Generally, three nodes of the communication system are relevant: the Radio Network Controller RNC, a Node B, and a user equipment UE. The Node B is interchangeably referred to as a base transceiver station BTS, and the UE is interchangeably referred to as a mobile station MS. The RNC and Node B are elements of the network, whereas the UE communicates with the network but is not considered a part thereof. Multiple Node Bs are typically under the control of one RNC, and typically multiple UEs are under the control of one Node B. Power control is an important feature in any packet-switched wireless system to enable multiple users to access the system simultaneously.
In HSUPA (High Speed Uplink Packet Access) involves enhancements of the uplink dedicated transport channel (DCH), hereafter referred to as E-DCH, for packet data-traffic as per Release 6 of 3GPP TS 25-321. In HSUPA one enhancement of interest relates to distributing some of the packet scheduler functionality to Node Bs (which may also be referred to as base transceiver station equipment). One reason for making this type of redistribution is to achieve a more rapid scheduling of bursty (e.g., packetized), non real-time (e.g., data rather than voice) traffic than can be accomplished using the Layer 3 (L3) of the Radio Network Controller (RNC). The basic premise is that with faster adaptation of the radio link it is possible to more efficiently share the uplink power resource between packet data users. For example, when data packets have been transmitted from one UE the scheduled resource can be made available immediately to another UE. This approach seeks to avoid the peaked variability of noise rise, when high data rates are being allocated to users running bursty, high data-rate applications.
In the current system-level architecture the packet scheduler is located in the RNC and, therefore, is limited in its ability to adapt to the instantaneous traffic due at least to bandwidth constraints on the Radio Resource Control (RRC) signaling interface between the RNC and the UE. Hence, to accommodate the variability the packet scheduler is designed to be conservative in allocating uplink power in order to take into account the influence from inactive users in a next scheduling period. However, this conservative approach is spectrally inefficient for allocated high data-rates and long release timer values.
With E-DCH, much of the packet scheduler functionality is transferred to the Node B, i.e., there is defined a Node B scheduler that is responsible for allocating uplink resources.
For this type of scheduling to be performed efficiently, the Node B needs to obtain a data rate request from the UE. After a scheduling decision is made the Node B can inform the UE of the decision by sending absolute and relative grants. With an absolute grant a certain power is allocated to the E-DCH data packet channel E-DPDCH (wherein the prefix E before a channel indicates a channel within the regime of enhancements to uplink dedicated data channel architecture). This power is given relative to the power on the dedicated physical control channel DPCCH (e.g., a ratio of E-DPDCH power to DPCCH power). The relative grant channels E-RGCH contain UP/KEEP/DOWN commands, which the UE responds to as follows. When the UE receives an UP command, the UE increases its transmit power allocation by a certain step size, and when the UE receives a DOWN command it reduces its power allocation by a certain step size. The possible step sizes are sent by the RNC to the UE.
Currently, the E-DPDCH to DPCCH power ratio (power ratio between the E-DPDCH and DPCCH) is defined to be in the range of −10, . . . , +21 dB, with a uniform 1 dB granularity, i.e., the uplink power control range is defined as 32, 1 dB steps. For example, when a Node B desires the UE to change its transmit power on E-DPDCH, it sends an UP or DOWN command on the relative grant channel. The UE responds by adjusting its power, which was received on the absolute grant channel as a ratio of E-DPDCH to DPCCH, either +1 dB or −1 dB, respectively. Further UP and DOWN commands further adjust the UE's transmit power on E-DPDCH by +/−1 dB for each command. This leads to slower link adaptation where the desired power change is more than +/−1 dB, regardless of whether the Node B or the RNC is originally determining the desired power for the UE to transmit.