IQ Imbalance Compensation Scheme in the Presence of Frequency Offset and Dynamic DC Offset for a Direct Conversion Receiver

Abstract

A direct conversion architecture reduces the cost and power consumption of a receiver. However, a direct conversion receiver may suffer from direct current (DC) offset, frequency offset, and IQ imbalance. This paper presents an IQ imbalance estimation scheme for orthogonal frequency division multiplexing (OFDM) direct conversion receivers. The proposed IQ imbalance estimation scheme operates in the presence of dynamic DC offset and frequency offset. The proposed scheme calculates IQ imbalance from a simple equation. It employs the knowledge of the preamble symbols of the IEEE 802.11 a/g standards, while it does not require the impulse response of the channel. Numerical results through computer simulation show that the bit error rate (BER) performance for the proposed IQ imbalance estimation scheme has a degradation of about 4dB with a large DC offset, frequency offset, and 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.…”

A Closed-Loop Reciprocity Calibration Method for Massive MIMO in Terrestrial Broadcasting Systems

“…However, because of the hardware impairments of the transceivers, the DL and UL channel are not always reciprocal [14], [15], especially when the BS uses a direct conversion transceiver (DCT) and cheap components with aim of reducing hardware costs in massive MIMO systems. Despite the advantages of low-cost, simplicity and flexibility of DCT, some practical problems arise when implementing a direct-conversion transmitter because of the non-linearity of the radio frequency (RF) component, such as in-phase (I) and quadrature (Q) mismatches, clock jitter, power amplifier (PA) distortion and inter-modulation [16]- [22]. The reciprocity of the channel is broken severely by the impairments which makes reciprocity calibration one of the main challenges of massive MIMO systems' implementation.…”

Joint estimation of CFO and receiver I/Q imbalance using virtual subcarriers for OFDM systems

“…In [9], assuming sending at least 3 repeated OFDM blocks, a closed-form solution for CFO and I/Q estimation was derived. In [10], the authors studied the I/Q and CFO estimation by using a differential filter to suppress the direct current offset in direct conversion receivers. In [11], a subspace method was proposed to solve the joint estimation problem.…”