Realtime multi-user multi-antenna downlink measurements

In this paper, we present real-time broadband multi-user multi-antenna measurements in typical indoor and outdoor scenarios. For the first time, essential frequency-selective functions of a new medium access control (MAC) layer, namely fair resource assignment to multiple users, spatial mode selection and adaptive modulation, have been implemented in real-time on standard digital signal processing hardware. The new MAC layer is steered over wireless feedback and control channels in a closed loop manner. Our implementation uses parameters close to the forthcoming long-term evolution (LTE) of the 3G air interface, thus illustrating the feasibility of the new functions in next-generation cellular radio systems. The paper describes our real-time implementation and reports several test results. Benefits of the frequency-selective multi-user MIMO MAC are validated in realistic mobile propagation environments.