GB2531690A - TDMA data exchange - Google Patents

TDMA data exchange Download PDF

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Publication number
GB2531690A
GB2531690A GB1405530.5A GB201405530A GB2531690A GB 2531690 A GB2531690 A GB 2531690A GB 201405530 A GB201405530 A GB 201405530A GB 2531690 A GB2531690 A GB 2531690A
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Prior art keywords
payload data
data
time slots
transmission
communication system
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GB1405530.5A
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GB2531690B (en
GB201405530D0 (en
Inventor
Nezou Patrice
El Kolli Yacine
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Canon Inc
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Canon Inc
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Priority to GB1405530.5A priority Critical patent/GB2531690B/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/40—Bus networks
    • H04L12/407—Bus networks with decentralised control
    • H04L12/413—Bus networks with decentralised control with random access, e.g. carrier-sense multiple-access with collision detection [CSMA-CD]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2643—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/16—Time-division multiplex systems in which the time allocation to individual channels within a transmission cycle is variable, e.g. to accommodate varying complexity of signals, to vary number of channels transmitted
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/20—Arrangements for detecting or preventing errors in the information received using signal quality detector
    • H04L1/203—Details of error rate determination, e.g. BER, FER or WER

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

The invention relates to a method for exchanging data between a destination node and a source node in a communication system using a time division multiple access (TDMA) protocol comprising a first TDMA mode 310 and a second TDMA mode 300. The first TDMA mode enables the transmission of payload data 306, such as image data from a camera, preferably in addition to control data. The second TDMA mode 300 is dedicated to transmission of control data 301-305 only, such as data for controlling image transmission. The second TDMA mode is preferably an asynchronous TDMA mode. At a destination node a transmission quality metric is monitored. The quality metric may be pixel error rate, or alternatively a measure of latency. The TDMA mode is switched from the payload data mode to the control data mode as soon as it is determined that the quality metric falls below a predetermined constraint. In another embodiment, the source node (101, Fig. 1) may request that a centralised control node (102, Fig. 1) grants the source node an extension slot to extend its slot allocation, if the source node determines that payload data to be transmitted is invalid. This could occur if payload data to be transmitted was unavailable at the time a time slot allocated to the source node was available.

Description

TDMA data exchange
FIELD OF THE INVENTION
The present invention relates to wireless communication. It relates more particularly to wireless communication systems using at least two different TDMA modes for the transmission of data. TDMA (Time Division Multiple Access) is a known channel access principle for networks using a shared medium. It allows several users to share the same frequency channel by dividing the signal into time slots. TDMA is a general method: an infinite numbers of modes (in which the length of each time slot is defined, as well the allocation of the time slots, and so on) may be defined, to best suit a given application, and several TDMA modes may be used in a TDMA protocol.
The invention may be implemented in the context of a wireless communication network comprising several nodes. In such a communication network, the nodes may be for example mobile or fixed stations. The data exchanges between the nodes or stations of the network may be ensured through a TDMA protocol driven by a main station.
BACKGROUND OF THE INVENTION
The invention is applicable to any wireless communication network using more than two TDMA modes of a TDMA protocol. By way of example, the invention will be described hereafter in the context of a wireless communication network comprising several stations, and using a TDMA protocol comprising two TDMA modes. For example:
- a first TDMA mode may be used to transmit payload data, such as images, video data, music, and so on;
- a second TDMA mode may be used to transmit system control data, i.e. any
FIELD OF THE INVENTION
The present invention relates to wireless communication. It relates more particularly to wireless communication systems using at least two different TDMA modes for the transmission of data. TDMA (Time Division Multiple Access) is a known channel access principle for networks using a shared medium. It allows several users to share the same frequency channel by dividing the signal into time slots. TDMA is a general method: an infinite numbers of modes (in which the length of each time slot is defined, as well the allocation of the time slots, and so on) may be defined, to best suit a given application, and several TDMA modes may be used in a TDMA protocol.
The invention may be implemented in the context of a wireless communication network comprising several nodes. In such a communication network, the nodes may be for example mobile or fixed stations. The data exchanges between the nodes or stations of the network may be ensured through a TDMA protocol driven by a main station.
BACKGROUND OF THE INVENTION
The invention is applicable to any wireless communication network using more than two TDMA modes of a TDMA protocol. By way of example, the invention will be described hereafter in the context of a wireless communication network comprising several stations, and using a TDMA protocol comprising two TDMA modes. For example:
- a first TDMA mode may be used to transmit payload data, such as images, video data, music, and so on;
- a second TDMA mode may be used to transmit system control data, i.e. any kind of data except payload.
The invention is for example applicable in a system comprising a mobile station having a camera that communicates through a wireless network for the transmission of images with one main fixed station or many fixed stations forwarding the received data to a main station.
In this example, the two TDMA modes may be:
* a first TDMA mode, namely an “image TDMA mode” used to transmit the payload data, i.e. data corresponding to an encoded image in this example, when the mobile station transmits an uncompressed high definition image. The uncompressed high definition image may be encapsulated in data blocks and transmitted to multiple receivers (destination stations); and
* a second TDMA mode, namely an “asynchronous TDMA mode” used to exchange asynchronous transactions to control the transmission of an uncompressed high definition image, i.e. system control data. Thus, in a communication system using TDMA, multiple TMDA modes
(or profiles) may be used to provide different priorities in data transmissions. When a large bandwidth for the transmission of payload data must be ensured, a dedicated TDMA profile with long time slots (the “image TDMA mode” in the given example) is well adapted. The asynchronous transactions, i.e. the transmission of control data, become less important and the associated latency is not optimized.
When control data with high priority must be sent, another TDMA profile with short time slots (the “asynchronous TDMA mode” in the given example) is set to reduce the latency between the source node and the destination node. All the transactions or data transmissions, mainly asynchronous, are delay-sensitive, so that a small-enough latency has to be guaranteed (the term latency referring to any of several kinds of delays typically incurred in processing of network data). It is then necessary to implement a mechanism which allows fast switching between the TDMA modes. If such a mechanism is not implemented, the latency requirement cannot be ensured and part of the bandwidth is lost. Moreover, due to possible buffering problems at the mobile station end and possible transmission errors in the wireless medium, unexpected delays may be created, which increase latency.
Some mechanisms for switching from one TDMA mode to another are known.
Most of them are driven by the wireless medium conditions. For instance the document US8249519 discloses a method of determining the instant of consideration of a modification of the radio conditions in a communication system which does not have a centralized architecture.
Another common reason for switching from one TDMA profile to another is a modification in the bandwidth requirements of the source nodes. In the known switching mechanisms, the requirements are typically transmitted through asynchronous transactions and are taken into account (or not) by a controller. That is, for instance, the kind of mechanism described in the document W02008010652. More specifically, that document discloses a method in which the modification of the TDMA profiles is driven by the bandwidth requirements of the source nodes. No method is known to modify the TDMA profiles (i.e. set a TDMA mode) based on the application requirements at the destination side (destination node(s)). The requirements may be for example a maximum acceptable latency and/or a maximum error rate in data transmission before and/or after application of a process to solve transmission error such as multi-copy decoding. Thus, it is desirable to provide a method allowing fast TDMA mode switching based on the application requirements at the destination node.
SUMMARY OF THE INVENTION
A first aspect of the invention relates to a method a method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of control data, wherein the method comprises at the destination node:
- upon reception of a payload data transfer request comprising information on the size of the payload data, setting the transmission protocol to the first TDMA mode, and determining and allocating a minimum set of time slots for receiving said payload data; - computing a transmission quality metric of the data received in a time slot comprising at least one quality parameter, and comparing said at least one parameter to a corresponding predefined quality constraint; and
- setting the communication system to the second TDMA mode as soon as the comparison of the at least one quality parameter to the predefined quality constraint indicates that said quality constraint is not met.
The quality parameter may be a latency computed based on data received in a time slot, and the corresponding quality constraint is a maximum permissible delay at application level.
In a particular application of the method, the payload data correspond to an encoded image, said data defining pixels of said image. In this case, the quality parameter may be a pixel rate computed as function of identified erroneous packets transporting the image data and the quality constraint is an admissible pixel error rate.
The method may further comprise updating the set of time slots by extending the set of time slots if an extension request has been received. For instance, the set of time slots may be extended by one time slot if an extension request has been received.
The method may further comprise setting the communication system to the second TDMA mode as soon as the entire determined set of time slots has been received.
In an embodiment of the invention, the method further comprises at the source node:
- transmitting a payload data transfer request, said request comprising the payload data size;
- receiving information from the destination node on time slots forming a set of time slots allocated for the transmission of the payload data;
- upon detection of invalid data payload, sending an extension slot request and updating the set of time slots; - transmitting the payload data in packets in said set of time slots.
A second aspect of the invention relates to a method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of the control data, wherein the method comprises at the source node:
- transmitting a payload data transfer request, said request comprising the payload data size; - receiving information from the destination node on time slots forming a set of time slots allocated for the transmission of the payload data;
- upon detection of invalid payload data, requesting an extension slot and updating the set of time slots;
- transmitting the payload data in packets in said set of time slots. For example, invalid payload data may be detected when a packet of payload data to be transmitted is unavailable at the time a time slot of the set of time slots should be filled with said packet.
Updating the set of time slots may consist in extending the set of time slots if an acknowledgement of the extension request has been received from the destination node. For instance, the set of time slots may be extended by one time slot if an acknowledgement of the extension request has been received from the destination node.
In a particular application of the method the payload data correspond to an encoded image, said data defining pixels of said image.
A third aspect of the invention relates to a communication system comprising a destination node and a source node, the communication system being configured to implement a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of control data, wherein the destination node comprises :
- means configured to receive a payload data transfer request comprising information on the size of the payload data;
- means configured to determine and allocate a minimum set of time slots for receiving the payload data, based on the received information on the size of the payload data;
- means to set the transmission protocol to the first TDMA mode
- means configured to compute a transmission quality metric comprising at least one quality parameter, and compare the at least one parameter to a corresponding predefined quality constraint; and
- means to set the communication system to the second TDMA mode as soon as the comparison of the at least one quality parameter to the predefined quality constraint indicates that said quality constraint is not met.
The means configured to compute a transmission quality metric may comprise means to determine latency.
The means configured to compute a transmission quality metric may comprise means to compute a pixel error rate of an image.
In such a communication system, the source node may comprise: - means configured to transmit and receive data blocks exchanged over a wireless medium;
- means configured to send a payload data transfer request including information on the size of the payload data ;
- means configured to receive information on allocated time slots forming a set of time slots for the transmission of the payload data;
- means configured to send a dedicated packet or flag with the payload data to request an extension of the set of time slots.
DETAILLED DESCRIPTION OF EMBODIEMENTS OF THE INVENTION
Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which:
Figure 1 illustrates an example of a wireless communication system in which the invention may be applicable;
Figure 2 is a block diagram illustrating a schematic configuration of a communication apparatus which may be used in an embodiment of the invention;
Figure 3 illustrates a TDMA protocol having two TDMA modes;
Figure 4 is a flowchart describing a method according to an embodiment of the invention, implemented at a source node of a wireless network to transmit an image.
Figure 5 is a flowchart describing a method according to an embodiment of the invention, implemented at a destination node of a wireless network to receive an image.
As shown in Figure 1 , a wireless communication system may comprise: a transmission channel or wireless medium 100, multiple stations, comprising a source station 101 denoted SRC, a set of destination stations 103-106 denoted Dest, (“i” being a station number) and a master system controller 102. The destination stations 103-106 and the master system controller 102 are destination nodes of the communication system.
In this example, the master system controller is connected to the set of destination stations 103-106 by wires. The set of destination stations 103-106 and the SRC station are connected by a wireless medium 100. The SRC station is in charge of image transmission to the master system controller via the set of destination stations 103-106. The wireless protocol is a TDMA protocol implementing two TDMA modes or “profiles”. In this example, the two TDMA modes may be an “image TDMA mode” as first TDMA mode, and an “asynchronous TDMA mode” as second TDMA mode. The image TDMA mode is used to transmit uncompressed high definition images from the source station 101 to the destination stations 103-106 over the wireless medium 100
Next, each destination station 103-106 forwards the image data blocks to a main station, namely the Master system controller 102 that performs a multi copy decoding process to solve transmission errors.
The asynchronous TDMA mode is used to exchange asynchronous transactions to control the transmission of the image, i.e. system control data.
Figure 2 is a block diagram illustrating by way of example a schematic configuration of a communication apparatus 200 representing a transmitting node or a receiving node adapted to be used in some embodiments of the invention.
The depicted communication apparatus 200 uses a layered communication protocol stack comprising three layers: the lower layer comprises a physical layer block 203, usually called PHY layer block, the intermediate layer comprises a Media Access Control layer block 204, usually called MAC layer block, and the higher layer is an application layer 201.
The PHY layer block 203 is in charge of formatting data packets and sending data packets on the wireless medium (preferably using the 60GHz band).
The MAC layer block 202 is composed of a TDMA MAC layer 204 in charge of managing the access over the wireless medium and two additional blocks allowing implementation of a method according to an embodiment of the invention: an image transfer module 205 in charge of transmitting or receiving image data blocks to or from the application layer 201 and an image transfer controller block 206 in charge of managing the image block transmission over the 60GHz wireless medium. The image transfer controller 206 handles image transmission at source node(s) and at destination node(s). A method according to an embodiment of the invention implemented at a source node will be detailed below in relation with Figure 4. A method according to an embodiment of the invention implemented at a destination node will be detailed below in relation with Figure 5.
Figure 3 illustrates a TDMA protocol having two TDMA modes. This TDMA protocol is used by the communication system of Figure 1. In the represented protocol, the time is divided into TDMA superframes (300, 310, 320 ... ). Each TDMA superframe 300, 310, 320, 330 is divided into time slots 301 -305 and, depending on the current TDMA mode, an optional image slot 306. In Figure 3, the superframes are numbered n, n+1 , n+2 etc. Superframes n and n+1 are consecutive. Each node of the network owns one (or several) time slots. In other words, each time slot is assigned to a node of the network. In the represented example, the destination stations 103-106 own the slots 301 -304. The first slot 301 is assigned to the first destination station 103, the second slot 302 is assigned to the second destination station 104 and so on. The slot 305 is assigned to the source station 101.
When the image TDMA mode is set, the image slot 306 is used by the SRC station to transmit image data blocks. This image slot 306 is much longer than all other time slots 301 -305 used to transmit control data.
When the asynchronous TDMA mode is set, the image slot 306 is not available in the superframe: the superframe comprises only the time slots 301 to 305 for transmission of control data.
To avoid the use of a heavy synchronization mechanism, the system master node (master system controller 102) drives the time slot allocation. It controls the starting time of each time slot allocated to the destination stations 103-106. The starting time of the time slots allocated to the source station(s) is transmitted by the set of destination stations during their associated time slots. Consequently the starting time of the time slots allocated to the source stations for a superframe n+1 (for example) are transmitted in the previous superframe n.
It implies a delay corresponding to one superframe to allow the source station to decode the information about its allocated time slots.
The delay due to this decoding process may have a significant impact on latency and bandwidth. In addition, in the formerly known TDMA protocols, the end of an image transmission is detected by detecting an empty image time slot, meaning that no more data corresponding to the images are transmitted. In that case, any switching from the image TDMA mode to the asynchronous TDMA mode needs one superframe delay. Thus, some bandwidth is lost. Moreover, if some buffering problems occur at the source station (e.g. buffer underflow), some image time slots can remain empty because no image data blocks are ready to send. This could be interpreted as the end of the transmission of an image.
In addition, if the transfer of an image takes too much time, said image can be obsolete when decoded at the destination side. In such a case, it would be better to cancel the current image transfer and to start another image transfer.
Another issue is related to reception quality. A high pixel error rate (e.g. one erroneous pixel per image), which may be caused by multiple transmission errors, leads to rejection of the image. All this may lead to an excessive bandwidth loss. This may be an important issue when the constraints of maximum latency and maximum pixel error rate are significant.
The developed invention provides a reliable and fast switching mechanism between the TDMA modes of a TDMA protocol, which reduces latency when switching from one TDMA mode to another TDMA mode. This solves the above mentioned issues.
Figure 4 is a flowchart describing a method according to an embodiment of the invention, implemented at a source node of a wireless network to transmit an image. More specifically, Figure 4 is a flowchart describing the image transmission procedure implemented at the source station 101 to transmit an image to the master system controller 102. This flowchart corresponds to the detail of the steps performed at the image transfer controller 206, in the source station 101. Upon reception of an image to transfer at step 410, the source station
101 sends an image transfer request to the system master controller 102 at step 420. The source station 101 provides the image size to allow the system master controller 102 to allocate the correct bandwidth (i.e. the needed number of image slots) for transmission of the entire image. However, if a transmission problem or error occurs at the source station 101 or in the wireless medium, the transfer is stopped.
The system master controller 102 acknowledges the image transfer request and sets the TDMA mode to the image TDMA mode. The TDMA mode of the TDMA protocol used is then switched from the asynchronous TDMA mode (second TDMA mode) to the image TDMA mode (first TDMA mode).
As the TDMA mode is set to the image TDMA mode, the next TDMA superframe comprises an image slot. When an image slot occurs at step 430, the source station 101 checks if image data blocks are available for transmission (step 440). If no image data block is available when an image slot occurs, the image slot remains empty and the source station 101 requests extra bandwidth for image transmission at step 450 to the system master controller 102 (by sending a request for an extension slot). This is done because, in an initial reservation request, the system master controller 102 only reserves and allocates the needed bandwidth (and not more) for image transmission, depending on the size of the image. Next, the method returns to step 430, where the source station 101 waits for the next image time slot.
If at least one image data block is available (i.e. ready for transmission) when an image slot occurs, the source station 101 transmits the data blocks in the current image slot at step 460. At step 470, it is checked whether the image transfer is finished. If the end of the transfer of the image is not detected, the process returns to step 430 where another image time slot is awaited. If the end of the transfer of the image is detected, the process returns to step 410 where new image transfer is awaited.
Figure 5 is a flowchart describing a method according to an embodiment of the invention, implemented at a destination node of a wireless network to receive an image. More specifically, Figure 5 is a flowchart describing the image transmission procedure implemented at a destination station 101 to transmit an image to the master system controller 102. This flowchart corresponds to the detail of the steps performed at the image transfer controller 206, in the destination station 103-106 or in the master system controller 102. Upon reception of an image transfer request from the source station 101 at step 510, the image size, which is included in said request, is decoded from the received request and converted at step 520 into a number of image slots required to transmit all associated image data blocks.
Then at step 530, the system master controller switches the TDMA mode from the asynchronous TDMA mode to the image TDMA mode to enable the image transmission.
Next at step 540, the system master controller checks whether an image slot occurred. The received data are analyzed and the estimated pixel error rate (denoted PER) associated with the current image transfer is computed. At step 550, the estimated PER is computed based on the identified erroneous image data blocks transmitted through the image slot. The pixel error rate may be used as a parameter to define a quality metric used to assess whether the quality of image transmission is good enough. In the same way, an estimated latency can be computed. The estimated latency is the estimated delay to well receive the complete image for the current image transfer.
At step 560, it is assessed whether the quality constraints are met or not. The estimated PER is compared to a predefined pixel error rate that may correspond to a maximum admissible pixel error rate as quality constraint. In the same way, the estimated latency is compared to a predefined latency that may correspond to a maximum admissible latency to well receive a complete image for the current image transfer.
If the computed pixel error rate is higher than the predefined pixel error rate, the received image is not acceptable for the application layer 201 , and the quality constraint is not met. This can be determined even if the image reception is not completed (i.e. before the end of reception of an image).
If the computed latency is greater than a predefined latency defined by the application layer, a quality constraint is not met.
If it has been determined before the end of transmission of an image that a quality constraint will not be met, it is useless to continue the image transfer. Consequently, the system master controller immediately ends the image transfer by setting the TDMA mode to the asynchronous TDMA mode at step 580. This saves bandwidth and allows fast switching of TDMA mode to be performed.
Next the process returns to step 510 and another image transfer is awaited.
If the computed pixel error rate is lower than the predefined pixel error rate or if the computed latency is lower than a predefined latency defined by the application layer, it is checked at step 561 if additional time to receive the complete image was requested by the sender.
If such a request is received, the acknowledgment of this request is sent only if the quality constraints are met, e.g. if the pixel error rate and its associated latency computed at step 550 are below given values. And the number of required image slots to receive the complete image is updated. Afterwards it is assessed at step 570 whether the image reception is finished. In other words it is checked whether the end transmission of the image has been detected. The end of the transmission is detected when all the slots allocated to the image have elapsed, i.e. the slots initially allocated plus the potential extension slots. When the end of the transfer of the image is detected, the master system controller 102 switches the TDMA mode from the image TDMA mode to the asynchronous TDMA mode at step 580.
At least parts of the methods according to the invention may be computer implemented. Accordingly, 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. Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.
The present invention thus provides a secure and fast TDMA mode switching mechanism, method and associated hardware communication system, associated with a multi-modal TDMA protocol. In the present invention, the TDMA switching mechanism is driven by a destination node of the communication system, Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention.
Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.
In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. e.g. a master system controller at the destination end.
According to embodiments of the invention, the end of the transmission of payload data (e.g. an image) is detected earlier than in the prior art, allowing a fast TDMA mode switching. Moreover thanks to a quality metric computation and analysis, the current image transmission may be broken if a quality constraint is not met, and TDMA mode quickly switched.
Contrary to what is done in most methods known in the prior art, the latency is driven by the application requirement. If the transmitted payload data is an image, the pixel error rate at the application layer may be also used to drive the choice of the TDMA profile to be set.
The present invention aims at minimized latency, especially optimizing latency for asynchronous transactions, while bandwidth consumption is also minimized.
Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention.
Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.
In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims (19)

CLAIMS A method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of control data, wherein the method comprises at the destination node: - upon reception of a payload data transfer request comprising information on the size of the payload data, setting the transmission protocol to the first TDMA mode, and determining and allocating a minimum set of time slots for receiving said payload data; - computing a transmission quality metric of the data received in a time slot comprising at least one quality parameter, and comparing said at least one parameter to a corresponding predefined quality constraint; and - setting the communication system to the second TDMA mode as soon as the comparison of the at least one quality parameter to the predefined quality constraint indicates that said quality constraint is not met. 2. A method according to claim 1 wherein a quality parameter is a pixel error rate computed on packets received in a time slot and the corresponding quality constraint is a maximum permissible pixel error rate. 3. A method according to claim 1 , wherein a quality parameter is a latency computed based on data received in a time slot, and the corresponding quality constraint is a maximum permissible delay. 4. A method according to any one of the preceding claims, wherein the payload data correspond to an encoded image, said data defining pixels of said image. A method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of control data, wherein the method comprises at the destination node: - upon reception of a payload data transfer request comprising information on the size of the payload data, setting the transmission protocol to the first TDMA mode, and determining and allocating a minimum set of time slots for receiving said payload data; - computing a transmission quality metric of the data received in a time slot comprising at least one quality parameter, and comparing said at least one parameter to a corresponding predefined quality constraint; and - setting the communication system to the second TDMA mode as soon as the comparison of the at least one quality parameter to the predefined quality constraint indicates that said quality constraint is not met. 2. A method according to claim 1 wherein a quality parameter is a pixel error rate computed on packets received in a time slot and the corresponding quality constraint is a maximum permissible pixel error rate. 3. A method according to claim 1 , wherein a quality parameter is a latency computed based on data received in a time slot, and the corresponding quality constraint is a maximum permissible delay. 4. A method according to any one of the preceding claims, wherein the payload data correspond to an encoded image, said data defining pixels of said image. 7. A method according to any of the preceding claims, further comprising setting the communication system to the second TDMA mode as soon as the entire determined set of time slots has been received. 8. A method for exchanging data according to claim 1 , wherein the method further comprises at the source node : - transmitting a payload data transfer request, said request comprising the payload data size; - receiving information from the destination node on time slots forming a set of time slots allocated for the transmission of the payload data; - upon detection of invalid data payload, sending an extension slot request and updating the set of time slots; - transmitting the payload data in packets in said set of time slots. 9. A method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of the control data, wherein the method comprises at the source node : - transmitting a payload data transfer request, said request comprising the payload data size; 5. A method according to any one of the preceding claims, further comprising updating the set of time slots by extending the set of time slots if an extension request has been received. 6. A method according to claim 5, wherein the set of time slots is extended by one time slot if an extension request has been received. 7. A method according to any of the preceding claims, further comprising setting the communication system to the second TDMA mode as soon as the entire determined set of time slots has been received. 8. A method for exchanging data according to claim 1 , wherein the method further comprises at the source node : - transmitting a payload data transfer request, said request comprising the payload data size; - receiving information from the destination node on time slots forming a set of time slots allocated for the transmission of the payload data; - upon detection of invalid data payload, sending an extension slot request and updating the set of time slots; - transmitting the payload data in packets in said set of time slots. 9. A method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of the control data, wherein the method comprises at the source node : - transmitting a payload data transfer request, said request comprising the payload data size; - receiving information from the destination node on time slots forming a set of time slots allocated for the transmission of the payload data; - upon detection of invalid payload data, requesting an extension slot and updating the set of time slots; - transmitting the payload data in packets in said set of time slots. 10. A method according to claim 8 or claim 9, wherein invalid payload data is detected when a packet of payload data to be transmitted is unavailable at the time a time slot of the set of time slots should be filled with said packet. 1 1. A method according to any one of claims 8 to 10, wherein updating the set of time slots consists in extending the set of time slots if an acknowledgement of the extension request has been received from the destination node. 12. A method according to claim 11 , wherein the set of time slots is extended by one time slot if an acknowledgement of the extension request has been received from the destination node. 13. A method according to any one of the claims 8 to 12 wherein the payload data correspond to an encoded image, said data defining pixels of said image. 14. A communication system comprising a destination node and a source node, the communication system being configured to implement a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of control data, wherein the destination node comprises : - means configured to receive a payload data transfer request comprising information on the size of the payload data; - means configured to determine and allocate a minimum set of time slots for receiving the payload data, based on the received information on the size of the payload data; - means configured to set the transmission protocol to the first TDMA mode; - means configured to compute a transmission quality metric comprising at least one quality parameter, and compare the at least one parameter to a corresponding predefined quality constraint; and - means configured to set the communication system to the second TDMA mode as soon as the comparison of the at least one quality parameter to the predefined quality constraint indicates that said quality constraint is not met. 15. A communication system according to claim 14 wherein the means configured to compute a transmission quality metric comprises means to determine latency. 16. A communication system according to claim 14 or claim 15, wherein the means configured to compute a transmission quality metric comprises means to compute a pixel error rate of an image. 17. A communication system according to any one of the claims 14 to 16, wherein the source node comprises : - means configured to transmit and receive data blocks exchanged over a wireless medium; - means configured to send a payload data transfer request including information on the size of the payload data ; - means configured to receive information on allocated time slots forming a set of time slots for the transmission of the payload data; - means configured to send a dedicated packet or flag with the payload data to request an extension of the set of time slots. 18. A method for exchanging data between a destination node and a source node in a communication system, said method comprising at the destination node a method as hereinbefore described with reference to, and as shown in Figure 5. 19. The method of claim 18, further comprising at the source node a method as hereinbefore described with reference to, and as shown in Figure 4.
1. A method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of control data only, wherein the method comprises at the destination node: - upon reception of a payload data transfer request comprising information on the size of the payload data, setting the transmission protocol to the first TDMA mode, and determining and allocating a minimum set of time slots for receiving said payload data; - computing a transmission quality metric of the data received in a time slot comprising at least one quality parameter, and comparing said at least one parameter to a corresponding predefined quality constraint; and - setting the communication system to the second TDMA mode as soon as the comparison of the at least one quality parameter to the predefined quality constraint indicates that said quality constraint is not met.
1. A method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of control data only, wherein the method comprises at the destination node: - upon reception of a payload data transfer request comprising information on the size of the payload data, setting the transmission protocol to the first TDMA mode, and determining and allocating a minimum set of time slots for receiving said payload data; - computing a transmission quality metric of the data received in a time slot comprising at least one quality parameter, and comparing said at least one parameter to a corresponding predefined quality constraint; and - setting the communication system to the second TDMA mode as soon as the comparison of the at least one quality parameter to the predefined quality constraint indicates that said quality constraint is not met.
2. A method according to claim 1 wherein a quality parameter is a pixel error rate computed on packets received in a time slot and the corresponding quality constraint is a maximum permissible pixel error rate.
2. A method according to claim 1 wherein a quality parameter is a pixel error rate computed on packets received in a time slot and the corresponding quality constraint is a maximum permissible pixel error rate.
3. A method according to claim 1 , wherein a quality parameter is a latency computed based on data received in a time slot, and the corresponding quality constraint is a maximum permissible delay.
3. A method according to claim 1 , wherein a quality parameter is a latency computed based on data received in a time slot, and the corresponding quality constraint is a maximum permissible delay.
4. A method according to any one of the preceding claims, wherein the payload data correspond to an encoded image, said data defining pixels of said image.
4. A method according to any one of the preceding claims, wherein the payload data correspond to an encoded image, said data defining pixels of said image.
5. A method according to any one of the preceding claims, further comprising updating the set of time slots by extending the set of time slots if an extension request has been received.
6. A method according to claim 5, wherein the set of time slots is extended by one time slot if an extension request has been received.
7. A method according to any of the preceding claims, further comprising setting the communication system to the second TDMA mode as soon as the entire determined set of time slots has been received.
8. A method for exchanging data according to claim 1 , wherein the method further comprises at the source node : - transmitting a payload data transfer request, said request comprising the payload data size; - receiving information from the destination node on time slots forming a set of time slots allocated for the transmission of the payload data; - upon detection of invalid data payload, sending an extension slot request and updating the set of time slots; - transmitting the payload data in packets in said set of time slots.
9. A method for exchanging data between a destination node and a source node in a communication system, the communication system using a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of the control data only, wherein the method comprises at the source node : - transmitting a payload data transfer request, said request comprising the payload data size; - receiving information from the destination node on time slots forming a set of time slots allocated for the transmission of the payload data; - upon detection of invalid payload data, requesting an extension slot and updating the set of time slots; - transmitting the payload data in packets in said set of time slots.
10. A method according to claim 8 or claim 9, wherein invalid payload data is detected when a packet of payload data to be transmitted is unavailable at the time a time slot of the set of time slots should be filled with said packet.
11. A method according to any one of claims 8 to 10, wherein updating the set of time slots consists in extending the set of time slots if an acknowledgement of the extension request has been received from the destination node.
12. A method according to claim 11 , wherein the set of time slots is extended by one time slot if an acknowledgement of the extension request has been received from the destination node.
13. A method according to any one of the claims 8 to 12 wherein the payload data correspond to an encoded image, said data defining pixels of said image.
14. A communication system comprising a destination node and a source node, the communication system being configured to implement a TDMA protocol comprising a first TDMA mode for the transmission of payload data and a second TDMA mode for the transmission of control data only, wherein the destination node comprises : - means configured to receive a payload data transfer request comprising information on the size of the payload data; - means configured to determine and allocate a minimum set of time slots for receiving the payload data, based on the received information on the size of the payload data; - means configured to set the transmission protocol to the first TDMA mode; - means configured to compute a transmission quality metric comprising at least one quality parameter, and compare the at least one parameter to a corresponding predefined quality constraint; and - means configured to set the communication system to the second TDMA mode as soon as the comparison of the at least one quality parameter to the predefined quality constraint indicates that said quality constraint is not met.
15. A communication system according to claim 14 wherein the means configured to compute a transmission quality metric comprises means to determine latency.
16. A communication system according to claim 14 or claim 15, wherein the means configured to compute a transmission quality metric comprises means to compute a pixel error rate of an image.
17. A communication system according to any one of the claims 14 to 16, wherein the source node comprises : - means configured to transmit and receive data blocks exchanged over a wireless medium; - means configured to send a payload data transfer request including information on the size of the payload data ; - means configured to receive information on allocated time slots forming a set of time slots for the transmission of the payload data; 18. A method for exchanging data between a destination node and a source node in a communication system, said method comprising at the destination node a method as hereinbefore described with reference to, and as shown in Figure 5. 19. The method of claim 18, further comprising at the source node a method as hereinbefore described with reference to, and as shown in Figure 4. - means configured to send a dedicated packet or flag with the payload data to request an extension of the set of time slots.
18. A method for exchanging data between a destination node and a source node in a communication system, said method comprising at the destination node a method as hereinbefore described with reference to, and as shown in Figure 5.
19. The method of claim 18, further comprising at the source node a method as hereinbefore described with reference to, and as shown in Figure 4.
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