Method and system for device discovery in a wireless video area network

A method and system for device discovery in a wireless network is provided. The device discovery involves directionally transmitting a data unit from a transmitting station over a channel in different directions to emulate omni-directional transmission, receiving the data unit transmissions from different directions at a receiving station, determining the quality of the transmissions received from the different directions, and detecting location information for the transmitting station relative to the receiving station based on the highest quality transmission among the transmissions received from the different directions. Further, if a channel has sufficient bandwidth to satisfy direct link communication between two stations, then during a direct link set-up stage, the two stations conduct a probing message exchange using omni-direction transmission, and upon successful probing, obtain communication link status information and set proper communication configurations for the two stations based on the communication link status information.

FIELD OF THE INVENTION

The present invention relates to device discovery in networks, and in particular to device discovery for a wireless video area network (WVAN).

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 which can require multiple gigabit per second (Gbps) in bandwidth for transmission. As such, when transmitting such HD video between devices, conventional transmission approaches compress the HD video to a fraction of its size to lower the required transmission bandwidth. The compressed video is then decompressed for consumption. However, with each compression and subsequent decompression of the video data, some data 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 video signals.

The OSI standard provides a seven-layered hierarchy between an end user and a physical device through which different systems can communicate. Each layer is responsible for different tasks, and the OSI standard specifies the interaction between layers, as well as between devices complying with the standard. The OSI standard includes a physical layer, a data link layer, a network layer, a transport layer, a session layer, a presentation layer and an application layer. The IEEE 802 standard provides a three-layered architecture for local networks that approximate the physical layer and the data link layer of the OSI standard. The three-layered architecture in the IEEE 802 standard 200 includes a physical (PHY) layer, a media access control (MAC) layer, and a logical link control (LLC) layer. The PHY layer operates as that in the OSI standard. The MAC and LLC layers share the functions of the data link layer in the OSI standard. The LLC layer places data into frames that can be communicated at the PHY layer, and the MAC layer manages communication over the data link, sending data frames and receiving acknowledgement (ACK) frames. Together the MAC and LLC layers are responsible for error checking as well as retransmission of frames that are not received and acknowledged.

Wireless personal area networks (WPANs) as defined by the IEEE 802 standard and similar technologies can suffer interference issues when several devices are connected which do not have enough bandwidth to carry the uncompressed HD signal, and do not provide an air interface to transmit uncompressed video over a 60 GHz band. The IEEE 802.15.3 specifies channel access methods for transmission of audio/visual information over WPANs. However, in IEEE 802.15.3, channel access control is complicated and is only for access to a single channel. It does not allow efficient device discovery in a wireless network, nor establishing direct communication link based on device discovery.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method and system for device discovery in a wireless network. In one embodiment, device discovery involves directionally transmitting a data unit from a transmitting station over a channel in different directions to emulate omni-directional transmission, receiving the data unit transmissions from different directions at a receiving station, determining the quality of the transmissions received from the different directions, and detecting location information for the transmitting station relative to the receiving station, based on the highest quality transmission among the transmissions received from the different directions.

In another embodiment, the present invention provides a direct link wireless data communication process, which includes: receiving a request for wireless communication between two wireless stations over a wireless channel; determining if the channel has sufficient bandwidth to satisfy the communication request; if the channel has sufficient bandwidth to satisfy the communication request, establishing a direct communication link between the two stations over the channel. The step of establishing the direct communication link, including the steps of: during a direct link set-up stage, the two stations conduct a probing message exchange using omni-direction transmission; and upon successful probing, obtaining communication link status information and setting proper communication configurations for the two stations based on the communication link status information.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and system for device discovery in a wireless video area network (WVAN) such as a wireless high definition (WiHD) WVAN including wireless devices. For device discovery, the same data is directionally transmitted by a transmitter over a channel in different directions to emulate omni-directional transmission. One or more receivers utilize the quality of the signal received from those different directions to detect the location of the transmitter. The receivers obtain the location information and update their location information by analyzing periodically received beacons. The location information can be used for direct link support and reduction of the PHY preamble length in the PHY header and the PHY payload size.

FIG. 1shows a functional block diagram of a wireless network10that includes wireless communication stations12and14implementing uncompressed HD video communication, according to an embodiment of the present invention. The wireless communication stations12comprise a coordinator12such as a WiHD coordinator. The wireless communication devices14include devices4(e.g., Dev-1, . . . , Dev-n). The coordinator12and the devices14utilize a low-rate (LR) channel16(shown by dashed lines inFIG. 1) and a high-rate (HR) channel18(shown by heavy solid lines inFIG. 1) for communication therebetween.

In this embodiment, the coordinator12is a sink of video and/or audio data implemented, for example, in a HDTV set in a home wireless network environment which is a type of WLAN. Each device14comprises a device that can be the source of uncompressed video or audio. Examples of each device14can be a set-top box, a DVD player, etc. A device14can also be an audio sink. In another example, the coordinator12can be a source of a video stream. In yet another example, the coordinator provides channel coordination functions for wireless communication between a sink station and a source station. The coordinator functions such as channel access functions, according to the present invention can also be implemented in a stand-alone device, in a sink device and/or in a source device. A device can be the source of uncompressed video or audio like set-top box or DVD player. A device can also be an audio sink.

In order to establish a WVAN for communication, available channel frequencies are scanned to determine available channels (i.e., not in use by neighboring networks). All LR channels are scanned to find channels with minimal interference with other networks. Then, the frequency band of the HR channels is scanned for interference, and a channel with minimal interference is selected.

A total of j channels in the frequency range of 57-66 GHz are defined by a High-Rate Plan (HRP) for the HR frequency. Due to regulatory restrictions, not all of these channels are available in all geographic regions. For example, when j=4, four channels are indexed by a HRP channel index. These HRP frequency channels are defined by example in Table 1 below.

Each HRP channel has a start frequency, a center frequency and a stop frequency. The start and stop frequencies define a HRP frequency channel.

A Low-Rate-PHY frequency Plan for the LRP uses the same frequency bands as the HRP, wherein within each of the HRP channels, a number k of LRP channels are defined. In this example, for k=3, three LR channels are defined for each of the four HRP bands. Only one LRP channel is used by a WVAN at a time. This allows multiple WVANs to use the same HRP frequency channel in close proximity, while minimizing channel interference. Each LRP channel is defined relative to the center frequency of the corresponding HRP channel, fc(HRP). As such, within each of the HRP channels, three LRP channels are defined near the center frequency of the HRP channel. The LRP frequency channels, indexed by a LRP channel index, are defined by example in Table 2 below.

Each LRP channel has a start frequency, a center frequency and a stop frequency. The start and stop frequencies define a LRP frequency channel. In this example, each LRP frequency band is an 80 MHz band, the LRP channels are separated by 120 MHz bands, and the center frequencies of the LRP channels are separated by 200 MHz bands.

The LRP channel implements orthogonal frequency division multiplexing (OFDM) and offers both omni-directional and beam-steered (i.e., directional) modes. Directional transmission in different directions according to the present invention comprises beam steered transmission in different directions. The transmission data rates for the LRP range from 2.5 Mb/s to 10 Mb/s for the omni-directional mode and 20 Mb/s to 40 Mb/s for the beam-steered mode. Channel coding includes ⅓, ½ and ⅔ convolutional coding. For the omni-directional mode, coding includes 4-times (i.e., 4×) or 8-times (i.e., 8×) replication coding, while for the beam-steered mode there is no replication. A summary of the LRP modes is provided by example in Table 3 below in indexed form.

The LRP modes are utilized in a device discovery process which involves a station location map set-up procedure, a location information update procedure and a location and distance information query procedure, as described below. The device location information can then be utilized for direct link transmission, frame preamble and payload size reduction for unicast transmissions, and LRP preamble and payload size reduction for multicast transmissions, as described further below.

FIG. 2shows an example process17for device discovery according to the present invention, including the steps of: directionally transmitting a data unit over a channel in different directions from a transmitting station in the network to emulate omni-directional transmission (step19); receiving the data unit transmissions from the different directions at a receiving station in the network (step21); determining the quality and parameters of the transmissions received from the different directions (step23); and determining location information for the transmitting station relative to the receiving station based on the highest quality received transmission among the received transmissions received from the different directions (step25). The above steps are described in more detail below.

Device Discovery

Location Map Set-Up

In omni-directional emulation mode, the same information is retransmitted (repeated) in N different directions on the LRP channel by beamforming to emulate omni-directional transmission, according to the present invention.

During an association stage wherein the stations are associated for communication, MAC frames are exchanged in omni-directional emulation mode between stations. For example, as shown inFIG. 3, in the LRP modes1through3, a data unit (e.g., a frame or packet) is transmitted from a transmitting station at a location13to N=8 different directions15(e.g., direction sections1,2, . . . ,8, each covering a 45 degree angle) to emulate omni-directional transmission. When a frame is received, a receiving station can measure and compare the signal quality (and other parameters) of the received frame, with that of other copies of the frame received from the transmitting station in other directions. Then, based on such measurement and comparison, the receiving station determines the direction of the transmitting station relative to the receiving station, as location information. The direction of the transmitting station is one of the sections15inFIG. 3(or section boundary) along which the highest quality transmission of the frame from the transmitting station was measured. The receiving station maintains the location information for each associated station. Further, each associated station also maintains location information for itself and other stations identified in broadcast beacons.

For example, in an association the coordinator12is associated with a device14for communication, wherein MAC frames are exchanged in omni-directional emulation mode between the coordinator12and the device14. When a frame is received, the coordinator12or the device14can measure and compare the signal quality (and other parameters) of the frame, with that of other copies of the frame from other directions. Then, based on such measurement and comparison, the coordinator12or device14determines the direction of the device14relative to the coordinator12, as location information. The direction of the device14is along a section inFIG. 3(or section boundary) along which the highest receive signal level was measured. The coordinator12maintains the location information for each associated device in a device list. Further, each associated device14also maintains the location information for itself and other devices14identified in broadcast beacons.

The term “location” as used herein is an abstract concept related to geographic location, but not exactly equal to geographic location. Usually geographically proximate stations are close to each other in location, however, there can be exceptions due to environmental and channel conditions. The location information can be represented as a location map comprising a location vector. For N directional retransmissions (i.e., Nx or N repetitions) of a data unit in a LRP mode along N corresponding directions, the location vector includes N elements. Each element describes the signal quality or other parameters of the data transmission for one of the N directions.

Location Information Update

In one implementation, the coordinator12periodically transmits a data unit comprising a beacon frame in omni-directional emulation mode, wherein N copies of the beacon frame are directionally transmitted in N different directions, as described. When receiving a beacon frame from the coordinator12, a receiving device14measures and compares the signal quality (and other parameters) for copies of the beacon frame received from the coordinator12in different directions. The receiving device14utilizes comparison of such signal quality and parameters to determine a new location vector for the coordinator12. Then a “distance” between the new location vector and the existing location vector (e.g., in a device list) is determined. The term “distance” as used herein is an abstract concept, related to geographic distance but not exactly equal to geographic distance.

If the distance is larger than a pre-defined threshold, then the device14attempts to send a location updating control frame to the coordinator12within an un-reserved channel time block (FIGS. 5A-B, described further below). An optional acknowledgement (ACK) can be sent back from the coordinator12to announce the successful reception of the location updating control frame. The coordinator12updates the location information for the device12stored in its device list. Optionally, the coordinator12announces the new (updated) location information for the device14in a next beacon transmission from the coordinator12.

Location and Distance Information Query

For direct link transmission between the devices14, a first device14may require location information for one or more other devices in the network and also the corresponding distance information. The coordinator12maintains the location information for the devices14relative to the coordinator12. The first device14sends a location query request control frame for location information of one or more devices14to the coordinator12(e.g., transmitted within an un-reserved channel time block). An optional ACK can be sent back from the coordinator12to announce the successful reception of the location query request control frame. The coordinator12then responds to the device14with a location query response command frame which provides location information including distance information for one or more devices in the network. The first device then determines location information of a second device relative to the first device using the location information of the first device relative to the coordinator and the location information of the second device relative to the coordinator.

An example inFIG. 4shows a device14designated as Device A, another device14designated as Device B and the coordinator12. Device A knows its location vector VCAin relation to the coordinator12, and Device B knows its location vector VCBin relation to the coordinator12. Device A requires location information for Device B. Device A obtains the location information of Device B (i.e., VCB), from the coordinator12by location query signaling, as described. Then, Device A estimates the distance information from Device A to Device B as VAB=VCA−VCB, where “−” is a type of vector subtraction operation. Alternatively, the coordinator12can calculate VABdirectly and send it to Device A directly. Due to influence of environmental and channel conditions, the actual distance from Device A to Device B can be different from VAB. However, usually VABis a good estimate of the actual distance between Device A and Device B.

Device discovery and location detection according to the present invention does not require additional signaling or signaling modules other than the coordinator12and devices14themselves. Further, using the location and distance information for the devices, the PHY preamble overhead in the PHY headers, and PHY payload size are reduced. Thus, the overall throughput of WiHD network is improved.

Channel Access Control

The coordinator12uses a LR channel16and a HR channel18, for communication of video information with the devices14. Each device14uses the LR channel16for communications with other devices14. The HR channel18only supports single direction unicast transmission with, e.g., multi-Gb/s bandwidth to support uncompressed HD video transmission. The LR channel16can support bi-directional transmission, e.g., with at most 40 Mbps throughput. The LR channel16is mainly used to transmit control frames such as acknowledgement (ACK) frames. Some low-rate data such as audio and compressed video can be transmitted on the LR channel between two devices14directly.

The HR channel only supports single direction unicast transmission with multi-Gb/s bandwidth to support uncompressed HD video. The LR channel can support bi-directional transmission with at most 40 Mbps throughput. A low-rate channel is mainly used to transmit control frames such as ACK frames. It is also possible some low-rate data like audio and compressed video can be transmitted on the low-rate channel between two devices directly.

As shown by the example timing diagram inFIG. 5, TDD scheduling is applied to the LR and HR channels16and18, whereby at any one time the LR and HR channels16and18, cannot be used in parallel for transmission. In the example ofFIG. 6, beacon and ACK packets/frames are transmitted over the LR channel16in between transmission of packets of data (e.g., video, audio and control message) information over the HR channel18. Beamforming technology can be used in both the LR and HR channels. The LR channel can also support omni-direction transmissions. The HR channel and the LR channel are logical channels.

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 MAC layer and a 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 (including a 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.

There are two approaches for a wireless station (STA) to access a shared wireless communication channel. One approach is a contention-free arbitration (CF) method, and the other is a contention based arbitration (CB) method. There are multiple channel access methods for a CF period. For example, a point coordinator function (PCF) can be utilized to control access to the channel. When a PCF is established, the PCF polls registered STAs for communications and provides channel access to the STAs based upon polling results. The CB access method utilizes a random back-off period to provide fairness in accessing the channel. In the CB period, a STA monitors the channel, and if the channel has been silent for a pre-defined period of time, the STA waits a certain period of time, such that if the channel remains silent, the STA transmits on the channel.

The coordinator and the non-coordinator devices share the same bandwidth, wherein the coordinator coordinates the sharing of that bandwidth. Standards have been developed to establish protocols for sharing bandwidth in a wireless personal area network (WPAN) setting. As noted, the IEEE standard 802.15.3 provides a specification for the PHY layer and the MAC layer in such a setting where bandwidth is shared using a form of time division multiple access (TDMA). According to the present invention, the MAC layer defines a superframe structure, described below, through which the sharing of the bandwidth by the non-coordinator devices14is managed by the coordinator12and/or the non-coordinator devices14.

According to the present invention, in a contention-free period, instead of PCF polls, time scheduling is utilized wherein beacons provide information about scheduled channel time blocks for devices. A superframe-based channel access control for transmission of uncompressed video over wireless channels, according to the present invention, is applied based on a superframe structure shown by example inFIGS. 6A-B.FIG. 6Ashows a sequence of superframes20, andFIG. 6Bshows the details of a superframe20for the LR and HR channels including multiple schedules30. Each schedule30includes one or more periodical reserved channel time blocks (CTBs)32which are reserved for transmission of isochronous data streams. Each schedule30includes multiple reserved CTBs32, wherein duration of a schedule is divided between multiple CTBs32. Each reserved CTB32is allocated to a portion of the corresponding schedule, wherein T1indicates the time period between the start of each Schedule1 interval, and T2indicates the time period between the start of each Schedule2 interval.

The schedules30represent reserved CTBs32, and the time periods between the schedules30are unreserved CTBs. As such, each superframe20includes two CTB categories: reserved CTBs32and unreserved CTBs37. Such a superframe20is useful for channel access control using CTBs for transmission of uncompressed video over wireless channels (e.g., the HR channel18and the LR channel16). Beacons are used to separate channel time into multiple superframes. In each superframe there are contention periods and contention-free periods. In each CFP there are one or more schedules. A superframe includes a contention-based control period (CBCP), a CFP including multiple reserved channel time blocks (RCTBs) and/or unreserved channel time blocks (UCTBs). Specifically, the superframe20includes:1. A beacon frame (“beacon”)22which is used to set timing allocations and to communicate management information for the network10(e.g., WiHD sub-net). It is assumed that beacon signals are always transmitted omni-directionally.2. A CBCP24is used to communicate Consumer Electronic Commands (CECs) and MAC control and management commands on the LR channel16. No information can be transmitted on the HR channel18within the CBCP period. There can also be a beam-search period (BSP) between the CBCP24and the CFP28to search transmission beams and to adjust beamforming parameters (e.g., every 1˜2 seconds a BSP can appear in the corresponding superframe20).3. The CFP28which includes said CTBs comprising one or more reserved CTBs32and one or more unreserved CTBs37.

The reserved CTBs32are reserved by one or multiple devices14for transmission of commands, isochronous streams and asynchronous data connections. The reserved CTBs32are used to transmit commands, isochronous streams and asynchronous data connections. Each reserved CTB32can be used for transmitting a single data frame or multiple data frames. The schedules30organize the reserved CTBs32. In each superframe20, a schedule30can have one reserved CTB32(e.g., for pre-scheduled beam-searching or bandwidth reservation signaling) or multiple periodical reserved CTBs32(e.g., for an isochronous stream). Unreserved CTBs37are typically used to transmit CECs (and MAC control and management commands on the LR channel. No beamforming transmission is allowed within the unreserved CTBs. Unreserved CTBs37can also be used for transmission of control and management packets between devices14if direct link support (DLS) is allowed. During an unreserved CTB37, only the LR channel, operating in an omni-direction mode, can be utilized. No information can be transmitted on the HR channel during an unreserved CTB37. Different contention-based medium access mechanisms, such as a carrier sense multiple access (CSMA) scheme or a slotted Aloha scheme can be used during an unreserved CTB37.

A beacon22is transmitted periodically to identify the start of every superframe20. Configuration of the superframe20and other parameters are included in the beacon22. For example, the beacon22indicates the start time and length of the periods CBCP24and the CFP28. In addition, the beacon22dictates allocation of the CTBs in the CFP28to different devices14and streams. Since devices can implicitly know the timing information of unreserved CTBs, a beacon frame need not carry timing information for unreserved CTBs.

For reservation-based time allocation, data transmissions using beamforming must be reserved in advance. A device14requests send-bandwidth from the coordinator12for the transmission of both isochronous streams and asynchronous data. If there is enough bandwidth, the coordinator12allocates a schedule for the requesting device. Each schedule includes a series of evenly distributed reserved CTBs32having equal durations. A schedule can include multiple reserved CTBs32, or one reserved CTB32in a superframe20, or one reserved CTB32in every N superframes20. Usually an isochronous stream is transmitted within one schedule for each superframe20. However, it is also possible to allocate multiple schedules for one isochronous or asynchronous stream. Multiple streams belonging to the same device can also be transmitted within one schedule. Each data packet31transmitted from a device to a destination has a corresponding ACK packet33sent back from that destination, wherein each data packet31and corresponding ACK packet33form a data-ACK pair. A CTB32can include a single data-ACK pair or multiple data-ACK pairs.

A schedule can be reserved for periodic beam-searching in which one reserved CTB32appears every 1˜2 seconds. Periodic beam-searching can also be performed within unreserved CTBs. In addition to periodic beam-searching, event-driven beam-searching (i.e., dynamic beam-searching) can be triggered by factors such as bad channel status. If event-driven beam-searching is to be implemented without affecting other reserved schedules, the length of any reserved CTB for a schedule (Treserved—CTB) plus the length of unreserved CTBs immediately after the reserved CTB (Tun—reserved—CTB) should not be less than the length of a beam-searching period Tbeam-searching(e.g., 400 μs as default). As such, Treserved—CTB+Tun—reserved—CTB≧Tbeam-searching.

Utilization of Device Location Information for Communication Using a Superframe

As noted, the device location information can be utilized for direct link transmission, frame preamble and payload size reduction for unicast transmissions, and LRP preamble and payload size reduction for multicast transmissions, as described below.

Direct Link Transmission

A device14in the WVAN can communicate with another device14using direct link transmission, according to the present invention. During a direct link set-up stage, the two devices14conduct a probing message exchange using a LRP mode omni-direction transmission to ensure that the two devices14can receive signals from each other successfully. After a successful probing, indicating that the two devices14can receive signals from each other successfully, a link assessment/recommendation or beam-searching/steering process can be conducted to obtain accurate communication link status information, and to set proper transmission/receiving configurations for the two devices.

FIG. 7shows an example management entity (ME)40for implementing such direct link transmission, wherein the ME40includes a MAC layer management entity (MLME) function48for managing MAC layer operations and a device management entity (DME) function46for establishing a channel and controlling channel access. The DME function46and the MLME function48can be implemented in the same device or on difference devices. Further, the coordinator12and each of the devices14can include a ME40. The ME40further provides monitoring and control functions to a MAC layer42and a PHY layer44, and facilitates communication between the upper layers45and the MAC layer42. The MLME messages below are defined by the IEEE 802.15.3 standard (“Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for High Rate Wireless Personal Areas Networks (WPANs),” 2003). The operations of the DME and MLME functions in response to the MLME messages are according to the present invention, as described below by example in relation toFIG. 8.

FIG. 8shows an example process50for direct link communication between two devices14such as a device n (Dev-n) and a device m (Dev-m). When the Dev-n desires to set-up a direct link transmission with the Dev-m, in step52the Dev-n sends a bandwidth reservation request command (indicating the amount of bandwidth requested) to the coordinator12within an unreserved CTB. In step54the coordinator12checks the available channel bandwidth and also the availability of the Dev-m, and in step56the coordinator12sends back a bandwidth response command to the Dev-n. Specifically, in step56if the available bandwidth is sufficient to satisfy the request, and the Dev-m is available, the coordinator12reserves CTBs for the requested bandwidth and responds to the Dev-n with a bandwidth response command that grants the bandwidth reservation request; otherwise, the coordinator12responds with a bandwidth response command that rejects the bandwidth reservation request.

After obtaining the reserved bandwidth, during a reserved CTB for direct link transmission, in step58the Dev-n probes the Dev-m by sending a direct link transmission (DLT) probe request command frame as a MAC command in omni-directional emulation mode in a LRP, and waits for a DLT probe response from the Dev-m. Upon successful reception of the DLT probe request frame, in step60the Dev-m measures and compares the signal quality and other parameters of repetition copies of the DLT probe request frame received in different directions from the Dev-n, and determines the direction of the Dev-n relative to Dev-m. Then, in step62the Dev-m sends back a DLT probe response command with channel coefficients information to the Dev-n. If the Dev-n cannot obtain a DLT probe response command after a waiting period (e.g., mDLTProbeWaitTime), the Dev-n may then repeatedly send the DLT probe request command a number of times (e.g., mMaxDLTProbing times).

Upon receiving a DLT probe response command from the Dev-m, a DLT probe request/response exchange may be repeated between the Dev-n and Dev-m up to a threshold (e.g., mMaxDLTProbingNum times). After the probing procedure, if probing of the Dev-m by the Dev-n in omni-directional mode at the LRP is successful, then in step64, the MAC layer of the Dev-n reports a successful DLT set-up to the DME with a MLME-DLS.cfm primitive message; otherwise, the Dev-n sends a bandwidth request command to the coordinator12to release the reserved CTBs and reports a DLT set-up failure to the DME with a MLME-DLS.cfm primitive message in step64.

Then in step66, a link assessment/recommendation or beam-searching/steering in directional mode at the HRP or LRP may be conducted to obtain accurate link status information in directional mode and set proper transmission/reception configurations before starting transmission of audio/video or data streams over the channels. Then, in step68, communication of audio/video/data streams in the reserved CTBs between the Dev-n and Dev-m commences.

LRP Preamble and Payload Size Reduction for Unicast Transmission

A device14knows its location relative to the coordinator12by receiving beacons periodically transmitted from the coordinator12. Based on such location information, the device14only needs to send a PHY preamble and PHY payload at the directions with good signal quality. Thus the device14can reduce the size of the PHY preamble and payload in the MAC frames it transmits to the coordinator12. Specifically, the device14can reduce the size of the PHY preamble and PHY payload from N-times (i.e., Nx) to M-times (i.e., Mx) wherein N≧M, according to the location vector of device14and without requiring accurate beam-searching, provided that all devices14are within M direction sections (FIG. 3) of the coordinator12. Similarly, if the coordinator12only wants to transmit a MAC frame to one device14, the coordinator12can reduce the size of the PHY preamble and the payload in the MAC frames it transmits to the device14from Nx to Mx (wherein N≧M) according to the location vector of the coordinator12, without requiring accurate beam-searching since the coordinator12can obtain location updates from the device14.

LRP Preamble and Payload Size Reduction for Omni-Direction Multicast Transmission

When the coordinator12is a multicast source in a multicast group, since the coordinator12knows the locations of all destination devices14in the multicast group, the coordinator12can reduce the PHY preamble and payload size in its multicast MAC frames from Nx to Mx (N≧M), provided that all destination devices14are within M direction sections (FIG. 3) of the coordinator12.

When a device14is a multicast source in a multicast group, the device14can obtain the locations of all devices in the multicast group using location query exchanges, and then calculate the location vectors of all other devices in relation to the multicast source. Then, the device14can reduce the size of the PHY preamble and payload in its multicast MAC frames from Nx to Mx (N≧M), provided all destination devices are within M direction sections (FIG. 3) of the multicast source device14.

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.