DURATION-SHORTENED OFDM SYMBOLS

• US 20090185476A1
• Filed: 01/15/2009
• Published: 07/23/2009
• Est. Priority Date: 01/16/2008
• Status: Abandoned Application

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: TSAI, Shiau-He, CHEN, Tsao-Tsen, ERNSTROM, Per
• Application Number:
  US12/354,159
• Publication Number:
  US 20090185476A1
• Time in Patent Office: Days
• US Class Current: 370/210
• CPC Class Codes: H04L 1/1812 Hybrid protocols; Hybrid automatic repeat request [HARQ]
• CPC Class Codes: H04L 27/26025 Numerology, i.e. varying one or more of symbol duration, subcarrier spacing, Fourier transform size, sampling rate or down-clocking allocating sub-channels of the transmission path H04L5/003
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365

Abstract

A communications network comprises a base station (28) and a wireless terminal (30) which communicate a frame (F) of information over an air interface (32). The frame (F) is prepared or processed to accommodate duration-shortened symbols. The preparation or processing the frame occurs in a manner whereby: (1) at least some of OFDM symbols of the frame have a symbol duration T_base in accordance with a base frequency 1/T_base of subcarriers employed for the frame; and (2) at least one duration-shortened OFDM symbol of the frame has a symbol duration T_base/N, wherein N is an integer greater than one and wherein a subset of subcarriers are utilized for the select OFDM symbol, the subset of subcarriers being frequencies which are integer multiples of a N^th harmonic of the base frequency 1/T_base. In an example embodiment, the duration-shortened symbol is inserted in a portion of the frame corresponding to a transition gap for at least one version of the frame.

Claims

1. A method of operating a communications network comprising a base station and a wireless terminal which communicate a frame of information over an air interface with the base station, the method comprising:

preparing or processing the frame in a manner whereby;

(1) at least some of OFDM symbols of the frame have a symbol duration T_base in accordance with a base frequency 1/T_base of subcarriers employed for the frame;

(2) at least one duration-shortened OFDM symbol of the frame has a symbol duration T_base/N, wherein N is an integer greater than one and wherein a subset of subcarriers are utilized for the select OFDM symbol, the subset of subcarriers being frequencies which are integer multiples of a N^th harmonic of the base frequency 1/T_base; and

transmitting the frame over the interface.

2. The method of claim 1, further comprising inserting the duration-shortened symbol in a portion of the frame corresponding to a transition gap for at least one version of the frame.

3. The method of claim 2, further comprising inserting an integer number of the duration-shortened symbols in a portion of the frame corresponding to the transition gap.

4. The method of claim 1, wherein the frame is a time division duplex (TDD) frame or a frequency division duplex (FDD) frame.

5. A base station comprising:

a transceiver configured to communicate a frame over an air interface with a wireless terminal; and

a frame handler arranged to prepare or process the frame in a manner whereby;

(1) at least some of OFDM symbols of the frame have a symbol duration T_base in accordance with a base frequency 1/T_base of subcarriers employed for the frame;

(2) at least one duration-shortened OFDM symbol of the frame has a symbol duration T_base/N, wherein N is an integer greater than one and wherein a subset of subcarriers are utilized for the select OFDM symbol, the subset of subcarriers being frequencies which are integer multiples of a N^th harmonic of the base frequency 1/T_base.

6. The apparatus of claim 5, wherein the frame handler is further arranged to insert the duration-shortened symbol in a portion of the frame corresponding to a transition gap for at least one version of the frame.

7. The apparatus of claim 6, wherein the frame handler is further arranged to insert an integer number of the duration-shortened symbols in a portion of the frame corresponding to the transition gap.

8. The apparatus of claim 5, wherein the frame handler further comprises an Inverse Fast Fourier Transform (IFFT) unit or an inverse Discrete Fourier Transform (IDFT) configured to transform modulated subcarriers into a sequence of time domain samples for both the duration-shortened OFDM symbol and the symbols having symbol duration T_base.

9. The apparatus of claim 5, wherein the frame is a time division duplex (TDD) frame or a frequency division duplex (FDD) frame.

10. A wireless terminal comprising:

a transceiver configured to receive a frame over an air interface from a base station; and

a frame handler arranged to demodulate the frame in a manner whereby;

(1) at least some of OFDM symbols of the frame have a symbol duration T_base in accordance with a base frequency 1/T_base of subcarriers employed for the frame;

(2) at least one duration-shortened OFDM symbol of the frame has a symbol duration T_base/N, wherein N is an integer greater than one and wherein a subset of subcarriers are utilized for the select OFDM symbol, the subset of subcarriers being frequencies which are integer multiples of a N^th harmonic of the base frequency 1/T_base.

11. The apparatus of claim 10, wherein the frame handler is further arranged to obtain the duration-shortened symbol from a portion of the frame corresponding to a transition gap for at least one version of the frame.

12. The apparatus of claim 11, wherein the frame handler is further arranged to obtain an integer number of the duration-shortened symbols in a portion of the frame corresponding to the transition gap.

13. The apparatus of claim 10, wherein the frame is a time division duplex (TDD) frame or a frequency division duplex (FDD) frame.

14. The apparatus of claim 10, wherein the frame handler further comprises a Fast Fourier Transform (FFT) unit or a Discrete Fourier Transform unit configured to convert the time domain waveform to the frequency domain for both the duration-shortened OFDM symbol and the symbols having symbol duration T_base.