Pulse shaping for data transmission in an orthogonal frequency division multiplexed system

• US 5,790,516 A
• Filed: 07/14/1995
• Issued: 08/04/1998
• Est. Priority Date: 07/14/1995
• Status: Expired due to Term

• Current Assignee: Wi-Fi One, LLC (Inception Holdings, LLC)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Brismark, Lars Gustav, Anderson, Per-Olof, Gudmundson, Perols Leif Mikael
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): NGO, RICKY QUOC
• Application Number:
  US08/502,633
• Time in Patent Office: 1,117 Days
• Field of Search: 370/203, 370/208, 370/210, 370/536, 370/537, 370/281, 370/295, 370/482, 370/485, 375/295, 375/298, 375/316
• US Class Current: 370/210
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/26035 Maintenance of orthogonality, e.g. for signals exchanged between cells or users, or by using covering codes or sequences using different training sequence per antenna H04B7/0684; code allocation H04J13/16

Abstract

A method and system for data transmission in a orthogonal frequency division multiplexed (OFDM) system is provided. In the invention each of a plurality of data symbols C_k, having a symbol period T, are modulated onto one of a plurality of subcarriers comprising a first data signal. The first data signal is then multiplied by a pulseshaping function over the period T to generate a second data signal. The second data signal is then transmitted on a system carrier over a communications channel of the OFDM system.

Claims

1. In a telecommunications system in which communications between a transmitter and a receiver are carried on a plurality of subcarriers over a communications channel on a system carrier, a method of transmitting data over said communications channel, said method comprising the steps of:

modulating each of a plurality of data symbols onto one of a plurality of subcarriers to generate a plurality of modulated subcarriers, said modulated subcarriers comprising a first data signal;

multiplying said first data signal by a pulseshaping waveform to generate a second data signal, said pulseshaping waveform comprising a function having at least one first and second amplitude wherein said first amplitude is greater than said second amplitude; and

transmitting said second data signal on said system carrier.

2. The method of claim 1 in which said system carrier has a frequency f_c and said step of modulating comprises:

modulating each of a plurality of data symbols C_k, having a symbol period T, onto a subcarrier having a frequency f_k, for k=0, . . . , N'"'"'-1, wherein f_k =f_c +∝

k/T and ∝

is a constant greater than 1, said modulated subcarriers comprising said first data signal.

3. The method of claim 2 further comprising the steps of:

receiving a third data signal y(t) at a receiver, said third data signal comprising said second data signal after transmission on said system carrier; and

detecting said set of data symbols C_k, k=0, . . . , N'"'"'-1, at said receiver.

4. The method of claim 2 wherein said pulseshaping waveform comprises a raised cosine pulse having a predetermined rolloff factor.

5. The method of claim 4 wherein said pulseshaping waveform comprises a Hanning function.

6. The method of claim 1 in which said step of modulating comprises:

performing an N'"'"'-point inverse fast fourier transform (IFFT) on a plurality of data symbols to generate said first data signal.

7. The method of claim 6 in which said step of multiplying comprises:

cyclicly extending said first data signal to generate an extended data signal; and

multiplying said extended data signal by a time discrete pulseshaping function to generate said second data signal.

8. The method of claim 7 further comprising the steps of:

receiving a third data signal at a receiver, said third data signal comprising said second data signal after transmission on said communication channel;

combining said third data signal to generate a fourth data signal; and

performing an N'"'"'-point fast fourier transform (FFT) on said fourth data signal to generate said set of data symbols.

9. The method of claim 7 wherein said pulseshaping function comprises a time discrete raised cosine function having a predetermined rolloff factor.

10. The method of claim 9 wherein said pulseshaping function comprises a time discrete Hanning function.

11. The method of claim 1 in which said system carrier has a frequency f_c, and said step of modulating comprises:

performing an N'"'"'-point inverse fast fourier transform (IFFT) on said data symbols, said data symbols comprising a plurality of symbols C_k, k=0, . . . , N'"'"'-1, each having a symbol period T, to generate a first data signal, said first data signal comprising a signal z_n comprising N'"'"' time discrete values each of said time discrete values being associated with a frequency f_k, for k=0, . . . , N'"'"'-1, in the frequency domain, where f_k =f_c +∝

k/T and ∝

is a constant greater than one.

12. The method of claim 11 in which said step of multiplying comprises:

cyclicly extending said first data signal z_n over said symbol period T to generate an extended data signal an comprising N time discrete values; and

multiplying said extended data signal a_n by a time discrete pulseshaping function w_n =w₀, w₁, . . . , w_N-1, over said period T to generate said second data signal x_n =w_n a_n, n=0, . . . , N-1, said pulseshaping function having a first amplitude w_n1, and a second amplitude w_n2, wherein said first amplitude is greater than said second amplitude.

13. The method of claim 12 further comprising the steps of:

receiving a third data signal b_n at a receiver, said third data signal comprising said second data signal x_n after transmission on said communications channel;

combining said third data signal b_n over said symbol period T to generate a fourth data signal y_n comprising N'"'"' time discrete values; and

performing an N'"'"'-point fast fourier transform (FFT) on said fourth data signal y_n to generate said set of data symbols C_k, k=0, . . . , N'"'"'-1.

14. The method of claim 12 wherein said pulseshaping function w_n comprises a time discrete raised cosine function having a predetermined rolloff factor.

15. The method of claim 14 wherein said pulseshaping function w_n comprises a time discrete Hanning function.

16. An apparatus for transmitting data in a telecommunications system in which communications between a transmitter and a receiver are carried on a plurality of subcarriers over a communications channel on a system carrier, said apparatus comprising:

inverse fast fourier transform (IFFT) circuitry for performing an IFFT on a plurality of data symbols and generating a first data signal;

a multiplier for multiplying said first data signal by a pulseshaping function in a time domain to generate a second data signal, the pulse shaping function comprising a raised cosine pulse having a predetermined rolloff factor; and

a transmitter for transmitting said second data signal on said communications channel.

17. The apparatus of claim 16 wherein said multiplier comprises:

cyclic extender circuitry for cyclically extending said first data signal to generate an extended signal; and

a multiplier for multiplying said extended signal by a pulseshaping function in the time domain to generate said second data signal.

18. The apparatus of claim 16 wherein said plurality of data symbols comprises a first plurality of data symbols, and said apparatus further comprises:

a serial to parallel converter for converting a serial digital data stream into said first plurality of data symbols.

19. The apparatus of claim 16 wherein said plurality of data symbols comprises a plurality of data symbols C_k, k=0, . . . , N'"'"'-1, each having a symbol period T, and said first data signal comprises a signal z_n comprising N'"'"' time discrete values, each of said time discrete values being associated with a frequency f_k, for k=0, . . . , N'"'"'-1, in the frequency domain, where f_k =f_c +∝

k/T and ∝

is a constant greater than one.

20. The apparatus of claim 19 wherein said multiplier comprises:

cyclic extender circuitry for cyclically extending said first data signal z_n to generate an extended signal a_n comprising N discrete time values; and

a multiplier for multiplying said extended signal a_n by a pulseshaping function in the time domain over said period T to generate said second data signal.

21. The apparatus of claim 20 wherein said multiplier comprises a multiplier for multiplying said extended signal a_n by a pulseshaping function w_n =w₀, w₁, . . . , w_n, over said period T to generate said second data signal, said second data signal comprising a signal x_n =w_n a_n, n=0, . . . , N-1, and said pulseshaping function having at least a first amplitude w_n1 and second amplitude w_n2, wherein said first amplitude is greater than said second amplitude.

22. The apparatus of claim 21 wherein said multiplier comprises a plurality of multipliers, each of said multipliers for multiplying a value a_n of said extended signal by the corresponding value w_n in the time domain to generate said second data signal.

23. The apparatus of claim 21 wherein said pulseshaping function comprises a time discrete raised cosine pulse.

24. The apparatus of claim 23 wherein said pulseshaping function comprises a Hanning function.

25. An apparatus for receiving data in a telecommunications system in which communications between a transmitter and a receiver are carried on a plurality of subcarriers over a communications channel on a system carrier having a frequency f_c, said apparatus comprising:

a receiver for receiving a first data signal transmitted on said communications channel and providing a second data signal b_n comprising N discrete time values;

combiner circuitry for combining said second data signal b_n to generate a combined signal y_n comprising N discrete time values; and

fast fourier transform (FFT) circuitry for performing an FFT on said combined signal y_n and generating a plurality of data symbols C_k, k=0, . . . , N'"'"'-1, each of said time discrete values of y_n being associated in said FFT with a frequency f_k =f_c +∝

k/T and ∝

is a constant greater than one.

26. The apparatus of claim 25 wherein said receiver comprises a receiver for receiving said first data signal and a serial to parallel converter for converting said first data signal into said second data signal.

27. The apparatus of claim 25 further comprising a parallel to serial converter for converting said plurality of data symbols into serial data.

28. In a telecommunication system in which communication between the transmitter and receiver are carried on a plurality of subcarriers over a communications channel on a system carrier having a frequency f_c, a method of transmitting data over said communications channel, said method comprising the steps of:

modulating each of a plurality of data symbols C_k, having a symbol period T, onto a subcarrier having a frequency f_k, where k=0, . . . , N'"'"'-1, wherein f_k =f_c +∝

k/T and ∝

is a constant greater than one, to generate a plurality of modulated subcarriers, said modulated subcarriers comprising a first data signal;

multiplying said first data signal by a pulseshaping waveform to generate a second data signal, said pulse-shaping waveform comprising a function having at least one first and second amplitude, wherein said first amplitude is greater than said second amplitude; and

transmitting said second data signal on said system carrier.