HK1037090A - A method of establishing the carrier-to-interference ratio in a radio communication system and a communication device for carrying out the method - Google Patents

Description

Method for establishing carrier-to-interference ratio in wireless communication system and communication device for implementing the method

Field of the invention

The present invention relates to a method of establishing a carrier-to-interference ratio in a wireless communication system. The invention also relates to a communication device implementing such a method.

Description of the prior art

In a communication system comprising a plurality of radio base stations and a mobile communication device, communication can be established between the mobile communication device and the base stations via a radio channel, which can also be considered as a transmission link. Channel access may be achieved through, for example, Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), or a combination thereof.

When a transmission link between a base station and a mobile communication device is established, it is important to be able to measure the quality of the link. Various methods have been used for this purpose. According to one of these methods, a received signal strength indication (RSSI or RXLEV) is employed. It is simply assumed here that the received signal strength indication is related to the quality of the transmission link. However, the received signal strength contains both carrier and interference, and therefore it is not a good measure of the transmission link measurements. In another preferred method, the bit error rate, RXQUAL, is used to estimate the quality of the transmission link, i.e. a small bit error rate corresponds to a high transmission link quality and vice versa. But since the information is subjected to data compression before being transmitted over the transmission link, the bit error rate can reach a smaller level (e.g. a total of eight levels in a GSM communication system). This method therefore only gives a rough indication of the transmission link. Furthermore, the channel coding method used is also unlikely to detect all erroneous bits, and the bit error rate is only an estimate of the quality of the transmission link. This is also true, for example, for the channel coding scheme employed in GSM. Also, the quality of the estimate for small bit error rates is generally better than for large bit error rates.

The ratio of the received carrier signal strength to the received interference signal strength, i.e. C/I, is a relatively good measure of the quality of the transmission link. This parameter is used in the development of channel coding schemes and speech coding algorithms, for example, to design cellular radio communication systems. This parameter is also important in the cell planning process (i.e. determining the location of the base station and measuring power values at different locations of the system). Furthermore, during use of the communication system, the communication system can obtain valuable information if the base station or the mobile communication device can measure the C/I. For example, the measured C/I information can be used by the communication system to opportunistically complete a handover to a high quality transmission link.

Separate C/I measurement devices are already known in the prior art. However, the high quality receiver and advanced filtering techniques that we employ are very expensive and therefore unlikely to be applied to normal mobile communication devices. There are several ways to estimate the C/I parameters.

A method is given in SE-a-469580 in which at least two base stations are involved, which method can only be used for the uplink, i.e. the transmission link from the mobile communication terminal to the base station. The method measures the strength of a carrier signal by a base station that establishes a communication link with a mobile communication device. At the same time, the second base station measures the signal strength originating from the same mobile communication terminal. The signal strength is then used as an interference estimate and an estimate of the C/I parameter. The main disadvantage of this method is that two base stations have to work together and only the C/I in the uplink can be estimated.

Another method is given in JP-A-08/182042. The method measures the strength of the carrier signal on an established communication link and estimates interference by measuring the signal strength of the current clear channel. However, since the interference experienced at an established communication link is very different from the interference measured on a clear channel (i.e. on a different radio frequency), the accuracy of the C/I estimate provided by this method is very poor.

The method set forth in US-A-5583886 relates to A cdmA system. Each of the plurality of transmitters transmits one of a plurality of signals known to the receiver. Multiple channel responses may be estimated by measuring the known signal in the receiver. These channel responses are then used to determine the C/I parameters. The disadvantages of this method are: it requires the receiver to know the multiple signals and their timing. Moreover, the transmission of known signals also occupies system resources.

WO-A-92/17953 relates to the measurement of carrier to interference ratio within A target channel selected prior to handover. The mobile communication device measures the received signal strength indication within the selected target channel in the event of transmission on the channel and interruption of the channel transmission. The measurement results are sent to a source base station which decides the C/I parameter and determines whether a handover to the selected target channel should be made based on the measurement values. The disadvantages of this method are: the C/I is measured only in the target channel and not in the source channel, and measurements can only be made occasionally. This method does not allow continuous measurement.

It is an object of the present invention to provide a method of measuring C/I parameters which overcomes or alleviates the above problems.

The invention also relates to a communication device comprising a method for measuring C/I parameters.

Summary of The Invention

According to an aspect of the present invention, there is provided a method of estimating a carrier-to-interference ratio in a wireless communication system, the method comprising the steps of: selecting a wireless communication channel allowing discontinuous transmission; measuring received signal strength in the communication channel during the transmission interruption; measuring a received signal strength in a communication channel during transmission; and calculating an estimated value of the carrier-to-interference ratio of the channel according to the signal strength measured in the above steps.

According to another aspect of the present invention, there is also provided a wireless communication device comprising a wireless receiver adapted to receive a signal selected by an antenna within a selected channel; means for measuring received signal strength within the selected channel; controller means for establishing a time period within the selected channel corresponding to the transmission or the interrupted transmission, respectively; and a calculation means for estimating the carrier-to-interference ratio C/I based on the transmission interruption period and the signal strength measured during the transmission.

The method and the device have the advantages that: the carrier-to-interference ratio can be continuously estimated and the estimation does not affect the communication in the channel.

These benefits may be obtained by measuring signal strength in the channel during transmission and transmission interruptions. This can be done continuously without having to affect the communication in the channel.

Furthermore, the ratio can be measured and estimated using relatively simple hardware and software solutions, and thus the method can be allowed for use in some small physical applications such as portable communication devices.

This benefit can be achieved by using a conventional RSSI detector.

According to another aspect of the present invention, there is also provided a method of controlling channel selection in a wireless communication system including at least two communication devices, the method comprising the steps of: establishing a communication channel between the first and second communication devices; providing a set of frequencies that can be used by the communication channel and determining for each frequency whether discontinuous transmission is active, and if so, measuring received signal strength on that frequency during transmission interruptions and during transmission; and calculating the carrier-to-interference ratio estimation value on the frequency according to the signal strength measured in the previous two steps; sorting the set of frequencies according to the corresponding C/I estimate values; transmitting information representative of at least one frequency having a maximum C/I to at least first and second communication devices; and establishing a communication channel between the first and second communication devices using at least the one frequency having the largest C/I.

The method has the following advantages: a communication channel can be established with the largest C/I and the C/I ratio is measured and estimated without interfering with the communication in the channel.

This advantage can be achieved by measuring the signal strength within the channel during transmission and interruption of transmission. This may not necessarily affect the communication in the channel.

Preferably, information representative of at least two frequencies having the largest C/I is transmitted to at least the first and second communication devices, and in the frequency hopping scheme, at least the two frequencies having the largest C/I are used at least between the first and second communication devices to establish the communication channel.

This has the advantages of: the frequency hopping scheme can be implemented on the basis of the estimated C/I ratio without having to make measurements for estimating the C/I ratio that would affect the communication on the respective frequency.

This advantage can be achieved by measuring the signal strength at this frequency during transmission and during an interruption of transmission. This may not necessarily affect communication on that frequency.

Preferably, it can be based on the formula (C/I)_dB≈((C+I)／I)_dB=(C+I^*)-(I^*) To calculate an estimate of C/I, where (I)^*) Indicating the measured signal strength (in dBm) during a transmission interruption, (C + I)^*) Representing the measured signal strength (in dBm) during transmission.

The benefits of this are: the calculations required to estimate C/I in dB are simple and therefore can be easily implemented in a device and are low cost.

This advantage can be achieved by estimating C/I by a simple subtraction.

Preferably, if according to the formula (C/I)_dB≈((C+I)／I)_dB=(C+I^*)-(I^*) Calculating the estimated value of C/I, the estimated value of C/I thus obtained can be corrected according to a correction function.

This has the advantages that: errors due to the smaller C/I value (due to the simultaneous measurement of the signal strength of the carrier and the interference) can be compensated.

This advantage can be achieved by the correction function.

Preferably, the method comprises the steps of: reading a pre-stored correction value corresponding to the C/I estimate from the memory; correction values read out according to a correction function are used to correct the C/I estimated value.

Preferably, the apparatus comprises: a memory for storing at least one pre-stored correction value, wherein each pre-stored correction value is associated with a respective C/I; reading means for reading the correction value from the memory and supplying it to the computing means. Furthermore, the calculation means is adapted to correct the estimated C/I value by the correction value read out from the correction function.

The method and the device have the advantages that: the correction value or values can be pre-calculated and pre-stored and can therefore be retrieved quickly when needed.

This advantage can be achieved by pre-calculating and pre-storing single or multiple correction values in a memory.

According to another aspect of the present invention, there is provided a method of operating a communication device comprising a radio receiver and a radio transmitter, the method comprising the steps of: selecting a wireless communication channel allowing discontinuous transmission; measuring a strength of a received signal in the communication channel during the transmission interruption; measuring the strength of a received signal within a communication channel during transmission; and transmitting information representative of the signal strength measured in the above step by the transmitter.

According to another aspect of the present invention, there is also provided a wireless communication apparatus, including: a wireless receiver adapted to receive a signal selected by the antenna within the selected channel; means for measuring received signal strength measured in the selected channel; controller means for establishing time periods within the selected middle channel corresponding to the transmission and the interrupted transmission, respectively; a transmitter for transmitting information representative of the measured signal strength from the communication device during the transmission interruption and during the transmission.

The above advantages are obtained by the method and apparatus, although the measurements required for establishing the C/I ratio are made by the communication device, and the device need not be equipped with calculation means for calculating the C/I estimate.

This advantage can be achieved by sending a measured signal strength from the communication device.

Brief Description of Drawings

FIG. 1 illustrates a communication system in accordance with an aspect of the present invention;

FIG. 2 illustrates an exemplary speech pattern within a communication system in accordance with an aspect of the present invention;

fig. 3 shows an example of a subset of TDMA frames that are transmitted at all times during a transmission break;

FIG. 4 is a flow chart illustrating one aspect of the present invention;

FIG. 5 is a flow chart illustrating one aspect of the present invention; and

fig. 6 illustrates a communication device according to an embodiment of the present invention.

Detailed description of the embodiments

Although the description that follows is given in the context of a cellular communication system, including portable or mobile radiotelephones and/or personal communication networks, it will be appreciated by those skilled in the art that the invention may be adapted for use in other communication applications.

Fig. 1 shows a communication system comprising: a plurality of radio base stations BS110, 111, 112 connected to a base station controller BSC120, and a mobile communication device 130. The cells 140, 141, 142 are defined by the radio coverage of each base station 110, 111, 112. These cells are represented by the hexagonal pattern in fig. 1. Communication between the mobile communication device and the base station is established by a wireless channel. Channel access may be accomplished through, for example, Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), or a combination thereof.

Typically, C/I is set equal to the ratio of the carrier signal strength (referred to as C) to the interfering signal strength (referred to as I) within a wireless channel, where the interfering signal originates from a base station or mobile communication device using the same frequency (same time slot for a TDMA system). Other signals, however, may also interfere with the carrier signal, such as signal power from adjacent frequencies that leaks into the radio channel frequency (referred to as a), and the average radio noise level (referred to as N). In a metro cellular network, a and N are much smaller than I. While in rural areas N is usually greater than I. Here, C/I^*Is defined as the ratio of the carrier signal strength to the interference signal strength, i.e. I^*Equal to the sum of A, N and I.

The C/I value will typically change very fast due to the effects of fast fading. The contribution given by fast fading is typically zero-mean. Thus, the C/I values are typically averaged over a predetermined period of time, and if the period of time is chosen to be sufficiently long, the fluctuations can be eliminated.

Most access systems allow the use of Discontinuous Transmission (DTX) and Discontinuous Reception (DRX). Discontinuous transmission may be used, for example, to transmit speech signals only when speech is present. A typical speech pattern 200 within a communication system is given in fig. 2. The speech pattern includes speech active periods 201 mixed with silence periods 202 or non-speech active periods. Several benefits may be achieved by interrupting transmission during periods of silence or no voice activity. In this way, the capacity of the wireless communication system can be used more efficiently, the power consumption, which is important for the mobile communication system, is reduced, and the amount of radio interference in the wireless communication system is reduced.

In GSM, which is a TDMA system, the structure of time frames, time slots and bursts is discussed in version 5.3.0 of ETSI standard GSM 05.01 (see in particular fig. 1), and discontinuous transmission is discussed in version 5.5.0 of ETSI standard GSM 05.08 (see in particular fig. 1). The contents of release 5.3.0 of the ETSI standard GSM 05.01 and release 5.5.0 of the ETSI standard GSM 05.08 are incorporated herein by reference. Within chapter 8.3 of release 5.5.0 of the ETSI standard GSM 05.08, a subset of frames TCH of a traffic channel is defined, which should always be transmitted. For example, the frame sequence numbers (modulo 104)52 through 59 are included in a subset of full rate TDMA frames that are always transmitted. This is illustrated in fig. 3. Another different scheme employs half rate transmission. For speech, these TDMA frames are occupied by silence descriptor (SID) speech frames when no signaling or speech is sent. In another case, when no information is required to be transmitted, for example, in a data channel, the padding frame, reference L2, should be transmitted as a fast associated control channel in the subset of TDMA frames that are to be transmitted at all times.

Also in other TDMA systems, FDMA systems and CDMA systems discontinuous transmission is possible. An example of discontinuous transmission in A cdmA system is discussed in US-A-5295153, which is also incorporated herein by reference.

The present invention takes advantage of discontinuous transmission operation. Measuring signal strength (C + I) of carrier signal and interference during transmission^*) Measuring the signal strength (I) of the interference during the interruption of the transmission^*). By signal strength C + I from carrier signal and interference in dBm^*Internally subtracting the interference signal strength I in dBm^*To calculate (C/I)_dBEstimated value of (a): (C/I)_dB≈(C+I^*)-(I^*)

The method is further illustrated in the flow chart of fig. 4. If C is much larger than I, the error of the C/I estimated value calculated by the method is smaller, and vice versa. However, in many cases, our interest is focused on cases where the C/I is less than 10 dB. A more accurate estimate is given by:

wherein (C + I)^*) And (I)^*) All in dBm. However, this formula is relatively complex, and therefore the calculation takes a relatively long time and requires a relatively large calculation power.

In another alternative, first by calculating (C + I)^*)-(I^*) To estimate ((C + I)/I)_dBThen the correction term ct is added to the result. The correction term ct is calculated by the following mathematical expression:the C/I estimate can be calculated by: (C/I)_dB=ct+((C+I^*)-(I^*))

Wherein the ct term is calculated according to the formula (C + I)^*) And (I)^*) In dBm. The advantage of calculating C/I by means of the correction term ct is that a table of correction values can be created, which can be for different ((C + I)/I)_dBThe values are obtained by precalculation. For example, the signal strength (C + I) of the carrier signal and the interference is first measured during transmission^*) Measuring the signal strength (I) of the interference during the interruption of the transmission^*). Suppose (C + I)^*) And (I)^*) In dBm. Next, by the slave (C + I)^*) Minus (I)^*) To calculate ((C + I)/I)_dBAn estimate of (d). Calculated in this way ((C + I)/I)_dBThe values are different from those stored in the table ((C + I)/I)_dBThe values are compared and can be compared with ((C + I)/I)_dBCalculated value of ((C + I)/I)_dBThe correction term corresponding to the stored value of (b) is read from the table. Finally, by (C + I)/I)_dBAnd the calculated value of (C) is added to the read correction value ct to estimate C/I. The method is further illustrated by the flow chart in fig. 5. By using this method to estimate C/I, the estimate can be made quickly, with little error, and without the need for computationally complex mathematical formulas. This is particularly advantageous in mobile communication terminals, such as cellular telephones, where both power consumption and computing power are valuable resources. It should be understood that, for example, for less than 10dB ((C + I)/I)_dBValues, corrected by correction termsOptionally only within a predetermined interval. It should also be understood that the correction term read in the above method is in the sum ((C + I)/I)_dBThe calculated values may optionally be modified using an interpolation algorithm prior to addition. For example, a linear interpolation algorithm (of order n, n being an integer greater than zero) using the calculated ((C + I)/I) may be used_dBValue, stored ((C + I)_dB) A value and a stored correction term.

According to another method, a correction factor cf is determined instead of a correction term. In this case, ((C + I)/I)_dBAn estimated value of, i.e., (C + I)^*)-(I^*) The correction can be obtained by multiplication with a correction factor cf, namely:

(C／I)_dB=cf×((C+I^*)-(I^*))

where x represents a multiplication operation, the correction factor may be obtained by calculating the following equation:

in this method, a stored and corresponding ((C + I)/I) is also created in the manner described above_dBValues are associated with a pre-calculated table of correction factors for use.

As for the GSM (full rate) system described above, the subset of TDMA frames that should always be transmitted contains the frame sequence numbers (modulo 104)52 to 59 (see fig. 3) when discontinuous transmission is active. In frames not to be transmitted, i.e. with frame numbers 0 to 51And measuring interference signal strength (I) within frames of 60 to 103 (96 frames in total)^*). SID frames are transmitted within frames having sequence numbers 52 to 59, or L2 padding frames are transmitted when data is transmitted. Measuring the carrier plus interference signal strength (C + I) within these frames^*). If the transmission is known to occur, the measurements can be improved by measuring at other frames, for example at those frames where it is specified that control information is to be included.

The signal strength measurements may be made within one frame or multiple frames. In the latter case the measured values are averaged. For example, assuming a frame in a GSM system having a time of 480ms, the measurement period may be n times 480ms, where n is an integer greater than zero. In this case, fast fading can be tracked over 480ms, or eliminated by averaging over a large number of frames, so that a long-term average can be obtained. It is noted that these measurements do not affect the communication in the transmission link. Furthermore, the measurement may be performed continuously, e.g. may not necessarily be limited to the moment when the transmission link is established. Also, the same hardware and/or software may be used as used for measuring received signal strength indication, RSSI, or RXLEV.

The method of establishing C/I according to the present invention can be used not only in mobile communication devices such as cellular phones, but also in other communication devices such as base stations. The only requirement is that discontinuous transmission can be activated, especially in the case of data transmission, which is interrupted by at least one frame. For example, if one mobile communication device is to be allowed to judge C/I in the downlink direction (i.e., in the direction from the base station to the mobile communication terminal), discontinuous transmission must be activated at the base station. It is apparent that if the base station is allowed to judge the uplink radio channel (i.e., in the direction from the mobile communication terminal to the base station) to judge the C/I, discontinuous transmission must be activated in the mobile communication terminal.

According to the invention, in case of activation or deactivation of discontinuous transmission within the mobile communication device according to a command from the base station, the same command can be used by the mobile communication device to activate or deactivate, respectively, the required measurements for estimating the C/I.

In a wireless communication system utilizing frequency hopping, the benefits are: the C/I is measured for each frequency of the frequency hopping scheme and the scheme can therefore be adjusted to avoid using frequencies with low C/I values. The method of establishing C/I according to the invention can be used to advantage for carrying out this measurement. For example, the base station may require the mobile communication device to measure and report the C/I on the unused frequencies or used by the communication device over time. This information may then be used by the base station to determine a preferred frequency hopping scheme. One way to do this is to order the frequencies according to the corresponding C/I values. Returning again to the GSM (full rate) example described above, for a frequency hopping scheme using up to 8 frequencies, the signal strength (C + I) of the interfering carrier signal is within 104 frame intervals^*) At least one measurement is made (see fig. 3) and the signal strength (I) to interference is measured in the same time interval^*) Up to 12 measurements are made (96 frames divided by 8 frequencies equals 12). Thus, the carrier signal plus the interfering signal strength (C + I)^*) Is relatively small, which can be compensated by long-term measurements and averaging the results.

Fig. 6 presents a block diagram of a communication device 600 for illustrating an example of a method of establishing C/I implemented in accordance with the present invention. The block diagram in fig. 6 is prepared for the purpose of illustrating various aspects of the present invention. Some well-known components of a communication device have not been given detailed detail. The receiver 601 is connected to an antenna 602 for receiving wireless signals. A first output of the receiver 601 is connected to an input of a DTX detector 603 and further to an input of a C/I measurement controller 604 and to other circuits of the communication device identified by the controller 605. A second output of the receiver 601 is connected to a C/I estimator 606. An output of the DTX detector 603 and an output of the C/I measurement controller 604 are connected to two separate inputs of a C/I estimator 606. The C/I measurement controller 604 and the DTX detector 603 are also interconnected. The output of the C/I estimator 606 is also connected to the controller 605. Which in turn is connected to an input of a transmitter 607. The output of transmitter 607 is connected to antenna 602.

In operation, antenna 602 selects wireless signals and transmits these signals to receiver 601. The receiver 601 provides these received signals to a DTX detector 603, a C/I measurement controller 604 and a controller 605 for further processing of the signals. The receiver 601 also establishes a received signal strength RSSI. The RSSI is sent to the C/I estimator 606. The C/I estimator 606 and the C/I measurement controller 604 are also started when the DTX detector 603 detects that discontinuous transmission is activated. C/I measurement controller 604 establishes a signal strength for carrier signal plus interference (C + I)^*) RSSI signal period of time, and for interference signal strength I^*And passes this information to the C/I estimator 606. The C/I estimator 606 estimates the C/I based on information obtained from the receiver 601. the results are sent by the DTX detector 603 and the C/I measurement controller 604 to the controller 605 according to any of the methods described above, thus allowing the communication device 600 to optionally use the C/I value. In the case of using a correction term or a correction factor, the term includes ((C + I)/I)_dBA table of values and associated correction terms/factors is stored in a memory (not shown). The C/I estimator 606 may access the table through a read circuit (not shown).

It should be understood that the present invention can be embodied in many different forms. For example, the communication device may measure the signal strength (C + I) of the carrier signal plus interference^*) And interference signal strength (I)^*) Rather than estimating the C/I itself and sending the measurements via transmitter 607 to the base station, which in turn performs the necessary calculations to estimate the C/I. This has the advantages that: the communication device does not have to perform the calculations required to estimate the C/I ratio. This is particularly advantageous in portable communication devices where power and computing power are valuable resources.

Claims (33)

1. A method of establishing a carrier-to-interference ratio in a wireless communication system, comprising the steps of:

selecting a wireless communication channel allowing discontinuous transmission;

measuring received signal strength within the communication channel during the transmission interruption;

measuring received signal strength within the communication channel during transmission;

and calculating an estimated value of the carrier-to-interference ratio in the channel according to the signal strength measured in the step.

2. The method of claim 1, wherein the step of selecting a wireless communication channel that activates discontinuous transmission comprises the steps of:

a determination is made whether the interrupted transmission is activated on the selected channel based on the signal received from that channel.

3. A method of controlling channel selection in a wireless communication system including at least two communication devices, comprising the steps of:

establishing a communication channel between the first and second communication devices;

providing a list of frequencies available for communication channels; and

for each frequency in the list the following steps are performed:

determining whether discontinuous transmission is activated, if so:

measuring received signal strength at the frequency during the transmission interruption;

measuring received signal strength at the frequency during transmission;

calculating the estimated value of the carrier-to-interference ratio on the frequency according to the signal intensity obtained by the previous two steps of measurement;

sorting the frequencies in the list according to the estimated values of the corresponding C/I;

transmitting information representing at least one frequency having a maximum C/I to at least first and second communication devices;

a communication channel is established between the first and second communication devices using at least one frequency having a maximum C/I.

4. The method of controlling channel selection according to claim 3, wherein information indicating at least two frequencies having the largest C/I is transmitted to at least the first and second communication devices, and in the frequency hopping scheme, a communication channel is established between the at least first and second communication devices using the at least two frequencies having the largest C/I.

5. A method according to any one of the preceding claimsWherein the signal strength I measured during the corresponding transmission interruption is determined in dBm^*And corresponding to the signal strength c + I measured during transmission^*And C/I in dB is calculated according to the following formula:

(C/I)_dB≈((C+I)/I)_dB=(C+I^*)-(I^*)。

6. the method of claim 5, further comprising the step of:

and correcting the C/I estimated value according to the correction function.

7. The method of claim 6, wherein the correction function comprises the step of adding a correction term.

8. A method according to claim 7, wherein the correction term ct is calculated according to the formula:。

9. the method of claim 6, wherein the correction function comprises the step of multiplying the correction factor.

lO. the method according to claim 9, wherein the correction factor cf is calculated according to the formula:。

11. a method according to any one of claims l to 5, further comprising the step of:

reading a correction value corresponding to the C/I estimated value from a memory; and

the correction value read according to the correction function is used to correct the C/I estimate.

12. The method of claim 11, wherein the step of correcting the estimated C/I value includes the step of adding the correction value to the estimated C/I value.

13. The method of claim 11, wherein the step of correcting the estimated C/I value includes the step of multiplying the correction value by the estimated C/I value.

14. A method according to any one of claims 11 to 13, wherein the step of reading from the memory comprises the step of comparing the estimated C/I value with at least two pre-stored C/I values, and reading the correction value corresponding to the pre-stored C/I value that is closest to the estimated C/I value.

15. A method as claimed in any one of claims 1 to 4, wherein the signal strength I measured during a transmission interruption is determined in dBm^*And corresponding to the signal strength c + I measured during transmission^*And C/I estimate in dB based onThe calculation is made as follows:。

16. a method of operating a communication device comprising a wireless receiver and a wireless transmitter, comprising the steps of:

selecting a wireless communication channel allowing discontinuous transmission;

measuring received signal strength within the communication channel during the transmission interruption;

measuring received signal strength within the communication channel during transmission;

information representative of the signal strength measured in the above step is transmitted by the transmitter.

17. The method of claim 16, wherein the step of selecting a wireless communication channel comprises the steps of:

a determination is made whether the interrupted transmission is active on the selected channel based on a signal received from the channel.

18. The method according to claim 16 or 17, further comprising the step of:

information representative of the wireless communication channel to be selected is received by the receiver within the communication channel.

19. A wireless communication device (600), comprising:

a radio receiver (601) adapted to receive a signal selected by an antenna on a selected channel,

means (601) for measuring received signal strength in the selected channel,

controller means (604) for establishing periods corresponding to transmissions and transmission interruptions, respectively, within the selected channel,

and a calculating means (606) for estimating the carrier-to-interference ratio C/I based on the signal strength measured during the interruption of the transmission and the signal strength measured during the transmission.

20. A communication device according to claim 19, wherein the calculating means (606) is adapted to calculate the C/I estimate in dB according to the formula:

(C／I)_dB≈((C+I)／I)_dB=(C+I^*)-(I^*)，

wherein I^*Representing the signal strength, C + I, measured in dBm, corresponding to the duration of the transmission interruption^*Representing the signal strength in dBm corresponding to the measured signal strength during transmission.

21. The communication device of claim 20, wherein the computing means (606) is further adapted to correct the estimated C/I according to a correction function.

22. A communications device according to claim 21, wherein the correction function includes an additional correction term.

23. A communication device according to claim 22, wherein the correction term ct is calculated according to the formula:。

24. the communications apparatus of claim 21, wherein the correction function comprises a multiplicative correction factor.

25. The communications device in claim 24, wherein the correction factor cf is calculated according to the formula:。

26. the communications apparatus in any one of claims 19 to 25, further comprising:

a memory for storing at least one pre-stored correction value, each pre-stored correction value being associated with a corresponding C/I value,

a reading device for reading the correction value from the memory and supplying the read correction value to the calculating device (606), and

wherein the computing means (606) corrects the C/I estimate by correction values read out in accordance with the correction function.

27. The communications apparatus of claim 26, wherein the correction function involves adding the correction value to the C/I estimate.

28. The communications apparatus of claim 26 wherein the correction function involves multiplying the correction value by the estimated C/I value.

29. The communication device of any one of claims 26 to 28, further comprising:

a comparator for comparing the C/I estimated value with at least two pre-stored C/I values.

30. A communication device according to claim 29, wherein the reading means is arranged to read the correction value corresponding to the pre-stored C/I value closest to the estimated C/I value.

31. The communication device of claim 19, wherein the computing means (606) is adapted to estimate C/I in dB according to:

wherein I^*Representing the signal strength, C + I, measured in dBm, corresponding to the duration of the transmission interruption^*Representing the signal strength in dBm corresponding to the measured signal strength during transmission.

32. A wireless communication device (600), comprising:

a radio receiver (601) adapted to receive a signal selected by the antenna in a selected channel,

means (601) for measuring received signal strength in the selected channel,

controller means (604) for establishing periods corresponding to transmissions and transmission interruptions, respectively, within the selected channel,

a transmitter (607) for transmitting information from the communication device indicative of the signal strength measured during the transmission interruption and information indicative of the signal strength measured during the transmission.

33. The communications device in claim 32, further comprising:

means for deciding whether the interrupted transmission is activated on the selected channel based on a signal received from the channel.