Packet Retransmission Method in a Wireless Transmitter with Possibility of Suspension

Technical field [0001] The present invention relates to wireless transmissions, in particular to a retransmission mechanism.

BACKGROUND OF THE INVENTION [0002] This part is intended to introduce the reader to various aspects of this technical field that may be related to various aspects of the present invention which are described and / or claimed below. It is believed that this discussion will be helpful in providing the reader with basic information to facilitate a better understanding of various aspects of the present invention. Accordingly, it should be understood that these claims are to be read in this light, and not as prior art.

[0003] The home entrance gate is adapted to connect the home network to the internet. It allows you to receive and distribute certain video content over the home network via the Internet Protocol (IP). Video can be transferred inside the home network via a wired or wireless network. If a wired network would prove useful for transmitting video services, this would require that home appliances be plugged into the wired network. This does not meet the requirements for device mobility. Wireless technologies such as IEEE 802.11 are more practical to reach the device on a local network, but do not provide sufficient quality of services required for video applications. In particular, wireless interfaces deteriorate wireless transmission and, as a result, video quality. The specifications of the IEEE 802.11 Medium Access Control (MAC) standard for the local wireless network and Physical Layer (PHY) from June 12, 2007, 802.11 mentioned here, determine the retransmission mechanism in Chapter 9.2.5.3 for recovery procedures and repetitive restrictions transmission. The retransmission mechanism is part of the distributed coordination coordination function (DCF) specified in chapter 9.2. In particular, when exchanging frames, the transmitter supports a mechanism to repair errors by repeated transmission attempts for a frame exchange sequence. He performs the retransmission until the retransmission fails or until the retry limit is reached. Typically, the retry limit is set to seven. Such a mechanism is not sufficient to allow satisfactory transmission of video frames via a wireless medium.

BACKGROUND ART [0004] Draft standard "802.11 TGN of the IEEE 802.11 n Working Group Part 11: Specifications of the IEEE802.11 Standard Access Control Medium (MAC) of the local wireless network and Physical Layer (PHY): Extensions for Increased Bandwidth", published in IEEE P802 .11N / D6.01 shows how the packet is transmitted taking into account the duration value and, in the event of a transmission failure, the retry limit.

[0005] US-B1-7668968 discloses a method that avoids losing packets in an overloaded network by causing a break until network traffic is restored again.

SUMMARY OF THE INVENTION [0006] The present invention seeks to correct at least some of the drawbacks associated with transmitting prior art packets by providing a transmission mechanism adapted to video services.

[0007] The present invention relates to a retransmission mechanism that increases the quality of services in wireless networks for video services.

[0008] Until now, the present invention has concerned a method in a wireless device for transmitting a packet, the method comprising setting a lifetime value for the packet to be transmitted and transmitting the packet. According to the present invention, if the transmission fails, and the retransmission fails, and the packet's lifetime is not exceeded, this method includes the step of retransmitting the packet until the retry limit is reached, and waiting the pause time before retransmitting the packet until reaching the retry limit.

[0009] Unexpectedly, and unlike what is usually accomplished in wireless transmission systems, repeat transmission occurs in several stages, including numerous repeat transmissions. It is not based on several continuous packet retransmissions. It suspends and resumes repeated transmissions to avoid a period of interference. It turns out that such a retransmission mechanism provides better quality services for video services. Instead of re-transmitting the packet several times in a short period of time, the mechanism delays the repeated transmission. This at least allows you to bypass the interference problem again.

[0010] The retransmission mechanism has proven its usefulness when used for video transmission. It significantly reduces the packet error rate. Such a retransmission mechanism also advantageously saves the wireless medium, unlike what a standard implementation gives.

[0011] According to an embodiment of the present invention, the pause time is appropriate for the time needed to send the packet as many times as specified by the retry limit.

[0012] According to another embodiment of the present invention, the pause time is appropriate to the time needed to send the packet as many times as the retry limit at the lowest transfer rate determines.

[0013] According to an embodiment of the present invention, the method is only used for audio and video packages.

[0014] Another object of the present invention is a wireless device comprising a wireless interface for connecting to a wireless network, and retransmission means for setting the lifetime value of the packet to be transmitted, and until the lifetime expires and the packet transmission fails, to sending the packet until reaching the limit of repeated attempts, and suspending the transmission of the packet for the pause before transmitting the packet until the retry limit is reached.

[0015] According to an embodiment, the wireless device includes interference detection means to detect interference in a wireless network.

[0016] Another object of the present invention is a computer program product comprising program code instructions for performing the steps of the present method according to the present invention when the program is executed on a computer. By "computer program product" is meant not only the computer program support, which may include not only the storage space containing the program, such as computer memory, but also a signal, such as an electrical or optical signal.

[0017] Below are some aspects including the embodiments shown. It should be understood that these aspects are provided solely to provide the reader with a general summary of some of the embodiments of the present invention that he may take, and that these aspects are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE FIGURES [0018] The invention will be better understood and illustrated by the following non-limiting embodiments and implementations with reference to the attached figures, in which:

- Fig. 1 is a block diagram of an access point in accordance with the present embodiment

- Fig. 2 shows the retransmission mechanism according to this embodiment; and

- Fig. 3 is a flow chart of the retransmission mechanism of this embodiment.

[0019] In Fig. 1, the blocks shown are only functional units, which do not necessarily correspond to physically separate units. Namely, they can be developed in the form of hardware or software, or they can be implemented in one or several integrated circuits.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0020] It is understood that the drawings and descriptions of the present invention have been simplified to illustrate the components essential for a clear understanding of the present invention, while depriving, for the sake of clarity, of many other components present in traditional digital multimedia content delivery methods and systems . However, because such ingredients are well known in the art, this document does not provide a detailed discussion of them. The present disclosure is directed to all such variations and modifications known to those skilled in the art.

[0021] The exemplary embodiment is within the scope of the IEEE 802.11 structure, but the invention is not limited to this particular environment, and may be used within other structures in which retransmission occurs in a similar manner to that defined in the IEEE 802.11 standard.

[0022] The AP in the form of a device 1 according to an embodiment is shown in Fig. 1. It consists of a wireless interface 11 in accordance with the IEEE 802.11 standard. AP 1 includes a interference detection module 13 adapted to detect interference in a wireless medium. The interference detection mechanism is outside the scope of the present invention. The AP includes a retransmission module 14 adapted to perform the retransmission as described below. The interference detection module is also adapted to inform the retransmission module when interference is detected. The AP 1 also includes a memory 12 for storing packets that are transmitted via a wireless medium.

[0023] Even if the present embodiment applies to the AP, the mechanism of this embodiment is also applicable in a wireless base station.

[0024] The retransmission mechanism according to the present embodiment will be described below. The retransmission module controls two parameters. The first parameter is the packet's lifetime. The packet's lifetime corresponds to the time that the packet is stored in memory. When the packet's lifetime expires and the packet has not been sent, the packet is removed from memory. When the packet is sent, it falls out of memory.

[0025] The lifetime of the packet can be selected with the following restrictions. It is longer than the expected duration of interference. Is shorter than the maximum AP buffer capacity; which depends on the video bandwidth and available memory. And it is also shorter than the amount of video buffered in the receiving station. In particular, certain values ​​may be as follows: AP buffer capacity around 5 seconds, video player buffer capacity around 10 seconds, and packet life 2.5 seconds.

[0026] The second parameter is the retransmission_suspend value. It sets the time during which the AP accesses transmissions between two series of retransmissions.

[0027] The mechanism is summarized below as shown in Fig. 3. The AP is equipped with a packet to be sent to the station, step S1. It sets the packet's lifetime value for this packet, step S2. The packet was not received correctly by the station, this is detected by the AP because the AP did not receive the acknowledgment packet. The AP re-transmits the packet according to the mechanism defined by the IEEE 802.11 specification, step S3. If necessary, re-transmit this packet up to the retry limit. If the retransmission is successful, the AP may send the next packet, step S4. If the retransmission still has no effect, the interference detection module informs the retransmission module of the occurrence of interference. A retransmission mechanism in accordance with the present invention is set. If the packet's lifetime expires, step S5, the AP leaves this packet and sends the next one. If the packet's lifetime has not expired, the AP suspends retransmissions, step S6, and starts another set of retransmissions, step S3. The repeat attempt limit in this embodiment is affected by the ShortRetryLimit parameter specified in chapter 9.2.4 of the IEEE 802.11 standard. Of course, this mechanism can also apply to the LongRetryLimit parameter.

[0028] The AP device sends several series of retransmission packets, separated by break periods. This is illustrated in Fig. 2, where each vertical line corresponds to a transmission attempt and the length of the line indicates the transmission speed. The transfer speed can be changed within a series of retransmissions or between two series. As shown in Fig. 2, the AP copes with sending a retransmission packet after twenty-four failed retransmissions. The repeat transmissions have been grouped into a series of seven repeat transmissions. If the seventh retransmission fails, the AP will suspend retransmission until it starts another set of retransmissions. Between series of repeated transmissions it releases the transmission medium. During this interruption, the same AP may transfer data to other related stations or other devices on the same channel capable of transmitting data. The AP does not contaminate the wireless medium with unnecessary repeated transmissions and allows other devices to use this medium.

[0029] This corresponds to the repeated use of the standard retransmission mechanism, with the retry limit set to seven. In the standard mechanism, after the retransmission limit has been reached, the packet is removed. Here, the AP uses the standard retransmission mechanism several times, with intervals between them, until the packet's lifetime is reached.

[0030] This mechanism can be configured depending on the quality of service (QoS) class. The IEEE 802.11 standard, in particular IEEE 802.11e for Medium Access Control for Service Quality Extensions, defines four classes: background, best volume, voice and video. According to the present embodiment, the load class for voice and video uses this mechanism, while the background load class and best intensity do not use it. A proper application that supports video transmission to many stations at the same time must have four QoS queues per station so that problems with transmission to one station do not affect the quality of the video on another.

[0031] The interval between two series of retransmissions may be as long as the time needed to retransmit one series. For example, the retransmission_suspend value can be set to 25 milliseconds.

[0032] In particular, the pause time corresponds to the time needed for the repeated transmission of the series of the retransmission packet with the lowest transfer rate from BSSBasicRateSet, which is specified in 7.3.2.2 of the IEEE 802.11 specification. This corresponds to the time needed to re-transmit the series in the worst case.

[0033] In other words, the AP, according to an embodiment of the present invention, is a standard AP with an additional retransmission module and interference detection module. The standard AP includes a recovery module that performs repeated transmissions as specified in the IEEE 802.11 standard, using among others the retry limit parameter. Standard AP performs retransmission up to the retry limit.

[0034] The retransmission module performs retransmission using the properties of the recovery module. In particular, it first requests the recovery module to retransmit to the retry limit. If the retransmission fails, it again requests the recovery module to retransmit. Typically, the retransmission module is adapted to control the recovery module, according to parameters such as retransmission_suspend value, number of retry limit and packet lifetime. The retransmission_suspend value can be set through the AP user interface.

[0035] The retransmission module may also check, before using the retransmission mechanism of the present embodiment, whether the receiver supports this retransmission mechanism. It checks the receiver's buffering capacity to estimate the maximum packet lifetime that can be set. If the packet's lifetime is too short, the retransmission mechanism is not used and only standard recovery procedures are used. This may be carried out in a reserved manner that is outside the scope of the present invention.

[0036] References disclosed herein, claims and drawing figures may be provided separately or in another suitable combination. According to the demand, the properties can be implemented in hardware, software or as a combination of the two.

[0037] The expressions used herein "some embodiment" or "embodiment" mean that the particular property, structure or characteristic described in connection with this embodiment can be included in at least one embodiment of the present invention. The expressions "in one embodiment" appearing in many places in this specification are not necessarily all refer to the same embodiment, nor are they separate or interchangeable embodiments necessarily mutually exclusive to other embodiments.

[0038] Reference numerals in the claims are for illustrative purposes only and should not limit the scope of the claims.