CN1242889A - Cellular radio system and method for measuring interference level - Google Patents

Abstract

The object of the invention is a cellular radio system and a method for measuring the interference level. The system has means for measuring the interference level on at least one radio frequency channel, means for reporting the measured interference level, and means for making decisions on system level actions using the measured interference levels as an aid. The measured interference levels are used as an aid in estimating how many new air interface communication links the system is able to tolerate.

Description

Cellular radio system and method for measuring interference level

The present invention relates to a cellular radio system comprising: at least one base transceiver station BTS; at least one mobile station MS; and an air interface communication link between the BTS and the MS, the air interface communication link being on at least one radio frequency channel send.

In the United States, the Federal Communications Commission (FCC) regulates the use of the radio frequency (RF) spectrum, determining which industry sectors get certain frequencies. Since the RF spectrum is limited, only a small portion of the spectrum can be allocated to each industry sector. Therefore, the allocated frequency spectrum must be used effectively, so that as many end users (users) as possible can obtain the services provided by the allocated frequency spectrum. Organizations similar to the FCC exist in every country, with the same responsibilities and rights.

Multiple access modulation techniques are some of the most efficient techniques for utilizing the RF spectrum. Examples of such modulation techniques include: Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA), all of which are suitable for use in cellular radio systems.

In Fig. 1, a typical cellular radio system is shown. In this example, the system is limited to three base transceiver stations, BTS 120, 122, 124. Each BTS has its own reception area, cell 160,162,164. The BTS is the network element that maintains the air interface. It manages air interface signaling, encryption, and methods to ensure an error-free connection between the MS and the BTS. The BTS is controlled by a base station controller BSC 110. The BSC controls the radio network. For example, this means the following things: connection establishment, liquidity management and collection of statistics. The BSC has a (usually terrestrial) communication link 150 to the BTS. There are also three mobile stations, MS 130, 132, 134. MS is a user terminal, which may be hand-held, vehicle-mounted, fixed, or similar devices used for communication. Each MS has an air interface communication link 140, 142, 144 to the BTS.

Obviously, Figure 1 is a simplified diagram. In current systems, there are thousands or even millions of mobile station users. The infrastructure of the cellular radio system excluding the MSs can be referred to as the network part. And the connection of BSC with mobile switching center and network management system has not been drawn yet. The mobile switching center also has connections to other networks, for example, to the global public switched telephone network. Since these are not essential to explaining the invention, they will not be described in detail.

In Fig. 1, the different types of interference experienced in a cellular radio system are drawn. The downlink is the link from the BTS to the MS, and the uplink is the link from the MS to the BTS. The downlink interference experienced by the BTS 120 includes interference caused by the active connection 140 of the BTS itself to the MS 130. The active connection 142, 144 of each neighboring cell 162, 164 also causes downlink interference. There is also other ambient noise 170 that causes downlink interference. This noise can originate in the system itself, or can come from outside the system (extra-system interference).

Similar interference exists in the uplink direction. These disturbances are caused by active connections 140 via the system itself, active connections 142, 144 of neighboring cells 162, 164, and other ambient noise 170.

Cellular radio systems have a certain capacity given certain limitations, which are the number of simultaneous connections that the system can handle. These limitations arise from infrastructure hardware capacity, frequency bands, theoretical capacity that the technology and/or access method can support, actual capacity with certain limits within which the system remains functional.

An operator of a communication system has obtained a license for a frequency band(s), allowing the operator to operate the system using that RF spectrum. In this frequency band, there are one or more RF channels. Since it is known how much of this frequency band is used by one RF channel of the communication system, the number of RF channels that the system can access can be easily calculated. Different multiple access modulation techniques (eg, FDMA, TDMA, CDMA) occupy this resource (frequency band) differently, because these techniques utilize different bandwidths of RF channels.

Knowing the frequency band width and number of RF channels, and estimating the number of users/connections that need to be handled in each geographical area, the operator has estimated the required BTS and other infrastructure (BSC, mobile switching centers, etc.) to support the required number of users. The communication system was initially built and later expanded according to these plans for hardware requirements.

So, knowing the frequency band, you know the number of connections that the infrastructure can handle, and you know the multiple access modulation technique to choose. Using certain multiple access modulation techniques (FDMA, TDMA), the number of simultaneous connections can be derived directly from the number of radio frequencies that the infrastructure can support with a certain amount of hardware, these radio frequencies being within the limits of the licensed frequency band. In short, an FDMA system has as many connections as there are radio frequencies in an area. A TDMA system has a certain number of connections (time slots) per radio frequency, so the total number of connections in any area is the number of connections per radio frequency multiplied by the number of radio frequencies in that area. With both technologies (FDMA and TDMA), the theoretical and practical capacity of the technology is about the same. With CDMA technology, the situation is slightly different. In the present invention, we focus on solving the practical capacity problems presented by CDMA.

CDMA modulation uses spread spectrum technology for information transmission. Spread spectrum systems utilize modulation techniques for transmitting signals over an extended wide frequency band. Typically, this frequency band is substantially wider than the minimum bandwidth required to transmit the signal. Spread spectrum technology is achieved by modulating each baseband data signal to be transmitted with a unique wideband spreading code. Using this technique, a signal with a bandwidth of only a few kHz can be extended to a bandwidth greater than 1MHz.

Spreading the transmitted signal over a wide frequency range results in a form of frequency diversity. Typically, since only the 200-300kHz signal is affected by frequency selective fading, the rest of the transmitted signal spectrum is not affected. Therefore, receivers receiving spread spectrum signals are less affected by frequency selective fading conditions.

In a CDMA-type digital radiotelephone system, multiple signals are transmitted simultaneously on the same frequency. A specific receiver then recognizes the spreading code in the signal. Without a particular spreading code for a particular receiver, the signal at that frequency appears to be noise to that receiver and is thus ignored. As the number of connections increases, the noise level (interference) experienced by each connection also increases (due to other connections).

In order to distinguish each service channel under the same radio frequency, the number of codes used in CDMA is the theoretical limit that one RF channel of this technology can support the number of simultaneous connections. In general, since the interference level increases with the number of connections in the system, it is by no means possible to exploit the theoretical maximum of this technique. The reason for this is that as the number of connections increases, the interference experienced by a connection (any one connection) eventually reaches such a level that the spreading codes can no longer be used to distinguish the channels of the connections. Moreover, since all connections are on the same frequency, each connection simultaneously suffers the same severe consequences (poor connection or even loss of connection). The system has reached the limit of its practical spectrum capacity, which never happens in a CDMA system because the entire system may have collapsed.

There are various reports and opinions (and even measurements) as to how far the practical limits of CDMA technology are. This is by no means what is discussed in the Summary of the Invention, nor does it make any difference to the actual invention. What's more, even though it is impossible to reach the theoretical maximum, every effort is being made to have a greater number of connections available without pushing the system to the limit of its capacity.

The main problem is that in a CDMA system, the actual capacity of the system is not known and varies as a function of time, location, temperature, etc. The first and often only indication of the fact that the system is reaching its capacity limits and the overall interference has become too great is that several connections in the system are simultaneously experiencing high frame erasure rates (FER). Therefore, the system must take certain actions to reduce the interference level: handover the interfering connection to other BTSs, block new connections, not allow handover to the interfering BTS, reduce the overall The transmission power, even forced to release the connection.

Other actions may also be taken. The serious problem here is that in some cases these operations may be too late. The system had reached its capacity limit and crashed despite precautionary actions. In less severe cases, only some connections may run into trouble: FER may increase a bit more, connections (perhaps just established) may be lost, handoffs may fail, etc. Even these are not allowed.

As mentioned above, in the worst case, a CDMA digital wireless telephone system can be very unstable if the capacity limits of the system and technology are being approached. Therefore, there is a clear need for an apparatus and method that has a reliable way of estimating and measuring the total interference in the system, and uses the measured interference to estimate how much theoretical system resources are available for practical use.

The object of the present invention is to overcome the above-mentioned problems.

The present invention provides a cellular radio system comprising: at least one base transceiver station BTS; at least one mobile station MS; an air interface communication link between the BTS and the MS, the air interface communication link being on at least one radio frequency channel means for measuring the level of interference on at least one radio frequency channel; means for reporting the measured level of interference; and means for making decisions about system-level operations using the measured level of interference.

Numerous advantages are obtained with the present invention. The biggest advantage is that the system becomes more stable. Its operation is carried out according to the plan, and the communication link will not be interrupted suddenly due to the overload of the system. This brings benefits both in the planning phase and in the operation of the system. Where the upper limit of the system is reached, the system is gradually improved.

The broader applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that while the detailed description and specific examples, which show the preferred embodiment of the invention are given for illustration only, various changes and modifications will be apparent from this detailed description which will be made within the spirit and scope of the invention. of.

The present invention can be more fully understood from the detailed description given below and the accompanying drawings which are for illustration only, and therefore should not be considered as limiting the invention, in which:

Figure 1 is a cellular radio system with interference;

Figure 2 is a cellular radio system according to the invention.

Figure 2 schematically depicts a cellular radio system and the sources of interference affecting the system. In other embodiments, the cellular radio system may be any analog or digital radio communication system utilizing FDMA, TDMA and/or CDMA as a modulation technique, but a preferred cellular radio system implementation is a CDMA digital cellular radio system. telephone system.

We now study Figure 2. The cellular radio system includes: at least one base station controller BSC 110; at least one base transceiver station BTS 120, 122, 124; and at least one mobile station MS 130, 132, 134. A communication link 150 exists between the BSC 110 and the BTSs 120, 122, 124. There are also air interface communication links 140, 142, 144 between the BTSs 120, 122, 124 and the MSs 130, 132, 134. These air interface communication links 140, 142, 144 are transmitted on at least one radio frequency channel.

The invention is characterized in the network part of a cellular radio system. Referring to Figure 2, this is represented by elements BSC 110 and BTS 120. According to the invention there are means 250 for measuring the interference level in the air interface communication link 140 in both uplink and downlink directions. This is achieved using the existing measurement receivers in the BTS 120 or adding a new HW capable of doing this measurement. Every possible RF channel in use can be measured. In addition, there is means 252 for reporting the measured interference level. This is best accomplished using state-of-the-art reporting mechanisms. Reporting is to certain elements in the network part, eg to BSC 110. There is also means 254 for making decisions on system level operation using the measured interference levels. These system-level operations include: handover, power control, new call initiation, call release, and other operations that affect the system or affect the nature and environment of one or more elements of the system. In this way, the system can estimate the amount of interference the system can tolerate, and then make decisions to keep the quality of service provided at a high level, avoiding high FER in connections or even loss of connections. Decisions are made in certain network elements, eg in BSC 110. The best way to realize the above-mentioned means 250, 252, 254 is by means of software: in this case, one program instructs the functional implementation of the measuring receiver to obtain the action of the above-mentioned means 250, and another program completes the report to obtain the action of the means 252 /function, there is also a program that makes decisions on system-level operations to obtain the role/function of the device 254. Other possible implementations include: integrated circuits, programmable signal processors, and other hardware devices. Professionals clearly know that the above-mentioned devices 250, 252, 254 can also be realized in other ways or in some other network elements not described above (for example, mobile switching center), but this is completely according to the spirit of the present invention Achieved.

According to one embodiment of the invention, the network part comprises means 254 for estimating, using the measured interference levels, how many new air interface communication links the system can tolerate. Therefore, the operation of the system is in accordance with the prior plan, avoiding the problems caused by overloading.

Since it is impossible to determine the source of the interference, the measurement of the interference level follows the following three steps:

A) After the BTS 120 has been installed and put into use, measure the interference outside the system when it is ready for actual use,

B) When adjacent BTSs 122, 124 are in use, measure their impact on interference levels,

C) Measure the total interference while the BTS 120 is in use.

The interference level measured in step A) serves as the noise background, ie, the reference point against which the interference level reported in step C) is in normal operation. This is a good point of reference, since the system itself has no active connections at this point. Interference values are reported as dB relative to the noise background. The noise background is the initial specified value for the BTS 120, which is used as the factory set value, or as an initialization parameter to negate the factory set value.

Interference levels measured in steps A) and B) as a function of time and/or temperature, or other parameters. Since the measured noise background is a function of time, BTS 120 is able to change its noise background is also a function of time, so considering such a situation, the noise background on site is higher than 4 PM-6 PM in the morning or during office hours, and the commute peak time or near midnight. For example, the function of time can also be extended to include days of the week or even seasons. Certain venues may experience higher noise backgrounds, for example, during weekends or holiday seasons. The noise background as a function of temperature is obtained in such a way that while the noise background is measured as a function of time, the measured results are also stored as a function of that site temperature.

The BSC 110 stores the noise background for each BTS 120, 122, 124 it controls. Therefore, the interference level measured at the BSC can easily be used in the estimation process described above. In the case of multiple measured interference levels as a function of time and/or temperature, the BSC 110 stores them all or the BTS reports the interference level measured at that time and/or temperature in relation to the BSC 110 noise background value .

Because conditions do change in cellular wireless systems and their environments, the noise background measured by the BTS 120 is updated periodically or on a random basis. Following this idea, the noise background reflects the real environment of the system.

The best way to implement the improved basic invention is by software. Other possible implementations include: integrated circuits, programmable signal processors, and other hardware devices. It is clear to those skilled in the art that the above functions can also be implemented in some other network elements not described above (eg, mobile switching center), but this is implemented entirely according to the spirit of the present invention.

It will be obvious that there may be various modifications of the invention described above. Such changes are not to be regarded as a departure from the spirit and scope of the present invention, and such changes which are obvious to those skilled in the art should be included within the scope of the following claims.

Claims (16)

1. A cellular radio system comprising: at least one base transceiver station BTS; at least one mobile station MS; and an air interface communication link between the BTS and the MS, the air interface communication link being at least on one radio frequency channel send on; means for measuring the level of interference on at least one radio frequency channel; means for reporting measured interference levels; and A device that uses measured interference levels as an aid in making decisions about system-level operations. 2. A system according to claim 1, further comprising means for estimating how many new air interface communication links the system can accommodate, aided by the measured interference levels. 3. The system according to claim 1, wherein the measurement of the interference level follows the following three steps: A) After the BTS 120 has been installed and put into use, measure the interference outside the system when it is ready for actual use, B) measure the impact of adjacent BTSs on the interference level when they are in use, C) Measure the total interference when the BTS is in use. 4. A system according to claim 3, wherein the interference level measured in steps A) and B) is a function of time and/or temperature, or any other parameter. 5. A system according to claim 3, wherein the interference level measured in step A) serves as a noise background, ie a relative reference point to the interference level reported in step C) during normal operation. 6. The system according to claim 5, wherein the noise background is a value given to the BTS as a factory setting, or as an initialization parameter negating the factory setting. 7. The system according to claim 5, wherein the BSC stores the noise background of each BTS it controls. 8. The system according to claim 5, wherein the BTS is updated periodically or measures the noise background on a random basis. 9. A method of measuring interference levels in a cellular radio system comprising: at least one base transceiver station BTS; at least one mobile station MS; and an air interface communication link between the BTS and the MS, The air interface communication link is transmitted on at least one radio frequency channel; the method comprising the steps of: measuring the interference level on at least one radio frequency channel, report the measured interference level, Use the measured interference levels as an aid in making system-level operational decisions. 10. A method according to claim 9, further comprising the step of estimating how many new air interface communication links the system can accommodate, aided by the measured interference levels. 11. The method according to claim 9, wherein the measurement of the interference level follows the following three steps: A) After the BTS 120 has been installed and put into use, measure the interference outside the system when it is ready for actual use, B) Measure their impact on interference levels when adjacent BTSs are in use, C) Measure the total interference when the BTS is in use. 12. A method according to claim 11, wherein the interference level measured in steps A) and B) is a function of time and/or temperature, or any other parameter. 13. A method according to claim 11, wherein the interference level measured in step A) serves as a noise background, ie a reference point against which the interference level reported in step C) is in normal operation. 14. The method according to claim 13, wherein the noise background is a value given to the BTS as a factory setting, or as an initialization parameter negating the factory setting. 15. A method according to claim 13, wherein the BSC stores the noise floor of each BTS it controls. 16. The method of claim 13, wherein the BTS is updated periodically or measures the noise background on a random basis.

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