Patent Publication Number: US-2011059703-A1

Title: User equipment-initiated precoding subset restriction for communication systems

Description:
This application claims the benefit of U.S. Provisional Application No. 60/976,106 entitled “UE-Initiated Precoding Subset Restriction for MIMO Networks,” filed on Sep. 28, 2007, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates, in general, to communications systems and, more particularly, to user equipment (“UE”)-initiated restriction of a precoding subset in a communication system. 
     BACKGROUND 
     The third generation partnership project (“3GPP”) long term evolution (“LTE”) describes an ongoing effort across the industry to improve the universal mobile telecommunications system (“UMTS”) for mobile communications to cope with continuing new requirements and the growing base of users. The goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards. The 3GPP LTE work project should result in new recommendations for standards for the UMTS. 
     Advancement of the access network to the core communication network is also a topic of interest within the 3GPP. The access network, referred to as the universal terrestrial radio access network (“UTRAN”), deals with the part of the communication network that generally consists of radio network controllers (“RNCs”), which control access to radio resources and the base stations/Node Bs or enhanced Node Bs (“eNode Bs”) lying between an interface (referred to as the “Iu”) of the RNCs with the core communication network and an interface (referred to as the “Uu”) of the UTRAN with user equipment (“UE”) or terminals. The core communication network is accessed through mobile switching centers (“MSCs”), cell broadcast centers (“CBCs”), general packet radio service (“GPRS”) support nodes (“SGSN”), and the like. 
     For the LTE, one of the targets is to achieve high peak data rates combined with high spectral efficiency. To obtain this, a number of features are considered, such as hybrid automatic repeat requests (“HARQ”), to keep the spectral efficiency high, and multiple-input, multiple-output (“MIMO”) transmission, mainly to reach high peak data rates, but also to improve the average communication system throughput. Two of the MIMO communication operation modes are the downlink (“DL”) single user (“SU”) and multi-user (“MU”) MIMO communication modes (also referred to as “SU-MIMO” and “MU-MIMO,” respectively), which may be based on precoded multi-stream transmission to single or multiple users. 
     Precoding in MIMO is typically related to multi-layer beamforming. In single-layer beamforming, the same signal is emitted from each of the transmit antennas with the appropriate phase and gain weighting in an attempt to maximize the signal power at a receiver. The benefits of beamforming are to increase the signal gain from constructive combining of multiple signals and to reduce multipath fading effects. When the receiver has multiple antennas, as is typically the case in MIMO communication systems, the transmit beamforming cannot simultaneously maximize the signal level at all of the receive antennas. Therefore, precoding is used to increase that signal level. Implementation of precoding generally requires knowledge of the channel state information (“CSI”) at the transmitter. This precoded multi-stream transmission, therefore, effectively boosts the user data rates. Precoding is typically based on codebooks known by the eNode B and UE as configured according to 3GPP TS 36.211 entitled “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Channels and Modulation (Release 8),” V.1.2.0 (June 2007), V.2.0.0 (September 2007) and V.8.0.0 (September 2007) which are incorporated herein by reference. 
     The eNode B may restrict the code words that are currently available to UEs in the codebook through code word subset restriction. An eNode B may restrict the codebook for various reasons, including eNode B capabilities, physical antenna array geometry, and the like. Once the eNode B restricts the codebook, the UEs receiving this code word subset restriction are generally bound to use only the restricted subset of code words. The eNode Bs may restrict the codebook entries used for UE reporting and eNode B transmission independently for each transmission rank. The independent restriction is typically performed through higher level signaling. This means that the eNode Bs may restrict the code words to be used by the UE and the eNode Bs. Thus, the UE are restricted to calculating the UE feedback related to rank, precoding weight, and corresponding channel quality identifier (“CQI”) values based on the restricted codebook. 
     Even with code words restricted from the codebook, it may still be quite large. For example, in a system or device with four transmit antennas, the restricted codebook may employ up to 16 code words. This large-size codebook creates additional baseband calculation complexity for the UE in selecting the preferred rank and precoding weight. Depending on the UE or terminal class, the computational complexity may cause problems at the UE. 
     Accordingly, what is needed in the art is a system and method that provide precoding code word subset restrictions for communication systems that overcome the deficiencies in the prior art. 
     SUMMARY 
     These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by embodiments of the present invention, which include a user equipment-initiated restriction of a precoding subset in a communication system. In one embodiment, a communication system includes an apparatus (e.g., user equipment) having an antenna array. The user equipment includes a processor including a code word subset instruction module configured to generate a user equipment-specific code word subset instruction compatible with the user equipment. The user equipment also includes a transceiver configured to transmit the user equipment-specific code word subset instruction to a base station. The transceiver is further configured to receive a user equipment-specific code word subset as a function of the user equipment-specific code word subset instruction and user data precoded with the user equipment-specific code word subset via the antenna array from the base station. The processor of the user equipment is configured to decode the user data with the user equipment-specific code word subset. 
     In another aspect, the communication system includes an apparatus (e.g., a base station) having an antenna array. The base station includes a transceiver configured to receive a user equipment-specific code word subset instruction compatible with a user equipment via the antenna array. The base station also includes a processor including a code word subset restriction module configured to generate a user equipment-specific code word subset as a function of the user equipment-specific code word subset instruction for transmission to the user equipment. The processor of the base station is configured to precode user data for transmission to the user equipment via the antenna array with the user equipment-specific code word subset. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  illustrates a system level diagram of an embodiment of a communication system constructed according to the principles of the present invention; 
         FIG. 2  illustrates a block diagram of an embodiment of a computer system in accordance with the systems, subsystems and modules of the present invention; 
         FIG. 3  illustrates a set diagram illustrating an exemplary relationship between code word subsets in a communication system according to the principles of the present invention; 
         FIGS. 4 and 5  illustrate block diagrams of embodiments of communication systems constructed according to the principles of the present invention; and 
         FIG. 6  illustrates a flowchart demonstrating an exemplary method of operating a communication system in accordance with the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The making and using of the presently presented advantageous embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. The present invention will be described with respect to exemplary embodiments in a specific context, namely, a LTE DL MIMO communication system. The invention may also be applied, however, to other types of communication systems, especially communication systems that employ MIMO functionality. 
     Referring initially to  FIG. 1 , illustrated is a system level diagram of an embodiment of a communication system constructed according to the principles of the present invention. In the illustrated embodiment, the communication system is employable with a MIMO communication network and includes a first eNode B  110  with an antenna array  120  in communication with a second eNode B  130  and a plurality of UE or terminals (referred to as a first UE  140 , a second UE  150  and a third UE  160 ). Each of UEs  140 ,  150 ,  160  has transceiver(s) coupled to an antenna array. In operation of the communication system, a code word set or codebook is used in communications between the eNode Bs and UEs, such as the first eNode B  110  and the UEs  140 ,  150 ,  160 . A codebook is defined for the particular communication network that includes each code word in the set for that communication network. Each of the eNode Bs may include a full codebook designed for the communication network (e.g., the MIMO communication network). 
     Instead of sending the entire codebook to the UEs, the first eNode B  110  may use subset restriction to create a subset of code words to transmit to a UE such as the first UE  140 . The communication network, however, may include capabilities beyond the processing power of the first UE  140 . Therefore, in order to keep calculation delays down, the first UE  140  can signal the first eNode B  110  to further restrict the code word subset to a new code word subset with even fewer code words that the first UE  140  is specifically programmed to work with in an efficient manner. 
     The UEs  140 ,  150 ,  160  may each signal a different number of code words for a subset, whether the subset is a small set of code words of the codebook, or whether the subset is the entire network codebook. The UEs  140 ,  150 ,  160  use the subset of code words for feedback to the first eNode B  110  regarding rank, precoding weight, CQI values, and the like. Based on this feedback, the first eNode B  110  may form the appropriate beams, attempting to maximize the signal transmissions between the first eNode B  110  and the UEs  140 ,  150 ,  160 . Of course, analogous principles can also apply to the second eNode B  130  in communication with the UEs  140 ,  150 ,  160 . 
     Before describing the system and method of the present invention in more detail,  FIG. 2  illustrates a block diagram of an embodiment of a computer system in accordance with the systems, subsystems and modules of the present invention. The computer system is adapted to perform various functions such as storing and/or executing software associated with the systems, subsystems and modules as described herein. A central processing unit (“CPU”)  205  is coupled to a system bus  210 . The CPU  205  may be any general purpose computer and embodiments of the present invention are not restricted by the architecture of the CPU  205 . The bus  210  is coupled to a random access memory (“RAM”)  215 , which may be a static random access memory (“SRAM”), dynamic random access memory (“DRAM”), or synchronous dynamic random access memory (“SDRAM”). A read only memory (“ROM”)  220  is also coupled to the bus  210 , which may be programmable read only memory (“PROM”), erasable programmable read only memory (“EPROM”), or electrically erasable programmable read only memory (“EEPROM”). The RAM  215  and the ROM  220  hold user and system data and programs as are well known in the art. 
     The bus  210  is also coupled to input/output (“I/O”) adapter  225 , communications adapter  230 , user interface adapter  240 , and display adapter  245 . The I/O adapter  225  connects storage devices  250 , such as one or more of a hard drive, a compact disc (“CD”) drive, a floppy disk drive, or a tape drive, to the computer system. The I/O adapter  225  is also connected to a printer (not shown), which would allow the system to print paper copies of information such as documents, photographs, articles, and the like. Note that the printer may be a printer (e.g., dot matrix, laser, and the like), a fax machine, scanner, or a copier machine. 
     Turning now to  FIG. 3 , illustrated is a set diagram illustrating an exemplary relationship between code word subsets in a communication system employable with a MIMO communication network according to the principles of the present invention. The communication network codebook, which includes all code words for use in the communication system, is represented by Ω NW    310 . When restricting the codebook and forming a particular code word subset for use with any particular UE or transmission, a code word subset may be generated by the eNode B, which is represented by Ω eNode B    320 . The eNode B code word subset Ω eNode B    320  may include the entire set of code words Ω NW    310  or some subset of the code words of the codebook. The UE may then also assist in formation of a UE-specific code word subset represented by Ω uE    330 . As with the code word subset Ω eNode B    320  created through subset restriction by the eNode B, the UE-specific code word subset Ω UE    330  may also include all of the code words Ω NW    310  of the communication network or up to any number of the code word subset Ω eNode B    320  provided by the eNode B, depending on the capabilities of the particular UE. Thus, the eNode B code word subset Ω eNode B   ⊂ Ω NW  and the UE-specific code word subset Ω UE   ⊂ Ω eNode B . 
     Turning now to  FIG. 4 , illustrated is a block diagram of an embodiment of a communication system employable with a MIMO communication network constructed according to the principles of the present invention. A base station or an eNode B  410  includes an antenna array  420  accessible through an antenna interface (“ANT I/F”)  430 , a transceiver  435 , a processor  440 , and a memory  450  with code words embodied in a codebook. The codebook contains the set of all code words designed for the MIMO communication network. In establishing communication with first and second UEs  460 ,  480 , a code word subset restriction (“CWSR”) module  445  operated in accordance with the processor  440  generates an eNode B code word subset Ω Node B1  based on the capabilities of the eNode B  410 , the physical antenna array geometry, and the first UE  460 . The eNode B  410  (via the transceiver  435 , antenna interface  430  and antenna array  420 ) transmits the eNode B code word subset Ω eNode B1  to the first UE  460 . 
     In response to the eNode B code word subset Ω eNode B1 , the first UE  460 , which includes an antenna array  463 , an antenna interface (“ANT I/F”)  466 , a transceiver  469 , a processor  472  (with a code word subset instruction (“CWSI”) module  475 ) and memory  478 , determines a need to further restrict the eNode B code word subset Ω eNode B1  according to its own baseband computational capabilities. The code word subset instruction module  475  in accordance with the processor  472  generates and the first UE  460  (via the transceiver  469 , antenna interface  466  and antenna array  463 ) transmits a higher layer signal of its own to the eNode B  410  with a UE-specific code word subset instruction Ω UE1 INST  for further restricting the eNode B code word subset Ω eNode B1 . The UE-specific code word subset instruction Ω UE1 INST  is provided in accordance with UE-specific computational capabilities of the first UE  460 . Using the UE-specific code word subset instructions Ω UE1 INST , the code word subset restriction module  445  generates a UE-specific code word subset Ω UE1  and the eNode B  410  transmits the same to the first UE  460  for final application. The processor  440  in conjunction with the transceiver  435  is configured to precode user data for transmission to the first UE  460  via the antenna array  420  with the UE-specific code word subset Ω UE1 . The first UE  460 , which receives the user data via the antenna array  463 , is configured to decode the user data (in accordance with the processor  472 ) employing the UE-specific code word subset Ω UE1 , thereby more efficiently communicating the user data between the eNode B  410  and the first UE  460 . 
     It should be noted that the communications between the UEs and eNode Bs of the various embodiments of the present invention may be implemented over any appropriate signaling protocol, from lower physical (“PHY”) layer and media access control (“MAC”) layer signaling to higher layer signaling, such as radio resource control (“RRC”) signaling, and the like. The various embodiments of the present invention are not limited to any specific communication or signaling scheme. Also, the UEs and eNode Bs employ the respective subsystems and modules such as the transceivers, antenna interfaces and antenna arrays to perform the intended communications therebetween. 
     Since the restricted subsets may be generated independently based, at least in part, on the particular UE, the code word subset restriction module  445  generates an eNode B code word subset Ω eNode B2  and transmits the same (via the transceiver  435 , antenna interface  430  and antenna array  420 ) to the second UE  480 . In response thereto, the second UE  480 , which includes an antenna array  483 , an antenna interface (“ANT I/F”)  486 , a transceiver  489 , a processor  492  (with a code word subset instruction (“CWSI”) module  495 ) and memory  498 , determines a need to further restrict the eNode B code word subset Ω eNode B2  according to its own baseband computational capabilities. The code word subset instruction module  495  in accordance with the processor  492  generates and the second UE  480  (via the transceiver  489 , antenna interface  486  and antenna array  483 ) transmits a higher layer signal of its own to the eNode B  410  with a UE-specific code word subset instruction Ω UE2 INST  for further restricting the eNode B code word subset Ω eNode B2 . The UE-specific code word subset instruction Ω UE2 INST  is provided in accordance with UE-specific computational capabilities of the second UE  480 . Using the UE-specific code word subset instruction Ω UE2 INST , the code word subset restriction module  445  generates a UE-specific code word subset Q uE   2  and the eNode B  410  transmits the same to the second UE  480  for final application. The processor  440  in conjunction with the transceiver  435  is configured to precode user data for transmission to the second UE  480  via the antenna array  420  with the UE-specific code word subset Ω UE2 . The second UE  480 , which receives the user data via the antenna array  483 , is configured to decode the user data (in accordance with the processor  492 ) employing the UE-specific code word subset Ω UE2 , thereby more efficiently communicating the user data between the eNode B  410  and the second UE  480 . 
     The code words and subsets thereof may be stored in the respective memories of the communication elements of the communication system. It should be noted that the UE-specific code word subsets Ω UE1 , Ω UE2  may contain different code words, depending on the capabilities of the first and second UEs  460 ,  480 , respectively. Moreover, the UE-specific code word subset instructions Ω UE2 INST , Ω UE2 INST  may take various forms, such as the number of codebook sizes each UE uses, exact codebook entries, or the like. 
     Turning now to  FIG. 5 , illustrated is a block diagram of an embodiment of a communication system employable with a MIMO communication network constructed according to the principles of the present invention. A base station or an eNode B  510  includes an antenna array  520  accessible through an antenna interface (“ANT I/F”)  530 , a transceiver  535 , a processor  540  (with a code word subset restriction (“CWSR”) module  545 ), and a memory  550  with code words embodied in a codebook. The codebook contains the set of all code words designed for the MIMO communication network. The eNode B  510  communicates with first and second UEs  560 ,  580 . The first UE  560  includes an antenna array  563 , an antenna interface (“ANT I/F”)  566 , a transceiver  569 , a processor  572  (with a code word subset instruction (“CWSI”) module  575 ) and memory  578 . The second UE  580 , includes an antenna array  583 , an antenna interface (“ANT I/F”)  586 , a transceiver  589 , a processor  592  (with a code word subset instruction (“CWSI”) module  595 ) and memory  598 . 
     In establishing communication between the first UE  560  and the eNode B  510 . the code word subset instruction module  575  in accordance with the processor  572  generates and the first UE  560  (via the transceiver  569 , antenna interface  566  and antenna array  563 ) transmits a signal to the eNode B  510  with a UE-specific code word subset instruction Ω UE1 INST . The UE-specific code word subset instruction Ω UE1 INST  restricts the codebook to a code word subset compatible with the first UE  560 . The UE-specific code word subset instruction Ω UE1 INST  is provided in accordance with UE-specific computational capabilities of the first UE  560 . Using the UE-specific code word subset instruction Ω UE1 INST , the code word subset restriction module  545  generates a UE-specific code word subset Ω UE1  and the eNode B  510  transmits the same to the first UE  560  for final application. The processor  540  in conjunction with the transceiver  535  is configured to precode user data for transmission to the first UE  560  via the antenna array  520  with the UE-specific code word subset Ω UE1 . The first UE  560 , which receives the user data via the antenna array  563 , is configured to decode the user data (in accordance with the processor  572 ) employing the UE-specific code word subset Ω UE1 , thereby more efficiently communicating the user data between the eNode B  510  and the first UE  560 . 
     In establishing communication between the second UE  580  and the eNode B  510 . the code word subset instruction module  595  in accordance with the processor  592  generates and the second UE  580  (via the transceiver  589 , antenna interface  586  and antenna array  583 ) transmits a signal to the eNode B  510  with a UE-specific code word subset instruction Ω UE2 INST . The UE-specific code word subset instruction Ω UE2 INST  restricts the codebook to a code word subset compatible with the second UE  580 . The UE-specific code word subset instruction Ω UE2 INST  is provided in accordance with UE-specific computational capabilities of the second UE  580 . Using the UE-specific code word subset instruction Ω UE2 INST , the code word subset restriction module  545  generates a UE-specific code word subset Ω UE2  and the eNode B  510  transmits the same to the second UE  580  for final application. The processor  540  in conjunction with the transceiver  535  is configured to precode user data for transmission to the second UE  580  via the antenna array  420  with the UE-specific code word subset Ω UE2 . The second UE  580 , which receives the user data via the antenna array  583 , is configured to decode the user data (in accordance with the processor  592 ) employing the UE-specific code word subset Ω UE2 , thereby more efficiently communicating the user data between the eNode B  510  and the second UE  580 . 
     Turning now to  FIG. 6 , illustrated is a flowchart demonstrating an exemplary method of operating a communication system in accordance with the principles of the present invention. The capabilities of an eNode B and a UE, the physical antenna array geometry, and the like are analyzed in a step  610 . Thereafter, a subset of code words is restricted from a plurality of code words. In accordance therewith, an eNode B code word subset Ω eNode B  is generated and transmitted during a step  620 . The eNode B code word subset Ω eNode B  may be transmitted to a UE over a signaling protocol in accordance with a PHY and MAC layer signaling or higher layer signaling in accordance with an RRC. The UE generates and transmits a UE-specific code word subset instruction Ω UE INST , in a step  630 , indicating a further restricted code word subset designed for the UE&#39;s capabilities including, without limitation, a list of specific code words, a number of supportable code words, or the like. Based on the UE-specific code word subset instruction Ω UE INsT , a UE-specific code word subset Ω UE  is generated and transmitted to the UE at a step  640 . One skilled in the art should understand that selected steps may be added or omitted from the aforementioned method of operating the communication system and still fall within the broad scope of the present invention. For instance, the generation and transmission of an eNode B code word subset Ω eNode B  in accordance with step  620  may be omitted from the method introduced above. 
     Thus, representative embodiments of the present invention are directed to methods for precoding subset restrictions in a communication system. The method includes receiving a signal from one or more UEs requesting a restricted compatible code word subset compatible with the one or more UEs. In response to this signal (including a UE-specific code word subset instruction), an eNode B generates a UE-specific code word subset containing the code word subset defined by the signal. The eNode B then transmits the UE-specific code word subset to one or more UEs. In addition, the eNode B first generates a restricted subset of code words (e.g., an eNode B code word subset) wherein the restricted subset of codes is based at least in part on the eNode B capabilities, the physical antenna array geometry, and/or the UE. The eNode B then transmits the eNode B code word subset to one or more of the UEs. Also, the UE transmits the UE-specific code word subset instruction in response to receiving the eNode B code word subset. Additionally, the UE-specific code word subset instruction transmitted by the UE includes either a list of compatible code words to include in the UE-specific code word subset or a number of code words that the UE can support. In addition, the aforementioned signals are transmitted using a higher layer signaling protocol. 
     In accordance with another embodiment of the present invention, a UE is provided for a communication system. The UE includes a processor, code word subset instruction module and memory. A set of code words or a codebook is stored in the memory that includes the code words compatible with the UE. The UE includes an antenna array with transceiver(s) to transmit instructions to an eNode B and receive a UE-specific code word subset from an eNode B. The UE-specific code word subset from the eNode B is based on the code limits provided by the code word subset instruction module of the UE. 
     In accordance with another embodiment of the present invention, an eNode B is provided for a communication system. The eNode B includes a processor, code word subset restriction module and memory. A codebook of each of the code words approved for a communication network is maintained in the memory. The eNode B includes an interface with an antenna array that transmits subsets of the codebook (e.g., an eNode B code word subset) compiled by the code word subset restriction module and receives UE-specific code word subset instructions from one or more UEs in communication with the eNode B. The antenna transmits updated subsets (e.g., a UE-specific code word subset) from the codebook to the UE based on the subset modification instructions. 
     The program or code segments making up the various embodiments of the present invention may be stored in a computer readable medium or transmitted by a computer data signal embodied in a carrier wave, or a signal modulated by a carrier, over a transmission medium. The “computer readable medium” may include any medium that can store or transfer information. Examples of the computer readable medium include an electronic circuit, a semiconductor memory device, a ROM, a flash memory, an erasable ROM (“EROM”), a floppy diskette, a compact disk CD-ROM, an optical disk, a hard disk, a fiber optic medium, a radio frequency (“RF”) link, and the like. The computer data signal may include any signal that can propagate over a transmission medium such as electronic network channels, optical fibers, air, electromagnetic links, RF links, and the like. The code segments may be downloaded via computer networks such as the Internet, Intranet, and the like. 
     As described above, the exemplary embodiment provides both a method and corresponding apparatus consisting of various modules providing functionality for performing the steps of the method. The modules may be implemented as hardware (including an integrated circuit such as an application specific integrated circuit), or may be implemented as software or firmware for execution by a computer processor. In particular, in the case of firmware or software, the exemplary embodiment can be provided as a computer program product including a computer readable storage structure embodying computer program code (i.e., software or firmware) thereon for execution by the computer processor. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the features and functions discussed above can be implemented in software, hardware, or firmware, or a combination thereof. 
     Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.