US 20070253467 A1
Techniques and apparatus for identifying the target mobile stations for data transmission in a wireless communication network.
1. A method for increasing the number of MACIndex, which is used for identifying mobile stations in a wireless communication system, the method comprising:
generating a first N-symbol bi-orthogonal sequence from Walsh functions based on a first portion of the MACIndex;
applying the first N-symbol bi-orthogonal sequence to one of an In-phase branch and an Quadrature branch channel of a complex signal meanwhile grounding the other branch according to a mean that is based on the second portion of the MACIndex; and
time-multiplexing the complex preamble signal with the data, pilot, and MAC portion in a slot.
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6. A method as in
generating the second N-symbol sequence based on the second portion of the MACIndex;
applying symbols of the first N-symbol bi-orthogonal sequence, whose corresponding symbol of the second N-symbol sequence is the first value, to the In-phase branch; and
applying symbols of the first N-symbol bi-orthogonal sequence, whose corresponding symbol of the second N-symbol sequence is the second value, to the Quadrature branch.
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generating the second N-symbol sequence based on the second portion of the MACIndex;
generating the third N-symbol sequence by taking the complementary value of the second N-symbol sequence symbol-by-symbol;
multiplying the first N-symbol bi-orthogonal sequence with the third N-symbol sequence to produce the fourth N-symbol sequence;
applying the fourth N-symbol sequence to, the In-phase branch;
multiplying the first N-symbol bi-orthogonal sequence with the second N-symbol sequence to produce the fifth N-symbol sequence; and
applying the fifth N-symbol sequence to the Quadrature branch.
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12. An apparatus for generating the preamble within a wireless communication system, comprising:
mapping elements configured to receive a sequence of bits and to output a sequence of symbols +1, −1 accordingly;
a memory of bi-orthogonal sequences specified in terms of the N-ary Walsh functions and respective bit-by-bit complements;
covering elements configured to spread the outputs of the mapping elements with different bi-orthogonal sequences;
repetition elements configured to repeat the outputs of the covering elements according to the preamble length; and
a switching element to switch the output of the repetition element onto one branch of the in-phase branch and quadrature branch of the carrier.
13. An apparatus as in
14. An apparatus as in
15. An apparatus as in
16. An apparatus as in
17. An apparatus as in
18. A method for the mobile station to detect its MACIndex, the method comprising:
reconstructing the received first N-symbol bi-orthogonal sequence from the received I-Branch or Q-Branch signal according to the symbol-by-symbol switching pattern that the base station is expected to use to applied the first N-symbol bi-orthogonal sequence to the I-Branch or Q-Branch;
generating the sixth N-symbol bi-orthogonal sequence from the first portion of the expected MACIndex;
de-spreading the reconstructed first N-symbol bi-orthogonal sequence with the sixth N-symbol bi-orthogonal sequence;
estimating the power of the de-spread signal;
estimating the noise variance;
calculating the signal-to-noise ratio of the received preamble signal; and
comparing the signal-to-noise ratio with a threshold to determine the detection result.
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This application claims the benefit of U.S. Provisional Application No. 60/713,177 entitled PREAMBLE FOR IDENTIFYING MOBILE STATIONS IN A WIRELESS COMMUNICATION NETWORK and filed on Aug. 30, 2005.
This application relates to wireless communication networks.
Wireless communication systems provide voice or data services to a plurality of wireless or mobile stations situated within a geographic region by dividing the region into a number of cells, conceptually represented by a hexagon in a honeycomb pattern. In practice, however, each cell may have an irregular shape, depending on various factors including the terrain surrounding the cell and traffic density. Each cell may be further divided into two or more sectors. Each cell contains system communication equipment such as a base station that transmits communication signals to the mobile stations on the forward link and receives communication signals from the mobile stations on the reverse link.
One exemplary wireless communication system designed for high speed packet data services is 1xEV-DO, which is also known as High Date Rate (HDR) or High Rate Packet Data (HRPD) system. 1xEV-DO has been standardized as C.S0024 in the international standard group Third Generation Project Partnership Two (3GPP2) and has been published as IS-856 Revision 0 and Revision A standards in the United States.
In 1xEV-DO system, a mobile station, which is also known as the access terminal or AT, determines and reports the data rate that can be supported on the forward link in the Data Rate Control (DRC) message. The base station, which is also known as the access network or AN, selects one Physical Layer packet for forward link transmission at a particular time slot, based on the DRC messages received from various mobile stations. The Physical Layer packet may be given more than one time slot for transmission. In this case, the transmit slots of a Physical Layer packet are separated by three intervening slots, during which the slots of other Physical Layer packets can be transmitted. If a positive acknowledgement (ACK) is received on the reverse link ACK Channel before all of the allocated slots have been transmitted, the remaining un-transmitted slots will not be transmitted and the next allocated slot may be used for the first slot of a new Physical Layer packet transmission. This technique is known as Hybrid Automatic Repeat Request (HARQ).
In a 1xEV-DO system, in order to identify the target mobile station of the forward data packet, the base station transmits a preamble on the I-branch, which is the in-phase branch of the complex signal, before the data packet. Meanwhile, no signals are transmitted on the Q-branch, which is the quadrature branch of the complex signal. The preamble contains the repetition of 32-chip bio-orthogonal sequence as in IS-856 Revision 0 standard, or repetition of 64-chip bio-orthogonal sequence as in IS-856 Revision A standard. The 32-chip bi-orthogonal sequence is defined in terms of the 32-ary Walsh functions and their bit-by-bit complements by
where i=0, 1, . . . , 63 is the MACIndex value and
where i=0, 1, . . . , 127 is the MACIndex value and
where N is a power of 2, HN denotes the Hadamard sequences with a length of N,
where WN denotes the Walsh functions with a length of N. Therefore, IS-856 Revision A standard doubles the MACIndex numbers while supporting the legacy mobile stations that comply with the IS-856 Revision 0 standard in an IS-856 Revision A network. The length of the preamble is variable from 64 chips to 1024 chips, depending on the data packet format. A maximum of 128 MACIndex values can be supported in an IS-856 Revision A system.
As 1xEV-DO evolves to provide broadband services, particularly with a multi-carrier based solution, the system may need to support more than 128 mobile stations for each sector. The industry is currently investigating methods that can increase the MACIndex numbers while maintaining backward compatibility in such a way that the legacy mobile stations can be supported in the same upgraded system.
This application describes, among others, techniques and apparatus for identifying target mobile stations for transmission of data packets in a wireless communication system.
In one aspect, a method for increasing the number of MACIndex for identifying mobile stations in a wireless communication system can include: generating a 64-symbol bi-orthogonal sequence from the Walsh functions based on the first portion of the MACIndex; repeating the 64-symbol bi-orthogonal sequence according to the preamble length; applying the repetition of the 64-symbol bi-orthogonal sequence to one of the In-phase branch and Quadrature branch on the complex signal meanwhile grounding the other branch, symbol-by-symbol according to a particular pattern that is determined by the second portion of the MACIndex; time-multiplexing the complex preamble signal with the data, pilot, and MAC portion in a slot.
In some implementations, the switching between I-Branch and Q-Branch can be implemented before the repetition or after the repetition.
In other implementations, the switching between I-Branch and Q-Branch can be implemented as a switch that is controlled by a binary bit sequence, or as a puncturing element that is controlled by a binary bit sequence, or as a multiplier that multiplies with a binary bit sequence. The binary bit sequence is determined by the second portion of the MACIndex.
When backward compatibility is desirable, the switching pattern can be restricted for preamble that is target for the legacy mobile stations such that all the preamble symbols are applied on the I-Branch, meanwhile the Q-branch is grounded.
In yet another aspect, an apparatus for generating the preamble within a wireless communication system is presented. One example of this apparatus can include mapping elements configured to receive a sequence of bits and output a sequence of symbols +1, −1 accordingly; a memory of bi-orthogonal sequences specified in terms of the 64-ary Walsh functions and their bit-by-bit complements; covering elements configured to spread the outputs of the mapping elements with different bio-orthogonal sequences; repetition elements configured to repeat the outputs of the covering elements according to the preamble length; a switching element configured to apply the output of the repetition element onto one branch of the in-phase branch or quadrature branch of the carrier while simultaneously grounding the other branch according to certain pattern that is determined by the second portion of the MACIndex.
Variations of realization of such an apparatus include, for example, changing the locations of repetition element and the switching element. Variations of realization of such an apparatus also include implementing the switching element as a switch that is controlled by a binary bit sequence, or as a puncturing element that is controlled by a binary bit sequence, or as a multiplier that multiplies with a binary bit sequence. The binary bit sequence is determined by the second portion of the MACIndex.
In yet another aspect, a method is described for the mobile station to reconstruct the 64-symbol sequence from the received I-Branch or Q-Branch, symbol-by-symbol according to the same pattern that the base station uses to applied the preamble symbols to the I-Branch or Q-Branch, and to further calculate the signal-to-noise ratio of the received preamble signal in order to determine the detection result.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the invention will become apparent from the description, the drawings, and the claims.
For clarity, several exemplary realizations are described herein using 10-bit B9B8B7B6B5B4B3B2B1B0 representation of MACIndex to illustrate the techniques that increase the number of MACIndex values to 1024. More or less MACIndex numbers can be represented with more or less bits.
In one implementation, the 64-bit sequence can be generated by using the most significant bits B9B8B7 of MACIndex to select a row or column index number of HN in equation (5). Table 1 below lists one example of such selection rules.
In another implementation, the 64-bit sequence can be generated by using the most significant bits B9B8 of MACIndex to select a row or column index number of HN in equation (5) and using the bit B7 of MACIndex to determine whether bit-by-bit complements of HN should be used as the 64-bit sequence. Table 2 below lists one example of such selection rules.
The complex preamble signal from the output of switch 308 is then time-division multiplexed (TDM) by multiplexer 320 with the complex signals of Data 140 modulation symbols, Pilot 120 symbols, and MAC 130 symbols, as illustrated in
Table 1 and Table 2 are provided only as examples for mapping B9B8B7 to the 64-bit Sequence that controls the switch 308. Other mapping rules can also be implemented. However, to ensure backward compatibility, when B9B8B7=000 a 64-bit sequence of all 0 shall be applied to the switch 308 such that all the symbols of the legacy preamble are applied on the I-branch only, meanwhile the Q-branch is grounded.
The complex preamble signal formed with the outputs from multiplier 508 on the I-branch and with the outputs from multiplier 510 on the Q-branch is then time-division multiplexed (TDM) by multiplexer 520 with the complex signals of Data 140 modulation symbols, Pilot 120 symbols, and MAC 130 symbols, as illustrated in
The multipliers 508, 510, 606, and 608 can also be implemented as puncturing elements, wherein a bit of 0 will puncture the corresponding bi-polar symbol into zero value or zero power, and a bit of 1 will let the corresponding bi-polar symbol go through with full power.
Thus a method is provided to expand the MACIndex numbers by applying the repetition of the 64-symbol bi-orthogonal sequence to the In-phase branch or Quadrature branch on the complex signal symbol-by-symbol according to a particular pattern that is determined by the most significant bits of the MACIndex, e.g. B9B8B7 in the examples illustrated above, wherein the 64-symbol bi-orthogonal sequence is determined by the least significant bits B6B5B4B3B2B1B0 of the MACIndex. For legacy mobile stations, whose B9B8B7 of MACIndex will be 000 be default, the pattern will be restrict such as all the preamble symbols will be applied on the I-Branch, meanwhile the Q-branch will be grounded.
A new mobile station, after being assigned a MACIndex via channel assignment message, can understand by what pattern the base station will apply the preamble that is target for him, symbol-by-symbol on the I-Branch or Q-branch. Therefore, after the quantization, dispreading, and channel-compensation for the received preamble signal, the mobile station reconstructs the received 64-symbol bi-orthogonal sequence following the same pattern that is determined by the most significant bits B9B8B7 of MACIndex. Then the mobile station despreads the received 64-symbol bi-orthogonal sequence with the bio-orthogonal cover that is generated from the seven least significant bits B6B5B4B3B2B1B0 of its MACIndex and estimates the despread signal power. The mobile station further estimates the noise variance with the same symbol-by-symbol pattern over the I-branch or Q-branch. Then the mobile station calculates the preamble Signal-to-Noise Ratio (SNR) by dividing the estimated despread signal power by the estimated noise variance. The mobile station further determines whether the Preamble SNR is greater than the threshold. If it is greater than the threshold, the mobile station concludes that the Preamble is detected. If it is less than the threshold, the mobile station concludes that the Preamble is not detected.
Hadamard codes in Equation (5) are used in various examples described in this specification. Hadamard codes have perfect orthogonality with respect to one another and thus are beneficial in implementing the present techniques. Other alternative codes can also be used, such as pseudo-noise (PN) codes or complementary codes, as long as good correlation properties hold among the different codes.
The expanded bits B9B8B7 of MACIndex may be implemented as a separated Preamble Pattern field instead of a part of the MACIndex in the implementation.
The various illustrative logical blocks, modules, and circuits described in connection with the embodiment 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.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be implemented or performed directly in hardware, in a software module executed by a processor, or in combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, or any other form of storage medium in the art.
The disclosed and other embodiments and the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term data processing apparatus encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.
A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.
The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).
Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data.
While this specification contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a particular order, this should not be understand as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.
Thus, particular embodiments have been described. Other embodiments are within the scope of the following claims.