Abstract:
A multiple output transmitter is configured for transmitting a single input data stream over two or more spatial channels using OFDM signals. The transmitter includes a commutator to select bits from the single input data stream for two or more bit streams and two or more encoders each to encode bits of one of the bit streams. The commutator operates at a bit rate and sequentially provides the selected bits of the input data stream to the encoders. A spatial bit sequencer selects groups of encoded bits from each of the encoders and assigns individual bits of a selected group at the bit-rate to block permuters in a sequential manner to distribute bits from the selected group across the block permuters. The block permuters produce interleaved blocks of bits for an associated spatial stream. The commutator assigns bits of the input bit stream to more than one encoder to allow each encoder to operate at a lower rate.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 10/990,026, filed on Nov. 16, 2004 which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD  
       [0002]    Embodiments of the present invention pertain to electronic communications. Some embodiments pertain to the transmission of OFDM symbols over two or more spatial channels. 
       BACKGROUND 
       [0003]    Many wireless communication systems employ an interleaving scheme to reduce errors in transmission. Interleaving, for example, may help reduce the number of uncorrected error bursts, especially in fading channels. Interleaving is generally performed after channel encoding and permutes bits in a regular or predetermined fashion prior to modulation and transmission. Upon reception and after demodulation, a deinterleaving process is performed to restore the original bit sequence. Some orthogonal frequency division multiplexed (OFDM) systems use coding and frequency interleaving to help overcome problems associated with transmitting data over frequency-selective (i.e., fading) channels. Interleaving may exploit this frequency diversity by spreading adjacent bits across the transmission bandwidth. 
         [0004]    Some multicarrier transmitters transmit more than one spatial stream on the same multicarrier communication channel. Conventional interleaving schemes may not provide sufficient bit separation between the subcarriers of these spatial channels. Conventional interleaving schemes may also not provide sufficient bit separation between bit positions of symbols. Thus there are general needs for multicarrier transmitters and methods of interleaving suitable for the transmission of more than one spatial stream. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a block diagram of a multicarrier transmitter in accordance with some embodiments of the present invention; 
           [0006]      FIG. 2  illustrates the operation of a commutator in accordance with some embodiments of the present invention; 
           [0007]      FIG. 3  illustrates the operation of a spatial-bit sequencer in accordance with some embodiments of the present invention; 
           [0008]      FIG. 4  illustrates an example output of a block permuter in accordance with some embodiments of the present invention; 
           [0009]      FIGS. 5A and 5B  illustrate the operations of bit-grouping shifters and bit-position permuters in accordance with some embodiments of the present invention; and 
           [0010]      FIG. 6  is a flow chart of a spatial stream transmission procedure in accordance with some embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The following description and the drawings illustrate specific embodiments of the invention sufficiently to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. Embodiments of the invention set forth in the claims encompass all available equivalents of those claims. Embodiments of the invention may be referred to, individually or collectively, herein by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. 
         [0012]      FIG. 1  is a block diagram of a multicarrier transmitter in accordance with some embodiments of the present invention. Multicarrier transmitter  100  may transmit two or more spatial streams with antennas  120  from input bit stream  101 . In some embodiments, multicarrier transmitter  100  includes scrambler  102  to scramble bits of input bit stream  101  to generate scrambled bit stream  103 . In some embodiments, scrambler  102  may generate pseudo-random bits. Multicarrier transmitter  100  also includes commutator  104  to assign bits of bit stream  103  to one of a plurality of data streams  105 , and encoders  106  associated with data streams  105  to receive the assigned bits from commutator  104 . Encoders  106  may perform an encoding operation on the assigned bits. Multicarrier transmitter  100  also includes spatial-bit sequencer  108  to select groups of bits from each of data streams  107  to generate two or more spatial streams  109 . Multicarrier transmitter  100  also includes block permuters  110  associated with each of the spatial streams to perform a block interleaving operation on bits of spatial streams  109  provided by spatial-bit sequencer  108 . 
         [0013]    In some embodiments, commutator  104  may sequentially assign bits of bit stream  103  to one of data streams  105 , and spatial-bit sequencer  108  may sequentially select groups of bits from each of the data streams  107  to generate up to four or more spatial streams  109 , although the scope of the invention is not limited in this respect. 
         [0014]    The operation of commutator  104  is illustrated in  FIG. 2  in which a bit clock operating at a bit rate may select individual bits of bit stream  103  and provide each selected bit sequentially to one of encoders  106 . In these example embodiments, every fourth bit may be assigned to one of encoders  106 . In some embodiments, because commutator  104  may assign bits of bit stream  103  to more than one encoder  106 , the rate at which an encoder may operate can be reduced. In some embodiments, encoders  106  may comprise convolutional encoders and may generate encoded bits. In some embodiments, encoders  106  may employ error-correcting techniques, although the scope of the invention is not limited in this respect. Each encoder  106  may generate encoded bits associated with a particular data stream  107 . Although  FIGS. 1 &amp; 2  illustrate four encoders  106  in which each encoder is associated with one of four data streams  107 , the scope of the invention is not limited in this respect. 
         [0015]    In some embodiments, spatial-bit sequencer  108  may select groups of four bits from each data stream  107  to generate more than one of spatial streams  109 . An example of the operation spatial-bit sequencer  108  is illustrated in  FIG. 3 . In  FIG. 3 , spatial-bit sequencer  108  may select bits from encoders  106  at ¼ the bit clock and may provide the selected bits to permuters  110  at the bit clock rate. In these example embodiments, groups of four encoded bits may be selected from each of encoders  106  and provided individually to permuters  110 . For example, spatial-bit sequencer  108  may select four encoded bits from the first encoder, and may provide the first bit to first permuter  110 A, the second bit to second permuter  110 B, the third bit to third permuter  110 C, and the fourth bit fourth permuter  110 D. 
         [0016]    Although  FIGS. 1 &amp; 3  illustrates spatial-bit sequencer  108  receiving four data streams  107  and generating four spatial streams  109 , some embodiments of the present invention do not require such a one-to-one correspondence between data streams  107  and spatial streams  109 . In some embodiments, the number of data streams  107  may differ from the number of spatial streams  109 . 
         [0017]    Referring to  FIG. 1 , multicarrier transmitter  100  also includes one or more bit-grouping shifters (BGS)  112 B- 112 D to shift symbol-bit groupings of an associated spatial stream (e.g., spatial streams  111 B- 111 D) among subcarriers of a multicarrier communication signal. Multicarrier transmitter  100  also includes one or more bit-position permuters (BPP)  114 B- 114 D to rotate bits among bit positions within subgroupings of the symbol-bit groupings of an associated spatial stream. The operations of bit-grouping shifters  112 B- 112 D and bit-position permuters  114 B- 114 D are described in more detail below. 
         [0018]    Multicarrier transmitter  100  also includes mappers  116 A- 116 D associated with a spatial stream to map bits from within bit positions to symbols. Mappers  116 A- 116 D may also symbol-modulate the mapped symbol-bit groupings and may generate symbol-modulated subcarriers  117 A- 117 D associated with a spatial stream. Multicarrier transmitter  100  also includes transmission (TX) circuitry  118 A- 118 D associated with each spatial stream. Each spatial stream may be transmitted by one of a plurality of transmit antennas  120 . In these embodiments, one antenna may be used to transmit an associated spatial stream. In some embodiments, the number of antennas may be at least as great as the number of spatial streams being transmitted. In some embodiments, transmitter  100  may further comprise a beamformer (not separately illustrated) to operate on symbol-modulated subcarriers representing the spatial streams to generate combined signals for transmission by transmit antennas  120 . 
         [0019]    Transmission circuitry  118 A- 118 D may include, among other things, inverse fast Fourier transformation (IFFT) circuitry to generate time-domain samples from the frequency domain samples comprising symbol-modulated subcarriers  117 A- 117 D. Transmission circuitry  118 A- 118 D may also include analog-to-digital conversion circuitry to generate analog I and Q signals, and radio-frequency (RF) circuitry to generate RF signals for transmission by an associated one of antennas  120 . 
         [0020]      FIG. 4  illustrates example output  400  of one of block permuters  110  ( FIG. 1 ). This example illustrates a modulation level of 64-QAM in six bits comprise each symbol (i.e., three I bits and three Q-bits). The assigned subcarriers of the multicarrier communication channel correspond to the different rows. In  FIG. 4 , the numbers in the table refer to a sequence number of the bits of a bit sequence received at the input of one of block permuters  110  ( FIG. 1 ). At the output of one of block permuters  110  ( FIG. 1 ), bits may be provided by row in the order illustrated. In some embodiments, block permuters  110  ( FIG. 1 ) may perform a block interleaving operation in accordance with the IEEE 802.11a standard referenced below, although the scope of the invention is not limited in this respect. Other block permuting operations are also suitable for use by block permuters  110  ( FIG. 1 ). As illustrated in the example of  FIG. 4 , sequential bits at the input of one of permuters  110  ( FIG. 1 ) are separated by three subcarriers which result from a block permutation, although the scope of the invention is not limited in this respect. 
         [0021]      FIGS. 5A and 5B  illustrate the operations of bit-grouping shifters and bit-position permuters in accordance with some embodiments of the present invention.  FIG. 5A  illustrates bits of first spatial stream  502  and  FIG. 5B  illustrates bits of second spatial stream  522 . The values of the numbers in  FIGS. 5A and 5B  correspond to sequential bits from each of encoders  106  ( FIG. 1 ) where the first digit corresponds to the decoder number. In this example, bits from four decoders are illustrated. In this example, bit “ 1001 ” is a first bit provided by a first of the decoders, and bit “ 4097 ” is a ninety seventh bit provided by the fourth of the decoders. 
         [0022]    Each spatial stream  202  and  222  may comprise symbol-bit groupings  508  or  528  which comprise in-phase (I) subgroupings  504  and quadrature-phase (Q) subgroupings  506 . First spatial stream  502  may correspond to first spatial stream  111 A ( FIG. 1 ) and second spatial stream  522  may refer to second spatial stream  111 B ( FIG. 1 ). In  FIGS. 5A and 5B , each row of bits may be associated with a subcarrier frequency (e.g., tone) of a multicarrier communication signal. For clarity, only a few of symbol-bit groupings  508  are  528  are circled. Third spatial stream  111 C ( FIG. 1 ) and fourth spatial stream  111 D ( FIG. 1 ) may be similar. 
         [0023]    Referring to  FIGS. 1 ,  5 A and  5 B together, in some embodiments, multicarrier transmitter  100  may use two or more antennas  120  for transmitting at least first and second spatial streams  111 A &amp;  111 B. In these embodiments, first bit-grouping shifter  112 B may shift symbol-bit groupings  528  of second spatial stream  522  among the subcarriers of the multicarrier communication signal. In these embodiments, bit-position permuter  114 B may rotate bits among bit positions  510 - 514  within I subgrouping  504  and may rotate bits among bit positions  516 - 520  within Q subgrouping  506  of second spatial stream  522  to generate output bit stream  115 B. 
         [0024]    In some embodiments, symbol-bit groupings  528  may be quadrature-amplitude-modulation (QAM) bit groupings. In some embodiments, bit-position permuter  114 B circularly rotates bits among positions within I subgroupings  504  and within Q subgroupings  506 . 
         [0025]    In some embodiments, the QAM bit groupings may have a predetermined number of bits associated therewith. The predetermined number of bits per QAM bit grouping may range from two-bits per symbol (BPSK) or four bits per symbol (16-QAM) to eight or more bits per symbol (256-QAM). In some embodiments, the QAM bit groupings may have a predetermined number of bits.  FIGS. 5A and 5B  illustrate a modulation level of 64-QAM, which communicates six bits per symbol, although the scope of the invention is not limited in this respect. Modulation levels with lower and higher data communication rates per subcarrier may also be used. 
         [0026]    In some embodiments, the number of subcarriers that bit-grouping shifters  112 B- 112 D shifts the QAM bit groupings may be based on a spatial stream index. The spatial stream index may be different for each spatial stream. For example, first spatial stream  111 A may have an index of zero, the second spatial stream  111 B may have an index of 1, third spatial stream  111 C may have an index of two, and fourth spatial stream  111 D may have an index of three. The spatial stream index may be used by bit-grouping shifters  112 B- 112 D and bit-position permuters  114 B- 114 D to provide differing amounts of bit shifting and bit position rotating for each spatial stream as described below. In some embodiments, the spatial stream index may be arbitrarily assigned. 
         [0027]    The number of bit positions within I subgroupings  504  and within Q subgroupings  506  of QAM symbol-bit groupings  528  that the bits are circularly rotated by bit-position permuters  114 B- 114 D may also based on the spatial stream index. Although multicarrier transmitter  100  is illustrated as having bit-grouping shifters  112 B- 112 D in a signal processing path prior to bit-position permuters  114 B- 114 D, in some other embodiments, the order of these operations may be interchanged. 
         [0028]    In some embodiments, first spatial stream  111 A may have an index of zero and therefore the QAM bit groupings are not shifted by a bit-grouping shifter and bits are not rotated among bit positions within I and Q subgroupings by a bit-position permuter. In these embodiments, second spatial stream  111 B may have an index of one and therefore the QAM bit groupings may be shifted by three subcarriers (e.g., three times the index) by bit-grouping shifter  112 B, and the bits within the I subgroupings  504  and within Q subgroupings  506  may be rotated by one bit position (e.g., one times the index) by bit-position permuter  114 B. In these embodiments, third spatial stream  111 C may have an index of two and therefore the QAM bit groupings may be shifted by six subcarriers (e.g., three times the index) by bit-grouping shifter  112 C, and the bits within the I subgroupings and within the Q subgroupings may be rotated by two bit positions (e.g., one times the index) by bit-position permuter  114 C. In these embodiments, fourth spatial stream  111 D may have an index of three and therefore the QAM bit groupings may be shifted by nine subcarriers (e.g., three times the index) by bit-grouping shifter  112 D, and the bits within the I subgroupings and within Q subgroupings may be rotated by three bit positions (e.g., one times the index) by bit-position permuter  114 D. In this way, QAM symbol shifting and bit-position rotation may be performed on all spatial streams but one (e.g., the first one). 
         [0029]    Although  FIG. 5  illustrates an example for 64-QAM with four spatial streams in which the QAM groupings are shifted a number of subcarriers based on a factor of three times the spatial stream index, the scope of the invention is not limited in this respect. Different amounts of shifting may be performed depending on the type of permuting performed by block permuters  110  to help provide a maximal subcarrier separation between adjacent bit and near adjacent bits at the output of the bit-grouping shifters. 
         [0030]    In some embodiments, first bit-position permuter  114 B may circularly rotate bits among bit-positions with I subgroupings and within Q subgroupings of each of QAM bit groupings  528 . Each of QAM bit groupings  528  may be associated with one subcarrier of the multicarrier communication signal, and first bit-grouping shifter  112 B shifts QAM bit groupings  528  by a plurality of subcarriers of the multicarrier communication signal. 
         [0031]    In some embodiments, bit-position permuter  114 B may rotate bits of I subgroupings  504  in columns  510 ,  512  and  514  left by one column (i.e., one bit position) so that bits originally in column  510  reside in column  514 , bits originally in column  512  reside in column  510 , and bits originally in column  514  now reside in column  512 . Similarly bit-position permuter  114 B may rotate bits of Q subgroupings  506  in columns  516 ,  518  and  512  left by one column (i.e., one bit position) so that bits originally in column  516  reside in column  520 , bits originally in column  518  reside in column  516 , and bits originally in column  520  now reside in column  516 . The shift may be performed in either direction. In the case of a three bit position shift, the bits result in their original position because there are three bits per I or Q subgrouping as illustrated, however, the scope of the invention is not limited in this respect. In some other embodiments, the I and Q subgroupings may comprise a higher number of bits per symbol grouping. 
         [0032]    In some embodiments, first QAM mapper  116 A may include a first symbol modulator to symbol-modulate QAM symbol-bit groupings of first spatial stream  111 A to generate a first plurality of symbol-modulated subcarriers  117 A. Second QAM mapper  116 B may include a second symbol modulator to symbol-modulate the QAM symbol-bit groupings of the second spatial stream  115 B after operation of first bit-grouping shifter  112 B and first bit-position permuter  114 B to generate a second plurality of symbol-modulated subcarriers  117 B. The first plurality of symbol-modulated subcarriers  117 A may comprise a first orthogonal frequency division multiplexed (OFDM) symbol for subsequent transmission by first antenna  120 A, and the second plurality of symbol-modulated subcarriers  117 B may comprise a second OFDM symbol for subsequent transmission by second antenna  120 B. 
         [0033]    In some embodiments, first block permuter  110 A may perform a block interleaving operation on bits  109  associated with the first spatial stream. Second block permuter  110 B may perform the block interleaving operation on bits associated with the second spatial stream prior operation of bit-grouping shifter  112 B and bit-position permuter  114 B. 
         [0034]    In some embodiments, first bit-grouping shifter  112 B may shift each symbol-bit grouping  528  of second spatial stream  522  by a predetermined number of subcarriers based on a spatial stream index of the second spatial stream, and first bit-position permuter  114 B may rotate bits within the I subgroupings and within the Q subgroupings of symbol-bit groupings  528  of second spatial stream  522  by a predetermined number of bit positions for all of the subcarriers of the multicarrier communication signal. The predetermined number bit positions may be based on the spatial stream index of the second spatial stream. In some embodiments, first bit-grouping shifter  112 B may shift each symbol-bit grouping  528  of second spatial stream  522  by three subcarriers, and first bit-position permuter  114 B may rotate bits within I subgroupings  504  and within Q subgroupings  506  of the symbol-bit groupings  528  of second spatial stream  522  by one bit position, although the scope of the invention is not limited in this respect. 
         [0035]    In some embodiments that transmit more than two spatial streams, multicarrier transmitter  100  also comprises second bit-grouping shifter  112 C to shift symbol-bit groupings of third spatial stream  111 C by a predetermined number of subcarriers based on a spatial stream index of third spatial stream  111 C. Multicarrier transmitter  100  may also include second bit-position permuter  114 C to rotate bits within the I subgroupings and within the Q subgroupings of the symbol-bit groupings of third spatial stream  111 C by a predetermined number of bit-positions for all of the subcarriers of the multicarrier communication signal. The predetermined number of bit positions may be based on the spatial stream index of third spatial stream  111 C. In these embodiments, multicarrier transmitter  100  may also include third QAM mapper  116 C to symbol-modulate the symbol-bit groupings of third spatial stream  115 C after operation of second bit-grouping shifter  112 C and second bit-position permuter  114 C to generate a third plurality of symbol-modulated subcarriers  117 C. The third plurality of symbol-modulated subcarriers  117 C may comprise a third orthogonal frequency division multiplexed symbol for subsequent transmission by third antenna  120 C. 
         [0036]    In some embodiments, second bit-grouping shifter  112 C shifts each QAM symbol-bit grouping of third spatial stream  111 C by six subcarriers. In these embodiments, second bit-position permuter  114 C may rotate bits within the I subgroupings and within the Q subgroupings of the QAM symbol-bit groupings of third spatial stream  111 C by two bit positions, although the scope of the invention is not limited in this respect. 
         [0037]    In some embodiments that transmit more than three spatial streams, multicarrier transmitter  100  may also comprise third bit-grouping shifter  112 D to shift QAM symbol-bit groupings of fourth spatial stream  111 D by a predetermined number of subcarriers based on a spatial stream index of fourth spatial stream  111 D. Multicarrier transmitter  100  may also include third bit-position permuter  114 D to rotate bits within the I subgroupings and within the Q subgroupings of the QAM symbol-bit groupings of fourth spatial stream  111 D by a predetermined number of bit-positions for all of the subcarriers of the multicarrier communication signal. The predetermined number may be based on the spatial stream index of fourth spatial stream  111 D. In these embodiments, multicarrier transmitter  100  may include symbol mapper  116 D to symbol-modulate the QAM symbol-bit groupings of fourth spatial stream  115 D after operations of third bit-grouping shifter  112 D and third bit-position permuter  114 D to generate a fourth plurality of symbol-modulated subcarriers  117 D. The fourth plurality of symbol-modulated subcarriers  117 D may comprise a fourth OFDM symbol for subsequent transmission by fourth antenna  120 D. In some of these embodiments, third bit-grouping shifter  112 D may shift each QAM symbol-bit grouping of fourth spatial stream  111 D by nine subcarriers, and third bit-position permuter  114 D may rotate bits within the I subgroupings and within the Q subgroupings of the QAM symbol-bit groupings of fourth spatial stream  111 C by three bit positions, although the scope of the invention is not limited in this respect. 
         [0038]    In some embodiments, multicarrier transmitter  100  generates a multicarrier symbol for each of the spatial streams. Each multicarrier symbol may comprise a plurality of symbol-modulated subcarriers of a multicarrier communication signal. In some embodiments, each antenna may transmit an OFDM symbol on the same frequency subcarriers as the other antennas. In these embodiments, antenna diversity is employed to allow the transmission of additional data (e.g., more than one spatial stream) without an increase in frequency bandwidth. 
         [0039]    Although multicarrier transmitter  100  is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, processing elements may comprise one or more microprocessors, DSPs, application specific integrated circuits (ASICs), and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, some functional elements of multicarrier transmitter  100  may refer to one or more processes operating on one or more processing elements. 
         [0040]    In some embodiments, multicarrier transmitter  100  may transmit an OFDM packet on a multicarrier communication channel. The multicarrier communication channel may be within a predetermined frequency spectrum. The multicarrier communication channel may comprise a plurality of orthogonal subcarriers. In some embodiments, the orthogonal subcarriers of a multicarrier communication channel may be closely spaced OFDM subcarriers. To achieve orthogonality between closely spaced subcarriers, in some embodiments, the subcarriers of a particular multicarrier communication channel may have a null at substantially a center frequency of the other subcarriers of that channel. 
         [0041]    In some embodiments, multicarrier transmitter  100  may communicate with one or more other communication stations over an OFDM communication channel. In some embodiments, the OFDM communication channel may comprise one or more spatial channels associated with each subchannel. In some embodiments, spatial channels associated with a particular multicarrier channel may overlap in frequency (i.e., use the same subcarriers) and orthogonality may be achieved through beamforming and/or antenna diversity. 
         [0042]    In some embodiments, the frequency spectrums for a multicarrier communication channel may comprise either a 5 GHz frequency spectrum or a 2.4 GHz frequency spectrum, although the scope of the invention is not limited in this respect. In these embodiments, the 5 GHz frequency spectrum may include frequencies ranging from approximately 4.9 to 5.9 GHz, and the 2.4 GHz spectrum may include frequencies ranging from approximately 2.3 to 2.5 GHz, although the scope of the invention is not limited in this respect, as other frequency spectrums are equally suitable. 
         [0043]    In some embodiments, multicarrier transmitter  100  may be part of a wireless communication device. The wireless communication device may be a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point or other device that may receive and/or transmit information wirelessly. In some embodiments, multicarrier transmitter  100  may transmit and/or receive RF communications in accordance with specific communication standards, such as the Institute of Electrical and Electronics Engineers (IEEE) standards including IEEE 802.11(a), 802.11(g/h) and/or 802.11(n) standards for wireless local area networks (WLANs) and/or 802.16 standards for wireless metropolitan area networks (WMANs), although multicarrier transmitter  100  may also be suitable to transmit and/or receive communications in accordance with other techniques. 
         [0044]    Each of antennas  120  may be a directional or omnidirectional antenna, including, for example, a dipole antenna, a monopole antenna, a patch antenna, a loop antenna, a microstrip antenna or other type of antenna suitable for transmission of multicarrier signals. 
         [0045]      FIG. 6  is a flow chart of a spatial stream transmission procedure in accordance with some embodiments of the present invention. Procedure  600  may be performed by a multicarrier transmitter, such as multicarrier transmitter  100  ( FIG. 1 ), although other multicarrier and OFDM transmitters may also be suitable. 
         [0046]    Operation  602  scrambles bits of an input bit stream. Operation  602  may be performed by scrambler  102  ( FIG. 1 ), although the scope of the invention is not limited in this respect. 
         [0047]    Operation  604  assigns bits of the bit stream to one of a plurality of data streams. Operation  604  may be performed by commutator  104  ( FIG. 1 ), although the scope of the invention is not limited in this respect. 
         [0048]    Operation  606  separately encodes bits of each data stream. Operation  606  may be performed by encoders  106  ( FIG. 1 ), although the scope of the invention is not limited in this respect. 
         [0049]    Operation  608  assigns the encoded bits in groups from the data streams to each of a plurality of spatial streams. Operation  608  may be performed by spatial-bit sequencer  108  ( FIG. 1 ), although the scope of the invention is not limited in this respect. 
         [0050]    Operation  610  separately performs block interleaving operations on blocks of bits of each of the spatial streams. Operation  610  may be performed by block permuters  110 A- 111 D ( FIG. 1 ), although the scope of the invention is not limited in this respect. 
         [0051]    Operation  612  shifts QAM bit groupings by a number of subcarriers based on the spatial stream index associated with the spatial stream. Operation  612  may be performed by bit-grouping shifters  112 B- 112 D ( FIG. 1 ) for some of the spatial streams, although the scope of the invention is not limited in this respect. 
         [0052]    Operation  614  rotates bits among bit positions of I and Q subgroupings of the QAM symbol-bit groupings based on the spatial stream index associated with the spatial stream. Operation  614  may be performed by bit-position permuters  114 B- 114 D ( FIG. 1 ) for some of the spatial streams, although the scope of the invention is not limited in this respect. 
         [0053]    Operation  616  maps the QAM bit groupings to QAM symbols to generate a multicarrier symbol for reach spatial stream. Operation  616  may be performed by QAM mappers  116 A- 116 D ( FIG. 1 ) for each spatial stream, although the scope of the invention is not limited in this respect. 
         [0054]    Operation  618  generates multicarrier communication signals for each spatial stream for transmission by a corresponding antenna. Operation  618  may be performed by transmit circuitry  118 A- 118 D ( FIG. 1 ), although the scope of the invention is not limited in this respect. 
         [0055]    Although the individual operations of procedure  600  are illustrated and described as separate operations, one or more of the individual operations may be performed concurrently, and nothing requires that the operations be performed in the order illustrated. 
         [0056]    Unless specifically stated otherwise, terms such as processing, computing, calculating, determining, displaying, or the like, may refer to an action and/or process of one or more processing or computing systems or similar devices that may manipulate and transform data represented as physical (e.g., electronic) quantities within a processing system&#39;s registers and memory into other data similarly represented as physical quantities within the processing system&#39;s registers or memories, or other such information storage, transmission or display devices. Furthermore, as used herein, computing device includes one or more processing elements coupled with computer-readable memory that may be volatile or non-volatile memory or a combination thereof. 
         [0057]    Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable medium, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable medium may include any mechanism for storing in a form readable by a machine (e.g., a computer). For example, a computer-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and other storage devices and media. 
         [0058]    The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. 
         [0059]    In the foregoing detailed description, various features are occasionally grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, invention may lie in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment.