Method and system for establishing a connection on a secondary frequency channel for wireless communication

A method and system for establishing a subnet in a wireless network is provided for wireless transmission of information between two stations in the network. A subnet access process in a wireless communication system establishes a subnet comprising a direct wireless link on a secondary frequency channel for wireless transmission of data between two stations.

FIELD OF THE INVENTION

The present invention relates to wireless communication, and in particular, to communication of video information over a wireless communication medium.

BACKGROUND OF THE INVENTION

With the proliferation of high quality video, an increasing number of electronics devices (e.g., consumer electronics devices) utilize high definition (HD) video signals. Conventionally, most systems compress the HD signal, which can be around multi-Mbps (megabits per second) in bandwidth, to a fraction of its size to allow for efficient transmission between devices. However, with each compression and subsequent decompression of the signal, some video information can be lost and the picture quality can be reduced.

The High-Definition Multimedia Interface (HDMI) specification allows transfer of uncompressed HD signals between devices via a cable. While consumer electronics makers are beginning to offer HDMI-compatible equipment, there is not yet a suitable wireless (e.g., radio frequency) technology that is capable of transmitting uncompressed HD signals between devices.

Wireless local area network (WLAN) and similar technologies can suffer interference issues when several devices are connected and they do not have the bandwidth to carry the uncompressed HD signal by providing an air interface to transmit uncompressed video. Referring toFIG. 1, the IEEE 802.11e draft (IEEE P802.11e/D13.0 (January 2005), “Amendment: Medium Access Control (MAC) Quality of Service (QoS) Enhancements”), provides a 4-step process for a Direct Link Protocol (DLP) which is used to set up a peer-to-peer link between two stations in a WLAN. This allows video frame transmission between two stations (STAs) without going through a coordinator. However, the direct link is established on the same channel that an access point (AP) utilizes for communication. This reduces available bandwidth for video frame transmissions between two stations. There is, therefore, a need for a method and system for communication of video information between two stations in a network, which address the above shortcomings.

BRIEF SUMMARY OF THE INVENTION

A method and system for establishing a subnet in a wireless network is provided for wireless transmission of information between two stations in the network. A subnet access process in a wireless communication system establishes a subnet comprising a direct wireless link on a secondary frequency channel for wireless transmission of data between two stations.

In one implementation, the subnet access process includes the steps of: receiving a request for wireless communication between two wireless stations over a primary frequency channel; establishing a direct wireless communication link between the two stations over a secondary frequency channel; and performing wireless communication between the two stations over the direct communication link via the secondary frequency channel.

The step of establishing the direct communication link between the two stations further includes the steps of: determining if the primary frequency channel has sufficient bandwidth to satisfy the communication request; and if the primary frequency channel has insufficient bandwidth to satisfy the communication request, then establishing the direct communication link between the two stations over the secondary frequency channel.

For establishing the direct communication link between the two stations, the two stations perform remote channel scans and provide the scan results by a remote scan response command. The scan results include information about the channels scanned, and the quality of each scanned channel.

Based on the remote channel scans, a common frequency set is determined. Then, a frequency channel is selected from the common frequency set as the secondary frequency channel. Selecting a frequency channel from the common frequency set as the secondary frequency channel can include the steps of selecting a frequency channel with the highest quality in the common frequency set.

The requesting stations perform communication therebetween with directed peer-to-peer data exchange over the direct communication link via the secondary frequency channel. One or both of the requesting stations can further periodically broadcast NULL frames for fixed duration on the secondary frequency channel to prevent other stations from transmitting on the secondary frequency channel. Further, an AP or coordinator on the primary frequency channel can transmit duplicates of a primary frequency channel beacon on the second frequency channel to prevent other stations from transmitting on the secondary frequency channel.

Upon completion of communications between the two stations, the requesting stations switch back to communication on the primary frequency channel, and the direct link on the secondary frequency channel is ended.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and system for establishing a subnet in a wireless network for wireless transmission of information such as video information between two stations in the network. In one embodiment, this involves implementing a subnet access method in a wireless communication system for establishing a subnet, comprising a direct wireless link on a secondary frequency channel for wireless transmission of data (e.g., uncompressed video signals) between two stations. In one example, if due to insufficient available bandwidth on a primary frequency channel a transmission request between a pair of stations cannot be satisfied, then a subnet access controller establishes a subnet (or a direct link) on a secondary frequency channel so that said pair of stations can access the secondary channel for communication therebetween.

An implementation of a subnet access process according to the present invention for establishing a direct link or subnet on a secondary frequency channel for wireless transmission of uncompressed high definition television (HDTV) signals is now described.

FIG. 2shows a functional block diagram of a wireless communication system100(e.g., a 60 GHz WPAN) implementing an example subnet access process, according to the present invention. The system100includes an access point (AP)102and multiple stations (STA A, . . . , STA Z)104. The AP implements a coordinator106. Although the coordinator106is shown as implemented in the AP102inFIG. 2, the coordinator106can also be implemented in one or more other device in the system100. Further, the coordinator106can be implemented as a standalone module apart from the AP102.

In many wireless communication systems, a frame structure is used for data transmission between wireless stations such as a transmitter and a receiver. For example, the IEEE 802.11 standard uses frame aggregation in a Media Access Control (MAC) layer and a physical (PHY) layer. In a typical transmitter, a MAC layer receives a MAC Service Data Unit (MSDU) and attaches a MAC header thereto, in order to construct a MAC Protocol Data Unit (MPDU). The MAC header includes information such a source addresses (SA) and a destination address (DA). The MPDU is a part of a PHY Service Data Unit (PSDU) and is transferred to a PHY layer in the transmitter to attach a PHY header (i.e., PHY preamble) thereto to construct a PHY Protocol Data Unit (PPDU). The PHY header includes parameters for determining a transmission scheme including a coding/modulation scheme. Before transmission as a packet from a transmitter to a receiver, a preamble is attached to the PPDU, wherein the preamble can include channel estimation and synchronization information.

The AP102implements a MAC layer on top of a PHY layer for wireless communication. The AP102provides central coordination for the stations104. The AP102and stations104normally communicate on said primary frequency channel. The coordinator106implements a subnet access process according to the present invention, which establishes and manages said secondary frequency channel as necessary.

FIG. 3shows protocol architecture for each station104in the system ofFIG. 2. Each station104includes a PHY layer110and a MAC layer112.FIG. 3also shows an example protocol architecture for the coordinator106, including a PHY layer120, a MAC layer122and a subnet access control module124implementing a subnet access process according to the present invention. The PHY layers110and120implement radio frequency (RF) communication for transmit/receive signals.

If due to insufficient available bandwidth on the primary frequency channel, a new transmission request between a pair of stations (e.g., requesting STA A and STA B inFIG. 2) cannot be satisfied, the coordinator106establishes a subnet comprising a direct link on a secondary frequency channel, such that the pair of requesting stations can access the secondary channel for communication therebetween. As such, the coordinator106starts a subnet (or a direct link) so that the pair of requesting stations can be admitted and allocated a contention-free data period on the secondary channel for communication therebetween.

FIG. 4shows multiple superframe structures130for wireless communication over a shared channel (such as the primary or secondary frequency channel) by the stations inFIG. 2, according to an embodiment of the present invention. In each superframe structure130, a contention-based (CB) channel time period132is used for transmission of control messages, and a contention-free (CF) channel time period134is used for transmission of asynchronous or isochronous data during scheduled slots136.

The coordinator106includes a scheduler125that is responsible for managing the CB and CF periods132and134, respectively, wherein a CB period132and a CF period134form a superframe130.FIG. 4illustrates multiple superframes130(superframe 0,. . . , superframe N+1). The coordinator106periodically transmits a beacon frame138(omni-directionally) on the primary channel to disseminate various timing information such as CF and CP control periods, CF data periods, time synchronization, etc., to the stations. Each superframe begins subsequent to a beacon frame138.

FIG. 5shows a flowchart of the steps of an example subnet access process200involving the coordinator106(e.g., coordinator C) and two stations104(e.g., stations A and B), for establishing a secondary frequency channel between the two stations, according to an embodiment of the present invention. The process200includes the following steps:Step201: The coordinator C detects that a new request for communication between stations A and B on the primary frequency channel cannot be satisfied because the requested bandwidth exceeds the available bandwidth on the primary frequency channel. The new request cannot be admitted on the primary frequency channel, whereby the coordinator C invokes establishment of a secondary channel (i.e., a subnet or a direct link) for the stations A and B to satisfy the new request.Step202: Since the coordinator C can be busy receiving or transmitting data, or managing the primary channel, the coordinator C commands/requests that the stations A and B perform a remote scan (FIG. 6), and report back the scan results to the coordinator. The remote scan command can be similar to that described in the IEEE 802.15.3 specifications, such as IEEE 802.15.3 Working Group. Part 15.3: Wireless medium access control (MAC) and physical layer (PHY) specifications for high rate wireless personal area networks (WPAN).Step204: Each of the stations A and B performs a remote channel scan (FIG. 7) and reports back the remote scan results to the coordinator C using the remote scan response commands such as in said IEEE 802.15.3 specifications. The two remote scan results include the channels scanned by each of the stations A and B and the quality of the scanned channels.Step206: The coordinator C determines a common frequency channel set based on the two remote channel scan results from the stations A and B. In one example, the common frequency channel set includes frequencies of similar scanned quality for both stations A and B.Step208: The coordinator C selects a frequency channel from the common frequency set as a secondary frequency channel. If more than one common frequency is determined in the frequency set, then the coordinator C selects the one with the highest channel quality as the secondary frequency channel.Step210: The coordinator C conveys information about the secondary frequency channel to the stations A and B.Step212: For establishing a subnet comprising a direct link between the stations A and B, the stations A and B exchange Probe request-and-response commands on the selected secondary channel in omni-directional mode as shown by example inFIG. 8. The Probe commands can be similar to that described in said IEEE 802.15.3 specifications. The perimeters103shown around the stations A, B, and the controller C, reflect their omni-directional transmission range. The station initiating a direct link setup (e.g., station A) sends a Probe request command and the peer station (e.g., station B) responds with a Probe response command. The Probes are exchanged to ensure that the two stations A and B are within range and successfully communicate on the secondary channel. After successfully exchanging the Probes, the two stations A and B have successfully established a direct link on the selected secondary channel.Step214: The coordinator C assigns schedules (CF periods134) on the secondary channel, as communicated in a beacon frame138. Then, the stations A and B wirelessly exchange directional data via directional beams on the secondary frequency channel as shown by example inFIG. 9, wherein each directional beam comprises a main lobe m and one or more side lobes s.Step216: Upon completion of the directional communication, the stations A and B relinquish the secondary frequency channel, and the coordinator C terminates the direct link.

As such, the coordinator C invokes establishment of a subnet for the stations A and B when the coordinator C determines that a new request for communication between the stations A and B cannot be satisfied on the primary frequency channel. The stations A and B communicate on the subnet (i.e., the direct link) by exchanging directional data therebetween, without needing a third device such as the coordinator.

Referring to the example inFIG. 10, because data exchange on the secondary frequency channel between the stations A and B is directional, another station (e.g., a station X associated with another coordinator, or a station Y wishing to start a new personal area network or piconet), may mistakenly interpret that the secondary frequency channel is free (or available for use). This is because directional beams comprising main lobes m and side lobes s, from the stations A and B are very dynamic. It is possible that at one instant in time, the stations X or Y do not observe/detect directional beam signal energy from main and side lobes of stations A and B, as shown by the perimeters105inFIG. 10reflecting the wireless sensitivity range of the stations X and Y. While stations A and B are exchanging data, stations X or Y may mistakenly interpret the secondary channel to be free for transmission, and interfere with the ongoing transmissions between stations A and B (i.e., causing collisions). However, as shown by example inFIG. 11, some time later, stations X and Y may receive signal energy from the main and/or side lobes of directional beams from stations A and/or B, and therefore, may create interference with the ongoing directional transmission between the stations A and B.

According to the present invention, to reduce such possibility, in one example either of stations A or B can periodically broadcast NULL frames for a fixed duration on the secondary frequency channel, for as long as stations A and B remain active (communicate) on the secondary frequency channel. When peer-to-peer stations A and B with direct link on the secondary channel have no further data to exchange, the stations A and B switch back to communicate on the primary frequency channel, and stop broadcasting NULL frames. At this point the coordinator terminates the subnet, relinquishing the secondary frequency channel.

In another example, the coordinator C on the primary frequency channel transmits duplicates of the primary channel beacon138on the secondary frequency channel138as shown in the example timing diagram ofFIG. 12. When peer-to-peer stations A and B with direct link on the secondary channel have no further data to exchange, the stations A and B switch back to communicate on the primary frequency channel, and the coordinator stops duplicating beacons on the secondary frequency channel. At this point the coordinator terminates the subnet, relinquishing the secondary frequency channel.

Using a subnet access method to provide a direct link between stations on a secondary frequency for peer-to-peer communication according to the present invention, allows more stations to be admitted in an existing wireless network such as a personal area network (PAN). Further, quality of service is improved since without a secondary channel such peer-to-peer transmissions could not occur.

In one example, the system100(FIG. 2) allows uncompressed video transmissions via the secondary frequency channel over a 60 GHz band millimeter-wave (mmwave) technology to support a PHY layer data of 3-4 gigabits per second (Gbps), such as transmitting uncompressed HDTV signals wirelessly. The system100utilizes multiple antennas107for directional transmission beams for transmitting/receiving HD data.

FIG. 13shows an example wireless network400implementing a subnet access process according to an embodiment of the present invention, wherein in one scenario a set-top box (STB)402is transmitting uncompressed HD video (e.g., 1080p) to one or more currently active stations404(e.g., HD TV 1) over a primary channel, while a coordinator406receives a new request for wireless data communication between a pair of requesting stations408and410. The pair of requesting stations408and410can be, e.g., a media server such as a DVD player requesting to record DVD content to a personal video recorder (PVR), or transmit uncompressed HD video (e.g., 1080i) for display on another HD TV 1, HD TV 2.

Considering an 8-bit quantization and 60 frames/second, one second of uncompressed video (1080p RGB format) can be expressed as 60×3×8×1920×1080=2.98 Gbits and one second of uncompressed video (1080i RGB format) can be expressed as 30×3×8×1920×1080=1.492 Gbits. Thus, to support both 1080p and 1080i streams on the primary channel, a wireless link supporting at least 4.478 Gbps is required. Considering a 60 GHz wireless system which supports a PHY rate of 3.8 Gbps, once a 1080p stream is active on a primary frequency channel411between the STB402and the HD TV 1404, there remains insufficient bandwidth on the primary frequency channel411to satisfy the request from the DVD player408to transmit uncompressed HD 1080i video stream to the HD TV 2410.

Based on the subnet access process, the coordinator406establishes a subnet (or a direct link)412on a secondary frequency channel so that the DVD player408can transmit 1080i video stream DVD content to the HD TV 2410on the secondary frequency channel.

Although in the examples herein the secondary channel is an established transmission of video information, the present invention is equally useful in establishing a secondary channel for transmission of information in general (not limited to video information), regardless of whether the primary channel is used for transmission of video or other types of information.

As is known to those skilled in the art, the aforementioned example architectures described above, according to the present invention, can be implemented in many ways, such as program instructions for execution by a processor, as logic circuits, as an application specific integrated circuit, as firmware, etc. The present invention has been described in considerable detail with reference to certain preferred versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.