934 research outputs found
Outage rates and outage durations of opportunistic relaying systems
Opportunistic relaying is a simple yet efficient cooperation scheme that
achieves full diversity and preserves the spectral efficiency among the
spatially distributed stations. However, the stations' mobility causes temporal
correlation of the system's capacity outage events, which gives rise to its
important second-order outage statistical parameters, such as the average
outage rate (AOR) and the average outage duration (AOD). This letter presents
exact analytical expressions for the AOR and the AOD of an opportunistic
relaying system, which employs a mobile source and a mobile destination
(without a direct path), and an arbitrary number of (fixed-gain
amplify-and-forward or decode-and-forward) mobile relays in Rayleigh fading
environment
Jointly Optimal Channel Pairing and Power Allocation for Multichannel Multihop Relaying
We study the problem of channel pairing and power allocation in a
multichannel multihop relay network to enhance the end-to-end data rate. Both
amplify-and-forward (AF) and decode-and-forward (DF) relaying strategies are
considered. Given fixed power allocation to the channels, we show that channel
pairing over multiple hops can be decomposed into independent pairing problems
at each relay, and a sorted-SNR channel pairing strategy is sum-rate optimal,
where each relay pairs its incoming and outgoing channels by their SNR order.
For the joint optimization of channel pairing and power allocation under both
total and individual power constraints, we show that the problem can be
decoupled into two subproblems solved separately. This separation principle is
established by observing the equivalence between sorting SNRs and sorting
channel gains in the jointly optimal solution. It significantly reduces the
computational complexity in finding the jointly optimal solution. It follows
that the channel pairing problem in joint optimization can be again decomposed
into independent pairing problems at each relay based on sorted channel gains.
The solution for optimizing power allocation for DF relaying is also provided,
as well as an asymptotically optimal solution for AF relaying. Numerical
results are provided to demonstrate substantial performance gain of the jointly
optimal solution over some suboptimal alternatives. It is also observed that
more gain is obtained from optimal channel pairing than optimal power
allocation through judiciously exploiting the variation among multiple
channels. Impact of the variation of channel gain, the number of channels, and
the number of hops on the performance gain is also studied through numerical
examples.Comment: 15 pages. IEEE Transactions on Signal Processin
Jointly Optimal Channel Pairing and Power Allocation for Multichannel Multihop Relaying
We study the problem of channel pairing and power allocation in a
multichannel multihop relay network to enhance the end-to-end data rate. Both
amplify-and-forward (AF) and decode-and-forward (DF) relaying strategies are
considered. Given fixed power allocation to the channels, we show that channel
pairing over multiple hops can be decomposed into independent pairing problems
at each relay, and a sorted-SNR channel pairing strategy is sum-rate optimal,
where each relay pairs its incoming and outgoing channels by their SNR order.
For the joint optimization of channel pairing and power allocation under both
total and individual power constraints, we show that the problem can be
decoupled into two subproblems solved separately. This separation principle is
established by observing the equivalence between sorting SNRs and sorting
channel gains in the jointly optimal solution. It significantly reduces the
computational complexity in finding the jointly optimal solution. It follows
that the channel pairing problem in joint optimization can be again decomposed
into independent pairing problems at each relay based on sorted channel gains.
The solution for optimizing power allocation for DF relaying is also provided,
as well as an asymptotically optimal solution for AF relaying. Numerical
results are provided to demonstrate substantial performance gain of the jointly
optimal solution over some suboptimal alternatives. It is also observed that
more gain is obtained from optimal channel pairing than optimal power
allocation through judiciously exploiting the variation among multiple
channels. Impact of the variation of channel gain, the number of channels, and
the number of hops on the performance gain is also studied through numerical
examples.Comment: 15 pages. IEEE Transactions on Signal Processin
Performance Analysis of Two-Hop Cooperative MIMO transmission with Relay Selection in Rayleigh Fading Channel
Wireless relaying is one of the promising solutions to overcome the channel
impairments and provide high data rate coverage that appears for beyond 3G
mobile communications. In this paper we present an end to end BER performance
analysis of dual hop wireless communication systems equipped with multiple
decode and forward relays over the Rayleigh fading channel with relay
selection. We select the best relay based on end to end channel conditions. We
apply orthogonal space time block coding (OSTBC) at source, and also present
how the multiple antennas at the source terminal affects the end to end BER
performance. This intermediate relay technique will cover long distance where
destination is out of reach from source.Comment: 5 figures, 4th International Conference on Wireless Communications,
Networking and Mobile Computing, 2008. WiCOM '0
A Comparative Study of Relaying Schemes with Decode-and-Forward over Nakagami-m Fading Channels
Utilizing relaying techniques to improve performance of wireless systems is a
promising avenue. However, it is crucial to understand what type of relaying
schemes should be used for achieving different performance objectives under
realistic fading conditions. In this paper, we present a general framework for
modelling and evaluating the performance of relaying schemes based on the
decode-and-forward (DF) protocol over independent and not necessarily
identically distributed (INID) Nakagami-m fading channels. In particular, we
present closed-form expressions for the statistics of the instantaneous output
signal-to-noise ratio of four significant relaying schemes with DF; two based
on repetitive transmission and the other two based on relay selection (RS).
These expressions are then used to obtain closed-form expressions for the
outage probability and the average symbol error probability for several
modulations of all considered relaying schemes over INID Nakagami-m fading.
Importantly, it is shown that when the channel state information for RS is
perfect, RS-based transmission schemes always outperform repetitive ones.
Furthermore, when the direct link between the source and the destination nodes
is sufficiently strong, relaying may not result in any gains and in this case
it should be switched-off.Comment: Submitted to Journal of Computer Systems, Networks, and
Communication
Outage Performance of Two-Hop OFDM Systems with Spatially Random Decode-and-Forward Relays
In this paper, we analyze the outage performance of different multicarrier
relay selection schemes for two-hop orthogonal frequency-division multiplexing
(OFDM) systems in a Poisson field of relays. In particular, special emphasis is
placed on decode-and-forward (DF) relay systems, equipped with bulk and
per-subcarrier selection schemes, respectively. The exact expressions for
outage probability are derived in integrals for general cases. In addition,
asymptotic expressions for outage probability in the high signal-to-noise ratio
(SNR) region in the finite circle relay distribution region are determined in
closed forms for both relay selection schemes. Also, the outage probabilities
for free space in the infinite relay distribution region are derived in closed
forms. Meanwhile, a series of important properties related to cooperative
systems in random networks are investigated, including diversity, outage
probability ratio of two selection schemes and optimization of the number of
subcarriers in terms of system throughput. All analysis is numerically verified
by simulations. Finally, a framework for analyzing the outage performance of
OFDM systems with spatially random relays is constructed, which can be easily
modified to analyze other similar cases with different forwarding protocols,
location distributions and/or channel conditions
- …