407 research outputs found
Network coded modulation for two-way relaying
Network coding compresses multiple traffic flows with the aid low-complexity algebraic operations, hence holds the potential of significantly improving both the power and bandwidth efficiency of wireless networks. In this contribution, the novel concept of Network Coded Modulation (NCM) is proposed for jointly performing network coding and modulation in bi-directional/duplex relaying. Each receiver is colocated with a transmitter and hence has prior knowledge of the message intended for the distant receiver. As in classic coded modulation, the Euclidian distance between the symbols is maximized, hence the Symbol Error Ratio (SER) is minimized. Specifically, we conceive NCM methods for PSK, PAM and QAM based on modulo addition of the normalized phase or amplitude. Furthermore, we propose low complexity decoding algorithms based on the corresponding conditional minimum distance criteria. Our performance analysis and simulations demonstrate that NCM relying on PSK is capable of achieving a SER at both receivers of the NCM scheme as if the relay transmitted exclusively to a single receiver only. By contrast, when our NCM concept is combined with PAM/QAM, an SNR loss (<1.25dB) is imposed at one of the receivers, usually at the one having a lower data rate in a realistic different rate scenario. Finally, we will demonstrate that the proposed NCM is compatible with existing physical layer designs
Achieving full diversity in multi-antenna two-way relay networks via symbol-based physical-layer network coding
This paper considers physical-layer network coding (PNC) with M-ary phase-shift keying (MPSK) modulation in two-way relay channel (TWRC). A low complexity detection technique, termed symbol-based PNC (SPNC), is proposed for the relay. In particular, attributing to the outer product operation imposed on the superposed MPSK signals at the relay, SPNC obtains the network-coded symbol (NCS) straightforwardly without having to detect individual symbols separately. Unlike the optimal multi-user detector (MUD) which searches over the combinations of all users’ modulation constellations, SPNC searches over only one modulation constellation, thus simplifies the NCS detection. Despite the reduced complexity, SPNC achieves full diversity in multi-antenna relay as the optimal MUD does. Specifically, antenna selection based SPNC (AS-SPNC) scheme and signal combining based SPNC (SC-SPNC) scheme are proposed. Our analysis of these two schemes not only confirms their full diversity performance, but also implies when SPNC is applied in multi-antenna relay, TWRC can be viewed as an effective single-input multiple-output (SIMO) system, in which AS-PNC and SC-PNC are equivalent to the general AS scheme and the maximal-ratio combining (MRC) scheme. Moreover, an asymptotic analysis of symbol error rate (SER) is provided for SC-PNC considering the case that the number of relay antennas is sufficiently large
Performance Analysis of Adaptive Physical Layer Network Coding for Wireless Two-way Relaying
The analysis of modulation schemes for the physical layer network-coded two
way relaying scenario is presented which employs two phases: Multiple access
(MA) phase and Broadcast (BC) phase. It was shown by Koike-Akino et. al. that
adaptively changing the network coding map used at the relay according to the
channel conditions greatly reduces the impact of multiple access interference
which occurs at the relay during the MA phase. Depending on the signal set used
at the end nodes, deep fades occur for a finite number of channel fade states
referred as the singular fade states. The singular fade states fall into the
following two classes: The ones which are caused due to channel outage and
whose harmful effect cannot be mitigated by adaptive network coding are
referred as the \textit{non-removable singular fade states}. The ones which
occur due to the choice of the signal set and whose harmful effects can be
removed by a proper choice of the adaptive network coding map are referred as
the \textit{removable} singular fade states. In this paper, we derive an upper
bound on the average end-to-end Symbol Error Rate (SER), with and without
adaptive network coding at the relay, for a Rician fading scenario. It is shown
that without adaptive network coding, at high Signal to Noise Ratio (SNR), the
contribution to the end-to-end SER comes from the following error events which
fall as : the error events associated with the removable
singular fade states, the error events associated with the non-removable
singular fade states and the error event during the BC phase. In contrast, for
the adaptive network coding scheme, the error events associated with the
removable singular fade states contributing to the average end-to-end SER fall
as and as a result the adaptive network coding scheme
provides a coding gain over the case when adaptive network coding is not used.Comment: 10 pages, 5 figure
Relay Selection for Two-way Relaying with Amplify-and-Forward Protocols
In this paper, we propose a relay selection amplify-and-forward (RS-AF)
protocol in general bi-directional relay networks with two sources and
relays. In the proposed scheme, the two sources first transmit to all the
relays simultaneously, and then a single relay with a minimum sum symbol error
rate (SER) will be selected to broadcast the received signals back to both
sources. To facilitate the selection process, we propose a simple sub-optimal
Min-Max criterion for relay selection, where a single relay which minimizes the
maximum SER of two source nodes will be selected. Simulation results show that
the proposed Min-Max selection has almost the same performance as the optimal
selection with lower complexity. We also present a simple asymptotic SER
expression and make comparison with the conventional all-participate
amplify-and-forward (AP-AF) relaying scheme. The analytical results are
verified through simulations. To improve the system performance, optimum power
allocation (OPA) between the sources and the relay is determined based on the
asymptotic SER. Simulation results indicate that the proposed RS-AF scheme with
OPA yields considerable performance improvement over an equal power allocation
(EPA) scheme, specially with large number of relay nodes.Comment: 19 pages, 6 figure
Self-concatenated coding for wireless communication systems
In this thesis, we have explored self-concatenated coding schemes that are designed for transmission over Additive White Gaussian Noise (AWGN) and uncorrelated Rayleigh fading channels. We designed both the symbol-based Self-ConcatenatedCodes considered using Trellis Coded Modulation (SECTCM) and bit-based Self- Concatenated Convolutional Codes (SECCC) using a Recursive Systematic Convolutional (RSC) encoder as constituent codes, respectively. The design of these codes was carried out with the aid of Extrinsic Information Transfer (EXIT) charts. The EXIT chart based design has been found an efficient tool in finding the decoding convergence threshold of the constituent codes. Additionally, in order to recover the information loss imposed by employing binary rather than non-binary schemes, a soft decision demapper was introduced in order to exchange extrinsic information withthe SECCC decoder. To analyse this information exchange 3D-EXIT chart analysis was invoked for visualizing the extrinsic information exchange between the proposed Iteratively Decoding aided SECCC and soft-decision demapper (SECCC-ID). Some of the proposed SECTCM, SECCC and SECCC-ID schemes perform within about 1 dB from the AWGN and Rayleigh fading channels’ capacity. A union bound analysis of SECCC codes was carried out to find the corresponding Bit Error Ratio (BER) floors. The union bound of SECCCs was derived for communications over both AWGN and uncorrelated Rayleigh fading channels, based on a novel interleaver concept.Application of SECCCs in both UltraWideBand (UWB) and state-of-the-art video-telephone schemes demonstrated its practical benefits.In order to further exploit the benefits of the low complexity design offered by SECCCs we explored their application in a distributed coding scheme designed for cooperative communications, where iterative detection is employed by exchanging extrinsic information between the decoders of SECCC and RSC at the destination. In the first transmission period of cooperation, the relay receives the potentially erroneous data and attempts to recover the information. The recovered information is then re-encoded at the relay using an RSC encoder. In the second transmission period this information is then retransmitted to the destination. The resultant symbols transmitted from the source and relay nodes can be viewed as the coded symbols of a three-component parallel-concatenated encoder. At the destination a Distributed Binary Self-Concatenated Coding scheme using Iterative Decoding (DSECCC-ID) was employed, where the two decoders (SECCC and RSC) exchange their extrinsic information. It was shown that the DSECCC-ID is a low-complexity scheme, yet capable of approaching the Discrete-input Continuous-output Memoryless Channels’s (DCMC) capacity.Finally, we considered coding schemes designed for two nodes communicating with each other with the aid of a relay node, where the relay receives information from the two nodes in the first transmission period. At the relay node we combine a powerful Superposition Coding (SPC) scheme with SECCC. It is assumed that decoding errors may be encountered at the relay node. The relay node then broadcasts this information in the second transmission period after re-encoding it, again, using a SECCC encoder. At the destination, the amalgamated block of Successive Interference Cancellation (SIC) scheme combined with SECCC then detects and decodes the signal either with or without the aid of a priori information. Our simulation results demonstrate that the proposed scheme is capable of reliably operating at a low BER for transmission over both AWGN and uncorrelated Rayleigh fading channels. We compare the proposed scheme’s performance to a direct transmission link between the two sources having the same throughput
JOINT NETWORK-CHANNEL CODING WITH C-MRC BASED DEMODULATE AND FORWARD PROTOCOL IN TWO-WAY RELAY CHANNELS
Sayısal aktarma tabanlı işbirlikli telsiz ağlarının sistem karmaşıklığını ve enerji sarfiyatını azaltmak için yapılan araştırma faaliyetleri rölenin aldığı işaretlerde kod çözme yerine kipleme çözme yaptığı kipleme çöz ve ilet tasarımını ortaya çıkarmıştır. Öte yandan işbirlikli en yüksek oranlı birleştirme (İEYOB), iletim verimini düşüren çevrimsel artıklık denetimi (ÇAD) kodlardan faydalanmaksızın sayısal aktarmada hata yayılımı ile mücadele etmede kullanılan yüksek performanslı düşük karmaşıklıklı önemli bir başka tekniktir. Bu çalışmada iki kullanıcının bir röle aracılığı ile veri alışverişi yaptığı iki yönlü röle kanalları için İEYOB tabanlı kipleme çöz ve ilet protokolünü önerilmektedir. İletim süresi, birinci ve ikinci fazların kullanıcıların kodlamasız veya konvolüsyonel kodlamalı verilerinin iletimine tahsis edildiği zamanda üç faza ayrılmıştır. Röle, demodülasyondan sonra bit düzeyinde XOR‟lanmış paketi üçüncü fazda kullanıcılara iletmektedir. Rayleigh sönümlemeli kanallardaki sayısal sonuçlar önerilen yaklaşımın tam çeşitleme seviyesi sağladığını göstermektedir. Research activities to reduce the system complexity and energy consumption of digital relaying based cooperative wireless networks have yielded the demodulate-forward scheme where the relay performs demodulation, instead of decoding, on the received signals. On the other hand, cooperative maximal ratio combining (C-MRC) is another high-performance low-complexity technique used to combat error propagation in digital relaying without exploiting CRC codes which decreases the transmission efficiency. In this study, we propose a C-MRC based demodulate and forward protocol for two-way relay channels where two users exchange information via a relay. The transmission is divided into three phases in time where the first and second phases are allocated to the transmissions of uncoded or convolutionally encoded data of the users. After demodulation, the relay broadcasts the bit-wise XOR-ed packet to the users in the third phase. The numerical results for Rayleigh fading show that the proposed approach provides full diversity gain
Self-interference cancellation for full-duplex MIMO transceivers
PhD ThesisIn recent years, there has been enormous interest in utilizing the full-duplex
(FD) technique with multiple-input multiple-output (MIMO) systems to complement
the evolution of fifth generation technologies. Transmission and reception
using FD-MIMO occur simultaneously over the same frequency band
and multiple antennas are employed in both sides. The motivation for employing
FD-MIMO is the rapidly increasing demand on frequency resources,
and also FD has the ability to improve spectral efficiency and channel capacity
by a factor of two compared to the conventional half-duplex technique.
Additionally, MIMO can enhance the diversity gain and enable FD to acquire
further degrees of freedom in mitigating the self-interference (SI). The
latter is one of the key challenges degrading the performance of systems operating
in FD mode due to local transmission which involves larger power
level than the signals of interest coming from distance sources that are significantly
more attenuated due to path loss propagation phenomena. Various
approaches can be used for self-interference cancellation (SIC) to tackle SI
by combining passive suppression with the analogue and digital cancellation
techniques. Moreover, active SIC techniques using special domain suppression
based on zero-forcing and null-space projection (NSP) can be exploited
for this purpose too. The main contributions of this thesis can be summarized
as follows. Maximum-ratio combining with NSP are jointly exploited in order
to increase the signal-to-noise ratio (SNR) of the desired path and mitigate
the undesired loop path, respectively, for an equalize-and-forward (EF) relay
using FD-MIMO. Additionally, an end-to-end performance analysis of the
proposed system is obtained in the presence of imperfect channel state information
by formulating mathematically the exact closed-form solutions for
the signal-to-interference-plus-noise ratio (SINR) distribution, outage probability,
and average symbol-error rate for uncoded M-ary phase-shift keying
over Rayleigh fading channels and in the presence of additive white Gaussian
noise (AWGN). The coefficients of the EF-relay are designed to attain
the minimum mean-square error (MMSE) between the transmission symbols.
Comparison of the results obtained with relevant state-of-the-art techniques
suggests significant improvements in the SINR figures and system capacity.
Furthermore, iterative detection and decoding (IDD) are proposed to mitigate
the residual self-interference (SI) remaining after applying passive suppression
along with two stages of SI cancellation (SIC) filters in the analogue
and digital domains for coded FD bi-directional transceiver based multiple
antennas. IDD comprises an adaptive MMSE filter with log-likelihood ratio
demapping, while the soft-in soft-out decoder utilizes the maximum a posteriori
(MAP) algorithm. The proposed system’s performance is evaluated in
the presence of AWGN over non-selective (flat) Rayleigh fading single-input
multiple-output (SIMO) and MIMO channels. However, the results of the
analyses can be applied to multi-path channels if orthogonal frequency division
multiplexing is utilised with a proper length of cyclic prefix in order to
tackle the channels’ frequency-selectivity and delay spread. Simulation results
are presented to demonstrate the bit-error rate (BER) performance as a
function of the SNR, revealing a close match to the SI-free case for the proposed
system. Furthermore, the results are validated by deriving a tight upper
bound on the performance of rate-1=2 convolutional codes for FD-SIMO and
FD-MIMO systems for different modulation schemes under the same conditions,
which asymptotically exhibits close agreement with the simulated BER
performance.Ministry of Higher Education and Scientific Research
(MoHESR), and the University of Mosul and to the Iraqi Cultural Attache in
London for providing financial support for my PhD scholarship
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