Design issues toward a cost effective physical layer for multiband OFDM (ECMA-368) in consumer products

The creation of Wireless Personal Area Networks (WPANs) offers the Consumer Electronics industry a mechanism to truly unwire consumer products, leading to portability and ease of installation as never seen before. WPAN's can offer data-rates exceeding those that are required to convey high quality broadcast video, thus users can easily connect to high quality video for multimedia presentations in education, libraries, advertising, or have a wireless connection at home. There have been many WPAN proposals, but this paper concentrates on ECMA-368 as this standard has the largest industrial and implementers' forum backing. With the aim to effective consumer electronic define and create cost equipment this paper discusses the technology behind ECMA-368 physical layer, the design freedom availabilities, the required processing, buffer memory requirements and implementation considerations while concentrating on supporting all the offered data-rates(1)

Spectrum control and iterative coding for high capacity multiband OFDM

The emergence of Multiband Orthogonal Frequency Division Modulation (MB-OFDM) as an ultra-wideband (UWB) technology injected new optimism in the market through realistic commercial implementation, while keeping promise of high data rates intact. However, it has also brought with it host of issues, some of which are addressed in this thesis. The thesis primarily focuses on the two issues of spectrum control and user capacity for the system currently proposed by the Multiband OFDM Alliance (MBOA). By showing that line spectra are still an issue for new modulation scheme (MB-OFDM), it proposes a mechanism of scrambling the data with an increased length linear feedback shift register (compared to the current proposal), a new set of seeds, and random phase reversion for the removal of line spectra. Following this, the thesis considers a technique for increasing the user capacity of the current MB-OFDM system to meet the needs of future wireless systems, through an adaptive multiuser synchronous coded transmission scheme. This involves real time iterative generation of user codes, which are generated over time and frequency leading to increased capacity. With the assumption of complete channel state information (CSI) at the receiver, an iterative MMSE algorithm is used which involves replacement of each users s signature with its normalized MMSE filter function allowing the overall Total Squared Correlation (TSC) of the system to decrease until the algorithm converges to a fixed set of signature vectors. This allows the system to be overloaded and user\u27s codes to be quasi-orthogonal. Simulation results show that for code of length nine (spread over three frequency bands and three time slots), ten users can be accommodated for a given QoS and with addition of single frequency sub-band which allows the code length to increase from nine to twelve (four frequency sub-bands and three time slots), fourteen users with nearly same QoS can be accommodated in the system. This communication is overlooked by a central controller with necessary functionalities to facilitate the process. The thesis essentially considers the uplink from transmitting devices to this central controller. Furthermore, analysis of this coded transmission in presence of interference is carried to display the robustness of this scheme through its adaptation by incorporating knowledge of existing Narrowband (NB) Interference for computing the codes. This allows operation of sub-band coexisting with NB interference without substantial degradation given reasonable interference energy (SIR=-l0dB and -5dB considered). Finally, the thesis looks at design implementation and convergence issues related to code vector generation whereby, use of Lanczos algorithm is considered for simpler design and faster convergence. The algorithm can be either used to simplify design implementation by providing simplified solution to Weiner Hopf equation (without requiring inverse of correlation matrix) over Krylov subspace or can be used to expedite convergence by updating the signature sequence with eigenvector corresponding to the least eigenvalue of the signature correlation matrix through reduced rank eigen subspace search

Design and implementation of frequency synthesizers for 3-10 ghz mulitband ofdm uwb communication

The allocation of frequency spectrum by the FCC for Ultra Wideband (UWB) communications in the 3.1-10.6 GHz has paved the path for very high data rate Gb/s wireless communications. Frequency synthesis in these communication systems involves great challenges such as high frequency and wideband operation in addition to stringent requirements on frequency hopping time and coexistence with other wireless standards. This research proposes frequency generation schemes for such radio systems and their integrated implementations in silicon based technologies. Special emphasis is placed on efficient frequency planning and other system level considerations for building compact and practical systems for carrier frequency generation in an integrated UWB radio. This work proposes a frequency band plan for multiband OFDM based UWB radios in the 3.1-10.6 GHz range. Based on this frequency plan, two 11-band frequency synthesizers are designed, implemented and tested making them one of the first frequency synthesizers for UWB covering 78% of the licensed spectrum. The circuits are implemented in 0.25µm SiGe BiCMOS and the architectures are based on a single VCO at a fixed frequency followed by an array of dividers, multiplexers and single sideband (SSB) mixers to generate the 11 required bands in quadrature with fast hopping in much less than 9.5 ns. One of the synthesizers is integrated and tested as part of a 3-10 GHz packaged receiver. It draws 80 mA current from a 2.5 V supply and occupies an area of 2.25 mm2. Finally, an architecture for a UWB synthesizer is proposed that is based on a single multiband quadrature VCO, a programmable integer divider with 50% duty cycle and a single sideband mixer. A frequency band plan is proposed that greatly relaxes the tuning range requirement of the multiband VCO and leads to a very digitally intensive architecture for wideband frequency synthesis suitable for implementation in deep submicron CMOS processes. A design in 130nm CMOS occupies less than 1 mm2 while consuming 90 mW. This architecture provides an efficient solution in terms of area and power consumption with very low complexity

Cross-Layer Design for Multi-Antenna Ultra-Wideband Systems

Ultra-wideband (UWB) is an emerging technology that offers great promises to satisfy the growing demand for low cost and high-speed digital wireless home networks. The enormous bandwidth available, the potential for high data rates, as well as the potential for small size and low processing power long with low implementation cost, all present a unique opportunity for UWB to become a widely adopted radio solution for future wireless home-networking technology. Nevertheless, in order for UWB devices to coexist with other existing wireless technology, the transmitted power level of UWB is strictly limited by the FCC spectral mask. Such limitation poses significant design challenges to any UWB system. This thesis introduces various means to cope with these design challenges. Advanced technologies including multiple-input multiple-output (MIMO) coding, cooperative communications, and cross-layer design are employed to enhance the performance and coverage range of UWB systems. First a MIMO-coding framework for multi-antenna UWB communication systems is developed. By a technique of band hopping in combination with jointly coding across spatial, temporal, and frequency domains, the proposed scheme is able to exploit all the available spatial and frequency diversity, richly inherent in UWB channels. Then, the UWB performance in realistic UWB channel environments is characterized. The proposed performance analysis successfully captures the unique multipath-rich property and random-clustering phenomenon of UWB channels. Next, a cross-layer channel allocation scheme for UWB multiband OFDM systems is proposed. The proposed scheme optimally allocates subbands, transmitted power, and data rates among users by taking into consideration the performance requirement, the power limitation, as well as the band hopping for users with different data rates. Also, an employment of cooperative communications in UWB systems is proposed to enhance the UWB performance and coverage by exploiting the broadcasting nature of wireless channels and the cooperation among UWB devices. Furthermore, an OFDM cooperative protocol is developed and then applied to enhance the performance of UWB systems. The proposed cooperative protocol not only achieves full diversity but also efficiently utilizes the available bandwidth

Multiple antenna system and channel estimation for multiband orthogonal frequency division multiplexing in ultra-wideband systems

Multiband Orthogonal Frequency Division Multiplexing (OFDM) has been deployed for practical implementation of low cost and low power Ultra-Wideband (UWB) devices due to its ability to mitigate the narrowband interference and multipath fading effects. In order to achieve high data rates, the deployment of multiple antenna techniques into a UWB system has gained considerable research interest. In a UWB system, both the spatial and multipath diversities exist in UWB system can be exploited via the use of Multiple-Input Multiple-Output (MIMO) antenna system and Space-Time Codes (STC) by leveraging Alamouti scheme. This work shows that MIMO system outperforms Alamouti technique in providing a power combining gain in the receiver. Given that channel estimation for timefrequency multiplexed such as a multiband OFDM system is unexplored largely, this thesis also addresses this issue. In literature, most of the conventional Channel Frequency Response (CFR) estimations require either pre-storing a large matrix or performing real-time matrix inversion. In general, these requirements are prohibitive for practical implementation of UWB devices. In this thesis, the implementation issues of STC-based on Alamouti scheme are investigated for the multiband OFDM system. The research quantifies and analyses existing channel estimation in frequency domain such as Least-Square (LS) and Minimum Mean Square Error (MMSE) techniques. Consequently, low-complexity channel estimation based on Singular Value Decomposition (SVD) technique is developed for multiband OFDM system evaluates under modified Saleh-Valuenzela (S-V) channel modelling represents the realistic wireless indoor environment. This work implies that the SVD technique gives an improvement of 3-5 dB compared to LS technique. Even though SVD performs similarly to MMSE, it managed to reduce significantly the complexity by or to 57.8%

IR-UWB and OFDM-UWB Transceiver Nodes for Communication and Positioning Purposes

Résumé Ultra-wideband (UWB) a suscité l'intérêt de chercheurs et de l'industrie en raison de ses nombreux avantages tels que la faible probabilité d'interception et de la possibilité de combiner la communication des données de positionnement dans un seul système. Il existe plusieurs UWB couche physique (PHY) présentées initialement à la norme IEEE qui convergent en deux propositions principales: des porte-UWB ou Orthogonal Frequency-Division Multiplexing (OFDM-UWB), et à court d'impulsion porteuse à-UWB ou Impulse Radio-(IR-UWB). Une des plus grandes tâches difficiles pour les chercheurs est de nos jours la conception d'émetteurs-récepteurs UWB optimisés qui satisfont à des conditions rigoureuses, dont la simplicité caractéristiques large bande, à faible coût et de conception. Des études antérieures ont montré que les récepteurs à conversion directe basée sur Wave-radio interféromètre (WRI) circuits représentent un bon candidat pour les applications UWB. Circuits IRG ont plusieurs avantages tels que l'exploitation à large bande, à faible coût et la simplicité. Des travaux antérieurs sur l'IRG circuit, cependant, a enquêté sur le circuit de l'IRG sur la base du concept de porteuse unique signaux (par exemple, les signaux sinusoïdaux). L'objectif de ce projet est de fournir les résultats de conception, de simulation, de mise en oeuvre et le test d'un émetteur-récepteur WRI basé sur ce que peut être utilisé comme un noeud ou un pico-réseau dans un détecteur sans fil / réseau de données. Nous allons passer par les étapes de conception et de mise en oeuvre de propositions UWB deux: IR-UWB et OFDM-UWB. Pour la proposition porteuse à nous concentrer sur la conception et la mise en oeuvre de l'émetteur-récepteur en intégrant les opérations de transmission / réception dans un prototype unique, alors que pour la proposition des porte-nous concevoir et mettre en oeuvre l'émetteur-récepteur avec le circuit de l'IRG dans le récepteur seulement utilisé en tant que convertisseur abaisseur directe. Résultats expérimentaux, de simulation et d'analyse ont été obtenus et sont présentés dans cette thèse.----------Abstract Ultra-wideband (UWB) technology has attracted interest from both researchers and the industry due to its numerous advantages such as low probability of interception and the possibility of combining data communication with positioning in a single system. There are several different UWB physical layer (PHY) proposals originally submitted to IEEE which converged into two main proposals: carrier‐based UWB or Orthogonal-Frequency Division Multiplexing (OFDM‐UWB), and short‐pulse carrierless‐UWB or Impulse-Radio (IR-UWB). One of the biggest challenging tasks for researchers nowadays is the design of optimized UWB transceivers that would satisfy rigorous conditions, among which wideband characteristics, low-cost and design simplicity. Previous studies have shown that direct-conversion receivers based on Wave-Radio Interferometer (WRI) circuits represent a suitable candidate for UWB applications. WRI circuits have several advantages such as wideband operation, low cost, and simplicity. Previous works on WRI circuit, however, investigated the WRI circuit based on the concept of single-carrier signals (i.e., sinusoidal signals). The objective of this project is to provide the design, simulation, implementation and testing results of a WRI-based transceiver that can be utilized as a node or a piconet in a wireless sensor/data network. We will go through the design and implementation steps for both UWB proposals: IR-UWB and OFDM-UWB. For the carrierless proposal we will focus on designing and implementing the transceiver by integrating the transmitter/receiver operations in a single prototype, while for the carrier‐based proposal we will design and implement the transceiver with the WRI circuit in the receiver only utilized as a direct downconverter

A digital polar transmitter for multi-band OFDM Ultra-WideBand

Linear power amplifiers used to implement the Ultra-Wideband standard must be backed off from optimum power efficiency to meet the standard specifications and the power efficiency suffers. The problem of low efficiency can be mitigated by polar modulation. Digital polar architectures have been employed on numerous wireless standards like GSM, EDGE, and WLAN, where the fractional bandwidths achieved are only about 1%, and the power levels achieved are often in the vicinity of 20 dBm. Can the architecture be employed on wireless standards with low-power and high fractional bandwidth requirements and yet achieve good power efficiency? To answer these question, this thesis studies the application of a digital polar transmitter architecture with parallel amplifier stages for UWB. The concept of the digital transmitter is motivated and inspired by three factors. First, unrelenting advances in the CMOS technology in deep-submicron process and the prevalence of low-cost Digital Signal processing have resulted in the realization of higher level of integration using digitally intensive approaches. Furthermore, the architecture is an evolution of polar modulation, which is known for high power efficiency in other wireless applications. Finally, the architecture is operated as a digital-to-analog converter which circumvents the use of converters in conventional transmitters. Modeling and simulation of the system architecture is performed on the Agilent Advanced Design System Ptolemy simulation platform. First, by studying the envelope signal, we found that envelope clipping results in a reduction in the peak-to-average power ratio which in turn improves the error vector magnitude performance (figure of merit for the study). In addition, we have demonstrated that a resolution of three bits suffices for the digital polar transmitter when envelope clipping is performed. Next, this thesis covers a theoretical derivation for the estimate of the error vector magnitude based on the resolution, quantization and phase noise errors. An analysis on the process variations - which result in gain and delay mismatches - for a digital transmitter architecture with four bits ensues. The above studies allow RF designers to estimate the number of bits required and the amount of distortion that can be tolerated in the system. Next, a study on the circuit implementation was conducted. A DPA that comprises 7 parallel RF amplifiers driven by a constant RF phase-modulated signal and 7 cascode transistors (individually connected in series with the bottom amplifiers) digitally controlled by a 3-bit digitized envelope signal to reconstruct the UWB signal at the output. Through the use of NFET models from the IBM 130-nm technology, our simulation reveals that our DPA is able to achieve an EVM of - 22 dB. The DPA simulations have been performed at 3.432 GHz centre frequency with a channel bandwidth of 528 MHz, which translates to a fractional bandwidth of 15.4%. Drain efficiencies of 13.2/19.5/21.0% have been obtained while delivering -1.9/2.5/5.5 dBm of output power and consuming 5/9/17 mW of power. In addition, we performed a yield analysis on the digital polar amplifier, based on unit-weighted and binary-weighted architecture, when gain variations are introduced in all the individual stages. The dynamic element matching method is also introduced for the unit-weighted digital polar transmitter. Monte Carlo simulations reveal that when the gain of the amplifiers are allowed to vary at a mean of 1 with a standard deviation of 0.2, the binary-weighted architecture obtained a yield of 79%, while the yields of the unit-weighted architectures are in the neighbourhood of 95%. Moreover, the dynamic element matching technique demonstrates an improvement in the yield by approximately 3%. Finally, a hardware implementation for this architecture based on software-defined arbitrary waveform generators is studied. In this section, we demonstrate that the error vector magnitude results obtained with a four-stage binary-weighted digital polar transmitter under ideal combining conditions fulfill the European Computer Manufacturers Association requirements. The proposed experimental setup, believed to be the first ever attempted, confirm the feasibility of a digital polar transmitter architecture for Ultra-Wideband. In addition, we propose a number of power combining techniques suitable for the hardware implementation. Spatial power combining, in particular, shows a high potential for the digital polar transmitter architecture. The above studies demonstrate the feasibility of the digital polar architecture with good power efficiency for a wideband wireless standard with low-power and high fractional bandwidth requirements