CN101137233B

CN101137233B - Preamble code for identifying mobile stations in a wireless communication network

Info

Publication number: CN101137233B
Application number: CN2007101401201A
Authority: CN
Inventors: 杨云松
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2006-08-30
Filing date: 2007-08-06
Publication date: 2010-11-17
Anticipated expiration: 2027-08-06
Also published as: CN101137233A

Abstract

Techniques and apparatus for identifying the target mobile stations for data transmission in a wireless communication network.

Description

Preamble for identifying mobile stations in a wireless communication network

Technical Field

The present application relates to wireless communication networks.

Background

A wireless communication system provides voice or data services to a plurality of wireless or mobile stations located in a geographical area by dividing the area into a plurality of cells, wherein the cells are conceptually represented by hexagons in the form of cells. However, in practice, each cell may have an irregular shape depending on a number of factors including the terrain around the cell and the traffic density. Each cell may be further divided into two or more sectors. Each cell includes system communication equipment, such as a base station, which transmits communication signals to and receives communication signals from mobile stations on the forward link.

One exemplary wireless communication system designed for High-Rate Packet Data services is 1xEV-DO, which is also known as a High Data Rate (HDR) or High Rate Packet Data (HRPD) system. 1xEV-DO has been standardized in International standards group third Generation partnership project two (3GPP2) as C.S0024 and published in the United states as the IS-856 revision 0 and revision A standards.

In a 1xEV-DO system, a mobile station, also referred to as an access terminal or AT, determines and reports the Data Rate that can be supported on the forward link in a Data Rate Control (DRC) message. Based on DRC messages received from different mobile stations, a base station, also referred to as a visited network or AN, selects one physical layer packet for forward link transmission at a particular time slot. More than one slot may be given to the physical layer packet for transmission. In this case, the transmission slots of a physical layer packet are separated by three intervening slots during which the slots of other physical layer packets may be transmitted. If an Acknowledgement (ACK) is received on the reverse link ACK channel before all allocated slots have been transmitted, the remaining untransmitted slots will not be transmitted and the next allocated slot may be used as the first slot for a new physical layer packet transmission. This technique is called Hybrid Automatic Repeat Request (HARQ).

In a 1xEV-DO system, to identify the target mobile station of a 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. At the same time, no signal is transmitted on the Q-branch, which is the quadrature branch of the complex signal. The preamble includes a repetition of a 32-chip biorthogonal sequence as in the IS-856 revision 0 standard, or a repetition of a 64-chip biorthogonal sequence as in the IS-856 revision a standard. The 32-chip biorthogonal sequence is determined from a 32-ary (ary) Walsh function and its bitwise complement:

W_i/2 ³²wherein i ═ 0, 2, ·, 62, (1)

Wherein i ═ 1, 3, ·, 63, (2)

Wherein i ═ 0, 1,. and 63 are MACIndex values, and

Figure S071E0120120070815D00002175553QIETU

is the bit-wise complement of the 32-chip Walsh function of sequence i. The MACIndex is a number assigned by the base station to identify the mobile stations in the system. Some MACIndex values are used as common values for all mobile stations,to identify control channels, broadcast, or multi-user packet transmissions. The 64-chip biorthogonal sequence is determined from the 64-ary Walsh function and its bit-wise complement:

W_i/2 ⁶⁴wherein i ═ 0, 2, ·, 126, (3)

Wherein i ═ 1, 3, ·, 127, (4)

Wherein i ═ 0, 1,. and 127 are MACIndex values, andis the bit-wise complement of the 64-chip Walsh function of sequence i. Since the Walsh function can be generated by the following recursive procedure (recursive procedure), the repetition of the 32-chip biorthogonal sequence is a subset of the 64-chip biorthogonal sequence:

H₁＝0，

H_{2} = \begin{matrix} 0 & 0 \\ 0 & 1 \end{matrix},

H_{4} = \begin{matrix} 0 & 0 & 0 & 0 \\ 0 & 1 & 0 & 1 \\ 0 & 0 & 1 & 1 \\ 0 & 1 & 1 & 0 \end{matrix},

<math> <mrow> <msub> <mi>H</mi> <msup> <mn>2</mn> <mi>N</mi> </msup> </msub> <mo>=</mo> <mrow> <mfenced open='' close='' separators=''> <mtable> <mtr> <mtd> <msub> <mi>H</mi> <mi>N</mi> </msub> </mtd> <mtd> <msub> <mi>H</mi> <mi>N</mi> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>H</mi> <mi>N</mi> </msub> </mtd> <mtd> <msub> <mover> <mi>H</mi> <mo>&OverBar;</mo> </mover> <mi>N</mi> </msub> </mtd> </mtr> </mtable> </mfenced> <mo>,</mo> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>5</mn> <mo>)</mo> </mrow> </mrow> </mrow></math>

where N is a power of 2, H_NRepresenting a Hadamard sequence of length N,

represents H_NAnd the bit-by-bit complementation is carried out. Additionally, in the IS-856 standard, a Walsh function IS generated by mapping a binary bit (e.g., "0" or "1") of a Hadamard sequence to a bipolar symbol +1 or-1 as follows:

W^N＝1-2H_N (6)

wherein, W^NRepresenting a Walsh function of length N. Thus, the IS-856 revision A standard doubles the number of the MACIndex when legacy mobile stations that conform to the IS-856 revision 0 standard are supported in an IS-856 revision A network. The length of the preamble may vary from 64 chips to 1024 chips depending on the format of the packet. The maximum of 128 MACIndex values can be supported in the IS-856 revision A system.

The development of 1xEV-DO provides broadband services and, in particular, multi-carrier based solutions, the system may require more than 128 mobile stations to be supported per zone. The industry is currently investigating a method that can add MACIndex numbers while maintaining backward compatibility to support legacy mobile stations in the same upgraded system.

Disclosure of Invention

This application describes, among other things, techniques and apparatus for identifying a target mobile station for data packet transmission in a wireless communication system.

According to one aspect, a method for increasing a number for identifying a MACIndex of a mobile station in a wireless communication system may include: generating a 64-symbol (64-symbol) biorthogonal sequence according to a Walsh function based on the first part of the MACIndex; repeating the 64-symbol biorthogonal sequence according to the length of the preamble; applying a repetition of a 64-symbol biorthogonal sequence to one of the in-phase and quadrature branches on the complex signal, symbol by symbol, while grounding the other branch, according to a specific pattern determined by the second part of the MACIndex; the complex preamble signal is time division multiplexed with data, pilot (pilot), and MAC portions in the slot.

In some embodiments, switching between the I-branch and the Q-branch may be performed before or after the repetition.

In other embodiments, the switching between the I-branch and the Q-branch may be implemented as a switch controlled by a sequence of binary bits, or as a puncturing element controlled by a sequence of binary bits, or as a multiplier that multiplies a sequence of binary bits. The sequence of binary bits is determined by the second part of the MACIndex.

When backward compatibility is required, the switching pattern can be limited to the preamble targeted by legacy mobile stations to apply all preamble symbols to the I-branch while grounding the Q-branch.

According to another aspect, an apparatus for generating a preamble in a wireless communication system is provided. An example of the apparatus may include: a mapping element configured to receive a sequence of bits and to output a sequence of symbols +1, -1 accordingly; a memory for complementing the assigned biorthogonal sequences bit by bit according to the 64-ary Walsh function; a masking element (coverage element) configured to spread the output of the mapping element with different biorthogonal sequences; a repetition element configured to repeat an output of the mask element according to a length of the preamble; a switching element configured to apply the output of the repeating element to one of the in-phase branch or the quadrature branch of the carrier while grounding the other branch according to a certain pattern determined by the second part of the MACIndex.

For example, various implementations of such devices include changing the position of the repeating elements and switching elements. Various implementations of such a device also include implementing the switching elements as switches controlled by the binary bit sequence, or as puncturing elements controlled by the binary bit sequence, or as multipliers with which the binary bit sequence is multiplied. The sequence of binary bits is determined by the second part of the MACIndex.

According to yet another aspect, a method is described for a mobile station to repair (reconstruct) a 64-symbol sequence from a received I-branch or Q-branch according to the same manner, the base station using the above manner to apply preamble symbols to the I-branch or Q-branch and further calculating a signal-to-noise ratio of the received preamble signal to determine a 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.

Drawings

FIG. 1 is a diagram of a forward link slot structure in a 1xEV-DO system;

FIG. 2 is a schematic diagram showing circuitry for generating a preamble structure in an existing 1xEV-DO system;

fig. 3 is a diagram of one example of a circuit for generating a preamble structure according to a first embodiment of the present invention;

FIG. 3A shows an example for symbols on the I-branch and the Q-branch in a 10-bit sequence based on an existing switch between the I-branch and the Q-branch;

fig. 4 is a diagram of an example of a circuit for generating a preamble structure according to a second embodiment of the present invention;

fig. 5 is a diagram of an example of a circuit for generating a preamble structure according to a third embodiment of the present invention; and

fig. 6 is a diagram of an example of a circuit for generating a preamble structure according to a fourth embodiment of the present invention.

Detailed Description

FIG. 1 shows a slot structure in a 1xEV-DO system. In each slot, the preamble 110, pilot 120 symbols, Medium Access Control (MAC)130 symbols, and data 140 symbols for the first slot transmission of each data packet are time division multiplexed and transmitted at the same power level (level).

Fig. 2 illustrates circuitry for generating a preamble structure in an existing 1xEV-DO system. The circuit is used for a transmission part of a base station. The preamble consists of all- "0" symbols. Signal point mapping 210 maps an all- "0" symbol to a "+ 1" sequence. The sequence is then spread with a 64-chip bio-orthogonal cover by multiplier 220. The sequence repeater 230 generates repetition of the biorthogonal mask sequence with repetition coefficients of 1 to 16 according to the length of the preamble. The preamble signal is then applied to the I-branch while the Q-branch is switched off. Then, as shown in fig. 1, signals of the data 140 modulation symbols, the pilot 120 symbols, and the MAC130 symbols are Time Division Multiplexed (TDM) by the multiplexer 240. The time division multiplexed signal is further spread by a despreader 250, filtered by baseband filters 260, 262, and modulated by modulators 270, 272, respectively, with an in-phase cosine curve cos (W)_ct) and an orthogonal sinusoid sin (W)_ct) is modulated onto the carrier frequency. The modulated I-branch and Q-branch signals are added by adder 280 to generate waveform s (t) to be transmitted.

For clarity, the 10-position B of MACIndex is utilized herein₉B₈B₇B₆B₅B₄B₃B₂B₁B₀The notation is used to describe several exemplary implementations to illustrate techniques for increasing the number of MACIndex values to 1024. How many of the MACIndex numbers can be expressed in terms of how many bits.

Fig. 3 illustrates a method for generating a preamble in a base stationAn embodiment of a circuit of the channel structure of (1). The preamble sequence consists of all- "0" symbols. Signal point mapping element 302 maps an all- "0" symbol to a "+ 1" sequence. The output sequence is spread with a 64-chip biorthogonal mask by multiplier 304. From the seven least significant bits B of the MACIndex according to equations (3) and (4)₆B₅B₄B₃B₂B₁B₀Generating a 64-chip biorthogonal mask on the preamble, wherein the sequence i is B of MACIndex₆B₅B₄B₃B₂B₁B₀The value of (c). The sequence repeater 306 generates repetition of the biorthogonal mask sequence with a repetition factor of 1 to 16 according to the length of the preamble. Then, a double-pole double-throw switch (double-pole double-throw switch)308 is based on the most significant bit B according to MACIndex₉B₈B₇The resulting bit values of the 64-bit sequence, the output sequence of sequence repeater 306 is applied to the in-phase branch (I-branch) or the quadrature branch (Q-branch) bit by bit. The 64-bit sequence is adjusted and synchronized with each repetition of the 64-symbol biorthogonal sequence from sequence repeater 306. When a particular bit of the 64-bit sequence is "0", the corresponding symbol of the output sequence from sequence repeater 306 is applied to the I-branch, while the Q-branch is tied to zero or ground. When a particular bit of the 64-bit sequence is "1", the corresponding symbol of the output sequence from sequence repeater 306 is applied to the Q-branch, while the I-branch is tied to zero or ground.

Fig. 3A further shows an example of symbols on the I-branch and the Q-branch in a 10-bit sequence based on an existing switch between the I-branch and the Q-branch.

In one embodiment, the most significant bit B of the MACIndex can be used₉B₈B₇Generating a 64-bit sequence to select H in equation (5)_NRow or column index number. Table 1 below lists one example of such a selection rule.

TABLE 1

In another embodiment, the most significant bit B of the MACIndex can be used₉B₈Generating a 64-bit sequence to select H in equation (5)_NAnd uses bit B of the MACIndex₇To determine whether H should be replaced_NThe bit-wise complement of (a) is used as the 64-bit sequence. Table 2 below lists one example of such a selection rule.

TABLE 2

Wherein,

represents H_NAnd the bit-by-bit complementation is carried out.

Then, as shown in fig. 1, the composite preamble signal from the output of the switch 308 is time division multiplexed with the complex signal of the data 140 modulation symbol, the pilot 120 symbol, and the MAC130 symbol by the multiplexer 320. As shown in fig. 2, the time-division multiplexed signal is further spread by a complex spreader 250, filtered by baseband filters 260 and 262, and modulated onto a carrier frequency by modulators 270 and 272, and added by an adder 280 to generate a waveform s (t) to be transmitted.

Tables 1 and 2 are provided only as examples for B₉B₈B₇Mapped as an example of a 64-bit sequence that controls the switch 308. Other mapping rules may also be implemented. However, to ensure backward compatibility, when B₉B₈B₇A sequence of 64-bits of all "0" would be "000Is applied to switch 308 to apply all symbols of the legacy preamble to only the I-branch while grounding the Q-branch.

Fig. 4 shows a similar but different implementation as the structure of the preamble channel. First, the output sequence from the multiplier 404 is switched symbol-by-symbol on the I-branch or the Q-branch by a switch 406 controlled by a 64-bit sequence, and then the signals on the I-branch and the Q-branch are repeated by

sequence repeaters

408 and 410, respectively, according to the length of the preamble. The 64-bit sequence for control switch 406 in fig. 4 is generated in the same manner as described above and shown in table 1 or table 2.

Fig. 5 shows another different implementation of a preamble channel structure. The output sequence of the multiplier 504 is repeated by a sequence repeater 506 according to the length of the preamble. The output of the sequence repeater 506 is further coupled to B according to MACIndex by

multipliers

510 and 508, respectively₉B₈B₇The resulting 64-bit sequence is multiplied by the bit-wise complement of the 64-bit sequence and the outputs are then applied to the I-branch and Q-branch, respectively. The 64-bit sequence multiplied by multiplier 510 is generated in the same manner as described above and shown in table 1 or table 2. The bit-wise complement of the same 64-bit sequence is multiplied by multiplier 508. Since the 64-bit sequence and its bitwise complement are binary values, i.e., "0" or "1," the "0" bit is multiplied by the repeated bipolar symbol of the 64-symbol biorthogonal sequence from sequence repeater 506, thereby generating 0 power on the corresponding in-phase or quadrature branch, while the "1" bit is multiplied by the repeated bipolar symbol of the 64-symbol biorthogonal sequence from sequence repeater 506, thereby applying the bipolar symbol with full power on the corresponding in-phase or quadrature branch. During the preamble, the total power of the complex signal of the preamble is kept constant.

Then, as shown in fig. 1, the complex preamble signal formed by the output from the multiplier 508 on the I-branch and the output from the multiplier 510 on the Q-branch is time division multiplexed with the complex signals of the data 140 modulation symbols, the pilot 120 symbols, and the MAC130 symbols by the multiplexer 520. As shown in fig. 2, the time-division multiplexed signal is further spread by a complex spreader (complex) 250, filtered by baseband filters 260 and 262, and modulated onto a carrier frequency by modulators 270 and 272, and added by an adder 280 to generate a waveform s (t) to be transmitted.

Fig. 6 shows yet another implementation of a preamble channel structure. In this design, the output sequence of multiplier 604 is further symbol-by-symbol concatenated with B according to MACIndex by

multipliers

608 and 606, respectively₉B₈B₇The resulting 64-bit sequence is multiplied by the bit-wise complement of the 64-bit sequence. The output of multiplier 606 is repeated by sequence repeater 610 and applied to the I-branch according to the length of the preamble. The output of multiplier 608 is repeated by sequence repeater 612 and applied to the Q-branch according to the length of the preamble. The 64-bit sequence multiplied by multiplier 608 is generated in the same manner as described above and shown in table 1 or table 2. The bit-wise complement of the same 64-bit sequence is multiplied by multiplier 606. Since the 64-bit sequence and its bitwise complement is a binary value, i.e., 0 or 1, the "0" bit is multiplied by the bipolar symbol of the 64-symbol biorthogonal sequence from multiplier 604, thereby generating 0 power on the corresponding in-phase branch or quadrature branch, while the "1" bit is multiplied by the bipolar symbol of the 64-symbol biorthogonal sequence from multiplier 604, thereby applying the bipolar symbol with full power on the corresponding in-phase branch or quadrature branch. During the preamble, the total power of the complex signal of the preamble is kept constant.

Multipliers

508, 510, 606, and 608 may also be implemented as puncturing elements (puncturing elements), wherein a "0" bit will puncture a corresponding bipolar symbol to a zero value or zero power, and a "1" bit will cause a corresponding bipolar symbol to always be at full power.

Thus, a method is provided for determining the most significant bit (e.g., B in the above example) based on the MAC index₉B₈B₇) The specific pattern determined by repeating the biorthogonal sequence of 64-symbols one by oneSpreading the MACIndex number by applying the symbols to either the in-phase or quadrature branches of a complex signal, where a 64-symbol biorthogonal sequence consists of the least significant bits B of the MACIndex₆B₅B₄B₃B₂B₁B₀And (4) determining. B of MACIndex for a legacy mobile station₉B₈B₇By default "000", the pattern will be limited, e.g., all preamble symbols will be applied to the I-branch while grounding the Q-branch.

After assigning the MACIndex through the channel assignment message, the new mobile station can know the way for the base station to apply the preamble, which is his target, to the I-branch or Q-branch symbol by symbol. Therefore, after quantizing, despreading, and channel compensating the received preamble signal, the mobile station will compare the most significant bit B of the mac index with the most significant bit B of the preamble signal₉B₈B₇The determined pattern is the same pattern to repair the received 64-symbol biorthogonal sequence. The mobile station then despreads the received 64-symbol biorthogonal sequence using a biorthogonal mask generated from the seven least significant bits of its mac index, and then estimates the power of the despread signal. The mobile station further estimates the noise variance in the same symbol-by-symbol pattern on either the I-branch or the Q-branch. Then, the mobile station calculates a signal-to-noise ratio (SNR) of the preamble by dividing the despread signal power estimated from the estimated noise variance. The mobile station further determines whether the SNR of the preamble is greater than a threshold. If greater than the threshold, the mobile station concludes that a preamble is detected. If less than the threshold, the mobile station concludes that no preamble has been detected.

The Hadamard code in equation (5) is used for the various examples described in this disclosure. Hadamard codes are advantageous for implementing the techniques of the present invention because they have excellent orthogonality with respect to each other. Other alternative codes, such as Pseudo Noise (PN) codes or complementary codes, may also be used as long as good correlation is maintained between the different codes.

In this embodiment, the extended bit B of the MACIndex₉B₈B₇Can be implemented asIs a separate preamble pattern field rather than part of the MACIndex.

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.

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. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, or any other form of storage medium known in the art.

The disclosed and other embodiments and 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 combination of objects that affects a machine-readable propagated signal, or a combination of one or more of them. The term "data processing apparatus" includes 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 for creating an execution environment for the computer program to be resolved (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 application, script, or code) can be written in any form of programming language, including compatible 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 peer files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be run on one computer or on multiple computers 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 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 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 executing 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 the 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 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 combination. Furthermore, 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.

Also, while operations are depicted in the drawings in a particular order, it should not be understood that these operations must be performed in the particular order shown or in sequential order, or that all of the operations shown, must be performed, to achieve desirable results. In some cases, 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 elements and systems can generally be integrated in a single software product or packaged into multiple software products.

Thus, specific embodiments have been described. Other embodiments are within the scope of the following claims.

Claims

1. A method for increasing the number of macindexes used to identify mobile stations in a wireless communication system, the method comprising:

generating a first N-symbol biorthogonal sequence by a Walsh function based on the first part of the MACIndex;

applying said first N-symbol biorthogonal sequence to one of an in-phase branch and a quadrature branch channel of a complex signal while grounding the other branch according to a method based on the second part of the MACIndex; and

time division multiplexing the complex preamble signal with data, pilot, and MAC portions in a time slot; wherein the first part of the MACIndex is seven least significant bits of the MACIndex, and the second part of the MACIndex is the rest bits of the MACIndex except the seven least significant bits.

2. The method of claim 1, wherein N is 64.

3. The method of claim 1, wherein the first N-symbol biorthogonal sequence is repeated according to a length of the preamble before being applied to one of the in-phase branch and the quadrature branch on the complex signal.

4. The method of claim 1, wherein the in-phase branch or the quadrature branch on applying the first N-symbol biorthogonal sequence to the complex signal

After one of the branches, the complex signals on the in-phase branch and the quadrature branch are repeated according to the length of the preamble.

5. The method of claim 1, wherein applying the first N-symbol biorthogonal sequence to one of the in-phase and quadrature branches on the complex signal while grounding the other branch comprises:

generating a second N-symbol sequence based on the second portion of the MACIndex;

applying the symbols of the first N-symbol biorthogonal sequence to the in-phase branch, wherein the symbols of the first N-symbol biorthogonal sequence corresponding to the symbols of the second N-symbol sequence are a first value; and

applying the symbols of the first N-symbol biorthogonal sequence to the orthogonal branches, wherein the symbols of the first N-symbol biorthogonal sequence corresponding to the symbols of the second N-symbol sequence are second values.

6. The method of claim 5, wherein each symbol of the second N-symbol sequence corresponds to one symbol of the first N-symbol biorthogonal in the sequence order.

7. The method of claim 6, wherein the first value is "0" and the second value is "1".

8. The method of claim 1, wherein applying the first N-symbol biorthogonal sequence to one of the in-phase and quadrature branches on the complex signal while grounding the other branch comprises:

generating a third N-symbol sequence by complementing the second N-symbol sequence symbol by symbol;

multiplying the first N-symbol biorthogonal sequence with the third N-symbol sequence to generate a fourth N-symbol sequence;

applying the fourth N-symbol sequence to the in-phase branch;

multiplying the first N-symbol biorthogonal sequence with the second N-symbol sequence to generate a fifth N-symbol sequence; and

applying the fifth N-symbol sequence to the orthogonal branch.

9. The method of claim 8, wherein the first N-symbol biorthogonal sequence is repeated according to a length of the preamble before being multiplied by the second N-symbol sequence and the third N-symbol sequence.

10. The method of claim 8, wherein the complex signals on the in-phase branch and the quadrature branch are repeated according to a length of the preamble after multiplying the first N-symbol biorthogonal sequence with the second N-symbol sequence and the third N-symbol sequence.

11. An apparatus for generating a preamble in a wireless communication system, comprising:

a mapping element configured to receive a sequence of bits and to output a sequence of symbols +1, -1 accordingly;

a memory of biorthogonal sequences, wherein the biorthogonal sequences are assigned according to N-ary Walsh functions and respective bit-wise complements;

a masking element configured to spread the output of the mapping element with different biorthogonal sequences;

a repetition element configured to repeat an output of the mask element according to a length of the preamble; and

a switching element for switching the output of the repeating element to one of an in-phase branch and a quadrature branch of a carrier.

12. The apparatus of claim 11, wherein N is 64.

13. The apparatus of claim 11, wherein the switching element is configured to apply the output of the repeating element to one of an in-phase branch and a quadrature branch of the carrier while grounding the other branch according to a particular pattern determined by the second part of MACIndex.

14. The apparatus of claim 13, wherein the second portion of the MACIndex is the remaining bits of the MACIndex except for the seven least significant bits.

15. The apparatus of claim 11, wherein the switching element is configured to apply an output of the masking element to one of an in-phase branch and a quadrature branch of the carrier while grounding the other branch according to the particular pattern determined by the second portion of the MACIndex, and the repeating element is configured to repeat the output of the switching element according to a length of the preamble. 16. The apparatus of claim 15, wherein the second portion of the MACIndex is the remaining bits of the MACIndex except for the seven least significant bits.

17. A method for a mobile station to detect its MACIndex, the method comprising: repairing a first N-symbol biorthogonal sequence received from the received I-branch or Q-branch signal according to a symbol-by-symbol switching pattern, wherein a base station is used to apply the first N-symbol biorthogonal sequence to the I-branch or the Q-branch using the symbol-by-symbol switching pattern;

generating a sixth N-symbol biorthogonal sequence from the first portion of the expected MACIndex, wherein the first portion of the expected MACIndex is the seven least significant bits of the expected MACIndex;

despreading the repaired first N-symbol biorthogonal sequence with the sixth N-symbol biorthogonal sequence;

estimating a power of the despread signal;

estimating a noise variance;

calculating a signal-to-noise ratio of the received preamble signal; and

comparing the signal-to-noise ratio with a threshold to determine a detection result.

18. The method of claim 17, wherein N is 64.

19. The method of claim 17, wherein the symbol-by-symbol pattern is based on a second portion of a desired MACIndex, and wherein the base station is configured to apply the first N-symbol biorthogonal sequence to the I-branch or the Q-branch using the symbol-by-symbol switching pattern.

20. The method of claim 19, wherein the desired MACIndex is

The second part is the remaining bits of the desired MACIndex, except for the seven least significant bits.