Patent Application
20050226185
The present invention relates generally to wireless communication systems, and in particular to a method and apparatus for communicating via a wireless local-area network.
Communication devices are currently being developed to take advantage of local access points for placing/receiving calls from near the access point. For example, Motorola Inc. is developing a dual-mode phone that operates using both a wireless local-area network (WLAN) protocol and a cellular protocol (e.g., GSM, CDMA, iDEN, . . . , etc.). During operation, a local access point is utilized for placing/receiving calls within the geographic area of the access point, while a wide-area network (WAN) (preferably a cellular network) is utilized for placing/receiving calls when outside the coverage of the WAN. As is known in the art, communication with an access point takes place utilizing a much lower power level than communication with the WAN. This greatly increases battery life, as well as decreasing overall system interference.
Because communication with a WLAN takes place at such low power, a problem exists in that RF conditions can degrade very rapidly, causing a handover the WAN. For example, local RF conditions change so rapidly (such as a door closing) that the communication device may not be able to communicate via the WLAN, and will be forced to switch to the WAN. As is evident, it would be beneficial for any communication via a WLAN to be able to tolerate temporary degradations in communication without having to de-register with the WLAN. Therefore a need exists for a method and apparatus for communicating via a WLAN that can tolerate temporary degradations in RF conditions.
To address the above-mentioned need a method and apparatus for communicating via a wireless local-area network is provided herein. During operation a device will utilize a wireless local-area network when within the coverage area of the wireless local-area network, and will utilize a wide-area network when outside of the coverage area of the wireless local-area network. The device will also utilize both the local-area, and wide-area networks for soft handoff purposes when both systems are available for communication.
Because communication can take place simultaneously with both the local-area and wide-area networks, a lower overall power can be utilized by the device when compared to the power necessary for sole communication with the wide-area network. In addition, because there exists redundancy in communication links, the local-area network can tolerate larger degradations in RF conditions than prior-art systems. Finally soft handoff avoids potential erasures (voice quality issues) associated with hard handoffs.
The present invention encompasses a method for communicating via a wireless local-area network. The method comprises the steps of receiving data and splitting the data into a plurality of redundant data streams. A first redundant data stream is transmitted to a Wireless Local Area Network (WLAN), while a second redundant data stream is transmitted to a Wide Area Network (WAN).
The present invention additionally encompasses an apparatus comprising a signal splitter receiving data and splitting the data into a plurality of redundant data streams, first transmit circuitry transmitting a first redundant data stream to a Wireless Local-Area Network (WLAN), and second transmit circuitry transmitting a second redundant data stream to a Wide-Area Network (WAN).
The present invention additionally encompasses an apparatus comprising means for receiving a data stream, means for splitting the data stream into a plurality of redundant data streams, means for transmitting a first redundant data stream to a Local-Area Network (LAN) utilizing a first communication system protocol, and means for transmitting a second redundant data stream to a Wide-Area Network (WAN) utilizing a second communication system protocol.
Turning now to the drawings, wherein like numerals designate like components,
During operation, local access point 104 is utilized for placing/receiving calls within the geographic area of the access point (e.g., within building 102), while a wide-area network (e.g., a cellular network) is utilized for placing/receiving calls when outside the coverage of access point 104. As discussed above, because communication with access point 104 takes place at such low power, a problem exists in that RF conditions can degrade very rapidly, causing a handover to base station 107. In order to address this issue, in the preferred embodiment of the present invention device 101 utilizes simultaneous communication (i.e., soft handoff) with both access point 104 and base station 107.
In
Device 101 preferably comprises a dual-mode transceiver that is capable of communication with both WAN 207 and/or WLAN 206 via communication signals 203 and 202, respectively. Similarly, both WAN 207 and WLAN 206 are capable of communicating with device 101 via downlink communication signals 204 and 205, respectively. It should be noted that while device 101 is preferably a dual-mode cellular telephone, one of ordinary skill in the art will recognize that device 101 may comprise other dual-mode devices such as, but not limited to a personal digital assistant (PDA), a personal computer, or any device (voice, data, or video) that can operate in dual mode systems.
During operation device 101 will utilize WLAN 206 when within the coverage area of WLAN 206, and will utilize WAN 207 when outside of the coverage area of WLAN 206. Device 101 will also utilize both WLAN 206 and WAN 207 for soft handoff purposes when both systems are available for communication. When in coverage of WLAN 206, device 101 will access WLAN 206 through any number of access points 111 (only one shown in
Eventually the uplink data transmitted via communication signals 202 and 203 reach selection and distribution unit (SDU) 214 where they are properly combined. Uplink communication signals 202 that are received via access point 104 may be routed to SDU 214 via one of several paths. For example, access point 104 may simply act as a wireless repeater by wirelessly re-broadcasting uplink communication signal 202 (via signal 212) to base station 107. Access point 104 may pass data received via uplink communication signal 202 through enterprise internet 208 to SDU 214 via internet 211. Finally, circuit-switched data may be directed towards SDU 214 by converting uplink communication signal 202 to circuit-switched data and passing the data through Private Branch Exchange (PBX) 209 to Public-Switched Telephone Network (PSTN) 210 and eventually to SDU 214 through MSC 213.
In a similar manner, device 101 may take advantage of soft handoff by simultaneously receiving downlink communication signals via base station 107 and access point 104. During such operation data exits SDU 214 and is directed towards base station 107, and eventually ends up at device 101 via downlink signal 204. Data may reach access point 104 via several signal paths. A first signal path simply exists through base station 107 to access point 104 via communication signal 212. A second signal path exists through internet 211 to access point 104 via intranet 208. Finally SDU may direct data to MSC 213 to PBX 209 through PSTN 210.
Regardless of the technique utilized for uplink and downlink soft handoff, data passing through WLAN 206 may be substantially delayed when compared to data that is transmitted/received through WAN 207. If the delay is too great, device 101 will be unable to use both signals for performing soft handoff. In order to address this issue, time-delay circuitry is utilized to delay all transmissions that are not directed through WLAN 206. By delaying transmissions not directed through WLAN 206, the communication signals entering SDU 214 can be appropriately time-aligned. This is illustrated in
Referring to
Assume “N” is the processing time required to translate data received on path 103 to data transmitted on path 105 and vice versa. Data transmitted over path 103 and 105 will require a longer time (N) to reach its destination when compared to data transmitted over path 106. This time difference must be corrected in order to perform soft handoff between WLAN 206 and WAN 207. “N” is a deterministic fixed delay in each direction. The fixed delay could be hard coded within the WLAN 206 and communicated back to the device 101 via messaging. The fixed delay is easily measured by sending known patterns and taking timing measurements. The WLAN supplier can then have this programmed into the WLAN device.
In the preferred embodiment of the present invention WLAN 206 communicates to both WAN 207 and device 101 the delay (N). Both device 101 and WAN 207 would delay their transmissions over path 106 by N. Thus, if data is available at time X for transmission over path 106, device 101 and WAN 207 will have to delay the transition over path 106 until time X+N. This would be the time when the WLAN 206 would first be able to transmit the data. Thus, WAN 207 and device 101 would receive both signals essentially simultaneously, allowing soft handoff to occur.
As discussed above, the redundant data stream is delayed an amount of time equal to the processing time required to translate, or convert the data received on path 103 to the data transmitted on path 105 and vice versa. Both non-delayed redundant data and delayed redundant data exit SDU 214 where they are transmitted to a WLAN and a WAN, respectively. Non-delayed, and delayed redundant data streams enter access point 104 and base station 107, respectively.
As discussed above, path 105 may comprise one of many paths to access point 104. For simplicity, the various paths available for data exiting SDU 214 are not shown in
As discussed above, because passing data through access point 104 will add appreciable delay to any signal transmitted to device 101, soft handoff may be precluded. However, by delaying any transmission through base station 107, signals 103 and 106 will arrive at device 101 simultaneously, allowing for soft handoff to occur. Additionally, it should be noted that while
While the invention has been particularly shown and described with reference to a particular embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. For example, the above description was given with respect to delaying transmit times for signal paths not utilizing WLAN 206. One of ordinary skill in the art will recognize that the same results may be achieved by delaying the received signals at WAN 207 and device 101. Thus, in an alternate embodiment of the present invention, the transmissions from WAN 207 and device 101 are not delayed. Instead all received signals (not passing through WLAN 206) are delayed at the receiver so that they are received at the same time as signals passing through WLAN 206. Additionally, it is contemplated that the above system will not need to delay data at all when conversion times are adequate. It is intended that such changes come within the scope of the following claims.
