80 research outputs found
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
Distributed space-time coding including the golden code with application in cooperative networks
This thesis presents new methodologies to improve performance of wireless cooperative networks using the Golden Code. As a form of space-time coding, the Golden Code can achieve diversity-multiplexing tradeoff and the data rate can be twice that of the Alamouti code. In practice, however, asynchronism between relay nodes may reduce performance and channel quality can be degraded from certain antennas.
Firstly, a simple offset transmission scheme, which employs full interference cancellation (FIC) and orthogonal frequency division multiplexing (OFDM), is enhanced through the use of four relay nodes and receiver processing to mitigate asynchronism. Then, the potential reduction in diversity gain due to the dependent channel matrix elements in the distributed Golden Code transmission, and the rate penalty of multihop transmission, are mitigated by relay selection based on two-way transmission. The Golden Code is also implemented in an asynchronous one-way relay network over frequency flat and selective channels, and a simple approach to overcome asynchronism is proposed. In one-way communication with computationally efficient sphere decoding, the maximum of the channel parameter means is shown to achieve the best performance for the relay selection through bit error rate simulations.
Secondly, to reduce the cost of hardware when multiple antennas are available in a cooperative network, multi-antenna selection is exploited. In this context, maximum-sum transmit antenna selection is proposed. End-to-end signal-to-noise ratio (SNR) is calculated and outage probability analysis is performed when the links are modelled as Rayleigh fading frequency flat channels. The numerical results support the analysis and for a MIMO system
maximum-sum selection is shown to outperform maximum-minimum selection. Additionally, pairwise error probability (PEP) analysis is performed for maximum-sum transmit antenna selection with the Golden Code and the diversity order is obtained.
Finally, with the assumption of fibre-connected multiple antennas with finite buffers, multiple-antenna selection is implemented on the basis of maximum-sum antenna selection. Frequency flat Rayleigh fading channels are assumed together with a decode and forward transmission scheme. Outage probability analysis is performed by exploiting the steady-state stationarity of a Markov Chain model
Enhanced Huffman Coded OFDM with Index Modulation
In this paper, we propose an enhanced Huffman coded orthogonal
frequency-division multiplexing with index modulation (EHC-OFDM-IM) scheme. The
proposed scheme is capable of utilizing all legitimate subcarrier activation
patterns (SAPs) and adapting the bijective mapping relation between SAPs and
leaves on a given Huffman tree according to channel state information (CSI). As
a result, a dynamic codebook update mechanism is obtained, which can provide
more reliable transmissions. We take the average block error rate (BLER) as the
performance evaluation metric and approximate it in closed form when the
transmit power allocated to each subcarrier is independent of channel states.
Also, we propose two CSI-based power allocation schemes with different
requirements for computational complexity to further improve the error
performance. Subsequently, we carry out numerical simulations to corroborate
the error performance analysis and the proposed dynamic power allocation
schemes. By studying the numerical results, we find that the depth of the
Huffman tree has a significant impact on the error performance when the
SAP-to-leaf mapping relation is optimized based on CSI. Meanwhile, through
numerical results, we also discuss the trade-off between error performance and
data transmission rate and investigate the impacts of imperfect CSI on the
error performance of EHC-OFDM-IM
Implementation of uplink network-coded modulation for two-hop networks
With the fast growing number of wireless devices and demand of user data, the
backhaul load becomes a bottleneck in wireless networks. Physical layer network
coding (PNC) allows Access Points (APs) to relay compressed, network coded user
data, therefore reducing the backhaul traffic. In this paper, an implementation
of uplink Network Coded Modulation (NetCoM) with PNC is presented. A 5-node
prototype NetCoM system is established using Universal Software Radio
Peripherals (USRPs) and a practical PNC scheme designed for binary systems is
utilised. An orthogonal frequency division multiplexing (OFDM) waveform
implementation and the practical challenges (e.g. device synchronisation and
clock drift) of applying OFDM to NetCoM are discussed. To the best of our
knowledge this is the first PNC implementation in an uplink scenario in radio
access networks and our prototype provides an industrially-applicable
implementation of the proposed NetCoM with PNC approach
Radio Communications
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