Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-03-13
2001-02-06
Olms, Douglas W. (Department: 2732)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S320000, C370S441000, C370S479000, C375S130000
Reexamination Certificate
active
06185200
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is one of the following five U.S. patent applications filed on the same date: Ser. No. 09/039,151 filed as attorney docket no. Prasad 11, Ser. No. 09/642,397 filed as attorney docket no. Prasad 12, Ser. No. 09/039,157 filed as attorney docket no. Prasad 13, Ser. No. 09/039,158 filed as attorney docket no. Prasad 14, and Ser. No. 09/039,154 filed as attorney docket no. Prasad 15, the teachings of all of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to telecommunication systems conforming to the cdmaOne standard.
2. Description of the Related Art
The cdmaOne™ communication standard is an interim standard for mobile telecommunication systems in which communications to and from each mobile unit are supported by one of a set of base stations strategically located over the system coverage area. The cdmaOne standard specifies a common air interface for code division multiple access (CDMA) systems on the cellular (900 MHz) and the PCS (1900 MHz) bands for mobile telephony. In addition, the same air interface is used for different wireless loop equipment supplied by a significant number of manufacturers. The term “cdmaOne” is used to refer collectively to the IS-95, IS-95A, and IS-95B family of communication standards.
The cdmaOne standard specifies that the symbols encoded in both the forward-link signal transmitted from the base station to the mobile unit and the reverse-link signal transmitted from the mobile unit to the base station be interleaved in the signal stream. Interleaving is performed to make burst errors during transmission look like random errors that are separated from one another in the de-interleaved symbol stream. In that case, the decoder in a receiver can perform error correction to reconstruct the original symbol stream notwithstanding the presence of burst errors.
According to the cdmaOne standard, a mobile unit transmits reverse-link data on an Access channel at 4800 bps and four Traffic (or Fundamental) channels at 9600, 4800, 2400, and 1200 bps. Each frame in a reverse-link channel contains 576 symbols. At 9600 bps, each symbol occurs once per frame. At 4800 bps, each symbol occurs two times in a row; four times at 2400 bps; and eight times at 1200 bps. The data rates of 9600, 4800, 2400, and 1200 bps correspond to the set of four unpunctured rates under the cdmaOne standard referred to as Rate Set 1.
The cdmaOne standard also supports a second set of data rates referred to as Rate Set 2. In Rate Set 2, punctured convolutional codes are used to transmit data at 14400, 7200, 3600, and 1800 bps, corresponding to the unpunctured rates of 9600, 4800, 2400, and 1200 bps, respectively. By using punctured convolutional codes, the number of symbols per frame is maintained, and the interleaving structure for the four rates of Rate Set 2 is the same as the interleaving structure for the four rates of Rate Set 1.
The cdmaOne standard specifies the reverse-link interleaving process at the mobile unit by means of a table.
FIG. 1
shows the order in which the 576 symbols of each frame of un-interleaved reverse-link data may be sequentially (or linearly) arranged within a matrix of 32 rows and 18 columns in the mobile unit. The symbols are written columnwise, beginning with the first column on the left, successively from the top row to the bottom row. The interleaving process involves reading the rows of the matrix in
FIG. 1
(left to right) in a specified order. For the Access channel at 4800 bps, the rows are read in the following sequence:
1 17 9 25 5 21 13 29 3 19 11 27 7 23 15 31 2 18 10 26 6 22 14 30 4 20 12 28 8 24 16 32
For the Traffic channel at 9600 bps (or 14400 bps, if the Rate Set 2 option is activated), the rows are read in the following sequence:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
For the Traffic channel at 4800 bps (or 7200 bps, if the Rate Set 2 option is activated), the rows are read in the following sequence:
1 3 2 4 5 7 6 8 9 11 10 12 13 15 14 16 17 19 18 20 21 23 22 24 25 27 26 28 29 31 30 32
For the Traffic channel at 2400 bps (or 3600 bps, if the Rate Set 2 option is activated), the rows are read in the following sequence:
1 5 2 6 3 7 4 8 9 13 10 14 11 15 12 16 17 21 18 22 19 23 20 24 25 29 26 30 27 31 28 32
For the Traffic channel at 1200 bps (or 1800 bps, if the Rate Set 2 option is activated), the rows are read in the following sequence:
1 9 2 10 3 11 4 12 5 13 6 14 7 15 8 16 17 25 18 26 19 27 20 28 21 29 22 30 23 31 24 32
The de-interleaving process at the base station must perform the reverse of these operations to recover a de-interleaved symbol stream for subsequent processing. Although the cdmaOne standard does not specify the de-interleaving process, typical existing telecommunication systems implement the reverse-link de-interleaving process by an algorithmic deconstruction of the interleaving process. This can be implemented at a reasonable cost only in software.
SUMMARY OF THE INVENTION
The present invention is directed to a de-interleaving process for cdmaOne base stations in which the reverse-link interleaved symbol stream is de-interleaved by hardware and/or software that implements closed-form expressions corresponding to the table-based procedure specified in the cdmaOne standard.
According to one embodiment, a closed-form expression relating each interleaved symbol position in an interleaved symbol stream to a corresponding de-interleaved symbol position is used to generate a de-interleaved symbol position for each symbol in the interleaved symbol stream. A de-interleaved symbol stream is generated from the interleaved symbol stream using the de-interleaved symbol positions.
In one hardware implementation, the present invention is an integrated circuit having a de-interleaver for de-interleaving a reverse-link channel of a cdmaOne communication system. The de-interleaver comprises a symbol buffer and an address generation unit. The address generation unit is adapted to generate symbol addresses for reading interleaved symbols from or writing de-interleaved symbols to the symbol buffer. For each interleaved channel, the address generation unit implements a closed-form expression relating each interleaved symbol position to a corresponding de-interleaved symbol position to generate a de-interleaved symbol position for each symbol in the interleaved symbol stream.
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“Realization of Optimum Interleaver”, by John L. Ramsey, IEEE Transactions on Information Theory, vol. IT-16, No. 3, May 1970, pp. 338-345.
Hom Shick
Lucent Technologies - Inc.
Mendelsohn Steve
Olms Douglas W.
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