deserialization standards and application-specific (silicon) devices for their implementations. This proprie- tary nature eliminated standard products from being used for large portions of the base sta- tion and forced the use of ASICs and field programmable gate arrays-both of which are highly proprietary and costly. As system performance requirements increased over time, the base station architecture evolved to separate into two main components: The Network Interface Card (NIC) and the Line Card, as shown for a three-sector base station. This evolution allows better scalability to increase performance from a single sector to three sector, six sector, and above. It also defines a new interface between the Line Card and the NIC. Physical interfaces used included PCIe, serial Rapid IO (sRIO), Asynchronous Transfer Mode, and Ethernet. The logical interface or Application Programming Interface (API) remained vendor proprietary, making decoupling of NIC from Line Card impossible. Even lower level components had a wide choice of imple- mentation options. Consider MPU/controller devices with instruction sets from ARM, MIPS, PowerPC, or x86, DSP architectures from Analog Devices (Tigersharc), Freescale (StarCore), or Texas Instruments (C66 family of devices), as well as many proprietary architectures and implementations. This broad technology portfolio was clearly not sustainable. At the same time, the system vendor landscape changed during the 3G and 4G decades. 3G and first-generation base stations were developed by many companies including, Alcatel, Ericsson, Fujitsu, Huawei, Lucent, Motorola, NEC, Nokia, Nortel, Samsung, Siemens, and Chapter 1 Open radio access network overview Facing intense competition, the industry went through a sequence of mergers during the 3G/4G period, with the "famous five": Ericsson, Huawei, Nokia, Samsung, and ZTE capturing ~95% of the infrastructure market. 5G base station architectures In the previous chapter, we discussed traditional base station architectures as deployed for macro sit