GB2519093A - Method and apparatus for wireless video transmission using reflection - Google Patents

Abstract

The invention relates to a video projection system in which a transmission channel is established between a wireless transceiver,101, in a video source device, 102, and a beam forming antenna, 401, embedded in a video projector, 104, through a reflection of the radio signal on a projection screen, 400. The invention enables the source to be located behind the video projector while allowing a good radio transmission with the video projector by using the projection screen as a reflector for the radio signal. Further disclosed is a video projector comprising a beam forming antenna and a method for configuring the beam-forming antenna of a video projector. The invention may be used to establishing a high bandwidth wireless transmission for uncompressed video transmission between a source device and a video projector using a 60 GHz-based communication system.

Description

Intellectual Property Office Applicacion Nc,. (lB 1317794.4 RTM Date:24 March 2014 The following terms are registered trade marks and should he rcad as such wherever they occur in this document: Bluetooth (page 19) DisplayPort (page 1) HDMI (page 1) Wi-Fi (page 1. 9, 19) WiGig (page 2) Inlelleclual Property Office is an operaling name of the Pateni Office www.ipo.gov.uk

METHOD AND APPARATUS FOR WIRELESS VIDEO TRANSMISSION

USING REFLECTION

The present invention concerns a method and a device for wireless video transmission using reflection for video projection. It concerns a method for establishing a high bandwidth wireless transmission for uncompressed video transmission between a source device and a video projector.

Video projection is becoming popular as a solution for large display in various situations like show room, conference, business presentation, home cinema. Usually a video projector is connected to a video source device through a cable using a standard interface like HDMI, DVI, DisplayPort. The drawback of wired connection is that it sometimes requires long and costly cables. For very long distances, some repeaters shall be added to guarantee correct signals shape at video projector input. Also especially for outdoor installation, it may be difficult to install cables from the video source to a projector.

To solve the burden of cabling, the appropriate wireless technology shall be integrated in the video source equipment and in the video projector. Wi-Fi connectivity is now widely deployed in multimedia products. However the available bandwidth, below 100Mbps, prevents from pure cable replacement.

With such wireless technology, data compression is a mandatory feature. For instance a full HD uncompressed video stream requires a throughput of about 3Gbps corresponding to 1920x1080 pixels, 24bit/pixel and 60 frames per second.

As the performance of newest wireless technology is greatly improving in term of throughput, it becomes feasible to wirelessly transmit uncompressed video data. The advantage of transferring uncompressed video is to benefit from the highest quality as there is no compression, and to provide a very low latency system allowing interactivity with the user, for instance for simulation tools. Obviously, transferring uncompressed video requires large bandwidth, in the order of several Gbps, but it becomes reachable with most recent wireless technologies like technology using 60GHz millimeter wave operating in the 57- 66 GHz unlicensed spectrum.

60 0Hz-based communication systems are widely studied, for example in the IEEE 802usd Task Group. This technology is also used in the following standards: IEEE 802.15.3c standard; WirelessHD initiative by the WirelessHD consortium; WiGig by the Wireless Gigabit Alliance. The research community proposes several solutions and methods to transport the audio and video applications with a desired quality of service.

The approach of wireless video projection is not new as shown by the publication US20040217948, depicting a 600Hz millimeter wave connection between a laptop and a video projector. The drawback of using 60GHz millimeter wave connection is that 60GHz signals are subjected to high attenuation by obstacle like a human body. Therefore, the quality of communications may be poor or subjected to masking conditions. To mitigate the effect of fading, directional antennas are preferable in order to increase the antenna gain in a given direction. However, using directional antennas does not prevent from shadowing conditions due to obstacle between the emitter and the receiver. It is the case of the link between the video source and a video projector, as typically, the video source is located at the ground level while a video projector is hanged to the roof or to a metallic structure. When the link quality is altered between a video source and a video projector, then the bit error rate increases and some pixels displayed by the video projector are erroneous. In the worst case, the video projector is no longer visible from the source, and the video projector cannot display anything.

Some solutions may use smart antennas that allow controlling the direction of antenna radiation pattern. This type of antenna allows the implementation of the technique known as beam forming to create the radiation pattern in a main desired direction. The ability to change the main direction of the radiation pattern is known as beam steering. Despite these techniques, the area covered by an antenna will not exceed the space equivalent to the half of a sphere. Typically, using these techniques implies a location of the source in front of the projector.

The present invention has been devised to address one or more of the foregoing concerns. It concerns the establishment of a transmission channel between the source and the video projector through a reflection of the radio signal on the screen used for the projection. Accordingly, the source may be located behind the video projector while allowing a good radio transmission with the video projector.

According to a first aspect of the invention there is provided a video projection system comprising a projection screen; a video source connected to a wireless transceiver; a video projector embedding a beam forming antenna; and wherein the video projector and the wireless transceiver are configured to wirelessly communicate through a reflection on said projection screen.

Accordingly, more freedom is given to the user for the location of the source by using the projection screen as a reflector for the radio signal.

In an embodiment, the video projector and the wireless transceiver are configured to wirelessly transmit multimedia data to the video projector through a reflection on the projection screen.

According another aspect of the invention there is provided a video projector, comprising a video projection lens; a beam forming antenna with a main beam direction; control means to vary an antenna beam direction around the main beam direction for wirelessly communicating with a remote device; and wherein the beam forming antenna is configured to have its main beam direction to correspond to the projection direction of the video projection lens.

The video projector may communicate with the remote device in emission or in reception. In case of receiving image data from the remote device acting as a video data source, the main beam direction corresponds to a main reception direction and the control means varies an antenna reception direction around the main reception direction.

In an embodiment, the projection direction of the lens corresponds to a projection axis representative of the direction of the light beam emitted by the video projector lens.

In an embodiment, the beam forming antenna is configured to keep the radiation pattern of the beam(s) within the projection cone.

In an embodiment, the control means allows adjusting the antenna beam direction to communicate with the remote device through reflection on a projection screen associated to the video projector.

In an embodiment, the main beam direction corresponds to a main reception direction and the control means allows adjusting the antenna reception direction around the main reception direction for wirelessly receiving image data from the remote device acting as a video data source.

In an embodiment, the video projection lens being adjustable, the video projector further comprises means to store in memory parameters used to set up the adjustable lens; means to determine from these parameters the projection axis; and means to configure the beam forming antenna to have its main beam direction corresponding to the determined projection axis.

In an embodiment, the video projector further comprises means for conducting a discovery process at initialization to discover the best emission or reception direction for the beam forming antenna; means to get the actual focus parameter of the projection lens; means to determine the actual projection cone of the video projection; and means to adapt the discovery process to restrain the discovery within the determined projection cone.

In an embodiment, the radiation pattern of the beam(s) is narrow in azimuth and wide in elevation.

According another aspect of the invention there is provided a method for configuring the beam forming antenna of a video projector comprising an adjustable projection lens, comprising storing in memory parameters used to set up the adjustable lens; determining from these parameters a projection axis corresponding to the projection direction of the adjustable projection lens; and configuring the beam forming antenna to have its main beam direction corresponding to the determined projection axis.

Accordingly the adjustment is made more accurate and the use of the projection screen as a reflector is privileged.

In an embodiment, the method further comprises conducting a discovery process at initialization to discover the best emission or reception direction for the beam forming antenna; getting the actual focus parameter of the projection lens; determining the actual projection cone of the video projection; and means to adapt the discovery process to restrain the discovery within the determined projection cone.

According another aspect of the invention there is provided a computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing a method according to the invention, when loaded into and executed by the programmable apparatus.

According another aspect of the invention there is provided a computer-readable storage medium storing instructions of a computer program for implementing a method according to the invention.

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 that may all generally be referred to herein as a "circuit", "module" or "system". 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.

Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RE signal.

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 a video projection system according to prior art; Figure 2 illustrates the hardware architecture of a video projector according to an embodiment of the invention; Figure 3 illustrates the hardware architecture of a video projector according to an embodiment of the invention; Figure 4 illustrates a video projection system according to an embodiment of the invention; Figure 5a illustrates a top view of an antenna used in an embodiment of the invention; Figure Sb illustrates a side view of an antenna used in an embodiment of the invention; Figure 6 shows an example of the TDMA sequence for communications between the video source and the video projector; Figure 7 illustrates the antenna discovery process according to an embodiment of the invention; Figure 8 is a flow chart of the algorithm executed at the initialization of a video projector according to an embodiment of the invention; Figure 9 is a flow chart of the algorithm executed at the initialization of a video source device according to an embodiment of the invention; Figure 10 illustrates the projection and emitting directions in a video projector according to an embodiment of the invention; Figure 11 is a flow chart of the algorithm executed for adjusting the emitting direction of the antenna of a video projector in an embodiment of the invention.

Figure 1 shows an example of a 60GHz wireless video projection system according to the prior art, composed of one video projector 104 installed on metallic structure 111 hooked to the ceiling 110 of a room, and wirelessly connected to the video source device 102. For that a 60GHz wireless transceiver 101 is attached to the video source device 102; the wireless transceiver embeds an antenna system 103. The antenna system 103 may be composed of two antennas, one for data transmission and one for data reception. The video projector is equipped with an optical zoom lens 105 adjusted to a given focal length, and with 60GHz wireless communications means having an antenna system 106. The antenna 106 may be separated into two antennas, one for data transmission and one for data reception. The radiation pattern of antenna system 106 allows the coverage of the area delimited by the shape 107 represented by dotted line. Used antenna technology is either omni-directional antenna or beam forming antenna able to generate simultaneous beams in various directions. As the antenna will be placed on one side of the video projector, the covered area is limited to half sphere. Moreover, long transmission distance is not guaranteed because the radiated energy is spread over several directions and the resulting signal power is rapidly decreasing due to fading. Therefore, using one antenna limits the possible position for the video source device. In the example of Figure 1, the source device 102 with the wireless transceiver 101 must be placed in front of the video projector 104. The video source device 102 may be a digital video camera, a hard-disk or solid-state drive, a digital video recorder, a personal computer, a set-top box, a video game console or similar.

The aim of the invention is to give more freedom to the user for the location of the source by using the projection screen as a reflector for the radio signal. By setting up the radio communication channel between the source and the video projector through a signal reflection on the projection screen, it is possible to locate the source behind the projector. According to an embodiment of the invention the initialization of the system is adapted to favor the establishment of the communication through a reflection on the screen. In particular, when a discovery process is implemented to find the best configuration for directional antennas used in the source and the video projector, the discovery process may be limited to emitting direction to the screen. The radio controller of the video projector may use some projection parameters to determine the projection direction and use this information for the configuration of the antenna.

Figure 2 shows the functional block diagram of the video projector displayed on Figure 3 according to an embodiment of the invention. It comprises a main controller 201 in charge of the whole control of the device, a radio physical layer unit (denoted PHY) 211 in charge of the radio communication with the source device, an optical system 239 including a projection lamp and a projection lens 240 in charge of the actual projection of video received by the radio physical layer 211 and processed by the main controller 201.

The main controller 201 is itself composed of a Random Access Memory (denoted RAM) 233, a Read-Only Memory (denoted ROM) 232, a micro-controller or Central Processing Unit (denoted CPU) 231, a user interface controller 234, a medium access controller (denoted MAC) 238, a video processing controller 235, a video interface controller 236, a video Random Access Memory (denoted video RAM) 237. All these components communicate through a communication bus 244. The main controller 231 controls the overall operation of the video projector as it is capable of executing, from the memory RAM 233, instructions pertaining to a computer program, once these instructions have been loaded from the memory ROM 232.

The video projector may be set up by the user using the user interface 234. This interface can be a wired interface (like Ethernet, Universal Serial Bus USB) or a wireless interface (infrared, WiFi). The user's settings are stored in RAM memory 233.

The video processing controller 235 performs all necessary transformations of video data which are temporary stored in video RAM 237.

The video processing controller 235 receives video image from the MAC 238, and it delivers the video image to the optical system 239. Prior to this transfer, video processing controller 235 may have to apply some digital adaptation like a digital zoom, or like an upscale to a higher video resolution. The optical system 239 will perform operation in the analogue domain, and will transmit the analogue signal to the projection lens 240.

MAC 238 is in charge of controlling the emission and reception of MAC frames conveying control data and video data. For physical transmission and reception, the MAC 238 relies on one physical layer units 211. Preferably, the physical layer unit operates in the 60GHz band. Typically, useful throughput between MAC 238 and the physical layer unit is in the order of 3.5Gbps.

The physical layer unit 211 embeds a modem 212, a radio module 213 and antenna 214. The radio module 213 is responsible for processing a signal output by the modem 212 before it is sent out by means of the antenna 214. For example, the processing can be done by frequency transposition and power amplification processes. Conversely, the radio module 213 is also responsible for processing a signal received by the antenna 214 before it is provided to the modem 212. The modem 212 is responsible for modulating and demodulating the digital data exchanged with the radio module 213. For instance, the modulation and demodulation scheme applied is of Orthogonal Frequency-Division Multiplexing (OFDM) type. In the preferred embodiment, antenna 214 includes antenna for transmission and antenna for reception. In a preferred embodiment, the antenna technology is sectored beam forming antenna as described in Figure 5a and 5b, but the invention is not limited to this type of antenna. Smart antennas with configurable directional radiation pattern may be used, provided that the radiated energy focuses in a selectable direction. The radio module 213 is mainly in charge of up-converting and down-converting signals frequency. For transmission, it provides up-conversion from the low frequency of the modem to the high frequency (e.g. 6GHZ) of radio signals. For reception, it provides the reverse operation (down-conversion from high to low frequency). The elements of physical layer 211 are driven by the main controller 231 through the MAC 238.

MAC 238 acts as a synchronization control unit, which controls scheduling of transmissions via the network. It means that MAC 238 schedules the beginning and the end of an emission of radio frames over the medium, as well as the beginning and the end of a reception of frames from the medium.

Regarding the reception, the modem of physical layer unit 211 collects the radio frames received from the radio module through the reception antenna, and transmits radio frames to the MAC 238. The MAC 238 is therefore able to detect if a radio frame is missing. This detection is made when the MAC 238 is expecting a radio frame payload during a scheduled receiving time slot but no data come from the physical layer unit. This situation occurs when the modem has failed to recognize the radio frame preamble: the synchronization was unsuccessful because the signal-to-noise ratio (SNR) or received signal strength indication (RSSI) was too low, meaning that the signal has been indiscernible from noise. Also, MAC 238 is able to detect transmission errors within a radio frame. As radio frame payload can be divided into several packets. A control sum, for example a CRC (Cyclic Redundancy Check) computed by MAC 238 can be appended at the end of each packet. For a given packet received in a destination node, if CRC computation result is different from the one received with the packet, then MAC 238 can decide to drop this packet as it is very likely to contain one or several erroneous data. Therefore MAC 238 can indicate to video processing controller 235 if some packets are missing or may contain errors. Then, any appropriate concealment mechanism can be applied in the video processing controller 235. To synchronize video image display, a time stamping technique may be used. Then each MAC frame conveying video data corresponding to the beginning of new video image, will include a timestamp value indicating at what time shall be displayed this new video image.

The wireless transceiver 101, not represented, shares the same architecture without the optical system 239 and lenses 240. It is composed of similar elements, a main controller 201, one physical layer unit 211. The main controller 201 of wireless transceiver 101 is itself composed of a Random Access Memory 233, a Read-Only Memory 232, a micro-controller or Central Processing Unit 231, a user interface controller 234, a medium access controller 238.

Figure 3 shows an example of hardware architecture of the video projector 104 according to an embodiment of the invention. Inside the casing is represented the main elements of Figure 2: the main controller 201, the optical system 239, the projection lens 240 and the physical layer unit 211. Due to the strong attenuation of 60GHz millimeter wave signals crossing materials, it is advantageous to locate antennas close to the casing of the product, in a place where there is almost no obstacle due to mechanical parts. The physical layer unit embedding the antenna is therefore located close to the edge of the video projector casing. Advantageously, the antenna is placed on the front side of the video projector. This arrangement will enable communications between the video source device 102 and with the video projector 104 either with line of sight communications or through a reflection against a surface able to reflect 60GHz radio signals.

Figure 4 represents an example of a video projection system for displaying video according to an embodiment of the invention. This system is similar to the system described in Figure 1, except that the wireless adapter/transceiver 101 and the video projector 104 are equipped with beam forming antenna, respectively 403 and 401. These antennas are able to concentrate the radiated energy in a selectable direction. An example of radiation pattern obtained for the antenna 401 is illustrated by the shape 402.

The communication between the wireless adapter/transceiver 101 and the video projector 104 is performed through a reflection on a surface. This has the effect to extend the coverage and to allow locating the video source device 102 in front of or behind the video projector 104. In this example the display screen 400 is used as a reflector. One advantage is that this surface is always present in a video projection system, and the area between the screen and the video projector is usually free of obstacle. Besides, the display screen is often of white color with good properties for radio signals reflection as the white color usually comprises metallic pigments typically of zinc or titanium.

The antenna used for the communication in the video projector and the wireless adapter is typically adapted to present a directional beam in a privileged direction. The antenna is a beam forming antenna radiating in a given direction. This antenna has a main reception direction. Advantageously, it may be controlled by steering means to choose the orientation of the beam around the main reception direction in order to favor a given transmission path around this main reception direction. By using this kind of directional antenna, it is possible to direct the antenna of the video projector toward the wireless adapter in order to establish a good transmission path between the two elements. The same applies to the antenna of the wireless adapter. When a direct path is not suitable between the video projector and the wireless adapter, the path may be chosen to use a reflection through a reflection surface, typically the projection screen. It is an aspect of the invention to adapt the steering means to favor a transmission path using the projection screen as a reflection surface for the transmission. We speak of the reception direction or the emitting direction which is assumed to be the same direction and this independently of the fact that the projector uses one antenna for emission and reception or two antennas, one for emission and one for reception.

Figure 5a represents a top view of antenna that may be used in an embodiment of the invention. The antenna 502 is made of a dielectric lens powered by waveguides within a substrate 501. Here eight waveguides are represented and referred 521 to 528. Figure Sb represents a side view of antenna 502. To be able to perform transmission and reception, one can install two antenna systems like the one presented in Figure 5a and 5b.

The lens is inhomogeneous with focusing and beam forming capabilities.

In such lens, the refraction index n(r) inside the lens follows a radial distribution. The most known example is the Luneburg' lens, here employed in this particular embodiment. In this case, the refraction index law is given by the following formula: n2(r) = 8(r) = 2 -r2, where r is the normalized radial position.

In a classical Luneburg lens, the dielectric constant varies from 2 in the center of the lens and decreases to 1 on its surface. These rough values are indicative as an example in this particular embodiment. A plate Luneburg lens is here considered resulting in narrow beam in azimuth and large beam in the elevation plane. The antenna gain value depends on the radius of the lens 502; l5dBi can be obtained with a radius or around 30mm.

The antenna lens 502 is illuminated by 8 RE sources. These sources are antenna elements placed on the circular surface of the cylindrical lens. On this particular embodiment, these antenna elements are wave guides 521 to 528.

The wave guides can be supplied directly without additional component by the input. To multiply the possible configurations, it can be useful to integrated RF electronic components directly on the feeder substrate. These RF electronics components can be RF switches, Power Amplifier (PA), Low Noise Amplifier ([NA), RE or IE mixer. Eor transmission, an on/off command on the power amplifier enables to activate/disable each single beam. Activation of amplifier connected to waveguide 521 will produce the beam 511. In the same way, the beam 515 is activated through the waveguide 525 and the beam 518 is activated through the waveguide 528. Similarly in reception, on/off command on the low noise amplifier enables to activate each single beam. If only one waveguide is supplied, therefore the antenna forms a narrow beam through the lens, characterized by a width of 200 in the azimuth plan. However, several waveguides can be activated simultaneously to form a larger beam by aggregation. If all waveguides are supplied, the result is a wide beam.

Advantageously, the generated beam is narrow in azimuth while being wide in elevation.

On Figure 5b, the beam 515 is represented with the resulting aperture in elevation plan in the order of 70°. It can be noticed that the orientation of this antenna relative to the projector position is not unique. For instance, the view of figure 5a can correspond to the top view of the video projector, and the antenna beam can be adjusted from the left edge to the right edge of the video projector.

In another embodiment, the antenna can be placed so that the view of figure 5a corresponds to the side view of the video projector. In that case, the antenna beam can be adjusted from the bottom edge to the top edge of the video projector.

This antenna design is proposed as an example of antenna that fits to the invention. Other type of antenna can be used, like phased array antenna allowing the generation of beam in any direction towards the front of the video projector.

Figure 6 shows an example of the TDMA (Time Division Multiple Access) sequence for communications between the video source and the video projector. In the preferred embodiment, access to the medium is scheduled according to a TDMA scheme, where each transmission time slot is associated to only one device. A single MAC frame is transmitted during each transmission slot. The set of MAC frames transmitted during one TDMA sequence is called a super-frame. Typically, the duration of a super-frame is 2Oms and the duration of a time slot does not exceed 200ps.

Among the devices, one is in charge of defining the beginning of each super-frame cycle. For instance the wireless transceiver 101 may be deemed as the master transmitting a first MAC frame at fixed periodic intervals. This MAC frame is generally called a beacon frame marking the beginning of the super4rame. The other device can then determine the beginning of each super-frame cycle according to the reception time of the beacon frame from the master node.

The Figure 6 represents one superframe timeline corresponding to a superframe cycle N, with several time slots referred 601, 602, 603 for data transmission. The wireless transceiver 101 transmits control data during the time slot 601, the video projector transmits control data during the time slot 602, and the wireless transceiver 101 transmits video data during the time slot 603.

For time slots 601 and 602, the transmission and reception can be performed using a robust modulation at low data rate and by activating all beams of antenna using an omni directional setting. Control data exchanged during time slots 601 and 602 can be used to synchronize antenna discovery step. This step is necessary to identify the single beam to use in wireless adapter 101 and video projector 104 in order to optimize video transmission at very high speed.

During this step, test pattern can be transmitted during the time slot 603. This test pattern will allow the destination device to perform antenna scan process described in Figure 8.

The discovery process is the process used to determine the best orientation for the couple of antennas, the antenna of the video projector and the antenna of the wireless adapter, to establish the communication. Depending of the particular embodiment, it consists basically in testing all the possible configurations and to keep the configuration giving the best signal noise ratio (SNR).

Figure 7 illustrates the antenna discovery process according to an embodiment of the invention. An aim of the invention is to accelerate the detection of a combination of a video projector antenna reception beam and a wireless adaptor antenna transmission beam using the projector screen as a reflector. The possible combinations are considered according to a process described in detail below and in the Figure 8, until a quality value is reached.

The wireless adapter 101 of the source device 102 initiates the antenna discovery process starting the transmission of test pattern using a first antenna setting transmission creating a beam 711.

This beam is the closest to a predefined reference direction 710 which is chosen here to be the direction of the video screen. Then the video projector will proceed to antenna scan, testing various beams for reception, starting with beam 701. This beam is the closest one to a predefined reference direction 700 which is chosen here to be the direction of video projection. After performing the link assessment with this configuration, the video projector switches to next beam 702 for reception, which is the closest to the previous one. Link assessment may consist in measuring the received signal length, or measuring the bit error rate. The antenna scan can be stopped when a peak value is identified for the link assessment. Advantageously, the scanning operation will continue if the best received signal strength is not above a predefined threshold.

Then the wireless adapter 101 can switch to the next beam 712 for transmission, which is the closest to the previous one, and the video projector 104 performs a new complete scan. The process stops when a peak value has been identified for the link assessment, which in the example of Figure 7 is obtained with transmission beam 715 and reception beam 702. Accordingly, the antenna discovery is optimized, the reflection on the projection screen is privileged, and the time spent for this step is limited.

Figure 8 is a flow chart of the algorithm executed at the initialization of a video projector according to an embodiment of the invention. This algorithm is typically executed by the processor 231 of the video projector.

In step 801, the video projector 104 proceeds to network synchronization probing the RF channel (all beams activated) waiting for the reception of a beacon frame. When it is done, in step 802, it uses its time slot to send to the wireless adapter 101 a message indicating it is ready to perform antenna discovery. In step 803, the video projector waits for the reception of a message from the wireless adapter indicating the start of test pattern transmission. When received, in step 804, it sets first antenna setting for reception and it proceeds to link assessment in step 805. According to the result of this assessment, the video projector decides in step 806 if antenna scan is over for the associated transmission setting in the wireless adapter. For example, the processor 231 checks if a peak value has been detected. If not, a new antenna setting is selected for the reception in step 807 before going back to step 805 for link assessment. The new selected beam is the next beam spatially closest to the first tested beam If the antenna scan is over in step 806, then a message is sent to the wireless adapter to indicate the status. This message indicates to the wireless adapter that the scan is complete for this antenna setting. This is performed in step 808 before going back to step 803. In step 803, if no test pattern transmission is detected, the processor 231 checks in step 809 if the antenna discovery is over, meaning that link assessment shows a peak value for a couple of antenna setting in transmission and in reception. If not, it returns to step 803, otherwise it goes to step 810 to set the best antenna setting found and waits in 811 for the reception of video data.

Figure 9 is a flow chart of the algorithm executed at the initialization of a wireless adapter for a video source device according to an embodiment of the invention. This algorithm is typically executed by the processor 231 of the wireless adapter.

After power on, in step 901, the wireless adapter starts sending a beacon frame to enable network synchronization of the video projector. In step 902, the processor 231 checks if the video projector is synchronized, it means if a specific message or acknowledgment has been received from the video projector 104.

Next, in step 903, the processor 231 sets first antenna setting and starts transmitting a signal until the reception of a report status message from the video projector. This is tested in step 904. When received, it is then checked (step 905) if the antenna scan is over for this antenna transmission setting. This is indicated, for example, in the status report message from the video projector.

If yes, it is also checked in step 907 if the antenna discovery is over. It is also indicated in the status report message from the video projector. If not, a new antenna setting for transmission is selected in step 906 before going back to the check 904. The new selected beam is the next beam spatially closest to the first tested beam. Otherwise it is checked in step 907 if the antenna discovery is over. It is also advantageously indicated in the status report message from the video projector. If the antenna discovery is over, the CPU 231 can go to step 908 to set the best antenna setting found by the video projector and it starts in step 909 the transmission of video data.

The control messages exchanged between the video projector and the wireless adapter are transmitted in this embodiment using the radio link using a robust modulation and omni directional emission. In some embodiment, the control messages may be exchanged using any transmission link established between the video projector and the wireless adapter. This transmission link may be wired or wireless, using for example, WiFi or Bluetooth technology.

Figure 10 illustrates a video projector 1001 with adjustable projection lens 240. Most of the video projectors allow adjusting the video projection direction in order to aim at the video screen. By this mechanism, the location of the video projector may be chosen more freely with respect to the screen. But this mechanism makes the projection direction to be different from the global front direction. For more precision in the discovery process described in the foregoing and to insure that the radio beams emitted by the antenna aim at the projection screen, it is advantageous to take into account the actual projection direction of an adjustable lens. By doing so, the main emission direction 1003 corresponds to the actual projection axis. The projection axis is representative of the direction of the light beam emitted by the video projector lens. More precisely, the projection axis corresponds to the central ray of the light beam emitted by the video projector. Advantageously the emission beams of the antenna are kept within the projection cone 1002 of the projector. The actual projection direction of the adjustable lens is typically set up by the user using set up parameters stored in the video projector memory. By accessing these set up parameters used to adjust the actual projection direction, the discovery process may be adapted to have a main emitting direction corresponding to the actual projection direction. Advantageously, the discovery process is adapted to keep the emission beams within the projection cone. To increase the knowledge of the actual projection cone, the current focus parameter of the projection may also be used. In an alternative embodiment, these parameters may be used, even with a nonadjustable lens to keep the emission beam within the projection cone.

Figure 11 illustrates the main further steps of the algorithm executed at the initialization of a video projector according to an improved embodiment.

In a step 1100, the processor 231 of the video projector gets some parameters of the setting of the adjustable lens. These parameters allow determining the actual projection direction of the adjustable lens corresponding to the direction of the projection screen. In a step 1101, the discovery process is adapted to use this actual projection direction to be the main direction of the antenna during the discovery process. This direction corresponds to the direction 700 on Figure 7. In some embodiments, additional parameters, typically related to the actual focus used by the adjustable lens are used to determine precisely the projection cone. In these embodiments, the discovery process is adapted to restrain the discovery within this projection cone.

Accordingly, the projection beams of the antenna are guaranteed to aim at the projection screen.

Any step of the algorithm shown in Figure 8, 9 and 11 may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC ("Personal Computer"), a DSP ("Digital Signal Processor") or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA ("Field-Programmable Gate Array") or an ASIC ("Application-Specific Integrated Circuit").

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 (16)

1. CLAIMS1. A video projection system comprising: -a projection screen; -a video source connected to a wireless transceiver; -a video projector embedding a beam forming antenna; wherein: the video projector and the wireless transceiver are configured to wirelessly communicate through a reflection on said projection screen.
2. 2. The video projection system of claim 1 wherein the video projector and the wireless transceiver are configured to wirelessly transmit multimedia data to the video projector through a reflection on the projection screen.
3. 3. A video projector, comprising: -a video projection lens; -a beam forming antenna with a main beam direction; -control means to vary an antenna beam direction around the main beam direction for wirelessly communicating with a remote device; wherein: -the beam forming antenna is configured to have its main beam direction to correspond to the projection direction of the video projection lens.
4. 4. The video projector of claim 3, wherein the projection direction of the lens corresponds to a projection axis representative of the direction of the light beam emitted by the video projector lens.
5. 5. The video projector of claim 3 or 4 wherein the beam forming antenna is configured to keep the radiation pattern of the beams within the projection cone.
6. 6. The video projector of any claim 3 to 5 wherein the control means allows adjusting the antenna beam direction to communicate with the remote device through reflection on a projection screen associated to the video projector.
7. 7. The video projector of any claim 3 to 6 wherein the main beam direction corresponds to a main reception direction and wherein the control means allows adjusting the antenna reception direction around the main reception direction for wirelessly receiving image data from the remote device acting as a video data source.
8. 8. The video projector of claim 5 wherein the video projection lens being adjustable and wherein the video projector further comprises: -means to store in memory parameters used to set up theadjustable lens;-means to determine from these parameters the projection axis; and -means to configure the beam forming antenna to have its main beam direction corresponding to the determined projection axis.
9. 9. The video projector of claim 5, wherein the video projector further comprises: -means for conducting a discovery process at initialization to discover the best emission or reception direction for the beam forming antenna; -means to get the actual focus parameter of the projection lens; -means to determine the actual projection cone of the video projection; and -means to adapt the discovery process to restrain the discovery within the determined projection cone.
10. 10. The video projector of any one claim 5 to 9, wherein the radiation pattern of the beams is narrow in azimuth and wide in elevation.
11. 11.A method for configuring the beam forming antenna of a video projector comprising an adjustable projection lens, comprising: -storing in memory parameters used to set up the adjustable lens; -determining from these parameters a projection axis corresponding to the projection direction of the adjustable projection lens; and -configuring the beam forming antenna to have its main beam direction corresponding to the determined projection axis.
12. 12. The method of claim 11, wherein the method further comprises: -conducting a discovery process at initialization to discover the best emission or reception direction for the beam forming antenna; -getting the actual focus parameter of the projection lens; -determining the actual projection cone of the video projection; and -means to adapt the discovery process to restrain the discovery within the determined projection cone.
13. 13.A computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing a method according to any one of claims 11 and 12, when loaded into and executed by the programmable apparatus.
14. 14.A computer-readable storage medium storing instructions of a computer program for implementing a method according to any one of claims 11 and 12.
15. 15.A video projector substantially as hereinbefore described with reference to, and as shown in Figure 2, 3, 4, 5a, 5b, 7 and 10.
16. 16.A video projection system substantially as hereinbefore described with reference to, and as shown in Figure 1, 4 and 7.