EP1543695A2

EP1543695A2 - Preparation of an intersystem connection transfer

Info

Publication number: EP1543695A2
Application number: EP03750587A
Authority: EP
Inventors: Andreas Höynck; Stefan Oestreich
Original assignee: Siemens AG; Nokia Siemens Networks GmbH and Co KG
Current assignee: Nokia Solutions and Networks GmbH and Co KG
Priority date: 2002-09-27
Filing date: 2003-09-19
Publication date: 2005-06-22
Also published as: BRPI0314698B1; CN1685757A; WO2004032549A3; BR0314698A; UA79817C2; DE10245113A1; CN100450267C; WO2004032549A2; AU2003270230A8; KR20050048643A; AU2003270230A1; KR101004233B1

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

description

Preparation of an intersystem call forwarding

The invention relates to a method for preparing a handover of a subscriber terminal compatible with different radio communication systems from a radio cell of a first one of these radio communication systems to a radio cell of a second radio communication system. The radio communication systems can belong to the same or different radio communication standards (eg GSM, UTRA-TDD, UTRA-FDD, ...), with at least the first radio communication system being a TDMA system (Time Divi Multiple access), d. H. data is transmitted in successive frames divided into time slots, the time slots being allocated to individual subscriber terminals within a frame. The invention can be used in particular for a call forwarding between digital mobile radio systems of the second and third generation with different transmission methods.

In radio communication systems, information such as voice, image information or other data is transmitted with the aid of electromagnetic waves via a radio interface between a transmitting and a receiving radio station, such as a base station or a mobile station in the case of a mobile radio system , The electromagnetic waves are emitted at carrier frequencies that lie in the frequency band provided for the respective system. In the known GSM mobile radio system (Global System for Mobile Communication), the carrier frequencies are in the range of 900 MHz, 1800 MHz and 1900 MHz. For future mobile radio systems with CDMA and

TD / CDMA transmission methods via the radio interface, such as UMTS (Universal Mobile Telecommunication System) or other 3rd generation systems, carrier frequencies in the range of approx. 2000 MHz are provided.

A problem-free connection forwarding should be made possible between the different digital mobile radio systems of the second and third generation, since a complete coverage or coverage is not provided, especially at the beginning of the expansion of the third generation systems. For example, initially only metropolitan areas are to be equipped with the third generation system, whereas rural areas continue to be supplied exclusively with systems based on the second generation mobile radio system. Accordingly, at least in this initial phase, there will be subscriber terminals that use both the second generation transmission method, for example GSM, and one or more third generation transmission methods, for example TDD (Time Division Duplex) and / or FDD mode (Frequency Division Duplex). support.

If such a so-called multimode subscriber terminal operates a communication link via a third-generation mobile radio system, it must be possible to measure the transmission properties of parallel existing mobile radio systems so that a connection can be forwarded to such a mobile radio system if necessary.

In TDMA (Time Division Multiple Access) communication systems such as GSM or UMTS (TDD mode), the time is divided into frames, which in turn are divided into time slots. Each subscriber terminal sends and receives within certain time slots that are allocated to it by the system. Between two successive time slots, the

Receiver and transmitter of the subscriber terminal can be used for other purposes, e.g. B. to listen to neighboring radio cells or base stations and thus the requirements for one create possible connection forwarding to another radio cell. The receiver of the subscriber terminal must be tuned briefly to the frequency of an adjacent radio cell, carries out measurements on its radio signal and is then tuned back again.

A subscriber terminal, which is compatible with two different radio communication systems, should be able to carry out measurements on radio cells of the second system while there is a transmission connection with a first system, in order to be able to switch the connection from the first to the second system if necessary. Ationssystemen under "different radio communi- ^{^',} understood as a different network operators operating according to different standards systems here, for example, both after the same standard operating systems.

In order to be able to switch to the second system, the subscriber terminal must receive synchronization information from the second system before the actual measurement. This requires a relatively long reception time, so that the time period between two time slots of the first system allocated to the subscriber terminal can be insufficient for this. In addition, parts of this synchronization information, such as a frame number, are only transmitted at fixed times within a frame. If the time between the frames of the two radio communication systems is unfavorable, it may be impossible to receive the complete information.

EP 1 005 246 A2 discloses a method for handing over radio connections in TDMA-based cordless communication systems, in which a mobile station tries on a time slot during a radio connection with a first base station, on at least one other time slot. slot to establish a radio connection with a second base station.

WO 96/05707 A1 discloses a method for forwarding the connection between two radio communication systems, in which a subscriber terminal communicates simultaneously over the two systems for a certain period of time.

Finally, from DE 100 08 058 Cl a method is known in which so-called downtime slots are assigned to a subscriber terminal, in which signals of another radio communication system can be received in preparation for a call forwarding, the currently supplying radio communication system during this Downtime slots do not transmit any data to the subscriber terminal.

As part of the standardization of the so-called 1.28 Mcps mode of the above-mentioned 3GPP TDD standard, also called TDD low chip rate mode (LCR) or TDSCDMA, the organization of the measurements described is currently being investigated in preparation for an intersystem call forwarding. The purpose of this is to enable the subscriber terminals (UE - User Equipment) to measure and, if necessary, evaluate certain signals from neighboring radio cells using the same or different transmission standard. Such signals can be, for example, the primary and secondary SCH in the case of an adjacent GSM radio cell and the FCCH and SCH (synchronization channel) and in the case of an adjacent FDD or HCR TDD radio cell (HCR - 3.84 Mcps TDD high chip rate mode) ,

With certain configurations of the allocation of time slots for the uplink (UL - uplink) and downlink (DL - downlink) to connections of a subscriber terminal, it can for this it would be impossible to measure signals from neighboring radio cells because the available measuring time is too short and / or the switching times, ie the change to another frequency are too long. The switching times for low-cost user terminals, so-called low cost UE, are typically 0.8 ms. Such short measurement times have the disadvantage that either the relevant signals of the neighboring radio cell (s) cannot be received or that this requires a very long period of time, within which a connection breakdown may already occur.

This problem is exemplified with reference to FIG 2. A sequence of two so-called sub-frames is shown, each with a length of 5 ms. This frame structure corresponds to the structure of the TDD LCR mode described. In each subframe, signals in the upward and downward direction are sent from or to subscriber terminals in time slots (ts0 ... ts6 - timeslot). A fixed and a flexibly positionable switching point (SP - switching point) are provided between the transmission directions within a subframe. In the example in FIG. 2, a subscriber terminal is considered to which radio resources for the transmission of data or other signaling information have been allocated both in the upward and in the downward direction. This is characterized by an upward-pointing arrow for the upward direction in time slot ts1 or by an downward-pointing arrow for the downward direction in time slot ts4. No radio resources are assigned to the subscriber terminal in the further time slots of the subframes, but these may be used for data transmission from / to other subscriber terminals. In the time intervals MTA, MTB (Measurement Time) between the assigned time slots tsO and ts4, signals from neighboring radio cells can thus be received by the subscriber terminal in order, if necessary, to Initiate connection forwarding to one of these neighboring radio cells.

In the example in FIG. 2, it is assumed that the subscriber terminal receives signals (MTA, MTB) from a neighboring base station supporting an FDD mode during the time intervals. The frame structure of the FDD neighboring radio cell is shown as an example below the subframes described. Due to the fact that neighboring radio systems are usually not synchronized, there is usually a certain time lag between the beginning of each

Framework on, as it is also given as an example. The base station of the FDD neighboring radio cell sends signals of a synchronization channel SCH at regular intervals within the frame, which are received by the observing subscriber terminal. As can be seen from FIG. 2, the respective time intervals (MTA, MTB) are too small to receive a sufficient number of successive signals of the synchronization channel for identifying the radio cell. An identification is only ensured after receipt of at least three consecutive synchronization sequences, so-called secondary SCH codes (SSC).

In order to ensure sufficiently long time intervals for receiving signals from neighboring radio cells, it is currently proposed that the subscriber terminal be assigned different time slots for signal transmission from time to time by means of dynamic channel allocation (DCA) in order to assign the longest possible time interval for observing neighboring radio cells to generate. This can be done, for example, as shown in FIG. 3, by time-limited reallocation of the signal transmission in the downward direction from the originally assigned time slot ts4 in FIG. 2 to the time slot ts3. This reallocation makes the time interval MTB one time slot extended and thus enables the reception of three successive synchronization sequences SCH.

In the standardization document 3GPP 3G TR 25.888, V0.2.0 (2002-8), "Improvement of inter-frequency and inter-system measurement for 1.28Mcps TDD ¹ (Release 6), it is further proposed a timed reallocation of both the transmission to carry out in the upward as well as in the downward direction, as is exemplarily shown in FIG.

However, the above-described methods of reallocation all lead disadvantageously to a large signaling outlay due to the necessary signaling of the newly allocated resources, to a high logistical outlay in the DCA algorithm for the provision of free resources and, if appropriate, to problems in the control of transmission power , adaptive antennas and synchronization in the upward direction.

The invention has for its object to provide a method which avoids the disadvantages of the known methods. This task is accomplished by the procedure according to the

Features of independent claim 1 solved. Further developments of the invention can be found in the dependent claims.

The invention advantageously makes use of the fact that signals of the same connection are transmitted in two successive subframes. This applies to both the upward and the downward direction. Furthermore, it is advantageously used that the data transmission takes place with a certain redundancy, ie even data that is not completely received can be reconstructed on the basis of a so-called error protection in the receiving base station or subscriber terminal. The method according to the invention is explained in more detail with the aid of graphic representations. Show

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

2 shows a first exemplary configuration of subframes according to the prior art,

3 shows a second exemplary configuration of subframes according to the prior art,

4 shows a third exemplary configuration of subframes according to the prior art,

5 shows a third exemplary configuration of subframes according to the invention, and

6 a and b: exemplary configurations within a nesting frame according to the prior art and according to the invention.

The mobile radio systems shown in FIG. 1 as an example of known radio communication systems each consist of a large number of network elements, in particular of mobile switching centers MSC (Mobile Switching Center), radio network controllers RNC (Radio Network Controller) and base stations NB (Node B), with only a base station NB-TDD or NB-FDD are shown. For example, the first system supports a TDD-LCR mode and the second system supports an FDD mode of the UMTS system.

Each system comprises a plurality of mobile switching centers, which are each networked within a system and which provide access to a fixed network PSTN (Public Switched Telephone Network). Farther these mobile switching centers are connected to radio network controllers for allocating radio resources. Each of these radio network controls in turn enables connections to base stations. A base station NB can establish and trigger connections to subscriber terminals UE, for example mobile or stationary subscriber terminals, via a radio interface. For the sake of simplicity, FIG. 1 shows a single user terminal UE that is able to communicate either with the first TDD or with the second system FDD. There is an active transmission connection, for example a call connection, between the subscriber terminal UE and a 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 hierarchical radio cell structures, several radio cells are also supplied per base station. Radio cells of the different systems can overlap geographically.

A respective operation and maintenance center (OMC - Operation and Maintenance) (not shown) implements control and maintenance functions for the mobile radio system or for parts thereof. The functionality of this structure can be transferred to other radio communication systems, in particular for subscriber access networks with a wireless subscriber line.

The method according to the invention is explained below using the example of FIG. 5. The fact that a physical transmission channel is always allocated symmetrically in both subframes #i and #i + l is advantageously used, ie the assignment of a resource unit applies to both subframes. According to the example in FIG. 2, the subscriber terminal is assigned a resource unit for data transmission in the upward direction in the time slot tsl, wherein this assignment applies to both the first and the second subframe. The same applies to resource units that are used for data transmission in the downward direction from the base station.

Furthermore, the fact that data is provided with error protection before transmission via the radio interface is advantageously used. This is also commonly referred to as FEC (Forward Error Correction). Typically, data from a service such as voice data transmission is encoded at a coding rate of, i.e. the original data of a message are duplicated, one bit becomes two coded bits. The encoded bits generated are then equally divided between the two subframes, so that each subframe contains the complete message. The additional information is pure redundancy, which enables a reconstruction of messages received incorrectly due to transmission errors on the receiving side. To further increase the security against errors, the message is also nested on four subframes (corresponds to 20 ms), i.e. four successive subframes contain parts of an encoded data signal. This is described in detail below for FIG. 6.

As shown by way of example in FIG. 5, according to the invention, the signal transmission from / to the subscriber terminal is interrupted in one (# 1 + 1) of the two subframes. As a result, the time interval MTB for observing and identifying the SCH of the neighboring FDD radio cell is significantly extended. In order to ensure secure reception of the transmitted part of the message despite the non-reception of the redundant part of the message which occurs as a result, both in the upward and the downward direction are used in the other subframe (#) used for the transmission an increased transmission power. An increased transmission power can advantageously result from the interruption called lower FEC (there is practically no redundancy) can be compensated. This interruption can also be carried out in several successive subframe pairs until the subscriber terminal has successfully completed identification of the neighboring radio cell. Furthermore, the transmission power can also be increased over several subframes preceding and / or following the interrupted subframe. This can be controlled, for example, depending on the nesting factor described.

According to the currently standardized methods for the transmission power control for the TDD LCR mode, a subscriber terminal cannot carry out an autonomous increase in the transmission power, but is instead dependent on signaling of the base stations. In addition, the subscriber terminal is not permitted to request a higher transmission power from the base station by means of so-called TPC commands (Transmit Power Control) if the target signal to interference ratio (target SIR) is fulfilled.

According to a first method according to the invention, the subscriber terminal, contrary to the standardized method described above, requests an increase in the transmission power of the base station and likewise autonomously increases the transmission power for a certain number of subframes preceding and / or following the interrupted subframes. After a successful measurement and identification of the neighboring radio cell, a lowering of the transmission power of the base station can advantageously be requested by the subscriber terminal and / or a reduction of the own transmission power can be controlled autonomously. The change in the transmission power of the base station is signaled, for example, via the known signaling for transmission power control. According to an alternative or supplementary second method according to the invention, the subscriber terminal signals to the base station that it will not send any data in the upstream direction in a subsequent subframe or that it will use a subframe to observe neighboring radio cells. This signaling takes place, for example, by means of one or more bits of the synchronization sequences sent in the upward direction by the subscriber terminal in the so-called UpPTS (uplink pilot timeslot) which are not used according to the current standard. By using two bits, for example, it could be signaled which of four associated, nested subframes should be used by the subscriber terminal for observing neighboring radio cells. This signaling means that the base station is aware of the unused subframe and accordingly knows that it cannot or does not have to receive any data from the subscriber terminal in this subframe. In the same way, the base station can suspend its own transmission to the subscriber terminal in this subframe, for example in order to advantageously reduce the interference influence of parallel transmissions in this subframe.

As an alternative to the first method according to the invention, as a consequence of this knowledge of an upcoming subframe for observing neighboring radio cells, the base station can autonomously increase its own transmission power without additional signaling of the subscriber terminal being required. Furthermore, as an alternative to this, the base station can autonomously increase its transmission power and instruct the subscriber terminal via TPC commands to likewise increase the transmission power, this being particularly advantageous for all further subframes of an interleaving frame.

According to a third alternative method, the subscriber terminal signals the need for a time interval for observing neighboring radio cells to the base station. The Ba- sisstation then defines a suitable subframe and signals this to the subscriber terminal using suitable known signaling mechanisms. In accordance with the previously described methods, the respective transmission power is increased in the preceding and / or subsequent subframes or in the further subframes of the interleaving frame. This can in turn be done autonomously by the subscriber terminal or by an instruction from the base station. The knowledge of the base station, if any, of the relative time structure of the neighboring radio cells or radio systems can advantageously be used for the definition of an optimally suitable time interval for observation.

The first method according to the invention is explained below using FIGS. 6a and 6b as an example. 6a and 6b show the data transmission between a subscriber terminal and a base station, for example in the configuration shown in FIG. 1. For the transmission in the upward direction to the base station, one or more resource units, for example CDMA codes, are assigned to the subscriber terminal in the time slot tsl. In the same way, one or more resource units are assigned for the transmission in the downward direction. A message, ie a certain amount of data to be transmitted, is interleaved via four subframes, the so-called interleaving frame or TTI (Transmission Time Interval). In the time intervals MTA and MTB between the respective transmissions in the upward and downward direction, the subscriber terminal can carry out an observation of neighboring radio cells. However, as shown in FIG. 6a, these time intervals are not sufficiently long for secure reception of at least three successive synchronization sequences to ensure neighboring FDD base station. Based on this problem, the subscriber terminal interrupts the transmission of signals to the currently serving base station and the reception of signals from this base station for a subframe, as shown in FIG. 6b. In the resulting very long time interval MTB, the subscriber terminal can receive and identify a sufficient number of synchronization sequences of the synchronization channel of the neighboring FDD base station. In order to ensure secure reception of the data signals despite the interrupted transmission and reception to / from the currently supplying base station, the subscriber terminal requests an increase in the transmission power of the base station by, for example, 2 dB by signaling corresponding TPC commands to the base station or he - increases the value for the target signal to noise ratio (target SIR) by 2dB and signals this to the base station. In the upward direction, the subscriber terminal also sends the data signals with a transmission power increased by 2 dB during the further subframes in the interleaving frame in order to enable the base station to detect and correct errors sufficiently without knowing the interrupted transmission, since the remaining data signals thereby result in a have higher detection reliability.

Claims

claims

1. Method for preparing a call forwarding of a subscriber terminal (UE) compatible with two different radio communication systems (TDD, FDD) from a first base station (NB-TDD) of a first one

(TDD) of these radio communication systems to a second base station (NB-FDD) of a second (FDD) of these radio communication systems, wherein at least from / to the first base station (NB-TDD) data in successive frames divided into time slots (ts) (Subframe) are transmitted, in which the transmission from and / or to the subscriber terminal (UE) is suspended during a frame (subframe).

2. The method according to claim 1, wherein the data in at least one frame before and / or after the frame without

Transmission with an increased transmission power can be transmitted.

3. The method according to claim 2, wherein the increase in the transmission power of the first base station (NB-TDD) is requested by the subscriber terminal (UE).

4. The method according to claim 2 or 3, wherein the subscriber terminal (UE) autonomously controls an increase in its own transmission power.

5. The method according to claim 2 or 3, wherein the increase in the transmission power of the subscriber terminal (UE) is controlled by the first base station (NB-TDD).

6. The method according to claim 1 or 2, wherein the first (TDD) and the second radio communication system (FDD) support different transmission standards. Radio communication system for performing the method according to claim 1.