## 2 System Model and Design Objective
The assumed design criteria in this study are the following:  
* The femtocell coverage area shall correspond to \(PL_{femto}\);
* The femtocell coverage area shall be defined as the total received power divided by the thermal noise power [1], assuming a NR target of 6 dB for the MNB. Figure 1: Basic simulation model with hexagonal macro area and HNBs deployed in either single houses (suburban) or in apartments of three-floor buildings (dense urban). * HUEs shall be offered a minimum data rate of \(\text{ReqThp}_{DL}\) and \(\text{ReqThp}_{UL}\) for the downlink and uplink, respectively, in the entire home/apartment of the end-user. \(\text{ReqThp}_{DL}\) and \(\text{ReqThp}_{UL}\) are planning parameters;
* The generated uplink NR at the nearest MNB from each HUE must be limited to \(NR_{HUE}\). \(NR_{HUE}\) is a planning parameter that depends on the HNB density and the expected offload effect (for instance \(NR_{HNB}\) divided by maximum number of simultaneously active HNBs per macrocell area);
* After fulfilling the above requirements, the generated HNB interference towards the macro UEs shall be minimized (save power, improve macro performance). In this paper, the femtocell coverage area is defined as the area where the RSCP of the specific femtocell is higher than the RSCP for all other cells. Even though only a single HNB is shown in the above figure, our proposed algorithm is not limited to the single HNB case. It is an advantageous design choice not to consider inter-HNB interference when calculating the HNB powers, as this prevents HNBs from entering a transmit power race where strongly coupled HNBs keep increasing the total transmit power. Such an event would not improve the target performance indicators in the region between the competing femtocells, but would in turn result in increased interference towards the macro network and, thus, lower the overall utility of the network. Depending on the radio and interference conditions, it may be impossible to fulfill all of the listed design criteria. As an example, if the HNB coverage area is close to the MNB, fulfilling both the requirement on HUE uplink data rate and maximum generated NR towards the macro may be conflicting. In case of such conflicting requirements, it is considered most important to protect the macro performance. The interference management algorithm for dealing with these issues is derived in Section 3. Table 1 lists the parameters used in the derivation of the interference management algorithm in Section 3. Given the outlined design objectives, the key performance indicators (KPI) considered in this study are user experienced throughput in uplink and downlink, as well as the corresponding outage probabilities for experiencing data rates below certain targets. Such information is extracted from an empirical cumulative distribution function (cdf) of user data rates, obtained from extensive Monte-Carlo simulations. We also consider the transmission power aspects, both in terms of downlink transmission powers from the HNBs, as well as HUE uplink transmission powers. Figure 2: Overview of system model and design objectives. It is noted that the setting of the parameters depends on the deployment conditions and the provisioning strategy of the operator. We provide some examples in Table 2 of how the algorithm can be configured for various deployment use-cases.