A Novel Multiuser Detection Algorithm for CDMA-Based MIMO-OFDM System

1Introduction Recently,MultipleInputMultipleOutput(MIMO)wirelesstechnologieshavecapturedalotofresearchin terest,giventhatthecapacityincreaseturnsouttobe achievable[1-2].OrthogonalFrequencyDivisionMulti plexing(OFDM)techniquehastheremarkablecharac teristic…     

Performance Analysis and Optimal Power Allocation for Space–Time and Amplify-and-Forward Cooperative System

In this paper, we consider a space?Ctime and amplify-and-forward (ST-AF) cooperative system which consists of two-antenna source, single-antenna relay and destination. Source transmits Alamouti space?Ctime coding symbols to destination with cooperation of relay which adopts AF strategy. Closed-form symbol error rate (SER) is derived for the ST-AF system with PSK signals. Moreover, a SER approximation is developed to show the asymptotic performance of the ST-AF cooperative system in medium and high SNR regimes. For comparison, the SER approximation of another cooperative space?Ctime coding (C-STC) scheme is also derived. Theoretical analysis shows that the ST-AF can obtain more diversity gain and achieve higher diversity order than C-STC. Statistical optimal power allocation (OPA) algorithm for the ST-AF cooperative system is presented based on the SER performance. It turns out the OPA only depends on the channel links related to the relay, not depend on the direct link between source and destination. Finally, numerical simulations validate the theoretical analysis.     

A New Semiblind Scheme Based on Second and Fourth Order Statistics for Decoding of Space–Time Data in Time Selective MIMO Channels

In this paper we propose a novel semiblind scheme based on second and fourth order statistics of Space–Time data in time varying MIMO channels. This scheme combines a new blind estimator of frequency offsets and an iterative decoder. Space–Time Codes have a periodic property which is used to find a simple and efficient blind estimator of carrier offsets. The iterative decoder is a data aided decoder which provides the best estimates of channel, noise co-variance and S–T data in its category. As a result of this the new semiblind scheme performs very efficiently in time-selective channels and is able to reduce the training overhead required by the data-aided estimators to a large extent, and increase the effective throughput.

A Novel Complex Orthogonal Design for Space–Time Coding in Sensor Networks

In this paper, we propose a complex orthogonal design based on the theory of Finite projective plane. As most of the orthogonal designs incur low ratio of time diversity, the proposed complex orthogonal design has a relatively high ratio of time diversity. In addition, the proposed scheme has the following characteristics: (1) full spatial diversity (2) low rate (3) linear processing. We compare the proposed scheme with another complex design to show the tradeoffs. The proposed scheme can be of use for certain applications such as sensor networks and deep space exploration where there might be an imposed limit on the peak transmit power.     

Space–Time/Space–Frequency/Space–Time–Frequency Block Coded MIMO-OFDM System with Equalizers in Quasi Static Mobile Radio Channels Using Higher Tap Order

In 4G broadband wireless communications, multiple transmit and receive antennas are used to form multiple input multiple output (MIMO) channels to increase the capacity (by a factor of the minimum number of transmit and receive antennas) and data rate. In this paper, the combination of MIMO technology and orthogonal frequency division multiplexing (OFDM) systems is analyzed for wideband transmission which mitigates the intersymbol interference and hence enhances system capacity. In MIMO-OFDM systems, the coding is done over space, time, and frequency domains to provide reliable and robust transmission in harsh wireless environment. Also, the performance of space time frequency (STF) coded MIMO-OFDM is analyzed with space time and space frequency coding as special cases. The maximum achievable diversity of STF coded MIMO-OFDM is analyzed and bit error rate performance improvement is verified by simulation results. Simulations are carried out in harsh wireless environment, whose effect is mitigated by using higher tap order channels. The complexity is resolved by employing sphere decoder at the receiver.     

Variational Bayes Based Multiuser Detection for On–Off Random Access Channels

This paper considers on–off random access channels where the users transmit either a one or a zero to a base station or fusion center, and it is assumed that only a small fraction of users are active during any channel use. Under these assumptions, the problem of identifying the active users reduces to that of recovering a sparse binary vector from noisy random linear measurements. A hierarchical Bayesian approach is proposed in this paper to recover the set of active users. A fast approximate Bayesian inference based on Variational Bayes (VB) is then developed. Extensive simulation results are then provided to compare the performance of the proposed VB based Bayesian MUD approach to sparse estimation techniques such as OMP and LASSO. It is observed that the proposed approach is robust to variations in noise as well as sparsity levels. Further, for a given BER performance, the proposed approach requires substantially smaller dimensional codes as compared to OMP and LASSO, thus improving the spectral efficiency.     

Two Schemes of Blind MMSE Multiuser Receiver for Space-Time Coded CDMA Systems

1　IntroductionIthasbeenshownthatthecapacityofwirelesscommunicationsystemscanbeincreaseddramatical lybyemployingmultipletransmittingandreceivingantennas.Space timecodinghasbeenpaidmoreat tentionrecentlybecauseitisaneffectivewaytoex ploitspatialandtemporaldiversity[1～2 ] .Despitealossincodingadvantage,space timeblockcodingcanofferthemaximumdiversitygainbasedononlythelinearprocessingatthereceiver[3～ 4] andhasbeenproposedtobeusedin 3Gsystems.InterferencesuppressionismorechallenginginCDMAsyste…     

Performance Bound for LDPC Coded Unitary Space–Time Modulation

This paper is concerned with the bit error probability (BEP) of coded unitary space–time modulation systems based on finite-length low density parity check (LDPC) codes. The union bound on the BEP of the maximum likelihood (ML) decoding is derived for any code rate, unitary space–time constellation and mapping. The tightness of the bound is checked with simulation results of the ordered statistic decoding (OSD). Numerical and simulation results show that the union bound is also close to the error performance of the sum–product (SP) decoding at low BEP levels when Gray mapping is employed. The derived bound is useful to benchmark the error performance of finite-length coded unitary space–time modulation systems, especially for those that employ short-to-medium length LDPC codes.

Efficient Decoding for Generalized Quasi-Orthogonal Space–Time Block Codes

Space–time coding can achieve transmit diversity and power gain over spatially uncoded systems without sacrificing bandwidth. There are various approaches in coding structures, including space–time block codes. A class of space–time block codes namely quasi-orthogonal space–time block codes can achieve the full rate, but the conventional decoders of these codes experience interference terms resulting from neighboring signals during signal detection. The presence of the interference terms causes an increase in the decoder complexity and a decrease in the performance gain. In this article, we propose a modification to the conventional coding/decoding scheme that will improve performance, reduce decoding complexity, and improve robustness against channel estimation errors as well.     

A New UWB Receiver in the Indoor Multipath Environment

1IntroductionUWBtechnology has receivedincreasing attentionforits broad applicability to short-range wireless communi-cations andradar applications as well .The basic conceptis to transmit , and receive an i mpulse like stream ofverylowpower density for its lowduty cycle and ultra-short duration pulses———typically shorter than a fewnanoseconds .One of the main propagation characteristics of UWBis that signals are spread over a long train of pulses duetothe reflection ,diffractions and sca…     

A Space Vector PWM Scheme for Multilevel lnverters Based on Two-Level Space Vector PWM

1. INTRODUCTION MULTILEVEL inverters are increasingly being used in high-power medium voltage applications due to their superior performance compared to two-level inverters, such as lower common-mode voltage, lower dv/dt, lower harmonics in output voltage and current, and reduced voltage on the power switches.     

A Space Vector PWM Scheme for Multilevel Inverters Based on Two-Level Space Vector PWM

Ⅰ. INTRODUCTION MULTILEVEL inverters are increasingly being used in high-power medium voltage applications due to their superior performance compared to two-level inverters, such as lower common-mode voltage, lower dv/dt, lower harmonics in output voltage and current, and reduced voltage on the power switches.     

Simplified Semi-Blind Channel Estimation for Space–Time Coded MIMO-OFDM Systems

The combination of Space–Time Coded Multiple Input Multiple Output systems (STC-MIMO) with Orthogonal Frequency Division Multiplexing (OFDM) is recently being investigated as an effective means of providing high-speed data transmission over dispersive wireless channels. The strengths of the two techniques coalesce and render MIMO-OFDM systems robust to ISI and IBI. However, the decoding and demodulation of STC-OFDM needs reliable channel knowledge at the receiver, unless differential modulation techniques are used. Semi-blind methods for channel estimation are seen to provide the best trade-off in terms of bandwidth overhead, computational complexity and latency. The conventional Expectation-Maximization (EM) algorithm for semi-blind channel estimation improves a pilot-based estimate with a two step process; however, it is computationally complex to implement. In this paper, we propose a variant of the EM method, referred to as ML-EM, for semi-blind estimation of doubly dispersive channels in space–time coded MIMO-OFDM systems. Here, the conventional EM algorithm is coupled with the ML decoder for space time block codes (STBCs). The technique shows good performance, even in highly correlated antenna arrays, and is computationally simpler than conventional EM. The method incurs a training overhead of less than 1%, and performs close to exact CSI through iterative processing at the receiver.     

Block Diagonal Differential Space–Time–Frequency Codes for Four Transmit Antennas

For Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system with four transmit antennas, this paper presents a novel block diagonal differential space–time–frequency (DSTF) coded scheme with full diversity and rate one. It overcomes the rate loss of the traditional differential orthogonal space–time–frequency coded scheme for four transmit antennas. The coding and decoding method are described in detail. After analyzing the system error performance, this paper provides two measures to improve the system error performance. One measure is to design good codes which achieve large coding gain. Thus, linear constellation decimation (LCD) codes are imported. The optimal decimation factors are given in the Table 1 under different design parameters. Another measure is to select a good subcarrier grouping method. A grouping method is proposed that all groups have the same subcarrier spacing. By the derived rule of evaluating subcarrier grouping, the optimal subcarrier spacing is obtained by computer search under different channels. Simulation results are presented to illustrate the performance of block diagonal DSTF codes and the proposed subcarrier grouping method.

A Novel Pulse Design Based on Hermite Functions for UWB Communications

1IntroductionUltra-Wide Band(UWB)technology is foreseen as apossible solution for future short-range high-data-ratewireless communications.Unlike the conventional carrier-based wireless communication systems,a carrier-freeUWB radio system usually transmit…     

Learning-Based Relay Selection for Cooperative Networks with Space–Time Network Coding

Wireless Personal Communications - Space–time network coding has recently been used in cooperative communication to mitigate the problem of transmission delay in wireless systems as well as...     

A Common Function of Different Union Bounds for Optimization and BER Evaluation of Space–Time codes

Optimizing Space-Time (S–T) codes, in terms of minimum error rates, based on Union bounds often produces results which vary with signal-to-noise ratio (SNR) and so are not easy to use. Error-rate evaluation of S–T codes using Union bounds sometimes requires very heavy computational loads and so is impractical. In this paper, a Common function shared by different Union bounds is derived and proposed for optimization of S–T codes. The Common function produces the optimization results which are SNR independent and so requires a substantially lower computation load. Results of Monte-Carlo simulation on two 2 × 2 rotation-based diagonal S–T codes (D codes) and two Linear-Dispersion codes (LDCs) show that the bit-error-rate (BER) performances using the optimization results based on the Common function, the exact Union bound (EUB) and Chernoff Union bound (CUB) are all nearly identical. The Common function is subsequently used to develop a modified Union bound (MUB) and modified Chernoff Union bound (MCUB). Results of numerical calculations show that the MUB can provide a good compromise between the accuracy and computational load for BER evaluation.

A New Anti-Collision Algorithm for Multi-Target Real Time Recognitionin RFID System

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