Wireless telecommunication systems are well known in the art. In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2 G) and was followed by its revision (2.5 G). GPRS and EDGE are examples of 2.5 G technologies that offer relatively high speed data service on top of (2 G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3 GPP) was formed in December 1998. 3 GPP continues to work on a common third generational mobile radio standard.
A typical UMTS system architecture in accordance with current 3 GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3 GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), known as User Equipments (UEs) in 3 GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3 GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs are connected to each RNC via an interface known as Iub in 3 GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.
Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station's timing. In 3 GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3 GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator's networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers. The gateway mobile services switching center also receives and administers connection requests from subscribers from external networks.
The RNCs generally control internal functions of the UTRAN. The RNCs also provides intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS.
Typically a RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3 GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection.
In many wireless communication systems, adaptive transmission power control algorithms are used. In such systems, many communications may share the same radio frequency spectrum. When receiving a specific communication, all the other communications using the same spectrum cause interference to the specific communication. As a result, increasing the transmission power level of one communication degrades the signal quality of all other communications within that spectrum. However, reducing the transmission power level too far results in undesirable received signal quality, such as measured by signal to interference ratios (SIRs) at the receivers.
Various methods of power control for wireless communication systems are well known in the art. Examples of open and closed loop power control transmitter systems for wireless communication systems are illustrated in FIGS. 2 and 3, respectively. The purpose of such systems is to rapidly vary transmitter power in the presence of a fading propagation channel and time-varying interference to minimize transmitter power while insuring that data is received at the remote end with acceptable quality.
In communication systems such as Third Generation Partnership Project (3 GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems, multiple shared and dedicated channels of variable rate data are combined for transmission. Background specification data for such systems are found at 3 GPP TS 25.223 v3.3.0, 3 GPP TS 25.222 v3.2.0, 3 GPP TS 25.224 v3.6 and Volume 3 specifications of Air-Interface for 3 G Multiple System Version 1.0, Revision 1.0 by the Association of Radio Industries Businesses (ARIB). A fast method and system of power control adaptation for data rate changes resulting in more optimal performance is taught in International Publication Number WO 02/09311 A2, published 31 Jan. 2002 and corresponding U.S. patent application Ser. No. 09/904,001, filed Jul. 12, 2001 owned by the assignee of the present invention.
In 3 GPP W-CDMA systems, power control is used as a link adaptation method. Dynamic power control is applied for dedicated physical channels (DPCH), such that the transmit power of the DPCHs is adjusted to achieve a quality of service (QoS) with a minimum transmit power level, thus limiting the interference level within the system.
One approach is to divide transmission power control into separate processes, referred to as outer loop power control (OLPC) and inner loop power control (ILPC). The power control system is generally referred to as either open or closed dependent upon whether the inner loop is open or closed. The outer loops of both types of systems as illustrated in the examples depicted in FIGS. 2 and 3 are closed loops. The inner loop in the open loop type of system illustrated in FIG. 2 is an open loop.
In outer loop power control, the power level of a specific transmitter is based on a target SIR value. As a receiver receives the transmissions, the quality of the received signal is measured. The transmitted information is sent in units of transport blocks (TBs), and the received signal quality can be monitored on a block error rate (BLER) basis. The BLER is estimated by the receiver, typically by a cyclic redundancy check (CRC) of the data. This estimated BLER is compared to a target quality requirement, such a target BLER, representative of QoS requirements for the various types of data services on the channel. Based on the measured received signal quality, a target SIR adjustment control signal is sent to the transmitter. The transmitter adjusts the target SIR in response to these adjustment requests.
In third generation partnership program (3 GPP) wideband code division multiple access (W-CDMA) systems utilizing time division duplex (TDD) mode, the UTRAN (SRNC-RRC) sets the initial target SIR to the WTRU at the call/session establishment and then subsequently continuously adjusts the target SIR of the WTRU during the life term of the call as dictated by the observation of the uplink (UL) BLER measurement.
In inner loop power control, the receiver compares a measurement of the received signal quality, such as SIR, to a threshold value (i.e., the target SIR). If the SIR exceeds the threshold, a transmit power command (TPC) to decrease the power level is sent. If the SIR is below the threshold, a TPC to increase the power level is sent. Typically, the TPC is multiplexed with data in a dedicated channel to the transmitter. In response to received TPC, the transmitter changes its transmission power level.
Conventionally, the outer loop power control algorithm in a 3 GPP system sets an initial target SIR for each coded composite transport channel (CCTrCH) based on the required target BLER, using a fixed mapping between BLER and SIR, assuming a particular channel condition. A CCTrCH is commonly employed for transmitting various services on a physical wireless channel by multiplexing several transport channels (TrCHs), each service on its own TrCH. In order to monitor the BLER level on a CCTrCH basis, a reference transport channel (RTrCH) may be selected among the transport channels multiplexed on the considered CCTrCH. For example, a TrCH-1 may be selected for RTrCH as it may be regarded as a mid-point of all channel conditions on the CCTrCH, including an AWGN channel. A mismatch between a target BLER and a target SIR may vary significantly depending on the given channel condition, especially at very low BLER. For instance, the target SIR at a target BLER=0.01 for TrCH-1 in the Case 1 channel condition may require more than 4 dB over the target SIR for another transport channel in the AWGN channel condition, (i.e., TrCH-1 requires a stronger signal). When the WTRU converts the target BLER to an initial target SIR, there may be an error caused by this channel condition mismatch, since the target SIR required for a target BLER varies with channel conditions. As a result, the iterative process for target SIR determination has an initial differential that must be overcome by convergence to the required target, compounded by allowing the CRC process to occur, which altogether creates an undesirable delay for target SIR convergence.
The entire power control algorithm may suffer degraded performance as a result of the delay. The delay is denoted in terms of the transmission rate unit, a transmission time interval (TTI). The smallest interval is one frame of data, typically defined as 10 ms for a 3 GPP communication system. In a 3 GPP system, TTIs are in lengths of 10, 20, 40, or 80 ms.
Also, a wireless channel can transmit a variety of services, such as video, voice, and data, each having different QoS requirements. For non-real time (NRT) data services, data is transmitted in many bursts of short duration. In a 3 GPP system for example, these data bursts are mapped as transport blocks on a temporary dedicated channel (Temp-DCH). This mapping is also referred to in terms of Temp-DCH allocations. One or more transport blocks are mapped onto the channel per TTI. Thus, each service is mapped across several TTIs, while target SIR adjustments are made on a TTI basis during OLPC for the Temp-DCH allocations.
When comparing voice and data types of transmissions, a real time (RT) voice transmission is more likely have a target BLER that is more tolerant (i.e., higher BLER value), while a NRT data transmission requires a lower rate of error with a lower target BLER. Accordingly, the expected delays to ensure QoS are longer for a data download than for a voice transmission. Further, the required transient step size for target SIR adjustments is set depending on the service's QoS requirement. While the initial target SIR for RT data will always converge to the desired target SIR, the initial target SIR for NRT data, which is newly assigned per Temp-DCH allocation, may not converge to the desired target SIR due to short duration of Temp-DCH allocation.
This invention recognizes that Temp-DCH allocation duration can be used as an additional parameter to enhance power control.