Hsi-Lu Chao

A cloud model and concept prototype for cognitive radio networks

The FCCs approval for the first commercial operation in TV white space gives new momentum to the development of cognitive radio in TVWS. On the other hand, the rapid growth of Cloud computing makes it possible and more economical to build a CR metropolitan area network with commodity hardware. In view of the opportunity and challenges brought about by these two technologies, we propose a CR cloud networking model that is able to support CR access in TVWS. Making use of the flexible and vast computing capacity of the cloud, a database and a cooperative spectrum sensing algorithm that estimates the radio power map of licensed users are realized on a CR cloud implemented with Microsoft¿s Windows Azure Cloud platform. The CRC can support CSS, dynamic spectrum access and mobility management. A medium access control protocol is also developed for this CRCN model to collect sensing reports and provide access to the TVWS and CRC services. Through this CRCN prototype, important network parameters such as the mean squared errors in CSS, the CR channel vacating delay, and the cloud-based handover time are measured for the design and deployment of the CRCN concept.

Sum Throughput-Improved Resource Allocation for LTE Uplink Transmission

Long Term Evolution (LTE) is a promising technology for 4G mobile networks. Due to utilize OFDMA in downlink and SC-FDMA in uplink, the LTE system is expected to provide significantly high throughput with 20 MHz spectrum allocation. To increase the cell throughput and multi-user diversity gain, channel dependent scheduling (CDS) is implemented for the OFDMA-based multi-user scenario to allocate resource blocks (RBs) to users experiencing better channel conditions. Nevertheless, CDS may not perform well in SC-FDMA due to its two inherent constraints¿|one is contiguous RB assignment and the other is robust modulation and coding mode. In this paper, the formulation of resource allocation for a SC-FDMA system upon considering two inherent constraints is proposed. Since the optimization problem of resource allocation in SC-FDMA is NP-hard, we further propose two heuristic algorithms to find feasible solutions. We evaluate the proposed formulation and heuristic algorithms by conducting simulation. The simulation results show that our methods achieve significant performance improvement not only in system sum throughput but also in transmission delay.

An efficient measurement report mechanism for Long Term Evolution networks

LONG-TERM EVOLUTION (LTE) is expected to ensure 3GPPs competitive edge over other cellular technologies. The advantages of LTE include improving end-user throughputs, and reducing latency. LTE systems utilize a network-controlled and the user equipment (UE) assisted handover procedure for mobility in connected mode. In this paper, we first introduce the measurement report mechanism defined in the specification of LTE systems. We further explore possible problems and the impact on handover decision. Followed, we propose rules for timer adjustment, including timeToTrigger and reportInterval. Our mechanism aims at reducing incorrect handover decisions and maximizing the throughput performance. By conducting simulation, we evaluate the designed mechanism. The simulation results show that our proposed mechanism does achieve our design goals.

A novel channel-aware frequency-domain scheduling in LTE uplink

Due to the power consumption issue of user equipment (UE), Single-Carrier FDMA (SC-FDMA) has been selected as the uplink multiple access scheme of 3GPP Long Term Evolution (LTE). Similar to OFDMA downlink, SCFDMA enables multiple UEs to be served simultaneously in uplink as well. However, the single carrier characteristic requires that all the allocated subcarriers to a UE must be contiguous in frequency with each time slot. Moreover, a UE should adopt the same modulation and coding scheme at all allocated subcarriers. These two constraints do limit the scheduling flexibility. In this paper, we formulate the UL scheduling problem with taking two constraints into consideration. Since this optimization had been proven to be an NP-hard problem, we further develop a heuristic algorithm with low complexity. We demonstrate that competitive performance can be achieved in terms of system throughput, which is evaluated by using 3GPP LTE system model simulations.

On synchronized channel sensing and accessing for cognitive radio users in IEEE 802.11 wireless networks

One of the most challenging issues in cognitive radio systems is channel sensing and channel accessing. In this paper, a synchronized channel-sensing and accessing for cognitive radio users in IEEE 802.11 wireless networks is proposed. The mechanism consists of two phases: fast channel sensing and proactive channel vacating. Fast channel sensing is for a pair of cognitive radio users to search an available channel time-efficiently; proactive channel vacating is for the pair of cognitive radio users to be aware of the presence of primary users and vacate the occupied channel as quick as possible. We utilize the concept of channel hopping to reduce the average channel sensing time of cognitive radio users. Besides, through the designed interruption mechanism, cognitive radio users can create opportunities for primary users to claim the spectrum and thus minimize the caused interference to primary users. From the simulation results, our proposed protocol can efficiently balance the tradeoff between throughput performance of a cognitive radio network and waiting time of primary users to claim channels.

F2-MAC: an efficient channel sensing and access mechanism for cognitive radio networks

One of the most challenging issues in cognitive radio (CR) systems is channel sensing and accessing. In this paper, a CR channel access mechanism is proposed. The mechanism consists of two phases: fast channel accessing and proactive channel vacating. In fast channel accessing, a pair of CR users time-efficiently searches an available channel to deliver data. In proactive channel vacating, a pair of CR users periodically makes channel access opportunities to primary users (PUs) and vacates the occupied channel as quick as possible. We utilize the concept of channel hopping to reduce the average channel searching time. Furthermore, our vacating mechanism allows CR users to create opportunities for PUs to claim the spectrum and thus minimize the caused interference to PUs. We evaluate the performance of our approach through a two-dimensional Markov chain model as well as simulations. The performance study indicates that the proposed protocol achieves low channel searching time, high throughput, and fairness.

On fair scheduling for mobile ad hoc networks with channel errors

In this paper, we study fair scheduling in ad hoc networks, accounting for channel errors. Since wireless channels are susceptible to failures, to ensure fairness it may be necessary to compensate those flows with error-prone channels. Existing compensation mechanisms need the support of base stations and only work for one-hop wireless channels. Therefore, they are not suitable for multihop wireless networks. Existing fair scheduling protocols for ad hoc networks can be classified into timestamp-based and credit-based approaches. None of them takes channel errors into account. In this paper, we investigate the compensation issue of fair scheduling and propose a timestamp-based fair scheduling mechanism for multihop mobile ad hoc networks, called timestamp-based compensation protocol (TBCP). We evaluate the performance of the proposed mechanism by simulation and also analyze its long-term throughput. The results show that our analytical result provides accurate approximation for the proposed mechanism.

Cooperative spectrum sharing and scheduling in self-organizing femtocell networks

A cooperative spectrum sharing, power allocation and user scheduling method is studied in this work under the framework of LTE self-organizing femtocell networks. Making use of dynamic channel and power allocation, and interference control, all femto access points (APs) in a self-organizing network (SON) can share the channels available to the SON with guaranteed quality of service. Simulation results show that the effective channel usage ratio can reach 75% in average even with no explicit cellular planning inside the service area of an SON. This result supports the feasibility of randomly deploying large numbers of femto APs in metropolitan areas based on the concept of SON.

Green Spectrum Sharing in a Cloud-Based Cognitive Radio Access Network

Based on the vast and elastic cloud computing resource, a cloud-based cognitive radio access networking (C2-RAN) service model is studied in this work. Integrating the cross-layer C2-RAN functions of computing and spectrum resource sharing, channel and power allocation, as well as user scheduling and medium access control in a public cloud platform, we explore the feasibility and potential of deploying a green yet broadband wireless RAN service in TV white space with tens of thousands of low-power cognitive radio (CR) access points (APs). Through an experimental and simulated study of C2-RAN in a wireless metropolitan area network (MAN), the system throughput and power consumption of the proposed C2-RAN MAN is compared with that of a simulated 3G MAN. Simulatio results show that the C2-RAN MAN can offer an aggregate 726.4 Gbps system capacity with a total power consumption of 203.6 kilowatt over a maximum of 180 MHz bandwidth, while the 3G system provides an 8 Gbps system capacity with 940.2 kilowatt over 15 MHz bandwidth. The proposed C2-RAN appears to be a promising solution for future broadband wireless access.

Scheduling with Reusability Improvement for Millimeter Wave Based Wireless Personal Area Networks

IEEE 802.15.3c has recently been formed for developing a millimeter-wave (mmWave)-based wireless personal area networks (WPANs). It utilizes 60 GHz license-free spectrum and provides very high data rate (over 3 Gbps). To deal with the problems of high propagation attenuation and path loss, beamforming antennas are utilized. In this paper, we consider the characteristics of beamforming to design an efficient scheduling algorithm. Specifically, we integrate axis alignment and location determination into scheduling mechanism. The designed scheduling algorithm improves the degree of spatial and directional channel reusability and the overall system performance. We evaluate our approach through simulations. The simulation results show that the designed scheduling algorithm performs well and does achieve its objectives.