Abstract:
A method and apparatus is provided for determining coupled path loss in a small geographical which is served by a plurality of transmitters and is subject to broad signal level variation. A method is also provided for determining performance of a signal received by a wireless device located within a bin of a cell of a cellular communication system. The method comprises determining the value of the received signal level as a function of the sum of the signal levels received from a primary base station at a primary cell divided by a number of signal level measurements from the primary base station.

Description:
The disclosure claims the filing-date benefit of Provisional Application No. 60/681,475 filed May 17, 2005, the specification of which is incorporated herein in its entirety; the disclosure also relates to application entitled “Method and Apparatus for Determining Path Loss by Combining Geolocation with Interference Suppression” and application entitled “Method and Apparatus for Determining Path Loss by Active Signal Detection filed simultaneously herewith and assigned to the assignee of the instant disclosure, the specification of each of said related application is incorporated herein in its entirety for background information. 
    
    
     BACKGROUND 
     Signal geo-coding is the process of assigning geographic coordinates to a signal. The signal coordinates can include the geographic coordinate of the transmitter as well as that of the receiver. In many locations there may be an abundance of events within a small area called a bin. A bin may include a multi-story building with a number of subscribers at each floor or it may include some other structure. While some bins can generate a number of events, others may show a lack of activity. If there are many events in a bin, a histogram of signal levels and corresponding path loss data can be constructed. If sufficient data is unavailable for a sector, interpolation techniques can be used from other bins to construct a working model. The model can provide some guidelines in frequency reuse planning and interference avoidance. 
     Typically there are too few measurements of interference from a sector in the vicinity of the bin to determine an accurate service level. If a sufficient amount of data has been collected, ignoring sector interference may be justified. However, in most cases the system administrator relies on information that only provide average signal level (or path loss) at a bin. The system administrator does not know whether the average values were determined based on a few or many measurements. Moreover, the average values often misrepresent signal propagation characteristics of a bin. 
     In bins that have an abundance of data, there may be a range of signal levels and interference levels. In these situations relying on average signal level values will prove ineffective as these values do not reflect the true propagation characteristics of the bin. In many instances the signal levels are known to change dramatically within a distance of, for example, ten meters. This is especially true in-building measurements are considered. 
     Conventional planning tools produce an average estimate of the signal level or path loss value per bin for each sector under consideration. Such measurements ignore a tremendous amount of valuable information about the propagation characteristics within a bin. For example, when power levels or antennas are being optimized to minimize overall network interference it is valuable to maintain paired signal levels or path losses that consider the location of the transmitter and the receiver as well as the signal attributes transmitted therebetween. 
     Consider a situation where a bin contains a tall building and the serving cell antenna is located some distance away on top of another tall building. At street level and in the lower levels of the building the serving signal level and the interfering signal level may both be low. On the upper levels of the building the interfering signal levels may increase as would the serving signal level. Relying on an average signal level for the entire building will dilute this valuable information. Using the average serving and interfering signal levels grossly undermines the true propagation characteristics of the bin and leads to a substantial over-estimate of the severity of the interference. 
     On the other hand, in a situation where a serving cell antenna is located nearby on the tall building on a two- or three-story building, the serving cell may be substantially stronger and interference substantially weaker for the lower levels of the building. For the higher levels of the tall building, the serving level may be lower but the interference level may be higher. In this case, the serving and the interfering signal levels would be negatively correlated. Again, an average serving signal level, interference or path loss calculation will not provide sufficient detail of the propagation characteristics. Therefore, there is a need for obtaining propagation information which accurately couples signal levels at different locations within a bin with the serving base stations that provide the signal at said locations. 
     SUMMARY 
     In one embodiment, the disclosure relates to an improved method for assigning a value for an attribute of a signal received by a wireless device located in a bin in a cell of a cellular communication system. Whereas conventionally the value is determined as a function of an average value of the attribute of a first plurality of signals received from a second plurality of base stations, in one embodiment the improvement comprises assigning the value as a function of an average value of the attribute of a third plurality of signals from one of the second plurality of base stations. 
     In another embodiment, the disclosure relates to a method for determining a value for an attribute of a signal received by a wireless device located in a bin in a cell of a cellular communication system comprising the steps of: (a) receiving a first plurality of signals from a first plurality of base stations; (b) measuring a first attribute of the first plurality of signals; (c) determining a primary base station from the first plurality of base stations as a function of the measured first attributes of the first plurality of signals; (d) receiving a second plurality of signals from the primary base station; (e) measuring a second attribute of the second plurality of signals; and (f) determining a value for the second attribute for the wireless device as a function of the measured attributes of the second plurality of signals. 
     In still another embodiment, the disclosure relates to a system for determining a value for an attribute of a signal received by a wireless device located in a bin in a cell of a cellular communication system comprising the wireless device having a receiver for receiving a first plurality of signals from a first plurality of base stations; measuring circuitry for measuring a first attribute of the first plurality of signals; circuitry including a microprocessor for determining a primary base station from the first plurality of base stations as a function of the measured first attributes of the first plurality of signals; said receiver for receiving a second plurality of signals from the primary base station; said measuring circuitry for measuring a second attribute of the second plurality of signals; and said circuitry including a microprocessor for determining a value for the second attribute for the wireless device as a function of the measured attributes of the second plurality of signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the disclosures are described in relation with the following exemplary and non-limiting embodiments, in which: 
         FIG. 1  is a schematic representation of a conventional cellular communication system implementing one embodiment of the disclosure; and 
         FIG. 2  is a flow chart depicting an exemplary method according to one embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic representation of a conventional cellular communication system implementing one embodiment of the disclosure.  FIG. 1  shows cellular communication system  100 , divided into several cells. Conventionally, a cellular communication system defines a cell as a six-side polygon. According to the conventional frequency reuse concept, a single high-power transmitter (for a large area) is replaced by multiple low-power transmitters, each covering only a small portion of the larger area. In this scheme, each base station transmitter is allocated a number of frequency channels from the total number of available channels. To avoid interference, neighboring base stations are assigned different groups of channels. 
     Referring once again to  FIG. 1 , wireless device  102  is located in a bin in cell  122 . The wireless device may be one or more of: wireless transmitter, radio frequency transmitter, mobile telephone, cellular phone, text messaging device, portable computer, laptop computer, personal digital assistant, vehicle security device, vehicle tracking device, pager, base station and wireless location sensor. The wireless device  102  may be referred to herein as a receiver. 
     The wireless device  102  receives signals from each of the base stations  110 ,  112 ,  114 ,  116  and  118 , respectively located at cells  120 ,  123 ,  124 ,  126  and  128 . Because of the intangibles associated with all wireless radio communications, certain received signals may be stronger at the location of the wireless device  102  than others. For example, at street level wireless device  102  may receive its strongest signal from base station  118 . In contrast, if the wireless device is positioned on a roof-top of a tall building in cell  122 , the strongest signal level may come from base station  114  which has a clear line of sight to wireless device  102 . When applied to a bin, the signal level can vary depending on the location where the signal is received in the bin. That is, while all base stations transmit the same signal on the same communication channel, the strongest signal received by the wireless device  102  can vary depending on the exact location and the altitude of the wireless device. When the bin includes a building or a large structure in a metropolitan area, the variation can affect network performance drastically. Any information which couples received signal strength with a location within the bin is useful in frequency reuse planning and network administration. 
       FIG. 2  shows an exemplary method according to one embodiment of the disclosure. The exemplary method outlined in  FIG. 2  is particularly suitable for obtaining signal propagation data for a receiver located in a bin of a cellular communication system. In step  210 , the receiver receives a plurality of signals from several base stations. This information can be received and processed in a relatively short period of time such that it would be reasonable to assume that the mobile terminal has not moved significantly. 
     The quality of the received signals from the several base stations is usually not consistent and typically the signal from one base station stands out as providing the highest comparative quality. Signal quality can be measured as a function of signal level or as a function of other signal attributes. Signal attributes may include signal-to-noise ratio, signal-to-interference ratio, inter-symbol interference, bit error rate, carrier-to-interference ratio or other similar quantifiable indicia known in the art. In step  220 , the receiver identifies the primary signal. Optionally, the receiver can identify the source of the primary signal as the primary base station. In another embodiment, the receiver reports an attribute of the received signals to a central node or to an auxiliary device tasked with monitoring signal propagation in the bin. 
     Once a primary signal is selected, in step  230 , the receiver (or the central node) identifies the primary base station associated with the primary signal. In one embodiment, the primary base station is the base station which transmits the primary signal. The primary base station can also be a relay station configured to amplify and relay a weaker signal received from another transmitter. In addition to identifying the primary base station, the cell and the sector housing said base station may also be identified. This identification can provide additional propagation data. 
     In step  240 , the receiver&#39;s location is identified. This step can be implemented by using any of the conventional geo-location methods. For example, the receiver can be equipped with a geo-positioning system (“GPS”) or it can use a wireless location sensor executing conventional methods such as time-difference of arrival (“TDOA”) or angle of arrival (“AOA”) information, or some combination, to determine the location of the receiver. For an embodiment where the receiver is located in a bin, the latitude and longitude may not vary as much as the altitude. In any event, the receiver&#39;s location can be determined independently of the bin, for example, by latitude, longitude and altitude, or it can be determined in relation to the bin (i.e., at altitude of 200 meters at a given bin location). 
     In step  250 , the location of the receiver and the primary base station serving the receiver at said location may be paired together to provide data points. The data points may additionally include such information as the serving cell&#39;s ID, the base station&#39;s ID, the received signal level and/or other signal attributes. Secondary information including path loss value between the primary base station and the receiver&#39;s location may also be calculated and compiled. Steps  210 - 250  can be repeated for a number of different receiver locations throughout the bin in order to provide, for example, an accurate understanding of the number of base stations serving different locations of the bin (see step  255 ). In step  260 , a database is formed with the compiled data. The database can be used to study and modify the frequency reuse plan. Importantly, these steps can be implemented within the existing communication infrastructure and do not require additional network overlay or expansion. 
     For example, the collected information can be used to build a multivariate histogram of the signal levels or path loss values between the primary base station and the wireless device. This information can also be used to produce interference analyses that are more accurate than the conventional methods which only compare average measurements of each sector. Additionally, the same information can be expanded to take into account the speed and direction of the receiver as it moves through the bin. 
     The steps outlined in the exemplary embodiment of  FIG. 2  can be used to determine a primary base station for the entire bin. According to this embodiment, a representative database can be compiled based on the signal propagation characteristics of the primary base station at one or more locations throughout the bin. 
     In an alternative embodiment where different locations throughout the bin identify different base stations as the primary base stations, the principles disclosed herein can be applied to each primary base station to obtain signal propagation characteristics specific to each location. For example, referring to  FIG. 1 , wireless device  102  may receive its strongest signal from base station  118  if the wireless device is at the first floor of the building. On the other hand, wireless device  102  may receive its strongest signal from base station  114  if the wireless device is positioned on a roof-top of the same building. Wireless device  102  may additionally receive its strongest signal from base station  116  if the wireless device is at the mid-building level and at a southeast corner of the building. Applying the principles of  FIG. 2  to this scenario, a database can be constructed for each of the three locations. Thus, a primary base station can be identified at each location of the building, signal attributes for each location can be determined as a function of the primary base station serving that particular location and the propagation characteristics of each location can be compiled to form a database. 
     A system according to one embodiment of the disclosure may include a plurality of transmitters or base stations communicating with one or more receivers located within a bin within the communication system. The receiver can be a wireless transmitter, a mobile telephone, a cellular phone, a text messaging device, a portable computer, a laptop computer, a personal digital assistant, a vehicle security device, a vehicle tracking device, a pager, a base station or a wireless location sensor. 
     The base stations may be located at different locations from each other and from the receiver. The base stations can transmit a signal to the receiver on the same communication channel, however because of structural and environmental obstacles, for example, the received signal levels at the receiver may vary. The receiver may identify the signal with the most favorable signal attributes from among the received signals. The identification step can be implemented by the receiver or by an auxiliary circuitry in communication with the receiver. The circuitry can include one or more microprocessors. Once the signal with the most favorable attributes (i.e., the primary signal) has been identified, the system (e.g., the receiver or an auxiliary circuit) can identify the source of the signal as the primary base station. In the event that the signal is received from a repeater or a relay station, the primary base station can be the repeater or the relay station. The source can be identified by, for example, base station number, cell and/or sector location. 
     The system may also include a geo-location device for determining the exact location of the receiver. For example, the receiver may include GPS capabilities that can determine its location simultaneously with receiving and identifying the primary signal. In an alternative embodiment, the system may include a wireless location sensor (“WLS”) overlay configured to detect the location of the receiver based on conventional methods of TDOA and AOA. 
     Finally, the system may include one or more memory modules for receiving and storing information identifying signal strength or signal attributes, location of the receiver and the identity of the primary base station. The memory modules can be co-located with the receiver or they can be implemented at an auxiliary circuit. In an alternative embodiment, the receiver selects the primary base station and reports pertinent signal information to a central node which will then compile a database for the bin. As the number of measurements increase, the database can provide valuable information to the service provider. 
     According to another embodiment of the disclosure, the receiver reports either the signals or their attributes to a central node, allowing the central node to identify the primary signal and the primary base station. Once identified, the central node communicates the identity of the primary base station to the receiver. The receiver can then monitor the primary signals received from the primary base station and report the appropriate signal information to the central node. 
     While the exemplary embodiments of the present invention have been described, it is to be understood that the embodiments described are illustrative only and that the scope of the invention is to be defined solely by the appended claims when accorded a full range of equivalence, many variations and modifications naturally occurring to those of skill in the art from a perusal hereof.