1,721,644 research outputs found
Exit Chart Aided Irregular Convolutional Code Design for Iterative Downlink SDMA Systems using Imperfect Channel State Information
Full text linkWe analyze a precoded and iteratively detected downlink multiuser system employing imperfect Spatio-Temporal Channel Impulse Response at the Transmitters (ST-CIRT) with the aid of Extrinsic Information Transfer (EXIT) charts. A Precoded Iterative DownLink Space Division Multiple Access (PI-DLSDMA) system proposed in our previous research is further improved and shown to be capable of maintaining an infinitesimally low BER, despite using imperfect ST-CIRT. A further novel feature of the PI-DL-SDMA system is that we design an IrRegular Convolutional Code (IRCC) with the aid of EXIT chart analysis for creating an open EXIT tunnel between the inner decoder’s and outer decoder’s EXIT curve at a reduced Eb/N0 value and hence maintain an infinitesimally low BER. Index Terms— SDMA, downlink, iterative, EXIT char
Spatial modulation and space-time shift keying: optimal performance at a reduced detection complexity
Full text linkAbstract—In this paper, we propose a comprehensive reduced-complexity detector both for hard-decision-aided as well as for the soft-decision-assisted Spatial Modulation (SM)/Space-Time Shift Keying (STSK). More explicitly, the detection of the SM scheme, which activates a single one out of M antennas to transmit a single LPSK/QAM symbol, may be carried out by detecting the antenna activation index m and the LPSK/QAM symbol sl separately, so that the detection complexity may be reduced from the order of O(M · L) to the lower bound of O(M + log2 L). However, the QAM aided STSK hard detection proposed in [1] results in a performance loss. Furthermore, the Max-Log-MAP algorithm proposed for soft STSK detection in [2] only takes into account the maximum a posteriori probabilities, which also imposed a performance degradation. Therefore, in this paper, we propose a novel solution for hard-decision-aided SM/STSK detection, which retains its optimal performance, despite its reduced detection complexity, when either LPSK or LQAM is employed. Furthermore, we propose the reduced-complexity Approx-Log-MAP algorithm conceived for the soft-decision-aided SM/STSK detector, in order to replace the sub-optimal Max-Log-MAP algorithm
Maximum bandwidth broadcast in single and multi-interface networks
No full textA maximum bandwidth broadcast problem in multi-interface
networks is considered, where each transmission, simultaneously
serving a group of nodes, achieves a total bandwidth
equal to the product between the smallest node bandwidth
in the group and the cardinality of the group. Two variants
of the problem are studied, called the K-Maximum
Bandwidth Broadcast in Single-Interface Networks (MBB)
and K-Maximum Bandwidth Broadcast in Multiple-Interface
Networks (MBBM) problems. It is shown that the former
problem can be optimally solved in polynomial time, while
the latter one is computationally intractable (i.e. NP-hard).
Polynomial time algorithms are devised for optimally solving
some particular cases of MBBM where a common order
holds and the number of used interfaces is polylogarithmic
in the number of nodes
The Probability of Multiple Correct Packet Reception in Coded Synchronous Frequency-Hopped Spread-Spectrum Networks
No full textIn this paper we present a computationally efficient method of evaluating the probability of multiple correct packet reception in coded synchronous frequency-hopped spread-spectrum (FHSS) networks. We show that the approximation using the independent receiver operation assumption (IROA), which has been frequently employed in the literature without rigorous validation, produces reasonable results in most network load conditions when compared to the exact computations derived from our proposed method. Specifically, the expected value of the absolute error was in the range of 0.0055%–18.21% in the investigated scenarios
On the Computation of 16-QAM and 64-QAM Performance in Rayleigh-Fading Channels
No full textSUMMARY Quadrature Amplitude Modulation (QAM) schemes are attractive in terms of bandwidth efficiency and offer a number of subchannels with different integrities via both Gaussian and Rayleigh-fading channels, Specifically, the 16-QAM phasor constellation has two, while the 64-QAM possesses three such subchannels, which become dramatically different via Rayleigh-fading channels. The analytically derived bit error rate (BER) formulae yield virtually identical curves with simulation results, exhibiting adequate BERs for the highest integrity subchannels of both 16-QAM and 64-QAM to be further reduced by forward error correction coding (FEC). However, the BERs of the lower integrity subchannels require fading compensation to reduce their values for FEC techniques to become effective. This property creates ground for a variety of carefully matched, embedded mobile transmission schemes of different complexities. The practical implementation of such an embedded scheme is demonstrated by a low-cost, low-complexity and low consumption 50 kBd mobile video telephone scheme offering adequate speech and image quality for channel SNRs in excess of about 20 dB via Rayleigh-fading channels. key words: QAM theory; modulation for microcellular fading channels
Social sharing of connectivity resources: control and encouragement of unselfishness in mobile environments
No full textIn the last years has clearly emerged the opportunity of extending traditional single-hop wireless technologies for Internet connectivity, by introducing practical effective solutions to dynamically use the best multi-hop heterogeneous paths available at runtime. Our primary idea is to enable, via proper, context-aware, and effective middleware, the mass of mobile devices already in the market to collaborate together toward innovative forms of Multi-hop Multi-path Heterogeneous Connectivity. Potential advantages are multiple, from extended wireless coverage to "green" cost reduction via cooperative sharing, from balancing energy consumption of collaborative nodes to maximizing overall bandwidth. In particular, this work-in-progress paper originally concentrates on the challenging issue of promoting connectivity sharing via effective forms of network management and control, capable of i) monitoring the selfish/collaborative behaviors of participants in a very lightweight way, ii) fairly distributing relay duties in order not to penalize too much "generous" nodes, and iii) rewarding cooperativeness by limiting the consumption of shared resources and by privileging unselfish participants. To that purpose, the paper presents original solution guidelines based on the regional fairness principle to achieve effectiveness and limited overhead; they can relevantly contribute to encourage connectivity sharing in open and dynamic deployment environments
Mobile Ad Hoc Networks: Challenges and Solutions for Providing Quality of Service Assurances
No full textMobile Ad Hoc Networks: Challenges and Solutions for Providing Quality of Service Assurances Lajos Hanzo (II.)1 and Rahim Tafazolli University of Surrey, ..
Mobile Ad Hoc Networks: Challenges and Solutions for Providing Quality of Service Assurances
No full textMobile Ad Hoc Networks: Challenges and Solutions for Providing Quality of Service Assurances Lajos Hanzo (II.)1 and Rahim Tafazolli University of Surrey, ..
Three-stage turbo MBER Multiuser beamforming receiver using irregular convolutional codes
No full textBased on extrinsic information transfer (EXIT) charts, the convergence behavior of a three-stage serially concatenated multiuser beamforming receiver is presented. This system uses a linear minimum bit error rate (BER) multiuser detector as the inner module. Due to the nonrecursive nature of this inner module, a unity-rate memory-1 recursive precoder is placed in front of the channel to provide the required recursive structure. Irregular convolutional codes (IRCCs) are constructed to be used as the outer code to achieve near-capacity performance. Our simulations show that this system outperforms the traditional two-component iterative structure and is capable of significantly educing the error floor
Partial Equalization for MC–CDMA Systems in Non-Ideally Estimated Correlated Fading
No full textMulticarrier code-division multiple access (MC–CDMA) can support high data rates in next-generation multiuser wireless communication systems. Partial equalization (PE) is a low-complexity technique for combining the signals of subcarriers to improve the achievable performance of MC–CDMA systems in terms of their bit error probability (BEP) and bit error outage (BEO) in comparison with maximal ratio combining, orthogonality restoring combining, and equal-gain combining techniques. We analyze the performance of the multiuser MC–CDMA downlink and derive the optimal PE parameter expression, which minimizes the BEP. Realistic imperfect channel estimation and frequency-domain (FD) block-fading channels are considered. More explicitly, the analytical expression of the optimum PE parameter is derived as a function of the number of subcarriers, number of active users (i.e., the system load), mean signal-to-noise ratio (SNR), and variance of the channel-estimation errors for the aforementioned FD block-fading channel. We show that the choice of the optimal PE technique significantly increases the achievable system load for the given target BEP and BEO
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