WO2013185319A1

WO2013185319A1 - Joint power control and rate adjustment scheme for voip

Info

Publication number: WO2013185319A1
Application number: PCT/CN2012/076896
Authority: WO
Inventors: Minghai Feng; Hao Xu; Madhavan S. Vajapeyam; Yongbin Wei; Zhifei Fan; Jilei Hou
Original assignee: Qualcomm Incorporated
Priority date: 2012-06-14
Filing date: 2012-06-14
Publication date: 2013-12-19

Abstract

A method, an apparatus, and a computer program product for wireless communication are provided in which a radio access network such as LTE combats uplink channel fading using a combination of power control and rate control, including where fixed rate traffic is handled, including voice and video traffic. A modulation and coding scheme is selected for transmitting a packet at a substantially fixed data rate on a packet data network based on an expected channel condition. Transmission power is then adjusted based on a difference between the expected channel condition and the measured channel condition.

Description

JOINT POWER CONTROL AND RATE ADJUSTMENT SCHEME FOR VOIP

BACKGROUND

Field

[0001] The present disclosure relates generally to communication systems, and more particularly, to wireless packet data networks.

Background

[0002] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

[0003] These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple- input multiple- output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

In an aspect of the disclosure, a radio access network (RAN) such as LTE may combat uplink channel fading using a combination of power control and rate control. Power control and rate control may be made for a variety of types of data to be transmitted with quality of service (QoS) requirements, including where the QoS requirements define a fixed rate for transmission including, for example, voice over Internet Protocol (VoIP) traffic.

In an aspect of the disclosure, a modulation and coding scheme (MCS) is selected for transmitting a packet at a substantially fixed data rate on a packet data network. The MCS may be selected based on an expected channel condition. A difference between the expected channel condition and a corresponding measured channel condition is determined during transmission of the packet, and transmission power is adjusted based on the difference between the expected channel condition and the measured channel condition, wherein the transmission power is adjusted to maintain the fixed data rate.

In an aspect of the disclosure, the substantially fixed data rate may be defined by a quality of service requirement associated with the packet.

In an aspect of the disclosure, the substantially fixed data rate is defined based on a type of the packet. The packet comprises voice over internet protocol data.

In an aspect of the disclosure, the expected channel condition comprises an expected uplink signal to interference plus noise ratio (SINR) of a user equipment (UE) transmitting the packet. The expected SINR may be based on an average SINR measured for the UE. Determining the difference between the expected channel condition and the measured channel condition may include determining an updated SINR for the UE during transmission of the packet. The updated SINR may be determined based on a difference between a block error rate (BLER) measured during transmission of the packet and a predefined target BLER. In one example, the UE transmission power may be adjusted at the UE based on the updated SINR. In another example, the transmission power of the UE based on an SINR measured during transmission of the packet.

[0009] In an aspect of the disclosure, MCS is reselected periodically repeated. The difference between the expected channel condition and the corresponding measured condition may be determined and the transmission power may be adjusted more than once between successive selections of the MCS.

[0010] In an aspect of the disclosure, the MCS may be selected by determining whether transmission of a packet from a previous period has completed at the commencement of a current period, and selecting an MCS to provide additional capacity sufficient to complete transmission of all packets available for transmission at the commencement of the current period.

[0011] In an aspect of the disclosure, the MCS is reselected based on an adjustment responsive to a group MCS command sent to a UE when the UE is configured using semi-persistent scheduling.

[0012] In an aspect of the disclosure, the MCS is selected by determining whether transmission of a packet from a previous period has completed at the start of a current period, and selecting an MCS with sufficient physical resource blocks to complete transmission of all packets available for transmission at the start of the current period.

[0013] In an aspect of the disclosure, transmission power is adjusted by enabling a UE to obtain additional power compensation through a radio resource control signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a diagram illustrating an example of a network architecture.

[0015] FIG. 2 is a diagram illustrating an example of an access network.

[0016] FIG. 3 is a diagram illustrating an example of a DL frame structure in LTE.

[0017] FIG. 4 is a diagram illustrating an example of an UL frame structure in LTE.

[0018] FIG. 5 is a diagram illustrating an example of a radio protocol architecture for the user and control planes.

[0019] FIG. 6 is a diagram illustrating an example of an evolved Node B and user equipment in an access network.

[0020] FIG. 7 is a timing diagram illustrating rate control and power control in an access network. [0021] FIG. 8 is a diagram illustrating selection of transport block size in an access network.

[0022] FIG. 9 is a flow chart of a method of wireless communication.

[0023] FIG. 10 is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus.

[0024] FIG. 11 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements"). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a "processing system" that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0028] Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer- readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0029] FIG. 1 is a diagram illustrating an LTE network architecture 100. The LTE network architecture 100 may be referred to as an Evolved Packet System (EPS) 100. The EPS 100 may include one or more UE 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 104, an Evolved Packet Core (EPC) 110, a Home Subscriber Server (HSS) 120, and an Operator's IP Services 122. The EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown. As shown, the EPS provides packet- switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit- switched services.

[0030] The E-UTRAN includes the evolved Node B (eNB) 106 and other eNBs 108.

The eNB 106 provides user and control planes protocol terminations toward the UE 102. The eNB 106 may be connected to the other eNBs 108 via a backhaul (e.g., an X2 interface). The eNB 106 may also be referred to as a base station, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The eNB 106 provides an access point to the EPC 110 for a UE 102. Examples of UEs 102 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, or any other similar functioning device. The UE 102 may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

[0031] The eNB 106 is connected by an SI interface to the EPC 110. The EPC 110 includes a Mobility Management Entity (MME) 112, other MMEs 114, a Serving Gateway 116, and a Packet Data Network (PDN) Gateway 118. The MME 112 is the control node that processes the signaling between the UE 102 and the EPC 110. Generally, the MME 112 provides bearer and connection management. All user IP packets are transferred through the Serving Gateway 116, which itself is connected to the PDN Gateway 118. The PDN Gateway 118 provides UE IP address allocation as well as other functions. The PDN Gateway 118 is connected to the Operator's IP Services 122. The Operator's IP Services 122 may include the Internet, the Intranet, an IP Multimedia Subsystem (IMS), and a PS Streaming Service (PSS).

[0032] FIG. 2 is a diagram illustrating an example of an access network 200 in an LTE network architecture. In this example, the access network 200 is divided into a number of cellular regions (cells) 202. One or more lower power class eNBs 208 may have cellular regions 210 that overlap with one or more of the cells 202. The lower power class eNB 208 may be a femto cell (e.g., home eNB (HeNB)), pico cell, micro cell, or remote radio head (RRH). The macro eNBs 204 are each assigned to a respective cell 202 and are configured to provide an access point to the EPC 110 for all the UEs 206 in the cells 202. There is no centralized controller in this example of an access network 200, but a centralized controller may be used in alternative configurations. The eNBs 204 are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway 116.

[0033] The modulation and multiple access scheme employed by the access network

200 may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the DL and SC-FDMA is used on the UL to support both frequency division duplexing (FDD) and time division duplexing (TDD). As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W- CDMA) and other variants of CDMA, such as TD-SCDMA; Global System for Mobile Communications (GSM) employing TDMA; and Evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDM employing OFDM A. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.

[0034] The eNBs 204 may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNBs 204 to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data steams may be transmitted to a single UE 206 to increase the data rate or to multiple UEs 206 to increase the overall system capacity. This is achieved by spatially precoding each data stream (i.e., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the DL. The spatially precoded data streams arrive at the UE(s) 206 with different spatial signatures, which enables each of the UE(s) 206 to recover the one or more data streams destined for that UE 206. On the UL, each UE 206 transmits a spatially precoded data stream, which enables the eNB 204 to identify the source of each spatially precoded data stream.

[0035] Spatial multiplexing is generally used when channel conditions are good. When channel conditions are less favorable, beamforming may be used to focus the transmission energy in one or more directions. This may be achieved by spatially precoding the data for transmission through multiple antennas. To achieve good coverage at the edges of the cell, a single stream beamforming transmission may be used in combination with transmit diversity.

[0036] In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system supporting OFDM on the DL. OFDM is a spread- spectrum technique that modulates data over a number of subcarriers within an OFDM symbol. The subcarriers are spaced apart at precise frequencies. The spacing provides "orthogonality" that enables a receiver to recover the data from the subcarriers. In the time domain, a guard interval (e.g., cyclic prefix) may be added to each OFDM symbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak- to-average power ratio (PAPR).

[0037] FIG. 3 is a diagram 300 illustrating an example of a DL frame structure in LTE.

A frame (10 ms) may be divided into 10 equally sized sub-frames. Each sub-frame may include two consecutive time slots. A resource grid may be used to represent two time slots, each time slot including a resource block. The resource grid is divided into multiple resource elements. In LTE, a resource block contains 12 consecutive subcarriers in the frequency domain and, for a normal cyclic prefix in each OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84 resource elements. For an extended cyclic prefix, a resource block contains 6 consecutive OFDM symbols in the time domain and has 72 resource elements. Some of the resource elements, as indicated as R 302, 304, include DL reference signals (DL-RS). The DL-RS include Cell-specific RS (CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS) 304. UE-RS 304 are transmitted only on the resource blocks upon which the corresponding physical DL shared channel (PDSCH) is mapped. The number of bits carried by each resource element depends on the modulation scheme. Thus, the more resource blocks that a UE receives and the higher the modulation scheme, the higher the data rate for the UE.

[0038] FIG. 4 is a diagram 400 illustrating an example of an UL frame structure in

LTE. The available resource blocks for the UL may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The UL frame structure results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section.

[0039] A UE may be assigned resource blocks 410a, 410b in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks 420a, 420b in the data section to transmit data to the eNB. The UE may transmit control information in a physical UL control channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in a physical UL shared channel (PUSCH) on the assigned resource blocks in the data section. A UL transmission may span both slots of a subframe and may hop across frequency.

[0040] A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH) 430. The PRACH 430 carries a random sequence and cannot carry any UL data/signaling. Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried in a single subframe (1 ms) or in a sequence of few contiguous subframes and a UE can make only a single PRACH attempt per frame (10 ms).

[0041] FIG. 5 is a diagram 500 illustrating an example of a radio protocol architecture for the user and control planes in LTE. The radio protocol architecture for the UE and the eNB is shown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1 (LI layer) is the lowest layer and implements various physical layer signal processing functions. The LI layer will be referred to herein as the physical layer 506. Layer 2 (L2 layer) 508 is above the physical layer 506 and is responsible for the link between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control (MAC) sublayer 510, a radio link control (RLC) sublayer 512, and a packet data convergence protocol (PDCP) 514 sublayer, which are terminated at the eNB on the network side. Although not shown, the UE may have several upper layers above the L2 layer 508 including a network layer (e.g., IP layer) that is terminated at the PDN gateway 118 on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radio bearers and logical channels. The PDCP sublayer 514 also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNBs. The RLC sublayer 512 provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ). The MAC sublayer 510 provides multiplexing between logical and transport channels. The MAC sublayer 510 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNB is substantially the same for the physical layer 506 and the L2 layer 508 with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516 is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE.

FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650 in an access network. In the DL, upper layer packets from the core network are provided to a controller/processor 675. The controller/processor 675 implements the functionality of the L2 layer. In the DL, the controller/processor 675 provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE 650 based on various priority metrics. The controller/processor 675 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE 650.

[0046] The transmit (TX) processor 616 implements various signal processing functions for the LI layer (i.e., physical layer). The signal processing functions includes coding and interleaving to facilitate forward error correction (FEC) at the UE 650 and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase- shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols are then split into parallel streams. Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 674 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 650. Each spatial stream is then provided to a different antenna 620 via a separate transmitter 618TX. Each transmitter 618TX modulates an RF carrier with a respective spatial stream for transmission.

[0047] At the UE 650, each receiver 654RX receives a signal through its respective antenna 652. Each receiver 654RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 656. The RX processor 656 implements various signal processing functions of the LI layer. The RX processor 656 performs spatial processing on the information to recover any spatial streams destined for the UE 650. If multiple spatial streams are destined for the UE 650, they may be combined by the RX processor 656 into a single OFDM symbol stream. The RX processor 656 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, is recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB 610. These soft decisions may be based on channel estimates computed by the channel estimator 658. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB 610 on the physical channel. The data and control signals are then provided to the controller/processor 659.

The controller/processor 659 implements the L2 layer. The controller/processor can be associated with a memory 660 that stores program codes and data. The memory 660 may be referred to as a computer-readable medium. In the UL, the controller/processor 659 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then provided to a data sink 662, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink 662 for L3 processing. The controller/processor 659 is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.

In the UL, a data source 667 is used to provide upper layer packets to the controller/processor 659. The data source 667 represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNB 610, the controller/processor 659 implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNB 610. The controller/processor 659 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB 610.

Channel estimates derived by a channel estimator 658 from a reference signal or feedback transmitted by the eNB 610 may be used by the TX processor 668 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 668 are provided to different antenna 652 via separate transmitters 654TX. Each transmitter 654TX modulates an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNB 610 in a manner similar to that described in connection with the receiver function at the UE 650. Each receiver 618RX receives a signal through its respective antenna 620. Each receiver 618RX recovers information modulated onto an RF carrier and provides the information to a RX processor 670. The RX processor 670 may implement the LI layer. The controller/processor 675 implements the L2 layer. The controller/processor 675 can be associated with a memory 676 that stores program codes and data. The memory 676 may be referred to as a computer-readable medium. In the UL, the control/processor 675 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE 650. Upper layer packets from the controller/processor 675 may be provided to the core network. The controller/processor 675 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

A RAN such as LTE may combat uplink channel fading using a combination of power control and rate control. The selection between power control and rate control may be made based on the type of data to be transmitted and QoS considerations associated with the data to be transmitted. Rate control is typically adopted for best effort traffic, and involves selecting an MCS according to channel condition to exploit the channel capacity. Power control is typically used for traffic that is subject to strict QoS control and has data transmission rates that are fixed or nearly constant. In one example, VoIP packets typically arrive at a fixed rate (every 20ms), and power control is more effective than rate control for guaranteeing low packet delay for VoIP traffic.

In the example of an LTE network, power control for PUSCH traffic may be calculated according to the equation: where:

the configured UE maximum transmitted power;

number of resource blocks valid for subframe ^:" ; and

is the downlink path-loss estimate calculated in the UE in dB. An eNB may adjust the power of the UE to satisfy the QoS requirement while maintaining a fixed data transmission rate for the UE's rate or TB size (TBS) is fixed, or may apply a power offset &^€itar?k) and use a different rate.

In an LTE network, rate control may be used to maintain relatively constant transmit power. The eNB may adapt the MCS and resource block (RB) allocations according to the estimated channel conditions for the UE. A power control algorithm used for VoIP traffic may result in a user's rate or transport block (TB) size being fixed and the eNB may consequently adjust a user's power to satisfy QoS requirement. While a power control arrangement offers increased efficiencies for VoIP over rate control schemes from a QoS perspective, it is relatively inefficient with regard to VoIP capacity because rate adaptation generally achieves better link efficiency than power control in fading channels.

[0056] Certain embodiments provide systems and methods that improve VoIP system performance by adjusting both power and rate from the perspective of the eNB. FIG. 7 is a diagram 700 illustrating a processing timeline for joint power and rate control. In certain embodiments, power control and rate adjustments may be jointly considered for VOIP uplink transmission. In the example depicted in FIG. 7, a user's average uplink SINR may be calculated during a rate adjustment period *i by assuming uplink transmit power tsisiis obtained under open loop power control: where denotes maximum transmit power, is the number of assigned RBs resource assigned, and ^ is the path-loss. Actual transmit power may be known based on power control command and power headroom.

[0057] At the beginning 702 of each rate adjustment period !l 724, an MCS and number of physical resource blocks (PRBs) may be selected according to the user's average SINR, which may be calculated as described above, for example. The MCS and number of PRBs may be determined based on average SINR during rate adjustment period ll 724, assuming open loop power control. With reference also to FIG. 8, a TBS with higher equivalent coding rate can be selected for higher average SINRs. For example, TBS candidates may include the combinations identified at coordinates (16,1), (10,2), (7,3), (5,4), (4,5), (3,6), (2,8), (1,9), (0,12) in the table 800. Each candidate has an actual block size of 328 bits for VoIP packets. The coordinates identify an index of transport block size (I_TBS) 804, and a number of PRBs (N_PRB) 802, each candidate being denoted by coordinates (I_TBS, N_PRB). AS discussed below, other TBS can be selected when multiple VOIP packets are combined for transmission.

[0058] Within the rate adjustment period * 724, outer loop power control 722 may be used to adjust a target SINR 704 for the selected rate by comparing the average BLER with a predefined target BLER. Inner loop power control 726 may be employed to adjust the user's power by comparing decoded SINR with the target SINR at 706. In some embodiments, MCS may be reselected 708 when another rate adjustment period occurs and power control may be implemented accordingly. One or more power adjustments may occur between MCS reselections.

[0059] Referring again to FIG. 8, certain embodiments employ joint power control and rate control in conjunction with packet aggregation. FIG. 8 illustrates a transport block size lookup table that may be used for TBS/MCS/PRB selection in a VoIP system which uses rate adaption. In one example, a TBS of 328 with higher equivalent coding rate selected for higher average SINRs may be found for various combinations of I_TBs and N_PRB (including at 806). In some embodiments, the power and rate control algorithms described herein are combined with packet aggregation, which may result, for example, in a TBS 680 (e.g. at 808) being selected during TBS/MCS/PRB selection for a VoIP system. The larger TBS may be selected when multiple packets are to be transmitted simultaneously. For example, when a VoIP packet arrives or is queued for transmission before a prior VOIP packet has been transmitted, then a TB size can be selected which is roughly twice the size used for one VoIP packet. As illustrated in FIG. 9, increasing TB size may be accomplished by increasing MCS and/or increasing PRB.

[0060] In certain embodiments, MCS may be dynamically adjusted using semi- persistent scheduling (SPS), which may be used for certain VoIP traffic to reduce PDCCH overhead. However, the grant is typically fixed when SPS is used and rate and/or TB size cannot be changed as a consequence. In some embodiments, group MCS control may be used. A group MCS adjustment command may be defined in similar terms as a group power control command through which group power can be changed. In group MCS adjustment, the eNB can signal the UE for a one time MCS adjustment. The MCS adjustment range can be predefined or preconfigured according to operator preferences and policies, or in accordance with industry standards. In some embodiments the MCS adjustment range is signaled in RRC transmitted to the UE.

[0061] Upon reception of a group MCS control command, a UE may adopt an increased or decreased MCS. Group MCS control commands and other information may be signaled to a group of UEs to reduce the signaling overhead in a manner similar to that of group power control command signaling. Certain embodiments provide methods for optimizing delta JACS. Rate control, power control may be combined with a delta JACS adjustment in a manner similar to that used for the power control formula described elsewhere herein. The variable delta_MCS may be used in LTE, for example, to control the uplink modulation coding scheme. The delta JACS variable may be signaled by RRC. In one example, delta_MCS may be turned on for VoIP traffic, as shown in the power control formula, when joint rate and power control are used. Accordingly, VoIP traffic can have additional power as needed. In another example, delta_MCS may be disabled for obtaining additional power compensation, and thereafter closed loop power control correction may be relied upon. In another example, a group MCS command may be used to dynamically turn the delta_MCS on or off.

FIG. 9 is a flow chart 900 of a method of wireless communication. The method may be performed by an eNB. At step 902, the eNB selects an MCS for transmitting a packet at a substantially fixed data rate on a packet data network. The MCS may be selected based on an expected channel condition. The substantially fixed data rate may be defined as a minimum or target data rate by a quality of service requirement associated with the packet and/or a type of the packet. For example, when the packet comprises a VoIP data packet, a QoS setting may be define a minimum data rate for the packet to ensure that time- sensitive data is received in a timely manner. Data rate may be dictated for other types of traffic, including video traffic. The actual data rate achieved during transmission may be more or less than the target data rate because of BLER for the transmission.

At step 904, the eNB determines a difference between the expected channel condition and a corresponding measured channel condition during transmission of the packet. The expected channel condition may comprise an expected uplink SINR of a UE transmitting the packet. The expected SINR may be based on an average SINR measured for the UE.

In some embodiments, the difference between the expected channel condition and the measured channel condition may be determined or expressed as an updated SINR for the UE during transmission of the packet. The updated SINR may be determined based on a difference between a BLER measured during transmission of the packet and a predefined target BLER for the selected MCS.

At step 906, the eNB adjusts transmission power based on the difference between the expected channel condition and the measured channel condition. The transmission power may be adjusted to maintain the fixed data rate. In one example, the transmission power of the UE may be adjusted based on the updated SINR. In another example, the transmission power of the UE may be adjusted based on an SINR measured during transmission of the packet.

In some embodiments, the MCS may be periodically reselected at predefined intervals. The difference between the expected channel condition and the corresponding measured condition may be determined and the transmission power may be adjusted more frequently than reselecting an MSC and thus the transmission power may be adjusted more than once between successive steps of selecting the MCS.

In some embodiments, the MCS is selected based on a determination of whether transmission of a packet from a previous period has completed at the commencement of a current period. Such previous packet may be partially transmitted or may be queued for transmission. An MCS may be selected to provide additional capacity for transmitting the previous packet or packets, in addition to one or more current or newly queued packets. The MCS may be selected to provide sufficient capacity for completion of the VoIP or other fixed rate data within the required time. In some embodiments, the eNB may allocate sufficient bandwidth to the fixed rate channel to complete transmission of all packets available for transmission at the commencement of the current period by the end of the current period.

In some embodiments, the MCS is selected and/or reselected by determining whether transmission of a packet from a previous period has completed at the start of a current period and selecting an MCS with sufficient physical resource blocks to complete transmission of all packets available for transmission at the start of the current period.

In some embodiments, the MCS is reselected based on an adjustment responsive to a group MCS command that may be sent to one or more UEs when semi- persistent scheduling is used.

In some embodiments, transmission power is adjusted by enabling a UE to obtain additional power compensation through a delta_MCS parameter transmitted using an RRC signal.

FIG. 10 is a conceptual data flow diagram 1000 illustrating the data flow between different modules/means/components in an exemplary apparatus 1002. The apparatus may comprise an eNB. The apparatus includes a receiving module 1004 that receives and decodes signals from a UE, a channel determining module that module 1006 that determines channel conditions and differences between the expected channel condition and a corresponding measured channel condition during transmission, a power adjusting module 1008 responsive to differences between the expected channel condition and the measured channel condition, a rate determining module 1010 that selects a MCS for transmitting a packet, including packets to be transmitted at a substantially fixed data rate, and a transmission module 1012 for transmitting signals to the UE.

[0073] The apparatus may include additional modules that perform each of the steps of the algorithm in the aforementioned timing chart of FIG. 7 and flow chart of FIG. 9. As such, each step in the aforementioned flow charts of FIGs. 7 and 9 may be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

[0074] FIG. 11 is a diagram 1100 illustrating an example of a hardware implementation for an apparatus 1002' employing a processing system 1114. The processing system 1114 may be implemented with a bus architecture, represented generally by the bus 1124. The bus 1124 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1114 and the overall design constraints. The bus 1124 links together various circuits including one or more processors and/or hardware modules, represented by the processor 1104, the modules 1004, 1006, 1008, 1010, 1012, and the computer-readable medium 1106. The bus 1124 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

[0075] The processing system 1114 may be coupled to a transceiver 1110. The transceiver 1110 is coupled to one or more antennas 1120. The transceiver 1110 provides a means for communicating with various other apparatus over a transmission medium. The processing system 1114 includes a processor 1104 coupled to a computer-readable medium 1106. The processor 1104 is responsible for general processing, including the execution of software stored on the computer- readable medium 1106. The software, when executed by the processor 1104, causes the processing system 1114 to perform the various functions described supra for any particular apparatus. The computer-readable medium 1106 may also be used for storing data that is manipulated by the processor 1104 when executing software. The processing system further includes at least one of the 1004, 1006, 1008, 1010, and 1012. The modules may be software modules running in the processor 1104, resident/stored in the computer readable medium 1106, one or more hardware modules coupled to the processor 1104, or some combination thereof. The processing system 1114 may be a component of the eNB 610 and may include the memory 676 and/or at least one of the TX processor 616, the RX processor 670, and the controller/processor 675.

[0076] In one configuration, the apparatus 1002/1002' for wireless communication includes means 1010 for selecting an MCS for transmitting a packet at a substantially fixed data rate on a packet data network, means 1006 for determining a difference between the expected channel condition and a corresponding measured channel condition during transmission of the packet, and means 1008 for adjusting transmission power based on the difference between the expected channel condition and the measured channel condition.

[0077] The aforementioned means may be one or more of the aforementioned modules of the apparatus 1002 and/or the processing system 1114 of the apparatus 1002' configured to perform the functions recited by the aforementioned means. As described supra, the processing system 1114 may include the TX Processor 616, the RX Processor 670, and the controller/processor 675. As such, in one configuration, the aforementioned means may be the TX Processor 616, the RX Processor 670, and the controller/processor 675 configured to perform the functions recited by the aforementioned means.

[0078] It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

[0079] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more." Unless specifically stated otherwise, the term "some" refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase "means for."

WHAT IS CLAIMED IS:

Claims

1. A method of wireless communication, comprising:

selecting a modulation and coding scheme (MCS) for transmitting a packet at a substantially fixed data rate on a packet data network, wherein the MCS is selected based on an expected channel condition;

determining a difference between the expected channel condition and a corresponding measured channel condition during transmission of the packet; and

adjusting transmission power based on the difference between the expected channel condition and the measured channel condition, wherein the transmission power is adjusted to maintain the fixed data rate.

2. The method of claim 1, wherein the substantially fixed data rate is defined by a quality of service requirement associated with the packet.

3. The method of claim 1, wherein the substantially fixed data rate is defined based on a type of the packet.

4. The method of claim 3, wherein the packet comprises voice over internet protocol data.

5. The method of claim 1, wherein the expected channel condition comprises an expected uplink signal to interference plus noise ratio (SINR) of a user equipment (UE) transmitting the packet.

6. The method of claim 5, wherein the expected SINR is based on an average SINR measured for the UE.

7. The method of claim 5, wherein determining the difference between the expected channel condition and the measured channel condition includes determining an updated SINR for the UE during transmission of the packet.

8. The method of claim 7, wherein the updated SINR is determined based on a difference between a block error rate (BLER) measured during transmission of the packet and a predefined target BLER.

9. The method of claim 8, wherein adjusting transmission power includes adjusting transmission power of the UE based on the updated SINR.

10. The method of claim 5, wherein adjusting transmission power includes adjusting transmission power of the UE based on a SINR measured during transmission of the packet.

11. The method of claim 1, further comprising periodically repeating the step of selecting the MCS, wherein the steps of determining the difference between the expected channel condition and the corresponding measured condition and adjusting the transmission power are performed more than once between successive steps of selecting the MCS.

12. The method of claim 11, wherein selecting the MCS includes:

determining whether transmission of a packet from a previous period has completed at the commencement of a current period; and

selecting an MCS to provide additional capacity sufficient to complete transmission of all packets available for transmission at the commencement of the current period.

13. The method of claim 11, wherein the MCS is reselected based on an adjustment responsive to a group MCS command sent to a UE when the UE is configured using semi-persistent scheduling.

14. The method of claim 11, wherein selecting the MCS includes:

determining whether transmission of a packet from a previous period has completed at the start of a current period; and

selecting an MCS with sufficient physical resource blocks to complete transmission of all packets available for transmission at the start of the current period.

15. The method of claim 1, wherein adjusting transmission power includes enabling a UE to obtain additional power compensation through a radio resource control signal.

16. An apparatus for wireless communication, comprising:

means for selecting a modulation and coding scheme (MCS) for transmitting a packet at a substantially fixed data rate on a packet data network, wherein the MCS is selected based on an expected channel condition;

means for determining a difference between the expected channel condition and a corresponding measured channel condition during transmission of the packet; and means for adjusting transmission power based on the difference between the expected channel condition and the measured channel condition, wherein the transmission power is adjusted to maintain the fixed data rate.

17. The apparatus of claim 16, wherein the substantially fixed data rate is defined by a quality of service requirement associated with the packet.

18. The apparatus of claim 16, wherein the substantially fixed data rate is defined based on a type of the packet.

19. The apparatus of claim 18, wherein the packet comprises voice over internet protocol data.

20. The apparatus of claim 16, wherein the expected channel condition comprises an expected uplink signal to interference plus noise ratio (SINR) of a user equipment (UE) transmitting the packet.

21. The apparatus of claim 20, wherein the expected SINR is based on an average SINR measured for the UE.

22. The apparatus of claim 20, wherein the difference between the expected channel condition and the measured channel condition is determined by determining an updated SINR for the UE during transmission of the packet.

23. The apparatus of claim 22, wherein the updated SINR is determined based on a difference between a block error rate (BLER) measured during transmission of the packet and a predefined target BLER.

24. The apparatus of claim 23, wherein transmission power is adjusted by adjusting transmission power of the UE based on the updated SINR.

25. The apparatus of claim 20, wherein transmission power is adjusted by adjusting transmission power of the UE based on an SINR measured during transmission of the packet.

26. The apparatus of claim 16, wherein the MCS is periodically reselected, and wherein the difference between the expected channel condition and the corresponding measured condition is determined and the transmission power is adjusted more than once between successive reselections of the MCS.

27. The apparatus of claim 26, wherein the MCS is selected by determining whether transmission of a packet from a previous period has completed at the commencement of a current period, and selecting an MCS to provide additional capacity sufficient to complete transmission of all packets available for transmission at the commencement of the current period.

28. The apparatus of claim 26, wherein the MCS is reselected through an adjustment responsive to a group MCS command sent to a UE when the UE is configured using semi-persistent scheduling.

29. The apparatus of claim 26, wherein the MCS is selected by determining whether transmission of a packet from a previous period has completed at the start of a current period, and selecting an MCS with sufficient physical resource blocks to complete transmission of all packets available for transmission at the start of the current period.

30. The apparatus of claim 16, wherein the transmission power is adjusted by enabling a UE to obtain additional power compensation through a radio resource control signal.

31. An apparatus for wireless communication, comprising:

a processing system configured to:

select a modulation and coding scheme (MCS) for transmitting a packet at a substantially fixed data rate on a packet data network, wherein the MCS is selected based on an expected channel condition;

determine a difference between the expected channel condition and a corresponding measured channel condition during transmission of the packet; and

adjust transmission power based on the difference between the expected channel condition and the measured channel condition, wherein the transmission power is adjusted to maintain the fixed data rate.

32. The apparatus of claim 31, wherein the substantially fixed data rate is defined by a quality of service requirement associated with the packet.

33. The apparatus of claim 31, wherein the substantially fixed data rate is defined based on a type of the packet.

34. The apparatus of claim 33, wherein the packet comprises voice over internet protocol data.

35. The apparatus of claim 31, wherein the expected channel condition comprises an expected uplink signal to interference plus noise ratio (SINR) of a user equipment (UE) transmitting the packet.

36. The apparatus of claim 35, wherein the expected SINR is based on an average SINR measured for the UE.

37. The apparatus of claim 35, wherein the processing system determines the difference between the expected channel condition and the measured channel condition by determining an updated SINR for the UE during transmission of the packet.

38. The apparatus of claim 37, wherein the updated SINR is determined based on a difference between a block error rate (BLER) measured during transmission of the packet and a predefined target BLER.

39. The apparatus of claim 38, wherein the processing system adjusts transmission power by adjusting transmission power of the UE based on the updated SINR.

40. The apparatus of claim 35, wherein the processing system adjusts transmission power by adjusting transmission power of the UE based on an SINR measured during transmission of the packet.

41. The apparatus of claim 31, wherein the processing system reselects the MCS repetitively, wherein the processing system determines the difference between the expected channel condition and the corresponding measured condition and adjusting the transmission power more than once between successive reselections of the MCS.

42. The apparatus of claim 41, wherein the processing system selects the MCS by determining whether transmission of a packet from a previous period has completed at the commencement of a current period, and selecting an MCS to provide additional capacity sufficient to complete transmission of all packets available for transmission at the commencement of the current period.

43. The apparatus of claim 41, wherein the MCS is reselected based on an adjustment responsive to a group MCS command sent to a UE when the UE is configured using semi-persistent scheduling.

44. The apparatus of claim 41, wherein the processing system selects the MCS by determining whether transmission of a packet from a previous period has completed at the start of a current period, and selecting an MCS with sufficient physical resource blocks to complete transmission of all packets available for transmission at the start of the current period.

45. The apparatus of claim 31, wherein the processing system adjusts transmission power by enabling a UE to obtain additional power compensation through a radio resource control signal.

46. A computer program product, comprising:

a computer-readable medium comprising code for:

during transmission of the packet, determining a difference between the expected channel condition and a corresponding measured channel condition; and

47. The computer program product of claim 46, wherein the substantially fixed data rate is defined by a quality of service requirement associated with the packet.

48. The computer program product of claim 46, wherein the substantially fixed data rate is defined based on a type of the packet.

49. The computer program product of claim 48, wherein the packet comprises voice over internet protocol data.

50. The computer program product of claim 46, wherein the expected channel condition comprises an expected uplink signal to interference plus noise ratio (SINR) of a user equipment (UE) transmitting the packet.

51. The computer program product of claim 50, wherein the expected SINR is based on an average SINR measured for the UE.

52. The computer program product of claim 50, wherein the difference between the expected channel condition and the measured channel condition is determined by determining an updated SINR for the UE during transmission of the packet.

53. The computer program product of claim 52, wherein the updated SINR is determined based on a difference between a block error rate (BLER) measured during transmission of the packet and a predefined target BLER.

54. The computer program product of claim 53, wherein transmission power is adjusted by adjusting transmission power of the UE based on the updated SINR.

55. The computer program product of claim 50, wherein transmission power is adjusted by adjusting transmission power of the UE based on an SINR measured during transmission of the packet.

56. The computer program product of claim 46, further comprising periodically reselecting the MCS, wherein the difference between the expected channel condition and the corresponding measured condition is determine and the transmission power is adjusted more than once between successive reselections of the MCS.

57. The computer program product of claim 56, wherein the MCS is selected by determining whether transmission of a packet from a previous period has completed at the commencement of a current period, and selecting an MCS to provide additional capacity sufficient to complete transmission of all packets available for transmission at the commencement of the current period.

58. The computer program product of claim 56, wherein the MCS is reselected based on an adjustment responsive to a group MCS command sent to a UE when the UE is configured using semi-persistent scheduling.

59. The computer program product of claim 56, wherein the MCS is selected by determining whether transmission of a packet from a previous period has completed at the start of a current period, and selecting an MCS with sufficient physical resource blocks to complete transmission of all packets available for transmission at the start of the current period.

60. The computer program product of claim 46, wherein transmission power is adjusted by enabling a UE to obtain additional power compensation through a radio resource control signal.