Rahman Doost-Mohammady

Smart Radios for Smart Vehicles: Cognitive Vehicular Networks

This article discusses the current state-of-the-art research on CRV networks. While it is envisaged that this technology will help to realize high-bandwidth multimedia applications, the research on CRV networks is still at a preliminary stage. The spectrum management functions proposed for general-purpose CR networks will need to be revisited by taking into account the characteristics of the vehicular environment, such as the role of the mobility, and the cooperation possibilities. The lack of realistic test beds and of simulation tools is a serious limitation, and effort needs to be invested in building such evaluation platforms that can provide realistic insights on the performance of CRV networks before the potential for this technology can be fully realized.

Transforming healthcare and medical telemetry through cognitive radio networks

The Wireless Medical Telemetry Services (WMTS) band has been established by the FCC in the United States for transmission of data related to a patient¿s health, and similar reserved channels exist for life-critical communications throughout the world. However, transmissions in the WMTS band are severely hampered by interferences from adjacent digital television channels, and due to non-uniform access priority, as this band is also shared by utility telemetry and government installations. In this article, we propose the use of cognitive radio technology to dynamically utilize the WMTS frequencies based on the activity patterns of the high priority users, and the quality of service constraints of the patients¿ data, while ensuring protection to existing higher priority transmissions and the safe operation of sensitive medical equipment. The priority users here are utility telemetry transmissions in certain portions of the WMTS band, government run radar sites, and legacy medical telemetry equipment without cognitive radio capability. We provide the first measurements on the complete WMTS spectrum activity at two major hospital locations in the Boston area, and outline an optimization framework that assigns frequency and transmission power jointly in this setting. The article also discusses the current state of the art and the major challenges in the implementation of this new cognitive radio assisted medical telemetry paradigm.

Cooperation and communication in Cognitive radio networks based on TV spectrum experiments

Cognitive radio (CR) ad hoc networks are composed of wireless nodes that may opportunistically transmit in licensed frequency bands without affecting the primary users of that band. In such distributed networks, gathering the spectrum information is challenging as the nodes have a partial view of the spectrum environment based on the local sensing range. Moreover, individual measurements are also affected by channel uncertainties and location-specific fluctuations in signal strength. To facilitate the distributed operation, this paper makes the following contributions: (i) First, an experimental study is undertaken to measure the signal characteristics for indoor and outdoor locations for the TV channels 21 – 51, and these results are used to identify the conditions under which nodes may share information. (ii) Second, a Cooperative reinforcement LearnIng scheme for Cognitive radio networKs (CLICK) is designed for combining the spectrum usage information observed by a node and its neighbors. (iii) Finally, CLICK is integrated within a MAC protocol for testing the benefits and overhead of our approach on a higher layer protocol performance. The proposed learning framework and the protocol design are extensively evaluated through a thorough simulation study in ns-2 using experimental traces of channel measurements.

Spectrum Allocation and QoS Provisioning Framework for Cognitive Radio With Heterogeneous Service Classes

Cognitive radio (CR) networks will enable dynamic spectrum re-use and thereby accelerate the adoption of high bandwidth services in available licensed frequencies with better channel characteristics. However, the possibility of the licensed user reclaiming the channel raises additional concerns on how best to reserve resources for secondary users (SUs) that are likely to have different qualities of service (QoSs) depending on their application requirements. This paper addresses the problem of spectrum resource management for co-located SUs with both streaming and intermittent data by efficiently identifying the number of backup channels that will ensure seamless end to end service. The contributions of this paper are threefold: First, a comprehensive analytical framework based on queueing theory is devised to calculate the theoretical delay in accessing the spectrum depending on the required QoS, with guidelines on how to optimize the set of back-up channels for possible future use; second, a method of spectrum allocation for SUs with these different QoS demands is formulated, especially as they co-exist and affect the performance of each other; third, a case study of applying these techniques in a novel application area of wireless medical telemetry is presented. Results reveal that the simulated spectral efficiency of the channel allocation using our approach matches closely with our theoretical predictions, within a 5% bound.

Device characterization and cross-layer protocol design for RF energy harvesting sensors

Energy harvesting from ambient radio frequency waves has the potential for realizing long lived wireless sensor networks, by reducing their dependence on the limited and irreplaceable on-board batteries. We propose two cross-layer approaches, called device-agnostic (DA) and device-specific (DS) protocols, for such networks composed of energy harvesting boards connected to off-the-shelf available sensors. These protocols determine the routing paths and the harvesting-transmission duty cycle at each hop under different conditions. The DA scheme relies purely on the local measurements on the harvesting capability of a node after the sensors are deployed, and is useful for single-flow networks. The DS scheme provides a joint hardware-software optimization by allowing the selection of the energy storing capacitor, apart from the route and duty cycle determination. Both schemes rely on a rich set of device-level experimental studies that help provide exact performance characteristics in practical scenarios, and results reveal significant performance improvement over other existing schemes.

Enhancing wireless medical telemetry through dynamic spectrum access

Wireless Medical Telemetry Systems (WMTS) currently operate on FCC designated bands for transmitting critical patient health information to distant receivers within hospitals. However, the current devices experience intermittent interference from digital TV transmissions in neighboring channels; are prohibited from transmitting multimedia data; and must operate with a secondary access priority in portions of the WMTS band, also shared with utility metering. We propose a fundamentally new communication paradigm for medical telemetry through dynamic spectrum access technology that adheres to the access rules in the WMTS band, and yet addresses the above concerns. The contributions of the paper are as follows: (i) we undertake a spectrum measurement study at hospital locations in the Boston area to model spectrum usage and activities in the medical band, (ii) we formulate the channel and power allocation task as an optimization problem under constrains of permissible electromagnetic interference to sensitive medical equipment, and latency, bandwidth thresholds of the medical data. Simulation results reveal the potential benefit of the use of dynamic spectrum access to improve medical telemetry and promises long-term improvement in the healthcare domain.

Leveraging Deliberately Generated Interferences for Multi-Sensor Wireless RF Power Transmission

Wireless RF power transmission promises battery-less, resilient, and perpetual wireless sensor networks. Through the action of controllable Energy Transmitters (ETs) that operate at-a- distance, the sensors can be re-charged by harvesting the radiated RF energy. However, both the charging rate and effective charging range of the ETs are limited, and thus multiple ETs are required to cover large areas. While this action increases the amount of wireless energy injected into the network, there are certain areas where the RF energy combines destructively. To address this problem, we propose a duty-cycled random- phase multiple access (DRAMA). Non-intuitively, our approach relies on deliberately generating random interferences, both destructive and constructive, at the destination nodes. We demonstrate that DRAMA optimizes the power conversion efficiency, and the total amount of energy harvested. Through real-testbed experiments, we prove that our proposed scheme provides significant advantages over the current state of the art in our considered scenario, as it requires up to 70% less input RF power to recharge the energy buffer of the sensor in the same time.

Accurate physical to Network LTE simulation framework

We present a unified LTE PHY/MAC/NET framework with a realistic Physical layer implementation and a standards-compliant MAC layer and Network Level simulation capabilities based on NS-3 and MATLAB LTE system toolbox.