Patent Application
20050105494
This application claims the benefit under 35 U.S.C. § 119(a) of an application entitled “Method and Apparatus for Transmitting/Receiving Control Signal on High Speed Shared Control Channel in a Hybrid Automatic Retransmission Request System” filed in the Korean Intellectual Property Office on Nov. 14, 2003 and assigned Serial No. 2003-80755, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to a method and apparatus for transmitting/receiving a High Speed Shared Control Channel (HS-SCCH) to support High Speed Downlink Packet Access (HSDPA) in a Wideband Code Division Multiple Access (WCDMA) wireless communication system. In particular, the present invention relates to a transmitting/receiving method and apparatus for preventing data loss that may be encountered with conventional systems through effective utilization of a New data Indicator (NI) included in a HS-SCCH.
2. Description of the Related Art
Mobile communication systems have evolved from a voice-based system to a high-speed, high-quality wireless packet data transmission system for provisioning data service and multimedia service. Standardization efforts dedicated to High Speed Downlink Packet Access (HSDPA) and Evolution-Data and Voice (1xEV-DV) primarily by the 3rd Generation Partnership Project (3GPP) and 3GPP2 committees is clear evidence of efforts to find a solution to 2 Mbps or higher-speed, high-quality wireless data packet transmission. 4th generation mobile communication systems aim to provide higher-speed, higher-quality multimedia service.
In wireless communications, the radio channel environment is an obstacle to high-speed, high-quality data service. For example, the radio channel environment varies often due to fading-incurred signal power change, shadowing, Doppler effects caused by mobile movement and frequent mobile velocity changes, interference from other users, and multipath interference as well as Additive White Gaussian Noise (AWGN). Thus it follows that an advanced technology is needed to improve adaptability to the channel changes beyond the technologies of conventional 2nd generation and 3rd generation mobile communication systems in order to provide high-speed wireless data packet service. Although fast power control adopted in conventional systems improves adaptability to the channel changes, the 3GPP and 3GPP2 dedicated to standardization of a high-speed data packet transmission system commonly address Adaptive Modulation and Coding Scheme (AMCS) and Hybrid Automatic Repeat Request (HARQ).
AMCS is a method of changing a modulation scheme and a coding rate adaptively according to the change of a downlink channel environment. Generally, a User Equipment (UE) measures the Signal-to-Noise Ratio (SNR) of a downlink signal and reports it to a Node B. The Node B then estimates the downlink channel environment based on the SNR information and determines an appropriate modulation scheme and coding rate according to the estimation. Therefore, a system using AMCS applies a higher-order modulation scheme such as 16-ary Quadrature Amplitude Modulation (16 QAM ) or 64 QAM and a high coding rate such as 3/4 to a UE near a Node B, that is, a UE in a good channel status. To a UE at a cell boundary, that is, a UE in a bad channel status, the system applies a lower-order modulation scheme such as Binary Phase Shift Keying (BPSK), Quadrature PSK (QPSK), or 8PSK (8-ary PSK) and a low coding rate such as 1/2. AMCS improves system performance on average by reducing interference relative to the conventional fast power control method.
HARQ is a scheme of, when an error is generated in an initially transmitted data packet, retransmitting the packet to compensate for the error. The HARQ scheme comprises Chase Combining (CC), Full Incremental Redundancy (FIR), and Partial Incremental Redundancy (PIR).
In the CC, the same packet as initially transmitted is retransmitted. A receiver combines the retransmitted packet and the buffered initially transmitted packet in a predetermined method, thereby increasing the reliability of coded bits input to a decoder and thus achieving a total system performance gain. The combining of the same two packets virtually gives the effect of repetition coding. Hence, an average performance gain of about 3 dB is achieved.
The FIR improves decoding performance at the receiver by transmitting a packet having only parity bits generated from a channel encoder instead of the same initially transmitted packet. The decoder uses the new parity bits as well as the initial transmission information. The resulting decrease in coding rate increases decoding performance. It is well known in coding theory that a performance gain at a low coding rate is higher than that achieved from repetition coding. Thus, the FIR offers good performance over the CC in terms of performance gain.
Unlike the FIR, the PIR transmits a data packet comprised of information bits and new parity bits at a retransmission. At decoding, the initially transmitted information bits are combined with the retransmitted information bits, leading to the effect of the CC, and the use of the parity bits leads to the effect of the IR. The PIR uses a higher coding rate than the FIR. Thus, the PIR falls between the FIR and the CC in terms of performance.
While the AMC and HARQ are independent techniques to increase adaptability to the change of links, a combination of the AMC and HARQ can improve the system performance considerably. That is, a transmitter in a Node B determines a modulation scheme and a coding rate for a channel encoder adaptively according to the downlink channel status and transmits a data packet correspondingly. A receiver in a UE, if it fails to decode the data packet, requests a retransmission. The Node B retransmits a predetermined data packet in a predetermined HARQ scheme in response to the retransmission request.
To support the above-described schemes, a UE and a Node B need to exchange related control signals. Especially a control channel that delivers the control channels in a Universal Mobile Telecommunication Service (UMTS) communication system is called a HS-SCCH. The HS-SCCH delivers control signals related to a (High Speed Physical Downlink Shared Channel (HS-PDSCH) for transmitting user data at a high rate.
Referring to
Referring to
A multiplexer (MUX) 222 generates a bit stream in a slot format by multiplexing the channelization code set information, MS information (e.g. redundancy and constellation information), NI, HARQ process information, RV, and TB size information. A Cyclic Redundancy Check (CRC) coder 224 attaches a CRC to the bit stream. The CRC may be masked with a UE ID. A serial to parallel converter (SPC) 226 converts the CRC-attached control information bits to parallel information bits and outputs them separately as an in-phase (I) part and a quadrature-phase (Q) part to a spreader 228.
The spreader 228 generates an I channel signal and a Q channel signal by spreading the I part and the Q part with a predetermined spreading code COVSF. A summer 230 sums the I channel signal and the Q channel signal and outputs the sum in the form of a complex signal to a scrambler 232.
The scrambler 232 scrambles the complex signal with a predetermined scrambling code CScramble. A channel gain controller 234 multiplies the scrambled signal by a channel gain and a modulator 236 modulates the gain-controlled signal in a predetermined modulation scheme. A Radio Frequency (RF) module 238 upconverts the modulated signal to an RF signal and transmits it through an antenna 240.
The structure of a receiving apparatus for receiving the HS-SCCH from the transmitting apparatus of
Referring to
A complex I/Q stream converter 310 separates the complex signal from the multiplier 308 into an I bit stream and a Q bit stream. Multipliers 312 and 314 multiply the I and Q bit streams by the same spreading code COVSF used in the Node B. Thus, the multipliers 312 and 314 act as despreaders. A channel compensator 316 compensates for the distortion of the despreaded signals caused during transmission over the air from the Node B.
A parallel to serial converter (PSC) 320 serializes the compensated signals. A CRC decoder 322 checks the CRC of the serial signal from the PSC 320. If no errors are detected, the CRC decoder 322 outputs the serial signal to a demultiplexer (DEMUX) 324. The DEMUX 324 demultiplexes the received signal into a channelization code set information, MS information, an NI, HARQ process information, an RV, and a TB size.
A control information interpreter 342 interprets the control information. If the control information indicates a new data packet, the previously received data is cleared and instead, the current received data is stored. If the control information indicates a retransmitted packet, the previous data is combined with the current data and stored.
An ACK/NACK is processed in two ways: fixed and toggled. In the fixed method, the NI is set to 1 at an initial transmission and to 0 at retransmissions.
As illustrated in
However, if initially transmitted or retransmitted packet is missing over the air, errors may be generated in the above fixed HARQ scheme, as illustrated in
Referring to
The other approach, the toggled method maintains the NI until a packet is completely transmitted. That is, if a particular packet is transmitted with the NI set to 1, the NI is maintained at 1 until an ACK is received for the packet. Upon receipt of the ACK, the NI is toggled to 0 for the next packet.
When the UE receives packet C with the NI set to 1 and transmits an ACK, the Node B transmits packet D with the NI set to 0. If the packet D is lost and the Node B interprets no response from the UE as an ACK, the Node B transmits packet E with the NI set to 1. However, the UE discards the packet E, considering that the packet E is a retransmission of the already received packet C according to the NI of the packet E. In this case, the UE also experiences packet loss.
The fixed and toggled NI transmission schemes can be summarized as follows.
When an initially transmitted packet is lost, the Node B determines no response for the packet from the UE as an ACK or NACK. In the case of an NACK, data loss occurs to the fixed HARQ scheme. On the contrary, in the case of an ACK, data loss occurs to both the fixed and toggled HARQ schemes. Therefore, packet loss is inevitable to both schemes. In this context, there is a need for a transmitting/receiving method and apparatus for overcoming the data loss.
An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide a transmitting/receiving method and apparatus for preventing packet loss by efficiently transmitting control information in a Hybrid Automatic Repeat Request (HARQ) communication system.
Another object of the present invention is to provide a transmitting/receiving method and apparatus for preventing packet loss on a physical channel by using fixed and toggled NI transmission schemes in combination in a HARQ communication system.
A further object of the present invention is to provide a transmitting/receiving method and apparatus for preventing packet loss to thereby improve system throughput in a HARQ communication system.
The above objects are achieved by providing a method and apparatus for transmitting/receiving control information to support High Speed Downlink Packet Access (HSDPA) in a Wideband Code Division Multiple Access
(WCDMA) communication system According to one aspect of the present invention, in a method of transmitting control information for HARQ in a wireless communication system, when packet data is initially transmitted, a new data indicator is set to a specific bit value indicating an initial transmission for the packet data. Upon receipt of a retransmission request for the packet data, the new data indicator is set to an inverse of a previous new data indicator corresponding to a retransmission of a previous packet data.
According to another aspect of the present invention, in a method of receiving control information for HARQ in a wireless communication system, control information is received, including a new data indicator and a redundancy/constellation version for packet data to be received. If the redundancy/constellation version is a specific value indicating an initial transmission and the new packet data indicator is a specific bit value indicating an initial transmission, the packet data is interpreted as initial transmission data. If the redundancy/constellation version is not the specific value and the new packet data indicator is an inverse of a previous new data indicator corresponding to a retransmission of a previous packet data, the packet data is interpreted as retransmission data.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
An embodiment of the present invention will now be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail for conciseness.
The present invention is intended to minimize packet loss by optimizing transmission of control information related to a packet retransmission in a Hybrid Automatic Repeat Request (HARQ) communication system.
In a High Speed Downlink Packet Access (HSDPA) communication system supporting HARQ, packet data is transmitted on a High Speed Physical Downlink Shared Channel (HS-PDSCH) and control information about the HS-PDSCH is transmitted on a High Speed Shared Control Channel (HS-SCCH) at the same time. The control information includes channelization code set information, modulation information, a Transport Block (TB) size, HARQ process information, a redundancy and constellation version, a New data Indicator (NI), and a User Equipment Identifier (UE ID).
The control information related to packet transmission will be detailed.
HS-DSCH Channelization Code Set
In a HSDPA system that increases communication efficiency using Adaptive Modulation and Coding Scheme (AMCS) and HARQ, some of the total downlink transmission resources are shared among a plurality of UEs. The downlink transmission resources include Orthogonal Variable Spreading Factor (OVSF) codes being orthogonal codes. The HSDPA communication system uses up to 15 OVSF codes with an SF of 16.
Referring to
In
Modulation Scheme (MS) information
As described above, the AMCS scheme adaptively changes a modulation scheme for a modulator and a coding rate for a channel encoder according to the change in condition the downlink channel environment. Typically, a UE measures the Signal to Noise Ratio (SNR) of a downlink signal and feeds back the SNR information to a Node B as an indication of a downlink channel status. The Node B estimates the downlink channel status based on the received information and selects an appropriate modulation scheme and coding rate according to the estimation.
When QPSK and 16QAM are used, the Node B must inform the UE the modulation scheme and coding rate of a current packet at each packet transmission. Because the coding rate is matched with a transport block combination, a High Speed Downlink Shared CHannel (HS-DSCH) channelization code set, and a modulation scheme, the Node B only has to transmit the MS information to the UE.
TB Size
TB size information indicates the size of a TB on a transport channel mapped to a physical channel.
Redundancy and Constellation Version (RV)
In a type of HARQ, IR, when an initial transmission data packet has errors, new parity bits related to the packet are transmitted at a retransmission. The RV indicates the ID of the bit combination transmitted. If a high-order modulation, 16QAM is used for the HS-PDSCH, a different version of constellation is adopted at each retransmission to change signal point locations to which transmission bits are mapped. The constellation version information indicates the version of a constellation used at a retransmission. The redundancy and constellation version (RV) information is represented in three bits to indicate a bit combination and a constellation version together.
NI
An NI indicates whether a current packet is initially transmitted or retransmitted. The NI is represented in one bit.
UE ID
The UE ID is specific to each UE. The UE determines whether the HS-SCCH and the HS-PDSCH are addressed to it in each time slot using its UE ID.
HARO Process ID
HARQ is a special case of ARQ with the following two schemes introduced to increase transmission efficiency. One is to transmit a retransmission request and a response between a UE and a Node B and the other is to temporarily store data having errors and combine the data with retransmitted data at a receiver.
Meanwhile, a typical Stop And Wait (SAW) ARQ scheme allows transmission of the next packet data only when an ACK is received for the current packet data. Then even if the packet data can be transmitted, the ACK is awaited. An n-channel SAW ARQ provided to solve this problem allows transmission of successive packet data without receiving an ACK for the current packet data.
That is, n time-divided logical channels are established between the UE and the Node B. The Node B tells the UE which logical channel delivers specific packet data using a predetermined time slot or channel number. The UE reorders packet data received at a particular time point in the original order using the HARQ process information or soft-combines the packet data.
Specifically, the UE is enabled to recover the packet data as much as can be using the NI flag in an embodiment of the present invention. According to the embodiment of the present invention, the NI flag is toggled at each new packet transmission and always fixed to a specific value (e.g. 1) at the initial transmission of each packet.
Referring to
The HARQ controller 806 reads an ACK or NACK received from the UE. In the case of an ACK, the HARQ controller 806 determines the RV as 000 and the NI as 1, and stores the inverse of prev_NI as the prev_NI. The prev_NI indicates a previous NI corresponding to a retransmission of a previous packet data and may be set to ‘0’ initially. The reason for setting the RV to 000 is that it is regulated to use the first redundancy/constellation version at an initial packet transmission. In the case of an NACK, an RV is selected and the NI is set to the prev_NI. If the RV is 000, the NI is set to 0.
The MUX 822 generates a bit stream in a slot format by multiplexing the channelization code set information, MS information, NI, HARQ process information, RV, and TB size information. A CRC coder 824 attaches a CRC to the bit stream. The CRC may be masked with a UE ID. An SPC 826 converts the CRC-attached control information bits to parallel information bits and outputs them separately as an in-phase (I) part and a quadrature-phase (Q) part to a spreader 828.
The spreader 828 spreads the I part and the Q part with a predetermined spreading code COVSF and provides an I channel signal and a Q channel signal separately to a summer 830. The summer 830 sums the I channel signal and the Q channel signal and outputs the sum in the form of a complex signal to a scrambler 832. The scrambler 832 scrambles the complex signal with a predetermined scrambling code CScramble.
A channel gain controller 834 multiplies the scrambled signal by a channel gain, and a modulator 836 modulates the gain-controlled signal using a predetermined modulation scheme. A Radio Frequency (RF) module 838 upconverts the modulated signal to a RF signal and transmits it through the antenna 840.
Referring to
On the contrary, if the response signal is an ACK, the HARQ controller 806 sets the RV to “000” and the NI to “1” to transmit a new packet in step 960 and stores the inverse of the stored prev_NI as prev_NI in step 970.
The structure of a receiving apparatus for receiving the HS-SCCH from the transmitting apparatus of
Referring to
A complex I/Q stream converter 1010 separates the complex signal from the multiplier 1008 into an I bit stream and a Q bit stream. Multipliers 1012 and 1014 multiply the I and Q bit streams by the same spreading code COVSF used in the Node B. Thus, the multipliers 1012 and 1014 act as despreaders. A channel compensator 1016 compensates for the distortion of the despreaded signals caused during transmission over the air from the Node B.
A PSC 1020 serializes the compensated signals. A CRC decoder 1022 checks the CRC of the serial signal from the PSC 1020. If no errors are detected, the CRC decoder 1022 outputs the signal to the DEMUX 1024. The DEMUX 1024 demultiplexes the received signal into channelization code set information, MS information, an NI, HARQ process information, an RV, and a TB size.
The control information interpreter 1042 interprets the control information. Especially the control information interpreter 1042 determines whether a current received packet is initially transmitted or retransmitted by the RV and NI included in the control information. Thus, it can be determined whether the current packet is initially transmitted or retransmitted based on the RV and NI.
With reference to
Referring to
On the other hand, if the NI is identical to the prev_NI in step 1130, the UE determines that the data received on the HS-PDSCH is a retransmission packet, combines the received data with the buffered data, and stores the combined data in the buffer in step 1150. In step 1160, the UE sets prev_NI to the current NI.
On the other hand, if the RV is 000, the UE determines whether the NI is 1 in step 1170. If the RV is 000 and the NI is 1, the UE clears the data from the HS-PDSCH buffer and stores the current received packet data in the buffer, assuming that the current packet data is a new packet in step 1180. In step 1190, the UE inverts the stored prev_NI and stores the inverse as prev_NI.
Referring to
If the Node B considers no response as a NACK and thus retransmits the packet B, the NI of the packet B is set to 0 at the retransmission, toggled from the NI of the retransmissions of the packet A. Thus, the UE recognizes the transmission of a new packet according to the NI of the retransmission packet B.
Then, the Node B receives an ACK for packet C from the UE and transmits packet D. If the packet D is lost during the initial transmission, the UE does not transmit a response signal (ACK/NACK). If the Node B considers no response as an ACK, it transmits packet E with an RV set to 000 and an NI set to 1. Therefore, the UE recognizes the transmission of a new packet.
As described above, the combination of the fixed and toggled NI transmission methods in the present invention minimizes packet loss.
In accordance with an embodiment of the present invention, packet loss is prevented by efficient transmission of the NI and thus retransmission through a higher layer is prevented in a physical layer, for high-speed packet data transmission/reception in a Wideband Code Division Multiple Access (WCDMA) wireless communication system. As a result, system throughput is improved.
While the invention has been shown and described with reference to a certain preferred embodiment thereof, it should 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-80755 | Nov 2003 | KR | national |
