Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-08-13
2001-09-25
Vu, Huy D. (Department: 2735)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C455S069000, C455S522000
Reexamination Certificate
active
06295289
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates, generally, to power control in radio transmission systems.
FIG. 1
shows a cellular radio communication system. The system
100
includes cells
101
-
107
. Each cell
101
-
107
includes a radio frequency transmitting and receiving base station
111
-
117
that allows downlink (base station to mobile unit) and uplink (mobile unit to base station) channels to be established. The uplink and downlink channels provide paths for communication between each mobile unit
120
and an associated base station
111
-
117
. The system
100
may be implemented in accordance with Telecommunications Industry Association standard TIA/EIA IS-95 Mobile Station-Base Station Compatibility Standar ds for Dual-Mode Wideband Spread Spectrum Cellular System (“IS-95”) or in accordance with the Japanese Association of Radio Industries and Businesses (ARIB) standard Specification of Mobiles station for 3G Mobile Station System Version 1.0, (3G CDMA) or other wideband CDMA (WCDMA) or multi-carrier CDMA (MC-CDMA) standard. An IS-95 CDMA, 3G CDMA, WCDMA, or MC-CDMA transmission system generally use code division multiple access (CDMA) protocols and quadrature phase shift keying (QPSK) modulation to establish a communication channel between a base station and a mobile receiver.
In a CDMA system, multiple uplink CDMA channels can share the same frequency spectrum. Similarly, multiple downlink channels can share another frequency spectrum. To enable this frequency sharing, each channel's baseband data signal is multiplied by a spreading code which uniquely spreads the channel's data over the entire uplink or downlink transmission spectrum. At a receiver, the unique spreading code assigned to a particular channel is used to despread a received signal and discriminate the desired channel from others occupying the same frequency spectrum. The technique may also be referred to as “spread spectrum” communication.
The use of the same frequency spectrum by multiple CDMA mobile units can increase the bandwidth efficiency of a communications system. However, this spectrum sharing also causes a gradual degradation of the performance of the system as the number of users increases. This gradual degradation occurs because mobile unit receiver s detect signals from other mobile units as noise. In general, the stronger the signal from a mobile unit, the more interference the base station experiences when receiving and demodulating signals from other mobile units. Ultimately, the power from one mobile unit may be great enough to terminate communications of other mobile units. Accordingly, it is extremely important in wireless CDMA communication systems to control the transmission power of all mobile units. In general, transmission power must be controlled both when a mobile unit initiates a channel to a base station, and for the duration of that channel's use.
In an IS-95 implementation, when a mobile unit initiates a CDMA channel with a base station, the mobile unit has not yet received power control information from the base station and, therefore, does not know the power level needed for effective transmission. If the mobile unit begins transmitting at a power level that is too high, it may interfere with the communications of other mobile units and may even terminate the communications of other mobile units. If the initial transmission power level is too low, the mobile unit will not be detected by the base station and a communication link will not be established. To resolve this issue, IS-95 includes a start up protocol whereby a mobile unit begins transmission at a low power level and gradually increases power until a channel is established with the base station.
After the channel has been established, the strength of a radio signal received over that channel may vary due to fades and reinforcements. Channel fading can cause degradation of the received signal and loss of the connection. Reinforcements may cause interference with other transmitters and/or receivers in the mobile radio system. Because of these time varying changes in the radio propagation environment, a mobile unit will need to adjust its transmission power during the use of a channel. To regulate power during use of a channel, a closed-loop power control system can be used. In a closed-loop system, a base station periodically sends power control messages to a mobile unit instructing the mobile unit to increase or decrease its transmission power level. In an IS-95 implementation, the power control messages are sent as a series of power control bits in an overhead portion of a downlink communications channel.
Delay exists between the transmission of a signal from a mobile unit on an uplink channel, the calculation of power control information from that uplink signal at a base station, and the receipt and processing of that power control information back at the mobile unit. In a rapidly varying propagation environment, this delay may result in unsuitable power control information being received and acted upon by the mobile unit. As a result, performance of the mobile unit and/or radio system may degrade. Consequently, improved means of setting a mobile unit's transmission power are desired.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention features a receiving and transmitting apparatus. The apparatus includes receiver circuitry, sampling circuitry, downlink prediction circuitry, uplink prediction circuitry and gain calculation circuitry. A downlink signal is received at the receiver and sampled at the sampling circuitry. Downlink and uplink prediction circuitry is used to estimate transmission properties of the downlink and uplink signals, respectively. The downlink and uplink prediction circuitry estimates downlink and uplink signal properties based on a sequence of previous downlink signal samples and the uplink estimates, respectively, as well as corresponding sequences of tap coefficients. The gain calculation circuitry is coupled to the uplink prediction circuitry and to a transmitter and can set a transmitter gain level based on the predicted uplink signal properties.
In general, in another aspect, the invention features a method of controlling power in a wireless communication device. The method includes storing a sequence of downlink signal samples (which may be derived using a spectral estimation method to compute the first sequence of tap coefficients, for example, by using autoregressive moving average (ARMA) models, or other models to derive the tap coefficients), calculating a downlink signal estimate and an uplink signal estimate, and setting a transmission power level based on the estimated uplink signal. The downlink signal estimate is calculated using the sequence of downlink signal samples and a first sequence of tap coefficients. The uplink signal estimate is calculated using a sequence of previous uplink signal estimates and a second sequence of tap coefficients.
Implementations of the invention may include one or more of the following features. The methods and apparatuses may be implemented in a mobile unit for use in a CDMA cellular phone system. The tap coefficients used for uplink and downlink prediction may be the same or the tap coefficients used for uplink prediction may be derived from those used for downlink prediction. The tap coefficients also may be feedback refined. Downlink signal samples may be determined by sampling a received signal in a downlink CDMA channel. The downlink CDMA channel may include a pilot channel and the received signal samples may be samples of the pilot channel signal envelope (which may be squared after combining different sources of diversity, e.g., multipath). Stored uplink signal estimates may be modified based on power control information received from a base station. The power control information may be in the form of delta modulated power control bits. A transmitter gain setting may be modified by a threshold amount based on the power control bits and/or uplink predictions. The power control information may
Ionescu Dumitru Mihai
Mandyam Giridhar
Fraccaroli Federico
Jones Prenell
Mahon James V.
Nokia Mobile Phones Ltd.
Vu Huy D.
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