Analysis of Clock Distribution and Delay Management for IMT-Advanced Distributed Wireless Base Station Systems

摘要

Modern wireless Base Station (BS) systems for future commercial 4G networks fulfilling the IMT-Advanced (IMT-A) requirements and including the 3GPP LTE and LTE-Advanced are increasingly leveraging distributed BS architectures. The usage of Software Defined Radio (SDR) concepts within the available technology is compromising with the cost targets of data-driven commercial mobile networks and desired software flexibility. Thereby, the concept of Remote Radio Heads (RRH) has been introduced from the industry. RRHs represent a mean to lower overall system installations and operating costs while increasing the software flexibility in the radio system front-end, that is interconnected to BSs via optical fiber using CPRI (Common Public Radio Interface) or OBSAI RP3-01 (Open Base Station Architecture Initiative) interfacing standards. These interfacing standards impose strict physical layer requirements in terms of clock performances and link delay measurement accuracy between the BS and the remotely located antennas, ensuring sufficient margins for the inaccuracies introduced from the serialization/de-serialization process and the optical media. This paper analyze the clock recovery and delay measurement blocks when applied to single-hop and multi-hop RRH applications, the latter representing the worst-case scenario delay and clocking performance wise. We analyzed the clock recovery PLL blocks in a single-hop connection and we present a simulation model for cascaded PLLs and the achieved results. Likewise, we analyzed the serial interface delay budget contributions presenting a novel approach for the design of a generic serial receiver architecture that provides sub-nanosecond delay measurement resolution. The receiver architecture is generic and equally applicable to either CPRI or OBSAI RP3-01 interfaces and implementable in any RTL technology including cost-effective low-end FPGAs.