Mohamed El-Tanany

Analytical modeling and simulation of phase noise interference in OFDM-based digital television terrestrial broadcasting systems

This paper deals with the problem of modeling of phase noise in OFDM systems and the impact it may have on the bit error rate performance of such systems subject to a number of system variables and to a number of channel conditions which may be encountered when such systems are deployed for certain applications such as high speed wireless LANs and Digital Television Terrestrial Broadcasting (DTTB). The phase noise processes, the sources of which are the transmitters and receivers local oscillator, are modeled using what is believed to be commercially realizable phase noise masks. Such masks represent the long-term averaged power spectral densities of the local oscillator output signal.

Experimental evaluation of space/frequency/polarization diversity in the indoor wireless channel

A series of experiments that were conducted to evaluate the relative merits of frequency, space, and polarization diversities in indoor portable radio channels at 900 MHz are described. Unmodulated tones were used to probe the channel in a typical university work environment. The statistics of the signal envelopes were analyzed to determine the correlation of the field strengths when the signals are separated in space, frequency or polarization. According to the results presented here, the performance of a narrowband system ( >

Robust near-field adaptive beamforming with distance discrimination

This paper proposes a robust near-field adaptive beamformer for microphone array applications in small rooms. Robustness against location errors is crucial for near-field adaptive beamforming due to the difficulty in estimating near-field signal locations especially the radial distances. A near-field regionally constrained adaptive beamformer is proposed to design a set of linear constraints by filtering on a low rank subspace of the near-field signal over a spatial region and frequency band such that the beamformer response over the designed spatial-temporal region can be accurately controlled by a small number of linear constraint vectors. The proposed constraint design method is a systematic approach which guarantees real arithmetic implementation and direct time domain algorithms for broadband beamforming. It improves the robustness against large errors in distance and directions of arrival, and achieves good distance discrimination simultaneously. We show with a nine-element uniform linear array that the proposed near-field adaptive beamformer is robust against distance errors as large as /spl plusmn/32% of the presumed radial distance and angle errors up to /spl plusmn/20/spl deg/. It can suppress a far field interfering signal with the same angle of incidence as a near-field target by more than 20 dB with no loss of the array gain at the near-field target. The significant distance discrimination of the proposed near-field beamformer also helps to improve the dereverberation gain and reduce the desired signal cancellation in reverberant environments.

Synchronization of OFDM systems over frequency selective fading channels

A joint initial frame synchronization and initial channel estimation algorithm for OFDM systems is developed, and its performance with carrier frequency offset and with additive white Gaussian noise in frequency selective channels is evaluated. Transmission of a short pre-frame synchronization burst is proposed and slow fading is assumed, so that the channel can be considered time invariant for the duration of the synchronization burst.

Filtered decision feedback channel estimation for OFDM-based DTV terrestrial broadcasting system

Orthogonal frequency division multiplexing (OFDM) is one of the transmission techniques used for digital television (DTV) terrestrial broadcasting. A high quality channel estimator with a low training overhead is the key to the successful delivery of DTV services which require high spectrum efficiency and robustness to strong and dynamic ghosts. Robustness to multipath distortion is especially important in a single frequency emission environment. This paper presents an application of a filtered decision feedback channel estimator for OFDM-based DTV systems using high order QAM modulations. The implementation and the performance of the channel estimator are discussed. Computer simulations were conducted to evaluate the performance of the channel estimator. The channel estimation loss is about 1.2 dB from the ideal case where the channel is assumed to be known by the receiver. For a given multipath spread, the loss can be further reduced by increasing the FFT size. The FFT size is however subject to an upper limit imposed by the Doppler spread.

Millimeter-wave channel measurements with space diversity for indoor wireless communications

Indoor wireless communication systems experience deep multipath fading due to the presence of people, antenna movement, and other environmental factors. The objective of this paper is to present results concerning envelope fading and large-scale attenuation properties of the signal based on narrowband measurements carried out at 21.6 and 37.2 GHz with and without antenna diversity. By using various transmitter-receiver arrangements in measurements which were taken over one floor of a university building, envelope statistics of received signal are produced with and without antenna diversity. It is shown that the statistical distributions follow the Rayleigh curve and hence a diversity gain close to 10 dB can be obtained for an availability of 99%. Power law exponents and wall loss factors are also calculated to assist in the design of future indoor radio systems in the millimeter frequency range. >

A novel adaptive structure of the energy detector applied to cognitive radio networks

The energy detector (ED) is one of the spectrum sensing techniques that is used in the cognitive radio networks to detect the presence of the primary user (PU) in a certain spectrum band. This technique assumes that the PU is either present or absent during the sensing time. However, the EDs performance degrades in a scenario when the PU is absent and then appears during the sensing time. The EDs performance is evaluated for this scenario and a novel adaptive ED structure is proposed to improve the detector performance. Analytical performance evaluation of the adaptive ED along with simulation results show that the proposed ED structure improves the probability of detection compared to the conventional ED.

Millimeter-wave channel measurements for indoor wireless communications

Propagation losses for the indoor radio channel at 21.6 GHz and 37.2 GHz are examined. The propagation measurements carried out are used to quantitatively present, through enveloped distribution, the effects of spatial fading, which is due to multipath propagation, and temporal fading, which is due to people moving in the building. Attenuation is given in the form of the exponent of the distance-power law.<<ETX>>

Suboptimal Detectors for Alpha-Stable Noise: Simplifying Design and Improving Performance

The design of detectors for binary signals in symmetric alpha-stable noise is considered. Since the optimal detector is impractically complex, many suboptimal detectors have been proposed such as the Gaussian, soft limiter, myriad and Cauchy detectors. However, no adequate explanation for the difference in performance between these detectors has been proposed. In this paper, we propose a novel framework, based on the optimal decision regions, that is used to justify the performance of many suboptimal detectors and compare them to the optimal one. Moreover, the analysis of the framework provides a novel method to significantly improve the performance of the soft limiter detector by employing an adaptive threshold that is a function of the signal level. As the number of samples per symbol increases, the performance of the proposed adaptive detector approaches the optimal performance at almost no additional complexity over the conventional Gaussian detector.

A discrete multi carrier multiple access technique for wireless communications

A discrete multi carrier multiple access (MCMA) technique is proposed for multi user wireless communications. An interleaved set of subcarriers is dedicated to each user to provide with a high order of frequency diversity. A reduced complexity digital implementation of the technique is discussed. Both inter-symbol interference and other-user interference are mitigated using a proper cyclic extension, provided that the relative propagation delays of the users are an integer multiple of a symbol period. The effect of other-user interference due to non-integer propagation delays is investigated using computer simulations. The bit error rate performance is presented for an example system over both an additive white Gaussian noise (AWGN) and a frequency selective Rayleigh fading channel. The amount of other-user interference is shown to be reduced increasing the number of subcarriers per user.