In prior art CDMA wireless communication systems that only support voice communications, shown illustratively in FIG. 1, a mobile terminal 101 transmits an encoded voice signal and a pilot signal in a digital form over a propagation channel 102 to a base station receiver 103. The analog voice signal is encoded and transmitted by the mobile terminal 101 on a Fundamental Channel (FCH) 104 in a fixed frame format that incorporates a Cyclic Redundancy Code (CRC) in each frame. The pilot signal, consisting of a fixed bit pattern, is transmitted on a Pilot Channel (PICH) 105. The FCH and PICH are code-division multiplexed (CDM) and kept orthogonal through the use of different Walsh codes. At the base station receiver 103, the pilot signal is used for the detection of the FCH. Also, at the mobile terminal 101, a fixed relationship is maintained between the power level of the pilot signal, referred to as the pilot Eb/N0 level, and the power level of the FCH. At the receiver, after the FCH and pilot signal are demultiplexed from the received CDM signal, a channel estimator 106 operates on the demultiplexed pilot signal and is used by the FCH detector/decoder 110 to derive the frame-formatted bit stream representing the frame-formatted encoded voice signal transmitted by the mobile terminal on the FCH channel in a manner well known in the art. Using the CRC in a received frame, a CRC checker 107 compares the received frame and the CRC in the received frame to determine whether or not the frame has been received in error. A mobile target Eb/N0 setup device 108 then derives a step-up or step-down signal in response to the comparison, which is transmitted by the base station 102 on the downlink channel 109 to the mobile terminal 101. If the frame passes its CRC check, the base station 103 transmits a step-down signal to the mobile terminal 101 to reduce the pilot signal Eb/N0 level and concomitant with that the power level of the transmitted FCH. This mitigates continued transmission by the mobile terminal at a power level could be high enough to be causing interference with other mobile terminals. If the received frame fails its CRC check, the base station transmits a step-up signal to the mobile terminal to increase its pilot signal Eb/N0 level and thus also the power level of the transmitted FCH. This mitigates continued transmission by the mobile terminal at a power level that is too low for accurate detection by the base station.
FIG. 2 shows the relationship between the FCH Frame Error Rate (FER) and the pilot Eb/N0 level of the mobile terminal 101. In order to achieve a particular FER, the Eb/N0 level of the mobile terminal should be at the level that corresponds with that particular FER. To achieve an overall desired FER of X, a step-up size, step_up, equal to
      (                  1        FER            -      1        )    ×  step_downis used, where step_down is equal to X Δ dB. For example, for a typical FER of 10−2, the step_up is set at 99×step_down. Δ is typically a value between 0.3 and 1. Thus, in order to achieve an FER of 10−2, a typical step-down size of between 0.003 dB and 0.01 dB is used, with a corresponding step-up size of approximately between 0.3 and 1.0 dB.
In CDMA2000 systems, in addition to the FCH and PICH channels, which are code-division-multiplexed together for transmission from the mobile terminal to the base station, the mobile terminal code-division multiplexes a Dedicated Control Channel (DCCH) that is used for transmitting control data, a Supplemental Channel (SCH) that is used for transmitting packet data, a Channel Quality Indicator Channel (CQICH) that is used for indicating downlink received pilot strength, and an Acknowledgement Channel (ACKCH) that is used for indicating to the base station whether a received data packet on the downlink has been successfully decoded. The latter two channels are used to support downlink high-speed data transmission, with the ACKCH being muted when the mobile terminal is not receiving any data on the downlink. When packet data is being transmitted on the SCH or DCCH by the mobile terminal, the FCH is not transmitted to conserve power since maintaining it in a NULL state is wasteful of the mobile terminal's power resources. The FCH is thus not always available from which a feedback signal for controlling the mobile terminal's pilot Eb/N0 level. The SCH and DCCH, which do use a CRC are discontinuous channels that are only active when data is being transmitted on them and thus also are not always available to derive a feedback signal for controlling the mobile terminal's pilot Eb/N0 level. The ACKCH, which is not coded, does not therefore use a CRC. The CQICH, which is coded, doesn't use a CRC. Thus, with a discontinuous FCH, and discontinuous DCCH and SCH, no mechanism is available for continuously adjusting the mobile terminal's pilot Eb/N0 level up or down in response to a comparison of a received frame and its associated CRC in order to achieve a desired overall frame error rate on the FCH. Since all the channel levels transmitted by the mobile terminal are referenced to the pilot Eb/N0 level, a mechanism is needed, therefore, to set up and maintain the pilot Eb/N0 level so that a desired frame error rate for the referenced FCH is achieved at the base station and the other channels are maintained at their corresponding appropriate levels.
USPTO Backgrounds
USPTO Backgrounds