Given the rapid development of current wireless communication systems has led to two major challenges: energy conservation and interference avoidance. Addressing these challenges is critical for sustaining modern green communications. This paper proposes two energy-efficient schemes for a heterogeneous network environment. The schemes include a cell switching strategy and a power control technique. The proposed schemes can save energy while maintaining the service quality for users. Simulation results showed that compared with conventional schemes, the proposed schemes reduced energy consumption by up to 18% more and further enhanced the system energy efficiency by up to 22% without using any switch-off procedure.

This paper focuses on system level simulation of heterogeneous networks (HetNet). Aiming at the imbalance offloading of macro cell and pico cell under the macro-pico coexistence case, we propose an adaptive cell-specific association strategy for HetNet to ensure that users can be served equitably by both macro cell and pico cell. The traditional cell range expansion (CRE) scheme with bias-based cell association has fixed bias values for all pico cells. Our proposal, on the other hand, sets different thresholds of attached users for all MeNB (macro enhanced node B) and PeNBs (pico enhanced node B), and all cell-specific biases are obtained by the proposed adaptive association strategy according to different cell-specific predefined thresholds. With this strategy, the load imbalance between MeNB and different PeNBs is well alleviated, and hence the entire network performance is elevated. Moreover, due to the newly deployed low-power nodes in HetNets, the achieved spectral efficiency of users, especially for cell edge users, is also affected by the downlink inter-cell interference. The idea we put forward is to combine the frequency and power coordination, and so suppress the inter-cell interference. Finally in this paper, we present some numerical results to verify the effectiveness of our proposed approach.

In order to support the increasing amount of mobile data traffic, Third Generation Partnership Project (3GPP) is actively discusses cell range expansion (CRE) and time domain multiplexing – inter-cell interference coordination (TDM-ICIC). They have shown to be attractive techniques for heterogeneous network (HetNet) deployment where pico base stations (BSs) overlay macro BSs. There are two control schemes of the TDM-ICIC. One, named ZP-scheme, stops radio resource assignments for data traffic in predetermined radio resources in the time domain (subframes). The other, named RP-scheme, maintains the resource assignment whereas it reduces the transmission power at macro BSs at predetermined subframes. In this paper, we clarify the effective ranges of both ZP-scheme and RP-scheme by conducting the system level simulations. Moreover, the appropriate power reduction value at predetermined subframes is also clarified from the difference in the effective range of various power reduction values. The comprehensive evaluation results show that both ZP-scheme and RP-scheme are not effective when the CRE bias value is 0 dB or less. If the CRE bias value is larger than 0 dB, they are effective when the ratio of predetermined subframes in all subframes is set to appropriate values. These values depend on the CRE bias value and power reduction in the predetermined subframes. The effective range is expanded when the power reduction in the predetermined subframes changes with the CRE bias value. Therefore, the effective range of RP-scheme is larger than that of ZP-scheme by setting an appropriate power reduction in the predetermined subframes.

Scheduling restriction is attracting much attention in LTE-Advanced as a technique to reduce the power consumption and network overheads in interference coordinated heterogeneous networks (HetNets). Such a network with inter-cell interference coordination (ICIC) provides two radio resources with different channel quality statistics. One of the resources is protected (unprotected) from inter-cell interference (hence, called protected (non-protected) resource) and has higher (lower) average channel quality. Without scheduling restriction, the channel quality feedback would be doubled to reflect the quality difference of the two resources. We present a simple scheduling restriction scheme that addresses the problem without significant performance degradation. Users with relatively larger (smaller) average channel quality difference between the two resources are scheduled in the protected (non-protected) resource only, and a boundary user, determined by a proportional fair resource allocation (PFRA) under simplified static channels, is scheduled on one of the two resources or both depending on PFRA. Having most users scheduled in only one of the resources, the power consumption and network overheads that would otherwise be required for the channel quality feedback on the other resource can be avoided. System level simulation of LTE-Advanced downlink shows that the performance degradation due to our scheduling restriction scheme is less than 2%, with the average feedback reduction of 40%.