HK1142731A - Method and apparatus for multiplexing and power control of uplink control channels in a wireless communication system - Google Patents

Description

Method and apparatus for multiplexing and power controlling uplink control channel in wireless communication system

The present application claims priority from U.S. provisional application No.60/938,995 entitled "a METHOD and apparatus FOR UPLINK CONTROL CHANNEL multi-level feeding and controller CONTROL", filed on day 18, 5/2007, which is assigned to the assignee of the present application and is hereby expressly incorporated herein by reference.

Technical Field

The present disclosure relates generally to communication, and more specifically to techniques for sending control information in a wireless communication system.

Background

Wireless communication systems have been widely deployed to provide various communication content such as voice, video, packet data, messaging, broadcast, and so on. These wireless systems are multiple-access systems capable of supporting multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA (OFDMA) systems, and single-carrier FDMA (SC-FDMA) systems.

In a wireless communication system, a node B may transmit traffic data to a User Equipment (UE) on a downlink and/or receive traffic data from the UE on an uplink. The downlink (or forward link) refers to the communication link from the node bs (node bs) to the UEs, and the uplink (or reverse link) refers to the communication link from the UEs to the node bs. The UE may send Channel Quality Indicator (CQI) information to the node B indicating the downlink channel quality. The node B may select a rate or a transport format according to the CQI information and may transmit traffic data to the UE at the selected rate or transport format. The UE may send Acknowledgement (ACK) information for traffic data received from the node B. The node B may determine whether to retransmit the unfinished traffic data or transmit new traffic data to the UE according to the ACK information. To achieve good performance, ACK and CQI information needs to be reliably transmitted.

Disclosure of Invention

Techniques for transmitting control information in a wireless communication system are described herein. The system supports different control channels, e.g., ACK channels and CQI channels, which may have different performance requirements and different target signal-to-noise ratios (SNRs).

In an aspect, ACKs and CQIs from different UEs may be multiplexed on the same resource block. The ACK and CQI channels may be power controlled to achieve their target SNRs. In this case, interference from the CQI channel may degrade performance of the ACK channels. In one design, the transmit power for the CQI channel may be set as follows: (i) setting the CQI channel to achieve a nominal target SNR for the CQI when not multiplexed with the ACK channels; (ii) when multiplexed with the ACK channels, the CQI channels are reduced or backed off to achieve a lower target SNR. In another design, the transmit power for the ACK channels may be set as follows: (i) setting the ACK channel to achieve a nominal target SNR for ACK when not multiplexed with the CQI channel; (ii) when the ACK channel is multiplexed with the CQI channels, it is boosted to achieve a higher target SNR. In another design, a combination of backoff for the CQI channels and boost for the ACK channels may be employed when multiplexing the channels together.

Using a lower target SNR for the CQI channel and/or a higher target SNR for the ACK channel may reduce CQI performance when multiplexing the CQI channel and the ACK channel together. In one design, the CQI channel from the UE may hop randomly, such that the CQI channel may not always be multiplexed with the ACK channels and thus may experience performance degradation. In another design, the node B may perform erasure detection for the CQI channel when multiplexed with the ACK channels. The node B receives CQI reports from the CQI channel and uses the CQI reports if the CQI channel is reliable enough, otherwise it is discarded. In another design, the node B may perform detection with interference cancellation when the ACK and CQI channels are multiplexed together. The node B may first detect the ACK channel (which may be more reliable), then estimate and cancel the interference caused by the detected ACK channel, and then detect the CQI channel (which may be less reliable).

Various aspects and features of the disclosure are described in further detail below.

Drawings

Fig. 1 shows a wireless communication system.

Fig. 2 shows exemplary downlink and uplink transmissions.

Fig. 3 shows an exemplary transmission structure for uplink.

Fig. 4 shows an exemplary ACK structure.

Fig. 5 shows an exemplary CQI structure.

Fig. 6 shows a process for transmitting control information.

Fig. 7 shows an apparatus for transmitting control information.

Fig. 8 shows a process for transmitting a CQI channel.

Fig. 9 shows an apparatus for transmitting a CQI channel.

Fig. 10 shows a process for receiving control information.

Fig. 11 shows an apparatus for receiving control information.

Fig. 12 shows a block diagram of a node B and a UE.

Detailed Description

The techniques described herein may be used for various wireless communication systems, such as: CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other systems. The terms "system" and "network" are often used interchangeably. A CDMA system may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes wideband-CDMA (W-CDMA) and other CDMA variants. Further, cdma2000 covers IS-2000, IS-95 and IS-856 standards. TDMA systems may implement wireless technologies such as global system for mobile communications (GSM). OFDMA systems may implement, for example, evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-Etc. wireless technologies. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System (UMTS). 3GPP Long Term Evolution (LTE) is a release of UMTS that uses E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from an organization named "third Generation partnership project" (3 GPP). In addition, cdma2000 and UMB are described in documents from an organization named "third Generation Partnership Project 2(3rd Generation Partnership Project 2)" (3GPP 2). For clarity, certain aspects of these techniques are described below for LTE, and the terminology of LTE is used in much of the description below.

Fig. 1 illustrates a wireless communication system 100 with multiple node bs 110. A node B may be a fixed station that communicates with UEs and may also be referred to as an evolved node B (enb), a base station, an access point, etc. UEs 120 may be distributed throughout the system, and each UE may be stationary or mobile. A UE may also be called a mobile station, terminal, access terminal, subscriber unit, station, etc. The UE may be a cellular phone, a Personal Digital Assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop, a cordless phone, and so on. In this application, the terms "UE" and "user" may be used interchangeably.

Fig. 2 shows an exemplary downlink transmission by a node B and an exemplary uplink transmission by a UE. The transmission timeline may be divided into subframe units, each subframe having a predetermined duration, e.g., 1 millisecond (ms). The UE periodically estimates the quality of the downlink channel for the node B and sends CQI information on the CQI channel to the node B. The node B may use the CQI information and/or other information to select a UE for downlink transmission and an appropriate transmission format (e.g., modulation and coding scheme) for the UE. The node B processes the transport blocks to obtain corresponding codewords (codewords). The node B then sends the codeword transmission to the UE on a Physical Downlink Shared Channel (PDSCH) and corresponding control information to the UE on a Physical Downlink Control Channel (PDCCH). The UE processes the codeword transmission received from the node B and sends ACK information on an ACK channel. The ACK and CQI channels are part of a Physical Uplink Control Channel (PUCCH). If the codeword is decoded correctly, the ACK information includes ACK; the ACK information includes a Negative Acknowledgement (NAK) if the codeword is decoded with an error. The node B sends another transmission of the codeword if a NAK is received and sends a transmission of a new codeword if an ACK is received. Fig. 2 shows an example in which ACK information is delayed by two subframes. The ACK information may be delayed by other amounts of time.

Fig. 3 shows a design of a transmission structure 300 that may be used for the uplink. Each subframe may be divided into two slots. Each slot includes a fixed or configurable number of symbol periods, e.g., six symbol periods in the case of an extended cyclic prefix and seven symbol periods in the case of a normal cyclic prefix.

For the uplink, a total of K subcarriers are available and grouped into resource blocks. Each resource block includes N subcarriers (e.g., N-12 subcarriers) in one slot. The available resource blocks may be divided into a data portion and a control portion. The control portion is formed at both edges of the system bandwidth as shown in fig. 3. The control portion may have a configurable size, which may be selected according to the amount of control information transmitted by the UE on the uplink. The resource blocks in the control portion may be allocated to the UE for transmitting ACK information, CQI information, and the like. The data section includes all resource blocks not included in the control section. In general, any subset of the available resource blocks may be used for transmitting control information, and the remaining resource blocks may be used for transmitting traffic data.

The UE may be assigned resource blocks in the control portion to send ACK and/or CQI information to the node B. The ACK information may convey whether each transport block sent by the node B to the UE was decoded correctly or in error by the UE. The amount of ACK information to be sent by the UE depends on the number of transport blocks sent to the UE. In one design, the ACK information may include one or two ACK bits depending on whether one or two transport blocks are transmitted to the UE. In other designs, the ACK information may include more ACK bits.

The CQI information may convey the downlink channel quality estimated by the UE for the node B. The amount of CQI information sent by the UE depends on various factors such as the number of spatial channels available for downlink transmission, the format used to report the downlink channel quality, the granularity needed in the reported downlink channel quality, and so on. In one design, the CQI information may include 8,9, or 10 bits. In other designs, the CQI information may include fewer or more bits.

The UE may send ACK and/or CQI information on the PUCCH, which may be mapped to resource blocks in the control portion. In one design, two PUCCH structures are supported and may be referred to as an ACK structure and a CQI structure. The ACK structure is used only for sending ACK information. The CQI structure may be used for transmitting only CQI information or for transmitting ACK and CQI information. The ACK and CQI structure may also be referred to by other names. For example, the ACK structure may also be referred to as PUCCH format 0 or 1 depending on whether one or two ACK bits are transmitted. The CQI structure may also be referred to as PUCCH format 2.

Fig. 4 shows a design of an ACK structure 400 for the case where each slot includes 7 symbol periods. In each subframe, the left slot includes seven symbol periods 0 to 6, and the right slot includes seven symbol periods 7 to 13. A group of UEs may simultaneously send ACK information on a resource block pair, including: (i) one resource block in the top control portion in the left slot and one resource block in the bottom control portion in the right slot, as shown in fig. 4; or (ii) one resource block in the bottom control portion in the left slot and one resource block in the top control portion in the right slot (shown with diagonal lines in fig. 4). In the design shown in fig. 4, each resource block for ACK includes four symbol periods for data and three symbol periods for pilot. The data and pilot for the ACK may also be sent in other manners within the resource block.

Fig. 5 shows a design of a CQI structure 500 for the case where each slot includes seven symbol periods. In the design shown in fig. 5, each resource block for CQI includes five symbol periods for data and two symbol periods for pilot. The data and pilot for the CQI may also be sent in other manners within the resource block.

Table 1 lists some characteristics of the ACK and CQI structures consistent with one design.

TABLE 1-PUCCH structure

	ACK structure	CQI Structure
			Number of information bits	1 or 2	8 to 10
Encoding	Is free of	Block coding
			Modulation scheme	BPSK or QPSK	QPSK
Number of modulation symbols	1	10
			Number of symbol periods for data per slot	4	5
Number of channels supported	A maximum of 18 ACK channels	A maximum of 6 CQI channels

The ACK and CQI information may be sent in various ways. In one design, the UE may send ACK and CQI information using a reference signal sequence with good correlation properties. Different UEs may send ACK and/or CQI information on the same resource block using different reference signal sequences and may generate these reference signal sequences with a base sequence (base sequence). The base sequence may be a CAZAC (constant amplitude zero autocorrelation) sequence such as a Chu sequence, a Zardoff-Chu sequence, a Frank sequence, a generalized chirp-like (GCL) sequence, and the like. The base sequence may also be a sequence defined to have good correlation properties.

In one design, six reference signal sequences of length N-12 may be generated with six different cyclic shifts of a base sequence of length 12. In general, any number of reference signal sequences may be generated. In one design, the UE may use a single reference signal sequence for all symbol periods of a subframe. In another design, the UE may use different reference signal sequences for different symbol periods or different slots of the subframe. Such hopping can randomize interference.

The UE may send the ACK information in various ways. In one design, the UE first maps one or two bits of the ACK to a modulation symbol d (0) based on BPSK or QPSK, respectively. Then, the UE modulates the reference signal sequence r (n) allocated to the UE with the modulation symbol d (0), as follows:

y (N) ═ d (0) · r (N) where N ═ 0.., N-1 formula (1)

Where y (n) is the modulation sequence for ACK.

Then, the UE spreads (spread) the modulation sequence as follows:

z_m(N) ═ w (m) y (N) where N is 0

Where w (m) is the orthogonal sequence allocated to the UE for ACK data,

z_m(n) is the data sequence of ACK in symbol period m.

Four orthogonal sequences may be defined by a 4 x 4 Walsh matrix and one of the four orthogonal sequences may be assigned to the UE. In the design shown in equation (2), the UE may generate four data sequences z (x (y)) by multiplying the modulation sequence y (n) by four symbols w (0) to w (3) in the orthogonal sequence w (m) assigned to the UE, respectively₀(n) to z₃(n) of (a). Then, as shown in fig. 4, the UE may transmit the four data sequences in the four symbol periods 0, 1, 5, and 6 of the left-hand slot, and also in the four symbol periods 7, 8, 12, and 13 of the right-hand slot.

The UE may send the pilot for the ACK in various ways. In one design, the UE is assigned an orthogonal sequence q (m), where the orthogonal sequence is a set of three orthogonal sequences q (m) defined from a 3 x 3 Discrete Fourier Transform (DFT) matrix₀(m)、q₁(m) and q₂(m) is selected from (m). The UE spreads its reference signal sequence r (n) with three symbols q (0) to q (2) of q (m) in the orthogonal sequence allocated to it to obtain three pilot sequences p₀(n) to p₂(n) of (a). Then, as shown in fig. 4, the UE may transmit the three pilot sequences in three symbol periods 2, 3, and 4 of the left slot, and also in three symbol periods 9, 10, and 11 of the right slot.

A maximum of 18 UEs may use six reference signal sequences and three orthogonal sequences q₀(m)、q₁(m) or q₂(m) to simultaneously transmit the pilot for the ACK. A maximum of 24 UEs may use six reference signal sequences and four orthogonal sequences w₀(m) to w₃(m) simultaneously transmitting data of the ACK. In one design, 18 ACK channels may be defined with six reference signal sequences, three orthogonal sequences for pilot, and four orthogonal sequences for data. The number of ACK channels is limited to the number of UEs that can send pilots simultaneously. Each ACK channel is associated with a designated reference signal sequence r (n), a designated orthogonal sequence q (m) for pilot, and a designated orthogonal sequence w (m) for data. Up to 18 UEs may send their ACK information simultaneously on up to 18 ACK channels on the same resource block pair. These UEs may be distinguished by: (i) the distinction of the reference signal sequence in the frequency domain, (ii) the broadening in the time domain with orthogonal sequences.

The UE may send the CQI information in various ways. In one design, the UE may first encode 8 to 10 information bits for the CQI to obtain 20 code bits and map the 20 code bits to ten modulation symbols d (0) to d (9). The UE then modulates its reference signal sequence r (n) with each modulation symbol d (m), as follows:

c_m(N) ═ d (m) · r (N) where N ═ 0., N-1 and m ═ 0., 9 formula (2)

Wherein, c_m(n) is a data sequence of CQI in symbol period m. The UE generates ten data sequences c for ten modulation symbols d (0) to d (9), respectively₀(n) to c₉(n) of (a). The UE transmits the ten data sequences in ten symbol periods for CQI data in one resource block pair, e.g., as shown in fig. 5.

The UE may send the pilot for the CQI in various ways. In one design, the UE may use its reference signal sequence r (n) directly as a pilot sequence and may send its reference signal sequence in each symbol period of the pilot, e.g., as shown in fig. 5.

In one design, six CQI channels may be defined with six reference signal sequences. Each CQI channel is associated with a designated reference signal sequence r (n). Up to six UEs may simultaneously send data and pilot for CQI on up to six CQI channels on the same resource block pair. These UEs can be distinguished by the above-mentioned difference of the reference signal sequences in the frequency domain.

In one design, for the case of six symbol periods per slot, the data for the ACK may be sent in four symbol periods and the pilot for the ACK may be sent in two symbol periods. Data for CQI may also be sent in five symbol periods and pilot for CQI may be sent in one symbol period. Four reference signal sequences may be defined. Four CQI channels or eight ACK channels may be supported with one resource block pair.

In general, the number of ACK channels and the number of CQI channels that can be supported depends on various factors such as the number of symbol periods per slot, the number of symbol periods for data, the number of symbol periods for pilot, the number of reference signal sequences, and so on. For clarity, the following description assumes the designs shown in fig. 4 and 5 and table 1.

Up to 18 ACK channels may be sent on the same resource block pair, e.g., as shown in fig. 4. Up to six CQI channels may be sent on the same resource block pair as shown in fig. 5. The ACK and CQI channels may also be multiplexed on the same resource block pair. Each available reference signal sequence may be used for ACK or CQI. Each reference signal sequence may support three ACK channels or one CQI channel. These reference signal sequences are orthogonal to each other in the frequency domain. Thus, when the ACK and CQI channels are multiplexed on the same resource block, the pilot for CQI may overlap with the data for ACK and the pilot for ACK may overlap with the data for CQI. Table 2 lists seven configurations for multiplexing ACK and CQI channels and gives the number of ACK channels and the number of CQI channels in each configuration.

TABLE 2 multiplexing of ACK and CQI

Configuration of	Number of reference signal sequences for ACK	Number of reference signal sequences for CQI	Number of ACK channels	Number of CQI channels
					0	0	6	0	6
1	1	5	3	5
					2	2	4	6	4
3	3	3	9	3
					4	4	2	12	2
5	5	1	15	1
					6	6	0	18	0

In one design, the ACK resources may be implicitly allocated to the UE. The ACK resources allocated to a given UE include a resource block for ACK, a reference signal sequence r (n), an orthogonal sequence w (m) for data, and an orthogonal sequence q (m) for pilot. The node B may send control information to the UE on the PDCCH, as shown in fig. 2. Different PDCCH resources (or indices) may be mapped to different ACK resources. The UE determines ACK resources allocated to the UE according to PDCCH resources used to transmit control information to the UE. In one design, CQI resources may be explicitly allocated to a UE and signaled to the UE. The ACK and CQI resources may also be allocated in other manners.

The ACK channel may have certain performance requirements and certain received signal quality requirements. Similarly, a CQI channel may also have certain performance requirements and certain received signal quality requirements. These performance requirements may be given by a target block error rate (BLER), a target Bit Error Rate (BER), a target Packet Error Rate (PER), a target erasure rate (erasure rate), etc. These received signal quality requirements may be given by a target SNR, a target Power Spectral Density (PSD), a target received signal level, etc. The PSD and received signal level indicate the received power of the ACK or CQI channel at the node B. SNR is the ratio of received power to noise at the node B. When the noise is constant or known, the SNR and PSD are equivalent. The SNR may be given by the energy per symbol to noise ratio (Es/No), the energy per bit to total noise ratio (Eb/Nt), and so on.

When ACK channels from different UEs are multiplexed on the same resource block, power control can be utilized to adjust the transmit power of each ACK channel to achieve the target SNR for ACK. This target SNR is selected to achieve a target BLER for ACKs. Similarly, when CQI channels from different UEs are multiplexed on the same resource block, the transmit power of each CQI channel may be adjusted with power control to achieve the target SNR for CQI. This target SNR is chosen to achieve a target BLER for CQI. Orthogonality between ACK or CQI channels multiplexed on the same resource block may be maintained according to the following conditions:

the time delay spread (time delay spread) of the radio channel should be smaller than the time domain cyclic shift of the reference signal sequence;

power control should keep the long-term received SNR of the multiplexed ACK or CQI channels at a similar level;

the correlation time of the wireless channel should be longer than the walsh spreading for the ACK channel. For example, length-4 orthogonal sequences may be used for speeds below 120km/hr, while length-2 orthogonal sequences may be used for high speeds such as 350 km/hr.

Computer simulations indicate that the performance of the ACK channel is highly dependent on accurate power control. When ACK channels from different UEs have different long-term received SNRs, the performance of these ACK channels varies greatly and the performance of some ACK channels is not satisfactory. Simulation results indicate that power control should maintain the long-term received SNR of different ACK channels multiplexed on the same resource block at similar levels in order to achieve good performance for these ACK channels. Similarly, power control should also maintain the long-term received SNR of the different CQI channels multiplexed on the same resource blocks at similar levels in order to achieve good performance for these CQI channels.

The ACK and CQI channels from different UEs may be multiplexed together on the same resource block, e.g., as shown in configurations 1 through 5 in table 2. Power control may attempt to maintain each ACK channel at its target SNR and each CQI channel at its target SNR. However, even with power control operation as designed above, the overall performance of the ACK and CQI channels may be affected by the following reasons. The ACK and CQI channels may have different target SNRs. Thus, power control may result in a difference in PSD of the ACK and CQI channels. The difference in PSD may reduce the orthogonality between the ACK and CQI channels, resulting in mutual interference between these channels and resulting performance degradation.

Various schemes may be used to address the performance degradation caused by multiplexing the ACK and CQI channels on the same resource block. In one scheme, ACK and CQI channels from different UEs are sent on different resource blocks and are not multiplexed together. The ACK resources may be implicitly mapped to PDCCH resources. The node B then sends control information to the UE on the PDCCH, so that only ACK channels are multiplexed together. The node B may allocate CQI resources to the UE such that the CQI channels are not multiplexed with the ACK channels. The transmit power for the ACK channels and the transmit power for the CQI channels may be separately controlled to achieve the desired performance for ACK and CQI. This scheme may limit the operation of the scheduler of the node B.

In an aspect, ACK and CQI channels from different UEs may be multiplexed together on the same resource block. This allows the node B to freely send control information to the UE on the PDCCH without having to ensure that only ACK channels are multiplexed together. The target BLER and target SNR for the ACK channel may be different from the target BLER and target SNR for the CQI channel. For example, the target BLER for the ACK channel is 0.1% and the target SNR for each antenna is approximately 2.8 dB. In contrast, the target BLER for the CQI channel is 1%, and the target SNR per antenna is about 7 dB. If the ACK and CQI channels are separately power controlled to achieve their target SNRs, the performance of the ACK channels may be significantly degraded for the reasons described above. This degradation in ACK performance may be mitigated in various ways.

In one design, the transmit power for the CQI channel may be: (i) when the CQI channel is not multiplexed with the ACK channel, it is set to achieve a nominal target SNR (SNR)_{target_nom} ^CQI) (ii) a (ii) When multiplexed with the ACK channels, the CQI channels are throttled down or backed off to achieve a lower target SNR (SNR)_{target_lower} ^CQI)。SNR_{target_lower} ^CQISpecific SNR_{target_nom} ^CQILow X decibels (dB), where X is the backoff factor and may be a predetermined magnitude. In this design, when the CQI channel is not multiplexed with the ACK channels on the same resource blocks, the transmit power of the CQI channel may be adjusted in the normal manner to achieve the target BLER for the CQI. When the CQI channel is multiplexed with the ACK channels on the same resource blocks, the transmit power of the CQI channel may be reduced from a nominal value by a backoff factor of X dB in order to maintain good performance for the ACK channels.

In another design, the transmit power for the ACK channel may be: (i) when the ACK channel is not multiplexed with the CQI channels, it is set to achieve a nominal target SNR (SNR)_{target_nom} ^ACK) (ii) a (ii) When the ACK channel is multiplexed with the CQI channel, it is boosted to achieve a higher target SNR (SNR)_{target_higher} ^ACK)。SNR_{target_higher} ^ACKSpecific SNR_{target_nom} ^ACKThe height of the beam is Y dB higher,where Y is a boost factor and may be a predetermined magnitude. In this design, when the ACK channel is not multiplexed with the CQI channels on the same resource blocks, the transmit power of the ACK channel may be adjusted in the normal manner to achieve the target BLER for ACK. When the ACK channel is multiplexed with the CQI channels on the same resource block, the transmit power of the ACK channel may be increased from the nominal value by a boost factor of Y dB to maintain good performance for the ACK channel.

In another design, a combination of backoff for the CQI channels and boost for the ACK channels may be used when multiplexing the channels together. The transmit power of the CQI channel may be reduced by a backoff factor of X dB from the nominal value of the CQI. The transmit power of the ACK channel may be increased by a boost factor of Y dB from the nominal value of ACK.

The backoff factor and/or the boost factor may be selected according to a tradeoff between ACK performance and CQI performance. In general, a larger backoff factor and/or a larger boost factor may improve ACK performance at the expense of CQI performance, and vice versa. In one design, the backoff factor and/or the boost factor may be fixed values and may be used whenever the ACK and CQI channels are multiplexed on the same resource block. In another design, the backoff factor and/or the boost factor may depend on one or more parameters such as the number of multiplexed CQI channels and the number of ACK channels, a nominal target SNR for the CQI channels, and/or the like.

The transmit power of a given transmission (e.g., a pilot channel or a CQI channel) from a UE may be adjusted with power control to maintain the received SNR of this transmission at a target SNR. The transmit power of another transmission (e.g., an ACK channel) from the UE may be set a Δ dB higher or lower than the transmit power of the designated transmission. In one design, signaling (e.g., a 1-bit indication) may be sent to a UE to indicate whether its CQI channel is multiplexed with ACK channels from other UEs. In another design, signaling may be sent to a UE to indicate whether its ACK channel is multiplexed with CQI channels from other UEs. In any event, the UE may apply a backoff factor to the CQI channel and/or a boost factor to the ACK channel whenever the signaling indicates that the CQI channel (or the ACK channel) is multiplexed with ACK channels (or the CQI channels) from other UEs. The signaling may be sent periodically or only when the multiplexing status changes.

Using a lower target SNR for the CQI channel and/or a higher target SNR for the ACK channel may degrade CQI performance when multiplexing the CQI channel and the ACK channel together. Various techniques may be used to mitigate the impact on CQI performance due to multiplexing of ACK and CQI channels. In one design, the CQI channel from the UE may hop randomly such that the CQI channel is not always multiplexed with the ACK channels and thus experiences a higher BUER. Such random hopping can be achieved by allocating different resource blocks for the CQI channel in different sub-frames, different reference signal sequences in different slots or symbol periods to the UEs. Different reference signal sequences may be derived from the same base sequence or different base sequences assigned to the node bs. Random hopping will cause the CQI channel to: (i) multiplexed with the ACK channels at some times and only the CQI channels at other times; and/or (ii) multiplexed with ACK channels from different UEs in different subframes. A UE assigned a reference signal sequence with a given cyclic shift is more susceptible to interference from UEs assigned reference signal sequences with neighboring cyclic shifts. The ACK and CQI channels may be assigned reference signal sequences with non-adjacent cyclic shifts in order to reduce interference.

In another design, to account for the higher BLER of the CQI caused by multiplexing with the ACK channels, the node B may perform erasure detection for the CQI channels when multiplexed with the ACK channels. For erasure detection, the node B receives a CQI report from the UE on a CQI channel, and uses the report if the CQI channel is sufficiently reliable, otherwise discards the report. In one design of erasure detection, the node B calculates a metric for a codeword received from the UE on the CQI channel. This metric may be based on a correlation between the received codeword and each possible codeword that can be sent on the CQI channel. The node B may calculate the difference between the two best correlation calculations and compare this difference to a threshold. When the difference is greater than the threshold, the node B uses the received CQI report. When the difference is less than the threshold, the node B then discards the received CQI report and uses the previous CQI report or the average CQI. The node B may also perform erasure detection in other ways, e.g., using other metrics.

In another design, the node B may perform detection using interference cancellation when the ACK and CQI channels are multiplexed together. If the transmit power of the ACK channel is increased from its nominal value and/or the transmit power of the CQI channel is decreased from its nominal value, the reliability of the CQI channel may be worse than normal. In this case, the node B first detects the ACK channel, then estimates and cancels the interference caused by the ACK channel, and then detects the CQI channel. When multiplexing the ACK and CQI channels together, the reliability of the ACK channel is worse than normal if the transmit power of these channels is maintained at their nominal value. In this case, the node B first detects the CQI channel, then estimates and cancels the interference caused by the CQI channel, and then detects the ACK channel. In general, the node B may first detect a more reliable control channel, then estimate and cancel the interference caused by detecting the control channel, and then detect a less reliable control channel.

Techniques described herein may enable multiplexing ACK and CQI channels from different UEs on the same resource block in order to improve utilization of available time-frequency resources. When multiplexing the ACK and CQI channels together, power control for the ACK and/or CQI channels may be jointly optimized to account for the difference between the PSDs of the ACK and CQI channels and reduce the impact on ACK performance. Techniques such as random hopping, erasure detection, and interference cancellation may be used to mitigate the impact on CQI performance when multiplexing ACK and CQI channels together.

Different transmit power levels may be used for the ACK channel from a UE even when this ACK channel is only multiplexed with ACK channels from other UEs. In one design, different transmit power levels may be used for the ACK and NAK to achieve different BLERs for the ACK and NAK. An "ACK-NAK error" due to the detection of a transmitted ACK as a NAK may result in additional transmissions of transport blocks that have been correctly decoded by the UE. A "NAK-ACK error" due to the detection of a transmitted NAK as an ACK can result in the termination of a transport block that was decoded incorrectly by the UE. Therefore, NAK-ACK errors are more catastrophic than ACK-NAK errors. To achieve a lower NAK-ACK error rate, the transmit power of the NAK may be set higher than the transmit power of the ACK.

In another design, different transmit power levels may be used for the ACK channels depending on the number of ACK bits sent. A Single Input Multiple Output (SIMO) UE may transmit one ACK bit with BPSK and a Multiple Input Multiple Output (MIMO) UE may transmit two ACK bits with QPSK. An ACK channel carrying two ACK bits has a higher target SNR than an ACK channel carrying one ACK bit. Different transmit power levels may be used for the ACK channels from SIMO UEs and MIMO UEs multiplexed together on the same resource block. The transmit power of the ACK channel from the MIMO UE may be set higher to achieve a higher target SNR; also, the transmit power of the ACK channel from the SIMO UEs may be set lower to achieve a lower target SNR.

In another design, different transmit power levels may be used for the CQI channel depending on the number of information bits transmitted. When ten information bits are carried, the CQI channel has a higher target SNR; it has a lower target SNR when carrying eight information bits. Different transmit power levels may be used for the CQI channel in order to meet the target SNR for different numbers of information bits.

Fig. 6 illustrates a process 600 for transmitting control information in a wireless communication system. Process 600 may be performed by a UE or some other entity. The UE transmits the first control channel at a first transmit power level if the first control channel is not multiplexed with second control channels from other UEs (block 612). If the first control channel is multiplexed with second control channels from other UEs, the UE transmits the first control channel at a second transmit power level different from the first transmit power level (block 614). When the first and second control channels are multiplexed together, the channels have different target SNRs and therefore different received signal levels. The spreading may be used for the first control channel but not for the second control channel, and vice versa.

In one design, the first control channel may comprise a CQI channel, the second control channel may comprise an ACK channel, and the second transmit power level may be lower than the first transmit power level. The first transmit power level may achieve a first target SNR for the CQI channel if the CQI channel is not multiplexed with ACK channels from other UEs. The second transmit power level may achieve a second target SNR for the CQI channel if multiplexed with the ACK channels from the other UEs. The second target SNR may be lower than the first target SNR.

In another design, the first control channel may comprise an ACK channel, the second control channel may comprise a CQI channel, and the second transmit power level may be higher than the first transmit power level. The first transmit power level may achieve the first target SNR if the ACK channels are not multiplexed with CQI channels from other UEs. The second transmit power level may achieve a second target SNR for the ACK channels if multiplexed with CQI channels from other UEs. The second target SNR may be higher than the first target SNR.

In another design, the first control channel may include an ACK channel carrying a first number of bits. The second control channel includes an ACK channel carrying a second number of bits different from the first number of bits. The first and second control channels may also comprise other types of control channels.

The UE may adjust its transmit power according to power control. The UE may determine the first or second transmit power based on the first or second power offset and the adjusted transmit power of the UE, respectively. The UE may receive signaling indicating whether the first control channel is multiplexed with second control channels from other UEs. The UE then selects either the first or second transmit power level for the first control channel based on the signaling. The first control channel may hop to randomize multiplexing of the first control channel with the second control channel from other UEs.

Fig. 7 shows a design of an apparatus 700 for transmitting control information in a wireless communication system. The apparatus 700 comprises: means 712 for transmitting the first control channel at a first transmit power level if the first control channel is not multiplexed with second control channels from other UEs; means 714 for transmitting the first control channel at a second transmit power level different from the first transmit power level if the first control channel is multiplexed with second control channels from other UEs.

Fig. 8 shows a design of a process 800 for transmitting control information in a wireless communication system. Process 800 may be performed by a UE or some other entity. The UE may generate a plurality of data sequences for the CQI channel based on the reference signal sequence (block 812). The UE may send the CQI channel at a first transmit power level if the CQI channel is not multiplexed with ACK channels from other UEs (block 814). If the CQI channel is multiplexed with ACK channels from other UEs, the UE may transmit the CQI channel at a second transmit power level that is lower than the first transmit power level (block 816). The data sequence for the ACK channel from the other UEs may be generated with at least one other reference signal sequence and spread using orthogonal sequences. The reference signal sequence for the CQI channel and the at least one other reference signal sequence for the ACK channel may correspond to different cyclic shifts of the base sequence. The UE may send multiple data sequences for the CQI channel in multiple symbol periods of a resource block. The data sequence for the ACK channel from the other UEs may be sent on the same resource block.

Fig. 9 shows a design of an apparatus 900 for transmitting control information in a wireless communication system. The apparatus 900 comprises: a module 912 for generating a plurality of data sequences for a CQI channel from a reference signal sequence; a module 914 for transmitting the CQI channel at a first transmit power level if the CQI channel is not multiplexed with ACK channels from other UEs; a module 916 for transmitting the CQI channel at a second transmit power level lower than the first transmit power level if the CQI channel is multiplexed with ACK channels from other UEs.

Fig. 10 shows a design of a process 1000 for receiving control information in a wireless communication system. Process 1000 may be performed by a node B or some other entity. The first control channel is received from the UE at a first received SNR if the first control channel is not multiplexed with second control channels from other UEs (block 1012). If the first control channel is multiplexed with second control channels from other UEs, the node B receives the first control channel at a second received SNR that is different from the first received SNR (block 1014). In one design, the node B may perform detection on the first and second control channels with interference cancellation if they are multiplexed together.

In one design, the first control channel may comprise a CQI channel, the second control channel may comprise an ACK channel, and the second received SNR may be lower than the first received SNR. The node B performs erasure detection for the CQI channel if it is multiplexed with the ACK channels, and skips erasure detection for the CQI channel if it is not multiplexed with the ACK channels. For erasure detection, the node B may determine from the metric whether the CQI channel is reliable, use the CQI report received from the CQI channel if it is deemed reliable, and discard the CQI report otherwise. In another design, the first control channel may comprise an ACK channel, the second control channel may comprise a CQI channel, and the second received SNR may be higher than the first received SNR.

Fig. 11 shows a design of an apparatus 1100 for receiving control information in a wireless communication system. The apparatus 1100 comprises: a module 1112 for receiving a first control channel from the UE at a first received SNR if the first control channel is not multiplexed with second control channels from other UEs; means 1114 for receiving the first control channel at a second received SNR different from the first received SNR if the first control channel is multiplexed with second control channels from other UEs.

The modules in fig. 7, 9, and 11 comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, etc., or any combination of the preceding.

Fig. 12 shows a block diagram of a design of node 110 and UE 120, which are one of the node bs and one of the UEs in fig. 1. In this design, UE 120 is equipped with T antennas 1232a through 1232T and node B110 is equipped with R antennas 1252a through 1252R, where, in general, T ≧ 1 and R ≧ 1.

At UE 120, a transmit processor 1220 receives traffic data from a data source 1212, processes (e.g., encodes and symbol maps) the traffic data, and provides data symbols. Transmit processor 1220 may also receive control information (e.g., ACK and/or CQI information) from a controller/processor 1240, process the control information as described above, and provide control symbols (e.g., for data sequences). Transmit processor 1220 may also generate pilot symbols (e.g., for pilot sequences) and multiplex the pilot symbols with the data symbols and control symbols. A MIMO processor 1222 processes (e.g., precodes) the symbols from transmit processor 1220 and provides T output symbol streams to T Modulators (MODs) 1230a through 1230T. MIMO processor 1222 may be omitted if UE 120 is equipped with a single antenna. Each modulator 1230 may process its output symbol stream (e.g., for SC-FDMA) to obtain an output sample stream. Each modulator 1230 may also condition (e.g., convert to analog, filter, amplify, and upconvert) its output sample stream to generate an uplink signal. The T uplink signals from modulators 1230a through 1230T may be transmitted through T antennas 1232a through 1232T, respectively.

At node B110, antennas 1252a through 1252r receive the uplink signals from UE 120 and/or other UEs. Each antenna 1252 may provide a received signal to a corresponding demodulator (DEMOD) 1254. Each demodulator 1254 may condition (e.g., filter, amplify, downconvert, and digitize) its received signal to obtain samples and further process the samples (e.g., for SC-FDMA) to obtain received symbols. A MIMO detector 1256 may detect for the received symbols from all R demodulators 1254a through 1254R and provide detected symbols. A receive processor 1260 may process (e.g., demodulate and decode) the detected symbols, provide decoded traffic data to a data store 1262, and provide decoded control information to a controller/processor 1270. In general, the processing by MIMO detector 1256 and receive processor 1260 is complementary to the processing by MIMO processor 1222 and transmit processor 1220, respectively, at UE 120.

Node B110 may send traffic data and/or control information to UE 120 on the downlink. Traffic data from a data source 1278 and/or control information from controller/processor 1270 may be processed by a transmit processor 1280 and further processed by a MIMO processor 1282 to obtain R output symbol streams. R modulators 1254a through 1254R may process the R output symbol streams (e.g., for OFDM) to obtain R output sample streams and may further condition the output sample streams to obtain R downlink signals, which may be transmitted via R antennas 1252a through 1252R. At UE 120, the downlink signals from node B110 may be received by antennas 1232a through 1232t, conditioned and processed by demodulators 1230a through 1230t, and further processed by a MIMO detector 1236 (if applicable) and a receive processor 1238 to recover the traffic data and control information sent to UE 120. Receive processor 1238 provides traffic data to a data sink 1239 and control information to controller/processor 1240.

Controllers/processors 1240 and 1270 may direct the operation at UE 120 and node B110, respectively. Controller/processor 1240 may perform or direct process 600 in fig. 6, process 800 in fig. 8, and/or other processes for the techniques described herein. Controller/processor 1270 may perform or direct process 1000 in fig. 10 and/or other processes for the techniques described herein. Memories 1242 and 1272 may store data and program codes for UE 120 and node B110, respectively. A scheduler 1274 schedules UEs for transmission of data on the downlink and/or uplink and allocates resources for the scheduled UEs. Scheduler 1274 may also explicitly and/or implicitly allocate ACK and CQI resources for the UEs for transmission of ACK and CQI information. The ACK and CQI resources may include resource blocks, reference signal sequences, orthogonal sequences for pilot, orthogonal sequences for data, and so on.

Those of skill in the art would also understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the present disclosure may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more example designs, 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 transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, 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 means in the form of instructions or data structures and that can be accessed by a computer. Further, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source over a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. 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.

The previous description of the invention is provided to enable any person skilled in the art to make or use the invention. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (41)

1. A method for wireless communication, comprising the steps of:

transmitting a first control channel at a first transmit power level if the first control channel is not multiplexed with second control channels from other User Equipments (UEs);

transmitting the first control channel at a second transmit power level different from the first transmit power level if the first control channel is multiplexed with the second control channel from the other UE.

2. The method of claim 1, wherein:

the first control channel comprises a Channel Quality Indicator (CQI) channel;

the second control channel comprises an Acknowledgement (ACK) channel;

the second transmit power level is lower than the first transmit power level.

3. The method of claim 2, wherein:

the first transmit power level achieves a first target signal-to-noise ratio (SNR) for the CQI channel if the CQI channel is not multiplexed with the ACK channels from the other UEs;

the second transmit power level achieves a second target SNR for the CQI channel if the CQI channel is multiplexed with the ACK channels from the other UEs, the second target SNR being lower than the first target SNR.

4. The method of claim 1, wherein:

the first control channel comprises an Acknowledgement (ACK) channel;

the second control channel comprises a Channel Quality Indicator (CQI) channel;

the second transmit power level is higher than the first transmit power level.

5. The method of claim 4, wherein:

the first transmit power level achieves a first target signal-to-noise ratio (SNR) for the ACK channel if the ACK channel is not multiplexed with the CQI channels from the other UEs;

the second transmit power level achieves a second target SNR for the ACK channel if the ACK channel is multiplexed with the CQI channels from the other UEs, the second target SNR being higher than the first target SNR.

6. The method of claim 1, wherein:

the first control channel includes an Acknowledgement (ACK) channel carrying a first number of bits:

the second control channel includes an ACK channel carrying a second number of bits, the second number being different from the first number.

7. The method of claim 4, wherein:

the step of transmitting the first control channel at the first transmit power level comprises the steps of: sending an ACK at the first transmit power level or a Negative Acknowledgement (NAK) at a third transmit power level if the ACK channel is not multiplexed with the CQI channels from the other UEs, the third transmit power level higher than the first transmit power level;

the step of transmitting the first control channel at the second transmit power level comprises the steps of: sending an ACK at the second transmit power level or a NAK at a fourth transmit power level if the ACK channel is multiplexed with the CQI channels from the other UEs, the fourth transmit power level being higher than the second transmit power level.

8. The method of claim 1, further comprising the steps of:

hopping the first control channel to randomize multiplexing of the first control channel with the second control channel from the other UEs.

9. The method of claim 1, wherein spreading is used for one of the first and second control channels but not for the other of the first and second control channels.

10. The method of claim 1, wherein the first and second control channels have different target signal-to-noise ratios (SNRs) and also have different received signal levels when multiplexed together.

11. The method of claim 1, further comprising the steps of:

receiving signaling indicating whether the first control channel is multiplexed with the second control channels from the other UEs;

selecting the first or second transmit power level for the first control channel in accordance with the signaling.

12. The method of claim 1, further comprising the steps of:

adjusting a transmit power of a User Equipment (UE) according to the power control;

determining the first or second transmit power level based on the first or second power offset and the adjusted transmit power of the UE, respectively.

13. An apparatus for wireless communication, comprising:

at least one processor configured to:

transmitting a first control channel at a first transmit power level if the first control channel is not multiplexed with second control channels from other User Equipments (UEs);

transmitting the first control channel at a second transmit power level different from the first transmit power level if the first control channel is multiplexed with the second control channel from the other UE.

14. The apparatus of claim 13, wherein:

the first control channel comprises a Channel Quality Indicator (CQI) channel;

the second control channel comprises an Acknowledgement (ACK) channel;

the second transmit power level is lower than the first transmit power level.

15. The apparatus of claim 13, wherein:

the first control channel comprises an Acknowledgement (ACK) channel;

the second control channel comprises a Channel Quality Indicator (CQI) channel;

the second transmit power level is higher than the first transmit power level.

16. The apparatus of claim 13, wherein the at least one processor is configured to: hopping the first control channel to randomize multiplexing of the first control channel with the second control channel from the other UEs.

17. The apparatus of claim 13, wherein the at least one processor is configured to:

adjusting a transmit power of a User Equipment (UE) according to the power control;

determining the first or second transmit power level based on the first or second power offset and the adjusted transmit power of the UE, respectively.

18. An apparatus for wireless communication, comprising:

a first sending module to: transmitting a first control channel at a first transmit power level if the first control channel is not multiplexed with second control channels from other User Equipments (UEs);

a second sending module to: transmitting the first control channel at a second transmit power level different from the first transmit power level if the first control channel is multiplexed with the second control channel from the other UE.

19. The apparatus of claim 18, wherein:

the first control channel comprises a Channel Quality Indicator (CQI) channel;

the second control channel comprises an Acknowledgement (ACK) channel;

the second transmit power level is lower than the first transmit power level.

20. The apparatus of claim 18, wherein:

the first control channel comprises an Acknowledgement (ACK) channel;

the second control channel comprises a Channel Quality Indicator (CQI) channel;

the second transmit power level is higher than the first transmit power level.

21. The apparatus of claim 18, further comprising:

a hopping module for hopping the first control channel to randomize multiplexing of the first control channel with the second control channel from the other UEs.

22. The apparatus of claim 18, further comprising:

an adjustment module to adjust a transmit power of a User Equipment (UE) according to power control;

a determining module to determine the first or second transmit power level based on a first or second power offset and the adjusted transmit power of the UE, respectively.

23. A computer program product, comprising:

a computer-readable medium, comprising:

first transmission code for causing at least one computer to transmit a first control channel at a first transmit power level when the first control channel is not complex with a second control channel from other User Equipment (UE);

a second transmission code for causing the at least one computer to transmit the first control channel at a second transmit power level different from the first transmit power level when the first control channel is multiplexed with the second control channel from the other UE.

24. A method for wireless communication, comprising the steps of:

transmitting a Channel Quality Indicator (CQI) channel at a first transmit power level if the CQI channel is not multiplexed with Acknowledgement (ACK) channels from other User Equipments (UEs);

transmitting the CQI channel at a second transmit power level lower than the first transmit power level if the CQI channel is multiplexed with the ACK channels from the other UEs.

25. The method of claim 24, further comprising the steps of:

generating a plurality of data sequences of the CQI channel which are not widened;

wherein the step of transmitting the CQI channel at the second transmit power level comprises the steps of: transmitting the plurality of data sequences in a plurality of symbol periods of a resource block at the second transmit power level;

wherein the ACK channel from the other UEs is transmitted by being widened in the resource block.

26. The method of claim 24, further comprising the steps of:

generating a plurality of data sequences for the CQI channel from a reference signal sequence;

wherein the step of transmitting the CQI channel at the second transmit power level comprises the steps of: transmitting the plurality of data sequences in a plurality of symbol periods of a resource block at the second transmit power level;

wherein the data sequence of the ACK channel from the other UEs is generated with at least one other reference signal sequence;

wherein the reference signal sequence and the at least one other reference signal sequence correspond to different cyclic shifts of a base sequence.

27. An apparatus for wireless communication, comprising:

at least one processor configured to:

transmitting a Channel Quality Indicator (CQI) channel at a first transmit power level if the CQI channel is not multiplexed with Acknowledgement (ACK) channels from other User Equipments (UEs);

transmitting the CQI channel at a second transmit power level lower than the first transmit power level if the CQI channel is multiplexed with the ACK channels from the other UEs.

28. The apparatus of claim 27, wherein:

the at least one processor is configured to:

generating a plurality of data sequences of the CQI channel which are not widened;

transmitting the plurality of data sequences in a plurality of symbol periods of a resource block at the second transmit power level;

the ACK channel from the other UEs is sent by spreading in the resource block.

29. The apparatus of claim 27, wherein:

the at least one processor is configured to:

generating a plurality of data sequences for the CQI channel from a reference signal sequence;

transmitting the plurality of data sequences in a plurality of symbol periods of a resource block at the second transmit power level;

the data sequence of the ACK channel from the other UE is generated with at least one other reference signal sequence;

the reference signal sequence and the at least one other reference signal sequence correspond to different cyclic shifts of a base sequence.

30. A method for wireless communication, comprising the steps of:

receiving a first control channel from a User Equipment (UE) at a first received signal-to-noise ratio (SNR) if the first control channel is not multiplexed with second control channels from other UEs;

receiving the first control channel at a second received SNR different from the first received SNR if the first control channel is multiplexed with the second control channel from the other UE.

31. The method of claim 30, wherein:

the first control channel comprises a Channel Quality Indicator (CQI) channel;

the second control channel comprises an Acknowledgement (ACK) channel;

the second received SNR is lower than the first received SNR.

32. The method of claim 31, further comprising the steps of:

performing erasure detection for the CQI channel if the CQI channel is multiplexed with the ACK channels from the other UEs;

skipping erasure detection for the CQI channel if the CQI channel is not multiplexed with the ACK channels from the other UEs.

33. The method of claim 31, further comprising the steps of:

determining whether the CQI channel is reliable according to a metric;

using a CQI report received from the CQI channel if the CQI channel is deemed reliable;

discarding the CQI report if the CQI channel is deemed unreliable.

34. The method of claim 30, wherein:

the first control channel comprises an Acknowledgement (ACK) channel;

the second control channel comprises a Channel Quality Indicator (CQI) channel;

the second received SNR is higher than the first received SNR.

35. The method of claim 30, further comprising the steps of:

detecting the first and second control channels is performed with interference cancellation if the first and second control channels are multiplexed together.

36. An apparatus for wireless communication, comprising:

at least one processor configured to:

receiving a first control channel from a User Equipment (UE) at a first received signal-to-noise ratio (SNR) if the first control channel is not multiplexed with second control channels from other UEs;

receiving the first control channel at a second received SNR different from the first received SNR if the first control channel is multiplexed with the second control channel from the other UE.

37. The apparatus of claim 36, wherein:

the first control channel comprises a Channel Quality Indicator (CQI) channel;

the second control channel comprises an Acknowledgement (ACK) channel;

the second received SNR is lower than the first received SNR.

38. The apparatus of claim 37, wherein the at least one processor is configured to:

performing erasure detection for the CQI channel if the CQI channel is multiplexed with the ACK channels from the other UEs;

skipping erasure detection for the CQI channel if the CQI channel is not multiplexed with the ACK channels from the other UEs.

39. The apparatus of claim 37, wherein the at least one processor is configured to:

determining whether the CQI channel is reliable according to a metric;

using a CQI report received from the CQI channel if the CQI channel is deemed reliable;

discarding the CQI report if the CQI channel is deemed unreliable.

40. The apparatus of claim 36, wherein:

the first control channel comprises an Acknowledgement (ACK) channel;

the second control channel comprises a Channel Quality Indicator (CQI) channel;

the second received SNR is higher than the first received SNR.

41. The apparatus of claim 36, wherein the at least one processor is configured to: detecting the first and second control channels is performed with interference cancellation if the first and second control channels are multiplexed together.