 an LTE system, if I = 16 bits and Q = 16 bits, then one AxC is 32 bits. Each 256 basic frames make up a hyperframe and 150 hyper- frames are needed to transport an LTE 10 ms frame. Data in a basic frame is encoded with 8B/10B encoding, that is, 8 bits of data are encoded in 10 bits. The extra bits are used to detect link failures. Some of the CPRI rates support 64B/66B encoding scheme and this CPRI option 1 (basic frame structure (128 bits/260.42 ns) 16 bits/260.42 ns 16 bits/260.42 ns- 8B/10B encoding CPRI line rate 614.4 Mbps W = 15 CPRI payload (I/Q data block 120 bits) 16 bits/260.42 ns 64 bits CPRI payload (I/Q data block 120 bits) 16 bits/260.42 ns 32 bits 16 bits/260.42 ns 16 bits 8 Bits Option (payload = 120 bits) Option 2 (payload = 240 bits) Option 3 (payload = 480 bits) Option 5 (payload = 960 bits) Radio Radio equipment control equipment (REC) LTE/NR upper LTE/NR PHY LTE/NR RF layers Control and management IP backhaul Timing and synchronization Figure 1.28 CPRI frame structure 60]. 76 Chapter 1 extension is used to detect sync header impairments and link failures. Note that 8B/10B and 64B/66B encodings incur 20% and 3% overhead, thus the latter would be a significant improvement in overhead reduction. The CPRI specification specifies the maximum allowed effect of the fronthaul jitter on the frequency accuracy of the clock recovered at the RRH relative to a master reference clock at the BBU. One of the CPRI technical requirements defines the clock frequency accuracy of RRH as + 0.002 ppm. This requirement states that the maximum impact of jitter from the CPRI fronthaul on the frequency accuracy of RRH should be less than + 0.002 ppm. In addition to jitter, there are other factors that may affect the accuracy of clock frequency. CPRI requires very high reliability with bit error rates (BERs) of V 10-12. The CPRI framing process is illustrated in Fig. 1.29. User data is transported as baseband digital I/Q stream in a data block of a CPRI basic frame. The RRH, upon receiving the data, converts it into an