Technique for adaptive multiuser equalization in code division multiple access systems
First Claim
1. A method for receiving digital data information that is user-unique and is transmitted from a plurality of user transmitting terminals over multipath and multiple-access interference channels to a receiving terminal with one or more diversity antennas containing associated received diversity signals, wherein the user transmitting terminal adds error-correcting coding and interleaving to the digital data information to provide a sequence of digital data symbols at a user symbol rate that is the reciprocal of a user integer multiple of a system period and subsequently multiplies the digital data symbols by a user-unique direct-sequence spread spectrum (DSSS) signal to provide a modulated signal for transmission to the receiving terminal, and wherein the receiving terminal produces within a data frame successive user decisions corresponding to transmitted digital data symbols for a set of λ
- detected users, said receiving method comprising the steps at the receiving terminal of;
time-sampling and grouping received diversity signals into a receiver time block that has a time duration that is no more than one-half of the interleaving delay;
producing DSSS replicas of the user-unique DSSS signals for K=μ
+λ
mutually-interfering user signals where K>
1 and μ
is equal to the number of interfering users that are not detected;
estimating a set of channel parameters associated with the receiver time block;
formatting the DSSS replicas to provide a set of sequence signals;
sequence combining the received diversity signals and sequence signals to provide sequence matched signals;
channel combining the sequence matched signals and channel parameters to provide channel matched signals, which depend on a subdecision interval that corresponds to a digital data subsymbol equal in duration to the system period and which further depend on subsymbol delay offsets that are relative to the subdecision interval;
processing the channel parameters and sequence signals to provide forward and backward filter parameters;
creating past interference signals that depend on the subdecision interval;
subtracting the past interference signals from the channel matched signals to provide equalization signals that depend on the subdecision interval and subsymbol delay offsets;
forward combining the equalization signals and the forward filter parameters to provide λ
user subsymbol estimates for successive subdecision intervals within the data frame;
summing the user integer multiple successive subsymbol estimates to provide a user symbol estimate of the transmitted user digital data symbol;
selecting, at the user symbol rate for users in the set of λ
detected users, the user decision as the possibly transmitted digital data symbol that is closest to the user symbol estimate;
partitioning the user decisions into subdecisions associated with subdecision intervals;
symbol deinterleaving and error-correcting decoding user symbol estimates to recover digital data information; and
wherein the creating step further comprises;
multiplying the backward filter parameters and subdecisions from previous subdecision intervals to provide the past interference signals.
0 Assignments
0 Petitions
Accused Products
Abstract
A radio communication method and system for transmitting multiple-user digital data information in a Code Division Multiple Access (CDMA) format over multipath and mutual-interfering channels to a receiving terminal with diversity antennas and equalization signal processing. At the receiving terminal, diversity antenna signals are grouped into time blocks and replicas are generated of the user-unique CDMA sequence signals for a set of K mutually interfering users. Within each time block the multiuser channel is estimated, equalization parameters are calculated, and decision-feedback equalization is used to produce multiuser estimates associated with a subset λ of the K users. These estimates are deinterleaved and error-correction decoded to recover transmitted digital data information for the subset of λ users. The invention includes embodiments for a CDMA sequence period that is equal to or longer than the transmitted data symbol interval with applications to current CDMA reverse link and forward link standards. Also embodiments for both decision-directed and reference-directed channel estimation are given.
47 Citations
30 Claims
-
1. A method for receiving digital data information that is user-unique and is transmitted from a plurality of user transmitting terminals over multipath and multiple-access interference channels to a receiving terminal with one or more diversity antennas containing associated received diversity signals, wherein the user transmitting terminal adds error-correcting coding and interleaving to the digital data information to provide a sequence of digital data symbols at a user symbol rate that is the reciprocal of a user integer multiple of a system period and subsequently multiplies the digital data symbols by a user-unique direct-sequence spread spectrum (DSSS) signal to provide a modulated signal for transmission to the receiving terminal, and wherein the receiving terminal produces within a data frame successive user decisions corresponding to transmitted digital data symbols for a set of λ
- detected users, said receiving method comprising the steps at the receiving terminal of;
time-sampling and grouping received diversity signals into a receiver time block that has a time duration that is no more than one-half of the interleaving delay;
producing DSSS replicas of the user-unique DSSS signals for K=μ
+λ
mutually-interfering user signals where K>
1 and μ
is equal to the number of interfering users that are not detected;
estimating a set of channel parameters associated with the receiver time block;
formatting the DSSS replicas to provide a set of sequence signals;
sequence combining the received diversity signals and sequence signals to provide sequence matched signals;
channel combining the sequence matched signals and channel parameters to provide channel matched signals, which depend on a subdecision interval that corresponds to a digital data subsymbol equal in duration to the system period and which further depend on subsymbol delay offsets that are relative to the subdecision interval;
processing the channel parameters and sequence signals to provide forward and backward filter parameters;
creating past interference signals that depend on the subdecision interval;
subtracting the past interference signals from the channel matched signals to provide equalization signals that depend on the subdecision interval and subsymbol delay offsets;
forward combining the equalization signals and the forward filter parameters to provide λ
user subsymbol estimates for successive subdecision intervals within the data frame;
summing the user integer multiple successive subsymbol estimates to provide a user symbol estimate of the transmitted user digital data symbol;
selecting, at the user symbol rate for users in the set of λ
detected users, the user decision as the possibly transmitted digital data symbol that is closest to the user symbol estimate;
partitioning the user decisions into subdecisions associated with subdecision intervals;
symbol deinterleaving and error-correcting decoding user symbol estimates to recover digital data information; and
wherein the creating step further comprises;
multiplying the backward filter parameters and subdecisions from previous subdecision intervals to provide the past interference signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
- detected users, said receiving method comprising the steps at the receiving terminal of;
-
18. For use in a multiuser communication system wherein digital data information that is user-unique is transmitted from a plurality of user transmitting terminals, that may be geographically separate or collocated at a central station, over multipath and multiple-access interference channels, and wherein the user transmitting terminal adds error-correcting coding and interleaving to the digital data information to provide a sequence of digital data symbols at a user symbol rate that is the reciprocal of a user integer multiple of a system period and subsequently multiplies the digital data symbols by a user-unique direct-sequence spread spectrum (DSSS) signal to provide a modulated signal for transmission, a receiver apparatus, that is associated with one or more diversity antennas containing associated received diversity signals, for producing within a data frame successive user decisions corresponding to transmitted digital data symbols for a set of λ
- detected users, comprising;
converters for time-sampling and grouping received diversity signals into a receiver time block that has a time duration that is no more than one-half of the interleaving delay;
DSSS replica generator for producing user-unique DSSS signals for K=μ
+λ
mutually-interfering user signals where K>
1 and μ
is equal to the number of interfering users that are not detected;
channel estimator for estimating channel parameters associated with the receiver time block;
sequence signal generator for formatting the DSSS replicas into a set of sequence signals;
sequence matched filter that combines the received diversity signals and sequence signals to provide a set of sequence matched signals;
channel matched filter that combines the sequence matched signals and channel parameters to provide a set of channel matched signals, which depend on a subdecision interval that corresponds to a digital data subsymbol equal in duration to the system period and which further depend on subsymbol delay offsets that are relative to the subdecision interval;
equalizer calculator that computes a set of forward and backward filter parameters from the channel parameters and sequence signals;
backward filter that generates past interference signals and subtracts the past interference signals from the channel matched signals to provide equalization signals that depend on the subdecision interval and subsymbol delay offsets;
forward filter that combines the equalization signals and the forward filter parameters to provide λ
user subsymbol estimates for successive subdecision intervals within the data frame;
multiuser quantizer that sums the user integer multiple successive subsymbol estimates to provide a symbol estimate of the transmitted user digital data symbol, and further selects, at the user symbol rate for users in the set of λ
detected users, the user decision as the possibly transmitted digital data symbol that is closest to the user symbol estimate, and further partitions the user decisions into subdecisions associated with subdecision intervals;
symbol deinterleaver and error-correcting decoder that processes user symbol estimates to recover digital data information; and
wherein the backward filter further comprises;
means that multiply the backward filter parameters and subdecisions from previous subdecision intervals to provide the past interference signals. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
- detected users, comprising;
Specification