Introduction to OFDM and MIMOOFDM
01 Jan 2011-pp 1-36
TL;DR: In this article, the authors present an OFDM history of OFDM Schematic Channel Estimation for Multi-carrier Systems Channel estimation for MIMO-OFDM Signal Detection in MIMI-OFD Systems Iterative Signal Processing for SDM-OF DM System Model SDM -OFDM System Model Novel Aspects and Outline of the Book Chapter Summary
Abstract: This chapter contains sections titled: OFDM History OFDM Schematic Channel Estimation for Multi-carrier Systems Channel Estimation for MIMO-OFDM Signal Detection in MIMO-OFDM Systems Iterative Signal Processing for SDM-OFDM System Model SDM-OFDM System Model Novel Aspects and Outline of the Book Chapter Summary
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TL;DR: For the first time, a multi-carrier based DM framework using antenna arrays is developed, where simultaneous data transmission over multiple frequencies can be achieved, so that a much higher data rate can be obtained.
Abstract: Directional modulation (DM) has been developed based on narrowband antenna arrays, which can form the desired constellation values in the directions of interest while scrambling the values and simultaneously maintaining a magnitude response as low as possible in other directions. In this study, for the first time, the authors develop a multi-carrier based DM framework using antenna arrays, where simultaneous data transmission over multiple frequencies can be achieved, so that a much higher data rate can be obtained. In addition, such a framework allows possible frequency division based multi-user access to the system and also provides the flexibility of using different modulation schemes at different frequencies. Then, they study the antenna location optimisation problem for multi-carrier based DM using a compressive sensing based approach by employing the group sparsity concept. Examples are provided for both the design of weight coefficients and the optimisation of antenna locations.
20 citations
TL;DR: The resultant beam patterns, phase patterns, and complementary cumulative distribution function (CCDF) of PAPR are presented to demonstrate the effectiveness of the proposed design.
Abstract: Multi-carrier-based waveform design for directional modulation (DM) is studied, where simultaneous data transmission over multiple frequencies can be achieved, with given phase distribution at the main lobe and as random as possible over sidelobe regions for each frequency. The design can be implemented efficiently by the inverse discrete Fourier transform (IDFT) structure. However, the problem of multi-carrier design is the high peak-to-average-power ratio (PAPR) of the resultant signals, leading to non-linear distortion when signal peaks pass through saturation regions of a power amplifier. To solve the problem, the $\text {PAPR}\leq \rho ~(\rho \geq 1)$ constraint is considered in the design, and a solution called wideband beam and phase pattern formation by Newton's method (WBPFN) is proposed. The resultant beam patterns, phase patterns, and complementary cumulative distribution function (CCDF) of PAPR are presented to demonstrate the effectiveness of the proposed design.
14 citations
20 Jul 2019
TL;DR: To solve the problem, planar antenna arrays are introduced in the design, where both the elevation angle and azimuth angle are considered and a magnitude constraint for weight coefficients is introduced.
Abstract: Directional modulation (DM) has been applied to linear antenna arrays to increase security of signal transmission. However, only the azimuth angle is considered in the design, due to inherent limitation of the linear array structure, since linear antenna array lacks the ability to scan in the three dimensional (3-D) space. To solve the problem, planar antenna arrays are introduced in the design, where both the elevation angle and azimuth angle are considered. Moreover, a magnitude constraint for weight coefficients is introduced. Design examples are provided to verify the effectiveness of the proposed design.
2 citations
DOI•
01 Jan 2014
TL;DR: In this paper, the effect of reactive load in Chireix combiner with stubs (a parallel inductor and capacitor), while distinguishing between its capacitive and inductive parts is analyzed.
Abstract: New generations of wireless communication systems require linear efficient RF power amplifiers (PAs) for higher transmission data rates and longer battery life. On the contrary, conventional PAs are normally designed for peak efficiency under maximum output power (Pout). Thus, in power back-off, the overall efficiency degrades significantly and the average efficiency is much lower than the efficiency at maximum Pout. Chireix outphasing PA, also called LINC (Linear amplification using Non-linear Components), is one of the most promising techniques to improve the efficiency at power back-off. In this method, a variable envelope input signal is first decomposed into two constant-envelope phase-modulated signals and then amplified using two highly efficient non-linear PAs. The output signals are combined preferably in a loss-less power combiner to build the desired output signal. In this way, the PA exhibits high efficiency with good linearity. In this thesis, first we analyze a complex model of outphasing combiner considering its nonidealities such as reflection and loss in transmission lines (TL). Then we propose a compact model with analytical formula that is validated through several comparative tests using ADS and Spectre RF. Furthermore, we analyze the effect of reactive load in Chireix combiner with stubs (a parallel inductor and capacitor), while distinguishing between its capacitive and inductive parts. It is demonstrated that only the capacitive part of the reactive load degrades the performances. Based on this, a new architecture (Z LINC) is proposed where the power combiner is designed to provide a zero capacitive load to the PAs whatever the outphasing angle. The theory describing the operations of the system is developed and a 900 MHz classical LINC and Z-LINC PAs are designed and measured. In addition, a miniaturization technique is proposed which employs I»/8 or smaller TLs instead of conventional I»/4 TLs in outphasing power combiner. This technique is applied to implement a 900 MHz PA using LDMOS power transistors. Besides single-band PAs, dual-band PAs are more and more needed because of an increasing demand for wireless communication terminals to handle multi-band operation. In chapter 5, a new compact design approach for dual-band transmitters based on a reconfigurable outphasing combiner is proposed. The objective is to avoid the cumbersome implementations where several PAs and matching network are used in parallel. The technique is applied to design a dual band PA with a fully integrated power combiner in 90 nm CMOS technology. An inverter-based class D PA topology, particularly suitable for outphasing and multimode operations is presented. The TLs in the combiner, realized using a network of on-chip series inductors and parallel capacitors, are reconfigurable from I»/4 in 1800 MHz to I»/8 in 900 MHz. In order to maximize the efficiency, the on-chip inductors are implemented using high quality factor on chip slab inductors. The measured maximum Pout at 900/1800 MHz are 24.3 and 22.7 dBm with maximum efficiencies of 51% and 34% respectively.