This work analyzed the trade-off between the area spectral efficiency and outage user rates in heterogeneous cellular networks with overlapping picocells. We considered two different models for the spectrum allocation and cell association. The first model employs a spectrum overlapping strategy with an SINR-based cell association. The second model avoids the interference between macrocell and picocell through a spectrum splitting strategy. Furthermore, picocell range expansion was also considered for the later to enable a load balancing between the macrocell and picocells. Our results showed that while the spectrum overlapping provides the highest spectral efficiency, its outage rate performance is very poor. In contrast, the spectrum splitting offered a trade-off by guaranteeing a minimum QoS for the weak user rates and by flexibly varying the spectrum splitting ratio and picocell range.
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