Energy-Efficient User Access Control and Resource Allocation in HCNs with Non-Ideal Circuitry

In this paper, we study the energy-efficient user access control (UAC) based on resource allocation (RA) in heterogeneous cellular networks (HCNs) with the required downlink data rate under non-ideal power amplifiers (PAs) and circuit power. It is proved that the energy consumption minimization is achieved when the typical user accesses only one base station (BS), while the other BSs remain in idle mode on the transmission resource allocated to this user. For this purpose, we reformulate the original non-convex optimization problem into a series of convex optimization problems where, in each case, the transmit power and duration of the accessed BS are determined. Then, the BS with the minimal energy consumption is selected for transmission. Considering the approximate situation, it is showed that the optimal transmit duration of the accessed BS can be estimated in closed form. The benefits of our proposed UAC and RA schemes are validated using numerical simulations, which also characterize the effect that non-ideal PAs have on the total energy consumption of different transmission schemes.Comment: 6 pages, 4 figures, 2017 9th International Conference on Wireless Communications and Signal Processing (WCSP

Optimal Pilot Symbols Ratio in terms of Spectrum and Energy Efficiency in Uplink CoMP Networks

In wireless networks, Spectrum Efficiency (SE) and Energy Efficiency (EE) can be affected by the channel estimation that needs to be well designed in practice. In this paper, considering channel estimation error and non-ideal backhaul links, we optimize the pilot symbols ratio in terms of SE and EE in uplink Coordinated Multi-point (CoMP) networks. Modeling the channel estimation error, we formulate the SE and EE maximization problems by analyzing the system capacity with imperfect channel estimation. The maximal system capacity in SE optimization and the minimal transmit power in EE optimization, which both have the closed-form expressions, are derived by some reasonable approximations to reduce the complexity of solving complicated equations. Simulations are carried out to validate the superiority of our scheme, verify the accuracy of our approximation, and show the effect of pilot symbols ratio.Comment: 5 pages, 3 figures, 2017 IEEE 85th Vehicular Technology Conference (VTC Spring

Joint Multi-Cell Resource Allocation Using Pure Binary-Integer Programming for LTE Uplink

Due to high system capacity requirement, 3GPP Long Term Evolution (LTE) is likely to adopt frequency reuse factor 1 at the cost of suffering severe inter-cell interference (ICI). One of combating ICI strategies is network cooperation of resource allocation (RA). For LTE uplink RA, requiring all the subcarriers to be allocated adjacently complicates the RA problem greatly. This paper investigates the joint multi-cell RA problem for LTE uplink. We model the uplink RA and ICI mitigation problem using pure binary-integer programming (BIP), with integrative consideration of all users' channel state information (CSI). The advantage of the pure BIP model is that it can be solved by branch-and-bound search (BBS) algorithm or other BIP solving algorithms, rather than resorting to exhaustive search. The system-level simulation results show that it yields 14.83% and 22.13% gains over single-cell optimal RA in average spectrum efficiency and 5th percentile of user throughput, respectively.Comment: Accepted to IEEE Vehicular Technology Conference (VTC Spring), Seoul, Korea, May, 201

Ultrasound mediated luminescence tomography using contrast agents

The achievable spatial resolution of fluorescence and bioluminescence imaging in deep tissue is severely limited by strong tissue scattering and absorption. The hybrid technique ultrasound (US) mediated fluorescence tomography (USMFT) has been investigated in the past decade, with the aim to obtain fluorescence images with optical contrast and US resolution. However, the very low modulation depth due to the intrinsic incoherent properties of fluorescence leads to low signal-to-noise ratio. In this thesis, the techniques of US mediated luminescence tomography (USMLT, including US mediated bioluminescence tomgoraphy (USMBLT) and USMFT) are investigated with the aim to improve the effect of US on light intensity via application of contrast agents. The mechanisms of USMBLT are firstly studied through incorporating the effect of US into NIRFAST, an open source software package for simulation of light propagation. The influence of US on optical properties (reduced scattering coefficient, absorption coefficient, and refractive index) and concentration of source particles are studied. Effects of US pressure, US position, and source particle concentration on the modulation depth are investigated and the signal-to-noise ratio for in vivo detection is calculated. It is demonstrated that the dominant effect in the generation of USMBL signal is US induced variation in the concentration of the source particles, and this effect is at least two orders of magnitude greater than that caused by changes in the optical properties. It is also found that modulation depth increases linearly with increase of US pressure. The maximum modulation depth can be obtained when the US focal zone overlaps the bioluminescence source region. The modulated fluence rate increases linearly with increase of the concentration but the modulation depth is independent of the concentration. Results for signal-to-noise ratio calculation confirm the feasibility of applying USMBLT in preclinical imaging of mice to improve the spatial resolution of bioluminescence imaging. Secondly, fluorophore labelled microbubbles are studied as a contrast agent to increase the modulation depth of USMFT. Upon application of US the size of the microbubbles oscillate changing the intermolecular distances of the fluorophores labelled on the monolayer of the microbubbles resulting in modulated fluorescence emission intensity. Increased modulation depth is observed both from simulation and experiment. The influence of factors including microbubble radius, US pressure, labelling concentration on the US modulated fluorescence emission are simulated. It was shown that the effects of the three factors are closely related to each other, and it is difficult to decouple their effects. Generally the maximum modulated signal can be obtained within the region C ∈ (2 mol% 5 mol%) and R0 ∈ (1.5μm 5μm). However microbubbles with a higher fluorophore labelling concentration or a bigger radius require higher US pressure to obtain its maximum volumeric oscillation and the highest modulated signal. The results suggest that it is desirable to produce microbubble suspensions with narrow size distribution, so that most of the microbubbles can be labelled by an optimized concentration and exposed to an appropriate US pressure. Thirdly, liposome based contrast agents are studied for use in USMFT for the first time. Compared with microbubbles, liposomes have the advantages that they have better stability, less US scattering, and can be manufactured with a defined size in nanometer scale. Liposomes are labelled with pyrene which has well-known concentration dependent excimer formation characteristic. The acousto-fluorescence dynamics of liposomes containing lipids with pyrene labelled on the fatty acid tail group (PyPC) and the head group (PyPE) were compared. An increase in excimer emission intensity following exposure to US was observed for both cases studied. The increased intensity and rise time constants were found to be different for the PyPC and PyPE labelled liposomes, and dependent on the applied US pressure and exposure time. The greatest US On-to-Off ratio of excimer emission intensity (130%) and smallest rise time constant (0.33 s) are achieved through the use of the PyPC labelled liposomes. Possible mechanisms underlying the observed increase of the excimer emission intensity in PyPC system is considered to arise from the "wagging" of acyl chains which involves fast response and requires lower US energy. This is accompanied with the increased lipid lateral diffusivity, mechanisms also active in the PyPE system. Finally, DiD-DiR labelled liposomes based on fluorescence resonance energy transfer (FRET) are studied. The excitation and emission spectra are located close or within near-infrared window, where the penetration depth is up to several centimetres. Measurements of emisison spectra show that strong FRET and self-quenching exist in the DiD-DiR labelled liposomes. The fluorescence emission intensity changes upon application of US, with the change trend dependent on fluorophore types, detection wavelength, and fluorophore concentration. Line scanning of a tube buried at a depth of 1 cm in a heavily scattering phantom shows a contrast of 8.5% can be obtained using 0.5 mol% DiD-DiR labelled liposomes through detection at DiR emission wavelength (around 740nm - 790 nm). The resolution can be improved by a factor of 6.3 compared with its no US counterpart. These results suggest that DiD-DiR labelled liposome has potential to be used as contrast agent of USMFT for deep tissue imaging. Further application for in vivo imaging is discussed