Patent Application
20080161000
The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer program products and, more specifically, relate to techniques for handing off a mobile device from one fixed wireless network node to another.
Various abbreviations that appear in the description are defined as follows:
Handover is a process in which a MS migrates from the air-interface provided by one BS to the air-interface provided by another BS. According to the current IEEE 802.16e 2005 (published in February 2006) standard, the HO process includes the following main steps (reference can also be made to
A. Cell reselection: The MS may use neighbor BS information acquired from a decoded MOB_NBR-ADV (neighbor BS advertisement) message, or may make a request to schedule scanning intervals or sleep-intervals to scan, and possibly range, neighbor BSs for the purpose of evaluating MS interest in handover to potential target BS. The cell reselection process need not occur in conjunction with any specific, contemplated HO decision.
B. HO decision and initiation: A handover begins with a decision for the MS to handover from a serving BS to a target BS. The decision may originate either at the MS or at the serving BS. The HO decision consummates with a notification of the MS intent to handover through a MOB_MSHO-REQ (MS HO request) message (Message 1 in
C. Synchronization to target BS downlink: The MS synchronizes to the DL transmissions of the target BS and obtains DL and UL transmission parameters. If the MS had previously received a MOB_NBR-ADV message that included a target BS ID, physical frequency, downlink channel descriptor (DCD) and uplink channel description (UCD), this process may be shortened. If the target BS had previously received a HO notification from the serving BS over the backbone network, then the target BS may allocate a non-contention-based initial ranging opportunity indicated by UL-MAP.
D. Ranging: The MS and the target BS conduct handover ranging. The purpose of the ranging processing is to obtain adjustment parameters for timing, frequency and power from the target BS.
E. Termination of MS context: the final step in handover. Termination of the MS context is defined as the serving BS termination of all connections belonging to the MS and the context associated with them.
After step D, the MS can set up a connection with the target BS.
A very reasonable requirement for mobile WiMAX is to support the continuity of the connections, especially in the case of a real time application such as VoIP and real-time streaming. In these exemplary cases the HO disruption time should be minimized.
According to the HO procedure as currently specified it is necessary for the MS to receive the subchannel allocation information from the UL-MAP (message 7 in
In an exemplary aspect of the invention there is a method, comprising receiving a mobile station handover request at a target base station, and prior to receiving a handover confirm message at the target base station, sending information descriptive of a mobile station handover resource allocation towards the mobile station.
In an exemplary aspect of the invention there is a method, comprising sending a mobile station handover request to a target base station, and prior to sending a handover confirm message to the target base station, receiving information descriptive of a mobile station handover resource allocation with a handover response message from the target base station.
In another exemplary aspect of the invention, there is a method, comprising sending from a mobile station to a currently serving base station a mobile station handover request, and prior to sending from a mobile station information descriptive of a mobile station handover indication message, receiving information at the mobile station descriptive of a mobile station handover resource allocation.
In another exemplary aspect of the invention, there is a computer program product comprising program instructions embodied on a tangible computer-readable medium, execution of the program instructions resulting in operations comprising receiving a mobile station handover request at a target base station, and prior to receiving a handover confirm message at the target base station, sending information descriptive of a mobile station handover resource allocation towards the mobile station.
In another exemplary aspect of the invention, there is a base station, comprising a receiver, a transmitter, and a processor, wherein when operating as a target base station, the receiver is adapted to receive a signal, wherein said signal comprises a mobile station handover request, the processor is adapted to allocate resources for the mobile station handover in response to the mobile station handover request prior to the receiver receiving a handover confirm message; and the transmitter is adapted to send information descriptive of the mobile station handover resource allocation.
In yet another exemplary aspect of the invention, there is a mobile station, comprising a processor, a transmitter adapted to send a handover request, and a handover indication message; and a receiver adapted to receive information descriptive of a resource allocation of a target base station, where the information is received after sending the handover request and before sending the handover indication message.
The foregoing and other aspects of embodiments of this invention are made more evident in the following Detailed Description, when read in conjunction with the attached Drawing Figures, wherein:
The exemplary embodiments of this invention relate in general to mobility management in a mobile wireless WiMAX communication network. In particular, the exemplary embodiments of this invention provide a technique to achieve fast HO in order to reduce total HO-related data transmission disruption time.
The exemplary embodiments of this invention address and solve the problem of HO latency by introducing an efficient network signaling to achieve faster HO. In greater detail, by providing a protocol for the MS to receive the UL-MAP message much earlier than the conventional case shown in
It should be noted at the outset while the exemplary embodiments of this invention will be described in the context of the mobile wireless WiMAX communication network (i.e., IEEE 802.16e), the exemplary embodiments of this invention are not limited for use only with this particular mobile wireless network type, and may be used in whole or in part and/or adapted for use in whole or in part in other types of mobile wireless networks where a mobile device HO can occur between a serving network node and a target network node.
Before further describing the exemplary embodiments of this invention reference is made to
Shown for completeness in
It can also be noted that the illustrated connection of the data link 13 between the BS 12 and BS 12′ is not intended to indicate a direct connection, and in practice this connection may be made through a network backhaul with one or more interposed network elements.
In general, the various embodiments of the MS 10 can include, but are not limited to, cellular phones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.
The exemplary embodiments of this invention may be implemented by computer software executable by the DP 12A of the BSs 12 and 12′ in cooperation with the DP 10A of the MS 10, or by hardware, or by a combination of software and hardware.
The MEMs 10B, 12B and 14B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The DPs 10A, 12A and 14A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.
The exemplary embodiments of this invention provide efficient techniques for the MS 10 to receive the UL-MAP message soon after it is synchronized to the target BS 12′. Due to the operation of the MOB_NBR-ADV and scanning procedure, the synchronization time with the target BS 12′ can be very short.
For scenarios in which the HO decision is originated from MS 10, two different techniques to provide an early UL-MAP, which includes the Fast_Ranging_IE, are described. A first technique to send the UL-MAP message early (earlier than would be done in accordance with conventional practice).is to set a Timer 12E at the target BS 12′, the timer here is also called as end Timer, in which the Timer 12E is set for the target BS 12′ to begin allocating the unique subchannel and CDMA codes to the MS 10 and send the UL-MAP. A different Timer to release the reserved resource can also be set. Note in
The second technique operates such that, after the serving BS 12 sends back the MOB_BSHO-RSP to the MS 10 (see message 4 in
For the scenarios in which the HO decision is originated from the BS 12 or at some other place in the network 1I in addition to the two techniques above, another technique includes the UL-MAP in a MOB_BSHO-REQ message which is derived from a HO Response from the target BS 12′. At the same time, the serving BS 12 informs the selection result to the target BS 12′ and other neighbor BSs. Therefore, only the target BS 12′ keeps the resource for the MS 10 and all other BSs release the ranging code and ranging subchannel after receiving a HO Cancellation message, thereby conserving radio resources.
Network re-entry begins with the MS 10 detaching from the serving BS 12 and attempting to synchronize with the target BS 12′. The synchronization processing procedure can be made faster if the target BS 12′ parameters obtained from the MS scanning procedure are still valid. Only after receiving the UL-MAP from the target BS 12′ can the MS 10 begin to send the ranging request to the target BS 12′.
In the case of the MS 10 making the decision as to the final target BS 12′, the exemplary embodiments of this invention consider two implementation options in order for the MS 10 to obtain the UL-MAP message as early as possible (described in
It is noted that all other HO-related processing procedures not specifically mentioned in the ensuing descriptions of
Discussed first are those embodiments where the MS 10 makes the decision about the HO target. In
Referring to
As there may be more than one BS 12′ included in the MOB_MSHO-REQ/MOB_BSHO-RSP messages, it is preferred that all of the potential target BSs 12′ run a second Timer #2 to control how long the ranging subchannel and CDMA ranging codes will be allocated for the MS 10. In a case where the target BS 12′ receives the HO Confirm message from the serving BS 12 (message 6), the Timer #2 is stopped automatically. If no HO Confirm message is received from the serving BS 12,.the target BS(s) 12′ (those not selected for the HO to the-MS 10) release the resources allocated for the MS 10 when the Timer #2 expires.
This implementation minimizes any impact due to a long transport latency between BSs in that at least some of the signaling and related operations occur in-parallel E : as opposed to in series as in the case of
It should be noted that the implementation of the first option shown in
In practice the target BS 12′ indicates in the UL-MAP message the position of the Uplink-frame (slot) where each MS associated with this BS should place their transmitted UL data. An UL slot is reserved for the MS 10 (according to the Fast Ranging IE delivered to the source BS 12 and the MS 10 in the HO_Response and MOB_BSHO-RSP) that is handing over, and is indicated in consecutive UL-MAP messages until the Timer #2 expires. The Timer #2 guarantees that the reserved uplink resource will be released for other MSs 10, such as for a case where the HO fails. The exemplary embodiments of this invention assume that the MS 10 is capable of receiving the UL-MAP message 7′, after which it is able to send data to the target BS (Ranging Request message), and that the target BS 12′ begins to allocate/schedule uplink transmission opportunities to the MS 10 as usual.
Another implementation option is illustrated in
As in the conventional processing, after receiving the HO Request from the serving BS 12, the target BS 12′ (at least one target BS 12′) sends the HO Response. The serving BS 12 receives the response message and sends to the MS 10 the MOB_BSHO-RSP as a response message to the MOB_MSHO-REQ. In addition, after processing the HO response messages from possibly different target BSs 12′, the serving BS 12 sends to the selected target BS(s) 12′ at step 6′ HO Pre-confirm information. The content of this “HO Pre-confirm” message (this name being simply descriptive of the functionality of the message) is different for those target BSs 12′ within a selected target group (“Yes”) and outside of the group (“No”). The selection criterion is implementation dependent and may be the same as the selection criterion for the BSs included in the message MOB_BSHO-RSP.
Those BSs 12′ that receive the HO Pre-confirm messages prepare to allocate the ranging subchannel and ranging CDMA codes for the MS 10. And the target BS 12′ sends out the UL-MAP message to the MS 10. Since there can be more than one BS 12′ that receives the HO Pre-confirm message it is preferred to define the Timer #2 to control how long the target BS 12′ will keep resources allocated for the MS 10. Timer #2 automatically stops if the HO Confirm message (message 6) is received.
Note that in the embodiments of
In a case where the network or the BS selects the final target BS 12′, this corresponds to a scenario where there is only one target BS 12′ included in the MOB_BSHO-REQ as shown in
The basic processing principle for this embodiment is as follows. In step 1 the serving BS 12 checks the availability of the neighbor BSs for the MS 10 HO via a HO Request message. If one neighbor BS agrees to the HO, this BS includes the ranging subchannel and ranging CDMA code information in the HO Response message to the serving BS 12 (in message 2). While this information is shown as a “Fast_Ranging_IE”, the particular name is illustrative and not limiting. At the same time, the neighbor BS starts Timer #2 to control the amount of time to maintain the resource allocation for the MS 10. Based on some criteria (possibly implementation specific) the serving BS 12 selects the final target BS 12′ and includes the UL-MAP (Fast_Ranging_IE) from the selected target BS 12′ in the MOB_BSHO-REQ message in step 3. The serving BS 12 also informs the non-selected neighbor BSs with a HO Cancellation message (3′) and, upon receiving the HO Cancellation message 3′ from the serving BS 12, these BSs release the resources reserved for the MS 1.0 (and automatically stop the Timer #2). At the same time the serving BS 12 may send the HO Pre-Confirm message 3” to the selected target BS 12′ to inform the selected target BS 12′ of the HO of the MS 10. The selected target BS 12′ maintains the allocated resources for the MS 10 for some time. After the MS 10 makes the final decision of HO target and sends out the MOB_HO-IND (message 4) to the serving BS 12, it detaches from the serving BS 12 and can immediately utilize the UL-MAP message included in the MOB_BSHO-REQ to determine the ranging resource information without waiting for any further information from the target BS 12′. Thus, the UL-MAP (message 6) is not needed. In a case where the MS 10 does not HO, the target BS 12′ releases the-resources-reserved for the MS 10 where the Timer #2 expires.
It should be noted that the embodiments described above with respect to
By the use of these exemplary embodiments the HO latency and HO disruption time can be reduced significantly.
The advantages include, but are not limited to, providing simple and efficient techniques to improve HO performance. Further, improved conservation of radio resources in the candidate target BS(s) can be realized. Note that the assignment of the Fast_Ranging_IE during the HO preparation phase can achieve significantly improved HO latency performance. Further, the embodiment described in reference to
(A) Based on the foregoing it should be apparent that the exemplary embodiments of this invention provide a method, apparatus and computer program product(s) to reduce HO latency by sending information descriptive of a MS HO resource allocation from at least one potential target BS prior to the target BS receiving a HO Confirm message from a currently serving BS.
(B) The method, apparatus and computer program product(s) as in the previous paragraph, where the information descriptive of the MS HO resource allocation is sent in response to expiration of a Timer that is started after receiving a HO Request from the currently serving BS.
(C) The method, apparatus and computer program product(s) as in paragraph (A), where the information descriptive of the MS HO resource allocation is sent in response to a receipt of an affirmative HO Pre-confirm message received from the currently serving BS after sending the currently serving BS a HO Response message.
(D) The method, apparatus and computer program product(s) as in paragraph (A), where the information descriptive of the MS HO resource allocation is sent with a HO Response message in response to a receipt of a HO Request message.
(E) The method, apparatus and computer program product(s) as in paragraphs (B) and (C), where the information descriptive of the MS HO resource allocation is sent directly to the MS.
(F) The method, apparatus and computer program product(s) as in paragraph (D), where the information descriptive of the MS HO resource allocation is sent to the currently serving BS, which forwards the information descriptive of the MS HO resource allocation to the MS as part of a MOB_BSHO-REQ message.
(G) The method, apparatus and computer program product(s) as in paragraphs (A)-(F), further comprising the potential target BS initiating a release Timer upon sending the information descriptive of the MS HO resource allocation, and subsequently releasing the MS HO resource allocation upon an expiration of the release Timer.
(H) The method, apparatus and computer program product(s) as in paragraphs (A)-(G), where the information descriptive of the MS HO resource allocation comprises information descriptive of allocated unique CDMA ranging codes and ranging subchannels.
(I) The method, apparatus and computer program product(s) as in paragraphs (A)-(H), embodied in a network compatible with IEEE 802.16e.
In general, the various message flows and blocks shown in
In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general-purpose hardware or controller or other computing devices, or some combination thereof.
As such, it should be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be fabricated on a semiconductor substrate. Such software tools can automatically route conductors and locate components on a semiconductor substrate using well established rules of design, as well as libraries of pre-stored design modules. Once the design for a semiconductor circuit has been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility for fabrication as one or more integrated circuit devices.
Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this invention.
For example, while the exemplary embodiments have been described above in the context of the WiMAX IEEE 802.16-type system, it should again be noted that the exemplary embodiments of this invention are not limited for use with only this one particular type of wireless communication system, and that they may be used to advantage in other wireless communication systems.
Furthermore, some of the features of the various non-limiting and exemplary embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.
This patent application claims priority under 35 U.S.C. §119(e) from Provisional Patent Application No. 60/877,487, filed Dec. 28, 2006, the disclosure of which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60877487 | Dec 2006 | US |
