Patent Publication Number: US-8995341-B2

Title: Pilot shifting

Description:
TECHNICAL FIELD 
     Some example embodiments presented herein may be directed towards a method in a Base Station for the dynamic shifting of pilot resources in an overlay communications system. Some example embodiments may be directed towards a method in an user equipment for the estimation of channels in an overlay communications system as a function of the dynamic shifting. 
     BACKGROUND 
     The use of mobile broadband (MBB) services is rapidly increasing in all regions of the world as a result of the ongoing transition from cellular telephony to MBB. Mobile data surpassed voice during December 2009 and yearly traffic increases in the order of 200% to 300% have been measured in real networks. This increase is predicted to continue. 
     Mobile operators now face the challenge of handling this immense traffic increase in their networks. One trend in radio research and regulation is based on the observation that many legacy systems are not using their spectrum very efficiently. While replanning of such legacy systems could free up spectrum for licensed mobile use, significant efforts in research, standardization, and regulation are being spent on finding ways of getting higher spectrum utilization in these bands by means of secondary usage of said spectrum. 
     A secondary user in this context is an user which is not using the spectrum for its licensed purpose and has obligations to not cause harmful interference to the licensed, or primary, usage. The broadcast TV systems have become the prime target for secondary spectrum usage and regulatory bodies already have rules in place for secondary usage. The main reasons for the interest in the TV spectrum are the stationary and predictability characteristics of the TV transmitters as well as the high value of the TV spectrum bands. 
     The presence of secondary users implies some sharing of spectrum bands between primary and secondary systems. The sharing of spectrum between two systems is usually grouped into one of the following three categories or approaches: (1) the overlay approach; (2) the underlay approach; or (3) the interweave approach. 
     The underlay approach uses a very low power per unit of bandwidth such that the interference caused to the primary system is kept below a defined level denoted the interference temperature. This level could be on the order of, or below, the thermal noise. 
     The interweave approach is the primary-secondary spectrum sharing approach. In this approach the signals of the secondary systems are orthogonalized to the primary signals in the time, frequency, and/or spatial domain(s). This can be achieved by, e.g., letting the secondary systems communicate on time/frequency resources that are unused by primary systems. Another type of interweave is spatial/frequency orthogonalization where channels unused by the primary system at certain locations can be used by secondary systems. 
     In the overlay approach the secondary system cooperates with the primary system and uses the same spectrum resources for its communication. This can be achieved by, e.g., letting the secondary system forward the primary signals while also transmitting secondary signals on the same communication resources. The approach involves interference management by the secondary system where one possible mechanism is interference cancellation at the secondary receivers in which the primary signal is decoded, reconstructed and subtracted from the received signal which then, ideally, only contains the secondary signal. 
     Studies show that the channel estimation performance may be an important parameter for the sharing of communication resources. For example, if the channel estimates are poor, the achievable secondary system SNRs will be very low. A straightforward implementation of a shared system transmitter just superimposes the secondary signals on the primary signals without making any modifications of the signal design. This results in the optimal channel estimation performance not being achieved, which limits the performance of the secondary system. 
     SUMMARY 
     Thus, at least one object of some of the example embodiments herein may be to provide an improved method of signaling transmission. Some example embodiments may be directed towards a method in a network node for transmitting a combined wireless communication signal. The combined wireless communication signal comprises a primary and a secondary signal component. The network node is comprised in a Radio Network. The method comprises transmitting the secondary signal component to be received by an user equipment. The secondary signal component comprises secondary pilot resources that are dynamically shifted. The dynamic shifting is based on a current estimation procedure. 
     Some example embodiments may be directed towards a method in an user equipment for estimating a primary and a secondary channel, wherein the secondary channel is a subset of the primary channel. The user equipment is comprised in a Radio Network. The method comprises receiving from a network node a combined wireless communication signal. The combined wireless communication signal comprises primary and secondary signal components, where the secondary pilot resources of the secondary signal component are shifted based on a current estimation procedure. The method also comprises estimating the primary channel when the current estimation procedure is a primary channel estimation procedure, and estimating the secondary channel when the current estimation procedure is a secondary channel estimation procedure. 
     Some example embodiments may be directed towards a network node for transmitting a combined wireless communication signal, the combined wireless communication signal comprises a primary and a secondary signal component. The network node is comprised in a Radio Network. The network node comprises a communications port that may be configured to transmit the secondary signal component to an user equipment. The network node also comprises a shifting unit that is configured to dynamically shift secondary pilot resources of the secondary signal component based on a current estimation procedure. 
     Some example embodiments may be directed towards an user equipment for estimating a primary and a secondary channel, wherein the secondary channel is a subset of the primary channel. The user equipment is comprised in a Radio Network. The user equipment comprises a communications port that is configured to receive from a network node a combined wireless communication signal. The combined wireless communication signal comprises primary and secondary signal components, where secondary pilot resources of the secondary signal component are shifted based on a current estimation procedure. The user equipment also comprises an estimation unit that is configured to estimate the primary channel when the current estimation procedure is a primary channel estimation procedure. The estimation unit is also configured to estimate the secondary channel when the current estimation procedure is a secondary channel estimation procedure. 
     Thus, as described above, the example embodiments presented herein describe secondary system pilot resource shifting for improving channel estimation performance. For example, an amount of pilot resource shifting of the secondary system may be selected in order to obtain a desired degree of overlap between the primary and secondary system pilots. This results in a decrease of interference cased by the secondary and primary systems thereby improving the accuracy of the channel estimations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of the example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the example embodiments. 
         FIG. 1  is a schematic of an overlay communications system, according to some of the example embodiments; 
         FIG. 2  is a schematic of an overlay communications system comprising a cognitive transmitter, according to some of the example embodiments; 
         FIG. 3  is a schematic of a Base Station, according to some of the example embodiments; 
         FIG. 4  is a schematic of an user equipment, according to some of the example embodiments; 
         FIG. 5  is a flow diagram depicting example operations for secondary channel estimation which may be performed by the user equipment of  FIG. 4 , according to some of the example embodiments; 
         FIGS. 6A and 6B  are illustrative examples of common taps between two communication channels, according to some of the example embodiments; 
         FIG. 7  is a flow diagram depicting example operations for pilot resource shifting which may be performed by the Base Station and/or the user equipment of  FIG. 3  and  FIG. 4 , respectively, according to some of the example embodiments; 
         FIG. 8  is a flow diagram depicting example operations for cognitive signal transmission and channel estimation which may be performed by the Base Station and/or the user equipment of  FIG. 3  and  FIG. 4 , respectively, according to some of the example embodiments; 
         FIG. 9  is a flow diagram depicting example operations for primary channel estimation which may be performed by the Base Station and/or user equipment of  FIG. 3  and  FIG. 4 , respectively, according to some of the example embodiments; and 
         FIGS. 10A and 10B  are illustrative example of signal suppression, according to some of the example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular components, elements, techniques, etc. in order to provide a thorough understanding of the example embodiments. However, the example embodiments may be practiced in other manners that depart from these specific details. In other instances, detailed descriptions of well-known methods and elements are omitted so as not to obscure the description of the example embodiments. 
     Introduction 
       FIG. 1  depicts an example of an overlay communication system. An overlay communication system is a system which utilizes spectrum sharing in the transmission of wireless communications. An overlay system typically involves a primary and secondary communication system. In the example provided by  FIG. 1 , the primary system may comprise a television broadcast system. The television broadcast system may comprise any number of transmitters  101  that may be configured to transmit wireless television signals, X TV , (e.g., a primary signal component) on a primary channel, h TV ,  103 . The primary channel may also be configured to transmit secondary signal components from a secondary system, as explained below. 
     In the example provided by  FIG. 1 , the secondary system may comprise a mobile communication system. The mobile broadband communications system may comprise any number of transmitters or Base Stations  105  that may be configured to simultaneously transmit a combined wireless signal on a secondary channel, h SS ,  107 . The combined wireless signal may comprise the wireless television signal, X TV , (e.g., the primary signal component) as well as a wireless communication signal, X SS , (e.g., a secondary signal component). 
     Since the secondary channel, h SS , conveys both primary and secondary signal components, the secondary channel may be considered a sub-set of the overall primary channel, h TV , as shown in  FIG. 1 . Therefore, the secondary channel, h SS , and the primary channel, h TV , may comprise common sub-components. 
     It should be appreciated that the television broadcast and mobile broadband systems are used merely as examples. The example embodiments disclosed herein may be applied to any system utilized for transmitting any form of wireless data known in the art. 
       FIG. 2  illustrates a cognitive overlay communications system. In the cognitive overlay communications system, cognitive secondary system transmitters  105 A may be configured to transmit the primary signal and secondary wireless signal simultaneously  201 , as described in relation to  FIG. 1 . The cognitive secondary system transmitters  105 A may also be configured to transmit the primary signal and secondary wireless signal according to a transmission pattern  203 . An example of a transmission pattern  203  may be an alternate transmission of the primary and secondary signals, such that the primary and secondary signals are not transmitted simultaneously. It should be appreciated that the alternate transmission pattern need not occur during the entire duration of the transmission, for example, transmission patterns may be applied during predetermined periods of transmission. It should be appreciated that any other type of transmission pattern may be employed. For example, the primary signal may be continuously transmitted while the secondary signal is transmitted at predetermined time intervals. 
     A mobile device, for example user equipment  100 , may be configured to receive communications from transmitters belonging to both the primary and secondary systems. The received signal may be represented, for example, as follows:
 
 Y=H   TV   X   TV   +H   SS   X   SS   +E   1   +H   SS   E   2   +N   (1)
 
where Y is the combined received signal, X TV  is the primary signal component (e.g., television broadcast signal), X SS  is the secondary signal component (e.g., cellular communication signal), N is thermal noise and interference, H TV  is the superposition of wireless channels that participate in the single-frequency broadcast of television signals, H SS  describes the wireless channel experienced by the signal transmitted from the secondary system, E 2  is the Error Vector Magnitude (EVM) noise generated by transmitters used to generate X SS  and X TV , and E 1  is the EVM noise generated by all other transmitters in the overlay system and filtered by the channel.
 
     After channel estimation, decoding, reconstruction, and cancellation of the primary television signal X TV , the residual signal becomes:
 
 Y   SS =( H   1   −H   est ) X   TV   +H   SS   X   SS   +E   1   +H   SS   E   2   +N   (2)
 
where H est  denotes the estimated primary channel. It should be noted that the primary signal remains due to imperfect channel estimation. The channel estimation performance (e.g., how similar H est  is to H TV ) plays a role when it comes to evaluation of the achievable Signal to Interference plus Noise Ratio (SINR) of Y SS .
 
     Thus, at least one object of some of the example embodiments herein may be to provide an improved method of signaling transmission. The technical effect of this object may be to provide improved channel estimations without greatly increasing the amount hardware components or system resources. 
     Specifically, some example embodiments presented herein may be directed towards an improved channel estimation. Some example embodiments may be applied to a Base Station and/or user equipment node. Some example embodiments may be applied to methods of primary and/or secondary channel estimations. Some example embodiments may utilize pilot resource shifting in conjunction with the primary and/or secondary channel estimations. It should be appreciated that the example embodiments may be applied to other nodes in a Radio network. 
     The example embodiments will be further described below according to the respective sub-headings. First example configurations of a Base Station and user equipment will be provided. Thereafter, some example embodiments directed towards secondary channel estimation will be described. Thereafter, some example embodiment directed towards pilot resource shifting will be provided. Pilot resource shifting may be related to a method of signal transmission which may be utilized for channel estimations. Example embodiments directed towards cognitive transmission will also be provided. Thereafter, some example embodiments directed towards primary channel estimation will be provided. 
     It should be appreciated that a primary channel estimation procedure herein refers to the primary channel being estimated and the secondary channel may be estimated with use of the primary channel estimation (i.e., based on the primary pilot resources). A secondary channel estimation procedure refers to the use of secondary pilot resources to estimate the secondary channel. 
     Base Station Configuration 
       FIG. 3  provides an illustrative example of a Base Station network node configuration, according to some of the example embodiments. The Base Station  101 ,  105 , or  105 A may comprise any number of communication ports  307 . The communication ports  307  may be configured to receive and transmit any form of communications data  303  and  305 , respectively. It should be appreciated that the Base Station  101 ,  105 , or  105 A may alternatively comprise a single transceiver port. It should further be appreciated that the communication or transceiver port may be in the form of any input/output communications port known in the art. 
     The Base Station  101 ,  105 , or  105 A may further comprise at least one memory unit  309  that may be in communication with the communication ports  307 . The memory unit  309  may be configured to store received, transmitted, and/or measured data of any kind and/or executable program instructions. The memory unit  309  be any suitable type of computer readable memory and may be of a volatile and/or non-volatile type. 
     The Base Station  101 ,  105 , or  105 A may also comprise a shifting unit  313  that may be configured to shift pilot resources of the primary and/or secondary signals. The Base Station  101 ,  105 , or  105 A may further comprise a suppression unit  315  that may be configured to suppress, puncture, and/or mute the transmission of the primary and/or secondary signal components. The Base Station  101 ,  105 , or  105 A may also comprise a general processing unit  311 . 
     It should be appreciated that the shifting unit  313 , the suppression unit  315 , and/or the processing unit  311  may be any suitable type of computation unit, e.g. a microprocessor, digital signal processor (DSP), field programmable gate array (FPGA), or application specific integrated circuit (ASIC). It should also be appreciated that the shifting unit  313 , the suppression unit  315 , and/or the processing unit  311  need not be comprised as separate units. The shifting unit  313 , the suppression unit  315 , and/or the processing unit  311  may be comprised as a single computational unit or any number of units. 
     User Equipment Configuration 
       FIG. 4  provides an illustrative example of an user equipment network node configuration, according to some of the example embodiments. The user equipment  100  may comprise any number of communication ports  407 . The communication ports  407  may be configured to receive and transmit any form of communications data  403  and  405 , respectively. It should be appreciated that the user equipment  100  may alternatively comprise a single transceiver port. It should further be appreciated that the communication or transceiver port may be in the form of any input/output communications port known in the art. 
     The user equipment  100  may further comprise at least one memory unit  409  that may be in communication with the communication ports  407 . The memory unit  409  may be configured to store received, transmitted, and/or measured data of any kind and/or executable program instructions. The memory unit  409  be any suitable type of computer readable memory and may be of a volatile and/or non-volatile type. 
     The user equipment  100  may also comprise an estimation unit  413  that may be configured to estimate the primary and/or secondary signals and/or the primary and/or secondary communication channels. The user equipment  100  may further comprise an evaluation unit  415  that may be configured to determine common sub-components between the primary and secondary communication channels. The user equipment  100  may also comprise a general processing unit  411 . 
     It should be appreciated that the estimation unit  413 , the evaluation unit  415 , and/or the processing unit  411  may be any suitable type of computation unit, e.g. a microprocessor, digital signal processor (DSP), field programmable gate array (FPGA), or application specific integrated circuit (ASIC). It should also be appreciated that the estimation unit  413 , the evaluation unit  415 , and/or the processing unit  411  need not be comprised as separate units. The estimation unit  413 , the evaluation unit  415 , and/or the processing unit  411  may be comprised as a single computational unit or any number of units. It should also be appreciated that the user equipment  100  may be a mobile phone, a Personal Digital Assistant (PDA), or any other wireless communications network unit capable to communicate with a base station over a radio channel. 
     Secondary Channel Estimation 
     Some example embodiments may be directed towards providing improved secondary channel estimations. In general, the secondary system channel estimate used for demodulation in the secondary system may be improved by utilizing the channel estimate from the primary system. If the primary signal is transmitted from multiple sources whereas the secondary signal is transmitted from a single source also, example embodiments may be used to identify common sub-components in the primary and secondary channel estimates, respectively, and utilize this information to derive an improved secondary system channel estimate. 
     By design the primary system may have more power than the secondary system. Therefore, the channel estimate formed in the primary system may be of higher quality and may be used in the secondary system. Thus, if the primary signal is transmitted by a single source, the channel estimate obtained in the primary system may be used and forwarded to the secondary system receiver. Alternatively, the user equipment may comprise a primary channel estimator which may forward the estimation information. The estimation may comprise an interpolation of the primary system channel estimate to make it compatible with the secondary system, e.g., if the primary and secondary systems are OFDM systems with different time/frequency grids. It could also comprise an extrapolation if the secondary system utilizes a larger bandwidth or larger time duration than the primary system. Alternatively, the channel estimate may be parameterized and the parameterized model may be forwarded to the secondary system. 
     Potentially the primary signal may be transmitted from multiple sources, e.g., neighbouring Base Stations in a Single Frequency Network (SFN) or a high tower TV transmitter. In this case the channels of the primary and secondary systems are not identical. Therefore, the primary channel may be a combination of the channel from the “other” primary system transmitters (those that are not also sending the secondary signal of interest) and the primary signal transmitter that is sending the secondary signal of interest. 
       FIG. 5  illustrates a flow diagram that provides example operations which may be utilized by the user equipment network node  100  of  FIG. 4  in providing secondary channel estimation, using primary channel estimation, for a multiple source scenario. 
     Operation  500 : 
     Some example embodiments directed towards improved secondary channel estimation may comprise an user equipment  100  receiving  500  from a network node (e.g., a Base Station  101 ,  105  or  105 A) a combined wireless communication signal (e.g., comprising primary and secondary signal components) through at least a portion of the primary channel. 
     The receiving  500  may be provided via the communications port  407 . Specifically, the communications port  407  is configured to receive from the network node (e.g., Base Station  101 ,  105  or  105 A) the combined wireless communication signal through at least a portion of the primary channel. 
     Operation  500 A: 
     Prior to the performance of any channel estimations, operations may also comprise the user equipment  100  sending  500 A information to a network node (e.g., Base Station  105  or  105 A). The information may provide an indication of a current estimation procedure. 
     Such information may be used by a cognitive Base Station  105 A in determining the transmission pattern of the primary and secondary signals. For example, if the user equipment  100  is under going a primary channel estimation procedure, the Base Station  105 A may utilize the sent  500 A information and transmit only the primary signal and the resources used for the primary channel estimation procedure. Similarly, if the user equipment  100  is under going a secondary channel estimation procedure, the Base Station  105 A may utilize the sent  500 A information and transmit the secondary signal such that the interference from the primary signal on the secondary pilot resources is reduced. 
     The information regarding the current estimation procedure may also be utilized for pilot resource shifting, which will be explained in greater detail below. For example, if the user equipment  100  is under going a primary channel estimation procedure, the sent  500 A information may be utilized by the Base Station  105  or  105 A to maximize an overlap between pilot resources of the primary and secondary signals. It should be appreciated that the maximizing may comprise any overlap percentage above a certain user programmable threshold. Similarly, if the user equipment  100  is under going a secondary channel estimation procedure, the Base Station  105  or  105 A may utilize the sent  500 A information and minimize an overlap between pilot resources of the primary and secondary signals. It should be appreciated that the minimizing may comprise any overlap percentage below a certain user programmable threshold. 
     Operation  501 : 
     Upon receiving the combined wireless communication signal, operations in the user equipment  100  also comprise determining  501  an estimate of the primary channel. The estimation unit  413  and/or processing unit  411  are configured to estimate the primary channel. 
     Operation  502 : 
     In some example embodiments, the determining  501  of the estimation of the primary channel may further comprise the user equipment  100  reconstructing  502  the primary signal component of the combined wireless communication signal. The reconstruction  502  may be performed with the use of the estimation unit  413  and/or the processing unit  411 . 
     Operation  503 : 
     The determining  501  operation may further comprise the user equipment  100  re-estimating the primary channel using the reconstructed signal as a pilot resource. The operation of reconstruction  503  may be performed with the use of the estimation unit  413  and/or the processing unit  411 . 
     Re-estimation of the primary channel with the utilization of the reconstructed signal as a pilot resource may increase the accuracy of the primary channel estimation. 
     Operation  505 : 
     After the determination  501  of the primary channel estimate has been obtained, operations further comprise the user equipment  100  determining  505  an estimate of the secondary channel. The estimation of the secondary channel may be obtained with a reconstructed secondary signal component. The reconstructed secondary signal component may be obtained by subtracting the primary signal component from the received signal. The estimation unit  413  and/or the processing unit  411  is configured to estimate the secondary channel. 
     Operation  506 : 
     Upon determining  505  the secondary channel, operations further comprise determining  506  at least one common sub-component (e.g., at least one common tap) between the estimations of the primary and secondary channels. An evaluation unit  415  and/or the processing unit  411  is configured to determine the at least one common sub-component between the estimations of the primary and secondary channels. A common sub-component may be a portion of the primary and secondary channels which correspond or are similar. 
     Operation  507 : 
     In determining  506  the at least one common sub-component, operations may further comprise the operation of the user equipment  100  constructing  507  a first and second time and/or frequency representation or any other parameterized representation of the estimated primary and secondary channel. The evaluation unit  415  and/or the processing unit  411  may be configured to perform the constructing  507 . 
     Examples of time and frequency domain representations are provided in  FIGS. 6A and 6B , respectively. In  FIGS. 6A and 6B , the upper graph represents the estimated channel comprising the primary and secondary channels, and the lower graph in  6 A represents the secondary channel (in this case represented as taps), whereas the lower graph in  6 B shows both the primary (excluding the secondary component) and secondary channels which together build up the joint channel, i.e., that is illustrated in the upper graph. The x-axis of all the graphs in  FIGS. 6A and 6B  represent the time and frequency, respectively. 
     Specifically,  FIG. 6A  illustrates an example of a constructed time domain representation comprising scatter responses of the estimated primary channel, H TV ,  601 A.  FIG. 6A  also illustrates an example of a constructed time domain representation of the estimated secondary channel H SS ,  603 A. 
       FIG. 6B  illustrates an example of a constructed frequency domain representation of the estimated primary channel, H TV ,  601 B.  FIG. 6B  also illustrates an example of a constructed frequency domain representation of the estimated secondary channel H SS ,  603 B. 
     Operation  508 : 
     Once the time and/or frequency domain representations or any other parameterized representation have been constructed  507 , operations may further comprise the user equipment  100  comparing  508  the first and second time and/or frequency domain representations or any other parameterized representation. The comparing  508  may be performed by the evaluation unit  415  and/or the processing unit  411 . 
     Operation  509 : 
     The comparing  508  may aid in the user equipment  100  determining  509  at least one similar delay component and/or a similar complex exponential waveform or any other similar parameter of the first and second time and/or frequency representations, respectively. The determining  509  may be performed by the evaluation unit  415  and/or the processing unit  411 . 
     The common sub-component (e.g., common tap) may be determined by comparing the time domain representation, or scatter responses, of the primary channel, H TV ,  601 A with the time domain representation of the secondary channel, H SS ,  603 A. As shown in  FIG. 6A , a common tap may be found where the primary and secondary time domain representations  601 A and  603 A, respectively, are similar such as the taps marked by  605 . 
       FIG. 6B  illustrates an example of a common tap in the frequency domain. The two complex exponential waveforms on the bottom of  FIG. 6B  correspond to channels of the secondary and primary system (excluding the secondary component) respectively, as denoted in the legend. The sum of those two waveforms, depicted in the upper graph of  FIG. 6B  corresponds to the estimated primary channel. This waveform may be compared with the complex exponential waveform of the secondary channel to determine the common complex exponential waveform. The common waveform can be transformed to the time domain to yield the common tap(s), which is similar to what is illustrated in  FIG. 6A . 
     The common sub-components may represent a portion of the estimated channel which stems from the transmitter which transmits the secondary signal. It should be appreciated that in the determination of the common sub-components, the common sub-component portions of the time or frequency domain representations need not be identical. For example, a common sub-component may be determined if the common sub-component portions of the time or frequency domain representations are similar with respect to a threshold percentage. The threshold percentage may be based on any percentage of similarity and may further be user programmable. 
     Operation  510 : 
     Operations further comprise the user equipment determining  510  an updated estimation of the secondary channel based on the at least one common sub-component (e.g., at least one common tap). The channel estimation of the primary channel comprising the at least one common sub-component can be used as estimate for the secondary channel for those sub-components. The determining estimation unit  413  and/or the processing unit  411  is configured to update the estimate of the secondary channel based on the at least one sub-component. For example, the secondary channel estimate may be obtained by taking the estimated values from the primary channel of the at least one common sub-component. 
     Therefore, as described above, an improved estimation of the secondary channel may be provided by obtaining a more precise estimation of the primary channel. According to some example embodiments this may be achieved with the use of the reconstructing  502  and re-estimation  503 . Furthermore, estimations are further improved by utilizing common sub-components  506  in the estimation of the secondary channel  510 . Thus, relative interference and noise levels in the secondary channel estimation may be reduced. 
     Pilot Resource Shifting 
     Some example embodiments may be directed towards pilot resource shifting. Pilot resource shifting may be applicable if the secondary system allows for pilot shifting in the time and/or frequency domain. An example of such a system is a Long Term Evolution (LTE) system where the pilot resources may be shifted in time and/or frequency. Presumably overlap between the pilot resources of the primary and secondary systems may be different based upon the pilot resource shifting in the secondary system. Thus, some example embodiments may be directed towards the optimal shifting of pilot resources of the secondary system. It should be appreciated that some example embodiments may also comprise pilot resource shifting of the primary system. 
     If the secondary system uses the channel estimate of the primary system as described above the pilot shifting may be selected to maximize the overlap between the pilots, assuming that the non-overlapping pilots of the secondary system are enough to give a rough estimate of the sub-components in the channel representation if needed (e.g., as explained in operation  506 ). The overlapping pilots may then be suppressed since they will not be used (or will at least not be used for decoding). The suppression may comprise puncturing or muting, which will be described in greater detail below. This allows a larger portion of the secondary resources to be used for data. 
     The optimization of the pilot shifting is not a time critical parameter to compute since it may be part of configuration (e.g., can be computed off-line).  FIG. 7  illustrates a flow diagram depicting example operations which are utilized in the Base Station  105  or  105 A and the user equipment  100  of  FIGS. 3 and 4 , respectively, in providing the shifting of pilot resources and estimation based on the shifting. 
     Operation  700 : 
     The shifting of pilot resources comprises transmitting  700  from the network node (e.g., Base Station  105  or  105 A) the secondary signal component to be received by an user equipment  100 . The secondary signal component comprises secondary pilot resources that are dynamically shifted. The dynamic shifting is based on a current estimation procedure. 
     The communications port  307  is configured to transmit the secondary signal component to an user equipment  100 . A shifting unit  313  is configured to dynamically shift secondary pilot resources of the secondary signal component based on a current estimation procedure. 
     Operation  701 : 
     In this operation the network node (e.g., Base Station  105  or  105 A) may determine  701  a value of the current estimation procedure. The determining  701  may be performed by the shifting unit  313  and/or the processing unit  311 . 
     Operation  702 : 
     The operation of determining  701  may further comprise the operation of the network node (e.g., Base Station  105  or  105 A) determining  702  the value of the current estimation procedure and thereafter sending said value to the user equipment  100 . The value of the current estimation may be useful such that the user equipment  100  may have knowledge of how it should perform channel estimation. Since the determining  702  occurs within the network node, it is the network node which may dictate the value of the estimation procedure and the shifting of pilot resources. The operation of determining  702  may be performed by the shifting unit  313  and/or the processing unit  311 . 
     Operation  703 : 
     The operation of determining  701  may comprise the operation of the network node (e.g., Base Station  105  or  105 A) obtaining  703  the value of the current estimation procedure from the user equipment  100 . In such an instance, it is the user equipment  100  which may dictate the current estimation mode and the shifting of pilot resources. The operation of obtaining  703  may be performed by the communications ports  307 . 
     Operation  704 : 
     Pilot resource shifting may also comprise the operation of dynamically shifting  704  the secondary pilot resources to provide a maximum overlap with primary pilot resources of the primary signal component, e.g., when the current estimation procedure is a primary estimation procedure. It should be appreciated that the maximizing may comprise any overlap percentage above a certain threshold, wherein the threshold may be an user programmable threshold of any value. The operation of shifting  704  may be performed by the shifting unit  313  or the processing unit  311 . 
     Operation  705 : 
     Pilot resource shifting may also comprise the operation of dynamically shifting  705  the secondary pilot resources to provide a minimum overlap with primary pilot resources of the primary signal component, e.g., when the current estimation procedure is a secondary channel estimation procedure. It should be appreciated that the minimizing may comprise any overlap percentage below a certain threshold, wherein the threshold may be an user programmable threshold of any value. It should further be appreciated that any other threshold may be employed. The operation of shifting  705  may be performed by the shifting unit  313  or the processing unit  311 . 
     Operation  706 : 
     Pilot resource shifting may also comprise a number of operations performed within the user equipment  100 , for example operations  706 - 711 . Example operations may comprise the operation of the user equipment  100  receiving  706  from a network node (e.g., Base Station  101 ,  105  or  105 A) a combined wireless communication signal comprising primary and secondary signal components. Secondary pilot resources of the secondary signal component being shifted based on a current estimation procedure. 
     A communications port  407  is configured to receive from a network node (e.g., Base Station  101 ,  105  or  105 A) a combined wireless communications signal comprising primary and secondary signal components, secondary pilot resources of the secondary signal component are shifted based on a current estimation procedure. 
     Operation  707 : 
     Operations may also comprise determining  707  the value of the current estimation procedure within the user equipment  100 . The operation of determining  707  may be performed by the estimation unit  413  or the processing unit  411 . 
     Operation  708 : 
     The operation of determining  707  may comprise the user equipment  100  determining  708  the value of the current estimation procedure and sending said value to the network node. The network node may receive the sent value as described in relation to operation  703 . The operation of determining  708  may be performed by the estimation unit  413  or the processing unit  411 . 
     Operation  709 : 
     The operation of determining  707  may comprise the user equipment  100  obtaining  709  the value of the current estimation procedure from the network node. The value obtained from the network node may be provided as explained in relation to operation  702 . The operation of obtaining may be performed by the communications port  407 . 
     Operation  710 : 
     Operations further comprise the user equipment  100  estimating  710  the secondary channel when the current estimation procedure is a secondary channel estimation procedure. 
     The estimation unit  413  and/or the processing unit  411  are further configured to estimation the secondary channel when the current estimation procedure is a secondary channel estimation procedure. 
     Operation  711 : 
     Operations further comprise the user equipment  100  estimating  711  the primary channel when the current estimation procedure is a primary channel estimation procedure. 
     The estimation unit  413  and/or the processing unit  411  are further configured to estimation the primary channel when the current estimation procedure is a primary channel estimation procedure. 
     Thus, as described above, the shifting of pilot resources may be useful in providing optimized channel estimations. Specifically, during primary channel estimation a maximum overlap of pilot resources may enable a greater number of secondary resources to be used for data. During secondary channel estimation a minimum overlap of pilot resources may reduce interference caused by the primary system on the secondary pilot resources. 
     It should be appreciated that the shifting of pilot resources may be provided by a series of computer executable instructions stored on a computer readable medium. The optimization of the pilot shifting is not a time critical parameter to compute since it is part of configuration (i.e., can be computed off-line). An example algorithm, or computer executable instructions, for computing an optimal pilot shift is outlined below.
         1 Decide the target pilot overlap (e.g., “maximum”, “minimum” or somewhere in between (e.g., 30%)), alternatively define a performance metric to optimize.   2 For each possible pilot shift i in the set S where S contains all allowed pilot shifts, compute the pilot overlap (alternatively the metric to optimize) and store it in O(i) where O is an array.   3 Select the pilot shift i where O(i) corresponds best to the target pilot overlap (where the performance metric is optimized) decided in step 1.       

     It should be appreciated that the instructions provided above were done so merely to provide an example. Any other form of instructions may be utilized. 
     Cognitive Transmission and Estimation 
     In some example embodiments, cognitive transmission and estimation may be employed.  FIG. 8  is a flow diagram depicting example operations performed by a network node (e.g., Base Station  105 A) and the user equipment  100  for handling primary and secondary channels, wherein the secondary channel is a sub-component of the primary channel, according to some of the example embodiments. 
     Operation  801 : 
     Cognitive transmission and estimation may comprise a network node (e.g., Base Station  105 A) sending  801  combined wireless communication signals on the secondary channel, which is a subpart of the primary channel, according to a predetermined pattern. The communication ports  307  is configured to send combined wireless communication signals on the secondary channel, which is a subpart of the primary channel, according to a predetermined pattern. Specifically, some example embodiments may comprise an alternating between sending  801  combined wireless communication signals and being quiet (e.g., not sending any signals at all) according to the predetermined pattern. 
     Operation  802 : 
     Operations may also comprise a network node sending  802  control signals to a cognitive user equipment  100 , or an user equipment capable of receiving cognitive data, the control signals may comprise information indicative of the predetermined pattern. The communications port  307  may be further configured to send the control signals to a cognitive user equipment  100 , where the control signals may comprise the predetermined pattern. The sending  802  of control signals may be useful to the user equipment  100 , as the user equipment may adjust its current estimation procedure based on what is currently being sent. 
     Operation  803 : 
     Cognitive transmission and estimation may also comprise an user equipment  100  receiving  803  combined wireless communication signals on the primary and secondary channels according to a predetermined pattern. 
     The communications port  407  is configured to receive combined wireless combination signals on the primary and secondary channels according to a predetermined pattern. Specifically, some example embodiments may comprise alternately receiving  803  combined wireless communication signals on the primary and secondary channels and the primary signal only on the primary channel (from  101  since  105 ,  105   a  is quiet). 
     Operation  804 : 
     Operations may further comprise the operation of the user equipment  100  estimating  804  the primary and secondary channels as a function of the predetermined pattern. As described in relation to operation  802 , the user equipment may gain knowledge of the current signal being transmitted via the control signals. It should be appreciated that in some example embodiments, the user equipment  100  may be configured to send a request to the network node that either the primary or secondary signal be sent at any given time. 
     Thus, as described above, cognitive transmission and estimation may provide improved channel estimations such that when the primary or secondary channel is being estimated, the secondary or primary signal, respectively, may not be transmitted from the cognitive transmitter, according to some example embodiments. Thus, channel estimation interference may be reduced. 
     Primary Channel Estimation 
     As described above, in relation to equation (2), the channel estimation performance (e.g., how similar H est  is to H) may play a role when it comes to evaluation of the achievable Signal to Interference plus Noise Ratio (SINR) of Y SS . However, the overlaid secondary system may add interference to the pilots of the primary system and therefore effect the channel estimation. Thus, some example embodiments may be directed towards increasing the primary system channel estimation performance by suppressing the resources of the secondary system which overlaps with the pilot resources of the primary system. In some example embodiments, suppression may comprise puncturing or muting of the pilot resources. 
     In an Orthogonal Frequency Division Multiplexing (OFDM) scenario, this means that no or little power may be allocated to the time and/or frequency resources of the secondary system which overlap with the time and/or frequency resources used for channel estimation (e.g., pilots, or reference symbols) in the primary system. According to some example embodiments, a margin could be introduced such that slightly larger resources are left empty in the secondary system. This may reduce leakage effects from the non-empty resources of the secondary system to the pilot resources of the primary system. Leaving larger resource regions empty may be useful if OFDM system parameters do not coincide since then orthogonality between the two systems is not given. Potentially complete OFDM symbol(s) needs to be punctured or muted. 
     In the suppression of pilot resources, puncturing may be utilized. Puncturing may comprise the process or replacing resource elements with a zero element after rate matching resulting in empty regions. It should also be appreciated that such empty regions may already be considered during rate matching, i.e. no information is mapped onto those resources. This process is referred to as muting. It should further be appreciated that a cancelling signal may be applied to the regions of interest, such that the applied canceling signal results in a reduced power region. 
       FIG. 9  is a flow diagram illustrating example operations which may be performed by a network node (e.g., Base Station  105  or  105 A) and an user equipment  100  with regard to primary channel estimation, according to some of the example embodiments. 
     Operation  900 : 
     Primary channel estimation may comprise a network node (e.g., Base Station  105  or  105 A) transmitting  900  to an user equipment  100  the secondary signal component according to a secondary transmission scheme such that the secondary signal component at least partially overlaps with the primary signal component with respect to a signal domain. 
     The communications port  307  may be configured to transmit to the user equipment  100  the secondary signal component according to a secondary transmission scheme such that the secondary signal component at least partially overlaps with the primary signal component with respect to a signal domain. 
     It should be appreciated that the signal domain may be a time, frequency, and/or code domain. It should also be appreciated that the primary and secondary signal components may be transmitted with respect to a domain grid transmission scheme. 
       FIG. 10A  illustrates an example of an overlapping signal transmission comprising primary and secondary signal transmission using a time and frequency domain grid transmission. The primary signal may be transmitted according to a time-frequency primary grid  205 . The secondary signal may be transmitted according to a time-frequency secondary grid  207 . As illustrated from  FIG. 10A , the secondary domain grid may comprise a secondary grid spacing which may be different from a primary grid spacing of a primary domain grid transmission scheme. An example of a primary pilot resource  206  is also provided in  FIG. 10A . 
     Operation  901 : 
     Primary channel estimation also comprises the network node simultaneously suppressing  901  at least one portion of the secondary signal component during the transmission of the primary signal component. The suppression unit  315  and/or processing unit  311  are configured to suppress at least one portion of the secondary signal during a transmission of the primary signal component 
       FIG. 10B  provides an example of signal suppression. In the center of the primary grid  205  an ‘X’  206  represents a pilot resource symbol. As shown in  FIG. 10B , portions of the secondary grid which overlap with the pilot resources of the primary grid  205  may be suppressed (denoted in  FIG. 10B  as shaded areas). Thus, as the primary channel is being estimated (e.g., with the utilization of the primary pilot resources  206 ), any interference from the secondary system may be greatly reduced due to the suppression. It should be appreciated that while  FIGS. 10A and 10B  illustrate the use of a time-frequency grid, any type of grid in the time, frequency, or code domain may be employed. 
     Operation  902 : 
     As described above, the suppression may comprise the network node puncturing or muting  902  the at least one portion of the secondary signal component which overlaps with pilot resources of the primary signal component. The operation of puncturing or muting  902  may be performed by the suppression unit  315  and/or the processing unit  311 . It should be appreciated that the puncturing or muting may be performed together with a cancelling signal such that once the cancelling signal is combined with the secondary signal; the combined signal may experience a reduced (e.g., zero or close to zero) amplitude in the predetermined grid cells. 
     Operation  903 : 
     Operations may further comprise the network node suppressing  903  at least one region of the secondary domain grid. The operation of suppression  903  may be performed by the suppression unit  315  and/or the processing unit  311 . 
     As shown in  FIG. 10B , in some example embodiments for any portion of the secondary grid  207  which overlaps with the primary pilot resource ‘X’  206 , an entire region of the grid cell may be suppressed. For example, only a portion of the secondary grid cell  208  overlaps with the pilot symbol  206 . However, in some example embodiments the entire region of the secondary grid cell  208  may be suppressed in order to improve the primary channel estimation performance. Similarly, in some example embodiments, an entire region of a secondary grid cell  210  may be suppressed even if the cell does not overlap with the primary pilot resource  206 . Specifically, secondary grid cells surrounding or in close proximity to the primary pilot resource may be suppressed as well. 
     Operation  904 : 
     Operations may further comprise the network node being a secondary transmitter and the secondary transmitter obtaining  904  information regarding a transmission pattern of a pilot resource of the primary signal component. A secondary transmitter may be a secondary system transmitter which solely transmits the secondary communication signal. The operation of obtaining  904  may be performed by the communications port  307  and/or the processing unit  311 . 
     Operation  905 : 
     The operation of obtaining  904  may further comprise the secondary transmitter suppressing  905  the at least one portion of the secondary signal component as a function of the information. The operation of suppressing  905  may be performed by the suppression unit  315  and/or the processing unit  311  of the secondary transmitter. 
     Operation  906 : 
     Operations may further comprise an user equipment  100  receiving  906  a combined wireless communication signal. The primary and secondary signal components being received according to a primary and secondary transmission scheme associated with a primary and secondary signal domain, respectively. 
     The communications port  407  is configured to receive from a network node (e.g., Base Station  105  or  105 A) a combined wireless communication signal comprising primary and secondary signal components, the primary and secondary signal components being received according to a primary and secondary transmission scheme, associated with a primary and secondary signal domain. 
     Operation  907 : 
     Operations also comprise an user equipment  100  estimating  907  the primary channel when the secondary signal component is suppressed. The estimation unit  413  and/or processing unit  411  are configured to estimate the primary channel during a period when the secondary channel is suppressed. 
     Operation  908 : 
     The operation of estimating  907  may comprise the User Equipment  100  estimating  908  the primary channel during a period when the at least one portion of the secondary signal component overlaps with a pilot resource of the primary signal component. For example, even if only a small portion of a grid cell overlaps with the pilot resource, an entire region of the grid cell of the secondary signal may be suppressed, as explained in relation to operation  903 . The operation of estimating may be performed by the estimation unit  413  and/or the processing unit  411 . 
     Thus, as described above, primary channel estimation may be improved with the use of suppression, according to some example embodiments. The use of suppression may reduce interference during estimation. 
     Conclusion 
     Some example embodiments may comprise a portable or non-portable telephone, media player, Personal Communications System (PCS) terminal, Personal Data Assistant (PDA), laptop computer, palmtop receiver, camera, television, radar and/or any appliance that comprises a transducer designed to transmit and/or receive radio, television, microwave, telephone and/or radar signals. The device according to the example embodiments is however intended for use particularly, but not exclusively for high frequency radio equipment. 
     The foregoing description of the example embodiments, have been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products. 
     It should be noted that the word “comprising” does not necessarily exclude the presence of other elements or steps than those listed and the words “a” or “an” preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the example embodiments may be implemented at least in part by means of both hardware and software, and that several “means”, “units” or “devices” may be represented by the same item of hardware. 
     A “device” as the term is used herein, is to be broadly interpreted to comprise a radiotelephone having ability for Internet/intranet access, web browser, organizer, calendar, a camera (e.g., video and/or still image camera), a sound recorder (e.g., a microphone), and/or global positioning system (GPS) receiver; a personal communications system (PCS) terminal that may combine a cellular radiotelephone with data processing; a personal digital assistant (PDA) that can comprise a radiotelephone or wireless communication system; a laptop; a camera (e.g., video and/or still image camera) having communication ability; and any other computation or communication device capable of transceiving, such as a personal computer, a home entertainment system, a television, etc. 
     The various example embodiments described herein is described in the general context of method steps or processes, which may be implemented in one aspect by a computer program product, embodied in a computer-readable medium, including computer-executable instructions, such as program code, executed by computers in networked environments. A computer-readable medium may comprise removable and non-removable storage devices including, but not limited to, Read Only Memory (ROM), Random Access Memory (RAM), compact discs (CDs), digital versatile discs (DVD), etc. Generally, program modules may comprise routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes.