KR20030019572A - Maximum distance block coding scheme - Google Patents

Abstract

In data communication systems capable of variable rate transmission, high speed packet data transmission improves the use of the forward link and reduces transmission delay. Data transmission on the forward link is time multiplexed and the base station 4 is determined at each time slot at the high data rate supported by the forward link for one mobile station 6. The data rate is determined by the maximum C / I measurement of the forward link signal measured at the mobile station 6. Upon determination of the data packet received by mistake, the mobile station 6 sends a NACK message back to the base station 4. The NACK message results in the transmission of a data packet received by mistake. The data packet can be sent from the sequence using the sequence number to identify each data unit in the data packet. On the reverse link, the reverse speed indicator symbol is encoded at the mobile station 6 to achieve the maximum distance between different codewords.

Description

Maximum distance block coding method {MAXIMUM DISTANCE BLOCK CODING SCHEME}

Current communication systems are required to support multiple applications. Some communication systems are code division multiple access (CDMA) systems that conform to the "TIA / EIA / IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System", which will be referred to as the IS-95 standard. CDMA systems enable data and voice communications between users over land links. The use of CDMA technology in a multiple access communication system is US Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", and "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM". US Patent No. 5,103,459, which is assigned to the assignee of the present invention and is cross-referenced herein.

In this specification, a base station refers to hardware with which a mobile station communicates. A cell refers to a local cover area or hardware depending on the environment in which the term is used. A sector is part of a cell. Since sectors in a CDMA system have cell characteristics, what is represented by a cell can easily be extended to sectors.

In a CDMA system, communication between users is performed through one or more base stations. A first user of a mobile station communicates with a second user at a second mobile station by transmitting data to the base station on the reverse link. The base station may receive data and route the data to other base stations. Data is transmitted to the second mobile station on the forward link of the same base station or second base station. The forward link refers to the transmission from the base station to the mobile station, and the reverse link refers to the transmission from the mobile station to the base station. In an IS-95 system, the forward link and the reverse link are assigned separate frequencies.

The mobile station communicates with at least one base station while communicating. The CDMA mobile station can communicate with several base stations during soft handoff. Soft handoff is the process of establishing a link with a new base station before the link with the previous base station is broken. Soft handoff minimizes the chance of an interruption of a call. A method and system for providing communication with one or more base stations and a mobile station during soft handoff is assigned to the assignee of the present invention and cross-referenced herein to a US patent number entitled " MOBILE ASSISTED SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM. &Quot; 5,267,261. Softer handoff is a communication process that occurs in several sectors served by the same base station. The softer handoff procedure is assigned to the assignee of the present invention and is cross-referenced herein, and US Patent No. 5,933,787, filed August 3, 1999, entitled "METHOD ANDAPPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMON BASE STATION." It is disclosed in detail.

As the demand for wireless data applications increases, the demand for highly effective wireless data communication systems is increasing. The IS-95 standard can transmit traffic data and voice data on the forward and reverse links. A method of transmitting traffic data in a fixed size code channel frame is assigned to U.S. Patent No. 5,504,773 assigned to the assignee of the present invention and cross-referenced herein and designated "METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION." It is disclosed in detail. According to the IS-95 standard, traffic data or voice data is divided into code channel frames having 20 msec at a data rate as high as 14.4 Kbps.

An important difference between voice service and data service is that voice service imposes strict and fixed delay requirements. In general, the total one-way delay of the voice frame should be less than 100 msec. In contrast, the data delay may be a variable parameter used to optimize the efficiency of the data communication system. In particular, a more effective error correction coding scheme may be used that requires a larger delay than can be tolerated by the voice service. An effective data coding scheme is disclosed in U.S. Patent No. 5,933,462, issued August 3, 1999, assigned to the assignee of the present invention, cross-referenced herein, and designated as "SOFT DECISION OUTPUT DECODER FOR DECODING CONVOLUTIONALLY ENCODED CODEWORDS". have.

Another big difference between voice and data services is that voice services require a fixed and common class of services (GOS) for all users. In general, for digital systems that provide voice services, this is fixed for all users and interpreted as the maximum allowable value for the same rate and error rate of the voice frame. In contrast, for data services, the GOS may be different between users and may be a parameter optimized to increase the overall efficiency of the data transmission system. The GOS of a data communication system is generally defined as the total delay incurred in the transmission of a certain amount of data to be referred to as a data packet.

Another major difference between voice service and data service is that voice service requires a reliable communication link provided by soft handoff in a typical CDMA communication system. Soft handoff results in redundant transmissions from two or more base stations to improve reliability. However, this additional reliability is not required for data transmission because accidentally received data packets can be transmitted. For data services, the transmit power used to support soft handoff can be used more effectively to transmit additional data.

Parameters that measure the quality and effectiveness of a data communication system are the average throughput of the system and the transmission delay required to transmit the data packet. Transmission delay does not have the same effect of data communication as voice communication, but is an important measure of the quality of a data communication system. Average throughput is a measure of the efficiency of the data transmission capacity of a communication system.

In a cellular system, the signal-to-noise and interference ratio (C / I) of a user is a function of the user's position within the cover area. To maintain a given level of service, TDMA and FDMA systems rely on frequency reuse techniques, ie not all frequency channels and / or time slots are used for each base station. In a CDMA system, the same frequency allocation is reused in all cells of the system, thereby improving the overall efficiency. The C / I reached by a user's mobile station determines the information that can be supported from a base station to a particular link to the user's mobile station. In the particular modulation and error correction method used for transmission, the present invention seeks to optimize data transmission, and a given level of performance is reached at that level of C / I. For an ideal cellular system that uses a common frequency in all cells and has a hexagonal cell layout, the distribution of C / I achieved in the ideal cell can be calculated.

The C / I achieved by a user is a function of path loss and increases from r ³ to r ⁵ for terrestrial cellular systems, where r is the distance to the radiation source. In addition, path loss is attributed to random variables due to artificial or natural obstructions in the path of radio waves. This random variable is generally modeled as a lognormal shadowing random process with a standard variation of 8 dB. The final C / I distribution achieved for the ideal hexagonal cellular deployment with shadowing process with 8 dB standard variation, r ⁴ propagation rule and omni base station antenna is shown in FIG. 10.

At any moment and at any location, only the obtained C / I distribution can be achieved if the mobile station is serviced by the best base station defined as reaching a maximum C / I value regardless of the physical distance to each base station. . Due to the random nature of the path loss described above, the signal with the best C / I value may be different from the minimum physical distance from the mobile station. On the contrary, since the mobile station can communicate only through the base station of the minimum distance, the C / I can be significantly degraded. Therefore, it is advantageous for the mobile station to communicate with the serving base station at the same time, thus achieving an optimum C / I value. In addition, in the ideal model shown in FIG. 10 and described above, it is observed that the range of the values of C / I achieved can be as large as 10,000, the difference between the highest and lowest values. In practice, the range is generally limited to approximately 1: 100 or 20 dB. Therefore, the CDMA base station can serve the mobile at an information bit rate that can vary by a factor of 100, which maintains the following manner.

(One)

Where R _b represents the information rate for a particular mobile station, W is the total bandwidth occupied by the spread spectrum signal, and Eb / Io is the energy per bit at the interference density required to achieve a given level of performance. For example, if a spread-spectrum signal requires a bandwidth of 1.2288 MHz and an average Eb / Io equal to 3 dB, then a mobile station that achieves a C / I value of 3 dB at the best base station communicates at a high data rate such as 1.2288 Mbps. can do. On the other hand, if the mobile station is subject to actual interference from the near base station and can only achieve a C / I of -7 dB, reliable communication will not be provided at speeds higher than 122.88 Kbps. Communication systems designed to optimize average throughput will support each remote user from the best serving base station at the highest data rate (Rb) that the remote user can reliably support. It would be advantageous to provide a data communication system that utilizes the features described above and optimizes data throughput from the CDMA base station to the mobile station.

It is also advantageous to use a more stringent channel for the mobile station when indicating the reverse link data rate at which data is being transmitted. In a data communication system, the reverse link data rate indicator is a relatively "low" channel that requires transmission only in the short time that the pilot channel is transmitted. In general, an orthogonal encoding scheme with a relatively high rate of repeatability is used. In order to improve the coding gain, it is desirable to increase the minimum distance (number of symbols of different encoder output code words) between different encoder output code words of the coding scheme. Therefore, a need exists for a way to improve coding gain in high data rate communication systems.

The present invention relates to a maximum distance rate 3/128 block coding scheme for use in data communications, in particular high speed packet data communications systems.

1 is a diagram of a data communication system including multiple cells, multiple base stations, and multiple mobile stations.

2 is a block diagram of a subsystem of the data communication system of FIG.

3A-3B are block diagrams of typical forward link structures.

4A is a diagram of a typical forward link frame structure.

4B-4C are diagrams of typical forward traffic channels and power control channels, respectively.

4D is a diagram of a punctured packet.

4E-4G are diagrams of typical two data packet formats and control channel capsules, respectively.

5 is a timing diagram illustrating high speed data packet transmissions on the forward link.

6 is a block diagram of a typical reverse link structure.

7A is a diagram of a typical reverse link frame structure.

7B is a diagram of a typical reverse link access channel.

8 is a typical timing diagram illustrating high speed data transmission on the reverse link.

9 is a typical state diagram illustrating the transition between various operating states of a mobile station.

10 is a plot of the cumulative distribution function (CDF) of the C / I distribution in an ideal hexagonal cellular arrangement.

11 is a block diagram of a reverse rate indicator (RRI) encoder of the reverse link structure of FIG.

The present invention relates to a method for improving coding gain in a high speed data communication system. Thus, in one aspect of the invention, a method of encoding data is provided. The method advantageously comprises block encoding the data to produce a plurality of code words; And repeating each code word for a predetermined number of times.

In one embodiment, the method advantageously comprises block encoding the data into a matrix of three columns and 32 rows and repeating each code word four times, the first column of the matrix from left to right. Is a binary number with a hexadecimal value of 2292DBBF following two zeros, and the second column of the matrix from left to right is a binary number with a hexadecimal value of 2492DBBF following two zeros, and from zero to left of the matrix. Column 3 is a binary number with a hexadecimal value of 2492DBBF followed by two zeros.

The invention is described in detail below with reference to the drawings.

According to a typical embodiment of a data communication system, forward link data transmission occurs from one base station to one mobile station (shown in FIG. 1) at or near the maximum data rate that can be supported by the forward link and the system. Reverse link data communication occurs from one mobile station to one or more base stations. The calculation of the maximum data rate for forward link transmission is described in detail below. Data is divided into data packets, each data packet being transmitted over one or more time slots. In each time slot, the base station can direct data transmission to any mobile station in communication with the base station.

First, the base station establishes communication with the base station using a predetermined access procedure. In this connected state, the mobile station can receive data and control messages from the base station and can receive data and control messages from the base station. The mobile station then monitors the forward link for transmission from the base station in the mobile station's active set. The active set includes a list of base stations in communication with the mobile station. In particular, the mobile station measures the signal-to-noise ratio and the interference ratio (C / I) of the forward link pilot from the base station, which is the active set received at the mobile station. If the received pilot signal is above the predetermined addition threshold or below the predetermined interruption threshold, the mobile station informs the base station of this. Subsequent messages from the base station instruct the mobile station to either add or remove the base station from its active set, respectively. Various operating states of the mobile station are described below.

If there is no data to be transmitted, the mobile station returns to the idle state and stops transmitting data rate information to the base station. While the mobile station is in the idle state, the mobile station monitors control channels from one or more base stations in the active set for paging messages.

If there is no data to be transmitted to the mobile station, this data is transmitted by the central controller to all base stations in the active set and stored in each base station in sequence. The paging message is then sent by the one or more base stations on each control channel to the mobile station. A base station can send the paging message simultaneously to multiple base stations to ensure reception while the mobile station is switching between base stations. The mobile station demodulates and decodes a signal on one or more control channels to receive a paging message.

When decoding the paging message, for each time slot until the data transmission is complete, the mobile station measures the C / I of the forward link signal from the base station that is the active set as received at the mobile station. The C / I of the forward link signal can be obtained by measuring individual pilot signals. The mobile station then selects the best base station based on a set of parameters. The parameter set includes current and previous C / I measurements and bit error rate or packet error rate. For example, the best base station may be selected based on the maximum C / I measurement. The mobile station then identifies the best base station and sends a data request message (hereinafter referred to as DRC message) in the data request channel (hereinafter referred to as DRC channel) to the selected base station. The DRC message may include an indication of the requested data rate or optionally the quality of the forward link channel (eg, C / I measurement itself, bit error rate or packet error rate). In an exemplary embodiment, the mobile station may direct the transmission of DRC messages to a particular base station by the use of a Walsh code that uniquely identifies the base station. DRC message symbols are XORed with a unique Walsh code. Since each base station in the mobile station that is the active set is identified by a unique Walsh code, only selected base stations with the same XOR operation performed by the mobile station with the correct Walsh code can correctly decode the DRC message. The base station uses the speed control information from each mobile station to effectively transmit the forward link data at the highest possible speed.

In each time slot, the base station may select a paged mobile station for data transmission. The base station then determines the data at the data rate at which it transmits data to the selected mobile station based on the most recent value of the DRC message received from the mobile station. The base station also uniquely identifies the transmission for a particular mobile station using a spreading code unique to that mobile station. In a typical embodiment, this spreading code is a long similar noise (PN) code defined by the IS-95 standard.

The mobile station to which the data packet is directed receives the data transmission and decodes the data packet. Each data packet includes a number of data units. In a typical embodiment, the data unit contains eight information bits, but different data unit sizes may be defined within the scope of the present invention. In a typical embodiment, each data unit is associated with a sequence number, and the mobile station can identify either lost or duplicate transmissions. In this case, the mobile station conveys the sequence number of the lost data unit via the reverse link data channel. The base station controller receiving the data message from the mobile station then instructs all base stations that communicate with the particular mobile station that the data unit is not received by the mobile station. The base station then schedules retransmission of the data unit.

Each mobile station in the data communication system can communicate with several base stations on the reverse link. In a typical embodiment, the data communication system of the present invention supports soft handoff and softer handoff on the reverse link for several reasons. First, soft handoff does not consume additional capacity on the reverse link, but allows the mobile station to transmit data at the minimum power level at which at least one base station can reliably transmit data. Second, the reception of the reverse link signal by many base stations increases the reliability of the transmission and only requires additional hardware at the base station.

In a typical embodiment, the forward link capacity of the data transmission system is determined by the data request of the mobile station. Additional gains in forward link capacity can be achieved by direct antennas and / or adaptive spatial filters. Typical methods and devices for providing additional transmissions are US Patent Nos. 5,857,147, issued January 5, 1999 and entitled "METHOD AND APPARATUS FOR DETERMINING THE TRANSMISSION DATA RATE IN A MULTI-USER COMMUNICATION SYSTEM". Disclosed in US Patent Application No. 08 / 925,521, filed May 8 and entitled “METHOD AND APPARATUS FOR PROVIDING ORTHOGONAL SPOT BEAMS, SECTORS, AND PICOCELLS,” both of which are assigned to the assignee of the present invention and Cross-referenced.

I. System overview

1 illustrates an exemplary data communication system according to one embodiment including several cells 2a-2g. Each cell 2 is served by a corresponding base station 4. Several mobile stations 6 propagate through the data communication system. In a typical embodiment, each mobile station 6 communicates with at least one base station 4 on the forward link in each timeslot, but one or more base stations 4 on the reverse link depending on whether the mobile station 6 is soft handoff. ) Can be communicated with. For example, base station 4a exclusively transmits data to mobile station 6a on the forward link in timeslot n, base station 4b exclusively transmits data to mobile station 6b, and base station 4c. ) Exclusively transmits data to the mobile station 6c. In Fig. 1, the solid arrow indicates the data transmission from the base station 4 to the mobile station 6. Arrow dotted lines indicate that the mobile station 6 receives the pilot signal but there is no data transmission from the base station 4. Reverse link communication is not shown in FIG. 1 for simplicity.

As shown in Fig. 1, each base station 4 preferably transmits data to one mobile station 6 at a given moment. The mobile station 6, especially the mobile station located close to the cell boundary, can receive pilot signals from several base stations 4. If the pilot signal is above a predetermined threshold, the mobile station 6 may request that the base station 4 be added to the mobile station 6 in the active set. In a typical embodiment, the mobile station 6 may receive data transmissions from zero or one member of the active set.

A block diagram illustrating the basic subsystem of the data communication system of FIG. 1 is shown in FIG. The base station controller 10 interfaces with all base stations 4, PSTN 30 and packet network interface 24 of the data communication system (only one base station 4 is shown in FIG. 2 for simplicity). The base station controller 10 regulates communication between the mobile station 6 and the packet network interface 24 and other users connected to the PSTN 30 of the data communication system. The PSTN 30 interfaces with the user through a standard telephone network (not shown in FIG. 2).

Base station controller 10 includes several selector elements 14, but only one is shown in FIG. 2 for simplicity. One selector element 14 is assigned to control communication between one or more base stations 4 and one mobile station 6. If the selector element 14 has not been assigned to the mobile station 6, the call control processor 16 informs the need of paging the mobile station 6. The call control processor 16 then instructs the base station 4 to page the mobile station 6.

The data source 20 contains data to be sent to the mobile station 6. Data source 20 provides data to packet network interface 24. The packet network interface 24 receives the data and routes the data to the selector element 14. The selector element 14 sends data to each base station 4 in communication with the mobile station 6. Each base station 4 maintains a data queue 40 containing data to be transmitted to the mobile station 6.

In a typical embodiment, on the forward link, a data packet represents a certain amount of data regardless of the data rate. The data packet is formatted and encoded with other control and coding bits. If data transmission occurs on multiple Walsh channels, the encoded packets are demultiplexed into parallel streams, with each stream transmitted on one Walsh channel.

Data is sent from the data queue 40 to the channel element 42 in a data packet. For each data packet, the channel element 42 inserts the necessary control fields. Data packets, control fields, frame check sequence bits, and code back bits include formatted packets. Channel element 42 then encodes one or more formatted packets and interleaves (or rearranges) the symbols within the encoded packets. Next, the interleaved packet is scrambled with a scrambling sequence, covered with a Walsh cover, and spread with a long PN code and short PN ₁ and PN _Q codes. Spread data is orthogonally modulated, filtered, and amplified by a transmitter in the RF unit 44. The forward link signal is transmitted in the air through the antenna 46 in the forward link 50.

At the mobile station 6, the forward link signal is received by the antenna 60 and routed to a receiver in the front end 62. The receiver filters, amplifies, quadrature demodulates, and quantizes the signal. The digital signal is provided to a demodulator 64, where it is despread with a long PN code and a short PN ₁ and PN _Q code, decovered with a Walsh cover, and descrambled with the same scrambling sequence. The demodulated data performs the reverse function of the signal processing function performed at the base station 4, in particular the deinterleaving, decoding and frame check functions. The decoded data is provided to the data sink 68. The hardware described above supports the transmission of data, messaging, voice, video, and other communications on the forward link.

System control and scheduling functions can be achieved by various implementations. The location of the channel scheduler 48 is based on whether central or distributed control / scheduling processing is desired. For example, for distributed processing, channel scheduler 48 may be located in each base station 4. In contrast, for central processing, the channel scheduler 48 may be located in the base station controller 10 and may be designed to coordinate the data transmission of the various base stations 4. Other ways of performing the above functions may be considered within the scope of the present invention.

As shown in FIG. 1, the mobile station 6 can be spread over a data communication system and communicate with zero or one base station 4 on the forward link. In a typical embodiment, the channel scheduler 48 regulates forward link data transmission of one base station 4. In a typical embodiment, channel scheduler 48 connects to channel element 42 and data queue 40 in base station 4 and receives queue size, which queues the DRC messages from mobile station 6 and the < RTI ID = 0.0 > 6) shows the amount of data transferred. Channel scheduler 48 schedules high-speed data transmissions to optimize system objectives such as optimal data throughput and minimum transmission delay.

In a typical embodiment, data transmission is scheduled based in part on the quality of the communication link. A typical communication system that selects a transmission rate based on link quality is disclosed in US patent application Ser. No. 08 / 741,320, filed on September 11, 1996 and entitled "METHOD AND APPARATUS FOR PROVIDING HIGH SPEED DATA COMMUNICATION IN A CELLULAR ENVIRONMENT." This application is assigned to the assignee of the present invention and cross-referenced herein. In the disclosed embodiment, the scheduling of the data communication may be based on the user's GOS, queue size, data type, degree of delay already experienced, and error rate of data transmission. These considerations are filed on Feb. 11, 1997, and filed on US Patent Application Nos. 08 / 798,951 and filed on August 20, 1997, entitled "METHOD AND APPARATUS FOR FORWARD LINK RATE SCHEDULING," and "METHOD AND APPARATUS FOR REVERSE LINK. Details are disclosed in US patent application Ser. No. 08 / 914,928, entitled " RATE SCHEDULING. &Quot; Other elements may be considered when scheduling data transmissions within the scope of the present invention.

The data communication system of the disclosed embodiment advantageously supports data and message transmission on the reverse link. In mobile station 6, controller 76 handles data or message transmission by routing data or messages from data source 70 to encoder 72. Controller 76 may be a microcontroller, a microprocessor, a digital signal processing (DSP) chip, or an ASIC programmed to perform the functions described below.

In a typical embodiment, encoder 72 encodes a message that matches the blank and burst signaling data format disclosed in US Pat. No. 5,504,773. The encoder 72 then generates and adds a set of CRC bits, adds a set of code trailing bits, encodes the data and the added bits, and rearranges the symbols in the encoded data. Interleaved data is provided to a modulator (MOD) 74.

Modulator 74 may be implemented in various embodiments. In a typical embodiment (see FIG. 6), interleaved data is covered with Walsh codes, spread with long PN codes, and spread with short PN codes. Spread data is provided to a transmitter in the front 62. The transmitter transmits the reverse link signal over the air in reverse link 52 through modulation, filtering, amplification and antenna 60.

In a typical embodiment, the mobile station 6 spreads the reverse link data according to the long PN code. Each reverse link channel is defined according to a temporary offset of a common long PN sequence. At two different offsets, the final modulation sequence is uncorrelated. The offset of the mobile station 6 is determined in accordance with the unique number identification of the mobile station 6 to which the mobile station 6 assigns an identification number in a typical embodiment of IS-95. Therefore, the mobile station 6 transmits on an uncorrelated reverse link channel determined according to its unique electronic serial number.

At base station 4, the reverse link signal is received by antenna 46 and provided by RF unit 44. The RF unit 44 filters, amplifies, demodulates and quantizes the signal and provides a digital signal to the channel element 42. Channel element 42 also performs Walsh code decovering and pilot and DRC extraction. The channel element 42 then rearranges the demodulated data, decodes the deinterleaved data and performs a CRC check function. Decoded data, such as data or a message, is provided to the selector element 14. The selector element 14 routes data and messages to the appropriate destination. Channel element 42 may also forward the quality indicator for selector element 14 that indicates the status of the received data packet.

In a typical embodiment, the mobile station 6 may be in one of three operating states. An exemplary state diagram showing the transition between the various operating states of the mobile station 6 is shown in FIG. In the access state 902, the mobile station 6 transmits an access probe and waits for channel assignment by the base station 4. Channel allocations include resource allocations such as power control channels and frequency allocations. The mobile station 6 may transition from the access state 902 to the connected state 904 if the mobile station 6 is paged to warn of upcoming data transmissions or if the mobile station 6 transmits data on the reverse link. In the connected state 904, the mobile station 6 exchanges (eg, transmits or receives) data and performs a handoff operation. Upon completing the release procedure, the mobile station 6 transitions from the connected state 904 to the idle state 906. The mobile station 6 may also transition from the access state 902 to the idle state 906 when the connection with the base station 4 is refused. In idle state 906, mobile station 6 receives and decodes messages in the forward control channel and performs an idle handoff procedure to listen for the overhead and paging messages. The mobile station 6 may initiate the access procedure to transition to the access state 902. The state diagram shown in FIG. 9 is merely a typical state definition for illustration. Other state diagrams may be used within the scope of the present invention.

II. Forward link data transmission

In a typical embodiment, the start of communication between the mobile station 6 and the base station 4 takes place in the same way as a CDMA system. After the call setup is complete, the mobile station 6 monitors the control channel of the paging message. In the connected state, the mobile station 6 starts transmitting the pilot signal on the reverse link.

An exemplary flow diagram of forward high speed data transfer is shown in FIG. If the base station 4 has data to be sent to the mobile station 6, the base station 4 sends a paging message addressed to the mobile station 6 in the control channel at block 502. The paging message may be sent to one or more base stations 4 depending on the handoff state of the mobile station 6. Upon receiving the paging message, the mobile station 6 begins the C / I measurement process at block 504. The C / I of the forward link signal is calculated in one or more combinations of the methods described below. The mobile station 6 then selects the requested data rate based on the best C / I measurement and sends a DRC message of the DRC channel at block 506.

In the same time slot, the base station 4 receives the DRC message at block 508. If the next timeslot can be used for data transmission, the base station 4 transmits data to the mobile station 6 in the data requested at block 510. Mobile station 6 receives the data transmission at block 512. If the next timeslot is available, the base station 4 sends the remainder of the packet at block 514 and the mobile station 6 receives the data transmission at block 516.

In one embodiment, the mobile station 6 can communicate with one or more base stations 4 at the same time. The action taken by the mobile station 6 depends on whether the mobile station 6 is soft handoff. These two cases are described separately below.

III. If there is no handoff

In the absence of handoff, the mobile station 6 communicates with one base station 4. 2, data destined for a particular base station 6 is provided to a selector element 14 which is assigned to control communication with the mobile station 6. The selector element 14 forwards the data to the data queue 40 in the base station 4. The base station 4 queues the data and sends a paging message on the control channel. The base station 4 then monitors the reverse DRC channel for the DRC channel from the mobile station. If no signal is selected in the DRC channel, the base station 4 may send a paging message until a DRC message is detected. After a predetermined number of transmissions have been attempted, the base station 4 may terminate or resume processing the call with the mobile station 6.

In a typical embodiment, the mobile station 6 sends the requested data rate in the form of a DRC message to the base station 4 in the DRC channel. In an alternative embodiment, the mobile station 6 sends an indication of the quality of the forward link channel (eg, C / I measurement) to the base station 4. In a typical embodiment, the 3-bit DRC message is decoded by the base station 4 into a soft decision. In a typical embodiment, the DRC message is sent in the first half of each timeslot. The base station 4 then has the remaining half of the time slot to decode the DRC message, and hardware for data transmission in the next subsequent time slot if that time slot is available for data transmission to this mobile station 6. Configure If the next subsequent time slot is not available, the base station 4 waits for the next available time slot and continuously monitors the DRC channel for a new DRC message.

In the first embodiment, the base station 4 transmits the requested data rate. This embodiment provides the mobile station 6 with an important decision regarding the choice of data rate. Transmission at the requested data rate has the advantage that the mobile station 6 always knows what data rate is excluded. Therefore, the mobile station 6 only demodulates and decodes the traffic channel according to the requested data rate. The base station 4 does not have to send a message to the mobile station 6 indicating that the data rate is to be used by the base station 4.

In the first embodiment, after receiving the paging message, the mobile station 6 attempts data demodulation continuously at the requested data rate. The mobile station 6 demodulates the forward traffic channel and provides a soft decision symbol to the decoder. The decoder performs a frame check on the decoded packet to decode the symbol and determine if the packet is received correctly. If a packet is received by mistake or directed to another mobile station 6, the frame check will indicate a packet error. Optionally, in the first embodiment, the mobile station 6 demodulates data in the slot by the slot basis. In a typical embodiment, the mobile station 6 is directed there on the basis of the preamble integrated in each transmitted data packet, as described below. Therefore, the mobile station 6 may terminate the decoding process if it is determined that this transmission is destined for the other mobile station 6. In either case, the mobile station 6 sends a negative acknowledgment (NACK) message to the base station 4 to inform the incorrect reception of the data unit. When receiving a NACK message, the error received data unit is retransmitted.

The transmission of the NACK message may be performed similarly to the transmission of the error indicator bit (EIB) of the CDMA system. Methods of using and performing EIB transmissions are disclosed in US Pat. No. 5,568,483, entitled "METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION." Optionally, a NACK may be sent with the message.

In the second embodiment, the data rate is determined by the base station 4 according to the input from the mobile station 6. The mobile station 6 performs C / I measurements and sends an indication of link quality (e.g., C / I measurements) to the base station 4. The base station 4 may adjust the requested data rate based on sources available to the base station 4 such as queue size and available transmit power. The regulated data rate may be transmitted to the mobile station 6 before or at the time of data transmission at the regulated data rate or may be performed in the encoding of the data packet. In the first case, when the mobile station 6 receives the adjusted data rate before data transmission, the mobile station 6 demodulates and decodes the received packet in the manner disclosed in the first embodiment. In the second case, if the adjusted data rate is transmitted to the mobile station 6 at the time of data transmission, the mobile station 6 can demodulate the forward traffic channel and store the demodulated data. Upon receiving the adjusted data rate, the mobile station 6 decodes the data according to the adjusted data rate. In the third case, if the adjusted data rate is performed on the encoded data packet, the mobile station 6 demodulates and decodes all candidate rates and determines the subsequent transmission rate for the selection of the decoded data. Methods and apparatus for performing rate determinations are US Patent Nos. 5,751,725 and 8 August 1997, entitled "METHOD AND APPARATUS FOR DETERMINING THE RATE OF RECEIVED DATA IN A VARIABLE RATE COMMUNICATION SYSTEM" And is disclosed in detail in U.S. Patent Application No. 08 / 908,866, entitled "METHOD AND APPARATUS FOR DETERMINING THE RATE OF RECEIVED DATA IN A VARIABLE RATE COMMUNICATION SYSTEM", the two inventions being assigned to the assignee of the present invention and Cross-referenced from For all the cases described above, the mobile station 6 transmits a NACK message as described above when the result of the frame check is negative.

The following description is based on the first embodiment in which the mobile station 6 transmits to the base station 4 a DRC message indicating the requested data rate except for other indications. However, the disclosed advantages can equally be used in the second embodiment in which the mobile station 6 transmits an indication of the link quality of the base station 4.

Ⅳ. For handoff

In the case of handoff, the mobile station 6 communicates with several base stations 4 on the reverse link. In a typical embodiment, data transmission for a particular mobile station 6 on the forward link occurs from one station 4. However, the mobile station 6 can simultaneously receive pilot signals from several base stations 4. If the C / I measurement of the base station 4 is above a predetermined threshold, the base station 4 is added to the mobile station 6 in the active set. During the soft handoff command message, the new base station 4 assigns the mobile station 6 to the reverse power control (RPC) Walsh channel described below. Each base station 4 in soft handoff with the mobile station 6 monitors the reverse link transmission and transmits an RPC bit in its respective RPC Walsh channel.

Referring to FIG. 2, the selector element 14 assigned to control communication with the mobile station 6 forwards data to all base stations 4 of the mobile station 6 that are active sets. Every base station 4 receiving data from the selector element 14 sends a paging message to the mobile station 6 in its respective control channel. When the mobile station 6 is in the connected state, the mobile station 6 performs two functions. First, the mobile station 6 selects the best base station 4 based on a set of parameters that may be the best C / I measurements. The mobile station 6 then selects a data rate corresponding to the C / I message and sends a DRC message to the selected base station 4. The mobile station 6 may instruct the specific base station 4 to transmit the DRC message by covering the DRC message assigned to that particular base station 4 with a Walsh cover. Second, the mobile station 6 attempts to demodulate the forward link signal according to the requested data rate in each subsequent time slot.

After sending the paging message, all base stations 4 in the active set monitor the DRC channel for DRC messages from the mobile station 6. In addition, since the DRC message is covered with a Walsh code, the selected base station 4 assigned the same Walsh cover can discover the DRC message. Upon receiving the DRC message, the selected base station 4 sends data to the mobile station 6 in the next available time slot.

In a typical embodiment, the base station 4 transmits data to the mobile station 6 in a packet comprising a plurality of data units at the requested data rate. If the data unit was incorrectly received by the mobile station 6, a NACK message is sent on the reverse link to all base stations 4 that are in the active set. In an exemplary embodiment, the NACK message is demodulated and decoded by the base station 4 and forwarded to the selector element 14 for processing. When processing a NACK message, the data unit can be retransmitted using the procedure described above. In a typical embodiment, the selector element 14 combines the NACK signal received from all base stations 4 with the NACK message and sends the NACK message to all base stations 4 in the active set.

In a typical embodiment, the mobile station 6 can detect changes in the best C / I measurements and dynamically request data transmissions from different base stations 4 in each time slot to improve efficiency. In a typical embodiment, since data transmissions originate from only one base station 4 in any given time slot, the other base station 4 in the active set is sent to the mobile station 6 if any data units are present. You may not know. In a typical embodiment, the transmitting base station 4 informs the selector element 14 of the data transmission. The selector element 14 then sends a message to all base stations 4 that are in the active set. In a typical embodiment, it is assumed that the transmitted data has been correctly received by the mobile station 6. Therefore, if the mobile station 6 requests data transmission from different base stations 4 which are the active set, the new base station 4 transmits the remaining data units. In a typical embodiment, the new base station 4 transmits from the selector element 14 according to the remaining transmission update. Optionally, the new base station 4 selects the next data unit to transmit using the previous scheme from the selector element 14 and the prediction scheme based on metrics such as the average transmission rate. This mechanism minimizes replicated retransmission of the same data unit by several base stations 4 in different time slots resulting in a loss of efficiency. If a previous transmission was received by mistake, the base station 4 may retransmit the data units from the sequence since each data unit is identified by a unique sequence number described below. In a typical embodiment, if a hole (or untransmitted data unit) is created (eg, as a result of a handoff between one base station 4 and another base station 4), the lost data unit is accidentally received. It is considered to be. The mobile station 6 sends a NACK message according to the lost data units and these data units are retransmitted.

In a typical embodiment, each base station 4 in the active set maintains an independent data queue 40 containing data to be transmitted to the mobile station 6. In addition to the retransmission of the data unit and signaling message received by mistake, the selected base station 4 sequentially transmits the data present in its data queue 40. In a typical embodiment, the transmitted data unit is cleared from the queue 4 after the transmission.

Ⅴ. Other Considerations for Forward Link Data Transmission

An important consideration in the data communication system of the described embodiment is the accuracy of the C / I estimates for selecting the data rate for future transmission. In a typical embodiment, the C / I measurements are performed on the pilot signal for a time interval when the base station 4 transmits the pilot signal. In a typical embodiment, since only the pilot signal is transmitted during the pilot time interval, the effects of multipath and interference are minimal.

If the pilot signal is transmitted continuously in an orthogonal code channel, similar to an IS-95 system, the effects of multipath and interference can distort the C / I measurements. Similarly, when performing C / I measurements in data transmissions instead of pilot signals, multipath and interference may also degrade C / I measurements. In both cases, when one base station 4 is transmitting to one mobile station 4, the mobile station 6 can accurately measure the C / I of the forward link signal since no other interfering signal is present. However, when the mobile station 6 is soft handoff and receives pilot signals from several base stations 4, the mobile station 6 does not know if the base station 4 transmits data. In the worst case, the mobile station 6 may measure a high C / I in the first time slot when no base station 4 transmits data to any base station 6, and all base stations 4 have the same time. When transmitting data in a slot, it is possible to receive data transmission in a second time slot. C / I measurements in the first time slot, because the state of the data communication system changes when all the base stations 4 are idle, gives a distortion indication of the forward signal quality in the second time slot. Indeed, the actual C / I in the second time slot may be degraded at points where reliable decoding is not possible at the requested data rate.

The opposite case exists when the C / I estimate by the mobile station 6 is based on the minimum interference. However, the actual transmission occurs when only the selected base station is transmitted, where the C / I estimate and the selected data rate are preserved, and the transmission occurs at a lower rate than the reliable decoding, thereby reducing the transmission efficiency.

If the C / I measurements are performed on consecutive pilot or traffic signals, the prediction of C / I in the second time slot is based on three measurements in the second time slot based on the measurement of C / I in the first time slot. The embodiment can be made more accurately. In the first embodiment, data transmission from base station 4 is controlled so that base station 4 does not continuously toggle between transmission and idle states in successive time slots. This can be achieved by queuing enough data (e.g., a predetermined number of bits of information) before the actual data transmission for the mobile station 6.

In the second embodiment, each base station 4 transmits a forward active bit (hereinafter referred to as the FAC bit) that indicates whether the transmission occurs in the next half frame. The use of the FAC bit is described in detail below. The mobile station 6 performs C / I measurements taking into account the FAC bits received from each base station 4.

In a third embodiment corresponding to the manner in which the indication of the link quality is transmitted to the base station 4 and corresponding to the method using the central scheduling scheme, one of the base stations 4 represents data transmitted in each time slot. Scheduling information may be used in the channel scheduler 48. The channel scheduler 48 may receive the C / I measurements from the mobile station 6 and adjust the C / I measurements based on the recognition of the presence or absence of data transmissions from each base station 4 of the data communication system. . For example, the mobile station 6 may measure C / I in the first time slot when no neighbor base station 4 is transmitted. The measured C / I is provided to the channel scheduler 48. The channel scheduler 48 knows that no data is transmitted in the first time slot because no base station 4 is scheduled by the channel scheduler 48. When scheduling data transmission in the second time slot, the channel scheduler 48 knows whether one or more neighboring base stations 4 will transmit data. The channel scheduler 48 adjusts the C / I measurements in the first time slot to account for additional interference, and the mobile station 6 may be received in the second time slot due to data transmission by the proximity base station 4. will be. Optionally, if the C / I is measured in the first time slot when the near base station 4 is transmitting and these near base stations 4 are not transmitted in the second time slot, then the channel scheduler 8 takes into account additional information. You can adjust the C / I measurements.

Another important consideration is to minimize redundant retransmissions. Redundant retransmissions may result from having the mobile station 6 select data transmissions from different base stations 4 in consecutive time slots. The best C / I measurements may be toggled over consecutive time slots where the mobile station 6 measures approximately the same C / I measurements for these base stations 4 between two or more base stations 4. This toggle may be due to variations in C / I measurements and / or changes in channel conditions. The transmission of data at different base stations 4 in consecutive time slots can lead to a loss of efficiency.

Toggling problems can be explained by hysteresis. Hysteresis may be performed in a signal level method, a timing method, or a combination of signal level and timing methods. In a typical signal level scheme, better C / I measurements of different base stations 4 that are active sets do not exceed the C / I measurements of different base stations 4 of base stations 4 currently transmitting by at least the amount of hysteresis. Will not be selected. For example, it is assumed that hysteresis is 1.0 dB, the C / I measurement of the first base station 4 is 3.5 dB, and the C / I measurement of the second base station 4 is 3.0 dB in the first time slot. In the next time slot, the second base station 4 will not be selected unless the C / I measurement is at least 1.0 dB higher than the first base station 4. Therefore, if the C / I measurement of the first base station 4 is still 3.5 dB in the next time slot, the second base station 4 will not be selected unless the C / I measurement is at least 4.5 dB.

In a typical timing scheme, the base station 4 transmits data packets to the mobile station 6 for a predetermined number of time slots. The mobile station 6 is not allowed to select different transmitting base stations 4 within a predetermined number of time slots. The mobile station 6 continuously measures the C / I of the base station 4 currently transmitting in each time slot and selects the data rate according to the C / I measurement.

Another important consideration is the efficiency of data transfer. According to Figures 4E and 4F, each data packet format 410, 430 includes data and overhead bits. In a typical embodiment, the overhead bit number is fixed for all data rates. At the highest data rate, the percentage of overhead is relatively small compared to the packet size and the efficiency is high. At low data rates, the overhead bits may comprise a high percentage of the packet. Efficiency at low data rates can be improved by sending variable length data bits to the mobile station 6. Variable length data packets may be divided and transmitted to the mobile station 6 in several time slots. Advantageously, variable length data packets are sent to the mobile station 6 in consecutive time slots to simplify processing. The disclosed embodiments will use different packet sizes at different supported data rates to improve overall transmission efficiency.

Ⅵ. Forward link structure

In a typical embodiment, the base station 4 transmits at the maximum power available to the base station 4 and at the maximum data rate supported by the data communication system to a single mobile station 6 in a given slot. The maximum data rate that can be supported is dynamic and follows the C / I of the forward link signal measured by the mobile station 6. Advantageously, the base station 4 transmits only one mobile station 6 in a given time slot.

To facilitate data transmission, the forward link includes four multiplexed channels: pilot, channel, power control channel, control channel and traffic channel. Each function and method of performing these channels is described below. In a typical embodiment, the traffic and power control channels each comprise multiple orthogonal spreading Walsh channels. In one embodiment, the traffic channel is used to send traffic data and paging messages to the mobile station 6. When used to send a paging message, a traffic channel is referred to herein as a control channel.

In a typical embodiment, the bandwidth of the forward link is chosen to be 1.2288 MHz. This bandwidth selection enables the use of existing hardware components designed for CDMA systems that conform to the IS-95 standard. However, the data communication system of the present invention can be modified to use different bandwidths in order to conflict with system requirements and / or to improve capacity. For example, 5 MHz bandwidth can be used to increase capacity. In addition, the bandwidths of the forward link and the reverse link may be different for closer matching of the link capacity (eg, 5 MHz bandwidth on the forward link and 1.2288 MHz bandwidth on the reverse link).

In a typical embodiment, the short PN ₁ and PN _Q codes are 2 ¹⁵ PN codes of the same length specified by the IS-95 standard. At 1.2288 MHz chip rate, the short PN sequence repeats every 26.67 msec (26.67 msec = 2 ¹⁵ /1.2288*10 ⁶ ). In a typical embodiment, the same short PN code is used by all base stations 4 in the data communication system. However, each base station 4 is identified by the unique offset of the basic short PN sequence. In a typical embodiment, this offset is an increment of 64 chips. Other bandwidths and PN codes may be used within the scope of the present invention.

Iii. Forward link traffic channel

A block diagram of a typical forward link structure is shown in FIG. 3A. The data is divided and provided to the CRC encoder 112. For each data packet, the CRC encoder 112 generates a frame check bit (eg, CRC parity bit) and inserts a code trailing bit. The formatted packet from the CRC encoder 112 includes data, frame check and code back bits, and other overhead bits described below. The formatted packet is provided to an encoder 114 that encodes the packet according to the encoding format disclosed in U. S. Patent No. 5,933, 462 described above. Other encoding formats may also be used within the scope of the present invention. The encoded packet from encoder 114 is provided to interleaver 116 which relocates code symbols into the packet. Interleaved packets are provided to frame puncture element 118 that removes portions of the packet in a manner described below. The punctured packet is provided from the scrambler 122 to the multiplexer 120 which scrambles the data using the scrambling sequence. Puncture elements 118 and scrambler 122 are described in detail below. The output from the multiplexer 120 includes scrambled packets.

The scrambled packet is provided to a variable speed controller 130 that demultiplexes the packet into K parallel in-phase and quadrature channels, where K follows the data rate. In a typical embodiment, the scrambled packets are first demultiplexed into in-phase (I) and quadrature (Q) streams. In a typical embodiment, the I stream contains even indexed symbols and the Q stream contains odd indexed symbols. Each stream is demultiplexed into K parallel channels so that the symbol rate of each channel is fixed for all data rates. The K channel of each stream is provided to a Walsh cover element 132 that covers each channel using a Walsh function to provide an orthogonal channel. Orthogonal channel data is provided to a gain element 134 that scales the data to maintain the same total energy per chip (and the same output power) for all data rates. The scaled data from the gain element 134 is provided to a multiplexer (MUX) 160 which multiplexes the data into a preamble. The preamble is described in detail below. The output from MUX 160 is provided to a multiplexer (MUX) 162 that multiplexes traffic data, power control bits and pilot data. The output of the MUX 162 includes an I Walsh channel and a Q Walsh channel.

A block diagram of a typical modulator used to modulate data is shown in FIG. 3B. The I Walsh channel and the Q Walsh channel are provided to summers 212a and 212b that sum the K Walsh channels to provide I _SUM and Q _SUM , respectively. The I _SUM and Q _SUM signals are provided to the complex multiplier 214. Complex multiplier 214 receives the PN_I and PN_Q signals from multipliers 236a and 236b, respectively, and multiplies the two complex inputs according to the following equation.

(2)

Where I _mult and Q _mult are output from complex multiplier 214 and j is a complex representation. The I _mult and Q _mult signals are provided to filters 216a and 216b that respectively filter the signal. The filtered signal from the filters 216a, 216b is provided to a summator 218a, 218b that multiplies the signal with the in-phase sinusoidal COS (wct) and the orthogonal sinusoidal SIN (wct), respectively. The I modulated and Q modulated signals are provided to a summer 220 that sums the signals to provide a forward modulation waveform S (t).

In a typical embodiment, data packets are spread with long PN codes and short pn codes. The long PN code scrambles the packet so that only the mobile station 6 to which the packet is directed will scramble the packet. In a typical embodiment, the pilot and power control bits and control channel packets are spread with short PN codes, but long PN codes do not allow all mobile stations 6 to receive these bits. The long PN sequence is generated by the long code generator 232 and provided to a multiplexer (MUX) 234. The long PN mask determines the offset of the long PN sequence and is uniquely assigned to the destination mobile station 6. The output from MUX 234 is a long PN sequence during the data portion of the transmission, otherwise zero (eg, during the pilot and power control portion). The long PN sequence gated from MUX 234 and the short PN _I and PN _Q sequences from short code generator 238 are fed to multipliers 236a and 236b that multiply two sets of sequences to form PN_I and PN_Q signals, respectively. Is provided. The PN_I and PN_Q signals are provided to the complex multiplier 214.

The block diagram of the typical traffic channel provided in FIG. 3A is one of several structures that support data encoding and modulation on the forward link. Other structures, such as those for the forward link traffic channel of CDMA systems conforming to the IS-95 standard, can be used within the scope of the present invention.

In a typical embodiment, the data rates supported by the base station 4 are determined and each supported data rate is assigned a unique rate index. The mobile station 6 selects one of the supported data rates according to the C / I measurements. The requested data rate needs to be transmitted to the machine tool 4, instructing the base station 4 to transmit data at the requested data rate, and identifying the requested data rate and the number of data rates supported for trade off. It is made between the required number of bits. In a typical embodiment, the number of data rates supported is seven, and a three bit index is used to identify the data rates requested. A typical definition of the supported data rates is shown in Table 1. Different definitions of supported data rates may be considered within the scope of the present invention.

In a typical embodiment, the minimum data rate is 38.4 Kbps and the maximum data rate is 2.4576 Mbps. The minimum data rate is chosen based on the system's worst C / I measurements, the system's processing gain, the design of the error correction code, and the desired level of performance. In a typical embodiment, the supported data rate is chosen such that the difference in successive supported data rates is 3 dB. The 3 dB increase is negotiated among several factors including the accuracy of the C / I measurements that can be achieved by the mobile station 6, and the loss (inefficiency) is based on the C / I measurements of the data rate. This results in quantization, and the number of bits (or bit rate) is needed to transmit the requested data rate from the mobile station 6 to the base station 4. More supported data rates require more bits to identify the requested data rate but allow for more efficient use of the forward link due to small quantization errors between the maximum data rate being calculated and the supported data rate. The present invention may use other speeds and supported data rates than those shown in Table 1.

Table 1-Traffic Channel Parameters

A diagram of a typical forward link frame structure of the present invention is shown in FIG. 4A. Traffic channel transmissions are divided into frames, which in a typical embodiment are defined by short PN sequences or lengths of 26.67 msec. Each frame may carry or empty control channel information (control channel frames) addressed to all mobile stations 6, traffic data (traffic frames) addressed to specific mobile stations 6 (idle frames). The content of each frame is determined by the scheduling performed by transmitting the mobile station 4. In a typical embodiment, each frame includes 16 time slots, each time slot having a duration of 1.667 msec. A time slot of 1.667 msec is suitable for the mobile station 6 to make C / I measurements of the forward link signal. The time slot of 1.667 msec also represents sufficient time for efficient packet data transmission. In a typical embodiment, each time slot is also divided into four quarter slots.

In one embodiment, each data packet is sent in one or more time slots as shown in Table 1. In a typical embodiment, each forward link data packet includes 1024 or 2048 bits. Therefore, the number of time slots is required to transmit each data packet, and each data packet follows the data rate and range of one time slot at speeds of 1.2288 Mbps or more from 16 time slots at 38.4 Kbps.

A diagram of a typical forward link slot structure is shown in FIG. 4B. In a typical embodiment, each slot includes a 3/4 multiplexed channel, a traffic channel, a control channel, a pilot channel and a power control channel. In a typical embodiment, the pilot and power control channels are transmitted in power control bursts located at the same location of two pilots and each time slot. Pilot and power control bursts are described in detail below.

In an exemplary embodiment, interleaved packets from interleaver 116 are punctured to accommodate pilot and power control bursts. In an exemplary embodiment, each interleaved packet includes 4096 code symbols, and the first 512 code symbols are punctured as shown in FIG. 4D. The remaining code symbols are sloped in time to assign to the traffic channel transmission interval.

The punctured code symbols are scrambled to randomize the data before applying orthogonal Walsh cover. Randomization limits the peak-to-average envelope in the modulated waveform S (t). The scrambling sequence can be generated using a linear feedback shift register in a known manner. In a typical embodiment, the scrambler 122 is located in the LC state at the beginning of each slot. In a typical embodiment, the clock of scrambler 122 is synchronized with the clock of interleaver 116 but is mounted during pilot and power control bursts.

In a typical embodiment, the forward Walsh channel (traffic channel and power control channel) is orthogonally spread to the 16-bit Walsh cover at a fixed chip rate of 1.2288 Mcps. The parallel orthogonal channel K in orthogonal signal and in phase is a function of data rate as shown in Table 1. In a typical embodiment, at low data rates, in-phase and quadrature Walsh covers are selected for orthogonal sets to minimize crosstalk to demodulator phase estimation errors. For example, for a 16 Walsh channel, typical Walsh assignments are W ₀ to W ₇ for in-phase signals and W ₈ to W ₁₅ for orthogonal signals.

In a typical embodiment, QPSK demodulation is used for data rates below 1.2288 Mbps. In the case of QPSK modulation, each Walsh channel contains one bit. In a typical embodiment, at a maximum data rate of 2.4576, 16 QAMs are used, scrambled data is demultiplexed into 32 parallel streams, each 2 bits, 16 parallel streams for in-phase signals and 16 parallel streams for orthogonal signals. Demultiplexed. In a typical embodiment, the LSB of each two bit symbol is an early symbol output of interleaver 116. In a typical embodiment, the QAM modulation inputs of (0,1,3,2) are mapped to modulation values of (+ 3, + 1, -1, -3), respectively. Other modulation schemes such as m-th phase shift keying (PSK) can be used within the scope of the present invention.

In-phase and quadrature Walsh channels are scaled prior to modulation to maintain a constant total transmit power independent of data rate. The gain setting is normalized to the same single criteria as the demodulated BPSK. The gain G of the normalized channel as a function of the number of Walsh channels (or data rates) is shown in Table 2. Also listed in Table 2 is the average power per phase Walsh channel (in phase or quadrature) where the total standard power has a single value. The channel gain for 16 QAM considers that the normalized energy per Walsh chip is 1 for QPSK and 5 for 16 QAM.

Table 2-Traffic Channel Orthogonal Channel Gain

In one embodiment, the preamble is punctured into each traffic frame to assist the mobile station 6 in synchronizing the first slot of each variable rate transmission. In a typical embodiment, the preamble is all zero sequences that are spread with long PN codes for traffic frames but not with long PN codes for control channel frames. In a typical embodiment, the preamble is demodulated BPSK that is orthogonally spread to Walsh cover W1. The use of a single orthogonal channel minimizes the peak-to-average envelope. In addition, the use of non-zero Walsh cover W1 minimizes false pilot detection in case of traffic frames, pilot spreads to Walsh cover W0, and pilot and preambles do not spread to long PN codes.

The preamble is multiplexed into the traffic channel stream at the beginning of the packet for a time that is a function of the data rate. The length of the preamble is nearly constant at all data rates, while the preamble minimizes the chances of approximately false detection. A summary of the frames as a function of data rate is shown in Table 3. The preamble contains less than 3.1 percent of the data packets.

Table 3- Preamble Parameters

Iii. Forward link graphics frame format

In a typical embodiment, each data packet is formatted by the addition of frame check bits, code back bits and other control fields. In this specification, an octet defines eight information bits, and the data unit is a single octet and includes eight information bits.

In a typical embodiment, the forward link supports the two data packet formats shown in FIGS. 4E and 4F. The packet format 410 includes five fields and the packet format 430 includes nine fields. The packet information 410 is used when the data packet to be sent to the mobile station 6 contains enough data to completely fill all octets available in the DATA field 418. If the amount of data to be transmitted is less than the available octets of the DATA field 418, the packet format 430 is used. Unused octets are padded with all zeros and designed with the PADDING field 446.

In an embodiment, the frame check sequence (FCS) fields 412 and 432 contain CRC parity bits generated by the CRC generator 112 in accordance with a predetermined generator polynomial (see FIG. 3A). In an embodiment, the CRC polynomial is g (x) = x ¹⁶ + x ¹² + x ⁵ +1, although other polynomials can be used, which is within the scope of the present invention. In an embodiment, the CRC bits are calculated for the FMT, SEQ, LEN, DATA and PADDING fields. This provides error detection for all bits except the code tail bits in the TAIL fields 420 and 448, transmitted on traffic channels on the forward link. In an alternative embodiment, the CRC bits are only calculated for the DATA field. In an embodiment, the FCS fields 412 and 432 contain 16 CRC parity bits, but other CRC generators providing other numbers of parity bits may be used, which is within the scope of the present invention. Although the FCS fields 412 and 432 disclosed herein are disclosed as CRC parity bits, other frame check sequences may be used and this is within the scope of the present invention. For example, the check sum can be calculated for the packet and provided in the FCS field.

In an embodiment, the frame format (FMT) fields 414 and 434 contain only data octets (packet format 410) or data and padding octets and zero or more messages (packet format 430). In an embodiment, the low value of the FMT field 414 corresponds to the packet format 410. Optionally, the high value of the FMT field 434 corresponds to the packet format 430.

Sequence number (SEQ) fields 416 and 442 identify the first data unit in data fields 418 and 444, respectively. The sequence number allows data to be sent to the mobile station 6 for retransmission of packets received in error in non-sequence form. The allocation of sequence numbers at the data unit level removes the requirement for the frame fragmentation protocol for retransmission. The sequence number also allows the mobile station 6 to detect duplicate data units. Upon receiving the FMT, SEQ, and LEN fields, the mobile station 6 may detect whether a data unit was received in each time slot without using a specific signaling message.

The number of bits allocated to represent the sequence number depends on the maximum number of data units that can be transmitted in one time slot and in the worst case data retransmission is delayed. In an embodiment, each data unit is identified by a 24-bit sequence number. At a 2.4576 Mbps data rate, the maximum number of data units that can be transmitted in each slot is approximately 256. Eight bits are required to identify each data unit. Moreover, the worst case data retransmission delay can be calculated to be less than 500 milliseconds. The retransmission delay includes the time required for the NACK message by the mobile station 6, the retransmission of data, and in the worst case the number of retransmission attempts caused by the execution of the burst error. Thus, the 24 bits enable the mobile station 6 to properly identify the data unit that is received unambiguously. The number of bits in the SEQ fields 416 and 442 may increase or decrease depending on the size of the DATA field 418 and the retransmission delay. The use of different numbers of bits for SEQ fields 416,442 is within the scope of the present invention.

If the base station 4 has less data to transmit to the mobile station 6 than is available in the DATA field 418, the packet format 430 is used. The packet format 430 allows the base station 4 to transmit any number of data units to the mobile station 6 up to the maximum number of data units available. In an embodiment, a high value for the FMT field 434 indicates that the base station 4 transmits the packet format 430. Within packet format 430, LEN field 440 contains a value of the number of data units sent in the packet. In an embodiment, LEN field 440 is 8 bits long because DATA field 444 may be in the range of 0 to 255 octets.

DATA fields 418 and 444 contain data to be transmitted to the mobile station 6. In an embodiment, for packet format 410, each data packet includes 1024 bits, of which 992 bits are data bits. However, variable length data packets can be used to increase the number of information bits, which is within the scope of the present invention. For packet format 430, the DATA size is determined by LEN field 440.

In an embodiment, packet format 430 may be used to send zero or more signaling messages. The signaling length (SIG LEN) field 436 contains the length of consecutive signaling messages in octets. In an embodiment, the SIG LEN field 436 is 8 bits long. The SIGNALING field 438 contains a signaling message. In an embodiment, each signaling message includes a MESSAGE ID field, a message length (LEN) field and a message payload as described below.

PADDING field 446 has a padding octet that is a set of 0x00 (hex) in an embodiment. The PADDING field 446 may have data octets to be transmitted to the mobile station 6 by the base station 4 less than the number of octets available in the DATA field 418. In this case, the PADDING field 446 contains enough padding octets to fill the unused data fields. PADDING field 446 is of variable length and depends on the length of DATA field 444.

The final fields 410 and 430 of the packet format are the TAIL fields 420 and 448 respectively. The TAIL fields 420 and 448 contain 0 (0x0) code tail bits used to bring the encoder 114 (see Figure 3A) to a known state at the end of each data packet. The code tail bits allow the encoder 114 to concisely split the packets so that only bits from one packet are used in the encoding process. The code tail bits also allow the decoder in mobile station 6 to determine packet boundaries during the decoding process. The number of bits in the TAIL fields 420 and 448 depends on the encoder 114 design. In an embodiment, the TAIL fields 420 and 448 are long enough for the encoder 114 to be in a known state.

The two packet formats described above are exemplary formats that can be used to facilitate data and signaling message transmission. Different packet formats can be generated to meet the requirements of a particular communication system. In addition, the communication system can be designed to accommodate more formats than the two packet formats described above.

Iii. Forward Link Control Channel Frame

Also in one embodiment, the traffic channel is used to transmit a message from the base station 4 to the mobile station 6. The message type sent includes the following messages: (1) handoff direction message, (2) (to page a particular mobile station 6 for which data is present in the queue for mobile station 6). A paging message, (3) a short data packet for a particular mobile station 6, and (4) an ACK or NACK message for reverse link data transmission (to be described later). Other types of messages may also be sent on the control channel, which are within the scope of the present invention. Upon completing the call set up phase, the mobile station 6 monitors the control channel to page the message and initiates transmission of the reverse link pilot signal.

In an embodiment, the control channel is the time multiplied by the traffic data on the traffic channel as shown in FIG. 4A. The mobile station 6 detects the preamble covered by the predetermined PN code to identify the control message. In the embodiment, the control message is transmitted at a fixed rate determined by the mobile station 6 during collection. In a preferred embodiment, the data rate of the control channel is 76.8 Kbps.

The control channel sends a message in a control channel capsule. A diagram of an exemplary control channel capsule is shown in FIG. 4G. In an embodiment, each capsule includes a preamble 462, a control payload, and a CRC parity bit 474. The control payload contains one or more messages and, if necessary, includes padding bits 472. Each message includes a message identifier (MSG ID) 464, a message length (LEN) 466, and (if the message is specific). Mobile station 6) and a select address (ADDR) 468, and message payload 470. In an embodiment, the message matches an octet boundary. The example control channel capsule shown in FIG. 4G includes two broadcast messages for all mobile stations 6 and one message affected at a particular mobile station 6. The MSG ID field 464 determines whether the message requires an address field (whether it is a broadcast message or a specific message).

Iii. Forward Link Pilot Channel

In the embodiment disclosed herein, the forward link pilot channel provides a pilot signal used by the mobile station 6 for initial acquisition, phase recovery, time recovery, and speed combination. Their use is similar to that of the CDMA communication system known as the IS-95 standard. In an embodiment, the pilot signal is also used by the mobile station 6 to perform C / I measurements.

A block diagram of an exemplary forward link pilot channel is shown in FIG. 3A. Pilot data includes a sequence of all zeros (or all ones) provided to multiplier 156. Multiplier 156 uses the Walsh code W ₀ to cover the pilot data. Since the Walsh code W ₀ is a sequence of all zeros, the output of multiplier 156 is pilot data. The pilot data is time multiplied by MUX 162 and provided to the I Walsh channel spread by the short PN _I code (see FIG. 3B) in compound multiplier 214. In an embodiment, the pilot data is not spread by the long PN code, which is gated off during the pilot burst by the MUX 234 so that it can be accommodated by all mobile stations 6. Thus, the pilot signal is an unmodulated BPSK signal.

A diagram illustrating the pilot signal is shown in FIG. 4B. In an embodiment, each time slot includes two pilot bursts 306a and 306b that occur at the ends of the first and third quarters of the time slot. In an embodiment, each pilot burst 306 is 64 chips (Tp = 64 chips) in duration. In the absence of traffic data or control channel data, the base station 4 only transmits pilot and power control bursts, which results in discontinuous waveforms bursting at a periodic rate of 1200 Hz. Pilot modulation parameters are tabulated in Table 4.

ⅩⅠ. Reverse Link Power Control

In the embodiment disclosed herein, the forward link power control channel is used to transmit a power control command used to control the transmit power of the reverse link transmission from the remote station 6. In the reverse link, each transmitting mobile station 6 acts as an interference source for all other mobile stations 6 in the network. In order to minimize interference on the reverse link and maximize capacity, the transmit power of each mobile station 6 is controlled by two power control loops. In an embodiment, the power control loop is a CDMA system disclosed in the specification of US Pat. No. 5,056,109 entitled "METHOD AND APPARATUS FOR CONTROLLING TRANMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM", assigned to the assignee of the present invention and incorporated herein by reference. Similar to that of Other power control mechanisms may also be considered and are within the scope of the present invention.

The first power control loop regulates the transmit power of the mobile station 6 so that the reverse link signal quality is maintained at the set level. The signal quality is measured as bit-to-noise plus interference rate E _b / I _o per energy of the reverse link signal received at the base station 4. The set level is referred to as an Eb / Io set point. The second power control loop adjusts the set point to maintain the desired level of performance as measured by the frame error rate (FER). Power control is important for the reverse link since the transmit power of each mobile station 6 is an interference to other mobile stations 6 in the communication system. Minimizing reverse link transmit power reduces interference and increases reverse link capacity.

Within the first power control loop, E _b / I _o of the reverse link signal is measured at the base station 4. The base station 4 then compares the measured E _b / I _o with the set point. If the measured E _b / I _o is greater than the set point, the base station 4 sends a power control message to the mobile station 6 to reduce the transmit power. Optionally, if the measured E _b / I _o is below the set point, the base station 4 sends a power control message to the mobile station 6 to increase the transmit power. In an embodiment, the power control message is implemented with one power control bit. In the embodiment, a high value for the power control bit commands the mobile station 6 to increase the transmit power and a low value commands the mobile station 6 to decrease the transmit power.

In one embodiment, the power control bits for all mobile stations 6 in the communication with each base station 4 are transmitted in a power control channel. In an embodiment, the power control channel includes up to 32 orthogonal channels spread over a 16-bit Walsh cover. Each Walsh channel transmits one Reverse Power Control (RPC) bit or one FAC bit at periodic intervals. For transmission of the defined RPC bit stream to each mobile station 6, each operating mobile station 6 is given an RPC index which forms a Walsh cover and a QPSK modulation phase (same or quadrature phase). In an embodiment, an RPC index of zero is reserved for the FAC bit.

A block diagram of an exemplary power control channel is shown in FIG. 3A. RPC bits are provided to the symbol iterator 150 which repeats each RPC bit for a predetermined number of times. The repeated RPC bits are provided to the Walsh cover element 152 which covers the bits using the Walsh cover corresponding to the RPC indicator. The covered bits are provided to a gain element 154 that scales the bits prior to modulation to maintain a constant overall transmit power. In an embodiment, the gain of the RPC Walsh channel is averaged such that the total RPC channel power is equal to the total available transmit power. While maintaining reliable RPC transmissions for all operating mobile stations 6, the gain of the Walsh channel can be varied as a function of time for effective use of the total base station transmit power. In the embodiment, the Walsh channel gain of the inactive mobile station 6 is set to zero. Automatic power control of the RPC Walsh channel enables to calculate the forward link quality measurement of the corresponding DRC channel from the mobile station 6. The scaled RPC bits of the gain element 154 are provided to the MUX 162.

In an embodiment, RPC indicators from ₀ to ₁₅ are assigned to Walsh covers W ₀ to W ₁₅ , respectively, and transmitted around the first pilot burst (RPC burst 304 of FIG. 4C) in the slot. RPC indicators of 16 to 31 are assigned to Walsh covers W ₀ to W _{15 ′} , respectively, and transmitted around the first pilot burst (RPC burst 308 in FIG. 4C) in the slot. In an embodiment, the RPC bits use an even number of Walsh covers (W ₀ , W ₂ , W _4, etc.) modulated in the same phase and odd Walsh covers (W ₁ , W ₃ , W _5, etc.) modulated in the quadrature phase. Is the modulated BPSK. In order to reduce the peak to average envelope, it is desirable to balance in phase and quadrature power. In addition, in order to minimize cross-talk due to demodulation phase estimate error, it is desirable to assign orthogonal covers to in-phase and quadrature signals.

In a typical embodiment, up to 31 RPC bits may be sent in the 31 RPC Walsh channel in each timeslot. In a typical embodiment, 15 RPC bits are sent in the first 1/2 slot and 16 RPC bits are sent in the second 1/2 slot. The RPC bits are combined by adder 212 (see FIG. 3B) and the hybrid waveform of the power control channel is shown in FIG. 4C.

The timing diagram of the power control channel is shown in FIG. 4B. In a typical embodiment, the RPC bit rate is 600 bps or one RPC bit per time slot. Each RPC bit is time multiplexed and transmitted in two RPC bursts (eg, RPC bursts 304a and 304b) as shown in FIGS. 4B and 4C. In a typical embodiment, each RPC burst is 32 PN chips (or 2 Walsh symbols) in width (Tpc = 32 chips), and the total width of each RPC bit is 64 PN chips (or 4 Walsh symbols). Other RPC chip rates can be obtained by varying the number of symbol repetitions. For example, an RPC bit rate of 1200 bps (to simultaneously support 63 mobile stations 6 or to increase power control rate) may be used in the first set of 31 RPC bits and RPC bursts 308a and 308b in RPC bursts 304a and 304b. Can be obtained by transmitting a second set of 32 RPC bits. In this case, all Walsh covers are used for in-phase and quadrature signals. The modulation parameters of the RPC bits are summarized in Table 4.

Table 4-Pilot Power Control Modulation Parameters

The power control channel is bursty because the number of mobile stations 6 in communication with each base station 4 may be less than the number of available RPC Walsh channels. In this environment, some RPC Walsh channels are set to zero by appropriate adjustment of the gain of the gain element 1554.

In a typical embodiment, the RPC bits are sent to the mobile station 6 without coding or interleaving to minimize processing delays. In addition, erroneous reception of power control bits is not detrimental to the data communication system of the present invention since the error can be corrected in the next time slot by the power control loop.

In the disclosed embodiment, the mobile station 6 may be softhanded off with several base stations 4 on the reverse link. Methods and apparatus for reverse link power control for mobile station 6 in soft handoff are disclosed in US Pat. No. 5,056,109 and US Pat. No. 5,267,261, both of which are assigned to the assignee of the present invention and are mutually interchanged herein. Reference is made. Mobile station 6 in soft handoff monitors the RPC Walsh channel for each G4 station that is the active set and combines the RPC bits according to the method disclosed in U.S. Patent Nos. 5,056,109 and 5,267,261 described above. In the first embodiment, the mobile station 6 performs a logic OR of the down power command. The mobile station 6 will reduce the transmit power if one of the received PRC bits commands the mobile station 6 to reduce the transmit power. In the second embodiment, the mobile station 6, which is a soft handoff, may combine the soft decisions of the RPC bits before making a hard decision. Other embodiments for the processing of received RPC bits may be considered within the scope of the present invention.

In one embodiment, the FAC bit indicates that the mobile station 6 will transmit the traffic channel of that pilot channel in the next half frame. The use of the FAC bits improves the C / I estimate and therefore the data rate request by the mobile station 6 by broadcasting the recognition of interfering activity. In a typical embodiment, only the FAC bits are changed at half frame boundaries and repeated for eight consecutive time slots, resulting in a bit rate of 75 bps. The parameters for the FAC bits are listed in Table 4.

Using the FAC bit, the mobile station 6 can calculate the C / I measurement as follows.

(3)

Where (C / I) _i is the C / I measurement of the i th forward link signal, C _i is the total received power of the i th forward link signal, C _j is the received power of the j th forward link signal, and I Is the total interference when all base stations 4 are transmitting, and α _j may be 0 or 1 following the FAC bit and the FAC bit of the j th forward link signal.

XII. Reverse link data transmission

In the disclosed embodiment, the reverse link supports variable rate data transmission. Variable rates provide availability and allow the mobile station 6 to be transmitted at one of several data rates depending on the amount of data to be transmitted to the base station 4. In a typical embodiment, the mobile station 6 may transmit data at the lowest data rate at any time. In a typical embodiment, data transmission at high data rates requires permission by the base station 4. This implementation minimizes reverse link transmission delay while providing effective use of reverse link sources.

A flow diagram of reverse link data transmission is shown in FIG. First, in slot n, mobile station 6 performs an access probe as disclosed in US Pat. No. 5,289,527 to establish the lowest rate data channel on the reverse link at block 802. In the same slot n, the base station 4 demodulates the access probe and receives the access message at block 804. The base station 4 grants the request of the data channel, sends this grant in slot n + 2 and sends the RPC index assigned to the control channel in block 806. In slot n + 2, the mobile station 6 receives this grant and is power controlled by the base station 4 in block 808. Starting at slot n + 3, mobile station 6 begins to transmit a pilot signal and has immediate access to the lowest rate data channel on the reverse link.

If the mobile station 6 has traffic data and requires a fast data channel, the mobile station 6 may begin the request at block 810. In slot n + 3, base station 4 receives the high speed data request in block 812. In slot n + 5, base station 4 sends a grant on the control channel at block 814. In slot n + 5, the mobile station 6 receives the grant at block 816 and begins fast data transmission on the reverse link starting at slot n + 6 at block 818.

XIII. Reverse link structure

In the data transmission system of the disclosed embodiment, reverse link transmission differs from forward link transmission in several ways. In the forward link, data transmission typically takes place from one base station 4 to one mobile station 6. However, on the reverse link, each base station 4 can receive data transmissions from several mobile stations 6 simultaneously. In a typical embodiment, each mobile station 6 may transmit at one of several data rates depending on the amount of data to be transmitted to the base station 4. This system design reflects the symmetrical nature of data communications.

In a typical embodiment, the time base unit on the reverse link is the same as the time base unit on the forward link. In a typical embodiment, the forward link and reverse link data transmissions occur during a time slot of 1.667 msec. However, since data transmission on the reverse link generally occurs at low data rates, long time base units can be used to improve efficiency.

In a typical embodiment, the reverse link supports two channels, a pilot / DRC / RRI channel and a data channel. The function and method of performing each channel are described below. Pilot / DRC / RRI channels are used to transmit pilot signals, DRC messages and RRI symbols (described below), and data channels are used to transmit traffic data. RRI (Reverse Speed Indicator) indicates the speed of the reverse link traffic channel.

A diagram of a typical reverse link frame structure is shown in FIG. 7A. In a typical embodiment, the reverse link frame structure is similar to the forward link frame structure shown in FIG. 4A. However, on the reverse link, pilot / DRC / RRI data and traffic data are transmitted simultaneously on in-phase and orthogonal channels. In one embodiment, each slot is 2048 chips long, and the file signal is time multiplexed at an alternate 64 chip interval with the DRC message. The RRI channel symbol is punctured with a pilot (1/30 second of the slot) or 64 chips per slot for 1/16 of the pilot symbol.

In a typical embodiment, the mobile station 6 sends a DRC message on the pilot / DRC / RRI channel in each time slot each time the mobile station 6 receives a high speed data transmission. Optionally, when the mobile station 6 does not receive high speed data transmission, the entire slot in the pilot / DRC / RRI channel contains a pilot signal. The pilot signal is used to receive and use the base station 4 for various functions with the help of the data channel as a source for initial acquisition and closed loop reverse link power control as the phase reference of the pilot / DRC.

In a typical embodiment, the bandwidth of the reverse link is selected to 1.2288 MHz. This bandwidth selection enables the use of existing hardware designed for CDMA systems that conform to the IS-95 standard. However, other bandwidths can be used to meet system requirements and / or increase capacity. In a typical embodiment, equally long PN codes and short PN _I and PN _Q codes specified by the IS-95 standard can be used to spread the reverse link signal. In a typical embodiment, the reverse link channel is transmitted using QPSK modulation. Optionally, OQPSK modulation can be used to minimize the peak-to-average amplitude variation of the modulated signal resulting in improved performance. The use of different system bandwidths, PN codes, and modulation schemes may be considered within the scope of the present invention.

In a typical embodiment, if the transmit power of the reverse link transmission in the pilot / DRC / RRI channel and data channel is controlled, the Eb / Io of the reverse link signal measured at the base station 4 is disclosed in U.S. Patent No. 5,506,109 described above. It is held at a given Eb / Io set point. Power control is maintained by the base station 4 in communication with the mobile station 6 and the command is transmitted as the RPC bits described above.

XIV. Reverse link data channel

A block diagram of a typical reverse link structure is shown in FIG. This data is divided into data packets and provided to the encoder 612. For each data packet, encoder 612 generates CRC parity bits, inserts code trailing bits, and encodes the data. In a typical embodiment, the encoder 612 encodes the packet according to the encoding format disclosed in U.S. Patent Application Serial No. 08 / 743,688 described above. Other encoding formats may also be used within the scope of the present invention. The encoded packet from encoder 612 is provided to a block interleaver 614 that relocates the code symbols into the packet. The interleaved packet is provided to a multiplier 616 that covers the data with a Walsh cover and provides the covered data to the gain element 618. Gain element 618 scales the data to maintain the same energy Eb per bit, regardless of the data rate. Scaled data from gain element 618 is provided to multipliers 650b and 650d that spread the data into PN_Q and PN_I sequences, respectively. Spread data from multipliers 650b and 650d are provided to filters 652b and 652d that respectively filter the data. Signals filtered from filters 652a and 652b are provided to adder 654a and signals filtered from filters 652c and 652d are provided to adder 654b. Adder 654 sums the signals from the pilot / DRC / RRI channels with the signals of the data channels. The outputs of adders 654a and 654b include IOUT and QOUT modulated with in-phase sinusoidal COS (wct) and quadrature sinusoidal SIN (wct) (as forward link), respectively (not shown). . In a typical embodiment, traffic data is transmitted in in-phase and quadrature sinusoidal phases.

In a typical embodiment, data is spread using long PN codes and short PN codes. The long PN code scrambles the data so that the receiving base station 4 can identify the transmitting mobile station 6. Short PN codes spread the signal at system bandwidth. The long PN sequence is generated by the long code generator 642 and provided to the multiplier 646. Short PN _I and PN _Q sequences are generated by short code generator 644 and provided to multipliers 646a and 646b that multiply two sets of sequences to form PN_I and PN_Q, respectively. Timing / control circuit 640 provides a timing reference.

A typical block diagram of the data channel structure is shown in FIG. 6, which is one of several structures that support data encoding and modulation on the reverse link. For high speed data transmission, a structure similar to a forward link using multiple orthogonal channels may be used. Other structures, such as the structure for the reverse link traffic channel of a CDMA system conforming to the IS-95 standard, can be considered within the scope of the present invention.

In a typical embodiment, the reverse link data channel supports the four data rates shown in Table 5. Additional data rates and / or different data rates may be supported within the scope of the present invention. In a typical embodiment, the packet size of the reverse link follows the data rates shown in Table 5. As disclosed in U. S. Patent No. 5,933, 462 described above, improved decoder performance can be obtained for large packet sizes. Therefore, packet sizes different from those shown in Table 5 can be used to improve performance within the scope of the present invention. In addition, the packet size can make a parameter independent of the data rate.

Table 5- Pilot and Power Control Modulation Parameters

As shown in Table 5, the reverse link supports multiple data rates. In a typical embodiment, the lowest data rate of 9.6 Kbps is assigned to each mobile station 6 when registering the base station 4. In a typical embodiment, the mobile station 6 may transmit data in the lowest data rate channel in any time slot without having a request grant from the base station. In a typical embodiment, data transmission at high data rates is allowed by the selected base station 4 based on a set of system parameters such as system loading, fairness and total throughput. Scheduling mechanisms for typical high speed data transfers are disclosed in detail in US patent application Ser. No. 08 / 798,951.

ⅩⅤ. Reverse Link Pilot / DRC / RRI Channel

A block diagram of the pilot / DRC / RRI channel is shown in FIG. 6. The DRC message is provided to a DRC encoder 626 that encodes the message according to a predetermined coding format. Coding of DRC messages is important because incorrect forward link data rate determination affects system throughput performance. In a typical embodiment, the DRC encoder 626 is a ratio (8,4) orthogonal block encoder that encodes a 3-bit DRC message into an 8-bit code word. The encoded DRC message is provided to a multiplier 628 that covers the message with a Walsh code that uniquely identifies the destination base station 4 to which the DRC message is directed. The Walsh code is provided by Walsh generator 624. The covered DRC message is provided to a multiplexer (MUX) 630 that multiplexes the DRC message with pilot data and then multiplies it by an 8 chip Walsh cover (not shown). After multiplexing by the MUX 630, the pilot data is multiplied by the same 8 chip Walsh cover (not shown). The RRI symbol is provided to an RRI encoder 627 that encodes the RRI symbol according to one embodiment disclosed in accordance with FIG. 11. The encoded RRI symbols are provided to the MUX 630, which multiplexes the RRI symbols with pilot data and DRC messages and then multiplied by the same 8-chip Walsh cover (not shown). The RRI message, DRC message and pilot data are provided to multipliers 650a and 650c which spread the data into PN_I and PN_Q signals, respectively. Therefore, pilot data, RRI symbols, and DRC messages are transmitted in both sinusoidal in-phase and quadrature phases. An eight chip Walsh cover is advantageously a predetermined Walsh function. In one embodiment, all zero Walsh functions are used. In an alternative embodiment, the 8 chip Walsh cover will be multiplied by the pilot data, RRI symbol and DRC message before the pilot data, RRI symbol and DRC message are multiplexed by MUX 630.

In a typical embodiment, the DRC message is sent to the selected base station 4. This is accomplished by covering the DRC message with a Walsh code identifying the selected base station 4. In a typical embodiment, the Walsh code is 128 chips long. The variation of the 128 chip Walsh code is known. One unique Walsh code is assigned to each base station 4 in communication with the mobile station 6. Each base station 4 discovers the signal in the DRC channel with an assigned Walsh code. The selected base station 4 may recover the DRC message and transmits the data in response to the requesting mobile station 6 on the forward link in response. The other base station 4 may determine whether the requested data rate will not be headed here because these base stations 4 are assigned different Walsh codes.

In a typical embodiment, the reverse link short PN codes for all base stations 4 of the data communication system are the same, and there is no offset in the short PN sequence that distinguishes the different base stations 4. Data communication systems advantageously support soft handoff on the reverse link. Using the same short PN code without any offset allows several base stations 4 to receive the same reverse link transmission from the mobile station 6 during soft handoff. Short PN codes provide spread spectrum but do not allow for identification of the base station 4.

In a typical embodiment, the DRC message carries the data rate requested by the mobile station 6. In an alternative embodiment, the DRC message carries an indication of forward link quality (eg, C / I information measured by mobile station 6). At the same time mobile station 96 receives the forward link pilot signal from one or more base stations 4 and performs C / I measurements on each received pilot signal. The mobile station 6 then selects the best base station 4 based on a set of parameters that may include current and past C / I measurements. Rate control information is formatted into a DRC message that can be conveyed to the base station 4 in one of several embodiments.

In the first embodiment, the mobile station 6 sends a DRC message based on the requested data rate. The requested data rate is the highest supported data rate that yields satisfactory performance in the C / I measured by the mobile station 6. From the C / I measurements, the mobile station 6 calculates a maximum data rate that yields a satisfactory performance. The maximum data rate is then quantized to one of the supported data rates and designed as the requested data rate. The data rate index corresponding to the requested data rate is sent to the selected base station 4. A typical set of supported data rates and corresponding data rate indexes are shown in Table 1.

In the second embodiment, the mobile station 6 sends an indication of the forward link quality to the selected base station 4 and the mobile station 6 sends a C / I index representing the quantization of the C / I measurements. C / I measurements are mapped to tables and associated with C / I indexes. Using more bits to represent the C / I index enables finer quality of C / I measurements. In addition, the mapping can be linear or predistorted. For linear mapping, each increment of the C / I index represents the corresponding increment of the C / I measurements. For example, each step of the C / I index may represent a 2.0 dB increase in the C / I measurement. In the case of pre-distorted mapping, each increase in the C / I index may represent a different increase in the C / I measurement. As an example, pre-distorted mapping may be used to quantize C / I measurements to match the cumulative allocation function (CDF) curve of the C / I assignment shown in FIG. 10.

Other embodiments of conveying speed control information from the mobile station 6 to the base station 4 may be considered within the scope of the present invention. In addition, the use of different number of bits representing the speed control information is within the scope of the present invention. In most specifications, the disclosed embodiments are described in the context of the first embodiment, and DRC messages are used to carry the requested data rate for simplicity.

In a typical embodiment, C / I measurements may be performed on the forward link pilot signal in a manner similar to that used in CDMA systems. Methods and devices for performing C / I measurements are disclosed in US Pat. No. 5,903,554, filed May 11, 1999 and entitled "METHOD AND APPARATUS FOR MEASURING LINK QUALITY IN A SPREAD SPECTRUM COMMUNICATIO0N SYSTEM." The invention is assigned to the assignee of the present invention and cross-referenced herein. In summary, the C / I measurements in the pilot signal can be obtained by despreading the received signal using a short PN code. C / I measurements in the pilot signal may include inaccuracies if the channel state changes between the time of the C / I measurements and the actual data transfer time. In one embodiment, the use of the FAC bit causes the mobile station 6 to consider forward link activity when determining the requested data rate.

In alternative embodiments, C / I measurements may be performed on the forward link traffic channel. The traffic channel signal is first despread with the long PN code and the short PN code and then covered with the Walsh code. The C / I measurement of the signal in the data channel may be more accurate because a large percentage of the transmitted power is allocated for data transmission. Other methods of measuring the C / I of the forward link signal received by the mobile station 6 can be considered within the scope of the present invention.

In a typical embodiment, the DRC message is sent in the first half of the timeslot (see FIG. 7A). For a typical time slot of 1.667 msec, the DRC message includes 0.83 msec or the first 1024 chips of the time slot. The remaining 1024 chip time is used by the base station 4 to demodulate and decode the message. The transmission of the DRC message in the earlier time slot portion causes the base station 4 to decode the DRC message in the same time slot, and can transmit data at the requested data rate in the immediately following time slot. The short processing delay allows the communication system of the present invention to quickly adapt to changes in the operating environment.

In an alternative embodiment, the requested data rate is conveyed to the base station 4 using absolute reference and relative reference. In this embodiment, an absolute criterion containing the requested data rate is sent periodically. The absolute reference causes the base station 4 to determine the exact data rate requested by the mobile station 6. For each time slot between absolute references, the mobile station 6 sends a relative reference to the base station 4 indicating whether the upcoming time slot is higher, lower or equal to the data rate requested for the previous time slot. Periodically, the mobile station 6 transmits an absolute reference. Periodic transmission of the data rate index ensures that the requested data rate is set to a known state and ensures that the failure reception of negative criteria does not accumulate. The use of absolute and relative criteria can reduce the transmission rate of DRC messages to the base station 6. Other protocols for transmitting the requested data rate may be considered within the scope of the present invention.

ⅩⅥ. Reverse Link RRI Encoding

In an exemplary embodiment, RRI encoder 627 includes an encoder 1002 connected to code word repetition generator 1004. A 3-bit RRI symbol per 16 slot packet is provided to the encoder 1002. In one embodiment, encoder 1002 is a (32,3) linear block encoder. Encoder 1002 generates 32 binary RRI symbols per packet, as described below, and provides the encoded RRI symbols to code word repetition generator 1004. In one embodiment, code word repetition generator 1004 is configured to perform factor 4 repetition of the encoded RRI symbols, thereby generating 128 binary RRI symbols per packet. The encoded and repeated RRI symbols are provided to the MUX 630 which multiplexes the RRI symbols into pilot symbols and DCR symbols. The multiplexed data stream output from MUX 630 is provided to signal point mapping logic 1006 in accordance with one embodiment of mapping digital zero values to +1 and digital 1 to -1. Signal point mapping logic 1006 provides the multiplier 1008 with multiplexed pilot, DRC, and RRI values. Multiplier 1008 also receives an 8 chip Walsh function, which is a predetermined Walsh function of 8 plus 1 value. In one embodiment, multiplier 1008 multiplies the multiplexed pilot, DRC and RRI values with the Walsh function to produce an output data stream at a chip rate of 1.2288 megachips per second.

The RRI encoder 627 thus performs (128,3) encoding, including (32,3) linear encoding, preceded by the code word repetition using a repetition factor of four. Advantageously, no puncturing is necessary. All iterations are code word iterations. The (32,3) code has a weight variance of 2 code words with a weighted zero value, 6 code words with a weight of 16 and 1 codeword with a weight of 20. After four iterations, the weight is increased four times. Those skilled in the art will understand that (n, k) encoding (or (n, k) coding) indicates that k bits are encoded to produce n symbols, where n is greater than k depending on the code rate of k / n. . Those skilled in the art will understand that the weight of a given code word is equal to the sum of the digital values of the code word. The (32,3) linear code can be described in the order of the following 3 * 32 generator matrix (G).

In the generator matrix G, the 30 symbols (g0 to g29 (left to right)) can be represented by g in any three columns. The first column of generator metrics G is simply g 0 0. The second column is 0 g 0. The third column is 0 0 g. In one embodiment, the binary value of g is the same as the hexadecimal representation of 2492DBBF. The eight code words are all eight combinations of a bit-to-bit XOR combination of columns (i.e., addition mode 2), a column of generator metrics G in which the appropriate columns are turned on or off based on the 3-bit input RRI symbol values. According to one embodiment, this mapping is shown in Table 6, where the outermost row represents the 3-bit input RRI symbol value, and the eighth row represents the corresponding code word output from the encoder 1002, where the generator matrix (G). The bottom row of) can be used as g.

Table 6-RRI (32,3) Encoder Mapping

The particular value of g is advantageously chosen to achieve the maximum possible distance between different code words. The distance between code words is the number of output symbol positions where the two code words differ. The large distance makes it easier to distinguish between two code words if there is noise. For (32,3) linear block codes, the maximum possible distance of the different code words is 18, which is A.E. Brouwer & T. Verhoeff, "An Updated Table of Minimun Distance Bounds for Binary Codes," IEEE Trans. on Information Theory, Vol. 39, No. 2, Mar. 1993, pp. 662-677. After 4 iterations, the distance is 72 in the (128,3) code. (The (32,3) codes described above are 1 code word with a weight zero value after iteration of the code word by 4, 6 code words with a weight of 72 (18 times 4) and 1 code with a weight of 80 (20 times 4). Has a weight distribution with words.)

Those skilled in the art will appreciate that other block sizes and repeating elements may be used (large block size with small repeating factor or small block size with large repeating factor). In one embodiment, the (128,3) code is formed using the (8,3) linear block code and 16 repetition factors, yielding a distance of 64. In another embodiment, the (128,3) code is formed using the (16,3) linear block code and 8 repetition factors, yielding a distance of 64. In the above-described embodiment with reference to FIG. 11, the (128,3) code is formed using the (32,3) linear block code and the repetition factor of 4, yielding 72 distances. In another embodiment, the (128,3) code is formed using the (64,3) linear block code and 2 repeating factors, yielding 72 distances. In another embodiment, the (128,3) code is formed without using any iterations, yielding 72 distances. In another embodiment described below, the (133,3) code is formed using the (7,3) linear block code and the repetition factor of (19) (which yields a minimum distance of 76). The (133,3) code is then punctured at five specific symbol positions to produce (128,3).

In the final alternative embodiment described above, the RRI symbol is provided to a (7,3) single encoder. (7,3) A single encoder is advantageously constructed from orthogonal code by puncturing the first symbol of every code word. The encoded symbol is then provided to the code word repetition generator using 19 repetition factors. The output of the code word repetition generator is provided to symbol puncturing logic that performs five symbol puncturing on a preselected symbol in each code word. The disadvantage of this embodiment is that puncturing (and greater coder complexity) is required to achieve (128,3) code.

Iii. Reverse link access channel

The access channel is used by the mobile station 6 to send a message to the base station 4 during the registration phase. In a typical embodiment, the access channel is performed using a slotted structure as shown in FIG. 7B, with each slot randomly accessed by the mobile station 6. In a typical embodiment, the access channel is multiplexed onto the DRC channel.

In a typical embodiment, the access channel sends a message in an access channel capsule. In an exemplary embodiment, the access channel frame format is the same as specified by the IS-95 standard except that the 26.67 msec frame is timing instead of the 20 msec frame specified by the IS-95 standard. A diagram of a typical access channel capsule is shown in FIG. 7B. In an exemplary embodiment, each access channel capsule 712 includes a preamble 722, one or more message capsules 724, and padding bits 726. Each message capsule 724 includes a message length (MSG LEN) field 732, a message body 734, and a CRC parity bit 736.

Iii. Reverse Link NACK Channel

In one embodiment, the mobile station 6 sends a NACK message on the data channel. A NACK message is generated for each packet error received by the mobile station 6. In an exemplary embodiment, the NACK message may be sent using the blank and burst signaling data format disclosed in US Pat. No. 5,504,773.

Although the disclosed embodiments have been described in the context of a NACK protocol, the use of the ACK protocol may be considered within the scope of the present invention.

Iii. conclusion

So far a new and improved maximum distance velocity 3/128 block coordination scheme has been described. In the above embodiment, the mobile station 6 may be referred to as a subscriber unit. The subscriber unit can be, for example, a wireless telephone, a PDA, a laptop computer, a telephone connected to a computer, a handset connected to a handfree kit or any other form of access terminal. Those skilled in the art will understand that data, instructions, commands, information, signals, bits, symbols and chips described in the foregoing specification may advantageously be voltage, current, electromagnetic waves, magnetic fields or particles, light wavelengths or particles or combinations thereof. Those skilled in the art will also appreciate that various logic blocks, modules, circuits, and algorithm steps associated with the disclosed embodiments may be performed in electronic hardware, computer software, or combinations thereof. Various illustrative components, blocks, modules, circuits, and steps have been described generally functionally. The function is performed as hardware or software that conforms to the specific application and design constraints imposed on the overall system. Those skilled in the art will recognize how to best perform the interchange of hardware and software and the disclosed functionality for each particular application under such circumstances. For example, the various illustrative logic blocks, modules, circuits, and algorithm steps described in connection with the above-described embodiments may be digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other programmable. It can be performed using logic devices, discrete gate or transistor logic, discrete hardware components such as registers and FIFOs, a processor that executes a set of firmware instructions, any conventional programmable software modules and processors, or a combination thereof. The processor may advantageously be a microprocessor, and optionally may be any conventional processor, controller, microcontroller or state machine. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disks, removable disks, CD-ROMs, or other known storage media. A typical processor is advantageously connected to a storage medium to enable reading information from or writing information to the storage medium. The processor and the storage medium reside in an ASIC. The ASIC can reside in the phone. In addition, the processor and the storage medium may reside in a telephone. The processor may be performed in a combination of a DSP and a microprocessor or a combination of two microprocessors associated with a DSP core.

The previous descriptions of the preferred embodiments have been provided to enable any person skilled in the art to practice the invention. However, those skilled in the art will understand that various embodiments are possible without departing from the scope of the present invention. Accordingly, the invention is limited only by the following claims.

Claims (33)

As a way to encode data: Block encoding the data to produce a plurality of code words; And Repeating each said code word for a predetermined time. 2. The method of claim 1, wherein encoding the block comprises encoding data into a matrix having three columns and thirty-two rows. The method of claim 1, wherein the predetermined time is four. 2. The method of claim 1, wherein the block encoding step comprises encoding data into a matrix having three columns and thirty-two rows, wherein the predetermined number is four. 5. The method of claim 4, wherein each column of the matrix is a binary number with two zero values and a hexadecimal value of 2492 DBBF. 6. The method of claim 5, wherein the first column of the matrix from left to right is binary with a hexadecimal value of 2292 DBBF followed by two zero values, and the second column of matrix from left to right follows two zero values. A binary number with a hexadecimal value of 2492DBBF, and the third column of the matrix from left to right is a binary number with a hexadecimal value of 2492DBBF following two zero values. 2. The method of claim 1, wherein the block encoding step encodes data into a matrix having three columns and eight rows, wherein the predetermined number is sixteen. 2. The method of claim 1, wherein the block encoding step encodes data into a matrix having three columns and sixteen rows, wherein the predetermined number is eight. 2. The method of claim 1, wherein the block encoding step encodes data into a matrix having three columns and 64 rows, wherein the predetermined number is two. 2. The method of claim 1, wherein the block coding step encodes data into a matrix having three columns and 128 rows, wherein the predetermined number is zero. The method of claim 1, wherein the block coding step encodes a matrix with three columns and seven rows, wherein the predetermined number is 19, wherein each set of repeated code words is punctured at five positions. The method further comprises a step. 2. The method of claim 1, wherein the data includes a transmission data rate indicator from a subscriber unit of a data communication system. 13. The method of claim 12, further comprising multiplexing the encoded, repeated rate indicator data with the encoded rate request message and pilot signal to produce a multiplexed signal. 14. The method of claim 13, further comprising covering the multiplexed signal with an orthogonal code. 15. The method of claim 14, wherein the orthogonal code is a Walsh function with eight chips. Means for block encoding data to generate a plurality of code words; And And means for repeating each code word for a predetermined number of times. 17. The apparatus of claim 16, wherein the block coding means comprises means for encoding data as a matrix having three columns and thirty-two rows, wherein the predetermined number is four and the first column of the matrix from left to right is two. Binary with a hexadecimal value of 2292DBBF following the zero value of, and the second column of the matrix from left to right is a binary number with a hexadecimal value of 2492DBBF following two zero values, and a third column of the matrix from left to right. Is a binary number with a hexadecimal value of 2492DBBF followed by two zero values. A processor; And A storage medium connected to said processor that includes a set of instructions that can be encoded by the processor to block encode data to produce a plurality of code words and to repeat the respective code words for a predetermined number of times. Subscriber unit. 19. The method of claim 18, wherein the instruction set is performed by the processor to encode data as a matrix having three columns and 32 rows, repeating each code word four times, the matrix from left to right The first column of is a binary number with a hexadecimal value of 2292DBBF following two zeros, and the second column of the matrix from left to right is a binary number with a hexadecimal value of 2492DBBF following two zeros, and from left to right. Wherein the third column of the matrix is a binary number with a hexadecimal value of 2492 DBBF followed by two zero values. Block encoder; And And a code word repetition generator coupled to the block encoder. 21. The method of claim 20, wherein the block encoder comprises a (32,3) linear block encoder configured to encode data as a matrix having three columns and 32 rows to produce at least one code word, wherein the code word repetition And the generator is configured to repeat each code word for a predetermined number of times. 22. The subscriber unit of claim 21 wherein the code word repetition generator is configured to repeat the respective code word four times. 23. The system of claim 22, wherein each column of the matrix comprises binary and two zero values having a hexadecimal value of 2492 DBBF. 24. The method of claim 23, wherein the first column of the matrix from left to right is binary with a hexadecimal value of 2292 DBBF followed by two zero values, and the second column of matrix from left to right is subsequent to two zero values. A binary number having a hexadecimal value of 2492DBBF, and the third column of the matrix from left to right is a binary number having a hexadecimal value of 2492DBBF following two zero values. 21. The apparatus of claim 20, wherein the block encoder comprises an (8,3) linear block encoder adapted to encode data as a matrix having three columns and eight rows to produce at least one code word. A repetition generator is configured to repeat each code word 16 times. 21. The apparatus of claim 20, wherein the block encoder comprises a (16,3) linear block encoder adapted to encode data as a matrix having three columns and sixteen rows to produce at least one code word. And the repetition generator is configured to repeat each code word eight times. 21. The apparatus of claim 20, wherein the block encoder comprises a (64,3) linear block encoder adapted to encode data as a matrix with three columns and 64 rows to produce at least one code word. A repetition generator is configured to repeat each code word twice. 21. The apparatus of claim 20, wherein the block encoder comprises a (128,3) linear block encoder adapted to encode data as a matrix having three columns and 128 rows to produce at least one code word. A repetition generator is configured to repeat each codeword zero times. 21. The apparatus of claim 20, wherein the block encoder comprises a (7,3) linear block encoder configured to encode data into a matrix having three columns and seven rows to generate at least one code word. A symbol configured to repeat the at least one code word 19 times to generate at least one repeated code word set, the symbol being connected to the code word repeat generator and configured to puncture the at least one repeated code word set at five locations And a puncturing element. 22. The system of claim 21, wherein said data comprises a transmission data rate indicator from a subscriber unit of a data communication system, said data transmission system residing in said subscriber unit. 31. The apparatus of claim 30, further comprising a multiplexer connected to the codeword repetition generator and configured to multiplex the encoded repeated rate indicator data with encoded rate request data and pilot signals to produce a multiplexed signal. Data transmission system. 32. The system of claim 31 further comprising a multiplier connected to said multiplexer and multiplying each bit of an orthogonal code and a multiplexed signal. 33. The system of claim 32, wherein the orthogonal code is a Walsh function with eight chips.