Burst shaping

Abstract: The present invention concerns a system for generating a band limited burst-like waveform. The system is responsive to an information bit sequence and a burst control signal and is essentially characterised by a constellation mapping device feeding a pair of pulse shaping filters and a pair of appropriately controlled storage devices maintaining burst opening and burst closing waveforms. The output of the pulse shaping filters and the storage devices are multiplexed to produce the band limited burst-like waveform. The stored waveforms may have a sinusoidal form, while the associated control logic may be realised by a finite state machine. If the invention is used in a wireless transmission system, additional gating circuitry improves the spectrum characteristics of the emitted signal. Transmission systems employing offset modulation formats such as OQPSK can easily be implemented in this framework. The invention more particularly applies to wireline and wireless access systems, to satellite links, and to mobile radio communications.

Description: BACKGROUND OF THE INVENTION This invention relates to the generation of a band limited burst-like waveform in burst data transmission systems such as the time division multiple access (TDMA) communication systems, where spectral spread due to the burst gating process must be prevented and the transition time of burst opening and burst closing must be minimized, allowing minimal guard time between consecutively transmitted data bursts. In burst transmission systems the transmission of the modulated waveform consists of burst-like segments separated by guard time intervals where no power is emitted. Gating the transmitted waveform can cause spectral spread resulting waste of expensive spectrum. For wireless systems in particular, gating can be obtained by properly switching on and off the modulator circuit, switching the power amplifier output, switching the input or the output of the pulse shaping filter, or even using a combination of the above. The trade-off involved in the overall gating problem hinges in the fact that as the transition time for muting the transmitter output becomes shorter the spectral spread becomes larger. Performing burst shaping in a way so that spectral spread is prevented while at the same time the required gating time is kept minimal results best resource exploitation both in time and frequency domain. FIG.1 shows a typical prior art burst shaping circuit 100 used in a wireless burst transmitter system. Referring to FIG.1, the burst shaping circuit is coupled to receive as input a binary sequence DATA and a control signal BC and produce a band limited baseband complex waveform (FI,FQ) . The sequence DATA feeds a constellation mapping circuit 105 that produces the in-phase I and quadrature Q symbol sequences. The burst control signal BC is properly delayed and the resulting delayed signal controls the gating of the symbol sequences I and Q . The gated symbol sequences GI and GQ undergo pulse shaping to produce the complex waveform (FI,FQ) . FIG.2A through FIG.2E illustrate the waveforms related to the operation of the burst shaping circuit in FIG. 1. Successive steps of digital to analogue conversion, frequency up-conversion to a radio frequency, signal amplification, gating with a properly timed version of the control signal BC and radio transmission follow. The pulse shaping filters being placed after the baseband signal gating are responsible for the prevention of the spectral spread. This scheme is suggested in U.S.Pat. No 4485478 issued to Takada M. in 1984. A more efficient burst shaping structure employs a simple digital logic ensuring that the first and last symbols of a transmitted data burst are respectively preceded and followed by their antipodal signals. In this way, a zero crossing is introduced at the burst opening and burst closing points assisting the gating procedure. Both U.S.Pat. No 4483000 issued to Yamamoto K. and Atobe M. in 1984 and U.S.Pat. No 4843352 issued to Kamisaka T., Yagi K., Takahashi Y. and Nakamura S. in 1989 follow this principle. A different route is taken in the Pat No EP631398 filed by Takai H., Kai K. and Yamasaki H. in 1994, where all possible signal transitions are stored in memory blocks. These transitions are categorized in burst opening, burst closing and payload data transitions. A control circuit is responsible for shifting out of the memory the appropriate stored sequence of samples and multiplexing the outputs of these memories. In this approach, pulse shaping is solely based on multiplexing pre-stored waveforms, while the well established practice of filter based pulse shaping is avoided. In this way, the transitions are controlled very accurately implying a tight control over the trade-off of frequency domain and time domain signal characteristics. However there is a penalty on the implementation complexity especially when the method is applied on dense constellation signalling such as 64 QAM. SUMMARY OF THE INVENTION According to the invention, a system for generating a band limited burst-like waveform is presented. The system combines filter based pulse shaping for the payload with multiplexing pre-stored waveforms for burst opening and burst closing. In this way, we obtain low complexity implementation and flexible control of the time-frequency signal characteristics at the same time. In particular, the system is responsive to an information bit sequence and a burst control signal and is essentially characterised by a symbol mapping device feeding a pair of pulse shaping filters and a pair of appropriately controlled storage devices maintaining burst opening and burst closing waveforms. The output of the pulse shaping filters and the storage devices are multiplexed to produce the band limited burst-like waveform. The stored waveforms may have a sinusoidal form, while the associated control logic may be realised by a finite state machine. If the invention is used in a wireless transmission system, additional gating circuitry improves the attenuation characteristics of the emitted gated signal. Transmission systems employing offset modulation formats such as OQPSK can easily be implemented in this framework. Waveform shaping using waveform pattern storage has been proposed in the context of pulse shaping filters (U.S.Pat. No 4745628 issued to McDavid W.T. and Bryce W.W. in 1988). Nevertheless, introducing the use of stored waveform patterns for shaping the opening and closing of the burst waveform yields an amplitude attenuation change exceeding 30dB within a time interval equal to half a symbol period, while maintaining the spectrum efficiency of the continuous transmission. This result is very important since it allows the use of small guard time intervals between consecutively transmitted data bursts even in multipoint TDMA systems, where the reception power of the consecutive bursts may differ by several decades of decibels. Finally, one may observe that reducing the guard time overhead in a system translates to higher transmission bit rate and further spectrum efficiency. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the invention will be more apparent from the detailed description hereunder taken in conjunction with the accompanying drawings, wherein: FIG.1 is a schematic block diagram of a prior art wireless burst transmitter system employing gating logic; FIG.2A through FIG.2E illustrate the waveforms useful to explain the operation of the circuit referred to in FIG. 1; FIG.3 illustrates an embodiment of a burst shaping circuit according to the invention; FIG.4A through FIG.4I illustrate the waveforms useful to explain the operation of the circuit referred to in FIG. 3; FIG.5 is an example of schematic block diagram of a wireless burst transmitter system employing the burst shaping circuit according to the invention; FIG.6 is an example of schematic block diagram details of the waveform memory and recovery means referred to in FIG.3; FIG.7A through FIG.7B illustrate an example of flow diagram details of the control logic means referred to in FIG.6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments described hereunder suggest realisations of the invention as examples without constituting any limitation whatsoever. Referring to FIG.3, there is shown a specific embodiment of a burst shaping system 300 for generating a band limited baseband burst-like complex sequence (FI, FQ) in accordance with the invention. The system is responsive to an information bit sequence DATA and a first burst control signal BC shown in FIG.4A and FIG.4C respectively. FIG.4B illustrates a synchronisation clock for the bit sequence DATA . The burst-like complex wave (FI, FQ ) carries segments of information of the input bit sequence DATA , where a sequence segment is emitted at consecutive time instances in a time interval specified by an "ON" pulse of the burst control signal BC . The information bit sequence DATA is mapped on a complex symbol sequence (I, Q) by a constellation mapping means 305. This mapping comprises encoding a subsequence of K information bits DATA(l-K+1),DATA(l-K+2) ,..., DATA(l) emitted at K consecutive time instances l-K+1, l-K+2 , ..., l on one complex symbol (I(l), Q(l)) , where the said encoding is carried out in accordance with a specified constellation mapping of 2 K points on the plane and the said consecutive instances are separated by a bit period T b . The said subsequence of K consecutive information bits dictate a K -bit symbol identifier SYMBOL _ID(l) indexed by the time instance l . FIG.4E illustrates a waveform of the symbol sequence I (or Q) for the special case where K takes a value equal to 4. FIG.4D illustrates the associated clock signal. The said sequence of complex symbols (I, Q) undergoes pulse shaping by a pair of real filters 310 and 320 preceded by a pair of interpolators. These interpolators generate N-1 zeros for each incoming complex symbol. So, the interpolation factor is equal to an integer number N and the interpolated complex sequence has a sampling period equal to an amount of time T . In other words, an interpolator functions as sample rate alteration means. The output of the pulse shaping filters, shown in FIG.4F, is a band limited complex sequence (PI, PQ) and it is produced with an input to output latency time equal to D. A waveform memory and recovery means 315 is coupled to receive as a first input the real component PI of the said band limited sequence (PI, PQ) , as a second input the sequence of said symbol identifiers SYMBOL_ID and as a third input the said first burst control signal BC in order to produce a sequence EI and a second burst control signal BCI . The sequence EI incorporates the burst opening and burst closing waveforms synchronised to the second burst control signal BCI . The signals BCI and EI are illustrated in FIG.4G and FIG.4H respectively. The said burst opening and burst closing waveforms are selected from a bank of memory stored waveforms. A waveform memory and recovery means 320 is coupled to receive as a first input the imaginary component PQ of the said band limited sequence (PI, PQ), as a second input the sequence of said symbol identifiers SYMBOL_ID and as a third input the said first burst control signal BC in order to produce a sequence EQ and a third burst control signal BCQ. The said sequence EQ incorporates the burst opening and burst closing waveforms synchronised to the third burst control signal BCQ . The signals BCQ and EQ are illustrated again in FIG.4G and FIG.4H respectively. The said burst opening and burst closing waveforms are selected from a bank of memory stored waveforms. Two 2-input real multiplexer means 330 and 335 are visualised as a complex 2-input multiplexer coupled to receive as input the said complex sequence (PI,PQ) and the complex sequence (EI.EQ) in order to produce the said baseband burst-like complex sequence (FI.FQ) . In the latter, the real component sequence FI , illustrated in FIG.4I, is produced at a certain time instance n by assigning to FI the value of PI if the second burst control signal BCI is on state "ON" at that instance and assigning to FI the value of EI otherwise. Similarly, the imaginary component sequence FQ , illustrated in FIG.4I, is produced at a certain time instance n by assigning to FQ the value of PQ if the third burst control signal BCQ is on state " ON " at that instance and assigning to FQ the value of EQ otherwise. A burst transmission system employing a modulation format exhibiting time offset between the in-phase and the quadrature components, such as the OQPSK modulation format, can be obtained according to the invention by simply appending a proper delay element at one of the output components. More specifically, referring to FIG.3, a delay means 340 coupled to receive as input the quadrature component sequence FQ of the band limited baseband burst-like complex sequence (FI, FQ) introduces a delay equal to half a symbol period and produces a delayed quadrature component sequence FQ_DEL . Referring to FIG.5, there is shown a specific embodiment of a system for generating a band limited modulated waveform in accordance with the invention. The system is coupled to receive as inputs an information bit sequence DATA and a burst control signal BC . The said modulated waveform carries segments of the bit sequence DATA, in which a sequence segment is emitted at consecutive instances in a time interval specified by an " ON" pulse of the burst control signal BC . The system comprises a burst shaping means 300, digital-to-analogue converter means 510 and 515, frequency up-conversion means 520, a delay and expansion means 530 and 545, gating means 525 and 540, an amplifier 535 and radio transmitter equipment 550. The burst shaping means 300 is coupled to receive the information bit sequence DATA and the burst control signal BC and carry out the processing stages previously described with reference to FIG.3 and FIG.4 to produce a band limited baseband burst-like complex sequence (FI, FQ) or (FI, FQ_DEL) . The digital-to-analogue converter means 510 and 515 are coupled to receive this complex sequence and produce a baseband analogue complex waveform. The frequency up-conversion means 520 is coupled to receive as input the said baseband analogue complex waveform and produce a modulated carrier signal MC. The delay and expansion means 530 is coupled to receive as input the said burst control signal BC and produce another burst control signal BC4 by successive delaying the signal BC and expanding the pulses of the resulting delayed signal. The delay is specified by the amount of time equal to the latency time introduced between emitting an information bit from the said bit sequence DATA and producing the associated fragment of the modulated carrier MC. The expanding process is carried out so as the pulse width in signal BC4 becomes no smaller than the time elapsing between the generation of the first sample of the in-phase and quadrature opening waveforms and the last sample of the in-phase and quadrature closing waveforms in the associated data burst. The gating means 525 is responsible for gating the modulated carrier signal MC in response to the burst control signal BC4 to produce a first gated signal. The amplifier 535 amplifies the said first gated signal producing an amplified waveform. The delay and expansion means 545 is coupled to receive as input the burst control signal BC and produces a burst control signal BC5 by successive delaying of the signal BC and expanding the pulses of the resulting delayed signal. The delay is specified by the amount of time equal to the latency introduced between emitting an information bit from the said bit sequence DATA and producing the associated fragment of the amplified waveform. The expanding process for signal BC5 is similar to the one used for generating signal BC4 . The gating means 540 is responsible for gating the said amplified waveform in response to the burst control signal BC5 and produce a second gated signal. The RF transmission equipment 550 transmits the said second gated signal over the air. Referring to FIG.6, a preferred embodiment of the waveform memory and recovery means 315 (325) is coupled to receive as a input the real or the imaginary component P of the band limited sequence (PI, PQ) along with the sequence of symbol identifiers SYMBOL_ID and the first burst control signal BC producing accordingly the real or the imaginary component E of the complex sequence (EI, EQ) and the associated burst control signal BC_OUT . The waveform memory and recovery means comprises a delay and shrink means 610, a sequential logic means 690, a delay means 615, a memory means 670 and a control logic means 680. The delay and shrink means 610 is coupled to receive as input the first burst control signal BC and it produces the burst control signal BC_DS by delaying the said signal BC by a time interval equal to the latency time D, and by shrinking the pulse width of the resulting delayed signal by a time interval equal to one symbol period. The latency time D has been defined with reference to FIG.3. The delay means 615 is coupled to receive as input the said symbol identifier sequence SYMBOL_ID and it produces a delayed symbol identifier sequence SYMBOL_ID_DEL by introducing a time delay equal to the said latency time D . The sequential logic means 690 is coupled to receive as input the said burst control signal BC_DS and it produces an EDGE_FLAG sequence and an OPEN_CLOSE_FLAG sequence. These sequences take binary values according to the following truth table: BC_DS EDGE_FLAG OPEN_CLOSE_FLAG Time instant: n-1 n n n " OFF " " OFF " " OFF " " X " " OFF " "ON" "ON" "ON" "ON" " OFF " "ON" " OFF " "ON" "ON" " OFF " " X " The time index n denotes successive time instances separated by a time interval equal to the said period T , while " X " signifies the don't care condition. An example circuitry implementing the above truth table is included in FIG.6. The burst control signal BC_DS feeds a flip-flop 620. A two-input and-gate 630 receives as inputs the burst control signal BC_DS and the output of the flip-flop 620 inverted by an inverter 625. Another two-input and-gate 640 receives as inputs the output of the flip-flop 620 and the burst control signal BC_DS inverted by an inverter 635. The OPEN_CLOSE_FLAG is produced as the output of a set-reset flip-flop that is set when the output of the and-gate 630 goes "ON" and is reset when the output of the and-gate 640 goes "ON". The EDGE_FLAG is produced as the output of a two-input or-gate 650 receiving as inputs the outputs of the two and-gates 630 and 640. The memory means 670 is responsible for storing a number of no more than 2 K+1 waveforms comprising M samples each one. Half of these waveforms constitute burst opening waveforms, while the other half are the burst closing waveforms. Each waveform is associated to the in-phase (or the quadrature component) of a complex symbol in the said constellation mapping. The memory means is accessed by specifying a waveform identifier WF_ID and an address pointer ADDR to extract the memory content WF_ID[ADDR] . The waveform identifier WF_ID comprises K+1 information bits, that is the opening-closing one-bit information and the K-bit associated symbol identifier. The address pointer ADDR ranges from 0 to M-1 . We assume that the closing waveforms contain a zero valued sample WF _ ID[M-1] at the position M-1 . An example of burst opening and burst closing waveforms are respectively given by the expressions and in which the sample index j takes values j=0,1,...,M-1 and A signifies a factor independent of j , associated to a specific waveform. The control logic means 680 comprises a five-state state machine coupled to receive as a first input the said band limited sequence component P , as a second input the said delayed symbol identifier sequence SYMBOL_ID_DEL , as a third input the said EDGE_FLAG sequence, as a fourth input the said OPEN_CLOSE_FLAG sequence and as a fifth input a memory content WF_ID[ADDR] , where the waveform identifier WF_ID and the address pointer ADDR are produced by the said control logic means along with the said output sequence E and the associated burst control signal BC_OUT . The said state machine is initialised in a "zero" state and operates at successive time instances separated by a time interval equal to the said period Tas follows: a. If the "zero" state is active the said identifier WF_ID specifies an arbitrary closing waveform as a current waveform, the address pointer ADDR takes the value M-1 implying a value for the output value E equal to the stored sample WF_ID[M-1] , that is zero by assumption. The burst control signal BC_OUT takes the value " OFF " and if a first exit condition becomes true at time instant n then the waveform identifier WF_ID specifies as the current waveform the opening waveform of the symbol dictated by the value of SYMBOL_ID_DEL at instance n, the address pointer ADDR takes the value 0 and a "opening" state is introduced at instance n+1 . The said first exit condition is given below: (EDGE_FLAG = "ON") AND ( OPEN_CLOSE_FLAG = " ON "). b. If the "opening" state is active at time instance n the value of the address pointer ADDR is increased by one and the value of the stored waveform sample WF_ID[ADDR] is assigned to the output E. If a second exit condition becomes true at instance n then the address pointer ADDR takes the value 0 , the burst control signal BC_OUT takes the value "ON" and a " normal " state is introduced at instance n+1 . The said second exit condition is given below: (ABS(WF_ID[ADDR]) > ABS(P)) OR (ADDR=M) in which " ABS " signifies the extraction of the absolute value. c. If the "normal" state is active, the "ON" value of the burst control signal BC_OUT is maintained and if a third exit condition becomes true at time instance n then the waveform identifier WF_ID specifies as the current waveform the closing waveform of the symbol dictated by the value of SYMBOL_ID_DEL at instance n , the address pointer ADDR takes the value 0 and a "switching" state is introduced at instance n+1 . The said third exit condition is given below: (EDGE_FLAG = " ON ") AND ( OPEN_CLOSE_FLAG = " OFF "). d. If the "switching " state is active at time instance n the value of the address pointer ADDR is increased by one and the value of the stored waveform sample WF_ID[ADDR] is assigned to the output E . If a fourth exit condition becomes true at instance n then the address pointer ADDR takes the value 0 , the burst control signal BC_OUT takes the value "OFF" and a "closing" state is introduced at instance n+1 . The said fourth exit condition is given below: ABS(WF_ID[ADDR]) < ABS(P) in which " ABS " signifies the extraction of the absolute value. e. If the "closing" state is active at time instance n the value of the address pointer ADDR is increased by one and the value of the stored waveform sample WF_ID[ADDR] is assigned to the output E . If a fifth exit condition becomes true at instance n then the said "zero" state is introduced at instance n+1 . The said fifth exit condition is given below: ADDR=M. Although the specific embodiments described so far comprise a two-component in-phase and quadrature baseband burst signal generation, the present invention applies to burst shaping of one-component baseband signals as well, such as BPSK or PAM modulation formatted signals. This can be achieved by simply omitting the circuitry implementing the processing stages of the quadrature phase component.

Claims: A system for generating a band limited baseband burst-like complex sequence (FI, FQ) responsive to an information bit sequence DATA and a first burst control signal BC , said burst-like complex sequence carrying segments of said bit sequence DATA, in which a sequence segment is emitted at consecutive time instants in a time interval specified by an " ON " pulse of said first burst control signal BC , wherein the system comprises: means (305) for mapping the information bit sequence DATA on a complex symbol sequence (I, Q) , said mapping comprising encoding a subsequence of K information bits DATA(I-K+1),DATA(l-K+2), ..., DATA(l) emitted at K consecutive time instants l-K+1, l-K+2, ..., l on one complex symbol (I(l), Q(l)) , said consecutive time instants being separated by a bit period T b , said subsequence of K consecutive information bits dictating a K -bit symbol identifier SYMBOL_ID(l) produced at time instant l , said encoding being carried out in accordance with a specified constellation mapping of 2 K points on a plane; means for interpolating the said sequence of complex symbols (I, Q) by an interpolation factor equal to an integer number N to produce an interpolated complex sequence having a period equal to an amount of time T ; a pulse shaping filter means (310,320) coupled to receive as input the said interpolated complex sequence and to produce a band limited complex sequence (PI, PQ) , said filter means introducing a latency time D ; a waveform memory and recovery means (315) coupled to receive as a first input the real component PI of the said band limited sequence (PI, PQ) , as a second input the sequence of said symbol identifiers SYMBOL_ID and as a third input the said first burst control signal BC and to produce a sequence EI and a second burst control signal BCI , said sequence EI comprising the burst opening and burst closing waveforms synchronised to the secpnd burst control signal BCI , said burst opening and burst closing waveforms being selected from a bank of memory stored waveforms; a waveform memory and recovery means (325) coupled to receive as a first input the imaginary component PQ of the said band limited sequence (PI, PQ) , as a second input the sequence of said symbol identifiers SYMBOL_ID and as a third input the said first burst control signal BC and to produce a sequence EQ and a third burst control signal BCQ , said sequence EQ comprising the burst opening and burst closing waveforms synchronised to the third burst control signal BCQ , said burst opening and burst closing waveforms being selected from a bank of memory stored waveforms; a multiplexer means (330,335) coupled to receive as input the said complex band limited sequence (PI,PQ) and the complex sequence (EI , EQ) and to produce the said baseband burst-like complex sequence (FI,FQ) in which the real component sequence FI is produced by assigning to FI at a certain time instant n the value of PI if the second burst control signal BCI is on state "ON" at that time instant and assigning to FI the value of EI otherwise the imaginary component sequence FQ is produced by assigning to FQ at a certain time instant n the value of PQ if the third burst control signal BCQ is on state "ON" at that time instant and assigning to FQ the value of EQ otherwise. A system according to claim 1, where the waveform memory and recovery means (315,325) are coupled to receive as an input the real or the imaginary component P of the band limited sequence (PI, PQ) along with the sequence of symbol identifiers SYMBOL_ID and the first burst control signal BC to produce accordingly the real or the imaginary component E of the complex sequence (EI, EQ) and the associated burst control signal BC_OUT , the system comprising: a delay and shrink means (610) coupled to receive as input the first burst control signal BC and to produce a burst control signal BC_DS by delaying the said signal BC by a time interval equal to the said latency time D , and by shrinking the pulse width of the resulting delayed signal at the leading edge of a pulse by a time interval equal to one symbol period; a sequential logic means (690) coupled to receive as input the said burst control signal BC_DS and to produce an EDGE_FLAG sequence and a OPEN_CLOSE_FLAG sequence, said sequences taking binary values at successive time instants separated by a time interval equal to the said period T and being specified at each time instant n by the following truth table: BC_DS EDGE_FLAG OPEN_CLOSE_FLAG Time instant: n-1 n n n " OFF " " OFF " "OFF" " X " "OFF" " ON " " ON " " ON " " ON " " OFF " " ON " "OFF" " ON " " ON " " OFF " " X " in which " X " signifies the don't care condition; a delay means (615) coupled to receive as input the said symbol identifier sequence SYMBOL_ID and to produce a delayed symbol identifier sequence SYMBOL_ID_DEL by introducing a time delay equal to the said latency time D; memory means (670) for storing a number of no more than 2 K+1 waveforms comprising a number of no more than 2 K burst opening waveforms and an equal number of burst closing waveforms, each waveform comprising a number of samples equal to an integer number M and being associated to the in-phase or the quadrature component of a complex symbol in the said constellation mapping, said memory means is being accessed by specifying a waveform identifier WF_ID and an address pointer ADDR to extract the memory content WF_ID[ADDR] , said waveform identifier WF_ID carrying the opening-closing one-bit information and the K -bit associated symbol identifier, said address pointer ADDR ranging from 0 to M-1 , said closing waveforms contain a 0 valued sample WF_ID[M-1] of rank M-1 ; a control logic means (680) comprising a five-state state machine coupled to receive as a first input the said band limited sequence component P , as a second input the said delayed symbol identifier sequence SYMBOL_ID_DEL , as a third input the said EDGE_FLAG sequence, as a fourth input the said OPEN CLOSE FLAG sequence and as a fifth input a memory content WF_ID[ADDR] , wherein the waveform identifier WF_ID and the address pointer ADDR are produced by the said control logic means along with the said output sequence E and the associated burst control signal BC_OUT , said state machine being initialised in a "zero" state and operating at successive time instants separated by a time interval equal to the said period T as follows: if the "zero" state is active the said identifier WF_ID specifies an arbitrary closing waveform as a current waveform, the said address pointer ADDR takes the value M-1 implying a value for the said output value E equal to the stored sample WF_ID[M-1] of rank M-1 of the said waveform, said burst control signal BC_OUT takes the value " OFF " and if a first exit condition becomes true at time instant n then the waveform identifier WF_ID specifies as the current waveform the opening waveform of the symbol dictated by the value of SYMBOL_ID _ DEL at time instant n , the address pointer ADDR takes the value 0 and a "opening" state is introduced at time instant n+1 , said first exit condition being: (EDGE_FLAG = "ON") AND ( OPEN_CLOSE_FLAG = " ON "); if the "opening" state is active at time instant n the value of the said address pointer ADDR is increased by one, the value of the stored waveform sample WF_ID[ADDR] of rank ADDR in the said current waveform is assigned to said output E , and if a second exit condition becomes true at time instant n then the said address pointer ADDR takes the value 0 , the said burst control signal BC_OUT takes the value "ON" and a "normal" state is introduced at time instant n+1 , said second exit condition being: (ABS(WF_ID[ADDR]) > ABS(P)) OR (ADDR=M) in which " ABS " signifies the extraction of the absolute value; if the "normal" state is active the "ON" value of the said burst control signal BC_OUT is maintained and if a third exit condition becomes true at time instant n then the waveform identifier WF_ID specifies as the current waveform the closing waveform of the symbol dictated by the value of SYMBOL_ID_DEL at time instant n, the address pointer ADDR takes the value 0 and a "switching" state is introduced at time instant n+1 , said third exit condition being (EDGE_FLAG = "ON") AND ( OPEN_CLOSE_FLAG = " OFF ") ; if the "switching" state is active at time instant n the value of the said address pointer ADDR is increased by one, the value of the stored waveform sample WF_ID[ADDR] of rank ADDR in the said current waveform is assigned to said output E, and if a fourth exit condition becomes true at time instant n then the said address pointer ADDR takes the value 0 , the said burst control signal BC_OUT takes the value " OFF " and a "closing" state is introduced at time instant n+1 , said fourth exit condition being: ABS(WF_ID[ADDR]) < ABS(P) in which " ABS " signifies the extraction of the absolute value; if the "closing" state is active at time instant n the value of the said address pointer ADDR is increased by one, the value of the stored waveform sample WF_ID[ADDR] of rank ADDR in the said current waveform is assigned to said output E, and if a fifth exit condition becomes true at time instant n then the said "zero" state is introduced at time instant n+1 , said fifth exit condition being ADDR=M . A system for generating a band limited baseband burst-like complex sequence (FI,FQ_DEL) responsive to an information bit sequence DATA and a first burst control signal BC , said burst-like complex sequence exhibiting a time offset between the two components and carrying segments of said bit sequence DATA , in which a sequence segment is emitted at consecutive time instants in a time interval specified by an "ON" pulse of said first burst control signal BC , wherein the system comprises: a means (300) for generating a band limited baseband burst-like complex sequence (FI, FQ) responsive to the information bit sequence DATA and the first burst control signal BC according to claim 1; a delay means (340) coupled to receive as input the quadrature component sequence FQ of the band limited baseband burst-like complex sequence (FI, FQ) and to produce a delayed quadrature component sequence FQ_DEL . A system according to claim 1, wherein the values of the samples of the burst opening and burst closing memory stored waveforms are characterised by the expressions: and respectively, in which A signifies a constant factor associated to a specific waveform and the index j takes values j = 0,1, ...,M-1 . A system for generating a band limited modulated waveform responsive to an information bit sequence DATA and a first burst control signal BC , said modulated waveform carrying segments of said bit sequence DATA , in which a sequence segment is emitted at consecutive time instants in a time interval specified by an " ON " pulse of said first burst control signal BC , wherein the system comprises: a means (300) for generating a band limited baseband burst-like complex sequence (FI, FQ) responsive to the information bit sequence DATA and the first burst control signal BC according to claim 1 or claim 3; digital-to-analogue converter means (510,515) coupred to receive as input the complex sequence (FI, FQ) and to produce a baseband analogue complex waveform; frequency up-conversion means (520) coupled to receive as input the said baseband analogue complex waveform and to produce a modulated carrier signal MC; a delay and expansion means (530) coupled to receive as input the said first burst control signal BC and to produce a fourth burst control signal BC4 by successive delaying of the signal BC and expanding the pulses of the resulting delayed signal, said delaying is specified by an amount of time equal to the latency time introduced between emitting an information bit in the said bit sequence DATA and producing the associated segment of the modulated carrier MC, said expanding is carried out so as the pulse width in signal BC4 becomes no smaller than the time elapsing between the generation of the first sample of the in-phase and quadrature opening waveforms and the last sample of the in-phase and quadrature closing waveforms of the associated data burst; means (525) for gating the modulated carrier signal MC in response to the fourth burst control signal BC4 to produce a first gated signal; means (535) for amplifying the said first gated signal to produce an amplified waveform; a delay and expansion means (545) coupled to receive as input the said first burst control signal BC and to produce a fifth burst control signal BC5 by successive delaying of the signal BC and expanding the pulses of the resulting delayed signal, said delaying is specified by an amount of time equal to the latency time introduced between emitting an information bit in the said bit sequence DATA and producing the associated segment of the amplified waveform, said expanding is carried out so as the pulse width in signal BC5 becomes no smaller than the time elapsing between the generation of the first sample of the in-phase and quadrature opening waveforms and the last sample of the in-phase and quadrature closing waveforms of the associated data burst; means (540) for gating the said amplified waveform in response to the fifth burst control signal BC5 to produce a second gated signal; means (550) for transmitting the said second gated signal.

Inventors: FRANTZESKAKIS MANOLIS, POSONIDIS ARIS, FRANTZESKAKIS, MANOLIS, POSONIDIS, ARIS, Frantzeskakis, Manolis, c/o INTRACOM S.A., Posonidis, Aris, c/o INTRACOM S.A.
Applicants: INTRACOM S A HELLENIC TELECOMM, INTRACOM S.A. HELLENIC TELECOMMUNICATIONS & ELECTRONICS INDUSTRY
Application year: 1999
Main classification: H04L25
IPC codes: H04L25