Performance of frequency offset estimation in the presence of IQ imbalance for OFDM direct conversion receivers

Abstract

In WLAN receivers, a direct conversion architecture has been implemented in recent years. Though this architecture reduces cost and power consumption, it may suffer from direct current (DC) offset and frequency offset. To reduce the effect of DC offset, a frequency offset estimation scheme with a differential filter for orthogonal frequency division multiplexing (OFDM) direct conversion receivers has been proposed. However, the receiver may also suffer from IQ imbalance, which deteriorates the performance of frequency offset estimation. In this paper, the performance analysis of the frequency offset estimation scheme with the differential filter in the presence of IQ imbalance is derived. The numerical results obtained through computer simulations show that the derived analysis provides close approximation to the performance of the frequency offset estimation scheme. It also clarifies the dependency of the mean square error on the waveform of the preamble symbols, which is caused by IQ imbalance.

Carrier frequency offset estimation for OFDM systems with time-varying DC Offset

“…τ is referred to as time constant, which is inverse to cut-off frequency of the HPF. In order to keep low degree of intersymbol interference, a HPF with low cut-off frequency is usually used [20,[28][29][30][31][32][33][34][35][36]. Thus, (2) can be approximated by a linear model …”

“…The linear model of TV-DCO in (4) was also widely adopted in literatures [28][29][30][31][32][33][34][35][36] as a valid approximation of TV-DCO at output of HPF. For notation simplicity, we replace '≈' with '=' and then rewrite (4) in matrix form as…”

“…In order to cover the high dynamic range of faded OFDM signals, low noise amplifier (LNA) with multiple gain modes [20][21][22][23][24][25][26][27] is usually employed by DCR in OFDM systems. During the gain mode switch stage shown in Figure 2, a sudden change of DCO level may occur [20,[28][29][30][31][32][33][34][35][36] and high frequency components of the sudden change may pass through the HPF succeeding LNA, which results in TV-DCO [28][29][30][31][32][33][34][35][36]. Only a few works were reported to address CFO estimation for OFDM systems with TV-DCO.…”

“…Yunus et al presented a least square estimation (LSE) algorithm in [34,35], which http://asp.eurasipjournals.com/content/2012/1/156 achieves better performance than DFE at costs of higher computation efforts. The DFE and LSE algorithms were respectively extended in [28,30] and [36] to address CFO estimation for OFDM systems with both TV-DCO and in-phase/quadrature (I/Q) imbalance.…”

A New Estimation Algorithm for CFO and I/Q Imbalance in Wideband Direct-Conversion Receivers

“…Both the CFO and I/Q imbalance can significantly deteriorate the system performance [2], [3]. It has also been shown [4] that in order to obtain an accurate CFO estimate, the presence of I/Q imbalance must be taken into account.…”