Adaptive quantization method and apparatus for an OFDM receiver
AssigneeIntegrated System Solution Corp.
InventorsJeng-Hong Chen, Yumin Lee, Yuh-Chun Lin
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Abstract
A quadrature frequency division multiplexing (“OFDM”) wireless receiver, including methods and devices for adaptive quantization of OFDM signals according to modulation and coding schemes and sub-carrier frequency responses, is provided. Efficient quantization may be utilized to reduce the large dynamic range of signals to achieve circuit simplification and chip area reduction. In one embodiment, a quantization circuit includes a quantization selector to select quantization thresholds according to modulation and coding schemes and sub-carrier frequency responses, and a non-uniform quantizer to reduce input dynamic range so that an output is represented by fewer bits than an input.
Claims21
A method of dynamic quantization in an orthogonal frequency division multiplexing (OFDM) system, the method comprising:
- receiving quadrature amplitude modulation (QAM) symbols for each of a number of “m” sub-carrier channels, m being an integer greater than 1;
- computing a channel power PCH(i)=|GCH(i)|2 for each of the m sub-carrier channels, where Gch(i) is the i-th sub-carrier channel frequency response, i being an integer from 0 to m−1;
- computing
- P
- max
- =
- max
- i
-
- {
- P
- CH
-
- (
- i
- )
- }
- ,
- where the max{ } function computes the maximum value of PCH(i);
- computing
- P
- min
- =
- min
- i
-
- {
- P
- CH
-
- (
- i
- )
- }
- ,
- where the min{ } function computes the minimum value of PCH(i);
- setting a first frequency selectivity indicator (FSI) value if Pmax≧T*Pmin and setting a second FSI value if Pmax<T*Pmin, wherein T is a predetermined threshold value;
- determining a quantization parameter, K, which is a positive real number selected according to the first or second FSI value;
- applying an exponential function to the received QAM symbol, xi for the i-th subcarrier, according to the following equation:
- g
-
- (
- x
- j
- )
- =
- sgn
-
- (
- x
- j
- )
-
- [
- 1
- -
- exp
-
- (
- -
-
- x
- j
-
- K
- )
- ]
- ,
- sgn
-
- (
- x
- j
- )
- =
- {
- 1
- ,
- x
- j
- >
- 0
- 0
- ,
- x
- j
- =
- 0
- -
- 1
- ,
- x
- j
- <
- 0
- ,
- where g(xi) is a transform output of xi;
- determining a set of (2q−1) quantization thresholds according to the first and second FSI values for a q-bit quantization output in the OFDM system, wherein q is a positive integer;
- and
- quantizing the exponential function outputs, g(xi) for all the sub-carriers.
A receiver for dynamic quantization in an orthogonal frequency division multiplexing (OFDM) system, the receiver comprising:
- a channel power calculator to compute a channel power PCH(i)=|GCH(i)|2 for each of “m” sub-carrier channels, where Gch(i) is the i-th sub-carrier channel frequency response, i being an integer from 0 to m−1;
- and
- a channel frequency selectivity detector to compute
- P
- max
- =
- max
- i
-
- {
- P
- CH
-
- (
- i
- )
- }
- ,
- where the max{ } function computes the maximum value of PCH(i), compute
- P
- min
- =
- min
- i
-
- {
- P
- CH
-
- (
- i
- )
- }
- ,
- where the min{ } function computes the minimum value of PCH(i), and set a first frequency selectivity indicator (FSI) value if Pmax≧T*Pmin and a second FSI value if Pmax<T*Pmin , wherein T is a predetermined threshold value;
- and
- a q-bit exponential quantizer comprising
- processing the received QAM symbols, xi, for the i-th subcarrier, according to the following exponential equation:
- g
-
- (
- x
- j
- )
- =
- sgn
-
- (
- x
- j
- )
-
- [
- 1
- -
- exp
-
- (
- -
-
- x
- j
-
- K
- )
- ]
- ,
- sgn
-
- (
- x
- j
- )
- =
- {
- 1
- ,
- x
- j
- >
- 0
- 0
- ,
- x
- j
- =
- 0
- -
- 1
- ,
- x
- j
- <
- 0
- ,
- where g(xi) is a transform output of xi, and the quantization parameter K is a positive real number;
- where x is either one real value of the received complex QAM symbol xi, and the quantization parameter K is a positive real number;
- determining a set of (2q−1) quantization thresholds according to the first or second FSI value for a q-bit quantization output in the OFDM system, wherein q is a positive integer;
- and
- quantizing the exponential function outputs, for all the subcarriers.
Dependencies are inferred from the claim text.