The PACS radio interface is the leading low-tier candidate for standardization in North America. This radio interface was originally conceived to serve pedestrian and fixed-distribution applications; there has been significant recent interest in extending this technology into high-mobility environments. In such environments, rapid channel variations significantly degrade the performance of the preselection diversity scheme proposed for use in PACS handsets. This paper quantifies this degradation and proposes a modified preselection diversity scheme using shorter diversity measurement lengths. This scheme yields good performance in both low-mobility and high-mobility environments.

In our highly mobile society, the provision of voice and data communications to a person away from his/her wireline telephone has become a major communications frontier. The early penetration of this frontier has been based on very limited portable communications approaches, e.g., cordless telephones, mobile radio telephones, and radio paging. Each of these approaches only partially satisfies portable communications needs. This paper describes an approach to providing universal digital portable communications integrated into telephone networks. A system configuration employing time-division multiple-access radio link architecture and frequency reuse is described. Issues affecting radio link transmission rates and radio system coverage are discussed. Characteristics and parameters of a possible system to supplement the wire (or fiber) loop are indicated.

This paper presents the measured performance of a 64 kbit/s switched-diversity FSK receiver subjected to simulated frequency-selective Rayleigh fading. The single receiver input is switched between two, three, or four uncorrelated Rayleigh-fading signals whenever the instantaneous receiver output falls below a threshold. The optimum level of this threshold relative to the mean signal level is relatively insensitive to frequency selectivity and vehicle speed. A nearly optimum threshold may be determined using an AGC amplifier and fixed comparator. Switched diversity is a powerful tool for combating frequency selectivity and Rayleigh fading. Two-branch switched diversity can achieve 10-2BER, with 6 dB lower SNR than that needed without diversity. In the absence of frequency selectivity, two-branch switched diversity can perform within 3 dB SNR of maximal-ratio diversity and within 1 dB of selection diversity. Switched diversity can achieve BER's lower than the irreducible single-channel BER produced by frequency selectivity. Four-branch switched diversity typically requires 4 dB lower SNR to achieve a given BER than does two-branch switched diversity.

We present the analysis and design of an efficient hybrid digital/analog multichannel hardware simulator for frequencyselective Rayleigh-fading mobile radio paths. The simulator has eight RF outputs and is linear and reciprocal. All outputs exhibit mutually independent Rayleigh fading over a 45 dB range and have identical time delay spreads. Analog RF techniques are combined with a digital signal processor (DSP) to generate random path modulation. Frequency selectivity from time delay spread is created using several RF path delay elements. Simulated vehicle velocity is continuously variable from 6 to 60 mph. The simulator is thus a flexible tool for the study of mobile radio transmission techniques.

This paper presents measured error-rate performance of binary FSK with discriminator detection in simulated Rayleigh fading with time delay spread. Measured relations between error rate and carrier-to-noise ratio are shown for a range of time delay spreads. We have verified that the effect of time delay spread on error rate can be described by only one parameter, the ratio of the rms delay spread to the transmitted baud time. Intersymbol interference from time delay spread causes an irreducible error rate for FSK, even for infinite carrier-to-noise ratio. For 64 kbit/s binary FSK, the 2.6μs rms delay spread typical of the urban environment produces an irreducible error rate of 3 percent. The measured irreducible error rate for binary FSK with discriminator detection is proportional to the fourth power of the ratio of rms delay spread to baud time. This functional dependence is identical to that predicted analytically for FSK with incoherent matched-filter detection.

This paper presents distributions of the intervals between fades measured on a hardware-simulated Rayleigh-fading mobile radio channel. For intervals between deep fades, these distributions take on a Poisson form. Measured results are in good agreement with a simple analytical model. Distributions for the intervals between shallower fades exhibit preferred durations caused by peaks in the Doppler fading spectrum.

Signal attenuation due to rain is the primary source of outages on earth-satellite radio links operating above 10 GHz. Measurements of the durations of rain fades are also useful in assessing link performance since the effect of many short outages is clearly different than that of fewer long outages. In this paper the authors present a set of measurements of the number and duration of rain fades measured at 19.04 GHz along an earth-satellite path with 18.5 degree elevation. Since rain attenuation is seasonally dependent, one would expect some seasonal variation in at least the rate of occurrence, and possibly the durations of rain fades. This paper briefly examines this dependence. Another factor affecting the performance of earth-satellite RF links is the distribution of time intervals between rain fades, called here `interfade intervals'. If the probability of short interfade intervals were high, this could adversely influence the link performance for services with long holding times. This paper presents measured distributions of these intervals.

This paper presents measured fade duration and levelcrossing statistics of a hardware-simulated mobile radio channel. These measurements were taken over a wide range of fade depths. The measurements agree well with existing analytical results and extend them to show the distribution of fade durations for shallow fades. Fine detail in the fade-duration distributions for shallow fades is produced by peaks in the fading spectrum.

Relationships between rain and ice attenuation and depolarization at 19 GHz have been determined for linear incident polarizations ± 4 and\pm 8\degfrom vertical. These relationships are based on measurements made using beacon transmissions from a COMSTAR satellite. A technique is used to bound depolarization magnitude at any incident polarization from a depolarization magnitude measurement made at another polarization. This technique makes use of previous observations that depolarization is minimal at vertical and horizontal incident polarizations. The bounds are compared with the results from the COMSTAR measurements.

Three experimental programs at Bell Laboratories, Crawford Hill, NJ, have collected rain attenuation data at three frequencies in the 10-30 GHz range for over 2 years. As expected from a simple geometrical model, rain attenuation statistics scale approximately as the cosecant of the path elevation angle. Thus, greater attenuation is encountered on lower elevation angle paths. The increased rain attenuation at higher frequencies is illustrated by comparing cumulative rain attenuation distributions at three widely separated frequencies. Typical year-to-year variations in these distributions are presented. Periods of severe rain attenuation are shown to occur more frequently during the summer months and during the afternoon hours. Cumulative attenuation distributions are compared for these and other time periods.

Cumulative attenuation distributions for one year and relationships between attenuations at 19 GHz and 28 GHz are presented for an earth-space propagation path terminating at Crawford Hill, New Jersey. An example from the distributions indicates that 20 dB attenuation was exceeded for 0.012% of the year at 19.04 GHz and for 0.06% at 28.56 GHz. For both frequencies the polarization was linear and oriented 21° from vertical at the receiver. When the attenuation at 19 GHz was less than 20 dB, the attenuation in dB at 28 GHz averaged 2.1 times that at 19 GHz. This ratio was lower at higher attenuations.