# A 4-Element MIMO Baseband Receiver with >35dB 80MHz Spatial Interference Cancellation

## TL;DR

This paper presents a novel 4-element MIMO baseband receiver that employs a discrete-time delay technique and Hadamard transform to achieve over 35dB interference cancellation across 80MHz bandwidth, significantly improving interference mitigation in wideband systems.

## Contribution

It introduces a scalable discrete-time delay method combined with a Hadamard transform for wideband interference cancellation in MIMO receivers, with practical implementation and measurement results.

## Key findings

- Achieves >35dB interference cancellation over 80MHz bandwidth.
- Demonstrates 592x improvement over prior interference cancellation methods.
- Implemented in 65nm CMOS with effective digital delay and Hadamard transform techniques.

## Abstract

Next-generation communication systems with wide bandwidths need to operate in interference-limited networks. A discrete-time delay (TD) technique in a baseband receiver array is proposed for canceling wide modulated bandwidth spatial interference and reducing the ADC dynamic range requirements. The proposed discrete TD technique first aligns the interference using non-uniform sampled phases followed by uniform cancellation using a Truncated Hadamard Transform implemented with antipodal binary coefficients. A digital timeinterleaver with 5 ps resolution spanning 15 ns implements a scalable discrete TD to compensate the inter-element delay, while the multiply-accumulate in the signal path is simplified by implementing a 1-bit differential truncated Hadamard matrix. Measured results demonstrate greater than 35 dB cancellation over 80 MHz modulated bandwidth in 65 nm CMOS with a 592x improvement over prior-art demonstration of wide modulated bandwidth interference cancellation.

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Source: https://tomesphere.com/paper/1908.00631