This paper proposes an iterative estimator for bit interleaved coded modulation (BICM) with an iterative soft-input soft-output (SISO) receiver over time-varying flat fading channels. More specifically, the system imp...
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This paper proposes an iterative estimator for bit interleaved coded modulation (BICM) with an iterative soft-input soft-output (SISO) receiver over time-varying flat fading channels. More specifically, the system implements signal space diversity (SSD) where the QAM symbols are rotated. The use of an iterative Kalman filter shows good results using superimposed training sequence and Gauss-Markov channel model for fast tracking of the channel variation. The proposed soft iterative estimator uses the soft extrinsic information from the decoder as well as the superimposed training sequence to update the channel coefficients for data detection. To analyze the results, an analytical bound for the asymptotic bit error rate (BER) for BICM-ID-SSD over correlated fading channels is computed with perfect channel state information (CSI).
In this work we design efficient soft output demodulators (also referred to as fast soft demodulators) for the 2 × 2 Golden code, which is a promising candidate space time block code in the evolving IEEE and 3GPP...
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In this work we design efficient soft output demodulators (also referred to as fast soft demodulators) for the 2 × 2 Golden code, which is a promising candidate space time block code in the evolving IEEE and 3GPP cellular standards. For this code, the naive approach for maximum likelihood (ML) hard decision as well as soft-output demodulation entails a complexity of O(M 4 ), where M denotes the cardinality of the QAM constellation from which the underlying modulated symbols are drawn. In contrast, our efficient demodulator exploits the structure of the code and yields the ML decision and soft outputs in the form of exact max-log log-likelihood ratios (LLRs) with an O(M 2.5 ) complexity. Moreover, we also design a sub-optimal soft output demodulator that has an O(M 0.5 ) complexity comparable to that of the linear minimum mean square error (LMMSE) based demodulator but results in substantial performance gains.
When code-division multiple access (CDMA) signals are linearly multiplexed (phase-coherently summed) at a transmit terminal, a receiver demodulating information from one component signal experiences multiple access in...
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When code-division multiple access (CDMA) signals are linearly multiplexed (phase-coherently summed) at a transmit terminal, a receiver demodulating information from one component signal experiences multiple access interference (MAI) from all others to the extent that the waveforms are not strictly orthogonal. Under a model for which: (1) the users are homogeneous, i.e., identical in those parameters that govern the amount of MAI they produce at a receiver, and (2) the various codes are random binary sequences, one may develop an expression for the amount of induced MAI as a function of the spread-spectrum chip delays and phases. It is not immediately obvious from this expression, however, what selection of delays and phases produces the most benign distribution of MAI among users. This paper presents an analytic characterization of MAI for linear multiplexing of a set of CDMA codes, culminating in a deterministic design of delays and phases that achieves MAI noise levels substantially smaller than those predicted by worst-case or random assignment results. It is believed that the design achieves the minimum MAI level, although it is not proved.
We propose specific modulation block codes for weakly-constrained coding and demonstrate that their performance is close to the theoretical limit. We also show that when such codes are used for the mitigation of patte...
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We propose specific modulation block codes for weakly-constrained coding and demonstrate that their performance is close to the theoretical limit. We also show that when such codes are used for the mitigation of patterning effects in optical fibre communications, a gain of about 1 dB is possible under realistic conditions, if only at the expense of small redundancy (¿ 10%).
Multi-carrier modulation (MCM) and especially orthogonal frequency division multiplexing (OFDM) are currently used in many radio transmission standards. Among these modulations, OFDM offset QAM (OFDM/OQAM) is an inter...
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Multi-carrier modulation (MCM) and especially orthogonal frequency division multiplexing (OFDM) are currently used in many radio transmission standards. Among these modulations, OFDM offset QAM (OFDM/OQAM) is an interesting alternative to OFDM. However, differently to OFDM, OFDM/OQAM modulation cannot directly use Alamouti coding scheme due to the remaining interference. In this paper, we propose a scheme which permits to adapt OFDM/OQAM to multiple-input multiple-output (MIMO) Alamouti system. The simulation results illustrate its efficiency.
Orthogonal modulations are powerful techniques for digital data transmission, very well suited to radio channels. They use orthogonal basis, whose elements will be the ldquosubcarriersrdquo used in transmission. Some ...
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Orthogonal modulations are powerful techniques for digital data transmission, very well suited to radio channels. They use orthogonal basis, whose elements will be the ldquosubcarriersrdquo used in transmission. Some advantages of the wavelet functions compared to the windowed complex exponentials used in orthogonal frequency division multiplexing (OFDM) are highlighted. Thus, theoretical proof that Daubechies wavelets have better time-frequency localization is provided, opening new paths towards modern orthogonal modulation approaches, based on wavelets.
Resource allocation (RA) is a crucial task in the operation of wireless communication systems, which in many cases aims at meeting the users' quality of service (QoS) requirements with the minimum amount of resour...
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Resource allocation (RA) is a crucial task in the operation of wireless communication systems, which in many cases aims at meeting the users' quality of service (QoS) requirements with the minimum amount of resources. In this work, we consider the QoS-provisioning RA problem at the downlink of a multicarrier system, where the total transmit power consumption is to be minimized. Two RA schemes, one employing Lagrange dual methods and a greedy primal recovery scheme, and the other heuristic with a three-step approach, are proposed under the same cross-layer framework, where power allocation, adaptive modulation and coding as well as retransmission protocols are jointly modeled. Though both suboptimal, the two schemes are advantageous for their low complexity and small amount of online computations required. Their performances are illustrated and compared based on simulation results. The work also provides a quantitative comparison on the two commonly used retransmission protocols, namely automatic repeat request (ARQ) and hybrid automatic repeat request (HARQ).
Since the maximum likelihood (ML) decoding results too complex when the modulation order and the number of receive antennas increase, an efficient reduced complexity ML-based decoding scheme applied to a multiple-inpu...
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Since the maximum likelihood (ML) decoding results too complex when the modulation order and the number of receive antennas increase, an efficient reduced complexity ML-based decoding scheme applied to a multiple-input-multiple-output (MIMO) antenna systems with quasi-orthogonal space-time block code (QO-STBC) is proposed, and named reduced cluster search ML decoding (RCS-ML). Its performance and complexity aspects are compared to the conventional ML decoding approach. High-order modulation indexes and short low density parity check codes (LDPC) are considered. Numerical results have indicated no degradation in the performance and an increasing reduction in the complexity of RCS-ML decoding with respect to the conventional ML when the modulation order increases.
Multicarrier modulations such as orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC-CDMA) have been widely developed for wideband cellular communications. MC-CDMA modu...
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Multicarrier modulations such as orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC-CDMA) have been widely developed for wideband cellular communications. MC-CDMA modulation scheme benefits from the advantages of both MC and CDMA techniques: high spectral efficiency, robustness in frequency selective channels with a low-complexity at receiver considering simple one-tap equalization and multiple access capability with high flexibility. In this paper, we propose a simple and efficient receiver design for frame based MC-CDMA in multipath Nakagami-m fading channels which have been found to be a very good fitting for the mobile radio channel. We also illustrate the performance of the proposed model for different values of fading parameter m, different modulation schemes (4, 16 and 64 QAM) and different number of users.
In this paper issues in the implementation of a recursive least squares (RLS) multiple-input multiple-output (MIMO) decision-directed channel estimation (DDCE) and tracking algorithm for spatial multiplexing are discu...
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In this paper issues in the implementation of a recursive least squares (RLS) multiple-input multiple-output (MIMO) decision-directed channel estimation (DDCE) and tracking algorithm for spatial multiplexing are discussed. Problems addressed are a simple calculation of the inverse autocorrelation matrix and schemes of training data or pilot symbols. While there is much work spend in evaluating pilot performances, the choice of pilot symbols cannot be decided based only on simulations. Three proposed schemes are discussed regarding off-the-shelf RF components' compatibility of an experimental MIMO system where polyphase pilots fail to yield good results. Because decision-directed channel estimation is prone to error propagation, we propose a scheme which makes a check on recovered symbol plausability by using the result from the channel decoder thus preventing error propagation.
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