1,722,478 research outputs found
OFDM turbo transceivers
No full textIn this thesis a variety of different techniques designed for the sake of improving the attainable efficiency of wireless system are considered in the context of Orthogonal Frequency Division Multiplexing (OFDM). More explicitly, powerful turbo transceivers invoking Sphere Packing (SP) modulation are designed using EXtrinsic Information Transfer (EXIT) charts for both single-user and multi-user transmission. In order to provide an attractive suite of single-user OFDM transceivers, we contrive a SP-aided OFDM scheme for maximizing the achievable coding advantage. The corresponding capacity equation shows that the SP-OFDM scheme exhibits a higher capacity than its counterpart dispensing with SP. Furthermore, a carefully designed Sphere Packing symbol To Sub-Carrier Mapping (SPTSCM) scheme is contrived, which results in an improved Discrete Input Continuous Output Memoryless Channel (DCMC) capacity. This is achieved by reducing the correlation between the multiple OFDM sub-carriers conveying a specific SP symbol. In order to enhance the attainable BER performance of the SP-OFDM scheme, iterative detection is invoked for exchanging extrinsic information between the SP symbol-to-bit demapper and the channel decoder. In contrast to the classic SP signal construction, sophisticated SP schemes are designed with the aid of EXIT charts for the sake of improving the convergence behaviour of the iteratively detected schemes. Explicitly, an approximately 0.15bit/s/Hz DCMC capacity improvement is achieved and the proposed iterative detection aided SP-OFDM scheme becomes capable of performing within 2.1dB of the maximum achievable rate limit obtained using EXITcharts at BER = 10-4. Some of the proposed advances are then extended to a multi-user Space Division MultipleAccess (SDMA) OFDM scheme. Novel turbo MUDs are designed and investigated in terms of their complexity, EXIT characteristics and BER performance. More explicitly, the linear turbo MUDs considered include the Complex-valued Minimum Mean Square Error (SIC-CMMSE) scheme, the Soft Interference Cancellation based Real-valued Minimum Mean Square Error (SIC-RMMSE) arrangement and the Soft Interference Cancellation based Minimum Bit-Error Rate (SIC-MBER) MUD schemes. The SIC-RMMSE is only applicable in the context of BPSK modulated schemes. A Reduced-complexity Minimum Bit-Error Rate (RMBER) is also designed for the sake of arriving at a complexity reduction by slightly compromising the attainable performance in comparison to the SIC-MBER MUD. Furthermore, a hybrid scheme was designed to eliminate the performance degradation imposed by the RMBER MUD. In contrast to above-mentioned linear schemes, Bayesian turbo MUD and the K-best iterative Sphere Decoder (SD) belong to the family of non-linear MUDs. Then a general complexity reduction technique was contrived in order to reduce the complexity imposed by the turboMUDs, which was referred to as the A-priori-LLR-Threshold (ALT) aided MUD algorithm, which was introduced for the sake of striking an attractive trade-off between the attainable complexity-reduction and the performance degradation imposed. Finally, the novel framework of Transmit Domain Processing based Detectors (TDPD) was contrived for a generalized multi-access or multiplexing based channel model in orderto circumvent the exponentially increasing complexity imposed by the Maximum Likelihood(ML) MUD as a function of both the number of antennas and the number of bits per symbol. Explicitly, the TDPD may be separated into three basic steps including the MUD’s Search Center (SC) calculation, detection candidate list generation and LLR output calculation. A range of different schemes were considered for each of the three steps, and the SIC-CMMSESC aided hybrid K-best subset combination based iterative TDPD was capable of achieving a similar BER performance to the optimal ML detector at a significantly reduced complexity
EXIT chart analysis aided turbo MUD designs for the rank-deficient multiple antenna assisted OFDM uplink
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Three-stage irregular convolutional coded iterative center-shifting K-best sphere detection for soft-decision SDMA-OFDM
No full textEXIT-charts-aided hybrid multiuser detector for multicarrier interleave-division multiple access
No full textA generically applicable hybrid multiuser detector (MUD) concept is proposed by appropriately activating different MUDs in consecutive turbo iterations based on the mutual information (MI) gain. It is demonstrated that the proposed hybrid MUD is capable of approaching the optimal Bayesian MUD's performance despite its reduced complexity, which is at a modestly increased complexity in comparison with that of the suboptimum soft interference cancellation (SoIC) MU
Enhancing Network Security through Software Defined Networking (SDN)
No full textSoftware Defined Networking (SDN) is an emerging technology that attracts significant attention from both industry and academia recently. By decoupling the control logic from the closed and proprietary implementations of traditional network devices, it enables researchers and practitioners to design new innovative network functions/protocols in a much more flexible, powerful, and easier way. We believe SDN provides new research opportunities to security, and it can greatly impact network security research in many different ways. However, till today, SDN has not been well recognized by the security community yet. In this systematic survey on SDN security, we investigate how the new features provided by SDN can help enhance network security and information security process. By systematically reasoning the opportunities introduced by SDN to network security, we hope to provide new insights for future research in this important area.
Index Terms—Software-Defined Networking, Network Securit
Generic iterative search-centre-shifting K-best sphere detection for rank-deficient SDM-OFDM systems
No full textA generic sphere-detection (SD) scheme is proposed, which substantially reduces the detection complexity by decomposing it into two stages, namely the generic iterative search-centre-update phase and the reduced-complexity search around it. This two-stage philosophy circumvents the high complexity of channel-coded soft-decision aided SDs
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