The Algorithm for Blind Multi-user Detector Based on Subspace Tracking

Abstract: Multi-user detection (MUD) is an efficient technique for interference suppression that reduces the Multiple access interference (MAI) and improves the performance and increases the capacity of the system. Nowadays most of the research to MUD focuses on the blind multi-user detector because it does not require training sequences and can save the spectrum resource. By applying an improved subspace tracking algorithm to a modified subspace-based linear MMSE multi-user detector, a blind multi-user detector is presented. For the improved subspace tracking algorithm can reduce considerably computational complexity while keeping satisfactory convergence speed and stability and the modified MMSE multi-user detector doesn’t require the estimation of eigenvalue matrix, there can be significant elevation in the detection performance. Simulation results demonstrate preliminarily the conclusions above. Copyright © 2014 IFSA Publishing, S. L

The puzzle of anomalously large isospin violations in η(1405/1475)→3π\eta(1405/1475)\to 3\pi

The BES-III Collaboration recently report the observation of anomalously large isospin violations in $J/\psi\to \gamma\eta(1405/1475) \to \gamma \pi^0 f_0(980)\to \gamma +3\pi$, where the $f_0(980)$ in the $\pi\pi$ invariant mass spectrum appears to be much narrower ($\sim$ 10 MeV) than the peak width ($\sim$50 MeV) measured in other processes. We show that a mechanism, named as triangle singularity (TS), can produce a narrow enhancement between the charged and neutral $K\bar{K}$ thresholds, i.e., $2m_{K^\pm}\sim 2m_{K^0}$. It can also lead to different invariant mass spectra for $\eta(1405/1475)\to a_0(980)\pi$ and $K\bar{K}^*+c.c.$, which can possibly explain the long-standing puzzle about the need for two close states $\eta(1405)$ and $\eta(1475)$ in $\eta\pi\pi$ and $K\bar{K}\pi$, respectively. The TS could be a key to our understanding of the nature of $\eta(1405/1475)$ and advance our knowledge about the mixing between $a_0(980)$ and $f_0(980)$.Comment: 4 pages and 7 eps figures; Journal-matched versio