712 research outputs found
Channel estimation and tracking algorithms for vehicle to vehicle communications
The vehicle-to-vehicle (V2V) communications channels are highly time-varying, making reliable communication difficult. This problem is particularly challenging because the standard of the V2V communications (IEEE 802.11p standard) is based on the WLAN IEEE 802.11a standard, which was designed for indoor, relatively stationary channels; so the IEEE 802.11p standard is not customized for outdo or, highly mobile non-stationary channels. In this thesis,We propose Channel estimation and tracking algorithms that are suitable for highly-time varying channels. The proposed algorithms utilize the finite alphabet property of the transmitted symbol, time domain truncation, decision-directed as well as pilot information. The proposed algorithm s improve the overall system performance in terms of bit error rates, enabling the system to achieve higher data rates and larger packet lengths at high relative velocities. Simulation results show that the proposed algorithms achieve improved performance for all the V2V channel models with different velocities, and for different modulation schemes and packet sizes as compared to the conventional least squares and other previously proposed channel estimation techniques for V2V channels
WIMAX INNER RECEIVER DESIGN
"Igniting broadband wireless access". That is the vision for WiMAX, which is
defined in the 802.16 standards to cover the frequency bands within the 2 to 66 GHz
region. It promises an OFDM air interface with data rates comparable to wireline
services (cable and xDSL). Coupled with QoS provisioning and support for NLOS
propagation, WiMAX offers the platform for real time multimedia communications in
addition to being able to replace the existing legacy PSTN. WiMAX also becomes the
perfect launch pad for service providers to roll out triple play. The standard based
products and availability of internet to anyone, anywhere and anytime will almost
guarantee the widespread adoption ofWiMAX everywhere.
This FYP attempts to simulate the working mechanism of a WiMAX receiver,
with focus on synchronization (inner receiver), via simulation in Simulink. The
undertaking will involve the baseband physical radio link. The proposed method of
synchronization is a novel hybrid of a modified version of the Schmidl and Cox
technique and the double sliding window packet detection. The inner receiver deals
with synchronization issues such as FFT timing offset and carrier frequency offset.
Offsets and impairments are deliberately introduced into the system to ensure that the
receiver is totally blind and to fully test the proposed algorithm.
Results indicate that the proposed method can harness the best features of both
worlds. Frame timing synchronization is achieved accurately without uncertainties of
detecting a plateau. On the other hand, frequency offsets are dealt with efficiently
using the tried and tested Schmidl and Cox technique. All in all, the proposed
synchronization scheme is very well suited for WiMAX systems. The proposed
method can achieve rapid synchronization with low overhead
WIMAX TESTBED
WiMAX, the Worldwide Interoperability for Microwave Access, is a
telecommunications technology aimed at providing wireless data over long distances
in a variety of ways, from point-to-point links to full mobile cellular type access. It is
based on the IEEE 802.16 standard, which is also called Wire IessMAN. The name
WiMAX was created by the WiMAX Forum, which was formed in June 2001 to
promote conformance and interoperability of the standard. The forum describes
WiMAX as a standards-based technology enabling the delivery of last mile wireless
broadband access as an alternative to cable and DSL. This Final Year Project attempts
to simulate via Simulink, the working mechanism of a WiMAX testbed that includes
a transmitter, channel and receiver. This undertaking will involve the baseband
physical radio link. Rayleigh channel model together with frequency and timing
offsets are introduced to the system and a blind receiver will attempt to correct these
offsets and provide channel equalization. The testbed will use the Double Sliding
Window for timing offset synchronization and the Schmid! & Cox algorithm for
Fractional Frequency Offset estimation. The Integer Frequency Offset
synchronization is achieved via correlation of the incoming preamble with its local
copy whereas Residual Carrier Fr~quency Offset is estimated using the L th extension
method. A linear Channel Estimator is added and combined with all the other blocks
to form the testbed. From the results, this testbed matches the standard requirements
for the BER when SNR is 18dB or higher. At these SNRs, the receiver side of the
testbed is successful in performing the required synchronization and obtaining the
same data sent. Sending data with SNR lower than 18dB compromises its
performance as the channel equalizer is non-linear. This project also takes the first
few steps of hardware implementation by using Real Time Workshop to convert the
Simulink model into C codes which run outside MATLAB. In addition, the Double
Sliding Window and Schmid! & Cox blocks are converted to Xilinx blocks and
proven to be working like their Simulink counterparts
SYNCHRONIZATION AND RESOURCE ALLOCATION IN DOWNLINK OFDM SYSTEMS
The next generation (4G) wireless systems are expected to provide
universal personal and multimedia communications with seamless connection
and very high rate transmissions and without regard to the users’ mobility and
location. OFDM technique is recognized as one of the leading candidates to
provide the wireless signalling for 4G systems. The major challenges in
downlink multiuser OFDM based 4G systems include the wireless channel, the
synchronization and radio resource management. Thus algorithms are required
to achieve accurate timing and frequency offset estimation and the efficient
utilization of radio resources such as subcarrier, bit and power allocation.
The objectives of the thesis are of two fields. Firstly, we presented the
frequency offset estimation algorithms for OFDM systems. Building our work
upon the classic single user OFDM architecture, we proposed two FFT-based
frequency offset estimation algorithms with low computational complexity.
The computer simulation results and comparisons show that the proposed
algorithms provide smaller error variance than previous well-known algorithm.
Secondly, we presented the resource allocation algorithms for OFDM
systems. Building our work upon the downlink multiuser OFDM architecture,
we aimed to minimize the total transmit power by exploiting the system
diversity through the management of subcarrier allocation, adaptive
modulation and power allocation. Particularly, we focused on the dynamic
resource allocation algorithms for multiuser OFDM system and multiuser
MIMO-OFDM system. For the multiuser OFDM system, we proposed a lowiv
complexity channel gain difference based subcarrier allocation algorithm. For
the multiuser MIMO-OFDM system, we proposed a unit-power based
subcarrier allocation algorithm. These proposed algorithms are all combined
with the optimal bit allocation algorithm to achieve the minimal total transmit
power. The numerical results and comparisons with various conventional nonadaptive
and adaptive algorithmic approaches are provided to show that the
proposed resource allocation algorithms improve the system efficiencies and
performance given that the Quality of Service (QoS) for each user is
guaranteed.
The simulation work of this project is based on hand written codes in the
platform of the MATLAB R2007b
Timing synchronization in MIMO-OFDM systems
OFDM (Orthogonal Frequency Division Multiplexing) provides a promising physical layer for
4G and 3GPP LTE Systems in terms of efficient use of bandwidth and high data rates. It is used
in several applications likeWiFi (IEEE 802.11n),WiMax (IEEE 802.16), Digital Audio Broadcasting
(DAB), Digital Video Broadcasting (DVB) and so on. OFDM suffers from inter-symbol
interference and inter-carrier interference in wireless and fading environments and it is important
to estimate and correct the start of OFDM symbol efficiently to reduce timing and frequency
offset errors. Synchronization issues in OFDM are crucial and can lead to certain amount of
information loss if they are not properly addressed. There are two modes of implementation
forDigital Video Broadcasting-Terrestrial (DVB-T) and this thesis implements the 2K mode. It
highlights the implementation of OFDM in DVB-T according to the European Telecommunications
Standards Institute (ETSI) . It mainly focuses on the timing offset problem present in
OFDM systems and its proposed solution using Cyclic Prefix (CP) as a modified Schmidl and
Cox’s (SC) algorithm. Simulations were performed to compare the different synchronization
methods with different amount of timing offsets and under different channel environments
- …