extensive researches on wireless sensor networks (wsns) have been performed and many techniques have been developed for the data link (mac) layer. most of them assume single-channel mac protocols. in the usual dense deployment of the sensor networks, single-channel mac protocols may be deficient because of radio collisions and limited bandwidth. hence, using multiple channels can significantly ...

In this paper, Ultra-wideband (UWB) multiple access relay channel with correlated noises at the relay and receiver is investigated. We obtain outer and inner bounds for the IEEE 802.15.3a UWB multiple access relay channel, and also, a diversity gain bound. Finally, we evaluate some results numerically and show that noise correlation coefficients play important role in determining relay position.

introduction: a limited number of studies have evaluated factors influencing the retention of fixed prostheses cemented to implant abutments. the aim of this study was to compare the effect of varying degrees of screw access channel obturation on retention of implant-supported cast fixed restorations. materials  & methods: in this experimental study, 40 implant abutments with a diameter of 4.5 ...

background and aims. because of compromised angulations of implants, the abutments are sometimes prepared. the purpose of this study was to investigate the effect of removing one wall of the implant abutment on the retention of cement-retained crowns. materials and methods. four prefabricated abutments were attached to analogues and embedded in acrylic resin blocks. the first abutment was left ...

ieee 802.11e standard is proposed to support quality of service (qos) in wireless local area networks (wlans). the distributed access method of 802.11e, enhanced distributed channel access (edca), prioritizes traffic generated by delay-sensitive applications by increasing probability to access medium for this type of traffic. edca resets the contention window (cw) of mobile stations to a minimu...

statement of the problem: one disadvantage of cement-retained crowns is the lack of predictable irretrievability. this problem can be overcome through designing a screw access hole in the metal substructure of cement-retained restoration and using porcelain stain to define this area. purpose: this study aimed to evaluate the influence of existence of screw access hole on porcelain fracture resi...

In recent years, there has been considerable interest in the use of CDMA in mobile communications. Bit error rate is one of the most important parameters in the evaluation of CDMA systems. In this paper, we develop a technique to find an accurate approximation to the probability of bit error for asynchronous direct–sequence code division multiple–access (DS/CDMA) systems by modeling the multipl...

In this study, we introduce a new two-way relay channel and obtain an inner bound and an outer bound for the discrete and memoryless multiple access relay channels with receiver-source feedback via two-way relay channel in which end nodes exchange signals by a relay node. And we extend these results to the Gaussian case. By numerical computing, we show that our inner bound is the same with o...

We study the problem of simulating a two-user multiple-access channel (MAC) over multiple access network noiseless links. Two encoders observe independent and identically distributed (i.i.d.) copies source random variable each, while decoder observes i.i.d. side-information variable. There are rate-limited communication links between each encoder decoder, there is pairwise shared randomness all...

In this channel,we study rate region of a Gaussian two-way diamond channel which operates in half-duplex mode. In this channel, two transceiver (TR) nodes exchange their messages with the help of two relay nodes. We consider a special case of the Gaussian two-way diamond channels which is called Compute-and-Forward Multiple Access Channel (CF-MAC). In the CF-MAC, the TR nodes transmit their mes...