FI104875B - Data communication method in a base station system in a cellular radio network - Google Patents

Description

104875

Communication method in a cellular radio base station system

Field of the Invention

The present invention relates to a data transmission method in a base station system of a cellular radio network 5, comprising at least one base station and one base station controller, where

Background of the Invention

In cellular radio networks, there is an increasing need for packet switched data transmission in addition to circuit switched speech and data transmission. New solutions have been developed to enable existing cellular radio networks to be modified to provide the most cost-effective and efficient cellular network transmission possible.

GPRS (General Packet Radio Service) is a new GSM-based service in which the air interface circuit-free capacity is used for packet transmission.

One kind of bottleneck remains the transfer of packet switched data and packet switch signaling between the base station and the base station controller 20. As a solution, a separate data link for the implementation of the transfer has been proposed. However, the solution is not very attractive to operators as it causes: · Constant additional usage costs.

Since circuit switching signaling is performed using a specific signaling channel, it has also been proposed that packet transmission and packet switching signaling be performed using the free capacity of that signaling channel. Such a signaling channel may be called, for example, a LAPD channel according to the protocol used. The problem is, however, that generally one transceiver, i.e. eight traffic channels, has one 16 kbit / s LAPD channel in use, and that capacity is hardly available for use in packet transmission and packet switching signaling. There are also solutions where, for example, the signaling of five transceivers is carried on a single 64 kbit / s channel. However, even if the LAPD channel had no circuit switching signaling running, its capacity would not be very high.

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One possibility would be to increase the rate of said LAPD channel from 16 kbit / s to 64 kbit / s, in which case the packet transfer capacity could be 50 kbit / s. However, the problem again arises out of costs: the solution will incur fixed and fixed additional costs, independent of the use of packet transmission, for the operator. In the worst case scenario, the 2 Mbit / s PCM link used by the operator for transmission is so full that the proposed increase in capacity would require the introduction of a new PCM link. This is not only expensive but also difficult.

Brief Description of the Invention

It is therefore an object of the invention to provide a method and an apparatus implementing the method 10 so that the above problems can be solved. This is achieved by a method of the type disclosed in the introduction, which is characterized in that in a circuit-switched transmission connection, data is transmitted in TRAUs (Transcoder and Rate Adapter Unit) formed for transcoding.

The invention further relates to a base station system of a cellular radio network comprising at least one base station and one base station controller configured to transfer bi-directional data-switched data-to-circuit data transmission, and a base station and a base station controller in the circuit switching connection.

According to the invention, the base station system is characterized in that the base station system is arranged in a circuit-switched transmission connection to transmit data in the TRAU (Transcoder Γ and Rate Adapter Unit) formed for transcoding.

Preferred embodiments of the invention are claimed in the dependent claims.

The invention is based on the fact that the adaptivity of transmission at the air interface between circuit switched and packet switched data transmission is also utilized between the base station and the base station controller Abis ·; 30 at the interface. When the air interface has free channels for packet transmission, at the same time, the Abis interface also has free capacity for circuit switching communication to be used for packet transmission and packet switching signaling.

The method and system of the invention provide several advantages. Capacity free of circuit-switched data transfer can be optimally utilized. No additional data transmission capacity is needed between the base station and the base station controller, which saves the network operator investment and / or operating costs. When operating in accordance with the invention, a much higher transmission rate is achieved in the manner described below than when using the LAPD channel. The transfer is reliable because synchronization is already secured before the transfer begins.

5 Brief Description of the Drawings

The invention will now be further described in connection with preferred embodiments, with reference to the accompanying drawings, in which:

Fig. 1 is a block diagram of a cellular radio network;

Figure 2 shows the structure of a single transceiver; Figure 3 shows the channels of the Abis interface;

Figure 4 shows the structure of a TRAU frame;

Figure 5 shows a normal circuit switched call;

FIG. 6 illustrates packet switched data transmission.

DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1, a typical structure of a cellular radio network according to the invention and its interfaces to a fixed telephone network and a packet transmission network will be described. Figure 1 contains only the blocks relevant to explaining the invention, but it will be apparent to one skilled in the art that the conventional cellular radio network also includes other functions and structures which need not be further described herein. The invention is applicable to basic GSM cellular radio networks and networks developed therefrom, for example GSM1800 and GSM1900 rigid systems. Most preferably, the invention is used:. In GSM 2 + Phase Packet Transfer, GPRS (General Packet

Radio Service).

The cellular radio network typically comprises a fixed network infrastructure, i.e., a network part, and subscriber terminal 150, which may be fixed, in-vehicle, or portable terminal equipment. The network part has base stations 100. Multiple base stations 100 are centrally controlled by the associated base station controller 102. Base station 100 30 has transceivers 114. Typically, base station 100 has one to sixteen transceivers 114. One transceiver 114 provides radio capacity for one TDMA. so typically for eight time slots.

The base station 100 has a control unit 118 which controls the operation of the transceivers 114 and the multiplexer 116. The multiplexer 116 places 35 traffic and control channels used by a plurality of transceivers 114 on a single transmission link 160. The structure of the transmission link 160 is well defined and is called the Abis interface. Transmission connection 160 is typically implemented using a 2 Mbit / s connection, i.e., a PCM (Pulse Coded Modulation) link, which provides 31 x 64 kbit / s transmission capacity with a time slot 0 reserved for synchronization. 3 and 4, the structure of the Abis interface and the implementation of the transmission link will be discussed in greater detail.

From the transceivers 114 of the base station 100, there is a connection to an antenna unit 112 which provides a bidirectional radio link 170 to the subscriber terminal 150. Also, the structure of the coils to be transmitted in the bidirectional radio link 170 is well defined and called an air interface.

The subscriber terminal 150 may be, for example, a normal GSM mobile phone and may, for example, be equipped with an additional card to connect a laptop 152 which may be used for packet transmission to order and process packets.

Figure 2 illustrates in more detail the structure of a single transceiver 114. The receiver 200 comprises a filter that blocks frequencies outside the desired frequency band. The signal is then converted to intermediate frequency or directly to baseband, where the signal in the form is sampled and quantized in an analog / digital converter 202. Equalizer 204 compensates for interference, for example, interference caused by multipath propagation. Demodulator 206 extracts a bit stream from the equalized signal, which is transmitted to demultiplexer 208. Demultiplexer 208 separates the bit stream from different time slots into its own logical channels. The channel codec 216 decodes the bit stream of the various logical channels, i.e., decides whether the bit stream is signaling information transmitted to the control unit 214, or whether the bit stream is speech transmitted to the base station controller: ·. 25 men 102 to speech codec 122. Channel codec 216 also performs error correction. The control unit 214 performs internal control tasks by controlling the different units. Burst generator 228 adds the training sequence and tail to data from channel codes 216. Multiplexer 226 assigns to each burst its time slot. Modulator 224 modulates digital signals for radio frequency 30 wave. This function is analog in nature, so a digital / analog converter 222 is required to perform it. The transmitter 220 comprises a filter for limiting bandwidth. In addition, transmitter 220 controls the transmission output power. Synthesizer 212 provides the necessary frequencies for different units. The clock contained in synthesizer 212 may be locally controlled or may be centrally controlled elsewhere, e.g. from base station controller 102. Synthesizer 212 generates the required frequencies, for example by a voltage controlled oscillator.

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The base station controller 102 comprises a group switching field 120 and a control unit 124. The group switching field 120 is used for switching speech and data, and for connecting signaling circuits. Additionally, the Base Station Subsys-5 tem formed by the Base Station 100 and the Base Station Controller 102 includes a Transcoder and Rate Adapter Unit (TRAU) 122. The Transcoder 122 is generally located as close as possible to the mobile switching center 132 because voice can be transmitted in cellular radio 122 and base station controller 102.

The transcoder 122 converts the various digital coding formats of speech used between the public telephone network and the cellular radio network, for example, from a 64 kbit / s fixed network to another (e.g., 13 kbit / s) format, and vice versa. The control unit 124 performs call control, mobility management, statistics collection and signaling.

As illustrated in Figure 1, group switching field 120 can connect (depicted with black balls) to both a Public Switched Telephone Network (PSTN) 134 via a mobile switching center 132 and a packet data network 142. In a public switched network 134, a typical terminal 136 is a standard or ISDN Digital Network).

A connection node 140 (SGSN = Serving GPRS Support Node) establishes the connection between the packet transmission network 142 and the group switching field 120. The function of the support node 140 is to transfer packets between the base station system and the port node (GGSN =: 25 Gateway GPRS Support Node) 144, and must keep track of the location of the subscriber terminal 150 in its area.

The gateway node 144 connects the public packet transmission network 146 and the packet transmission network 142. An interface or X.25 protocol may be used at the interface. The gateway node 144 hides by encapsulating the internal structure of the packet transmission network 142 from the public packet transmission network 146, thus the packet transmission network. '142 appears to the public packet transmission network 146 as a subnet, to which the subscriber terminal 150 may assign packets to and receive packets from the public packet transmission network.

The packet transmission network 142 is typically a private network using the Internet protocol 35 which carries signaling and tunneled user data. The structure of the network 142 may vary from operator to operator, both in architecture and protocol, below the internet protocol layer.

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The public packet transmission network 146 may be, for example, a global Internet network to which the terminal 148, for example a server computer, wishes to transfer packets to the subscriber terminal 150.

Figure 3 illustrates the channels of the Abis interface 160, i.e. logical channels used for bidirectional communication between base station 100 and base station controller 102. In the example, base station 100 comprises two transceivers 114. Since one transceiver 114 provides radio capacity for eight air interface time slots, in the example of FIG. 3 there are twice eight traffic channels TO, T1, ..., T7, each with a capacity of 10 to 16 kbit / s. Typically, time slot 0 of the first transceiver 114 is not used for speech transmission because the BCCH (Broadcast Control Channel) is transmitted in that time slot. However, in the Abis interface 160, this channel TO is allocated even though it is not in use. Each of the transceivers 114 has one 16 kbit / s signaling channel S1, S2 in use. Signaling channels S1, S2 can also be called LAPD channels.

According to the prior art, packet switched transmission at Abis interface 160 would be performed either using signaling channels S1.S2 as such or extended to 64 kbit / s. Another possibility would be to dedicate its own bearer to the packet link or to use the available capacity available on the PCM link. The disadvantages would be the previously mentioned slow transfer speeds, the costs of additional capacity, or even the high costs of a new PCM link.

At the air interface 170, slots free from circuit-switched transmission are used for packet transmission. For packet transmission, capacity is allocated dynamically, i.e., when a data transmission request is received, any available channel may be allocated for use in packet transmission. The arrangement is flexible in nature, with circuit-switched connections taking precedence over packet-switched connections. If necessary, the circuit switched transmission overrides the packet switched transmission, i.e., the time slot used for the packet transmission is made available for the circuit switched transmission. This can be done because packet transmission is well tolerated by such interruptions: transfer only: resume for another allocation period. The arrangement may also be implemented without giving absolute priority to circuit-switched transmission, but serving both circuit-switched and packet-switched transmission requests in their inputs.

In accordance with the invention, the charge dynamics of the air interface 170 is also utilized at the Abis interface 160. When the air interface 170 has a free circuit-switched transmission, the corresponding capacity of the Abis interface 160 is also free from the circuit-switched transmission circuit. Thus, using the free circuit switching link capacity of the Abis interface 160, packet-5 switching data and packet switching signaling can be transmitted bidirectionally between base station 100 and base station controller 102. Mimicking the air interface 170, the Abis interface 160 also has a flexible nature of packet-switched transmission: if necessary, the circuit-switched transmission cancels the packet transmission.

For example, suppose that the slots surrounded by the bold frame in FIG. 3, i.e. the slots T1, T2, T3, T5 and T7 of the first transceiver TRX1 and the slots TO and T3 of the second transceiver TRX2, are reserved for circuit-switched communication. The end capacity, i.e. three timeslots in TRX1 and six timeslots in TRX2, are free to be used for transmitting packet switched data and packet switching signaling. Of course, the maximum transceiver 114 could have all, i.e., eight time slots for free packet transmission. The capacity would then theoretically be 8x16 kbit / s, or 128 kbit / s. In practice, capacity is slightly lower due to the identification information (e.g., transaction identifier and sequence number) that is added to the time slots required for segmentation and assembly.

Figure 4 illustrates how typically, in the Abis interface, time slot information is placed in a Transcoder and Rate Adapter Unit (TRAU) formed for transcoding. In the subscriber terminal 150, 260 bits of speech containing 20 ms are encoded such that the main 50 bits of class 1a and 132 bits of class Ib are convolutionally coded. In addition, 25 bits of error correction are added to give a total of 378 bits. To these 378 bits are added the less important II class 78 bits. This gives a total of 456 bits, which in principle could fit into four radio bursts. However, for security reasons, they are spread over eight radio bursts in 57-bit sub-blocks. Each burst is transmitted at 577 microseconds.

30 Channel codec 216 collects speech bits sent from eight consecutive bursts *. The convolutional coding is decoded and the original 260 speech bits are placed in the TRAU frame.

The bits 0-15 of the word 0 of the TRAU frame word are always zero to separate successive TRAU frames. The 19 least significant 0-bit of each of the following words 1-35 is always a synchronization bit of 1.

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The original 260 bits received from the air interface are placed in bits 1-15 of words 2-18 of the TRAU frame and bits 1-5 of word 19.

In addition, channel codec 216 sets the values of control bits C1-C21 in word 1 in bits 1-15 and in word 19 in bits 6-11. Similarly, in channel-5, the codec 216 sets the timing bits T1-T4 located in bits 12-15 of the word 19.

260 bits designated P in FIG. 4 are available for packet transmission according to the invention. As previously described, perhaps 240 bits, or 30 bytes, would be available for payload transmission. This gives the aforementioned 12 kbit / s transmission rate per slot.

Structured optimized frames could also be used to transmit packet switched data and packet switching signaling. A slightly higher transfer rate would then be achieved. On the other hand, when using standard TRAU frames, the solution of the invention is better compatible with existing base station base station systems.

5 and 6, how the base station system of the invention operates. All components described in Figures 5 and 6 occur in and are described in Figure 1, so that the description will not be repeated here.

Figure 5 illustrates how a circuit switched transmission connection is established between a subscriber terminal 150 and a public telephone network terminal 136. The figures illustrate with an enhanced line how data travels through the system at air interface 170, from antenna 112 to transceiver 114, and thereafter in multiplexer 116, multiplexed over circuit switching link 160 to group 25 switching field 120, which connects to transcoder 122 and outputs 132 at base station 100, the control unit 118 controls the multiplexer 116 in performing the transfer, and in the base station controller 102, the control unit 124 controls the group-30 switching field 120 to perform the correct connection. The data traverses the transponder from the channel codec 216 to the transcoder 122 bidirectionally to form a control loop to ensure synchronization.

FIG. 6 advances to a situation where the circuit-switched transmission link 160 used in FIG. 5 has been released from circuit-switched data transmission. The Ti-35 broadband terminal 150 is now connected to a laptop computer 152. The enhanced line illustrates how the data to be transferred goes from the server computer 148 to the laptop computer 104875g. The data can of course also be transmitted in the reverse direction from laptop computer 152 to the server computer 148. from antenna 112 to transceiver 114 and thence in multiplexer 116 multiplexed from circuit switched-5 field data transmission over free circuit switching link 160 to group switching field 120, where connection to outgoing port 144 is provided to port 140, to the server computer 148.

In FIG. 5, a single time slot is used for circuit-switched transmission, while in FIG. 6, the free capacity of a circuit-switched transmission link 160 corresponding to all free time slots of the air interface 170 can be used. As previously described, this may be organized into TRAUs. For the sake of clarity, Figures 5 and 6 do not illustrate a case where both circuit and packet switched data are transmitted simultaneously. However, this is entirely possible and is, in fact, the most common embodiment of the invention since the free capacity of circuit switched data transmission can be flexibly utilized for implementing packet switched transmission or packet switching signaling. It is also possible to build a network where no circuit switched data is transmitted at all, but only packet data. The structure of the network can then be simplified.

When using the packet transfer according to the invention, there are various possible options for control loop control. For example, one base station controller 102 may have up to 380 transceivers 114 to be managed. In this case, 25 380 x 8 = 3040 parallel loops must be managed. Management could, in theory, be entrusted to support node 140. However, it is more sensible to terminate the loops already in the base station controller 102. One possible solution is that for each PCM link 160, the base station controller 102 has a separate processor card (not illustrated) capable of processing control loops of 12-15 separate transceivers 114. In addition to controlling the control loop, these processor cards then separate packet data from incoming traffic for transmission to support node 140.

With the described control loop procedure, initial synchronization of the packet transfer is very easy and is not required in practice since the transfer units are already synchronized by the control loops. The advantage is thus faster operation. In addition, the reliability of the packet transfer is significantly increased when there is no risk of failure of initial synchronization and consequent data corruption at the beginning of the transfer.

Preferably, the invention is implemented programmatically, wherein the invention requires relatively simple software changes within a narrowly defined area to base station 100 control unit 118 and base station controller 102 control unit 124. Also, group switching field 120 must be similar to allowing slots to be coupled to transcoder 122 or base node 140.

Although the examples are described only for point-to-point packet transmission connection between two parties, the invention is in no way 10 limited, but a person skilled in the art will appreciate how the described arrangement can also be used, for example, a point-to-multipoint connections, where one party send information to several other parties at the same time. Also, the connection need not be bidirectional: the invention allows bidirectional connections, but the connection can also be a one-way broa-15 dcast, in which the sender receives no acknowledgment from the receiver that the transmission has been received. Various combinations are also possible, for example, point-to-multipoint broadcast.

Although the invention has been described above with reference to the example of the accompanying drawings, it is to be understood that the invention is not limited thereto, but that it can be modified in many ways within the scope of the inventive idea set forth in the appended claims.

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Claims (13)

A method for transmitting data in a base station system for a cellular radio network, said base station system comprising at least one base station (100) and a base station controller (102), in which system circuitry data is transmitted bi-directionally between the base station (100) and the base station controller (102) circuit-switching transmission link (160) and packet-switched data and packet-switched signaling are transmitted in a circuit-switching transmission link (160), which is free from transmission of circuit-switched data, characterized by decreased data transmitted in circuit-switching transmission link (160) transcoding. 2. A method according to claim 1, characterized by reduced packet transmission by GPRS (General Packet Radio Service). Method according to claim 1, characterized in that the circuit switching transmission link (160) is dynamically reserved for transmission of packet switched data and packet switched signaling. Method according to claim 1, characterized in that synchronization of transmission of packet switched data and packet switched signaling in both transmission directions is performed by using the control loop of the circuit switching transmission (160) between the base station (100) and the base station controller (102). Method according to claim 1, characterized in that for transmitting packet switched data and packet switching signal TRAU frames of standard structure are used. Method according to claim 1, characterized in that frames which are optimized for the structure are used for transmitting packet-switched data and packet-switched signaling. A base station system for a cellular radio network, comprising at least one base station (100) and one base station controller (102), which base station (100) and base station controller (102) are arranged to transmit bi-directional data switched circuitry in a circuit switching transmission link ( 160), and the base station (100) and the base station controller (102) are arranged to transmit packet switched data and packet switched signaling in a circuit switching transmission link (160) which is free from transmission of circuit switched data, characterized in that the base station system is arranged to be in the circuit of the circuit 160) transmitting data in the Transcoder and Rate Adapter Unit (TRAU) frames created for transcoding. ,. 14 Base station system according to claim 7, characterized in that the base station system is arranged to perform packet transmission using GPRS (General Packet Radio Service). Base station system according to claim 7, characterized in that the base station system is arranged to dynamically reserve a circuit-switching transmission link (160), which is free from transmission of circuit-switched data, for transmission of packet-switched data and packet-switched signaling. Base station system according to claim 7, characterized in that the base station system is arranged to perform synchronization of transmission of packet switched data and packet switched signaling in the bed transmission directions by using the control circuit of the base station (100) and base station (100) control link (100). . Base station system according to claim 7, characterized in that the base station system is arranged to use standard structure TRAU frames for transmitting packet switched data and packet switched signaling. Base station system according to claim 7, characterized in that the base station system is arranged to use frames which are optimized for the structure for transmitting packet switched data and packet switched signaling. • · 1 i • <