V-BLAST-Based Virtual MIMO for Distributed Wireless Sensor Networks

A novel three-hop cooperative diversity system model is proposed in this paper comparing to conventional dual-hop cooperative systems, assuming all terminals have only one antenna for size limitation. This system model avoids complex relay selection criterions and data forwarding strategies which are necessary for conventional cooperative systems to optimize their performance. Both source node and destination node request free nodes around them to perform as virtual antenna arrays based on the simplest selection criterion, and then a virtual multiple-input multiple-output (MIMO) system is constructed. Different from the systems reported in literatures, signals from source node need three hops before arriving at destination. We show that if channels between destination node and its virtual antennas are better than channels between source and destination, symbol error rate (SER) of this virtual MIMO system can approximate the performance of actual MIMO system.

In this paper, a downlink wireless transmission scheme is proposed for roadside deployment. The scheme is based on orthogonal frequency-division multiplexing (OFDM) technology, and it also employs virtual multiple input multiple output (MIMO) to further improve system capacity. In the "virtual" MIMO scheme proposed in this paper, signals can be sent from two base stations (BS) to one user, which creates a virtual MIMO system that may offer additional capacity gains in fading channels. This scheme is especially fit for the bi-sectional BSs with zonal coverage along roadside. Simulation results show that the proposed scheme can support both high and low speed users on road, and achieve a high system capacity gain especially in the cell edge. Within this scheme, the OFDM symbols are characterized into two groups: localized resource group (LRG), which is continuous in time-frequency (TF) domain; and distributed resource group (DRG) which is TF discrete. As LRG is fit for low-speed users to utilize the slowly varying channel while DRG is fit for high-speed users with rapid varying channels, the combination of them makes the allocation of OFDM subchannel more elastic to support users with different speed

Long Term Evolution-Advanced (LTE-Advanced) and other advanced technologies like IEEE802.16e and IEEE802.11g base their physical layer transmission on multiple input multiple output (MIMO). The concept of multiple antennas at both receiver and transmitter ends is attributed with advantages of spatial multiplexing and diversity, however, the Implementation on small size UEs has its own limitations. Hence a concept of virtual multiple input multiple output (VMIMO) has evolved to accommodate higher throughput for LTE-Advanced system. This paper formulates a scheme that provides maximum uplink throughput in LTE-ADVANCED environment keeping minimum level of fairness within grouped user equipment (UEs) in VMIMO. Groups/Pairs are formed from single antenna UEs to obtain multiplexing gain. Round Robin (RR), Proportional Fair (PF) and Random Pairing (RP) are Conventional pairing scheme. Fairness is prime consideration in RR and PF but RP ignores both fairness and throughput. In this paper, a Modified Random Pair (M-RP) has been introduced that maximizes throughput 2.10%, 2.07% & 2.02% in Lower group VMIMO and .96%, .96% & .95% Higher group VMIMO from RP, RR and PF respectively while keeping minimum level of fairness in the legal UEs within Femtocell scenario.

An integrated design of a joint distributed source coding and an adaptive signal processing scheme for a virtual multiple input multiple output (V-MIMO) communications-based, cooperative wireless sensor network is proposed. We employ a distributed coding scheme that exploits inherent correlations among sensor data and an adaptive correlation tracking technique based on recursive least squares (RLS) algorithm that provides improved energy efficiency compared to previously proposed such joint coding and signal processing schemes for single input single output (SISO) communications based systems. An integration scheme with virtual space-time block coding based M-ary quadrature amplitude modulation (M-QAM) communication is also developed. The system efficiency is analyzed for various transmission distances and various channel conditions. Our results show that the proposed system achieves significant energy savings compared to conventional designs beyond certain transmission distances. The achieved energy efficiencies and low decoding error rates justify the application of the proposed scheme in energy constrained wireless sensor networks.

Wireless sensor networks (WSNs) have been paid more attention in recent years. However, energy efficiency is still a troublesome issue in real WSN applications. In this paper, we studied the performance of a virtual multiple-input multiple-output (VMIMO)-based communications architecture for WSN applications. By analyzing the bit error rate (BER) of each cooperative branch, we presented the closed-form expressions for optimal transmitting power (TP) scheme in K×1 VMIMO cluster-based system. Then, the impact of the number of cooperating nodes on energy efficiency with energy-perusefulbit (EPUB) metric was studied. Performance enhancement of the strategy with optimal TP assignment was verified by extensive simulations under different scenes. A thorough explanation of optimally choosing the number of cooperating nodes was also delivered by the aid of simulation verifications.

In the conventional Vertical Bell Laboratory Layered Space-Time (V-BLAST) receiver with successive interference cancellation (SIC) decoding, the diversity order for the first detected symbol is the lowest, hence its error probability dominates the overall average error probability. In this thesis, a new SIC scheme was presented, called iterative post SIC (IP-SIC) that can increase the diversity order to a fixed desired value for all symbols, thereby significantly reduce the overall average error probability. The key to the technique is that after the interference from all substreams is subtracted from the received vector (the resulting vector will be referred to as the modified received vector), the detected symbol times its channel vector is added to the modified received vector one at a time and the symbol is detected again. Important features of the proposed approach are the increase in diversity order for those symbols detected earlier and the flexibility of balancing the increase in diversity order and the suppression of remaining interference. The latter feature can be used to further reduce the average error probability. The proposed technique is applied to the V-BLAST and space-time block coded V-BLAST system and its performance and computational complexity are analyzed.

To monitor physical conditions, wireless sensor networks (WSNs) employ a large number of sensor nodes. These nodes have limited energy resources that is major issue in wireless communication systems. Virtual MIMO (vMIMO) is a technology that can enhance energy efficiency in WSNs by transmitting or receiving data from numerous nodes, enhancing signal quality, and lowering power. This research offers Energy-Efficient Virtual MIMO Communication (EE-VMC), a novel solution to addressing the energy efficiency dilemma in Wireless Sensor Networks (WSNs). EE-VMC presents a viable option for long-term deployments in cluster-based cooperative WSNs by exploiting virtual Multiple-Input Multiple-Output (MIMO) communication. The suggested method employs an optimized LEACH (OLEACH) protocol to promote energy efficiency by promoting effective communication while minimizing energy consumption. The simulation findings show that the OLEACH algorithm performs well in wireless sensor networks. At an SNR of -10dB, OLEACH has the highest Packet Delivery Ratio (PDR), showing improved performance in low signal-to-noise ratio conditions. Increasing the number of antennas also improves OLEACH's data delivery performance. When compared to state-of-the-art protocols (LEACH, HEED, BRICH, and B-LEACH), OLEACH regularly beats them in terms of PDR, SNR values, and data transfer rounds. Furthermore, OLEACH has greater remaining energy levels, indicating better energy management and increased network lifespan. The results back up the conclusion that OLEACH is a promising algorithm for optimizing energy consumption, improving packet delivery, and improving overall network performance in wireless sensor networks.

The virtual multiple input multiple output (MIMO) technique can dramatically improve the performance of a multi-cell distributed antenna system (DAS), thanks to its great potentials for inter-cell interference mitigation. One of the most challenging issues for virtual MIMO is the acquisition of channel state information at the transmitter (CSIT), which usually leads to an overwhelming amount of system overhead. In this work, we focus on the case that only the slowly-varying large-scale channel state is required at the transmitter, and explore the performance gain that can be achieved by coordinated transmissions for virtual MIMO with large-scale CSIT. Aiming at maximizing the achievable ergodic sum rate, the input covariances for all the mobile terminals (MTs) are jointly optimized, which turns out to be a complicated non-convex problem with a non-closed-form objective function. Further analysis reveals that the coordinated transmission problem can be recast as a Max-Min problem with a closed-form objective function and linear constraints. Then, by appealing to the successive approximation method and the saddle-point theory of concave-convex functions, we propose an iterative algorithm for coordinated transmissions with large-scale CSIT and establish its convergence. Simulation results corroborate that the proposed scheme converges quickly, and it yields significant performance gains compared to the existing schemes. Moreover, it is observed that the proposed scheme can achieve a nearly globally-optimal point under the diagonal input covariance constraint. Since the acquisition of large-scale CSIT is far less demanding than that of full CSIT, we believe that the proposed coordinated transmissions with large-scale CSIT in DASs shed some light on virtual MIMO in the making.

Installing multiple antennas at user equipments (UEs) may pose great challenges. In virtual multiple-input multiple-output (MIMO) concept, multiple single-antenna UEs can be grouped to transmit signals at the same time. Their signals can be separated at the base station (BS) by the same methods already used in conventional point-to-point MIMO scenarios. An important problem in virtual MIMO application is which users can be scheduled simultaneously to achieve a good balance between various system targets, e.g. aggregate throughput and user fairness. In this paper, a novel scheduling scheme is proposed which combines the advantages of proportional fair and maximum rate rules, based on successive interference cancellation (SIC) MIMO receiver architecture. Simulation results show that the proposed scheme can achieve a good tradeoff between system throughput and user fairness. Compared with other scheduling schemes already proposed in virtual MIMO context, e.g., orthogonality pairing scheduling (OPS), the proposed scheme can be justified by its low computational complexity and flexibility.

We consider large-scale virtual multiple-input multiple-output (MIMO) systems, in which a large number of user terminals communicate with a large number of cooperative bases stations (BSs). We focus on a training-based scheme and investigate the throughput maximization over various system parameters including pilot symbols, the time allocation coefficient a, the power allocation coefficient γ, and the user number K. Our main contribution is to derive simple throughput expressions by utilizing the random matrix theory, based on which closed-form optimal solutions of (K, γ, α) are obtained. We show that, for a large but finite coherent time T, the optimal K for throughput optimization satisfies K > T/2 and converges to T/2 as the signal-to-noise ratio goes to infinity.

Virtual MIMO (Multiple Input Multiple Output) groups multiple single-antenna mobile devices to form an antenna array, offering higher degrees of freedom and improved spatial diversity gain as a real MIMO does, yet with much lower costs. In this paper, we focus on the user grouping problem in uplink transmission from multiple single-antenna users to one multiple-antenna base station. State-of-the-art solutions mostly target two single-antenna users, solving a pairing problem. Having more than two uplink users in a grouping has yet to be addressed. Intuitively, a higher number of users in a VMIMO group offers better spectrum efficiency, and thus more throughput gains could be expected; the group dynamics however becomes higher too, making fairness harder to be achieved with reasonable computation overhead. To address these challenges, we present a novel solution that decomposes the VMIMO user grouping into two steps. We lighten the computations in user grouping by using instantaneous signal to noise ratio (SNR) as selection criteria, and combining it with proportional fairness for larger groups of users. Lightweight computation in using instantaneous SNR in our solution allows faster grouping and feasible scheduling for a large number of users, as well as fast decision on the efficiency of the number of users in each group. We have evaluated our solution under different network configurations, and the results demonstrate that it achieves much higher data throughput as compared to existing solutions and also well preserves fairness.

The innovation of Wireless communication has been developed very fast in order to improve the performance of communication systems. Especially, a concept of Multiple Input Multiple Output (MIMO) is purposed to fulfill a high data rate service such as high quality video conference. However, a limitation in size and power of mobile device in the latest version of cellular system i.e. third Generation (3G) and fourth Generation (4G) causes difficulty to implement MIMO on mobile unit. Hence, Cooperative communication has been created to operate as a virtual MIMO in modern wireless communication. The objective of this paper, the performance analysis of Hybrid Decode-Amplify and Forward (HDAF) Cooperative communication using Orthogonal Space-Time Block Code (OSTBC) is derived in term of Symbol Error Rate (SER) against Signal-to-Noise Ratio (SNR) when the system applies different type of modulation techniques. Additionally, the error performance is derived base on Moment Generating Function (MGF) of the Rayleigh fading channel. We only focus on the downlink direction. Assuming that multiple antennas can be equipped into a transmitter which operates as base station in cellular system, mobile unit can be equipped with only single antenna due to the size limitation which operates as relays and destination. Moreover, the receiver uses Maximum Ratio Combining (MRC) to receive the transmitted signal.

Virtual multiple-input multiple-output (VMIMO) enables the implementation of conventional MIMO on mobile devices equipped with insufficient numbers of antennas via cooperation. This paper considers a spectral efficient broadcasting network in which selected mobile devices form a VMIMO system to relay the broadcasted data to help other devices decode the source data more reliably. In particular, the relay selection problem, a fundamental issue in the construction of VMIMO, is examined. We first review existing selection schemes for users operating in the amplify-and-forward (AF) mode. We then propose a distributed selection scheme based on post-processing SNR. In the proposed scheme, each user individually finds the most favorable candidates for VMIMO construction and then all users obtain a joint decision through a voting process. Simulation results show that the proposed distributed scheme outperforms existing distributed selection schemes and achieves a near-optimal performance with lower complexity compared to the centralized scheme.

In this paper, optimized transmit schemes for multiple-input multiple-output (MIMO) systems with simplified receivers are proposed for the downlink of high-speed wireless communication systems. In these systems, MIMO signal preprocessing is performed at the transmitter or base station with the receiver at the mobile station having a simplified structure that requires only limited signal processing. An important potential application for our transmit MIMO techniques is in the downlink of high-speed wireless communication systems with Vertical Bell Laboratories Layered Space-Time (V-BLAST) or a similar technique utilized in the uplink, creating a high-speed duplex system with a simplified mobile station transceiver structure. Two approaches are introduced and these depend on whether or not receive diversity is employed at the receiver. Both methods require that channel state information be available at the transmitter. In addition, some important associated issues such as peak-to-average power ratio requirements at the transmitter and robustness to downlink channel errors are also investigated and various solutions are proposed. Simulation results are provided and these show that performance improvement can be achieved when compared with other MIMO transmit schemes.

In intermittently connected delay tolerant wireless sensor networks, sensor data generated at sensor nodes should be delivered to a sink node using opportunistic contacts between intermittently connected nodes. Since there is no stable end-to-end routing path from a source node to a sink node in intermittently connected network, an opportunistic routing protocol to deliver sensor data efficiently is needed. In this paper, an improved opportunistic routing protocol is proposed, where both current delivery predictability and maximum delivery predictability are used together to decide whether sensor data should be forwarded or not to a contact node. The proposed protocol can reduce buffer overflow and thus increase the delivery ratio, which is one of the most important performance measures in delay tolerant wireless sensor networks. The performance of the proposed routing protocol is compared with that of PRoPHET protocol and FREAK protocol, by varying buffer sizes and the number of nodes, in terms of delivery ratio, overhead ratio, and delivery latency. Performance analysis results show that the proposed protocol has better delivery ratio, overhead ratio, and delivery latency than the PRoPHET protocol and FREAK protocol have, in most considered parameter values, with appropriate selection of message dissemination thresholds.