In this thesis, we investigate and implement the channel estimation schemes for digital video broadcasting - handheld (DVB-H) and IEEE 802.16d world interoperability for micro-wave access (WiMAX). Both systems are based on the orthogonal frequency division multiplexing (OFDM) technique. The performance of the channel estimation schemes is first verified by using simulation experiments. Then, the channel estimation algorithms are realized by hardware implementation. For the DVB-H systems, since the mobile device may have a relatively high speed, the channel condition is time-varying, leading to serious degradation in channel estimation. In this thesis, the decision feedback mechanism is adopted to improve the performance of the channel estimation. The adopted structure for channel estimation is realized by using Verilog hardware description language (HDL). Then, all the baseband signal processing related algorithms, which include timing synchronization, frequency offset estimation/compensation, and scattered pilot detection, are integrated together using 0.18 ASIC process. For the IEEE 802.16d WiMAX, since it is dedicated for fixed wireless applications, the channel condition is basically stationary and easier to obtain. Therefore, the decision feedback mechanism is not adopted to save hardware complexity. The system performance is verified by conducting simulation experiments. The adopted channel estimation algorithm is implemented by using Verilog HDL. Finally, the whole baseband receiver is realized by using the field programmable gate array (FPGA) and verified by using the Agilent logic analyzer.

Error free transmission is one of the main aims in wireless communications. With the increase in multimedia applications, large amount of data is being transmitted over wireless communications. This requires error free transmission more than ever and to achieve error free transmission multiple antennas can be implemented on both stations i.e. base station and user terminal with proper modulation scheme and coding technique. The 4th generation of wireless communications can be attained by Multiple-Input Multiple-Output (MIMO) in combination with Orthogonal Frequency Division Multiplexing (OFDM). MIMO multiplexing (spatial multiplexing) and diversity (space time coding) having OFDM modulation scheme are the main areas of focus in our thesis study. MIMO multiplexing increases a network capacity by splitting a high signal rate into multiple lower rate streams. MIMO allows higher throughput, diversity gain and interference reduction. It also fulfills the requirement by offering high data rate through spatial multiplexing gain and improved link reliability due to antenna diversity gain. Alamouti Space Time Block Code (STBC) scheme is used with orthogonal designs over multiple antennas which showed simulated results are identical to expected theoretical results. With this technique both Bit Error Rate (BER) and maximum diversity gain are achieved by increasing number of antennas on either side. This scheme is efficient in all the applications where system capacity is limited by multipath fading.

The low complexity of layered processing makes the layered structure a promising candidate for MIMO systems with a large number of transmit antennas and higher order modulation. For broadband systems, orthogonal frequency division multiplexing (OFDM) appears promising for its immunity against delay spread. In addition, OFDM is especially suitable for frequency selective MIMO systems since the introduction of orthogonal subcarriers makes system design and implementation as simple as those for flat fading channels. Therefore, the combination of layered structure with OFDM is a promising technique for high-speed wireless data transmission. The proposed research is focused on the layered structure for MIMO-OFDM systems, where several techniques are proposed for performance enhancement, namely, channel estimation based on subspace tracking, parallel detection of group-wise space-time codes by predictive soft interference cancellation, quasi-block diagonal low-density parity-check codes (LDPC) coding and statistical data rate allocation for layered systems. For MIMO-OFDM systems, rank reduction by some linear transform matrix is necessary for channel estimation. In the proposed research, we propose a channel estimation algorithm for MIMO-OFDM systems, which uses the optimum low-rank channel approximation obtained by tracking the frequency autocorrelation matrix of the channel response. Then parallel detection algorithm is proposed for a modified layered system with group-wise space-time coding, where the structure of particular component space-time code trellises is exploited using partial information from the Viterbi decoder of the simultaneously decoded interfering component codes. Next we incorporate the layered structure with LDPC to develop a quasi-block diagonal LDPC space-time structure. The lower triangular structure of the parity check matrix introduces correlation between layers. Each layer, as a part of the whole codeword, can be decoded while taking information from other undetected layers to improve the decoding performance. In the end, a modified layered structure is proposed where the layer detection order is fixed and the data rate for each layer is allocated based on the detection order and channel statistics. With Gaussian approximation of layer capacities, we derive the optimum data rate allocation.

Orthogonal frequency division multiplexing systems are much more sensitive to timing and frequency error, therefore there were several methods to estimate time and frequency offset. In the thesis, a novel timing offset estimation method for OFDM systems is proposed, it transmits a specific training symbol in the time domain at transmitter. At the receiver, it estimate the timing offset by using a specific timing metric. The proposed scheme isn¡¦t affected by the frequency offset compare with Zhang¡¦s method, and it can estimate timing offset more accurately than Schmidl¡¦s method and Minn¡¦s method. We will analyze the statistical characteristic of the timing metric we proposed at correct time. According to the analysis and simulation result, it can show the accuracy of our analysis. Finally from the simulation result, it demonstrates that the proposed scheme has better performance.

In this paper, there are two major contents about OFDM synchronization issue in wireless communication. The first of all, a joint MLE and MMSE synchronization scheme is proposed for OFDM timing and frequency offset. Secondly, a novel pilot-aided inter-carrier interference (ICI) self-cancellation scheme is proposed for use in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme maps both modulated data symbols and pre-defined pilot symbols onto non-neighboring sub-carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols, a more accurate estimation of frequency offsets can be obtained, and the ICI self-cancellation demodulation can be operated properly.

Multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) technology has been used widely in many wireless communication systems. Signals will be distorted when they are transmitted in wireless channels. For the reason that wireless channel is time or location variant, we have to estimate the channel impulse response and use the channel state information to compensate the channel distortion. Pilot signals can be spaced separated in the transmitted symbols. In the receiver, the channel impulse response can be estimated at the positions of pilot signals. The other channel information at the data signals can be obtained by interpolating the estimated channel impulse response. However, error caused by channel interpolation can not be avoided. In this paper we propose a pilot-aided iterative maximum likelihood (ML) channel estimation algorithm for MIMO OFDM systems. At first, an ML channel estimate is obtained by using pilot tones. The receiver uses the estimated channel to help the detection/decision of data signals. And then the channel estimation treats the detected signals as known data to perform a next stage channel estimation iteratively. By utilizing the iterative channel estimation and signal detection process we can reduce the estimation error caused by channel interpolation between pilots. The accuracy of the channel estimation can be improved by increasing the number of iteration process. Simulation results demonstrate the iterative ML channel estimation algorithm can provide better mean-square-error and bit-error-rate performance than conventional methods. By changing the system parameters we can see that the improvement provided by this algorithm is different. Systems with fewer pilots have more improvement from the iterative ML algorithm. On the other hand, systems with more pilots have less improvement from the iterative algorithm. Finally, several channel environments are also considered in this thesis to compare the performance improvement introduced by the iterative algorithm.

In this thesis, the performance comparison of orthogonal frequency division multiple access (OFDMA) and complete complementary code based CDMA system is studied. The complete complementary code is composed of several sets of auto-complementary codes, any two of which are cross-complementary codes. The perfect correlation between code sets is the distinguishing feature of complete complementary code. OFDMA is used in the 4th. generation Mobile Communication systems. The OFDMA architecture can offer an MAI-free operation in both down-link (synchronous channel) and up-link (asynchronous channel) transmission under the AWGN channel.

This thesis aims to implement a power-line communication (PLC) adaptor to use power lines as transmission media for network communication between different floors in buildings. The PLC adaptor is based on a turbo-mode chip that adopts OFDM modulation technique with 4.5-21 MHz bandwidth and can accord with the HomePlug 1.0 standard. The other components include a physical-layer chip, a flash memory, a TX/RX filter, and a switching power supply with three outputs. All the above components are integrated into a PCB to form a PLC adaptor. The PCB layout has included EMI solutions to reduce interference to the communication signal. After burning process for the flash memory to record the MAC address, the PLC adaptor becomes a network node. Point-to-point communication test is performed between two PLC adaptors located on different floors of a building. The testing items include signal attenuation test and signal throughput test.

orthogonal frequency division multiplexing (OFDM) systems are very sensitive to synchronization errors. Therefore, OFDM systems require the knowledge of symbol timing and frequency offset. Most OFDM synchronization algorithms proposed in the literature are data-aided estimation structures. Data-aided estimators use pilot symbols or training sequences to perform synchronization. However, the use of training data reduces the transmission data rate. The alternative, which we consider in this thesis, is nondata-aided methods that perform synchronization by utilizing the redundant guard interval or cyclic prefix. Recently, cyclo-stationarity of signals is applied for estimating synchronization error. Gini and Giannakis utilized the property for single carrier systems and Bolcskei applied the property for OFDM systems. In this thesis, we proposed a modified synchronization algorithm, which is extended from Giannakis and Bolcskei algorithms, in additive white Gaussian noise (AWGN) environment. According to Park¡¦s study, additional sub-carrier weightings are not needed to enhance the estimation performance. From simulation results, the proposed modified blind synchronization algorithm can achieve better performance.

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