Research On Estimation And Compensation Method Of Non - Ideal Factors In OFDM System

With the fast development of science and technology, consumer electronic devices, such as smart phones, tablet PCs, high definition digital TVs and set-top boxes, have become necessaries in modern life. These devices require higher transmission rate of communication system. Because of its high transmission rate, Wireless Personal Area Network (WPAN) becomes a prospective application market. Ultra-wideband (UWB) technology has become the most promising scheme in WPAN market because of its advantages such as high transmission rate, low power consumption, low cost, flexible spectrum occupation and robustness to interference. The Federal Communication Commission formally approved in2002to allocate7.5GHz of spectrum for unlicensed use of UWB devices. Since then, UWB technology has grown faster and faster. Orthogonal Frequency Division Multiplexing (OFDM) is a kind of modulation with high spectrum efficiency, robustness to both channel fading and inter-symbol interference (ISI). So Multi-Band (MB) OFDM-based UWB has become the mainstream standard in the world.However, OFDM technology also has some disadvantages. One of those is that it is sensitive to analog front-end imperfections in the receiver side such as Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO) and I/Q mismatch. Both CFO and SFO can incur phase rotation and inter-carrier interference (ICI) to the expected signal in frequency domain, and I/Q mismatch causes mirror interference to sub-carriers. These interferences will degrade the performance of the decoder and increase the Packet Error Rate (PER). So it is very important to estimate these imperfections and compensate there adverse effects on the communication system.Previous studies focus on how to tackle one analog front-end imperfection at a time. However, these imperfections are simultaneous in practical OFDM systems and affect mutually, so it is more accurate to deal with these imperfections at the same time. In this paper, a joint estimation and compensation scheme is proposed to tackle these imperfections. First of all, three consecutive preamble sequences (PS) are employed to jointly estimate CFO and SFO, and then two channel estimation (CE) preambles are utilized to jointly estimate I/Q imbalance and channel fading, at last the frame payload is recovered using these estimated parameters.