Field trials of LTE with 4x4 MIMO

MIMO) enables single-layer transmission to several users who simultaneously share the same frequency allocation. In closed-loop spatial multiplexing (mode 4), one or more layers are transmitted using a precoder matrix that is selected from a predefi ned codebook. The precoder selections are typically based on channel measurements made by the UE. The precoders are applied to the layers transmitted from the eNB with the goal of maximizing performance according to the instantaneous channel conditions. Depending on the confi gured uplink feedback mode, the UE may feed back multiple preferred precoder matrix indicators (PMIs), where each PMI is valid for a particular sub-band (frequency-selective precoding); or one PMI that is valid for all sub-bands (wide-band precoding). Transmission mode 6 is similar to transmission mode 4, except that it is restricted to rank-one transmission. The various transmission modes specifi ed in the standard may be used with any antenna setup, and the codebooks are designed for a wide range of antenna setups and scenarios. Nevertheless, the choice of antenna setup is critical, and the best choice is dependent on the target performance profi le and propagation environment.