Digital Compensation for Analog Front-Ends: A New Approach to Wireless Transceiver Design

4

Impact of the Non-Ideal Front-Ends on the System Performance

Because of the limited frequency bandwidth, on the one hand, and the limited battery autonomy of terminal stations, on the other hand, spectral and power efficiencies of future communication systems should be as high as possible. New air interfaces, often derived from OFDM, are considered to meet the new requirements. Though OFDM is robust against the interference caused by the multi-path propagation, it is sensitive to the system non-idealities that destroy the orthogonality between the sub-carriers.

The CFO and the SCO, caused by the local oscillators at the transmitter and receiver, and the IQ imbalance, caused by the use of analog quadrature generation, are especially destructive. Since CFO, SCO and IQ imbalance are constant over each block of symbols (compared, for example, to additive noise or phase noise), it is important to study their effect based on a well-established model to assess if they can be compensated. Sections 4.1 and 4.2 are devoted to the study of the impact of CFO, SCO and IQ imbalance on the OFDM and SC-FDE air interfaces. The CFO and SCO can be equivalently defined at the transmitter or at the receiver. We limit the analysis to the IQ imbalance generated at the receiver (both the transmit and the receive IQ imbalance have a similar effect, except that the transmit IQ imbalance is generated before the channel convolution, making the performance degradation smaller in that case – see the analysis ...