KR20050048643A - Preparation of an intersystem connection transfer - Google Patents

Abstract

Disclosed is a method for preparing a connection transfer of a user terminal which is compatible with two different wireless communication systems from a first base station of a first of said wireless communication systems to a second base station of a second of said wireless communication systems, data being transmitted at least from/to the first base station within frames that are divided into time slots. According to the inventive method, transmission from and/or to the user terminal is interrupted during one frame.

Description

PREPARATION OF AN INTERSYSTEM CONNECTION TRANSFER}

The present invention relates to a method for preparation for connection switching (handover) of a user terminal, wherein the user terminal comprises: from a wireless cell of a first wireless communication system to a wireless cell of a second wireless communication system, Communicate with the different wireless communication systems. The wireless communication systems may belong to the same or different wireless communication standards (e.g., GSM, UTRA-TDD, UTRA-FDD, etc.), wherein the at least the first wireless communication system is A Time Division Multiple Access (TDMA) system, that is, a system in which data is transmitted in successive frames divided into time slots, wherein the time slots in the frame are each assigned to individual user terminals. The invention can be used in particular to switch the connection between the second and third generation digital mobile wireless communication systems using different transmission schemes.

In a wireless communication system, information such as, for example, voice, image information or other data is transmitted using electromagnetic waves over a wireless interface between a transmitting and receiving wireless station, for example a base station or mobile station in the case of a mobile wireless communication system. do. Electromagnetic waves are emitted here at carrier frequencies in the frequency band provided for each system. In the case of a known Global System for Mobile Communication (GSM) mobile wireless communication system, carrier frequencies exist in the 900 MHz, 1800 MHz, and 1900 MHz ranges. Carrier frequencies in the range of approximately 2000 MHz are prepared for future mobile wireless communication systems using CDMA and TD / CDMA transmission schemes over an air interface, for example Universal Mobile Telecommunication System (UMTS) or third generation systems. .

Seamless connection switching should be possible between different second and third generation digital mobile wireless communication systems, since not all preparation or coverage is provided, especially at the beginning of the use of the third generation system. For example, rural areas are supplied with systems based solely on second generation mobile wireless communication systems, whereas only urban areas are initially supplied with third generation systems. Thus, at least in this initial stage, at least one second generation transmission scheme, including, for example, GSM, and, for example, a Time Division Duplex (TDD) mode and / or a Frequency Division Duplex (FDD) mode. There should be user terminals that support all 3G transmission schemes.

When the multi-mode user terminal performs a communication connection through the third generation mobile wireless communication system, the multi-mode user terminal coexists with the existing mobile wireless communication in order to enable connection switching to the existing mobile wireless communication system. Must have the capability to measure transmission characteristics for the systems.

In a Time Division Multiple Access (TDMA) communication system including GSM or UMTS (TDD mode), time is divided into frames, and frames are divided into time slots. Each user terminal will transmit and receive within defined time slots assigned to it by the system. Between two consecutive time slots, the receiver and transmitter of the user terminal can be used for other purposes, for example, to create a precondition that monitors adjacent radio cells or base stations and thus enables a switch of access to another radio cell. have. The receiver of the user terminal must in this case be tuned to the frequency of the adjacent radio cell for a short time; The receiver performs measurements on its radio signal and then tunes back.

If necessary, while a transport connection is present in the first system to enable the switch of the connection from the first system to the second system, the user terminal compatible with the two other wireless communication systems is the wireless cells of the second system. It is designed to allow measurements to be taken. The term "other wireless communication systems" is understood herein to refer to both, for example, systems operating in accordance with the same standard and systems operating in accordance with other standards.

In order to be able to begin the transition to the second system, the user terminal must receive synchronization information for the second system prior to the actual measurement. This requires a relatively long reception period, so the time interval between two time slots of the first system assigned to the user terminal may be insufficient for this purpose. Also, portions of this synchronization information, such as for example frame numbers, are transmitted only at fixed times within the frame. If the time conditions between the frames of the two wireless communication systems are not met, it may be impossible to receive the synchronization information completely.

From European patent application EP 1005246 A2, in a TDMA-based wireless communication system a mobile station attempts to establish a wireless connection with a second base station in at least one other time slot during a wireless connection with the first base station in one time slot. Methods for switching connections are known.

From WO 96/05707 A1, a method is known for switching a connection between two wireless communication systems, in which a user terminal communicates simultaneously via two wireless communication systems for a defined time period.

Finally, from DE 10008058 C1 it is known how so-called downtime slots are allocated to the user terminal. During these downtime slots, signals of additional wireless communication systems may be received to prepare for switchover, and currently providing wireless service does not transmit any data to the user terminal.

The configuration of the described method for preparing a system-to-system connection switch is currently under consideration as part of the standardization of the so-called 1.28 Mcps mode of the aforementioned 3GPP TDD standard, also called TDD Low Chiprate Mode (LCR) or TDSCDMA. The purpose here is to allow user equipment (UE) to measure and possibly evaluate defined signals of adjacent radio cells using the same or different transmission standards. Such signals may be, for example, FCCH and Synchronization Channel (SCH) in the case of an adjacent GSM radio cell, and in the case of an adjacent FDD or HCR TDD radio cell (HCR: 3.84 Mcps TDD High Chiprate Mode), for example. For example, it may be a first SCH and a second SCH.

In the case of certain configurations that allocate time slots for the uplink (UL) and downlink (DL) to connections of the user terminal, the available measurement time is too short and / or switchover times, ie different If the times for switching in frequency are too long, it may be impossible for the user terminal to measure the signal of adjacent radio cells. Switchover times for low cost UEs are typically 0.8 ms. Such short measurement times may lead to situations in which relevant signals of adjacent radio cell (s) cannot be received, or may undesirably cause situations where a very long period of time is required, in which disconnection may occur. .

An embodiment for this problem is illustrated by FIG. A sequence for two so-called sub-frames, each 5 ms in length, is indicated. This frame structure matches the structure of the described TDD LCR mode. In each sub-frame, signals are transmitted from or to the user terminal in both the uplink and downlink during the time slots ts0 ... ts6. Between the transmission directions in the sub-frame, a switching point SP in a fixed position and a switching point SP that can be flexibly positioned are provided. In the embodiment shown in FIG. 2, a user terminal assigned radio resources for transmitting data or other signaling information in both uplink and downlink is examined. This is identified by an arrow pointing up for the uplink in time slot ts1 and an arrow pointing down for the downlink in time slot ts4. No radio resources are allocated to the user terminal during additional time slots of sub-frames, but these are used to transfer data from / to the terminal, if applicable. During the time intervals (measurement times; MTA, MTB) between the assigned time slots ts0 and ts4, the signals from neighboring radio cells are thus adapted to initiate a connection switch to one of the neighboring radio cells, if applicable. Can be received by a user terminal.

In the embodiment shown in FIG. 2, it is assumed that the user terminal receives signals during time intervals (MTA, MTB) of an adjacent base station supporting the FDD mode. For example, the frame structure of adjacent FDD radio cells is shown below the described subframes. Due to the fact that adjacent wireless communication systems are largely out of sync, any time skew generally occurs between the beginning of each frame, as indicated in the embodiment. Base stations of adjacent FDD radio cells transmit signals of a synchronization channel (SCH) in a frame at regular intervals, the signals of which are received by a monitoring user terminal. As shown in FIG. 2, each of the time intervals MTA, MTB is too short to receive a suitable number of consecutive sync channel signals to identify a radio cell. Identification is ensured only by subsequent reception of at least three consecutive synchronization sequences, which are the so-called second SCH codes (SSC).

In order to ensure long enough time intervals for receiving signals of neighboring radio cells, different time slots for signal transmission are sometimes caused by dynamic channel assignment (DCA) to generate as long a time interval as possible to monitor neighboring radio cells. It is currently proposed to assign to a user terminal. This is, for example, by time-limited reallocation of the signal transmission in the downlink from the originally assigned time slot ts4 to time slot ts3, as shown in FIG. Can be done. By this reassignment, the time interval MTB is extended by one time slot, thereby allowing the reception of three consecutive synchronization sequences (SCH).

In the standardization document 3GGP 3G TR 25.888, V0.2.0 (2002-8), "Improvement of inter-frequency and inter-system measurement for 1.28 Mcps TDD" (Release 6), for example, as shown in FIG. It is also proposed that a temporarily matched reassignment is performed for both transmission on the link and transmission on the downlink.

However, the reassignment schemes described above, together with the large signaling outlay due to signaling for newly allocated resources that are undesirably required, a high logistic outlay in the DCA algorithm to provide idle resources. And control problems for transmission power, adaptive antennas, and synchronization in the uplink.

1 shows a block diagram of two wireless communication systems, in particular mobile wireless communication systems.

2 shows a first exemplary configuration of sub-frames according to the prior art.

3 shows a second exemplary configuration of sub-frames according to the prior art.

4 shows a third exemplary configuration of sub-frames according to the prior art.

5 shows a third exemplary configuration of sub-frames according to the invention.

6A and 6B show an exemplary configuration within an interleaving frame according to the prior art and the present invention.

It is an object of the present invention to detail a method for avoiding the problems described with respect to known methods. This object is achieved from a method according to the features of independent claim 1. Further features of the invention are set out in the dependent claims.

The invention preferably takes advantage of the fact that signals for the same connection are transmitted in each case during two consecutive sub-frames. This applies to both uplink and downlink. The use of the present invention is also preferably accomplished by data transfer being carried out through a certain amount of redundancy. That is, even data that is not completely received may be reconstructed using a so-called error protection function at the receiving base station or the user terminal.

The method of the present invention is described in more detail with reference to the drawings.

The mobile wireless communication systems shown in FIG. 1 as examples of known wireless communication systems each have a large number of network components, in particular mobile switching centers (MSCs), wireless network controllers (RNCs) and base station NBs (Node Bs). Only one base station NB-TDD or NB-FDD is shown in each case. The first system supports, for example, the TDD-LCR mode and the second system supports the FDD mode of the UMTS system.

Each system is each comprised of a plurality of mobile switching centers that in each case are connected to each other within the system and establish access to a Public Switched Telephone Network (PSTN) fixed network. These mobile switching centers are also connected with radio network controllers for allocating radio facility resources. Each of these wireless network controllers may in turn connect to base stations. The base station NB may establish and release connections with user terminals (UEs) over the air interface, including, for example, mobile or fixed user terminals. 1 illustrates one user terminal (UE) that can optionally communicate with both a first TDD system and a second FDD system for simplicity. An active transport connection, including for example a voice connection, exists between the user terminal (UE) and the base station NB-TDD of the first system.

At least one radio cell Z-TDD or Z-FDD is formed by each base station NB-TDD, NB-FDD. In the case of sectorization or in the case of hierarchical radio cell structures, a plurality of radio cells are also provided for each base station. Wireless cells of different systems may be geographically overlapped in a random manner.

Each Operational Maintenance Center (OMC) (not shown) implements control and maintenance functions for a mobile wireless communications system or portions of the system. The function of this structure can be transferred to other wireless communication systems, in particular wireless communication systems for subscriber access networks using wireless subscriber connections.

The method of the present invention will be described exemplarily below with reference to FIG. 5. The preferred use here is that the physical transport channel is always symmetrically allocated in both subframes #i and # i + 1, ie the allocation of resource units is applied to all of the sub-frames. According to the example of FIG. 2, a resource unit is allocated to a user terminal for transmitting data on the uplink in time slot ts1, and this allocation applies to both the first sub-frame and the second sub-frame. The same manner of allocation applies equally to the resource units used to transmit data from the base station to the downlink.

Furthermore, the preferred use is also made by having error protection before data is transmitted over the air interface. This is commonly referred to as Forward Error Correction (FEC). In general, data of a service such as voice data transmission is coded at a coding rate of 1/2. That is, the original data of the message is copied, so that one bit becomes two coded bits. The coded bits generated such that each sub-frame contains a complete message is divided evenly between the two sub-frames. The additional information can be 100% redundant, causing incompletely received messages to be reconstructed at the receiver end due to transmission failures. To further extend the error protection, the message is interleaved between four (20 ms equivalent) sub-frames. That is, four consecutive sub-frames contain portions of the coded data signal. This is described in detail below with respect to FIG. 6.

For example, as shown in FIG. 5, the signal transmission from / to the terminal is interrupted in one sub-frame (# i + 1) of two sub-frames in accordance with the present invention. The time interval (MTB) for monitoring and identifying the SCHs of adjacent FDD radio cells is significantly extended by this means. Although not receiving the redundant portion of the message, another sub-frame (#i), which is still used for transmission, is transmitted over the increased transmit power to ensure secure reception of the transmitted portion of the message. Occurs on both the uplink and the downlink. With increased transmit power, the low FEC caused by the interruption can preferably be compensated for (in fact there is no further redundancy). This interruption can also be implemented in several consecutive sub-frame pairs until the user terminal has successfully identified the adjacent radio cell. Furthermore, an increase in transmit power may also be achieved through a plurality of sub-frames that precede and / or follow the interrupted sub-frame. This can be controlled dependently, for example, by the interleaving factors described.

According to currently standardized methods for the TDD LCR mode with regard to the adjustment of the transmit power, the user terminal cannot implement autonomous increase of the transmit power, in that it relies on the signaling of the base stations. In addition, if the target signal-to-interference ratio (target SIR) is satisfied, the user terminal is not allowed to request higher transmit power to the base station by so-called transmit power control (TPC) commands.

According to the first method of the present invention, the user terminal, in contrast to the previously described standardized method, defines a defined number of requests that increase the transmit power of the base station and also precedes and / or follows the interrupted sub-frame. Increase transmit power autonomously for sub-frames. After successful measurement and identification for an adjacent radio cell, the reduction in the transmit power of the base station may in turn be requested by the user terminal and / or the decrease in the transmit power of the base station may be controlled autonomously. The change signaling for the transmit power of the base station can be performed here using, for example, known signaling for transmit power control.

According to an alternative or supplementary second method of the invention, the user terminal signals to the base station that it will not transmit any data on the uplink in the next sub-frame or will use the sub-frame to monitor adjacent cells. Such signaling is achieved by one or more bits, which are not used in the current standard, for example of synchronization sequences transmitted uplink by the user terminal in a so-called Uplink Pilot Time Slot (UpPTS). For example, two bits may be used to signal which of the four related interleaved sub-frames will be used by the user terminal to monitor adjacent cells. Through this signaling, the base station recognizes that the sub-frame is not in use and thus recognizes that it cannot or should not receive any data from the user terminal during this sub-frame. In the same way, the base station can suspend its emission to the user terminal during this sub-frame, for example, to preferably reduce the interference effect of parallel transmissions.

As an alternative to the first method of the present invention, the base station recognizes that a sub-frame for monitoring adjacent radio cells is imminent, so that additional signaling for the user terminal is not required and can autonomously increase its transmit power. Can be. Furthermore, as an alternative to this, the base station can autonomously increase its transmit power and likewise instruct the user terminal to increase the transmit power via TPC commands. This is particularly preferably done for all further sub-frames of the interleaving frame.

According to an alternative third method, the user terminal signals to the base station that it needs a time interval to monitor adjacent radio cells. The base station then identifies the appropriate sub-frame and signals the sub-frame identified by the user terminal by appropriate known signaling mechanisms. According to the previously described method, each transmit power is increased in the preceding and / or following sub-frames or in additional sub-frames of the interleaving frame. This may in turn be done autonomously by the user terminal or by a command from the base station. Any existing knowledge about the base station with respect to the relative time structure of adjacent radio cells or wireless communication systems may be preferably used here to define an optimally suitable time interval for monitoring.

The first method of the present invention is exemplarily described below with reference to FIGS. 6A and 6B. For example, as shown in FIG. 1, data transmission between a user terminal and a base station is shown in FIGS. 6A and 6B. In uplink data transmission to a base station, one or more resource units, including for example CDMA codes, are allocated to the user terminal in time slot ts1. In the same way, one or more resource units are allocated for downlink transmission. The defined amount of data for the message, i. E. The transmission, is interleaved and transmitted via four sub-frames, the so-called interleaving frame or Transmission Time Interval (TTI). In the time intervals (MTA and MTB) between respective emissions in the uplink and downlink, the user terminal can perform monitoring for adjacent radio cells. However, as shown in FIG. 6A, these time intervals are not long enough to ensure secure reception for at least three consecutive synchronization sequences of adjacent FDD base stations.

To solve this problem, the user terminal, as shown in FIG. 6B, stops radiating signals from and receiving signals from the base station currently serving the sub-frame. In the resulting very long time interval MTB, the user terminal can receive and identify a sufficient number of sync sequences for the sync channel of the adjacent FDD base station. Despite interrupted transmission and reception to / from the currently served base station, in order to ensure safe reception of the data signals, the user terminal signals the appropriate TPC commands to the base station to increase the base station's transmit power, for example 2 dB. Request to increase or increase the value of the target signal to interference ratio (target SIR) by 2 dB and signal this fact to the base station. In order to enable proper detection and error correction for the base station even without knowledge of transmission interruption, in the uplink, the user terminal is in the interleaving frame during additional sub-frames, with the transmission power increased by 2 dB as well, Signals, and the remaining data signals in this manner are easier to detect.

Claims (7)

Two mutually from the first base station (NB-TDD) of the first wireless communication system (TDD) of the wireless communication systems to the second base station (NB-FDD) of the second wireless communication system (FDD) of the wireless communication systems. A method for preparing to switch access of a user terminal (UE) compatible with other wireless communication systems, Data is transmitted from / to at least the first base station (NB-TDD) in successive frames (sub-frames) divided into time slots (ts), and from / to the user terminal (UE). Or the transmission to the user terminal is interrupted for one frame (sub-frame). The method of claim 1, Data is transmitted in each case with increased transmit power in at least one frame before and / or after said frame without transmission. The method of claim 2, The increase in transmit power of the first base station (NB-TDD) is requested by the user terminal (UE). The method of claim 2 or 3, And the user terminal (UE) autonomously controls an increase in its transmit power. The method of claim 2 or 3, The increase in transmit power of the user terminal (UE) is controlled by the first base station (NB-TDD). The method according to claim 1 or 2, And said first wireless communication system (TDD) and said second wireless communication system (FDD) support different transmission standards. A wireless communication system for implementing the method according to claim 1.