13,029 research outputs found
Sub-graph based joint sparse graph for sparse code multiple access systems
Sparse code multiple access (SCMA) is a promising air interface candidate technique for next generation mobile networks, especially for massive machine type communications (mMTC). In this paper, we design a LDPC coded SCMA detector by combining the sparse graphs of LDPC and SCMA into one joint sparse graph (JSG). In our proposed scheme, SCMA sparse graph (SSG) defined by small size indicator matrix is utilized to construct the JSG, which is termed as sub-graph based joint sparse graph of SCMA (SG-JSG-SCMA). In this paper, we first study the binary-LDPC (B-LDPC) coded SGJSG- SCMA system. To combine the SCMA variable node (SVN) and LDPC variable node (LVN) into one joint variable node (JVN), a non-binary LDPC (NB-LDPC) coded SG-JSG-SCMA is also proposed. Furthermore, to reduce the complexity of NBLDPC coded SG-JSG-SCMA, a joint trellis representation (JTR) is introduced to represent the search space of NB-LDPC coded SG-JSG-SCMA. Based on JTR, a low complexity joint trellis based detection and decoding (JTDD) algorithm is proposed to reduce the computational complexity of NB-LDPC coded SGJSG- SCMA system. According to the simulation results, SG-JSGSCMA brings significant performance improvement compare to the conventional receiver using the disjoint approach, and it can also outperform a Turbo-structured receiver with comparable complexity. Moreover, the joint approach also has advantages in terms of processing latency compare to the Turbo approaches
Crossing by a single scalar field coupling with matter and the observational constraints
Motivated by Yang-Mills dark energy model, we propose a new model by
introducing a logarithmic correction. we find that this model can avoid the
coincidence problem naturally and gives an equation of state smoothly
crossing -1 if an interaction between dark energy and dark matter exists. It
has a stable tracker solution as well. To confront with observations based on
the combined data of SNIa, BAO, CMB and Hubble parameter, we obtain the best
fit values of the parameters with errors for the
noncoupled model: ,
, and for the coupled model with a decaying
rate : ,
. In particular, it is found that the
non-coupled model has a dynamic evolution almost undistinguishable to
CDM at the late-time Universe.Comment: 12 pages, 3 figures, the published versio
- …