LMMSE-based RAKE receiver with channel tap assignment
View Patent ↗Methods of recovering data in a received signal sent in a communications media are disclosed. Composite channel impulse responses are first estimated. Channel-tap locations are then assigned to suppress the interference noises by sequential search schemes or heuristic search schemes based on estimated composite channel impulse responses. A sequential search scheme optimizes a predetermined design criterion in a sequential manner. Also described are recursive evaluations of the design criterion and the inverses of the noise covariance matrices based on the composite channel impulse response during a sequential search. A heuristic search scheme selects channel-tap locations based on a set of pre-selected channel-tap locations. The set of pre-selected channel-tap locations is determined according to the estimated composite channel impulse response. A method of estimating energy levels of known interference sources is also described.
1. A method of recovering data in a received signal sent in a communications media, comprising:
(a) estimating at least one composite channel impulse response from said received signal,
(b) estimating a set of noise covariances based on said composite channel impulse response,
(c) assigning a set of channel-tap locations by a sequential search based on said composite channel impulse response, with each said channel tap depending on said composite channel impulse response,
(d) computing a set of weight coefficients for said set of channel-tap locations based on said composite channel impulse response, and
(e) demodulating data in said received signal with said set of channel-tap locations and said set of weight coefficients.
2. The method of claim 1 , wherein estimating said set of noise covariances based on said composite channel impulse response comprises:
(a) decomposing said noise variance into a one-dimensional part, a cyclostationary part, and a two-dimensional part,
(b) pre-computing and tabulating said one-dimensional part of said noise variance using a one-dimensional table,
(c) pre-computing and tabulating said cyclostationary part of said noise variance using a plurality of one-dimensional tables,
(d) accessing said one-dimensional tables to retrieve said one-dimensional part and said cyclostationary part of said noise covariance, and
(e) computing said two-dimensional part of said noise covariance.
3. The method of claim 1 , wherein said sequential search comprises:
(a) determining a search region based on said composite channel impulse response,
(b) pre-selecting a first set of channel-tap locations in said search region based on said composite channel impulse response, if said first set is predetermined to be non-empty, and
(c) sequentially selecting a second set of channel-tap locations in said search region, based on said first set of channel-tap locations, to optimize a design criterion.
4. The method of claim 3 , wherein said search region is a contiguous region comprising a span of said composite channel impulse response, a pre-composite-channel-impulse-response section, and a post-composite-channel-impulse-response section.
5. The method of claim 3 , wherein said search region is a union of a set of path regions and a set of mirror image regions.
6. The method of claim 3 , wherein pre-selecting said first set of channel-tap locations comprises choosing a number of strongest channel taps according to said composite channel impulse response, the distances among which are equal to or larger than a predetermined minimum distance.
7. The method of claim 3 , wherein said design criterion is mean square error, whereby said mean square error is computed based on said composite channel impulse response.
8. The method of claim 3 , wherein said design criterion is signal-to-noise ratio, whereby said signal-to-noise ratio is computed based on said composite channel impulse response.
9. The method of claim 3 , wherein sequentially selecting said second set of channel-tap locations to optimize said design criterion comprises choosing a new channel-tap location that optimizes said design criterion based on a recursive evaluation that explicitly depends on:
(a) a set of previously evaluated functions of all previously chosen channel-tap locations, and
(b) a set of functions of said new channel-tap location, whereby said recursive evaluation can reduce the amount of computations.
10. The method of claim 9 , wherein said recursive evaluation comprises:
(a) a function of said design criterion,
(b) a recursive equation of said function of said design criterion,
(c) a difference between two consecutive recursion values of said function of said design criterion, which is to be optimized by said new channel-tap location, and
(d) a recursive equation of a noise variance matrix.
11. The method of claim 3 , wherein sequentially selecting said second set of channel-tap locations to optimize said design criterion comprises choosing a new channel-tap location that optimizes said design criterion based on an approximate recursive evaluation that explicitly depends on:
(a) a set of previously evaluated functions of all previously chosen channel-tap locations, and
(b) a set of functions of said new channel-tap location,
whereby said approximate recursive evaluation can further reduce the amount of computations.
12. The method of claim 11 , wherein said approximate recursive evaluation comprises:
(a) a function of said design criterion,
(b) a recursive equation of said function of said design criterion,
(c) a simplified and approximate difference between two consecutive recursion values of said function of said design criterion, which is to be optimized by said new channel-tap location, and
(d) a recursive equation of the inverse of a noise variance matrix.
13. The method of claim 3 , wherein sequentially selecting said second set of channel-tap locations to optimize said design criterion can be terminated early before a predetermined number of channel-tap locations has been selected, if the difference between the value of said design criterion before a new tap is selected and the value of said design criterion after said new tap is selected is below a predetermined threshold.
14. The method of claim 1 , wherein recovering data in said received signal sent in said communications media is performed at 2× oversampling.
15. A method of recovering data in a received signal sent in a communications media, comprising:
(a) estimating at least one composite channel impulse response from said received signal,
(b) estimating a set of noise covariances based on said composite channel impulse responses,
(c) assigning a set of channel-tap locations by a heuristic search based on said composite channel impulse response, with each said channel tap depending on said composite channel impulse response,
(d) computing a set of weight coefficients for said set of channel-tap locations based on said composite channel impulse response, and
(e) demodulating data in said received signal with said set of channel-tap locations and said set of weight coefficients.
16. The method of claim 15 , wherein said heuristic search comprises:
(a) pre-selecting a first set of channel-tap locations based on said composite channel impulse response, and
(b) selecting a second set of channel-tap locations in said search region by a heuristic search scheme based on said first set of channel-tap locations.
17. The method of claim 16 , wherein pre-selecting said first set of channel-tap locations comprises choosing a number of strongest channel taps according to said composite channel impulse response, the distances among which are equal to or larger than a predetermined minimum distance.
18. The method of claim 16 , wherein said heuristic search scheme comprises choosing a number of channel taps, where the distance of a thus-chosen channel tap to another thus-chosen channel tap or to a pre-selected channel tap equals to the distance between a pair of pre-selected channel taps.
19. The method of claim 16 , wherein said heuristic search scheme comprises choosing a number of channel taps, where the distance between a thus-chosen channel tap and a pre-selected channel tap equals to the distance between a pair of pre-selected channel taps.
20. The method of claim 15 , wherein recovering data in said received signal sent in said communications media is performed at 2× oversampling.
21. A method of recovering data in a received signal sent in a communications media, comprising:
(a) estimating at least one composite channel impulse response from said received signal,
(b) estimating a set of noise covariances based on said composite channel impulse responses,
(c) assigning a set of filter-tap locations by a sequential search, with each said filter tap depending on said composite channel impulse response,
(d) computing a set of filter coefficients for said set of filter-tap locations, and
(e) filtering said received signal with said set of filter-tap locations and said set of filter coefficients.
22. The method of claim 21 , wherein recovering data in said received signal sent in said communications media is performed at a fractional oversampling rate.