Millimeter wave (mmWave) frequency bands offer a new frontier for cellular wireless systems to enable multigigabit communication. However, the availability and reliability of mmWave links are significantly limited due to its propagation characteristics. To mitigate the impact of such links and provide uninterrupted network services, the study of changing link condition is important. This paper proposes a reference signal (RS) transmission scheme for a mmWave cellular system using highly directional antenna beams. The aim of RS is to estimate the channel condition, which can be used for various purposes, e.g., initial access, beam alignment, and channel state information measurement. In particular, the objective of our proposed scheme is to enable efficient RS transmission in terms of angular coverage while ensuring a fair number of RS reception at all UEs within cell coverage. In addition, we provide a framework for studying the tradeoff between RS transmission overhead and RS measurement accuracy. Through theoretical analysis and simulation, we show that the proposed scheme achieves higher efficiency, especially in a small-cell scenario with smaller number of UE presence.