1. Technical Field of the Invention
This invention relates to cellular mobile telecommunications systems, and more particularly, to a system and method for automatically verifying and setting the optimal base station and mobile station radio channel output power values.
2. Description of Related Art
Wireless communication systems, including cellular mobile telephone communications systems, provide telephony services between mobile users and landline users. A system may be analog only, digital only or a dual mode system capable of both analog and digital operation. Analog cellular communication systems employ conventional frequency modulation of speech for broadcasting, while digital Time Division Multiple Access (TDMA) cellular telecommunications systems convert speech into digital samples utilizing voice coders in both the mobile and the base station. These digitized samples are transmitted between a mobile station and a base station according to the TDMA structure specified for a particular communications system. The speech samples are encoded with error protection which enables the measurement of the quality of the transmitted signal by calculating the Bit Error Rate (BER) at the receiving end. A low level of BER depends on a good quality radio channel that is undisturbed by interference.
Conventionally, the output power of each of the radio channels in the base station is set manually by an operator. The operator usually selects the same value of output power level for all channels of the base station, including the analog control and voice channels, as well as the digital control and voice channels. The base station output power values remain fixed until the operator manually sets and defines a new value.
On the other hand, the output power of the mobile station on the digital or analog voice channel during conversation is normally regulated in accordance with commands received from the base station. The levels specified by the transmitted commands are typically according to measurements made at the base station on the analog or digital voice channel. However, the initial power level the mobile station assumes when a conversation is first started on either an analog or digital voice channel is set according to an operator-defined parameter transmitted by the base station on the control channel. Further, the mobile station power output level when transmitting on the control channel is also set according to an operator-defined value.
One of the problems associated with the aforementioned methods of setting the output power for either mobile or base stations is that these methods fail to adequately optimize the power levels needed for good quality transmission and reception. If the power level of a base station is set too high, excessive radio interference is created within the coverage area of other base stations which reuse the same channel frequencies. If the power level is too low, on the other hand, unacceptable reception in the mobile or base stations results from insufficient signal strength.
Since the operator normally sets the requisite power levels based on a worst case scenario, it has been observed in many mobile radio communication systems that the power levels used are significantly higher than necessary to provide good radio coverage within the range of the base stations.
A separate commonly assigned patent application, Ser. No. 08/061,000, filed May 14, 1993 now U.S. Pat. No. 5,574,982, describes an invention entitled "Method and Apparatus for Transmission Power Regulation in a Radio System". According to this invention, reports of BER during conversations on the digital voice channel are monitored and the transmitting station output power on the digital voice channel is continuously adjusted to improve performance. The transmitting station can be either the base station or mobile station. The aim of the invention is not to obtain a perfect transmission on each digital voice channel, which would require high power signals from the mobile and base stations, but to optimize the balance between power and quality in order to obtain an acceptable level of bit errors on the digital voice channels.
This method, however, cannot be applied to analog voice channels because there is no means for the receiving mobile station to report to the transmitting base station on the quality of the received signal. Also, this method cannot be applied to digital or analog control channels because the control signal is used to communicate with multiple mobile stations at different ranges within the control area of the base station. Thus the operator still needs to define a base station output power level for analog voice channels, and an output power level for both the mobile and base station digital and analog control channels. Initial values for the mobile station analog and digital voice channels also must be defined. In addition the operator also needs to define a maximum power level value that must not be exceeded by the output power regulation mechanism in the digital voice channels of both the mobile and base stations.
Accordingly, it would be a distinct advantage to have a system and method for setting fixed system parameters such as power levels for the base station analog and digital control channels, the base station analog voice channels, the mobile station analog and digital control channels, and for setting initial power levels for the mobile station analog and digital voice channels. It would also be an advantage to have a system and method for setting a maximum power level for the power regulation mechanism in the digital voice channels of both the mobile and base stations. The present invention provides such a system and method.