Method and apparatus for wireless device performance testing

A method and apparatus for obtaining a set of optimized angles of arrival for a corresponding set of radio links. The set of radio links model a radio environment of a wireless unit operating at a particular location within in a radio system. Each radio link represents a different propagation path between the wireless unit and transmitting antenna operating within the radio system. Each optimized angle of arrival represents an angle of arrival of one radio link with reference to the wireless unit. Each probe antenna of a set of probe antennas is positioned at a corresponding angle of the set of optimized angles of arrival. A corresponding set of probe radio signals is transmitted from the set of probe antennas.

FIELD OF THE INVENTION

The present invention relates generally to electromagnetic communications, and more specifically to determining wireless device performance using standardized system modeling.

BACKGROUND

Standardized radio system modeling has been used extensively for determining the performance of wireless units, such as vehicular phones, cell phones, laptops, and wireless tablets. Standardized radio system testing provides for comparison of different models of wireless devices and can be useful during development of wireless devices when the standardized system model sufficiently models the real world environment. As systems have become more sophisticated, so have the standardized radio system models. Today there are well defined radio system models that use two dimensional modeling, wherein a wireless device under test is placed at a test position within an anechoic chamber that has a plurality of probe antennas placed at regular intervals at 90 degrees elevation and 360 degrees azimuth with reference to a normal position of the wireless device under test. (Note that for this document an elevation angle of zero is along an upper half of an axis that is vertical with reference to the horizontal plane.) With the increasing use of multiple-input-multiple-output antennas within devices, more complex mathematical algorithms are proposed to model the radio systems using radio propagation channels in three dimensional models. This results in greater numbers of antenna probes within anechoic test chambers that have been proposed to improve the modeling of the real world environment. The greater number of antenna probes includes probe antennas that are placed anywhere within the full elevation range of 0 to 180 degrees, that are not used in two dimensional models, and at smaller azimuth angular intervals One result of more antenna probes is the need for a larger anechoic chamber to reduce antenna coupling to limits. The increased size and complexity of the test setups can cost substantially more per unit test to run than earlier test systems.

DETAILED DESCRIPTION

Before describing in detail the following embodiments, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to testing of wireless devices in an anechoic chamber, in which a minimum number of antenna probes transmit modified forms of a particular test signal to a device under test. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

Referring toFIG. 1, a geometric block diagram of a radio system model100that is used as a basis of modeling radio signal propagation in actual radio systems is shown, in accordance with certain embodiments. The radio system model100may closely represent an actual radio system or may be a channel model of a type of radio system. The characteristics of propagation of the transmitted radio energy in these radio system models are commonly referred to as the channel model. Channel models have been defined for environments such as an urban micro-cell (whichFIG. 1represents), an indoor micro-cell a suburban macro-cell, or a rural macro-cell. The modeling of radio signal propagation in some embodiments is provided for radio energy that propagates from one transceiver105to one wireless unit110. The wireless unit can be any wireless device. The wireless unit may be any client device, of which just a few example are a cellular phone, a vehicular communication device, a PC or a tablet. In some cases the wireless device may not be considered a client device, such as a node of a local area network. Some of these embodiments are described in standardized channel models used in a channel modeling process for wireless unit test procedures, such as channel models and processes described in Chapter 5 of “MIMO Signal Processing”, Sebastian Miron (Ed.), ISBN: 978-953-7619-91-6, InTech. Chapter 5, “MIMO Channel Modelling” was authored by Faisal Darbari, Robert W. Stewart and Ian A. Glover of the University of Strathclyde, Galsgow, United Kingdom. Included in Chapter 5 are descriptions of newer radio system models such as SCME (extended spatial channel model), WINNER II, as well as some older models. These standardized channel models are included in specifications or documents issued by agencies such as CTIA, 3GPP, and WINNER. CTIA refers to “CTIA—the Wireless Association” located at 1400 16th Street, NW, Suite 600 Washington, D.C. 20036. 3GPP refers to the 3rd Generation Partnership Project, having a location at 3GPP Mobile Competence Centre, c/o ETSI, 650, route des Lucioles, 06921 Sophia-Antipolis Cedex, France. WINNER is a consortium co-ordinated from Nokia Siemens Networks GmbH and Co. KG, SN MN PG NT RA, St. Martinstrasse 76, 81617 Munich, Germany. These channel modeling processes may use random selection techniques to perform many instances of channel propagation emulation in order to determine the performance of a wireless unit in a particular channel model (e.g., an urban micro-cell)

It will appreciated that these radio system models are not only useful in methods used for testing wireless units to determine their performance according to published standards; these radio system models may alternatively be used for other purposes, such as optimizing the locations of a wireless unit and transceiver relative to each other when both units are going to operated in fixed positions.

Referring again toFIG. 1, in some embodiments the radio signal received at the wireless unit is analyzed for a situation of the wireless unit in which the wireless unit is moving at defined speeds and directions within the radio system, using a particular channel model. InFIG. 1, a wireless unit110is shown as moving along a path114that is shown as a dashed line starting at location111, curving behind a building155, and ending at location113. The radio energy received by the wireless unit110along the path114can be modeled as a set of radio links that include clusters of rays, or sub-paths. Each ray is affected by an environment that is characterized by a variety of propagation parameters. The channel model defines some of these propagation parameters. Some of the propagation parameters are classified as large scale parameters, which are parameters that do not change significantly over distances of a few tens of wavelengths, and therefore for which an average value may be used. Other propagation parameters may vary within distances of a few tens of wavelengths. In order to provide tractable analysis of the performance of a wireless unit operating in a particular channel model, a concept is used in some embodiments that is called a drop, which reduces the distance and time over which the channel model is analyzed to near zero. Propagation parameters are determined from the channel model for each drop and many drops are simulated to determine the performance of the wireless unit in the system model for the channel model.

Three drops for the wireless unit110are shown inFIG. 1as wireless drops111,112, and113. There may be a plurality of drops at one wireless location, representing changing characteristics of the radio propagation at various times at the one location. The links for the wireless unit when at location111are illustrated inFIG. 1. Energy is radiated from the antenna107of transceiver105. (The antenna107is mounted on tower or base station106.) Some of the energy arrives at the wireless unit110along each of six multipath routes, each of which involves a reflection. Each reflection is modeled as being at a particular position on buildings125,130,135,140,145,150. There is no multipath to the wireless unit110at location111for building155; it is blocking a direct line of sight path to the wireless unit. The positions on the buildings are such that the reflected energy arrives at the wireless unit110. One of the paths comprises path127from the antenna107to a position126on the building125, then path128from the position126to the wireless unit110at location111. The energy arriving that is reflected off of position126on building125arrives at a specific angle with reference to the wireless unit110. This is the angle of arrival of the energy.

The effects of the environment on this energy are modeled in the form of a radio link conveying energy at the angle of arrival of the path128. The radio link is characterized by propagation parameters of the channel model that modify the energy transmitted by antenna107, for a particular drop (i.e., for the particular location of the wireless unit, the particular angle of arrival, and the particular time of the drop). The values of the propagation parameters correspond to conditions that would occur along paths127and128in the type of environment being modeled (e.g., the amplitude may be modified for range and fading effects). The energy received at the wireless unit110for this channel model is reduced to six or fewer radio links having different propagation characteristics and each having an associated angle of arrival at the wireless unit110.

The angle of arrival for the radio link127-128is the angle of path128with reference to the wireless unit110at location111, as shown inFIG. 1. This angle of arrival has an azimuth angle161and an elevation angle160. In this example there is a horizontal plane that common to the base of the wireless unit100and the buildings125,130,135,140,145,150. An azimuth axis125that is within the horizontal plane is defined relative to the wireless unit110(at a corner of the base of the wireless unit110). The azimuth angle161is the angle between the projection129of path128onto the horizontal plane and the azimuth axis125. The elevation angle160is the angle between the path128and an axis that is perpendicular to the horizontal plane at the corner of the base of the wireless unit110. Each of the links132-133,137-138,142-143,147-148,152-153has a (typically different) angle of arrival for the drop of wireless unit110at location111. These angles of arrival are determined using the same wireless unit based coordinate system. Wireless unit110will also have additional sets of up to six links, each having an associated angle of arrival, for every drop, including drops112and113. The coordinate system used to define the angles of arrival need not be the same as the one described for this example, where it is a polar coordinate system with a plane of 90 degree elevation (a horizontal plane in this example) that is common to the wireless unit110and the base of the buildings125,130,135,140,145,150.

It will be appreciated that this modelling can be used to provide standardized comparison testing of a wireless unit by radiating the wireless unit with a quantity of radio signals equal to the number of radio links. Such standardized wireless unit testing may be required as a part of a procurement process by radio system operators, such as AT&T, Sprint, Verizon, T-Mobile, and Vodaphone, just to name a few well-known radio system operators. A particular radio system operator may require channel model wireless unit testing performed according to a standard issued by a standards agency, such as CTIA and 3GPP, wherein the standard incorporates channel models such as those described herein. Alternatively, a radio system operator could require the use of a channel model test method for wireless unit performance testing as described herein, issued by other engineering groups or the operator itself. Each radio signal is generated at its respective angle of arrival with reference to the wireless unit and transmitted by a probe antenna. Each probe radio signal is derived as a modified form of one test signal. The test signal may include information for the wireless unit to decode, allowing the determination of an error rate. The probe radio signals are determined using propagation parameters whose values are determined for each radio set of links for a particular drop. The drops may be determined using a randomized selection process. The angles of arrival and propagation characteristics can then be determined for a large enough number different drops to determine performance of the wireless unit for a particular environment (e.g., urban macro-cell). The angles of arrival and path lengths may be determined by a channel modeling process. The signal characteristics of the modified radio signal transmitted by each probe antenna may be determined from the channel model and specific parameters such as the path lengths of the links. The signal characteristics includes such items as carrier amplitude, carrier phase shift and phase spread, and polarization shift.

In some embodiments, a mathematical model of the geometry of a particular system may be used to analyze the performance characteristics of a wireless unit, which may be for such purposes as optimizing the position of a fixed wireless unit in a system. In such an instance, a mathematical model of the system geometry (for example, the mathematical model of the system shown inFIG. 1), implementation of which is known, can determine the angles of arrival doe different positions of the wireless unit. Probe antennas can then be placed at those angles and test signals used to optimize the location of the wireless unit.

Referring toFIG. 2, a geometric diagram200of one cluster226of a radio link in the model of the wireless system is shown, in accordance with certain embodiments. The radio link corresponds to path128. The reflection of a signal at a position such as position126inFIG. 1is enhanced in certain embodiments (e.g., SCME and WINNER II) to include a one or more rays at some or all of the reflection positions. The collection of rays is called a cluster. Each ray is also referred to as a sub-path. This is illustrated inFIG. 2, where reflection position126is cluster226. As shown inFIG. 2, in some embodiments used for standardized testing the clusters may include up to 20 sub-paths (e.g., sub-paths221-222and231-232), each having a small deviation around a parent path. The parent path127-128inFIGS. 1 and 2in some embodiments may be one of the sub paths shown inFIG. 2. In some embodiments the parent path may be determined by an average of the angles of the rays in the cluster.

Referring toFIG. 3, a view of a three dimensional geometric representation300of a distribution of antenna probes is shown, in accordance with certain prior art embodiments. A few of these are identified inFIG. 3with reference number310. Prior art solutions providing an environment for determining the performance of a wireless unit in a radio system typically involve placing a wireless unit under test in an anechoic chamber. The anechoic chamber is typically equipped with sufficient probe antennas at defined fixed positions to allow testing of any drop expected to be used for a testing a class of wireless units. During a test, a wireless unit305is positioned at a test position in the anechoic chamber. The number of probe antennas required and their fixed positions are determined by the angles of arrival in the channel model being emulated. The fixed positions are at regular intervals, so that the test setup can be used for a wide variety of purposes, which may include system models having angles of arrival at many azimuth angles For more sophisticated radio systems employing multiple-input-multiple-output (MIMO) antenna systems, angles of arrival may also include elevation angles other than +90 degrees. For example, elevations within the ranges of +45 to +135 degrees may occur in some embodiments.

The probe antennas must be located sufficiently apart from each other to achieve an acceptably low level of antenna to antenna coupling. Hence the volume of the sphere upon which the probe antennas are positioned is larger for wireless units requiring a larger volume and is larger when more probe antennas are used. In embodiments that use probe antennas distributed around the test position in patterns, the angle of arrival of the test signal for each radio link in a drop is provided by coupling the test signal to several probe antennas at signal strengths calculated so that the resultant energy comes for the correct angle of arrival. To accomplish this requires that the probe antennas be sufficiently close to each other so that the combined signal is a plane wave at the test volume, but far enough to avoid coupling. All of these constraints result in a relatively large radius of the sphere at which the probe antennas are mounted. For example, 48 probe antenna locations are described in “3D Channel Model Emulation in a MIMO OTA Setup” authored by Wei Fan, Pekka Kyösti, Fan Sun, Jesper Nielsen, Xavier Carreño, Gert F. Pedersen, and Mikael B. Knudsen, 2013, Department of Electronic Systems, Faculty of Engineering and Science, Aalborg University, Denmark.

Referring toFIG. 4, a geometric diagram400of one radio link427,428in the model of the wireless system100is shown, in accordance with certain embodiments. The angle of arrival of this radio link is the angle of path428, which is a consolidated angle of arrival derived from the cluster of rays described with reference toFIG. 2. By using one consolidated angle of arrival derived from the angles of arrivals of all of the sub-paths in each cluster, the quantity of angles of arrival is substantially reduced in comparison to models using radio links having multiple angles of arrival for each cluster. The signal characteristics for the consolidated radio link that now represents a cluster are derived by using a combination of the signal characteristics (e.g., amplitude and phase shift) the signals for each sub-path that have been determined by using the propagation parameters for each ray. The combination may be a combination weighted by amplitude. Testing of models using multiple drops for both approaches (that is, with multiple rays for each cluster versus a consolidated radio link for each cluster) show that the difference in wireless performance is less than +−5% when the consolidated angle of arrival is the average of the angles of arrival of each sub-path. Other versions of consolidated angles of arrival may be used, for example, a consolidated angle of arrival that is the parent angle of arrival, or an amplitude weighted average of the angles of arrival of each ray. The use of a consolidated angle of arrival for each radio link allows for a unique probe positioning technique that greatly reduces the amount of equipment needed to perform wireless unit analysis, as described below. This technique may be used as a modification in standard channel modeling processes.

Referring toFIGS. 5-6two views of a three dimensional geometric representation500of a distribution of antenna probes are shown, in accordance with certain embodiments. The view inFIG. 5is an elevation view of six probe antennas505,510,515,520,525,530. The view inFIG. 6is a plan view (top view) of the same six probe antennas505,510,515,520,525,530. The probe antennas505,510,515,520,525,530are positioned equidistant in space from a wireless unit535. Each probe antenna is positioned at the angle of a radio link of a model radio system. The performance of a wireless unit in a radio system is therefore modeled by a number of probe antennas that is equivalent to the number of angles of arrival in the radio system model and based on the principle that the consolidated angle of arrival is the average of the angel of arrival for a number of sub-paths. The azimuth and elevation positions of the antennas are changed for different instances of wireless devices, reflectors, and transceiver antenna locations. This approach requires fewer probe antennas, and in some embodiment comparisons, far fewer probe antennas than in prior art radio system models in which the prone antennas are at fixed equidistant positions at regular angular intervals, such as the embodiment described with reference toFIG. 3.

In some embodiments the probe antennas505,510,515,520,525,530are movably attached to a rail having the form of an arc of a sphere that is rotatably attached to a base540at point580. The rails inFIGS. 5 and 6are illustrated as being approximately 180 degree arcs capable of providing an elevation range close to 180 degrees. In other embodiments, if the radio systems being modeled do not require a full range of elevation angles, the arc shaped rails550,555,560,565,570,575can be shortened at both ends and be designed to move in a circular path on the base540, in which case the base would be raised closer to the test position). The range of elevation and azimuth angles needed may be determined by tests defined in one or more radio testing standards, or may be determined by a specific set of variations of geometry of a radio system being modeled. When a two dimensional channel model is emulated, the antenna probes505,510,515,520,552,530are typically placed at the elevation of 90 degrees. In some embodiments the probe antennas and the wireless unit are within an anechoic chamber. In some embodiments, the probe antennas are dual polarized horn antennas. The use of fewer probe antennas has benefits of reducing cost of emulations because each probe antenna may, for example be driven by a dedicated amplifier. In comparison, when many fixed probe antennas are used, either a larger number of dedicated complex amplifiers are needed and/or high quality radio frequency switches are used, which costs substantially. Also, the distance of the probe antennas from the wireless unit must be larger to prevent antenna coupling, which also increases costs.

The embodiment described here uses six probe antennas for six consolidated radio links. In embodiments used for some standardized testing, complex environments such as urban microcells are modeled as having six main propagation paths from the transceiver to the wireless unit. This number of propagation paths is deemed sufficiently diverse to provide a realistic model without using more paths. The six probe antenna embodiment described with reference toFIGS. 5 and 6would be sufficient for these 6 path models. The number of probes used for this unique approach of using a set of probe antennas wherein each probe antenna is positioned at an angle of arrival of a radio link can be increased or decreased as needed for other radio system models. Other means of positioning the probe antennas could be used. For example, rails that are straight vertical rails could be used, as long as the probe antennas are able to be directed at the wireless unit535. The test signals would have to be compensated for the differing distances of the probe antennas, and for embodiments in which an anechoic chamber is used, the chamber would have to be large enough to accommodate rails that are tall enough to achieve a desired range of elevation angles. The size of the chamber would have to allow for reduction of antennas coupling to acceptable levels. A free space arrangement may avoid the use of an anechoic chamber, as long as the strength of interference signals and reflections off of the nearest ground plane and other reflectors are sufficiently small.

It will be appreciated that the technique of radio system modeling described above with reference toFIGS. 1-2,4-6can be used for purposes other than comparative testing of wireless units operating in a radio system. For example, the technique could be used to optimize the locations of a transmitter and receiver in a fixed environment, by making measurements of performance of the receiver when the angles of arrival are determined for various relative positions of the transmitter and receiver with the fixed environment. An example is the placement of a transmitter and receiver in an environment for which the position and orientation of the reflecting surfaces is known, and the number of such reflecting surfaces (and therefore, the number of probe antennas) is a cost effective approach. Another example is the placement of a transmitter and receiver in an environment to optimize a given location or range of known locations for a wireless unit.

Referring toFIG. 7, a flow chart700of some steps of a method for modeling a radio system is shown, in accordance with certain embodiments. At step705, a set of optimized angles of arrival for a corresponding set of radio links is obtained. The set of radio links model a radio environment of a wireless unit operating at a particular location within in a radio system. In some embodiments, the location is a location of a drop that may be used for performance comparison of wireless units. In some embodiments, the location is a relative location of the wireless unit with reference to the transmitting antenna in a system model used for optimizing relative locations of the wireless unit and the transmitter antenna. In some embodiments the location is a relative location of the wireless unit relative to a system in a system model used to optimize the location of the wireless unit. Other uses may be made of a system model having a wireless unit at a location, such as optimizing the design of the wireless unit. The radio links represent different propagation paths between the wireless unit and another transceiver operating within the radio system. Each optimized angle of arrival represents an angle of arrival of one radio link with reference to the wireless unit. At step710a corresponding set of probe antennas is positioned. Each probe antenna is positioned at a corresponding one of the set of optimized angles of arrival. At step715a corresponding set of probe radio signals is transmitted from the set of probe antennas. In some embodiments, the optimized angles of arrival may include sub-paths. In those embodiments the optimized angles of arrival are derived from the sub-paths. Otherwise, each angle of arrival is the optimized angle of arrival.

Referring toFIG. 8, a flow chart800of some steps of a method for modeling a radio system is shown, in accordance with certain embodiments. At step805wireless a wireless unit under test is positioned as a test position within an anechoic chamber. At step810, a set of optimized angles of arrival for a particular drop is obtained. A channel model of a radio system that includes a wireless unit and a transceiver that transmits radio signals to the wireless unit is used to determine the angles of arrival. At step815, a corresponding set of probe antennas are positioned within the anechoic chamber. Each probe antenna is positioned at one of the set of optimized angles of arrival. At step820, a test is performed using a corresponding set of probe radio signals that is transmitted from the set of probe antennas. Each probe radio signal is a modified form of one selected test signal. Each modification is defined by the channel model.

Referring toFIG. 9, a flow chart900of one step of a method for modeling a radio system is shown, in accordance with certain embodiments. The method may be one of the methods described with reference toFIGS. 7 and 8. At step905, the optimized angle of arrival of each radio link referred to in step705(FIG. 7) and step810(FIG. 8) is derived from one of a mathematical model and a channel model.

Referring toFIG. 10, a flow chart1000of one step of a method for modeling a radio system is shown, in accordance with certain embodiments. The method may be one of the methods described with reference toFIGS. 7 and 8. At step1005, each radio signal is generated by modifying the signal characteristics of a test radio signal, wherein the modification is derived from a channel model. The channel model establishes propagation parameters associated with the radio link for a particular location, or drop, of the wireless unit.

Referring toFIG. 11a flow chart1100of one step of a method for modeling a radio system is shown, in accordance with certain embodiments. The method may be one of the methods described with reference toFIGS. 7 and 8. At step1105, the optimized angle of arrival of a radio link is derived from angles of arrival of one or more sub-paths in a cluster of sub-paths of the radio link, wherein each sub-path has an angle of arrival with reference to the wireless device.