Perfect Channel Research Articles

Turbo Processing for Joint Channel Estimation, Synchronization, and Decoding in Coded MIMO-OFDM Systems

This paper proposes a turbo joint channel estimation, synchronization, and decoding scheme for coded multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The effects of carrier frequency offset (CFO), sampling frequency offset (SFO), and channel impulse responses (CIRs) on the received samples are analyzed and explored to develop the turbo decoding process and vector recursive least squares (RLSs) algorithm for joint CIR, CFO, and SFO tracking. For burst transmission, with initial estimates derived from the preamble, the proposed scheme can operate without the need of pilot tones during the data segment. Simulation results show that the proposed turbo joint channel estimation, synchronization, and decoding scheme offers fast convergence and low mean squared error (MSE) performance over quasistatic Rayleigh multipath fading channels. The proposed scheme can be used in a coded MIMO-OFDM transceiver in the presence of multipath fading, carrier frequency offset, and sampling frequency offset to provide a bit error rate (BER) performance comparable to that in an ideal case of perfect synchronization and channel estimation over a wide range of SFO values.

Supporting Asymmetric Traffic in a TDD/CDMA Cellular Network via Interference-Aware Dynamic Channel Allocation and Space–Time LMMSE Joint Detection

In a time-division duplexing (TDD)/code-division multiple-access (CDMA) cellular network with asymmetric data traffic, dynamic channel allocation (DCA) enhances resource utilization compared with fixed channel allocation (FCA). However, it also induces base-to-base and mobile-to-mobile crossed-slot intercell interference, which can severely degrade system performance. To deal with this problem, a decentralized scheme is proposed, which combines an interference-aware DCA algorithm with space-time linear minimum-mean-square-error (LMMSE) joint detection at the base and mobile stations. The former assigns active links to timeslots in a way that crossed-slot interference is mitigated, while the latter suppresses the remaining intercell interference (along with intersymbol and intracell interference), exploiting its spatio-temporal autocorrelation statistics. The performance of this scheme is evaluated in terms of downlink and uplink signal-to-interference-plus-noise ratio (SINR) outage and average throughput via analytical approximations and Monte Carlo simulations, and it is compared with that of benchmark random DCA (RDCA) and FCA schemes. The cases of single- and dual-antenna reception with perfect and imperfect channel state information are examined. It is shown that the proposed scheme achieves higher average throughput than FCA (particularly for dual-antenna reception) as well as RDCA (for heavy traffic loads). These throughput gains are more significant in uplink than in downlink.

Joint Stream-Wise THP Transceiver Design for the Multiuser MIMO Downlink

This paper addresses the problem of joint transceiver design for Tomlinson-Harashima Precoding (THP) in the multiuser multiple-input-multiple-output (MIMO) downlink under both perfect and imperfect channel state information at the transmitter (CSIT). For the case of perfect CSIT, we differ from the previous work by performing stream-wise (both inter-user and intra-user) interference pre-cancelation at the transmitter. A minimum total mean square error (MT-MSE) criterion is used to formulate our optimization problem. By some convex analysis of the problem, we obtain the necessary conditions for the optimal solution. An iterative algorithm is proposed to handle this problem and its convergence is proved. Then we extend our designed algorithm to the robust version by minimizing the conditional expectation of the T-MSE under imperfect CSIT. Simulation results are given to verify the efficacy of our proposed schemes and to show their superiorities over existing MMSE-based THP schemes.

An Improved Analytical Model for IEEE 802.11 Distributed Coordination Function under Finite Load

In this paper, an improved analytical model for IEEE 802.11 distributed coordination function (DCF) under finite load is proposed by closely following the specifications given in IEEE 802.11 standard. The model is investigated in terms of channel throughput under perfect and slow Rayleigh fading channels. It is shown that the proposed model gives better insight into the operation of DCF.

Improved iterative detection and achieved throughputs of OFDM systems under imperfect channel estimation

Assuming imperfect channel estimation, we propose an improved detector for orthogonal frequency-division multiplexing (OFDM) systems over a frequency-selective fading channel. By adopting a Bayesian approach involving the statistics of the channel estimation errors, we formulate an improved maximum-likelihood (ML) detection metric taking into account the characteristics of the channel estimates. As a first step, we propose a modified iterative detector based on a maximum a posteriori receiver formulation which reduces the impact of channel uncertainty on the decoder performance, by an appropriate use of this metric. The results are compared to those obtained by using a detector based on a mismatched ML metric, which uses the channel estimate as if it was the perfect channel. In a second step, we calculate the information rates achieved by both the improved and mismatched ML detectors, in terms of achievable outage rates. These outage rates are compared to those provided by a theoretical (not practical) decoder defined as the best decoder in the presence of channel estimation errors. Numerical results over both uncorrelated Rayleigh fading channels and realistic ultra wideband channels show that the improved detector outperforms the classically-used mismatched approach in terms of bit error rate and achievable outage rates, without any increase in the receiver complexity.

TWO FORMS OF THE THREE-QUBIT STATE FOR PERFECT TELEPORTATION

Two forms of the three-qubit pure state for teleporting an unknown one-particle entangled state are presented, where the successful possibilities and fidelities of the two schemes both reach one unit. It is worthwhile noticing that GHZ states and W-states are special cases of those two forms of a perfect quantum channel. Furthermore, the orthogonal complete measurement bases are given.

Distributed Generalized Low-Density Codes for Wireless Relay Networks

Distributed generalized low-density (GLD) codes are proposed for cooperative networks with multiple relays. Specifically, every relay can decode and forward one or several constituent codes of the GLD code to cooperatively construct a distributed GLD code using the partial error-detecting and error-correcting capabilities of the GLD code. The scheme can be flexibly adjusted to the variation of the relay number and work effectively under both perfect and imperfect source-relay channels verified by simulations.

Analysis of maximal-ratio of transmitting/receiving antenna selection with perfect and partial channel information

To improve system performance and reduce the complexity and cost of receiver hardware, we investigated a new multiple-input multiple-output (MIMO) scheme combining maximal-ratio transmitting and receiver antenna selection (MRT/RAS). In this scheme, a single receiving antenna, which maximizes the signalto-noise ratio (SNR) at the receiver, is selected for demodulation. The closed-form outage probability and the bit error rate (BER) of the MRT/RAS system are both presented. The simulation demonstrates that the MRT/RAS scheme can achieve a full diversity order as if all the receiving antennas were used. It is shown that the MRT/RAS scheme outperforms some more complex space-time codes of the same spectral efficiency. The analytical results are verified by simulation. In the end, we also analyze the MRT/RAS system based on partial channel information.

AMC와 SFC기법을 적용한 MIMO-OFDM 시스템의 성능 분석

Adaptive modulation and Coding(AMC) scheme is promising technique to support the demands for high data rates and wideband proposed for 4G mobile communication system standards. In this paper, adaptive modulation and coding(AMC) based on OFDM system is analyzed through simulation for single user case and compared with SISO-OFDM and SFBC(Space frequency block coding)-OFDM. The performance analysis in terms of capacity for downlink system environments with different values of constellation size under multipath fading channel is done. The adaptive modulation and coding technique is based on perfect estimation channel. It has been observed that SFBC(Space-frequency block coding)-OFDM system gives better performance in terms of capacity.

Performance evaluation of multi-hop csma/ca networks in fading environments

The performance of multi-hop CSMA/CA networks has in most cases been evaluated via simulations, or analytically using a perfect collision channel model. Using such methods, one can neither have access to the capture nature of the terminals nor evaluate the performance of the network in a fading environment. In this paper a new analytical framework that takes into account these capture and fading effects is presented. The network investigated in this paper has an infinite number of nodes which is assumed to be spatially Poisson distributed. The approach is to develop analytical expressions for the transition probabilities between states of nodes in the network by approximating these states as a Markov chain. A fast algorithm to solve these equations is also given. Numerical results show that the model agrees with simulation results for both omni-directional networks and networks employing beamforming.

Performance Analysis of Single-User Ultra-Wide Band Impulse Radio (UWB-IR) with Super-Orthogonal Turbo Codes (SOTC)

Low-complexity low-rate super-orthogonal turbo codes (SOTC) are proposed in this work to replace the implicit repetition code (RC) in ultra-wide band impulse radio (UWB-IR) systems to improve the transmission range and system throughput. Various receivers, including the matched-filter and the RAKE receivers, are examined for data detection in the additive white Gaussian noise (AWGN) channel and the indoor IEEE 802.15.3a channels. The performance of SOTC-coded UWB with perfect and imperfect timing and channel information is analyzed and corroborated by computer simulation. It is demonstrated that the SOTC-based UWB-IR system can achieve significant performance improvement over the conventional direct-sequence UWB (DS-UWB) system encoded by RC over both ISI and ISI-free channels.

Dynamic resource allocation with beamforming for MIMO OFDM systems: performance and effects of imperfect CSI

We propose three different dynamic resource allocation algorithms using adaptive beamforming for multiple-input multiple-output (MIMO) OFDM systems, and investigate their performance over multipath fading channels under perfect and imperfect channel state information (CSI). These approaches involve the use of adaptive modulation, adaptive frequency-domain power allocation, and/or adaptive sub-channel allocation. By employing the proposed approaches in MIMO/OFDM systems, significant performance improvement can be achieved compared to the conventional adaptive antenna array based OFDM. The investigation of the effects of imperfect CSI reveals that the adaptive-modulation based approach is too sensitive to channel estimation errors, and that its performance is worse than the adaptive frequency-domain power allocation and/or adaptive sub-channel allocation approaches. The performance analysis also shows that combining adaptive power allocation with sub-channel allocation yields the best performance under imperfect CSI while being robust to channel estimation errors.

Quantum calculations for the effects of dislocations on channeling and channeling radiation

The channeling process in a crystal bent by dislocations is considered. The Schrödinger equation for the channeled particle motion is separated between longitudinal and transverse parts. The transverse potential and the frequency of channeling radiation in the perfect channel and the two regions of dislocation affected channels are calculated. The corresponding wave functions for the transverse and longitudinal motions are also calculated. In this work, we specifically investigate the effects of longitudinal motion of the particle on the dechanneling parameter and the frequency. The continuity of wave functions and their derivatives is used at the three boundaries and reflection and transmission coefficients are found using these boundary conditions. Finally, we consider the two cases of maximum and minimum dechanneling probabilities.

Teleportation via multi-qubit channels

We investigate the problem of teleporting an unknown qubit state to a recipient via a channel of $2{\mathcal L}$ qubits. In this procedure a protocol is employed whereby ${\mathcal L}$ Bell state measurements are made and information based on these measurements is sent via a classical channel to the recipient. Upon receiving this information the recipient determines a local gate which is used to recover the original state. We find that the $2^{2\mathcal L}$-dimensional Hilbert space of states available for the channel admits a decomposition into four subspaces. Every state within a given subspace is a perfect channel, and each sequence of Bell measurements projects $2{\mathcal L}$ qubits of the system into one of the four subspaces. As a result, only two bits of classical information need be sent to the recipient for them to determine the gate. We note some connections between these four subspaces and ground states of many-body Hamiltonian systems, and discuss the implications of these results towards understanding entanglement in multi-qubit systems.

Some Insights into MIMO Mutual Information: The High SNR Case

We consider mutual information of multiple-input multiple-output (MIMO) wireless channels with complex isotropic Gaussian input in the case where the receiver has perfect channel, knowledge. For arbitrary fading statistics, a mutual information lower bound is decomposed in a sum of three terms involving: a) average SNR; b) channel fading; and c) a term characterizing the "effective rank", or eigenvalue dispersion, of the channel matrix. The decomposition suggests that spatial multiplexing efficiency of a MIMO channel can be characterized by the so-called ellipticity statistic. Distribution functions, means and variances of the random terms in the decomposition for the case of Rayleigh fading are also derived

Numerical investigation on frictional pressure loss in a perfect square micro channel with roughness and particles

A numerical study is performed to investigate the effect of inner surface roughness and microparticles on adiabatic single phase frictional pressure drop in a perfect square micro channel. With the variation of particles sizes (0.1 to 1 μm) and occupied volume ratio (0.01 to 10%) by particles, the Eulerian multi-phase model is applied to a 100 μm hydraulic diameter perfect square micro channel in laminar flow region. Frictional pressure loss is affected significantly by particle size than occupied volume ratio by particles. The particle properties like density and coefficient of restitution are investigated with various particle materials and the density of particle is found as an influential factor. Roughness effect on pressure drop in the micro channel is investigated with the consideration of roughness height, pitch, and distribution. Additionally, the combination effect by particles and surface roughness are simulated. The pressure loss in microchannel with 2.5% relative roughness surface can be increased more than 20% by the addition of 0.5 μm diameter particles.

Optimal power loading for multiple-input single-output ofdm systems with bit-level interleaving

We derive a power loading procedure optimizing the bit-error rates of multiple-input single-output (MISO) bit-interleaved coded modulation (BICM) orthogonal frequency-division multiplexing (OFDM) systems performing hard-decisions at the receiver and ideal interleaving. The adaptive subcarrier power allocation is based on either perfect or outdated channel state information at the transmitter. The scheme has the same complexity as the one for the single transmit antenna case. For a standard BICM-OFDM system in Rayleigh fading, Monte Carlo simulations show that the relative signal-to-noise ratio gain by the adaptation is up to 4 dB at an average bit-error rate level of 10-66. The relative gain in MISO systems decreases to 1.05 dB for increasing the number of transmit antennas. The achievable gain decreases for decreasing cross-correlation of the outdated and the actual channel state

Error probability of coded STBC systems in block fading environments

In this letter, a union bound on the error probability of coded multi-antenna systems over block fading channels is derived. The bound is based on uniform interleaving of the coded sequence prior to transmission over the channel. Using this argument the distribution of error bits over the fading blocks is computed and the corresponding pair wise error probability (PEP) is derived. We consider coded systems that concatenate a binary code with a space-time block code (STBC). Coherent detection is assumed with perfect and imperfect channel state information (CSI) at the receiver, where imperfect CSI is obtained using pilot-aided estimation. Under channel estimation environments, the tradeoff between channel diversity and channel estimation is investigated and the optimal channel memory is approximated analytically. Results show that the performance degradation due to channel memory decreases as the number of transmit antennas is increased. Moreover, the optimal channel memory increases with increasing the number of transmit antennas.

Comprehensive Analysis of the IEEE 802.11

Wireless Local Area Networks (WLANs) have attracted significant research interest over the past few years. The IEEE 802.11 standard is the most mature technology for WLANs and has been widely adopted for wireless networks. This paper outlines a new performance analysis for IEEE 802.11 Distributed Coordinated Function (DCF) using Direct Sequence Spread Spectrum (DSSS) in terms of the channel throughput, packet processing rate, packet loss probability and average packet delay using a perfect channel as well as a slow Rayleigh fading channel. The theoretical results are subsequently compared with the simulation results. It is shown that there is a good match between these two results, which validates the analytical model.

Analytic model for ion channeling in successive implantations in crystalline silicon

Successive ion implantations are frequently used in the fabrication of silicon devices. Each ion implantation increases the crystal damage in the region near the surface. For successive implantations, the ion channeling in perfect crystal channels is reduced and the channeling tail is lowered. In the process simulation, the impurity distribution after ion implantation is often calculated as the sum of two Pearson functions, of which the second covers the channeling ions. In this work, we present a general model for the reduction of channeling in successive implantations. The crystal damage from the implantations is monitored and used for the calculation of a differential channel dose. The model allows a fast analytic calculation of impurity profiles in 1D, 2D, and 3D process simulators. It provides a similar accuracy as Monte Carlo simulations and gives excellent agreement with SIMS data of successive ion implantations.