HK1082850B - Method for code combining at an outer decoder on a communication system - Google Patents

Description

Method for code combining at an outer decoder of a communication system

Technical Field

The present invention relates to broadcast communications, otherwise known as point-to-multipoint communications, in wired or wireless communication systems. More particularly, the present invention relates to a system and method for code combining at an outer decoder in such a broadcast communication system.

Background

Communication systems have evolved to allow the transmission of information signals from an origination station to a physically different destination station. In transmitting an information signal from an origination station over a communication channel, the information signal is first converted into a form suitable for efficient transmission over the communication channel. The conversion, i.e. modulation, of the information signal involves varying a parameter of the carrier in accordance with the information signal in such a way that the spectrum of the resulting modulated carrier is confined within the bandwidth of the communication channel. At the destination station, the original information signal is replicated from a modulated carrier wave received over the communication channel. Such a copy is typically obtained by using the inverse of the modulation process used by the origination station.

Modulation also facilitates multiple access, i.e., the simultaneous transmission and/or reception of several signals over a common communication channel. Multiple-access communication systems often include multiple subscriber stations requiring intermittent service of relatively short duration rather than continuous access to a common communication channel. Many multiple access techniques are known in the art, such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and amplitude modulation multiple Access (AM). Another type of multiple access technique IS Code Division Multiple Access (CDMA) spread spectrum systems that conform to the "TIA/EIA/IS-95 mobile station-base station compatibility standard for dual mode wideband spread spectrum cellular systems," hereinafter the IS-95 standard. The use of CDMA techniques in multiple access communication systems is disclosed in U.S. patent No. 4,901,307, entitled "spread spectrum multiple access communication system using satellite or terrestrial repeaters," and U.S. patent No. 5,103,459, entitled "system and method for generating waveforms in a CDMA cellular telephone system," all of which are assigned to the assignee of the present invention.

Multiple-access communication systems may be wireless or wired and may communicate voice and/or data. An example of a communication system that communicates voice and data IS a system in accordance with the IS-95 standard, which specifies communicating voice and data signals over a communication channel. A method for transmitting data in fixed size code channel frames is described in detail in U.S. patent No. 5,504,773, entitled "method and apparatus for formatted transmission of data," which is assigned to the assignee of the present invention. In accordance with the IS-95 standard, data or sound IS divided into 20 millisecond wide coded channel frames at data rates up to 14.4 Kbps. Further examples of communication systems for transmitting voice and data include those compliant with the "third generation partnership project" (3GPP), which IS included in a group of documents including the 3G TS25.211, 3G TS 25.212, 3G TS 25.213, 3G TS 25.214(W-CDMA standard) number, or the "TR-45.5 physical layer standard for CDMA2000 spread spectrum systems, version C" (IS-2000 standard), also proposed as 1 xEV-DV.

An example of a data only communication system IS a high data rate (HD) communication system that conforms to the TIA/EIA/IS-856 industry standard, hereinafter referred to as the IS-856 standard. The HDR system is based on a communication system: it is disclosed in co-pending application serial No. 08/963,386 entitled "METHOD AND APPARATUS FOR high rate packet data transmission" (METHOD AND APPARATUS FOR HIGH RATE PACKET datarange transmission), filed on 3.12.1997 AND assigned to the assignee of the present invention. The HDR communication system defines a set of data rates, ranging from 38.4kbps to 2.4Mbps, AT which an Access Point (AP) can send data to a subscriber station (access terminal, AT). Because the AP is similar to the base station, the terminology regarding cells and sectors is the same as that regarding voice systems.

In a multiple access communication system, communication between users is conducted through one or more base stations. A first user on a first subscriber station communicates to a second user on a second subscriber station by transmitting data on a reverse link to a base station. The base station receives the data and routes the data to another base station. Data is transmitted on the forward link of the same or other base station to the second subscriber station. The forward link refers to transmission from a base station to a subscriber station, and the reverse link refers to transmission from a subscriber station to a base station. Likewise, communication may also be between a first user of the first subscriber station and a second user of the landline station. The base station receives data from the subscriber on the reverse link and routes the data to a second subscriber via the Public Switched Telephone Network (PSTN). In many communication systems, such as IS-95, W-CDMA, IS-2000, the forward link and the reverse link are assigned separate frequencies.

The wireless communication device described above is an example of a point-to-point communication service. In contrast, broadcast services provide point-to-multipoint communication services. The basic model of a broadcast system consists of a user broadcast network served by one or more central stations, which transmits information to the users with certain content, such as news, movies, sporting events, etc. Each broadcast network user's subscriber station monitors a common broadcast forward link signal. Because the central station fixedly determines the content, the user generally does not return a communication. Examples of common uses of broadcast service communication systems are television broadcasts, radio broadcasts, and the like. Such communication systems are generally highly specialized and well-defined communication systems. With recent advances in wireless cellular telephone systems, there has been interest in using the existing infrastructure of cellular telephone systems, which are primarily point-to-point, for broadcast services. (As used herein, the term "cellular" system includes communication systems using both cellular and PCS frequencies.)

Information signals exchanged in terminals of a communication system are often organized into a plurality of packets. For the purposes of this description, a packet refers to a group of bytes, including data (payload) and control elements, formatted specifically. The control elements include, for example, a preamble and a quality metric. Quality metrics include, for example, Cyclic Redundancy Check (CRC), parity bits (parity bits), and other types of metrics known in the art. The packet is typically formatted into a message in accordance with a communication channel structure. The message, appropriately modulated, transmitted between the originating terminal and the destination terminal is affected by characteristics of the communication channel, such as signal-to-noise ratio, fading, time variance (timeariance), and other such characteristics. These characteristics have different effects on the modulated signal in different communication channels. As a result, the transmission of modulated signals over wireless communication channels requires different considerations than the transmission of modulated signals over similar wired communication channels, such as coaxial or fiber optic cables.

In addition to selecting a modulation appropriate for a particular communication channel, other methods for protecting information signals have been devised. These methods include, for example, encoding, symbol repetition, interleaving, and other methods known to those of ordinary skill in the art. However, these methods add additional overhead. Therefore, engineering must make a compromise between the reliability of the message delivery and the amount of additional overhead. Even with the information protection discussed above, the condition of the communication channel degrades to the point that some of the packets making up the message may not be decoded (erased) by the destination station. In data-only communication systems, the strategy is to retransmit the undecoded packet using an automatic repeat request (ARQ) made by the destination station to the originating station. However, as discussed, the subscriber station does not communicate back with the base station. Moreover, even if the subscriber station is allowed to transmit ARQ, such communication may overload the system. Therefore, other ways of information protection are needed.

An outer code (outer code) and an inner code (inner code) are used in a communication system to provide information protection. The outer code includes an outer encoder at the base station controller and an outer decoder at the subscriber station. The inner code includes an inner encoder at the base station and an inner decoder at the subscriber station. The outer and inner codes relate to encoding and decoding of information blocks. The outer and inner codes add redundant information to improve protection. This redundancy allows decoding of information from less than one complete encoded information block.

The bit stream of information to be transmitted is provided to a transmit buffer and an outer code encoder communicatively coupled to the transmit buffer for encoding. Redundant bits are provided to each transmit buffer and then the contents of the transmit buffer are multiplexed and encoded by an inner encoder to further improve information protection. The receiving subscriber station provides a reverse process, decoding, to recover the transmitted information.

A co-pending application serial No. 09/933,912 entitled "METHOD and system FOR using an outer DECODER IN a BROADCAST SERVICES communication system" (METHOD AND SYSTEM FOR iterative OF output DECODER IN a BROADCAST DECODER) filed on 8/20/2001 and assigned to the assignee OF the present invention, discusses the use OF an outer DECODER IN a BROADCAST system IN detail. Co-pending application serial No. 10/226/058, entitled "METHOD and SYSTEM for delivering CONTENT over a BROADCAST services communication SYSTEM" (METHOD AND SYSTEM for communicating CONTENT ON a BROADCAST services communication SYSTEM), filed ON day 21/8/2002 and assigned to the assignee of the present invention, also discusses in detail the use of an outer decoder in a BROADCAST SYSTEM and focusing ON the time realignment of two transmissions of the same CONTENT from two base stations to alleviate the problem of truncating frames.

A co-pending application serial No. 09/976,591 entitled "METHOD and SYSTEM FOR reducing decoding complexity IN a COMMUNICATION SYSTEM (METHOD AND SYSTEM FOR decoding OF decoding performance IN a COMMUNICATION SYSTEM"), filed on 12/10/2001 and assigned to the assignee OF the present invention, discusses IN detail the transmit buffer FOR outer codes IN a broadcast SYSTEM.

Even with the use of outer and inner codes, the subscriber station may not be able to create this information bit stream from the decoded received packet from a particular base station. Therefore, there is a need in the art for a method and system that can create the information bit stream even when the subscriber station cannot create the information bit stream from the decoded received packet from a particular base station.

Disclosure of Invention

The embodiments disclosed herein address the needs set forth above by providing a method for coding combining at an outer decoder on a communication system.

Drawings

Fig. 1 illustrates a conceptual block diagram of a High Speed Broadcast Service (HSBS) communication system;

fig. 2 illustrates the concept of physical and logical channels for HSBS;

FIG. 3 illustrates a prior art inner code in accordance with one embodiment;

FIG. 4 illustrates physical layer processing in accordance with one embodiment;

FIG. 5 illustrates a transmit buffer for outer codes in accordance with one embodiment;

FIG. 6 shows a block diagram of an outer encoder, an inner decoder, and an outer decoder, in accordance with one embodiment; while

Fig. 7 shows a representation of the combining process of an embodiment applied to an example, where only the combination of the first 100 symbols is shown.

Detailed Description

Definition of

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

The term "point-to-point communication" is used herein to mean communication between two subscriber stations over a dedicated communication channel.

The term "broadcast communication" or "point-to-multipoint communication" is used herein to mean a communication in which multiple subscriber stations receive communications from one source.

The term "packet" is used herein to mean a set of bits comprising data (payload) and control elements arranged in a particular format. Control elements include, for example, preamble sequences, quality metrics, and other control elements known to those skilled in the art. Quality metrics include, for example, Cyclic Redundancy Check (CRC), parity bits, and other quality metrics known in the art.

The term "access network" is used herein to mean a collection of Base Stations (BSs) and one or more base station controllers. The access network transports data packets between multiple subscriber stations. The access network may be further connected to additional networks outside it, such as an intranet or the internet, and may transport data packets between each access terminal and such outside networks.

The term "base station" is used herein to refer to the hardware through which subscriber stations communicate. A "cell" refers to the hardware or a geographic coverage area, depending on the context in which the term is used. A "sector" is a portion of a cell. Because a sector has the properties of a cell, the teachings described herein with respect to a cell can be readily extended to a sector.

The term "subscriber station" is used herein to mean the hardware through which an access network communicates. A subscriber station may be mobile or stationary. A subscriber station may be any data device that communicates through a wireless channel or through a wired channel, for example using fiber optic or coaxial cables. A subscriber station further may be any of a number of types of devices including, but not limited to, PC card, flash memory card, external or internal modem, or wireless or wireline phone. A subscriber station that is in the process of establishing an active traffic channel connection with a base station is said to be in a connection setup state. A subscriber station that has established an active traffic channel connection with a base station is called an active subscriber station and is said to be in a communication state.

The term "physical channel" is used herein to refer to the communication route over which a signal propagates, described in terms of modulation characteristics and coding.

The term "logical channel" is used herein to mean a communication route within the protocol layer of a base station or subscriber station.

The term "communication channel/link" is used herein to mean either a physical channel or a logical channel in a contextual sense.

The term "reverse channel/link" is used herein to refer to a communication channel/link through which a subscriber station sends signals to a base station.

A "forward channel/link" is used herein to refer to a communication channel/link through which a base station transmits signals to a subscriber station.

The term "soft handoff" is used herein to refer to communication between a subscriber station and two or more sectors, where each sector belongs to a different cell. The reverse link communication is received by all sectors and is communicated upon the forward links of two or more sectors simultaneously.

The term softer handoff is used herein to refer to communication between a subscriber station and two or more sectors, each of which belongs to the same cell. The reverse link communication is received by all sectors and the forward link communication is simultaneously conducted on the forward link of one of the two or more sectors.

The term "erasure" is used herein to mean that a message cannot be identified.

The term "dedicated channel" is used herein to mean a channel modulated by information specific to an individual subscriber station.

The term "common channel" is used herein to mean a channel modulated by information shared among all subscriber stations.

Description of the invention

The basic model of a broadcast system consists of a user broadcast network served by one or more central stations, which delivers information to users with certain content, such as news, movies, sporting events, etc. Each broadcast network user's subscriber station monitors a common broadcast forward link signal. Fig. 1 illustrates a conceptual block diagram of a communication system 100 capable of performing High Speed Broadcast Services (HSBS) in accordance with one embodiment.

The broadcast content is from a Content Server (CS) 102. The content server may be located within the operator network (not shown) or external Internet (IP) 104. The content is delivered in packets to a Broadcast Packet Data Serving Node (BPDSN) 106. The term BPDSN is used because although a BPDSN may be physically located the same, or may be identical to a conventional PSDN (not shown), the BPDSN may be logically distinct from the conventional PSDN. The BPDSN 106 delivers the packet to a Packet Control Function (PCF)108 based on the packet's destination. The PCF is the control entity that the HSBS controls the functions of the base station 110, since the base station controller is for regular voice and data services. To illustrate the high-level concept of HSBS interfacing with a physical access network, fig. 1 shows a PCF that has the same or even equivalent physical address, but is logically different from a Base Station Controller (BSC). The BSC/PCF 108 provides the packets to a base station 110.

Communication system 100 facilitates High Speed Broadcast Services (HSBS) by introducing a high data rate forward broadcast shared channel (F-BSCH)112 that can be received by a large number of subscriber stations 114. The term "forward broadcast shared channel" is used herein to mean a single forward link physical channel that carries broadcast traffic. A single F-BSCH can carry one or more BSBS channels multiplexed in TDM fashion within the single F-BSCH. The term "HSBS channel" is used herein to mean a single logical HSBS broadcast session defined by the broadcast content of the session. Each session is defined by broadcast content that varies over time, e.g., 7-point-news, 8-point-weather, 9-point-movies, etc. Fig. 2 illustrates the above-described concept of physical and logical channels for an HSBS according to one embodiment.

As illustrated in fig. 2, the HSBS is provided on two F-BSCHs 202, each transmitting on a separate frequency fx, fy. Thus, for example, in the above-referenced cdma2000 communication system, such physical channels may include, for example, a forward supplemental channel (F-SCH), a forward broadcast control channel (F-BCCH), a forward common control channel (F-CCCH), other common and dedicated channels, and combinations of channels. The use of common and dedicated channels for information broadcast is disclosed in co-pending U.S. patent application No. 10/113,098 entitled "method and apparatus for channel management for point-and-multipoint services in a communication system", filed on 28/3/2002 and assigned to the assignee of the present invention. Those of ordinary skill in the art will appreciate that other communication systems use channels to perform similar functions; thus, the teachings of the present invention are applicable to other communication systems as well.

The F-BSCH 202 transmits broadcast traffic that may include one or more broadcast sessions. The F-BSCH1 carries two HSBS channels 204a, 204b multiplexed on the F-BSCH1202 a. The F-BSCH2202b carries one HSBS channel 204 c. The content of the HSBS channel is formatted into packets containing a payload 206 and a header 208.

Those of ordinary skill in the art will recognize that the steps of the HSBS broadcast service illustrated in fig. 2 are merely instructional. Thus, in a given sector, the HSBS broadcast service may be deployed in a number of ways depending on the features supported by the implementation of the particular communication system. These implementation features include, for example, the number of HSBS sessions supported, the number of frequency allocations, the number of broadcast physical channels supported, and other implementation features known to those skilled in the art. Thus, for example, more than two frequencies and the F-BSCH may be configured in a sector. Also, more than two HSBS channels may be multiplexed on one F-BSCH. Furthermore, a single HSBS channel may be multiplexed on more than one broadcast channel in a sector, on multiple different frequencies to serve subscribers residing in those frequencies.

As discussed, communication systems often transmit information in frames or blocks that are protected by encoding against adverse conditions affecting the communication channel. Examples of such systems include cdma2000, WCDMA, UMTS. As shown in fig. 3, an information bit stream 302 to be transmitted originating from higher layers is provided on the physical layer to an (inner) encoder 304. The encoder receives a block of information of length S bits. This block of S bits of information typically includes some additional overhead such as tail bits for the inner encoder, Cyclic Redundancy Check (CRC), and other additional overhead information known to those of ordinary skill in the art. This overhead bit helps the inner decoder at the receiving end to determine the success or failure of the decoding. The encoder then encodes the S bits with the selected code to produce an encoded information block of length P ═ S + R, where R is the number of redundant bits.

Those of ordinary skill in the art would appreciate that although the embodiments are described in the context of a hierarchical model, the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the physical layer may be implemented as electronic hardware, computer software, or combinations of both for instructional purposes. Thus, for example, the implementation or execution of inner encoder 304 may be as follows: a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

According to one embodiment, as shown in fig. 4, an information bit stream 402 to be transmitted is first encoded by an outer encoder 406, and the encoded information stream is then provided to an inner encoder (not shown) residing within a physical layer 408. The transmit buffer 404 is provided with a stream of information bits to be transmitted 402 originating from a higher layer. This transmit buffer is illustrated in more detail in fig. 5. Referring to fig. 5, the bits fill the systematic portion 504 of the transmit buffer 404 (of fig. 4) row by row from left to right. The system portion 504 includes k rows 508 of length L. In one embodiment, as shown in fig. 5, the length L of the buffer coincides with the length of the radio frame without additional overhead (e.g., CRC to aid the inner decoder and tail bits for the inner encoder). Returning to FIG. 4, once the systematic portion 504 (of FIG. 5) is filled, the outer block encoder 406 is activated to perform column-wise encoding of bits within the systematic portion 504 to generate (n-k) additional rows 510 (of FIG. 5) of parity bits (of FIG. 5). This column-wise operation is performed column-wise on the binary outer code, i.e. m is 1, where m is the dimension of the code. For non-binary coding, i.e., m > 1, every m adjacent columns within a row are treated as an m-bit symbol. The m-bit symbols along the top k rows are read by the outer encoder to produce n-k m-bit symbols that fill the corresponding lower n-k rows of the columns.

In another embodiment, the length L of the buffer is equal to the number of bits carried by the inner encoded frame divided by the dimension m encoded by the outer encoder. In this embodiment, the first m lines from the transmit buffer are sent in the first intra-coded frame and the second m bit lines are sent in the second intra-coded frame until the entire buffer is transferred. Returning to FIG. 4, once the systematic portion 504 (of FIG. 5) is filled, the outer block encoder 406 is activated to perform column-wise encoding of bits within the systematic portion 504 (of FIG. 5) to generate m (n-k) additional rows 510 of parity bits (of FIG. 5). This per-column operation is performed column by column for binary outer code, i.e., m is 1. For non-binary encoding, i.e., m > 1, every m rows of a column form an m-bit symbol. The outer encoder reads k symbols from the top k m rows in a column to produce (n-k) m-bit symbols that fill the corresponding lower m (n-k) rows of the column.

In one embodiment, the outer encoder comprises a systematic Reed-Solomon (R-S) encoder. The contents of the transmit buffer 404 are then provided to the physical layer 408. At the physical layer 408, the individual frames are encoded by an inner encoder (not shown), which results in encoded frames. The structure of the inner decoder may be, for example, the structure of fig. 3. The systematic rows and parity rows of the buffer may be interleaved during transmission, which may reduce the chance of a large number of systematic rows being erased when the total number of inner code erasures exceeds the outer code's correction capability. The frames are further processed according to the selected modulation scheme. In one embodiment, this processing IS performed in accordance with the IS-2000 standard. The processed frames are then transmitted over the communication channel 410.

The transmitted frames are received at the destination station and provided to physical layer 412. At the physical layer 412, the individual frames are demodulated and provided to an inner decoder (not shown). In one embodiment, the inner decoder decodes each frame and, if the decoding is successful, outputs a correctly decoded frame; or declare an erasure if the decode is unsuccessful. The success or failure of decoding must be determined with high accuracy. In one embodiment, this is achieved by including a long (e.g., 16-bit) Cyclic Redundancy Check (CRC) within the frame after outer encoding but before inner encoding. However, one of ordinary skill in the art recognizes that other mechanisms for frame quality indication may also be used. The incorporated CRC obtained from the decoded frame is compared to the CRC calculated from the decoded frame and if both CRCs are the same, a successful decode is declared. Further decoding at the physical layer proceeds in accordance with the results of the inner decoding decision.

The correctly decoded frame is provided to the appropriate line of the receive buffer 414. If all k frames of the system are decoded correctly by the inner decoder, the system frames from the system portion 414(1) of the receive buffer 414 are passed to higher layers (not shown) for further processing without outer decoding.

If the inner decoder is unable to decode the frame, the decoder declares an erasure and provides an indication to the outer block decoder 416 that the frame has been lost. This process continues until as many parity frames as erased systematic frames are correctly received and passed to the parity portion 414(2) of the receive buffer 414. The receiver stops receiving any remaining frames and an outer decoder (not shown) is activated to recover the erased frames. The recovered system frame is passed to the upper layer.

If the total number of correctly received frames in the receive buffer 414 is less than k, the outer decoder is not activated, in accordance with one embodiment of the present invention, because decoding success cannot be guaranteed. Correctly received systematic frames are passed to higher layers along with an identification of the missing bits. In another embodiment, the receiver uses the bits decoded from the inner decoder (which are unreliable as indicated by the failed CRC checks) to recover the bits for the systematic bits. According to one embodiment, the receiver decodes the unreliable bits from the inner decoder and finds the most likely codeword. In another embodiment, the receiver uses a measure of the signal quality of erased frames in the buffer to select enough erroneously received frames with the highest signal-to-noise ratio to form a sub-buffer with k rows. The receiver then performs a bit flip (changing the bit value 0 to the bit value 1 and vice versa at a row at a time) and checks whether the bit flip results in a codeword. In one embodiment, the bit flipping is performed first on the least reliable bits and is performed continuously in order of increasing reliability of the bits. The reliability of the bits may be determined in accordance with metrics of inner decoding such as the ratio of signal to noise and interference within a frame, yamamoto (yamamoto) metrics, re-encoded symbol error rate, re-encoded energy metrics, and other metrics known to one of ordinary skill in the art. If no codeword is found, the bit flipping continues in all remaining columns of all unreliable rows. If no codeword is found, the bit flipping continues with more bits being flipped (i.e., 2 bits at a time, then 3 bits until the maximum number of bits), 0 until a codeword is found or all combinations are exhausted. In another embodiment, the CRC from the unreliable rows is used to check the overall success of the decoding in this case. These frames are passed to the higher layer only if the CRCs from all rows match; otherwise, only bits from the reliable rows are passed to the higher layers.

In another embodiment, to improve the reliability of decoding, demodulation and inner decoding are performed for more than k correctly received frames in the buffer. In accordance with yet another embodiment, the demodulation and inner decoding are performed for all frames in the buffer. In both embodiments, the outer decoding is performed on the k (or km) line with the highest quality. The quality may be determined in accordance with inner decoding metrics such as the signal-to-noise-and-interference ratio within a frame, similar yamamoto metrics, re-encoded symbol error rate, re-encoded energy metrics, and other metrics known to those of ordinary skill in the art, or a combination of these metrics. The use of quality metrics for quality estimation is disclosed in detail in U.S. patent No. 5,751,725, entitled "method and apparatus for determining received data rate in a variable rate communication system" and U.S. patent No. 5,777,496, entitled "method and apparatus for determining data rate of transmitted variable rate data in a communication receiver", both of which are assigned to the assignee of the present invention.

Even in a broadcast communication system using outer coding and inner coding, a subscriber station may not be able to create a stream of information bits from a decoded received packet from a particular base station.

Fig. 6 shows an outer encoder 612 of a base station controller, inner encoders 622,632 of base stations 620,630, respectively, an inner decoder 642 of a subscriber station 640, and an outer decoder 648 of a subscriber station 640, in accordance with one embodiment. Those skilled in the art will appreciate that outer encoder 612 may be located elsewhere than at the base station controller.

Assuming that the outer encoder 612, which is an 1/2 rate encoder, is provided with a 1k stream of information bits, 2k bits are output from the outer encoder 612. In one embodiment, the 2k bits are broadcast to the base stations 620, 630. Assuming that the inner encoder 622 of the first base station (BS1)620 operates on frames of size 100 bits and is a rate 1/3 encoder, 300 bits are output for each data frame from the inner encoder 622. Assuming that the inner encoder 632 of the second base station (BS2)630 operates on frames of size 200 bits and is a 1/4 rate encoder, 800 bits are output for each data frame from the inner encoder 622. Those skilled in the art will appreciate that variable rate encoders and decoders may be used in embodiments.

The inner decoder 642 of the subscriber station 640 decodes the 300 bits from the first base station 620 and the 800 bits from the second base station 630 and outputs 100 inner decoded symbols representing the bits from the first base station 620 and 200 inner decoded symbols representing the bits of the second base station 630. Those skilled in the art will appreciate that these symbols may be any type of symbols known in the art. In one embodiment, these symbols are hard symbols as known in the art. In another embodiment, the symbols are soft symbols as known in the art. The hard symbol may take the value 0 or 1. Soft symbols indicate the likelihood of a received signal being 0 or 1 and generally take on a continuous value.

The subscriber station 640 includes a combiner 644 that combines the inner code decoded symbols from the first base station 620 and the second base station 630 and places the combined symbols into an outer decoder buffer 646. Those skilled in the art will appreciate that the combiner 644 may reside in either the inner decoder 642 or the outer decoder 648. Those skilled in the art will also appreciate that the combiner 644 can apply any combination scheme known in the art that improves the reliability of the corresponding bits by combining symbols.

The inner decoded symbols from the first base station 620 and the second base station 630 are combined according to their corresponding positions in the 2k information bit stream originally at the output of the outer encoder 612. For example, the first 100 symbols representing bits from the first base station 620 correspond to the first 100 bits of the 2k stream of information bits originally at the output of the outer encoder 612. Likewise, the first 200 symbols representing bits from the second base station 630 correspond to the first 200 bits of the 2k stream of information bits originally at the output of the outer encoder 612. Thus, the first 100 symbols representing bits from the first base station 620 are combined by the combiner in groups with the first 100 symbols of the 200 symbols representing bits from the second base station 630 described above. The combiner 644 then places the combined 100 symbols at the front end of the output decode buffer 646.

In one embodiment, a block of information is encoded at a control center, such as a BSC. The encoded symbols are then allocated to a plurality of base stations. Each base station may then transmit some or all of the encoded symbols.

In one embodiment, the BSC allocates all of the encoded signals to each base station. Then, each base station decides whether all or part of the symbols are to be transmitted based on its own available communication resources (power, Walsh code, duration), modulates the selected symbols and transmits them. In this case, there is no cooperation between the base stations.

In another embodiment, each base station periodically reports its available communication resources (power, walsh codes, duration) to the BSC. The BSC then decides which base station sends what portion of the encoded signal. The BSC operates to reduce the overlap of the parts transmitted by different base stations and to reduce the occurrence of the same encoded symbol being transmitted by multiple base stations. Thus, there is some cooperation between base stations. As a result of the cooperation, the effective code rate can be reduced.

In one embodiment, at the receiver, the subscriber station accounts how to combine symbols received from different base stations. From the F-PDCH information associated with the F-PDCH, the subscriber station can resolve how many binary symbols are transmitted from each base station. However, additional information is still required in order to combine symbols from different base stations.

In one embodiment, the rules indicating which base stations transmit which symbols are defined in advance. In one embodiment, each base station has a default starting point within each bit stream of symbols to be transmitted and the subscriber station knows the starting point. In another embodiment, the first base station always transmits symbols starting from the beginning of the bit stream, and the second base station always processes the bit stream from the end of the bit stream backwards and forwards.

In one embodiment, explicit signaling is used. Each base station signals to the subscriber station what symbols are being transmitted from the base station. The signaling may be a specification of a range of selection symbols. It will be apparent to those skilled in the art that there are other ways in which a subscriber station may be signaled to indicate what symbol is being transmitted from a base station.

Fig. 7 shows a representation of a combining process, in which only the combination of the first 100 symbols is shown. The 100 symbols representing the bits from the first base station 620 are combined with the 100 symbols of the 200 symbols representing the bits from the second base station 630 described above and the combined result is placed in the output decoder buffer 646. The 100 symbols representing the bits from the first base station 620 are denoted S1, i, the 100 symbols of the 200 symbols representing the bits from the second base station 630 are denoted S2, i, and the result of the combination put into the outer decoding buffer 646 is denoted Ci, where i is 1, 2. The "+" operator is defined as a combining function.

The combiner 644 performs a combining operation including a verification operation. The verify operation verifies each bit of data. The verification operation determines whether a particular bit of data has been inner decoded without error. If that particular bit of data has been inner decoded without error, then that bit is correct and can be combined.

When the hard symbols are combined, they may be combined based on a majority vote. In one embodiment, the hard symbols received from one base station but not the symbols corresponding to the same bits at the other base stations are used for outer decoding. In another embodiment, hard symbols corresponding to the same bit are received from a number of base stations, and a majority vote of the received hard symbols is used for outer decoding.

When soft symbols are combined, they can be combined to improve overall likelihood. In one embodiment, the combining method is additive logarithm probabilistic.

Once the symbols are combined and placed in outer decoder buffer 646, an outer decoder 648 decodes the combined symbols and uses the decoded results by subscriber station 640.

The combiner 644 has selection diversity if all outer-coded bits are sent to all base stations and all base stations transmit all outer-coded bits. Selection diversity means that the combiner can select symbols derived from a variety of, i.e., different, base stations and place them in an external decoding buffer.

If all outer-coded bits are transmitted to all base stations, the combiner 644 has not only selection diversity (if bits are transmitted from more than one base station, i.e., different base stations transmit different portions with overlapping outer-coded bits), but also code combining gain (code rate reduction and thus lower SNR requirements) when different base stations forward different portions of the outer-coded bits.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative logical blocks, modules, circuits, and algorithm steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in RAM memory, flash memory. ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Exemplary storage media read information from, and write information to, the storage media. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a subscriber unit. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

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

A portion of the disclosure of a patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the patent and trademark office patent file or records, but otherwise reserves all copyright rights whatsoever.

Claims (14)

1. A method of assembly comprising the steps of:

externally encoding a set of bits;

allocating a first subset of the outer-coded bits to a first station;

allocating a second subset of the outer-coded bits to a second station;

at the first station, inner-coding the first subset of outer-coded bits, thereby creating a first subset of inner-coded bits;

at the second station, inner-coding the second subset of outer-coded bits, thereby creating a second subset of inner-coded bits;

modulating the first subset of inner-coded bits, the modulating step creating a first subset of modulated inner-coded bits;

modulating the second subset of inner-coded bits, the modulating step creating a second subset of modulated inner-coded bits;

transmitting a first subset of the modulated intra-coded bits to a third station;

transmitting a second subset of the modulated intra-coded bits to a third station;

demodulating the first subset of modulated intra-coded bits, the demodulating step creating a demodulated first subset of bits;

demodulating a second subset of the modulated intra-coded bits, the demodulating step creating a demodulated second subset of bits;

inner decoding the modulated first subset of bits;

inner decoding the modulated second subset of bits; and

combining the inner decoded first subset of bits with the inner decoded second subset of bits, thereby creating a combined set of bits,

wherein the combining step includes a verifying operation that determines whether each bit of the data has been inner decoded without error and determines that a particular bit of the data is correct for combining if the particular bit of the data has been inner decoded without error.

2. The method of claim 1, further comprising outer decoding the combined set of bits.

3. The method of claim 1, wherein the first and second stations are base stations.

4. The method of claim 1, wherein the third station is a subscriber station.

5. The method of claim 1, wherein the combining step is performed based on an a priori rule indicating a first subset of bits and a second subset of bits.

6. The method of claim 1, wherein the combining step is performed based on signaling from the first station and the second station to the third station, wherein the signaling from the first station indicates the first subset of bits and the signaling from the second station indicates the second subset of bits.

7. The method of claim 1, wherein the first station transmits the first subset of modulated inner coded bits to the third station based on communication resources.

8. The method of claim 7, wherein the communication resource is power.

9. The method of claim 7, wherein the communication resource is a number of walsh codes available for transmission.

10. The method of claim 7, wherein the communication resource is an availability of transmission time.

11. The method of claim 1, further comprising: a first subset of modulated inner coded bits and a second subset of modulated inner coded bits are determined based on communication resources available to the first station and communication resources available to the second station.

12. The method of claim 1, further comprising: reporting communication resources available to the first and second stations to a fourth station, wherein the fourth station determines a first subset of modulated inner coded bits and a second subset of modulated inner coded bits.

13. The method of claim 11, wherein the transmitting step is over a forward data packet channel.

14. The method of claim 13, wherein the third station determines how many bits were transmitted from the first station based on information from the first station on a forward data packet control channel, and determines how many bits were transmitted from the second station based on information from the second station on the forward data packet control channel.