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User equipment for controlling transmission power levelsRelated Patent Categories: Pulse Or Digital Communications, Spread SpectrumUser equipment for controlling transmission power levels description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070030882, User equipment for controlling transmission power levels. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. application Ser. No. 10/435,796, filed May 12, 2003, which is a continuation of U.S. application Ser. No. 09/533,423, filed Mar. 22, 2002, which issued on Aug. 5, 2003 as U.S. Pat. No. 6,603,797; which are incorporated herein by reference as if fully set forth. FIELD OF INVENTION [0002] 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. BACKGROUND [0003] FIG. 1 depicts a wireless spread spectrum time division duplex (TDD) communication system. The system has a plurality of base stations 30.sub.1-30.sub.7. Each base station 30.sub.1 communicates with user equipment (UEs) 32.sub.1-32.sub.3 in its operating area. Communications transmitted from a base station 30.sub.1 to a UE 32.sub.1 are referred to as downlink communications and communications transmitted from a UE 32.sub.1 to a base station 30.sub.1 are referred to as uplink communications. [0004] 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.sub.1-36.sub.n,, such as sixteen time slots. In such systems, a communication is sent in selected time slots 36.sub.1-36.sub.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. [0005] 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.sub.1 or base station 30.sub.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. [0006] 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. [0007] 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 [0008] The present invention is directed to a user equipment (UE) for controlling transmission power levels in a system employing a spread spectrum time division duplex (TDD) technique having frames with timeslots for communication. The UE comprises a measuring device configured to receive, during a first time slot, a communication including a power level and measure the power level of the received communication and an interference power level. A pathloss estimation device determines a pathloss estimate and a long term pathloss estimate, based in part on the measured power level and the received power level. A quality measurement device determines a first quality factor, .alpha., and a second quality factor, 1-.alpha., of the pathloss estimate based in part on a number of timeslots, D, between the first and a second timeslot. A transmit power calculation device sets a transmission power level for transmission during the second timeslot. BRIEF DESCRIPTION OF THE DRAWINGS [0009] FIG. 1 illustrates a prior art TDD system. [0010] FIG. 2 illustrates time slots in repeating frames of a TDD system. [0011] FIG. 3 is a flow chart of outer loop/weighted open loop power control. [0012] FIG. 4 is a diagram of components of two communication stations using outer loop/weighted open loop power control. [0013] FIG. 5 is a graph of the performance of outer loop/weighted open loop, weighted open loop and closed loop power control systems. [0014] FIG. 6 is a graph of the three systems performance in terms of Block Error Rate (BLER). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) [0015] The preferred embodiments will be described with reference to the drawing figures where like numerals represent like elements throughout. Outer loop/weighted open loop power control will be explained using the flow chart of FIG. 3 and the components of two simplified communication stations 110, 112 as shown in FIG. 4. For the following discussion, the communication station having its transmitter's power controlled is referred to as the transmitting station 112 and the communication station receiving power controlled communications is referred to as the receiving station 110. Since outer loop/weighted open loop power control may be used for uplink, downlink or both types of communications, the transmitter having its power controlled may be associated with the base station 30.sub.1, UE 32.sub.1 or both. Accordingly, if both uplink and downlink power control are used, the receiving and transmitting station's components are associated with both the base station 30.sub.1 and UE 32.sub.1. [0016] The receiving station 110 receives various radio frequency signals including communications from the transmitting station 112 using an antenna 78, or alternately, an antenna array, step 38. The received signals are passed thorough an isolator 66 to a demodulator 68 to produce a baseband signal. The baseband signal is processed, such as by a channel estimation device 70 and a data estimation device 72, in the time slots and with the appropriate codes assigned to the transmitting station's communication. The channel estimation device 70 commonly uses the training sequence component in the baseband signal to provide channel information, such as channel impulse responses. The channel information is used by the data estimation device 72, the interference measurement device 74, and the transmit power calculation device 76. The data estimation device 72 recovers data from the channel by estimating soft symbols using the channel information. ior to transmission of the communication from the transmitting station 112, the data signal of the communication is error encoded using an error detection/correction encoder 110. The error encoding scheme is typically a circular redundancy code (CRC) followed by a forward error correction encoding, although other types of error encoding schemes may be used.Using the soft symbols produced by the data estimation device 72, an error detection device 112 detects errors in the soft symbols. A processor 111 analyzes the detected error and determines an error rate for the received communication, step 39. Based on the error rate, the processor 111 determines the amount, if any, a target level, such as a target signal to interference ration (SIR.sub.TARGET), needs to be changed at the transmitting station 112, step 40. Based on the determined amount, a target adjustment signal is generated by the target adjustment generator 114. The target adjustment is subsequently sent to the transmitting station, step 41. The target adjustment is signaled to the transmitting station 112, such as using a dedicated or a reference channel as shown in FIG. 4, step 41. [0017] One technique to determine the amount of adjustment in the target level uses an upper and lower threshold. If the determined error rate exceeds an upper threshold, the target level is set at an unacceptably low level and needs to be increased. A target level adjustment signal is sent indicating an increase in the target level. If the determined error rate is below a second threshold, the target level is set at an unnecessarily high level and the target level can be decreased. By reducing the target level, the transmitting station's power level is decreased reducing interference to other communications using the same time slot and spectrum. To improve performance, as soon as the error rate exceeds the upper limit, a target adjustment is sent. As a result, high error rates are improved quickly and lower error rates are adjusted slowly, such as once per 10 seconds. If the error rate is between the thresholds, a target adjustment is not sent maintaining the same target level. [0018] Applying the above technique to a system using CRC and FEC encoding follows. Each CRC block is checked for an error. Each time a frame is determined to have an error, a counter is incremented. As soon as the counter exceeds an upper threshold, such as 1.5 to 2 times the desired block error rate (BLER), a target adjustment is sent increasing the target level. To adjust the SIR.sub.TARGET at the transmitting station 112, the increase in the SIR.sub.TARGET is sent (SIR.sub.INC), which is typically in a range of 0.25 dB to 4 dB. If the number of CRC frames encountered exceeds a predetermined limit, such as 1000 blocks, the value of the counter is compared to a lower threshold, such as 0.2 to 0.6 times the desired BLER. If the number of counted block errors is below the lower threshold, a target adjustment signal is sent decreasing the target level, SIR.sub.DEC. A typical range of SIR.sub.DEC is 0.25 to 4 dB. The value of SIR.sub.DEC may be based on SIR.sub.INC and a target block error rate, BLER.sub.TARGET. The BLER.sub.TARGET is based on the type of service. A typical range for the BLER.sub.TARGET is 0.1% to 10%. Equation 1 illustrates one such approach for determining SIR.sub.DEC.SIR.sub.DEC=SIR.sub.INC.times.BLER.sub.TARGET/(1-BLER.sub.TAR- GET) Equation 1 Continue reading about User equipment for controlling transmission power levels... Full patent description for User equipment for controlling transmission power levels Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this User equipment for controlling transmission power levels patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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