MIMO Schemes in 16m ( WiMAX 2.0)

16m supports several advanced multi-antenna techniques including single and multi-user MIMO (spatial multiplexing and beamforming) as well as a number of transmit diversity schemes.

SU-MIMO: Single-user MIMO (SU-MIMO) schemes are used to improve the link performance, by providing robust transmissions with spatial diversity, or large spatial multiplexing gain and peak data rate to a single AMS, or beamforming gain.

Both open-loop SU-MIMO and closed-loop SU-MIMO are supported for the antenna configurations presented above.

For open-loop SU-MIMO, both spatial multiplexing and transmit diversity schemes are supported. For closed-loop SU-MIMO, codebook based precoding is supported for both TDD and FDD systems. CQI, PMI, and rank feedback can be transmitted by the mobile station to assist the base station’s scheduling, resource allocation, and rate adaptation decisions. CQI, PMI, and rank feedback may or may not be frequency dependent. For closed-loop SU-MIMO, sounding based precoding is supported for TDD systems.

MU-MIMO: Multi-user MIMO (MU-MIMO) schemes are used to enable resource allocation to communicate data to two or more AMSs. MU-MIMO enhances the system throughput.

Multi-user transmission with one stream per user is supported for MU-MIMO. MU-MIMO includes the MIMO configuration of 2Tx antennas to support up to 2 users, and 4Tx or 8Tx antennas to support up to 4 users. Both unitary and non-unitary MU-MIMO linear precoding techniques are supported.

For open-loop MU-MIMO, CQI and preferred stream index feedback may be transmitted to assist the base station’s scheduling, transmission mode switching, and rate adaptation. The CQI is frequency dependent.

For closed-loop multi -user MIMO, codebook based precoding is supported for both TDD and FDD systems. CQI and PMI feedback can be transmitted by the mobile station to assist the base station’s scheduling, resource allocation, and rate adaptation decisions. CQI and PMI feedback may or may not be frequency dependent. For closed-loop multi -user MIMO, sounding based precoding is supported for TDD systems.

Multi BS MIMO

Multi-BS MIMO techniques are supported for improving sector throughput and cell-edge throughput through multi-BS collaborative precoding, network coordinated beamforming, or inter-cell interference nulling. Both open-loop and closed-loop multi-BS MIMO techniques can be considered. For closed-loop multi-BS MIMO, CSI feedback via codebook based feedback or sounding channel will be used. The feedback information may be shared by neighboring BSs via network interface.

COMP – Coordinated multi-point (CoMP) is a new class of transmission schemes for interference reduction in the 16m technology. Enabling features such as network synchronization, cell- and user-specific pilots, feedback of multicell channel state information and synchronous data exchange between the base stations can be used for interference mitigation and for possible macro diversity gain. The collaborative MIMO (Co-MIMO) and the closed-loop macro diversity (CL-MD) techniques are examples of the possible options. For downlink Co-MIMO, multiple BSs perform joint MIMO transmission to multiple MSs located in different cells. Each BS performs multi-user precoding towards multiple MSs, and each MS is benefited from Co-MIMO by receiving multiple streams from multiple BSs. For downlink CL-MD, each group of antennas of one BS performs narrow-band or wide-band single-user precoding with up to two streams independently, and multiple BSs.

Downlink MIMO Modes

Uplink MIMO Modes

Performance of Different MIMO Schemes