Semi-blind time-domain equalization for MIMO-OFDM systems

In this paper, a semi-blind time-domain equalization technique is proposed for general multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. The received OFDM symbols are shifted by more than or equal to the cyclic prefix (CP) length, and a blind equalizer is designed to completely suppress both intercarrier interference (ICI) and intersymbol interference (ISI) using second-order statistics of the shifted received OFDM symbols. Only a one-tap equalizer is needed to detect the time-domain signals from the blind equalizer output, and one pilot OFDM symbol is utilized to estimate the required channel state information for the design of the one-tap equalizer. The technique is applicable irrespective of whether the CP length is longer than, equal to, or shorter than the channel length. Computer simulations show that the proposed technique outperforms the existing techniques, and it is robust against the number of shifts in excess of the CP length. © 2008 IEEE.published_or_final_versio

Novel multiple antenna techniques for improved diversity in wireless communication systems

The focus of this thesis is to enhance the performance of wireless communication systems through the exploitation of multiple antennas at both the transmitter and the receiver ends of a communication link. Such a multiple-input multiple-output (MIMO) connection can theoretically provide spatially independent channels which can be exploited to provide diversity gain and thereby mitigate the problem of channel fading. To integrate such MIMO technology with emerging wireless systems such as third generation code division multiple access (CDMA) and fourth generation orthogonal division multiple access (OFDMA) based-approaches novel advanced signal processing techniques are required. The major advantages of MIMO systems, including array, diversity and multiplexing gains, are initially reviewed. Diversity gain is identified as the key property, which leverages the spatial independent channels to increase the robustness of the communication link. The family of space-time block codes is then introduced as a low computational complexity scheme to benefit from diversity gain within wireless systems. In particular, extended-orthogonal and quasi-orthogonal space-time block codes (EO-/QO-STBCs) are introduced for systems with four transmit antennas which can operate either in open or closed-loop forms. New EO-STBC and QO-STBC wideband CDMA transmission schemes are proposed which when operating in closed-loop mode, i.e. channel state information is exploited at the transmitter, is shown to attain full diversity and thereby outperform previous schemes in terms of attain able symbol error rate performance. This advantage is then utilized in MIMO-OFDM transmission schemes and similar frame error rate (FER) performance advantage is attained. Finally, to mitigate multiuser interference within the proposed MIMO-OFDM system a novel two-step combined parallel interference canceller and multiuser detection scheme is proposed. Simulation studies based upon FER confirm the efficacy of the technique

Estudio experimental de algoritmos espacio-temporales para sistemas multiantena en túneles

[SPA] Las comunicaciones inalámbricas se han convertido hoy en día en una herramienta imprescindible en la sociedad en la que vivimos. En la actualidad los hábitos de consumo en las comunicaciones inalámbricas exigen aumentar la capacidad para transmitir contenidos multimedia. Día a día se trabaja en conseguir mejorar las prestaciones de estos sistemas inalámbricos y así poder afrontar dichas necesidades. Por ello, surgen los sistemas conocidos como Multiple-Input Multiple-Output (MIMO), que utilizan múltiples antenas en transmisión y múltiples antenas en recepción, permitiendo así alcanzar eficiencias espectrales mucho mayores a las alcanzadas en los sistemas convencionales. Por otro lado, en los últimos años se ha dado mucha importancia a poder comunicarse en entornos especiales, como es el caso de los túneles donde la naturaleza de los fenómenos físicos que permiten la propagación de las ondas es diferente al de otros entornos. En este tipo de entornos la energía es conducida por un medio guiado, de tal forma que la energía llega al receptor con un ángulo muy reducido en comparación con otros entornos. Además, la comunicación debe ser continua, fiable y de alta capacidad. Así pues, para cubrir dichas necesidades esta tesis está enmarcada en el estudio de los entornos tipo túnel, centrándose en el comportamiento y el rendimiento de los algoritmos espacio-temporales, ya que en este tipo de entornos se ha investigado muy poco sobre ello. Por ello, el objetivo principal de esta tesis es estudiar detalladamente, tanto de forma teórica como experimental, el comportamiento de los sistemas MIMO en túneles. Para ello se estudian los algoritmos más representativos de los sistemas multiantena: el algoritmo Vertical Bell Labs Space Time (VBLAST), los códigos Orthogonal Space Time Block Codes (OSTBC) y los códigos Quasy-Orthogonal Space Time Block Codes (QSTBC). El rendimiento de estos algoritmos, según la tasa de error de bit (BER, Bit Error Rate), se relaciona con las propiedades intrínsecas del canal radio tanto en banda estrecha como en banda ancha. [ENG] Wireless communications have become an indispensable tool in the society in which we live. In fact, the consumption habits of wireless communications require increasing capacity to transmit multimedia contents. Therefore, in order to meet these needs, work is continually being carried out in order to achieve the best performance possible from these wireless systems. The Multiple-Input Multiple-Output (MIMO) systems appear to achieve greater spectral efficiencies than the convectional systems. Furthermore, in recent years, communications in special contexts have acquired great importance. This thesis is focused on an environment type tunnel where the nature of the physical phenomena is different from other contexts. The energy is driven by a guided environment, therefore the energy arrives at the receiver with a smaller angle than in other environments. In addition, a continuous, reliable and effective communication is demanded. To meet the needs mentioned above, this thesis analyses the performance of space-time algorithms in tunnels. The main objective of this thesis is to study in detail both theoretically and experimentally the behaviour of the MIMO systems in tunnels combined with space-time algorithms. Moreover, this study covers both narrow and wide bands. The studied algorithms are the most representative: the Vertical Bell Labs Space Time (VBLAST), the Orthogonal Space Time Block Code (OSTBC) and the Quasy-Orthogonal Space Time Block Code (QSTBC). The performances in terms of Bit Error Rate (BER) have been compared, assuming a fixed bit rate, and interpreted from the MIMO channel characteristics.[ENG] Wireless communications have become an indispensable tool in the society in which we live. In fact, the consumption habits of wireless communications require increasing capacity to transmit multimedia contents. Therefore, in order to meet these needs, work is continually being carried out in order to achieve the best performance possible from these wireless systems. The Multiple-Input Multiple-Output (MIMO) systems appear to achieve greater spectral efficiencies than the convectional systems. Furthermore, in recent years, communications in special contexts have acquired great importance. This thesis is focused on an environment type tunnel where the nature of the physical phenomena is different from other contexts. The energy is driven by a guided environment, therefore the energy arrives at the receiver with a smaller angle than in other environments. In addition, a continuous, reliable and effective communication is demanded. To meet the needs mentioned above, this thesis analyses the performance of space-time algorithms in tunnels. The main objective of this thesis is to study in detail both theoretically and experimentally the behaviour of the MIMO systems in tunnels combined with space-time algorithms. Moreover, this study covers both narrow and wide bands. The studied algorithms are the most representative: the Vertical Bell Labs Space Time (VBLAST), the Orthogonal Space Time Block Code (OSTBC) and the Quasy-Orthogonal Space Time Block Code (QSTBC). The performances in terms of Bit Error Rate (BER) have been compared, assuming a fixed bit rate, and interpreted from the MIMO channel characteristics.Universidad Politécnica de CartagenaTecnologías de la Información y Comunicacione

Enhanced Air-Interfaces for Fifth Generation Mobile Broadband Communication

In broadband wireless multicarrier communication systems, intersymbol interference (ISI) and intercarrier interference (ICI) should be reduced. In orthogonal frequency division multiplexing (OFDM), the cyclic prefix (CP) guarantees to reduce the ISI interference. However, the CP reduces spectral and power efficiency. In this thesis, iterative interference cancellation (IIC) with iterative decoding is used to reduce ISI and ICI from the received signal in multicarrier modulation (MCM) systems. Alternative schemes as well as OFDM with insufficient CP are considered; filter bank multicarrier (FBMC/Offset QAM) and discrete wavelet transform based multicarrier modulation (DWT-MCM). IIC is applied in these different schemes. The required components are calculated from either the hard decision of the demapper output or the estimated decoded signal. These components are used to improve the received signal. Channel estimation and data detection are very important parts of the receiver design of the wireless communication systems. Iterative channel estimation using Wiener filter channel estimation with known pilots and IIC is used to estimate and improve data detection. Scattered and interference approximation method (IAM) preamble pilot are using to calculate the estimated values of the channel coefficients. The estimated soft decoded symbols with pilot are used to reduce the ICI and ISI and improve the channel estimation. The combination of Multi-Input Multi-Output MIMO and OFDM enhances the air-interface for the wireless communication system. In a MIMO-MCM scheme, IIC and MIMO-IIC-based successive interference cancellation (SIC) are proposed to reduce the ICI/ISI and cross interference to a given antenna from the signal transmitted from the target and the other antenna respectively. The number of iterations required can be calculated by analysing the convergence of the IIC with the help of EXtrinsic Information Transfer (EXIT) charts. A new EXIT approach is proposed to provide a means to define performance for a given outage probability on quasi-static channels

Signal processing for future MIMO-OFDM wireless communication systems

The combination of multiple-input multiple-output (MIMO) technology and orthogonal frequency division multiplexing (OFDM) is likely to provide the air-interface solution for future broadband wireless systems. A major challenge for MIMO-OFDM systems is the problem of multi-access interference (MAI) induced by the presence of multiple users transmitting over the same bandwidth. Novel signal processing techniques are therefore required to mitigate MAI and thereby increase link performance. A background review of space-time block codes (STBCs) to lever age diversity gain in MIMO systems is provided together with an introduction to OFDM. The link performance of an OFDM system is also shown to be sensitive to time-variation of the channel. Iterative minimum mean square error (MMSE) receivers are therefore proposed to overcome such time-variation. In the context of synchronous uplink transmission, a new two-step hard-decision interference cancellation receiver for STBC MIMO-OFDM is shown to have robust performance and relatively low complexity. Further improvement is obtained through employing error control coding methods and iterative algorithms. A soft output multiuser detector based on MMSE interference suppression and error correction coding at the first stage is shown by frame error rate simulations to provide significant performance improvement over the classical linear scheme. Finally, building on the "turbo principle", a low-complexity iterative interference cancellation and detection scheme is designed to provide a good compromise between the exponential computational complexity of the soft interference cancellation linear MMSE algorithm and the near-capacity performance of a scheme which uses iterative turbo processing for soft interference suppression in combination with multiuser detection.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Signal processing for future MIMO-OFDM wireless communication systems

The combination of multiple-input multiple-output (MIMO) technology and orthogonal frequency division multiplexing (OFDM) is likely to provide the air-interface solution for future broadband wireless systems. A major challenge for MIMO-OFDM systems is the problem of multi-access interference (MAI) induced by the presence of multiple users transmitting over the same bandwidth. Novel signal processing techniques are therefore required to mitigate MAI and thereby increase link performance. A background review of space-time block codes (STBCs) to lever age diversity gain in MIMO systems is provided together with an introduction to OFDM. The link performance of an OFDM system is also shown to be sensitive to time-variation of the channel. Iterative minimum mean square error (MMSE) receivers are therefore proposed to overcome such time-variation. In the context of synchronous uplink transmission, a new two-step hard-decision interference cancellation receiver for STBC MIMO-OFDM is shown to have robust performance and relatively low complexity. Further improvement is obtained through employing error control coding methods and iterative algorithms. A soft output multiuser detector based on MMSE interference suppression and error correction coding at the first stage is shown by frame error rate simulations to provide significant performance improvement over the classical linear scheme. Finally, building on the "turbo principle", a low-complexity iterative interference cancellation and detection scheme is designed to provide a good compromise between the exponential computational complexity of the soft interference cancellation linear MMSE algorithm and the near-capacity performance of a scheme which uses iterative turbo processing for soft interference suppression in combination with multiuser detection