Characterization of Interference in OFDMA Small-Cell Networks

The increase in mobile Internet access is pushing mobile network operators toward deploying smaller cells ( femtocells ) and sophisticated air interface technologies, Orthogonal Frequency Division Multiple Access (OFDMA). The expected high density of deployment and uncoordinated operations of femtocells, however, make interference management both critical and extremely challenging. A significant challenge stems from the fact that femtocells have to use the same synchronous access technology as traditional macrocells. Given this, understanding the impact of the multitude of design choices (originally tailored to well-planned macrocellular networks) on interference management forms an essential first step toward designing efficient solutions for next-generation femtocell networks. This in turn is the focus of our paper.  With the help of extensive measurements from our femtocell testbed, we characterize the impact of various system design choices on interference in OFDMA femtocell deployments. The design choices that we examine are categorized across three broad dimensions: 1) resource isolation at the logical (MAC) level across femtocells, 2) resource mapping through sub-channelization at the physical (PHY) level within each femtocell, and 3) synchronization (or lack thereof) between interfering cells. Based on the insights from our measurement study, we discuss several implications on the choice of system design features for multicell operations. We also provide guidelines for the design of efficient interference management solutions for femtocell networks.