Wireless device that receives data and scans for another access point

A wireless device comprises a plurality of receivers and logic coupled to the receivers. The logic causes at least one receiver to receive data communications from an access point while at least one other receiver concurrently scans for another access point.

BACKGROUND

Wireless communication devices communicate with network nodes (e.g., access points). A structure such as a building may have multiple network nodes, some of which may be tuned to different carrier frequencies (i.e., channels). A wireless device “associates” with an access point, but, from time to time, may scan for another access point with which improved communication quality is possible (e.g., fewer dropped transmission packets, improved signal-to-noise ratio, etc.). While scanning for a better access point, the wireless device unfortunately does not receive data communications. Further, the scanning process is time-consuming.

NOTATION AND NOMENCLATURE

DETAILED DESCRIPTION

FIG. 1shows a wireless device30in accordance with embodiments of the invention. In some embodiments, wireless device30comprises a portable device such as laptop or hand-held computer, personal data assistant (PDA), etc., while in other embodiments is not portable. Device30comprises a plurality of receiver chains40,42, and44coupled to summation and scan logic62. The summation and scan logic62also couples to host logic70. In embodiments in which the device30comprises a computer, the host logic70comprises any one or more of a processor, memory, an input device (e.g., keyboard, mouse), an output device (e.g., display), etc.

Although three receiver chains40-44are shown in the example ofFIG. 1, any number of receiver chains can be provided. Each receiver chain40-44comprises an antenna and a receiver. Each receive chain receives wireless communications from the access point (FIG. 2) with which the device30is currently associated. Receiver chain40comprises antenna50and receiver56. Receiver chain42comprises antenna52and receiver58, while receiver chain44comprises antenna54and receiver60. The antennas50-54may be included within, or otherwise coupled to, the wireless device30. In general, the antennas50-54are associated with the wireless device30. Communications from the wireless device30to an access point may be transmitted through a transmitter coupled to one or more of the antennas.

The system30implements a multiple input/multiple output (MIMO) communication scheme in which data communications can be received concurrently by the system30via multiple receive chains40-44. A data communication comprises any information received from an access point other than a “beacon.” A beacon comprises a periodic signal transmitted by each access point that wireless devices use to determine with which access point to associate. The received signals from the receive chains are provided to the summation and scan logic62which combines the signals in a suitable manner to provide a signal representative of the multiple received signals to the host logic70.

FIG. 2shows a wireless network comprising multiple access points80,82, and84to which the wireless device30can communicate. The wireless device30generally receives data communications from, and transmits data communications to, one of the access points80-84. The wireless device30thus “associates” itself with one of the access points. As the wireless device30is moved relative to the access points80-84(in the embodiment in which wireless device30is portable), the wireless device30may become closer to another access point and associate with that access point to have higher quality communications (e.g., communications that have fewer errors). In general, the wireless device associates with the access point with which wireless communications are best, or at least better than the current access point.

The summation and scan logic62(FIG. 1) monitors the quality of the communications received from an associated access point and compares the quality level to a threshold to determine if the threshold has been violated. Examples of suitable thresholds comprise a rate of “dropped” packets, signal-to-noise ratio, etc. A dropped packet is a packet transmitted between an access point and a wireless device that is not correctly received and decoded and thus a retry request is issued to the packet sender to have the packet retransmitted. A threshold based on the rate of dropped packets is violated if the rate of dropped packets associated with the wireless device exceeds the threshold. A threshold based on the signal-to-noise ratio is violated if the signal-to-noise ratio associated with the wireless falls below the threshold. If the communication quality violates the threshold, the summation and scan logic62configures a receiver in at least one of the receive chains40-44to perform a scan for another access point. In accordance with embodiments of the invention, the summation and scan logic62thus configures at least one receiver to receive data communications from an access point while at least one other receiver concurrently scans for another access point. By scanning via at least one receive chain and continuing to receive data communications on at least one other receive chain, the device30need not completely cease receiving data communications while scanning. If a better access point is discovered (i.e., one which results in higher communication quality), the summation and scan logic62causes the device30to associate with the newly discovered access point.

In addition to, or instead of, a scan for an access point being triggered by the violation of a communication threshold, a scan may also be triggered by a software event. For example, the user of device30may interact in the device to cause a scan to occur. Further, scanning may occur in accordance with a predetermined schedule, such as once every n units of time (e.g., once every 10 minutes).

Referring toFIG. 3, a method100comprises one or more actions102-108. At the beginning of method100, one or more of the receiver chains40-44have been configured to receive data communications from an associated access point. The summation and scan logic62monitors the received data communications and compares a predetermined communication characteristic to a threshold. The predetermined characteristic comprises any one or more of such exemplary characteristics as the rate of dropped packets, signal-to-noise ratio, etc. The predetermined characteristic may be directly measured or computed. At decision102, the summation and scan logic62determines if the predetermined communication characteristic violates a threshold. For example, the summation and scan logic62determines whether the rate of dropped packets exceed a related threshold or whether a signal-to-noise ratio falls below a related threshold.

If the predetermined characteristic violates a threshold, the summation and scan logic62causes a scan to occur to discover a new access point that provides for better communications, for example, communications whose communication characteristic does not violate the threshold. In accordance with embodiments of the invention, at least one of the receive chains40-44are configured by the summation and scan logic62to scan for another access point with which to the wireless device30should associate. Thus, while at least one receive chain40-44continues receiving data communications, at least one other receive chain40-44is used to scan for another access point. In embodiments in which only two receive chains are provided, one receive chain is thus used to receive data communications while the other receive chain is used to scan for another access point. In embodiments having three or more receive chains, at least one receive chain can be used to scan for an access point while at least one other receive chain concurrently receives data communications. If two or more receive chains are used to scan, then each receive chain can scan for a different predetermined set of communication channels while another receive chain is used to scan on another set of channels. The summation and scan logic62processes information from the scanning receive chains to determine with which, if any, access point the wireless device should now associate. Accordingly, all of the communication channels are scanned in less time than a single receive chain would have taken to scan all of the channels.

In accordance with various embodiments of the invention, each access point80-84transmits a beacon with a predetermined period. For example, an access point may transmit a beacon once every 100 milliseconds (ms). Accordingly, when scanning, a receive chain40-44tunes itself sequentially to each of the possible channels to which an access point may be tuned. The receive chain is tuned to each channel for a period of time that is greater than the beacon period. In an exemplary embodiment, if an access point transmits a beacon once every 100 ms, the receive chain in the wireless device30tunes itself to each channel for a duration of approximately 200 ms per channel to ensure sufficient time to receive a beacon.

In other embodiments, all receive chains can be used to scan for another access point. If the device30was already associated with an access point and was receiving data communications, data communications cease to be received by the wireless device during the scan, but scanning for a new access point is expedited as multiple receive chains40-44are used to concurrently seek out a new access point. If the device30was not currently associated with an access point (e.g., the device30was just initialized or was outside the coverage area of any access points), multiple (e.g., all) of the receive chains can be used to scan for an access point faster than if fewer (e.g., one) receive chains were used, for the scan.

Referring still toFIG. 3, if the summation and scan logic62discovers a more suitable access point (action106), then at108the wireless device30discontinues its association with its current access point and establishes an association with the newly discovered access point.

Various embodiments discussed above disclose each receive chain comprising a receiver and an antenna in a MIMO configuration. Other embodiments of the wireless device30comprise the device30having a receive chain that receives data communications from an access point and having at least one other receive chain that, while not necessarily used to receive data communications, can be used to perform a scan. Thus, when a scan is performed, the receive chain used for data communications and at least one other non-data communication receive chain are used to perform the scan. In effect, such a wireless device comprises a dedicated scan receive chain.

FIG. 4shows another embodiment of a wireless device120. Device120comprise an antenna122, a switch124(or duplexer), transmitter126, an amplifier128, a power splitter130, a plurality of receivers132(RCVR1, RCVR2, . . . RCVRn), base-band processing and scan logic134and host70. Through the base-band processing and scan logic134, the host70sends data to the transmitter126to be transmitted from the device30by the antenna122. The switch124is controlled by the base-band processing and scan logic134to provide transmissions from the transmitter126to the antenna122or to provide in-coming transmissions from the antenna122to the amplifier128. The amplifier128may be implemented as any suitable low-noise amplifier.

In the embodiment ofFIG. 4, power splitter130receives amplified signals from the amplifier128and splits the signal among the various receivers132. Each receiver132can be tuned to a different channel during a scan operation. Thus, in the embodiment ofFIG. 4, multiple receivers132are used with a single antenna122to perform a scan. If desired, at least one receiver132can be allowed to continue receiving data communications while at least one other receiver is used in the scan operation. Although the embodiment ofFIG. 4shows one antenna122being used by multiple receivers132, in other embodiments, multiple antennas can be used by multiple receivers132, with one antenna per receiver or fewer antennas than receivers. When not performing an access point scan, one or more of the receivers132are used to receive data communications.