Software-only TDOA/RTF positioning for 3G WCDMA wireless network

A hybrid location finding technique based oil time difference of arrival (TDOA) with round-trip time (RTT) measurements is proposed for a wideband code division Multiple access (WCDMA) network. In this technique, a mobile station measures timing from at least three base stations using user equipment receive-transmit (UE Rx-Tx) time difference and at least three base stations measure timing from the mobile station using RTT. The timing measurements of mobile and base stations are then combined to solve for both the location of the mobile and the synchronization offset between base stations. A software-only geolocation system based on the above mobile/base stations timing measurements is implemented in Matlab platform and the performance of the system is investigated using large-scale propagation models

SGD Frequency-Domain Space-Frequency Semiblind Multiuser Receiver with an Adaptive Optimal Mixing Parameter

A novel stochastic gradient descent frequency-domain (FD) space-frequency (SF) semiblind multiuser receiver with an adaptive optimal mixing parameter is proposed to improve performance of FD semiblind multiuser receivers with a fixed mixing parameters and reduces computational complexity of suboptimal FD semiblind multiuser receivers in SFBC downlink MIMO MC-CDMA systems where various numbers of users exist. The receiver exploits an adaptive mixing parameter to mix information ratio between the training-based mode and the blind-based mode. Analytical results prove that the optimal mixing parameter value relies on power and number of active loaded users existing in the system. Computer simulation results show that when the mixing parameter is adapted closely to the optimal mixing parameter value, the performance of the receiver outperforms existing FD SF adaptive step-size (AS) LMS semiblind based with a fixed mixing parameter and conventional FD SF AS-LMS training-based multiuser receivers in the MSE, SER and signal to interference plus noise ratio in both static and dynamic environments

Doppler spread estimation in mobile fading channels

The Doppler spread, or equivalently, the mobile speed, is a measure of the spectral dispersion of a mobile fading channel. Accurate estimation of the mobile speed is important in wireless mobile applications which require such as knowledge of the rate of channel variations. In this dissertation, first the performance of classical crossing- and covariance-based speed estimators is studied. Next, the problem of mobile speed estimation using diversity combining is investigated. Then, a nonparametric estimation technique is proposed that is robust to different channel variations. Finally, cyclostationarity-based speed estimators which can be applied either blindly or with the aid of pilot data, are developed. A unified framework for the performance analysis of well-known crossing and covariance based speed estimation techniques is presented. This allows a fair analytical comparison among all the methods. Interestingly, it is proved that all these methods are asymptotically equivalent, i.e., for large observation intervals. The extensive performance analysis, supported by Monte Carlo simulations, has revealed that depending on the channel condition and the observation interval, one needs to use a crossing or a covariance based technique to achieve the desired estimation accuracy over a large range of mobile speeds. Two common diversity schemes, selection combining (SC) and maximal ratio combining (MRC), are considered for Doppler spread estimation. Four new estimators are derived which rely on the inphase zero crossing rate, inphase rate of maxima, phase zero crossing rate, and the instantaneous frequency zero crossing rate of the output of SC. Two estimators, which work based on the level crossing rates of the envelopes at the output of SC and MRC, are also proposed. The performances of all these estimators are investigated in realistic noisy environments with different kinds of scatterings and different numbers of diversity branches. Then a novel speed estimation technique is proposed that is applicable to both mobile and base stations, based on the characteristics in the power spectrum of mobile fading channels. The analytic performance analysis, verified by Monte Carlo simulations, shows that this low-complexity estimator is not only robust to both Gaussian and non-Gaussian noises, but also insensitive to nonisotropic scattering observed at the mobile. The estimator performs very well in both two- and three-dimensional propagation environments. By taking advantage of resolvable paths in wideband fading channels, the robustness against both nonisotropic scattering and line of sight can be further increased, due to the differences among the Doppler spectra observed at different paths. This technique is also extended to base stations with antenna arrays. By exploiting the spatial information, the proposed space-time estimator exhibits excellent performance over a wide range of noise power, nonisotropic scattering, and the line-of-sight component. This is all verified by simulation. The utility of the new method is further demonstrated by applying it to the measured data. Finally, to design robust blind and data-aided mobile speed estimators, a proposal is made to exploit the inherent cyclostationarity of linearly modulated signals transmitted through fading channels. Two categories of cyclic-correlation- and cyclic-spectrum-based methods are developed. Extension to space-time speed estimation at the base station in macrocells is also provided. In comparison with the existing methods, the new estimators can be used without any need for pilot tones and are robust to additive stationary noise or interference of any color or distribution. Unlike the conventional multi-antenna based method, the proposed space-time speed estimator does not assume the receiver noise to be spatially white. A suboptimal training sequence is also devised for pilot-symbol assisted methods, to reduce the estimation error. The performance of the proposed estimators are illustrated via extensive Monte Carlo simulations

Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions

Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio (NR) and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing of 8 terminals). Coarse and even error-prone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.Comment: submitted to IEEE transactions on signal processin

信頼性の高い大容量公共用移動通信システムを実現するためのソフトウェア無線およびコグニティブ無線に関する研究

Public safety mobile wireless communication systems (PMCSs) are widely used by public safety personnel, such as firefighters and police, as well as local governments. PMCSs are crucial to protect safety and security of communities. Conventional PMCSs effectively cover underpopulated areas as well as urban areas by employing long-zone scheme. Since the PMCSs can cover areas that are not covered by commercial cellule systems, they play the important role as the only communication tool. Moreover, the conventional PMCSs have enhanced robustness and reliability. The conventional PMCSs can keep their services even if backbone lines are cut off. In contrast, short-zone scheme systems cannot offer stable and wide service area without backbone line connection. For example, the Great East Japan Earthquake in Japan, police mobile communication systems had kept their functions while cellular phones became disabled. PMCSs are required to be quite high robustness and reliability in order to save human life. Recently, conventional PMCSs are required to realize further expansion of service areas and high speed transmission although they have stably provided users with wide service areas so far. Nowadays, in order to solve complicated public affair quickly, more stable service areas and broadband communication are required. Compared with conventional PMCSs in urban areas, commercial wireless mobile communication systems (CWMCSs) such as cellular systems supply stable service areas and broadband communication in times of peace. In accordance with development of wireless technology, PMCSs need to keep pace with CWMCSs. However, conventional PMCSs can hardly realize further stable service areas and high speed transmission because of large-zone scheme. In terms of realization of further stable service areas, no-service areas cannot be eliminated easily. This is because no-service areas are mostly attributed to shadowing; in large-zone scheme, a no-service area that must essentially be covered by a certain base station is seldom covered by other neighboring base stations. Although new allocation of base stations is fundamental answer to solve no-service area problem in PMCSs, building new base stations of PMCSs that are not used for a commercial purpose is restricted by national and local budget. Realization of high speed transmission of PMCSs is also difficult because of large-zone scheme. To realize high speed transmission, increase of transmit power or shrinking of service area coverage is required to compensate Signal to Noise Power Ratio (SNR) deterioration caused by expanding bandwidth. Increase of transmission power of mobile station used in large-zone scheme systems is almost impossible because transmission power of mobile station is originally high. Thus, shrinking of service areas is necessary for high speed communication. Currently, to realize high speed transmission, next generation broadband PMCSs (BPMCSs) employing short-or middle-zone scheme are being developed. In the 3GPP, it is considered that the Long Term Evolution (LTE) is used for communication of public safety. In Japan, National Institute of Information and Communications Technology (NICT) has researched and developed Public Broadband Wireless Communication System (PBWCS), which employs 200MHz as carrier frequency. The PBWCS has already been equipped in national police agency in Japan. However, we consider that the conventional narrowband PMCSs (NPM-CSs) are not replaced with the BPMCSs completely. This is because the BPMCSs cannot cover all the areas that the conventional NPM-CSs have covered. Moreover, there are problems of robustness and reliability when accidents happen. Hence, users of PMCSs will utilize both of NPMCSs and BPMCSs in accordance with the situation. In this case, users equipping several terminals feel inconvenient and also radio resources are not used effectively. The best solution to realize optimal PMCSs is employing heterogeneous cognitive radio (HCR) for PMCSs. By applying the HCR to PMCSs, service areas expansion and high speed transmission in PM-CSs will be realized effectively. We propose an integrated system combining NPMCSs with CWMCSs and BPMCSs to make communication quality of the PMCSs improve. The proposed HCR recognizes communication conditions of several systems and then provides PMCS\u27s users with optimal communication quality. Although software defined radio techniques (SDR) are ideal to operate cognitive radio more flexibly, we deal with HCR mainly to realize combined systems in this thesis. We study advantages, problems, and their solution to realize the HCR for PMCSs. Firstly, we research service area expansion of NPMCSs using HCR. The proposed HCR is utilized for stabilization of NPMCS\u27s service area. If communication quality of a NPMCS deteriorates owing to shadowing, the proposed HCR terminal obtains a part of NPMCS\u27s data called subsidiary information (SI) from CWMCSs or BPMCSs. The proposed HCR terminal can improve PMCS\u27s bit error rate (BER) performance by combining the SI with received signals of the NPMCS and then decoding the combined signals using forward error correction (FEC). Since convolutional codes are often used in FEC of NPMCSs, we consider BER improvement methods of the convolutional code. We derive modified Viterbi algorithm from maximum likelihood sequence estimation (MLSE) of the combined signals. Moreover, we introduce the distance spectrum to evaluate characteristics of the convolutional codes. The distance spectrum is used for estimating improvement of BER performances. Next, we consider synchronization methods to realize the proposed HCR. In the HCR, there are two types of synchronization method; one is the self-synchronization method to synchronize each system itself. The other is the co-synchronization method to combine different systems. In this thesis, we consider self-synchronization methods of NPMCSs mainly. This is because the HCR aims to improve communication quality of NPMCSs equipping conventional self-synchronization methods that are not probably available in low SNR environments. In this environment, since NPMCSs can hardly obtain their self-synchronization alone, powerful self-synchronization methods using HCR techniques are required. We propose two synchronization methods that are utilization of global portioning system (GPS) signals and utilization of the SI, respectively. The synchronization methods utilizing GPS signals can acquire timing synchronization. To obtain timing synchronization, the proposed HCR acquires accurate time and own location using the GPS signals. The HCR also gets the location of base stations and the frame timing by making the SI convey their information. Since the HCR can know accurate time and distance between the base station and the HCR, synchronization timing can be calculated. However, in GPS based method, preciseness of timing synchronization may be deteriorated by measurement error of GPS signals, diffraction caused by mountains, and propagation delay caused by reection. For this reason, we consider a mitigation method of the timing error and then evaluate BER performances using computer simulation. Moreover, we propose a SI based synchronization method that can obtain timing synchronization without GPS signals. The proposed method is employed when a NPMCS uses differential coded π/4 shift QPSK as the modulation scheme. The notable feature of the proposed method is to convey the phase rotation of the π/4 shift QPSK as the SI. The HCR can forecast PMCS\u27s envelopes from the obtained SI and then obtain the timing synchronization by correlating the forecasted envelopes with real received envelopes. Since the proposed method can also be used for co-synchronization and BER improvement, CWMCS\u27s resource consumption to convey the SI is suppressed. Finally, we consider HCRs combining several PMCSs. In this thesis, the combination of NPMCSs and the combination of a NPMCS and a BPMCS are researched. In the combination of NPMCSs, we consider that several PMCSs are integrated by SDR. In the combination of a NPMCS and a BPMCS, we propose site diversity based on HCR to improve uplink communication quality of the BPMCS. In this diversity, since uplink interference must be avoided, we employ combination of the adaptive array and HCR techniques. Moreover, we propose information compression methods for narrow band backbone lines so that received data can be conveyed to head office with little BER deterioration. PMCSs will have played an important role to ensure social safety. In the thesis, we consider the one of the next generation PMCSs employing SDR and HCR. Using this research, we can obtain a direction of optimal PMCSs. The next step that we need to perform is to apply our proposed method to actual radio systems. We must continue this research so that high reliable and compact PMCSs can be realized.電気通信大学201

Bit error rate estimation in WiMAX communications at vehicular speeds using Nakagami-m fading model

The wireless communication industry has experienced a rapid technological evolution from its basic first generation (1G) wireless systems to the latest fourth generation (4G) wireless broadband systems. Wireless broadband systems are becoming increasingly popular with consumers and the technological strength of 4G has played a major role behind the success of wireless broadband systems. The IEEE 802.16m standard of the Worldwide Interoperability for Microwave Access (WiMAX) has been accepted as a 4G standard by the Institute of Electrical and Electronics Engineers in 2011. The IEEE 802.16m is fully optimised for wireless communications in fixed environments and can deliver very high throughput and excellent quality of service. In mobile communication environments however, WiMAX consumers experience a graceful degradation of service as a direct function of vehicular speeds. At high vehicular speeds, the throughput drops in WiMAX systems and unless proactive measures such as forward error control and packet size optimisation are adopted and properly adjusted, many applications cannot be facilitated at high vehicular speeds in WiMAX communications. For any proactive measure, bit error rate estimation as a function of vehicular speed, serves as a useful tool. In this thesis, we present an analytical model for bit error rate estimation in WiMAX communications using the Nakagami-m fading model. We also show, through an analysis of the data collected from a practical WiMAX system, that the Nakagami-m model can be made adaptive as a function of speed, to represent fading in fixed environments as well as mobile environments

The Multi-Input Multi-Output (MIMO) Channel Modeling, Simulation and Applications

This thesis mainly focus on the Multi-Input Multi-Output (MIMO) channel modeling, simulation and applications. There are several ways to design a MIMO channel. Most of the examples are given in Chapter 2, where we can design channels based on the environments and also based on other conditions. One of the new MIMO channel designs based on physical and virtual channel design is discussed in Unitary-Independent- Unitary (UIU) channel modeling. For completeness, the different types of capacity are discussed in details. The capacity is very important in wireless communication. By understanding the details behind different capacity, we can improve our transmission efficiently and effectively. The level crossing rate and average duration are discussed.One of the most important topics in MIMO wireless communication is estimation. Without having the right estimation in channel prediction, the performance will not be correct. The channel estimation error on the performance of the Alamouti code was discussed. The design of the transmitter, the channel and the receiver for this system model is shown. The two different types of decoding scheme were shown - the linear combining scheme and the Maximum likelihood (ML) decoder. Once the reader understands the estimation of the MIMO channel, the estimation based on different antenna correlation is discussed. Next, the model for Mobile-to-Mobile (M2M) MIMO communication link is proposed. The old M2M Sum-of-Sinusoids simulation model and the new two ring models are discussed. As the last step, the fading channel modeling using AR model is derived and the effect of ill-conditioning of the Yule-Walker equation is also shown. A number of applications is presented to show how the performance can be evaluated using the proposed model and techniques