49 research outputs found
A channel estimation method for MIMO-OFDM Mobile WiMax systems
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Design and Investigation of CDMA Baseband Transceiver Based Fourier Signals for Different Channel Estimation Algorithms in SUI Channels
Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) and are the technology used in all third generation cellular communications networks, and it is a promising candidate for the definition of fourth generation standards. This paper refers to channel estimation based on time-domain channel statistics. Using a general model for Stanford University Interim SUI channels model, the aim of the paper is to find out the most suitable channel estimation algorithms for the existing CDMA and modified the bit error rate for this system. Starting with the analysis of channel estimation algorithms, we present the Minimum Mean Square Error (MMSE (and Least Square (LS (estimators and compromising between performances under different channel scenarios. The bit error rate for a 16-QAM system is presented by methods of Matlab simulation results. Keywords: CDMA, OFDM, MMSE, LS, SUI
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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
Design and Performance of LTE 3GPP Baseband Transceiver Based Wavelet Signals for Different Channel Estimation Algorithms
Long Term Evolution (LTE) 3GPP advanced is a mobile communication standard. It was formally submitted as a candidate 4G system. This paper refers to channel estimation based on time-domain channel statistics. Using a general model for Stanford University Interim (SUI) channel models, the aim of the paper is to find out the most suitable channel estimation algorithms for the modified Long Term Evolution (LTE) 3GPP baseband transceiver based wavelet signals and improvement the bit error rate for this system. Starting with the analysis of channel estimation algorithms, we present the Minimum Mean Square Error (MMSE (and Least Square (LS (estimators and compromising between performances under different channel scenarios. The bit error rate for a 16-QAM and OFDM system based wavelet signals is presented by methods of Matlab simulation results. Keywords: LTE 3GPP, DWT, SUI, OFDM, MMSE, LS, 16-QAM
GCL Based Synchronization and Time Domain Frequency Offset Correction in OFDM System
Orthogonal Frequency Division Multiplexing (OFDM) is a modulation technique that has become the technology of choice in most wireless communication networks of today. Despite the advantages the OFDM system offers, it has some disadvantages like sensitivity to synchronization and high power-to-average-power ratio (PAPR). Any time offset leads to inter-symbol interference (ISI) whereas any frequency offset results in inter-carrier interference (ICI) and, as a result, the system performance degrades.
The studies of preamble based time synchronization show that, the standard PN sequence based preamble in IEEE 802.16a is less robust to frequency offset when used in Park’s method of time synchronization - a method that gives more accurate result as compared to other methods. Time domain channel estimation cannot be carried out in the presence of integer frequency offset.
This thesis has three specific objectives. Firstly, to design and evaluate a new preamble by making use of a generalized chirp-like (GCL) sequence that has low PAPR and good time and also frequency correlation properties. Secondly, to design a new receiver scheme that estimates and corrects the integer-frequency offset in the time domain and evaluate its performance. And lastly, having corrected the frequency offset in time domain, to estimate the wireless channel in time domain and evaluate its performance.
The results show that, the proposed GCL based preamble has better and more robust performance than the standard PN sequence (IEEE 802.16 standard) based preamble in the time and integer frequency synchronization and also in the time domain channel estimation.
In the new receiver scheme, the presence of symmetrical correlation shows that received signal is frequency corrected. The results show that the new receiver scheme is able to detect the symmetrical correlation quite accurately. The receiver also works well even in low SNR environment
Design and Investigation of LTE 3GPP Baseband Transceiver Based Fourier Signals for Different Channel Estimation Algorithms in SUI Channels
3GPP LTE is the evolution of the UMTS in response to ever?increasing demands for high quality multimedia services according to users’ expectations. These technologies have been selected for LTE 3GPP. Pilot?assisted channel estimation is a method in which known signals, called pilots, are transmitted along with data to obtain channel knowledge for proper decoding of received signals. This paper refers to channel estimation based on time-domain channel statistics. Using a general channels model for Stanford University Interim (SUI) Channel Models, the aim of the paper is to find out the most suitable channel estimation algorithms for the existing LTE 3GPP Baseband Transceiver and modified the bit error rate for this system. Starting with the analysis of channel estimation algorithms, we present the Minimum Mean Square Error (MMSE (and Least Square (LS (estimators and compromising between performances under different SUI channel scenarios. Performance of these algorithms has been measured in terms of Bit Error Rate (BER). The bit error rate for a 16-QAM system is presented by methods of Matlab simulation results. Keywords: LTE 3GPP, MMSE, LS, OFDM, SUI