Multistage reception of code division multiple access transmissions

• US 7,630,344 B1
• Filed: 03/14/2007
• Issued: 12/08/2009
• Est. Priority Date: 03/30/2001
• Status: Active Grant

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Potter, Michael, Carson, Steve, Slocumb, Travis H., Kilfoyle, Daniel B.
• Primary Examiner(s): Pham; Chi H
• Assistant Examiner(s): Wong; Warner
• Application Number:
  US11/717,743
• Time in Patent Office: 1,000 Days
• Field of Search: 370/252, 370/333, 714/699, 714/701
• US Class Current: 370/334
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0048 in conjunction with detection of multiuser or interfering signals, e.g. iteration between CDMA or MIMO detector and FEC decoder for spatial equalizer H04L25/03286
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04W 52/12 Outer and inner loops
• CPC Class Codes: H04W 52/26 using transmission rate or quality of service QoS [Quality of Service]
• CPC Class Codes: H04W 52/343 taking into account loading or congestion level
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

Reducing multiple access interference in the radio frequency communications path between the network base station and UE. The preferred methods include interleaving STAP and MUD in a plurality of stages in a base station receiver. Specific embodiments accomplish this by selecting certain UE connections for MUD processing by stage. Then, in two or more stages, demodulating the UE connections selected for MUD processing using STAP, and MUD canceling UE connections selected for MUD processing. Within the latency requirements of the network, preferred embodiments of the present invention also command a transmit power for each UE connections in order to exploit the effect of interleaved STAP and MUD processing.

Claims

1. In a communications network comprising a base station and a plurality of user equipment (UE), the network having at least one radio frequency communications path between each UE and the base station, the base station comprising a plurality of antennas and at least one base station receiver, a method of reducing multiple access interference in at least one radio frequency communications path between the base station and at least one UE, the method comprising:

interleaving space-time adaptive processing (STAP) and multi-user detection (MUD) in a first plurality of stages in a base station receiver, by;

selecting at least one UE connection for MUD processing by stage, and in a second plurality of stages;

demodulating the UE connections selected for MUD processing in a current stage, the demodulation employing STAP, and

performing MUD cancellation on UE connections selected for MUD processing in the current stage; and

acquiring new UE connections after at least one stage of MUD cancellation; and

commanding transmit power for each UE connection;

at least one UE connection being characterized by a target E_b/N₀ at least equal to a corresponding threshold target E_b/N₀, and

selecting UE connections for MUD processing by stage comprises estimating the multiple access interference contribution of each UE connection having a target E_b/N₀ at least equal to the corresponding threshold target E_b/N₀; and

UE connections characterized by a target E_b/N₀ at least equal to a corresponding threshold target E_b/N₀ are selected for MUD processing in order of descending multiple access interference contribution.

2. The method recited in claim 1, the at least one stage of MUD cancellation is a final stage within the second plurality of stages.

3. The method recited in claim 1, performing MUD cancellation further comprises group-wise subtractive interference cancellation.

4. The method recited in claim 3, the group-wise subtractive interference cancellation is group-wise serial subtractive interference cancellation.

5. The method recited in claim 1, performing MUD cancellation further comprises canceling each UE connection selected for canceling down to the ambient multiple access interference level of voice UE connections in the network.

6. The method recited in claim 1 wherein the threshold target E_b/N₀ for each UE connection is a function of a spreading factor of the UE connection.

7. The method recited in claim 1 further comprising:

determining data rates for UE connections; and

if no high data rate UE connections then commanding one or more low rate burst-enabled UE connections to sequentially burst at higher data rates.

8. The method recited in claim 2 further comprising:

after the final stage, demodulating remaining UE connections.

9. The method recited in claim 1 wherein commanding transmit power for each UE connection further comprises:

determining a base target E_b/N₀ as a function of at least one data quality metric (DQM);

estimating a received E_b/N₀ for each UE connection, and for each UE connection designated for MUD processing, adjusting the base target E_b/N₀ upward;

for each UE connection not designated for MUD processing, where the estimated E_b/N₀ is less than the base target E_b/N₀, commanding increased UE connection transmit power; and

for each UE connection designated for MUD processing, where the estimated E_b/N₀ is less than the adjusted base target E_b/N₀, commanding increased UE connection transmit power.

10. In a communications network comprising a base station and a plurality of user equipment (UE), the network having at least one radio frequency communications path between each UE and the base station, the base station comprising a plurality of antennas and at least one base station receiver, a method of reducing multiple access interference in at least one radio frequency communications path between the base station and at least one UE, the method comprising:

interleaving space-time adaptive processing (STAP) and multi-user detection (MUD) in a first plurality of stages in a base station receiver, by;

selecting at least one UE connection for MUD processing by stage by;

multiplexing a plurality of UE connections into an aggregate UE connection, and performing MUD cancellation on the aggregate UE connection as on a non-aggregate user system connection;

and in a second plurality of stages;

demodulating the at least one UE connection selected for MUD processing in a current stage, the demodulation employing STAP, and

performing MUD cancellation on UE connections selected for MUD processing in the current stage;

acquiring new UE connections after at least one stage of MUD cancellation; and

commanding transmit power for each UE connection;

performing MUD cancellation on UE connections further comprises;

at least one UE connection being characterized by a target E_b/N₀ less than a corresponding threshold target E_b/N₀, and

selecting at least one UE connection for MUD processing by stage comprises;

increasing the target E_b/N₀ of at least one UE connection having the lowest spreading factor from among the UE connections characterized by a target E_b/N₀ less than a corresponding threshold target E_b/N₀, by an amount sufficient to characterize the at least one UE connection as having an increased target E_b/N₀ at least equal to a corresponding threshold target E_b/N₀.

11. The method recited in claim 10, the at least one stage of MUD cancellation is a final stage within the second plurality of stages.

12. The method recited in claim 11 further comprising:

after the final stage, demodulating remaining UE connections.

13. The method recited in claim 10:

the set of UE connections selected for MUD processing are characterized by a range of target E_b/N₀ not greater than 3 dB.

14. The method recited in claim 10, commanding transmit power for each UE connection further comprises:

determining a base target E_b/N₀ as a function of at least one data quality metric (DQM);

estimating a received E_b/N₀ for each UE connection,

estimating a STAP gain for each UE connection, and

adjusting the base target E_b/N₀ down by the amount of estimated STAP gain for each UE connection where the estimated E_b/N₀ is less that the adjusted base target E_b/N₀, commanding increased UE connection transmit power.

15. The method recited in claim 10 wherein performing MUD cancellation further comprises:

group-wise subtractive interference cancellation.

16. The method recited in claim 15 wherein the group-wise subtractive interference cancellation is group-wise serial subtractive interference cancellation.

17. The method recited in claim 10 further comprising:

determining data rates for UE connections; and

if no high data rate UE connections then command one or more low rate burst-enabled UE connections to sequentially burst at higher data rates.

18. In a communications network comprising a base station and a plurality of user equipment (UE), the network having at least one radio frequency communications path between each UE and the base station, the base station comprising a plurality of antennas and at least one base station receiver, a method of reducing multiple access interference in at least one radio frequency communications path between the base station and at least one UE, the method comprising:

interleaving space-time adaptive processing (STAP) and multi-user detection (MUD) in a first plurality of stages in a base station receiver, by;

selecting at least one UE connection for MUD processing by stage, and in a second plurality of stages;

demodulating the UE connections selected for MUD processing in a current stage, the demodulation employing STAP, and

performing MUD cancellation on UE connections selected for MUD processing in the current stage; and

acquiring new UE connections after at least one stage of MUD cancellation; and

commanding transmit power for each UE connection;

wherein commanding transmit power for each UE connection further comprises;

determining a base target E_b/N₀ as a function of at least one data quality metric (DQM);

estimating a received E_b/N₀ for each UE connection, and for each UE connection designated for MUD processing, adjusting the base target E_b/N₀ upward;

for each UE connection not designated for MUD processing, where the estimated E_b/N₀ is less than the base target E_b/N₀, commanding increased UE connection transmit power; and

for each UE connection designated for MUD processing, where the estimated E_b/N₀ is less than the adjusted base target E_b/N₀, commanding increased UE connection transmit power.

19. In a communications network comprising a base station and a plurality of user equipment (UE), the network having at least one radio frequency communications path between each UE and the base station, the base station comprising a plurality of antennas and at least one base station receiver, a method of reducing multiple access interference in at least one radio frequency communications path between the base station and at least one UE, the method comprising:

interleaving space-time adaptive processing (STAP) and multi-user detection (MUD) in a first plurality of stages in a base station receiver, by;

selecting at least one UE connection for MUD processing by stage by;

multiplexing a plurality of UE connections into an aggregate UE connection, and performing MUD cancellation on the aggregate UE connection as on a non-aggregate user system connection;

and in a second plurality of stages;

demodulating the at least one UE connection selected for MUD processing in a current stage, the demodulation employing STAP, and

performing MUD cancellation on UE connections selected for MUD processing in the current stage;

acquiring new UE connections after at least one stage of MUD cancellation; and

commanding transmit power for each UE connection;

commanding transmit power for each UE connection further comprises;

determining a base target E_b/N₀ as a function of at least one data quality metric (DQM);

estimating a received E_b/N₀ for each UE connection,

estimating a STAP gain for each UE connection, and

adjusting the base target E_b/N₀ down by the amount of estimated STAP gain for each UE connection where the estimated E_b/N₀ is less that the adjusted base target E_b/N₀, commanding increased UE connection transmit power.