Enabling opportunistic channel access in a wireless communication system

Abstract

The present subject matter relates to a method comprising using at least one value of a first set of one or more channel metrics at a first time scale to determine a short-term link state of a communication channel; using values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale to determine a long-term link state of the communication channel; determining a comparative link quality using the short-term link state and the long-term link state, wherein the comparative link quality is indicative of a difference between the short-term link state and the long-term link state; controlling access to the communication channel based on the determined comparative link quality for enabling transmission of the data on the communication channel.

Description

[0001] ENABLING OPPORTUNISTIC CHANNEL ACCESS IN A WIRELESS COMMUNICATION SYSTEM

[0002] Technical Field

[0003]

[0001] Various example embodiments relate to telecommunication systems, and more particularly to an apparatus for enabling transmission of data in a communication channel.

[0004] Background

[0005]

[0002] The Distributed Coordination Function (DCF) may be provided as the standard channel access mechanism in unlicensed spectrum, combining medium state assessment (idle or busy) with self-adaptive congestion control using Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) and Binary Exponential Backoff (BEB). DCF’s randomized channel access follows fairness principles based on Listen Before Talk (LBT). BEB determines when a device can access the channel by selecting a random backoff value between a minimum and maximum contention window (CW), which decreases while the channel is idle. Transmission occurs once the counter reaches zero. Although this distributed approach may ensure all devices have equal access opportunities, it may suffer from inefficiencies, notably the "performance anomaly," where slower devices occupy more channel resources, hampering the performance of faster devices.

[0006] Summary

[0007]

[0003] Example embodiments provide an apparatus for enabling transmission of data in a communication channel, the apparatus comprising at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: use at least one value of a first set of one or more channel metrics at a first time scale to determine a short-term link state of the communication channel; use values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale to determine a long-term link state of the communication channel; determine a comparative link quality using the short-term link state and the long-term link state, the comparative link quality being indicative of a difference between the shortterm link state and the long-term link state; control access to the communication channel, for enabling transmission of the data on the communication channel, based on the determined comparative link quality.

[0004] Example embodiments provide a method (access method) for enabling transmission of data in a communication channel, the method comprising: using at least one value of a first set of one or more channel metrics at a first time scale to determine a short-term link state of the communication channel; using values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale to determine a long-term link state of the communication channel; determining a comparative link quality using the short-term link state and the long-term link state, wherein the comparative link quality is indicative of a difference between the short-term link state and the long-term link state; controlling access to the communication channel based on the determined comparative link quality for enabling transmission of the data on the communication channel.

[0008]

[0005] Example embodiments provide a non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least the method.

[0009]

[0006] Example embodiments provide a computer program comprising instructions for causing an apparatus for performing at least the following: using at least one value of a first set of one or more channel metrics at a first time scale to determine a short-term link state of a communication channel; using values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale to determine a long-term link state of the communication channel; determining a comparative link quality using the short-term link state and the long-term link state, wherein the comparative link quality is indicative of a difference between the short-term link state and the long-term link state; controlling access to the communication channel based on the determined comparative link quality for enabling transmission of the data on the communication channel.

[0010]

[0007] “ First,” “Second,” etc. as used herein, these terms are used as labels for nouns that they precede, and do not necessarily imply any type of ordering (e.g., spatial, temporal, logical) unless explicitly defined as such.

[0011] Brief Description of the Drawings

[0012]

[0008] The accompanying figures are included to provide a further understanding of examples, and are incorporated in and constitute part of this specification. In the figures:

[0013] FIG. 1 illustrates an example wireless communication system in which the present subject matter may be implemented in accordance with an example;

[0014] FIG. 2 is a flowchart of a method for transmission of data in a communication channel of a wireless communication system in accordance with an example of the present subject matter; FIG. 3 is a flowchart of a method for computing of backoff time for enabling transmission of data in a communication channel of a wireless communication system in accordance with an example of the present subject matter;

[0015] FIG. 4 is a flowchart of a method for transmission of data in a communication channel of a wireless communication system in accordance with an example of the present subject matter;

[0016] FIG. 5 is a diagram illustrating a method for maintenance of a link state of a communication channel of a wireless communication system in accordance with an example of the present subject matter;

[0017] FIG. 6 is a diagram illustrating a method for computing a backoff time for access to a communication channel of a wireless communication system in accordance with an example of the present subject matter; FIG. 7A and FIG. 7B are diagrams illustrating the status of access to the communication channel used by an access point and a station, comparing a method for computing the backoff time without considering the link state in FIG. 7A, and with considering the link state in FIG. 7B, in accordance with an example of the present subject matter;

[0018] FIG. 8 is a block diagram showing an example of an apparatus according to an example of the present subject matter.

[0019] Detailed Description

[0020]

[0009] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc., in order to provide a thorough understanding of the examples. However, it will be apparent to those skilled in the art that the disclosed subject matter may be practiced in other illustrative examples that depart from these specific details. In some instances, detailed descriptions of well-known devices and / or methods are omitted so as not to obscure the description with unnecessary detail.

[0021]

[0010] In modern communication systems, the dynamic nature of wireless channels presents challenges for maintaining efficient and reliable data transmission. Factors such as interference, signal fading, and fluctuating traffic conditions cause the quality of communication channels to vary over time. To address these challenges, the present subject matter may monitor and analyze the communication channel at multiple time scales. By determining both short-term link states, which capture rapid fluctuations in channel conditions, and long-term link states, which reflect averaged and stable trends over extended periods, a more comprehensive understanding of communication channel behavior can be achieved. By leveraging both short-term and long-term link states, the apparatus may adapt dynamically to channel variations, ensuring robust performance even in complex and changing wireless environments. Specifically, a comparative link quality may be derived from the difference between these states, providing a real-time assessment of whether the channel is in a "better" or "worse" condition than its usual performance. As a result, the present subject matter may enable opportunistic channel access, allowing the apparatus to leverage favorable conditions (alternatively, avoid unfavorable conditions) in real-time within a wireless communication system.

[0022]

[0011] An apparatus may be configured to access a communication channel of the wireless communication system. This access may involve transmitting data using the communication channel. The communication channel may refer to a specific frequency range, and transmitting data through this communication channel may involve encoding the data into signals that correspond to the frequency within that range. The communication channel may have a state, which may be referred to as link state. The link state may refer to one or more conditions of the communication channel, such as availability, signal quality, interference level, capacity, fading characteristics, and error rates. However, these conditions may be dynamic and may change over time due to factors such as environmental conditions, traffic load, and other variables. The present subject matter may use channel metrics descriptive of these conditions to collect and process link state information over varying time granularities, to make real-time adjustments to transmission parameters. The channel metric may be a metric. The channel metric may be a measurable property or parameter that provides information about the communication channel's condition(s). A value of the channel metric may be a scalar, vector, or matrix, depending on the nature of the channel metric.

[0023]

[0012] The apparatus may be configured to use at least one value of a first set of channel metrics at a first time scale to determine a short-term link state of the communication channel. The first set of channel metrics may comprise one or more channel metrics. For example, a (large) group of channel metrics may be provided. The first set of channel metrics may, for example, be selected from the group of channel metrics. Alternatively, the first set of channel metrics may comprise the group of channel metrics. The first set of channel metrics being at the first time scale may mean that measurements and potentially additional computations may be performed during the first time scale in order to obtain the at least one value of the first set of channel metrics. This may enable to focus on key metrics to get a precise and real-time snapshot of the communication channel’s condition on a short time level. The first time scale may refer to either an instantaneous point in time or a short period during which the first set of channel metrics are measured and evaluated. The short period may be a period shorter than a predefined evaluation time window. The first time scale may focus on capturing immediate and rapidly changing aspects of the communication channel. The short-term link state may thus provide an immediate condition of the communication channel reflecting the current quality and reliability of the communication channel. The short-term link state may, for example, be the at least one value of the first set of channel metrics. Alternatively, the short-term link state may be a combination of the values of the first set of channel metrics.

[0024]

[0013] The short-term link state may further be enhanced with another layer of analysis that uses values from a second set of channel metrics which are measured over a longer time scale, a second time scale, to determine a long-term link state of the communication channel. The second time scale may be longer than the first time scale. For example, the second time scale may refer to a period longer than the predefined evaluation time window. Specifically, the apparatus may be configured to use values of the second set of channel metrics at the second time scale that is longer than the first time scale to determine the long-term link state of the communication channel. The second set of channel metrics may comprise one or more channel metrics. The second set of channel metrics may, for example, be selected from the group of channel metrics. Alternatively, the second set of channel metrics may comprise the group of channel metrics. The values of the second set of channel metrics on a larger time scale may provide a holistic view of the communication channel’s conditions for averaging out short-term fluctuations and thus capturing the communication channel’s behavior in stable conditions rather than momentary changes. The long-term link state may, for example, be the values of the second set of channel metrics. Alternatively, the long-term link state may be a combination of the values of the second set of channel metrics.

[0025]

[0014] By incorporating both short-term and long-term link states, the apparatus may capture immediate fluctuations while also identifying persistent trends in the communication channel's performance. Forthat, the apparatus may be configured to determine a comparative link quality using the short-term link state and the long-term link state. The comparative link quality is indicative of a difference between the shortterm link state and the long-term link state. The term "difference" should be understood in a broad and qualitative sense, rather than exclusively referring to mathematical subtraction. The difference may refer to any form of comparison or contrast between the short-term link state and long-term link state, reflecting the relationship or disparity between them. For example, the difference may refer to various operations or evaluations beyond simple subtraction. It may involve calculating a ratio or proportion between the shortterm and long-term link states to quantify deviations, comparing the states against a threshold to trigger specific actions, or making a qualitative judgment to assess if the short-term conditions are better, worse, or similar to the long-term performance. The comparative link quality may be a metric that quantifies the difference between the short-term and long-term link states. The comparative link quality may provide a relative measure of how the communication channel is performing at any given moment compared to its average or expected performance. For example, if the short-term link state is significantly better than the long-term link state, this may indicate that the communication channel is temporarily in a "better-than- usual" condition. Conversely, if the short-term link state is worse, it may suggest temporary degradation or interference in the communication channel.

[0026]

[0015] Hence, by determining the comparative link quality based on the short-term link state and the long-term link state, the apparatus may evaluate the current performance of the communication channel relative to its average behavior. This comparative analysis may allow the apparatus to dynamically adjust transmission parameters, backoff time and power control, optimizing network performance. For example, the apparatus may be configured to control access to the communication channel based on the determined comparative link quality for enabling transmission of the data on the communication channel. Controlling access to the communication channel may involve managing when and how the apparatus may transmit data over the communication channel. For example, if the short-term link state is significantly better than the long-term link state, the apparatus may prioritize data transmission, while if the short-term link state is worse than the long-term link state, the apparatus may delay transmission or lower its priority. This may allow the apparatus to optimize the timing of transmissions, making use of favorable conditions and avoiding periods of poor performance. Alternatively, or additionally, if the short-term link state is better than the long-term link state, the apparatus may choose to increase transmission rates, use higher-order modulation, or reduce transmission power to conserve energy, while if the short-term link state is worse than the long-term link state, the apparatus may lower transmission rates, or switch to more robust coding schemes.

[0027]

[0016] According to one example, the apparatus may be configured to control the access to the communication channel by at least: compute a backoff time based on the determined comparative link quality.

[0028]

[0017] The backoff time may be a delay period that the apparatus waits before transmission of the data on the communication channel. The backoff time may be computed based on the comparative link quality. For example, if the comparative link quality is favorable (e.g., current conditions are better than average), the apparatus may compute a shorter backoff time to allow quicker access to the communication channel. Conversely, if the link quality is poor (worse than the long-term link state), the apparatus may increase the backoff time, delaying access to avoid transmitting under suboptimal conditions.

[0018] According to one example, the apparatus may be configured to start a backoff timer configured to implement the backoff time. This may trigger the apparatus to access to the communication channel and transmit the data upon expiry of the backoff timer. The backoff time may, for example, be computed after or before determining a need to transmit the data by the apparatus.

[0029]

[0019] For example, when the backoff timer reaches zero, the apparatus may be granted permission to attempt accessing the communication channel and begin transmitting its data. The expiration of the backoff timer may signal that the apparatus may proceed with transmission of the data. In one example, the expiration of the backoff timer may signal that the apparatus may proceed with transmission, and if the communication channel is idle, the apparatus transmits the data. If the communication channel is still busy, the apparatus may recalculate the backoff time using the comparative link quality and reset the backoff timer, entering another round of waiting.

[0030]

[0020] Controlling access to the communication channel through the computation of backoff time based on the comparative link quality, and implementing this through a backoff timer, may allow the apparatus to regulate transmission timing effectively. The backoff time may dynamically adapt to real-time channel conditions, optimizing access based on whether current conditions are better or worse than the long-term average. Starting the backoff timer may ensure that the apparatus may wait to access the communication channel, reducing collisions.

[0031]

[0021] In one example, the apparatus may be configured to control the access to the communication channel by adapting transmission resources for the transmission of the data. For example, if the shortterm link quality is better than the long-term average of the link quality, the apparatus may choose to increase transmission rates, use higher-order modulation, or reduce transmission power to conserve energy. If the short-term link quality is worse than the long-term link state, the apparatus may lower transmission rates, or switch to more robust coding schemes.

[0032]

[0022] According to one example, the apparatus may be configured to perform the control of access to the communication channel in response to an event. The event comprises at least one of the following: a channel quality variation of the communication channel exceeding a threshold, a channel feature variation of the communication channel exceeding a threshold, the age of the short-term link state and the longterm link state exceeding a freshness threshold, the comparative link quality fulfilling a quality condition, or a coherence timer being shorter than a corresponding channel coherence time.

[0033]

[0023] For example, the channel access control may be triggered by one or more of the following exemplified events: a significant change in channel quality, such as signal-to-noise ratio or interference levels, exceeding a set threshold; a variation in channel features, like bandwidth or latency, beyond normal values; the short-term and long-term link states aging beyond a freshness threshold, indicating that the information is outdated and unreliable; the comparative link quality meeting a defined quality condition, reflecting a difference between short-term and long-term link states that triggers an action; or the coherence timer becoming shorter than the channel coherence time, prompting a decision on channel access before the channel conditions change. These events may serve as triggers for the apparatus to adapt in real time to changing channel conditions, allowing it to optimize channel access by prioritizing transmissions during favorable conditions and delaying them when the channel is unstable.

[0034]

[0024] According to one example, the apparatus may be configured to perform the determining operations and the control of access to the communication channel in response to that event. That is, the access method may be performed in response to detecting the event, wherein the event comprises at least one of the following: a channel quality variation of the communication channel exceeding a threshold, a channel feature variation of the communication channel exceeding a threshold, the age of the shortterm link state and the long-term link state exceeding a freshness threshold, the comparative link quality fulfilling a quality condition, or a coherence timer being shorter than a corresponding channel coherence time.

[0035]

[0025] The two operations of determining by the apparatus the short-term link state and the long-term link state may form a (overall) link state determination operation. That is, the process of combining the two operations (determining the short-term and long-term link states) into a single, unified operation is referred to as the overall link state determination operation. According to one example, the apparatus may be configured to repeatedly perform the link state determination operation, wherein the comparative link quality is determined using the last determined short-term link state and the last determined long-term link state. In this context, the term “last” is to be understood to refer to temporal order, i.e. last in time. In one example, the determination of the comparative link quality may be performed in each iteration of the link state determination operation. Alternatively, the comparative link quality may be determined less frequently, such as after a predefined number of iterations or only when the control of the access to the communication is to be performed e.g., when the backoff time is to be computed.

[0036]

[0026] The apparatus being configured to repeatedly execute the overall link state determination operation, may, for example, mean that it continually updates both the short-term and long-term link states at regular intervals. Repeated updates may allow for continuous adaptation to changing channel conditions, ensuring that the apparatus remains responsive to both short-term variations and long-term trends.

[0027] The apparatus may be configured to determine the comparative link quality using the most recent short-term and long-term link states. For instance, when performing the operation to determine the comparative link quality, the apparatus may be configured to verify which short-term and long-term link states were obtained from the most recent execution or iteration of the link state determination operation. In this way, the apparatus may ensure that it is using up-to-date information for its comparison.

[0037]

[0028] According to one example, the apparatus may be configured to perform the link state determination operation by at least further: determining a channel coherence time using at least part of at least one of: the first set of channel metrics or the second set of channel metrics. The channel coherence time may refer to the duration over which the communication channel's conditions may remain stable. For example, the apparatus may be configured to iteratively perform the link state determination operation, which includes both short-term and long-term link state determinations. In addition to these determinations, the apparatus may also determine the channel coherence time— the duration over which the channel conditions may remain stable— using at least part of either the first set (short-term) or second set (long-term) of channel metrics. This may mean that in each iteration, both the link state determination operation and the determination of the channel coherence time are performed. Alternatively, the apparatus may be configured to determine the channel coherence time less frequently, only after a predefined number of iterations of the link state determination operation, or when certain threshold conditions are met, such as significant changes in channel metrics. By adjusting the frequency of channel coherence time determination, the apparatus may optimize resource usage and computation, ensuring that coherence time is evaluated only when necessary. Alternatively, the apparatus may prioritize the determination of the channel coherence time more frequently, while performing the link state determination operation less often. In this case, the channel coherence time may allow the apparatus to make quick adjustments to transmission behavior without needing to constantly perform detailed link state evaluations.

[0038]

[0029] The repeated execution of the link determination operation may be referred to a first iterative process while the repeated determination of the channel coherence time may be referred to as second iterative process.

[0039]

[0030] Regardless of whether the first and second iterative processes occur at the same frequency or at different frequencies, the apparatus may be further configured to perform actions in parallel (e.g., asynchronously) with the first and second iterative processes. For example, the apparatus may be configured to start a coherence timer using the last determined channel coherence time, such that the status of (e.g., expiration) of the coherence timer indicates the end time of the current channel coherence period. In other words, the coherence timer is set based on the channel coherence time derived from the most recent execution of the second iterative process.

[0040]

[0031] The status of the coherence timer may be the state or the current value of the coherence time. The end time of the channel coherence time may be defined based on the status of the coherence timer before it expires. The end time of the channel coherence time is the remaining duration of the coherence timer, indicating how much time is left before the channel coherence time ends.

[0041]

[0032] The apparatus may advantageously use the coherence timer as follows. The apparatus may be configured to perform the computation of the backoff time based on the determined comparative link quality in response to determining that a time comprising a start time and end time of an upcoming transmission of the data by the apparatus on the communication channel is shorter than the end time of the channel coherence time. Indeed, the apparatus may utilize the coherence timer to determine whether the upcoming data transmission will fit within the current stable period of the communication channel (e.g., the channel coherence time). The apparatus may check if the time window required for an upcoming data transmission (from its start time to its anticipated end time) falls within the remaining channel coherence time (i.e., before the coherence timer expires). If the entire transmission window is shorter than the remaining coherence time (e.g., it may be completed before the channel conditions become unstable), the apparatus may then proceed to compute the backoff time based on the comparative link quality. However, in response to determining that the time of the upcoming transmission exceeds the end time of the channel coherence time, the apparatus may be configured to perform a default backoff time computation for computing the backoff time. For example, if the apparatus determines that the duration of the upcoming data transmission (from its start to its end time) would extend beyond the current channel coherence time, it triggers the fallback or default backoff time computation. This may happen because, once the channel coherence time ends, the channel conditions are expected to change or become unstable, and the apparatus may not rely on the comparative link quality anymore to compute an optimal backoff time. The default backoff time may be more conservative or based on a generalized strategy, designed to ensure that the apparatus waits an appropriate amount of time before to transmit data even when future channel conditions are uncertain or expected to fluctuate. Hence, by using the default backoff time, the apparatus may ensure that it can still regulate access to the communication channel when precise optimization (based on comparative link quality) may no longer be possible due to the anticipated expiration of channel coherence.

[0042]

[0033] The term "default" in default backoff time computation is used for naming purposes to refer to an alternative method to compute the backoff time.

[0034] The time comprising the start time and end time of the upcoming data transmission by the apparatus on the communication channel being shorter than the channel coherence time may be explained as follows. The start time (ts) and end time (te) of the upcoming transmission form the time interval [ts, te]. The channel coherence time refers to the remaining period during which the channel conditions are expected to remain stable, indicated by the coherence timer, and is represented as the interval [t1 , t2], For the interval [ts, te] (representing the transmission start and end times) to be shorter than [t1 , t2] (representing the remaining channel coherence time), the entire transmission period must fit within the remaining channel coherence time. This means that the transmission must start at a time ts that is after or equal to t1 (the beginning of the remaining coherence time), and it must end at a time te that is before or equal to t2 (the end of the channel coherence time). In other words, both the start time ts must occur no earlier than t1 , and the end time te must occur no later than t2. This may ensure that the transmission occurs entirely within the period of stable channel conditions, avoiding any risk of transmission errors that could arise if the transmission extends beyond the coherence time at t2, where channel conditions may change.

[0043]

[0035] The interval [ts, te] is not shorter than (i.e. is exceeding) [t1 , t2], may mean that either part or the entire transmission may fall outside the stable period defined by the remaining channel coherence time. This may occur in different ways: if ts < t1 , the transmission starts before the beginning of the remaining channel coherence time. If te > t2, the transmission ends after the remaining channel coherence time. If ts > t2 or te < t1 , the entire transmission falls outside the remaining channel coherence time.

[0044]

[0036] For example, the default backoff computation may be a predefined algorithm, involving a fixed contention window (CW) range. For example, the default backoff computation may select a random backoff time uniformly from a range [0, CW], The apparatus may, for example, implement a hybrid backoff logic. The apparatus may be equipped with a logic to dynamically switch between these two backoff computation strategies.

[0045]

[0037] According to one example, the time of the upcoming transmission is determined as being shorter than the end time of the channel coherence time by a margin. The apparatus may check the start time and end time of the planned transmission and compares it with the remaining channel coherence time (as determined by the coherence timer). The phrase "by a margin" may indicate that the apparatus does not simply ensure the transmission fits exactly within the remaining coherence time, but rather allows for a buffer or safety margin between the transmission’s end time and the expiration of the channel coherence time. This buffer may account for potential uncertainties or fluctuations in channel conditions as the coherence time approaches its end. Following the above example definition involving the time intervals [ts, te] and [t1, t2], the same definition applies in this case by using [ts, te + A] instead of [ts, te], where A represents the margin.

[0046]

[0038] According to one example, the apparatus may be configured to start a freshness timer indicating an age of the last determined short-term link state and the long-term link state, wherein the coherence and freshness timers have the same clock frequency, wherein the comparative link quality is determined further using the age indicated by the freshness timer.

[0047]

[0039] The freshness timer may be a mechanism that starts counting from the moment the most recent short-term and long-term link states are determined. The freshness timer may record how much time has passed since these link states were last updated, effectively tracking their "age". The coherence timer and the freshness timer operate on the same clock frequency, meaning they count time at the same rate. This synchronization may ensure that both timers are comparable in terms of time measurement. Even though the first iterative process and the second iterative process may operate at different iteration frequencies, the timers themselves are synchronized to the same clock, allowing the apparatus to track both channel coherence and the recency of the link state information consistently. The comparative link quality may be the metric that compares the short-term and long-term link states to evaluate the current condition of the communication channel, wherein the age of the link state data (tracked by the freshness timer) may be factored into this comparison. The freshness of the link state data may be advantageous because, as time passes, the previously determined link states may become outdated and no longer accurately reflect the current channel conditions. The apparatus may, for example, use the age of the data (from the freshness timer) as a weight factor to weight the computed comparative link quality.

[0048]

[0040] According to one example, the apparatus may be configured to perform the computing of the backoff time based on the determined comparative link quality by at least: determining whether the comparative link quality fulfills a quality condition. In response to determining that the comparative link quality fulfills the quality condition, the apparatus may be configured to use the comparative link quality to compute the backoff time. In response to determining that the comparative link quality does not fulfill the quality condition, the apparatus may be configured to use the default backoff time computation to compute the backoff time.

[0049]

[0041] By evaluating whether the comparative link quality fulfills the predefined quality condition, the apparatus may dynamically adjust its backoff time computation based on real-time channel conditions. If the comparative link quality meets the quality condition, the apparatus uses it to calculate a more accurate and adaptive backoff time, allowing faster access to the channel when conditions are favorable. On the other hand, if the comparative link quality does not meet the quality condition (indicating unstable or poor channel conditions), the apparatus switches to the default backoff time computation, ensuring more conservative and reliable behavior under uncertain conditions.

[0050]

[0042] According to one example, the quality condition may be that the difference between the shortterm link state and the long-term link state exceeds a threshold. The threshold may act as a cutoff point to determine whether the channel conditions are sufficiently good to allow adaptive backoff time computation based on the comparative link quality.

[0051]

[0043] According to one example, the apparatus may be configured to determine the comparative link quality by at least: determining a first composite value of the values of the first set of channel metrics representing the short-term link state. A second composite value of the values of the second set of channel metrics representing the long-term link state may be determined. The first and second composite values may be combined, resulting in a combined value, wherein the comparative link quality is the combined value.

[0052]

[0044] The first composite value may, for example, be a representation of the short-term link state, which may be derived from the one or more channel metrics of the first set of channel metrics. In the case of a single metric, the first composite value may simply be the value of that individual metric. Alternatively, if the first set of channel metrics comprises more than one channel metric, the first composite value may be an aggregated or combined value of values of the first set of channel metrics representing the overall short-term link state. Similarly, the second composite value may, for example, be a representation of the long-term link state, which may be derived from the second set of channel metrics, where the second composite value may be an aggregated or combined value of values of the second set of channel metrics.

[0053]

[0045] The combination (or aggregation) of metric values as used herein may involve different methods, such as averaging, where individual metrics are averaged to generate a composite value. Alternatively, weighted averaging may be used, for performing the combination e.g., when certain metrics have more influence on the overall link state than others, such as giving more weight to SNR compared to interference levels. Additionally, in order to perform the combination, a normalization may be applied to bring the metrics to a common scale (e.g., normalizing SNR and bit error rate to a range of 0 to 1 ), ensuring that each metric contributes fairly to the composite value, and the combination may be performed using the normalized values.

[0054]

[0046] After determining both the first composite value (representing the short-term link state) and the second composite value (representing the long-term link state), the apparatus may combine these two values using a mathematical or logical method to calculate the comparative link quality. This combination may involve operations such as taking the difference or ratio between the two composite values to reflect how current short-term conditions compare to the long-term conditions. For instance, the apparatus may subtract the long-term composite value from the short-term composite value or compute a ratio, allowing it to quantify the relative difference between the short-term link state and the long-term link state.

[0055]

[0047] According to one example, the first set of channel metrics and the second set of channel metrics are partially or completely overlapping.

[0056]

[0048] The first set of channel metrics and the second set of channel metrics being partially or completely overlapping may allow for greater flexibility by enabling the two sets to share some or all metrics, covering a wider range of implementations. When the same or overlapping metrics are used for both the short-term and long-term link states evaluations, it may simplify the comparison between these two states, as the apparatus may be assessing similar or identical parameters across different time scales. This overlap may also reduce computational complexity by minimizing the need to gather and process entirely different sets of data for each evaluation. However, by using distinct metrics for short-term and long-term link states evaluations, the apparatus may capture different aspects of the channel's behavior that may not be fully reflected by shared metrics alone.

[0057]

[0049] According to one example, the first set of channel metrics is the second set of channel metrics.

[0058]

[0050] The first set of channel metrics being the second set of channel metrics may indicate that the two sets are identical. By using the same set of metrics to evaluate both the short-term and long-term link states, the apparatus may reduce computational overhead since it only needs to gather, process, and analyze a single set of metrics for both time scales. Additionally, when the same metrics are used for both short-term and long-term evaluations, it may ensure a consistent basis for comparison between the two link states.

[0059]

[0051] According to one example, the short-term link state is associated with first metadata, wherein the long-term link state is associated with second metadata, wherein the comparative link quality is determined further using the first and second metadata.

[0060]

[0052] This example may introduce the use of metadata to provide additional context for both the shortterm and long-term link states, improving the accuracy and relevance of the comparative link quality determination. Metadata may refer to supplementary information that provides context about when and how the link state was determined, enhancing the apparatus's ability to interpret and use the link states effectively.

[0053] According to one example, the first metadata comprises a timestamp indicating when the shortterm link state is determined. The second metadata comprises the second time scale and a periodicity of acquisitions of the values of the second set of channel metrics.

[0061]

[0054] The timestamp may record exactly when the short-term link state was determined. This timestamp may be advantageous because short-term conditions can change rapidly and knowing precisely when the short-term link state was measured may allow the apparatus to judge whether the information is still relevant for real-time decisions.

[0062]

[0055] The second time scale and the periodicity of acquisitions (how frequently the long-term metrics are sampled) may provide insight into the stability and reliability of the long-term link state, helping the apparatus understand whether the long-term data represents an accurate reflection of the channel's typical behavior.

[0063]

[0056] According to one example, the apparatus may be configured to determine the short-term link state of the communication channel by at least: using the values of the first set of channel metrics at the first time scale to determine an initial short-term link state of the communication channel, and using a statistical model to estimate the short-term link state from the initial short-term link state and the long-term link state, the statistical model having a decay slope defined by a channel coherence time.

[0064]

[0057] This example may refine the short-term link state through the use of the statistical model that accounts for both short-term and long-term channel conditions, while factoring in the channel coherence time. The statistical model may smooth the short-term link state over time, pulling it closer to the longterm link state based on the decay rate. As time passes, the short-term link state (which initially deviates from the long-term link state) may decay towards the long-term link state. The channel coherence time may determine how long this short-term link state remains valid before significant deviations in channel conditions occur. By incorporating the decay slope, influenced by the channel coherence time, the apparatus may adapt to fast or slow channel dynamics. This refined short-term link state may enable better decision-making, allowing the apparatus to adjust transmission strategies based on channel stability.

[0065]

[0058] In one example, the statistical model may be defined as follows: m(t) = mLT+ ekt(m - mLT, where mLTis the long-term link state, m(t) is the estimate of the link state after t seconds have elapsed from the previous short-term link state, k < 1 is the decay constant, depending on the coherence time. As an example, one can use k = - - , m is a previously available Tc estimate of the short-term link state, e.g., after an update step of a Bayesian tracking.

[0066]

[0059] According to one example, the channel metric comprises at least one of: channel gain, Channel State Information (CSI), Received Signal Strength Indicator (RSSI), Received Channel Power Indicator (RCPI), Received Signal to Noise Indicator (RSNI), retry counts, Signal-to-Noise Ratio (SNR), Signal-to- Interference-plus-Noise Ratio (SINR), or ACK failure counts. ACK stands for acknowledgement.

[0067]

[0060] The present subject matter may seamlessly be integrated in existing wireless communication systems such as Wi-Fi systems. The wireless communication system according to the present subject matter may be a Wi-Fi system, but it is not limited to Wi-Fi alone. It can also be adapted for use in other wireless communication systems, such as cellular networks, and any other protocols that involve managing access to a shared communication channel.

[0068]

[0061] In one example, the wireless communication system may comprise basic service sets (BSSs), wherein the apparatus is any one of access points and stations of interfering BSSs of the BSSs. For example, the communication channel may not be exclusively accessible by the apparatus, as other apparatuses of the wireless communication system may compete with it to use the same communication channel. Consequently, these apparatuses, including the apparatus, may form a set of interfering apparatuses. The present method may be implemented by each apparatus of the interfering apparatuses.

[0069]

[0062] FIG. 1 illustrates an example wireless communication system in which the present subject matter may be implemented in accordance with an example. The wireless communication system 100 is a Wi-Fi system comprising a BSS including an access point AP1 and two stations STA1 and STA2.

[0070]

[0063] As illustrated in FIG. 1 , the access point AP1 and the station STA1 may be a pair of apparatuses that define a communication link L1 through a communication channel, with one apparatus functioning as the transmitter and the other apparatus as the receiver. Furthermore, the access point AP1 and the station STA2 may be a pair of apparatuses that define a communication link L2 through the communication channel, with one apparatus functioning as the transmitter and the other apparatus as the receiver.

[0071]

[0064] The access point AP1 may have a coverage area, which is the geographical region around the access point AP1 where its wireless signal may be received by stations at a certain power level. As the distance from the access point AP1 increases, the signal strength may typically decrease, creating zones of both good and poor coverage within the overall coverage area. This is illustrated in FIG. 1 , where the good coverage area, represented by the innermost dashed circle, surrounds the access point AP1 and indicates the region where user devices, such as station STA1 , experience strong, reliable signal strength and high connection quality. In contrast, the poor coverage area, shown by the larger outer dashed circle, is farther from the access point AP1 and signifies a region with weaker signal strength. User devices in this area, such as station STA2, may likely experience reduced connection quality, lower data rates, and higher error rates due to the weaker signal.

[0072]

[0065] The application of a conventional contention-based channel access mechanism, in the system of FIG. 1, may suffer from inefficiencies, notably the 'performance anomaly,' because while it may promote fairness by giving all devices equal opportunities to access the channel, it may lead to performance issues when each device locally implements the mechanism. For instance, station STA1 , located in the good coverage area, experiences strong signals, while station STA2, in the poor coverage area, faces weaker signals. As a result, station STA2, with poorer conditions, may require more time and resources to transmit data, monopolizing channel access. This causes station STA1 , despite its ability to operate at higher speeds, to wait, reducing overall system efficiency. The present subject matter may address this anomaly by enabling a channel access mechanism e.g., as described with reference to FIG. 2, that may prioritize link state over throughput fairness, preventing delays that degrade the performance of high-capacity devices such as station STA1 .

[0073]

[0066] For simplicity, only one wireless network (e.g., BSS) is illustrated, with the network consisting of one access point and two stations. However, it is not limited to as this configuration can be expanded to include multiple networks and multiple access points and stations within each network, depending on the specific requirements or use case.

[0074]

[0067] FIG. 2 is a flowchart of a method for transmission of data in a communication channel of a wireless communication system in accordance with an example of the present subject matter. The method of FIG. 2 may, for example, be implemented in an apparatus such as the access point or station illustrated and described in reference to FIG. 1 or apparatus illustrated and described in reference to FIG. 8 but is not limited to this implementation.

[0075]

[0068] At least one value of a first set of one or more channel metrics at a first time scale may be used in step 201 to determine a short-term link state of the communication channel.

[0076]

[0069] Values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale may be used in step 203 to determine a long-term link state of the communication channel.

[0070] A comparative link quality may be determined in step 205 using the short-term link state and the long-term link state. The comparative link quality is indicative of a difference between the short-term link state and the long-term link state.

[0077]

[0071] Access to the communication channel may be controlled in step 207 based on the determined comparative link quality for enabling transmission of the data on the communication channel.

[0078]

[0072] FIG. 3 is a flowchart of a method for computation of backoff time for enabling transmission of data in a communication channel of a wireless communication system in accordance with an example of the present subject matter. The method of FIG. 3 may, for example, be implemented in an apparatus such as the access point or station illustrated and described in reference to FIG. 1 or apparatus illustrated and described in reference to FIG. 8 but is not limited to this implementation.

[0079]

[0073] In step 301 , sub-steps 301 A through 301 C may be repeatedly performed. In steps 301 A through 301 B, the link state determination operation may be performed, wherein the comparative link quality is determined (in step 301 C) using the last determined short-term link state and the last determined longterm link state.

[0080]

[0074] In this context, the term “last” is to be understood to refer to temporal order, i.e. last in time.

[0081]

[0075] In step 303, a channel coherence time determination may repeatedly be performed using at least part of at least one of: the first set of channel metrics or the second set of channel metrics.

[0082]

[0076] In step 305, a coherence timer may be started with the last determined channel coherence time, the expiration of the coherence timer indicating the end time of the channel coherence time. For example, step 305 may automatically be performed in response to or upon expiry of the coherence timer. That is, upon expiry of the coherence timer, most recent determined channel coherence time may be used to set again the coherence timer.

[0083]

[0077] In step 307, a time (transmission time) comprising a start time and end time of an upcoming transmission of the data by the apparatus may be determined.

[0084]

[0078] It may be determined in step 309 whether the transmission time is shorter than the end time of the channel coherence time. This check may be performed by comparing the status of the coherence timer with the transmission time.

[0085]

[0079] If the transmission time is shorter than the end time of the channel coherence time, the backoff time may be computed in step 311 based on the determined comparative link quality.

[0080] If the transmission time is not shorter than the end time of the channel coherence time,

[0086]

[0081] a default backoff time computation may be performed in step 313 for computing the backoff time.

[0087]

[0082] FIG. 4 is a flowchart of a method for transmission of data in a communication channel of a wireless communication system in accordance with an example of the present subject matter. The method of FIG. 4 may, for example, be implemented in an apparatus such as the access point or station illustrated and described in reference to FIG. 1 or apparatus illustrated and described in reference to FIG. 8 but is not limited to this implementation.

[0088]

[0083] In step 401 , the method begins with link state acquisition and tracking. The link state may be characterized by two sets of measurements for the determination of a current (short-term) link state (SST) and an average (long-term) link state (SLT). The short-term link state SSTmay be used to detect fast variations in the communication channel, allowing the apparatus to adopt an opportunistic approach. The short-term link state SSTmay be derived from channel metrics whose values represent most recent channel measurements, such as Channel State Information (CSI), Received Signal Strength Indicator (RSSI), interference levels, and additional information like current traffic load and the priority of upcoming packets. To ensure accuracy, the acquisition of the short-term link state SSTmay be accompanied by temporal context, such as timestamps, to assess the freshness of the current short-term link state. In contrast, the long-term link state SLTmay capture the stable performance of the communication channel over time. The long-term link state SLTmay aggregate channel metric values representing several past channel measurement samples, e.g., using a moving average or similar functions, and includes metadata that details aspects such as the calculation window and measurement periodicity.

[0089]

[0084] For the determination of both short-term and long-term link states, the channel metrics may be evaluated using established mechanisms across various communication standards and protocols.

[0090]

[0085] The output of step 401 which is a combination or an integration of the short-term link state SSTand the long-term link state SLT, denoted as S, serves as input to step 403, which involves computing the Backoff (BO) time for channel access by the apparatus based on the current link state S. This dynamic adjustment of the channel access policy may enable efficient use of the communication channel.

[0091]

[0086] In step 405, the apparatus may enter the channel contention phase, where it may compete with other devices for channel access to the communication channel using the computed backoff time to minimize the risk of collisions. Upon expiration of the backoff timer, the method advances to step 407, where packet transmission by the apparatus takes place. If the transmission fails or necessitates re- evaluation, the apparatus may loop back to earlier steps, particularly steps 401 and 403, ensuring continuous monitoring and optimization. The flowchart also includes feedback loops indicating the apparatus's adaptive nature, as changes in link state can trigger recalculations in the channel access policy.

[0092]

[0087] FIG. 5 is a diagram illustrating a method for maintenance of a link state of a communication channel of a wireless communication system in accordance with an example of the present subject matter. The method of FIG. 5 may, for example, be implemented in an apparatus such as the access point or station illustrated and described in reference to FIG. 1 or apparatus illustrated and described in reference to FIG. 8 but is not limited to this implementation.

[0093]

[0088] The method of FIG. 5 may involve two stages, 501 and 510. In stage 501 , a link state S maintenance method may be implemented based on a channel coherence window, which is concurrently maintained in stage 510. The channel coherence window may represent the remaining time of an initial channel coherence time (Tc), during which the communication channel properties are expected to remain stable. The channel coherence time Tcmay be defined as a predefined time interval during which any potential channel access may occur before the end time (Tc-end) of the channel coherence time Tc.

[0094]

[0089] In stage 501 , the method begins with step 502, gathering various input measurements, such as those specified in IEEE standards (e.g., 802.11 h, 802.11 k) or other protocols (e.g., USP-based), in order to provide values of channel metrics which may be used for the determination and / or update in step 503 of the link state S comprising the short-term link state SSTand the long-term link state SLT. In step 504, it may be determined whether new updates are available meaning whether the short-term link state SSTand the long-term link state SLThave been updated in step 503. If the new updates are available, the apparatus may reset in step 505 a freshness timer Tm(Tm= 0) to indicate the freshness of the link state S. In step 506, the channel coherence time Tcmay be updated using the input measurements. The steps of stage 501 may be repeatedly performed in order to regularly update the link state S and the channel coherence time Tc.

[0095]

[0090] In stage 510, the method begins with step 51 1 , which involves maintaining the freshness timer Tmand a coherence timer (Tc-end), representing the end time of the channel coherence time Tc. As time progresses, '++t' indicates the rate at which the apparatus increments the freshness timer (Tm= Tm+ t) and decrements the coherence timer (Tc-end= Tc-end- 1). Both timers track the passage of time, with the freshness timer Tmmeasuring how long it has been since the last link state S update, and the coherence timer Tc-endmeasuring the remaining channel coherence time before the channel conditions are expected to change. As illustrated in FIG. 5, the freshness timer Tmand the coherence timer Tc-endhave the same clock frequency to ensure synchronized time tracking, allowing the apparatus to make consistent and timely decisions based on the current link state and channel coherence time. Step 51 1 may involve a waiting phase e.g., while enabling updates of the link state S and the channel coherence time Tcin stage 501 . In step 512, the apparatus may check if the coherence timer Tc-endhas reached zero; if Tc-end= 0, the apparatus may reset in step 513 the coherence timer using the updated coherence time Tc(resulting from step 506).

[0096]

[0091] Before the method begins, an initialization phase (Start) may set up the link state S and the two timers. The method steps of stage 501 may be repeatedly performed, and the method steps of stage 510 may be repeatedly performed concurrently. The frequency of repetitions for each stage may or may not be the same, depending on the specific implementation. For instance, the steps in stage 510 related to the timers may be performed at a higher frequency to ensure precise tracking of time-sensitive parameters, while the steps in stage 501 , which maintain the link state S, may be repeated at a lower frequency to account for more gradual changes in channel conditions. The asynchronous nature of these repetitions may allow the apparatus to optimize its operations, adapting to the varying time scales of different channel parameters.

[0097]

[0092] FIG. 6 is a diagram illustrating a method for computing a backoff time for access to a communication channel of a wireless communication system in accordance with an example of the present subject matter. The method of FIG. 6 may, for example, be implemented in an apparatus such as the access point or station illustrated and described in reference to FIG. 1 or apparatus illustrated and described in reference to FIG. 8 but is not limited to this implementation. The method of FIG. 6 may, for example, be executed concurrently with the execution of the method of FIG. 5.

[0098]

[0093] A trigger event may be detected in step 601 indicating the need to compute a new backoff time for a next transmission attempt. The trigger event may, for example, be at least one of: a channel quality variation of the communication channel exceeding a threshold, a channel feature variation of the communication channel exceeding a threshold, the age of the short-term link state and the long-term link state exceeding a freshness threshold, the comparative link quality fulfilling a quality condition, or a coherence timer being shorter than a corresponding channel coherence time. Upon detection of the event in step 601, the most recent link state S may be retrieved in step 602, along with the relevant time window parameters, including the channel coherence time (Tc), its end time (Tc-end), and the freshness timer (Tm). Following this, step 603 involves calculating the upcoming transmission time (Ttx), based on factors such as the payload size and the intended modulation and coding scheme (MCS). The apparatus then proceeds to step 604, where it checks if the transmission can be completed within the current channel coherence time, the end of which is indicated by the coherence timer Tc-end. For this check, an optional channel access margin A may be added to the transmission time Ttxto account for possible delays caused by network conditions, including neighboring interference. If the transmission time plus the margin is within the end time indicated by the coherence timer (e.g., Ttx+ A < Tc-end), the apparatus identifies that the transmission may occur within the current coherence period, allowing for a more refined decisionmaking process. In this case, the apparatus proceeds to select an opportunistic policy in steps 605-606, where the short-term and long-term link states (SSTand SLT, respectively) may be used by a function f(S) to compute the backoff time accordingly. The function f(S) may adopt various forms, such as ratio between the short-term link state SSTand the long-term link state SLT. For instance, when the short-term channel properties are favorable compared to the long-term link state, f(S) might reduce the backoff time, granting priority for transmission, whereas unfavorable conditions may result in a more conservative approach. Alternatively, a threshold-based strategy may be implemented, where the difference between the shortterm and long-term link states SSTand SLTmay be compared to a predefined threshold £ to decide whether to employ an aggressive or conservative channel access policy. On the other hand, if the transmission time plus the margin is not within the end time indicated by the coherence timer, the apparatus may assume that the short-term conditions have either passed or are about to pass, and thus adopt a BEB policy in step 607. Here, the backoff time may be uniformly selected within the range [0, CW], with "CW" representing the contention window size. The BEB policy may, for example, provide a default BO computation of the apparatus.

[0099]

[0094] FIG. 7A and FIG. 7B are diagrams illustrating the status of access to the communication channel used by an access point AP1 and a station STA1 , comparing a method for computing the backoff time without considering the link state in FIG. 7A, and with considering the link state in FIG. 7B, in accordance with an example of the present subject matter. In this example, the access point AP1 and the station STA1 may exchange data through the communication channel, with the access point AP1 functioning as the transmitter and the station STA1 as the receiver. To provide an equal basis for evaluating the two methods shown in FIG. 7A and FIG. 7B, the same link state 701 of the communication channel is assumed. The link state 701 is depicted along the x-axis, with variations between poor and good link states over time. The poor link states correspond to periods 702A and 702C, while the good link states correspond to periods 702B and 702D. Line 703 may, for example, indicate a long-term average signal strength or other signal threshold that may differentiate between good and bad link status. Both the access point AP1 and the station STA1 have a timeline in FIG. 7A and FIG. 7B that outlines the operations they carry out.

[0100]

[0095] Referring to FIG. 7A, when the access point AP1 is ready to transmit data to the station STA1 , it may compute a new backoff time within a range of [0, 16] and start a backoff timer with the calculated time (705). Once the backoff timer expires, the access point AP1 transmits the data (706). However, due to the lack of link state information, a high (aggressive) MCS, such as 512-QAM, is applied. This MCS may increase throughput but is prone to errors if the communication channel is in poor condition, which is the case in the period 702A. Following a waiting time period defined by the extended interframe space (EIFS), an ACK timeout (707) caused by an RX error (represented by the "X"), the access point AP1 detects that the transmission has failed. As a result, the access point AP1 computes a new, longer backoff time in the range of [0, 32] (708) to delay the next transmission attempt, allowing time for the channel to stabilize. The backoff timer is restarted with this newly computed time. After the backoff timer expires, the access point AP1 transmits the data again (709), but this time, a more robust, low MCS, such as 16-QAM, is applied. While this modulation is more suitable for poor link states and less prone to errors, it may offer lower data rates. In this instance, the RX (reception) is successful, as indicated by the RX success signal.

[0101]

[0096] Referring to FIG. 7B, when the access point AP1 is ready to transmit data to the station STA1 , it computes a new backoff time within a range of [64, 128] and starts a backoff timer with the calculated time (715). Once the backoff timer expires, the access point AP1 transmits the data using a fast MCS, such as 4K-QAM, due to the good link state observed during period 702B (716). This high-order modulation may increase throughput but rely on favorable channel conditions. After the transmission, the access point AP1 may wait for a period defined by the arbitration interframe space (AIFS) and then successfully receives the acknowledgment (RX success), confirming the transmission (717). However, as the channel condition worsens during period 702C, the access point AP1 computes a new, longer backoff time within the range of [98, 128] to delay the next transmission and allow the communication channel to stabilize (718). Following this, when the backoff timer expires, the access point AP1 transmits the data, applying the fast MCS (4K-QAM) due to the good link state during period 702D, which allows for another successful reception, indicated by RX success (719). Throughout these steps, the access point AP1 dynamically adjusts the backoff times based on the fluctuating link state (701) as it moves between poor and good conditions, represented by 702A and 702B respectively.

[0097] Hence, the method used for channel access in FIG. 7A computes backoff values without considering the link state, which can lead to issues such as reception errors. For example, an ACK timeout occurs when an overly aggressive MCS is applied during a temporary period of poor link conditions. This also results in inefficiencies, such as slow transmissions when a lower MCS is unnecessarily applied, even when conditions improve. In contrast, FIG. 7B illustrates the present method, which addresses these inefficiencies by computing BO values that take the link state into account. In this approach, channel access is delayed by using a larger BO during poor link states, allowing the access point to apply a higher- order MCS and perform faster transmissions when the link state improves. As a result, the system's overall efficiency is enhanced by optimizing the timing and modulation schemes based on real-time link conditions.

[0102]

[0098] In FIG. 8, a block circuit diagram illustrating a configuration of an apparatus 1070 is shown, which is configured to implement at least part of the present subject matter. The apparatus may be a user equipment or an access point for wireless communication. It is to be noted that the apparatus 1070 shown in FIG. 8 may comprise several further elements or functions besides those described herein below, which are omitted herein for the sake of simplicity as they are not essential for the understanding. Furthermore, the apparatus may be also another device having a similar function, such as a chipset, a chip, a module etc., which can also be part of an apparatus or attached as a separate element to the apparatus 1070, or the like. The apparatus 1070 may comprise a processing function or processor, or controller 1071 , such as a central processing unit (CPU) or the like, which executes instructions given by programs or the like related to a flow control mechanism. The processor 1071 may comprise one or more processing portions dedicated to specific processing as described below, or the processing may be run in a single processor. Portions for executing such specific processing may be also provided as discrete elements or within one or more further processors or processing portions, such as in one physical processor like a CPU or in several physical entities, for example. Reference sign 1072 denotes transceiver or input / output (I / O) units (interfaces) connected to the processor 1071. The I / O units 1072 may be used for communicating with one or more other network elements, entities, terminals or the like. The I / O units 1072 may be a combined unit comprising communication equipment towards several network elements or may comprise a distributed structure with a plurality of different interfaces for different network elements. Reference sign 1073 denotes a memory usable, for example, for storing data and instructions, such as programs to be executed by the processor 1071 and / or as a working storage of the processor 1071.

[0099] The processor 1071 is configured to execute processing related to the above described subject matter. In particular, the apparatus 1070 may be configured to perform the method as described in connection with FIG. 2, 3, 4, 5 or 6.

[0103]

[0100] For example, the processor 1071 is configured to perform: using at least one value of a first set of one or more channel metrics at a first time scale to determine a short-term link state of a communication channel; using values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale to determine a long-term link state of the communication channel; determining a comparative link quality using the short-term link state and the long-term link state, wherein the comparative link quality is indicative of a difference between the short-term link state and the long-term link state; controlling access to the communication channel based on the determined comparative link quality for enabling transmission of the data on the communication channel.

[0104]

[0101] As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as an apparatus, method, computer program or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer executable code embodied thereon. A computer program comprises the computer executable code or "program instructions".

[0105]

[0102] Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable storage medium. A ‘computer-readable storage medium’ as used herein encompasses any tangible storage medium which may store instructions which are executable by a processor of a computing device. The computer-readable storage medium may be referred to as a computer-readable non-transitory storage medium. The computer-readable storage medium may also be referred to as a tangible computer readable medium. In some embodiments, a computer-readable storage medium may also be able to store data which is able to be accessed by the processor of the computing device.

[0106]

[0103] ‘Computer memory’ or ‘memory’ is an example of a computer-readable storage medium. Computer memory is any memory which is directly accessible to a processor. ‘Computer storage’ or ‘storage’ is a further example of a computer-readable storage medium. Computer storage is any non- volatile computer-readable storage medium. In some embodiments computer storage may also be computer memory or vice versa.

[0107]

[0104] A ‘processor’ as used herein encompasses an electronic component which is able to execute a program or machine executable instruction or computer executable code. References to the computing device comprising “a processor” should be interpreted as possibly containing more than one processor or processing core. The processor may for instance be a multi-core processor. A processor may also refer to a collection of processors within a single computer system or distributed amongst multiple computer systems. The term computing device should also be interpreted to possibly refer to a collection or network of computing devices each comprising a processor or processors. The computer executable code may be executed by multiple processors that may be within the same computing device or which may even be distributed across multiple computing devices.

[0108]

[0105] Computer executable code may comprise machine executable instructions or a program which causes a processor to perform an aspect of the present invention. Computer executable code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages and compiled into machine executable instructions. In some instances the computer executable code may be in the form of a high level language or in a pre-compiled form and be used in conjunction with an interpreter which generates the machine executable instructions on the fly.

[0109]

[0106] Generally, the program instructions can be executed on one processor or on several processors. In the case of multiple processors, they can be distributed over several different entities. Each processor could execute a portion of the instructions intended for that entity. Thus, when referring to a system or process involving multiple entities, the computer program or program instructions are understood to be adapted to be executed by a processor associated or related to the respective entity.

Claims

27CLAIMS1. An apparatus for enabling transmission of data in a communication channel, the apparatus comprising at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: use at least one value of a first set of one or more channel metrics at a first time scale to determine a short-term link state of the communication channel; use values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale to determine a long-term link state of the communication channel; determine a comparative link quality using the short-term link state and the long-term link state, the comparative link quality being indicative of a difference between the short-term link state and the long-term link state; control access to the communication channel, for enabling transmission of the data on the communication channel, based on the determined comparative link quality.

2. The apparatus of claim 1 , wherein execution of the instructions further causes the apparatus to control the access to the communication channel by at least: computing a backoff time based on the determined comparative link quality.

3. The apparatus of any of the preceding claims, wherein execution of the instructions further causes the apparatus to: perform the control of access to the communication channel or the determining operations and the control of access to the communication channel in response to an event, the event comprising at least one of the following: a channel quality variation of the communication channel exceeding a threshold, a channel feature variation of the communication channel exceeding a threshold, an age of the short-term link state and the long-term link state exceeding a freshness threshold, the comparative link quality fulfilling a quality condition, or a coherence timer being shorter than a corresponding channel coherence time.

4. The apparatus of any of the preceding claims 1 to 2, wherein the determining of the short-term link state and the long-term link state form a link state determination operation, wherein execution of the instructions further causes the apparatus to: repeatedly perform the link state determination operation, wherein the comparative link quality is determined using the last determined short-term link state and the last determined long-term link state.

5. The apparatus of claim 4, wherein execution of the instructions further causes the apparatus to perform the link state determination operation by at least further: determining a channel coherence time using at least part of at least one of: the first set of channel metrics or the second set of channel metrics; wherein execution of the instructions further causes the apparatus to: start a coherence timer with the last determined channel coherence time, a status of the coherence timer indicating the end time of the channel coherence time; perform the computing of the backoff time based on the determined comparative link quality in response to determining that a time comprising a start time and end time of an upcoming transmission of the data by the apparatus on the communication channel is shorter than the end time of the channel coherence time; perform a default backoff time computation for computing the backoff time in response to determining that the time of the upcoming transmission exceeds the end time of the channel coherence time.

6. The apparatus of claim 5, wherein the time of the upcoming transmission is determined as being shorter than the end time of the channel coherence time by a margin.

7. The apparatus of claim 5 or 6, wherein execution of the instructions further causes the apparatus to start a freshness timer indicating an age of the last determined short-term link state and the long-term link state, wherein the coherence and freshness timers have the same clock frequency, wherein the comparative link quality is determined further using the age indicated by the freshness timer.

8. The apparatus of any of the preceding claims 5 to 7, wherein execution of the instructions further causes the apparatus to perform the computing of the backoff time based on the determined comparative link quality by at least: determine whether the comparative link quality fulfills a quality condition; in response to determining that the comparative link quality fulfills the quality condition using the comparative link quality to compute the backoff time; or in response to determining that the comparative link quality does not fulfill the quality condition using the default backoff time computation to compute the backoff time.

9. The apparatus of claim 8, wherein the quality condition is that the difference between the shortterm link state and the long-term link state exceeds a threshold.

10. The apparatus of any of the preceding claims, wherein execution of the instructions further causes the apparatus to determine the comparative link quality comprising: determine a first composite value of the values of the first set of channel metrics representing the short-term link state; determine a second composite value of the values of the second set of channel metrics representing the long-term link state; combining the first and second composite values, wherein the comparative link quality is the combined composite value.11 . The apparatus of claim 10, wherein the combined composite value comprises the ratio of the first and second composite values.

12. The apparatus of any of the preceding claims, the first set of channel metrics and the second set of channel metrics being partially or completely overlapping.

13. The apparatus of any of the preceding claims, the first set of channel metrics being the second set of channel metrics.

14. The apparatus of any of the preceding claims, wherein the first time scale represents a time value and the second time scale covers a time interval.

15. The apparatus of any of the preceding claims, wherein the short-term link state is associated with first metadata, wherein the long-term link state is associated with second metadata, wherein the comparative link quality is determined further using the first and second metadata.

16. The apparatus of claim 15, the first metadata comprising a timestamp indicating when the shortterm link state is determined, the second metadata comprising the second time scale and a periodicity of acquisitions of the values of the second set of channel metrics.

17. The apparatus of any of the preceding claims, wherein execution of the instructions further causes the apparatus to determine the short-term link state of the communication channel by at least: using the values of the first set of channel metrics at the first time scale to determine an initial short-term link state of the communication channel, and using a statistical model to estimate the short-term link state from the initial short-term link state and the long-term link state, the statistical model having a decay slope defined by a channel coherence time.

18. The apparatus of any of the preceding claims, wherein the channel metric comprises at least one of: channel gain, Channel State Information (CSI), Received Signal Strength Indicator (RSSI), Received Channel Power Indicator (RCPI), Received Signal to Noise Indicator (RSNI), retry counts, Signal-to-Noise Ratio (SNR), Signal-to-lnterference-plus-Noise Ratio (SINR), or ACK failure counts.

19. A method for enabling transmission of data in a communication channel, the method comprising: using at least one value of a first set of one or more channel metrics at a first time scale to determine a short-term link state of the communication channel; using values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale to determine a long-term link state of the communication channel; determining a comparative link quality using the short-term link state and the long-term link state, wherein the comparative link quality is indicative of a difference between the short-term link state and the long-term link state; controlling access to the communication channel based on the determined comparative link quality for enabling transmission of the data on the communication channel.

20. A computer program comprising instructions for causing an apparatus for performing at least the following: using at least one value of a first set of one or more channel metrics at a first time scale to determine a short-term link state of a communication channel; using values of a second set of one or more channel metrics at a second time scale that is longer than the first time scale to determine a long-term link state of the communication channel; determining a comparative link quality using the short-term link state and the long-term link state, wherein the comparative link quality is indicative of a difference between the short-term link state and the long-term link state; controlling access to the communication channel based on the determined comparative link quality for enabling transmission of the data on the communication channel.

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