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Articles by Zhongzhao Zhang
Total Records ( 4 ) for Zhongzhao Zhang
  Jingning Wang , Xuejun Sha , Linan Sun and Zhongzhao Zhang
  In this study, a cooperative diversity scheme with decoded-and-forward plus amplify-and-forward is proposed by employing truncated stop-and-wait automatic repeat request for error control. All the transmission channels are assumed to exhibit Nakagami-m fading and the cross-layer performance is analyzed for the proposed scheme, such as the channel efficiency in physical layer, throughput and packet loss rate in link layer. The simulation results show that, the proposed scheme has the better cross-layer performance than other cooperative systems. By choosing a suitable partner, the proposed cooperative scheme can provide better performance than non-cooperative systems and spatial diversity gain can be obtained.
  Wei Wu , Zhongzhao Zhang , Xuejun Sha and Chenguang He
  Some auto rate protocols at the MAC layer have been proposed to improve the throughput of Ad Hoc networks with multiple rates support at physical layer. However, all of them neglect the influence of network congestion. The network performance will deteriorate as a result of transmitting data to a congested node. In this study, an auto rate protocol based on congestion detection called auto rate based on congestion detection (ARCD) is proposed. In the ARCD protocol, congestion level is detected at the receiving nodes and fed back to the sending nodes along with the rate selection information and then the sending nodes transmit a limited number of back-to-back packets at appropriate rates. The simulation results show that the ARCD protocol can not only improve the throughput and packet delivery ratio of Ad Hoc networks by taking full advantage of channel condition, but also achieve hop-by-hop congestion control.
  Weilin Jiang , Zhongzhao Zhang , Yubin Xu and Linan Sun
  In this study, we consider the joint application of adaptive Soft Frequency Reuse (SFR) and Maximum Ratio Combining (MRC) to dynamic Inter-Cell Interference (ICI) cancellation. The ICI is the dominant factor in system performance degradation for uplink in multi-cell Orthogonal Frequency Division Multiple Access (OFDMA) systems. This study firstly investigates the problem of ICI for uplink. Then dynamic ICI cancellation for uplink in OFDMA systems is proposed. When loading is small, low complexity and practical adaptive soft frequency reuse is adopted. As users in the boundary grow larger, MRC is applied to improve edge user performance, which can also cancel ICI by reducing user transmission power. Analysis results show the proposed scheme can provide better reuse efficiency over the adaptive SFR and also can mitigate ICI significantly. Simulation results indicate that the ergodic capacity proposed scheme increases larger 14.5% than not using MRC for Es/N0 around 10 dB. Higher spectral efficiency is achieved for large number of users in multi-cell environments, especially for users at the cell boundary.
  Linan Sun , Zhun Ye and Zhongzhao Zhang
  In order to effectively cancel Co-Channel Interference (CCI) and reduce Bit Error Rate (BER) in multi-cell MIMO cellular systems, performance of several Multi-User Detection (MUD) techniques based on coordinated multi-point processing (COMP) is studied. Several neighboring base stations coordinate with each other and form a virtual antenna array, serving for users in the coordinated region. Receivers of Zero Forcing (ZF), Minimum Mean-Square-Error (MMSE) and their combination with Successive Interference Cancellation (SIC) are designed and adept by the coordinated base stations and BER of above methods is studied. Simulation results show that BER performance of those COMP methods significantly outperforms single cell processing when interference is considered and is even better than it when interference is free at medium to high SNR. Furthermore, MMSE outperforms ZF and performance is even better when combined with SIC and will still increase with the number of antennas. Finally, MMSE-SIC COMP is shown to be most feasible and effective for interference cancellation in multi-cell MIMO cellular systems.
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