**Author details**

24 Recent Trends in Multiuser MIMO Communications

Mu-Opportunistic Mu-Threshold

r≥24

N = 10 N = 20 N = 30 N = 40 N = 50

Number of Users N

**Figure 15.** Throughput performance comparison versus the number of users

remarkable conclusions are summarized as follows:

(a) Channel *ChA*

m=4 r≥24

m=3 r≥24

best configuration for Mu-Threshold :

m=4

0 5 10 m=3 r≥48 m=5 r≥48

slot number threshold

ChD Model

Mu-Opportunistic Mu-Threshold

m=5 r≥54

N = 10 N = 20 N = 30 N = 40 N = 50

Number of Users N

(b) Channel *ChD*

m=6 r≥54

best configuration for Mu-Threshold :

m=7 r≥54

oughput (Mbps)

Thro

fact that it only requires partial CSI information at the transmitter side, in the form of SNIR measurements acquired by the downlink users. Since the IEEE 802.11n/ac specifications support beamforming, MOB can be easily implemented with minor modifications in the

On the other hand, in order to exploit the potential of the MOB technique in a realistic scenario, it is necessary to design appropriate MAC layer mechanisms to handle multiuser transmissions. In this chapter, three MAC layer schemes have been proposed. The first scheme, Mu-Basic, implemented a simple random scheduling multiuser scheme, meant to serve as a performance reference. Then, two opportunistic schemes have been proposed, Mu-Opportunistic and Mu-Threshold, that enhance performance by extracting the multiuser

The performance evaluation of the proposed multiuser schemes has led to many interesting observations. The lessons learned can be employed to improve the proposed algorithms but also as more general guidelines in the design of multiuser MAC schemes. The more

• When the best set of users is opportunistically selected depending on their measured channel quality, the gain achieved by multiuser transmissions can be significant.

• Multiuser diversity gain increases with the number of system users, since there is a higher probability of finding a high-rate set of users among a larger user pool. On the other hand, more users come with a cost of additional control overhead for the CSI acquisition. Mu-Threshold handles efficiently multiple users by setting appropriately the slot number

0 5 10

diversity gain.

m=2 r≥24 m=2 r≥24

slot number threshold

ChA Model

beamforming steering matrices.

oughput (Mbps)

Thro

Elli Kartsakli1,<sup>⋆</sup>, Nizar Zorba1, Luis Alonso2 and Christos Verikoukis<sup>3</sup>

<sup>⋆</sup> Address all correspondence to: ellik@tsc.upc.edu

1 Signal Theory and Communications Department of Technical University of Catalunya (UPC), Barcelona, Spain

2 Electrical Engineering Department of The University of Jordan, Jordan

3 Telecommunications Technological Center of Catalunya (CTTC), Barcelona, Spain
