) = antenna/carrier count (A X C) X bit- width (IQ) X signal rate/carrier (SR). This bandwidth is equal for uplink and downlink. An alternative physical implementation for this interface is Ethernet through standards such as (more about that later) CPRI over Ethernet or eCPRI. Moving to Ethernet removes the proprietary aspects of the standard but does not fix the high bandwidth requirements associated with baseband interfacing. Partial mitigation of the bandwidth challenge can be achieved by sample compression, either in CPRI/OBSAI interfaces or on Ethernet interfaces. Split 7. In the LTE air interface, only ~60% of available subcarriers are used for commu- nication (1200 out of 2048 in a 20 MHz carrier), with the remainder carriers defined as guard carriers. Combined with cyclic prefix-associated overheads, we see that roughly half of the fronthaul bandwidth can be eliminated by moving the frequency time conversion (FFT functionality) to the radio head. In addition, note that the FFT function is computationally (as counted in multiply-accumulates) intensive though highly regular and well understood with optimized implementations widely available. When combined with DFE functions such as signal conditioning/filtering and RACH (Random Access Channel) processing, this consti- tutes the bulk of the compute requirements in the physical layer chain: Within the Option 7 split, we define three subcategories of incremental offload to the radio head as shown in Fig. 1-20. Option 7-1 strictly offloads the (i)FFT per the description given earlier. Incrementally, we can off- load resource element mapping and beamforming components to the radio head to make Option 7- 2. To understand the benefit of this option, consider massive MIMO systems where the number of logical layers is (much) smaller (say, 8 layers) than the number of physical antennas (say, 64 anten- nas). See Fig. 1-21 for the downlink (transmit) chain only-but assume equivalent for the uplink. Compute and IQ sample IO bandwidths scale with number of layers before 