Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1997-09-16
2002-05-14
Pham, Chi H. (Department: 2664)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S543000
Reexamination Certificate
active
06389000
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to communications. More particularly, the present invention relates to a novel and improved method and apparatus for maximizing system throughput and increasing signal diversity by dynamically multiplexing signals onto multiple carriers in a spread spectrum communication system.
II. Description of the Related Art
The present invention is concerned with transmitting data at rates which are higher than the maximum data rate of a single CDMA channel. A traditional CDMA channel (as standardized for cellular communication in the United States) is capable of carry digital data at a maximum rate of 9.6 bits per second using a 64 bit Walsh spreading function at 1.2288 MHz.
Many solutions to this problem have been proposed. One solution is to allocate multiple channels to the users and allow those users to transmit and receive data in parallel on the plurality of channels available to them. Two methods for providing multiple CDMA channels for use by a single user are described in U.S. Pat. No. 6,005,855, entitled “METHOD AND APPARATUS FOR PROVIDING VARIABLE RATE DATA IN A COMMUNICATIONS SYSTEM USING STATISTICAL MULTIPLEXING”, filed Apr. 28, 1997 and U.S. Pat. No. 5,777,990, entitled “METHOD AND APPARATUS FOR PROVIDING VARIABLE RATE DATA IN A COMMUNICATIONS SYSTEM USING NON-ORTHOGONAL OVERFLOW CHANNELS”, filed Apr. 16, 1997, both of which are assigned to the assignee of the present invention and are incorporated by reference herein. In addition, frequency diversity can be obtained by transmitting data over multiple spread spectrum channels that are separated from one another in frequency. A method and apparatus for redundantly transmitting data over multiple CDMA channels is described in U.S. Pat. No. 5,166,951, entitled “HIGH CAPACITY SPREAD SPECTRUM CHANNEL”, which is incorporated by reference herein.
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes such as amplitude companded single sideband (ACSSB) are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these other modulation techniques for multiple access communication systems.
The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS”, assigned to the assignee of the present invention and incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM”, assigned to the assignee of the present invention and incorporated by reference herein. Code division multiple access communications systems have been standardized in the United States in Telecommunications Industry Association Interim Standard IS-95, entitled “Mobile Station-Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System”, which is incorporated by reference herein.
The CDMA waveform by its inherent nature of being a wideband signal offers a form of frequency diversity by spreading the signal energy over a wide bandwidth. Therefore, frequency selective fading affects only a small part of the CDMA signal bandwidth. Space or path diversity on the forward/reverse link is obtained by providing multiple signal paths through simultaneous links to/from a mobile user through two or more antennas, cell sectors or cell-sites. Furthermore, path diversity may be obtained by exploiting the multipath environment through spread spectrum processing by allowing a signal arriving with different propagation delays to be received and processed separately. Examples of the utilization of path diversity are illustrated in copending U.S. Pat. No. 5,101,501 entitled “SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM”, and U.S. Pat. No. 5,109,390 entitled “DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM”, both assigned to the assignee of the present invention and incorporated by reference herein.
FIG. 1
illustrates a transmission scheme for a multiple-carrier code division multiple access (CDMA) system in which each carrier carries a fixed fraction of the transmitted data. Variable rate frame of information bits are provided to encoder
2
which encodes the bits in accordance with a convolutional encoding format. The encoded symbols are provided to symbol repetition means
4
. Symbol repetition means
4
repeats the encoded symbols so as to provide a fixed rate of symbols out of symbol repetition means
4
, regardless of the rate of the information bits.
The repeated symbols are provided to block interleaver
6
rearranges the sequence in which the symbols are to be transmitted. The interleaving process, coupled with the forward error correction, provides time diversity which aids in the reception and error recovery of the transmitted signal in the face of burst errors. The interleaved symbols are provided to data scrambler
12
. Data scrambler
12
multiplies each interleaved symbol by (+1 or −1) according to a pseudonoise (PN) sequence. The pseudonoise sequence is provided by passing a long PN sequence generated by long code generator
8
at the chip rate through decimator
10
which selectively provides a subset of the chips of the long code sequence at the rate of the interleaved symbol stream.
The data from data scrambler
12
is provided to demultiplexer (DEMUX)
14
. Demultiplexer
14
divides the data stream into three equal sub-streams. The first sub-stream is provided to transmission subsystem
15
a
, the second sub-stream to transmission subsystem
15
b
and the third sub-stream to transmission subsystem
15
c
. The subframes are provided to serial-to-parallel converters (BINARY TO 4 LEVEL)
16
a
-
16
c
. The outputs of serial to parallel converters
16
a
-
16
c
are quaternary symbols (2bits/symbol) to be transmitted in a QPSK modulation format
The signals from serial-to-parallel converters
16
a
-
16
c
are provided to Walsh coders
18
a
-
18
c
. In Walsh coders
18
a
-
18
c
, the signals from converters
16
a
-
16
c
is multiplied by a Walsh sequence consisting of □1 values. The Walsh coded data is provided to QPSK spreaders
20
a
-
20
c
, which spread the data in accordance with two short PN sequences. The short PN sequence spread signals are provided to amplifiers
22
a
-
22
b
which amplify the signals in accordance with a gain factor.
The system described above suffers from a plurality of drawbacks. First, because the data is to be provided in equal sub-streams on each of the carriers, the available numerology is limited to frames with a number of code symbols that will divide evenly by a factor of three. Table 1 below illustrates the limited number of possible rate sets which are available using the transmission system illustrated in FIG.
1
.
TABLE 1
Walsh
Number
Function
Number of
Length of
Symbol
of
(QPSK
Walsh
Walsh
Rate [sps]
Symbols
Symbol)
Functions
Function
(After
per 20
Rate [sps]
per 20 ms
[chips]
Repetition)
ms.
1228800
24576
3*2{circumflex over ( )}13
1
2457600
49152
3*2{circumflex over ( )}14
614400
12288
3*2{circumflex over ( )}12
2
1228800
24576
3*2{circumflex over ( )}13
307200
6144
3*2{circumflex over ( )}11
4
614400
12288
3*2{circumflex over ( )}12
153600
3072
3*2{circumflex over ( )}10
8
307200
61444
3*2{circumflex over ( )}11
76800
1536
3*2{circumflex over ( )}9
16
153600
3072
3*2{circumflex over ( )}10
38400
768
3*2{circumflex over ( )}8
32
7
Baker Kent D.
Beladi S. Hossain
Nguyen Steven
Pham Chi H.
Qualcomm Incorporated
LandOfFree
Method and apparatus for transmitting and receiving high... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for transmitting and receiving high..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for transmitting and receiving high... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2893178