Chapter 17: MIMO III: Multi-User MIMO

Learning Objectives

• Characterise the capacity region of the K-user MIMO multiple-access channel (MAC) and explain the role of successive interference cancellation in achieving corner points
• State the BC-MAC duality theorem and derive the broadcast channel capacity region from the dual MAC under a sum power constraint
• Design zero-forcing and regularised zero-forcing (MMSE) linear precoders for the multi-user MISO downlink and quantify their sum-rate gap to dirty paper coding
• Formulate the weighted sum-rate maximisation problem, derive the WMMSE algorithm, and prove its convergence to a stationary point
• Explain the concept of interference alignment, state the Cadambe-Jafar K/2 degrees-of-freedom result, and construct closed-form alignment solutions for the 3-user interference channel
• Describe semi-orthogonal user selection (SUS) and multi-user diversity, and prove the log log K scaling of opportunistic scheduling gain
• Compare practical multi-user MIMO techniques (ZF, MMSE, WMMSE, IA, scheduling) in terms of performance, complexity, and CSI requirements for modern wireless systems