Abstract:
Embodiments of the present disclosure describe orthogonal frequency division multiple access (OFDMA) transmissions using a plurality of antennas and/or transmit chains. Still other embodiments may be described and claimed.

Description:
FIELD 
       [0001]    Embodiments of the present disclosure relate to the field of wireless access networks, and more particularly, to narrowband transmissions using a plurality of antennas. 
       BACKGROUND 
       [0002]    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. 
         [0003]    OFDMA-based communication systems are well known to have high peak-to-average power (PAPR) ratios. A high PAPR may reduce transmitter power amplifier (PA) power efficiency by increasing PA back off in order to comply with constraints imposed by regulatory spectral masks limit emissions outside of a designated frequency band. 
         [0004]    Communication devices that operate under these transmission power constraints often employ multiple antennas to increase spatial diversity to improve the quality and reliability of a wireless link. For example, a communication device may employ a cyclic delay diversity (CDD) scheme that transmits a signal over a number of antennas with each transmitted signal being provided with a different degree of cyclic delay. 
         [0005]    In another example, communication devices using distributed OFDMA allocations, e.g., uplink—partially used subchannel (UL-PUSC) schemes, may transmit different portions of a signal over different antennas. To provide CDD in these schemes, consecutive portions of the signal are interleaved over the different antennas. 
     
    
     
       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 an OFDMA wireless neighborhood in accordance with some embodiments. 
           [0008]      FIG. 2  illustrates a physical resource mapping in accordance with some embodiments. 
           [0009]      FIG. 3  is a flowchart depicting operations of the station in accordance with some embodiments. 
           [0010]      FIG. 4  illustrates a computing device capable of implementing an OFDMA communication system in accordance with some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    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. 
         [0012]    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. 
         [0013]    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). 
         [0014]    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. 
         [0015]    Embodiments of the present disclosure provide apparatuses and methods for narrowband OFDMA transmissions using a plurality of antennas/transmit chains. The method may work by dividing a frequency band into contiguous frequency partitions and transmitting physical resource units within each of the partitions over an antenna/transmit chain uniquely designated for transmissions in the respective partition. 
         [0016]    These methods and systems may be applied to OFDMA communications as presented in, e.g., the Institute of Electrical and Electronics Engineers (IEEE) 802.16-2004 standard along with any amendments, updates, and/or revisions, 3 rd  Generation Partnership Project (3GPP) long-term evolution (LTE) project, ultra mobile broadband (UMB) project, etc. 
         [0017]      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 two wireless communication devices, e.g., station  104  and station  108 , communicatively coupled to one another via an over-the-air (OTA) communication link  112 . 
         [0018]    In some embodiments, the station  104  may be a mobile/fixed station while the station  108  may be a base station that provides the station  104  access to a wider network. In these embodiments, a transmission from the station  104  to the station  108  may be referred to as an uplink transmission. In other embodiments, the station  104  may be the base station and the station  108  may be the mobile/fixed station and the transmission from the station  104  to the station  108  may be referred to as a downlink transmission. 
         [0019]    The station  104  may include a modulator  116  to receive an input data stream from upper layers of the station  104 . The modulator  116  may generate a wideband transmission that represents the input data stream. The wideband transmission may be one or more OFDMA symbols distributed across a number of logical resource units. 
         [0020]    The wideband transmission may be provided to the mapper  120 . The mapper  120  may generate a plurality of narrowband transmissions that collectively make up the wideband transmission. In some embodiments, the mapper  120  may generate the plurality of narrowband transmissions by mapping logical resource units to physical resource units. A physical resource unit, as used herein, may be a unit of a resource used for transmitting communications over a communication link. In some embodiments, a physical resource unit may include a first number of contiguous subcarriers over a second number of OFDM symbols. For example, in embodiments in which the transmission is an UL-PUSC transmission, the resource unit may be a tile that includes, e.g., four contiguous subcarriers over three OFDMA symbols. 
         [0021]    The mapper  120  may provide each narrowband transmission to a respective transmit chain. In this embodiment, three transmit chains are shown: transmit chain  124 , transmit chain  128 , and transmit chain  132 . Each of the transmit chains may include a transmitter coupled to an antenna. The transmitters may include a variety of elements to facilitate processing and transmission of the physical resource units. These elements may include, but are not limited to, inverse fast Fourier transformers (IFFTs), filters, radio frequency power amplifiers, etc. While three transmit chains are shown in station  104 , other embodiments may have a different number. 
         [0022]    In some embodiments, the mapper  120  may provide the narrowband transmissions to the transmit chains as an ordered mapping of the physical resource units based on frequency partitions within which the physical resource units reside. For example, in the embodiment with three transmit chains, a frequency band may be divided into three frequency partitions with each frequency partition having a one-to-one correspondence with one of the transmit chains. 
         [0023]    Each frequency partition may be a range of contiguous frequencies that is assigned to a respective transmit chain. Therefore, each transmit chain will be dedicated to transmitting physical resource units within a designated frequency partition. While the frequency partitions may be equally sized in many embodiments, they may have different sizes in other embodiments. 
         [0024]    In various embodiments, the mapper  120  may use one or more filters  136  to provide a narrowband transmission of desired frequencies to its respective transmit chain. In these embodiments, a filter may be provided for each transmit chain to filter out frequencies outside of a range of frequencies that is assigned to a particular transmit chain. 
         [0025]      FIG. 2  illustrates a physical resource mapping  200  that may be used in an UL-PUSC transmission in accordance with various embodiments. The mapping  200  may include tiles that belong to two different subchannels, e.g., subchannel x and subchannel y. Each of the subchannels may include six tiles with a tile located in each of six equal frequency subpartitions, e.g., subpartitions  204 ,  208 ,  212 ,  216 ,  220 , and  224 . Each subpartition may be paired with an adjacent subpartition into a frequency partition that is directly and uniquely mapped to a respective transmit chain. Specifically, tiles within subpartitions  204  and  208  may be mapped to transmit chain  124 ; tiles within subpartitions  212  and  216  may be mapped to transmit chain  128 , and tiles within subpartitions  220  and  224  may be mapped to transmit chain  132 . 
         [0026]    As can be seen in  FIG. 2 , the frequency partitions, which may account for the entire spectrum of the frequency band to accommodate the entire wideband transmission generated by the modulator  116 , may be adjacent to, and contiguous with, one another. 
         [0027]    With each transmit chain only being responsible for transmitting tiles that fall within in a relatively narrow bandwidth, e.g., one-third of the frequency band, the out-of-band emissions may also be narrower. This may allow the transmitters of the respective transmit chains to transmit with more power without exceeding limitations imposed by the regulatory spectral mask. 
         [0028]    Simulation results with ideal PAs, e.g., hard clippers or non-linear PAs with ideal pre-distortion, show a gain of 1 dB in transmit power for embodiments of this disclosure. So, while a communication device transmitting a wideband, e.g., full bandwidth, transmission over each transmit chain may be associated with a threshold transmit power of 22.6 dBm, a communication device transmitting a narrowband, e.g., a ⅓ bandwidth, transmission over each transmit chain may be associated with a threshold transmit power of 23.6 dBm. Accordingly, embodiments of the present disclosure may transmit 23 dBm signals using three PAs, in three separate transmit chains, when each PA is capable of transmitting 17.3 dBm at full bandwidth and 18.3 dBm at ⅓ bandwidth by 18.3+10 log 10 (3)=23 dBm. 
         [0029]    When using a plurality of transmit chains with each transmit chain transmitting the full bandwidth, as is done in conventional CDD schemes, out-of-band emission from each antenna is summed, at least in power. Accordingly, a gap of 10 log 10 (N TX ) dB, where N TX  is a number of antennas, may be taken from each transmit chain to stay under the regulatory spectral mask. However, when transmitting only a narrowband transmission over each of the plurality of transmit chains, e.g., as described above with respect to the station  104 , the spectral skirt provided by the mask may be asymmetric to the transmission profile  312 . This may translate to a sum of the out-of-band emissions being much smaller. Taking this into account, an additional ˜1.5 dB in transmit power may be achieved for a three transmit chain embodiment as described herein. 
         [0030]      FIG. 3  is a flowchart  300  depicting operations of the station  104  in accordance with some embodiments. 
         [0031]    At block  304 , the modulator  116  may receive an input data stream from upper levels of the station  104 . 
         [0032]    At block  308 , the modulator  116  may generate a wideband transmission, e.g., one or more OFDMA symbols, based at least in part on the input data stream. The OFDMA symbols may be distributed across a plurality of physical resource units of a frequency band, this distribution may be done by the modulator  116  and/or the mapper  120 . 
         [0033]    At block  312 , the mapper  120  may generate a number of narrowband transmissions by, e.g., mapping sets of physical resource units to corresponding transmit chains. A set of the physical resource units may be defined by frequency partitions, e.g., a range of contiguous frequencies, assigned to a particular transmit chain. In some embodiments, a set may include at least two physical resource units that are adjacent in frequency. Referring to  FIG. 2 , for example, a set of tiles that may be mapped to transmit chain  124  may be defined by a frequency partition that comprises the bottom third of the frequency band. Any tiles that occur within that frequency partition will, therefore, belong to the set that is mapped to the transmit chain  124 . In this embodiment, each set may include two tiles for each subchannel. 
         [0034]    At block  316 , the transmit chains may transmit corresponding sets of the physical resource units via the OTA link  112 . 
         [0035]    The station  104  may be implemented into a system using any suitable hardware and/or software to configure as desired.  FIG. 4  illustrates, for one embodiment, an example system  400  comprising one or more processor(s)  404 , system control logic  408  coupled to at least one of the processor(s)  404 , system memory  412  coupled to system control logic  408 , non-volatile memory (NVM)/storage  416  coupled to system control logic  408 , and one or more communications interface(s)  420  coupled to system control logic  408 . 
         [0036]    System control logic  408  for one embodiment may include any suitable interface controllers to provide for any suitable interface to at least one of the processor(s)  404  and/or to any suitable device or component in communication with system control logic  408 . 
         [0037]    System control logic  408  for one embodiment may include one or more memory controller(s) to provide an interface to system memory  412 . System memory  412  may be used to load and store data and/or instructions, for example, for system  400 . System memory  412  for one embodiment may include any suitable volatile memory, such as suitable dynamic random access memory (DRAM), for example. 
         [0038]    System control logic  408  for one embodiment may include one or more input/output (I/O) controller(s) to provide an interface to NVM/storage  416  and communications interface(s)  420 . 
         [0039]    NVM/storage  416  may be used to store data and/or instructions, for example. NVM/storage  416  may include any suitable non-volatile memory, such as flash memory, for example, and/or may include any suitable non-volatile storage device(s), such as one or more hard disk drive(s) (HDD(s)), one or more compact disc (CD) drive(s), and/or one or more digital versatile disc (DVD) drive(s), for example. 
         [0040]    The NVM/storage  416  may include a storage resource physically part of a device on which the system  400  is installed or it may be accessible by, but not necessarily a part of, the device. For example, the NVM/storage  416  may be accessed over a network via the communications interface(s)  420 . 
         [0041]    System memory  412  and NVM/storage  416  may include, in particular, temporal and persistent copies of mapping logic  424 , respectively. The mapping logic  424  may include instructions that when executed by at least one of the processor(s)  404  result in the system  400  performing the mapping as described in conjunction with the mapper  120  described herein. In some embodiments, the mapping logic  424  may additionally/alternatively be located in the system control logic  408 . 
         [0042]    Communications interface(s)  420  may provide an interface for system  400  to communicate over one or more network(s) and/or with any other suitable device. Communications interface(s)  420  may include any suitable hardware and/or firmware. Communications interface(s)  420  for one embodiment may include, for example, a network adapter, a wireless network adapter, a telephone modem, and/or a wireless modem. For wireless communications, communications interface(s)  420  for one embodiment may use one or more antenna(s). 
         [0043]    For one embodiment, at least one of the processor(s)  404  may be packaged together with logic for one or more controller(s) of system control logic  408 . For one embodiment, at least one of the processor(s)  404  may be packaged together with logic for one or more controllers of system control logic  408  to form a System in Package (SiP). For one embodiment, at least one of the processor(s)  404  may be integrated on the same die with logic for one or more controller(s) of system control logic  408 . For one embodiment, at least one of the processor(s)  404  may be integrated on the same die with logic for one or more controller(s) of system control logic  408  to form a System on Chip (SoC). 
         [0044]    In various embodiments, system  400  may have more or less components, and/or different architectures. 
         [0045]    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.