Equalization scheme for DSL receivers in presence of an under-sampled or over-sampled transmit IDFT
View Patent ↗A circuit and method is provided for reducing the effect of having potentially different sizes for an Inverse Discrete Fourier Transform (IDFT) at a transmitter and a Discrete Fourier Transform (DFT) at a receiver in a telecommunications system without requiring a change in the DFT's size. The method includes following steps. The first step includes determining whether the IDFT size is greater than, equal to, or less than the DFT size. The second step includes selecting a target impulse response length from a predefined set of impulse response lengths in accordance with a result the previous step. The third step includes training an equalizer at the receiver to the target impulse response length. The circuit comprises hardware and software for implementing the method.
1. A method of reducing an effect of having potentially different sizes for an Inverse Discrete Fourier Transform (IDFT) at a transmitter and a Discrete Fourier Transform (DFT) at a receiver in a telecommunications system without requiring a change to a DFT size of said DFT, said method comprising the steps of:
(a) determining whether an IDFT size of said IDFT is greater than, equal to, or less than said DFT size;
(b) selecting a target impulse response length of a desired channel impulse response from a predefined set of impulse response lengths in accordance with a result of step (a); and
(c) training an equalizer at said receiver to said target impulse response length.
2. A method as defined in claim 1 , wherein said predefined set of impulse response lengths is defined such that transients in a transmission signal coincide with a cyclic prefix of said transmission signal.
3. A method as defined in claim 2 , wherein an initial transient coincides with a cyclic prefix of an associated signal and a final transient coincides with a cyclic prefix of a following signal that follows said associated signal.
4. A method as defined in claim 1 , wherein if said IDFT size is equal to said DFT size, said target impulse response length is set to a value equal to or less than a cyclic prefix length at either said transmitter or said receiver plus one.
5. A method as defined in claim 1 , wherein if said IDFT size is less than said DFT size, said target impulse response length is set to a value equal to or less than a cyclic prefix length at said receiver plus a ratio between said DFT size and said IDFT size.
6. A method as defined in claim 1 , wherein if said IDFT size is greater than said DFT size, said target impulse response length is set to a value equal to or less than a cyclic prefix length at said transmitter plus one.
7. A method as defined by claim 1 , wherein said step (a) is achieved by comparing said IDFT size and said DFT size communicated between said transmitter and said receiver.
8. A method as defined in claim 7 , wherein said IDFT size and said DFT size are communicated between said transmitter and said receiver during handshaking.
9. A method as defined in claim 1 , wherein said step (a) comprises the following steps:
(d) training said equalizer with a plurality of impulse response lengths;
(e) estimating a per-bin signal-to-noise ratio for each of said plurality of impulse response lengths;
(f) determining a highest signal-to-noise ratio; and
(g) selecting an impulse response length associated with said highest signal-to- noise ratio for use as said target impulse response length.
10. A method as defined in claim 9 , wherein said plurality of impulse response lengths include impulse response lengths ranging from a cyclic prefix length at said receiver to a cyclic prefix length at said receiver plus a maximum expected ratio between said DFT size and said IDFT size.
11. A method as defined in claim 9 , wherein said plurality of impulse response lengths includes an impulse response length equal to a cyclic prefix length at said transmitter plus one.
12. A method as defined in claim 1 , wherein said equalizer is trained at a impulse response length representing said IDFT size greater than said DFT size, farther comprising the steps of:
(d) defining a time advance interval;
(e) estimating a per-bin signal-to-noise ratio for each of a plurality of predefined values in said time advance interval;
(f) determining a highest signal-to-noise ratio; and
(g) selecting a value in said time advance interval associated with said highest signal-to-noise ratio for selecting an optimal frame alignment.
13. A method as defined in claim 1 , wherein said equalizer is a time domain equalizer (TDLQ).
14. A method as defined in claim 1 , wherein said equalizer is a frequency domain equalizer (FDLQ).
15. A method as defined in claim 1 , wherein said IDFT is an Inverse Fast Fourier Transform and said DFT is a Fast Fourier Transform.
16. A digital subscriber line (DSL) telecommunications system including a transmitter and a receiver, said transmitter having an Inverse Discrete Fourier Transform (IDFT) and said receiver having a Discrete Fourier Transform (DFT), said DSL telecommunications system including circuitry to perform processing comprising the steps of:
(a) determining whether an IDFT size of said IDFT is greater than, equal to, or less than a DFT size of said DFT;
(b) selecting a target impulse response length of a desired channel impulse response from a predefined set of impulse response lengths in accordance with a result of step (a); and
(c) training an equalizer at said receiver to said target impulse response length.