asis. The reported CQIs from UEs indicating the downlink channel quality can be used at the eNodeB for the following purposes: selection of modulation and coding scheme; time/frequency selective scheduling; interference management; and transmission power control for physical channels. The eNodeB establishes the time and frequency resources that can be used by each UE to report CQI values. In LTE, a UE is configured by higher layers to feed back a wideband CQI as well as one CQI for each sub-band in a predefined set of sub-bands (see Figure 3.9). The specifications also allow the UE to select only the M Information referring to multiple antenna transmission is also reported and used to adapt transmitted signal to channel conditions. These procedures are described in detail in Section 3.2.5. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Instantaneous SNR at UE Wideband mean signal level (for Wideband CQI) Sub-band mean signal level (CQI in each sub-band) Frequency System bandwidth divided into a set of sub-bands Figure 3.9 Wideband CQI versus sub-band CQI. best sub-bands within the predefined set to be reported. In both cases, the CQI of each sub-band is encoded differentially with respect to the wideband CQI. The CQI reporting may be periodic or aperiodic, with a minimum reporting interval of one subframe for the latter. The aperiodic report is performed by each UE after receiving an indication sent by the eNodeB in a scheduling grant. In both cases, the time and frequency resources that can be used by the UE to report are controlled by the eNodeB. Although beyond the scope of this section, an important practical issue related to CQI reporting is worthy of mention. Due to several factors, a received CQI may be outdated, inexact, or even corrupted, which potentially leads to a degradation of system performance (Morales-Jimenez et al. 2008). For instance, potential delays introduced by the feedback channel imply that reported CQIs from the receivers do not match th