In this article, we study the coding advantage of spacetime-frequency block codes (STFBCs). Since in MIMO-OFDM coding there is the potential of exploiting space, time and frequency diversities and as the frequency ton...
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In this article, we study the coding advantage of spacetime-frequency block codes (STFBCs). Since in MIMO-OFDM coding there is the potential of exploiting space, time and frequency diversities and as the frequency tones of OFDM modulation are relatively substantial, the intricate structure of STFBCs makes it almost impossible to optimize the parameters of the code as the number of symbols increases in each block. Consequently, we investigate how to optimize the code parameters independently to reduce the computational complexity. Furthermore, code permutation is an important part of the STFBCs. However, due to elaborate structure of the STFBCs, it is very hard to calculate the optimum permutation. Therefore, we put forth a technique to decompose the coding advantage of the STFBCs. Using this technique, the permutation parameter can be easily introduced and optimized for STFBCs. We then design a novel STFBC based on any given STBC and apply the proposed scheme on the proposed STFBC to illustrate the application of this technique by designing the optimum permutation for the code. Simulation results confirm that the proposed STFBC outperforms the best existing STFBCs in the literature.
The Langberg-Medard k-Unicast Conjecture states that for any strongly reachable k-pair network, there exists a multi-flow with rate (1, 1, ..., 1). In this paper, for k = 3, 4, we construct multi-flows with rate (11/1...
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ISBN:
(纸本)9781538647813
The Langberg-Medard k-Unicast Conjecture states that for any strongly reachable k-pair network, there exists a multi-flow with rate (1, 1, ..., 1). In this paper, for k = 3, 4, we construct multi-flows with rate (11/12, 11/12, ..., 11/12), which improves the previous result (8/9, 8/9, ..., 8/9), and we further prove that our constructions are optimal within the proposed framework.
Multi-input multi-output-orthogonal frequency-division multiplexing is the foundation of next generation of wireless communication systems and space-time-frequency block coding (STFBC) is considered one of the best sc...
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Multi-input multi-output-orthogonal frequency-division multiplexing is the foundation of next generation of wireless communication systems and space-time-frequency block coding (STFBC) is considered one of the best schemes for implementing these systems. STFBCs have very complex structures and many parameters affect their performance. Studies have shown that permutation parameter plays a very important and sensitive role in the construction of STFBCs so much so that a small variation of this parameter could cause a significant change in the value of the coding advantage (CA) which alters the code's performance. In this study, first the authors explore how the permutation parameter affects STFBCs and demonstrate that existing permutation methods do not guarantee to attain the maximum possible CA. Next, they introduce a new structure for STFBCs permutation, which is the basis for the design of a modified model of one recently published STFBC. Comparison of the simulation results from the original and modified codes confirms the latter improves the performance by up to 3 dB. This is an achievement that is also verified by theoretical analysis.
Space-frequency (SF) group codes are designed for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. A rather general channel model is assumed, where the channel is frequenc...
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Space-frequency (SF) group codes are designed for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. A rather general channel model is assumed, where the channel is frequency-selective Rayleigh fading with arbitrary power-delay profile. It is shown that the SF group code has a symmetric distance structure like the space-time group code, if the group consists of diagonal matrices. A scenario where the multiple codewords are loaded onto the subcarriers of the OFDM system in parallel is considered. The optimality condition on the choice of subcarrier allocation is found, and an optimal subcarrier-allocation scheme is proposed. A transmit scheme where rotated versions of the same signal are transmitted from different transmit antennas is proposed, and it is shown that it satisfies the optimality condition. Then matrix groups are designed which guarantee that the resulting SF codes are full rank. Numerical comparisons with recently published techniques in the literature verify our improved performance.
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