|Publication number||USRE39375 E1|
|Application number||US 09/255,325|
|Publication date||Nov 7, 2006|
|Filing date||Feb 23, 1999|
|Priority date||May 3, 1994|
|Also published as||CN1085013C, CN1112346A, DE69523663D1, DE69523663T2, EP0681406A1, EP0681406B1, US5640395|
|Publication number||09255325, 255325, US RE39375 E1, US RE39375E1, US-E1-RE39375, USRE39375 E1, USRE39375E1|
|Inventors||Jari Hamalainen, Zhi Chun Honkasalo, Harri Jokinen|
|Original Assignee||Nokia Mobile Phones Ltd|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (27), Non-Patent Citations (10), Referenced by (15), Classifications (16), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to the transmission of packet information in the air interface of a packet radio system. The general range of application is any digital cellular system based on TDMA, Time Division Multiple Access.
The majority of current cellular networks provide effective data and speech services based on circuit switched technology. However, the utilization or transmission resources in circuit switching is unoptimal, because the transmission connection is maintained throughout the contact irrespective of the fact whether information is transmitted or not at a given moment. Transmission resources are shared by multiple users, which means that the reservation of circuit switched connection for one subscriber only unnecessarily uses by transmission resources from other subscribers. The burstiness of data services also is a drawback in circuit switched systems. The utilization of the channel can actually be enhanced by applying packet switched information transmission. On the other hand, packet switching should be used only when an actual need arises, because the burstiness of data services is high and this may cause interference in circuit switching.
The future third generation cellular system UMTS (Universal Mobile Telecommunications System) must be able to transmit both circuit switched and packet data transmission, such as ISDN (Integrated Services Digital Network) and ATM (Asynchronous Transfer Mode) transmission. Now the key factor is the air interface, where an advanced multiple access technology is employed; by means of this, the channels supporting different types of services must be effectively multiplexed in the air interface both to and from the radio channel. The conference publication “Mobile and Personal Communications, 13-15 December 1993, Conference Publication No. 387, IEE 1993” includes the article “A Reservation Based Multiple Access Scheme for a Future Universal Mobile Telecommunications System” by J. M. DeVille, which describes the requirements to be set for the air interface of a UMTS system. For example, multiple access must be able to utilize the Inactivity of the Information source by granting a physical channel only when there is activity on the logical channel, and to support different bit rates so that time slots in the frame are allocated to the logical channel according to the needs of the situation.
In order to satisfy these and other requirements, there is suggested the multiple access control method PRMA++ (Packet Reservation Multiple Access), which is part of a design for third generation cellular systems related to the transmission of packetized speech and data. PRMA++ can thus be used as multiple access control bath In packet switched and circuit switched transmission. The PRMA++ method concentrates on using one time slot in the transmission of packet data.
On the radio channel, PRMA++ uses Time Division Multiple Access TDMA. This allows the subscriber to share the transmission resources of the radio channel. The TDMA frame is divided into time slots, where the transmitted burst carries the data as well as signals connected to channel coding, notifications etc. In the uplink direction, which is the direction from the mobile station to the network (base station:), there are two types of time slots: reservation or R-slots, where only channel request bursts are transmitted, and information transmission or I-slots, which are only used for transmitting information bursts. In the channel request burst, the mobile station uses an Air-Interface Channel Identifier containing the network address of the mobile station, which address identifies the logical channel, and where it requests one or more time slots from the frame, according to the needs of the moment. In the downlink direction, i.e. from the network (base station) to the mobile station, there are likewise two types of time slots: I-slots reserved from transmitting information, and acknowledgement or A-slots. When the mobile station requests access to the network, the base station acknowledges the request on A-slots by transmitting the address of the subscriber and the number of the I-slot. From this onward, the said I-slot is reserved for the use of the mobile station.
Let us suppose that the number N of the PRMA++ time slots in one TDMA frame is a system configuration parameter. On the uplink channel, one TDMA frame now contains one R-slot and N-1 numbers of I-slots. All mobile stations start transmission by transmitting a channel request on the R-slot, and if several mobile stations use the same R-slot for transmitting the request, collisions may occur. The downlink TDMA frame includes, in addition to the above mentioned A-slot for acknowledging channel requests transmitted on the R-slot and I-slots, also a fast FP (Fast Paging) slot constituting the fast paging channel, on which the mobile station is notified of incoming data transmission and of information transmission slots.
The mobile station starts transmission by channel request on the uplink channel on an R-slot, which is used for this purpose by all mobile stations of the same cell. The base station acknowledges the received channel request on the acknowledgement burst on the downlink A-slot. If no requests are transmitted on the R-slot, or if on the channel there are collisions, identified by the base station, the base station transmits an idle flag on the acknowledgement burst of the respective A-slot, so that the mobile station understands to repeat the channel request after some time. In case The channel request sent on the R-slot was correctly received, but there are no free time slots for the transmission, the mobile station is notified of this on the next downlink time slot. The mobile station queues for access until a free time slot is found.
The R-slot contains a training sequence, address of the mobile station, number of requested information slots and a circuit switched flag. The flag informs whether the reservation is valid for the duration of the packet or longer. The channel is reserved, until an order for cancelling the reservation arrives. The A-slot acknowledgement burst contains the address of the requesting mobile station as well as the channels that are granted for traffic. The mobile station receives the acknowledgement burst, whereafter it tunes the receiver and transmitter to the allocated channel. Traffic on this channel is started, and it continues as long as there is data or speech to be transmitted. In packet data transmission, the number of bursts—bursts here meaning packets that are transmitted after one channel request—can be constant.
The base station uses the fast paging slot, FP-slot, to notify the mobile station of an incoming packet. The mobile station listens to the FP-channel and decodes all received messages in order to notice its own identifier. The time slot on the fast paging channel contains a list of those I-slots that are allocated for the mobile station. The mobile station acknowledges its own paging by transmitting an acknowledgement in the FP-acknowledgement slot.
According to what was said above, it is characteristic of the suggested UMTS system both in the uplink and in the downlink directions that physical channels are not allocated for connections which are not active at a given moment, and hence they do not reserve capacity in vain. The channels are always reserved by the same protocol, both in the case of circuit switched and packet transmission. The allocation of the channels is not dynamic, wherefore the channels reserved for packet usage cannot easily be altered. Reservation, fast paging and acknowledgement slots are given slots, and the state of the art does not comment on altering these. Moreover, the known method does not pay particular attention to the symmetricity or asymmetricity of packet transmission when creating a transmission channel.
The present invention relates to a packet data transmission system in an air interface, the said system having eliminated the above described drawbacks. In accordance with the invention, there is created a flexible system whereby channels can be flexibly created and altered according to the situation in hand, which enables an extremely effective utilization of the channel resources and provides possibilities for using different data rates. Here the system is called Variable Rate Reservation Access VRRA.
Aspects of the invention are defined in the appended claims.
Channels are allocated dynamically so that a variable number of time slots in the cell is reserved for packet usage, and the rest of the time slots are used for circuit switched services, including speech, The mobile station can select the number of employed time slots, and the network adjusts to that, so that even a simple one-slot mobile station can use the packet services. In case several time slots are reserved for the mobile station, each of which slots constitutes a sub-channel, for each slot there is designed error correction, interleaving and a corresponding frame length. If several time slots are required for one mobile station, there are reserved several of the said sub-channels, and each sub-channel uses the same error correction and interleaving algorithm. Thus there is needed only one algorithm. In the information transmission of the subscriber, the MAC layer at the transmitting end distributes the subscriber data to be carried through several sub-channels, and the MAC layer at the receiving end receives the frames of the sub-channels and compiles them to a complete subscriber data. From the point of view of the base station, each time slot is thus similar on the physical level. Now one and the same mobile station can use for instance two time slots, or one mobile station can use one and another can use the other. The prior art applies algorithms for units of one, two, three etc. time slots, in which case the base station respectively deals with channels comprised of one, two, three etc. time slots. A data stream conducted to the radio channel through the radio interface is multiplexed into several “pipes”, i.e. into said independent sub-channels, and after receiving the packets, the data is again demultiplexed from the “pipes” to a data stream.
As exemplary embodiment of the invention is further described with reference to the appended drawings, where:
In the examples below, it is assumed that the frame structure in the network is such that one TDMA frame consists of eight time slots, in the same fashion as in the known GSM system, but it is understood that the number of time slots is a system configuration of free choice. The number of those time slots that are allocated for packet radio can depend on the use demand for packet data in the cell. If there are only a few packet service subscribers, it is sufficient to allocate just a few time slots in the frame for packet data, and if there are several subscribers, all eight time slots are reserved. It is up to the operator to configure how many time slots must be reserved.
The logical channel structure may be different in different cases where the number of time slots reserved for packet data also differs. If two times slots are reserved for packet data, one of them can be used for data only and the other for control (FP, A, R). Another possibility is to use one for data only, and the other for both control and data, because there is not much need for control with only two time slots in use. In this case a combined control/data slot has a smaller data capacity. When all I-channels are reserved for transmitting the user's packets, control is not needed any more. Now the control slot or the logical control channel can be granted for transmitting information data, i.e. more I-capacity is obtained. As soon as an I-channel becomes free, a new logical control channel must be created.
If the Invention is applied for example to the GSM or PCN systems, the suitable fields for paging and acknowledgement bursts would be such as are illustrated in
In the drawing of
In the receiver side the carrier frequency signal is received from the radio channel 20 and is demodulated to the baseband frequency in a demodulation block 24. The signal is then decrypted in decryption block 26 and de-interleaved in a de-interleaving block 28, which also yields the stealing bit information for the control block 22. The error decoding is performed in a channel decoding block 30, and if the received data is speech, speech decoding is accomplished in a speech decoding block 32. All the mentioned transmitter and receiver blocks are controlled by the control block 22.
A more detailed description of the functions of the transmitter and receiver blocks can be found in, e.g., a publication by Michel Mouly and Marie-Bernadette Pautet; The GSM System for Mobile Communications, 1992, France.
In the above specification we have explained channel formation in general, but we have not paid attention to the direction of data packets. User information, i.e. data packets, are transmitted on I-slots reserved for the transmission of data packets by using normal bursts. Naturally a radio channel can be reserved symmetrically, by reserving an equal number of time slots in both directions. Generally data transmission is, however, asymmetric, and symmetric reservation means that resources are wasted in one of the directions.
An asymmetric transmission can be realized in two different ways. In the first alternative the MAC (Media Ascess Control) protocol is half duplex. The Information slots, I-slots, are reserved only in one direction at a time. MAC first investigates which direction the packet is going to be transmitted to, and reserves either an uplink or a downlink channel, according to the required direction. Acknowledgement is not used with information slots on the MAC level. Acknowledgements are carried by the link layer protocol, and for acknowledgement transmission there is reserved an information slot in similar fashion as for the user's data.
In the case of
Another possibility for asymmetric transmission is to use only one slot for acknowledgements and as many slots as are needed for information transmission.
The mobile station MS and the packet arrangement in the network may exchange various parameters at the beginning of the packet session. This is useful because thus the mobile station informs the network as to the number of the slots in the TDMA frame that it can handle during data transmission. The mobile station can be so simple in structure that it is capable of dealing with only one slot, whereas the network can handle all slots of the frame. When the mobile station informs the network of this feature at the beginning of the session, the network immediately knows to allocate only one slot for the mobile station. At the beginning the network also informs the mobile station as to the packet slots in the network, so that the mobile station finds out what kind of logical channel structure the cell has.
Irrespective of the form of the access burst, the system allows for a priority value to be included in the reservation request on the R-slot. There can be several different priority levels with different binary values. In the base station, the queue system may observe the priority of the data transmission requests. There is a maximum time value, for the duration when random access is valid. This prevents an incorrect use of the timing advance. When the base station receives the R-slot, it arranges the received requests in a queue. The channels reserved in the requests are allocated either in the FCFS order, or based on the priorised FCFS, if the request includes a priority value. The base station must include a time stamp for each received R-slot in order to keep track of the requests for which the maximum timing has been exceeded. Timing reserves a given duration for the request to be valid, and if the timer elapses before the request is fulfilled, it is removed from the queue.
If there are not as many free slots as was requested, there are two possibilities: 1) the request is queued until a sufficient amount of free capacity is found, or 2) the mobile station is given as many slots as there are free. In the first case, a message must be sent to the mobile station on the acknowledgement slot. This prevents unnecessary timer expiration. For those R-slots for which the time has elapsed, a retransmission algorithm is used,
The present invention can be applied to any digital TDMA cellular system. It is not necessary to alter the burst structure of the systems where the invention is applied, for instance GSM and PCN systems. The structure of logical channels renders several different possibilities and enables a dynamic allocation of resources and a flexible access protocol.
When applying the system of the invention to a GSM system, there are three different modes available:
1. Idle: the mobile station does not use packet data services, but only circuit switched services. Now it works as the current GSM phone.
2. Packet half active: the mobile station is in virtual connection state for packet services (no physical channel), but is currently not in the receiving or transmitting data state. It is listening to the standard GSM paging channel to receive data packets. In this mode, only the paging channel is listened to, which saves the batteries because listening takes place fairly seldom. When a packet is coming in, there is transmitted an ordinary paging, the reason code being “arrival of packet”. Now the mobile station shifts to mode 3, where it listens to the FP channel and can receive the packet.
3. Packet active: the mobile station is transmitting or receiving packet data. When not actively transmitting a packet, it listens to the FP channel to receive packets, as well as to the standard GSM paging to receive speech. This is called the FP DRX state (Fast Paging Discontinuous Reception).
When the transmission of packets in mode 3 is interrupted for some reason, the timer is started. When it elapses to a predetermined value, the mobile station is shifted from mode 3 to mode 2, so that the physical channel becomes free. When the mobile station requests to initiate virtual connection, it exchanges parameters with the network, such as exchange of encryption keys, initiation of encryption, identification etc. At the beginning of the virtual connection, the mobile station informs the network of the number of time slots that it is made for. Thus the network knows not to transmit data on eight slots, if the mobile station is made for one slot only.
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|U.S. Classification||370/322, 370/337|
|International Classification||H04W72/14, H04B7/26, H04W28/26, H04B7/212|
|Cooperative Classification||H04L1/0083, H04L1/1854, H04L1/0071, H04L1/0059, H04W72/042, H04B7/2656, H04W28/26, H04W72/0446|
|European Classification||H04B7/26T10, H04W72/04|