9,296 research outputs found
The Degrees of Freedom of the MIMO Y-channel
The degrees of freedom (DoF) of the MIMO Y-channel, a multi-way communication
network consisting of 3 users and a relay, are characterized for arbitrary
number of antennas. The converse is provided by cut-set bounds and novel
genie-aided bounds. The achievability is shown by a scheme that uses
beamforming to establish network coding on-the-fly at the relay in the uplink,
and zero-forcing pre-coding in the downlink. It is shown that the network has
min{2M_2+2M_3,M_1+M_2+M_3,2N} DoF, where M_j and N represent the number of
antennas at user j and the relay, respectively. Thus, in the extreme case where
M_1+M_2+M_3 dominates the DoF expression and is smaller than N, the network has
the same DoF as the MAC between the 3 users and the relay. In this case, a
decode and forward strategy is optimal. In the other extreme where 2N
dominates, the DoF of the network is twice that of the aforementioned MAC, and
hence network coding is necessary. As a byproduct of this work, it is shown
that channel output feedback from the relay to the users has no impact on the
DoF of this channel.Comment: 5 pages, 4 figures, ISIT 201
A New DoF Upper Bound and Its Achievability for -User MIMO Y Channels
This work is to study the degrees of freedom (DoF) for the -user MIMO Y
channel. Previously, two transmission frameworks have been proposed for the DoF
analysis when , where and denote the number of antennas at
each source node and the relay node respectively. The first method is named as
signal group based alignment proposed by Hua et al. in [1]. The second is named
as signal pattern approach introduced by Wang et al. in [2]. But both of them
only studied certain antenna configurations. The maximum achievable DoF in the
general case still remains unknown. In this work, we first derive a new upper
bound of the DoF using the genie-aided approach. Then, we propose a more
general transmission framework, generalized signal alignment (GSA), and show
that the previous two methods are both special cases of GSA. With GSA, we prove
that the new DoF upper bound is achievable when . The DoF
analysis in this paper provides a major step forward towards the fundamental
capacity limit of the -user MIMO Y channel. It also offers a new approach of
integrating interference alignment with physical layer network coding.Comment: 6 pages, 3 figures, submitted to IEEE ICC 2015. arXiv admin note:
text overlap with arXiv:1405.071
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