Performance of spatially multiplexed MC-CDM with zero-forcing unified successive interference cancellation detection

Spatially multiplexed multicarrier code-division multiplexing (SM-MC-CDM) is a multiple-input multiple-output, orthogonal frequency division multiplexing (MIMO-OFDM) communication technique with multiple antennas used for spatial multiplexing and with frequency domain spreading on each antenna. Unified successive interference canceller (U-SIC) is an efficient detector recently introduced for SM-MC-CDM. This paper presents an analytical approach to the performance of zero-forcing (ZF) U-SIC for SM-MC-CDM communications. For a system with an equal number of transmit and receive antennas, an approximation for the probability density function of post-detection signal-to-noise ratio (SNR) is used to derive a closed-form analytical upper bound and approximations for the probability of error and ergodic capacity. It is shown that SM-MC-CDM with ZF U-SIC is able to achieve higher diversity order than that achieved by ZF and minimum mean squared error (MMSE) V-BLAST detectors used on each subcarrier of a MIMO-OFDM system with the same number of subcarriers. The diversity order obtained increases with the number of subcarriers. It is also shown that the ergodic capacity of the system decreases with increasing number of subcarriers.     

Target localisation techniques and tools for multiple-input multiple-output radar

This study presents a comparative study of coherent and non-coherent target localisation techniques for multiple-input multiple-output (MIMO) radar systems with widely distributed elements. Performance is evaluated based on closed-form solutions developed for the best linear unbiased estimator (BLUE) for each of the localisation methods. These estimators afford insights into the relation between radar locations, target location and localisation accuracy. In particular, the means squared error of the BLUE is factored into a term dependent on signal and processing characteristics and a term dependent on sensor locations. The latter is referred to as geometric dilution of precision (GDOP). The best achievable accuracy for the coherent case is obtained, and a comparative study with the non-coherent case is presented. MIMO radar systems with coherent processing are shown to benefit from a gain because of coherent processing among sensors. This gain is referred to as coherent localisation gain, and it is proportional to the ratio of the signal carrier frequency to the effective bandwidth (a large ratio for typical signals). The footprint of multiple transmit/ receive sensors results in a gain, referred to as MIMO gain, for both processing techniques. The MIMO gain is proportional to the product of the number of transmitting and receiving sensors. Analysis of the MIMO gain through the use of GDOP contour maps demonstrate the achievable accuracy at various target locations for a given layout of sensors.     

Performance of multiantenna multicarrier direct-sequence code division multiple access using orthogonal variable spreading factor codes-assisted space?time spreading in time-selective fading channels

A downlink (base-to-mobile) multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) system employing multiple antennas at both the base station and each of the mobile terminals is investigated, when communicating over fast time-varying fading channels resulting in time-selective fading. In the considered multiantenna MC DS-CDMA, space-time spreading (STS) based on the family of orthogonal variable spreading factor (OVSF) codes is proposed in order to achieve the time diversity because of the time-selective fading, in addition to the transmit/receive diversity. In this contribution, the closed-form expressions for the single-user bit-error rate (BER) are derived, in order to gain insight into the achievable BER performance of the multiantenna MC DS-CDMA. The BER performance of the multiantenna MC DS-CDMA system is investigated, when communicating over correlated time-selective Rayleigh fading channels. The study and performance results show that the multiantenna MC DS-CDMA using OVSF codes-assisted STS constitutes a high-efficiency downlink space-time transmission scheme. It is capable of achieving the full diversity provided by the time- selective fading and multiple transmit/receive antennas. Furthermore, the proposed multiantenna MC DS-CDMA is capable of achieving a self-balance between the time diversity achieved and the multiuser interference suppression capability, when using low-complexity correlation detection.     

Full-rate full-diversity space-time block codes for any odd number of transmit antennas

The authors propose a new class of space-time block codes (STBCs) achieving full-rate and full spatial diversity for general quadrature amplitude modulation (QAM) when using any odd number of transmit antennas under quasi-static Rayleigh fading channels. These codes are the extended works of the conventional Alamouti-ST constellation-rotating (CR) codes which are designed by serially concatenating CR precoders with the Alamouti scheme for an even number of transmit antennas. From the computer simulation results, it is observed that the best code in this class outperforms the existing ST-CR code and also exhibits error performance within only about 1-dB of the maximal ratio combining receiver. The codes possessing quasi-orthogonal (QO) characteristic are also included in this class, allowing simple maximum likelihood (ML) decoding with almost the same error performance as the best code in this class and the conventional QO-STBCs with full diveristy. These codes have identical or much lowered ML decoding complexity compared with the conventional QO-STBCs.     

Virtual multiple input multiple output in multiple high-altitude platform constellations

Multiple-input multiple-output (MIMO) technology, which makes use of the spatial dimension by utilising multiple antennas at the transmitter and receiver, has proved an efficient solution for providing higher data throughput and/or link reliability in wireless systems. In this study, the authors investigate a virtual MIMO (V-MIMO) technique, based on a constellation of multiple high-altitude platforms (HAPs), providing broadband wireless access to high-speed trains under predominantly line-of-sight (LOS) propagation conditions. They analyse the performance of transmit diversity based on space?time block coding (STBC), in particular Alamouti and extended Alamouti schemes, using fixed wide-lobe receive antennas, and compare it to the reference receive diversity scheme based on best HAP selection that requires highly directional and steerable antennas. Simulation results for different diversity schemes are based on the calculation of carrier to interference-plus-noise ratio (CINR) along representative railway lines in a realistic terrain configuration. The CINR levels obtained are mapped onto transmission modes specified by standards developed for two wireless systems operating at distinct frequency bands, the DVB-S2 assumed for operation in mm-wave bands and the IEEE 802.16e (mobile WiMAX) for operation at 3.5 GHz. Simulation results show that the use of transmit diversity schemes in a multiple HAP constellation decreases the link outage and also increases the average spectral efficiency, but requires a marked increase in transmit power, especially for the system operating in mm-wave bands.     

Joint channel tracking and intercarrier-interference equalisation for vertical Bell Labs layered space time-orthogonal frequency division multiplexing in vehicle ad hoc network

Vertical Bell Labs layered space time-orthogonal frequency division multiplexing (VBLAST-OFDM) systems can achieve high spectral efficiency in quasi-stationary links and with channel state information (CSI) matrix knowledge. Owing to the high speeds of nodes in vehicle ad hoc network (VANET), the channel is fast fading thus raising the need for channel tracking. Furthermore, inter-carrier interference (ICI) causes an error floor at high signal-to-noise ratio (SNR) even with perfect CSI knowledge. In this paper we investigate channel tracking and ICI mitigation for VBLAST-OFDM. The analysis of ICI shows that it increases with speed, number of subcarriers and/or number of transmit antennas. The authors then introduce a simple channel tracking algorithm for VBLAST-OFDM. Simulation results show that our algorithm reduces the bit error rate (BER) of a 2 x 4 VBLAST system by 102² at 40 dB SNR and 100 km/h speed compared to obtaining a channel estimate from a training sequence only. The change in the channel response is estimated using the channel tracking algorithm and then passed to an ICI equaliser to enhance performance and reduce the error floor caused by ICI at high SNR. Equalising five pairs of subcarriers gives 4 dB improvement for 2 x 4 VBLAST at 180 km/h relative speed. The performance is enhanced as more subcarriers are included in the ICI equaliser at the expense of increased receiver complexity.     

Free-space measurement of complex permittivity and complexpermeability of magnetic materials at microwave frequencies

A free-space measurement system operating in the 8.2-40-GHz frequency range is used to measure the reflection and transmission coefficients, S₁₁ and S₂₁, of planar samples. The complex electric permittivity and the magnetic permeability are calculated from the measured values of S₁₁ and S₂₁. The measurement system consists of transmit and receive horn lens antennas, a network analyzer, mode transitions, and a computer. Diffraction effects at the edges of the sample are minimized by using spot-focusing lens antennas. Errors due to multiple reflections between antennas via the surface of the sample are corrected by using a free-space TRL (thru, reflect, line) calibration technique. For thin, flexible samples, the sample had to be sandwiched between two half-wavelength (at mid-band) quartz plates to eliminate sagging. Results are reported in the frequency range of 8.6-13.4 GHz for materials such as Teflon, sodium borosilicate glass, and microwave-absorbing materials     

一种基于跳波束天线的通信方式及其性能分析

提出了一种新的基于跳波束天线(Beam Hopping为Antennas，BHA)的通信方式，并对其在存在强方向性干扰的情况下的平均信干噪声比(SINR)性能进行了初步的分析。结果表明，相对于传统单波束天线(Single Beam．Antennas，SBA)的通信方式，这种新的BHA通信方式能够有效地改善存在强方向性干扰时的通信质量，从而提高系统的性能。     

Antenna selection technique for MIMO-OFDM systems over frequency selective Rayleigh fading channel

A joint transmit and receive antenna selection technique for MIMO-OFDM is presented. By appropriately ordering and tabulating the minimum channel sub-matrix's sub-stream signal to noise ratio in all subcarriers, an optimal antenna subset can be obtained. This procedure can be simplified further by analysing the inter-subcarrier correlation and by exploiting group selection methods. Complexity analyses on the proposed algorithm are presented, and performance improvements achievable are demonstrated through simulation studies     

Synthetic aperture imaging for small scale systems

Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored. Array apertures are synthesized using an active multi-element receive subaperture and a multi-element transmit subaperture defocused to emulate a single-element spatial response with high acoustic power. Echo signals are recorded independently by individual elements of the receive subaperture. Each method uses different spatial frequencies and acquisition strategies for imaging, and therefore different sets of active transmit/receive element combinations. Following acquisition, image points are reconstructed using the complete data set with full dynamic focus on both transmit and receive. Various factors affecting image quality have been evaluated and compared to conventional imagers through measurements with a 3.5 MHz, 128-element transducer array on different gel phantoms. Multielement synthetic aperture methods achieve higher electronic signal to noise ratio and better contrast resolution than conventional synthetic aperture techniques, approaching conventional phased array performance     

Channel correlation of transmit diversity FSO systems with partially coherent optical beams

Spatial diversity, including transmit diversity, has been proven to be a promising technique to mitigate turbulence-induced signal fading. However, due to the limitation of size in compact FSO (free-space optical) terminals, the transmit antennas cannot always be separated far enough from each other, resulting in increased channel correlation and deteriorated diversity performance. In this paper, we focus on the channel correlation statistics of transmit diversity FSO systems with two transmit beams. Specifically, we consider partially coherent optical beams, which reduce scintillation over fully coherent optical beams. We perform theoretical analysis and obtain some interesting numerical results, such as the degree of channel correlation which changed mainly with source correlation radius from 0.001 to 0.1 m. These results can be helpful for designing transmit diversity FSO systems with partially coherent beams.     

Outage probability of multiuser transmit antenna selection/maximal-ratio combining systems over arbitrary nakagami-m fading channels

The outage probability of multiuser diversity (MUD) in transmit antenna selection/maximal-ratio combining (TAS/MRC) systems is derived as an exact closed expression in independent and identically distributed (i.i.d.) Nakagami-m channels with an integer fading parameter. For a non-integer fading parameter, the exact outage probability is derived as a single infinite series of incomplete Gamma function. At high signal-to-noise ratios (SNRs), the analytical results deduce that the multiuser TAS/MRC systems can achieve a full diversity order equal to the product of the fading parameter, number of users, number of transmit antennas and number of receive antennas. The advantage of the total diversity gain becomes more pronounced on a severe fading channel. The achieved results provide an analytical framework for the assessment of multiuser TAS/MRC systems. All the derived expressions are verified by Monte Carlo simulations.     

Receive maximal-ratio combining with outdated arbitrary transmit antenna selection in Nakagami-m fading

The use of transmit antenna selection algorithms in multiple-antenna systems enables significant reduction in implementation cost and complexity while maintaining acceptable performance. An attractive and quite flexible selection algorithm is to allow the receiver to pick any of the transmit antennas that can satisfy a predetermined performance target. Such an algorithm is referred to as the arbitrarily ordered transmit antenna selection algorithm. However, the effectiveness of transmit antenna selection is decreased by several propagation impairments over the feedback channel from the receiver to the transmitter. Of these impairments, the feedback channel time delay may impose a significant impact on the achieved performance. This paper aims to investigate the impact of this time delay on the performance of receive maximal-ratio combining (MRC) diversity employing the arbitrarily ordered transmit antenna selection algorithm. In order to obtain quantitative measures for this impact, new expressions for various performance criteria are obtained by using the new derived formulas for the probability density function (pdf) and the moment generating function (MGF) of the combined signal-to-noise ratio (SNR). Numerical and simulation results are presented to illustrate the effect of delayed (i.e. outdated) feedback information on the system performance for various transmit antenna selection scenarios.     

A free-space bistatic calibration technique for the measurement ofparallel and perpendicular reflection coefficients of planarsamples

A free-space bistatic measurement system suitable for operation in the frequency range of 5.85-40 GHz is calibrated to measure the parallel and perpendicular reflection coefficients of metal-backed planar samples for obliquely incident waves. The measurement system consists of transmit and receive antennas in the bistatic configuration, mode transitions, precision coaxial cables, and the network analyzer. Diffraction effects of the edges of the sample are minimized by using spot-focusing horn lens antennas, which focus most of the energy on a one-wavelength-diameter circular section of the sample. A new free-space bistatic calibration technique is developed to eliminate errors due to multiple reflections between transmit and receive antennas via the surface of the sample. The effect of defocusing due to the obliquely incident plane wave with focused antennas is minimized by introducing correction factors which modify measured reflection coefficients. Details of the calibration procedure and a discussion of the experimental results obtained for planar samples of Teflon and Eccogel 1365-90 in the frequency range 12.4-18 GHz are presented     

Transmit beamforming methods for improved received signal-to-noise ratio in equivalent isotropic radiated power-constrained systems

A novel methodology of transmit beamforming for systems subjected to equivalent isotropic radiated power restrictions is presented in this paper. Based on the properties of the radiation due to the optimal beamforming method compared with that due to the eigen-beamforming, beamforming vectors are designed by perturbing the scaled eigen-beamforming vector such that the peak-to-average power ratio of the spatial radiation is reduced. Two algorithms incorporating this general methodology are presented. With a computational complexity less than the optimal method, both are shown to outperform conventional suboptimal beamforming methods. For example, in an investigated system with four transmit and one receive antennas, performance is improved by more than 1 dB at a packet-error-rate of 10^-3.     

BER analysis of space-time diversity in CDMA systems over frequency-selective fading channels

The performance of direct-sequence code division multiple access (DS-CDMA) using space-time spreading system, over frequency-selective fading channels, is investigated. The underlying transmit diversity scheme, previously introduced in the literature, is based on two transmit and one receive antenna. It was shown that when employed in flat fast-fading channels, the received signal quality can be improved by utilising the spatial and temporal diversities at the receiver side. We study the problem of multiuser interference in asynchronous CDMA systems that employ transmit/receive diversity using space-time spreading. To overcome the effects of interference, a decorrelator detector is used at the base station. Considering binary phase-shift keying transmission, we analyse the system performance in terms of its probability of bit error. In particular, we derive the probability of error over frequency-selective Rayleigh fading channels for both fast and slow-fading channels. For the fast-fading channel, both simulations and analytical results show that the full system diversity is achieved. On the other hand, when considering a slow-fading channel, we show that the scheme reduces to conventional space-time spreading schemes where the diversity order is half of that of fast-fading.     

Thickness dependence of electrical properties of PZT films deposited on metal substrates by laser-assisted aerosol deposition

Dependence of electrical properties-dielectric, ferroelectric, and piezoelectric properties-on film thickness was studied for lead-zirconate-titanate (PZT) thick films directly deposited onto stainless-steel (SUS) substrates in actuator devices by using a carbon dioxide (CO₂), laser-assisted aerosol deposition technique. Optical spectroscopic analysis data and laser irradiation experiments revealed that absorption at a given wavelength by the film increased with increasing film thickness. Dielectric constant epsiv, remanent polarization value P_r, and coercive field strength E_c of PZT films directly deposited onto a SUS-based piezoelectric actuator substrate annealed by CO₂ laser irradiation at 850degC improved with increasing film thickness, and for films thicker than 25 mum, e > 800, Pr > 40 muC/cm², and E_c < 45 kV/cm. In contrast, the displacement of the SUS-based actuator with the laser-annealed PZT thick film decreased with increasing film thickness.     

Cross-entropy optimisation of multiple-input multiple-output capacity by transmit antenna selection

Radio channel capacity can be increased dramatically using a multiple-input multiple-output (MIMO) scheme, but at the expense of hardware complexity. An efficient approach for complexity reduction is antenna subset selection at the transmitter and/or receiver. A novel transmit antenna selection algorithm is presented using the cross-entropy optimisation method to maximise channel capacity. In contrast with the existing work, the proposed algorithm guarantees a result to within 99% of the true optimum (i.e. the maximal capacity with selected transmit antennas) with substantially low complexity. The simulation results indicate that the proposed algorithm is independent of the relationship between the selected transmit array size and receive array size. The proposed scheme has the potential to make practical MIMO systems with high performance simpler to implement.     

Performance analyses of selection combining diversity receiver over α?μ fading channels in the presence of co-channel interference

An approach to the performance analyses of dual selection combining (SC) diversity receiver over correlated a ?m fading channels with the arbitrary parameters is presented. Fading between the diversity branches and interferers is correlated and distributed with α ? μ distribution. Infinite series expressions are obtained for the output SIR?s probability density function (PDF), cumulative distribution function (CDF) and an important measure of the system?s performances, the outage probability (OP). An average error probability is efficiently evaluated for coherent and non-coherent modulation schemes such as coherent frequency-shift keying (CFSK), coherent phase-shift keying (CPSK), binary frequency-shift keying (BFSK) and binary differentially phase-shift keying (BDPSK). Numerical results are presented to show the effects of various parameters such as fading severity, input SIR unbalance and the level of correlation between received desired signals and interferences on system?s performances.     

Joint rate and power adaptation for radio resource management in uplink wideband code division multiple access systems

The benefits of adaptive joint power control and rate allocation for uplink transmission in a wideband code division multiple access cellular system are investigated. Closed-loop power control (CLPC), to adaptively adjust the transmit power, has the effect of maintaining a target signal-to-interference ratio and bit error rate (BER) performance. On the other hand, rate adaptation requires less transmit power, although the BER performance may be poorer. The authors differentiate the power update interval from the data rate update interval, analyse and evaluate the performance of two joint rate/power adaptation algorithms in a fading environment: optimal spreading factor-power control (OSF-PC) and greedy rate packing-power control (GRP-PC). Numerical results show that GRP-PC exhibits superior throughput performance compared with other three adaptation schemes. CLPC alone exhibits throughput and BER performances comparable to those of the OSF-PC scheme, but consumes a significantly higher amount of transmit power. Rate adaptation only is not efficient in enhancing throughput, but its power consumption is minimal.