CDMA method with increased capacity

• US 6,434,131 B1
• Filed: 06/24/1999
• Issued: 08/13/2002
• Est. Priority Date: 04/21/1999
• Status: Expired due to Term

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Alcatel SA (Nokia Corporation)
• Inventors: Sari, Hikmet
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): Lee, John J.
• Application Number:
  US09/339,232
• Time in Patent Office: 1,146 Days
• Field of Search: 370/320, 370/335, 370/342, 370/411, 370/208, 370/209, 375/130, 375/142, 375/150
• US Class Current: 370/335
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04J 13/0022 PN, e.g. Kronecker

Abstract

Using CDMA encoding and spectrum spreading with a factor N, more than N messages are transmitted although N is a theoretical limit for this type of encoding. Encoding uses orthogonal sequences for a first group of N messages and random or pseudo-random sequences PN for a second group of M-N additional messages. On reception, the N messages of the first group are decoded and detected. Their interference is subtracted from the second group of M-N messages before detecting the M-N messages. In a second iteration, the interference of the M-N messages using PN sequences is estimated and subtracted from the N first messages before a second detection on the first group of N messages. Detection is then repeated for the second group of M-N messages after subtracting the interference of the first group of N messages and the mutual interference of the M-N messages.

Claims

1. A spread spectrum transmission method, in particular of the CDMA type, for transmitting a plurality of messages each containing a series of symbols, in which method:

each symbol to be transmitted is encoded using a sequence of N bits to obtain for each symbol a sequence of N contributions-known as chips,

the chips of the various messages are combined to obtain a transmitted signal,

the transmitted signal is received, characterized in that;

if N symbols at most are transmitted simultaneously, orthogonal sequences are chosen for the sequences of bits used,

if M symbols are transmitted simultaneously, where M is greater than N, N orthogonal sequences of N bits are chosen for N symbols and random or pseudo-random sequences of N bits are chosen for the M-N remaining symbols,

a sequence of N bits being random or pseudo-random if for subsequent symbols of the same message to be transmitted the sequences of N bits are reproduced only with a period greater than N.

2. A method according to claim 1, characterized in that the following steps are executed:

a) the transmitted signal received is decoded using the N orthogonal sequences and N quantified decoded signals (X1) are obtained, the N quantified decoded signals are detected and N estimates (â

₁) of the symbols of the N messages are obtained,

b) the transmitted signal received is decoded using the M-N random or pseudo-random additional sequences and M-N quantified decoded additional signals (XN+1, XN+2, . . . ) are obtained,

c) interference synthesized from the N estimates of the symbols of the N messages is subtracted from each of the M-N quantified decoded additional signals, the results (YN+1) of the subtractions are detected and M-N additional estimates (â

_N+1) of the symbols of the M-N messages are obtained.

3. A method according to claim 2, characterized in that:

f) interference synthesized from the M-N additional estimates (â

_N+1) of the symbols of the M-N messages are subtracted from each of the N quantified decoded signals (X1) and the N resulting subtracted quantified decoded signals are detected and N second estimates (â

₁) of the symbols of the N messages are obtained,

e) step c) is reiterated, replacing the N estimates of the symbols of the N messages by the N second estimates of the symbols of the N messages.

4. A method according to claim 3, characterized in that, in step e), M-N−

1 mutual interferences synthesized from the M-N−

1 estimates of the symbols of the M-N−

1 other messages are subtracted from each of the M-N quantified decoded additional signals and the results of such subtractions are detected.

5. A method according to claim 1, characterized in that, from the R^th symbol of the M messages to the (R+1)^th symbol of the M messages, encoding of the messages using orthogonal sequences is replaced by encoding using random or pseudo-random sequences.