Patent Application
20090303865
This invention relates to improvements in codes used in wireless communications, and more specifically to preamble codes.
The invention relates to improvements in preamble codes used in Orthogonal Frequency Division Multiple Access (OFDMA) for the physical layer (PHY).
The invention may be used, for example, to improve the communication performance in systems within the IEEE 802.16 Standard for Broadband Wireless Access. Such improvements may better adapt the OFDMA to a mobile environment.
The improvements may be used in the OFDMA PHY/MAC layers.
An important parameter in such communications is the Peak to Average Power Ratio (PAPR). Wideband signals may exhibit high values of PAPR, which pose high demands on the linearity performance of the system. That is, a large dynamic range is required to convey the high amplitude peaks associated with such signals.
It may be highly desirable to reduce the PAPR, to allow improved performance while concurrently reducing the costs of communication systems.
It is important to achieve improved performance in short codes, of length 128, 512 and 1K, in the preamble.
The communications may use various Fast Fourier Transform (FFT) values, thus improvements preferably should be capable at operating at these values.
This invention describes improved preamble codes having a lower PAPR value. For example, the preambles used in the 2K OFDMA mode were devised so as to have a lower PAPR, this having many advantages. For example, a lower PAPR allows to boost the preamble to get better performance in the estimation/acquisition/cell monitoring, etc.
The present disclosure includes improvements in the 1024, 512 and 128 FFT OFDMA modes.
Tables with series to modulate, for different FFT sizes, are disclosed in the present application.
The present disclosure includes, by way of example, improvements in the 1024, 512 and 128 FFT OFDMA modes.
Tables with series to modulate, for different FFT sizes, are disclosed in the present application.
The following tables detail Pseudo Noise (PN) sequences that may be used to modulate the pilot carriers in the preamble signal. Pilot carriers are modulated every third carrier.
Table 1 describes the parameters used for each FFT size.
The series length is determined by mapping the carriers up to the last allowed carrier, then truncated if the series is too long.
The following tables illustrate series required for different FFT sizes.
The PN series are shown in hexadecimal format, wherein each digit represents values from 0 to 15 decimal (0, 1, 2, 3 . . . 9, A, B, C, D, E, F), thus each digit may represent four bits of code.
Where required, the binary series may be lengthened by padding with zeros at the end of a sequence so the number of bits is a multiple of 4 (each hexa digit represents 4 bits) or a multiple of 8 (each byte represents 8 bits). The series may be then converted to hexa from the MSB to LSB.
Table 2 illustrates a preambles modulation series per segment and Cellid, for the 1K FFT mode.
Suggested title: Table 307b, if included in the IEEE Standard.
Table 3 illustrates a preambles modulation series per segment and Cellid, for the 512 FFT mode.
Suggested title: Table 307c, if included in the IEEE Standard.
Table 4 illustrates a preambles modulation series per segment and Cellid, for the 128 FFT mode.
Suggested title: Table 307d, if included in the IEEE Standard.
As disclosed in the U.S. provisional application No. 60/605,497 filed on 31 Aug. 2004 by the present applicant, the present invention may also be included as an improvement in the IEEE Standard P802.18e/D3 change, by adding on page 79 the paragraph in page 556 IEEE802.16d-2004 to read:
The PN series modulating the pilots are defined in Tables 307a-307d. The series modulated depends on the segment used and IDcell parameter. The defined series shall be mapped onto the preamble subcarriers in ascending order. Tables 307a-307d include the PN sequence in Hexadecimal format. The value of the PN may be obtained by converting the series to a binary series (Wk) and starting mapping the PN from the MSB of each symbol to the LSB. Thus, for example, 0 may be mapped to +1 and 1 to −1.
For example, in Table 307a for the 2K mode Index=0, segment=0, Wk=110000010010 . . . and the mapping may be:
−1, −1, +1, +1, +1, +1, +1, −1, +1, +1, −1, +1 . . .
Table 5 illustrates another embodiment of a preambles modulation series per segment and Cellid, for the 1K FFT mode.
Suggested title: Table 307b, if included in the IEEE Standard.
Table 6 illustrates another embodiment of a preambles modulation series per segment and Cellid, for the 512 FFT mode.
Suggested title: Table 307c, if included in the IEEE Standard.
Table 7 illustrates another embodiment of a preambles modulation series per segment and Cellid, for the 128 FFT mode.
Suggested title: Table 307d, if included in the IEEE Standard.
Preamble properties: the preambles were chosen using a computer search which minimizes the PAPR and cross-correlation properties (or a coherent/slow or differential/fast cell search).
The graphs in
The following method may be used to compute codes such as those presented in this disclosure, see
To evaluate the performance of each code, a cellular model was used, see
Each cell may have three sectors separated in frequency, groups F1, F2 and F3; in another embodiment, the cells may have six sectors each.
F1, F2, F3 each may refer to an orthogonal set of subcarriers.
For a group of 19 cells with 6 segments each, the total number is 19×6=144
We are looking for a randomizer that will achieve best performance from the aspects of Crest Factor/PAPR and/or Cross-correlation, for the above possible scenarios.
The various codes generated as detailed below have been evaluated with reference to the above model, see also
1. For each of the FFT modes: 128, 512, 1024, performing the following steps (2-4) [21]:
2. Generating various codes, pseudo-random simulation [22]
3. Codes evaluation in a predefined model, including a wireless cell, a first tier including 6 cells and a second tier including 12 cells, 19 cells in total [23].
Compute Crest Factor, PAPR
Compute Cross-correlation among codes
4. Selecting the highest performance codes according to predefined criteria in PAPR and/or Cross-correlation [24]
The present invention refers to improvements in wireless communications. It describes improved preamble codes having a lower PAPR value.
A lower PAPR allows to boost the preamble to get better performance in the estimation/acquisition/cell monitoring, etc.
The present disclosure includes improvements in the 1024, 512 and 128 FFT OFDMA modes.
Tables with series to modulate, for different FFT sizes, are disclosed in the present application.
It will be recognized that the foregoing is but one example of an apparatus and method within the scope of the present invention and that various modifications will occur to those skilled in the art upon reading the disclosure set forth hereinbefore.
The present application is related to, and claims priority from, the U.S. provisional application No. 60/582,820 filed on 28 Jun. 2004 and entitled “Preambles design for OFDMA PHY layer, FFT sizes of 1024, 512, and 128” and from U.S. provisional application No. 60/605,497 filed on 31 Aug. 2004 and entitled “Preambles design for OFDMA PHY layer, FFT sizes of 1024, 512, and 128”, both filed by the present applicant and inventor.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL05/00684 | 6/28/2005 | WO | 00 | 8/15/2008 |
| Number | Date | Country | |
|---|---|---|---|
| 60582820 | Jun 2004 | US | |
| 60605497 | Aug 2004 | US |
