346 research outputs found
A Cross Layer Routing Protocol for OFDMA Based Mobile Ad Hoc Networks.
PhDMobile ad hoc networks are of growing interest because of their unique characteristics
and advantages in many practical applications. QoS provision acts as a major challenge
in the routing protocol design in the real-world mobile ad hoc networks, especially for
the real-time services. OFDM is a new technology which has many advantages over the
other modulation schemes. Because of its prominent features, many popular wireless
standards have adopted it as physical layer modulation, such as IEEE 802.11 series,
WiMAX, 3GPP LTE etc, and it is extended to multiuser environment known as OFDMA.
So far none of the existing ad hoc routing protocols fully account for the OFDMA based
mobile ad hoc networks. In this thesis, a QoS routing protocol is proposed for OFDMA
based mobile ad hoc networks. A signal strength-based sub-channel allocation scheme is
proposed in the routing protocol aiming to reduce the signalling overhead and cochannel
interference. The performance of the proposed routing protocol is compared
with other alternative proposals through simulations using OPNET simulator. Moreover,
a partial time synchronization and a null subcarrier based frequency synchronization
algorithms are also proposed for OFDMA based ad hoc network to further support and
facilitate the proposed sub-channel allocation scheme and routing protocol
Comparative Analysis between OFDMA and SC-FDMA: Model, Features and Applications
This paper represents Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SCFDMA) techniques along with the Orthogonal Frequency Division Multiplexing (OFDM). The concept, model, features, scopes, applications and limitation for both types of multiple access have been discussed in this paper. In present 4G and 5G cellular communication system, both OFDMA and SC-FDMA have a notable applications. Dividing the available spectrum into overlapping orthogonal narrowband sub bands, OFDMA ensures high spectral efficiency. Besides by allocating multiple sub carriers to each user, OFDMA provides high data rate, reduces inter blockage interference, minimizes frequency selective fading and so on. But it suffers from high peak to average power ration (PAPR) which results in high power consumption at the transmitter end. SC-FDMA is one of the most promising techniques to solve the PAPR problems. Besides it also removes the capacity problem of wireless cellular systems and provides higher spectral efficiency, depending on multiplexing signals based on their spatial signature. On the other hand, in OFDM due to fixed subcarrier allocations for each user and its performance can suffer from narrowband fading and interference
A Link Quality Model for Generalised Frequency Division Multiplexing
5G systems aim to achieve extremely high data rates, low end-to-end latency
and ultra-low power consumption. Recently, there has been considerable interest
in the design of 5G physical layer waveforms. One important candidate is
Generalised Frequency Division Multiplexing (GFDM). In order to evaluate its
performance and features, system-level studies should be undertaken in a range
of scenarios. These studies, however, require highly complex computations if
they are performed using bit-level simulators. In this paper, the Mutual
Information (MI) based link quality model (PHY abstraction), which has been
regularly used to implement system-level studies for Orthogonal Frequency
Division Multiplexing (OFDM), is applied to GFDM. The performance of the GFDM
waveform using this model and the bit-level simulation performance is measured
using different channel types. Moreover, a system-level study for a GFDM based
LTE-A system in a realistic scenario, using both a bit-level simulator and this
abstraction model, has been studied and compared. The results reveal the
accuracy of this model using realistic channel data. Based on these results,
the PHY abstraction technique can be applied to evaluate the performance of
GFDM based systems in an effective manner with low complexity. The maximum
difference in the Packet Error Rate (PER) and throughput results in the
abstraction case compared to bit-level simulation does not exceed 4% whilst
offering a simulation time saving reduction of around 62,000 times.Comment: 5 pages, 8 figures, accepted in VTC- spring 201
Software Implementation of Orthogonal Frequency Division Multiplexing (OFDM)Scheme for Mobile Radio Channel
Orthogonal Frequency Division Multiplexing (OFDM) is a transmission technique which ensures efficient utilization of the spectrum by allowing overlap of carriers. OFDM is a combination of modulation and multiplexing that is used in the transmission of information and data. Compared with the other wireless transmission techniques like Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), OFDM has numerous advantages like high spectral density, its robustness to channel fading, its ability to overcome several radio impairment factors such as effect of AWGN, impulse noise, multipath fading, etc. Due to this it finds wide application in Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), and Wireless LAN. Most of the wireless LAN standards like IEEE 802.11a or IEEE 802.11g use the OFDM as the main multiplexing scheme for better use of spectrum. In fact in the 4G telecommunication system OFDMA is the backbone of it.
This project deals with the software simulation of this OFDM system in a mobile radio channel using the software tools of MATLAB® and SIMULINK®. From this simulation the performance of OFDM system in mobile radio channel is studied. Apart from this we also compare the OFDM system performance with the performance of the DS-CDMA system in the mobile radio channel
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Performance evaluation of fixed WiMax physical layer under high fading channels
This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.A radio channel characteristic modelling is essential in every network planning. This project deals with the performance of WiMax networks in an outdoor environment while using fading channel models. The radio channels characteristics are analyzed by simulations have been done using Matlab programming. Stanford University Interim(SUI) Channels set was proposed to simulate the fixed broadband wireless access channel environments where IEEE 802.16d is to be deployed. It has six channel models that are grouped into three categories according to three typical different outdoor Terrains, in order to give a comprehensive study of fading channels on the overall performance of the system, WiMax system has been tested under SUI channels that modified into account for 30o directional antennas, with 90% cell coverage and with 99.9% reliability in its geographical covered area. Furthermore, in order to combat the fading which occurs in urban areas and improve the capacity and the throughput of the system, multiples antennas at both ends of communication link are used, the transmission gain obtained when using multiple antennas instead of only a single antenna. Space-time coding and maximum ratio combining for more than one transmit and receive antenna is implemented to allow performance investigations in various MIMO scenarios. It has been concluded that uses multiple antennas at the receiver offers a significant improvement of 3 dB of gain in the channel SNR. This thesis also contain implementation of all compulsory features of the WiMax OFDM physical layer specified in IEEE 802.16-2004 using Matlab coding. In order to combat the temporal variations in quality on a multipath fading channel, an adaptive modulation technique is used. This technique employs multiple modulation schemes to instantaneously adapt to the variations in the channel SNR, thus maximizing the system throughput and improving BER performance. WiMax transceiver has been tested with and without encoding and studied the effect of encoding on multipath channel. Testing the system with flexible channel bandwidth has been part of this thesis. Finally it has been explained in this thesis the affect of increasing the size of cyclic prefix on overall performance of WiMax system
PROCESS FOR BREAKING DOWN THE LTE SIGNAL TO EXTRACT KEY INFORMATION
The increasingly important role of Long Term Evolution (LTE) has increased security concerns among the service
providers and end users and made security of the network even more indispensable. The main thrust of this thesis is to
investigate if the LTE signal can be broken down in a methodical way to obtain information that would otherwise be
private; e.g., the Global Positioning System (GPS) location of the user equipment/base station or identity (ID) of the
user. The study made use of signal simulators and software to analyze the LTE signal to develop a method to remove
noise, breakdown the LTE signal and extract desired information. From the simulation results, it was possible to
extract key information in the downlink like the Downlink Control Information (DCI), Cell-Radio Network
Temporary Identifier (C-RNTI) and physical Cell Identity (Cell-ID). This information can be modified to cause
service disruptions in the network within a reasonable amount of time and with modest computing resources.Defence Science and Technology Agency, SingaporeApproved for public release; distribution is unlimited
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