OFDM-Lite Architecture for HomePlug

• US 20100272192A1
• Filed: 04/27/2010
• Published: 10/28/2010
• Est. Priority Date: 04/28/2009
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Kim, Il Han, Varadarajan, Badri, Dabak, Anand, Du, Shu
• Granted Patent: US 8,649,443 B2
• Time in Patent Office: Days
• US Class Current: 375/257
• CPC Class Codes: H04L 27/2613 Structure of the reference signals

Abstract

A device for communicating digital data over power lines includes a power line interface for transmitting data over at least one band of frequencies. An orthogonal frequency division multiplexing (OFDM) modulation unit generates OFDM symbols using a set of tones for the frequency band. A preamble generation unit generates preamble sequences for the frequency band by using the set of tones used by the OFDM modulation unit. The tones used by the preamble generation unit have a constant magnitude, and a set of phases obtained by quantizing to a small alphabet the phase of a set of tones obtained by taking an IFFT of a portion of a preamble used by a non-interoperable powerline access device. The device may transmit on two or more bands using a sampling frequency clock, wherein a lower band clock frequency is equal to or an integer divisor of a higher band clock frequency.

Claims

1. A device for communicating digital data over power lines, the device comprising:

a power line interface for transmitting data over one or more of a low band and a high band of frequencies;

a clock generation unit configured to generate a sampling frequency clock, wherein a lower band clock frequency is equal to or an integer divisor of a higher band clock frequency;

an orthogonal frequency division multiplexing (OFDM) modulation unit to generate OFDM symbols using a set of tones for the one or more bands;

a preamble generation unit to generate preamble sequences for the one or more bands using one or more of the sampling frequency clocks; and

a preamble detection unit to detect preamble sequences for the one or more bands using one or more of the sampling frequency clocks.

2. The device of claim 1, wherein the OFDM modulation unit is configured to form OFDM symbols using a data sampling frequency Fs/m, where m is an integer, and Fs is a data sampling frequency used by other devices coupled to the power lines.

3. The device of claim 1, wherein the set of tones used for the lower band is a subset of the set of tones used for the high band.

4. The device of claim 1, wherein the preamble sequence for the lower band occupies a subset of the set of tones occupied by the preamble sequence of the high band.

5. The device of claim 1, wherein the preamble sequence detection unit is configured to detect more preamble sequences than can be generated by the preamble sequence generation unit.

6. The device of claim 1, wherein the preamble detection unit is configured to detect a preamble in the high band and the OFDM generation unit can only generate OFDM symbols for the low band.

7. The device of claim 1, wherein the device further comprises a power control module that is configured to place the device in sleep mode;

and

wherein the power line interface is configured to receive a periodic beacon signal while the device is in sleep mode, such that when the beacon signal contains an indication of data available, the power control module is configured to awaken the device so that the device is operable to receive the data.

8. A device for communicating digital data over power lines, the device comprising:

a power line interface for transmitting data over at least one band of frequencies;

a clock generation unit configured to generate a sampling frequency clock for the at least one band;

an orthogonal frequency division multiplexing (OFDM) modulation unit to generate OFDM symbols using a set of tones for the at least one band; and

a preamble generation unit to generate preamble sequences for the at least one band using the sampling frequency clock, wherein the preamble generation unit generates a portion of the preamble by using the set of tones used by the OFDM modulation unit;

wherein the tones used by the preamble generation unit have a constant magnitude, and a set of phases obtained by quantizing to a small alphabet the phase of a set of tones obtained by taking an IFFT of a portion of a preamble used by a non-interoperable powerline access device.

9. The device of claim 8, wherein the non-interoperable powerline access technology is Homeplug C &

C, and the small alphabet of phases is (π

/4)*k radians, where k=0, 1, 2, 3, 4, 5, 6, 7.

10. The device of claim 8, further comprising:

a preamble detection unit to detect one or more preamble sequences for the at least one band; and

an orthogonal frequency division multiplexing (OFDM) demodulation unit to recover data from the OFDM symbols using a set of tones for the at least one band.

11. The device of claim 10, further comprising a backoff unit coupled to the preamble detection unit and to the power line interface, wherein the preamble detection unit is configured to detect a preamble sequence that is generated by a non-interoperable device, wherein the non-interoperable device cannot demodulate the OFDM symbols generated by the device;

and

wherein the backoff unit is configured to cause postponement of data transmission by the power line interface when the preamble detection unit detects a preamble from the non-interoperable device.

12. A method for communicating digital data over power lines, the method comprising:

generating a sampling frequency clock within a device coupled to the power line, wherein a lower band sampling frequency clock has a sampling frequency Fs equal to or an integer divisor of a higher band sampling frequency clock;

generating orthogonal frequency division multiplexing (OFDM) symbols within the device using a set of tones for one or more of a low band and a high band of frequencies;

generating preamble sequences for the one or more bands using the sampling frequency clock; and

detecting preamble sequences received from other devices coupled to the power line for the one or more bands using the sampling frequency clock.

13. The method of claim 12, wherein generating OFDM symbols is performed using a data sampling frequency Fs/m, where m is an integer, and a fast Fourier transform having length N, whereby interoperability is achieved with other high band devices coupled to the power line that form OFDM symbols using a data sampling frequency Fs and a fast Fourier transform having length N.

14. The method of claim 12, wherein the set of tones used for generating OFDM symbols for the lower band is a subset of the set of tones used for the high band.

15. The method of claim 12, wherein the preamble sequences for the lower band occupy a subset of the set of tones occupied by the preamble sequences of the high band.

16. The method of claim 12, further comprising receiving data OFDM symbols at a data bandwidth, wherein detecting a preamble from the high band device is performed on a bandwidth B(preamble-Rx) that is larger than the data bandwidth.

17. The method of claim 12, further comprising postponing data transmission by the device when a preamble from a non-interoperable device is detected, wherein generating the preamble sequence by the device for the low band forms a preamble that is similar to a preamble generated by the non-interoperable device, such that the preamble detection unit is operable to detect a preamble from another interoperable device and also from the non-interoperable device.

18. A method for communicating digital data over power lines, the method comprising:

generating a sampling frequency clock within a device coupled to the power line;

generating orthogonal frequency division multiplexing (OFDM) symbols within the device using a set of tones for at least one band of frequencies; and

generating preamble sequences for the at least one band using the sampling frequency clock and the set of tones;

wherein the tones used for preamble generation have a constant magnitude, and a set of phases obtained by quantizing to a small alphabet the phase of a set of tones obtained by taking an IFFT of a portion of a preamble used by a non-interoperable powerline access technology, whereby the preamble sequence is detectable by a non-interoperable device coupled to the powerline.

19. The method of claim 18, wherein generating a preamble for the at least one band is performed according to

S_Preamble—

_LB[n]=S<sub>SYNC—

LB</sub>[(n)mod 512] for 0≦

n≦

2·

512−

1.

20. The method of claim 19, wherein