Performance analysis of a COFDM/FM in-band digital audiobroadcasting system

In this paper, we present a performance analysis of a coded orthogonal frequency division multiplexing DAB system that is power multiplexed over a commercial FM station. We model the mobile channel with a time-frequency scattering function. Results show that the performance of the FM demodulator is crucial, since the level of the residual FM signal has a strong influence on the BER performance of the COFDM system. As with other mobile communication systems, the use of interleaving greatly enhances the performances     

Channel codes based on hidden puncturing with applications to hybrid in band on channel digital audio broadcasting systems

In this work, a new approach of designing channel codes for partial band interference channels based on "Hidden Puncturing" is introduced. This technique does not require explicit estimation of the interferer. We investigate the performance of specially designed rate 1/2 convolutional codes with Viterbi decoding and rate 1/2 Turbo codes in an example scenario with partial band FM interference. For comparison, we also give results for Turbo codes for schemes with no interference. We show by means of simulations that for Gaussian as well as for a variety of multipath fading profiles, a significant Turbo channel coding gain compared to a conventional Viterbi system can be achieved. Thereby the performance of optimal combining, which requires optimal estimation of the interferer, can be approached very closely in various scenarios.     

OFDM和FM带内同频广播系统同步技术研究

介绍了带内数模混叠同播的CDRadio数字调频广播技术,通过对三种现有算法的改进和性能仿真,可以看出Park适用算法可以有效地降低算法的复杂度,并且能够显著提高系统的性能,对于同步算法来说,是一个较好的选择。     

四通道调频广播数字调制电路

为了覆盖无线广播信号的接收盲点,设计了一种微型化的四通道调频广播补点覆盖设备。其中的调制电路选用FPGA作为核心器件,采用小数分频的数字调频调制技术,把数字传输的广播声音电压信号直接变换成中频信号。这种调制电路不仅非常简单,而且从根本上解决了传统多通道模拟调制器的串音问题。     

A code division multiplexing scheme for satellite digital audiobroadcasting

Several systems are being considered for digital audio broadcasting (DAB) and some of these systems will be deployed for commercial use. In this paper, we consider a code division multiplex (CDM) scheme for satellite DAB. For diversity purposes, this system makes use of at least two satellites, and in urban areas, where the satellite signals are shadowed by large structures, a terrestrial network is employed. We present a forward error protection (FEC) scheme that is robust under a variety of channel conditions, especially in cases where the received signal is severely attenuated because of highway underpasses and tunnels. This FEC scheme makes use of time diversity, and this introduces a large delay. Such delays will not affect the performance of broadcast systems; however, the delay will be an issue during tuning when a switch to another channel occurs. We introduce a separate low-delay low-rate tuning channel to facilitate tuning. Extensive simulation results are given to examine the performance of the system, and it is shown that about 70 audio channels, each with a rate of 96 kbit/s, can be satisfactorily supported in a bandwidth of approximately 12.5 MHz in most of the channel conditions considered     

Technical considerations of channel 6/FM combining systems

Currently there are approximately 58 commercial channel 6 facilities in the United States. Noncommercial FM stations must protect these facilities from interference by using only antennas. It is argued that this could be avoided by collocating the FM and TV facilities thus broadcasting from the same antenna. TV facilities could generate significant capital by allowing FM broadcasters, commercial and noncommercial, to multiplex onto their current antenna system     

Error rates for narrow-band digital FM with discriminator detectionin mobile radio systems

Error rates for a narrowband digital FM system with discriminator detection in a land mobile radio channel characterized by fading and Doppler frequency shift are obtained using a new analytical method. The fading rate is assumed to be much slower than the bit rate so that signal distortion through a narrow bandpass filter can be analyzed via a quasistatic approach. An experiment was conducted using a Rayleigh fading simulator, and the error rate measurements are shown to agree well with the calculated results, except at high SNR (signal-to-noise ratio) where an irreducible error rate was observed     

Effects of channel narrowing in small zone FM mobile communication systems

In small zone (cellular) FM mobile communication systems, greater geographical reuse is achieved when the modulation index is larger. A large index, however, imposes a small number of channels. The spectrum utilization factor in total thus is determined as a synthesis of available channel number and geographical frequency reuse. From this viewpoint, relationship between the modulation index and spectrum utilization factor is discussed under the Rayleigh fading condition, with and without diversity. To take into account the actual traffic condition not only uniform but also a concentrated traffic distribution condition is considered. It is shown that the optimum peak deviation that realizes the most efficient spectrum utilization is from 3 to 4 kHz for uniform traffic distribution, and 2 kHz for concentrated traffic distribution. These results show that narrow channel spacing, such as 12.5 kHz, is better than the conventional 25 kHz or wider channel spacing to achieve efficient spectrum utilization.     

GaAs digital IC for FM demodulator

A middle-scale GaAs digital IC for a pulse-counting FM demodulator has been designed and fabricated for use in microwave communication systems. The IC is constructed with the normally-on (depletion) MESFET logic with epitaxial active layers. It exhibits a high-speed pulse train with a rise time of 150 ps and with an output voltage of 2.3 V into a 300-Ω load. Output pulsewidth can be altered by the external voltage for tuning the IC to give the highest demodulation sensitivity. By merely implementing a low-pass filter at the output of the chip, the pulse-counting FM demodulator can be realized at high frequencies where the use of Si IC's has never before been possible. We estimate the demodulation sensitivity to be 20 mV/MHz at the microwave IF band.     

Transmitter diversity for a digital FM paging system

Multipath fading is one of the most serious problems for the signal transmission in mobile radio. To combat this problem, the application of transmitter diversity to a digital FM paging system is described. The method is to transmit two digital FM paging signals with different modulation indices, each of which is modulated by an identical binary signal, from separate antennas. It is shown that the same action obtained with the well-known selection diversity can be achieved when the difference between the modulation indices is equal to two. The diversity effect on the bit-error-rate (BER) performance is theoretically analyzed. The diversity effect on the BER performance in a 600-bit/s Manchester-coded digital FM system is verified by the laboratory simulation tests using a Rayleigh fading simulator.     

Equalization problems in a digital FM receiver

In some recent papers a new all-digital intermediate frequency unit for the application in commercial broadcast FM receivers was introduced. Serious problems of an efficient hardware solution are the dynamic requirements of the input analog-to-digital converters, which can be solved by narrow-band analog pre-filtering, only. In this paper a digital nonrecursive equalization network is described, which can be used to compensate the non-ideal characteristics of the analog pre-filters. Furthermore, it will be shown that this equalization technique can be applied to multipath echo cancellation, as well. Some examples will be given to illustrate the reduction of nonlinear distortions after demodulation, if digital equalization is carried out.     

Integrated selectivity for narrow-band FM IF systems

An 18th-order all-pole continuous-time bandpass filter for IF (intermediate frequency) filtering purposes has been designed and integrated in a 3-μm CMOS process. Implemented using nine fully balanced, transconductor-capacitor coupled resonators, the filter features a 20-kHz bandwidth at 200-kHz center frequency and 54-dB dynamic range (IM3<-40 dB) and consumes 300 μA from a single 4-V supply. With the use of conventional phase-locked loop techniques for automatic tuning, the accuracy of the filter response is comparable to that of ceramic filters. As expected, the fundamental limitations of such an active implementation compared to a passive realization are noise and distortion     

A note on necessary bandwidth in FM systems

A digital computer simulation has been used in an effort to define the RF bandwidth needed for good transmission in FM systems in terms of given amounts of interchannel distortion. The computed results have been converted into a relationship that is similar to Carson's rule but perhaps more meaningful.     

A 10 ns hybrid number system data execution unit for digital signalprocessing systems

A high-performance data execution unit suitable for computation-intensive digital signal processing systems is described. This unit uses the hybrid number system approach to speed up the basic arithmetic operations while remaining compatible with a standard IEEE 32-b floating-point format. However, all the arithmetic operations are performed in the 32 b logarithmic number system (LNS) domain. This chip is designed using a 3.4 V 0.8 μm CMOS technology with double-layer metallization. Conversion algorithms, chip architecture, design methodology, and major circuit components are discussed. A macrocell design methodology is adopted in order to achieve high-performance custom design circuits with the convenience of an automatic layout system. Computer simulations indicate that all the 32 b floating-point arithmetic operations (multiplication, division, squaring, and square root) can be executed in 10 ns. Extension of this unit into a 64 b double-precision floating-point system and multiply-accumulation applications are also presented     

Digital audio broadcasting in the FM band based on continuous phase modulation

A method for broadcasting digital audio signals simultaneously with existing analog frequency modulation radio (88-108 MHz) in adjacent channels is presented. The digital transmission is based on continuous phase modulation (CPM) and a proper reduced-state sequence estimator. With the proposed method, the power level and the symbol rate of the transmitter signal is determined in a manner that the interference the CPM signal poses for the analog FM signal in adjacent channels remains below a level according to the radio frequency emission mask defined by international rules. Due to the multipath propagation of the transmitted signal, the transmission behavior of the radio channel is determined by high dispersion up to 85 /spl mu/s. With the selected bit rate, the receiver has to cope with a channel memory of up to 17 bits. Since Viterbi detection is not feasible due to the number of channel states, detection is performed by a reduced-state sequence estimator that is able to eliminate the complete channel interference by decision feedback. Simulation results show that the detector almost achieves the detection quality of the optimum receiver. CPM achieves data rates of up to 200 kb/s inside a 200 kHz FM channel, which is sufficient for transmission of digital compressed audio signals at compact disc quality. The encouraging results of field tests will be published in another paper.     

An efficient hybrid strategy for uplink channel estimation in massive MIMO systems based on spatially correlated channels

The channel estimation (CE) process is an important phase that has a considerable influence on the performance of massive multiple-input multiple-output systems, in particular, in a more realistic scenario where the channels are spatially correlated (ScD). Thereby, in this work, the uplink (UL) CE process and channel hardening (CH) feature is addressed for ScD Rayleigh fading channels using the statistical Bayesian minimum mean square error estimator. The spatial correlation (SC) of the channels is described using different models, namely, the Gaussian local scattering (GLS) model, the uniform local scattering model, and the proposed hybrid model. Each model (i.e., GLS model and the uniform local scattering model) is studied using two arrangements, that is, for a uniform linear array (ULA) and uniform planar array (UPA). Moreover, the CH feature is investigated under SC of the channels using different models. Furthermore, this study proposes an efficient hybrid strategy based on SC of the channels for UL CE; that is, this work proposes a hybrid covariance matrix (CM) for UPA arrangement by relying on the Kronecker product of the CMs generated through two ULA arrangements, where the first CM is generated through horizontal ULA using GLS model, whereas the second CM is generated through vertical ULA using uniform local scattering model (i.e., one-ring model). Numerical results regarding CE and CH are provided to assert the theoretical expressions, where the CE is evaluated using the normalized mean square error, whereas the CH is assessed using the variance of CH.     

Impairment of digital transmission through a Ka band satellite channel due to weather conditions

This paper describes an analytical derivation of the performance impairment of a non-coherent FSK signal and a coherent PSK signal due to fading caused by weather conditions at Ka band. Analytical results on the effect of signal phase variation on a coherent PSK signal are included. Numerical values in terms of probability of bit error are given for the two digital signals. These results should be useful to a system designer of satellite communications systems at Ka band. © 1998 John Wiley & Sons, Ltd.