HK1142181A - Pseudo-random sequence mapping in wireless communications - Google Patents

Description

Pseudo-random sequence mapping in wireless communications

Cross Reference to Related Applications

The application claims priority of U.S. provisional patent application entitled "A METHOD AND DAPPARATUS FOR PSEUDO-RANDOM SEQUENCE (PRS) MAPPING FORLTE", serial No. 60/942,201, filed on 5.6.2007, AND U.S. provisional patent application entitled "METHOD AND APPARATUS FOR PRP SEUDO-RANDOM SEQUENCE (PRS) MAPPING FOLTE", serial No. 60/945,073, filed on 19.6.2007. The entire contents of the above application are incorporated herein by reference.

Technical Field

The following description relates generally to wireless communications, and more specifically to pseudo-random sequence mapping for a physical layer communication channel.

Background

Wireless communication networks are widely deployed to provide various communication content such as voice, data, and so on. A typical wireless communication system may be a multiple-access system capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, and the like. In addition, these systems are capable of complying with specifications such as third generation partnership project (3GPP), 3GPP Long Term Evolution (LTE), Ultra Mobile Broadband (UMB), and the like.

In general, a wireless multiple-access communication system can simultaneously support communication for multiple mobile devices. Each mobile device may communicate with one or more base stations via forward link and reverse link transmissions. The forward link (or downlink) refers to the communication link from base stations to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to base stations. Moreover, communications between mobile devices and base stations can be established via single-input single-output (SISO) systems, multiple-input single-output (MISO) systems, multiple-input multiple-output (MIMO) systems, and so forth. In addition, mobile devices can communicate with other mobile devices (and/or base stations with other base stations) in a point-to-point wireless network configuration.

MIMO systems typically employ multiple pairs (N)_TSub) transmitting antenna and multi-pair (N)_RAnd) a receive antenna for data transmission. In one example, antennas can be associated with base stations and mobile devices to enable bi-directional communication between devices on a wireless network. Transmissions over multiple antennas are sometimes scrambled, allowing independent communication from many cells over the antennas. This has previously been achieved by using pseudo-random signals, which are random over multiple cells, and an Orthogonal Sequence (OS) of complex numbers, which is used to orthogonalize reference signals from different sectors in the same base station. However, in communications with an extended Cyclic Prefix (CP), e.g., to account for long range echo (faraway echo) in certain environments, it is desirable for the communication channel to become more frequency selective, which can cause a significant loss of orthogonality of the orthogonal sequences at the receiver.

Disclosure of Invention

The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

In accordance with one or more embodiments and corresponding disclosure thereof, various aspects are described in the context of: that is, scrambling for wireless communications of cells without the use of Orthogonal Sequences (OS) is facilitated or at least not provided for a particular communications subframe based at least in part on a Cyclic Prefix (CP) of the particular communications subframe. In one example, scrambling can be performed with a synchronization code pair comprising a Primary Synchronization Code (PSC), which can have varying reuse values, and a Secondary Synchronization Code (SSC), which is mapped to a pseudo-random signal, as opposed to a conventional PSC. The PSC/SSC combination identifies a cell and maps directly to a sequence used to scramble communications from that cell.

According to a related aspect, a method for interpreting downlink reference signals in a wireless communication network is provided. The method can comprise the following steps: receiving a scrambled downlink reference signal from a transmitter; a pseudo-random sequence is determined based at least in part on the received primary and secondary synchronization codes. The method further comprises the following steps: descrambling a portion of subframes of the downlink reference signal according to the pseudo-random sequence and a determined cyclic prefix length of one or more of the portion of subframes.

Another aspect relates to a wireless communications apparatus. The wireless communication apparatus may include: at least one processor configured to determine a cyclic prefix length of one or more subframes of a downlink reference signal and select descrambling based at least in part on the cyclic prefix length. The wireless communication apparatus may further include: a memory coupled to the at least one processor.

Another aspect relates to a wireless communications apparatus that receives and interprets downlink reference signals. The wireless communication apparatus may include: means for receiving a scrambled downlink reference signal from a transmitter; means for associating a pseudo-random sequence with at least a primary and a secondary synchronization code in the downlink reference signal. The wireless communication apparatus may further include: means for descrambling a portion of the downlink reference signal according to the pseudorandom sequence.

Another aspect relates to a computer program product that may have a computer-readable medium comprising: code for causing at least one computer to receive a scrambled downlink reference signal from a transmitter. The computer readable medium may further include: code for causing the at least one computer to determine a pseudo-random sequence using at least a primary and a secondary synchronization code. Further, the computer readable medium may include: code for causing the at least one computer to descramble a portion of subframes of the downlink reference signal according to the pseudo-random sequence and a determined cyclic prefix length of one or more of the portion of subframes.

According to another aspect, a method for transmitting downlink reference signals in a wireless communication network is provided. The method comprises the following steps: a downlink reference signal is generated that includes primary and secondary synchronization codes. The method further comprises the following steps: scrambling the downlink reference signal based at least in part on a pseudo-random sequence corresponding to a combination of the primary and secondary synchronization codes; transmitting the scrambled downlink reference signal.

Another aspect relates to a wireless communications apparatus. The wireless communication apparatus may include: at least one processor configured to obtain a pseudo-random sequence associated with a selected primary and secondary synchronization code combination and scramble a downlink reference signal using the pseudo-random sequence. The wireless communication apparatus may further include: a memory coupled to the at least one processor.

Another aspect relates to a wireless communications apparatus for scrambling downlink reference signals in a wireless communications network. The wireless communication apparatus may include: means for generating a downlink reference signal comprising a primary synchronization code and a secondary synchronization code. The wireless communication apparatus may further include: means for scrambling the downlink reference signal based at least in part on a pseudo-random sequence corresponding to a combination of the primary and secondary synchronization codes.

Another aspect relates to a computer program product that may have a computer-readable medium comprising: code for causing at least one computer to generate a downlink reference signal comprising a primary synchronization code and a secondary synchronization code. Further, the computer readable medium may include: code for causing the at least one computer to scramble the downlink reference signal based at least in part on a pseudo-random sequence corresponding to a combination of the primary and secondary synchronization codes.

To the accomplishment of the foregoing and related ends, the one or more embodiments comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects of the one or more embodiments. These aspects are indicative, however, of but a few of the various ways in which the principles of various embodiments may be employed and the described embodiments are intended to include all such aspects and their equivalents.

Drawings

Fig. 1 is an illustration of a wireless communication system in accordance with various aspects set forth herein.

Fig. 2 is an illustration of an example communications apparatus that is employed in a wireless communication environment.

Fig. 3 is an illustration of an example wireless communication system that effectuates transmitting scrambled downlink reference signals.

Fig. 4 is an illustration of an example methodology that facilitates transmitting scrambled downlink reference signals.

Fig. 5 is an illustration of an example methodology that facilitates interpreting scrambled downlink reference signals.

Fig. 6 is an illustration of an example methodology that facilitates interpreting reference signals based on a cyclic prefix.

Fig. 7 is an illustration of an example mobile device that facilitates interpreting scrambled reference signals.

Fig. 8 is an illustration of an example system that facilitates transmitting downlink reference signals.

Fig. 9 is an illustration of an example wireless network environment that can be employed in conjunction with the various systems and methods described herein.

FIG. 10 is an illustration of an example system that descrambles scrambled reference signals.

Fig. 11 is an illustration of an example system that scrambles downlink reference signals.

Detailed Description

Various embodiments will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments.

As used in this application, the terms "component," "module," "system," and the like are intended to refer to a computer-related entity, either hardware, firmware, a combination of hardware and software, or software in execution. For example, a component may be, but is not limited to being: a process running on a processor, an object, an executable, a thread of execution, a program, and/or a computer. By way of illustration, both an application running on a computing device and the computing device can be a component. One or more components can reside within a process and/or thread of execution and a component can be localized on one computer and/or distributed between two or more computers. In addition, these components can execute from various computer readable media having various data structures stored thereon. The components may communicate by way of local processes and/or remote processes such as in accordance with a signal having one or more data packets (e.g., data from one component interacting with another component in a local system, distributed system, and/or across a network such as the internet with other systems by way of the signal).

Furthermore, various embodiments are described herein in connection with a mobile device. A mobile device can also be called a system, subscriber unit, subscriber station, mobile, remote station, remote terminal, access terminal, user terminal, wireless communication device, user agent, user device, or User Equipment (UE). The mobile device may be a cellular telephone, a cordless telephone, a Session Initiation Protocol (SIP) phone, a Wireless Local Loop (WLL) station, a Personal Digital Assistant (PDA), a handheld device having wireless connection capability, a computing device, or other processing device connected to a wireless modem. Furthermore, various embodiments are described herein in connection with a base station. A base station can be utilized for communicating with mobile device(s) and can also be referred to as an access point, node B, evolved node B (eNode B or eNB), base transceiver station, or some other terminology.

Moreover, various aspects or features described herein can be implemented as a method, apparatus, or article of manufacture using standard programming and/or engineering techniques. The term "article of manufacture" as used herein is intended to encompass a computer program accessible from any computer-readable device, carrier, or media. For example, computer-readable media may include, but are not limited to: magnetic storage devices (e.g., hard disk, floppy disk, magnetic strips, etc.), optical disks (e.g., Compact Disk (CD), Digital Versatile Disk (DVD), etc.), smart cards, and flash memory devices (e.g., EPROM, card, stick, key drive, etc.). In addition, various storage media described herein can represent one or more devices and/or other machine-readable media for storing information. The term "machine-readable medium" can include, without being limited to, wireless channels and various other media capable of storing, containing, and/or carrying instruction(s) and/or data.

The techniques described herein may be used for various wireless communication systems such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), single carrier frequency domain multiplexing (SD-FDMA), and others. The terms "system" and "network" are often used interchangeably. A CDMA system may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA2000, and so on. UTRA includes wideband CDMA (W-CDMA) and other variants of CDMA. CDMA2000 covers IS-2000, IS-95 and IS-856 standards. TDMA systems may implement wireless technologies such as global system for mobile communications (GSM). OFDMA systems may implement wireless technologies such as evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM, and so forth. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System (UMTS). The 3GPP Long Term Evolution (LTE) is an upcoming release of UMTS that employs E-UTRA, which uses OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE, and GSM are described in documents of the organization entitled "third Generation partnership project" (3 GPP). CDMA2000 and UMB are described in a document entitled "third generation partnership project 2" (3GPP 2).

Referring now to fig. 1, a wireless communication system 100 is shown in accordance with various embodiments presented herein. System 100 comprises a base station 102, and base station 102 can comprise multiple antenna groups. For example, one antenna group can include antennas 104 and 106, another group can include antennas 108 and 110, and an additional group can include antennas 112 and 114. Two antennas are shown for each antenna group; however, more or fewer antennas may be used for each group. Base station 102 can additionally include a transmitter chain and a receiver chain, each of which can in turn comprise a plurality of components associated with signal transmission and reception (e.g., processors, modulators, multiplexers, demodulators, demultiplexers, antennas, etc.), as will be appreciated by one skilled in the art.

Base station 102 can communicate with one or more mobile devices (e.g., mobile device 116 and mobile device 122); however, it should be appreciated that base station 102 can communicate with substantially any number of mobile devices similar to mobile devices 116 and 122. For example, mobile devices 116 and 122 can be cellular phones, smart phones, laptops, handheld communication devices, handheld computing devices, satellite radios, global positioning systems, PDAs, and/or any other suitable device for communicating over wireless communication system 100. As depicted, mobile device 116 is in communication with antennas 112 and 114, where antennas 112 and 114 transmit information to mobile device 116 over a forward link 118 and receive information from mobile device 116 over a reverse link 120. In addition, mobile device 122 is in communication with antennas 104 and 106, where antennas 104 and 106 transmit information to mobile device 122 over a forward link 124 and receive information from mobile device 122 over a reverse link 126. In a Frequency Division Duplex (FDD) system, forward link 118 can utilize a different frequency band than that used by reverse link 120, and forward link 124 can employ a different frequency band than that employed by reverse link 126. Further, in Time Division Duplex (TDD), forward link 118 and reverse link 120 can utilize a common frequency band and forward link 124 and reverse link 126 can utilize a common frequency band.

Each group of antennas and/or the area in which they are designated to communicate can be referred to as a sector of base station 102. For example, antenna groups can be designed to communicate to mobile devices in a sector of the areas covered by base station 102. In communication over forward links 118 and 124, the transmitting antennas of base station 102 can utilize beamforming to improve signal-to-noise ratio of forward links 118 and 124 for mobile devices 116 and 122. Moreover, when base station 102 utilizes beamforming to transmit to mobile devices 116 and 122 scattered randomly through an associated coverage, mobile devices in neighboring cells can be subject to less interference as compared to base station 102 transmitting through a single antenna to all its mobile devices. In addition, mobile devices 116 and 122 can communicate directly with each other using the depicted point-to-point or ad hoc (ad hoc) techniques.

According to an example, system 100 can be a multiple-input multiple-output (MIMO) communication system. Moreover, system 100 can utilize substantially any type of duplexing technique (e.g., FDD, TDD, etc.) to divide communication channels (e.g., forward link, reverse link). Further, one or more multiplexing schemes (e.g., OFDM) may be used to modulate multiple signals on the frequency subcarriers forming one or more communication channels. In one example, a transmitter of a channel (e.g., base station 102 and/or mobile devices 116 and 122) can additionally transmit a pilot or reference signal to facilitate synchronizing communications with another device or estimating a channel. For example, a downlink Reference Signal (RS) transmitted from a sector in base station 102 can be a function of one or more synchronization codes. In an example, the RS can have a duration equal to a number of subframes (e.g., 10 subframes), and the synchronization code can be within one or more subframes (in one example, subframes 0 and 5).

According to an example, the synchronization code used can uniquely determine a pseudo-random sequence (PRS) used to scramble the RS. In one example, the RS is scrambled by performing an XOR operation with the PRS. As noted above, previous systems utilized orthogonal sequences and PRSs to provide cell-specific scrambling uniquely associated with cell identities; however, it is expected that transmissions with an extended Cyclic Prefix (CP) will result in higher channel selectivity, thereby gradually losing orthogonality of the orthogonal sequences starting at the receiver (e.g., mobile device 116 and/or 122). The subject matter described herein utilizes a Primary Synchronization Code (PSC) and a Secondary Synchronization Code (SSC) mapped to a PRS to scramble the RS according to multiple PRSs, wherein the PSC is used not only for conventional slot boundary detection, but also as a dynamic reuse factor for PRSs. The PSC/SSC combination can also be used to identify the transmitter of the RS (e.g., a particular sector in base station 102, mobile devices 116 and 122, or a transmitting cell associated with them). Thus, rather than using a PRS and orthogonal sequence, only a PRS based on a PSC/SSC combination is used. The described invention provides for substantially the same number of combinations that can utilize orthogonal sequences, as the number of PSCs can be substantially the same as the number of previous orthogonal sequences. It should be appreciated, however, that where orthogonal signals may provide substantial advantages when the subframe has a normal CP (or a CP below a given threshold), such signals may still optionally be used with PRSs to provide cell-specific scrambling uniquely associated with a cell identity.

Turning to fig. 2, illustrated is a communications apparatus 200 that employs in a wireless communication environment. Communications apparatus 200 can be a base station sector or a portion thereof, a mobile device or a portion thereof, or substantially any communications apparatus that can be employed to receive data transmitted in a wireless communication environment. The communication device 200 may include: a reference signal definer 202 that generates an RS for broadcasting to one or more different communication apparatuses; a scrambler 204 that scrambles the RS according to one or more synchronization codes; a transmitter 206 that transmits the scrambled RS.

According to an example, the communications apparatus 200 can transmit a downlink RS such that a receiver can utilize the downlink RS to determine information related to transmissions from the communications apparatus 200. In one example, the reference signal definer 202 can generate an RS that can be utilized to identify the communications apparatus 200, or the like, or to synchronize with the communications apparatus 200. The synchronization code can include the PSC and SSC related to cell-specific scrambling used for RS transmission. The SSC can uniquely determine the corresponding PRS, and the PSC can uniquely determine a reuse factor for the PRS. Thus, the number of available PRSs is substantially equal to the product of the available PSCs and the available SSCs.

The PSC and SSC utilized by the communications apparatus 200 can relate to a PRS utilized by the scrambler 204 to scramble the RS. It may also be used to identify the communication device 200 associated with a surrounding transmitting device. In the example of 3GPP LTE, 170 SSCs can correspond to 170 PRSs that the scrambler 204 can utilize to scramble the RS. Additionally, the 3 PSCs can provide a reuse factor to provide 510 PRSs that can be utilized to scramble the RS and uniquely identify the communication apparatus 200 or a cell thereof related to the communication apparatus receiving the RS. The scrambled RS can be transmitted to one or more such devices by utilizing the transmitter 206. It should be appreciated that the above examples may reduce the use of orthogonal sequences when scrambling RSs, e.g., when utilizing subframes with extended CP or subframes with longer CP (e.g., when susceptible to remote echoes and the like).

However, orthogonalizing the RS can be beneficial when orthogonality can be maintained, as is desirable when using conventional CP lengths. Thus, if an extended CP (e.g., a CP whose length exceeds a specified threshold) is utilized, the above PSC/SSC combination can determine the PRS used by the scrambler 204 from the RS. Alternatively, if the CP does not exceed the threshold or is of a conventional length, the PRS used may relate only to the SSC and the signal may be orthogonalized according to a conventional orthogonal sequence. In the example of 3GPP LTE, 170 SSCs can correspond to 170 PRSs, which can thus be used by the scrambler 204 to scramble the RS. In addition, 3 orthogonal sequences can be used to orthogonalize the RS to provide 510 combinations of orthogonal sequences and PRSs that can be used to scramble the RS and uniquely identify the communications apparatus 200 or its cell.

Referring now to fig. 3, illustrated is a wireless communication system 300 that transmits downlink RSs scrambled with a cell identification code. The system 300 includes: a base station sector 302 that communicates with a mobile device 304 (and/or any number of disparate mobile devices (not shown)). Base station sector 302 can transmit information to mobile device 304 over a forward link channel or a downlink channel; in addition, base station sector 302 can receive information from mobile device 304 over a reverse link channel or an uplink channel. Additionally, system 300 can be a MIMO system. Additionally, in one example, components and functionality illustrated and described below in base station sector 302 can also be present in mobile device 304, and vice versa; for ease of illustration, the illustrated construction does not include these components.

Base station sector 302 includes: a reference signal definer 306 that generates an RS for transmission to the mobile device 304, wherein the RS can include information for interpreting signals transmitted from the base station sector 302; a scrambler 308 that can scramble the RS by utilizing a source that identifies the PRS; a transmitter 310, which may transmit the scrambled RS. As described above, the PRS can correspond to the SSC and/or PSC/SSC pair stored in the RS. For example, in the case of orthogonalizing the RS using a normal CP subframe and an orthogonal sequence, the PRS may correspond to the SSC; and in the case of utilizing subframes with extended CP, the PRS can correspond to a PSC/SSC pair, as described above.

The mobile device 304 includes: a receiver 312 that can receive the transmitted signal; a reference signal detector 314, which may determine the signal as RS; a descrambler 316 that may descramble the RS according to the information received therein. In one example, the receiver 312 can receive one or more reference signals, and the reference signal detector 314 can determine that the signal is an RS and extract synchronization information from one or more subframes of the RS. The descrambler 316 may descramble the reference signal based on the extracted information to obtain other information.

In one example, the reference signal definer 306 can generate the RS, as described above; the scrambler 308 can scramble the RS using the PRS corresponding to the PSC/SSC combination, as described above. The RS can also store the PSC and SSC. Transmitter 310 can then transmit an RS to one or more mobile devices (e.g., mobile device 304) to provide synchronization/identity information of base station sector 302 for communicating with base station sector 302. The RS can be received by the receiver 312 of the mobile device 304 and detected as an RS by the reference signal detector 314. The reference signal detector 314 can detect the signal at least in part by determining a PSC and/or SSC for the signal (e.g., from subframe 0 of the RS). Upon determining the PSC/SSC combination, the reference signal detector 314 can identify a PRS for scrambling the RS, and the descrambler 316 can descramble the RS according to the PRS.

As described above, the conventional orthogonal sequence step in the scrambling process brings disadvantages while using the extended CP. Thus, utilizing only PRSs while extending the number of available PRSs to provide substantially the same number as PRS/orthogonal sequence combinations enables similar versatility for identifying base station sectors 302 without the need for additional orthogonalization steps. However, as described above, it is beneficial to utilize orthogonal sequences while using a conventional CP; thus, for example, a PSC/SSC combination can be used in a subframe with extended CP utilizing orthogonal sequences in such a scenario.

In this example, the mobile device 304 can receive the RS through the receiver 312, and the reference signal detector 314 can determine whether subframe 0 of the RS is transmitted in a subframe with an extended CP or a subframe with a normal CP. If an extended CP is detected in subframe 0, the reference signal detector 314 can determine that orthogonal ordering is not used for the given subframe when scrambling the RS. Thus, the PRS is constructed from a unique mapping of the PSC/SSC combination, which is used solely to scramble the RS. On the other hand, if a normal CP is detected in subframe 0, the reference signal detector 314 may determine that orthogonal ordering is used for the given subframe when scrambling the RS. Thus, the PRS is constructed from only the mapping to the SSC and scrambles the RS using the PRS together with the orthogonal sequence. The descrambler 316 may utilize this information to descramble the RS.

Additionally, in this example, if the reference signal detector 314 detects an extended CP in subframe 0, then, in one example, the extended CP may be assumed for the remaining subframes. Accordingly, the descrambler 316 can utilize the extracted PSC/SSC combination to descramble the remaining subframes. However, if the reference signal detector 314 detects a normal CP in subframe 0, then the Physical Broadcast Channel (PBCH) (which is typically in subframe 0) or the Dynamic Broadcast Channel (DBCH) may indicate which subframes use extended CP and which subframes use normal CP. If the remaining subframes use regular CP, then the SSC can be correlated with PRS used to scramble the corresponding subframes, and the reference signal detector 314 can assume that orthogonal sequences are used in these subframes; if the remaining subframes use extended CP, the PSC/SSC combination can be correlated with the PRS used to scramble the corresponding subframe, and no orthogonal ordering is used. It should be appreciated that in the case of subframe 0 using extended CP, the dynamic BCH may additionally specify subframes with normal CP and subframes with extended CP, such that the above distinction can be utilized for the remaining subframes. In addition, it should be appreciated that the PSC/SSC combination can be utilized in all subframes regardless of CP length, for example.

Referring to fig. 4-6, methodologies relating to scrambling downlink reference signals based upon primary and secondary synchronization codes are illustrated. While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more embodiments, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with one or more embodiments.

Turning to fig. 4, illustrated is a methodology 400 that facilitates generating and transmitting a scrambled downlink RS. At 402, a downlink RS is generated that includes information related to a transmitter of the RS. For example, the information may include a synchronization code, data in a primary broadcast channel, and so on. At 404, a unique PRS corresponding to a primary and secondary synchronization code used by a transmitter of the RS can be determined. The code combination may be mapped directly to the PRS; therefore, other transmitters in the vicinity may also transmit RSs using different PRSs in order to distinguish between RSs. Also in this regard, the PRS may enable a receiver of the RS to identify the transmitter.

At 406, the PRS is used to scramble the downlink reference signal. In one example, this may be performed via an XOR operation between the RS and the PRS. At 408, the scrambled downlink RS is transmitted. Thus, RS scrambling can be performed without using orthogonal sequences, while maintaining the number of possible scrambles, where the number of available PSCs matches the previously available orthogonal sequences. This is beneficial in subframes with extended CP, where the benefits of orthogonal ordering are lost due to the expected high channel frequency selectivity, as described above.

Turning to fig. 5, illustrated is a methodology 500 that facilitates scrambling a reference signal based at least in part on a synchronization code. At 502, a downlink RS is received; in one example, this may come from a transmitter with which it is desired to communicate. At 504, primary and secondary synchronization codes are determined to be associated with the RS. These codes may be extracted from specific time/frequency locations in specific subframes (e.g., subframes 0 and 5). At 506, a PRS is determined based at least in part on the primary and secondary synchronization codes; this may also be based at least in part on the CP duration, as described above. For example, the codes can be related to PRS used to scramble the RS prior to transmission, and at 508, the PRS can be used to descramble the RS. In one example, the secondary synchronization code can be directly related to the PRS while the primary synchronization code is a reuse factor for the PRS, or vice versa.

Turning to fig. 6, illustrated is a methodology 600 that facilitates descrambling a downlink RS based at least in part on a size of a cyclic prefix associated with one or more frames or subframes of the RS. At 602, a downlink RS comprising one or more subframes is received. The method starts with subframe 0 being the current subframe. At 604, the CP length of the current subframe is evaluated. If the CP is extended (e.g., has a length greater than a specified threshold), the previously extracted PSC/SSC combination can be used to determine the PRS for descrambling the RS. It is to be appreciated that at 606, the PSC/SSC combination can be extracted using substantially any of the methods described herein. At 608, it may be determined whether there are subsequent subframes in the RS. If so, it may be assumed that the remaining subframes also have extended prefixes, and thus, at 610: since subframe 0 has an extended CP, the next subframe may become the current subframe and similarly evaluated at step 606 until there are no subsequent subframes. When there are no subsequent subframes, the method continues to 612, where at 612, the RS is interpreted.

If it is determined at 604 that subframe 0 does not have an extended CP, at 614, a directly related PRS can be determined using the previously extracted SSC to descramble the subframe along with the orthogonal sequence. In this regard, for either an unexpanded CP or a conventional CP, the orthogonal sequence is used by a scrambler in the transmitter. However, in this case, it cannot be assumed that the remaining subframes have an unexpanded CP; thus, at 608, if there are still subsequent subframes, then at 610, the method returns to 604 to evaluate the CP of the next subframe, since subframe 0 has no extended CP. However, if no subframe exists, then at 612, the RS is interpreted. Thus, the method may be such that: orthogonal sequences are utilized in normal CP subframes in order to retain their advantages while at the same time removing orthogonal ordering from subframes with extended CP, as described herein, so that the advantages of orthogonal ordering may be hindered by the expected channel frequency selectivity.

It is to be appreciated that, in accordance with one or more aspects described herein, inferences can be made regarding: the PSC and/or SSC for a given transmitter is determined, as described above. As used herein, the term to "infer" or "inference" refers generally to the process of reasoning about or inferring states of the system, environment, and/or user from a set of observations as captured via events and/or data. Inference can be employed to identify a specific context or action, or can generate a probability distribution over states, for example. The inference can be probabilistic-that is, the computation of a probability distribution over states of interest based on a consideration of data and events. Inference can also refer to techniques employed for composing higher-layer events from a set of events and/or data. Such inference results in the construction of new events or actions from a set of observed events and/or stored event data, whether or not the events are correlated in close temporal proximity, and whether the events and stored event data come from one or several event and data sources.

According to an example, one or more of the methods presented above can include making inferences pertaining to: determining a PSC/SSC combination, determining a PRS associated therewith, determining an identity of a transmitter based on the PSC/SSC combination, determining an orthogonal sequence used in a subframe having a normal CP, determining a cyclic prefix length for one or more subframes, and the like.

Fig. 7 is an illustration of a mobile device 700 that facilitates descrambling received downlink RSs. Mobile device 700 comprises a receiver 702 that receives a signal from, for instance, a receive antenna (not shown), performs typical actions thereon (e.g., filters, amplifies, downconverts, etc.) the received signal, and digitizes the conditioned signal to obtain samples. Receiver 702 can comprise a demodulator 704 that can demodulate received symbols and provide them to a processor 706 for channel estimation. Processor 706 can be a processor dedicated to analyzing information received by receiver 702 and/or generating information for transmission by a transmitter 716, a processor that controls one or more components of mobile device 700, and/or a processor that both analyzes information received by receiver 702, generates information for transmission by transmitter 716, and controls one or more components of mobile device 700.

Moreover, mobile device 700 can comprise memory 708 that is operatively coupled to processor 706, and memory 708 can store data to be transmitted, received data, information related to available channels, data associated with analyzed signal and/or interference strength, information related to an assigned channel, power, rate, or the like, and any other suitable information for estimating a channel and transmitting via the channel. Further, memory 708 can store protocols and/or algorithms associated with estimating a channel and/or utilizing a channel (e.g., performance based, capacity based, etc.).

It will be appreciated that the data store (e.g., memory 708) described herein can be either volatile memory or nonvolatile memory, or can include both volatile and nonvolatile memory. By way of example, and not limitation, nonvolatile memory can include Read Only Memory (ROM), Programmable ROM (PROM), Electrically Programmable ROM (EPROM), Electrically Erasable PROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM), which acts as external cache memory. By way of example, and not limitation, RAM may be available in a variety of forms such as Synchronous RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), Synchronous Link DRAM (SLDRAM), and Direct Rambus RAM (DRRAM). The memory 708 of the subject systems and methods is intended to comprise, without being limited to, these and any other suitable types of memory.

Processor 706 and/or receiver 702 can additionally be operatively coupled to a reference signal detector 710 that determines whether a received signal is a downlink RS. Further, the reference signal detector 710 can determine a PRS used by the transmitter to scramble the RS prior to transmission. In one example, this can be based at least in part on an extracted PSC/SSC combination provided in the RS related to a given PRS. Further, the combination may be used to identify the transmitter of the RS. In another example, the reference signal detector 710 can determine an orthogonal sequence that is also used to scramble the RS, e.g., if the cyclic prefix is conventional. Using this information, the descrambler 712 can descramble the RS.

According to an example, the reference signal detector 710 can determine a cyclic prefix length of one or more subframes of the RS and determine whether to descramble with a PRS related to a PSC/SSC combination or with a PRS related to an SSC along with an orthogonal sequence. As described above, the former may be used in a subframe with an extended CP because orthogonality is likely to be lost due to frequency selectivity due to the extended CP; while the latter may be used for subframes with normal CP. Alternatively, in substantially all cases, a PSC/SSC combination can be mapped to a PRS. Mobile device 700 still further comprises a modulator 714 and a transmitter 716, modulator 714 modulating a signal and transmitter 716 transmitting the signal to, for instance, a base station, another mobile device, etc. Although shown as being separate from the processor 706, it is to be appreciated that the reference signal detector 710, descrambler 712, demodulator 704, and/or modulator 714 can be part of the processor 706 or multiple processors (not shown).

Fig. 8 is an illustration of a system 800 that facilitates generating and scrambling a downlink RS for transmission thereof. System 800 includes a base station 802 (e.g., an access point) having: a receiver 810 that receives signals from one or more mobile devices 804 via multiple receive antennas 806; a transmitter 824 that transmits signals to one or more mobile devices 804 via the transmit antenna 808. Receiver 810 can receive information from receive antennas 806 and is operatively associated with a demodulator 812 that demodulates received information. Demodulated symbols can be analyzed by a processor 814, wherein processor 814 is similar to that described above with respect to fig. 7, processor 814 is coupled to a memory 816, and memory 816 stores information related to estimated signal (e.g., pilot) strength and/or interference strength, data intended for or received from mobile device 804 (or a disparate base station (not shown)), and/or any other suitable information related to performing the various acts and functions described herein. Processor 814 is further coupled to a reference signal generator 818 that generates an RS that can be utilized to determine synchronization, identity, and/or other information related to base station 802, and a scrambler 820 that scrambles the RS.

According to an example, the reference signal generator 818 can generate an RS that includes a primary synchronization code and a secondary synchronization code. These codes can uniquely identify the base station 802, and can also directly correspond to one of a plurality of PRSs. The scrambler 820 may scramble the RS using PRS (e.g., via an XOR operation). In one example, in a subframe with a normal CP, the PRS can be correlated with the SSC and the RS can also be scrambled with an orthogonal sequence. The scrambled RS can be transmitted from the transmitter 824 to one or more mobile devices 804. Further, while reference signal generator 818, scrambler 820, demodulator 812, and/or modulator 822 are shown as being separate from processor 814, it is to be appreciated that such components may be part of processor 814 or multiple processors (not shown).

Fig. 9 illustrates an example wireless communication system 900. For simplicity, wireless communication system 900 illustrates only one base station 910 and one mobile device 950. However, it is to be appreciated that system 900 can include more than one base station and/or more than one mobile device, wherein other base stations and/or mobile devices can be substantially similar or different from example base station 910 and mobile device 950 described below. Moreover, it is to be appreciated that base station 910 and/or mobile device 950 can employ the systems (FIGS. 1-3 and 7-8) and/or methods (FIGS. 4-6) described herein to facilitate wireless communication there between.

At base station 910, traffic data for a number of data streams can be provided from a data source 912 to a Transmit (TX) data processor 914. According to one example, each data stream is transmitted over a respective antenna. TX data processor 914 formats, codes, and interleaves the traffic data stream based on a particular coding scheme selected for that data stream to provide coded data.

The coded data for each data stream can be multiplexed with pilot data using Orthogonal Frequency Division Multiplexing (OFDM) techniques. Additionally or alternatively, the pilot symbols may be Frequency Division Multiplexed (FDM), Time Division Multiplexed (TDM), or Code Division Multiplexed (CDM). The pilot data is typically a known data pattern that is processed in a known manner and can be used at mobile device 950 to estimate channel response. The multiplexed pilot and coded data for each data stream can be modulated (e.g., symbol mapped) based on a particular modulation scheme (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM), etc.) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream can be determined by instructions performed or provided by processor 930.

The modulation symbols for the data streams can be provided to a TX MIMO processor 920, and the modulation symbols (e.g., for OFDM) can be further processed by TX MIMO processor 920. The TXMMIMO processor 920 then forwards the N to_TN are provided by transmitters (TMTR)922a through 922t_TA stream of modulation symbols. In various embodiments, TX MIMO processor 920 may be configured to perform symbol-wise processing on the data streamsAnd the antenna used to transmit the symbol applies beamforming weights.

Each transmitter 922 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. In addition, from N respectively_TN from transmitters 922a through 922t are transmitted by antennas 924a through 924t_TA modulated signal.

At mobile device 950, by N_REach antenna 952a through 952r receives the transmitted modulated signal and provides a received signal from each antenna 952 to a respective receiver (RCVR)954a through 954 r. Each receiver 954 conditions (e.g., filters, amplifies, and downconverts) a respective signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding "received" symbol stream.

RX data processor 960 can vary from N according to a particular receiver processing technique_RA receiver 954 receives and processes N_RA received symbol stream is processed to provide N_TA "detected" symbol stream. RX data processor 960 can demodulate, deinterleave, and decode each detected symbol stream to recover the traffic data for the data stream. The processing by RX data processor 960 is complementary to that performed by TX MIMO processor 920 and TX data processor 914 at base station 910.

A processor 970 can periodically determine which precoding matrix to use as discussed above. Further, processor 970 formulates a reverse link message comprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message can be processed by a TX data processor 938, which TX data processor 938 also receives traffic data for a number of data streams from a data source 936, modulates it by modulator 980, conditions it by transmitters 954a through 954r, and transmits it back to base station 910.

At base station 910, the modulated signals from mobile device 950 are received by antennas 924, conditioned by receivers 922, demodulated by a demodulator 940, and processed by a RX data processor 942 to extract the reverse link message transmitted by mobile device 950. Further, processor 930 can process the extracted message to determine which precoding matrix to use for determining the beamforming weights.

Processors 930 and 970 can direct (e.g., control, coordinate, manage, etc.) operation at base station 910 and mobile device 950, respectively. Processors 930 and 970 can be associated with memory 932 and 972, respectively, that store program codes and data. Processors 930 and 970 can also perform computations to derive frequency and impulse response estimates for the uplink and downlink, respectively.

It is to be understood that the embodiments described herein may be implemented in hardware, software, firmware, middleware, microcode, or any combination thereof. For a hardware implementation, the processing units may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

When the embodiments are implemented in software, firmware, middleware or microcode, program code or code segments, they can be stored in a machine-readable medium, such as a storage component. A code segment may be represented by a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, etc.

For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

Referring to fig. 10, illustrated is a system 1000 that descrambles a received downlink RS according to a PRS. For example, system 1000 can reside at least partially within a base station, mobile device, etc. It is to be appreciated that system 1000 is represented as including functional blocks, which can be functional blocks that represent functions implemented by a processor, software, or combination thereof (e.g., firmware). System 1000 includes a logical grouping 1002 of electrical components that can act in conjunction. For example, logical grouping 1002 can include: an electrical component 1004 for receiving the scrambled downlink RS. For example, an RS can be received from a transmitter, which can include synchronization information and/or identification information related to the transmitter, e.g., a unique synchronization code that can be selected from a set of available codes. Further, logical grouping 1002 can include: an electrical component 1006 for associating the PRS with at least the primary and secondary synchronization codes in the downlink RS. For example, the unique synchronization code may correspond to a PRS; the unique characteristic may help identify the transmitter of the RS. Further, logical grouping 1002 can include: an electrical component 1008 for descrambling a portion of the downlink RS according to the PRS. The RS can then be interpreted to extract other information as needed. Additionally, system 1000 can include a memory 1010 that retains instructions for executing functions associated with electrical components 1004, 1006, and 1008. While electrical components 1004, 1006, and 1008 are illustrated as being located outside of memory 1010, it is to be understood that one or more of electrical components 1004, 1006, and 1008 can exist within memory 1010.

Turning to fig. 11, illustrated is a system 1100 that generates and scrambles RSs for transmission over a wireless communication network. System 1100 can reside within a base station, mobile device, etc., for instance. As depicted, system 1100 includes functional blocks that can represent functions implemented by a processor, software, or combination thereof (e.g., firmware). The system 1100 includes: logical grouping 1102 of electrical components that facilitate generating and scrambling the RS. Logical grouping 1102 may include: an electrical component 1104 for generating a downlink RS including primary and secondary synchronization codes. Such information not only allows the receiver to identify the transmitter of the information, but also to obtain information about synchronization with the transmitter for subsequent communications. In addition, such information can facilitate determining which PRS to use to scramble the RS prior to transmitting the RS. Further, logical grouping 1102 can include: an electrical component 1106 for scrambling a downlink RS based at least in part on a PRS corresponding to a combination having a primary and secondary synchronization code. Thus, there may be a set of PRSs that map directly to the synchronization code combination, which may be used by the transmitter. In this regard, depending on the number of PRS/synchronization code mappings, as the number of mappings increases, the chances of using similar PRSs by different transmitters that may cause interference are reduced. Once scrambled, the RS can be transmitted or broadcast to various receiving devices. Additionally, system 1100 can include a memory 1108 that retains instructions for executing functions associated with electrical components 1104 and 1106. While shown as being external to memory 1108, it is to be understood that electrical components 1104 and 1106 can exist within memory 1108.

What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term "includes" is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term "comprising" as "comprising" is interpreted when employed as a transitional word in a claim.

Claims (45)

1. A method for interpreting downlink reference signals in a wireless communication network, comprising:

receiving a scrambled downlink reference signal;

determining a pseudo-random sequence based at least in part on the received primary and secondary synchronization codes;

descrambling a portion of subframes of the downlink reference signal according to the pseudo-random sequence and a determined cyclic prefix length of one or more of the portion of subframes.

2. The method of claim 1, the primary and secondary synchronization codes are received in different signals from a transmitter.

3. The method of claim 1, the descrambling performed for a subframe with a cyclic prefix length greater than a specified threshold.

4. The method of claim 1, further comprising: descrambling a portion of subframes of the downlink reference signal having a cyclic prefix length less than a specified threshold based at least in part on a pseudo-random sequence and an orthogonal sequence corresponding to the secondary synchronization code.

5. The method of claim 1, further comprising: a first subframe is evaluated to determine a cyclic prefix length of the first subframe and possible cyclic prefix lengths of remaining subframes.

6. The method of claim 5, a dynamic broadcast channel in a subframe provides a cyclic prefix length for the remaining subframes.

7. The method of claim 1, further comprising: identifying a transmitter based at least in part on the primary and secondary synchronization codes.

8. The method of claim 1, further comprising: extracting the primary and secondary synchronization codes from the downlink reference signal.

9. A wireless communications apparatus, comprising:

at least one processor configured to:

determining a cyclic prefix length of one or more subframes of a downlink reference signal,

selecting descrambling based at least in part on the cyclic prefix length;

a memory coupled to the at least one processor.

10. The wireless communications apparatus of claim 9, the cyclic prefix length of the one or more subframes exceeds a specified threshold, the descrambling is performed utilizing a pseudo-random sequence determined from a combination of a primary and a secondary synchronization code in the reference signal.

11. The wireless communications apparatus of claim 10, a combination of the primary and secondary synchronization codes identifies a transmitter of the reference signal.

12. The wireless communications apparatus of claim 9, the one or more subframes have a cyclic prefix length that is less than a specified threshold, the descrambling is performed utilizing a pseudo-random sequence determined from a secondary synchronization code in the reference signal and a determined orthogonal sequence.

13. The wireless communications apparatus of claim 9, the one or more subframes are a first subframe of the reference signal.

14. The wireless communications apparatus of claim 13, the cyclic prefix of the first subframe has a regular length, the at least one processor further configured to determine cyclic prefix lengths of remaining subframes by evaluating a dynamic broadcast channel in the downlink reference signal.

15. The wireless communications apparatus of claim 13, the cyclic prefix of the first subframe has an extended length, the at least one processor further configured to determine remaining subframes having extended cyclic prefix lengths.

16. A wireless communications apparatus that receives and interprets downlink reference signals, comprising:

means for receiving a scrambled downlink reference signal;

means for associating a pseudo-random sequence with at least a primary and a secondary synchronization code in the downlink reference signal;

means for descrambling a portion of the downlink reference signal according to the pseudorandom sequence.

17. The wireless communications apparatus of claim 16, further comprising: means for determining a cyclic prefix length of one or more subframes in the portion of the downlink reference signal.

18. The wireless communications apparatus of claim 17, the descrambling is performed for at least one subframe with a cyclic prefix length greater than a specified threshold.

19. The wireless communications apparatus of claim 17, further comprising: means for descrambling at least one subframe with a cyclic prefix length less than a specified threshold based at least in part on a pseudo-random sequence and an orthogonal sequence corresponding to the secondary synchronization code.

20. The wireless communications apparatus of claim 17, further comprising: means for evaluating a first subframe to determine a cyclic prefix length of the first subframe and possible cyclic prefix lengths of remaining subframes.

21. The wireless communications apparatus of claim 20, a dynamic broadcast channel in a frame provides a cyclic prefix length for the remaining subframes.

22. The wireless communications apparatus of claim 16, further comprising: means for identifying a transmitter based at least in part on the primary and secondary synchronization codes.

23. The wireless communications apparatus of claim 16, further comprising: means for extracting the primary and secondary synchronization codes from the downlink reference signal.

24. A computer program product, comprising:

a computer-readable medium comprising:

code for causing at least one computer to receive a scrambled downlink reference signal;

code for causing the at least one computer to determine a pseudo-random sequence using at least a primary and a secondary synchronization code;

code for causing the at least one computer to descramble a portion of subframes of the downlink reference signal according to the pseudo-random sequence and a determined cyclic prefix length of one or more of the portion of subframes.

25. The computer program product of claim 24, the computer-readable medium further comprising: for causing the at least one computer to determine a cyclic prefix length of one or more of the portion of subframes of the downlink reference signal.

26. A method for transmitting downlink reference signals in a wireless communication network, comprising:

generating a downlink reference signal comprising a primary synchronization code and a secondary synchronization code;

scrambling the downlink reference signal based at least in part on a pseudo-random sequence corresponding to a combination of the primary and secondary synchronization codes;

transmitting the scrambled downlink reference signal.

27. The method of claim 26, the scrambling is performed in a portion of subframes of the downlink reference signal having a cyclic prefix length greater than a specified threshold.

28. The method of claim 27, further comprising:

scrambling a portion of subframes of the reference signal having a cyclic prefix length less than or equal to the threshold based at least in part on a pseudorandom sequence corresponding to the secondary synchronization code;

applying an orthogonal sequence to the scrambled subframes of the reference signal having a cyclic prefix length less than or equal to the threshold.

29. The method of claim 26, the pseudo-random sequence corresponds to the secondary synchronization code, and the primary synchronization code is a reuse factor of the pseudo-random sequence.

30. The method of claim 26, the combination of the primary and secondary synchronization codes identifies a transmitter of the reference signal.

31. A wireless communications apparatus, comprising:

at least one processor configured to:

a pseudo-random sequence associated with a selected primary and secondary synchronization code combination is obtained,

scrambling a downlink reference signal using the pseudo-random sequence;

a memory coupled to the at least one processor.

32. The wireless communications apparatus of claim 31, the at least one processor further configured to transmit a scrambled pseudo-random sequence.

33. The wireless communications apparatus of claim 31, the at least one processor scrambles a portion of subframes of the downlink reference signal having a cyclic prefix length greater than a specified threshold.

34. The wireless communications apparatus of claim 33, the at least one processor further configured to:

scrambling subframes of different portions of the reference signal having a cyclic prefix length less than the threshold based at least in part on different pseudo-random sequences corresponding to the secondary synchronization codes;

applying orthogonal sequences to the different portions of the subframe.

35. The wireless communications apparatus of claim 31, the pseudo-random sequence corresponds to the secondary synchronization code, and the primary synchronization code is a reuse factor of the pseudo-random sequence.

36. The wireless communications apparatus of claim 31, a combination of the primary and secondary synchronization codes identifies the wireless communications apparatus.

37. A wireless communications apparatus for scrambling downlink reference signals in a wireless communications network, comprising:

means for generating a downlink reference signal comprising a primary synchronization code and a secondary synchronization code;

means for scrambling the downlink reference signal based at least in part on a pseudo-random sequence corresponding to a combination of the primary and secondary synchronization codes.

38. The wireless communications apparatus of claim 37, further comprising means for transmitting a scrambled downlink reference signal.

39. The wireless communications apparatus of claim 37, the scrambling is performed in a portion of subframes of the downlink reference signal having a cyclic prefix length greater than a specified threshold.

40. The wireless communications apparatus of claim 39, further comprising:

means for scrambling a portion of subframes of the reference signal having a cyclic prefix length less than the threshold based at least in part on a pseudorandom sequence corresponding to the secondary synchronization code;

means for applying an orthogonal sequence to the scrambled subframes of the reference signal having a cyclic prefix length less than the threshold.

41. The wireless communications apparatus of claim 37, the pseudo-random sequence corresponds to the secondary synchronization code, and the primary synchronization code is a reuse factor of the pseudo-random sequence.

42. The wireless communications apparatus of claim 37, a combination of the primary and secondary synchronization codes identifies a transmitter of the reference signal.

43. A computer program product, comprising:

a computer-readable medium comprising:

code for causing at least one computer to generate a downlink reference signal comprising a primary synchronization code and a secondary synchronization code;

code for causing the at least one computer to scramble the downlink reference signal based at least in part on a pseudo-random sequence corresponding to a combination of the primary and secondary synchronization codes.

44. The computer program product of claim 43, the computer-readable medium further comprising: code for causing the at least one computer to transmit the scrambled downlink reference signal.

45. The computer program product of claim 43, the scrambling is performed in a portion of subframes of the downlink reference signal having a cyclic prefix length greater than a specified threshold.