recoding are in the remote unit All other PHY functions are in the distributed unit In downlink only, the encoder resides in the distributed unit All other PHY functions are in the remote unit ~ 503 RF chains are in the remote unit All other PHY functions are in the distributed unit 4 NG-RAN Architecture The compression is not a mandatory feature - it is up to the vendor whether or not to implement it. Data compression can be very helpful in reducing fronthaul bandwidth requirements; however, there is a cost as data compression may cause signal precision loss, and compression/decompression may increase RU complexity. 4.5.3.2 Low-Level Functional Split Details Generally, the lower the RAN is split, the more functions can be centralized, and the higher gains due to centralized scheduling and resource sharing can be achieved. On the other hand, lower splits increase fronthaul bandwidth and transport latency requirements, and the RU complexity. Therefore, a good NG-RAN split design needs to balance between these considerations. Those contradicting objectives are hard to address with a single solution. To better understand the issue we first consider the physical layer processing flows using the Physical Downlink Shared Channel (PDSCH) as an example. Generally, PHY Tx pro- cessing includes two stages - bit block processing and complex value symbol processing. The bit stream codeword is scrambled with a 3GPP-defined scrambling bit sequence (3GPP TS 38.211) before the modulation. Scrambling randomizes transmitted bits and makes them less prone to interference. The modulation function converts the bit block into a complex value modulation symbol using 3GPP-specified modulation schemes (3GPP TS 38.211), for example, QPSK, 16QAM, 64QAM, and 256QAM. The next processing function is the layer mapping, which maps the symbols into one or multiple layers. The layer mapping prepares the symbols to be transmitted using spatial multiplexing. The precoding function and beam- forming function are used to maximize the radio signal pow