A method and apparatus for controlling the use of idle frames

A method and apparatus implementing the method for controlling the use of idle frames by a mobile station operating in a wireless communication network. The control unit of the mobile station comprises information on the measures that can be performed during idle frames according to the operating mode of the mobile station. For each idle frame, the mobile station checks said mode of operation and the actions to be performed, and determines which of the actions to be performed is the most important as determined from said mode of operation. For example, the number of idle frames used to search for a synchronization burst can be arranged as large as possible, and thus enhance synchronization.

Förfarande and apparatus for styrning av lediga ramar med mobilaparat som fungerar i ett teleclordst telommunikationssystem. The mobile device is equipped with information on the mobile phone that is enhanced by the mobile device status under the LED frame. For the purpose of determining the current status of the mobile device, the status of the mobile device may be based on the status of the mobile device. Tili exempel kan antalet lediga ramar som kan användas för sökande efter en synkroniseringsskur vid behov anordnas at var ö ä höjligt, varvid synkroniseringen effektiviseras.

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I ¹ 106331

Method and apparatus for controlling the use of idle frames

The present invention relates to a method and an apparatus implementing the method for controlling the use of idle frames in a mobile station operating in a wireless telecommunication network. The method divides data transmission based on time division multiplexing into frames containing a constant number of time slots, and frames into time slots containing bursts between a mobile station and a base station. The selected number of consecutive frames forms a superframe of the mobile station, which essentially comprises traffic frames for the transmission of traffic information and idle frames for radio path measurements and measurement results transmission measures between the mobile station and the base station system.

In digital cellular network systems, data transmission was originally implemented in a circuit-switched manner, whereby a permanent transmission path is formed between the telecommunications terminals for the duration of the connection. Indeed, the data flow related to speech transmission is relatively continuous, so that the circuit-switched transmission format is usually sufficiently efficient for the utilization of a radio resource. However, the data stream associated with data calls is typically bursty, unnecessarily wasting the radio path for long-term slot allocation of the circuit-switched transmission mode.

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As the demand for data services in digital 'cellular network systems' can be seen to be growing rapidly, the European Telecommunications Institute (ETSI) has launched preparations to standardize a new GSM-based · · (Global System for Mobile Communications) packet-switched data service. The new service is known as the General Packet Radio Service. . (General Packet Radio Service, GPRS) and has been developed to work together • · · λ '.. with traditional circuit-switched GSM data transmission so that the radio path • · · can be efficiently utilized for both data and voice transmission.

• · · ·

In the GSM system, communication between a mobile station (Mobile Station, MS) and ^:... · between the Base Station Subsystem (BSS) is implemented by • ««: · 'transmitting data via a radio channel, the radio channel being formed from the time slots allocated for the connection of the used radio frequency band. GPRS offers the possibility to dynamically adjust the capacity so that time slots are reserved for the connection only when there is data to be transmitted, and the time slots for data transmission from the mobile station to the base station and for data transmission from the base station to the mobile station are determined separately. When data is to be transferred, the data transfer is faster due to the large capacity, and when there is no data to be transferred, the capacity can be used for the needs of other connections.

The advantage offered by packet-switched data transmission is substantially realized when the data transmission connection can be established quickly. If the connection to transfer a data packet is slow, a GPRS-type service for transferring small data packets is not justified. In order to establish a fast connection in the GPRS system, a kind of virtual connection is established between the mobile station MS and the serving GPRS access point, whereby data transmission can be started quickly without having to create or transfer all the information needed for connection. In order to achieve the optimized establishment and maintenance of said virtual connections, the mobile station must be able to continuously receive information from the surrounding cells as it moves from one access point to another. This requires a kind of pre-synchronization with the surrounding • II^: 20 cells so that the necessary cellular information can be sent and received. The speed at which a mobile station is able to connect to a cell affects * * · • «« '·' connection establishment and thus the efficiency of the entire packet-switched data transmission. Especially in an urban environment where there are a lot of • · · surrounding cells and the mobile station has to monitor its surroundings at a fast pace, «· · '·' '25 synchronization as soon as possible is important.

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λ. It is an object of the present invention to provide a method and apparatus implementing the method for enabling efficient utilization of idle frames in wireless packet-switched data transmission.

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In the method of the invention, data transmission based on time division multiple access ί is divided into frames containing a constant number of time slots, and frames into time slots containing bursts between a mobile station and a base station, and the selected i

the plurality of consecutive frames forms a superframe of the mobile station, comprising essentially traffic frames for the transmission of traffic information and idle frames for radio path measurements and measurement results transmission measures between the mobile station and the base station system.

The method is characterized in that the mobile station checks the radio path measurements and the transmission of measurement results that can be performed during the idle frame, as well as the operating status of the mobile station; determining the priority between the measures according to the operating mode of the mobile station; and performing the highest priority operation on the mobile station during the idle frame.

The invention also relates to a mobile station for a wireless communication system according to claim 5, wherein the time division multiple access communication is divided into frames comprising a constant number of time slots, and frames into time slots containing bursts between the mobile station and the base station, and the selected number of consecutive frames forming a mobile station frame. comprising essentially traffic frames for the transmission of traffic information and idle frames for the measurement of the radio path between the mobile station and the base station system and the measures related to the transmission of the measurement results.

· '' 20 The method is characterized in that the mobile station comprises means for checking the '··' radio path measurements and the transmission of measurement results that can be performed during the idle frame; to determine the operating status of the mobile station; to determine the priority between the actions according to the operating mode of the mobile station; and to initiate the highest priority «« «•« · '25 actions during the idle frame.

.... The invention is based on the idea that the control unit of a mobile station comprises information about the measures which, according to the operating mode of the mobile station, can be performed during idle frames. For each idle frame, the mobile station 30 checks said operating mode and the operations to be performed, and determines^:... · of the measures to be taken, whichever is the most important in the light of the said mode of operation. In the solution according to the invention, for example, the methods used to search for the synchronization burst transmitted from the base station system&gt;

⁴ The number of idle frames 106331 can be arranged as large as possible with the mobile station, whereby the probability of the simultaneous occurrence of the timing burst and said idle frame for burst search of the mobile station is maximized.

The invention will now be described in detail with reference to the accompanying drawings, in which:

the diagram of Figure 1 illustrates Time Division Multiple Access (TDMA) according to the prior art;

the diagram of Figure 2 illustrates the search for a frequency correction burst in a prior art arrangement:

Fig. 3 is a block diagram showing the architecture of a GSM / GPRS network;

Fig. 4 is a block diagram illustrating a structure of a mobile station supporting a GPRS service;

Fig. 5 is a diagram illustrating a frame structure followed by a GPRS mobile station according to the invention;

Fig. 6 is a diagram illustrating a procedure for determining a timing advance in a mobile station according to the invention;

^: Fig. 7 is a flow chart illustrating a first embodiment of a method according to the invention;

aa · • aa '·' 'The flow chart of Figure 8 illustrates decision making related to the method according to the invention;

The diagram of Fig. 9 illustrates the utilization of the solution according to the invention in retrieving a frequency correction signal.

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J. '.. The GPRS system follows Time Division Multiple Access (TDMA) according to the GSM system, the principle of which is illustrated «· · ··; in Figure 1. Various bursts of constant duration are transmitted over the radio path, which a »are channelized in a transmission phase for a time interval of 10/26 milliseconds 10. The carrier of each a ι« may comprise eight physical channels, whereby the TDMA frame 12

Il «: consists of eight time slots 10, and the physical channel is basically a continuation of one time slot (modulo 8) in a series of consecutive TDMA frames. The TDMA5 106331 frames are combined for the transmission of different types of logical channels into two different types of superframes, which are a 120 ms long superframe 14 containing 26 TDMA frames, mainly related to the transmission of traffic channels, and

A 3060/13 ms long superframe 16 containing 51 TDMA frames, primarily associated with signaling channel transmission. The smallest common multiple of these superframes is a superframe 18 containing a 26x51 = 1326 TDMA frame. TDMA frames are numbered with respect to this frame (modulo 8x26x51x2048 = 2715648), so at least the hyperframe contains all possible channel types.

In order to be able to communicate with each other, the functions of the cellular network mobile station MS and the base transceiver station (BTS) must be synchronized with each other. The base stations are provided with a broadcast channel, through which the base station periodically (23 octets every 0.235 seconds) transmits the selected base station data. Based on the information received from the broadcast channel of the base station, the mobile stations can synchronize with the base station and, if necessary, correct their frequency level to match the base station. The mobile station must constantly listen to the data sent by the neighboring cells, which, however, requires a kind of pre-synchronization with the neighboring cells in order for the mobile station to be able to decode the necessary cell information from the data sent by the base station.

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Y 'In order to enable the monitoring of neighboring cells, the base station system transmits to the mobile station a list of base stations surrounding its location, on the basis of which the * * * mobile station e.g. know at what frequency the surrounding cells transmit

V »· • · · '25 (beacon frequency). From these base stations, the mobile station tries to retrieve

... a frequency correction burst in order to then receive a synchronization burst, • · after which demodulation the mobile station arrives at the timing of each base station.

According to the 30 GSM channel structure, a Synchronization Burst (SB) always follows a Frequency Correction Burst (FEB) «· · · 'at the same frequency in the same time slot during the next TDMA frame. The frequency correction burst, on the other hand, is relatively easily identifiable⁶ 106331 structure corresponding to an unmodulated carrier with a certain frequency offset with respect to the nominal carrier frequency (148 bits, all of which have a value of 0). Thanks to the modulation technique chosen, the signal is a pure sine wave, and burst search is often referred to as PSW (Pure Sinwave Search). Thus, in order to find the synchronization burst SB, the mobile station MS searches the transmission of the base station BTS for a frequency correction burst FEB, and upon finding it, is able to receive a synchronization burst containing more detailed information related to the base station timing. The mobile station then updates its own neighbor channel counters based on the synchronization burst information to match the base station timing.

Figure 2 illustrates the implementation of a frequency correction burst search in a time division multiple access structure of a GSM system according to the prior art. The superframe containing 26 TDMA frames (A0-A25) contains 24 TDMA frames (A0-A11, A13-A24) containing bursts of traffic channels, one

A frame (A12) and one idle frame (A25) reserved for the SACCH control channel. During the idle frame, the mobile station typically does not send or receive, so it is then possible to perform e.g. search to find a frequency correction burst. The base station transmits the FCCH of the frequency correction burst in a superframe containing 51 TDMA frames such that there are ten TDMA frames between the first four frames containing the FCCH (BO, B10, B20, B30, B40) and eleven TDMA frames between the fourth and fifth (B51).

It can be seen from the figure that the mobile station detects the first superframe HFO of the FEB • · · burst transmitted by the base station in the idle frame A51. New search. . starts in idle frame B25 of the next superframe HF1. Point where BTS • · · .λ ·. the next time a FEB burst is transmitted during the idle frame of the mobile station, t · · is found in the idle frame A25 of the sixth superframe HF5, whereby 8 · 26 + 1 = 209 TDMA frames (approximately 0.965 seconds) elapsed during the search. 30 Correspondingly, when the next search starts in the idle frame A51 of the sixth superframe HF5, there is a point where the BTS sends a frequency correction burst «· ': during the idle frame of the mobile station only in the last frame A51 of the eleventh superframe HF10, in which 10 * 26 + 1 = 261 TDMA7 frames time (about 1.205 seconds). Accelerating these acceptable paging times in the GSM system has a beneficial effect on the operation of the GPRS system, especially in an urban operating environment consisting of a large number of regionally small cells.

The block diagram of Figure 3 illustrates the architecture of a GPRS network. The mobile stations MS are in radio communication with the base stations BTS. The base stations BTS are still connected to a base station controller BSC, which controls and manages several base stations. An entity formed by a plurality of base stations BTS (typically some tens of base stations) and a single base station controller BSC controlling them is called a base station system BSS. The base station controller BSC communicates with the Mobile Services Switching Center (MSC), which coordinates the connections to the mobile stations by means of the subscriber registers HLR and VLR. The connection is still obtained outside the mobile network via the mobile switching center MSC.

GPRS is logically implemented in the GSM structure by means of two network elements, the Gateway GPRS Support Node (GGSN) and the Serving GPRS Support Node (SGSN). A GGSN is a • «node to which data packets addressed to a GPRS server are assigned a PDP address of the packets.^:J. ' (Packet Data Protocol, e.g., IP or X.25). The GGSN contains «« 1 «4 I 'subscriber routing information, on the basis of which data packets from the data network can be routed to the subscriber's current access point SGSN. If necessary, the GGSN can also • · · '•' f query the home location register HLR for subscriber location information. The GGSN is the first • · · '25 PDN (Packet Data Network) access point in GSM that supports GPRS. . online. The SGSN is an access point serving the mobile station MS. In GPRS connection «·«

J. '., SGSN sets up mobility management functionality to route • · &lt;

data packets in the direction of the mobile station, and PDP functionality in the direction of the data network • · · · ”· to route the data packets to the GGSN. If necessary, the SGSN can update the location information of the mobile station to the VLR. The SGSN and GGSN may be connected to the same »« »physical node or may be located on different nodes. The SGSN and GGSN include IPI «routing functionality and can be connected to IP routers.

&lt;11 • II • Il β 106331

The block diagram of Figure 4 illustrates a structure of a mobile station according to the invention suitable for a GPRS service. For more detailed operation of GPRS functions, reference is made to GSM specification 03.64 Digital cellular Telecommunication system, Phase 2+; General Packet Radio Service (GPRS);

Overall description of the GPRS radio interface; Stage 2. For radio communication, the mobile station includes a radio unit RU comprising a transmitter branch 410 (comprising channel coding, interleaving, modulation and transmission function blocks) known to a conventional mobile station, a receiver branch 412 (comprising reception, demodulation, deinterleaving and channel decoding) and 414.

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The central controlling element of the mobile station is the control unit CU, which coordinates the functions of substantially all the blocks, including the transmission and reception timing of the mobile station. Current control units typically comprise three different counters for communication between base stations and a mobile station. The quarter bit number QN (values ​​0-624) is set according to the training period contained in the received synchronization burst. The time slot number TN (Timeslot number, values ​​0-7) is reset upon receipt of the synchronization burst, and TN increases by one as the counter QN changes from 624 to 0. The value of the TDMA timeslot number FN (TDMA timeslot number, values ​​02715647) is read from the synchronization burst, and FN increases by one TN moves from 7 to 0. However, the number of counters and the mechanism of mutual interaction are not essential to the invention, but other alternatives are possible. The functions of the control circuit are typically implemented by one or more microprocessors.

In the implementation shown in Figure 4, a first memory M1 is connected to the main control circuit CU, which may be an intermittent memory, for example RAM, in which the CU stores in-service data. In addition, the terminal comprises a second memory M2, which is preferably a non-volatile memory in which application programs performing various services of the terminal, other information relevant to the operation of the data station and any other information to be permanently stored are stored.

In addition to the above, the terminal comprises a user interface UI, which may comprise a display

432, a possible speaker 434 for voice calls and a keypad 430.

In the GPRS system, mobile stations implement time division multiplexing, the frame structure superframe 501 of which, like the second GSM superframe, comprises 52 TDMA frames. The TDMA frames are divided into radio blocks 502 consisting of four consecutive TDMA frames and idle frames 503 between them, as shown in Fig. 5. Thus, one superframe 501 comprises a total of 12 radio blocks B0-B11 and four idle frames.

According to the GPRS specifications, mobile stations must perform approximately the same measurements on 15 radio paths as in the GSM system. The information about the measurements made by the mobile station typically travels with the data to be transmitted in the Packet Associated Control Channel (PACCH) whenever necessary, which means data packets stolen from the communication capacity for signaling purposes. These are identified as signaling data by the ri: 20 identification bits included in the burst. A charge similar to the SACCH control frame (A12) in Figure 2: The GPRS system thus does not include. However, in the GPRS configuration, it is recommended to perform the frequency correction pulse search in every other idle frame.

According to the GSM system.

* · A ·

In order to determine and take into account the propagation delay, the GPRS configurations present a continuous timing advance procedure, for a more detailed explanation of which is referred to in Continuous timing advance update of the GSM specification 03.64 (clause 6.5.7.2 in version 5.2.0). To determine the propagation delay, a mobile station communicating with a particular base station must send an Uplink Packet Timing Control Channel (PTCCH) signal in the uplink once per group of eight superframes. When a mobile station switches to a base station, the base station system notifies the mobile station of the OR index (Timing »· · ·

Advance Index), which indicates to the mobile station in which idle frame the mobile station should transmit said random access signal. Based on the random access signal, the base station system calculates a timing advance for that mobile station, and sends a response to the downlink in the idle frames indicated by the OR value.

The calculation of the timing advance is illustrated by the diagram of Figure 6, which comprises a set of eight superframes. As shown in Figure 5, each superframe comprises 12 radio blocks and 4 idle frames, of which at most every other one is used for determining the timing advance. In each idle frame, random access signals may be transmitted (uplink PTCCH) by mobile stations to which the base station system has reported the value of the OR index marked above the idle frame. Below the idle frames are marked messages in which the mobile station listens to the timing preset value sent by the network (downlink

PTCCH). For example, a mobile station sending a random access message in idle frame 0, 2, 4, or 6 receives an updated timing preset value from the base station system in the message TA_message_2. The mobile station only needs to listen to one downlink PTCCH message, so up to five idle frames out of eight superframes are used to determine the timing advance.

• · «. . ·. During the idle frames, other states of the mobile station can be implemented and / '; measures related to the operating environment. For example, a GPRS network may comprise base stations and mobile stations in which the transmission power can be adjusted to eliminate interference visible to receivers. If the network wants to use power control: T: 25 in the transmission of the base station to eliminate the effect of the interference signal visible to the mobile station, the network instructs the mobile station to perform interference measurements during idle frames to determine the transmission power of the base station. ^: optimize. In a cell using constant powers, interference measurements do not need to be made. Similarly, for example, in small cells, the network may instruct to use a constant value for the timing advance, which is related to the timing measurement. no signaling is required. However, the details relating to the performance of the measurements and the transmission of the measurement results are not essential to the invention. In principle, it only needs to be taken into account that various measures related to the state and operating environment of the mobile station are performed during idle frames.

The solution according to the invention utilizes the idea that the number of frames to be allocated for the implementation of the measures related to the use of said radio path 5 varies considerably from one application and space to another on a mobile station supporting the GPRS service. It is added to the control part of the mobile station according to the invention to check in the case of idle frames what kind of measures are to be performed and what is the mutual order of priority of the measures in terms of the state and operating environment of the mobile station. For example, if there is no other data to be transmitted, or the synchronization function is selected to be more important than other data transmission according to the current state of the mobile station, the described frequency correction pulse search can be configured to be performed in all possible idle frames. For example, the synchronization function may be selected to be accelerated in situations where the mobile station receives from the base station system an updated neighbor cell list comprising information about new cells for which the mobile station has no information about the timing.

The decision-making according to the invention related to the use of the idle frame according to the first embodiment of the invention is illustrated in Figure 7. _: using a flowchart. In step 71, the control unit checks which actions to be performed during idle frames should be performed by the mobile station during the next idle frame. After identifying possible actions, the control unit performs a priority check between possible actions (item 72), and initiates: 25 actions selected based on the priority review to be performed during the idle frame (items 73a, 73b, 73c).

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V · • · · ^: In the priority check, the control unit checks the operating status of the mobile station and ·: · selects the action to be performed during the idle frame based on the operating status. //: 30 Operating mode refers to selected information related to the current operation of the mobile station and influencing decision making, such as information about measurement commands issued by the network, success and necessity of data transmission related to timing advance, information contained in the updated cell list, etc.

Said priority review is based on a code to be determined on the basis of GPRS configurations and application-specific selections, in which the selected operating modes of the mobile station are assigned a mutual priority for possible measures.

The flowchart of Figure 8 illustrates a simple example of such a code for the two operations described above, timing advance determination and frequency correction pulse retrieval. In the case of an idle frame, the control unit according to the invention is configured to check whether new cells have entered the updated cell list received from the base station system, the timing of which the mobile station has no previous information (point 81). If such a new cell is detected, the control unit prioritizes the frequency correction pulse search over the interference measurements specified by the network (step 82). Otherwise, the interference measurements are performed in the normal way (paragraph 83).

The example described above illustrates decision-making related to the allocation of the entire idle frame. This is a realistic option when searching for a frequency correction pulse, as the PSW search takes up the entire idle frame and it is not possible to perform other measures during the same idle frame. On the other hand, for example, a random access message related to the determination of the timing advance is sent in a certain proportion to the limits of the idle frame, in relation to which the network informs_; f. in connection with channel allocation OR in connection with the declaration of value. If a random access message needs to be sent at the beginning of the idle frame, the remaining time slots of the idle frame can be used to measure the interference values. If the «« · random access message has to be sent towards the end of the idle frame, the time slots at the beginning of the idle frame can be used to measure the interference values. Thus, the options for action under the code described above may also consist of actions that can be taken during a single idle frame. ^: combination of measures. For example, the action options associated with one idle frame may be: PSW paging, interference measurement,: 30 transmission of a random access message, reception of a random access message,. ··. interference measurement + transmission of a random access message in selected idle frame time slots, interference measurement + reception of a random access message in selected₁₃ 106331 idle frame time slots. The action to be taken in the idle frame is selected according to the current operating state of the mobile station.

As described above, depending on the type of connection and the operating environment, there will be situations in the use of the mobile station 5 in which no data transmission related to the determination of the timing preset value or other use of the radio path is required. In this case, in principle, all idle frames can be used to retrieve the frequency correction pulse.

Correspondingly, there are situations in the operation of the mobile station in which the mobile station must at least update the timing advance by sending and receiving the PTCCH.

In this case, five of the 32 idle frames included in the eight superframes are used to update the timing advance, and 27 can be utilized to retrieve the frequency correction pulse. In some cases, the network may also instruct the mobile station, for example, to measure interference values ​​from its own frequency, in which case half of the idle frames have to be used for these measurements. However, even in a more unfavorable situation in terms of PSW15 priority, the number of idle frames allocated for PSW paging (16 out of 32 idle frames) according to the arrangement according to the invention corresponds to the situation according to the prior art.

The normal operation of a mobile station consists of a variable combination of the situations described above, i.e. in the superframes of the mobile station there are always _; consecutive idle frames that are not required to perform other radio path measurements. By utilizing these as described above, it is possible to: //: speed up the search for the frequency correction pulse and, accordingly, the synchronization with the neighboring cells. The diagram of Figure 9 illustrates a solution according to the invention: 25 implementations adapted to a GRPS connection in terms of PSW paging. The presented solution is optimized for PSW search, so the pattern does not take the position of others

V · for the implementation of measurements during idle frames. Example of Figure 2^: In this way, the mobile station detects the FEB burst transmitted by the base station ·; · in idle frame A51. A new search starts in idle frame B25 of the following superframe HF1: /, / - 30. The point where the BTS transmits a FEB burst during the idle frame of the mobile station is already found in the idle frame A38 of the third superframe HF2, whereby a time corresponding to 5 * 13 + 1 = 66 TDMA frames has elapsed during the search (about 0.305 seconds). Similarly, when the PSW search starts the sixth superframe¹⁴ 106331

HF5 in idle frame A51, there is a point where the BTS sends a frequency correction burst during the idle frame of the mobile station in the second idle frame A12 of the ninth superframe HF8, whereby only 9 * 13 + 1 = 118 TDMA frames have elapsed (approximately 0.545 seconds). Compared to the times in Figure 2, the benefit achieved is significant.

The implementation and embodiments of the invention are presented here by way of examples. It will be apparent to those skilled in the art that the invention is not limited to the details of the above embodiments and that the invention may be embodied in other forms without departing from the features of the invention. The disclosed embodiments should be considered as illustrative but not restrictive. Thus, the possibilities of implementation and use of the invention are limited only by the appended claims. Thus, the various embodiments of the invention defined by the claims, including equivalent embodiments, are within the scope of the invention.