Performance analysis of beamforming for femtocellular applications
Date
2010
Authors
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Publisher
University of Delaware
Abstract
In recent wireless applications, the demand for higher data rates has dramatically increased, and over 70% of mobile tra c is generated by indoor users. The deployment of femtocells could be one promising solution to this demand. The objective in using femtocells is to expand wireless coverage for indoor users with low-power consumption. In this thesis, we study and analyze the impact of MIMO beamforming schemes in a femtocellular environment. Speci cally, we consider a variety of beamforming techniques such as transmit beamforming (TX-BF), transmit beamforming with nulling (TX-BF with nulling), and codebook-based beamforming (CB-BF). We apply these techniques to the femtocellular environment and compare the performance of each technique. When each femtocellular base station (FBS) employs multiple antennas, beamforming can greatly improve the femtocellular user equipment (FUE) performance, regardless of the number of femtocells. Since the FBSs are installed in the existing macrocell, a technique that protects the macrocellular user equipment (MUE) is required. In this light, TX-BF with nulling at the MUE can obtain the best performance for the FUE while minimizing the interference to the MUE. CB-BF also can be used for each FBS to reduce the computational complexity. This technique can achieve good performance from the FUE point of view, but the MUE performance is not signi cantly improved until half of all the codewords are restricted. Furthermore, as the number of precoding matrix index (PMI) restriction increases to protect the MUE, the FUE performance degrades. In addition, we have proposed using cooperative transmission among femtocells to improve the FUE and MUE performance at the same time. Speci cally, in a high-density femtocellular environment, this technique might be useful. In reality, however, it is hard to form the cooperative group since the use of femtocells is more likely for personal applications.