19156667
Double-orthogonal coded space-time-frequency spreading CDMA scheme
In this paper, we propose double-orthogonal coded space-time-frequency spreading code-division multiple-access (DOC-STFS-CDMA) scheme for the downlink orthogonal frequency-division multiplexing (OFDM) systems employing multiple transmit and receive antennas. First, we introduce the so-called STFS-CDMA and the corresponding minimum mean-square error (MMSE) detection algorithms for three scenarios with different user information. Then, we propose a new class of spreading codes, called double-orthogonal code (DOC), to match the MMSE detection algorithms for STFS-CDMA system. With the special double orthogonality, DOC can effectively exploit space, time, and frequency diversity to enhance the performance of MMSE detectors, and provide the well-balanced signal-to-interference-and-noise ratio to different users. Finally, the performance gain of the proposed scheme over conventional schemes is shown by computer simulation.
36101226
A Novel Fast Recursive MMSE-SIC Detection Algorithm for V-BLAST Systems
A novel fast recursive minimum mean square error successive interference cancellation (MMSE-SIC) algorithm with optimal detection order for vertical Bell Laboratories layered space-time (V-BLAST) systems is proposed. In this algorithm, the MMSE Alter matrices and the optimal detection order are successively computed from the previously obtained filter matrices according to simple recursive pseudoinverse formulas, so that the algorithmic complexity is reduced significantly, especially for the practical number of transmit/receive antennas.
18196020
Linear Precoding Based on Sub-Channel Permutation in Post-Combining MIMO-HARQ Systems
A powerful HARQ-based linear precoding scheme is proposed to utilize the flexibility of post-combining HARQ strategy in MIMO communications systems. The scheme selects the appropriate symbols and transmit powers for each eigen-mode to acquire more performance gains. Simulation results show that the proposed scheme achieves about 5.5dB signal-to-noise ratio gains over original spatial multiplexing scheme at an average bit error rate of 10 -4 . Furthermore, the gap between the two schemes increases with the number of transmissions.
9646774
An uplink analytical model for two-tiered 3G femtocell networks
This paper proposes an analytical model to investigate the impact of interference on the uplink capacity and coverage in a WCDMA network where macrocell and femtocells co-exist. Geometric modeling for the hierarchical system is used where the randomly deployed femtocells are within the planned macrocells' topology. The interference effects among femtocells and between femtocells and macrocells are studied analytically to quantify the system capacity and coverage based on the practical target signal-to-interference ratio (SIR). Interference level splitting results show that the macrocell attached User Equipment (UE) to Home Node B (HNB) interference has severe impact on the capacity and coverage of femtocell network. Further study suggests that advanced receivers which cancel interference at the femtocell could minimize the effect brought by different interferences in a cost-effective manner.
694816
Distributed file system support for virtual machines in grid computing
This paper presents a data management solution which allows fast virtual machine (VM) instantiation and efficient run-time execution to support VMs as execution environments in grid computing. It is based on novel distributed file system virtualization techniques and is unique in that: 1) it provides on-demand access to VM state for unmodified VM monitors; 2) it supports user-level and write-back disk caches, per-application caching policies and middleware-driven consistency models; and 3) it supports the use of meta-data associated with files to expedite data transfers. The paper reports on its performance in a WAN setup using VMware-based VMs. Results show that the solution delivers performance over 30% better than native NFS and can bring application-perceived overheads below 10% relatively to a local disk setup. The solution also allows a VM with 1.6GB virtual disk and 320MB virtual memory to be cloned within 160 seconds when it is first instantiated (and within 25 seconds for subsequent clones).
9529180
Joint Power and Channel Resource Allocation for F/TDMA Decode and Forward Relay Networks
In this paper, we study the joint power and channel resource allocation problem for a multiuser F/TDMA decode-and-forward (DF) relay network under per-node power constraints and a total channel resource constraint. Our goal is to maximize the total throughput achieved by the systems. To that end, we formulate a joint power and channel resource allocation problem. We develop an iterative optimization algorithm to solve this problem, whose convergence and optimality are guaranteed. Due to the per-node power constraints, more than one relay node may be needed for a single data stream. Our solution also provides a way of finding the optimal relays among the assisting relay nodes.
3677775
Relaying Schemes for MIMO Broadcast Channels: Coexistence of Direct-Link and Relay-Link Users
The combination of relay and Multiple-Input Multiple-Output (MIMO) techniques can significantly benefit the signal transmission in cellular networks. In this work, we propose a novel relaying scheme for the relay assisted MIMO broadcast channel including user classification and precoding. The users are firstly classified as Direct Link (DL) users and Relay Link (RL) users according to their channel conditions. After classification, both DL and RL users may coexist in the system, and Zero-Forcing (ZF) precoding is employed at both the BS and the relay for interference cancellation. Analysis and simulation results show that the proposed relaying scheme can effectively combat the large scale fading of the channels and provide significant performance gain compared with the conventional MIMO relaying schemes without user classification.