There are ever increasing demands for additional capacity in wireless communications to handle voice, data, and wideband Internet applications. These demands are constrained by the bandwidth that was allocated to wireless communications. The spectral efficiencies in present day wireless systems hover around 1 bit/s/Hz. Bell-labs Layered Space-Time (BLAST) is a communication technique for achieving very high spectral efficiencies in highly scattering environments using multiple transmit and receive antennas. A measurement campaign was undertaken to assess the BLAST gains in spectral efficiency in the suburban outdoor environment for stationary subscribers. The measurements employed directive antennas to better control interference from adjacent cells. The measurements were performed over a narrow band at 2.44 GHz with five transmitting and seven receiving antennas, respectively. Extensive calibration methods, assisted by simulations, were developed to assure accurate results for the BLAST capacities of the measured remote subscriber sites. Initial results indicate that BLAST capacities of C/sub B//spl ges/38 bits/s/Hz at 20% of the measured locations and C/sub B//spl ges/24 bits/s/Hz at 50% of these locations are feasible, for reasonable link parameters and negligible interference.

We present the results of propagation measurements at 2.485 GHz for fixed wireless loops. Path loss measurements were performed and characterized at 43 subscriber locations around a base station antenna located on top of Crawford Hill in Holmdel, NJ. This suburban location is characterized by rolling hills, foliage, and terrain blockages. Temporal and horizontal motion path loss fluctuations were found to be uncorrelated, each characterized by a different Ricean distribution. Lower r.m.s. delay spreads were obtained with directive subscriber antennas than with omni-directional antennas. No substantial gain loss (less than 2 dB) of subscribers' directive antennas was observed. The effects of trees, with foliage, surrounding the base station upon the path loss and the ratio of scattered power to specular power are also examined. The distance exponent of path loss versus distance (about 1.5) was observed to be less than free-space. Diffraction loss from hilltop trees, shadowing the base station, are suspected to be the cause. This loss decreases as the remote moves further away and comes out of the shadow. Scattered power from directions other than line-of-sight was observed to be as high as one half of the specular contribution when tree scattering near the base station was significant.

Recent breakthroughs in the application of information theory have shown great capacity increase by deploying multiple transmitting and multiple receiving antennas as compared to conventional single antenna systems. This work presents an experimental verification of the theoretical capacity prediction and a summary of measurement results for 16 fixed wireless locations in suburban New Jersey.

Resource auction multiple access (RAMA) is a technique for rapidly assigning communication resources (e.g., frequency carriers and/or TDMA time slots) in a wireless environment. This scheme is deterministic in that, barring errors caused by fading and noise, a resource assignment is made in each and every assignment cycle. Previous papers reported on the ultimate call assignment capacity of this technique, limited only by propagation delays, and also demonstrated its capabilities for statistical speech multiplexing in a PCS environment. We extend the previous work in two directions: (1) we examine the effects of channel fading and noise; and (2) we consider both GSM and IS-54 cellular environments. Propagation is modeled, for purposes of this study, as flat Rayleigh fading, with mean propagation loss as a parameter. We focus on the subscriber-to-base link and consider several forms of diversity at the base. We also consider two RAMA modes (call assignment without and with statistical speech multiplexing). We show that a simple form of two-branch diversity can be very effective. In both GSM and IS-54, for example, using simple diversity and an average transmit power of 100 mw yields assignment error probabilities of only 1% for losses as high as 151 dB.>

An architecture for a combined personal, mobile, and (possibly) loop access microcellular communications system in which calls are digitized and packetized is presented. A network of microcells is utilized to communicate with the various subscribers via radio. A fast handoff/resource assignment process is introduced. It is subscriber-controlled and is jointly performed by the subscribers and base station employing the resource auction multiple access (RAMA) algorithm. In this deterministic algorithm, resource utilization is independent of traffic load. Using selected GSM parameters with RAMA, for the purpose of illustration, it is shown that, in microcells with delays of 1 mu s, 1080 resource assignments per second are feasible: and with delays as high as 45 mu s, 216 assignments per second are feasible.>

Recent analysis/simulation studies have quantified the multipath outage statistics of digital radio systems using ideal adaptive equalization. In this paper, we consider the use of finite-tap delay line equalizers, with the aim of determining how many taps are needed to approximate ideal performance. To this end, we assume anM-level QAM system using cosine rolloff spectral shaping and an adaptive equalizer with either fractionally spaced or synchronously spaced taps. We invoke a widely used statistical model for the fading channel and computer-simulate thousands of responses from its ensemble. For each trial, we compute a detection signal-to-distortion measure, suitably maximized with respect to the tap gains. We can thereby obtain probability distributions of this measure for specified combinations of system parameters. These distributions, in turn, can be interpreted as outage probabilities (or outage seconds) versus the number of modulation levels. A major finding of this study is that, for the assumed multipath fading model, very few taps (the order of five) are needed to approximate the performance of an ideal infinite-tap equalizer. We also find that a simple, suboptimal form of timing recovery is generally quite adequate, and that fractionally spaced equalizers are more advantageous than synchronously spaced equalizers with the same number of taps. This advantage is minor for rolloff factors of 0.5 and larger but increases dramatically as the rolloff factor approaches zero.

The design and implementation of a high-speed, lowpower, and TTL-compatible driver for a 12 GHz digital p-i-n phase shifter are shown. The switching performance of the phase shifter, combined with its driver in a compact module, is presented. Measurements of 40 phase shifter/driver modules show that the longest time required to change phase states (switching time) is under 8 ns. The maximum driving power consumption is 36 mW at a phase switching repetition rate of 1 MHz. Each module can handle 800 mW of CW RF power. The performance and compactness of the phase shifter/driver make this module especially attractive for satellite and airborne applications.

A 4-PSK microstrip modulator operating at data rates of up to 800 Mbits/s at 12 GHz is described. The circuit is made of two cells in series. Each cell consists of a 3-dB branch-line hybrid coupler and two BTL p-i-n diodes. One cell provides 0° or 90° phase shifts, and the Other 0° or 180° phase shifts, so that four carrier phase values are obtained by appropriately exciting the two cells. The switching time of each cell is 200 ps. Simultaneous switching of both cells increases the switching time to a maximum value of 400 ps. The phase waveforms are nearly rectangular at the above-mentioned data rates. RF insertion loss is 1 dB ± 0.1dB for the four phase values over the 11.7-12.2 GHz frequency band.

The signal-to-noise ratio (SNR) statistics of a crosspolarized interference cancellation scheme is derived in terms of the statistics of nondispersive fading of the signals in the radio channels. The results are applied to certain digital radio channels subjected to nondispersive fading. It is found that error rates not exceeding 10-6could be maintained during 99 percent of the duration of a 30 dB fade in a 26.4 mi path. The method and data presented support the feasibility of cross polarization interference cancellation. They are applicable to the determination of SNR budget in the transmission system.