Control and data signaling in SC-FDMA communication systems

Abstract

A method for transmitting uplink information by a user equipment in a wireless communication system, the user equipment, a method for receiving uplink information by a base station in a wireless communication system, and the base station are provided. The method for transmitting uplink information by a user equipment in a wireless communication system includes mapping a reference signal on a first symbol in a slot; mapping acknowledgement information in response to reception of downlink data on a second symbol placed directly after the first symbol in the slot; and transmitting a signal including mapped data of the reference signal and the acknowledgement information in the slot.

Claims

1. A method for transmitting uplink information by a user equipment in a wireless communication system, the method comprising: mapping a reference signal on a first symbol in an uplink channel; mapping acknowledgement information in response to reception of downlink data on a second symbol first placed after the first symbol in the uplink channel; and transmitting a signal including mapped data of the reference signal and the acknowledgement information in the uplink channel, wherein a part of channel quality indicator (CQI) information is further mapped on at least one symbol, except for the first symbol, in case that the CQI information is present for transmission on the uplink channel.

2. The method of claim 1, wherein the reference signal is used for demodulation.

3. The method of claim 1, wherein the acknowledgement information and the part of the CQI information are respectively multiplexed on corresponding resource elements in the second symbol of the uplink channel.

4. The method of claim 1, wherein one or more symbols, except the first and second symbols, are additionally used to map the acknowledgement information in case that further transmission of the acknowledgement information is needed.

5. A user equipment (UE) for transmitting uplink information in a wireless communication system, the UE comprising: a transceiver; and a controller coupled with the transceiver and configured to: map a reference signal on a first symbol in an uplink channel; map acknowledgement information in response to reception of downlink data on a second symbol, first placed after the first symbol in the uplink channel; and transmit a signal including mapped data of the reference signal and the acknowledgement information in the uplink channel, wherein a part of channel quality indicator (CQI) information is further mapped on at least one symbol, except for the first symbol, in case that the CQI information is present for transmission on the uplink channel.

6. The UE of claim 5, wherein the reference signal is used for demodulation.

7. The UE of claim 6, wherein the acknowledgement information and the part of the CQI information are respectively multiplexed on corresponding resource elements in the second symbol of the uplink channel.

8. The UE of claim 5, wherein the controller is further configured to additionally use one or more symbols, except the first and second symbols, to map the acknowledgement information in case that further transmission of the acknowledgement information is needed.

9. A method for receiving uplink information by a base station in a wireless communication system, the method comprising: receiving a signal including mapped data of a reference signal and acknowledgement information in an uplink channel; de-mapping the reference signal on a first symbol in the uplink channel; and de-mapping the acknowledgement information in response to transmission of downlink data on a second symbol, first placed after the first symbol in the uplink channel, wherein a part of channel quality indicator (CQI) information is further de-mapped on at least one symbol, except for the first symbol, in case that the CQI information is present for reception on the uplink channel.

10. The method of claim 9, wherein the reference signal is used for demodulation.

11. The method of claim 9, wherein the acknowledgement information and the part of the CQI information are respectively de-multiplexed on corresponding resource elements in the second symbol of the uplink channel.

12. The method of claim 9, wherein one or more symbols, except the first and second symbols, are additionally used to de-map the acknowledgement information in case that further reception of the acknowledgement information is needed.

13. A base station for receiving uplink information in a wireless communication system, the base station comprising: a transceiver; and a controller coupled with the transceiver and configured to: receive a signal including mapped data of a reference signal and acknowledgement information in an uplink channel; de-map the reference signal on a first symbol in the uplink channel; and de-map the acknowledgement information in response to transmission of downlink data on a second symbol first placed after the first symbol in the uplink channel, wherein a part of channel quality indicator (CQI) information is further de-mapped on at least one symbol, except for the first symbol, in case that the CQI information is present for reception on the uplink channel.

14. The base station of claim 13, wherein the reference signal is used for demodulation.

15. The base station of claim 13, wherein the acknowledgement information and the part of the CQI information are respectively de-multiplexed on corresponding resource elements in the second symbol of the uplink channel.

16. The base station of claim 13, wherein the controller is further configured to additionally use one or more symbols, except the first and second symbols, to de-map the acknowledgement information in case that further reception of the acknowledgement information is needed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other aspects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a block diagram illustrating an exemplary sub-frame structure for the SC-FDMA communication system;

(3) FIG. 2 is a block diagram illustrative of a first exemplary SC-FDMA transmitter for multiplexing data bits, CQI bits, and ACK/NAK bits in a transmission sub-frame;

(4) FIG. 3 is another block diagram illustrative of a second exemplary SC-FDMA transmitter or multiplexing data bits, CQI bits, and ACK/NAK bits in a transmission sub-frame;

(5) FIG. 4 is a block diagram illustrative of an exemplary SC-FDMA receiver, corresponding to the first exemplary SC-FDMA transmitter, for de-multiplexing data bits, CQI bits, and ACK/NAK bits in a reception sub-frame;

(6) FIG. 5 presents un-coded bit error rate (BER) results as a function of the symbol number (symbol position) in the sub-frame slot and the UE velocity;

(7) FIG. 6 is a block diagram illustrating a first method for the selection of the sub-frame symbols carrying the transmission of CQI bits and ACK/NAK bits;

(8) FIG. 7 is a block diagram illustrating a first method for the selection of the sub-frame symbols carrying the transmission of ACK/NAK bits;

(9) FIG. 8 is a block diagram illustrating a first method for the selection of the sub-frame symbols carrying the transmission of CQI bits;

(10) FIG. 9 is a block diagram illustrating a second method for the selection of the sub-frame symbols carrying the transmission of ACK/NAK bits with reduced overhead; and

(11) FIG. 10 is a block diagram illustrating a second method for the selection of the sub-frame symbols carrying the transmission CQI bits and ACK/NAK bits.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(12) The present invention now will be described more fully hereinafter with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

(13) Additionally, although the invention assumes a single-carrier frequency division multiple access (SC-FDMA) communication system, it also applies to all FDM systems in general and to OFDMA, OFDM, FDMA, DFT-spread OFDM, DFT-spread OFDMA, single-carrier OFDMA (SC-OFDMA), and single-carrier OFDM in particular.

(14) Basically, the system and methods of the embodiments of the present invention solve problems related to the need for providing the desired reliability for the reception of control signaling under indicative transmission sub-frame structures and provide additional advantages such as the reduction of resource overhead for the transmission of control signals.

(15) A first observation for the sub-frame structure illustrated in FIG. 1 is that the reference signal (RS) exists only in the middle symbol of each slot. In case of a mobile terminal, or user equipment (UE), with high speed, this can substantially degraded channel estimation for symbols located further away from the RS (that is, for symbols near the beginning and end of each slot) due to the faster variation of the channel medium as the UE velocity increases. This may be acceptable for data transmission that is coded, which has typically a relatively large target block error rate (BLER), such as 10% or above, and can benefit from retransmissions though a conventional HARQ process. Conversely, the CQI and particularly the ACK/NAK have much stricter performance requirements, HARQ typically does not apply to the corresponding transmissions, and providing an accurate channel estimate is essential in achieving the desired reception reliability.

(16) A brief set of simulation results for the un-coded (raw) bit error rate (BER) is provided to illustrate the impact of inaccurate channel estimation on the reception quality as a function of the symbol position in the slot and the UE speed. Table 1 provides the simulation setup under optimistic conditions for the performance loss due to imperfect channel estimation at symbols further away from the RS for the following reasons: Transmission bandwidth is 1 RB. This maximizes power per sub-carrier. Channel frequency selectivity is large and there are 2 uncorrelated Node B receiver antennas. This maximizes the slope of the un-coded (raw) BER curve and minimizes the relative performance loss due to imperfect channel estimation for a target BER value. Operating signal-to-interference and noise ratio (SINR) is large. This minimizes the impact of inaccurate channel estimation.

(17) TABLE-US-00001 TABLE 1 Simulation Assumptions Parameters Assumptions Operating Bandwidth @ 5 MHz @ 2.6 GHz Carrier Frequency Modulation Scheme Quadrature Phase Shift Keying (QPSK) Data Transmission 1 RB Bandwidth (BW) UE Speed 3, 30, 120 and 350 Kilometers per hour (Kmph) Transmission Type Localized (at same RB) over the sub-frame at 3, 30 Kmph Frequency Hopping Between Slots at 120 and 350 Kmph Channel Model GSM - Terrestrial-Urban with 6 paths (TU6) Number of Node B 2 Receiver Antennas Number of UE 1 Transmitter Antennas

(18) FIG. 5 presents the un-coded BER. At symbol locations symmetric to the RS, the BER is typically the same. At 120 Kmph and 350 Kmph, the transmission in the first slot is assumed to occur at a different BW than the one in the second slot (frequency hopped transmission per slot). As only 1 RS per slot is available for channel estimation, the BER is the same at symbols symmetric (equidistant) to the RS. At low speeds, such as 3 Kmph, this is also the case because the channel does not change over the sub-frame duration. Some small variability does exist for medium UE speeds, such as 30 Kmph, but, for simplicity, the average BER of symbols equidistant to the RS is only shown.

(19) Even under the previous optimistic assumptions for the un-coded (raw) BER degradation due to degraded channel estimation at symbols further away from the RS, at 350 Kmph the BER saturates at the 1.sup.st/7.sup.th and 2.sup.nd/6.sup.th symbols. However, the impact on the BER of the 3.sup.rd/5.sup.th symbols is rather contained and saturation is avoided (the difference relative to the BER at 3 Kmph is also partly due to the fact that the latter uses both RS in the sub-frame for channel estimation which therefore effectively operates with twice as much SINR). The BER at 120 Kmph is also degraded by about 3 dB for the 1.sup.st/7.sup.th symbols and by about 1.5 dB for the 2.sup.nd/6.sup.th symbols relative to the one of the 3.sup.rd/5.sup.th symbols at about the 1% point. Obviously, due to the flattening of the BER curves for the 1.sup.st/7.sup.th and 2.sup.nd/6.sup.th symbols, the degradation will be much larger for BER operating points below 1% as it is typically needed for the NAK reception.

(20) Based on the results in FIG. 5 it becomes apparent that the control transmission should be placed with priority immediately next to the RS.

(21) FIG. 6 illustrates such a placement when a UE transmits both ACK/NAK bits 610 and CQI bits 620 during a sub-frame. These control bits are placed on symbols next to the RS 630 while the data bits 640 are included in symbols transmitted over the entire sub-frame (with the obvious exception of the symbols carrying the RS transmission). Due to the requirement for better reception reliability, the ACK/NAK bits are placed closer to the RS than the CQI bits.

(22) FIG. 7 illustrates the case in which the UE transmits only ACK/NAK bits 710 together with data bits 720 during a sub-frame. The ACK/NAK bits are placed at the two symbols next to the RS 730 in each of the two sub-frame slots while the data bits are included in symbols transmitted over the entire sub-frame.

(23) FIG. 8 illustrates the case in which the UE transmits only CQI bits 810 together with data bits 820 during a sub-frame. The CQI bits are placed at the two symbols next to the RS 830 in each of the two sub-frame slots while the data bits are included in symbols transmitted over the entire sub-frame.

(24) To minimize channel estimation losses, the ACK/NAK bits should be placed with priority in the symbol after the first symbol carrying the RS. This does not impact demodulation latency as a channel estimate is available only after this first RS symbol. To address low SINR or coverage issues, the ACK/NAK bits can also be placed in the symbol before the second RS. For medium UE speeds, this second placement of ACK/NAK bits benefits from improved channel estimation and time diversity while for high UE speeds, it benefits from frequency and time diversity. This is illustrated in FIG. 9 where the ACK/NAK bits 910 are placed in only one symbol next to the RS 920 in each slot, these two symbols (one in each slot) are located between the two RS, while the data bits 930 are transmitted throughout the sub-frame (with the obvious exception of the symbols carrying the RS).

(25) Provisioning for the transmission of ACK/NAK bits in the sub-carriers over 2 symbols is typically adequate to achieve the desired BER for the ACK reception. Nevertheless, because the NAK reception has typically a lower BER target, it is appropriate to have the ACK/NAK transmission over the number of sub-carriers in 1 symbol in each slot. If further ACK/NAK transmissions are needed, because of low SINR or coverage issues, the other symbols next to the RS in the 2 slots may also be used as illustrated in FIG. 6 and FIG. 7.

(26) Depending on the number of information bits carried in the CQI reporting, which are typically several times more than the ACK/NAK information bits, the symbols immediately adjacent to the RS may not suffice for the CQI transmission, especially for coverage or SINR limited UEs that are also typically assigned small bandwidth allocations (a small number of RBs). In such cases, the CQI transmission may also extend to one or more symbols that are adjacent to the symbols also carrying CQI information that are adjacent to the symbols carrying the RS. An exemplary embodiment of this principle is illustrated in FIG. 10. As previously discussed, the location of the ACK/NAK bits 1010 remains in symbols next to the RS 1030 but the CQI bits 1020 are located in symbols throughout the transmission sub-frame, similarly to the data symbols 1040.

(27) While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.