An Agile and Efficient MAC for Wireless Access over TV Whitespaces

The FCC mandate of allowing TV Whitespaces for unlicensed access has the potential for dramatic improvements in wireless access data rates. We argue that an ideal MAC should account for diverse user-location and spectrum dependent channel rates to provide fair data rates and efficient utilization. Furthermore, due to limited tunable bandwidth of a radio and fragmented spectrum, the AP should support multiple radios.

We make the following contributions by designing a MAC for wireless LAN access over TV Whitespace. (i) We propose an architecture and beaconing mechanism to enable such a MAC. Our MAC is an evolution of 802.11 MAC. (ii) We propose an algorithm that chooses the Whitespaces for the different radios of the AP and assigns clients to the radios. Our algorithm has provable guarantee and is near-optimal in many scenarios. (iii) Extensive simulation over OMNET platform demonstrates the benefit of our design over a frequency and client-location agnostic Wi-Fi-like MAC. The typical throughput gain is 30-76 percent, whereas, the reduction in collisions is up to 80 percent. (iv) We implemented a proof-of-concept prototype (by modifying madWiFi drivers) that demonstrates feasibility of our design, robustness to temporal variation of available spectrum, and system throughput.

A comprehensive survey of TDD-based mobile communication systems from TD-SCDMA 3G to TD-LTE(A) 4G and 5G directions

TDD (Time Division Duplex) is one of the two duplex modes. TD-SCDMA (Time Division Synchronous CDMA) is the first TDD-based cellular mobile system which is commercialized in wide area and large scale and TD-SCDMA is also the first cellular mobile system which adopted smart antenna technology (also called as beamforming). As the long term evolution of TD-SCDMA, TD-LTE(A) (Time Division-Long Term Evolution, and TD-LTE Advanced) introduced OFDM (Orthogonal Frequency Division Multiplexing) and enhanced smart antenna technology together with MIMO (Multiple Input Multiple Output), which are adopted by LTE FDD (Frequency Division Duplex) either.

It is indicated that TD-SCDMA and TD-LTE(A) have opened a sustainable utilization era of TDD and smart antenna technologies in the wireless mobile communication. This paper aims to present a systematic introduction to TDD-based mobile communications from TD-SCDMA to TD-LTE and beyond, with particular focuses on TDD key technologies, principles of TDD cellular mobile systems, TDD evolution path, and future TDD 5G directions. The comparisons between TDD and FDD are also included. We hope that this paper will provide a comprehensive overview of TDD technology upgrade and its standard evolution, and serve as a valuable reference for research on 5G mobile communicationsystems. It is believed that TDD will play more important role in 5G.

Cognitive and Energy Harvesting-Based D2D Communication in Cellular Networks: Stochastic Geometry Modeling and Analysis

While cognitive radio enables spectrum-efficient wireless communication, radio frequency (RF) energy harvesting from ambient interference is an enabler for energy-efficient wireless communication. In this paper, we model and analyze cognitive and energy harvesting-based device-to-device (D2D)communication in cellular networks. The cognitive D2D transmitters harvest energy from ambient interference and use one of the channels allocated to cellular users (in uplink or downlink), which is referred to as the D2D channel, to communicate with the corresponding receivers. We investigate two spectrum access policies for cellular communication in the uplink or downlink, namely, random spectrum access (RSA) policy and prioritized spectrum access (PSA) policy. In RSA, any of the available channels including the channel used by the D2D transmitters can be selected randomly for cellular communication, while in PSA the D2D channel is used only when all of the other channels are occupied.

A D2D transmitter can communicate successfully with its receiver only when it harvests enough energy to perform channel inversion toward the receiver, the D2D channel is free, and the signal-to-interference-plus-noise ratio (SINR) at the receiver is above the required threshold; otherwise, an outage occurs for the D2D communication. We use tools from stochastic geometry to evaluate the performance of the proposed communication system model with general path-loss exponent in terms of outage probability for D2D and cellular users. We show that energy harvesting can be a reliable alternative to power cognitive D2D transmitters while achieving acceptable performance. Under the same SINR outage requirements as for the non-cognitive case, cognitive channel access improves the outage probability for D2D users for both the spectrum access policies. When compared with the RSA policy, the PSA policy provides a better performance to the D2D users. Also, using an uplink channel provides improved performanc- to the D2D users in dense networks when compared to a downlink channel. For cellular users, the PSA policy provides almost the same outage performance as the RSA policy.

Throughput and delay of single-hop and two-hop aeronautical communication networks

Aeronautical communication networks (ACN) is an emerging concept in which aeronautical stations (AS) are considered as a part of multi-tier network for the future wireless communication system. An AS could be a commercial plane, helicopter, or any other low orbit station, i.e., Unmanned air vehicle, high altitude platform. The goal of ACN is to provide high throughput and cost effective communicationnetwork for aeronautical applications (i.e., Air traffic control (ATC), air traffic management (ATM)communications, and commercial in-flight Internet activities), and terrestrial networks by using aeronautical platforms as a backbone. In this paper, we investigate the issues about connectivity, throughput, and delay in ACN. First, topology of ACN is presented as a simple mobile ad hoc network and connectivity analysis is provided. Then, by using information obtained from connectivity analysis, we investigate two communication models, i.e., single-hop and two-hop, in which each source AS is communicating with its destination AS with or without the help of intermediate relay AS, respectively.

In our throughput analysis, we use the method of finding the maximum number of concurrent successful transmissions to derive ACN throughput upper bounds for the two communication models. We conclude that the two-hop model achieves greater throughput scaling than the single-hop model for ACN and multi-hop models cannot achieve better throughput scaling than two-hop model. Furthermore, since delay issue is more salient in two-hop communication, we characterize the delay performance and derive the closed-form average end-to-end delay for the two-hop model. Finally, computer simulations are performed and it is shown that ACN is robust in terms of throughput and delay performances.

Selective DF Protocol for MIMO STBC Based Single/Multiple Relay Cooperative Communication: End-to-End Performance and Optimal Power Allocation

In this paper, we consider the performance of a selective decode-and-forward (DF) relaying based multiple-input multiple-output (MIMO) space-time block coded (STBC) cooperative communicationsystem with single and multiple relays. We begin with a single relay based MIMO STBC system and derive the closed form expression for the end-to-end PEP of coded block detection at the destination node. It is also demonstrated that the MIMO STBC cooperative communication system achieves the full diversity order of the system. We also derive the optimal source relay power allocation, which minimizes the end-to-end decoding error of the cooperative system for a given power budget. Subsequently, for the multiple relay scenario, we consider two different relaying protocols based on two-phase and multi-phase communication.

For each of these multi-relay protocols, we derive the closed form expressions for the end-to-end error rate, diversity order, and optimal power allocation. Simulation results are presented to validate the performance of the proposed single and multiple relay based cooperative communication schemes and the derived analytical results. Further, these schemes can also be seen to lead to a performance improvement compared to several other relaying schemes in existing literature.

Dual band microstrip patch antenna for MIMO system

This work targets design of microstrip patch antenna that will resonate at two different band of frequencies which can be used as elements of array for MIMO system. The proposed dual band antenna operates at ISM band (2.37Ghz-2.48Ghz) and Wimax band (3.46 GHz-3.56 GHz).Bandwidth of operation offered by the given microstrip antenna in ISM band is around 110 Mhz while in Wimax band is 110 Mhz.

The designed dual band antenna was optimized using simulation tool CAD-FEKO_v6.2 which works on Method of Moments. Antenna was manufactured on FR4 substrate having εr= 4.4.The results obtained from simulating antenna with the help of simulation software matches with results of manufactured antenna obtained from Antritsu vector network analyzer.

A Study on Energy Saving and co2 Emission Reduction on Signal Countdown Extension by Vehicular Ad Hoc Networks

Research on the broadcasting of signal countdown messages (SCMs) to vehicles via vehicular ad hocnetwork (VANET) technology has shown that it can reduce CO2 emissions and energy consumption; however, past studies have lacked consideration of car following and vehicle gliding mode. In this paper, two green driving suggestion models, namely, the Maximize Throughput Model (MaxTM) and the Minimize Acceleration and Deceleration Model (MinADM), are proposed to minimize the CO2 emissions by considering real-time traffic information nearby the intersection. The two proposed strategies are compared with an open traffic light control model (OTLCM).

The main facts this paper demonstrate are that traffic models lack consideration of car following, which would make the simulation result unrealistic, that the proposed MaxTM can reduce more CO2 emissions than the MinADM and the OTLCM, and the total travel time in the MaxTM is also better than the other two models so that the general traffic performance can be improved. Simulation results show that the performance of CO2emissions of the MaxTM is 5%-102% better than the MinADM and 13%-209% better than the OTLCM in the simulation cases, and the performance of CO2 emissions of the MaxTM is 8%-14% better than the MinADM and 15%-231% better than the OTLCM in the real traffic cases.

Impact of Location Popularity on Throughput and Delay in Mobile Ad Hoc Networks

With the advent of smart portable devices and location-based applications, user’s mobility pattern is found to be highly dependent on varying locations. In this paper, we analyze asymptotic throughput-delay performance of mobile ad hoc networks (MANETs) under a location popularity based scenario, where users are more likely to visit popular locations. This work provides a complementary perspective compared with previous studies on fundamental scaling laws for MANETs, mostly assuming that nodes move uniformly in the network. Specifically, we consider a cell-partitioned network model with cells of known popularity, which follows a Zipf’s law distribution with popularity exponent α. We first conduct the analysis under traditional store-carry-forward paradigm, and find that location heterogeneity affects thenetwork performance negatively, which is due to the waste of potential transmission opportunities in popular cells.

Motivated by this observation, we further propose a novel store-carry-accelerate-forward paradigm to enhance the network communication, exploiting these potential transmissions. Theoretical results demonstrate that our proposed scheme outperforms all delay-capacity results obtained in conventional scheme for any α. In particular, when α = 1, it can achieve a constant capacity with an average delay of Θ(√n) (except for a polylogarithmic factor), while the delay is Θ(n) in conventional scheme. And by letting α = 0, our results can cover Neely’s scaling laws. Moreover, we show that the delay-capacity tradeoff ratio satisfies ≥Θ(√n), revealing that exploiting location popularity can effectively improve the performance in MANETs.

Simple Clustering Methods for Multi-Hop Cooperative Device-to-Device Communication

This paper studies the gain that cooperative multi-hop transmission provides when used to boost the data rate in Device-to-Device (D2D) communication. Both D2D transmitter and receiver are located in the coverage area of the same Macro Base Station, who is in charge of the control signaling to construct the cooperative cluster(s) of low-cost Relay Nodes (RNs) that Decode-and-Forward information non-coherently from source to destination. Communication resources are divided into two or three equal orthogonal parts for two- and three-hop cooperative transmissions, respectively.

For the three-hop cooperative case, backward Interference Cancellation (IC) is also considered in the RNs of the first cluster to reduce multiplexing loss (using two orthogonal portions of communication resources instead of three). The end-to-end data rate of different multi-hop cooperative transmission strategies is studied for different clustering algorithms and measurement reports (i.e., SNR and SINR). Based on obtained performance results, it is possible to conclude that three-hop cooperative transmission with backward IC provides better performance than its two-hop counterpart.

Regulation of arterial venous stem cell differentiation on PEG hydrogels using immobilized and soluble developmental signals

Vascular endothelial cells differentiated from pluripotent stem cells have potential in a variety of therapeutic areas such as tissue engineered vascular grafts and revascularization of ischemic tissues. However, there remain limitations in the control of stem cell differentiation into the desired functional phenotypes with current methods. During vascular development, it has been demonstrated that the early arterial-venous cell fate is genetically programmed, with the expression of transmembrane proteins ephrinB2 and EphB4 as the first distinction, prior to hemodynamic cues [1].

Here, we hypothesize that arterial venous differentiation is influenced, not only from the Notch activation pathway, but also from the bidirectional signaling of these transmembrane ligand-receptor proteins. Our results show ephrinB2/EphB4 immobilized signaling in combination with soluble factors can influence arterial venous differentiation in mouse embryonic stem cells (mESCs).