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A Cost-Effective Preamble-Assisted Engine With Skew Calibrator for Frequency-Dependent I/Q Imbalance in 4x4 MIMO-OFDM Modem

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3 Author(s)
Wei-Chi Lai ; Dept. of Comput. Sci., Nat. Chiao Tung Univ., Hsinchu, Taiwan ; Yuan-Te Liao ; Terng-Yin Hsu

Variations in I/Q gains, phases, and filters of the RF frontend, namely frequency-dependent I/Q imbalance (FDI), are an important factor in OFDM-based wireless access. To enable the proper function of a 4 × 4 MIMO-OFDM receiver this work proposes a low-complexity preamble-assisted solution using only one complex divider and one complex multiplier to handle significant FDI distortions. An all-digital multiphase and multi-rate clock generator (MPRCG) was built to support fast dynamic frequency scaling for FDI estimation and compensation and for efficient implementation. Based on the proposed MPRCG, a skew calibration was also realized to tune I/Q timing coherently via multiphase A/D clocking. Performance evaluation showed that the proposed approach incurs an SNR loss of 1.5 dB to maintain a packet-error rate of less than 10% under a 1 dB gain error, 15 phase error and worse filter mismatch. Thus, this solution not only provides adequate performance, but also makes FDI estimation and compensation more cost-effective.

Published in:

Circuits and Systems I: Regular Papers, IEEE Transactions on  (Volume:60 ,  Issue: 8 )