ADJACENT CHANNEL INTERFERENCE MITIGATION DURING THE ACQUISITION PHASE IN OFDM COMMUNICATIONS
Methods and apparatuses for adjacent channel interference mitigation during the acquisition phase in OFDM communications use a Discrete Fourier Transform (DFT) to detect the energy of a received channel without adding latency. In particular embodiments, the communications are vehicular OFDM communications and the DFT is a sliding DFT of variable length. In a typical acquisition procedure, RF gain is set based on received total energy, which includes energies of the received and adjacent channels. A modified state machine waits until the energy of a received channel is detected, then the RF gain is adjusted to fulfill an enhanced adjacent channel rejection criterion requirement.
1 . A method for adjacent channel interference mitigation during the acquisition phase in OFDM communications, comprising the steps of:
a) setting an RF gain based on received total energy;
b) waiting until energy of a received channel is detected; and
c) adjusting the RF gain based on the detected energy of the received channel, thereby fulfilling an enhanced adjacent channel rejection criterion requirement in the OFDM communications.
2 . The method of claim 1 , wherein the step of waiting includes waiting while using a discrete Fourier transform (DFT) to detect the received channel energy.
3 . The method of claim 2 , wherein the DFT is a sliding DFT.
4 . The method of claim 2 , wherein the DFT is a dynamic DFT with variable length.
5 . The method of claim 2 , wherein the using a DFT includes calculating a subset of the DFT for the duration of a short preamble (SP).
6 . The method of claim 4 , wherein the subset is selected from the group consisting of a subset of 4 subcarriers and a subset of 2 subcarriers.
7 . The method of claim 1 , wherein the OFDM communications are vehicular OFDM communications.
8 . A method for adjacent channel interference mitigation during the acquisition phase in OFDM communications, comprising the steps of:
a) using a DFT to detect the energy of a received channel; and
b) adjusting an RF gain based on the detected energy of the received channel, thereby fulfilling an adjacent channel rejection criterion requirement in the OFDM communications.
9 . The method of claim 8 , wherein the DFT is a sliding DFT.
10 . The method of claim 8 , wherein the DFT is a dynamic DFT with variable length.
11 . The method of claim 8 , wherein the using a DFT includes calculating a subset of the DFT for the duration of a short preamble (SP).
12 . The method of claim 11 , wherein the subset is selected from the group consisting of a subset of 4 subcarriers and a subset of 2 subcarriers.
13 . The method of claim 8 , further comprising the step of performing a stability test which demands a substantially constant result representing stable energy, thereby separating the received channel transmission from out-of-band emission of an adjacent channel.
14 . An apparatus for adjacent channel interference mitigation during the acquisition phase in OFDM communications, comprising:
a) a receive signal strength indicator (RSSI) estimator for measuring total energy of input signals;
b) a Discrete Fourier Transform (DFT) for measuring energy of a received channel; and
c) a state machine used for processing the measured total energy and received channel energy to fulfill an enhanced adjacent channel rejection criterion requirement in the OFDM communications.
15 . The apparatus of claim 14 , wherein the DFT is a sliding DFT.
16 . The apparatus of claim 14 , wherein the DFT is a dynamic DFT with variable length
17 . The apparatus of claim 14 , wherein the OFDM communications are vehicular OFDM communications.
18 . The apparatus of claim 14 , wherein the DFT includes a DFT subset calculated during a short preamble period.
19 . The apparatus of claim 18 , wherein the DFT subset includes four subcarriers.
20 . The apparatus of claim 18 , wherein the DFT subset includes two subcarriers.