 separate ACK/ NAK channel is needed in the DL. Retransmissions are requested with UL allo- cation (implicit NAK), and a UL allocation for a new transmission implies that retransmissions are not continued. Though the ACK/NAK channel still exists in terms of 3GPP agreement, it is overridden by UL allocation signaling. 10.6.2.5 Interference Aware Packet Scheduling for LTE UL As proposed in [24,26], an interference aware packet scheduling method to allevi- ate the co-channel interference for larger cells (e.g., macro cell Case 3 [27]) could be used. Briefly, the method is as follows: First, users in the same sector are sorted on the basis of DL path loss measurement. Second, UEs closer to BS are allocated into middle frequencies and UEs at the cell edge are allocated into edge frequen- cies. The SNR target is first set to cell edge users, and the SNR target of users closer to BS may be gradually increased. In other words, the basic idea in this method is that users with similar path loss use the same frequency in all sectors/cells. Hence, with this method the interference level is comparable to the useful signal level, but, © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Total bandwidth: Figure 10.14 IC scheme for large cell. as can be seen from Figure 10.14, the cell edge users may interfere with each other. Therefore, for small cells (e.g., macro cell Case 1 [27]), different re-use patterns to minimize intercell interference can be used. This is depicted in Figure 10.15. Similarly, as for the interference control scheme for larger cells, UEs are sorted according to DL path-loss measurements. Then, the required transmission power levels of UEs are fi gured out according to the SNR target. The SNR target is the same for all UEs in the network; that is, for re-use a factor three power sequence [0 -4 -4] is used. The key point here is that users with similar path loss use dif- ferent frequencies in different sectors within one cell. Hence, the cell edge users in Total 