Optimal filtering and upconversion in OFDM systems
AssigneeCisco Technology, Inc.
InventorsVincent K. Jones, IV, James M. Gardner, Michael Pollack
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Abstract
Systems and methods for converting a baseband OFDM signal to an IF signal while minimizing lengthening of the impulse response duration experienced by the OFDM signal. A conversion technique according to the present invention provides sufficient filtering to limit the effects of spurious frequency domain components caused by transitions between successive OFDM bursts. In one embodiment, the filtering is provided by a combination of a finite impulse response (FIR) filter having non-linear phase characteristics and a cyclic convolution filter. Conversion from the frequency domain into the time domain, upsampling, and cyclic filtering may be combined into one operation.
Claims18
Apparatus for transmitting OFDM signals comprising:
- a transform processor that transforms a frequency domain burst of symbols into a time domain burst of symbols;
- and
- a signal processing system that receives said time domain burst of symbols and performs operations on said time domain burst of symbols to develop a filtered time domain burst of symbols, said signal processing system comprising an FIR filter having non-linear phase characteristics, said signal processing system comprising a shifter that frequency shifts an output of said FIR filter to a desired IF.
Apparatus for transmitting OFDM signals comprising:
- a transform processor that transforms a frequency domain burst of symbols into a time domain burst of symbols;
- and
- a signal processing system that receives said time domain burst of symbols and performs operations on said time domain burst of symbols, said signal processing system comprising:
- a cyclic convolution filter that provides a filtered time domain symbol burst as output;
- and
- a first upsampler that receives said time domain burst of symbols and provides a first upsampled time domain burst as input to said cyclic convolution filter.
A method for transmitting OFDM signals comprising:
- receiving an N-symbol frequency domain symbol burst;
- zero-padding said N-symbol frequency domain symbol burst to form an M*N-symbol frequency domain burst;
- and
- transforming said M*N-symbol frequency domain symbol burst into an M*N-symbol time domain burst, wherein operations of upsampling, cyclic filtering, and conversion from the frequency domain to the time domain are accomplished by said transforming.
Dependencies are inferred from the claim text.