Uplink interference mitigation in FEMTO- Cell networks

Abstract

Femto-cells or Femto-Access Points (FAPs) are small, low cost, short ranged (10-30m), low powered (10-100mW) home base-stations which are installed by the consumer for better indoor voice and data reception. Ad hoc nature of user deployed femto-cells has made interference (both co-tier and cross-tier) a key issue in its implementation. Many interference management approaches for femto-cell networks have been reported in the literature both for uplink and downlink. Most of them are application specific and their performance degrades sharply in specific circumstances or they perform well but at the price of high computational complexity. Keeping in view the advantages and disadvantages and ongoing wireless standardization a Hybrid MMSE/Max-log-MAP MIMO detector has been proposed for uplink interference mitigation in OFDMA based femtocell environment. This two-stage hybrid detector is characterized by the lower complexity of linear detection and superior performance of maximum likelihood (ML) detection. The first stage is a linear filter that adapts the system dimension in accordance with the processing capability of the second stage, which is a non linear low complexity ML detector. This thesis considers the pragmatic ranges of MIMO systems (2×2, 3×3, 4×4, and 5×5) and looks at the effect of distribution of streams amongst the two stages. Adaptability of the system in the form of stream allocation to the two stages allows having a tradeoff between the complexity and performance of detection. Performance of the proposed hybrid detector as shown by MATLAB simulations improves as the number of streams to be suppressed in the first stage decreases but it is coupled with the increase in cost of complexity.