WO2001003394A1 - Pulse shaping device for mobile communication systems - Google Patents
Pulse shaping device for mobile communication systems Download PDFInfo
- Publication number
- WO2001003394A1 WO2001003394A1 PCT/IB2000/000978 IB0000978W WO0103394A1 WO 2001003394 A1 WO2001003394 A1 WO 2001003394A1 IB 0000978 W IB0000978 W IB 0000978W WO 0103394 A1 WO0103394 A1 WO 0103394A1
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- WO
- WIPO (PCT)
- Prior art keywords
- pulse
- telecommunications system
- pulses
- digital telecommunications
- criteria
- Prior art date
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/20—Modulator circuits; Transmitter circuits
- H04L27/2003—Modulator circuits; Transmitter circuits for continuous phase modulation
- H04L27/2007—Modulator circuits; Transmitter circuits for continuous phase modulation in which the phase change within each symbol period is constrained
- H04L27/2017—Modulator circuits; Transmitter circuits for continuous phase modulation in which the phase change within each symbol period is constrained in which the phase changes are non-linear, e.g. generalized and Gaussian minimum shift keying, tamed frequency modulation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03828—Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties
- H04L25/03834—Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties using pulse shaping
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
- H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
- H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
- H04B2201/70707—Efficiency-related aspects
Definitions
- serial bit streams of data are transmitted over-the- air.
- the bit streams are used to modulate a carrier.
- modulation scheme used to transmit data carried by the bit stream.
- GSM the modulation scheme used is Gaussian Minimum Shift Keying (GMSK)
- GMSK Gaussian Minimum Shift Keying
- QPSK QPSK
- GMSK is a phase modulation that converts a serial bit stream into a phase shift of a carrier wave.
- the function of the modulation is to convert the incoming serial bit stream into analog signals that modulate the carrier of the transmitter.
- the outgoing phase shift is filtered.
- the Gaussian function acts as a filter, removing the sharp edges of the digital pulses. Without this filtering the required bandwidth to transmit the signal would be far greater. Even with the gaussian filter it is acknowledged that the GSM system is spectrally inefficient.
- the GMSK modulation does, however, provide a constant amplitude signal that is power efficient.
- QPSK phase modulation technique
- orthogonal signals are transmitted which double the data rate relative to MSK modulation.
- QPSK modulation the outgoing phase shift is Nyquist filtered to provide root raised cosine shaped pulses that increase the spectral efficiency and reduced bit error rate by eliminating intersymbol interference.
- QPSK with root raised cosine pulse shaping is spectrally efficient allowing a high data rate and providing a low BER.
- a digital telecommunications system in which first and second communications devices communicate by respectively transmitting pulses indicative of data in accordance with a predetermined modulation scheme, the first and second devices each comprise means for shaping the respective data pulses prior to transmission, the shaping being applied in accordance with respective system criteria.
- the first and second devices may be different types of communications device, for example a fixed station and a mobile station.
- the pulse shape most appropriate for each modulation scheme is quite clear.
- the system designer makes a decision on which modulation scheme based on its strengths and weaknesses and selects the appropriate pulse shape.
- the single variable of the mathematical function is set to provide an acceptable balance in the defined relationship between the cost parameters.
- the shape of the pulse is defined in order to meet desired cost parameters or system criteria. There is freedom to select new pulse shapes that allow many system criteria to be balanced against each other. The trade-off relationship between two parameters is no longer so restricted.
- the derivative of the pulse functions (which at this stage are still unknown) are required. This derivative can be approximated as being proportional to the difference between two adjacent pulse values.
- the major operating elements in a telecommunications system are fixed stations and mobile stations. The considerations for each of these are somewhat different. Both have bandwidth constraints imposed by the systems in which they are operating. However, whereas the base station is relatively free from concern about power output, the mobile station is limited in the amount of power it can practically transmit.
- the present invention allows the pulse shaping for the up-link to a fixed station and the down-link to a mobile station to be optimised independently to take account of the specific requirements of each.
- the respective system criteria may therefore be designed to enhance the performance of the respective devices.
- both criteria can be optimised to suit the weakest device.
- the invention may be applied to any modulation scheme.
- Preferably two functions are used to optimise the pulse shape as this provides more optimal pulse shaping than just using one function.
- the method can be implemented as follows :
- PULSE is unknown as yet, but, in this embodiment it is read, non zero and of maximum length 8.
- equation (3) can be identified as to whether it is real or imaginary (assuming that the pulse function is real).
- Equation 3 e.g. for a simple receiver
- the bit cc N _ 4 is transmitted at time(N + 4)r as it is on its own. It is imaginary, and the interfering (ie other imaginary) pulses must be taken into account.
- the real terms in this expression can be totally ignored both for the interfering terms and the absolute value of the pulses.
- the interference should be minimised.
- the BER performance can, for example, be improved by making the terms Pulse [0] at (N + 4)T large compared to the absolute value of all the other terms.
- the absolute value of the pulse at time AT can be calculated in terms of the unknown pulses.
- the pulse is required to meet certain criteria with regard to power, BER, AFC and bandwidth. Hence, error functions for these are determined.
- the oversampling rate can be altered depending upon the level of pulse sampling required.
- the amplitude and BER costs are calculated for AT taking each of the above values.
- the total cost for each is the addition of all the 8 expressions obtained over the possible sequences.
- the pulse can be specifically designed based on system requirements by weighting the above error functions (for example 0.3 for power, 0.3 for BER and 0.4 for bandwidth or if a system requires only, for example, bandwidth considerations, 0 for power and BER and 1 for bandwidth). More weight can be added to whatever is causing a problem. The only restriction is that the total weighting must equal + 1.
- this expression is minimised using a conventional off-the-shelf optimiser, for example.
- This method provides an additional system criteria that can be varied to produce a pulse design and that is the number of pulse components used for shaping.
- the number of components used for the respective transmission directions can be different.
- This method can be used to determine the optimum parameters for the up-link of say a CDMA or GSM system using a determined set of weighted cost parameters and then recalculated using a different set of cost parameters for the down-link.
- a transceiver for a digital telecommunications system in which first and second communications devices communicate by transmitting information in accordance with a predetermined modulation scheme, the first and second communications devices transmitting pulses shaped prior to transmission indicative of data
- the transceiver comprising a processor for providing a string of data bits, a filter for shaping the transmitted pulse in accordance with a first set of system criteria and a filter operating in accordance with a second set of system criteria predetermined for receiving a string of data bits having a pulse shape determined in accordance with a second set of system criteria different from the first set of system criteria.
- FIG. 1 is a GSM transmitter according to an embodiment of the present invention
- FIG. 1 shows the GSM frame structure
- FIG. 3 is a GSM receiver according to an embodiment of the present invention
- FIG. 4 is a CDMA transmitter according to an embodiment of the present invention
- FIG. 5 is a CDMA receiver according to an embodiment of the present invention.
- Figure 6(a) is a CDMA receiver according to a preferred embodiment of the present invention.
- Figure 6(b) is a CDMA receiver demodulator stage according to a preferred embodiment of the present invention.
- the duration of the phase pulse In order to design a transmitter one of the first decisions that has to be made is the duration of the phase pulse. This is practically a decision on how to determine how the pulse shaping is to be achieved. The duration of the phase pulse determines how much history is included in each signal.
- the 'history' ie the impact of previous data bits on the current data bit lasts for 4T. The tails of the previous 3 bits are therefore superimposed onto the current bit and there are 2 4 possibilities for each bit.
- the handset or mobile unit In most systems, the handset or mobile unit is restricted in terms of power available and one of the most significant considerations is power consumption. An important factor in power consumption, and therefore talk and standby times, is the efficiency of the power amplifier. The handset is a consumer item cost, and therefore complexity, are also issues.
- the shaping of the pulses including composition of the transmission output for the up and down links respectively can be used to have a positive effect on handset performance.
- the up-link (handset to base station) is to be optimised for ACP (amplitude variation on the modulated signal).
- ACP amplitude variation on the modulated signal.
- the Laurent-type pulse shaping for a handset will typically be achieved by calculating the shape of the Laurent pulses by optimising for Amplitude to give a power consumption advantage. For GSM, if amplitude is the prime cost function, this will mean a closer approximation to a gaussian.
- the BT product is 0.3 and a phase pulse of duration 4T can be used in practice, the lower the BT product, the longer the duration of pulses.
- the computational overhead during demodulation is effected by the manner of the pulse transmission to the handset in the down-link (base station to handset). This could be quantified and added to the optimisation routine.
- the power amplifier efficiency is by no means as important as for the handset. This is because the source of power is less restricted. The designer then has a choice.
- the transmission at the base station could be optimised for power and other costs with weightings determined for the efficient operation of the base station.
- the power efficiency of the handset is the critical element in the system it is sensible to consider the handset when designing the output of the base station as the handset will be required to demodulate the signal and the type and the composition of the signal will have an impact on the computational overhead of the handset and consequently the power consumption.
- the base station has far more available power than the handset. This means that when a gaussian-like pulse is desirable and the pulse is generated by the superposition of pulse components a single pulse component can carry enough power to convey the data. Superposing two pulses to provide the output pulses at the base station although having some benefit in the power efficiency at the base station complicates the transmission process and provides little if any advantage to the handset.
- the number of pulses used to shape the modulated signal transmitted by the bases station should therefore be kept to one.
- GSM conventionally comprises a frame structure as shown in Figure 2.
- Figure 1 illustrates a GSM transmitter suitable for use in a handset in accordance with an embodiment of the present invention.
- a bit sequence 101 to be transmitted is input to a frame builder 102 of the transmitter, which puts the bits in the appropriate portion of a burst within a time slot of a TDMA frame.
- the bit stream is then forwarded to a modulator 104.
- this modulator would be a GMSK modulator.
- the signal is not put through a Gaussian filter.
- a lookup table 106 defines a pulse function whose shape has formed from a calculation of the first two pulses of a Laurent-type series.
- a multi-tap FIR digital filter with characteristics calculated to provide pulse shaping equivalent to the first two Laurent-type pulses of the optimisation could be used.
- a clock 105 provides the carrier signal as is conventional.
- the modulated signal is input to a digital analogue converter 107.
- This analogue signal is then reconstructed by reconstruction filter 108.
- This filter might typically comprise a switch capacitor filter for performing some of the spectral shaping and an analogue filter, such as an RC filter, for mainly dealing with residual shaping.
- the signal is amplified by a power amplifier 109 and is transmitted via antenna 110.
- the transmitter at the base station will look the same, but the look-up table or multi-tap FIR digital filter will hold data that provides a pulse function whose shape is formed from only the first pulse of a Laurent-type series.
- the efficiency of the base station transmitter will inevitably be not as great as that of the handset.
- the power constraints can be tolerated and the cost involved in providing a PA with greater linearity at the system level, is less critical than for the handset that is a consumer product, this trade off is easily acceptable.
- FIG. 3 shows a GSM receiver in accordance with an embodiment of the invention. Similar receivers can be utilized by both the handset and the base station.
- the handset will receive a pulse transmitted by the base station formed by the first pulse of a Laurent-type series.
- the base station will receive a pulse transmitted by a handset.
- This pulse will be composed of two Laurent-type pulses to optimise the power efficiency at the handset. Because for a gaussian shape the majority of the power is in the first pulse of the Laurent-type series, there is typically sufficient power in the first Laurent-type pulse to make this the only pulse that needs to be decoded by the base station. If circumstances were such that the was insufficient power in the first pulse, the base station could be designed to decode both the first and second pulses of the series.
- the receiver For a receiver decoding a single component pulse, the receiver down converts the received signal to the baseband of the receiver 120. This signal is then provided to the complex number sequencer 121 and then to a demodulator 122 to provide a bit sequence 123 in a conventional fashion.
- the power output of a handset is very important as the typical, root raised cosine shaping selected for bandwidth efficiency of the output pulses is ACP inefficient for use with non-linear amplifiers as the constant amplitude variation is much greater than for GSM using GMSK shaping.
- CDMA Code Division Multiple Access
- an important design factor for the handset is the efficiency of the power amplifier in providing sufficient output power to be received by a base station.
- the power is limited as the handset is mobile and carries its power supply with it. Because the amplitude variation is significant, the non-linearity of the power amplifier causes the spectrum to spread more widely than is ideal for the typical root raised cosine pulse shape.
- CDMA conventionally comprises a frame made up of a dedicated physical data channel (DPDCH) and a dedicated physical control channel (DPCCH).
- DPDCH dedicated physical data channel
- DPCCH dedicated physical control channel
- This Gold Code Encoder 303 operates as follows.
- the output of the Gold Code Encoder 303 is a sequence with N x M terms having the following elements :
- a modulator 304 modulates these MN chips output by the Gold Code Encoder 303 on to a carrier, which is output by clock 305.
- the modulator 304 generally used in CDMA systems such as IS95 is a linear QPSK modulator.
- the bandwidth of the signal output by the modulator 304 is directly related to the spectrum of the pulses that are used to make up a look-up table 306. Conventionally, for a CDMA system, this lookup table would comprise data defining a root raised cosine.
- the look-up table defines a different pulse whose shape has been optimised with reference to desired cost functions and is produced using a look-up table holding data representing the first two AM pulses according to Laurent's superposition theory, these pulses being a fixed family of pulses which are functions of cos and sin as described earlier.
- the first two AM pulses according to Laurent's superposition theory, these pulses being a fixed family of pulses which are functions of cos and sin as described earlier.
- ACP is optimised for a non-linear power amplifier.
- the output of the modulator 304 is input to a digital-to-analogue converter 307.
- the analogue signal is then reconstructed by a reconstruction filter 308.
- a reconstruction filter might typically comprise a switch capacitor filter for performing some spectral shaping and an analogue filter, such as an RC filter network, for mainly dealing with residual spectral shaping.
- FIG. 5 is a block diagram of a spread spectrum receiver with a demodulator.
- the receiver complements the CDMA transmitter of Figure 4. It comprises an antenna for receiving a spread signal, frequency downconverting circuitry 401 , analogue to digital converter 402, means for storing the receiver's code and a despreader 404.
- the despreader comprises means 405 for transforming the receiver's code according to the present invention, a correlator 406 for correlating the received signal and the transformed code, and a comparator 407 for determining the sign of the received signal.
- the code transformer 405 may solely comprise the transformation for detecting a + 1 bit.
- the comparator assumes it is a +1 if the value of the correlated signal output by correlator 406 is above a certain threshold, and -1 if it is below this threshold.
- this type of receiver requires more complex demodulation. Simpler demodulation is possible if the transformer 405 also has a transformation for detecting a -1. In this event the comparator determines the sign which produces the largest value. That value should be well above the noise floor, and hence, no complex demodulation is required to determine whether in fact the received signal is a -1 , intended for that receiver, or noise resulting from signals for other receivers.
- Figures 6a and 6b show a CDMA receiver according to a preferred embodiment, which complements a transmitter which transmits a signal constructed using the superposition of a plurality of amplitude modulated pulses. In the case of the present embodiment, two pulses.
- the frequency downconverting circuitry 401 comprises at least 1 IF stage 501 , mixers 502a, 502b and low pass filters 503a and 503b.
- a received signal is put through the IF stage(s) 501 to reduce its frequency to a base band frequency and then the signal is split into its I and Q components and the carrier is removed from the signal, using mixers 502a and 502b and low pass filters 503a and 503b.
- the signal is then converted from an analogue signal into a digital signal by A/D converters 504a and 504b and forwarded to the demodulator stage 404.
- Figure 6(b) shows this demodulator stage in more detail.
- the correlator 406 performs a correlation of each transformed code with the respective pulse of the received signal. For example, the transformed Gold Code associated with the first AM pulse for detecting a + 1 is correlated with the 1 st AM pulse of the received signal (x h ,x q1 ) by correlator
- the absolute value z of the correlated signal y is forwarded to the comparator 407. The same stages occur for the first AM pulse for detecting a
- the comparator 407 determines whether the received signal is +/- 1. This is achieved by a comparison of the absolute values (z, - z 4 ) received from the comparator with expected absolute of the values (E., - E 4 ) assuming the received signal is of the sign being detected.
- the values E, - E 4 can be precalculated and stored in the receiver. In this embodiment, if the received signal is a + 1 , then the value of z 1 and z 3 will be close to their associated expected values E, and E 3 , so that the values of h 1 and h 3 will be small. In contrast z 2 and z 4 will be much smaller in value than E 2 and E 4 , so that the values of h 2 and h 4 will be large.
- the comparator determines that a + 1 is received as h 1 + h 3 ⁇ h 2 + h 4 .
- the value of z 2 and z 4 will be close to their expected values E 2 and E 4 , so that the values of h 2 + h 4 will be small, whereas z, and z 3 will be much smaller than E and E 3 , so that h 1 and h 3 will be larger values.
- the comparator determines that a - 1 is received as h 2 + h 4 ⁇ h, + h 3 .
- the receiver need only perform the correlations for the first pulse.
- Jointly optimising pulses in general provides more scope for reducing the cost function e.g.
- the non-linearity of the PA was better compensated for (with regard to phone noise and spectrum error) by optimising two pulses jointly rather than optimising each pulse separately.
- two pulses tends to give the bulk of the improvement.
- N pulses can be used.
- the transmitted pulse is another variable in the system that can be used to provide maximum advantage.
- the pulse shape and the formation of the pulse can be tailored to meet the particular needs of one or more of the elements in the system.
- the present invention includes any novel feature or combination of features disclosed herein either explicitly or any generalisation thereof irrespective of whether or not it relates to the claimed invention or mitigates any or all of the problems addressed.
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Nonlinear Science (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Power Engineering (AREA)
- Mobile Radio Communication Systems (AREA)
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
Abstract
Description
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Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP00944140A EP1198937A1 (en) | 1999-07-01 | 2000-06-30 | Pulse shaping device for mobile communication systems |
JP2001508132A JP2003531507A (en) | 1999-07-01 | 2000-06-30 | Pulse shaping device for mobile communication system |
AU58374/00A AU5837400A (en) | 1999-07-01 | 2000-06-30 | Pulse shaping device for mobile communication systems |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9915434A GB2351633A (en) | 1999-07-01 | 1999-07-01 | Optimising pulse shaping for radio telephones |
GB9915434.6 | 1999-07-01 |
Publications (1)
Publication Number | Publication Date |
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WO2001003394A1 true WO2001003394A1 (en) | 2001-01-11 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/IB2000/000978 WO2001003394A1 (en) | 1999-07-01 | 2000-06-30 | Pulse shaping device for mobile communication systems |
Country Status (6)
Country | Link |
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EP (1) | EP1198937A1 (en) |
JP (1) | JP2003531507A (en) |
CN (1) | CN1367973A (en) |
AU (1) | AU5837400A (en) |
GB (1) | GB2351633A (en) |
WO (1) | WO2001003394A1 (en) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6956910B2 (en) * | 2002-11-20 | 2005-10-18 | Sandbridge Technologies, Inc. | Fast transmitter based on table lookup |
DE102009033788A1 (en) * | 2009-07-17 | 2011-03-03 | Astrium Gmbh | Method for receiving a signal and receiver |
JP4917136B2 (en) | 2009-09-29 | 2012-04-18 | インターナショナル・ビジネス・マシーンズ・コーポレーション | Method, circuit, and program for digitally filtering (pulse shape) a signal |
JP6070252B2 (en) * | 2013-02-21 | 2017-02-01 | 日本電気株式会社 | Signal detection apparatus, signal detection method, and reception apparatus |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4737969A (en) * | 1987-01-28 | 1988-04-12 | Motorola, Inc. | Spectrally efficient digital modulation method and apparatus |
US4750192A (en) * | 1986-06-24 | 1988-06-07 | Bbc Brown Boveri Ag | Method for transmitting digital data by means of continuous phase modulation |
DE19713175A1 (en) * | 1997-03-27 | 1998-10-08 | Siemens Ag | Method and arrangement for the transmission of data |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US5440594A (en) * | 1993-12-09 | 1995-08-08 | Bell Communications Research, Inc. | Method and apparatus for joint optimization of transmitted pulse shape and receiver timing in digital systems |
GB2333673A (en) * | 1998-01-21 | 1999-07-28 | Nokia Mobile Phones Ltd | Despreading a signal which has been spread by a code and modulated according to a non-linear modulation scheme |
GB2333674B (en) * | 1998-01-21 | 2003-08-27 | Nokia Mobile Phones Ltd | A radio telephone |
GB2337670B (en) * | 1998-01-21 | 2003-08-27 | Nokia Mobile Phones Ltd | Method and Apparatus for Generating a Pulse Function |
-
1999
- 1999-07-01 GB GB9915434A patent/GB2351633A/en not_active Withdrawn
-
2000
- 2000-06-30 CN CN 00809792 patent/CN1367973A/en active Pending
- 2000-06-30 EP EP00944140A patent/EP1198937A1/en not_active Withdrawn
- 2000-06-30 JP JP2001508132A patent/JP2003531507A/en not_active Withdrawn
- 2000-06-30 AU AU58374/00A patent/AU5837400A/en not_active Abandoned
- 2000-06-30 WO PCT/IB2000/000978 patent/WO2001003394A1/en not_active Application Discontinuation
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
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US4750192A (en) * | 1986-06-24 | 1988-06-07 | Bbc Brown Boveri Ag | Method for transmitting digital data by means of continuous phase modulation |
US4737969A (en) * | 1987-01-28 | 1988-04-12 | Motorola, Inc. | Spectrally efficient digital modulation method and apparatus |
DE19713175A1 (en) * | 1997-03-27 | 1998-10-08 | Siemens Ag | Method and arrangement for the transmission of data |
Non-Patent Citations (1)
Title |
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JUNG P: "LAURENT'S REPRESENTATION OF BINARY DIGITAL CONTINUOUS PHASE MODULATED SIGNALS WITH MODULATION INDEX 1/2 REVISITED", IEEE TRANSACTIONS ON COMMUNICATIONS,US,IEEE INC. NEW YORK, vol. 42, no. 2/03/04, 1 February 1994 (1994-02-01), pages 221 - 224, XP000445935, ISSN: 0090-6778 * |
Also Published As
Publication number | Publication date |
---|---|
GB2351633A (en) | 2001-01-03 |
AU5837400A (en) | 2001-01-22 |
GB9915434D0 (en) | 1999-09-01 |
CN1367973A (en) | 2002-09-04 |
EP1198937A1 (en) | 2002-04-24 |
JP2003531507A (en) | 2003-10-21 |
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