A 28.8 Mb/s 4 x 4 MIMO 3G CDMA receiver for frequency selective channels

This paper describes a silicon receiver for a multiple-input multiple-output (MIMO) wireless channel that supports up to 28.8 Mb/s using a 4 x 4 QPSK configuration over a 5-MHz frequency selective channel. The architecture has two key components: a space-time equalizer that mitigates both spatial and temporal effects of the channel, and a maximum likelihood detector with approximate a posterior probability (ML-APP) soft estimates of the transmit vectors over the MIMO configuration. The space-time equalizer uses an adaptive tap training process that includes a pilot correlator to reduce adaptation noise. The device is 685 k effective logic gates (11.6 mm(2)) in 0.18-mum 6LM CMOS.