Current Issue : January - March Volume : 2012 Issue Number : 1 Articles : 6 Articles
Cutting-edge wireless networking approaches are required to efficiently differentiate traffic and handle it according to its special characteristics. The current Medium Access Control (MAC) scheme which is expected to be sufficiently supported by well-known networking vendors comes from the IEEE 802.11e workgroup. The standardized solution is the Hybrid Coordination Function (HCF), that includes the mandatory Enhanced Distributed Channel Access (EDCA) protocol and the optional Hybrid Control Channel Access (HCCA) protocol. These two protocols greatly differ in nature and they both have significant limitations. The objective of this work is the development of a high-performance MAC scheme for wireless networks, capable of providing predictable Quality of Service (QoS) via an efficient traffic differentiation algorithm in proportion to the traffic priority and generation rate. The proposed Adaptive Weighted and Prioritized Polling (AWPP) protocol is analyzed, and its superior deterministic operation is revealed....
An ultra-high data rate time reversal (TR) multiple-input multiple-output (MIMO) ultra-wideband (UWB) communication system with space-time precoding is proposed. When the symbol duration is set to approach the duration of UWB monocycles, the data rate is close to the limit, resulting in the severe intersymbol interference (ISI). The zero-forcing (ZF) criterion-based space-time precoding presented in this paper eliminates both ISI and multistream interference (MSI) caused by spatial multiplexing at the sampling time. With less demand for the degree of freedom (the number of antennas) than other existing schemes, the proposed scheme enables the data rate to reach the order of Gbps without losing bit error rate (BER) performance. Since TR signal preprocessing and the proposed precoding both require the channel state information (CSI), a simple but effective channel estimation algorithm is also proposed to evaluate the impact of channel estimation on the proposed scheme....
Recently, the growing success of new wireless applications and services has led to overcrowded licensed bands, inducing the governmental regulatory agencies to consider more flexible strategies to improve the utilization of the radio spectrum. To this end, cognitive radio represents a promising technology since it allows to exploit the unused radio resources. In this context, the spectrum sensing task is one of the most challenging issues faced by a cognitive radio. It consists of an analysis of the radio environment to detect unused resources which can be exploited by cognitive radios. In this paper, three different cognitive radio architectures, namely, stand-alone single antenna, cooperative and multiple antennas, are proposed for spectrum sensing purposes. These architectures implement a relatively fast and reliable signal processing algorithm, based on a feature detection technique and support vector machines, for identifying the transmissions in a given environment. Such architectures are compared in terms of detection and classification performances for two transmission standards, IEEE 802.11a and IEEE 802.16e. A set of numerical simulations have been carried out in a challenging scenario, and the advantages and disadvantages of the proposed architectures are discussed....
Background\nThe emerging market of mobile phone technology and its use in the health sector is rapidly expanding and connecting even the most remote areas of world. Distributing diagnostic images over the mobile network for knowledge sharing, feedback or quality control is a logical innovation.\nObjective\nTo determine the feasibility of using mobile phones for capturing microscopy images and transferring these to a central database for assessment, feedback and educational purposes.\nMethods\nA feasibility study was carried out in Uganda. Images of microscopy samples were taken using a prototype connector that could fix a variety of mobile phones to a microscope. An Information Technology (IT) platform was set up for data transfer from a mobile phone to a website, including feedback by text messaging to the end user.\nResults\nClear images were captured using mobile phone cameras of 2 megapixels (MP) up to 5MP. Images were sent by mobile Internet to a website where they were visualized and feedback could be provided to the sender by means of text message.\nConclusion\nThe process of capturing microscopy images on mobile phones, relaying them to a central review website and feeding back to the sender is feasible and of potential benefit in resource poor settings. Even though the system needs further optimization, it became evident from discussions with stakeholders that there is a demand for this type of technology....
The performance of adaptive algorithms, including direct data domain least square, can be significantly degraded in the presence\nof mutual coupling among array elements. In this paper, a new adaptive algorithm was proposed for the fast recovery of the signal\nwith one snapshot of receiving signals in the presence of mutual coupling, based on the two-dimensional direct data domain least\nsquares (2-D D3LS) for uniform rectangular array (URA). In this method, inverse mutual coupling matrix was not computed.\nThus, the computation was reduced and the signal recovery was very fast. Taking mutual coupling into account, a method was\nderived for estimation of the coupling coefficient which can accurately estimate the coupling coefficient without any auxiliary\nsensors. Numerical simulations show that recovery of the desired signal is accurate in the presence of mutual coupling....
Slotted Aloha is an effective random access protocol and can also be an important element of more advanced media access protocols. This paper investigates slotted Aloha in a radio environment with multiple access points. Specifically, we examine the impact of multi-access-point (multi-AP) diversity on the performance of slotted Aloha. The paper considers both omni-directional (OM) and beamforming (BF) antennas at transmission nodes. This leads to the investigation and comparison of four different network scenarios, i.e., OM with multi-AP diversity, OM without multi-AP diversity, BF with multi-AP diversity and BF without multi-AP diversity. Performance evaluations and comparisons are presented in terms of throughput and average packet delay....
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