1,218 research outputs found
Two-Layered Superposition of Broadcast/Multicast and Unicast Signals in Multiuser OFDMA Systems
We study optimal delivery strategies of one common and independent
messages from a source to multiple users in wireless environments. In
particular, two-layered superposition of broadcast/multicast and unicast
signals is considered in a downlink multiuser OFDMA system. In the literature
and industry, the two-layer superposition is often considered as a pragmatic
approach to make a compromise between the simple but suboptimal orthogonal
multiplexing (OM) and the optimal but complex fully-layered non-orthogonal
multiplexing. In this work, we show that only two-layers are necessary to
achieve the maximum sum-rate when the common message has higher priority than
the individual unicast messages, and OM cannot be sum-rate optimal in
general. We develop an algorithm that finds the optimal power allocation over
the two-layers and across the OFDMA radio resources in static channels and a
class of fading channels. Two main use-cases are considered: i) Multicast and
unicast multiplexing when users with uplink capabilities request both
common and independent messages, and ii) broadcast and unicast multiplexing
when the common message targets receive-only devices and users with uplink
capabilities additionally request independent messages. Finally, we develop a
transceiver design for broadcast/multicast and unicast superposition
transmission based on LTE-A-Pro physical layer and show with numerical
evaluations in mobile environments with multipath propagation that the capacity
improvements can be translated into significant practical performance gains
compared to the orthogonal schemes in the 3GPP specifications. We also analyze
the impact of real channel estimation and show that significant gains in terms
of spectral efficiency or coverage area are still available even with
estimation errors and imperfect interference cancellation for the two-layered
superposition system
Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks
In this paper, a practical multi-user cooperative transmission scheme denoted as Virtual Maximum Ratio
Transmission (VMRT) for Multiple-Input Multiple-Output - Orthogonal Frequency Division Multiple Access
(MIMO-OFDMA) Relay-based networks is proposed and evaluated in the presence of a realistic channel estimation
algorithm. It is shown that this scheme is robust against channel estimation errors and offers diversity and array
gain keeping the complexity low, although the multi-user and multi-antenna channel estimation algorithm is simple
and efficient. Diversity gains larger than 4 can be easily obtained with reduced number of relays. Thus, this scheme
can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays
Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks
In this paper, a practical multi-user cooperative transmission scheme denoted as Virtual Maximum Ratio
Transmission (VMRT) for Multiple-Input Multiple-Output - Orthogonal Frequency Division Multiple Access
(MIMO-OFDMA) Relay-based networks is proposed and evaluated in the presence of a realistic channel estimation
algorithm. It is shown that this scheme is robust against channel estimation errors and offers diversity and array
gain keeping the complexity low, although the multi-user and multi-antenna channel estimation algorithm is simple
and efficient. Diversity gains larger than 4 can be easily obtained with reduced number of relays. Thus, this scheme
can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays
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