Preamble design for television white space transmissions

Abstract

A method for generating a Physical Layer Convergence Protocol Packet Data Unit (PPDU) having a preamble and a payload for television white space transmission (TVWS) is provided. The symbols of the PPDU each include 128 total (orthogonal frequency-division multiplexing) OFDM tones or 256 total OFDM tones. The preamble includes a signal (SIG) field symbol having 108 OFDM data tones if the symbols of the PPDU include 128 total OFDM tones or having 234 OFDM data tones if the symbols of the PPDU include 256 total OFDM tones. The SIG field symbol indicates at least one of an amount of data in the payload or a length of time that the PPDU will occupy the television broadcast frequency spectrum. The PPDU is generated by down-clocking an 802.11ac signal by a factor so that the bandwidth of the PPDU decreases down to one appropriate for use in a TVWS channel.

Description

[0001] priority claim [0002] This patent application claims priority to US Provisional Application No. 61 / 488,092, filed May 19, 2011, which is hereby expressly incorporated by reference. technical field [0003] In general, various features relate to wireless communication devices and systems, and in particular, various features relate to methods and apparatus for generating preambles for TV white space transmissions. Background technique [0004] Access terminals such as laptop computers, personal digital assistant devices, mobile or cellular telephones, personal media players, or other devices with a processor that communicate by wireless signals are becoming increasingly popular and more frequently use. Many access terminals are used to communicate over wireless local area networks (WLANs) and several emerging wireless communication standards have been and are being developed to facilitate these WLANs. [0005] The Institute of Electronics and Electrical Engineers (I...

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Problems solved by technology

[0009] In some cases, generating a 5MHz TVWS signal by down-converting a 20MHz 802.11ac signal may result in too short a cyclic prefix duration, which makes the resulting signal susceptible to high delay spread

In contrast, down-converting a larger bandwidth (e.g., 40MHz, 80MHz, etc.) 802.11ac signal to generate a 5MHz TVWS signal can result in a preamble that lasts too long

That is, the preamble duration occupies an unacceptably large fraction of the total time allocated to the WLAN device for a given TVWS transmission (i.e., the preamble overhead for the physical layer Convergence Protocol Packet Data Unit (PPDU) may be too large )

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