mically. DL L1/L2 control 20 ms UL allocation: UL VolP packet: Retransmission: Reserved resource: Release: Figure 10.11 Talk spurt based persistent allocation in uplink. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Semi-persistent Dynamic Number of dynamically scheduled users per TTI Figure 10.12 Cumulative distribution function for the dynamically scheduled users per TTI (Out of the maximum 10 users). The impact of the semi-persistent resource allocation method on DL control overhead is illustrated in Figure 10.12, which contains the cumulative distribution function (CDF) of the dynamically scheduled users per TTI. As is evident from the figure, with the semi-persistent resource allocation method, DL control over- head is approximately 40% of the control channel overhead of fully dynamic PS. In Figure 10.13 the CDF for the number of scheduled PRBs per OFDM subframe is presented. Performance of fully dynamic PS is control channel limited; that is, there are not enough control channel resources to utilize the total transmission bandwidth: with fully dynamic PS, only 70% of the total transmission bandwidth (5 MHz - 25 PRBs) is used on average. Here we assume that packets are used for the dynamic scheduler. Semi-persistent PS does not suffer from control channel limitation, but its performance is data limited: on average only 10% of the total transmission bandwidth is unused. 10.6.2.3 Means to Overcome CQI Imperfections CQI feedback is utilized by the channel aware scheduler at eNodeB when selecting the scheduled users and allocating resources for them. Additionally, CQI reports are used by the link adaptation algorithm when selecting the used modulation and coding schemes for the scheduled users. CQI feedback is subject to reporting delays © 2009 by Taylor & Francis Group, LLC Radio Access Network VolP Optimization Semi-persistent Dynamic Number of RBs scheduled per TTI [-] Figure 10.13 Cumulative distribution function for scheduled PRBs per TTI. and UE measureme