Source: https://patents.google.com/patent/US8289836B2/en
Timestamp: 2019-05-22 01:07:49
Document Index: 634324523

Matched Legal Cases: ['art 16', 'Application No. 05736547', 'Application No. 200480005282', 'Application No. 200480005282', 'Application No. 200480005282', 'Application No. 20048005282', 'Application No. 20058000623', 'Application No. 94104653', 'Application No. 2005', 'Application No. 2005']

US8289836B2 - Apparatus and associated methods to introduce diversity in a multicarrier communication channel - Google Patents
Apparatus and associated methods to introduce diversity in a multicarrier communication channel Download PDF
US8289836B2
US8289836B2 US10/788,657 US78865704A US8289836B2 US 8289836 B2 US8289836 B2 US 8289836B2 US 78865704 A US78865704 A US 78865704A US 8289836 B2 US8289836 B2 US 8289836B2
US10/788,657
US20040257978A1 (en
2004-02-27 Priority to US10/788,657 priority patent/US8289836B2/en
2004-08-27 Assigned to INTEL CORPORATION reassignment INTEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ROY, SUMIT, SANDHU, SUMEET, SHAO, LEI
2004-12-23 Publication of US20040257978A1 publication Critical patent/US20040257978A1/en
2012-10-16 Publication of US8289836B2 publication Critical patent/US8289836B2/en
In broadband wireless access (BWA) networks (e.g., those described in the IEEE 802.16a standard, referred to below), deep fades may occur that can persist over a significant period of time. Further, such wide-area wireless channels encounter significant dispersion due to multipath propagation that limits the maximum achievable rates. Since BWA is intended to compete with cable modems and xDSL where the channel is static and non-fading, such system designs must counteract these key challenges and provide high data-rate access at almost wireline quality. To date, conventional techniques such as space-time block encoding, etc. fail to sustain the coding rate while providing the diversity gain as the number of transmit antenna increase past two (2). In this regard, such conventional techniques for providing broadband wireless access typically have to trade data rate (or, throughput) for received channel quality.
According to one embodiment, network 100 may represent a broadband wireless access (BWA) network wherein one or more of device(s) 102, 104 may establish a wireless communication channel in accordance with the specification of the Institute for Electrical and Electronics Engineers IEEE Std 802.16-2001 IEEE Std. 802.16-2001 IEEE Standard for Local and Metropolitan area networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems, and its progeny including, e.g., IEEE Std 802.16a-2003 (Amendment to IEEE Std 802.16-2001), although the invention is not limited in this regard.
As used herein, network 120 is intended to represent any of a broad range of communication networks including, for example a plain-old telephone system (POTS) communication network, a local area network (LAN), metropolitan area network (MAA), wide-area network (WAN), global area network (Internet), cellular network, and the like. According to one example implementation, device 102 represents an access point (AP), while device 104 represents a station (STA), each of which suitable for use within an IEEE 802.11n wireless local area network (WLAN), and each utilizing the innovative space-frequency interleaving and transmit diversity techniques introduced above, and developed more fully below.
As used herein, serial-to-parallel (S/P) transform 202 may receive information (e.g., bits, bytes, frames, symbols, etc.) from a host device (or, an application executing thereon, e.g., email, audio, video, etc.) for processing and subsequent transmission via the communication channel. According to one embodiment, the received information is in the form of quadrature amplitude modulated (QAM) symbols (i.e., wherein each symbol represents two bits, bi and bj). That is, according to one embodiment, the received content is modulated into symbols (e.g., QAM, BPSK, QPSK, 8-PSK, 16-PSK, 128-PSK, 256-PSK, and the like), and may be convolutionally encoded at a rate of one or more of e.g., ½, ⅔, ¾., ⅚, ⅞, 1, 4/3 and the like. According to an alternate embodiment, one or more of the bit mapping (modulation) and convolutional encoding may well be performed within transmitter 200, and may be performed by diversity agent 204. Unlike the conventional coding systems, where the coding rate must be reduced as the number of antenna(s) increase, the rate-one, space frequency block coding technique described herein has no such limitations.
According to one embodiment, the serial-to-parallel transform 202 may generate a number of parallel substreams of symbols, which are passed to one or more instances of diversity agent 204. Although depicted as a separate functional element, serial to parallel transform 202 may well be included within embodiments of diversity agent 204, or another element of the transmitter 200.
As used herein, any of a number of sphere decoder's may well be used as the sphere decoder(s) 266A . . . Y. According to one embodiment, described more fully below, the sphere decoder searches for the closest point among lattice points within a sphere of given radius centered at the receive point. For example, in the case of a QAM constellation, the sphere decoder may traverse the part of a lattice inside of a sphere (of sufficient radius) to identify signal vectors, and then filter out any vectors that are too far away from the received point, although the scope of the invention is not limited in this regard.
According to one example embodiment, the rate-one, space-frequency code employed herein contemplate use within a MIMO-OFDM system with M transmit and N receive antennas and Nc subcarriers, where Nc>>M,N, although the scope of the invention is not limited to such systems and is, indeed, extensible to any multicarrier communication system with any number of subcarriers, transmit antenna(e) and receive antenna(e). Let C and E be two different space-frequency code words represented by matrices of size M×Nc. Assuming that the MIMO channel consists of L (matrix) taps, an upper bound on the expected pairwise error probability (averaged over the, e.g., general Rayleigh fading channel realizations) was derived. For the special case of no spatial fading correlation and a uniform power delay profile, the upper bound can be expressed as:
P ⁡ ( C -> E ) ≤ ∏ i = 0 rank ⁡ ( S ) - 1 ⁢ ⁢ ( 1 + λ i ⁡ ( S ) ⁢ ρ 4 ) - N ( 1 )
where ρ is the average signal-to-noise ratio (SNR), λi(S) is the i-th nonzero eigenvalue of S. S=G(C,E)GH(C,E) has dimension Nc×Nc where G(C,E) is the Nc×ML matrix G(C,E)=[(C−E)TD(C−E)T . . . DL−1(C−E)T] and
D = { ⅇ - j ⁢ 2 ⁢ π Nc ⁢ k } k = 0 Nc - 1 .
Rate-one Space-frequency Encoding
According to one embodiment, the content is received by one or more pre-coders 212A . . . Z of diversity agent 204, which may begin the encoding process by dividing the received content into a number (G) of groups, block 304. According to one embodiment, the Nc×1 vector of input symbols s=[s0 Ts1 T . . . sG−1 T]T is divided into G groups of size ML×1 vectors {sG}g=0 G−1, although the invention is not limited in this regard.
In block 306, at least a subset of the vector of input symbols, sg is multiplied by a constellation-rotation (CR) pre-coder (e.g., within pre-coder 212)Θ. According to one embodiment, the same constellation-rotation Θ is applied to each of the Nc×1 vector of input symbols sG by left-multiplying the vector by the constellation rotation, although the invention is not limited in this regard. According to one embodiment, the constellation rotation Θ is of dimension ML×ML to produce size ML-vector vg=Θsg=[Θ1 Tsg, . . . ,ΘML Tsg]T, where Θi T denotes the ith row of Θ.
In block 308, at least a subset of the vectors vg is divided into L, M×1 subvectors, which are used to generate an M×M diagonal matrix Ds g ,k=diag{ΘM×(k−1)+1 Tsg, . . . ,ΘM×k Tsg} for k=1 . . . L. According to one example embodiment, L submatrices are regarded to be in the same group.
According to one embodiment, the rate-one, space-frequency encoder described above leverages the following desirable property of Θ: for all distinct pairs {sg,{tilde over (s)}g} and vg=Θsg, and {tilde over (v)}g=Θ{tilde over (s)}g, the corresponding error vector eg=(vg−{tilde over (v)}g) has substantially all nonzero elements. As a result, generating D{tilde over (s)} g ,k, for k=1 . . . L from {tilde over (s)}g, then the L diagonal matrices (Ds g ,k−D{tilde over (s)} g ,k) have all diagonal elements that are nonzero. Accordingly, all distinct pairs {sg,{tilde over (s)}g} give rise to L full-rank diagonal error matrices, which may be used to prove that the space-frequency codes proposed herein can achieve the maximum diversity gain of M N L. This proof is provided below.
Λ k , g j = diag ⁢ { H 1 , ( k - 1 ) ⁢ GM + gM j H 2 , ( k - 1 ) ⁢ GM + gM + 1 j ⋮ H M , ( k - 1 ) ⁢ GM + ( g + 1 ) ⁢ M - 1 j } ( 3 )
r j = ⁢ [ r j , 1 , 0 ⁢ r j , 1 , 1 ⁢ ⁢ … ⁢ ⁢ r j , L , G - 2 ⁢ r j , L , G - 1 ] T = ⁢ [ b j , 1 , 0 ⁢ b j , 1 , 1 ⁢ ⁢ … ⁢ ⁢ b j , L , G - 2 ⁢ b j , L , G - 1 ] T + ⁢ [ w j , 1 , 0 ⁢ w j , 1 , 1 ⁢ ⁢ … ⁢ ⁢ w j , L , G - 2 ⁢ w j , L , G - 1 ] T ⁢ ⁢ where ( 4 ) b j , k , g = Λ k , g j ⁡ [ Θ ( k - 1 ) ⁢ M + 1 T Θ ( k - 1 ) ⁢ M + 2 T ⋮ Θ kM T ] ⁢ s g ( 5 )
r j , g = ⁢ [ r j , 1 , g ⁢ r j , 2 , g ⁢ ⁢ … ⁢ ⁢ r j , L , g ] T ⁢ ⁢ = [ Λ 1 , g j ⋱ Λ L , g j ] ︸ Λ g j ⁢ Θ ⁢ ⁢ s g + w j , g ( 6 )
According to one embodiment, combining the information from the gth group over the N receive antennas is performed using a maximal ratio combiner element(s) 264, which yields:
y g = ( ( ∑ ( Λ g j ) H ⁢ Λ g j ) ︸ ∑ g ) - 1 / 2 × [ ( Λ g 1 ) H ⁢ ⁢ … ⁢ ⁢ ( Λ g N ) H ] ⁢ r g ( 7 )
=Σg 1/2Θsg+ηg (8)
Turning to FIGS. 5-7, graphical representations of various performance comparison's are provided, according to one example embodiment, each of which will be addressed in turn. According to one embodiment, for purposes of these simulations, an OFDM system conforming to the 802.16.3 standard was used with FFT size of 256. Modulation symbols used were BPSK, 4QAM (or, 16QAM) where the total average symbol energy on M transmit antennas Es=1.
From the equation (1) defining the upper bound on the expected pairwise error probability for the BWA communication environment, proving the diversity gain is substantially equivalent to proving that rank(S)=M L. Since S=G(C,E)GH(C,E) and rank(S)=rank(G(C,E)) is equivalent to rank(G(C,E)T), it suffices to show that rank(G(C,E)T)=M L, where G(C,E)T is a ML×Nc matrix:
G ⁡ ( C , E ) T =  ( C - E ) ( C - E ) ⁢ D ⋮ ( C - E ) ⁢ D L - 1  ( 9 )
D = diag ⁢ { ⅇ - j ⁢ 2 ⁢ π Nc ⁢ k } k = 0 Nc - 1 .
Consider the Nc×1 vectors s=[s0 T s1 T . . . sG−1 T]T, and {tilde over (s)}=[{tilde over (s)}0 T{tilde over (s)}1 T . . . {tilde over (s)}G−1 T]T and that s≠{tilde over (s)} for some g that is an element of {0, . . . , G−1}. Without loss of generality, let s0≠{tilde over (s)}0.
D = diag ⁢ { ⅇ - j ⁢ 2 ⁢ π Nc ⁢ k } k = 0 GL
( C - E ) ⁢ D i = ⁢ [ A 1 ⁢ ⁢ … ⁢ ⁢ A GL ] ⁡ [ D 1 i 0 … 0 ⋱ 0 0 … D GL i ] = ⁢ [ D 1 i ⁢ ⁢ … ⁢ ⁢ D GL i ] ⁡ [ A 1 0 … 0 ⋱ 0 0 … A GL ] ( 10 )
since both Aj and Dj i are diagonal matrices. Therefore we can show:
G ⁡ ( C , E ) T = [ I M I M ⋯ I M D 1 D 2 ⋯ D GL ⋮ ⋮ ⋮ ⋮ D 1 L - 1 D 2 L - 1 ⋯ D GL L - 1 ] × [ A 1 0 ⋯ 0 ⋱ 0 0 ⋯ A GL ] ( 11 )
receiving content, at a diversity agent, the content for transmission from a wireless communication system having M transmit antennae and N receive antennae and Nc subcarriers, where Nc>>M,N, the received content for transmission from more than two of the M transmit antennae, wherein the received content is a vector of input symbols (s) of size Nc×1, and wherein the Nc subcarriers is the number of subcarriers of a multicarrier wireless communication channel of the wireless communication system;
generating a rate-one, space-frequency code matrix from the received content for transmission via the more than two of the M transmit antennae by dividing the vector of input symbols into a number G of groups to generate subgroups and multiplying at least a subset of the subgroups by a constellation rotation precoder to produce a number G of pre-coded vectors (vg), wherein successive symbols from the same group transmitted from the same antenna are at a frequency distance that is multiples of MG subcarrier spacings;
wherein the diversity agent comprises an encoder to generate the rate one, space-frequency code matrix from the received content using a space frequency code; and
wherein the method further comprises the encoder applying the space frequency code to the received content to generate the rate-one, space-frequency code matrix, wherein the space frequency code only consumes one multicarrier communication channel block duration.
creating an M×M diagonal matrix Ds g ,k=diag{ΘM×(K−1)+1 Tsg, . . . , ΘM×k Tsg}, where k=1 . . . L from the subvectors.
3. A method according to claim 2, further comprising: interleaving the L submatrices from the G groups to generate an M×Nc space-frequency matrix.
4. A method according to claim 3, wherein the space-frequency matrix provides M N L channel diversity, while preserving a code rate of 1 for any number of the transmit antennae M, receive antennae N and channel tap(s) L.
5. A method according to claim 1, wherein the space-frequency matrix provides M N L channel diversity, while preserving a code rate of 1 for any number of the transmit antennae M, receive antennae N and channel tap(s) L.
transmitting the space frequency code in one OFDM block duration.
a diversity agent:
to receive content for transmission from a wireless communication system having M transmit antennae and N receive antennae and Nc subcarriers, where Nc>>M,N, the received content for transmission via a multicarrier wireless communication channel of the wireless communication system, wherein the received content is a vector of input symbols (s) of size Nc×1, and wherein the Nc subcarriers is the number of subcarriers of the multicarrier wireless communication channel;
to generate a rate-one, space-frequency code matrix from the received content for transmission on the multicarrier wireless communication channel from more than two of the M transmit antennae by dividing the vector of input symbols into a number G of groups to generate subgroups and multiplying at least a subset of the subgroups by a constellation rotation precoder to produce a number G of pre-coded vectors (vg), wherein successive symbols from the same group transmitted from the same antenna are at a frequency distance that is multiples of MG subcarrier spacings;
wherein the diversity agent comprises an encoder to generate the rate one, space-frequency code matrix from the received content using a space frequency code, and
8. An apparatus according to claim 7, the diversity agent further comprising:
the encoder embodying a space-frequency encoding element to, responsive to the pre-coder element, divide each of the pre-coded vectors into a number of LM×1 subvectors, and to create an M×M diagonal matrix Ds g ,k=diag{ΘM×(k−1)+1 Tsg, . . . , ΘM×k Tsg}, where k=1 . . . L from the subvectors.
9. An apparatus according to claim 8, wherein the space-frequency encoding element interleaves the L submatrices from the G groups to generate an M×Nc space-frequency matrix.
10. An apparatus according to claim 9, wherein the space-frequency matrix provides M N L channel diversity, while preserving a code rate of 1 for any number of the transmit antennae M, receive antennae N and channel tap(s) L.
11. An apparatus according to claim 7, wherein the space-frequency matrix provides M N L channel diversity, while preserving a code rate of 1 for any number of the transmit antennae M, receive antennae N and channel tap(s) L.
a number M of omnidirectional antennas, wherein M comprises more than two omnidirectional antennas;
a number N of receive antennae;
a number Nc of subcarriers of a multicarrier wireless communication channel of the wireless communication system, where Nc>>M,N; and
to receive content for transmission via the multicarrier wireless communication channel, wherein the received content is a vector of input symbols (s) of size Nc×1, and
to generate a rate-one, space-frequency code matrix from the received content for transmission on the multicarrier wireless communication channel from at least a subset of the M omnidirectional antennas by dividing the vector of input symbols into a number G of groups to generate subgroups and multiplying at least a subset of the subgroups by a constellation rotation precoder to produce a number G of pre-coded vectors (vg), wherein successive symbols from the same group transmitted from the same antenna are at a frequency distance that is multiples of MG subcarrier spacings;
13. A wireless communication system according to claim 12, the diversity agent further comprising:
14. A wireless communication system according to claim 13, wherein the space-frequency encoding element interleaves the L submatrices from the G groups to generate an M×Nc space-frequency matrix.
15. A wireless communication system according to claim 14, wherein the space-frequency matrix provides M N L channel diversity, while preserving a code rate of 1 for any number of the omnidirectional antennas M, receive antennae N and channel tap(s) L.
16. A wireless communication system according to claim 12, wherein the space-frequency matrix provides M N L channel diversity, while preserving a code rate of 1 for any number of the omnidirectional antennas M, receive antennae N and channel tap(s) L.
passing the rate-one, space-frequency code matrix as encoded content from the diversity agent to one or more inverse discrete Fourier transform (IDFT) elements; and
transforming the encoded content from frequency domain into time domain content.
18. The method of claim 17, wherein a quantity of the IDFT elements is commensurate with a quantity of the M transmit antennae.
passing the time domain content to one or more cyclical prefix insertion (CPI) elements to introduce a cyclical prefix or a guard interval prior to transmission via the M transmit antennae.
US10/788,657 2003-02-27 2004-02-27 Apparatus and associated methods to introduce diversity in a multicarrier communication channel Expired - Fee Related US8289836B2 (en)
US10/788,657 US8289836B2 (en) 2003-02-27 2004-02-27 Apparatus and associated methods to introduce diversity in a multicarrier communication channel
EP20050736547 EP1721404A1 (en) 2004-02-27 2005-02-14 An apparatus and associated methods to introduce diversity in a multicarrier communication channel
CN 200580006236 CN1938978A (en) 2004-02-27 2005-02-14 Apparatus and associated methods to introduce diversity in a multicarrier communication channel
PCT/US2005/004478 WO2005093987A1 (en) 2004-02-27 2005-02-14 An apparatus and associated methods to introduce diversity in a multicarrier communication channel
TW94104653A TW200534628A (en) 2004-02-27 2005-02-17 An apparatus and associated methods to introduce diversity in a multicarrier communication channel
US20040257978A1 US20040257978A1 (en) 2004-12-23
US8289836B2 true US8289836B2 (en) 2012-10-16
ID=34966163
US10/788,657 Expired - Fee Related US8289836B2 (en) 2003-02-27 2004-02-27 Apparatus and associated methods to introduce diversity in a multicarrier communication channel
US (1) US8289836B2 (en)
EP (1) EP1721404A1 (en)
CN (1) CN1938978A (en)
TW (1) TW200534628A (en)
WO (1) WO2005093987A1 (en)
2004-02-27 US US10/788,657 patent/US8289836B2/en not_active Expired - Fee Related
2005-02-14 CN CN 200580006236 patent/CN1938978A/en not_active Application Discontinuation
2005-02-14 EP EP20050736547 patent/EP1721404A1/en not_active Withdrawn
2005-02-14 WO PCT/US2005/004478 patent/WO2005093987A1/en active Application Filing
2005-02-17 TW TW94104653A patent/TW200534628A/en unknown
Final Office Action for U.S. Appl. No. 10/789,387, mailed May 13, 2009, 11 pgs.
Final Office Action for U.S. Appl. No. 10/789,387, mailed Sep. 20, 2007, 6 pgs.
Gowrisankar, A Rate-one Full-diversity Low-complexity Space-Time-Frequency Block Code (STFBC) for 4-Tx MIMO-OFDM, 2005, vol. 2, pp. 2090-2094. *
Helmut Bolcskei, et al., "Space-Frequency Coded Broadband OFDM Systems" 2000 IEEE Wireless Communications and Networking Conference, Sep. 23, 2000, pp. 1-6, vol. 1.
International Preliminary Report on Patentability for Application No. PCTUS2004005968, mailed Sep. 2, 2005, 7 pages.
International Preliminary Report on Patentability for Application No. PCTUS2005004478, mailed Aug. 30, 2006, 5 pages.
International Search Report for Application No. PCTUS2004005968, mailed Aug. 30, 2004, 4 pages.
International Search Report for Application No. PCTUS2005004478, mailed Apr. 8, 2005, 5 pages.
King F. Lee, et al., "A Space-Frequency Transmitter Diversity Technique for OFDM Systems", Globecomm 2000, IEEE Global Telecommunications Conference, Nov. 27, 2000, pp. 1473-1477, vol. 3, San Francisco, CA USA.
Lei Shao, et al., "Rate-one Space Frequency Block Codes with Maximum Diversity Gain for MIMO-OFDM", IEEE Global Telecommunications Conference Globecom 2003, Dec. 1, 2003, pp. 809-813, vol. 2.
Li Lihua, "A Practical Space-Frequency Block Coded OFDM Scheme for Fast Fading Broadband Channels", IEEE International symposium on personal indoor and mobile radio communications, PIMRC, Sep. 15, 2002, pp. 212-216, vol. 1, Sections II, IV.
Maxime Guillaud, et al., "Full-Rate Full-Diversity Space-Frequency Coding for MIMI OFDM Systems" Proceedings of the 3rd Benelux Signal Processing Symposium, Mar. 21, 2002, pp. S02-1-S02-4, Section 2, Leuven, Belgium.
Office Action for Application No. 05736547.0, dated Mar. 5, 2010, 5 pgs.
Office Action for Application No. 200480005282.9, dated Dec. 18, 2009, 18 pgs.
Office Action for Application No. 200480005282.9, dated May 28, 2008, 25 pgs.
Office Action for Application No. 200480005282.9, dated Sep. 29, 2011, 13 pages.
Office Action for Application No. CN200580006236.5, dated Mar. 24, 2010, 14 pgs.
Office Action for Application No. PI 20050794, dated Nov. 30, 2011, 3 pages.
Office Action for China Patent Application No. 20048005282.9, mailed May 28, 2008, 25 pgs.
Office Action for Chinese Patent Application No. 20058000623.5, mailed Apr. 17, 2009, 10 pgs.
Office Action for Malaysian Patent Application No. PI 20050652, mailed Oct. 14, 2008, 10 pgs.
Office Action for Malaysian Patent Application No. PI 20050794, mailed Jun. 13, 2008, 7 pgs.
Office Action for Taiwan Patent Application No. 94104653, mailed May 16, 2008.
Office Action for U.S. Appl. No. 10/789,387, mailed Apr. 20, 2007, 14 pgs.
Office Action for U.S. Appl. No. 10/789,387, mailed Dec. 30, 2008, 6 pgs.
Office Action for U.S. Appl. No. 10/789,387, mailed Mar. 17, 2008, 5 pgs.
Office Action for U.S. Appl. No. 10/789,387, mailed Nov. 10, 2009, 11 pgs.
Office Action for U.S. Appl. No.10/789,387, mailed Sep. 4, 2008, 8 pgs.
Tirkkonen, Olav et al., "Minimal Non-Orthogonality Rate 1 Space-Time Block Code for 3+ Tx Antennas", Spread Spectrum Techniques and Applications, 2000 IEEE Sixth International Symposium on, Publication Date: 2000, vol. 2, pp. 429-432.
Translation of Office Action for Japanese Patent Application No. 2005-518591, mailed Feb. 29, 2008, 7 pgs.
Translation of Office Action for Korean Patent Application No. 2005-7015839, mailed Dec. 12, 2008, 2 pgs.
Written Opinion for Application No. PCTUS2004005968, mailed Aug. 26, 2004, 6 pages.
Written Opinion for Application No. PCTUS2005004478, mailed Aug. 2, 2005, 4 pages.
US20040257978A1 (en) 2004-12-23
CN1938978A (en) 2007-03-28
EP1721404A1 (en) 2006-11-15
TW200534628A (en) 2005-10-16
WO2005093987A1 (en) 2005-10-06
US20170163383A1 (en) 2017-06-08 Method and apparatus for implementing space time processing
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SHAO, LEI;ROY, SUMIT;SANDHU, SUMEET;REEL/FRAME:015733/0229;SIGNING DATES FROM 20040728 TO 20040817
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SHAO, LEI;ROY, SUMIT;SANDHU, SUMEET;SIGNING DATES FROM 20040728 TO 20040817;REEL/FRAME:015733/0229