d channel rank and precoding matrix reports bundled together with the CQI report in order to support multiantenna transmission at the eNode B. More details on the RRM function controlling the multiantenna transmission are discussed in Section 4.2.7. To obtain channel-quality information on the uplink channel at the eNode B is somewhat easier than for the downlink channel because the eNode B can perform measurements on the UL transmission of the UE. Reference symbols similar to those in the downlink are inserted in each RB in the uplink. Note, however, that the channel quality can be estimated only on RBs on which the UE is actually transmitting. Because the UE typically does not transmit in the full bandwidth, the eNode B gets (relative) channel quality information only on RBs that it has assigned to the UE, while the RB assignment should be done according to best RB quality selected from the full bandwidth. (To obtain precise absolute channel qual- ity, including uplink path loss, is made difficult by the fact that the UE exercises power control for uplink transmissions.) In order to allow the eNode B to estimate the channel quality on all RBs from the same UE, it is possible to transmit so-called channel sounding reference signals © 2009 by Taylor & Francis Group, LLC Long Term Evolution: GPP LTE Radio and Cellular Technology from the UE. The UE transmits the sounding signal for one symbol duration within a subframe occupying the entire bandwidth, if the eNode B instructs the UE to do SO. Recall that the flexibility of the RB assignments in the UL is constrained by the single carrier property. Therefore, realizing a fully flexible channel-dependent scheduling in the uplink is difficult, even if full bandwidth channel quality infor- mation is available. 4.2.2.2 Obtaining Buffer Status Information What was difficult in obtaining channel quality information for the downlink versus the uplink is now the opposite case for the buffer status information. Downlink buf- fer status information is naturally available for 