Random access preamble design

Abstract

A communication method performed by a base station in a wireless communication network is disclosed. The base station notifies a terminal of a cyclic shift increment N.sub.CS configuration information indicating an N.sub.CS value. The base station then receives from the terminal a random access preamble related to the N.sub.CS value indicated by the N.sub.CS configuration information. The N.sub.CS value belongs to a set of cyclic shift increments including all of the following cyclic shift increments of 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167, 279, and 419.

Claims

1. A communication method performed in a wireless communication network, comprising: notifying a terminal of cyclic shift increment N.sub.CS configuration information indicating an N.sub.CS value, the N.sub.CS value belonging to a set of cyclic shift increments including following cyclic shift increments: 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167, 279, and 419; and receiving, from the terminal, a random access preamble corresponding to the N.sub.CS value.

2. The communication method according to claim 1, further comprising: determining a time advance in accordance with the random access preamble; and transmitting the time advance to the terminal.

3. The communication method according to claim 1, further comprising: sending a downlink synchronization signal to the terminal for downlink synchronization with the terminal.

4. The communication method according to claim 1, wherein a cyclic shift increment 0 in the set of cyclic shift increments indicates that one preamble sequence is generated from one root sequence.

5. The communication method according to claim 4, wherein the cyclic shift increment 0 in the set of cyclic shift increments corresponds to a same cyclic shift as that of a cyclic shift increment 839.

6. An apparatus operable to communicate in a wireless communications network, the apparatus comprising: a processor; and a non-transitory computer readable storage medium storing programming for execution by the processor coupled to the storage medium, the programming including instructions that cause the apparatus to: notify a terminal of a cyclic shift increment N.sub.CS configuration information indicating an N.sub.CS value, the N.sub.CS value belonging to a set of cyclic shift increments including following cyclic shift increments: 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167, 279, and 419; and receive, from the terminal, a random access preamble corresponding to the N.sub.CS value.

7. The apparatus according to claim 6, wherein the programming further includes instructions that cause the apparatus to: determine a time advance in accordance with the random access preamble; and transmit the time advance to the terminal.

8. The apparatus according to claim 6, wherein the programming further includes instructions that cause the apparatus to: send a downlink synchronization signal to the terminal for downlink synchronization with the terminal.

9. The apparatus according to claim 6, wherein a cyclic shift increment 0 in the set of cyclic shift increments indicates that one preamble sequence is generated from one root sequence.

10. The apparatus according to claim 9, wherein the cyclic shift increment 0 in the set of cyclic shift increments corresponds to a same cyclic shift as that of a cyclic shift increment 839.

11. A communication method performed in a wireless communication network, comprising: receiving, from a base station, cyclic shift increment N.sub.CS configuration information indicating an N.sub.CS value, the N.sub.CS value belonging to a set of cyclic shift increments including following cyclic shift increments: 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167, 279, and 419; generating a random access preamble based on the N.sub.CS value; and sending the random access preamble to the base station.

12. The communication method according to claim 11, further comprising: receiving, from the base station, a time advance that is determined in accordance with the random access preamble.

13. The communication method according to claim 11, further comprising: receiving a downlink synchronization signal from the base station to be synchronized with the base station in downlink.

14. The communication method according to claim 11, wherein a cyclic shift increment 0 in the set of cyclic shift increments indicates that one preamble sequence is generated from one root sequence.

15. The communication method according to claim 14, wherein the cyclic shift increment 0 in the set of cyclic shift increments corresponds to a same cyclic shift as that of a cyclic shift increment 839.

16. An apparatus operable to communicate in a wireless communications network, the apparatus comprising: a processor; and a non-transitory computer readable storage medium storing programming for execution by the processor coupled to the storage medium, the programming including instructions that cause the apparatus to: receive from a base station, cyclic shift increment N.sub.CS configuration information indicating an N.sub.CS value, the N.sub.CS value belonging to a set of cyclic shift increments including following cyclic shift increments: 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167, 279, and 419; generate a random access preamble based on the N.sub.CS value; and send the random access preamble to the base station.

17. The apparatus according to claim 16, wherein the programming further includes instructions that cause the apparatus to: receive, from the base station, a time advance that is determined in accordance with the random access preamble.

18. The apparatus according to claim 16, wherein the programming further includes instructions that cause the apparatus to: receive a downlink synchronization signal from the base station to be synchronized with the base station in downlink.

19. The apparatus according to claim 16, wherein a cyclic shift increment 0 in the set of cyclic shift increments indicates that one preamble sequence is generated from one root sequence.

20. The apparatus according to claim 19, wherein the cyclic shift increment 0 in the set of cyclic shift increments corresponds to a same cyclic shift as that of a cyclic shift increment 839.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart illustrating an method embodiment of the disclosure;

(2) FIG. 2 is a diagram illustrating the relationship between the maximum number of preambles and the cell radius according to an embodiment of the disclosure;

(3) FIG. 3 is a diagram illustrating the value of maximum relative difference in the cell radius interval k according to an embodiment of the disclosure;

(4) FIG. 4 is a block diagram of the base station according to an embodiment of the disclosure; and

(5) FIG. 5 is a diagram illustrating the mobile communication system according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(6) The general solution of an embodiment of the disclosure is described first, incorporating FIG. 1. As illustrated in FIG. 1, the embodiment includes:

(7) Step 101: The length of the root sequence is determined.

(8) Step 102: A set of ZCZ lengths is selected so that, for any cell radius, the maximum number of preambles determined from a ZCZ length which is selected from the selected set of ZCZ lengths, and is applicable to the cell and capable of determining a maximum number of preambles, is closest to the maximum number of preambles obtained from a ZCZ length which is selected from the set of all integers, and is applicable to the cell and capable of determining a maximum number of preambles, wherein the maximum number of preambles is determined from the length of the root sequence and a ZCZ length selected.

(9) In an embodiment of the disclosure, it should be ensured that the product of a ZCZ length and the symbol period of the sequence is greater than the sum of the round trip time and the delay spread of a cell, i.e., T×T.sub.s>T.sub.r+T.sub.d, in which, T is the length of ZCZ, T.sub.s is the symbol period, T.sub.r is the round trip time, and T.sub.d is the delay spread.

(10) Since the maximum round trip time T.sub.r in a cell is determined by the cell radius R, i.e., T.sub.r=2R/c, where c is the speed of light, T×T.sub.s>T.sub.r+T.sub.d may be rewritten as T×T.sub.s>2R/c+T.sub.d.

(11) Furthermore, since T=N.sub.CS−1, T×T.sub.s>2R/c+T.sub.d may be rewritten as (N.sub.CS−1)×T.sub.s>2R/c+T.sub.d. Therefore, N.sub.CS>1+(2R/c+T.sub.d)/T.sub.s.

(12) Additionally, since N.sub.pre=N.sub.ZC/N.sub.CS , N.sub.pre<N.sub.ZC+(2R/c+T.sub.d)/T.sub.s). Thus, N.sub.pre may be a function of the cell radius R. Of course, the cell radius may also be varying; and the value of N.sub.pre decreases as the value of N.sub.CS increases.

(13) In an embodiment of the disclosure, a limited set of N.sub.CS values is constructed, i.e., for a certain cell radius, the N.sub.pre corresponding to the minimum N.sub.CS value which is selected from the limited set and is applicable to the cell, is closest to the N.sub.pre corresponding to the minimum N.sub.CS value which is selected from the set of all integers and is applicable to the cell. Furthermore, a maximum relative difference may be constructed from N.sub.pre. This maximum relative difference is between the N.sub.pre(R), which is determined from the minimum N.sub.CS value selected from the set of integers and is applicable to the cell, and the N.sub.pre(R), which is determined from the minimum N.sub.CS value selected from the limited set and is applicable to the cell. If the finally determined or selected limited set is such a set that the maximum relative difference between the N.sub.pre(R), which is determined from the minimum N.sub.CS value selected from the set of integers and is applicable to the cell, and the N.sub.pre(R), which is determined from the minimum N.sub.CS value selected from the limited set and is applicable to the cell, is minimized in a cell of any radius, this limited set is a required one.

(14) As illustrated in FIG. 2, curve A indicates that for any one cell radius, an integer from the set of all integers may be selected as N.sub.CS of the cell, wherein a maximum number of preamble sequences may be generated based on the integer selected, and the generated preamble sequences are applicable to the cell. Curve B indicates a set of N.sub.CS including a limited number of N.sub.CS. When the limited number of N.sub.CS is applied in cells of all radii, within a certain interval of cell radii, a same N.sub.CS will be used for all cell radii. Thus, the N.sub.CS should be determined according to the maximum cell radius in the interval of cell radii. Compared with A, the preamble number generated according to B decreases.

(15) Under these conditions, if the selected limited set ensures that the maximum relative difference between the N.sub.pre(R) determined from a N.sub.CS value selected from any integer and the N.sub.pre(R) determined from a N.sub.CS value selected from the limited set is minimized, and it is assumed that the N.sub.pre(R) determined from a N.sub.CS value selected from any integer is A(R) and the N.sub.pre(R) determined from a N.sub.CS value selected from the limited set is B(R), and then A(R) and B(R) are respectively illustrated in FIG. 2.

(16) As seen from FIG. 2, there is a small deviation between A(R) and B(R). For a certain cell radius R, the deviation of B(R) from A(R) for some cell radius R may increase the number of required root sequences for that cell radius R. The increase of the number of root sequences becomes very important for large cell radii where N.sub.pre is small. For example, if A(R)=.sub.3 and B(R)=2, the number of root sequences increases significantly, from 64/3=22 to 64/2=32. An appropriate measure of the deviation of B from A should therefore weigh the difference A-B with higher weight for small N.sub.pre, e.g. by considering the maximum relative difference between A(R) and B(R), i.e., [A(R)−B(R)]/A(R). We will adopt the maximum relative difference between A(R) and B(R) over all cell radii as the measurement of the deviation of B(R) from A(R), and find a set of N.sub.CS values that minimizes this measurement. This set may consist of one N.sub.CS=0 and K+1 non-zero N.sub.CS values. The total number of N.sub.CS values in the set is K+2.

(17) For example, in a relatively small cell, it would be possible to generate 64 ZCZ preambles from a single root sequence if N.sub.CS=N.sub.ZC/64. This value is the smallest value in the set N.sub.CS(k).

(18) The maximum value, N.sub.CS(K), is the one that allows for having 2 ZCZ sequences from a set single root sequence, so it is N.sub.ZC/2.

(19) For the largest cells there is only one RAP generated from each root sequence. Therefore, N.sub.CS(K+1)=0.

(20) The maximum relative difference between A(R) and B(R), i.e., [A(R)−B(R)]/A(R), is non-increasing with radius R within the interval of [(r(k−1), r(k)] and the interval being k, as illustrated in FIG. 2. In FIG. 2, r(k) denotes the kth cell radius arranged orderly from small ones to large ones. The reason is that B(R) is constant in the interval, whereas A is inversely proportional to the smallest possible N.sub.CS for given R. This value of N.sub.CS increases with the round trip time and hence with R.

(21) If it is assumed that the maximum number of preamble sequences of the set A(R) is N.sub.pre(k−1)−1 in the cell radius interval of [(r(k−1), r(k)], the maximum number of preamble sequences of the set B(R) generated in this interval associate with the cell radius r(k), i.e., the maximum number of preamble sequences is N.sub.pre(k). The maximum relative difference D.sub.k in the interval k may be obtained from the following equation:

(22) $D_k=\frac{N_{\mathrm{pre}}\left(k-1\right)-1-N_{\mathrm{pre}}\left(k\right)}{N_{\mathrm{pre}}\left(k-1\right)-1}$

(23) If D.sub.k and N.sub.pre(k−1) are given, N.sub.pre(k) may be obtained by rearranging the above equation, i.e.:
N.sub.pre(k)=(1−D.sub.k)(N.sub.pre(k−1)−1)

(24) The maximum relative difference D.sub.max for all cell radii may be given by
D.sub.max=max{D.sub.k}.sub.k=1.sup.K.

(25) For N.sub.pre(k), we will first allow N.sub.pre(k) to be a real number, and then round the result to the nearest integer. Additionally, N.sub.pre(0) and N.sub.pre(K) are fixed.

(26) Then D.sub.max is minimized if all D.sub.k are equal, i.e. D.sub.k=D, k=1, 2, . . . , K, as will be proved in the following.

(27) A set of values {N.sub.pre.sup.(1)(k)}.sub.k=0.sup.K is constructed with the constraint that N.sub.pre.sup.(1)(k)=N.sub.pre(k) for k=0 and k=K, so that D.sub.k.sup.(1)=D, k=1, 2, . . . , K. For this set, D.sub.max=D.

(28) Next, another set of values {N.sub.pre.sup.(2)(k)}.sub.k=0.sup.K is constructed with the constraint that for N.sub.pre.sup.(2)(k)=N.sub.pre.sup.(k) for k=0 and k=K, so that D.sub.max<D, i.e. D.sub.k.sup.(2)<D.sub.k.sup.(1), k=1, 2, . . . , K.

(29) When k=1, since D.sub.k.sup.(2)<D.sub.k.sup.(1) and N.sub.pre.sup.(2)(0)=N.sub.pre.sup.(1)(0), N.sub.pre.sup.(2)(1)>N.sub.pre.sup.(1)(1) is obtained according to N.sub.pre(k)=(1−D.sub.k)(N.sub.pre(k−1)−1).

(30) When k=2, since D.sub.2.sup.(2)<D.sub.2.sup.(1) and N.sub.pre.sup.(2)(1)>N.sub.pre.sup.(1)(1), N.sub.pre.sup.(2)(2)>N.sub.pre.sup.(1)(2) is obtained according to N.sub.pre(k)=(1−D.sub.k)(N.sub.pre(k−1)−1).

(31) Similarly, for all k, since N.sub.pre.sup.(2)(K)=N.sub.pre.sup.(1)(K)=N.sub.pre(K), N.sub.pre.sup.(2)(k)>N.sub.pre.sup.(1)(k) is impossible.

(32) Thus, it is impossible to construct a set of values N.sub.pre.sup.(k) such that D.sub.max<D, which proves that D.sub.max is minimized if all D.sub.k are equal, i.e. D.sub.k=D, k=1, 2, . . . , K.

(33) In this way, the set of values {N.sub.pre(k)}.sub.k=0.sup.K which minimizes D.sub.max may be found.

(34) Replacing D.sub.k by D in N.sub.pre(k)=(1−D.sub.k)(N.sub.pre(k−1)−1) and rearranging the equation, a linear difference equation is obtained as follows:
N.sub.pre(k)−aN.sub.pre(k−1)=−a,wherein a=(1−D).

(35) By recursion, it is obtained from the above equation:

(36) $\begin{array}{cc}{N}_{\mathrm{pre}}\left(k\right)=N_{\mathrm{pre}}\left(0\right)a^k+\frac{a}{1-a}\left(a^k-1\right)& \left(3\right)\end{array}$

(37) From the above equation and the boundary conditions N.sub.pre(0) and N.sub.pre(K), a may be determined numerically.

(38) For example, the maximum number of preambles generated from one root sequence is 64, i.e., N.sub.pre(0)=64. The minimum number of preamble obtained by cyclic shift is 2, for example, N.sub.pre(14)=2. Thus, a=0.856 may be obtained from these two parameters, and all N.sub.pre(k), k=1, 2, . . . may further be obtained.

(39) The maximum relative difference is minimized through an approximate minimization by a sub-optimal algorithm, i.e., by minimizing the maximum relative difference for fictive real-valued maximum number of ZCZ RAPs, and the maximum number of the ZCZ RAPs is thereafter quantized. The method is specified below.

(40) By first rounding the fictive real-valued N.sub.pre(k) in

(41) 0$N_{\mathrm{pre}}\left(k\right)=N_{\mathrm{pre}}\left(0\right)a^k+\frac{a}{1-a}\left(a^k-1\right),$
the following equation is obtained:
N.sub.CS(k)=N.sub.ZC/[N.sub.pre(0)×a.sup.k+a/(1−a)×(a.sup.k−1)](4)

(42) where x denotes the maximum integer not greater than x, N.sub.ZC is the length of the root sequence, N.sub.pre(0) denotes the maximum number of preambles generated from the root sequence.

(43) Still taking the above example as an example, if N.sub.pre(0)=64 and N.sub.pre(14)=2, a=0.856 is obtained based on equation (3). Next, when N.sub.ZC=839, N.sub.cs(k), k=0, 1, 2, . . . , 14 obtained based on equation (4) is illustrated in table 1:

(44) TABLE-US-00001 TABLE 1 k N.sub.CS(k) 0 13 1 15 2 18 3 22 4 26 5 32 6 38 7 46 8 59 9 76 10 93 11 119 12 167 13 279 14 419

(45) If only one preamble sequence is obtained for a very large cell, which is the sequence itself, then N.sub.CS=0. Adding this value into the above table, table 2 is obtained:

(46) TABLE-US-00002 TABLE 2 k N.sub.CS(k) 0 13 1 15 2 18 3 22 4 26 5 32 6 38 7 46 8 59 9 76 10 93 11 119 12 167 13 279 14 419 15 0

(47) Finally, the true integer value of N.sub.pre(k) is obtained from N.sub.pre(k)=N.sub.ZC/N.sub.CS(k) that for some values of k N.sub.ZC/N.sub.CS(k) are greater than the rounded values N.sub.pre(k). As illustrated in FIG. 3, when K=14, the value of D.sub.k obtained from the real number value of N.sub.pre(k) is D=0.144. It can be seen from FIG. 3 that the true integer values of N.sub.pre(k) will cause D.sub.k to deviate from D. But the deviation is still very small for all cells except the two largest cells. Thus, the selected limited set of values of N.sub.CS is applicable.

(48) It should be noted that if the limited set of values of N.sub.CS is determined, the limited set of lengths of ZCZ may also be determined, for instance, according to T=N.sub.CS−1.

(49) Correspondingly, the disclosure provides an embodiment of an apparatus of determining a set of ZCZ lengths. As illustrated in FIG. 4, the apparatus includes: a length determination unit 410, configured to determine a length of a root sequence; and a set selection unit 420, configured to select such a set of ZCZ lengths that, for any cell radius, the maximum number of preambles determined from a ZCZ length which is selected from the selected set of ZCZ lengths, and is applicable to the cell and capable of determining a maximum number of preambles, is closest to the maximum number of preambles determined from a ZCZ length which is selected from the set of all integers, and is applicable to the cell and capable of determining a maximum number of preambles, wherein the maximum number of preambles is determined by the length of the root sequence and a ZCZ length selected.

(50) The set selection unit 420 may include: a module 421 adapted for the selection of a set of cyclic shift increments, wherein, the module 421 is configured to select such a set of cyclic shift increments that, for any cell radius, the maximum number of preambles determined from a cyclic shift increment which is selected from the selected set of cyclic shift increments, and is applicable to the cell, is closest to the maximum number of preambles determined from a cyclic shift increment which is selected from the set of all integers and is applicable to the cell, wherein the maximum number of preambles is determined by the root sequence length and a cyclic shift increment selected; and a module 422 adapted to obtain a set of ZCZ lengths, wherein the module is configured to obtain the set of ZCZ lengths according to the selected set of cyclic shift increments.

(51) In above apparatus embodiment, the cyclic shift increment selected from the selected set of cyclic shift increments is the minimum cyclic shift increment in the selected set of cyclic shift increments; and the cyclic shift increment selected from the set of all integers is the minimum cyclic shift increment in the set of all integers.

(52) The disclosure provides an embodiment of a base station, as illustrated in FIG. 4, which includes: a length determination unit 410, configured to determine a length of a root sequence; and a set selection unit 420, configured to select such a set of ZCZ lengths that, for any cell radius, the maximum number of preambles determined from a ZCZ length which is selected from the selected set of ZCZ lengths, and is applicable to the cell and capable of determining a maximum number of preambles, is closest to the maximum number of preambles determined from a ZCZ length which is selected from the set of all integers, and is applicable to the cell and capable of determining a maximum number of preambles, wherein the maximum number of preambles is determined from the length of the root sequence and a ZCZ length selected.

(53) The disclosure further provides an embodiment of a mobile communication system, as illustrated in FIG. 5. The system comprises a base station 400 and a mobile terminal 500. The base station 400 is configured to interact with the mobile terminal 500, and to specify a ZCZ length from a set of ZCZ lengths for the mobile terminal 500; the mobile terminal 500 is configured to generate a preamble according to the ZCZ length specified by the base station 400, and to transmit an uplink signal to the base station 400 using the preamble; the set of ZCZ lengths is such a set of ZCZ lengths that, for any cell radius, the maximum number of preambles determined from a ZCZ length which is selected from the selected set of ZCZ lengths, and is applicable to the cell and capable of determining a maximum number of preambles, is closest to the maximum number of preambles determined from a ZCZ length which is selected from the set of all integers, and is applicable to the cell and capable of determining a maximum number of preambles, wherein the maximum number of preambles is determined from the length of the root sequence and a ZCZ length selected.

(54) In above embodiment of the mobile communication system, the cyclic shift increment selected from the selected set of cyclic shift increments is the minimum cyclic shift increment applicable to the cell in the selected set of cyclic shift increments, the cyclic shift increment selected from the set of all integers is the minimum cyclic shift increment applicable to the cell in the set of all integers.

(55) In general, in embodiments of the disclosure, the selected limited set of N.sub.CS values should be such a set that, in a plurality of intervals of cell radii, the maximum relative difference between the maximum number of the ZCZ RAPs determined from the minimum N.sub.CS value of the limited set, which is applicable to the plurality of cells, and the maximum number of the ZCZ RAPs determined from a plurality of N.sub.CS values of a set of integers which are applicable to the plurality of cells is minimized. Furthermore, a limited set of ZCZ lengths may be selected. Of course, in a plurality of intervals of cell radii, the maximum relative difference between the maximum number of the ZCZ RAPs determined from the minimum ZCZ length of the limited set of ZCZ lengths, which is applicable to the plurality of cells, and the maximum number of the ZCZ RAPs determined from a plurality of ZCZ lengths of the set of all integers which are applicable to the plurality of cells is minimized.

(56) What are described above are only preferred embodiments of the disclosure. It should be noted that, for a person skilled in the art, variations and improvements may be made without deviating from the principle of the disclosure. Those variations and improvements are all regarded to be within the scope of the disclosure.