Patent Application
20090161632
NOT APPLICABLE
NOT APPLICABLE
NOT APPLICABLE
The present invention relates to mobile telecommunications. More particularly, and not by way of limitation, the present invention is directed to a system and method for selecting power-efficient Enhanced Uplink Transport Format Combinations (E-TFCs) for power control of uplink transmissions.
Conventional mobile communication systems set up communication among multiple mobile terminals (for example, User Equipment (UE) devices) and base stations on a multitude of channels, where uplink transmissions are transmissions from the UE to the base station and downlink transmissions are transmissions from the base station to the UE. Some signaling protocols specify uplink transmissions on more than one channel, such as a control channel and a data channel. Thus, transmitter circuitry of the UE may transmit on one or more adjacent channels, possibly leading to adjacent channel interference. Accordingly, it is necessary to control the transmitter circuitry to avoid such issues.
In wide-band CDMA (WCDMA), the transmitter circuitry can be controlled to reduce adjacent channel interference problems by performing rate selection, which includes selecting the data rate and coding scheme (also known as Transport Format Combination (TFC) selection) for a signal transmission or burst to control the transmitter's power amplifier. In newer specifications for WCDMA, there are at least five channels that need to be supported for uplink transmission: the Dedicated Physical Control Channel (DPCCH), the Dedicated Physical Data Channel (DPDCH), the High Speed Dedicated Physical Control Channel (HS-DPCCH), the Enhanced Dedicated Physical Control Channel (E-DPCCH), and the Enhanced Dedicated Physical Data Channel (E-DPDCH). The rate selection for the enhanced uplink channels (E-DPCCH and E-DPDCH) is referred to as enhanced transport format combination (E-TFC). Each channel has a corresponding gain factor (βc, βd, βhs, βec, βed) determining the power offsets between the channels, and each channel has a corresponding spreading factor, I or Q branch assignment, and channelization code. In addition, there can be 1, 2, or 4 E-DPDCHs. Many thousands of different transmitter configurations are possible given the range of values possible for the gain parameters, number of codes, and spreading factors.
In the 3GPP release 99, the Radio Network Controller (RNC) controls resources and user mobility. Resource control in this context relates to admission control, congestion control, and channel switching (roughly changing the data rate of a connection). Furthermore, a dedicated connection is carried over a Dedicated Channel (DCH), which is realized as the DPCCH and the DPDCH.
In the evolved 3G standards, the trend is to decentralize decision making, and in particular the control over the short term data rate of the user connection. The uplink data is allocated to an Enhanced Dedicated Channel (E-DCH), which operates similarly to the DCH. The E-DCH is realized as the DPCCH, which is continuous; the E-DPCCH for data control; and the E-DPDCH for data. The two latter channels are only transmitted when there is uplink data in the send buffer to send. Hence the Node B uplink scheduler determines which transport formats each user may use over the E-DPDCH. The RNC, however, is still responsible for admission control.
For the DCH, the outer loop power control mechanism 12 adjusts the DPCCH_SIR target 16 to ensure that the DPDCH operates at the correct power level by monitoring whether or not the transport blocks are correctly received.
The data transmission configuration over E-DPDCH is predefined as a number of E-TFCs. Each E-TFC is associated with a number of data blocks, each with 320 data bits; a spreading factor; a number of scrambling codes; a power offset, which determines the E-DPDCH power relative the DPCCH power; a code rate for each transmission and subsequent retransmissions, if needed; and the like. Many aspects must be considered when determining how these parameters should be configured. The power offsets per E-TFC may be signaled to the UE, or may be computed by the UE. If the UE computes the E-TFC power offsets, the computation is based on the signaled power offsets of a set of reference E-TFCs.
The Node B scheduler allocates resources to UEs by signaling a maximum allowed power offset over the Absolute Grant Channel (AGCH). By comparing this maximum allowed power offset to the power offset per E-TFC, this restricts which E-TFCs the UE is allowed to use. The available power in the UE and the amount of data in the UE send buffer may further restrict which E-TFC that the UE will use when transmitting data.
The required E-DPDCH power to fulfill the outer loop depends primarily on the data rate and the code rate. The power increases with the data rate if the code rate is constant, and the power increases with the code rate. When transport formats are configured in a way that uses high code rates (>0.5), these transport formats provide relatively little data protection in terms of coding, and require relatively high signal quality at the receiver.
If the (signaled or calculated) power offset between the DPCCH and the E-DPDCH for a particular transport format is insufficient, it leads to many retransmissions. In response, the DPCCH_SIR target is increased in the outer loop power control, and therefore it has an impact on the transmitted power of all channels, including both the E-DPDCH and DPCCH, during the time period after the high code rate was used until the outer loop power control has converged to a lower level again. The increased DPCCH_SIR target also causes too many retransmissions of the current transport block since the outer loop is at a level too low for the E-TFC. The block error rate (BLER) also increases, as does retransmission at the RLC layer, which further increases the delay and the used power per transport block. This has a negative impact on the required power per bit for successful communication.
It would be advantageous to have a system and method that overcomes the disadvantages of the prior art by avoiding the power inefficient transport formats for data transmission. The present invention provides such a system and method.
The present invention provides a system and method that identifies power-inefficient transport formats and avoids them. The power inefficient transport formats may be identified, for example, by the code rate of the first transmission. The invention enables the use of high data rates while decreasing required power. The power reduction may be in the range of 25-30 percent.
Thus, in one aspect, the present invention is directed to a method in a mobile terminal for selecting a transport format for an uplink transmission to a base station. The method includes the steps of receiving parameters from the base station that describe a radio bearer configuration upon establishing a radio connection with the base station; generating a set of transport formats based upon the radio bearer parameters; and classifying each of the transport formats in the set as either power-efficient or power-inefficient. The method also includes receiving a grant from the base station; utilizing the grant to derive a set of allowed transport formats; and selecting a transport format that is both power-efficient and included in the set of allowed transport formats.
In another aspect, the present invention is directed to an arrangement in a mobile terminal for selecting a transport format for an uplink transmission to a base station. The arrangement includes means for generating a set of transport formats based upon parameters of a radio bearer for a radio connection with the base station; means for classifying each of the transport formats in the set as either power-efficient or power-inefficient; means for utilizing a grant received from the base station to derive a set of allowed transport formats; and means for selecting a transport format that is both power-efficient and included in the set of allowed transport formats.
In yet another aspect, the present invention is directed to a transport format selector in a mobile terminal for selecting a transport format for an uplink transmission to a base station, wherein the selector selects a transport format from a set of transport formats which are generated based upon parameters of a radio connection established with the base station. The selector includes means for accessing information regarding which transport formats in the set are power-efficient transport formats; means for accessing information regarding which transport formats in the set are allowed based upon a grant received from the base station; and means for selecting a transport format that is both power-efficient and allowed.
In one embodiment, the means for selecting a transport format includes means for selecting an allowed power-efficient transport format having the highest data rate that can be filled with the data in the mobile terminal send buffer. Hence, there is no meaning selecting a transport format with a higher data rate than what can be filled with the currently available data in the send buffer. In another embodiment, the selector determines a first allowed transport format having the highest data rate that can be be filled with the data in the mobile terminal send buffer, and if the determined first transport format is not power-efficient, the selector temporarily selects an allowed power-efficient second transport format with a data rate lower than the determined first transport format. This gradually increases the amount of data in the send buffer, and eventually the selector determines that there is enough data in the send buffer to fill an allowed power-efficient third transport format. This determined third transport format is then used for data transmission until the amount of data in the send buffer is decreased to a level that cannot fill the power-efficient third transport format. The selector then returns to an allowed power-efficient second transport format. The selector may continue to alternate between allowed power-efficient transport formats with data rates lower and higher than the determined first transport format, thereby averaging a data rate approximately equal to the highest data rate that corresponds to the amount of data in the send buffer, while utilizing only power-efficient transport formats. In some cases, if the send buffer has excess capacity, the selector may select a maximum-allowed transport format that is inefficient so as not to limit the maximum throughput of the mobile terminal.
In the following section, the invention will be described with reference to exemplary embodiments illustrated in the figures, in which:
The present invention provides a system and method that identifies power-inefficient transport formats and avoids them. When the radio bearer is established, the UE identifies the power-inefficient E-TFCs by computing the code rate of the first transmission attempt. Then, E-TFCs with a first transmission code rate of a threshold code rate (Cmax) or higher are considered power-inefficient. In different embodiments of the present invention, the threshold Cmax may be:
constant and predefined;
updated based on mode selections in the UE (for example, via selection of a power saving mode);
adapted to the battery status of the UE;
updated based on the number of retransmissions per E-TFC (code rate); or
updated based on the noise level in the network.
In a first embodiment of a process for selecting an E-TFC, the UE always avoids power-inefficient E-TFCs. Step 43 is characterized by setting Cmax at a threshold level to determine the number of power-inefficient E-TFCs that are excluded from use. For example, referring again to
In another embodiment, a first E-TFC is only considered power-inefficient if there exists at least one power-efficient second E-TFC, and the data rate of the second E-TFC is higher than the data rate of the first E-TFC. Using this power-inefficiency classification, groups A and B are classified as power inefficient (only group B for Cmax=0.6), while groups C and D are classified as power efficient since there are no power-efficient E-TFCs with higher data rates.
Each E-TFC is numbered by an EUL Transport Format Combination Indicator (E-TFCI) increasing with data rate. The UE may select an E-TFC using the following procedure. At step 51, the UE determines whether the data in the UE's send buffer can fill the maximum allowed E-TFC. If so, the process moves to step 52 where the UE selects the maximum E-TFC. The selection process then ends at step 53. However, if there is not enough data in the UE's send buffer to fill the maximum allowed E-TFC, the process moves to step 54, where the UE determines the highest E-TFC that data in the UE's send buffer can fill. This E-TFC is denoted as E-TFCI_1. At step 55, the UE determines whether E-TFCI_1 is power-efficient. If E-TFCI_1 is defined as power-efficient, the process moves to step 56 where E-TFC_1 is selected. The process then ends at step 57.
However, if E-TFCI_1 is defined as power-inefficient at step 55, the process moves to step 58 where the UE selects the highest power-efficient E-TFC among all E-TFCs lower than E-TFCI_1. With this process, the UE utilizes a lower data rate than required by the amount of data in the send buffer. However this, in turn, increases the amount of data in the send buffer size over time. Thus, in future TTIs, when the process is run again, the larger amount of data in the send buffer will result in the process moving to step 52 or step 56 where either the maximum allowed E-TFC or a power-efficient E-TFC_1 will be selected. Over a longer period of time, by alternating between data rates above and below the data rate corresponding to the power-inefficient E-TFCI_1, the average data rate approximates the data rate corresponding to the power-inefficient E-TFCI_1, while utilizing only power-efficient transport formats.
The RX 62 also receives a grant 68 from the BS 64. The grant is passed to an allowed E-TFC unit 69, which utilizes the grant to derive a set of allowed E-TFCs 71 that the UE is entitled to use. Identifiers of the power-efficient E-TFCs 72 and the allowed E-TFCs 71 are passed to an E-TFC selector 73, which selects an E-TFC for the transmission considering the allowed E-TFCs as well as whether the E-TFCs are power-efficient.
In one embodiment of the present invention, the E-TFC selector 73 sends a query 74 to a send buffer controller 75 requesting the amount of data in the UE's send buffer. The send buffer controller returns an indication of the amount of data in the send buffer. The E-TFC selector then determines whether the data in the send buffer can fill the maximum allowed E-TFC. If so, the E-TFC selector selects the maximum allowed E-TFC. However, if the data in the send buffer cannot fill the maximum allowed E-TFC, the E-TFC selector determines the highest E-TFC that data in the UE's send buffer can fill (i.e., E-TFCI_1). The E-TFC selector then determines whether E-TFCI_1 is power-efficient. If E-TFCI_1 is defined as power-efficient, the E-TFC selector selects E-TFC_1. However, if E-TFCI_1 is not power-inefficient, the E-TFC selector selects the highest power-efficient E-TFC among all E-TFCs lower than E-TFCI_1.
If E-TFCI_1 is not a power-efficient E-TFC, the E-TFC selector 73 performs the process illustrated in steps 56-58 of
The selected E-TFC 78 is sent to an encoder 79 and a transmitter (TX) 80 for uplink transmission to the base station 64.
It should also be recognized that in other embodiments of the present invention, different combinations of some or all of the E-TFC generator 65, power-efficiency classifier 67, allowed E-TFC unit 69, E-TFC selector 73, and to some extent the send buffer controller 75 may be implemented in a single unit referred to as an E-TFC selector.
As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed above, but is instead defined by the following claims.
