Mmwave MIMO Channel with One-Bit ADCs
Millimeter wave (mmWave) is a technology that can provide high bandwidth communication links in cellular systems. As mmWave uses larger bandwidths, the corresponding sampling rate of the analog-to-digital converter (ADC) scales up. Unfortunately, high speed, high resolution (e.g., 6-12 bits) ADCs are costly and power-hungry for portable devices. A possible solution is to use special ADC structures like a time interleaved ADC (TI-ADC) architecture where a number of low-speed, high-precision ADCs operate in parallel. The main challenge of the TI-ADC is the mismatch among the sub-ADCs in gain, timing and voltage offset which can cause error floors in receiver performance. An alternative solution is to live with ultra low resolution ADCs (1-3 bits), which reduces power consumption and cost.
To break through the ADC bottleneck, WNCG graduate student Jianhua Mo and WNCG Professor Robert Heath investigated the capacity of multiple-input multiple-output (MIMO) system in which a one-bit ADC is used for each inphase and quadrature baseband received signal. The main advantage of this architecture is the ADCs can be implemented with very low power consumption. The architecture also simplifies the overall complexity of the circuit, for example, automatic gain control may not be required. They have studied the channel capacity of the MIMO system with one-bit ADCs with channel state information at the transmitter establish exact results in some cases and high SNR bounds in others. They also showed that multipath is helpful in improving the channel capacity in the context of mmWave networks.