COMM-8.1

Orthogonal Pulse Shape Design via Semidefinite Programming
Timothy N Davidson, Zhi-Quan Luo (Communications Research Laboratory, McMaster University, Hamilton, Ontario, Canada), Kon M Wong (Communications Research Laboratory)

In digital communications, orthogonal pulse shapes are often used to represent message symbols for transmission through a channel. The design of such pulse shapes is formulated as a convex semidefinite programming problem, from which a globally optimal pulse shape can be efficiently found using interior point methods. The formulation is used to design filters which achieve the minimal bandwidth for a given filter length, and the minimal filter length for a given bandwidth. The effectiveness of the method is demonstrated by the design of waveforms with substantially improved performance over the `chip' waveforms specified in recent standards for digital mobile telecommunications.

COMM-8.2

Reed-Solomon Codes and Their Performance for FCMA Systems in Fading Satellite Channel
Mahmoud Ahmed Attia Ali, Atef Abou-El-Azm, M.F. Marie (Faculty of Electronic Engineering)

Fading in mobile satellite communications severely degrades the performance of data transmission. The emphasis in this paper is on the performance of uncoded and coded FCMA in the fading environment. The channel is modeled with nonfrequency selective Rice and Rayleigh fading using noncoherent demodulation with Reed-Solomon (RS) codes and hard decision decoding. Berlekamp-Massey decoding of RS codes is used to compensate for the fading. The bit error rate (BER) after decoding is calculated for specific codes and for different values of Rician channel parameters. The results of this paper are obtained by simulation techniques. They show that substantial coding gains are obtained compared to the uncoded reference system. They are also useful as reference for validating the results of simulation studies.

COMM-8.3

Highly Efficient Signal Processing for Frequency Agile Power Line Communications
Maja Sliskovic (Faculty of Electrical Engineering and Computing, Zagreb, Croatia)

A modified frequency hopping signaling scheme has recently received a considerable attention by the designers of power line communication systems because of its insensitivity to frequency-selective and time-variant attenuation and high level of interference. In frequency hopping system, the increase of the data rate without increase of the hop rate is possible only if the receiver can detect all information-bearing tones simultaneously. This paper presents the structure of the noncoherent optimum receiver that minimizes number of required multiplications and memory locations. The receiver structure is based on computation of equidistant DFT coefficients. The proposed demodulator can be used in systems with variable bit rate. With slightly modified algorithm, rough synchronization can also be achieved. Comparison of computational complexity confirms superiority of presented algorithm over direct DFT calculation and FFT algorithm.

COMM-8.4

Synchronization by Pilot Signal
Jyrki J Joutsensalo, Tapani - Ristaniemi (University of Jyvaskyla)

In this paper, we propose a novel approach for code acquisition in the code-division multiple access (CDMA) communication system. The essential assumption is that the pilot signal of the desired user is available. If the codes are exactly orthogonal, the method can be derived from an optimization criterion. Using the pilot signal, the performance can be greatly improved without increasing computational complexity. Simulations show that our method clearly outperforms minimum variance method, eigenvector-based MUSIC, and matched filter.

COMM-8.5

Nonlinear Prediction of Mobile Radio Channels: Measurements and MARS Model Designs
Torbjrn Ekman (Signals and Systems Group, Uppsala University), Gernot Kubin (Institute of Communications and Radio-Frequency Engineering, Vienna University of Technology)

The rapid time variation of mobile radio channels is often modeled as a random process with second order moments reflecting vehicle speed, bandwidth and the scattering environment. These statistics typically show that there is little room for prediction of channel properties such as received power or complex taps of the impulse response coefficients, at least when linear predictor structures are considered. We use mutual information estimation to measure statistical dependencies in sequences of wideband mobile radio channel data and find significant nonlinear dependencies, far exceeding the linear component. Based on these upper limits for the predictability of channel evolution over time intervals up to 30 ms ahead, we develop practical nonlinear predictor systems using Multivariate Adaptive Regression Splines (MARS). We demonstrate computationally efficient schemes that increase the prediction horizon beyond 10 ms, compared to less than 4 ms with linear predictors at comparable prediction gains.

COMM-8.6

Multi-Stage Adaptive Predistortion of HPA Saturation Effects for Digital Television Transmission
John T Stonick, Virginia L Stonick (ECE Dept., Oregon State University), Jose' M. F. Moura (ECE Dept., Carnegie Mellon University)

This paper presents a new structure for adaptive predistortion of memoryless, nonlinear saturation effects caused by High Power Amplifiers (HPA). Timely compensation of HPA distortions is critical for cost-effective prevention of the cliff effect during terrestrial transmission of digital broadcast television. The new structure provides a two-stage approach: First, the forward model is identified using measured data, and then its inverse is computed. Replacing the analog system by the HPA forward model eliminates measurement noise and analog system delays during inverse modeling, yielding faster adaptation and reduced solution bias. Additionally, block processing reduces noise in the forward modeling. In the inverse modeling stage, the use of synthetic data and a closed form expression for the gradient result in more efficient convergence and more accurate solutions. Simulation results using measured HPA data demonstrate about a 5 dB improvement in SINAD over standard SNR operating conditions.

COMM-8.7

CO-CHANNEL INTERFERENCE CANCELLATION FOR HDTV RECEIVERS
Monisha Ghosh (Lucent Technologies)

A new method of co-channel interference rejection for digital television receivers is presented that uses a different rejection filter from the comb filter that was used in the prototype built by Zenith. This filter is optimized for rejection of co-channel NTSC interference in the presence of white noise and hence suffers a penalty of only 0.4 dB in AWGN as compared to 3.5 dB with the comb. The receiver structure with this filter, including required equalizer and trellis decoder modifications is presented, along with simulation results showing the improvement in performance in co-channel-plus-AWGN interference and hence in coverage area.

COMM-8.8

Optimum Codec Companding for High-Speed PCM Data Transmission in Telephone Networks
Nirmal Warke, Murtaza Ali (DSP R&D center, Texas Instruments Inc.)

Codecs used in telephone networks in the United States have a mu-law companding characteristic solely designed for the purpose of transmitting voice signals. These mu-law codecs are not well suited for the latest generation of high-speed digital voiceband modems requiring PCM data transmission at the quantization levels of the codec. In this paper, we have shown that using a linear codec in the telephone network is optimal for PCM transmission in terms of a minimum symbol error rate performance of these PCM modems without any increase in the complexity of the modem. In practice, it would be necessary and relatively simple to implement an additional feature in the mu-law codec to detect a voiceband modem during the initial phase of training and switch to a linear companding characteristic.

COMM-8.9

Information measure based stochastic system identification of ATM network traffic
Baibing Li, Bart De Moor (SISTA-ESAT, Dept. of Electrical Engineering, Katholieke Universiteit Leuven)

For ATM network traffic, a new approach based on the Kullback-Leibler information measure is proposed for stochastic system identification of packet traffic. This approach, equivalent to the maximum marginal likehood estimate, can overcome the over-modeling problem in [1] such that much more parsimonious model order N can be obtained, and then lead significant reduction in the latter queueing analysis involving in O(N3) computational complexity. A practical case study is provided for a set of Internet traffic data.

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Last Update: February 4, 1999 Ingo Höntsch