 Therefore, to evaluate uplink SNR requirement for a given throughput target it is necessary to know how the eNodeB link adaptation allocates uplink bandwidth; obviously, this is a vendor-specific eNodeB implementation issue. This noteworthy point will be further illustrated in the sequel where an example of RSRP versus throughput measurement is presented. Figure 15.7 gives the full buffer throughput versus average SNR in low mobility. For a wideband system such as LTE, low SNRs can exhibit high throughput if the whole bandwidth is used for transmission. Even for the low spectral efficiency of 0.1 bits per second per Hz (corresponding to SNR = -9 dB in Figure 15.7), a MHz system would still have a respectable 2 Mbps downlink data rate. In practice this is difficult to realize due to the control channel link budget limitations; in practice the link budget limitation often comes from the control channels and not PDSCH or PUSCH. As shown in Table 15.9 the control channel performance depends on UE speed, radio channel, channel coding parameters and receive antenna configuration. Based on the 3GPP requirements in [10], in high mobility with two transmit antennas PCFICH/PDCCH with 8 CCE aggregation starts limiting below about Inter-layer Mobility Optimization Table 15.9 Example of uplink control channel SNR requirements from 3GPP Control channel and number of receive antennas SNR (dB) Notes PUCCH A/N 2Rx The ACK missed detection probability is the probability of not detecting an ACK when an ACK was sent. Target is 1% PUCCH A/N 4Rx The ACK missed detection probability is the probability of not detecting an ACK when an ACK was sent. Target is 1% PUCCH CQI 2Rx The CQI missed detection block error probability shall not exceed 1% PRACH burst format 0 2Rx The probability of detection shall be equal to or exceed 99% PRACH burst format 0 4Rx -12.1 The probability of detection shall be equal to or exceed 99% PUSCH msg3 80 bits 2Rx 1 PRB, 3 retransmissions, residual BLER = 1% [3GPP R1-081856] SNR = -3 dB (PDCCH misdetection prob