Characterizing outage capacity for space-time communication over wideband wireless channels

In this paper, an enhanced scheme of Index Modulation for Orthogonal Frequency Division Multiplexing (IM-OFDM), called Repeated IM-OFDM with Diversity Reception (ReIM-OFDM) is proposed. ReIM-OFDM achieves performance improvement over the convetional IM-OFDM at the same spectral efficiency by providing additional space and frequency diversity. Similar to IM-OFDM, the proposed ReIM-OFDM also activates K out of total N subcarriers to convey information bits using both the active sub-carriers and their indices. However, it differs from IM-OFDM in that all activated sub-carriers are modulated by the same M-ary data symbol. For signal combining, either Maximal Ratio Combining (MRC) or Selection Combining (SC) can be used in the spatial and sub-carriers domain to help ReIM-OFDM achieve both space and frequency diversity gain. In order to analyze performance of the system, the Moment Generating Function (MGF) is used to obtain the closed-form expressions for the pairwise index error probability (PEP) and the symbol error probability (SEP) in both cases: ReIM-OFDM-MRC and ReIM-OFDM-SC. Effects of various system parameters on the SEP are analyzed to select the best ReIM-OFDM configuration with minimum error probability. Our analysis proves the effectiveness of ReIM-OFDM over IM-OFDM at the same spectral efficiency.

International audience

This chapter is attempted to provide a survey of the advanced concepts and related issues involved in Multiple Input Multiple Output (MIMO) systems. MIMO system technology has been considered as a really significant foundation on which to build the next and future generations of wireless networks. The chapter addresses advanced MIMO techniques such as polarization diversity and antenna selection. We gradually provide an overview of the MIMO features from basic to more advanced topics. The first sections of this chapter start by introducing the key aspects of theMIMO theory. TheMIMO systemmodel is first presented in a genericway. Then, we proceed to describe diversity schemes used in MIMO systems. MIMO technology could exploit several diversity techniques beyond the spatial diversity. These techniques essentially cover frequency diversity, time diversity and polarization diversity. We further provide the reader with a geometrically based models for MIMO systems. The virtue of this channel modeling is to adopt realisticmethods for modeling the spatio-temporal channel statistics from a physical wave-propagation viewpoint. Two classes for MIMO channel modeling will be described. These models involve the Geometry-based Stochastic ChannelModels (GSCM) and the Stochastic channel models. Besides the listedMIMO channel models already described, we derive and discuss capacity formulas for transmission over MIMO systems. The achieved MIMO capacities highlight the potential of spatial diversity for improving the spectral efficiency of MIMO channels. When Channel State Information (CSI) is available at both ends of the transmission link, the MIMO system capacity is optimally derived by using adaptive power allocation based on water-filling technique. The chapter continues by examining the combining techniques for multiple antenna systems. Combining techniques are motivated for MIMO systems since they enable the signal to noise ratio (SNR) maximization at the combiner output. The fundamental combing techniques are the Maximal Ratio Combining (MRC), the Selection Combining (SC) and the Equal Gain Combining(EGC). Once the combining techniques are analyzed, the reader is introduced to the beamforming processing as an optimal strategy for combining. The use of multiple antennas significantly improves the channel spectral efficiency. Nevertheless, this induces higher system complexity of the communication system and the communication system performance is effected due to correlation between antennas that need to be deployed at the same terminal. As such, the antenna selection algorithm for MIMO systems is presented. To elaborate on this point, we introduce Space time coding techniques for MIMO systems and we evaluate by simulation the performance of the communication system. Next, we emphasis on multi polarization techniques for MIMO systems. As a background, we presume that the reader has a thorough understanding of antenna theory. We recall the basic antenna theory and concepts that are used throughout the rest of the chapter. We rigorously introduce the 3D channel model over the Non-Line of Sight (NLOS) propagation channel for MIMO system with polarized antennas. We treat the depolarization phenomena and we study its effect on MIMO system capacity. The last section of the chapter provides a scenario for collaborative sensor nodes performing distributed MIMO system model which is devoted to sensor node localization in Wireless Sensor Networks. The localization algorithm is based on beamforming processing and was tested by simulation. Our chapter provides the reader by simulation examples for almost all the topics that have been treated for MIMO system development and key issues affecting achieved performance.

In this paper, we propose a space-time coding and carrier block spreading based multiple-input-multiple-output (MIMO) orthogonal-frequency-division-multiplexing (OFDM) system. The proposed system exploits the potential spatial and frequency diversity of MIMO systems in frequency-selective fading environments through a two-stage procedure. In the first stage, we use space-time coding to exploit the spatial diversity, and in the second stage, we adopt block spreading among blocks of OFDM carriers to obtain frequency diversity. Moreover, by using rotated Hadamard matrix or rotated discrete Fourier transform (DFT) matrix as the carrier spreading matrix, the system can also possess a certain degree of modulation diversity. Our proposed system enjoys the advantage of high flexibility and low complexity. It allows the use of any existing space-time coding scheme as its component space-time code, and the diversity gains are obtained with only moderate transmit and receive processing complexity. Simulation results show that our proposed system can achieve desired spatial and frequency diversity with low detection complexity. Comparing to some existing space-frequency coding schemes, our proposed system enjoys the merit of low complexity, although it could suffer from some performance degradation, which is caused by the separation of space-time coding and frequency-domain spreading process.

Southern Railway have collected extensive data on microwave propagation over their 2000 KM net-work for over five years. The main problem of long path communication link is the occurrence of momentary deep fades of 10 to 40 dB for very short duration of 1 to 2 seconds. These dropouts. account for 80% of the total severe fading and about 60% of the total outage occur. in pre-summer months viz., February, March and April. The probability occurrence of deep fades increases very rapidly with distance and a computerised study indicate. that it is proportional to (Distance)10. Comparative study of Space Diversity and Frequency Diversity for long path indicates that Space Diversity reduces the outage time by 50% whereas Frequency Diversity wih even a small frequency separation of 1% reduces the outage by as much as 90%. Frequency Diversity, therefore, appears to be definitely more suited to tropical areas subjected to heavy momentary outages tban Space Diversity.

In this paper, the rate-2 pcu STF coding schemes that can be efficiently implemented for use in multiband UWB-MIMO systems has been presented. These proposed STF codes are constructed based on the multi-dimensional constellation preceding so that the rotated version of the information symbols are spread across adjacent subcarriers and sent over M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> transmit antennas and Mb time periods, allowing effective exploitation of space, time and frequency diversity. The performance of these STF codes with two transmit antennas over the IEEE 802.15.SG3a channel models are compared at the same spectral efficiency. It is shown that our proposed codes outperform well known schemes found in the literature such as rate-1 SF codes, which guarantee full diversity. In addition, we devise a random interleaving method to incorporate into the proposed codes and the simulation results show that further gains can be achieved depending on the level of SNR.

DHT-based GFDM and STC-GFDM systems for beyond 5G wireless networks

Literature indicates that frequency diversity can be utilized to compensate channel uncertainties such as multipath fading. Therefore, in this paper it is exploited for improving accuracy in locating stationary and mobile objects in the indoor environment. First, frequency diversity technique is introduced for small scale and temporal variation compensation of received signals and demonstrated analytically that it in fact enhances location accuracy. A novel metric is introduced in selection combining in order to achieve location accuracy through the addition of frequency diversity upon two of the available location determination schemes. The results are evaluated experimentally against the case where there is no frequency diversity for reception by using low cost wireless RF devices such as motes. An asset location tracking system is then devised to both improve accuracy and predict asset movement. Frequency diversity in terms of channel spacing of 55 MHz is evaluated and shown to provide a reduction in location determination error between 18 and 23% when compared to a system without frequency diversity. Finally, results from frequency diversity are compared against the spatial diversity techniques in terms of improvement in location accuracy, power consumption of the transmitter, and hardware and software costs.

We propose an information theoretic waveform design algorithm for target tracking in a low-grazing angle (LGA) scenario. We incorporate realistic physical and statistical effects, such as Earth's curvature, vertical refractivity gradient of lower atmosphere, and compound-Gaussian characteristics of sea-clutter, into our model. We employ a co-located multiple-input-multiple-output (MIMO) radar configuration using wideband orthogonal frequency division multiplexing (OFDM) signalling scheme. The frequency diversity of OFDM provides richer information about the target as different scattering centers resonate at different frequencies. Additionally, we use polarization-sensitive transceivers to resolve the multipath signals with small separation angles. Thus, we track the scattering coefficients of the target at different frequencies along with its position and velocity. We apply a sequential Monte Carlo method (particle filter) to track the target. Our tracker works in a closed-loop fashion with an integrated optimal waveform design technique based on mutual information (MI) criterion. We seek the optimal OFDM waveform at the current pulse duration to maximize the MI between the state and measurement vectors at the next pulse duration utilizing all the measurement history up to the current pulse. Our numerical examples demonstrate the importance of realistic physical modeling, effects of frequency diversity through OFDM MIMO configuration, and achieved performance improvements due to adaptive OFDM waveform design.

Spectrum sensing is a critical and challenging issue in cognitive radio networks. Prior research has demonstrated that using spatial diversity or temporal diversity can lead to more efficient spectrum sensing. Based on Neyman-Pearson criterion, this paper derives a novel spectrum sensing algorithm which exploits spatial diversity among multiple cognitive sensors and temporal diversity among consecutive time slots jointly. The numerical results not only verify the improvement of the sensing performance comparing with singular (spatial or temporal) diversity is applied, but also show the reduction of sensing overhead in low signal-noise-ratio (SNR) regime.

In this paper, a planar multiple input multiple output MIMO UWB array is proposed for 3D microwave imaging applications. According to the virtual array concept, the advantage of the MIMO array lies on improving the angular resolution with a reduced number of antennas, and achieve the same resolution as a fully populated conventional arrays. In addition, the UWB systems provide a better range resolution thanks to their large bandwidth. The frequency diversity and its influence on the system's resolution is also studied. For the MIMO array, an optimal UWB antenna element is designed with more than 128% of fractional bandwidth with no considerable distortion of the transmitted impulse. For the imaging algorithm, the Back-projection algorithm is implemented and used for the reconstruction of the images. In order to study the performance of the designed system, the full-wave electromagnetic simulator CST MWS is used which allow the modelling in three-dimensions (3D). The resulting images of a different target materials and dielectric properties confirm the reliability of the proposed system and the impact of the spatial and frequency diversity in the resolution improvement while considerably reducing the cost of the MIMO UWB array.

This paper presents frequency diversity effects of localized transmission, clustered transmission, and intra-subframe frequency hopping (FH) using a frequency domain equalizer (FDE) for discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). In the evaluations, we employ the normalized frequency mean square covariance (NFMSV) as a measure of the frequency diversity effect, i.e., randomization level of the frequency domain interleaving associated with turbo coding. Link-level computer simulation results show that frequency diversity is very effective in decreasing the required average received signal-to-noise power ratio (SNR) at the target average block error rate (BLER) using a linear minimum mean-square error (LMMSE) based FDE according to the increase in the entire transmission bandwidth for DFT-precoded OFDMA. Moreover, we show that the NFMSV is an accurate measure of the frequency diversity effect for the 3 transmission schemes for DFT-precoded OFDMA. We also clarify the frequency diversity effects of the 3 transmission schemes from the viewpoint of the required average received SNR satisfying the target average BLER for the various key radio parameters for DFT-precoded OFDMA in frequency-selective Rayleigh fading channels.

The widespread deployment of WiFi infrastructure has facilitated the development of Time-of-Flight (ToF) based sensing applications. ToF estimation, however, is a challenging task due to the complexity of multipath effect. In this paper, we propose a phase difference based method for ToF estimation and uncover the potential of signal cancellation to mitigate the impact of multipath and noise on phase differences among subcarriers. To separate the moving target path from the complex multipath for ToF estimation, we suggest employing specific elimination methods tailored to the characteristics of different signal components. For dynamic multipath, we observe that when a given subcarrier propagates along two paths to the receiver, with path lengths differing by half a wavelength, the phase difference introduced by these two paths cancels each other out. Therefore, we propose two metrics to identify signals that satisfy this condition, utilizing both frequency diversity and spatial diversity. Additionally, we propose leveraging time diversity to eliminate the static multipath component and reduce the impact of noise. We implemented the methods with off-the-shelf WiFi devices and achieved mean errors of 15.36 cm and 21.05 cm for distance estimation in outdoor and indoor scenarios, outperforming state-of-the-art ToF estimation method by 50% error reduction.

This paper deals with the study of received signal strength (RSS) as an input reference used in Bluetooth Low Energy (BLE) Indoor Positioning System (IPS) for location estimation. In the IPS where there are fixed scanners and portable advertisers which are sending no additional data, the RSS is the only reference for location process. Therefore, it is important to suppress RSS fluctuation caused by fading. The proposed method uses spatial diversity (SIMO approach) in combination with frequency diversity. Two different distances between four antennas were tested and for a quarter of the wavelength additional arrangement using back-side reflector was taken.

Orthogonal frequency and code division multiplexing (OFCDM) has been spotlighted as a next generation communication system. Cooperative OFCDM relaying system has advantages that provide the high reliability while maintaining high data rate because of getting the frequency diversity and the spatial diversity. However, this system decreases a throughput performance when it employs many relays. Therefore, in this letter, we present that the proposed system combines CDD due to complement throughput performance problem. In addition to that, the proposed system based on orthogonal frequency and code division multiple access (OFCDMA) which efficiently communicates each other through assigning the subcarrier and the channel code according to channel state or other environments.