Virtual Multiple-input Single-output Research Articles

Virtual MISO with joint device relaying and beamforming in 5G networks

In this paper, a novel scheme is proposed in which mobile users organize a virtual multiple-input single-output (MISO) structure with the aid of relaying based on device to device (D2D) communication in a 5G cellular network. The performance of distributed quasi-orthogonal space–time code (D-QOSTC) based virtual MISO for the cooperation among four communication nodes is investigated. Error propagation in the second hop of relaying in decode and forward (DF) relaying protocols, is one of the main challenges of virtual MISO systems and it can be mitigated by the joint use of selection relaying and beamforming techniques. We propose a novel beamforming technique for removing the end to end inter-symbol interference (ISI) of D-QOSTC scheme. By means of our proposed scheme, even though we have error propagation in the second hop of relaying, without any loss in bandwidth or rate, the full diversity order can be achieved. Moreover, the performance of bit error rate (BER) with closed form result is analyzed and compared to the simulation results. The results exhibit that the theoretical BER curves coincide with the simulation ones and the system achieves full diversity order. The simulation results also indicate a significant gain in power efficiency for the optimal selection relaying and fixed relaying compared to conventional schemes.

Spectrum-aware outage minimizing cooperative routing in cognitive radio sensor networks

This paper investigates the optimal path selection problem for end-to-end (e2e) outage probability minimization in clustered cognitive radio sensor networks. In order to improve outage performance of the optimal path, under a high node density regime, we consider feasibility of virtual multiple-input single-output (v-MISO) links in addition to conventional single-input single-output (SISO) links in the path. Since sensor nodes in such networks are allowed to access the spectrum of the primary network only in an opportunistic manner, the path selection problem is studied under the constraints of probabilistic interference to PU receivers and only single use of any PU channel along the path. The above problem is formulated as a joint hop-constrained routing, spectrum assignment and transmit power control problem. A convex optimization framework is used to find a closed form expression for the optimal transmit power of each transmitting node along the optimal route. Extension of the analytical result facilitates design of a novel routing algorithm, called spectrum aware-minimum outage intelligent cooperative routing (SA-MOICR) algorithm, which not only selects the minimum outage path for a given routing session, but also determines the number of nodes and the unique PU channel to be used for transmission in each hop along the path. Simulation results are found to corroborate our analytical results and quantify the significant improvement of the SA-MOICR scheme over only SISO or only v-MISO based routing solutions in terms of the achievable e2e outage probability.

Analysis of link asymmetry in virtual multiple-input-single-output (VMISO) systems

Cooperative transmission (CT) is an effective technique to mitigate multi-path fading through spatial diversity. In CT, spatially separated wireless nodes collaborate to form a virtual multiple-input-single-output (VMISO) link, which provides signal-to-noise ratio advantage over the conventional single-input-single-output (SISO) communications. In this paper, we consider link asymmetry of the VMISO links between two neighboring CT clusters in wireless multi-hop networks. Link asymmetry is important because it impacts the performance of link and routing layer protocols. While most of the existing studies on CT simplify analysis on CT-based networks with co-located approximation that ignores disparate path losses in VMISO links by assuming co-located transmitting nodes, this paper presents the impact of disparate path losses on link asymmetry by allowing the relay locations to be random. Assuming exclusive signal detection by cluster heads, we identify two main causes of the VMISO link asymmetry, which do not appear in the conventional SISO-based networks: independent fading and path disparity. We evaluate the degree of link asymmetry in terms of three metrics: the power correlation, the power ratio, and the probability that the power gap is 3 dB or higher. Also, the simulation results reveal how system parameters and channel conditions impact the VMISO link asymmetry.

Energy-efficient cooperative communication in wireless sensor networks using turbo codes

Energy efficiency is the main issue in the wireless sensor network. In this paper, we have developed the energy model for Virtual-Multiple Input Single Output cooperative communication using turbo codes. We have compared the energy consumption of uncoded cooperative communication with coded cooperative communication. The effect of code rate, number of participating nodes, channel conditions, target bit error rate on the energy consumption is also investigated. The simulation results show that significant energy saving can be obtained through the proposed turbo coded cooperative communication.

The Effects of Multiple Carrier Frequency Offsets on the Performance of Virtual MISO FSK Systems

In this letter, a virtual multiple-input single-output (VMISO) network employing non-coherent frequency shift keying (FSK) is considered. In the VMISO network, spatially separated single-antenna nodes transmit the same information cooperatively to a single receiver where each received signal is affected by an independent carrier frequency offset (CFO). The existing works in this area assume a perfect carrier synchronization between the nodes. However, in this letter, the effects of CFOs on the performance degradation of this network are analyzed. For that purpose, the expression for the probability of symbol error has been derived. The results indicate that the performance is degraded due to CFOs, which is dependent upon the magnitude of CFOs, signal-to-noise ratio (SNR), number of transmitting nodes, and the modulation order of FSK. At high SNR, the CFOs affect the system severely and the performance margin is minimum.

On cooperative transmission range extension in multi-hop wireless ad-hoc and sensor networks: A review

Range extension is a promising feature offered by cooperative transmission (CT), also known as virtual multiple-input–single-output (VMISO). Many authors have considered how the diversity and array gains from CT may benefit a wireless multi-hop network, when the gains are used for increasing link reliability and reducing transmit power. However, relatively less attention has been given to the benefits of CT range extension and few testbed implementations of CT have been demonstrated. In this paper, we focus on how CT range extension can impact the lower three layers, especially medium access control (MAC) and routing for ad hoc and sensor multi-hop networks (AHSMNs). We assume cooperators decode and forward the packets. Various analytical models, performance analyses, and experimental results using software-defined radios in an indoor office environment are discussed. For wireless sensor networks (WSNs), we review CT range extension at the network layer, to eliminate the energy hole that forms around sink nodes in non-CT networks, and we review cooperator selection and duty cycle scheduling algorithms at Layer 2, to maximize the lifetime of a multi-hop WSN. For ad hoc networks, we emphasize a family of lightweight broadcasting and unicasting protocols based on a simple form of CT called the opportunistic large array (OLA). Experimental results, including OLA-based unicast routing and diversity order effects in two-hop CT networks, are discussed.

Statistical Analysis of Array Gain for Cooperative MISO Transmitters without CSI

Virtual Multiple-Input Single-Output (MISO) is recently proposed to extend the benefits of transmitter space diversity to networks in which the deployment of antenna arrays on individual nodes is infeasible from a practical point of view. Ad-hoc and sensor networks are examples of these type of networks. In these scenarios, nodes equipped with single antenna can cooperatively transmit to emulate an antenna array. However, cooperative transmissions require knowledge of the channel state either at the transmitter side or the receiver side in order to achieve full performance gains. Several solutions are proposed in the literature under these assumptions, but at the expense of increased overhead and energy consumption. In this paper, the array gain at the receiver from the non-coherent combining of the signals from multiple transmitters is analyzed in statistical sense, under the assumption that the channel knowledge is unavailable. The transmitters are assumed to be randomly spread over a circular region. More specifically, exact or very accurate closed-form expressions for the expectation and variance of the array gain are obtained, and then a complete statistical distribution is postulated and validated by means of heuristic procedures, goodness-of-fit tests and specialized software. The results obtained in this paper can be especially useful for the implementation of two-tiered wide area sensor networks.

Proteus: Multiflow Diversity Routing for Wireless Networks with Cooperative Transmissions

In this paper, we consider the use of cooperative transmissions in multihop wireless networks to achieve Virtual Multiple Input Single Output (VMISO) links. Specifically, we investigate how the physical layer VMISO benefits translate into network level performance improvements. We show that the improvements are nontrivial (15 to 300 percent depending on the node density) but rely on two crucial algorithmic decisions: the number of cooperating transmitters for each link; and the cooperation strategy used by the transmitters. We explore the tradeoffs in making routing decisions using analytical models and derive the key routing considerations. Finally, we present Proteus, an adaptive diversity routing protocol that includes algorithmic solutions to the above two decision problems and leverages VMISO links in multihop wireless network to achieve performance improvements. We evaluate Proteus using NS2-based simulations with an enhanced physical layer model that accurately captures the effect of VMISO transmissions.

Energy-efficient cooperative beamforming in clustered wireless networks

Recently, due to the growing concern over the ever-increasing energy consumption, much attention has been given to the energy-efficient design of wireless communication systems. Various strategies for improving the energy efficiency, which is defined as the transmitted bits per total energy consumed (in bits/Joule), have been proposed. In this paper, we analyze the energy efficiency of clustered cooperative beamforming where distributed relay nodes construct a virtual Multiple-Input Single-Output beamforming system with a maximum transmit power constraint, and compare its performance with that of direct communications. All the energy consumption overheads incurred are taken into account in the energy efficiency analysis assuming a constant circuit-power consumption model. We then study the number of relay nodes that maximizes the efficiency for a given outage constraint. In addition, we propose a mode switching algorithm which optimally chooses between using cooperative beamforming or direct communications for transmission. We show that cooperative beamforming significantly outperforms direct communications in energy efficiency, as well as in spectral efficiency, even though a much larger amount of circuit power is consumed.

Multihop Hybrid Virtual MIMO Scheme for Wireless Sensor Networks

Wireless sensor network devices commonly use a single antenna for transmission and reception, as well as for relaying packets over multiple hops to a final destination, which is referred to as single-input-single-output (SISO) multihop transmission. Advancements in multiple antenna systems enable reliable broadband wireless communications using multiple-input-multiple-output (MIMO) transmission technology. In addition, through collaboration of several single-antenna-equipped devices, cooperative MIMO communication is possible in the form of virtual MIMO (V-MIMO), virtual multiple-input-single-output (V-MISO), and virtual single-input-multiple-output (V-SIMO), which are collectively called V-MIMO technology. In this paper, a multihop hybrid V-MIMO (HV-MIMO) networking scheme is proposed to configure a minimum energy consuming route (MECR) that provides high end-to-end connectivity while satisfying end-to-end data rate and bit error rate (BER) requirements by using the best cooperative MIMO configuration for each hop. In the proposed scheme, first, the source-to-destination path is divided into long wireless communication hops, and the minimum energy consuming V-MIMO configuration is applied to each hop. Next, the long communication hops are individually evaluated for replacement with two half-length V-MIMO hops, where changes are applied only when a gain in energy consumption is obtainable. If no gain is obtainable for a certain hop, then the hop configuration is not changed, and that hop is no longer compared for replacement. This procedure of testing for possible replacement with two half-length hops is repeated individually for all hops until no further changes are made in the source-to-destination path, which is when the HV-MIMO MECR is complete. For equivalent end-to-end data rate and BER requirements, the proposed HV-MIMO multihop scheme provides a significant energy saving (e.g., 52.32% energy saving at the node density of 0.003 nodes/m2) compared with the conventional SISO multihop path's MECR. In addition, the HV-MIMO scheme always results in an energy saving gain and a significantly higher end-to-end multihop MECR connection probability compared with using the same type of cooperative MIMO configuration for each hop (i.e., homogeneous V-MIMO configuration).

Collaborative-Relay Beamforming With Perfect CSI: Optimum and Distributed Implementation

This letter studies the collaborative use of amplify-and-forward (AF) relays to form a virtual multiple-input single-output (MISO) beamforming system with the aid of perfect channel state information (CSI) in a flat-fading channel. In particular, we optimize the relay weights jointly to maximize the received signal-to-noise ratio (SNR) at the destination terminal with both individual and total power constraints at the relays. We show that the optimal collaborative-relay beamforming (CRB) solution achieves the full diversity of a MISO antenna system. Another main contribution of this letter is a distributed algorithm that allows each individual relay to learn its own weight, based on the Karush-Kuhn-Tucker (KKT) analysis.

Reliable Multi-hop Routing with Cooperative Transmissions in Energy-Constrained Networks

We present a novel approach in characterizing the optimal reliable multi-hop virtual multiple-input single-output (vMISO) routing in ad hoc networks. Under a high node density regime, we determine the optimal cardinality of the cooperation sets at each hop on a path minimizing the total energy cost per transmitted bit. Optimal cooperating set cardinality curves are derived, and they can be used to determine the optimal routing strategy based on the required reliability, transmission power, and path loss coefficient. We design a new greedy geographical routing algorithm suitable for vMISO transmissions, and demonstrate the applicability of our results for more general networks.