The present invention relates to measuring and reporting link quality in a cellular telecommunication system. More particularly, the present invention relates to using frame erasure rates (also sometimes referred to as xe2x80x9cframe error ratesxe2x80x9d) in link quality measurement to improve network quality observation.
In most radiocommunication systems, such as cellular telephone systems, one or both of the base station and the mobile unit typically evaluate and report on the signal quality of the communication link (herein referred to as link quality) between the mobile and the base station. In older analog systems such as the Advanced Mobile Phone Service (AMPS) and Extended Total Access Communication System (ETACS), mobile units participate in the evaluation of link quality by transmitting a pilot tone to the base station. The base station then measures the signal strength of the pilot tone to estimate uplink and downlink signal quality.
In more contemporary digital systems such as the Global System for Mobile communication (GSM), used as a standard in Europe, and the Digital Advanced Mobile Phone Service (D-AMPS), used as a standard in North America, the mobile units measure the downlink quality and then report the measurements back to the base station. Typically, mobile units measure and report the bit error rate (BER). In addition to measuring and reporting the signal quality of the downlink between the base station and the mobile unit, each mobile unit is also capable of measuring and reporting the received signal strength (RSS) for a number of alternative frequency channels herein referred to as candidate channels. In a similar manner, the base station may measure the received signal strength and BER for the uplink. Both uplink and downlink quality information can then be reported to the network for storage and analysis by the operator. If necessary, remedial action can be taken at the base station to improve a connection""s signal quality.
For example, if the BER for the frequency channel currently being used for the downlink is greater than desirable and the corresponding signal strength is less than desirable, the base station may take remedial action. The base station may exchange the current frequency channel with one of the candidate channels or may even decide to xe2x80x9chandoffxe2x80x9d the mobile unit to a neighboring base station. These remedial actions help to insure that the user of the mobile unit experiences the best possible signal quality.
To avoid taking unnecessary remedial action in response to a few poor link quality measurements, existing systems average the link quality measurements in accordance with a time constant. The time constant will, in general, vary from a few milliseconds to several seconds depending upon the data rate, the communication protocol, and the frequency of the communication channel. For example, systems operating in accordance with GSM estimate the BER for each 20 ms speech frame and average the estimated BERs over half second intervals. Unfortunately, averaging the link quality measurements made using BER information tends to present an inaccurate measure of link quality. This is especially true when the operating environment is subjected to the effects of Rayleigh fading or other time dependent interference which increase the peak-to-average ratio of the signal quality measurements by approximately 3 to 4 decibels, i.e., degrade link quality without significantly affecting the average BER measurement.
This, in turn, makes it difficult for network operators to accurately determine the actual quality perceived by users in different parts of the network. Applicants have recognized that the problems underlying these conventional link quality reporting techniques involve the usage of RSS and/or BER information to estimate perceived link quality. In particular, the correlation between these parameters and perceived signal quality may be low and, moreover, the quality of the BER estimate itself may be poor.
Accordingly, it would be desirable to provide new systems and techniques for estimating and reporting link quality in a radiocommunication system.
Exemplary embodiments of the present invention provide techniques and systems for measuring and reporting frame erasures in either or both the uplink and downlink of communication channels. This information is used by the network operator to more accurately estimate perceived signal quality in the system.
According to some exemplary embodiments, the frame erasure rate is measured and reported. According to other exemplary embodiments, the time distribution of the frame erasures is also reported.
Various processing techniques are used according to the present invention to present the network operator with the link quality information needed to optimize system parameters. For example, frame erasure information can be presented on a per connection, per cell or system-wide basis. Moreover, the link quality information associated with connections that have recently been handed-off can be highlighted to alert network operators to potential problems in a particular area""s handoff algorithm. If the data reported by the system to the network operator is at a higher level than the desired presentation of that data, then exemplary embodiments of the present invention provide for transforming the received data to provide an estimate of the lower level presentation data.