Patent Publication Number: US-2015072636-A1

Title: Dual Channel Reception

Description:
FIELD 
     The invention relates generally to dual channel reception with one receiver. 
     BACKGROUND 
     It is an ongoing challenge to enhance the data rate in a mobile communication network. This may be pursued by developing completely new systems. An example of this type of evolution is the change in network architectures from a Global System for Mobile Communications (GSM) to a Universal Mobile Telecommunications System (UMTS) applying Wideband Code Division Multiple Access (WCDMA) and further to Long Term Evolution (LTE). Alternatively, the increase of the data rate may be obtained by developing the existing architectures. For example, a general packet radio service (GPRS) and enhanced data rates for global evolution (EDGE) were developed on top of the existing GSM network. Further, high-speed downlink packet access (HSDPA) was developed to coexist with the UMTS network. 
     One possible way to increase the data rate is to enable the dual channel reception in the mobile communication network. This technique is called a dual cell (DC) HSDPA. According to possible solutions for DC-HSDPA, a mobile terminal would require two separate receivers. Both of the receivers could separate the in-phase (I) and the quadrature (Q) branch from the received signal. The use of two receivers is, however, a highly space- and money-consuming solution. Alternatively, a diversity receiver of the mobile terminal could be applied together with the original receiver (such as a direct conversion receiver) for receiving two data channels simultaneously. 
     BRIEF DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     An object of the embodiments of the invention is to provide a novel solution for receiving two radio frequency signals comprised in one signal simultaneously in a mobile communication network. 
     According to an aspect of the invention, there is provided a method as specified in claim  1 . 
     According to an aspect of the invention, there is provided apparatuses as specified in claims  8 ,  15  and  22 . 
     According to an aspect of the invention, there is provided a computer program product as specified in claim  23 . 
     Embodiments of the invention are defined in the dependent claims. 
    
    
     
       LIST OF DRAWINGS 
       In the following, the examples of the invention will be described in greater detail with reference to the embodiments and the accompanying drawings, in which 
         FIG. 1  illustrates transmission of two signals; 
         FIG. 2  shows a general architecture of an apparatus capable of receiving and separating the transmitted two radio frequency signals, comprised in one radio frequency signal, simultaneously, according to an embodiment of the invention; 
         FIG. 3  shows how the received signals may be located in a frequency domain; and 
         FIG. 4  illustrates a method for performing the dual channel reception according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following embodiments are exemplary. Although the specification may refer to “an”, “one”, or “some” embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. 
       FIG. 1  illustrates transmission of two signals  104 ,  106  from a central node  100  to a target node  102 . The central node  100  and the target node  102  may be located within one cell or the target node  102  may be located in a different cell than the central node  100  and the transmitted signals  104 ,  106  may be forwarded to the target node  102  by a relay node or a similar network element. The central node  100  and the target node  102  may occupy radio resources of the GSM, UMTS, LTE, or any other well-known network architecture. Thus, even though the embodiments of the invention are described using the UMTS and the HSDPA as a basis, the scope of the invention is not limited to it but is applicable to any network where the reception of two signals  104 ,  106  simultaneously is desired. Similarly, the scope of the invention is not limited to a downlink transmission but the embodiments of the invention can be applied in an uplink transmission as well. 
     The central node  100  may be a base station, an evolved node B as in the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN). Further, the central node  100  may be a radio network controller (RNC) or any other apparatus capable of controlling a radio communication within the network. The target node  102  may be a mobile terminal, user equipment, palm computer, circuit, or any other apparatus capable of receiving radio frequency signals. 
     In the downlink transmission, the central node  100  may simultaneously transmit two separate radio frequency signals  104 ,  106  to the target node  102 . The signals  104 ,  106  may be located within two separate frequency bands. That is, the signal  104  may be located within a frequency band of a downlink channel and the signal  106  may be located within a frequency band of a different downlink channel. In the target node, the two signals  104 ,  106  may be received as one radio frequency signal comprising the two signals  104 ,  106 . The signals  104 ,  106  may be information-carrying data signals, pilot signals, control signals or any other signals that may need to be transmitted from the central node  100  to the target node  102 . Thus, according to the embodiment, the target node  102  may simultaneously receive the two separate radio frequency signals  104 ,  106  using methods and radio network elements described below. 
     A very general architecture of an apparatus  200  capable of receiving and separating the transmitted two radio frequency signals, comprised in one radio frequency signal, simultaneously according to an embodiment of the invention is shown in  FIG. 2 .  FIG. 2  shows the elements and functional entities required for understanding the reception of the two radio frequency signals according to an embodiment of the invention. Other components have been omitted for reasons of simplicity. The implementation of the elements and functional entities may vary from that shown in  FIG. 2 . The connections shown in  FIG. 2  are logical connections, and the actual physical connections may be different. It is apparent to a person skilled in the art that the apparatus  200  may also comprise other functions and structures. 
     The apparatus  200  may comprise an interface  204 . According to an embodiment of the invention, the interface  204  is capable of receiving radio frequency electromagnetic energy from the air interface. Consequently, the interface  204  may comprise an antenna. Alternatively, the reception may occur via a wire such as a coaxial cable or a similar transmission medium. The interface  204  may include computer ports for providing communication capabilities. The interface  204  may perform signal-processing operations for enabling a physical channel connection, if needed. According to an embodiment of the invention, the interface  204  receives a combined radio frequency signal  202  comprising a first and a second signal, the first and the second signal being on frequency bands of a first and a second channel, respectively, wherein the channels have different center frequencies. 
     Before discussing further with regards to  FIG. 2 , let us take a look at how the first and the second signal may be located in a frequency domain. This is shown in  FIG. 3 . The axis  330  represents the frequency domain with lower frequencies on the left-hand side of the axis, and higher frequencies on the right-hand side of the axis. 
     The first and the second signal  308  and  310  may be received by the apparatus  200  of  FIG. 2  on frequency bands of first and second channels  300  and  302 . That is, according to an embodiment, the first and the second signal  308  and  310  are located within bandwidths of the first and the second channel  300  and  302 . The center frequencies of the first and the second channel  300  and  302  are shown with dotted lines and with reference numbers  304  and  306 . Center frequencies  304  and  306  in the HSDPA network topology may be within a range from 700 MHz to 2200 MHz. The base-band representation of the first and the second signal  308  and  310  are shown with reference numbers  312  and  314 . Base-band values for the first and the second signal  308  and  310  may be within a range from 0 Hz to 5 MHz. The base-band signals  312  and  314  may have been used in a transmitter (central node in the downlink transmission or mobile terminal in the uplink transmission) together with a local oscillator of the transmitter to form the radio frequency signals  308  and  310 . 
     According to an embodiment of the invention, the center frequencies  304  and  306  of the first and the second channel  300  and  302  are separated by a channel bandwidth applied in the reception of the combined radio frequency signal. According to an embodiment of the invention, the channel bandwidth is, at the maximum, 5 MHz. 
     The first and the second signal  308  and  310  in  FIG. 3  are merely examples of signals received from the air interface. They may be sine signals that are used in testing the communication network, or they may represent modulated radio frequency signals at a certain point of time. For example, in the HSDPA topology applied together with the WCDMA, the radio frequency signals are hopping arbitrarily according to the spreading code of the WCDMA within the whole frequency band of the channel. Thus, at any point of time, the frequency bands  300  and  302  may be occupied by a large number of signals  308  and  310  with different spreading codes used to separate them from each other. Even though the description of the embodiments of the invention aims at separating one first signal  308  and one second signal  310  from the combined radio frequency signal, the embodiments of the invention are not limited to separating signals with certain spreading codes but can be applied to a separation of any first and second signals located anywhere within the frequency bands of the first and the second channel  300  and  302 , wherein the signals  308  and  310  may have any known spreading code. 
     Let us now discuss further with regard to  FIG. 2 . According to an embodiment, the combined radio frequency signal  202  is divided into an in-phase component  210  and a quadrature component  212 . 
     Thus, according to an embodiment, mixing a first oscillating signal  214  with the combined radio frequency signal  202  at a mixer  218  leads to obtaining the in-phase component  210  of the combined radio frequency signal  202 . The frequency of the first oscillating signal may be in the middle of the center frequencies of the first and the second channel. This is shown in  FIG. 3  with reference number  320 .  FIG. 3  also shows intermediate frequencies (IF)  316  (IF 1 ) and  318  (IF 2 ). They represent the differences between the frequency of the first oscillating signal  320  (O 1 ) to the first signal  308  (S 1 ) and to the second signal  310  (S 2 ), respectively. That is, they may be given as 
         f   IF1   =f   O1   −f   S1 , and  (1)
 
         f   IF2   =f   S2   −f   O1 .  (2)
 
     Further, from (1) and (2) we can derive representations for the first signal  308  (S 1 ) and the second signal  310  (S 2 ) as 
         S 1=sin(2·π· f   O1 −2·π· f   IF1 ) t =sin(ω O1 −ω IF1 ) t , and  (3)
 
         S 2=sin(2·π· f   O1 +2·π· f   IF2 ) t =sin(ω O1 +ω IF2 ) t,   (4)
 
     where 2·π·f O1 =ω O1 , 2·π·f IF1 =ω IF1  and 2·π·f IF2 =ω IF2 . 
     Further, mixing of a quadrature  216  of the first oscillating signal  214  with the combined radio frequency signal  202  at a mixer  220  may lead to obtaining the quadrature component  212  of the combined radio frequency signal  202 . 
     The mixers  218  and  220  may output two mixing results: one in which the two signals to be mixed are summed (added) and another where the two signals to be mixed are subtracted from each other. According to an embodiment of the invention, only the outputs that which comprise the subtracted results, are applied. Consequently, at least one filter may be applied to filter out the summed outputs of each of the mixers  218  and  220 . For example, a filter  224  filters out the summed output of the mixer  218 , and a filter  226  filters out the summed output of the mixer  220 . The filters  224 ,  226  may be implemented with one or more filters. That is,  FIG. 2  has separate filters for the reasons of simplicity and the actual implementation may be different. 
     Further, the in-phase component  210  and the quadrature component  212  may be converted to digital form. This may be performed by at least one converter  228  and  230 . That is,  FIG. 2  has separate converters for the reasons of simplicity and the actual implementation may be different. The at least one converter may be an analog-to-digital converter (ADC), in which an analog input is digitized on the basis of a characteristic of the analog input. The characteristic may be, for example, an amplitude or a phase of the analog input. The apparatus  200  may naturally comprise other components, for example, a power amplifier prior to quantization even though not shown in  FIG. 2 . 
     Consequently, the in-phase component  232  (I) of the combined radio frequency signal  202  after filtration and digitization may be represented as 
         I =[sin(ω O1 −ω IF1 ) t +sin(ω O1 +ω IF2 ) t ]−sin(ω O1   t )=sin(ω IF1   t )+sin(ω IF2   t ).  (5)
 
     Similarly, the quadrature component  234  (Q) of the combined radio frequency signal  202  after filtration and digitization may be represented as 
         Q =[sin(ω O1 −ω IF1 ) t +sin(ω O1 +ω IF2 ) t ]−sin(ω O1   t+ 90°)=sin(ω IF1   t− 90°)+sin(ω IF2   t+ 90°).  (6)
 
     Thus, after applying the first oscillating signal  214  and the quadrature  216  of the first oscillating signal  214  to form the IF representation of the in-phase  232  and quadrature component  234  of the combined radio frequency signal  202 , the further object of the apparatus  200  is to separate the base-band representation of the in-phase and quadrature components of the first and the second signal from the IF representation of the in-phase  232  and quadrature components  234  of the combined radio frequency signal  202 . 
     According to an embodiment of the invention, separating in-phase and quadrature components of the first and the second signal from the in-phase  232  and quadrature components  234  of the combined radio frequency signal  202  is performed next. The separation may be performed with digital signal processing manners. 
     According to an embodiment of the invention, a second oscillating signal  244  and a quadrature  246  of the second oscillating signal  244  are mixed in mixers with the in-phase  232  and quadrature component  234  of the combined radio frequency signal  202 . The use of the second oscillating signal  244  and the quadrature  246  of the second oscillating signal  244  may enable the converting of the first and the second signal from the IF frequencies  316  and  318  of  FIG. 3  to base-band frequencies  312  and  314 . The first base-band frequency signal (B 1 ) and the second base-band frequency signal (B 2 ) may be represented as 
         B 1=sin(2·π· f   B1 ) t =sin(ω B1   t )  (7)
 
         B 2=sin(2·π· f   B2 ) t =sin(ω B2   t ).  (8)
 
     The use of the second oscillating signal  244  and the quadrature  246  of the second oscillating signal  244  may also be advantageous in terms of combating the unwanted mirror frequencies caused by the mixers  218  and  220 . That is, the in-phase component  232  and the quadrature component  234 , generated by the mixers  218  and  220  and being  90  degrees phase shifted compared to each other, may lead to unwanted mirror frequencies. The mirror frequency can be attenuated by performing another frequency shift of 90 degrees. This may be obtained by applying the second oscillating signal  244  and the quadrature  246  of the second oscillating signal  244  to the in-phase  232  and quadrature components  234  of the combined radio frequency signal  202 . 
     The first oscillating signal  214  and the second oscillating signal  244  may be originated from a frequency synthesizer associated with one or more frequency dividers. This may enable the original frequency of a local oscillating signal, before the frequency dividers, to be at a different frequency than at the frequency of the received combined radio frequency signal  202 . The dividers may also be used to produce phase shifts of the signals, that is, the quadrature of the first oscillating signal  216  and the quadrature of the second oscillating signal  246 . Other means for providing a phase shift naturally exists and may be applied. In other words, the quadrature component of a signal has a 90 degrees phase difference compared to the in-phase component of the signal. 
     The use of mixers together with the second oscillating signal  244  and the quadrature  246  of the second oscillating signal  244  will be described next. According to an embodiment, the mixers mix the second oscillating signal  244  with the in-phase  232  and quadrature  234  components of the combined radio frequency signal  202 . Further, the mixers mix the quadrature  246  of the second oscillating signal  244  with the quadrature  234  and with the in-phase component  232  of the combined radio frequency signal  202 . The frequency of the second oscillating signal  244  may be a half of the difference between the center frequencies of the first and the second channel. This is shown in  FIG. 3  with reference number  322 . For example, if the channel bandwidth, separating the two channels  300  and  302 , is 5 MHz, the frequency of the second oscillating signal  322  may be 2.5 MHz. 
     The apparatus  200  may comprise a mixer  236 . The mixer  236  mixes the second oscillating signal  244  with the in-phase component  232  of the combined radio frequency signal  202 . That is, the output  264  of the mixer  236  may be represented as 
         Ii =sin(ω B1   t )+sin(ω B2   t ).  (9)
 
     The apparatus  200  may further comprise a mixer  238 . The mixer  238  mixes the second oscillating signal  244  with the quadrature component  234  of the combined radio frequency signal  202 . The output  266  of the mixer  238  may be represented as 
         Qi =sin(ω B1   t− 90°)+sin(ω B2   t+ 90°).  (10)
 
     The apparatus  200  may further comprise a mixer  240 . The mixer  240  mixes the quadrature  246  of the second oscillating signal  244  with the quadrature component  234  of the combined radio frequency signal  202 . The output  262  of the mixer  240  may be represented as 
         Qq =sin(ω B1   t− 90°+90°)+sin(ω B2   t+ 90°+90°).  (11)
 
     The apparatus  200  may further comprise a mixer  242 . The mixer  242  mixes the quadrature  246  of the second oscillating signal  244  with the in-phase component  232  of the combined radio frequency signal  202 . The output  268  of the mixer  242  may be represented as 
         Iq =sin(ω B1   t+ 90°)+sin(ω B2   t+ 90°).  (12)
 
     The mixers  218 ,  220 ,  236  to  242  may be implemented with one or more mixers. That is,  FIG. 2  has separate mixers for reasons of simplicity and the actual implementation may be different. For example, the apparatus  200  may comprise a multiplexing element in which the signals to be mixed are, in turns, processed and mixed. 
     In an embodiment, the outputs of the mixers  236 ,  238 ,  240  and  242  are fed as inputs to adders and subtractors. The adders and the subtractors may be applied to separate the in-phase and quadrature components of the first and the second signal. This will be described next. 
     The apparatus  200  may further comprise an adder  254 . The adder  254  adds the second oscillating signal  244  mixed with the in-phase component  232  of the combined radio frequency signal  202  to the quadrature  246  of the second oscillating signal  244  mixed with the quadrature component  234  of the combined radio frequency signal  202  to obtain the in-phase component of the first signal  270  (I 1 ). The output of the adder  254  may be represented as 
         I 1 =Qq+Ii= sin(ω B1   t− 90°+90°)+sin(ω B2   t+ 90°+90°)+sin(ω B1   t )+sin(ω B2   t )=2 sin(ω B1   t ).  (13)
 
     The apparatus  200  may further comprise a subtractor  256 . The subtractor  256  subtracts the quadrature  246  of the second oscillating signal  244  mixed with the quadrature component  234  of the combined radio frequency signal  202  from the second oscillating signal  244  mixed with the in-phase component  232  of the combined radio frequency signal  202  to obtain the in-phase component of the second signal  272  (I 2 ). The output of the subtractor  256  may be represented as 
         I 2= Ii−Qq =sin(ω B1   t )+sin(ω B2   t )−(sin(ω B1   t− 90°+90°)+sin(ω B2   t+ 90°+90°))=2 sin(ω B2   t ).  (14).
 
     The apparatus  200  may further comprise an adder  258 . The adder  258  adds the second oscillating signal  244  mixed with the quadrature component  234  of the combined radio frequency  202  signal to the quadrature  246  of the second oscillating signal  244  mixed with the in-phase component  232  of the combined radio frequency signal  202  to obtain the quadrature component of the second signal  276  (Q 2 ). The output of the adder  258  may be represented as 
         Q 2= Qi+Iq =sin(ω B1   t− 90°)+sin(ω B2   t+ 90°)+sin(ω B1   t+ 90°)+sin(ω B2   t+ 90°)=2 cos(ω B2   t ).  (15)
 
     The apparatus  200  may further comprise a subtractor  260 . The subtractor  260  subtracts the second oscillating signal  244  mixed with the quadrature component  234  of the combined radio frequency signal  202  from the quadrature  246  of the second oscillating signal  244  mixed with the in-phase component  232  of the combined radio frequency signal  202  to obtain the quadrature component of the first signal  274  (Q 1 ). The output of the subtractor  260  may be represented as 
         Q 1= Iq−Qi =sin(ω B1   t+ 90°)+sin(ω B2   t+ 90°)−(sin(ω B1   t− 90°)+sin(ω B2   t+ 90°))=2 cos(ω B1   t ).  (b 16).
 
     Thus, it is shown that the in-phase component  270  (I 1 ) and the quadrature component  274  (Q 1 ) of the first signal and the in-phase component  272  (I 2 ) and the quadrature component  276  (Q 2 ) of the second signal may be extracted from the combined radio frequency signal  202  received as input to the apparatus  200 , wherein the combined radio frequency signal  202  comprises the first and the second signal. 
     The adders and the subtractors  254  to  260  may be implemented with one or more adders and the subtractors. So  FIG. 2  has separate adders and the subtractors for the reasons of simplicity and the actual implementation may be different. 
     According to an embodiment of the invention, the functional blocks in  FIG. 2 , including the one or more mixers, the one or more filters, the one or more amplifiers, the one or more converters, the one or more adders, the one or more distractors, etc., may be realized with one or more processors. The processors may be implemented with separate digital signal processors, provided with suitable software embedded on a computer readable medium, or with separate logic circuits, such as application specific integrated circuits (ASIC). The processors may comprise interfaces such as computer ports for providing communication capabilities. 
     According to an embodiment of the invention, the apparatus  200  of  FIG. 2  may further comprise a processor. The processor may be implemented with a separate digital signal processor provided with suitable software embedded on a computer readable medium, or with a separate logic circuit, such as an ASIC. The processor may comprise an interface, such as a computer port for providing communication capabilities to other functional elements of the apparatus  200 . 
     According to an embodiment of the invention, the processor controls the function of the apparatus  200 . That is, the processor controls the utilization of the first oscillating signal  214 , the quadrature  216  of the first oscillating signal  214 , the second oscillating signal  244  and the quadrature  246  of the second oscillating signal  244 . Further, the processor may control the mixing, filtering amplifying, adding, subtracting, etc. The processor may further control the utilization of other functional elements of the apparatus  200  including, for example, the one or more mixers, the one or more filters, the one or more amplifiers, the one or more converters, the one or more adders, the one or more distractors, etc. 
     According to an embodiment of the invention, the apparatus  200  is employed during high-speed downlink packet access (HSDPA) reception. However, the embodiments of the invention are not limited to HSDPA, but can be applied in any network where dual channel reception is desired. 
       FIG. 4  illustrates a method for dual channel reception according to an embodiment of the invention. The method begins in step  400 . In step  402 , reception of the combined radio frequency signal comprising the first and the second signal is performed. The first and the second signal are on frequency bands of the first and the second channel, respectively, wherein the channels have different center frequencies. 
     Step  404  of the method comprises dividing the combined radio frequency signal into the in-phase component and the quadrature component. This step may also comprise the utilization of mixers in order to form the in-phase and quadrature components of the combined radio frequency signal. Further, filters, amplifiers and analog-to-digital converters may be applied in this step. 
     In step  406 , the converting of the in-phase and quadrature components of the combined radio frequency signal into digital form takes place. The converting may be performed with an analog-to-digital converter. 
     Step  408  of the method comprises separating the in-phase and quadrature components of the first and the second signal from the in-phase and quadrature components of the combined radio frequency signal. This step may also comprise the utilization of digital signal processing in order to form the in-phase and quadrature components of the first and the second signal. The method ends in step  410 . 
     The techniques and methods described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatus may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chip set (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and/or complimented by additional components in order to facilitate the achieving of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art. 
     Thus, according to an embodiment, the apparatus for performing the tasks of  FIGS. 2 and 4  comprises means for receiving the combined radio frequency signal comprising the first and the second signal, the first and the second signal being on frequency bands of the first and the second channel, respectively, wherein the channels have different center frequencies. Further, the apparatus comprises means for dividing the combined radio frequency signal into the in-phase and quadrature components, and means for separating the in-phase and quadrature components of the first and the second signal from the in-phase and quadrature components of the combined radio frequency signal. 
     Embodiments of the invention may be implemented as a computer program in the apparatus according to the embodiments of the invention. The computer program comprises instructions for executing a computer process for performing the dual channel reception. The computer program implemented in the apparatus may carry out, but is not limited to, the tasks related to  FIGS. 2 and 4 . 
     The computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, an electric, magnetic, optical, infrared or semiconductor system, device or transmission medium. The computer program medium may include at least one of the following media: a computer readable medium, a program storage medium, a record medium, a computer readable memory, a random access memory, an erasable programmable read-only memory, a computer readable software distribution package, a computer readable signal, a computer readable telecommunications signal, computer readable printed matter, and a computer readable compressed software package. 
     Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.