Novel carrier frequency offset mitigation in IEEE802.11a/g/n systems

The newly balloted IEEE 802.11n standard uses both orthogonal frequency division modulation (OFDM) and multi-input multi-output (MIMO) techniques. A requirement of the new standard is backward compatibility to legacy 802.11a/g systems through the use of legacy preambles. Taking advantage of pilots in the legacy signal field (L-SIG), and in the newly added high throughput (HT) signal fields (HT-SIG), a novel carrier frequency offset (CFO) mitigation scheme is developed. With the maximum CFO (40 ppm) requirement specified by the standard, the proposed scheme provides more than 3 dB gains than conventional methods to yield a less than 1 kHz residue CFO. Simulation results also show that the performance degradation due to residual CFO is within 1.5 dB for various TGn channels, modulation and coding schemes, transmit antenna excitation schemes and OFDM MIMO transceiver configurations.