BRPI9813885B1 - A method and equipment for high speed packet data transmission from at least one base station to a mobile station, and a method and equipment for high speed packet data transmission from at a base station to a mobile station - Google Patents

Description

"METHOD AND EQUIPMENT FOR HIGH-SPEED PACKAGE DATA FROM AT LEAST ONE BASE STATION FOR A MOBILE STATION, AND METHOD AND EQUIPMENT FOR HIGH-SPEED PACKAGE DATA FROM A BASE STATION" FIELD OF THE INVENTION The present invention relates to data communication. More particularly, the present invention relates to a new and improved method and equipment for high rate packet data transmission.

BACKGROUND DESCRIPTION

A communication system today must support a variety of applications. One such communication system consists of a code division multiple access (CDMA) system in accordance with "TIA / EIA / IS-95A, Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System" , hereinafter referred to as the IS-95 standard. The CDMA system allows voice and data communications between users over a terrestrial link. The use of CDMA techniques in a multiple access communication system is described in US Patent No. 4,901,307 entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS" and US Patent No. 5,103,459 entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM ", both on behalf of the Applicant of the present invention.

In this descriptive report, the base station refers to the hardware with which mobile stations communicate. Cell refers to hardware or geographic area, depending on the context in which the term is used. A sector is a partition of a cell. Because a sector of a CDMA system has the attributes of a cell, the teachings described in terms of cells can be readily extended to the sectors.

In the CDMA system, communications between users are conducted through one or more base stations. A first user on a mobile station communicates with a second user on a second mobile station by transmitting data via reverse link to a base station. The base station receives the data and can direct it to another base station. Data is transmitted over the direct link from the same base station, or from a second base station, to the second mobile station. Direct link refers to transmission from the base station to a mobile station and reverse link refers to transmission from the mobile station to a base station. On IS-95 systems, forward link and reverse link are allocated at separate frequencies.

The mobile station communicates with at least one base station during a communication. CDMA mobile stations are capable of communicating with multiple base stations simultaneously during soft handoff. Soft handoff is the process of establishing a link with a new base station before breaking the link with the previous base station. Soft handoff minimizes the likelihood of dropped calls. The method and system for providing communication with a mobile station through more than one base station during the soft handoff process is described in US Patent No. 5,267,261, entitled "MOBILE STATION ASSISTED SOFT HANDOFF IN A CDMA CELLULAR COMMUNICATIONS SYSTEM", on behalf of the Applicant of the present invention. Softer handoff is the process by which communication occurs across multiple sectors that are served by the same base station. The handoff process is described in detail in US Patent Serial No. 08 / 763,498, entitled "METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMON BASE STATION", filed December 11, 1996, on behalf of the Applicant of the present invention.

Given the growing demand for wireless data applications, the need for very efficient wireless data communication systems has become increasingly significant. The IS-95 standard is capable of transmitting traffic data and voice data via forward and reverse links. A method for transmitting traffic data in fixed length code channel frames is described in detail in U.S. Patent No. 5,504,773 entitled "METHOD AND APPARATUS FOR DATA FOR TRANSMISSION" on behalf of the Applicant of the present invention. According to IS-95, traffic data or voice data is partitioned into code channel frames that have a duration of 20 ms at data rates up to 14.4 kbps.

A significant difference between voice services and data services is the fact that the former imposes strict and fixed delay requirements. Typically, the overall unidirectional delay of speech frames should be less than 100 ms. In contrast, data delay can become a variable parameter used to optimize the efficiency of the data communication system. Specifically, more efficient error correction coding techniques that require significantly longer delays than can be tolerated by voice services can be used. An exemplary efficient coding scheme for data is described in US Patent Application Serial No. 08 / 743,688 entitled "SOFT DECISION OUTPUT DECODER FOR DECODING CONVOLUTIONALLY ENCODED CODEWORDS" filed November 6, 1996 on behalf of the Applicant. present invention.

Another significant difference between voice services and data services is that voice services require a fixed and common service level (GOS) for all users. Typically, for digital systems providing voice services, this translates into a fixed and equal transmission rate for all users and a tolerable maximum value for speech frame error rates. In contrast, for data services, GOS may differ from user to user and may be an optimized parameter to increase the overall efficiency of the data communication system. The GOS of a data communication system is typically defined as the total delay incurred in transferring a predetermined amount of data, hereinafter referred to as a data packet.

Yet another significant difference between voice and data services is that voice services require a reliable communication link, which in the exemplary CDMA communication system is provided by soft handoff. Soft handoff results in redundant transmissions from two or more base stations to improve reliability. However, such additional reliability is not required for data transmission as erroneously received data packets may be retransmitted. For data services, the transmit power used to support soft handoff can be used more efficiently for additional data transmission.

Parameters that measure the quality and effectiveness of a data communication system are the transmission delay required to transfer a data packet and the average system throughput. Transmission delay does not have the same impact on data communication as it does for voice communication, but is a relevant measure for measuring the quality of the data communication system. Average throughput is a measure of the efficiency of the communication system's data transmission capacity. It is well known that in cellular systems the signal / noise and interference ratio, C / I, for any user is a function of the user's location within the coverage area. To maintain a given level of service, the TDMA and FDMA systems use frequency reuse techniques, ie not all frequency channels and / or timeslots are used at each base station. In a CDMA system, the same frequency allocation is reused in all cells of the system, thereby improving overall efficiency. The C / I achieved by any user mobile station determines the rate of information that can be supported for such a particular link from the base station to the user's mobile station. Given the specific error modulation and correction method used for transmission, which the present invention seeks to optimize for data transmissions, a given level of performance is achieved at a corresponding C / I level. For an idealized cellular system with hexagonal cell layouts and using a common frequency across all cells, the C / I distribution achieved within the idealized cells can be calculated. The C / I achieved by any given user is a function of path loss, which for terrestrial cellular systems increases in proportion r3 to r5, where r is the distance to the irradiation source. In addition, path loss is subject to random variations due to natural or man-made obstructions within the radio wave path. Such random variations are typically modeled as a random log-normal shading process with a standard deviation of 8 dB. The resulting C / I distribution achieved for optimal hexagonal cellular layout with omnidirectional base station antennas, r4 propagation law and 8 dB standard deviation shading process is shown in Figure 10. The obtained C / I distribution can only be This is achieved if, at any time in time and in any location, the mobile station is served by the best base station, which is defined as the one that achieves the highest C / I value, regardless of the physical distance to each base station. Due to the random nature of the path loss as described above, the signal with the highest C / I value may be one that is at a different physical distance from the minimum than the mobile station. In contrast, if a mobile station is to communicate only through the short distance base station, C / I can be substantially degraded. It is therefore beneficial for mobile stations to communicate with and from the best service base station at all times, thereby achieving the optimal C / I value. It can also be observed that the range of C / I values achieved in the model idealized above, and as shown in Figure 10, is such that the difference between the highest and the lowest value can be up to 10,000. In a practical implementation, the range is typically limited to approximately 1: 100 or 20 dB. It is therefore possible for a CDMA base station to serve mobile stations with bit rates that can vary by a factor of up to 100, since the following ratio applies: (D where Rh represents the information rate for a specific mobile station W is the total bandwidth occupied by the spread spectrum signal and Eb / 10 is the energy per bit over the interference density required to achieve a given performance level. bandwidth, W, 1.2288 MHz and reliable communication requires an average Eb / I0 of 3 dB, so a mobile station that achieves a C / I value of 3 dB for the best base station can communicate at a rate On the other hand, if a mobile station is subjected to substantial interference from adjacent base stations and can only achieve -7 dB C / I, reliable communication cannot be supported. 122.88 kbps A communication system designed to optimize the average throughput will therefore attempt to serve each remote user from the best service base station and at the highest Rb data rate than the remote user. can withstand reliably. The data communication system of the present invention exploits the above characteristics and optimizes the data transfer rate from CDMA base stations to mobile stations.

Attention is directed to US-A 5,093,924 which describes a general designation method for use in mobile communication systems in which a base station selects in response to a communication connection request a radio communication channel having a level of interference wave reception that is obtained by a measurement unit and satisfies a quality condition of a communication channel from a plurality of radio communication channels, and transmits radio communication channel information to a mobile station as an object. of the communication connection request. The mobile station selects the radio communication channel transmitted by the base station, measures an interference wave reception level, and transmits the measurement result to the base station. The base station checks that the measurement results satisfy the quality conditions of a communication path, and assigns the requested communication radio channel when the measurement results satisfy the quality conditions of the communication path.

SUMMARY OF THE INVENTION The present invention is a new and improved method and apparatus for high rate packet data transmission in a CDMA system. The present invention improves the efficiency of a CDMA system by providing mechanisms for transmitting data via forward and reverse links. Each mobile station communicates with one or more base stations and monitors the control channels for the duration of communication with the base stations. Control channels can be used by base stations to transmit small amounts of data, paging messages addressed to a specific mobile station, and broadcast messages to all mobile stations. The alert message informs the mobile station that the base station has a large amount of data to transmit to the mobile station. It is an object of the present invention to improve the utilization of forward and reverse link capability in the data communication system. Upon receipt of alert messages from one or more base stations, the mobile station measures the signal-to-noise and interference (C / I) ratio of the direct link signals (for example the direct link pilot signals) in each partition. time and selects the best base station using a set of parameters that can comprise current and previous C / I measurements. In the exemplary embodiment, at each time partition, the mobile station transmits to the selected base station, via a dedicated data request channel (DRC), a request for transmission at the highest data rate that the measured C / I can support. reliably. The selected base station transmits data in data packets at a data rate that does not exceed the data rate received from the mobile station on the DRC channel. By transmitting from the best base station on all time partitions, an increase in throughput and transmission delay is achieved. It is another object of the present invention to improve performance by transmitting from the selected base station at maximum transmit power for the duration of one or more time partitions to a mobile station at the data rate requested by the mobile station. In the exemplary CDMA communication system, base stations operate at a predetermined back-off (e.g. 3 dB) from available transmit power to compensate for variations in usage. Thus, the average transmit power is half of the maximum (peak) power. However, in the present invention, since high speed data transmissions are programmed and power is typically not shared (for example, between transmissions), a retreat from the maximum available transmission power is not required. It is yet another object of the present invention to increase efficiency by allowing base stations to transmit data packets to each mobile station for a variable number of time partitions. The ability to transmit from different time partition base stations to time partition enables the data communication system of the present invention to adapt quickly to changes in the operating environment. In addition, the ability to transmit a data packet over noncontiguous time partitions is possible in the present invention due to the use of a sequence number to identify the data units within a data packet. It is yet another object of the present invention to increase the flexibility by issuing data packets addressed to a specific mobile station from a central controller to all base stations that are members of the active mobile station set. In the present invention, data transmission may occur from any base station in the active mobile station set in each time partition. Since each base station comprises a queue containing the data to be transmitted to the mobile station, efficient direct link transmission can occur with minimal processing delay. It is yet another object of the present invention to provide a relay mechanism for erroneously received data units. In the exemplary embodiment, each data packet comprises a predetermined number of data units, with each data unit being identified by a sequence number. Upon incorrect reception of one or more data units, the mobile station sends a negative acknowledgment (NACK) through the reverse link data channel indicating the sequence numbers of the missing data units for relay from the base station. The base station receives the message NACK and can relay the units of data received in error. It is yet another object of the present invention for the mobile station to select the best base station candidates for communication based on the procedure described in US Patent Application Serial No. 08 / 790,497 entitled "METHOD AND APPARATUS FOR PERFORMING SOFT HANDOFF IN A WIRELESS" COMMUNICATION SYSTEM ", filed January 29, 1997, on behalf of the Applicant of the present invention. In the exemplary embodiment, the base station may be added to the active set of the mobile station if the received pilot signal is above a predetermined plus limit and withdrawn from the active set if the received pilot signal is below a predetermined lower limit. In the alternative embodiment, the base station may be added to the active set if the additional energy of the base station (for example as measured by the pilot signal) and the energy of the base stations already in the active set exceeds a predetermined limit. Using this alternative embodiment, a base station whose transmitted energy comprises a non-substantial amount of the total energy received at the mobile station is not added to the active set. It is still another object of the present invention that mobile stations transmit data rate requests through the DRC channel so that only the base station selected from the base stations communicating with the mobile station is capable of distinguishing DRC messages, thus ensuring direct link transmission on any time partition is from the selected base station. In the exemplary embodiment, each base station communicating with the mobile station is assigned a unique Walsh code. The mobile station covers the DRC message with the Walsh code corresponding to the selected base station. Other codes may be used to cover DRC messages, although orthogonal codes are typically used and Walsh codes are preferred.

BRIEF DESCRIPTION OF THE FIGURES

The features, objects, and advantages of the present invention will become clearer from the following detailed description when read in conjunction with the drawings, in which the same numerical references identify corresponding items and in which: Figure 1 is a diagram of a system data communication device of the present invention, comprising a plurality of cells, a plurality of base stations and a plurality of mobile stations; Figure 2 is an example block diagram of the data communication system subsystems of the present invention;

Figures 3A and 3B are block diagrams of an example of the forward link architect of the present invention; Figure 4A is a diagram of an example of the forward link frame structure of the present invention;

Figures 4B and 4C are example diagrams of the direct traffic channel and the power control channel, respectively; Figure 4D is a punctured packet diagram of the present invention;

Figures 4E to 4G are diagrams of two examples of data packet and control channel capsule formats, respectively; Figure 5 is an example of a timing diagram showing high rate packet transmission over the forward link; Figure 6 is a block diagram of the example reverse link argumentar of the present invention; Figure 7A is a diagram of an example reverse link frame structure of the present invention; Figure 7B is a diagram of the example reverse link access channel; Figure 8 is an example of timing diagram showing high rate data transmission over reverse link; Figure 9 is an example state diagram showing the transitions between the various operating states of the mobile station; and Figure 10 is a diagram of the cumulative distribution function (CDF) of the C / I distribution in an ideal hexagonal cellular layout.

DETAILED DESCRIPTION OF THE INVENTION

According to an exemplary embodiment of the data communication system of the present invention, direct link data transmission takes place from a base station to a mobile station (see Figure 1) at or near the maximum data rate that can be supported by direct link and system. Reverse link data communication can occur from one mobile station to one or more base stations. The calculation of the maximum data rate for direct link transmission is described in detail below. Data is partitioned into data packets, with each data packet being transmitted across one or more time partitions (or partitions). At each time partition, the base station may direct data transmission to any mobile station communicating with the base station.

Initially, the mobile station establishes communication with a 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 is capable of transmitting data and control messages to the base station. The mobile station then monitors the direct link for transmissions from base stations in the active mobile station set. The active set contains a listing of base stations in communication with the mobile station. Specifically, the mobile station measures the signal-to-noise ratio and interference (C / I) of the direct link pilot coming from the base stations in the active set as received at the mobile station. If the received pilot signal is above a predetermined addition limit or below a predetermined withdrawal limit, the mobile station reports this to the base station. Subsequent messages from the base station direct the mobile station to add or remove the base station (s) to / from its active set, respectively. The various operating states of the mobile station are described below.

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

If data is to be transmitted to the mobile station, data is sent by a central controller to all base stations in the active set and stored in a queue at each base station. An alert message is then sent by one or more base stations to the mobile station in the respective control channels. The base station can transmit all of these alert messages at the same time through several base stations to ensure reception even when the mobile station is switching between base stations. The mobile station demodulates and decodes signals on one or more control channels to receive alert messages.

By decoding the alert messages, and for each time partition until data transmission is complete, the mobile station measures the C / I of direct link signals coming from the active set base stations as received at the mobile station. The C / I of the direct link signals can be obtained by measuring the respective pilot signals. The following mobile station selects the best base station based on a set of parameters. The parameter set may comprise current and previous C / I measurements and the bit error rate or packet error rate. As an example, the best base station may be selected based on the highest C / I measurement. The following mobile station identifies the best base station and transmits to the selected base station a data request message (hereinafter referred to as the DRC message) via the data request channel (hereinafter referred to as the DRC channel). The DRC message may contain the requested data rate or, alternatively, an indication of the quality of the direct link channel (for example, the C / I measurement itself, the bit error rate, or the packet error rate). In the exemplary embodiment, the mobile station may direct transmission of the DRC message to a specific base station using a Walsh code that uniquely identifies the base station. The DRC message symbols are OR-Exclusive (XOR) with unique Walsh code. Since each base station in the mobile station's active set is identified by a unique Walsh code, only the selected base station that performs the same OR-Exclusive operation as the mobile station with the correct Walsh code can correctly decode the message. DRC The base station uses rate control information from each mobile station to efficiently transmit deep link data at the highest possible rate.

In each time partition, the base station can select any of the mobile stations alerted for data transmission. The base station then determines the data rate at which to transmit data to the selected mobile station based on the most recent value of the DRC message received from the mobile station. Additionally, the base station uniquely identifies a transmission to a specific mobile station by the use of a spreading code that is unique to this mobile station. In the exemplary embodiment, such a spreading code is the long pseudo noise (PN) code which is defined by the IS-95 standard. The mobile station for which the data packet is intended receives the data transmission and decodes the data packet. Each data packet comprises a plurality of data units. In the exemplary embodiment, a data unit comprises eight bits of information, although different sizes of data units may be defined and are within the scope of the present invention. In the exemplary embodiment, each data unit is associated with a sequence number and mobile stations are capable of identifying missing or duplicate transmissions. In such cases, mobile stations communicate through the reverse link data channel the sequence numbers of the missing data units. The base station controllers, which receive data messages from mobile stations, then indicate to all base stations that communicate with such mobile station which specifies which data units were not received by the mobile station. The base stations then schedule a relay of such data units.

Each mobile station in the data communication system can communicate with multiple base stations on the reverse link. In the exemplary embodiment, the data communication system of the present invention supports soft handoff and reverse reverse handoff for various reasons. Firstly, soft handoff does not consume additional reverse link capacity, but rather allows mobile stations to transmit data at the minimum power level so that at least one of the base stations can decode the data reliably. Second, receiving reverse link signals from more base stations increases transmission reliability and requires only additional hardware at base stations.

In the exemplary embodiment, the direct link capability of the data transmission system of the present invention is determined by rate requests from mobile stations. Additional gains in direct link capacity can be achieved by using directional antennas and / or adaptive space filters. An example of a method and equipment for providing directional transmissions is described in US Patent Application Serial No. 08 / 575,049 entitled "METHOD AND APPARATUS FOR DETERMINING THE TRANSMISSION DATA RATE IN A MULTI-USER COMMUNICATION SYSTEM" filed 20 December 1995 and in US Patent Application Serial No. 08 / 925,521 entitled "METHOD AND APPARATUS FOR PROVIDING ORTHOGONAL SPOT BEAMS, SECTORS AND PICOCELLS", filed September 8, 1997, both on behalf of the Applicant of the present invention.

! SYSTEM DESCRIPTION

Referring to the Figures, Figure 1 represents the exemplary data communication system of the present invention comprising multiple cells 2a-2g. Each cell 2 is served by a corresponding base station 4. Several mobile stations 6 are dispersed throughout the data communication system. In the exemplary embodiment, each mobile station 6 communicates with at most one base station 4 via the direct link on each time partition, but may be in communication with one or more base stations 4 via the reverse link, depending on whether the station Mobile 6 is in soft handoff. As an example, base station 4a transmits data exclusively to mobile station 6a, base station 4b transmits data exclusively to mobile station 6b and base station 4c transmits data exclusively to mobile station 6c via the direct link in time partition n. In Figure 1, the solid line with the arrow indicates a data transmission from base station 4 to mobile station 6. A dashed line with the arrow indicates that mobile station 6 is receiving the pilot signal, but no data transmission, from base station 4. Reverse link communication is not shown in Figure 1 for simplicity.

As shown in Figure 1, each base station 4 preferably transmits data to a mobile station 6 at a given time. Mobile stations 6, especially those located near a cell boundary, may receive pilot signals from multiple base stations 4. If the pilot signal is above a predetermined limit, mobile station 6 may request that base station 4 be added to the active set of mobile station 6. In the exemplary embodiment, mobile station 6 can receive data transmissions from none or one member of the active set.

A block diagram illustrating the basic subsystems of the data communication system of the present invention is shown in Figure 2. Base station controller 10 interfaces with packet network interface 24, PSTN 30 and all base stations 4 in the system. data communication (only one base station 4 is shown in Figure 2 for simplicity). Base station controller 10 coordinates communication between mobile stations 6 in the data communication system and other users connected to packet network interface 24 and PSTN 30. PSTN 30 interfaces with users via the standard telephone network ( not shown in Figure 2). Base station controller 10 contains several selector elements 14, although only one is shown in Figure 2 for simplicity. A selector element 14 is designed to control communication between one or more base stations 4 and a mobile station 6. If the selector element 14 has not been assigned to mobile station 6, call control processor 16 is informed of the need to alert mobile station 6. Call control processor 16 then directs base station 4 to alert mobile station 6. Data source 20 contains the data to be transmitted to mobile station 6. Data source 20 provides data for packet network interface 24. Packet network interface 24 receives data and directs data to selector element 14. 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 the data to be transmitted to mobile station 6.

In the exemplary embodiment, in direct link, a data packet refers to a predetermined amount of data that is independent of the data rate. The data packet is formatted with other control and encoding bits and encoded. If data transmission occurs over multiple Walsh channels, the encoded packet is demultiplexed in parallel streams, with each stream being transmitted over one Walsh channel.

Data is sent in data packets from data queue 40 to channel element 42. For each data packet, channel element 42 inserts the required control fields. The data packet, control fields, frame check sequence bits, and code tail bits constitute a formatted packet. The channel element 42 then encodes one or more formatted packets and interleaves (or reorders) the symbols within the encoded packets. Next, the interleaved packet is shuffled with a scramble sequence, covered with Walsh covers and spread with long PN code and short PNi and PNQ codes. The scattered data is quadrature modulated, filtered and amplified by a transmitter within the RF unit 44. The forward link signal is transmitted over the air through antenna 46 on forward link 50.

At mobile station 6, the forward link signal is received by antenna 60 and directed to a receiver within a front end 62. The receiver filters, amplifies, quadrature demodulates and quantizes the signal. The digitized signal is provided to demodulator 64 where it is spread out with the long PN code and the short PNn codes; and PNQ, uncovered with the Walsh covers and scrambled with an identical scramble sequence. The demodulated data is provided to the decoder 66 which performs the inverse of the signal processing functions performed at base station 4, specifically the deinterleaving, decoding and frame checking functions. The decoded data is provided to the data store 68. The hardware, as described above, supports data transmission, message exchange, voice, video and other communications over the direct link.

System control and programming functions can be performed by various implementations. The location of channel programmer 48 depends on whether centralized or distributed control / programming processing is desired. As an example, for distributed processing, channel scheduler 48 may be located within base station 4. In contrast, for centralized processing, channel scheduler 48 may be located within base station controller 10 and may be designed to coordinate data transmissions from multiple base stations 4. Other implementations of the functions described above may be contemplated and are within the scope of the present invention.

As shown in Figure 1, mobile stations 6 are dispersed throughout the data communication system and may be in communication with none or a base station 4 via the direct link. In the exemplary embodiment, the channel scheduler 48 coordinates the direct link data transmissions of a base station 4. In the exemplary embodiment, the channel scheduler 48 connects to a data queue 40 and channel element 42 within the base station. 4 and receive the queue size, which is indicative of the amount of data to be transmitted to mobile station 6, and DRC messages from mobile stations 6. Channel programmer 48 schedules high rate data transmission such that system goals for maximum data throughput and minimum transmission delay are optimized.

In the exemplary embodiment, data transmission is programmed in part based on the quality of the communication link. An example of a communication system that selects the baud rate based on link quality is described in US Patent Application Serial No. 08 / 741,320 entitled "METHOD AND APPARATUS FOR PROVIDING HIGH SPEED DATA COMMUNICATIONS IN A CELLULAR ENVIRONMENT" filed on September 11, 1996, on behalf of the Applicant of the present invention. In the present invention, data communication programming may be based on additional considerations such as user GOS, queue size, data type, amount of delay already experienced, and error rate of data transmission. Such considerations are described in detail in US Patent Application Serial No. 08 / 798,951, entitled "METHOD AND APPARATUS FOR FORWARD LINK RATE SCHEDULING", filed February 11, 1997, and US Patent Application Serial No. 08 / 914,928, entitled "METHOD AND APPARATUS FOR REVERSE LINK RATE SCHEDULING", filed August 20, 1997, both on behalf of the Applicant of the present invention. Other factors may be considered in the programming of data transmissions and are within the scope of the present invention. The data communication system of the present invention supports reverse link data and message transmissions. Within mobile station 6, controller 76 processes the transmission of data or messages by directing the data or messages to encoder 72. Controller 76 may be implemented in a microcontroller, a microprocessor, a digital signal processing chip (DSP), or an ASIC programmed to perform the function as described herein.

In the exemplary embodiment, encoder 72 encodes the message consistent with the Blank & Burst signaling data format described in U.S. Patent No. 5,504,773 mentioned above. Encoder 72 then generates and appends a CRC bit set, appends a code termination bit set, encodes the attached data and bits, and reorders the symbols within the encoded data. Interleaved data is provided to modulator (MOD) 74. Modulator 74 can be implemented in various embodiments. In the exemplary embodiment (see Figure 6), the interleaved data is covered with Walsh codes, spread with a long PN code and further spread with short PN codes. The spread data is provided to a transmitter within front end 62. The transmitter modulates, filters, amplifies and transmits the reverse link signal through the air via antenna 46 on reverse link 52.

In the exemplary embodiment, mobile station 6 spreads the reverse link data according to a long PN code. Each reverse link channel is defined according to the temporal offset of a common long PN sequence. With two different offsets, the resulting modulation sequences are uncorrelated. The displacement of a mobile station 6 is determined according to a unique numerical identification of mobile station 6 which, in the exemplary embodiment of mobile stations 6 IS-95 is the mobile station specific identification number. Thus, each mobile station 6 broadcasts 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 to RF unit 44. RF unit 44 filters, amplifies, demodulates and quantizes the signal and provides the digitized signal to channel element 42. The element channel 42 splits the digitized signal with short PN codes and long PN code. Channel element 42 also performs Walsh code discovery and pilot and DRC extraction. Channel element 42 then reorders the demodulated data, decodes the deinterleaved data, and performs the CRC check function. The decoded data, for example the data or message, is provided to selector element 14. Selector element 14 directs the data and message to the appropriate destination. Channel element 42 may also output a quality indicator to selector element 14 indicative of the condition of the received data packet.

In the exemplary embodiment, mobile station 6 may be in one of three operating states. An example state diagram showing the transitions between the various operating states of mobile station 6 is shown in Figure 9. In access state 902, mobile station 6 sends access probes and waits for channel assignment by base station 4. Channel assignment comprises resource allocation, such as a power control channel and frequency allocation. Mobile station 6 may transition from access state 902 to connected state 904 if mobile station 6 is alerted and warned of the arrival of a data transmission, or if mobile station 6 transmits data via reverse link. In connected state 904, mobile station 6 exchanges (for example transmits or receives) data and performs handoff operations. Upon completion of the release procedure, mobile station 6 transitions from connected state 904 to idle state 906. Mobile station 6 can also transition from access state 902 to idle state 906 when a connection to base station 4 is rejected. In idle state 906, mobile station 6 listens for overhead and paging messages for receiving and decoding messages on the direct control channel and performs the idle handoff procedure. Mobile station 6 may transition to access state 902 by initializing the procedure. The state diagram shown in Figure 9 is only an exemplary state definition, which is shown for illustration. Other state diagrams may also be used and are within the scope of the present invention.

II. DIRECT LINK DATA TRANSMISSION

In the exemplary embodiment, the initiation of communication between mobile station 6 and base station 4 occurs similarly to the CDMA system. Upon completion of call establishment, mobile station 6 monitors the control channel for alert messages. When in the connected state, mobile station 6 begins transmission of the pilot signal through the reverse link.

An example of the direct link high rate data transmission flowchart of the present invention is shown in Figure 5. If base station 4 has data for transmission to mobile station 6, base station 4 sends an alert message addressed to the mobile station 6 on the control channel in block 502. The alert message may be sent from one or multiple base stations 4, depending on the handoff state of mobile station 6. Upon receipt of the alert message, mobile station 6 initiates the C / I measurement process in block 504. AC / I of the forward link signal is calculated from one or a combination of methods described below. Mobile station 6 then selects a requested data rate based on the best C / I measurement and transmits a DRC message through the DRC channel in block 506.

Within the same time partition, base station 4 receives the DRC message in block 508. If the next time partition is available for data transmission, base station 4 transmits data to mobile station 6 at the requested data rate. at block 510. Mobile station 6 receives data transmission at block 512. If the next time partition is available, base station 4 transmits the remainder of the packet at block 514 and mobile station 6 receives data transmission at block 512. 516.

In the present invention, mobile station 6 may be in communication with one or more base stations 4 simultaneously. The actions taken by mobile station 6 depend on whether or not mobile station 6 is in soft handoff. These two cases are described separately below.

III. NON-HANDOFF CASE

In the case of non-handoff, mobile station 6 communicates with a base station 4. Referring to Figure 2, data destined for a specific mobile station 6 is provided to the selector element 14 which has been designated to control communication with such a station. The selector element 14 outputs data to data queue 40 within base station 4. Base station 4 queues the data and transmits an alert message through the control channel. Base station 4 then monitors the reverse link DRC channel for DRC messages from mobile station 6. If no signal is detected on the DRC channel, base station 4 can relay the alert message until the DRC message is detected. After a predetermined number of retransmission attempts, base station 4 may terminate the process or restart a call with mobile station 6.

In the exemplary embodiment, mobile station 6 transmits the requested data rate, in the form of a DRC message, to base station 4 via the DRC channel. In the alternative embodiment, mobile station 6 transmits an indication of the quality of the forward link channel (e.g., C / I measurement) to base station 4. In the exemplary embodiment, the 3-bit DRC message is decoded with smooth decisions by base station 4. In the exemplary embodiment, the message is transmitted within the first half of each time partition. Base station 4 then has the remaining half of the time partition to decode the DRC message and configure hardware for data transmission on the next successive time partition, if such a time partition is available for data transmission to the mobile station. 6. If the next successive time partition is not available, base station 4 waits for the next available time partition and continues to monitor the DRC channel for new DRC messages.

In the first embodiment, base station 4 transmits at the requested data rate. This mode gives mobile station 6 the important decision to select the data rate. Always transmitting at the requested data rate has the advantage that mobile station 6 knows which data rate to expect. Thus, mobile station 6 only demodulates and decodes the traffic channel according to the requested data rate. Base station 4 does not have to transmit a message to mobile station 6 indicating which data rate is being used by base station 4.

In the first embodiment, upon receipt of the alert message, mobile station 6 continuously attempts to demodulate the data at the requested data rate. Mobile station 6 demodulates the direct traffic channel and provides the soft decision symbols to the decoder. The decoder decodes the symbols and checks frames on the decoded packet to determine if the packet was received correctly. If the packet was received in error, or if the packet was directed to another mobile station 6, frame checking would indicate a packet error. Alternatively in the first embodiment, mobile station 6 demodulates the data on a partition by partition basis. In the exemplary embodiment, mobile station 6 is able to determine if a data transmission is directed to it based on the preamble that is incorporated into each transmitted data packet as described below. Thus, mobile station 6 can terminate the decoding process if it is determined that transmission is directed to another mobile station 6. In either case, mobile station 6 transmits a negative acknowledgment message (NACK) to base station 4 to confirm incorrect reception of data units. Upon receipt of the NACK message, data units received in error are retransmitted. NACK message transmission can be implemented similarly to error indicator bit (EIB) transmission in the CDMA system. The implementation and use of EIB transmission are described in U.S. Patent No. 5,568,483 entitled "METHOD AND APPARATUS FOR DATA FOR TRANSMISSION" on behalf of the Applicant of the present invention. Alternatively, NACK may be transmitted with the messages.

In the second embodiment, the data rate is determined by base station 4 input from mobile station 6. Mobile station 6 performs C / I measurement and transmits a link quality indication (for example, C / I measurement) for base station 4. Base station 4 can adjust the requested data rate based on the resources available for base station 4, such as queue size and available transmit power. The set data rate may be transmitted to the mobile station 6 before or concurrently with the data transmission at the set data rate, or may be implicit in the encoding of the data packets. In the first case, wherein mobile station 6 receives the set data rate prior to data transmission, mobile station 6 demodulates and decodes the received packet as described in the first embodiment. In the second case, where the adjusted data rate is transmitted to the mobile station 6 concurrently with the data transmission, the mobile station 6 may demodulate the direct traffic channel and store the demodulated data. Upon receipt of the set data rate, mobile station 6 decodes the data according to the set data rate. And in the third case, where the adjusted data rate is implicit in the encoded data packets, the mobile station 6 demodulates and decodes all candidate rates and determines a posteriorly the baud rate for selection of the decoded data. The method and equipment for determining the rate is described in detail in US Patent Application Serial No. 08 / 730,863 entitled "METHOD AND APPARATUS FOR DETERMINING THE RATE OF RECEIVED DATE IN A VARIABLE RATE COMMUNICATION SYSTEM" filed 18 October 1996, and in US Patent Application Serial No. 08 / 908,866, also entitled "METHOD AND APPARATUS FOR DETERMINING THE RATE OF RECEIVED DATE IN A VARIABLE RATE COMMUNICATION SYSTEM", filed August 8, 1997, both in name of the Applicant of the present invention. For all of the above cases, mobile station 6 transmits a NACK message as described above if the frame check result is negative. The following description is based on the first embodiment, wherein mobile station 6 transmits to base station 4 the DRC message indicative of the requested data rate, unless otherwise indicated. However, the inventive concept described herein may also apply to the second embodiment wherein mobile station 6 transmits an indication of link quality to base station 4.

IV. HANDOFF CASE

In the case of handoff, mobile station 6 communicates with multiple base stations 4 via reverse link. In the exemplary embodiment, direct link data transmission to a specific mobile station 6 takes place from a base station 4. However, mobile station 6 can simultaneously receive pilot signals from multiple base stations 4. If measurement C / I of a base station 4 is above a predetermined limit, base station 4 is added to the active set of mobile station 6. During the soft handoff routing message, the new base station 4 assigns mobile station 6 to a channel Reverse power control (RPC) walsh which is described below. Each soft handoff base station 4 with mobile station 6 monitors reverse link transmission and sends an RPC bit on its respective Walsh RPC channels.

Referring to Figure 2, selector element 14 designed to control communication with mobile station 6 outputs data to all base stations 4 in the active set of mobile station 6. All base stations 4 receiving data from selector element 14 transmit an alert message to mobile station 6 on their respective control channels. When mobile station 6 is in the connected state, mobile station 6 performs two functions. In the first, mobile station 6 selects the best base station 4 based on a set of parameters that may be the best C / I measurement. The following mobile station 6 selects a data rate corresponding to the C / I measurement and transmits a DRC message to the selected base station 4. Mobile station 6 may direct DRC message transmission to a specific base station 4 by covering the DRC message with Walsh coverage assigned to the specific base station 4. In the second, mobile station 6 attempts to demodulate the forward link signal according to the requested data rate in each subsequent time partition.

After the alert messages are transmitted, all base stations 4 in the active set monitor the DRC channel for a DRC message from mobile station 6. Again, because the DRC message is covered with a Walsh code, base station 4 selected designation with identical Walsh coverage is capable of DRC message discovery. Upon receiving the DRC message, the selected base station 4 transmits data to mobile station 6 in the next available time partitions.

In the exemplary embodiment, base station 4 transmits packet data comprising a plurality of data units at the requested data rate to mobile station 6. If data units are incorrectly received by mobile station 6, a NACK message is transmitted on the links. reverse for all base stations 4 in the active set. In the exemplary embodiment, the NACK message is demodulated and decoded by the base stations 4 and sent to the selector element 14 for processing. When processing the NACK message, data units are relayed using the procedure as described above. In the exemplary embodiment, selector element 14 combines received NACK signals from all base stations 4 into one NACK message and sends the NACK message to all base stations 4 in the active set.

In the exemplary embodiment, mobile station 6 can detect changes in the best C / I measurement and dynamically request data transmissions from different base stations 4 at each time partition to improve efficiency. In the exemplary embodiment, since data transmission takes place from only one base station 4 in any time partition, other base stations 4 in the active set may not be told which data units, if any, have been transmitted to the base station. mobile station 6. In the exemplary embodiment, the transmitting base station 4 informs the selector element 14 about the data transmission. The selector element 14 below sends a message to all base stations in the active set. In the exemplary embodiment, the transmitted data is assumed to have been correctly received by mobile station 6. Therefore, if mobile station 6 requests data transmission from a different base station 4 in the active set, the new base station 4 transmits the data. data units left. In the exemplary embodiment, the new base station 4 transmits according to the last transmission update from selector element 14. Alternatively, the new base station 4 selects the next data units to transmit using metric-based predictive schemes such as rate. average transmission and prior updates from selector element 14. Such mechanisms minimize duplicate retransmissions of the same data units by multiple base stations 4 over different time partitions, resulting in a loss of efficiency. If a previous transmission was received in error, base stations 4 may retransmit those data units out of sequence as each data unit is identified by a unique sequence number as described below. In the exemplary embodiment, if a "hole" (or non-transmitted data units) is created (for example, as a result of the handoff between a base station 4 to another base station 4), the missing data units are considered to have been received. with error. Mobile station 6 transmits NACK messages corresponding to the missing data units and these data units are relayed.

In the exemplary embodiment, each base station 4 in the active set maintains an independent data queue 40, which contains the data to be transmitted to mobile station 6. The selected base station 4 transmits the data in its data queue 40 in an order. sequential, except for retransmissions of data units received in signaling and error messages. In the exemplary embodiment, the transmitted data units are deleted from queue 40 after transmission.

V. OTHER CONSIDERATIONS ON DIRECT LINK DATA TRANSMISSIONS

An important consideration in the data communication system of the present invention is the accuracy of C / I estimates for the purpose of selecting the data rate for future transmissions. In the exemplary embodiment, C / I measurements are performed on the pilot signals during the time interval at which base stations 4 transmit the pilot signals. In the exemplary embodiment, since only pilot signals are transmitted during such a pilot time interval, multipath and interference effects are minimal.

In other embodiments of the present invention where pilot signals are continuously transmitted through an orthogonal code channel, similar to that of IS-95 systems, the multipath and interference effect may distort C / I measurements. Similarly, performing C / I measurement on data transmissions in place of pilot signals, multipath and interference can also degrade C / I measurements. In either case, when a base station 4 is transmitting to a mobile station 6, mobile station 6 is able to accurately measure C / I of the forward link signal as no other interference signal is present. However, when mobile station 6 is in soft handoff and receives pilot signals from multiple base stations 4, mobile station 6 is not able to discern whether or not base stations 4 were transmitting data. At worst, mobile station 6 can measure high C / I in a first time partition, when no base station 4 was transmitting data to any mobile station 6, and receive data transmission in a second time partition, when all 4 base stations were transmitting data on the same time partition. C / I measurement in the first time partition, when all base stations 4 are idle, gives a false indication of the direct link signal quality in the second time partition, as the status of the data communication system has changed. . In fact, the actual C / I in the second time partition may be degraded to the point where reliable decoding at the requested data rate is not possible. The opposite extreme scenario occurs when an estimate of C / I by mobile station 6 is based on maximum interference. However, actual transmission occurs when only the selected base station is transmitting. In this case, the C / I estimate and the selected data rate are conservative and transmission occurs at a lower rate than could be reliably decoded, thereby reducing transmission efficiency.

In the implementation where C / I measurement is performed on a continuous pilot signal or traffic signal, C / I prediction in the second time partition based on C / I measurement in the first time partition can be made more accurate. by the three modalities. In the first embodiment, data transmissions from base stations 4 are controlled such that base stations 4 are not constantly toggle between transmission and idle states in successive time partitions. This can be achieved by queuing sufficient data (e.g., a predetermined number of information bits) prior to actual data transmission to mobile stations 6.

In the second embodiment, each base station 4 transmits a direct activity bit (hereinafter referred to as the FAC bit) indicating whether a transmission will occur in the next half frame. The use of the FAC bit will be described in detail below. Mobile station 6 performs C / I measurement taking into account the received FAC bit from each base station 4.

In the third embodiment, which corresponds to the scheme in which an indication of link quality is transmitted to base station 4 and which uses a centralized scheduling scheme, programming information indicating which of the base stations 4 transmitted data in each time partition, are made available to channel programmer 48. channel programmer 48 receives C / I measurements from mobile stations 6 and can adjust C / I measurements based on their knowledge of the presence or absence of data transmission from each base station 4 in the data communications system. As an example, mobile station 6 may measure C / I in the first time partition when no adjacent base station 4 is transmitting. Measured AC / I is provided to channel programmer 48. Channel programmer 48 knows that none of the adjacent base stations 4 transmitted data in the first time partition, since none was programmed by channel programmer 48. In the second time partition, the channel scheduler 48 knows if one or more adjacent base stations 4 will transmit data. Channel scheduler 48 may adjust the measured C / I in the first time partition taking into account the additional interference that mobile station 6 will receive in the second time partition due to data transmissions by adjacent base stations 4. Alternatively, if C / I is measured in the first time partition when adjacent base stations 4 are transmitting and such adjacent base stations 4 are not transmitting in the second time partition, channel programmer 48 may adjust C / I measurement by taking additional information into account.

Another important consideration is to minimize redundant retransmissions. Redundant retransmissions may result from allowing mobile station 6 to select data transmissions from different base stations 4 in successive time partitions. The best C / I measurement may alternate between two or more base stations 4 during successive time partitions if mobile station 6 measures approximately equal C / I for such base stations 4. The alternation may be due to deviations in C / I measurements and / or changes in channel condition. Data transmission by different base stations 4 in successive time partitions may result in a loss of efficiency. The problem of alternation can be addressed by the use of hysteresis. Hysteresis can be implemented with a signal level scheme, a timing scheme, or a combination of the signal level and timing schemes. In the exemplary signal level scheme, the best C / I measurement of a different base station 4 in the active set is not selected unless it exceeds the C / I measurement of the base station 4 currently transmitting by at least one. hysteresis amount. As an example, the hysteresis is assumed to be 1.0 dB and the C / I measurement of the first base station 4 to 3.5 dB and the C / I measurement of the second base station 4 to 3.0 dB in the first time partition. In the next time partition, the second base station 4 is not selected unless its C / I measurement is at least 1.0 dB higher than that of the first base station 4. Thus, if the C / I measurement of the first base station If base station 4 is still 3.5 dB at the next time partition, second base station 4 is not selected unless its C / I measurement is at least 4.5 dB.

In the exemplary timing scheme, base station 4 transmits data packets to mobile station 6 for a predetermined number of time partitions. Mobile station 6 is not allowed to select a different transmitting base station 4 within the predetermined number of time partitions. Mobile station 6 continues to measure the base station 4 C / I currently transmitting on each time partition and selects the data rate in response to the C / I measurement.

Yet another important consideration is the efficiency of data transmission. Referring to Figures 4E and 4F, each data packet format 410 and 430 contains data and overhead bits. In the exemplary embodiment, the number of overhead bits is fixed for all data rates. At the highest data rate, the percentage of overhead is small relative to packet size and efficiency is high. At lower data rates, overhead bits may comprise a larger percentage of the packet. Inefficiency at lower data rates can be improved by transmitting variable length data packets to mobile station 6. Variable length data packets can be partitioned and transmitted to mobile station 6 across multiple time partitions. Preferably, variable length data packets are transmitted to mobile station 6 for successive time partitions to simplify processing. The present invention is directed to the use of various packet sizes for the various data rates supported to improve overall transmission efficiency. SAW. DIRECT LINK ARCHITECTURE

In the exemplary embodiment, base station 4 transmits at the maximum available power for base station 4 and at the maximum data rate supported by the data communication system for a single mobile station 6 in any given partition. The maximum data rate that can be supported is dynamic and depends on the C / I of the forward link signal as measured by mobile station 6. Preferably, base station 4 transmits to only one mobile station 6 at any given time partition.

To facilitate data transmission, the direct link comprises four time-multiplexed channels: the pilot channel, the power control channel, the control channel and the traffic channel. The function and implementation of each of these channels will be described below. In the exemplary embodiment, the traffic and power control channels each comprise a number of orthogonally spread out Walsh channels. In the present invention, the traffic channel is used for the transmission of traffic data and alert messages to mobile stations 6. When used for the transmission of alert messages, the traffic channel is also referred to as the control channel in present descriptive report.

In the exemplary embodiment, the direct link bandwidth is selected to be 1.2288 MHz. Such bandwidth selection allows the use of existing hardware components designed for an IS-95 compliant CDMA system. However, the data communication system of the present invention may be adopted for use with different bandwidths to improve capacity and / or conform to system requirements. As an example, a 5 MHz bandwidth can be used to increase capacity. In addition, the forward link and reverse link bandwidths may differ (for example, 5 MHz bandwidth on the forward link and 1.2288 MHz on the reverse link) to better match link capacity to demand.

In the exemplary embodiment, short PNi and PNQ codes are the same length as PN 215 codes that are specified by IS-95. At the 1.2288 MHz chip rate, short PN sequences are repeated every 26.67 ms {26.67 ms = 215 / 1.2288x106}. In the exemplary embodiment, the same short PN codes are used by all base stations 4 within the data communication system. However, each base station 4 is identified by a single offset of the basic short PN sequences. In the exemplary embodiment, the offset is incremented by 64 chips. Other bandwidths and PN codes may be used and are within the scope of the present invention. VII. DIRECT LINK TRAFFIC CHANNEL

Figure 3A shows a block diagram of the exemplary forward link architecture of the present invention. Data is partitioned into data packets and provided to the CRC encoder 112. For each data packet, the CRC encoder 112 generates the frame check bits (for example, the CRC parity bits) and inserts the code terminating bits. (code tail bits). The formatted packet of the CRC encoder 112 comprises the data, the frame check and code termination bits, and other overhead bits that will be described later. The formatted packet is provided to encoder 114 which, in exemplary embodiment, encodes the packet according to the encoding format described in U.S. Patent Application. Serial No. 08 / 743,688 mentioned above. Other encoding formats may also be used and are within the scope of the present invention. The encoded packet from encoder 114 is provided to interleaver 116, which reorders the code symbols in the packet. The interleaved pack is provided to the frame punching element 118 which removes a fraction of the pack as described below. The punctured packet is provided to the multiplier 120, which scrambles the data with the scrambler scrambling sequence 122. The punching element 118 and scrambler 122 will be described in detail below. The output of multiplier 120 comprises the scrambled packet. The scrambled packet is provided to the variable rate controller 130 which demultiplexes the packet into K phase and quadrature parallel channels, where K depends on the data rate. In the exemplary embodiment, the scrambled packet is first demultiplexed in phase (I) and quadrature (Q) flows. In the exemplary embodiment, flow I comprises even indexed symbols and flow Q comprises odd indexed symbols. Each stream is further demultiplexed into K parallel channels such that the symbol rate of each channel is set for all data rates. The K channels of each stream are provided with the Walsh cover element 132, which covers each channel with a Walsh function to provide the orthogonal channels. Orthogonal channel data is provided to gain element 134 which scales the data to maintain a constant total chip power (and thus a constant output power) for all data rates. The staggered data from the gain element 134 is provided to multiplexer (MUX) 160 which multiplexes the data with the preamble. The preamble is commented in detail below. The output of the MUX 160 is provided to multiplexer (MUX) 162 which multiplexes traffic data, power control bits and pilot data. The MUX 162 output comprises Walsh I channels and Walsh Q channels.

A block diagram of the exemplary modulator used to modulate the data is illustrated in Figure 3B. Walsh I channels and Walsh Q channels are provided to adder 212a and 212b, respectively, which add the Walsh K channels to provide the Isoma and Q signals, respectively. Signals Isoma and Qs0ma are provided to complex multiplier 214. Complex multiplier 214 also receives signals PN_I and PN_Q from multipliers 236a and 236b, respectively, and multiplies the two complex inputs according to the following equation: where Imult and Qmutl are the outputs of the complex multiplier 214 and j is the complex representation. Imult and Qmult signals are provided to filters 216a and 216b, respectively, which filter the signals. The filtered signals from filters 216a and 216b are provided to multipliers 218a and 218b, respectively, which multiply the signals by the C0S phase sine (wct) and the quadrature sinusoid SEN (wct), respectively. Modulated I and modulated Q signals are provided to adder 220 which sum the signals to provide the direct modulated waveform S (t).

In the exemplary embodiment, the data packet is spread with long PN code and short PN codes. The long PN code scrambles the packet such that only the mobile station 6 for which the packet is intended is capable of unscrambling the packet. In the exemplary embodiment, the pilot and power control bits and the control channel packet are spread with short PN codes but not long PN codes to allow all mobile stations 6 to receive such bits. The long PN sequence is generated by the long code generator 232 and provided to the multiplexer (MUX) 234. The long PN mask determines the displacement of the long PN sequence and is assigned exclusively to the destination mobile station 6. The output of the MUX 234 is the long PN sequence during the transmission data portion and zero otherwise (for example, during pilot and power control portion). The long gated PN sequence from MUX 234 and the short sequences PNi and PNq from short code generator 238 are provided to multipliers 236a and 236b respectively, which multiply the two sequence sets to form signals PN_I and PN_Q respectively. The signals PN_I and PN_Q are provided to the complex multiplier 214. The exemplary traffic channel block diagram shown in Figures 3A and 3B is one of numerous architectures that support direct link data coding and modulation. Other architectures, such as the architecture for the direct link traffic channel in the CDMA system according to IS-95, may also be used and are within the scope of the present invention.

In the exemplary embodiment, the data rates supported by base stations 4 are predetermined and each supported data rate is assigned a unique rate index. Mobile station 6 selects one of the supported data rates based on C / I measurement. Since the requested data rate must be sent to a base station 4 to direct such base station 4 to transmit data at the requested data rate, a trade-off is made between the number of supported data rates and the number of bits required to transmit. identify the requested data rate. In the exemplary embodiment, the number of supported data rates is seven and a 3-bit rate index is used to identify the requested data rate. An exemplary definition of supported data rates is illustrated in Table 1. Different definitions of supported data rates may be contemplated and are within the scope of the present invention.

In the exemplary embodiment, the minimum data rate is 38.4 kbps and the maximum data rate is 2.457 6 Mbps. The minimum data rate is selected based on the worst case C / I measurement in the system, system processing gain, design of error correction codes and desired level of performance. In the exemplary embodiment, the supported data rates are chosen such that the difference between successive supported data rates is 3 dB. The 3 dB increment is a balance between several factors, including the C / I measurement accuracy that can be achieved by mobile station 6, the losses (or inefficiencies) that result from quantizing data rates based on the C / I measurement. and the number of bits (or bitrate) required to transmit the requested data rate from mobile station 6 to base station 4. More supported data rates require more bits to identify the requested data rate but allow more efficient use of the direct link due to a smaller quantization error between the calculated maximum data rate and the supported data rate. The present invention is directed to the use of any number of supported data rates and other data rates other than those listed in Table 1.

Table 1 - Traffic Channel Parameters Note: (1) 16-QAM modulation.

A diagram of the exemplary forward link frame structure of the present invention is illustrated in Figure 4A. The traffic channel transmission is partitioned into frames which, in the exemplary embodiment, are defined as the length of the short PN sequences, or 26.67 ms. Each frame may carry control channel information addressed to all mobile stations 6 (control channel frame), traffic data addressed to a specific mobile station 6 (traffic frame), or may be empty (idle frame). The content of each frame is determined by the programming performed by the transmitting base station 4. In the exemplary embodiment, each frame comprises 16 time partitions, with each time partition having a duration of 1.667 ms. A time partition of 1.667 ms is suitable to allow mobile station 6 to perform C / I measurement of the forward link signal. A time partition of 1.667 ms also represents a sufficient amount of time for efficient packet data transmission. In the exemplary embodiment, each time partition is further partitioned into four quarters of partition.

In the present invention, each data packet is transmitted over one or more time partitions, as shown in Table 1. In the exemplary embodiment, each forward link data packet comprises 1024 or 2048 bits. Thus, the number of time partitions required to transmit each data packet depends on the data rate and ranges from 16 time partitions for the 38.4 kbps rate to 1 time partition for the 1.2288 Mbps rate and higher.

An exemplary diagram of the forward link partition structure of the present invention is shown in Figure 4B. In the exemplary embodiment, each partition comprises three or four time multiplexed channels, the traffic channel, the control channel, the pilot channel and the power control channel. In the exemplary embodiment, the pilot and power control channels are transmitted in two pilot and power control bursts which are located at the same positions in each time partition. Pilot and power control bursts are described in more detail below.

In the exemplary embodiment, the interleaved package from interleaver 116 is punctured to accommodate pilot and power control bursts. In the exemplary embodiment, each interleaved packet comprises 4096 code symbols and the first 512 code symbols are punctured as shown in Figure 4D. The remaining code symbols are shifted in time to align with the transmission intervals of the traffic channel.

Punctured code symbols are scrambled to randomize data prior to applying orthogonal Walsh coverage. Randomization limits the peak / mean envelope in the modulated waveform S (t). The scramble sequence can be generated with a linear feedback deviation register, known to those skilled in the art. In the exemplary embodiment, scrambler 122 is loaded with the LC state at the beginning of each partition. In the exemplary embodiment, scrambler clock 122 is synchronous with interleaver clock 116 but is stopped during pilot and power control bursts.

In the exemplary embodiment, direct Walsh channels (for the traffic channel and power control channel) are orthogonally spread with 16-bit Walsh overlays at the fixed 1.2288 Mcps chip rate. The number of K orthogonal parallel channels per phase and quadrature signal is a function of the data rate, as shown in Table 1. In the exemplary embodiment, for lower data rates, phase and quadrature Walsh covers are chosen. to be orthogonal sets to minimize cross talk of demodulator phase estimation errors. As an example, for 16 Walsh channels, an exemplary Walsh assignment is W0 to W7 for the phase signal and W% to W15 for the quadrature signal.

In the exemplary embodiment, QPSK modulation is used for data rates of 1.2288 Mbps and lower. For QPSK modulation, each Walsh channel comprises one bit. In the exemplary embodiment, at the highest data rate of 2.4576 Mbps, 16-QAM is used and the scrambled data is demultiplexed into 32 parallel streams each having a 2-bit width, 16 parallel streams for the signal. phase and 16 parallel flows for the quadrature signal. In the exemplary embodiment, the LSB of each 2-bit symbol is the previous symbol output from interleaver 116. In the exemplary embodiment, the QAM modulation inputs of (0, 1, 3, 2) map the modulation values of (+ 3, +1, -1, -3) respectively. The use of other modulation schemes, such as PSK m-phase shift switching, may be contemplated and is 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 that is independent of the data rate. Gain adjustments are normalized to an unmodulated BPSK equivalent unit reference. The normalized channel gains, G, as a function of the number of Walsh channels (or data rate) are in Table 2. Also listed in Table 2 is the average power per Walsh channel (in phase or quadrature) in such a way. that the total normalized power is equal to the unit. Note that the channel gain for 16-QAM considers the fact that Walsh chip normalized power is 1 for QPSK and 5 for 16-QAM.

Table 2 - Traffic Channel Orthogonal Channel Gains In the present invention, a preamble is punctured in each traffic frame to assist mobile station 6 in synchronizing with the first partition of each variable rate transmission. In the exemplary embodiment, the preamble is an entire sequence of zeros that for a traffic frame is spread with long PN code but for a control channel frame is not spread with long PN code. In the exemplary embodiment, the preamble is unmodulated BPSK, which is orthogonally spread with the Walsh Jψ covering. Using a single orthogonal channel minimizes the peak / average envelope. In addition, the use of a non-zero Walsh Wx cover minimizes false pilot detection since, for traffic frames, the pilot is spread with the Walsh W0 coverage and both the pilot and the preamble are not spread with the pilot. long PN code. The preamble is multiplexed into the traffic channel stream at the beginning of the packet for a duration that is a function of the data rate. The preamble length is such that preamble overhead is approximately constant for all data rates, while minimizing the likelihood of erroneous detection. A summary of the preamble as a function of data rates is given in Table 3. Note that the preamble comprises 3.1 percent or less of a data packet.

Table 3 - Preamble Parameters VIII. DIRECT LINK TRAFFIC TABLE FORMAT

In the exemplary embodiment, each data packet is formatted by the addition of frame check bits, code termination bits, and other control fields. In the present report, an octet is defined as 8 bits of information and a unit of data is a single octet and comprises 8 bits of information.

In the exemplary embodiment, the direct link supports two data packet formats which are illustrated in Figures 4E and 4F. Packet format 410 comprises five fields and packet format 430 comprises nine fields. Packet format 410 is used when the data packet to be transmitted to mobile station 6 contains sufficient data to completely fill all available octets in the DATA field 418. If the amount of data to be transmitted is less than the available octets in the DATA field 418, the 430 packet format is used. The unused octets are all padded with zeros and designated as field FILL 446.

In the exemplary embodiment, frame check sequence (FCS) fields 412 and 432 contain the CRC parity bits that are generated by the CRC generator 112 (see Figure 3A) according to a predetermined generator polynomial. In the exemplary embodiment, the CRC polynomial is g (x) = x16 + x12 + x5 +1, although other polynomials may be used and are within the scope of the present invention. In the exemplary embodiment, the CRC bits are calculated over the FMT, SEQ, LEN, DATA, and FILL fields. This provides error detection on all bits except code termination bits in TERMINATION fields 420 and 448 transmitted through the traffic channel on the forward link. In the alternative embodiment, CRC bits are calculated only in the DATA field. In the exemplary embodiment, FCS fields 412 and 432 contain 16 CRC parity bits, although other CRC generators providing a different number of parity bits may be used and are within the scope of the present invention. Although the FCS fields 412 and 432 of the present invention have been described in the context of CRC parity bits, other frame check sequences may be used and are within the scope of the present invention. As an example, a check sum may be calculated for the packet and provided in the FCS field.

In the exemplary embodiment, frame format (FMT) fields 414 and 434 contain a control bit indicating whether the data frame contains only data octets (packet format 410) or data octets and padding and zero or more messages. (430 package format). In the exemplary embodiment, a low value for field FMT 414 corresponds to packet format 410. Alternatively, a high value for field FMT 434 corresponds to 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 transmitted out of sequence to mobile station 6, for example for retransmission of packets that were received in error. Assigning the data unit level sequence number eliminates the need for a frame fragmentation protocol for retransmission. The sequence number also allows mobile station 6 to detect duplicate data units. Upon receipt of the FMT, SEQ, and LEN fields, mobile station 6 is able to determine which data units have been received in each time partition without the use of special signaling messages. The number of bits assigned to represent the sequence number depends on the maximum number of data units that can be transmitted in a time partition and in the worst cases of data retransmission delay. In the exemplary embodiment, each data unit is identified by a 24-bit sequence number. At the data rate of 2.4576 Mbps, the maximum number of data units that can be transmitted in each partition is approximately 256. Eight bits are required to identify each of the data units. In addition, it can be estimated that the worst cases of data retransmission delay are less than 500 ms. Retransmission delays include the time required for a NACK message by the mobile station 6, the retransmission of the data, and the number of retransmission attempts caused by the worst case burst error operation. Therefore, 24 bits allow mobile station 6 to properly identify data units being unambiguously received. The number of bits in SEQ 416 and 442 fields may be increased or decreased depending on the size of DATA field 418 and retransmission delays. The use of a different number of bits for SEQ 416 and 442 fields is within the scope of the present invention.

When base station 4 has less data to transmit to mobile station 6 than the space available in the DATA field 418, packet format 430 is used. Packet format 430 allows base station 4 to transmit any number of data units, up to the maximum number of data units available, to mobile station 6. In the exemplary embodiment, a high value for field FMT 434 indicates that the base station 4 is transmitting packet format 430. Within packet format 430, field LEN 440 contains the value of the number of data units being transmitted in this packet. In the exemplary embodiment, the LEN field 440 is 8 bits long, as the DATA field 444 can range from 0 to 255 octets.

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

In the exemplary embodiment, packet format 430 may be used for transmitting zero or more signaling messages. The signaling length (SIG LEN) field 436 contains the Length of subsequent signaling messages, in octets. In the exemplary embodiment, the SIG LEN 436 field is 8 bits long. The 438 SIGNALING field contains the signaling messages. In the exemplary embodiment, each signaling message comprises a message ID field, a message length field (LEN), and a message payload as described below. Fill field 446 contains fill octets which, in exemplary mode, are set to 0x00 (hex). FILL field 446 is used because base station 4 may have fewer data octets for transmission to mobile station 6 than the number of octets available in DATA field 418. When this occurs, FILL field 446 contains enough fill octets to fill the field. unused data field. FILL field 446 is variable length and depends on the length of DATA field 444. The last field of packet formats 410 and 430 is that of TERMINATION fields 420 and 448, respectively. The TERMINATION fields 420 and 448 contain the zero (0x0) code termination bits that are used to force encoder 114 (see Figure 3A) to a known state at the end of each data packet. Code termination bits allow encoder 114 to succinctly partition the packet, so that only bits of a packet are used in the encoding process. The code termination bits also allow the decoder within mobile station 6 to determine packet limits during the decoding process. The number of bits in TERMINATION fields 420 and 448 depends on the design of encoder 114. In the exemplary embodiment, TERMINATION fields 420 and 448 are long enough to force encoder 114 to a known state.

The two packet formats described above are exemplary formats that can be used to facilitate data message transmission and signaling. Several other packet formats can be created to meet the needs of a specific communication system. In addition, a communication system may be designed to accommodate more than the two packet formats described above.

IX · DIRECT LINK CONTROL CHANNEL FRAMEWORK

In the present invention, the traffic channel is also used for transmitting messages from base station 4 to mobile stations 6. The types of messages transmitted include: (1) handoff routing messages, (2) alert messages (e.g. , to alert a mobile station 6 specifies that data is queued for such mobile station 6), (3) short data packets for a specific mobile station 6, and (4) ACK or NACK messages for reverse link data transmissions. (to be described later). Other types of messages may also be transmitted through the control channel and are within the scope of the present invention. Upon completion of the call establishment stage, mobile station 6 monitors the control channel for alert messages and initiates reverse link pilot signal transmission.

In the exemplary embodiment, the control channel is time multiplexed with traffic data on the traffic channel as shown in Figure 4A. Mobile stations 6 identify the control message by detecting a preamble that has been covered with a predetermined PN code. In the exemplary embodiment, control messages are transmitted at a fixed rate, which is determined by mobile station 6 during acquisition. In the preferred embodiment, the control channel data rate is 7 6.8 kbps. The control channel transmits messages in control channel capsules. The diagram of a typical control channel capsule is shown in Figure 4G. In the exemplary embodiment, each capsule comprises preamble 462, the control payload and the CRC parity bits 474. The control payload comprises one or more messages and, if necessary, filler bits 472. Each message comprises a handle identifier. (MSG ID) 464, the length of the message (LEN) 466, an optional address (ADDR) 468 (for example, if the message is directed to a specific mobile station 6) and the payload of message 470. In the exemplary embodiment , the messages are aligned to the octet boundaries. The exemplary control channel capsule illustrated in Figure 4G comprises two broadcast messages destined for all mobile stations 6 and one message directed to a specific mobile station 6. The MSG ID 464 field determines whether or not the message requires an address field (that is, whether it is a broadcast or specific message).

X. DIRECT LINK PILOT CHANNEL

In the present invention, a direct link pilot channel provides a pilot signal that is used by mobile stations 6 for initial acquisition, phase recovery, timing recovery and rate matching. Such uses are similar to those of CDMA communication systems that conform to the IS-95 standard. In the exemplary embodiment, the pilot signal is also used by mobile stations 6 to perform C / I measurement.

An exemplary block diagram of the forward link pilot channel of the present invention is shown in Figure 3A. The pilot data comprises a whole sequence of zeros (or all of ones) which is provided to multiplier 156. Multiplier 156 covers the pilot data with Walsh code W0. Since the Walsh code W0 is an entire sequence of zeros, the output of multiplier 156 is the pilot data. Pilot data is time multiplexed by MUX 162 and provided to the Walsh I channel which is spread by the short PNj code within complex multiplier 214 (see Figure 3B). In the exemplary embodiment, the pilot data is not spread with the long PN code which is gated off during the pilot burst by the MUX 234 to allow reception by all mobile stations 6. The pilot signal is therefore a signal. Unmodulated BPSK.

A diagram illustrating the pilot signal is shown in Figure 4B. In the exemplary embodiment, each time partition comprises two pilot bursts 306a and 306b occurring at the end of the first and third quarters of the time partition. In the exemplary embodiment, each pilot burst 306 has a duration of 64 chips (Tp = 64 chips). In the absence of traffic data or control channel data, base station 4 transmits only pilot and power control bursts, resulting in a burst waveform in bursts at the periodic rate of 1200 Hz. pilot are tabulated in Table 4. XI. REVERSE LINK POWER CONTROL

In the present invention, the forward link power control channel is used to send the power control command which is used to control the reverse link transmission transmit power from remote station 6. At the reverse link, each station The transmitting mobile 6 acts as a source of interference for all other mobile stations 6 in the network. To minimize reverse link interference and maximize capacity, the transmit power of each mobile station 6 is controlled by two power control loops. In the exemplary embodiment, the power control loops are similar to the CDMA system described in detail in US Patent No. 5,056,109 entitled "METHOD AND APPARATUS FOR CONTROLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM" on behalf of the Applicant herein. invention. Other power control mechanisms may also be contemplated and are within the scope of the present invention. The first power control loop adjusts the transmitting power of mobile station 6 such that the reverse link signal quality is maintained at an adjusted level. Signal quality is measured as the power-to-noise ratio plus interference Eb / I0 of the reverse link signal received at base station 4. The set level is referred to as the set point Eb / I0. The second power control loop adjusts the setpoint such that the desired level of performance as measured by the frame error rate (FER) is maintained. Power control is critical in reverse link, because the transmitting power of each mobile station 6 is interference with other mobile stations 6 in the communication system. Minimizing reverse link transmission power reduces interference and increases reverse link capacity.

Within the first power control loop, the reverse link signal Eb / I0 is measured at base station 4. Base station 4 then compares the measured Eb / I0 to the setpoint. If the measured Eb / I0 is greater than the setpoint, base station 4 transmits a power control message to mobile station 6 to reduce transmit power. Alternatively, if the measured Eb / I0 is below the setpoint, base station 4 transmits a power control message to mobile station 6 to increase transmit power. In the exemplary embodiment, the power control message is implemented with a power control bit. In the exemplary embodiment, a high value for the power control bit commands mobile station 6 to increase its transmit power and a small value controls the mobile station to reduce its transmit power.

In the present invention, the power control bits for all mobile stations 6 in communication with each base station 4 are transmitted through the power control channel. In the exemplary embodiment, the power control channel comprises up to 32 orthogonal channels that are spread with 16-bit Walsh covers. Each Walsh channel transmits a reverse power control (RPC) bit or a FAC bit at periodic intervals. Each active mobile station 6 is assigned an RPC index which defines the Walsh coverage and the QPSK modulation phase (i.e., in phase or quadrature) for transmitting the RPC bitstream destined for such mobile station 6. In the exemplary embodiment, the RPC index of 0 is reserved for the FAC bit. The exemplary block diagram of the power control channel is shown in Figure 3A. The RPC bits are provided to symbol repeater 150, which repeats each RPC bit a predetermined number of times. The repeated RPC bits are provided with the Walsh cover element 152 which covers the bits with the Walsh covers corresponding to the RPC indices. The covered bits are provided with the gain element 154 which scales the bits prior to modulation to maintain a constant total transmit power. In the exemplary embodiment, Walsh RPC channel gains are normalized so that the total RPC channel power equals the total available transmit power. Walsh channel gains can be varied as a function of time for efficient utilization of the base station's total transmit power while maintaining reliable RPC transmission for all active mobile stations 6. In the exemplary embodiment, Walsh channel gains from idle mobile stations 6 are set to zero. Automatic power control of Walsh RPC channels is possible by using direct link quality measurement estimates from the corresponding DRC channel from mobile stations 6. Scaled RPC bits from gain element 154 are provided to the MUX 162 .

In the exemplary embodiment, RPC indices from 0 to 15 are assigned to Walsh wraps W0 to W15, respectively, and are transmitted around the first pilot burst within a partition (RPC bursts 304 in Figure 4C). The RPC indices 16 through 31 are assigned to Walsh covers W0 through W15, respectively, and are transmitted around the second pilot burst within a partition (RPC burst 308 in Figure 4C). In the exemplary embodiment, the RPC bits are modulated in BPSK with even Walsh covers (eg W0, W2, W4, etc.) modulated in the phase signal and odd Walsh covers (eg W1, W3, W5 etc.). ) modulated in the quadrature signal. To reduce the peak / average envelope, it is preferable to balance the power in phase and quadrature. In addition, to minimize cross talk due to demodulator phase estimation errors, it is preferable to assign orthogonal coverage to the phase and quadrature signals.

In the exemplary embodiment, up to 31 RPC bits may be transmitted over 31 Walsh RPC channels in each time partition. In the exemplary embodiment, 15 RPC bits are transmitted in the first half partition and 16 RPC bits are transmitted in the second half partition. The RPC bits are combined by the adder 212 (see Figure 3B) and the power control channel composite waveform is as shown in Figure 4C.

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

Table 4 - Pilot Modulation and Power Control Parameters The power control channel has a bursty nature, since the number of mobile stations 6 in communication with each base station 4 may be less than number of Walsh RPC channels available. In such a situation, some Walsh RPC channels are set to zero by appropriately adjusting gain element gains 154.

In the exemplary embodiment, the RPC bits are transmitted to mobile stations 6 without coding or interleaving to minimize processing delays. Furthermore, erroneous reception of the power control bit is not detrimental to the data communication system of the present invention as the error can be corrected in the next time partition by the power control loop.

In the present invention, mobile stations 6 may be in soft handoff with multiple base stations 4 on the reverse link. The method and apparatus for reverse link power control for the soft handoff mobile station 6 is described in U.S. Patent No. 5,056,109 mentioned above. The soft handoff mobile station 6 monitors the Walsh RPC channel for each base station 4 in the active set and combines the RPC bits according to the method described in the above-mentioned U.S. Patent No. 5,056,109. In the first embodiment, mobile station 6 performs the OR (OR) logic of the power reduction commands. Mobile station 6 reduces transmit power if any of the received RPC bits command mobile station 6 to reduce transmit power. In the second embodiment, the soft handoff mobile station 6 can combine the soft decisions of the RPC bits before making a hard decision. Other modalities for processing received RPC bits may be contemplated and are within the scope of the present invention.

In the present invention, the FAC bit tells mobile stations 6 whether or not the associated pilot channel traffic channel is transmitting in the next half frame. The use of the FAC bit improves the C / I estimate by mobile stations 6, and thus the data rate request, by spreading knowledge of interference activity. In the exemplary embodiment, the FAC bit only changes at half-frame limits and is repeated for eight successive time partitions, resulting in a bit rate of 75 bps. The parameters for the FAC bit are listed in Table 4.

Using the FAC bit, mobile stations 6 can compute the C / I measurement as follows: '(Λ c, j * i where (C //) ,. is the C / I measurement of the same direct link signal, Cj is the total received power of the nth direct link signal, C. is the received power of jes, m the direct link signal, I is the total interference if all base stations 4 are transmitting, it is the jes FAC bit, m0 direct link signal and can be 0 or 1, depending on the FAC bit.

XII. REVERSE LINK DATA TRANSMISSION

In the present invention, reverse link supports variable rate data transmission. The variable rate provides flexibility and allows mobile stations 6 to transmit at one of several data rates, depending on the amount of data to be transmitted to base station 4. In the exemplary embodiment, mobile station 6 may transmit data at the data rate. lowest at any time. In the exemplary embodiment, data transmission at higher data rates requires a concession by base station 4. Such an implementation minimizes the reverse link transmission delay while providing for the effective use of reverse link resources.

An exemplary illustration of the reverse link data transmission flowchart of the present invention is shown in Figure 8. Initially, in partition n, mobile station 6 performs an access probe, as described in US Patent No. 5,289, 527 mentioned above, to establish the lowest rate reverse channel data channel on block 802. In the same partition n, base station 4 demodulates access polling and receives the access message on block 804. Base station 4 grants request for the data channel and, on partition n + 2, transmits the lease and the assigned RPC index through the control channel on block 806. On partition n + 2, mobile station 6 receives the lease and is controlled in base station 4 in block 808. Starting at partition n + 3, mobile station 6 begins transmission of the pilot signal and gains immediate access to the lower rate data channel on the reverse link.

If mobile station 6 has traffic data and requests a high rate data channel, mobile station 6 can initiate the request at block 810. In partition n + 3, base station 4 receives the high-speed data request, at block 812. At partition n + 5, base station 4 transmits the lease on the control channel at block 814. At partition n + 5, mobile station 6 receives the lease at block 816 and initiates high data transmission reverse link speed, starting at partition n + 6, block 818.

XIII. REVERSE LINK ARCHITECTURE

In the data communication system of the present invention, reverse link transmission differs from direct link transmission in several ways. On direct link, data transmission typically occurs from base station 4 to mobile station 6. However, on reverse link, each base station 4 can concurrently receive data transmissions from multiple mobile stations 6. In the exemplary embodiment , each mobile station 6 may transmit at one of several data rates, depending on the amount of data to be transmitted to base station 4. Such a system scheme reflects the asymmetric characteristic of data communication.

In the exemplary embodiment, the reverse link time base unit is identical to the forward link time base unit. In the exemplary embodiment, forward link and reverse link data transmissions occur on time partitions lasting 1.667 ms. However, since reverse link data transmission typically occurs at a lower data rate, a longer time base unit can be used to improve efficiency.

In the exemplary embodiment, the reverse link supports two channels: the pilot / DRC channel and the data channel. The function and implementation of each of these channels will be described below. The pilot / DRC channel is used to transmit the pilot signal and DRC messages and the data channel is used to transmit traffic data.

A diagram of the exemplary reverse link frame structure of the present invention is illustrated in Figure 7A. In the exemplary embodiment, the reverse link frame structure is similar to the forward link frame structure shown in Figure 4A. However, in reverse link, pilot / DRC data and traffic data are transmitted concomitantly on the phase and quadrature channels.

In the exemplary embodiment, mobile station 6 transmits a DRC message on the pilot / DRC channel at each time partition whenever mobile station 6 is receiving a high speed data transmission. Alternatively, when mobile station 6 is not receiving high speed data transmission, the entire partition on the pilot / DRC channel comprises the pilot signal. The pilot signal is used by the receiving base station 4 for a variety of functions: as an initial pickup aid, as a phase reference for the pilot / DRC and data channels, and as the source for loop reverse loop power control. closed loop.

In the exemplary embodiment, the reverse link bandwidth is selected to be 1.2288 MHz. Such bandwidth selection allows the use of existing hardware designed for a CDMA system that meets the IS-95 standard. However, other bandwidths may be used to increase capacity and / or meet system requirements. In the exemplary embodiment, the same long PN code and short PN codes as those specified by IS-95 are used to spread the reverse link signal. In the exemplary embodiment, reverse link channels are transmitted using QPSK modulation. Alternatively, OQPSK modulation can be used to minimize peak / average amplitude variation of the modulated signal, which may result in better performance. The use of different system bandwidths, PN codes and modulation schemes may be contemplated and is within the scope of the present invention.

In the exemplary embodiment, the transmission power of reverse link transmissions on the pilot / DRC channel and data channel is controlled such that the Eb / I0 of the reverse link signal as measured at base station 4 is maintained at a predetermined setpoint Eb / 10 as described in above-mentioned US Patent No. 5,506,109. Power control is maintained by base stations 4 in communication with mobile station 6 and commands are transmitted in the form of RPC bits as described above.

XIV. REVERSE LINK DATA CHANNEL

A block diagram of the exemplary reverse link architecture of the present invention is shown in Figure 6. Data is partitioned into data packets and provided to encoder 612. For each data packet, encoder 612 generates the CRC parity bits, inserts the code terminating bits and encodes the data. In the exemplary embodiment, encoder 612 encodes the packet according to the encoding format described in U.S. Patent Application Serial No. 08 / 743,688 mentioned above.

Other encoding formats may also be used and are within the scope of the present invention. The encoded packet from encoder 612 is provided to block interleaver 614 which reorders the code symbols in the packet. The interleaved packet is provided to the multiplier 616, which covers the data with Walsh overlay and provides the data covered to the gain element 618. The gain element 618 scales the data to maintain a constant energy per bit, Eb, independent of the data rate. The scaled data from gain element 618 is provided to multipliers 650b and 650d, which scatter the data with sequences PN_Q and PN_I, respectively. The scattered data from multipliers 650b and 650d are provided to filters 652b and 652d, respectively, which filter the data. Filtered signals from filters 652a and 652b are provided to adder 654a and filtered signals from filter 652c and 652d are provided to adder 654b. Adders 654 sum the data channel signals with the pilot / DRC channel signals. The outputs of the additions 654a and 654b consist of IOUT and QOUT, respectively, which are modulated by the COS phase sine (wct) and quadrature sinusoid SEN (wct), respectively (as in the direct link) and summed (not shown in Figure 6). In the exemplary embodiment, traffic data is transmitted in both the phase phase and quadrature phase of the sinusoid.

In the exemplary embodiment, data is spread with long PN code and short PN codes. The long PN code scrambles the data such that the receiving base station 4 is able to identify the transmitting mobile station 6. The short PN code spreads the signal across the system bandwidth. The long PN sequence is generated by the long code generator 642 and provided to multipliers 64 6. The short PNj and PNg sequences are generated by the short code generator 644 and are also provided to multipliers 646a and 646b, respectively, which multiply the two. sequence sets to form signals PN_I and PN_Q, respectively. Timing / Control Circuit 640 provides the timing reference. The exemplary block diagram of the data channel architecture as shown in Figure 6 is one of a number of architectures that support reverse link encoding and modulation. For high rate data transmission, a similar architecture of this direct link using multiple orthogonal channels can also be used. Other architectures, such as the reverse link traffic channel architecture in the CDMA system that conforms to the IS-95 standard, may also be contemplated and are within the scope of the present invention.

In the exemplary embodiment, the reverse link data channel supports four data rates, which are tabulated in Table 5. Additional data rates and / or different data rates may be supported and are within the scope of the present invention. In the exemplary embodiment, the packet size for the reverse link depends on the data rate as shown in Table 5. As described in the above-mentioned US Patent Serial No. 08 / 743,688, better decoder performance can be obtained. for larger package sizes. Accordingly, packet sizes other than those listed in Table 5 may be used to improve performance and are within the scope of the present invention. In addition, the packet size may have a parameter that is independent of the data rate.

Table 5 - Pilot Modulation and Power Control Parameters As shown in Table 5, the reverse link supports a plurality of data rates. In the exemplary embodiment, the lowest data rate of 9.6 kbps is allocated to each mobile station 6 upon registration with base station 4. In the exemplary embodiment, mobile stations 6 may transmit data over the highest rate data channel. low on any time partition without having to request permission from base station 4. In the exemplary embodiment, data transmission at the highest data rates is granted by the selected base station 4 based on a set of system parameters such as system load, equality and total throughput. An exemplary programming mechanism for high speed data transmission is described in detail in the above-mentioned U.S. Serial Patent Application 08 / 798,951.

XV. REVERSE LINK PILOT / DRC CHANNEL

The exemplary block diagram of the pilot / DRC channel is shown in Figure 6. The DRC message is provided to the DRC encoder 626 encoding the message according to a predetermined encoding format. DRC message encoding is important since the probability of error in the DRC message must be sufficiently low as incorrect data rate determination on the direct link impacts system throughput performance. In the exemplary embodiment, the DRC encoder 626 is a rate CRC block encoder (8.4) which encodes the 3-bit DRC message into an 8-bit codeword. The encoded DRC message is provided to multiplier 628 which covers the message with the Walsh code that uniquely identifies the destination base station 4 to which the DRC message is directed. The Walsh code is provided by the Walsh generator 624. The covered DRC message is provided to the multiplexer (MUX) 630, which multiplexes the message with the pilot data. The DRC message and pilot data are provided to multipliers 650a and 650c, which spread the data with signals PN_I and PN_Q, respectively. In this way, the pilot and the DRC message are transmitted in both the phase phase and quadrature phase of the sinusoid.

In the exemplary embodiment, the DRC message is transmitted to the selected base station 4. This is achieved by covering the DRC message with the Walsh code identifying the selected base station 4. In the exemplary embodiment, the Walsh code has a length of 128 chips. The 128-chip Walsh code derivation is known to those skilled in the art. A unique Walsh code is assigned to each base station 4 which is in communication with mobile station 6. Each base station 4 decovers the signal on the DRC channel with the assigned Walsh code. The selected base station 4 is capable of discovering the DRC message and transmitting the data to the requesting mobile station 6 via the direct link in response thereto. Other base stations 4 will be able to determine that the requested data rate is not directed to them, as such base stations 4 are assigned different Walsh codes.

In the exemplary embodiment, the reverse link short PN codes for all base stations 4 in the data communication system are the same and there is no shift in short PN sequences to distinguish different base stations 4. The data communication system of the present invention supports soft handoff on reverse link. Using the same short, non-offset PN codes allows multiple base stations 4 to receive the same reverse link transmission from mobile station 6 during a soft handoff. Short PN codes provide spectral spreading, but do not allow identification of base stations 4.

In the exemplary embodiment, the DRC message carries the data rate requested by mobile station 6. In the alternative embodiment, the DRC message carries an indication of direct link quality (e.g. C / I information as measured by mobile station 6) . Mobile station 6 can simultaneously receive direct link pilot signals from one or more base stations 4 and perform C / I measurement on each pilot signal received. Mobile station 6 then selects the best base station 4 based on a set of parameters that can comprise current and previous C / I measurements. Rate control information is formatted in the DRC message that can be conveyed to base station 4 in one of several forms.

In the first embodiment, mobile station 6 transmits a DRC message based on the requested data rate. The requested data rate is the highest supported data rate, which provides satisfactory C / I performance measured by mobile station 6. From C / I measurement, mobile station 6 first calculates the maximum data rate that provides performance. satisfactory. The maximum data rate is then quantized to one of the supported data rates and designated as the requested data rate. The data rate index corresponding to the requested data rate is transmitted to the selected base station 4. An exemplary set of supported data rates and corresponding data rate indices are presented in Table 1.

In the second embodiment, wherein mobile station 6 transmits a direct link quality indication to the selected base station 4, mobile station 6 transmits a C / I index representing the quantized value of the C / I measurement. The C / I measurement can be mapped to a table and associated with a C / I index. Using more bits to represent the C / I index allows for a finer quantization of C / I measurement. In addition, the mapping may be linear or pre-distorted. For a linear mapping, each increment in the C / I index represents a corresponding increase in the C / I measurement. For example, each step in the C / I index may represent a 2.0 dB increase in C / I measurement. For pre-distorted mapping, each increment in the C / I index may represent a different increase in C / I measurement. As an example, a distorted mapping can be used to quantize the C / I measurement to fit the cumulative distribution function (CDF) curve of the C / I distribution as shown in Figure 10.

Other embodiments for conducting rate control information from mobile station 6 to base station 4 may be contemplated and are within the scope of the present invention. In addition, the use of different bit numbers to represent rate control information is also within the scope of the present invention. For much of the disclosure, the present invention is described for simplicity in the context of the first embodiment using a DRC message to drive the requested data rate.

In the exemplary embodiment, C / I measurement can be performed on the direct link pilot signal, similar to that used in the CDMA system. A method and apparatus for performing C / I measurement are described in US Patent Application Serial No. 08 / 722,763 entitled "METHOD AND APPARATUS FOR MEASURING LINK QUALITY IN A SPREAD SPECTRUM COMMUNICATION SYSTEM" filed September 27, 1996, on behalf of the Applicant of the present invention. In short, the C / I measurement on the pilot signal can be obtained by straying the signal received with short PN codes. The C / I measurement on the pilot signal may contain inaccuracies if the channel condition has changed between the C / I measurement moment and the current moment of data transmission. In the present invention, the use of the FAC bit enables mobile stations 6 to account for direct link activity when determining the requested data rate.

In the alternative embodiment, the C / I measurement may be performed on the direct link traffic channel. The signal from the traffic channel is initially unscrambled with the long PN code and the short PN codes and uncovered with the Walsh code. The C / I measurement of signals on data channels may be more accurate as a higher percentage of transmit power is allocated for data transmission. Other methods for measuring C / I of the forward link signal received by mobile station 6 may also be contemplated and are within the scope of the present invention.

In the exemplary embodiment, the DRC message is transmitted in the first half of the time partition (see Figure 7A). For an exemplary 1.666 ms time partition, the DRC message comprises the first 1024 chips or 0.83 ms of the time partition. The remaining 1024 time chips are used by base station 4 to demodulate and decode the message. Transmission of the DRC message in the initial portion of the time partition allows base station 4 to decode the DRC message within the same time partition and possibly transmit data at the requested data rate in the immediately successive time partition. The short processing delay allows the communication system of the present invention to quickly adapt to changes in the operating environment.

In the alternative embodiment, the requested data rate is conducted to base station 4 by using an absolute reference and a relative reference. In this embodiment, the absolute reference comprising the requested data rate is transmitted periodically. Absolute reference allows base station 4 to determine the exact data rate requested by mobile station 6. For each time partition between absolute reference transmissions, mobile station 6 transmits a reference relative to base station 4, which indicates whether the Requested data rate for next time partition is higher, lower, or equal to requested data rate for previous time partition. Periodically, mobile station 6 transmits an absolute reference. Periodic transmission of the data rate index allows the requested data rate to be set to a known state and ensures that erroneous receptions of relative references do not accumulate. The use of absolute references and relative references may reduce the transmission rate of DRC messages to base station 6. Other protocols for transmitting the requested data rate may also be contemplated and are within the scope of the present invention. XVI. REVERSE LINK ACCESS CHANNEL The access channel is used by mobile station 6 to transmit messages to base station 4 during the registration phase. In the exemplary embodiment, the access channel is implemented using a partitioned structure with each partition being randomly accessed by mobile station 6. In the exemplary embodiment, the access channel is time multiplexed with the DRC channel.

In the exemplary embodiment, the access channel transmits messages in access channel capsules. In the exemplary embodiment, the access channel frame format is identical to that specified by IS-95, except that the timing is 26, 67 ms frames instead of the 20 ms frames specified by IS-95. . The diagram of an exemplary access channel capsule is shown in Figure 7B. In exemplary embodiment, each access channel capsule 712 comprises preamble 722, one or more message capsules 724 and filler bits 726. Each message capsule 724 comprises message length field (MSG LEN) 732, the body of the message 734 and the CRC parity bits 736.

XVI1 · channel NACK OF LINK REVERSE

In the present invention, mobile station 6 transmits NACK messages through the data channel. NACK message is generated for each packet received in error by mobile station 6. In the exemplary embodiment, NACK messages may be transmitted using the Blank & Burst signaling data format as described in U.S. Patent No. 5,504,773 mentioned above.

Although the present invention has been described in the context of a NACK protocol, the use of an ACK protocol may be contemplated and is within the scope of the present invention.

Claims (8)

Transmitter for high-speed packet data transmission, characterized in that it comprises: an encoder (114) for receiving data packets and encoding such data packets into encoded packets; a frame punching element (118) for receiving the coded packets and punching a portion of the coded packets to provide punctured packets; a variable rate controller (130) connected to the frame punching element for receiving the punctured packets and demultiplexing the punctured packets into parallel channels; a Walsh covering element (132) connected to the variable rate controller (130) for receiving parallel channels and covering parallel channels with Walsh covers to provide orthogonal channels; and a gain element (134) connected to the Walsh cover element (132) for receiving orthogonal channels and scaling orthogonal channels to provide staggered channels. Transmitter according to claim 1, characterized in that each of the parallel channels has a fixed data rate. Transmitter according to claim 1, characterized in that it further comprises: a multiplexer (160) connected to the gain element, the multiplexer (160) multiplexing pilot and power control bursts with the scaled channels to provide Walsh channels. Transmitter according to claim 3, characterized in that the pilot and power control bursts are located in fixed positions within each time partition. Transmitter according to claim 3, characterized in that the pilot and power control bursts are provided in two positions within each time partition. Transmitter according to claim 1, characterized in that it further comprises: a multiplexer (160) connected to the gain element, the multiplexer (160) multiplexing a preamble with the scaled channels to provide Walsh channels. Transmitter according to claim 1, characterized in that it further comprises: a scrambler (122) interposed between the frame punching element (118) and the variable rate controller (130), the scrambler (122) shuffling the punctured packages with a scramble sequence. Transmitter according to claim 1, characterized in that each of the Walsh covers is 16 bits long.