csi or 2° CB (per sector) Control: 8 . dcsi or 4 d (per sector) WLopt: WLopt: simulcast of control & data simulcast of control & data from CU to RNs small CB instead of CSI ideally no performance degradation UE-RN contr UE-RN contr RN-UE RN-UE RN-CU contr RN-CU contr CU-RN CU-RN CU-RN contr CU-RN contr WL WLopt WL WLopt (f) Cooperative Relaying (e) Distributed Cooperation Over the Air w/Mirror NBs Figure 7.11 (Continued). MCSs on NB-RN and RN-UE links separately (see also reference 15), which is important to avoid unnecessary overhead. For A&S&F instead of quantized data values, as for D&F, analogue Tx signals are sent to the RNs. For this reason, there will always be one channel use per Tx sample compared to the transmission of several bits for the D&F case. The inherent assumption is that the radio channels from NB to RNs have very high SNRs avoiding noise enhancement effects and that polarization multiplexing can be used, thus allowing for effi- cient data transmission on eNB-RN links. C 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology (F4) Cooperative Relaying: Self organizing Over the Air Control: scheduling requests/grants etc. WLopt: simulcast of control & data to/from CU to RNs; small CB instead of CSI UE-RN contr RN-UE RN-CU contr CU-RN CU-RN contr WLopt Figure 7.11 (Continued). For (f3), the CU at the serving eNB has been replaced by two mirror CUs at both RNs per sector. D&F relays are assumed, but instead of pre- coded data, the "pure" data signals for all UEs are broadcasted to both RNs. Control and CSI information is exchanged between both RNs wirelessly over the serving eNB. Therefore, channel information might be outdated to some extent for this solution, which might limit maxi- mum supportable mobile speed. To overcome this limitation, in (f4) CSI or PMIs as well as other control information are exchanged between RNs over the air with help from the UEs. Because wireless links are less reliable, a hardened UL chan- nel for this control information sho