Modified preamble structure for IEEE 802.11a extensions to allow for coexistence and interoperability between 802.11a devices and higher data rate, MIMO or otherwise extended devices
View Patent ↗A modified preamble is used by extended devices that operate at higher rates, MIMO or other extensions relative to strict 802.11a-compliant devices. The extended devices might use multiple antenna techniques (MIMO), where multiple data streams are multiplexed spatially and/or multi-channel techniques, where an extended transmitter transmits using more than one 802.11 a channel at a time. Such extensions to IEEE 802.11 a can exist in extended devices. The modified preamble is usable for signaling, to legacy devices as well as extended devices, to indicate capabilities and to cause legacy devices or extended devices to defer to other devices such that the common communication channel is not subject to unnecessary interference. The modified preamble is also usable for obtaining MIMO channel estimates and/or multi-channel estimates. The modified preamble preferably includes properties that facilitate detection of conventional and/or extended modes (“mode detection”) and provides some level of coexistence with legacy IEEE 802.11 a devices.
1. A method of transmitting signals using a plurality of transmit channels, the method comprising:
allocating data to be transmitted among the plurality of transmit channels, wherein at least one of the plurality of transmit channels transports a subset of said data that is not transmitted over another of said plurality of transmit channels; and
transmitting a modified preamble from each of the plurality of transmit channels, wherein the modified preamble is distinguishable at a receiver from a conventional 802.11a preamble and includes information in an out-of-band component unused in a conventional 802.11a preamble
wherein the plurality of transmit channels comprise a plurality of frequency channels; and,
wherein the out-of-band component comprises a frequency band at a junction of adjacent 20 MHz channels comprising a portion of each channel that is attenuated by conventional 802.11a communication devices.
2. In a communications system having a channel divided into a plurality of adjacent frequency bands separated by out-of-band frequency ranges, wherein data is transmitted within bands of the plurality of adjacent frequency bands, a method of increasing data capacity of the channel comprising:
for data to be transmitted from a transmitter, allocating a first portion of the data among the plurality of adjacent frequency bands and allocating a second portion of the data to at least one out-of-band frequency range when the first portion is allocated to adjacent frequency bands, wherein the at least one out-of-band frequency range includes an out-of-band frequency range between the adjacent frequency bands that is attenuated by legacy devices operating in the communication system;
transmitting the first portion of the data within the plurality of adjacent frequency bands; and
transmitting the second portion of the data within the at least one out-of-band frequency range.
3. The method of claim 2 , further comprising:
prior to transmitting at least the second portion of the data, transmitting one or more training symbols usable for a receiver to estimate transmission characteristics of the out-of-band frequency ranges; and
using received signals of the one or more training symbols to modify processing of a received signal corresponding to the second portion of the data to account for the transmission characteristics of the out-of-band frequency ranges.
4. A method of transmitting an extended mode packet intended for extended 802.11 receivers in a wireless medium, the method comprising:
transmitting a modified preamble, the modified preamble comprising data transmitted on subcarriers considered out-of-band subcarriers and unused for data transmission by conventional 802.11a receivers, the modified preamble comprising a plurality of fields decodable by a conventional 802.11a receiver such that a conventional 802.11a receiver that receives the extended mode packet can detect the extended mode packet or defer processing for a time corresponding to a remainder of a length of the extended mode packet; and
transmitting a remainder of the extended mode packet,
wherein said transmitting the modified preamble comprises transmitting the modified preamble over a 40 MHz channel comprising two adjacent 20 MHz channels, and
wherein the out-of-band subcarriers comprises subcarriers at adjoining edge portions of the adjacent 20 MHz channels that are attenuated by conventional 802.11a devices.