The present invention is generally related to telecommunications and, more particularly, to methods and systems for improving reciprocal communications in wireless telecommunication systems.
Interference in a wireless communications system can arise from a number of sources. In a cellular system, if the interference comes from another cell with the same uplink (UL-from the mobile station to the base station) and downlink (DL-the opposite direction) frequencies, then it is generally true that the UL interference is similar to that in the DL direction in the same cellxe2x80x94this is called reciprocity. This phenomenon, however, may not always be true because UL interference generally comes from mobile transmitters broadcasting relatively weak omnidirectional signals from a number of locations within a coverage area of another cell, while the DL interference generally comes from a single, relatively powerful base station antenna that is often directional.
In wireless cells, the difference in signal strength between base station (BS) and mobile station (MS) transmitters is generally compensated by an equivalent difference in antenna sensitivity. Thus, even though the UL interference signal is relatively weak it may be picked up by a sensitive (high gain) base station antenna in a cell that is not the serving cell. Conversely, although a DL interference source is relatively powerful, in order to cause problems it has to be picked up by the insensitive antennas in wireless mobile systems. Thus, either type of interface could be a problem in such systems; but it is often true that UL and DL interference comes from different cells experiencing different levels of disturbance. Other differences, such as different directionality of the signals and different geographical distribution of the sources, may also change this equation. Furthermore, interference may be caused by non-cellular radio sources. In this case there may be no matching UL and DL frequencies and the interferences may be wildly divergent.
In many wireless communication systems it is difficult to measure and analyze the interfering signal itself in either direction. Typically the UL interference is much easier to measure because the base station antenna can be connected to sophisticated measuring devices, computing devices, and memory devices. This may not be the case for the mobile station, which, apart from the difficulty in collecting measurements, must generally transmit any measurements it makes back to the base station over the same link as the voice or data transmission. Any such use of the transmission channel decreases the rate at which voice or data information can be transmitted.
It would therefore be desirable in the wireless telecommunications art to improve the measurement of signal reciprocity, thus allowing network engineers to efficiently determine how to concentrate their efforts towards system maintenance and improvements.
The problem of interference has been addressed in the past via visual inspection of available measurement data and vague, xe2x80x9crule of thumbo value judgements. The shortcoming of visual inspections is that such methods are not objective and do not allow for the ability to automate detection of problems or production of alarms or reports. There is apparently an absence of applied mathematical methods or systems that use available wireless communication system measurements to compare UL and DL interference in order to facilitate a solution to wireless system interference. If such techniques were to exist, they could be used for analyzing the performance of a wireless network in an objective and automatic way.
The shortcomings of the prior art are met with the present invention wherein statistical measurements of correlation and relative ranges between uplink (UL) and downlink (DL) interferences are obtainedxe2x80x94making it possible to render improved reciprocal communication in wireless systems. An aspect of the invention provides for several simultaneous measurements of Bit Error Rate (BER), BER class, or other measure of interference that are compared for UL and DL. In the prior art, the comparison may be visual whereby a computer-generated plot is examined by trained personnel. The plot is made over a range of traffic conditions from low to high. For example, if the interference comes from another cell, then it should vary with the traffic. A range of traffic conditions therefore may result in a range of interference conditions. With the present invention, the DL and the UL interferences may also be automatically correlated and analyzed by a computer using published statistical techniques well known and well accepted in the statistical arts, and signal adjustments/corrections may be based on the computerxc2xa7s analysis.
In addition to measuring the correlation, the system and methods of the present invention can determine the spread of values, e.g., as standard deviations. If statistics of the same type (e.g., UL and DL BERs) are being compared, a conclusion can be drawn from any statistically significant difference in the sizes of the spread. The same would apply measures of spread to other than standard deviation, such as the 90% quantile, etc. If non-corresponding types of data are being compared, such as the UL interfering signal strength and the DL BER, then one can compare the results of a number of cells and see if the ranges compare in the same ways. For example, if in one cell the ratio of interference signal strength to BER differs in statistically significant ways from that in most other cells, this could be an indication of a transmission/receive problem in that cell.