High Data Rate Wireless Communication Research Articles

ICI Reduction using Extended Kalman Filter in OFDM System

Orthogonal frequency division multiplexing (OFDM) is emerging as preferred modulation scheme in modern high data rate wireless communication systems. A well known problem of OFDM system is sensitivity to frequency offset between the transmitted and received signals, which may be caused by Doppler shift in the channel or by the difference between the transmitter and receiver local oscillator frequencies. This carrier frequency offset causes loss of orthogonality between sub carriers and the signal transmitted on each carrier are not independent of each other, leading to inter carrier interference (ICI)[1]-[4]. In this paper, the effects of ICI have been analyzed and two solutions to combat ICI have been presented. The first method is a self cancellation scheme, in which redundant data is transmitted onto adjacent subcarriers such that the ICI between adjacent sub carriers cancels out at the receiver. The other technique the Extended Kalman Filter (EKF) method statistically estimate the frequency offset and correct the offset using the estimated value at the receiver.

MIMO Channel Gain Mechanisms Relative to SISO Channel

In contrast to the rest of wireless communication technologies, multiple-input multiple-output (MIMO) technology enjoys different gain mechanisms that make it very attractive for reliable high data rate wireless communications. This paper presents a study on these gain mechanisms with particular emphasis on the case of high average received signal to noise ratio (SNR) where the MIMO system deployment is most promising. We write the MIMO channel capacity in terms of gains relative to a single- input single-output (SISO) wireless channel. Doing so, spatial multiplexing gain and power gain of MIMO wireless channels become more insightful. Based on this analysis a switching scheme between spatial multiplexing and transmit diversity is proposed. We support our discussion with numerical results which show that under a high data rate spatial multiplexing scheme the contribution of each gain mechanism to the total channel capacity depends on the channel Ricean factor, the average received SNR, and the MIMO system size. The proposed switching scheme gives about 2 dB gain in bit error rate performance relative to the spatial multiplexing mode.

Pilot Designs for Channel Estimation of MIMO OFDM Systems with Frequency-Dependent I/Q Imbalances

Multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems facilitate high data rate wireless communications, and require reliable channel estimates to fully materialize their advantages. The semiconductor downscaling trend has exacerbated device impairments such as inphase and quadrature (I/Q) imbalances which cause inter-carrier interferences in OFDM systems which cannot be remedied by increasing signal power. Different RF chains of MIMO branches can cause different I/Q imbalances which further complicates MIMO OFDM channel estimation. This paper proposes several pilot designs for the estimation of the combined responses of MIMO frequency-selective channels and frequency-dependent I/Q imbalances. The proposed designs require much smaller pilot overhead than the existing designs, and also provide estimation mean-squares error optimality (under white noise) and general applicability to preamble as well as pilot-data-multiplexed symbols in MIMO systems with or without null guard tones. Performance analyses and simulation results corroborate advantages of the proposed designs.

OFDM Systems for Wireless Communications

Orthogonal Frequency Division Multiplexing (OFDM) systems are widely used in the standards for digital audio/video broadcasting, WiFi and WiMax. Being a frequency-domain approach to communications, OFDM has important advantages in dealing with the frequency-selective nature of high data rate wireless communication channels. As the needs for operating with higher data rates become more pressing, OFDM systems have emerged as an effective physical-layer solution. This short monograph is intended as a tutorial which highlights the deleterious aspects of the wireless channel and presents why OFDM is a good choice as a modulation that can transmit at high data rates. The system-level approach we shall pursue will also point out the disadvantages of OFDM systems especially in the context of peak to average ratio, and carrier frequency synchronization. Finally, simulation of OFDM systems will be given due prominence. Simple MATLAB programs are provided for bit error rate simulation using a discrete-time OFDM representation. Software is also provided to simulate the effects of inter-block-interference, inter-carrier-interference and signal clipping on the error rate performance. Different components of the OFDM system are described, and detailed implementation notes are provided for the programs. The program can be downloaded here. Table of Contents: Introduction / Modeling Wireless Channels / Baseband OFDM System / Carrier Frequency Offset / Peak to Average Power Ratio / Simulation of the Performance of OFDM Systems / Conclusions

60-GHz Two-Dimensionally Scanning Array Employing Wideband Planar Switched Beam Network

A two-dimensionally (2-D) scanning array employing a planar switched beam network (SBN) is proposed for 60-GHz high data rate wireless communication. SBNs offer a number of advantages including low cost, multibeam operation, simple direction finding, and minimal power consumption. Unlike existing switched beam arrays operating at 60 GHz, the proposed array scans in both planes. Also, in contrast to 2-D scanning stacks of Butler matrices and Rotman lenses, the proposed SBN is uniplanar and, hence, leads to low-cost manufacturing and integration with 60-GHz radios. The network produces eight 2-D beam states and demonstrates beamforming capability across the entire band of interest (57-64 GHz) with the aid of dummy crossover structures. It is printed on a Rogers Duroid 5880 substrate along with a 2 × 4 patch array. This letter describes the design, operation, and realization of the beamforming array. Simulated and measured performance results are presented to verify the design.

PSSK Modulation Scheme for High-Data Rate Implantable Medical Devices

In this paper, we propose a new modulation scheme for high-data rate wireless body area network inbody communication systems. Simulation results are presented in terms of performance, modulation options, spectrum regrowth by nonlinearity and roll-off values of a pulse shaping filter. In addition, the planning for link budget explains that the proposed modulation approach is appropriate for high-data rate applications in the body channel environment.

Design considerations for photonically integrated antennas [Application Notes

It is generally well accepted that photonic technology, along with the low-loss, electromagnetic interference (EMI)-free and wide bandwidth signal transport of optical fiber, offers the potential for providing new capabilities, significant performance improvements, as well as design flexibility to analog radio frequency (RF) and microwave systems. The growing spectral demands of current defense systems and new technology opportunities such as high data rate wireless communications offer the possibility of photonics seeing significant technology insertion opportunities in the near as well as the far future.

An overview of peak-to-average power ratio reduction schemes for OFDM signals

Orthogonal frequency division multiplexing (OFDM) has been adopted as a standard for various high data rate wireless communication systems due to the spectral bandwidth efficiency, robustness to frequency selective fading channels, etc. However, implementation of the OFDM system entails several difficulties. One of the major drawbacks is the high peak-to-average power ratio (PAPR), which results in intercarrier interference, high out-of-band radiation, and bit error rate performance degradation, mainly due to the nonlinearity of the high power amplifier. This paper reviews the conventional PAPR reduction schemes and their modifications for achieving the low computational complexity required for practical implementation in wireless communication systems.

Two new space-time codes for UWB range extension

Ultrawideband (UWB) radio is a promising solution for low and high data rate wireless communications over short ranges. Space-time (ST) coding techniques are known to be simple and practical ways to increase both the spectral efficiency and the capacity in wireless communications. So far, few contributions have looked over multiple-inputs multiple-outputs (MIMO) UWB systems. In this paper we introduce two new families of ST codes suitable for binary pulse modulated (BPM) and pulse position modulated (PPM) UWB systems. The codes are characterised by full-rate, full-diversity and low complexity at the receiver side. The probability of error resulting from the use of these space-time codes in a typical MIMO UWB channel is analytically derived. Simulations support analysis for various numbers of transmit and receive antennas in order to show that the two methods can effectively enlarge the transmission range of UWB devices.

Information-guided channel-hopping for high data rate wireless communication

In this letter, we introduce information-guided channel-hopping, a new scheme for high data rate communication over Rayleigh fading channel using multiple transmit antennas. This scheme is proposed based on the fact that the independence character of multi-channel can be used as an additional information transmitting channel, and the maximum likelihood decoding can be achieved in a simple way by decoupling of the signals conveyed by different methods. The analysis results prove that the capacity behavior of this scheme is better than that of the space-time block coding for more than two transmit antennas.

OFDM 시스템을 위한 순환 지연을 사용하는 협력 다이버시티 기법

Orthogonal Frequency Division Multiplexing (OFDM) is one of the most promising technologies for high data rate wireless communications. OFDM has been adopted in wireless standards such as digital audio/video broadcasting. The combination of OFDM and cooperative diversity techniques can provide the diversity gain and/or increased capacity. In this paper, the cooperative coding using cyclic delay diversity (CDD) for multiuser OFDM systems is introduced. To improve the beneficial effects of relays`s cooperation, CDD is adopted in cooperative transmission of relays. Simulation results show the bit error rate (BER) for various consideration. The proposed scheme provides improved performance compared to delay.

An efficient joint channel estimation and decoding algorithm for turbo-coded space–time orthogonal frequency division multiplexing receivers

The challenging problem in the design of digital receivers of today's and future high-speed, high data-rate wireless communication systems is to implement the optimal decoding and channel estimation processes jointly in a computationally feasible way. Without realising such a critical function perfectly at receiver, the whole system will not work properly within the desired performance limits. Unfortunately, direct implementation of such optimal algorithms is not possible mainly due to their mathematically intractable and computationally prohibitive nature. A novel algorithm that reaches the performance of the optimal maximum a posteriori (MAP) algorithm with a feasible computational complexity is proposed. The algorithm makes use of a powerful statistical signal processing tool called the expectation–maximisation (EM) technique. It iteratively executes the MAP joint channel estimation and decoding for space–time block-coded orthogonal frequency division multiplexing systems with turbo channel coding in the presence of unknown wireless dispersive channels. The main novelty of the work comes from the facts that the proposed algorithm estimates the channel in a non-data-aided fashion and therefore except a small number of pilot symbols required for initialisation, no training sequence is necessary. Also the approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen–Loeve (KL) orthogonal expansion and finds MAP estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MAP estimator. Moreover, optimal rank reduction is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the iterative estimation approach.

Low Complexity Turbo Equalization for High Data Rate Wireless Communications

Soft interference cancellers (SICs) have been proposed in the literature as a means for reducing the computational complexity of the so-called turbo equalization receiver architecture. Soft-input-soft output (SISO) equalization algorithms based on linear filters have a tremendous complexity advantage over trellis-diagram-based SISO equalizers, especially for high-order modulations and long-delay spread frequency selective channels. In this paper, we modify the way in which the SIC incorporates soft information. In existing literature the input to the cancellation filter is the expectation of the symbols based solely on the apriori probabilities coming from the decoder, whereas here we propose to use the conditional expectation of those symbols, given both the apriori probabilities and the received sequence. This modification results in performance gains at the expense of increased computational complexity, as compared to previous SIC-based schemes. However, by introducing an approximation to the aforementioned algorithm a linear complexity SISO equalizer can be derived. Simulation results for an 8-PSK constellation and hostile radio channels have shown the effectiveness of the proposed algorithms in mitigating the intersymbol interference (ISI).

Super-orthogonal space-time codes with rectangular constellations and two transmit antennas for high data rate wireless communications

We demonstrate super-orthogonal space-time (ST) trellis codes with rectangular signal constellations for wireless communications with a spectral efficiency of 4 bits/s/Hz. Considering a mobile wireless communications system with two transmit antennas, we form a 4D signal constellation as Cartesian product of two 2D rectangular signal sets, a 4D point being transmitted by the first antenna as two concatenated 2D points in two consecutive channel uses. The 2D symbols transmitted by the second antenna are not independent, but so chosen as to form, together with the symbols transmitted by the first antenna, the entries of a 2 times 2 orthogonal matrix. This can be done in four different ways, resulting in four sets of 2 times 2 orthogonal matrices. To obtain a higher data rate, the union of two of them forms a super-orthogonal signal set. With 2 times 2 orthogonal matrices, we then label the state transitions of a trellis diagram describing the operation of the encoder. We perform simulations using a model that takes into account the Doppler effect as well as the effect of spatial antenna correlation at both the base station (BS) and at the mobile station (MS). The frame error rate (FER) and the bit error rate (BER) performance results show an excellent behaviour of our proposed super-orthogonal ST trellis code, which clearly outperforms all known simple ST trellis codes of same spectral efficiency using 16QAM or 16PSK

Modeling and Estimation of Wireless OFDM Channels by Using Time-Frequency Analysis

Orthogonal frequency division multiplexing (OFDM) has become a very popular method for high data rate wireless communications because of its advantages over single carrier modulation schemes on multipath, frequency selective fading channels. However, intercarrier interference, due to Doppler frequency shifts, and multipath fading severely degrade the performance of OFDM systems. Estimation of channel parameters is required at the receiver. In this paper, we present a channel modeling and estimation method based on the time-frequency representation of the received signal. The discrete evolutionary transform provides a time-frequency procedure to obtain a complete characterization of the multipath, fading, and frequency selective channels. Simulations are used to illustrate the performance of the proposed procedure and to compare it with other time-varying channel estimation techniques.

V-Band Patch-Fed Rod Antennas for High Data-Rate Wireless Communications

This paper presents the design and the prototyping of a patch-fed dielectric rod antenna at V band. The proposed antenna requires small space on printed circuit boards and eliminates the difficulty for a millimeter-wave probe feed. The details of simulation and manufacturing are described and measurements are conducted to examine the antenna performance. The patch and the rod have been fabricated using Duroid substrates and Teflon respectively. The impedance bandwidth of the antenna is 3 GHz. Its measured gain is up to 16 dBi at 61 GHz. Radiation characteristics, circular polarizations and beam tilting are also examined and discussed. As the proposed antenna can achieve high gain with relatively low profile, multiple patch-fed rods can be built as a beam-switching array or a multiple-input-multiple-output array for high data rate wireless communications.

Production test technique for measuring BER of ultra-wideband (UWB) devices

Ultra-wideband is an emerging standard for short-range high data-rate wireless communication. In a production test environment, ultra-wideband devices are tested for bit error rate (BER) in the presence of an external interferer. As the target BER values are small at low interference levels, it requires a long test sequence for measuring BER, incurring a long test time. This paper describes a novel production test technique for BER testing of orthogonal frequency-division multiplexing transceivers. By adjusting the phase values of the baseband signal, the proposed manufacturing test methodology reduces the overall test time considerably (up to 20/spl times/), while keeping the error vector magnitude and peak-to-average ratio of the transmitted signal unchanged. This method can be extended to any phase modulation scheme to reduce the test time for BER.

Direct Implementation of Space-Time MC-CDMA Receiver with Adaptive Linearly Constrained Constant Modulus Algorithm

SUMMARY To support high data rate wireless communications, in this paper, based on the linearly constrained constant modulus (LCCM) criterion, the reverse link performance of the multi-carrier code division multiple access (MC-CDMA) receiver, with frequency combiner, and having smart antenna arrays beamformer in base station, has been investigated over the Rayleigh fading channel. By using the Kronecker product an equivalent direct formulation, which integrates the information of spatial-domain as well as temporal-domain, with constraint matrix could be obtained. In consequence, the modified normalized LCCM-gradient algorithm is devised to adaptively implement the direct constrained optimal weights solution of the fully space-time MC-CDMA detector. We show that the proposed method outperforms the constrained minimum output energy (CMOE) algorithm and is more robust against to the signal mismatch, due to imperfect channel and direction-of-arrival estimation used in the array beamformer.

Modeling and Optimization of Interference Limited Wireless Communications

AbstractMultiple access interference (MAI) limits the system capacity of wireless communications systems applying code division multiple access (CDMA). Provided that channel knowledge is available in the transmitter, the transmitted signal can be preprocessed by multiuser transmission (MUT) methods. As optimization criterion, the bit error probability/rate (BER) is chosen. On the transmit signal, a limited power constraint is imposed, which is a quadratic function of the transmit signal. The nonlinear optimization problem is modeled in this paper. Unfortunately, the problem is non‐convex. However, with iterative nonlinear optimization methods like SQP, local minima can be found with a performance outperforming other MUT methods.The main remaining challenge are low‐complexity optimization algorithms to allow for a real‐time implementation in highdata rate wireless communications. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Rotationally invariant space-time trellis codes with 4-D rectangular constellations for high data rate wireless communications

We demonstrate rotationally invariant space-time (ST) trellis codes with a 4-D rectangular signal constellation for data transmission over fading channels using two transmit antennas. The rotational invariance is a good property to have that may alleviate the task of the carrier phase tracking circuit in the receiver. The transmitted data stream is segmented into eight bit blocks and quadrature amplitude modulated using a 256 point 4-D signal constellation whose 2-D constituent constellation is a 16 point square constellation doubly partitioned. The 4-D signal constellation is simply the Cartesian product of the 2-D signal constellation with itself and has 32 subsets. The partition is performed on one side into four subsets A, B, C, and D with increased minimum-squared Euclidian distance, and on the other side into four rings, where each ring includes four points of equal energy. We propose both linear and nonlinear ST trellis codes and perform simulations using an appropriate multiple-input multiple-output (MIMO) channel model. The 4-D ST codes constructed here demonstrate about the same frame error rate (FER) performance as their 2-D counterparts, having however the added value of rotational invariance.