29 research outputs found
Recommended from our members
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
A Quantitative Assessment of the Compatibility of Ultra Wideband with Broadband Wireless Access and Radar Services
In July 2008, following a request made by the Radio Spectrum Policy Unit in DG INFSO (Unit B4), a pilot phase of twelve months was agreed with Member States representatives in the Radio Spectrum Committee. During this time the Institute for the Protection and Security of the Citizen of the EC Joint Research Centre (IPSC-JRC) has been mandated to provide testing facilities to support the development of Community spectrum legal measures under the Radio Spectrum Decision (676/2002/EC). In the frame of this pilot phase, IPSC-JRC has successfully completed the implementation and extensive testing of both a state-of-the-art laboratory test-bed and a simulation tool, which have been specifically designed for two different coexistence studies. Firstly, the coexistence between broadband wireless access (BWA) and ultra wideband (UWB) services in the 3.5 GHz frequency band; and secondly, the coexistence between radiolocation (i.e. radar) and UWB services in the 3.1-3.4 GHz frequency band. The selection of these two coexistence scenarios is not casual and has been made based on the fact that they have been considered highly relevant in the CEPT-ECC studies on UWB mandated by the European Commission.JRC.G.6-Security technology assessmen
A Novel Seed Based Random Interleaving for OFDM System and Its PHY Layer Security Implications
Wireless channels are characterized by multipath and fading that can often cause long
burst of errors. Even though, to date, many very sophisticated error correcting codes have
been designed, yet none can handle long burst of errors efficiently. An interleaver, a
device that distributes a burst of errors, possibly caused by a deep fade, and makes them
appear as simple random errors, therefore, proves to a very useful technique when used in
conjunction with an efficient error correcting code.
In this work, a novel near optimal seed based random interleaver is designed. An optimal
interleaver scatters a given burst of errors uniformly over a fixed block of data - a
property that is measured by so called âspreadâ. The design makes use of a unique seed
based pseudo-random sequence generator or logistic map based chaotic sequence
generator to scramble the given block of data. Since the proposed design is based on a
seed based scrambler, the nature of input is irrelevant. Therefore, the proposed interleaver
can interleave either the bits or the symbols or the packets or even the frames.
Accordingly, in this work, we analyze the suitability of interleaver when introduced
before or after the modulation in single carrier communication systems and show that
interleaving the bits before modulation or interleaving the symbols after modulation has
same advantage. We further show that, in an orthogonal frequency division multiplexing
(OFDM) systems, the position of interleaver, whether before or after constellation
mapper, has no significance, and is interchangeable. However, scrambling symbols is
computationally less expensive than scrambling bits.
For the purpose of analyzing the performance of the proposed seed based random
interleaver, simulations are carried out in MATLABÂŽ. Results show that our proposed
seed based random interleaver has near optimal properties of âspreadâ and âdispersionâ.
Furthermore, the proposed interleaver is evaluated in terms of bit error rate (BER) versus
length of burst error in a single carrier system both before and after modulation. The
proposed interleaver out-performs the built in RANDINTLV in MATLABÂŽ when used in
the same system. It shows that proposed interleaver can convert greater amount of burst
errors into simple random errors than that of MATLABÂŽ interleaver. The proposed
interleaver is also tested in IEEE 802.16e based WiMAX system with Stanford University Interim (SUI) channels to compare the performance of average BER versus
SNR for both pre modulation and post modulation interleaver. Results show that pre
modulation interleaver and post modulation has same performance.
There is also a side advantage of this seed based interleaver, in that it generates a variety
of unique random-looking interleaving sequences. Only a receiver that has the knowledge
of the input seed can generate this sequence and no one else. If the interleaving patterns
are kept secure then it can possibly be used to introduce an extra layer of security at
physical (PHY) layer. In that way, at PHY layer, one builds an additional entry barrier to
break through and it comes with no extra cost. This property has been investigated by
carrying out key sensitivity analysis to show that the attacks to guess key can be very
futile, as difference at 4th decimal place in the initial condition can lead to entirely
different scrambling
Chicken Swarm Optimization for PTS based PAPR Reduction in OFDM Systems
Partial transmit sequence (PTS) is a well-known
PAPR reduction scheme for the OFDM system. One of the major
challenge of this scheme is to find an optimal phase vector using
exhaustive search over all the allowed phase factor combinations.
This leads to increased search complexity which grows
exponentially as the number of sub-blocks is increased. In this
paper, chicken swarm optimization (CSO) based PTS system is
designed that aims to find an optimal solution in less number of
average iterations and therefore results in reduced computational
complexity of the system. We have proposed two categories of the
algorithm: (i) CSO-PTS system without threshold limit on PAPR
(ii) CSO-PTS system with threshold limit on PAPR. Both the
schemes offer effective trade-offs between the computational
complexity and the PAPR reduction capability of the system.
Simulation results confirm that our proposed schemes perform
well in terms of low computational complexity, lesser number of
average iterations and improved PAPR reduction capability of
the OFDM signal without any loss in BER performance of the
system