Grace Oletu

The performance of turbo codes for wireless communication systems

Turbo codes play an important role in making communications systems more efficient and reliable. This paper provides a description of two turbo codes algorithms. Soft-output Viterbi algorithm and logarithmic-maximum a posteriori turbo decoding algorithms are the two candidates for decoding turbo codes. Soft-input soft-output (SISO) turbo decoder based on soft-output Viterbi algorithm (SOVA) and the logarithmic versions of the MAP algorithm, namely, Log-MAP decoding algorithm. The bit error rate (BER) performances of these algorithms are compared. Simulation results are provided for bit error rate performance using constraint lengths of K=3, over AWGN channel, show improvements of 0.4 dB for log-MAP over SOVA at BER 10−4.

Impact of Vehicular Traffic on Information Capacity of Cellular Wireless Network at Carrier Frequencies Greater Than 3 GHz

In this paper we describe a simulation study of the impact of vehicular traffic on the performance of cellular wireless network at microwave carrier frequencies above 3 GHz and up to 15 GHz, where the first and subsequent tiers co-channel interfering cells are active. The uplink information capacity of the cellular wireless network is used for the performance analysis. The simulation results show that vehicular traffic causes a decrease in the information apacity of a cellular wireless network. Results also show that for both light and heavy vehicular traffic environment, the nclusion of subsequent tier co-channel interferences caused a decrease of between 3 - 12

Modified Iterative Decision Feedback Equalization for Communication Systems

\%

The Smearing Filter Design Techniques for Data Transmission

in the information capacity of the cellular wireless network as compared to the case, when only the first tier co-channel interferences are active.

Adaptive MMSE multiuser detection for MIMO OFDM over Turbo-Equalization for Single-Carrier Transmission wireless channel

A number of reduced-complexity methods for turbo equalization have recently been introduced in which MAP equalization is replaced with sub optimal, low complexity approaches. In this paper, we investigate the inefficiency of the conventional decision feedback algorithm when higher-level modulation is used in Inter Symbol Interference channels. We estimates the data using the apriori information from the SISO channel decoder and also the a priori detected data from previous iteration to minimize error propagation. The proposed algorithm for 8-phase shift keying, 16-phase shift keying and 64 quadrature amplitude modulation was verified by assuming a statistical model for the a priori information combined with equalizer output to improve the interference cancellation. The simulation results show that the proposed low complexity DFE algorithm improves considerable compared to the conventional DFE when higher-level modulation are used. It was shown that at higher level modulation, the modified DEF has 1.6dB gain over the conventional DEF after seven iterations.

Performance of iterative decoding with imperfect MMSE DFE

Reducing Impulse noise is a very active research area in communication systems. This paper presents a digital smear-desmear technique (SDT) applied to data transmission over band limited channels. A generalized set of filter design criteria based on minimizing the average bit error probability is introduced. The design criteria were applied to a practical digital filter implementing SDT techniques. The SDT is simulated and combined with coded communication systems for high data transmission rate. Simulation results show that the SDT yields a significant improvement in bit error rates for coded systems subject to impulse noise, relative to the systems with no SDT. The technique also completely removes the error floor caused by the impulse noise.

Minimization of Channel Impulse Noise using Digital Smear Filter

This paper presents an adaptive multiuser receivers scheme for MIMO OFDM over Turbo-Equalization for Single-Carrier Transmission. It involves the joint adaptive minimum mean square error multiuser detection and decoding algorithm with prior information of the channel and interference cancelation in the spatial domain. A partially filtered gradient LMS (Adaptive) algorithm is also applied to improve the convergence speed and tracking ability of the adaptive detectors with slight increase in complexity. The proposed technique is analyzed in a slow and fast Rayleigh fading channels in MIMO OFDM systems. The adaptive multiuser detection for MIMO OFDM (AMUD MIMO OFDM) perform as well as the iterative equalization for single-carrier.

Channel impulse noise minimization using digital smear and desmear filter

The MMSE-DFE is a well established Intersymbol Interference (ISI) mitigating structure on linear, noisy, and dispersive channels. Time invariant communication channels exhibits ISI for severe frequency-selective channels. In this paper we investigate the iterative decoding with imperfect MMSE decision feedback equalizer using different modulation scheme. We assume that soft outputs from channel decoder are independent identically distributed Gaussian random variables with known mean and variance. The Imperfect MMSE DFE using different modulation outperforms other turbo equalization algorithms of similar computational complexity in terms of bit-error rate. The achieved improvement is up to 3dB for severe frequency-selective channels.

Interference Cancellation Using Iterative Equalization for Communication Networks

The paper describes a digital smear-desmear technique (SDT) based on polyphase multilevel sequences of unlimited length with good autocorrelation properties. A design procedure for digital implementation of SDT is defined and sequences with power efficiency higher than 50% are generated. These sequences are applied to the design of digital smear/desmear filters and combined with uncoded and coded ITU-T V.150.1 communication systems. The impulse noise is modeled as a sequence of Poisson arriving delta functions with gaussian amplitudes. The impulse noise parameters are computed from experimental data. Simulation results shows that the SDT filter design method yields a significant improvement in bit error rates for both systems subject to impulse noise, relative to systems with no SDT. The technique also completely removes the error floor caused by impulse noise.

Minimum Cell Size for Information Capacity Increase in a Shadowed Environment of Cellular System Operating at Higher Carrier Frequency

The paper describes a digital smear-desmear technique (SDT) based on polyphase sequences with good autocorrelation properties. These sequences are applied to the design of digital smear/desmear filters and combined with Trellis-coded modulation (TCM) codes. The scheme has been investigated for 16-QAM and 64-QAM modulation. The impulse noise is modeled as a sequence of Poisson arriving delta functions with gaussian amplitudes. The impulse noise parameters are computed from experimental data. Results shows that the SDT filter design method yields a significant improvement in bit error rates as when subject to impulse noise, relative to systems with no SDT.