Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
  • H04L27/12—Modulator circuits; Transmitter circuits

Definitions

• the invention relates to a data transmission method using continuous phase modulation, and in which method a signal to be transmitted is mul- tiplied by a modulation index, and which signal may have different data rates.
• the quality of a channel, or a radio path varies continuously. On many occasions the channel quality is good. However, on many occasions the channel quality may also be poor. In radio systems, the channel quality is affected by many factors. A signal propagating from a transmitter to a receiver is affected by multipath propagation, fading and interference from the surroundings, among other things.
• An object of the invention is to provide a data transmission method and transmitter to make it possible to transmit different data rates. This is achieved by the method of the type presented in the introduction, which is characterized in that the modulation index used is changed according to the data rate of the signal to be transmitted.
• the invention also relates to a transmitter comprising an encoder, first means for multiplying a signal to be transmitted by a modulation index, and a frequency modulator, the signal to be transmitted possibly having different data rates.
• the transmitter of the invention is characterized in that the transmitter comprises means for multiplying the signal to be transmitted by the modulation index which depends on the data rate of the signal to be transmitted.
• the preferred embodiments of the invention are disclosed in the dependent claims.
• the method and arrangement of the invention provide many advantages.
• the method of the invention enables the optimization of the transmission capacity of a frequency band with respect of propagation conditions and transmission needs at a given time.
• the channel quality is bad, a smaller amount of information can be reliably transmitted.
• the transmission capacity can be increased. Consequently, in good propagation conditions no underutilization of the channel occurs, which is the case in the existing methods.
• Figure 1 illustrates an example of a system to which the invention can be applied
• Figure 2 is a block diagram illustrating a first example of the struc- ture of the transmitter of the invention
• Figure 3 is a block diagram illustrating a second example of the structure of the transmitter of the invention
• Figure 4 is a block diagram illustrating a third example of the structure of the transmitter of the invention.
• the method of the invention can be applied to any data transmission system in which continuous phase modulation is used and in which method a signal to be transmitted is multiplied by a modulation index, the signal possibly having different data rates.
• the invention is particularly advanta- geous when applied to wireless data transmission systems, such as cellular radio systems of the GSM type using either the FDMA multiple access method or the TDMA multiple access method or a combination thereof.
• Figure 1 illustrating an example of a cellular radio system to which the method of the invention can be applied.
• the figure shows a base station 100 communicating 102 to 106 with terminals 108 to 112 within its area.
• the base station communicates with a base station controller 114 controlling the operation of the base station and forwarding the connections to other parts of the network.
• One base station controller can control several base stations.
• the base station controller and the base stations controlled by it constitute a base station system.
• the data rate may vary on the different connections 102 to 106, and, on the other hand, the data rate may change in the middle of the connection.
• a different modulation index can be used in the different transmission directions.
• the modulation index used on each connection can be determined at a call set-up stage.
• the modulation index can also be changed during the connection, if required.
• the modulation index used on each connection between the terminal and the base station is determined in the base station system.
• the decision may be affected by not only the data rate required but also the quality of a transmission channel.
• the connection quality is poor, small modulation indices cannot be used, because with small modulation indices, providing a high data rate, the connection is more prone to errors than with higher modulation indices.
• FIG. 2 presents a radio system transmitter structure essential to the invention.
• the transmitter may be either the transmitter of the base station or that of the terminal.
• the apparatus to be implemented must also include other components apart from those presented in Figure 2, as it is obvious to those skilled in the art. However, for the sake of clarity, they are not dealt with in the figure and description.
• the arrangement comprises a data source 200 generating a digital signal 202 to be transmitted.
• the data source may comprise a microphone connected to a speech encoder, for example.
• the signal to be transmitted comprises speech in digital form.
• Other data sources may include a computer or a modem, for example.
• a symbol rate is 1/T, where T is the length of the data symbol.
• the encoded symbols are of the form 0 or 1.
• the values so obtained are further applied to mapping means 206 performing conversion in which symbols [-1 , 1] represent the symbols [0,
• a receiver includes the first switch and a second switch 208, 218 by means of which a modulation index used is selected.
• the transmitter can use two modulation indices, and the switches 208, 218 can select one or the other from the two feasible options. Naturally, even more than two options may exist.
• the modulation index is changed, the data rate of the signal 202 to be transmitted is also concurrently changed.
• Each signal path comprises a filter 210, 214 and a multiplier 212,
• the filter is se- lected according to the modulation index used. The same filter can also be used with different modulation indices. Let us study an upper signal branch, for example.
• the signal is applied from the first switch 208 to the filter 210 filtering the signal in accordance with a spectral pattern desired.
• a transfer function following the Gaussian distribution can preferably be selected as the transfer function of the filter.
• a function h(t) can be selected by
• B stands for a 3-dB bandwidth of the filter with the impulse response h(t) and T is thus the length of the data symbol.
• the signal so obtained is further applied to the multiplier 212 to be multiplied by a factor h of the form ⁇ /(2m), where m is a positive integer greater than one.
• the signal so obtained is further applied to the second switch 218.
• another filtering for example a cosine-type root raised cosine RRC filtering, is possibly performed to the signal.
• the filtered signal is multiplied by a modulation index of the form ⁇ /(2m), where m is a positive integer greater than one, but different from the one of the upper branch.
• the signal so obtained is further applied to the sec- ond switch 218.
• the signal is further applied from the second switch to a frequency modulator 220 performing prior art frequency modulation by a voltage- controlled oscillator, for example.
• a time reference t' is the start of the data to be transmitted.
• the modulated signal is further applied to radio frequency parts 222 which can be implemented according to the prior art. It is an advantage of the invention that the radio frequency parts of the GSM system, for example, can be used as the radio frequency parts, although when the modulation method of the invention is used and m is given a value 2, the data rate T can be doubled as compared with the GSM system.
• the modulated RF signal can be ex- pressed in the form
• E c is the energy of a modulating symbol
• f 0 is a centre frequency
• ⁇ 0 is a random phase which is constant for a period of one burst.
• a C-class amplifier can thus be used, which is a significant advantage particularly as far as portable terminals are concerned.
• the signal is applied from the radio frequency parts to an antenna 224.
• the transmitter of the invention further comprises a control processor 226 controlling the operation of the other components of the apparatus.
• the control processor controls the switches 208, 218 by means of which the modulation index and the data rate used are selected on the basis of the control coming from the base station system.
• the base station system transmits the control to the control processor of the terminal by using prior art methods, i.e. by using control channels.
• Figure 3 illustrates a second embodiment of the invention.
• a first switch is located after a data source 200. The signal is switched from the switch to one of the two or more branches.
• each branch also includes the encoder 204, 300.
• the encoding used is changed according to the data rate and the modulation index used.
• the branch may not comprise a filter after the encoder.
• Each branch also includes their own mapping means 206, 302 after the encoder.
• the solution is similar to the one described above.
• the solutions of Figures 2 and 3 can preferably be implemented using digital signal processing in such a way that the encoder, mapping means, filters and multipliers are implemented by software with a signal processor or a general processor. In that case, when the modulation index is changed, the actual multiplier is not changed, but the multiplier is changed by software.
• Figure 4 illustrates a second alternative embodiment of the frequency modulator of the transmitter of the invention.
• a signal 400 coming from the second switch 218 is applied to an integrator 402 and further to a phase modulator 404 from which the signal is further applied to the radio frequency parts, providing the desired frequency modulation.
• the solution is similar to the one described in connection with Figures 2 and 3.

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Transmitters (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8550111

Family Applications (1)

Country Status (7)

Cited By (3)

Citations (2)

• 1997
  • 1997-12-11 FI FI974495A patent/FI106233B/fi active
• 1998
  • 1998-12-10 WO PCT/FI1998/000964 patent/WO1999033237A1/en not_active Application Discontinuation
  • 1998-12-10 AU AU14907/99A patent/AU748114B2/en not_active Ceased
  • 1998-12-10 EP EP98958945A patent/EP1036452A1/en not_active Withdrawn
  • 1998-12-10 JP JP2000526022A patent/JP2002500453A/ja active Pending
  • 1998-12-10 CN CN 98812058 patent/CN1281610A/zh active Pending
• 2000
  • 2000-06-09 NO NO20002974A patent/NO20002974L/no not_active Application Discontinuation

Patent Citations (2)

Non-Patent Citations (1)

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