CN1695333A - A system of QS-CDMA with two-level spreading scheme and LS sequences - Google Patents
A system of QS-CDMA with two-level spreading scheme and LS sequences Download PDFInfo
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Abstract
The presented invention is to provide a system of QS-CDMA with two-level spreading scheme and LS sequences, the said system comprising: means for designating a user in the system to a user group according to the cell or the sector it belongs to; means for spreading the information signals both by the FL and SL spreaders; one-level despreading means coupled to the said means to simplify the receiver structure of the two-level spreading system; means for communicating information signals between users in the same user-group without MAI; means for communicating information signals between users in different user-group with suppressed MAI; means for employing the LS sequences as the spreading sequences so as to suppress the MAI. The presented invention can obtain satisfactory system error performance and system capacity.
Description
Technical Field
The present invention relates to CDMA systems, and more particularly, to a QS-CDMA system having a two-stage spreading scheme and LS sequences.
Background
In a CDMA system, many users share the same frequency band and time slot. Multiple access transmission can be achieved by means of the assigned spreading sequences, i.e. address sequences. Depending on the spreading sequence used, current CDMA systems can be classified into: orthogonal CDMA (O-CDMA) systems and pseudo-noise CDMA (PN-CDMA) systems.
Orthogonal sequences and sequences with Zero Correlation Zone (ZCZ) properties are commonly used in the first category and assume system synchronization or quasi-synchronization (QS). Conventional orthogonal spreading sequences, such as Walsh sequences and Orthogonal Variable Spreading Factor (OVSF) sequences, can be used in synchronous CDMA systems to maintain orthogonality between users. For the forward link in mobile wireless communications, all users in the same cell are naturally synchronized and can be assigned orthogonal spreading sequences. In this case, if there is no multipath propagation problem, multi-user access interference (MAI) in the cell is not generated. However, for the reverse link, maintaining synchronization between different users may be more difficult. But in microcellular and indoor environments the transmission delay is relatively small and it is therefore feasible to model the reverse link as a synchronous system with a synchronization timing error limited to a threshold, the so-called quasi-synchronous CDMA system (QS-CDMA). In QS-CDMA systems, orthogonality between orthogonal sequences is destroyed by synchronization errors.
To solve the problems of said QS-CDMA system, PCT application No. PCT/CN00/00028, the inventor proposes, for the litterbook patent on LS codes, a set of sequences with Interference Free Window (IFW) properties, called loose set of synchronization sequences (LS sequences), hereinafter denoted S (L) sequences，Ms，IFW，Lgap) Wherein L iss，MsIFW and LgapRespectively length, family size, IFW width and one-sided slot width. In a QS-CDMA system, by using LS sequences as spreading sequences, interference can be eliminated if the time delay between user signals falls within the Interference Free Window (IFW) of the set of LS sequences.
Based on the above analysis, it can be seen that for the first class of CDMA systems, the capacity of the system is limited mainly by the size of the limited set of sequences, since multiple access transmission interference can be effectively suppressed by the excellent correlation properties of the spreading sequences. In practice, there is a trade-off between the size of the family and the zero correlation region in order to obtain superior correlation properties. For example, assuming a spreading factor L of 128, the maximum time delay τ between usersmThe LS set S (128, 32, 7, 3) can be used to suppress the existing interference, which is 3 chips. The capacity of the system is then 32/134 ═ 0.239/Tc(bps), wherein the capacity of the system is determined based on the maximum total bit rate of all users in the system.
In the second class of CDMA systems, where PN sequences are used as spreading sequences, the systems are typically in an asynchronous mode. In such a system, although a large number of spreading sequences are available, the capacity of the system is limited by interference caused by non-orthogonality of the PN sequences. Especially in QS-CDMA systems, such CDMA systems are often not satisfactory to implement because the time delay is evenly distributed over a limited interval.
From the above discussion, it can be seen how to obtain more usable sequences and how to simultaneously suppress Multiple Access Interference (MAI) in CDMA systems is the key to increasing system capacity.
In synchronous CDMA systems, different approaches, such as two-stage spreading-despreading schemes, have been proposed to increase the capacity of the system. Chinese patent application No. 001109301.3 proposes an invention for downlink transmission in CDMA systems that includes a two-stage variable chip rate spreading and despreading method. The total spreading gain is the product of the two-stage spreading factors. Orthogonal sequences, ZCZ sequences and pseudo-noise sequences may be used as the First (FL) and Second (SL) stage sequences. The invention aims to improve the error code performance in the downlink channel of the CDMA system.
Disclosure of Invention
An object of the present invention is to provide a quasi-synchronous code division multiple access (QS-CDMA) system with a two-stage spreading scheme and LS sequences to obtain satisfactory system error performance and system capacity.
A QS-CDMA system with a two-level spreading scheme and LS sequences includes:
a user group designating device for designating a user in the system to a user group according to the cell or sector to which the user belongs;
means for spreading the information signal by the FL spreader and the SL spreader;
a primary spreading device coupled to the device to simplify a receiver structure of the secondary spreading system;
means for transmitting information signals between users of the same user group without the MAI;
means for transmitting information signals between users of different user groups with suppressed MAI;
a device for suppressing multiple access interference using an LS sequence as a spreading sequence.
The QS-CDMA system utilizes the set of LS sequences S1 (L) when only one user group existss，Ls/2，IFW＝3，Lgap1) as FL spreading sequences to accommodate multiple users in the system. FL spreading factor L1＝Ls+2Lgap(ii) a Can accommodate at most L in the systemsAnd 2 active users.
The QS-CDMA system utilizes the set of LS sequences S2 (L) when only one user group exists2，L2/2，IFW＝1，Lgap0) as an SL spreading sequence to provide multi-channel transmission for each user, which may have L at maximum2A plurality of parallel channels; SL spreading factor of L2。
The SL spreading factor of the two-level QS-CDMA system is close to the number of chips with the largest relative time delay among users when only one user group exists.
When a plurality of user groups exist, the user group specifying device comprises a device which enables the receiver to adopt a directional antenna and enables users in the same sector to belong to the same user group; users of different sectors are assigned to different groups.
When a plurality of user groups exist, the user group designating means includes means for causing the receiver to use an omnidirectional antenna and causing users in the same cell to belong to the same user group; users in different cells are made to belong to different groups.
Wherein said user group designating means comprises means for assigning users in the same sector to the same user group; further comprising means for limiting the relative time delays between all users to within a threshold range; SL spreading factor L2The number of chips is chosen to be equal to the maximum time delay between all users.
Wherein said user group assigning means comprises user group splitting means for assigning users in the same cell or sector to the same user group, said QS-CDMA system using m-sequences as SL spreading sequences to provide multiple group splitting.
Wherein the user group segmentation apparatus further comprises: the long m-sequence is cleaved to a length L2Each segment is used as a SL sequence for each bit duration, and different segments may be used for different bit durations.
Wherein the user group segmentation apparatus further comprises: in different user groups, long m-sequences of different phases are cut and used as means for SL sequences.
Wherein said user group specifying means includes means for making users in the same sector belong to the same user group and for limiting the maximum time delay to not more than L2TcThe phase-shifted long segment of the m-sequence is used as the SL spreading sequence, and the QS-CDMA system utilizes the set of LS sequences S1 (L)s，Ls/2，IFW＝3，Lgap1) as FL spreading sequences to provide intra-group user segmentation; FL spreading factor L1＝Ls+ 2; each group can contain at most LsActive user of/2; MAI within the group was eliminated by the IFW property of the FL sequence; inter-group interference is further suppressed by the IFW cross-correlation properties of FL sequences and sectored antennas.
Wherein said user group specifying means includes means for making users of the same cell belong to the same user group and making the maximum time delay between users of the same group be limited to not more than L2TcA segment of the phase-shifted long m-sequence is used as the SL spreading sequence. The QS-CDMA system utilizes a set of LS sequences S1 (L)s，Ls/2，IFW＝3，Lgap) As an FL spreading sequence to provide multiple sets of partitions; FL spreading factor L1＝Ls+2Lgap，LgapNot less than 1; each group can contain at most Ls2 active users; MAI within the group is eliminated by the IFW property of the FL sequence.
Wherein LS set S1 (L)s，Ls/2，IFW＝3，Lgap) Is used for FL spreading sequence, LgapDepending on the number of chips of the largest relative time delay among the users between the groups; considering the cells of 2 or 3 layers around the ideal cell, LgapMay be equal to 3 or 4; the MAI between groups, i.e., Adjacent Cell Interference (ACI), is suppressed by the IFW characteristic and path loss of the FL sequence.
Wherein the data information is spread by both FL and SL spreaders. Despreading the spread spectrum signal by only one despreader using a local despreading sequence; the local despreading sequences are constructed by linking FL and SL sequences at FL and SL chip rates, respectively.
The present invention provides a quasi-synchronous (QS) Code Division Multiple Access (CDMA) system that utilizes a two-level spreading scheme and a relaxed synchronization (LS) sequence to suppress Multiple Access Interference (MAI) in the system and increase the performance and capacity of the system.
Drawings
Fig. 1 is a schematic diagram of a spread signal of a channel (r, k) after two-stage spreading in the case of a single user group;
fig. 2 is a schematic diagram of the spread signals of users (k, c) after two-stage spreading in the case of a multi-user group;
FIG. 3 is a schematic diagram of a transmitter and channel model for a single user group case;
FIG. 4 is a diagram of a transmitter and channel model for a multi-user group case;
fig. 5 is a constructed local despreading sequence used by the despreader for the jth bit duration.
Detailed Description
The reverse link is modeled as a QS-CDMA system and considered assuming that transmissions from different users travel different paths through the ideal signal and the interfering signalThe access timing error between is limited. In this case, using a two-stage spreading scheme, the FL and SL spreading factors are L1And L2。
An LS sequence with an IFW width of 3 is used as the FL spreading sequence to provide user segmentation. In addition, an LS sequence with an IFW width of 1 and a phase shifted long m-sequence are used as SL spreading sequences in single and multiple sets, respectively, to provide a partitioning of the channel or user set.
Case of a single user group:
first consider LS set S1 (L)s1，Ls1/2, 3, 1) and S2 (L)s2，L s21, 0) are used as FL and SL spreading sequences, respectively. In this case, only one L can be accommodated in the systems1A user group of 2 users, each user having at most Ls2A number of parallel channels. And the spreading factors of FL and SL are L respectively1＝Ls1+2 and L2＝Ls2. In this section, the k-th segment FL and the s-th segment SL spreading sequences are denoted G, respectivelykAnd WkWherein k is 0, 1s1/2，s＝0，1，...，Ls2。
Based on the method proposed in chinese patent application No. 001109301.3, each data bit is spread to L ═ L after a two-stage spreading scheme1L2A chip, where L is the system spreading factor. Let (r, k) denote the r channel, T, of the k usercIndicating the chip duration. In general, let channel (q, i) be the ideal channel, where we consider the 0 th data bit. Based on the results obtained previously, it can be concluded that if the time delay τ between the ideal signal and the interfering signal is not greater than L2TcThe interference caused by the channel (r, k) is
Wherein <math> <mrow> <msubsup> <mi>θ</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>i</mi> </mrow> <mi>g</mi> </msubsup> <mrow> <mo>(</mo> <mi>j</mi> <mo>)</mo> </mrow> <mo>=</mo> <munderover> <mi>Σ</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>L</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msubsup> <mi>g</mi> <mi>n</mi> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msubsup> <msubsup> <mi>g</mi> <mrow> <mi>n</mi> <mo>+</mo> <mi>j</mi> </mrow> <mrow> <mo>(</mo> <mi>i</mi> <mo>)</mo> </mrow> </msubsup> <mo>=</mo> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <mi>L</mi> <mo>,</mo> <mi>forj</mi> <mo>=</mo> <mn>0</mn> <mo>,</mo> <mi>k</mi> <mo>=</mo> <mi>i</mi> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> <mo>,</mo> <mi>forj</mi> <mo>=</mo> <mn>0</mn> <mo>,</mo> <mo>,</mo> <mi>k</mi> <mo>≠</mo> <mi>i</mi> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> <mo>,</mo> <mi>for</mi> <mn>0</mn> <mo><</mo> <mo>|</mo> <mi>j</mi> <mo>|</mo> <mo>≤</mo> <mi>Z</mi> </mtd> </mtr> </mtable> </mfenced> </mrow> </math> Is the periodic correlation function of the FL code;ρr，q w(τ) andthe partial correlation function, which is continuous for the SL sequence, can be expressed as
l is equal to or less than tau/Tcδ ═ t (τ -lT)c)/TcAnd
is a discrete partial correlation function of the SL sequence.
Because the channels of the same user are synchronized, the interference within the user can be obtained as
Where R is the number of channels per user. Due to the orthogonality of the SL spreading sequences, the value of equation (4) is 0.
The interference between users can be obtained as
Where K is the number of users in the system. Set of LS codes S1 (L) since k ≠ is1，Ls1/2，3，1)， <math> <mrow> <msubsup> <mi>θ</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>i</mi> </mrow> <mi>g</mi> </msubsup> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <mn>0</mn> </mrow> </math> And <math> <mrow> <msubsup> <mi>θ</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>i</mi> </mrow> <mi>g</mi> </msubsup> <mrow> <mo>(</mo> <mn>0</mn> <mo>)</mo> </mrow> <mo>=</mo> <mn>0</mn> <mo>,</mo> </mrow> </math> the value of equation (5) is therefore 0.
Based on the above discussion, it is explained if the interference signal and the ideal signalThe time delay between the numbers is not more than L2TcNo interference is present in the system. So that each user can have at most L2A plurality of channels, and at most L can be accommodated in the system1And 2 users.
Table 1 gives an example of a current single-user two-level spread spectrum system, where τmRepresenting the maximum time delay allowed if the relative time delay between users is not greater than τmThen no interference is present. It can be seen that τ is increasedmThen a larger SL spreading factor L is needed2And the system will accommodate fewer users. But at the same time the number of channels per user increases and the three example systems all have the same capacity in terms of the capacity of the system, i.e. the total bit rate provided. It can be concluded that: for the same L1×L2Value, L2The smaller the value of (c), the more users are accommodated, but the smaller the time delay that can be tolerated. When the timing error is larger, L2Can be increased to ensure that no interference occurs, it is noted that the total bit rate can only be achieved if all parallel channels of each user are utilized, which means that in this case users with high data rates are preferred.
Table 2 shows an example of a level 1 spread spectrum system using LS sequences. From a comparison of these two tables, it is clear that when τ is present in both systemsmAlmost the same, the QS-CDMA system proposed here has a higher system capacity than the level 1 orthogonal spread spectrum system.
Table 3 shows the chip rate 1/T of the current system and the O-CDMA systemc(Bandwidth) equal and bit rate r per user in both systemsbComparison of two systems when close together. It can be concluded that: when two systems provide almost the same τmCurrent systems can accommodate more users at each user's bit rate and system bandwidth.
TABLE 1 Secondary example System of spreading Using LS codes as FL spreading sequences in Single user scenarios
| Parameter(s) | System-I | System-II | System-III |
| Spread spectrum code | FLS1(32，16，3，1) | FL：S1(16，8，3，1) | FL：S1(8，4，3，1) |
| SL：S2(4，4，1，0) | SL：S2(8，8，1，0) | SL：S2(16，16，1，0) | |
| FLSFL1 | 34 | 18 | 10 |
| SLSFL2 | 4 | 8 | 16 |
| System SFL | 136 | 144 | 160 |
| Number of channels per user | 4 | 8 | 16 |
| Number of users | 16 | 8 | 4 |
| Bit rate per channel (1/T)c) | 1/136 | 1/144 | 1/160 |
| Bit rate per user (1/T)c) | 1/34 | 1/18 | 1/10 |
| Total bit rate (1/T)c) | 0.471 | 0.444 | 0.4 |
| Maximum time delay allowed taum | 4Tc | 8Tc | 16Tc |
TABLE 2 example system for 1-level orthogonal spreading with LS codes
| Parameter(s) | System-I | System-II | System-III |
| Spread spectrum code | S(128，32，7，3) | S(128，16，15，7) | S(128，8，31，15) |
| System SFL | 128+3×2＝134 | 128+7×2＝142 | 128+15×2＝158 |
| Number of channels per | 1 | 1 | 1 |
| Number of users | 32 | 16 | 8 |
| Bit rate per channel (1/T)c) | 1/134 | 1/142 | 1/158 |
| Total bit rate (1/T)c) | 32/134＝0.238 | 16/142＝0.113 | 8/158＝0.051 |
| Maximum time delay allowed taum | 3Tc | 7Tc | 15Tc |
TABLE 3 comparison of Current System with O-CDMA System
| Current systems | τm | 4Tc | 8Tc | 16Tc |
| Set of spreading codes | S1(64，32，3，1) | S1(64，32，3，1) | S1(64，32，3，1) | |
| S2(4，4，1，0) | S2(8，8，1，0) | S2(16，16，1，0) | ||
| L1 | 64 | 64 | 64 | |
| L2 | 4 | 8 | 16 | |
| S | 4 | 8 | 16 | |
| K | 32 | 32 | 32 | |
| rbTc | 1/66 | 1/66 | 1/66 | |
| RTc | 0.485 | 0.485 | 0.485 | |
| O-CDMA system | τm | 3Tc | 7Tc | 9Tc |
| Set of spreading codes | LS(64，16，7，3) | LS(64，16，15，7) | LS(64，16，31，15) | |
| K | 16 | 8 | 4 | |
| rbTc | 1/70 | 1/77 | 1/94 | |
| RTc | 0.229 | 0.103 | 0.043 |
Case of multi-user group:
in this case, the system may accommodate multiple groups of users, each with only one channel.
Users in the system are assigned to different user groups according to the cell or sector to which the user belongs. When using directional antennas, users in different sectors belong to different user groups, and when using omni-directional antennas, users in different cells belong to the same user group.
In the case of sector-based grouping, since the relative time delay limits are the same for all user groups, the LS set S1 (L1) is the same as in the single-group cases1，Ls1/2, 3, 1) is used as the FL spreading sequence. However, in the case of cell-based components, the LS set S1 (L)s1，Ls1/2，3，Lgap≧ 1) is used as the FL sequence, and LgapThe selection of (a) depends on the maximum relative time delay among the users between the groups. If cells of the first, second and third layers are considered, L is assumedgapEither 3 or 4 is feasible.
To provide multiple sets of communications, a long m-sequence is cut into segments, each of which in turn serves as an SL sequence in each bit duration in place of an SL set with an IFW width of 1. Furthermore, the phase-shifted m-sequence Tc[P(Lp)]Is cut into SL sequences of length L by the c-th user grouppM sequence of (a), Tc[·]An operator that moves the vector around to the left by c-space. The SL factor is selected based on the maximum time delay among users between groups. Hereinafter Tc[P(Lp) Simply denoted as Pc. The k-th FL sequence and the c-th SL sequence are respectively denoted as GkAnd PcWherein k is 0, 1s1And C is 0, 1, C-1, C being the number of groups.
Based on the method proposed by the Chinese patent application with the application number of 001109301.3, each data bit is spread to L after passing through a two-stage spreading scheme1L2One chip. The spread signal is shaped by a chip-pulse-shaping filter ψ (t) and then modulated by Binary Phase Shift Keying (BPSK). From different usersThe emitted signals are subject to different time delays. Assuming that a rectangular wave chip waveform is considered at this time, the input signal received by the base station receiver can be represented as
Wherein,is a sequence of warp dataA modulated spread spectrum signal; g(k)Is the k FL sequence; p(c)Is the SL sequence assigned to group c; pr (Pr) ofk，cFor the average power of the received users (k, c), when sophisticated power control techniques are introduced into each group of users, Pr is used for the users in the groupk，cIs the same and can be expressed as Prc；fcAnd thetak，cFrequency and phase, τ, of the (k, c) th carrier, respectivelyk，cTime delay for the (k, c) th user.
The received signal added with the channel noise n (t) is BPSK modulated, and passes through a waveform matching filter, and then passes through a despreader. Based on the above discussion, the despreader outputs for user (k, c) can be written as
Wherein L is L ═ L1L2Is the system spreading factor. The first term of equation (7) is the ideal signal; the second term is the interference within the group and is limited as long as the maximum relative time delay between users within the group is not greater than the SL spreading factor, i.e., τm，d≤L2It can be expressed as
Wherein phik，d＝*k，d-*k，dIs the phase shift of the user (k, d) relative to the user (i, d) and is assumed to be uniformly distributed over the interval [ O, 2 π]. Since when k ≠ i, S1 (L) is applied to the set of LS codess1，Ls1/2，3，1)， <math> <mrow> <msubsup> <mi>θ</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>i</mi> </mrow> <mi>g</mi> </msubsup> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <mn>0</mn> </mrow> </math> And <math> <mrow> <msubsup> <mi>θ</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>i</mi> </mrow> <mi>g</mi> </msubsup> <mrow> <mo>(</mo> <mn>0</mn> <mo>)</mo> </mrow> <mo>=</mo> <mn>0</mn> <mo>,</mo> </mrow> </math> equation (8) equals 0. No interference is then generated within the group.
The third term of equation (7) is the interference between groups, which can be written as
Wherein,
the number of FL chips which is the relative time delay between the users (k, c) between the groups and the ideal user, where c ≠ d. If τk，c≤L2TcThen m isc，k0, and since k ≠ i, <math> <mrow> <msubsup> <mi>θ</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>i</mi> </mrow> <mi>g</mi> </msubsup> <mrow> <mo>(</mo> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <mn>0</mn> <mo>,</mo> </mrow> </math> the interference of the ideal user (i, d) is then mainly caused by the user (i, C), where C is 0, 1.., C-1 and C ≠ d, which is the case where only one user in each group contributes to the interference portion of the ideal user in a sector-based group system, as a result of which the interference present in the current system is effectively suppressed compared to the conventional PN-CDMA system. However, in a cell-based packet system, since signals propagating from distant cells experience longer delays, then mc，kIs greater than 0. In this case, though due to IFW in the LS sequenceNon-zero correlation values in the squares can cause interference, but as long as the gap length Lgap≥(mc，k)maxThe IFW characteristic of the LS code further suppresses the interference between groups effectively.
It can then be concluded that: in current multi-group QS-CDMA systems, there is no intra-group interference and the splitting of the groups is provided by phase-shifted m-sequences, which are SL spreading sequences. At the same time, MAI between groups is further suppressed by the IFW characteristic of the LS sequence used as the FL spreading sequence.
A primary despreader:
to simplify the receiver structure, the despreaders used in current systems are similar to conventional correlators, but the received signal is multiplexed by a constructed local despreading sequence and then in the interval 0, Tb]And (4) internal integration. The local despreading sequence is constructed by concatenating the FL and SL sequences, but since the chip rates of the two spreaders are not the same, the concatenation process is based on a different two-level chip rate.
Embodiments of the present invention are described below with reference to the drawings.
FIG. 1 shows a spread spectrum signal of a channel (r, k) after two-stage spreading in case of a single user group, where (r, k) denotes the r-th channel of the k-th user, gm kSet of presentation codes S1 (L)s1，Ls1M-th chip of k-th code in/2, 3, 1), wn rThe set of presentation codes S2 (L)s2，Ls2N-th chip of the r-th code,/2, 1, 0), TcFor the chip duration, b denotes the data bit to be transmitted, L1＝Ls1+2 and L2＝Ls2FL and SL spreading factors, respectively, L ═ L1L2Is the system spreading factor.
Fig. 2 shows the spread signals of users (k, C) after two-stage spreading in the case of a multi-user group, where (k, C) represents the kth user in the C-th group, and C is 0, 1m kSet of presentation codes S1 (L)s1，Ls1/2，31) mth chip of the kth code, Pn cRepresents an m-sequence TcN-th chip of P, TcIs the chip duration, TfFor the duration of each frame, L ═ L1L2Is the system spreading factor. From fig. 2, it can be seen that each frame consists of LpEach data bit b in each framek，c(j) From the same FL sequence gm k，m＝0，1，...，L1-1} but PN sequence { Pn c，n＝jL2，jL2+1，...，(j+1)L2-1} wherein j is 0, 1p-1。
FIG. 3 shows a transmitter and channel model for the single user group case, where the data bit b from the kth user is transmittedkData bits b serial/parallel converted to R channel, s channelskIs first FL sequence GkSpread to have a chip duration T1＝Tb/L1L of1Chip, TbWherein is the bit duration, GkIs the k-th FL sequence. Then each FL chip bs，kgk m(m＝0，1，...，L1-1) is again SL sequence WsFurther spreading, resulting in a chip duration Tc＝Tb/(L1×L2)。
FIG. 4 shows a transmitter and channel model for a multi-user group case, where the data bits b from the kth user in group ck，cIs first FL sequence GkSpread to have a chip duration T1＝Tb/L1L of1A chip, wherein TbIs bit duration, GkIs the k-th FL sequence. Then each FL chip bk，cgk m(m＝0，1，...，L1-1) is further lengthened by a length L2SL sequence T ofccP is further spread, resulting in a chip duration Tc＝Tb/(L1×L2)。
Fig. 5 shows the structure of a constructed local spreading sequence used by the despreaders of a user (K, C) during the jth bit duration, where K is 0, 1.
The present invention is to provide a QS-CDMA system with a two-stage spreading scheme and LS sequences. The system of the invention can obtain satisfactory system error code performance and system capacity.
Although the invention has been described in detail with reference to a preferred embodiment, anyone skilled in the art knows that many variations can be made to the embodiment without departing from the scope of the invention. Accordingly, this invention is to be limited only by the following claims, which are intended to cover such modifications and all equivalents.
Claims (19)
1. A QS-CDMA system with a two-level spreading scheme and LS sequences, comprising:
a user group designating means for designating a user in the system to a user group according to a cell or sector to which the user belongs;
means for spreading the information signal by the FL and SL spreaders;
a primary spreading means coupled to said means for simplifying the receiver structure of a two-stage spread spectrum system;
means for communicating information signals between users within the same user group without the MAI;
means for communicating information signals between users of different user groups in the presence of suppressed MAI;
and means for suppressing the MAI using the LS sequence as a spreading sequence.
2. A QS-CDMA system with a two-stage spreading scheme and LS sequences according to claim 1, characterized in that: there is only one user group, and the QS-CDMA system uses a length LsS1 as FL spreading sequences to accommodate multiple users in the system; FL spreading factor L1＝Ls+ 2; can accommodate at most L in the systemsAnd 2 active users.
3. A QS-CDMA system with a two-stage spreading scheme and LS sequences according to claim 1, characterized in that: there is only one user group, and the QS-CDMA system uses a length L2S2 as an SL spreading sequence provides multi-channel transmission for each user, each user having at most L2A plurality of parallel channels; SL spreading factor of L2。
4. A QS-CDMA system with a two-stage spreading scheme and LS sequences as in claim 1, wherein: there is only one user group, and the QS-CDMA system uses a length LsS1 as FL spreading sequences to accommodate multiple users in the system; FL spreading factor L1＝Ls+ 2; can accommodate at most L in the systems2 active users;
the QS-CDMA system utilizes a length L2S2 as an SL spreading sequence provides multi-channel transmission for each user, each user having at most L2A plurality of parallel channels; SL spreading factor of L2。
5. A QS-CDMA system with two-stage spreading scheme and LS sequences according to any of claims 1 to 4 characterized in that: there is only one user group and the SL spreading factor of the two-stage QS-CDMA system is selected to be approximately the maximum number of chips relative to the time delay among the users.
6. A QS-CDMA system with a two-stage spreading scheme and LS sequences according to claim 1, characterized in that: there are multiple user groups and the user group assignment means comprises a means for the receiver to use directional antennas and to have users in the same sector belong to the same user group and to have users in different sectors belong to different groups.
7. A QS-CDMA system with a two-stage spreading scheme and LS sequences according to claim 1, characterized in that: there are multiple user groups and the user group assignment means comprises means for using an omni-directional antenna at the receiver and for enabling users in the same cell to belong to the same user group and for enabling users in different cells to belong to different groups.
8. The QS-CDMA system with two-level spreading scheme and LS sequence of claim 6, wherein said user group assigning means includes means for making users of the same sector belong to the same user group; further comprising means for limiting the relative time delay between all users to within a threshold; and selects the number of chips with SL spreading factor equal to the maximum time delay between all users.
9. A QS-CDMA system with a two-level spreading scheme and LS sequence as in claim 7, wherein said user group assignment means includes means for causing users of the same cell to belong to the same user group, the maximum time delay between users in a group being limited to a threshold; and selects SL spreading factor L2The number of chips equal to the maximum time delay between users in the group.
10. A QS-CDMA system with a two-stage spreading scheme and LS sequence according to claim 8, wherein: the user group assignment means includes sector division means for making users in the same sector belong to the same user group, and the QS-CDMA system provides multi-sector division using an m-sequence as an SL spreading sequence.
11. A QS-CDMA system with a two-stage spreading scheme and LS sequence according to claim 9, wherein: the user group assignment means includes cell division means for making users in the same cell belong to the same user group, and the QS-CDMA system provides multi-cell division using an m-sequence as an SL spreading sequence.
12. A QS-CDMA system with a two-stage spreading scheme and LS sequence according to claim 10, characterized in that: the sector division device further comprises a long m sequence which is cut into a length L2And each segment is used as a SL sequence in each bit duration, different segments belonging to different bit durations.
13. A QS-CDMA system with a two-stage spreading scheme and LS sequence according to claim 11, wherein: the cell division device further comprises a long m sequence which is cut into a length L2And each segment is used as a SL sequence in each bit duration, different segments belonging to different bit durations.
14. A QS-CDMA system with a two-stage spreading scheme and LS sequence according to claim 12, wherein: the sector division means further comprises means for cutting out long m-sequences of different phases at different sectors and using them as SL sequences.
15. The system of claim 13, wherein: the cell division means further comprises means for cutting long m-sequences of different phases in different cells and using them as SL sequences.
16. A QS-CDMA system with a two-level spreading scheme and LS sequences according to claim 8, 10, 12 or 14, wherein the user group specifying means comprises: means for making users of the same sector belong to the same user group, the maximum time delay being limited to not more than L2TcA phase-shifted segment of the long m-sequence is used as the SL spreading sequence, and the QS-CDMA system utilizes a set of SL sequences S1 as the FL spreading sequence to provide segmentation of users in the group; FL spreading factor L1＝Ls+ 2; each group can contain at most Ls2 active users; MAI within the group is eliminated by the IFW property of the FL sequence; interference between groups is further suppressed by the IFW cross-correlation properties of the FL sequence and the sector antenna.
17. A QS-CDMA system with a two-level spreading scheme and LS sequences according to claim 9, 11, 13 or 15, wherein the user group assignment means comprises: means for users of the same cell belonging to the same group of users, the maximum time delay between users in the same group being limited to not more than L2TcA phase-shifted segment of the long m-sequence is used as the SL spreading sequence, and the QS-CDMA system utilizes a set of SL sequences S1 as the FL spreading sequence to provide a split of groups; FL spreading factor L1＝Ls+2Lgap，LgapNot less than 1; each group can contain at most Ls2 active users; MAI within the group is eliminated by the IFW property of the FL sequence.
18. A QS-CDMA system with a two-stage spreading scheme and LS sequence as in claim 17, wherein: LS set S1 is used as FL spreading sequence, LgapDepends on the maximum relative time delay between users between groups; considering the 2 or 3 layers of cells around the ideal cell, LgapMay be equal to 3 or 4; IFW characteristics and paths of ACI by FL sequenceThe loss is suppressed.
19. A QS-CDMA system with a two-stage spreading scheme and LS sequences according to claim 1, characterized in that: the data information is spread by FL and SL spreaders, the spread signal is despread by only one despreader using a local despreading sequence; the local spreading sequences are constructed by linking the chip rate FL and SL sequences of FL and SL, respectively.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/CN2002/000847 WO2004049612A1 (en) | 2002-11-26 | 2002-11-26 | A system of qs-cdma with two-level spreading scheme and ls sequences |
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| CN1695333A true CN1695333A (en) | 2005-11-09 |
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| CN02829815.2A Pending CN1695333A (en) | 2002-11-26 | 2002-11-26 | A system of QS-CDMA with two-level spreading scheme and LS sequences |
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| CN (1) | CN1695333A (en) |
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| US5103459B1 (en) * | 1990-06-25 | 1999-07-06 | Qualcomm Inc | System and method for generating signal waveforms in a cdma cellular telephone system |
| KR100277925B1 (en) * | 1997-12-22 | 2001-02-01 | 서평원 | Multiuser defectors for DS-CDMA systems and it's method |
| US6452916B1 (en) * | 1999-01-04 | 2002-09-17 | Lucent Technologies Inc. | Space-time spreading method of CDMA wireless communication |
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2002
- 2002-11-26 AU AU2002350378A patent/AU2002350378A1/en not_active Abandoned
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| AU2002350378A1 (en) | 2004-06-18 |
| WO2004049612A1 (en) | 2004-06-10 |
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