Analysis of Alternative Metrics for the PAPR Problem in OFDM Transmission

The effective PAPR of the transmit signal is the standard metric to capture the effect of nonlinear distortion in OFDM transmission. A common rule of thumb is the log$(N)$ barrier where $N$ is the number of subcarriers which has been theoretically analyzed by many authors. Recently, new alternative metrics have been proposed in practice leading potentially to different system design rules which are theoretically analyzed in this paper. One of the main findings is that, most surprisingly, the log$(N)$ barrier turns out to be much too conservative: e.g. for the so-called amplifier-oriented metric the scaling is rather $\log[ \log(N)]$. To prove this result, new upper bounds on the PAPR distribution for coded systems are presented as well as a theorem relating PAPR results to these alternative metrics.Comment: 5 pages, IEEE International Symposium on Information Theory (ISIT), 2011, accepted for publicatio

On multicarrier signals where the PMEPR of a random codeword is asymptotically log n

Multicarrier signals exhibit a large peak-to-mean envelope power ratio (PMEPR). In this correspondence, without using a Gaussian assumption, we derive lower and upper probability bounds for the PMEPR distribution when the number of subcarriers n is large. Even though the worst case PMEPR is of the order of n, the main result is that the PMEPR of a random codeword C=(c/sub 1/,...,c/sub n/) is logn with probability approaching one asymptotically, for the following three general cases: i) c/sub i/'s are independent and identically distributed (i.i.d.) chosen from a complex quadrature amplitude modulation (QAM) constellation in which the real and imaginary part of c/sub i/ each has i.i.d. and even distribution (not necessarily uniform), ii) c/sub i/'s are i.i.d. chosen from a phase-shift keying (PSK) constellation where the distribution over the constellation points is invariant under /spl pi//2 rotation, and iii) C is chosen uniformly from a complex sphere of dimension n. Based on this result, it is proved that asymptotically, the Varshamov-Gilbert (VG) bound remains the same for codes with PMEPR of less than logn chosen from QAM/PSK constellations

Comparison of Automotive FMCW and OFDM Radar Under Interference

Automotive radars are subject to interference in spectrally congested environments. To mitigate this interference, various waveforms have been proposed. We compare two waveforms (FMCW and OFDM) in terms of their radar performance and robustness to interference, under similar parameter settings. Our results indicate that under proper windowing both waveforms can achieve similar performance, but OFDM is more sensitive to interference

Hardware Realization of a Transform Domain Communication System

The purpose of this research was to implement a Transform Domain Communication System (TDCS) in hardware and compare experimental bit error performance with results published in literature. The intent is to demonstrate the effectiveness or ineffectiveness of a TDCS in communicating binary data across a real channel. In this case, an acoustic channel that is laden with narrowband interference was considered. A TDCS user pair was constructed to validate the proposed design using Matlab™ to control a PC sound card. The proposed TDCS design used the Bartlett method of spectrum estimation, the spectral notching algorithm found in TDCS literature, quadrature phase shift keying, and minimum mean square error transverse equalization to mitigate the effects of noise and intersymbol interference. Water-filling was evaluated as an alternative to spectral notching for performing waveform design and is shown to perform equivalently. Validated software was migrated to code suitable for use onboard a Digital Signal Processor Starter Kit (DSK). Two DSK boards were used, one for transmission and reception, and bit error performance results were obtained. Bit error analysis reveals that the TDCS hardware performs approximately the same as literature suggests

Adjustable dynamic range for paper reduction schemes in large-scale MIMO-OFDM systems

In a multi-input-multi-output (MIMO) communication system there is a necessity to limit the power that the output antenna amplifiers can deliver. Their signal is a combination of many independent channels, so the demanded amplitude can peak to many times the average value. The orthogonal frequency division multiplexing (OFDM) system causes high peak signals to occur because many subcarrier components are added by an inverse discrete Fourier transformation process at the base station. This causes out-of-band spectral regrowth. If simple clipping of the input signal is used, there will be in-band distortions in the transmitted signals and the bit error rate will increase substantially. This work presents a novel technique that reduces the peak-to-average power ratio (PAPR). It is a combination of two main stages, a variable clipping level and an Adaptive Optimizer that takes advantage of the channel state information sent from all users in the cell. Simulation results show that the proposed method achieves a better overall system performance than that of conventional peak reduction systems in terms of the symbol error rate. As a result, the linear output of the power amplifiers can be minimized with a great saving in cost

Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing

To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation. This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation framework, the problem of symbol time offset (STO) and carrier frequency offset (CFO) estimation is investigated and synchronization approaches, which can operate in burst and continuous transmissions, are designed. The first part of this work presents the modulation principles of prominent 5G candidate waveforms and then focuses on the GFDM basic and advanced attributes. The GFDM concept is extended towards the use of OQAM, introducing the novel frequency-shift OQAM-GFDM, and a new low complexity model based on signal processing carried out in the time domain. A new prototype filter proposal highlights the benefits obtained in terms of a reduced out-of-band (OOB) radiation and more attractive hardware implementation cost. With proper parameterization of the advanced GFDM, the achieved gains are applicable to other filtered OFDM waveforms. In the second part, a search approach for estimating STO and CFO in GFDM is evaluated. A self-interference metric is proposed to quantify the effective SNR penalty caused by the residual time and frequency misalignment or intrinsic inter-symbol interference (ISI) and inter-carrier interference (ICI) for arbitrary pulse shape design in GFDM. In particular, the ICI can be used as a non-data aided approach for frequency estimation. Then, GFDM training sequences, defined either as an isolated preamble or embedded as a midamble or pseudo-circular pre/post-amble, are designed. Simulations show better OOB emission and good estimation results, either comparable or superior, to state-of-the-art OFDM system in wireless channels

Sequences design for OFDM and CDMA systems

With the emergence of multi-carrier (MC) orthogonal frequency division multiplexing (OFDM) scheme in the current WLAN standards and next generation wireless broadband standards, the necessitation to acquire a method for combating high peak to average power ratio (PMEPR) becomes imminent. In this thesis, we will explore various sequences to determine their PMEPR behaviours, in hopes to find some sequences which could potentially be suitable for PMEPR reduction control under MC system settings. These sequences include $m$ sequences, Sidelnikov sequences, new sequences, Golay sequences, FZC sequences and Legendre sequences. We will also examine the merit factor properties of these sequences, and then we will derive a bound between PMEPR and merit factor. Moreover, in the design of code division multiple access (CDMA) spreading sequence sets, it is critical that each sequence in the set has low autocorrelations and low cross-correlation with other sequences in the same set. In the thesis, we will present a class of GDJ Golay sequences which contains a large zero autocorrelation zone (ZACZ), which could satisfy the low autocorrelation requirement. This class of Golay sequences could potentially be used to construct new CDMA spreading sequence sets

Index Modulation Techniques for Energy-efficient Transmission in Large-scale MIMO Systems

This thesis exploits index modulation techniques to design energy- and spectrum-efficient system models to operate in future wireless networks. In this respect, index modulation techniques are studied considering two different media: mapping the information onto the frequency indices of multicarrier systems, and onto the antenna array indices of a platform that comprises multiple antennas. The index modulation techniques in wideband communication scenarios considering orthogonal and generalized frequency division multiplexing systems are studied first. Single cell multiuser networks are considered while developing the system models that exploit the index modulation on the subcarriers of the multicarrier systems. Instead of actively modulating all the subcarriers, a subset is selected according to the index modulation bits. As a result, there are subcarriers that remain idle during the data transmission phase and the activation pattern of the subcarriers convey additional information. The transceivers for the orthogonal and generalized frequency division multiplexing systems with index modulation are both designed considering the uplink and downlink transmission phases with a linear combiner and precoder in order to reduce the system complexity. In the developed system models, channel state information is required only at the base station. The linear combiner is designed adopting minimum mean square error method to mitigate the inter-user-interference. The proposed system models offer a flexible design as the parameters are independent of each other. The parameters can be adjusted to design the system in favor of the energy efficiency, spectrum efficiency, peak-to-average power ratio, or error performance. Then, the index modulation techniques are studied for large-scale multiple-input multiple-output systems that operate in millimeter wave bands. In order to overcome the drawbacks of transmission in millimeter wave frequencies, channel properties should be taken in to account while envisaging the wireless communication network. The large-scale multiple-input multiple-output systems increase the degrees of freedom in the spatial domain. This feature can be exploited to focus the transmit power directly onto the intended receiver terminal to cope with the severe path-loss. However, scaling up the number of hardware elements results in excessive power consumption. Hybrid architectures provide a remedy by shifting a part of the signal processing to the analog domain. In this way, the number of bulky and high power consuming hardware elements can be reduced. However, there will be a performance degradation as a consequence of renouncing the fully digital signal processing. Index modulation techniques can be combined with the hybrid system architecture to compensate the loss in spectrum efficiency to further increase the data rates. A user terminal architecture is designed that employs analog beamforming together with spatial modulation where a part of the information bits is mapped onto the indices of the antenna arrays. The system is comprised a switching stage that allocates the user terminal antennas on the phase shifter groups to minimize the spatial correlation, and a phase shifting stage that maximizes the beamforming gain to combat the path-loss. A computationally efficient optimization algorithm is developed to configure the system. The flexibility of the architecture enables optimization of the hybrid transceiver at any signal-to-noise ratio values. A base station is designed in which hybrid beamforming together with spatial modulation is employed. The analog beamformer is designed to point the transmit beam only in the direction of the intended user terminal to mitigate leakage of the transmit power to other directions. The analog beamformer to transmit the signal is chosen based on the spatial modulation bits. The digital precoder is designed to eliminate the inter-user-interference by exploiting the zero-forcing method. The base station computes the hybrid beamformers and the digital combiners, and only feeds back the digital combiners of each antenna array-user pair to the related user terminals. Thus, a low complexity user architecture is sufficient to achieve a higher performance. The developed optimization framework for the energy efficiency jointly optimizes the number of served users and the total transmit power by utilizing the derived upper bound of the achievable rate. The proposed transceiver architectures provide a more energy-efficient system model compared to the hybrid systems in which the spatial modulation technique is not exploited. This thesis develops low-complexity system models that operate in narrowband and wideband channel environments to meet the energy and spectrum efficiency demands of future wireless networks. It is corroborated in the thesis that adopting index modulation techniques both in the systems improves the system performance in various aspects.:1 Introduction 1 1.1 Motivation 1 1.2 Overview and Contribution 2 1.3 Outline 9 2 Preliminaries and Fundamentals 13 2.1 Multicarrier Systems 13 2.2 Large-scale Multiple Input Multiple Output Systems 17 2.3 Index Modulation Techniques 19 2.4 Single Cell Multiuser Networks 22 3 Multicarrier Systems with Index Modulation 27 3.1 Orthogonal Frequency Division Multiplexing 28 3.2 Generalized Frequency Division Multiplexing 40 3.3 Summary 52 4 Hybrid Beamforming with Spatial Modulation 55 4.1 Uplink Transmission 56 4.2 Downlink Transmission 74 4.3 Summary 106 5 Conclusion and Outlook 109 5.1 Conclusion 109 5.2 Outlook 111 A Quantization Error Derivations 113 B On the Achievable Rate of Gaussian Mixtures 115 B.1 The Conditional Density Function 115 B.2 Tight Bounds on the Differential Entropy 116 B.3 A Bound on the Achievable Rate 118 C Multiuser MIMO Downlink without Spatial Modulation 121 Bibliograph

Optical techniques for broadband in-building networks

Optical fibres, which can easily handle any bandwidth demand, have been rolled out to more than 32 million consumer’s homes and professional buildings worldwide up to 2010. The basic technological and economical challenges of fibre-to-the-home (FTTH) has been solved. The current FTTH technology can now providing baseband Gbit Ethernet and high definition TV services to the gates of homes. Thus, the bottleneck for delivery of broadband services to the end users is shifting from the access network to the in-building network. In the meantime, the need for high-capacity transmission between devices inside the building, e.g. between desktop PC and data services, are also rapidly increase. How to bring high bandwidth to the mobile terminals such as laptops, PDAs or cell phones as well as to the fixed terminals such as desktop PCs and HDTV equipment in an all-in-one network infrastructure is a challenge we are facing. Building on the flexibility of the wireless access networks and the latent vast bandwidth of a fibre infrastructure, radio-over-fibre (RoF) techniques have been proposed as a cost-effective solution to the future integrated broadband services in in-building networks. This thesis investigates techniques to deliver high data rate wireless services via in-building networks: high capacity RoF links employing optical frequency multiplication (OFM) and sub-carrier multiplexing (SCM) techniques, with single- or multi-carrier signal formats. The orthogonal frequency division multiplexing (OFDM) format is investigated for the RoF transmission system, particularly with regard to the optical system nonlinearity. For low-cost short-range optical backbone networks, RoF transmission over large-core diameter plastic optical fibre (POF) links has been studied, including the transmission of the WiMedia-compliant multiband OFDM UWB signal over bandwidth-limited large-core POF as well as a full-duplex bi-directional UWB transmission over POF. In order to improve the functionalities for delivery of wireless services of in-building networks, techniques to introduce flexibility into the network architecture and to create dynamic capacity allocation have been investigated. By employing optical switching techniques based on optical semiconductor amplifiers (SOA), an optically routed RoF system has been studied. The dynamic capacity allocation is addressed by investigating one-dimensional and two-dimensional routing using electrical SCM and optical wavelengths. In addition, next to RoF networking, this thesis explores techniques for wired delivery of baseband high capacity services over POF links by employing a multi-level signal modulation format, in particular discrete multi-tone (DMT) modulation. Transmission of 10 Gbit/s data over 1 mm core diameter PMMA POF links is demonstrated, as a competitor to more expensive fibre solutions such as silica single and multimode fibre. A record transmission rate of more than 40 Gbit/s is presented for POF whose core diameter is comparable with silica multimode fibre. Finally, from the network perspective, the convergence of wired and wireless multi-standard services into a single fibre-based infrastructure has been studied. Techniques have been designed and demonstrated for in-building networks, which can convey both high capacity baseband services and broadband radio frequency (RF) services over a POF backbone link. The multi-standard RoF signals carry different wireless services at different radio frequencies and with different bandwidths, including WiFi, WiMax, UMTS and UWB. System setups to carry them together over the same multimode optical fibre based network have been designed and experimentally shown. All the concepts, designs and system experiments presented in this thesis underline the strong potential of multimode (silica and plastic) optical fibre techniques for the delivery of broadband services to wired and wireless devices in in-building networks, in order to extend to the end user the benefits of the broadband FTTH networks which are being installed and deployed worldwide