Interference Alignment in 2-user X Channel System with Orthogonal and quasi-orthogonal Space-time Block Codes

본 논문에서는 각 단말에 2개 이상의 안테나의 간섭 정렬을 이용한 X채널에서 직교 및 준직교 시공간 블록 부호를 통하여 더 높은 다이버시티와 전력 이득을 달성하고자 했다. 제안한 방법으로 다이버시티 차수는 직교 시공간 블록부호에서 최대에 도달한 반면, 준직교 시공간 블록 부호에서는 유효 채널 행렬의 비 직교성에 의해 약간의 성능 저하가 나타났다. 수신기의 유효 채널 행렬에서의 유리한 구조에 의해 단순 제로 포싱 수신기는 최대 다이버시티 차수를 달성하는 반면, 간섭 제거 수신기는 성능이 저하되었다. 기존의 방법과 비교했을 때, 시뮬레이션 결과는 제안된 방법이 같은 스펙트럼 효율을 얻으면서, 3-4개의 안테나의 각 단의 직교 시공간 블록 부호의 경우 각각 목표 비트 에러율 10-4 에서 14dB와 16.5bB의 이득을 얻는 것을 증명하였다. 또한 4개의 안테나의 각 단의 준직교 시공간 블록 부호의 경우 같은 목표 비트 에러율에서 10dB의 이득을 얻었다

Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks

In this paper, a practical multi-user cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for Multiple-Input Multiple-Output - Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) Relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm. It is shown that this scheme is robust against channel estimation errors and offers diversity and array gain keeping the complexity low, although the multi-user and multi-antenna channel estimation algorithm is simple and efficient. Diversity gains larger than 4 can be easily obtained with reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays

Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks

In this paper, a practical multi-user cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for Multiple-Input Multiple-Output - Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) Relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm. It is shown that this scheme is robust against channel estimation errors and offers diversity and array gain keeping the complexity low, although the multi-user and multi-antenna channel estimation algorithm is simple and efficient. Diversity gains larger than 4 can be easily obtained with reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays

Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks

In this paper, a practical multi-user cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for Multiple-Input Multiple-Output - Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) Relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm. It is shown that this scheme is robust against channel estimation errors and offers diversity and array gain keeping the complexity low, although the multi-user and multi-antenna channel estimation algorithm is simple and efficient. Diversity gains larger than 4 can be easily obtained with reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays

GOODPUT BASED ADAPTIVE MODULATION AND CODING ALGORITHM FOR BIC-OFDM SYSTEMS

WiMAX IEEE 802.16m standard description and implementation of simulation software. SISO and MIMO techniques(open loop and closed loop) implementation and resultis validation. A novel physical abstraction and Link layer prediction for 802.16m MIMO BIC-OFDM system based on goodput maximization: Effective SNR mapping, with low complexity but same performance or even better compared with MIESM, called novel kESM. Theoretical derivation of novel kESM physical abstraction technique, comparison between kESM and MI-ESM / EESM. Goodput oriented adaptive modulation and coding algorithm for BIC-OFDM wireless system based on above-mentioned abstraction. Theoretical derivation and dissertation. Simulations of 802.16m WiMAX system using C++ and C++ with IT++ libraries(used in NEWCOMM++ project). Various graphic rapresentation for different modulation and coding schemas, dissertation abuot visual and practical results

Block-Orthogonal Space-Time Code Structure and Its Impact on QRDM Decoding Complexity Reduction

Full-rate space time codes (STC) with rate = number of transmit antennas have high multiplexing gain, but high decoding complexity even when decoded using reduced-complexity decoders such as sphere or QRDM decoders. In this paper, we introduce a new code property of STC called block-orthogonal property, which can be exploited by QR-decomposition-based decoders to achieve significant decoding complexity reduction without performance loss. We show that such complexity reduction principle can benefit the existing algebraic codes such as Perfect and DjABBA codes due to their inherent (but previously undiscovered) block-orthogonal property. In addition, we construct and optimize new full-rate BOSTC (Block-Orthogonal STC) that further maximize the QRDM complexity reduction potential. Simulation results of bit error rate (BER) performance against decoding complexity show that the new BOSTC outperforms all previously known codes as long as the QRDM decoder operates in reduced-complexity mode, and the code exhibits a desirable complexity saturation property.Comment: IEEE Journal of Selected Topics in Signal Processing, Vol. 5, No. 8, December 201

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