WO2001050648A1

WO2001050648A1 - Method and device in a diversity receiver

Info

Publication number: WO2001050648A1
Application number: PCT/SE2000/002224
Authority: WO
Inventors: Timo Pohjanvuori; Erik Stare
Original assignee: Teracom Ab
Priority date: 1999-12-29
Filing date: 2000-11-14
Publication date: 2001-07-12
Also published as: EP1247362A1; AU1428701A; SE9904842L; SE515967C2; SE9904842D0

Abstract

A method and a device for test receiving alternative frequencies without interrupting the reception of the current reception frequency in a spatial diversity receiver. According to the invention, test receptions of alternative frequencies are done by using momentarily not-needed reception paths/branches. By performing test receptions with reception paths that are not used for reception of the current reception frequency, the current program/information transfer is not interrupted at all during the test receptions. A subsequently determined frequency changeover can thereafter, with a high probability, be performed without any noticeable interruption.

Description

Method and device in a diversity receiver

FIELD OF THE INVENTION

The present invention relates generally to a method and a device for change of reception frequency in a diversity radiofrequency receiver, especially mobile diversity radiofrequency receivers, in the intersection area between radio broadcasting regions with different broadcasting frequencies, especially in a diversity radiofrequency receiver for a digital audio/video broadcasting system (DAB/DVB) .

BACKGROUND TO THE INVENTION

Diversity reception/combining is a well-known concept within the area of mobile telephony. Diversity reception is used to avoid the poor reception quality when a receiver and a transmitter mutually move in relation to each other, i.e. a stationary transmitter and a mobile receiver (for example a car radio) , a mobile transmitter (for example a mobile phone) and a stationary receiver (for example a base station), or a mobile transmitter and a mobile receiver. There are several types of diversity reception, such as spatial/space diversity and frequency diversity. The use of spatial diversity, which uses a plurality of antennas physically spaced apart one or more wavelengths, is based on the assumption that there is a high probability that not all antennas will be in a fading area at the same time. When a receiver, such as a mobile telephone, analog radio/TV receiver, or digital radio/TV receiver, moves between different broadcasting areas/regions covered by transmitters of different frequencies then the receiver has to change reception frequency. A diversity receiver will only solve reception problems within a region/cell. The necessary change of reception frequency when moving between regions/cells of different frequencies will necessitate test receptions of alternative frequencies, unless a random trial method is used.

Digital mobile telephony uses Time Division Multiplex Access (TDMA) and can thus use the time frames when there is no reception or transmission, for test receiving alternative frequencies.

Digital radio/TV broadcasting systems, digital audio broadcasting (DAB) and digital video broadcasting (DVB) uses coded orthogonal frequency division multiplexing (COFDM) modulation. DAB and DVB was primarily intended as single frequency network (SFN) systems. In a single frequency network a DAB/DVB receiver does not have to switch reception frequency when travelling between regions covered by different transmitters as all regions of the single frequency network transmit the same programs/ information with the same frequency. COFDM modulation technique provides a robust method of information transfer and is very suitable for SFNs. But due to, for example, the interleaving and the decoding of the digital data stream, the digital data stream cannot be interrupted for a test reception of an alternative frequency to thereby implement an unnoticeable method of test receiving alternative frequencies.

To somewhat provide a solution to the problem of finding alternative frequencies for a current program, the DAB system broadcasts alternative frequencies of the current program so that a list of these can be maintained in the receiver in a manner comparable to that of the RDS system. The DAB receiver will, in accordance to the methods used previously in other systems, when the field strength of the received program falls below a preset threshold or according to a tendency of the field strength, interrupt the reception of the program and perform test receptions of the alternative frequencies in the list. The reception of the current program is unfortunately interrupted for a time interval, which can be considered annoying. As an alternative, a DAB receiver can arbitrarily choose one of the alternative frequencies on the list and perform a frequency change in between two information frames. If such a method is used then there exists a certain probability that the correct frequency is selected and that therefore no interruption will occur. On the other hand there is also a high probability that the frequency is incorrect and that several frequency changes has to be performed with a considerable interruption of the program as a result of this. There is thus a need to improve the methods of providing test receptions in diversity receivers .

SUMMARY OF THE INVENTION

An object of the invention is to define a method and a device which are able to test receive an alternative reception frequency for evaluation purposes in a diversity radiofrequency receiver, especially a mobile DAB or DVB diversity receiver, without interrupting the currently received program/information.

The aforementioned objects are achieved according to the invention by a method and a device for test receiving alternative frequencies without interrupting the reception of the current reception frequency in a spatial diversity receiver. According to the invention, test receptions of alternative frequencies are done by using momentarily not- needed reception paths/branches. By performing test receptions with reception paths that are not used for reception of the current reception frequency, the current program/information transfer is not interrupted at all during the test receptions. A subsequently determined frequency changeover can thereafter, with a high probability, be performed without any noticeable interruption.

The aforementioned objects are also achieved according to the invention by a method of test receiving an alternative reception frequency in a space/spatial diversity receiver comprising at least two receive paths. According to the invention the method comprises a number of steps in the spatial diversity receiver. A first step of receiving a first signal having a first radio frequency being a reception frequency in at least two of the at least two receive paths with a diversity reception. A second step of determining a quality of reception of the first signal in the receive paths in question. A third step of determining which receive path or paths should be removed from the diversity reception. A fourth step of removing at least one of the determined receive path or paths from the diversity reception. A fifth step of switching the reception frequency of at least one of the removed receive path or paths from the first radio frequency of the first signal to an alternative reception frequency, the alternative reception frequency being different from the first radio frequency of the first signal. A sixth step of receiving the alternative reception frequency by the at least one removed receive path or paths. A seventh step of determining a quality of reception of the alternative reception frequency. To thereby enable a test reception of an alternative reception frequency without interrupting the reception of the first signal having the first radio frequency.

Advantageously the third step of determining which receive path or paths should be removed from the diversity reception, comprises the substep of determining which of the receive paths is a lowest quality receive path or paths and the substep of determining that at least one of the receive path or paths that are the determined lowest quality receive path or paths, should be the path or paths that should be removed from the diversity reception.

Alternatively the third step of determining which receive path or paths should be removed from the diversity reception, can advantageously comprise the substep of determining which of the receive paths is a highest quality receive path or paths and the substep of determining that at least one of the receive path or paths that are different from the determined highest quality receive path or paths, should be the path or paths that should be removed from the diversity reception.

The diversity reception can preferably be a selection diversity method or a maximum ratio combining diversity method.

Preferably the second step of determining the quality of reception of the first signal, further comprises the substep of determining a top quality tendency of the at least two receive paths and the substep of suspending further steps until the top quality tendency is equal or below a predetermined top value. The second step of determining the quality of reception of the first signal, can also or either further comprise the substep of determining a top quality tendency of the at least two receive paths and the substep of suspending further steps until the top quality tendency is equal or above a predetermined minimum value. The second step of determining the quality of reception of the first signal, can also or either further comprise the substep of determining a top quality of the at least two receive paths and the substep of determining a lowest quality of the at least two receive paths and the substep of suspending further steps until the difference between the top quality and the lowest quality is equal or greater than a predetermined value.

The method can advantageously further comprise the steps of evaluating which is a best quality reception frequency: the quality of reception of the first signal having the first radio frequency, or the quality of reception of the alternative reception frequency, and of switching the reception frequency of the at least two receive paths to the best quality reception frequency. The step of switching the reception frequency of the at least two receive paths to the best quality reception frequency can preferably further comprise the substep of suspending the switching of the reception frequency until the best quality signal is properly synchronized in the diversity receiver.

The method can further preferably comprise the steps of determining a list of alternative frequencies, and of systematically performing test receptions of the alternative frequencies on the determined list. The method preferably further comprises the steps of evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency, and of switching the reception frequency of the at least two receive paths to the best quality reception frequency. The alternative frequencies on the determined list can systematically be test received at least once each before evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency. Alternatively The alternative frequencies on the determined list are systematically test received only once each before evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency. Alternatively the alternative frequencies on the determined list are systematically test received at least twice each before evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency. The step of evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency, is preferably based on calculated tendency of the quality of reception of each alternative frequency on the determined list.

In some versions the second step of determining the quality of reception of the first signal, further comprises the substeps of determining a top quality tendency of the at least two receive paths, and of, if the top quality tendency is below a must change value, then determining if there is an alternative reception frequency which has recently been test received with an adequate quality, and of, if it is determined that there is no test received alternative reception frequency with an adequate quality, then performing one or more emergency test receptions of alternative reception frequencies at least until an alternative reception frequency with an adequate quality is found or the top quality tendency comes above the must change value.

One or more of the features of the above described different methods according to the invention can be combined in any desired manner, as long as the features are not contradictory.

The aforementioned objects are achieved in accordance with the invention also by a device for test receiving an alternative reception frequency in a space/spatial diversity receiver. The diversity receiver comprising at least two receive paths receiving a first signal having a first radio frequency being a reception frequency in at least two of the at least two receive paths with a diversity reception. According to the invention the device comprises a plurality of means arranged to carry out the invention. A first means arranged to determine a quality of reception of the first signal in the receive paths in question. A second means arranged to determine which receive path or paths should be removed from the diversity reception. A third means arranged to remove at least one of the determined receive path or paths from the diversity reception. A fourth means arranged to switch the reception frequency of at least one of the removed receive path or paths from the first radio frequency of the first signal to an alternative reception frequency, the alternative reception frequency being different from the first radio frequency of the first signal. A fifth means arranged to receive the alternative reception frequency by the at least one removed receive path or paths. And a sixth means arranged to determine a quality of reception of the alternative reception frequency. Thereby a test reception of an alternative reception frequency is possible without interrupting the reception of the first signal having the first radio frequency.

Different embodiments of the device according to the invention can be reached according to additional features mentioned above in connection with the description of the method according to the invention. The features of the above described different embodiments of a device according to the invention can be combined in any desired manner, as long as no conflict occurs.

By providing a device and a method for test receiving alternative frequencies without interrupting the current program/information, a plurality of advantages over prior art systems are obtained. Under favorable conditions even a data transfer can be changed from one reception frequency to another without any loss of information. The device and method according to the invention will work just as well in a mobile or portable receiver as in a stationary receiver. A stationary receiver might be located in an area which is an intersection of two or more broadcasting areas with different transmitter frequencies in such a way that under certain conditions, weather conditions for example, one reception frequency is better than the other (s), and under different conditions another reception frequency is superior. The invention can also advantageously be utilized in a single frequency network where a full coverage DAB/DVB network is not yet achieved and where analog FM or AM broadcasting is utilized to complement the DAB network and thereby provide complete coverage for regional and/or national programs. The difference being that test receptions are performed on alternative FM or AM frequencies instead of on DAB/DVB frames and that the evaluation of the test receptions are adapted according to the type of test reception performed. DESCRIPTION OF THE FIGURES

The invention will now be described in more detail for explanatory, and in no sense limiting, purposes, with reference to the following figures, in which

Fig. 1 shows a block diagram of one DAB frame,

Fig. 2 shows a frequency coverage map,

Fig. 3 shows a block diagram of a diversity receiver according to the invention, and

Fig. 4 shows a flow chart of how at least one alternative reception frequency is measured and possibly changed to in a receiver according to one method of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In order to clarify the system according to the invention, some examples of its use will now be described in connection with Figures 1 to 4.

Figure 1 shows a block diagram of one DAB frame, which is merely provided for a deeper understanding of the DAB system in particular and to understand in general the principles of transmission coding systems, such as DVB, that cannot be interrupted.

DAB frames are sent in succession. A DAB frame mainly comprises a synchronization channel 101, 102, a fast information channel (FIC) 103, and a main service channel

(MSC) 104. The synchronization channel comprises a null symbol 101 and at least one phase reference symbol 102. The fast information channel (FIC) 103 is, for example, used for multiplex configuration information (MCI) and service information (SI) . The main service channel 104 carries the desired useful information, which can be a number of coded audio programs/channels, one or more digital information transfers, or a combination of these. Usually more than one program/channel or information transfer is coded into the main service channel.

A DAB frame is configured to provide a robust way of transferring information, i.e. packets of digital information, from a transmitter to a receiver without any feedback through, for example, a back channel. In the transmitter a DAB frame is assembled in the following manner; Packets of digital information are coded, error protected, and then time interleaved. These are thereafter multiplexed into the main service channel 104 according to a predetermined, but changeable, service configuration. The multiplexer output is frequency interleaved and combined with multiplex control and service information which travel in the fast information channel 103 in order to avoid the time interleaving process. Finally, very rugged synchronization symbols 102 are added before applying orthogonal frequency division multiplexing (OFDM) and differential quadrature phase- shift keying (QPSK) modulation onto a large number of carriers to form the DAB signal.

Due to, among other things, the interleaving, not only within a single frame but also between different frames, the fast information channel 103 and the main service channel 104 cannot be interrupted for any substantial length of time without causing a substantial interruption of the received program/information before the interleaving is complete again. A frequency switch between a currently received frequency to an alternative frequency should not be preceded with interruptions of the currently received frequency for the purpose of test receiving alternative frequencies. If a diversity receiver knows which alternative frequency it should switch to when a currently received frequency deteriorates, then there is no need to perform test receptions of alternative frequencies for an evaluation of which alternative frequency the receiver should switch to. Unfortunately this is rarely or never the case. Therefore there is a need to test receive alternative frequencies, to thereby be able to evaluate which is a, for the moment, superior reception frequency.

Figure 2 shows a frequency coverage map over four different broadcasting regions 211, 212, 213, 214, each region broadcasting with a different frequency. Each broadcasting region 211, 212, 213, 214, has at least one transmitter 221, 231, 222, 232, 242, 223, 224. A first broadcasting region 211 comprises two transmitters 221, 231, to be able to cover the whole first region 211. The two transmitters 221, 231, of the first region 211 transmit at the same frequency and thereby take advantage of a single frequency network (SFN) such as that of the DAB and DVB broadcasting systems. A second broadcasting region 212 comprises three transmitters 222, 232, 242, to cover the whole second region 212. The number of necessary transmitters can, for example, depend on the geography of the region or transmitter output power level. The first and second regions 211, 212, are single frequency networks on a small scale.

Each one of the third and fourth broadcasting regions 213,

214 comprises a single respective transmitter 223, 224. These broadcasting regions 213, 214 can be of the DAB,

DVB, FM, or AM type. The invention is not restricted to what type of broadcasting system a mobile receiver enters or a stationary receiver is in the vicinity of. The invention is however mainly directed toward the problems when the currently received program is transmitted from for example a DAB or DVB system since the invention deals with performing test receptions of alternative frequencies by a diversity receiver without interruption of the currently received program and thus for example the received DAB or DVB frames. It will be assumed in the following that all of the broadcasting regions 211, 212, 213, 214, are of the DAB or DVB type. Further it will be assumed that at least two of the broadcasting regions 211, 213, (the first and third 211, 213) broadcast at least one common program/ information channel, the program being the one that our mobile receiver 290 is receiving when travelling along a road 200 that goes through the first and third broadcasting regions 211, 213, in our example.

If the same program were not available, a diversity receiver would preferably change to an alternative frequency that transmits the same type of program that is currently received. In these circumstances it would be preferable if the change to an alternative frequency is a bit more reluctant, i.e. the current frequency and therefore current program would be allowed to degrade a bit more before a change is performed than when the same program/information is available and a change back and forth can be performed without, for example, a listener noticing these changes. The DAB standard has provisions for not only broadcasting alternative frequencies that transmit the same program to the receiver, but also alternative frequencies that transmit the same type of program, i.e. news, pop music, jazz, sport etc.

Test receptions of alternative frequencies is preferably done more or less continuously, but change to an alternative frequency will usually only be close at hand when a receiver is located in a region/intersection 219 between two or more broadcasting regions 211, 213, as is illustrated in figure 2. The recieved signal level will then be lower which gives an increased sensitivity to fading, which is at least in part compensated by a spatial diversity receiver.

If, for example, according to figure 2, a mobile receiver 290 travels along a road/path 200 through a first broadcasting region 211 towards a third broadcasting region 213 and currently is located in a region 219 which is an intersection of the first 211 and third 213 regions, then a currently received frequency is assumed to be that of the first region 211. According to the invention, test receptions of alternative frequencies can either be performed more or less continuously or only when the reception level of the currently received frequency starts to deteriorate and for example an error bitrate rises. In the example, test receptions will preferably be performed at least when the mobile receiver 290 is on its way to enter a new broadcasting region 213.

According to the invention, test receptions of alternative frequencies in a spatial diversity receiver are performed by one or more reception paths/branches that are not

"needed" during a test reception interval. Which paths/branches that are not "needed" is determined either by determining which path/branch or paths/branches have the worst reception quality for the moment and/or possibly predicted to have in the near future and then use these, or by determining which path/branch or paths/branches have the best reception quality for the moment and/or possibly predicted to have in the near future and then use one or more of the other, i.e. not best reception quality, paths/branches. By using momentarily superfluous reception branches the reception of the currently received frequency is not interrupted and nor is the quality of reception degraded. The currently received frequency is meant to denote the frequency that is received when the procedure of the method according to the invention commences. This procedure of test receiving alternative frequencies can be repeated several times until the receiver determines that an alternative frequency will provide a superior reception quality compared to the currently received frequency, which is when a change of reception frequency is initiated.

As mentioned previously, the alternative frequencies are not necessarily DAB or DVB transmissions and even if they are, it is not necessary for the invention that they are synchronized. Independently of what is received during these test receptions of the alternative frequencies, an evaluation of the received signals is performed. A prediction as to the tendency, stronger and stronger or weaker and weaker, of the received signal can also possibly be done to support the determination as to what alternative frequency a change should be executed to and also when this should happen. Depending on the specific embodiment of the invention, the evaluation may comprise a determination of what type of signals are received, i.e. DAB, DVB, FM, or AM, so that an evaluation may take into account not only the received signal strength but also the received signal strength in view of the type of received signals. The method and device used for evaluation and prediction is outside the scope of this invention and within the capability of the man skilled in the art to implement and will therefore not be discussed any further herein .

Figure 3 shows a block diagram of a diversity receiver according to the invention. The receiver according to the example only comprises two reception paths/branches, a first branch 301, 311, 321, 325, 331, 341 and a second branch 302, 312, 326, 322, 332, the minimum required by the invention, there is no upper limit to the number of reception branches used. The receiver according to figure 3 comprises two antennas 301, 302, which are suitably physically separated one or more wavelengths from each other. Mounted in a car, the antennas 301, 302 can suitably be placed in the vicinity of different corners of the car perimeter. Each branch then comprises a corresponding preamplifier and possible filter 311, 312, a local oscillator 321, 322, a mixer 325, 326 for a frequency shift to the baseband and possibly a filter 331, 332. The diversity receiver also comprises a diversity combiner 360, which determines if an output signal 390 should be derived from only one reception branch and in that case which branch, or if the output signal 390 should be derived from some sort of combining of the received signals from two or more branches. The diversity combiner 360 makes use of a quality checker 350 when combining the received signals from the attached branches. The quality checker 350 can for example determine the received signal strength, bit error rate, and/or tendencies for use as a quality base. According to the invention at least one branch comprises a switch 341 which removes a branch in question and directs the signal of the branch to a quality checker, preferably being the quality checker 350 of the receiver. Preferably each branch of the receiver comprises a corresponding switch 341, 342 such that any branch can be disconnected from the diversity reception and instead be connected to a quality checker for evaluation of alternatively received frequencies in the disconnected branches. However, by using only one switch 341 there is a cost and space saving, with the disadvantage of only being able to test receive alternative frequencies in one branch. During operation the quality checker 350 will determine when the quality of the currently received signals from a currently received reception frequency has deteriorated to such a degree that there is a need to change reception frequency, and thus a need to determine to which alternative frequency a change should be made, by means of test receptions. In certain embodiments or modes of the invention test receptions are performed at regular or irregular intervals instead of waiting for an acute need. When it has been determined that a test reception of an alternative frequency should be made, then it is determined which reception branch that is not momentarily needed for a proper reception of the currently received signals of the current reception frequency. Preferably the quality checker 350 is used to determine which branch is not momentarily needed, i.e. determined not needed during a time period of sufficient length for at least one test reception of one alternative frequency. The differences in reception quality between the different antennas/reception paths in a spatial diversity receiver is most likely due to fading. Fading can in principle be divided into two basic types, a first type which is dependent on the relative movement between a transmitter and a receiver and a second type which is dependent on the spatial relationship between the transmitter and the receiver which brings in geographical and atmospherical conditions. The first type of fading is periodically varying and is dependent on factors such as the relative speed between receiver and transmitter and used frequency. The periods can be measured and will give a possibility to predict length of availability of a path/branch for test receptions and also when this will occur. Unfortunately the periods become shorter and shorter (i.e. the frequency of change increases) with increasing relative speed between transmitter and receiver, which means that if the speed is above a certain limit, the available time for test receptions will be to short. The second type of fading is unpredictable and will vary even if receiver and transmitter are not moving relative each other. The second type of fading is more difficult to predict, but it is possible during favorable conditions. According to the invention it is possible to interupt a test reception and return one or more used paths for reception of the original reception frequency if the fading takes an unexpected negative turn, i.e. the reception quality deteriorates, on the path or paths used for receiving the current reception frequency.

The determination of which branch (or branches in a spatial diversity reception system with more than two branches) that is not needed can be based on which branch

(or branches) that have the determined worst reception quality, or which branch (or branches) that do not have the determined best reception quality, or which branch (or branches) that is not determined needed for providing an adequate reception quality of the currently received signals of the current reception frequency. For example, according to figure 3, if the first branch 301, 311, 321, 325, 331 is determined not needed then it is removed/disconnected from the diversity combiner 360 by a switch 341 of the branch in question. In this example, the diversity combiner 360 will then only receive signals from the second branch 302, 312, 326, 322, 332. The local oscillator 321 of the first branch is then changed so that an alternative frequency is received. The received signals of the alternative frequency are directed to a quality checker, preferably the quality checker 350 so that the quality of the alternative frequency can be measured. At this point a plurality of alternative frequencies can be test received by simply adjusting the local oscillator 321 of the first branch, or the first branch is returned to receiving the current signal of the current reception frequency and a new evaluation/determination of which path is not needed is made.

Fig. 4 shows a flow chart of how at least one alternative reception frequency is test received, measured and possibly changed to in a receiver according to one method of the invention. In a first step 410 or actually a receive state 410, a current frequency is received by the different paths/branches of a diversity receiver. In a second step 420, a quality determination step 420, the quality of reception of the currently received frequency is determined. The quality determination can, for example, be based on measured field strength, number of bit errors, or tendencies, i.e. is the situation getting worse or better. In a first optional step 431, it is determined if it is necessary to measure any alternative frequencies, i.e. is there a need, presently or in the near future, to change to a better reception frequency? A measured field strength or for example an error bitrate of the currently received frequency is either compared to a fixed threshold value or used in a prediction computation with which a tendency is computed and thereafter compared with model tendencies. Model tendencies can be either computated from knowledge of for example fading behaviour, such as described above, and/or from previous measurements, a car receiver which travels the same route day after day. If the field strength is above the fixed threshold or does not show a weakening tendency, then the procedure returns to the receive state 410. On the other hand, if, for example, the field strength is below a fixed threshold or shows a weakening tendency, then the procedure proceeds to a second optional step 433, or if there is no optional step 433 directly to a third step 440 which will be described in full below. The procedure can also possibly be suspended if the received quality is below a threshold, below which it is determined that all or most paths/branches are needed to ensure that the reception is not interrupted.

The first optional step 431 is optional, the method according to the invention, as described below, can be performed continuously, initiated by another program, or initiated on demand by other methods/devices than by the method which has been described in relation to the first optional step 431. The second optional step 433 determines a list of alternative frequencies that can be suitable to test receive. The list might consist of only one alternative frequency or a plurality. The currently received frequency can preferably be included in the list. The list might be assembled from all or selected frequencies from those included in the information received by the currently received, for example DAB or DVB, transmissions, preprogrammed frequencies, one or more random frequencies generated, for example, from a random generator, all or selected frequencies in the neighborhood of the currently received frequency, or all or selected frequencies in the frequency range of the receiver or a combination of any of these possibilities.

In the third step 440 one or more branches are removed from use for reception of the currently received frequency, i.e. this or these branches are not to be used for diversity reception, but for reception of alternative reception frequencies. The method for removing one or more branches can be determined in different manners in dependence on the specific embodiment of the invention. The branch or branches that are determined to have the currently received frequency' s worst reception quality can be the one or ones that are removed. In other embodiments it can be the one or more branches that are removed that is/are not or do not belong the group of branches that are determined to have the currently received frequency's highest quality reception.

Thereafter in a fourth step 450 at least one branch of the removed branch or branches have their reception frequency switched to an alternative reception frequency. When the reception frequency of at least one removed reception branch has been switched in the fourth step 450, then in a fifth step the alternative reception frequency is received. In a sixth step 470 the quality of the received alternative frequency is determined. As mentioned previously, the quality determination can, for example, be based on measured field strength, number of bit errors, or tendencies, i.e. is the situation getting worse or better.

The procedure according to the method according to the invention can then optionally comprise a third optional step 481. The third optional step 481 will determine if there are more alternative frequencies to measure/test receive. If, for example, there is a list of alternative reception frequencies to measure, then preferably all of them should be measured at least once, maybe even more times to thereby be able to calculate reception tendencies. If all alternative frequencies have been measured then the procedure will optionally continue with a 483 fourth optional step. On the other hand, if it is determined that more alternative frequencies should be measured, then the procedure can, for example either continue the fourth step 450, or to the first step 410, with or without returning the removed branch or branches to the current frequency, for starting the procedure from the top. In the fourth optional step 483, it is determined if an alternative frequency is better than the currently received frequency. Basically a comparison of the results from the second step 420 and the sixth step 470 is made, i.e. the quality of the received frequency is compared with the quality of alternative frequency or frequencies. If the currently received frequency is determined as having a better quality, i.e. being the most preferable, then the procedure preferably either exits from the procedure or returns to the top with the first step 410 to start the procedure over again. On the other hand, if it is determined that an alternative frequency is of a better quality then the procedure preferably continues with possibly a fifth optional step 485 and a sixth optional step 487.

The fifth optional step 485 suspends further processing until the alternative frequency it has been determined has a better quality, has been properly synchronized. When the alternative frequency has been properly synchronized then the procedure continues with the sixth optional step 487, which switches reception of preferably all the reception branches to the alternative frequency. Thereafter the procedure exists or returns to the top of the procedure and starts over again with the first step 410.

The present invention can be put into apparatus-form either as pure hardware, as pure software or as a combination of hardware and software. If the method according to the invention is realized in the form of software, it can be completely independent or it can be one part of a larger program. The software can suitably be located in a general-purpose computer or in a dedicated computer. As a summary, the invention can basically be described as a device and a method which provide test receptions of alternative reception frequencies to thereby enable a change of reception frequency in a spatial diversity receiver without interrupting reception of the currently received frequency.

The invention is not limited to the embodiments described above but may be varied within the scope of the appended patent claims.

FIG 1

101 null symbol

102 phase reference symbol

103 FIC fast information channel

104 MSC main service channel - audio programs

FIG 2

200 road;

211 frequency 1 coverage;

212 frequency 2 coverage;

213 frequency 3 coverage;

221144 frequency 4 coverage;

219 overlap between 211 and 213;

221 transmitter 1 frequency 1,

222 transmitter 1 frequency 2;

223 transmitter 1 frequency 3,

222244 transmitter 1 frequency 4

231 transmitter 2 frequency 1,

232 transmitter 2 frequency 2

242 transmitter 3 frequency 2,

290 receiver / mobile receiver / car;

F FIIGG 33

301 antenna branch 1

302 antenna branch 2

311 preamplifier and filters branch 1

331122 preamplifier and filters branch 2

321 local oscillator branch 1

322 local oscillator branch 2

325 mixer branch 1

326 mixer branch 2

333311 filter branch 1

332 filter branch 2 341 switch branch 1

342 optional switch branch 2

350 quality checker for measurement of quality 360 diversity combiner 390 output signal for further processing

FIG 4

410 first step - receive;

420 second step - determine quality of received signal;

431 first optional step - is it necessary to measure alternative frequencies; 433 second optional step - determine list of alternative frequencies; 440 third step - remove one or more branches;

450 fourth step - switch frequency of removed branch (s) ; 460 fifth step - removed branch (s) receive alternative frequency; 470 sixth step - determine quality of received alternative frequency; 481 third optional step - are there more alternative frequencies to measure; 483 fourth optional step - is an alternative frequency better than currently received frequency, signal; 485 fifth optional step - synchronize alternative frequency, signal; 487 sixth optional step - switch reception to alternative frequency;

Claims

1. A method of test receiving an alternative reception frequency in a space/spatial diversity receiver comprising at least two receive paths, characterized in that the method comprises the following steps in the spatial diversity receiver: receiving a first signal having a first radio frequency being a reception frequency in at least two of the at least two receive paths with a diversity reception; - determining a quality of reception of the first signal in the receive paths in question; determining which receive path or paths should be removed from the diversity reception; removing at least one of the determined receive path or paths from the diversity reception; switching the reception frequency of at least one of the removed receive path or paths from the first radio frequency of the first signal to an alternative reception frequency, the alternative reception frequency being different from the first radio frequency of the first signal; receiving the alternative reception frequency by the at least one removed receive path or paths; determining a quality of reception of the alternative reception frequency; thereby enabling a test reception of an alternative reception frequency without interrupting the reception of the first signal having the first radio frequency.

2. The method according to claim 1, characterized in that the step of determining which receive path or paths should be removed from the diversity reception, comprises the substeps of: - determining which of the receive paths is a lowest quality receive path or paths; determining that at least one of the receive path or paths that are the determined lowest quality receive path or paths, should be the path or paths that should be removed from the diversity reception.

3. The method according to claim 1, characterized in that the step of determining which receive path or paths should be removed from the diversity reception, comprises the substeps of: determining which of the receive paths is a highest quality receive path or paths; determining that at least one of the receive path or paths that are different from the determined highest quality receive path or paths, should be the path or paths that should be removed from the diversity reception.

4. The method according to any one of claims 1 to 3, characterized in that the diversity reception is a selection diversity method.

5. The method according to any one of claims 1 to 3, characterized in that the diversity reception is a maximum ratio combining diversity method.

6. The method according to any one of claims 1 to 5, characterized in that the step of determining the quality of reception of the first signal, further comprises the substeps of: determining a top quality tendency of the at least two receive paths; suspending further steps until the top quality tendency is equal or below a predetermined top value.

7. The method according to any one of claims 1 to 6, characterized in that the step of determining the quality of reception of the first signal, further comprises the substeps of: determining a top quality tendency of the at least two receive paths; suspending further steps until the top quality tendency is equal or above a predetermined minimum value.

8. The method according to any one of claims 1 to 7, characterized in that the step of determining the quality of reception of the first signal, further comprises the substeps of: determining a top quality of the at least two receive paths; determining a lowest quality of the at least two receive paths; - suspending further steps until the difference between the top quality and the lowest quality is equal or greater than a predetermined value.

9. The method according to any one of claims 1 to 8, characterized in that the method further comprises the steps of: evaluating which is a best quality reception frequency: the quality of reception of the first signal having the first radio frequency, or the quality of reception of the alternative reception frequency; switching the reception frequency of the at least two receive paths to the best quality reception frequency.

10. The method according to claim 9, characterized in that the step of switching the reception frequency of the at least two receive paths to the best quality reception frequency further comprises the substep of: suspending the switching of the reception frequency until the best quality signal is properly synchronized in the diversity receiver.

11. The method according to any one of claims 1 to 8, characterized in that the method further comprises the steps of: determining a list of alternative frequencies; systematically performing test receptions of the alternative frequencies on the determined list.

12. The method according to claim 11, characterized in that the method further comprises the steps of: evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency; switching the reception frequency of the at least two receive paths to the best quality reception frequency.

13. The method according to claim 11 or 12, characterized in that the alternative frequencies on the determined list are systematically test received at least once each before evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency.

14. The method according to claim 11 or 12, characterized in that the alternative frequencies on the determined list are systematically test received only once each before evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency.

15. The method according to claim 11 or 12, characterized in that the alternative frequencies on the determined list are systematically test received at least twice each before evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency.

16. The method according to any one of claims 11 to 15, characterized in that the step of evaluating which of the quality of reception of the first signal and the quality of reception of the alternative reception frequencies on the determined list is a best quality reception frequency, is based on calculated tendency of the quality of reception of each alternative frequency on the determined list .

17. The method according to any one of claims 1 to 16, characterized in that the step of determining the quality of reception of the first signal, further comprises the substeps of: determining a top quality tendency of the at least two receive paths; if the top quality tendency is below a must change value, then determining if there is an alternative reception frequency which has recently been test received with an adequate quality; - if it is determined that there is no test received alternative reception frequency with an adequate quality, then performing one or more emergency test receptions of alternative reception frequencies at least until an alternative reception frequency with an adequate quality is found or the top quality tendency comes above the must change value.

18. A device for test receiving an alternative reception frequency in a space/spatial diversity receiver comprising at least two receive paths receiving a first signal having a first radio frequency being a reception frequency in at least two of the at least two receive paths with a diversity reception, characterized in that the device comprises : - means arranged to determine a quality of reception of the first signal in the receive paths in question; means arranged to determine which receive path or paths should be removed from the diversity reception; means arranged to remove at least one of the determined receive path or paths from the diversity reception; means arranged to switch the reception frequency of at least one of the removed receive path or paths from the first radio frequency of the first signal to an alternative reception frequency, the alternative reception frequency being different from the first radio frequency of the first signal; means arranged to receive the alternative reception frequency by the at least one removed receive path or paths; means arranged to determine a quality of reception of the alternative reception frequency; thereby enabling a test reception of an alternative reception frequency without interrupting the reception of the first signal having the first radio frequency.