A novel MC DS-CDMA system scheme with high spectral efficiency

1 Introduction Recently, some studies [1, 2] have shown that the Multi- Carrier code-division multiple-access (CDMA) systems can exhibit excellent performance in beyond 3G or 4G mobile communication systems. In general, multicarrier (MC) CDMA systems have…     

Adaptive modulation for space–frequency block coded OFDM systems

The growing popularity of both multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) systems has created the need for adaptive modulation to integrate temporal, spatial and spectral components together. In this article, an overview of some adaptive modulation schemes for OFDM is presented. Then a new scheme consisting of a combination of adaptive modulation, OFDM, high-order space-frequency block codes (SFBC), and antenna selection is presented. The proposed scheme exploits the benefits of space–frequency block codes, OFDM, adaptive modulation and antenna selection to provide high-quality transmission for broadband wireless communications. The spectral efficiency advantage of the proposed system is examined. It is shown that antenna selection with adaptive modulation can greatly improve the performance of the conventional SFBC–OFDM systems.     

A Comparison Study Between Pre-Equalization Schemes for Single and Multi Carrier Modulation Systems

In this paper, frequency domain pre-equalization (Pre-FDE) is developed for broadband cyclic prefix-code division multiple access (CP-CDMA) as a single carrier transmission scheme, and for multi carrier-CDMA (MC-CDMA) and orthogonal frequency division multiplexing (OFDM) as multi carrier transmission schemes. A comparison study is held between these schemes and the traditional equalization schemes. Experimental results show that pre-equalization improves significantly the performance of the single and multi carrier communication systems with a very low complexity at the receiver. The comparative study between MIMO pre-equalization for single carrier systems and for multi carrier systems shows that MIMO pre-equalization for single carrier systems outperforms that for multi carrier systems in terms of bit error rate (BER) performance since single carrier transmission has more frequency diversity than multi carrier transmission in the uncoded case.     

Novel semi-blind ICI equalization algorithm for wireless OFDM systems

Intercarrier interference is deemed as one of the crucial problems in the wireless orthogonal frequency division multiplexing (OFDM) systems. The conventional ICI mitigation schemes involve the frequency-domain channel estimation or the additional coding, both of which require the spectral overhead and hence lead to the significant throughput reduction. Besides, the OFDM receivers using the ICI estimation rely on a large-dimensional matrix inverter with high computational complexity especially for many subcarriers such as digital video broadcasting (DVB) systems and wireless metropolitan-area networks (WMAN). To the best of our knowledge, no semi-blind ICI equalization has been addressed in the existing literature. Thus, in this paper, we propose a novel semi-blind ICI equalization scheme using the joint multiple matrix diagonalization (JMMD) algorithm to greatly reduce the intercarrier interference in OFDM. However, the well-known phase and permutation indeterminacies emerge in all blind equalization schemes. Hence we also design a few OFDM pilot blocks and propose an iterative identification method to determine the corresponding phase and permutation variants in our semi-blind scheme. Our semi-blind ICI equalization algorithm integrating the JMMD with the additional pilot-based iterative identification is very promising for the future high-throughput OFDM systems. Through Monte Carlo simulations, the QPSK-OFDM system with our proposed semi-blind ICI equalizer can achieve significantly better performance with symbol error rate reduction in several orders-of-magnitude. For the 16QAM-OFDM system, our scheme can also improve the performance over the plain OFDM system to some extent.     

A new complex sphere detector with SE enumeration

Multiple-Input Multiple-Output (MIMO) techniques are promising in wireless communication systems for its high spectral efficiency. Sphere Detector (SD) is favoured in MIMO detection to achieve Maximum-Likelihood (ML) performance. In this paper, we proposed a new SD method for MIMO-Orthogonal Frequency Division Multiplexing (OFDM) systems based on IEEE802.11n, which uses Singular Value Decomposition (SVD) in complex domain to reduce the computation complexity. Furthermore, a new Schnorr-Euchner (SE) enumeration algorithm is also discussed in detail. The computer simulation result shows that the computational complexity and the number of visited nodes can be reduced significantly compared with conventional SD detectors with the same Bit Error Rate (BER) performance.     

Bit Interleaved Time-Frequency Coded Modulation for OFDM Systems Over Time-Varying Channels

Bit Interleaved Time-Frequency Coded Modulation for OFDM Systems Over Time-Varying Channels Orthogonal frequency-division multiplexing (OFDM) is a promising technology in broadband wireless communications with its ability in transforming a frequency selective fading channel into multiple flat fading channels. However, the time-varying characteristics of wireless channels induce the loss of orthogonality among OFDM sub-carriers, which was generally considered harmful to system performance. In this paper, we propose a bit interleaved time–frequency coded modulation (BITFCM) scheme for OFDM to achieve both time and frequency diversity inherent in broadband time-varying channels. We will show that the time-varying characteristics of the channel are beneficial to system performance. Using the BITFCM scheme and for relatively low maximum normalized Doppler frequency, a reduced complexity Maximum Likelihood (ML) decoding approach is proposed to achieve good performance with low complexity as well. For high maximum normalized Doppler frequency, the inter-carrier interference (ICI) can be large and an error floor will be induced. To solve this problem, we propose two ICI mitigation schemes by taking advantage of the second order channel statistics and the complete channel information, respectively. It will be shown that both schemes can reduce the ICI significantly.     

An Improved ICI Reduction Method in OFDM Communication System

Orthogonal frequency division multiplexing (OFDM) is a promising technique for the broadband wireless communication system. However, the inter-sub-carrier-interference (ICI) produced by the phase noise of transceiver local oscillator is a serious problem. Bit error rate (BER) performance is degraded because the orthogonal properties between the sub-carriers are broken down. In this paper, ICI self-cancellation of data-conjugate method is studied to reduce ICI effectively. CPE (common phase error), ICI and CIR (carrier to interference power ratio) are derived and discussed by the linear approximation of the phase noise. Then, the system performance of the data-conjugate method is compared with those of the original OFDM and the conventional data-conversion method. As results, it can be shown that CPE becomes zero in the OFDM of the data-conjugate method. Besides, in the OFDM system with phase noise, the data-conjugate method can make remarkable improvement of the BER performance and it is better than the data-conversion method and the original OFDM with or without convolution coding.     

Effects of phase noise on performance of OFDM systems using an ICI cancellation scheme

This paper investigates the effects of phase noise on the performance of orthogonal frequency division multiplexing (OFDM) systems using an intercarrier interference (ICI) cancellation scheme. In this case, the common phase error (CPE) and ICI caused by phase noise depend on the overall spectrum of each weighted group of subcarriers rather than on the spectrum of each individual subcarrier. This means that the system performance can be improved by filtering the phase noise to fit a particular spectrum. It is shown that the ICI cancellation scheme can significantly improve the bit error rate (BER) performance in the presence of phase noise.     

An OFDM-TDMA/SA MAC Protocol with QoS Constraints for Broadband Wireless LANs

Orthogonal frequency division multiplexing (OFDM) is an important technique to support high speed transmission of broadband traffic in wireless networks, especially broadband wireless local area networks (LANs). Based on OFDM, a new multiple access scheme, called OFDM-TDMA with subcarrier allocation (OFDM-TDMA/SA), is proposed in this paper. It provides more flexibility in resource allocation than other multiple access schemes such as OFDM-TDMA, OFDM-frequency division multiple access (OFDM-FDMA), and orthogonal frequency division multiple access (OFDMA). With OFDM-TDMA/SA, a medium access control (MAC) is designed for broadband wireless LANs. It optimizes bit allocation in subcarriers so that maximum bits are transmitted in each OFDM symbol under a frequency selective fading environment. The OFDM-TDMA/SA MAC protocol also supports three classes of traffic such as guaranteed, controlled-load, and best effort services. Based on the optimum subcarrier bit-allocation algorithm and considering heterogeneous QoS constraints of multimedia traffic, a hierarchical scheduling scheme is proposed to determine the subcarriers and time slots in which a mobile terminal can transmit packets. In such a way, the OFDM-TDMA/SA MAC protocol significantly increases system throughput in a frequency selective fading environment and guarantees QoS of multimedia traffic. Computer simulation is carried out to evaluate the performance of the OFDM-TDMA/SA MAC protocol. Results show that the new MAC protocol outperforms other MAC protocols for OFDM-based wireless LANs. This work was supported by the State of Georgia Yamacraw Project (E21-105).     

Progressive image transmission over space-time coded OFDM-based MIMO systems with adaptive modulation

This paper considers a progressive image transmission system over wireless channels by combining joint source-channel coding (JSCC), space-time coding, and orthogonal frequency division multiplexing (OFDM). The BER performance of the space-time coded OFDM-based MIMO system based on a newly built broadband MIMO fading model is first evaluated by assuming perfect channel state information at the receiver for coherent detection. Then, for a given average SNR (hence, BER), a fast local search algorithm is applied to optimize the unequal error protection design in JSCC, subjected to fixed total transmitted energy for various constellation sizes. This design allows the measurement of the expected reconstructed image quality. With this end-to-end system performance evaluation, an adaptive modulation scheme is proposed to pick the constellation size that offers the best reconstructed image quality for each average SNR. Simulation results of practical image transmissions confirm the effectiveness of our proposed adaptive modulation scheme.     

KLT-CRKCN: Hyperspectral Image Classification via Karhunen Loeve Transformation and Collaborative Representation-Based K Closest Neighbor

Nowadays, there is a great demand for ultra-high data rate (UHDR) transmission on most 5th generation wireless networks. In this concern, the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) scheme is used on a large scale to achieve UHDR transmission with reduced inter-symbol interference (ISI) and inter-carrier interference (ICI). Discrete wavelet transform-based OFDM (DWT-OFDM) provides better orthogonality due to presence of orthogonal wavelets, which mitigates the effects caused by ISI and ICI. Also, it has extended bandwidth than the traditional OFDM systems. But a major drawback in this system is that it suffers from down sampling. The down-sampling effect reduces the actual size of the input bit streams. As a result, the system performance is degraded. For solving this problem, a multilevel redundant discrete wavelet transform (ML-RDWT) is used instead of DWT to achieve improved spectral performance. Here, complex down-sampling operation is eliminated. From the simulation outcomes, it is clearly viewed that effects caused by ICI, ISI and BER are mitigated by improving the performance of CIR. The proposed method employs optimal red deer algorithm (ORDA) to locate the optimized weights for the ICI cancellation system. This algorithm enhances the spectral efficiency by achieving high CIR with reduced BER, ISI and ICI. The BER in the proposed MIMO-ML-RDWT-OFDM-ORDA method is 68%, 76%, 38% and 75%, which is very low when compared to the BER in the existing techniques like MIMO-DWT-OFDM-RDA, MIMO-RNS-OFDM-PNMA, MIMO-OFDM-BMA and MIMO-OFDM-ICIMA. The ISI in the proposed method is 94%, 91%, 95% low when compared to the ISI in the existing techniques. The ICI in the proposed work is 71%, 57%, 73% and 86% low when compared to the ICI in the existing techniques. Therefore, the general performance of the proposed MIMO-ML-RDWT-OFDM-ORDA method is improved in an efficient way with less complexity, error rate and processing delay.

     

Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems

Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and data symbols encoded by space–time codes can be steered to these eigenmodes similar to MIMO wireless communication systems with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G TDD.     

An efficient radio resource management strategy for adaptive OFDM cellular systems

This paper presents an efficient Radio Resource Management （RRM） strategy for adaptive Orthogonal Frequency Division Multiplexing （OFDM） cellular systems. In the proposed strategy, only those users who have the same distance from their base stations can reuse a same subcarrier. This can guarantee the received Carrier-to-Interference ratio （C/I） of each subcarrier to be acceptable as required by system planning. Then by employing different modulation scheme on each subcarrier according to its received C/I, system spectral efficiency can be gracefully increased. Analytical and simulation results show that the spectral efficiency is improved by 40% without sacrificing the Bit Error Rate （BER） performance and call blocking probability and system capacity of the proposed strategy is better than conventional systems.     

Peak‐to‐average power ratio reduction in space–time coded MIMO‐OFDM via preprocessing

In this paper, we propose a trellis exploration algorithm based preprocessing strategy to lower the peak‐to‐average power ratio (PAPR) of precoded MIMO‐OFDM. We first illustrate the degradation in PAPR due to optimal linear precoding in MIMO‐OFDM systems. Then we propose two forms of multi‐layer precoding (MLP) schemes to reduce PAPR. In both schemes, the inner‐layer precoder is designed to optimize system capacity/BER performance. In the first MLP scheme (MLP‐I), a common outer‐layer polyphase precoding matrix is employed. In the second MLP scheme (MLP‐II), data stream corresponding to every transmit antenna is precoded with a different outer‐layer polyphase precoding matrix. Both outer‐layer precoders are custom designed using the trellis exploration algorithm by applying the aperiodic autocorrelation of OFDM data symbols as the metric to minimize. Simulation results indicate that both MLP schemes show superior PAPR performance over conventional MIMO‐OFDM with and without precoding. In addition, MLP better exploits frequency diversity resulting in BER performance gains in multi‐path environments. Copyright © 2010 John Wiley & Sons, Ltd.     

Bandwidth‐Efficient Selective Retransmission for MIMO‐OFDM Systems

In this work, we propose an efficient selective retransmission method for multiple‐input and multiple‐output (MIMO) wireless systems under orthogonal frequency‐division multiplexing (OFDM) signaling. A typical received OFDM frame may have some symbols in error, which results in a retransmission of the entire frame. Such a retransmission is often unnecessary, and to avoid this, we propose a method to selectively retransmit symbols that correspond to poor‐quality subcarriers. We use the condition numbers of the subcarrier channel matrices of the MIMO‐OFDM system as a quality measure. The proposed scheme is embedded in the modulation layer and is independent of conventional hybrid automatic repeat request (HARQ) methods. The receiver integrates the original OFDM and the punctured retransmitted OFDM signals for more reliable detection. The targeted retransmission results in fewer negative acknowledgements from conventional HARQ algorithms, which results in increasing bandwidth and power efficiency. We investigate the efficacy of the proposed method for optimal and suboptimal receivers. The simulation results demonstrate the efficacy of the proposed method on throughput for MIMO‐OFDM systems.     

Interference Cancellation with Space Diversity for Downlink MC-CDMA Systems

Modern wireless communications require an efficient spectrum usage and high channel capacity and throughput. Multiple-input and multiple-output (MIMO), Linear equalizers, multi-user detection and multicarrier code-division multiple access (MC-CDMA) are possible solutions to achieve spectral efficiency, high channel capacity, eliminate multiple access interference (MAI), eliminate Inter symbol interference (ISI) and robustness against frequency selective fading. In this paper, we combine all these techniques and investigate BER performance. We propose a low complexity receiver structure for Single-input Multiple-output (SIMO) downlink MC-CDMA systems. It employs an interference cancellation scheme to suppress the interference caused by the multipath fading channel. Also, the proposed scheme is developed for MIMO MC-CDMA system. The performance analysis of Downlink MIMO MC-CDMA systems with V-BLAST over frequency selective fading channel is investigated under various number of transmit and receive antennas. The simulation results show proposed SIMO equalization with parallel interference cancellation scheme is effective in reducing the ISI and the MAI. It improves the performance significantly and the simulation results show that MIMO MC-CDMA with V-BLAST multi-user detection provides high data rate and the BER significant improvement.     

Bandwidth efficient MT-DS-SS via reduced subcarrier frequency spacing

We investigate modifications to conventional multitone direct-sequence spread spectrum (MT-DS-SS) signaling to improve spectral efficiency, for high-data-rate systems with small processing gain. Reduction in subcarrier frequency spacing to half the symbol rate improves bandwidth efficiency at no cost in complexity or performance. Via both analysis and simulations, we provide example results that illustrate the attractive performance and throughputs attainable with reduced frequency spacing. We extend study to synchronous multiuser transmission, and show that our best spectrally efficient MT-DS-SS scheme outperforms the conventional MT-DS-SS in a dispersive multiuser environment.     

A Radon-Multiwavelet Based OFDM System Design and Simulation Under Different Channel Conditions

Finite Radon transform (FRAT) mapper has the ability to increase orthogonality of sub-carriers, it is non sensitive to channel parameters variations, and has a small constellation energy compared with conventional fast Fourier transform (FFT) based orthogonal frequency division multiplexing (OFDM). It is also able to work as a good interleaver which significantly reduces the bit error rate (BER). Due to its good orthogonality, discrete Multiwavelet transform (DMWT) is attractive for implementation in OFDM systems which reduces inter-symbol interference (ISI) and inter-carrier interference (ICI) and eliminates the need for cyclic prefix and increases the spectral efficiency of the design. In this paper both FRAT and DMWT are implemented in a new design for OFDM. The new structure was tested and compared with conventional FFT-based OFDM, Radon-based OFDM, and DMWT-based OFDM for additive white Gaussian noise channel, flat fading channel, and multi-path selective fading channel. Simulation tests were generated for different channels parameters values. The obtained results showed that proposed system has increased spectral efficiency, reduced ISI and ICI, and improved BER performance compared with other systems.     

Binomial distribution based grey wolf optimization algorithm for channel estimation in wireless communication system

Several input high-data-rate transmissions over broadband wireless channels are possible using multiple input multiple output (MIMO) systems paired with orthogonal frequency division multiplexing (OFDM) technology. Channel estimation is an essential technique and a necessary component of MIMO-OFDM systems. However, the noise will be there in MIMO-OFDM due to the environment. As a result, the wireless system performs degrades in terms of bit error rate (BER). The suggested method offers a better pilot pattern strategy for MIMO-OFDM and an efficient power allocation to address this issue. The binomial distribution-based grey wolf optimization (BDGWO) algorithm is proposed to identify the optimal pilot patterns. The power is then adaptively distributed to each transmit antenna to increase the spectral efficiency and maximum channel capacity through an adaptive neuro-fuzzy inference system with a sigmoid membership function (SMFANFIS). The best pilot patterns in PDGSIP (pilot design with generalized shift invariant property) were determined using the BDGWO algorithm based on the binomial distribution. According to the simulation results, the proposed BDGWO established pilot design with generalized shift invariant property (BDGWO-DGSIP) achieves higher performance compared other existing approaches such as PDGSIP, TPDGSIP, and LS in terms of NMSE, BER, and SER. Compared to the PDGSIP technique, the proposed PDGSIP-BDGWO system minimizes NMSE at 10%, BER at about 12%, and SER at 15%.     

Joint scheduling and mapping in support of downlink fairness and spectral efficiency in ieee 802.16e OFDMA system

The next generation broadband wireless networks deploy orthogonal frequency division multiple access (OFDMA) as the enabling technologies for broadband data transmission with QoS capabilities. In such broadband wireless systems, one major issue is how to utilize radio resource efficiently while maintaining fairness between sessions as well as providing adequate QoS. In this work, we propose an approach for OFDMA/time division duplex (TDD) downlink suitable for IEEE802.16e WiMAX systems that combines scheduling and burst mapping algorithms for a trade‐off between session fairness, QoS, and spectral efficiency. While optimizing radio resources under QoS and fairness constraints is an NP‐hard problem, we follow a heuristic approach that simplifies the complexity of the algorithm. Performance results show that while the new scheme outperforms the Proportional Fair algorithm in terms of fairness, it also improves the overall system spectral efficiency. Copyright © 2016 John Wiley & Sons, Ltd.