rence. The rest of the chapter is organized as follows: The packet scheduling solutions for interfer- ence mitigation are shown in Section 7.2, eICIC in Section 7.3, eCoMP in Section 7.4, CoMP in Section 7.5 and the summary is presented in Section 7.6. 7.2 Packet Scheduling Solutions 3GPP has standardized the interfaces very carefully but not the network-side algorithms. The radio resource management (RRM) algorithms in eNodeB can be developed and optimized by the network vendors together with the mobile operators. Therefore, there may be differences in the algorithms between the different LTE networks globally. The packet scheduler is key part of LTE RRM algorithms. The packet scheduler has more flexibility in LTE than in 2G or 3G networks since the scheduling optimization can be done in multiple domains: frequency domain, time domain, power domain and spatial antenna domain. The frequency- domain scheduling is a powerful solution for avoiding interfered PRBs and faded PRBs. The frequency-domain scheduling was not possible in CDMA-based systems where the signal is always spread over the whole transmission bandwidth. LTE technology uses frequency-domain transmission both in downlink and in uplink which enables frequency-domain scheduling. The time-domain scheduling is utilized in eICIC and it can also be utilized for quality of service (QoS) differentiation by transmitting high-priority packets first before low-priority packets. The power domain can use power control and can also change the relative power levels of the adjacent cells for the intra-frequency load balancing. The scheduling can also be done in spatial domain with antennas by using CoMP or beamforming. The different scheduling domains are illustrated in Figure 7.1. LTE Small Cell Optimization Frequency - Avoid interfered PRBs - Avoid faded PRBs - Quality of Service eICIC Power - Power control - Load balancing Spatial (antennas) - CoMP - Beamforming Figure 7.1 LTE packet scheduler can operate in multiple domains One of the main objectives of LTE sched