Pilot based MMSE Channel Estimation for Spatial Modulated OFDM Systems

Due to the multifold growth in demands of multimedia services and mobile data, the request for increased channel capacity in mobile and wireless communication has been quickly increasing. Developing a wireless system with more spectral efficiency under varying channel condition is a key challenge to provide more bit rates with limited spectrum. Multiple Input Multiple Output(MIMO) system with Orthogonal Frequency Division Multiplexing (OFDM) gives higher gain by using the direct and the reflected signals, thus facilitating the transmission at high data rate. An integration of Spatial Modulation (SM) with OFDM (SM OFDM) is a newly evolved transmission technique and has been suggested as a replacement for MIMO -OFDM transmission. In practical scenarios, channel estimation is significant for detecting transmitted data coherently. This paper proposes pilot based, Minimum Mean Square Error (MMSE) channel estimation for the SM OFDM communication system. We have focused on analyzing Symbol Error Rate (SER) and Mean Square error (MSE) under Rayleigh channel employing International Telecommunication Union (ITU) specified Vehicular model of Pilot based MMSE channel estimator using windowed Discrete Fourier Transform (DFT) and MMSE weighting function. Simulation output shows that proposed estimator’s SER performance lies close to that of  the MMSE optimal estimator in minimizing aliasing error and suppressing channel noise by using frequency domain data windowing and time domain weighting function. Usage of the Hanning window eliminates error floor and has a compact side lobe level compared to Hamming window and Rectangular window. Hanning window has a larger MSE at low Signal to Noise Ratio (SNR) values and decreases with high SNR values. It is concluded that data windowing technique can minimize the side lobe level and accordingly minimize channel estimation error when interpolation is done. MMSE weighting suppresses channel noise and improves estimation performance. Since Inverse Discrete Fourier Transform(IDFT)/DFT transforms can be implemented with fast algorithms Inverse Fast Fourier Transform( IFFT)/Fast Fourier Transform(FFT) computational complexity can be remarkably reduced

Metamaterial-Inspired Quad-Band Notch Filter for LTE Band Receivers and WPT Applications

A new compact quad-band notch filter (QBNF) based on the extended composite right and left-handed transmission line (E-CRLH TL) has been presented. As known, E-CRLH TL behaves like a quad-band structure. A microstrip TL which is loaded with an open-ended ECRLH TL is presented as a QBNF. Four unwanted frequencies were used in a dual-band LTE receiver as four notch frequencies which must be eliminated (0.9 GHz, 1.3 GHz, 2.55 GHz, and 3.35 GHz). Also, this QBNF can be applied to simultaneous wireless power and data transfer (SWPDT) system to isolate the wireless power circuit from the data communication circuit. A design technique for the proposed QBNF is presented and its performance is validated using full-wave simulation results and theoretical analysis. The main advantage of this design is an overall rejection greater than 20dB at selected unwanted frequencies. Good agreements between the fullwave simulation and equivalent circuit model results have been achieved which verified the effectiveness of the proposed circuit model. The proposed QBNF is designed on an FR-4 substrate and the dimension of the proposed QBNF is 20 * 22 mm

Optimal Power Allocation by Imperfect Hardware Analysis in Untrusted Relaying Networks

CCBY By taking a variety of realistic hardware imperfections into consideration, we propose an optimal power allocation (OPA) strategy to maximize the instantaneous secrecy rate of a cooperative wireless network comprised of a source, a destination and an untrusted amplify-and-forward (AF) relay. We assume that either the source or the destination is equipped with a large-scale multiple antennas (LSMA) system, while the rest are equipped with a single-antenna. To prevent the untrusted relay from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as destination-based cooperative jamming (DBCJ). Given this system model, novel closed-form expressions are presented in the high signal-to-noise ratio (SNR) regime for the ergodic secrecy rate (ESR) and the secrecy outage probability (SOP). We further improve the secrecy performance of the system by optimizing the associated hardware design. The results reveal that by beneficially distributing the tolerable hardware imperfections across the transmission and reception radio-frequency (RF) front ends of each node, the system & #x2019;s secrecy rate may be improved. The engineering insight is that equally sharing the total imperfections at the relay between the transmitter and the receiver provides the best secrecy performance. Numerical results illustrate that the proposed OPA together with the most appropriate hardware design significantly increases the secrecy rate

Radio resource management for V2V multihop communication considering adjacent channel interference

This paper investigates schemes for multihop scheduling and power control for vehicle-to-vehicle (V2V) multicast communication, taking into account the effects of both co-channel interference and adjacent channel interference, such that requirements on latency or age of information (AoI) are satisfied. Optimal performance can be achieved by formulating and solving mixed Boolean linear programming (MBLP) optimization problems for various performance metrics, including network throughput and connectivity. Fairness among network nodes (vehicles) is addressed by considering formulations that maximizes the worst-case network node performance. Solving the optimization problem comes at the cost of significant computational complexity for large networks and requires that (slow) channel state information is gathered at a central point. To address these issues, a clustering method is proposed to partition the optimization problem into a set of smaller problems, which reduces the overall computational complexity, and a decentralized algorithm that does not need channel state information is provided

Linearity of Outphasing Radio Transmitters

The outphasing transmitter is a promising technique, which can simultaneously achieve high linearity and power efficiency, thereby addressing the major design requirements of next generation transmitters. It employs highly non-linear power amplifier (PA) classes in a linear manner, in principle transmitting a distortion-free signal. Due to symmetric nature of the outphasing architecture, its linearity performance is constrained by any mismatches and non-linear effects encountered in the RF paths. This thesis analyzes the linearity performance of outphasing transmitters (in terms of ACLR specification) for LTE base station applications, under the non-linear effects and tolerances present in practical implementations. The system-level model, built in Matlab software, investigates the important non-linear effects present in outphasing transmitters, including gain and phase imbalance, IQ modulator mismatches, delay imbalance, and the non-linear effects of PAs and Chireix combiners. The path and delay mismatches result in only partial cancellation of the wideband quadrature signal, and thus create interference in both the in-band and out-of-band frequency regions. The misalignment in IQ modulators, such as gain/phase imbalance and carrier leakage, introduces amplitude and phase modulation in the outphased signals. The quadrature modulator mismatches, in conjunction with amplifier nonlinearity, result in spectral regrowth around the carrier frequency. The transmitter linearity performance is also affected by mismatches in the non-linear characteristics of the PAs. Realistic square-wave signals, exhibiting finite rise- and fall- time, also create spectral leakage for distinct rise/fall times in each outphasing branch. Furthermore, the Chireix combiner severely degrades the linearity of outphasing transmitters; it produces ACLR well below the specified limit for LTE base stations. This makes mandatory the compensation of Chireix combiner induced non-linearity in outphasing transmitters. The strict linearity requirements (for LTE downlink applications) present a small tolerance window for mismatches experienced in practical circuits. The relatively small tolerance margin indicates the need of linearization and compensation techniques in outphasing transmitters

Cell-Free Multi-User Massive MIMO Under Channel Non-Reciprocity

In Cell-Free (CF) Massive multiple-input multiple-output (MIMO), a large number of access points (AP) are geographically distributed over the coverage area, and jointly serve a smaller number of users on the same time/frequency resources. In this thesis, we study the impact of non-reciprocal channels (NRC) and imperfect channel state information (CSI) on Cell-Free massive MIMO systems performance. As non-reciprocity sources, we consider transceiver frequency response mismatches and mutual-coupling mismatches in uplink and downlink analogue processing chains. We study both single-antenna and multi-antenna AP configurations, and in this last case, we also include non-reciprocal mutual coupling in addition to transceiver frequency responses. We present a novel non-reciprocal channel model based on experimental results from massive MIMO reciprocity calibration tests. Previous models consider that channel non-reciprocity characteristics are fast-varying like random variables; conversely, we consider a model where non-reciprocity values change substantially slower in time, as demonstrated in experimental results. Besides, we derive closed-form analytical expressions of capacity lower bounds for zero-forcing and conjugate beamforming schemes. The conclusion is that non-reciprocal channels can be a limiting factor for Cell-Free systems performance; nevertheless, only AP mismatches impact on performance while UE mismatches do not affect performance. Furthermore, only phase non-reciprocity degrades MRT performance, whereas both phase and amplitude non-reciprocity degrade ZF performance. Therefore, calibration requirements may dispense with amplitude compensation when APs use MRT scheme, and prioritise phase over amplitude compensation when APs use ZF scheme. Mutual coupling considerately affects both MRT and ZF precoders, but ZF to a greater extent. Hence, calibration procedures should always try to compensate for mutual coupling non-reciprocity

Digital predistortion of RF amplifiers using baseband injection for mobile broadband communications

Radio frequency (RF) power amplifiers (PAs) represent the most challenging design parts of wireless transmitters. In order to be more energy efficient, PAs should operate in nonlinear region where they produce distortion that significantly degrades the quality of signal at transmitter’s output. With the aim of reducing this distortion and improve signal quality, digital predistortion (DPD) techniques are widely used. This work focuses on improving the performances of DPDs in modern, next-generation wireless transmitters. A new adaptive DPD based on an iterative injection approach is developed and experimentally verified using a 4G signal. The signal performances at transmitter output are notably improved, while the proposed DPD does not require large digital signal processing memory resources and computational complexity. Moreover, the injection-based DPD theory is extended to be applicable in concurrent dual-band wireless transmitters. A cross-modulation problem specific to concurrent dual-band transmitters is investigated in detail and novel DPD based on simultaneous injection of intermodulation and cross-modulation distortion products is proposed. In order to mitigate distortion compensation limit phenomena and memory effects in highly nonlinear RF PAs, this DPD is further extended and complete generalised DPD system for concurrent dual-band transmitters is developed. It is clearly proved in experiments that the proposed predistorter remarkably improves the in-band and out-of-band performances of both signals. Furthermore, it does not depend on frequency separation between frequency bands and has significantly lower complexity in comparison with previously reported concurrent dual-band DPDs

Joint compensation of I/Q impairments and PA nonlinearity in mobile broadband wireless transmitters

The main focus of this thesis is to develop and investigate a new possible solution for compensation of in-phase/quadrature-phase (I/Q) impairments and power amplifier (PA) nonlinearity in wireless transmitters using accurate, low complexity digital predistortion (DPD) technique. After analysing the distortion created by I/Q modulators and PAs together with nonlinear crosstalk effects in multi-branch multiple input multiple output (MIMO) wireless transmitters, a novel two-box model is proposed for eliminating those effects. The model is realised by implementing two phases which provide an optimisation of the identification of any system. Another improvement is the capability of higher performance of the system without increasing the computational complexity. Compared with conventional and recently proposed models, the approach developed in this thesis shows promising results in the linearisation of wireless transmitters. Furthermore, the two-box model is extended for concurrent dual-band wireless transmitters and it takes into account cross-modulation (CM) products. Besides, it uses independent processing blocks for both frequency bands and reduces the sampling rate requirements of converters (digital-to-analogue and analogue-to-digital). By using two phases for the implementation, the model enables a scaling down of the nonlinear order and the memory depth of the applied mathematical functions. This leads to a reduced computational complexity in comparison with recently developed models. The thesis provides experimental verification of the two-box model for multi-branch MIMO and concurrent dual-band wireless transmitters. Accordingly, the results ensure both the compensation of distortion and the performance evaluation of modern broadband wireless transmitters in terms of accuracy and complexity