Shared-nothing architecture has been widely used in distributed databases to achieve good scalability. While it offers superior performance for local transactions, the overhead of processing distributed transactions can degrade the system performance significantly. The key contributor to the degradation is the expensive two-phase commit (2PC) protocol used to ensure atomic commitment of distributed transactions. In this paper, we propose a transaction management scheme called LEAP to avoid the 2PC protocol within distributed transaction processing. Instead of processing a distributed transaction across multiple nodes, LEAP converts the distributed transaction into a local transaction. This benefits the processing locality and facilitates adaptive data repartitioning when there is a change in data access pattern. Based on LEAP, we develop an online transaction processing (OLTP) system, L-Store, and compare it with the state-of-the-art distributed in-memory OLTP system, H-Store, which relies on the 2PC protocol for distributed transaction processing, and H^L-Store, a H-Store that has been modified to make use of LEAP. Results of an extensive experimental evaluation show that our LEAP-based engines are superior over H-Store by a wide margin, especially for workloads that exhibit locality-based data accesses.

This paper presents the design, implementation, and evaluation of FAST (Full-duplex Attachment System), a cross layer system to solve both Hidden terminal problem and exposed terminal problems. The main reason that CSMA-like protocol cannot well solve hidden and exposed terminal problem both at once lies in the fact that they cannot obtain accurate Channel Usage Information (CUI, who is transmitting or receiving nearby) with low cost. FAST successfully obtains cost CUI in a cost-efficient way, thus can know exactly what are the neighborhood doing currently. FAST includes Attachment Coding in PHY layer to provide cost-effective CUI, and Attachment Sense in MAC layer to utilize CUI to identify hidden and exposed nodes in real time. Extensive simulation results show FAST can well solve both hidden and exposed terminal problems, and improves an average throughput to 200% over CSMA in practical ad-hoc networks.

By introducing the leakage concept, the maximum signal-to-leakage-and-noise ratio (SLNR) scheme has been served as a candidate precoding scheme in the advanced long term evolution (LTE-Advanced) communication system. However, the original scheme allocates every user the same transmit power and takes the matched filter to decode the receive signals, which results in the limited bit error rate (BER) performance. With the antenna correlation at BS and the channel estimation error for every user, we design a modified matrix by minimizing the system Mean Square Error (MMSE) after maximizing the SLNR under the total transmit power constraint. At each user, a linear decoder is calculated based on the MMSE criteria in the presence of imperfect channel state information (ICSI). Due to the dynamic power allocation during the parallel data streams and the linear MMSE (LMMSE) receiver, the proposed scheme can mitigate the residual interference induced by ICSI and improve the system BER performance efficiently.

In this paper, we proposed an effective and unified transmit power allocation (TPA) scheme for the Singular Value Decomposition (SVD)-Assisted multi-user multiple-input multiple-output (MU-MIMO) downlink (DL) and uplink (UL) transmissions in the presence of imperfect channel state information (ICSI). The existing power allocation policies for the SVD-Assisted MU-MIMO system, such as equal power allocation (EPA) in the DL and maximum signal-to-noise ratio (MSNR) policy in UL have been developed under the perfect CSI case. However, the EPA scheme doesn't exploit the CSI and ignores the Bit Error Rate (BER) difference among all singular values meanwhile the MSNR method neglects the noise enhancement caused by the decoding operation at Base Station (BS). Aiming at solving these problems, the proposed TPA scheme takes the smallest singular value and the noise enhancement into account and derives an unified expression for DL and UL. Under the ICSI, the proposed scheme can exploit the power allocation operation to mitigate the residual interference induced by ICSI and improve the system BER performance efficiently.

Hybrid subcarrier exclusivity and sharing (HSEnS) scheme with optimized bit loading in uplink multicell OFDMA system is proposed in this paper. Optimizing bit loading under subcarrier exclusivity (SE) and subcarrier sharing (SS) schemes in two adjacent cells is analyzed. Bit loading criteria and boundary setting procedures for convex optimizing bit loading under SS scheme are proposed. And bit loading boundaries for convex optimizing bit loading under SE and SS scheme can be obtained. The HSEnS scheme is proposed to combine the advantages of SE and SS schemes for making tradeoff between throughput performance and algorithm failure rate when interference is strong, moderate or weak. Simulations support our proposals and HSEnS with optimized bit loading outperforms other schemes.