We propose a new graphical model approach to cooperative multiple-input multiple-output (MIMO) cellular networks. The objective is to optimize downlink transmit beamforming at each BS in order to maximize the sum thro...
详细信息
We propose a new graphical model approach to cooperative multiple-input multiple-output (MIMO) cellular networks. The objective is to optimize downlink transmit beamforming at each BS in order to maximize the sum throughput over the entire network. While ideal centralized beamforming requires full channel state information (CSI) sharing among all BSs in the network and huge computational complexity for combinatorial optimization, the proposed graphical model enables distributed beamforming which requires only local CSI sharing between neighboring BSs and efficiently solves the optimization problem in a distributed manner. As distributed solvers for this problem, we derive message-passing algorithms which can be implemented with polynomial-time computational complexity. Furthermore, we make a slight approximation on the objective function to derive a simpler graphical model, providing further complexity saving. Simulation results indicate that the proposed distributed downlink beamforming achieves average cell throughput typically within just 2% of ideal centralized beamforming.
As an effective technique for combating multipath fading and for high-bit-rate transmission over wireless channels, orthogonal frequency division multiplexing (OFDM) is extensively used in high-rate wireless communica...
详细信息
As an effective technique for combating multipath fading and for high-bit-rate transmission over wireless channels, orthogonal frequency division multiplexing (OFDM) is extensively used in high-rate wireless communication systems, such as, the wireless local area network (WLAN) and the digital television terrestrial broadcasting (DTTB) systems, to support high performance bandwidth-efficient multimedia services. multiple antennas and transmit or receive diversity, multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM), can be used to improve error performance and capacity of wireless systems. In this paper, we consider the effects of carrier frequency offset and channel estimation errors on the performance of MIMO-OFDM systems in spatially correlated channels. Theoretical calculations and computer simulations are done to analyze the performance degradation of MIMO-OFDM systems in spatially correlated channels due to carrier frequency offset and channel estimation errors, and the theoretical and simulated results match well.
The outdated channel state information (CSI) at the transmitter and receiver, which is resulted from time variation of channels, is considered in multiple-input multiple-output systems employing maximal ratio combinin...
详细信息
The outdated channel state information (CSI) at the transmitter and receiver, which is resulted from time variation of channels, is considered in multiple-input multiple-output systems employing maximal ratio combining. Closed-form expressions for the cumulative distribution function of output signal-to-noise ratio and symbol error rate under time-varying channels are presented to evaluate the effect of outdated CSI. The analytical results are compared with Monte Carlo simulations and a good agreement is obtained.
In this paper, we propose a new QR-based selection criterion with reduced complexity for the development of switching between spatial multiplexing (SM) and spatial diversity (SD) transmission. Then, we investigate an ...
详细信息
In this paper, we propose a new QR-based selection criterion with reduced complexity for the development of switching between spatial multiplexing (SM) and spatial diversity (SD) transmission. Then, we investigate an effect of the QR-decomposition processes by exploiting orthogonal structure of channel matrix. Additionally, to solve the problem of the error transmission mode in transmitter, we claim that the proposed QR-based detection at receiver can be used to form the successive interference cancellation (SIC) detection and orthogonal space-time block code (O-STBC) decoding for the SM transmission and the SD transmission, respectively. Simulation results show that the proposed scheme is capable of achieving optimum performance, but at a low-complexity level.
In conventional concatenations of Convolutional Codes (CC) and Space-Time Block Codes (STBC), the CC and STBC are utilized to provide coding gain and spatial diversity, respectively. We propose a concatenated code tha...
详细信息
In conventional concatenations of Convolutional Codes (CC) and Space-Time Block Codes (STBC), the CC and STBC are utilized to provide coding gain and spatial diversity, respectively. We propose a concatenated code that achieves the full system diversity by appropriately selecting the outer CC with an inner reduced-rank STBC. The advantage of the lower rank STBC is that the number of RF chains can be reduced. For any number of RF chains, R, we show that a desirable diversity order Y can be easily achieved i.e., 1 <= R <= Y. Using trellis diagram, we formalize the method to determine the maximum diversity.
An efficient pruning method is proposed for the infinity-norm sphere decoding based on Schnorr-Euchner enumeration in multiple-input multiple-output spatial multiplexing systems. The proposed method is based on the ch...
详细信息
An efficient pruning method is proposed for the infinity-norm sphere decoding based on Schnorr-Euchner enumeration in multiple-input multiple-output spatial multiplexing systems. The proposed method is based on the characteristics of the infinity norm, and utilizes the information of the layer at which the infinity-norm value is selected in order to decide unnecessary sub-trees that can be pruned without affecting error-rate performance. Compared to conventional pruning, the proposed pruning decreases the average number of tree-visits by up to 37.16% in 4 x 4 16-QAM systems and 33.75% in 6 x 6 64-QAM systems.
Dynamic spectrum sharing in cognitive radio networks is an open research issue. This paper propose, a limited feedback opportunistic spectrum sharing (LFOSS) technique for heterogeneous multiple-input multiple-output ...
详细信息
ISBN:
(纸本)9783037851036
Dynamic spectrum sharing in cognitive radio networks is an open research issue. This paper propose, a limited feedback opportunistic spectrum sharing (LFOSS) technique for heterogeneous multiple-input multiple-output (MIMO) uplink system based on the concept learning automata. Simulation results show that our proposed algorithm can substantially improve the average mutual information of each secondary user under the interference temperature constraint and the maximum data substream constraint compared to the random selection scheme.
For error-correction codes, the optimal coding rate can vary and depend on factors including channel, time-varying fading, environmental interference, power, bandwidth allocation, communication content, and applicatio...
详细信息
ISBN:
(纸本)9781467303231
For error-correction codes, the optimal coding rate can vary and depend on factors including channel, time-varying fading, environmental interference, power, bandwidth allocation, communication content, and application. Rate adaptive coding schemes are thus important for robust communications. This writeup proposes and studies a rate adaptive low density parity check (LDPC) coding scheme using non-binary Galois fields (GF). The algorithm uses a single low complexity encoding structure, but maintains strong near-capacity performance at arbitrary rational rates. The rate adaptive encoder can be used in a space-time code for multiple-input multiple-output (MIMO) communication systems and is shown to achieve near capacity performance at various rates and different MIMO configurations.
In this paper, we consider an interference multiple-input multiple-output (MIMO) relay system where multiple source nodes communicate with their desired destination nodes with the aid of distributed relay nodes. An it...
详细信息
ISBN:
(纸本)9781457703881
In this paper, we consider an interference multiple-input multiple-output (MIMO) relay system where multiple source nodes communicate with their desired destination nodes with the aid of distributed relay nodes. An iterative algorithm is developed to minimize the total source and relay transmit power such that a minimum signal-to-interference-plus-noise ratio (SINR) threshold is maintained at each receiver. The proposed algorithm exploits the network beamforming technique at the relay nodes and the receive beamforming technique at the destination nodes to mitigate the interferences from the unintended sources in conjunction with transmit power control. In particular, we apply the semidefinite relaxation technique to transform the relay transmission power minimization problem into a semidefinite programming (SDP) problem which can be efficiently solved by interior point-based methods. Numerical simulations are performed to demonstrate the effectiveness of the proposed iterative algorithm.
We investigate the performance of cooperative diversity when employed in convolutionally coded direct-sequence code-division multiple-access (DS-CDMA) systems over frequency-selective fading channels. The performance ...
详细信息
ISBN:
(纸本)9781612842332
We investigate the performance of cooperative diversity when employed in convolutionally coded direct-sequence code-division multiple-access (DS-CDMA) systems over frequency-selective fading channels. The performance of the coded system is evaluated through bit error rate upper bounds and compared with simulations. In our analysis, we obtain closed form expressions for the bit error rate upper bounds for multi-relay cooperative systems employing multiuser detection at both the relay and base station receivers. We show that the full benefits of cooperative diversity cannot be achieved if no interference suppression is employed at both the cooperative user and base station receiver. Both simulation and analytical results are presented to validate and demonstrate the performance gain with different system parameters.
暂无评论