 shown in figure 1 is that the

communication transmitter 400 further comprises a detection and calibration unit 401. In a calibration mode of the communication transmitter 400 the communication transmitter 400 is configured to transmit only one of the first and the second frequency channels of the communication signal at a time and the detection and calibration unit 401 is configured to measure the leakage signal at the other frequency channel. In a transmission mode of the communication transmitter 400 the detection and calibration unit 401 configures a digital signal processor (DSP) 403 to pre-distort the first and/or the second frequency channel to suppress any measured leakage signals. Figure 5 shows a schematic diagram of a communication transmitter 500 according to an embodiment. The main difference between the communication transmitter 500 shown in figure 5 and the communication transmitter 100 shown in figure 1 is that the

communication transmitter 500 further comprises a fourth modulator 103d being configured to modulate a fourth base band frequency channel on the basis of a fourth local oscillator frequency f_L04 to obtain a fourth modulated signal including a fourth frequency channel situated around a frequency f_RF4 and a fifth modulator 103e being configured to modulate a fifth base band frequency channel on the basis of a fifth local oscillator frequency f_Los to obtain a fifth modulated signal situated around a frequency f_RF5- In the embodiment shown in figure 5 the first combiner 105 is configured to add the first modulated signal, the second modulated signal, the fourth modulated signal and the fifth modulated signal to obtain a combined modulated signal. In the embodiment shown in figure 5 the mixer 107 is configured to mix the combined modulated signal with a square- wave signal having a mixing frequency f_c for generating the communication signal, as schematically indicated in figure 5, such that the communication signal comprises the down-converted first frequency channel of the combined modulated signal, the up- converted second frequency channel of the combined modulated signal, the down- converted fourth frequency channel of the combined modulated signal and the up- converted fifth frequency channel of the combined modulated signal.

In an embodiment, the frequency†RF40† the fourth frequency channel, the fourth local oscillator frequency f_L04 and the mixing frequency are related by f_L04 =†RF4 + 3f_c, and the frequency fRFs Of the fifth frequency channel, the fifth local oscillator frequency f_Los and the mixing frequency are related by f_Los =†RFS - 3f_c.

As the person skilled in the art will appreciate, the use of a square-wave mixing signal in the embodiment shown in figure 5, in principle, allows processing even more than five frequency or communication channels, provided a corresponding number of modulators are available. Figure 6 shows a schematic diagram illustrating the process of generating the mutual spectral range of interest of a communication signal, comprising 5

communication channels and the respective f_c and harmonics, by the communication transmitter 500 of figure 5.

Figure 7 shows a schematic diagram of a method 700 of transmitting a communication signal including a plurality of frequency channels according to an embodiment. The plurality of frequency channels comprise a first frequency channel situated around a frequency f_RFi and a second frequency channel situated around a frequency f_RF2 and define a mutual spectral range of interest having a spectral bandwidth Af and being situated around a frequency f_RF. The method 700 comprises the steps of: modulating 701 a first base band frequency channel on the basis of a first local oscillator frequency _οι to obtain a first modulated signal including the first frequency channel situated around a frequency f_RFi ; modulating 703 a second base band frequency channel on the basis of a second local oscillator frequency f_L02 to obtain a second modulated signal including the second frequency channel situated around a frequency f_RF2; adding 705 the first modulated signal and the second modulated signal to obtain a combined modulated signal; and mixing 707 the combined modulated signal with a periodic mixing signal having a mixing frequency f_c for generating the communication signal such that the communication signal comprises the down-converted first frequency channel of the combined modulated signal and the up-converted second frequency channel of the combined modulated signal.

One skilled in the art appreciates that at least some of the above steps can be performed serially, in parallel, or a combination thereof. For example, steps 701 and 703 can be performed in parallel to each other and in series vis-a-vis steps 705 and 707.

The devices described herein may be implemented as optical circuit within a chip or an integrated circuit or an application specific integrated circuit (ASIC). The invention can be implemented in digital and/or analogue electronic and optical circuitry.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms "coupled" and "connected", along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other. Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein. Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.

Claims

CLAIMS:

1. A communication transmitter (100; 400; 500) for transmitting a communication signal including a plurality of frequency channels, the plurality of frequency channels comprising a first frequency channel situated around a frequency f_RFi and a second frequency channel situated around a frequency†RF2 and defining a mutual spectral range of interest having a spectral bandwidth Af and being situated around a frequency f_RF, the communication transmitter (100; 400; 500) comprising: a first modulator (103a) being configured to modulate a first base band frequency channel on the basis of a first local oscillator frequency _οι to obtain a first modulated signal including the first frequency channel; a second modulator (103b) being configured to modulate a second base band frequency channel on the basis of a second local oscillator frequency f_L02 to obtain a second modulated signal including the second frequency channel; a first combiner (105) being configured to add the first modulated signal and the second modulated signal to obtain a combined modulated signal; and a mixer (107) being configured to mix the combined modulated signal with a periodic mixing signal having a mixing frequency fc for generating the communication signal, wherein the communication signal comprises the down-converted first frequency channel of the combined modulated signal and the up-converted second frequency channel of the combined modulated signal.

2. The communication transmitter (100; 400; 500) of claim 1 , wherein the frequency f_RFi of the first frequency channel, the first local oscillator frequency f_Loi and the mixing frequency are related by f_Loi =†RFI + fc, and wherein the frequency f_RF2 of the second frequency channel, the second local oscillator frequency _02 and the mixing frequency are related by f_L02 =†RF2 - fc-

3. The communication transmitter (100; 400; 500) of claim 1 , wherein the communication transmitter (100; 400; 500) further comprises a third modulator (103c) being configured to modulate a third base band frequency channel on the basis of a third local oscillator frequency†LO3 to obtain a third modulated signal including a third frequency channel, wherein the third frequency channel is situated around a frequency f_RF3, wherein the third local oscillator frequency is given by f_L03 =†RF3, wherein the communication transmitter (100; 400; 500) comprises a second combiner (109) being configured to add the third modulated signal to the communication signal generated by the mixer (107).

4. The communication transmitter (100; 400; 500) of claim 3, wherein the

communication transmitter (100; 400; 500) further comprises a first local oscillator configured to provide a first local oscillator signal having the first local oscillator frequency fi_oi , a second local oscillator configured to provide a second local oscillator signal having the second local oscillator frequency f_L02 and a third local oscillator configured to provide a third local oscillator signal having the third local oscillator frequency f_L03-

5. The communication transmitter (100; 400; 500) of claims 3 or 4, wherein the first, the second or the third modulator (103a-c) comprises a modulator mixer (1 11 a-c), wherein the modulator mixer (1 1 1 a) of the first modulator (103a) is configured to mix the first base band frequency channel with a mixing signal having the first local oscillator frequency _οι , wherein the modulator mixer (1 1 1 b) of the second modulator (103b) is configured to mix the second base band frequency channel with a mixing signal having the second local oscillator frequency fi_02, and wherein the modulator mixer (1 1 1 c) of the third modulator (103c) is configured to mix third base band frequency channel with a mixing signal having the third local oscillator frequency f_L03.

6. The communication transmitter (100; 400; 500) of claim 5, wherein the first, the second or the third modulator (103a-c) further comprises a low-pass filter (1 13a-c) being configured to filter the respective base band frequency channel.

7. The communication transmitter (100; 400; 500) of anyone of claims 1 to 6, wherein the communication transmitter (100; 400; 500) further comprises a power amplifier (1 15) being configured to amplify the communication signal generated by the mixer (107).

8. The communication transmitter (1 00; 400; 500) of claim 7, wherein the frequency of the mixing signal f_c is higher than spectral bandwidth A†_BPF of the mutual spectral range of interest of the communication signal.

9. The communication transmitter (400) of claim 8, wherein the communication transmitter (400) further comprises a detection and calibration unit (401 ) configured to measure a leakage signal at the first frequency channel or the second frequency channel and a digital signal processor (403) configured to pre-distort the first base band frequency channel and/or the second base band frequency channel to suppress any leakage signal on the basis of the measurement of the detection and calibration unit (401 ).

1 0. The communication transmitter (1 00; 400; 500) of any one of the preceding claims, wherein the communication transmitter (1 00; 400; 500) further comprises a band-pass filter (1 1 6) configured to filter the communication signal generated by the mixer ( 1 07), wherein the bandwidth A†_BPF of the band-pass filter (1 1 6) is situated around the frequency f_RF.

1 1 . The communication transmitter (100; 400; 500) of any one of the preceding claims, wherein the periodic mixing signal is a sinusoidal mixing signal.

12. The communication transmitter (500) of any one of the preceding claims, wherein the communication transmitter (500) further comprises: a fourth modulator (103d) being configured to modulate a fourth base band frequency channel situated around a frequency†RF4 on the basis of a fourth local oscillator frequency _04 to obtain a fourth modulated signal including a fourth frequency channel; and a fifth modulator (103e) being configured to modulate a fifth base band frequency channel situated around a frequency†RFS on the basis of a fifth local oscillator frequency _05 to obtain a fifth modulated signal including a fifth frequency channel; wherein the first combiner (105) is configured to add the first modulated signal, the second modulated signal, the fourth modulated signal and the fifth modulated signal to obtain a combined modulated signal; and wherein the mixer (107) is configured to mix the combined modulated signal with a square-wave signal having a mixing frequency f_c for generating the communication signal, wherein the communication signal comprises the down-converted first frequency channel of the combined modulated signal, the up-converted second frequency channel of the combined modulated signal, the down-converted fourth frequency channel of the combined modulated signal and the up-converted fifth frequency channel of the combined modulated signal.

13. The communication transmitter (500) of claim 12, wherein the frequency f_RF4 of the fourth frequency channel, the fourth local oscillator frequency f_L04 and the mixing frequency are related by f_L04 =†RF4 + 3f_c, and wherein the frequency fRFs Of the fifth frequency channel, the fifth local oscillator frequency f_Los and the mixing frequency are related by f_L05 =†RFS - 3f_c.

14. A method (700) of transmitting a communication signal including a plurality of frequency channels, the plurality of frequency channels comprising a first frequency channel situated around a frequency f_RFi and a second frequency channel situated around a frequency†RF2 and defining a mutual spectral range of interest having a spectral bandwidth Af and being situated around a frequency†RF, the method comprising the steps of: modulating (701 ) a first based band frequency channel on the basis of a first local oscillator frequency _οι to obtain a first modulated signal including the first frequency channel; modulating (703) a second base band frequency channel on the basis of a second local oscillator frequency f_L02 to obtain a second modulated signal including the second frequency channel; adding (705) the first modulated signal and the second modulated signal to obtain a combined modulated signal; and mixing (707) the combined modulated signal with a periodic mixing signal having a mixing frequency fc for generating the communication signal, wherein the communication signal comprises the down-converted first frequency channel of the combined modulated signal and the up-converted second frequency channel of the combined modulated signal.

15. A computer program comprising a program code for performing the method of claim 14 when executed on a computer.