Transmission Outage Probability Research Articles

Cognitive antenna selection relay for green heterogeneous healthcare networks

This article presents the latest progress on green healthcare research in heterogeneous networks (HetNet), where devices are capable of switching between multiple radio access technologies (RAT) and each RAT operates on a different frequency channel. After outlining the design features and challenges of a medical service paradigm for green cognitive medical body area networks (MBAN), measurements are made to investigate the turn-on characteristics of a power amplifier (PA) in terms of excess energy consumption and turn-on delay. We then present a multi-mode PA architecture for an MBAN relay system. An energy-efficient PA switch/stay mechanism is also presented. This allows the proposed PA architecture to operate given a transmission outage probability and transmission delay constraint. Antenna selection between two heterogeneous RATs is exploited to improve the transmission reliability. Both measurement and numerical results are provided to corroborate the performance of the proposed architecture and its switch/stay mechanism.

Wireless Information Transfer with Opportunistic Energy Harvesting

Energy harvesting is a promising solution to prolong the operation of energy-constrained wireless networks. In particular, scavenging energy from ambient radio signals, namely wireless energy harvesting (WEH), has recently drawn significant attention. In this paper, we consider a point-to-point wireless link over the narrowband flat-fading channel subject to time-varying co-channel interference. It is assumed that the receiver has no fixed power supplies and thus needs to replenish energy opportunistically via WEH from the unintended interference and/or the intended signal sent by the transmitter. We further assume a single-antenna receiver that can only decode information or harvest energy at any time due to the practical circuit limitation. Therefore, it is important to investigate when the receiver should switch between the two modes of information decoding (ID) and energy harvesting (EH), based on the instantaneous channel and interference condition. In this paper, we derive the optimal mode switching rule at the receiver to achieve various trade-offs between wireless information transfer and energy harvesting. Specifically, we determine the minimum transmission outage probability for delay-limited information transfer and the maximum ergodic capacity for no-delay-limited information transfer versus the maximum average energy harvested at the receiver, which are characterized by the boundary of so-called outage-energy region and region, respectively. Moreover, for the case when the channel state information (CSI) is known at the transmitter, we investigate the joint optimization of transmit power control, information and energy transfer scheduling, and the receiver's mode switching. The effects of circuit energy consumption at the receiver on the achievable rate-energy trade-offs are also characterized. Our results provide useful guidelines for the efficient design of emerging wireless communication systems powered by opportunistic WEH.

Joint Optimal Sensing Time and Power Allocation for Amplify-and-Forward Cognitive Relay Networks

In this letter, we investigate the joint optimization of sensing time and power allocation for amplify-and-forward cognitive relay networks. By jointly considering the sensing slot and the data transmission slot, the optimization problems are respectively formulated to maximize the average network throughput and minimize the approximate outage probability of secondary transmission under the average transmit power constraint of secondary users and the average interference power constraint of primary user. The optimal algorithms are developed to acquire the optimal sensing time and power allocation. Simulation results demonstrate that significant improvements in the average throughput and outage behavior are achieved through the joint optimization.

무선 네트워크에서 네트워크 코딩 재전송 기법의 점근적 이득

In this paper, we derive the gain of network coding when it is utilized for retransmission in wireless networks. To the end, we derive the outage probability of the network-coded transmission and express the diversity order as a function of the number of nodes and the node`s listening probability. From the outage probability, we formulate the -outage capacity. The network-coding gain is the ratio of the -outage capacities between network-coded and non-coded transmissions. Under our system model, we find that the network-coding gain is a function of the diversity order. Moreover, when there are infinitely many nodes, we show that the network coding gain approaches .

Performance analysis of dual-hop fixed-gain AF relaying systems with OSTBC over Nakagami-m fading channels

In this paper, we present outage probability and symbol error rate (SER) performance analyses of a dual-hop transmission using fixed-gain amplify-and-forward relaying in flat Nakagami-m fading channels. The system under consideration is equipped with multiple antennas at source and destination adopting orthogonal space-time block coding to provide transmit diversity and maximum ratio combining to provide receive diversity, respectively. For integer and half-integer m values, closed forms of exact outage probability and moment generating function (MGF) expressions are derived through cumulative distribution function (CDF) of the overall system signal-to-noise ratio. Closed-form exact SER expressions based on the overall CDF are obtained for binary phase shift keying, binary frequency shift keying and M-ary pulse amplitude modulation. Exact SER expressions based on the MGF method are also obtained for binary differential phase shift keying, M-ary phase shift keying and M-ary quadrature amplitude modulation. Moreover, the asymptotic diversity order analysis is performed through derivations of asymptotic outage probability and SER. Theoretical analyses are validated by Monte Carlo simulations showing perfect match between each other.

Secrecy Outage in MISO Systems With Partial Channel Information

Secrecy on the physical layer is a promising technique to simplify the overall cross-layer secrecy concept. In many recent works on the multiple antenna wiretap channel, perfect channel state information to the intended receiver as well as the passive eavesdropper are assumed. In this paper, the transmitter has only partial information about the channel to the eavesdropper, but full information on the main channel to the intended receiver. The applied channel model is the flat-fading multiple-input single-output wiretap channel. We minimize the outage probability of secure transmission under single-stream beamforming and the use of artificial noise in the null space of the main channel. Furthermore, we derive a suboptimal beamforming scheme based on a Markov bound, which performs reasonably well. The results generalize the cases with perfect as well as without channel state information of the eavesdropper channel. Numerical simulations illustrate the secrecy outage probability over the degree of channel knowledge and confirm the theoretical results.

Difference Antenna Selection and Power Allocation for Wireless Cognitive Systems

In this paper, we propose an antenna selection method in a wireless cognitive radio (CR) system, which we term difference selection, whereby a single transmit antenna is selected at the secondary transmitter out of M possible antennas such that the weighted difference between the channel gains of the data link and the interference link is maximized. We analyze the mutual information and the outage probability of the secondary transmission in a CR system with difference antenna selection, and propose a method of optimizing these performance metrics subject to practical constraints on the peak secondary transmit power and the average interference power as seen by the primary receiver. The optimization is performed over two parameters: the peak secondary transmit power and the difference selection weight δ∈[0,1]. Furthermore, we show that the diversity gain of a CR system employing difference selection is an impulsive function of δ, in that a value of δ=1 yields the full diversity order of M and any other value of δ gives no diversity benefit. Finally, we demonstrate through extensive simulations that, in many cases of interest, difference selection using the optimal values of these two parameters is superior to the so-called ratio selection method disclosed in the literature.

On Secrecy of Codebook-Based Transmission Beamforming under Receiver Limited Feedback

We investigate the secrecy performance of a codebook based transmission beamforming for a sensitive data link against passive eavesdropping. We characterize the secrecy outage probability of a communication link that is being eavesdropped. We consider a limited feedback scenario where the transmitter is using a predefined codebook known to both transmitter and receiver for beamforming, and analyze the secrecy outage probability of the link when it being eavesdropped. Our analysis also provides the secrecy outage probability of the beamforming transmission in the direction of the intended receiver. We characterize how the secrecy outage probability improves as the number of transmit antennas increases. We further analyze the effect of codebook design on secrecy enhancement and provide bounds on the secrecy outage probability of codebook beamforming.

Optimal Power Allocation Strategies for Fading Cognitive Radio Channels with Primary User Outage Constraint

In this paper, we consider a cognitive radio (CR) network where a secondary (cognitive) user shares the spectrum for transmission with a primary (non-cognitive) user over block-fading (BF) channels. It is assumed that the primary user has a constant-rate, constant-power transmission, while the secondary user is able to adapt transmit power and rate allocation over different fading states based on the channel state information (CSI) of the CR network. We study a new type of constraint imposed over the secondary transmission to protect the primary user by limiting the maximum transmission outage probability of the primary user to be below a desired target. We derive the optimal power allocation strategies for the secondary user to maximize its ergodic/outage capacity, under the average/peak transmit power constraint along with the proposed primary user outage probability constraint. It is shown by simulations that the derived new power allocation strategies can achieve substantial capacity gains for the secondary user over the conventional methods based on the interference temperature (IT) constraint to protect the primary transmission, with the same resultant primary user outage probability.

Computational Modeling of Transmission Capacity With Outage Constraints in Ad-Hoc Networks

In this paper, the transmission capacity of two existing wireless networks (the primary (PR) network and the secondary (SR) network) operating in the same geographical region and sharing the same spectrum is studied. We define transmission capacity as a product of the following signal propagation parameters: the density of transmission, the transmission rate and transmission outage probability. The PR network has a higher priority to access the spectrum regardless of the SR network, while the SR network limits its interference on PR network by carefully controlling the density of the transmitters. We quantify the transmission capacity for both networks and study their tradeoffs using computer simulation. Simulation results show that the proposed model has minimized mutual interference by significantly increasing the network spectrum efficiency per unit area and the transmission capacity.

Subcarrier-pair based resource allocation for cooperative multi-relay OFDM systems

In this paper, we study the joint allocation of three types of resources, namely, power, subcarriers and relay nodes, in multi-relay assisted dual-hop cooperative OFDM systems. All the relays adopt the amplify-and-forward protocol and assist the transmission from the source to destination simultaneously but on orthogonal subcarriers. The objective is to maximize the system transmission rate subject to individual power constraints on each node or a total network power constraint. We formulate such a problem as a subcarrier-pair based resource allocation that seeks the joint optimization of subcarrier pairing, subcarrier-pair-to-relay assignment, and power allocation. Using a dual approach, we solve this problem efficiently in an asymptotically optimal manner. Specifically, for the optimization problem with individual power constraints, the computational complexity is polynomial in the number of subcarriers and relay nodes, whereas the complexity of the problem with a total power constraint is polynomial in the number of subcarriers.We further propose two suboptimal algorithms for the former to trade off performance for complexity. Simulation studies are conducted to evaluate the average transmission rate and outage probability of the proposed algorithms. The impact of relay location is also discussed.

Cooperative Multiplexing: Toward Higher Spectral Efficiency in Multiple-Antenna Relay Networks

Previous work on cooperative communications has concentrated primarily on the diversity benefits of such techniques. This paper, instead, considers the multiplexing benefits of cooperative communications. First, a new interpretation on the fundamental tradeoff between the transmission rate and outage probability in multiple-antenna relay networks is given. It follows that multiplexing gains can be obtained at any finite signal-to-noise ratio (SNR), in full-duplex multiple-antenna relay networks. Thus, relaying can offer not only stronger link reliability, but also higher spectral efficiency. Specifically, the decode-and-forward protocol is applied and networks that have one source, one destination, and multiple relays are considered. A receive power gain at the relays, which captures the network large-scale fading characteristics, is also considered. It is shown that this power gain can significantly affect the system diversity-multiplexing tradeoff for any finite SNR value. Several relaying protocols are proposed and are shown to offer nearly the same outage probability as if the transmit antennas at the source and the relay(s) were colocated, given certain SNR and receive power gains at the relays. Thus, a higher multiplexing gain than that of the direct link can be obtained if the destination has more antennas than the source. Much of the analysis in the paper is valid for arbitrary channel fading statistics. These results point to a view of relay networks as a means for providing higher spectral efficiency, rather than only link reliability.

Performance comparison of MRC and IC under transmit diversity

This work explores the performance of MIMO (multiple-input/multiple-output) systems in Rayleigh fading channels with co-channel interference (CCI) and thermal noise. We provide analytical expressions for the outage probability of maximal ratio transmission combined with one of two different receive antenna array schemes, maximal ratio combining (MRC) and interference cancellation (IC) via null steering of the array pattern. We derive the statistics of the signal to interference-plus- noise ratio (SINR) for each technique in a closed-form and obtain an integral expression to calculate the average bit error rate (BER) or symbol error rate (SER). Our results show the conditions under which IC yields significantly better performance than MRC and vice versa. We also determine the impact on performance of the number of antennas in the transmit array.

An Analytical Model for the Reverse Link of WCDMA Systems With Repeaters in Nonuniform Traffic Distributions

The current extensive third generation network deployment has to cope with the existence of nonhomogeneous spatial traffic distributions, which are usually in the form of areas with high density of traffic. The concentration of users in some areas, particularly those far away from the base stations, can result in quality-of-service degradation due to high propagation losses. In this context, repeaters have turned out to be cost-effective nodes that are capable of mitigating these negative effects. This paper describes and models a multicellular/multiservice wideband code division multiple access system with repeaters in an environment with spatial nonuniformities. An analytical model is presented, and the expressions for the required transmission power, outage probability, and block error rate are derived for the reverse link. The implications of the noise amplification caused by the deployment of the repeaters as well as the variation of the propagation loss have been taken into account. Results focus on determining the maximum load factor for a given outage probability. In particular, special attention is paid to the effect of key parameters such as the gain between the base station and the repeaters, denoted as coupling gain, and the location of the different repeaters.

Outage Performance of Cognitive Radio with Multiple Receive Antennas

Outage performance of cognitive radios is analyzed in this paper. The scenario under consideration requires the cognitive radio to sense whether the primary user (PU) link is free (i. e. a spectrum hole exists) before making an active transmission using that link. Multiple antennas are available at the cognitive radio link to provide array gains at the sensing stage. We derive a closed-form expression of the outage probability for cognitive transmission by classifying it into several cases. A sensing threshold is deduced according to the PU arrival model illustrated in this paper. Simulation results verify our analysis.

MWSN for Large Scale Mobile Sensing

This paper reviews the state-of-the-art features introduced by sink mobility into wireless sensor networks (WSN), and introduces the architecture of mobile enabled Wireless Sensor Network (mWSN) to realize large-scale information gathering via networked wireless sensors and mobile sinks. After introducing the mobile sensing scenarios, some fundamental design parameters in mWSN have been investigated, such as cluster size, sink velocity, transmission range, and packet length. Our contributions include: (1) A cluster formation method has been proposed via multihop forwarding to form a cluster around the expected position of a mobile sink, in order to guarantee packet delay and minimize energy consumption. (2) Analysis of the performance influence by sink mobility leads to the conclusion that the optimal sink velocity must make a compromise between sink-sensor meeting delay and message delivery delay. (3) Finding that large transmission range and short packet length are both of benefit to lower the outage probability of packet transmission. Extensive simulations have been designed to evaluate the performance of mWSN in terms of packet delay, energy consumption and outage probability of packet transmission.

Minimum outage probability transmission with imperfect feedback for MISO fading channels

We study optimal transmission strategies in terms of minimum outage probability for a fading channel with multiple transmit antennas and a single receive antenna. We consider two cases of imperfect channel state information (CSI) feedback: mean feedback and covariance feedback. In both cases, the optimum strategy is shown to be transmission of multiple data streams to the same directions as when maximizing the ergodic channel capacity, but with different power allocation strategies which are closely related to the target rate. In the mean feedback case, the optimal power allocation strategy is also related to the accuracy of the feedback CSI, which affects significantly the achievable outage capacity.

Outage probability of multihop transmission over Nakagami fading channels

We present a general analytical framework for the evaluation of the end-to-end outage probability of multihop wireless communication systems with nonregenerative relays over Nakagami fading channels. It is shown that the presented results can either be exact or tight lower bounds on the performance of these systems depending on the choice of the relay gain. More specifically, we obtain a closed-form expression for the moment generating function of the reciprocal of the end-to-end signal-to-noise ratio (SNR) and we then use this expression to calculate the outage probability via numerical inversion of the Laplace transform. Numerical examples show that regeneration is more crucial at low average SNR and for multihop systems with a large number of hops.