KR100491520B1 - Method and apparatus for high rate data transmission in a spread spectrum communication - Google Patents

Abstract

The present invention is a method and apparatus for transmitting a high speed data packet in a CDMA communication system. The transmission system sends a first channel assignment message indicating at least one additional channel to be used to hold the high speed data packet. The first assignment message is sent before the start of the high speed data communication. In addition, the present invention provides a dual channel assignment message in a first frame of high speed data. The remote receiver uses a channel assignment message to initialize demodulation elements 114 and 120 to receive additional information carried on at least one additional channel.

Description

METHOD AND APPARATUS FOR HIGH RATE DATA TRANSMISSION IN A SPREAD SPECTRUM COMMUNICATION}

The present invention relates to communication. In particular, the present invention relates to a new and improved communication system in which a user transmits data on a primary channel.

However, when the user's message exceeds the capacity of the primary channel, the user is provided with an additional channel or set of channels along with the primary channel for transmitting high speed data. The present invention provides dynamic channel allocation for high speed data transmission and provides a very effective system for the transmission of variable rate data.

The present invention relates to multiple users sharing communication resources, as in cellular CDMA systems. The use of code division multiple access (CDMA) modulation technology is one of several techniques to enable communication where multiple system users exist. Other multiple access communication techniques such as time division multiple access (TDMA), frequency division multiple access (FDMA), and AM modulation methods such as amplitude expansion single sideband (ACSSB) are already known. However, CDMA's spread spectrum modulation technique has significant advantages over the other modulation techniques for multiple access communication systems. A method of using CDMA technology in a multiple access communication system is disclosed in U.S. Patent No. 4,901,307, entitled "Spectrum Spread Multiple Access Communication System Using Satellite or Terrestrial Repeater," assigned to the assignee of the present invention and incorporated herein by reference. do. A method of using CDMA technology in a multiple access communication system is assigned to the assignee of the present invention and incorporated herein by reference, US Patent No. 5,103,459 entitled "System and Method for Generating Signal Waveforms in CDMA Cellular Telephone Systems". Is initiated.

Due to the inherent nature of wideband signals, CDMA provides a kind of frequency diversity by spreading signal energy over a wideband. Therefore, frequency selective fading affects only a small portion of the CDMA signal bandwidth. Path diversity is obtained by developing a multipath environment through spread spectrum processing by allowing signals to arrive with different propagation delays to be received and processed respectively. In addition, spatial or path diversity is obtained by providing multiple signal paths through simultaneous connections between a mobile user and two or more base stations. An embodiment of the use of path diversity is US Patent No. 5,109,390, entitled "Diversity Receiver in a CDMA Cellular Telephone System," assigned to the assignee of the present invention and incorporated herein by reference, and the name "CDMA Cell". "Soft Handoff of Modem Phone Systems", US Pat. No. 5,101,501.

Another technique that can increase the allocation efficiency of communication resources is to allow the user of the resource to provide data at a variable rate, using only the minimum amount of communication resources to meet the user's service needs. One example of a variable speed data source is a variable speed vocoder described in detail in US Pat. No. 5,414,796, entitled "Variable Speed Vocoder" assigned to the assignee of the present invention and incorporated herein by reference. Since speech inherently includes silent periods, i.e., interruption periods, the amount of data required to represent these periods is reduced. Variable rate vocoding is used very effectively by reducing the data rate during these silent periods.

Variable rate speech encoders actively speak to a speaker, providing speech data at full rate when using the full capacity of a transmission frame. If the variable rate voice coder provides voice data at a rate below the maximum rate, there is excessive capacity overrun in the transmission frame. The method for the data source to provide data at a variable rate and the additional data to be transmitted in a fixed sized transmission frame is handed over to the assignee of the present invention and hereby incorporated by reference the name "formatting data for transmission". US Pat. No. 5,504,773, which discloses a method and device for doing the same. The patent application described above discloses a method and apparatus for combining different types of data from different sources into data packets for transmission.

1 is a diagram illustrating an embodiment of the invention in a mobile communication system.

2 is a block diagram of a transmission system of the present invention.

3 is a block diagram of a receiver system of the present invention.

Communication resources are typically divided into communication channels. The present invention is described for a CDMA communication system, where each channel is provided by spreading data by different spreading sequences. In an exemplary embodiment, the spreading sequence used is an orthogonal Walsh sequence.

In the present invention, each user is provided with a dedicated channel referred to herein as the primary channel. In addition, each user is provided with an optional connection towards a common channel called an additional channel that can be shared by all users of the communication system.

If the user transmission rate exceeds the primary channel capacity, the communication system determines if enough additional channels are available for high speed data transmission. If enough additional channels are available, additional channels are assigned to the user for high speed data transmission.

In the present invention, after determining that additional channels are sufficiently available, before the start of the fast transmission, the transmitter sends a message called a first channel assignment message to the receiver to indicate the next fast data transmission. In an exemplary embodiment, the channel assignment message identifies additional channels to be used to maintain the high speed data service. In an exemplary embodiment, the first channel assignment message is sent two frames before the high speed transmission. By using the first channel assignment message, the receiving system does not need to demodulate all possible channels that greatly reduce the power consumption of the mobile station.

In an improved embodiment, a second channel assignment message comprising the same information as the first channel assignment message is provided on the primary channel at the start of the high speed data communication. This provides a second indication for reliable high speed data transmission if the frame carrying the first channel assignment message is not properly received.

In the present invention, the receiving system initializes an additional demodulator set to demodulate high speed data according to the information provided in the first channel assignment message. Fast data is demodulated by a primary channel demodulator and an additional channel demodulator, and the demodulated frames are combined and provided to a user.

If frame deletion occurs, the receiving system demodulates all possible additional channels as though the first channel assignment message was received in the deleted frame. The receiving system then uses the second channel assignment message to recombine the frames and initialize an additional demodulator for receiving the next frame.

The features, objects, and advantages of the present invention will become more apparent from the detailed description given with reference to the drawings in which like reference numerals designate the same.

Multiple access communication resources are divided into channels. This division is generally called multiplexing, and three specific forms of the multiplexing are as follows. Frequency division multiplexing (FDM), time division multiplexing (TDM), and code division multiplexing (CDM). The basic unit of information transmitted and received in a communication system is called a frame.

1 shows an embodiment of the present invention in a mobile communication system. The mobile station 10 transmits the information to the cell base station 12 and receives the information from the cell base station 12. Cell base station 12 in turn transmits information to and receives information from MTSO 14. The MTSO 14 in turn transmits and receives information to a public telephone access network (not shown).

In an exemplary embodiment, the signal transmitted by the cell base station 12 to the mobile station 10 is a spread spectrum signal, such as the signal transmitted from the mobile station 10 to the cell base station 12. The generation of the spread spectrum communication signal is described in detail in US Pat. Nos. 4,901,307 and 5,103,459, supra. An exemplary embodiment of the invention is described herein in terms of a method for providing a high speed data packet from a cell base station 12 to a mobile station 10 called forward link transmission. However, the present invention is equally applicable to reverse link transmission of data from mobile station 10 to cell base station 12.

In an exemplary embodiment, the mobile station 10 is assigned a primary channel for communicating with the base station 12. In an exemplary embodiment, a single channel is provided by a unique Walsh spreading sequence as detailed in US Pat. Nos. 4,901,307 and 5,103,459, above. In the present invention, cell base station 12 uses an additional channel to provide high speed data transmission to mobile station 10.

As mentioned above, high speed data packets require more capacity than the primary channel for transmission. In an exemplary embodiment, the data is sent in packets. If the packet contains high speed data, the content of the high speed data is divided into a number of frames, each frame being transmitted on a single channel and recombined at the receiver.

2 shows a block diagram of an exemplary embodiment of the transmission system of the present invention. Data source 20 provides a data packet for transmission from cell base station 12 to mobile station 10. Data source 20 is provided for illustration. Base station 12 typically relays information from remote locations and data source 20 is a convenient way to describe a packet source of data for transmission. The data source 20 can provide data packets that are smaller than the capacity limit of the primary channel, and high speed data requiring the use of one or more additional channels in the primary channel for carrying the packets.

If the data packet to be transmitted can be transmitted using only the assigned primary channel, then the data source 20 provides the data packet to the primary formatter 24 via the demultiplexer (DE-MUX) 22. In an exemplary embodiment, the primary formatter 24 generates a set of redundant bits for the packet in accordance with conventionally known error correction and detection methods. In an exemplary embodiment, formatter 24 generates a set of cyclic redundancy check (CRC) bits and a set of code tail bits and adds the sets of bits to the outgoing packet. The generation of the bit sets is described in detail in US Pat. No. 5,550,773.

The primary formatter 24 outputs the packet to the primary encoder 26 which encodes the packet and provides the encoded symbol. In an exemplary embodiment, the primary encoder 26 is a half speed convolutional encoder, the construction and implementation of which is already known in the art. In an exemplary embodiment, the convolutional encoder is implemented using a digital shift register. The primary encoder 26 provides the encoded data packet to the primary interleaver 28.

The primary interleaver 28 reconstructs the binary digits of the encoded packet according to a predetermined reconstruction format. In an exemplary embodiment, the primary interleaver 28 is a block interleaver. In a block interleaver, data is written to columns in memory and output in rows. With respect to error correction codes, interleaving increases the time diversity of the data and therefore increases the robustness to bursty channel errors.

The interleaved packet is provided to the primary modulator 30 by the primary interleaver 28. The primary modulator 30 modulates the frame to provide a frame on the assigned primary channel. In an embodiment modulator 30 is a code division multiple access (CDMA) modulator as described in detail in US Pat. Nos. 4,901,307 and 5,103,459. In an exemplary embodiment, each frame is spread by a Walsh sequence W _{n that} is unique to the primary channel and orthogonal to all other Walsh sequences used by all other channels while data is being transmitted from the base station 12. . In an exemplary embodiment, the data on the primary channel may be variable speed in accordance with an industry standard TIA / EIA / IS-95-mobile-base station compatible standard for dual mode wideband spread spectrum cellular systems, but provided on additional channels. The data is designed at a fixed rate.

In an exemplary embodiment, the spread frame is covered using a pseudo noise (PN) sequence that provides each base station 12 with greater separation and identification of code space. Each channel is uniquely distinguished by a Walsh sequence. Since the available orthogonal sequences are limited, as the number of users to be transmitted at high speed increases, the number of users that can be accommodated by the base station 12 becomes smaller. The modulator 30 transmits the modulated frame to the transmitter TMTR 34, the transmitter 34 upconverts and amplifies the modulated frame, and transmits a signal through the antenna 36.

The data source 20 provides a request signal REQ to the cell controller 40 of the cell base station 12 when preparing to transmit a high speed data packet. The cell controller 40 responds by providing an acknowledgment (ACK) signal. The cell controller 40 selects an additional channel to be used for the transmission of high speed data. In an exemplary embodiment, possible additional channels that may be used for the transmission of high speed data may be selected by simple masking techniques as predefined and well known in the art. In another exemplary embodiment an additional channel set is predefined and the channel assignment message identifies one of the predetermined sets. In an improved embodiment, the predetermined set consists of a number of additional channels. The cell controller 40 generates a channel assignment message indicating an additional Walsh channel or channels to be used to carry high speed data (40 ms) after two frames, and provides the message to the primary formatter 24.

The channel assignment message may be provided with its own CRC check bits to provide additional reliability, or may be sent without its own check bits using only minimal additional bits. When the present invention is used in a time division multiple access communication system, the channel assignment message will specify additional time slots for the data to be provided to the mobile station 10. Similarly, when the present invention is used in a frequency division multiple access communication system, the channel assignment message will specify an additional frequency to be used to provide data to the mobile station 10.

In an exemplary embodiment, the channel assignment message is provided as additional signal transmission data combined with outgoing data on the primary channel. The channel assignment message sent before the start of the high speed data transfer is referred to herein as the first channel assignment message. A method for combining signaling data with outgoing traffic data is described in detail in US Pat. No. 5,550,773. In an alternative embodiment, the first channel assignment message is punctured into a starting data frame on the primary channel by methods well known in the art.

The frame containing the first channel assignment message is formatted by the primary formatter 24 as described above and encoded by the primary encoder 26 as described above. The encoded symbol is then provided to the primary interleaver 28 which reconstructs the symbol as described above. In an exemplary embodiment, the channel assignment message, signaling message (if present), control message (if present) and some of the data are all transmitted on the primary channel by the primary modulator 30 and the additional The channel carries only data. In an exemplary embodiment, where there are power control bits, they are punctured with primary channel data to provide closed loop power control of the type described in US Pat. No. 5,109,501 described above. The primary channel can be variable or fixed speed or used as a dedicated control channel. The modulated frame is upconverted and amplified by transmitter 34 and transmitted via antenna 36.

In an exemplary embodiment, the first channel assignment message is provided two frames earlier than a high speed data transmission to provide sufficient time for the receiver (shown in FIG. 3) to prepare for its reception. In an exemplary embodiment, while establishing a call, additional channels are grouped by cell controller 40 and sent to mobile station 10. In an exemplary embodiment, this additional group of channels may be updated during the call. Defining an additional set of channels possible in advance, the channel assignment message only needs a few bits to identify the channel to be used. Instead of sending a signal identifying the additional channel to be used, the base station may send a mask signal that allows the fast demodulation controller 117 to identify the additional channel.

Since there is a possibility that the first channel assignment message is received in an error state, the present invention provides channel assignment information in addition to the secondary channel assignment message transmitted on the primary channel.

At the start of a high speed data transfer, the data source 20 provides a high speed data packet to the demultiplexer 22. Demultiplexer 22 divides the high speed data packet into two parts. The first part is included in the frame to be transmitted on the primary channel. The second part is included in the frame to be transmitted on the additional channel. Frames to be transmitted on the primary channel are processed as described above.

Data bits for additional channels are provided to additional formatter 25. Additional formatter 25 generates a set of CRC bits for incoming data and a set of code tail bits. The formatted data from the additional formatter 25 is provided to an additional encoder 27 that encodes the data to provide an encoded symbol. In an exemplary embodiment, the additional encoder 27 is a convolutional encoder.

The encoded symbol is provided to an additional interleaver 29, which additionally reconstructs the encoded symbol as described above according to a predetermined alignment format. In the first embodiment of the primary interleaver 28 and the additional interleaver 29, the interleavers use the same number of addresses and variable word sizes to accommodate different sized data blocks for interleaving. In alternative embodiments of the primary interleaver 28 and the additional interleaver 29, the interleavers use a variable number of addresses and a fixed word size to accommodate variable block sizes. The reconstructed encoded symbol is provided to a demultiplexer (DE-MUX) that divides additional frames into frames, each of which is carried on an additional channel.

Each additional frame from demultiplexer 35 is provided to a different one of additional modulators 32a-32n. In an exemplary embodiment, modulated additional frames from additional modulators 32a-32n are combined with modulated frames from primary modulator 30 by transmitter 34 prior to transmission. The transmitter 34 upconverts and amplifies the combined signal and transmits it through the antenna 36.

Referring to FIG. 3, signal transmission via antenna 36 of FIG. 2 is received by antenna 110 and provided to receiver (RCVR) 112. Receiver 112 downconverts, filters, and amplifies the received signal and provides the received signal to demodulation circuit 111.

When such a structure is used, the demodulation circuit 111 represents the "finger" of one of the RAKE receivers. In a rake receiver implementation, the multipath signal received at the mobile station 10, with different propagation path delays, is demodulated separately and the result of the resulting demodulation operation is combined at the finger combiner 128. The construction and implementation of the rake receiver is described in detail in US Pat. No. 5,109,390, above.

In an exemplary embodiment, the primary demodulator 114 and the additional demodulators 120a-120n are CDMA demodulators as described in US Pat. Nos. 4,901,307 and 5,103,459 described above. In an exemplary embodiment, the primary demodulator 114 and the additional demodulators 120a-120n are quadrature phase shift keying (QPSK) demodulators.

The primary demodulator 114 despreads the received signal according to the assigned primary channel Walsh sequence and the PN code. The despread primary frame is provided to the improved finger combiner 128, which combines the primary frame soft decision from the finger demodulator 111 with the soft decision from the other finger to produce an improved soft decision. to provide. The improved soft decision is provided to the primary deinterleaver 118 which reconstructs the demodulated soft decision according to a given reconstruction format. The configuration of the deinterleaver and its implementation are conventional. In an exemplary embodiment, the deinterleavers 118 and 124 operate using a fixed number of addresses and variable word size, or a fixed word size and variable number of addresses to accommodate different sized data packets.

The deinterleaver 118 provides the reconstructed frame to the primary decoder 122 which reconstructs the frame. In an exemplary embodiment, the primary decoder 122 and the additional decoder 126 are Viterbi decoders, and the configuration and implementation of the Viterbi decoder is conventional. The decoded frame from the primary decoder 122 is provided to the data sink 130, which may be a user of the mobile station 10 or another additional processing element via the multiplexer 127.

If a frame containing the first channel assignment message has been received without error, then the decoded channel assignment message is provided to the fast data controller 117. The high speed data controller can be implemented using a microprocessor programmed to perform the required functions. The fast data controller 117 provides the additional demodulators 120a-120n with Walsh sequence identification and PN code information needed to demodulate the additional data.

The RF signal is received by the antenna 110 and provided to the receiver 112. Receiver 112 amplifies and downconverts the received signal and provides the received signal to primary demodulator 114 and additional demodulators 120a-120n.

The demodulated primary frame from the primary channel is provided to the finger combiner 128 to provide an improved demodulation soft decision as described above. The improved soft decision is provided to the primary deinterleaver 118 which reconstructs the soft decision as described above. The reconstructed frame is provided to a primary decoder 122 that decodes the deinterleaved frame and provides the decoded frame to a multiplexer (MUX) 127.

The received signal is provided to additional demodulators 120a-120n that demodulate the signal according to the channel information provided in the first channel assignment message. Demodulated data frames from additional demodulators 120a-120n are provided to finger combiner 128 to produce an improved soft decision for each additional frame. The improved soft decision of the demodulated frame provides the multiplexer (MUX) 123 to recombine the packets containing additional data. In an exemplary embodiment, the multiplexer 123 indicates additional demodulators currently in use and operates according to a method of reassembling packets containing signals and additional data from the fast demodulation controller 117.

The recombined packet of additional data is provided to an additional deinterleaver 124 that reconstructs the soft decision according to the desired deinterleaving format. The reconstructed soft decision is provided to the additional decoder 126. Although shown as two separate blocks, primary decoder 122 and additional decoder 126 may use the same hardware, such as a microprocessor programmed to perform a specific function or an application specific integrated circuit (ASIC) designed to perform a specific function. Can be performed using. Additional decoder 126 decodes additional data packets and provides decoded bits to multiplexer 127.

Multiplexer (MUX) 127 combines the decoded data transmitted on the primary channel with the decoded data transmitted on the additional channel. The recombined data packet is provided to the data sink 103.

If frame deletion occurs and the content of the first channel assignment message is unknown, the receiver system will operate based on the worst case scenario. The receiver will demodulate the maximum set of additional channels as possible and demodulate the final set used. This will determine which frame from the additional channel will be used as valid data if the second channel assignment message for the current data packet is properly decoded.

If both frames containing the first and second channel assignment messages are received in error, the corresponding received data will be discarded and an erase status will be declared.

The present invention is equally applicable to variable rate data transmission and fixed speed transmission. For fixed rate transmission, channel assignment message data will remain constant throughout the service. However, if additional channels are needed for signaling or other data traffic, the channel assignment message will change to indicate that additional channels will be used for the transmission of the data.

For variable rate transmission, a method is employed that allows as many additional channels as necessary for the current data packet size to be allocated. The number of additional channels to be allocated depends on the amount of data to be transmitted. This can be done in units of frames.

The foregoing description of the preferred embodiments is provided to enable any person skilled in the art to practice the invention. Other variations of these embodiments will be apparent to those skilled in the art and the general principles defined herein may be applied to other embodiments without using the inventive capabilities. Thus, the invention is not limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (4)

An apparatus for transmitting high speed packet data, Define channel groups such that each group includes additional selected channels for the primary channel; Correlating the groups with a predetermined indication; Generate a group message indicating which additional channels are associated with each indication; And A cell controller comprising a processor capable of generating a first channel assignment message comprising at least one of the indications indicating which additional channels will be used to support the high speed data packet transmission; And Sending the group message during call setup, sending the first channel assignment message on the primary channel after call setup, and on at least one additional channel associated with the primary channel and the indicated group And a transmitter capable of transmitting the high speed data packet. 2. The apparatus of claim 1, wherein the first channel assignment message is transmitted before the high speed data packet. 3. The apparatus of claim 2, wherein the first channel assignment message is transmitted two frames before the fast data packet. The method of claim 1, The first channel assignment message is transmitted before the high speed data, The cell controller may also generate a redundant second channel assignment message for the first channel assignment message; And the transmitter is further capable of transmitting a second channel assignment message in a first frame of the fast data packet.