James F. Kepler

An experimental OFDM system for broadband mobile communications

We present an overview of an experimental 20 MHz 2/spl times/2 MIMO-OFDM system for operation at 3.65 GHz. The transmitted signal characteristics, data collection setup, measurement analysis, and timing acquisition algorithms are described. Field trials from a base station with two transmit antennas to a two-antenna mobile receiver are planned in a coverage area having a two mile radius. The first phase of the development process of this experimental system is complete, and initial laboratory results in the area of MIMO channel estimation and demodulation are presented for an indoor pedestrian MIMO channel.

Delay spread measurements on a wideband MIMO channel at 3.7 GHz

This paper summarizes the delay spread characteristics of a 20 MHz MIMO channel at a carrier frequency of 3.676 GHz. The signals are transmitted from a two-antenna base to a two-antenna mobile receiver, and the experiments were conducted in a suburban setting outside Chicago, Illinois. The results include a statistical description of the delay spread environment. In addition, a case study of the temporal behavior of the channel is presented along with a one-bounce analysis to locate macro scatterers.

Wideband MIMO mobile impulse response measurements at 3.7 GHz

This paper summarizes the propagation characteristics of a 20 MHz channel at a carrier frequency of 3.676 GHz transmitted from a two-antenna base to a two-antenna mobile receiver. The experiments were conducted in a moderate density suburban setting outside Chicago, Illinois. The transmit and receive systems are described, as are the data collection procedures and data analysis. The results include path loss measurements and various metrics of the MIMO channel, such as channel impulse responses, rms delay spread, and other spatial characteristics.

Experimental MIMO Comparisons of a 4-Element Uniform Linear Array to an Array of Two Cross Polarized Antennas at 3.5 GHz

Motorola has developed a 20 MHz experimental widearea mobile multi-antenna system at 3.5 GHz for characterizing the spatial channel. With this system, simultaneous channel measurements were taken using both a uniform linear array (ULA) and an array of two cross-polarized (XP) antennas for locations near the Motorola Schaumburg campus. The ULA consists of eight vertically-polarized elements with half wavelength spacing between elements and the XP array consists of two XP panels spaced at two wavelengths where each XP panel consists of two co-located antennas with one antenna having a +45° polarization while the other has a -45° polarization. The receive array consists of eight vertically-polarized antennas in a uniform circular array with a radius of 2.62 wavelengths. This paper compares the antenna correlation and the downlink performance of a ULA (with both half wavelength and one wavelength spacings) and the XP array in a power-fair scenario with four transmit elements for each array type in each sector. Eigen beamforming (EBF) for TDD, DOA-beamforming for FDD, and single-user MIMO (SUMIMO) algorithms are compared.

Frequency hopped systems for PCS

The application of frequency hopping methods to cellular and personal communication systems (PCS) is studied. The performance enhancements due to the use of frequency hopping (FH) is initially reviewed followed by a brief summary of previously designed cellular/PCS systems that have incorporated FH methods. A slow frequency hop (SFH) prototype (which incorporated a hybrid form of multiple access, in particular slow frequency hopping CDMA combined with time division multiple access (TDMA)) was developed for PCS applications is then described. Performance results using the SFH prototype in laboratory and field trials are provided. These results demonstrate the excellent performance that may be obtained in PCS environments using a SFH architecture which has a complexity level that is suitable for PCS implementation.<<ETX>>

Field data showing the downlink adaptive beamforming gains in an experimental IEEE 802.16e-2005 OFDMA system

Transmit adaptive beamforming can be applied on the subcarriers of an OFDM system to obtain a coherent processing gain at the receiver. The IEEE 802.16e-2005 standard for mobile broadband wireless access contains signaling strategies that facilitate the use of downlink adaptive beam- forming which leverages time-division duplex (TDD) channel reciprocity. Motorola Labs has developed an experimental mobile multi-antenna OFDM system that implements a realtime, adaptive beamformer that uses these strategies. This paper describes key components and parameters of this experimental system and describes the results of field experiments that show the performance gains realized by this platform.

An Experimental Adaptive Beamforming System for the IEEE 802.16e-2005 OFDMA Downlink

Transmit adaptive beamforming can be applied on the subcarriers of an OFDM system to obtain a coherent processing gain at the receiver. The IEEE 802.16e-2005 standard for mobile broadband wireless access contains signaling strategies that facilitate the use of downlink adaptive beamforming which leverages time-division duplex (TDD) channel reciprocity. Using these strategies, Motorola Labs has developed an experimental mobile multi-antenna OFDM system that implements a real-time, adaptive beamformer. This paper describes key components and parameters of this experimental system and describes the results of initial field experiments that show the performance gains realized by this platform

Seasonal variations in path loss in the 3.7 GHz band

This work presents path loss measurements through a 20 MHz wireless channel at a carrier frequency of 3.676 GHz in a suburban setting outside Chicago, Illinois. The data collection system is described and the measurement environment is characterized. Results are presented for two seasons, winter and summer, demonstrating that tree foliage creates an average excess path loss of between 3 and 7 dB.

Field measurements of a prototype slow frequency hop personal communication system

A 500 kbps, high-mobility, personal communication system (PCS) employing slow frequency hopping (SFH) and time-division multiple access is investigated for the 1.8 GHz band. In order to verify the concepts which drove the system design and to characterize the SFH propagation environment, extensive field tests have been conducted with the prototype units. This paper summarizes the findings and draws conclusions on the effectiveness of the space, frequency, and time diversity. Results are presented for the forward and reverse transmission paths. On the forward path, both mobile and portable receiver antenna configurations have been examined. The complementary set of diversity techniques incorporated within the system has been found to allow robust operation even on the severe multipath fading channels characteristic of the expanded PCS propagation environment.

Estimating Statistical Eigen-Beamforming Gains Using Spatial Channel Correlation

Statistical eigen-beamforming (EBF) is a widely used multiple antenna transmission technique in which one antenna weight is used over potentially a large bandwidth (e.g., all subcarriers in OFDM). With N transmit antennas, the maximum gain for EBF at a receiver is 20 log N decibels over a single antenna transmission (assuming a power unfair comparison where each transmit antenna has a fixed power so the addition of new antennas brings a beamforming gain as well as a total transmit power increase). Based on statistical analysis of field data and observations, this gain is nearly achievable with line-of-sight transmissions. While useful for characterizing the benefits of EBF, the statistical analysis does not indicate the realizable gain for a particular location. This paper presents a relationship between the EBF gain, spatial correlation of the channel, and the number of transmit antennas. The conjectured gain is compared to the expected gain based on an analysis of field data. The results of this comparison show that the spatial correlation as defined in this paper can be used to predict the EBF gain accurately for a variety of antenna spacings and polarizations.