OFDM communication system with multiple OFDM symbol sizes

Abstract

Techniques to use OFDM symbols of different sizes to achieve greater efficiency for OFDM systems. The system traffic may be arranged into different categories (e.g., control data, user data, and pilot data). For each category, one or more OFDM symbols of the proper sizes may be selected for use based on the expected payload size for the traffic in that category. For example, control data may be transmitted using OFDM symbols of a first size, user data may be transmitted using OFDM symbols of the first size and a second size, and pilot data may be transmitted using OFDM symbols of a third size or the first size. In one exemplary design, a small OFDM symbol is utilized for pilot and for transport channels used to send control data, and a large OFDM symbol and the small OFDM symbol are utilized for transport channels used to send user data.

What is claimed is:  
     
         1 . A method of transmitting data in an orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 transmitting a first block of data in a first OFDM symbol of a first size; and    transmitting a second block of data in a second OFDM symbol of a second size that is different from the first size.    
     
     
         2 . The method of  claim 1 , wherein the first block of data comprises control data and the second block of data comprises user data.  
     
     
         3 . The method of  claim 2 , wherein the first size is selected based on an expected payload size for the control data and the second size is selected based on an expected payload size for the user data.  
     
     
         4 . The method of  claim 1 , wherein the first and second blocks of data are for a data packet.  
     
     
         5 . The method of  claim 1 , wherein the first block of data is intended for multiple receivers and the second block of data is intended for a single receiver.  
     
     
         6 . The method of  claim 1 , further comprising: 
 transmitting a pilot in a third OFDM symbol.    
     
     
         7 . The method of  claim 6 , wherein the pilot is a steered reference.  
     
     
         8 . The method of  claim 1 , wherein each pair of modulation symbols for the second OFDM symbol is concurrently transmitted on a pair of subbands from two antennas.  
     
     
         9 . The method of  claim 1 , wherein cyclic prefixes for the first and second OFDM symbols have the same length.  
     
     
         10 . The method of  claim 1 , wherein cyclic prefixes for the first and second OFDM symbols have different lengths.  
     
     
         11 . The method of  claim 1 , wherein the second block of data is coded to obtain an error detection value that is transmitted in the second OFDM symbol.  
     
     
         12 . The method of  claim 1 , wherein the first and second blocks of data are interleaved with the same interleaving scheme.  
     
     
         13 . The method of  claim 1 , wherein the first and second sizes are related by a power of two.  
     
     
         14 . An apparatus in an orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 means for transmitting a first block of data in a first OFDM symbol of a first size; and    means for transmitting a second block of data in a second OFDM symbol of a second size that is different from the first size.    
     
     
         15 . The apparatus of  claim 14 , further comprising: 
 means for transmitting a pilot in a third OFDM symbol of the first size.    
     
     
         16 . A transmitter unit in an orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 a transmit (TX) data processor operative to process a first block of data to obtain a first set of modulation symbols and to process a second block of data to obtain a second set of modulation symbols; and    a modulator operative to process the first set of modulation symbols to obtain a first OFDM symbol of a first size and to process the second set of modulation symbols to obtain a second OFDM symbol of a second size that is different from the first size.    
     
     
         17 . The transmitter unit of  claim 16 , wherein the modulator is further operative to process a third set of modulation symbols for a pilot to obtain a third OFDM symbol for the pilot.  
     
     
         18 . A method of transmitting data in an orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 transmitting control data in a first time segment with a first OFDM symbol of a first size; and    transmitting user data in a second time segment with a second OFDM symbol of a second size that is different from the first size.    
     
     
         19 . The method of  claim 18 , further comprising: 
 transmitting user data in the second time segment with a third OFDM symbol of a third size that is different from the second size.    
     
     
         20 . The method of  claim 18 , further comprising: 
 transmitting a pilot in a third time segment with a third OFDM symbol.    
     
     
         21 . The method of  claim 18 , wherein the first and second sizes are fixed.  
     
     
         22 . The method of  claim 18 , wherein the first and second sizes are configurable.  
     
     
         23 . A method of receiving data in an orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 receiving a first OFDM symbol of a first size for a first block of data; and    receiving a second OFDM symbol of a second size for a second block of data, the second size being different from the first size.    
     
     
         24 . The method of  claim 23 , wherein the first block of data comprises control data and the second block of data comprises user data.  
     
     
         25 . The method of  claim 23 , wherein the first and second blocks of data are for a data packet.  
     
     
         26 . The method of  claim 23 , further comprising: 
 receiving a third OFDM symbol for a pilot.    
     
     
         27 . The method of  claim 26 , further comprising: 
 processing the third OFDM symbol to obtain a channel estimate for each of a plurality of subbands.    
     
     
         28 . The method of  claim 27 , further comprising: 
 interpolating channel estimates for the plurality of subbands to obtain a channel estimate for an additional subband not among the plurality of subbands.    
     
     
         29 . An apparatus in an orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 means for receiving a first OFDM symbol of a first size for a first block of data; and    means for receiving a second OFDM symbol of a second size for a second block of data, the second size being different from the first size.    
     
     
         30 . The apparatus of  claim 29 , further comprising: 
 means for receiving a third OFDM symbol for a pilot; and    means for processing the third OFDM symbol to obtain a channel estimate for each of a plurality of subbands.    
     
     
         31 . The apparatus of  claim 30 , comprising: 
 means for interpolating channel estimates for the plurality of subbands to obtain a channel estimate for an additional subband not among the plurality of subbands.    
     
     
         32 . A receiver unit in an orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 a demodulator operative to process a first OFDM symbol of a first size to obtain a first set of received modulation symbols and to process a second OFDM symbol of a second size to obtain a second set of received modulation symbols, wherein the second size is different from the first size; and    a receive (RX) data processor operative to process the first set of received modulation symbols to obtain a first block of data and to process the second set of received modulation symbols to obtain a second block of data.    
     
     
         33 . The receiver unit of  claim 32 , wherein the demodulator is further operative to process a third OFDM symbol for a pilot to provide a channel estimate for each of a plurality of subbands.  
     
     
         34 . The receiver unit of  claim 33 , further comprising: 
 a controller operative to interpolate channel estimates for the plurality of subbands to obtain a channel estimate for an additional subband not among the plurality of subbands.    
     
     
         35 . A method of processing a pilot in a multiple-input multiple-output (MIO) orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 receiving a first set of OFDM symbols from a set of antennas for the pilot;    processing the first set of OFDM symbols to obtain a channel response matrix for each of a plurality of subbands; and    decomposing the channel response matrix for each of the plurality of subbands to obtain a unitary matrix of eigenvectors for the channel response matrix, wherein the decomposition is performed in a manner to avoid arbitrary phase rotations from subband to subband.    
     
     
         36 . The method of  claim 35 , wherein the arbitrary phase rotations from subband to subband are avoided by constraining first element in each column of the unitary matrix to be a non-negative value.  
     
     
         37 . The method of  claim 36 , further comprising: 
 generating a steered reference based on a particular column of the unitary matrix for each of the plurality of subbands; and    transmitting a second set of OFDM symbols from the set of antennas for the steered reference.    
     
     
         38 . A method of processing a steered reference in a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 receiving a set of OFDM symbols from a set of antennas for the steered reference;    processing the set of OFDM symbols to obtain a steering vector for each of a plurality of subbands; and    interpolating steering vectors for the plurality of subbands to obtain a steering vector for an additional subband not among the plurality of subbands.    
     
     
         39 . A method of transmitting a data unit having a data unit size in an orthogonal frequency division multiplexing (OFDM) communication system, the method comprising: 
 selecting a first OFDM symbol size from a set of OFDM symbol sizes, wherein the set of OFDM symbol sizes comprises a large OFDM symbol size and a small OFDM symbol size that is smaller than the large OFDM symbol size; and    transmitting a first portion of the data unit in an OFDM symbol having the first OFDM symbol size.    
     
     
         40 . The method of  claim 39  wherein the selecting a first OFDM symbol size is based on the data unit size.  
     
     
         41 . The method of  claim 39  wherein the data unit has a data unit type, and wherein the selecting a first OFDM symbol size is based on the data unit type.  
     
     
         42 . The method of  claim 39  further comprising: 
 selecting a second OFDM symbol size from the set of OFDM symbol sizes; and  
 transmitting a second portion of the data unit in a second OFDM symbol having the second OFDM symbol size.  
 
     
     
         43 . The method of  claim 42 , wherein the first OFDM symbol size is equal to the second OFDM symbol size.  
     
     
         44 . The method of  claim 42 , wherein the first OFDM symbol size is larger than the second OFDM symbol size.  
     
     
         45 . An apparatus in an orthogonal frequency division multiplexing (OFDM) communication system, comprising 
 means for selecting a first OFDM symbol size from a set of OFDM symbol sizes, wherein the set of OFDM symbol sizes comprises a large OFDM symbol size and a small OFDM symbol size that is smaller than the large OFDM symbol size; and    means for transmitting a first portion of a data unit in an OFDM symbol having the first OFDM symbol size.    
     
     
         46 . The apparatus of  claim 45 , further comprising: 
 means for selecting a second OFDM symbol size from the set of OFDM symbol sizes; and    means for transmitting a second portion of the data unit in a second OFDM symbol having the second OFDM symbol size.    
     
     
         47 . The apparatus of  claim 45 , wherein the first OFDM symbol size is selected based on a data unit size of the data unit.  
     
     
         48 . The apparatus of  claim 45 , wherein the first OFDM symbol size is selected based on a data unit type of the data unit.  
     
     
         49 . A transmitter unit in an orthogonal frequency division multiplexing (OFDM) communication system, comprising: 
 a controller operative to select a first OFDM symbol size from a set of OFDM symbol sizes, wherein the set of OFDM symbol sizes comprises a large OFDM symbol size and a small OFDM symbol size that is smaller than the large OFDM symbol size; and    a modulator operative to process a first portion of a data unit to obtain an OFDM symbol having the first OFDM symbol size.    
     
     
         50 . The transmitter of  claim 49 , wherein the controller is further operative to select a second OFDM symbol size from the set of OFDM symbol sizes, and wherein the modulator is further operative to process a second portion of the data unit to obtain a second OFDM symbol having the second OFDM symbol size.