call for paper 2012, hard copy of journal, research paper publishing, where to publish research paper,
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
IOSR Journal of Electronics and Communication Engineering(IOSR-JECE) is an open access international journal that provides rapid publication (within a month) of articles in all areas of electronics and communication engineering and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in electronics and communication engineering. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
A Dynamic MAC Protocol for WCDMA Wireless Multimedia NetworksIDES Editor
Existing MAC protocols like TDMA and 802.11
have many disadvantages for scheduling multimedia traffic in
CDMA wireless networks. Our objective is to develop a
dynamic MAC protocol for WCDMA networks to avoid
congestion and improve the channel utilization and
throughput of the bulky real-time flows. In this paper, we
propose to develop a dynamic MAC protocol for wireless
multimedia networks. In the design, we combine the merits of
the CSMA, TDMA MAC protocols with WCDMA systems to
improve the throughput of the multimedia WLAN in a
cellular environment. We use these MAC protocols
adaptively, to handle both the low and high data traffics of the
mobile users. It uses multiple slots per frame allowing
multiple users to transmit simultaneously using their own
CDMA codes. By simulation results, we show that our
proposed MAC protocol achieves high channel utilization and
improved throughput with reduced average delay under low
and high data traffic.
IOSR Journal of Electronics and Communication Engineering(IOSR-JECE) is an open access international journal that provides rapid publication (within a month) of articles in all areas of electronics and communication engineering and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in electronics and communication engineering. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
A Dynamic MAC Protocol for WCDMA Wireless Multimedia NetworksIDES Editor
Existing MAC protocols like TDMA and 802.11
have many disadvantages for scheduling multimedia traffic in
CDMA wireless networks. Our objective is to develop a
dynamic MAC protocol for WCDMA networks to avoid
congestion and improve the channel utilization and
throughput of the bulky real-time flows. In this paper, we
propose to develop a dynamic MAC protocol for wireless
multimedia networks. In the design, we combine the merits of
the CSMA, TDMA MAC protocols with WCDMA systems to
improve the throughput of the multimedia WLAN in a
cellular environment. We use these MAC protocols
adaptively, to handle both the low and high data traffics of the
mobile users. It uses multiple slots per frame allowing
multiple users to transmit simultaneously using their own
CDMA codes. By simulation results, we show that our
proposed MAC protocol achieves high channel utilization and
improved throughput with reduced average delay under low
and high data traffic.
A simulation study of wi max based communication system using deliberately cl...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
A simulation study of wi max based communication system using deliberately cl...eSAT Journals
Abstract WiMAX is a highly sophisticated technology in the broadband wireless access communication system. Scalable Orthogonal Frequency Division Multiple Access (OFDMA) is a key technology behind mobile WiMAX and it is also expected to play a key role in 3GPP Long Term Evolution (LTE) standards. Designers and OEMs have to concentrate on flexibility, scalability and stability of the overall Orthogonal Frequency Division Multiplexing (OFDM) system along with its proper data processing and channeling process to achieve high performance and competitiveness. In this paper, the performance of a strictly band limited OFDM signal is examined using deliberate clipping method, one of the simplest signal distortion based way to reduce high Peak to Average Power Ratio (PAPR) and its effect on the resultant Bit Error Rate (BER) against Signal to Noise Ratio (SNR) performance. A simulation program using MATLAB software was developed to investigate performance of OFDM signal by optimization of different parameters such values of FFT size, Cyclic Prefix co-efficient (CPC) and The Voltage Clipping Ratio (VCR). The simulation results show that with the increment of VCR at optimized parameter values of FFT size and CP, the performance of BER vs SNR improves compared to the results found without clipping. Keywords: WiMAX, PAPR, OFDM, CPC, Voltage Clipping Ratio, Deliberately Clipped
There are several possible methods for increasing
transmission capacity over fixed bandwidth.
These include modulation employing different amplitude
levels, two orthogonal subcarriers and polarization.
In fact, the only remaining unused dimension is Space.
Performance Evaluation of QoS parameters in UMTS Network Using Qualnetijdpsjournal
A UMTS network based on the Wide Band-CDMA technology is a 3rd generation telecommunication system which provides various multimedia applications along with the conventional
telephony service. These various multimedia applications fall into four different categories, which are
differentiated from each other on the basis of required bit rate and delay tolerance etc. parameters. In
order to get best Quality of Service (QoS) for a particular application running on the subscriber
equipment the parameters of the respective category to which the application belong need to be in a
required range. In this work the performance of a UMTS network scenario is evaluated by using various values of the precedence bits of the CBR application. The simulation tool used is QUALNET 5.0. The performance of the scenario according to the respective precedence bits is analyzed by four metrics: average jitter, end to end delay, throughput and UMTS signals received and forwarded to MAC. The comparative analysis of all the four metrics according to the precedence bit values will be carried out and it will be concluded in the last section that which precedence bit gives the best performance for the simulated UMTS network scenario.
Modern Wireless Communication System
4.1 Evolution for 2.5 G TDMA
standards [12]
HSCSD for 2.5 G GSM
GPRS for 2.5 G GSM and IS-136
EDGE for 2.5G GSM and IS-136
IS-95B for 2.5 G CDMA.
4.2 IMT 2000 [04]
IMT 2000 Vision and Evolution Aspects.
Radio Spectrum for IMT -2000
Prospective of Fifth Generation Mobile Communications ijngnjournal
This paper explores future mobile systems with emphasis on re-configurability based on cognitive and software defined radios. 5G (Fifth Generation) network architecture consisting of reconfigurable multitechnology core and a single fully reconfigurable terminal able to autonomously operate in different heterogeneous access networks is proposed. The proposed network is enforced by nanotechnology, cloud
computing and based on All IP Platform. The paper highlights 5G main development challenges and illustrates why there is a need for 5G. It also reviews in brief the evolution of wireless and cellular systems focusing on four main key factors: radio access, data rates, bandwidth and switching schemes in addition to change in network architecture. The 3G transitional cellular and wireless systems toward 4G and the true 4G IMT-advanced systems are thoroughly presented.
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
call for paper 2012, hard copy of journal, research paper publishing, where to publish research paper,
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
call for paper 2012, hard copy of journal, research paper publishing, where to publish research paper,
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
A simulation study of wi max based communication system using deliberately cl...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
A simulation study of wi max based communication system using deliberately cl...eSAT Journals
Abstract WiMAX is a highly sophisticated technology in the broadband wireless access communication system. Scalable Orthogonal Frequency Division Multiple Access (OFDMA) is a key technology behind mobile WiMAX and it is also expected to play a key role in 3GPP Long Term Evolution (LTE) standards. Designers and OEMs have to concentrate on flexibility, scalability and stability of the overall Orthogonal Frequency Division Multiplexing (OFDM) system along with its proper data processing and channeling process to achieve high performance and competitiveness. In this paper, the performance of a strictly band limited OFDM signal is examined using deliberate clipping method, one of the simplest signal distortion based way to reduce high Peak to Average Power Ratio (PAPR) and its effect on the resultant Bit Error Rate (BER) against Signal to Noise Ratio (SNR) performance. A simulation program using MATLAB software was developed to investigate performance of OFDM signal by optimization of different parameters such values of FFT size, Cyclic Prefix co-efficient (CPC) and The Voltage Clipping Ratio (VCR). The simulation results show that with the increment of VCR at optimized parameter values of FFT size and CP, the performance of BER vs SNR improves compared to the results found without clipping. Keywords: WiMAX, PAPR, OFDM, CPC, Voltage Clipping Ratio, Deliberately Clipped
There are several possible methods for increasing
transmission capacity over fixed bandwidth.
These include modulation employing different amplitude
levels, two orthogonal subcarriers and polarization.
In fact, the only remaining unused dimension is Space.
Performance Evaluation of QoS parameters in UMTS Network Using Qualnetijdpsjournal
A UMTS network based on the Wide Band-CDMA technology is a 3rd generation telecommunication system which provides various multimedia applications along with the conventional
telephony service. These various multimedia applications fall into four different categories, which are
differentiated from each other on the basis of required bit rate and delay tolerance etc. parameters. In
order to get best Quality of Service (QoS) for a particular application running on the subscriber
equipment the parameters of the respective category to which the application belong need to be in a
required range. In this work the performance of a UMTS network scenario is evaluated by using various values of the precedence bits of the CBR application. The simulation tool used is QUALNET 5.0. The performance of the scenario according to the respective precedence bits is analyzed by four metrics: average jitter, end to end delay, throughput and UMTS signals received and forwarded to MAC. The comparative analysis of all the four metrics according to the precedence bit values will be carried out and it will be concluded in the last section that which precedence bit gives the best performance for the simulated UMTS network scenario.
Modern Wireless Communication System
4.1 Evolution for 2.5 G TDMA
standards [12]
HSCSD for 2.5 G GSM
GPRS for 2.5 G GSM and IS-136
EDGE for 2.5G GSM and IS-136
IS-95B for 2.5 G CDMA.
4.2 IMT 2000 [04]
IMT 2000 Vision and Evolution Aspects.
Radio Spectrum for IMT -2000
Prospective of Fifth Generation Mobile Communications ijngnjournal
This paper explores future mobile systems with emphasis on re-configurability based on cognitive and software defined radios. 5G (Fifth Generation) network architecture consisting of reconfigurable multitechnology core and a single fully reconfigurable terminal able to autonomously operate in different heterogeneous access networks is proposed. The proposed network is enforced by nanotechnology, cloud
computing and based on All IP Platform. The paper highlights 5G main development challenges and illustrates why there is a need for 5G. It also reviews in brief the evolution of wireless and cellular systems focusing on four main key factors: radio access, data rates, bandwidth and switching schemes in addition to change in network architecture. The 3G transitional cellular and wireless systems toward 4G and the true 4G IMT-advanced systems are thoroughly presented.
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
call for paper 2012, hard copy of journal, research paper publishing, where to publish research paper,
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
call for paper 2012, hard copy of journal, research paper publishing, where to publish research paper,
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
call for paper 2012, hard copy of journal, research paper publishing, where to publish research paper,
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
call for paper 2012, hard copy of journal, research paper publishing, where to publish research paper,
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
call for paper 2012, hard copy of journal, research paper publishing, where to publish research paper,
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
CDMA Transmitter and Receiver Implementation Using FPGAIOSR Journals
Abstract: Code Division Multiple Access (CDMA) is a spread spectrum technique that uses neither frequency channels nor time slots. With CDMA, the narrow band message (typically digitized voice data) is multiplied by a large bandwidth signal that is a pseudo random noise code (PN code). All users in a CDMA system use the same frequency band and transmit simultaneously. The transmitted signal is recovered by correlating the received signal with the PN code used by the transmitter. The DS - CDMA is expected to be the major medium access technology in the future mobile systems owing to its potential capacity enhancement and the robustness against noise. The CDMA is uniquely featured by its spectrum-spreading randomization process employing a pseudo-noise (PN) sequence, thus is often called the spread spectrum multiple access (SSMA). As different CDMA users take different PN sequences, each CDMA receiver can discriminate and detect its own signal, by regarding the signals transmitted by other users as noise- like interferences. In this project direct sequence principle based CDMA transmitter and receiver is implemented in VHDL for FPGA. Modelsim 6.2(MXE) tool will be used for functional and logic verification at each block. The Xilinx synthesis technology (XST) of Xilinx ISE 9.2i tool will be used for synthesis of transmitter and receiver on FPGA Spartan 3E. Keywords: CDMA, DSSS, BPSK, GOLD code.
I use this presentation for opening 4G Mobile Technology seminar sessions. Usually it will be continued with 1 other presentation on LTE, 1 on WiMAX II, and 1 on applications.
This is work done by MURTADHA ALI NSAIF SHUKUR student at MMU Mullana, Ambala, Haryana, India. With the help my teacher ( Dr.H.P.Sinha HOD (ECE) ) thank for Dr. H.P. sinha and all my teachers for help me. thank you
An Approach to Improve the Quality of Service in OFDMA Relay Networks via Re-...iosrjce
With the next-generation cellular networks making a transition toward smaller cells, two-hop
orthogonal frequency-division multiple access (OFDMA) relay networks have become a dominant, mandatory
component in the 4G standards (WiMAX802.16j, 3GPP LTE-Adv.). Here we are using the multicasting strategy
Given the growing importance of multimedia broadcast and multicast services (MBMS) in 4G networks, the
latter forms the focus of this project. The main aim of this project is to improve the performance of the OFDMA
based relay networks. The OFDMA transmission Scheme is a widely accepted scheme for improving the quality
and speed of communication over the 4G cellular network. There are two different models designed for OFDMA
relay networks .Distributed (DP) and Contiguous (CP) permutations. We are checking the performance of two
algorithms The linear programming algorithm and the greedy algorithm by using two models of OFDMA for
multicast scheduling and after performance evaluation we select the best model and the algorithm for
transmission. We further improve the throughput via retransmission of lost packets during data transfer over the
specified network. We can detect the packet loss by packet synchronization technique and a request will be sent
by the destination for re-sending the lost packets which is called as Re-Transmission.[1]
The tutorial is designed for all those readers who are planning or pursuing the CDMA course to make their career in this field. However, it is also meant for the common readers who simply want to understand − what is CDMA Technology?
A Novel Method for Prevention of Bandwidth Distributed Denial of Service AttacksIJERD Editor
Distributed Denial of Service (DDoS) Attacks became a massive threat to the Internet. Traditional
Architecture of internet is vulnerable to the attacks like DDoS. Attacker primarily acquire his army of Zombies,
then that army will be instructed by the Attacker that when to start an attack and on whom the attack should be
done. In this paper, different techniques which are used to perform DDoS Attacks, Tools that were used to
perform Attacks and Countermeasures in order to detect the attackers and eliminate the Bandwidth Distributed
Denial of Service attacks (B-DDoS) are reviewed. DDoS Attacks were done by using various Flooding
techniques which are used in DDoS attack.
The main purpose of this paper is to design an architecture which can reduce the Bandwidth
Distributed Denial of service Attack and make the victim site or server available for the normal users by
eliminating the zombie machines. Our Primary focus of this paper is to dispute how normal machines are
turning into zombies (Bots), how attack is been initiated, DDoS attack procedure and how an organization can
save their server from being a DDoS victim. In order to present this we implemented a simulated environment
with Cisco switches, Routers, Firewall, some virtual machines and some Attack tools to display a real DDoS
attack. By using Time scheduling, Resource Limiting, System log, Access Control List and some Modular
policy Framework we stopped the attack and identified the Attacker (Bot) machines
Hearing loss is one of the most common human impairments. It is estimated that by year 2015 more
than 700 million people will suffer mild deafness. Most can be helped by hearing aid devices depending on the
severity of their hearing loss. This paper describes the implementation and characterization details of a dual
channel transmitter front end (TFE) for digital hearing aid (DHA) applications that use novel micro
electromechanical- systems (MEMS) audio transducers and ultra-low power-scalable analog-to-digital
converters (ADCs), which enable a very-low form factor, energy-efficient implementation for next-generation
DHA. The contribution of the design is the implementation of the dual channel MEMS microphones and powerscalable
ADC system.
Influence of tensile behaviour of slab on the structural Behaviour of shear c...IJERD Editor
-A composite beam is composed of a steel beam and a slab connected by means of shear connectors
like studs installed on the top flange of the steel beam to form a structure behaving monolithically. This study
analyzes the effects of the tensile behavior of the slab on the structural behavior of the shear connection like slip
stiffness and maximum shear force in composite beams subjected to hogging moment. The results show that the
shear studs located in the crack-concentration zones due to large hogging moments sustain significantly smaller
shear force and slip stiffness than the other zones. Moreover, the reduction of the slip stiffness in the shear
connection appears also to be closely related to the change in the tensile strain of rebar according to the increase
of the load. Further experimental and analytical studies shall be conducted considering variables such as the
reinforcement ratio and the arrangement of shear connectors to achieve efficient design of the shear connection
in composite beams subjected to hogging moment.
Gold prospecting using Remote Sensing ‘A case study of Sudan’IJERD Editor
Gold has been extracted from northeast Africa for more than 5000 years, and this may be the first
place where the metal was extracted. The Arabian-Nubian Shield (ANS) is an exposure of Precambrian
crystalline rocks on the flanks of the Red Sea. The crystalline rocks are mostly Neoproterozoic in age. ANS
includes the nations of Israel, Jordan. Egypt, Saudi Arabia, Sudan, Eritrea, Ethiopia, Yemen, and Somalia.
Arabian Nubian Shield Consists of juvenile continental crest that formed between 900 550 Ma, when intra
oceanic arc welded together along ophiolite decorated arc. Primary Au mineralization probably developed in
association with the growth of intra oceanic arc and evolution of back arc. Multiple episodes of deformation
have obscured the primary metallogenic setting, but at least some of the deposits preserve evidence that they
originate as sea floor massive sulphide deposits.
The Red Sea Hills Region is a vast span of rugged, harsh and inhospitable sector of the Earth with
inimical moon-like terrain, nevertheless since ancient times it is famed to be an abode of gold and was a major
source of wealth for the Pharaohs of ancient Egypt. The Pharaohs old workings have been periodically
rediscovered through time. Recent endeavours by the Geological Research Authority of Sudan led to the
discovery of a score of occurrences with gold and massive sulphide mineralizations. In the nineties of the
previous century the Geological Research Authority of Sudan (GRAS) in cooperation with BRGM utilized
satellite data of Landsat TM using spectral ratio technique to map possible mineralized zones in the Red Sea
Hills of Sudan. The outcome of the study mapped a gossan type gold mineralization. Band ratio technique was
applied to Arbaat area and a signature of alteration zone was detected. The alteration zones are commonly
associated with mineralization. The alteration zones are commonly associated with mineralization. A filed check
confirmed the existence of stock work of gold bearing quartz in the alteration zone. Another type of gold
mineralization that was discovered using remote sensing is the gold associated with metachert in the Atmur
Desert.
Reducing Corrosion Rate by Welding DesignIJERD Editor
The paper addresses the importance of welding design to prevent corrosion at steel. Welding is
used to join pipe, profiles at bridges, spindle, and a lot more part of engineering construction. The
problems happened associated with welding are common issues in these fields, especially corrosion.
Corrosion can be reduced with many methods, they are painting, controlling humidity, and also good
welding design. In the research, it can be found that reducing residual stress on the welding can be
solved in corrosion rate reduction problem.
Preheating on 500oC and 600oC give better condition to reduce corosion rate than condition after
preheating 400oC. For all welding groove type, material with 500oC and 600oC preheating after 14 days
corrosion test is 0,5%-0,69% lost. Material with 400oC preheating after 14 days corrosion test is 0,57%-0,76%
lost.
Welding groove also influence corrosion rate. X and V type welding groove give better condition to reduce
corrosion rate than use 1/2V and 1/2 X welding groove. After 14 days corrosion test, the samples with
X welding groove type is 0,5%-0,57% lost. The samples with V welding groove after 14 days corrosion test is
0,51%-0,59% lost. The samples with 1/2V and 1/2X welding groove after 14 days corrosion test is 0,58%-
0,71% lost.
Router 1X3 – RTL Design and VerificationIJERD Editor
Routing is the process of moving a packet of data from source to destination and enables messages
to pass from one computer to another and eventually reach the target machine. A router is a networking device
that forwards data packets between computer networks. It is connected to two or more data lines from different
networks (as opposed to a network switch, which connects data lines from one single network). This paper,
mainly emphasizes upon the study of router device, it‟s top level architecture, and how various sub-modules of
router i.e. Register, FIFO, FSM and Synchronizer are synthesized, and simulated and finally connected to its top
module.
Active Power Exchange in Distributed Power-Flow Controller (DPFC) At Third Ha...IJERD Editor
This paper presents a component within the flexible ac-transmission system (FACTS) family, called
distributed power-flow controller (DPFC). The DPFC is derived from the unified power-flow controller (UPFC)
with an eliminated common dc link. The DPFC has the same control capabilities as the UPFC, which comprise
the adjustment of the line impedance, the transmission angle, and the bus voltage. The active power exchange
between the shunt and series converters, which is through the common dc link in the UPFC, is now through the
transmission lines at the third-harmonic frequency. DPFC multiple small-size single-phase converters which
reduces the cost of equipment, no voltage isolation between phases, increases redundancy and there by
reliability increases. The principle and analysis of the DPFC are presented in this paper and the corresponding
simulation results that are carried out on a scaled prototype are also shown.
Mitigation of Voltage Sag/Swell with Fuzzy Control Reduced Rating DVRIJERD Editor
Power quality has been an issue that is becoming increasingly pivotal in industrial electricity
consumers point of view in recent times. Modern industries employ Sensitive power electronic equipments,
control devices and non-linear loads as part of automated processes to increase energy efficiency and
productivity. Voltage disturbances are the most common power quality problem due to this the use of a large
numbers of sophisticated and sensitive electronic equipment in industrial systems is increased. This paper
discusses the design and simulation of dynamic voltage restorer for improvement of power quality and
reduce the harmonics distortion of sensitive loads. Power quality problem is occurring at non-standard
voltage, current and frequency. Electronic devices are very sensitive loads. In power system voltage sag,
swell, flicker and harmonics are some of the problem to the sensitive load. The compensation capability
of a DVR depends primarily on the maximum voltage injection ability and the amount of stored
energy available within the restorer. This device is connected in series with the distribution feeder at
medium voltage. A fuzzy logic control is used to produce the gate pulses for control circuit of DVR and the
circuit is simulated by using MATLAB/SIMULINK software.
Study on the Fused Deposition Modelling In Additive ManufacturingIJERD Editor
Additive manufacturing process, also popularly known as 3-D printing, is a process where a product
is created in a succession of layers. It is based on a novel materials incremental manufacturing philosophy.
Unlike conventional manufacturing processes where material is removed from a given work price to derive the
final shape of a product, 3-D printing develops the product from scratch thus obviating the necessity to cut away
materials. This prevents wastage of raw materials. Commonly used raw materials for the process are ABS
plastic, PLA and nylon. Recently the use of gold, bronze and wood has also been implemented. The complexity
factor of this process is 0% as in any object of any shape and size can be manufactured.
Spyware triggering system by particular string valueIJERD Editor
This computer programme can be used for good and bad purpose in hacking or in any general
purpose. We can say it is next step for hacking techniques such as keylogger and spyware. Once in this system if
user or hacker store particular string as a input after that software continually compare typing activity of user
with that stored string and if it is match then launch spyware programme.
A Blind Steganalysis on JPEG Gray Level Image Based on Statistical Features a...IJERD Editor
This paper presents a blind steganalysis technique to effectively attack the JPEG steganographic
schemes i.e. Jsteg, F5, Outguess and DWT Based. The proposed method exploits the correlations between
block-DCTcoefficients from intra-block and inter-block relation and the statistical moments of characteristic
functions of the test image is selected as features. The features are extracted from the BDCT JPEG 2-array.
Support Vector Machine with cross-validation is implemented for the classification.The proposed scheme gives
improved outcome in attacking.
Secure Image Transmission for Cloud Storage System Using Hybrid SchemeIJERD Editor
- Data over the cloud is transferred or transmitted between servers and users. Privacy of that
data is very important as it belongs to personal information. If data get hacked by the hacker, can be
used to defame a person’s social data. Sometimes delay are held during data transmission. i.e. Mobile
communication, bandwidth is low. Hence compression algorithms are proposed for fast and efficient
transmission, encryption is used for security purposes and blurring is used by providing additional
layers of security. These algorithms are hybridized for having a robust and efficient security and
transmission over cloud storage system.
Application of Buckley-Leverett Equation in Modeling the Radius of Invasion i...IJERD Editor
A thorough review of existing literature indicates that the Buckley-Leverett equation only analyzes
waterflood practices directly without any adjustments on real reservoir scenarios. By doing so, quite a number
of errors are introduced into these analyses. Also, for most waterflood scenarios, a radial investigation is more
appropriate than a simplified linear system. This study investigates the adoption of the Buckley-Leverett
equation to estimate the radius invasion of the displacing fluid during waterflooding. The model is also adopted
for a Microbial flood and a comparative analysis is conducted for both waterflooding and microbial flooding.
Results shown from the analysis doesn’t only records a success in determining the radial distance of the leading
edge of water during the flooding process, but also gives a clearer understanding of the applicability of
microbes to enhance oil production through in-situ production of bio-products like bio surfactans, biogenic
gases, bio acids etc.
Gesture Gaming on the World Wide Web Using an Ordinary Web CameraIJERD Editor
- Gesture gaming is a method by which users having a laptop/pc/x-box play games using natural or
bodily gestures. This paper presents a way of playing free flash games on the internet using an ordinary webcam
with the help of open source technologies. Emphasis in human activity recognition is given on the pose
estimation and the consistency in the pose of the player. These are estimated with the help of an ordinary web
camera having different resolutions from VGA to 20mps. Our work involved giving a 10 second documentary to
the user on how to play a particular game using gestures and what are the various kinds of gestures that can be
performed in front of the system. The initial inputs of the RGB values for the gesture component is obtained by
instructing the user to place his component in a red box in about 10 seconds after the short documentary before
the game is finished. Later the system opens the concerned game on the internet on popular flash game sites like
miniclip, games arcade, GameStop etc and loads the game clicking at various places and brings the state to a
place where the user is to perform only gestures to start playing the game. At any point of time the user can call
off the game by hitting the esc key and the program will release all of the controls and return to the desktop. It
was noted that the results obtained using an ordinary webcam matched that of the Kinect and the users could
relive the gaming experience of the free flash games on the net. Therefore effective in game advertising could
also be achieved thus resulting in a disruptive growth to the advertising firms.
Hardware Analysis of Resonant Frequency Converter Using Isolated Circuits And...IJERD Editor
-LLC resonant frequency converter is basically a combo of series as well as parallel resonant ckt. For
LCC resonant converter it is associated with a disadvantage that, though it has two resonant frequencies, the
lower resonant frequency is in ZCS region[5]. For this application, we are not able to design the converter
working at this resonant frequency. LLC resonant converter existed for a very long time but because of
unknown characteristic of this converter it was used as a series resonant converter with basically a passive
(resistive) load. . Here, it was designed to operate in switching frequency higher than resonant frequency of the
series resonant tank of Lr and Cr converter acts very similar to Series Resonant Converter. The benefit of LLC
resonant converter is narrow switching frequency range with light load[6] . Basically, the control ckt plays a
very imp. role and hence 555 Timer used here provides a perfect square wave as the control ckt provides no
slew rate which makes the square wave really strong and impenetrable. The dead band circuit provides the
exclusive dead band in micro seconds so as to avoid the simultaneous firing of two pairs of IGBT’s where one
pair switches off and the other on for a slightest period of time. Hence, the isolator ckt here is associated with
each and every ckt used because it acts as a driver and an isolation to each of the IGBT is provided with one
exclusive transformer supply[3]. The IGBT’s are fired using the appropriate signal using the previous boards
and hence at last a high frequency rectifier ckt with a filtering capacitor is used to get an exact dc
waveform .The basic goal of this particular analysis is to observe the wave forms and characteristics of
converters with differently positioned passive elements in the form of tank circuits.
Simulated Analysis of Resonant Frequency Converter Using Different Tank Circu...IJERD Editor
LLC resonant frequency converter is basically a combo of series as well as parallel resonant ckt. For
LCC resonant converter it is associated with a disadvantage that, though it has two resonant frequencies, the
lower resonant frequency is in ZCS region [5]. For this application, we are not able to design the converter
working at this resonant frequency. LLC resonant converter existed for a very long time but because of
unknown characteristic of this converter it was used as a series resonant converter with basically a passive
(resistive) load. . Here, it was designed to operate in switching frequency higher than resonant frequency of the
series resonant tank of Lr and Cr converter acts very similar to Series Resonant Converter. The benefit of LLC
resonant converter is narrow switching frequency range with light load[6] . Basically, the control ckt plays a
very imp. role and hence 555 Timer used here provides a perfect square wave as the control ckt provides no
slew rate which makes the square wave really strong and impenetrable. The dead band circuit provides the
exclusive dead band in micro seconds so as to avoid the simultaneous firing of two pairs of IGBT’s where one
pair switches off and the other on for a slightest period of time. Hence, the isolator ckt here is associated with
each and every ckt used because it acts as a driver and an isolation to each of the IGBT is provided with one
exclusive transformer supply[3]. The IGBT’s are fired using the appropriate signal using the previous boards
and hence at last a high frequency rectifier ckt with a filtering capacitor is used to get an exact dc
waveform .The basic goal of this particular analysis is to observe the wave forms and characteristics of
converters with differently positioned passive elements in the form of tank circuits. The supported simulation
is done through PSIM 6.0 software tool
Amateurs Radio operator, also known as HAM communicates with other HAMs through Radio
waves. Wireless communication in which Moon is used as natural satellite is called Moon-bounce or EME
(Earth -Moon-Earth) technique. Long distance communication (DXing) using Very High Frequency (VHF)
operated amateur HAM radio was difficult. Even with the modest setup having good transceiver, power
amplifier and high gain antenna with high directivity, VHF DXing is possible. Generally 2X11 YAGI antenna
along with rotor to set horizontal and vertical angle is used. Moon tracking software gives exact location,
visibility of Moon at both the stations and other vital data to acquire real time position of moon.
“MS-Extractor: An Innovative Approach to Extract Microsatellites on „Y‟ Chrom...IJERD Editor
Simple Sequence Repeats (SSR), also known as Microsatellites, have been extensively used as
molecular markers due to their abundance and high degree of polymorphism. The nucleotide sequences of
polymorphic forms of the same gene should be 99.9% identical. So, Microsatellites extraction from the Gene is
crucial. However, Microsatellites repeat count is compared, if they differ largely, he has some disorder. The Y
chromosome likely contains 50 to 60 genes that provide instructions for making proteins. Because only males
have the Y chromosome, the genes on this chromosome tend to be involved in male sex determination and
development. Several Microsatellite Extractors exist and they fail to extract microsatellites on large data sets of
giga bytes and tera bytes in size. The proposed tool “MS-Extractor: An Innovative Approach to extract
Microsatellites on „Y‟ Chromosome” can extract both Perfect as well as Imperfect Microsatellites from large
data sets of human genome „Y‟. The proposed system uses string matching with sliding window approach to
locate Microsatellites and extracts them.
Importance of Measurements in Smart GridIJERD Editor
- The need to get reliable supply, independence from fossil fuels, and capability to provide clean
energy at a fixed and lower cost, the existing power grid structure is transforming into Smart Grid. The
development of a smart energy distribution grid is a current goal of many nations. A Smart Grid should have
new capabilities such as self-healing, high reliability, energy management, and real-time pricing. This new era
of smart future grid will lead to major changes in existing technologies at generation, transmission and
distribution levels. The incorporation of renewable energy resources and distribution generators in the existing
grid will increase the complexity, optimization problems and instability of the system. This will lead to a
paradigm shift in the instrumentation and control requirements for Smart Grids for high quality, stable and
reliable electricity supply of power. The monitoring of the grid system state and stability relies on the
availability of reliable measurement of data. In this paper the measurement areas that highlight new
measurement challenges, development of the Smart Meters and the critical parameters of electric energy to be
monitored for improving the reliability of power systems has been discussed.
Study of Macro level Properties of SCC using GGBS and Lime stone powderIJERD Editor
One of the major environmental concerns is the disposal of the waste materials and utilization of
industrial by products. Lime stone quarries will produce millions of tons waste dust powder every year. Having
considerable high degree of fineness in comparision to cement this material may be utilized as a partial
replacement to cement. For this purpose an experiment is conducted to investigate the possibility of using lime
stone powder in the production of SCC with combined use GGBS and how it affects the fresh and mechanical
properties of SCC. First SCC is made by replacing cement with GGBS in percentages like 10, 20, 30, 40, 50 and
by taking the optimum mix with GGBS lime stone powder is blended to mix in percentages like 5, 10, 15, 20 as
a partial replacement to cement. Test results shows that the SCC mix with combination of 30% GGBS and 15%
limestone powder gives maximum compressive strength and fresh properties are also in the limits prescribed by
the EFNARC.
Study of Macro level Properties of SCC using GGBS and Lime stone powder
Welcome to International Journal of Engineering Research and Development (IJERD)
1. International Journal of Engineering Research and Development
e-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.com
Volume 5, Issue 11 (February 2013), PP. 86-94
Multiple Access Techniques For 4G Mobile Wireless
Networks
Dr Rupesh Singh,
Associate Professor & HOD ECE, HMRITM, New Delhi
Abstract:- A number of new technologies are being integrated by the telecommunications industry as
it prepares for the next generation mobile services. One of the key changes incorporated in the multiple
channel access techniques is the choice of Orthogonal Frequency Division Multiple Access (OFDMA)
for the air interface. This paper presents a survey of various multiple channel access schemes for 4G
networks and explains the importance of these schemes for the improvement of spectral efficiencies of
digital radio links. The paper also discusses about the use of Multiple Input/Multiple Output (MIMO)
techniques to improve signal reception and to combat the effects of multipath fading. A comparative
performance analysis of different multiple access schemes such as Time Division Multiple Access
(TDMA), FDMA, Code Division Multiple Access (CDMA) & Orthogonal Frequency Division
Multiple Access (OFDMA) is made vis-à-vis design parameters to highlight the advantages and
limitations of these schemes. Finally simulation results of implementing some access schemes in
MATLAB are provided.
I. INTRODUCTION
4G (also known as Beyond 3G), an abbreviation of Fourth-Generation, is used for describing the next
complete evolution in wireless communications. A 4G system will be a complete replacement for current
networks and will be able to provide a comprehensive and secure IP solution. Here, voice, data, and streamed
multimedia can be given to users on an "Anytime, Anywhere" basis, and at much higher data rates than the
previous generations [1], [2], [3]. 4G wireless communication standard has the following specifications:
A spectrally efficient system (in bits/s/Hz and bits/s/Hz/site)
High network capacity i.e., more simultaneous calls per cell
A nominal data rate of 100 Mbit/s when the client physically moves at high speeds relative to the
station, and 1 Gbit/s when client and base station are in relatively fixed positions Smooth handoff
across heterogeneous networks.
Seamless connectivity and global roaming across multiple networks.
High quality of service for next generation multimedia support e.g. real time audio, high speed data,
HDTV video content, mobile TV etc.
Interoperability with existing wireless standards.
An all-IP packet switched network.
Actually the 4G system should dynamically share and utilize the network resources to meet the
requirements of all the 4G enabled users. The principal design techniques to be exploited in 4G mobile
wireless networks are [4], [5], [6], [7]:
Adaptive radio interface
Modulation, spatial processing including multi-antenna and multi-user Multiple Input/Multiple Output
(MIMO) to attain ultra high spectral efficiency
Multiple access to exploit the frequency selective channel property
Turbo principle to minimize the required SNR at the reception side
Relaying, including fixed relay networks (FRNs), and the cooperative relaying concept, known as
multi-mode protocol
According to the 4G working groups, the infrastructure and the terminals of 4G will have almost all
the standards from 2G to 4G implemented. Although legacy systems are in place to adopt existing users, the
infrastructure for 4G will be only packet-based (all-IP). Some proposals suggest having an open internet
platform. With the wireless standards evolution, the access techniques used also increased in efficiency, capacity
and scalability. The first generation wireless standards used plain Time division Multiple Access (TDMA) and
Frequency Division Multiple Access (FDMA). In the wireless channels, TDMA is less efficient in handling the
high data rate channels because it requires large guard periods to alleviate the multipath impact. Again, FDMA
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2. Multiple Access Techniques For 4G Mobile Wireless Networks
consumes more bandwidth for guards for avoiding inter carrier interference. So two branches came in second
generation systems, one branch of standard used the combination of FDMA and TDMA and the other
introduced a new access scheme called Code Division Multiple Access (CDMA) [8]. Usage of CDMA increased
the system capacity. Data rate is also increased as CDMA is efficient to handle the multipath channel. This
enabled the third generation systems to use CDMA as the access scheme of IS-2000, UMTS, HSXPA, 1xEV-
DO, TD-CDMA and TD-SCDMA. The only issue with CDMA is that it suffers from poor spectrum flexibility
and scalability. Recently, new access schemes like Orthogonal Frequency Division Multiple Access (OFDMA),
Single Carrier FDMA (SC-FDMA), Interleaved FDMA (IFDMA) and Multi-carrier CDMA (MC-CDMA) are
gaining more importance for the next generation systems. WiMax uses OFDMA in the downlink and in the
uplink [9]. For the next generation UMTS, OFDMA is being considered for the downlink. By contrast, IFDMA
is being considered for the uplink since OFDMA contributes more to the Peak-to-Average Power Ratio (PAPR)
related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus
avoids amplifier issues. Similarly, MC-CDMA is in the proposal for the IEEE 802.20 standard. The advantages
of these access schemes are that they offer the same efficiencies as older technologies like CDMA, scalability
and higher data rates but they require less complexity for equalization at the receiver. This is an added
advantage especially in the MIMO environments as the spatial multiplexing transmission of MIMO systems
requires high complexity equalization at the receiver. With these advantages in these multiplexing systems,
improved modulation techniques are also used. At the present data rates of 15-30 Mbit/s, 4G is capable of
providing users with streaming high-definition television. At rates of 100 Mbit/s, the content of a DVD-5 (for
example a movie), can be downloaded within about 5 minutes for offline access [10]. The rest of the paper is
organized as follows. Section II provides descriptions of several multiple access schemes for 4G mobile wireless
networks. Section III provides a comparative performance analysis of the above schemes vis-àvis design
parameters of 4G mobile wireless networks viz., throughput, Access scheme, Bit Error Rate (BER), Intersymbol
Interference (ISI), equalization, Bandwidth and security issues. Simulation results of implementing CDMA and
OFDMA channel access schemes in MATLAB, is provided in section IV. Section V concludes the paper with
some highlights on future work.
II. MULTIPLE ACCESS SCHEMES FOR 4G MOBILE WIRELESS NETWORKS
A. FDMA
FDMA gives users an individual allocation of one or several frequency bands, or channels. It is a basic
technology in the analog Advanced Mobile Phone Service (AMPS), the most widely-installed cellular phone
system installed in North America. With FDMA, each channel can be assigned to only one user at a time.
FDMA is also used in the Total Access Communication System (TACS). The Digital-Advanced Mobile Phone
Service (D-AMPS) also uses FDMA but adds TDMA to get three channels for each FDMA channel, tripling the
number of calls that can be handled on a channel. The use of frequency division multiplexing is to provide
multiple and simultaneous transmissions to a single transponder. In FDMA, each transmitter is assigned a
distinct frequency channel so that receivers can discriminate among them by tuning to the desired channel.
TDMA and CDMA are always used in combination with FDMA, i.e., a given frequency channel may be used
for either TDMA or CDMA independently of signals on other frequency channels. In 1989, the Cellular
Telecommunications Industry Association (CTIA) chose TDMA over Motorola’s FDMA (today known as
narrowband analog mobile-phone service [NAMPS]) narrowband standard as the technology of choice for
existing 800 MHz cellular markets and for emerging 1.9 GHz markets. Crosstalk is a major limitation of
FDMA, which causes interference between the other frequency bands and disturbs the transmission. The
features of FDMA are as follows.
• FDMA requires high-performing filters in the radio hardware, in contrast to TDMA and CDMA.
• FDMA is not vulnerable to timing problems like TDMA. Since a predetermined frequency band is available
for the entire period of communication, stream data can easily be used with FDMA.
• As frequency filtering is there, FDMA is not sensitive to near-far problem which we get in CDMA.
• There is different frequency slot for every user transmission and reception happens at different frequencies.
There is a difference between FDMA and frequency-division duplexing (FDD). While FDMA allows
multiple users to simultaneously access a certain system, FDD refers to how the radio channel is shared between
the uplink and downlink (for instance, the traffic going back and forth between a mobilephone and a base-
station). Again, Frequency Division Multiplexing (FDM) is different from FDMA. FDM is a physical layer
technique that combines and transmits low bandwidth channels through a high-bandwidth channel. FDMA, on
the other hand, is an access method in the data link layer [11]. Low PAPR and low sensitivity to carrier
frequency offset are some of the useful properties of FDMA. A hybrid system may be formed by combining
TDMA and FDMA.
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3. Multiple Access Techniques For 4G Mobile Wireless Networks
B. TDMA
TDMA is a channel access method for shared medium networks. It allows several users to share the
same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession,
one after the other, each at his time slot. This allows multiple stations to share the same transmission medium
(e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G
cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular
(PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable
phones. It is also used extensively in satellite systems, and combat-net radio systems. TDMA is a method used
to enable multiple earth stations or VSAT terminals to transmit intermittently on the same frequency, but with
the timing of their transmissions so arranged that the bursts do not overlay when they arrive at the satellite but
arrive in sequence and thus are all successfully received by the teleport hub modem burst demodulator. The
operation of TDMA requires an out link control to all the remote sites which contains some control information.
This out link carrier also had a frame structure that provides accurate timing information for all the remote sites.
The teleport hub equipment computer tells each VSAT site what particular time slot to use in the TDMA frame
and this time plan information is broadcast to all sites periodically. The burst time plan may be fixed, so as to
allocate each site a particular proportion of the total TDMA frame time or is may be dynamic, whereby the time
slot allocated is adjusted in response to the traffic needs of each site [12]. Fig.1 shows the TDMA frame
structure where a data stream is divided into frames and those frames divided into time slots. TDMA is a type of
time-division multiplexing, with the special point that instead of having one transmitter connected to one
receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this
becomes particularly difficult because the mobile phone can move around and vary the timing advance required
to make its transmission match the gap in transmission from its peers. The features of TDMA are as follows.
• Shares single carrier frequency with multiple users
• Non-continuous transmission makes handoff simpler
• Slots can be assigned on demand in dynamic TDMA
• Less stringent power control than CDMA due to reduced intra cell interference
• Higher synchronization overhead than CDMA
• Advanced equalization may be necessary for high data rates if the channel is "frequency selective" and creates
Inter symbol interference
• Cell breathing (borrowing resources from adjacent cells) is more complicated than in CDMA
• Frequency/slot allocation complexity
• Pulsating power envelop: Interference with other devices
Fig. 1 TDMA Frrame Structure
TDMA can also be dynamic in nature. In dynamic TDMA, a scheduling algorithm dynamically
reserves a variable number of time slots in each frame to variable bit-rate data streams, based on the traffic
demand of each data stream. applications.HIPERLAN/2 broadband radio access network, IEEE 802.16a
WiMax, Bluetooth, Packet Radio Multiple Access (PRMA) method for combined circuit switched voice
communication and packet data, TD-SCDMA, ITU-T are some of the application areas of Dynamic TDMA.
C. CDMA
CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is
assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, TDMA
divides access by time, while FDMA divides it by frequency. CDMA is a form of "spreadspectrum" signaling,
since the modulated coded signal has a much higher data bandwidth than the data being communicated. CDMA
has been widely used in mobile phones and in satellite system for transportation logistics. The scheme of
CDMA is briefly described below. CDMA uses the spread spectrum technique, which spreads the bandwidth of
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4. Multiple Access Techniques For 4G Mobile Wireless Networks
the data uniformly for the same transmitted power. Spreading code is a pseudo-random code which has a narrow
ambiguity function unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher
rate than the data to be transmitted. Data for transmission is simply logically XOR (exclusive OR) added with
the faster code. The figure shows how spread spectrum signal is generated. The data signal with pulse duration
of Tb is XOR added with the code signal with pulse duration of Tc. (Note: bandwidth is proportional to 1 / T
where T = bit time) Therefore, the bandwidth of the data signal is 1 / Tb and the bandwidth of the spread
spectrum signal is 1 / Tc. Since Tc is much smaller than Tb, the bandwidth of the spread spectrum signal is
much larger than the bandwidth of the original signal. The ratio Tb / Tc is called spreading factor or processing
gain and determines to certain extent the upper limit of total number of users supported simultaneously by a
base station. Fig. 2 shows the frame structure of CDMA. Each user in a CDMA system uses a different code to
modulate their signal. Choosing the codes used to modulate the signal is very important in the performance of
CDMA systems. The best performance will occur when there is good separation between the signal of a desired
user and the signals of other users.
Fig. 2 CDMA Frame Structure
The separation of the signals is made by correlating the received signal with the locally generated code
of the desired user. If the signal matches the desired user's code then the correlation function will be high and
the system can extract that signal. If the desired user's code has nothing in common with the signal the
correlation should be as close to zero as possible (thus eliminating the signal); this is referred to as cross
correlation. If the code is correlated with the signal at any time offset other than zero, the correlation should be
as close to zero as possible. This is referred to as auto-correlation and is used to reject multi-path interference.
Flexible allocation of resources and privacy protection in due to antijamming capabilities of PN sequences are
some of the advantages of CDMA. Fig.3 shows 3-D representation of FDMA, TDMA/FDMA hybrid and
CDMA. FDMA shows that each narrow band channel is allocated to a single user; FDMA/TDMA hybrid shows
that the bandwidth is split into frequency channels and time slots; CDMA shows that each user is allocated a
different code in same frequency and time slot.
FDMA TDMA/FDMA Hybrid CDMA
Fig 3 3D Representation of Access Schemes
There are basically two types of CDMA: single carrier CDMA and multicarrier CDMA.
a) Single Carrier CDMA
Fig.4 shows the general structure of a single carrier transmission system. The transmitted symbols are
pulse formed by a transmitter filter. After passing the multipath channel in the receiver a filter matched to the
channel is used to maximize signal to noise ratio and the device used to extract the data. The scenario we are
dealing with is Digital Video Broadcasting-Terrestrial (DVB-T), which is characterized by the following
conditions [13]:
Transmission Rate: R =1/T = 7.4 M sym/s
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5. Multiple Access Techniques For 4G Mobile Wireless Networks
Maximum channel delay: τmax = 224 μs
ISI [14] : max /T 1600
b) Multi Carrier CDMA
The complexity involved in removing the interference in the receiver of single carrier CDMA is
tremendous. Using the approach in Fig.4 will only lead to sub-optimal results. This is the main reason why the
multi carrier approach shown in Fig.5 has become so popular. The original data stream of rate R is multiplexed
into N parallel data streams of rate Rmc = 1/ Tmc = R/N. Each of the data streams is modulated with a different
frequency and the resulting signals are transmitted together in the same band. Correspondingly the receiver
consists of N parallel receiver paths. Due to the prolonged distance in between transmitted symbols, the ISI for
each sub system reduces to tmax / Tmc = tmax / N*T. In the case of DVB-T we have N=8192 leading to an ISI
of tmax / Tmc = 0.2. Such little ISI can often be tolerated and no extra counter measure such as an equalizer is
needed. But as far as the complexity of a receiver is concerned a system with 8192 parallel paths still isn't
feasible. This asks for a slight modification of the approach which leads us to the concept of OFDM.
Fig. 5 Multi Carrier CDMA
D. OFDMA
OFDMA is a multi-user version of the popular OFDM digital modulation scheme. For achieving
multiple accesses subsets of subcarriers are provided to the individual users in OFDMA. This allows
simultaneous low data rate transmission from several users. OFDMA is also a candidate access method for the
IEEE 802.22 Wireless Regional Area Networks (WRAN). The project aims at designing the first cognitive radio
based standard operating in the VHF-low UHF spectrum (TV spectrum) [15]. FDMA also supports demand
assignment with fixed assignment. Demand assignment allows all users apparently continuous access of the
radio spectrum by assigning carrier frequencies on a temporary basis using a statistical assignment process.
Single-carrier FDMA (SC-FDMA) is a kind of FDMA scheme, which is basically a multi-user version of
Single-carrier Frequency-Domain-Equalization (SC-FDE) modulation scheme [16]. SC-FDE can be viewed as a
linearly precoded OFDM scheme, and SC-FDMA can as a linearly precoded OFDMA scheme, henceforth LP-
OFDMA. It can also be viewed as a single carrier multiple access scheme. One prominent advantage over
conventional OFDM and OFDMA is that the SC-FDE and LP-OFDMA/SC-FDMA signals have lower peak-to-
average power ratio (PAPR) because of its inherent single carrier structure [17].
A. Characteristics
Based on feedback information about the channel conditions, adaptive user-to-subcarrier assignment
can be achieved. If the assignment is done sufficiently fast, this further improves the OFDM robustness to fast
fading and narrow-band co channel interference, and makes it possible to achieve even better system spectral
efficiency. Different number of sub-carriers can be assigned to different users, for supporting different Quality
of Service (QoS), i.e. to control the data rate and error probability individually for each user. OFDMA resembles
CDMA spread spectrum, where users can achieve different data rates by assigning a different code spreading
factor or a different number of spreading codes to each user. OFDMA can be seen as an alternative to
combining OFDM with TDMA or time-domain statistical multiplexing, i.e. packet Mode communication. Low-
data-rate users can send continuously with low transmission power instead of using a "pulsed" high-power
carrier. Constant delay, and shorter delay, can be achieved. In OFDMA, the resources are partitioned in the
timefrequency space, and slots are assigned along the OFDM symbol index as well as OFDM sub-carrier index.
OFDMA is considered as highly suitable for broadband wireless networks, due to advantages including
scalability and MIMO friendliness, and ability to take advantage of channel frequency selectivity. In spectrum
sensing cognitive radio, OFDMA is a possible approach to filling free radio frequency bands adaptively.
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6. Multiple Access Techniques For 4G Mobile Wireless Networks
B. Principle of Operation
OFDM is a subset of FDM in which a single channel utilizes multiple sub-carriers on adjacent
frequencies. In addition the sub-carriers in an OFDM system are overlapping to maximize spectral efficiency.
Ordinarily, overlapping adjacent channels can interfere with one another. However, sub-carriers in an OFDM
system are precisely orthogonal to one another. Thus, they are able to overlap without interfering. Two
conditions must be considered for the orthogonality between the subcarriers [15].
1. Each subcarrier has exactly an integer number of cycles in the FFT interval.
2. The number of cycles between adjacent subcarriers differs by exactly one.
C. Orthogonality of Sub-Channel Carriers
OFDM communications systems are able to more effectively utilize the frequency spectrum through
overlapping subcarriers. These sub-carriers are able to partially overlap without interfering with adjacent sub-
carriers because the maximum power of each sub-carrier corresponds directly with the minimum power of each
adjacent channel. OFDM channels are different from band limited FDM channels how they apply a pulse-
shaping filter. With FDM systems, a sinc-shaped pulse is applied in the time domain to shape each individual
symbol and prevent ISI. With OFDM systems, a sinc-shaped pulse is applied in the frequency domain of each
channel. As a result, each sub-carrier remains orthogonal to one another.
D. Transmitter/Receiver
In order to use multiple sub-carriers to transmit an individual channel, an OFDM communications
system must perform several steps, described in Fig.6.
Fig. 6 OFDM Communication System
1. Serial to Parallel Conversion - In an OFDM system, each channel can be broken into various sub-carriers.
The use of sub-carriers makes optimal use out of the frequency spectrum but also requires additional processing
by the transmitter and receiver. This additional processing is necessary to convert a serial bit stream into several
parallel bit streams to be divided among the individual carriers. Once the bit stream has been divided among the
individual sub-carriers, each sub-carrier is modulated as if it was an individual channel before all channels are
combined back together and transmitted as a whole. The receiver performs the reverse process to divide the
incoming signal into appropriate sub-carriers and then demodulating these individually before reconstructing the
original bit stream.
2. Modulation with the Inverse FFT - The modulation of data into a complex waveform occurs at the Inverse
Fast Fourier Transform (IFFT) stage of the transmitter. Here, the modulation scheme can be chosen completely
independently of the specific channel being used and can be chosen based on the channel requirements. In fact,
it is possible for each individual sub-carrier to use a different modulation scheme. The role of the IFFT is to
modulate each sub-channel onto the appropriate carrier.
3. Cyclic Prefix Insertion - Wireless communications systems are susceptible to multi-path channel reflections; a
cyclic prefix is added to reduce ISI. A cyclic prefix is a repetition of the first section of a symbol that is
appended to the end of the symbol. In addition, it is important because it enables multipath representations of
the original signal to fade so that they do not interfere with the subsequent symbol. Fig.7 shows the block
diagram of Cyclic Prefix Insertion
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7. Multiple Access Techniques For 4G Mobile Wireless Networks
.
Fig. 7 Cycle Prefix Insertion
4. Parallel to Serial Conversion - Once the cyclic prefix has been added to the sub-carrier channels, they must
be transmitted as one signal. Thus, the parallel to serial conversion stage is the process of summing all sub-
carriers and combining them into one signal. As a result, all subcarriers are generated perfectly simultaneously.
Several common commercial protocols, such as DVB, asymmetric digital subscriber line (ADSL), and wireless
Ethernet (WiFI) implement OFDM. With WiFI, the IEEE 802.11a and IEEE 802.11g implementations
specifically use
OFDM techniques. With IEEE 802.11g, each channel occupies 16.25 MHz of bandwidth at the 2.4GHz
frequency range. In addition, each channel is divided into 52 sub-carriers of 312.5 kHz. Together, these sub-
carriers overlap to fully utilize the 16.25 MHz channel bandwidth dedicated per channel. In addition, each sub-
carrier can use a unique modulation scheme. More specifically, WiFI can use BPS, QPSK, 16-QAM, or 64-
QAM depending on the characteristics
of the physical channel being used. One of the newest wireless internet protocols, WiMAX, also used OFDM
technology.
III. PERFORMANCE ANALYSIS
Several parameters are considered here for the comparative performance analysis of the above schemes
vis-à-vis design parameters of 4G mobile wireless networks.
• Throughput: In communication networks, throughput or network throughput is the average rate of successful
message delivery over a communication channel. This data may be delivered over a physical or logical link, or
pass through a certain network node.
• Access Scheme: In telecommunications and computer networks, a channel access method or multiple access
method allows several terminals connected to the same multi-point transmission medium to transmit over it and
to share its capacity. Examples of shared physical media are wireless networks, bus networks, ring networks,
hub networks and half-duplex point-to-point links. A channel-access scheme is based on a multiplexing method,
which allows several data streams or signals to share the same communication channel or physical medium.
• Delay: In a network based on packet switching, transmission delay is the amount of time required to push all
of the packet's bits into the wire. In other words, this is the delay caused by the data-rate of the link.
Transmission delay is a function of the packet's length and has nothing to do with the distance between the two
nodes. This delay is proportional to the packet's length in bits, It is given by the following formula: DT = N / R
where DT is the transmission delay N is the number of bits, and R is the rate of transmission (say in bits per
second)
• Bandwidth: Bandwidth is the difference between the upper and lower frequencies in a contiguous set of
frequencies. It is typically measured in hertz, and may sometimes refer to passband bandwidth, sometimes to
baseband bandwidth, depending on context.
• Dynamic Power Management: Dynamic power management is a design methodology aiming at controlling
performance and power levels of digital circuits and systems, with the goal of extending the autonomous
operation time of battery powered systems, providing graceful performance degradation when supply energy is
limited, and adapting power dissipation to satisfy environmental constraints.
• BER: In digital transmission, the number of bit errors is the number of received bits of a data stream over a
communication channel that has been altered due to noise, interference, distortion or bit synchronization errors.
It is the number of bit errors divided by the total number of transferred bits during a studied time interval.
• ISI: In telecommunication, inter symbol interference (ISI) is a form of distortion of a signal in which one
symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have
similar effect as noise, thus making the communication less reliable
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8. Multiple Access Techniques For 4G Mobile Wireless Networks
• Equalization: It is the process of adjusting the volume of certain frequencies within a signal.
• Security: Communications security is the discipline of preventing unauthorized interceptors from accessing
telecommunications in an intelligible form, while still delivering content to the intended recipients
• PAPR: The peak-to-average power ratio (PAPR) is a measurement of a waveform, calculated from the peak
amplitude of the waveform divided by the RMS value of the waveform. Table I gives a comparative
performance analysis of FDMA, TDMA, CDMA and OFDMA with respect to these design parameters.
IV. SIMULATION RESULTS
This section provides the simulation results of implementing two different channel access schemes in
MATLAB. Our simulation is restricted to OFDMA as this technology surpass the other two technologies viz.,
FDMA and TDMA in terms of different network parameters for 4G mobile wireless networks as seen from
Table I. Fig. 8 show the frequency response characteristics of OFDMA signals as simulated in MATLAB.
Parameters FDMA TDMA CDMA OFDMA
Throughput Low Low Moderate High
Access Scheme Uses Frequency Uses Time Slots Uses Spread Uses Frequency
Slots Spectrum Selective
Channel
Delay Short Increases with Substantial Constant and
Users Shorter
Allocated 12.5 MHz 12.5 MHz 12.5 MHz 12.5 MHz
Bandwidth
Required .03 MHz .03 MHz 1.25 MHz 1.25 MHz-20
Channel MHz
Bandwidth
Dynamic No Yes Yes Yes
Bandwidth
Allocation
Dynamic Power No No Yes Yes
Management
BER High High Lower Lower
ISI Low Low Mitigated Absent
Calls/RF Channel 4 1 40 200
Table I Comparative Analysis
Fig 8 Frequency Response Characteristics of OFDMA Signal
V. CONCLUSION
Table I shows that OFDMA surpasses all the other schemes in terms of various parameters. So it is the
right choice of multiple channel access schemes for 4G mobile wireless networks. However in spite of all the
utilities of OFDMA, there are certain obstacles in using OFDM in transmission system in contrast to its
advantages. Firstly OFDM signal exhibits a very high PAPR. Therefore, RF power amplifiers should be
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9. Multiple Access Techniques For 4G Mobile Wireless Networks
operated in a very large linear region. Otherwise, the signal peaks get into non-linear region of the power
amplifier causing signal distortion. This signal distortion introduces inter modulation among the subcarriers and
out of band radiation. Thus, the power amplifiers should be operated with large power back-offs. On the other
hand, this leads to very inefficient amplification and expensive transmitters. Thus, it is highly desirable to
reduce the PAPR. Secondly it is very sensitive to frequency errors caused by frequency differences between the
local oscillators in the transmitter and the receiver. Hence carrier frequency offset causes a number of
impairments including attenuation and rotation of each of the subcarriers and ICI between subcarriers. In the
mobile radio environment, the relative
Movement between transmitter and receiver causes Doppler frequency shifts; in addition, the carriers
can never be perfectly synchronized. These random frequency errors in OFDM system distort orthogonality
between subcarriers and thus ICI occurs. A Number of methods have been developed to reduce this sensitivity
to frequency offset. Thirdly asynchronous data communication services such as web access are characterized by
short communication bursts at high data rate. Few users in a base station cell are transferring data
simultaneously at low constant data rate. Fourthly dealing with co-channel interference from nearby cells is
more complex in OFDM than in CDMA. It would require dynamic channel allocation with advanced
coordination among adjacent base stations.
REFERENCES
[1]. http://en.wikipedia.org/wiki/Channel_access_method
[2]. http://en.wikipedia.org/wiki/4G
[3]. Willie W Lu “4G Mobile research in Asia”, IEEE Communications Magazine, March 2003
[4]. www.telenor.com/telektronikk/Oien_Beyond3G.pdf
[5]. [MOBICOM 2005] R. Chakravorty, S. Agarwal, S. Banerjee and I. Pratt, MoB: A Mobile Bazaar for
Wide-area Wireless Services", Proceedings of ACM Mobicom, Sep. 2005.
[6]. R. Chakravorty, S. Banerjee, P. Rodriguez, J. Chesterfield and I. Pratt, Performance Optimizationsfor
Wireless Wide-area Networks: Comparative Study and Exp. Evaluation", Proceedings of ACM
Mobicom, 2004
[7]. R. Chakravorty, A. Clark and I. Pratt, GPRSWeb: Optimizing the Web for GPRS Links", Proceedings
of ACM Mobisys, 2003
[8]. Shihua Zhu and Jon W. Mark,``An Exposition on Third Generation CDMA
[9]. www.itr-rescue.org/bin/pubdocs/mtg-weekly/9-16-05 Intel_WiMAX_White_Paper (Hassib).pdf
[10]. http://burgami.com/4g
[11]. “Underwater Acoustic Networks” Ethem M. Sozer, Milica Stojanovic, and John G. Proakis, Life
Fellow, IEEE IEEE JOURNAL OF OCEANIC ENGINEERING, VOL. 25, NO. 1, JANUARY 2000
[12]. www.satsig.net/vsat-equipment/tdma-explanation.htm
[13]. http://en.wikipedia.org/wiki/DVB-T
[14]. http://en.wikipedia.org/wiki/Intersymbol_interference.
[15]. Hujun Yin and Siavash Alamouti (August 2007). "OFDMA: A Broadband Wireless Access
Technology". IEEE Sarnoff Symposium, 2006 (IEEE): pp. 1–4. doi:10.1109/SARNOF.2006.4534773
[16]. http://en.wikipedia.org/wiki/4G
[17]. http://en.wikipedia.org/wiki/Single-carrier_FDMA
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