WO2010041990A1

WO2010041990A1 - Systems and method for filtering channel quality indicator (cqi) values

Info

Publication number: WO2010041990A1
Application number: PCT/SE2008/051128
Authority: WO
Inventors: Karl Werner; Patrick Svedman; Mathias Riback
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2008-10-06
Filing date: 2008-10-06
Publication date: 2010-04-15

Abstract

The present application discloses systems and methods for filtering a channel quality indicator (CQI) value. In some embodiment, the method includes the steps of: obtaining an initial CQI value indicating a quality of a channel; determining whether the initial CQI value is within a certain range; in response to determining that the initial CQI value is outside of the certain range, then increasing or decreasing the initial CQI value to produce an output CQI value; and in response to determining that the initial CQI value is within the certain range, then setting the output CQI value equal to the initial CQI value.

Description

SYSTEMS AND METHOD FOR FILTERING CHANNEL QUALITY INDICATOR

(CQI) VALUES

TECHNICAL FIELD

[001] The present invention relates to wireless communications and, more specifically, to systems and methods for filtering channel quality indicator (CQI) values.

BACKGROUND

[002] Channel fading is a fundamental characteristic of a wireless communication channel. Channel fading is the variability over time of the instantaneous conditions of the wireless communication channel. Channel-dependent adaptation of a transmission is one way to handle channel fading. When a channel is in a good state, it is possible to transmit data using a low level of error protection on the channel. In contrast, when the channel is in a bad fading state, a higher level of error protection is necessary, which causes a reduction in the information data rate. The level of error protection may, for example, be varied by changing the modulation format and channel coding rate. The information data rate is the number of transmitted information bits per second. In many wireless communication systems, a transmission is divided into blocks. It is possible to detect erroneous reception of a block, usually through a cyclic redundancy check (CRC). The ratio of incorrectly received blocks, either including or not including retransmitted blocks, is called the block-error rate (BLER).

[003] In order to maximize the information data rate, the error protection level of the transmission should be adapted to the instantaneous channel conditions. This is often called "link adaptation." In practice, link adaptation is often implemented to aim at a fixed BLER (e.g., a target BLER).

[004] In a typical wireless communication system many parameters of the communication channel used by a transmitting device to transmit data to a receiving device (a.k.a., the forward channel) can not be reliably estimated from parameters of the reverse channel (i.e., the channel used by the receiving device to transmit data to the transmitting device). In practice, this means that the receiving device may be able to directly determine the instantaneous channel conditions of the forward channel, but the transmitting device is not able to do so. Accordingly, in order for the transmitting device to adapt its transmission to the receiving device, the receiver needs to feed back (e.g., transmit) information about the channel to the transmitter. In a wireless communication system where the parameters of the forward communication channel can be reliably estimated directly at the transmitter, the channel quality can be directly computed at the transmitter, without the need of feedback.

[005] Typically, a receiving device indicates the quality of a channel to the transmitter by transmitting to the transmitter one or more scalar quantities known as channel quality indicator (CQI) values that are channel realization dependent parameters indicating the quality of the channel, with the purpose of describing the channel's ability to support information transfer. For example, a CQI value can indicate the recommended modulation format and code-rate based on channel measurements. For instance, the CQI value can be an SINR value computed by the receiving device based on channel measurements. In a communication system with multiple parallel channels, there may be several CQI values, indicating the channel quality of each parallel channel or of subsets of parallel channels.

[006] For simplicity of exposition, it will be assumed that the CQI values are ordered so that the highest CQI value corresponds to the highest transmitted information data rate, whereas the lowest CQI value corresponds to the lowest transmitted information data rate.

[007] In a wireless communication system with CQI feedback, the CQI values used to adapt the channel are estimated (or predicted) at the receiver. There are several types of fundamental and implementation specific problems that may cause the receiver to produce inaccurate CQI values. Typically, the process of determining (estimating) CQI values involves estimation of parameters corresponding to the instantaneous realization of the communications channel. This estimation is subject to errors. These errors may result in inaccurate CQI estimates. Additionally, a model (functional or physical) of parts of the receiver and a model (functional or physical) of parts of the transmitter are typically used in the process of generating a CQI value, and inaccuracies in these models may affect the quality of the generated CQI value. For time-variant communication channels, the delay between channel estimation or prediction and the adaptation of the link induces additional inaccuracies in the CQI estimation. That is, if the channel changes rapidly in relation to the above mentioned delay, then the estimated CQI or CQIs may be outdated at the time they are used by the transmitter to adapt the transmission.

[008] It is desired to mitigate the effect of such errors to as large extent as possible because CQI estimates that are inaccurate may cause performance degradation. If, for example, an inaccurate CQI value causes the transmitter to apply more error protection than what is necessary, then less information is transmitted than would be the case if the correct CQI formed the basis for the link adaptation. Also, if, for example, an inaccurate CQI value causes the transmitter to select less error protection than necessary, then the probability of block error will be higher than the target block error, and performance will suffer.

[009] Accordingly, it is common practice to modify an estimated CQI (e.g., reduce or increase the estimated CQI by some amount), at the receiver, at the transmitter or on both sides. Modifying the estimated CQI is sometimes referred to as applying a "back-off to the estimated CQI. Applying a back-off to an estimated CQI typically increases the level of error protection compared to the originally estimated CQI, but it may also decrease the level of error protection. For example, if the CQI is in the form of a modulation and coding scheme, the back-off may decrease the code-rate of the coding scheme, thereby increasing the level of error protection, compared to the originally computed modulation and coding scheme.

[0010] Backing-off a computed CQI value as described above may mitigate the effects of using inadequate CQI estimates, but a back-off will not properly address problems caused by significant changes in the channel during the delay between CQI estimation and link adaptation based on the CQI value. That is, using a back-off will not change the variability of the CQI, but only offset the CQI values. If intermittent, high CQI values occur with a duration that is smaller than the time it takes for the system to adapt the transmission format, then the back-off needs to be high to avoid applying a too high transmission format. On the other hand, if an intermittent, low, CQI value occurs, then such a large back-off will cause a too high level of error protection. A back-off, also when it is adapted to historical BLER, does not properly address fast channel variability. [0011] A linear filter applied to the CQI values will be able to make the CQI variability smaller, but it will also affect the ability of the system to respond to fast changes in the channel, thereby, in effect, increasing the delay between CQI estimation and application of the resulting transmission format.

[0012] What is desired are improved systems and methods for filtering CQI values.

SUMMARY

[0013] In one aspect, the invention provides a method for filtering a channel quality indicator value. In some embodiments, this method includes the following steps:, obtaining an initial CQI value indicating a quality of a channel; determining whether the initial CQI value is within a certain range; in response to determining that the initial CQI value is outside of the certain range, then increasing or decreasing the initial CQI value to produce an output CQI value; and in response to determining that the initial CQI value is within the certain range, then setting the output CQI value equal to the initial CQI value. [0014] The step of determining whether the initial CQI value is within the certain range may include comparing the initial CQI value to a max threshold value and a min threshold value, and the method may further include increasing the initial CQI value if the result of the comparison indicates that the initial CQI value is below the min threshold value and decreasing the initial CQI value if the result of the comparison indicates that the initial CQI value is above the max threshold value. The max and min threshold values may be a function of a plurality of initial CQI values and a percentage value that were obtained prior to obtaining the initial CQI value that is being compared to the threshold values. In some embodiments, the max threshold value is determined by determining a value for which the percentage of the plurality of initial CQI values that is above the value equals the percentage value. The threshold value may also be a function of the initial CQI value. In some embodiments, the percentage value is a function of a time variability of the channel. For example, the percentage value may be a function of a speed of a transmitter relative to a speed of a receiver.

[0015] In another aspect, the present invention provides an apparatus for filtering CQI value. In some embodiments, the apparatus includes: determining means for determining whether the initial CQI value is within a certain range; means for increasing or decreasing the initial CQI value to produce an output CQI value in response to the determining means determining that the initial CQI value is outside of the certain range; and means for setting the output CQI value equal to the initial CQI value in response to determining that the initial CQI value is within the certain range. In some embodiments, the determining means is configured to compare the initial CQI value to a threshold value and the means for increasing or decreasing the initial CQI value is configured to increase the initial CQI value in response to the determining means determining that the initial CQI value is below the threshold value. In some embodiments, the determining means is configured to compare the initial CQI value to a second threshold value and the means for increasing or decreasing the initial CQI value is configured to decrease the initial CQI value in response to the determining means determining that the initial CQI value is above the second threshold value. The apparatus may also include a means for determining the threshold value, which may be a function of a plurality of initial CQI values and a percentage that were obtained prior to said initial CQI value. [0016] In other embodiments, the apparatus includes: a first module configured to determine whether the initial CQI value is within a certain range; a second module configured to increase or decrease the initial CQI value to produce an output CQI value in response to the first module determining that the initial CQI value is outside of the certain range; and a third module configured to set the output CQI value equal to the initial CQI value in response to determining that the initial CQI value is within the certain range.

[0017] The above and other aspects and embodiments are described below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. In the drawings, like reference numbers indicate identical or functionally similar elements. [0019] FIG. 1 illustrates a first communication device in communication with a second communication device.

[0020] FIG. 2 is a functional block diagram of a CQI reporting module according to some embodiments of the invention. [0021] FIG. 3 is a flow chart illustrating a process according to some embodiments of the invention.

[0022] FIG. 4 illustrates a histogram according to embodiments of the invention.

[0023] FIG. 5 is a flow chart illustrating a process, according to some embodiments, for setting threshold values.

[0024] FIG. 6. is a functional block diagram of a communication device according to some embodiments of the invention.

DETAILED DESCRIPTION

[0025] Referring now to FIG. 1, FIG. 1 illustrates a communication device 102 (e.g., a mobile terminal) in communication with a communication device 104 (e.g., a fixed terminal, such as a base station). As shown, device 102 transmits data to device 104 using a channel 1 10 and device 104 transmits data to device 102 using channel 108. As further illustrated, each communication device 102, 104 may include a CQI reporting module 106 (e.g., device 102 includes module 106a and device 104 includes module 106b). A CQI reporting module 106 is configured to generate CQI values, which may be transmitted to the other communication device so that the other communication device can adapt its transmission. As used herein, a CQI value is value indicating a quality of a communication channel. For the sake of simplicity, we shall refer to communication device 102 as the "receiver," communication device 104 as the "transmitter," channel 108 as the forward channel and channel 1 10 as the reverse channel. However, one skilled in the art will appreciate that designation could be reversed (i.e., device 102 could be transmitter, etc.). That is, one skilled in the art will appreciate that the embodiments of the present invention described herein can be implemented in either the receiver or the transmitter.

[0026] Receiver 102 uses CQI reporting module 106a to generate CQI values representing a condition of forward channel 108. These CQI values may be transmitted to transmitter 104 using the reverse channel 1 10, and transmitter 104 uses the received CQI values to adapt its transmission on the forward channel 108. As discussed above, there is a need for improved systems and methods for filtering CQI values. The CQI reporting modules 106 provide such an improvement. [0027] Referring now to FIG. 2, FIG. 2 is a functional block diagram of CQI reporting module 106 according to some embodiments of the invention. As shown in FIG. 2, in some embodiments, module 106 includes an initial CQI value generating module 202. This module may be configured to generate an initial CQI value based on real-time measurements of the condition of the forward channel. These initial CQI values are input to threshold value generator 204 and a CQI filtering module 206. Threshold value generator 204 is configured to produce one or more threshold values. CQI filtering module 206 is configured to use the threshold values to filter the input initial CQI value. [0028] For example, in some embodiments, threshold value generator 204 defines a CQI value range by producing a maximum threshold value (Tmax) and minimum threshold value (Tmin), and filtering module 206 either increases, decreases or maintains the initial CQI value depending on, for example, whether the initial CQI value falls below, above or within the defined CQI value range. For example, filtering module 206 may be configured to (a) increase the initial CQI value if the initial CQI value is less than the Tmin, (b) decrease the initial CQI value if the initial CQI value is greater than the Tmax, and (c) maintain the initial CQI value if the CQI value is greater than Tmin, but less than Tmax. This process is illustrated in FIG. 3.

[0029] Referring now to FIG. 3, FIG. 3 is a flow chart illustrating a process 300 for filtering CQI values. Process 300 may begin in step 302, where a CQI value range is specified. For example, in step 302, threshold value generator 204 may define a CQI value range by producing a maximum threshold value (Tmax) and minimum threshold value (Tmin). Next (step 304), an initial CQI value is obtained. For example, in step 304, initial CQI value generating module 202 may generate an initial CQI value (Vi) based on measurements regarding the condition of the forward channel. Next (step 306), CQI filtering module 206 determines whether Vi is less than Tmin. If it is, process 300 proceeds to step 308, otherwise it proceeds to step 310.

[0030] In step 308, filtering module 206 creates an output CQI value (Vo) that is a function of Vi and X, where X may be a constant or may be a function of one or more variables (e.g., Vi and Tmin). For example, Vo my be set equal to Vi + X, where X may equal Tmin - Vi. Thus, in some embodiments, if in step 308 filtering module 206 determines that Vi is less than Tmin, then filtering module 206 sets Vo equal to Tmin. Next (step 316), Vo is further modified or Vo is transmitted from the receiver 102 to the transmitter 104.

[0031] In step 310, CQI filtering module 206 determines whether Vi is greater than Tmax. If it is, process 300 proceeds to step 312, otherwise it proceeds to step 314. [0032] In step 312, filtering module 206 creates an output CQI value (Vo) that is a function of Vi and Y, where Y may be a constant or may be a function of one or more variables (e.g., Vi and Tmax). For example, Vo my be set equal to Vi - Y, where Y may equal Vi - Tmax. Thus, in some embodiments, if in step 312 filtering module 206 determines that Vi is greater than Tmax, then filtering module 206 sets Vo equal to Tmax. After step 312, the process proceeds to step 316. In step 314, Vo is set equal to Vi. After step 314, the process proceeds to step 316.

[0033] In the above manner, an initial CQI value (e.g., a CQI estimate) is filtered by adjusting the initial CQI value if the initial CQI value falls outside of a filtering window.

[0034] As illustrated in FIG. 2, the threshold values used by filtering module 206 need not be fixed. That is, the threshold values may be adapted. In some embodiments, the threshold values are a function of a set of historical initial CQI values (including or not including the most recently output initial CQI value) and a percentage value obtained from percentage value generator 208. A time window may specify the set of historical CQI values that are used to generate the threshold values.

[0035] As a specific example, in some embodiments, to determine a value for Tmin and a value for Tmax, threshold value generator 204 uses all of the initial CQI values that were generated in the last X seconds (X may be between 0.1 and 1 second or some other value) and a percentage value obtained from percentage value generator 208. For instance, threshold value generator 204 may set Tmax equal to the value for which the percentage of all of the initial CQI values generated in the last X seconds that is above the value equals the percentage value obtained from module 208. This process is illustrated graphically in FIG. 4. FIG. 4 shows a histogram for a set of historic initial CQI values (e.g., all of the initial CQI values that were generated in the last I second) and shows that Tmax is set equal to Vix. Tmax is set equal to Vix because Vix is the initial CQI value for which the percentage of all of the initial CQI values represented in the histogram that is greater than Vix is equal to the percentage value obtained from percentage value generator 208. That is the ratio of the shaded area under the curve to the entire area under the curve is equal to the percentage value obtained from percentage value generator 208. As the histogram changes due to a changing radio environment, the threshold would move. If the percentage is dependent on the speed of the receiver relative to the transmitter (CQI variability), then the area of the shaded portion would depend on the CQI variability, while the threshold would depend on both the CQI variability and the shape of the histogram. Embodiments of the invention may use other types of histograms (e.g., weighted histograms). For instance, older initial CQI values may be given lower weight than newer initial CQI values when deciding the thresholds. [0036] Referring now to FIG. 5, FIG. 5 is a flow chart that illustrates the above described process of determining the thresholds. The process may begin in step 502, where a set of previously obtained initial CQI values is stored (e.g., all of the initial CQI values that were obtained within a certain window of time (e.g., within the last 0.1 - I second) is stored). In step 504, frequency distribution data is generated based on the stored initial CQI values. In step 506, a percentage value is obtained. Next (step 508), using the frequency distribution data and the percentage value, the value for which the percentage of the plurality of initial CQI values that is above the value equals the obtained percentage value. Next (step 510), the threshold value (e.g., Tmax) is set equal to the value determined in step 508. Next (step 512) a second percentage value is obtained. Next (step 514), using the frequency distribution data and the percentage value, the value for which the percentage of the plurality of initial CQI values that is less than the value equals the obtained percentage value. Next (step 516), the threshold value (e.g., Tmin) is set equal to the value determined in step 514.

[0037] As illustrated in the drawings and described above, the thresholds may be adapted based on historical channel realizations. For example, the thresholds may be adapted based on the historical initial CQIs (including or not including the latest initial- CQI) that fall within a time window of a certain size. The adaptation may be such that the highest threshold (Tmax) represents a level that a certain proportion of the historical initial CQI in the time window is above and the lowest threshold (Tmin) is such that a certain proportion of the historical initial CQI values in the time window are below. The historical initial CQl values in the time window may be seen as a histogram of initial CQI values. The effect of the filtering window would then be to cut off, or compress, the tails of the histogram. As the channel would fade, the histogram would change accordingly. The invention may also be used with other types of time windowing, for instance such that give older initial CQI values less weight than newer initial CQI values when deciding the thresholds.

[0038] The percentages which define the filtering window may also, in turn, be adapted, possibly based on a time-variability of the channel realizations. For example, the percentages may be adapted based on the speed of the transmitter 104 relative to the receiver 102. The speed may be measured, for example, using the Doppler shift of the received signals, or some computed quantity related to the time-variability of the channel estimates. Accordingly, percentage value generator 208 may be configured to measure the speed of the receiver and/or transmitter and generate (e.g., calculate or select) a percentage values based on the speeds.

[0039] For example, if the speed of the transmitter 104 relative to the receiver 102 is high, then the channel can be expected to have a high variability during the delay between CQI computation and the application of the resulting transmission format. If the two percentages mentioned above are adapted to be large, then the output-CQI value will tend to the median of the initial CQI values. Hence the output-CQI values will not follow intermittent fast peaks in the channel. If the speed of the transmitter relative to the receiver is small, then the two percentages will be small, and most changes in initial CQI will be reflected in the applied transmission format.

[0040] Even if the two percentages and the length of the time window are fixed to suitable values, the output-CQI values will be able to track the fading peaks of a slowly fading channel and avoid the intermittent CQI peaks of a fast fading channel. This is possible if the time window is of the same order or shorter than the slowly fading channel coherence time. As a special case, the system can be configured so that the output-CQI is selected to be, minimum, maximum, median or a similar statistics of all initial CQI in a time window of historical initial CQI values.

[0041] Referring now to FIG. 6, FIG. 6 is a functional block diagram of a communication device 102,104 according to some embodiments of the invention. In general, the communication device may comprise a CPU 602, a data storage unit 606 (e.g., a non-volatile storage device) and computer software 608 stored on the storage unit 606. A set of historic initial CQI values 610 may also be stored in storage unit 606. The communication device also may comprise transmit/receive (Tx/Rx) circuitry 604 for transmitting data to and receiving data from another communication device. Software 608 is configured such that when processor 602 executes software 608, the communication device performs steps described above with reference to the flow charts shown in FIGs. 3 and 5. For example software 608 may include: computer instructions for: (a) defining a filtering window (e.g., defining threshold values), (b) determining whether an initial CQI values falls within the filtering window, (c) modifying the initial CQI value if it fall outside of the filtering window. The computer instructions for defining the filtering window may include computer instructions for: (a) storing a set of historic initial CQI values, (b) producing a percentage value, (c) determining a threshold based on the set of historic initial CQI values and the percentage value.

[0042] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments. [0043] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, and the order of the steps may be re-arranged.

Claims

What is claimed is:

1. A method of filtering a channel quality indicator (CQI) value, comprising: obtaining an initial CQI value indicating a quality of a channel; determining whether the initial CQI value is within a certain range; in response to determining that the initial CQI value is outside of the certain range, then increasing or decreasing the initial CQI value to produce an output CQI value; and in response to determining that the initial CQI value is within the certain range, then setting the output CQl value equal to the initial CQI value.

2. The method of claim 1, wherein the step of determining whether the initial CQI value is within the certain range comprises comparing the initial CQI value to a first threshold value.

3. The method of claim 2, wherein the method further includes (a) increasing the initial CQI value if the result of the comparison indicates that the initial CQI value is below the first threshold value or (b) decreasing the initial CQl value if the result of the comparison indicates that the initial CQI value is above the first threshold value.

4. The method of any one of claims 2-3, further comprising determining the first threshold value prior to comparing the initial CQI value to the first threshold value, wherein the first threshold value is a function of a plurality of initial CQI values that were obtained prior to obtaining the initial CQI value that is being compared to the first threshold value.

5. The method of claim 4, wherein the first threshold value is a further function of a percentage value.

6. The method of claim 5, wherein the step of determining the first threshold value comprises determining a value for which (a) the percentage of the plurality of initial CQI values that is above the value equals said percentage value or (b) the percentage of the plurality of initial CQI values that is below the value equals said percentage value.

7. The method of any one of claims 5-6, wherein the percentage value is a function of (i) a measure of the time variability of the channel and/or (ii) a speed of a transmitter and/or a speed of a receiver.

8. The method of any one of claims 4-7, wherein the threshold value is a further function of the initial CQI value.

9. The method of any one of claims 1-8, wherein the step of determining whether the initial CQI value is within the certain range comprises comparing the initial CQI value to a second threshold value, and the method further includes (a) increasing the initial CQI value if the result of the comparison indicates that the initial CQI value is below the first threshold value and (b) decreasing the initial CQI value if the result of the comparison indicates that the initial CQI value is above the second threshold value.

10. The method of claim 9, further comprising determining the second threshold value prior to comparing the initial CQI value to the second threshold value, wherein the second threshold value is a function of (i) a plurality of initial CQI values that were obtained prior to obtaining the initial CQI value that is being compared to the second threshold value and (ii) a percentage value.

11. A communication device capable of filtering an initial channel quality indicator (CQI) value, comprising: determining means for determining whether the initial CQI value is within a certain range; means for increasing or decreasing the initial CQI value to produce an output CQI value in response to the determining means determining that the initial CQI value is outside of the certain range; and means for setting the output CQI value equal to the initial CQI value in response to determining that the initial CQI value is within the certain range.

12. The communication device of claim 1 1 , wherein the determining means is configured to compare the initial CQI value to a first threshold value.

13. The communication device of claim 12, wherein the means for increasing or decreasing the initial CQl value is configured to (a) increase the initial CQI value in response to the determining means determining that the initial CQI value is below the first threshold value or (b) decrease the initial CQI value in response to the determining means determining that the initial CQI value is above the first threshold value.

14. The communication device of any one of claims 12-13, further comprising means for determining the first threshold value, wherein the first threshold value is a function of a plurality of initial CQI values that were obtained prior to said initial CQI value.

15. The communication device of claim 14, wherein the first threshold value is a further function of a percentage value.

16. The communication device of claim 15, wherein the means for determining the first threshold value is configured to determine a value for which (a) the percentage of the plurality of initial CQI values that is above the value equals said percentage value or (b) the percentage of the plurality of initial CQI values that is below the value equals said percentage value.

17. The communication device of any one of claims 15-16, wherein the percentage value is a function of (i) a measure of the time variability of the channel and/or (ii) a speed of a transmitter and/or a speed of a receiver.

18. The communication device of any one of claims 14-17, wherein the threshold value is a further function of the initial CQI value.

19. The communication device of any one of claims 1 1-18, wherein: the determining means is further configured to compare the initial CQl value to a second threshold value, and the means for increasing or decreasing the initial CQI value is configured to (a) increase the initial CQI value in response to the determining means determining that the initial CQI value is below the first threshold value and (b) decrease the initial CQI value in response to the determining means determining that the initial CQI value is above the second threshold value.

20. The communication device of claim 19, wherein the second threshold value is a function of (i) a plurality of initial CQI values that were obtained prior to said initial CQI value and (ii) a percentage value.

21. A communication device capable of filtering an initial channel quality indicator (CQI) value, comprising: a first module configured to determine whether the initial CQI value is within a certain range; a second module configured to increase or decrease the initial CQI value to produce an output CQI value in response to the first module determining that the initial CQl value is outside of the certain range; and a third module configured to set the output CQI value equal to the initial CQI value in response to determining that the initial CQI value is within the certain range.

22. The communication device of claim 21 , wherein the first module is configured to compare the initial CQI value to a first threshold value.

23. The communication device of claim 22, wherein the second module is configured to (a) increase the initial CQI value in response to the first module determining that the initial CQI value is below the first threshold value or (b) decrease the initial CQI value in response to the first module determining that the initial CQI value is above the first threshold value.

24. The communication device of any one of claims 22-23, further comprising a threshold determining module for determining the first threshold value, wherein the first threshold value is a function of a plurality of initial CQI values that were obtained prior to said initial CQI value.

25. The communication device of claim 24, wherein the first threshold value is a further function of a percentage value.

26. The communication device of claim 25, wherein the threshold determining module is configured to determine a value for which (a) the percentage of the plurality of initial CQI values that is above the value equals said percentage value or (b) the percentage of the plurality of initial CQI values that is below the value equals said percentage value.

27. The communication device of any one of claims 25-26, wherein the percentage value is a function of (i) a measure of the time variability of the channel and/or (ii) a speed of a transmitter and/or a speed of a receiver.

28. The communication device of any one of claims 24-27, wherein the first threshold value is a further function of the initial CQI value.

29. The communication device of any one of claims 21-28, wherein: the first module is further configured to compare the initial CQI value to a second threshold value, and the second module is configured to (a) increase the initial CQI value in response to the first module determining that the initial CQI value is below the first threshold value and (b) decrease the initial CQI value in response to the first module determining that the initial CQI value is above the second threshold value.

30. The communication device of claim 29, wherein the second threshold value is a function of (i) a plurality of initial CQI values that were obtained prior to said initial CQI value and (ii) a percentage value.