HK1063700B - Rescheduling scheduled transmissions - Google Patents

Description

Rescheduling scheduled transmissions

Technical Field

The present invention relates generally to communications, and more particularly to improving scheduling of data transmissions.

Background

The field of wireless communications has many applications including, for example: cordless telephones, paging, wireless local area networks (wlans), Personal Digital Assistants (PDAs), Internet telephony (Internet telephony), and satellite communication systems (satellite communication systems). One particularly important application is cellular telephone systems for mobile subscribers. (as used herein, the term "cellular" includes frequencies of cellular and personal communications services (PCS.) various air interfaces have been developed for such cellular telephone systems, including, for example: frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). In connection therewith, various national and international standards have been established including, for example: advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM), and Interim Standard 95 (IS-95). In particular, IS-95 and its derivatives IS-95A, IS-95B, ANSIJ-STD-008 (these are often collectively referred to herein as IS-95), and proposed high-data-rate systems for data, among others, are promulgated by the Telecommunications Industry Association (TIA), the International Telecommunications Union (ITU), and other well-known standards bodies.

Cellular telephone systems configured in accordance with the use of the IS-95 standard use CDMA signal processing techniques to provide efficient and robust cellular telephone service. Typical cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. patent nos.5,103,459 and 4,901,307, both assigned to the assignee of the present invention and incorporated herein by reference in their entirety. A typical system described using CDMA Technology is the CDMA2000ITU-R Radio Transmission Technology (RTT) Candidate recommendation issued by the TIA (referred to herein as CDMA 2000). The standard for cdma2000 IS given in the draft version of IS-2000 and has been approved by the TIA. The cdma2000 scheme IS downward compatible with IS-95 systems. Another CDMA standard is the W-CDMA standard, as included in document numbers 3G TS 25.211, 3G TS 25.213, and 3G TS 25.214 of 3rd Generation partnership project (3rd Generation partnership project) "3 GPP".

In the CDMA system described above, voice and data traffic may be transmitted using information frames (message frames) of different lengths. Typically, a remote station (remote station) within range of a base station must receive and decode a set of information frames in order to determine the complete speech and data payload information. A header is attached to the information frame to convey information, such as regarding the number of information frames that will send a given payload. In addition to the number of frames required to transmit the entire payload, the header may also transmit information identifying the target destination and the transmission rate of the information frames. Other information such as Radio Link Protocol (RLP) sequence numbers of the information frames may also be included. Thus, accurate decoding of an information frame relies on the detection and decoding of a header attached to the information frame.

It is desirable to optimize the throughput of the system with successful or unsuccessful decoding of the message by the frame header and associated information frame. In particular, it would be desirable to utilize such information to quickly change the transmission schedule of information frames.

SUMMARY

An ARQ (automatic repeat request) channel is implemented on the reverse link of the communication system, on which positive or negative acknowledgements are sent in response to received transmissions. The system proposed here changes the already existing transmission schedule based on the signal or lack of signal on the ARQ channel.

In one aspect, a method of improving transmission scheduling is presented. The method comprises the steps of sending a group of frame header sub-packet data and a group of data service sub-packet data in parallel according to the transmission scheduling; monitoring a signal on an acknowledgement channel; if no signal is detected, continuing to transmit according to the transmission schedule; if a signal is detected, determining whether a sender of the signal is a destination station; if the signal is from the target station, canceling the transmission schedule and forming a new transmission schedule with new data traffic if the signal is an acknowledgement, or continuing to transmit retransmissions in accordance with the transmission schedule if the signal is a negative acknowledgement; and if the signal is not from the target station, aborting retransmission within a time limit of less than or equal to one second if the signal is a negative acknowledgement, or transmitting retransmission if the signal is a positive acknowledgement.

In another aspect, an apparatus in a base station for adjusting an existing scheduling plan for transmitting redundant data packets is presented. The apparatus includes a frame header channel generator for transmitting a frame header sub-packet data; a data traffic channel generator for transmitting data traffic sub-packet data; a scheduling unit electrically connected to the frame header channel generator and the data service channel generator, the scheduling unit for controlling the packing of frame header information into the frame header sub packet data and data service into the data service sub packet data, and for controlling the transmission sequence of the frame header sub packet data and the transmission sequence of the data service sub packet data; and a receiver subsystem electronically connected to said scheduling unit, said receiver subsystem for detecting a signal from a remote station on an acknowledgment channel, wherein said scheduling unit controls the transmission sequence of said frame header subpacket data and the transmission sequence of said data service subpacket data according to said signal or the absence of said signal on said acknowledgment channel, wherein the arrival of said signal indicates that said frame header subpacket data was successfully decoded and the absence of said signal indicates that said frame header subpacket data was not successfully decoded.

According to the present invention there is provided a method of rescheduling scheduled transmissions between a base station and a target remote station comprising: scheduling frame header information and data traffic for transmission to the target remote station, wherein the scheduling includes grouping the frame header information and the data traffic into a plurality of frame header sub-packet data and a plurality of data traffic sub-packet data to be transmitted to the target remote station; according to the scheduling, at least one frame header sub-packet data in the plurality of frame header sub-packet data and at least one data service sub-packet data in the plurality of data service sub-packet data are sent; waiting for a signal to be transmitted on an acknowledgement channel; rescheduling transmission of frame header information and data traffic to the target remote station if no signal is received on the acknowledgment channel within a reasonable time; scheduling transmission of new frame header information and new data traffic if the signal received on the acknowledgement channel is a positive acknowledgement from the target remote station; continuing said scheduling by transmitting another one of said plurality of frame header sub-packet data and another one of said plurality of data traffic sub-packet data if the signal received on said acknowledgment channel is a negative acknowledgment from said target remote station; if the signal received on the acknowledgment channel is a positive acknowledgment from the wrong remote station, ignoring the signal and continuing the scheduling by sending another one of the plurality of frame header subpacket data and another one of the plurality of data traffic subpacket data; and if the signal received on the acknowledgement channel is a negative acknowledgement from the wrong remote station, ignoring the signal and interrupting all transmissions for a predetermined time.

According to the present invention there is also provided an apparatus for rescheduling scheduled transmissions between a base station and a target remote station, comprising: means for scheduling frame header information and data traffic for transmission to the target remote station, wherein the scheduling means groups frame header information and data traffic into a plurality of frame header sub-packets and a plurality of data traffic sub-packets to be transmitted to the target remote station, and the scheduling means is responsive to signals received on an acknowledgement channel, wherein if no signals are received on the acknowledgement channel within a reasonable time, the scheduling means reschedules transmission of the frame header information and data traffic to the target remote station, but if the signals received on the acknowledgement channel are positive acknowledgements from the target remote station, the scheduling means schedules transmission of new frame header information and new data traffic; and if the signal received on the acknowledgment channel is a negative acknowledgment from the target remote station, the scheduling means continues the scheduling by transmitting another one of the plurality of frame header sub-packet data and another one of the plurality of data traffic sub-packet data; and if the signal received on the acknowledgment channel is a positive acknowledgment from the wrong remote station, the scheduling means ignores the signal and continues the scheduling by transmitting another one of the plurality of frame header sub-packet data and another one of the plurality of data service sub-packet data; and if the signal received on the acknowledgement channel is a negative acknowledgement from an erroneous remote station, the scheduling means ignores the signal and interrupts all transmissions for a predetermined time; and means for transmitting at least one of the plurality of frame header sub packet data and at least one of the plurality of data service sub packet data according to the scheduling.

According to the present invention, there is also provided a method for enhancing transmission scheduling, comprising: according to the sending scheduling, sending a plurality of frame header sub-packet data and a plurality of data service sub-packet data in parallel; monitoring a signal on an acknowledgment channel; if no signal is detected, continuing to transmit according to the transmission scheduling; if the signal is detected, judging whether a sender of the signal is a target station or not; if the signal is from the target station, canceling the transmission scheduling and forming a new transmission scheduling by using new frame header information and new data service if the signal is a positive acknowledgement, otherwise, re-transmitting according to the transmission scheduling if the signal is a negative acknowledgement; and if the signal is not from the target station, interrupting the retransmission for a period of time if the signal is a negative acknowledgement, otherwise, performing the retransmission if the signal is a positive acknowledgement.

Drawings

Fig. 1 is a diagram of a typical communication system.

Fig. 2 is a block diagram of an apparatus that can be used to generate a frame header channel.

Fig. 3 is a block diagram of a frame header decoder.

Fig. 4 is a block diagram of an apparatus that can be used to generate an ARQ channel.

Fig. 5 is a flow chart illustrating the use of ACKs and NAKs at the base station to facilitate retransmission and new transmissions.

Fig. 6 is a flow chart illustrating the generation of ACKs and NAKs at the remote station and the use of ACKs and NAKs at the base station.

Detailed Description

As shown in fig. 1, a wireless communication network 10 generally includes a set of remote stations (also referred to as mobile stations or subscriber units or user equipment) 12a-12d, a set of base stations (also referred to as Base Transceiver Stations (BTSs) or node bs) 14a-14c, a Base Station Controller (BSC) (also referred to as radio network controller or packet control function) 16, a Mobile Switching Center (MSC) or switch 18, a Packet Data Serving Node (PDSN) or internetworking function (IWF)20, a Public Switched Telephone Network (PSTN)22 (typically a telephone company), and an Internet Protocol (IP) network 24 (typically the internet). For simplicity, four remote stations 12a-12d, three base stations 14a-14c, one BSC16, one MSC18, and one PDSN20 are shown. Those skilled in the art will appreciate that there may be any number of remote stations 12, base stations 14, BSCs 16, MSCs 18, and PDSNs 20.

In one embodiment the wireless communication network 10 is a packet data service network. The remote stations 12a-12d may be any of a number of different types of wireless communication device such as a mobile telephone, a cellular telephone connected to a laptop computer running IP-based web browser applications, a cellular telephone associated with a hands-free car kit, a Personal Data Assistant (PDA) running IP-based web browser applications, a wireless communication module incorporated into a portable computer, or a fixed location communication module such as might be found in a wireless local loop (wireless local loop) or meter reading system (meter reading system). In most general embodiments, the remote station may be any type of communication unit.

The remote stations 12a-12d may be configured to execute one or more wireless packet data protocols, such as the protocol described in EIA/TIA/IS-707. In one particular embodiment, the remote stations 12a-12d generate IP packets destined for the IP network 24 and encapsulate the IP packets into frames using a Point-to-Point protocol (PPP).

In one embodiment, the IP network 24 is connected to a PDSN20, the PDSN20 is connected to a MSC18, the MSC18 is connected to the BSC16 and the PSTN22, and the BSC16 is connected to the base stations 14a-14c via wireline configured to transport voice and/or data packets according to any of several known protocols, including, for example, E1, T1, Asynchronous Transfer Mode (ATM), IP, frame relay, HDSL, ADSL, or xDSL. In another embodiment, the remote stations 12a-12d communicate with the base stations 14a-14c over an RF interface as defined in "Physical Layer Standard for cdma2000 spread Spectrum Systems" ("Physical Layer Standard for cdma2000 spread Spectrum Systems") under 3GPP2 document No. C.P0002-A, TIA PN-4694 and published as TIA/EIA/IS-2002-2-A (draft modified version 30) (11/19/1999) in third Generation Partnership Project 2(3rd Generation Partnership Project 2) "3 GPP 2", which IS hereby incorporated by reference in its entirety.

During typical operation of the wireless communication network 10, the base stations 14a-14c receive and demodulate sets of reverse link signals from various remote stations 12a-12d engaged in telephone calls, web browsing, or other data communications. Each reverse link signal received by a given base station 14a-14c is processed at that base station 14a-14 c. Each base station 14a-14c may communicate with a group of remote stations 12a-12d by modulating and transmitting sets of forward link signals to the remote stations 12a-12 d. For example, as shown in FIG. 1, the base station 14a communicates with first and second remote stations 12a, 12b simultaneously, and the base station 14c communicates with third and fourth remote stations 12c, 12d simultaneously. As a result, the packet data is forwarded to the BSC16, and the BSC16 provides call resource allocation and mobility management functions including placing a soft handoff of a call from one base station 14a-14c to another base station 14a-14 c. For example, one remote station 12c is communicating with two base stations 14b, 14c simultaneously. Finally, when the remote station 12c moves far enough away from one base station 14c, the call will be handed off to another base station 14 b.

If a conventional voice call is being transmitted, the BSC16 forwards the received data to the MSC18, and the MSC18 provides other delivery services that interface with the PSTN 22. If the transmission is a packet-based transmission, such as a data call destined for the IP network 24, the MSC18 will pass the data packet to the PDSN20, and the PDSN20 will send the packet data to the IP network 24. Alternatively, the BSC16 passes the packet data directly to the PDSN20, and the PDSN20 sends the packet data to the IP network 24.

The process of transmitting both data and voice on the forward and reverse links can be problematic. In a system using variable rate coding and decoding of voice traffic, a base station will not transmit voice traffic at a fixed power level. The use of variable rate encoding and decoding translates speech characteristics into speech frames that are optimally encoded at a variable rate. In a typical CDMA system, these rates are full, half, quarter, and eighth rates. These encoded speech frames can then be transmitted at different power levels, and if the system is properly designed, a desired target Frame Error Rate (FER) can be achieved. The use of VARIABLE RATE encoding and decoding is described in detail in U.S. patent No.5,414,796 entitled "VARIABLE RATE decoder," which is assigned to the assignee of the present invention and is incorporated herein by reference. Since the transmission of voice traffic frames does not require the use of the maximum power level that the base station may transmit, data traffic of packet data may be transmitted using the remaining power.

Thus, if a speech frame is transmitted at a given time X (t) in XdB, but the base station has a maximum transmission capacity of YdB, then there is (Y-X) dB of remaining power available for data traffic to transmit packet data. Since the voice traffic frames are transmitted at different transmission power levels, the number (Y-X) is unpredictable. One way to deal with this uncertainty is to repackage the data traffic payload into duplicate and redundant sub-packets (subpackets). Redundant copies of the data payload are packed into frames or packets, sub-packets, or other system-related terminology, which may then be soft-combined at the receiving party. The soft combining process allows recovery of corrupted bits.

By combining one corrupted sub-packet with another corrupted sub-packet in a soft combining process, the transmission of duplicate and redundant sub-packets allows a system to transmit data at a minimum transmission rate. Transmitting duplicate and redundant sub-packets is particularly desirable in the presence of fading. Rayleigh fading (Rayleigh fading), also known as multipath interference (multipath), occurs when multiple copies of the same signal arrive at the receiving party in a destructive manner. True multipath interference can occur causing flat fading (flat fading) of the entire frequency bandwidth. If the remote station moves in a rapidly changing environment, deep fades often occur when arranging sub-packets for retransmission. When such a situation occurs, the base station needs additional transmission power to transmit the sub-packet data. There is a problem if the remaining power level is not sufficient to retransmit the sub-packet.

For example, if a scheduler unit (scheduler unit) within a base station receives a data payload to be transmitted to a remote station, the data payload is redundantly packed into a set of subpackets to be transmitted sequentially to a remote station. Redundancy refers to the transmission of substantially similar information by each sub-packet. When transmitting the sub-packet data, the scheduler unit may decide to transmit the sub-packet data either periodically or in a channel sensing manner.

For ease of explanation, the nomenclature of a cdma2000 system is used herein. Such use is not intended to limit the present invention to cdma2000 systems. In a typical CDMA system, data traffic may be transmitted in packet data, which consists of sub-packets occupying time slots. The slot length has been specified as 1.25ms, but it should be understood that the slot length in the embodiments described herein may vary without affecting the scope of the embodiments. In addition, the data traffic can be transmitted in information frames, which may be 5ms, 10ms, 20ms, 40ms, or 80ms in duration. The terms "time slot" and "frame" are terms used in relation to different data channels. A CDMA system includes many channels on the forward and reverse links, some of which are generated differently than others. Therefore, the terms describing some channels will differ according to the channel structure. For purposes of illustration only, the term "time slot" will be used hereinafter to describe a packet (packing) of a wirelessly propagated signal.

The forward link includes a set of channels including, but not limited to, a pilot channel (pilot channel), a synchronization channel (synchronization channel), a paging channel (paging channel), a quick paging channel (quick paging channel), a power control channel (power control channel), an allocation channel (assignment channel), a control channel (control channel), a dedicated control channel (dedicated control channel), a fundamental channel (fundamental channel), a supplemental channel (supplemental channel), a supplemental code channel (supplemental code channel), and a packet data channel (packet data channel). The reverse link also includes a set of channels. Each channel conveys different types of information to a target destination. Typically, voice traffic is transmitted on the fundamental channel, while data traffic is transmitted on the supplemental channel or packet channel. The supplemental channels are typically dedicated channels, while the packet data channels typically transmit signals assigned to different users in a time-multiplexed (time-multiplexed) manner. Alternatively, the packet data channel is also described as a common supplemental channel(s). For the purposes of describing embodiments herein, the supplemental channel and the packet data channel are generally referred to as a data traffic channel (data traffic channel).

The supplemental channel and the packet data channel can improve the average transmission rate of the system by allowing unexpected data messages to be transmitted to the destination. Since the remote station has no way of determining when a sub-packet addressed to itself arrives, a header with addressing information for the remote station must be associated with each sub-packet. If the sub-packet data transmission is periodic, the first sub-packet must have a frame header that is easy to detect and decode, and that also informs the receiving station of the time interval in which future sub-packets will arrive. Alternatively, the delay between periodic transmissions may be a system parameter known to the recipient. If subsequent sub-packet transmissions are aperiodic after the first sub-packet transmission, then there must also be a frame header for each subsequent sub-packet transmission.

In one embodiment, an ARQ channel is generated for the reverse link, so that the remote station can send an acknowledgement signal if a sub-packet has been decoded correctly. If a base station receives such a signal, there is no need to transmit redundant sub-packets, thus increasing the throughput of the system.

In this data transmission scheme, the remote station must be able to detect and decode the redundant sub-packets. The transmission of these further sub-packets may alternatively be referred to as "retransmission" since the further sub-packets transmit redundant data payload bits. To detect retransmission, it is desirable for the remote station to be able to detect the header bits of the frame, which typically precede the subpacket data.

It should be noted that if the retransmission is being sent at a lower available power, the frame header may also be sent at a lower power. Since it is crucial to decode the frame header accurately, there is a possibility: if the receiver cannot successfully decode the frame header with lower remaining power, the entire sub-packet data is lost.

Another consideration is the overhead occupied by the frame header. If the length of the frame header is M bits and the length of the whole sub-packet is N bits, a fixed percentage of the M/N transmitted code stream is put into the non-service information. This inefficiency means that a more optimal data transmission rate can be achieved if the frame header information can be transmitted more efficiently.

The embodiments described herein decode frame header information for those systems that send frame header information on a channel separate from the channel on which the user payload is sent. In addition, the positive and negative acknowledgements associated with the received frame header and decoding of the data sub-packet data can be used by the base station to optimize the scheduling of retransmissions.

In a system that includes an ARQ channel on the reverse link and a frame header channel and a data traffic channel on the forward link, the base station will send packetized data traffic on the data channel and frame header traffic on the frame header channel, wherein the frame header traffic informs the remote station that it is the target destination of sub-packet data on a time slot of the designated data traffic channel. The use of an ARQ channel on the reverse link informs the transmitting base station that its data communication has or has not been accurately decoded by the remote station. In one embodiment described herein, signals received on the ARQ channel are used to directly acknowledge receipt of data sub-packets on the data traffic channel and indirectly acknowledge receipt of a frame header on the frame header channel. Using these inferences about the received frame header, the scheduler unit in the base station can improve the scheduling of retransmissions and new data traffic payloads by making the scheduling more efficient.

An example of an apparatus that can be used to generate the frame header channel is shown in fig. 2. In fig. 2, for transmission on the forward link, a header sequence is generated using the equipment described by the functional units. In one embodiment, the Forward link Channel over which the frame header information is sent will be referred to as a Forward second Packet Data Control Channel (F-SPDCCH).

The incoming frame header information stream includes bits designated for use as a Medium Access Control (MAC) identifier, a sub-packet identifier, and an ARQ channel identifier. Additional information such as the size of the payload and the number of slots used per data traffic channel may be transmitted by the frame header information stream for use in a multi-channel system. In one embodiment, the data traffic channel is referred to as a forward packet data channel (F-PDCH).

In one embodiment, the frame header information code stream contains fifteen bits per N-slot F-SPDCCH sub-packet, where N is 1, 2, or 4. Of the fifteen bits, six bits are assigned to the MAC identifier, two bits to the sub-packet identifier, two bits to the ARQ channel, three bits to the payload size, and two bits to the number of slots that the payload occupies the traffic channel. The MAC identifier is assigned to the remote Station when the remote Station enters the communication system according to a unique International Mobile Station Identity (IMSI).

In one embodiment, an extra bit may be added to the header information code stream by the Cyclic Redundancy Check (CRC) encoding unit 210 so that the number of bits of the transmitted header information with higher spectral efficiency is suitable for Quadrature Amplitude Modulator (QAM).

In another embodiment, an additional set of bits may be added at the end of the header information sequence in zero-padding units, so that the convolutional encoding element 230 is reinitialized by each new header information stream. In one embodiment, the zero padding unit adds eight zero-valued bits on the frame header code stream.

After the zero padding, the frame header is input to the encoding unit 230. In one embodiment where twenty-four bit code symbols have been generated from the initial fifteen bit frame header code stream, a convolutional encoder with a constraint length of K9 and operating at a code rate of R1/2 is sufficient to generate forty-eight bit code symbols per F-SPDCCH.

In this embodiment, a repeating sequence of 48-bit code symbols is then made using the repeating unit 240. For a repetition factor N, there will be 48N symbols per N-slot F-SPDCCH subpacket. In an embodiment where the slot length is 1.25ms, the symbol rate of the repeated sequence is 38.4 kilosymbols per second (ksps). After repetition, the symbols are then interleaved by an interleaving unit 250 to protect against fading conditions inherent in mobile wireless communication transmissions.

The interleaved symbols are then split into in-phase (I) and quadrature-phase (Q) components using a Quadrature Phase Shift Keying (QPSK) modulator unit. In one embodiment, the I and Q symbols are then transmitted by the amplifiers 270, 280 using the jth 64-ary Walsh code function (jth 64-ary Walsh code function). It should be noted that for other CDMA systems, other orthogonal or quasi-orthogonal functions may be used in place of Walsh code functions. This resulting sequence is wirelessly transmitted to the destination station.

Fig. 3 is a block diagram of one embodiment of a frame header decoder located at a destination station. As discussed above, accurately decoding the frame headers on the F-SPDCCH is the basis for receiving data traffic on the forward link, particularly on the F-PDCH, which is a data traffic channel designed to start transmission in irregular situations. The frame header decoder depicted in fig. 3 is intended to be used in a communication system comprising at least one frame header channel and at least one data traffic channel. In one embodiment, the header and data traffic are sent in sub-packets and occupy the same slot position in parallel channels. That is, the time slot occupied by the frame header on the frame header channel has the same time limit as the time slot occupied by the data service sub-packet data on the data service channel.

In another embodiment, the number of frame header slots need not be the same as the number of slots occupied by data traffic. In the embodiment shown in fig. 3, the frame header sub-packet data is designed to occupy 1, 2 or 4 slots, while the data communication sub-packet may occupy 1, 2, 4 or 8 slots. The destination may use the MAC identifier sent by the frame header sub-packet data to determine the eight (8) slots of data traffic on the data traffic channel that correspond to the frame header.

Whether the number of frame header channel slots better reflects the number of traffic channel slots is independent of the novel frame header decoding apparatus and method described herein. For convenience of explanation, only one frame header decoder is described, which is used for a system for transmitting frame header sub-packet data using 1, 2, or 4 slots.

At the receiver (not shown) a demodulated sequence of soft decision values is input to a set of detection units 390a, 390b, 390c, which are arranged to accommodate data from a variable number of time slots. Each detection unit 390a, 390b, 390c receives a sequence of values from a variable number of time slots and inputs it into parallel deinterleaving units 300a, 300b, 300 c. In one embodiment, the first deinterleaving unit 300a deinterleaves over four (4) time slots. The second deinterleaving unit 300b deinterleaves over two (2) time slots. The third deinterleaving unit 300c deinterleaves over one (1) slot. The output of the first deinterleaving unit 300a is software-combined by the combining unit 310a so that four sequences each of which has occupied one slot are software-combined into one sequence. The outputs of the second deinterleaving unit 300b are software-combined by the combining unit 310b so that two sequences each of which has occupied one slot are software-combined into one sequence. The output of each combining unit 310a, 310b and the third deinterleaving unit 300c is each input to a separate decoding unit 320a, 320b, 320 c. In one embodiment, a convolutional decoder with constraint length K-9 and R-1/2 is used for each parallel stream. It should be understood that other decoders may be used without affecting the scope of this embodiment.

The output for each decoding unit 320a, 320b, 320c is a data sequence and a best path metric value. Thus, at this point in this embodiment, there are three data sequences and three best path metric values. Each of the three data sequences is input to one of a set of sequence checking units 330a, 330b, 330 c. The sequence check unit may be comprised of a processing unit and a memory unit, the sequence check unit configured to determine whether a bit value of a decoded symbol matches a known set of identifiers. In one embodiment, the known set of identifiers can include information such as a MAC identifier, an expected number of F-PDCH slots, and/or check bits.

Since the header sequence is initially encoded to occupy one, two or four time slots, only one output from the sequence checking units 330a, 330b, 330c should result in one data sequence. Other check units that do not match the data sequence to a known identifier will be set to output a null value.

However, if for some reason more than one data sequence is output from the sequence check elements 330a, 330b, 330c, a selection unit 340, consisting of a processing unit (not shown) and a memory (not shown), may be used to select one data sequence as the correct header sequence. The selection unit 340 is configured to receive the data sequence from the sequence checking unit 330a, 330b, 330c and the best path metric value from each decoding unit 320a, 320b, 320 c. Using the best path metric value, the selection unit 340 can select a data sequence as the header of the decoded frame and pass this data sequence to the receiver along with an indication of the time slot used to transmit this data sequence.

While the frame header decoder of fig. 3 is decoding information on the frame header channel, the receiver receives information on the data traffic channel. In one embodiment, a plurality of buffers are set up to receive and store slot information according to a slot size. For example, a first buffer is used to store the soft decision value for one time slot. A second buffer is used to store the soft decision values for both slots. A third buffer is used to store the soft decision values for the four time slots. A fourth buffer is used to store the soft decision values for 8 slots. Once the frame header decoder makes a decision regarding the number of slots to send the frame header or the number of slots indicated by the frame header contents, the control unit receives the slot number information and selects the appropriate buffer contents for decoding. Only the selected buffer contents need to be decoded.

An acknowledgement of the receipt of the information is desirable once the frame header information and data traffic are received and decoded at the receiving station. In one embodiment, the ARQ channel is configured to communicate acknowledgement information. However, in addition to direct acknowledgement of the active data traffic subpacket data, an acknowledgement signal may be used to make inferences as to whether the frame header is intact. Accordingly, an ARQ channel configured to acknowledge the reception of one channel can be used to acknowledge the reception of two channels.

An example of an apparatus for generating an ARQ channel structure is shown in fig. 4. The remote station (not shown) generates a bit, either 0 or 1, for each slot indicating that the sub-packet has or has not been decoded accurately. The bit is repeated a number of times in the repeat unit 400. In a system transmitting at a rate of 1.2288Mcps, the optimal repetition factor is twenty-four (24). The term "chip" is used to describe a bit in a spreading sequence, such as a bit pattern that is spread in a Walsh code. The output of the repetition unit 400 is mapped by the mapping unit to either +1 or-1. The output of the mapping unit 410 is taken care of by the diffusion unit 420. In one embodiment, spreading unit 420 may be an output amplifier spread mapped with ith64-ary Walsh code function (jth 64-ary Walsh codefunction). The use of Walsh codes provides channel selection and prevents phase errors in the receiver. It should be noted that for other CDMA systems, other orthogonal or quasi-orthogonal functions could be used in place of Walsh code functions.

Fig. 5 is a flow chart describing a method for scheduling retransmissions by a scheduler unit in a base station using information received on an ARQ channel or lost information. The method allows the base station to optimize the retransmission of data traffic to the target remote station in accordance with the acknowledgement sent by the target remote station on the ARQ channel. It should be noted that there are two ways to send redundant sub-packets or "retransmissions". First, a group of sub-packet data may be transmitted in a periodic manner. Although the first transmission may not be pre-determined, it is possible to implement a traffic channel in which all retransmissions of the first transmission occur after a predetermined delay. This predetermined delay may be a system parameter so that after the target station receives the first data transmission and the first frame header transmission, subsequent retransmissions do not send a frame header because the target station knows that the received subpacket is directed to itself after the predetermined delay. This periodic transmission method is called Synchronous Incremental Redundancy (SIR).

A second way to transmit redundant sub-packet data is to transmit sub-packet data in an aperiodic manner according to channel conditions. This channel sensing scheme requires the use of one frame header for each redundant sub-packet data being transmitted because the destination station cannot otherwise determine whether it is the correct target for the data traffic payload. This aperiodic transmission is referred to as asynchronous added redundancy (AIR).

In step 500, a scheduling unit, comprised of at least one control processor and a memory unit, in a base station (not shown) schedules transmission of frame headers and associated data service sub-packets of data over a set of slots in a frame header channel and a data service channel, respectively.

In step 505, a receiver subsystem in a base station receives a signal on an ARQ channel. If the signal is an ACK, the program flow process proceeds to step 510. If the signal is a NAK, program flow proceeds to step 515.

In step 510, the base station determines whether the ACK is a false alarm. A false alarm is an ACK from a remote station that is not the target station. The base station knows that the ACK is a false alarm because the base station can determine the identity of the remote station. In a CDMA system, the reverse link channel can be identified with a time shift in a long pseudo-random noise (PN) code. A detailed description of this identification process is provided in the aforementioned U.S. patent nos.5,103,459 and 4,901,307. If the remote station identity is correct, then the base station knows that the frame header was received and transmits the next data traffic payload instead of the retransmission of the previous data traffic payload in step 520. If the identity of the remote station is not correct, then the base station ignores this ACK signal and continues with the scheduled retransmission at step 530.

Since the remote station has sent an ACK in the event that the first transmission is deemed to be it, the retransmission of any more redundant sub-packet data will be a message to the remote station: the first transmission is an error. This remote station may be programmed to discard the first transmission if a retransmission occurs even after the ACK is sent.

In step 515, the base station has received the NAK and must confirm the identity of the sender of the NAK as the target station. Here, the receipt of the NAK tells the base station that the frame header was received, but that no data traffic subpacket data was received. If the NAK is from the target station, the base station transmits the next retransmission, step 525. If there is no scheduled retransmission, the base station reschedules a new series of redundant sub-packets that transmit the same data traffic payload. In step 535, the base station determines that the NAK is from an erroneous receiving station and overflows a timer common to both the base station and the erroneous station without retransmission. Since the base station intentionally ignores the negative acknowledgement of this remote station, this remote station will know that it is not the target of the frame header and data traffic because the retransmission was not received in time. The remote station may include a timer that starts counting when the first transmission is received and stops when the other is subsequently received. If no subsequent packet data arrives before the timer expires, the remote station knows that the first transmission is an error and discards the first transmission.

At step 540, the base station receives neither a positive nor a negative acknowledgement. If the signal is not received within a predetermined delay, the base station knows that the frame header has not been received. If the system is in accordance with the SIR transmission scheme, the base station knows that the first sub-packet data is not received and that subsequent retransmissions will not be received. Therefore, the entire data traffic payload must be rescheduled for transmission. In one embodiment, this problem may be avoided by sending two frame headers in the SIR system, one for the first transmission and the other for the first retransmission. If the first frame header is not received, it is possible that the second frame header may also be received and decoded. Then, the program flow can go to step 505. If, however, neither the first nor the second frame header is received within the allocated waiting period, the process flow will return to step 500 where the base station reschedules the old data traffic for another transmission mode.

Fig. 6 is a flow chart describing an error correction scheduling scheme between a base station (not shown) and a remote station (also not shown) when a transmission error occurs in an ARQ channel, a frame header channel, or a data traffic channel. At step 600, the remote station receives a frame header transmission and a sub-packet data transmission. The program flow is split into two paths since the remote station may erroneously determine itself as the target destination for this frame header transmission and sub-packet transmission. If the remote station is the correct target for the base station transmission, then program flow goes to step 610. If the remote station is not the correct target for the base station transmission, then program flow goes to 615.

If the remote station receiving the transmission is the intended recipient of the transmission, then at step 610 the remote station decodes the information conveyed by the frame header channel. A method of decoding frame header information is described in the foregoing. If the frame header is decoded correctly, the remote station decodes the associated sub-packet information on the data traffic channel at step 620. If the sub-packet can be decoded correctly, the remote station sends an ACK at step 622. When the ACK is received at a receiver subsystem in the base station, a scheduling unit in the base station stops the scheduled retransmission of the redundant sub-packet data on the forward link and schedules the transmission of a new data payload in step 624. It should be noted that this new data payload may be directed to the same remote station that sent the ACK, or the new data payload may be directed to another remote station within transmission range of the base station.

Due to interference during transmission, the ACK sent by the remote station may be tampered with and reduced to the point that the receiver subsystem in the base station reads a NAK on the ARQ channel instead of an ACK. When this occurs, the scheduling unit of the base station will continue with the scheduled retransmission. The remote station will then receive a redundant sub-packet that can be identified as a redundant transmission and will use a metric value from the decoder to determine which sub-packet to pass to the RLP layer. The RLP layer provides for the in-order delivery of RLP packets and detection of duplicate packets, which will reduce the radio link error rate as seen in higher layer protocols.

If the sub-packet data transmitted on the data traffic channel cannot be decoded, the remote station transmits a NAK at step 626. In step 628, the base station transmits a retransmission. The remote station retains the old sub-packet data in a buffer until a timer expires and delivers the old sub-packet data to the RLP layer as an error. If the retransmission arrives within the time allotted by the timer, the retransmission is decoded and passed to the RLP layer if the appended CRC bits pass the CRC check. If the retransmission cannot be decoded, the retransmission is passed to the RLP layer as an error.

Alternatively, if a NAK is tampered with during transmission and therefore it will be misread as an ACK, the base station will send a new data payload to the remote station. In this case, the remote station keeps the old sub-packet data in a buffer until a timer expires. If the timer overflows before a retransmission arrives, the old data sub-packet is delivered as an error to the RLP layer.

If the remote station sends a NAK, but the receiver subsystem in the base station does not detect an ACK or NAK, it will be assumed that the transmission of the old data payload was never set or rescheduled by the scheduling unit that did not receive the frame header. The remote station retains the old data sub-packet data until a timer expires. If the timer overflows before a retransmission arrives, the old data sub-packet is delivered as an error to the RLP layer.

If the remote station is unable to decode the frame header payload, i.e., information regarding the associated data traffic subpacket, then process flow transitions from step 610 to step 630, where the remote station does not send a transmission on the ARQ channel. If no positive or negative acknowledgement is received at the base station, the scheduling unit at the base station will be set to reschedule the old data payload to a new transmission schedule assuming that the frame header was not received from the scheduling unit. It should be noted that the ARQ channel is used to acknowledge receipt of the data service sub-packet data. If a NAK has been generated and received in this example, the scheduling unit will assume that the frame header has arrived completely and will only send a retransmission that has been scheduled, or will send a new data payload if a NAK has been tampered with and read as an ACK.

If the remote station fails to decode the header payload correctly, e.g., if the remote station fails to decode the sequence numbers of the sub-packets correctly, the remote station may become a collision when a subsequent sub-packet arrives, either with the same information or with an out-of-sequence number. In one embodiment, the remote station is programmed to either ignore newly arriving sub-packet data with collision information or use a metric to select between old sub-packet data and newly arriving sub-packet data stored in the buffer. If the remote station is programmed to ignore a newly arrived sub-packet with conflicting information, then no resources are required to decode the sub-packet. In either case, no signal is sent to the base station on the ARQ channel, so the base station reschedules the transmission of the old data payload.

In another path, if the remote station receives a transmission that the remote station is not the intended recipient, process flow proceeds from step 600 to step 615. At step 615, the remote station attempts to decode the frame header sequence received on the frame header channel. If the frame header can be decoded, then the remote station will attempt to decode the associated sub-packet data in step 625.

If the sub-packet data can be decoded correctly, the remote station will deliver the decoded transmission to the RLP layer and send an ACK in step 627. In step 699, the base station receives the ACK but ignores the signal because the signal is from an unwanted recipient. The base station is able to determine that the remote station is not the intended target because of the uniquely time-shifted identification of the long PN code. The scheduling unit of the base station continues without acknowledging this signal because the scheduling unit knows that the remote station is not the intended recipient of a previous transmission from the base station. At the remote station, the RLP layer has received the data of the data sub-packet and determined that the data of this data sub-packet was delivered in error.

If the ACK signal is tampered to the extent that the receiver subsystem of the base station detects the ACK as a NAK, the base station again ignores the signal because the base station has determined that the signal is a false alarm. The RLP layer of the remote station handles the error. If the base station does not detect a signal, the predetermined retransmission scheme continues and the RLP layer of the remote station handles the error.

If, at step 625, the remote station is unable to decode the sub-packet data, the remote station sends a NAK at step 631. In step 699, the base station determines that the remote station that has sent a NAK is not the intended recipient of the original transmission and ignores this signal. In one embodiment, a timer may be set in the base station and the remote station so that if the base station ignores the signal and refrains from transmitting a retransmission, the remote station is notified that the previous transmission is a false alarm. The remote station will keep the old transmission in the buffer and then pass the old transmission to the RLP as an error. If a retransmission is received before the timer expires, the remote station may either pass the retransmission to the RLP or the software combines the retransmission with the old transmission and passes the result of the software combination to the RLP. At the RLP layer, errors are detected and corrected.

If the receiver subsystem does not detect a NAK from the remote station, the base station will continue retransmission of the predetermined redundant sub-packet. This action will cause the remote station to buffer and decode retransmissions that are deemed spurious by the remote station. The information from the transmission with the best metric value is passed to the RLP, which corrects the erroneous information.

If the remote station is not able to decode the frame header, then process flow transitions from step 615 to step 635 where no signal is sent on the ARQ channel. The base station will continue with the predetermined retransmission scheme. However, since the remote station does not send an ARQ signal, the remote station can only expect a new transmission of the old data payload instead of a retransmission. Receipt of a retransmission will indicate to the remote station that it is the wrong recipient of that particular data payload. The remote station passes the old transmission to the RLP as an error.

If the receiver subsystem detects an appreciable ARQ signal due to reverse link interference, the base station will identify the remote station as an incorrect recipient of the data and ignore the appreciable ARQ signal. In one embodiment, a timer may be set at the base station and the remote station so that if the base station ignores the signal and refrains from transmitting a retransmission, the remote station is notified that the previous transmission was a false alarm.

Those skilled in the art will 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.

The skilled person will further understand that: the various logical units, modules, circuits, and arithmetic steps described in connection with the embodiments disclosed 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 units, modules, and circuits described in connection with the embodiments disclosed 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 bank 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 embodiments disclosed herein 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 storage medium 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.

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

Claims (5)

1. A method for rescheduling scheduled transmissions between a base station and a target remote station, comprising:

scheduling frame header information and data traffic for transmission to the target remote station, wherein the scheduling includes grouping the frame header information and the data traffic into a plurality of frame header sub-packet data and a plurality of data traffic sub-packet data to be transmitted to the target remote station;

according to the scheduling, at least one frame header sub-packet data in the plurality of frame header sub-packet data and at least one data service sub-packet data in the plurality of data service sub-packet data are sent;

waiting for a signal to be transmitted on an acknowledgement channel;

rescheduling transmission of frame header information and data traffic to the target remote station if no signal is received on the acknowledgment channel within a reasonable time;

scheduling transmission of new frame header information and new data traffic if the signal received on the acknowledgement channel is a positive acknowledgement from the target remote station;

continuing said scheduling by transmitting another one of said plurality of frame header sub-packet data and another one of said plurality of data traffic sub-packet data if the signal received on said acknowledgment channel is a negative acknowledgment from said target remote station;

if the signal received on the acknowledgment channel is a positive acknowledgment from the wrong remote station, ignoring the signal and continuing the scheduling by sending another one of the plurality of frame header subpacket data and another one of the plurality of data traffic subpacket data; and

if the signal received on the acknowledgment channel is a negative acknowledgment from the wrong remote station, the signal is ignored and all transmissions are interrupted for a predetermined time.

2. The method of claim 1, further comprising:

receiving at the target remote station at least one of a plurality of frame header sub-packet data and at least one of the plurality of data traffic sub-packet data;

transmitting the positive acknowledgement on the acknowledgement channel if at least one of the plurality of frame header sub packet data and at least one of the plurality of data traffic sub packet data can be decoded;

transmitting a negative acknowledgement on the acknowledgement channel if at least one of the plurality of frame header sub packet data can be decoded but at least one of the plurality of data service sub packet data cannot be decoded; and is

Refraining from transmitting on the acknowledgment channel if at least one of the plurality of frame header subpackets cannot be decoded.

3. The method of claim 1, further comprising:

receiving, at the erroneous remote station, at least one of the plurality of frame header sub-packet data and at least one of the plurality of data traffic sub-packet data;

transmitting a positive acknowledgement on the acknowledgement channel if at least one of the frame header sub packet data and at least one of the plurality of data service sub packet data can be decoded;

transmitting a negative acknowledgement on the acknowledgement channel if at least one of the plurality of frame header sub packet data can be decoded but at least one of the plurality of data service sub packet data cannot be decoded;

refraining from transmitting on the acknowledgement channel if at least one of the plurality of frame header subpackets cannot be decoded; and is

Passing the at least one data traffic subpacket as an error to a Radio Link Protocol (RLP) layer if no further transmission is received from the base station.

4. An apparatus for rescheduling scheduled transmissions between a base station and a target remote station, comprising:

means for scheduling frame header information and data traffic for transmission to the target remote station, wherein the scheduling means groups frame header information and data traffic into a plurality of frame header sub-packets and a plurality of data traffic sub-packets to be transmitted to the target remote station, and the scheduling means is responsive to signals received on an acknowledgement channel, wherein if no signals are received on the acknowledgement channel within a reasonable time, the scheduling means reschedules transmission of the frame header information and data traffic to the target remote station, but if the signals received on the acknowledgement channel are positive acknowledgements from the target remote station, the scheduling means schedules transmission of new frame header information and new data traffic; and if the signal received on the acknowledgment channel is a negative acknowledgment from the target remote station, the scheduling means continues the scheduling by transmitting another one of the plurality of frame header sub-packet data and another one of the plurality of data traffic sub-packet data; and if the signal received on the acknowledgment channel is a positive acknowledgment from the wrong remote station, the scheduling means ignores the signal and continues the scheduling by transmitting another one of the plurality of frame header sub-packet data and another one of the plurality of data service sub-packet data; and if the signal received on the acknowledgement channel is a negative acknowledgement from an erroneous remote station, the scheduling means ignores the signal and interrupts all transmissions for a predetermined time; and

means for transmitting at least one of the plurality of frame header sub packet data and at least one of the plurality of data service sub packet data according to the scheduling.

5. A method for enhancing transmission scheduling, comprising:

according to the sending scheduling, sending a plurality of frame header sub-packet data and a plurality of data service sub-packet data in parallel;

monitoring a signal on an acknowledgment channel;

if no signal is detected, continuing to transmit according to the transmission scheduling;

if the signal is detected, judging whether a sender of the signal is a target station or not;

if the signal is from the target station, canceling the transmission scheduling and forming a new transmission scheduling by using new frame header information and new data service if the signal is a positive acknowledgement, otherwise, re-transmitting according to the transmission scheduling if the signal is a negative acknowledgement; and

if the signal is not from the destination, the retransmission is interrupted for a period of time if the signal is a negative acknowledgement, otherwise the retransmission is performed if the signal is a positive acknowledgement.