9,525 research outputs found
Data mixing at the source, relay, and in the air in multiple-access relay networks
The concept of cooperative relay is an essential technique for future cellular networks such as wireless mesh networking or wireless ad-hoc networking. In a practical relay network, channel coding, network coding, and antenna arrays, will coexist and yet the joint optimization of these conventional coding schemes and cooperative relay is not well understood. To build a design guideline for relay network, this dissertation develop a joint optimization methodology for multiple coding schemes in multiple access relay network.
There are four major contributions in this thesis: First, we jointly optimize conventional coding schemes and radio resources of multiple access relay network with multiple antennas. The combined design of MIMO transmission modes, channel coding at the source, network coding at the relay have been investigated. We develop optimal design rule that minimize the end-to-end error probability. Second, we derive the fundamental tradeoff between achievable rate and reliability of multiple access relay network with multiple antennas. We consider three MIMO transmission modes, spatial multiplexing (SM), Alamouti coding as transmit diversity (TD), and Golden Coding, and random linear network coding at the relay. We compare the average decoding error probability of each transmission mode. Third, we present an interference cancellation scheme for multi-user MIMO. The proposed Log-likelihood-ratio (LLR) ordered successive interference cancellation (SIC) scheme provides 1 ~ 3 dB gain over the conventional SNR-ordered SIC and the gain increases with increasing number of users. Finally, we present a new architecture for MIMO receivers that cancel the co-channel interference (CCI) using a single radio frequency (RF) and baseband (BB) chain, while still achieving nearly the same bit error rate that can be provided by the conventional receiver requiring multiple RF/BB chains
Space-Time Coded Spatial Modulated Physical Layer Network Coding for Two-Way Relaying
Using the spatial modulation approach, where only one transmit antenna is
active at a time, we propose two transmission schemes for two-way relay channel
using physical layer network coding with space time coding using Coordinate
Interleaved Orthogonal Designs (CIOD's). It is shown that using two
uncorrelated transmit antennas at the nodes, but using only one RF transmit
chain and space-time coding across these antennas can give a better performance
without using any extra resources and without increasing the hardware
implementation cost and complexity. In the first transmission scheme, two
antennas are used only at the relay, Adaptive Network Coding (ANC) is employed
at the relay and the relay transmits a CIOD Space Time Block Code (STBC). This
gives a better performance compared to an existing ANC scheme for two-way relay
channel which uses one antenna each at all the three nodes. It is shown that
for this scheme at high SNR the average end-to-end symbol error probability
(SEP) is upper bounded by twice the SEP of a point-to-point fading channel. In
the second transmission scheme, two transmit antennas are used at all the three
nodes, CIOD STBC's are transmitted in multiple access and broadcast phases.
This scheme provides a diversity order of two for the average end-to-end SEP
with an increased decoding complexity of for an arbitrary
signal set and for square QAM signal set.Comment: 9 pages, 7 figure
Interference suppression with physical-layer network coding and MIMO for multi-way channels
Orthogonal techniques (such as TDMA – time division multiple access) are traditionally used when a set of terminals wants to exchange data and a relay is required when wireless terminals cannot communicate directly. This paper proposes two schemes to address multi-way channels when a set of terminals wants to exchange data. Both proposed schemes consist of a first phase based on virtual MIMO with lattice reduction-aided (LRA) detection at the relay, establishing a multiple access channel (MAC). Two new strategies are then proposed for the second (multicast) phase; one for single antenna terminals and another for multiple-input multiple-output (MIMO) terminals. The second strategy achieves interference suppression by successively combining physical layer network coding and MIMO detection (with LRA detectors also at the terminals). The paper assesses a 3 terminals network with a relay for which a TDMA-based scheme would require 6 time-slots, while the proposed strategy for MIMO terminals is able to exchange the information between all terminals using 2 time-slots only. This latter scheme is easily scalable to a higher number of terminals, and always able to accomplish the exchange of messages between all of them in just 2 time-slots, although limited by the number of antennas that the terminals can fit and also the MIMO processing complexity they can afford.info:eu-repo/semantics/acceptedVersio
User-Antenna Selection for Physical-Layer Network Coding based on Euclidean Distance
In this paper, we present the error performance analysis of a multiple-input
multiple-output (MIMO) physical-layer network coding (PNC) system with two
different user-antenna selection (AS) schemes in asymmetric channel conditions.
For the first antenna selection scheme (AS1), where the user-antenna is
selected in order to maximize the overall channel gain between the user and the
relay, we give an explicit analytical proof that for binary modulations, the
system achieves full diversity order of in the
multiple-access (MA) phase, where , and denote the number of
antennas at user , user and relay respectively. We present a
detailed investigation of the diversity order for the MIMO-PNC system with AS1
in the MA phase for any modulation order. A tight closed-form upper bound on
the average SER is also derived for the special case when , which is
valid for any modulation order. We show that in this case the system fails to
achieve transmit diversity in the MA phase, as the system diversity order drops
to irrespective of the number of transmit antennas at the user nodes.
Additionally, we propose a Euclidean distance (ED) based user-antenna selection
scheme (AS2) which outperforms the first scheme in terms of error performance.
Moreover, by deriving upper and lower bounds on the diversity order for the
MIMO-PNC system with AS2, we show that this system enjoys both transmit and
receive diversity, achieving full diversity order of in the MA phase for any modulation order. Monte Carlo simulations are
provided which confirm the correctness of the derived analytical results.Comment: IEEE Transactions on Communications. arXiv admin note: text overlap
with arXiv:1709.0445
Cooperative diversity in CDMA networks
Spatial diversity is one of the well known diversity methods used in combating fading channels. Recently, cooperative diversity has been widely studied in literature as a spatial diversity technique. Different from multiple-input multiple-output (MIMO) systems, each user in the cooperative network is employed with a single transmit/receive antenna. In this thesis, we propose a cooperative diversity technique for asynchronous direct sequence code division multiple access (D8-CDMA) over frequency selective slow fading environment. First we assume the single cooperation relay case, where the bit-error-rate performance of the system is studied for both cases of perfect and imperfect inter-user channel (user-relay link). In order to mitigate the multi-access interference (MAI), decorrelator multiuser detectors are introduced at both relay and base station sides. Its effect on performance is studied and compared to the performance of the conventional matched filter receiver. Additionally, the performance of the system is studied and compared for different multi-path diversity scenarios in the inter-user and uplink channel. Furthermore, a coded multi-relay cooperation technique is proposed, where channel coding is introduced to minimize errors over the inter-user channel. All users are embedded with convolutional encoder and a Viterbi decoder. We study the performance of the coded system for different number of cooperating relays and over different multi-path diversity scenarios. Both simulation and analytical results are compared. Finally, we conclude that for a communication network to benefit from the cooperation diversity technique, a reliable communication link between active users and the cooperating relays should be secured (inter-user channel). We show that for an active user cooperating with V relays over a P -path frequency-selective fading channel, the expected diversity degree is P ( V +1
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Weak Secrecy in the Multi-Way Untrusted Relay Channel with Compute-and-Forward
We investigate the problem of secure communications in a Gaussian multi-way
relay channel applying the compute-and-forward scheme using nested lattice
codes. All nodes employ half-duplex operation and can exchange confidential
messages only via an untrusted relay. The relay is assumed to be honest but
curious, i.e., an eavesdropper that conforms to the system rules and applies
the intended relaying scheme. We start with the general case of the
single-input multiple-output (SIMO) L-user multi-way relay channel and provide
an achievable secrecy rate region under a weak secrecy criterion. We show that
the securely achievable sum rate is equivalent to the difference between the
computation rate and the multiple access channel (MAC) capacity. Particularly,
we show that all nodes must encode their messages such that the common
computation rate tuple falls outside the MAC capacity region of the relay. We
provide results for the single-input single-output (SISO) and the
multiple-input single-input (MISO) L-user multi-way relay channel as well as
the two-way relay channel. We discuss these results and show the dependency
between channel realization and achievable secrecy rate. We further compare our
result to available results in the literature for different schemes and show
that the proposed scheme operates close to the compute-and-forward rate without
secrecy.Comment: submitted to JSAC Special Issue on Fundamental Approaches to Network
Coding in Wireless Communication System
Multi-Antenna Cooperative Wireless Systems: A Diversity-Multiplexing Tradeoff Perspective
We consider a general multiple antenna network with multiple sources,
multiple destinations and multiple relays in terms of the
diversity-multiplexing tradeoff (DMT). We examine several subcases of this most
general problem taking into account the processing capability of the relays
(half-duplex or full-duplex), and the network geometry (clustered or
non-clustered). We first study the multiple antenna relay channel with a
full-duplex relay to understand the effect of increased degrees of freedom in
the direct link. We find DMT upper bounds and investigate the achievable
performance of decode-and-forward (DF), and compress-and-forward (CF)
protocols. Our results suggest that while DF is DMT optimal when all terminals
have one antenna each, it may not maintain its good performance when the
degrees of freedom in the direct link is increased, whereas CF continues to
perform optimally. We also study the multiple antenna relay channel with a
half-duplex relay. We show that the half-duplex DMT behavior can significantly
be different from the full-duplex case. We find that CF is DMT optimal for
half-duplex relaying as well, and is the first protocol known to achieve the
half-duplex relay DMT. We next study the multiple-access relay channel (MARC)
DMT. Finally, we investigate a system with a single source-destination pair and
multiple relays, each node with a single antenna, and show that even under the
idealistic assumption of full-duplex relays and a clustered network, this
virtual multi-input multi-output (MIMO) system can never fully mimic a real
MIMO DMT. For cooperative systems with multiple sources and multiple
destinations the same limitation remains to be in effect.Comment: version 1: 58 pages, 15 figures, Submitted to IEEE Transactions on
Information Theory, version 2: Final version, to appear IEEE IT, title
changed, extra figures adde
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