Mohammed S. El-Tanany

Hardware nonlinearities in digital TV broadcasting using OFDM modulation

FFT-based coded orthogonal frequency division multiplexing (COFDM) is one of the techniques for digital TV broadcasting over multipath fading channels. A FFT-based OFDM signal is subject to various hardware nonlinearities in both the transmitter and receiver. Hardware nonlinearities not only affect the in-band performance of an FFT-based OFDM system but also may affect the system performance of an adjacent channel signal because of regenerated sidelobes of the transmitted signal. The paper investigates the in-band and out-of-band behaviour of a 64QAM-OFDM system under various nonlinear devices. It is shown that the inherent signal clipping in the IFFT processors with a limited word length reduces the required RF amplifier output backoff (OBO) where adjacent channel interference is the limiting factor. For a 0.25% clipping rate, an additional 2 dB OBO is required for the COFDM signal to achieve the same level of adjacent channel interference as for the single carrier system. The loss in SNR due to signal clipping is negligible in a coded OFDM system.

Space and frequency diversity measurements of the 1.7 GHz indoor radio channel using a four-branch receiver

The practical space and frequency diversity performance achievable inside a building at 1.75 GHz under fading conditions due to the motion of a portable terminal and due to the movement of people are investigated. Data are collected using a four-branch dual-frequency envelope receiver positioned throughout one floor of a university building of common construction type. The measurement environment is characterized for large-scale path loss and wall transmission loss. Envelope cross correlations are calculated, and performance of diversity is measured for various frequency separations and antenna spacings which would be applicable given the physical size of portable telephones and data terminals. Two-branch space diversity is directly compared to two-branch frequency diversity and to four-branch hybrid diversity based on simultaneous measurements of each using selection combining. The distributions of correlations and diversity gain at different locations are also investigated. Results indicate that two- and four-branch diversity can be a very effective way to combat signal fading for portable terminals in an indoor radio environment. >

An adaptive combiner for co-channel interference reduction in multi-user indoor radio systems

An efficient technique for co-channel interference suppression in multi-user indoor radio communication systems is presented. The proposed approach makes use of an antenna array in conjunction with an adaptive combiner that employs a training sequence to adjust the receiver to the desired co-user. A different training sequence known to the receiver is transmitted periodically with the information sequence of each co-user. Signals received at the diversity antennas are weighted and summed to produce a combined signal. The weight coefficients are adjusted such that the reception of the desired signal is enhanced and all interfering signals are attenuated. A complex least-mean-square algorithm based on the method of steepest descent is used for weight adjustment. Computer simulations are presented for a two-antenna system with coherent QPSK (quadrature phase-shift keying) signaling over frequency-nonselective Rayleigh fading channels, and in the presence of a single interferer.<<ETX>>

Mean-Square Error Optimization of Quadrature Receivers for CPM with Modulation Index 1/2

Detection of continuous phase modulation (CPM) signals can be accomplished using quadrature coherent detectors which include a pair of linear and time-invariant postdetection filters. Performance of the quadrature detectors is highly sensitive to the postdetection filters response. This paper presents a rigorous derivation of an optimum postdetection filter response. The derivation is based on minimizing the mean-square interference subject, to the constraint that the filter noise bandwidth is held constant. The amount of computations involved is fairly small and increases linearly with the receiver observation interval. Performance analysis results for several modulation techniques are presented.

On the performance of a coded MCM over multipath Rayleigh fading channels

Multicarrier modulation (MCM) is an effective and robust technique to combat ISI in wideband signalling over multipath radio channels. A coded MCM system is analyzed. An upper-bound is given for the average BER (bit error rate) performance of the system. An expression is provided to calculate the matched-filter bounds in terms of the symbol-spaced multipath intensity profile coefficients. It is shown that the system performance meets and in some cases exceeds the matched-filter bounds provided that a proper channel coding and interleaving is used. Computer simulation is performed to support and clarify the results of analysis.

Indoor radio path loss comparison between the 1.7 GHz and 37 GHz bands

Third generation indoor wireless systems providing broadband communications will make use of higher frequency millimeter wave bands. In the planning of these networks it would be useful to estimate coverage based on the many studies of indoor propagation at L-band coupled with knowledge of the building structure. This paper presents results of a comparison between path loss at 1.75 GHz and 37.2 GHz from 100 locations throughout four buildings. The authors analyze the large scale path loss in line of sight and obstructed paths, compare this with building layout and construction and then estimate transmission loss through walls. Results indicate that at 1.75 GHz the non line of sight signals decayed with distance to the exponent N=2.7 while for 37.2 GHz on average N=3.5. The propagation loss through walls at 37.2 GHz showed a much higher dependence on construction type than at 1.7 GHz.

Impact of adjacent channel interference on the performance of OFDM systems over frequency selective channels

This paper deals with the problem of modelling of adjacent channel interference 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 a number of channel conditions which may be encountered when such systems are deployed for certain applications such as high speed wireless LANs and DTTB.

Transmitter identification of ATSC DTV under mobile environment

The ATSC A/110 standard specifies a transmitter identification (TxID) system using RF water-mark. The system, using a 16-bit Kasami sequence, can identify up to 16 millions DTV Transmitters. With the recent development of the ATSC Mobile DTV (M/H), the implementation of transmitter identification will enable new capabilities to receivers in mobile environment. In this paper, we investigate the TxID reception over mobile channels with Doppler fading, dynamic multipath, carrier offset and clock offset, etc. Our simulation results have confirmed the validity of TxID scheme in mobile environment.

Characterization of 29.5 GHz broadband indoor radio channels using a steerable receiving antenna

This paper reports on the work performed on the broadband indoor 29.5-GHz radio channel measurements employing a directional-to-directional antenna configuration. The use of a programmable array antenna at the receiver allows investigations of the channel behavior for various reception angles. The reported results include the channel delay spread properties, the angle-dependent received power, and the correlation of two signals of different reception directions.

Performance of a novel discriminator based quaternary CPM receiver

A novel approach to the design of quaternary continuous phase modulation (CPM) modems, with discriminator detection, is presented. This approach is comparable in complexity to binary modems. The proposed detector yields several dB of signal-to-noise ratio (SNR) savings when compared to the conventional symbol-by-symbol data detector. The numerical results also indicate the superiority of the proposed scheme over binary CPM modems for the same data rate and same bandwidth occupancy. These advantages, however, come at the expense of higher sensitivity to timing errors. Several practical techniques for timing recovery have been tried in the study, and seem to give the desired accuracies.<<ETX>>