Method and transcoder for performing a distributed handover in the uplink direction
Abstract
The present invention relates to the technique of handover in mobile telephony. A new Transcoder and Rate Adaptation Unit (100, fig. 3) is introduced which provides two uplink (230, 250 respectively, fig. 3) and two downlink (240, 260 respectively, fig. 3) channels. The use of these two channels (230, 250 respectively, fig.3) on the uplink during handover provides for the use of distributed handover on the uplink. The result minimizes the audible interruption during handover by minimizing the loss of Traffic Channel frames to what is possible within the GSM standard. Additionally, interruption of the speech or background noise during these lost frames is masked by an error concealment algorithm, since the Transcoder and Rate Adaptation Unit (100, fig. 3) still has information from the Base Transceiver Station responsible for transmission before the handover.

Term
No projected expiry on record.
- Priority and filed
- Granted
- Today
3 claims: 2 independent, 1 dependent
- 1Patentkrav claim 1. Förfarande för att genomföra en handover från en första radiosändare/mottagare (340 fig. 4a) till en andra radiosändare/mottagare (350 fig. 4a), där den första radiosändaren/mottagaren (340 fig. 4a) sänder information till, och tar emot information från, en mobil station (310 fig. 4a), över en första luftgränssnittstrafikkanal (345 fig. 4a) motsvarande en första nedlänkkanal (370 fig. 4a) och en första upplänkkanal (360 fig. 4a) över vilken informationssignaler sänds från, respektive tas emot av, en signalkonverterar- och en hastighetsanpassningsenhet (100 fig. 4a), där den andra radiosändaren/mottagaren (350 fig. 4a) kan sända information över en andra luftgränssnittstrafikkanal (355 fig. 4a), kännetecknat av att tilldela (30 fig. 5) den andra luftgränssnittstrafikkanalen (355 fig. 4a) en andra upplänkkanal (380 fig. 4a) och en andra nedlänkkanal (390 fig. 4a) i signalkonverterar- och hastighetsanpassningsenheten (100 fig. 4a) . 1st Method of conducting a handover from a first radio transmitter / receiver (340 FIG. 4a) to a second radio transmitter / receiver (350 FIG. 4a), wherein the first radio transmitter / receiver (340 FIG. 4a) transmits information to, and receives information from, a mobile station (310 fig. 4a), over a first air interface traffic channel (345 fig. 4a) corresponding to a first downlink channel (370 fig. 4a) and a first uplink channel (360 fig. 4a) over which information signals are transmitted from, respectively received by, a signal converter and a speed matching unit (100 Fig. 4a), where the second radio transmitter / receiver (350 Fig. 4a) can transmit information over a second air interface traffic channel (355 Fig. 4a). ), characterized by assigning (30 FIG. 5) to the second air interface traffic channel (355 FIG. 4a) a second uplink channel (380 FIG. 4a) and a second downlink channel (390 FIG. 4a) in the signal converter and speed adjustment unit (100 Fig. 4a).
- 35) signal converter and speed adjustment unit (100 5) signalkonverterar- och hastighetsanpassningsenheten (100
Independent claims2
195 paragraphs in 2 sections, as filed
(54) (56) (57)
PATENT HOLDER Telefonaktiebolaget LM Ericsson, 126 25 Stockholm SE
INVENTOR'S OFFICE
Johan Karoly Peter Galyas, Täby SE Norin K
NAME Procedure and unit for distributed handover in uplink CALLED PUBLICATIONS: - - SUMMARY:
The invention relates to the method of handover in mobile telephony. A new signal converter and speed adjustment unit (100 fig. 3) is introduced which provides two uplink (230, 250 fig. 3) and two downlink channels (240 and 260 fig. 3, respectively). The use of these two channels (230 and 250, respectively, Fig. 3) on the uplink during handover enables the use of distributed handover on the uplink. The result minimizes audible interruption during handover by minimizing the loss of traffic channel frames to what is possible within the GSM standard.
In addition, interruptions of speech or background noise during these lost frames are masked by an error tracking algorithm, since the signal converter and speed matching unit (100 FIG.
3) still has information from the base transceiver station responsible for transmission prior to said handover.
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The numbers in brackets indicate International Identification! INID code. Letter Within the pinch indicates international document code.
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Field of the Invention
The invention relates generally to methods of handover in connection with mobile telephony, and in particular to the use of distributed handover in the uplink direction.
Technical area
In a typical mobile phone system, the architecture is divided into two parts: a base station subsystem and a switching subsystem. The task of the base station subsystem is to provide and administer transmission paths between a mobile station, or a plurality of mobile stations, and the switching subsystem machines. A machine in the switching subsystem is typically called a mobile telephone exchange. The base station subsystem administers the radio transmission over the air interface between the mobile stations and the rest of the mobile system. The switching subsystem must manage communications and connect mobile stations to relevant external networks (for example, the public telecommunications network). The switching subsystem does not have direct contact with a mobile station, nor does the base station subsystem have direct contact with an external network.
The task of the base station subsystem can be summarized as establishing the connection between the mobile station and other telecommunications users. On one side of the base station subsystem is the mobile telephone exchange, and there the base station subsystem has direct contact with the mobile telephone exchange. On the opposite side of the base station subsystem is the mobile station, and there the base station subsystem has direct contact with the mobile station that uses radio transmission or what is sometimes called the air interface.
The base station subsystem includes two types of machines: a base transceiver station, in contact with the mobile station
507 432 by radio transmission over the air interface, and the base station controller, where the latter has contact with both the switching system switches and the base transmitter station. There is to a great extent a functional division between transmission equipment, the base transceiver station, and its administrative equipment, the base station controller. In the GSM terminology, a base station subsystem means is a set with a base station controller and all base transceiver stations it controls.
The interface between the base station controller and the mobile telephone exchange, the MSC-BSC interface, is often called the A interface. It is so called in the Global System for Mobile Communication (GSM) system and is hereafter referred to in this description. The interface between the base station controller and the base transceiver station, the BSC-BTS interface, is called the Abis interface in GSM and is hereinafter referred to as.
The base transceiver station includes radio transmitting and receiving devices including antennas, and also all signal processing specific to the radio interface. An important component of the base transceiver station of the GSM architecture is the Transcoder and Rate Adaptation Unit (TRAU). TRAU is the equipment where speech encoding and decoding is performed, as well as speed adjustment in the case of data. In the previous approach, each base transceiver station was assigned a separate TRAU for each voice channel used by each mobile station in the cell covered by this base transceiver station. This is an important difference in the case of handover, as mentioned below.
The concept of channel is important in mobile communication. The main task of a communication system is to transmit user information, either speech or data. To limit the use of the radio spectrum, numbers in digital systems, such as GSM, are represented by a binary signal transmitted over specific radio frequencies. The user should be able to access this information by looking at the specific frequency and time 507 432 point at which the information is transmitted. This specifically identified part of the interface, the time and frequency, is called a channel.
In systems using only frequency multiplex (FDMA), a channel with a specific frequency is identified. In systems with time multiplex (TDMA) where the bit stream is transmitted over time, the time axis can be divided into shorter periods which can then be associated with specific channels. In addition, frequency jumps can be used, where the transfer jumps from one frequency to another and the channel is then the frequency sequence to which the jump occurred.
GSM, and other systems, use a mixture of FDMA, TDMA and frequency jumping. A basic concept of GSM is that the unit of transmission is a series of about 100 modulated bits, and is called a burst. Showers have a limit :; duration, and occupies a limited portion of the radio spectrum. They are transmitted in time and frequency windows, sometimes called hatches. Time slot is sometimes used to denote the door, its time value, or also the cycle that uses a door every eight hours in time.
Using a given channel in GSM means transmitting bursts at specific times, at specific frequencies. Defining a channel then consists of specifying which gaps can be used by, or are part of, the channel. Consequently, a channel has a temporary definition given, for each time slot, the number of slots that form part of the channel. The temporary definition is also cyclical, ie. it repeats itself over time. In parallel with the time definition, the frequency definition of a channel gives the frequency for each slot belonging to each channel. It basically consists of a function that assigns a frequency to each time slot where a channel has a slot. There are fixed frequency channels and frequency jump channels.
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Channels are also defined by reference to their time and frequency, they can also be designated by their function. A voice channel is a bidirectional channel intended for the user's call for its duration. These are sometimes called traffic channels. In addition to user data, signaling messages must also be communicated to support ongoing calls, including support for handovers.
At GSM, the system actually steals information from the voice channel to support the handover procedure. This specific use of the traffic channel is called in the GSM for fast associated control channel (FACCH) in the GSM. Said FACCH is then only a specific use of a traffic channel, where a speech frame is stolen to transmit signaling information. The receiver can then differentiate between both modes of use of the traffic channel by reading binary information transmitted on the traffic channel, which is called the theft flag.
Upon return to the TRAU, even though the specifications of the GSM consider the TRAU as part of the base transceiver station, it can be located far away from the base transceiver station, and can be located anywhere from the base transceiver station to the mobile telephone exchange itself. However, a more centralized location closer to the mobile telephone exchange saves significantly more transmission resources and thereby costs. As described below, said TRAU acts as an inter-network line between said 64 kbit / s transmission on the public telecommunications network (PSTN) and the mobile network of lower frequency. There must be ground links between the mobile telephone exchange (MSC) and the base transceiver station (BTS). Accordingly, these links can carry traffic at either the lower speed of the mobile part or the higher speed, which is much more expensive, for the public telecommunications network.
The cost of these internal ground links (between the base transceiver station and the base station controller, and between the base station controller and the mobile telephone exchange), which is usually
507 432 said by the operator, represents a considerable part of the operating cost. A transmission method that uses only 16 kbit / s for user data (signaling is kept at 64 kbit / s) leads to a cost reduction, even if they introduce a certain extra delay of transmission, and consequently lowers the overall voice transmission quality. With the interconnect line between 16 kbit / s and 64 kbit / s, the function of said TRAU, closer to the mobile telephone exchange, saves significantly more of these fixed management costs.
At the current phase of GSM, the incoming signal is transmitted from the mobile station at a speed of 13 kbit / s. The next GSM phase allows the use of other algorithms to compress the speech to even lower bit rates. For example, advanced speech encoders cut the current bit rate from 13 kbit / s to 5.6 kbit / s and the speech is transmitted on so-called half-speed channels. However, the standard used for transmission in the public telecommunications network is 64 kbit / s. Accordingly, each mobile telephone system must have some means to change all incoming 13 kbit / s mobile station signals to a 64 kbit / s signal transmitted to the fixed telephone network. This is the function of what is called TRAU in the invention. Although this nomenclature is the same as that of GSM, the invention can be applied to all similar agents used for voice coding and speed adjustment of other mobile telephone systems.
In a mobile telecommunication system, the mobile station can move from one geographical location to another in a process known as roaming. Because the coverage area of a mobile phone system is divided into cells, the mobile system performs roaming from one cell to another. The radio transmission and reception from a cell is controlled by a base transceiver station. Each individual cell has its own base transceiver station, which is responsible for transmission and reception in that cell.
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In the next step up in the hierarchy of the cellular structure of a cellular telephone system, a group of cells is organized in a location area. This is the area where a mobile station is located and then searched for an incoming call to the mobile station. All the cells in a location area can be controlled by one or more base station controllers, but they belong to only one mobile telephone exchange. A base station controller usually controls several base transceiver stations, with each base transceiver station covering a separate cell.
As the mobile station performs roaming from one cell to another, it is often necessary to carry out handover for the responsibility of controlling communication from one base transceiver station to the next. The base transceiver station that controls the radio interface of the cell that was occupied prior to said handover can be called BTS-old. The base transceiver station responsible for the radio interface in the cell occupied after the handover is completed can be called BTS-new.
Handovers are often distinguished by the switching point where there are three cases: first, BTS-new is controlled by the same base station controller as BTS-old; second, BTS-new is controlled by a different base station controller than BTS-old, but by the same mobile telephone exchange; and finally, BTS-new is controlled by a different mobile telephone exchange and base station controller than BTS-old.
A handover from one cell to another is called an intercell handover and the responsibility is transferred from one base transceiver station to another. An intercell handover where the same base station controller retains control is called an intraBSC handover. An intercell handover where BTS-new is controlled by another base station controller is called an inter-BSC handover. There are also intracell handovers where the responsibility is transferred from the base transceiver station to itself, but from one channel to another. All handover procedures in this section are intra-MSC handovers, since the same mobile telephone exchange be507 432 maintains the control before and after the handover is performed. It is these intra-MSC handovers that the invention relates to.
elevated
IN
A handover can be performed for a variety of reasons. These reasons include: attenuated signal strength, transmission bit error rate, lust, and increased scattering delay. the decision to try to carry out handover of the same base station controller, but the phonebook. Once the decision has been made, the transmission is coordinated by radio broadcasting and elevated distribution paths, in most cases, a given mobile phone mix is taken by mobile telephony and once the new cell has been selected, the actual one between the mobile station and the receiving machines must be old and the one administering the old cell ( BTSHandover can new cell (BTS new).
other ways. As the mobile is also distinguished on roaming through the cell system, the delay station varies the performance of the transfer to and from the base transceiver station. A mechanism has been designed to compensate for this In order to compensate for the delay mobile station its transmission time in the ground plane, which is deduced from the scour as indicated by the infrastructure, time delay in the GSM system. ning speeds up the relationship with its taking, with a time advantage. The base transceiver station continuously measures the time offset between its own burst and the receiving plane of the bursts of the mobile station. Based on these measurements, it can provide the mobile station with the required time advantage.
Since the time delay in transmission between two base transceiver stations is known, the two cells are synchronized. When the BTS old and BTS new cells in a handover are synchronized, the handover is called a synchronous handover. The mobile station can only measure and derive the difference in spread time between BTS-old and BTS-new to calculate the time advantage used by BTS-new after the said handover.
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In a handover between two cells that are not synchronized, no information can be used by either BTS-new or the mobile station to predict the time advantage. The mobile station is prohibited from transmitting its normal bursts until it knows the timing of BTS-ny. Since BTS new must receive something from the mobile station to reach the spread time, the mobile station must send access bursts with a time delay equal to zero. At GSM, these access bursts are broadcast on the direct access channel (RACH). With these access bursts, BTS-ny can calculate the time jump. This extended exchange between the mobile station and the BTS new extends the handover procedure between asynchronous cells, asynchronous handover, in relation to synchronized handover.
One problem with handovers is the handover break time. Since the physical path of transmission is switched by different machines, inevitably a certain delay occurs. This delay is different in different systems and it is one of the objects of the invention to reduce this handover interruption time.
An earlier approach to minimize handover downtime in the downlink direction was to introduce distributed handover in the downlink. This idea gives downlink numbers to both said BTS old and said BTS new by using a radio equipment in the switch. This reduces the downlink handover interrupt to only the interruption caused by the mobile station, signaling over the air interface and delay caused by interfoliation.
In the uplink direction, synchronous handover has been used to reduce the handover interruption time, due to reduced signaling over the air interface. One way to use synchronous handover is to have BTS new use the detection of the four RACH bursts transmitted by the mobile station, such as a criterion for transmitting the handover detected message to the base station controller in GSM.
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Another way to use synchronous handover is to have the BTS new transmitted handover detected-inset message to the base station controller upon receipt of a properly decoded signaling frame or a properly decoded TCH frame. In this case, no RACH bursts are needed, which reduces uplink interruption time by 20 ms. Accordingly, when using this solution, the transmission of RACH bursts at the mobile station is interrupted by handover command. The base station controller uses the receive handover detected message to initiate uplink channel switching. However, the handover detected message is received at a time when the first speech frame on the traffic channel has already been transmitted, or partially transmitted (i.e., the delay may be less than one frame), over the Abis interface. Consequently, the change of uplink channel may occur too late, depending on the signal load and the specific realization.
For an asynchronous handover, the switching of a delay factor may occur near optimization switching time. A delay is needed, as the mobile station must wait for the message physical information before any broadcast on the assigned traffic channel. The resulting switching time varies due to message queues on the Abis interface in the base station controller.
It is also known that one can use an equipment in the switch to connect a conference call between BTS old and BTS new. This is a form of distributed handover where, however, the switching is performed at 64 kbit / s and need not have the same advantages as the invention, where the switching is done at the sub-speed level.
One can see how previous approaches have used TRAU, and their non-optimal switching at handover. First, when two TRAUs are used, if the switching is done prematurely, the output of the old TRAU, which performs some masking based on the last received speech frame or the
507 432 most recently received SID frame. The new TRAU has no valid voice data or previous SID or voice information. It then begins to send silence. If switching occurs too late, speech information is lost. It should be noted that the accuracy is 125 με, since the switching is done on the PCM side of the plurality of TRAUs.
In these previous procedures using TRAU, if switching is done prematurely, the output of the old TRAU, which performs some masking based on the last received speech frame or the last received SID frame, progresses until the first speech frame or SID frame is received from the new BTS. If switching occurs too late, speech information is lost. It should be noted that the accuracy is 20 ms since the switching is performed on the Abis side of said TRAU. This means that even if only part of the frame is lost, a full 20 ms of speech information is lost. A further problem with this solution is that the switching moment is not in phase with said TRAU frames. At the time of switching, said TRAU considers the TRAU frames from said new BTS as a disturbance until they have been re-synchronized to the new phase.
Although different approaches exist to minimize handover interruption time, there is still room for improvement. It is still possible to optimize the switching opportunity in the uplink direction, and one way to do this is to introduce a distributed handover in the uplink direction.
Summary of the Invention
The invention uses the concept of distributed handover to minimize interruption of speech frames. This is similar to the idea of soft handover used at CDMA. However, the invention is applied to a digital TDMA system such as the GSM system.
Instead of assigning a new TRAU to BTS new in said handover, the invention uses the same TRAU and switching
507 432 is made on the Abis side of said TRAU, at full speed of 16 kbit / s or half speed of 8 kbit / s GSM, regardless of whether TRAU is located at the base transceiver station or somewhere more central, up to the mobile telephone exchange. The actual speed is not important, the invention can be applied to other systems, regardless of the transmission speed on the BTS side of said TRAU. Although other systems exist that use a TRAU for handover, they do not use the idea of the invention, which is to have two uplink channels for soft handover, where the best embodiment uses only one TRAU.
The new invention can be applied to both handover between cells controlled by the same base station controller, intra-BSC handovers and handover between cells controlled by different base station controllers, inter-BSC handovers. It can also be applied to intracell handovers from one channel to another at the same base transceiver station. It can also be applied to changed voice coding handovers where said TRAU uses two different speech encoders (for example, both half-speed and full-speed), and both voice and data services work with the invention.
By maintaining the same TRAU, interruptions caused by the switching of uplink traffic can be more easily masked by said TRAU, since said TRAU has information stored from BTS old regarding the speech frames being transmitted. Since the uplink handover interrupt with synchronous handover can be as short as 40-60 ms under ideal conditions, said TRAU probably generates partially attenuated speech from BTS-old, or perhaps safety noise, based on data received from BTS-old.
In the invention, switching is performed in the uplink of said TRAU based on the quality of the received data from both BTS old and BTS new. This new TRAU has two inputs and two outputs on the Abis interface, instead of one input and one output, such as the TRAU used in today's system. It also has an input and an output on the A interface,
507 432 as in today's system. This modified TRAU runs two Abis protocols in parallel, independently of one another, on an Abis channel
A and an Abis channel B.
An object of the construction in accordance with the invention is to minimize the loss of speech frames on the traffic channel to what is possible in the GSM standard. Time is lost only for frames stolen for signaling over the air interface, time is taken by the mobile station to physically switch to BTS-new, and the delay is caused by interleaving.
Another object of the invention is to mask each loss frame with an error tracking algorithm, since said TRAU already has information from BTS old.
A further object of the invention is to avoid the use of a radio structure in the gear or the sub-speed gear which may cause some interference in connection or disconnection. The radio function can then be used to monitor traffic.
Short figure description
The invention is now described in more detail with reference to preferred embodiments of the invention, which are given by way of example only, and are illustrated in the accompanying drawings, in which:
Fig. 1 shows an overview view of a mobile communication system comprising various essential elements and the location of the invention in relation to these elements, where the signal converter and the speed adjustment unit (TRAU) are located at the base station controller.
Fig. 1a shows a more detailed view of the switching used in the mobile communication system of Fig. 1.
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Fig. 2 shows an overview view of a mobile communication system with various essential elements and the arrangement of the invention in relation to these elements, where the signal converter and speed adjustment unit (TRAU) is located at the mobile telephone exchange.
Figure 2a shows a more detailed view of the switching used in the mobile communication system of Figure 2.
Fig. 3 shows a diagram of the functional elements of the signal converter and speed adjustment unit (TRAU) according to the invention.
Fig. 4a shows a diagram of the channel assignment during an intercell handover.
Fig. 4b shows a diagram of the channel assignment during an intracell handover.
Fig. 5 shows a flow chart of the steps of the method performed in accordance with the invention.
Fig. 6 shows a time diagram of the traffic flow in the channels as the method according to the invention is carried out.
Fig. 7 shows a more detailed time schedule of the timing of various events of the method according to the invention.
Detailed description
The invention applies to both intra-BSC handovers and interBSC handovers. The embodiment described here focuses on an intra-BSC handover, from a base transceiver station controlled by one base station controller to another base transceiver station controlled by the same base station controller.
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Typically, the base station controller makes all decisions regarding intra-BSC handovers, including the allocation of radio resources and ground lines. However, it is possible for the mobile switchboard to be responsible for the handover decision. In the preferred embodiment of the invention, said TRAU is located at the mobile telephone exchange, although it may be located more peripherally at the base station controller or base transceiver station.
In previous approaches with said TRAU located at the base station controller, each call to and from a mobile station has both uplink and downlink channels for this call which is controlled by a TRAU. Once a handover has been performed from one base transceiver station to another base transceiver station, the responsibility for voice coding for both uplink and downlink channels is transferred to a second TRAU, which handles the speech frames to and from the BTS new.
One aspect that distinguishes the invention from previous approaches is that only one TRAU is used where switching is performed on the Abis side at 16 kbit / s and that the TRAU is simultaneously connected to two base transceiver stations during ongoing handover. Earlier approaches either use two TRAUs for handover when switching is performed at 64 kbit / s, or one TRAU when switching is performed at 16 kbit / s and that one TRAU is connected to only one base transmitter station at a time during ongoing handover. Both approaches provided a less optimal switchover opportunity for handover. In the invention, new ground resources must be allocated to transmit the signal from said TRAU to BTS new, although only one TRAU is needed for voice coding and speed adjustment for both BTS old and BTS new.
A simplified overview of a mobile communication system is shown in Figure 1. The division of the system into a switching system (SS) 10 and a base station subsystem (BSS) 20 is shown. As previously pointed out, the base station subsystem administers
507 432 radio interface between the mobile station 30 and the rest of the mobile communication system. The switching system administers the connection of the mobile communication system with external networks, such as the public telecommunications network (PSTN).
The core of the switching system 10 is a mobile telephone exchange (MSC) 40 which has direct contact with a base station controller (BSC) 50. The base station controller 50 then contacts at least one base transmitter station (BTS) 60a-60c. Here are shown three base transceiver stations, BTS1 60a, BTS2 60b and BTS3 60c, although there may be an arbitrary number of base transceiver stations 60a-60c. These base transceiver stations 60a-60c then have direct contact with a mobile station 30 located in the geographical area covered by this particular base station
<td colspan="4">control unit 50.</td>
<td>A feature</td><td>at</td><td>The GSM system is the interface</td><td>between mobile</td>
<td>telephone exchange</td><td> 40</td><td>and the base station controller</td><td>50, MSC-BSC</td>
<td>interface,</td><td>as</td><td>is called the A interface (A</td><td>) 70 in GSM.</td>
The interface between the base station controller 50 and the base transceiver stations 60a-60c, the BSC-BTS interface is called the A-bis interface (A-BIS) 80 of the GSM. In most systems, communication over these interfaces is conducted along ground lines, while communication between the base transceiver stations 60a-60c and the mobile station 30 is performed over an air interface with radio transmission.
Communication over the public telecommunications network (PSTN) is 64 kbit / s, while over the air interface it is usually much slower to save bandwidth. In GSM, mobile station 30 transmits at an effective rate of 22.8 kbit / s to each base transceiver station 60a-60c, which in turn first removes the channel coding bits, which reduces the speed down to 13 kbit / s, and then adds various signaling information to increase the bandwidth of each channel to the base station controller 50 to 16 kbit / s. The purpose of the signal converter and speed adjustment unit (TRAU) 100 is to
507 432 acts as the network port function between the 16 kbit / s speed and 64 kbit / s speed.
Fig. 1a shows a more focused view of the switching according to the invention. A TRAU 100 is connected to two gears, a 64 kbit / s gear 110 and a 16 kbit / s gear 120. Although only one TRAU 100 is displayed, there are usually several TRAUs in the same location, depending on the realization and requirements of the system. The 16 kbit / s switch 120 has lines 125 going to each base transceiver station 60a-60c controlled by this particular base station controller 50. Three separate lines 125 are shown here, one for each base transceiver station 60a-60c. The 16 kbit / s switch is controlled by the base station controller 50 and controls the routing of signals between said TRAU 100 and the base transceiver station 60a-60c. When the mobile station 30 performs roaming from cell to cell 90a-90c, handovers are performed and during this process, the 16 kbit / s exchange directs the signals so that the transmission occurs between said TRAU 100 and the necessary base transceiver stations 60a-60c.
Each TRAU 100 is provided with two lines 105 between itself and 16 kbit / s switch 120. This is an aspect which distinguishes the invention from prior art. In the previous approach, only one line 105 was assigned between said TRAU 100 and 16 kbit / s switch 120 during a handover. As shown below, during handover, said TRAU 100 is simultaneously assigned two uplink and two downlink channels during the process. These two channel pairs are carried over two lines 105, one pair of uplink and downlink channels for each line 105.
A pair of uplink and downlink channels is then switched by 16 kbit / s switch 120 to the base transceiver station 90a-90c which communicates with the mobile station 30 prior to handover. A second pair of uplink and downlink channels is switched to the base transceiver station 90a-90c, which is responsible for communication with the mobile station 30 after the handover is performed. The function of the 16 kbit / s gear 120 is clearly shown in Fig. 1a. At the up 507 432 find, there are two lines 105 between said TRAU 100 and 16 kbit / s gear 120, each carrying an uplink and a downlink channel. The switch 120 switches these two lines 105 to two of the corresponding lines 125, three of which are shown here, between the 16 kbit / s switch 120 and two of the corresponding base transceiver stations 60a-60c.
Another switch is also shown in Fig. 1. This is a 64 kbit / s switch 110. There is a line 115 between each TRAU 100 at this BSC 50 and this 64 kbit / s switch 110. Each call involving a mobile station 30 must be connected up to 64 kbit / s before transmitting along the correct path. Here is shown a line 45 between 64 kbit / s switch 110 and the mobile telephone exchange 40. The mobile telephone exchange 40 then directs the call to said PSTN or perhaps to another base station controller 2 this mobile system.
In cases where the mobile station 30 communicates with another mobile station in the coverage area of the same base station controller 50, the 64 kbit / s switch 110 can only switch to another TRAU in the same base station controller 50 without first connecting to the mobile telephone exchange 40. However, even calls between mobile stations in the same cell are each connected up to 64 kbit / s in GSM before being sent to another mobile station. Also in the embodiment shown here, the transmission occurs at 64 kbit / s (lines 45, 115) and 16 kbit / s (lines 105, 125), which is specific to the GSM system. The invention is not limited to these speeds and works equally well in similar systems that use other transfer rates.
In the embodiment shown in Figures 1 and 1a, the TRAU 100 is located at the same physical location as the base station controller 50. However, the invention can also be applied to embodiments where the TRAU 100 is physically located at other locations. Said TRAU 100 may be located at other locations along the transmission chain, in between
507 432 the base transceiver stations 60a-60c and the mobile telephone exchange 40. From a functional point of view, the TRAU 100 belongs to the location of the base transceiver stations 60a-60c, and forms part of the A-bis interface 80 in accordance with the GSM specifications.
Fig. 2 shows the preferred embodiment wherein said TRAU 100 is located at the location of the mobile telephone exchange 40. The base station controller 50, such as a functional unit, is spread over its own location and the location of the mobile telephone exchange 40, and includes the link 125 between these two locations. On the other hand, the A interface 70, indicated by the dotted line, is located at the location of the mobile telephone exchange 40, over a very short distance. As shown in FIG. 2, compared to FIG. 1, the A interface 70 in the preferred embodiment is actually located at the physical location of the mobile telephone exchange 40. The reason for the somewhat artificial definitions of the various interfaces is to avoid the possibility of transmitting data at 16 kbit / s or 64 kbit / s at A interface 70.
As a result, since the GSM specifications do not strictly allow for functional location, even though they allow a physical location, of the TRAU 100 in the mobile telephone exchange 40, every call between two GSM users must undergo two conversions from 16 kbit / s to 64 kbit / s and back again. Accordingly, each call includes two signal conversions, and accordingly two TRAUs 100, one for each GSM user.
Similar to the embodiment of Figures 1 and 1a, in the preferred embodiment of Figure 2 there are two switches 110, 120 which are located at the mobile telephone exchange 40 and belong to the TRAU 100. These are 64 kbit / s switch 110 with a 64 kbit line 115 between itself and said TRAU 100, and a 16 kbit / s switch 120 with lines 105 carrying traffic at 16 kbit / s. These function similarly to their realization in the previous embodiment of FIG. 1 and 1a, where they were located in the base transceiver station 50.
507 432
A major difference of this preferred embodiment in relation to the embodiment of Fig. 1a is that the 16 kbit / switch 120 does not switch between different base transceiver stations 60a-60c. Instead, it switches between different base station controllers 50, 51. Here two base station controllers 50, 51 are shown, although there could be more. There are groups of lines 125, 126 that carry numbers or data between 16 kbit / s switch 120 and the base stations controller 50, 51. At the base station controller 50 there is also a 16 kbit / s switch 56 which switches signals to and from the appropriate base transceiver stations 90a-90c over 16 kbit / s lines 55.
The geographical area controlled by a base transceiver station 60a-60c is called here a cell 90. Here three different cells 90a-90c are shown. These cells 90a-90c are controlled by a base station controller 50, but different base transceiver stations 60a-60c. A mobile station 30 in the first cell 90a receives transmissions from, and transmits to, BTS1 60a. Likewise, when mobile station 30 is in second cell 90b, it receives and transmits to BTS2 60b, and when mobile station 30 is in third cell 90c, it receives and transmits to BTS3 60c.
As the mobile station 30 performs cell-to-cell roaming, it is often necessary that the responsibility for radio transmissions over the air interface be transferred from one base transceiver station to another. For example, as the mobile station 30 moves from the geographical area of the first cell 90a to the second cell 90b, the control of the radio transmissions over the air interface is transmitted from BTS1 60a to BTS2 60b. If mobile station 30 frequently performs roaming from one cell 90a-90c to another, interruptions can often occur due to handover.
In the method of the invention described below, said TRAU 100 may be located at either base station controller 50 location, as shown in Figure 1, and
507 432a, or at the mobile telephone exchange, as shown in Figures 2 and 2a. The TRAU 100 is an essential unit involved in handover. As the mobile station 30 performs roaming through the geographical area covered by the base station controller 50, it is often necessary for the base station controller 50 to switch control of the communication to the mobile station 30 between the various base transceiver stations 60a-60c. This is accomplished by a 16 kbit / s switch 120, in Fig. 1 and 1a or 56 in Figs. 2 and 2a, located at the base station controller.
One of the essential functions of the base station controller 50 is to control the switching between the various base transceiver stations 60a-60c under its control. In the embodiment shown in Figures 2 and 2a, the base station controller 50 still controls the switching performed by the TRAU 100 using its 16 kbit / s gear. It is possible for other embodiments, not shown, that the switching is controlled by the mobile telephone exchange 40 instead of the base station controller 50.
Fig. 2a shows a more concentrated view of the switching of the preferred embodiment of the invention. The preferred embodiment shown in Figure 2 illustrates an intraBSC handover. During said handover in accordance with the invention, there are two pairs of uplink and downlink channels simultaneously recorded for each TRAU 100. These two pairs occupy the two 16 kbit / s lines between said TRAU 100 and said 16 kbit / s switch 120 at the mobile telephone exchange 40. location, one channel pair for each line 105. They also occupy two of the 16 kbit / lines 125 between the 16 kbit / s switch 120 of the mobile telephone exchange 40 and 16 kbit / s switch 56 of the base station controller 50. They also occupy two 16 kbit / s lines 55 between the base station controller 50 and two of the base transceiver stations 60a-60c.
The responsibility for the 16 kbit / s switch 120 at the MSC 40 location is to direct the two lines 105 coming from said TRAU 100 to the correct base station controller 50.
507 432 intra-BSC handover shown here, the two lines 105 are routed to the same BSC 50. The 16 kbit / s switch 56 of this BSC 50 then directs these two channel pairs on the correct two lines 55 to the correct two base transceiver stations 60a. 60b. This shows some of the advantages of the preferred embodiment, where more transmission is performed at 16 kbit / s instead of at 64 kbit / s.
Although Figures 2 and 2a show an intra-BSC handover, the invention also works for an intra-MSC handover. The second base station controller 51 also has a similar switch to the first base station controller 50 and controls similar base stations which are not shown. If the mobile station 30 performs roaming from a cell 90a-90c in the control area of the first base station controller 50 to a cell not shown, under the control of the second base station controller 51, a handover in accordance with the invention can still be performed. Here, too, two pairs of uplink and downlink channels are used during said handover. In addition, two 16 kbit / s lines are used for these channels between said TRAU 100 and the base transceiver stations.
During said handover, the 16 kbit / s switch 120, located at the location of the mobile telephone exchange 40, connects a channel pair to the first base station controller 50 over one of the lines 125 between the mobile telephone exchange 40 and the first base station controller 50. 16 kbit / s switch 56 in the first base station controller 50, the first channel pair then connects to the correct base transceiver station 60a-60c over one of its 16 kbit / s lines 55. 16 kbit / s switch 120 at the location of mobile telephone exchange 40, the second channel pair connects to the second base station controller 51 over one of its 16 kbit / s lines 126. A 16 kbit / s switch, not shown, in the second base station controller 51 then switches these to the correct base transceiver station, which is also not shown, under its control and which is then responsible for transferring to, and from, the mobile station 30 upon completion of the handover.
507 432
Since each call involving this particular mobile station 30 must undergo a conversion from 16 kbit / s to 64 kbit / s, a TRAU 100 must be involved whenever there is a transmission of speech or data to or from this mobile station 30. in the current approaches, which use two separate TRAUs for handover between, for example, BTS1 60a to BTS2 60b, the responsibility for each speech coding is also transferred from one TRAU 100 to another. This makes sense from a functional point of view, since the TRAU 100 is a functional part of the base transceiver station 60a-60c.
However, the GSM specifications allow the placement of the TRAU 100 at the base station controller 50, as shown in Fig. 1 or 1a, or at the mobile telephone exchange, as shown in Fig. 2 or 2a, and some manufacturers realize it in one of these ways. In previous approaches, a separate TRAU 100 is used for each base transceiver station 60a-60c. In the invention, only one TRAU 100 is used for handovers between base transceiver stations 60a-60c which are controlled by a single base station controller 50, and the construction allows distributed handover on the uplink.
Fig. 3 shows a diagram of the construction of the TRAU 100 according to the invention. The various elements include a speech encoder (SPE) and a discontinuous transmission unit (DTX), which performs speech encoding on the downlink transmission. Here is also shown a speech decoder (SPD) and DTX unit 210 which performs speech decoding on the uplink transmission. Some digital mobile communication systems, such as GSM, use discontinuous transmission technology. This is sometimes called variable bit rate. It aims to increase the efficiency of the system by reducing the noise level, by preventing transmission of the radio signal during speech breaks.
A choice has been made by the system on a call per call basis as to whether to transfer in normal mode or DTX mode. This is because the DTX mod slightly deteriorates
507 432 transmission quality, especially when used on both uplink and downlink. In DTX mode, the goal is to encode the speech at a higher speed when the user is actually talking, 13 kbit / s GSM, and otherwise at a lower bit rate, about 500 kbit / s GSM.
This low speed is sufficient to encode the background noise, which is re-recorded to the listener so that he or she does not think the connection is broken. This is the definition of safety noise. Experience has shown that a user is significantly disturbed when the background noise behind the speech suddenly ceases. One way to avoid this interference is to generate an artificial noise when no signal is received. The background noise characteristic during the call is regularly upgraded and transmitted with specific frames called silence description frames (SID).
The speech decoder 210 and speech encoder 220 also performs coding on speech samples according to various algorithms which are not essential to the invention. The number is divided into 20 ms segments, which are digitized and coded to be transmitted over a certain channel with further added information, for a sum of 260 bits in GSM. After encoding the downlink signal, speech encoder 220 sends the signal on a line 221 which is then divided into two lines 222, 223 which go to said Abis handler DnL A 245 and Abis handler DnL B 265. In the embodiment shown, the signal is only divided when a copy is transmitted on both handlers 245, 265. As shown in the embodiment of Fig. 3, the signal transmitted over both Abis channel A, DnL (240 Fig. 3) and Abis channel B, DnL (260 Fig. 3) is identical.
The channel concept is a key concept in systems that use a TDMA procedure, such as GSM. A bit stream carried over the frequency of a carrier is sequentially divided into frames. The frames are then divided into time slots, eight time slots in GSM. A time slot in a TDMA frame on a carrier frequency is called a physical channel. Accordingly, there are eight physical channels per carrier frequency,
507 432 or only carrier waves, in GSM. The information transmitted during a time slot is called a burst.
Many different types of information must be transmitted between the base transceiver station and the mobile station, for example user data and control signaling. Depending on the type of information that needs to be transmitted, we refer to different logical channels. These logical channels are mapped onto the physical channels. For example, in GSM, speech is transmitted on the physical channel traffic channel, which is assigned to a particular physical channel during the transmission.
Also shown in Figure 3 is an error hiding module 200 which is responsible for implementing various algorithms for hiding lost speech frames. In addition, there are four Abis handlers 235-245255-265 who are responsible for the phase synchronization of voice coding to the air interface to reduce the delay. Abis handlers 235-245-255-265 also handle synchronization of frames from the base transceiver stations.
Although the embodiment shown in Fig. 3 shows four Abis handlers 235-245-255-265, it is a functional separation. There are two separate physical units, a channel A Abis handler which includes two functional subunits Abis handler DnL A 245 and Abis handler UpL A 235, and a channel B Abis handler which includes the two functional subunits Abis handler DnL B 265 and Abis Manager UpL B 255. The connection of the Abis handler DnL A 245 and the Abis handler UpL 235 to a unit is shown by the first dashed line 241. The connection of the Abis handler DnL B 265 and the Abis handler UpL B 255 to a unit is shown by the second dashed line 261.
In TRAU 100 there is also a management controller 280 and a switch 270. The Abis handler UpL A 235 has an input 237 to the switch 270 and the Abis handler UpL B 255 also has an input 257 to this switch 270. In addition, the Abis handler has the UpL A
507 432
235 an input 236 to the management controller 280 and the Abish handler UpL B 255 has an input 256 to this management controller 280. The management controller 280, in turn, has an input 281 to the switch 270.
At the beginning of this process, a mobile station (Fig. 1) transmits speech frames to, and receives speech frames from, a first base transmitter station (60a Fig. 1). Before a handover is initiated, speech frames are received in the signal converter and speed matching unit (100 Fig. 3) from the first base transceiver station (60a Fig. 1) on Abis channel UpL A 230 and sent to the Abis handler UpL A 235 for synchronization. The Abish handler UpL A 235 then sends these frames to the switch 270 and the handling controller 280. Since there is no input to the handling controller 280 from the Abis handler UpL B 235 at this time, the management controller 280 instructs the switch 270 to allow only the signal from the Abis handler UpL A 235 is transmitted through switch 270 to the error decay module 200 through its input (271 Fig. 3). The error sensing module 200 then transmits this signal through its input (201 fig. 3) to the speech decoder 210.
After a handover has been initiated, the transfer to said TRAU 100 begins from a second base transceiver station (60b Fig. 1) over Abis channel UpL B (250 Fig. 3). During the execution of a handover in accordance with the invention, transfers from the two involved base transceiver stations (60a, 60b Fig. 1) occur on both Abis channel A UpL 230 and Abis channel B UpL 250. After both the Abis handler UpL A 235 and the Abis handler UpL B 255 both perform their synchronization, they forward the signals to the management controller 280 and the switch 270. The management controller 280 then checks various quality measures of these signals using different quality measurement means that are not essential to the invention, and decides which channel to transmit through switch 270.
507 432
Before the mobile station (30 fig. 1) switches to the second base transceiver station (60b fig. 1), the speech frames it transmits to the first base transceiver station (60a fig. 1) are transmitted over Abis channel UpL A 230 to the Abis handler UpL A 235 and on to the switch 270 and the handling controller 280. These speech frames have an error frame indicator flag (BFI) indicating to the management controller 280 that these are valid speech frames (BFI = 0). This results in the management controller 280 directing the switch to transmit the signal from the Abish handler UpL A 235. After the mobile station (30 Fig. 1) has switched, it starts transmitting to the second base transceiver station (60b Fig. 1). These speech frames are then transmitted over the Abis channel UpL B 250 to the Abis handler UpL B 255 and on to the switch 270 and the handling controller 280. These speech frames have an error frame indicator flag indicating to the management controller 280 that these are valid speech frames (BFI = 0). At the same time, the Abis handler UpL A 235 receives speech frames from the first base transceiver station (60a Fig. 1) with an error frame indicator flag indicating invalid speech frames (BFI = 1). This results in the management controller 280 controlling the switch 270 to switch to the Abis handler UpL B 255 and allowing only the signal from the Abis handler UpL B 255 to be transmitted, and not the frames of the Abis handlers UpL A 235. Although the management controller 280 can use an error frame indicator flag to control the switching, it can also use any of a number of other quality indicators depending on the specific implementation. The specific quality indicators are not subject to the invention, which operates using any of these measurement methods in the management controller 280.
Fig. 4a shows the position of an intercell handover. We assume that a mobile station 310 transmits and receives on a carrier frequency 345 which includes either voice or data. The mobile station 310 is located in cell one 320 which is covered by a base transceiver station called BTS1 340. Initially, said TRAU 100 is assigned to BTS1 340. TRAU's 100 speech frames are transmitted to and
507 432 from mobile station 310 and received and fed on Abiskanal A 360-370, which includes both a downlink and an uplink portion.
The transfer direction from a base transceiver station, for example BTS1 340, to mobile station 310 is defined as the downlink and the opposite direction as the uplink. For Abis channel A 360-370, the uplink section is Abis channel A UpL 360 and the downlink section is Abis channel A DnL 370.
Likewise, Abis channel B 380-390 includes both a downlink and an uplink portion. The uplink portion is Abis channel B UpL 380 and the downlink portion is Abis channel B DnL 390. At this time, Abis channel B 380-390 is not connected to a base transceiver station and a sub-speed pattern is transmitted over this channel.
When mobile station 310 performs roaming 315 to another cell, here cell two 330, which is covered by another BTS, in this case BTS2 350, makes the base station controller, see BSC 50 Fig. 1, 1a, 2 or 2a, the decision to implement a handover from BTS1 340 to BTS2 350. Accordingly, the BTS old previously described is BTS1 340, and BTS new is BTS2 350. The decision made by the base station controller can be based on any of a number of parameters and is not subject to the invention. .
Fig. 4b shows the position of an intracell handover. The situation is similar to that in Fig. 4a except that there is only one base transceiver station, BTS 340, which performs handover in the same cell (ie intracell). This BTS 340 includes both the Abis channel A 360-370 and the Abis channel B 380-390. Instead of handover from Abis channel A 360-370 in one base transceiver station to Abis channel B 380-390 in another base transceiver station, said handover is performed from Abis channel A 360-370 to Abisk channel B 380-390 in this specific BTS 340.
507 432
Fig. 5 shows a flowchart of the method of a handover according to the invention, as applied in a GSM mobile communication system. Reference is also made to Fig. 4a, intercell handover, following the procedure of Fig. 5. After a decision has been made to carry out a handover, block 10, of the base station controller, the base station controller transmits a message channel activation, block 20, to BTS2, see BTS2 350 in Figure 4a. A message channel activation is a simple request and confirmation procedure that includes information specifying transfer mode, digit mode and continuous downlink and uplink transmission mode. In addition, they include the information that the mobile station 310 needs for access and first power control settings.
Said BTS2 350 begins upon receipt of this channel activation message information exchange on number line over Abis channel B 380-390 Fig. 4a, with said TRAU 100, to set basic transmission mode and discontinuous transmission mode; this is the time when synchronization between the mobile station 310 and said TRAU 100 normally begins. Thereafter, the TRAU 100, block 30 of Fig. 5, assigns the Abiskan channel B 380-390 for handover.
When Abis channel
B 380-390 has been assigned, block
30, a confirmation is sent fig.
5) from BTS2 of channel activation message,
350 to the base station controller.
block 40
The road through does
360-370 Fig. 4a, is not yet vacant. This allows the mobile station 310 to return to AbisAbis channel A channel
A 360-370 on handover would fail.
On Abis channel B DnL 390, said TRAU 100 commences the transmission of TRAU speech frames, block 50 Fig. 5, to said BTS2 350. This is done as confirmation that speech frames received from BTS2 350 in Abis handler UpL B 255 fig. 3. The speech information in these speech frames to BTS2 350 over Abis channel B DnL 390 is identical to that of the speech frames still being transmitted
507 432 to BTS1 340 over Abis channel A DnL 370. Accordingly, voice frames are transmitted parallel in the downlink direction to both BTS1 340 and BTS2 350 and then to mobile station 310. However, at this time, only mobile station 310 is switched for frequency transmission of BTS1 340 and does not actually receive the signal transmitted by BTS2 350.
The phase of speech coding with the same phase as it is unchanged, ie. synchronized
BTS1 340, which uses a timeContent of the uplink frames from the synchronization procedure.
said BTS2 350 along Abis channel B UpL 380 does not include any useful data at this time. The data is sent to the voice echo still there, see SPD 210 Fig. 3, coming from BTS1
340.
sends
The base station controller command specified
310 via BTS1 340 in GSM, then a handover block 60 mobile station Fig. 5, to the over Abis channel A DnL 370, Fig. 4a. You can mobile station this message or not. At
RACH transmission is then, block 70 choose to pass through
310 so that it either sends RACH bursts this embodiment off. The mobile Fig. 5, to the BTS2 350 circuit solution, upon receipt of the handover command.
it is assumed that said station 310 changes semed with its own
The reception of speech frames from mobile station 310 is then interrupted, block 80 Fig. 5, at BTS1 340. This is indicated for said TRAU 100 upon receipt of a fault frame indicator flag (BFI) along Abis channel A UpL 360, and said TRAU 100 begins to attenuate the frame. in accordance with an error tracking algorithm. This error tracking algorithm may be one described in PCT / SE96 / 00311, Arrangement and Method Relating to Speech Transmission and a Telecommunications System Comprising Such Arrangement, the contents of which are hereby incorporated by reference. Upon receipt, block 80 Fig. 5, of BTS2 350 of the first correctly coded signaling or traffic channel frame (TCH) from mobile station 310, BTS2 350 transmits
507 432 a handover detected message specified in GSM, block 90 Fig. 5, to the base station controller.
In the case where quality measures in said TRAU indicate, for example, where BFI = 0, the TRAU 100, block 100 Fig. 5, switches from BTS1 340 to BTS2 350 and sends the contents of the TRAU frame to the error tracking block, see error tracking na time sends the speech decoder, see SPD partially attenuated speech in case of a short nad, or possibly security noise, if
200 Fig.
210 Fig.
interrupting an appropriate algorithm
At the then or silent3, has been realized, in the case of a longer interruption. The number can then be increased or decoded without modification. At this time, Abis channel B DnL 390 receives the control from the speech coding phase, ie. the synchronization of the air interface timing at
BTS2 350 can now be achieved.
Thereafter, a handover terminated message, as specified in the GSM, is transmitted from the mobile station 310 to the base station controller, block 110 Fig. 5, releasing the channel on BTS1 340, disconnecting Abis channel A 360-370, block 120 Fig. 5, and marks this as free and ready for use in a new handover. The part-speed rest pattern is now broadcast on Abis channel A 360-370.
The method shown in Fig. 5 has been described above as applied to an intercell handover, as shown in Fig. 4a. The method works equally well for intracell handover, as shown in Fig. 4b. The difference in the method is that the functions of BTS2 in an intercell handover are performed by the same BTS in an intracell handover. For example, the ChL activation to BTS2, block 20 of Figure 5, is a channel activation to another channel in the same BTS at an intracell handover. When speech frames begin to BTS2, block 50 Fig. 5, in an intercell handover, the equivalent of an intracell handover is that the speech frames begin on the newly activated channel in the same BTS.
507 432
Further, when the mobile station switches to BTS2, block 70 Fig. 5, in an intercell handover, the corresponding action in an intracell handover is that the mobile station is switched only to the newly activated channel transmitted by the same BTS. The mobile station then interrupts transmission of speech frames to the old channel in said BTS and begins transmission of speech frames to the new channel in the same BTS, corresponding to a similar document for an intercell handover, block 80 Fig. 5.
The same BTS then sends a handover detected message, instead of BTS2 in an intercell handover, block 90 Fig. 5. TRAU then switches from one channel to another in the same BTS, instead of BTS1 to BTS2, as in an intercell cell. handover, block 100 Fig. 5. The final difference between intercell and intracell handover is the channel release. In an intercell handover, channel A must be released on BTS1, block 120 fig. 5, while in an intracell handover, channel A is only one other channel in the same BTS that must be released.
Fig. 6 shows an overview view of the timing of handover according to the invention. Up to the time of 510, voice traffic is only generated to BTS1. After receiving the handover command, a new channel to BTS2 is opened at time tl 510. After time tl 510 traffic on channels to both BTS1 and BTS2 is generated. After receiving the handover detection message, the channel is released to BTS1 at time t2 520 and traffic is generated to BTS2 only.
Fig. 7 shows a more detailed overview view of the timing of said handover according to the invention. The timing here begins with handover command 600 being sent to the mobile station from the base station controller. The base station controller steals 20 ms with speech on the traffic channel in the downlink to send this command. After a short delay, traffic in BTS1 610 stops as the mobile station prepares for frequency change 620 to the frequency for BTS2. After the mobile station has ceased broadcasting to
507 432
BTS1 610 is a short delay before frequency switching 620 caused by the time differences from the mobile station to BTS1 and BTS2. The mobile station must synchronize its multi-frame display with that of BTS2. The delay can be as small as 0 ms, if the transfer time to BTS1 and BTS2 is identical, up to 20 ms for an entire multi-frame.
After the mobile station has switched 620 to the new frequency and started transferring to BTS2, there is a further delay before the first speech frame 630 is processed. This delay is caused by interleaving. At GSM it is fixed and equal to 8 bursts, giving a total of about 4.6 ms.
The first speech frame 630 can be either 20 ms with speech or a handover terminated message, as described in Figure 5, which steals 20 ms with speech from the traffic channel.
Since switch 650 is based on handover detected message 640, the problem is that the time varies between the actual switching time and the optimal switching time. This is caused by three things: one, the time variation between detection of handover 640 in the base transceiver station relative to the first received speech frame; two, the time variation of the base station controller upon receiving handover detected 640 from BTS2 caused by message queue, signal delay, etc .; and three, the time variation of the base station controller when performing switching caused by the central processor load, signal delay, etc.
In a synchronous handover without direct access channel bursts, the base transceiver station uses the decoding of a correct fast associated control channel block or a correct traffic channel block to detect said handover. The Direct Access Channel (RACH) is a channel used by the mobile station to request assignment of a control channel! for signaling
507 432 during the connection of the call at BTS2. The fast associated control channel (FACCH) is actually a use of the traffic channel on the uplink where 20 ms bursts of speech, or data, are stolen for signaling purposes.
The use of a traffic channel or a fast associated control channel block is a realization specific to the mobile station. The delay in this case is caused by the length of the block, which is sometimes 20 ms of a full-speed traffic channel and 40 ms of a half-speed traffic channel.
In a synchronous handover with direct access channel bursts, the base transceiver station uses the decoding of the correct direct access channel burst to detect said handover. This is a realization specific to the mobile station if the first block it sends after direct access to the channel bursts is a fast associated control channel or a traffic channel. Accordingly, this means a delay of 20 ms for a full-speed traffic channel and 40 ms for a half-speed penalty channel.
For non-synchronous handover, the base transceiver station uses the decoding of correct direct access channel bursts from the mobile station to detect said handover. The bass transceiver transmits the physical information (for example, timing information) to the mobile station. There is then a specific realization in the mobile station about how long it takes until it broadcasts the first traffic channel or the fast associated control channel. Here, the delay here includes 20 ms for a full speed channel or 40 ms for a half speed channel plus the design-specific delay in the mobile station.
Since different hand poverty types (for example, synchronous and non-synchronous) can coexist in a network, many variations are added if the base station controller only turns on handover detecting 640 without any specific timer for each type of
507 432 handover. This would significantly increase the complexity of the software in the base station controller.
The described embodiment serves as an illustration and is not limiting. One of ordinary skill in the art will recognize that deviations can be made from the above-described embodiment without departing from the spirit and spirit of the invention. Accordingly, the invention should not be considered as limited to the examples described, but should instead be regarded as equal to the scope of the following claims.
507 432
Contents2
8 sheets
Sheet 1 Sheet 2 Sheet 3 Sheet 4 Sheet 5 Sheet 6 Sheet 7 Sheet 8
13 members in 9 offices
Priority claims2
| Document | Office | Kind | Date |
|---|---|---|---|
| 9603560 | Sweden | A | |
| SE19960003560 | – | – | – |
Members13
| Document | Office | Kind | |
|---|---|---|---|
| SE9603560D0 | Sweden | D0 | |
| SE9603560L | Sweden | L | |
| CA2267270A1 | Canada | A1 | |
| WO9815152A1 | World Intellectual Property Organization (WIPO) | A1 | |
| AU4478497A | Australia | A | |
| SE507432C2This record | Sweden | C2 | |
| EP0933000A1 | European Patent Office (EPO) | A1 | |
| BR9711425A | Brazil | A | |
| CN1239636A | China | A | |
| AU719645B2 | Australia | B2 | |
| US6138020A | United States of America | A | |
| JP2001508251A | Japan | A | |
| CN1109472C | China | C |
1 legal event, as the office reported them to INPADOC
Events
| Event | Code | |
|---|---|---|
| Patent has lapsedLapsedNUG | NUG |
Numbers
- Publication, DOCDB
- 507432
- Publication, EPODOC
- SE507432
- Application
- 9603560
- Application, DOCDB
- 9603560
- Application, EPODOC
- SE19960003560
Titles2
- Swedish
- Förfarande och enhet för distribuerad handover i upplänk
- English
- Procedure and unit for distributed handover in uplink
Classification
- CPC, 2
- H04W36/18
- G10L19/005
- IPC, 2
- G10L19 005
- H04W36 18