FI98019C - Procedure for using a mobile phone in a mobile telephone system as well as a mobile telephone - Google Patents

Abstract

The invention concerns a method for using a telephone device MS in a telephone device system, in which the telephone device MS when it is ready to function receives a signal on the control channel CC1 from a base station BS1 and examines the signal quality. The telephone device MS completes the reception on the control channel CC1 and performs a channel search to find a new control channel, when a particular criterion is fulfilled for the worsening of the signal received on the control channel CC1. When ready to function, the telephone device MS is further controlled in response to a received electricity economising order to switch repeatedly into the electricity economising condition and terminate the signal reception for a particular time, and upon expiration of the particular time to switch for another time to a new electricity economising order to receive the signal on the previous control channel CC1. According to the invention, other criteria are stated for the worsening of the control signal received on the control channel CC1, which are fulfilled prior to the aforesaid criterion, wherein when the other criteria are fulfilled the telephone device MS is made to perform the channel search during the contemplated electricity economising time. When the electricity economising time expires, the telephone device switches to receive on the control channel CC1, unless a new control channel CC2 has been found. The telephone device MS performs the channel search on the basis of certain criteria periodically during the times devoted to electricity economising. As a result of this, the channel switching is smooth and easy. If the signal does not worsen continuously, the telephone device does not offer electricity economising time for channel search. The invention also specifies a telephone device to be used with the method according to the invention. <IMAGE>

Description

, 98019

The invention relates to a method for using a mobile station in a mobile communication system and in particular to a method for changing a control channel in a mobile communication system. The invention further relates to a mobile station for use according to the method.

The mobile communication system has a plurality of base stations and corresponding control channels assigned to them for transmitting control signals to the mobile stations. Mobile communication systems today are generally cellular mobile communication systems in which the coverage area of the system is divided into cells, each of which generally has one base station assigned a control channel so that the base stations of adjacent cells have different control channels. The mobile station of the mobile communication system, when ready for operation, continuously receives a control signal on one of the control channels in order to obtain the calls addressed to it and other information provided by the system. When moving in the coverage area of the cellular network, the mobile station has to change the base station and the control channel from time to time when the coverage of the control channel decreases as the distance increases to the current base station or for other reasons.

The system specifications of the mobile communication systems define the mode of operation of the handover and the criteria by which the mobile station starts to search for a new control channel. Different control channel switching modes have been defined in different systems. The present invention is applicable to mobile communication systems in which the following conditions are met for control channel switching: a) the mobile station independently selects the control channel on which it receives the control signal, b) the mobile station receives only one control channel at a time and does not continuously measure the strengths of other control channels; 30 when the mobile station may not be listening to the control channel, i.e. directs the standby mobile station to operate in the so-called power-saving mode.

In mobile communication systems such as the one described, a criterion is set for degradation of a signal received on a control channel, for example in terms of signal strength and time, whereby the mobile station stops receiving There are some problems with this general procedure for changing the control channel. It may take a relatively long time to find a new control channel, and when a mobile station searches for a control channel, for example, it does not receive incoming calls and cannot receive a call. Since the handover criterion for the widest possible network coverage is set down in the systems, the mobile station 5 also often "hangs" on the old base station and the control channel for too long, even though it could already select a stronger control channel from another base station. On the other hand, signaling performed on a weak control channel with a remote base station is uncertain, and call set-up can easily fail. Some known handover solutions for such mobile communication systems are described below.

In the Nordic NMT system, in which an embodiment of the invention is described, the channel is considered lost according to the specification if the field is 75% below the reference level for 2 minutes. In this case, a new control channel ha-15 ku is started, which may take from a few seconds under favorable conditions to up to a minute when the situation is unfavorable. Incoming calls will be lost during this time. In addition, the system provides power-saving periods to the standby mobile station, during which the station does not have to receive a signal on the control channel but can enter a power-saving mode, so-called "sleep". In the NMT system, the mat-20 cavities message is always received separately from the system. a sleep command giving it the next waking time. Wake-up and sleep periods can be relatively regular for long periods of time if, for some reason, the signaling capacity of the system is not overloaded so that it is not sufficient to send sleep commands on a regular basis. When there is sufficient signaling capacity, the receiver may be awake and receive a control signal on the selected control channel, e.g. When examining the fulfillment of the handover criterion, the mobile station monitors the signal strength during the waking period and considers that the same intensity level continues during the next sleep period. The main disadvantage of the current solution in the NMT system is that the search for a new control channel for handovers only starts when the absolute criterion requiring a handover is met. In order to overcome this shortcoming and to make the most of the very useful power saving function in the system, a solution would still be needed to prepare for handover in advance by researching alternative channels without unnecessarily consuming the power of the mobile station batteries for channel search.

Il 3 98019

In connection with some other mobile communication systems, solutions have been proposed in which control channel switching can be prepared in advance by arrangements in which the capacity of the mobile station is shared between listening to the current control channel and exploring alternative control channels. EP 269 643 discloses a handover solution in a system in which the control signals transmitted by the base stations repeat a frame structure with a identifier identifying the destination mobile station or stations in the first part and a control message in the second part. The mobile station analyzes the identification part, and if the control message is not intended for it and if the control signal strength is below a certain level, the mobile station is directed to the operating mode for the control message, where it indicates the control channels of the alternative base stations and determines their signal quality. An essential feature of the solution is that the capacity used by the mobile station to receive irrelevant control messages can be better utilized by analyzing alternative control channels during that time. However, the disadvantage of the solution is that the assessment of the need to examine alternative channels is based only on the signal level received during the short duration of the feature, and thus may result in the mobile station examining the signal levels of the alternative control channels more or less continuously. Such a solution is not sufficient for combining power saving and optimal operation of a mobile station, and the solution of said EP publication, on the other hand, does not even set the goal of simultaneously saving the power consumption of the mobile station.

In the solution disclosed in JP 58-187 033, the acquisition of time for the mobile station to explore alternative control channels is based on the fact that the mobile stations are divided into call groups, each of which is sent calls within a certain predetermined time interval. The mobile station receives on the current paging channel only in its own group of time slots and can use the time slots of other groups to examine the signal levels of the control channels of other base stations. In the context of the solution, this publication does not consider at all the power consumption of the mobile station or an implementation by which the prior examination of alternative channels could be optimally limited for this purpose.

The object of the invention is to provide a method for using a mobile station in a mobile communication system according to the preamble of claim 1, in which control channel change can be prepared in advance so as to generally avoid a situation where a new control channel is requested only when the absolute handover criterion is met. unnecessarily used to explore alternative control channels at the expense of power savings. To this end, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

The solution according to the invention is based on the fact that in addition to the absolute handover criterion, at least one but most preferably several other criteria are set for the degradation of the signal received on the control channel. If a control channel 10 that meets the requirements is found during the power saving period, the mobile station switches to this channel. If, on the other hand, no better control channel is found, the mobile station switches to receive on the former control channel for the specified period at the end of the power saving period. Depending on how this is defined in the operating system, the mobile station may continue to scan control channels for subsequent power saving periods, always returning to the current control channel until all channels have been scanned. If a new control channel that meets the requirements is not found, and unless the signal quality on the current control channel continues to deteriorate, the mobile station will normally continue to use power saving cycles for full power saving. On the other hand, if the control channel signal further deteriorates so that the next possible second criterion is reached, the mobile station again uses the power-20 saving period to explore alternative control channels, and so on. In this way, the optimal mode of operation of the mobile station is achieved, in which the mobile station starts to prepare for handover in advance and, as the control signal continuously deteriorates, performs handover most likely before the degradation reaches the absolute handover criterion, so that handover is flexible and no interruption occurs. If, on the other hand, the signal does not deteriorate further, the charging is not continued unnecessarily, and the mobile station uses the power saving periods according to their original purpose for power saving.

The invention also relates to a mobile station 30 for use with the method according to the invention, which is characterized by what is set forth in claim 7.

The invention will be explained in more detail below with reference to the accompanying drawings, in which: Fig. 1 schematically shows a part of a cellular mobile communication system in which the invention can be applied, and illustrates the prior art and b) and c) illustrate the operation of a mobile station according to the method of the invention. in Fig. 5, Fig. 3 illustrates handover events a) prior art and b) when using the method according to the invention, and Fig. 4 shows a block diagram of an application of a mobile station for use with the method according to the invention.

10

Figure 1 schematically shows a part of a cellular mobile communication system in which cellular base stations BS1 to BS5 have control channels CC1 to CC5, respectively. The mobile station MS is moving from the coverage area of the base station BS1 to the area of the base station BS2 and is still receiving control signals on the control channel CC1 of the base station BS1. As the mobile station 15 MS continues to move away from the base station BS1, the strength of the signal received on the control channel CC1 decreases, and the handover begins to become topical.

As stated above in the general part of the description, the invention can be applied to an NMT ice system, for example. In the NMT system 20 according to the current specifications, the mobile station MS operates in the situation of Fig. 1 by receiving a signal from the base station BS1 on the control channel CC1 until the signal degradation reaches a certain criterion, even if the base station BS2 is much closer and its control signal on the channel CC2 is much stronger. on channel CC1. When said criterion is reached, the current control channel is considered lost, and the mobile station MS starts to search for a new control channel. The channel search procedure may comprise several rounds of scanning, possibly with several RF level criteria, as well as storing and processing the measurement results to find an acceptable channel. The mobile station may also have information provided to it by the system to enable it to delimit scannable channels. Since the invention does not address the details of the search procedure itself, they will not be discussed in more detail here. Essentially, in an NMT ice system, for example, the search for a new control channel can advantageously take a few seconds and at worst even about a minute, during which time the mobile station is not operational and unable to receive calls in a prior art system implementation. According to the NMT specifications, the criterion for signal degradation on the control channel is met and handover is considered necessary when the signal level has been 75% below the reference level for the past 2 minutes. This absolute handover criterion is considered in this application in the so-called as the first criterion and is denoted A. The NMT specifications define two different reference levels for different types of base stations that the mobile station MS can identify from certain bits of their signals, but it is sufficient to consider one power level denoted by L to explain the invention. The reference level more commonly used in the NMT system is nominally 10dB (lpV) E.M.F.

As also stated in the general part of the description, the invention relates in particular to a mobile communication system in which the so-called power saving operation, where the system creates an instruction to the mobile station when the mobile station should be "awake" i.e. receiving on the control channel and when it can correspondingly save power or "sleep" and not receive any signal. The NMT system gives mobile stations wake-up times based on their IDs. One possible wake-up time can be, for example, 2 signal frames, i.e. 278 ms, and the sleep time can be 3.3 seconds. These values have been used in the example of Figure 2, which illustrates the operation of the invention in more detail and is described below. The mobile station measures the signal strength during the 2 frames when it is awake and considers, when assessing the fulfillment of said handover criterion, that the same signal level continues during the next sleep or power saving period.

20

The diagrams of Figure 2 show an example of the operation of a mobile station according to the prior art on the one hand and according to the invention on the other hand in an NMT ice system as described above. Schemes a) to c) illustrate the wake-up and power-saving periods of a mobile station in a particular handover situation. The starting point in Fig. 2 25 is to consider two ready-to-operate mobile stations (represented by diagrams a) and b), respectively, starting from time t = 0. During mobile periods, the mobile stations receive on the current control channel, which in each diagram is denoted CC1. They have such identification numbers that their wake-up and power-saving periods are the same. The sections in this example have the regular lengths shown above. The operation of the mobile stations thus repeats the numbered periods described in the diagrams, which include the wake-up time TA and the power saving time TS, as shown in diagram a) at period number 10. The periods are numbered for ease of explanation only, and the numbering has nothing to do with the operation of the mobile station. In the example, the signal level received by the mobile stations on the control channel is constantly below the reference level L from the moment t = 0, and they do not receive calls during the considered period.

7 98019

Diagram a) of the prior art operation is simple. The mobile station monitors the signal levels measured during the wake periods, and when it detects at period 25 that the absolute handover criterion A is met, i.e. the signal level has been 75% below the reference level L for the past 2 minutes, it stops receiving on the current control channel and starts a new channel search. it is thought here to take about a long time, about 35 seconds, i.e. about the end of the time considered.

Schemes b) and c) illustrate two different alternatives to the operation according to the invention. In the operation of Kek-10 according to the invention, it is essential, firstly, that in addition to the absolute handover criterion, at least one other criterion is met which is fulfilled before it is fulfilled. It is recommended that several such criteria be defined, and in the example considered a total of five, ie criteria B to F, are defined, in this case as percentages which the signal for said elapsed 2 minutes must not be below the reference level L. Criteria including criterion A are given in Table 1 below.

Table 1 _

Kriteeri__Määrittely_

A__Signal 75% of 2 minutes below reference level L

B__Signal 30% of 2 minutes below reference level L

_C__Signal 40% of 2 minutes below reference level L

_D__Signal 50% of 2 minutes below reference level L

_E__Signal 60% of 2 minutes below reference level L

_F_ Signal 70% of 2 minutes below reference level L

In the method according to the invention for using a mobile station in a mobile communication network as described above, it is essential that the mobile station prepares for the upcoming handover using the time-saving periods to search for alternative control channels before fulfilling the absolute handover criterion A according to criteria B to F. Thus, following the operation according to the invention from the vessels of diagram b), it is seen that at the beginning of period 11 the mobile station detects that criterion B is met. Thus, the mobile station uses the channel search for the next power saving period, returning at the end of the period for two frames to the current control channel because no acceptable new control channel was found. In the implementation of this example, the mobile station does not continue the channel search during the next power saving period, but only stores the data received during the channel search period and then resumes normal power saving mode by monitoring the signal level of the current control channel during the wake periods. As stated above, the signal level in this example remains constantly below the reference level, and when criterion C is met at the beginning of period 14 5, the mobile station again uses one power saving period for channel search in the same manner and with the same results as the previous time. If the signal level received on the control channel had sometimes risen above the reference level for a significant time, the mobile station would have continued the normal power saving mode until, for example, criterion B was met at some point when the signal may be re-observed. When the signal level remains low, the mobile station detects that criterion D is met at the beginning of period 17 and proceeds to continue the channel search for the duration of the power saving period. If an acceptable channel is not found as shown in diagram b) now and the following criteria E and F are not yet met, for example because the mobile station has reached the periphery of the network where no acceptable signal level is received from any base station 15, then in this case criterion A is finally met and resumed in-depth channel search.

Under normal circumstances, however, the option shown in Figure c) is already likely to materialize. The periodic channel search of the mobile station, which has now been available for a total of about 9 seconds, results in the discovery of an acceptable new control channel CC2 during period 17 of diagram b), and the mobile station has time to switch to the new control channel before the power saving period ends. In the example shown in Figure 2, it is assumed that the signal level is also continuously below the reference level L for this new control channel CC2, which has been switched for the period of waking-25 starting in period 18 of diagram b), and thus criterion B at the beginning of period 11 of diagram c) is also met. C at the beginning of section 14, criterion D at the beginning of section 17, and so on, and the mobile station continues to perform the channel search periodically, sacrificing part of the power saving time.

30 Scheme c) in Figure 2 may not be the most likely to materialize in practice. Where, for example, the mobile station clearly moves from the coverage area of the base station BS1 to the coverage area of the base station BS2, as shown in Figure 1, the new control channel CC2 is likely to have a good signal level and result in flexible and unobtrusive handover without sacrificing significant power-saving time; in most cases, if criterion A is not met at all and the subsequent forced handover procedure is followed, a total of even more power saving time can be obtained for the mobile station overall than with the current specification mode of operation. The method 9 98019 according to the invention thus achieves an optimal mode of operation in which the levels of power saving can even be improved, while at the same time the handover is made to operate in such a way that it is prepared in advance. When a handover proves necessary, it is done flexibly, but when the need for a handover is shifted or eliminated, mobile resources are not sacrificed for contingency. This is particularly well accomplished with the implementation of the invention described herein, in which the periodic performance of handover is based on the use of a number of step-by-step criteria.

In the example solution shown above in connection with Figure 2, the mobile station uses only one of the other criteria for one power saving period for the channel search when one of the other criteria is met. This is a reasonable solution in this case, because the power saving period in the example is quite long, 3.3 seconds. Of course, the operation can also be implemented in such a way that the mobile station uses two or even more power saving periods in succession between the 15 current control channels if no new control channel is found, if at least one of the other criteria is fulfilled. Another implementation alternative is that the mobile station is controlled to always perform a certain part of the channel search at a time and to use the time required for it from successive power-saving periods. One skilled in the art can easily design other implementation options, taking into account the length of the power saving period and other system parameters.

In the example shown, all criteria are set with respect to time using the same signal strength reference level. It is clear that the criteria could equally well be defined by different reference levels, keeping their definition the same over time, or by varying both the signal strength reference levels and the definition over time in the criteria. One skilled in the art will also appreciate that as the signal quality gradually deteriorates, the criteria for signal strength and time may be set in other ways, or that the criteria for signal degradation may in some cases be set based on, for example, the bit error rate.

30

Figure 3 illustrates the improvement achieved by the method according to the invention in handover compared to the current method. Figure 3 (a) illustrates the current solution and shows the route of the mobile station MS through several cells having base stations BS1, BS2 and BS3, respectively. Points P1 and P2 35 indicate the points where handover in this example would probably take place. Upon moving away from the base station BS1, the mobile station does not switch to the control channel of the stronger base station BS2 in time but "hangs" on the control channel BS1 for as long as possible, i.e. until the signal quality is so poor when said absolute handover criterion is met that the control channel is lost. The same is repeated as the mobile station moves away from the base station BS2 and approaches the base station BS3. Figure 3 (b), using the same notations as in Figure 3 (a), shows in the same way the handover events when using the method according to the invention. When a mobile station periodically performs a channel search long before the absolute handover criterion is met, and when a stronger control channel of the approaching base station is available, the handover is also likely to occur much earlier than the method illustrated in Figure 3 (a).

10

Finally, an embodiment of a mobile station used by the method according to the invention is described, the block diagram of which is shown in Figure 4. The mobile station according to the described embodiment can be, for example, an NMT telephone. The operation of the blocks which are not essential to the invention will be explained only very briefly.

On the transmission side, the speech signal from the microphone 31 is processed in the audio processing block 32, and the baseband speech signal obtained in the modulator block 33 is modulated into an intermediate frequency RF signal and mixed with the channel frequency signal from the synthesizer 34. The transmitter block 35 amplifies the signal to the desired power level, and the duplex filter 36 filters it and prevents the transmitter signal from entering the frequency band of the receiver 38.

On the receiving side, the signal from the antenna 37 is filtered in a duplex filter 36 and mixed at the receiver 38 with the injection signal 25 produced by the synthesizer 34 to produce an intermediate frequency signal. In the demodulator block 39, the intermediate frequency signal is amplified in the limiter amplifiers and is detected, for example, by a quadrature detector. The detected audio level signal is further processed in the audio processing block 40 to produce a speech signal to the headset 41.

The operation of the mobile station is centrally controlled by a controller 43 built around the microprocessor, which has access to RAM and ROM 44 and 45.

The frequency synthesizer 34 has a voltage controlled oscillator, the frequency of which is divided down, and is then compared with the frequency produced by the reference oscillator. The reference voltage VC is used to feedback the oscillator to generate a stable frequency. The division number of the frequency oscillator is changed under the control of the controller 43 to select the desired channel frequency.

li 98019 11

The limiter amplifiers of the demodulator section 39 provide information about the field strength (RSSI), which is digitized by the A / D converter 42 and passed on to the controller 43. The controller 43 and the memories 44 and 45 set a signal strength and time criterion that is met as the signal deteriorates and decreases. below the set reference level for substantially long periods. When the criterion is met, handovers are performed for this purpose to find a new channel.

The channel search is performed by the controller 43 setting the desired split ratio for the splitter 34 and measuring the channel field strength (RSSI level) after the settling time 10. The measured level information is stored in RAM 44 and compared to the signal quality criteria set for channel acceptance. Based on the information thus obtained, the controller 43 scans through the possible channels according to a certain channel aging procedure.

System signaling is provided by a controller 43, the data bit stream of which is converted into a baseband data signal in a modem block 47, such as an FFSK modem. Correspondingly, the received baseband data signal is detected by the same modem circuit.

The power saving logic consists of a controllable power supply block 48 and the operation of a timer block 46. Timer block 46 is always kept current to produce time delays. When the so-called the Power Save Time set via the sleep command, i.e. the time of arrival of the next control signal, sets the controller 43 to the desired delay for the timer 46 and controls all the blocks of the telephone except the timer block. After the delay, the timer block 46 excites the controller 43 with the interrupt signal INT, under the control of which the operating voltages VI and V2 are connected to the required blocks. The operating voltages can be connected to different blocks depending on the operating mode of the mobile station. When operational, the mobile station returns at the end of the power saving time to receive a signal on the same control channel it had when it received the sleep-30 go.

When the controller 43 and the memories 44 and 45 set only the aforementioned first criterion A for degradation of the signal received on the control channel in the known mode of operation of the mobile station, leading to rejection of the current channel and execution of a channel search procedure to find a new control channel, the mobile station 43 44 and 45, at least one second criterion that is met before the first criterion is degraded. The first criterion A and the second criteria B, C, D, E, F in the NMT system may be, for example, those shown in Table 1.

The controller 43 and the memories 44 and 45 can also be used to change the above operation of the mobile station 5 so that when one of the other criteria B, C, D, E, F is met, the controller 43 does not control the sleep of the power saving period when the sleep or power save command is received and set by the timer block 46. other blocks to the power saving mode but instead directs the necessary blocks, such as the synthesizer 34, the receiver 38, the demodulator 39, and the A / D converter 42 itself 10, to perform a channel search according to a specified procedure during the set delay, i.e. the intended power saving period. When the delay lasts, the controller 43 controls the channel search normally, i.e. if a new channel is found in time, the controller 43 directs the mobile station to switch to this channel for the next wake-up period. If no new channel is found, the controller 43 interrupts the channel search at the end of the set time delay and 15 directs the mobile station to receive on the previous control channel in the same way as if the sleep period had been used for power saving.

The above setting of new criteria and changing the operation of the control is, for the mobile station control designer, mainly the programming work of the processor controlling the conventional mobile station 20 and the related redesign of the signaling between the blocks of the mobile station. It will also be easy for a person skilled in the art to see how functional additions and changes are implemented in the mobile station which make the mobile station operate in accordance with the various variations of the method according to the invention.

li

Claims (7)

A method of using a telecommunications device (MS) in a telecommunications system comprising multiple base stations (BS1, ..., BS5) and providing corresponding control channels (CC1, ..., CC5) for transmitting signals to the telecommunications devices, in which the telecommunications device (MS), as it is operable on any control channel 10 (CC1) of the base station receives a signal, reviews the quality of said signal, and terminates the reception on the control channel (CC 1) and performs channel search according to a determined procedure for find a new control channel, since the deterioration of the signal received on the control channel (CC1) at any instant corresponds to a first criterion (A) for the quality of the signal, which is the telecommunications device (MS), since it is functional ready and receives and examines the signal on the control channel (CC1) during a first period (TA), in response to a received power saver command is controlled by the party state and to terminate the signal reception for a second period (TS), and at the end of the second period (TS) to resume receiving and reviewing the signal on the control channel (CC1) during a new first period (TA), characterized in that, in the process, at least a second criterion (B, C, D, E, F) is stalled for the deterioration. of the control signal received on the control channel (CC1) before the first criterion (A) is filled, and when this second criterion is fulfilled, the telecommunications device (MS) performs channel search according to a certain procedure to find a new control channel during the second period (TS) and remedy If a new control channel (CC2) has not been found, the receiver channel (CC 1) is received during the first period (TA). Method according to claim 1 for using a telecommunication device in a telecommunication system, characterized in that said criteria (A, B, C, D, E, F) are set with respect to signal intensity and time. Method according to claim 2 for using a telecommunication device in a telecommunications system, characterized in that the criteria are set by determining one or more comparison levels of the signal intensity and corresponding times, during which a received signal can be at most below the comparison level. Method according to any of the preceding claims for use of a telecommunications device in a telecommunications system, characterized in that when any of the other criteria (B, C, D, E, F) are fulfilled, the telecommunications device (MS) performs channel search according to a certain procedure during a second period (TS). Method according to any one of claims 1-3 for using a telecommunications device in a telecommunications system, characterized in that when any of the other criteria (B, C, D, E, F) are filled, the telecommunications device (MS) performs under one or more successive second periods (TS) a fixed period of the channel search according to a particular procedure. 10 Method according to any of the preceding claims for the use of a telecommunications device in a telecommunications system, characterized in that the telecommunications device (MS), where it carried out channel search according to a certain procedure at any point during one or more other periods (TS) since the said criteria (B, C, D, E, F) were previously filled, where none of the other criteria (B, C, D, E, F) are filled, channel search continues according to a determined procedure at said point. Telecommunication device (MS) to be used with a method according to any preceding claim containing: means (37, 36, 38, 34, 39, 47, 43, 44, 45) to receive a signal on the control channel ( CC1) and to detect and decode the received signal one, means (39, 42, 43, 44, 45) to check the quality of the signal received, means (43, 44, 45) on the control channel (CC1) to set a first criterion (A) for the deterioration of the quality of the received signal and for controlling the telecommunications device (MS) to terminate the reception of the signal on the control channel (CC 1) and to perform channel search according to a determined procedure where the first criterion (A) ) are filled, means (34, 38, 39, 42, 43, 44, 45) for performing channel search according to a particular procedure, and means (43, 44, 45, 46, 48) for controlling the telecommunications device (MS) where it receives a signal on the control channel (CC1) during a first period (TA) in response to a received power saving order to pass on power part ill and terminating the signal reception during a second period (TS) and again receiving the signal on the control channel (CC1) as the second period (TS) ends during a new first period (TA), characterized in that it further comprises: means ( 43, 44, 45) to set at least a second criterion (B, C, D, E, F) which is filled when the signal quality deteriorates before the first criterion (A) is filled, and means (43, 44, 45) for to control the telecommunications device (MS), where some of the other criteria (B, C, D, E, F) are filled, in response to a received electricity saving order, to perform a channel search according to a determined procedure for a second period (TS) and returning to receive a signal on the control channel (CC1) for a first period (TA), if no new control channel was found.