1. A shopping cart liner for a shopping cart seat having a handle, a back support and two sides that extend between the handle and the back support, the shopping cart liner comprising:
a body configured to nest in the shopping cart seat, the body having a front with a front edge, a back with a back edge, and two sides which each have a side edge, the body defining one or more openings positioned at the front to enable the feet of a child seated in the shopping cart seat to protrude through the body beneath the handle, wherein, when nested in the shopping cart seat, the front edge is draped over the handle, the back edge is draped over the back support, and the two side edges are draped over the sides of the shopping cart seat;
a track comprising a flexible rod-like member, wherein the track is coupled to a portion of the shopping cart liner between the front edge and the one or more openings so that the child faces the track when the shopping cart liner is in use in the shopping cart seat, wherein the track projects away from the liner, and wherein the track is coupled to the liner such that the track is aligned with an elongate axis of the handle when the body is nested in the shopping cart seat; and
at least one clip slidingly engaged with the track, wherein the clip is slidable along the track so as to be moveable along the handle in the direction of the elongate axis.
2. The shopping cart liner of claim 1, wherein the body is padded.
3. The shopping cart liner of claim 1, wherein the clip includes a central opening.
4. The shopping cart liner of claim 1, further comprising a seat belt for securing the child to the shopping cart liner.
5. The shopping cart liner of claim 1, wherein the track comprises a continuous outer surface and is embedded by wrapping it in a fabric sleeve sewn into the shopping cart liner.
6. The shopping cart liner of claim 1, in combination with a pillow disposed within the shopping cart liner to support the child when the shopping cart liner and pillow are in use, wherein the pillow is generally arc shaped, having two curved arms extending from a midsection, to define an open well to receive the child.
7. The shopping cart liner of claim 1, further comprising a pocket in an outside surface of the shopping cart liner.
8. The shopping cart liner of claim 1, in combination with an item attached to the shopping cart liner via the clip.
9. The combination of claim 10, wherein the item comprises an item selected from the group consisting of a toy, a doll, a ball, a mirror, a block, a pyramid, a teething ring, a toy shaped like an animal or insect, a toy shaped like a plant or flower, an item that generates sound, an item that generates vibration, and an item that generates light.
10. The shopping cart liner of claim 3, in combination with an item to be attached to the shopping cart liner, the item comprising a main body larger than the opening in the clip, and the item including a compressible member connected to the main body, wherein the compressible member is larger than the opening when the compressible member is in an uncompressed state, and the compressible member is configured to be compressible to a size smaller than the opening so that the compressible member can be passed through the opening to place the compressible member and the main body on opposite sides of the opening.
11. The shopping cart liner of claim 10, wherein the main body comprises a book that is coupled to the compressible member by a tether.
12. The shopping cart liner of claim 1, wherein the track comprises a welt having at least a portion with a substantially circular cross section, wherein the welt is made of foam, rubber, or plastic and includes an integrally formed flange.
13. The shopping cart liner of claim 1, in combination with a tote bag.
14. A liner for a seat having a front rail, a back support and two sides that extend between the front rail and the back support, the liner comprising:
a body configured to nest in the seat, the body having a front with a front edge, a back with a back edge, and two sides that each have a side edge, the body defining one or more openings positioned at the front to enable the feet of a child seated in the seat to protrude through the body beneath the front rail, wherein, when nested in the seat, the front edge is draped over the front rail, the back edge is draped over the back support, and the two side edges are draped over the sides of the seat;
a track comprising a flexible rod-like member, wherein the track is coupled to a portion of the seat liner between the front edge and the one or more openings so that the child faces the track when the seat liner is in use in the seat, wherein the track projects away from the liner, and wherein the track is coupled to the liner such that the track is aligned with an elongate axis of the front rail when the body is nested in the seat; and
at least one clip slidingly engaged with the track, wherein the clip is slidable along the track so as to be moveable along the front rail in the direction of the elongate axis.
15. The liner for a seat of claim 14, wherein the seat liner is configured to nest in a seat portion of a high chair or a shopping cart.
16. The liner for a seat of claim 14, wherein the clip defines an opening for attaching an item to the seat liner.
17. The liner for a seat of claim 14, wherein the track comprises a continuous outer surface and is embedded by wrapping it in a fabric sleeve sewn into the shopping cart liner.
18. The liner for a seat of claim 14, in combination with an item to be attached to the liner, the item comprising a main body larger than an opening in the clip, and the item including a compressible member connected to the main body, wherein the compressible member is larger than the opening when the compressible member is in an uncompressed state, and the compressible member is configured to be compressible to a size smaller than the opening so that the compressible member can be passed through the opening to place the compressible member and the main body on opposite sides of the opening; and
wherein the main body comprises a book that is coupled to the compressible member by a tether.
19. A method of using a seat liner, the method comprising:
providing a seat liner comprising a body configured to nest in the seat, the body having a front with a front edge, a back with a back edge, and two sides that each have a side edge, the body defining one or more openings positioned at the front to enable the feet of a child seated in the seat to protrude through the body beneath the front rail, and a track comprising a flexible rod-like member, wherein the track is coupled to a portion of the seat liner between the front edge and the one or more openings so that the child faces the track when the seat liner is in use in the seat, wherein the track projects away from the liner, and wherein the track is coupled to the liner such that the track is aligned with an elongate axis of the front rail when the body is nested in the seat;
nesting the seat liner in a seat portion of a seat, wherein, when nested in the seat, the front edge is draped over a front rail of the seat, the back edge is draped over a back support of the seat, and the two side edges are draped over sides of the seat that extend between the front rail and the back support; and
seating the child in the seat liner so that the child faces the track; and
sliding the clip along the front rail in the direction of the elongate axis.
20. The method of claim 19, further comprising attaching an item to the clip via an opening in the clip.
21. The method of claim 20, further comprising adjusting the position of the item by sliding the clip along the track.
22. The method of claim 19, wherein the liner further includes a seat belt, the method further comprising securing the seat belt around the child.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An apparatus for pre-equalizing an optical signal at a transmitter, comprising:
a digital signal processor (DSP), for determining a target pre-equalized signal waveform associated with an expected distortion of the optical signal by a fiber link, wherein the DSP determines the target pre-equalized signal waveform by:
dividing the fiber link into N segments, wherein N is an integer greater than one, wherein the N-th segment is associated with a receiver and the first segment is associated with a transmitter; and
iteratively computing a plurality of pre-equalized signal waveforms for the respective plurality of segments;
wherein the pre-equalized signal waveforms are computed beginning with the N-th segment and ending with the first segment in a direction from the receiver toward the transmitter;
wherein, for the N-th segment, the pre-equalized signal waveform associated with the N-th segment is computed using as input a desired waveform to be received by the receiver;
wherein, for each of the remaining N-1 segments, the associated pre-equalized signal waveform computed for a current segment is computed using as input the pre-equalized signal waveform computed for the previous segment;
wherein the target pre-equalized signal waveform determined by the DSP is the pre-equalized signal waveform associated with the first segment;
digital to analog converters, for converting in-phase and quadrature-phase components of the target pre-equalized signal waveform into analog waveforms; and
an electro-optical modulator, for encoding the analog waveforms onto an optical carrier to form a pre-equalized optical signal;
wherein the DSP adaptively determines the target pre-equalized signal waveform according to receiver signal quality information received via a communication link.
2. The apparatus of claim 1, wherein the DSP further comprises a look-up table for storing information defining the target pre-equalized signal waveform determined by the DSP.
3. The apparatus of claim 2, wherein DSP operation is adapted by updating the lookup table in response to the receiver signal quality information.
4. The apparatus of claim 3, wherein the DSP uses values of a set of system parameters to determine each of the plurality of pre-equalized signal waveforms of the respective segments, wherein the DSP operates to iteratively adapt values of at least a portion of the set of system parameters to adapt the target pre-equalized signal waveform.
5. The apparatus of claim 1, wherein the DSP uses values of a set of system parameters to determine each of the plurality of pre-equalized signal waveforms of the respective segments, wherein the DSP selectively assigns nominal values for unknown system parameters or system parameters received from a network controller.
6. The apparatus of claim 1, wherein the DSP uses values of a set of system parameters to determine each of the plurality of pre-equalized signal waveforms of the respective segments, wherein the set of system parameters comprises a total chromatic dispersion (CD) of the fiber link, Dtotal, a mean total self-phase-modulation (SPM) induced nonlinear phase shift, \u03a6NL, a number of fiber segments, N, and a signal bit rate, BR.
7. The apparatus of claim 6, wherein the number of fiber segments N is approximately 10.
8. The apparatus of claim 6, wherein the mean total SPM induced nonlinear phase shift, \u03a6NL, is limited to within a range of approximately 0, 3.
9. The apparatus of claim 6, wherein the DSP determines the pre-equalized signal waveform at the beginning of the N-th segment, S(t,N), as
SD(N)= F{FS(t,L)\xb7e\u2212i\xb7f(DtotalN)}, S(t,N)=SD(N)\xb7e\u2212ja\xb7\u03a6NL\xb7|SD(N)|2N,
wherein S(t,L) represents the desired waveform to be received by the receiver, F(x) and F(y) are, respectively, the Fourier and inverse-Fourier transformation of signal x and y, j is the imaginary unit, f(D) represents the modification of the optical phase of the signal due to the dispersive effect resulting from a dispersion with a value of D, and \u201ca\u201d is a normalization constant.
10. The apparatus of claim 6, wherein, for each of the remaining N-1 segments, the DSP determines the pre-equalized signal waveform at the beginning of the i-th segment, S(t,i), as
SD(i)= F{FS(t,i+1)\xb7e\u2212i\xb7f(DtotalN)}, S(t,i)=SD(i)\xb7e\u2212ja\xb7\u03a6NL|SD(i)2N,
wherein S(t,1) represents the target pre-equalized signal waveform at the transmitter for simultaneous compensation of SPM and CD.
11. The apparatus of claim 1, wherein the electro-optical modulator comprises one of a dual-drive Mach-Zehnder modulator and a nested Mach-Zehnder modulator.
12. A method for determining a target pre-equalized signal waveform for use in pre-equalizing an optical signal at a transmitter to compensate for the distortion of the optical signal traversing a fiber link toward a receiver, comprising:
dividing the fiber link into N segments, wherein N is an integer greater than 1, wherein the N-th segment is associated with the receiver and the first segment is associated with the transmitter;
iteratively computing a plurality of pre-equalized signal waveforms for the respective plurality of segments;
wherein the pre-equalized signal waveforms are computed beginning with the N-th segment and ending with the first segment in a direction from the receiver toward the transmitter;
wherein, for the N-th segment, the associated pre-equalized signal waveform is computed using as input the desired waveform to be received by the receiver;
wherein, for each of the remaining N-1 segments, the associated pre-equalized signal waveform computed for a current segment is computed using as input the pre-equalized signal waveform computed for the previous segment;
wherein the target pre-equalized signal waveform determined by a digital signal processor (DSP) is the pre-equalized signal waveform associated with the first segment; and
populating a lookup table with the target pre-equalized signal waveform.
13. The method of claim 12, wherein each of the plurality of pre-equalized signal waveforms of the respective segments is determined using values of a set of system parameters, further comprising assigning initial values for unknown ones of the system parameters.
14. The method of claim 12, wherein each of the plurality of pre-equalized signal waveforms of the respective segments is determined using values of a set of system parameters, further comprising assigning at least one value of at least one of the system parameters based on information from a network controller.
15. The method of claim 12, wherein each of the plurality of pre-equalized signal waveforms of the respective segments is determined using values of a set of system parameters, wherein the set of system parameters comprises a total chromatic dispersion (CD) of the fiber link, Dtotal, a mean total self phase modulation (SPM) induced nonlinear phase shift, \u03a6NL, a number of fiber segments, N, and a signal bit rate, BR.
16. The method of claim 15, wherein the number of fiber segments N is about 10.
17. The method of claim 15, wherein the mean total SPM induced nonlinear phase shift, \u03a6NL, is limited to within a range of approximately 0, 3.
18. The method of claim 12, wherein the pre-equalized signal waveform at the beginning of the N-th segment, S(t,N), is computed as:
SD(N)= F{FS(t,L)\xb7e\u2212i\xb7f(DtotalN)}, S(t,N)=SD(N)\xb7e\u2212ja\xb7\u03a6NL\xb7|SD(N)|2N,
wherein S(t,L) represents the desired waveform to be received by the receiver, F(x) and F(y) are, respectively, the Fourier and inverse-Fourier transformation of signal x and y, j is the imaginary unit, f(D) represents the modification of the optical phase of the signal due to the dispersive effect resulting from a dispersion with a value of D, and \u201ca\u201d is a normalization constant.
19. The method of claim 12, wherein, for each of the remaining N-1 segments, the pre-equalized signal waveform computed at the beginning of the i-th segment, S(t,i), is computed as:
SD(i)= F{FS(t,i+1)\xb7e\u2212i\xb7f(DtotalN)}, S(t,i)=SD(i)\xb7e\u2212ja\xb7\u03a6NL\xb7|SD(i)|2N,
wherein S(t,1) represents the target pre-equalized signal waveform at the transmitter for simultaneous compensation of self phase modulation and chromatic dispersion.
20. The method of claim 12, wherein each of the plurality of pre-equalized signal waveforms of the respective segments is determined using values of a set of system parameters, and further comprising:
adapting the target pre-equalized signal waveform using updated values of at least a portion of the system parameters to obtain thereby improved received signal quality, wherein the received signal quality is measured by the bit error rate (BER).
21. The method of claim 12, wherein each of the plurality of pre-equalized signal waveforms of the respective segments is determined using values of a set of system parameters, and further comprising:
adapting the target pre-equalized signal waveform using updated values of at least a portion of the system parameters to obtain thereby improved received signal quality, wherein the improved received signal quality is measured using an eye diagram.
22. The method of claim 12, further comprising establishing the lookup table using a training bit sequence.
23. The method of claim 22, wherein the training bit sequence is a pseudo random bit sequence (PRBS).
24. The method of claim 12, wherein each of the plurality of pre-equalized signal waveforms of each of the segments is determined using values of a set of system parameters, and further comprising:
updating the set of system parameters, to obtain thereby improved received signal quality, with a fixed value of a mean total self phase modulation (SPM) induced nonlinear phase shift, \u03a6NL.
25. The method of claim 24, wherein the \u03a6NL is fixed at about 1 radian.
26. The method of claim 12, wherein the step of iteratively computing changes a value of a mean total self phase modulation induced nonlinear phase shift, \u03a6NL, within the range of approximately 0, 3 by a step size of about 0.3 radians.