Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-03-13
2001-03-06
Ton, Dang (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S320000, C370S441000, C370S501000, C370S342000
Reexamination Certificate
active
06198732
ABSTRACT:
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 base station transmits forward-link data on a Pilot channel (used for timing acquisition), a Sync channel (used for synchronization) at 4800 bps, Paging channels at either 9600 or 4800 bps, and four Traffic (or Fundamental) channels at 9600, 4800, 2400, and 1200 bps. Each frame in a forward-link Paging or Traffic channel contains 384 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.
Since only null data is sent on the Pilot channel, no interleaving is used on this channel. However, the cdmaOne specification does require interleaving for the rest of the forward-link channels.
For example, the cdmaOne standard specifies the forward-link interleaving process at the base station for the Paging and Traffic channels by means of a table.
FIG. 1A
shows the order in which the 384 symbols of each frame of un-interleaved forward-link Paging/Traffic data may be sequentially (or linearly) arranged within a matrix of 24 rows and 16 columns in the base station. The symbols are written columnwise, beginning with the first column on the left, successively from the top row to the bottom row.
FIG. 1B
shows the order in which the 384 symbols stored in the matrix of
FIG. 1A
are to be read in order to form a frame of interleaved forward-link Paging/Traffic data for the 9600-bps data rate. The sequence of symbols in
FIG. 1B
are listed columnwise, beginning with the first column on the left, successively from the top row to the bottom row. Thus, the symbol in position #
1
in
FIG. 1A
is the first symbol in an interleaved frame, followed by the symbol in position #
65
, followed by the symbol in position #
129
, etc.
The interleaving scheme for the three other data rates (i.e., 4800, 2400, and 1200 bps) is identical to that shown in
FIG. 1B
for the 9600-bps data rate. The only difference is that, for the 4800-bps data rate, for example, the symbols stored in positions #
1
and #
2
in
FIG. 1A
correspond to the two occurrences of the first symbol in the frame, positions #
3
and #
4
correspond to the two occurrences of the second symbol in the frame, etc. Similarly, for the 2400-bps data rate, each set of four consecutive positions in
FIG. 1A
correspond to a different symbol in the frame, and, for the 1200-bps data rate, each set of eight consecutive positions in
FIG. 1A
correspond to a different symbol in the frame. The interleaving scheme for the different data rates in Rate Set 2 is identical to that for the corresponding data rates in Rate Set 1.
The cdmaOne standard specifies that the forward-link interleaving process be implemented using a table-based procedure that can be implemented at a reasonable cost only in software.
SUMMARY OF THE INVENTION
The present invention is directed to an interleaving process for cdmaOne base stations in which the forward-link un-interleaved symbol stream is interleaved by hardware and/or software that implements closed-form expressions corresponding to the table-based procedures specified in the cdmaOne standard.
According to one embodiment, a closed-form expression relating each un-interleaved symbol position in a un-interleaved symbol stream to a corresponding interleaved symbol position is used to generate an interleaved symbol position for each symbol in the un-interleaved symbol stream. An interleaved symbol stream is generated from the un-interleaved symbol stream using the interleaved symbol positions.
In one hardware implementation, the present invention is an integrated circuit having an interleaver for interleaving a forward-link channel of a cdmaOne communication system. The interleaver comprises a symbol buffer and an address generation unit. The address generation unit is adapted to generate symbol addresses for reading un-interleaved symbols from or writing interleaved symbols to the symbol buffer. For each un-interleaved channel, the address generation unit implements a closed-form expression relating each un-interleaved symbol position to a corresponding interleaved symbol position to generate an interleaved symbol position for each symbol in the un-interleaved symbol stream.
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“Realization of Optimum Interleavers”, by John Ramsey, IEEE Transactions on Information Theory, vol.IT-16, No. 3, May 1970, pp. 337-345.
Lucent Technologies - Inc.
Mendelsohn Steve
Ton Anthony
Ton Dang
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