Abstract:
In directional antennas, spatial reuse involves enabling two communications to occur on the same link at the same time. The communications may be in the same or opposite directions. If no link of sufficient bandwidth is available that does not already have an active communication, a link with an active communication of sufficient bandwidth is located. Then an antenna training sequence may be implemented. A check determines whether the antenna training sequence was successful. If there was interference during the antenna training sequence, then the spatial reuse is not permitted. Otherwise, spatial reuse may be permitted.

Description:
RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/035,480, filed Mar. 11, 2008 and is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     This relates generally to directional antennas that radiate radio waves more effectively in some directions than in other directions. 
     Spatial reuse allows two or more communication links to simultaneously operate over the same channel within the same neighborhood. Generally, efficient spatial reuse is only possible with directional, as opposed to omnidirectional, antennas. Thus, two spaced devices may communicate in forward and reverse directions over the same channel, at the same time, within the same radio coverage range. 
     One application for direction antenna systems is in connection with wireless personal area networks (WPANs). A WPAN is a network for interconnecting devices centered around an individual person&#39;s work space in which the connections are wireless. For example, a WPAN may interconnect ordinary computing and communicating devices that many people have at their work place or it might serve a more specialized purpose, allowing a number of team members to communicate during a work task. 
     In some embodiments, the spatial reuse may be integrated with the antenna training stream for high performance. It may be used in both intra and inter piconet spatial reuse. The spatial reuse is triggered upon establishment of a new link and, therefore, it may be called a reactive or on demand system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction of a wireless network according to one embodiment; 
         FIGS. 2A-D  are communication sequences according to one embodiment; and 
         FIG. 3  is a flow chart for one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a wireless network, such as a piconet, may include at least three devices, including the device  42 , the device  42   a , and a piconet coordinator (PNC)  45 . In one embodiment, the wireless network is a wireless personal area network. 
     In one example, the n th  superframe used in the network is depicted in  FIG. 2A . On this superframe, the device  42  transmits a bandwidth request packet to the PNC  45  requesting to establish a link with duration T 1  to device  42   a . Since wireless resources are available, the PNC  45  allocates time within the next superframe for the link between devices  42  and  42   a . This allocation of time is announced on the PNC&#39;s beacon in a beacon period (BP) in the next superframe, as shown in  FIG. 2B . The devices  42  and  42   a  can then perform antenna training or beamforming and can proceed with actual data transmissions without any restrictions. 
     Directional high-gain antennas or antenna arrays are often used to support spatial reuse and provide adequate link budget and high data rate transmissions. In addition, many applications operate under potentially non-line-of-sight (NLOS) channels and quick adaptation to changing environments such as moving objects. Hence, an adaptive beamforming and beam-steering protocol may allow radios to establish a high-gain, directional LOS or NLOS beam between the transmitting and receiving stations. This process is referred to as antenna training (or beamforming). 
     Superframes later in the same example, the device  42   b  transmits a bandwidth request packet during a contention access period (CAP) to the PNC  45  to establish a link with device  42   c  for duration T 2 , as also shown in  FIG. 2B . The PNC  45  then determines that the superframe can no longer accommodate all the requested links. At this time, a spatial reuse scheme is triggered. 
     In the spatial reuse scheme, the PNC  45  goes through its current superframe reservations in search of a primary reservation R whose duration T 1  is greater than or equal to T 2  during a channel time allocation period (CTAP). Alternatively, the PNC  45  may combine reservations such that the total time T 1  is greater than or equal to T 2 . 
     The bandwidth request from device  42   b  is denied if the PNC  45  cannot find suitable reservations for this procedure. Otherwise, the PNC  45  creates an opportunistic (or secondary) reservation, as indicated in  FIG. 2C , of duration T 3 , where T 3  is less than or equal to T 2 , which is less than or equal to T 1 , over the primary reservation R. 
     During the time T 3 , the devices  42   b  and  42   c  will initiate antenna training in a sharing or non-sharing mode described later and illustrated in  FIG. 2C . 
     The antenna training can be done in a sharing or non-sharing mode. In a sharing mode, a clear channel assessment (CCA), such as energy or preamble detection, is performed before every transmission of a training sequence through a given direction. If a clear channel assessment is positive, because no signal is detected over a particular direction, a training sequence transmission is carried out normally in that particular direction. 
     Otherwise, if the clear channel assessment is negative because a signal is detected, the training sequence transmission is skipped. By skipping a direction, a node is implicitly disallowing this link to operate over this direction, avoiding interference with other ongoing links. Even when a direction is skipped, the antenna training algorithm compensates by delaying the antenna training process by an amount equivalent to the transmission of the training sequence. As a result, skipping a particular direction becomes transparent to the receiver and to the training algorithm. 
     Of course, it is not only the transmitter node that performs antenna training in sharing and non-sharing modes. The receiver can also perform the same procedure. Antenna training is a process that involves both of the transmitter and receiver of a link. By using both the transmitter and the receiver, the robustness of this reactive spatial reuse scheme may be improved, promoting a higher degree of spatial reusability in some embodiments. 
     The devices  42   b  and  42   d  then initiate antenna training in a sharing mode during the opportunistic reservation shown in  FIG. 2C . Even when the antenna training is done in sharing mode, there is a possibility that the devices  42   b  and  42   c  transmit a training sequence in a particular direction that may interfere with an ongoing transmission. In such case, the PNC  45  can periodically probe the devices participating in the primary reservation (devices  42  and  42   a  in this example) for their link status. This is shown in  FIG. 2D  in connection with superframe n+t. The PNC  45  sends a link status request to the devices  42  and  42   a , which can then each send a link status response as indicated. 
     Alternatively, the devices  42  and  42   a  can send an unsolicited link status response to the PNC  45 . Through this link status notification procedure, the PNC  45  keeps abreast of, say, the packet error rate, signal-to-interference noise ratio (SINR), etc., of the primary reservation and determines whether it will allow an opportunistic reservation to proceed over the next superframe or not. 
     Once the antenna training process of the opportunistic reservation comes to an end, the devices  42   b  and  42   c  inform the PNC  45  whether they were able to successfully beamform, or find a path toward each other, with adequate link quality. Also, the devices  42  and  42   a  can report to the PNC  45  their link status information during the CAP. If the beamforming between the devices  42   b  and  42   c  was successful and the devices  42  and  42   a  were not impacted during the process, the PNC  45  can safely confirm the opportunistic reservation between the devices  42   b  and  42   c  during the primary reservation R between the devices  42  and  42   a , as indicated in  FIG. 2D . Otherwise, if either the beam-forming was not successful or the communication C between the devices  42  and  42   a  was negatively impacted, the PNC  45  revokes the opportunistic reservation for the devices  42   b  and  42   c.    
     Once an opportunistic reservation is confirmed by the PNC  45 , actual data communication between the devices can commence. While both the primary and the opportunistic reservations are active, the PNC  45  can continuously monitor the link status of the primary reservation. Periodic link status updates allow the PNC  45  to determine whether it is safe to allow opportunistic reservations to proceed or not. 
     A reactive scheme can also be applied for spatial use across piconets, even though the scenario described above was for a single piconet. If increased spatial reuse among piconets is desirable, the PNC  45  can always require devices to perform antenna training in a sharing mode. In this way, inter-piconet spatial reuse can also be accomplished in embodiments where CCA is always employed. 
     While the scheme has been described in connection with a centralized medium access control (MAC) architecture, the same principles can be applied in distributed medium access control environments. All that is required is for the devices to perform antenna training in a sharing mode and also to make the link status notifications and beacon frames during the beacon period. 
     Referring to  FIG. 3 , in some embodiments, the reactive spatial reuse may be implemented using hardware, software, or firmware. In cases where the spatial reuse is implemented in software, a computer readable medium may be used to store the software. The computer readable medium may be the storage  46  in  FIG. 1  that may, for example, be a semiconductor memory or an optical or magnetic storage device, to mention a few examples. 
     Referring to  FIG. 3 , initially a check at diamond  10  determines whether there is a reservation request for a time T 2 . If the device  42  needs to establish a new link with a device  42   a , it makes a reservation request to the PNC  45  for the time T 2 . A check at diamond  12  determines if resources are available. If not, a search is implemented for reservations R, with duration T 1  greater than T 2 , as indicated at block  14 . The PNC  45  searches its ongoing reservations in search for reservations R, for which its duration T 1  is greater than or equal to T 2 . Alternatively, the PNC may combine reservations such that the total time T 1  is greater than or equal to T 2 . 
     The reservation request from the device  42  is denied if a reservation is not found and the process is aborted. Otherwise, the PNC  45  creates an opportunistic reservation of duration T 3 , which is less than or equal to T 2  and T 2  is less than or equal to T 1  over reservation R, during which the devices  42  and  42   a  initiate antenna training in sharing mode. 
     Thus, if a successful search results, then the opportunistic reservation of duration T 3  is undertaken, as indicated in block  18 . Next, antenna training occurs, as indicated in block  20 . 
     Thereafter, the devices  42  and  42   a  perform antenna training. In a sharing mode, before a training sequence transmission in a particular direction, a directional clear channel assessment is performed. If the signal is detected, the training sequence transmission is skipped. Otherwise, the training sequence is transmitted in that particular direction. 
     If the training is successful, as determined in diamond  22 , an overlapping reservation is configured in block  26 . Otherwise, the opportunistic reservation is revoked, as indicated in block  24 . 
     In a non-sharing mode, antenna training is carried out without constraints and without using CCA. 
     In the case of an opportunistic reservation, during or at the antenna training, the devices  42  and  42   a  notify the PNC  45  whether or not the antenna training was successful. The source and sink of the primary reservation notify the PNC  45  that they experienced interference. If the training is successful, the PNC  45  can safely confirm the overlapping reservation between the devices  42  and  42   a  during reservation R. Otherwise, the PNC  45  revokes the opportunistic reservation. 
     In the case of the yes prong at the detection of resources at diamond  12 , indicating that resources are available, the PNC  45  makes a primary reservation for the devices  42  and  42   a  to perform antenna training if needed, in either sharing or non-sharing mode. Then the data transmission is continued. 
     Some embodiments may be compliant with the Wireless Personal Area Network Standard IEEE 802.15.3, Telecommunications and Information Exchange between Systems available for IEEE New York, N.Y. 10016. 
     References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application. 
     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.