Heterogeneous Downlink Cellular Networks

We characterize the ergodic spectral efficiency of a non-cooperative and a cooperative type of K-tier heterogeneous networks with limited feedback. In the non-cooperative case, a multi-antenna base station (BS) serves a single-antenna user using maximum-ratio transmission based on limited feedback. In the cooperative case, a BS coordination set is formed by using dynamic clustering across the tiers, wherein the intra-cluster interference is mitigated by using multi-cell zero-forcing also based on limited feedback. Modeling the network based on stochastic geometry, we derive analytical expressions for the ergodic spectral efficiency as a function of the system parameters. Leveraging the obtained expressions, we formulate feedback partition problems and obtain solutions to maximize the ergodic spectral efficiency. Simulations show the spectral efficiency improvement by using the obtained feedback partitions. Our major findings are as follows: 1) In the non-cooperative case, the feedback is only useful in a particular tier if the mean interference is small enough. 2) In the cooperative case, allocating more feedback to stronger intra-cluster BSs is efficient. 3) In both cases, the obtained solutions do not change depending on instantaneous signal-to-interference ratio. J. Park and R. W. Heath Jr. are with the Wireless Networking and Communication Group (WNCG), Department of Electrical and Computer Engineering, The University of Texas at Austin, TX 78701, USA. (E-mail: { jeonghun, rheath}@utexas.edu) N. Lee is with Dept. of Electrical Engineering, POSTECH, 37673, Republic of Korea. (Email:[email protected]). This material is based upon work supported in part by the National Science Foundation under Grant No. NSF-CCF-1319556. A special case of this paper (feedback design in a cooperative single-tier network) appeared in IEEE Globecom Workshop 2016 [1]. ar X iv :1 70 8. 03 86 1v 1 [ cs .I T ] 1 3 A ug 2 01 7