HK1145737A - Reference signal generation in a wireless communication system - Google Patents

Description

Reference signal generation in a wireless communication system

This application claims priority to U.S. provisional application No.60/955,801, entitled "METHOD AND APPARATUS FOR REFERENCE SIGNAL GENERATION FOR E-UTRAN", filed on 8, 14, 2007, which is assigned to the assignee of the present application and incorporated herein by reference.

Technical Field

The present disclosure relates generally to communication, and more specifically to techniques for generating reference signals in a wireless communication system.

Background

Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These wireless systems may be multiple-access systems capable of supporting multiple users by sharing the available system resources. 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 FDMA (OFDMA) systems, and single-carrier FDMA (SC-FDMA) systems.

A wireless communication system may include any number of node bs that may support communication for any number of User Equipments (UEs). Each node B supports one or more cells and periodically transmits a reference signal for each cell. The reference signals may also be referred to as pilots. The reference signals from the cells may be used by the UE for various purposes, such as channel estimation, signal strength measurements, signal quality measurements, and so on. It may be desirable to generate the reference signals in some manner in order to provide good performance and simplify the reference signal processing procedures at the node B and the UE.

Disclosure of Invention

Techniques for generating reference signals in a wireless communication system are described. In one aspect, a set of Q reference signal sequences may be generated from G pseudo-random sequences and L scrambling sequences, where Q ═ G · L, G > 1, and L > 1. Each reference signal sequence may be generated according to a particular pseudo-random sequence and a particular scrambling sequence. The Q reference signal sequences may be used for Q cell Identities (IDs), one reference signal sequence per cell ID.

In one design, the node B may determine the first index and the second index based on a cell ID of the cell. The node B may generate a pseudo-random sequence based on the first index and a scrambling sequence based on the second index. The scrambling sequence may be generated from a maximal length sequence (M-sequence), a Golay complementary sequence, etc. The node B may generate a reference signal sequence from the pseudo-random sequence and the scrambling sequence, e.g., by symbol-by-symbol multiplying the pseudo-random sequence with the scrambling sequence. The node B may then generate a reference signal for the cell based on the reference signal sequence, e.g., by mapping the reference signal sequence onto a set of subcarriers and generating OFDM symbols using the reference signal sequence mapped to the set of subcarriers.

In one design, the UE may determine the first and second indices based on a cell ID of a cell detected by the UE. The UE may generate a pseudo-random sequence according to the first index, generate a scrambling sequence according to the second index, and generate a reference signal sequence according to the pseudo-random sequence and the scrambling sequence. The UE may process the reference signal received from the cell according to the reference signal sequence. The UE may perform channel estimation, signal strength measurement, signal quality measurement, time tracking, frequency tracking, noise estimation, and/or other functions based on reference signals from the cell.

Various aspects and features of the disclosure are described in further detail below.

Drawings

Fig. 1 shows a wireless communication system.

Fig. 2 shows an exemplary transmission of synchronization and reference signals.

Fig. 3 shows a design for generating a reference signal sequence.

Fig. 4A illustrates reference signal transmission for a conventional cyclic prefix.

Fig. 4B illustrates reference signal transmission for an extended cyclic prefix.

Fig. 4C shows reference signal transmission from two antennas.

Fig. 5 shows a block diagram of a node B and a UE.

Fig. 6 shows synchronization and reference signal generators at a node B.

Fig. 7 shows synchronization and reference signal generators at a UE.

Fig. 8 shows a process of generating synchronization and reference signals.

Fig. 9 shows an apparatus for generating synchronization and reference signals.

Fig. 10 shows a process for receiving synchronization and reference signals.

Fig. 11 shows an apparatus for receiving synchronization and reference signals.

Detailed Description

The techniques described herein may be used for various wireless communication systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other systems. 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, etc. UTRA includes wideband CDMA (wcdma) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards.TDMA systems may implement radio technologies such as global system for mobile communications (GSM). OFDMA systems may implement, for example, evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDMEtc. radio technologies. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System (UMTS). 3GPP Long Term Evolution (LTE) is a upcoming release of UMTS that uses E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE, and GSM are described in documents from an organization named "third Generation partnership project" (3 GPP). Cdma2000 and UMB are described in documents from an organization named "third generation partnership project 2" (3GPP 2). For clarity, certain aspects of the present technology are described below for LTE, and LTE terminology is used in much of the description below.

Fig. 1 shows a wireless communication system 100, which may be an LTE system. System 100 may include any number of node bs and other network entities. For simplicity, only three node bs 110a, 110B, and 110c are shown in fig. 1. A node B may be a fixed station that communicates with UEs and may also be referred to as an evolved node B (enb), a base station, an access point, etc. Each node B110 provides communication coverage for a particular geographic area 102. To improve system capacity, the overall coverage area of the node B may be divided into a number of smaller areas, e.g., three smaller areas 104a, 104B, and 104 c. Each smaller area may be served by a respective node B subsystem. In 3GPP, the term "cell" refers to the smallest coverage area of a node B and/or a node B subsystem serving this coverage area. In other systems, the term "sector" refers to the smallest coverage area of a base station and/or a base station subsystem serving this coverage area. For simplicity, the 3GPP concept of a cell is used in the following description.

In the example shown in fig. 1, each node B110 has three cells 1, 2, and 3, which cover different geographical areas. The cells of node bs 110a, 110B, and 110c may operate on the same frequency or different frequencies. For clarity, fig. 1 shows cells that do not overlap with each other. In practical configurations, adjacent cells typically overlap each other at the edges. This overlap of coverage edges ensures that the UE can be within the coverage of one or more cells anywhere the UE moves in the system.

UEs 120 may be dispersed throughout the system, and each UE may be fixed or mobile. A UE may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, etc. The UE may be a cellular phone, a Personal Digital Assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop, a cordless phone, etc. A UE may communicate with a node B via transmissions on the downlink and uplink. The downlink (or forward link) refers to the communication link from the node bs to the UEs, and the uplink (or reverse link) refers to the communication link from the UEs to the node bs. In fig. 1, a solid line with double arrows indicates communication between the node B and the UE. The dotted line with a single arrow indicates that the UE receives a downlink signal from the node B. The UE may perform cell search and other functions based on the downlink signals transmitted by the node B.

In system 100, each node B may periodically transmit a primary synchronization signal and a secondary synchronization signal for each cell in the node B. The UE may search for the primary and secondary synchronization signals in order to detect cells and obtain information such as cell IDs, timing and frequency offsets of the detected cells. Each node B may also periodically transmit a reference signal for each cell in the node B. The UE may use the reference signals from the detected cells for various functions, such as channel estimation, signal strength measurements, signal quality measurements, and so on.

Fig. 2 illustrates exemplary transmissions of primary and secondary synchronization signals and a reference signal for a cell in accordance with one design. The transmission timeline for the downlink may be divided into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be divided into 20 slots, with indices of 0 through 19. Each slot may cover a fixed or configurable number of symbol periods, e.g., 6 symbol periods for an extended cyclic prefix and 7 symbol periods for a normal cyclic prefix.

In the design shown in fig. 2, each slot includes 7 symbol periods with indices of 0 through 6. The primary and secondary synchronization signals may be transmitted in symbol periods 6 and 5 of each slot 0 and slot 10, respectively, of each radio frame. The reference signal may be transmitted in symbol periods 0 and 4 of each slot of each radio frame.

In general, each of the primary and secondary synchronization signals and the reference signal may each be transmitted at any rate, e.g., any number of times in each radio frame. The primary and secondary synchronization signals may be transmitted in any two symbol periods of the slot. The secondary synchronization signal may be transmitted in the vicinity of (e.g., immediately before or after) the primary synchronization signal, such that a channel estimate may be derived from the primary synchronization signal and used for coherent detection of the secondary synchronization signal. The reference signal may be transmitted in any number of symbol periods and in any symbol period of each slot. The reference signals may be spaced as uniformly as possible in the symbol period of each slot.

Each cell is assigned a cell ID that is unique among all cells within a certain range of the cell. The cell ID assignment allows each UE to uniquely identify all cells detected by the UE regardless of the UE's location. The system may support a set of Q cell IDs, Q may be any integer value. Each cell is then assigned a specific cell ID from the set of supported cell IDs.

In one design, the system supports a set of Q504 unique cell IDs. The 504 cell IDs may be grouped into 168 unique cell ID groups, each cell ID group including three unique cell IDs. The grouping is such that each cell ID is included in only one cell ID group.

In one design, the cell ID may be represented as:

C_ID3g + l, formula (1)

Wherein, C_IDE { 0., 503} is the cell ID,

g ∈ { 0.,. 167} is an index of a cell ID group to which the cell ID belongs;

l ∈ {0, 1, 2} is the index of the particular ID in the cell ID group.

In the design shown in equation (1), the cell ID may be defined by (i) a first number or range within 0 to 167 that represents the index of the group of cell IDs and (ii) a second number or range within 0 to 2 that represents the index of the IDs in the group of cell IDs.

In general, any number of cell IDs (q) may be supported, and the cell IDs may be grouped into any number of groups (G), each of which may include any number of cell IDs (l). For clarity, much of the description below is for the design described above with a total of 504 cell IDs, 168 cell ID groups and 3 cell IDs in each group.

Three Primary Synchronization Code (PSC) sequences can be defined for the three possible values of index/for the three cell IDs in each group. In addition, 168 Secondary Synchronization Code (SSC) sequences may be defined for 168 possible values of index g of the 168 possible cell ID groups. The PSC and SSC sequences can be represented as follows:

·d_psc，l(n) is the PSC sequence with index l, where l ∈ {0, 1, 2}

·d_ssc，g(n) is an SSC sequence of index g, where g ∈ { 0., 167},

where n ∈ { 0.,. 61} is the symbol index of the PSC and SSC sequences. The index g is also referred to as the SSC index and the index l is also referred to as the PSC index.

The PSC sequence can be generated from a Zadoff-Chu sequence. An SSC sequence can be generated based on one or more M sequences. The PSC and SSC sequences can be as publicly available under the designation "EVOLVED Universal Terrestrial Radio Access (E-UTRA); physical Channels and modulation (Release 8) "as described in 3GPP TS 36.211.

In one aspect, Q reference signal sequences may be generated from G pseudo-random sequences and L scrambling sequences, where Q is G · L. Each reference signal sequence may be generated according to a particular pseudo-random sequence and a particular scrambling sequence. Q reference signal sequences may be used for Q cell IDs, one reference signal sequence per cell ID. Each cell may generate a reference signal from a reference signal sequence corresponding to its cell ID.

In one design, the pseudorandom sequence, the scrambling sequence, and the reference signal sequence may be represented as follows:

·p_g(n) is a pseudorandom sequence of SSC indices g, where g ∈ { 0., 167}

·s_l(n) is the scrambling sequence of PSC index l, where l ∈ {0, 1, 2}

·r_g，l(n) is a reference signal sequence of PSC index l and SSC index g,

where N ∈ { 0.,. N-1} is the symbol index. N may be equal to 220 or some other value.

In the above design, the index g of the cell ID group is used for the index g of the pseudo random sequence. Thus, a pseudo-random sequence is linked to the SSC sequence. The index/of the ID in the cell ID group is used for the index/of the scrambling sequence. Thus, the scrambling sequence is linked to the PSC sequence. Each cell ID is mapped to a particular PSC sequence d_psc，l(n) a specific SSC sequence d_ssc，g(n) a specific pseudo-random sequence p_g(n) a specific scrambling sequence s_l(n) and a specific reference signal sequence r_g，l(n)。

The pseudo-random sequence may be generated in various ways. In one design, G pseudo-random sequences may be generated from an M sequence. In another design, the pseudo-random sequence may be generated from a Gold sequence c (n), which may be expressed as:

c(n)＝[x₁(n)+x₂(n)]mod 2 formula (2)

Wherein x is₁(n+31)＝[x₁(n+3)+x₁(n)]mod 2，

x₂(n+31)＝[x₂(n+3)+x₂(n+2)+x₂(n+1)+x₂(n)]mod 2, and

"mod" denotes a modulo operation.

In the formula (2), x₁(n) is a first M-sequence generated from a first generator polynomial, x₂(n) is a second M-sequence generated according to a second generator polynomial. Each M-sequence may be generated using a Linear Feedback Shift Register (LFSR), where the LFSR implements a generator polynomial for the M-sequence. Each LFSR may be initialized to an appropriate initial value. The first and second M sequences and the Gold sequence have a length of 2³¹-1. The Gold sequence c (n) has a value of 0 or 1 for each value of n.

The G pseudo-random sequences can be generated from the Gold sequence as follows:

formula (3)

In equation (3), the pseudo-random sequence p_g(n) by complex valued symbolsEach complex-valued symbol is defined by two consecutive symbols of a Gold sequence. The Gold sequence is based on an initial value c_initGenerated, the initial value may be determined according to the SSC index g. Different pseudo-random sequences may be generated with different initial values of the Gold sequence. Initial value c_initCan be used to initialize a first M-sequence x₁(n) LFSR and/or second M sequence x₂(n) LFSR.

In one design, a cell may use the same pseudo-random sequence for each symbol period in which a reference signal is transmitted. In this design, the initial value c_initCan be a function of the SSC index g, or c_initF (g), where f () may be any suitable function. In another design, the cell may use a different pseudo-random sequence for a different symbol period for each slot or for each subframe of two slots. In this design, the initial value c_initCan be a function of the SSC index g and the symbol period index t, or c_initF (g, t). In another design, the cell may use different pseudo-random sequences for different time slots or subframes. In this design, the initial value c_initMay be a function of the SSC index g and the slot or subframe index s, or c_initF (g, s). In another design, a cell may use different pseudo-random sequences for different symbol periods in different slots or subframes. In this design, the initial value c_initMay be a function of the SSC index g and the symbol period index t and the slot or subframe index s, or c_initF (g, t, s). In general, the pseudo-random sequence may (i) be static and used for all symbol periods in which reference signals are transmitted, or (ii) may vary for different symbol periods, different time slots, different subframes, etc.

The L scrambling sequences may be generated in various ways. In one design, scrambling sequences may be generated from the L M sequences, each scrambling sequence being generated from a different M sequence. In another design, the scrambling sequences may be generated from different cyclic shifts of a single M-sequence. In another design, the scrambling sequence may be generated from a Golay complementary sequence. Marcel j.e.golay in the title "comparative Series" IRE trans. inform. theory, IT-7: 82-87, 1961, describes a direct construction method for generating different Golay complementary sequence pairs of any length N. Different N pairs of Golay complementary sequences of length N can also be obtained by multiplying a pair of Golay complementary sequences of length N with an nxn Hadamard matrix. The scrambling sequence may also be generated in other ways, for example with other types of sequences with good correlation.

In one design, the scrambling sequence has the same length N as the pseudorandom sequence. In another design, a shorter scrambling sequence of length S may be extended by repeating as many times as necessary to obtain a scrambling sequence of length N. The shorter scrambling sequence may be extended as follows:

s_l(n+i·S)＝s′_l(n), where i ═ 0, 1.., formula (4)

Wherein, s'_l(n) is a shorter scrambling sequence for PSC index l.

In one design, a reference signal sequence may be generated from a pseudorandom sequence and a scrambling sequence as follows:

r_g，l(n)＝p_g(n)·s_l(n), where l ∈ {0, 1, 2} and g ∈ { 0., 167} formula (5)

LTE utilizes Orthogonal Frequency Division Multiplexing (OFDM) on the downlink. OFDM divides the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. The distance between adjacent subcarriers is fixed and the total number of subcarriers (K) depends on the system bandwidth. Each subcarrier may be modulated with data.

To generate OFDM symbols, real and/or complex-valued symbols may be mapped onto subcarriers used for transmission and 0 symbols having a signal value of 0 may be mapped onto subcarriers not used for transmission. A total of K symbols for the K total subcarriers are transformed with a K-point Inverse Fast Fourier Transform (IFFT) to obtain a useful portion containing K time-domain samples. The last C samples of the useful portion are copied and appended to the front of the useful portion to form an OFDM symbol containing K + C samples. The copied portion is called a cyclic prefix and is used to cope with inter-symbol interference (ISI) due to frequency selective fading. LTE supports a normal cyclic prefix with a normal value of C and an extended cyclic prefix with a larger value of C. A slot may include 7 symbol periods for a normal cyclic prefix or 6 symbol periods for an extended cyclic prefix.

Fig. 3 shows a design for generating reference signals for a cell. The pseudo-random sequence p can be generated_g(n) with a scrambling sequence s_l(n) symbol-by-symbol multiplying to generate a reference signal sequence r_g，l(n) as shown in formula (5). The N symbols of a reference signal sequence may be mapped to an index k for transmitting the reference signal₀To k_N-1On a set of N subcarriers. The subcarriers used for the reference signal are spaced apart from each other by a predetermined number of subcarriers, for example, 6 subcarriers. Subcarriers not used for reference signals may be used for transmitting data and/or other information.

Fig. 4A shows a design for transmitting reference signals from one antenna of one cell using a conventional cyclic prefix. In this design, each slot includes 7 symbol periods 0 through 6, and each reference signal is transmitted in symbol periods 0 through 4 of each slot. The reference signal is transmitted in symbol period 0 on a first set of subcarriers, which are spaced 6 subcarriers apart. The reference signal is transmitted in symbol period 4 on a second set of subcarriers, which are also spaced 6 subcarriers apart. The subcarriers in the second group are offset from the subcarriers in the first group by 3 subcarriers.

Fig. 4B shows a design for transmitting reference signals from one antenna of one cell with an extended cyclic prefix. In this design, each slot includes 6 symbol periods 0 through 5, and the reference signal is transmitted in symbol periods 0 and 3 of each slot. The reference signals are transmitted on a first set of subcarriers in symbol period 0 and on a second set of subcarriers in symbol period 3.

Fig. 4C shows a design for transmitting reference signals from two antennas of a cell using a conventional cyclic prefix. In this design, for antenna 0, the reference signal is sent on the first set of subcarriers in symbol period 0 of each slot and on the second set of subcarriers in symbol period 4 of each slot. For antenna 1, the reference signal is sent on the second set of subcarriers in symbol period 0 of each slot and on the first set of subcarriers in symbol period 4 of each slot. The subcarriers used by one antenna for transmission of the reference signal are not used by the other antennas for transmission.

In general, reference signals may be transmitted from any number of antennas. A reference signal may be transmitted from one antenna on a set of subcarriers in one symbol period and no signal is transmitted from other antennas on the set of subcarriers in order to avoid interference with the reference signal.

Fig. 5 shows a block diagram of a design of node B110 and UE 120, which are one of the node bs and one of the UEs in fig. 1. In this design, node B110 is equipped with T antennas 534a through 534T, and UE 120 is equipped with R antennas 552a through 552R, typically T ≧ 1 and R ≧ 1.

At node B110, a transmit processor 520 may receive data for one or more UEs from a data source 512, process the data for each UE according to a modulation and coding scheme selected for that UE, and provide data symbols for all UEs. Transmit processor 520 may also generate primary and secondary synchronization signals and reference signals for each cell and provide the symbols for the primary and secondary synchronization signals and reference signals for all cells in node B110. A Transmit (TX) multiple-input multiple-output (MIMO) processor 530 may multiplex the data symbols, pilot symbols, and symbols for the synchronization and reference signals. TX MIMO processor 530 may perform spatial processing (e.g., precoding) on the multiplexed symbols, if applicable, and may provide T output symbol streams to T Modulators (MODs) 532a through 532T. Each modulator 532 may process a respective output symbol stream (e.g., for OFDM) to obtain an output sample stream. Each modulator 532 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. T downlink signals from modulators 532a through 532T may be transmitted through T antennas 534a through 534T, respectively.

At UE 120, antennas 552a through 552r may receive downlink signals from node B110 and provide received signals to demodulators (DEMODs) 554a through 554r, respectively. Each demodulator 554 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples and further process the input samples (e.g., for OFDM) to obtain received symbols. A MIMO detector 556 may obtain received symbols from all R demodulators 554a through 554R, perform MIMO detection on the received symbols if available, and provide detected symbols. A receive processor 558 may process (e.g., demodulate, deinterleave, and decode) the detected symbols and provide decoded data for UE 120 to a data sink 560. In general, the processing by MIMO detector 556 and receive processor 558 is complementary to the processing by TX MIMO processor 530 and transmit processor 520 at node B110.

On the uplink, at UE 120, data from a data source 562 and signaling from controller/processor 580 may be processed by a transmit processor 564, further processed by a TXMIMO processor 566 if applicable, conditioned by modulators 554a through 554r, and transmitted to node B110. At node B110, the uplink signals from UE 120 may be received by antennas 534, conditioned by demodulators 532, processed by a MIMO detector 536 if appropriate, and further processed by a receive processor 538 to obtain the data and signaling sent by UE 120.

Controllers/processors 540 and 580 may direct operation at node B110 and UE 120, respectively. Memories 542 and 582 may store data and program codes for node B110 and UE 120, respectively. A scheduler 544 may schedule UEs for downlink and/or uplink transmissions and provide resource allocations for the scheduled UEs. A synchronization and reference signal processor 570 at UE 120 may perform processing for the primary and secondary synchronization signals and the reference signal.

Fig. 6 shows a block diagram of a design of synchronization and reference signal generator 600 of node B110. Generator 600 may be part of transmit processor 520 and/or modulator 532 in fig. 5. Generator 600 may receive a cell ID for cell x and generate primary and secondary synchronization signals for cell x and a reference signal.

In generator 600, index mapper 610 can receive a cell ID for cell x and provide a PSC index l and SSC index g corresponding to the cell ID, e.g., as shown in equation (1). The generator 622 can generate the PSC sequence for cell x based on the PSC index/. Generator 624 can generate a primary synchronization signal for cell x based on the PSC sequence, e.g., by mapping symbols of the PSC sequence onto subcarriers used for the primary synchronization signal and performing OFDM modulation on the mapped symbols.

The generator 632 can generate the SSC sequence for cell x based on the SSC index g and PSC index l. The generator 634 may generate a secondary synchronization signal for cell x based on the SSC sequence, e.g., by mapping symbols of the SSC sequence onto subcarriers used for the secondary synchronization signal and performing OFDM modulation on the mapped symbols.

The generator 642 may generate a pseudo-random sequence for cell x based on the SSC index g, e.g., as shown in equations (2) and (3). The generator 644 may generate a scrambling sequence for cell x based on the PSC index l. The generator 646 may generate a reference signal sequence for cell x based on the pseudo-random sequence and the scrambling sequence, e.g., as shown in equation (5). The generator 648 may generate a reference signal for cell x from the reference signal sequence, e.g., by mapping symbols of the reference signal sequence onto subcarriers for the reference signal and performing OFDM modulation on the mapped symbols.

The generator 600 may generate primary and secondary synchronization signals and a reference signal for all cells in the node B110. The generator 600 can generate primary and secondary synchronization signals for each cell based on different combinations of PSC and SSC sequences determined by the cell ID of the cell. The generator 600 may also generate reference signals for each cell based on different combinations of the pseudo-random sequence and the scrambling sequence determined by the cell ID for that cell.

Fig. 7 shows a block diagram of a design of synchronization and reference signal processor 570 at UE 120 in fig. 5. In this design, processor 570 includes sample buffer 710, a synchronization signal processor comprised of blocks 722, 724, and 726, and a reference signal processor comprised of blocks 732 through 744. Sample buffer 710 may receive and store input samples and provide the appropriate input samples when requested.

The synchronization signal processor may detect the primary synchronization signal and the secondary synchronization signal in order to search for a cell. In the synchronization signal processor, a detector 722 may detect the primary synchronization signal in each timing hypothesis (e.g., each sampling period). The detector 722 can correlate the input samples with different possible PSC sequences to obtain a correlation result for each timing hypothesis. The detector 722 can then determine whether a primary synchronization signal is detected based on the correlation result. If a primary synchronization signal is detected, detector 722 can provide the detected PSC sequence, symbol timing, and information transmitted in the primary synchronization signal (e.g., PSC index /).

Upon detecting the primary synchronization signal, the detector 724 may detect the secondary synchronization signal. Detector 724 may remove frequency offset from the input samples, convert the frequency-corrected samples to the frequency domain, and perform coherent detection on the frequency domain symbols with a channel gain derived from the detected primary synchronization signal to obtain input symbols. Detector 724 may then correlate the input symbols with different possible SSC sequences to obtain a correlation result and determine whether a secondary synchronization signal is detected based on the correlation result. If a secondary synchronization signal is detected, detector 724 can provide the detected SSC sequence, frame timing, and information sent in the secondary synchronization signal (e.g., SSC index g). The lookup table 726 can receive the detected PSC index l and SSC index g and provide the cell ID of the detected cell.

A reference signal processor may process reference signals from each detected cell. In the reference signal processor, a generator 732 can generate a scrambling sequence for a detected cell according to a PSC index/of the cell. The generator 734 may generate a pseudo-random sequence for a detected cell based on the SSC index g for the cell. The generator 736 may generate a reference signal sequence of the detected cell according to the pseudo-random sequence and the scrambling sequence. A detector 738 may remove the frequency offset from the input samples and convert the frequency corrected samples to the frequency domain to obtain received symbols. Detector 738 may multiply the received symbols with the symbols of the reference signal sequence to obtain detected symbols corresponding to all subcarriers used to transmit the reference signal.

Channel estimator 740 may derive a channel estimate for the detected cell based on the detected symbols. In one design, channel estimator 740 may convert detected symbols to the time domain to obtain channel taps, perform thresholding and low energy channel taps to 0, perform truncation, and convert the resulting channel taps to the frequency domain to obtain channel gains for subcarriers of interest. Channel estimator 740 may also perform channel estimation in other ways. The channel estimates may be used for spatial processing by MIMO detector 556 in fig. 5 and/or for coherent detection by other units at UE 120.

The signal strength measurement unit 742 may measure the signal strength of the detected cells from the detected symbols, e.g., by accumulating the power of the detected symbols. The signal strength measurements may be used to select a suitable cell for communication, make handover decisions, and so on. The signal quality measurement unit 744 may measure the received signal quality of the detected cell from the detected symbols, e.g., by dividing the power of the detected symbols by the estimated interference and noise power. Unit 744 may also derive Channel Quality Indicator (CQI) information for the detected cells based on the received signal quality. The CQI information may be sent to the node B, which may select an appropriate modulation and coding scheme for data transmission to UE 120 based on the CQI information. Although not shown in fig. 7, the detected symbols of the reference signal may also be used for other purposes, such as noise estimation, time tracking, frequency tracking, and the like.

A reference signal processor may process reference signals from each detected cell of interest. The reference signal processor may periodically process the reference signals from each detected cell as long as the reference signals are received from the cell.

Fig. 8 shows a design of a process 800 for generating synchronization and reference signals in a wireless communication system. Process 800 may be performed by a node B of a cell (as described below) or by some other entity.

The node B may determine the first index and the second index from the cell ID of the cell (block 812). The first index may be an SSC index g and the second index may be a PSC index l. The node B may generate a PSC sequence based on the second index (block 814) and may generate a SSC sequence based on the first index (block 816). The node B may generate a primary synchronization signal for the cell based on the PSC sequence (block 818) and may generate a secondary synchronization signal for the cell based on the SSC sequence (block 820).

The node B may generate a pseudo-random sequence based on the first index (block 822). The pseudo-random sequence may be one of G possible pseudo-random sequences corresponding to G possible values of the first index. The pseudo-random sequence may be fixed or may vary over a symbol period, slot, subframe, etc. The node B may generate a scrambling sequence based on the second index (block 824). There can be a one-to-one mapping between the PSC sequence and the scrambling sequence, which can be linked by a second index. The scrambling sequence may be one of L possible scrambling sequences corresponding to the L possible values of the second index. The scrambling sequence may be generated from an M-sequence, a Golay complementary sequence, or the like. The scrambling sequence may have the same length as the pseudorandom sequence. Alternatively, a short scrambling sequence may be repeated to obtain a scrambling sequence having the same length as the pseudorandom sequence, e.g., as shown in equation (4). The same pseudo-random sequence and the same scrambling sequence may be used for the normal cyclic prefix and the extended cyclic prefix.

The node B may generate a reference signal sequence based on the pseudorandom sequence and the scrambling sequence, e.g., by symbol-by-symbol multiplying the pseudorandom sequence and the scrambling sequence, as shown in equation (5) (block 826). The node B may then generate a reference signal for the cell based on the reference signal sequence (block 828). For block 828, the node B may map the reference signal sequence onto a set of subcarriers for the reference signal. The node B may then generate an OFDM symbol with the reference signal sequence mapped to the set of subcarriers. The OFDM symbol will include a reference signal. The node B may periodically transmit reference signals (e.g., as shown in fig. 4A, 4B, or 4C) for use by the UE for channel estimation, signal strength measurements, signal quality measurements, time tracking, frequency tracking, noise estimation, and so on.

Fig. 9 shows a design of an apparatus 900 for generating synchronization and reference signals in a wireless communication system. The apparatus 900 comprises: a module 912 configured to determine a first index and a second index according to a cell ID of a cell; a module 914 for generating a PSC sequence based on the second index; a module 916 for generating an SSC sequence according to the first index; a module 918 for generating a primary synchronization signal for the cell based on the PSC sequence; a module 920, configured to generate a secondary synchronization signal of the cell according to the SSC sequence; a module 922, configured to generate a pseudo-random sequence according to the first index; a module 924 configured to generate a scrambling sequence according to the second index; a module 926 for generating a reference signal sequence from the pseudorandom sequence and the scrambling sequence; and a module 928 for generating a reference signal for the cell from the reference signal sequence.

Fig. 10 shows a design of a process 1000 for receiving synchronization and reference signals in a wireless communication system. Process 1000 may be performed by a UE (as described below) or by some other entity. The UE may detect a PSC sequence from a cell (block 1012) and may detect an SSC sequence from the cell (block 1014). The UE may determine a first index (e.g., SSC index g) for the cell ID of the cell based on the detected SSC sequence (block 1016) and may determine a second index (e.g., PSC index l) for the cell ID based on the detected PSC sequence (block 1018).

The UE may generate a pseudo-random sequence based on the first index (block 1020) and may generate a scrambling sequence based on the second index (block 1022). The UE may generate a reference signal sequence from the pseudorandom sequence and the scrambling sequence (block 1024). The UE may process the reference signal received from the cell based on the reference signal sequence (block 1026). The UE may derive channel estimates, measure signal strength, measure signal quality, perform time tracking, perform frequency tracking, and/or perform other functions based on the reference signals from the cell.

Fig. 11 shows a design of an apparatus 1100 for receiving synchronization and reference signals in a wireless communication system. The apparatus 1100 comprises: a module 1112 for detecting a PSC sequence from a cell; a module 1114 for detecting an SSC sequence from the cell; a module 1116 for determining a first index of a cell ID of the cell based on the detected SSC sequence; a module 1118 for determining a second index for the cell ID based on the detected PSC sequence; a module 1120 configured to generate a pseudo-random sequence according to the first index; a module 1122 for generating a scrambling sequence according to the second index; a module 1124 for generating a reference signal sequence based on the pseudorandom sequence and the scrambling sequence; and a module 1126 for processing a reference signal received from the cell according to the reference signal sequence.

The processing in fig. 8 to 11 may be performed implicitly or explicitly. For example, since the cell ID of a cell may be fixed, the reference signal sequence of the cell may be calculated in advance and stored in the memory. The processes in blocks 822, 824, and 826 in fig. 8 and/or the processes in blocks 1020, 1022, and 1024 in fig. 10 may be performed implicitly by obtaining the reference signal sequence for the cell from memory.

The modules in fig. 9 and 11 may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, etc., or any combination thereof.

In an alternative design, the reference signal sequence may be generated differently for the normal cyclic prefix and the extended cyclic prefix. For a conventional cyclic prefix, 504 reference signal sequences may be generated from 168 pseudo-random sequences of length N and 3 orthogonal sequences of length 3. Each orthogonal sequence may be repeated to obtain a spread orthogonal sequence of length N. For an extended cyclic prefix, 504 reference signal sequences may be generated from 504 pseudorandom sequences of length N.

As described above, reference signal sequences generated based on pseudorandom sequences and scrambling sequences may provide some advantages not available from alternative designs. First, the scrambling sequence may provide improved performance for the reference signal sequence over the orthogonal sequence. Orthogonal sequences may degrade channel estimation performance for wireless channels with large delay spreads, while scrambling sequences may avoid this problem. Second, the same set of 168 pseudo-random sequences can be used for both the normal cyclic prefix and the extended cyclic prefix. This may simplify the implementation of the UE because (i) there is no need to generate different pseudo-random sequences for the normal cyclic prefix and the extended cyclic prefix, and (ii) a single receiver structure is used for channel estimation for both the normal cyclic prefix and the extended cyclic prefix. The mapping of cell IDs to PSC and SSC indices may also be used for the pseudo-random sequences and scrambling sequences due to (i) a one-to-one mapping between L scrambling sequences and L possible values of the PSC indices, and (ii) a one-to-one mapping between G pseudo-random sequences and G possible values of the SSC indices.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination of components designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium may be coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and transmission media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Further, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source over a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes Compact Disc (CD), laser disc, optical disc, Digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data electromagnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the present invention. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the present invention is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (32)

1. A method of generating a reference signal in a wireless communication system, comprising:

generating a pseudo-random sequence according to a cell Identification (ID) of a cell;

generating a scrambling sequence according to the cell ID;

generating a reference signal sequence according to the pseudo-random sequence and the scrambling sequence;

and generating the reference signal of the cell according to the reference signal sequence.

2. The method of claim 1, further comprising:

determining a first index and a second index from the cell ID, wherein generating the pseudo-random sequence comprises generating the pseudo-random sequence from the first index, and wherein generating the scrambling sequence comprises generating the scrambling sequence from the second index.

3. The method of claim 2, wherein generating the pseudorandom sequence according to the first index comprises generating the pseudorandom sequence as one of G possible pseudorandom sequences corresponding to G possible values of the first index, wherein G is an integer greater than 1, and wherein generating the scrambled sequence according to the second index comprises generating the scrambled sequence as one of L possible scrambled sequences corresponding to L possible values of the second index, wherein L is an integer greater than 1.

4. The method of claim 2, further comprising:

generating a Primary Synchronization Code (PSC) sequence based on the second index;

generating a Secondary Synchronization Code (SSC) sequence based on the first index;

generating a primary synchronization signal for the cell based on the PSC sequence;

generating a secondary synchronization signal for the cell based on the SSC sequence.

5. The method of claim 4, wherein the PSC sequences are one-to-one mapped to the scrambling sequence according to the second index.

6. The method of claim 1, wherein generating the scrambling sequence comprises: the scrambling sequence is generated from a maximal length sequence (M-sequence) or a Golay complementary sequence.

7. The method of claim 1, wherein the scrambling sequence has a same length as the pseudorandom sequence.

8. The method of claim 1, wherein generating the scrambling sequence comprises:

generating a first sequence having a shorter length than the pseudorandom sequence;

repeating the first sequence to obtain the scrambling sequence having the same length as the pseudorandom sequence.

9. The method of claim 1, wherein generating the reference signal sequence comprises: multiplying the pseudo-random sequence with the scrambling sequence symbol-by-symbol to obtain the reference signal sequence.

10. The method of claim 1, wherein generating the reference signal comprises: for each symbol period in which the reference signal is transmitted,

mapping the reference signal sequence to a set of subcarriers for the reference signal;

generating an Orthogonal Frequency Division Multiplexing (OFDM) symbol using the reference signal sequence mapped to the set of subcarriers, the OFDM symbol including the reference signal.

11. The method of claim 1, further comprising:

the reference signals are periodically transmitted for use by a User Equipment (UE) for channel estimation, signal strength measurement, signal quality measurement, time tracking, frequency tracking, noise estimation, or any combination thereof.

12. The method of claim 1, wherein the pseudo-random sequence and the scrambling sequence are for both a normal cyclic prefix and an extended cyclic prefix.

13. An apparatus for wireless communication, comprising:

at least one processor configured to generate a pseudo-random sequence based on a cell Identification (ID) of a cell; generating a scrambling sequence according to the cell ID; generating a reference signal sequence according to the pseudo-random sequence and the scrambling sequence; and generating the reference signal of the cell according to the reference signal sequence.

14. The apparatus of claim 13, wherein the at least one processor is further configured to: determining a first index and a second index according to the cell ID; generating the pseudo-random sequence according to the first index; and generating the scrambling sequence according to the second index.

15. The apparatus of claim 14, wherein the at least one processor is configured to: generating a Primary Synchronization Code (PSC) sequence based on the second index; generating a Secondary Synchronization Code (SSC) sequence based on the first index; generating a primary synchronization signal for the cell based on the PSC sequence; generating a secondary synchronization signal for the cell based on the SSC sequence.

16. The apparatus of claim 13, wherein the at least one processor is configured to: the scrambling sequence is generated from a maximal length sequence (M-sequence) or a Golay complementary sequence.

17. An apparatus for wireless communication, comprising:

means for generating a pseudo-random sequence from a cell Identification (ID) of a cell;

means for generating a scrambling sequence according to the cell ID;

means for generating a reference signal sequence from the pseudorandom sequence and the scrambling sequence;

means for generating a reference signal for the cell from the reference signal sequence.

18. The apparatus of claim 17, further comprising:

means for determining a first index and a second index from the cell ID, wherein the means for generating the pseudorandom sequence comprises means for generating the pseudorandom sequence from the first index, and wherein the means for generating the scrambled sequence comprises means for generating the scrambled sequence from the second index.

19. The apparatus of claim 18, further comprising:

means for generating a Primary Synchronization Code (PSC) sequence based on the second index;

means for generating a Secondary Synchronization Code (SSC) sequence based on the first index;

means for generating a primary synchronization signal for the cell based on the PSC sequence;

means for generating a secondary synchronization signal for the cell based on the SSC sequence.

20. The apparatus of claim 17, wherein the means for generating the scrambling sequence comprises: means for generating the scrambling sequence from a maximal-length sequence (M-sequence) or a Golay complementary sequence.

21. A computer program product, comprising:

a computer-readable medium comprising:

code for causing at least one computer to generate a pseudo-random sequence based on a cell Identification (ID) of a cell;

code for causing the at least one computer to generate a scrambling sequence from the cell ID;

code for causing the at least one computer to generate a reference signal sequence from the pseudorandom sequence and the scrambling sequence;

code for causing the at least one computer to generate a reference signal for the cell from the reference signal sequence.

22. A method of receiving a reference signal in a wireless communication system, comprising:

generating a pseudo-random sequence according to a cell Identification (ID) of a cell;

generating a scrambling sequence according to the cell ID;

generating a reference signal sequence according to the pseudo-random sequence and the scrambling sequence;

processing reference signals received from the cell according to the reference signal sequence.

23. The method of claim 22, wherein generating the pseudo-random sequence comprises generating the pseudo-random sequence according to a first index of the cell ID, and wherein generating the scrambling sequence comprises generating the scrambling sequence according to a second index of the cell ID.

24. The method of claim 23, further comprising:

detecting a Primary Synchronization Code (PSC) sequence from the cell;

determining the second index from the detected PSC sequence;

detecting a Secondary Synchronization Code (SSC) sequence from the cell;

determining the first index based on the detected SSC sequence.

25. The method of claim 22, wherein processing the reference signal comprises: multiplying the received symbols comprising the reference signal with the symbols of the reference signal sequence to obtain detected symbols.

26. The method of claim 22, further comprising:

deriving a channel estimate for the cell from the reference signal.

27. The method of claim 22, further comprising:

performing at least one of signal strength measurements, signal quality measurements, time tracking, frequency tracking, and noise estimation from the reference signal.

28. An apparatus for wireless communication, comprising:

at least one processor configured to generate a pseudo-random sequence based on a cell Identification (ID) of a cell; generating a scrambling sequence according to the cell ID; generating a reference signal sequence according to the pseudo-random sequence and the scrambling sequence; processing reference signals received from the cell according to the reference signal sequence.

29. The apparatus of claim 28, wherein the at least one processor is configured to: generating the pseudo-random sequence according to the first index of the cell ID; generating the scrambling sequence according to the second index of the cell ID.

30. The apparatus of claim 29, wherein the at least one processor is configured to: detecting a Primary Synchronization Code (PSC) sequence from the cell; determining the second index from the detected PSC sequence; detecting a Secondary Synchronization Code (SSC) sequence from the cell; determining the first index based on the detected SSC sequence.

31. The apparatus of claim 28, wherein the at least one processor is configured to: deriving a channel estimate for the cell from the reference signal.

32. The apparatus of claim 28, wherein the at least one processor is configured to: performing at least one of signal strength measurements, signal quality measurements, time tracking, frequency tracking, and noise estimation from the reference signal.