Cooperative Multi-input Multi-output Research Articles

Cooperative MIMO relay beamforming in overloaded DS/CDMA multicast networks

A new beamforming scheme is proposed for multi-input multi-output (MIMO) non-regenerative relays in an overloaded synchronous direct sequence code division multiple access (DS-CDMA) network in which the number of users is larger than the processing gain. In this scheme, several transmitters multicast their data to their groups of receivers through MIMO relays and DS-CDMA technique is utilised to decrease the level of multiple access interference (MAI) at the relays and the receivers. At the relays, the data of transmitters are despread, beamformed and re-spread. The aim of the beamformer is to minimise the total relays transmission power subject to the signal to interference and noise ratio (SINR) constraints at the receivers. This optimisation problem is an indefinite quadratic (non-convex) programming. Semi-definite programming (SDP) and second-order cone programming (SOCP) are two existing methods to solve the problem. However, they, respectively, suffer from high computational complexity and performance degradation when the number of antennas or users increase. To effectively mitigate these deficiencies, we propose a novel DC (difference of two convex functions) programming method. Our simulation results demonstrate the computational advantage of the proposed DC programming over SDP, while a better performance over SOCP is achieved. Moreover, the superiority of the proposed MIMO-CDMA scheme over other multiplexing schemes is shown by several scenarios.

Energy-Efficient Cooperative MIMO-Based Random Walk Routing for Wireless Sensor Networks

To improve energy efficiency of wireless sensor networks, this letter proposes a novel random walk routing algorithm based on the cooperative multi-input multi-output (MIMO) mechanism. For each hop of each walk, we investigate the adaption of communication modes [i.e., single-input single-output, virtual single-input multi-output, virtual multi-input single-output (vMISO), and virtual MIMO]. The parameters are jointly optimized for determining minimum energy consuming communication mode, including the number of transmitters and receivers, the set of cooperation nodes. Additionally, we consider only vMISO mode and derive the approximate optimal number of transmitters by exploiting the relationship with the transmission distances. The simulation results show that the proposed scheme can improve energy efficiency.

Energy Efficient Wireless Sensor Networks using Co-operative MIMO: A Technical Review

paper considers the wireless sensor networks and highlights its applications in present time and mainly focuses on the two main techniques for saving maximum energy in transmitting information in WSN and these are multi-input multi-output (MIMO) and cooperative MIMO (CMIMO). Under this paper there is a comparison of energy efficiency in MIMO and single-input single-output (SISO) system for both transmission energy and circuit energy. Then there will be the discussion of CMIMO advantages, its energy model, properties, comparison with the equivalent technique (DCA) and the most important strategy used under CMIMO system is node sleep strategy and its significance in front of non-node sleep strategy will be discuss in this paper. Keywordssensor networks, MIMO system, CMIMO technology, energy efficiency, node sleep strategy.

MIMO AND COOPERATIVE MIMO COMPARISON IN ENERGY CONSTRAINED WIRELESS SENSOR NETWORKS

In Wireless Sensor Network commonly referred as WSN, the hubs or nodes are operated by batteries so that the energy utilization should be diminished, while fulfilling the given throughput and given requirement. The paper studies about the performance and energy consumption of cooperative MIMO and MIMO (multi input multi output) based communication. The average energy usage comprises circuit energy and transmission energy consumption. The comparison between the multi-input- multi-output (MIMO) and cooperative MIMO techniques help us to choose the best scheme for energy constrained wireless sensor network application. The simulation result shows that energy efficiency of MIMO (multi-input-multi-output) and SISO (single-input-single-output) is better for longer distances and thud increase the system life time.

A Cooperative MIMO Framework for Wireless Sensor Networks

We explore the use of cooperative multi-input multi-output (MIMO) communications to prolong the lifetime of a wireless sensor network (WSN). Single-antenna sensor nodes are clustered into virtual antenna arrays that can act as virtual MIMO (VMIMO) nodes. We design a distributed cooperative clustering protocol (CCP), which exploits VMIMO's diversity gain by optimally selecting the cooperating nodes (CNs) within each cluster and balancing their energy consumption. The problem of optimal CN selection at the transmit and receive clusters is formulated as a nonlinear binary program. Aiming at minimizing the imbalance in the residual energy at various nodes, we decompose this problem into two subproblems: finding the optimal number of CNs (ONC) in a cluster and the CN assignment problem. For the ONC problem, we first analyze the energy efficiency of two widely used VMIMO methods: distributed Space Time Block Code (DSTBC) and distributed Vertical-Bell Laboratories-Layered-Space-Time (DVBLAST). Our analysis provides an upper bound on the optimal number of CN nodes, which greatly reduces the computational complexity of the ONC problem. The second subproblem is addressed by assigning CNs based on the residual battery energy. To make CCP scalable to large WSNs, we propose a multihop energy-balanced routing mechanism for clustered WSNs (C-EBR) with a novel cost metric. Finally, we derive sufficient conditions on the intra- and intercluster ranges, under which CCP guarantees connectivity of the intercluster topology. Extensive simulations show that the proposed approach dramatically improves the network lifetime.

Joint Grassmann-Stiefel Quantization for MIMO Product Codebooks

We consider product codebook strategy where a single small codebook is implemented at the receiver to quantize larger multi-input multi-output (MIMO) channels, e.g. aggregate channels of cooperative MIMO base stations. The present work focuses on the codebook design, codebook construction, and codeword selection under this scenario, for single- or multistream MIMO transmission. Designing point-to-point unitary precoding codebook is related to a discretization problem on the Grassmann manifold, where a Grassmannian codeword is an equivalence class of rectangular-unitary/Stiefel matrices. For practical needs, one has to choose the rectangular unitary matrix to represent each Grassmann codeword. In this paper, we choose appropriate representatives so that product codebook quantization becomes competitive with global Grassmannian quantization. For this, we propose a novel joint Grassmann-Stiefel codebook design aiming at good quantization/discretization of Grassmann and Stiefel manifolds with a single codebook. To find low-distortion codebooks, we present a vector quantizer generating a Stiefel codebook conditioned on a fixed Grassmann codebook. For this purpose, we provide an exact solution for computing centroids in the Stiefel manifold with chordal distance. Furthermore, concrete examples of analytical joint Grassmann-Stiefel packings are given. Finally, we discuss low-complexity codeword selection methods.

Performance Analysis of Cooperative Virtual MIMO Systems for Wireless Sensor Networks

Multi-Input Multi-Output (MIMO) techniques can be used to increase the data rate for a given bit error rate (BER) and transmission power. Due to the small form factor, energy and processing constraints of wireless sensor nodes, a cooperative Virtual MIMO as opposed to True MIMO system architecture is considered more feasible for wireless sensor network (WSN) applications. Virtual MIMO with Vertical-Bell Labs Layered Space-Time (V-BLAST) multiplexing architecture has been recently established to enhance WSN performance. In this paper, we further investigate the impact of different modulation techniques, and analyze for the first time, the performance of a cooperative Virtual MIMO system based on V-BLAST architecture with multi-carrier modulation techniques. Through analytical models and simulations using real hardware and environment settings, both communication and processing energy consumptions, BER, spectral efficiency, and total time delay of multiple cooperative nodes each with single antenna are evaluated. The results show that cooperative Virtual-MIMO with Binary Phase Shift Keying-Wavelet based Orthogonal Frequency Division Multiplexing (BPSK-WOFDM) modulation is a promising solution for future high data-rate and energy-efficient WSNs.

Clustering and power management for virtual MIMO communications in wireless sensor networks

Multi-input multi-output (MIMO) is a well-established technique for increasing the link throughput, extending the transmission range, and/or reducing energy consumption. In the context of wireless sensor networks (WSNs), even if each node is equipped with a single antenna, it is possible to group several nodes to form a virtual antenna array, which can act as the transmitting or receiving end of a virtual MIMO (VMIMO) link. In this paper, we propose energy-efficient clustering and power management schemes for virtual MIMO operation in a multi-hop WSN. Our schemes are integrated into a comprehensive protocol, called cooperative MIMO (CMIMO), which involves clustering the WSN into several clusters, each managed by up to two cluster heads (CHs); a master CH (MCH) and a slave CH (SCH). The MCH and SCH collect data from their cluster members during the intra-cluster communications phase and communicate these data to neighboring MCHs/SCHs via an inter-cluster VMIMO link. CMIMO achieves energy efficiency by proper selection of the MCHs and SCHs, adaptation of the antenna elements and powers in the inter-cluster communications phase, and using a cross-layer MIMO-aware route selection algorithm for multi-hop operation. We formally establish the conditions on the transmission powers of CHs and non-CHs that ensure the connectivity of the inter-cluster topology. Simulations are used to study the performance of CMIMO. The simulation results indicate that our proposed protocol achieves significant reduction in energy consumption and longer network life time, compared with non-adaptive clustered WSNs.

Adaptive bit allocation scheme in multi-cell cooperative block diagonalization systems with delayed and limited feedback

In multi-cell cooperative multi-input multi-output (MIMO) systems, base station (BS) can exchange and utilize channel state information (CSI) of adjacent cell users to manage co-channel interference. Users quantize the CSIs of desired channel and interference channels using finite-rate feedback links, then BS can generate cooperative block diagonalization (BD) precoding matrices using the obtained quantized CSI at transmitter to supress co-channel interference. In this paper, a novel adaptive bit allocation scheme is proposed to minimize the rate loss due to imperfect CSI. We derive the closed-form expression of rate loss caused by both channel delay and limited feedback. Based on the derived rate loss expression, the proposed scheme can adaptively allocate more bits to quantize the better channels with smaller delays and fewer bits to worse channels with larger delays. Simulation results show that the proposed scheme yields higher performance than other allocation schemes.

Cooperative MIMO Transmissions in WSN Using Threshold Based MAC Protocol

Sensor networks require robust and efficient communication protocols to maximise the network lifetime. Radio irregularity, channel fading and interference results in larger energy consumption and latency for packet transmission over wireless channel. Cooperative multi-input multi-output (MIMO) schemes when incorporated in wireless senor network (WSN) can significantly improve the communication performance. An inefficiently designed medium access control (MAC) protocol however, may diminish the performance gains of MIMO operation. Hence, this paper proposes a distributed threshold based MAC protocol for cooperative MIMO transmissions using space time block codes (STBC). The protocol uses a thresholding scheme that is updated dynamically based on the queue length at the sending node to achieve lesser energy consumption and minimise latency ensuring the stability of transmission queues at the nodes. STBC and code combining techniques are applied to utilise the inherent spatial diversity in wireless cooperative MIMO systems. Simulation results are provided to evaluate the performance of the proposed protocol and are compared with fixed group size cooperative MIMO MAC protocols with and without STBC coding. Results show that the proposed protocol outperforms point to point communication as well as cooperative MIMO MAC protocols that use fixed group sizes. STBC technique for the proposed MAC protocol provides significant energy savings and minimises the packet delay by leveraging MIMO diversity gains.

Energy efficiency of a per-hop relay selection scheme for sensor networks using cooperative MIMO

The energy efficiencies of cooperative Multi-Input Multi-Output (MIMO) schemes are analysed in the context of dense multi-hop wireless sensor networks. The framework of per-hop relay selection is employed, which decides on the next-hop relay based on a metric that captures the trade-off between the performance and the energy cost. Such a framework makes the analysis tractable and suggests a practical way to implement opportunistic cross-layer routing with physical layer adaptation. A few representative cooperative MIMO transmission schemes such as spatial multiplexing, Alamouti coding and selection diversity are analysed as well as an adaptive scheme that switches the transmission strategy based on channel conditions. Simulation results reveal that the cooperative MIMO schemes achieve significant performance enhancement over the Single-Input Single-Output (SISO) scheme when the circuit power consumption is small compared to the transmit power. However, when the circuit power consumption is not negligible compared to the transmit power, the cooperative MIMO may not be energy efficient in the cross-layer setting compared to the SISO scheme.

Spectrally efficient communication for wireless sensor networks using a cooperative MIMO technique

The multi-input multi-output (MIMO) communication framework is adopted for wireless sensor networks by having multiple sensors equipped with single-element antennas cooperate in transmission. A power method-based iterative algorithm is developed that computes the optimal transmit and receive eigen-filters distributively among the sensors while transferring most of the computational burden to the central collector node. Since the proposed algorithm implicitly exploits the channel state information (CSI) both at the receiver and the transmitter, it is expected that the resulting spectral efficiency is higher than what can be achieved by receive CSI-only space-time coding. This intuition is confirmed by employing a variable-rate adaptive modulation scheme for the eigen-transmission and comparing its spectral efficiency with that of orthogonal space time block codes (OSTBCs) at specific target bit error rates. The performance is also evaluated using realistic channel estimation as well as the least mean square (LMS) and recursive least square (RLS) algorithms for iterative eigencoding.