Pulse or digital communications – Spread spectrum
Reexamination Certificate
2002-02-22
2003-07-22
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Spread spectrum
C370S342000, C455S522000
Reexamination Certificate
active
06597724
ABSTRACT:
BACKGROUND
This application is a continuation of application Ser. No. 09/533,423, filed Mar. 22, 2000; which application is incorporated herein by reference.
This invention generally relates to spread spectrum time division duplex (TDD) communication systems. More particularly, the present invention relates to a system and method for controlling transmission power within TDD communication systems.
FIG. 1
depicts a wireless spread spectrum time division duplex (TDD) communication system. The system has a plurality of base stations
30
1
-
30
7
. Each base station
30
1
communicates with user equipment (UEs)
32
1
-
32
3
in its operating area. Communications transmitted from a base station
30
1
to a UE
32
1
are referred to as downlink communications and communications transmitted from a UE
32
1
to a base station
30
1
are referred to as uplink communications.
In addition to communicating over different frequency spectrums, spread spectrum TDD systems carry multiple communications over the same spectrum. The multiple signals are distinguished by their respective chip code sequences (codes). Also, to more efficiently use the spread spectrum, TDD systems as illustrated in
FIG. 2
use repeating frames
34
divided into a number of time slots
36
1
-
36
n,
, such as sixteen time slots. In such systems, a communication is sent in selected time slots
36
1
-
36
n
using selected codes. Accordingly, one frame
34
is capable of carrying multiple communications distinguished by both time slot and code. The combination of a single code in a single time slot is referred to as a resource unit. Based on the bandwidth required to support a communication, one or multiple resource units are assigned to that communication.
Most TDD systems adaptively control transmission power levels. In a TDD system, many communications may share the same time slot and spectrum. When a UE
32
1
or base station
30
1
is receiving a specific communication, all the other communications using the same time slot and spectrum cause interference to the specific communication. Increasing the transmission power level of one communication degrades the signal quality of all other communications within that time slot and spectrum. However, reducing the transmission power level too far results in undesirable signal to noise ratios (SNRs) and bit error rates (BERs) at the receivers. To maintain both the signal quality of communications and low transmission power levels, transmission power control is used.
One approach using transmission power control in a code division multiple access (CDMA) communication system is described in U.S. Pat. No. 5,056,109 (Gilhousen et al.). A transmitter sends a communication to a particular receiver. Upon reception, the received signal power is measured. The received signal power is compared to a desired received signal power. Based on the comparison, a control bit is sent to the transmitter either increasing or decreasing transmission power by a fixed amount. Since the receiver sends a control signal to the transmitter to control the transmitter's power level, such power control techniques are commonly referred to as closed loop.
Under certain conditions, the performance of closed loop systems degrades. For instance, if communications sent between a UE and a base station are in a highly dynamic environment, such as due to the UE moving, such systems may not be able to adapt fast enough to compensate for the changes. The update rate of closed loop power control in TDD is typically 100 cycles per second which is not sufficient for fast fading channels. Accordingly, there is a need for alternate approaches to maintain signal quality and low transmission power levels.
SUMMARY
Outer loop/weighted open loop power control controls transmission power levels in a spread spectrum time division duplex communication system. At a first communication station, errors are measured in a received communication from a second communication station. Based on in part the measured errors, an adjustment in a target level is determined. The first station transmits a communication and the target adjustment to the second station. The second station measures the first station's communication's received power level. Based on in part the received power level, a path loss is determined. The target level is adjusted in response to receiving the target adjustment. The quality of the path loss is determined with respect to a subsequent communication to be transmitted from the second station. The second station's transmission power level for the subsequent communication is adjusted based on in part the determined path loss, the determined quality and the adjusted target level.
REFERENCES:
patent: 4868795 (1989-09-01), McDavid et al.
patent: 5056109 (1991-10-01), Gilhousen et al.
patent: 5542111 (1996-07-01), Ivanov et al.
patent: 5839056 (1998-11-01), Hakkinen
patent: 5859838 (1999-01-01), Soliman
patent: 6101179 (2000-08-01), Soliman
patent: 6108561 (2000-08-01), Mallinckrodt
patent: 6175586 (2001-01-01), Lomp
patent: 6175745 (2001-01-01), Bringby et al.
patent: 6188678 (2001-02-01), Prescott
patent: 6373823 (2002-04-01), Chen et al.
patent: 6449462 (2002-09-01), Gunnarsson et al.
patent: 0462952 (1991-12-01), None
patent: 0610030 (1994-08-01), None
patent: 0682419 (1995-11-01), None
patent: 0500689 (1998-04-01), None
patent: 9749197 (1997-12-01), None
patent: WO98/45962 (1998-10-01), None
“Specification of Air-Interface for the 3G Mobile System”, Version 1.0, ARIB, Jan. 14, 1999.
“Combined Closed-Loop/Open-Loop Power Control Process for Time Division Duplexing”, Ariela Zeira, Sung-Hyuk Shin and Fatih Ozluturk, Apr. 1999.
“Performance of Weighted Open Loop Scheme for Uplink Power Control in TDD Mode”, Ariela Zeira and Sung-Hyuk Shin, May 1999.
“Text Proposal for S1.24”, Ariela Zeira, Sung-Hyuk Shin and Stephen Dick, May 1999.
Dick Steven G.
Shin Sung-Hyuk
Zeira Ariela
Ghebretinsae Temesghen
InterDigital Technology Corporation
Volpe and Koenig P.C.
LandOfFree
User equipment method employing a time division duplex... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with User equipment method employing a time division duplex..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and User equipment method employing a time division duplex... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3091532