Apparatus and method for detecting preambles according to IEEE 802.11A/B/G wireless LAN standards and its application to a 802.11 multimode receiver
The present invention relates to the field of wireless communication systems and in particular to an apparatus and a method for detecting preambles according to IEEE 802.11a/b/g wireless LAN standards and its application to an 802.11 multimode receiver. The proposed apparatus is capable of detecting 802.11a/b/g preambles by using two auxiliary low-resolution ADCs (down to 1 bit) coupled with a preamble detector. The purpose of this apparatus which is located within the RF section of the receiver upstream of the baseband section, is to offload or discharge the baseband functions by performing a signal discrimination and waking up the baseband functions only if the received signal is determined to embed either an 802.11a/g or 802.11b preamble. This results in significant power savings in a multimode 802.11 receiver since the baseband circuitry does not need to be woken up every time a “false” signal is received
1 . A 802.11a/b/g preamble detector, embedded in a 802.11 multimode receiver including a radio frequency section and a baseband section, and comprising:
a DC offset estimation and compensation block for performing a DC offset compensation on analog I/Q signals obtained from received and down converted radio signal, and for outputting analog DC offset compensated I/Q signals,
low-resolution analog to digital converters for converting the DC offset compensated analog I/Q signals to n-bit digital I/Q signal streams,
a preamble detector for detecting 802.11a/b/g preambles within the n-bit digital I/Q signal streams and for generating an output signal indicating the type of the detected preamble,
an RSSI block for measuring the in-band power of the analog DC offset compensated I/Q signals and for generating an output signal when the measured in-band power exceeds a preset threshold, and
an evaluation block comprising a state machine for generating a wakeup signal for the baseband section of the receiver when the measured in-band power exceeds a preset threshold and the preamble detector detects a 802.11a/b/g preamble.
2 . The 802.11a/b/g preamble detector according to claim 1 , characterized in that the low-resolution analog to digital converters are 1-bit ADCs.
3 . The 802.11a/b/g preamble detector according to claim 1 , characterized in that it is embedded in the radio frequency section of the receiver.
4 . The 802.11a/b/g preamble detector according to any claim 1 , characterized in that the preamble detector comprises of two sub-units, a first sub-unit for detecting 802.11a preambles and a second sub-unit for detecting 802.11b preambles.
5 . A method for detecting preambles according to 802.11a/b/g wireless standard in a 802.11 multimode receiver, comprising the steps of:
receiving and down converting a radio signal in a radio frequency section of the receiver for obtaining analog I/Q signals;
performing a DC offset compensation on the analog I/Q signals in a DC offset estimation and compensation block, for generating analog DC offset compensated I/Q signals;
applying a low-resolution analog to digital conversion to the DC offset compensated analog I/Q signals for generating n-bit digital I/Q signal streams, detecting 802.11a/b/g preambles within the n-bit digital I/Q signal streams in a preamble detector, and generating an output signal indicating the type of the detected preamble,
measuring the in-band power of the analog DC offset compensated I/Q signals in a RSSI block and generating an output signal when the measured in-band power exceeds a preset threshold, and
utilizing an evaluation block comprising a state machine for generating a wakeup signal for the baseband section of the receiver when the measured in-band power exceeds a preset threshold and the preamble detector detects a 802.11a/b/g preamble.
6 . The method according to claim 5 , characterized in that the steps of performing the DC offset compensation, the in-band power measurement and the preamble detection are performed at the same time in parallel.
7 . The method according claim 5 , characterized in that the DC offset compensated analog I/Q signals are converted into 1-bit digital I/Q signal streams.
8 . The 802.11a/b/g preamble detector according to claim 2 , characterized in that it is embedded in the radio frequency section of the receiver
9 . The 802.11a/b/g preamble detector according to claim 2 , characterized in that the preamble detector comprises of two sub-units, a first sub-unit for detecting 802.11a preambles and a second sub-unit for detecting 802.11b preambles.
10 . The 802.11a/b/g preamble detector according to claim 3 , characterized in that the preamble detector comprises of two sub-units, a first sub-unit for detecting 802.11a preambles and a second sub-unit for detecting 802.11b preambles.
11 . The method according claim 6 , characterized in that the DC offset compensated analog I/Q signals are converted into 1-bit digital I/Q signal streams.