GB2540185A - Method and system for wireless communications - Google Patents

Abstract

A method for wireless communications between a master transceiver device and a slave transceiver device, the master transceiver device and/or the slave transceiver device comprising a group of radio modules connected between them in a daisy chain manner. The method comprises configuring (504 fig.6) a data path for data communication between the master transceiver device and the slave transceiver device and determining (505 fig.6), at the master transceiver device, transmission processing latency. At the slave transceiver device, the transmission processing latency determined at the master transceiver device is obtained 712 and latency between the master transceiver device and the slave transceiver device through the configured data path is determined 713, taking into account the obtained transmission processing latency. A synchronization parameter is adjusted 714 according to the determined latency and the adjusted synchronization parameter is used when the slave transceiver device communicates with the master transceiver device.

Description

The present invention relates to a method and a system for wireless communications between a master transceiver device and a slave transceiver device, the master transceiver device and/or the slave transceiver device comprising a group of radio modules connected between them in a daisy chain manner.

The invention has a particular application in wireless communication of high definition (HD) video or images, both requiring a low Bit Error Rate (BER) and a low latency. Typically, radio bands of 2.4GHz, 5GHz or 60GHz are used for these wireless communications.

In wireless communications, sharing and accessing the transmission medium may be implemented according to several methods.

Methods based on allocating time slots such as Time Division Multiple Access (TDMA) method are well adapted for wireless communications requiring low latency since transmission medium resources are reserved and communications are not disturbed by collisions of data packets.

When TDMA is used in wireless communications between a transmitter device and a receiver device, the transmitter device is provided with a time slot which is defined by a start time and a predefined duration. A device may transmit data during the time slot it owns. A super frame is a time slots allocation scheme which is generated by a master device in the wireless network. The super frame is used in the wireless network for synchronizing all the devices in the wireless network. For that, the master device transmits the super frame to the slave devices in the wireless network.

The start time of the time slot owned by a device is determined with reference to a start event of a super frame. The super frame start event is the emission of a beacon. Thus, the time at which a beacon is emitted represents a synchronization parameter.

All the devices in the wireless network compute the beginning of a new super frame and the beginning of time slots with reference to the beacon.

As represented by Figure 1, when the master transceiver device transmits a generated super frame for the slave transceiver devices, the beacon arrival time seen by a slave device is delayed compared to the beacon transmission time seen by the master device.

Figure 1 represents a first timeline 200 illustrating events as seen by a master device and a second timeline 220 illustrates some events as seen by a slave device.

On the first timeline 200 a time slots allocation scheme or super frame 212 is represented. Start events 210, 211 represent respectively the beginning of two consecutive super frames 212, 214.

At the beginning of a super frame 212, 214, the master device emits a beacon 201, 207. The beacon 201, 207 emitted by the master device is used by all the other devices in the network as synchronization parameter, for example, to determine the beginning of super frames. After the beacon 201, 207, a plurality of time slots 202 to 206 are allocated respectively for a plurality of devices. Time slots duration may differ from one time slot to another.

Two consecutive time slots (e.g. 204, 205) are separated by an interframe gap 216 in order to ensure that no collision occurs on the transmission medium.

It may be noted that a beacon may for instance contain information such as time slots durations and identification of the time slot owner for each allocated time slot in the super frame.

According to an example, a device owning the time slot 203 waits for a predefined duration 213 after the beacon 201 to start transmitting its data.

In the second timeline 220, the events are shifted in time by a delay 215 compared to the first timeline 200.

This delay 215 corresponds to latency due to a communication between the master device and the slave device. In particular, the latency corresponds to the transmission processing latency at the master device, the crossing of the transmission medium, and the reception processing latency at the slave device. In more detail, the transmission processing latency corresponds to the time elapsed between the time at which a beacon transmission has been requested from a master device and the actual emission of the beacon over the medium, and the reception processing latency at the slave device corresponds to time needed to stamp beacon data 221 and to present it to the Medium Access Control (MAC) layer of the slave device.

In the second timeline 220, the event 230 defines a super frame start time. The beginning of the time slot 223 is defined with reference to the event 230, i.e. after a period of time 213 elapses from the event 230.

If the latency is great, the slave device allocated the time slot 223 overlaps with the next time slot (time slot corresponding to 204) and leads to data collision and data loss.

In systems for wireless communications in which the master device and/or the slave device comprises a group of radio modules connected in a daisy chain manner, the transmission or reception processing latency within the device comprising the group of radio modules may be great and may vary depending on the number of radio modules of the group. A solution to avoid data collision may be to increase the inter-frame gaps 216. However, reducing the inter-frame gaps 216 leads to increasing medium access overhead, and thus to reducing available bandwidth.

In document US2003/0153275, the latency due to the medium is determined based on the distance between a base station and a mobile device, the determined latency being balanced in order to ensure the integrity of communication slots.

However, when the master device and/or the slave device comprises a group of radio modules, the transmission or reception processing latency (i.e. the latency between the physical layer and the Medium Access Control layer or vice versa) may vary and thus the synchronization between a master device and a slave device is difficult to obtain without increasing guard times which is not suitable for communicating high quality and high resolution low latency video data.

The present invention is directed to providing a method for wireless communication between a master transceiver device and a slave transceiver device, the master transceiver device and/or the slave transceiver device comprising a group of radio modules which are connected between them in a daisy chain manner, providing correct synchronization of the master device and the slave device, without increasing the latencies in communications implemented between them.

To that end, according to a first aspect, the present invention concerns a method for wireless communications between a master transceiver device and a slave transceiver device, the master transceiver device and/or the slave transceiver device comprising a group of radio modules connected between them in a daisy chain manner.

The method comprises: at the master transceiver device and at the slave transceiver device: - configuring a data path for data communication between the master transceiver device and the slave transceiver device; at the master transceiver device: - determining a transmission processing latency; and at the slave transceiver device: - obtaining a transmission processing latency at the master transceiver device; - determining a latency between the master transceiver device and the slave transceiver device through the configured data path taking into account the obtained transmission processing latency, - adjusting a synchronization parameter according to the determined latency, - using the adjusted synchronization parameter when the slave transceiver device communicates with the master transceiver device.

Thus, latency between the master transceiver device and the slave transceiver device is taken into account when synchronizing the slave transceiver device with the master transceiver device.

The synchronization parameter is adapted continuously to each particular data path used when implementing a communication between the master transceiver device and the slave transceiver device.

As a consequence of the correct synchronization, data collision is avoided.

In addition, guard periods between two consecutive time slots or inter-frame gaps are not incremented unnecessarily.

According to a feature, the transmission processing latency is transmitted to the slave transceiver device.

According to an embodiment, determining the transmission processing latency comprises determining a first partial transmission processing latency corresponding to the baseband latency.

In this embodiment, the master transceiver device determines the PHY latency corresponding to the period of time elapsed between the time at which a signal is going to be transmitted and the actual emission of the signal.

According to another embodiment, determining the transmission processing latency further comprises: - determining a second partial transmission processing latency corresponding to the latency between a baseband module of a radio module and a MAC module of the master transceiver device, and - adding the determined first partial transmission processing latency and the second partial transmission processing latency in order to obtain the transmission processing latency.

In this embodiment, the master transceiver device comprises a plurality of baseband modules or a plurality of radio modules.

The determined latency corresponds to the MAC to PHY latency at the master transceiver device.

According to an embodiment, determining the second partial transmission processing latency comprises: - emitting from the MAC module a control message to a baseband module in a radio module; - the baseband module in the radio module returning back the control message to the MAC module; and - the MAC module determining the travel time, corresponding to the time which has elapsed between the emission of the control message and its reception, the transmission processing latency being half the determined travel time.

According to another embodiment, the second partial transmission processing latency is determined based on the number of radio modules of the data path and a predefined value representing the latency on passing through a radio module.

According to a feature, determining the latency between the master transceiver device and the slave transceiver device further comprises at the slave transceiver device: - determining a reception processing latency; and - adding the determined reception processing latency and the obtained transmission processing latency.

Thus, the determined latency corresponds to the latency between the MAC module of the master transceiver device and the MAC module of the slave transceiver device.

According to an embodiment, determining the reception processing latency comprises, at the slave transceiver device, determining a first partial reception latency corresponding to the reception baseband latency.

According to another embodiment, determining the reception processing latency further comprises: - determining a second partial reception processing latency corresponding to a latency between a baseband module of a radio module and a MAC module of the slave transceiver device, and - adding the determined first partial reception processing latency and the second partial reception processing latency in order to obtain the reception processing latency.

In this embodiment, the slave transceiver device comprises a plurality of baseband modules or a plurality or radio modules.

The reception processing latency corresponds to the PHY to MAC latency.

According to an embodiment, determining the second partial reception processing latency comprises: emitting from a MAC module a control message to a baseband module; the baseband module returning back the control message to the MAC module; and the MAC module determining the travel time, corresponding to the time which has been elapsed between the emission of the control message and its reception, the reception processing latency being half the determined travel time.

According to another embodiment, the second partial reception latency is determined based on the number of radio modules of the data path and a predefined value representing the latency on passing through a radio module.

According to a feature, adjusting a synchronization parameter comprises at the slave transceiver device: - receiving a message from the master transceiver device comprising a synchronization parameter, - time stamping the received synchronization parameter, and - subtracting the determined latency between the master transceiver device and the slave transceiver device from the stamped synchronization parameter.

Thus, the emission time (corresponding to 210 in Figure 1) of the message is obtained at the slave transceiver device.

According to an embodiment, configuring a data path comprises: - determining a value representing the reception quality of a signal received at each radio module in the group of radio modules; - selecting a radio module from the radio modules of the group on the basis of the determined value representing the reception quality, and - configuring the data path, the data path starting from the selected radio module and passing through a plurality of radio modules in the group for data communication between the master device and the slave device.

Thus, the data path is configured starting from the radio module presenting the best wireless communication quality between the master device and the slave device.

Selecting the wireless module presenting the best wireless transmission quality with the mobile device makes possible to improve the BER (bit error rate).

According to an embodiment, the value representing the reception quality is based on the Received Signal Strength Indication (RSSI).

According to another embodiment, the value representing the reception quality is based on the Signal-to-Noise Ratio (SNR).

According to an embodiment, configuring the data path comprises transmitting a control message to each radio module included in the data path, the control message comprising information about the configuration of a data stream selector module of the radio module according to the data path and to information obtained from a routing table.

According to an embodiment, the master transceiver device is a fixed device and the slave transceiver device is a mobile device.

According to another embodiment, the master transceiver device is a mobile device and the slave transceiver device is a fixed device.

In other embodiment, the master transceiver device and the slave transceiver device are both either mobile devices or fixed devices.

According to a feature, the master transceiver device comprises the group of radio modules, at least one of the radio modules being directly connected to a device controller.

According to a second aspect of the present invention, there is provided a system for wireless communications comprising a master transceiver device and a slave transceiver device, at least either the master transceiver device or the slave transceiver device comprising a group of radio modules connected between them in a daisy chain manner.

The system comprises: at the master transceiver device and at the slave transceiver device: - means for configuring a data path for data communication between the master transceiver device and the slave transceiver device; at the master transceiver device: - means for determining a transmission processing latency; and at the slave transceiver device: - means for obtaining the transmission processing latency determined at the master transceiver device; - means for determining a latency between the master transceiver device and the slave transceiver device through the configured data path taking into account the obtained transmission processing latency, - means for adjusting a synchronization parameter according to the determined latency, - means for using the adjusted synchronization parameter when the slave device communicates with the master transceiver device.

According to a feature, the system comprises means for transmitting the transmission processing latency to the slave transceiver device.

According to a feature, the means for determining the transmission processing latency comprise means for determining a first partial transmission processing latency corresponding to the transmission baseband latency.

According to a feature, the means for determining the transmission processing latency further comprise: - means for determining a second partial transmission latency corresponding to the latency between a baseband module and a MAC module, and - means for adding the determined first partial transmission processing latency and the second partial transmission processing latency in order to obtain the transmission processing latency.

According to a feature, the means for determining the second partial transmission processing latency comprise means for emitting from the MAC module a control message to a baseband module in a radio module; the baseband module in the radio module comprising means for returning back the control message to the MAC module; and the MAC module comprising means for determining the travel time, corresponding to the time which has elapsed between the emission of the control message and its reception, the transmission processing latency being half the determined travel time.

According to a feature, the means for determining the latency between the master transceiver device and the slave transceiver device further comprise at the slave transceiver device: - means for determining a reception processing latency; - means for obtaining the transmission processing latency determined at the master transceiver device; - means for adding the determined reception processing latency and the obtained transmission processing latency.

According to a feature, the means for determining the reception processing latency comprise, at the slave transceiver device, means for determining a first partial reception latency corresponding to the reception baseband latency.

According to a feature, the means for determining the reception processing latency further comprise: - means for determining a second partial reception processing latency corresponding to a latency between a baseband module and a MAC module, and - means for adding the determined first partial reception processing latency and the second partial reception processing latency in order to obtain the reception processing latency.

According to a feature, the means for determining the second partial reception processing latency comprise means for emitting from a MAC module a control message to a baseband module; the baseband module comprising means for returning back the control message to the MAC module; and the MAC module comprising means for determining the travel time, corresponding to the time which has been elapsed between the emission of the control message and its reception, the reception processing latency being half the determined travel time.

According to a feature, the means for adjusting a synchronization parameter comprise at the slave transceiver device: - means for receiving a message from the master transceiver device comprising a synchronization parameter, - means for time stamping the received synchronization parameter, and - means for subtracting the determined latency between the master transceiver device and the slave transceiver device from the stamped synchronization parameter.

According to a feature, the means for configuring a data path comprise: - means for determining a value representing the reception quality of a signal received at each radio module in the group of radio modules; - means for selecting a radio module from the radio modules of the group on the basis of the determined value representing the reception quality, and - means for configuring the data path, the data path starting from the selected radio module and passing through a plurality of radio modules in the group for data communication between the master device and the slave device.

According to a feature, the means for configuring the data path comprises means for transmitting a control message to each radio module included in the data path, the control message comprising information about the configuration of a data stream selector module of the radio module according to the data path and to information obtained from a routing table.

According to a feature, the master transceiver device is a fixed device and the slave transceiver device is a mobile device.

According to a third aspect of the present invention, there is provided a means for storing information which can be read by a computer or a microprocessor holding instructions of a computer program, for implementing a method for wireless communications according to the invention, when said information is read by said computer or said microprocessor.

The means for storing may be partially or totally removable.

According to a fourth aspect of the present invention, there is provided a computer program product which can be loaded into a programmable apparatus, comprising a sequence of instructions for implementing a method for wireless communications according to the invention when said computer program product is loaded into and executed by said programmable apparatus.

The advantages and particular features of the system for wireless communications, of the means for storing information and the computer program product are similar to those of the method for wireless communications.

Still other features and advantages of the invention will appear in the following description, made with reference to the accompanying drawings which are given by way of non-limiting example, and in which: - Figure 1 represents timelines illustrating events as seen by a master device and by a slave device; - Figure 2 represents a wireless communication system according to a first embodiment; - Figure 3 represents a functional block diagram of a mobile station in the wireless communication system according to an embodiment; - Figure 4 represents a functional block diagram of a radio module in the wireless communication system according to an embodiment; - Figure 5 represents a functional block diagram of a station controller in the wireless communication system according to an embodiment; - Figure 6 represents flowcharts illustrating a part of the method in accordance with an embodiment of the invention which is implemented by a master transceiver device and a slave transceiver device; - Figures 7a and 7b represent flowcharts illustrating a part of the method in accordance with an embodiment of the invention invention which is implemented by a master transceiver device and a slave transceiver device; - Figures 8a and 8b represents flowcharts illustrating an alternative to the part of the method illustrated by Figure 6; - Figures 9a and 9b represent flowcharts illustrating an alternative to the part of the method illustrated by Figures 7a and 7b; - Figure 10 represents an embodiment of a beacon message used by the method and the system according to the invention; and - Figures 11,12 and 13 represent a wireless communication system according respectively to a second, a third and a forth embodiment.

Figure 2 illustrates schematically a first embodiment of a wireless communication system 10. Such a wireless communication system 10 is called wireless multi-communication system or wireless multi-reception/transmission system. A wireless communication system 10 according to the invention may be installed for example in an outdoor environment such as the neighborhood of a city, or in an indoor environment such as an industrial building.

The wireless communication system 10 comprises a first radio device 1 which communicates with a second radio device 2. The first radio device 1 and the second radio device 2 are also called respectively mobile device 1 and fixed device 2.

According to the embodiment represented by Figure 1, the first radio device 1 is a mobile device which comprises a radio module or a radio transceiver node 12 which is called “mobile station”.

The second radio device 2 is a fixed device and comprises a group of radio modules or radio transceiver nodes 13-18 connected between them in a daisy chain manner, and a device controller 19. The radio modules 13-18 are called fixed stations 13-18.

It may be noted that in other embodiments (not represented in the figures), the first radio device is a mobile device and the second radio device is a fixed device; both the first radio device and the second radio device are fixed devices; or both the first radio device and the second radio device are mobile devices.

In this embodiment, a radio module or radio transceiver node 16 (here the radio transceiver node referenced 16), which is called “primary fixed station”, is connected to the device controller 19. The device controller 19 is called “station controller” 19.

The primary fixed station 16 is connected to the station controller 19 through a point to point link 60.

The remaining radio modules 13-15, 17, 18 of the group of radio modules 13-18 are called “secondary fixed stations”.

The station controller 19 implements network Medium Access Control (MAC) layer services, while the fixed stations 13-18 implements baseband and physical layer services.

The mobile station 12 may be connected to a video capture and/or display device 11 through a wired interface 40.

According to an example, the video capture and/or display device 11 may be an augmented reality video headset comprising for instance two HD video camcorders, and two HD display areas, a digital camera, a digital camcorder, a video surveillance camera or other device.

The wired interface 40 can be a single or double HDMI cable, a Camera Link cable, an Ethernet cable or other wired interface.

The mobile station 12 comprises at least one antenna 12a. The mobile station 12 processes the HD video or image data streams from the video capture and/or display device 11 and sends the processed data wirelessly through its antenna 12a. The mobile station 12 may also receive video or image data wirelessly through its antenna 12a. In this case, the mobile station 12 processes the data, and send it to video capture and/or display device 11.

The mobile station 12 can send and receive the data to and from several different stationary positions or while in motion.

Each of the fixed stations 13-18 comprises at least one antenna 13a- 18a.

The data stream sent by the mobile station 12 is received by at least one of the fixed stations 13-18 through its at least one antenna 13a - 18a.

The wireless communication system 10 illustrated in Figure 2 is dimensioned to cover the displacement of the mobile station 12, i.e. to allow good radio communication wherever the mobile station 12 is within a predefined area.

In the described embodiment, the second radio device or fixed device 2 comprises six fixed stations 13-18.

The fixed stations 13 - 18 are located in different positions to create spatial diversity. Thus, for a given position of the mobile station 12, there is a low probability that all fixed stations 13-18 are able to receive correctly the data sent by the mobile station 12.

Figure 2 represents an example where some obstacles 22a, 22b are situated between the mobile device 1 and the fixed device 2. The obstacles 22a and 22b can be metallic objects, human beings, furniture, buildings, street furniture or else.

In this example, for a given position of the mobile device 1 or the mobile station 12, some fixed stations 13-18 may be unable to receive correctly the data sent by the mobile station 12 due, for example to obstacles 22a, 22b or due to a too great distance between the mobile station 12 and the fixed stations 13-18.

In the example of the Figure 2, considering the position of the mobile station 12 and the positions of the obstacles 22a, 22b, only fixed stations referenced 15, 16 and 17 are able to receive correctly the data sent by the mobile station 12. Indeed, the obstacles 22a and 22b are masking respectively the fixed stations referenced 14 and 18 and the fixed station referenced 13 is out of range.

Flowever, the invention is not limited to this number or fixed stations 13 - 18. Thus, the wireless communication system 10 may include more or fewer fixed stations, depending on the communication area to be covered by the system.

It may be noted that the use of a group of radio modules on the fixed device side, allows greater coverage area of the wireless communication system. In addition, path shadowing is limited.

Among these fixed stations 13 - 18, the primary fixed station 16 is linked directly to the station controller 19, the secondary fixed stations being not directly linked to the station controller 19.

However, this configuration is not limitative. For example, any one of the fixed stations 13-18 might be the one connected to the station controller 19 (i.e. the primary fixed station).

As stated above, the fixed stations 13-18 are connected in a daisy chain manner. Thus, a fixed station 13 -18 is connected with two other fixed stations 13-18 through respectively two bidirectional point to point connections 50a-50f. Thus the fixed stations 13-18 are connected between them in series, for example in a ring. These connections 50a-50f may be implemented either through wired connections or wireless connections.

If using wired connections, fiber optic or copper cables could be used. If using wireless connections, microwave frequency band (6-38GHz) or mm wave frequency band (60GHz) could be used.

The connections 50a- 50f support the transmission of at least the amount of data exchanged between the mobile device 12 and the station controller 19, both directions being supported (i.e. the connections are full duplex connections).

For example, the setup of primary and secondary fixed stations is defined during system installation based on known physical considerations such as distance between mobile station and each fixed station, such as spatial diversity, such as the knowledge of the trajectory of the mobile station 12, etc.

According to an embodiment, a metric or value representing the reception quality of data emitted from the mobile device 12 at each fixed station 13-18 is stored in a dedicated register of memory of each fixed station 13-18.

The metric representing the reception quality of data may be of RSSI or SNR type, but is not limited to these examples. Any metric enabling determination of which fixed station is the best to handle data transmission and reception is valid.

Station controller 19 regularly reads metric values from the group of fixed stations 13- 18, and, as will be described later, based on read values, decides which fixed station 13-18 is currently the best to handle data communication between the mobile device 1 and the fixed device 2.

Next, the station controller 19 sends messages to fixed stations 13-18 to inform them about which one is selected to handle communications with the mobile station 12. The station controller 19 sends messages to the fixed stations 13 - 18 to also inform them about the selected data path to carry data between the selected fixed stations (here the fixed station referenced 15) and the station controller 19.

Fixed stations 13-18 then configure themselves in accordance with the messages received from the station controller 19 in order to be ready to process the received/transmitted data stream.

In the illustrated example, fixed station 15 presents the best metric value and is selected to handle communications between the mobile station 12 and the station controller 19. Fixed station 15 receives data from the mobile device 12. Next, data is processed and transmitted to the primary fixed station 16 through link 50c and fixed station 16 transmits data to station controller 19 through link 60.

As for the connections 50a-50f, the link 60 between the primary fixed station 16 and the station controller 19 may be implemented either through a wired connection or a wireless connection.

If fixed station 13 is selected to handle communications, data transmitted from station controller 19 to mobile device 12 will be carried through links 60, 50c, 50b and 50a to reach the selected fixed station 13 and to finally be transmitted to mobile device 12.

The mobile station 12 and the selected secondary fixed station 15 communicate through a bidirectional radio communication 30.

The bidirectional radio communication 30 is typically used for wireless transmission of HD video or image data stream.

The station controller 19 may be connected to a video processing device 20 either through a wired link 70 or a wireless link, for example if an augmented reality video headset is used.

The wired connection 70 can be a set of HDMI or DisplayPort cables, a USB cable or other connection.

Thus, the station controller 19 may forward video data streams received from the mobile device 12 to the video processing unit in a video processing device 20 through the wired link 70.

The video processing unit may input video stream and output it back to the station controller 19.

When the video processing device 20 transmits video data to the station controller 19, the station controller 19 transmits processed video stream to mobile device 1 for display.

An embodiment of a mobile station 12, a fixed station 13-18 and a station controller 19 will be described respectively with reference to Figures 3, 4 and 5.

Figure 3 represents a functional block diagram of the mobile station 12 in the wireless communication system 10 according to an embodiment.

The mobile station 12 comprises an I/O interface module 126, a Media Access Control (MAC) module 125, a baseband module 124, and a RF Front-End module 123.

The mobile station 12 further comprises a micro-controller 120, a Read-Only Memory (ROM) 122 and a Random Access Memory (RAM) 121. The ROM 122 and the RAM 121 are connected to the micro-controller 120.

The micro-controller 120 is connected to the I/O interface module 126, the MAC module 125, the base band module 124 and the RF Front-End module 123 via a bi-directional address/data bus 127. In particular, the directional address/data bus 127 allows the micro-controller 120 to initialize and configure the modules 123, 124, 125 and 126 at the start-up of the wireless communication system 10.

The I/O interface module 126 is connected to the video capture and/or display device 11 (shown in Figure 2) via the wired interface 40. The wired interface 40 can be an HDMI cable, a USB cable, a Camera Link cable, an Ethernet cable form of interface.

When the mobile station 12 transmits data to the fixed device 2: - The I/O interface module 126 retrieves the HD video or image content received from video capture and/or display device 11 and formats this HD video or image data in order to be processed by the MAC module 125. - The MAC module 125 builds MAC data packets from the data provided either by the I/O interface module 126 or by the micro-controller 120 (control messages). Typically the MAC module 125 builds the MAC data packets by adding header data and by adding Error Correction Code (ECC) redundancy bits. - The Baseband module 124 performs channel encoding, modulation and digital to analog conversion functions on the data packets received from the MAC module 125. - The RF Front-End module 123 is responsible for matching a signal coming from the Baseband block 124 and which is going to be sent to the fixed device 2 by means of the antenna 12a. For example, the matching consists of frequency transposition and power amplification processes.

When the mobile station 12 receives data from the fixed device 2: - the RF Front-End 123 is responsible for matching or adapting a signal received by the antenna 12a. Once the received signal is matched, the matched received signal is sent to the Baseband block 124. - The Baseband block 124 performs analog to digital conversion, demodulation and channel decoding functions on the signal received from the RF Front-End 123, and sends the signal to the MAC module 125. - The MAC module 125 processes the received data packets to retrieve the control/command data or video data sent by the station controller 19. Next, the retrieved control/command data is stored within internal registers in the MAC module 125 to be further processed by the micro-controller 120, and the retrieved video data is forwarded to I/O interface module 126. - The I/O interface module 126 formats video data received from MAC module data and forward it to the video capture and/or display device 11.

The ROM 122 contains a software program which can be used, when executed by the micro-controller 120 (using the RAM 121), to implement the method for wireless communications according to the present invention. The method for wireless communications will be described later with reference to Figures 6, 7a, 7b, 8a, 8b, 9a and 9b. The RAM 121 is used for the execution by the micro-controller 120 of the above-mentioned software program and for the processing of the different tasks performed by the micro-controller 120.

Figure 4 represents a functional block diagram of the radio modules or fixed stations 13 - 18 in the wireless communication system 10 according to an embodiment.

As explained above, the fixed stations may be either primary fixed stations (when the fixed station is directly connected to the station controller 19) or secondary fixed stations.

It may be noted, that in the embodiment of the wireless communication system 10 illustrated in Figure 2, the fixed station referenced 16 is a primary fixed station and the rest of fixed stations (13-15, 17 and 18) are secondary fixed stations. Both types of fixed stations comprise the same functional blocks.

Figure 4 represents the fixed station referenced 13. However, the description given with reference to Figure 4 applies to all the fixed stations.

The fixed station 13 comprises a RF Front-End Module 133, a Baseband module 134, a Data Stream Selector Module 135, a first I/O interface module 136, a second I/O interface module 137 and a second I/O interface module 138.

The fixed station 13 further comprises a micro-controller 130, a Read-Only Memory (ROM) 132 and a Random Access Memory (RAM) 131. The ROM 132 and the RAM 131 are connected to the micro-controller 130.

The micro-controller 130 is connected to the I/O interface modules 136, 137, 138, the data stream selector 135, the base band module 134 and the RF Front-End module 133 via a bi-directional address/data bus 139. In particular, the directional address/data bus 139 allows the micro-controller 130 to initialize and to configure the modules 133, 134, 135, 136, 137 and 138 at the start-up of the wireless communication system 10.

The ROM 132 contains a software program which can be used, when executed by the micro-controller 130 (using the RAM 131), to implement the method for wireless communications according to the present invention. The method for wireless communications will be described later with reference to Figures 6, 7a, 7b, 8a, 8b, 9a and 9b. The RAM 131 is used for the execution by the micro-controller 130 of the above-mentioned software program and for the processing of the different tasks performed by the micro-controller 130.

The RF Front-End module 133 is connected to the antenna 13a communicating with the mobile device 12.

When the fixed device 2 receives data from the mobile station 12: - the RF Front-End 133 is responsible for matching or adapting a signal received by the antenna 13a. Once the received signal is matched, the matched received signal is transmitted to the Baseband module 134. For example, matching consists of frequency transposition and power amplification processes. - The Baseband block 134 performs analog to digital conversion, demodulation and channel decoding functions on the signal received from the RF Front-End 133. The Baseband block 134 computes also a quality metric on the received data. This quality metric is an indicator of the quality of the radio path between the mobile station 12 and the fixed station 13. This quality metric may be a Signal to Noise Ratio (SNR) measurement, a Received Signal Strength Indicator (RSSI), an Error Vector measurement (EVM) or other metric. Finally, the Baseband block 134 sends the signal to the Data Stream Selector module 135.

When the fixed device 2 transmits data to the mobile station 12: - the Baseband block 134 performs channel encoding, modulation and digital to analog conversion functions on the data packets received from the Data Stream Selector module 135. - The RF Front-End 133 is responsible for matching or adapting the signal originating from the Baseband block 134. Once the signal is matched, the matched signal is sent to the mobile station 12 by means of the antenna 13a.

The first I/O interface module 136 makes it possible to connect the fixed station 16 to the station controller 19 through the point to point link 60.

The link 60 can be either a wire or a wireless link able to support a data rate up to several Gbps.

The first I/O interface module 136 is responsible for matching the data to be transmitted/received over the link 60. For example, the matching consists of channel encoding/decoding, modulation/demodulation, digital to analog conversion/analog to digital conversion, frequency transposition and/or power amplification processes.

The second I/O interface module 137 and the third I/O interface module 138 allows connection of the fixed station 13 in daisy chain manner respectively to the fixed station 14 through the link 50a and to the fixed station 18 through the link 50f.

The second I/O interface module 137 and the third I/O interface module 138 are similar.

The links 50a and 50f can be either wire or wireless links and are able to support data rates up to several Gbps.

The second I/O interface module 137 and the third I/O interface module 138 are responsible for matching the data to be transmitted/received over the links 50a and 50f. For example, the matching consists respectively of channel encoding/decoding, modulation/demodulation, digital to analog conversion/ analog to digital conversion, frequency transposition and/or power amplification processes.

If the fixed station 13 is a secondary fixed station, the Data Stream Selector module 135 makes it possible to select and route a selected data stream to the primary fixed station through the daisy chain connection 50x (x being a, b, c, d, e or f) with respect of a routing table.

According to an embodiment the routing table is computed and communicated to the fixed stations 13-18 by the Station Controller 19. According to another embodiment, the routing table is defined and configured in the station controller 19 by an operator at the setup of the wireless communication system 10.

Thus, the Data Stream Selector module 135 allows the following four selection and routing configurations: a. the data stream output by the Baseband block 134 is selected and routed to the secondary fixed station 18 through the third I/O interface module 138 and the daisy chain connection 50f. b. The data stream output by the Baseband block 134 is selected and routed to the secondary fixed station 14 through the second I/O interface module 137 and the daisy chain connection 50a. c. The data stream output by the secondary fixed station 18 is selected and routed to the secondary fixed station 14 respectively through the daisy chain connection 50f and the third I/O interface module 138 and the second I/O interface module 137 and the daisy chain connection 50a. d. the data stream output by the secondary fixed station 14 is selected and routed to the secondary fixed station 18 respectively through the daisy chain connection 50a and the second I/O interface module 137 and the third I/O interface module 138 and the daisy chain connection 50f.

If the fixed station 13 is a primary fixed station, the Data Stream Selector module 135 makes it possible to select and route a data stream to the station controller 19 through the point to point link 60, or to a secondary fixed station through the daisy chain connection 50x (x being a, b, c, d, e or f) with respect of a routing table.

According to an embodiment, the routing table is computed and communicated by the Station Controller 19.

According to another embodiment, the routing table is defined and configured in the station controller 19 by an operator at the setup of the wireless communication system 10.

Thus, in the case of the primary fixed station 16 the Data Stream Selector module 135 allows the following five selection and routing configurations: a. the data stream output by the Baseband module 134 is selected and routed to the station controller 19 through the first I/O interface module 136 and the point to point link 60. b. The data stream output by the secondary fixed station 15 is selected and routed to the station controller 19 respectively through the daisy chain connection 50c and the third I/O interface module 138 and the first I/O interface module 136 and the point to point connection 60. c. The data stream output by the secondary fixed station 17 is selected and routed to the station controller 19 respectively through the daisy chain connection 50d and the second I/O interface module 137 and the first I/O interface module 136 and the point to point connection 60. d. The data stream output by the Baseband module 134 is selected and routed to the secondary fixed station 17 through the second I/O interface module 137 and the daisy chain connection 50d; simultaneously, the data stream output by the secondary fixed station 15 is selected and routed towards the station controller 19 respectively through the daisy chain connection 50c and the third I/O interface module 138 and the first I/O interface module 136 and the point to point connection 60. e. The data stream output by the Baseband module 134 is selected and routed to the secondary fixed station 15 through the third I/O interface module 138 and the daisy chain connection 50c; simultaneously, the data stream output by the secondary fixed station 17 is selected and routed to the station controller 19 respectively through the daisy chain connection 50d and the second I/O interface module 137 and the first I/O interface module 136 and the point to point connection 60.

Those two last routing configurations (d, e) might be used for instance in relation with embodiment represented within Figure 11.

If the fixed station 13 is a primary fixed station, the Data Stream Selector module 135 also enables storage of the quality metric computed in the Baseband module 134 and the quality metrics computed in the associated secondary fixed stations connected through the daisy chain connection 50x (x being a, b, c, d, e orf).

Figure 5 represents a functional block diagram of the Station Controller 19 according to an embodiment.

The station controller 19 comprises a first I/O interface module 193, a Media Access Control module 195 and a second I/O interface module 196.

The first I/O interface module 193 is similar to the first I/O interface module 136 of the fixed station 13-18 described previously with reference to the Figure 4. The first I/O interface module 193 makes it possible to connect the station controller 19 to the primary fixed station 16 through the point to point link 60.

The station controller 19 is connected, by the second I/O interface module 196, to the video processing sink device 20 through a wired interface 70. A Data Streams Controller module 195a is embedded within the MAC module 195. The Data Streams Controller 195a gathers and processes quality metrics of all fixed stations to identify the fixed stations having the best reception/transmission quality with the mobile station 12. Then the Data Streams Controller 195a computes a corresponding routing table making it possible to configure the Data Stream Selector 135 of each fixed station 13-18 in order to route the data streams between a selected fixed station 13-18 and the Station Controller 19.

The station controller 19 further comprises a micro-controller 190, a Read- Only Memory (ROM) 192 and a Random Access Memory (RAM) 191. The ROM 192 and the RAM 191 are connected to the micro-controller 190.

The micro-controller 190 is connected to the first I/O interface module 193, the MAC module 195, and the second I/O interface module 196 via a bidirectional address/data bus 194. In particular, the directional address/data bus 194 allows the micro-controller 190 to initialize and configure the modules 193, 194 and 196 at the start-up of the wireless communication system 10.

The ROM 192 contains a software program which can be used, when executed by the micro-controller 190 (using the RAM 191), to implement the method for wireless communications according to the present invention. The method for wireless communications will be described later with reference to Figures 6, 7a, 7b, 8a, 8b, 9a and 9b.

The RAM 191 is used for the execution by the micro-controller 190 of the above-mentioned software program and for the processing of the different tasks performed by the micro-controller 190.

When the fixed device 2 receives data from the mobile station 12, the station controller 19 receives data stream sent by the mobile station 12 through the fixed stations selected via the current routing table loaded in each fixed station 13-18.

The data stream is transmitted by the primary fixed station 16 and received by the station controller 19 through its first I/O interface module 193. Next, the first I/O interface module 193 processes the received data and sends it to the MAC module 195.

The MAC module 195 processes the data stream provided by the first I/O interface module 193 in order to retrieve the control/command data or the HD video or image data sent by the mobile station 12. For example, the processing consists of removing the MAC header and removing the CRC redundancy bits.

Next, the received control/command data are stored within internal registers of the MAC module 195 to be further processed by the Data Streams Controller 195a and/or the micro-controller 190.

The received HD video or image data stream is provided to the second I/O interface module 196.

The second I/O interface module 196 receives the HD video or image data stream from the MAC module 195. Next, it matches the video or image data stream to be sent to the video processing sink device 20 through the wired interface 70.

When the fixed device 2 transmits data to the mobile station 12, the video processing sink device 20 sends video or image data stream to the second I/O interface module 196 through the wired interface 70. The second I/O interface module 196 matches the video or image data stream and provides it to the MAC module 195.

Next, the MAC module 195 sends control/command data either to the mobile station 12 or to the fixed stations 13-18.

According to an example, the MAC module 195 sends a request to the primary fixed station 16 to retrieve the quality metric of all fixed stations 13-18. Video data stream received by the second I/O interface module 196 is processed by MAC module 195, and provided to the first I/O interface module 193, to be further deliver to mobile device 12. The MAC module 195 apply any MAC layer related processing (including for instance, MAC header insertion, CRC computation and validation, data reordering protocol if needed, or network synchronization processing).

The mobile station 12 and the fixed device 2, in particular the station controller 19, may both have a system synchronization role of either a master or a slave in the wireless communication system 10. Only one device may be a master device, the rest of the devices in the wireless communication system 10 being slave devices.

The method for wireless communication according to the invention will be described here below with reference to Figure 6, Figure 7a and Figure 7b.

Figure 6 represents a part of the method for wireless communication which is implemented within the master device and the slave device as long as they include several radio modules or fixed stations 13-18.

Thus, in the embodiment of wireless communication system 10 represented by Figure 2, the part of the method according to the invention represented by Figure 6 is implemented in the fixed device 2.

In devices comprising only one baseband antenna, such as the mobile station 12 in the present embodiment, the part of the method represented by Figure 6 is partially implemented.

The method for wireless communications will be described for an embodiment wherein the master device or master transceiver device is the fixed device 2, in particular the station controller 19, and the slave device is the mobile station 12.

At the master device and the slave device, the method for wireless communication comprises configuring 504 a data path for data communication between the master transceiver device and the slave transceiver device.

Once the data path has been configured, the processing latencies at both the master transceiver device and the slave transceiver device are determined (505) based on the configured data path.

The processing latency at the master device is called “transmission processing latency” and the processing latency at the slave device is called “reception processing latency”.

It may be noted that in the described method, the master device transmits a beacon message to the slave device for synchronization of both devices.

The transmission processing latency comprises a first partial transmission processing latency and a second partial transmission processing latency.

The reception processing latency comprises a first partial reception processing latency and a second partial reception processing latency.

The first partial transmission latency and the first partial reception latency correspond respectively to the transmission baseband latency and to the reception baseband latency.

At the master device and the slave device, after the initialization 500 of the wireless communication system 10, the first partial transmission processing latency and the first partial reception processing latency are respectively determined 501. For that, the MAC module 125, 195 requests baseband latency calibration value for all baseband modules included in the device, i.e. one baseband module 124 in the mobile station 12 and one baseband module 134 in each fixed station 13-18.

For calibrating, the baseband module 124, 134 starts a timer and sends a message to a remote wireless device (the mobile station 12 or a fixed station 13-18). When the remote wireless device receives the message, its baseband module 124, 134 sent the message back to its emitter.

When the baseband module 124, 134 receives the message, it stops the timer. The value stored in the timer corresponds approximately to the sum of the baseband latency at the mobile station 12 and at the fixed station 13-18.

It may be noted that since in the context of present invention, distances between the mobile station 12 and the fixed stations 13-18 are short, time to travel in the air is meaningless, and thus, the baseband latency is determined as being half the timer value.

According to another embodiment, the baseband latency value is known from factory.

In the embodiment represented in Figure 2 wherein the mobile station 12 comprises only a baseband module 124, the transmission processing latency or reception processing latency comprises respectively only the first partial transmission processing latency or the first partial reception processing latency. Thus, only the step 501 of the flowchart illustrated by Figure 6 is implemented in the mobile station 12.

The following steps represented by the flowchart illustrated by Figure 6 are only implemented by the fixed device 1.

At step 502, a configuration timer is verified in order to check if the value of the configuration timer is a predetermined value. The configuration timer is initialized and started at system initialization. When the configuration timer has reached the predetermined value, the configuration timer is reset at an initialization value.

This step 502 allows to regularly check if the current data path is still the good one, even if no event (such as a poor reception quality metric (RSSI) detection 508) has been detected.

In addition, this step 502 allows to continuously update the data path.

Once the configuration timer has reached the predetermined value, or if a poor reception quality metric 508 is detected by the system ,the MAC module 195 requests the metric representing the reception quality of received data (for example RSSI or SNR) of the baseband module 134 of each fixed station 13-18. As indicated above the value or metric representing the reception quality of received data is determined by the baseband modules 134 when receiving a signal originating from the mobile station 12.

Once the values representing the reception quality determined by the baseband modules 134 have been received at the MAC module 195, the MAC module 195 selects the radio module or fixed station 13-18 from the group of radio modules or fixed stations 13-18 on the basis of the determined values representing the reception quality.

Thus, the MAC module 195 selects the fixed station 13-18 presenting the best value or metric representing the reception quality for the communications, in the embodiment described, for the communications with the mobile station 12.

Next, a data path between the MAC module 195 and the select fixed station 13-18 is determined and configured 504.

Configuring 504 the data path comprises sending a control message to each fixed station 13-18 on the data path, the control messages comprising information about the configuration of the data stream selector modules 135 of the fixed stations 13-18 according to the selected data path and to information obtained from a routing table.

It may be noted that in the described embodiment, this configuration will not be applied at this step 504 but preferably at step 507 (which will be described below), in order to avoid disturbing on-going data transfer.

The different configurations of the data stream selector modules 135 have been described with reference to Figure 4.

According to an embodiment, data path may be determined and preconfigured at system installation and setup.

According to another embodiment, data paths may be determined and configured dynamically, based on the daisy chain topology previously detected.

Once the data path has been configured, the second partial transmission or reception processing latency is determined 505, based on the determined data path properties and characteristics.

According to an embodiment, determining 505 the second partial transmission latency comprises the MAC module 195 starting a timer and emitting a control message to the baseband module 134 of the fixed station 13-18 which has been selected for communications.

Next, the selected baseband module 134 returns back the control message to the MAC module 195 and the MAC module 195 stops the timer at reception of the returned control message and determines the travel time which corresponds to the time elapsed between the emission of the control message and its reception (value of the timer).

The transmission processing latency is half the determined travel time.

According to another embodiment which will be described with reference to Figure 8a, the second partial transmission or reception processing latency is determined based on the number of daisy chains elements or radio modules of the data path and a predefined value representing the latency of a daisy chain element or radio module.

For instance, knowing the number of daisy chain elements included in the data path, and knowing, by measurement or by factory predetermination, the latency of a daisy chain element, the latency corresponding to the data path may be determined.

It may be noted that any other method known by the man of the art is suitable for determining the second partial transmission or reception processing latency.

Once the second partial transmission or reception processing latency (latency from the MAC module 195 to the selected fixed station (15 in Figure 2)) has been determined, the determined first partial transmission or reception processing latency and the second partial transmission or reception processing latency are added in order to obtain the transmission or reception processing latency.

The determined transmission or reception processing latency corresponds to the local MAC to PHY latency.

Next, the wireless communication system 10 waits 506 for the end of the current super frame.

Next, at step 507, the new configured data path is applied (MAC module sends a control message to all fixed station 13-18, requesting them to apply new configured data path in selectors 135).

Next, step 502 is reached again to wait for the configuration timer to reaches predetermined value.

Once the configuration timer has reached the predetermined value or if a poor reception quality metric 508 is detected, steps 503 to 507 are implemented again.

Figure 7a represents a part of a method for wireless communication implemented in the master device which in the described embodiment, is the fixed device 2, in particular the station controller 19,

Figure 7b represents a part of a method for wireless communication implemented in the slave device which in the described embodiment, is the mobile station 12.

The parts of methods represented in Figures 7a and 7b are implemented in parallel with the part of a method represented in Figure 6.

According to the described embodiment, at step 700, the wireless communication system 10 waits for generation of a beacon message. Once a beacon message has been generated, the determined transmission processing latency (local MAC to PFIY latency) is inserted in a dedicated beacon field 1001 (see Figure 10) at step 701.

Once the beacon message has been transmitted, the wireless communication system 10 waits for the next generation of a beacon message at step 700.

An example of a beacon message or beacon packet is illustrated by

Figure 10.

The beacon message or beacon packet comprises a first field 1000 containing a packet type identifier. By virtue of this field, the type of packet being processed may be identified. This packet type identifier may represent a beacon message, an intra-device control message, an extra-device control message, a video stream message, an audio message, etc.

The beacon message or beacon packet further comprises a second field 1001 containing the determined transmission processing latency determined at the master device or local MAC to PFIY latency of the master device.

The beacon message or beacon packet further comprises a third field 1002 containing the number of daisy chain elements crossed by the beacon message since it has been emitted by the MAC module of the master device.

The beacon message or beacon packet may comprise other fields containing different values adapted to each particular implementation. For instance, the fields may contain timeslot allocation, timeslot duration, and timeslot position information.

The fields of the beacon message are adapted to the implemented embodiment. For instance, when implementing the method for wireless communications represented in Figures 6, 7a, and 7b, only the first 1000 and the second field 1001 are mandatory.

As represented by Figure 7b, the slave device waits at step 710 for the reception of a beacon message from the master device.

Once the beacon message has arrived at the slave device, the slave device timestamps it at step 711.

According to the embodiment described, the transmission processing latency or MAC to PFIY latency previously determined at the master transceiver device is obtained at step 712. The transmission processing latency is extracted from the second field 1001 in the received beacon message.

Next, the obtained transmission processing latency is added to the reception processing latency which has been determined at the slave device according to Figure 6.

In the described embodiment, the slave device is the mobile station 12, and the determination of the reception processing latency implements only step 501 as explained above.

Thus, at step 713, the latency between the master transceiver device and the slave transceiver device, in particular the latency between the MAC module 195 of the station controller 19 and the MAC module 125 of the mobile station 12 is obtained. This latency is called MAC to MAC latency and is represented by the interval of time referenced 215 in Figure 1.

Finally, at step 714 a synchronization parameter is adjusted according to the determined MAC to MAC latency 215.

The synchronization parameter is the beacon arrival time seen by the slave device.

According to the example represented by Figure 1, the beacon arrival time which has been stamped by the slave device is referenced 230.

Adjusting the synchronization parameter or beacon arrival time 230 comprises subtracting the determined MAC to MAC latency 215 from the beacon arrival time 230. Thus, the time when the beacon message is emitted by the master device is obtained. The slave device uses this adjusted synchronization parameter as timing reference, for example for determining the start time of the timeslots.

By virtue of the application of the method for wireless communication according to the invention, all the devices in the wireless communication system 10 use a common timing reference and collisions of data are avoided.

Next, the wireless communication system 10 waits for the reception of a next beacon message at step 710.

Figures 8a, 8b, 9a and 9b represent a second embodiment of a method for wireless communications according to the invention.

Figure 8a illustrates the flowchart illustrated by Figure 6 wherein step 505 is omitted.

According to this embodiment, the second partial transmission (or reception) processing latency is determined based on the number of daisy chains elements of the data path and a predefined value representing the latency of a daisy chain element.

The determination of the second partial transmission (or reception) processing latency or PHY to MAC latency is implemented based on the idea that knowing the number of daisy chain elements included in the data path, and knowing, by measurement or by factory predetermination, the latency of a daisy chain element, the latency corresponding to the data path may be determined.

Thus, when a daisy chained element, i.e. a fixed station 13-18, is crossed by a beacon message (either at the master device or the slave device), the data stream selector module 135 of the fixed station 13-18 implements the algorithm represented by Figure 8b.

The data stream selector module 135 waits for a message. When a message arrives at the data stream selector module 135, the type of message is checked at step 801. At step 801, the first field 1000 of the message is checked. If the packet type identifier in the first field 1000 is of beacon type, the value of the third field 1002 is read at step 802 and incremented by 1 at step 803. Next, the incremented value is written back in the third field 1002 of the beacon message at step 804.

Thus, when the beacon message arrives at the MAC module 125 of the slave device, the third field 1002 of the beacon message contains the number of daisy chain elements or fixed stations 13-18 crossed by the beacon message.

The wireless communication system 10 is able to determinate the second partial transmission or reception processing latency or PHY to MAC latency, based on the value in the third field 1002 of the beacon message and the latency generated on passing through a daisy chain element.

Figure 9a illustrates a part of method for wireless communication implemented by the master device according to this second embodiment.

In the same way as for Figure 7a, at step 900, the wireless communication system 10 waits for generation of a beacon message. Once a beacon message has been generated, the baseband latency value determined at step 501 (in Figure 8a) is stored in the second field 1001 of the beacon message and the third field 1002 is initialized to 0 at step 901. Once the beacon message has been transmitted by the master device, the method returns to step 900 wherein the wireless communication system waits for the generation of a next beacon message.

It may be noted that the second field 1002 initialized by the master device at step 901, will be updated during the travel of the beacon message through the fixed stations 13-18.

Once the beacon message reaches MAC module 125 in the slave device, the part of the method for wireless communication which is illustrated by Figure 9b is implemented in the slave device.

Once the beacon message has arrived at the slave device, the slave device timestamps it at step 911.

Next, at step 912, the value stored in the second field 1001 (baseband latency at the master device) and in the third field 1002 (number of daisy chain elements crossed by the beacon message) are read.

The value read from the third field 1002 is multiplied by the latency on passing through a daisy chain element in order to determine the reception processing latency or local PHY to MAC latency.

Next, the local PHY to MAC latency is added to the baseband latency at the master device which has been read from the second field 1001 of the beacon message in order to obtain the latency between the master device and the slave device, in particular the latency between the MAC module 195 of the station controller 19 and the MAC module 125 of the mobile station 12. This latency is called MAC to MAC latency and is represented by the interval of time referenced 215 in Figure 1.

The latency on passing through a daisy chain element is known from the factory, and is stored in the fixed stations 13-18 at the initialization of the wireless communication system 10.

According to another embodiment, the beacon message is time stamped when arriving at a fixed station 13-18. The time stamped value is stored in a dedicated field of the beacon message. When the beacon message arrives at the next fixed station 13-18, the beacon message is time stamped. The latency on passing through a daisy chain element corresponds to the difference between the time stamped value at the current fixed station and the time stamped value stored in the beacon message.

Finally, at step 914, the determined full MAC to MAC latency 215 is used to adjust the synchronization parameter or beacon message arrival time as seen by the slave device. Step 914 is similar to step 714 of Figure 7b.

Next, the wireless communication system 10 waits for the reception of a next beacon message at step 910.

Figures 11, 12 and 13 illustrate different embodiments of a network communication system 10 for which the method for wireless communication according to the invention applies.

In Figure 11, the mobile device 1 comprises three radio modules nodes or radio transceiver nodes 12, 22, 23. In such an embodiment, both mobile device 1 and fixed device 2 implements determining the first partial transmission or reception processing latency (corresponding to the transmission or reception baseband latency), and determining the second partial transmission or reception processing latency (corresponding to the latency between the baseband module 134 of the selected fixed station 13-18 and the MAC module 195 or daisy chain path latency).

It may be noted that determining the second partial transmission or reception processing latency is carried out by any device (either master or slave) comprising a group of fixed stations connected in a daisy chained manner.

In Figure 12, the fixed device 2 comprises two fixed stations 14, 16 among stations 13-18 connected directly to the station controller 19 or two primary fixed stations.

In such an embodiment, several data paths may exist between a selected fixed station 13-18 and the station controller 19. Thus, a step of determining the best data path may be implemented, for instance during step 504 in Figure 6.

According to an embodiment, the best data path is selected according to a data path latency criterion.

In Figure 13, the fixed device 2 comprises two groups of fixed stations 13-18, each group of fixed stations 13-18 being connected respectively in a first daisy chain and a second daisy chain. Two fixed stations 14, 16 are directly connected to the station controller 19 respectively through two point to point links 60a, 60b.

In such an embodiment, at step 503 of Figures 6 and 8a, a metric representing the reception quality has to be requested for the fixed stations of each daisy chain.

Finally, the wireless communication system may comprise a plurality of mobile devices 1 and/or a plurality of fixed devices 2. It is worth noting that the method is independent from the number of fixed or mobile devices so that it can advantageously be used in systems comprising a plurality of mobile devices and/or a plurality of fixed devices.

As long as the devices share the same TDMA network, one of the devices is the master device and the other devices are slave devices.

Claims (36)

1. Method for wireless communications between a master transceiver device and a slave transceiver device, the master transceiver device and/or the slave transceiver device comprising a group of radio modules connected between them in a daisy chain manner, the method comprising: at the master transceiver device and at the slave transceiver device: - configuring a data path for data communication between the master transceiver device and the slave transceiver device; at the master transceiver device: - determining a transmission processing latency; and at the slave transceiver device: - obtaining the transmission processing latency determined at the master transceiver device; - determining a latency between the master transceiver device and the slave transceiver device through the configured data path taking into account the obtained transmission processing latency, - adjusting a synchronization parameter according to the determined latency, and - using the adjusted synchronization parameter when the slave transceiver device communicates with the master transceiver device.

2. Method according to claim 1, wherein the transmission processing latency is transmitted to the slave transceiver device.

3. Method according to any one of claims 1 or 2, wherein determining the transmission processing latency comprises determining a first partial transmission processing latency corresponding to the transmission baseband latency.

4. Method according to claim 3, wherein determining the transmission processing latency further comprises: - determining a second partial transmission latency corresponding to the latency between a baseband module of a radio module and a MAC module of the master transceiver device, and - adding the determined first partial transmission processing latency and the second partial transmission processing latency in order to obtain the transmission processing latency.

5. Method according to claim 4, wherein determining the second partial transmission processing latency comprises: - emitting from the MAC module a control message to a baseband module in a radio module; - the baseband module in the radio module returning back the control message to the MAC module; and - the MAC module determining the travel time, corresponding to the time which has elapsed between the emission of the control message and its reception, the transmission processing latency being half the determined travel time.

6. Method according to claim 4, wherein the second partial transmission latency is determined based on the number of radio modules of the data path and a predefined value representing the latency on passing through a radio module.

7. Method according to any one of claims 1 to 6, wherein determining the latency between the master transceiver device and the slave transceiver device further comprises at the slave transceiver device: - determining a reception processing latency; and - adding the determined reception processing latency and the obtained transmission processing latency.

8. Method according to claim 7, wherein determining the reception processing latency comprises, at the slave transceiver device, determining a first partial reception latency corresponding to the reception baseband latency.

9. Method according to claim 8, wherein determining the reception processing latency further comprises: - determining a second partial reception processing latency corresponding to a latency between a baseband module of a radio module and a MAC module of the slave transceiver device, and - adding the determined first partial reception processing latency and the second partial reception processing latency in order to obtain the reception processing latency.

10. Method according to claim 9, wherein determining the second partial reception processing latency comprises: emitting from a MAC module a control message to a baseband module; the baseband module returning back the control message to the MAC module; and the MAC module determining the travel time, corresponding to the time which has been elapsed between the emission of the control message and its reception, the reception processing latency being half the determined travel time.

11. Method according to claim 9, wherein the second partial reception latency is determined based on the number of radio modules of the data path and a predefined value representing the latency on passing through a radio module.

12. Method according to any one of claims 1 to 11, wherein adjusting a synchronization parameter comprises at the slave transceiver device: - receiving a message from the master transceiver device comprising a synchronization parameter, - time stamping the received synchronization parameter, and - subtracting the determined latency between the master transceiver device and the slave transceiver device from the stamped synchronization parameter.

13. Method according to any one of claims 1 to 12, wherein configuring a data path comprises: - determining a value representing the reception quality of a signal received at each radio module in the group of radio modules; - selecting a radio module from the radio modules of the group on the basis of the determined value representing the reception quality, and - configuring the data path, the data path starting from the selected radio module and passing through a plurality of radio modules in the group for data communication between the master device and the slave device.

14. Method according to claim 13, wherein the value representing the reception quality is based on the Received Signal Strength Indication (RSSI).

15. Method according to claim 13, wherein the value representing the reception quality is based on the Signal-to-Noise Ratio (SNR).

16. Method according to any one of claims 1 to 15, wherein configuring the data path comprises transmitting a control message to each radio module included in the data path, the control message comprising information about the configuration of a data stream selector module of the radio module according to the data path and according to information obtained from a routing table.

17. Method according to any one of claims 1 to 16, wherein the master transceiver device is a fixed device and the slave transceiver device is a mobile device.

18. Method according to any one of claims 1 to 17, wherein the master transceiver device comprises the group of radio modules, at least one of the radio modules being directly connected to a device controller.

19. System for wireless communications comprising a master transceiver device and a slave transceiver device, the master transceiver device and/or the slave transceiver device comprising a group of radio modules connected between them in a daisy chain manner, the system comprising: at the master transceiver device and at the slave transceiver device: - means for configuring a data path for data communication between the master transceiver device and the slave transceiver device; at the master transceiver device: - means for determining a transmission processing latency; and at the slave transceiver device: - means for obtaining the transmission processing latency determined at the master transceiver device; - means for determining a latency between the master transceiver device and the slave transceiver device through the configured data path taking into account the obtained transmission processing latency, - means for adjusting a synchronization parameter according to the determined latency, - means for using the adjusted synchronization parameter when the slave transceiver device communicates with the master transceiver device.

20. System according to claim 19, comprising means for transmitting the transmission processing latency to the slave transceiver device.

21. System according to any one of claims 19 or 20, wherein said means for determining the transmission processing latency comprises means for determining a first partial transmission processing latency corresponding to the transmission baseband latency.

22. System according to claim 21, wherein said means for determining the transmission processing latency further comprise: - means for determining a second partial transmission latency corresponding to the latency between a baseband module of a radio module and a MAC module of the master transceiver device, and - means for adding the determined first partial transmission processing latency and the second partial transmission processing latency in order to obtain the transmission processing latency.

23. System according to claim 22, wherein said means for determining the second partial transmission processing latency comprise means for emitting from the MAC module a control message to a baseband module in a radio module; the baseband module in the radio module comprising means for returning back the control message to the MAC module; and the MAC module comprising means for determining the travel time, corresponding to the time elapsed between the emission of the control message and its reception, the transmission processing latency being half the determined travel time.

24. System according to any one of claims 19 to 23, wherein said means for determining the latency between the master transceiver device and the slave transceiver device further comprise at the slave transceiver device: - means for determining a reception processing latency; and - means for adding the determined reception processing latency and the obtained transmission processing latency.

25. System according to claim 24, wherein said means for determining the reception processing latency comprise, at the slave transceiver device, means for determining a first partial reception latency corresponding to the reception baseband latency.

26. System according to claim 25, wherein said means for determining the reception processing latency further comprise: - means for determining a second partial reception processing latency corresponding to a latency between a baseband module of a radio module and a MAC module of the slave transceiver device, and - means for adding the determined first partial reception processing latency and the second partial reception processing latency in order to obtain the reception processing latency.

27. System according to claim 26, wherein said means for determining the second partial reception processing latency comprise means for emitting from a MAC module a control message to a baseband module; the baseband module comprising means for returning back the control message to the MAC module; and the MAC module comprising means for determining the travel time, corresponding to the time elapsed between the emission of the control message and its reception, the reception processing latency being half the determined travel time.

28. System according to any one of claims 19 to 27, wherein said means for adjusting a synchronization parameter comprise at the slave transceiver device: - means for receiving a message from the master transceiver device comprising a synchronization parameter, - means for time stamping the received synchronization parameter, and - means for subtracting the determined latency between the master transceiver device and the slave transceiver device from the stamped synchronization parameter.

29. System according to any one of claims 19 to 28, wherein said means for configuring a data path comprise: - means for determining a value representing the reception quality of a signal received at each radio module in the group of radio modules; - means for selecting a radio module from the radio modules of the group on the basis of the determined value representing the reception quality, and - means for configuring the data path, the data path starting from the selected radio module and passing through a plurality of radio modules in the group for data communication between the master device and the slave device.

30. System according to any one of claims 19 to 29, wherein said means for configuring the data path comprise means for transmitting a control message to each radio module included in the data path, the control message comprising information about the configuration of a data stream selector module of the radio module according to the data path and according to information obtained from a routing table.

31. System according to any one of claims 19 to 30, wherein the master transceiver device is a fixed device and the slave transceiver device is a mobile device.

32. Means for storing information which can be read by a computer or a microprocessor holding instructions of a computer program, for implementing a method for wireless communications according to any one of claims 1 to 18, when said information is read by said computer or said microprocessor.

33. Means for storing information according to claim 32, being partially or totally removable.

34. Computer program product which can be loaded into a programmable apparatus, comprising a sequence of instructions for implementing a method for wireless communication according to any one of claims 1 to 18, when said computer program product is loaded into and executed by said programmable apparatus.

35. Method for wireless communications substantially as hereinbefore described with reference to, and as shown in, Figures 6, 7a and 7b or Figures 8a, 8b,9a and 9b of the accompagnying drawings.

36. System for processing an image substantially as hereinbefore described with reference to, and as shown in, Figure 10, or Figure 11, or Figure 12, or Figure 13 of the accompagnying drawings.