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We present new frequency allocation schemes for wireless networks and show that they outperform all other published work. Two categories of schemes are presented: 1) those purely based on measurements and 2) those that use site-specific knowledge, which refers to knowledge of building layouts, the locations and electrical properties of access points (APs), users, and physical objects. In our site-specific knowledge-based algorithms, a central network controller communicates with all APs and has site-specific knowledge so that it can a priori predict the received power from any transmitter to any receiver. Optimal frequency assignments are based on predicted powers to minimize interference and maximize throughput. In our measurement-based algorithms, clients periodically report in situ interference measurements to their associated APs; then, the APs' frequency allocations are adjusted based on the reported measurements. Unlike other work, we minimize interference seen by both users and APs, use a physical model rather than a binary model for interference, and mitigate the impact of rogue interference. Our algorithms consistently yield high throughput gains, irrespective of the network topology, AP activity level, number of APs, rogue interferers, and available channels. Our algorithms outperform the best published work by 18.5%, 97.6%, and 1180% for median, 25th percentile, and 15th percentile user throughputs, respectively. Index Terms--Cellular networks, frequency allocation, radio spectrum management, site-specific knowledge, wireless local area network (WLAN).

This paper presents spatio-temporal measurements for the peer-to-peer radio channel at a center frequency of 1920 MHz with 140 MHz of radio-frequency bandwidth. The measurements were taken using a spread-spectrum channel sounder and an automated spatial probing system that uses precise computer-controlled positioning and orientation of omnidirectional and directional (30[degrees] beamwidth) antennas to measure both the angles-of-arrival and time-delays of multipath components. Transmitter-receiver configurations included six outdoor-to-outdoor cross-campus locations at Virginia Polytechnic Institute and State University (17-219 ns rms delay spread, 0.36--0.91 angular spread--using the unitless definition of angular spread defined in [1]), three outdoor-to-indoor locations (27-34 ns rms delay spread, 0.78-0.98 angular spread), and three indoor-to-indoor locations (29-45 ns rms delay spread, 0.73--0.90 angular spread). The paper also quantitatively describes a trend that shows how angular spread increases with increasing delay spread. Index Terms--Angle of arrival, fading channels, mobile communications, multipath channels, peer-to-peer, propagation.

Indoor parasitic cellular systems reuse the same frequencies as outdoor cellular (macrocellular) systems to provide wireless communications inside a building or campus. This paper provides a simulation strategy to determine future channel availability that is possible between in-building and outdoor cellular systems that share the same radio spectrum. Capacity that is currently available inside an urban office building is first derived from field-strength measurements of all the channels in the macrocellular system made inside the building. We then create a simulation that determines the effect of a growing outdoor cellular system on in-building frequency reuse. Future in-building frequency reuse is predicted over a 6-yr timeline in 3-mo intervals and includes the effect of height above ground inside the building. Results show that indoor reuse is practical as long as interference levels of about -85 dBm can be tolerated from the outdoor macrocellular system. Index Terms - In-building wireless, parasitic cellular, SitePlanner, spectrum sharing, WPBX.

This paper presents an experimental study of impulsive noise in urban hospitals and clinics. A receiver was designed to resolve impulsive noise bursts as short as 2 [Mu]'s in duration in the 450-MHz band. Extensive measurements were taken at three hospitals and three clinics in three major urban areas across the United States and empirical models are provided for the amplitude, interarrival time, and duration distributions of observed impulsive noise events. This work may be used in modeling the noise found in indoor wireless communication channels. Index Terms - Impulse noise, indoor radio communication.

This paper describes a geometrical optics based model to predict propagation within buildings for Personal Communication System (PCS) design. A ray tracing model for predicting propagation based on a building blueprint representation is presented for a transmitter and receiver located on the same floor inside a building. Measured and predicted propagation data are presented as power delay profiles that contain the amplitude and arrival time of individual multipath components. Measured and predicted power delay profiles are compared on a location-by-location basis to provide both a qualitative and a quantitative measure of the model accuracy. The concept of effective building material properties is developed, and the effective building material properties are derived for two dissimilar buildings based upon comparison of measured and predicted power delay profiles. Time delay comparison shows that the amplitudes of many significant multipath components are accurately predicted by this model. Path loss between a transmitter and receiver is predicted with a standard deviation of less than 5 dB over 45 locations in two different buildings.

In this paper, we examine the performance enhancements that can be achieved by employing spatial filtering in code division multiple access (CDMA) cellular radio systems. The goal is to estimate what improvements are possible using narrow-beam adaptive antenna techniques, assuming that adaptive algorithms and the associated hardware to implement these systems can be realized. Simulations and analytical results are presented which demonstrate that steerable directional antennas at the base station can dramatically improve the reverse channel performance of multicell mobile radio systems, and new analytical techniques for characterizing mobile radio systems which employ frequency reuse are described using the wedge-cell geometry of [1]. We also discuss the effects of using directional antennas at the portable unit. Throughout this paper we will use phased arrays and steerable, fixed pattern antennas to approximate the performance of adaptive antennas in multipath-free environments.

This paper presents results of wide-band path loss and delay spread measurements for five representative microcellular environments in the San Francisco Bay area at 1900 MHz. Measurements were made with a wide-band channel sounder using a 100-ns probing pulse. Base station antenna heights of 3.7 m, 8.5 m, and 13.3 m were tested with a mobile receiver antenna height of 1.7 m to emulate a typical microcellular scenario. The results presented in this paper provide insight into the satistical distributions of measured path loss by showing the validity of a double regression model with a break point at a distance that has first Fresnel zone clearance for line-of-sight topographies. The variation of delay spread as a function of path loss is also investigated, and a simple exponential overbound model is developed. The path loss and delay spread models are then applied to communication system design allowing outage probabilities, based on path loss or delay spread, to be estimated for a given microcell size.

Analysis techniques that quantitatively describe the impact of propagation path loss and user distributions on wireless direct-sequence code-division multiple-access (DS-CDMA) spread spectrum systems are presented. First, conventional terrestrial propagation models which assume a [d.sup.4] path loss law are shown to poorly describe modern cellular and personal communication system channels. Then, using both a two-ray propagation model and path loss models derived from field measurements, we analyze the impact of path loss on the frequency reuse efficiency of DS-CDMA cellular radio systems. Analysis is carried out for the reverse (subscriber-to-base) channel using a simple geometric modeling technique for the spatial location of cells, and inherent to the geometry is the ability to easily incorporate nonuniform spatial distributions of users and multiple layers of surrounding cells throughout the system. Our analysis shows the frequency reuse efficiency (F) of the reverse channel with a single ring of adjacent cells can vary between a maximum of 71% in [d.sup.4] channels with a favorable distribution of users, to a minimum of 33% in [d.sup.2] channels with a worst case user distribution. For three rings of adjacent users, F drops to 58% for the best [d.sup.4] case, and 16% for the worst [d.sup.2] case. Using the two-ray model, we show that F can vary over a wide range of values due to the fine structure of propagation path loss. The analysis techniques presented here can be extended to incorporate site-specific propagation data.

It is well known that cellular system capacity can be increased by reducing the cell cluster size N. Reducing the cluster size, however, increases cochannel interference. In recent years, several techniques have been proposed for controlling the cochannel interference and simultaneously reducing the cluster size. In this paper, we combine two proposed capacity improvement methods and explore the effectiveness of reducing cochannel interference using narrow-beam antennas ('smart antennas') with the fractional loading factor. As shown in this paper, it is possible to increase capacity by many times by decreasing the cluster size (i.e. increasing frequency reuse), although the proper combination of antenna specifications and fractional loading is surprisingly nonintuitive. The first cochannel mitigation technique uses base-station antennas with narrow beams in the direction of the desired mobile stations and significant side lobe attenuation in the direction of undesired users. The second technique exploits the fact that interference is related to the loading factor [p.sub.ch], which defines the probability that a given channel is in use within a cell. We show that large capacity gains with respect to a reference cellular system (N = 7, three sectors per cell) can be obtained by combining these two techniques. This paper provides insight for system-level deployment of high-capacity cellular systems and can be extended to fixed wireless systems as well. Index Terms--Adaptive narrow-beam antennas, cellular radio system, fixed wireless system, fractional loading factor, system capacity improvement.

This paper presents a new theory of multipath shape factors that greatly simplifies the description of small-scale fading statistics of a wireless receiver. A method is presented for reducing a multipath channel with arbitrary spatial complexity to three shape factors that have simple intuitive geometrical interpretations. Furthermore, these shape factors are shown to describe the statistics of received signal fluctuations in a fading multipath channel. Analytical expressions for level-crossing rate, average fade duration, envelope autocovariance, and coherence distance are all derived using the new shape factor theory and then applied to several classical examples for comparison. Index Terms---Angle of arrival, diversity, fading channels, mobile communications, multipath channels, propagation, scattering.