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The OFDM system with multiple transceiver antennas is attractive to increase the spectrum or energy efficiency. Depending on the channel state information (CSI), precoding techniques offer array and multiplexing gain in such systems. However, if terminal equipment is fast moving, the CSI feedback would be outdated when it is applied to data transmission. This paper proposes a novel channel prediction method applicable for high‐speed environment. Benefiting from the proposed structure, this method greatly improves the prediction accuracy, and meanwhile retains the low feedback overhead. Numerical results show that the performance of the proposed method outperforms conventional precoding methods in high‐speed scenarios.

This work analyzes the performance of the implementable detectors for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) technique under specific and realistic operation system condi- tions, including antenna correlation and array configuration. Time-domain channel model has been used to evaluate the system performance under realistic communication channel and system scenarios, including different channel correlation, modulation order and antenna arrays configurations. A bunch of MIMO-OFDM detectors were analyzed for the purpose of achieve high performance combined with high capacity systems and manageable computational complexity. Numerical Monte-Carlo simulations (MCS) demonstrate the channel selectivity effect, while the impact of the number of antennas, adoption of linear against heuristic-based detection schemes, and the spatial correlation effect under linear and planar antenna arrays are analyzed in the MIMO-OFDM context., Comment: 26 pgs, 16 figures and 5 tables

In this project, a compact monopoles Multiple-Input-Multiple-Output MIMO antenna with size 40 × 42 mm2 that operates at 7 GHz is designed and proposed for 5th Generation mobile networks (5G) application. The antenna is built by using FR-4 substrate and it consists of two planar antenna elements which arranged orthogonally to provide a good isolation between them. To further enhance the isolation and decrease the mutual coupling effect, a rod-like parasite element is added in the design. Initial simulation result shows that the antenna can operate from 4 GHz to 9 GHz while measurement result proves that it can operate from 5.5 GHz to 9 GHz. Both results show that isolation is below −20 dB.

Multiple-Input, Multiple-Output MIMO-orthogonal frequency division multiplexing OFDM is a promising technique in 5G wireless communications. In high-mobility scenarios, the transmission environments are time-varying and/or the relative moving velocity between the transmitter and receiver is also time-varying. In the literature, most of previous works mainly focused on fixed subcarrier group size and precoded the MIMO signals with unitary channel state information. In this way, the subcarrier grouping may naturally lead to big loss of channel capacity in high-mobility scenarios because of the channel state information difference on the subcarriers in each group. To employ the MIMO-OFDM technique, adaptive subcarrier grouping scheme may be an efficient way. In this paper, we first consider MIMO-OFDM systems over double-selective i.i.d. Rayleigh channels and investigate the quantitative relation between subcarrier group size and capacity loss theoretically. With developed theoretical results, we also propose an adaptive subcarrier grouping scheme to satisfy the preset capacity loss threshold by adjusting grouping size with the sensed environmental information and mobile velocity. Theoretical analysis and simulation results show that to achieve a better system capacity, a sparse scattering, lower signal-to-noise ratio, and lower velocity as well as properly large antenna number are matched with larger subcarrier group size. One important observation is that if the antenna number is too large and higher than a threshold, which will not bring any additional gain to the subcarrier grouping. That is, the system capacity loss will converge to a lower bound expeditiously with respect to antenna number, which is given in theory also. Copyright © 2016 John Wiley & Sons, Ltd.

This chapter first describes various optical fibers that can support space‐division multiplexing (SDM) transmission. It then reviews SDM transmission techniques that can be utilized in case the crosstalk between the spatial channels is small, for example, in multi‐core fibers (MCFs). The chapter also introduces the general principles for SDM transmission over optical fibers in the presence of coupling between the spatial channels, describes the basic properties of the fiber‐optic multimode channel, such as differential group delay (DGD) and mode‐dependent loss (MDL), as well as the strategies to reduce the impact of the DGD. It further discusses experimental results for multiple‐input multiple‐output (MIMO) transmission and MIMO digital signal processing (DSP) techniques specific to SDM systems. The second part of the chapter describes methods for SDM component characterization and components required for SDM transmission systems such as mode couplers, SDM wavelength‐selective switches (WSSs), and SDM optical amplifiers.

In this paper, a novel MIMO-OFDM transmission scheme is developed to effectively enable multi-access by joint code design across multiple antennas, subcarriers, OFDM frames, and users. It achieves better spectrum efficiency while improving bit error rate performance. The proposed scheme uses either parity bit selected or permutation techniques to assign spreading codes at the transmitter side. As a result, the detection at the receiver is greatly improved because of the fact that identifying the spreading codes directly yields the transmitted data symbols. The paper also investigates the field-programmable gate array implementation of the proposed algorithms; optimization techniques are proposed to reduce area, power, and time. These techniques include a pipelined architecture for inverse FFT/FFT blocks, an efficient low complexity algorithm for despreading based on counters and comparators and an optimized architecture for complex matrix inversion using Gauss-Jordan elimination GJ-elimination. Finally, the fixed-point optimized field-programmable gate array architecture for MIMO-OFDM transceiver is developed, where the maximum allowed performance loss because of quantization is defined, the tradeoffs between BER performance and area reduction are investigated. Copyright © 2015 John Wiley & Sons, Ltd.

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.

Multiple-input multiple-output orthogonal frequency division multiplexing has become an attractive air-interface solution for the next generation wireless networks because of its high spectrum efficiency. This paper addresses the security concern and proposes to achieve covert orthogonal frequency division multiplexing transmission using cyclic delay diversity featured multiple-input multiple-output technology. Particularly, our physical layer security scheme takes the advantage of cyclic delay diversity formed periodical frequency selective channel and utilizes uneven comb pilots to confuse unauthorized receivers and benefit authorized receivers. We conduct simulation study to evaluate the impact of different cyclic delay, antenna number, and interpolation algorithms on our scheme. Numerical results show that our scheme can provide authorized users with significant advantage over eavesdroppers without complicated upper-layer encryption and decryption. Moreover, the scheme has flexible choice of parameters and thus can be easily deployed in a variety of wireless networks with different requirements. Copyright © 2014 John Wiley & Sons, Ltd.

This paper studies energy-efficiency (EE) power allocation for cognitive radio MIMO-OFDM systems. Our aim is to minimize energy efficiency, measured by "Joule per bit" metric, while maintaining the minimal rate requirement of a secondary user under a total power constraint and mutual interference power constraints. However, since the formulated EE problem in this paper is non-convex, it is difficult to solve directly in general. To make it solvable, firstly we transform the original problem into an equivalent convex optimization problem via fractional programming. Then, the equivalent convex optimization problem is solved by a sequential quadratic programming algorithm. Finally, a new iterative energy-efficiency power allocation algorithm is presented. Numerical results show that the proposed method can obtain better EE performance than the maximizing capacity algorithm.

Beamforming technique is applied to significantly increase the performance of a MIMO system, if the channel information CI of the communication system is available at the transmitter. For the transmitter to obtain the entire CI, however, a considerable reverse-link bandwidth is required. To save the bandwidth, a limited-rate closed-loop system, therefore, uses a predetermined codebook which is derived from the CI. The codebook consists of a finite number of precoders out of which the index of the best one is transmitted from the receiver to the transmitter using only a few bits saving substantial bandwidth. However, the amount of bits that need to be fed back can still be significantly large for MIMO-OFDM systems when the precoding matrix index PMI for each subcarrier should be transmitted. Such per-subcarrier precoding scheme has high feedback overhead and also incurs huge computational cost to determine the best PMI for each subcarrier. We, therefore, propose a per-band precoding scheme that precodes a band group of subcarriers by only one precoder. More importantly, we develop, for the proposed per-band scheme, reduced-complexity precoding selection methods that lead to the design of efficient receivers. The effectiveness of the proposed scheme is investigated through computer simulations. Copyright © 2014 John Wiley & Sons, Ltd.

To achieve more high-speed communication systems, multiple-input multiple-output orthogonal frequency division multiplexing (MIMO/OFDM) is adopted in several standardisations. On the other hand, the conventional MIMO/OFDM requires many pilot signals to estimate the channel state information (CSI). To achieve an accurate CSI with the small number of pilot signals, high time resolution carrier interferometry (HTRCI) for MIMO/OFDM has been proposed. Moreover, QR decomposition with M-algorithm maximum likelihood detection (QRM-MLD) and channel ranking has been proposed to achieve both the reducing complexity and the improving system performance. However, the conventional HTRCI-MIMO/OFDM with the QRM-MLD and channel ranking did not consider the problem of the fast fading channel. In the fast fading environment, many errors are caused in the last part of the packet. To overcome this problem, the decision-direct method has been proposed. However, it requires large complexity because of the iterative processing. Therefore, in this paper, we propose the non-linear prediction method for an HTRCI-MIMO/OFDM with the QRM-MLD and channel ranking. Copyright © 2014 John Wiley & Sons, Ltd.

Single carrier-frequency division multiple access SC-FDMA has been adopted as the uplink transmission standard in fourth generation cellular network to enable the power efficiency transmission in mobile station. Because multiuser MIMO MU-MIMO is a promising technology to fully exploit the channel capacity in mobile radio network, this paper investigates the uplink transmission of SC-FDMA systems with orthogonal space frequency block codes SFBC. Two linear MU-MIMO receivers, orthogonal SFBC OSFBC and minimum mean square error MMSE, are derived for the scenarios with limited number of users or adequate receive antennas at base station. In order to effectively eliminate the multiple access interference MAI and fully exploit the capacity of MU-MIMO channel, we propose a turbo MU-MIMO receiver, which iteratively utilizes the soft information from maximum a posteriori decoder to cancel the MAI. By the simulation results in several typical MIMO channels, we find that the proposed MMSE MU-MIMO receiver outperforms the OSFBC receiver over 1dB at the cost of higher complexity. However, the proposed turbo MU-MIMO receivers can effectively cancel the MAI under overloaded channel conditions and really achieve the capacity of MU-MIMO channel. Copyright © 2014 John Wiley & Sons, Ltd.

In order to provide high quality services, current communication systems require high-data transmission rate and good error performance. Because single-carrier frequency division multiple access SC-FDMA is with the desirable characteristics of orthogonal frequency division multiple access and the low peak-to-average power ratio of single-carrier transmission schemes, it has been adopted as the uplink transmission scheme in 3GPP long-term evolution to approach the demand for data transmission rates and error performance. By combining multiple-input multiple-output MIMO techniques with the SC-FDMA modulation scheme, MIMO SC-FDMA systems can achieve high data rates over broadband wireless channels. In this paper, we propose the iterative multiuser detection scheme for the low-density parity-check-coded MIMO SC-FDMA communication systems. On the basis of the property of space-frequency block coding, we develop the frequency domain minimum mean-squared error and zero-forcing equalisers with multiuser interference cancellation technique on each subcarrier to recover the transmitted symbols. Some simulation examples for uplink scenario are given to demonstrate the effectiveness of the proposed schemes. Copyright © 2014 John Wiley & Sons, Ltd.

We consider the downlink of a multi-input multi-output orthogonal frequency-division multiplexing-based cooperative cognitive radio network in which the secondary users SUs with extra resources work as relay to help the SUs with less available resources to improve their utility in terms of the throughput and fairness by forming a coalition graph. We model the problem of joint relay selection and power allocation in multi-input multi-output orthogonal frequency-division multiplexing-based cooperative cognitive radio network as a two-level cooperative game problem, and the objectives of this work are twofold. Firstly, we assign each weak SU to one of the relays rich SUs through solving a problem achieved by a non-transferable utility coalition graph game, and this comprises the first level of the game. Secondly, we jointly allocate available channels to the SUs such that no subchannel is allocated to more than one SU and simultaneously optimise the transmit covariance matrices of nodes based on the Nash bargaining solution, which is the second level of the game. We further model the network as a multi-cell scenario with small serving areas. After relaxing the problem and convexifying the relaxed version, we develop an optimal distributed algorithm, using dual decomposition. Afterwards, we propose a dynamic distributed resource allocation algorithm for this purpose. Simulations confirm the convergence of our distributed algorithms to the globally optimal solution of the two-level game. Copyright © 2014 John Wiley & Sons, Ltd.

In this paper, a tone reservation TR method is employed to reduce the peak-to-average power ratio PAPR in multi-input multi-output orthogonal frequency division multiplexing systems with space frequency block coding SFBC. The key idea of the employed TR method is taking signals on multiple transmit antennas into account to design appropriate peak reduction symbols, which can significantly reduce the PAPR of SFBC multi-input multi-output orthogonal frequency division multiplexing signals. With the employed TR scheme, the SFBC structure can be maintained, whereas the traditional TR method would destroy it, resulting in the degradation of bit error rate BER performance. Simulation results demonstrate that the employed TR scheme can provide significantly better BER performance than the traditional TR method with slight PAPR reduction degradation. Copyright © 2013 John Wiley & Sons, Ltd.

An effective signal detection algorithm with low complexity is presented for multiple-input multiple-output orthogonal frequency division multiplexing systems. The proposed technique, QR-MLD, combines the conventional maximum likelihood detection (MLD) algorithm and the QR algorithm, resulting in much lower complexity compared to MLD. The proposed technique is compared with a similar algorithm, showing that the complexity of the proposed technique with T=1 is a 95% improvement over that of MLD, at the expense of about a 2-dB signalto-noise-ratio (SNR) degradation for a bit error rate (BER) of 10 –3 . Additionally, with T=2, the proposed technique reduces the complexity by 73% for multiplications and 80% for additions and enhances the SNR performance about 1 dB for a BER of 10 –3 .

SUMMARY Multi-hop communications equipped with parallel relay nodes is an emerging network scenario visible in environments with high node density. Conventional interference-free medium access control (MAC) has little capability in utilizing such parallel relays because it essentially prohibits the existence of co-channel interference and limits the feasibility of concurrent communications. This paper aims at presenting a cooperative multi-input multi-output (MIMO) space division multiple access (SDMA) design that uses each hop's parallel relay nodes to improve multi-hop throughput performance. Specifically, we use MIMO and SDMA to enable concurrent transmissions (from multiple Tx nodes to single/multiple Rx nodes) and suppress simultaneous links' co-channel interference. As a joint physical layer (MAC/PHY) solution, our design has multiple MAC modules including load balancing that uniformly splits traffic packets at parallel relay nodes and multi-hop scheduling taking co-channel interference into consideration. Meanwhile, our PHY layer modules include distributive channel sounding that exchanges channel information in a decentralized manner and link adaptation module estimating instantaneous link rate per time frame. Simulation results validate that compared with interference-free MAC or existing Mitigating Interference using Multiple Antennas (MIMA-MAC), our proposed design can improve end-to-end throughput by around 30% to 50%. In addition, we further discuss its application on extended multi-hop topology. Copyright © 2012 John Wiley & Sons, Ltd.

In this article, we propose and demonstrate an orthogonal frequency division multiplexing-radio over fiber (OFDM-ROF) system based on three channels sextupling-frequency scheme using an external modulation of a distributed feedback laser diode (DFB-LD) and dual drive Mach–Zehnder modulator (DD-MZM) for carrying 100 GHz W-band frequency multiple-input multiple-output (MIMO)-OFDM signals with 90 Gbps downstream. MIMO-OFDM algorithms effectively compensate for impairments in the wireless link. Without using costly W-band components, a transmission system with 50 km single mode fiber (SMF) and 4 m wireless transmission operation at 100 GHz is experimentally validated. The power penalties for MIMO-OFDM signals of base stations are less than 3 dBm. For the upstream transmission, wavelength reuse with 30 Gbps 4QAM upstream signals is experimentally demonstrated. The minimum optical spectral gap between residue downstream OFDM band and upstream OFDM band that guarantees a tolerable amount of optical interference has been determined through experiment. The frequency of local oscillator is reduced due to frequency sextupling scheme. The cost of the proposed system is largely reduced. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:93–99, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27251

This chapter contains sections titled: Benefits of MIMO Space Time Coding Multi‐User MIMO MIMO Network MIMO Cognitive Radio Network Summary

We analyze the relationship between channel coherence bandwidth and two complexity-reduced lattice reduction aided detection (LRAD) algorithms for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems in correlated fading channels. In both the adaptive LR algorithm and the fixed interval LR algorithm, we exploit the inherent feature of unimodular transformation matrix P that remains the same for the adjacent highly correlated subcarriers. Complexity simulations demonstrate that the adaptive LR algorithm could eliminate up to approximately 90 percent of the multiplications and 95 percent of the divisions of the brute-force LR algorithm with large coherence bandwidth. The results also show that the adaptive algorithm with both optimum and globally suboptimum initial interval settings could significantly reduce the LR complexity, compared with the brute-force LR and fixed interval LR algorithms, while maintaining the system performance. Keywords: MIMO, OFDM, coherence bandwidth, lattice reduction.

An approach of superimposed training ST-aided time-varying TV channel estimation for multiple-input multiple-output orthogonal frequency division multiplexing systems is presented. By modeling the TV channel with the truncated discrete basis expansion model, a two-step approach is adopted to estimate the TV channel. In addition, the mean square error MSE of the proposed channel estimation is analyzed, and its closed-form expression is derived, which is a function of the data-to-ST power ratio. Using the developed channel MSE, we case the problem of ST power-allocation by minimizing the lower bound on the average channel capacity. To enhance the performance of channel estimation, a low-complexity decision feedback mechanism is introduced to iteratively mitigate the unknown data interference. Numerical results verify the performances of the proposed approach. Copyright © 2012 John Wiley & Sons, Ltd.

Carrier frequency offset (CFO) is a factor that corrupts subchannel orthogonality resulting to performance degradation in multiple-input multiple-output orthogonal frequency division multiplexing systems. We investigate the effect of CFO on the channel estimation and the effect of both CFO and channel estimation on the system capacity. The main result of the paper is a lower bound on the capacity for a given CFO and channel estimation error covariance. The lower bound is based on the Gaussian bound of the multiplicative noise because of channel estimation errors. Copyright © 2012 John Wiley & Sons, Ltd.

We introduce 10 × 10 Gb/s RZ-DPSK-DWDM links in the architecture integration of MIMO-OFDM system. The optical communication performance and wireless communication performance is analyzed in the integrated system. The long distance transmission for RZ-DPSK WDM is done, and the demodulated RZ-DPSK signal is transformed to the binary data, which is given to MIMO-OFDM-QPSK wireless communication system. Two MIMO-OFDM-QPSK wireless system is designed with two transmit antennas and one receive antenna and four transmit antennas and one receive antenna. The BER performance of almost 10−3 is achieved at SNR of 11 dB with four transmit antennas and one receive antenna, which is better when compared to two transmit antennas and one receive antenna. The results prove that seamless integration of RZ-DPSK-DWDM optical links with MIMO-OFDM system is suitable to simultaneously offer higher receiver performance and simplify system configuration for fourth generation wide-area coverage mobile communication. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1679–1679, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26891

Space-time coded multiple-input multiple-output MIMO technology is an important technique that improves the performance of wireless communication systems significantly without consuming bandwidth resource. This paper first discusses the characteristics and limitations of traditional symbol-level space-time coding schemes, which work largely on the basis of an assumption that signals are sent to a block-fading channel. Therefore, the symbol-level space-time coding schemes rely on symbol-level signal processing. Taking advantage of orthogonal complementary codes, we propose a novel MIMO scheme, in this paper, based on chip-level space-time coding that is different from the traditional symbol-level space-time coding. With the help of space-time-frequency complementary coding and multicarrier modem, the proposed scheme is able to achieve multipath interference-free and multiuser interference-free communications with simple a correlator detector. The proposed chip-level space-time coded MIMO works well even in a fast fading channel in addition to its flexibility to achieve diversity and multiplexing gains simultaneously in varying channel environments. Copyright © 2012 John Wiley & Sons, Ltd.

Precoding in the multiple-input multiple-output orthogonal frequency division multiplexing system is investigated. In conventional wideband precoding (WBP), only one precoder, obtained from the decomposition of the subcarrier independent channel matrix, is used for all subcarriers. With an investigation of the relationship between the subcarrier independent channel matrix and the temporal/frequency channels, an improved WBP scheme is proposed for practical scenarios in which a part of subcarriers are allocated to a user. The improved WBP scheme is a generalized scheme of which narrow-band precoding and conventional WBP schemes are special modes. Simulation results demonstrate that the improved WBP scheme almost achieves the optimum performance of a single precoder and outperforms the conventional WBP scheme in terms of the bit error ratio and ergodic capacity with slight complexity increase. The largest advantage of the improved WBP scheme on signal-to-noise ratio in simulation results is over 2.1 dB.

This letter considers the channel estimation for two-way relay MIMO OFDM systems. A least square (LS) channel estimation algorithm under block-based training is proposed. The mean square error (MSE) of the LS channel estimate is computed, and the optimal training sequences with respect to this MSE are derived. Some numerical examples are presented to evaluate the performance of the proposed channel estimation method.

In Multiple Input Multiple Output (MIMO) communications, multiple antenna elements are employed both in the transmitter and the receiver, in order to obtain increased data rates or improved reliabi ...

In this paper, we consider multiple-input multiple-output MIMO multi-tone code division multiple access MT-CDMA uplink transmission over multipath fading channels. The zero-forcing vertical Bell Laboratories layered space-time architecture ZF V-BLAST algorithm and maximum ratio combining scheme are applied at the receiver. The average bit error rate BER expression is derived provided that the number of receive antennas is not less than that of transmit antennas. The BER expression is verified by simulations. Numerical results show that the numbers of transmit and receive antennas have significant effects on the BER performance of the considered system. Spatial and path diversity show different capabilities to improve the BER performance. The MIMO MT-CDMA system based on the ZF V-BLAST algorithm is capable of achieving a better BER performance and a higher capacity than the conventional MT-CDMA system. Copyright © 2011 John Wiley & Sons, Ltd.

This chapter contains sections titled: Potential Benefits for Millimeter Wave Systems Spatial and Temporal Diversity Spatial and Frequency Diversity Dynamic Spatial, Frequency, and Modulation Allocation References ]]>

Multiuser diversity beamforming (MDB) is investigated for downlink channels of multiuser multiple input multiple output (MIMO) systems. Since the use of multiple beams simultaneously results in a poor performance of MDB when the number of users is not sufficiently large, the use of single-beam at a time is considered to avoid performance degradation due to the interference from other beams. Furthermore, in order to share a common precoder by multiple users, modulation division multiplexing (MDM) with a higher order modulation for MDB is discussed. Performance criteria for precoder and user selection are derived under the assumption that the maximum likelihood (ML) detector is used. Copyright © 2011 John Wiley & Sons, Ltd.

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.

In this paper, we analyze the performance of evolutionary heuristic-aided linear detectors deployed in Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) systems, considering realistic operating scenarios. Hybrid linear-heuristic detectors under different initial solutions provided by linear detectors are considered, namely differential evolution (DE) and particle swarm optimization (PSO). Numerical results demonstrated the applicability of hybrid detection approach, which can improve considerably the performance of minimum mean-square error (MMSE) and matched filter (MF) detectors. Furthermore, we discuss how the complexity of the presented algorithms scales with the number of antennas, besides of verifying the spatial correlation effects on MIMO-OFDM performance assisted by linear, heuristic and hybrid detection schemes. The influence of the initial point in the performance improvement and complexity reduction is evaluated numerically., 19 pages, 7 figures and 5 tables

This paper considers covariance-feedback based linear precoding (LP) and nonlinear Tomlinson–Harashima precoding (THP) for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. Orthogonal space–time block coded (OSTBC)‡ OFDM and spatially-multiplexed (SM)§ OFDM are analysed. The main objective is to design precoders to mitigate the impact of transmit-antenna and path correlations. The impact of path correlations on the pairwise error probability (PEP) of MIMO OFDM is also analysed. Closed-form, waterfilling-based covariance precoders are derived to minimize the worst case PEP in OSTBC OFDM. An adaptive transmission strategy is also developed for switching between precoded SM OFDM and precoded OSTBC OFDM. The switching criterion is the minimum Euclidean distance of the received codebook. The switching decision sent to the transmitter requires one feedback bit per subcarrier. The proposed precoders considerably reduce the error rate in antenna and path-correlated channels; nonlinear precoders perform better than linear precoders. We show that the adaptive strategy can achieve full diversity gain, and it outperforms either SM or OSTBC applied individually in terms of the bit error rate (BER). Copyright © 2010 John Wiley & Sons, Ltd.

In this work, the effects of channel estimation errors on the performance of a maximum likelihood detector (MLD) in a MIMO OFDM system are assessed. The analysis is conducted in the framework of a long-term evolution (LTE) air interface and is based on a robust pilot aided channel estimator. The correlation coefficient between the estimate and the real channel is computed and the impact of interpolation errors on the detector is evaluated as a function of key design parameters such as the pilot spacing and the number of transmit antennas. The effect of partial knowledge of the channel statistics at the receiver side is studied with special emphasis on the role of the delay and Doppler spread of the channel. Our analysis accounts for both time and frequency selectivity of the channel and thus also for the intercarrier interference arising in a typical time varying propagation scenario. Copyright © 2010 John Wiley & Sons, Ltd.

In this paper, the recently introduced method of channel-coding-based peak-to-average power ratio (PAR) reduction is further developed. On the one hand, not only PAR is considered, but a broad class of signal parameters to be optimised is treated by defining a respective metric to be minimised. On the other hand, the candidate generation and assessment is done successively. If a given tolerable metric limit is met the procedure stops. Analytical expressions for the average number of tested candidates and the achieved performance are derived. Critical metric values, as generalisation of the ‘critical’ PAR value ξ = log(D), where D is the number of carriers, are defined. The theoretical statements are covered by means of numerical simulations using either PAR or cubic metric as desired signal parameter. Copyright © 2010 John Wiley & Sons, Ltd.

In this paper we present two resource allocation algorithms with minimum rate requirements for MIMO–OFDM systems, which have much a lower complexity than the optimal solution. The first method is based on a heuristic sum rate maximization algorithm using so-called eigenvalue updates. It has a very low complexity and performs quite well for high required minimum rates. The second algorithm has a higher complexity than the first one but still less than the optimal solution. It performs very well for low required minimum rates.