Research And Application Of IQ Imbalances Estimation On IEEE802.11a/b/n/ac Protocol RF Conformance Test

IQ-imbalance refers to mismatched magnitude and phase between the in-phase and quadrature branch of transceiver. IQ imbalances will destroy orthogonality between sub-carriers of OFDM system, resulting in imaging interference and degrading BER performance of the system. Therefore, how to improve the accuracy of IQ imbalance estimation and how to reduce and compensate the image disturbing caused by IQ imbalance effectively have become two very important research topics. This paper focuses on IQ imbalance estimation and compensation algorithms on the transmitter side, the main contents of this paper are organized as follows:Firstly, we introduce the basic principle and characteristics of IEEE 802.11b/ac, and study the standard of IEEE 802.11b/ac physical layer(PHY), including the frame format of the preamble and modulation scheme. On this basis, we analysis the advantages of IEEE 802.11ac.Secondly, study in depth the previous IQ imbalance estimation algorithm. A wide linear model of IQ imbalance on the transmitter side is then given. Based on this modle, we introduce several typical IQ imbalance estimation algorithms. One algorithm is based on specific training sequence and the other is a blind one. These lay a sound theoretical foundation for the following algorithm research.Thirdly, the problem of frequency-independent IQ imbalances caused by DSSS transmitter is investigated. And a time-domain IQ imbalance compensation model of the transmitter is proposed based on previous studies. To start with suppressing the image component of the compensation model obtained, we get a joint estimation method of IQ imbalance and channel based on time-domain. The time-domain blind compensation algorithm compensate IQ imbalance generated by the transmitter at the receiver side. Compared with the traditional estimation scheme, the time-domain blind estimation method proposed here owns higher efficiency.Thirdly, the problem of frequency-independent IQ imbalances caused by OFDM transmitter is investigated. And two frequency domain IQ imbalance estimation algorithms are presented. One is the frequency domain least squares estimation algorithm based on single-tap channel, the other is a joint estimation method of IQ imbalance and frequency-domain multi-tap channel. The former algorithm requires a relatively high quality of channel environment, the algorithm uses two long training sequences to estimate IQ imbalance and achieves a better estimation performance. While the latter one allows the presence of frequency selective channel, the algorithm uses two adjacent sequences to estimate IQ imbalance parameters.Last but not least, we conduct simulation for the three main algorithms presented in the article to verify the algorithms. Comparation results show that the algorithms confirgued in the article own a higher accuracy in both amplitude imbalance and phase imbalance estimation than the measured value obtained from Aeroflex analyzer to a certain extent. In addition, we give the the constellation of a particular sequence before and after IQ compensation to verify the efficient of our IQ compensation algorithm. And then we make a summary of this thesis and make a future research prospect.