US20160323074A1 - Reverse link pilot integrated with block codes - Google Patents
Reverse link pilot integrated with block codes Download PDFInfo
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- US20160323074A1 US20160323074A1 US15/211,521 US201615211521A US2016323074A1 US 20160323074 A1 US20160323074 A1 US 20160323074A1 US 201615211521 A US201615211521 A US 201615211521A US 2016323074 A1 US2016323074 A1 US 2016323074A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
- H04L5/005—Allocation of pilot signals, i.e. of signals known to the receiver of common pilots, i.e. pilots destined for multiple users or terminals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
- H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
- H04B7/2628—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0041—Arrangements at the transmitter end
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0061—Error detection codes
- H04L1/0063—Single parity check
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0064—Concatenated codes
- H04L1/0065—Serial concatenated codes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0064—Concatenated codes
- H04L1/0066—Parallel concatenated codes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0071—Use of interleaving
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/183—Multiresolution systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
- H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
- H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
- H04B2201/70701—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation featuring pilot assisted reception
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
Abstract
A method and apparatus for encoding digital communication signals is described herein. A wireless communication unit may comprise a processor configured to produce first symbols derived from data bits and parity bits. The wireless communication unit may transmit a wireless signal including the first symbols and reference symbols in a time interval including a plurality of symbol time intervals. In one of the symbol time intervals a plurality of the reference symbols may be transmitted in a predetermined pattern, which may have the reference symbols not adjacent to each other. A base station may receive a wireless signal including first and reference symbols. In one of the symbol time intervals a plurality of the reference symbols may be received in a predetermined pattern. The base station may then demodulate the first symbols using the reference symbols, wherein the first symbols are derived from data bits and parity bits.
Description
- This application is a continuation of U.S. patent application Ser. No. 14/480,116, filed on Sep. 8, 2014, which is a continuation of U.S. patent application Ser. No. 13/311,151, filed Dec. 5, 2011, which issued as U.S. Pat. No. 8,830,977 on Sep. 9, 2014, which is a continuation of U.S. patent application No. Ser. 12/290,755, filed Nov. 3, 2008, which issued as U.S. Pat. No. 8,072,958 on Dec. 6, 2011, which is a continuation of U.S. patent application Ser. No. 10/874,101, filed Jun. 22, 2004, which issued as U.S. Pat. No. 7,447,187 on Nov. 4, 2008, which is a continuation of U.S. patent application Ser. No. 09/728,575, filed Nov. 30, 2000, which issued as U.S. Pat. No. 6,804,223 on Oct. 12, 2004, the contents of which are all hereby incorporated by reference herein.
- The present invention relates to communications systems and in particular to a scheme for digital encoding of signals in a wireless system.
- Demand for wireless communications equipment and services continue to grow at an unprecedented rate throughout the world. Increasingly, such systems are commonly relied upon to provide voice and data communications to a growing sector of the public. While these systems originally depended upon analog signaling technology, there is essentially unanimous agreement that future systems will be based on various types of digital signal coding schemes.
- The typical wireless communication system is a point to multi-point type system in which a central base station communicates with a number of remote units located within a local geographic area of coverage known as a cell. This system provides for duplex communication such that signals may be sent in both a forward direction (from the base station to the remote unit) as well as in a reverse direction (from the mobile remote unit back to the base station). In order to support communication between the remote unit and networks such as the Public Switched Telephone Network (PSTN), or data networks such as the Internet, the wireless system must also provide for various logical components and functional entities.
- Consider the Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) digital systems presently in widespread use. Each of these systems provides for certain logical types of the radio channels that make up the forward link and reverse link. In particular, the forward link channels often include a pilot channel, paging channels, and multiple forward traffic channels. The traffic channels are used to carry the payload data between the base station and the mobile unit. A pilot channel is also typically required to allow the remote unit to maintain synchronization with the base station. The paging channels provide a mechanism for the base station to inform the remote unit of control information, such as the assignment of forward traffic channels to particular connections and/or subscriber units.
- Likewise, an access channel is provided in the reverse direction in addition to reverse traffic channels. The access channels allow the remote units to communicate control information with the base station, such as to send messages indicating the need to allocate or deallocate connections as required.
- Various environmental conditions will affect the performance of any wireless communications system. These elements include atmospheric signal path loss, which may often introduce fading and interference. Fading may include variations that are introduced as a result of the specific terrain within the cell, as well as other types of fading, such as multi-path fading, that occurs due to signal reflections from specific features, such as buildings that cause fluctuations in receive signal strength. Systems in which the remote unit may be a mobile unit, especially those potentially operating at higher speeds, such as the cellular telephones used in automobiles, are particularly susceptible to multi-path fading. In such an environment, the signal pathways are continually changing at a rapid rate.
- Certain techniques can be used to attempt to eliminate the detrimental effects of signal fading. One common scheme is to employ special modulation and/or coding techniques to improve the performance in a fading environment. Coding schemes such as block or convolutional coding add additional parity bits at the transmitter. These coding schemes thus provide increased performance in noisy and/or fading environments at the expense of requiring greater bandwidth to send a given amount of information.
- In addition, pilot signals may also be used to provide a reference for use in signal demodulation. For example, most digital wireless communications systems provide for a dedicated pilot channel on the forward link. This permits the remote units to remain in time synchronization with the base station. Certain systems, such as the IS-95 CDMA system specification promulgated by the Telecommunications Industry Association (TIA) use the pilot signals that include pseudorandom binary sequences. The pilot signals from each base station in such a system typically use the identical pseudorandom binary sequence, with a unique time offset being assigned to each base station. The offsets provide the ability for the remote stations to identify a particular base station by determining this phase offset in the forward link pilot channel. This in turn permits the remote units to synchronize with their nearest neighboring base station. Coding the pilot channel in this way also helps support other features, such as soft handoff for cell-to-cell mobility.
- The pilot signal, having a predictable frequency and rate, allows the remote units to determine the radio channel transfer characteristics. By making such determinations, the receiver may in turn further compensate for the distortion introduced in the channel during the process of estimating symbols being received.
- However, it is generally considered to be impractical to use pilot signals in the reverse link. In particular, this would lead to a situation where pilot signal channels would have to be dedicated for each remote unit. While this would not necessarily pose a problem in a point to point system, in point to multi-point systems such as a cellular telephone network, the architecture would quickly lead to inefficiency in use of the available radio spectrum. In addition, it is generally thought that the overhead associated with a system that assigned individual pilot channels to each remote unit would unnecessarily complicate the base station receiver processing.
- An alternative to allocating individual pilot channels is to make use of a sequence of pilot symbols. The pilot symbols are interleaved with data symbols on the traffic channel. This technique is generally referred to as pilot symbol assisted modulation. In such a system, the transmitter encodes the data to be sent on the traffic channel as a series of symbols. A pilot symbol interleaver then inserts a sequence of predetermined pilot symbols within the data symbol sequence. The pilot symbol augmented sequence is then modulated and transmitted over the radio channel. At the receiving station, a decimeter or deinterleaver and filter separate the pilot symbols from the data symbols.
- What is needed is a way to integrate pilot symbol assisted modulation techniques with block encoding schemes in a way which maximizes the probability that data and pilot symbols will be correctly received.
- The invention accomplishes this with a pilot symbol insertion scheme that proceeds as follows. The source data bits are first augmented with periodically inserted pilot symbols. In a preferred embodiment, the pilot symbols are inserted at a position corresponding to a power of two, such as for example, every fourth, eighth, sixteenth, or thirty-second symbol. Next, this pilot symbol augmented data sequence is presented to a deterministic block coder. Such a block coder may, for example, be a sub-rate two dimensional turbo product coder.
- The symbols of the resulting encoded block are then rearranged such that the pilot symbols will be in a predictable location. Because the pilot symbols are always in a known place in the input block coding matrix, their positions are therefore also known in the output block coding matrix. The encoded output pilot symbols can therefore be rearranged such that they are evenly distributed through the output coded space, prior to modulation and transmission.
- An optional embodiment makes use of an interleaving scheme in which parity symbols are interleaved with data and pilot symbols. In such a scheme, all symbols from the coded space, with the exception of the pilot symbols, are placed in a temporary storage area by row. Data is then read out of the temporary storage area to provide the interleaved output, by reading data from the temporary array in column order. For example, a first pilot signal is selected, a row is read out, a second pilot signal is selected, a second row is read out, and so on. As a result, the pilot symbols are output at predetermined positions preferably located within symbol positions which are a power of two away from each other.
- In an alternate embodiment, the symbols may be composed of pairs of input data bits, to form complex -valved symbols, which can then be modulated using Quadrature Phase Shift Keyed (QPSK) schemes. In this embodiment, the data, parity, and pilot bits are processed in pairs.
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FIG. 1 is a block diagram of a communication system which encodes pilot symbols according to the invention; -
FIG. 2 is a more detailed diagram of a transmit encoder and receive decoder; -
FIGS. 3A and 3B illustrate how a deterministic block encoder, such as a one-quarter rate turbo product encoder, distributes data and parity bits in an output matrix; -
FIGS. 3C and 3D illustrate how the pilot inserter and block encoder operate according to the invention; -
FIG. 4A illustrates how a first type of interleaver outputs pilot, data, and parity bits; -
FIGS. 4B and 4C illustrate how a second type of interleaver may order the data, parity, and pilot bits; and -
FIG. 4D illustrates how a third type of interleaver may order data, parity and pilot bits for use with a Quadrature Phase Shift Keyed (QPSK) type modulator. - The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
- A description of preferred embodiments of the invention follows.
- While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
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FIG. 1 is a block diagram of acommunication system 10 that interleaves pilot symbols with data symbols and uses a systematic block coder to ensure that the pilot symbols are located in predetermined locations. In the following description of a preferred embodiment, thecommunication system 10 is described such that the shared channel resource is a wireless or radio channel. However, it should be understood that the techniques described here may be applied to allow shared access to other types of media such as telephone connections, computer network connections, cable connections, and other physical media to which access is granted on a demand driven basis. - The
communication system 10 includes a number of Personal Computer (PC) devices 12-1, 12-2, . . . 12-h, . . . 12-l, corresponding Subscriber Access Units (SAUs) 14-1, 14-2, . . . 14-h, . . . 14-l, and associated antennas 16-1, 16-2, . . . 16-h, . . . 16-l. Centrally located equipment includes abase station antenna 18, and a Base Station Processor (BSP) 20. TheBSP 20 provides connections to and from anInternet gateway 22, which in turn provides access to a data network such as theInternet 24, andnetwork file server 30 connected to thenetwork 22. Thesystem 10 is a demand access, point to multi-point wireless communication system such that thePCs 12 may transmit data to and receive data fromnetwork server 30 through bi-directional wireless connections implemented overforward links 40 andreverse links 50. It should be understood that in a point to multi-point multiple accesswireless communication system 10 as shown, a givenbase station processor 20 typically supports communication with a number of differentsubscriber access units 14 in a manner which is similar to a cellular telephone communication network. - The
PCs 12 may typically be laptop computers 12-l, handheld units 12-h, Internet-enabled cellular telephones or Personal Digital Assistant (PDA)-type computers. ThePCs 12 are each connected to arespective SAU 14 through a suitable wired connection such as an Ethernet-type connection. - An
SAU 14 permits its associatedPC 12 to be connected to thenetwork file server 30 through theBSP 20,gateway 22 andnetwork 24. In the reverse link direction, that is, for data traffic traveling from thePC 12 towards theserver 30, thePC 12 provides an Internet Protocol (IP) level packet to theSAU 14. TheSAU 14 then encapsulates the wired framing (i.e., Ethernet framing) with appropriate wireless connection framing. The appropriately formatted wireless data packet then travels over one of the radio channels that comprise thereverse link 50 through theantennas BSP 20 then extracts the radio link framing, reformatting the packet in IP form and forwards it through theInternet gateway 22. The packet is then routed through any number and/or any type of TCP/IP networks, such as theInternet 24, to its ultimate destination, such as thenetwork file server 30. - Data may also be transmitted from the
network file server 30 to thePCs 12 in a forward direction. In this instance, an Internet Protocol (IP) packet originating at thefile server 30 travels through theInternet 24 through theInternet gateway 22 arriving at theBSP 20. Appropriate wireless protocol framing is then added to the IP packet. The packet then travels through theantenna receiver SAU 14. The receivingSAU 14 decodes the wireless packet formatting, and forwards the packet to the intendedPC 12 which performs the IP layer processing. - A given
PC 12 and thefile server 30 can therefore be viewed as the end points of a duplex connection at the IP level. Once a connection is established, a user at thePC 12 may therefore transmit data to and receive data from thefile server 30. - The
reverse link 50 actually consists of a number of different types of logical and/or physical radio channels including anaccess channel 51, multiple traffic channels 52-1, . . . 52-t, and amaintenance channel 53. The reverselink access channel 51 is used by theSAUs 40 to send messages to theBSP 20 to request that traffic channels be granted to them. The assignedtraffic channels 52 then carry payload data from theSAU 14 to theBSP 20. It should be understood that a given IP layer connection may actually have more than onetraffic channel 52 assigned to it. In addition, amaintenance channel 53 may carry information such as synchronization and power control messages to further support transmission of information over thereverse link 50. - Similarly, the
forward link 40 typically includes apaging channel 41. Thepaging channel 41 is used by theBSP 20 to not only inform theSAU 14 that forwardlink traffic channels 52 have been allocated to it, but also to inform theSAU 14 of allocatedtraffic channels 52 in the reverse link direction. Traffic channels 42-1 . . . 42-t on theforward link 40 are then used to carry payload information from theBSP 20 to theSAUs 14. Additionally, maintenance channels carry synchronization and power control information on theforward link 40 from thebase station processor 20 to theSAUs 14. - In the preferred embodiment, the logical channels 41-43 and 51-53 are defined by assigning each channel a unique pseudorandom channel (PN) code. The
system 10 is therefore a so-called Code Division Multiple Access (CDMA) system in which channels assigned to unique codes may use the same radio carrier frequency. The channel may also be further divided or assigned. Additional information as to one possible way to implement thevarious channels - Turning attention now to
FIG. 2 there is shown a generalized block diagram of the encoding process at the transmit side and decoding process at the receive side according to the invention. It should be understood that the invention is implemented on thereverse link 50, so that thetransmitter 100 may typically be one of theSAUs 14 and the receiver is the Base Station Processor (BSP) 20. However, in other implementations it is possible for the invention to be applied on theforward link 40, in which case the transmitter is implemented in theBSP 20 and the receivers is theSAUs 14. - In any event, a
transmitter 100 is implemented with apilot inserter 110,block encoder 120,pilot interleaver 130,channel coder 140 and radio frequency (RF)modulator 150. Thereceiver 200 includes anRF demodulator 250,channel decoder 240,pilot deinterleaver 230,block decoder 220,pilot removal 210, andpilot reference generator 205. - It should be understood that the
receiver 200 performs the inverse functions of the corresponding portions of thetransmitter 100. In such an instance, theRF demodulator 250 performs the inverse radio frequency to modulation process, thechannel decoder 240 decodes the channel codes reversing the operation of thechannel coder 140, thepilot deinterleaver 230 performs the inverse function of thespecific pilot interleaver 130 implemented in the transmitter, and theblock decode process 220 also undoes the block encodeprocess 120. Thepilot removal process 210 uses a pilotreference signal generator 205, for example, to multiply the received data in pilot stream via reference pilot signal to further aid in the recovery of the data. Apilot inserter 110 typically makes sense in thereverse link 50 given and that pilot symbols are preferably inserted with the data symbols or bits in this same channel. This is opposed to an arrangement where there are separate pilot channels devoted separately for simply sending pilot signals, which is typically more practical on theforward link 40, in which case a single pilot channel can be associated with and be shared bynumerous SAUs 14. - Before discussing the details of the
pilot inserter 110 andblock encoder 120 in more detail, it is instructed to consider the operation of a typical error coding process. In particular, consider an example situation in the use of a turbo product code which is to encode data at the rate of ¼. (We assume in the discussion of this first embodiment that data is real-valued only such that a “symbol” is a single data bit, and discuss a situation with complex-valued data symbols later on.) In the case shown inFIG. 3A , the inputdata bits data 1, data2 . . . data16 may thought of as being placed in the upper left hand corner of a matrix encoding space. Because the code is a ¼ rate code, the matrix encoding space consists of a matrix which is four times the size of the input data matrix space. In the current example the input data matrix space is 4×4, and the coded space is a matrix of 8×8. - For a typical prior art block coding operation, that is one without supplementation with pilot symbols according to the invention, the 16 input data bits are placed in an upper left hand corner of the 8×8 encoded space as shown in
FIG. 3A . - The encoded matrix is then presented to the block encoder to calculate and create the parity bits for an encoded space. In the example being discussed, in the case of a ¼ rate code, three times as many parity bits as data bits are calculated and created as shown in
FIG. 3B . This type of systematic turbo product code, is considered to be deterministic in the sense that input data bits appear in the same position in the output matrix as they do in the input matrix, with all of the parity bits taking up the other spaces in the matrix. - Returning attention to
FIG. 2 , thepilot inserter 110 andblock encoder 120 can now be understood more particularly. In the pilot insertion scheme employed by thepilot inserter 110, some of the input data symbols are replaced with pilot symbols. In the preferred embodiment, the goal is to have pilot symbols make up approximately 6.25% of the data symbols sent on the channel after encoding. That means for every 64 channel symbols there needs to be 4 pilot symbols inserted into the information space. - Turning attention to
FIG. 3C , we see that in considering a group of 16 data symbols, 4 of the symbols will be replaced with pilot symbols such that the input matrix becomes as shown. Thus a pilot symbol, pilot1, is followed by three data symbols, data1, data2, data3. The next pilot symbol, pilot2, is followed by data symbols data4, data5, data6 and so on. - As in the case of the standard turbo product code, the matrix in
FIG. 3C is then presented to theblock encoder 120 to create the encoded space shown inFIG. 3D . The parity symbols of this example will, in fact, be different from those for the situation where the non-inserted information space because the information space has changed between the two examples. In particular, of course, the information space inFIG. 3C is different from the information space inFIG. 3A , and so the parity symbols parity1, parity2 . . . parity48 are different. What is important to note here is that the pilot symbols pilot1, pilot2, pilot3 and pilot4 are still in the same identifiable positions in the matrix. - It is the job of the
pilot interleaver 130 to rearrange the output matrix in such a manner that the pilot symbols are evenly distributed among the data and parity symbols in a manner which makes sense. In the simplest instance, the data and parity symbols can be placed on the channel in, more or less, the order in which they appear in the matrix. This situation is shown inFIG. 4A . In particular, it is noted that the pilot symbols pilot1, pilot2, pilot3 are redistributed through the matrix so that they are read out once every 16 bits, or 6.25% of the time, as desired. The matrix can thus be interpreted as a set of instructions for ordering the output bits, by reading along the first row, and then reading the bits out along the second row, and then also the third row, and so on. - In certain other instances it is important to interleave the parity symbols among the pilot and data symbols as well. In this situation, the parity symbols and data symbols can be better distributed throughout the information space. In this approach, all except the pilot symbols may be placed in a temporary storage area 180 in row order fashion and then read out by column order. The goal in allocating rows and columns in the temporary storage area 180 is to remain as square as possible. Thus, in the example illustrated shown in
FIG. 4B , the data and parity symbols are first read out from a first row of the coded output matrix inFIG. 4A , while saving the pilot symbols in another temporary storage area. The result is a matrix having the data1, data2, data3, parity1, parity2, parity3 . . . parity47, parity48 symbol arrangement as shown. Data is then read out of this temporary storage area 180 by reading out the non-pilot symbols in column order. Thus, for example, as shown inFIG. 4C , a first pilot symbol is read out of the pilot matrix, and then fifteen symbols are read from the non-pilot storage area (data1, parity4, parity7, parity10, and so on) resulting in the order of symbols shown in the first row ofFIG. 4C . This results not only in the pilot symbols continuing to be distributed once every 16 symbols, but also in a situation such that the data symbols are more evenly disbursed throughout the encoded space. - In yet another example of the implementation of the
interleaver 130, it may be advantageous to apply data to the channel with Quadrature Phase Shift Keyed (QPSK) format modulation. In this case, individual input data bits are read in pairs so that for example, 2 pilot bits are required to make up respectively the In-phase (I) and the Quadrature (Q) portion of a complex valued data symbol. In this case, pilot bits are also read out in pairs so that two pilot bits comprise a pilot symbol. The result, as shown inFIG. 4D , is a situation in which pilot symbols (consisting of a pilot1 and pilot2 bit) still appear every 16 symbols or 6.25% of the time. - Using the systematic block encoder, the position of the pilot, information, and parity symbols is always known in the output matrix. This creates a structure where pilot symbols can be repositioned in a known fashion, to ensure that they repeat in a regular pattern in the modulated output signal.
- For example, a system timing requirement may demand that the ratio of pilot symbols to the ratio of data and parity symbols remain at a power of two, so that clock phasing requirements are much easier to meet. In particular, even if a block encoder produces a number of data and parity symbols as a power of 2, the additional pilot symbol insertions would create an output sequence which is not an exact power of 2. This makes it difficult to insert pilot symbols in blocks which do not remain in phase, and therefore “roll” with respect to the PN sequences used with
respective channel encoding 140. For example, in a case where pilot symbols need to be inserted 6.25% of the time, a block of 4096 would require 4096 for data and parity, plus 6% of 4096, or 256 symbols for pilots for a total of 4352 symbols per block. Because no PN channel code is such a length, to maintain synchronization, the position of the PN code would change at the start of every symbol block. However, with the invention, this difficulty is avoided, and the output symbol blocks are easily contrived to be in groups of 2N, including both parity and pilot symbols. Thus, PN code synchronization timing, as required to maintain the proper spread spectrum characteristics, is easy.
Claims (15)
1. A wireless communication unit comprising:
a processor configured to produce first symbols derived from data bits and parity bits; and
a transmitter configured to transmit a wireless signal including the first symbols and reference symbols in a time interval including a plurality of symbol time intervals, wherein in one of the symbol time intervals a plurality of the reference symbols are transmitted in a predetermined pattern, wherein the predetermined pattern has the reference symbols not adjacent to each other.
2. The wireless communication unit of claim 1 , wherein the predetermined pattern has the reference symbols with a single space separating the reference symbols.
3. The wireless communication unit of claim 1 , wherein the reference symbols are pilot symbols.
4. The wireless communication unit of claim 1 , wherein the first symbols are quadrature modulated.
5. The wireless communication unit of claim 1 , wherein the first symbols are produced by turbo coding the data bits.
6. A method for use in a wireless communication unit, the method comprising:
producing first symbols derived from data bits and parity bits; and
transmitting a wireless signal including the first symbols and reference symbols in a time interval including a plurality of symbol time intervals, wherein in one of the symbol time intervals a plurality of the reference symbols are transmitted in a predetermined pattern, wherein the predetermined pattern has the reference symbols not adjacent to each other.
7. The method of claim 6 , wherein the predetermined pattern has the reference symbols with a single space separating the reference symbols.
8. The method of claim 6 , wherein the reference symbols are pilot symbols.
9. The method of claim 6 , wherein the first symbols are quadrature modulated.
10. The method of claim 6 , wherein the first symbols are produced by turbo coding the data bits.
11. A base station comprising:
a receiver configured to receive a wireless signal, wherein the wireless signal includes first and reference symbols in a time interval including a plurality of symbol time intervals, wherein in one of the symbol time intervals a plurality of the reference symbols are received in a predetermined pattern, wherein the predetermined pattern has the reference symbols not adjacent to each other; and
a processor configured to demodulate the first symbols using the reference symbols, wherein the first symbols are derived from data bits and parity bits.
12. The base station of claim 11 , wherein the predetermined pattern has the reference symbols with a single space separating the reference symbols.
13. The base station of claim 11 , wherein the reference symbols are pilot symbols.
14. The base station of claim 11 , wherein the first symbols are quadrature modulated.
15. The base station of claim 11 , wherein the first symbols are produced by turbo coding the data bits.
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US15/211,521 US20160323074A1 (en) | 2000-11-30 | 2016-07-15 | Reverse link pilot integrated with block codes |
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US20020064182A1 (en) | 2002-05-30 |
US20120087364A1 (en) | 2012-04-12 |
US6804223B2 (en) | 2004-10-12 |
US20140376539A1 (en) | 2014-12-25 |
US9397808B2 (en) | 2016-07-19 |
US7447187B2 (en) | 2008-11-04 |
US8830977B2 (en) | 2014-09-09 |
US20090116469A1 (en) | 2009-05-07 |
US20040223514A1 (en) | 2004-11-11 |
US8072958B2 (en) | 2011-12-06 |
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