System and method for blind channel estimation and coherent differential equalization in an orthogonal frequency division multiplexing (ofdm) receiver

Patent metadata

Field	Value
Publication number	US-2022200825-A1
Application number	US-202017124561-A
Country	US
Kind code	A1
Filing date	Dec 17, 2020
Priority date	Dec 17, 2020
Publication date	Jun 23, 2022
Grant date	—

Abstract

In one aspect, an apparatus includes: a fast Fourier transform (FFT) engine to receive and convert a plurality of orthogonal frequency division multiplexing (OFDM) samples into a plurality of frequency carriers; a detector coupled to the FFT engine to determine a channel estimate for a first frequency carrier using a first channel estimate for the first frequency carrier and a plurality of other channel estimates, each of the plurality of other channel estimates for one of a plurality of neighboring frequency carriers within an evaluation window, and determine a log likelihood ratio (LLR) for the first frequency carrier using the channel estimate for the first frequency carrier; and a decoder coupled to the detector to decode a first OFDM symbol comprising the first frequency carrier using the LLR for the first frequency carrier.

First claim

What is claimed is:

1 . An apparatus comprising:
a front end circuit to receive incoming radio frequency (RF) signals and process the incoming RF signals into orthogonal frequency division multiplexing (OFDM) samples of a plurality of OFDM symbols; a fast Fourier transform (FFT) engine coupled to the front end circuit, the FFT engine to receive the plurality of OFDM samples and convert the plurality of OFDM samples into a plurality of frequency carriers; a detector coupled to the FFT engine, the detector to determine a channel estimate for a first frequency carrier using a first channel estimate for the first frequency carrier and a plurality of other channel estimates, each of the plurality of other channel estimates for one of a plurality of neighboring frequency carriers within an evaluation window, and determine a log likelihood ratio (LLR) for the first frequency carrier using the channel estimate for the first frequency carrier; and a decoder coupled to the detector to decode a first OFDM symbol comprising the first frequency carrier using the LLR for the first frequency carrier.

2 . The apparatus of claim 1 , wherein the detector is to determine the channel estimate for the first frequency carrier comprising an average value determined using the first channel estimate and the plurality of other channel estimates.

3 . The apparatus of claim 2 , wherein the evaluation window comprises a first plurality of frequency carriers of the first OFDM symbol and a second plurality of frequency carriers of a second OFDM symbol adjacent to the first OFDM symbol.

4 . The apparatus of claim 1 , wherein the detector is to:
calculate a plurality of metrics for the first frequency carrier and the plurality of neighboring frequency carriers within the evaluation window; and determine the LLR for a pair of frequency carriers comprising the first frequency carrier and a second frequency carrier based at least in part on the plurality of metrics.

5 . The apparatus of claim 4 , wherein the detector is to determine the LLR for the pair of frequency carriers comprising the first frequency carrier and the second frequency carrier comprising:
for a first bit of the first OFDM symbol, a difference between a first maximum metric of the plurality of metrics for a first value for the first bit and a second maximum metric of the plurality of metrics for a second value for the first bit; and for a second bit of the first OFDM symbol, a difference between a first maximum metric of the plurality of metrics for the first value for the second bit and a second maximum metric of the plurality of metrics for the second value for the second bit.

6 . The apparatus of claim 4 , wherein the detector comprises:
a channel estimation circuit to generate a plurality of channel estimates for the first frequency carrier, the plurality of channel estimates including the first channel estimate; and a channel estimation smoother to determine the channel estimate for the first frequency carrier using the first channel estimate and the plurality of other channel estimates.

7 . The apparatus of claim 6 , wherein the detector further comprises:
a metric calculator coupled to the channel estimation smoother to calculate the plurality of metrics using the first channel estimate; and a buffer to store the plurality of metrics.

8 . The apparatus of claim 7 , wherein the detector further comprises a determination circuit coupled to the metric calculator to determine the LLR for the pair of frequency carriers and the plurality of neighboring frequency carriers within the evaluation window.

9 . A method comprising:
determining, in a channel estimation circuit of a receiver, a plurality of channel estimates within an evaluation window having a plurality of frequency carriers including a first frequency carrier, each of the plurality of channel estimates for one of the plurality of frequency carriers; calculating, in a calculation circuit of the receiver, a plurality of metrics for each of the plurality of frequency carriers using at least some of the plurality of channel estimates; and determining a soft decision for the first frequency carrier based at least in part on the plurality of metrics.

10 . The method of claim 9 , wherein determining a first channel estimate for the first frequency carrier comprising calculating an average of an initial channel estimate for the first frequency carrier and initial channel estimates for a plurality of other frequency carriers of the plurality of frequency carriers.

11 . The method of claim 10 , further comprising selecting the initial channel estimate for the plurality of other frequency carriers comprising a channel estimate closest to the initial channel estimate for the first frequency carrier.

12 . The method of claim 9 , wherein calculating the plurality of metrics comprises:
calculating a first log likelihood ratio (LLR) metric for each of the plurality of frequency carriers of the evaluation window, the first LLR metric corresponding to a likelihood that a first bit of a modulation point of the frequency carrier is a first value; calculating a second LLR metric for each of the plurality of frequency carriers of the evaluation window, the second LLR metric corresponding to a likelihood that the first bit of the modulation point is a second value; calculating a third LLR metric for each of the plurality of frequency carriers of the evaluation window, the third LLR metric corresponding to a likelihood that a second bit of the modulation point is the first value; and calculating a fourth LLR metric for each of the plurality of frequency carriers of the evaluation window, the fourth LLR metric corresponding to a likelihood that the second bit of the modulation point is the second value.

13 . The method of claim 12 , further comprising determining a first LLR value and a second LLR value based at least in part on the first LLR metric, the second LLR metric, the third LLR metric, and the fourth LLR metric.

14 . The method of claim 13 , wherein the soft decision comprises the first LLR value and the second LLR value.

15 . The method of claim 9 , further comprising performing coherent demodulation for a differentially encoded quadrature phase shift keying orthogonal frequency division multiplexing symbol using the soft decision.

16 . An apparatus comprising:
means for determining a plurality of channel estimates within an evaluation window having a plurality of frequency carriers including a first frequency carrier, each of the plurality of channel estimates for one of the plurality of frequency carriers; means for calculating a plurality of metrics for each of the plurality of frequency carriers using at least some of the plurality of channel estimates; and means for determining a soft decision for the first frequency carrier based at least in part on the plurality of metrics.

17 . The apparatus of claim 16 , wherein the means for determining is to calculate an average of an initial channel estimate for the first frequency carrier and initial channel estimates for a plurality of other frequency carriers of the plurality of frequency carriers.

18 . The apparatus of claim 17 , further comprising means for selecting the initial channel estimate for the plurality of other frequency carriers comprising a channel estimate closest to the initial channel estimate for the first frequency carrier.

19 . The apparatus of claim 16 , wherein the means for calculating comprises:
means for calculating a first

Assignees

• Skyworks Solutions Inc

Inventors

• Kleinerman Alexander
• Wallace Bradley Arthur

Classifications

• H04L27/2647

  Arrangements specific to the receiver only (equalisation H04L27/01) · CPC title

• H04L27/2331

  wherein the received signal is demodulated using one or more delayed versions of itself · CPC title

• H04L25/067

  providing soft decisions, i.e. decisions together with an estimate of reliability (H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178) · CPC title

• H04L25/0238 Primary

  using blind estimation · CPC title

• H04L25/0204

  of multiple channels · CPC title