Amir Saemi

Synchronization algorithms for MIMO OFDMA systems

We propose in this paper a maximum likelihood (ML) estimator to jointly obtain time and frequency synchronization together with channel estimation in a MIMO OFDMA system. The proposed algorithm is planned to be implemented in a base station (BS) environment and so it is mainly devoted to uplink asynchronous transmission schemes. We propose a new EM based procedure which enables to convert a multidimensional maximization problem into a number of substantially smaller separate maximization problems. Simulation results are presented which clearly show the accuracy of our estimator and its ability to combat the near-far effect.

Joint ML time-frequency synchronisation and channel estimation algorithm for MIMO-OFDM systems

The maximum-likelihood (ML) time-frequency synchronisation algorithm combined with channel estimation for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems in frequency selective fading channels is addressed. In the proposed algorithm, the authors use two steps to maximise an ML metric to obtain first the frequency offset and then timing. A fast Fourier transform algorithm is used to estimate the frequency offset. Using these two estimates, the channel is identified. A simple iterative algorithm is proposed to improve the frequency offset estimation. The performance of the proposed synchronisation approach, in terms of timing failure probability and mean square error of the estimated frequency offset and bit error rate, is compared with others in the literature. Comparison of simulation results with the Cramer-Rao lower bound clearly illustrates the accuracy of the proposed algorithm, which outperforms the state-of-the-art synchroniser devices in the open literature.

New List Sphere Decoding (LSD) and Iterative Synchronization Algorithms for MIMO-OFDM Detection With LDPC FEC

New sphere decoding and synchronization algorithms for multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems are proposed in this paper. In particular, an iterative list branch-and-bound (BB) algorithm based on the basic BB algorithm is described to obtain a candidate list to compute soft information that is used in the iterative detector. Furthermore, an improved algorithm that uses prior information from the preceding iteration to calculate the lower bound is proposed, and the candidate list is updated every iteration. To obtain a complete modem architecture, we propose an efficient expectation-maximization (EM)-based iterative algorithm for synchronization and channel estimation to interface with the proposed list-sphere-decoding detector, and we investigate the performance of the designed MIMO-OFDM modem on a realistic fading channel. The obtained performance results show that it is possible to practically design a performing MIMO-OFDM modem with high spectral efficiency, i.e., 8 bit/s/Hz with a 4times4 16-QAM MIMO-OFDM system.

ML Time-Frequency Synchronization for MIMO-OFDM Systems in Unknown Frequency Selective Fading Channels

This paper addresses maximum-likelihood (ME) time-frequency synchronization algorithm joint with channel estimation for MIMO-OFDM systems in frequency selective fading channels. In proposed algorithm, we use two steps to maximize a proposed metric to obtain first frequency offset and then timing. Using these two estimates, the channel is identified. An iterative algorithm is proposed to improve frequency offset estimation. The performance of the proposed synchronization approach, in terms of timing failure probability and mean square error of the estimated frequency offset, was compared with literature. Based on simulation results, the Cramer-Rao lower bound is obtained with a few iterations

Iterative (turbo) expectation - maximisation-based time and frequency synchronisation for multiple-input multiple-output-orthogonal frequency-division multiplexing systems

An iterative expectation-maximisation time-frequency synchronisation algorithm joint with channel estimation for multiple-input multiple-output-orthogonal frequency-division multiplexing (OFDM) systems in frequency-selective fading channels is addressed. The receiver iterates between detection and estimation stages. For each iteration, the expectation of ODFM symbols is calculated first by using a posteriori probabilities provided by maximum a posteriori (MAP) decoder, and second, a proposed metric is maximised to obtain both frequency offset and symbol timing. The channel can be identified by means of these estimates. This algorithm can work in transmission mode, and thus, can be used to estimate the residual errors or track the change of the parameters. The performance of the proposed synchronisation approach, in terms of bit-error rate and mean-square error, is shown.

Mixed Analog and Digital Matched-Filter Design for High Rate WLAN

A mixed-signal programmable filter suitable for high- rate WLAN is addressed in this work. The proposed filter has analog input and analog-sampled outputs. The filter taps are stored in a digital memory and can be changed easily to meet any receiver requirements. The filter structure is based on a bank of digitally controlled transconductors realized by simple CMOS inverters and thus can be integrated efficiently with digital parts. A cosine rolloff filter is designed and investigated by simulation in frequency domains. Comparison with other recent works shows that the proposed structure has a good speed-complexity-consumption trade-off.

Mixed-Signal Realization of Matched-Filters for High Rate Communication Systems

A mixed-signal programmable filter suitable for high-rate communication systems is addressed in this work. The proposed filter has analog input and analog-sampled outputs. The filter taps are stored in a digital memory and can be changed on the fly which is desirable in many practical applications such as adaptive filtering. The filter structure is based on a bank of digitally controlled transconductors along with small capacitors. The employed transconductors are based on simple CMOS transistors and thus can be integrated efficiently with the digital parts of systems. A cosine rolloff filter is designed and investigated by simulation in frequency domains. The results show that the proposed structure has a good speed-complexity-consumption trade-off.

A Mixed-Signal Matched-Filter Design and Simulation

A 0.35 mu-CMOS mixed-signal programmable filter suitable for high-rate communication systems is designed and investigated. The proposed filter has analog input and analog-sampled outputs. Filter taps are stored in a digital memory and can be changed on the fly. The filter structure is based on a bank of digitally controlled transconductors along with small capacitors. The employed transconductors are based on simple inverter and thus can be integrated efficiently with the digital parts of a system. A FIR cosine rolloff filter is designed and investigated by simulation in time and frequency domains. The results show that the proposed structure has a good speed-complexity-consumption trade-off.

ML MIMO-OFDM Time Synchronization/Channel Estimation for Unknown Frequency Selective Fading Channels

This paper addresses maximum-likelihood (ML) time synchronization algorithm joint with channel estimation for MIMO-OFDM systems in frequency selective fading channels. For this purpose a SISO joint maximum likelihood (ML) synchronization algorithm with channel estimation is extended and generalised to MIMO systems. Timing failure probability is presented as a criterion to illustrate the robustness of the algorithm. The performance of the proposed synchronization approach, in terms of timing failure probability, was compared with SISO systems. Based on simulation results, the performance of the proposed algorithm is quite satisfying

MIMO-OFDM Iterative Time - Frequency Synchronization

This paper addresses an iterative expectation-maximization (EM) time-frequency synchronization algorithm joint with channel estimation for MIMO-OFDM systems in frequency selective fading channels. The receivers iterates between detection and estimation. For each iteration, we calculate first the expectation of ODFM symbols by using a posteriori probabilities provided by MAP decoder and second we maximise a proposed metric to obtain both frequency offset and then symbol-timing. The channel can be identified by means of these estimates. This algorithm can work in transmission mode and thus can be used to estimate the residual errors or track the change of the parameters. The performance of the proposed synchronization approach, in terms bit error rate and mean square error of the estimated frequency offset, is shown.