Packet duration estimation

Abstract

A radio receiver apparatus is provided. The radio receiver device is configured to: receive a radio signal comprising a data packet having a packet duration, the data packet comprising a first portion and a second portion; determining an initial estimate of the packet duration using the data included in the first portion; determining a correction factor for the initial estimate of the packet duration using the data included in the second portion; and combining the initial estimate and the correction factor to determine a precise estimate of the packet duration.

Description

Background Art

[0001] The present invention relates to an apparatus and method for estimating the duration of a radio packet.

[0002] Packet-based radio communication is common, where data is transmitted between devices in different chunks ("packets"). For example, the IEEE 802.11 wireless LAN ("Wi-Fi") standard defines various packet-based protocols for wireless network communication.

[0003] Each packet typically includes one or more preamble parts followed by a payload, where the payload contains the actual data to be transmitted and the preamble includes information that facilitates the ongoing communication. For example, the preamble part may include information identifying the packet structure and / or information for synchronizing the receiver with the time and frequency of the incoming packet.

[0004] Many radio communication protocols require the receiver to send an acknowledgement or other response to the received packet. In some IEEE 802.11 communications, the receiver may be required to send a reply to the packet at a specific time after the end of a given packet. The interval between the end of the data packet and the start of the response is called the Short Inter-Frame Space (SIFS). However, it may be difficult to directly identify the end point of a given packet with sufficient accuracy to time the response, and in any case, having to wait until the packet ends to determine the response time may limit the processing time for the content of the response to the SIFS itself (which may be very short).

[0005] Accordingly, some packet-based protocols (such as the IEEE 802.11 standard) include information in the preamble that allows the receiver to determine the duration of the packet. This can not only improve the accuracy with which the end point of the packet is identified, but also allow the receiver to calculate the necessary response time in advance, perhaps even before it has received most of the payload.

[0006] Traditional methods for using the preamble to identify the packet duration include multiplying the value indicating the number of bytes in the packet (e.g., determined from the LENGTH field of the IEEE 802.11 preamble) by the value indicating the data rate of the packet (e.g., determined from the RATE field of the IEEE 802.11 preamble).

[0007] However, for some implementations, this method may not be precise enough. For example, using the LENGTH field and the RATE field in the L-SIG part of an IEEE802.11ax packet as described above can provide an accuracy of up to ±4 μs, but the IEEE802.11ax standard includes a trigger-based multi-user protocol (HE TB) where response packets must be sent with an accuracy of ±0.4 μs. There are more precise methods of determining the packet duration based on preamble information suitable for meeting these requirements, but these methods may be complex to implement.

[0008] An improved method may be required. Summary of the Invention

[0009] According to a first aspect of the present invention, there is provided a radio receiver device configured to:

[0010] receive a radio signal comprising a data packet having a packet duration, the data packet comprising a first part and a second part;

[0011] use data comprised in the first part to determine an initial estimate of the packet duration;

[0012] use data comprised in the second part to determine a correction factor for the initial estimate of the packet duration; and

[0013] combine the initial estimate and the correction factor to determine an accurate estimate of the packet duration.

[0014] Thus, those skilled in the art will understand that by determining an initial estimate and then refining it with a correction factor to determine an accurate estimate of the packet duration, an accurate estimate of the packet duration can be provided with lower processing requirements than determining an equally accurate estimate by traditional direct calculation using data from several parts of the packet.

[0015] Combining the initial estimate with the correction factor may require fewer and / or simpler computational steps than alternative methods, and some of these steps can be optimized to further reduce the processing requirements. Reducing the processing requirements while maintaining accuracy can advantageously allow for a reduction in the cost, size, and / or power consumption of the radio receiver device.

[0016] Effectively determining an accurate estimate of the packet duration can facilitate accurate communication timing. For example, in a set of embodiments, a radio receiver device is arranged to use an accurate estimate of the packet duration to determine the end time of a data packet. For example, the radio receiver device can be arranged to detect the start time of a data packet (e.g., by detecting one or more preamble portions of a packet containing a predetermined pattern), and calculate the end time of the packet by adding the accurate estimate of the packet duration to the start time.

[0017] For example, accurately knowing the end time of a data packet can enable the radio receiver device to send an accurately timed response to the data packet. In a set of embodiments, the radio receiver device is arranged to use an accurate estimate of the packet duration to determine a response time for responding to the data packet. For example, the response time can be a fixed interval after the end time of the data packet (e.g., a short inter-frame space (SIFS)). The radio receiver device can be a radio transceiver device. The radio transceiver device can be arranged to transmit a radio signal including a response to the data packet at the determined response time.

[0018] The data packet can be distributed over multiple frequency bands. In some embodiments, at least a portion (and optionally all) of the data packet is modulated according to an orthogonal frequency division multiplexing (OFDM) scheme (e.g., an orthogonal frequency division multiple access (OFDMA) scheme), where the data packet is distributed over multiple orthogonal subcarrier frequencies (subcarriers). The first portion and the second portion can extend over all subcarriers or a subset of subcarriers.

[0019] The first portion and / or the second portion can include an encoded bit sequence. For example, the first portion and / or the second portion can include OFDM symbols, where their respective bit sequences are distributed over multiple frequency subcarriers and / or multiple time slots (e.g., each bit of an OFDM symbol is carried simultaneously in different subcarriers). The first portion and the second portion can use a phase shift keying modulation scheme, such as binary phase shift keying (BPSK) or quadrature BPSK (QBPSK). The radio receiver device can be arranged to decode and / or demodulate the first portion and / or the second portion as needed.

[0020] In certain sets of embodiments, the data packet follows the IEEE 802.11 protocol. For example, the data packet can be an IEEE 802.11ax data packet (e.g., an IEEE 802.11ax high-efficiency multi-user (HE-MU) format packet, or an IEEE 802.11ax high-efficiency single-user (HE-SU) format packet).

[0021] The data grouping may include a preamble followed by a payload (e.g., as described above, the payload contains the actual data to be transmitted, and the preamble includes information to facilitate ongoing communication). The first part and the second part may form part of the preamble.

[0022] In a set of embodiments, determining an initial estimate of the packet duration includes determining one or more values indicated by the first part. The radio receiver device may be arranged to determine one or more values from the first part and perform one or more mathematical operations on the values to determine the initial estimate. For example, the first part may include information identifying the amount of data contained in the data packet (e.g., the length of the data packet in bytes). The first part may include information identifying the data rate of the data packet (e.g., number of bytes per unit time). Determining the initial estimate of the packet duration may include combining the information (e.g., multiplying the amount of data by the data rate).

[0023] In a set of embodiments, the first part includes the legacy signal (L-SIG) part of an IEEE 802.11 data packet (e.g., an IEEE 802.11ax frame). The initial estimate of the packet duration can be calculated by combining the data amount information from the LENGTH field of the L-SIG part with the data rate information from the RATE field of the L-SIG part.

[0024] The initial estimate can provide a reasonably accurate estimate of the packet duration, which is then refined with a correction factor. In a set of embodiments, the initial estimate of the packet duration is accurate within 20 μs or less, 10 μs or less, or 4 μs or less.

[0025] Compared to the initial estimate, the correction factor can improve the accuracy of the refined estimate of the packet duration. In a set of embodiments, the refined estimate of the packet duration is accurate within 2 μs or less, 1 μs or less, 0.5 μs or less, or 0.4 μs or less. In some embodiments, the refined estimate can be considered an accurate assessment of the packet duration.

[0026] Obtaining this improved accuracy using the correction factor may require additional processing and / or other resources, i.e., processing additional information from the second part to determine the correction factor. Determining the correction factor may need to be optimized.

[0027] In a set of embodiments, determining the correction factor includes determining one or more values indicated by the second part. The radio receiver device may be arranged to determine one or more values from the second part and perform one or more mathematical operations on the values to determine the correction factor.

[0028] In a set of embodiments, the second part includes information identifying one or more of the following: the symbol duration in a data packet (e.g., the T SYM parameter) of an IEEE 802.11ax frame, the number of symbols in one or more fields of a data packet (e.g., the N HE_LTF parameter) of an IEEE 802.11ax frame, the duration of one or more fields in a data packet (e.g., the T HE LTF SYM parameter) of an IEEE 802.11ax frame, the middle code period of a data packet (e.g., the M MA parameter) of an IEEE 802.11ax frame, and packet extension information (e.g., the PE Disambiguity parameter of an IEEE 802.11ax frame). Determining the correction factor can include combining the information (e.g., using mathematical operations). In a set of embodiments, the second part includes the high-efficiency signal (HE-SIG) part of an IEEE 802.11ax data packet (e.g., an HE multi-user (MU) frame).

[0029] In a set of embodiments, determining the correction factor also utilizes the data included in the first part, such as the data volume information from the LENGTH field of the L-SIG part of an IEEE 802.11 frame and / or the data rate information from the RATE field of the L-SIG part of an IEEE 802.11 frame.

[0030] The inventors have recognized that determining the correction factor based on the information in the second part of a data packet can include one or more steps with a finite number of possible inputs and results. Thus, in a set of embodiments, determining the correction factor includes using one or more lookup tables that associate multiple input conditions with corresponding multiple results. The radio receiver device can include a memory storing one or more lookup tables for determining the correction factor (although alternatively, one or more lookup tables can be stored separately). Using a lookup for one or more calculation steps when determining the correction factor can reduce the processing power required to obtain an accurate packet duration estimate.

[0031] The input conditions for one or more lookup tables can include a single value determined based on the second part of the data packet, such that the lookup table links that value to a corresponding output. For example, the lookup table can include corresponding multiple possible values from the second part (e.g., the symbol duration of a data packet, such as the T SYMMultiple remainders of the value of the parameter (i.e., the fractional part between 0 and 1, or the value modulo 1). Since some fields in the second part may take only a limited number of values, it may be more efficient to use a lookup table to determine the remainders of these values than to provide processing resources for calculating the remainders.

[0032] Additionally or alternatively, in a set of embodiments, the input conditions for one or more lookup tables include a plurality of values determined from the second part of the data packet or from the first and second parts of the data packet. Such a lookup table can allow appropriate outputs to be determined for many different combinations of possible input values without the need for potentially complex processing steps. For example, the lookup table can include multiple remainders for corresponding multiple calculations involving several values that are extracted from the second part or the first and second parts (e.g., the product of the values of N HE_LTF and T HE_LTF_SYM parameters of an IEEE 802.11ax frame).

[0033] The radio receiver device can be arranged to perform one or more determination steps simultaneously with receiving a radio signal including a data packet. In other words, the determination of the initial estimate value, the correction factor, and / or the precise estimate value can be performed while the data packet is still being received. Determining an estimate value for the packet duration while the packet is still being received can provide the radio receiver device with more time to process the data packet, such as preparing an appropriate response for transmission immediately after the data packet ends.

[0034] According to a second aspect of the present invention, there is provided a method of operating a radio receiver device, comprising:

[0035] Receiving a radio signal including a data packet having a packet duration, the data packet including a first part and a second part;

[0036] Using the data included in the first part to determine an initial estimate value of the packet duration;

[0037] Using the data included in the second part to determine a correction factor for the initial estimate value of the packet duration; and

[0038] Combining the initial estimate value and the correction factor to determine a precise estimate value for the packet duration.

[0039] A radio receiver device may include one or more dedicated hardware components arranged to determine an initial estimate and / or a correction factor and / or an accurate estimate (e.g., the radio receiver device may include a pipeline architecture for determining an initial estimate and / or a correction factor and / or an accurate estimate). Additionally or alternatively, the radio receiver device may include a processor arranged to determine an initial estimate and / or a correction factor and / or an accurate estimate, for example, by executing appropriate software.

[0040] Accordingly, the invention extends to computer software which, when executed by a radio receiver device, causes the radio receiving device to perform the methods disclosed herein. The radio receiver device may include a memory storing the software. The radio receiver device may include a processor arranged to execute the software.

[0041] The invention extends to a radio communication system comprising:

[0042] a radio transmitter device arranged to transmit a radio signal comprising data packets having a packet duration; and

[0043] a radio receiver device as disclosed herein arranged to receive the radio signal and determine an accurate estimate of the packet duration for the data packets.

[0044] As described above, the radio receiver device may be a radio transceiver device arranged to transmit, at a response time determined using the accurate estimate of the packet duration, a radio signal comprising a response to the data packets. The radio transmitter device may be a radio transceiver device arranged to receive the response.

[0045] The ability to accurately estimate the data packet duration may be particularly useful for a number of user communication protocols (such as the 802.11ax OFDMA protocol), for example, accurately synchronizing responses from multiple users to a single trigger data packet may be beneficial.

[0046] In a set of embodiments, a radio communication system includes a second radio receiver device arranged to receive the radio signal and determine an accurate estimate of the packet duration for the data packet. The second radio receiver device may include any of the features described above with respect to the (first) radio receiver device, although the first radio receiver device and the second radio receiver device are not necessarily arranged identically. The second radio receiver device may include a second radio transceiver device arranged to transmit a radio signal including a response to the data packet at a response time determined using its accurate estimate of the packet duration. The first radio receiver device and the second radio receiver device may be arranged to synchronize their responses.

[0047] Where appropriate, the features of any aspect or embodiment described herein may be applied to any other aspect or embodiment described herein. When referring to different embodiments, it should be understood that these embodiments are not necessarily different but may overlap. It should be understood that all the preferred features of the first aspect above may also be applied to other aspects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] One or more non-limiting examples will now be described by way of example only and with reference to the drawings, in which:

[0049] Figure 1 is a schematic diagram of a radio communication system according to an embodiment of the present invention; and

[0050] Figure 2 is a timing and flow chart showing the operation of the radio communication system. DETAILED DESCRIPTION

[0051] As Figure 1 shown, the radio communication system 100 includes a first radio transceiver device 102, a second radio transceiver device 104, and a third radio transceiver device 105. In this example, the first radio transceiver device 102 is an IEEE 802.11 access point, and the second radio transceiver device 104 and the third radio transceiver device 105 are IEEE 802.11 client device stations. The first radio transceiver device 102, the second radio transceiver device 104, and the third radio transceiver device 105 are arranged to communicate according to the IEEE 802.11ax wireless local area network standard, particularly using orthogonal frequency division multiple access (OFDMA) IEEE high-efficiency multi-user (HE MU) transmission.

[0052] The first radio transceiver device 102 includes a memory 106 that stores software, which is executed by a processor 108 to cause the first radio transceiver device to prepare and send data packets to the second radio transceiver device 104 and the third radio transceiver device 105, and to receive and process data packets from the second radio transceiver device 104 and the third radio transceiver device 105. Similarly, the second radio receiver device 104 includes a memory 110 that stores software, which is executed by a processor 112 to cause the second radio transceiver device 104 to receive and process data packets from the first radio transceiver device 102, and to prepare and send data packets to the first radio transceiver device 102. The third radio transceiver device 105 is configured in the same manner as the second radio transceiver device 104.

[0053] Although Figure 1 not shown in, the first radio transceiver device 102, the second radio transceiver device 104, and the third radio transceiver device 105 also include additional radio communication and processing components to facilitate the sending and receiving of the data packets. For example, the processors 108, 112 can process (among other processes) physical layer (PHY) processes such as encoding, decoding, synchronization, and carrier frequency offset estimation, and the radio transceiver devices can also include an RF front-end portion that processes processes such as modulation, multiplexing, demultiplexing, and sampling (e.g., including one or more DACs, ADCs, mixers, filters, amplifiers, and / or baluns (balun transformers)).

[0054] Reference will now be made additionally to Figure 2 describe the operation of the radio communication system 100. This description will focus mainly on the operation of the second radio transceiver device 104, but the third radio transceiver device 105 also performs the same operations.

[0055] In use, the first radio transceiver device 102 broadcasts a trigger data packet 202, which is received by the second and third radio transceiver devices 104. In this example, the trigger data packet 202 uses an efficient multi-user (HE-MU) physical layer protocol data unit (PPDU) format (i.e., packet structure), which has several parts, including an L-STF part 201, an L-LTF part 203, an L-SIG part 204, a HE-SIG-A1 part 206, and a HE-SIG-A2 part 208. The parts of the packet 202 are surrounded by a guard interval 210.

[0056] The trigger data packet 202 has a duration TXTIME. After a short inter-frame space (SIFS) has elapsed since the end of the trigger data packet 202, the second radio transceiver device 104 sends a response data packet 212 to the first radio transceiver device 102. The third radio transceiver device 105 also sends a response data packet after the SIFS (not shown). The response data packet 212 can be a simple acknowledgment, or it can contain a substantial data payload. The response data packet 212 uses a High-Efficiency Trigger (HE-TB)-based Physical Layer Protocol Data Unit (PPDU) format. The response data packets from the second radio transceiver device 104 and the third radio transceiver device 105 must be sent exactly at the end of the SIFS (with an accuracy of ±0.4 μs) to avoid timing mismatches that may make the response data packets difficult or impossible to decode.

[0057] To send the response data packet 212 exactly at the end of the SIFS, the second radio transceiver device uses the information in the L-SIG part 204, the HE-SIG-A1 part 206, and the HE-SIG-A2 part 208 to estimate the duration TXTIME of the trigger data packet 202. This estimation is performed while the remainder of the trigger data packet 202 is still being received.

[0058] In an initial step, the second radio transceiver device 104 uses the preamble fields L-STF 201 and L-LTF 203 of the packet to estimate the start time of the trigger packet 202.

[0059] Then, the processor 112 decodes the L-SIG part 204 within the first decoding time 214.

[0060] Then, in step 216, the processor 112 extracts the LENGTH value and the RATE value from the decoded L-SIG part 204 and uses these values to calculate an initial estimated value TXTIME for the duration of the trigger data packet 202 L , as follows:

[0061]

[0062] where N DPBS is mapped from the RATE field and can take on the values 6, 9, 12, 18, 24, 36, 48, or 54.

[0063] The HE-SIG-A1 part 206 and the HE-SIG-A2 part 208 are decoded at the second decoding time 218.

[0064] Then, in step 220, the processor 112 extracts T SYM、 N HE_LTF , and T HE_LTF_SYM , M MA , and b PE-Disambiguity values from the decoded HE-SIG-A1 section 206 and HE-SIG-A2 section 208.

[0065] The T SYM value is used with the first lookup table 222 stored in the memory 110 to determine mod(T SYM , 1). T SYM can only take 3 different values: 13.6, 14.4, or 16, and the first lookup table 222 has three corresponding entries: 0.6, 0.4, or 0.

[0066] The N HE_LTF , and T HE_LTF_SYM values are used with the second lookup table 224 to determine mod(N HE_LTF ×T HE_LTF_SYM , 1). N HE_LTF can effectively take the values 1, 2, and 4, and T HE_LTF_SYM can effectively be 4, 7.2, 8, 13.6, or 16. The second lookup table 224 has five entries corresponding to the possible values of mod(N HE_LFT ×T HE_LTF_SYM , 1): 0, 0.2, 0.4, 0.6, or 0.8.

[0067] In step 226, the processor 112 determines the values of N SYM and N MA using the values extracted from the L-SIG section 204, HE-SIG-A1 section 206, and HE-SIG-A2 section 208 according to the following formula:

[0068]

[0069] where:

[0070] T HE-PREAMBLE = 4 + 8N HE_SIG_A + 4N HE_SIG_B + 4N HE_LTF T HE_LTF_SYM ,

[0071] and

[0072]

[0073] and,

[0074]

[0075] Wherein:

[0076] T MA = M MA T SYM + N HE_LTF T HE_LTF_SYM .

[0077] Next, in step 228, the determined values of N SYM and N MA are used to determine a correction factor TXTIME HE_CORR : TXTIME HE_CORR = N SYM × mod(T SYM , 1) + (N MA + 1) × mod(N HE_LTF × T HE_LTF_SYM , 1).

[0078] Finally, the correction factor TXTIME HE_CORR is combined with the initial estimated value TXTIME L to determine an accurate estimated value for the duration of the trigger data packet 202:

[0079] TXTIME HE = TXTIME L - TXTIME HE_CORR .

[0080] Thus, the second radio transceiver device 104 can determine an accurate estimated value for the duration of the trigger data packet 202 with only moderate processing resources. In particular, the use of lookup tables 222, 224 to determine mod(T SYM , 1) and mod(N HE_LTF × T HE_LTF_SYM , 1) avoids the need for complex circuitry that would otherwise be required to compute a highly accurate estimated value.

[0081] The processor 112 then adds the accurate estimated value TXTIME HE for the duration of the trigger data packet 202 and the SIFS to the detected start time to determine an appropriate response time. Then, the second radio transceiver device 104 can accurately transmit the response data packet 212 at the end of the SIFS. The third radio transceiver device 105 performs corresponding processing to transmit its own response data packet. Since the accurate estimated value for the duration of the trigger data packet 202 is accurate, the responses of the second radio transceiver device 104 and the third radio transceiver device 105 are well synchronized.

[0082] Although the present invention has been described in detail only in connection with a limited number of embodiments, it should be readily understood that the present invention is not limited to these disclosed embodiments. On the contrary, the present invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements that have not been previously described but are within the scope of the present invention. In addition, although various embodiments of the present invention have been described, it should be understood that various aspects of the present invention may include only some of the described embodiments. Accordingly, the present invention should not be regarded as being limited by the foregoing description, but only by the scope of the appended claims.

Claims

1. A radio receiver device, configured to: Receive a radio signal comprising data packets having a packet duration, the data packets comprising a first part and a second part; Use data comprised in the first part to determine an initial estimate of the packet duration; Use data comprised in the second part to determine a correction factor for the initial estimate of the packet duration; and Combine the initial estimate and the correction factor to determine an accurate estimate of the packet duration.

2. The radio receiver device according to claim 1, arranged to detect a start time of the data packet and calculate an end time of the packet by adding the accurate estimate of the packet duration to the start time.

3. The radio receiver device according to claim 1 or 2, wherein, The radio receiver device is a radio transceiver device, the radio transceiver device being arranged to use the accurate estimate of the packet duration to determine a response time for responding to the data packet and transmit a radio signal comprising a response to the data packet at the determined response time.

4. The radio receiver device according to any one of the preceding claims, wherein, At least a part of the data packet is modulated according to an orthogonal frequency division multiplexing (OFDM) scheme.

5. The radio receiver device according to any one of the preceding claims, wherein, The first part comprises information identifying the amount of data comprised in the data packet and information identifying the data rate of the data packet, and determining the initial estimate of the packet duration comprises combining the information.

6. The radio receiver device according to any one of the preceding claims, wherein the data packet is an IEEE802.11ax data packet.

7. The radio receiver device according to claim 6, wherein, The first part comprises a legacy signal (L-SIG) part of the IEEE802.11ax data packet.

8. The radio receiver device according to any one of the preceding claims, arranged to determine one or more values from the second part and perform one or more mathematical operations on the values to determine the correction factor.

9. The radio receiver device according to any one of the preceding claims, wherein, The second part comprises information identifying one or more of the following: symbol duration in the data packet, number of symbols in one or more fields of the data packet, duration of one or more fields in the data packet, middle code period of the data packet, and packet extension information.

10. The radio receiver device according to any one of the preceding claims, wherein, The second part comprises a high efficiency signal (HE-SIG) part of the IEEE802.11ax data packet.

11. The radio receiver device according to any one of the preceding claims, wherein, Determining the correction factor comprises using one or more look-up tables that associate multiple input conditions with corresponding multiple results.

12. The radio receiver device according to claim 11, which is arranged to use a lookup table, the lookup table including a plurality of remainders for corresponding multiple possible values from the second part.

13. The radio receiver device according to claim 11 or 12, which is arranged to use a lookup table, the lookup table including a plurality of remainders for corresponding multiple calculations involving a number of values, the number of values being extracted from the second part or the first part and the second part.

14. The radio receiver device radio according to any one of the preceding claims, which is arranged to perform one or more of the determination steps simultaneously with receiving a radio signal including the data packet.

15. The radio receiver device radio according to any one of the preceding claims, including a pipeline architecture for determining the initial estimate value and / or the correction factor and / or the accurate estimate value.

16. The radio receiver device radio according to any one of the preceding claims, including a processor, the processor being arranged to determine the initial estimate value and / or the correction factor and / or the accurate estimate value.

17. A method of operating a radio receiver device, comprising: receiving a radio signal including a data packet having a packet duration, the data packet including a first part and a second part; using the data included in the first part to determine an initial estimate value of the packet duration; using the data included in the second part to determine a correction factor for the initial estimate value of the packet duration; and combining the initial estimate value and the correction factor to determine an accurate estimate value for the packet duration.

18. A computer software which, when executed by a radio receiver device, causes the radio receiver device to perform the method according to claim 17.

19. A radio communication system, comprising: a radio transmitter device, which is arranged to transmit a radio signal including a data packet having a packet duration; and a radio receiver device according to any one of claims 1-16, which is arranged to receive the radio signal and determine an accurate estimate value for the packet duration of the data packet.

20. The radio communication system according to claim 19, wherein, the radio receiver device is a first radio transceiver device, the first radio transceiver device being arranged to transmit a radio signal including a response to the data packet at a response time determined using the accurate estimate value of the packet duration.

21. The radio communication system according to claim 20, including a second radio transceiver device, the second radio transceiver device being arranged to: receive the radio signal and determine an accurate estimate value for the packet duration of the data packet; and transmit a radio signal including a response to the data packet at a response time determined using the accurate estimate value of the packet duration.

22. The radio communication system according to claim 21, wherein, The first radio transceiver device and the second radio transceiver device are arranged to synchronize their responses.

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