Multi hop wireless networks face many challenges basically the
limitation of bandwidth, loss of packets because of many problems
in wireless medium also loss of paths because of the random and
unpredictable movement of wireless nodes, which reduce
the
performance of these networks. Recently, Network coding has been
used as promising technology that achieves the reliable transfer of
data in wireless networks with high throughput. Considering the
efficiency of this technology and with benefiting from both the
same cost paths and the broadcasting property of wireless medium,
a multi transmission mechanism for random linear network coding
has been proposed in multi hop wireless networks, which depends
on multicasting of coded packets on the same cost paths.
Services that demanded by users via internet network are classified in two main
kinds, Services work in real time such as video and voice in real time and use UDP
protocol, and other services that work in non-real time such as web browsing (HTTP) a
nd
file transfer (FTP) which use TCP Protocol.
In this research, we study and analyze algorithms that enhance the quality of service
for various applications. For real time application, we use queues disciplines, which gives
high priority for these services and achieves minimum delay. For non-real time application,
we study congestion control algorithms, which achieve best performance for reliable
transfer process with existing the congestion in the network. We used OPNET 14.5
program for simulating various services via internet network. Simulation results show
achieving minimum delay for voice service, and achieving high transmission rate for FTP
application with existing of packets loss in the network.
تطبيقات الزمن الحقيقي
التحكم بالازدحام
Congestion Control
تطبيقات الزمن غير الحقيقي
قواعد الرتل
خوارزمية البداية البطيئة
تجنب الازدحام
خوارزمية إعادة الإرسال السريع و الاستعادة السريعة
Real Time application
non-real time application
Queue disciplines
Slow start algorithms
Congestion avoidance algorithms
Fast retransmit and Fast recovery
المزيد..
Wireless communication has become more popular over the last decade. Although
there are many advantages to use wireless over fixed line systems, there is a major
disadvantage, which is a high transmission error rate in a temporal and permanent nois
y
environment. There are techniques to reduce effectiveness off transmission errors in
wireless communications. We have discussed in this paper. Many methods and techniques
have been implementing to deal and resist errors (by increasing transmission power,
switching modulation scheme) as well as evaluation the wireless connection performance
taking into account many factors.
This works aims to study the performance of the mobile system via studying the
effects of adaptive modulation technique on the data rate. Fuzzy logic technique is used as
a tool to analyze the data rate of the downlink connection depending on type
of
modulation, coverage quality and the distant between the receiver and the transmitter. For
parameters were considered as input parameters for the fuzzy logic system mainly are:
power of the station, quality of coverage, the type of modulation technique and the signal
to interface noise ratio. One parameter is used as an output of the fuzzy system which is
spectrum efficiency in bit per second per hertz. Analytical study to select the optimal data
rates for different modulation techniques will be considered. Additionally, studying the
input and output memberships of the data rate parameters using fuzzy logic will be
explained. Keywords: Data rate, downlink, signal to noise ratio, modulation type, Fuzzy
logic, spectrum efficiency.
Random Linear Network Coding (RLNC) is considered to be one of the promised
solutions to achieve the reliability of transmission in multi hop wireless networks, Since it
is based on correcting the loss of the packets in the medium through the conti
nuity of
transmitting coded packets from each segment until receiving acknowledgment of getting
the required number of these packets for decoding. However, because of the nature of
wireless medium and multi hops transfer, a loss or delay of the ACK may occur, which
causes transmitting extra packets and time delay to the next segments, consequently
decreasing the throughput of these networks.
In this research, we propose a new transmission mechanism for reliable transfer in
multi hops wireless networks through using the concepts of sliding window and fast
retransmit with RLNC, for transmitting packets of consequent segments in specific
continues flow and fast correcting the loss in these segments. Simulation results show that
proposed mechanism decreases the time delay for transmission process and increases the
transfer throughput of these networks.
In this research, We interest to studying two methods of ways to increase the reliability of wireless communication, namely: hybrid retransmission protocols (HARQ Protocols) and adaptive coding data (Adaptive Coding), in order for the wireless commun
ication system between two points: the first is fixed and represents the control and leadership station .The second represents a body moving and it is controlled from the command station , it performs various measurements and sent it to the command station.
This research aims to study the importance of serving efficiency in tennis. It is applied to nineteen labeled players, who have participated in the following international championships: 1-Masters-tennis tournament 2011 London; 2-Hamburg Tennis tourn
ament; -3-china open tennis tournament2013 4-shanghai rolex masters 2013.
Results of these tournaments have been analyzed and yielded the following results: the accuracy and efficiency of surving play a critical role in determining the result of the game, especially when levels of the two players are very close. Absence of focus and loss of accuracy in serving leads to increase in the number of double fault. That in turn leads to losing too many rounds in games and it also leads contender to win faultless rounds without any effort. When the player has too many aces in games, he will always be in attacking position. This is a conformation, which proves that the powerful efficiency of serving is confusing the contender and making him occupied with a defence position all the time.