lution: 3GPP LTE Radio and Cellular Technology RLC ARQ RLC ARQ RLC ARQ Figure 9.4 RLC operation with REC. same number of resources is allocated to the BS-RN link and the RN-UT link. This means that in every first TTI such as shown in Figure 9.3, a fixed number of resources is dedicated to the BS-RN transmission. In reality, this is not necessary because the actual number of resources dedicated to the BS-RN link depends on the scheduling and the traffic load. We use a Pareto distribution-based on-off traffic model to simulate the data traffic, of which the parameters are listed in Table 9.2. As in the REC, the relay area is not big and is supposed to serve a limited number of users; we always assume 16 users are served by the RN, which keeps the multiuser diversity. In order to simulate different traffic load scenarios, we assign different numbers of traffic flows to each user; each flow is independent of the other and follows the Pareto on-off traffic model. With the REC dimension and the pointed antenna beam from the BS to the RN (6-dB additional gain), the BS-RN link has a very stable and high signal-to-noise ratio (SNR) and the transmission on it has no errors. For the RN to UT link, we assume that chase combining HARQ could have, at most, three times of transmissions for one PDU. This would result in a HARQ residual PER of about 1.8%. Because we simulate only one REC cell and Table 9.2 Traffic Generator Parameters Period Shape (a) Location (B) 1,024 bytes 14,026 bytes 1 second 2.4939 seconds Pareto distribution Packet length 200 bytes Peal rate 150 kb/s Mean rate 31.5 kb/s © 2009 by Taylor & Francis Group, LLC User Plane Protocol Design for LTE System Throughput of RLC SDU Per-hop RLC Two-hop RLC RLC Window Size in the Number of PDUs Figure 9.5 Throughput of RLC operation with REC. leave interference out of consideration, the HARQ residual PER with a maximum of four times of transmission would be very small (about 0.1%). A residual PER that is too small makes RLC layer retransmission a rare event, and, hence,