Time- Versus Size-Based CPRI in Ethernet Encapsulation for Next Generation Reconfigurable Fronthaul

Abstract

The utilization of Ethernet in the cellular terrestrial cloud radio access network (C-RAN) fronthaul will potentially improve C-RAN reconfigurability and cost efficiency in terms of both capital and operational expenditures. Moreover, Common Public Radio Interface (CPRI) line bit rate dynamic reconfiguration may spare further capital expenditures by avoiding peak traffic capacity allocation. A possible solution for introducing Ethernet in the fronthaul is the encapsulation of CPRI in Ethernet. This solution is now part of the radio over Ethernet interface specified by the IEEE P1914 working group. However, it must be assured that fronthaul strict requirements on delay and jitter are still met. In this study, the combined impact of encapsulating CPRI in Ethernet and of the dynamic CPRI line bit rate reconfiguration on delay and jitter of the communication between radio equipment and a radio equipment controller is evaluated. The evaluation is both analytical and based on the presynthesis emulation of dynamic CPRI line bit rate reconfiguration. Both a size-based and a time-based encapsulation are considered. Results show that dynamic CPRI line bit rate reconfiguration can be achieved within about 1 ms. However, if a size-based encapsulation of CPRI in Ethernet is utilized, dynamic CPRI line bit rate reconfiguration might cause delay variations (i.e., jitter) up to few microseconds. Thus, to avoid jitter upon CPRI line bit rate reconfiguration, time-based encapsulation is preferable.