Performance analysis of a fully-connected, full-duplex CDMA ALOHA network with channel sensing and collision detection

In cases where machines having bursty data are equally likely to transmit to one another, code-division multiple-access (CDMA) ALOHA which allows for an individual "virtual channel" for each receiving station may be a better multiple-access protocol than simple ALOHA. With the use of "receiver-based code" multiple-access protocol, it is also possible for a station to listen to the channel of the intended receiver before transmission, and also abort transmission when it detects others transmitting on the same channel. This paper describes a model for a fully-connected, full duplex, and slotted CDMA ALOHA network where channel sensing and collision detection are used. The model is analyzed using a discrete time Markov chain and some numerical results are presented. For a system with a large number of users, where Markov analysis is impractical, equilibrium point analysis is used to predict the stability of the system, and estimate the throughput as well as the delay performance of the system when it is stable. Finally, a comparison is made with a simple channel sense multiple-access with collision detection (CSMA-CD) network, showing that a substantial improvement in the performance is achieved by the proposed network.published_or_final_versio

Performance comparison of single and multi-channel CSMA-CD wireless networks using equilibrium point analysis

Conference theme: Mobile Technology for the Human RaceA fundamental defect of simple CSMA-CD multiple access scheme is that messages meant for different stations can collide in the common channel. In this paper, a multi-channel form of CSMA-CD network, created by CDMA signalling, is analyzed. Its performance is shown to be superior to that of a single channel CSMA-CD network.published_or_final_versio

A model for evaluating the performance of code phase assignment CDMA LAN

Conference Theme: Wireless: Merging onto the Information SuperhighwayThis paper describes a model for a fully-connected, full duplex, and synchronized CDMA LAN where the receivers use the same maximal length sequence with different chip phase offset for receiving messages. ALOHA medium access is used. The performance of the model is analyzed by considering the succession of states the system is in as a Markov process. The behaviour of a 5-station system is shown.published_or_final_versio

Performance of multichannel CSMA networks

International Conference on Information, Communications and Signal Processing, Singapore, 9-12 September 1997Channel sense multiple access with collision detection (CSMA/CD) is a very simple and efficient way of allowing many stations to transmit messages to a central server down a shared channel. In wireless networks, however, collision detection is difficult to implement, and in such cases CSMA alone may have to be used. In this paper, it is shown that a multichannel CSMA network can be almost as efficient in utilizing the bandwidth available to the network as an equivalent single-channel CSMA/CD network. Furthermore, multichannel CSMA networks provide better throughput and delay performance than equivalent single channel CSMA systems, even when the message generation probability and the number of stations in the network are varied.published_or_final_versio

Performance analysis of a CDMA ALOHA network with channel sensing

It has been shown in [1] that the throughput-delay performance of a CDMA ALOHA network, where each station is assigned a spreading code so that each effectively has its own `virtual channel', and where channel sensing and collision detection are also used, is much better than that of a simple CSMA-CD network. Such a system, however, is difficult to implement. A simpler system that may provide good performance and that is easy to implement is a CDMA ALOHA network with just channel sensing. The channel sensing can be provided by a simple correlator and threshold device. In this paper, the performance of such a network is investigated, and some comparisons are made with those of the simple CSMA-CD network and the CDMA ALOHA network with both channel sensing and collision detection. It is shown that when the CDMA-CS network is stable, its performance is not much worse than that of a CDMA-CS/CD network, and much better than that of a simple single channel CSMA-CD system.published_or_final_versio

Delay-throughput comparison of single and multi-channel slotted ALOHA networks

In networks where stations are equally likely to transmit to one another, simple slotted ALOHA is not an appropriate form of multiple access protocol as messages meant for different stations can collide in the common channel. In this paper the performance of a single channel slotted ALOHA network is compared to that of a CDMA ALOHA network where each of the station is assigned a different spreading code with which to receive messages, and thus effectively possesses its own private 'virtual channel'.published_or_final_versio

Recording of natural head position using stereophotogrammetry: A new technique and reliability study

The purpose of this study was to develop a technique to record physical references and orient digital mesh models to natural head position (NHP) using stereo-photogrammetry (SP). The first step was to record the digital mesh model of a hanging reference board placed at the capturing position of the SP machine. The board was aligned to the true vertical using a plumb bob. It was also aligned with laser plane parallel to the hanging mirror which was located at the center of the machine. Parameter derived from the digital mesh model of the board was then used to adjust the roll, pitch and yaw of the subsequent captures of subjects. This information was valid until the next machine calibration. The board placement was repeatable with standard deviation of less than 0.1 degrees for both pitch and yaw; 0.15 degrees for roll angles.postprin

Performance evaluation of hybrid solar parabolic trough concentrator systems in Hong Kong

Author name used in this publication: Edward W. C. LoVersion of RecordPublishe

The factor validity of the Western Ontario Rotator Cuff Index

BACKGROUND: The Western Ontario Rotator Cuff Index (WORC) is a self-report questionnaire developed specifically to evaluate disability in persons with pathology of the rotator cuff of the shoulder. The authors created items in 5 categories based on a model of quality of life, but never validated this structure. The purpose of this study was to examine the validity of the original 5-domain model of the WORC by performing factor analysis. METHODS: Three hundred twenty nine subjects (age, mean: 52, SD: 12) were tested prior to undergoing surgery for rotator cuff pathologies. They completed the WORC, a self-report questionnaire, which has 21 items on the effect of the rotator cuff problem on symptoms, activities and emotions. Statistical calculations included correlations between items, Cronbach's alpha of the total scale and subscales, and principal component factor analysis with oblique rotation. RESULTS: Correlations ranged from .09 to .70 between all the items, from .29 to .70 between items within a subscale, and from .53 to .72 between subscale scores. Cronbach's alpha was .93 for the total scale, and .72 to .82 for the subscales. The factor analysis produced 3 factors that explained 57% of the variance. The first factor included symptoms and emotional items, the second included strength items and the third included daily activities. CONCLUSION: The results of this study did not support the 5-domain model of the WORC

Bilateral dilation of the urinary tract due to iliopsoas pyomyositis: a case report

<p>Abstract</p> <p>Introduction</p> <p>Pyomyositis is an acute bacterial infection of the skeletal muscles that arises from hematogenous spread and is caused predominantly by Gram-positive cocci.</p> <p>Case presentation</p> <p>We report a case of iliopsoas pyomyositis in a 25-year-old Greek Caucasian woman with a history of intravenous drug use. Her condition was complicated by bilateral dilation of the ureters and renal calyces as a result of mechanical pressure from inflammation and edema of the involved muscle. The patient did not present aggravation of renal function and was treated successfully solely with intravenous antibiotics, without surgical intervention. This is the first case report describing iliopsoas pyomyositis with reversible bilateral dilation of the urinary tract that was treated successfully with intravenous antibiotics, without surgical intervention.</p> <p>Conclusion</p> <p>We present the first described case of iliopsoas pyomyositis with reversible bilateral hydroureteronephrosis that was treated successfully with intravenous antibiotics, without the necessity of surgical intervention. To our knowledge, this is the first report of its kind in the literature regarding an unexpected event in the course of treating a patient with iliopsoas pyomyositis, and it should be of particular interest to different clinical medical specialties such as internal medicine, infectious disease and urology.</p