The present invention relates to wireless communication, and in particular to wireless communication by channel reuse.
With the proliferation of wireless communications, many wireless stations are in use in wireless networks. Such wireless stations can communicate over channels in infrastructure mode, ad hoc mode or other modes. In infrastructure mode, a wireless coordinator provides a coordination function by forwarding data and control messages for the wireless stations, enabling the wireless stations to establish connections with each other via communication links through the coordinator. A station can transmit an information request to the coordinator to obtain the information about other stations within a communication system such as a wireless network. Wireless stations can periodically receive control messages such as beacons from the coordinator, wherein the beacons indicate channel reservation and occupation information, allowing the stations to reserve a data channel based on such information.
In ad hoc mode communication, a coordinator is not required. A pair of wireless stations directly establish a connection without association to a coordinator. Establishing such a connection is achieved by signaling to reserve a data channel. Signaling includes communicating control messages, such as control messages, ad hoc beacons, etc. over a default control channel between the pair of stations.
Both in infrastructure mode and ad hoc mode communication, when connections between wireless stations need to be established it is desirable to utilize wireless data channel bandwidth efficiently.
The present invention provides a method and a system for wireless communication between wireless stations by spatial reuse. One embodiment involves establishing wireless communication between a first transmitter and a first receiver on the same wireless data channel used for ongoing transmission between a second transmitter and a second receiver. Establishing wireless communication between the first transmitter and the first receiver includes determining if the second receiver can receive signals from the first transmitter, and determining if the first receiver can receive signals from the second transmitter.
If the second receiver cannot receive signals from the first transmitter, and the first receiver cannot receive signals from the second transmitter, then a new transmission is performed from the first transmitter to the first receiver by spatial reuse of the wireless data channel, wherein both the first transmitter and the second transmitter can concurrently transmit on the data channel. The new transmission on said data channel is at least partially concurrent with said ongoing transmission on said data channel.
These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures.
In the drawings, like references refer to similar elements.
The present invention provides a method and system for wireless communication between wireless stations by spatial reuse. One embodiment involves reusing data channels for at least partially concurrent communications between pairs of wireless stations. A new transmission between a pair of wireless stations utilizes the same data channel used in an ongoing transmission between another pair of wireless stations.
A frame structure may be used for data transmission between wireless stations. Frame aggregation can be used in a Media Access Control (MAC) layer and a physical (PHY) layer. The MAC layer obtains a MAC Service Data Unit (MSDU) and attaches a MAC header thereto, in order to construct a MAC Protocol Data Unit (MPDU), for transmission. The MAC header includes information such as a source address (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.
At higher frequency bands such as 60 GHz there is much more free space loss than at lower frequencies such as 2 GHz or 5 GHz because free space loss increases quadratically with frequency increases. This higher free space loss can be compensated for, using multiple antennas with more pattern directivity, while maintaining small antenna pattern dimensions, known as beamforming. When beamforming is used, antenna obstruction (e.g., by an object) and mis-pointing, may easily cause a substantial drop in received transmission power. This may nullify the advantage of using multiple antennas. Therefore, dynamic beamsearching and beamtracking are used to maintain stable beamforming transmission. Beamtracking involves monitoring the quality of beamformed transmission on a beamforming channel, while beamsearching involves searching for new beamforming coefficients to provide satisfactory channel quality. At higher frequencies such as 60 GHz transmissions, directional antennas can be used, wherein one or more directional antennas at a sender can physically point to a receiver to compensate for higher free space loss. Usually there is no dynamic beamsearching when directional antennas are used.
In the example network 10 shown in
The data channel selection (e.g., determining which 60 GHz data channel to use) for data communication between two stations (wireless devices) is determined by bandwidth reservation signaling on a default control channel (e.g., sending a bandwidth reservation request message and obtaining a bandwidth reservation response indicating if the bandwidth is reserved). Multiple transmissions can share the same data channel at least partially concurrently by using directional transmission to avoid interference.
In one example, in ad hoc mode the involved stations inform each other via direct control messages (or indirectly via a coordinator in infrastructure mode) if transmission from station A to station B does not interfere with transmission from station X to station Y, such that stations X and Y can at least partially concurrently use the same data channel 18 as stations A and B, for at least a portion of the new communication.
As such, steps 21 and 22 involve interference detection. In this example, if station B (first receiver) does not receive signals on channel 16 from station X (second transmitter), and if station Y (second receiver) does not receive signals on channel 16 from station A (first transmitter), then stations X and Y can begin a new communication on the same data channel 18 as the ongoing data communication between stations A and B. In
In this example, the range of HRC transmission matches with the LRC transmission, and the invention allows exploitation of spatial reuse (channel reuse) for HRC communication. As noted, data communication between the stations A and B on an HRC (channel 18) is ongoing. To establish a new connection between stations X and Y for data communication on that same HRC (channel 18), first it is determined if the LRC transmission of station X (i.e., transmission from station X on the LRC (channel 16)) does not spatially overlap with the LRC transmission of station B. This means that while station X is transmitting, station X will not cause interference at station B. Then, it is determined if the LRC transmission of station A does not spatially overlap with the LRC transmission of station Y. This means that while station A is transmitting it will not cause interference at station Y. As such, if LRC transmission from station X does not interfere with LRC transmission at station B, and LRC transmission from station A does not interfere with LRC transmission at station Y, then it is clear that the two HRC transmissions (i.e., A→B and X→Y) will not interfere with each other, and can therefore at least partially concurrently utilize the same HRC (the same data channel 18), according to an implementation of the invention. In this example, it is assumed that the HRC antenna pattern is contained within the LRC antenna pattern. Even though LRC transmissions of stations A and X can spatially overlap with each other, it is safe to have concurrent HRC transmissions A→B and X→Y since transmissions from station A are not received by station Y, and transmissions from station X are not received by station B.
There are multiple options to avoid LRC contention such as transmission from A and X. For example, communications between stations A and B (i.e., A to B and B to A) and communications between stations X and Y (i.e., X to Y and Y to X), can use different LRC channels (the HRC antenna pattern is contained within the LRC antenna pattern). In another example, a contention-based scheme can be used to avoid collisions. Yet in another example, channel time division multiple access (TDMA) or channel reservation schemes can be used to avoid collisions.
While HRC transmissions from station A (first transmitter) to station B (second transmitter) are ongoing, as shown by the example channel access diagram 30 in
Steps 27 and 28 involve interference detection. In this example, before stations X and Y can start reusing the HRC for data transmission, the stations ensure that the ongoing HRC transmission (A→B) and the new HRC transmission (X→Y), will not interfere with each other. If the result is yes (i.e., the ongoing HRC transmission (A→B) and the new HRC transmission (X→Y) will not interfere with each other), then spatial reuse can be used. As such, stations X and Y perform beamforming towards each other and then perform interference detection (steps 27 and 28). As shown by the example channel access diagram 40 in
Once stations X and Y are beamformed towards each other on the HRC channel, during a first testing period 35, station Y listens on the HRC channel to determine if it can receive an HRC transmission from station A. If not, then either station X or station Y can signal stations A and B to also perform the same steps. That is while station X is transmitting to station Y, station A and station B beamform towards each other, and during a second testing period 37 station B checks if it can receive HRC transmissions from station X. If not, then stations X and Y can utilize HRC channel reuse and begin HRC transmissions that are at least partially concurrent HRC transmissions between stations A and B. As long as such concurrent HRC transmissions are active, the two pairs of stations may periodically detect interference from each other and other devices, and each pair can perform beamtracking/beamforming as needed to maintain a good connection. As shown in
The above interference detection steps can also be implemented where a coordinator (e.g., DevN in
Each CTAP 53 includes multiple test periods 54 (e.g., CTAP-1, CTAP-2) for detecting interference. Stations A and B are involved in ongoing data transmission on the HRC and stations X and Y desire to establish a new data transmission on that HRC. Although CTAP is shown being used for testing periods, the CAP may also be used for this purpose. The CTAP-1 period is allocated to transmissions from source station A to destination station B, and includes data transmissions from station A on the HRC channel and acknowledgment from station B. During the CTAP-1 period, stations X and Y detect if they can receive transmissions between station A and station B. Similarly, during the CTAP-2 period, stations X and Y communicate on the HRC channel, and stations A and B detect if they can receive transmissions between station X and station Y. Referring to the process 60 in
Assuming that the HRC antenna pattern is contained within the LRC antenna pattern, in steps 62 and 63 above, test data is first transmitted over the LRC. If both steps result in no detection, then spatial reuse is possible and the test over HRC is skipped. If steps 62 and 63 over LRC result in failure, i.e., spatial reuse is not possible, then steps 62 and 63 are executed over HRC. (Note that in the context of ad hoc mode the test is first performed over LRC (
In this example, station X functions as a transmitter (initiator or sender) and station Y functions as a receiver (responder). The station X includes a PHY layer 76 and a MAC layer 78. The MAC layer 78 implements a communication module 78C, a spatial reuse module 78B and may include a reservation module 78A. The station Y includes a PHY layer 75 and a MAC layer 77. The MAC layer 77 implements a communication module 77C, a spatial reuse module 77B, and may include a reservation module 77A. Each PHY layer 75, 76, may comprise one or multiple antennas.
The communication modules 77C, 78C enable the two stations X and Y to communicate over HRC and LRC channels. The stations X and Y select a data channel HRC from m channels in the, e.g., 60 GHz frequency band. Then, the spatial reuse modules 77B, 78B together implement channel reuse as discussed above (e.g.,
In one example, on each 60 GHz data channel, TDMA is used for different data stream transmissions. In addition, at least partially concurrent channel reuse with directional mode is provided, as described above to provide sufficient bandwidth for new transmissions. As noted, ongoing transmissions are announced by beacons on the control channel at both the sender and the receiver. A beacon can announce a schedule for one stream which can include one or multiple channel time blocks for one stream in between beacons. In each beacon for ad hoc transmission, there is a field which indicates the time left for each channel time reservation. In addition, another beacon field indicates which data channel or control channel the reservation is for. On the control channel, both a reservation-based and a contention-based channel control scheme can be used.
Concurrent, or partially concurrent, data channel reservations are made for communication between a pair of wireless stations. Time schedules are provided by beacons which include information about reserved channel time blocks for data communication. Time periods between the schedules are unreserved channel time blocks. The length of each reserved channel time block is defined in a schedule for a pair of stations. In one example, a beacon can include a bandwidth allocation information element (IE), indicating channel occupation information (e.g., a certain duration of a channel time block is reserved for communication).
The present invention is applicable to high throughput wireless communications, such as ECMA standards on millimeter wave (mm-wave) communication networks, and implementation of Wireless HD standard on uncompressed video transmission. An example implementation for a 60 GHz frequency band wireless network is described below, useful with ECMA and Wireless HD (WiHD) applications. ECMA is an international organization providing ECMA-60 GHz wireless protocol. An example implementation of the present invention for a 60 GHz frequency band wireless network can be useful with Wireless HD (WiHD) applications. Wireless HD is an industry-led effort to define a wireless digital network interface specification for wireless HD digital signal transmission on the 60 GHz frequency band, e.g., for consumer electronics (CE) and other electronic products. An example WiHD network utilizes a 60 GHz-band mmWave technology to support a physical (PHY) layer data transmission rate of multi-Gbps (gigabits per second), and can be used for transmitting uncompressed high definition television (HDTV) signals wirelessly. Another example application is for ECMA 60 GHz wireless radio standard for very high data rate short range communications (ECMA stands for European Computer Manufacturers Association, which provides international standards association for information and communication systems). The present invention is useful with other wireless communication systems as well.
As noted, a control channel (e.g., an out-of-band channel) is used for control message transmissions. This helps reduce collisions and interferences between adjacent transmissions on a data channel (in-band channel), whereby multiple streams can be essentially simultaneously transmitted on the same data channel using a directional transmission scheme. An out-of-band channel is a first physical channel that is out-of-band relative to a second physical channel (i.e., an in-band channel). The out-of-band channel is at a frequency different from an in-band channel. For example, an in-band data transmission channel may operate on a 60 GHz frequency band, whereas, an out-of-band channel may operate on a 5 GHz or 2.4 GHz (or even another 60 GHz) frequency band. Out-of-band frequency means a different frequency than in-band frequency, even if both are in the same frequency band. In an ad hoc mode wireless communication process, each wireless client in a network forwards data for other wireless clients as determined based on the network connectivity, by using control channels for communicating control information messages to facilitate communication on a data channel.
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.
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/881,444, filed on Jan. 19, 2007, incorporated herein by reference.
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