System and method for data distribution in VHF/UHF bands

• US 8,274,885 B2
• Filed: 10/03/2008
• Issued: 09/25/2012
• Est. Priority Date: 10/03/2008
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Quarterhill Inc. (f/k/a Wi-LAN Inc.)
• Inventors: Wu, Shiquan, Yee, Jung
• Primary Examiner(s): Ferris, Derrick
• Assistant Examiner(s): Taha, Shaq
• Application Number:
  US12/245,209
• Publication Number:
  US 20100085921A1
• Time in Patent Office: 1,453 Days
• Field of Search: 370/230
• US Class Current: 370/230
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 27/26265 Arrangements for sidelobes suppression specially adapted to multicarrier systems, e.g. spectral precoding
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

Whitespace devices can use unused television frequencies for transmission and reception of WiFi OFDM signals. Three contiguous bands, such as former channels 2, 3, and 4, may be bonded together to define a whitespace band. In order to fit a WiFi OFDM signal into this whitespace band, a whitespace device compresses the bandwidth of each WiFi OFDM signal using a specific spectrum mask. Very low transmission power is needed for the modified WiFi OFDM signals, eliminating the need for high power amplifiers and most of the WiFi OFDM designs such as PHY and MAC can be reused with minor modifications.

Claims

1. A method of transmitting user data within a very-high frequency/ultra-high frequency (VHF/UHF) band, over a local area network (LAN), comprising:

identifying in the VHF/UHF band a whitespace band B_WS available in an area of operation of the LAN, the whitespace band representing the band of three consecutive unused TV channels;

generating a baseband WiFi orthogonal frequency division multiplexing (OFDM) signal from user data;

reconfiguring the baseband WiFi OFDM signal into a modified WiFi OFDM signal using a transmit spectrum mask adapted to confine the bandwidth of the modified WiFi OFDM signal into the whitespace band, and adapted to attenuate the modified WiFi OFDM signal at the edges of the whitespace band for maintaining a performance of any neighboring TV channel unchanged; and

transmitting the modified WiFi OFDM signal over the whitespace band.

2. The method of claim 1, wherein the whitespace band extends over a band B_WS around a central frequency Fc in the portion of the spectrum allocated to digital TV between 54 MHz and 698 MHz.

3. The method of claim 1, wherein the whitespace band extends over an integer number of unused consecutive TV channels.

4. The method of claim 1, wherein B_WS is 18 MHz.

5. The method of claim 1, wherein a band effectively occupied by the modified WiFi OFDM signal in a band reserved for digital TV channels 2-4 is 16.25 MHz.

6. The method of claim 1, wherein a band effectively occupied by the modified WiFi OFDM signal in the band reserved for any three consecutive TV channels from digital TV channels 5-51 is 13 MHz.

7. The method of claim 1, wherein the modified WiFi OFDM signal is modulated over 48 data carriers and uses 4 pilot carriers in the whitespace band.

8. The method of claim 4, wherein the modified transmit spectrum mask has a plateau of 18 MHz around a central frequency Fc to enable a maximum amplitude for the modified WiFi OFDM signal and attenuates the modified WiFi OFDM signal to −

99 dB over 6 MHz from edges of the plateau.

9. The method of claim 8, wherein attenuation presented by the modified transmit spectrum mask includes a sharp attenuation of −

36 dB at the edges of the plateau over 500 kHz.

10. The method of claim 4, wherein the modified transmit spectrum mask is configured such that an effective spectrum occupied by the modified WiFi OFDM signal is 13 MHz.

11. The method of claim 4, wherein the reconfiguring and transmitting steps are performed such that a symbol duration for the modified WiFi OFDM signal is 5 μ

s, including 4 μ

s as a useful signal duration and 1 μ

s as a guard interval duration.

12. The method of claim 4, wherein a subcarrier spacing in the transmitting step for the modified WiFi OFDM signal is 250 KHz.

13. The method of claim 4, wherein a data rate in the transmitting step for the modified WiFi OFDM signal is 43.2 Mbps.

14. The method of claim 6, wherein the modified transmit spectrum mask has a plateau of 18 MHz between 54 MHz and 72 MHz around a central frequency of 63 MHz to enable a maximum amplitude for the modified WiFi OFDM signal, and the modified WiFi OFDM signal is attenuated to −

99 dB over 6 MHz from edges of the plateau.

15. The method of claim 14, wherein the attenuation presented by the modified transmit spectrum mask includes a sharp attenuation of −

36 dB at the edges of the plateau over 500 kHz.

16. The method of claim 6, wherein an effective spectrum of the modified transmit spectrum mask occupied by the modified WiFi OFDM signal is 16.25 MHz.

17. The method of claim 6, wherein a symbol duration of the modified transmit spectrum mask for the modified WiFi OFDM signal is 4 μ

s, including 3.2 μ

s as a useful signal duration and 0.8 μ

s as a guard interval duration.

18. The method of claim 6, wherein a subcarrier spacing of the modified transmit spectrum mask for the modified WiFi OFDM signal is 312.5 KHz.

19. The method of claim 6, wherein a data rate for the modified WiFi OFDM signal is 54 Mbps.

20. A transmitter that broadcasts user data over a local area network (LAN) within a whitespace band B_WS in the very-high frequency/ultra-high frequency (VHF/UHF) spectrum, where the band B_WS is not currently used in an area of operation of the LAN for transmission of TV signals, comprising:

a baseband generator to generate a baseband WiFi orthogonal frequency division multiplexing (OFDM) signal from the user data;

a frequency converter to reconfigure the baseband WiFi OFDM signal into a modified WiFi OFDM signal using a transmit spectrum mask adapted to confine the bandwidth of the modified WiFi OFDM signal into the whitespace band, and to attenuate the modified WiFi OFDM signal at the edges of the whitespace band for maintaining a performance of any neighboring TV channel unchanged, the whitespace band being the band of three consecutive unused TV channels; and

a transmitter to transmit the modified WiFi OFDM signal over the whitespace band.

21. The transmitter of claim 20, wherein the whitespace band extends over 18 MHz around a central frequency Fc in the portion of the spectrum allocated to digital TV between 54 MHz and 698 MHz.

22. The transmitter of claim 21, wherein a band effectively occupied by the modified WiFi OFDM signal in a band reserved for digital TV channels 2-4 is 16.25 MHz.

23. The transmitter of claim 20, wherein a band effectively occupied by the modified WiFi OFDM signal in the band reserved for any three consecutive TV channels from digital TV channels 5-51 is 13 MHz.

24. The transmitter of claim 20, wherein the modified WiFi OFDM signal is modulated over 48 data carriers and uses 4 pilot carriers in the whitespace band.

25. The transmitter of claim 21, wherein the modified transmit spectrum mask has a plateau of 18 MHz around a central frequency Fc to enable a maximum amplitude for the modified WiFi OFDM signal and attenuates the modified WiFi OFDM signal to −

99 dB over 6 MHz from edges of the plateau.

26. The transmitter of claim 25, wherein attenuation presented by the modified transmit spectrum mask includes a sharp attenuation of −

36 dB at the edges of the plateau over 500 kHz.

27. The transmitter of claim 21, wherein an effective spectrum of the modified transmit spectrum mask occupied by the modified WiFi OFDM signal is 13 MHz.

28. The transmitter of claim 21, wherein a symbol duration of the modified transmit spectrum mask for the modified WiFi OFDM signal is 5 μ

s, including 4 us as a useful signal duration and 1 μ

s as a guard interval duration.

29. The transmitter of claim 21, wherein the transmitter sets a subcarrier spacing of the modified transmit spectrum mask for the modified WiFi OFDM signal to be 250 KHz.

30. The transmitter of claim 21, wherein the transmitter sets a data rate for the modified WiFi OFDM signal to be 43.2 Mbps.

31. The transmitter of claim 22, wherein the modified transmit spectrum mask has a plateau of 18 MHz between 54 MHz and 72 MHz around a central frequency of 63 MHz to enable a maximum amplitude for the modified WiFi OFDM signal, and the modified WiFi OFDM signal is attenuated to −

99 dB over 6 MHz from edges of the plateau.

32. The transmitter of claim 31, wherein the attenuation presented by the modified transmit spectrum mask includes a sharp attenuation of −

36 dB at the edges of the plateau over 500 kHz.

33. The transmitter of claim 22, wherein an effective spectrum of the modified transmit spectrum mask occupied by the modified WiFi OFDM signal is 16.25 MHz.

34. The transmitter of claim 22, wherein a symbol duration of the modified transmit spectrum mask for the modified WiFi OFDM signal is 4 μ

s, including 3.2 μ

s as a useful signal duration and 0.8 μ

s as a guard interval duration.

35. The transmitter of claim 22, wherein the transmitter sets a subcarrier spacing for the modified WiFi OFDM signal to be 312.5 KHz.

36. The transmitter of claim 22, wherein the transmitter sets a data rate for the modified WiFi OFDM signal to be 54 Mbps.