Abstract:
Embodiments of the present invention provide a virtual multicarrier design for orthogonal frequency division multiple access communications. Other embodiments may be described and claimed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 14/563,956, filed Dec. 8, 2014, entitled, “VIRTUAL MULTICARRIER DESIGN FOR ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS COMMUNICATIONS,” which is a continuation of U.S. patent application Ser. No. 13/658,735, filed Oct. 23, 2012, entitled, “VIRTUAL MULTICARRIER DESIGN FOR ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS COMMUNICATIONS,” which is a continuation of U.S. patent application Ser. No. 12/242,755 filed Sep. 30, 2008, entitled, “VIRTUAL MULTICARRIER DESIGN FOR ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS COMMUNICATIONS,” the entire specification of which is hereby incorporated by reference in its entirety for all purposes. 
     
    
     FIELD 
       [0002]    Embodiments of the present disclosure relate to the field of wireless access networks, and more particularly, to virtual multicarrier design for orthogonal frequency division multiple access communications in said wireless access networks. 
       BACKGROUND 
       [0003]    Orthogonal frequency division multiple access (OFDMA) communications use an orthogonal frequency-division multiplexing (OFDM) digital modulation scheme to deliver information across broadband networks. OFDMA is particularly suitable for delivering information across wireless networks. 
         [0004]    The OFDM digital modulation scheme uses a large number of closely-spaced orthogonal subcarriers to carry information. Each subcarrier is capable of carrying a data stream across a network between OFDMA terminals. 
         [0005]    OFDMA-based communication systems are well known to have out of band emission (OOBE) issues that result in intercarrier interference (ICI). Prior art networks control this ICI by providing guard bands, e.g., unused subcarriers, between adjacent carriers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. 
           [0007]      FIG. 1  illustrates a wireless communication environment in accordance with embodiments of this disclosure. 
           [0008]      FIG. 2  is a flowchart depicting operations of a base station in accordance with some embodiments. 
           [0009]      FIG. 3  is a flowchart depicting operations of a mobile station in accordance with some embodiments. 
           [0010]      FIG. 4  is a graph illustrating OOBE on two adjacent carriers in accordance with some embodiments. 
           [0011]      FIG. 5  illustrates various views of a configuration of assigned bandwidth in accordance with some embodiments. 
           [0012]      FIG. 6  illustrates an OFDMA frame in accordance with some embodiments. 
           [0013]      FIG. 7  illustrates a multicarrier transmission being processed with and without reuse of guard band subcarriers in accordance with some embodiments. 
           [0014]      FIG. 8  illustrates how teachings of various embodiments facilitate a flexible deployment and upgrading of network equipment in accordance with some embodiments. 
           [0015]      FIG. 9  illustrates a computing device capable of implementing a virtual carrier terminal in accordance with some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments in accordance with the present invention is defined by the appended claims and their equivalents. 
         [0017]    Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding embodiments of the present invention; however, the order of description should not be construed to imply that these operations are order dependent. 
         [0018]    For the purposes of the present invention, the phrase “A and/or B” means “(A), (B), or (A and B).” For the purposes of the present invention, the phrase “A, B, and/or C” means “(A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).” 
         [0019]    The description may use the phrases “in an embodiment,” or “in embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present invention, are synonymous. 
         [0020]    Embodiments of the present disclosure describe virtual multicarrier designs for OFDMA communications as may be used by multicarrier transmission schemes presented in, e.g., the Institute of Electrical and Electronics Engineers (IEEE) 802.16-2004 standard along with any amendments, updates, and/or revisions (e.g., 802.16m, which is presently at predraft stage), 3 rd  Generation Partnership Project (3GPP) long-term evolution (LTE) project, ultra mobile broadband (UMB) project (also referred to as “3GPP2”), etc. 
         [0021]      FIG. 1  illustrates a wireless communication environment  100  in accordance with an embodiment of this disclosure. In this embodiment, the wireless communication environment  100  is shown with three wireless communication terminals, e.g., base station  104 , mobile station  108 , and mobile station  112 , communicatively coupled to one another via an over-the-air (OTA) interface  116 . 
         [0022]    In various embodiments, the mobile stations  108  and  112  may be a mobile computer, a personal digital assistant, a mobile phone, etc. The base station  104  may be a fixed device or a mobile device that may provide the mobile stations  108  and  112  with network access. The base station  104  may be an access point, a base transceiver station, a radio base station, a node B, etc. 
         [0023]    The wireless communication devices  104 ,  108 , and  112  may have respective antenna structures  120 ,  124 , and  128  to facilitate the communicative coupling. Each of the antenna structures  120 ,  124 , and  128  may have one or more antennas. An antenna may be a directional or an omnidirectional antenna, including, e.g., a dipole antenna, a monopole antenna, a patch antenna, a loop antenna, a microstrip antenna or any other type of antenna suitable for transmission/reception of radio frequency (RF) signals. 
         [0024]    Briefly, the base station  104  may have a baseband processing block (BPB)  132  coupled to a transmitter  136 . The BPB  132  may be configured to encode input data, which may be received in a binary format, as an OFDM signal on logical subcarriers of a virtual carrier. The logical subcarriers may be mapped to physical subcarriers from at least two adjacent physical carriers. The BPB  132  may then control the transmitter  136  to transmit the OFDM signal on the physical subcarriers. 
         [0025]      FIG. 2  is a flowchart depicting operations of the base station  104  in accordance with some embodiments. At block  204 , an encoder  140  of the BPB  132  may receive input data from upper layers of the base station  104 . 
         [0026]    At block  208 , the encoder  140  may encode the input data into frequency domain OFDM signal having logical subcarriers of a virtual carrier. 
         [0027]    At block  212 , the encoder  140  may map the logical subcarriers to physical subcarriers of one or more physical carriers according to a mapping scheme provided by the mapper  144 . 
         [0028]    In some embodiments, the mapping scheme may map indices of the logical subcarriers to indices of the physical subcarriers. For example, consider a simple embodiment in which the encoder  140  encodes an OFDMA signal onto 20 logical subcarriers of a virtual carrier. The logical subcarriers may have indices 1-20. A mapping scheme may map the logical subcarrier indices 1-20 to physical subcarrier indices 1-5 of a first physical carrier, physical subcarrier indices 1-5 of a second physical carrier, and physical subcarrier indices 1-10 of a third physical carrier. In an actual implementation, the number of subcarriers will be significantly higher. Furthermore, the total number of logical subcarriers need not be equal to the total number of physical subcarriers as is described in this example. 
         [0029]    The frequency domain OFDM signal may be provided to an inverse fast Fourier transformer (IFFT)  148  that transforms the signal into a time domain OFDM signal, having a plurality of time domain samples for associated physical subcarriers. 
         [0030]    At block  216 , the transmitter  136  may be controlled to transmit the physical subcarriers. The transmitter  136  may provide a variety of physical layer processing techniques, e.g., adding cyclic prefix, upconverting, parallel-to-serial conversion, digital-to-analog conversion, etc. to effectuate the transmission. 
         [0031]    The receiving process of the mobile stations may operate in a manner that complements the transmitting process described above. 
         [0032]      FIG. 3  is a flowchart depicting operations of the mobile station  108  in accordance with some embodiments. At block  304 , a receiver  152  of the mobile station  108  may receive the physical carriers that carry the OFDM signal via the OTA interface  116 , process the OFDM signal and present it, as a time domain OFDM signal, to a BPB  156 . The complementary physical layer processing techniques of the receiver  152  may include, e.g., removing cyclic prefix, down converting, serial-to-parallel conversion, analog-to-digital conversion, etc. to effectuate reception and facilitate subsequent processing. 
         [0033]    The BPB  156  may include a fast Fourier transformer (FFT)  160  to receive the time domain OFDM signal from the receiver  152 . The FFT  160  may generate a frequency domain OFDM signal and forward the signal to a decoder  164 . 
         [0034]    At block  308 , the decoder  164  may map the physical subcarriers of the physical carriers to logical subcarriers of the virtual carrier according to the mapping scheme provided by mapper  168 . In some embodiments, information related to the mapping scheme may be transmitted to the mobile station  108  from the base station  104  in, e.g., downlink (DL) control messages, DL broadcast channel messages, etc. 
         [0035]    At block  312 , the decoder  164  may decode the logical subcarriers to retrieve the transmitted data. This data may then be output to upper layers of the mobile station  108  at block  316 . 
         [0036]    The use of virtual multicarriers for communications between terminals may, for example, allow a base station to scale its bandwidth, provide support for mobile stations having various bandwidths, facilitate deployment and upgrading of network equipment due, at least in part, to legacy support, etc. These aspects will be discussed in further detail below. 
         [0037]    While the described embodiments discuss the base station  104  transmitting, and the mobile station  108  receiving, on virtual carriers, other embodiments may additionally/alternatively include the mobile station  108  transmitting, and the base station  104  receiving, on virtual channels. 
         [0038]    Furthermore, various embodiments of this disclosure describe aligning subcarriers of adjacent physical carriers of a virtual carrier. As used herein, subcarrier of adjacent physical carriers may be aligned if the spacing between a subcarrier of a first physical carrier and a subcarrier of a second physical carrier is equal to, or a multiple of, a spacing between adjacent subcarriers within the first (or second) physical carrier. This alignment may reduce, either in part or in total, ISI, which may, in turn, enable use of subcarriers traditional reserved for guard band. Using these subcarriers for data transmission may increase an overall spectrum utilization ratio. 
         [0039]    To understand the effect of subcarrier spacing between adjacent carriers, consider an OFDM signal that is expressed in the time domain as: 
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         [0040]    and in the frequency domain as: 
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         [0041]    where M is the number of used subcarriers, T u  is useful symbol duration, q k  is the position, or index, of the used subcarrier. Eq. 2 may be used to calculate the average power spectrum as: 
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         [0042]    where β is a misalignment factor that ranges from 0˜1, and σ s  is an expression of subcarrier energy. 
         [0043]      FIG. 4  is a graph illustrating OOBE on two adjacent carriers  404  and  408  that have a maximum misalignment factor of 0.5, a 10 MHz bandwidth, 840 subcarriers, and no low-pass filter. As can be seen, there is a 0 to −29 dB interference signal at guard band subcarriers. 
         [0044]    The power of the interference signal from a neighboring carrier may be: 
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         [0045]    When the subcarriers of adjacent carriers are aligned, as described in accordance with various embodiments, the alignment factor β=0 and the value of the expression “10 log(|sin(βπ| 2 )” of Eq. 5 will go to negative infinity. Accordingly, there will be no (or very little) interference due to OOBE after the neighboring carriers are well aligned. 
         [0046]    The alignment of the subcarriers in adjacent carriers may be accomplished in a variety of ways. In one embodiment, the IFFT  148  may be one transformer that utilizes all of the frequency domain samples corresponding to one virtual channel as one vector input group. In this manner, the subcarriers across an entire virtual carrier of, e.g., a 20 MHz band, may then be equally spaced. The 20 MHz band may be subdivided into various physical carriers, e.g., two 5 MHz and one 10 MHz carriers. 
         [0047]    In another embodiment, the IFFT  148  may include more than one transformer, e.g., it may include a transformer for each physical carrier, with each transformer producing a physical carrier. In this embodiment, each of the distinct transformers may perform transform functions on distinct vector input groups of the frequency domain samples. When separate transformers are used to independently produce physical carriers, care may be taken to ensure that subcarriers of adjacent carriers are aligned. In various embodiments, subcarrier alignment may be performed by changing the channel raster to, e.g., 175 kHz; by shifting the center frequency of adjacent carriers; and/or to change the subcarrier spacing to, e.g., 12.5 kHz. 
         [0048]      FIG. 5  illustrates various views of a configuration of assigned bandwidth  500  in accordance with embodiments of this disclosure. In this embodiment, the assigned bandwidth  500  may be a 20 MHz band. The base station  104  may configure the assigned bandwidth  500  as three physical carriers, e.g., physical carrier (PC)  504 , PC  508 , and PC  512 . PCs  504  and  508  may be 5 MHz bands, while the PC  512  may be a 10 MHz band. A “physical carrier,” as used herein, may refer to a continuous spectrum of radio frequencies in which at least one mobile station of the wireless communication environment  100  is capable of, and restricted to, communicating with the base station. 
         [0049]    The configured PCs may be viewed differently according to the capabilities of the receiving terminal. A terminal capable of communicating with virtual carriers (hereinafter also referred to as “VC terminal”) may have a VC terminal view  516 , while a terminal not able to communicate with virtual carriers (hereinafter also referred to as “legacy terminal”) may have a legacy terminal view  520 . The base station  104  may adapt communications accordingly. 
         [0050]    The base station  104  may communicate with a VC terminal having a 20 MHz receiver by a virtual carrier shown in the VC terminal view  516 . With the subcarriers of adjacent PCs being aligned, e.g., PC  504  and  508  and/or PC  508  and PC  512 , the base station  104  may utilize at least some of the edge subcarrier groups, which are reserved as guard band subcarriers in prior art systems, for communication. As used herein, “an edge subcarrier group” may be a group of consecutive subcarriers of a particular PC that includes a subcarrier that is adjacent to subcarriers of an adjacent PC. 
         [0051]    Edge subcarrier groups that are adjacent to a PC of a common virtual carrier may be referred to as interior edge subcarrier groups. In  FIG. 5 , the interior edge subcarrier groups may be groups  524 ,  528 ,  532 , and  536 . Given the subcarrier alignment, these interior edge subcarrier groups may be utilized for communications. However, in order to avoid ICI with PCs external to the virtual carrier, the groups  540  and  544 , or external edge subcarrier groups, may be reserved for a guard band. 
         [0052]    The base station  104  may communicate with legacy terminal by PC  504 ,  508 , or  512  as seen in the legacy terminal view  520 . Each legacy terminal will only be capable of receiving data communications on one of the PCs. Furthermore, unlike the VC terminals, a legacy terminal will see the edge subcarrier groups  524 ,  528 ,  532 , and  536  as being reserved for a guard band. Accordingly, the legacy terminal will not be able to transmit or receive on subcarriers within these groups. 
         [0053]    Communications between the base station  104  and a legacy terminal will not compromise a contemporaneous communication of the base station  104  and a VC terminal that uses the full range of available subcarriers. 
         [0054]      FIG. 6  illustrates an OFDM frame  600  in accordance with embodiments of the present disclosure. In this embodiment, PCs  604 ,  608 , and  612  are shown. PCs  604  and  608  may each have, e.g., a 10 MHz band, while PC  612  may have a 5 MHz band. Each PC may include a preamble  616 , edge subcarriers  620 , and a broadcast messaging section  624 . 
         [0055]    In one embodiment, the base station  104  may encode data onto a first virtual carrier (VC 1 ) that includes all three of the PCs  604 ,  608 , and  612 . In this embodiment, one or more receiving terminals including, e.g., mobile station  108 , may have a 25 MHz receiver that accommodates the entire range of VC 1 . 
         [0056]    The base station  104  may transmit allocation information on a common messaging section  628  to communicate DL and UL allocations to VC terminals. In this embodiment, the base station  104  may use the common messaging section  628  to inform the mobile station  108  that downlink communications will be sent to the mobile station  108  at resource  632  and that the mobile station  108  may upload information to the base station  104  at resource  636 . As can be seen, the resource  632  may incorporate edge subcarriers of PCs  604  and  608 . 
         [0057]    The base station  104  may also encode data onto other virtual carriers that include various subsets of adjacent PCs. For example, the base station  104  may encode data onto a second virtual carrier (VC 2 ) that includes only PC  604  and PC  608 . VC 2  may be used for communications with VC terminals having 20 MHz receivers. Hereinafter, a VC terminal having a 20 MHz receiver may also be referred to as a 20 MHz VC terminal. In this embodiment, the base station  104  may communicate, to a particular 20 MHz VC terminal, DL allocations at resource  640  and UL allocations at resource  644 , which also includes edge subcarrier groups of PC  604  and PC  608 . 
         [0058]    The base station  104  may additionally/alternatively encode data onto a third virtual carrier (VC 1 ) that includes only PC  608  and PC  612 . VC 3  may be used for communications with 15 MHz VC terminals. In this embodiment, the base station  104  may communicate, to a particular 15 MHz VC terminal, DL allocations at resource  652  and UL allocations at resource  656 , which may include edge subcarrier groups of PC  608  and PC  612 . 
         [0059]    The base station  104  may also use individual PCs to communicate with legacy terminals. In this embodiment, e.g., 10 MHz legacy terminals may communicate with the base station  104  on PC  608 . The base station  104  may communicate, to a particular 10 MHz legacy terminal, DL allocations at resource  660  and UL allocations at resource  664 . It may be noted that communications between the base station  104  and the legacy terminal may not use the edge subcarrier groups of the PC  608 . However, these same edge subcarrier groups of PC  608  may be used for communications between the base station  104  and VC terminals without adversely affecting the communications with the legacy terminal. 
         [0060]    Dividing an assigned bandwidth into various PCs, which may or may not have the same bandwidths, and utilizing the different PCs in various combinations to provide a variety of virtual carriers, may allow base stations endowed with teachings of this disclosure to scale communications to terminals configured to operate on any number of different bandwidths. 
         [0061]    In some embodiments, one or more of the PCs of a virtual carrier may be used as a data only pipe. For example, in VC 1  control and signaling information may be transmitted in PC  608  while the entire spectrum of PC  612  is reserved for data communications. However, if a PC is being used to communicate with a legacy terminal, some amount of control and signaling information may be desired in said PC. 
         [0062]      FIG. 7  illustrates a multicarrier transmission being processed with and without reuse of edge subcarriers in accordance with an embodiment of the present disclosure. Referring to  FIG. 7( a ) , a virtual carrier, including PCs  704  and  708 , may be used for transmissions to a VC terminal and PC  704  may be used for transmissions to a legacy terminal. Each of the PCs  704  and  708  may have 10 MHz bands. Data may be distributed among the PCs according to a partial usage subchannelization (PUSC) scheme with each PC having 841 subcarriers (not including edge carrier groups) over a 9.1984 MHz band. 
         [0063]    In order to align the two PCs, the center frequency of PC  708  may be shifted by 3.125 KHz, which may result in the center frequencies of the two bands being 9.996875 MHz apart. The value of this frequency shift is purely exemplary and may be adjusted in various embodiments according to, e.g., carrier bandwidth, subcarrier spacing, etc. 
         [0064]      FIG. 7( b )  illustrates subcarriers  712  that represent the 841 subcarriers of the PC  704 , subcarriers  716  that represent the 73 guard subcarriers, and subcarriers  720  that correspond to the 841 subcarriers of the PC  708 . The legacy terminal may include a 10 MHz band selection filter  724  that corresponds to the PC  704 . 
         [0065]      FIG. 7( c )  illustrates data tones that may result from the sampling of the subcarriers of  FIG. 7( b )  when all of the subcarriers, including the subcarriers  716 , are used for data transmission in accordance with an embodiment of the present disclosure. In this embodiment, a common sampling rate of 11.2 MHz for a 10 MHz carrier is used. 
         [0066]      FIG. 7( d )  illustrates data tones that may result from the sampling of the subcarriers of  FIG. 7( b )  when the subcarriers  716  are not used for data transmission in accordance with an embodiment of the present disclosure. 
         [0067]    As can be seen by  FIGS. 7( c ) and 7( d ) , the values of the subcarriers that are used by the legacy terminal, e.g., subcarriers  712 , are not impacted regardless of whether or not the guard band subcarriers  716  are used. 
         [0068]    Therefore, data transmissions to a legacy terminal will not be affected, even when the guard subcarriers of the PC  708  are used and the PC  708  is effectively shifted closer to the PC  704  due to the alignment processing. 
         [0069]      FIG. 8  illustrates how teachings of various embodiments facilitate a flexible deployment and upgrading of network equipment in accordance with various embodiments of this disclosure. At an initial stage  804 , 20 MHz of assigned bandwidth may be configured into two 10 MHz bands. The first band may be designated a PC  808  to be used only for communications with legacy terminals. The other 10 MHz band may be reserved. 
         [0070]    At deployment stage  812 , the formally reserved band may be configured as PC  816  to be used only for communications with VC terminals. 
         [0071]    At deployment stage  820 , the legacy-only PC  808  may be configured as PC  824  to be used for communications with legacy and/or VC terminals. This stage may be similar to the embodiment discussed with reference to  FIG. 6 . 
         [0072]    At deployment stage  828 , the legacy/VC PC  824  may be configured as PC  832  to be used only for communications with VC terminals. In this embodiment, the 20 MHz bandwidth may thus be used as two different 10 MHz bands or one 20 MHz band for various VC terminals of the wireless communication environment. 
         [0073]      FIG. 9  illustrates a computing device  900  capable of implementing a VC terminal in accordance with various embodiments. As illustrated, for the embodiments, computing device  900  includes processor  904 , memory  908 , and bus  912 , coupled to each other as shown. Additionally, computing device  900  includes storage  916 , and communication interfaces  920 , e.g., a wireless network interface card (WNIC), coupled to each other, and the earlier described elements as shown. 
         [0074]    Memory  908  and storage  916  may include in particular, temporal and persistent copies of coding and mapping logic  924 , respectively. The coding and mapping logic  924  may include instructions that when accessed by the processor  904  result in the computing device  900  performing encoding/decoding and mapping operations described in conjunction with various VC terminals in accordance with embodiments of this disclosure. In particular, these coding and mapping operations may allow a VC terminal, e.g., base station  104  and/or mobile station  108 , to transmit and/or receive communications over virtual carriers as described herein. 
         [0075]    In various embodiments, the memory  908  may include RAM, dynamic RAM (DRAM), static RAM (SRAM), synchronous DRAM (SDRAM), dual-data rate RAM (DDRRAM), etc. 
         [0076]    In various embodiments, the processor  904  may include one or more single-core processors, multiple-core processors, controllers, application-specific integrated circuits (ASICs), etc. 
         [0077]    In various embodiments, storage  916  may include integrated and/or peripheral storage devices, such as, but not limited to, disks and associated drives (e.g., magnetic, optical), universal serial bus (USB) storage devices and associated ports, flash memory, read-only memory (ROM), nonvolatile semiconductor devices, etc. 
         [0078]    In various embodiments, storage  916  may be a storage resource physically part of the computing device  900  or it may be accessible by, but not necessarily a part of, the computing device  900 . For example, the storage  916  may be accessed by the computing device  900  over a network. 
         [0079]    In various embodiments, computing device  900  may have more or less components, and/or different architectures. 
         [0080]    Although certain embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that embodiments in accordance with the present invention be limited only by the claims and the equivalents thereof.