LTE, LTE-Advanced and WiMAX: Towards IMT-Advanced Networks

Multiple Antenna Techniques

Another key technology for increasing the system capacity is the use of multiple transmit and multiple receive antennas, that is, using Multiple Input and Multiple Output (MIMO) techniques [6]. Over the past decade, MIMO techniques became a prominent capacity and reliability enhancement technology for many wireless communication standards including the LTE and WiMAX. Consequently, it is envisioned to remain and even to improve in IMT-Advanced networks.

MIMO techniques involve a variety of techniques aiming at different objectives in different scenarios. In general, they can be divided into Single User MIMO (SU-MIMO) and Multi User MIMO (MU-MIMO), see Figure 2.7. In SU-MIMO, the additional transmit and receive antennas are used to enhance the capacity as well as the reliability experienced by that user. These can be achieved by using space-time codes or beamforming. On the contrary, MU-MIMO generalizes these gains to multiple users. In particular, MU-MIMO exploits the multiuser diversity in allocating a group of users into the same time-frequency resource [7]. It facilitates achieving high transmission capacity while requiring simpler terminals. To elaborate, data streams on the UL can come from different MSs. The general setting assumes MSs transmitting normally to a BS utilizing more than one antenna. There is generally no coordination assumed between the MSs. Hence, the main challenge is how to schedule the MSs. As MSs are usually dispersed over the ...