Frequency Offset Estimation Scheme in the Presence of Time-Varying DC Offset and IQ Imbalance for OFDM Direct Conversion Receivers

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

“…MUE and NBE are ML CFO estimation algorithms for OFDM systems with respectively no DCO and only static DCO. CP-DFE and CP-LSE are blind versions of DFE [28] and LSE [34,35], respectively. Up to our awareness, DFE and LSE are the only algorithms reported for CFO estimation under TV-DCO.…”

“…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.…”