Base station utilizing a weighted open loop power control

Details Base station utilizing a weighted open loop power control Base station utilizing a weighted open loop power control

2002-02-26

2003-06-10

Ghebretinsae, Temesghen (Department: 2631)

Pulse or digital communications

Spread spectrum

C375S146000, C370S342000, C455S522000

Reexamination Certificate

active

06577669

ABSTRACT:

BACKGROUND
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 equipments (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 fifteen 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
36
1
--
36
n
and code. The use 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
32
1
and a base station
30
1
are in a highly dynamic environment, such as due to the UE
32
1
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 a typical TDD system is 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
The invention controls transmission power levels in a spread spectrum time division duplex communication station. A first communication station transmits a communication to a second communication station. The second station receives the communication and measures its received power level. Based on, in part, the received communication's power level and the communication's transmission power level, a path loss estimate is determined. The transmission power level for a communication from the second station to the first station is set based on, in part, weighting the path loss estimate and a long term pathloss estimate.


REFERENCES:
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“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.

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