Performance Trade-off Investigation of B-IFDMA

A performance trade-off investigation is carried out between different possible uplink multiple access schemes, that are based on Orthogonal Frequency Division Multiplexing (OFDM), for International Mobile Telecommunication (IMT) Advanced systems. Between the Discrete Fourier Transform (DFT) precoded systems with different subcarrier allocation mappings and systems lacking DFT-precoders, Block Interleaved Frequency Division Multiple Access (B-IFDMA) is shown to provide a good trade-off between the frequency diversity collected, envelope properties achieved, and channel estimation performance compared to the other mapping schemes. The schemes are analyzed in the presence of the different possible modules which include equalizers, modulators, interleavers, and channel codes. In particular, robust codes such as Turbo codes are able to collect the diversity provided by such schemes, and B-IFDMA systems is shown to be able to beat the other systems in bit error rate (BER) performance terms

LMS Based Adaptive Channel Estimation for LTE Uplink

In this paper, a variable step size based least mean squares (LMS) channel estimation (CE) algorithm is presented for a single carrier frequency division multiple access(SC-FDMA) system under the umbrella of the long term evolution (LTE). This unbiased CE method can automatically adapts the weighting coefficients on the channel condition. Therefore, it does not require knowledge of channel,and noise statistics. Furthermore, it uses a phase weighting scheme to eliminate the signal fluctuations due to noise and decision errors. Such approaches can guarantee the convergence towards the true channel coefficient. The mean and mean square behaviors of the proposed CE algorithm are also analyzed. With the help of theoretical analysis and simulation results, we prove that the proposed algorithm outperforms the existing algorithms in terms of mean square error (MSE) and bit error rate (BER) by more than around 2.5dB

Channel Estimation in Uplink of Long Term Evolution

Long Term Evolution is considered to be the fastest spreading communication standard in the world.To live up to the increasing demands of higher data rates day by day and higher multimedia services,the existing UMTS system was further upgraded to LTE.To meet their requirements novel technologies are employed in the downlink as well as uplink like Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier- Frequency Division Multiple Access (SC-FDMA).For the receiver to perform properly it should be able to recover athe transmittedadata accurately and this is done through channel estimation.Channel Estimation in LTE engages Coherent Detection where a prior knowledge of the channel is required,often known as Channel State Information (CSI).This thesis aims at studying the channel estimation methods used in LTE and evaluate their performance in various multipath models specified by ITU like Pedestrian and Vehicular.The most commonly used channel estimation algorithms are Least Squarea(LS) and Minimum MeanaSquare error (MMSE) algorithms.The performance of these estimators are evaluated in both uplink as well as Downlink in terms of the Bit Error Rate (BER).It was evaluated for OFDMA and then for SC-FDMA,further the performance was assessed in SC-FDMA at first without subcarrier Mapping and after that with subcarrier mapping schemes like Interleaved SC-FDMA (IFDMA) and Localized SC-FDMA (lFDMA).It was found from the results that the MMSE estimator performs better than the LS estimator in both the environments.And the IFDMA has a lower PAPR than LFDMA but LFDMA has a better BER performance

Performance study of air interface for broadband wireless packet access

Ph.DDOCTOR OF PHILOSOPH

Iterative receiver design for broadband wireless communication systems via expectation maximization (EM) based algorithms

Ph.DDOCTOR OF PHILOSOPH

SC-FDMA and OFDMA: The two competing technologies for LTE

One of the key requirements of next generation networks (NGNs) is the support of higher data rates. Although OFDM is capable of delivering the target peak data rates, its high PAPR raises questions as to its suitability in the uplink. SC-FDMA is examined in this paper as a promising alternative to OFDMA. Recent novel techniques offering performance gains are also considered

Spectrum Optimisation in Wireless Communication Systems: Technology Evaluation, System Design and Practical Implementation

Two key technology enablers for next generation networks are examined in this thesis, namely Cognitive Radio (CR) and Spectrally Efficient Frequency Division Multiplexing (SEFDM). The first part proposes the use of traffic prediction in CR systems to improve the Quality of Service (QoS) for CR users. A framework is presented which allows CR users to capture a frequency slot in an idle licensed channel occupied by primary users. This is achieved by using CR to sense and select target spectrum bands combined with traffic prediction to determine the optimum channel-sensing order. The latter part of this thesis considers the design, practical implementation and performance evaluation of SEFDM. The key challenge that arises in SEFDM is the self-created interference which complicates the design of receiver architectures. Previous work has focused on the development of sophisticated detection algorithms, however, these suffer from an impractical computational complexity. Consequently, the aim of this work is two-fold; first, to reduce the complexity of existing algorithms to make them better-suited for application in the real world; second, to develop hardware prototypes to assess the feasibility of employing SEFDM in practical systems. The impact of oversampling and fixed-point effects on the performance of SEFDM is initially determined, followed by the design and implementation of linear detection techniques using Field Programmable Gate Arrays (FPGAs). The performance of these FPGA based linear receivers is evaluated in terms of throughput, resource utilisation and Bit Error Rate (BER). Finally, variants of the Sphere Decoding (SD) algorithm are investigated to ameliorate the error performance of SEFDM systems with targeted reduction in complexity. The Fixed SD (FSD) algorithm is implemented on a Digital Signal Processor (DSP) to measure its computational complexity. Modified sorting and decomposition strategies are then applied to this FSD algorithm offering trade-offs between execution speed and BER

OFDM smart beamforming

Develop of OFDM blind smart beamforming techniques that reduce the overhead that the actual techniques requireOFDM is the existing modulation technology used in mobile communications, which has been studied over the years to give new extensions of its principles in order to improve the communication performance to the end-users. Taking into account its knowledge, the thesis is focused on the 3GPP LTE Uplink Single Carrier-Frequency Division Multiple Access (SC-FDMA) transmission. The entire blocks within its system are simulated with Matlab in order to generate the signals transmitted by the user to the Base Station. Furthermore, the user needs to send data together with Demodulation Reference Signals (DM-RS) to adapt the beamformer algorithm at the receiver so that the antenna array point to a specific User Equipment cancelling the other interferences coming from other users. A non-blind adaptive algorithm by Wiener solution design is applied for Channel Estimation and minimizing the Minimum Square Error, which performs the smart operation of the system without interfering in the quality between users.OFDM es la tecnología existente en modulación para las comunicaciones móviles, la cual ha sido estudiada a lo largo de los años para dar nuevas extensiones de sus principios para poder mejorar las prestaciones de comunicación a los usuarios finales. Teniendo en cuenta su conocimiento, la tesis se centra en estudiar la transmisión 3GPP LTE SC-FDMA para el canal ascendente donde todos sus bloques han sido simulados con Matlab para generar las señales transmitidas del usuario a la estación base. Por otro lado, el usuario necesita enviar información conjuntamente con señales de referencia (DM-RS) para adaptar el algoritmo de conformador de haz en el receptor para que el sistema de antenas apunte a un usuario específico cancelando las interferencias generadas por otros usuarios. Se ha aplicado un algoritmo adaptativo no ciego basado en la solución de Wiener para estimar el canal y minimizar el error cuadrático medio, el cual implementa la operación inteligente del sistema para no interferir en la calidad entre usuarios.OFDM és la tecnologia existent en modulació per a les comunicacions mòbils, la qual ha sigut estudiada al llarg dels anys per donar noves extensions dels seus principis per tal de millorar les prestacions de comunicació als usuaris finals. Tenint en compte el seu coneixement, la tesis es centra en estudiar la transmissió 3GPP LTE SC-FDMA per al canal ascendent on tots els seus blocs han estat simulats amb Matlab per tal de generar les senyals transmeses de l'usuari a l'estació base. Per una altra banda, l'usuari necessita enviar informació conjuntament amb senyals de referència per adaptar l'algoritme de conformador de feix en el receptor per tal que el sistema d'antenes apunti a un usuari específic cancel·lant les interferències generades per altres usuaris. S'ha aplicat un algoritme adaptatiu no cec basat en la solució de Wiener per estimar el canal i minimitzar l'error quadràtic mig, el qual implementa l'operació intel·ligent del sistema per no interferir en la qualitat entre usuaris

Papr analysis and channel estimation techniques for 3GPP LTE system

High data rates and secured data communication has become an unavoidable need of every mobile users. 3G technology provided greater data speed and secured networks compared to its predecessor 2G or 2.5G. The highest bit rates in commercially deployed wireless systems are achieved by means of Orthogonal Frequency Division Multiplexing (OFDM) [1]. The next advance in cellular systems, under investigation by Third Generation Partnership Project (3GPP), also anticipates the adoption of OFDMA to achieve high data rates. But a modified form of OFDMA i.e. SCFDMA (Single Carrier FDMA) having similar throughput performance and essentially the same complexity has been implemented as it has an edge over OFDMA having lower PAPR (peak to average power ratio) [2]. SCFDMA is currently a strong candidate for the uplink multiple access in the Long Term Evolution of cellular systems under consideration by the 3GPP. In our project we have worked on PAPR analysis of OFDMA, SCFDMA and various other SCFDMA (with different subcarrier mapping). Though SCFDMA had larger ISI it has lower PAPR which help in avoiding the need of an efficient linear power amplifier. We have analyzed various modulation techniques and implemented various kinds of pulse shaping filters and compared the PAPR for IFDMA, DFDMA and LFDMA (kinds of SCFDMA). Like other communication systems, in SCFDMA we encounter many trade-offs between design parameters (such as roll-off factor) and performance. The project report also constitutes the channel estimation techniques implemented in OFDM systems. Due to multipath fading the channel impulse response fluctuates for different subcarriers in different time slots. But with channel estimation OFDM systems can use coherent detection instead of differential. For MIMO system like OFDM channel information is vital for diversity combining and interference suppression [3]. So we need to estimate the channel as accurately as possible. As we have taken a slow Rayleigh fading channel in our study we used block type pilot arrangement channel estimation which uses LS (least square), MMSE (minimum mean square error) estimator. Due to higher complexity of the MMSE estimator, modified MMSE is implemented where tradeoff is made with performance. Here we have compared various channel estimation techniques used in OFDM systems. There are various other adaptive estimation techniques like LMS and RLS for estimating blind channels and comb type pilot arrangement estimation techniques for fast fading channels