Stochastic Geometric Analysis of the Uplink Throughput in Cognitive Radio Cellular Networks

This paper investigates the uplink throughput of Cognitive Radio Cellular Networks(CRCNs).As oppose to traditional performance evaluation schemes which mainly adopt complex system level simulations,we use the theoretical framework of stochastic geometry to provide a tractable and accurate analysis of the uplink throughput in the CRCN.By modelling the positions of User Equipments(UEs)and Base Stations(BSs)as Poisson Point Processes(PPPs),we analyse and derive expressions for the link rate and the cell throughput in the Primary(PR)and Secondary(SR)networks.The expressions show that the throughput of the CRCN is mainly affected by the density ratios between the UEs and the BSs in both the PR and SR networks.Besides,a comparative analysis of the link rate between random and regular BS deployments is concluded,and the results confirm the accuracy of our analysis.Furthermore,we define the cognitive throughput gain and derive an expression which is dominated by the traffic load in the PR network.

Energy Efficiency in ARQ-Based Multi-Hop Systems and the Tradeoff with Throughput

The minimum energy per bit(EPB)as the energy efficiency(EE)metric in an automatic retransmission request(ARQ)based multi-hop system is analyzed under power and throughput constraints.Two ARQ protocols including type-I(ARQ-I)and repetition redundancy(ARQ-RR)are considered and expressions for the optimal power allocation(PA)are obtained.Using the obtained optimal powers,the EE-throughput tradeoff(EETT)is analyzed and the EETT closed-form expressions for both ARQ protocols and in arbitrary average channel gain values are obtained.It is shown that how different throughput requirements,especially the high levels,affect the EE performance.Additionally,asymptotic analysis is made in the feasible high throughput values and lower and upper EETT bounds are derived for ARQ-I protocol.To evaluate the EE a distributed PA scenario,as a benchmark,is presented and the energy savinggain obtained from the optimal PA in comparison with the distributed PA for ARQ-I and ARQ-RR protocols is discussed in different throughput values and node locations.

Impacts of Packet Collisions on Link Throughput in CSMA Wireless Networks

It is known that packet collisions in wireless networks will deteriorate system performance, hence substantial efforts have been made to avoid collision in multi-user access designs. Also, there have been many studies on throughput analysis of CSMA wireless networks. However, for a typical CSMA network in which not all nodes can sense each other, it is still not well investigated how link throughputs are affected by collisions. We note that in practical 802.11-like networks, the time is divided into mini-timeslots and packet collisions are in fact unavoidable. Thus, it is desirable to move forward to explore how collisions in such a network will affect system performance. Based on the collision-free ideal CSMA network(ICN) model, this paper attempts to analyze link throughputs when taking the backoff collisions into account and examine the effect of collisions on link throughputs. Specifically, we propose an Extended Ideal CSMA Network(EICN) model to characterize the collision effects as well as the interactions and dependency among links in the network. Based on EICN, we could directly compute link throughputs and collision probabilities. Simulations show that the EICN model is of high accuracy. Under various network topologies and protocol parameter settings, the computation error of link throughputs using EICN is kept to 4% or below. Interestingly, we find that unlike expected, the effect of collisions on link throughputs in a modest CSMA wireless network is not significant, which enriches our understanding on practical CSMA wireless networks such as Wi-Fi.

Solar Energy Harvesting Using a Timer-Based Relay Selection

In this paper,the throughput and delay of cooperative communications are derived when solar energy is used and relay node is selected using a timer.The source and relays harvest energy from sun using a photo voltaic system.The harvested power is used by the source to transmit data to the relays.Then,a selected relay amplifies the signal to the destination.Opportunistic,partial and reactive relay selection are used.The relay transmits when its timer elapses.The timer is set to a value proportional to the inverse of its Signal to Noise Ratio(SNR).Therefore,the relay with largest SNR will transmit first and its signal will be detected by the other relays that will remain idle to avoid collisions.Harvesting duration is optimized to maximize the throughput.Packet’s waiting time and total delay are also computed.We also derive the statistics of SNR when solar energy is used.The harvested power from sun is proportional to the sum of a deterministic radiation intensity and a random attenuation due to weather effects and clouds occlusion.The fixed radiation intensity depends on season,month and time t in hour.The throughput of cooperative communications with energy harvesting from sun was not yet studied.

Improved picoliter-sized micro-reactors for high-throughput biological analysis

High-throughput pyrosequencing,carried out in millions of picoliter-sized reactors on a fiber-optic slide,is known for its longer read length.However,both optical crosstalk(which reduces the signal-to-noise ratio of CCD images)and chemical retention adversely affect the accuracy of chemiluminescence determination,and ultimately decrease the read length and the accuracy of pyrosequencing results.In this study,both titanium and oxidized aluminum films were deposited on the side walls and upper faces of micro-reactor slides to enhance optical isolation;the films reduced the inter-well crosstalk by one order of magnitude.Subsequently,chemical retention was shown to be caused by the lower diffusion coefficient of the side walls of the picolitersized reactors because of surface roughness and random pores.Optically isolated fiber-optic slides over-coated with silicon oxide showed smoother surface morphology,resulting in little chemical retention;this was further confirmed with theoretical calculations.Picoliter-sized micro-reactors coated with titanium-silicon oxide films showed the least inter-well optical crosstalk and chemical retention;these properties are expected to greatly improve the high-throughput pyrosequencing performance.

Cognitive Radio Networks Using Intelligent Reflecting Surfaces

In this article,we optimize harvesting and sensing duration for Cognitive Radio Networks(CRN)using Intelligent Reflecting Surfaces(IRS).The secondary source harvests energy using the received signal from node A.Then,it performs spectrum sensing to detect Primary Source PS activity.When PS activity is not detected,The Secondary Source SS transmits data to Secondary Destination SD where all reflected signals on IRS are in phase at SD.We show that IRS offers 14,20,26,32,38,44,50 dB enhancement in throughput using M=8,16,32,64,128,256,512 reflectors with respect to CRN without IRS.We also suggested to add a second IRS between A and SS to increase the harvested energy.The use of 2 IRS with M1=8 reflectors in the first IRS and M2=8 reflectors in the second IRS offers 18 dB gain(respectively 32 dB)gain with respect to a single IRS with M2=8 reflectors(respectively without IRS).The use of 2 IRS with M1=16 reflectors in the first IRS and M2=8 reflectors in the second IRS offers 28 dB gain(respectively 42 dB)gain with respect to a single IRS with M2=8 reflectors(respectively without IRS).Our results are valid for Nakagami channels of fading figure m.We also provide the throughput of IRS with energy harvesting.We have studied packet waiting time and total delay in the presence and absence or IRS.At Signal to Noise Ratio(SNR)per bit equal to 0 dB,packet waiting time is 0.9 ms when there is no IRS and 0.5 ms when there is an IRS with M=8 reflector.At SNR per bit equal to 0 dB,total transmission delay is 54 ms when there is no IRS and 1.5 ms when there is an IRS with M=8 reflectors.We show that the energy efficiency is larger when both harvesting and sensing durations are optimized.The maximum of energy efficiency is 260 Mbit/s/Hz/J when harvesting and sensing durations are optimized while the maximum is 80 Mbit/s/Hz/J when harvesting and sensing durations are not optimized.

Nanoelectrochemical architectures for high-spatial-resolution single cell analysis

The analysis of single cells instead of cell populations is important for characterizing cellular heterogeneity and elucidating the cellular signalling pathways. Nanoelectrodes have emerged as an increasingly important tool for biomolecule analyses at the single-cell level with high spatial or temporal resolution. Various electrochemical methods, such as amperometry and scanning electrochemical microscopy(SECM), have been applied. Research to date has focused on the development of new nanoelectrochemical architectures, such as arrays, to achieve higher spatial resolution and faster analysis rates for single-cell analysis. In this review, the fabrication of these new nanoelectrochemical architectures and their applications in high spatial resolution single-cell analyses are discussed. The recent progress of Chinese researchers is highlighted.