SDR BASED METHOD OF M U LTI- MODE RADIO TIMING SCHEDULING

FIELD OF THE INVENTION

The invention relates to a multi-mode radio timing scheduling method, and more specifically, to a Software Defined Radio (SDR) based radio timing scheduling method, and a mobile telecommunication system adopting the radio timing scheduling method which is capable of dealing with a required inter-mode monitoring, carrying out automatic handover at a very fine time resolution with cost-effective and lower power consumption.

TECHNICAL BACKGROUND OF THE INVENTION

It is known that the 2nd generation and the 3rd generation mobile communication standards require respective dedicated transmission/reception interfaces and protocols. An ideal global roaming service is still in question.

In order to make sufficient use of radio resources and realize global roaming seamlessly, it is desirable to design a mobile station in supporting multi-radio systems. However, it always takes precedence for a mobile station to design an analog transmission/reception front-end unit and various ASICs suitable for available standards in use. So, some conventional multi-mode (including multi-RAT) mobile stations realize switching among modes manually. Even though some mobile stations are capable of adapting automatically to multiple radio timing scheduling systems for an automatic handover, they need more gate count usage of ASICs since separate hardware sets should be provided within one

mobile station for each of available modes, resulting in increasing cost of mobile stations and power consumption.

Recently, a Software Defined Radio (hereafter "SDR") based telecommunication system was proposed, which provides a possibility and high flexibility in adapting a mobile station to various standards currently in use or in development. In this regard, providing a multi-mode radio timing scheduling with a very fine time resolution is one of tasks. As the radio timing scheduling method is quite different for different kinds of radio access mode, it is necessary to find a solution for a multi-mode timing scheduling method to facilitate inter-mode (including inter-RAT) handover and operation with less cost, high efficiency, and low power consumption.

SUMMARY OF THE INVENTION

In order to overcome the shortcoming of the prior art, the present invention is to provide a SDR based radio timing scheduling method for a mobile station.

In particular, the present invention is to provide a method and an apparatus of multiple radio access system based on Software Defined

Radio technology, which enables users to migrate seamlessly from one mode to another mode to support compelling data service without exposing to interruption in coverage.

To achieve the above object, the present invention provides a method of multi-mode radio timing scheduling for a multi-mode telecommunication system, said method comprises setting a shared operation pool table for containing all operations to be executed by two

modes; establishing an action table; checking the established action table to determine whether to proceed inter-mode processing; reloading a first timer for carrying out communication between a mobile station and a base station at a current mode; waking up a second timer if inter-mode processing is proceeded; and adapting the frequency and gain of a channel of the system to another communication mode upon completion of the communication between the mobile station and the base station.

According to an embodiment of the invention, the action table is preset into the system and comprises a Mode-Domain field for indicating whether the operation is an inter-mode processing; an OPCode field for identifying an operation corresponding to the shared operation pool table; an Absolute Starting Time field for indicating the start time for the operation; an Timing Length field for indicating the time length of processing the operation; and a Priority field for indicating whether the Timing Length field is active.

Preferably, the above-mentioned checking step is implemented by checking the Mode-Domain field of the action table.

Preferably, if the Mode-Domain field is "0", an intra-mode processing is proceeded. Otherwise, if the Mode-Domain field is "1 ", an inter-mode processing is proceeded, and a second timer is loaded while the first timer is still working for counting the communication. Moreover, the second timer may be triggered once the first timer stops.

Moreover, the method further comprises a step of inquiring the Priority field of the action table when the second timer is loaded.

Preferably, if the Priority field indicates that the Timing Length

field is inactive, the second timer is loaded with an initiate value according to relevant execution timing of the shared operation pool table; otherwise, if the Priority field indicates that the Timing Length field is active, the second timer is loaded with an initiate value according to relevant execution timing of the Timing Length field of the action table.

According to another embodiment of the invention, the shared operation pool table is a pre-recorded table in the process of manufacturing.

According to a further embodiment of the invention, the shared operation pool table is configured to be updated at the initial boot up of the system.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a schematic diagram of a multi-radio mobile station according to the invention;

Fig. 2 is a graph illustrating operations for monitoring another available mode TD-SCDMA when GSM mode is in service;

Fig. 3 is a schematic diagram showing shared operation pool structure in comparison with the separate conventional operation definition for each mode;

Fig. 4 is an action table showing the data structure of a radio timing scheduling; and

Fig. 5 is a flow chart of the inter-Mode Monitor processing.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention and various advantages thereof will be described with reference to exemplary embodiments in conjunction with the drawings.

Fig. 1 is one embodiment of the present invention, schematically showing a dual-mode radio telecommunication system according to the invention. It is easily understood for those skilled in the art that Fig. 1 and its relevant illustration are to exemplify the inventive concept of this invention. The present invention is not limited to this embodiment.

As shown in Fig.1 , a system 100 is a multiple accessible telecommunication system, comprising a dual-mode radio mobile station 6, a first mode base station 4a and a second mode base station 4b. To facilitate the understanding of this invention, the mobile station 6 of this embodiment may be a GSM/LCR-TDD dual mode mobile station. The first mode is GSM mode and the second mode is TD-SCDMA mode.

The station 6 is able to communicate with the base stations 4a and 4b, respectively, by transmitting and receiving radio signals 8a or 8b via an antenna assembly 20.

Radio signals 8a are organized, e.g. in frames of 1250 bits of information for GSM mode, and radio signals 8b are organized, e.g. in frames of 6400 chips for TD-SCDMA mode.

To receive or transmit such radio signals 8a and 8b, the mobile station 6 comprises a tunable radio-frequency subsystem 16 and a baseband processor 18. The subsystem 16 is used for converting radio signals received from base stations to base-band signals and outputting the converted signals through lines 22 to the base-band processor 18.

The subsystem 16 is also able to convert base-band signals received from the based-band processor 18 through lines 22 into radio signals to be transmitted to base stations.

The base-band processor 18 includes an interface 40, a calculator 70, a storage unit 72, and a memory 42.

The interface 40 includes blocks 54, 55, 56 and 58, a comparator 52, a controller 60 and two timers 50 and 51. Two clocks 80 and 81 are input into the timers 50 and 51 , respectively, in supporting two modes. The controller 60 may be a hardwired controller for controlling blocks 54, 55, 56 and 58.

The three-wire bus 24 connecting between the block 54 and the subsystem 16 is used to transmit control messages called 'telegrams". For example, such telegrams are used to change a frequency of channel of subsystem 16.

The digital lines 26 connecting between the block 56 and the subsystem 16 are two-state lines which can be set either in a logic "1 " state or logic "0" state. For example, the lines 26 are used to control an antenna front end switch (not shown in Fig. 1) in subsystem 16 to shift from a receiving mode to a transmitting mode and vice-versa.

Another digital lines 28 connecting between the block 58 and the subsystem 16 are used to send digital signals, which are used e.g. for controlling a reference frequency of subsystem 16 and for controlling a transmission power level.

The lines 25 connecting between the block 55 and the

subsystem 16 is specially designed for multi-mode access systems to change the sampling rate according to an action table 44 stored in the memory 42.

The calculator 70 preferably includes a main processor 74 and a coprocessor 76 to achieve faster performance.

The main processor 74 is a conventional programmable microcontroller to execute conventional operations as disclosed in the International Publication WO 2005/093969. The main processor 74 is also programmable to control every user interface of the mobile station 6, such as a displayer, keyboard, speaker, or the like.

The coprocessor 76 can be a Digital Signal Processor (DSP) chip. The coprocessor 76 is especially designed to process the base-band signals received through lines 22.

More specifically, the coprocessor 76 is also designed to process and update an action table 44, which will be explained in detail hereafter. To do so, the coprocessor 76 is connected to the memory 42 through a bus 46. The bus 46 is a shared resource between the interface 40 and the coprocessor 76. Since memory 42 can be accessible by different electronic applications of the mobile station 6 through the common bus 46, the memory is a general purpose memory.

The storage unit 72 allows data exchange between the main processor 74 and the coprocessor 76. The storage unit 72 can be, for example, a dual port random access memory (DPRAM).

To save space in the storage unit 72 and therefore reduce power

consumption, a special data structure 78 is used, which will be referred to as a shared operation pool hereafter. Moreover, the shared operation pool is of benefit to the development of modular handset. Specifically, as to designing of a modular handset, the unified interface between the subsystem 16 and the processor 18 is standardized for being shared in multi-mode or multi-RAT mobile station. In fact, the operations introduced in the shared operation pool are a part of the content of the unified interface between the subsystem 16 and the processor 18.

According to the present invention, in order to make the multi- mode mobile station work at multiple radio modes without any interruption, multiple reference clocks and multiple timers used for multiple available modes are introduced. Fig. 1 shows two timers 50 and 51 and two reference clocks 80 and 81 , respectively, in order to support the dual-mode communication.

As shown in Fig. 1 , one reference clock 80 is 1.0834MHz for

GSM mode and another Clock 81 is 10.24MHz for TD-SCDMA mode. The two reference clocks can be generated with one or more clock synthesizers inside the ASICs and be enabled or disabled by the processor 18.

In the embodiment, assuming that the mobile station 6 works at GSM mode, the time to send commands must be controlled with a time resolution as small as a one quarter-bit period, say, 923 ns.

If the mobile station should monitor another mode, like TD- SCDMA, the time to send a command must be scheduled with a time resolution as small as one eighth-chip period, namely, 97.65 ns.

Thus, as shown in Fig. 1 , the GSM timer 50 receives a reference clock 80 for counting the number of quarter-bit periods elapsed since the beginning of a GSM frame processing; and the TD-SCDMA timer 51 receives another reference clock 81 for counting the number of one eighth-chip period elapsed since the beginning of TD-SCDMA frame processing. The timer 50 and timer 51 are connected at a first input and a second input of the comparator 52, respectively.

A third input of the comparator 52 is designed to receive the output of the memory 42. The output of the comparator 52 is connected to an enable input of four blocks 54, 55, 56 and 58.

Compared with the mentioned prior publication of WO2005/093969, the block 55 and lines 25 between the block 55 and the subsystem 16 are specially designed according to the present invention. As shown in Fig. 1 , the first input of the block 55 receives an output of the controller 60 and the second input of the block 55 receives the output of the comparator 52. The output of the block 55 is sent to the subsystem 16 through AD/DA control lines 25. By means of the block 55 and lines 25, the Analog to Digital Converter (ADC) and Digital to Analog Converter (DAC) in the radio subsystem 16 (not shown in Fig. 1) can be controlled in order to change sampling rates of the ADC and DACs and switch the ADC and DAC to be "ON" or "OFF" condition according to the table 44.

Furthermore, the coprocessor 76 is also designed to execute multi-mode radio timing scheduling, except for its conventional functions as described in the prior art.

According to the present invention, the coprocessor 76 enables

the inter-mode monitoring by reloading the timers 50 or 51 with the initial value that is coincidence with the monitoring period. The timing scheduling mechanism of the present invention will be described in detail later with reference to Figs. 4 and 5.

The two reference clocks 80 and 81 and two timers 50 and 51 can be woken up by the coprocessor 76 according to the table 44. In detail, the coprocessor 76 is able to determine the current mode according to the action table 44 and to execute the required radio timing scheduling at the corresponding absolute event time according to the current mode.

In particular, the mobile station 6 is working at a certain mode, e.g. GSM mode and frames transmitted between the mobile station 6 and the base station 4a satisfy relevant GSM protocols. In order to normally work at the current GSM mode, the station 6 should regularly monitor an adjacent cell of the current mode so as to determine whether the communication is qualified. If the signals 8a received from the base station 4a is so weak that the normal communication cannot be guaranteed, the mobile station 6 sends a message to its upper-level system to inquiry a frame 10, as shown in Fig. 2, for monitoring whether another mode, e.g. TD-SCDMA mode is available. Upon processing the frame 10, the mobile station 6 determines whether it is necessary to execute an inter-mode handover from the current GSM to TD-SCDMA.

In other words, to make the mobile station 6 seamlessly roam from one mode to another, an inter-Mode processing is needed, including inter-Mode monitoring and inter-mode handover. The frame 10 is used for inter-mode monitoring. After processing the frame 10, the mobile station 6 reports to the system 100 the result of the monitoring so that the

system 100 makes a decision on whether to handover from one mode to another. As mentioned above, to successfully handover from one mode to another, the radio timing scheduling is a key factor for this solution.

Now, the inter-mode processing will be explained in detailed.

Especially, a SDR based radio timing scheduling method will be introduced.

Please refer to Fig. 2, which illustrates a frame 10 for monitoring TD-SCDMA mode while the station 6 is working at GSM, wherein curves

30, 31 , and 32 represent the timing variations of lines 26 during the processing of the frame 10 and a curve 34 represents the timing at which telegrams are sent on the bus 24 to process frame 10. Transmission of telegrams is illustrated by series of pulses, while an idle state is illustrated by a period of logic "0". The state of signal lines 25 could also be represented here.

It is known from Fig. 2 that the frame 10 could be divided into two parts. The first part I is from tO to t12 and the second part Il starts at t12 and ends at t15.

As a matter of fact, the first part I is the same as a normal frame for proceeding a normal communication between the mobile station 6 and the base station 4, including a RX slot, a TX slot, a "G-Mon" slot. During the RX slot, the station 6 receives information from the base station 4a at current mode, say GSM. During the TX slot, the station 6 transmits information for communication with the based station 4a at the current mode GSM. During the G-MON slot, the station monitors an adjacent cell of the same network for guaranteeing the quality of communication.

The second part Il is specially provided for monitoring. During T-

Mon slot, the mobile station 6 monitors another mode, say, TD-SCDMA.

In detail, during the TS-SCDMA slot, the mobile station 6 receives information from the base station 4b so as to monitor the power of another mode.

It is observed from Fig. 2 that processing a frame 10 includes a plurality of operations such as A1 between tO to t1 for shifting the mobile station 6 to a receiving state;

B1 between t2 to t3 for shifting the mobile station 6 out of the receiving state;

C between t4 to t5 for shifting the mobile station 6 into a transmitting state;

D between t6 to t7 for shifting the mobile station 6 out of the transmitting mode;

A2 between t8 to t9 for shifting the mobile station 6 into a receiving state in order to monitor an adjacent cell of the same network; and

B2 between t10 to t11 for shifting the mobile station 6 out of receiving state after completing the monitoring.

Up to now, the mobile station 6 carries out a normal communication as well as monitoring of its current network in use.

One more operation F1 is special given for monitoring another available mode between t12-t13 for shifting the mobile station 6 into a receiving mode to receive information in TD-SCDMA. Operation G1 between t14 to t15 is for shifting the mobile station 6 out of TD-SCDMA.

Obviously, in the process of dealing with so many operations, the mobile station 6 should be set or turned so as to keep the frequency and gain of channel consistent with the relevant protocols. In fact, up to hundreds of commands must be transmitted to the radio-frequency subsystem 16 in the process of processing one frame, wherein lots of commands similar for two modes, e.g., TX, and RX, must be repeatedly dealt with two or more times. The reason for this situation is that, in a traditional multi-mode system, one operation table is defined for each mode. Please refer to Fig. 3, upper of which shows two separate operation tables 1 and 2 for two modes 1 and 2, respectively. Obviously, this needs huge volume of a memory when multi-mode concerns. Moreover, it is not easy to support inter-Mode operation since each mode has its specific timing requirements, like inter-Mode Monitor and Handover.

According to the present invention, a shared operation pool is proposed by using a shared operation pool table 78, which contains all operations to be used for two modes. Please refer to Fig. 3, operations in the shared operation pool table can be classified into three catalogs.

The first catalog is the primary operations, including basic operations such as receiving data operation (RX) and transmitting data

(TX) operation, which are similar essentially in various modes since these operations for various available modes may adopt the same or similar parameters.

The second catalog is the secondary operations, including

RX/TX RF channel setup, or turn OFF related operations for one mode, such as RX_CH_ON_TD for Mode TD-SCDMA, RX_CH_ON_G for Mode

GSM, etc., and mode specific operations, such as Cell search operation, SYNC operation, etc. These operations are defined based on one single timing domain. As for this exemplified mobile station 6 which intends to work at two modes, the secondary operations for two modes are defined based on two timing domains, respectively.

The third catalog is inter-Mode operations, e.g. inter-Mode monitoring, handover, and etc. which are specially provided for multi- mode systems. Inter-Mode operations are defined across multiple timing domains.

It is understood from the above that, as to processing a frame, e.g., frame 10, there are operations A1 , B1 , C, D, A2, B2, F1 and G1 (Fig.

2), all of which are disposed in a shared operation pool. Among these operations, operations A1 , B1 , A2, B2, C and D may be shared by two modes, e.g. GSM and TD-SCDMA modes.

Typically, the size of an operation table for one mode is as large as 16k bits. Thus, 96,000 transistors will be used for implementing such a memory for 0.18um SRAM 6-T technology. In order to implement a multi-mode system, if separate operation tables are defined for each of modes, respectively, taking 3 modes as an example, the size of a memory for storing three operation tables will be as large as 48k bits. If a shared operation pool table is adopted, only a memory with the size of 17.6k bits is sufficient. That is, 180,000 transistors can be saved.

According to the present invention, the shared operation pool table 78 can be pre-recorded in the process of manufacturing the mobile station 6 like a mobile phone. More advantageous, the shared operation pool table 78 can be updated at the initial boot up of the system, which

will be helpful for sharing the basedband part, say processor 18 with different types of radio subsystems. Whenever the radio subsystem 16 is imposed with different characteristics, e.g., different synthesizer adjustment time, the processor 18 can be reused by simply modifying the initial boot up data accordingly.

In order to effectively process the operations for multi modes by using the above-mentioned shared operation pool, using separate radio timing scheduling methods for two modes is obviously not economic and practical. Thus, based on the idea of a share operation pool, a single unified method of multi-radio timing scheduling is also proposed to facilitate the multi-mode handover, instead of two separate timing scheduling methods for two modes of the prior art.

Fig. 4 shows the action table 44 in illustrating the data structure of a radio timing scheduling action according to the present invention. As shown in Fig.4, the action table 44, which is stored in the memory 42 of Fig. 1 , is preset with five fields. The action table 44 can be updated at an interval of every radio frame or every several frames, e.g. at the end of each radio frame, by co-processor 76 according to the command of the upper-layer protocol. An interrupt synchronized with the radio frame of the relevant mode is sent to the co-processor 76 for this purpose. Coprocessor 76 updates the action table 44 by bus 46 at the right timing in relation to the radio frame in response to the interruption. As a conventional technology, the introduction for generating a radio frame relating to an interruption is omitted here for the concision of illustration.

The first field is the Mode-Domain, in which "0" indicates that the operation is an intra-mode processing, without needing timing switch, while "1 " indicates the action is an inter-mode processing so that the

relevant circuits of the targeted mode is expected to be woken up for this event.

The second field is OPCode. OPCode is used to identify an operation to be executed by using the shared operation pool.

The third field is Absolute Starting Time field for indicating the start time for the operation.

The fourth field is Timing Length field for indicating the time length of processing the operation.

The fifth field is Priority field, in which "1 " indicates that the Timing Length field is active, while "0" indicates that the Timing Length field is inactive and the relevant execution time of the operations in the shared operation pool table will take effect. The priority field gives more flexibility to the usage of the shared operation pool, as the relevant execution time is generally fixed for some kind of operations in the conventional sense. For multi-mode operation, the execution time will be quite different for different modes, by defining the Priority field, it is able to execute the operations with required timing length for different modes by using the Timing Length Field in the action table which can be modified every frame.

As known in the prior art, a method for radio timing scheduling method in implementing inter-mode monitoring comprises the following steps: shifting the mobile station 6 which is working at model to mode 2 by changing the frequency of its receiving channel; adapting the gain and filter parameters of the receiving channel

to Mode 2; synchronizing the mobile station 6 to satisfy the requirements of mode 2 by changing sampling rate; performing switch control adaptive to mode 2; keeping the receiving channel to RX status to receive signals for inter-Mode Monitor from Mode 2 for a period as defined in the applied protocols; shifting the station 6 out from mode 2 and returning mode 1 by changing the frequency of the receiving channel; adapting the gain of the receiving channel to mode 1 ; changing sampling rate to adapt to mode 1 ; and performing switch control adaptive mode 1.

According to the present invention, by applying to the inventive idea of a shared operation pool, a method for radio timing scheduling including inter-Mode monitoring will be given in detail as below.

Referring to Fig. 1 again, it shows a multi mode telecommunication system with the multi mode mobile station 6, base station 4a at GSM mode and base station 4b at TD-SCDMA mode. As mentioned above, the current mode at which the station 6 works is GSM mode. The timer 50 and the reference clock 80 are used for GSM mode, and the timer 51 and the reference clock 81 are used for TD-SCDMA mode.

In step 301 , the action table 44 is updated by the coprocessor

76 in respect of each frame to be processed. Then, the coprocessor 76 checks Mode Domain of the action table 44 at the beginning of processing a frame in step 302 and determines whether there is a need to carry out inter-mode monitor in step 303.

If Mode Domain is "0", the procedure goes to step 304 to perform an intra-mode processing. In this case, the timer 50 is reloaded with an initial value as a ready for processing a frame of GSM mode in step 305 for conducting a normal communication.

To the contrary, if Mode Domain is "1 ", the coprocessor 76 checks OPCode of the action table 44 in step 306. It is understood by those skilled in the art, the timer 50 is still working as the following steps are preceded.

In step 307, the reference clock 81 and timer 51 will be woken up by the coprocessor 76.

In step 308, the coprocessor 76 checks Priority Field of the action table 44, and then determines whether the action table 44 is with high priority in step 309.

If the priority is low ("0"), the Timing Length field of the action table 44 is inactive and the procedure goes to step 310, during which the timer 51 is loaded with an initial value according to the relevant execution time defined in the shared operation pool table 78.

Otherwise, if the priority is high ("1 "), the Timing Length field of the action table 44is active, the procedure goes to step 311 , during which the timer 51 is loaded with an initial value according to Timing Length field of the action table 44.

As stated above, the output of timer 50 and the output of timer 51 are connected to the inputs of the comparator 52. In step 312, the

comparator 52 generates enable signals to the interface blocks 54, 55, 56 and 58 when timer 50 reaches the absolute starting time as defined in action table 44.

The timer 50 counts the number of quarter-bit periods with the loaded initial value corresponding to the current working GSM mode, and the comparator 52 compares the value of timer 50 with the absolute starting time of the next action to be processed. When the comparator 52 finds the current value of the timer 50 reaches the absolute starting time of the pending action, it generates an enable signal to the RF control interface blocks 55, 54, 56 and 58.

In step 313, RX_CH_OFF_G is executed according to the shared operation pool table 78 by the block 56, the GSM RX channel is put to a sleep mode under the control of the coprocessor 76.

In step 314, RX_CH_ON_TD is executed according to the shared operation pool table 78, and the RX channel of TD-SCDMA is set at a right frequency, right ADC sampling rate, AGC (automatic gain control) and filtering parameters by blocks 54, 55 and 56.

In step 315, the timer 51 is triggered after the operation

RX_CH_ON_TD of the operation of T-Mon is executed. Timer 50 and related clock circuit can be put to a sleep mode to save the power. The TD-SCDMA timing and monitoring can be acquired based on receiving data. The monitoring will end once the timer 51 counts down to 0.

In step 316, the operation RX_CH_OFF_TD is triggered and executed when the timer 51 counts the number of one eighth-chip periods down to 0. Timer 50 and its related clock circuit can be woken up

and the timer 51 and its related clock circuits can be put to sleep.

Step 317 is a resume step, during which the coprocessor 76 has to resume the RX channel into the mode 1 , say GSM state. Up to now, the scheduling in the process of inter-mode monitoring is completed.

Since the other inter-Mode processing, such as handover processing, is quite similar to the inter-mode Monitor processing, the description for the other inter-Mode processing is omitted herein.

As stated above, the embodiment discloses the radio timing scheduling method for handover from GSM mode to TD-SCDMA mode. However, it is understood by those skilled in the art that the radio timing scheduling method of the present invention is also suitable for handover from TD-SCDMA mode to GSM mode. The procedure of handover from TD-SCDMA mode to GSM mode will not be described in detail, since it is similar to the above-mentioned procedure.

As stated above, the embodiment discloses timing scheduling between GSM mode and TD-SCDMA mode. However, it is understood by those skilled in the art that the radio timing scheduling can also be used between multi-modes by re-configuring the reference clock blocks 80 and 81. The re-configuration of the clock blocks is a conventional technology, and will not be described here in detail.

Although a dual-mode (GSM/TD-SCDMA) mobile station is described, it is apparent for those skilled in the art that the present invention is not limited to it. The present invention can also be used in a radio telecommunication apparatus with multi-mode (e.g. D-AMPS, PDC, PHS, CDMA, and/or IMT-2000 mode).

In order to simplify the illustration of the invention, clocks 80 and 81 are described in this embodiment. However, it is understood that clocks 80 and 81 can also be the outputs of the clock synthesizer, like PLL in the chipset.

It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements.