1. Field of the Invention
The present invention relates generally to the field of telecommunications and, more particularly to a method and apparatus for detecting a reduction in capacity of a CDMA system.
2. Description of the Related Art
FIG. 1 illustrates a schematic diagram of a portion of a typical wireless telecommunications system 100. The system 100 provides wireless communication service to a number of wireless terminals 101-1, 101-2, 101-3 that are situated within a graphical region. The heart of a typical wireless telecommunications system 100 is the Wireless Switching Center (WSC) 120, which may also be known as a Mobile Switching Center (MSC) or Mobile Telephone Switching Office (MTSO). Typically, the WSC 120 is connected to a plurality of base stations 103-1, 103-2, 103-3, 103-4, 103-5 that are dispersed throughout the geographic area serviced by the system 100 and to local-offices (L.O.) 130, 138 and toll offices (T.O.) 140. The WSC 120 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal 150, which is connected to the system through local and/or long distance networks.
The geographic area serviced by the system 100 is partitioned into a number of spatially distinct areas called xe2x80x9ccellsxe2x80x9d. In FIG. 1 each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on the topology of the terrain serviced by the system 100. Typically, each cell contains a base station, such as for example base station 103-1, which includes the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with the WSC 120.
For example, when wireless terminal 101-1 desires to communicate with wireless terminal 101-2, wireless terminal 101-1 transmits the desired information to base station 103-1, which relays the information to WSC 120. Upon receipt of the information, and with the knowledge that the information is intended for wireless terminal 101-2, the WSC 120 returns the information back to base station 103-1, which relays the information to the wireless terminal 101-2.
In a CDMA wireless telecommunications system a base station process commonly referred to as xe2x80x9cpower controlxe2x80x9d regulates the transmitting power of wireless terminals communicating with the base station. This power control process ensures that all wireless terminals communicating with the base station have roughly the same power level at the base station to prevent unwanted signal interference and noise. The power control process determines the power level of each wireless terminal communicating with the base station and transmits messages to each wireless terminal indicating whether its power level should be increased, decreased, or remain the same.
The power control process also regulates the number of users that a cell can support at any one time. Analog and TDMA wireless telecommunications systems have a predetermined or xe2x80x9chard limitxe2x80x9d number of users per channel. CDMA systems, however, do not have such a hard limit. The only limit to the number of users a CDMA cell can handle (i.e., its capacity) is the amount of noise and interference present within the cell. A CDMA system has a xe2x80x9csoftxe2x80x9d capacity limit because the noise and interference can vary.
Since a CDMA wideband channel is reused in every cell, self interference caused by other users of the same cell and interference caused by users in other cells is the most limiting factor to the capacity of the cell and thus, the CDMA system. Due to fading and other channel impairments, maximum capacity is achieved when the signal-to-noise ratio (SNR) for every user is, on the average, at the minimum point needed to support an acceptable channel performance. Based on these and other principles, power control determines whether a new user (i.e., wireless terminal) or call can be added to a cell within a system. If power control determines that a new user or call cannot be added to a cell, it prevents the user from gaining access to the cell. The process of preventing a new user from gaining access to a cell is known as blocking.
Ensuring that a CDMA system operates to its full capacity is extremely important for a CDMA service provider in terms of its revenue, customer satisfaction, and reputation. Since the typical CDMA system has a soft capacity limit, it is difficult to determine whether the system is operating up to its full potential because, unlike analog and TDMA systems, there is no hard limit number of users to compare with the CDMA system""s current number of users. That is, it is difficult to determine if power control is blocking new users from gaining access to the system when the capacity of the system has not been reached.
This inappropriate blocking, referred to herein as a blocking fault, could be caused by various errors within the system. The CDMA service provider needs to detect these errors as soon as possible since they are affecting the operational capacity of the system. Although the typical CDMA system has error detection capabilities, these capabilities typically focus upon the engineering aspects of the system, such as over temperature problems, but not operational aspects such as a blocking fault resulting in a reduction of capacity (which in a CDMA system is difficult to determine). Thus, there is a desire and need for a mechanism for detecting a reduction in capacity of a CDMA system.
In view of the foregoing shortcomings, and for other reasons, the present invention is directed to detecting a reduction in capacity of a CDMA wireless telecommunications system. The invention comprises a computer implemented method and apparatus that utilizes call processing information associated with every sector/carrier within a base station to determine if any sector/carrier is operating at a reduced capacity while also being limited by power control (i.e., power control is blocking new users from gaining access to the sector/carrier even though the sector/carrier is operating at a reduced capacity). Thus, the present invention detects faults affecting the capacity of the CDMA system.
In one aspect of the present invention, a method of detecting a reduction in capacity of a telecommunications system is provided. The method includes the steps of: determining a number of calls that have been blocked by a process of the system during a predetermined interval; determining a minimum number of channel elements carrying calls when calls are being blocked by the process during the predetermined interval; comparing the number of calls being blocked to a first threshold; comparing the minimum number of channel elements carrying calls when calls are being blocked to a second threshold; and if the number of calls being blocked exceeds the first threshold and the minimum number of channel elements carrying calls when calls are being blocked is less than the second threshold, providing an indication that the system is operating at a reduced capacity.
In another aspect of the present invention, a wireless communications apparatus is provided. The apparatus includes: a programmed processor for determining a number of calls that have been blocked by a process of the system during a predetermined interval; determining a minimum number of channel elements carrying calls when calls are being blocked by the process during the predetermined interval; comparing the number of calls being blocked to a first threshold; comparing the minimum number of channel elements carrying calls when calls are being blocked to a second threshold; and if the number of calls being blocked exceeds the first threshold and the minimum number of channel elements carrying calls when calls are being blocked is less than the second threshold, for providing an indication that the system is operating at a reduced capacity.
In yet another aspect of the present invention, a test system is provided. The system includes: a test apparatus; and a base station connected to said test apparatus, said base station having a programmed processor for determining a number of calls that have been blocked by a process of the telecommunications system during a predetermined interval; determining a minimum number of channel elements carrying calls when calls are being blocked by the process during the predetermined interval; comparing the number of calls being blocked to a first threshold; comparing the minimum number. of channel elements carrying calls when calls are being blocked to a second threshold; and if the number of calls being blocked exceeds the first threshold and the minimum number of channel elements carrying calls when calls are being blocked is less than the second threshold, for providing an indication to the test apparatus that the telecommunications system is operating at a reduced capacity.
It is an object of the present invention is to provide an apparatus for detecting a reduction in capacity of a wireless telecommunications system.
It is another object of the invention to provide an apparatus for providing a fault indication whenever a portion of a wireless system is operating at a reduced capacity.
It is a further object of the present invention is to provide a method for detecting a reduction in capacity of a wireless telecommunications system.
It is yet another object of the invention to provide a method that provides a fault indication whenever a portion of a wireless system is operating at a reduced capacity.