KR20010104714A - Method for detecting and compensating for radio link timing errors - Google Patents

Abstract

The mobile station 16 may determine whether one or more radio link transmissions 14 from the network are outside or near the outside of the receive time window 18 of the mobile station 16 and report this information to the network for proper action. A method of detecting and compensating for radio link timing errors in a mobile communication system is described.

Description

{METHOD FOR DETECTING AND COMPENSATING FOR RADIO LINK TIMING ERRORS}

The operation of certain mobile communication systems, such as code division multiple access (CDMA) or time division multiple access (TDMA) mobile communication systems, depends on the use of timing criteria for synchronization purposes. In part, at the base station BS, this timing reference is generated by the internal oscillator. However, this internal oscillator can be locked and synchronized to an external long-term timing reference.

Certain design problems relate to the use of BS timing criteria for network time synchronization. For example, an oscillator used by a BS to generate an internal timing reference can drift frequently, reducing the accuracy of the timing reference that is generated. In addition, the timing of the BS (detected by the mobile station (MS)) can be displaced in time, which means that the MS is moving towards or from the BS (mobility), or the radio environment changes and moves over time (time variance). ) Because. This problem is sometimes referred to as "MS timing shift". In any case, it can be seen that the propagation delay over the radio link can change over time.

In a mobile communication network, each BS may form one or more cells. Each cell connects the BS (and radio network) to the appropriate MS via a unique radio link (wireless air interface connection). Typically, there is no specific timing problem between different / multiple radio links belonging to one BS and also towards one MS. However, if two or more cells belong to different BSs, the timing between these cells can cause serious design problems. In this regard, each MS has a "receive time window" or interval at which all radio link transmissions are received.

Timing criteria defined for mobile systems operating in accordance with the " IS-95 " and " CDMA200 " protocols allow the use of fairly accurate Global Positioning System (GPS) timing signals that provide relatively stable timing criteria for network nodes. Based. Thus, for example, in IS-95 and CDMA2000 systems, each BS has a fairly accurate timing reference with respect to inter-BS timing, which can maintain radio link transmission within the MS's receive time window. However, the radio link transmission may still move within the reception time window due to the impact of MS mobility and / or time dispersion. Whatever the case, there is a significant design problem for these mobile systems (CDMA) that use less accurate inter-BS synchronization methods, where some (one or more) of the radio links move out of the MS's receive time window. Because it can.

In existing and developing mobile communication systems (e.g., broadband CDMA or WCDMA systems), if the MS is connected to various cells of different BSs by radio link, synchronization between these cells may be drift topologically. This problem arises because these systems do not use (or do not plan to use) an absolute time reference (such as GPS) to synchronize the different BSs involved. In practice, the problem of inadequate "phase drift" in this context is that no absolute timing criteria are used for inter-BS synchronization, or some form of inadequate (eg, suboptimal or always available) network time synchronization method is being used. It can be regarded as occurring.

In existing cellular systems with macro-diversity, the solution for handover evaluation is based on the power level of the signal that the MS receives. However, in this method, the network typically cannot determine whether the radio link transmission is outside the MS's receive time window. Thus, there is a significant need for a method that enables a mobile communication system operating without an accurate network timing criterion to determine when one or more radio link transmissions move out of or near the MS's receive time window. As described in more detail below, the present invention successfully solves these and other related problems.

This application for a patent claims priority to the entire disclosure of pending US Provisional Application No. 60 / 174,064, filed December 30, 1999.

TECHNICAL FIELD The present invention relates to the field of mobile communications, and in particular, to a method that can be used in a mobile communications system to detect and compensate for radio link timing errors.

1A, 1B and 1C are related diagrams illustrating how radio link timing errors can be detected and compensated for in accordance with a preferred embodiment of the present invention.

2A and 2B are related diagrams illustrating a second feature of the preferred embodiment.

3A and 3B are related diagrams illustrating a third feature of the preferred embodiment.

4A and 4B are related diagrams illustrating a fourth feature of a preferred embodiment.

In accordance with a preferred embodiment of the present invention, radiolink timing, which allows the MS to determine whether one or more radiolink transmissions are outside or near the outside of the MS's receive time window, and report this information to the network for proper action. Methods and means for detecting errors are provided.

An important technical advantage of the present invention is to provide a method for mobile network time synchronization that does not require the use of absolute timing criteria such as GPS.

Another important technical advantage of the present invention is that it provides a method of minimizing the effects of phase drift between cells in a mobile communication system.

Another important technical advantage of the present invention is that it provides a method of improving the cell retrieval process by improving the accuracy of inter-BS timing in a mobile communication system, thereby reducing the uncertainty (for MS) of other BS timings.

A more complete understanding of the method and apparatus of the present invention may be made by reference to the following detailed description taken in conjunction with the accompanying drawings.

Preferred embodiments of the present invention and their advantages can be best understood by referring to Figs. 1A to 4B, and like numerals are used for like and corresponding parts in the drawings.

In essence, in accordance with a preferred embodiment of the present invention, a method is provided for detecting and compensating radio link timing errors such that the MS determines whether one or more radio link transmissions are outside or near the outside of the MS's receive time window, This information is reported to the network via the uplink for proper action. The threshold levels used to determine whether the radio link transmission is outside the MS's receive time window are transmitted from the MS to the network.

In particular, Figures 1A, 1B and 1C are related diagrams illustrating how to detect and compensate for radio link timing errors, in accordance with a preferred embodiment of the present invention. 1A, a section 10 of an exemplary mobile communication system is shown. For example, such a system may be a CDMA system that functions according to existing or future CDMA protocols (eg, IS-95, CDMA2000, or so-called third generation systems). However, the present invention is not limited to a system functioning according to a specific protocol, and may include any telecommunication system having a radio link timing problem to be solved.

System 10 includes a base station (BS) 12 connected to a network via a suitable communication link. In the configuration shown, BS 12 forms a single cell and associated radio link 14. As such, MS 16 may be connected to communicate with the network via radio link 14 and BS 12.

1B illustrates how the MS (eg, 16) determines whether a radio link (eg, 14) transmission moves out of (or nearly out of) the MS's receive time window (eg, 18). It is a timing chart explaining whether there exists. In general, one downlink (forward) code is used for each radio link. These codes must be orthogonal to the BS. Thus, in this exemplary embodiment, a new radio link setup should be assigned to the earliest 256-chip boundary. In third generation CDMA systems, since there is no strict / accurate inter-BS synchronization, the radio link can be located relatively close to the boundary of the MS's receive time window.

As shown, in this exemplary embodiment, one radio link 14 is involved. If the received radio link 14 is located very close to the center of the timing window 18 of the MS, and there is no sudden change in the distance of the MS from the BS or in the wireless environment, the MS sends the downlink signal at the timing of the uplink transmission. It can be followed relatively slowly and accurately. However, on the other hand, if the received radio link is located far enough from the center of the window 18, this situation can cause a more complicated problem (as described below, the present invention solves).

In this example scenario, referring to FIG. 1C, assume that the MS 16 has just completed handover from one or more other cells (not shown) to the cell associated with the BS 12 and the radio link 14. In addition, each of the other radio links (connected prior to handover) were released in connection with the MS 16. In this example, the remaining radio link 14 being received by the MS 16 is offset by approximately 128 chips from the center of the reception time window 18. In this example, since the width of the reception time window from the boundary line to the boundary line is slightly larger than 256 chips, the received radio link 14 is located near the boundary of the reception time window 18. Thus, slight movement of the radio link (eg, due to time dispersion or changes in the radio environment) can cause the radio link to deviate outside of the reception time window. As such, in accordance with a preferred embodiment of the present invention, the MS 16 may network (over the uplink) a message that reports that the radio link 14 has moved across boundaries where the wireless network previously signaled the MS. To transmit. These boundaries may exhibit a window size slightly smaller than the MS's receive time window 18. The network can then take appropriate action in response to these reports (as described in more detail below).

Instead, before the radio link 14 actually moves out of the receive time window, the MS 16 may send a message to the network reporting that the radio link 14 is near the boundary of the window 18. Once again, as described in more detail below, the network can take appropriate action in response to these reports. For example, the MS may be instructed to send a report message to the network informing that the radio link transmission is offset from the center of the timing window by an amount greater than the selected prescribed values (ie, each value associated with the "side" of the window). Can be. For example, the timing window may include two thresholds. One such value may be related to “less than” from the MS (eg, located to the left of the first boundary). Another threshold may be related to “greater” from the MS (eg, located to the right of the second boundary). As such, in response, an appropriate action by the network to adjust the radio link timing to reposition the radio link at an acceptable location within the window.

2A and 2B are related diagrams illustrating a second feature of a preferred embodiment. In this case, referring to FIG. 2A, the MS 16 is connected to the network by wireless links 14 and 114 (via BS 12 and 112, respectively). However, as shown in FIG. 2B, the two radio links 14 and 114 are significantly spaced apart in time (eg, BS 12 and 112 are connected to different BSs). In this case, the MS 16 may select one of the radio links to follow the reception time window (eg, the strongest radio link). Nevertheless, many different timing problems may arise.

For example, because of the influence of mobility or time dispersion along with the line-of-sight change between the transmitter and receiver (i.e., the radio link can move back and forth between the line of sight), one of the radio links May slightly deviate from others, or the radio link just disappears from the window and then pops out again (detected). In this example, in accordance with the present invention, the MS can send a message to the network reporting a radio link that has not been detected for a defined length of time. Among other things, one design choice (but which should not be considered as limiting the invention) is that two windows can be used to detect the radio link. The large window can be used to allow the MS (eg, user equipment or UE) to detect the radio link within this window. Smaller windows can also be used to allow the MS to report to the network that the radio link is located near the boundary of the large window. However, in this example, if the radio link pops out of a large window, the MS cannot detect the radio link and cannot report this information to the network.

3A and 3B are related diagrams illustrating a third feature of the preferred embodiment. In this case, referring to FIG. 3A, the MS 16 is connected to the network by three radio links 14, 114 and 214 (via BS 12, 112 and 212). Referring to FIG. 3B, the MS can determine what action to take according to the particular situation involved. Preferably, the MS reports all detected radio links to the network. In addition, if necessary, the network may request appropriate information from the MS regarding the measured cell (s) to determine what action to take. In particular, although the exemplary terminology “MS” is used in the text to indicate a mobile station, a mobile terminal, a mobile radio telephone, and the like, the equivalent terminology “user equipment or UE” can be used.

As another solution, according to a preferred embodiment of the present invention, if the weakest radio link (e.g., 214) moves out of the MS's receive time window, the MS 16 may indicate that the radio link 214 is outside the window. The reporting message can be sent to the network. On the other hand, if the strongest radio link (eg, 14) moves out of the window, the MS 16 keeps (and follows) the connection with the strongest radio link and commands from the network to terminate the connection with the two weak links. You can get As such, the network interprets the MS's radio link (or related) reports and instructs the MS to ignore or terminate the radio link for transmission power control timing on the uplink. Similar to the second aspect of the embodiment, the radio link may be slightly out of the receive time window.

4A and 4B are related diagrams illustrating a fourth feature of the preferred embodiment. In this case, referring to FIG. 4A, the MS 16 is connected to the network by four radio links 14, 114, 214 and 314. In this case, however, four radio links are associated with four BSs and two different timing domains (ie, radio links 14 and 114 associated with BS 12 and 112, and radios associated with BS 212 and 312). Link 214 and 314). Referring to FIG. 4B, if two of the radio links (eg, 214 and 314) move out of the timing window of the MS, the MS 16 indicates that two radio links were dropped from the active radio link set. As a report, it sends a message to the network that it can interpret. Among other things, according to 3GPP, the term "active set" can be defined as a set of radio links that are simultaneously involved in a particular communication service between a user equipment and a Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) access point have. A "UTRAN access point" can be defined as a conceptual point in the UTRAN that performs radio transmission and reception. A UTRAN access point is associated with one and a particular cell such that one UTRAN access point exists for each cell. The UTRAN access point is the UTRAN-side endpoint of the radio link.

In response to reports from the MS that the wireless link is outside or near the outside of the MS's receive time window, the wireless network may respond in a number of different ways. For example, the network deletes the radio link from the active set and waits until the MS sends a message reporting that the MS has detected a new neighbor cell and associated radio link to be located in the active set. The network then connects this radio link to the MS, which receives the transmission in the timing window. Alternatively, the network may connect directly to the radio link MS that was reported to be outside the timing window, and may also instruct the MS to include this radio link in the active set. As such, the network does not need to wait for a new neighbor cell report from the MS, and the network can also set up the radio link directly after the radio link is deleted.

As another alternative, the wireless network may connect another copy of the radio link that has been reported within the same cell, outside or near the outside of the MS's receive time window, and then remove the first radio link from the active set. have. As another alternative, the wireless network may update the active set by sending a " replace " message to the MS, then removing the first wireless link and adding a second wireless link as a replacement. In this case, the timing of the new radio link may be different from the timing of the first radio link.

Although the preferred embodiments of the method and apparatus of the present invention are illustrated in the accompanying drawings and described in the foregoing detailed description, the spirit of the present invention is not limited to the described embodiments of the present invention, but is defined by the following claims. It will be appreciated that various reconstructions, modifications and alternatives are possible without departing from the scope of the invention.

Claims (24)

A method for detecting and compensating a radio link timing error in a mobile communication network, Detecting a radio link transmission timing from the mobile communication network; Determining whether the detected radio link transmission timing is outside a reception time window; If the detected radio link transmission timing is outside a receiving time window, transmitting a message to the network indicating that the detected radio link transmission timing is outside the receiving time window. A method for detecting and compensating for radio link timing errors in a communication network. 2. The method of claim 1, wherein the determining step comprises the steps of: determining whether the detected radio link transmission timing is substantially outside of the reception timing window; If the detected radio link transmission timing is near the outside of the receiving time window, sending a message to the network indicating that the detected radio link transmission timing is near outside of the receiving time window. Characterized in that the method. 3. The method of claim 1 or 2, further comprising, in response to the message, the network adjusting the timing of the radio link transmission. 3. The method of claim 1 or 2, further comprising, in response to the message, the network removing the radio link from an active set. 5. The method of claim 4, further comprising connecting the radio link to a mobile station in response to the second message. 2. The method of claim 1, further comprising: in response to the message, the network connecting the radio link to a mobile station; Instructing the mobile station to include the radio link in an active set. The method according to claim 1 or 2, In response to the message, the network connecting a copy of the radio link in the same cell; Removing the radio link from the active set. The method according to claim 1 or 2, In response to the message, the network sending a replacement message to a mobile station to update an active set; Removing the radio link from the active set; Adding a first wireless link to the active set. The method of claim 1, wherein said network comprises a CDMA network. The method of claim 1, wherein the determining step, Receiving, by the mobile station, at least one radio link transmission timing threshold from the mobile communication network; Comparing the detected radio link transmission timing with the at least one radio link transmission timing threshold. A method of detecting and compensating a radio link timing error in a mobile communication network, Detecting a plurality of radio link transmission timings from the mobile communication network; Determining whether at least one of the plurality of detected radio link transmission timings is inside a reception time window; If the at least one of the plurality of detected radio link transmission timings is within the reception timing window, a second one of the plurality of detected radio link transmission timings is spaced apart from the center of the reception time window by a prescribed value And if so, sending a message to the network indicating that the second one of the plurality of detected radio link transmission timings is spaced apart from the center of the reception time window by the prescribed value. And detecting and compensating for a radio link timing error in a mobile communication network. The method of claim 11, In response to the message, the network further comprising adjusting a timing of the second of the detected plurality of radio link transmission timings. 12. The method of claim 11, wherein said network comprises a CDMA network. The method of claim 11, wherein the determining step, Receiving, by the mobile station, at least one radio link transmission timing threshold from the mobile communication network; Comparing the at least one of the plurality of detected radio link transmission timings with the at least one radio link transmission timing threshold. 12. The method of claim 11, wherein the prescribed value comprises a threshold that a mobile station receives from the mobile communication network. A system for detecting and compensating radio link timing errors in a mobile communication network, Means for detecting radio link transmission timing from the mobile communication network; Means for determining whether the detected radio link transmission timing is outside a reception time window; If the detected radio link transmission timing is outside the reception time window, means for transmitting a message to the network indicating that the detected radio link transmission timing is outside the reception time window. A system for detecting and compensating for radio link timing errors in a mobile communication network. 17. The apparatus of claim 16, wherein the means for detecting further comprises: means for determining whether the detected radio link transmission timing is substantially outside of the reception time window; Means for sending a message to the network indicating that the detected radio link transmission timing is substantially outside of the reception time window, if the detected radio link transmission timing is substantially outside of the receiving time window. System characterized in that. 18. The system of claim 16 or 17, further comprising means for adjusting the timing of the radio link transmission timing in response to the message. 18. The system of claim 16 or 17, further comprising means for removing the radio link from an active set in response to the message. The method of claim 16, And means for connecting the radio link to a mobile station in response to a second message. The method of claim 16, In response to the message, further comprising means for connecting the radio link to a mobile station and instructing the mobile station to include the radio link in an active set. The method according to claim 16 or 17, In response to the message, further comprising means for connecting a copy of the radio link within the same cell and removing the radio link from an active set. The method according to claim 16 or 17, In response to the message, further comprising means for sending a replacement message to the mobile station, removing the radio link from the active set and adding a second radio link to the active set. 17. The system of claim 16, wherein said network comprises a CDMA network.