Concept

Multi-user MIMO

Résumé
Multi-user MIMO (MU-MIMO) is a set of multiple-input and multiple-output (MIMO) technologies for multipath wireless communication, in which multiple users or terminals, each radioing over one or more antennas, communicate with one another. In contrast, single-user MIMO (SU-MIMO) involves a single multi-antenna-equipped user or terminal communicating with precisely one other similarly equipped node. Analogous to how OFDMA adds multiple-access capability to OFDM in the cellular-communications realm, MU-MIMO adds multiple-user capability to MIMO in the wireless realm. SDMA, massive MIMO, coordinated multipoint (CoMP), and ad hoc MIMO are all related to MU-MIMO; each of those technologies often leverage spatial degrees of freedom to separate users. MU-MIMO leverages multiple users as spatially distributed transmission resources, at the cost of somewhat more expensive signal processing. In comparison, conventional single-user MIMO (SU-MIMO) involves solely local-device multiple-antenna dimensions. MU-MIMO algorithms enhance MIMO systems where connections among users count greater than one. MU-MIMO may be generalized into two categories: MIMO broadcast channels (MIMO BC) and MIMO multiple-access channels (MIMO MAC) for downlink and uplink situations, respectively. Again in comparison, SU-MIMO may be represented as a point-to-point, pairwise MIMO. To remove ambiguity of the words receiver and transmitter, we can adopt the terms access point (AP) or base station, and user. An AP is the transmitter and a user the receiver for downlink connections, and vice versa for uplink connections. Homogeneous networks are freed from this distinction since they tend to be bi-directional. MIMO BC represents a MIMO downlink case where a single sender transmits to multiple receivers within the wireless network. Examples of advanced-transmit processing for MIMO BC are interference-aware precoding and SDMA-based downlink user scheduling. For advanced-transmit processing, qfz has to be known at the transmitter (CSIT).
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