Indoor Wideband Time/Angle of Arrival Multipath Propagation Results zy Quentin Spencer, Michael Rice, Brian Jeffs, and Michael Jensen Department of Electrical zyxwv 8~ Computer Engineering Brigham Young University Provo, Utah 84602 AbstTact- Most current indoor propagation experiments measure the time of arrival of characteristics of multipath reflections without regard to angle of arrival. Because of the increasing number of systems that are used indoors and which use multiple antenna systems to combat multipath in- terference, a need exists for indoor propagation data which takes angle of arrival into account. In this paper, a system is described which was used to collect simultaneous time and angle of arrival data in two indoor environments. A total of 65 data sets were taken in two buildings of differ- ent construction. The data confirmed the temporal model proposed by Saleh and Valenzuela zyxwvuts [l], and showed a unique clustering pattern in angle, which consisted of clusters uni- formly distributed in angle, with members of the clusters following a Laplacian distribution. I. INTRODUCTION Radio has recently become an increasingly viable option for indoor communications applications. The availability of new, higher frequency bands has made wireless an at- tractive option for high bandwidth digital communications in applications such as local area networks. Wireless net- works can be advantageous in situations where portability is desirable, or where installation of wiring is undesirable or impractical. Multipath interference, or interference due to the recep- tion of multiple copies of a signal due to reflections, is known to be a problem in many outdoor communication channels. As a result, much data has been collected in out- door environments to characterize various multipath sce- narios. However, multipath is also a problem in indoor en- vironments, but has characteristics distinct from outdoor multipath because of the presence of walls and large ob- jects which present very different reflection mechanisms. The increasing use of wireless in indoor applications de- mands greater study of the indoor multipath environment. Several other researchers have already collected various types of data on indoor multipath propagation. The foun- dation for much of today’s work was the paper by Turin, et a1 [2], which was a study of outdoor multipath propa- gation in an urban environment. This work eventually led to the paper by Saleh and Valenzuela, an important early reference on indoor multipath propagation. Their work consisted of collecting temporal data on indoor propaga- tion, from which they proposed a time domain model for indoor propagation. Their model is discussed in the paper by Spencer et a1 [3]. Until very recently, nearly all of the work in indoor mul- tipath propagation dealt with time domain data, but did not include any data on the angle of arrival. Knowledge of the angle associated with a multipath arrival is important because of the increasing use of multiple antenna systems in communications applications. Signals from multiple an- tennas can be exploited by using (for example) diversity combining, phased array beamforming, or adaptive array processing algorithms to overcome the effects of multipath. Additionally, multiple antenna systems have the potential to allow multiple users to simultaneously use the same fre- quency band, making efficient use of r.f. bandwidth. In order to predict the performance of these combining al- gorithms, knowledge of both the time and angle of each arrival in a multipath environment is needed. Studies on the distribution of angles of arrival for indoor channels have not been published until very recently. Lo and Litva [4] found that multipath arrivals tend to occur at varying angles indoors, but were not able to arrive at any conclusions based on their limited data. Guerin [5] used a data acquisition system similar to the one used in this present study to collect narrowband angle of arrival data and wideband time arrival data, but they did not collect any data in which the two were measured simultaneously. Wang, et a1 zyxw [6], used a rectangular antenna array to esti- mate both the elevation and azimuth angles of arrival for major multipaths, but did not measure the corresponding time of arrival. Litva, et al, [7] used a rectangular array to take simultaneous measurements of time and angle of arrival, similar to the format of the data presented here. They came to the preliminary conclusion that it is possible to make accurate measurements of this type and learn more about what is happening in the indoor multipath channel. However, their experiment was not extensive enough to make any conclusions about the channel. This paper expands on some of this recent research. A data acquisition system is described which was able to col- lect simultaneous measurements of both time and angle of multipath arrivals over short transmission distances. This enables a joint temporal-spatial characterization of the in- door channel response. Some of the results will be pre- sented, along with general observations about the patterns that were noticed. 11. DATA ACQUISITION SYSTEM The key to the data acquisition system was that the propagation distances in question were relatively short. This allowed for the possibility of the transmitter and the 0-7803-3659-3/97 $1 0.00 01 997 IEEE 1410